Flux transfer events: Reconnection without separators. [magnetopause

NASA Technical Reports Server (NTRS)

Hesse, M.; Birn, J.; Schindler, K.

1989-01-01

A topological analysis of a simple model magnetic field of a perturbation at the magnetopause modeling an apparent flux transfer event is presented. It is shown that a localized perturbation at the magnetopause can in principle open a closed magnetosphere by establishing magnetic connections across the magnetopause. Although the model field exhibits neutral points, these are not involved in the magnetic connection of the flux tubes. The topological substructure of a localized perturbation is analyzed in a simpler configuration. The presence of both signs of the magnetic field component normal to the magnetopause leads to a linkage of topologically different flux tubes, described as a flux knot, and a filamentary substructure of field lines of different topological types which becomes increasingly complicated for decreasing magnetic shear at the magnetopause.

Critical speeds and forced response solutions for active magnetic bearing turbomachinery, part 2

NASA Technical Reports Server (NTRS)

Rawal, D.; Keesee, J.; Kirk, R. Gordon

1991-01-01

The need for better performance of turbomachinery with active magnetic bearings has necessitated a study of such systems for accurate prediction of their vibrational characteristics. A modification of existing transfer matrix methods for rotor analysis is presented to predict the response of rotor systems with active magnetic bearings. The position of the magnetic bearing sensors is taken into account and the effect of changing sensor position on the vibrational characteristics of the rotor system is studied. The modified algorithm is validated using a simpler Jeffcott model described previously. The effect of changing from a rotating unbalance excitation to a constant excitation in a single plane is also studied. A typical eight stage centrifugal compressor rotor is analyzed using the modified transfer matrix code. The results for a two mass Jeffcott model were presented previously. The results obtained by running this model with the transfer matrix method were compared with the results of the Jeffcott analysis for the purposes of verification. Also included are plots of amplitude versus frequency for the eight stage centrifugal compressor rotor. These plots demonstrate the significant influence that sensor location has on the amplitude and critical frequencies of the rotor system.

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.

A voxel based comparative analysis using magnetization transfer imaging and T1-weighted magnetic resonance imaging in progressive supranuclear palsy

PubMed Central

Sandhya, Mangalore; Saini, Jitender; Pasha, Shaik Afsar; Yadav, Ravi; Pal, Pramod Kumar

2014-01-01

Aims: In progressive supranuclear palsy (PSP) tissue damage occurs in specific cortical and subcortical regions. Voxel based analysis using T1-weighted images depict quantitative gray matter (GM) atrophy changes. Magnetization transfer (MT) imaging depicts qualitative changes in the brain parenchyma. The purpose of our study was to investigate whether MT imaging could indicate abnormalities in PSP. Settings and Design: A total of 10 patients with PSP (9 men and 1 woman) and 8 controls (5 men and 3 women) were studied with T1-weighted magnetic resonance imaging (MRI) and 3DMT imaging. Voxel based analysis of T1-weighted MRI was performed to investigate brain atrophy while MT was used to study qualitative abnormalities in the brain tissue. We used SPM8 to investigate group differences (with two sample t-test) using the GM and white matter (WM) segmented data. Results: T1-weighted imaging and MT are equally sensitive to detect changes in GM and WM in PSP. Magnetization transfer ratio images and magnetization-prepared rapid acquisition of gradient echo revealed extensive bilateral volume and qualitative changes in the orbitofrontal, prefrontal cortex and limbic lobe and sub cortical GM. The prefrontal structures involved were the rectal gyrus, medial, inferior frontal gyrus (IFG) and middle frontal gyrus (MFG). The anterior cingulate, cingulate gyrus and lingual gyrus of limbic lobe and subcortical structures such as caudate, thalamus, insula and claustrum were also involved. Cerebellar involvement mainly of anterior lobe was also noted. Conclusions: The findings suggest that voxel based MT imaging permits a whole brain unbiased investigation of central nervous system structural integrity in PSP. PMID:25024571

Tunable magnetotransport in Fe/hBN/graphene/hBN/Pt(Fe) epitaxial multilayers

NASA Astrophysics Data System (ADS)

Magnus Ukpong, Aniekan

2018-03-01

Theoretical and computational analysis of the magnetotransport properties and spin-transfer torque field-induced switching of magnetization density in vertically-stacked multilayers is presented. Using epitaxially-capped free layers of Pt and Fe, atom-resolved magnetic moments and spin-transfer torques are computed at finite bias. The calculations are performed within linear response approximation to the spin-density reformulation of the van der Waals density functional theory. Dynamical spin excitations are computed as a function of a spin-transfer torque induced magnetic field along the magnetic easy axis, and the corresponding spin polarization perpendicular to the easy axis is obtained. Bias-dependent giant anisotropic magnetoresistance of up to 3200% is obtained in the nonmagnetic-metal-capped Fe/hBN/graphene/hBN/Pt multilayer architecture. Since this specific heterostructure is not yet fabricated and characterized, the predicted high performance has not been demonstrated experimentally. Nevertheless, similar calculations performed on the Fe/hBN/Co stack show that the tunneling magnetoresistance obtained at the Fermi-level is in excellent agreement with results of recent magnetotransport measurements on magnetic tunnel junctions that contain the monolayer hBN tunnel region. The magnitude of the spin-transfer torque is found to increase as the tunneling spin current increases, and this activates the magnetization switching process due to increased charge accumulation. This mechanism causes substantial spin backflow, which manifests as rapid undulations in the bias-dependent tunneling spin currents. The implication of these findings on the design of nanoscale spintronic devices with spin-transfer torque tunable magnetization density is discussed. Insights derived from this study are expected to enhance the prospects for developing and integrating artificially assembled van der Waals multilayer heterostructures as the preferred material platform for efficient engineering of spin switches for spintronic applications.

Dynamics of paramagnetic agents by off-resonance rotating frame technique in the presence of magnetization transfer effect

NASA Astrophysics Data System (ADS)

Zhang, Huiming; Xie, Yang

2007-02-01

The simple method for measuring the rotational correlation time of paramagnetic ion chelates via off-resonance rotating frame technique is challenged in vivo by the magnetization transfer effect. A theoretical model for the spin relaxation of water protons in the presence of paramagnetic ion chelates and magnetization transfer effect is described. This model considers the competitive relaxations of water protons by the paramagnetic relaxation pathway and the magnetization transfer pathway. The influence of magnetization transfer on the total residual z-magnetization has been quantitatively evaluated in the context of the magnetization map and various difference magnetization profiles for the macromolecule conjugated Gd-DTPA in cross-linked protein gels. The numerical simulations and experimental validations confirm that the rotational correlation time for the paramagnetic ion chelates can be measured even in the presence of strong magnetization transfer. This spin relaxation model also provides novel approaches to enhance the detection sensitivity for paramagnetic labeling by suppressing the spin relaxations caused by the magnetization transfer. The inclusion of the magnetization transfer effect allows us to use the magnetization map as a simulation tool to design efficient paramagnetic labeling targeting at specific tissues, to design experiments running at low RF power depositions, and to optimize the sensitivity for detecting paramagnetic labeling. Thus, the presented method will be a very useful tool for the in vivo applications such as molecular imaging via paramagnetic labeling.

Energy transfers in large-scale and small-scale dynamos

NASA Astrophysics Data System (ADS)

Samtaney, Ravi; Kumar, Rohit; Verma, Mahendra

2015-11-01

We present the energy transfers, mainly energy fluxes and shell-to-shell energy transfers in small-scale dynamo (SSD) and large-scale dynamo (LSD) using numerical simulations of MHD turbulence for Pm = 20 (SSD) and for Pm = 0.2 on 10243 grid. For SSD, we demonstrate that the magnetic energy growth is caused by nonlocal energy transfers from the large-scale or forcing-scale velocity field to small-scale magnetic field. The peak of these energy transfers move towards lower wavenumbers as dynamo evolves, which is the reason for the growth of the magnetic fields at the large scales. The energy transfers U2U (velocity to velocity) and B2B (magnetic to magnetic) are forward and local. For LSD, we show that the magnetic energy growth takes place via energy transfers from large-scale velocity field to large-scale magnetic field. We observe forward U2U and B2B energy flux, similar to SSD.

The magnetic nature of disk accretion onto black holes.

PubMed

Miller, Jon M; Raymond, John; Fabian, Andy; Steeghs, Danny; Homan, Jeroen; Reynolds, Chris; van der Klis, Michiel; Wijnands, Rudy

2006-06-22

Although disk accretion onto compact objects-white dwarfs, neutron stars and black holes-is central to much of high-energy astrophysics, the mechanisms that enable this process have remained observationally difficult to determine. Accretion disks must transfer angular momentum in order for matter to travel radially inward onto the compact object. Internal viscosity from magnetic processes and disk winds can both in principle transfer angular momentum, but hitherto we lacked evidence that either occurs. Here we report that an X-ray-absorbing wind discovered in an observation of the stellar-mass black hole binary GRO J1655 - 40 (ref. 6) must be powered by a magnetic process that can also drive accretion through the disk. Detailed spectral analysis and modelling of the wind shows that it can only be powered by pressure generated by magnetic viscosity internal to the disk or magnetocentrifugal forces. This result demonstrates that disk accretion onto black holes is a fundamentally magnetic process.

Compression of magnetized target in the magneto-inertial fusion

NASA Astrophysics Data System (ADS)

Kuzenov, V. V.

2017-12-01

This paper presents a mathematical model, numerical method and results of the computer analysis of the compression process and the energy transfer in the target plasma, used in magneto-inertial fusion. The computer simulation of the compression process of magnetized cylindrical target by high-power laser pulse is presented.

Amide proton transfer imaging with improved robustness to magnetic field inhomogeneity and magnetization transfer asymmetry using Saturation with Frequency Alternating RF Irradiation (SAFARI)

PubMed Central

Scheidegger, Rachel; Vinogradov, Elena; Alsop, David C

2011-01-01

Amide proton transfer (APT) imaging has shown promise as an indicator of tissue pH and as a marker for brain tumors. Sources of error in APT measurements include direct water saturation, and magnetization transfer (MT) from membranes and macromolecules. These are typically suppressed by post-processing asymmetry analysis. However, this approach is strongly dependent on B0 homogeneity and can introduce additional errors due to intrinsic MT asymmetry, aliphatic proton features opposite the amide peak, and radiation damping-induced asymmetry. Although several methods exist to correct for B0 inhomogeneity, they tremendously increase scan times and do not address errors induced by asymmetry of the z-spectrum. In this paper, a novel saturation scheme - saturation with frequency alternating RF irradiation (SAFARI) - is proposed in combination with a new magnetization transfer ratio (MTR) parameter designed to generate APT images insensitive to direct water saturation and MT, even in the presence of B0 inhomogeneity. The feasibility of the SAFARI technique is demonstrated in phantoms and in the human brain. Experimental results show that SAFARI successfully removes direct water saturation and MT contamination from APT images. It is insensitive to B0 offsets up to 180Hz without using additional B0 correction, thereby dramatically reducing scanning time. PMID:21608029

The characteristic of evaporative cooling magnet for ECRIS

NASA Astrophysics Data System (ADS)

Xiong, B.; Ruan, L.; Gu, G. B.; Lu, W.; Zhang, X. Z.; Zhan, W. L.

2016-02-01

Compared with traditional de-ionized pressurized-water cooled magnet of ECRIS, evaporative cooling magnet has some special characteristics, such as high cooling efficiency, simple maintenance, and operation. The analysis is carried out according to the design and operation of LECR4 (Lanzhou Electron Cyclotron Resonance ion source No. 4, since July 2013), whose magnet is cooled by evaporative cooling technology. The insulation coolant replaces the de-ionized pressurized-water to absorb the heat of coils, and the physical and chemical properties of coolant remain stable for a long time with no need for purification or filtration. The coils of magnet are immersed in the liquid coolant. For the higher cooling efficiency of coolant, the current density of coils can be greatly improved. The heat transfer process executes under atmospheric pressure, and the temperature of coils is lower than 70 °C when the current density of coils is 12 A/mm2. On the other hand, the heat transfer temperature of coolant is about 50 °C, and the heat can be transferred to fresh air which can save cost of water cooling system. Two years of LECR4 stable operation show that evaporative cooling technology can be used on magnet of ECRIS, and the application advantages are very obvious.

The characteristic of evaporative cooling magnet for ECRIS

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

Xiong, B., E-mail: xiongbin@mail.iee.ac.cn; University of Chinese Academy of Sciences, Beijing 100049; Ruan, L.

2016-02-15

Compared with traditional de-ionized pressurized-water cooled magnet of ECRIS, evaporative cooling magnet has some special characteristics, such as high cooling efficiency, simple maintenance, and operation. The analysis is carried out according to the design and operation of LECR4 (Lanzhou Electron Cyclotron Resonance ion source No. 4, since July 2013), whose magnet is cooled by evaporative cooling technology. The insulation coolant replaces the de-ionized pressurized-water to absorb the heat of coils, and the physical and chemical properties of coolant remain stable for a long time with no need for purification or filtration. The coils of magnet are immersed in the liquidmore » coolant. For the higher cooling efficiency of coolant, the current density of coils can be greatly improved. The heat transfer process executes under atmospheric pressure, and the temperature of coils is lower than 70 °C when the current density of coils is 12 A/mm{sup 2}. On the other hand, the heat transfer temperature of coolant is about 50 °C, and the heat can be transferred to fresh air which can save cost of water cooling system. Two years of LECR4 stable operation show that evaporative cooling technology can be used on magnet of ECRIS, and the application advantages are very obvious.« less

Unsteady Magnetized Flow and Heat Transfer of a Viscoelastic fluid over a Stretching Surface

NASA Astrophysics Data System (ADS)

Ghosh, Sushil Kumar

2017-12-01

This paper is to study the flow of heated ferro-fluid over a stretching sheet under the influence of magnetic field. The fluid considered in the present investigation is a mixture of blood as well as fluid-dispersed magnetic nano particles and under this context blood is found to be the appropriate choice of viscoelastic, Walter's B fluid. The objective of the present work is to study the effect of various parameters found in the mathematical analysis. Taking into account the blood has zero electrical conductivity, magnetization effect has been considered in the governing equation of the present study with the use of ferro-fluid dynamics principle. By introducing appropriate non-dimensional variables into the governing equations of unsteady two-dimensional flow of viscoelastic fluid with heat transfer are converted to a set of ordinary differential equations with appropriate boundary conditions. Newton's linearization technique has been employed for the solution of non-linear ordinary differential equations. Important results found in the present investigation are the substantial influence of ferro-magnetic parameter, Prandlt number and the parameter associated with the thermal conductivity on the flow and heat transfer. It is observed that the presence of magnetic dipole essentially reduces the flow velocity in the vertical direction and that helps to damage the cancer cells in the tumor region.

Nonhelical inverse transfer of a decaying turbulent magnetic field.

PubMed

Brandenburg, Axel; Kahniashvili, Tina; Tevzadze, Alexander G

2015-02-20

In the presence of magnetic helicity, inverse transfer from small to large scales is well known in magnetohydrodynamic (MHD) turbulence and has applications in astrophysics, cosmology, and fusion plasmas. Using high resolution direct numerical simulations of magnetically dominated self-similarly decaying MHD turbulence, we report a similar inverse transfer even in the absence of magnetic helicity. We compute for the first time spectral energy transfer rates to show that this inverse transfer is about half as strong as with helicity, but in both cases the magnetic gain at large scales results from velocity at similar scales interacting with smaller-scale magnetic fields. This suggests that both inverse transfers are a consequence of universal mechanisms for magnetically dominated turbulence. Possible explanations include inverse cascading of the mean squared vector potential associated with local near two dimensionality and the shallower k^{2} subinertial range spectrum of kinetic energy forcing the magnetic field with a k^{4} subinertial range to attain larger-scale coherence. The inertial range shows a clear k^{-2} spectrum and is the first example of fully isotropic magnetically dominated MHD turbulence exhibiting weak turbulence scaling.

Current control of time-averaged magnetization in superparamagnetic tunnel junctions

NASA Astrophysics Data System (ADS)

Bapna, Mukund; Majetich, Sara A.

2017-12-01

This work investigates spin transfer torque control of time-averaged magnetization in a small 20 nm × 60 nm nanomagnet with a low thermal stability factor, Δ ˜ 11. Here, the nanomagnet is a part of a magnetic tunnel junction and fluctuates between parallel and anti-parallel magnetization states with respect to the magnetization of the reference layer generating a telegraph signal in the current versus time measurements. The response of the nanomagnet to an external field is first analyzed to characterize the magnetic properties. We then show that the time-averaged magnetization in the telegraph signal can be fully controlled between +1 and -1 by voltage over a small range of 0.25 V. NIST Statistical Test Suite analysis is performed for testing true randomness of the telegraph signal that the device generates when operated at near critical current values for spin transfer torque. Utilizing the probabilistic nature of the telegraph signal generated at two different voltages, a prototype demonstration is shown for multiplication of two numbers using an artificial AND logic gate.

Development and Technology Transfer of the Syncro Blue Tube (Gabriel) Magnetically Guided Feeding Tube

DTIC Science & Technology

2017-06-01

other documentation. TITLE: Development and Technology Transfer of the Syncro Blue Tube (Gabriel) Magnetically Guided Feeding Tube REPORT DOCUMENTATION...TITLE AND SUBTITLE Development and Technology Transfer of the Syncro Blue Tube (Gabriel) Magnetically Guided Feeding Tube 5a. CONTRACT NUMBER W81XWH-09-2...Technical Abstract: Further Development and Technology Transfer of the Syncro BLUETUBE™ (Gabriel) Magnetically Guided Feeding Tube. New Primary

Thermal Analysis of Magnetically-Coupled Pump for Cryogenic Applications

NASA Technical Reports Server (NTRS)

Senocak, Inanc; Udaykumar, H. S.; Ndri, Narcisse; Francois, Marianne; Shyy, Wei

1999-01-01

Magnetically-coupled pump is under evaluation at Kennedy Space Center for possible cryogenic applications. A major concern is the impact of low temperature fluid flows on the pump performance. As a first step toward addressing this and related issues, a computational fluid dynamics and heat transfer tool has been adopted in a pump geometry. The computational tool includes (i) a commercial grid generator to handle multiple grid blocks and complicated geometric definitions, and (ii) an in-house computational fluid dynamics and heat transfer software developed in the Principal Investigator's group at the University of Florida. Both pure-conduction and combined convection-conduction computations have been conducted. A pure-conduction analysis gives insufficient information about the overall thermal distribution. Combined convection-conduction analysis indicates the significant influence of the coolant over the entire flow path. Since 2-D simulation is of limited help, future work on full 3-D modeling of the pump using multi-materials is needed. A comprehensive and accurate model can be developed to take into account the effect of multi-phase flow in the cooling flow loop, and the magnetic interactions.

Two-Dimensional Magnetotelluric Modelling of Ore Deposits: Improvements in Model Constraints by Inclusion of Borehole Measurements

NASA Astrophysics Data System (ADS)

Kalscheuer, Thomas; Juhojuntti, Niklas; Vaittinen, Katri

2017-12-01

A combination of magnetotelluric (MT) measurements on the surface and in boreholes (without metal casing) can be expected to enhance resolution and reduce the ambiguity in models of electrical resistivity derived from MT surface measurements alone. In order to quantify potential improvement in inversion models and to aid design of electromagnetic (EM) borehole sensors, we considered two synthetic 2D models containing ore bodies down to 3000 m depth (the first with two dipping conductors in resistive crystalline host rock and the second with three mineralisation zones in a sedimentary succession exhibiting only moderate resistivity contrasts). We computed 2D inversion models from the forward responses based on combinations of surface impedance measurements and borehole measurements such as (1) skin-effect transfer functions relating horizontal magnetic fields at depth to those on the surface, (2) vertical magnetic transfer functions relating vertical magnetic fields at depth to horizontal magnetic fields on the surface and (3) vertical electric transfer functions relating vertical electric fields at depth to horizontal magnetic fields on the surface. Whereas skin-effect transfer functions are sensitive to the resistivity of the background medium and 2D anomalies, the vertical magnetic and electric field transfer functions have the disadvantage that they are comparatively insensitive to the resistivity of the layered background medium. This insensitivity introduces convergence problems in the inversion of data from structures with strong 2D resistivity contrasts. Hence, we adjusted the inversion approach to a three-step procedure, where (1) an initial inversion model is computed from surface impedance measurements, (2) this inversion model from surface impedances is used as the initial model for a joint inversion of surface impedances and skin-effect transfer functions and (3) the joint inversion model derived from the surface impedances and skin-effect transfer functions is used as the initial model for the inversion of the surface impedances, skin-effect transfer functions and vertical magnetic and electric transfer functions. For both synthetic examples, the inversion models resulting from surface and borehole measurements have higher similarity to the true models than models computed exclusively from surface measurements. However, the most prominent improvements were obtained for the first example, in which a deep small-sized ore body is more easily distinguished from a shallow main ore body penetrated by a borehole and the extent of the shadow zone (a conductive artefact) underneath the main conductor is strongly reduced. Formal model error and resolution analysis demonstrated that predominantly the skin-effect transfer functions improve model resolution at depth below the sensors and at distance of ˜ 300-1000 m laterally off a borehole, whereas the vertical electric and magnetic transfer functions improve resolution along the borehole and in its immediate vicinity. Furthermore, we studied the signal levels at depth and provided specifications of borehole magnetic and electric field sensors to be developed in a future project. Our results suggest that three-component SQUID and fluxgate magnetometers should be developed to facilitate borehole MT measurements at signal frequencies above and below 1 Hz, respectively.

[Magnetic field numerical calculation and analysis for magnetic coupling of centrifugal blood pump for extracorporeal circulation].

PubMed

Hu, Zhaoyan; Lu, Lijun; Zhang, Tianyi; Chen, Zhenglong; Zhang, Tao

2013-12-01

This paper mainly studies the driving system of centrifugal blood pump for extracorporeal circulation, with the core being disc magnetic coupling. Structure parameters of disc magnetic coupling are related to the ability of transferring magnetic torque. Therefore, it is necessary to carry out disc magnetic coupling permanent magnet pole number (n), air gap length (L(g)), permanent magnet thickness (L(m)), permanent magnet body inside diameter (R(i)) and outside diameter (R(o)), etc. thoroughly. This paper adopts the three-dimensional static magnetic field edge element method of Ansys for numerical calculation, and analyses the relations of magnetic coupling each parameter to transmission magnetic torque. It provides a good theory basis and calculation method for further optimization of the disc magnetic coupling.

Metamaterial-enhanced coupling between magnetic dipoles for efficient wireless power transfer

NASA Astrophysics Data System (ADS)

Urzhumov, Yaroslav; Smith, David R.

2011-05-01

Nonradiative coupling between conductive coils is a candidate mechanism for wireless energy transfer applications. In this paper we propose a power relay system based on a near-field metamaterial superlens and present a thorough theoretical analysis of this system. We use time-harmonic circuit formalism to describe all interactions between two coils attached to external circuits and a slab of anisotropic medium with homogeneous permittivity and permeability. The fields of the coils are found in the point-dipole approximation using Sommerfeld integrals which are reduced to standard special functions in the long-wavelength limit. We show that, even with a realistic magnetic loss tangent of order 0.1, the power transfer efficiency with the slab can be an order of magnitude greater than free-space efficiency when the load resistance exceeds a certain threshold value. We also find that the volume occupied by the metamaterial between the coils can be greatly compressed by employing magnetic permeability with a large anisotropy ratio.

Thermal stability analysis of a superconducting magnet considering heat flow between magnet surface and liquid helium

NASA Astrophysics Data System (ADS)

Jang, J. Y.; Hwang, Y. J.; Ahn, M. C.; Choi, Y. S.

2018-07-01

This paper represents a numerical calculation method that enables highly-accurate simulations on temperature analysis of superconducting magnets considering the heat flow between the magnet and liquid helium during a quench. A three-dimensional (3D) superconducting magnet space was divided into many cells and the finite-difference method (FDM) was adopted to calculate the superconducting magnet temperatures governed by the heat transfer and joule heating of the each cell during a quench. To enhance the accuracy of the temperature calculations during a quench, the heat flow between the superconducting magnet surface and liquid helium, which lowers the magnet temperatures, was considered in this work. The electrical equation coupled with the governing thermal equation was also applied to calculate the change of the decay of the magnet current related to the joule heating. The proposed FDM method for temperatures calculation of a superconducting magnet during a quench process achieved results that were in good agreement with those obtained from an experiment.

Modulation of spin transfer torque amplitude in double barrier magnetic tunnel junctions

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

Clément, P.-Y.; Baraduc, C., E-mail: claire.baraduc@cea.fr; Chshiev, M.

2015-09-07

Magnetization switching induced by spin transfer torque is used to write magnetic memories (Magnetic Random Access Memory, MRAM) but can be detrimental to the reading process. It would be quite convenient therefore to modulate the efficiency of spin transfer torque. A solution is adding an extra degree of freedom by using double barrier magnetic tunnel junctions with two spin-polarizers, with controllable relative magnetic alignment. We demonstrate, for these structures, that the amplitude of in-plane spin transfer torque on the middle free layer can be efficiently tuned via the magnetic configuration of the electrodes. Using the proposed design could thus pavemore » the way towards more reliable read/write schemes for MRAM. Moreover, our results suggest an intriguing effect associated with the out-of-plane (field-like) spin transfer torque, which has to be further investigated.« less

Primary-Side Power Flow Control of Wireless Power Transfer for Electric Vehicle Charging

DOE PAGES

Miller, John M.; Onar, Omer C.; Chinthavali, Madhu

2014-12-22

Various noncontacting methods of plug-in electric vehicle charging are either under development or now deployed as aftermarket options in the light-duty automotive market. Wireless power transfer (WPT) is now the accepted term for wireless charging and is used synonymously for inductive power transfer and magnetic resonance coupling. WPT technology is in its infancy; standardization is lacking, especially on interoperability, center frequency selection, magnetic fringe field suppression, and the methods employed for power flow regulation. This paper proposes a new analysis concept for power flow in WPT in which the primary provides frequency selection and the tuned secondary, with its resemblancemore » to a power transmission network having a reactive power voltage control, is analyzed as a transmission network. Analysis is supported with experimental data taken from Oak Ridge National Laboratory s WPT apparatus. Lastly, this paper also provides an experimental evidence for frequency selection, fringe field assessment, and the need for low-latency communications in the feedback path.« less

On Electromagnetic Modulation of Flow Instabilities, Mixing and Heat Transfer in Conducting and Magnetized Fluids

NASA Astrophysics Data System (ADS)

Kenjeres, S.

2016-09-01

In the present paper we give a concise review of some recent highlights of our research dealing with electromagnetic control of flow, mixing and heat transfer of electrically conductive or magnetized fluids. We apply a combination of state-of-art numerical (DNS and LES) and experimental (PIV and LIF) techniques to provide fundamental insights into the complex phenomena of interactions between imposed (or induced) electromagnetic fields and underlying fluid flow. Our analysis covers an extensive range of working fluids, i.e. weakly- and highly-electrically-conductive, as well as magnetized fluids. These interactions are defined through the presence of different types of body forces acting per volume of fluid. A fully closed system of governing equations containing an extended set of the Navier-Stokes and a simplified set of the Maxwell equations is presented. The four characteristic examples are selected: the electromagnetic control of self-sustained jet oscillations, the electromagnetic enhancement of heat transfer in thermal convection, the wake interactions behind magnetic obstacles and finally, the thermo-magnetic convection in differentially heated cubical enclosure. The comparative assessment between experimental and numerical results is presented. It is concluded that generally good agreement between simulations and experiments is obtained for all cases considered, proving the concept of electromagnetic modulation, which can be used in numerous technological applications.

Peristaltic Transport of Prandtl-Eyring Liquid in a Convectively Heated Curved Channel

PubMed Central

Hayat, Tasawar; Bibi, Shahida; Alsaadi, Fuad; Rafiq, Maimona

2016-01-01

Here peristaltic activity for flow of a Prandtl-Eyring material is modeled and analyzed for curved geometry. Heat transfer analysis is studied using more generalized convective conditions. The channel walls satisfy complaint walls properties. Viscous dissipation in the thermal equation accounted. Unlike the previous studies is for uniform magnetic field on this topic, the radial applied magnetic field has been utilized in the problems development. Solutions for stream function (ψ), velocity (u), and temperature (θ) for small parameter β have been derived. The salient features of heat transfer coefficient Z and trapping are also discussed for various parameters of interest including magnetic field, curvature, material parameters of fluid, Brinkman, Biot and compliant wall properties. Main observations of present communication have been included in the conclusion section. PMID:27304458

Annealing pressure induced ions transfer in Cobalt-Ferrite thin films on amorphous SiO2/Si substrates

NASA Astrophysics Data System (ADS)

Huang, Shun-Yu; Chong, Cheong-Wei; Chen, Pin-Hui; Li, Hong-Lin; Li, Min-Kai; Huang, J. C. Andrew

2017-11-01

In this work, Cobalt-Ferrite (CFO) films were grown on silicon substrates with 300 nm amorphous silicon dioxide by Pulsed Laser Deposition (PLD) with different annealing conditions. The results of structural analysis prove that the CFO films have high crystalline quality with (1 1 1) preferred orientation. The Raman spectra and X-ray absorption spectra (XAS) indicate that the Co ions can transfer from tetrahedral sites to octahedral sites with increasing the annealing pressure. The site exchange of Co and Fe ions leads to the change of saturation magnetization in the CFO films. Our experiments provide not only a way to control the magnetism of CFO films, but also a suitable magnetic layer to develop silicon and semiconductor based spintronic devices.

Asymptotic Analysis of Melt Growth for Antimonide-Based Compound Semiconductor Crystals in Magnetic and Electric Fields

DTIC Science & Technology

2006-10-01

F. Bliss, Gerald W. Iseler and Piotr Becla, "Combining static and rotating magnetic fields during modified vertical Bridgman crystal growth ," AIAA...Wang and Nancy Ma, "Semiconductor crystal growth by the vertical Bridgman process with rotating magnetic fields," ASME Journal of Heat Transfer...2005. 15. Stephen J. LaPointe, Nancy Ma and Donald W. Mueller, Jr., " Growth of binary alloyed semiconductor crystals by the vertical Bridgman

Variable Delay Multi-Pulse Train for Fast Chemical Exchange Saturation Transfer and Relayed-Nuclear Overhauser Enhancement MRI

PubMed Central

Xu, Jiadi; Yadav, Nirbhay N.; Bar-Shir, Amnon; Jones, Craig K.; Chan, Kannie W. Y.; Zhang, Jiangyang; Walczak, P.; McMahon, Michael T.; van Zijl, Peter C. M.

2013-01-01

Purpose Chemical exchange saturation transfer (CEST) imaging is a new MRI technology allowing the detection of low concentration endogenous cellular proteins and metabolites indirectly through their exchangeable protons. A new technique, variable delay multi-pulse CEST (VDMP-CEST), is proposed to eliminate the need for recording full Z-spectra and performing asymmetry analysis to obtain CEST contrast. Methods The VDMP-CEST scheme involves acquiring images with two (or more) delays between radiofrequency saturation pulses in pulsed CEST, producing a series of CEST images sensitive to the speed of saturation transfer. Subtracting two images or fitting a time series produces CEST and relayed-nuclear Overhauser enhancement CEST maps without effects of direct water saturation and, when using low radiofrequency power, minimal magnetization transfer contrast interference. Results When applied to several model systems (bovine serum albumin, crosslinked bovine serum albumin, l-glutamic acid) and in vivo on healthy rat brain, VDMP-CEST showed sensitivity to slow to intermediate range magnetization transfer processes (rate < 100–150 Hz), such as amide proton transfer and relayed nuclear Overhauser enhancement-CEST. Images for these contrasts could be acquired in short scan times by using a single radiofrequency frequency. Conclusions VDMP-CEST provides an approach to detect CEST effect by sensitizing saturation experiments to slower exchange processes without interference of direct water saturation and without need to acquire Z-spectra and perform asymmetry analysis. PMID:23813483

Surface molecular imprinting onto fluorescein-coated magnetic nanoparticlesvia reversible addition fragmentation chain transfer polymerization: A facile three-in-one system for recognition and separation of endocrine disrupting chemicals

NASA Astrophysics Data System (ADS)

Li, Ying; Dong, Cunku; Chu, Jia; Qi, Jingyao; Li, Xin

2011-01-01

In this study, we present a general protocol for the making of surface-imprinted magnetic fluorescence beads viareversible addition-fragmentation chain transfer polymerization. The resulting composites were characterized by X-ray diffraction analysis, transmission electron microscopy, scanning electron microscopy, fluorescence spectroscopy, Fourier transform infrared spectroscopy, and energy dispersive spectroscopy. The as-synthesized beads exhibited homogeneous polymer films (thickness of about 5.7 nm), spherical shape, high fluorescence intensity and magnetic property (Magnetization (Ms) = 3.67 emu g-1). The hybrids bind the original template 17β-estradiol with an appreciable selectivity over structurally related compounds. In addition, the resulting hybrids performed without obvious deterioration after five repeated cycles. This study therefore demonstrates the potential of molecularly imprinted polymers for the recognition and separation of endocrine disrupting chemicals.In this study, we present a general protocol for the making of surface-imprinted magnetic fluorescence beads viareversible addition-fragmentation chain transfer polymerization. The resulting composites were characterized by X-ray diffraction analysis, transmission electron microscopy, scanning electron microscopy, fluorescence spectroscopy, Fourier transform infrared spectroscopy, and energy dispersive spectroscopy. The as-synthesized beads exhibited homogeneous polymer films (thickness of about 5.7 nm), spherical shape, high fluorescence intensity and magnetic property (Magnetization (Ms) = 3.67 emu g-1). The hybrids bind the original template 17β-estradiol with an appreciable selectivity over structurally related compounds. In addition, the resulting hybrids performed without obvious deterioration after five repeated cycles. This study therefore demonstrates the potential of molecularly imprinted polymers for the recognition and separation of endocrine disrupting chemicals. Electronic supplementary information (ESI) available: Supplementary figure S1. The hysteresis loop of Fe3O4 (a), Fe3O4@SiO2 (b), and Fe3O4@SiO2-Dye-SiO2 (c). See DOI: 10.1039/c0nr00614a

Anisotropy in electromagnetic field variations and its implication for lateral inhomogeneity of the electrical conductivity structure

NASA Astrophysics Data System (ADS)

Honkura, Y.; Watanabe, N.; Kaneko, Y.; Oshima, S.

1989-03-01

Two-dimensional analyses of magnetotelluric data provide information on anisotropic response for two different polarization cases; the so-called B-polarization and E-polarization cases. Similar anisotropy should also be observed in the horizontal components of magnetic field variations. On the assumption that a reference station provides the normal magnetic field, transfer functions for the horizontal magnetic fields can be derived in a fashion similar to the impedance analysis for magnetotelluric data. We applied this method to magnetic data obtained at some observation sites in a geothermal area in Japan. Transfer functions for the horizontal magnetic fields exhibit a strong anisotropy with the preferred direction nearly perpendicular to that for the electric field. This result implies the existence of strong electric currents flowing in the direction perpendicular to the above preferred direction for the magnetic field. The present method was also applied to the horizontal components of magnetic field variations observed at the seafloor. In this case, a magnetic observatory on land was taken as the reference station, and attenuation of the amplitude of horizontal magnetic field variation was examined. Anisotropy in attenuation was then found with the preferred direction perpendicular to the axis of the Okinawa trough where the seafloor measurement was undertaken.

An abnormal periventricular magnetization transfer ratio gradient occurs early in multiple sclerosis.

PubMed

Brown, J William L; Pardini, Matteo; Brownlee, Wallace J; Fernando, Kryshani; Samson, Rebecca S; Prados Carrasco, Ferran; Ourselin, Sebastien; Gandini Wheeler-Kingshott, Claudia A M; Miller, David H; Chard, Declan T

2017-02-01

In established multiple sclerosis, tissue abnormality-as assessed using magnetization transfer ratio-increases close to the lateral ventricles. We aimed to determine whether or not (i) these changes are present from the earliest clinical stages of multiple sclerosis; (ii) they occur independent of white matter lesions; and (iii) they are associated with subsequent conversion to clinically definite multiple sclerosis and disability. Seventy-one subjects had MRI scanning a median of 4.6 months after a clinically isolated optic neuritis (49 females, mean age 33.5 years) and were followed up clinically 2 and 5 years later. Thirty-seven healthy controls (25 females, mean age 34.4 years) were also scanned. In normal-appearing white matter, magnetization transfer ratio gradients were measured 1-5 mm and 6-10 mm from the lateral ventricles. In control subjects, magnetization transfer ratio was highest adjacent to the ventricles and decreased with distance from them; in optic neuritis, normal-appearing white matter magnetization transfer ratio was lowest adjacent to the ventricles, increased over the first 5 mm, and then paralleled control values. The magnetization transfer ratio gradient over 1-5 mm differed significantly between the optic neuritis and control groups [+0.059 percentage units/mm (pu/mm) versus -0.033 pu/mm, P = 0.010], and was significantly steeper in those developing clinically definite multiple sclerosis within 2 years compared to those who did not (0.132 pu/mm versus 0.016 pu/mm, P = 0.020). In multivariate binary logistic regression the magnetization transfer ratio gradient was independently associated with the development of clinically definite multiple sclerosis within 2 years (magnetization transfer ratio gradient odds ratio 61.708, P = 0.023; presence of T 2 lesions odds ratio 8.500, P = 0.071). At 5 years, lesional measures overtook magnetization transfer ratio gradients as significant predictors of conversion to multiple sclerosis. The magnetization transfer ratio gradient was not significantly affected by the presence of brain lesions [T 2 lesions (P = 0.918), periventricular T 2 lesions (P = 0.580) or gadolinium-enhancing T 1 lesions (P = 0.724)]. The magnetization transfer ratio gradient also correlated with Expanded Disability Status Scale score 5 years later (Spearman r = 0.313, P = 0.027). An abnormal periventricular magnetization transfer ratio gradient occurs early in multiple sclerosis, is clinically relevant, and may arise from one or more mechanisms that are at least partly independent of lesion formation. © The Author (2016). Published by Oxford University Press on behalf of the Guarantors of Brain. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

An abnormal periventricular magnetization transfer ratio gradient occurs early in multiple sclerosis

PubMed Central

Brown, J William L; Pardini, Matteo; Brownlee, Wallace J; Fernando, Kryshani; Samson, Rebecca S; Prados Carrasco, Ferran; Ourselin, Sebastien; Gandini Wheeler-Kingshott, Claudia A M; Miller, David H; Chard, Declan T

2017-01-01

Abstract In established multiple sclerosis, tissue abnormality—as assessed using magnetization transfer ratio—increases close to the lateral ventricles. We aimed to determine whether or not (i) these changes are present from the earliest clinical stages of multiple sclerosis; (ii) they occur independent of white matter lesions; and (iii) they are associated with subsequent conversion to clinically definite multiple sclerosis and disability. Seventy-one subjects had MRI scanning a median of 4.6 months after a clinically isolated optic neuritis (49 females, mean age 33.5 years) and were followed up clinically 2 and 5 years later. Thirty-seven healthy controls (25 females, mean age 34.4 years) were also scanned. In normal-appearing white matter, magnetization transfer ratio gradients were measured 1–5 mm and 6–10 mm from the lateral ventricles. In control subjects, magnetization transfer ratio was highest adjacent to the ventricles and decreased with distance from them; in optic neuritis, normal-appearing white matter magnetization transfer ratio was lowest adjacent to the ventricles, increased over the first 5 mm, and then paralleled control values. The magnetization transfer ratio gradient over 1–5 mm differed significantly between the optic neuritis and control groups [+0.059 percentage units/mm (pu/mm) versus −0.033 pu/mm, P = 0.010], and was significantly steeper in those developing clinically definite multiple sclerosis within 2 years compared to those who did not (0.132 pu/mm versus 0.016 pu/mm, P = 0.020). In multivariate binary logistic regression the magnetization transfer ratio gradient was independently associated with the development of clinically definite multiple sclerosis within 2 years (magnetization transfer ratio gradient odds ratio 61.708, P = 0.023; presence of T2 lesions odds ratio 8.500, P = 0.071). At 5 years, lesional measures overtook magnetization transfer ratio gradients as significant predictors of conversion to multiple sclerosis. The magnetization transfer ratio gradient was not significantly affected by the presence of brain lesions [T2 lesions (P = 0.918), periventricular T2 lesions (P = 0.580) or gadolinium-enhancing T1 lesions (P = 0.724)]. The magnetization transfer ratio gradient also correlated with Expanded Disability Status Scale score 5 years later (Spearman r = 0.313, P = 0.027). An abnormal periventricular magnetization transfer ratio gradient occurs early in multiple sclerosis, is clinically relevant, and may arise from one or more mechanisms that are at least partly independent of lesion formation. PMID:28043954

Magnetization reversal in ferromagnetic thin films induced by spin-orbit interaction with Slonczewski-like spin transfer torque

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

Li, Jia, E-mail: lijia@wipm.ac.cn

2014-10-07

We theoretically investigate the dynamics of magnetization in ferromagnetic thin films induced by spin-orbit interaction with Slonczewski-like spin transfer torque. We reproduce the experimental results of perpendicular magnetic anisotropy films by micromagnetic simulation. Due to the spin-orbit interaction, the magnetization can be switched by changing the direction of the current with the assistant of magnetic field. By increasing the current amplitude, wider range of switching events can be achieved. Time evolution of magnetization has provided us a clear view of the process, and explained the role of minimum external field. Slonczewski-like spin transfer torque modifies the magnetization when current ismore » present. The magnitude of the minimum external field is determined by the strength of the Slonczewski-like spin transfer torque. The investigations may provide potential applications in magnetic memories.« less

Force Balance at the Magnetopause Determined with MMS: Application to Flux Transfer Events

NASA Technical Reports Server (NTRS)

Zhao, C.; Russell, C. T.; Strangeway, R. J.; Petrinec, S. M.; Paterson, W. R.; Zhou, M.; Anderson, B. J.; Baumjohann, W.; Bromund, K. R.; Chutter, M.;

Noninvasive amide proton transfer magnetic resonance imaging in evaluating the grading and cellularity of gliomas.

PubMed

Bai, Yan; Lin, Yusong; Zhang, Wei; Kong, Lingfei; Wang, Lifu; Zuo, Panli; Vallines, Ignacio; Schmitt, Benjamin; Tian, Jie; Song, Xiaolei; Zhou, Jinyuan; Wang, Meiyun

2017-01-24

Using noninvasive magnetic resonance imaging techniques to accurately evaluate the grading and cellularity of gliomas is beneficial for improving the patient outcomes. Amide proton transfer imaging is a noninvasive molecular magnetic resonance imaging technique based on chemical exchange saturation transfer mechanism that detects endogenous mobile proteins and peptides in biological tissues. Between August 2012 and November 2015, a total number of 44 patients with pathologically proven gliomas were included in this study. We compared the capability of amide proton transfer magnetic resonance imaging with that of noninvasive diffusion-weighted imaging and noninvasive 3-dimensional pseudo-continuous arterial spin imaging in evaluating the grading and cellularity of gliomas. Our results reveal that amide proton transfer magnetic resonance imaging is a superior imaging technique to diffusion-weighted imaging and 3-dimensional pseudo-continuous arterial spin imaging in the grading of gliomas. In addition, our results showed that the Ki-67 index correlated better with the amide proton transfer-weighted signal intensity than with the apparent diffusion coefficient value or the cerebral blood flow value in the gliomas. Amide proton transfer magnetic resonance imaging is a promising method for predicting the grading and cellularity of gliomas.

Stability phase diagram of a perpendicular magnetic tunnel junction in noncollinear geometry

NASA Astrophysics Data System (ADS)

Strelkov, N.; Timopheev, A.; Sousa, R. C.; Chshiev, M.; Buda-Prejbeanu, L. D.; Dieny, B.

2017-05-01

Experimental measurements performed on MgO-based perpendicular magnetic tunnel junctions show a strong dependence of the stability voltage-field diagrams as a function of the direction of the magnetic field with respect to the plane of the sample. When the magnetic field is applied in-plane, systematic nonlinear phase boundaries are observed for various lateral sizes. The simulation results based on the phenomenological Landau-Lifshitz-Gilbert equation including the in-plane and out-of-plane spin transfer torques are consistent with the measurements if a second-order anisotropy contribution is considered. Furthermore, performing the stability analysis in linear approximation allowed us to analytically extract the critical switching voltage at zero temperature in the presence of an in-plane field. This study indicates that in the noncollinear geometry investigations are suitable to detect the presence of the second-order term in the anisotropy. Such higher order anisotropy term can yield an easy-cone anisotropy which reduces the thermal stability factor but allows for more reproducible spin transfer torque switching due to a reduced stochasticity of the switching. As a result, the energy per write event decreases much faster than the thermal stability factor as the second-order anisotropy becomes more negative. Easy-cone anisotropy can be useful for fast-switching spin transfer torque magnetic random access memories provided the thermal stability can be maintained above the required value for a given memory specification.

Spatial and Temporal Signatures of Flux Transfer Events in Global Simulations of Magnetopause Dynamics

NASA Technical Reports Server (NTRS)

Kuznetsova, Maria M.; Sibeck, David Gary; Hesse, Michael; Berrios, David; Rastaetter, Lutz; Toth, Gabor; Gombosi, Tamas I.

2011-01-01

Flux transfer events (FTEs) were originally identified by transient bipolar variations of the magnetic field component normal to the nominal magnetopause centered on enhancements in the total magnetic field strength. Recent Cluster and THEMIS multi-point measurements provided a wide range of signatures that are interpreted as evidence for FTE passage (e.g., crater FTE's, traveling magnetic erosion regions). We use the global magnetohydrodynamic (MHD) code BATS-R-US developed at the University of Michigan to model the global three-dimensional structure and temporal evolution of FTEs during multi-spacecraft magnetopause crossing events. Comparison of observed and simulated signatures and sensitivity analysis of the results to the probe location will be presented. We will demonstrate a variety of observable signatures in magnetic field profile that depend on space probe location with respect to the FTE passage. The global structure of FTEs will be illustrated using advanced visualization tools developed at the Community Coordinated Modeling Center

On the inverse transfer of (non-)helical magnetic energy in a decaying magnetohydrodynamic turbulence

NASA Astrophysics Data System (ADS)

Park, Kiwan

2017-12-01

In our conventional understanding, large-scale magnetic fields are thought to originate from an inverse cascade in the presence of magnetic helicity, differential rotation or a magneto-rotational instability. However, as recent simulations have given strong indications that an inverse cascade (transfer) may occur even in the absence of magnetic helicity, the physical origin of this inverse cascade is still not fully understood. We here present two simulations of freely decaying helical and non-helical magnetohydrodynamic (MHD) turbulence. We verified the inverse transfer of helical and non-helical magnetic fields in both cases, but we found the underlying physical principles to be fundamentally different. In the former case, the helical magnetic component leads to an inverse cascade of magnetic energy. We derived a semi-analytic formula for the evolution of large-scale magnetic field using α coefficient and compared it with the simulation data. But in the latter case, the α effect, including other conventional dynamo theories, is not suitable to describe the inverse transfer of non-helical magnetic energy. To obtain a better understanding of the physics at work here, we introduced a 'field structure model' based on the magnetic induction equation in the presence of inhomogeneities. This model illustrates how the curl of the electromotive force leads to the build up of a large-scale magnetic field without the requirement of magnetic helicity. And we applied a quasi-normal approximation to the inverse transfer of magnetic energy.

Experimental study on heat transfer enhancement of laminar ferrofluid flow in horizontal tube partially filled porous media under fixed parallel magnet bars

NASA Astrophysics Data System (ADS)

Sheikhnejad, Yahya; Hosseini, Reza; Saffar Avval, Majid

2017-02-01

In this study, steady state laminar ferroconvection through circular horizontal tube partially filled with porous media under constant heat flux is experimentally investigated. Transverse magnetic fields were applied on ferrofluid flow by two fixed parallel magnet bar positioned on a certain distance from beginning of the test section. The results show promising notable enhancement in heat transfer as a consequence of partially filled porous media and magnetic field, up to 2.2 and 1.4 fold enhancement were observed in heat transfer coefficient respectively. It was found that presence of both porous media and magnetic field simultaneously can highly improve heat transfer up to 2.4 fold. Porous media of course plays a major role in this configuration. Virtually, application of Magnetic field and porous media also insert higher pressure loss along the pipe which again porous media contribution is higher that magnetic field.

Field-cycling NMR experiments in an ultra-wide magnetic field range: relaxation and coherent polarization transfer.

PubMed

Zhukov, Ivan V; Kiryutin, Alexey S; Yurkovskaya, Alexandra V; Grishin, Yuri A; Vieth, Hans-Martin; Ivanov, Konstantin L

2018-05-09

An experimental method is described allowing fast field-cycling Nuclear Magnetic Resonance (NMR) experiments over a wide range of magnetic fields from 5 nT to 10 T. The method makes use of a hybrid technique: the high field range is covered by positioning the sample in the inhomogeneous stray field of the NMR spectrometer magnet. For fields below 2 mT a magnetic shield is mounted on top of the spectrometer; inside the shield the magnetic field is controlled by a specially designed coil system. This combination allows us to measure T1-relaxation times and nuclear Overhauser effect parameters over the full range in a routine way. For coupled proton-carbon spin systems relaxation with a common T1 is found at low fields, where the spins are "strongly coupled". In some cases, experiments at ultralow fields provide access to heteronuclear long-lived spin states. Efficient coherent polarization transfer is seen for proton-carbon spin systems at ultralow fields as follows from the observation of quantum oscillations in the polarization evolution. Applications to analysis and the manipulation of heteronuclear spin systems are discussed.

Thermal-hydraulic analysis of the coil test facility for CFETR.

PubMed

Ren, Yong; Liu, Xiaogang; Li, Junjun; Wang, Zhaoliang; Qiu, Lilong; Du, Shijun; Li, Guoqiang; Gao, Xiang

2016-01-01

Performance test of the China Fusion Engineering Test Reactor (CFETR) central solenoid (CS) and toroidal field (TF) insert coils is of great importance to evaluate the CFETR magnet performance in relevant operation conditions. The superconducting magnet of the coil test facility for CFETR is being designed with the aim of providing a background magnetic field to test the CFETR CS insert and TF insert coils. The superconducting magnet consists of the inner module with Nb 3 Sn coil and the outer module with NbTi coil. The superconducting magnet is designed to have a maximum magnetic field of 12.59 T and a stored energy of 436.6 MJ. An active quench protection circuit and the positive temperature coefficient dump resistor were adopted to transfer the stored magnetic energy. The temperature margin behavior of the test facility for CFETR satisfies the design criteria. The quench analysis of the test facility shows that the cable temperature and the helium pressure inside the jacket are within the design criteria.

T1, diffusion tensor, and quantitative magnetization transfer imaging of the hippocampus in an Alzheimer's disease mouse model.

PubMed

Whittaker, Heather T; Zhu, Shenghua; Di Curzio, Domenico L; Buist, Richard; Li, Xin-Min; Noy, Suzanna; Wiseman, Frances K; Thiessen, Jonathan D; Martin, Melanie

2018-07-01

Alzheimer's disease (AD) pathology causes microstructural changes in the brain. These changes, if quantified with magnetic resonance imaging (MRI), could be studied for use as an early biomarker for AD. The aim of our study was to determine if T 1 relaxation, diffusion tensor imaging (DTI), and quantitative magnetization transfer imaging (qMTI) metrics could reveal changes within the hippocampus and surrounding white matter structures in ex vivo transgenic mouse brains overexpressing human amyloid precursor protein with the Swedish mutation. Delineation of hippocampal cell layers using DTI color maps allows more detailed analysis of T 1 -weighted imaging, DTI, and qMTI metrics, compared with segmentation of gross anatomy based on relaxation images, and with analysis of DTI or qMTI metrics alone. These alterations are observed in the absence of robust intracellular Aβ accumulation or plaque deposition as revealed by histology. This work demonstrates that multiparametric quantitative MRI methods are useful for characterizing changes within the hippocampal substructures and surrounding white matter tracts of mouse models of AD. Copyright © 2018. Published by Elsevier Inc.

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.

A quantitative study of ramped radio frequency, magnetization transfer, and slab thickness in three-dimensional time-of-flight magnetic resonance angiography in a patient population.

PubMed

Goodrich, K C; Blatter, D D; Parker, D L; Du, Y P; Meyer, K J; Bernstein, M A

1996-06-01

The authors compare the effectiveness of various magnetic resonance (MR) angiography acquisition strategies in enhancing the visibility of small intracranial vessels. Blood vessel contrast-to-noise ratio (CNR) in time-of-flight MR angiography was studied as a function of vessel size and several selectable imaging parameters. Contrast-to-noise measurements were made on 257 vessel segments ranging in size from 0.3 mm to 4.2 mm in patients who recently had undergone intraarterial cerebral angiography. Imaging parameters studied included magnetization transfer, spatially variable radio frequency (RF) pulse profile (ramped RF), and imaging slab thickness. The combination of thin slabs (16 slices/slab), ramped RF, and magnetization transfer resulted in the highest CNR for all but the smallest vessel sizes. The smallest vessels (< 0.5 mm) had the highest CNR, using the thick slab (64 slices/slab) with ramped RF and magnetization transfer. Magnetization transfer always improved vessel CNR, but the improvement diminished as the slab thickness was reduced. The CNR increased with a decrease in slab thickness for all but the smallest vessel sizes. Overall, the results provide a quantitative demonstration that inflow enhancement of blood is reduced for small vessels. Thus, whereas magnetization transfer is important at all vessel sizes, it becomes the primary factor in improving the visibility of the smallest vessels.

Training Efficiency and Transfer Success in an Extended Real-Time Functional MRI Neurofeedback Training of the Somatomotor Cortex of Healthy Subjects

PubMed Central

Auer, Tibor; Schweizer, Renate; Frahm, Jens

2015-01-01

This study investigated the level of self-regulation of the somatomotor cortices (SMCs) attained by an extended functional magnetic resonance imaging (fMRI) neurofeedback training. Sixteen healthy subjects performed 12 real-time functional magnetic resonance imaging neurofeedback training sessions within 4 weeks, involving motor imagery of the dominant right as well as the non-dominant left hand. Target regions of interests in the SMC were individually localized prior to the training by overt finger movements. The feedback signal (FS) was defined as the difference between fMRI activation in the contra- and ipsilateral SMC and visually presented to the subjects. Training efficiency was determined by an off-line general linear model analysis determining the fMRI percent signal changes in the SMC target areas accomplished during the neurofeedback training. Transfer success was assessed by comparing the pre- and post-training transfer task, i.e., the neurofeedback paradigm without the presentation of the FS. Group results show a distinct increase in feedback performance (FP) in the transfer task for the trained group compared to a matched untrained control group, as well as an increase in the time course of the training, indicating an efficient training and a successful transfer. Individual analysis revealed that the training efficiency was not only highly correlated to the transfer success but also predictive. Trainings with at least 12 efficient training runs were associated with a successful transfer outcome. A group analysis of the hemispheric contributions to the FP showed that it is mainly driven by increased fMRI activation in the contralateral SMC, although some individuals relied on ipsilateral deactivation. Training and transfer results showed no difference between left- and right-hand imagery, with a slight indication of more ipsilateral deactivation in the early right-hand trainings. PMID:26500521

Confirmation of quasi-static approximation in SAR evaluation for a wireless power transfer system.

PubMed

Hirata, Akimasa; Ito, Fumihiro; Laakso, Ilkka

2013-09-07

The present study discusses the applicability of the magneto-quasi-static approximation to the calculation of the specific absorption rate (SAR) in a cylindrical model for a wireless power transfer system. Resonant coils with different parameters were considered in the 10 MHz band. A two-step quasi-static method that is comprised of the method of moments and the scalar-potential finite-difference methods is applied, which can consider the effects of electric and magnetic fields on the induced SAR separately. From our computational results, the SARs obtained from our quasi-static method are found to be in good agreement with full-wave analysis for different positions of the cylindrical model relative to the wireless power transfer system, confirming the applicability of the quasi-static approximation in the 10 MHz band. The SAR induced by the external electric field is found to be marginal as compared to that induced by the magnetic field. Thus, the dosimetry for the external magnetic field, which may be marginally perturbed by the presence of biological tissue, is confirmed to be essential for SAR compliance in the 10 MHz band or lower. This confirmation also suggests that the current in the coil rather than the transferred power is essential for SAR compliance.

Optimization of magnetization transfer measurements: statistical analysis by stochastic simulation. Application to creatine kinase kinetics.

PubMed

Rydzy, M; Deslauriers, R; Smith, I C; Saunders, J K

1990-08-01

A systematic study was performed to optimize the accuracy of kinetic parameters derived from magnetization transfer measurements. Three techniques were investigated: time-dependent saturation transfer (TDST), saturation recovery (SRS), and inversion recovery (IRS). In the last two methods, one of the resonances undergoing exchange is saturated throughout the experiment. The three techniques were compared with respect to the accuracy of the kinetic parameters derived from experiments performed in a given, fixed, amount of time. Stochastic simulation of magnetization transfer experiments was performed to optimize experimental design. General formulas for the relative accuracies of the unidirectional rate constant (k) were derived for each of the three experimental methods. It was calculated that for k values between 0.1 and 1.0 s-1, T1 values between 1 and 10 s, and relaxation delays appropriate for the creatine kinase reaction, the SRS method yields more accurate values of k than does the IRS method. The TDST method is more accurate than the SRS method for reactions where T1 is long and k is large, within the range of k and T1 values examined. Experimental verification of the method was carried out on a solution in which the forward (PCr----ATP) rate constant (kf) of the creatine kinase reaction was measured.

Effect of Longitudinal Magnetic Field on Vibration Characteristics of Single-Walled Carbon Nanotubes in a Viscoelastic Medium

NASA Astrophysics Data System (ADS)

Zhang, D. P.; Lei, Y.; Shen, Z. B.

2017-12-01

The effect of longitudinal magnetic field on vibration response of a sing-walled carbon nanotube (SWCNT) embedded in viscoelastic medium is investigated. Based on nonlocal Euler-Bernoulli beam theory, Maxwell's relations, and Kelvin viscoelastic foundation model, the governing equations of motion for vibration analysis are established. The complex natural frequencies and corresponding mode shapes in closed form for the embedded SWCNT with arbitrary boundary conditions are obtained using transfer function method (TFM). The new analytical expressions for the complex natural frequencies are also derived for certain typical boundary conditions and Kelvin-Voigt model. Numerical results from the model are presented to show the effects of nonlocal parameter, viscoelastic parameter, boundary conditions, aspect ratio, and strength of the magnetic field on vibration characteristics for the embedded SWCNT in longitudinal magnetic field. The results demonstrate the efficiency of the proposed methods for vibration analysis of embedded SWCNTs under magnetic field.

Numerical analysis of the shifting slabs applied in a wireless power transfer system to enhance magnetic coupling

NASA Astrophysics Data System (ADS)

Dong, Yayun; Yang, Xijun; Jin, Nan; Li, Wenwen; Yao, Chen; Tang, Houjun

2017-05-01

Shifting medium is a kind of metamaterial, which can optically shift a space or an object a certain distance away from its original position. Based on the shifting medium, we propose a concise pair of shifting slabs covering the transmitting or receiving coil in a two-coil wireless power transfer system to decrease the equivalent distance between the coils. The electromagnetic parameters of the shifting slabs are calculated by transformation optics. Numerical simulations validate that the shifting slabs can approximately shift the electromagnetic fields generated by the covered coil; thus, the magnetic coupling and the efficiency of the system are enhanced while remaining the physical transmission distance unchanged. We also verify the advantages of the shifting slabs over the magnetic superlens. Finally, we provide two methods to fabricate shifting slabs based on split-ring resonators.

Effect of polarized radiative transfer on the Hanle magnetic field determination in prominences: Analysis of hydrogen H alpha line observations at Pic-du-Midi

NASA Technical Reports Server (NTRS)

Bommier, V.; Deglinnocenti, E. L.; Leroy, J. L.; Sahal-Brechot, S.

1985-01-01

The linear polarization of the Hydrogen H alpha line of prominences has been computed, taking into account the effect of a magnetic field (Hanle effect), of the radiative transfer in the prominence, and of the depolarization due to collisions with the surrounding electrons and protons. The corresponding formalisms are developed in a forthcoming series of papers. In this paper, the main features of the computation method are summarized. The results of computation have been used for interpretation in terms of magnetic field vector measurements from H alpha polarimetric observations in prominences performed at Pic-du-Midi coronagraph-polarimeter. Simultaneous observations in one optically thin line (He I D(3)) and one optically thick line (H alpha) give an opportunity for solving the ambiguity on the field vector determination.

A numerical analysis for non-linear radiation in MHD flow around a cylindrical surface with chemically reactive species

NASA Astrophysics Data System (ADS)

Khan, Junaid Ahmad; Mustafa, M.

2018-03-01

Boundary layer flow around a stretchable rough cylinder is modeled by taking into account boundary slip and transverse magnetic field effects. The main concern is to resolve heat/mass transfer problem considering non-linear radiative heat transfer and temperature/concentration jump aspects. Using conventional similarity approach, the equations of motion and heat transfer are converted into a boundary value problem whose solution is computed by shooting method for broad range of slip coefficients. The proposed numerical scheme appears to improve as the strengths of magnetic field and slip coefficients are enhanced. Axial velocity and temperature are considerably influenced by a parameter M which is inversely proportional to the radius of cylinder. A significant change in temperature profile is depicted for growing wall to ambient temperature ratio. Relevant physical quantities such as wall shear stress, local Nusselt number and local Sherwood number are elucidated in detail.

A computational study of entropy generation in magnetohydrodynamic flow and heat transfer over an unsteady stretching permeable sheet

NASA Astrophysics Data System (ADS)

Saeed Butt, Adnan; Ali, Asif

2014-01-01

The present article aims to investigate the entropy effects in magnetohydrodynamic flow and heat transfer over an unsteady permeable stretching surface. The time-dependent partial differential equations are converted into non-linear ordinary differential equations by suitable similarity transformations. The solutions of these equations are computed analytically by the Homotopy Analysis Method (HAM) then solved numerically by the MATLAB built-in routine. Comparison of the obtained results is made with the existing literature under limiting cases to validate our study. The effects of unsteadiness parameter, magnetic field parameter, suction/injection parameter, Prandtl number, group parameter and Reynolds number on flow and heat transfer characteristics are checked and analysed with the aid of graphs and tables. Moreover, the effects of these parameters on entropy generation number and Bejan number are also shown graphically. It is examined that the unsteadiness and presence of magnetic field augments the entropy production.

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

Miller, John M.; Onar, Omer C.; Chinthavali, Madhu

Various noncontacting methods of plug-in electric vehicle charging are either under development or now deployed as aftermarket options in the light-duty automotive market. Wireless power transfer (WPT) is now the accepted term for wireless charging and is used synonymously for inductive power transfer and magnetic resonance coupling. WPT technology is in its infancy; standardization is lacking, especially on interoperability, center frequency selection, magnetic fringe field suppression, and the methods employed for power flow regulation. This paper proposes a new analysis concept for power flow in WPT in which the primary provides frequency selection and the tuned secondary, with its resemblancemore » to a power transmission network having a reactive power voltage control, is analyzed as a transmission network. Analysis is supported with experimental data taken from Oak Ridge National Laboratory s WPT apparatus. Lastly, this paper also provides an experimental evidence for frequency selection, fringe field assessment, and the need for low-latency communications in the feedback path.« less

Gating heat transport by manipulating convection in a magnetic nanofluid

NASA Astrophysics Data System (ADS)

Seshadri, Indira; Gardner, Alex; Mehta, Rutvik J.; Swartwout, Richard; Keblinski, Pawel; Borca-Tasciuc, Theo; Ramanath, Ganpati

2013-05-01

Gating thermal transport is a key requirement in smart heat exchangers used in a variety of applications such as electronics and energy generation. Here, we demonstrate a high on-off ratio thermal valve using magnetic nanofluids actuated by a non-uniform magnetic field. Using nanofluids comprised of magnetic nanoparticles in paraffin oil, we obtain on-off ratios as high as 16, which is more than 5-fold higher than that seen in comparable nanofluids with uniform magnetic fields. Analysis of these results using heat transfer modeling shows that the remarkable enhancement arises from magneto-thermally activated convection due to field gradients. Such convective thermal gating could be promising for applications.

Screening and Monitoring Response to Treatment Using Subsecond Molecular Imaging and Hyperpolarized Contrast Agents

DTIC Science & Technology

2013-05-01

Magnetization transfer MRI in multiple sclerosis . J Neuroimaging. 2007;17 Suppl 1:S22–S26. 82. Filippi M, Rocca MA. Magnetization transfer magnetic resonance... multiple sclerosis . Neuroimaging Clin N Am. 2009;19(1):27–36. 84. Lundbom N. Determination of magnetization transfer contrast in tissue: an MR... multiple RF coils intended for optimal direct and indirect detection of hyperpolarized contrast agents in vivo. 4.b. Y1Q3-Y1Q4. Low field MRI: pre

Evidence for Coherent Transfer of para-Hydrogen-Induced Polarization at Low Magnetic Fields.

PubMed

Kiryutin, Alexey S; Yurkovskaya, Alexandra V; Kaptein, Robert; Vieth, Hans-Martin; Ivanov, Konstantin L

2013-08-01

We have investigated the mechanism of para-hydrogen-induced polarization (PHIP) transfer from the original strongly aligned protons to other nuclei at low external magnetic fields. Although it is known that PHIP is efficiently transferred at low fields, the nature of the transfer mechanism, that is, coherent spin mixing or cross-relaxation, is not well established. Polarization transfer kinetics for individual protons of styrene was, for the first time, measured and modeled theoretically. Pronounced oscillations were observed indicating a coherent transfer mechanism. Spin coherences were excited by passing through an avoided level crossing of the nuclear spin energy levels. Transfer at avoided level crossings is selective with respect to spin order. Our work provides evidence that the coherent PHIP transfer mechanism is dominant at low magnetic fields.

Analysis of in situ electric field and specific absorption rate in human models for wireless power transfer system with induction coupling.

PubMed

Sunohara, Tetsu; Hirata, Akimasa; Laakso, Ilkka; Onishi, Teruo

2014-07-21

This study investigates the specific absorption rate (SAR) and the in situ electric field in anatomically based human models for the magnetic field from an inductive wireless power transfer system developed on the basis of the specifications of the wireless power consortium. The transfer system consists of two induction coils covered by magnetic sheets. Both the waiting and charging conditions are considered. The transfer frequency considered in this study is 140 kHz, which is within the range where the magneto-quasi-static approximation is valid. The SAR and in situ electric field in the chest and arm of the models are calculated by numerically solving the scalar potential finite difference equation. The electromagnetic modelling of the coils in the wireless power transfer system is verified by comparing the computed and measured magnetic field distributions. The results indicate that the peak value of the SAR averaged over a 10 g of tissue and that of the in situ electric field are 72 nW kg(-1) and 91 mV m(-1) for a transmitted power of 1 W, Consequently, the maximum allowable transmitted powers satisfying the exposure limits of the SAR (2 W kg(-1)) and the in situ electric field (18.9 V m(-1)) are found to be 28 MW and 43 kW. The computational results show that the in situ electric field in the chest is the most restrictive factor when compliance with the wireless power transfer system is evaluated according to international guidelines.

A survey of flux transfer events observed in the dayside magnetopause

NASA Astrophysics Data System (ADS)

Silveira, M. D.; Sibeck, D. G.; Lee, S. H.; Gonzalez, W.; Koga, D.

2017-12-01

Flux transfer events (FTE) have been interpreted to be results from transient magnetic reconnection and can be observed in the vicinity of the Earth's magnetopause, as well in other planets. FTE acts as a flux tube connecting the magnetosheath to the magnetosphere allowing the transference of particles, energy and momentum in both sides magnetopause. Their main signatures in satellite data are bipolar variation in the magnetic field component normal to the magnetopause, centered in an enhanced magnetic field strength. Other signatures such as pressure imbalance, bulk flow jets, and particle anisotropy distribution can be observed inside the those structures. We surveyed FTEs observed by MMS on the vicinity of the magnetopause (from x = 0 to 13Re and y = -12 to 12Re). Taking advantage of the MMS tetrahedron configuration we will employed timing analysis to determine the FTEs direction of motion and scale lengths. We will present information about occurrence related with IMF clock angle and other parameters, amplitude of the perturbations induced by the FTEs in the environment magnetic field and plasma; characteristic time and structure scale size. Using data from ACE, Wind and Artemis we can evaluate which is the best solar wind monitor for each FTE observed and then employ the appropriated lag time corresponding to FTE location and magnetic field orientation. The objective is to investigate the mechanisms of generation of FTEs comparing characteristics of the events observed on the dayside region and on the magnetopause flanks determining the motion and speed of FTEs.

Spectral Estimation Techniques for time series with Long Gaps: Applications to Paleomagnetism and Geomagnetic Depth Sounding

NASA Astrophysics Data System (ADS)

Smith-Boughner, Lindsay

Many Earth systems cannot be studied directly. One cannot measure the velocities of convecting fluid in the Earth's core but can measure the magnetic field generated by these motions on the surface. Examining how the magnetic field changes over long periods of time, using power spectral density estimation provides insight into the dynamics driving the system. The changes in the magnetic field can also be used to study Earth properties - variations in magnetic fields outside of Earth like the ring-current induce currents to flow in the Earth, generating magnetic fields. Estimating the transfer function between the external changes and the induced response characterizes the electromagnetic response of the Earth. From this response inferences can be made about the electrical conductivity of the Earth. However, these types of time series, and many others have long breaks in the record with no samples available and limit the analysis. Standard methods require interpolation or section averaging, with associated problems of introducing bias or reducing the frequency resolution. Extending the methods of Fodor and Stark (2000), who adapt a set of orthogonal multi-tapers to compensate for breaks in sampling- an algorithm and software package for applying these techniques is developed. Methods of empirically estimating the average transfer function of a set of tapers and confidence intervals are also tested. These methods are extended for cross-spectral, coherence and transfer function estimation in the presence of noise. With these methods, new analysis of a highly interrupted ocean sediment core from the Oligocene (Hartl et al., 1993) reveals a quasi-periodic signal in the calibrated paleointensity time series at 2.5 cpMy. The power in the magnetic field during this period appears to be dominated by reversal rate processes with less overall power than the early Oligocene. Previous analysis of the early Oligocene by Constable et al. (1998) detected a signal near 8 cpMy. These results suggest that a strong magnetic field inhibits reversals and has more variability in shorter term field changes. Using over 9 years of data from the CHAMP low-Earth orbiting magnetic satellite and the techniques developed here, more robust estimates of the electromagnetic response of the Earth can be made. The tapers adapted for gaps provide flexibility to study the effects of local time, storm conditions on Earth's 1-D electromagnetic response as well as providing robust estimates of the C-response at longer periods than previous satellite studies.

Studying the Transfer of Magnetic Helicity in Solar Active Regions with the Connectivity-based Helicity Flux Density Method

NASA Astrophysics Data System (ADS)

Dalmasse, K.; Pariat, É.; Valori, G.; Jing, J.; Démoulin, P.

2018-01-01

In the solar corona, magnetic helicity slowly and continuously accumulates in response to plasma flows tangential to the photosphere and magnetic flux emergence through it. Analyzing this transfer of magnetic helicity is key for identifying its role in the dynamics of active regions (ARs). The connectivity-based helicity flux density method was recently developed for studying the 2D and 3D transfer of magnetic helicity in ARs. The method takes into account the 3D nature of magnetic helicity by explicitly using knowledge of the magnetic field connectivity, which allows it to faithfully track the photospheric flux of magnetic helicity. Because the magnetic field is not measured in the solar corona, modeled 3D solutions obtained from force-free magnetic field extrapolations must be used to derive the magnetic connectivity. Different extrapolation methods can lead to markedly different 3D magnetic field connectivities, thus questioning the reliability of the connectivity-based approach in observational applications. We address these concerns by applying this method to the isolated and internally complex AR 11158 with different magnetic field extrapolation models. We show that the connectivity-based calculations are robust to different extrapolation methods, in particular with regard to identifying regions of opposite magnetic helicity flux. We conclude that the connectivity-based approach can be reliably used in observational analyses and is a promising tool for studying the transfer of magnetic helicity in ARs and relating it to their flaring activity.

Magnetic Shielding Design for Coupler of Wireless Electric Vehicle Charging Using Finite Element Analysis

NASA Astrophysics Data System (ADS)

Zhao, W. N.; Yang, X. J.; Yao, C.; Ma, D. G.; Tang, H. J.

2017-10-01

Inductive power transfer (IPT) is a practical and preferable method for wireless electric vehicle (EV) charging which proved to be safe, convenient and reliable. Due to the air gap between the magnetic coupler, the magnetic field coupling decreases and the magnetic leakage increases significantly compared to traditional transformer, and this may lead to the magnetic flux density around the coupler more than the safety limit for human. So magnetic shielding should be adding to the winding made from litz wire to enhance the magnetic field coupling effect in the working area and reduce magnetic field strength in non-working area. Magnetic shielding can be achieved by adding high-permeability material or high-conductivity material. For high-permeability material its magnetic reluctance is much lower than the surrounding air medium so most of the magnetic line goes through the high-permeability material rather than surrounding air. For high-conductivity material the eddy current in the material can produce reverse magnetic field to achieve magnetic shielding. This paper studies the effect of the two types of shielding material on coupler for wireless EV charging and designs combination shielding made from high-permeability material and high-conductivity material. The investigation of the paper is done with the help of finite element analysis.

Unusual negative permeability of single magnetic nanowire excited by the spin transfer torque effect

NASA Astrophysics Data System (ADS)

Han, Mangui; Zhou, Wu

2018-07-01

Due to the effect of spin transfer torque, negative imaginary parts of permeability (μ″ < 0) are reported in a ferromagnetic nanowire. It is found that negative μ″ values are resulted from the interaction of spin polarized conduction electrons with the spatially non-uniform distributed magnetic moments at both ends of nanowires. The results are well explained from the effect of spin transfer torque on the precession of magnetization under the excitation of both the pulsed magnetic field and static electric field.

ENERGY TRANSFERS IN THREE-FREQUENCY CIRCUITS WITH MAGNETIC COUPLING,

DTIC Science & Technology

core are studied. Rules are given to determine the type of nonlinear characteristic needed to make energy transfers possible for given frequency...combinations. General energy relations of the Manley Rowe type are discussed, examining the validity and limitations of these relations for the practical...case where the frequency ratios are not irrational. Examples of the use of the analysis are given for oscillators, subringers and amplifiers with a variety of frequency ratios. (Author)

Radially Magnetized Protoplanetary Disk: Vertical Profile

NASA Astrophysics Data System (ADS)

Russo, Matthew; Thompson, Christopher

2015-11-01

This paper studies the response of a thin accretion disk to an external radial magnetic field. Our focus is on protoplanetary disks (PPDs), which are exposed during their later evolution to an intense, magnetized wind from the central star. A radial magnetic field is mixed into a thin surface layer, wound up by the disk shear, and pushed downward by a combination of turbulent mixing and ambipolar and ohmic drift. The toroidal field reaches much greater strengths than the seed vertical field that is usually invoked in PPD models, even becoming superthermal. Linear stability analysis indicates that the disk experiences the magnetorotational instability (MRI) at a higher magnetization than a vertically magnetized disk when both the effects of ambipolar and Hall drift are taken into account. Steady vertical profiles of density and magnetic field are obtained at several radii between 0.06 and 1 AU in response to a wind magnetic field Br ˜ (10-4-10-2)(r/ AU)-2 G. Careful attention is given to the radial and vertical ionization structure resulting from irradiation by stellar X-rays. The disk is more strongly magnetized closer to the star, where it can support a higher rate of mass transfer. As a result, the inner ˜1 AU of a PPD is found to evolve toward lower surface density. Mass transfer rates around 10-8 M⊙ yr-1 are obtained under conservative assumptions about the MRI-generated stress. The evolution of the disk and the implications for planet migration are investigated in the accompanying paper.

Interaction transfer of silicon atoms forming Co silicide for Co/√(3)×√(3)R30°-Ag/Si(111) and related magnetic properties

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

Chang, Cheng-Hsun-Tony; Fu, Tsu-Yi; Tsay, Jyh-Shen, E-mail: jstsay@phy.ntnu.edu.tw

Combined scanning tunneling microscopy, Auger electron spectroscopy, and surface magneto-optic Kerr effect studies were employed to study the microscopic structures and magnetic properties for ultrathin Co/√(3)×√(3)R30°-Ag/Si(111). As the annealing temperature increases, the upward diffusion of Si atoms and formation of Co silicides occurs at temperature above 400 K. Below 600 K, the √(3)×√(3)R30°-Ag/Si(111) surface structure persists. We propose an interaction transferring mechanism of Si atoms across the √(3)×√(3)R30°-Ag layer. The upward transferred Si atoms react with Co atoms to form Co silicide. The step height across the edge of the island, a separation of 0.75 nm from the analysis of the 2 × 2 structure,more » and the calculations of the normalized Auger signal serve as strong evidences for the formation of CoSi{sub 2} at the interface. The interaction transferring mechanism for Si atoms enhances the possibility of interactions between Co and Si atoms. The smoothness of the surface is advantage for that the easy axis of magnetization for Co/√(3)×√(3)R30°-Ag/Si(111) is in the surface plane. This provides a possible way of growing flat magnetic layers on silicon substrate with controllable silicide formation and shows potential applications in spintronics devices.« less

Magnetic forces and localized resonances in electron transfer through quantum rings.

PubMed

Poniedziałek, M R; Szafran, B

2010-11-24

We study the current flow through semiconductor quantum rings. In high magnetic fields the current is usually injected into the arm of the ring preferred by classical magnetic forces. However, for narrow magnetic field intervals that appear periodically on the magnetic field scale the current is injected into the other arm of the ring. We indicate that the appearance of the anomalous-non-classical-current circulation results from Fano interference involving localized resonant states. The identification of the Fano interference is based on the comparison of the solution of the scattering problem with the results of the stabilization method. The latter employs the bound-state type calculations and allows us to extract both the energy of metastable states localized within the ring and the width of resonances by analysis of the energy spectrum of a finite size system as a function of its length. The Fano resonances involving states of anomalous current circulation become extremely narrow on both the magnetic field and energy scales. This is consistent with the orientation of the Lorentz force that tends to keep the electron within the ring and thus increases the lifetime of the electron localization within the ring. Absence of periodic Fano resonances in electron transfer probability through a quantum ring containing an elastic scatterer is also explained.

ARCADE IMPLOSION CAUSED BY A FILAMENT ERUPTION IN A FLARE

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

Wang, Juntao; Simões, P. J. A.; Fletcher, L.

Coronal implosions—the convergence motion of plasmas and entrained magnetic field in the corona due to a reduction in magnetic pressure—can help to locate and track sites of magnetic energy release or redistribution during solar flares and eruptions. We report here on the analysis of a well-observed implosion in the form of an arcade contraction associated with a filament eruption, during the C3.5 flare SOL2013-06-19T07:29. A sequence of events including the magnetic flux-rope instability and distortion, followed by a filament eruption and arcade implosion, lead us to conclude that the implosion arises from the transfer of magnetic energy from beneath the arcademore » as part of the global magnetic instability, rather than due to local magnetic energy dissipation in the flare. The observed net contraction of the imploding loops, which is found also in nonlinear force-free field extrapolations, reflects a permanent reduction of magnetic energy underneath the arcade. This event shows that, in addition to resulting in the expansion or eruption of an overlying field, flux-rope instability can also simultaneously implode an unopened field due to magnetic energy transfer. It demonstrates the “partial opening of the field” scenario, which is one of the ways in 3D to produce a magnetic eruption without violating the Aly–Sturrock hypothesis. In the framework of this observation, we also propose a unification of three main concepts for active region magnetic evolution, namely the metastable eruption model, the implosion conjecture, and the standard “CSHKP” flare model.« less

Energy transfer in compressible magnetohydrodynamic turbulence for isothermal self-gravitating fluids

NASA Astrophysics Data System (ADS)

Banerjee, Supratik; Kritsuk, Alexei G.

2018-02-01

Three-dimensional, compressible, magnetohydrodynamic turbulence of an isothermal, self-gravitating fluid is analyzed using two-point statistics in the asymptotic limit of large Reynolds numbers (both kinetic and magnetic). Following an alternative formulation proposed by Banerjee and Galtier [Phys. Rev. E 93, 033120 (2016), 10.1103/PhysRevE.93.033120; J. Phys. A: Math. Theor. 50, 015501 (2017), 10.1088/1751-8113/50/1/015501], an exact relation has been derived for the total energy transfer. This approach results in a simpler relation expressed entirely in terms of mixed second-order structure functions. The kinetic, thermodynamic, magnetic, and gravitational contributions to the energy transfer rate can be easily separated in the present form. By construction, the new formalism includes such additional effects as global rotation, the Hall term in the induction equation, etc. The analysis shows that solid-body rotation cannot alter the energy flux rate of compressible turbulence. However, the contribution of a uniform background magnetic field to the flux is shown to be nontrivial unlike in the incompressible case. Finally, the compressible, turbulent energy flux rate does not vanish completely due to simple alignments, which leads to a zero turbulent energy flux rate in the incompressible case.

Energy transfer in compressible magnetohydrodynamic turbulence for isothermal self-gravitating fluids.

PubMed

Banerjee, Supratik; Kritsuk, Alexei G

2018-02-01

Three-dimensional, compressible, magnetohydrodynamic turbulence of an isothermal, self-gravitating fluid is analyzed using two-point statistics in the asymptotic limit of large Reynolds numbers (both kinetic and magnetic). Following an alternative formulation proposed by Banerjee and Galtier [Phys. Rev. E 93, 033120 (2016)2470-004510.1103/PhysRevE.93.033120; J. Phys. A: Math. Theor. 50, 015501 (2017)1751-811310.1088/1751-8113/50/1/015501], an exact relation has been derived for the total energy transfer. This approach results in a simpler relation expressed entirely in terms of mixed second-order structure functions. The kinetic, thermodynamic, magnetic, and gravitational contributions to the energy transfer rate can be easily separated in the present form. By construction, the new formalism includes such additional effects as global rotation, the Hall term in the induction equation, etc. The analysis shows that solid-body rotation cannot alter the energy flux rate of compressible turbulence. However, the contribution of a uniform background magnetic field to the flux is shown to be nontrivial unlike in the incompressible case. Finally, the compressible, turbulent energy flux rate does not vanish completely due to simple alignments, which leads to a zero turbulent energy flux rate in the incompressible case.

Dynamics of intramolecular electron transfer reaction of FAD studied by magnetic field effects on transient absorption spectra.

PubMed

Murakami, Masaaki; Maeda, Kiminori; Arai, Tatsuo

2005-07-07

The kinetics of intermediates generated from intramolecular electron-transfer reaction by photo irradiation of the flavin adenine dinucleotide (FAD) molecule was studied by a magnetic field effect (MFE) on transient absorption (TA) spectra. Existence time of MFE and MFE action spectra have a strong dependence on the pH of solutions. The MFE action spectra have indicated the existence of interconversion between the radical pair and the cation form of the triplet excited state of flavin part. All rate constants of the triplet and the radical pair were determined by analysis of the MFE action spectra and decay kinetics of TA. The obtained values for the interconversion indicate that the formation of cation radical promotes the back electron-transfer reaction to the triplet excited state. Further, rate constants of spin relaxation and recombination have been studied by the time profiles of MFE at various pH. The drastic change of those two factors has been obtained and can be explained by SOC (spin-orbit coupling) induced back electron-transfer promoted by the formation of a stacking conformation at pH > 2.5.

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%.

Numerical investigation of MHD flow of blood and heat transfer in a stenosed arterial segment

NASA Astrophysics Data System (ADS)

Majee, Sreeparna; Shit, G. C.

2017-02-01

A numerical investigation of unsteady flow of blood and heat transfer has been performed with an aim to provide better understanding of blood flow through arteries under stenotic condition. The blood is treated as Newtonian fluid and the arterial wall is considered to be rigid having deposition of plaque in its lumen. The heat transfer characteristic has been analyzed by taking into consideration of the dissipation of energy due to applied magnetic field and the viscosity of blood. The vorticity-stream function formulation has been adopted to solve the problem using implicit finite difference method by developing well known Peaceman-Rachford Alternating Direction Implicit (ADI) scheme. The quantitative profile analysis of velocity, temperature and wall shear stress as well as Nusselt number is carried out over the entire arterial segment. The streamline and temperature contours have been plotted to understand the flow pattern in the diseased artery, which alters significantly in the downstream of the stenosis in the presence of magnetic field. Both the wall shear stress and Nusselt number increases with increasing magnetic field strength. However, wall shear stress decreases and Nusselt number enhances with Reynolds number. The results show that with an increase in the magnetic field strength upto 8 T, does not causes any damage to the arterial wall, but the study is significant for assessing temperature rise during hyperthermic treatment.

Preparation of magnetic molecularly imprinted polymers by atom transfer radical polymerization for the rapid extraction of avermectin from fish samples.

PubMed

You, Xiaoxiao; Gao, Lei; Qin, Dongli; Chen, Ligang

2017-01-01

A novel and highly efficient approach to obtain magnetic molecularly imprinted polymers is described to detect avermectin in fish samples. The magnetic molecularly imprinted polymers were synthesized by surface imprinting polymerization using magnetic multiwalled carbon nanotubes as the support materials, atom transfer radical polymerization as the polymerization method, avermectin as template, acrylamide as functional monomer, and ethylene glycol dimethacrylate as crosslinker. The characteristics of the magnetic molecularly imprinted polymers were assessed by using transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, vibrating sample magnetometry, X-ray diffraction, and thermogravimetric analysis. The binding characteristics of magnetic molecularly imprinted polymers were researched through isothermal adsorption experiment, kinetics adsorption experiment, and the selectivity experiment. Coupled with ultra high performance liquid chromatography and tandem mass spectrometry, the extraction conditions of the magnetic molecularly imprinted polymers as adsorbents for avermectin were investigated in detail. The recovery of avermectin was 84.2-97.0%, and the limit of detection was 0.075 μg/kg. Relative standard deviations of intra- and inter-day precisions were in the range of 1.7-2.9% and 3.4-5.6%, respectively. The results demonstrated that the extraction method not only has high selectivity and accuracy, but also is convenient for the determination of avermectin in fish samples. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Magnetic field transfer device and method

DOEpatents

Wipf, S.L.

1990-02-13

A magnetic field transfer device includes a pair of oppositely wound inner coils which each include at least one winding around an inner coil axis, and an outer coil which includes at least one winding around an outer coil axis. The windings may be formed of superconductors. The axes of the two inner coils are parallel and laterally spaced from each other so that the inner coils are positioned in side-by-side relation. The outer coil is outwardly positioned from the inner coils and rotatable relative to the inner coils about a rotational axis substantially perpendicular to the inner coil axes to generate a hypothetical surface which substantially encloses the inner coils. The outer coil rotates relative to the inner coils between a first position in which the outer coil axis is substantially parallel to the inner coil axes and the outer coil augments the magnetic field formed in one of the inner coils, and a second position 180[degree] from the first position, in which the augmented magnetic field is transferred into the other inner coil and reoriented 180[degree] from the original magnetic field. The magnetic field transfer device allows a magnetic field to be transferred between volumes with negligible work being required to rotate the outer coil with respect to the inner coils. 16 figs.

Magnetic field transfer device and method

DOEpatents

Wipf, Stefan L.

1990-01-01

A magnetic field transfer device includes a pair of oppositely wound inner coils which each include at least one winding around an inner coil axis, and an outer coil which includes at least one winding around an outer coil axis. The windings may be formed of superconductors. The axes of the two inner coils are parallel and laterally spaced from each other so that the inner coils are positioned in side-by-side relation. The outer coil is outwardly positioned from the inner coils and rotatable relative to the inner coils about a rotational axis substantially perpendicular to the inner coil axes to generate a hypothetical surface which substantially encloses the inner coils. The outer coil rotates relative to the inner coils between a first position in which the outer coil axis is substantially parallel to the inner coil axes and the outer coil augments the magnetic field formed in one of the inner coils, and a second position 180.degree. from the first position, in which the augmented magnetic field is transferred into the other inner coil and reoriented 180.degree. from the original magnetic field. The magnetic field transfer device allows a magnetic field to be transferred between volumes with negligible work being required to rotate the outer coil with respect to the inner coils.

Entropy Analysis in Mixed Convection MHD flow of Nanofluid over a Non-linear Stretching Sheet

NASA Astrophysics Data System (ADS)

Matin, Meisam Habibi; Nobari, Mohammad Reza Heirani; Jahangiri, Pouyan

This article deals with a numerical study of entropy analysis in mixed convection MHD flow of nanofluid over a non-linear stretching sheet taking into account the effects of viscous dissipation and variable magnetic field. The nanofluid is made of such nano particles as SiO2 with pure water as a base fluid. To analyze the problem, at first the boundary layer equations are transformed into non-linear ordinary equations using a similarity transformation. The resultant equations are then solved numerically using the Keller-Box scheme based on the implicit finite-difference method. The effects of different non-dimensional governing parameters such as magnetic parameter, nanoparticles volume fraction, Nusselt, Richardson, Eckert, Hartman, Brinkman, Reynolds and entropy generation numbers are investigated in details. The results indicate that increasing the nano particles to the base fluids causes the reduction in shear forces and a decrease in stretching sheet heat transfer coefficient. Also, decreasing the magnetic parameter and increasing the Eckert number result in improves heat transfer rate. Furthermore, the surface acts as a strong source of irreversibility due to the higher entropy generation number near the surface.

The study of structures and properties of PdnHm(n=1-10, m=1,2) clusters by density functional theory

NASA Astrophysics Data System (ADS)

Wen, Jun-Qing; Chen, Guo-Xiang; Zhang, Jian-Min; Wu, Hua

2018-04-01

The geometrical evolution, local relative stability, magnetism and charge transfer characteristics of PdnHm(n = 1-10, m = 1,2) have been systematically calculated by using density functional theory. The studied results show that the most stable geometries of PdnH and PdnH2 (n = 1-10) can be got by doping one or two H atoms on the sides of Pdn clusters except Pd6H and Pd6H2. It is found that doping one or two H atoms on Pdn clusters cannot change the basic framework of Pdn. The analysis of stability shows that Pd2H, Pd4H, Pd7H, Pd2H2, Pd4H2 and Pd7H2 clusters have higher local relative stability than neighboring clusters. The analysis of magnetic properties demonstrates that absorption of hydrogen atoms decreases the average atomic magnetic moments compared with pure Pdn clusters. More charges transfer from H atoms to Pd atoms for Pd6H and Pd6H2 clusters, demonstrating the adsorption of hydrogen atoms change from side adsorption to surface adsorption.

Heat Transfer to Anode of Arc as Function of Transverse Magnetic Field and Lateral Gas Flow Velocity

NASA Astrophysics Data System (ADS)

Zama, Yoshiyuki; Shiino, Toru; Ishii, Yoko; Maeda, Yoshifumi; Yamamoto, Shinji; Iwao, Toru

2016-10-01

Gas tungsten arc welding has useful joining technology because of high-energy and high-current characteristics. It can be flexible from the transverse magnetic field and lateral gas flow velocity. In this case, the weld defect occurs. In this research, the heat transfer to the anode of the arc as a function of the transverse magnetic field and lateral gas flow velocity is elucidated. That magnetic flux density and lateral gas velocity were varied from 0 to 3 mT and 0 to 50?m?s -1, respectively. The axial plasma gas argon flow rates were 3?slm. A transverse magnetic field is applied to the arc using Helmholtz coil. The anode is used by a water-cooled copper plate, and the heat transfer is measured by temperature of cooled water. As a result, the arc is deflected by the Lorentz force and lateral gas convection. Thus, the heat transfer to the anode of the arc decreases with increasing the transverse magnetic field and lateral gas flow velocity. In addition, the heat transfer to the anode changes with different attachments modes. The lateral gas flow causes a convective heat loss from the arc to the chamber walls.

Mathematical Model of the Processes of Heat and Mass Transfer and Diffusion of the Magnetic Field in an Induction Furnace

NASA Astrophysics Data System (ADS)

Perminov, A. V.; Nikulin, I. L.

2016-03-01

We propose a mathematical model describing the motion of a metal melt in a variable inhomogeneous magnetic field of a short solenoid. In formulating the problem, we made estimates and showed the possibility of splitting the complete magnetohydrodynamical problem into two subproblems: a magnetic field diffusion problem where the distributions of the external and induced magnetic fields and currents are determined, and a heat and mass transfer problem with known distributions of volume sources of heat and forces. The dimensionless form of the heat and mass transfer equation was obtained with the use of averaging and multiscale methods, which permitted writing and solving separately the equations for averaged flows and temperature fields and their oscillations. For the heat and mass transfer problem, the boundary conditions for a real technological facility are discussed. The dimensionless form of the magnetic field diffusion equation is presented, and the experimental computational procedure and results of the numerical simulation of the magnetic field structure in the melt for various magnetic Reynolds numbers are described. The extreme dependence of heat release on the magnetic Reynolds number has been interpreted.

Oscillation characteristics of zero-field spin transfer oscillators with field-like torque

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

Guo, Yuan-Yuan; Xue, Hai-Bin, E-mail: xuehaibin@tyut.edu.cn; Department of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan 030024

2015-05-15

We theoretically investigate the influence of the field-like spin torque term on the oscillation characteristics of spin transfer oscillators, which are based on MgO magnetic tunnel junctions (MTJs) consisting of a perpendicular magnetized free layer and an in-plane magnetized pinned layer. It is demonstrated that the field-like torque has a strong impact on the steady-state precession current region and the oscillation frequency. In particular, the steady-state precession can occur at zero applied magnetic field when the ratio between the field-like torque and the spin transfer torque takes up a negative value. In addition, the dependence of the oscillation properties onmore » the junction sizes has also been analyzed. The results indicate that this compact structure of spin transfer oscillator without the applied magnetic field is practicable under certain conditions, and it may be a promising configuration for the new generation of on-chip oscillators.« less

Environmentally-friendly oxygen-free roasting/wet magnetic separation technology for in situ recycling cobalt, lithium carbonate and graphite from spent LiCoO2/graphite lithium batteries.

PubMed

Li, Jia; Wang, Guangxu; Xu, Zhenming

2016-01-25

The definite aim of the present paper is to present some novel methods that use oxygen-free roasting and wet magnetic separation to in situ recycle of cobalt, Lithium Carbonate and Graphite from mixed electrode materials. The in situ recycling means to change waste into resources by its own components, which is an idea of "waste+waste→resources." After mechanical scraping the mixed electrode materials enrich powders of LiCoO2 and graphite. The possible reaction between LiCoO2 and graphite was obtained by thermodynamic analysis. The feasibility of the reaction at high temperature was studied with the simultaneous thermogravimetry analysis under standard atmospheric pressure. Then the oxygen-free roasting/wet magnetic separation method was used to transfer the low added value mixed electrode materials to high added value products. The results indicated that, through the serious technologies of oxygen-free roasting and wet magnetic separation, mixture materials consist with LiCoO2 and graphite powders are transferred to the individual products of cobalt, Lithium Carbonate and Graphite. Because there is not any chemical solution added in the process, the cost of treating secondary pollution can be saved. This study provides a theoretical basis for industrial-scale recycling resources from spent LIBs. Copyright © 2015 Elsevier B.V. All rights reserved.

Magnetic Silica-Supported Ruthenium Nanoparticles: An Efficient Catalyst for Transfer Hydrogenation of Carbonyl Compounds

EPA Science Inventory

One-pot synthesis of ruthenium nanoparticles on magnetic silica is described which involve the in situ generation of magnetic silica (Fe3O4@ SiO2) and ruthenium nano particles immobilization; the hydration of nitriles and transfer hydrogenation of carbonyl compounds occurs in hi...

Iterative optimization method for design of quantitative magnetization transfer imaging experiments.

PubMed

Levesque, Ives R; Sled, John G; Pike, G Bruce

2011-09-01

Quantitative magnetization transfer imaging (QMTI) using spoiled gradient echo sequences with pulsed off-resonance saturation can be a time-consuming technique. A method is presented for selection of an optimum experimental design for quantitative magnetization transfer imaging based on the iterative reduction of a discrete sampling of the Z-spectrum. The applicability of the technique is demonstrated for human brain white matter imaging at 1.5 T and 3 T, and optimal designs are produced to target specific model parameters. The optimal number of measurements and the signal-to-noise ratio required for stable parameter estimation are also investigated. In vivo imaging results demonstrate that this optimal design approach substantially improves parameter map quality. The iterative method presented here provides an advantage over free form optimal design methods, in that pragmatic design constraints are readily incorporated. In particular, the presented method avoids clustering and repeated measures in the final experimental design, an attractive feature for the purpose of magnetization transfer model validation. The iterative optimal design technique is general and can be applied to any method of quantitative magnetization transfer imaging. Copyright © 2011 Wiley-Liss, Inc.

Commissioning and Testing the 1970's Era LASS Solenoid Magnet in JLab's Hall D

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

Ballard, Joshua T.; Biallas, George H.; Brown, G.

2015-06-01

JLab refurbished and reconfigured the LASS1, 1.85m bore Solenoid and installed it as the principal analysis magnet for nuclear physics in the newly constructed, Hall D at Jefferson Lab. The magnet contains four superconducting coils within an iron yoke. The magnet was built in the early1970's at Stanford Linear Accelerator Center and used a second time at Los Alamos National Laboratory. The coils were extensively refurbished and individually tested by JLab. A new Cryogenic Distribution Box provides cryogens and their control valving, current distribution bus, and instrumentation pass-through. A repurposed CTI 2800 refrigerator system and new transfer line complete themore » system. We describe the re-configuration, the process and problems of re-commissioning the magnet and the results of testing the completed magnet.« less

Theory of atomistic simulation of spin-transfer torque in nanomagnets

NASA Astrophysics Data System (ADS)

Tay, Tiamhock; Sham, L. J.

2013-05-01

In spin-transfer torque (STT) for technological applications, the miniaturization of the magnet may reach the stage of requiring a fully quantum-mechanical treatment. We present an STT theory which uses the quantum macrospin ground and excited (magnon) states of the nanomagnet. This allows for energy and angular momentum exchanges between the current electron and the nano-magnet. We develop a method of magnetization dynamics simulation which captures the heating effect on the magnet by the spin-polarized current and the temperature dependence in STT. We also discuss the magnetostatics effect on magnon scattering for ferromagnetic relaxation in a thin film. Our work demonstrates a realistic step towards simulation of quantum spin-transfer torque physics in nanoscale magnets.

Field optimization method of a dual-axis atomic magnetometer based on frequency-response and dynamics

NASA Astrophysics Data System (ADS)

Xing, Li; Quan, Wei; Fan, Wenfeng; Li, Rujie; Jiang, Liwei; Fang, Jiancheng

2018-05-01

The frequency-response and dynamics of a dual-axis spin-exchange-relaxation-free (SERF) atomic magnetometer are investigated by means of transfer function analysis. The frequency-response at different bias magnetic fields is tested to demonstrate the effect of the residual magnetic field. The resonance frequency of alkali atoms and magnetic linewidth can be obtained simultaneously through our theoretical model. The coefficient of determination of the fitting results is superior to 0.995 with 95% confidence bounds. Additionally, step responses are applied to analyze the dynamics of the control system and the effect of imperfections. Finally, a noise-limited magnetic field resolution of 15 fT {{\\sqrt{Hz}}-1} has been achieved for our dual-axis SERF atomic magnetometer through magnetic field optimization.

Period Variations of the Eclipsing Binary Systems T LMi and VX Lac

NASA Astrophysics Data System (ADS)

Yılmaz, M.; İzci, D. D.; Gümüş, D.; Özavci, İ.; Selam, S. O.

2015-07-01

We present a period analysis of the two Algol-type eclipsing binary systems T LMi and VX Lac using all available times of minimum in the literature, as well as new minima obtained at the Ankara University Kreiken Observatory. The period analysis of T LMi suggests mass transfer between the components and also a third body that is dynamically bound to the binary system. The analysis of VX Lac also suggests mass transfer between the components, and the presence of a third and a fourth body under the assumption of a Light-Time Effect. In addition, the periodic variation of VX Lac was examined under the hypothesis of magnetic activity, and the corresponding parameters were derived. We report here the orbital parameters for both systems, along with the ones related to mass transfer, and those for the third and fourth bodies.

Electro-mechanical energy conversion system having a permanent magnet machine with stator, resonant transfer link and energy converter controls

DOEpatents

Skeist, S. Merrill; Baker, Richard H.

2006-01-10

An electro-mechanical energy conversion system coupled between an energy source and an energy load comprising an energy converter device including a permanent magnet induction machine coupled between the energy source and the energy load to convert the energy from the energy source and to transfer the converted energy to the energy load and an energy transfer multiplexer to control the flow of power or energy through the permanent magnetic induction machine.

Wireless power transfer magnetic couplers

DOEpatents

Wu, Hunter; Gilchrist, Aaron; Sealy, Kylee

2016-01-19

A magnetic coupler is disclosed for wireless power transfer systems. A ferrimagnetic component is capable of guiding a magnetic field. A wire coil is wrapped around at least a portion of the ferrimagnetic component. A screen is capable of blocking leakage magnetic fields. The screen may be positioned to cover at least one side of the ferrimagnetic component and the coil. A distance across the screen may be at least six times an air gap distance between the ferrimagnetic component and a receiving magnetic coupler.

Exchange magnon induced resistance asymmetry in permalloy spin-Hall oscillators

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

Langenfeld, S.; Walter Schottky Institut and Physik-Department, Technische Universität München, 85748 Garching; Tshitoyan, V.

2016-05-09

We investigate magnetization dynamics in a spin-Hall oscillator using a direct current measurement as well as conventional microwave spectrum analysis. When the current applies an anti-damping spin-transfer torque, we observe a change in resistance which we ascribe mainly to the excitation of incoherent exchange magnons. A simple model is developed based on the reduction of the effective saturation magnetization, quantitatively explaining the data. The observed phenomena highlight the importance of exchange magnons on the operation of spin-Hall oscillators.

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.

Steady MHD free convection heat and mass transfer flow about a vertical porous surface with thermal diffusion and induced magnetic field

NASA Astrophysics Data System (ADS)

Touhid Hossain, M. M.; Afruz-Zaman, Md.; Rahman, Fouzia; Hossain, M. Arif

2013-09-01

In this study the thermal diffusion effect on the steady laminar free convection flow and heat transfer of viscous incompressible MHD electrically conducting fluid above a vertical porous surface is considered under the influence of an induced magnetic field. The governing non-dimensional equations relevant to the problem, containing the partial differential equations, are transformed by usual similarity transformations into a system of coupled non-linear ordinary differential equations and will be solved analytically by using the perturbation technique. On introducing the non-dimensional concept and applying Boussinesq's approximation, the solutions for velocity field, temperature distribution and induced magnetic field to the second order approximations are obtained for large suction with different selected values of the established dimensionless parameters. The influences of these various establish parameters on the velocity and temperature fields and on the induced magnetic fields are exhibited under certain assumptions and are studied graphically in the present analysis. It is observed that the effects of thermal-diffusion and large suction have great importance on the velocity, temperature and induced magnetic fields and mass concentration for several fluids considered, so that their effects should be taken into account with other useful parameters associated. It is also found that the dimensionless Prandtl number, Grashof number, Modified Grashof number and magnetic parameter have an appreciable influence on the concerned independent variables.

EV Charging Through Wireless Power Transfer: Analysis of Efficiency Optimization and Technology Trends

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

Miller, John M; Rakouth, Heri; Suh, In-Soo

This paper is aimed at reviewing the technology trends for wireless power transfer (WPT) for electric vehicles (EV). It also analyzes the factors affecting its efficiency and describes the techniques currently used for its optimization. The review of the technology trends encompasses both stationary and moving vehicle charging systems. The study of the stationary vehicle charging technology is based on current implementations and on-going developments at WiTricity and Oak Ridge National Lab (ORNL). The moving vehicle charging technology is primarily described through the results achieved by the Korean Advanced Institute of Technology (KAIST) along with on-going efforts at Stanford University.more » The factors affecting the efficiency are determined through the analysis of the equivalent circuit of magnetic resonant coupling. The air gap between both transmitting and receiving coils along with the magnetic field distribution and the relative impedance mismatch between the related circuits are the primary factors affecting the WPT efficiency. Currently the industry is looking at an air gap of 25 cm or below. To control the magnetic field distribution, Kaist has recently developed the Shaped Magnetic Field In Resonance (SMFIR) technology that uses conveniently shaped ferrite material to provide low reluctance path. The efficiency can be further increased by means of impedance matching. As a result, Delphi's implementation of the WiTricity's technology exhibits a WPT efficiency above 90% for stationary charging while KAIST has demonstrated a maximum efficiency of 83% for moving vehicle with its On Line Vehicle (OLEV) project. This study is restricted to near-field applications (short and mid-range) and does not address long-range technology such as microwave power transfer that has low efficiency as it is based on radiating electromagnetic waves. This paper exemplifies Delphi's work in powertrain electrification as part of its innovation for the real world program geared toward a safer, greener and more connected driving. Moreover, it draws from and adds to Dr. Andrew Brown Jr.'s SAE books 'Active Safety and the Mobility Industry', 'Connectivity and Mobility Industry', and 'Green Technologies and the Mobility Industry'. Magnetic resonant coupling is the foundation of modern wireless power transfer. Its efficiency can be controlled through impedance matching and magnetic field shaping. Current implementations use one or both of these control methods and enable both stationary and mobile charging with typical efficiency within the 80% and 90% range for an air gap up to 25 cm.« less

Voltage-controlled magnetization switching in MRAMs in conjunction with spin-transfer torque and applied magnetic field

NASA Astrophysics Data System (ADS)

Munira, Kamaram; Pandey, Sumeet C.; Kula, Witold; Sandhu, Gurtej S.

2016-11-01

Voltage-controlled magnetic anisotropy (VCMA) effect has attracted a significant amount of attention in recent years because of its low cell power consumption during the anisotropy modulation of a thin ferromagnetic film. However, the applied voltage or electric field alone is not enough to completely and reliably reverse the magnetization of the free layer of a magnetic random access memory (MRAM) cell from anti-parallel to parallel configuration or vice versa. An additional symmetry-breaking mechanism needs to be employed to ensure the deterministic writing process. Combinations of voltage-controlled magnetic anisotropy together with spin-transfer torque (STT) and with an applied magnetic field (Happ) were evaluated for switching reliability, time taken to switch with low error rate, and energy consumption during the switching process. In order to get a low write error rate in the MRAM cell with VCMA switching mechanism, a spin-transfer torque current or an applied magnetic field comparable to the critical current and field of the free layer is necessary. In the hybrid processes, the VCMA effect lowers the duration during which the higher power hungry secondary mechanism is in place. Therefore, the total energy consumed during the hybrid writing processes, VCMA + STT or VCMA + Happ, is less than the energy consumed during pure spin-transfer torque or applied magnetic field switching.

Joule heating and spin-transfer torque investigated on the atomic scale using a spin-polarized scanning tunneling microscope.

PubMed

Krause, S; Herzog, G; Schlenhoff, A; Sonntag, A; Wiesendanger, R

2011-10-28

The influence of a high spin-polarized tunnel current onto the switching behavior of a superparamagnetic nanoisland on a nonmagnetic substrate is investigated by means of spin-polarized scanning tunneling microscopy. A detailed lifetime analysis allows for a quantification of the effective temperature rise of the nanoisland and the modification of the activation energy barrier for magnetization reversal, thereby using the nanoisland as a local thermometer and spin-transfer torque analyzer. Both the Joule heating and spin-transfer torque are found to scale linearly with the tunnel current. The results are compared to experiments performed on lithographically fabricated magneto-tunnel junctions, revealing a very high spin-transfer torque switching efficiency in our experiments.

Topology of magnetic flux ropes and formation of fossil flux transfer events and boundary layer plasmas

NASA Technical Reports Server (NTRS)

Lee, L. C.; Ma, Z. W.; Fu, Z. F.; Otto, A.

1993-01-01

A mechanism for the formation of fossil flux transfer events and the low-level boundary layer within the framework of multiple X-line reconnection is proposed. Attention is given to conditions for which the bulk of magnetic flux in a flux rope of finite extent has a simple magnetic topology, where the four possible connections of magnetic field lines are: IMF to MSP, MSP to IMF, IMF to IMF, and MSP to MSP. For a sufficient relative shift of the X lines, magnetic flux may enter a flux rope from the magnetosphere and exit into the magnetosphere. This process leads to the formation of magnetic flux ropes which contain a considerable amount of magnetosheath plasma on closed magnetospheric field lines. This process is discussed as a possible explanation for the formation of fossil flux transfer events in the magnetosphere and the formation of the low-latitude boundary layer.

Analysis and Optimization of Four-Coil Planar Magnetically Coupled Printed Spiral Resonators.

PubMed

Khan, Sadeque Reza; Choi, GoangSeog

2016-08-03

High-efficiency power transfer at a long distance can be efficiently established using resonance-based wireless techniques. In contrast to the conventional two-coil-based inductive links, this paper presents a magnetically coupled fully planar four-coil printed spiral resonator-based wireless power-transfer system that compensates the adverse effect of low coupling and improves efficiency by using high quality-factor coils. A conformal architecture is adopted to reduce the transmitter and receiver sizes. Both square architecture and circular architectures are analyzed and optimized to provide maximum efficiency at a certain operating distance. Furthermore, their performance is compared on the basis of the power-transfer efficiency and power delivered to the load. Square resonators can produce higher measured power-transfer efficiency (79.8%) than circular resonators (78.43%) when the distance between the transmitter and receiver coils is 10 mm of air medium at a resonant frequency of 13.56 MHz. On the other hand, circular coils can deliver higher power (443.5 mW) to the load than the square coils (396 mW) under the same medium properties. The performance of the proposed structures is investigated by simulation using a three-layer human-tissue medium and by experimentation.

Quantized spin-momentum transfer in atom-sized magnetic systems

NASA Astrophysics Data System (ADS)

Loth, Sebastian

2010-03-01

Our ability to quickly access the vast amounts of information linked in the internet is owed to the miniaturization of magnetic data storage. In modern disk drives the tunnel magnetoresistance effect (TMR) serves as sensitive reading mechanism for the nanoscopic magnetic bits [1]. At its core lies the ability to control the flow of electrons with a material's magnetization. The inverse effect, spin transfer torque (STT), allows one to influence a magnetic layer by high current densities of spin-polarized electrons and carries high hopes for applications in non-volatile magnetic memory [2]. We show that equivalent processes are active in quantum spin systems. We use a scanning tunneling microscope (STM) operating at low temperature and high magnetic field to address individual magnetic structures and probe their spin excitations by inelastic electron tunneling [3]. As model system we investigate transition metal atoms adsorbed to a copper nitride layer grown on a Cu crystal. The magnetic atoms on the surface possess well-defined spin states [4]. Transfer of one magnetic atom to the STM tip's apex creates spin-polarization in the probe tip. The combination of functionalized tip and surface adsorbed atom resembles a TMR structure where the magnetic layers now consist of one magnetic atom each. Spin-polarized current emitted from the probe tip not only senses the magnetic orientation of the atomic spin system, it efficiently transfers spin angular momentum and pumps the quantum spin system between the different spin states. This enables further exploration of the microscopic mechanisms for spin-relaxation and stability of quantum spin systems. [4pt] [1] Zhu and Park, Mater. Today 9, 36 (2006).[0pt] [2] Huai, AAPPS Bulletin 18, 33 (2008).[0pt] [3] Heinrich et al., Science 306, 466 (2004).[0pt] [4] Hirjibehedin et al., Science 317, 1199 (2007).

Dynamics of magnetization in ferromagnet with spin-transfer torque

NASA Astrophysics Data System (ADS)

Li, Zai-Dong; He, Peng-Bin; Liu, Wu-Ming

2014-11-01

We review our recent works on dynamics of magnetization in ferromagnet with spin-transfer torque. Driven by constant spin-polarized current, the spin-transfer torque counteracts both the precession driven by the effective field and the Gilbert damping term different from the common understanding. When the spin current exceeds the critical value, the conjunctive action of Gilbert damping and spin-transfer torque leads naturally the novel screw-pitch effect characterized by the temporal oscillation of domain wall velocity and width. Driven by space- and time-dependent spin-polarized current and magnetic field, we expatiate the formation of domain wall velocity in ferromagnetic nanowire. We discuss the properties of dynamic magnetic soliton in uniaxial anisotropic ferromagnetic nanowire driven by spin-transfer torque, and analyze the modulation instability and dark soliton on the spin wave background, which shows the characteristic breather behavior of the soliton as it propagates along the ferromagnetic nanowire. With stronger breather character, we get the novel magnetic rogue wave and clarify its formation mechanism. The generation of magnetic rogue wave mainly arises from the accumulation of energy and magnons toward to its central part. We also observe that the spin-polarized current can control the exchange rate of magnons between the envelope soliton and the background, and the critical current condition is obtained analytically. At last, we have theoretically investigated the current-excited and frequency-adjusted ferromagnetic resonance in magnetic trilayers. A particular case of the perpendicular analyzer reveals that the ferromagnetic resonance curves, including the resonant location and the resonant linewidth, can be adjusted by changing the pinned magnetization direction and the direct current. Under the control of the current and external magnetic field, several magnetic states, such as quasi-parallel and quasi-antiparallel stable states, out-of-plane precession, and bistable states can be realized. The precession frequency can be expressed as a function of the current and external magnetic field.

Effect of the ratio of radial gap to radius of the coils on the transmission efficiency of wireless power transfer via coupled magnetic resonances

NASA Astrophysics Data System (ADS)

Gao, Pengfei; Tian, Zijian; Wang, Xuqi; Wu, Jun; Gui, Weifeng

2018-03-01

Wireless power transfer (WPT) via coupled magnetic resonance is a promising technology to be applied in many fields. In general, there will be a radial gap in practical application, and some special application environments need to limit the radius of the coils. Therefore, in this paper, considering the comprehensive analysis of the radial gap and the radius of the coils, the concept of the ratio of radial gap to the radius of the coils was proposed. Based on the circuit theory, the formula between the ratio and transmission efficiency of WPT was deduced, and the effects of the ratio on the transmission efficiency were studied respectively at different axial distances. Simulation experiments were carried out and the results not only demonstrate the influence law of the ratio on transmission efficiency, but also validate the value of the ratio which the axial distance has the greatest effect on the transmission efficiency. Besides, the results shows the relationship between the effect of the ratio on the efficiency and the effect of the axial distance on the efficiency. The experimental results show that the theoretical analysis is correct, thus providing an useful theoretical reference for the design and further research on the wireless power transfer system in complicated environment.

Evolution of magnetic flux ropes associated with flux transfer events and interplanetary magnetic clouds

NASA Technical Reports Server (NTRS)

Wei, C. Q.; Lee, L. C.; Wang, S.; Akasofu, S.-I.

1991-01-01

Spacecraft observations suggest that flux transfer events and interplanetary magnetic clouds may be associated with magnetic flux ropes which are magnetic flux tubes containing helical magnetic field lines. In the magnetic flux ropes, the azimuthal magnetic field is superposed on the axial field. The time evolution of a localized magnetic flux rope is studied. A two-dimensional compressible MHD simulation code with a cylindrical symmetry is developed to study the wave modes associated with the evolution of flux ropes. It is found that in the initial phase both the fast magnetosonic wave and the Alfven wave are developed in the flux rope. After this initial phase, the Alfven wave becomes the dominant wave mode for the evolution of the magnetic flux rope and the radial expansion velocity of the flux rope is found to be negligible. Numerical results further show that even for a large initial azimuthal component of the magnetic field, the propagation velocity along the axial direction of the flux rope remains the Alfven velocity. It is also found that the localized magnetic flux rope tends to evolve into two separate magnetic ropes propagating in opposite directions. The simulation results are used to study the evolution of magnetic flux ropes associated with flux transfer events observed at the earth's dayside magnetopause and magnetic clouds in the interplanetary space.

Molecular orbital (SCF-X-α-SW) theory of Fe2+-Mn3+, Fe3+-Mn2+, and Fe3+-Mn3+ charge transfer and magnetic exchange in oxides and silicates

USGS Publications Warehouse

Sherman, David M.

1990-01-01

Metal-metal charge-transfer and magnetic exchange interactions have important effects on the optical spectra, crystal chemistry, and physics of minerals. Previous molecular orbital calculations have provided insight on the nature of Fe2+-Fe3+ and Fe2+-Ti4+ charge-transfer transitions in oxides and silicates. In this work, spin-unrestricted molecular orbital calculations on (FeMnO10) clusters are used to study the nature of magnetic exchange and electron delocalization (charge transfer) associated with Fe3+-Mn2+, Fe3+-Mn3+, and Fe2+-Mn3+ interactions in oxides and silicates. 

Effects of magnetic, radiation and chemical reaction on unsteady heat and mass transfer flow of an oscillating cylinder

NASA Astrophysics Data System (ADS)

Ahmed, Rubel; Rana, B. M. Jewel; Ahmmed, S. F.

2017-06-01

The effects of magnetic, radiation and chemical reaction parameters on the unsteady heat and mass transfer boundary layer flow past an oscillating cylinder is considered. The dimensionless momentum, energy and concentration equations are solved numerically by using explicit finite difference method with the help of a computer programming language Compaq visual FORTRAN 6.6a. The obtained results of this study have been discussed for different values of well-known parameters with different time steps. The effect of these parameters on the velocity field, temperature field and concentration field, skin-friction, Nusselt number, streamlines and isotherms has been studied and results are presented by graphically represented by the tabular form quantitatively. The stability and convergence analysis of the solution parameters that have been used in the mathematical model have been tested.

On-Chip Magnetic Bead Manipulation and Detection Using a Magnetoresistive Sensor-Based Micro-Chip: Design Considerations and Experimental Characterization

PubMed Central

Gooneratne, Chinthaka P.; Kodzius, Rimantas; Li, Fuquan; Foulds, Ian G.; Kosel, Jürgen

2016-01-01

The remarkable advantages micro-chip platforms offer over cumbersome, time-consuming equipment currently in use for bio-analysis are well documented. In this research, a micro-chip that includes a unique magnetic actuator (MA) for the manipulation of superparamagnetic beads (SPBs), and a magnetoresistive sensor for the detection of SPBs is presented. A design methodology, which takes into account the magnetic volume of SPBs, diffusion and heat transfer phenomena, is presented with the aid of numerical analysis to optimize the parameters of the MA. The MA was employed as a magnetic flux generator and experimental analysis with commercially available COMPEL™ and Dynabeads® demonstrated the ability of the MA to precisely transport a small number of SPBs over long distances and concentrate SPBs to a sensing site for detection. Moreover, the velocities of COMPEL™ and Dynabead® SPBs were correlated to their magnetic volumes and were in good agreement with numerical model predictions. We found that 2.8 μm Dynabeads® travel faster, and can be attracted to a magnetic source from a longer distance, than 6.2 μm COMPEL™ beads at magnetic flux magnitudes of less than 10 mT. The micro-chip system could easily be integrated with electronic circuitry and microfluidic functions, paving the way for an on-chip biomolecule quantification device. PMID:27571084

First-principles analysis of X-ray magnetic circular dichroism for transition metal complex oxides

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

Ikeno, Hidekazu, E-mail: h-ikeno@21c.osakafu-u.ac.jp

2016-10-14

X-ray magnetic circular dichroism (XMCD) is widely used for the characterization of magnetism of materials. However, information from XMCD related to the atomic, electronic, and magnetic structures is not fully utilized due to the lack of reliable theoretical tools for spectral analysis. In this work, the first-principles configuration interaction (CI) calculations for X-ray absorption spectra developed by the author were extended for the calculation of XMCD, where the Zeeman energy was taken into the Hamiltonian of the CI to mimic magnetic polarization in the solid state. This technique was applied to interpret the L{sub 2,3} XMCD from 3d transition metalmore » complex oxides, such as NiFe{sub 2}O{sub 4} and FeTiO{sub 3}. The experimental XMCD spectra were quantitatively reproduced using this method. The oxidation states as well as the magnetic ordering between transition metal ions on crystallographically different sites in NiFe{sub 2}O{sub 4} can be unambiguously determined. A first-principles analysis of XMCD in FeTiO{sub 3} revealed the presence of Fe{sup 3+} and Ti{sup 3+} ions, which indicates that the charge transfer from Fe to Ti ions occurs. The origin of magnetic polarization of Ti ions in FeTiO{sub 3} was also discussed.« less

On-Chip Magnetic Bead Manipulation and Detection Using a Magnetoresistive Sensor-Based Micro-Chip: Design Considerations and Experimental Characterization.

PubMed

Gooneratne, Chinthaka P; Kodzius, Rimantas; Li, Fuquan; Foulds, Ian G; Kosel, Jürgen

2016-08-26

The remarkable advantages micro-chip platforms offer over cumbersome, time-consuming equipment currently in use for bio-analysis are well documented. In this research, a micro-chip that includes a unique magnetic actuator (MA) for the manipulation of superparamagnetic beads (SPBs), and a magnetoresistive sensor for the detection of SPBs is presented. A design methodology, which takes into account the magnetic volume of SPBs, diffusion and heat transfer phenomena, is presented with the aid of numerical analysis to optimize the parameters of the MA. The MA was employed as a magnetic flux generator and experimental analysis with commercially available COMPEL™ and Dynabeads(®) demonstrated the ability of the MA to precisely transport a small number of SPBs over long distances and concentrate SPBs to a sensing site for detection. Moreover, the velocities of COMPEL™ and Dynabead(®) SPBs were correlated to their magnetic volumes and were in good agreement with numerical model predictions. We found that 2.8 μm Dynabeads(®) travel faster, and can be attracted to a magnetic source from a longer distance, than 6.2 μm COMPEL™ beads at magnetic flux magnitudes of less than 10 mT. The micro-chip system could easily be integrated with electronic circuitry and microfluidic functions, paving the way for an on-chip biomolecule quantification device.

Interferometric study on the mass transfer in cryogenic distillation under magnetic field

NASA Astrophysics Data System (ADS)

Bao, S. R.; Zhang, R. P.; Y Rong, Y.; Zhi, X. Q.; Qiu, L. M.

2017-12-01

Cryogenic distillation has long been used for the mass production of industrial gases because of its features of high efficiency, high purity, and capability to produce noble gases. It is of great theoretical and practical significance to explore methods to improve the mass transfer efficiency in cryogenic distillation. The negative correlation between the susceptibility of paramagnetic oxygen and temperature provides a new possibility of comprehensive utilization of boiling point and susceptibility differences in cryogenic distillation. Starting from this concept, we proposed a novel distillation intensifying method by using gradient magnetic field, in which the magnetic forces enhance the transport of the oxygen molecules to the liquid phase in the distillation. In this study, a cryogenic testbed was designed and fabricated to study the diffusion between oxygen and nitrogen under magnetic field. A Mach-Zehnder interferometer was used to visualize the concentration distribution during the diffusion process. The mass transfer characteristics with and without magnetic field, in the chamber filled with the magnetized medium, were systematically studied. The concentration redistribution of oxygen was observed, and the stable stratified diffusion between liquid oxygen and nitrogen was prolonged by the non-uniform magnetic field. The experimental results show that the magnetic field can efficiently influence the mass transfer in cryogenic distillation, which can provide a new mechanism for the optimization of air separation process.

On judgement of electron transfer between two regions divided by the separatrix of confronting divergent magnetic fields applied to an inductively coupled plasma

NASA Astrophysics Data System (ADS)

Sugawara, Hirotake; Yamamoto, Tappei

2016-09-01

In order to quantitatively evaluate the electron confinement effect of the confronting divergent magnetic fields (CDMFs) applied to an inductively coupled plasma, we analyzed the electron transfer between two regions divided by the separatrix of the CDMFs in Ar at 0.67 Pa at 300 K using a Monte Carlo method. A conventional transfer judgement was simply based on the electron passage across the separatrix from the upstream source region to the downstream diffusion region. An issue was an overestimation of the transfer due to temporary stay of electrons in the downstream region. Electrons may pass the downstream region during their gyration even in case they are effectively bound to the upstream region, where their guiding magnetic flux lines run. More than half of the transfers were temporary ones and such seeming transfers were relevantly excluded from the statistics by introducing a newly chosen criterion based on the passage of electron gyrocenters across the separatrix and collisional events in the downstream region. Simulation results showed a tendency that the ratio of the temporary transfers excluded was higher under stronger magnetic fields because of higher cyclotron frequency. Work supported by JSPS Kakenhi Grant Number 16K05626.

Spin Transfer Torque in Graphene

NASA Astrophysics Data System (ADS)

Lin, Chia-Ching; Chen, Zhihong

2014-03-01

Graphene is an idea channel material for spin transport due to its long spin diffusion length. To develop graphene based spin logic, it is important to demonstrate spin transfer torque in graphene. Here, we report the experimental measurement of spin transfer torque in graphene nonlocal spin valve devices. Assisted by a small external in-plane magnetic field, the magnetization reversal of the receiving magnet is induced by pure spin diffusion currents from the injector magnet. The magnetization switching is reversible between parallel and antiparallel configurations by controlling the polarity of the applied charged currents. Current induced heating and Oersted field from the nonlocal charge flow have also been excluded in this study. Next, we further enhance the spin angular momentum absorption at the interface of the receiving magnet and graphene channel by removing the tunneling barrier in the receiving magnet. The device with a tunneling barrier only at the injector magnet shows a comparable nonlocal spin valve signal but lower electrical noise. Moreover, in the same preset condition, the critical charge current density for spin torque in the single tunneling barrier device shows a substantial reduction if compared to the double tunneling barrier device.

RADIALLY MAGNETIZED PROTOPLANETARY DISK: VERTICAL PROFILE

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

Russo, Matthew; Thompson, Christopher

2015-11-10

This paper studies the response of a thin accretion disk to an external radial magnetic field. Our focus is on protoplanetary disks (PPDs), which are exposed during their later evolution to an intense, magnetized wind from the central star. A radial magnetic field is mixed into a thin surface layer, wound up by the disk shear, and pushed downward by a combination of turbulent mixing and ambipolar and ohmic drift. The toroidal field reaches much greater strengths than the seed vertical field that is usually invoked in PPD models, even becoming superthermal. Linear stability analysis indicates that the disk experiencesmore » the magnetorotational instability (MRI) at a higher magnetization than a vertically magnetized disk when both the effects of ambipolar and Hall drift are taken into account. Steady vertical profiles of density and magnetic field are obtained at several radii between 0.06 and 1 AU in response to a wind magnetic field B{sub r} ∼ (10{sup −4}–10{sup −2})(r/ AU){sup −2} G. Careful attention is given to the radial and vertical ionization structure resulting from irradiation by stellar X-rays. The disk is more strongly magnetized closer to the star, where it can support a higher rate of mass transfer. As a result, the inner ∼1 AU of a PPD is found to evolve toward lower surface density. Mass transfer rates around 10{sup −8} M{sub ⊙} yr{sup −1} are obtained under conservative assumptions about the MRI-generated stress. The evolution of the disk and the implications for planet migration are investigated in the accompanying paper.« less

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.

3D discrete angiogenesis dynamic model and stochastic simulation for the assessment of blood perfusion coefficient and impact on heat transfer between nanoparticles and malignant tumors.

PubMed

Yifat, Jonathan; Gannot, Israel

2015-03-01

Early detection of malignant tumors plays a crucial role in the survivability chances of the patient. Therefore, new and innovative tumor detection methods are constantly searched for. Tumor-specific magnetic-core nano-particles can be used with an alternating magnetic field to detect and treat tumors by hyperthermia. For the analysis of the method effectiveness, the bio-heat transfer between the nanoparticles and the tissue must be carefully studied. Heat diffusion in biological tissue is usually analyzed using the Pennes Bio-Heat Equation, where blood perfusion plays an important role. Malignant tumors are known to initiate an angiogenesis process, where endothelial cell migration from neighboring vasculature eventually leads to the formation of a thick blood capillary network around them. This process allows the tumor to receive its extensive nutrition demands and evolve into a more progressive and potentially fatal tumor. In order to assess the effect of angiogenesis on the bio-heat transfer problem, we have developed a discrete stochastic 3D model & simulation of tumor-induced angiogenesis. The model elaborates other angiogenesis models by providing high resolution 3D stochastic simulation, capturing of fine angiogenesis morphological features, effects of dynamic sprout thickness functions, and stochastic parent vessel generator. We show that the angiogenesis realizations produced are well suited for numerical bio-heat transfer analysis. Statistical study on the angiogenesis characteristics was derived using Monte Carlo simulations. According to the statistical analysis, we provide analytical expression for the blood perfusion coefficient in the Pennes equation, as a function of several parameters. This updated form of the Pennes equation could be used for numerical and analytical analyses of the proposed detection and treatment method. Copyright © 2014 Elsevier Inc. All rights reserved.

Current driven dynamics of magnetic domain walls in permalloy nanowires

NASA Astrophysics Data System (ADS)

Hayashi, Masamitsu

The significant advances in micro-fabrication techniques opened the door to access interesting properties in solid state physics. With regard to magnetic materials, geometrical confinement of magnetic structures alters the defining parameters that govern magnetism. For example, development of single domain nano-pillars made from magnetic multilayers led to the discovery of electrical current controlled magnetization switching, which revealed the existence of spin transfer torque. Magnetic domain walls (DWs) are boundaries in magnetic materials that divide regions with distinct magnetization directions. DWs play an important role in the magnetization reversal processes of both bulk and thin film magnetic materials. The motion of DW is conventionally controlled by magnetic fields. Recently, it has been proposed that spin polarized current passed across the DW can also control the motion of DWs. Current in most magnetic materials is spin-polarized, due to spin-dependent scattering of the electrons, and thus can deliver spin angular momentum to the DW, providing a "spin transfer" torque on the DW which leads to DW motion. In addition, owing to the development of micro-fabrication techniques, geometrical confinement of magnetic materials enables creation and manipulation of a "single" DW in magnetic nanostructures. New paradigms for DW-based devices are made possible by the direct manipulation of DWs using spin polarized electrical current via spin transfer torque. This dissertation covers research on current induced DW motion in magnetic nanowires. Fascinating effects arising from the interplay between DWs with spin polarized current will be revealed.

Optimal design of implants for magnetically mediated hyperthermia: A wireless power transfer approach

NASA Astrophysics Data System (ADS)

Lang, Hans-Dieter; Sarris, Costas D.

2017-09-01

In magnetically mediated hyperthermia (MMH), an externally applied alternating magnetic field interacts with a mediator (such as a magnetic nanoparticle or an implant) inside the body to heat up the tissue in its proximity. Producing heat via induced currents in this manner is strikingly similar to wireless power transfer (WPT) for implants, where power is transferred from a transmitter outside of the body to an implanted receiver, in most cases via magnetic fields as well. Leveraging this analogy, a systematic method to design MMH implants for optimal heating efficiency is introduced, akin to the design of WPT systems for optimal power transfer efficiency. This paper provides analytical formulas for the achievable heating efficiency bounds as well as the optimal operating frequency and the implant material. Multiphysics simulations validate the approach and further demonstrate that optimization with respect to maximum heating efficiency is accompanied by minimizing heat delivery to healthy tissue. This is a property that is highly desirable when considering MMH as a key component or complementary method of cancer treatment and other applications.

Magnetic field concentration using ferromagnetic material to propel a wireless power transfer based micro-robot

NASA Astrophysics Data System (ADS)

Kim, Dongwook; Park, Bumjin; Park, Jaehyoung; Park, Hyun Ho; Ahn, Seungyoung

2018-05-01

In this paper, we propose a novel coil structure, using a ferromagnetic material which concentrates the magnetic field, as the propulsion system of a wireless power transfer (WPT) based micro-robot. This structure uses an incident magnetic field to induce current during wireless power transfer, to generate a Lorentz force. To prevent net cancelation of the Lorentz force in the load coil, ferrite films were applied to one side of the coil segment. The demonstrated simplicity and effectiveness of the proposed micro-robot showed its suitability for applications. Simulation and experimental results confirmed a velocity of 1.02 mm/s with 6 mW power transfer capacity for the 3 mm sized micro-robot.

Theoretical and experimental study of a wireless power supply system for moving low power devices in ferromagnetic and conductive medium

NASA Astrophysics Data System (ADS)

Safour, Salaheddine; Bernard, Yves

2017-10-01

This paper focuses on the design of a wireless power supply system for low power devices (e.g. sensors) located in harsh electromagnetic environment with ferromagnetic and conductive materials. Such particular environment could be found in linear and rotating actuators. The studied power transfer system is based on the resonant magnetic coupling between a fixed transmitter coil and a moving receiver coil. The technique was utilized successfully for rotary machines. The aim of this paper is to extend the technique to linear actuators. A modeling approach based on 2D Axisymmetric Finite Element model and an electrical lumped model based on the two-port network theory is introduced. The study shows the limitation of the technique to transfer the required power in the presence of ferromagnetic and conductive materials. Parametric and circuit analysis were conducted in order to design a resonant magnetic coupler that ensures good power transfer capability and efficiency. A design methodology is proposed based on this study. Measurements on the prototype show efficiency up to 75% at a linear distance of 20 mm.

Two phase modeling of nanofluid flow in existence of melting heat transfer by means of HAM

NASA Astrophysics Data System (ADS)

Sheikholeslami, M.; Jafaryar, M.; Bateni, K.; Ganji, D. D.

2018-02-01

In this article, Buongiorno Model is applied for investigation of nanofluid flow over a stretching plate in existence of magnetic field. Radiation and Melting heat transfer are taken into account. Homotopy analysis method (HAM) is selected to solve ODEs which are obtained from similarity transformation. Roles of Brownian motion, thermophoretic parameter, Hartmann number, porosity parameter, Melting parameter and Eckert number are presented graphically. Results indicate that nanofluid velocity and concentration enhance with rise of melting parameter. Nusselt number reduces with increase of porosity and melting parameters.

Dynamic impedance compensation for wireless power transfer using conjugate power

NASA Astrophysics Data System (ADS)

Liu, Suqi; Tan, Jianping; Wen, Xue

2018-02-01

Wireless power transfer (WPT) via coupled magnetic resonances has been in development for over a decade. However, the frequency splitting phenomenon occurs in the over-coupled region. Thus, the output power of the two-coil system achieves the maximum output power at the two splitting angular frequencies, and not at the natural resonant angular frequency. According to the maximum power transfer theorem, the impedance compensation method was adopted in many WPT projects. However, it remains a challenge to achieve the maximum output power and transmission efficiency in a fixed-frequency mode. In this study, dynamic impedance compensation for WPT was presented by utilizing the compensator within a virtual three-coil WPT system. First, the circuit model was established and transfer characteristics of a system were studied by utilizing circuit theories. Second, the power superposition of the WPT system was carefully researched. When a pair of compensating coils was inserted into the transmitter loop, the conjugate power of the compensator loop was created via magnetic coupling of the two compensating coils that insert into the transmitter loop. The mechanism for dynamic impedance compensation for wireless power transfer was then provided by investigating a virtual three-coil WPT system. Finally, the experimental circuit of a virtual three-coil WPT system was designed, and experimental results are consistent with the theoretical analysis, which achieves the maximum output power and transmission efficiency.

Parameters assessment of the inductively-coupled circuit for wireless power transfer

NASA Astrophysics Data System (ADS)

Isaev, Yu N.; Vasileva, O. V.; Budko, A. A.; Lefebvre, S.

2017-02-01

In this paper, a wireless power transfer model through the example of inductively-coupled coils of irregular shape in software package COMSOL Multiphysics is studied. Circuit parameters, such as inductance, coil resistance and self-capacitance were defined through electromagnetic energy by the finite-element method. The study was carried out according to Helmholtz equation. Spatial distribution of current per unit depending on frequency and the coupling coefficient for analysis of resonant frequency and spatial distribution of the vector magnetic potential at different distances between coils were presented. The resulting algorithm allows simulating the wireless power transfer between the inductively coupled coils of irregular shape with the assessment of the optimal parameters.

On-chip cell sorting via patterned magnetic traps

NASA Astrophysics Data System (ADS)

Byvank, Tom; Prikockis, Michael; Chen, Aaron; Miller, Brandon; Chalmers, Jeffrey; Sooryakumar, Ratnasingham

2015-03-01

Due to their importance in research for the diagnosis and treatment of cancer, numerous schemes have been developed to sort rare cell populations, e.g., circulating tumor cells (CTCs), from a larger ensemble of cells. Here, we improve upon a previously developed microfluidic device (Lab Chip 13, 1172, (2013)) to increase throughput and sorting purity of magnetically labeled cells. The separation mechanism involves controlling magnetic forces by manipulating the magnetic domain structures of embedded permalloy microdisks with weak external fields. These forces move labeled cells from the input flow stream into an adjacent buffer flow stream. Such magnetically activated transfer separates the magnetic entities from their non-magnetic counterparts as the two flow streams split apart and move toward their respective outputs. Purity of the magnetic output is modulated by the withdrawal rate of the non-magnetic output relative to the inputs. A proof of concept shows that CTCs from metastatic breast cancer patients can be sorted, recovered from the device, and confirmed as CTCs using separate immunofluorescence staining and analysis. With further optimizations, the channel could become a useful device for high purity final sorting of enriched patient cell samples.

Mechanistic investigation for the axisymmetric transport of nanocomposite molybdenum disulfide-silicon dioxide in ethylene glycol and sphericity assessment of nanoscale particles

NASA Astrophysics Data System (ADS)

Azhar, Ehtsham; Maraj, E. N.; Iqbal, Z.

2018-03-01

The present paper provides a comparative analysis between nano and hybrid nanofluid axisymmetric flow towards a radially stretching porous surface along with heat transfer mechanism in the presence of magnetic force and internal heat source/sink. The effect of various shapes of nanoparticles is also taken into account. The physical flow problem is modeled and presented in cylindrical coordinates. Governing nonlinear equations are converted into a system of differential equations by using the similarity approach. Numerical results are computed by means of a well-established and stable numerical procedure. The main implication of this research is the influence of nanoparticle shapes, internal heating and applied magnetic field on fluid flow and heat transfer. Computational results are extracted out with the help of mathematics software MATLAB. One of the key findings of the present analysis is the fact that the maximum temperature is achieved for lamina-shaped SiO2 and MoS2-SiO2 nanoparticles and the lowest temperature is attained in the case of sphere-shaped nanoparticles.

Magnetic resonance imaging using chemical exchange saturation transfer

NASA Astrophysics Data System (ADS)

Park, Jaeseok

2012-10-01

Magnetic resonance imaging (MRI) has been widely used as a valuable diagnostic imaging modality that exploits water content and water relaxation properties to provide both structural and functional information with high resolution. Chemical exchange saturation transfer (CEST) in MRI has been recently introduced as a new mechanism of image contrast, wherein exchangeable protons from mobile proteins and peptides are indirectly detected through saturation transfer and are not observable using conventional MRI. It has been demonstrated that CEST MRI can detect important tissue metabolites and byproducts such as glucose, glycogen, and lactate. Additionally, CEST MRI is sensitive to pH or temperature and can calibrate microenvironment dependent on pH or temperature. In this work, we provide an overview on recent trends in CEST MRI, introducing general principles of CEST mechanism, quantitative description of proton transfer process between water pool and exchangeable solute pool in the presence or absence of conventional magnetization transfer effect, and its applications

Investigating spin-transfer torques induced by thermal gradients in magnetic tunnel junctions by using micro-cavity ferromagnetic resonance

NASA Astrophysics Data System (ADS)

Cansever, H.; Narkowicz, R.; Lenz, K.; Fowley, C.; Ramasubramanian, L.; Yildirim, O.; Niesen, A.; Huebner, T.; Reiss, G.; Lindner, J.; Fassbender, J.; Deac, A. M.

2018-06-01

Similar to electrical currents flowing through magnetic multilayers, thermal gradients applied across the barrier of a magnetic tunnel junction may induce pure spin-currents and generate ‘thermal’ spin-transfer torques large enough to induce magnetization dynamics in the free layer. In this study, we describe a novel experimental approach to observe spin-transfer torques induced by thermal gradients in magnetic multilayers by studying their ferromagnetic resonance response in microwave cavities. Utilizing this approach allows for measuring the magnetization dynamics on micron/nano-sized samples in open-circuit conditions, i.e. without the need of electrical contacts. We performed first experiments on magnetic tunnel junctions patterned into 6  ×  9 µm2 ellipses from Co2FeAl/MgO/CoFeB stacks. We conducted microresonator ferromagnetic resonance (FMR) under focused laser illumination to induce thermal gradients in the layer stack and compared them to measurements in which the sample was globally heated from the backside of the substrate. Moreover, we carried out broadband FMR measurements under global heating conditions on the same extended films the microstructures were later on prepared from. The results clearly demonstrate the effect of thermal spin-torque on the FMR response and thus show that the microresonator approach is well suited to investigate thermal spin-transfer-driven processes for small temperatures gradients, far below the gradients required for magnetic switching.

Magnetic nanoparticles stimulation to enhance liquid-liquid two-phase mass transfer under static and rotating magnetic fields

NASA Astrophysics Data System (ADS)

Azimi, Neda; Rahimi, Masoud

2017-01-01

Rotating magnetic field (RMF) was applied on a micromixer to break the laminar flow and induce chaotic flow to enhance mass transfer between two-immiscible organic and aqueous phases. The results of RMF were compared to those of static magnetic field (SMF). For this purpose, experiments were carried out in a T-micromixer at equal volumetric flow rates of organic and aqueous phases. Fe3O4 nanoparticles were synthesized by co-precipitation technique and they were dissolved in organic phase. Results obtained from RMF and SMF were compared in terms of overall volumetric mass transfer coefficient (KLa) and extraction efficiency (E) at various Reynolds numbers. Generally, RMF showed higher effect in mass transfer characteristics enhancement compared with SMF. The influence of rotational speeds of magnets (ω) in RMF was investigated, and measurable enhancements of KLa and E were observed. In RMF, the effect of magnetic field induction (B) was investigated. The results reveal that at constant concentration of nanoparticles, by increasing of B, mass transfer characteristics will be enhanced. The effect of various nanoparticles concentrations (ϕ) within 0.002-0.01 (w/v) on KLa and E at maximum induction of RMF (B=76 mT) was evaluated. Maximum values of KLa (2.1±0.001) and E (0.884±0.001) were achieved for the layout of RMF (B=76 mT), ω=16 rad/s and MNPs concentration of 0.008-0.01 (w/v).

MHD Forced Convective Laminar Boundary Layer Flow from a Convectively Heated Moving Vertical Plate with Radiation and Transpiration Effect

PubMed Central

Uddin, Md. Jashim; Khan, Waqar A.; Ismail, A. I. Md.

2013-01-01

A two-dimensional steady forced convective flow of a Newtonian fluid past a convectively heated permeable vertically moving plate in the presence of a variable magnetic field and radiation effect has been investigated numerically. The plate moves either in assisting or opposing direction to the free stream. The plate and free stream velocities are considered to be proportional to whilst the magnetic field and mass transfer velocity are taken to be proportional to where is the distance along the plate from the leading edge of the plate. Instead of using existing similarity transformations, we use a linear group of transformations to transform the governing equations into similarity equations with relevant boundary conditions. Numerical solutions of the similarity equations are presented to show the effects of the controlling parameters on the dimensionless velocity, temperature and concentration profiles as well as on the friction factor, rate of heat and mass transfer. It is found that the rate of heat transfer elevates with the mass transfer velocity, convective heat transfer, Prandtl number, velocity ratio and the magnetic field parameters. It is also found that the rate of mass transfer enhances with the mass transfer velocity, velocity ratio, power law index and the Schmidt number, whilst it suppresses with the magnetic field parameter. Our results are compared with the results existing in the open literature. The comparisons are satisfactory. PMID:23741295

Effects of magnetic fields on improving mass transfer in flue gas desulfurization using a fluidized bed

NASA Astrophysics Data System (ADS)

Zhang, Qi; Gui, Keting; Wang, Xiaobo

2016-02-01

The effects of magnetic fields on improving the mass transfer in flue gas desulfurization using a fluidized bed are investigated in the paper. In this research, the magnetically fluidized bed (MFB) is used as the reactor in which ferromagnetic particles are fluidized with simulated flue gas under the influence of an external magnetic field. Lime slurry is continuously sprayed into the reactor. As a consequence, the desulfurization reaction and the slurry drying process take place simultaneously in the MFB. In this paper, the effects of ferromagnetic particles and external magnetic fields on the desulphurization efficiency are studied and compared with that of quartz particles as the fluidized particles. Experimental results show that the ferromagnetic particles not only act as a platform for lime slurry to precipitate on like quartz particles, but also take part in the desulfurization reaction. The results also show that the specific surface area of ferromagnetic particles after reaction is enlarged as the magnetic intensity increases, and the external magnetic field promotes the oxidation of S(IV), improving the mass transfer between sulphur and its sorbent. Hence, the efficiency of desulphurization under the effects of external magnetic fields is higher than that in general fluidized beds.

Spin-transfer torque switched magnetic tunnel junctions in magnetic random access memory

NASA Astrophysics Data System (ADS)

Sun, Jonathan Z.

2016-10-01

Spin-transfer torque (or spin-torque, or STT) based magnetic tunnel junction (MTJ) is at the heart of a new generation of magnetism-based solid-state memory, the so-called spin-transfer-torque magnetic random access memory, or STT-MRAM. Over the past decades, STT-based switchable magnetic tunnel junction has seen progress on many fronts, including the discovery of (001) MgO as the most favored tunnel barrier, which together with (bcc) Fe or FeCo alloy are yielding best demonstrated tunnel magneto-resistance (TMR); the development of perpendicularly magnetized ultrathin CoFeB-type of thin films sufficient to support high density memories with junction sizes demonstrated down to 11nm in diameter; and record-low spin-torque switching threshold current, giving best reported switching efficiency over 5 kBT/μA. Here we review the basic device properties focusing on the perpendicularly magnetized MTJs, both in terms of switching efficiency as measured by sub-threshold, quasi-static methods, and of switching speed at super-threshold, forced switching. We focus on device behaviors important for memory applications that are rooted in fundamental device physics, which highlights the trade-off of device parameters for best suitable system integration.

Mass Transfer Process by Magneto-convection at a Solid-liquid Interface in a Heterogeneous Vertical Magnetic Field

NASA Astrophysics Data System (ADS)

Sugiyama, Atsushi; Morisaki, Shigeyoshi; Aogaki, Ryoichi

2003-08-01

When an external magnetic field is vertically imposed on a solid-liquid interface, the mass transfer process of a solute dissolving from or depositing on the interface was theoretically examined. In a heterogeneous vertical magnetic field, a material receives a magnetic force in proportion to the product of the magnetic susceptibility, the magnetic flux density B and its gradient (dB/dz). As the reaction proceeds, a diffusion layer of the solute with changing susceptibility is formed at the interface because of the difference of the the magnetic susceptibility on the concentration of the solute. In the case of an unstable condition where the dimensionless number of magneto-convection S takes a positive value, the magnetic force is applied to the layer and induces numerous minute convection cells. The mass transfer of the solute is thus accelerated, so that it is predicted that the mass flux increases with the 1/3rd order of B(dB/dz) and the 4/3rd order of the concentration. The experiment was then performed by measuring the rate of the dissolution of copper sulfate pentahydrate crystal in water.

Magnetic induced heating of nanoparticle solutions

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

Murph, S. Hunyadi; Brown, M.; Coopersmith, K.

2016-12-02

Magnetic induced heating of nanoparticles (NP) provides a useful advantage for many energy transfer applications. This study aims to gain an understanding of the key parameters responsible for maximizing the energy transfer leading to nanoparticle heating through the use of simulations and experimental results. It was found that magnetic field strength, NP concentration, NP composition, and coil size can be controlled to generate accurate temperature profiles in NP aqueous solutions.

Energy transport in cooling device by magnetic fluid

NASA Astrophysics Data System (ADS)

Yamaguchi, Hiroshi; Iwamoto, Yuhiro

2017-06-01

Temperature sensitive magnetic fluid has a great potential with high performance heat transport ability as well as long distance energy (heat) transporting. In the present study experimental set-up was newly designed and constructed in order to measure basic heat transport characteristics under various magnetic field conditions. Angular dependence for the device (heat transfer section) was also taken into consideration for a sake of practical applications. The energy transfer characteristic (heat transport capability) in the magnetically-driven heat transport (cooling) device using the binary TSMF was fully investigated with the set-up. The obtained results indicate that boiling of the organic mixture (before the magnetic fluid itself reaching boiling point) effectively enhances the heat transfer as well as boosting the flow to circulate in the closed loop by itself. A long-distance heat transport of 5 m is experimentally confirmed, transferring the thermal energy of 35.8 W, even when the device (circulation loop) is horizontally placed. The highlighted results reveal that the proposed cooling device is innovative in a sense of transporting substantial amount of thermal energy (heat) as well as a long distance heat transport. The development of the magnetically-driven heat transport device has a great potential to be replaced for the conventional heat pipe in application of thermal engineering.

Nonlinear Magnetic Dynamics and The Switching Phase Diagrams in Spintronic Devices

NASA Astrophysics Data System (ADS)

Yan, Shu

Spin-transfer torque induced magnetic switching, by which the spin-polarized current transfers its magnetic moment to the ferromagnetic layer and changes its magnetization, holds great promise towards faster and smaller magnetic bits in data-storage applications due to the lower power consumption and better scalability. We propose an analytic approach which can be used to calculate the switching phase diagram of a nanomagnetic system in the presence of both magnetic field and spin-transfer torque in an exact fashion. This method is applied to the study of switching conditions for the uniaxial, single domain magnetic layers in different spin-transfer devices. In a spin valve with spin polarization collinear with the easy axis, we get a modified Stoner-Wohlfarth astroid which represents many of the features that have been found in experiment. It also shows a self-crossing boundary and demonstrates a region with three stable equilibria. We demonstrate that the region of stable equilibria with energy near the maximum can be reached only through a narrow bottleneck in the field space, which sets a stringent requirement for magnetic field alignment in the experiments. Switching diagrams are then calculated for the setups with magnetic field not perfectly aligned with the easy axis. In a ferromagnet-heavy-metal bilayer device with strong spin Hall effect, the in plane current becomes spin-polarized and transfers its magnetic moment to the ferromagnetic layer by diffusion. The three-dimensional asymmetric phase diagram is calculated. In the case that the external field is confined in the vertical plane defined by the direction of the current and the easy axis, the spin-transfer torque shifts the conventional in-plane (IP) equilibria within the same plane, and also creates two out-of-plane (OOP) equilibria, one of which can be stable. The threshold switching currents for IP switching and OOP switching are discussed. We also address the magnetic switching processes. Damping switching and precessional switching are two different switching types that are typically considered in recent studies. In the damping mode the switching is slow and heavily depends on the initial deviation, while in the precessional mode the accurate manipulation of the field or current pulse is required. We propose a switching scenario for a fast and reliable switching by taking advantage of the out-of-plane stable equilibrium in the SHE induced magnetic switching. The magnetization is first driven by a pulse of field and current towards the OOP equilibrium without precession. Since it is in the lower half of the unit sphere, no backwards pulse is required for a complete switching. This indicates a potentially feasible method of reliable ultra-fast magnetic control.

Active Magnetic Regenerative Liquefier

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

Barclay, John A.; Oseen-Send, Kathryn; Ferguson, Luke

2016-01-12

This final report for the DOE Project entitled Active Magnetic Regenerative Liquefier (AMRL) funded under Grant DE-FG36-08GO18064 to Heracles Energy Corporation d.b.a. Prometheus Energy (Heracles/Prometheus) describes an active magnetic regenerative refrigerator (AMRR) prototype designed and built during the period from July 2008 through May 2011. The primary goal of this project was to make significant technical advances toward highly efficient liquefaction of hydrogen. Conventional hydrogen liquefiers at any scale have a maximum FOM of ~0.35 due primarily to the intrinsic difficulty of rapid, efficient compression of either hydrogen or helium working gases. Numerical simulation modeling of high performance AMRL designsmore » indicates certain designs have promise to increase thermodynamic efficiency from a FOM of ~0.35 toward ~0.5 to ~0.6. The technical approach was the use of solid magnetic working refrigerants cycled in and out of high magnetic fields to build an efficient active regenerative magnetic refrigeration module providing cooling power for AMRL. A single-stage reciprocating AMRR with a design temperature span from ~290 K to ~120 K was built and tested with dual magnetic regenerators moving in and out of the conductively-cooled superconducting magnet subsystem. The heat transfer fluid (helium) was coupled to the process stream (refrigeration/liquefaction load) via high performance heat exchangers. In order to maximize AMRR efficiency a helium bypass loop with adjustable flow was incorporated in the design because the thermal mass of magnetic refrigerants is higher in low magnetic field than in high magnetic field. Heracles/Prometheus designed experiments to measure AMRR performance under a variety of different operational parameters such as cycle frequency, magnetic field strength, heat transfer fluid flow rate, amount of bypass flow of the heat transfer fluid while measuring work input, temperature span, cooling capability as a function of cold temperature as a function of the amount of bypass flow of the heat transfer fluid. The operational AMRR prototype can be used to answer key questions such as the best recipe for multiple layers of different magnetic refrigerants in one or more integrated regenerators with varying amounts of bypass flow of the heat transfer fluid. Layered regenerators are necessary to span the AMRR range from 290 K to 120K. Our AMRR performance simulation model predicts that ~10-15 % of bypass flow should significantly improve the thermodynamic performance. Initial results obtained with regenerators made of gadolinium spheres were very encouraging; a temperature span of ~ 50 K (between 295K and 245 K) across both regenerators was achieved with zero bypass flow of the heat transfer fluid and with the magnetic field strength of ~4 T.« less

Highly Efficient Wireless Powering for Autonomous Structural Health Monitoring and Test/Evaluation Systems

DTIC Science & Technology

2016-07-27

ADDRESS (ES) U.S. Army Research Office P.O. Box 12211 Research Triangle Park, NC 27709-2211 Wireless Power Transfer , Structural Health Monitoring...efficient strongly coupled magnetic resonant systems, Wireless Power Transfer , (03 2014): 0. doi: 10.1017/wpt.2014.3 TOTAL: 1 Received Paper TOTAL...2016 Received Paper . Miniaturized Strongly Coupled Magnetic Resonant Systems for Wireless Power Transfer , 2016 IEEE Antennas Propagat. Society

Magnetization hysteresis electron paramagnetic resonance. A new null phase insensitive saturation transfer EPR technique with high sensitivity to slow motion.

PubMed Central

Vistnes, A I

1983-01-01

In electron paramagnetic resonance (EPR) nonlinear phenomena with respect to magnetic-field modulation are often studied by out-of-phase spectra recordings. The existence of a nonzero out-of-phase signal implies that the EPR signal is phase shifted relative to the modulation signal. This phase shift is called a magnetization hysteresis. The hysteresis angle varies during a sweep through the resonance conditions for a free radical. By recording this variation, a magnetization hysteresis (MH) spectrum results. In practice, a MH spectrum is computer calculated from two EPR spectra detected with a 90 degree difference in phase setting. There is no need for a careful null-phase calibration like that in traditional analysis of nonlinearities. The MH spectra calculated from second harmonic EPR spectra of spin labels were highly dependent on the rotational correlation time. The technique can therefore be used to study slow molecular motion. In the present work MH spectra and Hemminga and deJager's magnitude saturation transfer EPR spectra (Hemminga, M. A., and P. A. deJager, 1981, J. Magn. Reson., 43:324-327) have been analyzed to define parameters that can describe variations in the rotational correlation time. A novel modification of the sample holder and temperature regulation equipment is described. PMID:6309263

Density functional theory study of small X-doped Mg(n) (X = Fe, Co, Ni, n = 1-9) bimetallic clusters: equilibrium structures, stabilities, electronic and magnetic properties.

PubMed

Kong, Fanjie; Hu, Yanfei

2014-03-01

The geometries, stabilities, and electronic and magnetic properties of Mg(n) X (X = Fe, Co, Ni, n = 1-9) clusters were investigated systematically within the framework of the gradient-corrected density functional theory. The results show that the Mg(n)Fe, Mg(n)Co, and Mg(n)Ni clusters have similar geometric structures and that the X atom in Mg(n)X clusters prefers to be endohedrally doped. The average atomic binding energies, fragmentation energies, second-order differences in energy, and HOMO-LUMO gaps show that Mg₄X (X = Fe, Co, Ni) clusters possess relatively high stability. Natural population analysis was performed and the results showed that the 3s and 4s electrons always transfer to the 3d and 4p orbitals in the bonding atoms, and that electrons also transfer from the Mg atoms to the doped atoms (Fe, Co, Ni). In addition, the spin magnetic moments were analyzed and compared. Several clusters, such as Mg₁,₂,₃,₄,₅,₆,₈,₉Fe, Mg₁,₂,₄,₅,₆,₈,₉Co, and Mg₁,₂,₅,₆,₇,₉Ni, present high magnetic moments (4 μ(B), 3 μ(B), and 2 μ(B), respectively).

MHD boundary layer slip flow and heat transfer of ferrofluid along a stretching cylinder with prescribed heat flux.

PubMed

Qasim, Muhammad; Khan, Zafar Hayat; Khan, Waqar Ahmad; Ali Shah, Inayat

2014-01-01

This study investigates the magnetohydrodynamic (MHD) flow of ferrofluid along a stretching cylinder. The velocity slip and prescribed surface heat flux boundary conditions are employed on the cylinder surface. Water as conventional base fluid containing nanoparticles of magnetite (Fe3O4) is used. Comparison between magnetic (Fe3O4) and non-magnetic (Al2O3) nanoparticles is also made. The governing non-linear partial differential equations are reduced to non-linear ordinary differential equations and then solved numerically using shooting method. Present results are compared with the available data in the limiting cases. The present results are found to be in an excellent agreement. It is observed that with an increase in the magnetic field strength, the percent difference in the heat transfer rate of magnetic nanoparticles with Al2O3 decreases. Surface shear stress and the heat transfer rate at the surface increase as the curvature parameter increases, i.e curvature helps to enhance the heat transfer.

Magnetic metamaterial superlens for increased range wireless power transfer.

PubMed

Lipworth, Guy; Ensworth, Joshua; Seetharam, Kushal; Huang, Da; Lee, Jae Seung; Schmalenberg, Paul; Nomura, Tsuyoshi; Reynolds, Matthew S; Smith, David R; Urzhumov, Yaroslav

2014-01-10

The ability to wirelessly power electrical devices is becoming of greater urgency as a component of energy conservation and sustainability efforts. Due to health and safety concerns, most wireless power transfer (WPT) schemes utilize very low frequency, quasi-static, magnetic fields; power transfer occurs via magneto-inductive (MI) coupling between conducting loops serving as transmitter and receiver. At the "long range" regime - referring to distances larger than the diameter of the largest loop - WPT efficiency in free space falls off as (1/d)(6); power loss quickly approaches 100% and limits practical implementations of WPT to relatively tight distances between power source and device. A "superlens", however, can concentrate the magnetic near fields of a source. Here, we demonstrate the impact of a magnetic metamaterial (MM) superlens on long-range near-field WPT, quantitatively confirming in simulation and measurement at 13-16 MHz the conditions under which the superlens can enhance power transfer efficiency compared to the lens-less free-space system.

Quantum approach of mesoscopic magnet dynamics with spin transfer torque

NASA Astrophysics Data System (ADS)

Wang, Yong; Sham, L. J.

2013-05-01

We present a theory of magnetization dynamics driven by spin-polarized current in terms of the quantum master equation. In the spin coherent state representation, the master equation becomes a Fokker-Planck equation, which naturally includes the spin transfer and quantum fluctuation. The current electron scattering state is correlated to the magnet quantum states, giving rise to quantum correction to the electron transport properties in the usual semiclassical theory. In the large-spin limit, the magnetization dynamics is shown to obey the Hamilton-Jacobi equation or the Hamiltonian canonical equations.

Magnetic Nozzle and Plasma Detachment Experiment

NASA Technical Reports Server (NTRS)

Chavers, Gregory; Dobson, Chris; Jones, Jonathan; Martin, Adam; Bengtson, Roger D.; Briezman, Boris; Arefiev, Alexey; Cassibry, Jason; Shuttpelz, Branwen; Deline, Christopher

2006-01-01

High power plasma propulsion can move large payloads for orbit transfer (such as the ISS), lunar missions, and beyond with large savings in fuel consumption owing to the high specific impulse. At high power, lifetime of the thruster becomes an issue. Electrodeless devices with magnetically guided plasma offer the advantage of long life since magnetic fields confine the plasma radially and keep it from impacting the material surfaces. For decades, concerns have been raised about the plasma remaining attached to the magnetic field and returning to the vehicle along the closed magnetic field lines. Recent analysis suggests that this may not be an issue of the magnetic field is properly shaped in the nozzle region and the plasma has sufficient energy density to stretch the magnetic field downstream. An experiment was performed to test the theory regarding the Magneto-hydrodynamic (MHD) detachment scenario. Data from this experiment will be presented. The Variable Specific Impulse Magnetoplasma Rocket (VASIMR) being developed by the Ad Astra Rocket Company uses a magnetic nozzle as described above. The VASIMR is also a leading candidate for exploiting an electric propulsion test platform being considered for the ISS.

Computational Analysis of Enhanced Magnetic Bioseparation in Microfluidic Systems with Flow-Invasive Magnetic Elements

PubMed Central

Khashan, S. A.; Alazzam, A.; Furlani, E. P.

2014-01-01

A microfluidic design is proposed for realizing greatly enhanced separation of magnetically-labeled bioparticles using integrated soft-magnetic elements. The elements are fixed and intersect the carrier fluid (flow-invasive) with their length transverse to the flow. They are magnetized using a bias field to produce a particle capture force. Multiple stair-step elements are used to provide efficient capture throughout the entire flow channel. This is in contrast to conventional systems wherein the elements are integrated into the walls of the channel, which restricts efficient capture to limited regions of the channel due to the short range nature of the magnetic force. This severely limits the channel size and hence throughput. Flow-invasive elements overcome this limitation and enable microfluidic bioseparation systems with superior scalability. This enhanced functionality is quantified for the first time using a computational model that accounts for the dominant mechanisms of particle transport including fully-coupled particle-fluid momentum transfer. PMID:24931437

MHD effects on heat transfer and entropy generation of nanofluid flow in an open cavity

NASA Astrophysics Data System (ADS)

Mehrez, Zouhaier; El Cafsi, Afif; Belghith, Ali; Le Quéré, Patrick

2015-01-01

The present numerical work investigates the effect of an external oriented magnetic field on heat transfer and entropy generation of Cu-water nanofluid flow in an open cavity heated from below. The governing equations are solved numerically by the finite-volume method. The study has been carried out for a wide range of solid volume fraction 0≤φ≤0.06, Hartmann number 0≤Ha≤100, Reynolds number 100≤Re≤500 and Richardson number 0.001≤Ri≤1 at three inclination angles of magnetic field γ: 0°, 45° and 90°. The numerical results are given by streamlines, isotherms, average Nusselt number, average entropy generation and Bejan number. The results show that flow behavior, temperature distribution, heat transfer and entropy generation are strongly affected by the presence of a magnetic field. The average Nusselt number and entropy generation, which increase by increasing volume fraction of nanoparticles, depend mainly on the Hartmann number and inclination angle of the magnetic field. The variation rates of heat transfer and entropy generation while adding nanoparticles or applying a magnetic field depend on the Richardson and Reynolds numbers.

A method for transferring NASTRAN data between dissimilar computers. [application to CDC 6000 series, IBM 360-370 series, and Univac 1100 series computers

NASA Technical Reports Server (NTRS)

Rogers, J. L., Jr.

1973-01-01

The NASTRAN computer program is capable of executing on three different types of computers: (1) the CDC 6000 series, (2) the IBM 360-370 series, and (3) the Univac 1100 series. A typical activity requiring transfer of data between dissimilar computers is the analysis of a large structure such as the space shuttle by substructuring. Models of portions of the vehicle which have been analyzed by subcontractors using their computers must be integrated into a model of the complete structure by the prime contractor on his computer. Presently the transfer of NASTRAN matrices or tables between two different types of computers is accomplished by punched cards or a magnetic tape containing card images. These methods of data transfer do not satisfy the requirements for intercomputer data transfer associated with a substructuring activity. To provide a more satisfactory transfer of data, two new programs, RDUSER and WRTUSER, were created.

Synthesis of Natural Electric and Magnetic Time Series Using Impulse Responses of Inter-station Transfer Functions and a Reference

NASA Astrophysics Data System (ADS)

Wang, H.; Cheng, J.

2017-12-01

A method to Synthesis natural electric and magnetic Time series is proposed whereby the time series of local site are derived using an Impulse Response and a reference (STIR). The method is based on the assumption that the external source of magnetic fields are uniform, and the electric and magnetic fields acquired at the surface satisfy a time-independent linear relation in frequency domain.According to the convolution theorem, we can synthesize natural electric and magnetic time series using the impulse responses of inter-station transfer functions with a reference. Applying this method, two impulse responses need to be estimated: the quasi-MT impulse response tensor and the horizontal magnetic impulse response tensor. These impulse response tensors relate the local horizontal electric and magnetic components with the horizontal magnetic components at a reference site, respectively. Some clean segments of times series are selected to estimate impulse responses by using least-square (LS) method. STIR is similar with STIN (Wang, 2017), but STIR does not need to estimate the inter-station transfer functions, and the synthesized data are more accurate in high frequency, where STIN fails when the inter-station transfer functions are contaminated severely. A test with good quality of MT data shows that synthetic time-series are similar to natural electric and magnetic time series. For contaminated AMT example, when this method is used to remove noise present at the local site, the scatter of MT sounding curves are clear reduced, and the data quality are improved. *This work is funded by National Key R&D Program of China(2017YFC0804105),National Natural Science Foundation of China (41604064, 51574250), State Key Laboratory of Coal Resources and Safe Mining ,China University of Mining & Technology,(SKLCRSM16DC09)

Magnetically Recoverable Supported Ruthenium Catalyst for Hydrogenation of Alkynes and Transfer Hydrogenation of Carbonyl Compounds

EPA Science Inventory

A ruthenium (Ru) catalyst supported on magnetic nanoparticles (NiFe2O4) has been successfully synthesized and used for hydrogenation of alkynes at room temperature as well as transfer hydrogenation of a number of carbonyl compounds under microwave irradiation conditions. The cata...

Magnetically Suspended Linear Pulse Motor for Semiconductor Wafer Transfer in Vacuum Chamber

NASA Technical Reports Server (NTRS)

Moriyama, Shin-Ichi; Hiraki, Naoji; Watanabe, Katsuhide; Kanemitsu, Yoichi

1996-01-01

This paper describes a magnetically suspended linear pulse motor for a semiconductor wafer transfer robot in a vacuum chamber. The motor can drive a wafer transfer arm horizontally without mechanical contact. In the construction of the magnetic suspension system, four pairs of linear magnetic bearings for the lift control are used for the guidance control as well. This approach allows us to make the whole motor compact in size and light in weight. The tested motor consists of a double-sided stator and a transfer arm with a width of 50 mm and a total length of 700 mm. The arm, like a ladder in shape, is designed as the floating element with a tooth width of 4 mm (a tooth pitch of 8 mm). The mover mass is limited to about 1.6 kg by adopting such an arm structure, and the ratio of thrust to mover mass reaches to 3.2 N/kg under a broad air gap (1 mm) between the stator teeth and the mover teeth. The performance testing was carried out with a transfer distance less than 450 mm and a transfer speed less than 560 mm/s. The attitude of the arm was well controlled by the linear magnetic bearings with a combined use, and consequently the repeatability on the positioning of the arm reached to about 2 micron. In addition, the positioning accuracy was improved up to about 30 micron through a compensation of the 128-step wave current which was used for the micro-step drive with a step increment of 62.5 micron.

MESSENGER observations of magnetic reconnection in Mercury's magnetosphere.

PubMed

Slavin, James A; Acuña, Mario H; Anderson, Brian J; Baker, Daniel N; Benna, Mehdi; Boardsen, Scott A; Gloeckler, George; Gold, Robert E; Ho, George C; Korth, Haje; Krimigis, Stamatios M; McNutt, Ralph L; Raines, Jim M; Sarantos, Menelaos; Schriver, David; Solomon, Sean C; Trávnícek, Pavel; Zurbuchen, Thomas H

2009-05-01

Solar wind energy transfer to planetary magnetospheres and ionospheres is controlled by magnetic reconnection, a process that determines the degree of connectivity between the interplanetary magnetic field (IMF) and a planet's magnetic field. During MESSENGER's second flyby of Mercury, a steady southward IMF was observed and the magnetopause was threaded by a strong magnetic field, indicating a reconnection rate ~10 times that typical at Earth. Moreover, a large flux transfer event was observed in the magnetosheath, and a plasmoid and multiple traveling compression regions were observed in Mercury's magnetotail, all products of reconnection. These observations indicate that Mercury's magnetosphere is much more responsive to IMF direction and dominated by the effects of reconnection than that of Earth or the other magnetized planets.

Magnetization switching in ferromagnets by adsorbed chiral molecules without current or external magnetic field.

PubMed

Ben Dor, Oren; Yochelis, Shira; Radko, Anna; Vankayala, Kiran; Capua, Eyal; Capua, Amir; Yang, See-Hun; Baczewski, Lech Tomasz; Parkin, Stuart Stephen Papworth; Naaman, Ron; Paltiel, Yossi

2017-02-23

Ferromagnets are commonly magnetized by either external magnetic fields or spin polarized currents. The manipulation of magnetization by spin-current occurs through the spin-transfer-torque effect, which is applied, for example, in modern magnetoresistive random access memory. However, the current density required for the spin-transfer torque is of the order of 1 × 10 6  A·cm -2 , or about 1 × 10 25 electrons s -1 cm -2 . This relatively high current density significantly affects the devices' structure and performance. Here we demonstrate magnetization switching of ferromagnetic thin layers that is induced solely by adsorption of chiral molecules. In this case, about 10 13 electrons per cm 2 are sufficient to induce magnetization reversal. The direction of the magnetization depends on the handedness of the adsorbed chiral molecules. Local magnetization switching is achieved by adsorbing a chiral self-assembled molecular monolayer on a gold-coated ferromagnetic layer with perpendicular magnetic anisotropy. These results present a simple low-power magnetization mechanism when operating at ambient conditions.

Magnetization switching in ferromagnets by adsorbed chiral molecules without current or external magnetic field

PubMed Central

Ben Dor, Oren; Yochelis, Shira; Radko, Anna; Vankayala, Kiran; Capua, Eyal; Capua, Amir; Yang, See-Hun; Baczewski, Lech Tomasz; Parkin, Stuart Stephen Papworth; Naaman, Ron; Paltiel, Yossi

2017-01-01

Ferromagnets are commonly magnetized by either external magnetic fields or spin polarized currents. The manipulation of magnetization by spin-current occurs through the spin-transfer-torque effect, which is applied, for example, in modern magnetoresistive random access memory. However, the current density required for the spin-transfer torque is of the order of 1 × 106 A·cm−2, or about 1 × 1025 electrons s−1 cm−2. This relatively high current density significantly affects the devices' structure and performance. Here we demonstrate magnetization switching of ferromagnetic thin layers that is induced solely by adsorption of chiral molecules. In this case, about 1013 electrons per cm2 are sufficient to induce magnetization reversal. The direction of the magnetization depends on the handedness of the adsorbed chiral molecules. Local magnetization switching is achieved by adsorbing a chiral self-assembled molecular monolayer on a gold-coated ferromagnetic layer with perpendicular magnetic anisotropy. These results present a simple low-power magnetization mechanism when operating at ambient conditions. PMID:28230054

Nanofluid flow and heat transfer due to a stretching cylinder in the presence of magnetic field

NASA Astrophysics Data System (ADS)

Ashorynejad, H. R.; Sheikholeslami, M.; Pop, I.; Ganji, D. D.

2013-03-01

In this paper, flow and heat transfer of a nanofluid over a stretching cylinder in the presence of magnetic field has been investigated. The governing partial differential equations with the corresponding boundary conditions are reduced to a set of ordinary differential equations with the appropriate boundary conditions using similarity transformation, which is then solved numerically by the fourth order Runge-Kutta integration scheme featuring a shooting technique. Different types of nanoparticles as copper (Cu), silver (Ag), alumina (Al2O3) and titanium oxide (TiO2) with water as their base fluid has been considered. The influence of significant parameters such as nanoparticle volume fraction, nanofluids type, magnetic parameter and Reynolds number on the flow and heat transfer characteristics is discussed. It was found that the Nusselt number increases as each of Reynolds number or nanoparticles volume fraction increase, but it decreases as magnetic parameter increase. Also it can be found that choosing copper (for small of magnetic parameter) and alumina (for large values of magnetic parameter) leads to the highest cooling performance for this problem.

Maghemite nanoparticles with enhanced magnetic properties: one-pot preparation and ultrastable dextran shell.

PubMed

Di Corato, Riccardo; Aloisi, Alessandra; Rella, Simona; Greneche, Jean-Marc; Pugliese, Giammarino; Pellegrino, Teresa; Malitesta, Cosimino; Rinaldi, Rosaria

2018-05-10

In the field on nanomedicine, superparamagnetic nanoparticles are one of the most studied nanomaterials for theranostics. In this paper, a one-pot synthesis of magnetic nanoparticles is presented, with elevated control on particles size from 10 to 40 nm. The monitoring of vacuum level is here introduced as a crucial parameter for achieving a fine particle morphology. Magnetic properties of these nanoparticles are highly affected by disorders or mismatches in crystal structure. A prolonged oxidation step is applied to the obtained nanoparticles to transform the magnetic phases into a pure maghemite one, confirmed by a high resolution XPS analysis, by Mössbauer spectrometry and, indirectly, by increased performances in magnetization curves and in relaxation times. Afterward, the attained nanoparticles are transferred in water by a non-derivatized dextran coating. The thermogravimetric analysis confirms that the polysaccharide molecules replace the oleic acid on the surface by stabilizing the particles in aqueous phase and culture media. Preliminary in vitro test reveals as the dextran coated nanoparticles are not passively internalized from the cells. As proof of concept, a secondary layer of chitosan assures a positive charge to the nanoparticle surface, thus enhancing the cellular internalization.

Review of heat transfer problems associated with magnetically-confined fusion reactor concepts

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

Hoffman, M.A.; Werner, R.W.; Carlson, G.A.

1976-04-01

Conceptual design studies of possible fusion reactor configurations have revealed a host of interesting and sometimes extremely difficult heat transfer problems. The general requirements imposed on the coolant system for heat removal of the thermonuclear power from the reactor are discussed. In particular, the constraints imposed by the fusion plasma, neutronics, structure and magnetic field environment are described with emphasis on those aspects which are unusual or unique to fusion reactors. Then the particular heat transfer characteristics of various possible coolants including lithium, flibe, boiling alkali metals, and helium are discussed in the context of these general fusion reactor requirements.more » Some specific areas where further experimental and/or theoretical work is necessary are listed for each coolant along with references to the pertinent research already accomplished. Specialized heat transfer problems of the plasma injection and removal systems are also described. Finally, the challenging heat transfer problems associated with the superconducting magnets are reviewed, and once again some of the key unsolved heat transfer problems are enumerated.« less

Wireless Power Transfer for Space Applications

NASA Technical Reports Server (NTRS)

Ramos, Gabriel Vazquez; Yuan, Jiann-Shiun

2011-01-01

This paper introduces an implementation for magnetic resonance wireless power transfer for space applications. The analysis includes an equivalent impedance study, loop material characterization, source/load resonance coupling technique, and system response behavior due to loads variability. System characterization is accomplished by executing circuit design from analytical equations and simulations using Matlab and SPICE. The theory was validated by a combination of different experiments that includes loop material consideration, resonance coupling circuits considerations, electric loads considerations and a small scale proof-of-concept prototype. Experiment results shows successful wireless power transfer for all the cases studied. The prototype provided about 4.5 W of power to the load at a separation of -5 cm from the source using a power amplifier rated for 7 W.

Evaluation of the induced electric field and compliance procedure for a wireless power transfer system in an electrical vehicle.

PubMed

Laakso, Ilkka; Hirata, Akimasa

2013-11-07

In this study, an induced electric field in a human body is evaluated for the magnetic field leaked from a wireless power transfer system for charging an electrical vehicle. The magnetic field from the wireless power transfer system is modelled computationally, and its effectiveness is confirmed by comparison with the field measured in a previous study. The induced electric field in a human standing around the vehicle is smaller than the allowable limit prescribed in international guidelines, although the magnetic field strength in the human body is locally higher than the allowable external field strength. Correlation between the external magnetic field and the induced electric field is confirmed to be reasonable at least in the standing posture, which is the case discussed in the international standard. Based on this finding, we discussed and confirmed the applicability of a three-point magnetic field measurement at heights of 0.5, 1.0, and 1.5 m for safety compliance.

Spin Transfer torques in Antiferromagnets

NASA Astrophysics Data System (ADS)

Saidaoui, Hamed; Waintal, Xavier; Manchon, Aurelien; Spsms, Cea, Grenoble France Collaboration

2013-03-01

Spin Transfer Torque (STT) has attracted tremendously growing interest in the past two decades. Consisting on the transfer of spin angular momentum of a spin polarized current to local magnetic moments, the STT gives rise to a complex dynamics of the magnetization. Depending on the the structure, the STT shows a dominated In plane component for spin valves, whereas both components coexist for magnetic tunneling junctions (MTJ). For latter case the symmetry of the structure is considered to be decisive in identifying the nature and behavior of the torque. In the present study we are interested in magnetic structures where we substitute either one or both of the magnetic layers by antiferromagnets (AF). We use Non-equilibrium Green's function formalism applied on a tight-binding model to investigate the nature of the spin torque. We notice the presence of two types of torque exerted on (AF), a torque which tends to rotate the order parameter and another one that competes with the exchange interaction. We conclude by comparison with previous works.

1998 Conference on Precision Electromagnetic Measurements Digest. Proceedings.

NASA Astrophysics Data System (ADS)

Nelson, T. L.

The following topics were dealt with: fundamental constants; caesium standards; AC-DC transfer; impedance measurement; length measurement; units; statistics; cryogenic resonators; time transfer; QED; resistance scaling and bridges; mass measurement; atomic fountains and clocks; single electron transport; Newtonian constant of gravitation; stabilised lasers and frequency measurements; cryogenic current comparators; optical frequency standards; high voltage devices and systems; international compatibility; magnetic measurement; precision power measurement; high resolution spectroscopy; DC transport standards; waveform acquisition and analysis; ion trap standards; optical metrology; quantised Hall effect; Josephson array comparisons; signal generation and measurement; Avogadro constant; microwave networks; wideband power standards; antennas, fields and EMC; quantum-based standards.

Resonant-cavity antenna for plasma heating

DOEpatents

Perkins, F.W. Jr.; Chiu, S.C.; Parks, P.; Rawls, J.M.

1984-01-10

This invention relates generally to a method and apparatus for transferring energy to a plasma immersed in a magnetic field, and relates particularly to an apparatus for heating a plasma of low atomic number ions to high temperatures by transfer of energy to plasma resonances, particularly the fundamental and harmonics of the ion cyclotron frequency of the plasma ions. This invention transfers energy from an oscillating radio-frequency field to a plasma resonance of a plasma immersed in a magnetic field.

Controlling the column spacing in isothermal magnetic advection to enable tunable heat and mass transfer.

DOE PAGES

Solis, Kyle Jameson; Martin, James E.

2012-11-01

Isothermal magnetic advection is a recently discovered method of inducing highly organized, non-contact flow lattices in suspensions of magnetic particles, using only uniform ac magnetic fields of modest strength. The initiation of these vigorous flows requires neither a thermal gradient nor a gravitational field and so can be used to transfer heat and mass in circumstances where natural convection does not occur. These advection lattices are comprised of a square lattice of antiparallel flow columns. If the column spacing is sufficiently large compared to the column length, and the flow rate within the columns is sufficiently large, then one wouldmore » expect efficient transfer of both heat and mass. Otherwise, the flow lattice could act as a countercurrent heat exchanger and only mass will be efficiently transferred. Although this latter case might be useful for feeding a reaction front without extracting heat, it is likely that most interest will be focused on using IMA for heat transfer. In this paper we explore the various experimental parameters of IMA to determine which of these can be used to control the column spacing. These parameters include the field frequency, strength, and phase relation between the two field components, the liquid viscosity and particle volume fraction. We find that the column spacing can easily be tuned over a wide range, to enable the careful control of heat and mass transfer.« less

Low-current-density spin-transfer switching in Gd{sub 22}Fe{sub 78}-MgO magnetic tunnel junction

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

Kinjo, Hidekazu, E-mail: kinjou.h-lk@nhk.or.jp; Machida, Kenji; Aoshima, Ken-ichi

2014-05-28

Magnetization switching of a relatively thick (9 nm) Gd-Fe free layer was achieved with a low spin injection current density of 1.0 × 10{sup 6} A/cm{sup 2} using MgO based magnetic tunnel junction devices, fabricated for light modulators. At about 560 × 560 nm{sup 2} in size, the devices exhibited a tunneling magnetoresistance ratio of 7%. This low-current switching is mainly attributed to thermally assisted spin-transfer switching in consequence of its thermal magnetic behavior arising from Joule heating.

Magnetic and optoelectronic properties of gold nanocluster-thiophene assembly.

PubMed

Qin, Wei; Lohrman, Jessica; Ren, Shenqiang

2014-07-07

Nanohybrids consisting of Au nanocluster and polythiophene nanowire assemblies exhibit unique thermal-responsive optical behaviors and charge-transfer controlled magnetic and optoelectronic properties. The ultrasmall Au nanocluster enhanced photoabsorption and conductivity effectively improves the photocurrent of nanohybrid based photovoltaics, leading to an increase of power conversion efficiency by 14 % under AM 1.5 illumination. In addition, nanohybrids exhibit electric field controlled spin resonance and magnetic field sensing behaviors, which open up the potential of charge-transfer complex system where the magnetism and optoelectronics interact. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

IS VOYAGER 1 INSIDE AN INTERSTELLAR FLUX TRANSFER EVENT?

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

Schwadron, N. A.; McComas, D. J., E-mail: n.schwadron@unh.edu

Plasma wave observations from Voyager 1 have recently shown large increases in plasma density, to about 0.1 cm{sup –3}, consistent with the density of the local interstellar medium. However, corresponding magnetic field observations continue to show the spiral magnetic field direction observed throughout the inner heliosheath. These apparently contradictory observations may be reconciled if Voyager 1 is inside an interstellar flux transfer event—similar to flux transfer events routinely seen at the Earth's magnetopause. If this were the case, Voyager 1 remains inside the heliopause and based on the Voyager 1 observations we can determine the polarity of the interstellar magnetic field for the first time.

Wireless power transfer based on dielectric resonators with colossal permittivity

NASA Astrophysics Data System (ADS)

Song, Mingzhao; Belov, Pavel; Kapitanova, Polina

2016-11-01

Magnetic resonant wireless power transfer system based on dielectric disk resonators made of colossal permittivity (ɛ = 1000) and low loss (tan δ = 2.5 × 10-4) microwave ceramic is experimentally investigated. The system operates at the magnetic dipole mode excited in the resonators providing maximal power transfer efficiency of 90% at the frequency 232 MHz. By applying an impedance matching technique, the efficiency of 50% is achieved within the separation between the resonators d = 16 cm (3.8 radii of the resonator). The separation, misalignment and rotation dependencies of wireless power transfer efficiency are experimentally studied.

Improved methods for the measurement and analysis of stellar magnetic fields

NASA Technical Reports Server (NTRS)

Saar, Steven H.

1988-01-01

The paper presents several improved methods for the measurement of magnetic fields on cool stars which take into account simple radiative transfer effects and the exact Zeeman patterns. Using these methods, high-resolution, low-noise data can be fitted with theoretical line profiles to determine the mean magnetic field strength in stellar active regions and a model-dependent fraction of the stellar surface (filling factor) covered by these regions. Random errors in the derived field strength and filling factor are parameterized in terms of signal-to-noise ratio, wavelength, spectral resolution, stellar rotation rate, and the magnetic parameters themselves. Weak line blends, if left uncorrected, can have significant systematic effects on the derived magnetic parameters, and thus several methods are developed to compensate partially for them. The magnetic parameters determined by previous methods likely have systematic errors because of such line blends and because of line saturation effects. Other sources of systematic error are explored in detail. These sources of error currently make it difficult to determine the magnetic parameters of individual stars to better than about + or - 20 percent.

Magnetic field tunability of spin polarized excitations in a high temperature magnet

NASA Astrophysics Data System (ADS)

Holinsworth, Brian; Sims, Hunter; Cherian, Judy; Mazumdar, Dipanjan; Harms, Nathan; Chapman, Brandon; Gupta, Arun; McGill, Steve; Musfeldt, Janice

Magnetic semiconductors are at the heart of modern device physics because they naturally provide a non-zero magnetic moment below the ordering temperature, spin-dependent band gap, and spin polarization that originates from exchange-coupled magnetization or an applied field creating a spin-split band structure. Strongly correlated spinel ferrites are amongst the most noteworthy contenders for semiconductor spintronics. NiFe2O4, in particular, displays spin-filtering, linear magnetoresistance, and wide application in the microwave regime. To unravel the spin-charge interaction in NiFe2O4, we bring together magnetic circular dichroism, photoconductivity, and prior optical absorption with complementary first principles calculations. Analysis uncovers a metamagnetic transition modifying electronic structure in the minority channel below the majority channel gap, exchange splittings emerging from spin-split bands, anisotropy of excitons surrounding the indirect gap, and magnetic-field dependent photoconductivity. These findings open the door for the creation and control of spin-polarized excitations from minority channel charge charge transfer in NiFe2O4 and other members of the spinel ferrite family.

Towards sub-nanometer real-space observation of spin and orbital magnetism at the Fe/MgO interface

PubMed Central

Thersleff, Thomas; Muto, Shunsuke; Werwiński, Mirosław; Spiegelberg, Jakob; Kvashnin, Yaroslav; Hjӧrvarsson, Björgvin; Eriksson, Olle; Rusz, Ján; Leifer, Klaus

2017-01-01

While the performance of magnetic tunnel junctions based on metal/oxide interfaces is determined by hybridization, charge transfer, and magnetic properties at the interface, there are currently only limited experimental techniques with sufficient spatial resolution to directly observe these effects simultaneously in real-space. In this letter, we demonstrate an experimental method based on Electron Magnetic Circular Dichroism (EMCD) that will allow researchers to simultaneously map magnetic transitions and valency in real-space over interfacial cross-sections with sub-nanometer spatial resolution. We apply this method to an Fe/MgO bilayer system, observing a significant enhancement in the orbital to spin moment ratio that is strongly localized to the interfacial region. Through the use of first-principles calculations, multivariate statistical analysis, and Electron Energy-Loss Spectroscopy (EELS), we explore the extent to which this enhancement can be attributed to emergent magnetism due to structural confinement at the interface. We conclude that this method has the potential to directly visualize spin and orbital moments at buried interfaces in magnetic systems with unprecedented spatial resolution. PMID:28338011

Spin dynamics and frequency dependence of magnetic damping study in soft ferromagnetic FeTaC film with a stripe domain structure

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

Samantaray, B., E-mail: iitg.biswanath@gmail.com; Ranganathan, R.; Mandal, P.

Perpendicular magnetic anisotropy (PMA) and low magnetic damping are the key factors for the free layer magnetization switching by spin transfer torque technique in magnetic tunnel junction devices. The magnetization precessional dynamics in soft ferromagnetic FeTaC thin film with a stripe domain structure was explored in broad band frequency range by employing micro-strip ferromagnetic resonance technique. The polar angle variation of resonance field and linewidth at different frequencies have been analyzed numerically using Landau-Lifshitz-Gilbert equation by taking into account the total free energy density of the film. The numerically estimated parameters Landé g-factor, PMA constant, and effective magnetization are foundmore » to be 2.1, 2 × 10{sup 5} erg/cm{sup 3} and 7145 Oe, respectively. The frequency dependence of Gilbert damping parameter (α) is evaluated by considering both intrinsic and extrinsic effects into the total linewidth analysis. The value of α is found to be 0.006 at 10 GHz and it increases monotonically with decreasing precessional frequency.« less

Towards sub-nanometer real-space observation of spin and orbital magnetism at the Fe/MgO interface

NASA Astrophysics Data System (ADS)

Thersleff, Thomas; Muto, Shunsuke; Werwiński, Mirosław; Spiegelberg, Jakob; Kvashnin, Yaroslav; Hjӧrvarsson, Björgvin; Eriksson, Olle; Rusz, Ján; Leifer, Klaus

2017-03-01

While the performance of magnetic tunnel junctions based on metal/oxide interfaces is determined by hybridization, charge transfer, and magnetic properties at the interface, there are currently only limited experimental techniques with sufficient spatial resolution to directly observe these effects simultaneously in real-space. In this letter, we demonstrate an experimental method based on Electron Magnetic Circular Dichroism (EMCD) that will allow researchers to simultaneously map magnetic transitions and valency in real-space over interfacial cross-sections with sub-nanometer spatial resolution. We apply this method to an Fe/MgO bilayer system, observing a significant enhancement in the orbital to spin moment ratio that is strongly localized to the interfacial region. Through the use of first-principles calculations, multivariate statistical analysis, and Electron Energy-Loss Spectroscopy (EELS), we explore the extent to which this enhancement can be attributed to emergent magnetism due to structural confinement at the interface. We conclude that this method has the potential to directly visualize spin and orbital moments at buried interfaces in magnetic systems with unprecedented spatial resolution.

A chiral-based magnetic memory device without a permanent magnet

PubMed Central

Dor, Oren Ben; Yochelis, Shira; Mathew, Shinto P.; Naaman, Ron; Paltiel, Yossi

2013-01-01

Several technologies are currently in use for computer memory devices. However, there is a need for a universal memory device that has high density, high speed and low power requirements. To this end, various types of magnetic-based technologies with a permanent magnet have been proposed. Recent charge-transfer studies indicate that chiral molecules act as an efficient spin filter. Here we utilize this effect to achieve a proof of concept for a new type of chiral-based magnetic-based Si-compatible universal memory device without a permanent magnet. More specifically, we use spin-selective charge transfer through a self-assembled monolayer of polyalanine to magnetize a Ni layer. This magnitude of magnetization corresponds to applying an external magnetic field of 0.4 T to the Ni layer. The readout is achieved using low currents. The presented technology has the potential to overcome the limitations of other magnetic-based memory technologies to allow fabricating inexpensive, high-density universal memory-on-chip devices. PMID:23922081

A chiral-based magnetic memory device without a permanent magnet.

PubMed

Ben Dor, Oren; Yochelis, Shira; Mathew, Shinto P; Naaman, Ron; Paltiel, Yossi

2013-01-01

Several technologies are currently in use for computer memory devices. However, there is a need for a universal memory device that has high density, high speed and low power requirements. To this end, various types of magnetic-based technologies with a permanent magnet have been proposed. Recent charge-transfer studies indicate that chiral molecules act as an efficient spin filter. Here we utilize this effect to achieve a proof of concept for a new type of chiral-based magnetic-based Si-compatible universal memory device without a permanent magnet. More specifically, we use spin-selective charge transfer through a self-assembled monolayer of polyalanine to magnetize a Ni layer. This magnitude of magnetization corresponds to applying an external magnetic field of 0.4 T to the Ni layer. The readout is achieved using low currents. The presented technology has the potential to overcome the limitations of other magnetic-based memory technologies to allow fabricating inexpensive, high-density universal memory-on-chip devices.

Smelting reduction and kinetics analysis of magnetic iron in copper slag using waste cooking oil.

PubMed

Li, Bo; Wang, Xubin; Wang, Hua; Wei, Yonggang; Hu, Jianhang

2017-05-25

To improve the recovery of copper, the viscosity of copper molten slag is decreased by the reduction of magnetic iron, which, in turn, accelerates the settling and separation of copper droplets from the slag. A new technology is proposed in which waste cooking oil is used as a reductant to reduce magnetic iron in the copper smelting slag and consequently reduce carbon emissions in the copper smelting process. A kinetic model of the reduction of magnetic iron in copper slag by waste cooking oil was built using experimental data, and the accuracy of the model was verified. The results indicated that the magnetic iron content in the copper slag decreased with increasing reduction time and an increase in temperature more efficiently reduced magnetic iron in the copper slag. The magnetic iron in the copper slag gradually transformed to fayalite, and the viscosity of the copper molten slag decreased as the magnetic iron content decreased during the reduction process. The reduction of magnetic iron in the copper molten slag using waste cooking oil was a first-order reaction, and the rate-limiting step was the mass transfer of Fe 3 O 4 through the liquid boundary layer.

Ruthenium supported on magnetic nanoparticles: An efficient and recoverable catalyst for hydrogenation of alkynes and transfer hydrogenation of carbonyl compounds

EPA Science Inventory

Ruthenium supported on surface modified magnetic nanoparticles (NiFe2O4) has been successfully synthesized and applied for hydrogenation of alkynes at room temperature as well as transfer hydrogenation of a number of carbonyl compounds under microwave irradiation conditions. The ...

Serial Magnetization Transfer Imaging in Acute Optic Neuritis

ERIC Educational Resources Information Center

Hickman, S. J.; Toosy, A. T.; Jones, S. J.; Altmann, D. R.; Miszkiel, K. A.; MacManus, D. G.; Barker, G. J.; Plant, G. T.; Thompson, A. J.; Miller, D.H.

2004-01-01

In serial studies of multiple sclerosis lesions, reductions in magnetization transfer ratio (MTR) are thought to be due to demyelination and axonal loss, with later rises due to remyelination. This study followed serial changes in MTR in acute optic neuritis in combination with clinical and electrophysiological measurements to determine if the MTR…

In-situ electric field in human body model in different postures for wireless power transfer system in an electrical vehicle.

PubMed

Shimamoto, Takuya; Laakso, Ilkka; Hirata, Akimasa

2015-01-07

The in-situ electric field of an adult male model in different postures is evaluated for exposure to the magnetic field leaked from a wireless power transfer system in an electrical vehicle. The transfer system is located below the centre of the vehicle body and the transferred power and frequency are 7 kW and 85 kHz, respectively. The in-situ electric field is evaluated for a human model (i) crouching near the vehicle, (ii) lying on the ground with or without his arm stretched, (iii) sitting in the driver's seat, and (iv) standing on a transmitting coil without a receiving coil. In each scenario, the maximum in-situ electric fields are lower than the allowable limit prescribed by international guidelines, although the local magnetic field strength in regions of the human body is higher than the allowable external magnetic field strength. The highest in-situ electric field is observed when the human body model is placed on the ground with his arm extended toward the coils, because of a higher magnetic field around the arm.

Fermi Level shifting, Charge Transfer and Induced Magnetic Coupling at La0.7Ca0.3MnO3/LaNiO3 Interface

PubMed Central

Ning, Xingkun; Wang, Zhanjie; Zhang, Zhidong

2015-01-01

A large magnetic coupling has been observed at the La0.7Ca0.3MnO3/LaNiO3 (LCMO/LNO) interface. The x-ray photoelectron spectroscopy (XPS) study results show that Fermi level continuously shifted across the LCMO/LNO interface in the interface region. In addition, the charge transfer between Mn and Ni ions of the type Mn3+ − Ni3+ → Mn4+ − Ni2+ with the oxygen vacancies are observed in the interface region. The intrinsic interfacial charge transfer can give rise to itinerant electrons, which results in a “shoulder feature” observed at the low binding energy in the Mn 2p core level spectra. Meanwhile, the orbital reconstruction can be mapped according to the Fermi level position and the charge transfer mode. It can be considered that the ferromagnetic interaction between Ni2+ and Mn4+ gives rise to magnetic regions that pin the ferromagnetic LCMO and cause magnetic coupling at the LCMO/LNO interface. PMID:25676088

Generation and characterization of gas bubbles in liquid metals

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

Eckert, S.; Gerbeth, G.; Witke, W.

1996-06-01

There is an ongoing research performed in the RCR on local transport phenomena in turbulent liquid metal (LM) duct flows exposed to external magnetic fields. In this context so-called MHD flow phenomena can be observed, which are unknown in usual hydraulic engineering. The field of interest covers also the influence of magnetic fields on the behaviour of liquid metal - gas mixtures. Profound knowledge on these LMMHD two-phase flow plays an important role in a variety of technological applications, in particular, in the design of Liquid-Metal MHD generators or for several metallurgical processes employing gas-stirred reactors. However, the highly empiricalmore » nature of two-phase flow analysis gives little hope for the prediction of MHD two-phase flows without extensive experimental data. A summary is given about the authors research activities focussing on two directions: (a) Momentum transfer between gas and liquid metal in a bubbly flow regime to investigate the influence of the external magnetic field on the velocity slip ration S (b) Peculiarities of the MHD turbulence to use small gas bubbles as local tracers in order to study the turbulent mass transfer.« less

Dynamic nuclear polarization of (1)H, (13)C, and (59)Co in a tris(ethylenediamine)cobalt(III) crystalline lattice doped with Cr(III).

PubMed

Corzilius, Björn; Michaelis, Vladimir K; Penzel, Susanne A; Ravera, Enrico; Smith, Albert A; Luchinat, Claudio; Griffin, Robert G

2014-08-20

The study of inorganic crystalline materials by solid-state NMR spectroscopy is often complicated by the low sensitivity of heavy nuclei. However, these materials often contain or can be prepared with paramagnetic dopants without significantly affecting the structure of the crystalline host. Dynamic nuclear polarization (DNP) is generally capable of enhancing NMR signals by transferring the magnetization of unpaired electrons to the nuclei. Therefore, the NMR sensitivity in these paramagnetically doped crystals might be increased by DNP. In this paper we demonstrate the possibility of efficient DNP transfer in polycrystalline samples of [Co(en)3Cl3]2·NaCl·6H2O (en = ethylenediamine, C2H8N2) doped with Cr(III) in varying concentrations between 0.1 and 3 mol %. We demonstrate that (1)H, (13)C, and (59)Co can be polarized by irradiation of Cr(III) with 140 GHz microwaves at a magnetic field of 5 T. We further explain our findings on the basis of electron paramagnetic resonance spectroscopy of the Cr(III) site and analysis of its temperature-dependent zero-field splitting, as well as the dependence of the DNP enhancement factor on the external magnetic field and microwave power. This first demonstration of DNP transfer from one paramagnetic metal ion to its diamagnetic host metal ion will pave the way for future applications of DNP in paramagnetically doped materials or metalloproteins.

Dynamic Nuclear Polarization of 1H, 13C, and 59Co in a Tris(ethylenediamine)cobalt(III) Crystalline Lattice Doped with Cr(III)

PubMed Central

2015-01-01

The study of inorganic crystalline materials by solid-state NMR spectroscopy is often complicated by the low sensitivity of heavy nuclei. However, these materials often contain or can be prepared with paramagnetic dopants without significantly affecting the structure of the crystalline host. Dynamic nuclear polarization (DNP) is generally capable of enhancing NMR signals by transferring the magnetization of unpaired electrons to the nuclei. Therefore, the NMR sensitivity in these paramagnetically doped crystals might be increased by DNP. In this paper we demonstrate the possibility of efficient DNP transfer in polycrystalline samples of [Co(en)3Cl3]2·NaCl·6H2O (en = ethylenediamine, C2H8N2) doped with Cr(III) in varying concentrations between 0.1 and 3 mol %. We demonstrate that 1H, 13C, and 59Co can be polarized by irradiation of Cr(III) with 140 GHz microwaves at a magnetic field of 5 T. We further explain our findings on the basis of electron paramagnetic resonance spectroscopy of the Cr(III) site and analysis of its temperature-dependent zero-field splitting, as well as the dependence of the DNP enhancement factor on the external magnetic field and microwave power. This first demonstration of DNP transfer from one paramagnetic metal ion to its diamagnetic host metal ion will pave the way for future applications of DNP in paramagnetically doped materials or metalloproteins. PMID:25069794

Direct enhancement of nitrogen-15 targets at high-field by fast ADAPT-SABRE

NASA Astrophysics Data System (ADS)

Roy, Soumya S.; Stevanato, Gabriele; Rayner, Peter J.; Duckett, Simon B.

2017-12-01

Signal Amplification by Reversible Exchange (SABRE) is an attractive nuclear spin hyperpolarization technique capable of huge sensitivity enhancement in nuclear magnetic resonance (NMR) detection. The resonance condition of SABRE hyperpolarization depends on coherent spin mixing, which can be achieved naturally at a low magnetic field. The optimum transfer field to spin-1/2 heteronuclei is technically demanding, as it requires field strengths weaker than the earth's magnetic field for efficient spin mixing. In this paper, we illustrate an approach to achieve strong 15N SABRE hyperpolarization at high magnetic field by a radio frequency (RF) driven coherent transfer mechanism based on alternate pulsing and delay to achieve polarization transfer. The presented scheme is found to be highly robust and much faster than existing related methods, producing ∼ 3 orders of magnitude 15N signal enhancement within 2 s of RF pulsing.

Direct enhancement of nitrogen-15 targets at high-field by fast ADAPT-SABRE.

PubMed

Roy, Soumya S; Stevanato, Gabriele; Rayner, Peter J; Duckett, Simon B

2017-12-01

Signal Amplification by Reversible Exchange (SABRE) is an attractive nuclear spin hyperpolarization technique capable of huge sensitivity enhancement in nuclear magnetic resonance (NMR) detection. The resonance condition of SABRE hyperpolarization depends on coherent spin mixing, which can be achieved naturally at a low magnetic field. The optimum transfer field to spin-1/2 heteronuclei is technically demanding, as it requires field strengths weaker than the earth's magnetic field for efficient spin mixing. In this paper, we illustrate an approach to achieve strong 15 N SABRE hyperpolarization at high magnetic field by a radio frequency (RF) driven coherent transfer mechanism based on alternate pulsing and delay to achieve polarization transfer. The presented scheme is found to be highly robust and much faster than existing related methods, producing ∼3 orders of magnitude 15 N signal enhancement within 2 s of RF pulsing. Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.

Enhancement of Spin-transfer torque switching via resonant tunneling

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

Chatterji, Niladri; Tulapurkar, Ashwin A.; Muralidharan, Bhaskaran

We propose the use of resonant tunneling as a route to enhance the spin-transfer torque switching characteristics of magnetic tunnel junctions. The proposed device structure is a resonant tunneling magnetic tunnel junction based on a MgO-semiconductor heterostructure sandwiched between a fixed magnet and a free magnet. Using the non-equilibrium Green's function formalism coupled self consistently with the Landau-Lifshitz-Gilbert-Slonczewski equation, we demonstrate enhanced tunnel magneto-resistance characteristics as well as lower switching voltages in comparison with traditional trilayer devices. Two device designs based on MgO based heterostructures are presented, where the physics of resonant tunneling leads to an enhanced spin transfer torquemore » thereby reducing the critical switching voltage by up to 44%. It is envisioned that the proof-of-concept presented here may lead to practical device designs via rigorous materials and interface studies.« less

Liquid neon heat transfer as applied to a 30 tesla cryomagnet

NASA Technical Reports Server (NTRS)

Papell, S. S.; Hendricks, R. C.

1975-01-01

Since superconducting magnets cooled by liquid helium are limited to magnetic fields of about 18 teslas, the design of a 30 tesla cryomagnet necessitates forced convection liquid neon heat transfer in small coolant channels. As these channels are too small to handle the vapor flow if the coolant were to boil, the design philosophy calls for suppressing boiling by subjecting the fluid to high pressures. Forced convection heat transfer data are obtained by using a blowdown technique to force the fluid vertically through a resistance-heated instrumented tube. The data are obtained at inlet temperatures between 28 and 34 K and system pressures between 28 to 29 bars. Data correlation is limited to a very narrow range of test conditions, since the tests were designed to simulate the heat transfer characteristics in the coolant channels of the 30 tesla cryomagnet concerned. The results can therefore be applied directly to the design of the magnet system.-

Advances in cryogenic engineering. Volume 27 - Proceedings of the Cryogenic Engineering Conference, San Diego, CA, August 11-14, 1981

NASA Technical Reports Server (NTRS)

Fast, R. W. (Editor)

1982-01-01

Applications of superconductivity are considered, taking into account MHD and fusion, generators, transformers, transmission lines, magnets for physics, cryogenic techniques, electrtronics, and aspects of magnet stability. Advances related to heat transfer in He I are discussed along with subjects related to theat transfer in He II, refrigeration of superconducting systems, refrigeration and liquefaction, dilution and magnetic refrigerators, refrigerators for space applications, mass transfer and flow phenomena, and the properties of fluids. Developments related to cryogenic applications are also explored, giving attention to bulk storage and transfer of cryogenic fluids, liquefied natural gas operations, space science and technology, and cryopumping. Topics related to cryogenic instrumentation and controls include the production and use of high grade silicon diode temperature sensors, the choice of strain gages for use in a large superconducting alternator, microprocessor control of cryogenic pressure, and instrumentation, data acquisition and reduction for a large spaceborne helium dewar.

Wireless power using magnetic resonance coupling for neural sensing applications

NASA Astrophysics Data System (ADS)

Yoon, Hargsoon; Kim, Hyunjung; Choi, Sang H.; Sanford, Larry D.; Geddis, Demetris; Lee, Kunik; Kim, Jaehwan; Song, Kyo D.

2012-04-01

Various wireless power transfer systems based on electromagnetic coupling have been investigated and applied in many biomedical applications including functional electrical stimulation systems and physiological sensing in humans and animals. By integrating wireless power transfer modules with wireless communication devices, electronic systems can deliver data and control system operation in untethered freely-moving conditions without requiring access through the skin, a potential source of infection. In this presentation, we will discuss a wireless power transfer module using magnetic resonance coupling that is specifically designed for neural sensing systems and in-vivo animal models. This research presents simple experimental set-ups and circuit models of magnetic resonance coupling modules and discusses advantages and concerns involved in positioning and sizing of source and receiver coils compared to conventional inductive coupling devices. Furthermore, the potential concern of tissue heating in the brain during operation of the wireless power transfer systems will also be addressed.

Magnetic MIMO Signal Processing and Optimization for Wireless Power Transfer

NASA Astrophysics Data System (ADS)

Yang, Gang; Moghadam, Mohammad R. Vedady; Zhang, Rui

2017-06-01

In magnetic resonant coupling (MRC) enabled multiple-input multiple-output (MIMO) wireless power transfer (WPT) systems, multiple transmitters (TXs) each with one single coil are used to enhance the efficiency of simultaneous power transfer to multiple single-coil receivers (RXs) by constructively combining their induced magnetic fields at the RXs, a technique termed "magnetic beamforming". In this paper, we study the optimal magnetic beamforming design in a multi-user MIMO MRC-WPT system. We introduce the multi-user power region that constitutes all the achievable power tuples for all RXs, subject to the given total power constraint over all TXs as well as their individual peak voltage and current constraints. We characterize each boundary point of the power region by maximizing the sum-power deliverable to all RXs subject to their minimum harvested power constraints. For the special case without the TX peak voltage and current constraints, we derive the optimal TX current allocation for the single-RX setup in closed-form as well as that for the multi-RX setup. In general, the problem is a non-convex quadratically constrained quadratic programming (QCQP), which is difficult to solve. For the case of one single RX, we show that the semidefinite relaxation (SDR) of the problem is tight. For the general case with multiple RXs, based on SDR we obtain two approximate solutions by applying time-sharing and randomization, respectively. Moreover, for practical implementation of magnetic beamforming, we propose a novel signal processing method to estimate the magnetic MIMO channel due to the mutual inductances between TXs and RXs. Numerical results show that our proposed magnetic channel estimation and adaptive beamforming schemes are practically effective, and can significantly improve the power transfer efficiency and multi-user performance trade-off in MIMO MRC-WPT systems.

Heat transfer through the flat surface of Rutherford superconducting cable samples with novel pattern of electrical insulation immersed in He II

NASA Astrophysics Data System (ADS)

Strychalski, M.; Chorowski, M.; Polinski, J.

2014-05-01

Future accelerator magnets will be exposed to heat loads that exceed even by an order of magnitude presently observed heat fluxes transferred to superconducting magnet coils. To avoid the resistive transition of the superconducting cables, the efficiency of heat transfer between the magnet structure and the helium must be significantly increased. This can be achieved through the use of novel concepts of the cable’s electrical insulation wrapping, characterized by an enhanced permeability to helium while retaining sufficient electrical resistivity. This paper presents measurement results of the heat transfer through Rutherford NbTi cable samples immersed in a He II bath and subjected to the pressure loads simulating the counteracting of the Lorentz forces observed in powered magnets. The Rutherford cable samples that were tested used different electrical insulation wrapping schemes, including the scheme that is presently used and the proposed scheme for future LHC magnets. A new porous polyimide cable insulation with enhanced helium permeability was proposed in order to improve the evacuation of heat form the NbTi coil to He II bath. These tests were performed in a dedicated Claudet-type cryostat in pressurized He II at 1.9 K and 1 bar.

Testing of Prototype Magnetic Suspension Cryogenic Transfer Line

NASA Astrophysics Data System (ADS)

Fesmire, J. E.; Augustynowicz, S. D.; Nagy, Z. F.; Sojourner, S. J.; Shu, Q. S.; Cheng, G.; Susta, J. T.

2006-04-01

A 6-meter prototype cryogenic transfer line with magnetic suspension was tested for its mechanical and thermal performance at the Cryogenics Test Laboratory of NASA Kennedy Space Center (KSC). A test facility with two cryogenic end-boxes was designed and commissioned for the testing. Suspension mechanisms were verified through a series of tests with liquid nitrogen. The thermal performance of the prototype was determined using the new test apparatus. The tested prototype has incorporated temperature and vacuum pressure data acquisition ports, customized interfaces to cryogenic end-boxes, and instrumentation. All tests were conducted under simulated onsite transfer line working conditions. A static (boiloff rate measurement) testing method was employed to demonstrate the gross heat leak in the tested article. The real-time temperature distribution, vacuum level, levitation distance, and mass flow rate were measured. The main purpose of this paper is to summarize the testing facility design and preparation, test procedure, and primary test results. Special arrangements (such as turning on/off mechanical support units, observing levitation gap, and setting up the flowmeter) in testing of such a magnetically levitated transfer line are also discussed. Preliminary results show that the heat leak reduction of approximately one-third to one-half is achievable through such transfer lines with a magnetic suspension system.

The influence of eddy currents on magnetic actuator performance

NASA Technical Reports Server (NTRS)

Zmood, R. B.; Anand, D. K.; Kirk, J. A.

1987-01-01

The present investigation of the effects of eddy currents on EM actuators' transient performance notes that a transfer function representation encompassing a first-order model of the eddy current influence can be useful in control system analysis. The method can be extended to represent the higher-order effects of eddy currents for actuators that cannot be represented by semiinfinite planes.

EDITORIAL: Spin-transfer-torque-induced phenomena Spin-transfer-torque-induced phenomena

NASA Astrophysics Data System (ADS)

Hirohata, Atsufumi

2011-09-01

This cluster, consisting of five invited articles on spin-transfer torque, offers the very first review covering both magnetization reversal and domain-wall displacement induced by a spin-polarized current. Since the first theoretical proposal on spin-transfer torque—reported by Berger and Slonczewski independently—spin-transfer torque has been experimentally demonstrated in both vertical magnetoresistive nano-pillars and lateral ferromagnetic nano-wires. In the former structures, an electrical current flowing vertically in the nano-pillar exerts spin torque onto the thinner ferromagnetic layer and reverses its magnetization, i.e., current-induced magnetization switching. In the latter structures, an electrical current flowing laterally in the nano-wire exerts torque onto a domain wall and moves its position by rotating local magnetic moments within the wall, i.e., domain wall displacement. Even though both phenomena are induced by spin-transfer torque, each phenomenon has been investigated separately. In order to understand the physical meaning of spin torque in a broader context, this cluster overviews both cases from theoretical modellings to experimental demonstrations. The earlier articles in this cluster focus on current-induced magnetization switching. The magnetization dynamics during the reversal has been calculated by Kim et al using the conventional Landau--Lifshitz-Gilbert (LLG) equation, adding a spin-torque term. This model can explain the dynamics in both spin-valves and magnetic tunnel junctions in a nano-pillar form. This phenomenon has been experimentally measured in these junctions consisting of conventional ferromagnets. In the following experimental part, the nano-pillar junctions with perpendicularly magnetized FePt and half-metallic Heusler alloys are discussed from the viewpoint of efficient magnetization reversal due to a high degree of spin polarization of the current induced by the intrinsic nature of these alloys. Such switching can be further operated at high frequency resulting in an oscillator, as shown in the article by Sulka et al. These results provide fundamental elements for magnetic random access memories. The later articles discuss domain-wall displacement. Again this phenomenon is also described by Shibata et al based on the LLG equation with spin-torque terms. This analytical model can explain the details of the depinning mechanism and a critical current for the displacement. Experimental observation is presented in the subsequent article by Malinowski et al, showing the depinning processes for the cases of intrinsic and extrinsic pinning sites. Here, the detailed magnetic moment configurations within the wall hold the dominant control over the critical current. These results can be used for future 3-dimensional magnetic memories, such as racetrack memory proposed by IBM. We sincerely hope this cluster offers an up-to-date understanding of macroscopic behaviour induced by spin-transfer torque and contributes to further advancement in this exciting research field. We are grateful to all the authors for spending their precious time and knowledge submitting to this cluster. We would also like to thank Professor Kevin O'Grady for his kind offer of the opportunity to make this review accessible to a general audience.

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.

Fluid mechanics and mass transfer in melt crystal growth: Analysis of the floating zone and vertical Bridgman processes

NASA Technical Reports Server (NTRS)

Brown, R. A.

1986-01-01

This research program focuses on analysis of the transport mechanisms in solidification processes, especially one of interest to the Microgravity Sciences and Applications Program of NASA. Research during the last year has focused on analysis of the dynamics of the floating zone process for growth of small-scale crystals, on studies of the effect of applied magnetic fields on convection and solute segregation in directional solidification, and on the dynamics of microscopic cell formation in two-dimensional solidification of binary alloys. Significant findings are given.

Scientific Visualization to Study Flux Transfer Events at the Community Coordinated Modeling Center

NASA Technical Reports Server (NTRS)

Rastatter, Lutz; Kuznetsova, Maria M.; Sibeck, David G.; Berrios, David H.

2011-01-01

In this paper we present results of modeling of reconnection at the dayside magnetopause with subsequent development of flux transfer event signatures. The tools used include new methods that have been added to the suite of visualization methods that are used at the Community Coordinated Modeling Center (CCMC). Flux transfer events result from localized reconnection that connect magnetosheath magnetic field and plasma with magnetospheric fields and plasma and results in flux rope structures that span the dayside magnetopause. The onset of flux rope formation and the three-dimensional structure of flux ropes are studied as they have been modeled by high-resolution magnetohydrodynamic simulations of the dayside magnetosphere of the Earth. We show that flux transfer events are complex three-dimensional structures that require modern visualization and analysis techniques. Two suites of visualization methods are presented and we demonstrate the usefulness of those methods through the CCMC web site to the general science user.

Transient multi-physics analysis of a magnetorheological shock absorber with the inverse Jiles-Atherton hysteresis model

NASA Astrophysics Data System (ADS)

Zheng, Jiajia; Li, Yancheng; Li, Zhaochun; Wang, Jiong

2015-10-01

This paper presents multi-physics modeling of an MR absorber considering the magnetic hysteresis to capture the nonlinear relationship between the applied current and the generated force under impact loading. The magnetic field, temperature field, and fluid dynamics are represented by the Maxwell equations, conjugate heat transfer equations, and Navier-Stokes equations. These fields are coupled through the apparent viscosity and the magnetic force, both of which in turn depend on the magnetic flux density and the temperature. Based on a parametric study, an inverse Jiles-Atherton hysteresis model is used and implemented for the magnetic field simulation. The temperature rise of the MR fluid in the annular gap caused by core loss (i.e. eddy current loss and hysteresis loss) and fluid motion is computed to investigate the current-force behavior. A group of impulsive tests was performed for the manufactured MR absorber with step exciting currents. The numerical and experimental results showed good agreement, which validates the effectiveness of the proposed multi-physics FEA model.

Basic theory for polarized, astrophysical maser radiation in a magnetic field

NASA Technical Reports Server (NTRS)

Watson, William D.

1994-01-01

Fundamental alterations in the theory and resulting behavior of polarized, astrophysical maser radiation in the presence of a magnetic field have been asserted based on a calculation of instabilities in the radiative transfer. I reconsider the radiative transfer and find that the relevant instabilities do not occur. Calculational errors in the previous investigation are identified. In addition, such instabilities would have appeared -- but did not -- in the numerous numerical solutions to the same radiative transfer equations that have been presented in the literature. As a result, all modifications that have been presented in a recent series of papers (Elitzur 1991, 1993) to the theory for polarized maser radiation in the presence of a magnetic field are invalid. The basic theory is thus clarified.

Magnetic Proximity Effect in a Transferred Topological Insulator Thin Film on a Magnetic Insulator

NASA Astrophysics Data System (ADS)

Che, Xiaoyu; Murata, Koichi; Pan, Lei; He, Qinglin; Yin, Gen; Fan, Yabin; Bi, Lei; Wang, Kang Lung

Exotic physical phenomena such as the quantum anomalous Hall effect (QAHE) arise by breaking the time-reversal symmetry (TRS) in topological insulators. However, substantial efforts have been made in improving the temperature for realizing the QAHE via magnetically doping, while the proximity coupling is another approach to develop the magnetic order without the introduction of additional carriers or the presence of local Fermi level fluctuation. Here we demonstrate the experimental signature of magnetic proximity effect in a molecular beam epitaxy-grown TI thin film of Bi2Se3 transferred to a magnetic substrate of yttrium iron garnet using a wet transfer technique. Comparing to the TI/GaAs control sample, the magnetic order is manifested by the anomalous Hall effect in magneto-transport characterization. Furthermore, due to TRS breaking by the proximity effect we observed a constituent weak localization component accompanied with the weak antilocalization behavior. The present work takes a step further toward realizing QAHE at higher temperature and opens up a new path in TI device designs for applications. We acknowledge the support from the ARO program under contract 15-1-10561, the SHINES Center under Award # S000686, NSF DMR-1350122, and the FAME Center, one of six centers of STARnet, sponsored by MARCO and DARPA.

Layer and doping tunable ferromagnetic order in two-dimensional Cr S2 layers

NASA Astrophysics Data System (ADS)

Wang, Cong; Zhou, Xieyu; Pan, Yuhao; Qiao, Jingsi; Kong, Xianghua; Kaun, Chao-Cheng; Ji, Wei

2018-06-01

Interlayer coupling is of vital importance for manipulating physical properties, e.g., electronic band gap, in two-dimensional materials. However, tuning magnetic properties in these materials is yet to be addressed. Here, we found the in-plane magnetic orders of Cr S2 mono and few layers are tunable between striped antiferromagnetic (sAFM) and ferromagnetic (FM) orders by manipulating charge transfer between Cr t2 g and eg orbitals. Such charge transfer is realizable through interlayer coupling, direct charge doping, or substituting S with Cl atoms. In particular, the transferred charge effectively reduces a portion of Cr4 + to Cr3 +, which, together with delocalized S p orbitals and their resulting direct S-S interlayer hopping, enhances the double-exchange mechanism favoring the FM rather than sAFM order. An exceptional interlayer spin-exchange parameter was revealed over -10 meV , an order of magnitude stronger than available results of interlayer magnetic coupling. It addition, the charge doping could tune Cr S2 between p - and n -doped magnetic semiconductors. Given these results, several prototype devices were proposed for manipulating magnetic orders using external electric fields or mechanical motion. These results manifest the role of interlayer coupling in modifying magnetic properties of layered materials and shed considerable light on manipulating magnetism in these materials.

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.

Oscillatory noncollinear magnetism induced by interfacial charge transfer in superlattices composed of metallic oxides

DOE PAGES

Hoffman, Jason D.; Kirby, Brian J.; Kwon, Jihwan; ...

2016-11-22

Interfaces between correlated complex oxides are promising avenues to realize new forms of magnetism that arise as a result of charge transfer, proximity effects, and locally broken symmetries. We report on the discovery of a noncollinear magnetic structure in superlattices of the ferromagnetic metallic oxide La 2/3Sr 1/3MnO 3 (LSMO) and the correlated metal LaNiO 3 (LNO). The exchange interaction between LSMO layers is mediated by the intervening LNO, such that the angle between the magnetization of neighboring LSMO layers varies in an oscillatory manner with the thickness of the LNO layer. The magnetic field, temperature, and spacer thickness dependencemore » of the noncollinear structure are inconsistent with the bilinear and biquadratic interactions that are used to model the magnetic structure in conventional metallic multilayers. A model that couples the LSMO layers to a helical spin state within the LNO fits the observed behavior. We propose that the spin-helix results from the interaction between a spatially varying spin susceptibility within the LNO and interfacial charge transfer that creates localized Ni 2+ states. In conclusion, our work suggests a new approach to engineering noncollinear spin textures in metallic oxide heterostructures.« less

Helium Transfer System for the Superconducting Devices at NSRRC

NASA Astrophysics Data System (ADS)

Li, H. C.; Hsiao, F. Z.; Chang, S. H.; Chiou, W. S.

2006-04-01

A helium cryogenic plant with a maximum cooling power of 450 W at 4.5K was installed at the end of the year 2003. This plant has provide the cooling power for the test of one superconducting cavity and the commission of one superconducting magnet for nine months. In November 2004, we installed one helium transfer system in NSRRC's storage ring to fulfill the cooling requirement for the operation of one superconducting cavity and two superconducting magnets. This helium transfer system consists of a switch valve box and the nitrogen-shielding multi-channel transfer lines. The averaged heat leak to the helium process line (including the straight section, the joint, the elbow, the coupling) at liquid helium temperature is specified to be less than 0.1 W/m at 4.2K; the total heat leak of the switching valve box to helium process lines is less than 16 W at 4.2K. In this paper we present the function, design parameters and test result of the helium transfer system. Commissioning results of both the cavity and the magnets using this helium transfer system will be shown as well.

Theory and experimental results of transfer-NOE experiments. 1. The influence of the off rate versus cross-relaxation rates

NASA Astrophysics Data System (ADS)

Lippens, R. M.; Cerf, C.; Hallenga, K.

The theory of the transferred nuclear Overhauser effect is presented in the framework of an extended relaxation matrix representation. This matrix representation allows a coherent description of all one- and two-dimensional experiments. We present analytical solutions for the buildup of magnetization in the 2D transfer-NOE experiment, for all ratios of the off rate k to the cross-relaxation rates R involved. We show that systematic deviations in distance determination occur when the off rate becomes comparable to or smaller than the relaxation rates. Experimental results on the peptide/protein system oxytocin/neurophysin confirming this analysis are presented. The importance of residual mobility in the bound ligand, as demonstrated by the experimental data, is also discussed.

Flow and Heat Transfer in Sisko Fluid with Convective Boundary Condition

PubMed Central

Malik, Rabia; Khan, Masood; Munir, Asif; Khan, Waqar Azeem

2014-01-01

In this article, we have studied the flow and heat transfer in Sisko fluid with convective boundary condition over a non-isothermal stretching sheet. The flow is influenced by non-linearly stretching sheet in the presence of a uniform transverse magnetic field. The partial differential equations governing the problem have been reduced by similarity transformations into the ordinary differential equations. The transformed coupled ordinary differential equations are then solved analytically by using the homotopy analysis method (HAM) and numerically by the shooting method. Effects of different parameters like power-law index , magnetic parameter , stretching parameter , generalized Prandtl number Pr and generalized Biot number are presented graphically. It is found that temperature profile increases with the increasing value of and whereas it decreases for . Numerical values of the skin-friction coefficient and local Nusselt number are tabulated at various physical situations. In addition, a comparison between the HAM and exact solutions is also made as a special case and excellent agreement between results enhance a confidence in the HAM results. PMID:25285822

Undergraduate Laboratory on a Turbulent Impinging Jet

NASA Astrophysics Data System (ADS)

Ivanosky, Arnaud; Brezzard, Etienne; van Poppel, Bret; Benson, Michael

2017-11-01

An undergraduate thermal sciences laboratory exercise that includes both experimental fluid mechanics and heat transfer measurements of an impinging jet is presented. The flow field is measured using magnetic resonance velocimetry (MRV) of a water flow, while IR thermography is used in the heat transfer testing. Flow Reynolds numbers for both the heat transfer and fluid mechanics tests range from 20,000-50,000 based on the jet diameter for a fully turbulent flow condition, with target surface temperatures in the heat transfer test reaching a maximum of approximately 50 Kelvin. The heat transfer target surface is subject to a measured uniform Joule heat flux, a well-defined boundary condition that allows comparison to existing correlations. The MRV generates a 3-component 3-dimensional data set, while the IR thermography provides a 2-dimensional heat transfer coefficient (or Nusselt number) map. These data sets can be post-processed and compared to existing correlations to verify data quality, and the sets can be juxtaposed to understand how flow features drive heat transfer. The laboratory setup, data acquisition, and analysis procedures are described for the laboratory experience, which can be incorporated as fluid mechanics, experimental methods, and heat transfer courses

Exploration of perpendicular magnetic anisotropy material system for application in spin transfer torque - Random access memory

NASA Astrophysics Data System (ADS)

Natarajarathinam, Anusha

Perpendicular magnetic anisotropy (PMA) materials have unique advantages when used in magnetic tunnel junctions (MTJ) which are the most critical part of spin-torque transfer random access memory devices (STT-RAMs) that are being researched intensively as future non-volatile memory technology. They have high magnetoresistance which improves their sensitivity. The STT-RAM has several advantages over competing technologies, for instance, low power consumption, non-volatility, ultra-fast read and write speed and high endurance. In personal computers, it can replace SRAM for high-speed applications, Flash for non-volatility, and PSRAM and DRAM for high-speed program execution. The main aim of this research is to identify and optimize the best perpendicular magnetic anisotropy (PMA) material system for application to STT-RAM technology. Preliminary search for perpendicular magnetic anisotropy (PMA) materials for pinned layer for MTJs started with the exploration and optimization of crystalline alloys such as Co50Pd50 alloy, Mn50Al50 and amorphous alloys such as Tb21Fe72Co7 and are first presented in this work. Further optimization includes the study of Co/[Pd/Pt]x multilayers (ML), and the development of perpendicular synthetic antiferromagnets (SAF) utilizing these multilayers. Focused work on capping and seed layers to evaluate interfacial perpendicular anisotropy in free layers for pMTJs is then discussed. Optimization of the full perpendicular magnetic tunnel junction (pMTJ) includes the CoFeB/MgO/CoFeB trilayer coupled to a pinned/pinning layer with perpendicular Co/[Pd/Pt]x SAF and a thin Ta seeded CoFeB free layer. Magnetometry, simulations, annealing studies, transport measurements and TEM analysis on these samples will then be presented.

Wireless power transfer electric vehicle supply equipment installation and validation tool

DOEpatents

Jones, Perry T.; Miller, John M.

2015-05-19

A transmit pad inspection device includes a magnetic coupling device, which includes an inductive circuit that is configured to magnetically couple to a primary circuit of a charging device in a transmit pad through an alternating current (AC) magnetic field. The inductive circuit functions as a secondary circuit for a set of magnetically coupled coils. The magnetic coupling device further includes a rectification circuit, and includes a controllable load bank or is configured to be connected to an external controllable load back. The transmit pad inspection device is configured to determine the efficiency of power transfer under various coupling conditions. In addition, the transmit pad inspection device can be configured to measure residual magnetic field and the frequency of the input current, and to determine whether the charging device has been installed properly.

[Functional magnetic resonance imaging. What are the benefits expected in hand surgery?].

PubMed

Moutet, F; Delon-Martin, C; Martin, O; Sirigu, A; Delaquaize, F; Benali, H; Masquelet, A-C

2013-06-01

Functional MRI (fMRI) allowed considerable advances upon understanding of cerebral functioning. Cortical plasticity, which allows the voluntary command of a restored function by a transferred muscle remains to be investigated in its intimacy. The authors present here the round table held at the 48th annual meeting of the French Society for Surgery of the Hand on December 22nd, 2012. It tries to review the analysis of the phenomenon observed during multiple tendinous transfers for restoration of proximal radial nerve palsy. Were successively approached: 1) Methods of acquisition and analysis of the signals (C. D-M.); 2) Movement reorganization (O.M.); 3) Motor plasticity after hand allograft (A. S.); 4) The potential interest of the fMRI in hand rehabilitation (F. D.); 5) The analysis of cerebral plasticity in general (H. B.). A rather philosophical conclusion opens other fields to f MRI (A.M.). Copyright © 2013 Elsevier Masson SAS. All rights reserved.

Near-Field Magneto-Optical Microscope

DOEpatents

Vlasko-Vlasov, Vitalii; Welp, Ulrich; and Crabtree, George W.

2005-12-06

A device and method for mapping magnetic fields of a sample at a resolution less than the wavelength of light without altering the magnetic field of the sample is disclosed. A device having a tapered end portion with a magneto-optically active particle positioned at the distal end thereof in communication with a fiber optic for transferring incoming linearly polarized light from a source thereof to the particle and for transferring reflected light from the particle is provided. The fiber optic has a reflective material trapping light within the fiber optic and in communication with a light detector for determining the polarization of light reflected from the particle as a function of the strength and direction of the magnetic field of the sample. Linearly polarized light from the source thereof transferred to the particle positioned proximate the sample is affected by the magnetic field of the sample sensed by the particle such that the difference in polarization of light entering and leaving the particle is due to the magnetic field of the sample. Relative movement between the particle and sample enables mapping.

Current induced multi-mode propagating spin waves in a spin transfer torque nano-contact with strong perpendicular magnetic anisotropy

NASA Astrophysics Data System (ADS)

Mohseni, S. Morteza; Yazdi, H. F.; Hamdi, M.; Brächer, T.; Mohseni, S. Majid

2018-03-01

Current induced spin wave excitations in spin transfer torque nano-contacts are known as a promising way to generate exchange-dominated spin waves at the nano-scale. It has been shown that when these systems are magnetized in the film plane, broken spatial symmetry of the field around the nano-contact induced by the Oersted field opens the possibility for spin wave mode co-existence including a non-linear self-localized spin-wave bullet and a propagating mode. By means of micromagnetic simulations, here we show that in systems with strong perpendicular magnetic anisotropy (PMA) in the free layer, two propagating spin wave modes with different frequency and spatial distribution can be excited simultaneously. Our results indicate that in-plane magnetized spin transfer nano-contacts in PMA materials do not host a solitonic self-localized spin-wave bullet, which is different from previous studies for systems with in plane magnetic anisotropy. This feature renders them interesting for nano-scale magnonic waveguides and crystals since magnon transport can be configured by tuning the applied current.

Near Field Magneto-Optical Microscope

DOEpatents

Vlasko-Vlasov, Vitalii K.; Welp, Ulrich; Crabtree, George W.

2005-12-06

A device and method for mapping magnetic fields of a sample at a resolution less than the wavelength of light without altering the magnetic field of the sample is disclosed. A device having a tapered end portion with a magneto-optically active particle positioned at the distal end thereof in communication with a fiber optic for transferring incoming linearly polarized light from a source thereof to the particle and for transferring reflected light from the particle is provided. The fiber optic has a reflective material trapping light within the fiber optic and in communication with a light detector for determining the polarization of light reflected from the particle as a function of the strength and direction of the magnetic field of the sample. Linearly polarized light from the source thereof transferred to the particle positioned proximate the sample is affected by the magnetic field of the sample sensed by the particle such that the difference in polarization of light entering and leaving the particle is due to the magnetic field of the sample. Relative movement between the particle and sample enables mapping.

Achieving the broader frequency electromagnetic absorber by development of magnetic core-shell composite with tunable shell/core sizes

NASA Astrophysics Data System (ADS)

Cheng, Ye; Guo, Yuhang; Zhang, Zhenya; Dong, Songtao; Liu, Suwei; Wang, Hongying

2018-03-01

Magnetic absorber has been regarded as the advanced electromagnetic energy transfer material to solve the increasingly high frequency electromagnetic interference issue. Even so, the pure magnetic material, in particular magnetic metal nanoparticle, suffering from the poor chemical stability and strong eddy current effect, thus limits it further application. To overcome this shortage, surrounded the magnetic metal nanoparticle (MPs) with insulated oxide shell has been considered to be an efficient route to suppress such an eddy current effect. Meanwhile, the combined insulated shell with good impedance matching feature, shows a positive role on the electromagnetic energy transfer intensity. In this regard, the binary Fe@α-Fe2O3 composite with the average size of ∼ 20 nm was prepared by a facile self-oxidation reaction. Interestingly, both the core diameter and shell thickness is controllable by controlling the oxide degree. The electromagnetic energy transfer performance revealed the maximum absorption frequency bandwidth of the optimal Fe@α-Fe2O3 composite is up to 5.3 G(8.2-13.5 GHz)under a small coating thickness of 1.5 mm.

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

Kar, Durga P.; Nayak, Praveen P.; Bhuyan, Satyanarayan

In order to power or charge electronic devices wirelessly, a bi-directional wireless power transfer method has been proposed and experimentally investigated. In the proposed design, two receiving coils are used on both sides of a transmitting coil along its central axis to receive the power wirelessly from the generated magnetic fields through strongly coupled magnetic resonance. It has been observed experimentally that the maximum power transfer occurs at the operating resonant frequency for optimum electric load connected across the receiving coils on both side. The optimum wireless power transfer efficiency is 88% for the bi-directional power transfer technique compared 84%more » in the one side receiver system. By adopting the developed bi-directional power transfer method, two electronic devices can be powered up or charged simultaneously instead of a single device through usual one side receiver system without affecting the optimum power transfer efficiency.« less

Oliver E. Buckley Condensed Matter Prize Lecture: Transfer of spin momentum between magnets: its genesis and prospect

NASA Astrophysics Data System (ADS)

Slonczewski, John

2013-03-01

Consider two nanoscopic monodomain magnets connected by a spacer that is composed of a non-magnetic metal or a tunnel barrier. Any externally applied electric current flowing through these three layers contributes tiny pseudo-torques to both magnetic moments (J . S . 1989). Such a weak spin-transfer torque (STT) may counteract and overcome a comparably small torque caused by viscous dissipation (L. Berger1996; J . S . 1996). Any initial motion (e. g. excited by ambient temperature) of one moment (or both), may grow in amplitude and culminate in steady precession or a transient switch to a new direction of static equilibrium. In a memory element, the STT effect writes 0 or 1 in a magnetic-tunnel junction. Indeed, world-wide developments of memory arrays and radio-frequency oscillators utilizing current-driven STT today enjoy a nine-digit dollar commitment. But the fact that transfer of each half-unit of spin momentum h/4 π through a barrier requires the transfer of at least one unit of electric charge limits its efficiency. Arguably, STT should also arise from the flow of external heat, in either direction, between an insulating magnet, of ferrite or garnet (e. g. YIG) composition, and a metallic spacer (J . S . 2010). Whenever s-d exchange annihilates a hot magnon at the insulator/metal-spacer interface, it transfers one unit h/2 π of spin momentum to the spacer. Conduction electrons within the spacer will transport this spin momentum to the second magnet without requiring an electric current. Such a thermagnonicmethod, modestly powered by a Joule-effect heater, can substantially increase the efficiency of STT. Support for this prediction comes from (1) an estimate of the sd-exchange coefficient from data on spin relaxation in magnetically dilute (Cu,Ag,Au):Mn alloys; (2) a DFT computation (J. Xiao et al 2010); and (3) most persuasively, data from spin pumping driven across a YIG/Au interface by ferromagnetic resonance (B. Heinrich et al 2011; C. Burrowes et al 2012).

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.

Magnetic Flux Circulation During Dawn-Dusk Oriented Interplanetary Magnetic Field

NASA Technical Reports Server (NTRS)

Mitchell, E. J.; Lopez, R. E.; Fok, M.-C.; Deng, Y.; Wiltberger, M.; Lyon, J.

2010-01-01

Magnetic flux circulation is a primary mode of energy transfer from the solar wind into the ionosphere and inner magnetosphere. For southward interplanetary magnetic field (IMF), magnetic flux circulation is described by the Dungey cycle (dayside merging, night side reconnection, and magnetospheric convection), and both the ionosphere and inner magnetosphere receive energy. For dawn-dusk oriented IMF, magnetic flux circulation is not well understood, and the inner magnetosphere does not receive energy. Several models have been suggested for possible reconnection patterns; the general pattern is: dayside merging; reconnection on the dayside or along the dawn/dusk regions; and, return flow on dayside only. These models are consistent with the lack of energy in the inner magnetosphere. We will present evidence that the Dungey cycle does not explain the energy transfer during dawn-dusk oriented IMF. We will also present evidence of how magnetic flux does circulate during dawn-dusk oriented IMF, specifically how the magnetic flux reconnects and circulates back.

Powering the High-Luminosity Triplets

NASA Astrophysics Data System (ADS)

Ballarino, A.; Burnet, J. P.

The powering of the magnets in the LHC High-Luminosity Triplets requires production and transfer of more than 150 kA of DC current. High precision power converters will be adopted, and novel High Temperature Superconducting (HTS) current leads and MgB2 based transfer lines will provide the electrical link between the power converters and the magnets. This chapter gives an overview of the systems conceived in the framework of the LHC High-Luminosity upgrade for feeding the superconducting magnet circuits. The focus is on requirements, challenges and novel developments.

Advances in cryogenic engineering. Volume 33 - Proceedings of the Cryogenic Engineering Conference, Saint Charles, IL, June 14-18, 1987

NASA Technical Reports Server (NTRS)

Fast, R. W. (Editor)

1988-01-01

Papers are presented on superconductivity applications including magnets, electronics, rectifiers, magnet stability, coil protection, and cryogenic techniques. Also considered are insulation, heat transfer to liquid helium and nitrogen, heat and mass transfer in He II, superfluid pumps, and refrigeration for superconducting systems. Other topics include cold compressors, refrigeration and liquefaction, magnetic refrigeration, and refrigeration for space applications. Papers are also presented on cryogenic applications, commercial cryogenic plants, the properties of cryogenic fluids, and cryogenic instrumentation and data acquisition.

Assisted Writing in Spin Transfer Torque Magnetic Tunnel Junctions

NASA Astrophysics Data System (ADS)

Ganguly, Samiran; Ahmed, Zeeshan; Datta, Supriyo; Marinero, Ernesto E.

2015-03-01

Spin transfer torque driven MRAM devices are now in an advanced state of development, and the importance of reducing the current requirement for writing information is well recognized. Different approaches to assist the writing process have been proposed such as spin orbit torque, spin Hall effect, voltage controlled magnetic anisotropy and thermal excitation. In this work,we report on our comparative study using the Spin-Circuit Approach regarding the total energy, the switching speed and energy-delay products for different assisted writing approaches in STT-MTJ devices using PMA magnets.

Automated observatory in Antarctica: real-time data transfer on constrained networks in practice

NASA Astrophysics Data System (ADS)

Bracke, Stephan; Gonsette, Alexandre; Rasson, Jean; Poncelet, Antoine; Hendrickx, Olivier

2017-08-01

In 2013 a project was started by the geophysical centre in Dourbes to install a fully automated magnetic observatory in Antarctica. This isolated place comes with specific requirements: unmanned station during 6 months, low temperatures with extreme values down to -50 °C, minimum power consumption and satellite bandwidth limited to 56 Kbit s-1. The ultimate aim is to transfer real-time magnetic data every second: vector data from a LEMI-25 vector magnetometer, absolute F measurements from a GEM Systems scalar proton magnetometer and absolute magnetic inclination-declination (DI) measurements (five times a day) with an automated DI-fluxgate magnetometer. Traditional file transfer protocols (for instance File Transfer Protocol (FTP), email, rsync) show severe limitations when it comes to real-time capability. After evaluation of pro and cons of the available real-time Internet of things (IoT) protocols and seismic software solutions, we chose to use Message Queuing Telemetry Transport (MQTT) and receive the 1 s data with a negligible latency cost and no loss of data. Each individual instrument sends the magnetic data immediately after capturing, and the data arrive approximately 300 ms after being sent, which corresponds with the normal satellite latency.

Magnetic field enhancement of organic photovoltaic cells performance.

PubMed

Oviedo-Casado, S; Urbina, A; Prior, J

2017-06-27

Charge separation is a critical process for achieving high efficiencies in organic photovoltaic cells. The initial tightly bound excitonic electron-hole pair has to dissociate fast enough in order to avoid photocurrent generation and thus power conversion efficiency loss via geminate recombination. Such process takes place assisted by transitional states that lie between the initial exciton and the free charge state. Due to spin conservation rules these intermediate charge transfer states typically have singlet character. Here we propose a donor-acceptor model for a generic organic photovoltaic cell in which the process of charge separation is modulated by a magnetic field which tunes the energy levels. The impact of a magnetic field is to intensify the generation of charge transfer states with triplet character via inter-system crossing. As the ground state of the system has singlet character, triplet states are recombination-protected, thus leading to a higher probability of successful charge separation. Using the open quantum systems formalism we demonstrate that the population of triplet charge transfer states grows in the presence of a magnetic field, and discuss the impact on carrier population and hence photocurrent, highlighting its potential as a tool for research on charge transfer kinetics in this complex systems.

Super-Eddington radiation transfer in soft gamma repeaters

NASA Technical Reports Server (NTRS)

Ulmer, Andrew

1994-01-01

Bursts from soft gamma repeaters (SGRs) have been shown to be super-Eddington by a factor of 1000 and have been persuasively associated with compact objects. Super-Eddington radiation transfer on the surface of a strongly magnetic (greater than or equal to 10(exp 13) G) neutron star is studied and related to the observational constraints on SGRs. In strong magnetic fields, Thompson scattering is suppressed in one polarization state, so super-Eddington fluxes can be radiated while the plasma remains in hydrostatic equilibrium. We discuss a model which offers a somewhat natural explanation for the observation that the energy spectra of bursts with varying intensity are similar. The radiation produced is found to be linearly polarized to one part in 1000 in a direction determined by the local magnetic field, and intensity variations between bursts are understood as a change in the radiating area on the source. The net polarization is inversely correlated with burst intensity. Further, it is shown that for radiation transfer calculations in limit of superstrong magnetic fields, it is sufficient to solve the radiation transfer for the low opacity state rather than the coupled equations for both. With this approximation, standard stellar atmosphere techniques are utilized to calculate the model energy spectrum.

RF-SABRE: A Way to Continuous Spin Hyperpolarization at High Magnetic Fields.

PubMed

Pravdivtsev, Andrey N; Yurkovskaya, Alexandra V; Vieth, Hans-Martin; Ivanov, Konstantin L

2015-10-29

A new technique is developed that allows one to carry out the signal amplification by reversible exchange (SABRE) experiments at high magnetic field. SABRE is a hyperpolarization method, which utilizes transfer of spin order from para-hydrogen to the spins of a substrate in transient iridium complexes. Previously, it has been thought that such a transfer of spin order is only efficient at low magnetic fields, notably, at level anti-crossing (LAC) regions. Here it is demonstrated that LAC conditions can also be fulfilled at high fields under the action of a RF field. The high-field RF-SABRE experiment can be implemented using commercially available nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) machines and does not require technically demanding field-cycling. The achievable NMR enhancements are around 100 for several substrates as compared to their NMR signals at thermal equilibrium conditions at 4.7 T. The frequency dependence of RF-SABRE is comprised of well pronounced peaks and dips, whose position and amplitude are conditioned solely by the magnetic resonance parameters such as chemical shifts and scalar coupling of the spin system involved in the polarization transfer and by the amplitude of the RF field. Thus, the proposed method can serve as a new sensitive tool for probing transient complexes. Simulations of the dependence of magnetization transfer (i.e., NMR signal amplifications) on the frequency and amplitude of the RF field are in good agreement with the developed theoretical approach. Furthermore, the method enables continuous re-hyperpolarization of the SABRE substrate over a long period of time, giving a straightforward way to repetitive NMR experiments.

Magnetization transfer proportion: a simplified measure of dose response for polymer gel dosimetry.

PubMed

Whitney, Heather M; Gochberg, Daniel F; Gore, John C

2008-12-21

The response to radiation of polymer gel dosimeters has most often been described by measuring the nuclear magnetic resonance transverse relaxation rate as a function of dose. This approach is highly dependent upon the choice of experimental parameters, such as the echo spacing time for Carr-Purcell-Meiboom-Gill-type pulse sequences, and is difficult to optimize in imaging applications where a range of doses are applied to a single gel, as is typical for practical uses of polymer gel dosimetry. Moreover, errors in computing dose can arise when there are substantial variations in the radiofrequency (B1) field or resonant frequency, as may occur for large samples. Here we consider the advantages of using magnetization transfer imaging as an alternative approach and propose the use of a simplified quantity, the magnetization transfer proportion (MTP), to assess doses. This measure can be estimated through two simple acquisitions and is more robust in the presence of some sources of system imperfections. It also has a dependence upon experimental parameters that is independent of dose, allowing simultaneous optimization at all dose levels. The MTP is shown to be less susceptible to B1 errors than are CPMG measurements of R2. The dose response can be optimized through appropriate choices of the power and offset frequency of the pulses used in magnetization transfer imaging.

Collaborative Research: Polymeric Multiferroics

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

Ren, Shenqiang

2017-04-20

The goal of this project is to investigate room temperature magnetism and magnetoelectric coupling of polymeric multiferroics. A new family of molecular charge-transfer crystals has been emerged as a fascinating opportunity for the development of all-organic electrics and spintronics due to its weak hyperfine interaction and low spin-orbit coupling; nevertheless, direct observations of room temperature magnetic spin ordering have yet to be accomplished in organic charge-transfer solids. Furthermore, room temperature magnetoelectric coupling effect hitherto known multiferroics, is anticipated in organic donor-acceptor complexes because of magnetic field effects on charge-transfer dipoles, yet this is also unexplored. The PI seeks to fundamentalmore » understanding of the control of organic crystals to demonstrate and explore room temperature multiferroicity. The experimental results have been verified through the theoretical modeling.« less

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.

ON THE NATURE OF RECONNECTION AT A SOLAR CORONAL NULL POINT ABOVE A SEPARATRIX DOME

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

Pontin, D. I.; Priest, E. R.; Galsgaard, K., E-mail: dpontin@maths.dundee.ac.uk

2013-09-10

Three-dimensional magnetic null points are ubiquitous in the solar corona and in any generic mixed-polarity magnetic field. We consider magnetic reconnection at an isolated coronal null point whose fan field lines form a dome structure. Using analytical and computational models, we demonstrate several features of spine-fan reconnection at such a null, including the fact that substantial magnetic flux transfer from one region of field line connectivity to another can occur. The flux transfer occurs across the current sheet that forms around the null point during spine-fan reconnection, and there is no separator present. Also, flipping of magnetic field lines takesmore » place in a manner similar to that observed in the quasi-separatrix layer or slip-running reconnection.« less

Positive and negative effects of dielectric breakdown in transformer oil based magnetic fluids

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

Lee, Jong-Chul, E-mail: jclee01@gwnu.ac.kr; Lee, Won-Ho; Lee, Se-Hee

The transformer oil based magnetic fluids can be considered as the next-generation insulation fluids because they offer exciting new possibilities to enhance dielectric breakdown voltage as well as heat transfer performance compared to pure transformer oils. In this study, we have investigated the dielectric breakdown strength of the fluids with the various volume concentrations of nanoparticles in accordance with IEC 156 standard and have tried to find the reason for changing the dielectric breakdown voltage of the fluids from the magnetic field analysis. It was found that the dielectric breakdown voltage of pure transformer oil is around 12 kV withmore » the gap distance of 1.5 mm. In the case of our transformer oil-based magnetic fluids with 0.08% < Φ < 0.6% (Φ means the volume concentration of magnetic nanoparticles), the dielectric breakdown voltage shows above 40 kV, which is 3.3 times higher positively than that of pure transformer oil. Negatively in the case when the volume concentration of magnetic nanoparticles is above 0.65%, the dielectric breakdown voltage decreases reversely. From the magnetic field analysis, the reason might be considered as two situations: the positive is for the conductive nanoparticles dispersed well near the electrodes, which play an important role in converting fast electrons to slow negatively charged particles, and the negative is for the agglomeration of the particles near the electrodes, which leads to the breakdown initiation.« less

Amide Proton Transfer Imaging Allows Detection of Glioma Grades and Tumor Proliferation: Comparison with Ki-67 Expression and Proton MR Spectroscopy Imaging.

PubMed

Su, C; Liu, C; Zhao, L; Jiang, J; Zhang, J; Li, S; Zhu, W; Wang, J

2017-09-01

Prognosis in glioma depends strongly on tumor grade and proliferation. In this prospective study of patients with untreated primary cerebral gliomas, we investigated whether amide proton transfer-weighted imaging could reveal tumor proliferation and reliably distinguish low-grade from high-grade gliomas compared with Ki-67 expression and proton MR spectroscopy imaging. This study included 42 patients with low-grade ( n = 28) or high-grade ( n = 14) glioma, all of whom underwent conventional MR imaging, proton MR spectroscopy imaging, and amide proton transfer-weighted imaging on the same 3T scanner within 2 weeks before surgery. We assessed metabolites of choline and N -acetylaspartate from proton MR spectroscopy imaging and the asymmetric magnetization transfer ratio at 3.5 ppm from amide proton transfer-weighted imaging and compared them with histopathologic grade and immunohistochemical expression of the proliferation marker Ki-67 in the resected specimens. The asymmetric magnetization transfer ratio at 3.5 ppm values measured by different readers showed good concordance and were significantly higher in high-grade gliomas than in low-grade gliomas (3.61% ± 0.155 versus 2.64% ± 0.185, P = .0016), with sensitivity and specificity values of 92.9% and 71.4%, respectively, at a cutoff value of 2.93%. The asymmetric magnetization transfer ratio at 3.5 ppm values correlated with tumor grade ( r = 0.506, P = .0006) and Ki-67 labeling index ( r = 0.502, P = .002). For all patients, the asymmetric magnetization transfer ratio at 3.5 ppm correlated positively with choline ( r = 0.43, P = .009) and choline/ N -acetylaspartate ratio ( r = 0.42, P = .01) and negatively with N -acetylaspartate ( r = -0.455, P = .005). These correlations held for patients with low-grade gliomas versus those with high-grade gliomas, but the correlation coefficients were higher in high-grade gliomas (choline: r = 0.547, P = .053; N -acetylaspartate: r = -0.644, P = .017; choline/ N -acetylaspartate: r = 0.583, P = .036). The asymmetric magnetization transfer ratio at 3.5 ppm may serve as a potential biomarker not only for assessing proliferation, but also for predicting histopathologic grades in gliomas. © 2017 by American Journal of Neuroradiology.

Dynamic Nuclear Polarization and other magnetic ideas at EPFL.

PubMed

Bornet, Aurélien; Milani, Jonas; Wang, Shutao; Mammoli, Daniele; Buratto, Roberto; Salvi, Nicola; Segaw, Takuya F; Vitzthum, Veronika; Miéville, Pascal; Chinthalapalli, Srinivas; Perez-Linde, Angel J; Carnevale, Diego; Jannin, Sami; Caporinia, Marc; Ulzega, Simone; Rey, Martial; Bodenhausen, Geoffrey

2012-01-01

Although nuclear magnetic resonance (NMR) can provide a wealth of information, it often suffers from a lack of sensitivity. Dynamic Nuclear Polarization (DNP) provides a way to increase the polarization and hence the signal intensities in NMR spectra by transferring the favourable electron spin polarization of paramagnetic centres to the surrounding nuclear spins through appropriate microwave irradiation. In our group at EPFL, two complementary DNP techniques are under investigation: the combination of DNP with magic angle spinning at temperatures near 100 K ('MAS-DNP'), and the combination of DNP at 1.2 K with rapid heating followed by the transfer of the sample to a high-resolution magnet ('dissolution DNP'). Recent applications of MAS-DNP to surfaces, as well as new developments of magnetization transfer of (1)H to (13)C at 1.2 K prior to dissolution will illustrate the work performed in our group. A second part of the paper will give an overview of some 'non-enhanced' activities of our laboratory in liquid- and solid-state NMR.

Design and prototype fabrication of a 30 tesla cryogenic magnet

NASA Technical Reports Server (NTRS)

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

1977-01-01

A liquid neon cooled magnet was designed to produce 30 teslas in steady operation. To ensure the correctness of the heat transfer relationships used, supercritical neon heat transfer tests were made. Other tests made before the final design included tests on the effect of the magnetic field on pump motors, tensile shear tests on the cryogenic adhesives, and simulated flow studies for the coolant. The magnet will consist of two pairs of coils, cooled by forced convection of supercritical neon. Heat from the supercritical neon will be rejected through heat exchangers which are made of roll bonded copper panels and are submerged in a pool of saturated liquid neon. A partial mock up coil was wound to identify the tooling required to wind the magnet. This was followed by winding a prototype pair of coils. The prototype winding established procedures for fabricating the final magnet and revealed slight changes needed in the final design.

Kelvin-Helmholtz instability for flow in porous media under the influence of oblique magnetic fields: A viscous potential flow analysis

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

Moatimid, Galal M.; Obied Allah, M. H.; Hassan, Mohamed A.

2013-10-15

In this paper, the Kelvin-Helmholtz instability of viscous incompressible magnetic fluid fully saturated porous media is achieved through the viscous potential theory. The flow is considered to be through semi-permeable boundaries above and below the fluids through which the fluid may either be blown in or sucked out, in a direction normal to the main streaming direction of the fluid flow. An oblique magnetic field, mass, heat transfer, and surface tension are present across the interface. Through the linear stability analysis, a general dispersion relation is derived and the natural curves are plotted. Therefore, the linear stability condition is discussedmore » in some depth. In view of the multiple time scale technique, the Ginzburg–Landau equation, which describes the behavior of the system in the nonlinear approach, is obtained. The effects of the orientation of the magnetic fields on the stability configuration in linear, as well as nonlinear approaches, are discussed. It is found that the Darcy's coefficient for the porous layers plays a stabilizing role. The injection of the fluids at both boundaries has a stabilizing effect, in contrast with the suction at both boundaries.« less

Spin-Transfer Studies in Magnetic Multilayer Nanostructures

NASA Astrophysics Data System (ADS)

Emley, N. C.; Albert, F. J.; Ryan, E. M.; Krivorotov, I. N.; Ralph, D. C.; Buhrman, R. A.

2003-03-01

Numerous experiments have demonstrated current-induced magnetization reversal in ferromagnet/paramagnet/ferromagnet nanostructures with the current in the CPP geometry. The primary mechanism for this reversal is the transfer of angular momentum from the spin-polarized conduction electrons to the nanomagnet moment the spin transfer effect. This phenomenon has potential application in nanoscale, current-controlled non-volatile memory elements, but several challenges must be overcome for realistic device implementation. Typical Co/Cu/Co nanopillar devices, although effective for fundamental studies, are not advantageous for technological applications because of their large switching currents Ic ( 3-10 mA) and small R·A (< 1 mΩ·µm^2). Here we report initial results testing some possible approaches for enhancing spin-transfer device performance which involve the addition of more layers, and hence, more complexity, to the simple Co/Cu/Co trilayer structure. These additions include synthetic antiferromagnet layers (SAF), exchange biased layers, nano-oxide layers (NOL), and additional magnetic layers. Research supported by NSF and DARPA

Advances in cryogenic engineering. Volume 27 - Proceedings of the Cryogenic Engineering Conference, San Diego, CA, August 11-14, 1981

NASA Astrophysics Data System (ADS)

Fast, R. W.

Applications of superconductivity are considered, taking into account MHD and fusion, generators, transformers, transmission lines, magnets for physics, cryogenic techniques, electrtronics, and aspects of magnet stability. Advances related to heat transfer in He I are discussed along with subjects related to theat transfer in He II, refrigeration of superconducting systems, refrigeration and liquefaction, dilution and magnetic refrigerators, refrigerators for space applications, mass transfer and flow phenomena, and the properties of fluids. Developments related to cryogenic applications are also explored, giving attention to bulk storage and transfer of cryogenic fluids, liquefied natural gas operations, space science and technology, and cryopumping. Topics related to cryogenic instrumentation and controls include the production and use of high grade silicon diode temperature sensors, the choice of strain gages for use in a large superconducting alternator, microprocessor control of cryogenic pressure, and instrumentation, data acquisition and reduction for a large spaceborne helium dewar. For individual items see A83-43221 to A83-43250

Review of magnetic refrigeration system as alternative to conventional refrigeration system

NASA Astrophysics Data System (ADS)

Mezaal, N. A.; Osintsev, K. V.; Zhirgalova, T. B.

2017-10-01

The refrigeration system is one of the most important systems in industry. Developers are constantly seeking for how to avoid the damage to the environment. Magnetic refrigeration is an emerging, environment-friendly technology based on a magnetic solid that acts as a refrigerant by magneto-caloric effect (MCE). In the case of ferromagnetic materials, MCE warms as the magnetic moments of the atom are aligned by the application of a magnetic field. There are two types of magnetic phase changes that may occur at the Curie point: first order magnetic transition (FOMT) and second order magnetic transition (SOMT). The reference cycle for magnetic refrigeration is AMR (Active Magnetic Regenerative cycle), where the magnetic material matrix works both as a refrigerating medium and as a heat regenerating medium, while the fluid flowing in the porous matrix works as a heat transfer medium. Regeneration can be accomplished by blowing a heat transfer fluid in a reciprocating fashion through the regenerator made of magnetocaloric material that is alternately magnetized and demagnetized. Many magnetic refrigeration prototypes with different designs and software models have been built in different parts of the world. In this paper, the authors try to shed light on the magnetic refrigeration and show its effectiveness compared with conventional refrigeration methods.

Interface-induced phenomena in magnetism

DOE PAGES

Hellman, Frances; Hoffmann, Axel; Tserkovnyak, Yaroslav; ...

2017-06-05

Our article reviews static and dynamic interfacial effects in magnetism, focusing on interfacially-driven magnetic effects and phenomena associated with spin-orbit coupling and intrinsic symmetry breaking at interfaces. It provides a historical background and literature survey, but focuses on recent progress, identifying the most exciting new scientific results and pointing to promising future research directions. It starts with an introduction and overview of how basic magnetic properties are affected by interfaces, then turns to a discussion of charge and spin transport through and near interfaces and how these can be used to control the properties of the magnetic layer. Important conceptsmore » include spin accumulation, spin currents, spin transfer torque, and spin pumping. We provide an overview for the current state of knowledge and existing review literature on interfacial effects such as exchange bias, exchange spring magnets, spin Hall effect, oxide heterostructures, and topological insulators. Our article highlights recent discoveries of interface-induced magnetism and non-collinear spin textures, non-linear dynamics including spin torque transfer and magnetization reversal induced by interfaces, and interfacial effects in ultrafast magnetization processes.« less

Interface-Induced Phenomena in Magnetism

PubMed Central

Hoffmann, Axel; Tserkovnyak, Yaroslav; Beach, Geoffrey S. D.; Fullerton, Eric E.; Leighton, Chris; MacDonald, Allan H.; Ralph, Daniel C.; Arena, Dario A.; Dürr, Hermann A.; Fischer, Peter; Grollier, Julie; Heremans, Joseph P.; Jungwirth, Tomas; Kimel, Alexey V.; Koopmans, Bert; Krivorotov, Ilya N.; May, Steven J.; Petford-Long, Amanda K.; Rondinelli, James M.; Samarth, Nitin; Schuller, Ivan K.; Slavin, Andrei N.; Stiles, Mark D.; Tchernyshyov, Oleg; Thiaville, André; Zink, Barry L.

2017-01-01

This article reviews static and dynamic interfacial effects in magnetism, focusing on interfacially-driven magnetic effects and phenomena associated with spin-orbit coupling and intrinsic symmetry breaking at interfaces. It provides a historical background and literature survey, but focuses on recent progress, identifying the most exciting new scientific results and pointing to promising future research directions. It starts with an introduction and overview of how basic magnetic properties are affected by interfaces, then turns to a discussion of charge and spin transport through and near interfaces and how these can be used to control the properties of the magnetic layer. Important concepts include spin accumulation, spin currents, spin transfer torque, and spin pumping. An overview is provided to the current state of knowledge and existing review literature on interfacial effects such as exchange bias, exchange spring magnets, spin Hall effect, oxide heterostructures, and topological insulators. The article highlights recent discoveries of interface-induced magnetism and non-collinear spin textures, non-linear dynamics including spin torque transfer and magnetization reversal induced by interfaces, and interfacial effects in ultrafast magnetization processes. PMID:28890576

Modes of Action of Acarbose Hydrolysis and Transglycosylation Catalyzed by a Thermostable Maltogenic Amylase, the Gene for Which Was Cloned from a Thermus Strain

PubMed Central

Kim, Tae-Jip; Kim, Myo-Jeong; Kim, Byung-Cheon; Kim, Jae-Cherl; Cheong, Tae-Kyou; Kim, Jung-Wan; Park, Kwan-Hwa

1999-01-01

A maltogenic amylase gene was cloned in Escherichia coli from a gram-negative thermophilic bacterium, Thermus strain IM6501. The gene encoded an enzyme (ThMA) with a molecular mass of 68 kDa which was expressed by the expression vector p6xHis119. The optimal temperature of ThMA was 60°C, which was higher than those of other maltogenic amylases reported so far. Thermal inactivation kinetic analysis of ThMA indicated that it was stabilized in the presence of 10 mM EDTA. ThMA harbored both hydrolysis and transglycosylation activities. It hydrolyzed β-cyclodextrin and starch mainly to maltose and pullulan to panose. ThMA not only hydrolyzed acarbose, an amylase inhibitor, to glucose and pseudotrisaccharide (PTS) but also transferred PTS to 17 sugar acceptors, including glucose, fructose, maltose, cellobiose, etc. Structural analysis of acarbose transfer products by using methylation, thin-layer chromatography, high-performance ion chromatography, and nuclear magnetic resonance indicated that PTS was transferred primarily to the C-6 of the acceptors and at lower degrees to the C-3 and/or C-4. The transglycosylation of sugar to methyl-α-d-glucopyranoside by forming an α-(1,3)-glycosidic linkage was demonstrated for the first time by using acarbose and ThMA. Kinetic analysis of the acarbose transfer products showed that the C-4 transfer product formed most rapidly but readily hydrolyzed, while the C-6 transfer product was stable and accumulated in the reaction mixture as the main product. PMID:10103262

Analysis and design of an ultrahigh temperature hydrogen-fueled MHD generator

NASA Technical Reports Server (NTRS)

Moder, Jeffrey P.; Myrabo, Leik N.; Kaminski, Deborah A.

1993-01-01

A coupled gas dynamics/radiative heat transfer analysis of partially ionized hydrogen, in local thermodynamic equilibrium, flowing through an ultrahigh temperature (10,000-20,000 K) magnetohydrodynamic (MHD) generator is performed. Gas dynamics are modeled by a set of quasi-one-dimensional, nonlinear differential equations which account for friction, convective and radiative heat transfer, and the interaction between the ionized gas and applied magnetic field. Radiative heat transfer is modeled using nongray, absorbing-emitting 2D and 3D P-1 approximations which permit an arbitrary variation of the spectral absorption coefficient with frequency. Gas dynamics and radiative heat transfer are coupled through the energy equation and through the temperature- and density-dependent absorption coefficient. The resulting nonlinear elliptic problem is solved by iterative methods. Design of such MHD generators as onboard, open-cycle, electric power supplies for a particular advanced airbreathing propulsion concept produced an efficient and compact 128-MWe generator characterized by an extraction ratio of 35.5 percent, a power density of 10,500 MWe/cu m, and a specific (extracted) energy of 324 MJe/kg of hydrogen. The maximum wall heat flux and total wall heat load were 453 MW/sq m and 62 MW, respectively.

Chemical Exchange Saturation Transfer (CEST): what is in a name and what isn’t?

PubMed Central

van Zijl, Peter C.M.; Yadav, Nirbhay N.

2011-01-01

Chemical exchange saturation transfer (CEST) imaging is a relatively new MRI contrast approach in which exogenous or endogenous compounds containing either exchangeable protons or exchangeable molecules are selectively saturated and, after transfer of this saturation, detected indirectly through the water signal with enhanced sensitivity. The focus of this review is on basic MR principles underlying CEST and similarities to and differences with conventional magnetization transfer contrast (MTC). In CEST MRI, transfer of magnetization is studied in mobile compounds instead of semisolids. Similar to MTC, CEST has contributions of both chemical exchange and dipolar cross-relaxation, but the latter can often be neglected if exchange is fast. Contrary to MTC, CEST imaging requires sufficiently slow exchange on the MR time scale to allow selective irradiation of the protons of interest. As a consequence, magnetic labeling is not limited to radio-frequency saturation but can be expanded with slower frequency-selective approaches such as inversion, gradient dephasing and frequency labeling. The basic theory, design criteria, and experimental issues for exchange transfer imaging are discussed. A new classification for CEST agents based on exchange type is proposed. The potential of this young field is discussed, especially with respect to in vivo application and translation to humans. PMID:21337419

Graphene Derivative in Magnetically Recoverable Catalyst Determines Catalytic Properties in Transfer Hydrogenation of Nitroarenes to Anilines with 2-Propanol.

PubMed

Das, Vijay Kumar; Mazhar, Sumaira; Gregor, Lennon; Stein, Barry D; Morgan, David Gene; Maciulis, Nicholas A; Pink, Maren; Losovyj, Yaroslav; Bronstein, Lyudmila M

2018-06-14

Here, we report transfer hydrogenation of nitroarenes to aminoarenes using 2-propanol as a hydrogen source and Ag-containing magnetically recoverable catalysts based on partially reduced graphene oxide (pRGO) sheets. X-ray diffraction and X-ray photoelectron spectroscopy data demonstrated that, during the one-pot catalyst synthesis, formation of magnetite nanoparticles (NPs) is accompanied by the reduction of graphene oxide (GO) to pRGO. The formation of Ag 0 NPs on top of magnetite nanoparticles does not change the pRGO structure. At the same time, the catalyst structure is further modified during the transfer hydrogenation, leading to a noticeable increase of sp 2 carbons. These carbons are responsible for the adsorption of substrate and intermediates, facilitating a hydrogen transfer from Ag NPs and creating synergy between the components of the catalyst. The nitroarenes with electron withdrawing and electron donating substituents allow for excellent yields of aniline derivatives with high regio and chemoselectivity, indicating that the reaction is not disfavored by these functionalities. The versatility of the catalyst synthetic protocol was demonstrated by a synthesis of an Ru-containing graphene derivative based catalyst, also allowing for efficient transfer hydrogenation. Easy magnetic separation and stable catalyst performance in the transfer hydrogenation make this catalyst promising for future applications.

Bipyridinium array-type porous polymer displaying hydrogen storage, charge-transfer-type guest inclusion, and tunable magnetic properties.

PubMed

Yao, Qing-Xia; Pan, Long; Jin, Xu-Hui; Li, Jing; Ju, Zhan-Feng; Zhang, Jie

2009-11-09

A multifunctional pillared-layer porous coordination polymer, {[Mn(2)(Bpybc)(ox)(2)]8 H(2)O}(n), has been constructed based on a flexible viologen derivative, 1,1'-bis(4-carboxybenzyl)-4,4'-bipyridinium dichloride (H(2)BpybcCl(2)), and an oxalate (ox) coligand. Single-crystal X-ray analysis reveals that the compound possesses multichannels with dimensions of about 6.1x6.6 A along the [110] and [-110] directions and 4.2x7.6 A along [100], and a void space of about 41.4 %. Hydrogen adsorption measurements at 77 K and 1 atm indicate that the compound exhibits a hydrogen uptake of 0.71 wt %. Owing to the incorporation of bipyridinium acceptor units, the compound can selectively accommodate aromatic donors into its nanosized pores based on charge-transfer interactions in an elastic way, and afford a specific color to different guests. Furthermore, the effect of perturbation exerted by the guest molecules on its magnetic properties has been investigated. The results indicate that the donor inclusion has little effect on its antiferromagnetic behavior, whereas dehydration of the compound decreases the strength of the magnetic exchange couplings and results in a change of the antiferromagnetic transition temperature from 14.7 to 9.8 K.

Numerical simulation for flow and heat transfer to Carreau fluid with magnetic field effect: Dual nature study

NASA Astrophysics Data System (ADS)

Hashim; Khan, Masood; Alshomrani, Ali Saleh

2017-12-01

This article considers a realistic approach to examine the magnetohydrodynamics (MHD) flow of Carreau fluid induced by the shrinking sheet subject to the stagnation-point. This study also explores the impacts of non-linear thermal radiation on the heat transfer process. The governing equations of physical model are expressed as a system of partial differential equations and are transformed into non-linear ordinary differential equations by introducing local similarity variables. The economized equations of the problem are numerically integrated using the Runge-Kutta Fehlberg integration scheme. In this study, we explore the condition of existence, non-existence, uniqueness and dual nature for obtaining numerical solutions. It is found that the solutions may possess multiple natures, upper and lower branch, for a specific range of shrinking parameter. Results indicate that due to an increment in the magnetic parameter, range of shrinking parameter where a dual solution exists, increases. Further, strong magnetic field enhances the thickness of the momentum boundary layer in case of the second solution while for first solution it reduces. We further note that the fluid suction diminishes the fluid velocity and therefore the thickness of the hydrodynamic boundary layer decreases as well. A critical analysis with existing works is performed which shows that outcome are benchmarks with these works.

Pulse electromagnetic fields enhance extracellular electron transfer in magnetic bioelectrochemical systems.

PubMed

Zhou, Huihui; Liu, Bingfeng; Wang, Qisong; Sun, Jianmin; Xie, Guojun; Ren, Nanqi; Ren, Zhiyong Jason; Xing, Defeng

2017-01-01

Microbial extracellular electron transfer (EET) is essential in driving the microbial interspecies interaction and redox reactions in bioelectrochemical systems (BESs). Magnetite (Fe 3 O 4 ) and magnetic fields (MFs) were recently reported to promote microbial EET, but the mechanisms of MFs stimulation of EET and current generation in BESs are not known. This study investigates the behavior of current generation and EET in a state-of-the-art pulse electromagnetic field (PEMF)-assisted magnetic BES (PEMF-MBES), which was equipped with magnetic carbon particle (Fe 3 O 4 @N-mC)-coated electrodes. Illumina Miseq sequencing of 16S rRNA gene amplicons was also conducted to reveal the changes of microbial communities and interactions on the anode in response to magnetic field. PEMF had significant influences on current generation. When reactors were operated in microbial fuel cell (MFC) mode with pulse electromagnetic field (PEMF-MMFCs), power densities increased by 25.3-36.0% compared with no PEMF control MFCs (PEMF-OFF-MMFCs). More interestingly, when PEMF was removed, the power density dropped by 25.7%, while when PEMF was reintroduced, the value was restored to the previous level. Illumina sequencing of 16S rRNA gene amplicon and principal component analysis (PCA) based on operational taxonomic units (OTUs) indicate that PEMFs led to the shifts in microbial community and changes in species evenness that decreased biofilm microbial diversity. Geobacter spp. were found dominant in all anode biofilms, but the relative abundance in PEMF-MMFCs (86.1-90.0%) was higher than in PEMF-OFF-MMFCs (82.5-82.7%), indicating that the magnetic field enriched Geobacter on the anode. The current generation of Geobacter -inoculated microbial electrolysis cells (MECs) presented the same change regularity, the accordingly increase or decrease corresponding with switch of PEMF, which confirmed the reversible stimulation of PEMFs on microbial electron transfer. The pulse electromagnetic field (PEMF) showed significant influence on state-of-the-art pulse magnetic bioelectrochemical systems (PEMF-MBES) in terms of current generation and microbial ecology. EET was instantaneously and reversibly enhanced in MBESs inoculated with either mixed-culture or Geobacter . PEMF notably decreased bacterial and archaeal diversities of the anode biofilms in MMFCs via changing species evenness rather than species richness, and facilitated specific enrichment of exoelectrogenic bacteria ( Geobacter ) on the anode surface. This study demonstrates a new magnetic approach for understanding and facilitating microbial electrochemical activities.

Analysis on the power and efficiency in wireless power transfer system via coupled magnetic resonances

NASA Astrophysics Data System (ADS)

Liu, Mingjie

2018-06-01

The analysis of characteristics of the power and efficiency in wireless power transmission (WPT) system is the theoretical basis of magnetic coupling resonant wireless power transmission (MCR-WPT) technology. The electromagnetic field theory was employed to study the variation of the coupling degree of the two electromagnetic coils with the parameters of the coils. The equivalent circuit was used to analyze the influence of different factors on the transmission power and efficiency of the WPT system. The results show that there is an optimal radius ratio between the two coils, which makes the mutual inductance of the coils the largest. Moreover, when the WPT system operates in the under-coupling state, the transmission power of the system drops sharply, and there is a frequency splitting of the power when in the over-coupling state.

Resonant Spin-Transfer-Torque Nano-Oscillators

NASA Astrophysics Data System (ADS)

Sharma, Abhishek; Tulapurkar, Ashwin A.; Muralidharan, Bhaskaran

2017-12-01

Spin-transfer-torque nano-oscillators are potential candidates for replacing the traditional inductor-based voltage-controlled oscillators in modern communication devices. Typical oscillator designs are based on trilayer magnetic tunnel junctions, which have the disadvantages of low power outputs and poor conversion efficiencies. We theoretically propose using resonant spin filtering in pentalayer magnetic tunnel junctions as a possible route to alleviate these issues and present viable device designs geared toward a high microwave output power and an efficient conversion of the dc input power. We attribute these robust qualities to the resulting nontrivial spin-current profiles and the ultrahigh tunnel magnetoresistance, both of which arise from resonant spin filtering. The device designs are based on the nonequilibrium Green's-function spin-transport formalism self-consistently coupled with the stochastic Landau-Lifshitz-Gilbert-Slonczewski equation and Poisson's equation. We demonstrate that the proposed structures facilitate oscillator designs featuring a large enhancement in microwave power of around 1150% and an efficiency enhancement of over 1100% compared to typical trilayer designs. We rationalize the optimum operating regions via an analysis of the dynamic and static device resistances. We also demonstrate the robustness of our structures against device design fluctuations and elastic dephasing. This work sets the stage for pentalyer spin-transfer-torque nano-oscillator device designs that ameliorate major issues associated with typical trilayer designs.

Water-Soluble Phosphine-Protected Au₁₁ Clusters: Synthesis, Electronic Structure, and Chiral Phase Transfer in a Synergistic Fashion.

PubMed

Yao, Hiroshi; Iwatsu, Mana

2016-04-05

Synthesis of atomically precise, water-soluble phosphine-protected gold clusters is still currently limited probably due to a stability issue. We here present the synthesis, magic-number isolation, and exploration of the electronic structures as well as the asymmetric conversion of triphenylphosphine monosulfonate (TPPS)-protected gold clusters. Electrospray ionization mass spectrometry and elemental analysis result in the primary formation of Au11(TPPS)9Cl undecagold cluster compound. Magnetic circular dichroism (MCD) spectroscopy clarifies that extremely weak transitions are present in the low-energy region unresolved in the UV-vis absorption, which can be due to the Faraday B-terms based on the magnetically allowed transitions in the cluster. Asymmetric conversion without changing the nuclearity is remarkable by the chiral phase transfer in a synergistic fashion, which yields a rather small anisotropy factor (g-factor) of at most (2.5-7.0) × 10(-5). Quantum chemical calculations for model undecagold cluster compounds are then used to evaluate the optical and chiroptical responses induced by the chiral phase transfer. On this basis, we find that the Au core distortion is ignorable, and the chiral ion-pairing causes a slight increase in the CD response of the Au11 cluster.

Oxygen transport enhancement by functionalized magnetic nanoparticles (FMP) in bioprocesses

NASA Astrophysics Data System (ADS)

Ataide, Filipe Andre Prata

The enhancement of fluid properties, namely thermal conductivity and mass diffusivity for a wide range of applications, through the use of nanosized particles' suspensions has been gathering increasing interest in the scientific community. In previous studies, Olle et al. (2006) showed an enhancement in oxygen absorption to aqueous solutions of up to 6-fold through the use of functionalized nanosized magnetic particles with oleic acid coating. Krishnamurthy et al. (2006) showed a remarkable 26-fold enhancement in dye diffusion in water. These two publications are landmarks in mass transfer enhancement in chemical systems through the use of nanoparticles. The central goal of this Ph.D. thesis was to develop functionalized magnetic nanoparticles to enhance oxygen transport in bioprocesses. The experimental protocol for magnetic nanoparticles synthesis and purification adopted in this thesis is a modification of that reported by Olle et al. (2006). This is facilitated by employing twice the quantity of ammonia, added at a slower rate, and by filtering the final nanoparticle solution in a cross-flow filtration modulus against 55 volumes of distilled water. This modification in the protocol resulted in improved magnetic nanoparticles with measurably higher mass transfer enhancement. Magnetic nanoparticles with oleic acid and Hitenol-BC coating were screened for oxygen transfer enhancement, since these particles are relatively inexpensive and easy to synthesize. A glass 0.5-liter reactor was custom manufactured specifically for oxygen transport studies in magnetic nanoparticles suspensions. The reactor geometry, baffles and Rushton impeller are of standard dimensions. Mass transfer tests were conducted through the use of the sulphite oxidation method, applying iodometric back-titration. A 3-factor central composite circumscribed design (CCD) was adopted for design of experiments in order to generate sufficiently informative data to model the effect of magnetic nanoparticles on interfacial area and mass transfer coefficient. The parameters ranges used were: 250-750 rpm for stirring speed, 0-2 vvm for aeration and 0-0.00120 g g?1 magnetic nanoparticles mass fraction. It was found that 36 nm-sized nanoparticles produced during the course of this dissertation enhanced the volumetric mass transfer coefficient up to 3.3-fold and the interfacial area up to 3.3-fold in relation to gas-liquid dispersions without nanoparticles. These results are concordant with previously published enhancement data (kLa enhancement by 7.1-fold and a enhancement by 4.1-fold) (Olle et al. 2006). The magnetic nanoparticles synthesized in this thesis were stable (constant diameter) over a 1wide pH range (2-9). Statistical regression models showed that both kLa and a have high sensitivity to the nanoparticles loading. Empirical correlation models were derived for kLa and for interfacial area, a, as function of physical properties and nanoparticles loading. These correlations lay out a methodology that can help the scientific community to design and scale-up oxygen transfer systems that are based on nanoparticle suspensions. None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None None

Magnetohydrodynamic Heat Transfer Research Related to the Design of Fusion Blankets

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

Barleon, Leopold; Burr, Ulrich; Mack, Klaus Juergen

2001-03-15

Lithium or any lithium alloy like the lithium lead alloy Pb-17Li is an attractive breeder material used in blankets of fusion power reactors because it allows the breeding of tritium and, in the case of self-cooled blankets, the transfer of the heat generated within the liquid metal and the walls of the cooling ducts to an external heat exchanger. Nevertheless, this type of liquid-metal-cooled blanket, called a self-cooled blanket, requires specific design of the coolant ducts, because the interaction of the circulating fluid and the plasma-confining magnetic fields causes magnetohydrodynamic (MHD) effects, yielding completely different flow patterns compared to ordinarymore » hydrodynamics (OHD) and pressure drops significantly higher than there. In contrast to OHD, MHD flows depend strongly on the electrical properties of the wall. Also, MHD flows reveal anisotropic turbulence behavior and are quite sensitive to obstacles exposed to the fluid flow.A comprehensive study of the heat transfer characteristics of free and forced convective MHD flows at fusion-relevant conditions is conducted. The general ideas of the analytical and numerical models to describe MHD heat transfer phenomena in this parameter regime are discussed. The MHD laboratory being installed, the experimental program established, and the experiments on heat transfer of free and forced convective flow being conducted are described. The theoretical results are compared to the results of a series of experiments in forced and free convective MHD flows with different wall properties, such as electrically insulating as well as electric conducting ducts. Based on this knowledge, methods to improve the heat transfer by means of electromagnetic/mechanic turbulence promoters (TPs) or sophisticated, arranged electrically conducting walls are discussed, experimental results are shown, and a cost-benefit analysis related to these methods is performed. Nevertheless, a few experimental results obtained should be highlighted:1. The heat flux removable in rectangular electrically conducting ducts at walls parallel to the magnetic field is by a factor of 2 higher than in the slug flow model previously used in design calculations. Conditions for which this heat transfer enhancement is attainable are presented. The measured dimensionless pressure gradient coincides with the theoretical one and is constant throughout the whole Reynolds number regime investigated (Re = 10{sup 3} {yields} 10{sup 5}), although the flow turns from laminar to turbulent. The use of electromagnetic TPs close to the heated wall leads to nonmeasurable increase of the heat transfer in the same Re regime as long as they do not lead to an interaction with the wall adjacent boundary layers.2. Mechanical TPs used in an electrically insulated rectangular duct improved the heat transfer up to seven times compared to slug flow, but the pressure drop can increase also up to 300%. In a cost-benefit analysis, the advantageous parameter regime for applying this method is determined.3. Experiments performed in a flat box both in a vertical and a horizontal arrangement within a horizontal magnetic field show the expected increase of damping of the fluid motion with increasing Hartmann number M. At high M, buoyant convection will be completely suppressed in the horizontal case. In the vertical setup, the fluid motion is reduced to one large vortex leading to a decreasing heat transfer between heated and cooled plate to pure heat conduction.From an analysis of the experimental and theoretical results, general design criteria are derived for the orientation and shape of the first wall coolant ducts of self-cooled liquid metal blankets. Methods to generate additional turbulence within the flow, which can improve the heat transfer further are elaborated.« less

Numerical simulation of magnetic convection ferrofluid flow in a permanent magnet-inserted cavity

NASA Astrophysics Data System (ADS)

Ashouri, Majid; Behshad Shafii, Mohammad

2017-11-01

The magnetic convection heat transfer in an obstructed two-dimensional square cavity is investigated numerically. The walls of the cavity are heated with different constant temperatures at two sides, and isolated at two other sides. The cavity is filled with a high Prandtl number ferrofluid. The convective force is induced by a magnetic field gradient of a thermally insulated square permanent magnet located at the center of the cavity. The results are presented in the forms of streamlines, isotherms, and Nusselt number for various values of magnetic Rayleigh numbers and permanent magnet size. Two major circulations are generated in the cavity, clockwise flow in the upper half and counterclockwise in the lower half. In addition, strong circulations are observed around the edges of the permanent magnet surface. The strength of the circulations increase monotonically with the magnetic Rayleigh number. The circulations also increase with the permanent magnet size, but eventually, are suppressed for larger sizes. It is found that there is an optimum size for the permanent magnet due to the contrary effects of the increase in magnetic force and the increase in flow resistance by increasing the size. By increasing the magnetic Rayleigh number or isothermal walls temperature ratio, the heat transfer rate increases.

MESSENGER Observations of Mercury's Dynamic Magnetosphere During Three Flybys

NASA Astrophysics Data System (ADS)

Slavin, James; Krimigis, Stamatios; Anderson, Brian J.; Benna, Mehdi; Gold, Robert E.; Ho, George; McNutt, Ralph; Raines, James; Schriver, David; Solomon, Sean C.

MESSENGER's 14 January and 6 October 2008 and 29 September 2009 encounters with Mer-cury have provided new measurements of dynamic variations in the planet's coupled atmo-sphere-magnetosphere system. The three flybys took place under very different interplanetary magnetic field (IMF) conditions. Consistent with predictions of magnetospheric models for northward IMF, the neutral atmosphere was observed to have its strongest sources in the high latitude northern hemisphere for the first flyby. The southward IMF for the second encounter revealed a highly dynamic magnetosphere. Reconnection between the interplanetary and plan-etary magnetic fields is known to control the rate of energy transfer from the solar wind and to drive magnetospheric convection. The MESSENGER magnetic field measurements revealed that the rate at which interplanetary magnetic fields were reconnecting to the planetary fields was a factor of 10 greater than is usually observed at Earth. This extremely high reconnection rate results in a large magnetic field component normal to the magnetopause and the formation of flux transfer events that are much larger relative to the size of the forward magnetosphere than is observed at Earth. The resulting magnetospheric configuration allows the solar wind access to much of the dayside surface of Mercury. During MESSENGER's third Mercury flyby, a variable interplanetary magnetic field produced a series of several-minute-long enhancements of the tail magnetic field by factors of 2 to 3.5. The magnetic field flaring during these intervals indicates that they resulted from loading of the tail with magnetic flux transferred from the dayside magnetosphere. The unloading intervals were associated with plasmoids and traveling compression regions, signatures of tail reconnection. The peak tail magnetic flux during the smallest loading events equaled 30

Investigation of Deposits in Channels of Panels of a Heat-Transfer Agent

NASA Astrophysics Data System (ADS)

Koshoridze, S. I.; Levin, Yu. K.; Rabinskiy, L. N.; Babaytsev, A. V.

2017-12-01

An analysis of the behavior of nanosized colloidal particles in a supersaturated solution made it possible to substantiate the possibility of increasing the heat-transfer efficiency in a heat exchanger during magnetic treatment of a heat-transfer agent. A model is proposed to weaken the scale during magnetic treatment of a water stream. A colloidal solution is shown to decrease its stability—the coagulation of colloidal particles begins—because of the deformation of the double electrical layer. As a result of increasing the effective radius of curvature of nanoparticles, the solution becomes strongly supersaturated with respect to forming aggregates, which accelerates the solidification of dissolved salts on them. The influence of the interfacial layer of nanoobjects decreases the energy of formation of critical nuclei (size effect) and their sizes. Since coagulation tends to decrease the concentration of critical nuclei in the solution, their loss should be compensated via the homogeneous generation of new nuclei. As a result, the concentration of suspended particles increases additionally and the antiscale effect is enhanced. The solidification flux of dissolved salts is shown to deposit mainly on suspended nanoparticles due to an increase in their total surface area and to the fact that the coefficient of mass transfer to suspension is higher than that to the wall by four orders of magnitude. The mathematical model constructed on the basis of the detected set of physical processes can be used to perform quantitative estimates of the antiscale effect in real power plants.

SU-E-T-590: Optimizing Magnetic Field Strengths with Matlab for An Ion-Optic System in Particle Therapy Consisting of Two Quadrupole Magnets for Subsequent Simulations with the Monte-Carlo Code FLUKA

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

Baumann, K; Weber, U; Simeonov, Y

Purpose: Aim of this study was to optimize the magnetic field strengths of two quadrupole magnets in a particle therapy facility in order to obtain a beam quality suitable for spot beam scanning. Methods: The particle transport through an ion-optic system of a particle therapy facility consisting of the beam tube, two quadrupole magnets and a beam monitor system was calculated with the help of Matlab by using matrices that solve the equation of motion of a charged particle in a magnetic field and field-free region, respectively. The magnetic field strengths were optimized in order to obtain a circular andmore » thin beam spot at the iso-center of the therapy facility. These optimized field strengths were subsequently transferred to the Monte-Carlo code FLUKA and the transport of 80 MeV/u C12-ions through this ion-optic system was calculated by using a user-routine to implement magnetic fields. The fluence along the beam-axis and at the iso-center was evaluated. Results: The magnetic field strengths could be optimized by using Matlab and transferred to the Monte-Carlo code FLUKA. The implementation via a user-routine was successful. Analyzing the fluence-pattern along the beam-axis the characteristic focusing and de-focusing effects of the quadrupole magnets could be reproduced. Furthermore the beam spot at the iso-center was circular and significantly thinner compared to an unfocused beam. Conclusion: In this study a Matlab tool was developed to optimize magnetic field strengths for an ion-optic system consisting of two quadrupole magnets as part of a particle therapy facility. These magnetic field strengths could subsequently be transferred to and implemented in the Monte-Carlo code FLUKA to simulate the particle transport through this optimized ion-optic system.« less

Synchronization of spin-transfer torque oscillators by spin pumping, inverse spin Hall, and spin Hall effects

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

Elyasi, Mehrdad; Bhatia, Charanjit S.; Yang, Hyunsoo, E-mail: eleyang@nus.edu.sg

2015-02-14

We have proposed a method to synchronize multiple spin-transfer torque oscillators based on spin pumping, inverse spin Hall, and spin Hall effects. The proposed oscillator system consists of a series of nano-magnets in junction with a normal metal with high spin-orbit coupling, and an accumulative feedback loop. We conduct simulations to demonstrate the effect of modulated charge currents in the normal metal due to spin pumping from each nano-magnet. We show that the interplay between the spin Hall effect and inverse spin Hall effect results in synchronization of the nano-magnets.

High-time resolution measurements of upstream magnetic field and plasma conditions during flux transfer events at the Earth's dayside magnetopause

NASA Technical Reports Server (NTRS)

Jacob, Jamey D.; Carrell, Cynthia

1993-01-01

We present preliminary results of a study of upstream magnetic field and plasma conditions measured by IRM during flux transfer events observed at the Earth's magnetopause by CCE. This study was designed to determine the importance of various upstream factors in the formation of bipolar magnetic field signatures called flux transfer events (FTEs). Six FTE encounters were examined. In three cases, the two satellites were on similar magnetic field lines. Preliminary investigation showed that fluctuations occurred in the Bz component of the interplanetary magnetic field (IMF) resulting in a southward field preceding the FTE in all three of these cases. In two of these cases, the changes were characterized by a distinct rotation from a strong southward to a strong northward field. There were also accompanying changes in the dynamic and thermal pressure in the solar wind immediately before the FTE was encountered. Examination of the 3D plasma distributions showed that these pulses were due to the addition of energetic upstreaming foreshock particles. There were no consistent changes in either Bz or the plasma pressure at IRM for the three events when the satellites were not connected by the IMF.

Note: A calibration method to determine the lumped-circuit parameters of a magnetic probe.

PubMed

Li, Fuming; Chen, Zhipeng; Zhu, Lizhi; Liu, Hai; Wang, Zhijiang; Zhuang, Ge

2016-06-01

This paper describes a novel method to determine the lumped-circuit parameters of a magnetic inductive probe for calibration by using Helmholtz coils with high frequency power supply (frequency range: 10 kHz-400 kHz). The whole calibration circuit system can be separated into two parts: "generator" circuit and "receiver" circuit. By implementing the Fourier transform, two analytical lumped-circuit models, with respect to these separated circuits, are constructed to obtain the transfer function between each other. Herein, the precise lumped-circuit parameters (including the resistance, inductance, and capacitance) of the magnetic probe can be determined by fitting the experimental data to the transfer function. Regarding the fitting results, the finite impedance of magnetic probe can be used to analyze the transmission of a high-frequency signal between magnetic probes, cables, and acquisition system.

High-frequency flux transfer events detected near Mercury

NASA Astrophysics Data System (ADS)

Schultz, Colin

2013-01-01

The physical process that creates connections between the magnetic fields emanating from the Sun and a planet—a process known as magnetic reconnection—creates a portal through which solar plasma can penetrate the planetary magnetic field. The opening of these portals, known as flux transfer events (FTEs), takes place roughly every 8 minutes at Earth and spawns a rope of streaming plasma that is typically about half of the radius of the Earth. As early as 1985, scientists analyzing the Mariner 10 observations, collected during their 1974-1975 flybys, have known that FTEs also occur at Mercury. However, using the measurements returned from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft now orbiting Mercury, Slavin et al. found that Mercurial flux transfer events are proportionally much larger, stronger, and more frequent than those at Earth.

Interfacial spin-filter assisted spin transfer torque effect in Co/BeO/Co magnetic tunnel junction

NASA Astrophysics Data System (ADS)

Tang, Y.-H.; Chu, F.-C.

2015-03-01

The first-principles calculation is employed to demonstrate the spin-selective transport properties and the non-collinear spin-transfer torque (STT) effect in the newly proposed Co/BeO/Co magnetic tunnel junction. The subtle spin-polarized charge transfer solely at O/Co interface gives rise to the interfacial spin-filter (ISF) effect, which can be simulated within the tight binding model to verify the general expression of STT. This allows us to predict the asymmetric bias behavior of non-collinear STT directly via the interplay between the first-principles calculated spin current densities in collinear magnetic configurations. We believe that the ISF effect, introduced by the combination between wurtzite-BeO barrier and the fcc-Co electrode, may open a new and promising route in semiconductor-based spintronics applications.

Liquid neon heat transfer as applied to a 30 tesla cryomagnet

NASA Technical Reports Server (NTRS)

Papell, S. S.; Hendricks, R. C.

1975-01-01

A 30-tesla magnet design is studied which calls for forced convection liquid neon heat transfer in small coolant channels. The design also requires suppressing boiling by subjecting the fluid to high pressures through use of magnet coils enclosed in a pressure vessel which is maintained at the critical pressure of liquid neon. This high pressure reduces the possibility of the system flow instabilities which may occur at low pressures. The forced convection heat transfer data presented were obtained by using a blowdown technique to force the fluid to flow vertically through a resistance heated, instrumented tube.

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.

Cattaneo-Christov based study of {TiO}_2 -CuO/EG Casson hybrid nanofluid flow over a stretching surface with entropy generation

NASA Astrophysics Data System (ADS)

Jamshed, Wasim; Aziz, Asim

2018-06-01

In the present research, a simplified mathematical model is presented to study the heat transfer and entropy generation analysis of thermal system containing hybrid nanofluid. Nanofluid occupies the space over an infinite horizontal surface and the flow is induced by the non-linear stretching of surface. A uniform transverse magnetic field, Cattaneo-Christov heat flux model and thermal radiation effects are also included in the present study. The similarity technique is employed to reduce the governing non-linear partial differential equations to a set of ordinary differential equation. Keller Box numerical scheme is then used to approximate the solutions for the thermal analysis. Results are presented for conventional copper oxide-ethylene glycol (CuO-EG) and hybrid titanium-copper oxide/ethylene glycol ({TiO}_2 -CuO/EG) nanofluids. The spherical, hexahedron, tetrahedron, cylindrical, and lamina-shaped nanoparticles are considered in the present analysis. The significant findings of the study is the enhanced heat transfer capability of hybrid nanofluids over the conventional nanofluids, greatest heat transfer rate for the smallest value of the shape factor parameter and the increase in Reynolds number and Brinkman number increases the overall entropy of the system.

Passive shielding effect on space profile of magnetic field emissions for wireless power transfer to vehicles

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

Batra, T., E-mail: tba@et.aau.dk; Schaltz, E.

2015-05-07

Magnetic fields emitted by wireless power transfer systems are of high importance with respect to human safety and health. Aluminum and ferrite are used in the system to reduce the fields and are termed as passive shielding. In this paper, the influence of these materials on the space profile has been investigated with the help of simulations on Comsol for the four possible geometries—no shielding, ferrite, aluminum, and full shielding. As the reflected impedance varies for the four geometries, the primary current is varied accordingly to maintain constant power transfer to the secondary side. Surrounding magnetic field plots in themore » vertical direction show that maxima's of the two coils for the no shielding geometry are centered at the respective coils and for the remaining three are displaced closer to each other. This closeness would lead to more effective addition of the two coil fields and an increase in the resultant field from space point of view. This closeness varies with distance in the horizontal direction and vertical gap between the coils and is explained in the paper. This paper provides a better understanding of effect of the passive shielding materials on the space nature of magnetic fields for wireless power transfer for vehicle applications.« less

Modeling magnetization transfer effects of Q2TIPS bolus saturation in multi-TI pulsed arterial spin labeling.

PubMed

Petr, Jan; Schramm, Georg; Hofheinz, Frank; Langner, Jens; van den Hoff, Jörg

2014-10-01

To estimate the relaxation time changes during Q2TIPS bolus saturation caused by magnetization transfer effects and to propose and evaluate an extended model for perfusion quantification which takes this into account. Three multi inversion-time pulsed arterial spin labeling sequences with different bolus saturation duration were acquired for five healthy volunteers. Magnetization transfer exchange rates in tissue and blood were obtained from control image saturation recovery. Cerebral blood flow (CBF) obtained using the extended model and the standard model was compared. A decrease of obtained CBF of 6% (10%) was observed in grey matter when the duration of bolus saturation increased from 600 to 900 ms (1200 ms). This decrease was reduced to 1.6% (2.8%) when the extended quantification model was used. Compared with the extended model, the standard model underestimated CBF in grey matter by 9.7, 15.0, and 18.7% for saturation durations 600, 900, and 1200 ms, respectively. Results for simulated single inversion-time data showed 5-16% CBF underestimation depending on blood arrival time and bolus saturation duration. Magnetization transfer effects caused by bolus saturation pulses should not be ignored when performing quantification as they can cause appreciable underestimation of the CBF. Copyright © 2013 Wiley Periodicals, Inc.

Magnetization transfer studies of the fast and slow tissue water diffusion components in the human brain.

PubMed

Mulkern, Robert V; Vajapeyam, Sridhar; Haker, Steven J; Maier, Stephan E

2005-05-01

Magnetization transfer (MT) properties of the fast and slow diffusion components recently observed in the human brain were assessed experimentally. One set of experiments, performed at 1.5 T in healthy volunteers, was designed to determine whether the amplitudes of fast and slow diffusion components, differentiated on the basis of biexponential fits to signal decays over a wide range of b-factors, demonstrated a different or similar magnetization transfer ratio (MTR). Another set of experiments, performed at 3 T in healthy volunteers, was designed to determine whether MTRs differed when measured from high signal-to-noise images acquired with b-factor weightings of 350 vs 3500 s/mm2. The 3 T studies included measurements of MTR as a function of off-resonance frequency for the MT pulse at both low and high b-factors. The primary conclusion drawn from all the studies is that there appears to be no significant difference between the magnetization transfer properties of the fast and slow tissue water diffusion components. The conclusions do not lend support to a direct interpretation of the 'components' of the biexponential diffusion decay in terms of the 'compartments' associated with intra- and extracellular water. Copyright 2004 John Wiley & Sons, Ltd.

Stress analysis in high-temperature superconductors under pulsed field magnetization

NASA Astrophysics Data System (ADS)

Wu, Haowei; Yong, Huadong; Zhou, Youhe

2018-04-01

Bulk high-temperature superconductors (HTSs) have a high critical current density and can trap a large magnetic field. When bulk superconductors are magnetized by the pulsed field magnetization (PFM) technique, they are also subjected to a large electromagnetic stress, and the resulting thermal stress may cause cracking of the superconductor due to the brittle nature of the sample. In this paper, based on the H-formulation and the law of heat transfer, we can obtain the distributions of electromagnetic field and temperature, which are in qualitative agreement with experiment. After that, based on the dynamic equilibrium equations, the mechanical response of the bulk superconductor is determined. During the PFM process, the change in temperature has a dramatic effect on the radial and hoop stresses, and the maximum radial and hoop stress are 24.2 {{MPa}} and 22.6 {{MPa}}, respectively. The mechanical responses of a superconductor for different cases are also studied, such as the peak value of the applied field and the size of bulk superconductors. Finally, the stresses are also presented for different magnetization methods.

Electromagnetic deep-probing (100-1000 kms) of the Earth's interior from artificial satellites: Constraints on the regional emplacement of crustal resources

NASA Technical Reports Server (NTRS)

Hermance, J. F. (Principal Investigator)

1981-01-01

A spherical harmonic analysis program is being tested which takes magnetic data in universal time from a set of arbitrarily space observatories and calculates a value for the instantaneous magnetic field at any point on the globe. The calculation is done as a least mean-squares value fit to a set of spherical harmonics up to any desired order. The program accepts as a set of input the orbit position of a satellite coordinates it with ground-based magnetic data for a given time. The output is a predicted time series for the magnetic field on the Earth's surface at the (r, theta) position directly under the hypothetically orbiting satellite for the duration of the time period of the input data set. By tracking the surface magnetic field beneath the satellite, narrow-band averages crosspowers between the spatially coordinated satellite and the ground-based data sets are computed. These crosspowers are used to calculate field transfer coefficients with minimum noise distortion. The application of this technique to calculating the vector response function W is discussed.

Manipulating spins of magnetic molecules: Hysteretic behavior with respect to bias voltage

NASA Astrophysics Data System (ADS)

Płomińska, Anna; Misiorny, Maciej; Weymann, Ireneusz

2018-02-01

Formation of a magnetic hysteresis loop with respect to a bias voltage is investigated theoretically in a spin-valve device based on a single magnetic molecule. We consider a device consisting of two ferromagnetic electrodes bridged by a carbon nanotube, acting as a quantum dot, to which a spin-anisotropic molecule is exchange-coupled. Such a coupling allows for transfer of angular momentum between the molecule and a spin current flowing through the dot, and thus, for switching orientation of the molecular spin. We demonstrate that this current-induced switching process exhibits a hysteretic behavior with respect to a bias voltage applied to the device. The analysis is carried out with the use of the real-time diagrammatic technique in the lowest-order expansion of the tunnel coupling of the dot to electrodes. The influence of both the intrinsic properties of the spin-valve device (the spin polarization of electrodes and the coupling strength of the molecule to the dot) and those of the molecule itself (magnetic anisotropy and spin relaxation) on the size of the magnetic hysteresis loop is discussed.

DCE-MRI-Derived Volume Transfer Constant (Ktrans) and DWI Apparent Diffusion Coefficient as Predictive Markers of Short- and Long-Term Efficacy of Chemoradiotherapy in Patients With Esophageal Cancer.

PubMed

Ye, Zhi-Min; Dai, Shu-Jun; Yan, Feng-Qin; Wang, Lei; Fang, Jun; Fu, Zhen-Fu; Wang, Yue-Zhen

2018-01-01

This study aimed to evaluate both the short- and long-term efficacies of chemoradiotherapy in relation to the treatment of esophageal cancer . This was achieved through the use of dynamic contrast-enhanced magnetic resonance imaging-derived volume transfer constant and diffusion weighted imaging-derived apparent diffusion coefficient . Patients with esophageal cancer were assigned into the sensitive and resistant groups based on respective efficacies in chemoradiotherapy. Dynamic contrast-enhanced magnetic resonance imaging and diffusion weighted imaging were used to measure volume transfer constant and apparent diffusion coefficient, while computed tomography was used to calculate tumor size reduction rate. Pearson correlation analyses were conducted to analyze correlation between volume transfer constant, apparent diffusion coefficient, and the tumor size reduction rate. Receiver operating characteristic curve was constructed to analyze the short-term efficacy of volume transfer constant and apparent diffusion coefficient, while Kaplan-Meier curve was employed for survival rate analysis. Cox proportional hazard model was used for the risk factors for prognosis of patients with esophageal cancer. Our results indicated reduced levels of volume transfer constant, while increased levels were observed in ADC min , ADC mean , and ADC max following chemoradiotherapy. A negative correlation was determined between ADC min , ADC mean , and ADC max , as well as in the tumor size reduction rate prior to chemoradiotherapy, whereas a positive correlation was uncovered postchemoradiotherapy. Volume transfer constant was positively correlated with tumor size reduction rate both before and after chemoradiotherapy. The 5-year survival rate of patients with esophageal cancer having high ADC min , ADC mean , and ADC max and volume transfer constant before chemoradiotherapy was greater than those with respectively lower values. According to the Cox proportional hazard model, ADC mean , clinical stage, degree of differentiation, and tumor stage were all confirmed as being independent risk factors in regard to the prognosis of patients with EC. The findings of this study provide evidence suggesting that volume transfer constant and apparent diffusion coefficient as being tools allowing for the evaluation of both the short- and long-term efficacies of chemoradiotherapy esophageal cancer treatment.

Spin dependent transport and spin transfer in nanoconstrictions and current confined nanomagnets

NASA Astrophysics Data System (ADS)

Ozatay, Ozhan

In this thesis, I have employed point contact spectroscopy to determine the nature of electron transport across constrained domain walls in a ferromagnetic nanocontact and to uncover the relationship between ballisticity of electron transport and domain wall magnetoresistance. In the range of hole sizes studied (from 10 to 3 nm) the resulting magnetoresistance was found to be less than 0.5% and one that increases with decreasing contact size. I have used point contacts as local probes, to study the spin dependent transport across Ferromagnet/Normal Metal/Ferromagnet(FM/NM/FM) trilayers as well as the consequences of localized spin polarized current injection into a nano magnet on spin angular momentum transfer and high frequency magnetization dynamics. I have demonstrated that absolute values for spin transfer switching critical currents are reduced in this new geometry as compared to uniform current injection. I have also performed micromagnetic simulations to determine the evolution of magnetization under the application of magnetic fields and currents to gain more insights into experimental results. I have used Scanning Transmission Electron Microscopy (STEM), X-Ray Photoemission Spectroscopy (XPS) and Electron Energy Loss Spectroscopy (EELS) techniques to characterize the interfacial mixing and oxygen diffusion in the metallic multilayers of interest. I have shown that the Ta/CuOx bilayer structure provides a smooth substrate by improving interfacial roughness due to grain boundary diffusion of oxygen and reaction with Ta that fills in the grain boundary gaps in Cu. Analysis of the Py/AlOx interface proved a strong oxidation passivation on the Py surface by Al coating accompanied by Fe segregation into the alumina. I have utilized the characterization results to design a new nanomagnet whose sidewalls are protected from adventitious sidewall oxide layers and yields improved device performance. The oxide layers that naturally develop at the sidewalls of Py nanomagnets cause an enhancement in magnetic damping especially for temperatures below the blocking temperature of the AFM layer (≤40K). Studies with pillars protected by Al coating and ones with more NiO coating (˜2.5 nm) shed light onto the role of surface oxides in determining temperature dependent behaviour of both spin torque and field driven switching characteristics.

Detumbling of a rigid spacecraft via torque wheel assisted gyroscopic motion

NASA Astrophysics Data System (ADS)

Lin, Yiing-Yuh; Wang, Chin-Tzuo

2014-01-01

A time and energy efficient two-part method for detumbling a rigid spacecraft using an onboard torque wheel and a set of three-axis magnetic torquer is presented in this paper. Part-1 of the method manipulates the speed of the wheel, whose spin axis is parallel to a designated body axis of a tumbling spacecraft, and induces a desired gyroscopic-like motion to align the designated axis with its total angular momentum, H. The procedure in effect detumbles the spacecraft to rotate about the designated axis and distributes H, which is conserved during this control period, between the body and the wheel. After the alignment is achieved, Part-2 control, activated with a specified momentum transfer parameter, η, can either quickly stop the body rotation by transferring its angular momentum to the wheel or offload most of the momentum into space, using the wheel and the magnetic torquer. Convergence criteria and control laws for both parts are derived from the Lyapunov stability analysis and the method of feedback linearization. The wheel performs as a momentum storing and transferring device regulating the angular momentum between the wheel and the body. It can also provide gyroscopic stiffness to stabilize the system while the magnetic torquer is offloading the momentum. Simulation results from the included cases indicate that significantly fast detumbling of the spacecraft can be achieved with Part-1 of the proposed method. The results also show that, under the same condition, either by transferring almost all H to the wheel or dumping it, the two-part method, with a chosen η and final residual momentum condition, requires much less time and energy needed than the B-dot method does. Moreover, the stability nature of the two-part method is heuristically substantiated as the wheel torques and the dipole moment were constrained in the simulation.

Competing spin density wave, collinear, and helical magnetism in Fe 1 + x Te

DOE PAGES

Stock, C.; Rodriguez, E. E.; Bourges, P.; ...

2017-04-07

The Fe 1+xTe phase diagram consists of two distinct magnetic structures with collinear order present at low interstitial iron concentrations and a helical phase at large values of x with these phases separated by a Lifshitz point. In this paper, we use unpolarized single-crystal diffraction to confirm the helical phase for large interstitial iron concentrations and polarized single-crystal diffraction to demonstrate the collinear order for the iron-deficient side of the Fe 1+xTe phase diagram. Polarized neutron inelastic scattering shows that the fluctuations associated with this collinear order are predominately transverse at low-energy transfers, consistent with a localized magnetic moment picture.more » We then apply neutron inelastic scattering and polarization analysis to investigate the dynamics and structure near the boundary between collinear and helical orders in the Fe 1+xTe phase diagram. We first show that the phase separating collinear and helical orders is characterized by a spin density wave with a single propagation wave vector of (~0.45, 0, 0.5). We do not observe harmonics or the presence of a charge density wave. The magnetic fluctuations associated with this wave vector are different from the collinear phase, being strongly longitudinal in nature and correlated anisotropically in the (H,K) plane. The excitations preserve the C 4 symmetry of the lattice but display different widths in momentum along the two tetragonal directions at low-energy transfers. Finally, while the low-energy excitations and minimal magnetic phase diagram can be understood in terms of localized interactions, we suggest that the presence of the density wave phase implies the importance of electronic and orbital properties.« less

Analysis of self-heating of thermally assisted spin-transfer torque magnetic random access memory

DOE PAGES

Deschenes, Austin; Muneer, Sadid; Akbulut, Mustafa; ...

2016-11-11

Thermal assistance has been shown to significantly reduce the required operation power for spin torque transfer magnetic random access memory (STT-MRAM). Proposed heating methods include modified material stack compositions that result in increased self-heating or external heat sources. Here, we analyze the self-heating process of a standard perpendicular magnetic anisotropy STT-MRAM device through numerical simulations in order to understand the relative contributions of Joule, thermoelectric Peltier and Thomson, and tunneling junction heating. A 2D rotationally symmetric numerical model is used to solve the coupled electro-thermal equations including thermoelectric effects and heat absorbed or released at the tunneling junction. We comparemore » self-heating for different common passivation materials, positive and negative electrical current polarity, and different device thermal anchoring and boundaries resistance configurations. The variations considered are found to result in significant differences in maximum temperatures reached. Average increases of 3 K, 10 K, and 100 K for different passivation materials, positive and negative polarity, and different thermal anchoring configurations, respectively, are observed. Furthermore, the highest temperatures, up to 424 K, are obtained for silicon dioxide as the passivation material, positive polarity, and low thermal anchoring with thermal boundary resistance configurations. Interestingly it is also found that due to the tunneling heat, Peltier effect, device geometry, and numerous interfacial layers around the magnetic tunnel junction (MTJ), most of the heat is dissipated on the lower potential side of the magnetic junction. We have observed this asymmetry in heating and is important as thermally assisted switching requires heating of the free layer specifically and this will be significantly different for the two polarity operations, set and reset.« less

Magnetic enhancement of ferroelectric polarization in a self-grown ferroelectric-ferromagnetic composite

NASA Astrophysics Data System (ADS)

Kumar, Amit; Narayan, Bastola; Pachat, Rohit; Ranjan, Rajeev

2018-02-01

Ferroelectric-ferromagnetic multiferroic composites are of great interest both from the scientific and technological standpoints. The extent of coupling between polarization and magnetization in such two-phase systems depends on how efficiently the magnetostrictive and electrostrictive/piezoelectric strain gets transferred from one phase to the other. This challenge is most profound in the easy to make 0-3 ferroelectric-ferromagnetic particulate composites. Here we report a self-grown ferroelectric-ferromagnetic 0-3 particulate composite through controlled spontaneous precipitation of ferrimagnetic barium hexaferrite phase (BaF e12O19 ) amid ferroelectric grains in the multiferroic alloy system BiFe O3-BaTi O3 . We demonstrate that a composite specimen exhibiting merely ˜1% hexaferrite phase exhibits ˜34% increase in saturation polarization in a dc magnetic field of ˜10 kOe. Using modified Rayleigh analysis of the polarization field loop in the subcoercive field region we argue that the substantial enhancement in the ferroelectric switching is associated with the reduction in the barrier heights of the pinning centers of the ferroelectric-ferroelastic domain walls in the stress field generated by magnetostriction in the hexaferrite grains when the magnetic field is turned on. Our study proves that controlled precipitation of the magnetic phase is a good strategy for synthesis of 0-3 ferroelectric-ferromagnetic particulate multiferroic composite as it not only helps in ensuring a good electrical insulating character of the composite, enabling it to sustain high enough electric field for ferroelectric switching, but also the factors associated with the spontaneity of the precipitation process ensure efficient transfer of the magnetostrictive strain/stress to the surrounding ferroelectric matrix making domain wall motion easy.

Competing spin density wave, collinear, and helical magnetism in Fe 1 + x Te

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

Stock, C.; Rodriguez, E. E.; Bourges, P.

The Fe 1+xTe phase diagram consists of two distinct magnetic structures with collinear order present at low interstitial iron concentrations and a helical phase at large values of x with these phases separated by a Lifshitz point. In this paper, we use unpolarized single-crystal diffraction to confirm the helical phase for large interstitial iron concentrations and polarized single-crystal diffraction to demonstrate the collinear order for the iron-deficient side of the Fe 1+xTe phase diagram. Polarized neutron inelastic scattering shows that the fluctuations associated with this collinear order are predominately transverse at low-energy transfers, consistent with a localized magnetic moment picture.more » We then apply neutron inelastic scattering and polarization analysis to investigate the dynamics and structure near the boundary between collinear and helical orders in the Fe 1+xTe phase diagram. We first show that the phase separating collinear and helical orders is characterized by a spin density wave with a single propagation wave vector of (~0.45, 0, 0.5). We do not observe harmonics or the presence of a charge density wave. The magnetic fluctuations associated with this wave vector are different from the collinear phase, being strongly longitudinal in nature and correlated anisotropically in the (H,K) plane. The excitations preserve the C 4 symmetry of the lattice but display different widths in momentum along the two tetragonal directions at low-energy transfers. Finally, while the low-energy excitations and minimal magnetic phase diagram can be understood in terms of localized interactions, we suggest that the presence of the density wave phase implies the importance of electronic and orbital properties.« less

Competing spin density wave, collinear, and helical magnetism in Fe1 +xTe

NASA Astrophysics Data System (ADS)

Stock, C.; Rodriguez, E. E.; Bourges, P.; Ewings, R. A.; Cao, H.; Chi, S.; Rodriguez-Rivera, J. A.; Green, M. A.

2017-04-01

The Fe1 +xTe phase diagram consists of two distinct magnetic structures with collinear order present at low interstitial iron concentrations and a helical phase at large values of x with these phases separated by a Lifshitz point. We use unpolarized single-crystal diffraction to confirm the helical phase for large interstitial iron concentrations and polarized single-crystal diffraction to demonstrate the collinear order for the iron-deficient side of the Fe1 +xTe phase diagram. Polarized neutron inelastic scattering shows that the fluctuations associated with this collinear order are predominately transverse at low-energy transfers, consistent with a localized magnetic moment picture. We then apply neutron inelastic scattering and polarization analysis to investigate the dynamics and structure near the boundary between collinear and helical orders in the Fe1 +xTe phase diagram. We first show that the phase separating collinear and helical orders is characterized by a spin density wave with a single propagation wave vector of (˜0.45 , 0, 0.5). We do not observe harmonics or the presence of a charge density wave. The magnetic fluctuations associated with this wave vector are different from the collinear phase, being strongly longitudinal in nature and correlated anisotropically in the (H ,K ) plane. The excitations preserve the C4 symmetry of the lattice but display different widths in momentum along the two tetragonal directions at low-energy transfers. While the low-energy excitations and minimal magnetic phase diagram can be understood in terms of localized interactions, we suggest that the presence of the density wave phase implies the importance of electronic and orbital properties.

A simple hand-held magnet array for efficient and reproducible SABRE hyperpolarisation using manual sample shaking.

PubMed

Richardson, Peter M; Jackson, Scott; Parrott, Andrew J; Nordon, Alison; Duckett, Simon B; Halse, Meghan E

2018-07-01

Signal amplification by reversible exchange (SABRE) is a hyperpolarisation technique that catalytically transfers nuclear polarisation from parahydrogen, the singlet nuclear isomer of H 2 , to a substrate in solution. The SABRE exchange reaction is carried out in a polarisation transfer field (PTF) of tens of gauss before transfer to a stronger magnetic field for nuclear magnetic resonance (NMR) detection. In the simplest implementation, polarisation transfer is achieved by shaking the sample in the stray field of a superconducting NMR magnet. Although convenient, this method suffers from limited reproducibility and cannot be used with NMR spectrometers that do not have appreciable stray fields, such as benchtop instruments. Here, we use a simple hand-held permanent magnet array to provide the necessary PTF during sample shaking. We find that the use of this array provides a 25% increase in SABRE enhancement over the stray field approach, while also providing improved reproducibility. Arrays with a range of PTFs were tested, and the PTF-dependent SABRE enhancements were found to be in excellent agreement with comparable experiments carried out using an automated flow system where an electromagnet is used to generate the PTF. We anticipate that this approach will improve the efficiency and reproducibility of SABRE experiments carried out using manual shaking and will be particularly useful for benchtop NMR, where a suitable stray field is not readily accessible. The ability to construct arrays with a range of PTFs will also enable the rapid optimisation of SABRE enhancement as function of PTF for new substrate and catalyst systems. © 2017 The Authors Magnetic Resonance in Chemistry Published by John Wiley & Sons Ltd.

Antiproton powered propulsion with magnetically confined plasma engines

NASA Technical Reports Server (NTRS)

Lapointe, Michael R.

1989-01-01

Matter-antimatter annihilation releases more energy per unit mass than any other method of energy production, making it an attractive energy source for spacecraft propulsion. In the magnetically confined plasma engine, antiproton beams are injected axially into a pulsed magnetic mirror system, where they annihilate with an initially neutral hydrogen gas. The resulting charged annihilation products transfer energy to the hydrogen propellant, which is then exhausted through one end of the pulsed mirror system to provide thrust. The calculated energy transfer efficiencies for a low number density (10(14)/cu cm) hydrogen propellant are insufficient to warrant operating the engine in this mode. Efficiencies are improved using moderate propellant number densities (10(16)/cu cm), but the energy transferred to the plasma in a realistic magnetic mirror system is generally limited to less than 2 percent of the initial proton-antiproton annihilation energy. The energy transfer efficiencies are highest for high number density (10(18)/cu cm) propellants, but plasma temperatures are reduced by excessive radiation losses. Low to moderate thrust over a wide range of specific impulse can be generated with moderate propellant number densities, while higher thrust but lower specific impulse may be generated using high propellant number densities. Significant mass will be required to shield the superconducting magnet coils from the high energy gamma radiation emitted by neutral pion decay. The mass of such a radiation shield may dominate the total engine mass, and could severely diminish the performance of antiproton powered engines which utilize magnetic confinement. The problem is compounded in the antiproton powered plasma engine, where lower energy plasma bremsstrahlung radiation may cause shield surface ablation and degradation.

Proximity effects across oxide-interfaces of superconductor-insulator-ferromagnet hybrid heterostructure.

PubMed

Prajapat, C L; Singh, Surendra; Bhattacharya, D; Ravikumar, G; Basu, S; Mattauch, S; Zheng, Jian-Guo; Aoki, T; Paul, Amitesh

2018-02-27

A case study of electron tunneling or charge-transfer-driven orbital ordering in superconductor (SC)-ferromagnet (FM) interfaces has been conducted in heteroepitaxial YBa 2 Cu 3 O 7 (YBCO)/La 0.67 Sr 0.33 MnO 3 (LSMO) multilayers interleaved with and without an insulating SrTiO 3 (STO) layer between YBCO and LSMO. X-ray magnetic circular dichroism experiments revealed anti-parallel alignment of Mn magnetic moments and induced Cu magnetic moments in a YBCO/LSMO multilayer. As compared to an isolated LSMO layer, the YBCO/LSMO multilayer displayed a (50%) weaker Mn magnetic signal, which is related to the usual proximity effect. It was a surprise that a similar proximity effect was also observed in a YBCO/STO/LSMO multilayer, however, the Mn signal was reduced by 20%. This reduced magnetic moment of Mn was further verified by depth sensitive polarized neutron reflectivity. Electron energy loss spectroscopy experiment showed the evidence of Ti magnetic polarization at the interfaces of the YBCO/STO/LSMO multilayer. This crossover magnetization is due to a transfer of interface electrons that migrate from Ti (4+)-δ to Mn at the STO/LSMO interface and to Cu 2+ at the STO/YBCO interface, with hybridization via O 2p orbitals. So charge-transfer driven orbital ordering is the mechanism responsible for the observed proximity effect and Mn-Cu anti-parallel coupling in YBCO/STO/LSMO. This work provides an effective pathway in understanding the aspect of long range proximity effect and consequent orbital degeneracy parameter in magnetic coupling.

Tuning the photovoltaic effect of multiferroic CoFe2O4/Pb(Zr, Ti)O3 composite films by magnetic fields

NASA Astrophysics Data System (ADS)

Pan, Dan-Feng; Chen, Guang-Yi; Bi, Gui-Feng; Zhang, Hao; Liu, Jun-Ming; Wang, Guang-Hou; Wan, Jian-Guo

2016-05-01

The 0-3 type CoFe2O4-Pb(Zr,Ti)O3 (CFO-PZT) multiferroic composite films have been prepared by a sol-gel process and spin-coating technique. A confirmable photovoltaic effect is observed under ultraviolet light irradiation. Moreover, this photovoltaic effect can be tuned by external magnetic fields. The maximum magnetic modulation ratios of short-circuit current density and open-circuit voltage can reach as high as 13.7% and 12.8% upon the application of 6 kOe DC magnetic field. Through remnant polarization measurements under various magnetic fields and detailed analysis of the energy band structures, we elucidate the mechanism of tuning photovoltaic effect by magnetic fields and attribute it to the combination of two factors. One is the decreased ferroelectric-polarization-induced depolarization electric field and another is the band structure reconstruction at CFO-PZT interfaces, both of which are dominated by the magnetoelectric coupling via interfacial stress transferring at nanoscale. This work makes some attempts of coupling photo-induced effects with magnetoelectric effect in multiferroic materials and will widen the practical ranges of multiferroic-based applications.

Numerical study focusing on the entropy analysis of MHD squeezing flow of a nanofluid model using Cattaneo–Christov theory

NASA Astrophysics Data System (ADS)

Akmal, N.; Sagheer, M.; Hussain, S.

2018-05-01

The present study gives an account of the heat transfer characteristics of the squeezing flow of a nanofluid between two flat plates with upper plate moving vertically and the lower in the horizontal direction. Tiwari and Das nanofluid model has been utilized to give a comparative analysis of the heat transfer in the Cu-water and Al2O3-water nanofluids with entropy generation. The modeling is carried out with the consideration of Lorentz forces to observe the effect of magnetic field on the flow. The Joule heating effect is included to discuss the heat dissipation in the fluid and its effect on the entropy of the system. The nondimensional ordinary differential equations are solved using the Keller box method to assess the numerical results which are presented by the graphs and tables. An interesting observation is that the entropy is generated more near the lower plate as compared with that at the upper plate. Also, the heat transfer rate is found to be higher for the Cu nanoparticles in comparison with the Al2O3 nanoparticles.

Time-series analysis of energetic electron fluxes (1. 2 - 16 MeV) at geosynchronous altitude. Master's thesis

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

Halpin, M.P.

This project used a Box and Jenkins time-series analysis of energetic electron fluxes measured at geosynchronous orbit in an effort to derive prediction models for the flux in each of five energy channels. In addition, the technique of transfer function modeling described by Box and Jenkins was used in an attempt to derive input-output relationships between the flux channels (viewed as the output) and the solar-wind speed or interplanetary magnetic field (IMF) north-south component, Bz, (viewed as the input). The transfer function modeling was done in order to investigate the theoretical dynamic relationship which is believed to exist between themore » solar wind, the IMF Bz, and the energetic electron flux in the magnetosphere. The models derived from the transfer-function techniques employed were also intended to be used in the prediction of flux values. The results from this study indicate that the energetic electron flux changes in the various channels are dependent on more than simply the solar-wind speed or the IMF Bz.« less

Heat and momentum transfer for magnetoconvection in a vertical external magnetic field

NASA Astrophysics Data System (ADS)

Zürner, Till; Liu, Wenjun; Krasnov, Dmitry; Schumacher, Jörg

2016-11-01

The scaling theory of Grossmann and Lohse for the turbulent heat and momentum transfer is extended to the magnetoconvection case in the presence of a (strong) vertical magnetic field. The comparison with existing laboratory experiments and direct numerical simulations in the quasistatic limit allows to restrict the parameter space to very low Prandtl and magnetic Prandtl numbers and thus to reduce the number of unknown parameters in the model. Also included is the Chandrasekhar limit for which the outer magnetic induction field B is large enough such that convective motion is suppressed and heat is transported by diffusion. Our theory identifies four distinct regimes of magnetoconvection which are distinguished by the strength of the outer magnetic field and the level of turbulence in the flow, respectively. LIMTECH Research Alliance and Research Training Group GK 1567 on Lorentz Force Velocimetry, funded by the Deutsche Forschungsgemeinschaft.

Giant Spin Hall Effect and Switching Induced by Spin-Transfer Torque in a W /Co40Fe40B20/MgO Structure with Perpendicular Magnetic Anisotropy

NASA Astrophysics Data System (ADS)

Hao, Qiang; Xiao, Gang

2015-03-01

We obtain robust perpendicular magnetic anisotropy in a β -W /Co40Fe40B20/MgO structure without the need of any insertion layer between W and Co40Fe40B20 . This is achieved within a broad range of W thicknesses (3.0-9.0 nm), using a simple fabrication technique. We determine the spin Hall angle (0.40) and spin-diffusion length for the bulk β form of tungsten with a large spin-orbit coupling. As a result of the giant spin Hall effect in β -W and careful magnetic annealing, we significantly reduce the critical current density for the spin-transfer-torque-induced magnetic switching in Co40Fe40B20 . The elemental β -W is a superior candidate for magnetic memory and spin-logic applications.

Recyclable magnetic nanocluster crosslinked with poly(ethylene oxide)-block-poly(2-vinyl-4,4-dimethylazlactone) copolymer for adsorption with antibody.

PubMed

Prai-In, Yingrak; Boonthip, Chatchai; Rutnakornpituk, Boonjira; Wichai, Uthai; Montembault, Véronique; Pascual, Sagrario; Fontaine, Laurent; Rutnakornpituk, Metha

2016-10-01

Surface modification of magnetic nanoparticle (MNP) with poly(ethylene oxide)-block-poly(2-vinyl-4,4-dimethylazlactone) (PEO-b-PVDM) diblock copolymers and its application as recyclable magnetic nano-support for adsorption with antibody were reported herein. PEO-b-PVDM copolymers were first synthesized via a reversible addition-fragmentation chain-transfer (RAFT) polymerization using poly(ethylene oxide) chain-transfer agent as a macromolecular chain transfer agent to mediate the RAFT polymerization of VDM. They were then grafted on amino-functionalized MNP by coupling with some azlactone rings of the PVDM block to form magnetic nanoclusters with tunable cluster size. The nanocluster size could be tuned by adjusting the chain length of the PVDM block. The nanoclusters were successfully used as efficient and recyclable nano-supports for adsorption with anti-rabbit IgG antibody. They retained higher than 95% adsorption of the antibody during eight adsorption-separation-desorption cycles, indicating the potential feasibility in using this novel hybrid nanocluster as recyclable support in cell separation applications. Copyright © 2016 Elsevier B.V. All rights reserved.

Self-consistent models for Coulomb heated X-ray pulsar atmospheres

NASA Technical Reports Server (NTRS)

Harding, A.; Meszaros, S. P.; Kirk, J.; Galloway, D.

1983-01-01

Calculations of accreting magnetized neutron star atmospheres heated by the gradual deceleration of protons via Coulomb collisions are presented. Self consistent determinations of the temperature and density structure for different accretion rates are made by assuming hydrostatic equilibrium and energy balance, coupled with radiative transfer. The full radiative transfer in two polarizations, using magnetic cross sections but with cyclotron resonance effects treated approximately, is carried out in the inhomogeneous atmospheres.

Physiological Remediation of Cobalt Ferrite Nanoparticles by Ferritin

NASA Astrophysics Data System (ADS)

Volatron, Jeanne; Kolosnjaj-Tabi, Jelena; Javed, Yasir; Vuong, Quoc Lam; Gossuin, Yves; Neveu, Sophie; Luciani, Nathalie; Hémadi, Miryana; Carn, Florent; Alloyeau, Damien; Gazeau, Florence

2017-01-01

Metallic nanoparticles have been increasingly suggested as prospective therapeutic nanoplatforms, yet their long-term fate and cellular processing in the body is poorly understood. Here we examined the role of an endogenous iron storage protein - namely the ferritin - in the remediation of biodegradable cobalt ferrite magnetic nanoparticles. Structural and elemental analysis of ferritins close to exogenous nanoparticles within spleens and livers of mice injected in vivo with cobalt ferrite nanoparticles, suggests the intracellular transfer of degradation-derived cobalt and iron, entrapped within endogenous protein cages. In addition, the capacity of ferritin cages to accommodate and store the degradation products of cobalt ferrite nanoparticles was investigated in vitro in the acidic environment mimicking the physiological conditions that are present within the lysosomes. The magnetic, colloidal and structural follow-up of nanoparticles and proteins in the lysosome-like medium confirmed the efficient remediation of nanoparticle-released cobalt and iron ions by ferritins in solution. Metal transfer into ferritins could represent a quintessential process in which biomolecules and homeostasis regulate the local degradation of nanoparticles and recycle their by-products.

Physiological Remediation of Cobalt Ferrite Nanoparticles by Ferritin

PubMed Central

Volatron, Jeanne; Kolosnjaj-Tabi, Jelena; Javed, Yasir; Vuong, Quoc Lam; Gossuin, Yves; Neveu, Sophie; Luciani, Nathalie; Hémadi, Miryana; Carn, Florent; Alloyeau, Damien; Gazeau, Florence

2017-01-01

Metallic nanoparticles have been increasingly suggested as prospective therapeutic nanoplatforms, yet their long-term fate and cellular processing in the body is poorly understood. Here we examined the role of an endogenous iron storage protein – namely the ferritin – in the remediation of biodegradable cobalt ferrite magnetic nanoparticles. Structural and elemental analysis of ferritins close to exogenous nanoparticles within spleens and livers of mice injected in vivo with cobalt ferrite nanoparticles, suggests the intracellular transfer of degradation-derived cobalt and iron, entrapped within endogenous protein cages. In addition, the capacity of ferritin cages to accommodate and store the degradation products of cobalt ferrite nanoparticles was investigated in vitro in the acidic environment mimicking the physiological conditions that are present within the lysosomes. The magnetic, colloidal and structural follow-up of nanoparticles and proteins in the lysosome-like medium confirmed the efficient remediation of nanoparticle-released cobalt and iron ions by ferritins in solution. Metal transfer into ferritins could represent a quintessential process in which biomolecules and homeostasis regulate the local degradation of nanoparticles and recycle their by-products. PMID:28067263

MMS Observations of the Evolution of Ion-Scale Flux Transfer Events

NASA Astrophysics Data System (ADS)

Zhao, C.; Russell, C. T.; Strangeway, R. J.; Paterson, W.; Petrinec, S.; Zhou, M.; Anderson, B. J.; Baumjohann, W.; Bromund, K. R.; Chutter, M.; Fischer, D.; Gershman, D. J.; Giles, B. L.; Le, G.; Nakamura, R.; Plaschke, F.; Slavin, J. A.; Torbert, R. B.

2017-12-01

Flux transfer events are key processes in the solar wind-magnetosphere interaction. Previously, the observed flux transfer events have had scale sizes of 10,000 km radius in the cross-section and connect about 2 MWb magnetic flux from solar wind to the terrestrial magnetosphere. Recently, from the high-temporal resolution MMS magnetic field data, many ion-scale FTEs have been found. These FTEs contains only about 2 kWb magnetic flux and are believed to be in an early stage of FTE evolution. With the help of the well-calibrated MMS data, we are also able to determine the velocity profile and forces within the FTE events. We find that some ion-scale FTEs are expanding as we expect, but there are also contracting FTEs. We examine the differences between the two classes of FTEs and their differences with the larger previously studied class of FTE.

Ultralow-current-density and bias-field-free spin-transfer nano-oscillator

PubMed Central

Zeng, Zhongming; Finocchio, Giovanni; Zhang, Baoshun; Amiri, Pedram Khalili; Katine, Jordan A.; Krivorotov, Ilya N.; Huai, Yiming; Langer, Juergen; Azzerboni, Bruno; Wang, Kang L.; Jiang, Hongwen

2013-01-01

The spin-transfer nano-oscillator (STNO) offers the possibility of using the transfer of spin angular momentum via spin-polarized currents to generate microwave signals. However, at present STNO microwave emission mainly relies on both large drive currents and external magnetic fields. These issues hinder the implementation of STNOs for practical applications in terms of power dissipation and size. Here, we report microwave measurements on STNOs built with MgO-based magnetic tunnel junctions having a planar polarizer and a perpendicular free layer, where microwave emission with large output power, excited at ultralow current densities, and in the absence of any bias magnetic fields is observed. The measured critical current density is over one order of magnitude smaller than previously reported. These results suggest the possibility of improved integration of STNOs with complementary metal-oxide-semiconductor technology, and could represent a new route for the development of the next-generation of on-chip oscillators. PMID:23478390

Ultralow-current-density and bias-field-free spin-transfer nano-oscillator.

PubMed

Zeng, Zhongming; Finocchio, Giovanni; Zhang, Baoshun; Khalili Amiri, Pedram; Katine, Jordan A; Krivorotov, Ilya N; Huai, Yiming; Langer, Juergen; Azzerboni, Bruno; Wang, Kang L; Jiang, Hongwen

2013-01-01

The spin-transfer nano-oscillator (STNO) offers the possibility of using the transfer of spin angular momentum via spin-polarized currents to generate microwave signals. However, at present STNO microwave emission mainly relies on both large drive currents and external magnetic fields. These issues hinder the implementation of STNOs for practical applications in terms of power dissipation and size. Here, we report microwave measurements on STNOs built with MgO-based magnetic tunnel junctions having a planar polarizer and a perpendicular free layer, where microwave emission with large output power, excited at ultralow current densities, and in the absence of any bias magnetic fields is observed. The measured critical current density is over one order of magnitude smaller than previously reported. These results suggest the possibility of improved integration of STNOs with complementary metal-oxide-semiconductor technology, and could represent a new route for the development of the next-generation of on-chip oscillators.

Hydromagnetic flow of a Cu-water nanofluid past a moving wedge with viscous dissipation

NASA Astrophysics Data System (ADS)

M. Salem, A.; Galal, Ismail; Rania, Fathy

2014-04-01

A numerical study is performed to investigate the flow and heat transfer at the surface of a permeable wedge immersed in a copper (Cu)-water-based nanofluid in the presence of magnetic field and viscous dissipation using a nanofluid model proposed by Tiwari and Das (Tiwari I K and Das M K 2007 Int. J. Heat Mass Transfer 50 2002). A similarity solution for the transformed governing equation is obtained, and those equations are solved by employing a numerical shooting technique with a fourth-order Runge-Kutta integration scheme. A comparison with previously published work is carried out and shows that they are in good agreement with each other. The effects of velocity ratio parameter λ, solid volume fraction φ, magnetic field M, viscous dissipation Ec, and suction parameter Fw on the fluid flow and heat transfer characteristics are discussed. The unique and dual solutions for self-similar equations of the flow and heat transfer are analyzed numerically. Moreover, the range of the velocity ratio parameter for which the solution exists increases in the presence of magnetic field and suction parameter.

Transferable ordered ni hollow sphere arrays induced by electrodeposition on colloidal monolayer.

PubMed

Duan, Guotao; Cai, Weiping; Li, Yue; Li, Zhigang; Cao, Bingqiang; Luo, Yuanyuan

2006-04-13

We report an electrochemical synthesis of two-dimensionally ordered porous Ni arrays based on polystyrene sphere (PS) colloidal monolayer. The morphology can be controlled from bowl-like to hollow sphere-like structure by changing deposition time under a constant current. Importantly, such ordered Ni arrays on a conducting substrate can be transferred integrally to any other desired substrates, especially onto an insulting substrate or curved surface. The magnetic measurements of the two-dimensional hollow sphere array show the coercivity values of 104 Oe for the applied field parallel to the film, and 87 Oe for the applied field perpendicular to the film, which is larger than those of bulk Ni and hollow Ni submicrometer-sized spheres. The formation of hollow sphere arrays is attributed to preferential nucleation on the interstitial sites between PS in the colloidal monolayer and substrate, and growth along PSs' surface. The transferability of the arrays originates from partial contact between the Ni hollow spheres and substrate. Such novel Ni ordered nanostructured arrays with transferability and high magnetic properties should be useful in applications such as data storage, catalysis, and magnetics.

Design and prototype fabrication of a 30 tesla cryogenic magnet

NASA Technical Reports Server (NTRS)

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

1977-01-01

A liquid-neon-cooled magnet has been designed to produce 30 teslas in steady operation. Its feasibility was established by a previously reported parametric study. To ensure the correctness of the heat transfer relationships used, supercritical neon heat transfer tests were made. Other tests made before the final design included tests on the effect of the magnetic field on pump motors; tensile-shear tests on the cryogenic adhesives; and simulated flow studies for the coolant. The magnet will be made of two pairs of coils, cooled by forced convection of supercritical neon. Heat from the supercritical neon will be rejected through heat exchangers which are made of roll-bonded copper panels and are submerged in a pool of saturated liquid neon. A partial mock-up coil was wound to identify the tooling required to wind the magnet. This was followed by winding a prototype pair of coils. The prototype winding established procedures for fabricating the final magnet and revealed slight changes needed in the final design.

Spin-transfer torque in spin filter tunnel junctions

NASA Astrophysics Data System (ADS)

Ortiz Pauyac, Christian; Kalitsov, Alan; Manchon, Aurelien; Chshiev, Mairbek

2014-12-01

Spin-transfer torque in a class of magnetic tunnel junctions with noncollinear magnetizations, referred to as spin filter tunnel junctions, is studied within the tight-binding model using the nonequilibrium Green's function technique within Keldysh formalism. These junctions consist of one ferromagnet (FM) adjacent to a magnetic insulator (MI) or two FM separated by a MI. We find that the presence of the magnetic insulator dramatically enhances the magnitude of the spin-torque components compared to conventional magnetic tunnel junctions. The fieldlike torque is driven by the spin-dependent reflection at the MI/FM interface, which results in a small reduction of its amplitude when an insulating spacer (S) is inserted to decouple MI and FM layers. Meanwhile, the dampinglike torque is dominated by the tunneling electrons that experience the lowest barrier height. We propose a device of the form FM/(S)/MI/(S)/FM that takes advantage of these characteristics and allows for tuning the spin-torque magnitudes over a wide range just by rotation of the magnetization of the insulating layer.

Interaction mechanisms and biological effects of static magnetic fields

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

Tenforde, T.S.

1994-06-01

Mechanisms through which static magnetic fields interact with living systems are described and illustrated by selected experimental observations. These mechanisms include electrodynamic interactions with moving, ionic charges (blood flow and nerve impulse conduction), magnetomechanical interactions (orientation and translation of molecules structures and magnetic particles), and interactions with electronic spin states in charge transfer reactions (photo-induced electron transfer in photosynthesis). A general summary is also presented of the biological effects of static magnetic fields. There is convincing experimental evidence for magnetoreception mechanisms in several classes of lower organisms, including bacteria and marine organisms. However, in more highly evolved species of animals,more » there is no evidence that the interactions of static magnetic fields with flux densities up to 2 Tesla (1 Tesla [T] = 10{sup 4} Gauss) produce either behavioral or physiolocical alterations. These results, based on controlled studies with laboratory animals, are consistent with the outcome of recent epidemiological surveys on human populations exposed occupationally to static magnetic fields.« less

Quantification of in vivo pH-weighted amide proton transfer (APT) MRI in acute ischemic stroke

NASA Astrophysics Data System (ADS)

Zhou, Iris Y.; Igarashi, Takahiro; Guo, Yingkun; Sun, Phillip Z.

2015-03-01

Amide proton transfer (APT) imaging is a specific form of chemical exchange saturation transfer (CEST) MRI that probes the pH-dependent amide proton exchange.The endogenous APT MRI is sensitive to tissue acidosis, which may complement the commonly used perfusion and diffusion scans for characterizing heterogeneous ischemic tissue damage. Whereas the saturation transfer asymmetry analysis (MTRasym) may reasonably compensate for direct RF saturation, in vivo MTRasym is however, susceptible to an intrinsically asymmetric shift (MTR'asym). Specifically, the reference scan for the endogenous APT MRI is 7 ppm upfield from that of the label scan, and subjects to concomitant RF irradiation effects, including nuclear overhauser effect (NOE)-mediated saturation transfer and semisolid macromolecular magnetization transfer. As such, the commonly used asymmetry analysis could not fully compensate for such slightly asymmetric concomitant RF irradiation effects, and MTRasym has to be delineated in order to properly characterize the pH-weighted APT MRI contrast. Given that there is very little change in relaxation time immediately after ischemia and the concomitant RF irradiation effects only minimally depends on pH, the APT contrast can be obtained as the difference of MTRasym between the normal and ischemic regions. Thereby, the endogenous amide proton concentration and exchange rate can be solved using a dual 2-pool model, and the in vivo MTR'asym can be calculated by subtracting the solved APT contrast from asymmetry analysis (i.e., MTR'asym =MTRasym-APTR). In addition, MTR'asym can be quantified using the classical 2-pool exchange model. In sum, our study delineated the conventional in vivo pH-sensitive MTRasym contrast so that pHspecific contrast can be obtained for imaging ischemic tissue acidosis.

Effect of Cr doping on structural and magnetic properties of ZnS nanoparticles

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

Virpal,; Singh, Jasvir; Sharma, Sandeep

2016-05-23

The structural, optical and magnetic properties of pure and Cr doped ZnS nanoparticles were studied at room temperature. X-ray diffraction analysis confirmed the absence of any mixed phase and the cubic structure of ZnS in pure and Cr doped ZnS nanoparticles. Fourier transfer infrared spectra confirmed the Zn-S stretching bond at 664 cm{sup −1} of ZnS in all prepared nanoparticles. The UV-Visible absorption spectra showed blue shift which became even more pronounced in Cr doped ZnS nanoparticles. However, at relatively higher Cr concentrations a slower red shift was shown by the doped nanoparticles. This phenomenon is attributed to sp-d exchange interactionmore » that becomes prevalent at higher doping concentrations. Further, magnetic hysteresis measurements showed that Cr doped ZnS nanoparticles exhibited ferromagnetic behavior at room temperature.« less

Quantum renormalizations in anisotropic multisublattice magnets and the modification of magnetic susceptibility under irradiation

NASA Astrophysics Data System (ADS)

Val'kov, V. V.; Shustin, M. S.

2015-11-01

The dispersion equation of a strongly anisotropic one-dimensional magnet catena-[FeII(ClO4)2{FeIII(bpca)2}]ClO4 containing alternating high-spin (HS) ( S = 2) and low-spin (LS) ( S = 1/2) iron ions is obtained by the diagram technique for Hubbard operators. The analysis of this equation yields six branches in the excitation spectrum of this magnet. It is important that the crystal field for ions with spin S = 2 is described by the Hamiltonian of single-ion easy-plane anisotropy, whose orientation is changed by 90° when passing from one HS iron ion to another. The U( N) transformation technique in the atomic representation is applied to diagonalize a single-ion Hamiltonian with a large number of levels. It is shown that the modulation of the orientation of easy magnetization planes leads to a model of a ferrimagnet with easy-axis anisotropy and to the formation of energy spectrum with a large gap. For HS iron ions, a decrease in the mean value of the spin projection due to quantum fluctuations is calculated. The analysis of the specific features of the spectrum of elementary excitations allows one to establish a correspondence to a generalized Ising model for which the magnetic susceptibility is calculated in a wide range of temperatures by the transfer-matrix method. The introduction of a statistical ensemble that takes into account the presence of chains of different lengths and the presence of iron ions with different spins allows one to describe the experimentally observed modification of the magnetic susceptibility of the magnet under optical irradiation.

A low temperature transfer of ALH84001 from Mars to Earth.

PubMed

Weiss, B P; Kirschvink, J L; Baudenbacher, F J; Vali, H; Peters, N T; Macdonald, F A; Wikswo, J P

2000-10-27

The ejection of material from Mars is thought to be caused by large impacts that would heat much of the ejecta to high temperatures. Images of the magnetic field of martian meteorite ALH84001 reveal a spatially heterogeneous pattern of magnetization associated with fractures and rock fragments. Heating the meteorite to 40 degrees C reduces the intensity of some magnetic features, indicating that the interior of the rock has not been above this temperature since before its ejection from the surface of Mars. Because this temperature cannot sterilize most bacteria or eukarya, these data support the hypothesis that meteorites could transfer life between planets in the solar system.

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

NASA Technical Reports Server (NTRS)

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

1976-01-01

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

Solution of magnetohydrodynamic flow and heat transfer of radiative viscoelastic fluid with temperature dependent viscosity in wire coating analysis

PubMed Central

Khan, Muhammad Altaf; Siddiqui, Nasir; Ullah, Murad; Shah, Qayyum

2018-01-01

Wire coating process is a continuous extrusion process for primary insulation of conducting wires with molten polymers for mechanical strength and protection in aggressive environments. In the present study, radiative melt polymer satisfying third grade fluid model is used for wire coating process. The effect of magnetic parameter, thermal radiation parameter and temperature dependent viscosity on wire coating analysis has been investigated. Reynolds model and Vogel’s models have been incorporated for variable viscosity. The governing equations characterizing the flow and heat transfer phenomena are solved analytically by utilizing homotopy analysis method (HAM). The computed results are also verified by ND-Solve method (Numerical technique) and Adomian Decomposition Method (ADM). The effect of pertinent parameters is shown graphically. In addition, the instability of the flow in the flows of the wall of the extrusion die is well marked in the case of the Vogel model as pointed by Nhan-Phan-Thien. PMID:29596448

Magnetic field pattern synthesis and its application in targeted drug delivery: Design and implementation.

PubMed

Hajiaghajani, Amirhossein; Abdolali, Ali

2018-05-01

In cancer therapy, magnetic drug targeting is considered as an effective treatment to reduce chemotherapy's side effects. The accurate design and shaping of magnetic fields are crucial for healthy cells to be immune from chemotherapeutics. In this paper, arbitrary 2-dimensional spatial patterns of magnetic fields from DC to megahertz are represented in terms of spatial Fourier spectra with sinusoidal eigenfunctions. Realization of each spatial frequency was investigated by a set of elliptical coils. Therefore, it is shown that the desired pattern was synthesized by simultaneous use of coil sets. Currents running on each set were obtained via fast and straightforward analytical Fourier series calculation. Experimentally scanned sample patterns were in close agreement with full wave analysis. Discussions include the evaluation of the Fourier series approximation error and cross-polarization of produced magnetic fields. It was observed that by employing the controlled magnetic field produced by the proposed setup, we were able to steer therapeutic particles toward the right or left half-spheres of the breast, with an efficiency of 90%. Such a pattern synthesizer may be employed in numerous human arteries as well as other bioelectromagnetic patterning applications, e.g., wireless power transfer, magnetic innervation, and tomography. Bioelectromagnetics. 39:325-338, 2018. © 2018 Wiley Periodicals, Inc. © 2018 Wiley Periodicals, Inc.

First-order particle acceleration in magnetically driven flows

DOE PAGES

Beresnyak, Andrey; Li, Hui

2016-03-02

In this study, we demonstrate that particles are regularly accelerated while experiencing curvature drift in flows driven by magnetic tension. Some examples of such flows include spontaneous turbulent reconnection and decaying magnetohydrodynamic turbulence, where a magnetic field relaxes to a lower-energy configuration and transfers part of its energy to kinetic motions of the fluid. We show that this energy transfer, which normally causes turbulent cascade and heating of the fluid, also results in a first-order acceleration of non-thermal particles. Since it is generic, this acceleration mechanism is likely to play a role in the production of non-thermal particle distribution inmore » magnetically dominant environments such as the solar chromosphere, pulsar magnetospheres, jets from supermassive black holes, and γ-ray bursts.« less

Graphene-ferromagnet interfaces: hybridization, magnetization and charge transfer.

PubMed

Abtew, Tesfaye; Shih, Bi-Ching; Banerjee, Sarbajit; Zhang, Peihong

2013-03-07

Electronic and magnetic properties of graphene-ferromagnet interfaces are investigated using first-principles electronic structure methods in which a single layer graphene is adsorbed on Ni(111) and Co(111) surfaces. Due to the symmetry matching and orbital overlap, the hybridization between graphene pπ and Ni (or Co) d(z(2)) states is very strong. This pd hybridization, which is both spin and k dependent, greatly affects the electronic and magnetic properties of the interface, resulting in a significantly reduced (by about 20% for Ni and 10% for Co) local magnetic moment of the top ferromagnetic layer at the interface and an induced spin polarization on the graphene layer. The calculated induced magnetic moment on the graphene layer agrees well with a recent experiment. In addition, a substantial charge transfer across the graphene-ferromagnet interfaces is observed. We also investigate the effects of thickness of the ferromagnet slab on the calculated electronic and magnetic properties of the interface. The strength of the pd hybridization and the thickness-dependent interfacial properties may be exploited to design structures with desirable magnetic and transport properties for spintronic applications.

Superconducting applications in propulsion systems. Magnetic insulation for plasma propulsion devices

NASA Technical Reports Server (NTRS)

Gonzalez, Dora E.; Karr, Gerald R.

1990-01-01

The purpose of this paper is to review the status of knowledge of the basic concepts needed to establish design parameters for effective magnetic insulation. The objective is to estimate the effectiveness of the magnetic field in insulating the plasma, to calculate the magnitude of the magnetic field necessary to reduce the heat transfer to the walls sufficiently enough to demonstrate the potential of magnetically driven plasma rockets.

Molecular, dynamic, and structural origin of inhomogeneous magnetization transfer in lipid membranes.

PubMed

Swanson, Scott D; Malyarenko, Dariya I; Fabiilli, Mario L; Welsh, Robert C; Nielsen, Jon-Fredrik; Srinivasan, Ashok

2017-03-01

To elucidate the dynamic, structural, and molecular properties that create inhomogeneous magnetization transfer (ihMT) contrast. Amphiphilic lipids, lamellar phospholipids with cholesterol, and bovine spinal cord (BSC) specimens were examined along with nonlipid systems. Magnetization transfer (MT), enhanced MT (eMT, obtained with double-sided radiofrequency saturation), ihMT (MT - eMT), and dipolar relaxation, T 1D , were measured at 2.0 and 11.7 T. The amplitude of ihMT ratio (ihMTR) is positively correlated with T 1D values. Both ihMTR and T 1D increase with increasing temperature in BSC white matter and in phospholipids and decrease with temperature in other lipids. Changes in ihMTR with temperature arise primarily from alterations in MT rather than eMT. Spectral width of MT, eMT, and ihMT increases with increasing carbon chain length. Concerted motions of phospholipids in white matter decrease proton spin diffusion leading to increased proton T 1D times and increased ihMT amplitudes, consistent with decoupling of Zeeman and dipolar spin reservoirs. Molecular specificity and dynamic sensitivity of ihMT contrast make it a suitable candidate for probing myelin membrane disorders. Magn Reson Med 77:1318-1328, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

Engineering Topological Surface State of Cr-doped Bi2Se3 under external electric field

NASA Astrophysics Data System (ADS)

Zhang, Jian-Min; Lian, Ruqian; Yang, Yanmin; Xu, Guigui; Zhong, Kehua; Huang, Zhigao

2017-03-01

External electric field control of topological surface states (SSs) is significant for the next generation of condensed matter research and topological quantum devices. Here, we present a first-principles study of the SSs in the magnetic topological insulator (MTI) Cr-doped Bi2Se3 under external electric field. The charge transfer, electric potential, band structure and magnetism of the pure and Cr doped Bi2Se3 film have been investigated. It is found that the competition between charge transfer and spin-orbit coupling (SOC) will lead to an electrically tunable band gap in Bi2Se3 film under external electric field. As Cr atom doped, the charge transfer of Bi2Se3 film under external electric field obviously decreases. Remarkably, the band gap of Cr doped Bi2Se3 film can be greatly engineered by the external electric field due to its special band structure. Furthermore, magnetic coupling of Cr-doped Bi2Se3 could be even mediated via the control of electric field. It is demonstrated that external electric field plays an important role on the electronic and magnetic properties of Cr-doped Bi2Se3 film. Our results may promote the development of electronic and spintronic applications of magnetic topological insulator.

A wireless magnetic resonance energy transfer system for micro implantable medical sensors.

PubMed

Li, Xiuhan; Zhang, Hanru; Peng, Fei; Li, Yang; Yang, Tianyang; Wang, Bo; Fang, Dongming

2012-01-01

Based on the magnetic resonance coupling principle, in this paper a wireless energy transfer system is designed and implemented for the power supply of micro-implantable medical sensors. The entire system is composed of the in vitro part, including the energy transmitting circuit and resonant transmitter coils, and in vivo part, including the micro resonant receiver coils and signal shaping chip which includes the rectifier module and LDO voltage regulator module. Transmitter and receiver coils are wound by Litz wire, and the diameter of the receiver coils is just 1.9 cm. The energy transfer efficiency of the four-coil system is greatly improved compared to the conventional two-coil system. When the distance between the transmitter coils and the receiver coils is 1.5 cm, the transfer efficiency is 85% at the frequency of 742 kHz. The power transfer efficiency can be optimized by adding magnetic enhanced resonators. The receiving voltage signal is converted to a stable output voltage of 3.3 V and a current of 10 mA at the distance of 2 cm. In addition, the output current varies with changes in the distance. The whole implanted part is packaged with PDMS of excellent biocompatibility and the volume of it is about 1 cm(3).

A simple hand‐held magnet array for efficient and reproducible SABRE hyperpolarisation using manual sample shaking

PubMed Central

Richardson, Peter M.; Jackson, Scott; Parrott, Andrew J.; Nordon, Alison; Duckett, Simon B.

2018-01-01

Signal amplification by reversible exchange (SABRE) is a hyperpolarisation technique that catalytically transfers nuclear polarisation from parahydrogen, the singlet nuclear isomer of H2, to a substrate in solution. The SABRE exchange reaction is carried out in a polarisation transfer field (PTF) of tens of gauss before transfer to a stronger magnetic field for nuclear magnetic resonance (NMR) detection. In the simplest implementation, polarisation transfer is achieved by shaking the sample in the stray field of a superconducting NMR magnet. Although convenient, this method suffers from limited reproducibility and cannot be used with NMR spectrometers that do not have appreciable stray fields, such as benchtop instruments. Here, we use a simple hand‐held permanent magnet array to provide the necessary PTF during sample shaking. We find that the use of this array provides a 25% increase in SABRE enhancement over the stray field approach, while also providing improved reproducibility. Arrays with a range of PTFs were tested, and the PTF‐dependent SABRE enhancements were found to be in excellent agreement with comparable experiments carried out using an automated flow system where an electromagnet is used to generate the PTF. We anticipate that this approach will improve the efficiency and reproducibility of SABRE experiments carried out using manual shaking and will be particularly useful for benchtop NMR, where a suitable stray field is not readily accessible. The ability to construct arrays with a range of PTFs will also enable the rapid optimisation of SABRE enhancement as function of PTF for new substrate and catalyst systems. PMID:29193324

An optimized framework for quantitative magnetization transfer imaging of the cervical spinal cord in vivo.

PubMed

Battiston, Marco; Grussu, Francesco; Ianus, Andrada; Schneider, Torben; Prados, Ferran; Fairney, James; Ourselin, Sebastien; Alexander, Daniel C; Cercignani, Mara; Gandini Wheeler-Kingshott, Claudia A M; Samson, Rebecca S

2018-05-01

To develop a framework to fully characterize quantitative magnetization transfer indices in the human cervical cord in vivo within a clinically feasible time. A dedicated spinal cord imaging protocol for quantitative magnetization transfer was developed using a reduced field-of-view approach with echo planar imaging (EPI) readout. Sequence parameters were optimized based in the Cramer-Rao-lower bound. Quantitative model parameters (i.e., bound pool fraction, free and bound pool transverse relaxation times [ T2F, T2B], and forward exchange rate [k FB ]) were estimated implementing a numerical model capable of dealing with the novelties of the sequence adopted. The framework was tested on five healthy subjects. Cramer-Rao-lower bound minimization produces optimal sampling schemes without requiring the establishment of a steady-state MT effect. The proposed framework allows quantitative voxel-wise estimation of model parameters at the resolution typically used for spinal cord imaging (i.e. 0.75 × 0.75 × 5 mm 3 ), with a protocol duration of ∼35 min. Quantitative magnetization transfer parametric maps agree with literature values. Whole-cord mean values are: bound pool fraction = 0.11(±0.01), T2F = 46.5(±1.6) ms, T2B = 11.0(±0.2) µs, and k FB  = 1.95(±0.06) Hz. Protocol optimization has a beneficial effect on reproducibility, especially for T2B and k FB . The framework developed enables robust characterization of spinal cord microstructure in vivo using qMT. Magn Reson Med 79:2576-2588, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine.

Calculating the Motion and Direction of Flux Transfer Events with Cluster

NASA Technical Reports Server (NTRS)

Collado-Vega, Y. M.; Sibeck, D. G.

2012-01-01

For many years now, the interactions of the solar wind plasma with the Earth's magnetosphere has been one of the most important problems for Space Physics. It is very important that we understand these processes because the high-energy particles and also the solar wind energy that cross the magneto sphere could be responsible for serious damage to our technological systems. The solar wind is inherently a dynamic medium, and the particles interaction with the Earth's magnetosphere can be steady or unsteady. Unsteady interaction include transient processes like bursty magnetic reconnection. Flux Transfer Events (FTEs) are magnetopause signatures that usually occur during transient times of reconnection. They exhibit bipolar signatures in the normal component of the magnetic field. We use multi-point timing analysis to determine the orientation and motion of ux transfer events (FTEs) detected by the four Cluster spacecraft on the high-latitude dayside and flank magnetopause during 2002 and 2003. During these years, the distances between the Cluster spacecraft were greater than 1000 km, providing the tetrahedral configuration needed to select events and determine velocities. Each velocity and location will be examined in detail and compared to the velocities and locations determined by the predictions of the component and antiparallel reconnection models for event formation, orientation, motion, and acceleration for a wide range of spacecraft locations and solar wind conditions.

Assessment of the patellofemoral cartilage: Correlation of knee pain score with magnetic resonance cartilage grading and magnetization transfer ratio asymmetry of glycosaminoglycan chemical exchange saturation transfer.

PubMed

Lee, Young Han; Yang, Jaemoon; Jeong, Ha-Kyu; Suh, Jin-Suck

2017-01-01

Biochemical imaging of glycosaminoglycan chemical exchange saturation transfer (gagCEST) could predict the depletion of glycosaminoglycans (GAG) in early osteoarthritis. The purpose of this study was to evaluate the relationship between the magnetization transfer ratio asymmetry (MTR asym ) of gagCEST images and visual analog scale (VAS) pain scores in the knee joint. This retrospective study was approved by the institutional review board. A phantom study was performed using hyaluronic acid to validate the MTR asym values of gagCEST images. Knee magnetic resonance (MR) images of 22 patients (male, 9; female, 13; mean age, 50.3years; age range; 25-79years) with knee pain were included in this study. The MR imaging (MRI) protocol involved standard knee MRI as well as gagCEST imaging, which allowed region-of-interest analyses of the patellar facet and femoral trochlea. The MTR asym at 1.0ppm was calculated at each region. The cartilages of the patellar facets and femoral trochlea were graded according to the Outerbridge classification system. Data regarding the VAS scores of knee pain were collected from the electronic medical records of the patients. Statistical analysis was performed using Spearman's correlation. The results of the phantom study revealed excellent correlation between the MTR asym values and the concentration of GAGs (r=0.961; p=0.003). The cartilage grades on the MR images showed significant negative correlation with the MTR asym values in the patellar facet and femoral trochlea (r=-0.460; p=0.031 and r=-0.543; p=0.009, respectively). The VAS pain scores showed significant negative correlation with the MTR asym values in the patellar facet and femoral trochlea (r=-0.435; p=0.043 and r=-0.671; p=0.001, respectively). The pain scores were associated with the morphological and biochemical changes in articular cartilages visualized on knee MR images. The biochemical changes, visualized in terms of the MTR asym values of the gagCEST images, exhibited greater correlation with the pain scores than the morphological changes visualized on conventional MR images; these results provide evidence supporting the theory regarding the association of patellofemoral osteoarthritis with knee pain scores. Copyright © 2016 Elsevier Inc. All rights reserved.

Development of the active magnetic regenerative refrigerator operating between 77 K and 20 K with the conduction cooled high temperature superconducting magnet

NASA Astrophysics Data System (ADS)

Park, Inmyong; Jeong, Sangkwon

2017-12-01

The experimental investigation of an active magnetic regenerative refrigerator (AMRR) operating between 77 K and 20 K is discussed in this paper, with detailed energy transfer analysis. A multi-layered active magnetic regenerator (AMR) is used, which consists of four different rare earth intermetallic compounds in the form of irregular powder. Numerical simulation confirms that the AMR can attain its target operating temperature range. Magnetic field alternation throughout the AMR is generated by a high temperature superconducting (HTS) magnet. The HTS magnet is cooled by a two stage Gifford-McMahon (GM) cryocooler. Helium gas was employed as a working fluid and its oscillating flow in the AMR is controlled in accordance with the magnetic field variation. The AMR is divided into two stages and each stage has a different mass flow rate as needed to achieve the desired cooling performance. The temperature variation of the AMR during the experiment is monitored by temperature sensors installed inside the AMR. The experimental results show that the AMRR is capable of achieving no-load temperature of 25.4 K while the warm end temperature is 77 K. The performance of the AMRR is analyzed by observing internal temperature variations at cyclic steady state. Furthermore, numerical estimation of the cooling capacity and the temperature variation of the AMR are examined and compared with the experimental results.

Energy release and transfer in guide field reconnection

NASA Astrophysics Data System (ADS)

Birn, J.; Hesse, M.

2010-01-01

Properties of energy release and transfer by magnetic reconnection in the presence of a guide field are investigated on the basis of 2.5-dimensional magnetohydrodynamic (MHD) and particle-in-cell (PIC) simulations. Two initial configurations are considered: a plane current sheet with a uniform guide field of 80% of the reconnecting magnetic field component and a force-free current sheet in which the magnetic field strength is constant but the field direction rotates by 180° through the current sheet. The onset of reconnection is stimulated by localized, temporally limited compression. Both MHD and PIC simulations consistently show that the outgoing energy fluxes are dominated by (redirected) Poynting flux and enthalpy flux, whereas bulk kinetic energy flux and heat flux (in the PIC simulation) are small. The Poynting flux is mainly associated with the magnetic energy of the guide field which is carried from inflow to outflow without much alteration. The conversion of annihilated magnetic energy to enthalpy flux (that is, thermal energy) stems mainly from the fact that the outflow occurs into a closed field region governed by approximate force balance between Lorentz and pressure gradient forces. Therefore, the energy converted from magnetic to kinetic energy by Lorentz force acceleration becomes immediately transferred to thermal energy by the work done by the pressure gradient force. Strong similarities between late stages of MHD and PIC simulations result from the fact that conservation of mass and entropy content and footpoint displacement of magnetic flux tubes, imposed in MHD, are also approximately satisfied in the PIC simulations.

Batch extracting process using magneticparticle held solvents

DOEpatents

Nunez, Luis; Vandergrift, George F.

1995-01-01

A process for selectively removing metal values which may include catalytic values from a mixture containing same, wherein a magnetic particle is contacted with a liquid solvent which selectively dissolves the metal values to absorb the liquid solvent onto the magnetic particle. Thereafter the solvent-containing magnetic particles are contacted with a mixture containing the heavy metal values to transfer metal values into the solvent carried by the magnetic particles, and then magnetically separating the magnetic particles. Ion exchange resins may be used for selective solvents.

Radiative heat transfer in the extreme near field.

PubMed

Kim, Kyeongtae; Song, Bai; Fernández-Hurtado, Víctor; Lee, Woochul; Jeong, Wonho; Cui, Longji; Thompson, Dakotah; Feist, Johannes; Reid, M T Homer; García-Vidal, Francisco J; Cuevas, Juan Carlos; Meyhofer, Edgar; Reddy, Pramod

2015-12-17

Radiative transfer of energy at the nanometre length scale is of great importance to a variety of technologies including heat-assisted magnetic recording, near-field thermophotovoltaics and lithography. Although experimental advances have enabled elucidation of near-field radiative heat transfer in gaps as small as 20-30 nanometres (refs 4-6), quantitative analysis in the extreme near field (less than 10 nanometres) has been greatly limited by experimental challenges. Moreover, the results of pioneering measurements differed from theoretical predictions by orders of magnitude. Here we use custom-fabricated scanning probes with embedded thermocouples, in conjunction with new microdevices capable of periodic temperature modulation, to measure radiative heat transfer down to gaps as small as two nanometres. For our experiments we deposited suitably chosen metal or dielectric layers on the scanning probes and microdevices, enabling direct study of extreme near-field radiation between silica-silica, silicon nitride-silicon nitride and gold-gold surfaces to reveal marked, gap-size-dependent enhancements of radiative heat transfer. Furthermore, our state-of-the-art calculations of radiative heat transfer, performed within the theoretical framework of fluctuational electrodynamics, are in excellent agreement with our experimental results, providing unambiguous evidence that confirms the validity of this theory for modelling radiative heat transfer in gaps as small as a few nanometres. This work lays the foundations required for the rational design of novel technologies that leverage nanoscale radiative heat transfer.

Critical Role of CD8 T Cells in Mediating Sex-Based Differences in a Murine Model of Lupus

DTIC Science & Technology

2009-08-21

into  female  transfers  (fF)  mice  that  was  reduced  in  CD8  depleted  fF  mice.  Flow   cytometry   analysis  showed increased numbers of splenic...splenocytes were first analyzed by flow cytometry for CD4 and CD8 T cells and F1 mice received either: a) unfractionated splenocytes (CD8 intactF1...using magnetic beads purchased from Invitrogen (Carlsbad, CA) according to the manufacturer’s instructions. Flow cytometry analysis before cell

Advances in cryogenic engineering. Vols. 35A & 35B - Proceedings of the 1989 Cryogenic Engineering Conference, University of California, Los Angeles, July 24-28, 1989

NASA Astrophysics Data System (ADS)

Fast, R. W.

The book presents a review of literature on superfluid helium, together with papers under the topics on heat and mass transfer in He II; applications of He II for cooling superconducting devices in space; heat transfer to liquid helium and liquid nitrogen; multilayer insulation; applications of superconductivity, including topics on magnets and other devices, magnet stability and coil protection, and cryogenic techniques; and refrigeration for electronics. Other topics discussed include refrigeration of superconducting systems; the expanders, cold compressors, and pumps for liquid helium; dilution refrigerators; magnetic refrigerators; pulse tube refrigerators; cryocoolers for space applications; properties of cryogenic fluids; cryogenic instrumentation; hyperconducting devices (cryogenic magnets); cryogenic applications in space science and technology and in transportation; and miscellaneous cryogenic techniques and applications.

A study of flux transfer events at different planets

NASA Technical Reports Server (NTRS)

Russell, C. T.

1995-01-01

Flux transfer events (FTEs) are disturbances in and near the magnetopause current layer that cause a characteristic signature in the component of the magnetic field parallel to the average boundary normal. These disturbances have been observed at Mercury, Earth and Jupiter but not at Saturn, Uranus or Neptune. At Earth, FTEs last about 1 minute and repeat about every 8 but at Mercury, a much smaller magnetosphere, the events last seconds and are tens of seconds apart. These features have been interpreted in terms of magnetospheric flux ropes connected to the interplanetary magnetic field, arising as the result of reconnection. An analogous phenomenon occurs at Venus where magnetic flux ropes arise at the ionosphere, a boundary between a very strongly magnetized one. However, here the flux ropes do not appear to be due to reconnection.

Modeled ground magnetic signatures of flux transfer events

NASA Technical Reports Server (NTRS)

Mchenry, Mark A.; Clauer, C. Robert

1987-01-01

The magnetic field on the ground due to a small (not greater than 200 km scale size) localized field-aligned current (FAC) system interacting with the ionosphere is calculated in terms of an integral over the ionospheric distribution of FAC. Two different candidate current systems for flux transfer events (FTEs) are considered: (1) a system which has current flowing down the center of a cylindrical flux tube with a return current uniformly distributed along the outside edge; and (2) a system which has upward current on one half of the perimeter of a cylindrical flux tube with downward current on the opposite half. The peak magnetic field on the ground is found to differ by a factor of 2 between the two systems, and the magnetic perturbations are in different directions depending on the observer's position.

Alfvén wave dynamics at the neighborhood of a 2.5D magnetic null-point

NASA Astrophysics Data System (ADS)

Sabri, S.; Vasheghani Farahani, S.; Ebadi, H.; Hosseinpour, M.; Fazel, Z.

2018-05-01

The aim of the present study is to highlight the energy transfer via the interaction of magnetohydrodynamic waves with a 2.5D magnetic null-point in a finite plasma-β regime of the solar corona. An initially symmetric Alfvén pulse at a specific distance from a magnetic null-point is kicked towards the isothermal null-point. A shock-capturing Godunov-type PLUTO code is used to solve the ideal magnetohydrodynamic set equations in the context of wave-plasma energy transfer. As the Alfvén wave propagates towards the magnetic null-point it experiences speed lowering which ends up in releasing energy along the separatrices. In this line owing to the Alfvén wave, a series of events take place that contribute towards coronal heating. Nonlinear induced waves are by products of the torsional Alfvén interaction with magnetic null-points. The energy of these induced waves which are fast magnetoacoustic (transverse) and slow magnetoacoustic (longitudinal) waves are supplied by the Alfvén wave. The nonlinearly induced density perturbations are proportional to the Alfvén wave energy loss. This supplies energy for the propagation of fast and slow magnetoacoustic waves, where in contrast to the fast wave the slow wave experiences a continuous energy increase. As such, the slow wave may transfer its energy to the medium at later times, maintaining a continuous heating mechanism at the neighborhood of a magnetic null-point.

A small scale remote cooling system for a superconducting cyclotron magnet

NASA Astrophysics Data System (ADS)

Haug, F.; Berkowitz Zamorra, D.; Michels, M.; Gomez Bosch, R.; Schmid, J.; Striebel, A.; Krueger, A.; Diez, M.; Jakob, M.; Keh, M.; Herberger, W.; Oesterle, D.

2017-02-01

Through a technology transfer program CERN is involved in the R&D of a compact superconducting cyclotron for future clinical radioisotope production, a project led by the Spanish research institute CIEMAT. For the remote cooling of the LTc superconducting magnet operating at 4.5 K, CERN has designed a small scale refrigeration system, the Cryogenic Supply System (CSS). This refrigeration system consists of a commercial two-stage 1.5 W @ 4.2 K GM cryocooler and a separate forced flow circuit. The forced flow circuit extracts the cooling power of the first and the second stage cold tips, respectively. Both units are installed in a common vacuum vessel and, at the final configuration, a low loss transfer line will provide the link to the magnet cryostat for the cooling of the thermal shield with helium at 40 K and the two superconducting coils with two-phase helium at 4.5 K. Currently the CSS is in the testing phase at CERN in stand-alone mode without the magnet and the transfer line. We have added a “validation unit” housed in the vacuum vessel of the CSS representing the thermo-hydraulic part of the cyclotron magnet. It is equipped with electrical heaters which allow the simulation of the thermal loads of the magnet cryostat. A cooling power of 1.4 W at 4.5 K and 25 W at the thermal shield temperature level has been measured. The data produced confirm the design principle of the CSS which could be validated.

Aptamer-based detection of plasma proteins by an electrochemical assay coupled to magnetic beads.

PubMed

Centi, Sonia; Tombelli, Sara; Minunni, Maria; Mascini, Marco

2007-02-15

The DNA thrombin aptamer has been extensively investigated, and the coupling of this aptamer to different transduction principles has demonstrated the wide applicability of aptamers as bioreceptors in bioanalytical assays. The goal of this work was to design an aptamer-based sandwich assay with electrochemical detection for thrombin analysis in complex matrixes, using a simple target capturing step by aptamer-functionalized magnetic beads. The conditions for the aptamer immobilization and for the protein binding have been first optimized by surface plasmon resonance, and then transferred to the electrochemical-based assay performed onto screen-printed electrodes. The assay was then applied to the analysis of thrombin in buffer, spiked serum, and plasma and high sensitivity and specificity were found. Moreover, thrombin was generated in situ in plasma by the conversion of its precursor prothrombin, and the formation of thrombin was followed at different times. The concentrations detected by the electrochemical assay were in agreement with a simulation software that mimics the formation of thrombin over time (thrombogram). The proposed work demonstrates that the high specificity of aptamers together with the use of magnetic beads are the key features for aptamer-based analysis in complex matrixes, opening the possibility of a real application to diagnostics or medical investigation.

Batch extracting process using magnetic particle held solvents

DOEpatents

Nunez, L.; Vandergrift, G.F.

1995-11-21

A process is described for selectively removing metal values which may include catalytic values from a mixture containing same, wherein a magnetic particle is contacted with a liquid solvent which selectively dissolves the metal values to absorb the liquid solvent onto the magnetic particle. Thereafter the solvent-containing magnetic particles are contacted with a mixture containing the heavy metal values to transfer metal values into the solvent carried by the magnetic particles, and then magnetically separating the magnetic particles. Ion exchange resins may be used for selective solvents. 5 figs.

Interaction of proflavin with aromatic amines in homogeneous and micellar media: Photoinduced electron transfer probed by magnetic field effect

NASA Astrophysics Data System (ADS)

Chakraborty, Brotati; Basu, Samita

2010-02-01

Photoinduced electron transfer (PET) between proflavin (PF +) and two aromatic amines viz., dimethylaniline (DMA) and 4,4'-bis(dimethylamino)diphenylmethane (DMDPM) is studied in homogeneous and heterogeneous media using steady-state as well as time-resolved fluorescence spectroscopy and laser flash photolysis with an associated magnetic field. Ionic micelles have been used to study the effect of charge of proflavin on PET with amines. Magnetic field effect on PET reactions reveals that the parent spin-state of precursors of PET for DMA-PF + system is singlet while for DMDPM-PF + system is triplet, implying that the dynamics of PET is influenced by the structure of the donor.

Evidence for a "metabolically inactive" inorganic phosphate pool in adenosine triphosphate synthase reaction using localized 31P saturation transfer magnetic resonance spectroscopy in the rat brain at 11.7 T.

PubMed

Tiret, Brice; Brouillet, Emmanuel; Valette, Julien

2016-09-01

With the increased spectral resolution made possible at high fields, a second, smaller inorganic phosphate resonance can be resolved on (31)P magnetic resonance spectra in the rat brain. Saturation transfer was used to estimate de novo adenosine triphosphate synthesis reaction rate. While the main inorganic phosphate pool is used by adenosine triphosphate synthase, the second pool is inactive for this reaction. Accounting for this new pool may not only help us understand (31)P magnetic resonance spectroscopy metabolic profiles better but also better quantify adenosine triphosphate synthesis. © The Author(s) 2016.

Enhancing NMR of insensitive nuclei by transfer of SABRE spin hyperpolarization

NASA Astrophysics Data System (ADS)

Pravdivtsev, Andrey N.; Yurkovskaya, Alexandra V.; Zimmermann, Herbert; Vieth, Hans-Martin; Ivanov, Konstantin L.

2016-09-01

We describe the performance of methods for enhancing NMR (Nuclear Magnetic Resonance) signals of "insensitive", but important NMR nuclei, which are based on the SABRE (Signal Amplification By Reversible Exchange) technique, i.e., on spin order transfer from parahydrogen (H2 molecule in its nuclear singlet spin state) to a substrate in a transient organometallic complex. Here such transfer is performed at high magnetic fields by INEPT-type NMR pulse sequences, modified for SABRE. Signal enhancements up to three orders of magnitude are obtained for 15N nuclei; the possibility of sensitive detection of 2D-NMR 1H-15N spectra of SABRE complexes and substrates is demonstrated.

Self-consistent models for Coulomb-heated X-ray pulsar atmospheres

NASA Technical Reports Server (NTRS)

Harding, A. K.; Kirk, J. G.; Galloway, D. J.; Meszaros, P.

1984-01-01

Calculations of accreting magnetized neutron star atmospheres heated by the gradual deceleration of Protons via Coulomb collisions are presented. Self consistent determinations of the temperature and density structure for different accretion rates are made by assuming hydrostatic equilibrium and energy balance, coupled with radiative transfer. The full radiative transfer in two polarizations, using magnetic cross sections but with cyclotron resonance effects treated approximately, is carried out in the inhomogeneous atmospheres. Previously announced in STAR as N84-12012

Spin-transfer torque induced spin waves in antiferromagnetic insulators

DOE PAGES

Daniels, Matthew W.; Guo, Wei; Stocks, George Malcolm; ...

2015-01-01

We explore the possibility of exciting spin waves in insulating antiferromagnetic films by injecting spin current at the surface. We analyze both magnetically compensated and uncompensated interfaces. We find that the spin current induced spin-transfer torque can excite spin waves in insulating antiferromagnetic materials and that the chirality of the excited spin wave is determined by the polarization of the injected spin current. Furthermore, the presence of magnetic surface anisotropy can greatly increase the accessibility of these excitations.

Study the effect of chemical reaction and variable viscosity on free convection MHD radiating flow over an inclined plate bounded by porous medium

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

Ali, M., E-mail: ali.mehidi93@gmail.com; Department of Mathematics, Chittagong University of Engineering and Technology, Chittagong-4349; Alim, M. A., E-mail: maalim@math.buet.ac.bd

An analysis is performed to study the free convection heat and mass transfer flow of an electrically conducting incompressible viscous fluid about a semi-infinite inclined porous plate under the action of radiation, chemical reaction in presence of magnetic field with variable viscosity. The dimensionless governing equations are steady, two-dimensional coupled and non-linear ordinary differential equation. Nachtsgeim-Swigert shooting iteration technique along with Runge-Kutta integration scheme is used to solve the non-dimensional governing equations. The effects of magnetic parameter, viscosity parameter and chemical reaction parameter on velocity, temperature and concentration profiles are discussed numerically and shown graphically. Therefore, the results of velocitymore » profile decreases for increasing values of magnetic parameter and viscosity parameter but there is no effect for reaction parameter. The temperature profile decreases in presence of magnetic parameter, viscosity parameter and Prandtl number but increases for radiation parameter. Also, concentration profile decreases for the increasing values of magnetic parameter, viscosity parameter and reaction parameter. All numerical calculations are done with respect to salt water and fixed angle of inclination of the plate.« less

Rashba spin-orbit coupling and orbital chirality in magnetic bilayers

NASA Astrophysics Data System (ADS)

Lee, Hyun-Woo

2013-03-01

The phenomenon of the Rashba spin-orbit coupling is examined theoretically for an ultrathin magnetic layer in contact with a non-magnetic heavy metal layer. From first-principles calculation, large Rashba parameter of order 1 eV .Å is obtained, which is strong enough to generate large spin transfer torque of spin-orbit coupling origin. Large Rashba parameter is attributed to the orbital mixing of 3 d magnetic atoms and non-magnetic heavy elements with significant atomic spin-orbit coupling. Interestingly the magnitude and sign of the parameter vary from energy bands to bands, which we attribute to band-specific chiral ordering of orbital angular momentum. Through a simple tight-binding model analysis, we demonstrate that d-orbital hybridization allowed by the breaking of structural inversion symmetry generates band-specific chiral ordering of orbital angular momentum, which combines with atomic spin-orbit coupling to give rise to band-specific Rashba parameter. The band-dependence of the Rashba parameter is discussed in connection with recent experiments and we argue that the dependence may be utilized to enhance device application potentials. This work is supported by NRF grant (2010-0008529, 2011-0015631, 2010-0014109, 2011-0030789).

Magnetic Reconnection at a Thin Current Sheet Separating Two Interlaced Flux Tubes at the Earth's Magnetopause

NASA Astrophysics Data System (ADS)

Kacem, I.; Jacquey, C.; Génot, V.; Lavraud, B.; Vernisse, Y.; Marchaudon, A.; Le Contel, O.; Breuillard, H.; Phan, T. D.; Hasegawa, H.; Oka, M.; Trattner, K. J.; Farrugia, C. J.; Paulson, K.; Eastwood, J. P.; Fuselier, S. A.; Turner, D.; Eriksson, S.; Wilder, F.; Russell, C. T.; Øieroset, M.; Burch, J.; Graham, D. B.; Sauvaud, J.-A.; Avanov, L.; Chandler, M.; Coffey, V.; Dorelli, J.; Gershman, D. J.; Giles, B. L.; Moore, T. E.; Saito, Y.; Chen, L.-J.; Penou, E.

2018-03-01

The occurrence of spatially and temporally variable reconnection at the Earth's magnetopause leads to the complex interaction of magnetic fields from the magnetosphere and magnetosheath. Flux transfer events (FTEs) constitute one such type of interaction. Their main characteristics are (1) an enhanced core magnetic field magnitude and (2) a bipolar magnetic field signature in the component normal to the magnetopause, reminiscent of a large-scale helicoidal flux tube magnetic configuration. However, other geometrical configurations which do not fit this classical picture have also been observed. Using high-resolution measurements from the Magnetospheric Multiscale mission, we investigate an event in the vicinity of the Earth's magnetopause on 7 November 2015. Despite signatures that, at first glance, appear consistent with a classic FTE, based on detailed geometrical and dynamical analyses as well as on topological signatures revealed by suprathermal electron properties, we demonstrate that this event is not consistent with a single, homogenous helicoidal structure. Our analysis rather suggests that it consists of the interaction of two separate sets of magnetic field lines with different connectivities. This complex three-dimensional interaction constructively conspires to produce signatures partially consistent with that of an FTE. We also show that, at the interface between the two sets of field lines, where the observed magnetic pileup occurs, a thin and strong current sheet forms with a large ion jet, which may be consistent with magnetic flux dissipation through magnetic reconnection in the interaction region.

SAR in human head model due to resonant wireless power transfer system.

PubMed

Zhang, Chao; Liu, Guoqiang; Li, Yanhong; Song, Xianjin

2016-04-29

Efficient mid-range wireless power transfer between transmitter and the receiver has been achieved based on the magnetic resonant coupling method. The influence of electromagnetic field on the human body due to resonant wireless power transfer system (RWPT) should be taken into account during the design process of the system. To analyze the transfer performance of the RWPT system and the change rules of the specific absorption rate (SAR) in the human head model due to the RWPT system. The circuit-field coupling method for a RWPT system with consideration of the displacement current was presented. The relationship between the spiral coil parameters and transfer performance was studied. The SAR in the human head model was calculated under two different exposure conditions. A system with output power higher than 10 W at 0.2 m distance operating at a frequency of approximately 1 MHz was designed. The FEM simulation results show the peak SAR value is below the safety limit which appeared when the human head model is in front of the transmitter. The simulation results agreed well with the experimental results, which verified the validity of the analysis and design.

Exactly solved mixed spin-(1,1/2) Ising-Heisenberg diamond chain with a single-ion anisotropy

NASA Astrophysics Data System (ADS)

Lisnyi, Bohdan; Strečka, Jozef

2015-03-01

The mixed spin-(1,1/2) Ising-Heisenberg diamond chain with a single-ion anisotropy is exactly solved through the generalized decoration-iteration transformation and the transfer-matrix method. The decoration-iteration transformation is first used for establishing a rigorous mapping equivalence with the corresponding spin-1 Blume-Emery-Griffiths chain, which is subsequently exactly treated within the transfer-matrix technique. Apart from three classical ground states the model exhibits three striking quantum ground states in which a singlet-dimer state of the interstitial Heisenberg spins is accompanied either with a frustrated state or a polarized state or a non-magnetic state of the nodal Ising spins. It is evidenced that two magnetization plateaus at zero and/or one-half of the saturation magnetization may appear in low-temperature magnetization curves. The specific heat may display remarkable temperature dependences with up to three and four distinct round maxima in a zero and non-zero magnetic field, respectively.

Radiated flow of chemically reacting nanoliquid with an induced magnetic field across a permeable vertical plate

NASA Astrophysics Data System (ADS)

Mahanthesh, B.; Gireesha, B. J.; Athira, P. R.

Impact of induced magnetic field over a flat porous plate by utilizing incompressible water-copper nanoliquid is examined analytically. Flow is supposed to be laminar, steady and two-dimensional. The plate is subjected to a regular free stream velocity as well as suction velocity. Flow formulation is developed by considering Maxwell-Garnetts (MG) and Brinkman models of nanoliquid. Impacts of thermal radiation, viscous dissipation, temperature dependent heat source/sink and first order chemical reaction are also retained. The subjected non-linear problems are non-dimensionalized and analytic solutions are presented via series expansion method. The graphs are plotted to analyze the influence of pertinent parameters on flow, magnetism, heat and mass transfer fields as well as friction factor, current density, Nusselt and Sherwood numbers. It is found that friction factor at the plate is more for larger magnetic Prandtl number. Also the rate of heat transfer decayed with increasing nanoparticles volume fraction and the strength of magnetism.

An In-Rush Current Suppression Technique for the Solid-State Transfer Switch System

NASA Astrophysics Data System (ADS)

Cheng, Po-Tai; Chen, Yu-Hsing

More and more utility companies provide dual power feeders as a premier service of high power quality and reliability. To take advantage of this, the solid-state transfer switch (STS) is adopted to protect the sensitive load against the voltage sag. However, the fast transfer process may cause in-rush current on the load-side transformer due to the resulting DC-offset in its magnetic flux as the load-transfer is completed. The in-rush current can reach 2∼6 p.u. and it may trigger the over-current protections on the power feeder. This paper develops a flux estimation scheme and a thyristor gating scheme based on the impulse commutation bridge STS (ICBSTS) to minimize the DC-offset on the magnetic flux. By sensing the line voltages of both feeders, the flux estimator can predict the peak transient flux linkage at the moment of load-transfer and evaluate a suitable moment for the transfer to minimize the in-rush current. Laboratory test results are presented to validate the performance of the proposed system.

Design of single-winding energy-storage reactors for dc-to-dc converters using air-gapped magnetic-core structures

NASA Technical Reports Server (NTRS)

Ohri, A. K.; Wilson, T. G.; Owen, H. A., Jr.

1977-01-01

A procedure is presented for designing air-gapped energy-storage reactors for nine different dc-to-dc converters resulting from combinations of three single-winding power stages for voltage stepup, current stepup and voltage stepup/current stepup and three controllers with control laws that impose constant-frequency, constant transistor on-time and constant transistor off-time operation. The analysis, based on the energy-transfer requirement of the reactor, leads to a simple relationship for the required minimum volume of the air gap. Determination of this minimum air gap volume then permits the selection of either an air gap or a cross-sectional core area. Having picked one parameter, the minimum value of the other immediately leads to selection of the physical magnetic structure. Other analytically derived equations are used to obtain values for the required turns, the inductance, and the maximum rms winding current. The design procedure is applicable to a wide range of magnetic material characteristics and physical configurations for the air-gapped magnetic structure.

Determining magnetospheric ULF wave activity from external drivers using the most influential solar wind parameters

NASA Astrophysics Data System (ADS)

Bentley, S.; Watt, C.; Owens, M. J.

2017-12-01

Ultra-low frequency (ULF) waves in the magnetosphere are involved in the energisation and transport of radiation belt particles and are predominantly driven by the external solar wind. By systematically examining the instantaneous relative contribution of non-derived solar wind parameters and accounting for their interdependencies using fifteen years of ground-based measurements (CANOPUS) at a single frequency and magnetic latitude, we conclude that the dominant causal parameters for ground-based ULF wave power are solar wind speed v, interplanetary magnetic field component Bz and summed power in number density perturbations δNp. We suggest that these correspond to driving by the Kelvin-Helmholtz instability, flux transfer events and direct perturbations from solar wind structures sweeping past. We will also extend our analysis to a stochastic wave model at multiple magnetic latitudes that will be used in future to predict background ULF wave power across the radiation belts in different magnetic local time sectors, and to examine the relative contribution of the parameters v, Bz and var(Np) in these sectors.

Structural and magnetic properties of FeGen-/0 (n = 3-12) clusters: Mass-selected anion photoelectron spectroscopy and density functional theory calculations

NASA Astrophysics Data System (ADS)

Deng, Xiao-Jiao; Kong, Xiang-Yu; Liang, Xiaoqing; Yang, Bin; Xu, Hong-Guang; Xu, Xi-Ling; Feng, Gang; Zheng, Wei-Jun

2017-12-01

The structural, electronic, and magnetic properties of FeGen-/0 (n = 3-12) clusters were investigated by using anion photoelectron spectroscopy in combination with density functional theory calculations. For both anionic and neutral FeGen (n = 3-12) clusters with n ≤ 7, the dominant structures are exohedral. The FeGe8-/0 clusters have half-encapsulated boat-shaped structures, and the opening of the boat-shaped structure is gradually covered by the additional Ge atoms to form Gen cage from n = 9 to 11. The structures of FeGe10-/0 can be viewed as two Ge atoms symmetrically capping the opening of the boat-shaped structure of FeGe8, and those of FeGe12-/0 are distorted hexagonal prisms with the Fe atom at the center. Natural population analysis shows that there is an electron transfer from the Ge atoms to the Fe atom at n = 8-12. The total magnetic moment of FeGen-/0 and local magnetic moment of the Fe atom have not been quenched.

Transfluxor circuit amplifies sensing current for computer memories

NASA Technical Reports Server (NTRS)

Milligan, G. C.

1964-01-01

To transfer data from the magnetic memory core to an independent core, a reliable sensing amplifier has been developed. Later the data in the independent core is transferred to the arithmetical section of the computer.

Finite Element Modeling of Magnetically-Damped Convection during Solidification

NASA Technical Reports Server (NTRS)

deGroh, H. C.; Li, B. Q.; Lu, X.

1998-01-01

A fully 3-D, transient finite element model is developed to represent the magnetic damping effects on complex fluid flow, heat transfer and electromagnetic field distributions in a Sn- 35.5%Pb melt undergoing unidirectional solidification. The model is developed based on our in- house finite element code for the fluid flow, heat transfer and electromagnetic field calculations. The numerical model is tested against numerical and experimental results for water as reported in literature. Various numerical simulations are carried out for the melt convection and temperature distribution with and without the presence of a transverse magnetic field. Numerical results show that magnetic damping can be effectively applied to stabilize melt flow, reduce turbulence and flow levels in the melt and over a certain threshold value a higher magnetic field resulted in a greater reduction in velocity. Also, for the study of melt flow instability, a long enough running time is needed to ensure the final fluid flow recirculation pattern. Moreover, numerical results suggest that there seems to exist a threshold value of applied magnetic field, above which magnetic damping becomes possible and below which the 0 convection in the melt is actually enhanced.

Irradiation and Enhanced Magnetic Braking in Cataclysmic Variables

NASA Astrophysics Data System (ADS)

McCormick, P. J.; Frank, J.

1998-12-01

In previous work we have shown that irradiation driven mass transfer cycles can occur in cataclysmic variables at all orbital periods if an additional angular momentum loss mechanism is assumed. Earlier models simply postulated that the enhanced angular momentum loss was proportional to the mass transfer rate without any specific physical model. In this paper we present a simple modification of magnetic braking which seems to have the right properties to sustain irradiation driven cycles at all orbital periods. We assume that the wind mass loss from the irradiated companion consists of two parts: an intrinsic stellar wind term plus an enhancement that is proportional to the irradiation. The increase in mass flow reduces the specific angular momentum carried away by the flow but nevertheless yields an enhanced rate of magnetic braking. The secular evolution of the binary is then computed numerically with a suitably modified double polytropic code (McCormick & Frank 1998). With the above model and under certain conditions, mass transfer oscillations occur at all orbital periods.

Magnetization Transfer Ratio Relates to Cognitive Impairment in Normal Elderly

PubMed Central

Seiler, Stephan; Pirpamer, Lukas; Hofer, Edith; Duering, Marco; Jouvent, Eric; Fazekas, Franz; Mangin, Jean-Francois; Chabriat, Hugues; Dichgans, Martin; Ropele, Stefan; Schmidt, Reinhold

2014-01-01

Magnetization transfer imaging (MTI) can detect microstructural brain tissue changes and may be helpful in determining age-related cerebral damage. We investigated the association between the magnetization transfer ratio (MTR) in gray and white matter (WM) and cognitive functioning in 355 participants of the Austrian stroke prevention family study (ASPS-Fam) aged 38–86 years. MTR maps were generated for the neocortex, deep gray matter structures, WM hyperintensities, and normal appearing WM (NAWM). Adjusted mixed models determined whole brain and lobar cortical MTR to be directly and significantly related to performance on tests of memory, executive function, and motor skills. There existed an almost linear dose-effect relationship. MTR of deep gray matter structures and NAWM correlated to executive functioning. All associations were independent of demographics, vascular risk factors, focal brain lesions, and cortex volume. Further research is needed to understand the basis of this association at the tissue level, and to determine the role of MTR in predicting cognitive decline and dementia. PMID:25309438

Evidence for Neutron Star Formation from Accretion Induced Collapse of a White Dwarf

NASA Technical Reports Server (NTRS)

Paradijis, J. Van; VanDenHeuvel, E. P. J.; Kouveliotou, C.; Fishman, G. J.; Finger, M. H.; Lewin, W. H. G.

1997-01-01

The orbital parameters of the recently discovered transient burster/pulsar GRO J1744-28 indicate that this system is a low-mass X-ray binary in an advanced stage of its mass transfer, with several tenths of a solar mass already transferred from the donor to the compact star. All neutron stars known to have accreted such an amount have very weak magnetic fields, and this has led to the idea that the magnetic fields of neutron stars decay as a result of accretion. The observation of a strongly magnetized neutron star in GRO J1744-28 then suggests that this neutron star was formed recently as a result of the collapse of a white dwarf during an earlier stage of the current phase of mass transfer. It is shown that this model can consistently explain the observed characteristics of GRO J1744-28. Attractive progenitors for such an evolution are the luminous supersoft X-ray sources detected with ROSAT.

An optimized framework for quantitative magnetization transfer imaging of the cervical spinal cord in vivo

PubMed Central

Grussu, Francesco; Ianus, Andrada; Schneider, Torben; Prados, Ferran; Fairney, James; Ourselin, Sebastien; Alexander, Daniel C.; Cercignani, Mara; Gandini Wheeler‐Kingshott, Claudia A.M.; Samson, Rebecca S.

2017-01-01

Purpose To develop a framework to fully characterize quantitative magnetization transfer indices in the human cervical cord in vivo within a clinically feasible time. Methods A dedicated spinal cord imaging protocol for quantitative magnetization transfer was developed using a reduced field‐of‐view approach with echo planar imaging (EPI) readout. Sequence parameters were optimized based in the Cramer‐Rao‐lower bound. Quantitative model parameters (i.e., bound pool fraction, free and bound pool transverse relaxation times [ T2F, T2B], and forward exchange rate [k FB]) were estimated implementing a numerical model capable of dealing with the novelties of the sequence adopted. The framework was tested on five healthy subjects. Results Cramer‐Rao‐lower bound minimization produces optimal sampling schemes without requiring the establishment of a steady‐state MT effect. The proposed framework allows quantitative voxel‐wise estimation of model parameters at the resolution typically used for spinal cord imaging (i.e. 0.75 × 0.75 × 5 mm3), with a protocol duration of ∼35 min. Quantitative magnetization transfer parametric maps agree with literature values. Whole‐cord mean values are: bound pool fraction = 0.11(±0.01), T2F = 46.5(±1.6) ms, T2B = 11.0(±0.2) µs, and k FB = 1.95(±0.06) Hz. Protocol optimization has a beneficial effect on reproducibility, especially for T2B and k FB. Conclusion The framework developed enables robust characterization of spinal cord microstructure in vivo using qMT. Magn Reson Med 79:2576–2588, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. PMID:28921614

A 3D analysis of oxygen transfer in a low-cost micro-bioreactor for animal cell suspension culture.

PubMed

Yu, P; Lee, T S; Zeng, Y; Low, H T

2007-01-01

A 3D numerical model was developed to study the flow field and oxygen transport in a micro-bioreactor with a rotating magnetic bar on the bottom to mix the culture medium. The Reynolds number (Re) was kept in the range of 100-716 to ensure laminar environment for animal cell culture. The volumetric oxygen transfer coefficient (k(L)a) was determined from the oxygen concentration distribution. It was found that the effect of the cell consumption on k(L)a could be negligible. A correlation was proposed to predict the liquid-phase oxygen transfer coefficient (k(Lm)) as a function of Re. The overall oxygen transfer coefficient (k(L)) was obtained by the two-resistance model. Another correlation, within an error of 15%, was proposed to estimate the minimum oxygen concentration to avoid cell hypoxia. By combination of the correlations, the maximum cell density, which the present micro-bioreactor could support, was predicted to be in the order of 10(12) cells m(-3). The results are comparable with typical values reported for animal cell growth in mechanically stirred bioreactors.

A comparative study on heat and mass transfer of the Blasius and Falkner-Skan flow of a bio-convective Casson fluid past a wedge

NASA Astrophysics Data System (ADS)

Raju, C. S. K.; Sandeep, N.

2016-11-01

Nowadays, many theoretical models are available for analyzing the heat and mass transfer of flows through different geometries. Nevertheless, it is challenging for researchers to choose among these models, the most suitable for a particular geometry. In addition to this, the extrinsic magnetic field is capable to set the thermal and physical properties of magnetic fluids and regulate the flow and heat transfer characteristics. The strength of the applied magnetic field affects the thermal conductivity of the fluids and makes it anisotropic. With this incentive, we attempt to study the thermophoresis and Brownian motion effects on the magnetohydrodynamic radiative Casson fluid flow over a wedge filled with gyrotactic microorganisms by considering the Blasius and Falkner-Skan models. Numerical solutions are offered graphically as well as in tabular form with the aid of Runge-Kutta and Newton's methods. Results for Blasius and Falkner-Skan flow cases are exhibited through plots for the parameters of concern. For real life applications, we also calculated the heat and mass transfer rates. It is observed that thermal and concentration boundary layers are not uniform for Falkner-Skan and Blasius flow cases. It is also observed that the heat and mass transfer rate is high in Falkner-Skan flow when compared with Blasius flow.

A Novel Method Of Gradient Forming and Fluid Manipulation in Reduced Gravity Environments

NASA Technical Reports Server (NTRS)

Ramachandran N.; Leslie, F.

1999-01-01

The use of magnetic fields to control the motion and position of non-conducting liquids has received growing interest in recent times. The possibility of using the forces exerted by a nonuniform magnetic field on a ferrofluid to not only achieve fluid manipulation but also to actively control fluid motion makes it an attractive candidate for applications such as heat transfer in space systems. Terrestrial heat transfer equipment often relies on the normal gravitational force to hold liquid in a desired position or to provide a buoyant force to enhance the heat transfer rate. The residual gravitational force present in a space environment may no longer serve these useful functions and other forces, such as surface tension, can play a significant role in determining heat transfer rates. Although typically overwhelmed by gravitational forces in terrestrial applications, the body force induced in a ferrofluid by a nonuniform magnetic field can help to achieve these objectives in a microgravity environment. This paper will address the fluid manipulation aspect and will comprise of results from model fluid experiments and numerical modeling of the problem. Results from a novel method of forming concentration gradients that are applicable to low gravity applications will be presented. The ground based experiments are specifically tailored to demonstrate the magnetic manipulation capability of a ferrofluid and show that gravitational effects can be countered in carefully designed systems. The development of governing equations for the system will be presented along with a sampling of numerical results.

New method for determining central axial orientation of flux rope embedded within current sheet using multipoint measurements

NASA Astrophysics Data System (ADS)

Li, ZhaoYu; Chen, Tao; Yan, GuangQing

2016-10-01

A new method for determining the central axial orientation of a two-dimensional coherent magnetic flux rope (MFR) via multipoint analysis of the magnetic-field structure is developed. The method is devised under the following geometrical assumptions: (1) on its cross section, the structure is left-right symmetric; (2) the projected structure velocity is vertical to the line of symmetry. The two conditions can be naturally satisfied for cylindrical MFRs and are expected to be satisfied for MFRs that are flattened within current sheets. The model test demonstrates that, for determining the axial orientation of such structures, the new method is more efficient and reliable than traditional techniques such as minimum-variance analysis of the magnetic field, Grad-Shafranov (GS) reconstruction, and the more recent method based on the cylindrically symmetric assumption. A total of five flux transfer events observed by Cluster are studied using the proposed approach, and the application results indicate that the observed structures, regardless of their actual physical properties, fit the assumed geometrical model well. For these events, the inferred axial orientations are all in excellent agreement with those obtained using the multi-GS reconstruction technique.

Magnetic latching solenoid

DOEpatents

Marts, Donna J.; Richardson, John G.; Albano, Richard K.; Morrison, Jr., John L.

1995-01-01

This invention discloses a D.C. magnetic latching solenoid that retains a moving armature in a first or second position by means of a pair of magnets, thereby having a zero-power requirement after actuation. The first or second position is selected by reversing the polarity of the D.C. voltage which is enough to overcome the holding power of either magnet and transfer the armature to an opposite position. The coil is then de-energized.

Characterizing the magnetic memory signals on the surface of plasma transferred arc cladding coating under fatigue loads

NASA Astrophysics Data System (ADS)

Huang, Haihong; Han, Gang; Qian, Zhengchun; Liu, Zhifeng

2017-12-01

The metal magnetic memory signals were measured during dynamic tension tests on the surfaces of the cladding coatings by plasma transferred arc (PTA) welding and the 0.45% C steel. Results showed that the slope of the normal component Hp(y) of magnetic signal and the average value of the tangential component Hp(x) reflect the magnetization of the specimens. The signals increased sharply in the few initial cycles; and then fluctuated around a constant value during fatigue process until fracture. For the PTA cladding coating, the slope of Hp(y) was steeper and the average of Hp(x) was smaller, compared with the 0.45% C steel. The hysteresis curves of cladding layer, bonding layer and substrate were measured by vibrating sample magnetometer testing, and then saturation magnetization, initial susceptibility and coercivity were further calculated. The stress-magnetization curves were also plotted based on the J-A model, which showed that the PTA cladding coating has smaller remanence and coercivity compared with the 0.45% C steel. The microstructures of cladding coating confirmed that the dendritic structure and second-phase of alloy hinder the magnetic domain motion, which was the main factor influencing the variation of magnetic signal during the fatigue tests.

Site-specific gene delivery to stented arteries using magnetically guided zinc oleate-based nanoparticles loaded with adenoviral vectors

PubMed Central

Chorny, Michael; Fishbein, Ilia; Tengood, Jillian E.; Adamo, Richard F.; Alferiev, Ivan S.; Levy, Robert J.

2013-01-01

Gene therapeutic strategies have shown promise in treating vascular disease. However, their translation into clinical use requires pharmaceutical carriers enabling effective, site-specific delivery as well as providing sustained transgene expression in blood vessels. While replication-deficient adenovirus (Ad) offers several important advantages as a vector for vascular gene therapy, its clinical applicability is limited by rapid inactivation, suboptimal transduction efficiency in vascular cells, and serious systemic adverse effects. We hypothesized that novel zinc oleate-based magnetic nanoparticles (MNPs) loaded with Ad would enable effective arterial cell transduction by shifting vector processing to an alternative pathway, protect Ad from inactivation by neutralizing factors, and allow site-specific gene transfer to arteries treated with stent angioplasty using a 2-source magnetic guidance strategy. Ad-loaded MNPs effectively transduced cultured endothelial and smooth muscle cells under magnetic conditions compared to controls and retained capacity for gene transfer after exposure to neutralizing antibodies and lithium iodide, a lytic agent causing disruption of free Ad. Localized arterial gene expression significantly stronger than in control animal groups was demonstrated after magnetically guided MNP delivery in a rat stenting model 2 and 9 d post-treatment, confirming feasibility of using Ad-loaded MNPs to achieve site-specific transduction in stented blood vessels. In conclusion, Ad-loaded MNPs formed by controlled precipitation of zinc oleate represent a novel delivery system, well-suited for efficient, magnetically targeted vascular gene transfer.—Chorny, M., Fishbein, I., Tengood, J. E., Adamo, R. F., Alferiev, I. S., Levy, R. J. Site-specific gene delivery to stented arteries using magnetically guided zinc oleate-based nanoparticles loaded with adenoviral vectors. PMID:23407712

3D magneto-convective heat transfer in CNT-nanofluid filled cavity under partially active magnetic field

NASA Astrophysics Data System (ADS)

Al-Rashed, Abdullah A. A. A.; Kolsi, Lioua; Oztop, Hakan F.; Aydi, Abdelkarim; Malekshah, Emad Hasani; Abu-Hamdeh, Nidal; Borjini, Mohamed Naceur

2018-05-01

A computational study has been performed to investigate the effects of partially active magnetic field on natural convection heat transfer in CNT-nanofluid filled and three-dimensional differentially heated closed space. Two cases are considered to see this effect as magnetic field is applied to upper half (Case I) and lower half (Case II) while remaining walls are insulated. The finite volume method is used to solve governing equations and results are obtained for different governing parameters as Hartmann number (0 ≤ Ha ≤ 100), nanoparticle volume fraction (0 ≤ φ ≤ 0.05) and height of the active zone (0 ≤ LB ≤ 1). It is found that location of magnetic field plays an important role even at the same Hartmann number. Thus, it can be a good parameter to control heat and fluid flow inside the closed space.

Heat Transfer in MHD Mixed Convection Flow of a Ferrofluid along a Vertical Channel.

PubMed

Gul, Aaiza; Khan, Ilyas; Shafie, Sharidan; Khalid, Asma; Khan, Arshad

2015-01-01

This study investigated heat transfer in magnetohydrodynamic (MHD) mixed convection flow of ferrofluid along a vertical channel. The channel with non-uniform wall temperatures was taken in a vertical direction with transverse magnetic field. Water with nanoparticles of magnetite (Fe3O4) was selected as a conventional base fluid. In addition, non-magnetic (Al2O3) aluminium oxide nanoparticles were also used. Comparison between magnetic and magnetite nanoparticles were also conducted. Fluid motion was originated due to buoyancy force together with applied pressure gradient. The problem was modelled in terms of partial differential equations with physical boundary conditions. Analytical solutions were obtained for velocity and temperature. Graphical results were plotted and discussed. It was found that temperature and velocity of ferrofluids depend strongly on viscosity and thermal conductivity together with magnetic field. The results of the present study when compared concurred with published work.

Heat Transfer in MHD Mixed Convection Flow of a Ferrofluid along a Vertical Channel

PubMed Central

Gul, Aaiza; Khan, Ilyas; Shafie, Sharidan; Khalid, Asma; Khan, Arshad

2015-01-01

This study investigated heat transfer in magnetohydrodynamic (MHD) mixed convection flow of ferrofluid along a vertical channel. The channel with non-uniform wall temperatures was taken in a vertical direction with transverse magnetic field. Water with nanoparticles of magnetite (Fe 3 O 4) was selected as a conventional base fluid. In addition, non-magnetic (Al 2 O 3) aluminium oxide nanoparticles were also used. Comparison between magnetic and magnetite nanoparticles were also conducted. Fluid motion was originated due to buoyancy force together with applied pressure gradient. The problem was modelled in terms of partial differential equations with physical boundary conditions. Analytical solutions were obtained for velocity and temperature. Graphical results were plotted and discussed. It was found that temperature and velocity of ferrofluids depend strongly on viscosity and thermal conductivity together with magnetic field. The results of the present study when compared concurred with published work. PMID:26550837

The Substructure of a Flux Transfer Event Observed by the MMS Spacecraft

NASA Technical Reports Server (NTRS)

Hwang, K.-J.; Sibeck, D. G.; Giles, B. L.; Pollock, C. J.; Gershman, D.; Avanov, L.; Paterson, W. R.; Dorelli, J. C.; Ergun, R. E.; Russel, C. T.;

Convective Heat Transfer Enhancement Using Alternating Magnetic Fields and Particle Laden Fluid Applied to the Microscale

DTIC Science & Technology

2010-05-11

convective heat transfer , researchers have been drawn to the high heat flux potentials of microfluidic devices. Microchannel flows, with hydraulic...novel heat transfer enhancement technique proven on the conventional scale to the mini and microchannel scales. 1.3 Background: Conventional...S.G., 2004, “Single-Phase Heat Transfer Enhancement Techniques in Microchannel and Minichannel Flows,” International Conference on Microchannels

[Present status and trend of heart fluid mechanics research based on medical image analysis].

PubMed

Gan, Jianhong; Yin, Lixue; Xie, Shenghua; Li, Wenhua; Lu, Jing; Luo, Anguo

2014-06-01

With introduction of current main methods for heart fluid mechanics researches, we studied the characteristics and weakness for three primary analysis methods based on magnetic resonance imaging, color Doppler ultrasound and grayscale ultrasound image, respectively. It is pointed out that particle image velocity (PIV), speckle tracking and block match have the same nature, and three algorithms all adopt block correlation. The further analysis shows that, with the development of information technology and sensor, the research for cardiac function and fluid mechanics will focus on energy transfer process of heart fluid, characteristics of Chamber wall related to blood fluid and Fluid-structure interaction in the future heart fluid mechanics fields.

RIE-based Pattern Transfer Using Nanoparticle Arrays as Etch Masks

NASA Astrophysics Data System (ADS)

Hogg, Chip; Majetich, Sara A.; Bain, James A.

2009-03-01

Nanomasking is used to transfer the pattern of a self-assembled array of nanoparticles into an underlying thin film, for potential use as bit-patterned media. We have used this process to investigate the limits of pattern transfer, as a function of gap size in the pattern. Reactive Ion Etching (RIE) is our chosen process, since the gaseous reaction products and high chemical selectivity are ideal features for etching very small gaps. Interstitial surfactant is removed with an O2 plasma, allowing the etchants to penetrate between the particles. Their pattern is transferred into an intermediate SiO2 mask using a CH4-based RIE. This patterned SiO2 layer is finally used as a mask for the MeOH-based RIE which patterns the magnetic film. We present cross-sectional TEM characterization of the etch profiles, as well as magnetic characterization of the film before and after patterning.

Magnetization transfer from laser-polarized xenon to protons located in the hydrophobic cavity of the wheat nonspecific lipid transfer protein

PubMed Central

Landon, Céline; Berthault, Patrick; Vovelle, Françoise; Desvaux, Hervé

2001-01-01

Nonspecific lipid transfer protein from wheat is studied by liquid-state NMR in the presence of xenon. The gas–protein interaction is indicated by the dependence of the protein proton chemical shifts on the xenon pressure and formally confirmed by the first observation of magnetization transfer from laser-polarized xenon to the protein protons. Twenty-six heteronuclear nOes have allowed the characterization of four interaction sites inside the wheat ns-LTP cavity. Their locations are in agreement with the variations of the chemical shifts under xenon pressure and with solvation simulations. The richness of the information obtained by the noble gas with a nuclear polarization multiplied by ∼12,000 makes this approach based on dipolar cross-relaxation with laser-polarized xenon promising for probing protein hydrophobic pockets at ambient pressure. PMID:11274467

A wireless energy transfer platform, integrated at the bedside.

PubMed

De Clercq, Hans; Puers, Robert

2013-01-01

This paper presents the design of a wireless energy transfer platform, integrated at the bedside. The system contains a matrix of identical inductive power transmitters, which are optimised to provide power to a wearable sensor network, with the purpose of wirelessly recording vital signals over an extended period of time. The magnetic link, operates at a transfer frequency of 6.78MHz and is able to transfer a power of 3.3mW to the remote side at an inter-coil distance of 100mm. The total efficiency of the power link is 26%. Moreover, the platform is able to dynamically determine the position of freely moving sensor nodes and selectively induce a magnetic field in the area where the sensor nodes are positioned. As a result, the patient will not be subjected to unnecessary radiation and the specific absorption rate standards are met more easily.

Higher-order Brain Areas Associated with Real-time Functional MRI Neurofeedback Training of the Somato-motor Cortex.

PubMed

Auer, Tibor; Dewiputri, Wan Ilma; Frahm, Jens; Schweizer, Renate

2018-05-15

Neurofeedback (NFB) allows subjects to learn self-regulation of neuronal brain activation based on information about the ongoing activation. The implementation of real-time functional magnetic resonance imaging (rt-fMRI) for NFB training now facilitates the investigation into underlying processes. Our study involved 16 control and 16 training right-handed subjects, the latter performing an extensive rt-fMRI NFB training using motor imagery. A previous analysis focused on the targeted primary somato-motor cortex (SMC). The present study extends the analysis to the supplementary motor area (SMA), the next higher brain area within the hierarchy of the motor system. We also examined transfer-related functional connectivity using a whole-volume psycho-physiological interaction (PPI) analysis to reveal brain areas associated with learning. The ROI analysis of the pre- and post-training fMRI data for motor imagery without NFB (transfer) resulted in a significant training-specific increase in the SMA. It could also be shown that the contralateral SMA exhibited a larger increase than the ipsilateral SMA in the training and the transfer runs, and that the right-hand training elicited a larger increase in the transfer runs than the left-hand training. The PPI analysis revealed a training-specific increase in transfer-related functional connectivity between the left SMA and frontal areas as well as the anterior midcingulate cortex (aMCC) for right- and left-hand trainings. Moreover, the transfer success was related with training-specific increase in functional connectivity between the left SMA and the target area SMC. Our study demonstrates that NFB training increases functional connectivity with non-targeted brain areas. These are associated with the training strategy (i.e., SMA) as well as with learning the NFB skill (i.e., aMCC and frontal areas). This detailed description of both the system to be trained and the areas involved in learning can provide valuable information for further optimization of NFB trainings. Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.

Photocatalytic Conversion of Nitrobenzene to Aniline through Sequential Proton-Coupled One-Electron Transfers from a Cadmium Sulfide Quantum Dot

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

Jensen, Stephen C.; Bettis Homan, Stephanie; Weiss, Emily A.

2016-01-28

This paper describes the use of cadmium sulfide quantum dots (CdS QDs) as visible-light photocatalysts for the reduction of nitrobenzene to aniline through six sequential photoinduced, proton-coupled electron transfers. At pH 3.6–4.3, the internal quantum yield of photons-to-reducing electrons is 37.1% over 54 h of illumination, with no apparent decrease in catalyst activity. Monitoring of the QD exciton by transient absorption reveals that, for each step in the catalytic cycle, the sacrificial reductant, 3-mercaptopropionic acid, scavenges the excitonic hole in ~5 ps to form QD•–; electron transfer to nitrobenzene or the intermediates nitrosobenzene and phenylhydroxylamine then occurs on the nanosecondmore » time scale. The rate constants for the single-electron transfer reactions are correlated with the driving forces for the corresponding proton-coupled electron transfers. This result suggests, but does not prove, that electron transfer, not proton transfer, is rate-limiting for these reactions. Nuclear magnetic resonance analysis of the QD–molecule systems shows that the photoproduct aniline, left unprotonated, serves as a poison for the QD catalyst by adsorbing to its surface. Performing the reaction at an acidic pH not only encourages aniline to desorb but also increases the probability of protonated intermediates; the latter effect probably ensures that recruitment of protons is not rate-limiting.« less

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.

Magnetic refrigeration apparatus with heat pipes

DOEpatents

Barclay, John A.; Prenger, Jr., F. Coyne

1987-01-01

A magnetic refrigerator operating in the 4 to 20 K range utilizes heat pipes to transfer heat to and from the magnetic material at the appropriate points during the material's movement. In one embodiment circular disks of magnetic material can be interleaved with the ends of the heat pipes. In another embodiment a mass of magnetic material reciprocatingly moves between the end of the heat pipe of pipes that transmits heat from the object of cooling to the magnetic material and the end of the heat pipe or pipes that transmits heat from the magnetic material to a heat sink.

Magnetic refrigeration apparatus with heat pipes

DOEpatents

Barclay, J.A.; Prenger, F.C. Jr.

1985-10-25

A magnetic refrigerator operating in the 4 to 20 K range utilizes heat pipes to transfer heat to and from the magnetic material at the appropriate points during the material's movement. In one embodiment circular disks of magnetic material can be interleaved with the ends of the heat pipes. In another embodiment a mass of magnetic material reciprocatingly moves between the end of the heat pipe or pipes that transmits heat from the object of cooling to the magnetic material and the end of the heat pipe or pipes that transmits heat from the magnetic material to a heat sink.

Study of wave form compensation at CSNS/RCS magnets

NASA Astrophysics Data System (ADS)

Xu, S. Y.; Fu, S. N.; Wang, S.; Kang, W.; Qi, X.; Li, L.; Deng, C. D.; Zhou, J. X.

2018-07-01

A method of wave form compensation for magnets of the Rapid Cycling Synchrotron (RCS), which is based on transfer function between magnetic field and exciting current, was investigated on the magnets of RCS of Chinese Spallation Neutron Source (CSNS). By performing wave form compensation, the magnetic field ramping function for RCS magnets can be accurately controlled to the given wave form, which is not limited to sine function. The method of wave form compensation introduced in this paper can be used to reduce the magnetic field tracking errors, and can also be used to accurately control the betatron tune for RCS.

PARTICLE ACCELERATOR

DOEpatents

Teng, L.C.

1960-01-19

ABS>A combination of two accelerators, a cyclotron and a ring-shaped accelerator which has a portion disposed tangentially to the cyclotron, is described. Means are provided to transfer particles from the cyclotron to the ring accelerator including a magnetic deflector within the cyclotron, a magnetic shield between the ring accelerator and the cyclotron, and a magnetic inflector within the ring accelerator.

Spin-transfer-torque efficiency enhanced by edge-damage of perpendicular magnetic random access memories

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

Song, Kyungmi; Lee, Kyung-Jin, E-mail: kj-lee@korea.ac.kr; Department of Materials Science and Engineering, Korea University, Seoul 136-713

2015-08-07

We numerically investigate the effect of magnetic and electrical damages at the edge of a perpendicular magnetic random access memory (MRAM) cell on the spin-transfer-torque (STT) efficiency that is defined by the ratio of thermal stability factor to switching current. We find that the switching mode of an edge-damaged cell is different from that of an undamaged cell, which results in a sizable reduction in the switching current. Together with a marginal reduction of the thermal stability factor of an edge-damaged cell, this feature makes the STT efficiency large. Our results suggest that a precise edge control is viable formore » the optimization of STT-MRAM.« less

Dynamic aspects of antibody:oligosaccharide complexes characterized by molecular dynamics simulations and saturation transfer difference nuclear magnetic resonance.

PubMed

Theillet, François-Xavier; Frank, Martin; Vulliez-Le Normand, Brigitte; Simenel, Catherine; Hoos, Sylviane; Chaffotte, Alain; Bélot, Frédéric; Guerreiro, Catherine; Nato, Farida; Phalipon, Armelle; Mulard, Laurence A; Delepierre, Muriel

2011-12-01

Carbohydrates are likely to maintain significant conformational flexibility in antibody (Ab):carbohydrate complexes. As demonstrated herein for the protective monoclonal Ab (mAb) F22-4 recognizing the Shigella flexneri 2a O-antigen (O-Ag) and numerous synthetic oligosaccharide fragments thereof, the combination of molecular dynamics simulations and nuclear magnetic resonance saturation transfer difference experiments, supported by physicochemical analysis, allows us to determine the binding epitope and its various contributions to affinity without using any modified oligosaccharides. Moreover, the methods used provide insights into ligand flexibility in the complex, thus enabling a better understanding of the Ab affinities observed for a representative set of synthetic O-Ag fragments. Additionally, these complementary pieces of information give evidence to the ability of the studied mAb to recognize internal as well as terminal epitopes of its cognate polysaccharide antigen. Hence, we show that an appropriate combination of computational and experimental methods provides a basis to explore carbohydrate functional mimicry and receptor binding. The strategy may facilitate the design of either ligands or carbohydrate recognition domains, according to needed improvements of the natural carbohydrate:receptor properties. © The Author 2011. Published by Oxford University Press. All rights reserved.

A biofilm microreactor system for simultaneous electrochemical and nuclear magnetic resonance techniques.

PubMed

Renslow, R S; Babauta, J T; Majors, P D; Mehta, H S; Ewing, R J; Ewing, T W; Mueller, K T; Beyenal, H

2014-01-01

Nuclear magnetic resonance (NMR) techniques are ideally suited for the study of biofilms and for probing their microenvironments because these techniques allow for noninvasive interrogation and in situ monitoring with high resolution. By combining NMR with simultaneous electrochemical techniques, it is possible to sustain and study live biofilms respiring on electrodes. Here, we describe a biofilm microreactor system, including a reusable and a disposable reactor, that allows for simultaneous electrochemical and NMR techniques (EC-NMR) at the microscale. Microreactors were designed with custom radio frequency resonator coils, which allowed for NMR measurements of biofilms growing on polarized gold electrodes. For an example application of this system we grew Geobacter sulfurreducens biofilms on electrodes. EC-NMR was used to investigate growth medium flow velocities and depth-resolved acetate concentration inside the biofilm. As a novel contribution we used Monte Carlo error analysis to estimate the standard deviations of the acetate concentration measurements. Overall, we found that the disposable EC-NMR microreactor provided a 9.7 times better signal-to-noise ratio over the reusable reactor. The EC-NMR biofilm microreactor system can ultimately be used to correlate extracellular electron transfer rates with metabolic reactions and explore extracellular electron transfer mechanisms.

The puzzling orbital period evolution of the LMXB AX J1745.6-2901

NASA Astrophysics Data System (ADS)

Ponti, G.; De, K.; Munoz-Darias, T.; Stella, L.; Nandra, K.

2017-10-01

The discovery of gravitational waves through mergers of binary black holes raises the question of how such compact systems form, renewing issues related to the orbital evolution of binary systems. Eclipsing X-ray binaries are excellent tools to constrain the orbital period evolution and how the system loses angular momentum. I will present an X-ray eclipse timing analysis (spanning an interval of more than 20 yr) of one of such objects, AX J1745.6-2901. Its orbital period is decreasing at a rate Pdotorb=-4.03+-0.32 e-11 s s-1, at least one order of magnitude larger than expected from conservative mass transfer and angular momentum losses due to gravitational waves and magnetic braking, and it might result from either non-conservative mass transfer or magnetic activity changing the quadrupole moment of the companion star. I will also show that imprinted on the long-term evolution of the orbit, there are highly significant eclipse leads delays of 10-30 s, characterized by a clear state dependence in which, on average, eclipses occur earlier during the hard state. Finally, I will discuss whether accretion disc winds might have an impact onto the orbital evolution.

Natural convection in square cavity filled with ferrofluid saturated porous medium in the presence of uniform magnetic field

NASA Astrophysics Data System (ADS)

Javed, Tariq; Mehmood, Z.; Abbas, Z.

2017-02-01

This article contains numerical results for free convection through square enclosure enclosing ferrofluid saturated porous medium when uniform magnetic field is applied upon the flow along x-axis. Heat is provided through bottom wall and a square blockage placed near left or right bottom corner of enclosure as a heat source. Left and right vertical boundaries of the cavity are considered insulated while upper wall is taken cold. The problem is modelled in terms of system of nonlinear partial differential equations. Finite element method has been adopted to compute numerical simulations of mathematical problem for wide range of pertinent flow parameters including Rayleigh number, Hartman number, Darcy number and Prandtl number. Analysis of results reveals that the strength of streamline circulation is an increasing function of Darcy and Prandtl number where convection heat transfer is dominant for large values of these parameters whereas increase in Hartman number has opposite effects on isotherms and streamline circulations. Thermal conductivity and hence local heat transfer rate of fluid gets increased when ferroparticles are introduced in the fluid. Average Nusselt number increases with increase in Darcy and Rayleigh numbers while it is decreases when Hartman number is increased.

Analysis of SAR distribution in human head of antenna used in wireless power transform based on magnetic resonance.

PubMed

Gong, Feixiang; Wei, Zhiqiang; Cong, Yanping; Chi, Haokun; Yin, Bo; Sun, Mingui

2017-07-20

In this paper, a novel wireless power transfer antenna system was designed for human head implantable devices. The antenna system used the structure of three plates and four coils and operated at low frequencies to transfer power via near field. In order to verify the electromagnetic radiation safety on the human head, the electromagnetic intensity and specific absorption rate (SAR) were studied by finite-difference-time-domain (FDTD) method. A three-layer model of human head including skin, bone and brain tissues was constructed. The transmitting and receiving antenna were set outside and inside the model. The local and average SAR were simulated at the resonance frequency of 18.67 MHz in two situations, in one scenario both transmitting and receiving coil worked, while in the other scenario only the transmitting coil worked. The results showed that the maximum of 10 g SAR average value of human thoracic were 0.142 W/kg and 0.148 W/kg, respectively, both were lower than the international safety standards for human body of the ICNIRP and FCC, which verified the safety of the human body in wireless power transmission based on magnetic coupling resonance.

Chemiluminescence resonance energy transfer imaging on magnetic particles for single-nucleotide polymorphism detection based on ligation chain reaction.

PubMed

Bi, Sai; Zhang, Zhipeng; Dong, Ying; Wang, Zonghua

2015-03-15

A novel ligation chain reaction (LCR) methodology for single-nucleotide polymorphism (SNP) detection was developed based on luminol-H2O2-horseradish peroxidase (HRP)-mimicking DNAzyme-fluorescein chemiluminescence resonance energy transfer (CRET) imaging on magnetic particles. For LCR, four unique target-complement probes (X and X(⁎), YG and Y(⁎)) for the amplification of K-ras (G12C) were designed by modifying G-quadruplex sequence at 3'-end of YG and fluorescein at 5'-end of Y(⁎). After the LCR, the resulting products of XYG/X(⁎)Y(⁎) with biotin-labeled X(⁎) were captured onto streptavidin-coated magnetic particles (SA-MPs) via specific biotin-SA interaction, which stimulated the CRET reaction from hemin/G-quadruplex-catalyzed luminol-H2O2 CL system to fluorescein. By collecting signals by a cooled low-light CCD, a CRET imaging method was proposed for visual detection and quantitative analysis of SNP. As low as 0.86fM mutant DNA was detected by this assay, and positive mutation detection was achieved with a wild-type to mutant ratio of 10,000:1. This high sensitivity and specificity could be attributed to not only the exponential amplification and excellent discrimination of LCR but also the employment of SA-MPs. SA-MPs ensured the feasibility of the proposed strategy, which also simplified the operations through magnetic separation and separated the reaction and detection procedures to improve sensitivity. The proposed LCR-CRET imaging strategy extends the application of signal amplification techniques to SNP detection, providing a promising platform for effective and high-throughput genetic diagnosis. Copyright © 2014 Elsevier B.V. All rights reserved.

Magnetic field effect on Poiseuille flow and heat transfer of carbon nanotubes along a vertical channel filled with Casson fluid

NASA Astrophysics Data System (ADS)

Aman, Sidra; Khan, Ilyas; Ismail, Zulkhibri; Salleh, Mohd Zuki; Alshomrani, Ali Saleh; Alghamdi, Metib Said

2017-01-01

Applications of carbon nanotubes, single walls carbon nanotubes (SWCNTs) and multiple walls carbon nanotubes (MWCNTs) in thermal engineering have recently attracted significant attention. However, most of the studies on CNTs are either experimental or numerical and the lack of analytical studies limits further developments in CNTs research particularly in channel flows. In this work, an analytical investigation is performed on heat transfer analysis of SWCNTs and MWCNTs for mixed convection Poiseuille flow of a Casson fluid along a vertical channel. These CNTs are suspended in three different types of base fluids (Water, Kerosene and engine Oil). Xue [Phys. B Condens. Matter 368, 302-307 (2005)] model has been used for effective thermal conductivity of CNTs. A uniform magnetic field is applied in a transverse direction to the flow as magnetic field induces enhancement in the thermal conductivity of nanofluid. The problem is modelled by using the constitutive equations of Casson fluid in order to characterize the non-Newtonian fluid behavior. Using appropriate non-dimensional variables, the governing equations are transformed into the non-dimensional form, and the perturbation method is utilized to solve the governing equations with some physical conditions. Velocity and temperature solutions are obtained and discussed graphically. Expressions for skin friction and Nusselt number are also evaluated in tabular form. Effects of different parameters such as Casson parameter, radiation parameter and volume fraction are observed on the velocity and temperature profiles. It is found that velocity is reduced under influence of the exterior magnetic field. The temperature of single wall CNTs is found greater than MWCNTs for all the three base fluids. Increase in volume fraction leads to a decrease in velocity of the fluid as the nanofluid become more viscous by adding CNTs.

Chemical exchange rotation transfer (CERT) on human brain at 3 Tesla.

PubMed

Lin, Eugene C; Li, Hua; Zu, Zhongliang; Louie, Elizabeth A; Lankford, Christopher L; Dortch, Richard D; Does, Mark D; Gore, John C; Gochberg, Daniel F

2018-05-25

To test the ability of a novel pulse sequence applied in vivo at 3 Tesla to separate the contributions to the water signal from amide proton transfer (APT) and relayed nuclear Overhauser enhancement (rNOE) from background direct water saturation and semisolid magnetization transfer (MT). The lack of such signal source isolation has confounded conventional chemical exchange saturation transfer (CEST) imaging. We quantified APT and rNOE signals using a chemical exchange rotation transfer (CERT) metric, MTR double . A range of duty cycles and average irradiation powers were applied, and results were compared with conventional CEST analyses using asymmetry (MTR asym ) and extrapolated magnetization transfer (EMR). Our results indicate that MTR double is more specific than MTR asym and, because it requires as few as 3 data points, is more rapid than methods requiring a complete Z-spectrum, such as EMR. In white matter, APT (1.5 ± 0.5%) and rNOE (2.1 ± 0.7%) were quantified by using MTR double with a 30% duty cycle and a 0.5-µT average power. In addition, our results suggest that MTR double is insensitive to B 0 inhomogeneity, further magnifying its speed advantage over CEST metrics that require a separate B 0 measurement. However, MTR double still has nontrivial sensitivity to B 1 inhomogeneities. We demonstrated that MTR double is an alternative metric to evaluate APT and rNOE, which is fast, robust to B 0 inhomogeneity, and easy to process. © 2018 International Society for Magnetic Resonance in Medicine.

Imaging of endogenous exchangeable proton signals in the human brain using frequency labeled exchange transfer imaging.

PubMed

Yadav, Nirbhay N; Jones, Craig K; Hua, Jun; Xu, Jiadi; van Zijl, Peter C M

2013-04-01

To image endogenous exchangeable proton signals in the human brain using a recently reported method called frequency labeled exchange transfer (FLEX) MRI. As opposed to labeling exchangeable protons using saturation (i.e., chemical exchange saturation transfer, or CEST), FLEX labels exchangeable protons with their chemical shift evolution. The use of short high-power frequency pulses allows more efficient labeling of rapidly exchanging protons, while time domain acquisition allows removal of contamination from semi-solid magnetization transfer effects. FLEX-based exchangeable proton signals were detected in human brain over the 1-5 ppm frequency range from water. Conventional magnetization transfer contrast and the bulk water signal did not interfere in the FLEX spectrum. The information content of these signals differed from in vivo CEST data in that the average exchange rate of these signals was 350-400 s(-1) , much faster than the amide signal usually detected using direct saturation (∼30 s(-1) ). Similarly, fast exchanging protons could be detected in egg white in the same frequency range where amide and amine protons of mobile proteins and peptides are known to resonate. FLEX MRI in the human brain preferentially detects more rapidly exchanging amide/amine protons compared to traditional CEST experiments, thereby changing the information content of the exchangeable proton spectrum. This has the potential to open up different types of endogenous applications as well as more easy detection of rapidly exchanging protons in diaCEST agents or fast exchanging units such as water molecules in paracest agents without interference of conventional magnetization transfer contrast. Copyright © 2013 Wiley Periodicals, Inc.

Perceptual learning modifies the functional specializations of visual cortical areas.

PubMed

Chen, Nihong; Cai, Peng; Zhou, Tiangang; Thompson, Benjamin; Fang, Fang

2016-05-17

Training can improve performance of perceptual tasks. This phenomenon, known as perceptual learning, is strongest for the trained task and stimulus, leading to a widely accepted assumption that the associated neuronal plasticity is restricted to brain circuits that mediate performance of the trained task. Nevertheless, learning does transfer to other tasks and stimuli, implying the presence of more widespread plasticity. Here, we trained human subjects to discriminate the direction of coherent motion stimuli. The behavioral learning effect substantially transferred to noisy motion stimuli. We used transcranial magnetic stimulation (TMS) and functional magnetic resonance imaging (fMRI) to investigate the neural mechanisms underlying the transfer of learning. The TMS experiment revealed dissociable, causal contributions of V3A (one of the visual areas in the extrastriate visual cortex) and MT+ (middle temporal/medial superior temporal cortex) to coherent and noisy motion processing. Surprisingly, the contribution of MT+ to noisy motion processing was replaced by V3A after perceptual training. The fMRI experiment complemented and corroborated the TMS finding. Multivariate pattern analysis showed that, before training, among visual cortical areas, coherent and noisy motion was decoded most accurately in V3A and MT+, respectively. After training, both kinds of motion were decoded most accurately in V3A. Our findings demonstrate that the effects of perceptual learning extend far beyond the retuning of specific neural populations for the trained stimuli. Learning could dramatically modify the inherent functional specializations of visual cortical areas and dynamically reweight their contributions to perceptual decisions based on their representational qualities. These neural changes might serve as the neural substrate for the transfer of perceptual learning.

76 FR 52346 - Public Land Order No. 7760; Extension of Public Land Order No. 6839; Alaska; Correction

Federal Register 2010, 2011, 2012, 2013, 2014

2011-08-22

... Survey facility encumbers 45 acres for the Barrow Magnetic Observatory.'' is hereby corrected to read... Magnetic Observatory.'' Robert L. Lloyd, Supervisor, Lands, Realty and Title Transfer Program, Division of...

Virtual Compton scattering and the generalized polarizabilities of the proton at Q2=0.92 and 1.76 GeV2

NASA Astrophysics Data System (ADS)

Fonvieille, H.; Laveissière, G.; Degrande, N.; Jaminion, S.; Jutier, C.; Todor, L.; Di Salvo, R.; Van Hoorebeke, L.; Alexa, L. C.; Anderson, B. D.; Aniol, K. A.; Arundell, K.; Audit, G.; Auerbach, L.; Baker, F. T.; Baylac, M.; Berthot, J.; Bertin, P. Y.; Bertozzi, W.; Bimbot, L.; Boeglin, W. U.; Brash, E. J.; Breton, V.; Breuer, H.; Burtin, E.; Calarco, J. R.; Cardman, L. S.; Cavata, C.; Chang, C.-C.; Chen, J.-P.; Chudakov, E.; Cisbani, E.; Dale, D. S.; de Jager, C. W.; De Leo, R.; Deur, A.; d'Hose, N.; Dodge, G. E.; Domingo, J. J.; Elouadrhiri, L.; Epstein, M. B.; Ewell, L. A.; Finn, J. M.; Fissum, K. G.; Fournier, G.; Frois, B.; Frullani, S.; Furget, C.; Gao, H.; Gao, J.; Garibaldi, F.; Gasparian, A.; Gilad, S.; Gilman, R.; Glamazdin, A.; Glashausser, C.; Gomez, J.; Gorbenko, V.; Grenier, P.; Guichon, P. A. M.; Hansen, J. O.; Holmes, R.; Holtrop, M.; Howell, C.; Huber, G. M.; Hyde, C. E.; Incerti, S.; Iodice, M.; Jardillier, J.; Jones, M. K.; Kahl, W.; Kato, S.; Katramatou, A. T.; Kelly, J. J.; Kerhoas, S.; Ketikyan, A.; Khayat, M.; Kino, K.; Kox, S.; Kramer, L. H.; Kumar, K. S.; Kumbartzki, G.; Kuss, M.; Leone, A.; LeRose, J. J.; Liang, M.; Lindgren, R. A.; Liyanage, N.; Lolos, G. J.; Lourie, R. W.; Madey, R.; Maeda, K.; Malov, S.; Manley, D. M.; Marchand, C.; Marchand, D.; Margaziotis, D. J.; Markowitz, P.; Marroncle, J.; Martino, J.; McCormick, K.; McIntyre, J.; Mehrabyan, S.; Merchez, F.; Meziani, Z. E.; Michaels, R.; Miller, G. W.; Mougey, J. Y.; Nanda, S. K.; Neyret, D.; Offermann, E. A. J. M.; Papandreou, Z.; Pasquini, B.; Perdrisat, C. F.; Perrino, R.; Petratos, G. G.; Platchkov, S.; Pomatsalyuk, R.; Prout, D. L.; Punjabi, V. A.; Pussieux, T.; Quémenér, G.; Ransome, R. D.; Ravel, O.; Real, J. S.; Renard, F.; Roblin, Y.; Rowntree, D.; Rutledge, G.; Rutt, P. M.; Saha, A.; Saito, T.; Sarty, A. J.; Serdarevic, A.; Smith, T.; Smirnov, G.; Soldi, K.; Sorokin, P.; Souder, P. A.; Suleiman, R.; Templon, J. A.; Terasawa, T.; Tieulent, R.; Tomasi-Gustaffson, E.; Tsubota, H.; Ueno, H.; Ulmer, P. E.; Urciuoli, G. M.; Vanderhaeghen, M.; Van der Meer, R. L. J.; Van De Vyver, R.; Vernin, P.; Vlahovic, B.; Voskanyan, H.; Voutier, E.; Watson, J. W.; Weinstein, L. B.; Wijesooriya, K.; Wilson, R.; Wojtsekhowski, B. B.; Zainea, D. G.; Zhang, W.-M.; Zhao, J.; Zhou, Z.-L.

2012-07-01

Virtual Compton scattering (VCS) on the proton has been studied at the Jefferson Laboratory using the exclusive photon electroproduction reaction ep→epγ. This paper gives a detailed account of the analysis which has led to the determination of the structure functions PLL-PTT/ɛ and PLT and the electric and magnetic generalized polarizabilities (GPs) αE(Q2) and βM(Q2) at values of the four-momentum transfer squared Q2=0.92 and 1.76 GeV2. These data, together with the results of VCS experiments at lower momenta, help building a coherent picture of the electric and magnetic GPs of the proton over the full measured Q2 range and point to their nontrivial behavior.

Energy coupling during the August 2011 magnetic storm

NASA Astrophysics Data System (ADS)

Huang, C. Y.; Su, Y.; Sutton, E. K.; Weimer, D. R.; Davidson, R.

2013-12-01

We present results from an analysis of high-latitude ionosphere-thermosphere (IT) coupling to the solar wind during a moderate magnetic storm which occurred on 5-6 August 2011. During the storm, a multi-point set of observations of the ionosphere and thermosphere was available. We make use of ionospheric measurements of electromagnetic and particle energy made by the Defense Meteorological Satellite Program (DMSP), and neutral densities measured by the Gravity Recovery and Climate Experiment (GRACE) satellite to infer: (1) the energy budget and (2) timing of the energy transfer process during the storm. We conclude that the primary location for energy input to the IT system is the extremely high latitude region. We suggest that the total energy available to the IT system is not completely captured either by observation or empirical models.

Structural and electronic evolution of Cr[subscript 2]O[subscript 3] on compression to 55 GPa

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

Dera, Przemyslaw; Lavina, Barbara; Meng, Yue

2016-08-15

Synchrotron single-crystal x-ray diffraction experiments have been performed on corundum-type Cr{sub 2}O{sub 3} up to a pressure of 55 GPa in Ne and He pressure transmitting media. Diffraction experiments were complemented by measurements of optical absorption spectra with single crystal samples up to 60 GPa. Results of the diffraction data analysis rule out the earlier reported monoclinic distortion at 15-30 GPa, but indicate evidence of two discontinuous transitions of electronic or magnetic nature, most likely associated with a change in magnetic ordering and charge transfer. The compression mechanism established from single crystal refinements indicates much smaller distortion of the Cr{supmore » 3+} coordination environment than was previously assumed.« less

Design of Novel FBG-Based Sensor of Differential Pressure with Magnetic Transfer.

PubMed

Lyu, Guohui; Che, Guohang; Li, Junqing; Jiang, Xu; Wang, Keda; Han, Yueqiang; Gao, Laixu

2017-02-15

In this paper, a differential pressure sensor with magnetic transfer is proposed, in which the non-electric measurement based on the fiber Bragg grating (FBG) with the position limiting mechanism is implemented without the direct contact of the sensing unit with the measuring fluid. The test shows that the designed sensor is effective for measuring differential pressure in the range of 0~10 kPa with a sensitivity of 0.0112 nm/kPa, which can be used in environments with high temperature, strong corrosion and high overload measurements.

Analysis of gene transfer rate with immobilized retroviral vectors.

PubMed

Peng, Ching-An

2009-04-01

Efficient delivery of transgenes into the cell nucleus by retroviral vectors in a static culture system is limited by the intrinsic features of incompetent retroviruses (i.e., thermodynamically unstable envelope proteins and low titers). Although several physicochemical approaches (e.g., adding polycationic polymer and applying magnetic force) have been reported to augment the retroviral gene transfer rate, none are suitable for scaling up to a setting for clinical use. The study of using acoustic fields with the form of standing waves has recently been reported to be a feasible way to enhance retroviral gene delivery efficiency in large-scale settings. The concept of using ultrasound standing-wave fields to increase retrovirus-mediated gene transfer is based on quickly established cell bands on acoustic nodal planes as nucleating sites to capture unstable colloidlike retroviruses. In this study, instead of having retroviral nanoparticles circulated between nodal planes, we proposed to immobilize retroviruses onto acoustic transparent films arranged in an acoustic chamber. Then, cells inoculated into the acoustic chamber can be driven by the primary radiation forces to the retrovirus-coated films that are constructed on the nodal planes. To obtain the optimal time of immobilizing retroviruses onto the acoustic transparent film prior to the inception of acoustic fields, we developed a retroviral diffusion-reaction model to describe such a static retroviral system. Analysis of viral transport model has its merit to guide experimental design for attaining high gene transfer efficiency.

Gyrokinetic turbulence: between idealized estimates and a detailed analysis of nonlinear energy transfers

NASA Astrophysics Data System (ADS)

Teaca, Bogdan; Jenko, Frank; Told, Daniel

2017-04-01

Using large resolution numerical simulations of gyrokinetic (GK) turbulence, spanning an interval ranging from the end of the fluid scales to the electron gyroradius, we study the energy transfers in the perpendicular direction for a proton-electron plasma in a slab equilibrium magnetic geometry. The plasma parameters employed here are relevant to kinetic Alfvén wave turbulence in solar wind conditions. In addition, we use an idealized test representation for the energy transfers between two scales, to aid our understanding of the diagnostics applicable to the nonlinear cascade in an infinite inertial range. For GK turbulence, a detailed analysis of nonlinear energy transfers that account for the separation of energy exchanging scales is performed. Starting from the study of the energy cascade and the scale locality problem, we show that the general nonlocal nature of GK turbulence, captured via locality functions, contains a subset of interactions that are deemed local, are scale invariant (i.e. a sign of asymptotic locality) and possess a locality exponent that can be recovered directly from measurements on the energy cascade. It is the first time that GK turbulence is shown to possess an asymptotic local component, even if the overall locality of interactions is nonlocal. The results presented here and their implications are discussed from the perspective of previous findings reported in the literature and the idea of universality of GK turbulence.

MHD Convective Flow of Jeffrey Fluid Due to a Curved Stretching Surface with Homogeneous-Heterogeneous Reactions

PubMed Central

Imtiaz, Maria; Hayat, Tasawar; Alsaedi, Ahmed

2016-01-01

This paper looks at the flow of Jeffrey fluid due to a curved stretching sheet. Effect of homogeneous-heterogeneous reactions is considered. An electrically conducting fluid in the presence of applied magnetic field is considered. Convective boundary conditions model the heat transfer analysis. Transformation method reduces the governing nonlinear partial differential equations into the ordinary differential equations. Convergence of the obtained series solutions is explicitly discussed. Characteristics of sundry parameters on the velocity, temperature and concentration profiles are analyzed by plotting graphs. Computations for pressure, skin friction coefficient and surface heat transfer rate are presented and examined. It is noted that fluid velocity and temperature through curvature parameter are enhanced. Increasing values of Biot number correspond to the enhancement in temperature and Nusselt number. PMID:27583457

Current Sheet Properties and Dynamics During Sympathetic Breakout Eruptions

NASA Astrophysics Data System (ADS)

Lynch, B. J.; Edmondson, J. K.

2013-12-01

We present the continued analysis of the high-resolution 2.5D MHD simulations of sympathetic magnetic breakout eruptions from a pseudostreamer source region. We examine the generation of X- and O-type null points during the current sheet tearing and track the magnetic island formation and evolution during periods of reconnection. The magnetic breakout eruption scenario forms an overlying 'breakout' current sheet that evolves slowly and removes restraining flux from above the sheared field core that will eventually become the center of the erupting flux rope-like structure. The runaway expansion from the expansion-breakout reconnection positive feedback enables the formation of the second, vertical/radial current sheet underneath the rising sheared field core as in the standard CHSKP eruptive flare scenario. We will examine the flux transfer rates through the breakout and flare current sheets and compare the properties of the field and plasma inflows into the current sheets and the reconnection jet outflows into the flare loops and flux rope ejecta.

Fiber Bragg Grating Dilatometry in Extreme Magnetic Field and Cryogenic Conditions

PubMed Central

Corvalán Moya, Carolina; Weickert, Franziska; Zapf, Vivien; Balakirev, Fedor F.; Wartenbe, Mark; Rosa, Priscila F. S.; Betts, Jonathan B.; Crooker, Scott A.; Daou, Ramzy

2017-01-01

In this work, we review single mode SiO2 fiber Bragg grating techniques for dilatometry studies of small single-crystalline samples in the extreme environments of very high, continuous, and pulsed magnetic fields of up to 150 T and at cryogenic temperatures down to <1 K. Distinct millimeter-long materials are measured as part of the technique development, including metallic, insulating, and radioactive compounds. Experimental strategies are discussed for the observation and analysis of the related thermal expansion and magnetostriction of materials, which can achieve a strain sensitivity (ΔL/L) as low as a few parts in one hundred million (≈10−8). The impact of experimental artifacts, such as those originating in the temperature dependence of the fiber’s index of diffraction, light polarization rotation in magnetic fields, and reduced strain transfer from millimeter-long specimens, is analyzed quantitatively using analytic models available in the literature. We compare the experimental results with model predictions in the small-sample limit, and discuss the uncovered discrepancies. PMID:29117137

Fiber Bragg Grating Dilatometry in Extreme Magnetic Field and Cryogenic Conditions.

PubMed

Jaime, Marcelo; Corvalán Moya, Carolina; Weickert, Franziska; Zapf, Vivien; Balakirev, Fedor F; Wartenbe, Mark; Rosa, Priscila F S; Betts, Jonathan B; Rodriguez, George; Crooker, Scott A; Daou, Ramzy

2017-11-08

In this work, we review single mode SiO₂ fiber Bragg grating techniques for dilatometry studies of small single-crystalline samples in the extreme environments of very high, continuous, and pulsed magnetic fields of up to 150 T and at cryogenic temperatures down to <1 K. Distinct millimeter-long materials are measured as part of the technique development, including metallic, insulating, and radioactive compounds. Experimental strategies are discussed for the observation and analysis of the related thermal expansion and magnetostriction of materials, which can achieve a strain sensitivity ( ΔL/L ) as low as a few parts in one hundred million (≈10 -8 ). The impact of experimental artifacts, such as those originating in the temperature dependence of the fiber's index of diffraction, light polarization rotation in magnetic fields, and reduced strain transfer from millimeter-long specimens, is analyzed quantitatively using analytic models available in the literature. We compare the experimental results with model predictions in the small-sample limit, and discuss the uncovered discrepancies.

Fiber Bragg Grating Dilatometry in Extreme Magnetic Field and Cryogenic Conditions

DOE PAGES

Jaime, Marcelo; Corvalán Moya, Carolina; Weickert, Franziska; ...

2017-11-08

In this work, we review single mode SiO 2 fiber Bragg grating techniques for dilatometry studies of small single-crystalline samples in the extreme environments of very high, continuous, and pulsed magnetic fields of up to 150 T and at cryogenic temperatures down to <1 K. Distinct millimeter-long materials are measured as part of the technique development, including metallic, insulating, and radioactive compounds. Experimental strategies are discussed for the observation and analysis of the related thermal expansion and magnetostriction of materials, which can achieve a strain sensitivity (ΔL/L) as low as a few parts in one hundred million (≈10 -8). Themore » impact of experimental artifacts, such as those originating in the temperature dependence of the fiber’s index of diffraction, light polarization rotation in magnetic fields, and reduced strain transfer from millimeter-long specimens, is analyzed quantitatively using analytic models available in the literature. We compare the experimental results with model predictions in the small-sample limit, and discuss the uncovered discrepancies.« less

Currentless reversal of Néel vector in antiferromagnets

NASA Astrophysics Data System (ADS)

Semenov, Yuriy; Li, Xilai; Kim, Ki Wook

The bias driven perpendicular magnetic anisotropy is a magneto-electric effect that can realize 900 magnetization rotation and even 1800 flip along the easy axis in the ferromagnets with a minimal energy consumption. This study theoretically demonstrates a similar phenomenon of the Néel vector reversal via a short electrical pulse that can mediate perpendicular magnetic anisotropy in the antiferromagnets. The analysis based on the dynamical equations as well as the micromagnetic simulations reveals the important role of the inertial behavior in the antiferromagnets that facilitates the Néel vector to overcome the barrier between two free-energy minima of the bistable states along the easy axis. In contrast to the ferromagnets, this Néel vector reversal does not accompany angular moment transfer to the environment, leading to acceleration in the dynamical response by a few orders of magnitude. Further, a small switching energy requirement of a few attojoules illustrates an added advantage of the phenomenon in low-power spintronic applications.

Magnon condensation and spin superfluidity

NASA Astrophysics Data System (ADS)

Bunkov, Yury M.; Safonov, Vladimir L.

2018-04-01

We consider the Bose-Einstein condensation (BEC) of quasi-equilibrium magnons which leads to spin superfluidity, the coherent quantum transfer of magnetization in magnetic material. The critical conditions for excited magnon density in ferro- and antiferromagnets, bulk and thin films, are estimated and discussed. It was demonstrated that only the highly populated region of the spectrum is responsible for the emergence of any BEC. This finding substantially simplifies the BEC theoretical analysis and is surely to be used for simulations. It is shown that the conditions of magnon BEC in the perpendicular magnetized YIG thin film is fulfillied at small angle, when signals are treated as excited spin waves. We also predict that the magnon BEC should occur in the antiferromagnetic hematite at room temperature at much lower excited magnon density compared to that of ferromagnetic YIG. Bogoliubov's theory of Bose-Einstein condensate is generalized to the case of multi-particle interactions. The six-magnon repulsive interaction may be responsible for the BEC stability in ferro- and antiferromagnets where the four-magnon interaction is attractive.

Antiferromagnetic spintronics

NASA Astrophysics Data System (ADS)

Baltz, V.; Manchon, A.; Tsoi, M.; Moriyama, T.; Ono, T.; Tserkovnyak, Y.

2018-01-01

Antiferromagnetic materials could represent the future of spintronic applications thanks to the numerous interesting features they combine: they are robust against perturbation due to magnetic fields, produce no stray fields, display ultrafast dynamics, and are capable of generating large magnetotransport effects. Intense research efforts over the past decade have been invested in unraveling spin transport properties in antiferromagnetic materials. Whether spin transport can be used to drive the antiferromagnetic order and how subsequent variations can be detected are some of the thrilling challenges currently being addressed. Antiferromagnetic spintronics started out with studies on spin transfer and has undergone a definite revival in the last few years with the publication of pioneering articles on the use of spin-orbit interactions in antiferromagnets. This paradigm shift offers possibilities for radically new concepts for spin manipulation in electronics. Central to these endeavors are the need for predictive models, relevant disruptive materials, and new experimental designs. This paper reviews the most prominent spintronic effects described based on theoretical and experimental analysis of antiferromagnetic materials. It also details some of the remaining bottlenecks and suggests possible avenues for future research. This review covers both spin-transfer-related effects, such as spin-transfer torque, spin penetration length, domain-wall motion, and "magnetization" dynamics, and spin-orbit related phenomena, such as (tunnel) anisotropic magnetoresistance, spin Hall, and inverse spin galvanic effects. Effects related to spin caloritronics, such as the spin Seebeck effect, are linked to the transport of magnons in antiferromagnets. The propagation of spin waves and spin superfluids in antiferromagnets is also covered.

Initial Results from Lunar Electromagnetic Sounding with ARTEMIS

NASA Astrophysics Data System (ADS)

Fuqua, H.; Fatemi, S.; Poppe, A. R.; Delory, G. T.; Grimm, R. E.; De Pater, I.

2016-12-01

Electromagnetic Sounding constrains conducting layers of the lunar interior by observing variations in the Interplanetary Magnetic Field. Here, we focus our analysis on the time domain transfer function method locating transient events observed by two magnetometers near the Moon. We analyze ARTEMIS and Apollo magnetometer data. This analysis assumes the induced field responds undisturbed in a vacuum. In actuality, the dynamic plasma environment interacts with the induced field. Our models indicate distortion but not confinement occurs in the nightside wake cavity. Moreover, within the deep wake, near-vacuum region, distortion of the induced dipole fields due to the interaction with the wake is minimal depending on the magnitude of the induced field, the geometry of the upstream fields, and the upstream plasma parameters such as particle densities, solar wind velocity, and temperatures. Our results indicate the assumption of a vacuum dipolar response is reasonable within this minimally disturbed zone. We then interpret the ATEMIS magnetic field signal through a geophysical forward model capturing the induced response based on prescribed electrical conductivity models. We demonstrate our forward model passes benchmarking analyses and solves the magnetic induction response for any input signal as well as any 2 or 3 dimensional conductivity profile. We locate data windows according to the following criteria: (1) probe locations such that the wake probe is within 500km altitude within the wake cavity and minimally disturbed zone, and the second probe is in the free streaming solar wind; (2) a transient event consisting of an abrupt change in the magnetic field occurs enabling the observation of induction; (3) cross correlation analysis reveals the magnetic field signals are well correlated between the two probes and distances observed. Here we present initial ARTEMIS results providing further insight into the lunar interior structure. This method and modeling results are applicable to any airless body with a conducting interior, interacting directly with the solar wind in the absence of a parent body magnetic field as well as any two point magnetometer constellation.

Analysis of decoherence mechanisms in a single-atom quantum memory

NASA Astrophysics Data System (ADS)

Koerber, Matthias; Langenfeld, Stefan; Morin, Olivier; Neuzner, Andreas; Ritter, Stephan; Rempe, Gerhard

2017-04-01

While photons are ideal for the transmission of quantum information, they require dedicated memories for long-term storage. The challenge for such a photonic quantum memory is the combination of an efficient light-matter interface with a low-decoherence encoding. To increase the time before the quantum information is lost, a thorough analysis of the relevant decoherence mechanisms is indispensable. Our optical quantum memory consists of a single rubidium atom trapped in a two dimensional optical lattice in a high-finesse Fabry-Perot-type optical resonator. The qubit is initially stored in a superposition of Zeeman states, making magnetic field fluctuations the dominant source of decoherence. The impact to this type of noise is greatly reduced by transferring the qubit into a subspace less susceptible to magnetic field fluctuations. In this configuration, the achievable coherence times are no longer limited by those fluctuations, but decoherence mechanisms induced by the trapping beams pose a new limit. We will discuss the origin and magnitude of the relevant effects and strategies for possible resolutions.

A replaceable microreactor for on-line protein digestion in a two-dimensional capillary electrophoresis system with tandem mass spectrometry detection

PubMed Central

Li, Yihan; Wojcik, Roza; Dovichi, Norman J.

2010-01-01

We describe a two-dimensional capillary electrophoresis system that incorporates a replaceable enzymatic microreactor for on-line protein digestion. In this system, trypsin is immobilized on magnetic beads. At the start of each experiment, old beads are flushed to waste and replaced with a fresh plug of beads, which is captured by a pair of magnets at the distal tip of the first capillary. For analysis, proteins are separated in the first capillary. A fraction is then parked in the reactor to create peptides. Digested peptides are periodically transferred to the second capillary for separation; a fresh protein fraction is simultaneously moved to the reactor for digestion. An electrospray interface is used to introduce peptides into a mass spectrometer for analysis. This procedure is repeated for several dozen fractions under computer control. The system was demonstrated by the separation and digestion of insulin chain b oxidized and β-casein as model proteins. PMID:21030030

Light Curve and Orbital Period Analysis of VX Lac

NASA Astrophysics Data System (ADS)

Yılmaz, M.; Nelson, R. H.; Şenavcı, H. V.; İzci, D.; Özavcı, İ.; Gümüş, D.

2017-04-01

In this study, we performed simultaneously light curve and radial velocity, and also period analyses of the eclipsing binary system VX Lac. Four color (BVRI) light curves of the system were analysed using the W-D code. The results imply that VX Lac is a classic Algol-type binary with a mass ratio of q=0.27, of which the less massive secondary component fills its Roche lobe. The orbital period behaviour of the system was analysed by assuming the light time effect (LITE) from a third body. The O-C analysis yielded a mass transfer rate of dM/dt=1.86×10-8M⊙yr-1 and the minimal mass of the third body to be M3=0.31M⊙. The residuals from mass transfer and the third body were also analysed because another cyclic variation is seen in O-C diagram. This periodic variation was examined under the hypotheses of stellar magnetic activity and fourth body.

Tuning the heat transfer medium and operating conditions in magnetic refrigeration

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

Ghahremani, Mohammadreza, E-mail: mghahrem@shepherd.edu; Dept. of Electrical and Computer Engineering, The George Washington University, Washington DC 20052; Aslani, Amir

A new experimental test bed has been designed, built, and tested to evaluate the effect of the system’s parameters on a reciprocating Active Magnetic Regenerator (AMR) near room temperature. Bulk gadolinium was used as the refrigerant, silicon oil as the heat transfer medium, and a magnetic field of 1.3 T was cycled. This study focuses on the methodology of single stage AMR operation conditions to get a high temperature span near room temperature. Herein, the main objective is not to report the absolute maximum attainable temperature span seen in an AMR system, but rather to find the system’s optimal operatingmore » conditions to reach that maximum span. The results of this research show that there is a optimal operating frequency, heat transfer fluid flow rate, flow duration, and displaced volume ratio in any AMR system. By optimizing these parameters in our AMR apparatus the temperature span between the hot and cold ends increased by 24%. The optimized values are system dependent and need to be determined and measured for any AMR system by following the procedures that are introduced in this research. It is expected that such optimization will permit the design of a more efficient magnetic refrigeration system.« less

Quantitative measures of walking and strength provide insight into brain corticospinal tract pathology in multiple sclerosis.

PubMed

Fritz, Nora E; Keller, Jennifer; Calabresi, Peter A; Zackowski, Kathleen M

2017-01-01

At least 85% of individuals with multiple sclerosis report walking dysfunction as their primary complaint. Walking and strength measures are common clinical measures to mark increasing disability or improvement with rehabilitation. Previous studies have shown an association between strength or walking ability and spinal cord MRI measures, and strength measures with brainstem corticospinal tract magnetization transfer ratio. However, the relationship between walking performance and brain corticospinal tract magnetization transfer imaging measures and the contribution of clinical measurements of walking and strength to the underlying integrity of the corticospinal tract has not been explored in multiple sclerosis. The objectives of this study were explore the relationship of quantitative measures of walking and strength to whole-brain corticospinal tract-specific MRI measures and to determine the contribution of quantitative measures of function in addition to basic clinical measures (age, gender, symptom duration and Expanded Disability Status Scale) to structural imaging measures of the corticospinal tract. We hypothesized that quantitative walking and strength measures would be related to brain corticospinal tract-specific measures, and would provide insight into the heterogeneity of brain pathology. Twenty-nine individuals with relapsing-remitting multiple sclerosis (mean(SD) age 48.7 (11.5) years; symptom duration 11.9(8.7); 17 females; median[range] Expanded Disability Status Scale 4.0 [1.0-6.5]) and 29 age and gender-matched healthy controls (age 50.8(11.6) years; 20 females) participated in clinical tests of strength and walking (Timed Up and Go, Timed 25 Foot Walk, Two Minute Walk Test ) as well as 3 T imaging including diffusion tensor imaging and magnetization transfer imaging. Individuals with multiple sclerosis were weaker (p = 0.0024) and walked slower (p = 0.0013) compared to controls. Quantitative measures of walking and strength were significantly related to corticospinal tract fractional anisotropy (r > 0.26; p < 0.04) and magnetization transfer ratio (r > 0.29; p < 0.03) measures. Although the Expanded Disability Status Scale was highly correlated with walking measures, it was not significantly related to either corticospinal tract fractional anisotropy or magnetization transfer ratio (p > 0.05). Walk velocity was a significant contributor to magnetization transfer ratio (p = 0.006) and fractional anisotropy (p = 0.011) in regression modeling that included both quantitative measures of function and basic clinical information. Quantitative measures of strength and walking are associated with brain corticospinal tract pathology. The addition of these quantitative measures to basic clinical information explains more of the variance in corticospinal tract fractional anisotropy and magnetization transfer ratio than the basic clinical information alone. Outcome measurement for multiple sclerosis clinical trials has been notoriously challenging; the use of quantitative measures of strength and walking along with tract-specific imaging methods may improve our ability to monitor disease change over time, with intervention, and provide needed guidelines for developing more effective targeted rehabilitation strategies.

A Simple Approach to Evaluate the Kinetic Rate Constant for ATP Synthesis in Resting Human Skeletal Muscle at 7 T

PubMed Central

Ren, Jimin; Sherry, A. Dean; Malloy, Craig R.

2015-01-01

Inversion transfer (IT) is a well-established technique with multiple attractive features for analysis of kinetics. However, its application in measurement of ATP synthesis rate in vivo has lagged behind the more common ST techniques. One well-recognized issue with IT is the complexity of data analysis in comparison to much simpler analysis by ST. This complexity arises, in part, because the γ-ATP spin is involved in multiple chemical reactions and magnetization exchanges, whereas Pi is involved in a single reaction, Pi → γ-ATP. By considering the reactions involving γ-ATP only as a lumped constant, the rate constant for the reaction of physiological interest, kPi→γATP, can be determined. Here, we present a new IT data analysis method to evaluate kPi→γATP using data collected from resting human skeletal muscle at 7T. The method is based on the basic Bloch-McConnell equation, which relates kPi→γATP with ṁPi, the rate of Pi magnetization change. The kPi→γATP value is accessed from ṁPi data by more familiar linear correlation approaches. For a group of human subjects (n = 15), the kPi→γATP value derived for resting calf muscle was 0.066 ± 0.017 s−1, in agreement with literature reported values. In this study we also explored possible time-saving strategies to speed up data acquisition for kPi→γATP evaluation using simulations. The analysis indicates that it is feasible to carry out a 31P inversion transfer experiment in ~10 minutes or shorter at 7T with reasonable outcome in kPi→γATP variance for measurement of ATP synthesis in resting human skeletal muscle. We believe that this new IT data analysis approach will facilitate the wide acceptance of IT to evaluate ATP synthesis rate in vivo. PMID:25943328

The transition from natural convection to thermomagnetic convection of a magnetic fluid in a non-uniform magnetic field

NASA Astrophysics Data System (ADS)

Szabo, Peter S. B.; Früh, Wolf-Gerrit

2018-02-01

Magnetic fluid flow and heat transfer by natural and thermomagnetic convection was studied numerically in a square enclosure. The aim was to investigate the transition from natural convection to thermomagnetic convection by exploring situations where buoyancy and the Kelvin body force would be opposing each other such that the magnetic effects would in some cases be the dominant factor throughout the domain and in other cases only in a part of the fluid. The numerical model coupled the solution of the magnetostatic field equation with the heat and fluid flow equations to simulate the fluid flow under a realistic magnetic field generated by a permanent magnet. The results suggest that the domain of influence over the flow field is largely aligned with the domain of dominance of the respective driving force. The result is that the transition from a single buoyancy-driven convection cell to a single thermomagnetically driven cell is via a two-cell structure and that the local effect on the flow field leads to a global effect on the heat transfer with a minimum of the Nusselt number in the transition region.

Time-Resolved Magnetic Field Effects Distinguish Loose Ion Pairs from Exciplexes

PubMed Central

2013-01-01

We describe the experimental investigation of time-resolved magnetic field effects in exciplex-forming organic donor–acceptor systems. In these systems, the photoexcited acceptor state is predominantly deactivated by bimolecular electron transfer reactions (yielding radical ion pairs) or by direct exciplex formation. The delayed fluorescence emitted by the exciplex is magnetosensitive if the reaction pathway involves loose radical ion pair states. This magnetic field effect results from the coherent interconversion between the electronic singlet and triplet radical ion pair states as described by the radical pair mechanism. By monitoring the changes in the exciplex luminescence intensity when applying external magnetic fields, details of the reaction mechanism can be elucidated. In this work we present results obtained with the fluorophore-quencher pair 9,10-dimethylanthracene/N,N-dimethylaniline (DMA) in solvents of systematically varied permittivity. A simple theoretical model is introduced that allows discriminating the initial state of quenching, viz., the loose ion pair and the exciplex, based on the time-resolved magnetic field effect. The approach is validated by applying it to the isotopologous fluorophore-quencher pairs pyrene/DMA and pyrene-d10/DMA. We detect that both the exciplex and the radical ion pair are formed during the initial quenching stage. Upon increasing the solvent polarity, the relative importance of the distant electron transfer quenching increases. However, even in comparably polar media, the exciplex pathway remains remarkably significant. We discuss our results in relation to recent findings on the involvement of exciplexes in photoinduced electron transfer reactions. PMID:24041160

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.

On-resonance variable delay multipulse scheme for imaging of fast-exchanging protons and semisolid macromolecules.

PubMed

Xu, Jiadi; Chan, Kannie W Y; Xu, Xiang; Yadav, Nirbhay; Liu, Guanshu; van Zijl, Peter C M

2017-02-01

To develop an on-resonance variable delay multipulse (VDMP) scheme to image magnetization transfer contrast (MTC) and the chemical exchange saturation transfer (CEST) contrast of total fast-exchanging protons (TFP) with exchange rate above approximately 1 kHz. A train of high power binomial pulses was applied at the water resonance. The interpulse delay, called mixing time, was varied to observe its effect on the water signal reduction, allowing separation and quantification of MTC and CEST contributions as a result of their different proton transfer rates. The fast-exchanging protons in CEST and MTC are labeled together with the short T 2 components in MTC and separated out using a variable mixing time. Phantom studies of selected metabolite solutions (glucose, glutamate, creatine, myo-inositol), bovine serum albumin (BSA), and hair conditioner show the capability of on-resonance VDMP to separate out exchangeable protons with exchange rates above 1 kHz. Quantitative MTC and TFP maps were acquired on healthy mouse brains using this method, showing strong gray/white matter contrast for the slowly transferring MTC protons, whereas the TFP map was more uniform across the brain but somewhat higher in gray matter. The new method provides a simple way of imaging fast-exchanging protons and MTC components with a slow transfer rate. Magn Reson Med 77:730-739, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

Precessional switching of a perpendicular anisotropy magneto-tunneling junction without a magnetic field

NASA Astrophysics Data System (ADS)

Drobitch, Justine L.; Ahsanul Abeed, Md; Bandyopadhyay, Supriyo

2017-10-01

We describe an approach to implement precessional switching of a perpendicular-magnetic-anisotropy magneto-tunneling-junction (p-MTJ) without using any magnetic field. The switching is accomplished with voltage-controlled-magnetic-anisotropy (VCMA), spin transfer torque (STT) and mechanical strain. The soft layer of the p-MTJ is magnetostrictive and the strain acts as an effective in-plane magnetic field around which the magnetization of the soft layer precesses to complete a flip. A two-terminal energy-efficient p-MTJ based memory cell, that is compatible with crossbar architecture and high cell density, is designed.

Control of Thermal Convection in Layered Fluids Using Magnetic fields

NASA Technical Reports Server (NTRS)

Ramachandran, N.; Leslie, F. W.

2003-01-01

Immiscible fluid layers are found in a host of applications ranging from materials processing, for example the use of encapsulants in float zone crystal growth technique and a buffer layer in industrial Czochralski growth of crystals to prevent Marangoni convection, to heat transfer phenomena in day-to-day processes like the presence of air pockets in heat exchangers. In the microgravity and space processing realm, the exploration of other planets requires the development of enabling technologies in several fronts. The reduction in the gravity level poses unique challenges for fluid handling and heat transfer applications. The present work investigates the efficacy of controlling thermal convective flow using magnetic fluids and magnetic fields. The setup is a two-layer immiscible liquids system with one of the fluids being a diluted ferrofluid (super paramagnetic nano particles dispersed in carrier fluid). Using an external magnetic field one can essentially dial in a volumetric force - gravity level, on the magnetic fluid and thereby affect the system thermo-fluid behavior. The paper will describe the experimental and numerical modeling approach to the problem and discuss results obtained to date.

A modular designed ultra-high-vacuum spin-polarized scanning tunneling microscope with controllable magnetic fields for investigating epitaxial thin films.

PubMed

Wang, Kangkang; Lin, Wenzhi; Chinchore, Abhijit V; Liu, Yinghao; Smith, Arthur R

2011-05-01

A room-temperature ultra-high-vacuum scanning tunneling microscope for in situ scanning freshly grown epitaxial films has been developed. The core unit of the microscope, which consists of critical components including scanner and approach motors, is modular designed. This enables easy adaptation of the same microscope units to new growth systems with different sample-transfer geometries. Furthermore the core unit is designed to be fully compatible with cryogenic temperatures and high magnetic field operations. A double-stage spring suspension system with eddy current damping has been implemented to achieve ≤5 pm z stability in a noisy environment and in the presence of an interconnected growth chamber. Both tips and samples can be quickly exchanged in situ; also a tunable external magnetic field can be introduced using a transferable permanent magnet shuttle. This allows spin-polarized tunneling with magnetically coated tips. The performance of this microscope is demonstrated by atomic-resolution imaging of surface reconstructions on wide band-gap GaN surfaces and spin-resolved experiments on antiferromagnetic Mn(3)N(2)(010) surfaces.

Analysis of ferrite nanoparticles in the flow of ferromagnetic nanofluid.

PubMed

Muhammad, Noor; Nadeem, Sohail; Mustafa, M T

2018-01-01

Theoretical analysis has been carried out to establish the heat transport phenomenon of six different ferromagnetic MnZnFe2O4-C2H6O2 (manganese zinc ferrite-ethylene glycol), NiZnFe2O4-C2H6O2 (Nickel zinc ferrite-ethylene glycol), Fe2O4-C2H6O2 (magnetite ferrite-ethylene glycol), NiZnFe2O4-H2O (Nickel zinc ferrite-water), MnZnFe2O4-H2O (manganese zinc ferrite-water), and Fe2O4-H2O (magnetite ferrite-water) nanofluids containing manganese zinc ferrite, Nickel zinc ferrite, and magnetite ferrite nanoparticles dispersed in a base fluid of ethylene glycol and water mixture. The performance of convective heat transfer is elevated in boundary layer flow region via nanoparticles. Magnetic dipole in presence of ferrites nanoparticles plays a vital role in controlling the thermal and momentum boundary layers. In perspective of this, the impacts of magnetic dipole on the nano boundary layer, steady, and laminar flow of incompressible ferromagnetic nanofluids are analyzed in the present study. Flow is caused by linear stretching of the surface. Fourier's law of heat conduction is used in the evaluation of heat flux. Impacts of emerging parameters on the magneto-thermomechanical coupling are analyzed numerically. Further, it is evident that Newtonian heating has increasing behavior on the rate of heat transfer in the boundary layer. Comparison with available results for specific cases show an excellent agreement.

A dual flip angle 3D bSSFP magnetization transfer-like method to differentiate between recent and old myocardial infarction.

PubMed

Germain, Philippe; El Ghannudi, Soraya; Labani, Aissam; Jeung, Mi Y; Gangi, Afshin; Ohlmann, Patrick; Roy, Catherine

2018-03-01

Magnetic resonance imaging (MRI) tissue signal is modulated by magnetization transfer (MT) phenomena, intrinsically induced by balanced steady-state free precession (bSSFP) imaging. To investigate the possible value of such a MT-like bSSFP approach in two clinical settings involving focal myocardial lesions highligthed by late gadolinium enhancement (LGE+): edema induced by recent myocardial infarction (MI) and fibrotic scar related to chronic infarction. Population: 48 LGE + patients were studied: 26 with recent MI, 22 with chronic MI. 20 LGE-normal subjects were considered the control group. Field strength/sequence: Navigator-based short axis 3D-bSSFP sequences with 20° and 90° excitation flip angles were acquired (1.5T). Pixel-wise normalized MT Ratio (nMTR) parametric images were calculated according to: nMTR = 100*(S 20 -S 90 *k)/S 20 , with S 20 and S 90 signal intensity in 20° and 90° flip angle images and k = Blood 20 /Blood 90 as a normalization ratio. Statistical tests: analysis of variance (ANOVA), receiver operating characteristic (ROC) analysis. Overall normal myocardial nMTR was 50.2 ± 3.6%. In recent MI, nMTR values were significantly reduced in LGE + regions (-22.3 ± 9.9%, P < 0.0001). In cases of chronic infarct, nMTR was significantly increased in LGE + regions (14.2 ± 11.4%, P < 0.0001). Comparison between observed results and theoretical values obtained with the Freeman-Hill formula showed that most variations observed in MI are related to MT effects instead of relaxation effects. In contrast to LGE imaging, which may show a similar hyperenhancement in recent and old infarctions, nMTR imaging demonstrates an opposite pattern: decreased values for recent infarction and increased values for old infarction, thus allowing to discriminate between these two clinical conditions without gadolinium injection. 3 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;47:798-808. © 2017 International Society for Magnetic Resonance in Medicine.

Variable magnetic field (VMF) effect on the heat transfer of a half-annulus cavity filled by Fe3O4-water nanofluid under constant heat flux

NASA Astrophysics Data System (ADS)

Hatami, M.; Zhou, J.; Geng, J.; Jing, D.

2018-04-01

In this paper, the effect of a variable magnetic field (VMF) on the natural convection heat transfer of Fe3O4-water nanofluid in a half-annulus cavity is studied by finite element method using FlexPDE commercial code. After deriving the governing equations and solving the problem by defined boundary conditions, the effects of three main parameters (Hartmann Number (Ha), nanoparticles volume fraction (φ) and Rayleigh number (Ra)) on the local and average Nusselt numbers of inner wall are investigated. As a main outcome, results confirm that in low Eckert numbers, increasing the Hartmann number make a decrease on the Nusselt number due to Lorentz force resulting from the presence of stronger magnetic field.

Dissipative structures induced by spin-transfer torques in nanopillars

NASA Astrophysics Data System (ADS)

León, Alejandro O.; Clerc, Marcel G.; Coulibaly, Saliya

2014-02-01

Macroscopic magnetic systems subjected to external forcing exhibit complex spatiotemporal behaviors as result of dissipative self-organization. Pattern formation from a uniform magnetization state, induced by the combination of a spin-polarized current and an external magnetic field, is studied for spin-transfer nano-oscillator devices. The system is described in the continuous limit by the Landau-Lifshitz-Gilbert equation. The bifurcation diagram of the quintessence parallel state, as a function of the external field and current, is elucidated. We have shown analytically that this state exhibits a spatial supercritical quintic bifurcation, which generates in two spatial dimensions a family of stationary stripes, squares, and superlattice states. Analytically, we have characterized their respective stabilities and bifurcations, which are controlled by a single dimensionless parameter. This scenario is confirmed numerically.

Probing the magnetic field structure in Sgr A* on Black Hole Horizon Scales with Polarized Radiative Transfer Simulations

NASA Astrophysics Data System (ADS)

Gold, Roman; McKinney, Jonathan; Johnson, Michael; Doeleman, Sheperd; Event Horizon Telescope Collaboration

2016-03-01

Accreting black holes (BHs) are at the core of relativistic astrophysics as messengers of the strong-field regime of General Relativity and prime targets of several observational campaigns, including imaging the black hole shadow in SagA* and M87 with the Event Horizon Telescope. I will present results from general-relativistic, polarized radiatiative transfer models for the inner accretion flow in Sgr A*. The models use time dependent, global GRMHD simulations of hot accretion flows including standard-and-normal-evolution (SANE) and magnetically arrested disks (MAD). I present comparisons of these synthetic data sets to the most recent observations with the Event Horizon Telescope and show how the data distinguishes the models and probes the magnetic field structure.

Regional patterns of grey matter atrophy and magnetisation transfer ratio abnormalities in multiple sclerosis clinical subgroups: a voxel-based analysis study.

PubMed

Mallik, Shahrukh; Muhlert, Nils; Samson, Rebecca S; Sethi, Varun; Wheeler-Kingshott, Claudia A M; Miller, David H; Chard, Declan T

2015-04-01

In multiple sclerosis (MS), demyelination and neuro-axonal loss occur in the brain grey matter (GM). We used magnetic resonance imaging (MRI) measures of GM magnetisation transfer ratio (MTR) and volume to assess the regional localisation of reduced MTR (reflecting demyelination) and atrophy (reflecting neuro-axonal loss) in relapsing-remitting MS (RRMS), secondary progressive MS (SPMS) and primary progressive MS (PPMS). A total of 98 people with MS (51 RRMS, 28 SPMS, 19 PPMS) and 29 controls had T1-weighted volumetric and magnetisation transfer scans. SPM8 was used to undertake voxel-based analysis (VBA) of GM tissue volumes and MTR. MS subgroups were compared with controls, adjusting for age and gender. A voxel-by-voxel basis correlation analysis between MTR and volume within each subject group was performed, using biological parametric mapping. MTR reduction was more extensive than atrophy. RRMS and SPMS patients showed proportionately more atrophy in the deep GM. SPMS and PPMS patients showed proportionately greater cortical MTR reduction. RRMS patients demonstrated the most correlation of MTR reduction and atrophy in deep GM. In SPMS and PPMS patients, there was less extensive correlation. These results suggest that in the deep GM of RRMS patients, demyelination and neuro-axonal loss may be linked, while in SPMS and PPMS patients, neuro-axonal loss and demyelination may occur mostly independently. © The Author(s), 2014.

High-throughput microcoil NMR of compound libraries using zero-dispersion segmented flow analysis.

PubMed

Kautz, Roger A; Goetzinger, Wolfgang K; Karger, Barry L

2005-01-01

An automated system for loading samples into a microcoil NMR probe has been developed using segmented flow analysis. This approach enhanced 2-fold the throughput of the published direct injection and flow injection methods, improved sample utilization 3-fold, and was applicable to high-field NMR facilities with long transfer lines between the sample handler and NMR magnet. Sample volumes of 2 microL (10-30 mM, approximately 10 microg) were drawn from a 96-well microtiter plate by a sample handler, then pumped to a 0.5-microL microcoil NMR probe as a queue of closely spaced "plugs" separated by an immiscible fluorocarbon fluid. Individual sample plugs were detected by their NMR signal and automatically positioned for stopped-flow data acquisition. The sample in the NMR coil could be changed within 35 s by advancing the queue. The fluorocarbon liquid wetted the wall of the Teflon transfer line, preventing the DMSO samples from contacting the capillary wall and thus reducing sample losses to below 5% after passage through the 3-m transfer line. With a wash plug of solvent between samples, sample-to-sample carryover was <1%. Significantly, the samples did not disperse into the carrier liquid during loading or during acquisitions of several days for trace analysis. For automated high-throughput analysis using a 16-second acquisition time, spectra were recorded at a rate of 1.5 min/sample and total deuterated solvent consumption was <0.5 mL (1 US dollar) per 96-well plate.

Energy Transfer and Dual Cascade in Kinetic Magnetized Plasma Turbulence

NASA Astrophysics Data System (ADS)

Plunk, G. G.; Tatsuno, T.

2011-04-01

The question of how nonlinear interactions redistribute the energy of fluctuations across available degrees of freedom is of fundamental importance in the study of turbulence and transport in magnetized weakly collisional plasmas, ranging from space settings to fusion devices. In this Letter, we present a theory for the dual cascade found in such plasmas, which predicts a range of new behavior that distinguishes this cascade from that of neutral fluid turbulence. These phenomena are explained in terms of the constrained nature of spectral transfer in nonlinear gyrokinetics. Accompanying this theory are the first observations of these phenomena, obtained via direct numerical simulations using the gyrokinetic code AstroGK. The basic mechanisms that are found provide a framework for understanding the turbulent energy transfer that couples scales both locally and nonlocally.

Ion Acceleration by Flux Transfer Events in the Terrestrial Magnetosheath

NASA Astrophysics Data System (ADS)

Jarvinen, R.; Vainio, R.; Palmroth, M.; Juusola, L.; Hoilijoki, S.; Pfau-Kempf, Y.; Ganse, U.; Turc, L.; von Alfthan, S.

2018-02-01

We report ion acceleration by flux transfer events in the terrestrial magnetosheath in a global two-dimensional hybrid-Vlasov polar plane simulation of Earth's solar wind interaction. In the model we find that propagating flux transfer events created in magnetic reconnection at the dayside magnetopause drive fast-mode bow waves in the magnetosheath, which accelerate ions in the shocked solar wind flow. The acceleration at the bow waves is caused by a shock drift-like acceleration process under stationary solar wind and interplanetary magnetic field upstream conditions. Thus, the energization is not externally driven but results from plasma dynamics within the magnetosheath. Energetic proton populations reach the energy of 30 keV, and their velocity distributions resemble time-energy dispersive ion injections observed by the Cluster spacecraft in the magnetosheath.

Coupled Simulation of Thermomagnetic Energy Generation Based on NiMnGa Heusler Alloy Films

NASA Astrophysics Data System (ADS)

Kohl, Manfred; Gueltig, Marcel; Wendler, Frank

2018-03-01

This paper presents a simulation model for the coupled dynamic properties of thermomagnetic generators based on magnetic shape memory alloy (MSMA) films. MSMA thermomagnetic generators exploit the large abrupt temperature-induced change of magnetization at the first- or second-order magnetic transition as well as the short heat transfer times due to the large surface-to-volume ratio of films. These properties allow for resonant self-actuation of freely movable MSMA cantilever devices showing thermomagnetic duty cycles in the order of 10 ms duration, which matches with the period of oscillatory motion. We present a numerical analysis of the energy conversion processes to understand the effect of design parameters on efficiency and power output. A lumped element model is chosen to describe the time dependence of MSMA cantilever deflection and of temperature profiles as well as the magnitude and phase dependency of magnetization change. The simulation model quantitatively describes experimentally observed oscillatory motion and resulting power output in the order of 100 mW cm-3. Furthermore, it predicts a power output of 490 mW cm-3 for advanced film materials with temperature-dependent change of magnetization Δ M/Δ T of 4 A m2 (kg K)-1, which challenges state-of-the-art thermoelectric devices.

Coupled Simulation of Thermomagnetic Energy Generation Based on NiMnGa Heusler Alloy Films

NASA Astrophysics Data System (ADS)

Kohl, Manfred; Gueltig, Marcel; Wendler, Frank

2018-01-01

This paper presents a simulation model for the coupled dynamic properties of thermomagnetic generators based on magnetic shape memory alloy (MSMA) films. MSMA thermomagnetic generators exploit the large abrupt temperature-induced change of magnetization at the first- or second-order magnetic transition as well as the short heat transfer times due to the large surface-to-volume ratio of films. These properties allow for resonant self-actuation of freely movable MSMA cantilever devices showing thermomagnetic duty cycles in the order of 10 ms duration, which matches with the period of oscillatory motion. We present a numerical analysis of the energy conversion processes to understand the effect of design parameters on efficiency and power output. A lumped element model is chosen to describe the time dependence of MSMA cantilever deflection and of temperature profiles as well as the magnitude and phase dependency of magnetization change. The simulation model quantitatively describes experimentally observed oscillatory motion and resulting power output in the order of 100 mW cm-3. Furthermore, it predicts a power output of 490 mW cm-3 for advanced film materials with temperature-dependent change of magnetization ΔM/ΔT of 4 A m2 (kg K)-1, which challenges state-of-the-art thermoelectric devices.

Osmotically shrunken LIPOCEST agents: an innovative class of magnetic resonance imaging contrast media based on chemical exchange saturation transfer.

PubMed

Terreno, Enzo; Delli Castelli, Daniela; Violante, Elisabetta; Sanders, Honorius M H F; Sommerdijk, Nico A J M; Aime, Silvio

2009-01-01

The peculiar properties of osmotically shrunken liposomes acting as magnetic resonance imaging-chemical exchange saturation transfer (MRI-CEST) contrast agents have been investigated. Attention has been primarily devoted to assessing the contribution arising from encapsulated and incorporated paramagnetic lanthanide(III)-based shift reagents in determining the chemical shift of the intraliposomal water protons, which is a relevant factor for generating the CEST contrast. It is demonstrated that a highly shifted resonance for the encapsulated water can be attained by increasing the percentage of the amphiphilic shift reagent incorporated in the liposome bilayer. It is also demonstrated that the shift contribution arising from the bulk magnetic susceptibility can be optimized through the modulation of the osmotic shrinkage. In terms of sensitivity, it is shown that the saturation transfer efficiency can be significantly improved by increasing the size of the vesicle, thus allowing a high number of exchangeable protons to be saturated. In addition, the role played by the intensity of the saturating radiofrequency field has also been highlighted.

Abnormal Injury Response in Spontaneous Mild Ventriculomegaly Wistar Rat Brains: A Pathological Correlation Study of Diffusion Tensor and Magnetization Transfer Imaging in Mild Traumatic Brain Injury.

PubMed

Tu, Tsang-Wei; Lescher, Jacob D; Williams, Rashida A; Jikaria, Neekita; Turtzo, L Christine; Frank, Joseph A

2017-01-01

Spontaneous mild ventriculomegaly (MVM) was previously reported in ∼43% of Wistar rats in association with vascular anomalies without phenotypic manifestation. This mild traumatic brain injury (TBI) weight drop model study investigates whether MVM rats (n = 15) have different injury responses that could inadvertently complicate the interpretation of imaging studies compared with normal rats (n = 15). Quantitative MRI, including diffusion tensor imaging (DTI) and magnetization transfer imaging (MTI), and immunohistochemistry (IHC) analysis were used to examine the injury pattern up to 8 days post-injury in MVM and normal rats. Prior to injury, the MVM brain showed significant higher mean diffusivity, axial diffusivity, and radial diffusivity, and lower fractional anisotropy (FA) and magnetization transfer ratio (MTR) in the corpus callosum than normal brain (p < 0.05). Following TBI, normal brains exhibited significant decreases of FA in the corpus callosum, whereas MVM brains demonstrated insignificant changes in FA, suggesting less axonal injury. At day 8 after mild TBI, MTR of the normal brains significantly decreased whereas the MTR of the MVM brains significantly increased. IHC staining substantiated the MRI findings, demonstrating limited axonal injury with significant increase of microgliosis and astrogliosis in MVM brain compared with normal animals. The radiological-pathological correlation data showed that both DTI and MTI were sensitive in detecting mild diffuse brain injury, although DTI metrics were more specific in correlating with histologically identified pathologies. Compared with the higher correlation levels reflecting axonal injury pathology in the normal rat mild TBI, the DTI and MTR metrics were more affected by the increased inflammation in the MVM rat mild TBI. Because MVM Wistar rats appear normal, there was a need to screen rats prior to TBI research to rule out the presence of ventriculomegaly, which may complicate the interpretation of imaging and IHC observations.

Abnormal Injury Response in Spontaneous Mild Ventriculomegaly Wistar Rat Brains: A Pathological Correlation Study of Diffusion Tensor and Magnetization Transfer Imaging in Mild Traumatic Brain Injury

PubMed Central

Lescher, Jacob D.; Williams, Rashida A.; Jikaria, Neekita; Turtzo, L. Christine; Frank, Joseph A.

2017-01-01

Abstract Spontaneous mild ventriculomegaly (MVM) was previously reported in ∼43% of Wistar rats in association with vascular anomalies without phenotypic manifestation. This mild traumatic brain injury (TBI) weight drop model study investigates whether MVM rats (n = 15) have different injury responses that could inadvertently complicate the interpretation of imaging studies compared with normal rats (n = 15). Quantitative MRI, including diffusion tensor imaging (DTI) and magnetization transfer imaging (MTI), and immunohistochemistry (IHC) analysis were used to examine the injury pattern up to 8 days post-injury in MVM and normal rats. Prior to injury, the MVM brain showed significant higher mean diffusivity, axial diffusivity, and radial diffusivity, and lower fractional anisotropy (FA) and magnetization transfer ratio (MTR) in the corpus callosum than normal brain (p < 0.05). Following TBI, normal brains exhibited significant decreases of FA in the corpus callosum, whereas MVM brains demonstrated insignificant changes in FA, suggesting less axonal injury. At day 8 after mild TBI, MTR of the normal brains significantly decreased whereas the MTR of the MVM brains significantly increased. IHC staining substantiated the MRI findings, demonstrating limited axonal injury with significant increase of microgliosis and astrogliosis in MVM brain compared with normal animals. The radiological-pathological correlation data showed that both DTI and MTI were sensitive in detecting mild diffuse brain injury, although DTI metrics were more specific in correlating with histologically identified pathologies. Compared with the higher correlation levels reflecting axonal injury pathology in the normal rat mild TBI, the DTI and MTR metrics were more affected by the increased inflammation in the MVM rat mild TBI. Because MVM Wistar rats appear normal, there was a need to screen rats prior to TBI research to rule out the presence of ventriculomegaly, which may complicate the interpretation of imaging and IHC observations. PMID:26905805

Detection of rabbit IgG by using functional magnetic particles and an enzyme-conjugated antibody with a homemade magnetic microplate.

PubMed

Tsai, Hweiyan; Lu, Yi-Hsuan; Liao, Huan-Xuan; Wu, Shih-Wei; Yu, Feng-Yih; Fuh, Chwan Bor

2015-01-01

The enzyme-linked immunosorbent assay (ELISA) has been used for diagnosing medical and plant pathologies. In addition, it is used for quality-control evaluations in various industries. The ELISA is the simplest method for obtaining excellent results; however, it is time consuming because the immunoreagents interact only on the contact surfaces. Antibody-labeled magnetic particles can be dispersed in a solution to yield a pseudohomogeneous reaction with antigens which improved the efficiency of immunoreaction, and can be easily separated from the unreactive substances by applying a magnetic force. We used a homemade magnetic microplate, functional magnetic particles (MPs) and enzyme-labeled secondary antibody to perform the sandwich ELISA successfully. Using antibody-labeled MPs enabled reducing the analysis time to one-third of that required in using a conventional ELISA. The secondary antibody conjugated with horseradish peroxidase (HRP) was affinity-bound to the analyte (IgG in this study). The calibration curve was established according to the measured absorbance of the 3, 3', 5, 5'-tetramethybezidine-HRP reaction products versus the concentrations of standard IgG. The linear range of IgG detection was 114 ng/mL-3.5 ng/mL. The limit of detection (LOD) of IgG was 3.4 ng/mL. The recovery and coefficient of variation were 100% (±7%) and 116% (±4%) for the spiked concentrations of 56.8 ng/mL and 14.2 ng/mL, respectively. Pseudohomogeneous reactions can be performed using functional MPs and a magnetic microplate. Using antibody-labeled MPs, the analysis time can be reduced to one-third of that required in using a conventional ELISA. The substrate-enzyme reaction products can be easily transferred to another microplate, and their absorbance can be measured without interference by light scattering caused by magnetic microbeads. This method demonstrates great potential for detecting other biomarkers and in biochemical applications. Graphical AbstractA magnetic ELISA with convenient magnetic microplate.

Controlling Emergent Ferromagnetism at Complex Oxide Interfaces

NASA Astrophysics Data System (ADS)

Grutter, Alexander

The emergence of complex magnetic ground states at ABO3 perovskite heterostructure interfaces is among the most promising routes towards highly tunable nanoscale materials for spintronic device applications. Despite recent progress, isolating and controlling the underlying mechanisms behind these emergent properties remains a highly challenging materials physics problems. In particular, generating and tuning ferromagnetism localized at the interface of two non-ferromagnetic materials is of fundamental and technological interest. An ideal model system in which to study such effects is the CaRuO3/CaMnO3 interface, where the constituent materials are paramagnetic and antiferromagnetic in the bulk, respectively. Due to small fractional charge transfer to the CaMnO3 (0.07 e-/Mn) from the CaRuO3, the interfacial Mn ions are in a canted antiferromagnetic state. The delicate balance between antiferromagnetic superexchange and ferromagnetic double exchange results in a magnetic ground state which is extremely sensitive to perturbations. We exploit this sensitivity to achieve control of the magnetic interface, tipping the balance between ferromagnetic and antiferromagnetic interactions through octahedral connectivity modification. Such connectivity effects are typically tightly confined to interfaces, but by targeting a purely interfacial emergent magnetic system, we achieve drastic alterations to the magnetic ground state. These results demonstrate the extreme sensitivity of the magnetic state to the magnitude of the charge transfer, suggesting the potential for direct electric field control. We achieve such electric field control through direct back gating of a CaRuO3/CaMnO3 bilayer. Thus, the CaRuO3/CaMnO3 system provides new insight into how charge transfer, interfacial symmetry, and electric fields may be used to control ferromagnetism at the atomic scale.

Emergent magnetism at transition-metal–nanocarbon interfaces

PubMed Central

Al Ma’Mari, Fatma; Rogers, Matthew; Alghamdi, Shoug; Moorsom, Timothy; Lee, Stephen; Prokscha, Thomas; Luetkens, Hubertus; Valvidares, Manuel; Flokstra, Machiel; Stewart, Rhea; Ali, Mannan; Burnell, Gavin; Hickey, B. J.

2017-01-01

Charge transfer at metallo–molecular interfaces may be used to design multifunctional hybrids with an emergent magnetization that may offer an eco-friendly and tunable alternative to conventional magnets and devices. Here, we investigate the origin of the magnetism arising at these interfaces by using different techniques to probe 3d and 5d metal films such as Sc, Mn, Cu, and Pt in contact with fullerenes and rf-sputtered carbon layers. These systems exhibit small anisotropy and coercivity together with a high Curie point. Low-energy muon spin spectroscopy in Cu and Sc–C60 multilayers show a quick spin depolarization and oscillations attributed to nonuniform local magnetic fields close to the metallo–carbon interface. The hybridization state of the carbon layers plays a crucial role, and we observe an increased magnetization as sp3 orbitals are annealed into sp2−π graphitic states in sputtered carbon/copper multilayers. X-ray magnetic circular dichroism (XMCD) measurements at the carbon K edge of C60 layers in contact with Sc films show spin polarization in the lowest unoccupied molecular orbital (LUMO) and higher π*-molecular levels, whereas the dichroism in the σ*-resonances is small or nonexistent. These results support the idea of an interaction mediated via charge transfer from the metal and dz–π hybridization. Thin-film carbon-based magnets may allow for the manipulation of spin ordering at metallic surfaces using electrooptical signals, with potential applications in computing, sensors, and other multifunctional magnetic devices. PMID:28507160

Zn induced in-gap electronic states in La214 probed by uniform magnetic susceptibility: relevance to the suppression of superconducting T c

NASA Astrophysics Data System (ADS)

Islam, R. S.; Naqib, S. H.

2018-02-01

Substitution of isovalent non-magnetic defects, such as Zn, in the CuO2 plane strongly modifies the magnetic properties of strongly electron correlated hole doped cuprate superconductors. The reason for enhanced uniform magnetic susceptibility, χ, in Zn substituted cuprates is debatable. Generally the defect induced magnetic behavior has been analyzed mainly in terms of two somewhat contrasting scenarios. The first one is due to independent localized moments appearing in the vicinity of Zn arising because of the strong electronic/magnetic correlations present in the host compound and the second one is due to transfer of quasiparticle (QP) spectral weight and creation of weakly localized low-energy electronic states associated with each Zn atom in place of an in-plane Cu. If the second scenario is correct, one should expect a direct correspondence between Zn induced suppression of the superconducting transition temperature, T c, and the extent of the enhanced magnetic susceptibility at low temperature. In this case, the low-T enhancement of χ would be due to weakly localized QP states at low energy and these electronic states will be precluded from taking part in Cooper pairing. We explore this second possibility by analyzing the χ(T) data for La2-x Sr x Cu1-y Zn y O4 with different hole contents, p (=x), and Zn concentrations (y) in this paper. The results of our analysis support this scenario.

Decorrelation dynamics and spectra in drift-Alfven turbulence

NASA Astrophysics Data System (ADS)

Fernandez Garcia, Eduardo

Motivated by the inability of one-fluid magnetohydrodynamics (MHD) to explain key turbulence characteristics in systems ranging from the solar wind and interstellar medium to fusion devices like the reversed field pinch, this thesis studies magnetic turbulence using a drift-Alfven model that extends MHD by including electron density dynamics. Electron effects play a significant role in the dynamics by changing the structure of turbulent decorrelation in the Alfvenic regime (where fast Alfvenic propagation provides the fastest decorrelation of the system): besides the familiar counter-propagating Alfvenic branches of MHD, an additional branch tied to the diamagnetic and eddy-turn- over rates enters in the turbulent response. This kinematic branch gives hydrodynamic features to turbulence that is otherwise strongly magnetic. Magnetic features are observed in the RMS frequency, energy partitions, cross-field energy transfer and in the turbulent response, whereas hydrodynamic features appear in the average frequency, self-field transfer, turbulent response and finally the wavenumber spectrum. These features are studied via renormalized closure theory and numerical simulation. The closure calculation naturally incorporates the eigenmode structure of the turbulent response in specifying spectral energy balance equations for the magnetic, kinetic and internal (density) energies. Alfvenic terms proportional to cross correlations and involved in cross field transfer compete with eddy-turn-over, self transfer, auto-correlation terms. In the steady state, the kinematic terms dominate the energy balances and yield a 5/3 Kolmogorov spectrum (as observed in the interstellar medium) for the three field energies in the strong turbulence, long wavelength limit. Alfvenic terms establish equipartition of kinetic and magnetic energies. In the limit where wavelengths are short compared to the gyroradius, the Alfvenic terms equipartition the internal and magnetic energies resulting in a steep (-2) spectrum fall-off for those energies while the largely uncoupled kinetic modes still obey a 5/3 law. From the numerical simulations, the response function of drift-Alfven turbulence is measured. Here, a statistical ensemble is constructed from small perturbations of the turbulent amplitudes at fixed wavenumber. The decorrelation structure born out of the eigenmode calculation is verified in the numerical measurement.

Comptonization in Ultra-Strong Magnetic Fields: Numerical Solution to the Radiative Transfer Problem

NASA Technical Reports Server (NTRS)

Ceccobello, C.; Farinelli, R.; Titarchuk, L.

2014-01-01

We consider the radiative transfer problem in a plane-parallel slab of thermal electrons in the presence of an ultra-strong magnetic field (B approximately greater than B(sub c) approx. = 4.4 x 10(exp 13) G). Under these conditions, the magnetic field behaves like a birefringent medium for the propagating photons, and the electromagnetic radiation is split into two polarization modes, ordinary and extraordinary, that have different cross-sections. When the optical depth of the slab is large, the ordinary-mode photons are strongly Comptonized and the photon field is dominated by an isotropic component. Aims. The radiative transfer problem in strong magnetic fields presents many mathematical issues and analytical or numerical solutions can be obtained only under some given approximations. We investigate this problem both from the analytical and numerical point of view, provide a test of the previous analytical estimates, and extend these results with numerical techniques. Methods. We consider here the case of low temperature black-body photons propagating in a sub-relativistic temperature plasma, which allows us to deal with a semi-Fokker-Planck approximation of the radiative transfer equation. The problem can then be treated with the variable separation method, and we use a numerical technique to find solutions to the eigenvalue problem in the case of a singular kernel of the space operator. The singularity of the space kernel is the result of the strong angular dependence of the electron cross-section in the presence of a strong magnetic field. Results. We provide the numerical solution obtained for eigenvalues and eigenfunctions of the space operator, and the emerging Comptonization spectrum of the ordinary-mode photons for any eigenvalue of the space equation and for energies significantly lesser than the cyclotron energy, which is on the order of MeV for the intensity of the magnetic field here considered. Conclusions. We derived the specific intensity of the ordinary photons, under the approximation of large angle and large optical depth. These assumptions allow the equation to be treated using a diffusion-like approximation.

Redistribution of resonance radiation. II - The effect of magnetic fields.

NASA Technical Reports Server (NTRS)

Omont, A.; Cooper, J.; Smith, E. W.

1973-01-01

Previously obtained results for scattering of radiation in the presence of collisions are restated in a density matrix formalism which employs an irreducible-tensor description of the radiation field. This formalism is particularly useful for problems associated with radiative transfer theory. The redistribution is then extended to include the effect of a weak magnetic field. By averaging over a finite bandwidth which is on the order of the Doppler width, simplified expressions of physical significance for the scattering in the Doppler core and the Lorentz wings are obtained. Expressions are also obtained for the corresponding source function of radiative transfer theory.

Advances in cryogenic engineering. Vols. 37A & 37B - Proceedings of the 1991 Cryogenic Engineering Conference, Univ. of Alabama, Huntsville, June 11-14, 1991

NASA Technical Reports Server (NTRS)

Fast, Ronald W. (Editor)

1991-01-01

The present volume on advances in cryogenic engineering discusses heat and mass transfer in helium, heat transfer in cryogenic fluids, thermoacoustic oscillations, and insulation. Attention is given to applications of superconductivity with reference to magnetic stability and coil protection, cryogenic techniques, and refrigeration for electronics and superconducting systems. Topics addressed include compressors, expanders, and pumps for liquid helium, magnetic refrigerators, pulse tube refrigerators, and cryocoolers. Also examined are properties of cryogenic fluids, cryogenic applications in transportion and space science and technology, and cryogenic instrumentation.

Synthesis, photophysical analysis, and in vitro cytotoxicity assessment of the multifunctional (magnetic and luminescent) core@shell nanomaterial based on lanthanide-doped orthovanadates

NASA Astrophysics Data System (ADS)

Szczeszak, Agata; Ekner-Grzyb, Anna; Runowski, Marcin; Mrówczyńska, Lucyna; Grzyb, Tomasz; Lis, Stefan

2015-03-01

Rare earths orthovanadates (REVO4) doped with luminescent lanthanide ions (Ln3+) play an important role as promising light-emitting materials. Gadolinium orthovanadate exhibits strong absorption of ultraviolet radiation and as a matrix doped with Eu3+ ions is well known for its efficient and intense red emission, induced by energy transfer from the VO4 3- groups to Eu3+ ions. In the presented study, Fe3O4@SiO2@GdVO4:Eu3+ 5 % nanomaterial was investigated. The core@shell structures demonstrate attractive properties, such as higher thermal stability, enhanced water solubility, increased optical response, higher luminescence, longer decay times, and magnetic properties. Silica coating may protect nanocrystals from the surrounding environment. Therefore, such silica-covered nanoparticles (NPs) are successfully utilized in biomedical research. Multifunctional magnetic nanophosphors are very interesting due to their potential biomedical applications such as magnetic resonance imaging, hyperthermic treatment, and drug delivery. Therefore, the aim of our study was to investigate photophysical, chemical, and biological properties of multifunctional REVO4 doped with Ln3+. Moreover, the studied NPs did not affect erythrocyte sedimentation rate, cell membrane permeability, and morphology of human red blood cells.

Strange Quark Magnetic Moment of the Nucleon at the Physical Point.

PubMed

Sufian, Raza Sabbir; Yang, Yi-Bo; Alexandru, Andrei; Draper, Terrence; Liang, Jian; Liu, Keh-Fei

2017-01-27

We report a lattice QCD calculation of the strange quark contribution to the nucleon's magnetic moment and charge radius. This analysis presents the first direct determination of strange electromagnetic form factors including at the physical pion mass. We perform a model-independent extraction of the strange magnetic moment and the strange charge radius from the electromagnetic form factors in the momentum transfer range of 0.051  GeV^{2}≲Q^{2}≲1.31  GeV^{2}. The finite lattice spacing and finite volume corrections are included in a global fit with 24 valence quark masses on four lattices with different lattice spacings, different volumes, and four sea quark masses including one at the physical pion mass. We obtain the strange magnetic moment G_{M}^{s}(0)=-0.064(14)(09)μ_{N}. The four-sigma precision in statistics is achieved partly due to low-mode averaging of the quark loop and low-mode substitution to improve the statistics of the nucleon propagator. We also obtain the strange charge radius ⟨r_{s}^{2}⟩_{E}=-0.0043(16)(14)  fm^{2}.

Structural and magnetic properties of yttrium and lanthanum-doped Ni-Co and Ni-Co-Zn spinel ferrites

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

Stergiou, Charalampos, E-mail: stergiou@cperi.certh.gr; Litsardakis, George, E-mail: lits@eng.auth.gr

2014-11-05

Rare earth doping of Co-rich spinel ferrites is investigated through the preparation of two groups of polycrystalline Ni-Co and Ni-Co-Zn ferrites, where Fe is partly substituted by Y and La. The characterization of the sintered ferrites by means of X-ray powder diffraction and Rietveld profile analysis, indicates the subtle expansion of the spinel unit cell and the cation redistribution in the doped ferrites in order to accommodate the incorporation of Y and La in the lattice. The impurity traces, detected only in the Ni-Co-Zn group, is ascribed to the Zn population in the tetrahedral A-sites impeding the cation transfer. Moreover,more » the examined microstructure of the doped Ni-Co samples comprises enlarged and more homogeneous grains, whereas grain growth is moderated in the doped Ni-Co-Zn ferrites. The discussed characteristics of the crystal and magnetic structure along with the morphological aspects define the impact of Y and La doping on the static magnetic properties of Ni-Co and Ni-Co-Zn ferrites, saturation magnetization MS and coercivity HC, which were extracted from the respective hysteresis loops.« less

Phased Array Excitations For Efficient Near Field Wireless Power Transmission

DTIC Science & Technology

2016-09-01

relating to the improvement of wireless - power transfer (WPT) in the near field. Improvement to power reception in the near field requires that...improvement of wireless - power transfer (WPT) in the near field. Improvement to power reception in the near field requires that excitation correction methods...transverse electromagnetic TM transverse magnetic UAV unmanned aerial vehicles VSWR voltage standing wave ratio WPT wireless power transfer XML

Controlled enhancement of spin-current emission by three-magnon splitting.

PubMed

Kurebayashi, Hidekazu; Dzyapko, Oleksandr; Demidov, Vladislav E; Fang, Dong; Ferguson, A J; Demokritov, Sergej O

2011-07-03

Spin currents--the flow of angular momentum without the simultaneous transfer of electrical charge--play an enabling role in the field of spintronics. Unlike the charge current, the spin current is not a conservative quantity within the conduction carrier system. This is due to the presence of the spin-orbit interaction that couples the spin of the carriers to angular momentum in the lattice. This spin-lattice coupling acts also as the source of damping in magnetic materials, where the precessing magnetic moment experiences a torque towards its equilibrium orientation; the excess angular momentum in the magnetic subsystem flows into the lattice. Here we show that this flow can be reversed by the three-magnon splitting process and experimentally achieve the enhancement of the spin current emitted by the interacting spin waves. This mechanism triggers angular momentum transfer from the lattice to the magnetic subsystem and modifies the spin-current emission. The finding illustrates the importance of magnon-magnon interactions for developing spin-current based electronics.

Multiscale modeling of current-induced switching in magnetic tunnel junctions using ab initio spin-transfer torques

NASA Astrophysics Data System (ADS)

Ellis, Matthew O. A.; Stamenova, Maria; Sanvito, Stefano

2017-12-01

There exists a significant challenge in developing efficient magnetic tunnel junctions with low write currents for nonvolatile memory devices. With the aim of analyzing potential materials for efficient current-operated magnetic junctions, we have developed a multi-scale methodology combining ab initio calculations of spin-transfer torque with large-scale time-dependent simulations using atomistic spin dynamics. In this work we introduce our multiscale approach, including a discussion on a number of possible schemes for mapping the ab initio spin torques into the spin dynamics. We demonstrate this methodology on a prototype Co/MgO/Co/Cu tunnel junction showing that the spin torques are primarily acting at the interface between the Co free layer and MgO. Using spin dynamics we then calculate the reversal switching times for the free layer and the critical voltages and currents required for such switching. Our work provides an efficient, accurate, and versatile framework for designing novel current-operated magnetic devices, where all the materials details are taken into account.

Local light-induced magnetization using nanodots and chiral molecules.

PubMed

Dor, Oren Ben; Morali, Noam; Yochelis, Shira; Baczewski, Lech Tomasz; Paltiel, Yossi

2014-11-12

With the increasing demand for miniaturization, nanostructures are likely to become the primary components of future integrated circuits. Different approaches are being pursued toward achieving efficient electronics, among which are spin electronics devices (spintronics). In principle, the application of spintronics should result in reducing the power consumption of electronic devices. Recently a new, promising, effective approach for spintronics has emerged, using spin selectivity in electron transport through chiral molecules. In this work, using chiral molecules and nanocrystals, we achieve local spin-based magnetization generated optically at ambient temperatures. Through the chiral layer, a spin torque can be transferred without permanent charge transfer from the nanocrystals to a thin ferromagnetic layer, creating local perpendicular magnetization. We used Hall sensor configuration and atomic force microscopy (AFM) to measure the induced local magnetization. At low temperatures, anomalous spin Hall effects were measured using a thin Ni layer. The results may lead to optically controlled spintronics logic devices that will enable low power consumption, high density, and cheap fabrication.

Spin and Magnetism: Two Transfer Matrix Formulations of a Classical Heisenberg Ring in a Magnetic Field.

DTIC Science & Technology

1998-06-01

determination of the partition function could be attempted. According to Gatteschi et al, however, [Ref. 15] when commenting on the quantum mechanical...1995 15. Gatteschi , D. et al, "Large Clusters of Metal Ions: The Transition from Molecular to Bulk Magnets" Science vol. 265, pp. 1054-1058, August... Gatteschi , D. et al, "Spin Dynamics in Mesoscopic Size Magnetic Systems... ", Phys. Rev. B, vol. 55, no. 21, 01 June, 1997 18. Tejeda, J. etal, "Quantum

The efficiency of backward magnetic-pulse processing

NASA Astrophysics Data System (ADS)

Kudasov, Yu. B.; Maslov, D. A.; Surdin, O. M.

2017-01-01

The dependence of the efficiency of magnetic-pulse processing of materials on the pulsed magnetic-field shape has been studied. It is shown that, by using a pulse train instead of a single pulse in the fast-rising component of a magnetic field applied during the backward forming process, it is possible to increase the specific mechanical impulse transferred to a workpiece and, thus, improve the efficiency of processing. Possible applications of the proposed method to removing dents from car chassis and aircraft parts are considered

Numerical study of MHD nanofluid flow and heat transfer past a bidirectional exponentially stretching sheet

NASA Astrophysics Data System (ADS)

Ahmad, Rida; Mustafa, M.; Hayat, T.; Alsaedi, A.

2016-06-01

Recent advancements in nanotechnology have led to the discovery of new generation coolants known as nanofluids. Nanofluids possess novel and unique characteristics which are fruitful in numerous cooling applications. Current work is undertaken to address the heat transfer in MHD three-dimensional flow of magnetic nanofluid (ferrofluid) over a bidirectional exponentially stretching sheet. The base fluid is considered as water which consists of magnetite-Fe3O4 nanoparticles. Exponentially varying surface temperature distribution is accounted. Problem formulation is presented through the Maxwell models for effective electrical conductivity and effective thermal conductivity of nanofluid. Similarity transformations give rise to a coupled non-linear differential system which is solved numerically. Appreciable growth in the convective heat transfer coefficient is observed when nanoparticle volume fraction is augmented. Temperature exponent parameter serves to enhance the heat transfer from the surface. Moreover the skin friction coefficient is directly proportional to both magnetic field strength and nanoparticle volume fraction.

Role of magnetic exchange interaction due to magnetic anisotropy on inverse spin Hall voltage at FeSi3%/Pt thin film bilayer interface

NASA Astrophysics Data System (ADS)

Shah, Jyoti; Ahmad, Saood; Chaujar, Rishu; Puri, Nitin K.; Negi, P. S.; Kotnala, R. K.

2017-12-01

In our recent studies inverse spin Hall voltage (ISHE) was investigated by ferromagnetic resonance (FMR) using bilayer FeSi3%/Pt thin film prepared by pulsed laser deposition (PLD) technique. In ISHE measurement microwave signal was applied on FeSi3% film along with DC magnetic field. Higher magnetization value along the film-plane was measured by magnetic hysteresis (M-H) loop. Presence of magnetic anisotropy has been obtained by M-H loop which showed easy direction of magnetization when applied magnetic field is parallel to the film plane. The main result of this study is that FMR induced inverse spin Hall voltage 12.6 μV at 1.0 GHz was obtained across Pt layer. Magnetic exchange field at bilayer interface responsible for field torque was measured 6 × 1014 Ω-1 m-2 by spin Hall magnetoresistance. The damping torque and spin Hall angle have been evaluated as 0.084 and 0.071 respectively. Presence of Si atom in FeSi3% inhomogenize the magnetic exchange field among accumulated spins at bilayer interface and feebly influenced by spin torque of FeSi3% layer. Weak field torque suppresses the spin pumping to Pt layer thus low value of inverse spin Hall voltage is obtained. This study provides an excellent opportunity to investigate spin transfer torque effect, thus motivating a more intensive experimental effort for its utilization at maximum potential. The improvement in spin transfer torque may be useful in spin valve, spin battery and spin transistor application.

Heat and mass transfer in MHD free convection from a moving permeable vertical surface by a perturbation technique

NASA Astrophysics Data System (ADS)

Abdelkhalek, M. M.

2009-05-01

Numerical results are presented for heat and mass transfer effect on hydromagnetic flow of a moving permeable vertical surface. An analysis is performed to study the momentum, heat and mass transfer characteristics of MHD natural convection flow over a moving permeable surface. The surface is maintained at linear temperature and concentration variations. The non-linear coupled boundary layer equations were transformed and the resulting ordinary differential equations were solved by perturbation technique [Aziz A, Na TY. Perturbation methods in heat transfer. Berlin: Springer-Verlag; 1984. p. 1-184; Kennet Cramer R, Shih-I Pai. Magneto fluid dynamics for engineers and applied physicists 1973;166-7]. The solution is found to be dependent on several governing parameter, including the magnetic field strength parameter, Prandtl number, Schmidt number, buoyancy ratio and suction/blowing parameter, a parametric study of all the governing parameters is carried out and representative results are illustrated to reveal a typical tendency of the solutions. Numerical results for the dimensionless velocity profiles, the temperature profiles, the concentration profiles, the local friction coefficient and the local Nusselt number are presented for various combinations of parameters.

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

NASA Technical Reports Server (NTRS)

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

1990-01-01

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

"Magnetic" termite mound surfaces are oriented to suit wind and shade conditions.

PubMed

Jacklyn, Peter M

1992-09-01

The termites Amitermes meridionalis and A. laurensis construct remarkable meridional or "magnetic" mounds in northern Australia. These mounds vary geographically in mean orientation in a manner that suggests such variation is an adaptive response to local environmental conditions. Theoretical modelling of solar irradiance and mound rotation experiments show that maintenance of an eastern face temperature plateau during the dry season is the most likely physical basis for the mound orientation response. Subsequent heat transfer analysis shows that habitat wind speed and shading conditions also affect face temperature gradients such as the rate of eastern face temperature change. It is then demonstrated that the geographic variation in mean mound orientation follows the geographic variation in long-term wind speed and shading conditions across northern Australia such that an eastern face temperature plateau is maintained in all locations.

Dispersion relation and growth rate of a relativistic electron beam propagating through a Langmuir wave wiggler

NASA Astrophysics Data System (ADS)

Zirak, H.; Jafari, S.

2015-06-01

In this study, a theory of free-electron laser (FEL) with a Langmuir wave wiggler in the presence of an axial magnetic field has been presented. The small wavelength of the plasma wave (in the sub-mm range) allows obtaining higher frequency than conventional wiggler FELs. Electron trajectories have been obtained by solving the equations of motion for a single electron. In addition, a fourth-order Runge-Kutta method has been used to simulate the electron trajectories. Employing a perturbation analysis, the dispersion relation for an electromagnetic and space-charge waves has been derived by solving the momentum transfer, continuity, and wave equations. Numerical calculations show that the growth rate increases with increasing the e-beam energy and e-beam density, while it decreases with increasing the strength of the axial guide magnetic field.

Characterization of high-intensity, long-duration continuous auroral activity (HILDCAA) events using recurrence quantification analysis

NASA Astrophysics Data System (ADS)

Mendes, Odim; Oliveira Domingues, Margarete; Echer, Ezequiel; Hajra, Rajkumar; Everton Menconi, Varlei

2017-08-01

Considering the magnetic reconnection and the viscous interaction as the fundamental mechanisms for transfer particles and energy into the magnetosphere, we study the dynamical characteristics of auroral electrojet (AE) index during high-intensity, long-duration continuous auroral activity (HILDCAA) events, using a long-term geomagnetic database (1975-2012), and other distinct interplanetary conditions (geomagnetically quiet intervals, co-rotating interaction regions (CIRs)/high-speed streams (HSSs) not followed by HILDCAAs, and events of AE comprised in global intense geomagnetic disturbances). It is worth noting that we also study active but non-HILDCAA intervals. Examining the geomagnetic AE index, we apply a dynamics analysis composed of the phase space, the recurrence plot (RP), and the recurrence quantification analysis (RQA) methods. As a result, the quantification finds two distinct clusterings of the dynamical behaviours occurring in the interplanetary medium: one regarding a geomagnetically quiet condition regime and the other regarding an interplanetary activity regime. Furthermore, the HILDCAAs seem unique events regarding a visible, intense manifestations of interplanetary Alfvénic waves; however, they are similar to the other kinds of conditions regarding a dynamical signature (based on RQA), because it is involved in the same complex mechanism of generating geomagnetic disturbances. Also, by characterizing the proper conditions of transitions from quiescent conditions to weaker geomagnetic disturbances inside the magnetosphere and ionosphere system, the RQA method indicates clearly the two fundamental dynamics (geomagnetically quiet intervals and HILDCAA events) to be evaluated with magneto-hydrodynamics simulations to understand better the critical processes related to energy and particle transfer into the magnetosphere-ionosphere system. Finally, with this work, we have also reinforced the potential applicability of the RQA method for characterizing nonlinear geomagnetic processes related to the magnetic reconnection and the viscous interaction affecting the magnetosphere.

Integrating magnetic resonance imaging postprocessing results into neuronavigation for electrode implantation and resection of subtle focal cortical dysplasia in previously cryptogenic epilepsy.

PubMed

Wellmer, Jörg; Parpaley, Yaroslav; von Lehe, Marec; Huppertz, Hans-Jürgen

2010-01-01

Focal cortical dysplasias (FCDs) are highly epileptogenic lesions. Surgical removal is frequently the best treatment option for pharmacoresistant epilepsy. However, subtle FCDs may remain undetected even after high-resolution magnetic resonance imaging (MRI). Morphometric MRI analysis, which compares the individual brain with a normal database, can facilitate the detection of FCDs. We describe how the results of normal database-based MRI postprocessing can be used to guide stereotactic electrode implantation and subsequent resection of lesions that are suspected to be FCDs. A presurgical evaluation was conducted on a 19-year-old woman with pharmacoresistant hypermotor seizures. Conventional high-resolution MRI was classified as negative for epileptogenic lesions. However, morphometric analysis of the spatially normalized MRI revealed abnormal gyration and blurring of the gray-white matter junction, which was suggestive of a small and deeply seated FCD in the left frontal lobe. The brain region highlighted by morphometric analysis was marked as a region of interest, transferred back to the original dimension of the individual MRI, and imported into a neuronavigation system. This allowed the region of interest-targeted stereotactic implantation of 2 depth electrodes, by which seizure onset was confirmed in the lesion. The electrodes also guided the final resection, which rendered the patient seizure-free. The lesion was histologically classified as FCD Palmini and Lüders IIB. Transferring normal database-based MRI postprocessing results into a neuronavigation system is a new and worthwhile extension of multimodal neuronavigation. The combination of resulting regions of interest with functional and anatomic data may facilitate planning of electrode implantation for invasive electroencephalographic recordings and the final resection of small or deeply seated FCDs.

MMS Examination of FTEs at the Earth's Subsolar Magnetopause

NASA Astrophysics Data System (ADS)

Akhavan-Tafti, M.; Slavin, J. A.; Le, G.; Eastwood, J. P.; Strangeway, R. J.; Russell, C. T.; Nakamura, R.; Baumjohann, W.; Torbert, R. B.; Giles, B. L.; Gershman, D. J.; Burch, J. L.

2018-02-01

Determining the magnetic field structure, electric currents, and plasma distributions within flux transfer event (FTE)-type flux ropes is critical to the understanding of their origin, evolution, and dynamics. Here the Magnetospheric Multiscale mission's high-resolution magnetic field and plasma measurements are used to identify FTEs in the vicinity of the subsolar magnetopause. The constant-α flux rope model is used to identify quasi-force free flux ropes and to infer the size, the core magnetic field strength, the magnetic flux content, and the spacecraft trajectories through these structures. Our statistical analysis determines a mean diameter of 1,700 ± 400 km ( 30 ± 9 di) and an average magnetic flux content of 100 ± 30 kWb for the quasi-force free FTEs at the Earth's subsolar magnetopause which are smaller than values reported by Cluster at high latitudes. These observed nonlinear size and magnetic flux content distributions of FTEs appear consistent with the plasmoid instability theory, which relies on the merging of neighboring, small-scale FTEs to generate larger structures. The ratio of the perpendicular to parallel components of current density, RJ, indicates that our FTEs are magnetically force-free, defined as RJ < 1, in their core regions (<0.6 Rflux rope). Plasma density is shown to be larger in smaller, newly formed FTEs and dropping with increasing FTE size. It is also shown that parallel ion velocity dominates inside FTEs with largest plasma density. Field-aligned flow facilitates the evacuation of plasma inside newly formed FTEs, while their core magnetic field strengthens with increasing FTE size.

The advantages of complementing MT profiles in 3-D environments with geomagnetic transfer function and interstation horizontal magnetic transfer function data: results from a synthetic case study

NASA Astrophysics Data System (ADS)

Campanyà, Joan; Ogaya, Xènia; Jones, Alan G.; Rath, Volker; Vozar, Jan; Meqbel, Naser

2016-12-01

As a consequence of measuring time variations of the electric and the magnetic field, which are related to current flow and charge distribution, magnetotelluric (MT) data in 2-D and 3-D environments are not only sensitive to the geoelectrical structures below the measuring points but also to any lateral anomalies surrounding the acquisition site. This behaviour complicates the characterization of the electrical resistivity distribution of the subsurface, particularly in complex areas. In this manuscript we assess the main advantages of complementing the standard MT impedance tensor (Z) data with interstation horizontal magnetic tensor (H) and geomagnetic transfer function (T) data in constraining the subsurface in a 3-D environment beneath a MT profile. Our analysis was performed using synthetic responses with added normally distributed and scattered random noise. The sensitivity of each type of data to different resistivity anomalies was evaluated, showing that the degree to which each site and each period is affected by the same anomaly depends on the type of data. A dimensionality analysis, using Z, H and T data, identified the presence of the 3-D anomalies close to the profile, suggesting a 3-D approach for recovering the electrical resistivity values of the subsurface. Finally, the capacity for recovering the geoelectrical structures of the subsurface was evaluated by performing joint inversion using different data combinations, quantifying the differences between the true synthetic model and the models from inversion process. Four main improvements were observed when performing joint inversion of Z, H and T data: (1) superior precision and accuracy at characterizing the electrical resistivity values of the anomalies below and outside the profile; (2) the potential to recover high electrical resistivity anomalies that are poorly recovered using Z data alone; (3) improvement in the characterization of the bottom and lateral boundaries of the anomalies with low electrical resistivity; and (4) superior imaging of the horizontal continuity of structures with low electrical resistivity. These advantages offer new opportunities for the MT method by making the results from a MT profile in a 3-D environment more convincing, supporting the possibility of high-resolution studies in 3-D areas without expending a large amount of economical and computational resources, and also offering better resolution of targets with high electrical resistivity.

Multilayer solar cell waveguide structures containing metamaterials

NASA Astrophysics Data System (ADS)

Hamouche, Houria.; Shabat, Mohammed. M.; Schaadt, Daniel M.

2017-01-01

Multilayer antireflection coating structures made from silicon and metamaterials are designed and investigated using the Transfer Matrix Method (TMM). The Transfer Matrix Method is a very useful algorithm for the analysis of periodic structures. We investigate in this paper two anti-reflection coating structures for silicon solar cells with a metamaterial film layer. In the first structure, the metamaterial film layer is sandwiched between a semi-infinite glass cover layer and a semi-infinite silicon substrate layer. The second structure consists of a four layers, a pair of metamaterial-dielectric layer with opposite real part of refractive indices, is placed between the two semi-infinite cover and substrate. We have simulated the absorptivity property of the structures for adjustable thicknesses by using MAPLE software. The absorptivity of the structures achieves greater than 80% for incident electromagnetic wave of transverse magnetic (TM) polarization.

Neuroinflammation and its relationship to changes in brain volume and white matter lesions in multiple sclerosis.

PubMed

Datta, Gourab; Colasanti, Alessandro; Rabiner, Eugenii A; Gunn, Roger N; Malik, Omar; Ciccarelli, Olga; Nicholas, Richard; Van Vlierberghe, Eline; Van Hecke, Wim; Searle, Graham; Santos-Ribeiro, Andre; Matthews, Paul M

2017-11-01

Brain magnetic resonance imaging is an important tool in the diagnosis and monitoring of multiple sclerosis patients. However, magnetic resonance imaging alone provides limited information for predicting an individual patient's disability progression. In part, this is because magnetic resonance imaging lacks sensitivity and specificity for detecting chronic diffuse and multi-focal inflammation mediated by activated microglia/macrophages. The aim of this study was to test for an association between 18 kDa translocator protein brain positron emission tomography signal, which arises largely from microglial activation, and measures of subsequent disease progression in multiple sclerosis patients. Twenty-one patients with multiple sclerosis (seven with secondary progressive disease and 14 with a relapsing remitting disease course) underwent T1- and T2-weighted and magnetization transfer magnetic resonance imaging at baseline and after 1 year. Positron emission tomography scanning with the translocator protein radioligand 11C-PBR28 was performed at baseline. Brain tissue and lesion volumes were segmented from the T1- and T2-weighted magnetic resonance imaging and relative 11C-PBR28 uptake in the normal-appearing white matter was estimated as a distribution volume ratio with respect to a caudate pseudo-reference region. Normal-appearing white matter distribution volume ratio at baseline was correlated with enlarging T2-hyperintense lesion volumes over the subsequent year (ρ = 0.59, P = 0.01). A post hoc analysis showed that this association reflected behaviour in the subgroup of relapsing remitting patients (ρ = 0.74, P = 0.008). By contrast, in the subgroup of secondary progressive patients, microglial activation at baseline was correlated with later progression of brain atrophy (ρ = 0.86, P = 0.04). A regression model including the baseline normal-appearing white matter distribution volume ratio, T2 lesion volume and normal-appearing white matter magnetization transfer ratio for all of the patients combined explained over 90% of the variance in enlarging lesion volume over the subsequent 1 year. Glial activation in white matter assessed by translocator protein PET significantly improves predictions of white matter lesion enlargement in relapsing remitting patients and is associated with greater brain atrophy in secondary progressive disease over a period of short term follow-up. © The Author (2017). Published by Oxford University Press on behalf of the Guarantors of Brain. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

A Simple and Universal Gel Permeation Chromatography Technique for Precise Molecular Weight Characterization of Well-Defined Poly(ionic liquid)s

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

He, Hongkun; Zhong, Mingjiang; Adzima, Brian

2013-03-20

Poly(ionic liquid)s (PILs) are an important class of technologically relevant materials. However, characterization of well-defined polyionic materials remains a challenge. Herein, we have developed a simple and versatile gel permeation chromatography (GPC) methodology for molecular weight (MW) characterization of PILs with a variety of anions. PILs with narrow MW distributions were synthesized via atom transfer radical polymerization, and the MWs obtained from GPC were further confirmed via nuclear magnetic resonance end group analysis.

Analysis of Biologic Samples for Morphine and Morphine-Related Compounds by Gas Chromatographic-Mass Spectrometric Methods

DTIC Science & Technology

1976-04-01

spectra are obtained for each peak detected in the CC effluent stream. In this mode of operation, the "total ion current" is usually used as a guide...correcting drift for both magnetic field and electrical field instruments. The peak setting is usually made to the 47 nearest 0.1 amu, and adjustments...su stances by charge transfer from nitric oxide ions (No ), however, the M14 ions are the base peak . This obser- vation by Jardine and Fenselau (44

Magnetic gold nanocatalyst (nanocat-Fe–Au): catalytic applications for the oxidative esterification and hydrogen transfer reactions

EPA Science Inventory

An efficient and sustainable protocol is described for the oxidative esterification of aldehydes and the reduction of aromatic nitro compounds that uses magnetically separable and reusable maghemite-supported gold nanocatalyst (nanocat-Fe-Au) under mild conditions. The complex ch...

Magnetization transfer and adiabatic R 1ρ MRI in the brainstem of Parkinson's disease.

PubMed

Tuite, Paul J; Mangia, Silvia; Tyan, Andrew E; Lee, Michael K; Garwood, Michael; Michaeli, Shalom

2012-06-01

In addition to classic midbrain pathology, Parkinson's disease (PD) is accompanied by changes in pontine and medullary brainstem structures. These additional abnormalities may underlie non-motor features as well as play a role in motor disability. Using novel magnetic resonance imaging (MRI) methods based on rotating frame adiabatic R(1ρ) (i.e., measurements of longitudinal relaxation during adiabatic full passage pulses) and modified magnetization transfer (MT) MRI mapping, we sought to identify brainstem alterations in nine individuals with mild-moderate PD (off medication) and ten age-matched controls at 4 T. We discovered significant differences in MRI parameters between midbrain and medullary brainstem structures in control subjects as compared to PD patients. These findings support the presence of underlying functional/structural brainstem changes in mild-moderate PD. Copyright © 2012 Elsevier Ltd. All rights reserved.

Numerical investigation of MHD flow with Soret and Dufour effect

NASA Astrophysics Data System (ADS)

Hayat, Tasawar; Nasir, Tehreem; Khan, Muhammad Ijaz; Alsaedi, Ahmed

2018-03-01

This paper describes the flow due to an exponentially curved surface subject to Soret and Dufour effects. Nonlinear velocity is considered. Exponentially curved stretchable sheet induced the flow. Fluid is electrical conducting through constant applied magnetic field. The governing flow expressions are reduced to ordinary ones and then tackled by numerical technique (Built-in-Shooting). Impacts of various flow variables on the dimensionless velocity, concentration and temperature fields are graphically presented and discussed in detail. Skin friction coefficient and Sherwood and Nusselt numbers are studied through graphs. Furthermore it is observed that Soret and Dufour variables regulate heat and mass transfer rates. It is also noteworthy that velocity decays for higher magnetic variable. Skin friction magnitude decays via curvature and magnetic variables. Also mass transfer gradient or rate of mass transport enhances for higher estimations of curvature parameter and Schmidt number.

Development of atomic force microscope with wide-band magnetic excitation for study of soft matter dynamics

NASA Astrophysics Data System (ADS)

Kageshima, Masami; Chikamoto, Takuma; Ogawa, Tatsuya; Hirata, Yoshiki; Inoue, Takahito; Naitoh, Yoshitaka; Li, Yan Jun; Sugawara, Yasuhiro

2009-02-01

In order to probe dynamical properties of mesoscopic soft matter systems such as polymers, structured liquid, etc., a new atomic force microscopy apparatus with a wide-band magnetic cantilever excitation system was developed. Constant-current driving of an electromagnet up to 1 MHz was implemented with a closed-loop driver circuit. Transfer function of a commercial cantilever attached with a magnetic particle was measured in a frequency range of 1-1000 kHz in distilled water. Effects of the laser spot position, distribution of the force exerted on the cantilever, and difference in the detection scheme on the obtained transfer function are discussed in comparison with theoretical predictions by other research groups. A preliminary result of viscoelasticity spectrum measurement of a single dextran chain is shown and is compared with a recent theoretical calculation.

Reactions between NO/+/ and metal atoms using magnetically confined afterglows

NASA Technical Reports Server (NTRS)

Lo, H. H.; Clendenning, L. M.; Fite, W. L.

1977-01-01

A new method of studying thermal energy ion-neutral collision processes involving nongaseous neutral atoms is described. A long magnetic field produced by a solenoid in a vacuum chamber confines a thermal-energy plasma generated by photoionization of gas at very low pressure. As the plasma moves toward the end of the field, it is crossed by a metal atom beam. Ionic products of ion-atom reactions are trapped by the field and both the reactant and product ions move to the end of the magnetic field where they are detected by a quadrupole mass filter. The cross sections for charge transfer between NO(+) and Na, Mg, Ca, and Sr and that for rearrangement between NO(+) and Ca have been obtained. The charge-transfer reaction is found strongly dominant over the rearrangement reaction that forms metallic oxide ions.

Microtesla SABRE enables 10% nitrogen-15 nuclear spin polarization.

PubMed

Theis, Thomas; Truong, Milton L; Coffey, Aaron M; Shchepin, Roman V; Waddell, Kevin W; Shi, Fan; Goodson, Boyd M; Warren, Warren S; Chekmenev, Eduard Y

2015-02-04

Parahydrogen is demonstrated to efficiently transfer its nuclear spin hyperpolarization to nitrogen-15 in pyridine and nicotinamide (vitamin B(3) amide) by conducting "signal amplification by reversible exchange" (SABRE) at microtesla fields within a magnetic shield. Following transfer of the sample from the magnetic shield chamber to a conventional NMR spectrometer, the (15)N NMR signals for these molecules are enhanced by ∼30,000- and ∼20,000-fold at 9.4 T, corresponding to ∼10% and ∼7% nuclear spin polarization, respectively. This method, dubbed "SABRE in shield enables alignment transfer to heteronuclei" or "SABRE-SHEATH", promises to be a simple, cost-effective way to hyperpolarize heteronuclei. It may be particularly useful for in vivo applications because of longer hyperpolarization lifetimes, lack of background signal, and facile chemical-shift discrimination of different species.

Microtesla SABRE Enables 10% Nitrogen-15 Nuclear Spin Polarization

PubMed Central

2016-01-01

Parahydrogen is demonstrated to efficiently transfer its nuclear spin hyperpolarization to nitrogen-15 in pyridine and nicotinamide (vitamin B3 amide) by conducting “signal amplification by reversible exchange” (SABRE) at microtesla fields within a magnetic shield. Following transfer of the sample from the magnetic shield chamber to a conventional NMR spectrometer, the 15N NMR signals for these molecules are enhanced by ∼30,000- and ∼20,000-fold at 9.4 T, corresponding to ∼10% and ∼7% nuclear spin polarization, respectively. This method, dubbed “SABRE in shield enables alignment transfer to heteronuclei” or “SABRE-SHEATH”, promises to be a simple, cost-effective way to hyperpolarize heteronuclei. It may be particularly useful for in vivo applications because of longer hyperpolarization lifetimes, lack of background signal, and facile chemical-shift discrimination of different species. PMID:25583142

(LaTiO3)n/(LaVO3)n as a model system for unconventional charge transfer and polar metallicity

NASA Astrophysics Data System (ADS)

Weng, Yakui; Zhang, Jun-Jie; Gao, Bin; Dong, Shuai

2017-04-01

At interfaces between oxide materials, lattice and electronic reconstructions always play important roles in exotic phenomena. In this study, the density functional theory and maximally localized Wannier functions are employed to investigate the (LaTiO3)n/(LaVO3)n magnetic superlattices. The electron transfer from Ti3 + to V3 + is predicted, which violates the intuitive band alignment based on the electronic structures of LaTiO3 and LaVO3. Such unconventional charge transfer quenches the magnetism of LaTiO3 layer mostly and leads to metal-insulator transition in the n =1 superlattice when the stacking orientation is altered. In addition, the compatibility among the polar structure, ferrimagnetism, and metallicity is predicted in the n =2 superlattice.

Optimal and Miniaturized Strongly Coupled Magnetic Resonant Systems

NASA Astrophysics Data System (ADS)

Hu, Hao

Wireless power transfer (WPT) technologies for communication and recharging devices have recently attracted significant research attention. Conventional WPT systems based either on far-field or near-field coupling cannot provide simultaneously high efficiency and long transfer range. The Strongly Coupled Magnetic Resonance (SCMR) method was introduced recently, and it offers the possibility of transferring power with high efficiency over longer distances. Previous SCMR research has only focused on how to improve its efficiency and range through different methods. However, the study of optimal and miniaturized designs has been limited. In addition, no multiband and broadband SCMR WPT systems have been developed and traditional SCMR systems exhibit narrowband efficiency thereby imposing strict limitations on simultaneous wireless transmission of information and power, which is important for battery-less sensors. Therefore, new SCMR systems that are optimally designed and miniaturized in size will significantly enhance various technologies in many applications. The optimal and miniaturized SCMR systems are studied here. First, analytical models of the Conformal SCMR (CSCMR) system and thorough analysis and design methodology have been presented. This analysis specifically leads to the identification of the optimal design parameters, and predicts the performance of the designed CSCMR system. Second, optimal multiband and broadband CSCMR systems are designed. Two-band, three-band, and four-band CSCMR systems are designed and validated using simulations and measurements. Novel broadband CSCMR systems are also analyzed, designed, simulated and measured. The proposed broadband CSCMR system achieved more than 7 times larger bandwidth compared to the traditional SCMR system at the same frequency. Miniaturization methods of SCMR systems are also explored. Specifically, methods that use printable CSCMR with large capacitors, novel topologies including meandered, SRRs, and spiral topologies or 3-D structures, lower the operating frequency of SCMR systems, thereby reducing their size. Finally, SCMR systems are discussed and designed for various applications, such as biomedical devices and simultaneous powering of multiple devices.

An investigation into the torque density capabilities of flux-focusing magnetic gearboxes

NASA Astrophysics Data System (ADS)

Uppalapati, Krishna Kiran

Wind and many rotary based ocean energy conversion devices rely on a mechanical gearbox to increase their speed so as to match the requirements of the electromagnetic generator. However, mechanical gearboxes have a number of disadvantages such as the need for gear lubrication, no overload protection and the creation of acoustic noise. Frequently direct-drive generators are employed to overcome these issues, wherein the gearbox is removed and the shaft of the turbine is directly connected to the synchronous generator, either with an electrically excited or permanent magnet rotor. If the input speed to the generator is very low the torque must be very high in order to generate the necessary power. However, as the electrical loading of a synchronous generator is thermally limited, the size of the generator will become excessively large at high power levels. An alternative to these technologies is to consider replacing the mechanical gearbox with a magnetic gear. A magnetic gear can create speed change without any physical contact. It has inherent overload protection, and its non-contact operation offers the potential for high reliability. Despite significant progress, existing magnetic gear designs do not achieve torque densities that are competitive with mechanical gearboxes. This research has focused on designing a coaxial magnetic gear that can operate at a volumetric torque density that is comparable to a mechanical gearbox. A flux-focusing rotor topology also called spoke-type rotor magnet arrangement was adopted to improve the air-gap magnetic flux density which in turn improves the torque transferred between the rotors. Finite element analysis was utilized to conduct a parameter sweep analysis of the different geometric parameters of the magnetic gear. A sub-scale magnetic gear with a diameter of 110 mm and a scaled-up magnetic gear with a diameter of 228 mm was designed, constructed and experimentally evaluated. The torque and torque density of sub-scale design was measured to be 115 Nm and 151.2 Nm/L respectively and that of the scaled-up model was measured to be 731 Nm and 239 Nm/L respectively. An iterative magnetomechanical analysis technique was developed to study the deflection of the magnetic gear steel rotor bars due to the magnetic forces coming from the inner and outer rotor permanent magnets. The accuracy of the technique was validated by using an experimental test-stand. It was shown that the deflection is an important issue to consider especially if the air-gaps are small. A 2-D analytical based model was derived for the flux-focusing coaxial magnetic gear by using the separation of variables method to solve the Laplace and Poisson equation in each region. After applying the applicable Dirchlet and Neumann boundary conditions a set of 16 equations with 16 unknown Fourier coefficients was obtained. The 16 unknowns were solved numerically by putting the equations in a matrix form. It was shown that the analytical based model immensely reduced the torque and field computational time when compared to using finite element analysis. However, the analytical model does not take into consideration the non-linear properties of the steel. The benefits of using the analytical model was demonstrated by conducting a radial scaling and gear-ratio analysis.

Magnetothermal Convection of Water with the Presence or Absence of a Magnetic Force Acting on the Susceptibility Gradient.

PubMed

Maki, Syou

2016-01-01

Heat transfer of magnetothermal convection with the presence or absence of the magnetic force acting on the susceptibility gradient (fsc) was examined by three-dimensional numerical computations. Thermal convection of water enclosed in a shallow cylindrical vessel (diameter over vessel height = 6.0) with the Rayleigh-Benard model was adopted as the model, under the conditions of Prandtl number 6.0 and Ra number 7000, respectively. The momentum equations of convection were nondimensionalized, which involved the term of fsc and the term of magnetic force acting on the magnetic field gradient (fb). All the computations resulted in axisymmetric steady rolls. The values of the averaged Nu, the averaged velocity components U, V, and W, and the isothermal distributions and flow patterns were almost completely the same, regardless of the presence or absence of the term of fsc. As a result, we found that the effect of fsc was extremely small, although much previous research emphasized the effect with paramagnetic solutions under an unsteady state. The magnitude of fsc depends not only on magnetic conditions (magnitudes of magnetic susceptibility and magnetic flux density), but also on the thermal properties of the solution (thermal conductivity, thermal diffusivity, and viscosity). Therefore the effect of fb becomes dominant on the magnetothermal convection. Active control over the density gradient with temperature will be required to advance heat transfer with the effect of fsc.

Umbrella sampling of proton transfer in a creatine-water system

NASA Astrophysics Data System (ADS)

Ivchenko, Olga; Bachert, Peter; Imhof, Petra

2014-04-01

Proton transfer reactions are among the most common processes in chemistry and biology. Proton transfer between creatine and surrounding solvent water is underlying the chemical exchange saturation transfer used as a contrast in magnetic resonance imaging. The free energy barrier, determined by first-principles umbrella sampling simulations (EaDFT 3 kcal/mol) is in the same order of magnitude as the experimentally obtained activation energy. The underlying mechanism is a first proton transfer from the guanidinium group to the water pool, followed by a second transition where a proton is "transferred back" from the nearest water molecule to the deprotonated nitrogen atom of creatine.

Sub-millitesla magnetic field effects on the recombination reaction of flavin and ascorbic acid radicals

NASA Astrophysics Data System (ADS)

Evans, Emrys W.; Kattnig, Daniel R.; Henbest, Kevin B.; Hore, P. J.; Mackenzie, Stuart R.; Timmel, Christiane R.

2016-08-01

Even though the interaction of a <1 mT magnetic field with an electron spin is less than a millionth of the thermal energy at room temperature (kBT), it still can have a profound effect on the quantum yields of radical pair reactions. We present a study of the effects of sub-millitesla magnetic fields on the photoreaction of flavin mononucleotide with ascorbic acid. Direct control of the reaction pathway is achieved by varying the rate of electron transfer from ascorbic acid to the photo-excited flavin. At pH 7.0, we verify the theoretical prediction that, apart from a sign change, the form of the magnetic field effect is independent of the initial spin configuration of the radical pair. The data agree well with model calculations based on a Green's function approach that allows multinuclear spin systems to be treated including the diffusive motion of the radicals, their spin-selective recombination reactions, and the effects of the inter-radical exchange interaction. The protonation states of the radicals are uniquely determined from the form of the magnetic field-dependence. At pH 3.0, the effects of two chemically distinct radical pair complexes combine to produce a pronounced response to ˜500 μT magnetic fields. These findings are relevant to the magnetic responses of cryptochromes (flavin-containing proteins proposed as magnetoreceptors in birds) and may aid the evaluation of effects of weak magnetic fields on other biologically relevant electron transfer processes.

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.

Magnetotelluric investigation of the Vestfold Hills and Rauer Group, East Antarctica

USGS Publications Warehouse

Peacock, Jared R.; Selway, Katherine

2016-01-01

The Vestfold Hills and Rauer Group in East Antarctica have contrasting Archean to Neoproterozoic geological histories and are believed to be juxtaposed along a suture zone that now lies beneath the Sørsdal Glacier. Exact location and age of this suture zone are unknown, as is its relationship to regional deformation associated with the amalgamation of East Gondwana. To image the suture zone, magnetotelluric (MT) data were collected in Prydz Bay, East Antarctica, mainly along a profile crossing the Sørsdal Glacier and regions inland of the Vestfold Hills and Rauer Group islands. Time-frequency analysis of the MT time series yielded three important observations: (1) Wind speeds in excess of ∼8 m/s reduce coherence between electric and magnetic fields due to charged wind-blown particles of ice and snow. (2) Estimation of the MT transfer function is best between 1000 and 1400 UT when ionospheric Hall currents enhance the magnetic source field. (3) Nonplanar source field effects were minimal but detectable and removed from estimation of the MT transfer function. Inversions of MT data in 2-D and 3-D produce similar resistivity models, where structures in the preferred 3-D resistivity model correlate strongly with regional magnetic data. The electrically conductive Rauer Group is separated from the less conductive Vestfold Hills by a resistive zone under the Sørsdal Glacier, which is interpreted to be caused by oxidation during suturing. Though a suture zone has been imaged, no time constrains on suturing can be made from the MT data.

Analysis of FORTE data to extract ionospheric parameters

NASA Astrophysics Data System (ADS)

Roussel-Dupré, Robert A.; Jacobson, Abram R.; Triplett, Laurie A.

2001-01-01

The ionospheric transfer function is derived for a spherically symmetric ionosphere with an arbitrary radial electron density profile in the limit where the radio frequencies of interest ω are much larger than the plasma frequency ωpe. An expansion of the transfer function to second order in the parameter X (= ω2pe/ω2) is carried out. In this limit the dispersive properties of the ionosphere are manifested as a frequency-dependent time of arrival that includes quadratic, cubic, and quartic terms in 1/ω. The coefficients of these terms are related to the total electron content (TEC) along the slant path from transmitter to receiver, the product of TEC and the longitudinal magnetic field strength along the slant path, and refractive bending and higher-order electron density profile effects, respectively. By fitting the time of arrival versus frequency of a transionospheric signal to a polynomial in 1/ω it is possible to extract the TEC, the longitudinal magnetic field strength, the peak electron density, and an effective thickness for the ionosphere. This exercise was carried out for a number of transionospheric pulses measured in the VHF by the FORTE satellite receiver and generated by the Los Alamos Portable Pulser. The results are compared with predictions derived from the International Reference Ionosphere and the United States Geological Survey geomagnetic field model.

Utilization of the computational technique to improve the thermophysical performance in the transportation of an electrically conducting Al2O3 - Ag/H2O hybrid nanofluid

NASA Astrophysics Data System (ADS)

Iqbal, Z.; Azhar, Ehtsham; Maraj, E. N.

2017-12-01

In this study, we analyzed the induced magnetic field effect on stagnation-point flow of a Al2O3-Ag/water hybrid nanofluid over a stretching sheet. Hybrid nanofluid, a new type of conventional fluid has been used for enhancement of heat transfer within boundary layer flow. It is notable here that only 1% to 5% contribution of nanoparticles enhance thermal conductivity of water. Nonlinear governing equations are simplified into boundary layer equations under boundary layer approximation assumption. A coupled system of nonlinear partial differential equation is transformed into a nonlinear system of ordinary differential equation by implementing suitable similarity conversions. Numerical analysis is performed by means of Keller box scheme. Effects of different non-dimensional governing parameters on velocity, induced magnetic field and temperature profiles, along with skinfriction coefficient and local Nusselt number, are discussed and presented through graphs and tables. Hybrid nanofluid is considered by keeping the 0.1% volumetric fraction of silver. From this study it is observed that the heat transfer rate of hybrid nanofluid (Al2O3-Ag/water) is higher than nanofluid (Ag/water). Novel results computed are useful in academic studies of hybrid nanofluids in engineering and industry.

A biofilm microreactor system for simultaneous electrochemical and nuclear magnetic resonance techniques

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

Renslow, Ryan S.; Babauta, Jerome T.; Majors, Paul D.

2014-03-01

In order to fully understand electrochemically active biofilms and the limitations to their scale-up in industrial biofilm reactors, a complete picture of the microenvironments inside the biofilm is needed. Nuclear magnetic resonance (NMR) techniques are ideally suited for the study of biofilms and for probing their microenvironments because these techniques allow for non-invasive interrogation and in situ monitoring with high resolution. By combining NMR with simultaneous electrochemical techniques, it is possible to sustain and study live electrochemically active biofilms. Here, we introduce a novel biofilm microreactor system that allows for simultaneous electrochemical and NMR techniques (EC-NMR) at the microscale. Microreactorsmore » were designed with custom radiofrequency resonator coils, which allowed for NMR measurements of biofilms growing on polarized gold electrodes. For an example application of this system, we grew Geobacter sulfurreducens biofilms. NMR was used to investigate growth media flow velocities, which were compared to simulated laminar flow, and electron donor concentrations inside the biofilms. We use Monte Carlo error analysis to estimate standard deviations of the electron donor concentration measurements within the biofilm. The EC-NMR biofilm microreactor system can ultimately be used to correlate extracellular electron transfer rates with metabolic reactions and explore extracellular electron transfer mechanisms.« less

A thermo-electric-driven flowing liquid lithium limiter/divertor for magnetic confined fusion

NASA Astrophysics Data System (ADS)

Ruzic, D. N.; Xu, Wenyu; Curreli, Davide; Andruczyk, Daniel; Mui, Travis

2012-10-01

The concept of using a liquid metal, especially liquid lithium, as the plasma facing surface may provide the best path forward toward reactor designs. A liquid PFC can effectively eliminate the erosion and thermal stress problems compared to the solid PFC while transferring heat and prolong the lifetime limit of the PFCs. A liquid lithium surface can also suppress the hydrogen isotopes recycling and getter the impurities in fusion reactor. The Lithium/metal infused trench (LiMIT) concept successfully proved that the thermoelectric effect can induce electric currents inside liquid lithium and an external magnetic field can drive liquid lithium to flow within metallic open trenches. IR camera and thermocouple measurements prove the strong heat transfer ability of this concept. A new flowing lithium system with active control of the temperature gradient inside the lithium trenches and back flow channels has been designed. TEMHD driven liquid lithium run steady state and pulsed for a few seconds of high heat flux (˜15MW/m^2) has been used to investigate the transient reaction of the flowing lithium. A similar tray is scheduled to be tested in HT-7, Hefei, China as a limiter in Sept. 2012. Related movies and analysis will be 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.

ORIENTATION REQUIREMENT TO DETECT MAGNETIC FIELD-INDUCTED ALTERATION OF GAP JUNCTION COMMUNICATION IN EPITHELIAL CELLS

EPA Science Inventory

ORIENTATION REQUIREMENT TO DETECT MAGNETIC FIELD-INDUCED ALTERATION OF GAP JUNCTION COMMUNICATION IN EPITHELIAL CELLS.
OBJECTIVE: We have shown that functional gap junction communication as measured by Lucifer yellow dye transfer (DT) in Clone-9 rat liver epithelial cells, c...

47 CFR 51.217 - Nondiscriminatory access: Telephone numbers, operator services, directory assistance services...

Code of Federal Regulations, 2011 CFR

2011-10-01

... to have access to its directory assistance services, including directory assistance databases, so... provider, including transfer of the LECs' directory assistance databases in readily accessible magnetic.... Updates to the directory assistance database shall be made in the same format as the initial transfer...

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

Hoffman, Jason D.; Kirby, Brian J.; Kwon, Jihwan

Interfaces between correlated complex oxides are promising avenues to realize new forms of magnetism that arise as a result of charge transfer, proximity effects, and locally broken symmetries. We report on the discovery of a noncollinear magnetic structure in superlattices of the ferromagnetic metallic oxide La 2/3Sr 1/3MnO 3 (LSMO) and the correlated metal LaNiO 3 (LNO). The exchange interaction between LSMO layers is mediated by the intervening LNO, such that the angle between the magnetization of neighboring LSMO layers varies in an oscillatory manner with the thickness of the LNO layer. The magnetic field, temperature, and spacer thickness dependencemore » of the noncollinear structure are inconsistent with the bilinear and biquadratic interactions that are used to model the magnetic structure in conventional metallic multilayers. A model that couples the LSMO layers to a helical spin state within the LNO fits the observed behavior. We propose that the spin-helix results from the interaction between a spatially varying spin susceptibility within the LNO and interfacial charge transfer that creates localized Ni 2+ states. In conclusion, our work suggests a new approach to engineering noncollinear spin textures in metallic oxide heterostructures.« less

Nanoscale control of stripe-ordered magnetic domain walls by vertical spin transfer torque in La0.67Sr0.33MnO3 film

NASA Astrophysics Data System (ADS)

Wang, Jing; Wu, Shizhe; Ma, Ji; Xie, Lishan; Wang, Chuanshou; Malik, Iftikhar Ahmed; Zhang, Yuelin; Xia, Ke; Nan, Ce-Wen; Zhang, Jinxing

2018-02-01

Stripe-ordered domains with perpendicular magnetic anisotropy have been intensively investigated due to their potential applications in high-density magnetic data-storage devices. However, the conventional control methods (e.g., epitaxial strain, local heating, magnetic field, and magnetoelectric effect) of the stripe-ordered domain walls either cannot meet the demands for miniaturization and low power consumption of spintronic devices or require high strength of the electric field due to the small value of the magnetoelectric effect at room temperature. Here, a domain-wall resistive effect of 0.1% was clarified in La0.67Sr0.33MnO3 thin films between the configurations of current in the plane and perpendicular to the plane of walls. Furthermore, a reversible nanoscale control of the domain-wall re-orientation by vertical spin transfer torque across the probe/film interface was achieved, where a probe voltage of 0.1 V was applied on a manganite-based capacitor. We also demonstrated that the stripe-ordered magnetic domain-wall re-orientation strongly depends on the AC frequency of the scanning probe voltage which was applied on the capacitor.

Droplet-based microfluidic system to form and separate multicellular spheroids using magnetic nanoparticles.

PubMed

Yoon, Sungjun; Kim, Jeong Ah; Lee, Seung Hwan; Kim, Minsoo; Park, Tai Hyun

2013-04-21

The importance of creating a three-dimensional (3-D) multicellular spheroid has recently been gaining attention due to the limitations of monolayer cell culture to precisely mimic in vivo structure and cellular interactions. Due to this emerging interest, researchers have utilized new tools, such as microfluidic devices, that allow high-throughput and precise size control to produce multicellular spheroids. We have developed a droplet-based microfluidic system that can encapsulate both cells and magnetic nanoparticles within alginate beads to mimic the function of a multicellular tumor spheroid. Cells were entrapped within the alginate beads along with magnetic nanoparticles, and the beads of a relatively uniform size (diameters of 85% of the beads were 170-190 μm) were formed in the oil phase. These beads were passed through parallel streamlines of oil and culture medium, where the beads were magnetically transferred into the medium phase from the oil phase using an external magnetic force. This microfluidic chip eliminates additional steps for collecting the spheroids from the oil phase and transferring them to culture medium. Ultimately, the overall spheroid formation process can be achieved on a single microchip.

Selective heteronuclear Hartmann-Hahn: A multiple-pulse sequence for selective magnetization transfer in the structural elucidation of “isotagged” oligosaccharides

NASA Astrophysics Data System (ADS)

Meng, Xi; Nguyen, William H.; Nowick, James S.; Shaka, A. J.

2010-03-01

A new selective heteronuclear Hartmann-Hahn (SHEHAHA) multiple-pulse mixing sequence is proposed for the solution structure elucidation of milligram amounts of peracetylated oligosaccharides in which the acetyl groups are enriched in carbon-13, so-called “isotags”. SHEHAHA accomplishes exclusive in-phase magnetization transfer between the isotag carbonyl 13C and the proximal proton on the sugar ring. Relayed transfer around the sugar rings by proton-proton TOCSY is suppressed, while the heteronuclear transfer from the labeled carbonyl carbon to the proximal ring proton is maintained. The sequence is broadband in the sense that all acetyl groups simultaneously give good signal transfer to their respective nearest proton neighbors. The 1H-detected spectra have decent sensitivity and excellent resolution, giving patterns that unambiguously identify common structural subunits in human glycans. Peracetylated maltitol is shown as a test case of the method. Lineshapes are pure absorption, allowing facile measurement of vicinal proton-proton couplings. Linkage points can be deduced, and the 2D correlation spectra may be useful for more ambitious prediction algorithms and machine identification by a spectral database.

Preliminary Analysis of a Fully Solid State Magnetocaloric Refrigeration

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

Abdelaziz, Omar

Magnetocaloric refrigeration is an alternative refrigeration technology with significant potential energy savings compared to conventional vapor compression refrigeration technology. Most of the reported active magnetic regenerator (AMR) systems that operate based on the magnetocaloric effect use heat transfer fluid to exchange heat, which results in complicated mechanical subsystems and components such as rotating valves and hydraulic pumps. In this paper, we propose an alternative mechanism for heat transfer between the AMR and the heat source/sink. High-conductivity moving rods/sheets (e.g. copper, brass, iron, graphite, aluminum or composite structures from these) are utilized instead of heat transfer fluid significantly enhancing the heatmore » transfer rate hence cooling/heating capacity. A one-dimensional model is developed to study the solid state AMR. In this model, the heat exchange between the solid-solid interfaces is modeled via a contact conductance, which depends on the interface apparent pressure, material hardness, thermal conductivity, surface roughness, surface slope between the interfaces, and material filled in the gap between the interfaces. Due to the tremendous impact of the heat exchange on the AMR cycle performance, a sensitivity analysis is conducted employing a response surface method, in which the apparent pressure, effective surface roughness and grease thermal conductivity are the uncertainty factors. COP and refrigeration capacity are presented as the response in the sensitivity analysis to reveal the important factors influencing the fully solid state AMR and optimize the solid state AMR efficiency. The performances of fully solid state AMR and traditional AMR are also compared and discussed in present work. The results of this study will provide general guidelines for designing high performance solid state AMR systems.« less

Rhodium clustering process on defective (8,0) SWCNT: Analysis of chemical and physical properties using density functional theory

NASA Astrophysics Data System (ADS)

Ambrusi, Ruben E.; Luna, C. Romina; Sandoval, Mario G.; Bechthold, Pablo; Pronsato, M. Estela; Juan, Alfredo

2017-12-01

The Spin-polarized density functional theory is used to study the effect of a single vacancy in a (8,0) single-walled carbon nanotube (SWCNT) on the Rh clustering process. The vacancy is considered oxygenated and non-oxygenated and, in each case, different Rhn cluster sizes (n = 1-4) are taken into account. For the analysis of these systems some physical and chemical properties are calculated, such as binding energy (Eb), work function (WF), magnetic moment, charge transfer, bond length, band gap (Eg), and density of state (DOS). From this analysis it can be concluded that: a single Rh atom and Rh2 dimer are adsorbed on vacancy without oxygen, whereas Rh3 and Rh4 clusters prefer to be adsorbed on oxygenated vacancy. In all cases, Rh adsorption induces a magnetic moment. When the Rh atom and Rh2 dimer are bonded to the defective SWCNT, it has been found that they show a semiconductor behavior that could be interesting to use in the spintronic area. In the case of Rh3 and Rh4 clusters our results show a metallic behavior suggesting that these systems are good candidates for nanotube contact.

Magnetic Field Effect: An Efficient Tool To Investigate The Mechanism Of Reactions Using Laser Flash Photolysis Technique

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

Basu, Samita; Bose, Adity; Dey, Debarati

2008-04-24

Magnetic field effect combined with laser flash photolysis technique have been used to study the mechanism of interactions between two drug-like quinone molecules, Menadione (1,4-naphthoquinone, MQ) and 9, 10 Anthraquinone (AQ) with one of the DNA bases, Adenine in homogeneous acetonitrile/water and heterogeneous micellar media. A switchover in reaction mode from electron transfer to hydrogen abstraction is observed with MQ on changing the solvent from acetonitrile/water to micelle; whereas, AQ retains its mode of interaction towards Adenine as electron transfer in both the media due to its bulky structure compared to MQ.

Radiative transfer in scattering stochastic atmospheres

NASA Astrophysics Data System (ADS)

Silant'ev, N. A.; Alekseeva, G. A.; Novikov, V. V.

2017-12-01

Many stars, active galactic nuclei, accretion discs etc. are affected by the stochastic variations of temperature, turbulent gas motions, magnetic fields, number densities of atoms and dust grains. These stochastic variations influence on the extinction factors, Doppler widths of lines and so on. The presence of many reasons for fluctuations gives rise to Gaussian distribution of fluctuations. The usual models leave out of account the fluctuations. In many cases the consideration of fluctuations improves the coincidence of theoretical values with the observed data. The objective of this paper is the investigation of the influence of the number density fluctuations on the form of radiative transfer equations. We consider non-magnetized atmosphere in continuum.

(LaTiO3)n/(LaVO3)n as a model system for unconventional charge transfer and polar metallicity

NASA Astrophysics Data System (ADS)

Weng, Yakui; Zhang, Jun-Jie; Gao, Bin; Dong, Shuai

At interfaces between oxide materials, lattice and electronic reconstructions always play important roles in exotic phenomena. In this study, the density-functional theory and maximally localized Wannier functions are employed to investigate the (LaTiO3)n/(LaVO3)n magnetic superlattices. By considering lattice distortion and dimensional effect, many interesting interfacial physics have been found in the n = 1 superlattice, e.g. magnetic phase transition, unconventional charge transfer, and metal-insulator transition. In addition, the compatibility among the polar structure, ferrimagnetism, and metallicity is predicted in the n = 2 superlattice.

Magnetic Field Effect: An Efficient Tool To Investigate The Mechanism Of Reactions Using Laser Flash Photolysis Technique

NASA Astrophysics Data System (ADS)

Basu, Samita; Bose, Adity; Dey, Debarati

2008-04-01

Magnetic field effect combined with laser flash photolysis technique have been used to study the mechanism of interactions between two drug-like quinone molecules, Menadione (1,4-naphthoquinone, MQ) and 9, 10 Anthraquinone (AQ) with one of the DNA bases, Adenine in homogeneous acetonitrile/water and heterogeneous micellar media. A switchover in reaction mode from electron transfer to hydrogen abstraction is observed with MQ on changing the solvent from acetonitrile/water to micelle; whereas, AQ retains its mode of interaction towards Adenine as electron transfer in both the media due to its bulky structure compared to MQ.