Magnetic Behavior of Ni-Fe Core-Shell and Alloy Nanowires

NASA Astrophysics Data System (ADS)

Tripathy, Jagnyaseni; Vargas, Jose; Spinu, Leonard; Wiley, John

2013-03-01

Template assisted synthesis was used to fabricate a series of Ni-Fe core-shell and alloy nanowires. By controlling reaction conditions as well as pore structure, both systems could be targeted and magnetic properties followed as a function of architectures. In the core-shell structure coercivity increases with decrease in shell thickness while for the alloys, coercivity squareness improve with increase pore diameter. Details on the systematic studies of these materials will be presented in terms of hysteretic measurements, including first order reversal curves (FORC), and FMR data. Magnetic variation as a function of structure and nanowire aspect ratios will be presented and the origins of these behaviors discussed. Advanced Material Research Institute

3D measurements and simulations of ion and neutral velocity distribution functions in a magnetized plasma boundary

NASA Astrophysics Data System (ADS)

Thompson, Derek S.; Keniley, Shane; Curreli, Davide; Henriquez, Miguel F.; Caron, David D.; Jemiolo, Andrew J.; McLaughlin, Jacob W.; Dufor, Mikal T.; Neal, Luke A.; Scime, Earl E.; Siddiqui, M. Umair

2017-10-01

We present progress toward the first paired 3D laser induced fluorescence measurements of ion and neutral velocity distribution functions (I/NVDFs) in a magnetized plasma boundary. These measurements are performed in the presheath region of an absorbing boundary immersed in a background magnetic field that is obliquely incident to the boundary surface (ψ =74°). Parallel and perpendicular flow measurements demonstrate that cross-field ion flows occur and that ions within several gyro-radii of the surface are accelerated in the E-> × B-> direction. We present electrostatic probe measurements of electron temperature, plasma density, and electric potential in the same region. Ion, neutral and electron measurements are compared to Boltzmann simulations, allowing direct comparison between measured and theoretical distribution functions in the boundary region. NSF PHYS 1360278.

[The peculiarities of the application of transcranial magnetic therapy and electrical stimulation for the treatment of the patients presenting with various types of stroke].

PubMed

Melnikova, E A

2015-01-01

In this article, the results of the authors' research, including analysis of the clinical and instrumental data concerning 203 patients with, stroke are presented. It is shown that the clinical effectiveness of the transcranial methods incorporated in the combined rehabilitation programs depends on the type of stroke and localization of the lesions. Specifically, the patients presenting with ischemic stroke of hemispheric localization experienced a neurophysiologically confirmed significant clinical improvement that became apparent after the consistent application of transcranial magnetic therapy and micropolarization. In the patients with ischemic stroke of stem localization, the positive influence on psychomotor recovery was achieved with the application of transcranial magnetic therapy, but transcranial micropolarization did not have an appreciable effect on the recovery of such patients. The patients presenting with hemorrhagic stroke did not experience any significant improvement of psychomotor parameters from transcranial magnetic therapy and transcranial micropolarization. The likely mechanism underlying the recovery of psychomotor processes under effect of transcranial magnetic therapy in the patients with ischemic stroke is the normalization of the frequency of interaction between brain structures. In addition, in the patients with ischemic stroke of hemispheric localization and in the patients with hemorrhagic stroke electrical myostimulation has a marked impact on the psychomotor recovery only in case of functional treatment. In the patients suffering from ischemic stroke of stem localization non-functional electromyostimulation significantly improves motor functions and cognitive motor control.

Studies of aggregated nanoparticles steering during magnetic-guided drug delivery in the blood vessels

NASA Astrophysics Data System (ADS)

Hoshiar, Ali Kafash; Le, Tuan-Anh; Amin, Faiz Ul; Kim, Myeong Ok; Yoon, Jungwon

2017-04-01

Magnetic-guided targeted drug delivery (TDD) systems can enhance the treatment of diverse diseases. Despite the potential and promising results of nanoparticles, aggregation prevents precise particle guidance in the vasculature. In this study, we developed a simulation platform to investigate aggregation during steering of nanoparticles using a magnetic field function. The magnetic field function (MFF) comprises a positive and negative pulsed magnetic field generated by electromagnetic coils, which prevents adherence of particles to the vessel wall during magnetic guidance. A commonly used Y-shaped vessel was simulated and the performance of the MFF analyzed; the experimental data were in agreement with the simulation results. Moreover, the effects of various parameters on magnetic guidance were evaluated and the most influential identified. The simulation results presented herein will facilitate more precise guidance of nanoparticles in vivo.

Magnetism, structures and stabilities of cluster assembled TM@Si nanotubes (TM = Cr, Mn and Fe): a density functional study.

PubMed

Dhaka, Kapil; Bandyopadhyay, Debashis

2016-08-02

The present study reports transition metal (TM = Cr, Mn and Fe) doped silicon nanotubes with tunable band structures and magnetic properties by careful selection of cluster assemblies as building blocks using the first-principles density functional theory. We found that the transition metal doping and in addition, the hydrogen termination process can stabilize the pure silicon nanoclusters or cluster assemblies and then it could be extended as magnetic nanotubes with finite magnetic moments. Study of the band structures and density of states (DOS) of different empty and TM doped nanotubes (Type 1 to Type 4) show that these nanotubes are useful as metals, semiconductors, semi-metals and half-metals. These designer magnetic materials could be useful in spintronics and magnetic devices of nanoscale order.

High-permeability functionalized silicone magnetic microspheres with low autofluorescence for biomedical applications

PubMed Central

Evans, Benjamin A.; Ronecker, Julia C.; Han, David T.; Glass, Daniel R.; Train, Tonya L.; Deatsch, Alison E.

2017-01-01

Functionalized magnetic microspheres are widely used for cell separations, isolation of proteins and other biomolecules, in vitro diagnostics, tissue engineering, and microscale force spectroscopy. We present here the synthesis and characterization of a silicone magnetic microsphere which can be produced in diameters ranging from 0.5 to 50 μm via emulsion polymerization of a silicone ferrofluid precursor. This bottom-up approach to synthesis ensures a uniform magnetic concentration across all sizes, leading to significant advances in magnetic force generation. We demonstrate that in a size range of 5–20 μm, these spheres supply a full order of magnitude greater magnetic force than leading commercial products. In addition, the unique silicone matrix exhibits autofluorescence two orders of magnitude lower than polystyrene microspheres. Finally, we demonstrate the ability to chemically functionalize our silicone microspheres using a standard EDC reaction, and show that our folate-functionalized silicone microspheres specifically bind to targeted HeLa and Jurkat cells. These spheres show tremendous potential for replacing magnetic polystyrene spheres in applications which require either large magnetic forces or minimal autofluorescence, since they represent order-of-magnitude improvements in each. In addition, the unique silicone matrix and proven biocompatibility suggest that they may be useful for encapsulation and targeted delivery of lipophilic pharmaceuticals. PMID:26952493

Three-dimensional functional magnetic resonance imaging of human brain on a clinical 1.5-T scanner.

PubMed Central

van Gelderen, P; Ramsey, N F; Liu, G; Duyn, J H; Frank, J A; Weinberger, D R; Moonen, C T

1995-01-01

Functional magnetic resonance imaging (fMRI) is a tool for mapping brain function that utilizes neuronal activity-induced changes in blood oxygenation. An efficient three-dimensional fMRI method is presented for imaging brain activity on conventional, widely available, 1.5-T scanners, without additional hardware. This approach uses large magnetic susceptibility weighting based on the echo-shifting principle combined with multiple gradient echoes per excitation. Motor stimulation, induced by self-paced finger tapping, reliably produced significant signal increase in the hand region of the contralateral primary motor cortex in every subject tested. Images Fig. 2 Fig. 3 PMID:7624341

Verification of Anderson Superexchange in MnO via Magnetic Pair Distribution Function Analysis and ab initio Theory

NASA Astrophysics Data System (ADS)

Frandsen, Benjamin A.; Brunelli, Michela; Page, Katharine; Uemura, Yasutomo J.; Staunton, Julie B.; Billinge, Simon J. L.

2016-05-01

We present a temperature-dependent atomic and magnetic pair distribution function (PDF) analysis of neutron total scattering measurements of antiferromagnetic MnO, an archetypal strongly correlated transition-metal oxide. The known antiferromagnetic ground-state structure fits the low-temperature data closely with refined parameters that agree with conventional techniques, confirming the reliability of the newly developed magnetic PDF method. The measurements performed in the paramagnetic phase reveal significant short-range magnetic correlations on a ˜1 nm length scale that differ substantially from the low-temperature long-range spin arrangement. Ab initio calculations using a self-interaction-corrected local spin density approximation of density functional theory predict magnetic interactions dominated by Anderson superexchange and reproduce the measured short-range magnetic correlations to a high degree of accuracy. Further calculations simulating an additional contribution from a direct exchange interaction show much worse agreement with the data. The Anderson superexchange model for MnO is thus verified by experimentation and confirmed by ab initio theory.

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

PubMed

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

2017-09-12

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

Magnetic field effects on charge structure factors of gapped graphene structure

NASA Astrophysics Data System (ADS)

Rezania, Hamed; Tawoose, Nasrin

2018-02-01

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

Preparation and characterization of iron oxide magnetic nanoparticles functionalized by nisin.

PubMed

Gruskiene, Ruta; Krivorotova, Tatjana; Staneviciene, Ramune; Ratautas, Dalius; Serviene, Elena; Sereikaite, Jolanta

2018-05-08

Nisin is a known bacteriocin approved as a food additive for food preservation. It exhibits a wide spectrum antimicrobial activity against Gram-positive bacteria. Iron oxide magnetic nanoparticles were synthesized and characterized by X-ray diffraction method. A main part of iron oxide nanoparticles was found to be maghemite though a small quantity of magnetite could also be present. Magnetic nanoparticles were stabilized by citric, ascorbic, gallic or glucuronic acid coating. Stable iron oxide magnetic nanoparticles were functionalized by nisin using a simple and low cost adsorption method. Nisin loading was confirmed by FT-IR spectra, thermogravimetric analysis, dynamic light scattering and atomic force microscopy methods. Nisin-loaded iron oxide magnetic nanoparticles were stable at least six weeks as judged by the measurements of zeta-potential and hydrodynamic diameter. The antimicrobial activity of nisin-loaded iron oxide magnetic nanoparticles was demonstrated toward Gram-positive bacteria. Functionalized nanoparticles could therefore find the application as antimicrobials in innovative and emerging technologies based on the magnetic field. Copyright © 2018 Elsevier B.V. All rights reserved.

Muon collider interaction region design

DOE PAGES

Alexahin, Y. I.; Gianfelice-Wendt, E.; Kashikhin, V. V.; ...

2011-06-02

Design of a muon collider interaction region (IR) presents a number of challenges arising from low β* < 1 cm, correspondingly large beta-function values and beam sizes at IR magnets, as well as the necessity to protect superconducting magnets and collider detectors from muon decay products. As a consequence, the designs of the IR optics, magnets and machine-detector interface are strongly interlaced and iterative. A consistent solution for the 1.5 TeV center-of-mass muon collider IR is presented. It can too provide an average luminosity of 10 34 cm -2s -1 with an adequate protection of magnet and detector components.

Study of Permanent Magnet Focusing for Astronomical Camera Tubes

NASA Technical Reports Server (NTRS)

Long, D. C.; Lowrance, J. L.

1975-01-01

A design is developed of a permanent magnet assembly (PMA) useful as the magnetic focusing unit for the 35 and 70 mm (diagonal) format SEC tubes. Detailed PMA designs for both tubes are given, and all data on their magnetic configuration, size, weight, and structure of magnetic shields adequate to screen the camera tube from the earth's magnetic field are presented. A digital computer is used for the PMA design simulations, and the expected operational performance of the PMA is ascertained through the calculation of a series of photoelectron trajectories. A large volume where the magnetic field uniformity is greater than 0.5% appears obtainable, and the point spread function (PSF) and modulation transfer function(MTF) indicate nearly ideal performance. The MTF at 20 cycles per mm exceeds 90%. The weight and volume appear tractable for the large space telescope and ground based application.

Quantum Theory of Orbital Magnetization and Its Generalization to Interacting Systems

NASA Astrophysics Data System (ADS)

Shi, Junren; Vignale, G.; Xiao, Di; Niu, Qian

2007-11-01

Based on standard perturbation theory, we present a full quantum derivation of the formula for the orbital magnetization in periodic systems. The derivation is generally valid for insulators with or without a Chern number, for metals at zero or finite temperatures, and at weak as well as strong magnetic fields. The formula is shown to be valid in the presence of electron-electron interaction, provided the one-electron energies and wave functions are calculated self-consistently within the framework of the exact current and spin-density functional theory.

Multi-functional liposomes showing radiofrequency-triggered release and magnetic resonance imaging for tumor multi-mechanism therapy.

PubMed

Du, Bin; Han, Shuping; Li, Hongyan; Zhao, Feifei; Su, Xiangjie; Cao, Xiaohui; Zhang, Zhenzhong

2015-03-12

Recently, nanoplatforms with multiple functions, such as tumor-targeting drug carriers, MRI, optical imaging, thermal therapy etc., have become popular in the field of cancer research. The present study reports a novel multi-functional liposome for cancer theranostics. A dual targeted drug delivery with radiofrequency-triggered drug release and imaging based on the magnetic field influence was used advantageously for tumor multi-mechanism therapy. In this system, the surface of fullerene (C60) was decorated with iron oxide nanoparticles, and PEGylation formed a hybrid nanosystem (C60-Fe3O4-PEG2000). Thermosensitive liposomes (dipalmitoylphosphatidylcholine, DPPC) with DSPE-PEG2000-folate wrapped up the hybrid nanosystem and docetaxel (DTX), which were designed to combine features of biological and physical (magnetic) drug targeting for fullerene radiofrequency-triggered drug release. The magnetic liposomes not only served as powerful tumor diagnostic magnetic resonance imaging (MRI) contrast agents, but also as powerful agents for photothermal ablation of tumors. Furthermore, a remarkable thermal therapy combined chemotherapy multi-functional liposome nanoplatform converted radiofrequency energy into thermal energy to release drugs from thermosensitive liposomes, which was also observed during both in vitro and in vivo treatment. The multi-functional liposomes also could selectively kill cancer cells in highly localized regions via their excellent active tumor targeting and magnetic targeted abilities.

Continuous chemical operations and modifications on magnetic γ-Fe2O3 nanoparticles confined in nanoliter droplets for the assembly of fluorescent and magnetic SiO2@γ-Fe2O3.

PubMed

Ferraro, D; Lin, Y; Teste, B; Talbot, D; Malaquin, L; Descroix, S; Abou-Hassan, A

2015-12-11

We present a microfluidic platform that allows undergoing different chemical operations in a nanoliter droplet starting from the colloidal suspension of magnetic iron oxide (γ-Fe2O3) nanoparticles "NPs" (ferrofluid). These operations include: mixing, flocculation, magnetic decantation, colloidal redispersion, washing, surface functionalization, heating and colloidal assembly. To prove the platform capabilities, we produced fluorescent and magnetic nanoassemblies composed of fluorescent silica and magnetic NPs.

Analytic and numeric Green's functions for a two-dimensional electron gas in an orthogonal magnetic field

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

Cresti, Alessandro; Grosso, Giuseppe; Parravicini, Giuseppe Pastori

2006-05-15

We have derived closed analytic expressions for the Green's function of an electron in a two-dimensional electron gas threaded by a uniform perpendicular magnetic field, also in the presence of a uniform electric field and of a parabolic spatial confinement. A workable and powerful numerical procedure for the calculation of the Green's functions for a large infinitely extended quantum wire is considered exploiting a lattice model for the wire, the tight-binding representation for the corresponding matrix Green's function, and the Peierls phase factor in the Hamiltonian hopping matrix element to account for the magnetic field. The numerical evaluation of themore » Green's function has been performed by means of the decimation-renormalization method, and quite satisfactorily compared with the analytic results worked out in this paper. As an example of the versatility of the numerical and analytic tools here presented, the peculiar semilocal character of the magnetic Green's function is studied in detail because of its basic importance in determining magneto-transport properties in mesoscopic systems.« less

Functional magnetic resonance microscopy at single-cell resolution in Aplysia californica

PubMed Central

Radecki, Guillaume; Nargeot, Romuald; Jelescu, Ileana Ozana; Le Bihan, Denis; Ciobanu, Luisa

2014-01-01

In this work, we show the feasibility of performing functional MRI studies with single-cell resolution. At ultrahigh magnetic field, manganese-enhanced magnetic resonance microscopy allows the identification of most motor neurons in the buccal network of Aplysia at low, nontoxic Mn2+ concentrations. We establish that Mn2+ accumulates intracellularly on injection into the living Aplysia and that its concentration increases when the animals are presented with a sensory stimulus. We also show that we can distinguish between neuronal activities elicited by different types of stimuli. This method opens up a new avenue into probing the functional organization and plasticity of neuronal networks involved in goal-directed behaviors with single-cell resolution. PMID:24872449

Magnetic stem cell targeting to the inner ear

NASA Astrophysics Data System (ADS)

Le, T. N.; Straatman, L.; Yanai, A.; Rahmanian, R.; Garnis, C.; Häfeli, U. O.; Poblete, T.; Westerberg, B. D.; Gregory-Evans, K.

2017-12-01

Severe sensorineural deafness is often accompanied by a loss of auditory neurons in addition to injury of the cochlear epithelium and hair cell loss. Cochlear implant function however depends on a healthy complement of neurons and their preservation is vital in achieving optimal results. We have developed a technique to target mesenchymal stem cells (MSCs) to a deafened rat cochlea. We then assessed the neuroprotective effect of systematically delivered MSCs on the survival and function of spiral ganglion neurons (SGNs). MSCs were labeled with superparamagnetic nanoparticles, injected via the systemic circulation, and targeted using a magnetized cochlea implant and external magnet. Neurotrophic factor concentrations, survival of SGNs, and auditory function were assessed at 1 week and 4 weeks after treatments and compared against multiple control groups. Significant numbers of magnetically targeted MSCs (>30 MSCs/section) were present in the cochlea with accompanied elevation of brain-derived neurotrophic factor and glial cell-derived neurotrophic factor levels (p < 0.001). In addition we saw improved survival of SGNs (approximately 80% survival at 4 weeks). Hearing threshold levels in magnetically targeted rats were found to be significantly better than those of control rats (p < 0.05). These results indicate that magnetic targeting of MSCs to the cochlea can be accomplished with a magnetized cochlear permalloy implant and an external magnet. The targeted stem cells release neurotrophic factors which results in improved SGN survival and hearing recovery. Combining magnetic cell-based therapy and cochlear implantation may improve cochlear implant function in treating deafness.

Holographic superconductor vortices.

PubMed

Montull, Marc; Pomarol, Alex; Silva, Pedro J

2009-08-28

A gravity dual of a superconductor at finite temperature has been recently proposed. We present the vortex configuration of this model and study its properties. In particular, we calculate the free energy as a function of an external magnetic field, the magnetization, and the superconducting density. We also find the two critical magnetic fields that define the region in which the vortex configurations are energetically favorable.

Random Fields and Collective Effects in Molecular Magnets

DTIC Science & Technology

2018-01-29

longitudinal fields the final state consists of only partially reversed spins. Further, we measured the front speed as a function of applied magnetic...field. The theory of magnetic deflagration, together with a modification that takes into account the partial spin reversal, fits the transverse field...Conference Paper or Presentation Conference Name: APS March Meeting 2016 Conference Location: Baltimore, Paper Title: Time-resolved Measurements

Verification of Anderson Superexchange in MnO via Magnetic Pair Distribution Function Analysis and ab initio Theory.

PubMed

Frandsen, Benjamin A; Brunelli, Michela; Page, Katharine; Uemura, Yasutomo J; Staunton, Julie B; Billinge, Simon J L

2016-05-13

We present a temperature-dependent atomic and magnetic pair distribution function (PDF) analysis of neutron total scattering measurements of antiferromagnetic MnO, an archetypal strongly correlated transition-metal oxide. The known antiferromagnetic ground-state structure fits the low-temperature data closely with refined parameters that agree with conventional techniques, confirming the reliability of the newly developed magnetic PDF method. The measurements performed in the paramagnetic phase reveal significant short-range magnetic correlations on a ∼1  nm length scale that differ substantially from the low-temperature long-range spin arrangement. Ab initio calculations using a self-interaction-corrected local spin density approximation of density functional theory predict magnetic interactions dominated by Anderson superexchange and reproduce the measured short-range magnetic correlations to a high degree of accuracy. Further calculations simulating an additional contribution from a direct exchange interaction show much worse agreement with the data. The Anderson superexchange model for MnO is thus verified by experimentation and confirmed by ab initio theory.

Verification of Anderson superexchange in MnO via magnetic pair distribution function analysis and ab initio theory

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

Benjamin A. Frandsen; Brunelli, Michela; Page, Katharine

Here, we present a temperature-dependent atomic and magnetic pair distribution function (PDF) analysis of neutron total scattering measurements of antiferromagnetic MnO, an archetypal strongly correlated transition-metal oxide. The known antiferromagnetic ground-state structure fits the low-temperature data closely with refined parameters that agree with conventional techniques, confirming the reliability of the newly developed magnetic PDF method. The measurements performed in the paramagnetic phase reveal significant short-range magnetic correlations on a ~1 nm length scale that differ substantially from the low-temperature long-range spin arrangement. Ab initio calculations using a self-interaction-corrected local spin density approximation of density functional theory predict magnetic interactions dominatedmore » by Anderson superexchange and reproduce the measured short-range magnetic correlations to a high degree of accuracy. Further calculations simulating an additional contribution from a direct exchange interaction show much worse agreement with the data. Furthermore, the Anderson superexchange model for MnO is thus verified by experimentation and confirmed by ab initio theory.« less

Verification of Anderson superexchange in MnO via magnetic pair distribution function analysis and ab initio theory

DOE PAGES

Benjamin A. Frandsen; Brunelli, Michela; Page, Katharine; ...

2016-05-11

Here, we present a temperature-dependent atomic and magnetic pair distribution function (PDF) analysis of neutron total scattering measurements of antiferromagnetic MnO, an archetypal strongly correlated transition-metal oxide. The known antiferromagnetic ground-state structure fits the low-temperature data closely with refined parameters that agree with conventional techniques, confirming the reliability of the newly developed magnetic PDF method. The measurements performed in the paramagnetic phase reveal significant short-range magnetic correlations on a ~1 nm length scale that differ substantially from the low-temperature long-range spin arrangement. Ab initio calculations using a self-interaction-corrected local spin density approximation of density functional theory predict magnetic interactions dominatedmore » by Anderson superexchange and reproduce the measured short-range magnetic correlations to a high degree of accuracy. Further calculations simulating an additional contribution from a direct exchange interaction show much worse agreement with the data. Furthermore, the Anderson superexchange model for MnO is thus verified by experimentation and confirmed by ab initio theory.« less

Synthesis, characterization and applications of maghemite beads functionalized with rabbit antibodies.

PubMed

Rodriguez, A F R; Rocha, C O; Piazza, R D; Dos Santos, C C; Morales, M A; Faria, F S E D V; Iqbal, M Zubair; Barbosa, L; Chaves, Y O; Mariuba, L A; Jafelicci, M; Marques, R F C

2018-06-12

Magnetic nanoparticles (NPs) have attracted great attention owing to their applications in the biomedical field. In the present work, maghemite (γFe 2 O 3 ) NPs of 6.5 nm were prepared using a sonochemical method and used to prepare magnetic beads through silanization with 3-aminopropyltrimethoxysilane (APTS). Subsequently, amino groups in the resulting APTS-γFe 2 O 3 beads were converted to carboxylic acid (CARB-γFe 2 O 3 ) through the succinic anhydride reaction, as confirmed by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy and dynamic light scattering (DLS) measurements. The size of these beads was measured as 12 nm and their hydrodynamic diameter as 490 nm, using TEM analysis and DLS, respectively. The CARB-γFe 2 O 3 beads were further functionalized by immobilizing rabbit antibodies on their surfaces; the immobilization was confirmed by flow cytometry and ionic strength. The samples were further characterized by Mössbauer spectroscopy and DC magnetization measurements. Studies on magnetic relaxivities showed that magnetic beads present great potential for application in MR imaging.

Influence of the surface magnetic field of a cylindrical permanent magnet on the maximum levitation force in high-Tc superconductors

NASA Astrophysics Data System (ADS)

Zhao, Xian-Feng; Liu, Yuan

2006-06-01

In this paper we present the dependence of the maximum levitation force (FzMax) of a high-Tc superconductor on the surface magnetic field (Bs) of a cylindrical permanent magnet, based on the Bean critical state model and Ampère's law. A transition point of Bs is found at which the relation between FzMax and Bs changes: while the surface magnetic field is less than the transition point the dependence is subjected to a nonlinear function, otherwise it is a linear one. The two different relations are estimated to correspond to partial penetration of the shielding currents in the interior of the superconductor below the transition point and complete penetration above it, respectively. Furthermore, the influence of the geometrical properties of superconductors on the transition point of Bs is discussed, which shows a quadratic polynomial function between the transition points and the radii and the thickness of superconductors. Some optimum contours of the transition point of Bs are presented in order to achieve large levitation forces.

Magnetic resonance imaging findings of cellular angiofibroma of the tunica vaginalis of the testis: a case report.

PubMed

Ntorkou, Alexandra A; Tsili, Athina C; Giannakis, Dimitrios; Batistatou, Anna; Stavrou, Sotirios; Sofikitis, Nikolaos; Argyropoulou, Maria I

2016-03-31

Cellular angiofibroma represents a rare mesenchymal tumor typically involving the inguinoscrotal area in middle-aged men. Although the origin of this benign tumor is unknown, it is histologically classified as an angiomyxoid tumor. Cellular angiofibroma is characterized by a diversity of pathological and imaging features. An accurate preoperative diagnosis is challenging. Magnetic resonance imaging examination of the scrotum has been reported as a valuable adjunct modality in the investigation of scrotal pathology. The technique by providing both structural and functional information is useful in the differentiation between extratesticular and intratesticular diseases and in the preoperative characterization of the histologic nature of various scrotal lesions. There are few reports in the English literature addressing the magnetic resonance imaging findings of cellular angiofibroma of the scrotum and no reports on functional magnetic resonance imaging data. Here we present the first case of a cellular angiofibroma arising from the tunica vaginalis of the testis and we discuss the value of a multiparametric magnetic resonance protocol, including diffusion-weighted imaging, magnetization transfer imaging and dynamic contrast-enhanced magnetic resonance imaging in the preoperative diagnosis of this rare neoplasm. A 47-year Greek man presented with a painless left scrotal swelling, which had gradually enlarged during the last 6 months. Magnetic resonance imaging of his scrotum displayed a left paratesticular mass, in close proximity to the tunica vaginalis, with heterogeneous high signal intensity on T2-weighted images and no areas of restricted diffusion. The tumor was hypointense on magnetization transfer images, suggestive for the presence of macromolecules. On dynamic contrast-enhanced magnetic resonance imaging the mass showed intense heterogeneous enhancement with a type II curve. Magnetic resonance imaging findings were strongly suggestive of a benign paratesticular tumor, which was confirmed on pathology following lesion excision. Magnetic resonance imaging of the scrotum by combining conventional and functional magnetic resonance data provides useful diagnostic information in the preoperative characterization of scrotal masses. A possible diagnosis of a benign paratesticular tumor based on magnetic resonance imaging features may improve patient care and decrease the number of unnecessary radical surgical explorations.

Electron Cloud Trapping in Recycler Combined Function Dipole Magnets

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

Antipov, Sergey A.; Nagaitsev, S.

2016-10-04

Electron cloud can lead to a fast instability in intense proton and positron beams in circular accelerators. In the Fermilab Recycler the electron cloud is confined within its combined function magnets. We show that the field of combined function magnets traps the electron cloud, present the results of analytical estimates of trapping, and compare them to numerical simulations of electron cloud formation. The electron cloud is located at the beam center and up to 1% of the particles can be trapped by the magnetic field. Since the process of electron cloud build-up is exponential, once trapped this amount of electronsmore » significantly increases the density of the cloud on the next revolution. In a Recycler combined function dipole this multiturn accumulation allows the electron cloud reaching final intensities orders of magnitude greater than in a pure dipole. The multi-turn build-up can be stopped by injection of a clearing bunch of 1010 p at any position in the ring.« less

Unique system of FE/PD for magneto-optical recording and magnetic switching devices

DOEpatents

Liu, Chian Q.; Bader, Samuel D.

1992-01-01

A high density magneto-optical information storage medium utilizing the properties of an ultrathin iron film on a palladium substrate. The present invention comprises a magneto-optical medium capable of thermal and magnetic stability and capable of possessing a vertical orientation of the magnetization vector for the magnetic material. Data storage relies on the temperature dependence of the coercivity of the ultrathin film. Data retrieval derives from the Kerr effect which describes the direction of rotation of a plane of polarized light traversing the ultrathin magnetic material as a function of the orientation of the magnetization vector.

Peptide conjugated magnetic nanoparticles for magnetically mediated energy delivery to lung cancer cells.

PubMed

Hauser, Anastasia K; Anderson, Kimberly W; Hilt, J Zach

2016-07-01

In the present study, we examine the effects of internalized peptide-conjugated iron oxide nanoparticles and their ability to locally convert alternating magnetic field (AMF) energy into other forms of energy (e.g., heat and rotational work). Dextran-coated iron oxide nanoparticles were functionalized with a cell penetrating peptide and after internalization by A549 and H358 cells were activated by an AMF. TAT-functionalized nanoparticles and AMF exposure increased reactive oxygen species generation compared with the nanoparticle system alone. The TAT-functionalized nanoparticles induced lysosomal membrane permeability and mitochondrial membrane depolarization, but these effects were not further enhanced by AMF treatment. Although not statistically significant, there are trends suggesting an increase in apoptosis via the Caspase 3/7 pathways when cells are exposed to TAT-functionalized nanoparticles combined with AMF. Our results indicate that internalized TAT-functionalized iron oxide nanoparticles activated by an AMF elicit cellular responses without a measurable temperature rise.

Magnetic behavior study of samarium nitride using density functional theory

NASA Astrophysics Data System (ADS)

Som, Narayan N.; Mankad, Venu H.; Dabhi, Shweta D.; Patel, Anjali; Jha, Prafulla K.

2018-02-01

In this work, the state-of-art density functional theory is employed to study the structural, electronic and magnetic properties of samarium nitride (SmN). We have performed calculation for both ferromagnetic and antiferromagnetic states in rock-salt phase. The calculated results of optimized lattice parameter and magnetic moment agree well with the available experimental and theoretical values. From energy band diagram and electronic density of states, we observe a half-metallic behaviour in FM phase of rock salt SmN in while metallicity in AFM I and AFM III phases. We present and discuss our current understanding of the possible half-metallicity together with the magnetic ordering in SmN. The calculated phonon dispersion curves shows dynamical stability of the considered structures. The phonon density of states and Eliashberg functional have also been analysed to understand the superconductivity in SmN.

Reconfigurable logic via gate controlled domain wall trajectory in magnetic network structure

PubMed Central

Murapaka, C.; Sethi, P.; Goolaup, S.; Lew, W. S.

2016-01-01

An all-magnetic logic scheme has the advantages of being non-volatile and energy efficient over the conventional transistor based logic devices. In this work, we present a reconfigurable magnetic logic device which is capable of performing all basic logic operations in a single device. The device exploits the deterministic trajectory of domain wall (DW) in ferromagnetic asymmetric branch structure for obtaining different output combinations. The programmability of the device is achieved by using a current-controlled magnetic gate, which generates a local Oersted field. The field generated at the magnetic gate influences the trajectory of the DW within the structure by exploiting its inherent transverse charge distribution. DW transformation from vortex to transverse configuration close to the output branch plays a pivotal role in governing the DW chirality and hence the output. By simply switching the current direction through the magnetic gate, two universal logic gate functionalities can be obtained in this device. Using magnetic force microscopy imaging and magnetoresistance measurements, all basic logic functionalities are demonstrated. PMID:26839036

A Model of Anode Sheath Potential Evolution in a Transverse Magnetic Field

NASA Astrophysics Data System (ADS)

Foster, John E.; Gallimore, Alec D.

1996-11-01

It has been conjectured that the growth in the magnitude of the anode fall voltage with changing transverse magnetic field is a function of the ratio of available transverse current to the discharge current. It has been postulated that at small values of this ratio, the anode fall voltage and thus the near-anode electric field increases in order to assure that the prescribed discharge is maintained.footnote H. Hugel, IEEE Tran. Plas. Sci., PS-8,4, 1980 In this present work, a model is presented which predicts the behavior of the anode fall voltage as a function of transverse magnetic field. The model attempts to explain why the anode fall voltage depends so strongly on this ratio. In addition, it is further shown that because of the current ratio's strong dependence on local electron number density, ultimately it is the changes in near-anode ionization processes with varying transverse magnetic field that control the anode fall voltage.

Tailored functionalization of iron oxide nanoparticles for MRI, drug delivery, magnetic separation and immobilization of biosubstances.

PubMed

Hola, Katerina; Markova, Zdenka; Zoppellaro, Giorgio; Tucek, Jiri; Zboril, Radek

2015-11-01

In this critical review, we outline various covalent and non-covalent approaches for the functionalization of iron oxide nanoparticles (IONPs). Tuning the surface chemistry and design of magnetic nanoparticles are described in relation to their applicability in advanced medical technologies and biotechnologies including magnetic resonance imaging (MRI) contrast agents, targeted drug delivery, magnetic separations and immobilizations of proteins, enzymes, antibodies, targeting agents and other biosubstances. We review synthetic strategies for the controlled preparation of IONPs modified with frequently used functional groups including amine, carboxyl and hydroxyl groups as well as the preparation of IONPs functionalized with other species, e.g., epoxy, thiol, alkane, azide, and alkyne groups. Three main coupling strategies for linking IONPs with active agents are presented: (i) chemical modification of amine groups on the surface of IONPs, (ii) chemical modification of bioactive substances (e.g. with fluorescent dyes), and (iii) the activation of carboxyl groups mainly for enzyme immobilization. Applications for drug delivery using click chemistry linking or biodegradable bonds are compared to non-covalent methods based on polymer modified condensed magnetic nanoclusters. Among many challenges, we highlight the specific surface engineering allowing both therapeutic and diagnostic applications (theranostics) of IONPs and magnetic/metallic hybrid nanostructures possessing a huge potential in biocatalysis, green chemistry, magnetic bioseparations and bioimaging. Copyright © 2015 Elsevier Inc. All rights reserved.

Microfabricated magnetic traps for single molecule manipulation and measurement

NASA Astrophysics Data System (ADS)

Mirowski, Elizabeth; Moreland, John; Russek, Stephen; Donahue, Michael

2003-03-01

We have microfabricated patterned magnetic thin film traps for capturing superparamagnetic beads in microfluidic cells. The traps are based on a novel concept of using a magnetic force microsope cantilever for transporting magnetic beads from one trap to another along the surface of a thin silicon nitride membrane. We specifically address the optimal design criteria for the traps. In addition, we present measurements of the forces on a bead (attached to a functionalized cantilever tip) as a function of its position near the trap. Equivalent spring constants of various trap geometries are extrapolated from the force measurements. The force measurements will be compared to micromagnetic modelling of the system as well as the Brownian motion of the bead in the trap.

Methods for Dichoptic Stimulus Presentation in Functional Magnetic Resonance Imaging - A Review

PubMed Central

Choubey, Bhaskar; Jurcoane, Alina; Muckli, Lars; Sireteanu, Ruxandra

2009-01-01

Dichoptic stimuli (different stimuli displayed to each eye) are increasingly being used in functional brain imaging experiments using visual stimulation. These studies include investigation into binocular rivalry, interocular information transfer, three-dimensional depth perception as well as impairments of the visual system like amblyopia and stereodeficiency. In this paper, we review various approaches of displaying dichoptic stimulus used in functional magnetic resonance imaging experiments. These include traditional approaches of using filters (red-green, red-blue, polarizing) with optical assemblies as well as newer approaches of using bi-screen goggles. PMID:19526076

Stable, polymer-directed and SPION-nucleated magnetic amphiphilic block copolymer nanoprecipitates with readily reversible assembly in magnetic fields

NASA Astrophysics Data System (ADS)

Giardiello, Marco; Hatton, Fiona L.; Slater, Rebecca A.; Chambon, Pierre; North, Jocelyn; Peacock, Anita K.; He, Tao; McDonald, Tom O.; Owen, Andrew; Rannard, Steve P.

2016-03-01

The formation of inorganic-organic magnetic nanocomposites using reactive chemistry often leads to a loss of super-paramagnetisim when conducted in the presence of iron oxide nanoparticles. We present here a low energy and chemically-mild process of co-nanoprecipitation using SPIONs and homopolymers or amphiphilic block copolymers, of varying architecture and hydrophilic/hydrophobic balance, which efficiently generates near monodisperse SPION-containing polymer nanoparticles with complete retention of magnetism, and highly reversible aggregation and redispersion behaviour. When linear and branched block copolymers with inherent water-solubility are used, a SPION-directed nanoprecipitation mechanism appears to dominate the nanoparticle formation presenting new opportunities for tailoring and scaling highly functional systems for a range of applications.The formation of inorganic-organic magnetic nanocomposites using reactive chemistry often leads to a loss of super-paramagnetisim when conducted in the presence of iron oxide nanoparticles. We present here a low energy and chemically-mild process of co-nanoprecipitation using SPIONs and homopolymers or amphiphilic block copolymers, of varying architecture and hydrophilic/hydrophobic balance, which efficiently generates near monodisperse SPION-containing polymer nanoparticles with complete retention of magnetism, and highly reversible aggregation and redispersion behaviour. When linear and branched block copolymers with inherent water-solubility are used, a SPION-directed nanoprecipitation mechanism appears to dominate the nanoparticle formation presenting new opportunities for tailoring and scaling highly functional systems for a range of applications. Electronic supplementary information (ESI) available: Additional experimental details, NMR spectra, GPC chromatograms, kinetics experiments, graphs of nanopreciptate aggregation and cycling studies and SPION characterisation. See DOI: 10.1039/c6nr00788k

Engineering biofunctional magnetic nanoparticles for biotechnological applications

NASA Astrophysics Data System (ADS)

Moros, Maria; Pelaz, Beatriz; López-Larrubia, Pilar; García-Martin, Maria L.; Grazú, Valeria; de La Fuente, Jesus M.

2010-09-01

Synthesis and characterization of magnetic nanoparticles with excellent size control are showed here. Their functionalization using an amphiphilic polymer is also described. This strategy allows the stabilization of magnetic nanoparticles in aqueous solvents and in addition, the polymer shell serves as a platform to incorporate relevant biomolecules, such as poly(ethylene glycol) and a number of carbohydrates. Nanoparticles functionalized with carbohydrates show the ability to avoid unspecific interactions between proteins present in the working medium and the nanoparticles, so can be used as an alternative to poly(ethylene glycol) molecules. Results confirm these nanoparticles as excellent contrast agents for magnetic resonance imaging. Changes in the spin-spin transversal relaxation times of the surrounding water protons due to nanoparticle aggregation demonstrates the bioactivity of these nanoparticles functionalized with carbohydrates. To finish with, nanoparticle toxicity is evaluated by means of MTT assay. The obtained results clearly indicate that these nanoparticles are excellent candidates for their further application in nanomedicine or nanobiotechnology.Synthesis and characterization of magnetic nanoparticles with excellent size control are showed here. Their functionalization using an amphiphilic polymer is also described. This strategy allows the stabilization of magnetic nanoparticles in aqueous solvents and in addition, the polymer shell serves as a platform to incorporate relevant biomolecules, such as poly(ethylene glycol) and a number of carbohydrates. Nanoparticles functionalized with carbohydrates show the ability to avoid unspecific interactions between proteins present in the working medium and the nanoparticles, so can be used as an alternative to poly(ethylene glycol) molecules. Results confirm these nanoparticles as excellent contrast agents for magnetic resonance imaging. Changes in the spin-spin transversal relaxation times of the surrounding water protons due to nanoparticle aggregation demonstrates the bioactivity of these nanoparticles functionalized with carbohydrates. To finish with, nanoparticle toxicity is evaluated by means of MTT assay. The obtained results clearly indicate that these nanoparticles are excellent candidates for their further application in nanomedicine or nanobiotechnology. Electronic supplementary information (ESI) available: Chemical, physical and magnetic characterization; R2 maps; stability of NPs at different conditions; size of glucose NPs in the presence of Concanavalin A; MTT assays of the samples are shown in figures S1-S10. Table S1 represents the hydrodynamic size of PMAO NPs after being washed with different solvents. See DOI: 10.1039/c0nr00104j

Localized magnetism in liquid Al80Mn20 alloys: A first-principles investigation

NASA Astrophysics Data System (ADS)

Jakse, N.; LeBacq, O.; Pasturel, A.

2006-04-01

We present first-principles investigations of the formation of magnetic moments in liquid Al80Mn20 alloys as a function of temperature. We predict the existence of large magnetic moments on Mn atoms which are close to that of the single-impurity limit. The wide distribution of moments can be understood in terms of fluctuations in the local environment. Our calculations also predict that thermal expansion effects within the single-impurity model mainly explain the striking increase of magnetism with temperature.

Micromagnetic study of equilibrium states in nano hemispheroidal shells

NASA Astrophysics Data System (ADS)

Schultz, Keren; Schultz, Moty

2017-11-01

We present results of micromagnetic simulations of thin ferromagnetic nano hemispheroidal shells with sizes ranging from 5 to 50 nm (inside dimensions). Depending on the geometrical and magnetic parameters of the hemispheroidal shell, there exist three different magnetic phases: easy axis, onion and vortex. The profile for the vortex magnetization distribution is analyzed and the limitations and applicability of different vortex ansatzes are discussed. In addition, we investigate the total energy density for each of the magnetic distributions as a function of the hemispheroidal shell dimensions.

Preparation of magnetic chitosan and graphene oxide-functional guanidinium ionic liquid composite for the solid-phase extraction of protein.

PubMed

Ding, Xueqin; Wang, Yuzhi; Wang, Ying; Pan, Qi; Chen, Jing; Huang, Yanhua; Xu, Kaijia

2015-02-25

A series of novel cationic functional hexaalkylguanidinium ionic liquids and anionic functional tetraalkylguanidinium ionic liquids have been synthesized, and then magnetic chitosan graphene oxide (MCGO) composite has been prepared and coated with these functional guanidinium ionic liquids to extract protein by magnetic solid-phase extraction. MCGO-functional guanidinium ionic liquid has been characterized by vibrating sample magnetometer, field emission scanning electron microscopy, X-ray diffraction spectrometer and Fourier transform infrared spectrometer. After extraction, the concentrations of protein were determined by measuring the absorbance at 278 nm using an ultra violet visible spectrophotometer. The advantages of MCGO-functional guanidinium ionic liquid in protein extraction were compared with magnetic chitosan, graphene oxide, MCGO and MCGO-ordinary imidazolium ionic liquid. The proposed method has been applied to extract trypsin, lysozyme, ovalbumin and bovine serum albumin. A comprehensive study of the adsorption conditions such as the concentration of protein, the amount of MCGO-functional guanidinium ionic liquid, the pH, the temperature and the extraction time were also presented. Moreover, the MCGO-functional guanidinium ionic liquid can be easily regenerated, and the extraction capacity was about 94% of the initial one after being used three times. Copyright © 2015 Elsevier B.V. All rights reserved.

[The neurobiology of obsessive-compulsive disorder: new findings from functional magnetic resonance imaging (II)].

PubMed

Pena-Garijo, Josep; Ruipérez-Rodríguez, M Angeles; Barros-Loscertales, Alfonso

2010-05-01

In recent years, neuroscience has shown a growing interest in applying its methods to furthering the knowledge of psychiatric disorders, and one of the fundamental tools used to do so are neuroimaging techniques. Yet, in general, few studies have been conducted in which functional magnetic resonance has been applied in this field and findings are sometimes contradictory. In this study we review the specialised bibliography and present a critical discussion on the scientific literature published to date on the application of functional magnetic resonance and diffusion tensor imaging to one of the most widely studied disorders, from a neurobiological point of view, namely, obsessive-compulsive disorder. The study reviews the articles on the use of functional magnetic resonance imaging, as well as those dealing with neural connectivity, that have been indexed in the most commonly used medical databases on the topic since 1996. Most studies suggest that the prefrontal cortex (orbitofrontal and cingulate), the basal ganglia and the thalamus are involved in the pathogenesis of obsessive-compulsive disorder. Likewise, alterations in the white matter that affect neural connectivity have also been found. The contributions made by neuroimaging and, more specifically, by functional magnetic resonance imaging are and will undoubtedly continue to be a particularly interesting tool for explaining the aetiology of this disorder.

Design and Realization of a Three Degrees of Freedom Displacement Measurement System Composed of Hall Sensors Based on Magnetic Field Fitting by an Elliptic Function

PubMed Central

Zhao, Bo; Wang, Lei; Tan, Jiu-Bin

2015-01-01

This paper presents the design and realization of a three degrees of freedom (DOFs) displacement measurement system composed of Hall sensors, which is built for the XYθz displacement measurement of the short stroke stage of the reticle stage of lithography. The measurement system consists of three pairs of permanent magnets mounted on the same plane on the short stroke stage along the Y, Y, X directions, and three single axis Hall sensors correspondingly mounted on the frame of the reticle stage. The emphasis is placed on the decoupling and magnetic field fitting of the three DOFs measurement system. The model of the measurement system is illustrated, and the XY positions and θZ rotation of the short stroke stage can be obtained by decoupling the sensor outputs. A magnetic field fitting by an elliptic function-based compensation method is proposed. The practical field intensity of a permanent magnet at a certain plane height can be substituted for the output voltage of a Hall sensors, which can be expressed by the elliptic function through experimental data as the crucial issue to calculate the three DOFs displacement. Experimental results of the Hall sensor displacement measurement system are presented to validate the proposed three DOFs measurement system. PMID:26370993

Towards the blackbox computation of magnetic exchange coupling parameters in polynuclear transition-metal complexes: theory, implementation, and application.

PubMed

Phillips, Jordan J; Peralta, Juan E

2013-05-07

We present a method for calculating magnetic coupling parameters from a single spin-configuration via analytic derivatives of the electronic energy with respect to the local spin direction. This method does not introduce new approximations beyond those found in the Heisenberg-Dirac Hamiltonian and a standard Kohn-Sham Density Functional Theory calculation, and in the limit of an ideal Heisenberg system it reproduces the coupling as determined from spin-projected energy-differences. Our method employs a generalized perturbative approach to constrained density functional theory, where exact expressions for the energy to second order in the constraints are obtained by analytic derivatives from coupled-perturbed theory. When the relative angle between magnetization vectors of metal atoms enters as a constraint, this allows us to calculate all the magnetic exchange couplings of a system from derivatives with respect to local spin directions from the high-spin configuration. Because of the favorable computational scaling of our method with respect to the number of spin-centers, as compared to the broken-symmetry energy-differences approach, this opens the possibility for the blackbox exploration of magnetic properties in large polynuclear transition-metal complexes. In this work we outline the motivation, theory, and implementation of this method, and present results for several model systems and transition-metal complexes with a variety of density functional approximations and Hartree-Fock.

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

Lombardo, v.; Barzi, E.; Turrioni, D.

Superconducting magnets with magnetic fields above 20 T will be needed for a Muon Collider and possible LHC energy upgrade. This field level exceeds the possibilities of traditional Low Temperature Superconductors (LTS) such as Nb{sub 3}Sn and Nb{sub 3}Al. Presently the use of high field high temperature superconductors (HTS) is the only option available for achieving such field levels. Commercially available YBCO comes in tapes and shows noticeable anisotropy with respect to field orientation, which needs to be accounted for during magnet design. In the present work, critical current test results are presented for YBCO tape manufactured by Bruker. Shortmore » sample measurements results are presented up to 14 T, assessing the level of anisotropy as a function of field, field orientation and operating temperature.« less

Comprehensive evaluation of attitude and orbit estimation using real earth magnetic field data

NASA Technical Reports Server (NTRS)

Deutschmann, Julie; Bar-Itzhack, Itzhack

1997-01-01

A single, augmented extended Kalman filter (EKF) which simultaneously and autonomously estimates spacecraft attitude and orbit was developed and tested with simulated and real magnetometer and rate data. Since the earth's magnetic field is a function of time and position, and since time is accurately known, the differences between the computed and measured magnetic field components, as measured by the magnetometers throughout the entire spacecraft's orbit, are a function of orbit and attitude errors. These differences can be used to estimate the orbit and attitude. The test results of the EKF with magnetometer and gyro data from three NASA satellites are presented and evaluated.

Optical multichannel room temperature magnetic field imaging system for clinical application

PubMed Central

Lembke, G.; Erné, S. N.; Nowak, H.; Menhorn, B.; Pasquarelli, A.

2014-01-01

Optically pumped magnetometers (OPM) are a very promising alternative to the superconducting quantum interference devices (SQUIDs) used nowadays for Magnetic Field Imaging (MFI), a new method of diagnosis based on the measurement of the magnetic field of the human heart. We present a first measurement combining a multichannel OPM-sensor with an existing MFI-system resulting in a fully functional room temperature MFI-system. PMID:24688820

Iron pages of HTSC

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

Gasparov, V. A., E-mail: vgasparo@issp.ac.r

Experimental data are presented on the superconducting and electronic properties of iron-based high-temperature superconductors in the normal and superconducting states. The following topics are discussed: lattice structure; structure of magnetic vortices; magnetic penetration depth; Fermi surface; isotope effect; and critical magnetic fields both in oxide compounds of 1111 type and oxide-free compounds of 122, 111, and 011 types as a function of the doping level, temperature, and external pressure.

Fluorescent and Magnetic Mesoporous Hybrid Material: A Chemical and Biological Nanosensor for Hg2+ Ions

PubMed Central

Suresh, Moorthy; Anand, Chokkalingam; Frith, Jessica E.; Dhawale, Dattatray S.; Subramaniam, Vishnu P.; Strounina, Ekaterina; Sathish, Clastinrusselraj I.; Yamaura, Kazunari; Cooper-White, Justin J.; Vinu, Ajayan

2016-01-01

We introduce “sense, track and separate” approach for the removal of Hg2+ ion from aqueous media using highly ordered and magnetic mesoporous ferrosilicate nanocages functionalised with rhodamine fluorophore derivative. These functionalised materials offer both fluorescent and magnetic properties in a single system which help not only to selectively sense the Hg2+ ions with a high precision but also adsorb and separate a significant amount of Hg2+ ion in aqueous media. We demonstrate that the magnetic affinity of these materials, generated from the ultrafine γ-Fe2O3 nanoparticles present inside the nanochannels of the support, can efficiently be used as a fluorescent tag to sense the Hg2+ ions present in NIH3T3 fibroblasts live cells and to track the movement of the cells by external magnetic field monitored using confocal fluorescence microscopy. This simple approach of introducing multiple functions in the magnetic mesoporous materials raise the prospect of creating new advanced functional materials by fusing organic, inorganic and biomolecules to create advanced hybrid nanoporous materials which have a potential use not only for sensing and the separation of toxic metal ions but also for cell tracking in bio-separation and the drug delivery. PMID:26911660

Dynamical properties of magnetized two-dimensional one-component plasma

NASA Astrophysics Data System (ADS)

Dubey, Girija S.; Gumbs, Godfrey; Fessatidis, Vassilios

2018-05-01

Molecular dynamics simulation are used to examine the effect of a uniform perpendicular magnetic field on a two-dimensional interacting electron system. In this simulation we include the effect of the magnetic field classically through the Lorentz force. Both the Coulomb and the magnetic forces are included directly in the electron dynamics to study their combined effect on the dynamical properties of the 2D system. Results are presented for the velocity autocorrelation function and the diffusion constants in the presence and absence of an external magnetic field. Our simulation results clearly show that the external magnetic field has an effect on the dynamical properties of the system.

Functionalized magnetic-fluorescent hybrid nanoparticles for cell labelling.

PubMed

Lou, Lei; Yu, Ke; Zhang, Zhengli; Li, Bo; Zhu, Jianzhong; Wang, Yiting; Huang, Rong; Zhu, Ziqiang

2011-05-01

A facile method of synthesizing 60 nm magnetic-fluorescent core-shell bifunctional nanocomposites with the ability to label cells is presented. Hydrophobic trioctylphosphine oxide (TOPO)-capped CdSe@ZnS quantum dots (QDs) were assembled on polyethyleneimine (PEI)-coated Fe(3)O(4) nanoparticles (MNP). Polyethyleneimine was utilized for the realization of multifunction, including attaching 4 nm TOPO capped CdSe@ZnS quantum dots onto magnetite particles, altering the surface properties of quantum dots from hydrophobic to hydrophilic as well as preventing the formation of large aggregates. Results show that these water-soluble hybrid nanocomposites exhibit good colloidal stability and retain good magnetic and fluorescent properties. Because TOPO-capped QDs are assembled instead of their water-soluble equivalents, the nanocomposites are still highly luminescent with no shift in the PL peak position and present long-term fluorescence stability. Moreover, TAT peptide (GRKKRRQRRRPQ) functionalized hybrid nanoparticles were also studied due to their combined magnetic enrichment and optical detection for cell separation and rapid cell labelling. A cell viability assay revealed good biocompatibility of these hybrid nanoparticles. The potential application of the new magnetic-fluorescent nanocomposites in biological and medicine is demonstrated. © The Royal Society of Chemistry 2011

Identification of Lectins from Metastatic Cancer Cells through Magnetic Glyconanoparticles

PubMed Central

Kavunja, Herbert W.; Voss, Patricia G.

2016-01-01

Cancer cells can have characteristic carbohydrate binding properties. Previously, it was shown that a highly metastatic melanoma cell line B16F10 bound to galacto-side-functionalized nanoparticles much stronger than the corresponding less metastatic B16F1 cells. To better understand the carbohydrate binding properties of cancer cells, herein, we report the isolation and characterization of endogenous galactose binding proteins from B16F10 cells using magnetic glyconanoparticles. The galactose-coated magnetic glyconanoparticles could bind with lectins present in the cells and be isolated through magnet-mediated separation. Through Western blot and mass spectrometry, the arginine/serine rich splicing factor Sfrs1 was identified as a galactose-selective endogenous lectin, overexpressed in B16F10 cells, compared with B16F1 cells. In addition, galactin-3 was found in higher amounts in B16F10 cells. Finally, the glyconanoparticles exhibited a superior efficiency in lectin isolation, from both protein mixtures and live cells, than the corresponding more traditional microparticles functionalized with carbohydrates. Thus, the magnetic glyconanoparticles present a useful tool for discovery of endogenous lectins, as well as binding partners of lectins, without prior knowledge of protein identities. PMID:27110035

Antimicrobial function of Nd3+-doped anatase titania-coated nickel ferrite composite nanoparticles: a biomaterial system.

PubMed

Rana, S; Rawat, J; Sorensson, M M; Misra, R D K

2006-07-01

The present study describes and makes a relative comparison of the antimicrobial function of undoped and neodymium-doped titania coated-nickel ferrite composite nanoparticles processed by uniquely combining the reverse micelle and chemical hydrolysis approaches. This methodology facilitates the formation of undoped and doped photocatalytic titania shells and a magnetic ferrite core. The ferrite core is needed to help in the removal of particles from the sprayed surface using a small magnetic field. Doping of the titania shell with neodymium significantly enhances the photocatalytic and anti-microbial function of the core-shell composite nanoparticles without influencing the magnetic characteristics of the nickel ferrite core. The increased performance is believed to be related to the inhibition of electron-hole recombination and a decrease in the band gap energy of titania. The retention of magnetic strength ensures controlled movement of the composite nanoparticles by the magnetic field, facilitating their application as removable anti-microbial photocatalyst nanoparticles. The consistent behavior of the composite nanoparticles points to the viability of the synthesis process adopted.

A plasma model for reversed field pinch circuit design

NASA Astrophysics Data System (ADS)

Johnston, J. W.

1981-03-01

A plasma model has been developed for use in the design of circuits for reversed field pinch experiments. The magnetic field is assumed to evolve through a given series of relaxed states with the plasma resistivity specified as a function of time. At any instant the magnetic field configuration is determined by the field energy and the toroidal flux. If the Bessel function model is chosen as the relaxed state then the magnetic helicity can be used as an alternative to the magnetic energy without altering the results. Simulations of discharges on ZETA and ETA BETA II are presented. By suitable choices of the relaxed field configuration and plasma resistivity it is possible to obtain close agreement with the experimental waveforms. Application to the proposed RFX device is discussed.

A novel architecture of non-volatile magnetic arithmetic logic unit using magnetic tunnel junctions

NASA Astrophysics Data System (ADS)

Guo, Wei; Prenat, Guillaume; Dieny, Bernard

2014-04-01

Complementary metal-oxide-semiconductor (CMOS) technology is facing increasingly difficult obstacles such as power consumption and interconnection delay. Novel hybrid technologies and architectures are being investigated with the aim to circumvent some of these limits. In particular, hybrid CMOS/magnetic technology based on magnetic tunnel junctions (MTJs) is considered as a very promising approach thanks to the full compatibility of MTJs with CMOS technology. By tightly merging the conventional electronics with magnetism, both logic and memory functions can be implemented in the same device. As a result, non-volatility is directly brought into logic circuits, yielding significant improvement of device performances and new functionalities as well. We have conceived an innovative methodology to construct non-volatile magnetic arithmetic logic units (MALUs) combining spin-transfer torque MTJs with MOS transistors. The present 4-bit MALU utilizes 4 MTJ pairs to store its operation code (opcode). Its operations and performances have been confirmed and evaluated through electrical simulations.

Zero-field magnetic response functions in Landau levels

PubMed Central

Gao, Yang; Niu, Qian

2017-01-01

We present a fresh perspective on the Landau level quantization rule; that is, by successively including zero-field magnetic response functions at zero temperature, such as zero-field magnetization and susceptibility, the Onsager’s rule can be corrected order by order. Such a perspective is further reinterpreted as a quantization of the semiclassical electron density in solids. Our theory not only reproduces Onsager’s rule at zeroth order and the Berry phase and magnetic moment correction at first order but also explains the nature of higher-order corrections in a universal way. In applications, those higher-order corrections are expected to curve the linear relation between the level index and the inverse of the magnetic field, as already observed in experiments. Our theory then provides a way to extract the correct value of Berry phase as well as the magnetic susceptibility at zero temperature from Landau level fan diagrams in experiments. Moreover, it can be used theoretically to calculate Landau levels up to second-order accuracy for realistic models. PMID:28655849

Magnetic anisotropy behaviour of pyrrhotite as determined by low- and high-field experiments

NASA Astrophysics Data System (ADS)

Martín-Hernández, F.; Dekkers, M. J.; Bominaar-Silkens, I. M. A.; Maan, J. C.

2008-07-01

Here we report on the sources of magnetic anisotropy in pyrrhotite, an iron sulphide present in many rocks as an important carrier of the Natural Remanent Magnetization. While the magnetic hysteresis parameters of pyrrhotite are well known, the existing database concerning its anisotropy behaviour is patchy and ambiguous. Therefore, a collection of 11 seemingly single crystals of natural pyrrhotite was scrutinized. Before embarking on the anisotropy determinations the set of single crystals was extensively characterized rock magnetically by measuring Curie temperatures, hysteresis loops, IRM acquisition curves, and FORC diagrams (the latter three all at room temperature). First the variation of the low-field susceptibility as function of applied field and grain size was evaluated for fields ranging from 1 to 450 A m-1. Existing grain size dependent data and the present larger crystals show a logarithmic grain size dependence. This enables estimating the grain size for unimodal pyrrhotite distributions in rocks. Measured trends are better fitted with an exponential function than with a Rayleigh Law style function. Based on the rock magnetic characterization and the behaviour of the anisotropy of magnetic susceptibility six samples (of the original 11) were selected for the high-field anisotropy determinations within the basal plane. Those data were acquired with a torque cantilever-type magnetometer. As expected, most single crystals showed a pure 6-θ curve within their basal plane because of the easy axis configuration. In some crystals, however, lower harmonic terms overlapped the 6-θ term. This may be the dominant source of the observed variation in magnetic anisotropy properties. Torque data of three of the six samples were of sufficient quality to allow evaluation of K1. Re-evaluation of existing torque data and including the present newly derived determinations, yields for the anisotropy constant of pyrrhotite within the basal plane K1: (2.7 +/- 0.2) 104 Jm-3. This is over an order of magnitude more precise than the sparse existing K1 data; only the value reported by Mikami and co-authors in 1959 agrees with the new determination. With this firmly established K1 value meaningful anisotropy models are now possible for pyrrhotite-bearing rocks.

Modeling magnetic field amplification in nonlinear diffusive shock acceleration

NASA Astrophysics Data System (ADS)

Vladimirov, Andrey

2009-02-01

This research was motivated by the recent observations indicating very strong magnetic fields at some supernova remnant shocks, which suggests in-situ generation of magnetic turbulence. The dissertation presents a numerical model of collisionless shocks with strong amplification of stochastic magnetic fields, self-consistently coupled to efficient shock acceleration of charged particles. Based on a Monte Carlo simulation of particle transport and acceleration in nonlinear shocks, the model describes magnetic field amplification using the state-of-the-art analytic models of instabilities in magnetized plasmas in the presence of non-thermal particle streaming. The results help one understand the complex nonlinear connections between the thermal plasma, the accelerated particles and the stochastic magnetic fields in strong collisionless shocks. Also, predictions regarding the efficiency of particle acceleration and magnetic field amplification, the impact of magnetic field amplification on the maximum energy of accelerated particles, and the compression and heating of the thermal plasma by the shocks are presented. Particle distribution functions and turbulence spectra derived with this model can be used to calculate the emission of observable nonthermal radiation.

Smart multifunctional core-shell nanospheres with drug and gene co-loaded for enhancing the therapeutic effect in a rat intracranial tumor model

NASA Astrophysics Data System (ADS)

Wang, Hanjie; Su, Wenya; Wang, Sheng; Wang, Xiaomin; Liao, Zhenyu; Kang, Chunsheng; Han, Lei; Chang, Jin; Wang, Guangxiu; Pu, Peiyu

2012-09-01

Glioblastoma with high mortality has been one of the most serious cancers threatening human health. Because of the present treatment limitations, there is an urgent need to construct a multifunctional vesicle for enhancing the treatment of in situ malignant glioblastoma. In our study, drug and gene co-loaded magnetic PLGA/multifunctional polymeric liposome (magnetic PLGA/MPLs) core-shell nanospheres were constructed. They were mainly self-assembled from two parts: hydrophobic PLGA cores that can load drugs and magnetic nanocrystals; and polymeric lipid shells anchored with functional molecules such as PEG chains, TAT peptides and RGD peptides that can help the vectors to condense the gene, prolong the circulation time, cross the blood brain barrier and target delivery to the cancer tissue. The results showed that the magnetic PLGA/MPLs nanosphere has a nanosized core-shell structure, can achieve sustained drug release and has good DNA binding abilities. Importantly, compared with the control group and other groups with single functionality, it can co-deliver the drug and gene into the same cell in vitro and show the strongest inhibiting effect on the growth of the in situ malignant glioblastoma in vivo. All of these results indicated that the different functional components of magnetic PLGA/MPLs, can form an organic whole and none of them can be dispensed with. The magnetic PLGA/MPLs nanosphere may be another option for treatment of glioblastoma.Glioblastoma with high mortality has been one of the most serious cancers threatening human health. Because of the present treatment limitations, there is an urgent need to construct a multifunctional vesicle for enhancing the treatment of in situ malignant glioblastoma. In our study, drug and gene co-loaded magnetic PLGA/multifunctional polymeric liposome (magnetic PLGA/MPLs) core-shell nanospheres were constructed. They were mainly self-assembled from two parts: hydrophobic PLGA cores that can load drugs and magnetic nanocrystals; and polymeric lipid shells anchored with functional molecules such as PEG chains, TAT peptides and RGD peptides that can help the vectors to condense the gene, prolong the circulation time, cross the blood brain barrier and target delivery to the cancer tissue. The results showed that the magnetic PLGA/MPLs nanosphere has a nanosized core-shell structure, can achieve sustained drug release and has good DNA binding abilities. Importantly, compared with the control group and other groups with single functionality, it can co-deliver the drug and gene into the same cell in vitro and show the strongest inhibiting effect on the growth of the in situ malignant glioblastoma in vivo. All of these results indicated that the different functional components of magnetic PLGA/MPLs, can form an organic whole and none of them can be dispensed with. The magnetic PLGA/MPLs nanosphere may be another option for treatment of glioblastoma. Electronic supplementary information (ESI) available. See DOI: 10.1039/c2nr31263h

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)

Bi-layer graphene structure with non-equivalent planes: Magnetic properties study

NASA Astrophysics Data System (ADS)

Mhirech, A.; Aouini, S.; Alaoui-Ismaili, A.; Bahmad, L.

2018-05-01

In this paper, we study the magnetic properties of a ferromagnetic bi-layer graphene structure with non-equivalent planes. The geometry of the studied system is formed by two layers (A) and (B) consisting of the spins σ = 1 / 2 and S = 1 . For this purpose, the influence of the coupling exchange interactions, the external magnetic and the crystal fields are investigated and presented as well as the ground state phase diagrams. The Monte Carlo simulations have been used to examine the behavior of the partial and the total magnetizations as a function of the system parameters. These effects on the compensation and critical temperatures behavior are also presented in different phase diagrams, for the studied system.

Development of Metamaterial Composites for Compact High Power Microwave Systems and Antennas

DTIC Science & Technology

2016-05-01

for the eddy currents to decay and thus the reverse magnetizing field becomes significant at the surface of the material. This reverse field shields ...76 Appendix A: Ceramic Magnetics , Inc. Ferrite Data Sheets…………………………………81 Appendix B: Conference Presentations and Journal...Figure 21: Magnetic loss tangent as a function of frequency for each of the five ferrite composites

Magnetization dynamics driven by spin-polarized current in nanomagnets

NASA Astrophysics Data System (ADS)

Carpentieri, M.; Torres, L.; Azzerboni, B.; Finocchio, G.; Consolo, G.; Lopez-Diaz, L.

2007-09-01

In this report, micromagnetic simulations of magnetization dynamics driven by spin-polarized currents (SPCs) on magnetic nanopillars of permalloy/Cu/permalloy with different rectangular cross-sections are presented. Complete dynamical stability diagrams from initial parallel and antiparallel states have been computed for 100 ns. The effects of a space-dependent polarization function together with the presence of magnetostatic coupling from the fixed layer and classical Ampere field have been taken into account.

Peptide conjugated magnetic nanoparticles for magnetically mediated energy delivery to lung cancer cells

PubMed Central

Hauser, Anastasia K; Anderson, Kimberly W; Hilt, J Zach

2016-01-01

Aim: In the present study, we examine the effects of internalized peptide-conjugated iron oxide nanoparticles and their ability to locally convert alternating magnetic field (AMF) energy into other forms of energy (e.g., heat and rotational work). Materials & methods: Dextran-coated iron oxide nanoparticles were functionalized with a cell penetrating peptide and after internalization by A549 and H358 cells were activated by an AMF. Results: TAT-functionalized nanoparticles and AMF exposure increased reactive oxygen species generation compared with the nanoparticle system alone. The TAT-functionalized nanoparticles induced lysosomal membrane permeability and mitochondrial membrane depolarization, but these effects were not further enhanced by AMF treatment. Although not statistically significant, there are trends suggesting an increase in apoptosis via the Caspase 3/7 pathways when cells are exposed to TAT-functionalized nanoparticles combined with AMF. Conclusion: Our results indicate that internalized TAT-functionalized iron oxide nanoparticles activated by an AMF elicit cellular responses without a measurable temperature rise. PMID:27388639

Quantitative interpretation of magnetic properties as a way to characterize biogeophysical signatures of biodegraded contaminated sites

NASA Astrophysics Data System (ADS)

Ustra, A.; Kessouri, P.; Leite, A.; Mendonça, C. A.; Bandeira, N.

2017-12-01

Magnetic minerals in soils and rocks are one way to study biogechemical and paleoenvironmental processes. The ultrafine fraction of these minerals (superparmagnetic (SP) and stable single domain (SSD)) are usually investigated in environmental magnetism studies, since changes in mineralogy, concentration, size and morphology of the magnetic grains can be related to biogeochemical processes. In this study, we use low-field frequency dependent susceptibility (FDS) and isothermal remanent magnetization (IRM) to characterize the magnetic properties of materials in environmental magnetism. Magnetic susceptibility (MS) measurements are frequently used as a proxy of magnetic minerals present in soils and rocks. MS is a complex function of magnetic mineralogy and grain size, as well as magnitude and frequency of the applied field. This work presents a method for inverting low-field FDS data. The inverted parameters can be interpreted in terms of grain size variations of magnetic particles on the SP-SSD transition. This work also presents a method for inverting IRM demagnetization curves, to obtain the saturation magnetization, the individual magnetic moment for an assemblage of ultrafine SP minerals and estimate the concentration of magnetic carriers. IRM magnetization curves can be interpreted as resulting from distinct contributions of different mineral phases, which can be described by Cummulative Log-Gaussian (CLG) distributions. Each acquisition curve provides fundamental parameters that are characteristic of the respective mineral phase. The CLG decomposition is widely used in an interpretation procedure named mineral unmixing. In this work we present an inversion method for mineral unmixing, implementing the genetic algorithm to find the parameters of distinct components. These methodologies have been tested by synthetic models and applied to data from environmental magnetism studies. In this work we apply the proposed methodologies to characterize the magnetic properties of samples from the former Brandywine MD Defense Reutilization and Marketing Office (DRMO). The results from the magnetic properties characterization will provide additional information that may assist the interpretation of the biogeophysical signatures observed at the site.

A density functional theory study of the magnetic exchange coupling in dinuclear manganese(II) inverse crown structures.

PubMed

Vélez, Ederley; Alberola, Antonio; Polo, Víctor

2009-12-17

The magnetic exchange coupling constants between two Mn(II) centers for a set of five inverse crown structures have been investigated by means of a methodology based on broken-symmetry unrestricted density functional theory. These novel and highly unstable compounds present superexchange interactions between two Mn centers, each one with S = 5/2 through anionic "guests" such as oxygen, benzene, or hydrides or through the cationic ring formed by amide ligands and alkali metals (Na, Li). Magnetic exchange couplings calculated at B3LYP/6-31G(d,p) level yield strong antiferromagnetic couplings for compounds linked via an oxygen atom or hydride and very small antiferromagnetic couplings for those linked via a benzene molecule, deprotonated in either 1,4- or 1,3- positions. Analysis of the magnetic orbitals and spin polarization maps provide an understanding of the exchange mechanism between the Mn centers. The dependence of J with respect to 10 different density functional theory potentials employed and the basis set has been analyzed.

Optimizing the field distribution of a Halbach type permanent magnet cylinder using the soft iron and superhard magnet

NASA Astrophysics Data System (ADS)

Xu, Xiaonong; Lu, Dingwei; Xu, Xibin; Yu, Yang; Gu, Min

2018-01-01

When a conventional Halbach type Hollow Cylindrical Permanent Magnet Array (HCPMA) is used to generate magnetic induction over the magnitude of coercivity μ0Hc, some detrimental parasitic magnetic phenomena, such as the demagnetization, magnetization reversal, and vortexes of magnetization, can appear in the interior of the magnets. We present a self-consistent quantitative analysis of the magnetization and magnetic induction distributions inside the magnetic array by considering the anisotropic and nonlinear magnetization functions of the materials consisting of the array. These numeric simulations reveal novel magnetization structures resulted from the self-field of array. We demonstrate that both the field uniformity and magnetic flux in the pole gap can be modulated by partially substituting the magnets of high energy products with the soft irons and the superhard magnets. We also show how the optimized substitution parameters can be obtained for a HCPMA achieving the best field uniformity or the maximum magnetic flux.

Hemispheric asymmetries in dorsal language pathway white-matter tracts: A magnetic resonance imaging tractography and functional magnetic resonance imaging study.

PubMed

Silva, Guilherme; Citterio, Alberto

2017-10-01

Introduction Previous studies have shown that the arcuate fasciculus has a leftward asymmetry in right-handers that could be correlated with the language lateralisation defined by functional magnetic resonance imaging. Nonetheless, information about the asymmetry of the other fibres that constitute the dorsal language pathway is scarce. Objectives This study investigated the asymmetry of the white-matter tracts involved in the dorsal language pathway through the diffusion tensor imaging (DTI) technique, in relation to language hemispheric dominance determined by task-dependent functional magnetic resonance imaging (fMRI). Methods We selected 11 patients (10 right-handed) who had been studied with task-dependent fMRI for language areas and DTI and who had no language impairment or structural abnormalities that could compromise magnetic resonance tractography of the fibres involved in the dorsal language pathway. Laterality indices (LI) for fMRI and for the volumes of each tract were calculated. Results In fMRI, all the right-handers had left hemispheric lateralisation, and the ambidextrous subject presented right hemispheric dominance. The arcuate fasciculus LI was strongly correlated with fMRI LI ( r = 0.739, p = 0.009), presenting the same lateralisation of fMRI in seven subjects (including the right hemispheric dominant). It was not asymmetric in three cases and had opposite lateralisation in one case. The other tracts presented predominance for rightward lateralisation, especially superior longitudinal fasciculus (SLF) II/III (nine subjects), but their LI did not correlate (directly or inversely) with fMRI LI. Conclusion The fibres that constitute the dorsal language pathway have an asymmetric distribution in the cerebral hemispheres. Only the asymmetry of the arcuate fasciculus is correlated with fMRI language lateralisation.

Modulation of N400 in Chronic Non-Fluent Aphasia Using Low Frequency Repetitive Transcranial Magnetic Stimulation (rTMS)

ERIC Educational Resources Information Center

Barwood, Caroline H. S.; Murdoch, Bruce E.; Whelan, Brooke-Mai; Lloyd, David; Riek, Stephan; O'Sullivan, John D.; Coulthard, Alan; Wong, Andrew

2011-01-01

Low frequency Repetitive Transcranial Magnetic Stimulation (rTMS) has previously been applied to language homologues in non-fluent populations of persons with aphasia yielding significant improvements in behavioral language function up to 43 months post stimulation. The present study aimed to investigate the electrophysiological correlates…

Real-space transmission electron microscopy investigations of attachment of functionalized magnetic nanoparticles to DNA-coils acting as a biosensor.

PubMed

Akhtar, Sultan; Strömberg, Mattias; Zardán Gómez de la Torre, Teresa; Russell, Camilla; Gunnarsson, Klas; Nilsson, Mats; Svedlindh, Peter; Strømme, Maria; Leifer, Klaus

2010-10-21

The present work provides the first real-space analysis of nanobead-DNA coil interactions. Immobilization of oligonucleotide-functionalized magnetic nanobeads in rolling circle amplified DNA-coils was studied by complex magnetization measurements and transmission electron microscopy (TEM), and a statistical analysis of the number of beads hybridized to the DNA-coils was performed. The average number of beads per DNA-coil using the results from both methods was found to be around 6 and slightly above 2 for samples with 40 and 130 nm beads, respectively. The TEM analysis supported an earlier hypothesis that 40 nm beads are preferably immobilized in the interior of DNA-coils whereas 130 nm beads, to a larger extent, are immobilized closer to the exterior of the coils. The methodology demonstrated in the present work should open up new possibilities for characterization of interactions of a large variety of functionalized nanoparticles with macromolecules, useful for gaining more fundamental understanding of such interactions as well as for optimizing a number of biosensor applications.

Vertical bloch line memory

NASA Technical Reports Server (NTRS)

Katti, R.; Wu, J.; Stadler, H.

1990-01-01

Vertical Bloch Line (VBL) memory is a recently conceived, integrated, solid-state, block-access, VLSI memory which offers the potential of 1Gbit/sq cm real storage density, gigabit per second data rates, and sub-millisecond average access times simultaneously at relatively low mass, volume, and power values when compared to alternative technologies. VBL's are micromagnetic structures within magnetic domain walls which can be manipulated using magnetic fields from integrated conductors. The presence or absence of VBL pairs are used to store binary information. At present, efforts are being directed at developing a single-chip memory using 25Mbit/sq cm technology in magnetic garnet material which integrates, at a single operating point, the writing, storage, reading, and amplification functions needed in a memory. This paper describes the current design architecture, functional elements, and supercomputer simulation results which are used to assist the design process. The current design architecture uses three metal layers, two ion implantation steps for modulating the thickness of the magnetic layer, one ion implantation step for assisting propagation in the major line track, one NiFe soft magnetic layer, one CoPt hard magnetic layer, and one reflective Cr layer for facilitating magneto-optic observation of magnetic structure. Data are stored in a series of elongated magnetic domains, called stripes, which serve as storage sites for arrays of VBL pairs. The ends of these stripes are placed near conductors which serve as VBL read/write gates. A major line track is present to provide a source and propagation path for magnetic bubbles. Writing and reading, respectively, are achieved by converting magnetic bubbles to VBL's and vice versa. The output function is effected by stretching a magnetic bubble and detecting it magnetoresistively. Experimental results from the past design cycle created four design goals for the current design cycle. First, the bias field ranges for the stripes and the major line needed to be matched. Second, the magnetic field barrier between the stripe and the read/write gates needed to be reduced. Third, current conductor routing needed to be improved to reduce occurrences of open-circuiting, short-circuiting, and eddy-current shielding. Fourth, a modified Co-alloy was needed with an increased coercivity and controlled magnetization to allow VBL stabilization to occur without affecting stripe stability.

Modulated heat pulse propagation and partial transport barriers in chaotic magnetic fields

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

Castillo-Negrete, Diego del; Blazevski, Daniel

2016-04-15

Direct numerical simulations of the time dependent parallel heat transport equation modeling heat pulses driven by power modulation in three-dimensional chaotic magnetic fields are presented. The numerical method is based on the Fourier formulation of a Lagrangian-Green's function method that provides an accurate and efficient technique for the solution of the parallel heat transport equation in the presence of harmonic power modulation. The numerical results presented provide conclusive evidence that even in the absence of magnetic flux surfaces, chaotic magnetic field configurations with intermediate levels of stochasticity exhibit transport barriers to modulated heat pulse propagation. In particular, high-order islands andmore » remnants of destroyed flux surfaces (Cantori) act as partial barriers that slow down or even stop the propagation of heat waves at places where the magnetic field connection length exhibits a strong gradient. Results on modulated heat pulse propagation in fully stochastic fields and across magnetic islands are also presented. In qualitative agreement with recent experiments in large helical device and DIII-D, it is shown that the elliptic (O) and hyperbolic (X) points of magnetic islands have a direct impact on the spatio-temporal dependence of the amplitude of modulated heat pulses.« less

Hubbard pair cluster in the external fields. Studies of the magnetic properties

NASA Astrophysics Data System (ADS)

Balcerzak, T.; Szałowski, K.

2018-06-01

The magnetic properties of the two-site Hubbard cluster (dimer or pair), embedded in the external electric and magnetic fields and treated as the open system, are studied by means of the exact diagonalization of the Hamiltonian. The formalism of the grand canonical ensemble is adopted. The phase diagrams, on-site magnetizations, spin-spin correlations, mean occupation numbers and hopping energy are investigated and illustrated in figures. An influence of temperature, mean electron concentration, Coulomb U parameter and external fields on the quantities of interest is presented and discussed. In particular, the anomalous behaviour of the magnetization and correlation function vs. temperature near the critical magnetic field is found. Also, the effect of magnetization switching by the external fields is demonstrated.

A Green's function method for local and non-local parallel transport in general magnetic fields

NASA Astrophysics Data System (ADS)

Del-Castillo-Negrete, Diego; Chacón, Luis

2009-11-01

The study of transport in magnetized plasmas is a problem of fundamental interest in controlled fusion and astrophysics research. Three issues make this problem particularly challenging: (i) The extreme anisotropy between the parallel (i.e., along the magnetic field), χ, and the perpendicular, χ, conductivities (χ/χ may exceed 10^10 in fusion plasmas); (ii) Magnetic field lines chaos which in general complicates (and may preclude) the construction of magnetic field line coordinates; and (iii) Nonlocal parallel transport in the limit of small collisionality. Motivated by these issues, we present a Lagrangian Green's function method to solve the local and non-local parallel transport equation applicable to integrable and chaotic magnetic fields. The numerical implementation employs a volume-preserving field-line integrator [Finn and Chac'on, Phys. Plasmas, 12 (2005)] for an accurate representation of the magnetic field lines regardless of the level of stochasticity. The general formalism and its algorithmic properties are discussed along with illustrative analytical and numerical examples. Problems of particular interest include: the departures from the Rochester--Rosenbluth diffusive scaling in the weak magnetic chaos regime, the interplay between non-locality and chaos, and the robustness of transport barriers in reverse shear configurations.

Neural Correlates of Working Memory Performance in Adolescents and Young Adults with Dyslexia

ERIC Educational Resources Information Center

Vasic, Nenad; Lohr, Christina; Steinbrink, Claudia; Martin, Claudia; Wolf, Robert Christian

2008-01-01

Behavioral studies indicate deficits in phonological working memory (WM) and executive functioning in dyslexics. However, little is known about the underlying functional neuroanatomy. In the present study, neural correlates of WM in adolescents and young adults with dyslexia were investigated using event-related functional magnetic resonance…

Spin related transport in two pyrene and Triphenylene graphene nanodisks using NEGF method

NASA Astrophysics Data System (ADS)

Taghilou, Hamed; Fathi, Davood

2018-07-01

The present study is conducted to evaluate the spin polarization in two pyrene and Triphenylene graphene nanoflakes. All calculations are performed using non-equilibrium Green's function (NEGF) method. The obtained results show that, graphene has no magnetic property and using Pyrene nanoflake results in a better spin switching at extreme magnetic fields. On the contrary, when applying magnetized electrodes, depending on the direction of magnetization of the two electrodes (either parallel or anti-parallel), different spin polarization diagrams are obtained. In this situation, it is observed that, in the case of electrodes magnetization in Triphenylene nanoflake a better spin switching is reached.

Current induced perpendicular-magnetic-anisotropy racetrack memory with magnetic field assistance

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

Zhang, Y.; Klein, J.-O.; Chappert, C.

2014-01-20

High current density is indispensable to shift domain walls (DWs) in magnetic nanowires, which limits the using of racetrack memory (RM) for low power and high density purposes. In this paper, we present perpendicular-magnetic-anisotropy (PMA) Co/Ni RM with global magnetic field assistance, which lowers the current density for DW motion. By using a compact model of PMA RM and 40 nm design kit, we perform mixed simulation to validate the functionality of this structure and analyze its density potential. Stochastic DW motion behavior has been taken into account and statistical Monte-Carlo simulations are carried out to evaluate its reliability performance.

Magnetically-induced electric polarization in an organo-metallic magnet

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

Zapf, W S; Fabris, F W; Balakirev, F F

2009-01-01

The coupling between magnetic order and ferroelectricity has been under intense investigation in a wide range of transition metal oxides. The strongest coupling is obtained in so-called magnetically induced multiferroics where ferroelectricity arises directly from magnetic order that breaks inversion symmetry. However, it has been difficult to find non-oxide based materials in which these effects occur. Here we present a study of copper dimethyl sulfoxide dichloride (CDC), an organometallic quantum magnet containing S =1/1 Cu spins, in which a switchable electric polarization arises from field-tuned magnetic order. Fast magnetic field pulses allow us to perform sensitive measurements of the electricmore » polarization and demonstrate that the electric state is present only if the magnetic order is non-collinear. Furthermore, we show that the electric polarization can be switched in a stunning hysteretic fashion. Because the magnetic order in CDC is mediated by large organic molecules, our study shows that magnetoelectric interactions can exist in this important class of materials, opening the road to designing magnetoelectrics and multiferroics using large molecules as building blocks. Further, we demonstrate that CDC undergoes a magnetoelectric quantum phase transition -the first of its kind, where both ferroelectric and magnetic order emerge simultaneously as a function of magnetic field at very low temperatures.« less

Photospheric Magnetic Diffusion by Measuring Moments of Active Regions

NASA Astrophysics Data System (ADS)

Engell, Alexander; Longcope, D.

2013-07-01

Photospheric magnetic surface diffusion is an important constraint for the solar dynamo. The HMI Active Region Patches (HARPs) program automatically identify all magnetic regions above a certain flux. In our study we measure the moments of ARs that are no longer actively emerging and can thereby give us good statistical constraints on photospheric diffusion. We also present the diffusion properties as a function of latitude, flux density, and single polarity (leading or following) within each HARP.

One dimensional spatial resolution optimization on a hybrid low field MRI-gamma detector

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

Agulles-Pedrós, L., E-mail: lagullesp@unal.edu.co; Abril, A., E-mail: ajabrilf@unal.edu.co

Hybrid systems like Positron Emission Tomography/Magnetic Resonance Imaging (PET/MRI) and MRI/gamma camera, offer advantages combining the resolution and contrast capability of MRI with the better contrast and functional information of nuclear medicine techniques. However, the radiation detectors are expensive and need an electronic set-up, which can interfere with the MRI acquisition process or viceversa. In order to improve these drawbacks, in this work it is presented the design of a low field NMR system made up of permanent magnets compatible with a gamma radiation detector based on gel dosimetry. The design is performed using the software FEMM for estimation ofmore » the magnetic field, and GEANT4 for the physical process involved in radiation detection and effect of magnetic field. The homogeneity in magnetic field is achieved with an array of NbFeB magnets in a linear configuration with a separation between the magnets, minimizing the effect of Compton back scattering compared with a no-spacing linear configuration. The final magnetic field in the homogeneous zone is ca. 100 mT. In this hybrid proposal, although the gel detector do not have spatial resolution per se, it is possible to obtain a dose profile (1D image) as a function of the position by using a collimator array. As a result, the gamma detector system described allows a complete integrated radiation detector within the low field NMR (lfNMR) system. Finally we present the better configuration for the hybrid system considering the collimator parameters such as height, thickness and distance.« less

Polymer- and dendrimer-coated magnetic nanoparticles as versatile supports for catalysts, scavengers, and reagents.

PubMed

Kainz, Quirin M; Reiser, Oliver

2014-02-18

The work-up of chemical reactions by standard techniques is often time consuming and energy demanding, especially when chemists have to guarantee low levels of metal contamination in the products. Therefore, scientists need new ideas to rapidly purify reaction mixtures that are both economically and environmentally benign. One intriguing approach is to tether functionalities that are required to perform organic reactions to magnetic nanoparticles, for example, catalysts, reagents, scavengers, or chelators. This strategy allows researchers to quickly separate active agents from reaction mixtures by exploiting the magnetic properties of the support. In this Account, we discuss the main attributes of magnetic supports and describe how we can make the different nanomagnets accessible by surface functionalization. Arguably the most prominent magnetic nanoparticles are superparamagnetic iron oxide nanoparticles (SPIONs) due to their biologically well-accepted constituents, their established size-selective synthesis methods, and their diminished agglomeration (no residual magnetic attraction in the absence of an external magnetic field). However, nanoparticles made of pure metal have a considerably higher magnetization level that is useful in applications where high loadings are needed. A few layers of carbon can efficiently shield such highly reactive metal nanoparticles and, equally important, enable facile covalent functionalization via diazonium chemistry or non-covalent functionalization through π-π interactions. We highlight carbon-coated cobalt (Co/C) and iron (Fe/C) nanoparticles in this Account and compare them to SPIONs stabilized with surfactants or silica shells. The graphene-like coating of these nanoparticles offers only low loadings with functional groups via direct surface modification, and the resulting nanomagnets are prone to agglomeration without effective steric stabilization. To overcome these restrictions and to tune the dispersibility of the magnetic supports in different solvents, we can introduce dendrimers and polymers on Co/C and Fe/C platforms by various synthetic strategies. While dendrimers have the advantage of being able to array all functional groups on the surface, polymers need fewer synthetic steps and higher molecular weight analogues are easily accessible. We present the application of these promising hybrid materials for the extraction of analytes or contaminates from complex aqueous solutions (e.g. waste water treatments or blood analytics), for metal-, organo-, and biocatalysis, and in organic synthesis. In addition, we describe advanced concepts like magnetic protecting groups, a multistep synthesis solely applying magnetic reagents and scavengers, and thermoresponsive self-separating magnetic catalysts. We also discuss the first examples of the use of magnetic scaffolds manipulated by external magnetic fields in flow reactors on the laboratory scale. These hold promise for future applications of magnetic hybrid materials in continuous flow or highly parallelized syntheses with rapid magnetic separation of the applied resins.

Organic-dye-coupled magnetic nanoparticles encaged inside thermoresponsive PNIPAM Microcapsules.

PubMed

Guo, Jia; Yang, Wuli; Deng, Yonghui; Wang, Changchun; Fu, Shoukuan

2005-07-01

We present a new approach for the fabrication of thermoresponsive polymer microcapsules with mobile magnetic cores that undergo a volume phase-transition upon changing the temperature and are collected under an external magnetic field. We have prepared organic/inorganic composite microspheres with a well-defined core-shell structure that are composed of a crosslinked poly(N-isopropylacrylamide) (PNIPAM) shell and silica cores dotted centrally by magnetite nanoparticles. Since the infiltration of template-decomposed products is dependent on the permeability of PNIPAM shells triggered by changes of exterior temperature, the silica layer sandwiched between the magnetic core and the PNIPAM shell was quantitatively removed to generate PNIPAM microcapsules with mobile magnetic cores by treatment with aqueous NaOH solution. For development of the desired multifunctional microcapsules, modification of the unetched silica surface interiors can be realized by treatment with a silane coupling agent containing functional groups that can easily bind to catalysts, enzymes, or labeling molecules. Herein, fluorescein isothiocyanate (FITC), which is a common organic dye, is attached to the insides of the mobile magnetic cores to give PNIPAM microcapsules with FITC-labeled magnetic cores. In this system, it can be expected that an extension of the functionalization of the cavity properties of smart polymer microcapsules is to immobilize other target molecules onto the mobile cores in order to introduce other desired functions in the hollow cage.

Comparison of Flux-Surface Aligned Curvilinear Coordinate Systems and Neoclassical Magnetic Field Predictions

NASA Astrophysics Data System (ADS)

Collart, T. G.; Stacey, W. M.

2015-11-01

Several methods are presented for extending the traditional analytic ``circular'' representation of flux-surface aligned curvilinear coordinate systems to more accurately describe equilibrium plasma geometry and magnetic fields in DIII-D. The formalism originally presented by Miller is extended to include different poloidal variations in the upper and lower hemispheres. A coordinate system based on separate Fourier expansions of major radius and vertical position greatly improves accuracy in edge plasma structure representation. Scale factors and basis vectors for a system formed by expanding the circular model minor radius can be represented using linear combinations of Fourier basis functions. A general method for coordinate system orthogonalization is presented and applied to all curvilinear models. A formalism for the magnetic field structure in these curvilinear models is presented, and the resulting magnetic field predictions are compared against calculations performed in a Cartesian system using an experimentally based EFIT prediction for the Grad-Shafranov equilibrium. Supported by: US DOE under DE-FG02-00ER54538.

Dynamics of photogenerated carriers near magnetic field driven quantum phase transition in aperiodic multiple quantum wells

NASA Astrophysics Data System (ADS)

Tito, M. A.; Pusep, Yu A.

2018-01-01

Time-resolved magneto-photoluminescence was employed to study the magnetic field induced quantum phase transition separating two phases with different distributions of electrons over quantum wells in an aperiodic multiple quantum well, embedded in a wide AlGaAs parabolic quantum well. Intensities, broadenings and recombination times attributed to the photoluminescence lines emitted from individual quantum wells of the multiple quantum well structure were measured as a function of the magnetic field near the transition. The presented data manifest themselves to the magnetic field driven migration of the free electrons between the quantum wells of the studied multiple quantum well structure. The observed charge transfer was found to influence the screening of the multiple quantum well and disorder potentials. Evidence of the localization of the electrons in the peripheral quantum wells in strong magnetic field is presented.

Magnetic purification of curcumin from Curcuma longa rhizome by novel naked maghemite nanoparticles.

PubMed

Magro, Massimiliano; Campos, Rene; Baratella, Davide; Ferreira, Maria Izabela; Bonaiuto, Emanuela; Corraducci, Vittorino; Uliana, Maíra Rodrigues; Lima, Giuseppina Pace Pereira; Santagata, Silvia; Sambo, Paolo; Vianello, Fabio

2015-01-28

Naked maghemite nanoparticles, namely, surface active maghemite nanoparticles (SAMNs), characterized by a diameter of about 10 nm, possessing peculiar colloidal stability, surface chemistry, and superparamagnetism, present fundamental requisites for the development of effective magnetic purification processes for biomolecules in complex matrices. Polyphenolic molecules presenting functionalities with different proclivities toward iron chelation were studied as probes for testing SAMN suitability for magnetic purification. Thus, the binding efficiency and reversibility on SAMNs of phenolic compounds of interest in the pharmaceutical and food industries, namely, catechin, tyrosine, hydroxytyrosine, ferulic acid, coumaric acid, rosmarinic acid, naringenin, curcumin, and cyanidin-3-glucoside, were evaluated. Curcumin emerged as an elective compound, suitable for magnetic purification by SAMNs from complex matrices. A combination of curcumin, demethoxycurcumin, and bis-demethoxycurcumin was recovered by a single magnetic purification step from extracts of Curcuma longa rhizomes, with a purity >98% and a purification yield of 45%, curcumin being >80% of the total purified curcuminoids.

Spin-orbit driven magnetic insulating state with J eff=1/2 character in a 4d oxide

DOE PAGES

Calder, S.; Li, Ling; Okamoto, Satoshi; ...

2015-11-30

The unusual magnetic and electronic ground states of 5d iridates has been shown to be driven by intrinsically enhanced spin-orbit coupling (SOC). The influence of appreciable but reduced SOC in creating the manifested magnetic insulating states in 4d oxides is less clear, with one hurdle being the existence of such compounds. Here we present experimental and theoretical results on Sr 4RhO 6 that reveal SOC dominated behavior. Neutron measurements show the octahedra are both spatially separated and locally ideal, making the electronic ground state susceptible to alterations by SOC. Magnetic ordering is observed with a similar structure to an analogousmore » J eff=1/2 Mott iridate. We consider the underlying role of SOC in this rhodate with density functional theory and x-ray absorption spectroscopy and find a magnetic insulating ground state with J eff =1/2 character.The unusual magnetic and electronic ground states of 5d iridates have been shown to be driven by intrinsically enhanced spin-orbit coupling (SOC). The influence of appreciable but reduced SOC in creating the manifested magnetic insulating states in 4d oxides is less clear, with one hurdle being the existence of such compounds. Here, we present experimental and theoretical results on Sr 4RhO 6 that reveal SOC dominated behavior. Neutron measurements show the octahedra are both spatially separated and locally ideal, making the electronic ground state susceptible to alterations by SOC. Magnetic ordering is observed with a similar structure to an analogous J eff=1/2 Mott iridate. We consider the underlying role of SOC in this rhodate with density functional theory and x-ray absorption spectroscopy, and find a magnetic insulating ground state with J eff=12 character.« less

Real-time and quantitative isotropic spatial resolution susceptibility imaging for magnetic nanoparticles

NASA Astrophysics Data System (ADS)

Pi, Shiqiang; Liu, Wenzhong; Jiang, Tao

2018-03-01

The magnetic transparency of biological tissue allows the magnetic nanoparticle (MNP) to be a promising functional sensor and contrast agent. The complex susceptibility of MNPs, strongly influenced by particle concentration, excitation magnetic field and their surrounding microenvironment, provides significant implications for biomedical applications. Therefore, magnetic susceptibility imaging of high spatial resolution will give more detailed information during the process of MNP-aided diagnosis and therapy. In this study, we present a novel spatial magnetic susceptibility extraction method for MNPs under a gradient magnetic field, a low-frequency drive magnetic field, and a weak strength high-frequency magnetic field. Based on this novel method, a magnetic particle susceptibility imaging (MPSI) of millimeter-level spatial resolution (<3 mm) was achieved using our homemade imaging system. Corroborated by the experimental results, the MPSI shows real-time (1 s per frame acquisition) and quantitative abilities, and isotropic high resolution.

Propagation of electromagnetic waves parallel to the magnetic field in the nightside Venus ionosphere

NASA Technical Reports Server (NTRS)

Huba, J. D.; Rowland, H. L.

1993-01-01

The propagation of electromagnetic waves parallel to the magnetic field in the nightside Venus ionosphere is presented in a theoretical and numerical analysis. The model assumes a source of electromagnetic radiation in the Venus atmosphere, such as that produced by lightning. Specifically addressed is wave propagation in the altitude range z = 130-160 km at the four frequencies detectable by the Pioneer Venus Orbiter Electric Field Detector: 100 Hz, 730 Hz, 5.4 kHz, and 30 kHz. Parameterizations of the wave intensities, peak electron density, and Poynting flux as a function of magnetic field are presented. The waves are found to propagate most easily in conditions of low electron density and high magnetic field. The results of the model are consistent with observational data.

Dynamics of aging magnetic clouds. [interacted with solar wind

NASA Technical Reports Server (NTRS)

Osherovich, V. A.; Farrugia, C. J.; Burlaga, L. F.

1993-01-01

The dynamics of radially expanding magnetic clouds is rigorously analyzed within the framework of ideal MHD. The cloud is modelled as a cylindrically symmetric magnetic flux rope. In the force balance we include the gas pressure gradient and the Lorentz force. Interaction with the ambient solar wind due to expansion of the magnetic cloud is represented by a drag force proportional to the bulk velocity. We consider the self-similar expansion of a polytrope, and reduce the problem to an ordinary nonlinear differential equation for the evolution function. Analyzing the asymptotic behavior of the evolution function, we formulate theoretical expectations for the long-term behavior of cloud parameters. We focus on the temporal evolution of (1) the magnetic field strength; (2) the twist of the field lines; (3) the asymmetry of the total field profile; and (4) the bulk flow speed. We present data from two magnetic clouds observed at 1 AU and 2 AU, respectively, and find good agreement with theoretical expectations. For a peak magnetic field strength at 1 AU of 25 nT and a polytropic index of 0.5, we find that a magnetic cloud can be distinguished from the background interplanetary field up to a distance of about 5 AU. Taking larger magnetic fields and bigger polytropic indices this distance can double.

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.

Development of New Contrast Agents for Imaging Function and Metabolism by Magnetic Resonance Imaging

PubMed Central

Carvalho, Alexandra; Gonçalves, M Clara; Corvo, M Luísa; Martins, M Bárbara F

2017-01-01

Liposomes are interesting nanosystems with a wide range of medical application. One particular application is their ability to enhance contrast in magnetic resonance images; when properly loaded with magnetic/superparamagnetic nanoparticles, this means to act as contrast agents. The design of liposomes loaded with magnetic particles, magnetoliposomes, presents a large number of possibilities depending on the application from image function to metabolism. More interesting is its double function application as theranostics (diagnostics and therapy). The synthesis, characterization, and possible medical applications of two types of magnetoliposomes are reviewed. Their performance will be compared, in particular, their efficiency as contrast agents for magnetic resonance imaging, measured by their relaxivities r1 and r2 relating to their particular composition. One of the magnetoliposomes had 1,2-diacyl-sn-glycero-3-phosphocholine (soy) as the main phospholipid component, with and without cholesterol, varying its phospholipid to cholesterol molar ratios. The other formulation is a long-circulating liposome composed of 1,2-diacyl-sn-glycero-3-phosphocholine (egg), cholesterol, and 1,2-distearoyl-sn-glycerol-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000]. Both nanosystems were loaded with superparamagnetic iron oxide nanoparticles with different sizes and coatings. PMID:28804244

MAX UnMix: Introducing a new web application for unmixing magnetic coercivity distributions

NASA Astrophysics Data System (ADS)

Feinberg, J. M.; Maxbauer, D.; Fox, D. L.

2016-12-01

Magnetic minerals are present in a wide variety of natural systems and are often indicative of the natural or anthropogenic processes that led to their deposition, formation, or transformation. Unmixing the contribution of magnetic components to bulk field-dependent magnetization curves has become increasingly common in environmental and rock magnetic studies and has enhanced our ability to fingerprint the magnetic signatures of magnetic minerals with distinct compositions, grain sizes, and origins. A variety of programs have been developed over the past two decades to allow researchers to deconvolve field-dependent magnetization curves for these purposes, however many of these programs are either outdated or have obstacles that inhibit the programs usability. MAX UnMix is a new web application (available online at http://www.irm.umn.edu/maxunmix) built using the `shiny' package for R-studio that can be used to process coercivity distributions derived from magnetization curves (acquisition, demagnetization, or backfield data) via an online user-interface. Here, we use example datasets from lake sediments and paleosols to present details of the MAX UnMix model and the programs functionality. MAX UnMix is designed to be accessible, user friendly, and should serve as a useful resource for future research.

Asymptotic-preserving Lagrangian approach for modeling anisotropic transport in magnetized plasmas

NASA Astrophysics Data System (ADS)

Chacon, Luis; Del-Castillo-Negrete, Diego

2012-03-01

Modeling electron transport in magnetized plasmas is extremely challenging due to the extreme anisotropy between parallel (to the magnetic field) and perpendicular directions (the transport-coefficient ratio χ/χ˜10^10 in fusion plasmas). Recently, a novel Lagrangian Green's function method has been proposedfootnotetextD. del-Castillo-Negrete, L. Chac'on, PRL, 106, 195004 (2011); D. del-Castillo-Negrete, L. Chac'on, Phys. Plasmas, submitted (2011) to solve the local and non-local purely parallel transport equation in general 3D magnetic fields. The approach avoids numerical pollution, is inherently positivity-preserving, and is scalable algorithmically (i.e., work per degree-of-freedom is grid-independent). In this poster, we discuss the extension of the Lagrangian Green's function approach to include perpendicular transport terms and sources. We present an asymptotic-preserving numerical formulation, which ensures a consistent numerical discretization temporally and spatially for arbitrary χ/χ ratios. We will demonstrate the potential of the approach with various challenging configurations, including the case of transport across a magnetic island in cylindrical geometry.

Nuclear spin circular dichroism.

PubMed

Vaara, Juha; Rizzo, Antonio; Kauczor, Joanna; Norman, Patrick; Coriani, Sonia

2014-04-07

Recent years have witnessed a growing interest in magneto-optic spectroscopy techniques that use nuclear magnetization as the source of the magnetic field. Here we present a formulation of magnetic circular dichroism (CD) due to magnetically polarized nuclei, nuclear spin-induced CD (NSCD), in molecules. The NSCD ellipticity and nuclear spin-induced optical rotation (NSOR) angle correspond to the real and imaginary parts, respectively, of (complex) quadratic response functions involving the dynamic second-order interaction of the electron system with the linearly polarized light beam, as well as the static magnetic hyperfine interaction. Using the complex polarization propagator framework, NSCD and NSOR signals are obtained at frequencies in the vicinity of optical excitations. Hartree-Fock and density-functional theory calculations on relatively small model systems, ethene, benzene, and 1,4-benzoquinone, demonstrate the feasibility of the method for obtaining relatively strong nuclear spin-induced ellipticity and optical rotation signals. Comparison of the proton and carbon-13 signals of ethanol reveals that these resonant phenomena facilitate chemical resolution between non-equivalent nuclei in magneto-optic spectra.

Density functional perturbational orbital theory of spin polarization in electronic systems. II. Transition metal dimer complexes.

PubMed

Seo, Dong-Kyun

2007-11-14

We present a theoretical scheme for a semiquantitative analysis of electronic structures of magnetic transition metal dimer complexes within spin density functional theory (DFT). Based on the spin polarization perturbational orbital theory [D.-K. Seo, J. Chem. Phys. 125, 154105 (2006)], explicit spin-dependent expressions of the spin orbital energies and coefficients are derived, which allows to understand how spin orbitals form and change their energies and shapes when two magnetic sites are coupled either ferromagnetically or antiferromagnetically. Upon employment of the concept of magnetic orbitals in the active-electron approximation, a general mathematical formula is obtained for the magnetic coupling constant J from the analytical expression for the electronic energy difference between low-spin broken-symmetry and high-spin states. The origin of the potential exchange and kinetic exchange terms based on the one-electron picture is also elucidated. In addition, we provide a general account of the DFT analysis of the magnetic exchange interactions in compounds for which the active-electron approximation is not appropriate.

Strain-induced magnetization control in an oxide multiferroic heterostructure

NASA Astrophysics Data System (ADS)

Motti, Federico; Vinai, Giovanni; Petrov, Aleksandr; Davidson, Bruce A.; Gobaut, Benoit; Filippetti, Alessio; Rossi, Giorgio; Panaccione, Giancarlo; Torelli, Piero

2018-03-01

Controlling magnetism by using electric fields is a goal of research towards novel spintronic devices and future nanoelectronics. For this reason, multiferroic heterostructures attract much interest. Here we provide experimental evidence, and supporting density functional theory analysis, of a transition in L a0.65S r0.35Mn O3 thin film to a stable ferromagnetic phase, that is induced by the structural and strain properties of the ferroelectric BaTi O3 (BTO) substrate, which can be modified by applying external electric fields. X-ray magnetic circular dichroism measurements on Mn L edges with a synchrotron radiation show, in fact, two magnetic transitions as a function of temperature that correspond to structural changes of the BTO substrate. We also show that ferromagnetism, absent in the pristine condition at room temperature, can be established by electrically switching the BTO ferroelectric domains in the out-of-plane direction. The present results confirm that electrically induced strain can be exploited to control magnetism in multiferroic oxide heterostructures.

Two-dimensional electrodynamic structure of the normal glow discharge in an axial magnetic field

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

Surzhikov, S. T., E-mail: surg@ipmnet.ru

Results are presented from numerical simulations of an axisymmetric normal glow discharge in molecular hydrogen and molecular nitrogen in an axial magnetic field. The charged particle densities and averaged azimuthal rotation velocities of electrons and ions are studied as functions of the gas pressure in the range of 1–5 Torr, electric field strength in the range of 100–600 V/cm, and magnetic field in the range of 0.01–0.3 T. It is found that the axial magnetic field does not disturb the normal current density law.

Decreased Functional Brain Activation in Friedreich Ataxia Using the Simon Effect Task

ERIC Educational Resources Information Center

Georgiou-Karistianis, N.; Akhlaghi, H.; Corben, L. A.; Delatycki, M. B.; Storey, E.; Bradshaw, J. L.; Egan, G. F.

2012-01-01

The present study applied the Simon effect task to examine the pattern of functional brain reorganization in individuals with Friedreich ataxia (FRDA), using functional magnetic resonance imaging (fMRI). Thirteen individuals with FRDA and 14 age and sex matched controls participated, and were required to respond to either congruent or incongruent…

Statistical description and transport in stochastic magnetic fields

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

Vanden Eijnden, E.; Balescu, R.

1996-03-01

The statistical description of particle motion in a stochastic magnetic field is presented. Starting form the stochastic Liouville equation (or, hybrid kinetic equation) associated with the equations of motion of a test particle, the probability distribution function of the system is obtained for various magnetic fields and collisional processes. The influence of these two ingredients on the statistics of the particle dynamics is stressed. In all cases, transport properties of the system are discussed. {copyright} {ital 1996 American Institute of Physics.}

Active shielding of cylindrical saddle-shaped coils: application to wire-wound RF coils for very low field NMR and MRI.

PubMed

Bidinosti, C P; Kravchuk, I S; Hayden, M E

2005-11-01

We provide an exact expression for the magnetic field produced by cylindrical saddle-shaped coils and their ideal shield currents in the low-frequency limit. The stream function associated with the shield surface current is also determined. The results of the analysis are useful for the design of actively shielded radio-frequency (RF) coils. Examples pertinent to very low field nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) are presented and discussed.

An NV-Diamond Magnetic Imager for Neuroscience

NASA Astrophysics Data System (ADS)

Turner, Matthew; Schloss, Jennifer; Bauch, Erik; Hart, Connor; Walsworth, Ronald

2017-04-01

We present recent progress towards imaging time-varying magnetic fields from neurons using nitrogen-vacancy centers in diamond. The diamond neuron imager is noninvasive, label-free, and achieves single-cell resolution and state-of-the-art broadband sensitivity. By imaging magnetic fields from injected currents in mammalian neurons, we will map functional neuronal network connections and illuminate biophysical properties of neurons invisible to traditional electrophysiology. Furthermore, through enhancing magnetometer sensitivity, we aim to demonstrate real-time imaging of action potentials from networks of mammalian neurons.

Electronic and magnetic properties of bare armchair BC2N nanoribbons

NASA Astrophysics Data System (ADS)

Li, Hong; Xiao, Xiang; Tie, Jun; Lu, Jing

2017-03-01

We present the electronic and magnetic properties of bare armchair BC2N nanoribbons (ABC2NNRs) in the view of density functional calculations. We consider three types of edge terminations with a width of 0.75 2.10 nm. All the investigated ribbons exhibit magnetic ground states with the magnetic moments mainly located on the edge C atoms. Room temperature accessible magnetic stabilities are obtained for ABC2NNRs with NC-NC and NC-BC edge alignments. We find the ABC2NNRs have various electronic structures, where half-metal, metal, and semiconductor are all acquired depend on the edge alignment and magnetic coupling state. The results show the ABC2NNRs can be a promising candidate material in nanoelectronics and nanospintronics.

Efficient solution methodology for calibrating the hemodynamic model using functional Magnetic Resonance Imaging (fMRI) measurements.

PubMed

Zambri, Brian; Djellouli, Rabia; Laleg-Kirati, Taous-Meriem

2015-08-01

Our aim is to propose a numerical strategy for retrieving accurately and efficiently the biophysiological parameters as well as the external stimulus characteristics corresponding to the hemodynamic mathematical model that describes changes in blood flow and blood oxygenation during brain activation. The proposed method employs the TNM-CKF method developed in [1], but in a prediction/correction framework. We present numerical results using both real and synthetic functional Magnetic Resonance Imaging (fMRI) measurements to highlight the performance characteristics of this computational methodology.

Real-time functional magnetic imaging-brain-computer interface and virtual reality promising tools for the treatment of pedophilia.

PubMed

Renaud, Patrice; Joyal, Christian; Stoleru, Serge; Goyette, Mathieu; Weiskopf, Nikolaus; Birbaumer, Niels

2011-01-01

This chapter proposes a prospective view on using a real-time functional magnetic imaging (rt-fMRI) brain-computer interface (BCI) application as a new treatment for pedophilia. Neurofeedback mediated by interactive virtual stimuli is presented as the key process in this new BCI application. Results on the diagnostic discriminant power of virtual characters depicting sexual stimuli relevant to pedophilia are given. Finally, practical and ethical implications are briefly addressed. Copyright © 2011 Elsevier B.V. All rights reserved.

Frequency redistribution function for the polarized two-term atom

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

Casini, R.; Landi Degl'Innocenti, M.; Manso Sainz, R.

2014-08-20

We present a generalized frequency redistribution function for the polarized two-term atom in an arbitrary magnetic field. This result is derived within a new formulation of the quantum problem of coherent scattering of polarized radiation by atoms in the collisionless regime. The general theory, which is based on a diagrammatic treatment of the atom-photon interaction, is still a work in progress. However, the results anticipated here are relevant enough for the study of the magnetism of the solar chromosphere and of interest for astrophysics in general.

An Alternate Set of Basis Functions for the Electromagnetic Solution of Arbitrarily-Shaped, Three-Dimensional, Closed, Conducting Bodies Using Method of Moments

NASA Technical Reports Server (NTRS)

Mackenzie, Anne I.; Baginski, Michael E.; Rao, Sadasiva M.

2008-01-01

In this work, we present an alternate set of basis functions, each defined over a pair of planar triangular patches, for the method of moments solution of electromagnetic scattering and radiation problems associated with arbitrarily-shaped, closed, conducting surfaces. The present basis functions are point-wise orthogonal to the pulse basis functions previously defined. The prime motivation to develop the present set of basis functions is to utilize them for the electromagnetic solution of dielectric bodies using a surface integral equation formulation which involves both electric and magnetic cur- rents. However, in the present work, only the conducting body solution is presented and compared with other data.

Magneto Tuning of a Ferrite Dielectric Resonator Antenna Based on LiFe5O8 Matrix

NASA Astrophysics Data System (ADS)

de Morais, J. E. V.; de Castro, A. J. N.; Oliveira, R. G. M.; do Carmo, F. F.; Sales, A. J. M.; Sales, J. C.; Silva, M. A. S.; Gouveia, D. X.; Costa, M. M.; Rodrigues, A. R.; Sombra, A. S. B.

2018-04-01

LiFe5O8 (LFO) spinel-like material has been studied for use in ferrite resonator antennas (FRAs). Antenna parameters such as gain and return loss were greatly affected when an external magnetic field was applied to the FRA. The temperature coefficient of the resonant frequency (τ f ) for the FRA presented a value of - 482.16 ppm/°C. The magnetic hysteresis results showed that the LFO was a soft ferrite, considering the values of the remanent magnetization (M r = 5.95 emu g-1), coercive field (0.76 mT), and saturation magnetization (32.15 emu g-1). The magnetodielectric resonator presented a tuning effect in the resonant frequency as a function of the external magnetic field. The antenna bandwidth was also affected by the presence of the magnetic field. LFO is a soft ferrite with applications in microwave circuits, antennas, and devices for operation at microwave frequencies due to its magnetization and demagnetization properties. Impedance study revealed increasing conductivity from room to higher temperature with low activation energy (0.36 eV).

Note: Precise radial distribution of charged particles in a magnetic guiding field

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

Backe, H., E-mail: backe@kph.uni-mainz.de

2015-07-15

Current high precision beta decay experiments of polarized neutrons, employing magnetic guiding fields in combination with position sensitive and energy dispersive detectors, resulted in a detailed study of the mono-energetic point spread function (PSF) for a homogeneous magnetic field. A PSF describes the radial probability distribution of mono-energetic electrons at the detector plane emitted from a point-like source. With regard to accuracy considerations, unwanted singularities occur as a function of the radial detector coordinate which have recently been investigated by subdividing the radial coordinate into small bins or employing analytical approximations. In this note, a series expansion of the PSFmore » is presented which can numerically be evaluated with arbitrary precision.« less

Transverse particle acceleration and diffusion in a planetary magnetic field

NASA Technical Reports Server (NTRS)

Barbosa, D. D.

1994-01-01

A general model of particle acceleration by plasma waves coupled with adiabatic radial diffusion in a planetary magnetic field is developed. The model assumes that a spectrum of lower hybird waves is present to resonantly accelerate ions transverse to the magnetic field. The steady state Green's function for the combined radial diffusion and wave acceleration equation is found in terms of a series expansion. The results provide a rigorous demonstration of how a quasi-Maxwellian distribution function is formed in the absence of particle collisons and elucidate the nature of turbulent heating of magnetospheric plasmas. The solution is applied to the magnetosphere of Neptune for which a number of examples are given illustrating how the spectrum of pickup N(+) ions from Triton evolves.

Modeling of the gate-controlled Kondo effect at carbon point defects in graphene

NASA Astrophysics Data System (ADS)

May, Daniel; Lo, Po-Wei; Deltenre, Kira; Henke, Anika; Mao, Jinhai; Jiang, Yuhang; Li, Guohong; Andrei, Eva Y.; Guo, Guang-Yu; Anders, Frithjof B.

2018-04-01

We study the magnetic properties in the vicinity of a single carbon defect in a monolayer of graphene. We include the unbound σ orbital and the vacancy-induced bound π state in an effective two-orbital single-impurity model. The local magnetic moments are stabilized by the Coulomb interaction as well as a significant ferromagnetic Hund's rule coupling between the orbitals predicted by a density functional theory calculation. A hybridization between the orbitals and the Dirac fermions is generated by the curvature of the graphene sheet in the vicinity of the vacancy. We present results for the local spectral function calculated using Wilson's numerical renormalization group approach for a realistic graphene band structure and find three different regimes depending on the filling, the controlling chemical potential, and the hybridization strength. These different regions are characterized by different magnetic properties. The calculated spectral functions qualitatively agree with recent scanning tunneling spectra on graphene vacancies.

Magnetic field effect on photoionization cross-section of hydrogen-like impurity in cylindrical quantum wire

NASA Astrophysics Data System (ADS)

Mughnetsyan, V. N.; Barseghyan, M. G.; Kirakosyan, A. A.

2008-01-01

We consider the photoionization of a hydrogen-like impurity centre in a quantum wire approximated by a cylindrical well of finite depth in a magnetic field directed along the wire axis. The ground state energy and the wave function of the electron localized on on-axis impurity centre are calculated using the variational method. The wave functions and energies of the final states in an one-dimensional conduction subband are also presented. The dependences of photoionization cross-section of a donor centre on magnetic field and frequency of incident radiation both for parallel and perpendicular polarizations and corresponding selection rules for the allowed transitions are found in the dipole approximation. The estimates of photoionization cross-section for various values of wire radius and magnetic field induction for GaAs quantum wire embedded in Ga 1-xAl 1-xAs matrix are given.

Chitosan magnetic nanoparticles for drug delivery systems.

PubMed

Assa, Farnaz; Jafarizadeh-Malmiri, Hoda; Ajamein, Hossein; Vaghari, Hamideh; Anarjan, Navideh; Ahmadi, Omid; Berenjian, Aydin

2017-06-01

The potential of magnetic nanoparticles (MNPs) in drug delivery systems (DDSs) is mainly related to its magnetic core and surface coating. These coatings can eliminate or minimize their aggregation under physiological conditions. Also, they can provide functional groups for bioconjugation to anticancer drugs and/or targeted ligands. Chitosan, as a derivative of chitin, is an attractive natural biopolymer from renewable resources with the presence of reactive amino and hydroxyl functional groups in its structure. Chitosan nanoparticles (NPs), due to their huge surface to volume ratio as compared to the chitosan in its bulk form, have outstanding physico-chemical, antimicrobial and biological properties. These unique properties make chitosan NPs a promising biopolymer for the application of DDSs. In this review, the current state and challenges for the application magnetic chitosan NPs in drug delivery systems were investigated. The present review also revisits the limitations and commercial impediments to provide insight for future works.

A Hybrid Density Functional Study of Atomic Hydrogen and Oxygen Adsorptions on the (0001) Surface of Non-Magnetic DHCP Americium

NASA Astrophysics Data System (ADS)

Amdani-Moten, Shafaq; Atta-Fynn, Raymond; Ray, Asok

2010-03-01

As our group have recently shown^+, hybrid density functional theory (HDFT) which replaces a fraction (40%) of approximate DFT exchange with exact Hartree-Fock exchange yield structural, magnetic, and electronic properties for Americium-I that are in excellent agreement with experimental data. As a natural progression, ab initio calculations for atomic adsorptions on the (0001) surface of non-magnetic americium have been performed using HDFT. The americium surface is modeled by a seven-layer slab using inversion symmetry consisting of one atom per layer and non-magnetic ABAC stacking arrangement of these layers. Top, bridge, hcp and fcc chemisorption sites have been investigated with energies optimized with respect to the adatom distance from the surface. Details of the chemisorptions processes as well as comparisons of different sites will be presented. ^+ R. Atta-Fynn and A. K. Ray, Chemical Physics Letters, 482, 223-227 (2009).

Contribution functions for Zeeman-split lines, and line formation in photospheric faculae

NASA Technical Reports Server (NTRS)

Vanballegooijen, A. A.

1985-01-01

The transfer of polarized light in an inhomogeneous stellar atmosphere, and the formation of magnetically sensitive spectral lines, are discussed. A new method for the solution of the transfer equations is proposed. The method gives a natural definition of the contribution functions for Stokes' parameters, i.e., functions describing the contributions from different parts along the line-of-sight (LOS). The formalism includes all magneto-optical effects, and allows for an arbitrary variation of magnetic field, velocity field, temperature, density, etc., along the LOS. The formation of FeI lambda 5250.2 in photospheric faculae is described. A potential-field model of a facular element is presented, and spectra profiles and contribution functions are computed for the Stokes parameters I, Q, and V.

The properties and origin of magnetic fields in white dwarfs

NASA Astrophysics Data System (ADS)

Kawka, A.

2018-01-01

A significant fraction of white dwarfs harbour a magnetic field with strengths ranging from a few kG up to about 1000 MG. The fraction appears to depend on the specific class of white dwarfs being investigated and may hold some clues to the origin of their magnetic field. The number of white dwarfs with variable fields as a function of their rotation phase have revealed a large field structure diversity, from a simple offset dipole to structures with spots or multipoles. A review of the current challenges in modelling white dwarf atmospheres in the presence of a magnetic field is presented, and the proposed scenarios for the formation of magnetic fields in white dwarfs are examined.

Functionalization and Characterization of Magnetic Nanoparticles for the Detection of Ferritin Accumulation in Alzheimer's Disease.

PubMed

Fernández, Tamara; Martínez-Serrano, Alberto; Cussó, Lorena; Desco, Manuel; Ramos-Gómez, Milagros

2018-05-16

Early diagnosis in Alzheimer's disease (AD), prior to the appearance of marked clinical symptoms, is critical to prevent irreversible neuronal damage and neural malfunction that lead to dementia and death. Therefore, there is an urgent need to generate new contrast agents which reveal by a noninvasive method the presence of some of the pathological signs of AD. In the present study, we demonstrate for the first time a new nanoconjugate composed of magnetic nanoparticles bound to an antiferritin antibody, which has been developed based on the existence of iron deposits and high levels of the ferritin protein present in areas with a high accumulation of amyloid plaques (particularly the subiculum in the hippocampal area) in the brain of a transgenic mouse model with five familial AD mutations. Both in vitro and after intravenous injection, functionalized magnetic nanoparticles were able to recognize and bind specifically to the ferritin protein accumulated in the subiculum area of the AD transgenic mice.

Three-Dimensional Field Solutions for Multi-Pole Cylindrical Halbach Arrays in an Axial Orientation

NASA Technical Reports Server (NTRS)

Thompson, William K.

2006-01-01

This article presents three-dimensional B field solutions for the cylindrical Halbach array in an axial orientation. This arrangement has applications in the design of axial motors and passive axial magnetic bearings and couplers. The analytical model described here assumes ideal magnets with fixed and uniform magnetization. The field component functions are expressed as sums of 2-D definite integrals that are easily computed by a number of mathematical analysis software packages. The analysis is verified with sample calculations and the results are compared to equivalent results from traditional finite-element analysis (FEA). The field solutions are then approximated for use in flux linkage and induced EMF calculations in nearby stator windings by expressing the field variance with angular displacement as pure sinusoidal function whose amplitude depends on radial and axial position. The primary advantage of numerical implementation of the analytical approach presented in the article is that it lends itself more readily to parametric analysis and design tradeoffs than traditional FEA models.

Retained Austenite in SAE 52100 Steel Post Magnetic Processing and Heat Treatment

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

Pappas, Nathaniel R; Watkins, Thomas R; Cavin, Odis Burl

2007-01-01

Steel is an iron-carbon alloy that contains up to 2% carbon by weight. Understanding which phases of iron and carbon form as a function of temperature and percent carbon is important in order to process/manufacture steel with desired properties. Austenite is the face center cubic (fcc) phase of iron that exists between 912 and 1394 C. When hot steel is rapidly quenched in a medium (typically oil or water), austenite transforms into martensite. The goal of the study is to determine the effect of applying a magnetic field on the amount of retained austenite present at room temperature after quenching.more » Samples of SAE 52100 steel were heat treated then subjected to a magnetic field of varying strength and time, while samples of SAE 1045 steel were heat treated then subjected to a magnetic field of varying strength for a fixed time while being tempered. X-ray diffraction was used to collect quantitative data corresponding to the amount of each phase present post processing. The percentage of retained austenite was then calculated using the American Society of Testing and Materials standard for determining the amount of retained austenite for randomly oriented samples and was plotted as a function of magnetic field intensity, magnetic field apply time, and magnetic field wait time after quenching to determine what relationships exist with the amount of retained austenite present. In the SAE 52100 steel samples, stronger field strengths resulted in lower percentages of retained austenite for fixed apply times. The results were inconclusive when applying a fixed magnetic field strength for varying amounts of time. When applying a magnetic field after waiting a specific amount of time after quenching, the analyses indicate that shorter wait times result in less retained austenite. The SAE 1045 results were inconclusive. The samples showed no retained austenite regardless of magnetic field strength, indicating that tempering removed the retained austenite. It is apparent that applying a magnetic field after quenching will result in a lower amount of retained austenite but that the exact relationship, linear or other, is inconclusive. This project is a part of a larger, ongoing project investigating the application of a magnetic field during heat treatment and its influence on the iron-carbon phase-equilibria.« less

Priming With 1-Hz Repetitive Transcranial Magnetic Stimulation Over Contralesional Leg Motor Cortex Does Not Increase the Rate of Regaining Ambulation Within 3 Months of Stroke: A Randomized Controlled Trial.

PubMed

Huang, Ying-Zu; Lin, Li-Fong; Chang, Kwang-Hwa; Hu, Chaur-Jong; Liou, Tsan-Hon; Lin, Yen-Nung

2018-05-01

The potential benefits of repetitive transcranial magnetic stimulation (rTMS), applied either alone or as a combination treatment, on recovery of lower limbs after stroke have been insufficiently studied. The aim of the study was to evaluate the effect of priming with 1-Hz repetitive transcranial magnetic stimulation over contralesional leg motor area with a double-cone coil before physical therapy on regaining ambulation. Thirty-eight subacute stroke patients with significant leg disabilities were randomly assigned into the experimental group or control group to receive a 15-min real or sham 1-Hz repetitive transcranial magnetic stimulation, respectively, over the contralesional motor cortex representing the quadriceps muscle followed by 45-min physical therapy for 15 sessions for 3 wks. Functional measures, motor evoked potentials, and quality of life were assessed. There was no significant difference between experimental group and control group regarding the recovery in ambulation, balance, motor functions, and activity of daily living. No significant difference was found in other functional measures and the quality of life. Only the control group displayed significantly increased cortical excitability of the contralesional hemisphere after the intervention. The present study found that insufficient evidence that contralesional priming with 1-Hz repetitive transcranial magnetic stimulation improves ambulatory and other motor functions among patients with a severe leg dysfunction in subacute stroke.

Sector magnets or transverse electromagnetic fields in cylindrical coordinates

DOE PAGES

Zolkin, T.

2017-04-10

Laplace’s equation is considered for scalar and vector potentials describing electric or magnetic fields in cylindrical coordinates, with invariance along the azimuthal coordinate. In a series, we found special functions which, when expanded to lowest order in power series in radial and vertical coordinates, replicate harmonic polynomials in two variables. These functions are based on radial harmonics found by Edwin M. McMillan forty years ago. In addition to McMillan’s harmonics, a second family of radial harmonics is introduced to provide a symmetric description between electric and magnetic fields and to describe fields and potentials in terms of the same functions.more » Formulas are provided which relate any transverse fields specified by the coefficients in the power series expansion in radial or vertical planes in cylindrical coordinates with the set of new functions. Our result is important for potential theory and for theoretical study, design and proper modeling of sector dipoles, combined function dipoles and any general sector element for accelerator physics. All results are presented in connection with these problems.« less

Comparison of forcing functions in magnetohydrodynamics

NASA Astrophysics Data System (ADS)

McKay, Mairi E.; Linkmann, Moritz; Clark, Daniel; Chalupa, Adam A.; Berera, Arjun

2017-11-01

Results are presented of direct numerical simulations of incompressible, homogeneous magnetohydrodynamic turbulence without a mean magnetic field, subject to different mechanical forcing functions commonly used in the literature. Specifically, the forces are negative damping (which uses the large-scale velocity field as a forcing function), a nonhelical random force, and a nonhelical static sinusoidal force (analogous to helical ABC forcing). The time evolution of the three ideal invariants (energy, magnetic helicity, and cross helicity), the time-averaged energy spectra, the energy ratios, and the dissipation ratios are examined. All three forcing functions produce qualitatively similar steady states with regard to the time evolution of the energy and magnetic helicity. However, differences in the cross-helicity evolution are observed, particularly in the case of the static sinusoidal method of energy injection. Indeed, an ensemble of sinusoidally forced simulations with identical parameters shows significant variations in the cross helicity over long time periods, casting some doubt on the validity of the principle of ergodicity in systems in which the injection of helicity cannot be controlled. Cross helicity can unexpectedly enter the system through the forcing function and must be carefully monitored.

Sector magnets or transverse electromagnetic fields in cylindrical coordinates

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

Zolkin, T.

Laplace’s equation is considered for scalar and vector potentials describing electric or magnetic fields in cylindrical coordinates, with invariance along the azimuthal coordinate. In a series, we found special functions which, when expanded to lowest order in power series in radial and vertical coordinates, replicate harmonic polynomials in two variables. These functions are based on radial harmonics found by Edwin M. McMillan forty years ago. In addition to McMillan’s harmonics, a second family of radial harmonics is introduced to provide a symmetric description between electric and magnetic fields and to describe fields and potentials in terms of the same functions.more » Formulas are provided which relate any transverse fields specified by the coefficients in the power series expansion in radial or vertical planes in cylindrical coordinates with the set of new functions. Our result is important for potential theory and for theoretical study, design and proper modeling of sector dipoles, combined function dipoles and any general sector element for accelerator physics. All results are presented in connection with these problems.« less

Noninvasive and painless magnetic stimulation of nerves improved brain motor function and mobility in a cerebral palsy case.

PubMed

Flamand, Véronique H; Schneider, Cyril

2014-10-01

Motor deficits in cerebral palsy disturb functional independence. This study tested whether noninvasive and painless repetitive peripheral magnetic stimulation could improve motor function in a 7-year-old boy with spastic hemiparetic cerebral palsy. Stimulation was applied over different nerves of the lower limbs for 5 sessions. We measured the concurrent aftereffects of this intervention on ankle motor control, gait (walking velocity, stride length, cadence, cycle duration), and function of brain motor pathways. We observed a decrease of ankle plantar flexors resistance to stretch, an increase of active dorsiflexion range of movement, and improvements of corticospinal control of ankle dorsiflexors. Joint mobility changes were still present 15 days after the end of stimulation, when all gait parameters were also improved. Resistance to stretch was still lower than prestimulation values 45 days after the end of stimulation. This case illustrates the sustained effects of repetitive peripheral magnetic stimulation on brain plasticity, motor function, and gait. It suggests a potential impact for physical rehabilitation in cerebral palsy. Copyright © 2014 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All rights reserved.

EDTA functionalized magnetic nanoparticle as a multifunctional adsorbent for Congo red dye from contaminated water

NASA Astrophysics Data System (ADS)

Sahoo, Jitendra Kumar; Rath, Juhi; Dash, Priyabrat; Sahoo, Harekrushna

2017-05-01

The present work reports the applicability of magnetite iron nanoparticles (Fe3O4) functionalized with ethylenediaminetetraacetic acid (EDTA) as an efficient adsorbent for the removal of Congo red (CR) dye from contaminated water. Magnetic nanoparticles (Fe3O4) are prepared by chemical precipitation method in which Fe2+ and Fe3+ salt from aqueous solution were reacted in presence of ammonia solution. The surface of Fe3O4 nanoparticle was first coated with (3-aminopropyl) triethoxy silane (APTES) by a salinization reaction and then linked with EDTA via reaction between -NH2 and -COOH to form well dispersed surface functionalised biocompatible magnetic nanoparticles. The obtained EDTA functionalized magnetic nanoparticles are characterized in terms of their morphological, XRD, BET surface area analysis, Fourier transform infrared spectroscopy (FT-IR) and Vibrating sample magnetometer (VSM). The adsorption of CR on Fe3O4-APTES-EDTA nanocomposite corresponds well to the Langmuir model and the Freundlich model respectively. The adsorption processes for CR followed the pseudo-second-order model.

Magnetic spectroscopy and microscopy of functional materials

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

Jenkins, Catherine Ann

2011-05-01

Heusler intermetallics Mn 2Y Ga and X 2MnGa (X; Y =Fe, Co, Ni) undergo tetragonal magnetostructural transitions that can result in half metallicity, magnetic shape memory, or the magnetocaloric effect. Understanding the magnetism and magnetic behavior in functional materials is often the most direct route to being able to optimize current materials for todays applications and to design novel ones for tomorrow. Synchrotron soft x-ray magnetic spectromicroscopy techniques are well suited to explore the the competing effects from the magnetization and the lattice parameters in these materials as they provide detailed element-, valence-, and site-specifc information on the coupling ofmore » crystallographic ordering and electronic structure as well as external parameters like temperature and pressure on the bonding and exchange. Fundamental work preparing the model systems of spintronic, multiferroic, and energy-related compositions is presented for context. The methodology of synchrotron spectroscopy is presented and applied to not only magnetic characterization but also of developing a systematic screening method for future examples of materials exhibiting any of the above effects. The chapter progression is as follows: an introduction to the concepts and materials under consideration (Chapter 1); an overview of sample preparation techniques and results, and the kinds of characterization methods employed (Chapter 2); spectro- and microscopic explorations of X 2MnGa/Ge (Chapter 3); spectroscopic investigations of the composition series Mn 2Y Ga to the logical Mn 3Ga endpoint (Chapter 4); and a summary and overview of upcoming work (Chapter 5). Appendices include the results of a Think Tank for the Graduate School of Excellence MAINZ (Appendix A) and details of an imaging project now in progress on magnetic reversal and domain wall observation in the classical Heusler material Co 2FeSi (Appendix B).« less

The mechanisms of the effects of magnetic fields on cells

NASA Astrophysics Data System (ADS)

Kondrachuk, A.

The evolution of organisms in conditions of the Earth magnetism results in close dependence of their functioning on the properties of the Earth magnetic field. The magnetic conditions in space flight differ from those on the Earth (e.g. much smaller values of magnetic filed) that effect various processes in living organisms. Meanwhile the mechanisms of interaction of magnetic fields with cell structures are poorly understood and systemized. The goal of the present work is to analyze and estimate the main established mechanisms of "magnetic fields - cell" interaction. Due to variety and complexity of the effects the analysis is mainly restricted to biological effects of the static magnetic field at a cellular level. 1) Magnetic induction. Static magnetic fields exert forces on moving ions in solution (e.g., electrolytes), giving rise to induced electric fields and currents. This effect may be especially important when the currents changed due to the magnetic field application are participating in some receptor functions of cells (e.g. plant cells). 2) Magneto-mechanical effect of reorientation. Uniform static magnetic fields produce torques on certain molecules with anisotropic magnetic properties, which results in their reorientation and spatial ordering. Since the structures of biological cells are magnetically and mechanically inhomogeneous, the application of a homogeneous magnetic field may cause redistribution of stresses within cells, deformation of intracellular structures, change of membrane permeability, etc. 3) Ponderomotive effects. Spatially non-uniform magnetic field exerts ponderomotive force on magnetically non-uniform cell structures. This force is proportional to the gradient of the square of magnetic field and the difference of magnetic susceptibilities of the component of the cell and its environment. 4) Biomagnetic effects. Magnetic fields can exert torques and translational forces on ferromagnetic structures, such as magnetite and ferritins presented in the cells. 5) Electronic interactions. Static magnetic fields can alter energy levels and spin orientation of electrons. Similar interactions can also occur with nuclear spins, but these are very weak compared to electron interactions. 6) Free radicals. Magnetic fields alter the spin states of the radicals, which, in turn, changes the relative probabilities of recombination and other interactions, possibly with biological consequences. 7) Non-linear effects. A number of non-linear mechanisms of magnetic effects on cells were recently proposed to explain how the cell could extract a weak magnetic signal from noise (e.g. stochastic non-linear resonance, self-tuned Hopf bifurcations). These new models need further experimental testing.

Mechanism of orientation of stimulating currents in magnetic brain stimulation (abstract)

NASA Astrophysics Data System (ADS)

Ueno, S.; Matsuda, T.

1991-04-01

We made a functional map of the human motor cortex related to the hand and foot areas by stimulating the human brain with a focused magnetic pulse. We observed that each functional area in the cortex has an optimum direction for which stimulating currents can produce neural excitation. The present report focuses on the mechanism which is responsible for producing this anisotropic response to brain stimulation. We first obtained a functional map of the brain related to the left ADM (abductor digiti minimi muscles). When the stimulating currents were aligned in the direction from the left to the right hemisphere, clear EMG (electromyographic) responses were obtained only from the left ADM to magnetic stimulation of both hemisphere. When the stimulating currents were aligned in the direction from the right to the left hemisphere, clear EMG signals were obtained only from the right ADM to magnetic stimulation of both hemisphere. The functional maps of the brain were sensitive to changes in the direction of the stimulating currents. To explain the phenomena obtained in the experiments, we developed a model of neural excitation elicited by magnetic stimulation. When eddy currents which are induced by pulsed magnetic fields flow in the direction from soma to the distal part of neural fiber, depolarized area in the distal part are excited, and the membrane excitation propagates along the nerve fiber. In contrast, when the induced currents flow in the direction from the distal part to soma, hyperpolarized parts block or inhibit neural excitation even if the depolarized parts near the soma can be excited. The model explains our observation that the orientation of the induced current vectors reflect both the functional and anatomical organization of the neural fibers in the brain.

Magnetic pumping as a source of particle heating in the solar wind

NASA Astrophysics Data System (ADS)

Lichko, E. R.; Egedal, J.; Daughton, W. S.; Kasper, J. C.

2017-12-01

Magnetic pumping is a means of heating plasmas for both fusion and astrophysical applications. In this study a magnetic pumping model is developed as a possible explanation for the heating and the generation of power-law distribution functions observed in the solar wind plasma. In most previous studies turbulent energy is only dissipated at microscopic kinetic scales. In contrast, magnetic pumping energizes the particles through the largest scale turbulent fluctuations, thus bypassing the energy cascade. Kinetic simulations are applied to verify these analytic predictions. Previous results for the one-dimensional model, as well as initial results for a two-dimensional model which includes the effects of trapped and passing particles are presented. Preliminary results of the presence of this mechanism in the bow shock region, using spacecraft data from the Magnetospheric Multiscale mission, are presented as well.

Identification of prominence ejecta by the proton distribution function and magnetic fine structure in ICMEs in the inner heliosphere

NASA Astrophysics Data System (ADS)

Marsch, Eckart; Yao, Shuo; Tu, Chuanyi; Schwenn, Rainer

This work presents in-situ solar wind observations of three magnetic clouds that contain certain cold high-density material, when Helios 2 was located at 0.3 AU, on 9 May 1979, 0.5 AU on 30 March 1976, and 0.7 AU on 24 December 1978, respectively. In the cold high-density regions embedded in the ICMEs we find that (1) the number density of protons is higher than in other regions inside the magnetic cloud (MC), (2)the possible existence of He+, (3) the thermal velocity distribution functions (VDFs) are more isotropic and appear to be colder than in the other regions of the MC, and the proton temperature is lower than that of the ambient plasma, (4) the associated magnetic field configuration can for all three MC events be identified as a flux rope. This cold high-density region is located at the polarity inversion line in the center of the bipolar structure of the MC magnetic field (consistent with previous work of solar observation that a prominence lies over the neutral line of the related bipolar solar magnetic field ). It is the first time that prominence ejecta are identified by both the plasma and magnetic field features inside 1 AU, and that thermal ion velocity distribution functions are used to investigate the microstate of the prominence material. Overall, our in situ observations are consistent with the three-part CME models.

Magnetic damping phenomena in ferromagnetic thin-films and multilayers

NASA Astrophysics Data System (ADS)

Azzawi, S.; Hindmarch, A. T.; Atkinson, D.

2017-11-01

Damped ferromagnetic precession is an important mechanism underpinning the magnetisation processes in ferromagnetic materials. In thin-film ferromagnets and ferromagnetic/non-magnetic multilayers, the role of precession and damping can be critical for spintronic device functionality and as a consequence there has been significant research activity. This paper presents a review of damping in ferromagnetic thin-films and multilayers and collates the results of many experimental studies to present a coherent synthesis of the field. The terms that are used to define damping are discussed with the aim of providing consistent definitions for damping phenomena. A description of the theoretical basis of damping is presented from early developments to the latest discussions of damping in ferromagnetic thin-films and multilayers. An overview of the time and frequency domain methods used to study precessional magnetisation behaviour and damping in thin-films and multilayers is also presented. Finally, a review of the experimental observations of magnetic damping in ferromagnetic thin-films and multilayers is presented with the most recent explanations. This brings together the results from many studies and includes the effects of ferromagnetic film thickness, the effects of composition on damping in thin-film ferromagnetic alloys, the influence of non-magnetic dopants in ferromagnetic films and the effects of combining thin-film ferromagnets with various non-magnetic layers in multilayered configurations.

Real-space investigation of short-range magnetic correlations in fluoride pyrochlores NaCaCo 2F 7 and NaSrCo 2F 7 with magnetic pair distribution function analysis

DOE PAGES

Frandsen, Benjamin A.; Billinge, Simon J. L.; Ross, Kathryn A.; ...

2017-12-29

Here, we present time-of-flight neutron total scattering and polarized neutron scattering measurements of the magnetically frustrated compounds NaCaCo 2F 7 and NaSrCo 2F 7, which belong to a class of recently discovered pyrochlore compounds based on transition metals and fluorine. The magnetic pair distribution function (mPDF) technique is used to analyze and model the total scattering data in real space. We find that a previously-proposed model of short-range XY-like correlations with a length scale of 10-15 Å, combined with nearest-neighbor collinear antiferromagnetic correlations, accurately describes the mPDF data at low temperature, confirming the magnetic ground state in these materials. Thismore » model is further verified by the polarized neutron scattering data. From an analysis of the temperature dependence of the mPDF and polarized neutron scattering data, we find that short-range correlations persist on the nearest-neighbor length scale up to 200 K, approximately two orders of magnitude higher than the spin freezing temperatures of these compounds. These results highlight the opportunity presented by these new pyrochlore compounds to study the effects of geometric frustration at relatively high temperatures, while also advancing the mPDF technique and providing a novel opportunity to investigate a genuinely short-range-ordered magnetic ground state directly in real space.« less

Real-space investigation of short-range magnetic correlations in fluoride pyrochlores NaCaCo 2F 7 and NaSrCo 2F 7 with magnetic pair distribution function analysis

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

Frandsen, Benjamin A.; Billinge, Simon J. L.; Ross, Kathryn A.

Here, we present time-of-flight neutron total scattering and polarized neutron scattering measurements of the magnetically frustrated compounds NaCaCo 2F 7 and NaSrCo 2F 7, which belong to a class of recently discovered pyrochlore compounds based on transition metals and fluorine. The magnetic pair distribution function (mPDF) technique is used to analyze and model the total scattering data in real space. We find that a previously-proposed model of short-range XY-like correlations with a length scale of 10-15 Å, combined with nearest-neighbor collinear antiferromagnetic correlations, accurately describes the mPDF data at low temperature, confirming the magnetic ground state in these materials. Thismore » model is further verified by the polarized neutron scattering data. From an analysis of the temperature dependence of the mPDF and polarized neutron scattering data, we find that short-range correlations persist on the nearest-neighbor length scale up to 200 K, approximately two orders of magnitude higher than the spin freezing temperatures of these compounds. These results highlight the opportunity presented by these new pyrochlore compounds to study the effects of geometric frustration at relatively high temperatures, while also advancing the mPDF technique and providing a novel opportunity to investigate a genuinely short-range-ordered magnetic ground state directly in real space.« less

Magnetism in olivine-type LiCo(1-x)Fe(x)PO4 cathode materials: bridging theory and experiment.

PubMed

Singh, Vijay; Gershinsky, Yelena; Kosa, Monica; Dixit, Mudit; Zitoun, David; Major, Dan Thomas

2015-12-14

In the current paper, we present a non-aqueous sol-gel synthesis of olivine type LiCo1-xFexPO4 compounds (x = 0.00, 0.25, 0.50, 0.75, 1.00). The magnetic properties of the olivines are measured experimentally and calculated using first-principles theory. Specifically, the electronic and magnetic properties are studied in detail with standard density functional theory (DFT), as well as by including spin-orbit coupling (SOC), which couples the spin to the crystal structure. We find that the Co(2+) ions exhibit strong orbital moment in the pure LiCoPO4 system, which is partially quenched upon substitution of Co(2+) by Fe(2+). Interestingly, we also observe a non-negligible orbital moment on the Fe(2+) ion. We underscore that the inclusion of SOC in the calculations is essential to obtain qualitative agreement with the observed effective magnetic moments. Additionally, Wannier functions were used to understand the experimentally observed rising trend in the Néel temperature, which is directly related to the magnetic exchange interaction paths in the materials. We suggest that out of layer M-O-P-O-M magnetic interactions (J⊥) are present in the studied materials. The current findings shed light on important differences observed in the electrochemistry of the cathode material LiCoPO4 compared to the already mature olivine material LiFePO4.

Real-space investigation of short-range magnetic correlations in fluoride pyrochlores NaCaCo2F7 and NaSrCo2F7 with magnetic pair distribution function analysis

NASA Astrophysics Data System (ADS)

Frandsen, Benjamin A.; Ross, Kate A.; Krizan, Jason W.; Nilsen, Gøran J.; Wildes, Andrew R.; Cava, Robert J.; Birgeneau, Robert J.; Billinge, Simon J. L.

2017-12-01

We present time-of-flight neutron total scattering and polarized neutron scattering measurements of the magnetically frustrated compounds NaCaCo2F7 and NaSrCo2F7 , which belong to a class of recently discovered pyrochlore compounds based on transition metals and fluorine. The magnetic pair distribution function (mPDF) technique is used to analyze and model the total scattering data in real space. We find that a previously proposed model of short-range XY-like correlations with a length scale of 10-15 Å, combined with nearest-neighbor collinear antiferromagnetic correlations, accurately describes the mPDF data at low temperature, confirming the magnetic ground state in these materials. This model is further verified by the polarized neutron scattering data. From an analysis of the temperature dependence of the mPDF and polarized neutron scattering data, we find that short-range correlations persist on the nearest-neighbor length scale up to 200 K, approximately two orders of magnitude higher than the spin freezing temperatures of these compounds. These results highlight the opportunity presented by these new pyrochlore compounds to study the effects of geometric frustration at relatively high temperatures, while also advancing the mPDF technique and providing an opportunity to investigate a genuinely short-range-ordered magnetic ground state directly in real space.

Low temperature synthesis and enhanced electrical properties by substitution of Al3+ and Cr3+ in Co-Ni nanoferrites

NASA Astrophysics Data System (ADS)

Pervaiz, Erum; Gul, I. H.

2013-10-01

Aluminum and chromium substituted Co-Ni spinel nanoferrites were prepared by sol-gel auto combustion method. Structural parameters along with electrical and magnetic properties have been investigated in the present work. Crystallite sizes of nano ferrite estimated from the peak (311) lies in the range of 13-21 nm ±2 nm and compared with crystallite sizes calculated from Williamsons-Hall plots. DC electrical resistivity variations due to the concentration of aluminum and chromium in the host ferrite have been measured from 368 K to 573 K. Increase in the room temperature DC electrical resistivity was observed up to a concentration x=0.2 and then decreases for x >0.2. Dielectric parameters (real and imaginary part of complex permittivity, dielectric loss tangent) were studied as a function of frequency (20 Hz-5 MHz) and a decrease in the dielectric parameters was observed due to substitution of nickel, aluminum and chromium ions in cobalt nanoferrites. AC conductivity, complex impedance and complex electrical modulus were studied as a function of frequency for the conduction and relaxation mechanisms in the present ferrite system. Saturation magnetization, coercivity, canting angles and magneto crystalline anisotropy variations with composition were observed and presented for the present ferrites under an applied magnetic field of 10 kOe at room temperature. It was found that both magnetization and coercivity decreases with increase in the concentration of aluminum and chromium along with a decrease in the anisotropy parameters. High DC resistivity with low dielectric parameters of the present nanoferrites make them suitable for high frequency and electromagnetic wave absorbing devices. High purity mixed Co-Ni-Al-Cr nanoferrites have been prepared by sol-gel auto combustion method. DC electrical resistivity increases due to substitution of Al3+ and Cr3+. Complex permittivity decrease for Co-Ni-Al-Cr nanoferrites. Detailed AC response analysis has been presented for mixed Co-Ni-Al-Cr nanoferrites. Magnetization and coercively reduces for Al3+ and Cr3+ doped Co-Ni ferrite nanoparticles showing that material is becoming soft magnetic.

Intrinsic brain abnormalities in young healthy adults with childhood trauma: A resting-state functional magnetic resonance imaging study of regional homogeneity and functional connectivity.

PubMed

Lu, Shaojia; Gao, Weijia; Wei, Zhaoguo; Wang, Dandan; Hu, Shaohua; Huang, Manli; Xu, Yi; Li, Lingjiang

2017-06-01

Childhood trauma confers great risk for the development of multiple psychiatric disorders; however, the neural basis for this association is still unknown. The present resting-state functional magnetic resonance imaging study aimed to detect the effects of childhood trauma on brain function in a group of young healthy adults. In total, 24 healthy individuals with childhood trauma and 24 age- and sex-matched adults without childhood trauma were recruited. Each participant underwent resting-state functional magnetic resonance imaging scanning. Intra-regional brain activity was evaluated by regional homogeneity method and compared between groups. Areas with altered regional homogeneity were further selected as seeds in subsequent functional connectivity analysis. Statistical analyses were performed by setting current depression and anxiety as covariates. Adults with childhood trauma showed decreased regional homogeneity in bilateral superior temporal gyrus and insula, and the right inferior parietal lobule, as well as increased regional homogeneity in the right cerebellum and left middle temporal gyrus. Regional homogeneity values in the left middle temporal gyrus, right insula and right cerebellum were correlated with childhood trauma severity. In addition, individuals with childhood trauma also exhibited altered default mode network, cerebellum-default mode network and insula-default mode network connectivity when the left middle temporal gyrus, right cerebellum and right insula were selected as seed area, respectively. The present outcomes suggest that childhood trauma is associated with disturbed intrinsic brain function, especially the default mode network, in adults even without psychiatric diagnoses, which may mediate the relationship between childhood trauma and psychiatric disorders in later life.

Theoretical investigation of discharge parameters in magnetized radio frequency excited CO2 lasers

NASA Astrophysics Data System (ADS)

Tavassoli, H.; Sohbatzadeh, F.; Latifi, H.

2003-06-01

In the present paper the magnetic field effects on discharge parameters in rf excited CO2 lasers are calculated. A rf generated plasma imbedded in an external, constant, and homogeneous magnetic field is considered. The continuity equation is used to derive the electron density. Quasineutrality condition and ambipolar diffusion are used. Electron attachment coefficient is neglected. Local electric field, local electron density, and thickness of charge layers are derived as a function of distance from the electrodes and magnetic field. The thickness of charge layers in the presence of magnetic field is always smaller than one without the magnetic field. When the magnetic field increases, the electron density increases in all regions of discharge, and the electric field reduces in the charge layers but increases in the middle part of discharge.

Magnetic fields in noninvasive brain stimulation.

PubMed

Vidal-Dourado, Marcos; Conforto, Adriana Bastos; Caboclo, Luis Otávio Sales Ferreira; Scaff, Milberto; Guilhoto, Laura Maria de Figueiredo Ferreira; Yacubian, Elza Márcia Targas

2014-04-01

The idea that magnetic fields could be used therapeutically arose 2000 years ago. These therapeutic possibilities were expanded after the discovery of electromagnetic induction by the Englishman Michael Faraday and the American Joseph Henry. In 1896, Arsène d'Arsonval reported his experience with noninvasive brain magnetic stimulation to the scientific French community. In the second half of the 20th century, changing magnetic fields emerged as a noninvasive tool to study the nervous system and to modulate neural function. In 1985, Barker, Jalinous, and Freeston presented transcranial magnetic stimulation, a relatively focal and painless technique. Transcranial magnetic stimulation has been proposed as a clinical neurophysiology tool and as a potential adjuvant treatment for psychiatric and neurologic conditions. This article aims to contextualize the progress of use of magnetic fields in the history of neuroscience and medical sciences, until 1985.

Analytic solution of magnetic induction distribution of ideal hollow spherical field sources

NASA Astrophysics Data System (ADS)

Xu, Xiaonong; Lu, Dingwei; Xu, Xibin; Yu, Yang; Gu, Min

2017-12-01

The Halbach type hollow spherical permanent magnet arrays (HSPMA) are volume compacted, energy efficient field sources, and capable of producing multi-Tesla field in the cavity of the array, which have attracted intense interests in many practical applications. Here, we present analytical solutions of magnetic induction to the ideal HSPMA in entire space, outside of array, within the cavity of array, and in the interior of the magnet. We obtain solutions using concept of magnetic charge to solve the Poisson's and Laplace's equations for the HSPMA. Using these analytical field expressions inside the material, a scalar demagnetization function is defined to approximately indicate the regions of magnetization reversal, partial demagnetization, and inverse magnetic saturation. The analytical field solution provides deeper insight into the nature of HSPMA and offer guidance in designing optimized one.

A Definition of the Magnetic Transition Temperature Using Valence Bond Theory.

PubMed

Jornet-Somoza, Joaquim; Deumal, Mercè; Borge, Juan; Robb, Michael A

2018-03-01

Macroscopic magnetic properties are analyzed using Valence Bond theory. Commonly the critical temperature T C for magnetic systems is associated with a maximum in the energy-based heat capacity C p (T). Here a more broadly applicable definition of the magnetic transition temperature T C is described using the spin moment expectation value (i.e., applying the spin exchange density operator) instead of energy. Namely, the magnetic capacity C s (T) reflects variation in the spin multiplicity as a function of temperature, which is shown to be related to ∂[χT(T)]/∂T. Magnetic capacity C s (T) depends on long-range spin interactions that are not relevant in the energy-based heat capacity C p (T). Differences between C s (T) and C p (T) are shown to be due to spin order/disorder within the crystal that can be monitored via a Valence Bond analysis of the corresponding magnetic wave function. Indeed the concept of the Boltzmann spin-alignment order is used to provide information about the spin correlation between magnetic units. As a final illustration, the critical temperature is derived from the magnetic capacity for several molecular magnets presenting different magnetic topologies that have been experimentally studied. A systematic shift between the transition temperatures associated with C s (T) and C p (T) is observed. It is demonstrated that this shift can be attributed to the loss of long-range spin correlation. This suggests that the magnetic capacity C s (T) can be used as a predictive tool for the magnetic topology and thus for the synthetic chemists.

The influence of crystalline electrical field on magnetic and magnetocaloric properties in Er1-yTbyAl2 compounds

NASA Astrophysics Data System (ADS)

Ribeiro, P. O.; Alho, B. P.; Alvarenga, T. S. T.; Nóbrega, E. P.; de Sousa, V. S. R.; Carvalho, A. Magnus G.; Caldas, A.; Lopes, P. H. O.; von Ranke, P. J.

2017-11-01

We report the anisotropy of magnetic field-induced entropy change in rare earth Er1-yTbyAl2 compounds (y = 0.00, 0.25, 0.50, 0.75 and 1.00). In the present work, we use a model Hamiltonian that includes the crystalline electrical field anisotropy in both Er and Tb magnetic sublattices, chemical disorder in exchange interactions among Er-Er, Tb-Tb and Er-Tb magnetic ions and the Zeeman effect. We investigated the isothermal magnetic entropy change ΔST for a magnetic field of 1 T rotating from a hard 〈0 0 1〉 to the easy 〈1 1 1〉 direction. We also performed a systematic analysis of the reorientation temperature as a function of the magnetic field intensity. The anisotropic magnetocaloric effect highlights the applicability of this effect on the rotating magnetic refrigeration.

Magnetic-Nanoflocculant-Assisted Water-Nonpolar Solvent Interface Sieve for Microalgae Harvesting.

PubMed

Lee, Kyubock; Na, Jeong-Geol; Seo, Jung Yoon; Shim, Tae Soup; Kim, Bohwa; Praveenkumar, Ramasamy; Park, Ji-Yeon; Oh, You-Kwan; Jeon, Sang Goo

2015-08-26

Exploitation of magnetic flocculants is regarded as a very promising energy-saving approach to microalgae harvesting. However, its practical applicability remains limited, mainly because of the problem of the postharvest separation of magnetic flocculants from microalgal flocs, which is crucial both for magnetic-flocculant recycling and high-purity microalgal biomasses, but which is also a very challenging and energy-consuming step. In the present study, we designed magnetic nanoflocculants dually functionalizable by two different organosilane compounds, (3-aminopropyl)triethoxysilane (APTES) and octyltriethoxysilane (OTES), which flocculate negatively charged microalgae and are readily detachable at the water-nonpolar organic solvent (NOS) interface only by application of an external magnetic field. APTES functionalization imparts a positive zeta potential charge (29.6 mV) to magnetic nanoflocculants, thereby enabling microalgae flocculation with 98.5% harvesting efficiency (with a dosage of 1.6 g of dMNF/g of cells). OTES functionalization imparts lipophilicity to magnetic nanoflocculants to make them compatible with NOS, thus effecting efficient separation of magnetic flocculants passing through the water-NOS interface sieve from hydrophilic microalgae. Our new energy-saving approach to microalgae harvesting concentrates microalgal cultures (∼1.5 g/L) up to 60 g/L, which can be directly connected to the following process of NOS-assisted wet lipid extraction or biodiesel production, and therefore provides, by simplifying multiple downstream processes, a great potential cost reduction in microalgae-based biorefinement.

Dissipative MHD solutions for resonant Alfven waves in 1-dimensional magnetic flux tubes

NASA Technical Reports Server (NTRS)

Goossens, Marcel; Ruderman, Michail S.; Hollweg, Joseph V.

1995-01-01

The present paper extends the analysis by Sakurai, Goossens, and Hollweg (1991) on resonant Alfven waves in nonuniform magnetic flux tubes. It proves that the fundamental conservation law for resonant Alfven waves found in ideal MHD by Sakurai, Goossens, and Hollweg remains valid in dissipative MHD. This guarantees that the jump conditions of Sakurai, Goossens, and Hollweg, that connect the ideal MHD solutions for xi(sub r), and P' across the dissipative layer, are correct. In addition, the present paper replaces the complicated dissipative MHD solutions obtained by Sakurai, Goossens, and Hollweg for xi(sub r), and P' in terms of double integrals of Hankel functions of complex argument of order 1/3 with compact analytical solutions that allow a straight- forward mathematical and physical interpretation. Finally, it presents an analytical dissipative MHD solution for the component of the Lagrangian displacement in the magnetic surfaces perpen- dicular to the magnetic field lines xi(sub perpendicular) which enables us to determine the dominant dynamics of resonant Alfven waves in dissipative MHD.

Hyperthermia in low aspect-ratio magnetic nanotubes for biomedical applications

NASA Astrophysics Data System (ADS)

Gutierrez-Guzman, D. F.; Lizardi, L. I.; Otálora, J. A.; Landeros, P.

2017-03-01

A simple model for the magnetization reversal process of low aspect-ratio ferromagnetic nanotubes (MNTs) is presented. Because of advantages over other geometries, these structures are interesting for biomedical applications, such as magnetic hyperthermia cancer therapy, where the heat released during magnetic reversal is used to destroy tumors. For example, the tubular geometry provides two independent functional surfaces that may be selectively manipulated and also gives a storage cavity. Owing to their large surface to weight ratio and low mass density, MNTs are not decanted by gravity. We calculated magnetic phase diagrams, energy barriers, nucleation fields, and the amount of dissipated heat and specific absorption rate for magnetite nanotubes. The geometrical parameters were varied, and simple formulae were used to optimize the tube response under alternating excitation, as required for magnetic hyperthermia applications.

The transverse magnetic field effect on steady-state solutions of the Bursian diode

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

Pramanik, Sourav; Chakrabarti, Nikhil; Ender, A. Ya.

2015-04-15

A study of steady-states of a planar vacuum diode driven by a cold electron beam (the Bursian diode) under an external transverse magnetic field is presented. The regime of no electrons turned around by a magnetic field only is under the consideration. The emitter electric field is evaluated as a characteristic function for the existence of solutions depending on the diode length, the applied voltage, and the magnetic field strength. At certain conditions, it is shown that a region of non-unique solutions exists in the Bursian diode when the magnetic field is absent. An expression for the maximum current transmittedmore » through the diode is derived. The external magnetic field is put forth to control fast electronic switches based on the Bursian diode.« less

Magnetization reversal of the domain structure in the anti-perovskite nitride Co{sub 3}FeN investigated by high-resolution X-ray microscopy

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

Hajiri, T., E-mail: t.hajiri@numse.nagoya-u.ac.jp; Kuroki, Y.; Ando, H.

2016-05-14

We performed X-ray magnetic circular dichroism (XMCD) photoemission electron microscopy imaging to reveal the magnetic domain structure of anti-perovskite nitride Co{sub 3}FeN exhibiting a negative spin polarization. In square and disc patterns, we systematically and quantitatively determined the statistics of the stable states as a function of geometry. By direct imaging during the application of a magnetic field, we revealed the magnetic reversal process in a spatially resolved manner. We compared the hysteresis on the continuous area and the square patterns from the magnetic field-dependent XMCD ratio, which can be explained as resulting from the effect of the shape anisotropy,more » present in nanostructured thin films.« less

On the dependence of the domain of values of functionals of hypersonic aerodynamics on controls

NASA Astrophysics Data System (ADS)

Bilchenko, Grigory; Bilchenko, Nataly

2018-05-01

The properties of mathematical model of control of heat and mass transfer in laminar boundary layer on permeable cylindrical and spherical surfaces of the hypersonic aircraft are considered. Dependences of hypersonic aerodynamics functionals (the total heat flow and the total Newton friction force) on controls (the blowing into boundary layer, the temperature factor, the magnetic field) are investigated. The domains of allowed values of functionals of hypersonic aerodynamics are obtained. The results of the computational experiments are presented: the dependences of total heat flow on controls; the dependences of total Newton friction force on controls; the mutual dependences of functionals (as the domains of allowed values "Heat and Friction"); the dependences of blowing system power on controls. The influences of magnetic field and dissociation on the domain of "Heat and Friction" allowed values are studied. It is proved that for any fixed constant value of magnetic field the blowing system power is a symmetric function of constant dimensionless controls (the blowing into boundary layer and the temperature factor). It is shown that the obtained domain of allowed values of functionals of hypersonic aerodynamics depending on permissible range of controls may be used in engineering.

Phase-synchronization, energy cascade, and intermittency in solar-wind turbulence.

PubMed

Perri, S; Carbone, V; Vecchio, A; Bruno, R; Korth, H; Zurbuchen, T H; Sorriso-Valvo, L

2012-12-14

The energy cascade in solar wind magnetic turbulence is investigated using MESSENGER data in the inner heliosphere. The decomposition of magnetic field time series in intrinsic functions, each characterized by a typical time scale, reveals phase reorganization. This allows for the identification of structures of all sizes generated by the nonlinear turbulent cascade, covering both the inertial and the dispersive ranges of the turbulent magnetic power spectrum. We find that the correlation (or anticorrelation) of phases occurs between pairs of neighboring time scales, whenever localized peaks of magnetic energy are present at both scales, consistent with the local character of the energy transfer process.

Continuously distributed magnetization profile for millimeter-scale elastomeric undulatory swimming

NASA Astrophysics Data System (ADS)

Diller, Eric; Zhuang, Jiang; Zhan Lum, Guo; Edwards, Matthew R.; Sitti, Metin

2014-04-01

We have developed a millimeter-scale magnetically driven swimming robot for untethered motion at mid to low Reynolds numbers. The robot is propelled by continuous undulatory deformation, which is enabled by the distributed magnetization profile of a flexible sheet. We demonstrate control of a prototype device and measure deformation and speed as a function of magnetic field strength and frequency. Experimental results are compared with simple magnetoelastic and fluid propulsion models. The presented mechanism provides an efficient remote actuation method at the millimeter scale that may be suitable for further scaling down in size for micro-robotics applications in biotechnology and healthcare.

Neural coding using telegraphic switching of magnetic tunnel junction

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

Suh, Dong Ik; Bae, Gi Yoon; Oh, Heong Sik

2015-05-07

In this work, we present a synaptic transmission representing neural coding with spike trains by using a magnetic tunnel junction (MTJ). Telegraphic switching generates an artificial neural signal with both the applied magnetic field and the spin-transfer torque that act as conflicting inputs for modulating the number of spikes in spike trains. The spiking probability is observed to be weighted with modulation between 27.6% and 99.8% by varying the amplitude of the voltage input or the external magnetic field. With a combination of the reverse coding scheme and the synaptic characteristic of MTJ, an artificial function for the synaptic transmissionmore » is achieved.« less

Magnetically Actuated Soft Capsule With the Multimodal Drug Release Function

PubMed Central

Yim, Sehyuk; Goyal, Kartik; Sitti, Metin

2014-01-01

In this paper, we present a magnetically actuated multimodal drug release mechanism using a tetherless soft capsule endoscope for the treatment of gastric disease. Because the designed capsule has a drug chamber between both magnetic heads, if it is compressed by the external magnetic field, the capsule could release a drug in a specific position locally. The capsule is designed to release a drug in two modes according to the situation. In the first mode, a small amount of drug is continuously released by a series of pulse type magnetic field (0.01–0.03 T). The experimental results show that the drug release can be controlled by the frequency of the external magnetic pulse. In the second mode, about 800 mm3 of drug is released by the external magnetic field of 0.07 T, which induces a stronger magnetic attraction than the critical force for capsule’s collapsing. As a result, a polymeric coating is formed around the capsule. The coated area is dependent on the drug viscosity. This paper presents simulations and various experiments to evaluate the magnetically actuated multimodal drug release capability. The proposed soft capsules could be used as minimally invasive tetherless medical devices with therapeutic capability for the next generation capsule endoscopy. PMID:25378896

The dynamics of magnetic nanoparticles exposed to non-heating alternating magnetic field in biochemical applications: theoretical study

NASA Astrophysics Data System (ADS)

Golovin, Yuri I.; Gribanovsky, Sergey L.; Golovin, Dmitry Y.; Zhigachev, Alexander O.; Klyachko, Natalia L.; Majouga, Alexander G.; Sokolsky, Marina; Kabanov, Alexander V.

2017-02-01

In the past decade, magneto-nanomechanical approach to biochemical systems stimulation has been studied intensively. This method involves macromolecule structure local deformation via mechanical actuation of functionalized magnetic nanoparticles (f-MNPs) by non-heating low frequency (LF) alternating magnetic field (AMF). Specificity at cellular or molecular level and spatial locality in nanometer scale are its key advantages as compared to magnetic fluid hyperthermia. However, current experimental studies have weak theoretical basis. Several models of magneto-nanomechanical actuation of macromolecules and cells in non-heating uniform LF AMF are presented in the article. Single core-shell spherical, rod-like, and Janus MNPs, as well as dimers consisting of two f-MNPs with macromolecules immobilized on their surfaces are considered. AMF-induced rotational oscillations of MNPs can affect properties and functioning of macromolecules or cellular membranes attached to them via periodic deformations in nanometer scale. This could be widely used in therapy, in particular for targeted drug delivery, controlled drug release, and cancer cell killing. An aggregate composed of MNPs can affect associated macromolecules by force up to several hundreds of piconewton in the case of MNPs of tens of nanometers in diameter and LF AMF below 1 T. AMF parameters and MNP design requirements for effective in vitro and in vivo magneto-nanomechanical treatment are presented.

Zeeman relaxation of MnH (X7Σ+) in collisions with He3: Mechanism and comparison with experiment

NASA Astrophysics Data System (ADS)

Turpin, F.; Stoecklin, T.; Halvick, Ph.

2011-03-01

We present a theoretical study of the Zeeman relaxation of the magnetically trappable lowest field seeking state of MnH (7Σ) in collisions with He3. We analyze the collisional Zeeman transition mechanism as a function of the final diatomic state and its variation as a function of an applied magnetic field. We show that as a result of this mechanism the levels with ΔMj>2 give negligible contributions to the Zeemam relaxation cross section. We also compare our results to the experimental cross sections obtained from the buffer-gas cooling and magnetic trapping of this molecule and investigate the dependence of the Zeeman relaxation cross section on the accuracy of the three-body interaction at ultralow energies.

Intense laser field effects on a Woods-Saxon potential quantum well

NASA Astrophysics Data System (ADS)

Restrepo, R. L.; Morales, A. L.; Akimov, V.; Tulupenko, V.; Kasapoglu, E.; Ungan, F.; Duque, C. A.

2015-11-01

This paper presents the results of the theoretical study of the effects of non-resonant intense laser field and electric and magnetic fields on the optical properties in an quantum well (QW) make with Woods-Saxon potential profile. The electric field and intense laser field are applied along the growth direction of the Woods-Saxon quantum well and the magnetic field is oriented perpendicularly. To calculate the energy and the wave functions of the electron in the Woods-Saxon quantum well, the effective mass approximation and the method of envelope wave function are used. The confinement in the Woods-Saxon quantum well is changed drastically by the application of intense laser field or either the effect of electric and magnetic fields. The optical properties are calculated using the compact density matrix.

Experimental Investigation of Electron Cloud Containment in a Nonuniform Magnetic Field

NASA Technical Reports Server (NTRS)

Eninger, J. E.

1974-01-01

Dense clouds of electrons were generated and studied in an axisymmetric, nonuniform magnetic field created by a short solenoid. The operation of the experiment was similar to that of a low-pressure (approximately 0.000001 Torr) magnetron discharge. Discharge current characteristics are presented as a function of pressure, magnetic field strength, voltage, and cathode end-plate location. The rotation of the electron cloud is determined from the frequency of diocotron waves. In the space charge saturated regime of operation, the cloud is found to rotate as a solid body with frequency close to V sub a/phi sub a where V sub a is the anode voltage and phi suba is the total magnetic flux. This result indicates that, in regions where electrons are present, the magnetic field lines are electrostatic equipotentials (E bar, B bar = 0). Equilibrium electron density distributions suggested by this conditions are integrated with respect to total ionizing power and are found consistent with measured discharge currents.

3D ion flow measurements and simulations near a boundary at oblique incidence to a magnetic field

NASA Astrophysics Data System (ADS)

Thompson, Derek S.; Keniley, Shane; Khaziev, Rinat; Curreli, Davide; Good, Timothy N.; Henriquez, Miguel; McIlvain, Julianne; Siddiqui, M. Umair; Scime, Earl E.

2016-10-01

Boundaries at oblique incidence to magnetic fields are abundant in magnetic confinement plasmas. The ion dynamics near these boundaries has implications for applications such as tokamak divertor wall loading and Hall thruster channel erosion. We present 3D, non-perturbative measurements of ion velocity distribution functions (IVDFs), providing ion temperatures and flows upstream of a grounded stainless steel limiter plate immersed in an argon plasma, oriented obliquely to the background axial magnetic field (ψ = 74°). The spatial resolution of the measurements is sufficient to probe the kinetic details of magnetic presheath structures, which span several ion Larmor radii ( 1 cm). Furthermore, we report probe measurements of electron density and temperature, and of local electric potential. To complement these measurements, results from particle-in-cell and Boltzmann models of the same region are presented. These models allow for point-to-point comparison of simulated and measured electrostatic structures and IVDFs at high spatial resolution. NSF Award PHYS-1360278.

Lorentz-covariant coordinate-space representation of the leading hadronic contribution to the anomalous magnetic moment of the muon

NASA Astrophysics Data System (ADS)

Meyer, Harvey B.

2017-09-01

We present a Lorentz-covariant, Euclidean coordinate-space expression for the hadronic vacuum polarisation, the Adler function and the leading hadronic contribution to the anomalous magnetic moment of the muon. The representation offers a high degree of flexibility for an implementation in lattice QCD. We expect it to be particularly helpful for the quark-line disconnected contributions.

Quantitative Characterization of Magnetic Mobility of Nanoparticle in Solution-Based Condition.

PubMed

Rodoplu, Didem; Boyaci, Ismail H; Bozkurt, Akif G; Eksi, Haslet; Zengin, Adem; Tamer, Ugur; Aydogan, Nihal; Ozcan, Sadan; Tugcu-Demiröz, Fatmanur

2015-01-01

Magnetic nanoparticles are considered as the ideal substrate to selectively isolate target molecules or organisms from sample solutions in a wide variety of applications including bioassays, bioimaging and environmental chemistry. The broad array of these applications in fields requires the accurate magnetic characterization of nanoparticles for a variety of solution based-conditions. Because the freshly synthesized magnetic nanoparticles demonstrated a perfect magnetization value in solid form, they exhibited a different magnetic behavior in solution. Here, we present simple quantitative method for the measurement of magnetic mobility of nanoparticles in solution-based condition. Magnetic mobility of the nanoparticles was quantified with initial mobility of the particles using UV-vis absorbance spectroscopy in water, ethanol and MES buffer. We demonstrated the efficacy of this method through a systematic characterization of four different core-shell structures magnetic nanoparticles over three different surface modifications. The solid nanoparticles were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD) and saturation magnetization (Ms). The surfaces of the nanoparticles were functionalized with 11-mercaptoundecanoic acid and bovine serum albumin BSA was selected as biomaterial. The effect of the surface modification and solution media on the stability of the nanoparticles was monitored by zeta potentials and hydrodynamic diameters of the nanoparticles. Results obtained from the mobility experiments indicate that the initial mobility was altered with solution media, surface functionalization, size and shape of the magnetic nanoparticle. The proposed method easily determines the interactions between the magnetic nanoparticles and their surrounding biological media, the magnetophoretic responsiveness of nanoparticles and the initial mobilities of the nanoparticles.

Two design of the S4.BEN01 magnet for the CBETA splitter/merger

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

Tsoupas, N.; Berg, S.; Meot, F.

2017-04-10

The splitter/merger section of the CBETA project [1] consists of 4 beam lines as shown in Fig. 1. Two of the functions of the splitter’s/merger’s lines is to match the beam parameters at the exit of the Energy Recovery Linac (ERL) to the beam parameters at the entrance of the Fixed Field Alternating Gradient (FFAG) arc, and also place the reference particles of the beam bunches at the entrance of the FFAG arc on specified trajectories according to their energies. In this technical note we are presenting results from the 2D and 3D electromagnetic analysis of the S4.BEN01 magnet whichmore » is one of the dipole magnets of the 150 MeV line of the splitter/merger. In particular we present results from two designs of the S4.BEN01 magnet, one based on iron dominated current-excited magnet, and the other design based on Halbach-type permanent magnet. An evaluation of the two designs will be given in the section under “conclusion”.« less

Phonon-drag magnetoquantum oscillations in graphene

NASA Astrophysics Data System (ADS)

Kubakaddi, S. S.; Biswas, Tutul; Kanti Ghosh, Tarun

2017-08-01

A theory of low-temperature phonon-drag magnetothermopower Sxxg is presented in graphene in a quantizing magnetic field. Sxxg is found to exhibit quantum oscillations as a function of magnetic field B and electron concentration n e . The amplitude of the oscillations is found to increase (decrease) with increasing B (n e ). The behavior of Sxxg is also investigated as a function of temperature. A large value of Sxxg (˜few hundreds of μV K-1) is predicted. Numerical values of Sxxg are compared with the measured magnetothermopower S xx and the diffusion component Sxxd from the modified Girvin-Jonson theory.

Analysis of magnetic fields using variational principles and CELAS2 elements

NASA Technical Reports Server (NTRS)

Frye, J. W.; Kasper, R. G.

1977-01-01

Prospective techniques for analyzing magnetic fields using NASTRAN are reviewed. A variational principle utilizing a vector potential function is presented which has as its Euler equations, the required field equations and boundary conditions for static magnetic fields including current sources. The need for an addition to this variational principle of a constraint condition is discussed. Some results using the Lagrange multiplier method to apply the constraint and CELAS2 elements to simulate the matrices are given. Practical considerations of using large numbers of CELAS2 elements are discussed.

Two-range magnetoelectric sensor

NASA Astrophysics Data System (ADS)

Bichurin, M.; Petrov, V.; Leontyev, V.; Saplev, A.

2017-01-01

In this study, we present a two-range magnetoelectric ME sensor design comprising of permendur (alloy of Fe-Co-V), nickel, and lead zirconate titanate (PZT) laminate composite. A systematic study was conducted to clarify the contribution of magnetostrictive layers variables to the ME response over the applied range of magnetic bias field. The two-range behavior was characterized by opposite sign of the ME response when magnetic dc bias is in different sub-ranges. The ME coefficient as a function of magnetic bias field was found to be dependent on the laminate composite structure.

Absolute method of measuring magnetic susceptibility

USGS Publications Warehouse

Thorpe, A.; Senftle, F.E.

1959-01-01

An absolute method of standardization and measurement of the magnetic susceptibility of small samples is presented which can be applied to most techniques based on the Faraday method. The fact that the susceptibility is a function of the area under the curve of sample displacement versus distance of the magnet from the sample, offers a simple method of measuring the susceptibility without recourse to a standard sample. Typical results on a few substances are compared with reported values, and an error of less than 2% can be achieved. ?? 1959 The American Institute of Physics.

Viscosity and inertia in cosmic-ray transport - Effects of an average magnetic field

NASA Technical Reports Server (NTRS)

Williams, L. L.; Jokipii, J. R.

1991-01-01

A generalized transport equation is introduced which describes the transport and propagation of cosmic rays in a magnetized, collisionless medium. The equation is valid if the cosmic-ray distribution function is nearly isotropic in momentum, if the ratio of fluid speed to fluid-flow particle speed is small, and if the ratio of collision time to time for change in the macroscopic flow is small. Five independent cosmic-ray viscosity coefficients are found, and the ralationship of this viscosity to particle orbits in a magnetic field is presented.

Technological Innovations in Magnetic Resonance for Early Detection of Cardiovascular Diseases.

PubMed

Santarelli, Maria F; Positano, Vincenzo; Martini, Nicola; Valvano, Giuseppe; Landini, Luigi

2016-01-01

Most recent technical innovations in cardiovascular MR imaging (CMRI) are presented in this review. They include hardware and software developments, and novelties in parametric mapping. All these recent improvements lead to high spatial and temporal resolution and quantitative information on the heart structure and function. They make it achievable ambitious goals in the field of magnetic resonance, such as the early detection of cardiovascular pathologies. In this review article, we present recent innovations in CMRI, emphasizing the progresses performed and the solutions proposed to some yet opened technical problems.

Image Quality of the Helioseismic and Magnetic Imager (HMI) Onboard the Solar Dynamics Observatory (SDO)

NASA Technical Reports Server (NTRS)

Wachter, R.; Schou, Jesper; Rabello-Soares, M. C.; Miles, J. W.; Duvall, T. L., Jr.; Bush, R. I.

2011-01-01

We describe the imaging quality of the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) as measured during the ground calibration of the instrument. We describe the calibration techniques and report our results for the final configuration of HMI. We present the distortion, modulation transfer function, stray light,image shifts introduced by moving parts of the instrument, best focus, field curvature, and the relative alignment of the two cameras. We investigate the gain and linearity of the cameras, and present the measured flat field.

Exotic chemical arrangements and magnetic moment evolution of NixPt1-x (0 ≤x≤ 1) nanoparticles

NASA Astrophysics Data System (ADS)

Mokkath, Junais Habeeb

2018-06-01

We present a systematic study on the chemical ordering pattern and the magnetic properties of NixPt1-x (0 ⩽ x≤ 1) nanoparticles having a size of 1.5 nm by means of an approach which combines basin hopping structure sampling technique and spin-polarized density functional theory. We found exotic chemical ordering patterns for different Ni/Pt ratios. In addition, we observed a sharp phase transition from non-magnetic to ferromagnetic behaviour around x = 67%. We show that this is a direct consequence of a unique atomic arrangement on the surface in which Ni atoms club together causing the strong Ni-Ni magnetic interaction. The observed magnetic properties are correlated to the electronic density of states.

Quench Protection of SC Quadrupole Magnets

NASA Astrophysics Data System (ADS)

Feher, S.; Bossert, R.; Dimarco, J.; Mitchell, D.; Lamm, M. J.; Limon, P. J.; Mazur, P.; Nobrega, F.; Orris, D.; Ozelis, J. P.; Strait, J. B.; Tompkins, J. C.; Zlobin, A. V.; McInturff, A. D.

1997-05-01

The energy stored in a superconducting accelerator magnet is dissipated after a quench in the coil normal zones, heating the coil and generating a turn to turn and coil to ground voltage drop. Quench heaters are used to protect the superconducting magnet by greatly increasing the coil normal zone thus allowing the energy to be dissipated over a larger conductor volume. Such heaters will be required for the Fermilab/LBNL design of the high gradient quads (HGQ) designed for the LHC interaction regions. As a first step, heaters were installed and tested in several Tevatron low-β superconducting quadrupoles. Experimental studies in normal and superfluid helium are presented which show the heater-induced quench response as a function of magnet excitation current, magnet temperature and peak heater energy density.

Neuronal Effects of Auditory Distraction on Visual Attention

ERIC Educational Resources Information Center

Smucny, Jason; Rojas, Donald C.; Eichman, Lindsay C.; Tregellas, Jason R.

2013-01-01

Selective attention in the presence of distraction is a key aspect of healthy cognition. The underlying neurobiological processes, have not, however, been functionally well characterized. In the present study, we used functional magnetic resonance imaging to determine how ecologically relevant distracting noise affects cortical activity in 27…

High temperature spin dynamics in linear magnetic chains, molecular rings, and segments by nuclear magnetic resonance

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

Adelnia, Fatemeh; Lascialfari, Alessandro; Dipartimento di Fisica, Università degli Studi di Pavia and INSTM, Pavia

2015-05-07

We present the room temperature proton nuclear magnetic resonance (NMR) nuclear spin-lattice relaxation rate (NSLR) results in two 1D spin chains: the Heisenberg antiferromagnetic (AFM) Eu(hfac){sub 3}NITEt and the magnetically frustrated Gd(hfac){sub 3}NITEt. The NSLR as a function of external magnetic field can be interpreted very well in terms of high temperature spin dynamics dominated by a long time persistence of the decay of the two-spin correlation function due to the conservation of the total spin value for isotropic Heisenberg chains. The high temperature spin dynamics are also investigated in Heisenberg AFM molecular rings. In both Cr{sub 8} closed ringmore » and in Cr{sub 7}Cd and Cr{sub 8}Zn open rings, i.e., model systems for a finite spin segment, an enhancement of the low frequency spectral density is found consistent with spin diffusion but the high cut-off frequency due to intermolecular anisotropic interactions prevents a detailed analysis of the spin diffusion regime.« less

Effects of the magnetic field direction on the Tsallis statistic

NASA Astrophysics Data System (ADS)

González-Casanova, Diego F.; Lazarian, A.; Cho, J.

2018-04-01

We extend the use of the Tsallis statistic to measure the differences in gas dynamics relative to the mean magnetic field present from natural eddy-type motions existing in magnetohydrodynamical (MHD) turbulence. The variation in gas dynamics was estimated using the Tsallis parameters on the incremental probability distribution function of the observables (intensity and velocity centroid) obtained from compressible MHD simulations. We find that the Tsallis statistic is susceptible to the anisotropy produced by the magnetic field, even when anisotropy is present the Tsallis statistic can be used to determine MHD parameters such as the Sonic Mach number. We quantize the goodness of the Tsallis parameters using the coefficient of determination to measure the differences in the gas dynamics. These parameters also determine the level of magnetization and compressibility of the medium. To further simulate realistic spectroscopic observational data, we introduced smoothing, noise, and cloud boundaries to the MHD simulations.

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

Glioblastoma Presenting with Pure Alexia and Palinopsia Involving the Left Inferior Occipital Gyrus and Visual Word Form Area Evaluated with Functional Magnetic Resonance Imaging and Diffusion Tensor Imaging Tractography.

PubMed

Huang, Meng; Baskin, David S; Fung, Steve

2016-05-01

Rapid word recognition and reading fluency is a specialized cortical process governed by the visual word form area (VWFA), which is localized to the dominant posterior lateral occipitotemporal sulcus/fusiform gyrus. A lesion of the VWFA results in pure alexia without agraphia characterized by letter-by-letter reading. Palinopsia is a visual processing distortion characterized by persistent afterimages and has been reported in lesions involving the nondominant occipitotemporal cortex. A 67-year-old right-handed woman with no neurologic history presented to our emergency department with acute cortical ischemic symptoms that began with a transient episode of receptive aphasia. She also reported inability to read, albeit with retained writing ability. She also saw afterimages of objects. During her stroke workup, an intra-axial circumscribed enhancing mass lesion was discovered involving her dominant posterolateral occipitotemporal lobe. Given the eloquent brain involvement, she underwent preoperative functional magnetic resonance imaging with diffusion tensor imaging tractography and awake craniotomy to maximize resection and preserve function. Many organic lesions involving these regions have been reported in the literature, but to the best of our knowledge, glioblastoma involving the VWFA resulting in both clinical syndromes of pure alexia and palinopsia with superimposed functional magnetic resonance imaging and fiber tract mapping has never been reported before. Copyright © 2015 Elsevier Inc. All rights reserved.

Current Density Functional Theory Using Meta-Generalized Gradient Exchange-Correlation Functionals.

PubMed

Furness, James W; Verbeke, Joachim; Tellgren, Erik I; Stopkowicz, Stella; Ekström, Ulf; Helgaker, Trygve; Teale, Andrew M

2015-09-08

We present the self-consistent implementation of current-dependent (hybrid) meta-generalized gradient approximation (mGGA) density functionals using London atomic orbitals. A previously proposed generalized kinetic energy density is utilized to implement mGGAs in the framework of Kohn-Sham current density functional theory (KS-CDFT). A unique feature of the nonperturbative implementation of these functionals is the ability to seamlessly explore a wide range of magnetic fields up to 1 au (∼235 kT) in strength. CDFT functionals based on the TPSS and B98 forms are investigated, and their performance is assessed by comparison with accurate coupled-cluster singles, doubles, and perturbative triples (CCSD(T)) data. In the weak field regime, magnetic properties such as magnetizabilities and nuclear magnetic resonance shielding constants show modest but systematic improvements over generalized gradient approximations (GGA). However, in the strong field regime, the mGGA-based forms lead to a significantly improved description of the recently proposed perpendicular paramagnetic bonding mechanism, comparing well with CCSD(T) data. In contrast to functionals based on the vorticity, these forms are found to be numerically stable, and their accuracy at high field suggests that the extension of mGGAs to CDFT via the generalized kinetic energy density should provide a useful starting point for further development of CDFT approximations.

Magnetic nanoparticle detection method employing non-linear magnetoimpedance effects

NASA Astrophysics Data System (ADS)

Beato-López, J. J.; Pérez-Landazábal, J. I.; Gómez-Polo, C.

2017-04-01

In this work, a sensitive tool to detect magnetic nanoparticles (Fe3O4) based on a non-linear Giant Magnetoimpedance (GMI) effect is presented. The GMI sensor is designed with four nearly zero magnetostrictive ribbons connected in series and was analysed as a function of a constant external magnetic field and exciting frequency. The influence of the magnetic nanoparticles deposited on the ribbon surface was characterized using the first (fundamental) and second (non-linear) harmonics of the magnetoinductive voltage. The results show a clear enhancement of the sensor response in the high magnetic field region (H = 1.5 kA/m) as a consequence of the stray field generated by the magnetic nanoparticles on the GMI ribbons' surface. The highest sensitivity ratios are obtained for the non-linear component in comparison with the fundamental response. The results open a new research strategy in magnetic nanoparticle detection.

Towards magnetic-enhanced cellular uptake, MRI and chemotherapeutics delivery by magnetic mesoporous silica nanoparticles.

PubMed

Liu, Qian; Zhang, Jixi; Xia, Weiliang; Gu, Hongchen

2012-10-01

A type of nanoparticle with three functional modalities was prepared with the aim of providing a multifunctional drug delivery system. The nanoparticle was 50 nm in size, with 2.7 nm mesopores and a magnetic nanocrystal core, which was further doped with FITC to enable the tracking of cellular uptake. We demonstrated that the internalization of the nanoparticles in tumor cells could be enhanced by applying an external magnetic field and furthermore, this kind of nanoparticle could be used in magnetic targeted drug delivery. With high transverse relaxivity, the magnetic nanoparticles shortened proton relaxation time and induced high magnetic resonance imaging contrast in tumor cells. Studies on anticancer drug loading and delivery capacity of anticancer drugs also showed that this type of nanoparticles could load water-soluble doxorubicin, and produce a prominent inhibitive effect against tumor cells. Taken together, the presented nanoparticles could become a promising agent in cancer theranostics.

Magnetoacoustic tomography with magnetic induction for high-resolution bioimepedance imaging through vector source reconstruction under the static field of MRI magnet.

PubMed

Mariappan, Leo; Hu, Gang; He, Bin

2014-02-01

Magnetoacoustic tomography with magnetic induction (MAT-MI) is an imaging modality to reconstruct the electrical conductivity of biological tissue based on the acoustic measurements of Lorentz force induced tissue vibration. This study presents the feasibility of the authors' new MAT-MI system and vector source imaging algorithm to perform a complete reconstruction of the conductivity distribution of real biological tissues with ultrasound spatial resolution. In the present study, using ultrasound beamformation, imaging point spread functions are designed to reconstruct the induced vector source in the object which is used to estimate the object conductivity distribution. Both numerical studies and phantom experiments are performed to demonstrate the merits of the proposed method. Also, through the numerical simulations, the full width half maximum of the imaging point spread function is calculated to estimate of the spatial resolution. The tissue phantom experiments are performed with a MAT-MI imaging system in the static field of a 9.4 T magnetic resonance imaging magnet. The image reconstruction through vector beamformation in the numerical and experimental studies gives a reliable estimate of the conductivity distribution in the object with a ∼ 1.5 mm spatial resolution corresponding to the imaging system frequency of 500 kHz ultrasound. In addition, the experiment results suggest that MAT-MI under high static magnetic field environment is able to reconstruct images of tissue-mimicking gel phantoms and real tissue samples with reliable conductivity contrast. The results demonstrate that MAT-MI is able to image the electrical conductivity properties of biological tissues with better than 2 mm spatial resolution at 500 kHz, and the imaging with MAT-MI under a high static magnetic field environment is able to provide improved imaging contrast for biological tissue conductivity reconstruction.

Increase in stability of cellulase immobilized on functionalized magnetic nanospheres

NASA Astrophysics Data System (ADS)

Zhang, Wenjuan; Qiu, Jianhui; Feng, Huixia; Zang, Limin; Sakai, Eiichi

2015-02-01

Functionalized magnetic nanospheres were prepared by co-condensation of tetraethylorthosilicate with three different amino-silanes: 3-(2-aminoethylamino propyl)-triethoxysilane (AEAPTES), 3-(2-aminoethylamino propyl)-trimethoxysilane (AEAPTMES) and 3-aminopropyltriethoxysilane (APTES). Then three functionalized magnetic nanospheres were used as supports for immobilization of cellulase. The three functionalized magnetic nanospheres with core-shell morphologies exhibited higher capacity for cellulase immobilization than unfunctionalized magnetic nanospheres. The increasing of surface charge of functionalized magnetic nanospheres leads to an enhancement of the capacity of cellulase immobilization. Particularly, AEAPTMES with methoxy groups was favored to be hydrolyzed and grafted on unfunctionalized magnetic nanospheres than the others. AEAPTMES functionalized magnetic nanospheres with the highest zeta potential (29 mV) exhibited 87% activity recovery and the maximum amount of immobilized cellulase was 112 mg/g support at concentration of initial cellulase of 8 mg/mL. Immobilized cellulase on AEAPTMES functionalized magnetic nanospheres had higher temperature stability and broader pH stability than other immobilized cellulases and free cellulase. In particular, it can be used in about 40 °C, demonstrating the potential of biofuel production using this immobilized cellulase.

The DIII-D Map -- An Area-Preserving Map for Trajectories of Magnetic Field Lines in the DIII-D Tokamak

NASA Astrophysics Data System (ADS)

Punjabi, Alkesh; Ali, Halima; Boozer, Allen; Evans, Todd

2007-11-01

The EFIT data for the DIII-D shot 115467 3000 ms is used to calculate the generating function for an area-preserving map for trajectories of magnetic field lines in the DIII-D. We call this map the DIII-D map. The generating function is a bivariate polynomial in base vectors &1/2circ;cos(θ) and &1/2circ;sin(θ). ψ is toroidal flux and θ is poloidal angle. The generating function is calculated using a canonical transformation from (ψ,θ) to physical coordinates (R,Z) in the DIII-D [1] and nonlinear regression. The equilibrium generating function gives an excellent representation of the equilibrium flux surfaces in the DIII-D. The DIII-D map is then used to calculate effects of the magnetic perturbations in the DIII-D. Preliminary results of the DIII-D map will be presented. This work is supported by US DOE OFES DE-FG02-01ER54624 and DE-FG02-04ER54793. [1] A. Punjabi, H. Ali, T. Evans, and A. Boozer, Phys Lett A 364 140--145 (2007).

A new vibrator to stimulate muscle proprioceptors in fMRI.

PubMed

Montant, Marie; Romaiguère, Patricia; Roll, Jean-Pierre

2009-03-01

Studying cognitive brain functions by functional magnetic resonance imaging (fMRI) requires appropriate stimulation devices that do not interfere with the magnetic fields. Since the emergence of fMRI in the 90s, a number of stimulation devices have been developed for the visual and auditory modalities. Only few devices, however, have been developed for the somesthesic modality. Here, we present a vibration device for studying somesthesia that is compatible with high magnetic field environments and that can be used in fMRI machines. This device consists of a poly vinyl chloride (PVC) vibrator containing a wind turbine and of a pneumatic apparatus that controls 1-6 vibrators simultaneously. Just like classical electromagnetic vibrators, our device stimulates muscle mechanoreceptors (muscle spindles) and generates reliable illusions of movement. We provide the fMRI compatibility data (phantom test), the calibration curve (vibration frequency as a function of air flow), as well as the results of a kinesthetic test (perceived speed of the illusory movement as a function of vibration frequency). This device was used successfully in several brain imaging studies using both fMRI and magnetoencephalography.

Rapid and continuous magnetic separation in droplet microfluidic devices.

PubMed

Brouzes, Eric; Kruse, Travis; Kimmerling, Robert; Strey, Helmut H

2015-02-07

We present a droplet microfluidic method to extract molecules of interest from a droplet in a rapid and continuous fashion. We accomplish this by first marginalizing functionalized super-paramagnetic beads within the droplet using a magnetic field, and then splitting the droplet into one droplet containing the majority of magnetic beads and one droplet containing the minority fraction. We quantitatively analysed the factors which affect the efficiency of marginalization and droplet splitting to optimize the enrichment of magnetic beads. We first characterized the interplay between the droplet velocity and the strength of the magnetic field and its effect on marginalization. We found that marginalization is optimal at the midline of the magnet and that marginalization is a good predictor of bead enrichment through splitting at low to moderate droplet velocities. Finally, we focused our efforts on manipulating the splitting profile to improve the enrichment provided by asymmetric splitting. We designed asymmetric splitting forks that employ capillary effects to preferentially extract the bead-rich regions of the droplets. Our strategy represents a framework to optimize magnetic bead enrichment methods tailored to the requirements of specific droplet-based applications. We anticipate that our separation technology is well suited for applications in single-cell genomics and proteomics. In particular, our method could be used to separate mRNA bound to poly-dT functionalized magnetic microparticles from single cell lysates to prepare single-cell cDNA libraries.

Whole-head SQUID system in a superconducting magnetic shield.

PubMed

Ohta, H; Matsui, T; Uchikawa, Y

2004-11-30

We have constructed a mobile whole-head SQUID system in a superconducting magnetic shield - a cylinder of high Tc superconductor BSCCO of 65 cm in diameter and 160 cm in length. We compared the noise spectra of several SQUID sensors of SNS Josephson junctions in the superconducting magnetic shield with those of the same SQUID sensors in a magnetically shielded room of Permalloy. The SQUID sensors in the superconducting magnetic shield are more than 100 times more sensitive than those in a magnetically shielded room of Permalloy below 1 Hz. We tested the whole-head SQUID system in the superconducting magnetic shield observing somatosensory signals evoked by stimulating the median nerve in the right wrist of patients by current pulses. We present data of 64 and 128 traces versus the common time axis for comparison. Most sensory responses of human brains phase out near 250 ms. However monotonic rhythms still remain even at longer latencies than 250 ms. The nodes of these rhythm are very narrow even at these longer latencies just indicating low noise characteristics of the SQUID system at low-frequencies. The current dipoles at the secondary somatosensory area SII are evoked at longer latencies than 250 ms contributing to a higher-level brain function. The SQUID system in a superconducting magnetic shield will also have advantages when it is used as a DC MEG to study very slow activities and function of the brain.

Magnetic Navigation in Sea Turtles: Insights from Secular Variation

NASA Astrophysics Data System (ADS)

Putman, N. F.; Lohmann, K.

2011-12-01

Sea turtles are iconic migrants that posses a sensitive magnetic-sense that guides their long-distance movements in a variety of contexts. In the first few hours after hatching turtles use the magnetic field to maintain an offshore compass heading to reach deeper water, out of the reach of nearshore predators. Young turtles engage in directed swimming in response to regional magnetic fields that exist along their transoceanic migratory path. Older turtles also use magnetic information to relocate foraging sites and islands used for nesting after displacement. Numerous hypotheses have been put forth to explain how magnetic information functions in these movements, however, there is little consensus among animal navigation researchers. A particular vexing issue is how magnetic navigation can function under the constraints of the constant, gradual shifting of the earth's magnetic field (secular variation). Here, I present a framework based on models of recent geomagnetic secular variation to explore several navigational mechanisms proposed for sea turtles. I show that while examination of secular variation likely falsifies some hypothetical navigational strategies, it provides key insights into the selective pressures that could maintain other navigational mechanisms. Moreover, examination of secular variation's influence on the navigational precision in reproductive migrations of sea turtles offers compelling explanations for the population structure along sea turtle nesting beaches as well as spatiotemporal variation in nesting turtle abundance.

Rapid and continuous magnetic separation in droplet microfluidic devices

PubMed Central

Brouzes, Eric; Kruse, Travis; Kimmerling, Robert; Strey, Helmut H.

2015-01-01

We present a droplet microfluidic method to extract molecules of interest from a droplet in a rapid and continuous fashion. We accomplish this by first marginalizing functionalized super-paramagnetic beads within the droplet using a magnetic field, and then splitting the droplet into one droplet containing the majority of magnetic beads and one droplet containing the minority fraction. We quantitatively analysed the factors which affect the efficiency of marginalization and droplet splitting to optimize the enrichment of magnetic beads. We first characterized the interplay between the droplet velocity and the strength of the magnetic field and its effect on marginalization. We found that marginalization is optimal at the midline of the magnet and that marginalization is a good predictor of bead enrichment through splitting at low to moderate droplet velocities. Finally, we focused our efforts on manipulating the splitting profile to improve the enrichment provided by asymmetric splitting. We designed asymmetric splitting forks that employ capillary effects to preferentially extract the bead-rich regions of the droplets. Our strategy represents a framework to optimize magnetic bead enrichment methods tailored to the requirements of specific droplet-based applications. We anticipate that our separation technology is well suited for applications in single-cell genomics and proteomics. In particular, our method could be used to separate mRNA bound to poly-dT functionalized magnetic microparticles from single cell lysates to prepare single-cell cDNA libraries. PMID:25501881

Performance prediction for a magnetostrictive actuator using a simplified model

NASA Astrophysics Data System (ADS)

Yoo, Jin-Hyeong; Jones, Nicholas J.

2018-03-01

Iron-Gallium alloys (Galfenol) are promising transducer materials that combine high magnetostriction, desirable mechanical properties, high permeability, and a wide operational temperature range. Most of all, the material is capable of operating under tensile stress, and is relatively resistant to shock. These materials are generally characterized using a solid, cylindrically-shaped specimen under controlled compressive stress and magnetization conditions. Because the magnetostriction strongly depends on both the applied stress and magnetization, the characterization of the material is usually conducted under controlled conditions so each parameter is varied independently of the other. However, in a real application the applied stress and magnetization will not be maintained constant during operation. Even though the controlled characterization measurement gives insight into standard material properties, usage of this data in an application, while possible, is not straight forward. This study presents an engineering modeling methodology for magnetostrictive materials based on a piezo-electric governing equation. This model suggests phenomenological, nonlinear, three-dimensional functions for strain and magnetic flux density responses as functions of applied stress and magnetic field. Load line performances as a function of maximum magnetic field input were simulated based on the model. To verify the modeling performance, a polycrystalline magnetostrictive rod (Fe-Ga alloy, Galfenol) was characterized under compressive loads using a dead-weight test setup, with strain gages on the rod and a magnetic field driving coil around the sample. The magnetic flux density through the Galfenol rod was measured with a sensing coil; the compressive loads were measured using a load cell on the bottom of the Galfenol rod. The experimental results are compared with the simulation results using the suggested model, showing good agreement.

Bit patterned media with composite structure for microwave assisted magnetic recording

NASA Astrophysics Data System (ADS)

Eibagi, Nasim

Patterned magnetic nano-structures are under extensive research due to their interesting emergent physics and promising applications in high-density magnetic data storage, through magnetic logic to bio-magnetic functionality. Bit-patterned media is an example of such structures which is a leading candidate to reach magnetic densities which cannot be achieved by conventional magnetic media. Patterned arrays of complex heterostructures such as exchange-coupled composites are studied in this thesis as a potential for next generation of magnetic recording media. Exchange-coupled composites have shown new functionality and performance advantages in magnetic recording and bit patterned media provide unique capability to implement such architectures. Due to unique resonant properties of such structures, their possible application in spin transfer torque memory and microwave assisted switching is also studied. This dissertation is divided into seven chapters. The first chapter covers the history of magnetic recording, the need to increase magnetic storage density, and the challenges in the field. The second chapter introduces basic concepts of magnetism. The third chapter explains the fabrication methods for thin films and various lithographic techniques that were used to pattern the devices under study for this thesis. The fourth chapter introduces the exchanged coupled system with the structure of [Co/Pd] / Fe / [Co/Pd], where the thickness of Fe is varied, and presents the magnetic properties of such structures using conventional magnetometers. The fifth chapter goes beyond what is learned in the fourth chapter and utilizes polarized neutron reflectometry to study the vertical exchange coupling and reversal mechanism in patterned structures with such structure. The sixth chapter explores the dynamic properties of the patterned samples, and their reversal mechanism under microwave field. The final chapter summarizes the results and describes the prospects for future applications of these structures.

Novel Integration Radial and Axial Magnetic Bearing

NASA Technical Reports Server (NTRS)

Blumenstock, Kenneth; Brown, Gary

2000-01-01

Typically, fully active magnetically suspended systems require one axial and two radial magnetic bearings. Combining radial and axial functions into a single device allows for more compact and elegant packaging. Furthermore, in the case of high-speed devices such as energy storage flywheels, it is beneficial to minimize shaft length to keep rotor mode frequencies as high as possible. Attempts have been made to combine radial and axial functionality, but with certain drawbacks. One approach requires magnetic control flux to flow through a bias magnet reducing control effectiveness, thus resulting in increased resistive losses. This approach also requires axial force producing magnetic flux to flow in a direction into the rotor laminate that is undesirable for minimizing eddy-current losses resulting in rotational losses. Another approach applies a conical rotor shape to what otherwise would be a radial heteropolar magnetic bearing configuration. However, positional non-linear effects are introduced with this scheme and the same windings are used for bias, radial, and axial control adding complexity to the controller and electronics. For this approach, the amount of axial capability must be limited. It would be desirable for an integrated radial and axial magnetic bearing to have the following characteristics; separate inputs for radial and axial control for electronics and control simplicity, all magnetic control fluxes should only flow through their respective air gaps and should not flow through any bias magnets for minimal resistive losses, be of a homopolar design to minimize rotational losses, position related non-linear effects should be minimized, and dependent upon the design parameters, be able to achieve any radial/axial force or power ratio as desired. The integrated radial and axial magnetic bearing described in this paper exhibits all these characteristics. Magnetic circuit design, design equations, and magnetic field modeling results will be presented.

Modular magnetic tweezers for single-molecule characterizations of helicases.

PubMed

Kemmerich, Felix E; Kasaciunaite, Kristina; Seidel, Ralf

2016-10-01

Magnetic tweezers provide a versatile toolkit supporting the mechanistic investigation of helicases. In the present article, we show that custom magnetic tweezers setups are straightforward to construct and can easily be extended to provide adaptable platforms, capable of addressing a multitude of enquiries regarding the functions of these fascinating molecular machines. We first address the fundamental components of a basic magnetic tweezers scheme and review some previous results to demonstrate the versatility of this instrument. We then elaborate on several extensions to the basic magnetic tweezers scheme, and demonstrate their applications with data from ongoing research. As our methodological overview illustrates, magnetic tweezers are an extremely useful tool for the characterization of helicases and a custom built instrument can be specifically tailored to suit the experimenter's needs. Copyright © 2016 Elsevier Inc. All rights reserved.

Magnetic islands modelled by a phase-field-crystal approach

NASA Astrophysics Data System (ADS)

Faghihi, Niloufar; Mkhonta, Simiso; Elder, Ken R.; Grant, Martin

2018-03-01

Using a minimal model based on the phase-field-crystal formalism, we study the coupling between the density and magnetization in ferromagnetic solids. Analytical calculations for the square phase in two dimensions are presented and the small deformation properties of the system are examined. Furthermore, numerical simulations are conducted to study the influence of an external magnetic field on various phase transitions, the anisotropic properties of the free energy functional, and the scaling behaviour of the growth of the magnetic domains in a crystalline solid. It is shown that the energy of the system can depend on the direction of the magnetic moments, with respect to the crystalline direction. Furthermore, the growth of the magnetic domains in a crystalline solid is studied and is shown that the growth of domains is in agreement with expected behaviour.

Synthesis of magnetic microtubes decorated with nanowires and cells

NASA Astrophysics Data System (ADS)

Pomar, C. Diaz; Martinho, H.; Ferreira, F. F.; Goia, T. S.; Rodas, A. C. D.; Santos, S. F.; Souza, J. A.

2018-04-01

Antiferromagnetic and ferrimagnetic microtubes decorated with nanowires have been obtained during thermal oxidation process, which was assisted by in situ electrical resistivity measurements. The synthesis route including heat treatment and electrical current along with growth mechanism are presented. This simple method and the ability to tune in the magnetic moment of the obtained microtubes going from a nonmagnetic-like to a large magnetization saturation open an avenue for interesting applications. In vitro experiments involving adherence, migration, and proliferation of fibroblasts cell culture on the surface of the microtubes indicated the absence of cytotoxicity for this material. We have also calculated both torque and driving magnetic force for these microtubes with nanowires and cells as a function of external magnetic field gradient which were found to be robust opening the possibility for magnetic bio micro-robot device fabrication and application in biotechnology.

A guided enquiry approach to introduce basic concepts concerning magnetic hysteresis to minimize student misconceptions

NASA Astrophysics Data System (ADS)

Wei, Yajun; Zhai, Zhaohui; Gunnarsson, Klas; Svedlindh, Peter

2014-11-01

Basic concepts concerning magnetic hysteresis are of vital importance in understanding magnetic materials. However, these concepts are often misinterpreted by many students and even textbooks. We summarize the most common misconceptions and present a new approach to help clarify these misconceptions and enhance students’ understanding of the hysteresis loop. In this approach, students are required to perform an experiment and plot the measured magnetization values and thereby calculated demagnetizing field, internal field, and magnetic induction as functions of the applied field point by point on the same graph. The concepts of the various coercivity, remanence, saturation magnetization, and saturation induction will not be introduced until this stage. By plotting this graph, students are able to interlink all the preceding concepts and intuitively visualize the underlying physical relations between them.

Prussian blue nanocubes: multi-functional nanoparticles for multimodal imaging and image-guided therapy (Conference Presentation)

NASA Astrophysics Data System (ADS)

Cook, Jason R.; Dumani, Diego S.; Kubelick, Kelsey P.; Luci, Jeffrey; Emelianov, Stanislav Y.

2017-03-01

Imaging modalities utilize contrast agents to improve morphological visualization and to assess functional and molecular/cellular information. Here we present a new type of nanometer scale multi-functional particle that can be used for multi-modal imaging and therapeutic applications. Specifically, we synthesized monodisperse 20 nm Prussian Blue Nanocubes (PBNCs) with desired optical absorption in the near-infrared region and superparamagnetic properties. PBNCs showed excellent contrast in photoacoustic (700 nm wavelength) and MR (3T) imaging. Furthermore, photostability was assessed by exposing the PBNCs to nearly 1,000 laser pulses (5 ns pulse width) with up to 30 mJ/cm2 laser fluences. The PBNCs exhibited insignificant changes in photoacoustic signal, demonstrating enhanced robustness compared to the commonly used gold nanorods (substantial photodegradation with fluences greater than 5 mJ/cm2). Furthermore, the PBNCs exhibited superparamagnetism with a magnetic saturation of 105 emu/g, a 5x improvement over superparamagnetic iron-oxide (SPIO) nanoparticles. PBNCs exhibited enhanced T2 contrast measured using 3T clinical MRI. Because of the excellent optical absorption and magnetism, PBNCs have potential uses in other imaging modalities including optical tomography, microscopy, magneto-motive OCT/ultrasound, etc. In addition to multi-modal imaging, the PBNCs are multi-functional and, for example, can be used to enhance magnetic delivery and as therapeutic agents. Our initial studies show that stem cells can be labeled with PBNCs to perform image-guided magnetic delivery. Overall, PBNCs can act as imaging/therapeutic agents in diverse applications including cancer, cardiovascular disease, ophthalmology, and tissue engineering. Furthermore, PBNCs are based on FDA approved Prussian Blue thus potentially easing clinical translation of PBNCs.

Dependence of trapped-flux-induced surface resistance of a large-grain Nb superconducting radio-frequency cavity on spatial temperature gradient during cooldown through T c

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

Huang, Shichun; Kubo, Takayuki; Geng, R. L.

Recent studies by Romanenko et al. revealed that cooling down a superconducting cavity under a large spatial temperature gradient decreases the amount of trapped flux and leads to reduction of the residual surface resistance. In the present paper, the flux expulsion ratio and the trapped-flux-induced surface resistance of a large-grain cavity cooled down under a spatial temperature gradient up to 80K/m are studied under various applied magnetic fields from 5E-6 T to 2E-5 T. We show the flux expulsion ratio improves as the spatial temperature gradient increases, independent of the applied magnetic field: our results supports and enforces the previousmore » studies. We then analyze all RF measurement results obtained under different applied magnetic fields together by plotting the trapped- flux-induced surface resistance normalized by the applied magnetic field as a function of the spatial temperature gradient. All the data can be fitted by a single curve, which defines an empirical formula for the trapped- flux-induced surface resistance as a function of the spatial temperature gradient and applied magnetic field. The formula can fit not only the present results but also those obtained by Romanenko et al. previously. Furthermore, the sensitivity r fl of surface resistance from trapped magnetic flux of fine-grain and large-grain niobium cavities and the origin of dT/ds dependence of R fl/B a are also discussed.« less

Dependence of trapped-flux-induced surface resistance of a large-grain Nb superconducting radio-frequency cavity on spatial temperature gradient during cooldown through T c

DOE PAGES

Huang, Shichun; Kubo, Takayuki; Geng, R. L.

2016-08-26

Recent studies by Romanenko et al. revealed that cooling down a superconducting cavity under a large spatial temperature gradient decreases the amount of trapped flux and leads to reduction of the residual surface resistance. In the present paper, the flux expulsion ratio and the trapped-flux-induced surface resistance of a large-grain cavity cooled down under a spatial temperature gradient up to 80K/m are studied under various applied magnetic fields from 5E-6 T to 2E-5 T. We show the flux expulsion ratio improves as the spatial temperature gradient increases, independent of the applied magnetic field: our results supports and enforces the previousmore » studies. We then analyze all RF measurement results obtained under different applied magnetic fields together by plotting the trapped- flux-induced surface resistance normalized by the applied magnetic field as a function of the spatial temperature gradient. All the data can be fitted by a single curve, which defines an empirical formula for the trapped- flux-induced surface resistance as a function of the spatial temperature gradient and applied magnetic field. The formula can fit not only the present results but also those obtained by Romanenko et al. previously. Furthermore, the sensitivity r fl of surface resistance from trapped magnetic flux of fine-grain and large-grain niobium cavities and the origin of dT/ds dependence of R fl/B a are also discussed.« less

Biological effects due to weak magnetic field on plants

NASA Astrophysics Data System (ADS)

Belyavskaya, N. A.

2004-01-01

Throughout the evolution process, Earth's magnetic field (MF, about 50 μT) was a natural component of the environment for living organisms. Biological objects, flying on planned long-term interplanetary missions, would experience much weaker magnetic fields, since galactic MF is known to be 0.1-1 nT. However, the role of weak magnetic fields and their influence on functioning of biological organisms are still insufficiently understood, and is actively studied. Numerous experiments with seedlings of different plant species placed in weak magnetic field have shown that the growth of their primary roots is inhibited during early germination stages in comparison with control. The proliferative activity and cell reproduction in meristem of plant roots are reduced in weak magnetic field. Cell reproductive cycle slows down due to the expansion of G 1 phase in many plant species (and of G 2 phase in flax and lentil roots), while other phases of cell cycle remain relatively stabile. In plant cells exposed to weak magnetic field, the functional activity of genome at early pre-replicate period is shown to decrease. Weak magnetic field causes intensification of protein synthesis and disintegration in plant roots. At ultrastructural level, changes in distribution of condensed chromatin and nucleolus compactization in nuclei, noticeable accumulation of lipid bodies, development of a lytic compartment (vacuoles, cytosegresomes and paramural bodies), and reduction of phytoferritin in plastids in meristem cells were observed in pea roots exposed to weak magnetic field. Mitochondria were found to be very sensitive to weak magnetic field: their size and relative volume in cells increase, matrix becomes electron-transparent, and cristae reduce. Cytochemical studies indicate that cells of plant roots exposed to weak magnetic field show Ca 2+ over-saturation in all organelles and in cytoplasm unlike the control ones. The data presented suggest that prolonged exposures of plants to weak magnetic field may cause different biological effects at the cellular, tissue and organ levels. They may be functionally related to systems that regulate plant metabolism including the intracellular Ca 2+ homeostasis. However, our understanding of very complex fundamental mechanisms and sites of interactions between weak magnetic fields and biological systems is still incomplete and still deserve strong research efforts.

Vortex pinning properties in Fe-chalcogenides

NASA Astrophysics Data System (ADS)

Leo, A.; Grimaldi, G.; Guarino, A.; Avitabile, F.; Nigro, A.; Galluzzi, A.; Mancusi, D.; Polichetti, M.; Pace, S.; Buchkov, K.; Nazarova, E.; Kawale, S.; Bellingeri, E.; Ferdeghini, C.

2015-12-01

Among the families of iron-based superconductors, the 11-family is one of the most attractive for high field applications at low temperatures. Optimization of the fabrication processes for bulk, crystalline and/or thin film samples is the first step in producing wires and/or tapes for practical high power conductors. Here we present the results of a comparative study of pinning properties in iron-chalcogenides, investigating the flux pinning mechanisms in optimized Fe(Se{}1-xTe x ) and FeSe samples by current-voltage characterization, magneto-resistance and magnetization measurements. In particular, from Arrhenius plots in magnetic fields up to 9 T, the activation energy is derived as a function of the magnetic field, {U}0(H), whereas the activation energy as a function of temperature, U(T), is derived from relaxation magnetization curves. The high pinning energies, high upper critical field versus temperature slopes near critical temperatures, and highly isotropic pinning properties make iron-chalcogenide superconductors a technological material which could be a real competitor to cuprate high temperature superconductors for high field applications.

Spatially Resolved Large Magnetization in Ultrathin BiFeO 3

DOE PAGES

Guo, Er-Jia; Petrie, Jonathan R.; Roldan, Manuel A.; ...

2017-06-19

Complex interactions across the interface in heterostructures can generate novel functionalities not present in the constituent materials. Here, we create a unique ferromagnetic ground state out of normally antiferromagnetic BiFeO 3 (BFO) by interleaving it with layers of ferromagnetic La 0.7Sr 0.3MnO 3. Intriguingly, we found that the magnetization of BFO was aligned opposite to that of the manganite layers. Based on polarized neutron reflectometry (PNR) depth profiling of custom-designed layers, we obtained a net magnetization in the BFO layers of 275 kA/m (~1.83 B/Fe) at 10 K, which is two times larger than the previously reported values. Additionally, ferromagneticmore » order in the BFO persists up to 200 K, which is much higher than previously seen in BFO heterostructures. Our unprecedented understanding of the evolution of magnetism and functional coupling across the interface between antiferromagnetic and ferromagnetic layers provides a blueprint towards advanced spintronic devices.« less

Targeting the Cerebellum by Noninvasive Neurostimulation: a Review.

PubMed

van Dun, Kim; Bodranghien, Florian; Manto, Mario; Mariën, Peter

2017-06-01

Transcranial magnetic and electric stimulation of the brain are novel and highly promising techniques currently employed in both research and clinical practice. Improving or rehabilitating brain functions by modulating excitability with these noninvasive tools is an exciting new area in neuroscience. Since the cerebellum is closely connected with the cerebral regions subserving motor, associative, and affective functions, the cerebello-thalamo-cortical pathways are an interesting target for these new techniques. Targeting the cerebellum represents a novel way to modulate the excitability of remote cortical regions and their functions. This review brings together the studies that have applied cerebellar stimulation, magnetic and electric, and presents an overview of the current knowledge and unsolved issues. Some recommendations for future research are implemented as well.

Magnetically actuated tissue engineered scaffold: insights into mechanism of physical stimulation

NASA Astrophysics Data System (ADS)

Sapir-Lekhovitser, Yulia; Rotenberg, Menahem Y.; Jopp, Juergen; Friedman, Gary; Polyak, Boris; Cohen, Smadar

2016-02-01

Providing the right stimulatory conditions resulting in efficient tissue promoting microenvironment in vitro and in vivo is one of the ultimate goals in tissue development for regenerative medicine. It has been shown that in addition to molecular signals (e.g. growth factors) physical cues are also required for generation of functional cell constructs. These cues are particularly relevant to engineering of biological tissues, within which mechanical stress activates mechano-sensitive receptors, initiating biochemical pathways which lead to the production of functionally mature tissue. Uniform magnetic fields coupled with magnetizable nanoparticles embedded within three dimensional (3D) scaffold structures remotely create transient physical forces that can be transferrable to cells present in close proximity to the nanoparticles. This study investigated the hypothesis that magnetically responsive alginate scaffold can undergo reversible shape deformation due to alignment of scaffold's walls in a uniform magnetic field. Using custom made Helmholtz coil setup adapted to an Atomic Force Microscope we monitored changes in matrix dimensions in situ as a function of applied magnetic field, concentration of magnetic particles within the scaffold wall structure and rigidity of the matrix. Our results show that magnetically responsive scaffolds exposed to an externally applied time-varying uniform magnetic field undergo a reversible shape deformation. This indicates on possibility of generating bending/stretching forces that may exert a mechanical effect on cells due to alternating pattern of scaffold wall alignment and relaxation. We suggest that the matrix structure deformation is produced by immobilized magnetic nanoparticles within the matrix walls resulting in a collective alignment of scaffold walls upon magnetization. The estimated mechanical force that can be imparted on cells grown on the scaffold wall at experimental conditions is in the order of 1 pN, which correlates well with reported threshold to induce mechanotransduction effects on cellular level. This work is our next step in understanding of how to accurately create proper stimulatory microenvironment for promotion of cellular organization to form mature tissue engineered constructs.

Magnetically actuated tissue engineered scaffold: insights into mechanism of physical stimulation

PubMed Central

Sapir-Lekhovitser, Yulia; Rotenberg, Menahem Y.; Jopp, Juergen; Friedman, Gary; Polyak, Boris; Cohen, Smadar

2016-01-01

Providing the right stimulatory conditions resulting in efficient tissue promoting microenvironment in vitro and in vivo is one of the ultimate goals in tissue development for regenerative medicine. It has been shown that in addition to molecular signals (e.g. growth factors) physical cues are also required for generation of functional cell constructs. These cues are particularly relevant to engineering of biological tissues, within which mechanical stress activates mechano-sensitive receptors, initiating biochemical pathways which lead to the production of functionally mature tissue. Uniform magnetic fields coupled with magnetizable nanoparticles embedded within three dimensional (3D) scaffold structures remotely create transient physical forces that can be transferrable to cells present in close proximity to the nanoparticles. This study investigated the hypothesis that magnetically responsive alginate scaffold can undergo reversible shape deformation due to alignment of scaffold’s walls in a uniform magnetic field. Using custom made Helmholtz coil setup adapted to an Atomic Force Microscope we monitored changes in matrix dimensions in situ as a function of applied magnetic field, concentration of magnetic particles within the scaffold wall structure and rigidity of the matrix. Our results show that magnetically responsive scaffolds exposed to an externally applied time-varying uniform magnetic field undergo a reversible shape deformation. This indicates on possibility of generating bending/stretching forces that may exert a mechanical effect on cells due to alternating pattern of scaffold wall alignment and relaxation. We suggest that the matrix structure deformation is produced by immobilized magnetic nanoparticles within the matrix walls resulting in a collective alignment of scaffold walls upon magnetization. The estimated mechanical force that can be imparted on cells grown on the scaffold wall at experimental conditions is in the order of 1 pN, which correlates well with reported threshold to induce mechanotransduction effects on cellular level. This work is our next step in understanding of how to accurately create proper stimulatory microenvironment for promotion of cellular organization to form mature tissue engineered constructs. PMID:26790538

The Astromag superconducting magnet facility configured for a free-flying satellite

NASA Technical Reports Server (NTRS)

Green, M. A.; Smoot, G. F.

1992-01-01

The magnet parameters of a free-flying version of Astromag and the parameters of the space cryogenic system for the magnet are presented. Consideration is given to the free-flyer version of the Astromag magnet. The diameter of the magnet, its cryostat, the satellite and the two instruments is limited by the 4.27-m shroud diameter of the Atlas IIa. The magnet coil must use a stable reliable superconductor which can carry the full magnet current at 4.2 K at a peak induction in the coil of 7.5 T. The magnet must operate in the persistent mode. The changes in the overall design and operating requirements for the free-flying-design Astromag suggest that the coils, the cryogenic system, and the charging system can be simplified without a loss of required magnet function. Attention is given to switches, trim coils, and plumbing in the low field region between the coils; the magnet charging system and the quench protection system; and cooled helium supply to the magnet gas-cooled electrical leads.

Three dimensional lithospheric magnetization structures beneath Australia derived by inverse modeling of CHAMP satellite magnetic field model

NASA Astrophysics Data System (ADS)

Du, Jinsong; Chen, Chao; Lesur, Vincent; Li, Yaoguo; Lane, Richard; Liang, Qing; Wang, Haoran

2014-05-01

We present an inversion algorithm for magnetic anomaly data in spherical coordinates to image the three dimensional (3-D) susceptibility distributions in the lithosphere. The method assumes that remanent magnetization is absent and that the magnetic anomalies are solely the result of lateral variations in magnetic susceptibility. To take into account the curvature of the Earth, the 3-D model is comprised of a set of spherical prisms (referred to as tesseroids), each of which has a constant isotropic susceptibility. The inversion method is formulated with a specifically designed model objective function and radial weighting function in spherical coordinates. A Tikhonov regularization technique is used to obtain an optimal solution with data misfit consistent with the estimated error level. Results for regional synthetic models with different magnetized inclinations and declinations are presented to demonstrate the capability of the method to recover large scale lithospheric magnetic structures. We have applied the algoithm to study the lithospheric susceptibility structures in the Australia region using magnetic anomaly data from the GRIMM_L120v0.0 model, which is based on ten years of CHAMP satellite data. As a self-constrained inversion, the maximum depths variation of magnetization layer is estimated first and then incorporated to the three dimensional (3-D) inversion. Results showed that the susceptibility anomalies concentrate in the depth range from 25 km to 45 km, i.e., focused in the lower crust. In addition, the results showed that the susceptibilities in continental lithosphere are higher than those in oceanic lithosphere. The inverted 3-D susceptibility distribution in the region of Australia reveals significant features related to tectonics, surface heat-flux, crustal thickness and Curie isotherm depths. In general, the higher susceptibility anomalies correlate with Precambrian rocks, and the lower susceptibility anomalies correlate with younger orogenic belts, suture zones and modern uplifts. In details, the inverted susceptibility distribution shows differences in the magnetic structures between the eastern and western parts of the Yilgarn Craton, and three lower susceptibility belts from north to south in the Eromanga Basin and the Gawler Craton with high susceptibility that extend to the ocean and then to the west.

Impact of enzyme replacement therapy on cardiac morphology and function and late enhancement in Fabry's cardiomyopathy.

PubMed

Beer, Meinrad; Weidemann, Frank; Breunig, Frank; Knoll, Anita; Koeppe, Sabrina; Machann, Wolfram; Hahn, Dietbert; Wanner, Christoph; Strotmann, Jörg; Sandstede, Jörn

2006-05-15

The present study evaluated the evolution of cardiac morphology, function, and late enhancement as a noninvasive marker of myocardial fibrosis, and their inter-relation during enzyme replacement therapy in patients with Fabry's disease using magnetic resonance imaging and color Doppler myocardial imaging. Late enhancement, which was present in up to 50% of patients, was associated with increased left ventricular mass, the failure of a significant regression of hypertrophy during enzyme replacement therapy, and worse segmental myocardial function. Late enhancement may predict the effect of enzyme replacement therapy on left ventricular mass and cardiac function.

The Euclidean scalar Green function in the five-dimensional Kaluza-Klein magnetic monopole space-time

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

Bezerra de Mello, E.R.

2006-01-15

In this paper we present, in a integral form, the Euclidean Green function associated with a massless scalar field in the five-dimensional Kaluza-Klein magnetic monopole superposed to a global monopole, admitting a nontrivial coupling between the field with the geometry. This Green function is expressed as the sum of two contributions: the first one related with uncharged component of the field, is similar to the Green function associated with a scalar field in a four-dimensional global monopole space-time. The second contains the information of all the other components. Using this Green function it is possible to study the vacuum polarizationmore » effects on this space-time. Explicitly we calculate the renormalized vacuum expectation value <{phi}{sup *}(x){phi}(x)>{sub Ren}, which by its turn is also expressed as the sum of two contributions.« less

The Maximum Levitation Force of High- T c Superconductors

NASA Astrophysics Data System (ADS)

Zhao, Xian-Feng; Liu, Yuan

2007-11-01

In this paper we present the dependence of the maximum levitation force ( F {/z max }) of a high- T c superconductor (HTS) on the structural factors of high- T c superconducting systems based on the Bean critical state model and Ampère’s law. A transition point of the surface magnetic field ( B s ) of a permanent magnet (PM) is found at which the relation between F {/z max } and B s changes: while the surface magnetic field is less than the transition value the dependence is subject to a nonlinear function, otherwise it is a linear one. The two different relations are estimated to correspond to partial penetration of the shielding currents inside the superconductor below the transition point and complete penetration above it respectively. The influence of geometric properties of superconductors on the dependence is also investigated. In addition, the relation between F {/z max } and the critical current density ( J c ) of the HTS is discussed. The maximum levitation force saturates at high J c . An optimum function of the J c and the B s is presented in order to achieve large F {/z max }.

Magneto-exciton transitions in laterally coupled quantum dots

NASA Astrophysics Data System (ADS)

Barticevic, Zdenka; Pacheco, Monica; Duque, Carlos A.; Oliveira, Luiz E.

2008-03-01

We present a study of the electronic and optical properties of laterally coupled quantum dots. The excitonic spectra of this system under the effects of an external magnetic field applied perpendicular to the plane of the dots is obtained, with the potential of every individual dot taken as the superposition of a quantum well potential along the axial direction with a lateral parabolic confinement potential, and the coupled two- dot system then modeled by a superposition of the potentials of each dot, with their minima at different positions and truncated at the intersection plane. The wave functions and eigenvalues are obtained in the effective-mass approximation by using an extended variational approach in which the magneto- exciton states are simultaneously obtained [1]. The allowed magneto-exciton transitions are investigated by using circularly polarized radiation in the plane perpendicular to the magnetic field. We present results on the excitonic absorption coefficient as a function of the photon energy for different geometric quantum-dot confinement and magnetic-field values. Reference: [1] Z. Barticevic, M. Pacheco, C. A. Duque and L. E. Oliveira, Phys. Rev. B 68, 073312 (2003).

Influence of magnetic disorders on quantum anomalous Hall effect in magnetic topological insulator films beyond the two-dimensional limit

NASA Astrophysics Data System (ADS)

Xing, Yanxia; Xu, Fuming; Cheung, King Tai; Sun, Qing-feng; Wang, Jian; Yao, Yugui

2018-04-01

Quantum anomalous Hall effect (QAHE) has been experimentally realized in magnetic topological insulator (MTI) thin films fabricated on magnetically doped {({{Bi}},{{Sb}})}2{{{Te}}}3. In an MTI thin film with the magnetic easy axis along the normal direction (z-direction), orientations of magnetic dopants are randomly distributed around the magnetic easy axis, acting as magnetic disorders. With the aid of the non-equilibrium Green's function and Landauer–Büttiker formalism, we numerically study the influence of magnetic disorders on QAHE in an MTI thin film modeled by a three-dimensional tight-binding Hamiltonian. It is found that, due to the existence of gapless side surface states, QAHE is protected even in the presence of magnetic disorders as long as the z-component of magnetic moment of all magnetic dopants are positive. More importantly, such magnetic disorders also suppress the dissipation of the chiral edge states and enhance the quality of QAHE in MTI films. In addition, the effect of magnetic disorders depends very much on the film thickness, and the optimal influence is achieved at certain thickness. These findings are new features for QAHE in three-dimensional systems, not present in two-dimensional systems.

A model for the nonlocal transport and the associated distribution function deformation in magnetized laser-plasmas

NASA Astrophysics Data System (ADS)

Nicolaï, Ph.; Feugeas, J.-L.; Schurtz, G.

2006-06-01

We present a model of nonlocal transport for multidimensional radiation magneto hydrodynamic codes. In laser produced plasmas, it is now believed that the heat transfert can be strongly modified by the nonlocal nature of the electron conduction. Nevertheless other mechanisms as self generated magnetic fields may affect heat transport too. The model described in this work aims at extending the formula of G. Schurtz, Ph. Nicolaï and M. Busquet [1] to magnetized plasmas. A system of nonlocal equations is derived from kinetic equations with self-consistent electric and magnetic fields. These equations are analyzed and applied to a physical problem in order to demonstrate the main features of the model.

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

PubMed Central

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

2016-01-01

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

Proton magnetic resonance spectroscopy of tubercular breast abscess: report of a case.

PubMed

Das, Chandan Jyoti; Medhi, Kunjahari

2008-01-01

In vivo proton magnetic resonance spectroscopy (H-MRS) is a functional imaging modality. When magnetic resonance imaging is coupled with H-MRS, it results in accurate metabolic characterization of various lesions. Proton magnetic resonance spectroscopy has an established role in evaluating malignant breast lesions, and the increasing number of published literature supports the role of H-MRS in patients with breast cancer. However, H-MRS can be of help in evaluating benign breast disease. We present a case of tubercular breast abscess, initial diagnosis of which was suggested based on characteristic lipid pick on H-MRS and was subsequently confirmed by fine needle aspiration biopsy of the breast lesion.

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

PubMed

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

2016-07-18

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

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

NASA Astrophysics Data System (ADS)

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

2016-07-01

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

Integrated Vertical Bloch Line (VBL) memory

NASA Technical Reports Server (NTRS)

Katti, R. R.; Wu, J. C.; Stadler, H. L.

1991-01-01

Vertical Bloch Line (VBL) Memory is a recently conceived, integrated, solid state, block access, VLSI memory which offers the potential of 1 Gbit/sq cm areal storage density, data rates of hundreds of megabits/sec, and submillisecond average access time simultaneously at relatively low mass, volume, and power values when compared to alternative technologies. VBLs are micromagnetic structures within magnetic domain walls which can be manipulated using magnetic fields from integrated conductors. The presence or absence of BVL pairs are used to store binary information. At present, efforts are being directed at developing a single chip memory using 25 Mbit/sq cm technology in magnetic garnet material which integrates, at a single operating point, the writing, storage, reading, and amplification functions needed in a memory. The current design architecture, functional elements, and supercomputer simulation results are described which are used to assist the design process.

NMR shifts for polycyclic aromatic hydrocarbons from first-principles

NASA Astrophysics Data System (ADS)

Thonhauser, T.; Ceresoli, Davide; Marzari, Nicola

We present first-principles, density-functional theory calculations of the NMR chemical shifts for polycyclic aromatic hydrocarbons, starting with benzene and increasing sizes up to the one- and two-dimensional infinite limits of graphene ribbons and sheets. Our calculations are performed using a combination of the recently developed theory of orbital magnetization in solids, and a novel approach to NMR calculations where chemical shifts are obtained from the derivative of the orbital magnetization with respect to a microscopic, localized magnetic dipole. Using these methods we study on equal footing the 1H and 13 shifts in benzene, pyrene, coronene, in naphthalene, anthracene, naphthacene, and pentacene, and finally in graphene, graphite, and an infinite graphene ribbon. Our results show very good agreement with experiments and allow us to characterize the trends for the chemical shifts as a function of system size.

Fermionic vacuum polarization by an Abelian magnetic tube in the cosmic string spacetime

NASA Astrophysics Data System (ADS)

Maior de Sousa, M. S.; Ribeiro, R. F.; Bezerra de Mello, E. R.

2017-02-01

In this paper, we consider a charged massive fermionic quantum field in the idealized cosmic string spacetime and in the presence of a magnetic field confined in a cylindrical tube of finite radius. Three distinct configurations for the magnetic fields are taken into account: (i) a cylindrical shell of radius a , (ii) a magnetic field proportional to 1 /r , and (iii) a constant magnetic field. In these three cases, the axis of the infinitely long tube of radius a coincides with the cosmic string. Our main objectives in this paper are to analyze the fermionic condensate (FC) and the vacuum expectation value (VEV) of the fermionic energy-momentum tensor. In order to do that, we explicitly construct the complete set of normalized wave functions for each configuration of the magnetic field. We show that in the region outside the tube, the FC and the VEV of the energy-momentum tensor are decomposed into two parts: The first ones correspond to the zero-thickness magnetic flux contributions, and the second ones are induced by the nontrivial structure of the magnetic field, named core-induced contributions. The latter present specific forms depending on the magnetic field configuration considered. We also show that the VEV of the energy-momentum tensor is diagonal and obeys the conservation condition, and its trace is expressed in terms of the fermionic condensate. The zero-thickness contributions to the FC and VEV of the energy-momentum tensor depend only on the fractional part of the ration of the magnetic flux inside the tube by the quantum one. As to the core-induced contributions, they depend on the total magnetic flux inside the tube and, consequently, in general, are not a periodic function of the magnetic flux.

Novel Integrated Radial and Axial Magnetic Bearing

NASA Technical Reports Server (NTRS)

Blumenstock, Kenneth A.; Brown, Gary L.; Powers, Edward I. (Technical Monitor)

2000-01-01

Typically, fully active magnetically suspended systems require one axial and two radial magnetic bearings. Combining radial and axial functions into a single device allows for more compact and elegant packaging. Furthermore, in the case of high-speed devices such as energy storage flywheels, it is beneficial to minimize shaft length to keep rotor mode frequencies as high as possible. Attempts have been made to combine radial and axial functionality, but with certain drawbacks. One approach requires magnetic control flux to flow through a bias magnet reducing control effectiveness, thus resulting in increased resistive losses. This approach also requires axial force producing magnetic flux to flow in a direction into the rotor laminate that is undesirable for minimizing eddy-current losses resulting in rotational losses. Another approach applies a conical rotor shape to what otherwise would be a radial heteropolar magnetic bearing configuration. However, positional non-linear effects are introduced with this scheme and the same windings are used for bias, radial, and axial control adding complexity to the controller and electronics. For this approach, the amount of axial capability must be limited. It would be desirable for an integrated radial and axial magnetic bearing to have the following characteristics, separate inputs for radial and axial control for electronics and control simplicity, all magnetic control fluxes should only flow through their respective air gaps and should not flow through any bias magnets for minimal resistive losses, be of a homopolar design to minimize rotational losses, position related non-linear effects should be minimized, and dependent upon the design parameters, be able to achieve any radial/axial force or power ratio as desired. The integrated radial and axial magnetic bearing described in this paper exhibits all these characteristics. Magnetic circuit design, design equations, and analysis results will be presented.

Detailed relationship between local structure, polarons, and magnetizationfor La1-xCaxMnO3 (0.21≤x≤0.45)

NASA Astrophysics Data System (ADS)

Bridges, F.; Downward, L.; Neumeier, J. J.; Tyson, T. A.

2010-05-01

We present detailed local structure measurements (using the extended x-ray absorption fine structure technique) for the colossal magnetoresistive material La1-xCaxMnO3 (0.21

Computer simulations of equilibrium magnetization and microstructure in magnetic fluids

NASA Astrophysics Data System (ADS)

Rosa, A. P.; Abade, G. C.; Cunha, F. R.

2017-09-01

In this work, Monte Carlo and Brownian Dynamics simulations are developed to compute the equilibrium magnetization of a magnetic fluid under action of a homogeneous applied magnetic field. The particles are free of inertia and modeled as hard spheres with the same diameters. Two different periodic boundary conditions are implemented: the minimum image method and Ewald summation technique by replicating a finite number of particles throughout the suspension volume. A comparison of the equilibrium magnetization resulting from the minimum image approach and Ewald sums is performed by using Monte Carlo simulations. The Monte Carlo simulations with minimum image and lattice sums are used to investigate suspension microstructure by computing the important radial pair-distribution function go(r), which measures the probability density of finding a second particle at a distance r from a reference particle. This function provides relevant information on structure formation and its anisotropy through the suspension. The numerical results of go(r) are compared with theoretical predictions based on quite a different approach in the absence of the field and dipole-dipole interactions. A very good quantitative agreement is found for a particle volume fraction of 0.15, providing a validation of the present simulations. In general, the investigated suspensions are dominated by structures like dimmer and trimmer chains with trimmers having probability to form an order of magnitude lower than dimmers. Using Monte Carlo with lattice sums, the density distribution function g2(r) is also examined. Whenever this function is different from zero, it indicates structure-anisotropy in the suspension. The dependence of the equilibrium magnetization on the applied field, the magnetic particle volume fraction, and the magnitude of the dipole-dipole magnetic interactions for both boundary conditions are explored in this work. Results show that at dilute regimes and with moderate dipole-dipole interactions, the standard method of minimum image is both accurate and computationally efficient. Otherwise, lattice sums of magnetic particle interactions are required to accelerate convergence of the equilibrium magnetization. The accuracy of the numerical code is also quantitatively verified by comparing the magnetization obtained from numerical results with asymptotic predictions of high order in the particle volume fraction, in the presence of dipole-dipole interactions. In addition, Brownian Dynamics simulations are used in order to examine magnetization relaxation of a ferrofluid and to calculate the magnetic relaxation time as a function of the magnetic particle interaction strength for a given particle volume fraction and a non-dimensional applied field. The simulations of magnetization relaxation have shown the existence of a critical value of the dipole-dipole interaction parameter. For strength of the interactions below the critical value at a given particle volume fraction, the magnetic relaxation time is close to the Brownian relaxation time and the suspension has no appreciable memory. On the other hand, for strength of dipole interactions beyond its critical value, the relaxation time increases exponentially with the strength of dipole-dipole interaction. Although we have considered equilibrium conditions, the obtained results have far-reaching implications for the analysis of magnetic suspensions under external flow.

1H MAS NMR (magic-angle spinning nuclear magnetic resonance) techniques for the quantitative determination of hydrogen types in solid catalysts and supports.

PubMed

Kennedy, Gordon J; Afeworki, Mobae; Calabro, David C; Chase, Clarence E; Smiley, Randolph J

2004-06-01

Distinct hydrogen species are present in important inorganic solids such as zeolites, silicoaluminophosphates (SAPOs), mesoporous materials, amorphous silicas, and aluminas. These H species include hydrogens associated with acidic sites such as Al(OH)Si, non-framework aluminum sites, silanols, and surface functionalities. Direct and quantitative methodology to identify, measure, and monitor these hydrogen species are key to monitoring catalyst activity, optimizing synthesis conditions, tracking post-synthesis structural modifications, and in the preparation of novel catalytic materials. Many workers have developed several techniques to address these issues, including 1H MAS NMR (magic-angle spinning nuclear magnetic resonance). 1H MAS NMR offers many potential advantages over other techniques, but care is needed in recognizing experimental limitations and developing sample handling and NMR methodology to obtain quantitatively reliable data. A simplified approach is described that permits vacuum dehydration of multiple samples simultaneously and directly in the MAS rotor without the need for epoxy, flame sealing, or extensive glovebox use. We have found that careful optimization of important NMR conditions, such as magnetic field homogeneity and magic angle setting are necessary to acquire quantitative, high-resolution spectra that accurately measure the concentrations of the different hydrogen species present. Details of this 1H MAS NMR methodology with representative applications to zeolites, SAPOs, M41S, and silicas as a function of synthesis conditions and post-synthesis treatments (i.e., steaming, thermal dehydroxylation, and functionalization) are presented.

Towards hybrid biocompatible magnetic rHuman serum albumin-based nanoparticles: use of ultra-small (CeLn)3/4+ cation-doped maghemite nanoparticles as functional shell

NASA Astrophysics Data System (ADS)

Israel, Liron L.; Kovalenko, Elena I.; Boyko, Anna A.; Sapozhnikov, Alexander M.; Rosenberger, Ina; Kreuter, Jörg; Passoni, Lorena; Lellouche, Jean-Paul

2015-01-01

Human serum albumin (HSA) is a protein found in human blood. Over the last decade, HSA has been evaluated as a promising drug carrier. However, not being magnetic, HSA cannot be used for biomedical applications such as magnetic resonance imaging (MRI) and magnetic drug targeting. Therefore, subsequent composites building on iron oxide nanoparticles that are already used clinically as MRI contrast agents are extensively studied. Recently and in this context, innovative fully hydrophilic ultra-small CAN-stabilized maghemite ((CeLn)3/4+-γ-Fe2O3) nanoparticles have been readily fabricated. The present study discusses the design, fabrication, and characterization of a dual phase hybrid core (rHSA)-shell ((CeLn)3/4+-γ-Fe2O3 NPs) nanosystem. Quite importantly and in contrast to widely used encapsulation strategies, rHSA NP surface-attached (CeLn)3/4+-γ-Fe2O3 NPs enabled to exploit both rHSA (protein functionalities) and (CeLn)3/4+-γ-Fe2O3 NP surface functionalities (COOH and ligand L coordinative exchange) in addition to very effective MRI contrast capability due to optimal accessibility of H2O molecules with the outer magnetic phase. Resulting hybrid nanoparticles might be used as a platform modular system for therapeutic (drug delivery system) and MR diagnostic purposes.

Exploring graphene superlattices: Magneto-optical properties

NASA Astrophysics Data System (ADS)

Duque, C. A.; Hernández-Bertrán, M. A.; Morales, A. L.; de Dios-Leyva, M.

2017-02-01

We present a detailed study of magnetic subbands, wave functions, and transition strengths for graphene superlattices (SLs) subject to a perpendicular magnetic field. It is shown that, for a weak magnetic field, the flat subbands of a SL exhibiting extra Dirac points are grouped into subsets, each of which consists of a singlet subband and a nearly degenerate doublet subband, and one nearly degenerate triplet subband. It was found that the wave functions corresponding to a singlet or to a doublet are always located around the image in real space of the central or extra Dirac points in k-space. The latter properties were explained by assuming that the electron motion is quasi-classical. Our study revealed that, for an intermediate field, the general characteristics of the wave functions are very similar to those of the pristine graphene, while for weak field, their behavior is drastically different. The latter is characterized by rapid oscillations which were understood using the solutions provided by the formalism of Luttinger-Kohn. The study on transition strengths allows us to obtain, for SLs with extra Dirac points in a weak magnetic field and different polarizations, the conditions under which transitions between multiplets are approximately allowed. It was shown that these conditions correspond to an unusual selection rule that is broken when the magnetic field intensity increases from weak to an intermediate value.

A functional magnetic resonance imaging investigation of episodic memory after traumatic brain injury.

PubMed

Russell, Kathryn C; Arenth, Patricia M; Scanlon, Joelle M; Kessler, Lauren J; Ricker, Joseph H

2011-06-01

Traumatic brain injury often negatively impacts episodic memory; however, studies of the neural substrates of this impairment have been limited. In this study, both encoding and recognition of visually presented stimuli were examined with functional magnetic resonance imaging. Twelve adults with chronic complicated mild, moderate, and severe injuries were compared with a matched group of 12 controls. Behavioral task performance did not differentiate the groups. During neuroimaging, however, the group of individuals with traumatic brain injury exhibited increased activation, as well as increased bilaterality and dispersion as compared to controls. Findings are discussed in terms of increased resource recruitment.

Multi-scale modeling of spin transport in organic semiconductors

NASA Astrophysics Data System (ADS)

Hemmatiyan, Shayan; Souza, Amaury; Kordt, Pascal; McNellis, Erik; Andrienko, Denis; Sinova, Jairo

In this work, we present our theoretical framework to simulate simultaneously spin and charge transport in amorphous organic semiconductors. By combining several techniques e.g. molecular dynamics, density functional theory and kinetic Monte Carlo, we are be able to study spin transport in the presence of anisotropy, thermal effects, magnetic and electric field effects in a realistic morphologies of amorphous organic systems. We apply our multi-scale approach to investigate the spin transport in amorphous Alq3 (Tris(8-hydroxyquinolinato)aluminum) and address the underlying spin relaxation mechanism in this system as a function of temperature, bias voltage, magnetic field and sample thickness.

Design of magnetic coordination complexes for quantum computing.

PubMed

Aromí, Guillem; Aguilà, David; Gamez, Patrick; Luis, Fernando; Roubeau, Olivier

2012-01-21

A very exciting prospect in coordination chemistry is to manipulate spins within magnetic complexes for the realization of quantum logic operations. An introduction to the requirements for a paramagnetic molecule to act as a 2-qubit quantum gate is provided in this tutorial review. We propose synthetic methods aimed at accessing such type of functional molecules, based on ligand design and inorganic synthesis. Two strategies are presented: (i) the first consists in targeting molecules containing a pair of well-defined and weakly coupled paramagnetic metal aggregates, each acting as a carrier of one potential qubit, (ii) the second is the design of dinuclear complexes of anisotropic metal ions, exhibiting dissimilar environments and feeble magnetic coupling. The first systems obtained from this synthetic program are presented here and their properties are discussed.

A new quasi-thermal trap model for solar flare hard X-ray bursts - An electrostatic trap model

NASA Technical Reports Server (NTRS)

Spicer, D. S.; Emslie, A. G.

1988-01-01

A new quasi-thermal trap model of solar flare hard X-ray bursts is presented. The new model utilizes the trapping ability of a magnetic mirror and a magnetic field-aligned electrostatic potential produced by differences in anisotropies of the electron and ion distribution function. It is demonstrated that this potential can, together with the magnetic mirror itself, effectively confine electrons in a trap, thereby enhancing their bremsstrahlung yield per electron. This analysis makes even more untenable models involving precipitation of the bremsstrahlung-producing electrons onto a cold target.

Generation of dynamo magnetic fields in protoplanetary and other astrophysical accretion disks

NASA Technical Reports Server (NTRS)

Stepinski, T. F.; Levy, E. H.

1988-01-01

A computational method for treating the generation of dynamo magnetic fields in astrophysical disks is presented. The numerical difficulty of handling the boundary condition at infinity in the cylindrical disk geometry is overcome by embedding the disk in a spherical computational space and matching the solutions to analytically tractable spherical functions in the surrounding space. The lowest lying dynamo normal modes for a 'thick' astrophysical disk are calculated. The generated modes found are all oscillatory and spatially localized. Tha potential implications of the results for the properties of dynamo magnetic fields in real astrophysical disks are discussed.

Orientation-controlled parallel assembly at the air-water interface

NASA Astrophysics Data System (ADS)

Park, Kwang Soon; Hao Hoo, Ji; Baskaran, Rajashree; Böhringer, Karl F.

2012-10-01

This paper presents an experimental and theoretical study with statistical analysis of a high-yield, orientation-specific fluidic self-assembly process on a preprogrammed template. We demonstrate self-assembly of thin (less than few hundred microns in thickness) parts, which is vital for many applications in miniaturized platforms but problematic for today's pick-and-place robots. The assembly proceeds row-by-row as the substrate is pulled up through an air-water interface. Experiments and analysis are presented with an emphasis on the combined effect of controlled surface waves and magnetic force. For various gap values between a magnet and Ni-patterned parts, magnetic force distributions are generated using Monte Carlo simulation and employed to predict assembly yield. An analysis of these distributions shows that a gradual decline in yield following the probability density function can be expected with degrading conditions. The experimentally determined critical magnetic force is in good agreement with a derived value from a model of competing forces acting on a part. A general set of design guidelines is also presented from the developed model and experimental data.

Magnetic wire trap arrays for biomarker-based molecular detection

NASA Astrophysics Data System (ADS)

Vieira, Gregory; Mahajan, Kalpesh; Ruan, Gang; Winter, Jessica; Sooryakumar, R.

2012-02-01

Submicrometer-scale magnetic devices built on chip-based platforms have recently been shown to present opportunities for new particle trapping and manipulation technologies. Meanwhile, advances in nanoparticle fabrication allow for the building of custom-made particles with precise control of their size, composition, and other properties such as magnetism, fluorescence, and surface biomarker characteristics. In particular, carefully tailored surface biomarkers facilitate precise binding to targeted molecules, self-actuated construction of hybrid structures, and fluorescence-based detection schemes. Based on these progresses, we present an on-chip detection mechanism for molecules with known surface markers. Hybrid nanostructures consisting of micelle nanoparticles, fluorescent quantum dots, and superparamagnetic iron oxide nanoparticles are used to detect proteins or DNA molecules. The target is detected by the magnetic and fluorescent functionalities of the composite nanostructure, whereas in the absence of the target these signals are not present. Underlying this approach is the simultaneous manipulation via ferromagnetic zigzag nanowire arrays and imaging via quantum dot excitation. This chip-based detection technique could provide a powerful, low cost tool for ultrasensitive molecule detection with ramifications in healthcare diagnostics and small-scale chemical synthesis.

Magnetic Resonance Imaging and Arthroscopic Correlation in Shoulder Instability.

PubMed

Knapik, Derrick M; Voos, James E

2017-12-01

The shoulder is the most inherently unstable joint in the body, prone to high rates of anterior dislocations with subsequent injuries to soft tissue and bony stabilizing structures, resulting in recurrent shoulder instability. Advanced imaging utilizing magnetic resonance (MR) imaging and MR arthrography allows for thorough evaluation of lesions present in the unstable shoulder and is critical for preoperative planning. Arthroscopic shoulder stabilization in the appropriately selected patient can help restore stability and function. This review highlights correlations between MR imaging and arthroscopy of the most commonly reported soft tissue and bony injuries present in patients with shoulder instability.

A new polyester based on allyl α-hydroxy glutarate as shell for magnetite nanoparticles

NASA Astrophysics Data System (ADS)

Nan, Alexandrina; Feher, Ioana Coralia

2017-12-01

Allyl side-chain-functionalized lactide was synthesized from commercially available glutamic acid and polymerized by ring opening polymerization using 4-dimethylaminopyridine as an organocatalyst in the presence of magnetic nanoparticles. The resulting magnetic nanostructures coated with the allyl-containing polyester were then functionalized with cysteine by thiol-ene click reaction leading to highly functionalized magnetic nano-platforms of practical interest. The polyester precursors were characterized by nuclear magnetic resonance and mass spectrometry. The morphology of magnetic nanostructures based on the functionalized polyester was determined by transmission electron microscopy TEM, while the chemical structure was investigated by FT-IR. TGA investigations and the magnetic properties of the magnetic nanostructures are also described.

Computational investigation of spin-polarization in cobalt/graphite superlattices

NASA Astrophysics Data System (ADS)

Goto, Kim F.; Hill, Nicola A.; Sanvito, Stefano

2003-03-01

We present results of a computational investigation of the magnetic properties of cobalt/ graphite superlattices. This work was motivated by experimental data showing spin injection into carbon nanotubes via cobalt contacts [1] as well as the discovery of a magnetic meteorite made from graphite and magnetic particles, in which part of the magnetization is on the carbon atoms [2]. Using density functional theory within the local spin-density approximation (the SIESTA implementation), we show that cobalt induces both n-doping and a magnetic moment in the graphite layers adjacent to the cobalt-carbon interface. We also show that the magnetic properties are strongly affected by the orientation of the graphite. Finally, implications for spin injection and spin-polarized transport are discussed. [1] K. Tsukagoshi, B.W. Alphenaar, and H. Ago, Nature (London) 401, 572 (1999) [2] J.M.D. Coey, M. Venkatesan, C.B. Fitzgerald, A.P. Douvalis and I.S. Sanders, Nature (London) 420, 156 (2002)

Magnetic cluster expansion simulation and experimental study of high temperature magnetic properties of Fe-Cr alloys.

PubMed

Lavrentiev, M Yu; Mergia, K; Gjoka, M; Nguyen-Manh, D; Apostolopoulos, G; Dudarev, S L

2012-08-15

We present a combined experimental and computational study of high temperature magnetic properties of Fe-Cr alloys with chromium content up to about 20 at.%. The magnetic cluster expansion method is applied to model the magnetic properties of random Fe-Cr alloys, and in particular the Curie transition temperature, as a function of alloy composition. We find that at low (3-6 at.%) Cr content the Curie temperature increases with the increase of Cr concentration. It is maximum at approximately 6 at.% Cr and then decreases for higher Cr content. The same feature is found in thermo-magnetic measurements performed on model Fe-Cr alloys, where a 5 at.% Cr alloy has a higher Curie temperature than pure Fe. The Curie temperatures of 10 and 15 at.% Cr alloys are found to be lower than the Curie temperature of pure Fe.

Estimation of electrical conductivity distribution within the human head from magnetic flux density measurement.

PubMed

Gao, Nuo; Zhu, S A; He, Bin

2005-06-07

We have developed a new algorithm for magnetic resonance electrical impedance tomography (MREIT), which uses only one component of the magnetic flux density to reconstruct the electrical conductivity distribution within the body. The radial basis function (RBF) network and simplex method are used in the present approach to estimate the conductivity distribution by minimizing the errors between the 'measured' and model-predicted magnetic flux densities. Computer simulations were conducted in a realistic-geometry head model to test the feasibility of the proposed approach. Single-variable and three-variable simulations were performed to estimate the brain-skull conductivity ratio and the conductivity values of the brain, skull and scalp layers. When SNR = 15 for magnetic flux density measurements with the target skull-to-brain conductivity ratio being 1/15, the relative error (RE) between the target and estimated conductivity was 0.0737 +/- 0.0746 in the single-variable simulations. In the three-variable simulations, the RE was 0.1676 +/- 0.0317. Effects of electrode position uncertainty were also assessed by computer simulations. The present promising results suggest the feasibility of estimating important conductivity values within the head from noninvasive magnetic flux density measurements.

Probing non-collinear magnetism in Ca1-xSrxMn7O12 films by neutron scattering

NASA Astrophysics Data System (ADS)

Huon, Amanda; Grutter, Alexander; Kirby, Brian; Disseler, Steven; Borchers, Julie; Liu, Yaohua; Tian, Wei; Herklotz, Andreas; Lee, Ho Nyung; Fitzsimmons, Michael; May, Steven

CaMn7O12 has been reported to be a single-phase multiferroic quadruple manganite that exhibits both ferroelectricity and helical magnetism below 90 K, but presently no experimental data from bulk or thin films have demonstrated coupling between these two ordering types. Herein, we synthesized epitaxial Ca1-xSrxMn7O12 thin films grown by oxide molecular beam epitaxy and pulsed laser deposition. We utilized neutrons to map out the non-collinear magnetic wavevectors as a function of temperature. To verify whether this coupling is present in our thin films we performed both magnetic and electric field studies. The results highlight the scientific opportunities in using chemical pressure and strain to modify non-collinear magnetism and better understand the link between ferroelectricity and helical magnetism. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists, Office of Science Graduate Student Research (SCGSR) program. The SCGSR program is administered by the Oak Ridge Institute for Science and Education for the DOE under Contract Number DE-SC0014664.

INTERMITTENCY AND MULTIFRACTALITY SPECTRA OF THE MAGNETIC FIELD IN SOLAR ACTIVE REGIONS

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

Abramenko, Valentyna; Yurchyshyn, Vasyl

We present the results of a study of intermittency and multifractality of magnetic structures in solar active regions (ARs). Line-of-sight magnetograms for 214 ARs of different flare productivity observed at the center of the solar disk from 1997 January until 2006 December are utilized. Data from the Michelson Doppler Imager (MDI) instrument on board the Solar and Heliospheric Observatory operating in the high resolution mode, the Big Bear Solar Observatory digital magnetograph, and the Hinode SOT/SP instrument were used. Intermittency spectra were derived from high-order structure functions and flatness functions. The flatness function exponent is a measure of the degreemore » of intermittency. We found that the flatness function exponent at scales below approximately 10 Mm is correlated with flare productivity (the correlation coefficient is -0.63). The Hinode data show that the intermittency regime is extended toward small scales (below 2 Mm) as compared to the MDI data. The spectra of multifractality, derived from the structure functions and flatness functions, are found to be broader for ARs of higher flare productivity as compared to those of low flare productivity. The magnetic structure of high-flaring ARs consists of a voluminous set of monofractals, and this set is much richer than that for low-flaring ARs. The results indicate the relevance of the multifractal organization of the photospheric magnetic fields to the flaring activity. The strong intermittency observed in complex and high-flaring ARs is a hint that we observe a photospheric imprint of enhanced sub-photospheric dynamics.« less

Magnetic bearing reaction wheel. [for spacecraft attitude control

NASA Technical Reports Server (NTRS)

Sabnis, A.; Schmitt, F.; Smith, L.

1976-01-01

The results of a program for the development, fabrication and functional test of an engineering model magnetically suspended reaction wheel are described. The reaction wheel develops an angular momentum of + or - 0.5 foot-pound-second and is intended for eventual application in the attitude control of long-life interplanetary and orbiting spacecraft. A description of the wheel design and its major performance characteristics is presented. Recommendations for flight prototype development are made.

Development of a Novel Method for the Exploration of the Thermal Response of Superfluid Helium Cooled Superconducting Cables to Pulse Heat Loads

NASA Astrophysics Data System (ADS)

Winkler, T.; Koettig, T.; van Weelderen, R.; Bremer, J.; ter Brake, H. J. M.

Management of transient heat deposition in superconducting magnets and its extraction from the aforementioned is becoming increasingly important to bring high energy particle accelerator performance to higher beam energies and intensities. Precise knowledge of transient heat deposition phenomena in the magnet cables will permit to push the operation of these magnets as close as possible to their current sharing limit, without unduly provoking magnet quenches. With the prospect of operating the Large Hadron Collider at CERN at higher beam energies and intensities an investigation into the response to transient heat loads of LHC magnets, operating in pressurized superfluid helium, is being performed. The more frequently used approach mimics the cable geometry by resistive wires and uses Joule-heating to deposit energy. Instead, to approximate as closely as possible the real magnet conditions, a novel method for depositing heat in cable stacks made out of superconducting magnet-cables has been developed. The goal is to measure the temperature difference as a function of time between the cable stack and the superfluid helium bath depending on heat load and heat pulse length. The heat generation in the superconducting cable and precise measurement of small temperature differences are major challenges. The functional principle and experimental set-up are presented together with proof of principle measurements.

Experimental determination of the frequency and field dependence of Specific Loss Power in Magnetic Fluid Hyperthermia

NASA Astrophysics Data System (ADS)

Cobianchi, M.; Guerrini, A.; Avolio, M.; Innocenti, C.; Corti, M.; Arosio, P.; Orsini, F.; Sangregorio, C.; Lascialfari, A.

2017-12-01

Magnetic nanoparticles are promising systems for biomedical applications and in particular for Magnetic Fluid Hyperthermia, a therapy that utilizes the heat released by such systems to damage tumor cells. We present an experimental study of the physical properties that influences the capability of heat release, i.e. the Specific Loss Power, SLP, of three biocompatible ferrofluid samples having a magnetic core of maghemite with different diameter d = 10.2, 14.6 and 19.7 nm. The SLP was measured as a function of frequency f and intensity H of the applied alternating magnetic field, and it turned out to depend on the core diameter, as expected. The results allowed us to highlight experimentally that the physical mechanism responsible for the heating is size-dependent and to establish, at applied constant frequency, the phenomenological functional relationship SLP = c·Hx, with 2 ≤ x<3 for all samples. The x-value depends on sample size and field frequency, here chosen in the typical range of operating magnetic hyperthermia devices. For the smallest sample, the effective relaxation time τeff ≈ 19.5 ns obtained from SLP data is in agreement with the value estimated from magnetization data, thus confirming the validity of the Linear Response Theory model for this system at properly chosen field intensity and frequency.

Biogenic Magnetite and EMF Effects

NASA Astrophysics Data System (ADS)

Kirschvink, Joseph L.

1996-03-01

Magnetite biomineralization is a genetically-controlled biochemical process through which organisms make perfect ferrimagnetic crystals, usually of single magnetic domain size. This process is an ancient one, having evolved about 2 billion years ago in the magnetotactic bacteria, and presumably was incorporated in the genome of higher organisms, including humans. During this time, DNA replication, protein synthesis, and many other biochemical processes have functioned in the presence of strong static fields of up to 400 mT adjacent to these magnetosomes without any obvious deleterious effects. Recent behavioral experiments using short but strong magnetic pulses in honeybees and birds demonstrates that ferromagnetic materials are involved in the sensory transduction of geomagnetic field information to the nervous system, and both behavioral and direct electrophysiological experiments indicate sensitivity thresholds to DC magnetic fields down to a few nT. However, far more biogenic magnetite is present in animal tissues than is needed for magnetoreception, and the biological function of this extra material is unknown. The presence of ferromagnetic materials in biological systems could provide physical transduction mechanisms for ELF magnetic fields, as well for microwave radiation in the .5 to 10 GHz band where magnetite has its peak ferromagnetic resonance. Elucidation of the cellular ultrastructure and biological function(s) of magnetite might help resolve the question of whether anthropogenic EMFs can cause deleterious biological effects. This work has been supported by grants from the NIH and EPRI.

Experimental High Temperature Characterization of a Magnetic Bearing for Turbomachinery

NASA Technical Reports Server (NTRS)

Montague, Gerald; Jansen, Mark; Provenza, Andrew; Palazzolo, Alan; Jansen, Ralph; Ebihara, Ben

2003-01-01

Open loop, experimental force and power measurements of a radial, redundant-axis, magnetic bearing at temperatures to 1000 F (538 C) and rotor speeds to 15,000 RPM along with theoretical temperature and force models are presented in this paper. The experimentally measured force produced by a single C-core using 22A was 600 lb. (2.67 kN) at room temperature and 380 lb. (1.69 kN) at 1000 F (538 C). These values were compared with force predictions based on a 1D magnetic circuit analysis and a thermal analysis of gap growth as a function of temperature. Tests under rotating conditions showed that rotor speed has a negligible effect on the bearing s load capacity. One C-core required approximately 340 W of power to generate 190 lb. (8.45 kN) of magnetic force at 1000 F (538 C); however the magnetic air gap was much larger than at room temperature. The data presented is after the bearing had already operated six thermal cycles and eleven total (not consecutive) hours at 1000 F (538 C).

Dual immobilization and magnetic manipulation of magnetic nanoparticles

NASA Astrophysics Data System (ADS)

Yang, S. Y.; Jian, Z. F.; Horng, H. E.; Hong, Chin-Yih; Yang, H. C.; Wu, C. C.; Lee, Y. H.

By suitably bio-functionalizing the surfaces, magnetic nanoparticles are able to bind specific biomolecules, and may serve as vectors for delivering bio-entities to target tissues. In this work, the synthesis of bio-functionalized magnetic nanoparticles with two kinds of bio-probes is developed. Here, the stem cell is selected as a to-be-delivered bio-entity and infarcted myocardium is the target issue. Thus, cluster designation-34 (CD-34) on stem cell and creatine kinase-MB (CK-MB) (or troponin I) on infarcted myocardium are the specific biomolecules to be bound with bio-functionalized magnetic nanoparticles. In addition to demonstrating the co-coating of two kinds of bio-probes on a magnetic nanoparticle, the feasibility of manipulation on bio-functionalized magnetic nanoparticles by external magnetic fields is investigated.

Application of sensitivity-analysis techniques to the calculation of topological quantities

NASA Astrophysics Data System (ADS)

Gilchrist, Stuart

2017-08-01

Magnetic reconnection in the corona occurs preferentially at sites where the magnetic connectivity is either discontinuous or has a large spatial gradient. Hence there is a general interest in computing quantities (like the squashing factor) that characterize the gradient in the field-line mapping function. Here we present an algorithm for calculating certain (quasi)topological quantities using mathematical techniques from the field of ``sensitivity-analysis''. The method is based on the calculation of a three dimensional field-line mapping Jacobian from which all the present topological quantities of interest can be derived. We will present the algorithm and the details of a publicly available set of libraries that implement the algorithm.

Using Redundancy To Reduce Errors in Magnetometer Readings

NASA Technical Reports Server (NTRS)

Kulikov, Igor; Zak, Michail

2004-01-01

A method of reducing errors in noisy magnetic-field measurements involves exploitation of redundancy in the readings of multiple magnetometers in a cluster. By "redundancy"is meant that the readings are not entirely independent of each other because the relationships among the magnetic-field components that one seeks to measure are governed by the fundamental laws of electromagnetism as expressed by Maxwell's equations. Assuming that the magnetometers are located outside a magnetic material, that the magnetic field is steady or quasi-steady, and that there are no electric currents flowing in or near the magnetometers, the applicable Maxwell 's equations are delta x B = 0 and delta(raised dot) B = 0, where B is the magnetic-flux-density vector. By suitable algebraic manipulation, these equations can be shown to impose three independent constraints on the values of the components of B at the various magnetometer positions. In general, the problem of reducing the errors in noisy measurements is one of finding a set of corrected values that minimize an error function. In the present method, the error function is formulated as (1) the sum of squares of the differences between the corrected and noisy measurement values plus (2) a sum of three terms, each comprising the product of a Lagrange multiplier and one of the three constraints. The partial derivatives of the error function with respect to the corrected magnetic-field component values and the Lagrange multipliers are set equal to zero, leading to a set of equations that can be put into matrix.vector form. The matrix can be inverted to solve for a vector that comprises the corrected magnetic-field component values and the Lagrange multipliers.

Rapid and continuous magnetic separation in droplet microfluidic devices

DOE PAGES

Brouzes, Eric; Kruse, Travis; Kimmerling, Robert; ...

2014-12-03

Here, we present a droplet microfluidic method to extract molecules of interest from a droplet in a rapid and continuous fashion. We accomplish this by first marginalizing functionalized super-paramagnetic beads within the droplet using a magnetic field, and then splitting the droplet into one droplet containing the majority of magnetic beads and one droplet containing the minority fraction. We quantitatively analysed the factors which affect the efficiency of marginalization and droplet splitting to optimize the enrichment of magnetic beads. We first characterized the interplay between the droplet velocity and the strength of the magnetic field and its effect on marginalization.more » We found that marginalization is optimal at the midline of the magnet and that marginalization is a good predictor of bead enrichment through splitting at low to moderate droplet velocities. Finally, we focused our efforts on manipulating the splitting profile to improve the enrichment provided by asymmetric splitting. We designed asymmetric splitting forks that employ capillary effects to preferentially extract the bead-rich regions of the droplets. Our strategy represents a framework to optimize magnetic bead enrichment methods tailored to the requirements of specific droplet-based applications. We anticipate that our separation technology is well suited for applications in single-cell genomics and proteomics. In particular, our method could be used to separate mRNA bound to poly-dT functionalized magnetic microparticles from single cell lysates to prepare single-cell cDNA libraries.« less

Stabilization and functionalization of iron oxide nanoparticles for biomedical applications

NASA Astrophysics Data System (ADS)

Amstad, Esther; Textor, Marcus; Reimhult, Erik

2011-07-01

Superparamagnetic iron oxide nanoparticles (NPs) are used in a rapidly expanding number of research and practical applications in the biomedical field, including magnetic cell labeling separation and tracking, for therapeutic purposes in hyperthermia and drug delivery, and for diagnostic purposes, e.g., as contrast agents for magnetic resonance imaging. These applications require good NP stability at physiological conditions, close control over NP size and controlled surface presentation of functionalities. This review is focused on different aspects of the stability of superparamagnetic iron oxide NPs, from its practical definition to its implementation by molecular design of the dispersant shell around the iron oxide core and further on to its influence on the magnetic properties of the superparamagnetic iron oxide NPs. Special attention is given to the selection of molecular anchors for the dispersant shell, because of their importance to ensure colloidal and functional stability of sterically stabilized superparamagnetic iron oxide NPs. We further detail how dispersants have been optimized to gain close control over iron oxide NP stability, size and functionalities by independently considering the influences of anchors and the attached sterically repulsive polymer brushes. A critical evaluation of different strategies to stabilize and functionalize core-shell superparamagnetic iron oxide NPs as well as a brief introduction to characterization methods to compare those strategies is given.Superparamagnetic iron oxide nanoparticles (NPs) are used in a rapidly expanding number of research and practical applications in the biomedical field, including magnetic cell labeling separation and tracking, for therapeutic purposes in hyperthermia and drug delivery, and for diagnostic purposes, e.g., as contrast agents for magnetic resonance imaging. These applications require good NP stability at physiological conditions, close control over NP size and controlled surface presentation of functionalities. This review is focused on different aspects of the stability of superparamagnetic iron oxide NPs, from its practical definition to its implementation by molecular design of the dispersant shell around the iron oxide core and further on to its influence on the magnetic properties of the superparamagnetic iron oxide NPs. Special attention is given to the selection of molecular anchors for the dispersant shell, because of their importance to ensure colloidal and functional stability of sterically stabilized superparamagnetic iron oxide NPs. We further detail how dispersants have been optimized to gain close control over iron oxide NP stability, size and functionalities by independently considering the influences of anchors and the attached sterically repulsive polymer brushes. A critical evaluation of different strategies to stabilize and functionalize core-shell superparamagnetic iron oxide NPs as well as a brief introduction to characterization methods to compare those strategies is given. This article was submitted as part of a collection of articles on surface nanotechnology for biological applications. Other papers on this topic can be found in issue 2 of vol. 3 (2011). This issue can be found from the Nanoscale homepage [http://www.rsc.org/nanoscale].

Magnetism by embedding 3d transition metal atoms into germanene

NASA Astrophysics Data System (ADS)

Sharma, Durgesh Kumar; Kumar, Sudhir; Auluck, Sushil

2018-06-01

We have performed a series of first-principles calculations within the framework of density functional theory for germanene including mono vacancy (MV) and double vacancy (DV). Perdew–Burke–Ernzerhof generalized gradient approximation (GGA) in the form of exchange-correlation potential was used. Ten transition metals (TMs) i.e. Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn, have been embedded at MV and DV site for the purpose to introduce magnetism into germanene. We find TM embedded germanene is stable and the value of magnetic moment can be tune with the TM impurities. Further, carbon (C) or nitrogen (N) in the vicinity of MV has been considered to find its influence on stability and total magnetic moment. Present predictions indicate Mn impurity shows largest magnetic moment among considered ten TMs. The Heyd–Scuseria–Ernzerhof (HSE06) hybrid functional based calculations have been also carried out for Mn system only for shake of comparison standpoint. The GGA/HSE06 calculations show better stability of TM embedded germanene after doping of C or N in vicinity of TM. Our calculations may provide a promising approach to design germanene based spintronic devices.

An interchangeable scanning Hall probe/scanning SQUID microscope

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

Tang, Chiu-Chun; Lin, Hui-Ting; Wu, Sing-Lin

2014-08-15

We have constructed a scanning probe microscope for magnetic imaging, which can function as a scanning Hall probe microscope (SHPM) and as a scanning SQUID microscope (SSM). The scanning scheme, applicable to SHPM and SSM, consists of a mechanical positioning (sub) micron-XY stage and a flexible direct contact to the sample without a feedback control system for the Z-axis. With the interchangeable capability of operating two distinct scanning modes, our microscope can incorporate the advantageous functionalities of the SHPM and SSM with large scan range up to millimeter, high spatial resolution (⩽4 μm), and high field sensitivity in a widemore » range of temperature (4.2 K-300 K) and magnetic field (10{sup −7} T-1 T). To demonstrate the capabilities of the system, we present magnetic images scanned with SHPM and SSM, including a RbFeB magnet and a nickel grid pattern at room temperature, surface magnetic domain structures of a La{sub 2/3}Ca{sub 1/3}MnO{sub 3} thin film at 77 K, and superconducting vortices in a striped niobium film at 4.2 K.« less

Investigation of electronic and magnetic properties of Ni0.5Cu0.5Fe2O4: theoretical and experimental

NASA Astrophysics Data System (ADS)

Sharma, Uma Shankar; Shah, Rashmi

2018-05-01

In present study, Ni0.5Cu0.5Fe2O4 been was synthesized with Co-precipitation method and prepared samples were annealed at 300°C and 500°C. The single phase formation of nickel ferrite was confirmed through powder X-ray diffraction (XRD). The presence of various functional groups was confirmed through FTIR analysis. The effects of the annealing temperature on the particle sizes and magnetic properties of the ferrite samples were investigated and interpret with valid reasons. The structural and magnetic properties of the ferrite samples were strongly affected by the annealing temperature. The annealing temperature increases coercivity and saturation magnetization values are continuously increased. Spin­ polarization calculations are performed on the Ni0.5Cu0.5Fe2O4, compounds within density functional theory (DFT) and find out equilibrium lattice constants 8.2 Å and DOS show there exists large spin splitting between the spin up and spin down channels near the Fermi level confirm p-d hybridization. The theoretical calculated magnetic are slightly higher than our experimental results. The other results have been discussed in detail.

Particle acceleration magnetic field generation, and emission in Relativistic pair jets

NASA Technical Reports Server (NTRS)

Nishikawa, K.-I.; Ramirez-Ruiz, E.; Hardee, P.; Hededal, C.; Kouveliotou, C.; Fishman, G. J.

2005-01-01

Plasma waves and their associated instabilities (e.g., the Buneman instability, two-streaming instability, and the Weibel instability) are responsible for particle acceleration in relativistic pair jets. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic pair jet propagating through a pair plasma. Simulations show that the Weibel instability created in the collisionless shock accelerates particles perpendicular and parallel to the jet propagation direction. Simulation results show that this instability generates and amplifies highly nonuniform, small-scale magnetic fields, which contribute to the electron's transverse deflection behind the jet head. The "jitter' I radiation from deflected electrons can have different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants. The growth rate of the Weibel instability and the resulting particle acceleration depend on the magnetic field strength and orientation, and on the initial particle distribution function. In this presentation we explore some of the dependencies of the Weibel instability and resulting particle acceleration on the magnetic field strength and orientation, and the particle distribution function.

Functional cardiac magnetic resonance microscopy

NASA Astrophysics Data System (ADS)

Brau, Anja Christina Sophie

2003-07-01

The study of small animal models of human cardiovascular disease is critical to our understanding of the origin, progression, and treatment of this pervasive disease. Complete analysis of disease pathophysiology in these animal models requires measuring structural and functional changes at the level of the whole heart---a task for which an appropriate non-invasive imaging method is needed. The purpose of this work was thus to develop an imaging technique to support in vivo characterization of cardiac structure and function in rat and mouse models of cardiovascular disease. Whereas clinical cardiac magnetic resonance imaging (MRI) provides accurate assessment of the human heart, the extension of cardiac MRI from humans to rodents presents several formidable scaling challenges. Acquiring images of the mouse heart with organ definition and fluidity of contraction comparable to that achieved in humans requires an increase in spatial resolution by a factor of 3000 and an increase in temporal resolution by a factor of ten. No single technical innovation can meet the demanding imaging requirements imposed by the small animal. A functional cardiac magnetic resonance microscopy technique was developed by integrating improvements in physiological control, imaging hardware, biological synchronization of imaging, and pulse sequence design to achieve high-quality images of the murine heart with high spatial and temporal resolution. The specific methods and results from three different sets of imaging experiments are presented: (1) 2D functional imaging in the rat with spatial resolution of 175 mum2 x 1 mm and temporal resolution of 10 ms; (2) 3D functional imaging in the rat with spatial resolution of 100 mum 2 x 500 mum and temporal resolution of 30 ms; and (3) 2D functional imaging in the mouse with spatial resolution down to 100 mum2 x 1 mm and temporal resolution of 10 ms. The cardiac microscopy technique presented here represents a novel collection of technologies capable of acquiring routine high-quality images of murine cardiac structure and function with minimal artifacts and markedly higher spatial resolution compared to conventional techniques. This work is poised to serve a valuable role in the evaluation of cardiovascular disease and should find broad application in studies ranging from basic pathophysiology to drug discovery.

[Functional magnetic resonance imaging in psychiatry and psychotherapy].

PubMed

Derntl, B; Habel, U; Schneider, F

2010-01-01

technical improvements, functional magnetic resonance imaging (fMRI) has become the most popular and versatile imaging method in psychiatric research. The scope of this manuscript is to briefly introduce the basics of MR physics, the blood oxygenation level-dependent (BOLD) contrast as well as the principles of MR study design and functional data analysis. The presentation of exemplary studies on emotion recognition and empathy in schizophrenia patients will highlight the importance of MR methods in psychiatry. Finally, we will demonstrate insights into new developments that will further boost MR techniques in clinical research and will help to gain more insight into dysfunctional neural networks underlying cognitive and emotional deficits in psychiatric patients. Moreover, some techniques such as neurofeedback seem promising for evaluation of therapy effects on a behavioral and neural level.

Research with Transcranial Magnetic Stimulation in the Treatment of Aphasia

PubMed Central

Martin, Paula I; Naeser, Margaret A.; Ho, Michael; Treglia, Ethan; Kaplan, Elina; Baker, Errol H.; Pascual-Leone, Alvaro

2010-01-01

Repetitive transcranial magnetic stimulation (rTMS) has been used to improve language behavior, including naming, in stroke patients with chronic, nonfluent aphasia. Part 1 of this paper reviews functional imaging studies related to language recovery in aphasia. Part 2 reviews the rationale for using rTMS to treat nonfluent aphasia (based on functional imaging); and presents our current rTMS protocol. We present language results from our rTMS studies, and imaging results from overt naming fMRI scans obtained pre- and post- a series of rTMS treatments. Part 3 presents results from a pilot study where rTMS treatments were followed immediately by constraint-induced language therapy. Part 4 reviews our diffusion tensor imaging study that examined possible connectivity of arcuate fasciculus to different parts of Broca’s area (pars triangularis, PTr; pars opercularis, POp); and to ventral premotor cortex (vPMC). The potential role of mirror neurons in R POp and vPMC in aphasia recovery is discussed. PMID:19818232

Statistical Study of Interplanetary Coronal Mass Ejections with Strong Magnetic Fields

NASA Astrophysics Data System (ADS)

Murphy, Matthew E.

Coronal Mass Ejections (CMEs) with strong magnetic fields (B ) are typically associated with significant Solar Energetic Particle (SEP) events, high solar wind speed and solar flare events. Successful prediction of the arrival time of a CME at Earth is required to maximize the time available for satellite, infrastructure, and space travel programs to take protective action against the coming flux of high-energy particles. It is known that the magnetic field strength of a CME is linked to the strength of a geomagnetic storm on Earth. Unfortunately, the correlations between strong magnetic field CMEs from the entire sun (especially from the far side or non-Earth facing side of the sun) to SEP and flare events, solar source regions and other relevant solar variables are not well known. New correlation studies using an artificial intelligence engine (Eureqa) were performed to study CME events with magnetic field strength readings over 30 nanoteslas (nT) from January 2010 to October 17, 2014. This thesis presents the results of this study, validates Eureqa to obtain previously published results, and presents previously unknown functional relationships between solar source magnetic field data, CME initial speed and the CME magnetic field. These new results enable the development of more accurate CME magnetic field predictions and should help scientists develop better forecasts thereby helping to prevent damage to humanity's space and Earth assets.

Chemically engineered graphene-based 2D organic molecular magnet.

PubMed

Hong, Jeongmin; Bekyarova, Elena; de Heer, Walt A; Haddon, Robert C; Khizroev, Sakhrat

2013-11-26

Carbon-based magnetic materials and structures of mesoscopic dimensions may offer unique opportunities for future nanomagnetoelectronic/spintronic devices. To achieve their potential, carbon nanosystems must have controllable magnetic properties. We demonstrate that nitrophenyl functionalized graphene can act as a room-temperature 2D magnet. We report a comprehensive study of low-temperature magnetotransport, vibrating sample magnetometry (VSM), and superconducting quantum interference (SQUID) measurements before and after radical functionalization. Following nitrophenyl (NP) functionalization, epitaxially grown graphene systems can become organic molecular magnets with ferromagnetic and antiferromagnetic ordering that persists at temperatures above 400 K. The field-dependent, surface magnetoelectric properties were studied using scanning probe microscopy (SPM) techniques. The results indicate that the NP-functionalization orientation and degree of coverage directly affect the magnetic properties of the graphene surface. In addition, graphene-based organic magnetic nanostructures were found to demonstrate a pronounced magneto-optical Kerr effect (MOKE). The results were consistent across different characterization techniques and indicate room-temperature magnetic ordering along preferred graphene orientations in the NP-functionalized samples. Chemically isolated graphene nanoribbons (CINs) were observed along the preferred functionality directions. These results pave the way for future magnetoelectronic/spintronic applications based on promising concepts such as current-induced magnetization switching, magnetoelectricity, half-metallicity, and quantum tunneling of magnetization.

Comprehensive Evaluation of Attitude and Orbit Estimation Using Actual Earth Magnetic Field Data

NASA Technical Reports Server (NTRS)

Deutschmann, Julie K.; Bar-Itzhack, Itzhack Y.

2000-01-01

A single, augmented Extended Kalman Filter (EKF), which simultaneously and autonomously estimates spacecraft attitude and orbit has been developed and successfully tested with real magnetometer and gyro data only. Because the earth magnetic field is a function of time and position, and because time is known quite precisely, the differences between the computed and measured magnetic field components, as measured by the magnetometers throughout the entire spacecraft orbit, are a function of both orbit and attitude errors. Thus, conceivably these differences could be used to estimate both orbit and attitude; an observability study validated this assumption. The results of testing the EKF with actual magnetometer and gyro data, from four satellites supported by the NASA Goddard Space Flight Center (GSFC) Guidance, Navigation, and Control Center, are presented and evaluated. They confirm the assumption that a single EKF can estimate both attitude and orbit when using gyros and magnetometers only.

Non-invasive and high-sensitivity scanning detection of magnetic nanoparticles in animals using high-Tc scanning superconducting-quantum-interference-device biosusceptometry.

PubMed

Chieh, J J; Hong, C Y

2011-08-01

Although magnetic nanoparticles (MNPs) have been widely applied to animals in biomedicine, MNPs within animals should be examined in real time, in vivo, and without bio-damaged possibility to evaluate whether the bio-function of MNPs is valid or to further controls the biomedicinal process because of accompanying complex problems such as MNPs distribution and MNPs biodegradation. The non-invasive and high-sensitivity scanning detection of MNPs in animals using ac susceptometry based on a high-T(c) superconducting quantum interference device (SQUID) is presented. The non-invasive results and biopsy results show good agreement, and two gold-standard biomedicine methods, Prussian blue stain and inductively coupled plasma, prove the magnetic results. This confirms that the future clinical diagnosis of bio-functional MNPs could be operated by using scanning SQUID biosusceptometry as conveniently as an ultrasonic probe.

Self-constrained inversion of potential fields

NASA Astrophysics Data System (ADS)

Paoletti, V.; Ialongo, S.; Florio, G.; Fedi, M.; Cella, F.

2013-11-01

We present a potential-field-constrained inversion procedure based on a priori information derived exclusively from the analysis of the gravity and magnetic data (self-constrained inversion). The procedure is designed to be applied to underdetermined problems and involves scenarios where the source distribution can be assumed to be of simple character. To set up effective constraints, we first estimate through the analysis of the gravity or magnetic field some or all of the following source parameters: the source depth-to-the-top, the structural index, the horizontal position of the source body edges and their dip. The second step is incorporating the information related to these constraints in the objective function as depth and spatial weighting functions. We show, through 2-D and 3-D synthetic and real data examples, that potential field-based constraints, for example, structural index, source boundaries and others, are usually enough to obtain substantial improvement in the density and magnetization models.

Electrical conductivity of the Earth's mantle from the first Swarm magnetic field measurements

NASA Astrophysics Data System (ADS)

Civet, F.; Thébault, E.; Verhoeven, O.; Langlais, B.; Saturnino, D.

2015-05-01

We present a 1-D electrical conductivity profile of the Earth's mantle down to 2000 km derived from L1b Swarm satellite magnetic field measurements from November 2013 to September 2014. We first derive a model for the main magnetic field, correct the data for a lithospheric field model, and additionally select the data to reduce the contributions of the ionospheric field. We then model the primary and induced magnetospheric fields for periods between 2 and 256 days and perform a Bayesian inversion to obtain the probability density function for the electrical conductivity as function of depth. The conductivity increases by 3 orders of magnitude in the 400-900 km depth range. Assuming a pyrolitic mantle composition, this profile is interpreted in terms of temperature variations leading to a temperature gradient in the lower mantle that is close to adiabatic.

Beyond static measures: A review of functional magnetic resonance spectroscopy and its potential to investigate dynamic glutamatergic abnormalities in schizophrenia.

PubMed

Jelen, Luke A; King, Sinead; Mullins, Paul G; Stone, James M

2018-05-01

Abnormalities of the glutamate system are increasingly implicated in schizophrenia but their exact nature remains unknown. Proton magnetic resonance spectroscopy ( 1 H-MRS), while fundamental in revealing glutamatergic alterations in schizophrenia, has, until recently, been significantly limited and thought to only provide static measures. Functional magnetic resonance spectroscopy (fMRS), which uses sequential scans for dynamic measurement of a range of brain metabolites in activated brain areas, has lately been applied to a variety of task or stimulus conditions, producing interesting insights into neurometabolite responses to neural activation. Here, we summarise the existing 1 H-MRS studies of brain glutamate in schizophrenia. We then present a comprehensive review of research studies that have utilised fMRS, and lastly consider how fMRS methods might further the understanding of glutamatergic abnormalities in schizophrenia.

The converse approach to NMR chemical shifts from first-principles: application to finite and infinite aromatic compounds

NASA Astrophysics Data System (ADS)

Thonhauser, T.; Ceresoli, D.; Marzari, N.

2009-03-01

We present first-principles, density-functional theory calculations of the NMR chemical shifts for polycyclic aromatic hydrocarbons, starting with benzene and increasing sizes up to the one- and two-dimensional infinite limits of graphene ribbons and sheets. Our calculations are performed using a combination of the recently developed theory of orbital magnetization in solids, and a novel approach to NMR calculations where chemical shifts are obtained from the derivative of the orbital magnetization with respect to a microscopic, localized magnetic dipole. Using these methods we study on equal footing the ^1H and ^13C shifts in benzene, pyrene, coronene, in naphthalene, anthracene, naphthacene, and pentacene, and finally in graphene, graphite, and an infinite graphene ribbon. Our results show very good agreement with experiments and allow us to characterize the trends for the chemical shifts as a function of system size.

Colossal intrinsic magnetoelectric effect in Pb(Fe2/3W1/3)0.83Ti0.17O3

NASA Astrophysics Data System (ADS)

Fraygola, B.; Coelho, Adelino A.; Garcia, D.; Eiras, J. A.

2012-08-01

Dielectric and magnetic properties were investigated in Pb(Fe2/3W1/3)0.83Ti0.17O3 ceramics. The dielectric constant in these samples exhibits colossal changes at the magnetic ordering temperature under the presence of bias external electric fields, which presents a close connection with magnetoelectrics effects (ME), confirming the possibility to control magnetic proprieties with electric fields. The ferroelectromagnetoelastic coefficient was determined from the dielectric response as a function of the electric field. The analysis of magnetic and dielectric susceptibilities based on the Landau-Devonshire thermodynamic formalisms indicates that the ME effects is a contribution of intrinsic ME coupling and a field dependent term.

Modelling of resonant MEMS magnetic field sensor with electromagnetic induction sensing

NASA Astrophysics Data System (ADS)

Liu, Song; Xu, Huaying; Xu, Dehui; Xiong, Bin

2017-06-01

This paper presents an analytical model of resonant MEMS magnetic field sensor with electromagnetic induction sensing. The resonant structure vibrates in square extensional (SE) mode. By analyzing the vibration amplitude and quality factor of the resonant structure, the magnetic field sensitivity as a function of device structure parameters and encapsulation pressure is established. The developed analytical model has been verified by comparing calculated results with experiment results and the deviation between them is only 10.25%, which shows the feasibility of the proposed device model. The model can provide theoretical guidance for further design optimization of the sensor. Moreover, a quantitative study of the magnetic field sensitivity is conducted with respect to the structure parameters and encapsulation pressure based on the proposed model.

Electron beam therapy with coil-generated magnetic fields.

PubMed

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

2004-06-01

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

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

Sadovnikov, A. V., E-mail: sadovnikovav@gmail.com; Nikitov, S. A.; Kotel'nikov Institute of Radioengineering and Electronics, Russian Academy of Sciences, Moscow 125009

Using the space-resolved Brillouin light scattering spectroscopy we study the transformation of dynamic magnetization patterns in a bilayer multiferroic structure. We show that in the comparison with a single yttrium iron garnet (YIG) film magnetization distribution is transformed in the bilayer structure due to the coupling of waves propagating both in an YIG film (magnetic layer) and in a barium strontium titanate slab (ferroelectric layer). We present a simple electrodynamic model using the numerical finite element method to show the transformation of eigenmode spectrum of confined multiferroic. In particular, we demonstrate that the control over the dynamic magnetization and themore » transformation of spatial profiles of transverse modes in magnetic film of the bilayer structure can be performed by the tuning of the wavevectors of transverse modes. The studied confined multiferroic stripe can be utilized for fabrication of integrated dual tunable functional devices for magnonic applications.« less

Design of portable electric and magnetic field generators

NASA Astrophysics Data System (ADS)

Stewart, M. G.; Siew, W. H.; Campbell, L. C.; Stewart, M. G.; Siew, W. H.

2000-11-01

Electric and magnetic field generators capable of producing high-amplitude output are not readily available. This presents difficulties for electromagnetic compatibility testing of new measurement systems where these systems are intended to operate in a particularly hostile electromagnetic environment. A portable electric and a portable magnetic field generator having high pulsed field output are described in this paper. The output of these generators were determined using an electromagnetic-compatible measurement system. These generators allow immunity testing in the laboratory of electronic systems to very high electrical fields, as well as for functional verification of the electronic systems on site. In the longer term, the basic design of the magnetic field generator may be developed as the generator to provide the damped sinusoid magnetic field specified in IEC 61000-4-10, which is adopted in BS EN 61000-4-10.

Magnetic Flux Distribution of Linear Machines with Novel Three-Dimensional Hybrid Magnet Arrays

PubMed Central

Yao, Nan; Yan, Liang; Wang, Tianyi; Wang, Shaoping

2017-01-01

The objective of this paper is to propose a novel tubular linear machine with hybrid permanent magnet arrays and multiple movers, which could be employed for either actuation or sensing technology. The hybrid magnet array produces flux distribution on both sides of windings, and thus helps to increase the signal strength in the windings. The multiple movers are important for airspace technology, because they can improve the system’s redundancy and reliability. The proposed design concept is presented, and the governing equations are obtained based on source free property and Maxwell equations. The magnetic field distribution in the linear machine is thus analytically formulated by using Bessel functions and harmonic expansion of magnetization vector. Numerical simulation is then conducted to validate the analytical solutions of the magnetic flux field. It is proved that the analytical model agrees with the numerical results well. Therefore, it can be utilized for the formulation of signal or force output subsequently, depending on its particular implementation. PMID:29156577

Majority logic gate for 3D magnetic computing.

PubMed

Eichwald, Irina; Breitkreutz, Stephan; Ziemys, Grazvydas; Csaba, György; Porod, Wolfgang; Becherer, Markus

2014-08-22

For decades now, microelectronic circuits have been exclusively built from transistors. An alternative way is to use nano-scaled magnets for the realization of digital circuits. This technology, known as nanomagnetic logic (NML), may offer significant improvements in terms of power consumption and integration densities. Further advantages of NML are: non-volatility, radiation hardness, and operation at room temperature. Recent research focuses on the three-dimensional (3D) integration of nanomagnets. Here we show, for the first time, a 3D programmable magnetic logic gate. Its computing operation is based on physically field-interacting nanometer-scaled magnets arranged in a 3D manner. The magnets possess a bistable magnetization state representing the Boolean logic states '0' and '1.' Magneto-optical and magnetic force microscopy measurements prove the correct operation of the gate over many computing cycles. Furthermore, micromagnetic simulations confirm the correct functionality of the gate even for a size in the nanometer-domain. The presented device demonstrates the potential of NML for three-dimensional digital computing, enabling the highest integration densities.

Analytical modeling of hyperthermia using magnetic nanoparticles

NASA Astrophysics Data System (ADS)

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

2018-06-01

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

Magnetic Flux Distribution of Linear Machines with Novel Three-Dimensional Hybrid Magnet Arrays.

PubMed

Yao, Nan; Yan, Liang; Wang, Tianyi; Wang, Shaoping

2017-11-18

The objective of this paper is to propose a novel tubular linear machine with hybrid permanent magnet arrays and multiple movers, which could be employed for either actuation or sensing technology. The hybrid magnet array produces flux distribution on both sides of windings, and thus helps to increase the signal strength in the windings. The multiple movers are important for airspace technology, because they can improve the system's redundancy and reliability. The proposed design concept is presented, and the governing equations are obtained based on source free property and Maxwell equations. The magnetic field distribution in the linear machine is thus analytically formulated by using Bessel functions and harmonic expansion of magnetization vector. Numerical simulation is then conducted to validate the analytical solutions of the magnetic flux field. It is proved that the analytical model agrees with the numerical results well. Therefore, it can be utilized for the formulation of signal or force output subsequently, depending on its particular implementation.

Lens-free imaging of magnetic particles in DNA assays.

PubMed

Colle, Frederik; Vercruysse, Dries; Peeters, Sara; Liu, Chengxun; Stakenborg, Tim; Lagae, Liesbet; Del-Favero, Jurgen

2013-11-07

We present a novel opto-magnetic system for the fast and sensitive detection of nucleic acids. The system is based on a lens-free imaging approach resulting in a compact and cheap optical readout of surface hybridized DNA fragments. In our system magnetic particles are attracted towards the detection surface thereby completing the labeling step in less than 1 min. An optimized surface functionalization combined with magnetic manipulation was used to remove all nonspecifically bound magnetic particles from the detection surface. A lens-free image of the specifically bound magnetic particles on the detection surface was recorded by a CMOS imager. This recorded interference pattern was reconstructed in software, to represent the particle image at the focal distance, using little computational power. As a result we were able to detect DNA concentrations down to 10 pM with single particle sensitivity. The possibility of integrated sample preparation by manipulation of magnetic particles, combined with the cheap and highly compact lens-free detection makes our system an ideal candidate for point-of-care diagnostic applications.

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.

Composite iron oxide-Prussian blue nanoparticles for magnetically guided T1-weighted magnetic resonance imaging and photothermal therapy of tumors.

PubMed

Kale, Shraddha S; Burga, Rachel A; Sweeney, Elizabeth E; Zun, Zungho; Sze, Raymond W; Tuesca, Anthony; Subramony, J Anand; Fernandes, Rohan

2017-01-01

Theranostic nanoparticles offer the potential for mixing and matching disparate diagnostic and therapeutic functionalities within a single nanoparticle for the personalized treatment of diseases. In this article, we present composite iron oxide-gadolinium-containing Prussian blue nanoparticles (Fe 3 O 4 @GdPB) as a novel theranostic agent for T 1 -weighted magnetic resonance imaging (MRI) and photothermal therapy (PTT) of tumors. These particles combine the well-described properties and safety profiles of the constituent Fe 3 O 4 nanoparticles and gadolinium-containing Prussian blue nanoparticles. The Fe 3 O 4 @GdPB nanoparticles function both as effective MRI contrast agents and PTT agents as determined by characterizing studies performed in vitro and retain their properties in the presence of cells. Importantly, the Fe 3 O 4 @GdPB nanoparticles function as effective MRI contrast agents in vivo by increasing signal:noise ratios in T 1 -weighted scans of tumors and as effective PTT agents in vivo by decreasing tumor growth rates and increasing survival in an animal model of neuroblastoma. These findings demonstrate the potential of the Fe 3 O 4 @GdPB nanoparticles to function as effective theranostic agents.

Composite iron oxide–Prussian blue nanoparticles for magnetically guided T1-weighted magnetic resonance imaging and photothermal therapy of tumors

PubMed Central

Kale, Shraddha S; Burga, Rachel A; Sweeney, Elizabeth E; Zun, Zungho; Sze, Raymond W; Tuesca, Anthony; Subramony, J Anand; Fernandes, Rohan

2017-01-01

Theranostic nanoparticles offer the potential for mixing and matching disparate diagnostic and therapeutic functionalities within a single nanoparticle for the personalized treatment of diseases. In this article, we present composite iron oxide-gadolinium-containing Prussian blue nanoparticles (Fe3O4@GdPB) as a novel theranostic agent for T1-weighted magnetic resonance imaging (MRI) and photothermal therapy (PTT) of tumors. These particles combine the well-described properties and safety profiles of the constituent Fe3O4 nanoparticles and gadolinium-containing Prussian blue nanoparticles. The Fe3O4@GdPB nanoparticles function both as effective MRI contrast agents and PTT agents as determined by characterizing studies performed in vitro and retain their properties in the presence of cells. Importantly, the Fe3O4@GdPB nanoparticles function as effective MRI contrast agents in vivo by increasing signal:noise ratios in T1-weighted scans of tumors and as effective PTT agents in vivo by decreasing tumor growth rates and increasing survival in an animal model of neuroblastoma. These findings demonstrate the potential of the Fe3O4@GdPB nanoparticles to function as effective theranostic agents. PMID:28919744

Magnetically driven floating foams for the removal of oil contaminants from water.

PubMed

Calcagnile, Paola; Fragouli, Despina; Bayer, Ilker S; Anyfantis, George C; Martiradonna, Luigi; Cozzoli, P Davide; Cingolani, Roberto; Athanassiou, Athanassia

2012-06-26

In this study, we present a novel composite material based on commercially available polyurethane foams functionalized with colloidal superparamagnetic iron oxide nanoparticles and submicrometer polytetrafluoroethylene particles, which can efficiently separate oil from water. Untreated foam surfaces are inherently hydrophobic and oleophobic, but they can be rendered water-repellent and oil-absorbing by a solvent-free, electrostatic polytetrafluoroethylene particle deposition technique. It was found that combined functionalization of the polytetrafluoroethylene-treated foam surfaces with colloidal iron oxide nanoparticles significantly increases the speed of oil absorption. Detailed microscopic and wettability studies reveal that the combined effects of the surface morphology and of the chemistry of the functionalized foams greatly affect the oil-absorption dynamics. In particular, nanoparticle capping molecules are found to play a major role in this mechanism. In addition to the water-repellent and oil-absorbing capabilities, the functionalized foams exhibit also magnetic responsivity. Finally, due to their light weight, they float easily on water. Hence, by simply moving them around oil-polluted waters using a magnet, they can absorb the floating oil from the polluted regions, thereby purifying the water underneath. This low-cost process can easily be scaled up to clean large-area oil spills in water.

Magnetic pumping as a source of particle heating

NASA Astrophysics Data System (ADS)

Lichko, Emily; Egedal, Jan; Daughton, William; Kasper, Justin

2017-10-01

Magnetic pumping is a means of heating plasmas for both fusion and astrophysical applications. In this study a magnetic pumping model is developed as a possible explanation for the heating and the generation of power-law distribution functions observed in the solar wind plasma. In most previous studies turbulent energy is only dissipated at microscopic kinetic scales. In contrast, magnetic pumping energizes the particles through the largest scale turbulent fluctuations, thus bypassing the energy cascade. Kinetic simulations are applied to verify these analytic predictions. Previous results for the one-dimensional model, as well as initial results for a two-dimensional model which includes the effects of trapped and passing particles are presented. Preliminary results of the presence of this mechanism in the bow shock region, using spacecraft data from the Magnetospheric Multiscale mission, are presented as well. This research was conducted with support from National Defense Science and Engineering Graduate (NDSEG) Fellowship, 32 CFR 168, as well as from NSF Award 1404166 and NASA award NNX15AJ73G.

Energy levels of a hydrogenic impurity in a parabolic quantum well with a magnetic field

NASA Astrophysics Data System (ADS)

Zang, J. X.; Rustgi, M. L.

1993-07-01

In this paper, we present a calculation of the energy levels of a hydrogenic impurity (or a hydrogenic atom) at the bottom of a one-dimensional parabolic quantum well with a magnetic field normal to the plane of the well. The finite-basis-set variational method is used to calculate the ground state and the excited states with major quantum number less than or equal to 3. The limit of small radial distance and the limit of great radial distance are considered to choose a set of proper basis functions. The results in the limit that the parabolic parameter α=0 are compared with the data of Rösner et al. [J. Phys. B 17, 29 (1984)]. The comparison shows that the present calculation is quite accurate. It is found that the energy levels increase with increasing parabolic parameter α and increase with increasing normalized magnetic-field strength γ except those levels with magnetic quantum number m<0 at small γ.

Exchange-biased quantum tunnelling in a supramolecular dimer of single-molecule magnets.

PubMed

Wernsdorfer, Wolfgang; Aliaga-Alcalde, Núria; Hendrickson, David N; Christou, George

2002-03-28

Various present and future specialized applications of magnets require monodisperse, small magnetic particles, and the discovery of molecules that can function as nanoscale magnets was an important development in this regard. These molecules act as single-domain magnetic particles that, below their blocking temperature, exhibit magnetization hysteresis, a classical property of macroscopic magnets. Such 'single-molecule magnets' (SMMs) straddle the interface between classical and quantum mechanical behaviour because they also display quantum tunnelling of magnetization and quantum phase interference. Quantum tunnelling of magnetization can be advantageous for some potential applications of SMMs, for example, in providing the quantum superposition of states required for quantum computing. However, it is a disadvantage in other applications, such as information storage, where it would lead to information loss. Thus it is important to both understand and control the quantum properties of SMMs. Here we report a supramolecular SMM dimer in which antiferromagnetic coupling between the two components results in quantum behaviour different from that of the individual SMMs. Our experimental observations and theoretical analysis suggest a means of tuning the quantum tunnelling of magnetization in SMMs. This system may also prove useful for studying quantum tunnelling of relevance to mesoscopic antiferromagnets.

Enrichment of peptides in serum by C(8)-functionalized magnetic nanoparticles for direct matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis.

PubMed

Yao, Ning; Chen, Hemei; Lin, Huaqing; Deng, Chunhui; Zhang, Xiangmin

2008-03-21

Human serum contains a complex array of proteolytically derived peptides (serum peptidome), which contain biomarkers of preclinical screening and disease diagnosis. Recently, commercial C(8)-functionalized magnetic beads (1-10 microm) were widely applied to the separation and enrichment of peptides in human serum, prior to matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) analysis. In this work, laboratory-prepared C(8)-functionalized magnetic nanoparticles (about 50 nm) were prepared and applied to the fast separation and the enrichment of peptides from serum. At first, the C(8)-magnetic nanoparticles were synthesized by modifying amine-functionalized magnetic nanoparticles with chlorodimethyloctylsilane. These synthesized C(8)-amine-functionalized magnetic particles have excellent magnetic responsibility, high dispersibility and large surface area. Finally, the C(8)-magnetic nanoparticles were successfully applied to fast and efficient enrichment of low-abundance peptides from protein tryptic digestion and human serum followed by MALDI-TOF-MS analysis.

Morphological and functional evaluation of chronic pancreatitis with magnetic resonance imaging

PubMed Central

Hansen, Tine Maria; Nilsson, Matias; Gram, Mikkel; Frøkjær, Jens Brøndum

2013-01-01

Magnetic resonance imaging (MRI) techniques for assessment of morphology and function of the pancreas have been improved dramatically the recent years and MRI is very often used in diagnosing and follow-up of chronic pancreatitis (CP) patients. Standard MRI including fat-suppressed T1-weighted and T2-weighted imaging techniques reveal decreased signal and glandular atrophy of the pancreas in CP. In contrast-enhanced MRI of the pancreas in CP the pancreatic signal is usually reduced and delayed due to decreased perfusion as a result of chronic inflammation and fibrosis. Thus, morphological changes of the ductal system can be assessed by magnetic resonance cholangiopancreatography (MRCP). Furthermore, secretin-stimulated MRCP is a valuable technique to evaluate side branch pathology and the exocrine function of the pancreas and diffusion weighted imaging can be used to quantify both parenchymal fibrotic changes and the exocrine function of the pancreas. These standard and advanced MRI techniques are supplementary techniques to reveal morphological and functional changes of the pancreas in CP. Recently, spectroscopy has been used for assessment of metabolite concentrations in-vivo in different tissues and may have the potential to offer better tissue characterization of the pancreas. Hence, the purpose of the present review is to provide an update on standard and advanced MRI techniques of the pancreas in CP. PMID:24259954

Magnetic properties of spinels GeNi2-xCoxO4 systems: Green's function and high-temperature series expansions

NASA Astrophysics Data System (ADS)

El Grini, A.; Salmi, S.; Masrour, R.; Hamedoun, M.; Bouslykhane, K.; Marzouk, A.; Hourmatallah, A.; Benzakour, N.

2018-06-01

The Green's function theory and high-temperature series expansions technical have been developed for magnetic systems GeNi2-xCoxO4. We have applied the Green's function theory to evaluate thermal magnetization and magnetic susceptibility for different values of magnetic field and dilution x, considering all components of the magnetization when an external magnetic field is applied in (x,z)-plane. The second theory combined with the Padé approximants method for a randomly diluted Heisenberg magnet is used to deduce the magnetic phase diagram of GeNi2 - xCoxO4 systems. The critical exponents ? and ? associated with the magnetic susceptibility ? and the correlation length ξ, respectively, have been deduced. The theoretical results are compared with those given by magnetic measurements.

Setup presentation and clinical outcome analysis of treating highly language-eloquent gliomas via preoperative navigated transcranial magnetic stimulation and tractography.

PubMed

Sollmann, Nico; Kelm, Anna; Ille, Sebastian; Schröder, Axel; Zimmer, Claus; Ringel, Florian; Meyer, Bernhard; Krieg, Sandro M

2018-06-01

OBJECTIVE Awake surgery combined with intraoperative direct electrical stimulation (DES) and intraoperative neuromonitoring (IONM) is considered the gold standard for the resection of highly language-eloquent brain tumors. Different modalities, such as functional magnetic resonance imaging (fMRI) or magnetoencephalography (MEG), are commonly added as adjuncts for preoperative language mapping but have been shown to have relevant limitations. Thus, this study presents a novel multimodal setup consisting of preoperative navigated transcranial magnetic stimulation (nTMS) and nTMS-based diffusion tensor imaging fiber tracking (DTI FT) as an adjunct to awake surgery. METHODS Sixty consecutive patients (63.3% men, mean age 47.6 ± 13.3 years) suffering from highly language-eloquent left-hemispheric low- or high-grade glioma underwent preoperative nTMS language mapping and nTMS-based DTI FT, followed by awake surgery for tumor resection. Both nTMS language mapping and DTI FT data were available for resection planning and intraoperative guidance. Clinical outcome parameters, including craniotomy size, extent of resection (EOR), language deficits at different time points, Karnofsky Performance Scale (KPS) score, duration of surgery, and inpatient stay, were assessed. RESULTS According to postoperative evaluation, 28.3% of patients showed tumor residuals, whereas new surgery-related permanent language deficits occurred in 8.3% of patients. KPS scores remained unchanged (median preoperative score 90, median follow-up score 90). CONCLUSIONS This is the first study to present a clinical outcome analysis of this very modern approach, which is increasingly applied in neurooncological centers worldwide. Although human language function is a highly complex and dynamic cortico-subcortical network, the presented approach offers excellent functional and oncological outcomes in patients undergoing surgery of lesions affecting this network.

Egocentric virtual maze learning in adult survivors of childhood abuse with dissociative disorders: evidence from functional magnetic resonance imaging.

PubMed

Weniger, Godehard; Siemerkus, Jakob; Barke, Antonia; Lange, Claudia; Ruhleder, Mirjana; Sachsse, Ulrich; Schmidt-Samoa, Carsten; Dechent, Peter; Irle, Eva

2013-05-30

Present neuroimaging findings suggest two subtypes of trauma response, one characterized predominantly by hyperarousal and intrusions, and the other primarily by dissociative symptoms. The neural underpinnings of these two subtypes need to be better defined. Fourteen women with childhood abuse and the current diagnosis of dissociative amnesia or dissociative identity disorder but without posttraumatic stress disorder (PTSD) and 14 matched healthy comparison subjects underwent functional magnetic resonance imaging (fMRI) while finding their way in a virtual maze. The virtual maze presented a first-person view (egocentric), lacked any topographical landmarks and could be learned only by using egocentric navigation strategies. Participants with dissociative disorders (DD) were not impaired in learning the virtual maze when compared with controls, and showed a similar, although weaker, pattern of activity changes during egocentric learning when compared with controls. Stronger dissociative disorder severity of participants with DD was related to better virtual maze performance, and to stronger activity increase within the cingulate gyrus and the precuneus. Our results add to the present knowledge of preserved attentional and visuospatial mnemonic functioning in individuals with DD. Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.

The 15 cm diameter ion thruster research

NASA Technical Reports Server (NTRS)

Wilbur, P. J.

1974-01-01

The startup reliability of a 15 cm diameter mercury bombardment ion thruster which employs a pulsed high voltage tickler electrode on the main and neutralizer cathodes is examined. Startup of the thruster is achieved 100% of the time on the main cathode and 98.7% of the time on the neutralizer cathode over a 3640 cycle test. The thruster was started from a 20 C initial condition and operated for an hour at a 600 mA beam current. An energy efficiency of 75% and a propellant utilization efficiency of 77% was achieved over the complete cycle. The effect of a single cusp magnetic field thruster length on its performance is discussed. Guidelines are formulated for the shaping of magnetic field lines in thrusters. A model describing double ion production in mercury discharges is presented. The production route is shown to occur through the single ionic ground state. Photographs of the interior of an operating-hollow cathode are presented. A cathode spot is shown to be present if the cathode is free of low work-function surfaces. The spot is observed if a low work-function oxide coating is applied to the cathode insert. Results show that low work-function oxide coatings tend to migrate during thruster operation.

Design of a modified Halbach magnet for the CBETA Project

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

Tsoupas, Nicholaos; Berg, J. S.; Brooks, S.

A modified Halbach magnet has been designed to be installed in the splitter/merger section of the CBETA project which is under construction at Cornell University. The splitter/merger of the CBETA consists of 4 beam lines and is shown in Fig. 1. Two of the functions of the splitter/merger lines are; first to match the beam parameters at the exit of the Energy Recovery Linac (ERL) to those at the entrance of the Fixed Field Alternating Gradient (FFAG) arc, and second to place the trajectories of the reference particles of the beam bunches at the entrance of the FFAG arc onmore » specified trajectories as they determined by the beam optics of the FFAG arc. In this technical note we present results from the 2D and 3D electromagnetic analysis of the S4.BEN01 magnet which is one of the dipole magnets of the 150 MeV line of the splitter/merger. The present design of the S4.BEN01 magnet, is based on a modified Halbach-type permanent magnet. To justify our suggestion of using a Halbach type of magnet instead of an electromagnet for the S4.BEN01 magnet we devote an APPENDIX A in which we provide details on the design of an electromagnet for the S4.BEN01 magnet and in the section under conclusion will list the pros and cons of the two designs.« less

The Magsat magnetometer boom

NASA Technical Reports Server (NTRS)

Smola, J. F.; Radford, W. E.; Reitz, M. H.

1980-01-01

A lightweight extendable structure that can precisely position magnetically sensitive instruments safe distances from magnetic sources in a spacecraft is described as well as the major areas of concern that played dominant roles in its development. Weight, packaging volume, thermal distortion, mechanical misalignments, dimensional instability, launch environments, and low temperature functioning were areas that presented some formidable obstacles. The ways in which these obstacles were dealt with are examined for those involving the development of similar aerospace mechanisms with equally restrictive requirements.

g-factor measurements of isomeric states in 174W

NASA Astrophysics Data System (ADS)

Rocchini, M.; Nannini, A.; Benzoni, G.; Melon, B.; John, P. R.; Ur, C. A.; Avigo, R.; Bazzacco, D.; Blasi, N.; Bocchi, G.; Bottoni, S.; Bracco, A.; Camera, F.; Ceruti, S.; Crespi, F. C. L.; Georgiev, G.; Giaz, A.; Gottardo, A.; Leoni, S.; Menegazzo, R.; Mengoni, D.; Michelagnoli, C.; Million, B.; Modamio, V.; Morales, A. I.; Napoli, D. R.; Ottanelli, M.; Pellegri, L.; Perego, A.; Valiente-Dobon, J. J.; Wieland, O.

2016-05-01

The experimental setup GAMIPE used for gyro magnetic factor measurements at Laboratori Nazionali di Legnaro and a recent experimental work regarding K-isomers in 174W are described. Aim of the experiment is to study the detailed structure of the isomeric states wave functions, by the measurement of the magnetic dipole moments. This piece of information can provide interesting hints for theoretical models. Preliminary results concerning the population of the isomers of interest and half-lives are presented.

Dynamics of the EEG of human brain in the gradient magnetic fields of geological faults in different geographical and climatic zones

NASA Astrophysics Data System (ADS)

Pobachenko, S. V.; Sokolov, M. V.; Grigoriev, P. E.; Vasilieva, I. V.

2017-11-01

There are presented the results of experimental studies of the dynamics of indices of the functional state of a person located within the zones characterized by anomalous parameters of spatial distribution of magnetic field vector values. It is shown that these geophysical modifications have a pronounced effect on the dynamics of electrical activity indices of the human brain, regardless of geographic and climatic conditions.

Spacecraft observations of a Maxwell Demon coating the separatrix of asymmetric magnetic reconnection with crescent-shaped electron distributions

NASA Astrophysics Data System (ADS)

Egedal, J.; Le, A.; Daughton, W.; Wetherton, B.; Cassak, Pa; Chen, Lj; Lavraud, B.; Dorell, J.; Avanov, L.; Gershman, D.

2016-10-01

During asymmetric magnetic reconnection in the dayside magnetopause in situ spacecraft mea- surements show that electrons from the high density inflow penetrate some distance into the low density inflow. Supported by a kinetic simulation, we present a general derivation of an exclusion energy parameter, which provides a lower kinetic energy bound for an electron to jump across the reconnection region from one inflow region to the other. As by a Maxwell Demon, only high energy electrons are permitted to cross the inner reconnection region, strongly impacting the form of the electron distribution function observed along the low density side separatrix. The dynamics produce two distinct flavors of crescent-shaped electron distributions in a thin boundary layer along the separatrix between the magnetospheric inflow and the reconnection exhaust. The analytical model presented relates these salient details of the distribution function to the electron dynamics in the inner reconnection region.

Magnetic field amplification by small-scale dynamo action: dependence on turbulence models and Reynolds and Prandtl numbers.

PubMed

Schober, Jennifer; Schleicher, Dominik; Federrath, Christoph; Klessen, Ralf; Banerjee, Robi

2012-02-01

The small-scale dynamo is a process by which turbulent kinetic energy is converted into magnetic energy, and thus it is expected to depend crucially on the nature of the turbulence. In this paper, we present a model for the small-scale dynamo that takes into account the slope of the turbulent velocity spectrum v(ℓ)proportional ℓ([symbol see text])V}, where ℓ and v(ℓ) are the size of a turbulent fluctuation and the typical velocity on that scale. The time evolution of the fluctuation component of the magnetic field, i.e., the small-scale field, is described by the Kazantsev equation. We solve this linear differential equation for its eigenvalues with the quantum-mechanical WKB approximation. The validity of this method is estimated as a function of the magnetic Prandtl number Pm. We calculate the minimal magnetic Reynolds number for dynamo action, Rm_{crit}, using our model of the turbulent velocity correlation function. For Kolmogorov turbulence ([symbol see text] = 1/3), we find that the critical magnetic Reynolds number is Rm(crit) (K) ≈ 110 and for Burgers turbulence ([symbol see text] = 1/2) Rm(crit)(B) ≈ 2700. Furthermore, we derive that the growth rate of the small-scale magnetic field for a general type of turbulence is Γ proportional Re((1-[symbol see text])/(1+[symbol see text])) in the limit of infinite magnetic Prandtl number. For decreasing magnetic Prandtl number (down to Pm >/~ 10), the growth rate of the small-scale dynamo decreases. The details of this drop depend on the WKB approximation, which becomes invalid for a magnetic Prandtl number of about unity.

Fe3O4 nanoparticles and nanocomposites with potential application in biomedicine and in communication technologies: Nanoparticle aggregation, interaction, and effective magnetic anisotropy

NASA Astrophysics Data System (ADS)

Allia, P.; Barrera, G.; Tiberto, P.; Nardi, T.; Leterrier, Y.; Sangermano, M.

2014-09-01

Magnetite nanoparticles with a size of 5-6 nm with potential impact on biomedicine and information/communication technologies were synthesized by thermal decomposition of Fe(acac)3 and subsequently coated with a silica shell exploiting a water-in-oil synthetic procedure. The as-produced powders (comprised of either Fe3O4 or Fe3O4@silica nanoparticles) were mixed with a photocurable resin obtaining two magnetic nanocomposites with the same nominal amount of magnetic material. The static magnetic properties of the two nanopowders and the corresponding nanocomposites were measured in the 10 K-300 K temperature range. Magnetic measurements are shown here to be able to give unambiguous information on single-particle properties such as particle size and magnetic anisotropy as well as on nanoparticle aggregation and interparticle interaction. A comparison between the size distribution functions obtained from magnetic measurements and from TEM images shows that figures estimated from properly analyzed magnetic measurements are very close to the actual values. In addition, the present analysis allows us to determine the value of the effective magnetic anisotropy and to estimate the anisotropy contribution from the surface. The Field-cooled/zero field cooled curves reveal a high degree of particle aggregation in the Fe3O4 nanopowder, which is partially reduced by silica coating and strongly decreased by dissolution in the host polymer. In all considered materials, the nanoparticles are magnetically interacting, the interaction strength being a function of nanoparticle environment and being the lowest in the nanocomposite containing bare, well-separate Fe3O4 particles. All samples behave as interacting superparamagnetic materials instead of ideal superparamagnets and follow the corresponding scaling law.

Experimental evidence of a double layer in a large volume helicon reactor.

PubMed

Sutherland, O; Charles, C; Plihon, N; Boswell, R W

2005-11-11

The self-consistently generated current-free electric double layer (DL) is shown to scale up with the source tube diameter and appears not to be affected by rf driving frequency and changes in reactor geometry. This Letter presents the first simultaneous measurements of local plasma potential and beam energy as a function of axial position. The DL is shown to be no more than 5 mm thick (20 D lengths) and positioned just downstream of the maximum in the magnetic field gradient. Furthermore, its position relative to the magnetic field is observed to be invariant as the magnetic field is translated axially. Measurements of the potential drop across the DL are presented for pressures down to 0.09 mTorr and the DL strength (phiDL/T(e)) is determined to be between 5 and 7.

Collisionless distribution function for the relativistic force-free Harris sheet

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

Stark, C. R.; Neukirch, T.

A self-consistent collisionless distribution function for the relativistic analogue of the force-free Harris sheet is presented. This distribution function is the relativistic generalization of the distribution function for the non-relativistic collisionless force-free Harris sheet recently found by Harrison and Neukirch [Phys. Rev. Lett. 102, 135003 (2009)], as it has the same dependence on the particle energy and canonical momenta. We present a detailed calculation which shows that the proposed distribution function generates the required current density profile (and thus magnetic field profile) in a frame of reference in which the electric potential vanishes identically. The connection between the parameters ofmore » the distribution function and the macroscopic parameters such as the current sheet thickness is discussed.« less

Functional Magnetic Resonance Imaging in Alzheimer' Disease Drug Development.

PubMed

Holiga, Stefan; Abdulkadir, Ahmed; Klöppel, Stefan; Dukart, Juergen

2018-01-01

While now commonly applied for studying human brain function the value of functional magnetic resonance imaging in drug development has only recently been recognized. Here we describe the different functional magnetic resonance imaging techniques applied in Alzheimer's disease drug development with their applications, implementation guidelines, and potential pitfalls.

Peptide-functionalized iron oxide magnetic nanoparticle for gold mining

NASA Astrophysics Data System (ADS)

Shen, Wei-Zheng; Cetinel, Sibel; Sharma, Kumakshi; Borujeny, Elham Rafie; Montemagno, Carlo

2017-02-01

Here, we present our work on preparing a novel nanomaterial composed of inorganic binding peptides and magnetic nanoparticles for inorganic mining. Two previously selected and well-characterized gold-binding peptides from cell surface display, AuBP1 and AuBP2, were exploited. This nanomaterial (AuBP-MNP) was designed to fulfill the following two significant functions: the surface conjugated gold-binding peptide will recognize and selectively bind to gold, while the magnetic nano-sized core will respond and migrate according to the applied external magnetic field. This will allow the smart nanomaterial to mine an individual material (gold) from a pool of mixture, without excessive solvent extraction, filtration, and concentration steps. The working efficiency of AuBP-MNP was determined by showing a dramatic reduction of gold nanoparticle colloid concentration, monitored by spectroscopy. The binding kinetics of AuBP-MNP onto the gold surface was determined using surface plasmon resonance (SPR) spectroscopy, which exhibits around 100 times higher binding kinetics than peptides alone. The binding capacity of AuBP-MNP was demonstrated by a bench-top mining test with gold microparticles.

Exchange Interactions on the Highest-Spin Reported Molecule: the Mixed-Valence Fe42 Complex

NASA Astrophysics Data System (ADS)

Aravena, Daniel; Venegas-Yazigi, Diego; Ruiz, Eliseo

2016-04-01

The finding of high-spin molecules that could behave as conventional magnets has been one of the main challenges in Molecular Magnetism. Here, the exchange interactions, present in the highest-spin molecule published in the literature, Fe42, have been analysed using theoretical methods based on Density Functional Theory. The system with a total spin value S = 45 is formed by 42 iron centres containing 18 high-spin FeIII ferromagnetically coupled and 24 diamagnetic low-spin FeII ions. The bridging ligands between the two paramagnetic centres are two cyanide ligands coordinated to the diamagnetic FeII cations. Calculations were performed using either small Fe4 or Fe3 models or the whole Fe42 complex, showing the presence of two different ferromagnetic couplings between the paramagnetic FeIII centres. Finally, Quantum Monte Carlo simulations for the whole system were carried out in order to compare the experimental and simulated magnetic susceptibility curves from the calculated exchange coupling constants with the experimental one. This comparison allows for the evaluation of the accuracy of different exchange-correlation functionals to reproduce such magnetic properties.

The Role of Cortical Plasticity in Recovery of Function Following Allogeneic Hand Transplantation

DTIC Science & Technology

2015-10-01

transplantation, functional magnetic resonance imaging, hand replantation, cortical reorganization, functional recovery 16. SECURITY CLASSIFICATION OF: U...functional magnetic resonance imaging (fMRI) data suggest that areas of the sensory and motor cortex devoted to representing the hand prior to...function, recovery, functional magnetic resonance imaging 3. Accomplishments Major Goals Achieved: Year Two My lab is relocated to Washington University

Exact axially symmetric galactic dynamos

NASA Astrophysics Data System (ADS)

Henriksen, R. N.; Woodfinden, A.; Irwin, J. A.

2018-05-01

We give a selection of exact dynamos in axial symmetry on a galactic scale. These include some steady examples, at least one of which is wholly analytic in terms of simple functions and has been discussed elsewhere. Most solutions are found in terms of special functions, such as associated Lagrange or hypergeometric functions. They may be considered exact in the sense that they are known to any desired accuracy in principle. The new aspect developed here is to present scale-invariant solutions with zero resistivity that are self-similar in time. The time dependence is either a power law or an exponential factor, but since the geometry of the solution is self-similar in time we do not need to fix a time to study it. Several examples are discussed. Our results demonstrate (without the need to invoke any other mechanisms) X-shaped magnetic fields and (axially symmetric) magnetic spiral arms (both of which are well observed and documented) and predict reversing rotation measures in galaxy haloes (now observed in the CHANG-ES sample) as well as the fact that planar magnetic spirals are lifted into the galactic halo.

Magnetically guided release of ciprofloxacin from superparamagnetic polymer nanocomposites.

PubMed

Gupta, Rashmi; Bajpai, A K

2011-01-01

Tailored with superparamagnetic properties the magnetic nanocomposites have been thoroughly investigated in recent past because of their potential applications in the fields of biomedicine and bioengineering such as protein detection, magnetic targeted drug carriers, bioseparation, magnetic resonance imaging contrast agents and hyperthermia. Magnetic drug targeting has come up as a safe and effective drug-delivery technology, i.e., with the least amount of magnetic particles a maximum of drug may be easily administered and transported to the site of choice. In the present work novel magnetic drug-targeting carriers consisting of magnetic nanoparticles encapsulated within a smart polymer matrix with potential of controlled drug release is described. To make such magnetic polymeric drug-delivery systems, both the magnetic nanoparticles and antibiotic drug (ciprofloxacin) were incorporated into the hydrogel. The controlled release process and release profiles were investigated as a function of experimental protocols such as percent loading of drug, chemical composition of the nanocomposite, pH of release media and strength of magnetic field on the release profiles. The structure, morphology and compositions of magnetic hydrogel nanocomposites were characterized by FT-IR, TEM, XRD and VSM techniques. It was found that magnetic nanocomposites were biocompatible and superparamagnetic in nature and could be used as a smart drug carrier for controlled and targeted drug delivery.

Improved Frequency Fluctuation Model for Spectral Line Shape Calculations in Fusion Plasmas

NASA Astrophysics Data System (ADS)

Ferri, S.; Calisti, A.; Mossé, C.; Talin, B.; Lisitsa, V.

2010-10-01

A very fast method to calculate spectral line shapes emitted by plasmas accounting for charge particle dynamics and effects of an external magnetic field is proposed. This method relies on a new formulation of the Frequency Fluctuation Model (FFM), which yields to an expression of the dynamic line profile as a functional of the static distribution function of frequencies. This highly efficient formalism, not limited to hydrogen-like systems, allows to calculate pure Stark and Stark-Zeeman line shapes for a wide range of density, temperature and magnetic field values, which is of importance in plasma physics and astrophysics. Various applications of this method are presented for conditions related to fusion plasmas.

Brain regions sensitive to the face inversion effect: a functional magnetic resonance imaging study in humans.

PubMed

Leube, Dirk T; Yoon, Hyo Woon; Rapp, Alexander; Erb, Michael; Grodd, Wolfgang; Bartels, Mathias; Kircher, Tilo T J

2003-05-22

Perception of upright faces relies on configural processing. Therefore recognition of inverted, compared to upright faces is impaired. In a functional magnetic resonance imaging experiment we investigated the neural correlate of a face inversion task. Thirteen healthy subjects were presented with a equal number of upright and inverted faces alternating with a low level baseline with an upright and inverted picture of an abstract symbol. Brain activation was calculated for upright minus inverted faces. For this differential contrast, we found a signal change in the right superior temporal sulcus and right insula. Configural properties are processed in a network comprising right superior temporal and insular cortex.

A combined confocal and magnetic resonance microscope for biological studies

NASA Astrophysics Data System (ADS)

Majors, Paul D.; Minard, Kevin R.; Ackerman, Eric J.; Holtom, Gary R.; Hopkins, Derek F.; Parkinson, Christopher I.; Weber, Thomas J.; Wind, Robert A.

2002-12-01

Complementary data acquired with different microscopy techniques provide a basis for establishing a more comprehensive understanding of cell function in health and disease, particularly when results acquired with different methodologies can be correlated in time and space. In this article, a novel microscope is described for studying live cells simultaneously with both confocal scanning laser fluorescence optical microscopy and magnetic resonance microscopy. The various design considerations necessary for integrating these two complementary techniques are discussed, the layout and specifications of the instrument are given, and examples of confocal and magnetic resonance images of large frog cells and model tumor spheroids obtained with the compound microscope are presented.

Local and nonlocal parallel heat transport in general magnetic fields

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

Del-Castillo-Negrete, Diego B; Chacon, Luis

2011-01-01

A novel approach for the study of parallel transport in magnetized plasmas is presented. The method avoids numerical pollution issues of grid-based formulations and applies to integrable and chaotic magnetic fields with local or nonlocal parallel closures. In weakly chaotic fields, the method gives the fractal structure of the devil's staircase radial temperature profile. In fully chaotic fields, the temperature exhibits self-similar spatiotemporal evolution with a stretched-exponential scaling function for local closures and an algebraically decaying one for nonlocal closures. It is shown that, for both closures, the effective radial heat transport is incompatible with the quasilinear diffusion model.

Development of a cross-polarization scattering system for the measurement of internal magnetic fluctuations in the DIII-D tokamak

DOE PAGES

Rhodes, Terry L.; Peebles, William A.; Crocker, Neal A.; ...

2014-08-05

The design and performance of a new cross-polarization scattering (CPS) system for the localized measurement of internal magnetic fluctuations is presented. CPS is a process whereby magnetic fluctuations scatter incident electromagnetic radiation into a perpendicular polarization which is subsequently detected. A new CPS design that incorporates a unique scattering geometry was laboratory tested, optimized, and installed on the DIII-D tokamak. Plasma tests of signal-to-noise, polarization purity, and frequency response indicate proper functioning of the system. Lastly, CPS data show interesting features related to internal MHD perturbations known as sawteeth that are not observed on density fluctuations.

Magnetization of the Ising model on the Sierpinski pastry-shell

NASA Astrophysics Data System (ADS)

Chame, Anna; Branco, N. S.

1992-02-01

Using a real-space renormalization group approach, we calculate the approximate magnetization in the Ising model on the Sierpinski Pastry-shell. We consider, as an approximation, only two regions of the fractal: the internal surfaces, or walls (sites on the border of eliminated areas), with coupling constants JS, and the bulk (all other sites), with coupling constants Jv. We obtain the mean magnetization of the two regions as a function of temperature, for different values of α= JS/ JV and different geometric parameters b and l. Curves present a step-like behavior for some values of b and l, as well as different universality classes for the bulk transition.

Linear fixed-field multipass arcs for recirculating linear accelerators

DOE PAGES

Morozov, V. S.; Bogacz, S. A.; Roblin, Y. R.; ...

2012-06-14

Recirculating Linear Accelerators (RLA's) provide a compact and efficient way of accelerating particle beams to medium and high energies by reusing the same linac for multiple passes. In the conventional scheme, after each pass, the different energy beams coming out of the linac are separated and directed into appropriate arcs for recirculation, with each pass requiring a separate fixed-energy arc. In this paper we present a concept of an RLA return arc based on linear combined-function magnets, in which two and potentially more consecutive passes with very different energies are transported through the same string of magnets. By adjusting themore » dipole and quadrupole components of the constituting linear combined-function magnets, the arc is designed to be achromatic and to have zero initial and final reference orbit offsets for all transported beam energies. We demonstrate the concept by developing a design for a droplet-shaped return arc for a dog-bone RLA capable of transporting two beam passes with momenta different by a factor of two. Finally, we present the results of tracking simulations of the two passes and lay out the path to end-to-end design and simulation of a complete dog-bone RLA.« less

Magnetic and Structural characterization of Co nanowires using advanced electron microscopy techniques

NASA Astrophysics Data System (ADS)

Cantu-Valle, Jesus; Ruiz-Zepeda, Francisco; Sanchez, John Eder; Mendoza-Santoyo, Fernando; Ponnce, Arturo; UTSA Team

2015-03-01

We report the magnetic imaging and crystalline structure of high aspect ratio cobalt nanowires. Experimental results of magnetization reversal in cobalt nanowires are presented to illustrate the functionality of the in situ magnetization process through the manipulation of the objective lens. By making use of this applicability, we measure the magnetization and show experimental evidence of the magnetic flux distribution in polycrystalline cobalt nanowires using off-axis electron holography. The retrieved phase map can distinguishes the magnetic contribution from the crystalline contribution with high accuracy. To determine the size and orientation of the grains within the Co nanowires, PED-assisted orientation mapping was performed. Finally, the magnetic analysis performed at individual nanowires was correlated with the crystalline orientation map, obtained by PED-assisted crystal phase orientation mapping. The large shape anisotropy determines the mayor magnetization direction rather than the magneto-crystalline anisotropy in the studied nanowires. The combination of the two techniques allowed us to directly visualize the effects of the crystallographic texture on the magnetization of the nanowire. The authors would like to acknowledge Dr. B.J.H. Stadler for providing the samples and financial support from NSF PREM #DMR 0934218, CONACYT, #215762 and Department of Defense #64756-RT-REP.

Steel characteristics measurement system using Barkhausen jump sum rate and magnetic field intensity and method of using same

DOEpatents

Kohn, Gabriel; Hicho, George; Swartzendruber, Lydon

1997-01-01

A steel hardness measurement system and method of using same are provided for measuring at least one mechanical or magnetic characteristic of a ferromagnetic sample as a function of at least one magnetic characteristic of the sample. A magnetic field generator subjects the sample to a variable external magnetic field. The magnetic field intensity of the magnetic field generated by the magnetic field generating means is measured and a signal sensor is provided for measuring Barkhausen signals from the sample when the sample is subjected to the external magnetic field. A signal processing unit calculates a jump sum rate first moment as a function of the Barkhausen signals measured by the signal sensor and the magnetic field intensity, and for determining the at least one mechanical or magnetic characteristic as a function of the jump sum rate first moment.

Steel characteristics measurement system using Barkhausen jump sum rate and magnetic field intensity and method of using same

DOEpatents

Kohn, G.; Hicho, G.; Swartzendruber, L.

1997-04-08

A steel hardness measurement system and method of using same are provided for measuring at least one mechanical or magnetic characteristic of a ferromagnetic sample as a function of at least one magnetic characteristic of the sample. A magnetic field generator subjects the sample to a variable external magnetic field. The magnetic field intensity of the magnetic field generated by the magnetic field generating means is measured and a signal sensor is provided for measuring Barkhausen signals from the sample when the sample is subjected to the external magnetic field. A signal processing unit calculates a jump sum rate first moment as a function of the Barkhausen signals measured by the signal sensor and the magnetic field intensity, and for determining the at least one mechanical or magnetic characteristic as a function of the jump sum rate first moment. 7 figs.

Characteristics of magnetised plasma flow around stationary and expanding magnetic clouds

NASA Astrophysics Data System (ADS)

Dalakishvili, Giorgi

Studies of interplanetary magnetic clouds have shown that the characteristics of the region ahead of these objects, which are moving away from the Sun in the solar wind, play a role in determining their geo-efficiency, i.e. the kind and the degree of their effects on the Earth environment. Therefore, our main goal is to model and study the plasma parameters in the vicinity of interplanetary magnetic clouds. To this end we present a model in which the magnetic clouds are immersed in a magnetised plasma flow with a homogeneous magnetic field. We first calculate the resulting distortion of the external magnetic field and then determine the plasma velocity by employing the frozen-in condition. Subsequently, the plasma density and pressure are expressed as functions of the magnetic field and the velocity field. The plasma flow parameters are determined by solving the time-independent ideal MHD equations for both the stationary regime and for the case of an expand-ing cylindrical magnetic cloud, thus extending previous results that appeared in the literature.

Self-assembly with orthogonal-imposed stimuli to impart structure and confer magnetic function to electrodeposited hydrogels.

PubMed

Li, Ying; Liu, Yi; Gao, Tieren; Zhang, Boce; Song, Yingying; Terrell, Jessica L; Barber, Nathan; Bentley, William E; Takeuchi, Ichiro; Payne, Gregory F; Wang, Qin

2015-05-20

A magnetic nanocomposite film with the capability of reversibly collecting functionalized magnetic particles was fabricated by simultaneously imposing two orthogonal stimuli (electrical and magnetic). We demonstrate that cathodic codeposition of chitosan and Fe3O4 nanoparticles while simultaneously applying a magnetic field during codeposition can (i) organize structure, (ii) confer magnetic properties, and (iii) yield magnetic films that can perform reversible collection/assembly functions. The magnetic field triggered the self-assembly of Fe3O4 nanoparticles into hierarchical "chains" and "fibers" in the chitosan film. For controlled magnetic properties, the Fe3O4-chitosan film was electrodeposited in the presence of various strength magnetic fields and different deposition times. The magnetic properties of the resulting films should enable broad applications in complex devices. As a proof of concept, we demonstrate the reversible capture and release of green fluorescent protein (EGFP)-conjugated magnetic microparticles by the magnetic chitosan film. Moreover, antibody-functionalized magnetic microparticles were applied to capture cells from a sample, and these cells were collected, analyzed, and released by the magnetic chitosan film, paving the way for applications such as reusable biosensor interfaces (e.g., for pathogen detection). To our knowledge, this is the first report to apply a magnetic field during the electrodeposition of a hydrogel to generate magnetic soft matter. Importantly, the simple, rapid, and reagentless fabrication methodologies demonstrated here are valuable features for creating a magnetic device interface.

Magnetoacoustic tomography with magnetic induction for high-resolution bioimepedance imaging through vector source reconstruction under the static field of MRI magnet

PubMed Central

Mariappan, Leo; Hu, Gang; He, Bin

2014-01-01

Purpose: Magnetoacoustic tomography with magnetic induction (MAT-MI) is an imaging modality to reconstruct the electrical conductivity of biological tissue based on the acoustic measurements of Lorentz force induced tissue vibration. This study presents the feasibility of the authors' new MAT-MI system and vector source imaging algorithm to perform a complete reconstruction of the conductivity distribution of real biological tissues with ultrasound spatial resolution. Methods: In the present study, using ultrasound beamformation, imaging point spread functions are designed to reconstruct the induced vector source in the object which is used to estimate the object conductivity distribution. Both numerical studies and phantom experiments are performed to demonstrate the merits of the proposed method. Also, through the numerical simulations, the full width half maximum of the imaging point spread function is calculated to estimate of the spatial resolution. The tissue phantom experiments are performed with a MAT-MI imaging system in the static field of a 9.4 T magnetic resonance imaging magnet. Results: The image reconstruction through vector beamformation in the numerical and experimental studies gives a reliable estimate of the conductivity distribution in the object with a ∼1.5 mm spatial resolution corresponding to the imaging system frequency of 500 kHz ultrasound. In addition, the experiment results suggest that MAT-MI under high static magnetic field environment is able to reconstruct images of tissue-mimicking gel phantoms and real tissue samples with reliable conductivity contrast. Conclusions: The results demonstrate that MAT-MI is able to image the electrical conductivity properties of biological tissues with better than 2 mm spatial resolution at 500 kHz, and the imaging with MAT-MI under a high static magnetic field environment is able to provide improved imaging contrast for biological tissue conductivity reconstruction. PMID:24506649

Magnetism in (Semi)Conducting Macrocycles of pi conjugated Polymers

DTIC Science & Technology

2016-12-09

wise and avoiding a break in the continuity of the macrocycle. As a first criterion we tested the continuity of the electron orbitals over the...magnesium chloride) and post polymerization functionalization by a Sonogashira coupling reaction is required (scheme 2). Scheme 2: Synthetic...Sonogashira post - polymerization chain end functionalization and B isotopic model of the different population present in the final batch

Functional Brain Activation Differences in School-Age Children with Speech Sound Errors: Speech and Print Processing

ERIC Educational Resources Information Center

Preston, Jonathan L.; Felsenfeld, Susan; Frost, Stephen J.; Mencl, W. Einar; Fulbright, Robert K.; Grigorenko, Elena L.; Landi, Nicole; Seki, Ayumi; Pugh, Kenneth R.

2012-01-01

Purpose: To examine neural response to spoken and printed language in children with speech sound errors (SSE). Method: Functional magnetic resonance imaging was used to compare processing of auditorily and visually presented words and pseudowords in 17 children with SSE, ages 8;6[years;months] through 10;10, with 17 matched controls. Results: When…

Magnetoelectric effects in single crystals of the cubic ferrimagnetic helimagnet Cu2OSeO3

NASA Astrophysics Data System (ADS)

Belesi, M.; Rousochatzakis, I.; Abid, M.; Rößler, U. K.; Berger, H.; Ansermet, J.-Ph.

2012-06-01

We present magnetodielectric measurements in single crystals of the cubic spin-1/2 compound Cu2OSeO3. A magnetic-field-induced electric polarization (P) and a finite magnetocapacitance (MC) is observed at the onset of the magnetically ordered state (Tc=59 K). Both P and MC are explored in considerable detail as a function of temperature (T), applied field Ha, and relative field orientations with respect to the crystallographic axes. The magnetodielectric data show a number of anomalies which signal magnetic phase transitions, and allow us to map out the phase diagram of the system in the Ha-T plane. Below the 3-up-1-down collinear ferrimagnetic phase, we find two additional magnetic phases. We demonstrate that these are related to the field-driven evolution of a long-period helical phase, which is stabilized by the chiral Dzyaloshinskii-Moriya term DM·(∇×M) that is present in this noncentrosymmetric compound. We also present a phenomenological Landau-Ginzburg theory for the magnetic-field-induced electric polarization (MEH) effect, which is in excellent agreement with experimental data, and shows three main features: (i) the polarization P has a uniform as well as a long-wavelength spatial component that is given by the pitch of the magnetic helices, (ii) the uniform component of P points along the vector (HyHz,HzHx,HxHy), and (iii) its strength is proportional to η∥2-η⊥2/2, where η∥ is the longitudinal and η⊥ is the transverse (and spiraling) component of the magnetic ordering. Hence, the field dependence of P provides a clear signature of the evolution of a conical helix under a magnetic field. A similar phenomenological theory is discussed for the MC.

On the suitability of nanocrystalline ferrites as a magnetic carrier for drug delivery: functionalization, conjugation and drug release kinetics.

PubMed

Rana, S; Gallo, A; Srivastava, R S; Misra, R D K

2007-03-01

Superparamagnetic nickel ferrite nanoparticles functionalized with polyvinyl alcohol, polyethylene oxide and polymethacrylic acid (PMAA) polymers and subsequently conjugated with doxorubicin anti-cancer drug are studied for their use as a magnetic carrier for drug delivery. Fourier transform infrared spectroscopy enabled examination of the ability of the nanoparticles to be functionalized with polymers and conjugated with doxorubicin drug. The functionalized polymer-coated nanocrystalline nickel ferrites retain the magnetic characteristics of non-functionalized nanocrystalline nickel ferrites (superparamagnetism, absence of hysteresis, remanence and coercivity at room temperature), encouraging their application as a magnetic carrier for drug delivery. The PMAA-coated nanoferrites are demonstrated as being a potentially superior magnetically targeted drug carrier based on FTIR results and drug release kinetics in the absence and presence of an external magnetic field.

Contributions of structural connectivity and cerebrovascular parameters to functional magnetic resonance imaging signals in mice at rest and during sensory paw stimulation.

PubMed

Schroeter, Aileen; Grandjean, Joanes; Schlegel, Felix; Saab, Bechara J; Rudin, Markus

2017-07-01

Previously, we reported widespread bilateral increases in stimulus-evoked functional magnetic resonance imaging signals in mouse brain to unilateral sensory paw stimulation. We attributed the pattern to arousal-related cardiovascular changes overruling cerebral autoregulation thereby masking specific signal changes elicited by local neuronal activity. To rule out the possibility that interhemispheric neuronal communication might contribute to bilateral functional magnetic resonance imaging responses, we compared stimulus-evoked functional magnetic resonance imaging responses to unilateral hindpaw stimulation in acallosal I/LnJ, C57BL/6, and BALB/c mice. We found bilateral blood-oxygenation-level dependent signal changes in all three strains, ruling out a dominant contribution of transcallosal communication as reason for bilaterality. Analysis of functional connectivity derived from resting-state functional magnetic resonance imaging, revealed that bilateral cortical functional connectivity is largely abolished in I/LnJ animals. Cortical functional connectivity in all strains correlated with structural connectivity in corpus callosum as revealed by diffusion tensor imaging. Given the profound influence of systemic hemodynamics on stimulus-evoked functional magnetic resonance imaging outcomes, we evaluated whether functional connectivity data might be affected by cerebrovascular parameters, i.e. baseline cerebral blood volume, vascular reactivity, and reserve. We found that effects of cerebral hemodynamics on functional connectivity are largely outweighed by dominating contributions of structural connectivity. In contrast, contributions of transcallosal interhemispheric communication to the occurrence of ipsilateral functional magnetic resonance imaging response of equal amplitude to unilateral stimuli seem negligible.

Preparation of poly-L-lysine functionalized magnetic nanoparticles and their influence on viability of cancer cells

NASA Astrophysics Data System (ADS)

Khmara, I.; Koneracka, M.; Kubovcikova, M.; Zavisova, V.; Antal, I.; Csach, K.; Kopcansky, P.; Vidlickova, I.; Csaderova, L.; Pastorekova, S.; Zatovicova, M.

2017-04-01

This study was aimed at development of biocompatible amino-functionalized magnetic nanoparticles as carriers of specific antibodies able to detect and/or target cancer cells. Poly-L-lysine (PLL)-modified magnetic nanoparticle samples with different PLL/Fe3O4 content were prepared and tested to define the optimal PLL/Fe3O4 weight ratio. The samples were characterized for particle size and morphology (SEM, TEM and DLS), and surface properties (zeta potential measurements). The optimal PLL/Fe3O4 weight ratio of 1.0 based on both zeta potential and DLS measurements was in agreement with the UV/VIS measurements. Magnetic nanoparticles with the optimal PLL content were conjugated with antibody specific for the cancer biomarker carbonic anhydrase IX (CA IX), which is induced by hypoxia, a physiologic stress present in solid tumors and linked with aggressive tumor behavior. CA IX is localized on the cell surface with the antibody-binding epitope facing the extracellular space and is therefore suitable for antibody-based targeting of tumor cells. Here we showed that PLL/Fe3O4 magnetic nanoparticles exhibit cytotoxic activities in a cell type-dependent manner and bind to cells expressing CA IX when conjugated with the CA IX-specific antibody. These data support further investigations of the CA IX antibody-conjugated, magnetic field-guided/activated nanoparticles as tools in anticancer strategies.

A smart magnetic nanoplatform for synergistic anticancer therapy: manoeuvring mussel-inspired functional magnetic nanoparticles for pH responsive anticancer drug delivery and hyperthermia.

PubMed

Sasikala, Arathyram Ramachandra Kurup; GhavamiNejad, Amin; Unnithan, Afeesh Rajan; Thomas, Reju George; Moon, Myeongju; Jeong, Yong Yeon; Park, Chan Hee; Kim, Cheol Sang

2015-11-21

We report the versatile design of a smart nanoplatform for thermo-chemotherapy treatment of cancer. For the first time in the literature, our design takes advantage of the outstanding properties of mussel-inspired multiple catecholic groups - presenting a unique copolymer poly(2-hydroxyethyl methacrylate-co-dopamine methacrylamide) p(HEMA-co-DMA) to surface functionalize the superparamagnetic iron oxide nanoparticles as well as to conjugate borate containing anticancer drug bortezomib (BTZ) in a pH-dependent manner for the synergistic anticancer treatment. The unique multiple anchoring groups can be used to substantially improve the affinity of the ligands to the surfaces of the nanoparticles to form ultrastable iron oxide nanoparticles with control over their hydrodynamic diameter and interfacial chemistry. Thus the BTZ-incorporated-bio-inspired-smart magnetic nanoplatform will act as a hyperthermic agent that delivers heat when an alternating magnetic field is applied while the BTZ-bound catechol moieties act as chemotherapeutic agents in a cancer environment by providing pH-dependent drug release for the synergistic thermo-chemotherapy application. The anticancer efficacy of these bio-inspired multifunctional smart magnetic nanoparticles was tested both in vitro and in vivo and found that these unique magnetic nanoplatforms can be established to endow for the next generation of nanomedicine for efficient and safe cancer therapy.

Correlating size and composition-dependent effects with magnetic, Mössbauer, and pair distribution function measurements in a family of catalytically active ferrite nanoparticles

DOE PAGES

Wong, Stanislaus; Papaefthymiou, Georgia C.; Lewis, Crystal S.; ...

2015-05-06

The magnetic spinel ferrites, MFe₂O₄ (wherein 'M' = a divalent metal ion such as but not limited to Mn, Co, Zn, and Ni), represent a unique class of magnetic materials in which the rational introduction of different 'M's can yield correspondingly unique and interesting magnetic behaviors. Herein we present a generalized hydrothermal method for the synthesis of single-crystalline ferrite nanoparticles with 'M' = Mg, Fe, Co, Ni, Cu, and Zn, respectively, which can be systematically and efficaciously produced simply by changing the metal precursor. Our protocol can moreover lead to reproducible size control by judicious selection of various surfactants. Asmore » such, we have probed the effects of both (i) size and (ii) chemical composition upon the magnetic properties of these nanomaterials using complementary magnetometry and Mössbauer spectroscopy techniques. The structure of the samples was confirmed by atomic PDF analysis of X-ray and electron powder diffraction data as a function of particle size. These materials retain the bulk spinel structure to the smallest size (i.e., 3 nm). In addition, we have explored the catalytic potential of our ferrites as both (a) magnetically recoverable photocatalysts and (b) biological catalysts, and noted that many of our as-prepared ferrite systems evinced intrinsically higher activities as compared with their iron oxide analogues.« less

GMAG PhD Dissertation Research Award Talk: Dynamic Magnetic Traps for Particle Self-Assembly and Lab-on-Chip Applications

NASA Astrophysics Data System (ADS)

Chen, Aaron

2013-03-01

Micro-patterned Permalloy thin films serve as an excellent means to architect the spatial profile of magnetic fields with the tunable, high gradients required to manipulate objects with weak induced magnetic moments. In this presentation, I will highlight two projects carried out during my PhD studies. These findings demonstrate the functionalities achieved through carefully designed patterns of different sizes and shapes (e.g. circular, triangular, octagonal profiles): (i) By tuning a precessing magnetic field in conjunction with such Permalloy patterns, microsphere (i.e. dipole) cluster structures ranging from closely packed to frustrated and to plum-pudding-like planar lattices are stabilized. Such self-assembly of components at the micro to nanometer range not only support a rich variety of physical phenomena, but also have applications, for example, as filters or force probes and field-tunable photonic crystals. (ii) Mobile magnetic trap arrays consisting of Permalloy disks have enabled rapid transport of magnetic beads or immunomagnetically labeled cells across surfaces. Integration of these arrays with microfluidic droplet technology allows separation of labeled cells and their subsequent encapsulation into picoliter-sized droplets. The droplets serve as isolated containers for individual cells to be probed without cross-contamination. The separation-encapsulation function could become a critical component in point-of-care single-cell analysis platforms.

BOLDSync: a MATLAB-based toolbox for synchronized stimulus presentation in functional MRI.

PubMed

Joshi, Jitesh; Saharan, Sumiti; Mandal, Pravat K

2014-02-15

Precise and synchronized presentation of paradigm stimuli in functional magnetic resonance imaging (fMRI) is central to obtaining accurate information about brain regions involved in a specific task. In this manuscript, we present a new MATLAB-based toolbox, BOLDSync, for synchronized stimulus presentation in fMRI. BOLDSync provides a user friendly platform for design and presentation of visual, audio, as well as multimodal audio-visual (AV) stimuli in functional imaging experiments. We present simulation experiments that demonstrate the millisecond synchronization accuracy of BOLDSync, and also illustrate the functionalities of BOLDSync through application to an AV fMRI study. BOLDSync gains an advantage over other available proprietary and open-source toolboxes by offering a user friendly and accessible interface that affords both precision in stimulus presentation and versatility across various types of stimulus designs and system setups. BOLDSync is a reliable, efficient, and versatile solution for synchronized stimulus presentation in fMRI study. Copyright © 2013 Elsevier B.V. All rights reserved.

First principles statistical mechanics of alloys and magnetism

NASA Astrophysics Data System (ADS)

Eisenbach, Markus; Khan, Suffian N.; Li, Ying Wai

Modern high performance computing resources are enabling the exploration of the statistical physics of phase spaces with increasing size and higher fidelity of the Hamiltonian of the systems. For selected systems, this now allows the combination of Density Functional based first principles calculations with classical Monte Carlo methods for parameter free, predictive thermodynamics of materials. We combine our locally selfconsistent real space multiple scattering method for solving the Kohn-Sham equation with Wang-Landau Monte-Carlo calculations (WL-LSMS). In the past we have applied this method to the calculation of Curie temperatures in magnetic materials. Here we will present direct calculations of the chemical order - disorder transitions in alloys. We present our calculated transition temperature for the chemical ordering in CuZn and the temperature dependence of the short-range order parameter and specific heat. Finally we will present the extension of the WL-LSMS method to magnetic alloys, thus allowing the investigation of the interplay of magnetism, structure and chemical order in ferrous alloys. This research was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division and it used Oak Ridge Leadership Computing Facility resources at Oak Ridge National Laboratory.

How a High-Gradient Magnetic Field Could Affect Cell Life

NASA Astrophysics Data System (ADS)

Zablotskii, Vitalii; Polyakova, Tatyana; Lunov, Oleg; Dejneka, Alexandr

2016-11-01

The biological effects of high-gradient magnetic fields (HGMFs) have steadily gained the increased attention of researchers from different disciplines, such as cell biology, cell therapy, targeted stem cell delivery and nanomedicine. We present a theoretical framework towards a fundamental understanding of the effects of HGMFs on intracellular processes, highlighting new directions for the study of living cell machinery: changing the probability of ion-channel on/off switching events by membrane magneto-mechanical stress, suppression of cell growth by magnetic pressure, magnetically induced cell division and cell reprograming, and forced migration of membrane receptor proteins. By deriving a generalized form for the Nernst equation, we find that a relatively small magnetic field (approximately 1 T) with a large gradient (up to 1 GT/m) can significantly change the membrane potential of the cell and thus have a significant impact on not only the properties and biological functionality of cells but also cell fate.

Simulation of concomitant magnetic fields on fast switched gradient coils used in advanced application of MRI

NASA Astrophysics Data System (ADS)

Salinas-Muciño, G.; Torres-García, E.; Hidalgo-Tobon, S.

2012-10-01

The process to produce an MR image includes nuclear alignment, RF excitation, spatial encoding, and image formation. To form an image, it is necessary to perform spatial localization of the MR signals, which is achieved using gradient coils. MRI requires the use of gradient coils that generate magnetic fields, which vary linearly with position over the imaging volume. Safety issues have been a motivation to study deeply the relation between the interaction of gradient magnetic field and the peripheral nerve stimulation. In this work is presented a numerical modeling between the concomitant magnetic fields produced by the gradient coils and the electric field induced in a cube with σ conductivity by the gradient field switching in pulse sequences as Eco planar Imaging (EPI), due to this kind of sequence is the most used in advance applications of magnetic resonance imaging as functional MRI, cardiac imaging or diffusion.

How a High-Gradient Magnetic Field Could Affect Cell Life

PubMed Central

Zablotskii, Vitalii; Polyakova, Tatyana; Lunov, Oleg; Dejneka, Alexandr

2016-01-01

The biological effects of high-gradient magnetic fields (HGMFs) have steadily gained the increased attention of researchers from different disciplines, such as cell biology, cell therapy, targeted stem cell delivery and nanomedicine. We present a theoretical framework towards a fundamental understanding of the effects of HGMFs on intracellular processes, highlighting new directions for the study of living cell machinery: changing the probability of ion-channel on/off switching events by membrane magneto-mechanical stress, suppression of cell growth by magnetic pressure, magnetically induced cell division and cell reprograming, and forced migration of membrane receptor proteins. By deriving a generalized form for the Nernst equation, we find that a relatively small magnetic field (approximately 1 T) with a large gradient (up to 1 GT/m) can significantly change the membrane potential of the cell and thus have a significant impact on not only the properties and biological functionality of cells but also cell fate. PMID:27857227

Band-pass Fabry-Pèrot magnetic tunnel junctions

NASA Astrophysics Data System (ADS)

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

2018-05-01

We propose a high-performance magnetic tunnel junction by making electronic analogs of optical phenomena such as anti-reflections and Fabry-Pèrot resonances. The devices we propose feature anti-reflection enabled superlattice heterostructures sandwiched between the fixed and the free ferromagnets of the magnetic tunnel junction structure. Our predictions are based on non-equilibrium Green's function spin transport formalism coupled self-consistently with the Landau-Lifshitz-Gilbert-Slonczewski equation. Owing to the physics of bandpass spin filtering in the bandpass Fabry-Pèrot magnetic tunnel junction device, we demonstrate an ultra-high boost in the tunnel magneto-resistance (≈5 × 104%) and nearly 1200% suppression of spin transfer torque switching bias in comparison to a traditional trilayer magnetic tunnel junction device. The proof of concepts presented here can lead to next-generation spintronic device design harvesting the rich physics of superlattice heterostructures and exploiting spintronic analogs of optical phenomena.

Optical Pumping Spin Exchange 3He Gas Cells for Magnetic Resonance Imaging

NASA Astrophysics Data System (ADS)

Kim, W.; Stepanyan, S. S.; Kim, A.; Jung, Y.; Woo, S.; Yurov, M.; Jang, J.

2009-08-01

We present a device for spin-exchange optical pumping system to produce large quantities of polarized noble gases for Magnetic Resonance Imaging (MRI). A method and design of apparatus for pumping the polarization of noble gases is described. The method and apparatus enable production, storage and usage of hyperpolarized noble gases for different purposes, including Magnetic Resonance Imaging of human and animal subjects. Magnetic imaging agents breathed into lungs can be observed by the radio waves of the MRI scanner and report back physical and functional information about lung's health and desease. The technique known as spin exchange optical pumping is used. Nuclear magnetic resonance is implemented to measure the polarization of hyperpolarized gas. The cells prepared and sealed under high vacuum after handling Alkali metals into the cell and filling with the 3He-N2 mixture. The cells could be refilled. The 3He reaches around 50% polarization in 5-15 hours.

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.

Interaction quench dynamics in the Kondo model in the presence of a local magnetic field.

PubMed

Heyl, M; Kehrein, S

2010-09-01

In this work we investigate the quench dynamics in the Kondo model on the Toulouse line in the presence of a local magnetic field. It is shown that this setup can be realized by either applying the local magnetic field directly or by preparing the system in a macroscopically spin-polarized initial state. In the latter case, the magnetic field results from a subtlety in applying the bosonization technique where terms that are usually referred to as finite-size corrections become important in the present non-equilibrium setting. The transient dynamics are studied by analyzing exact analytical results for the local spin dynamics. The timescale for the relaxation of the local dynamical quantities turns out to be exclusively determined by the Kondo scale. In the transient regime, one observes damped oscillations in the local correlation functions with a frequency set by the magnetic field.

The effect of magnetic nanoparticle concentration on the structure organisation of a microferrogel

NASA Astrophysics Data System (ADS)

Ryzhkov, A. V.; Melenev, P. V.; Balasoiu, M.; Raikher, Yu L.

2018-03-01

Coarse-grained molecular dynamics simulation is applied to study the structural response of micro-sized magnetopolymer objects – microferrogels (MFG). The results for MFGs with different magnetic properties and concentrations of magnetic filler nanoparticles are analysed to detect the transition between non-aggregated configurations and the states with pronounced chains. The nanoparticles are assumed to be either magnetically isotropic or to possess infinite magnetic anisotropy. It is shown that, depending on the type of the particle anisotropy, an applied field in rather different ways affects the MFG structure and shape. Diagrams describing the degree of aggregation as a function of the parameter of the interparticle magnetodipolar interaction and concentration are presented. In particular, it is found that in the case of infinitely anisotropic nanoparticles the aggregation transitions undergoes via a non-trivial scenario. The effect of the structure transformations on the volume change of the MFG objects is studied as well.

Towards nanomedicines of the future: Remote magneto-mechanical actuation of nanomedicines by alternating magnetic fields☆

PubMed Central

Golovin, Yuri I.; Gribanovsky, Sergey L.; Golovin, Dmitry Y.; Klyachko, Natalia L.; Majouga, Alexander G.; Master, Alyssa M.; Sokolsky, Marina; Kabanov, Alexander V.

2015-01-01

The paper describes the concept of magneto-mechanical actuation of single-domain magnetic nanoparticles (MNPs) in super-low and low frequency alternating magnetic fields (AMFs) and its possible use for remote control of nanomedicines and drug delivery systems. The applications of this approach for remote actuation of drug release as well as effects on biomacromolecules, biomembranes, subcellular structures and cells are discussed in comparison to conventional strategies employing magnetic hyperthermia in a radio frequency (RF) AMF. Several quantitative models describing interaction of functionalized MNPs with single macromolecules, lipid membranes, and proteins (e.g. cell membrane receptors, ion channels) are presented. The optimal characteristics of the MNPs and an AMF for effective magneto-mechanical actuation of single molecule responses in biological and bio-inspired systems are discussed. Altogether, the described studies and phenomena offer opportunities for the development of novel therapeutics both alone and in combination with magnetic hyperthermia. PMID:26407671

Towards nanomedicines of the future: Remote magneto-mechanical actuation of nanomedicines by alternating magnetic fields.

PubMed

Golovin, Yuri I; Gribanovsky, Sergey L; Golovin, Dmitry Y; Klyachko, Natalia L; Majouga, Alexander G; Master, Аlyssa M; Sokolsky, Marina; Kabanov, Alexander V

2015-12-10

The paper describes the concept of magneto-mechanical actuation of single-domain magnetic nanoparticles (MNPs) in super-low and low frequency alternating magnetic fields (AMFs) and its possible use for remote control of nanomedicines and drug delivery systems. The applications of this approach for remote actuation of drug release as well as effects on biomacromolecules, biomembranes, subcellular structures and cells are discussed in comparison to conventional strategies employing magnetic hyperthermia in a radio frequency (RF) AMF. Several quantitative models describing interaction of functionalized MNPs with single macromolecules, lipid membranes, and proteins (e.g. cell membrane receptors, ion channels) are presented. The optimal characteristics of the MNPs and an AMF for effective magneto-mechanical actuation of single molecule responses in biological and bio-inspired systems are discussed. Altogether, the described studies and phenomena offer opportunities for the development of novel therapeutics both alone and in combination with magnetic hyperthermia.

THE TURBULENT DYNAMO IN HIGHLY COMPRESSIBLE SUPERSONIC PLASMAS

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

Federrath, Christoph; Schober, Jennifer; Bovino, Stefano

The turbulent dynamo may explain the origin of cosmic magnetism. While the exponential amplification of magnetic fields has been studied for incompressible gases, little is known about dynamo action in highly compressible, supersonic plasmas, such as the interstellar medium of galaxies and the early universe. Here we perform the first quantitative comparison of theoretical models of the dynamo growth rate and saturation level with three-dimensional magnetohydrodynamical simulations of supersonic turbulence with grid resolutions of up to 1024{sup 3} cells. We obtain numerical convergence and find that dynamo action occurs for both low and high magnetic Prandtl numbers Pm = ν/ηmore » = 0.1-10 (the ratio of viscous to magnetic dissipation), which had so far only been seen for Pm ≥ 1 in supersonic turbulence. We measure the critical magnetic Reynolds number, Rm{sub crit}=129{sub −31}{sup +43}, showing that the compressible dynamo is almost as efficient as in incompressible gas. Considering the physical conditions of the present and early universe, we conclude that magnetic fields need to be taken into account during structure formation from the early to the present cosmic ages, because they suppress gas fragmentation and drive powerful jets and outflows, both greatly affecting the initial mass function of stars.« less

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

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.

Magnetic field induced dynamical chaos.

PubMed

Ray, Somrita; Baura, Alendu; Bag, Bidhan Chandra

2013-12-01

In this article, we have studied the dynamics of a particle having charge in the presence of a magnetic field. The motion of the particle is confined in the x-y plane under a two dimensional nonlinear potential. We have shown that constant magnetic field induced dynamical chaos is possible even for a force which is derived from a simple potential. For a given strength of the magnetic field, initial position, and velocity of the particle, the dynamics may be regular, but it may become chaotic when the field is time dependent. Chaotic dynamics is very often if the field is time dependent. Origin of chaos has been explored using the Hamiltonian function of the dynamics in terms of action and angle variables. Applicability of the present study has been discussed with a few examples.

Ab-initio calculations of the Ruddlesden Popper phases CaMnO3, CaO(CaMnO3) and CaO(CaMnO3)2

NASA Astrophysics Data System (ADS)

Cardoso, C.; Borges, R. P.; Gasche, T.; Godinho, M.

2008-01-01

The present work reports ab-initio density functional theory calculations for the Ruddlesden-Popper phase CaO(CaMnO3)n compounds. In order to study the evolution of the properties with the number of perovskite layers, a detailed analysis of the densities of states calculated for each compound and for several magnetic configurations was performed. The effect of distortions of the crystal structure on the magnetic ground state is also analysed and the exchange constants and transition temperatures are calculated for the three compounds using a mean field model. The calculated magnetic ground state structures and magnetic moments are in good agreement with experimental results and previous calculations.

Spool pieces at the SSCL

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

Clayton, T.; Cai, Y.; Smellie, R.

1993-05-01

The basic features of the Superconducting Super Collider lattice are the two beamlines formed by superconducting dipoles (7736) and quadrupoles (1564). The dipoles constraint two 20 TeV proton beams into counterrotating closed orbits of 86.2 km. The quadrupoles (FODO) require cryogenic cooling the LHe temperatures. This requirement isolates the main magnets from the outside world. The interface required, the spool, is a crucial component of superconducting lattice design and machine operation. There are over 1588 spools in the Super Collider. We present hear SSCL spool designs which consist of (1) housing for superconducting closed orbit and multipole correction magnets, (2)more » cryogenic function, magnet quench protection, system power, and instrumentation interfaces, and (3) cold to warm transitions for ware magnet and warm instrumentation drift spaces.« less

Imaging of single magnetic dopants in III-V semiconductor hosts

NASA Astrophysics Data System (ADS)

Koenraad, Paul; Celebi, Cem; Silov, Andrei; Yakunin, Andrei; Tang, Jian-Ming; Flatte, Michael; Kaminska, Maria

2007-03-01

We present room-temperature cross-sectional scanning tunneling microscopy (STM) topographic measurements of the acceptor state wave function for Mn dopants in InP and compare with measurements for the nonmagnetic dopants Zn and Cd as well as with previous results for Mn in GaAs[1]. We find a strongly anisotropic ``bow-tie'' shape for the Mn acceptor state wave function in InP, similar to Mn in GaAs, which has a binding energy of 210 meV (compared to 113 meV for Mn in GaAs). The shape for Mn in InP is more symmetric with respect to the 001 plane than Mn in GaAs, which agrees with a general trend for the magnetic and nonmagnetic acceptor state symmetry as a function of acceptor binding energy. We present a new theoretical model based on the surface strain of GaAs (110) that explains why the 001-plane asymmetry of acceptor states seen in STM measurements is much larger than expected from bulk calculations. [1] A. M. Yakunin, et al., Phys. Rev. Lett. 92, 216806 (2004).

Energy anisotropy as a function of the direction of spin magnetization for a doublet system

NASA Astrophysics Data System (ADS)

Cherry, Peter J.; Malkin, Vladimir G.; Malkina, Olga L.; Asher, James R.

2016-11-01

This manuscript describes new phenomena that currently are not taken into account in both experimental EPR spectra interpretations and quantum chemical calculations of EPR parameters. This article presents an argument, with evidence, against the common belief that in the absence of an external magnetic field the total energy of a doublet system is independent of the spin orientation. Consequences of this phenomenon for interpretation of EPR experimental studies as well as for quantum chemical calculations of EPR parameters are discussed.

Contributions to the Fourth Solar Wind Conference. [interplanetary magnetic fields and medium

NASA Technical Reports Server (NTRS)

Acuna, M. H.; Behannon, K. W.; Burlaga, L. F.; Lepping, R.; Ness, N.; Ogilvie, K.; Pizzo, J.

1979-01-01

Recent results in interplanetary physics are examined. These include observations of shock waves and post-shock magnetic fields made by Voyager 1, 2; observations of the electron temperature as a function of distance between 1.36 AU and 2.25 AU; and observations of the structure of sector boundaries observed by Helios 1. A theory of electron energy transport in the collisionless solar wind is presented, and compared with observations. Alfven waves and Alvenic fluctuations in the solar wind are also discussed.

Non-Markovian Effects in Turbulent Diffusion in Magnetized Plasmas

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

Zagorodny, Anatoly; Weiland, Jan

2009-10-08

The derivation of the kinetic equations for inhomogeneous plasma in an external magnetic field is presented. The Fokker-Planck-type equations with the non-Markovian kinetic coefficients are proposed. In the time-local limit (small correlation times with respect to the distribution function relaxation time) the relations obtained recover the results known from the appropriate quasilinear theory and the Dupree-Weinstock theory of plasma turbulence. The equations proposed are used to describe zonal flow generation and to estimate the diffusion coefficient for saturated turbulence.

Advances in single-molecule magnet surface patterning through microcontact printing.

PubMed

Mannini, Matteo; Bonacchi, Daniele; Zobbi, Laura; Piras, Federica M; Speets, Emiel A; Caneschi, Andrea; Cornia, Andrea; Magnani, Agnese; Ravoo, Bart Jan; Reinhoudt, David N; Sessoli, Roberta; Gatteschi, Dante

2005-07-01

We present an implementation of strategies to deposit single-molecule magnets (SMMs) using microcontact printing microCP). We describe different approaches of microCP to print stripes of a sulfur-functionalized dodecamanganese (III, IV) cluster on gold surfaces. Comparison by atomic force microscopy profile analysis of the patterned structures confirms the formation of a chemically stable single layer of SMMs. Images based on chemical contrast, obtained by time-of-flight secondary ion mass spectrometry, confirm the patterned structure.

Convection in a nematic liquid crystal with homeotropic alignment and heated from below

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

Ahlers, G.

Experimental results for convection in a thin horizontal layer of a homeotropically aligned nematic liquid crystal heated from below and in a vertical magnetic field are presented. A subcritical Hopf bifurcation leads to the convecting state. There is quantitative agreement between the measured and the predicted bifurcation line as a function of magnetic field. The nonlinear state near the bifurcation is one of spatio-temporal chaos which seems to be the result of a zig-zag instability of the straight-roll state.

A non-axial superconducting magnet design for optimized patient access and minimal SAD for use in a Linac-MR hybrid: proof of concept.

PubMed

Yaghoobpour Tari, Shima; Wachowicz, Keith; Gino Fallone, B

2017-04-21

A prototype rotating hybrid magnetic resonance imaging system and linac has been developed to allow for simultaneous imaging and radiation delivery parallel to B 0 . However, the design of a compact magnet capable of rotation in a small vault with sufficient patient access and a typical clinical source-to-axis distance (SAD) is challenging. This work presents a novel superconducting magnet design as a proof of concept that allows for a reduced SAD and ample patient access by moving the superconducting coils to the side of the yoke. The yoke and pole-plate structures are shaped to direct the magnetic flux appropriately. The outer surface of the pole plate is optimized subject to the minimization of a cost function, which evaluates the uniformity of the magnetic field over an ellipsoid. The magnetic field calculations required in this work are performed with the 3D finite element method software package Opera-3D. Each tentative design strategy is virtually modeled in this software package, which is externally controlled by MATLAB, with its key geometries defined as variables. The optimization variables are the thickness of the pole plate at control points distributed over the pole plate surface. A novel design concept as a superconducting non-axial magnet is introduced, which could create a large uniform B 0 magnetic field with fewer geometric restriction. This non-axial 0.5 T superconducting magnet has a moderately reduced SAD of 123 cm and a vertical patient opening of 68 cm. This work is presented as a proof of principle to investigate the feasibility of a non-axial magnet with the coils located around the yoke, and the results encourage future design optimizations to maximize the benefits of this non-axial design.

A non-axial superconducting magnet design for optimized patient access and minimal SAD for use in a Linac-MR hybrid: proof of concept

NASA Astrophysics Data System (ADS)

Yaghoobpour Tari, Shima; Wachowicz, Keith; Fallone, B. Gino

2017-04-01

A prototype rotating hybrid magnetic resonance imaging system and linac has been developed to allow for simultaneous imaging and radiation delivery parallel to B 0. However, the design of a compact magnet capable of rotation in a small vault with sufficient patient access and a typical clinical source-to-axis distance (SAD) is challenging. This work presents a novel superconducting magnet design as a proof of concept that allows for a reduced SAD and ample patient access by moving the superconducting coils to the side of the yoke. The yoke and pole-plate structures are shaped to direct the magnetic flux appropriately. The outer surface of the pole plate is optimized subject to the minimization of a cost function, which evaluates the uniformity of the magnetic field over an ellipsoid. The magnetic field calculations required in this work are performed with the 3D finite element method software package Opera-3D. Each tentative design strategy is virtually modeled in this software package, which is externally controlled by MATLAB, with its key geometries defined as variables. The optimization variables are the thickness of the pole plate at control points distributed over the pole plate surface. A novel design concept as a superconducting non-axial magnet is introduced, which could create a large uniform B 0 magnetic field with fewer geometric restriction. This non-axial 0.5 T superconducting magnet has a moderately reduced SAD of 123 cm and a vertical patient opening of 68 cm. This work is presented as a proof of principle to investigate the feasibility of a non-axial magnet with the coils located around the yoke, and the results encourage future design optimizations to maximize the benefits of this non-axial design.

Rapid cycling medical synchrotron and beam delivery system

DOEpatents

Peggs, Stephen G [Port Jefferson, NY; Brennan, J Michael [East Northport, NY; Tuozzolo, Joseph E [Sayville, NY; Zaltsman, Alexander [Commack, NY

2008-10-07

A medical synchrotron which cycles rapidly in order to accelerate particles for delivery in a beam therapy system. The synchrotron generally includes a radiofrequency (RF) cavity for accelerating the particles as a beam and a plurality of combined function magnets arranged in a ring. Each of the combined function magnets performs two functions. The first function of the combined function magnet is to bend the particle beam along an orbital path around the ring. The second function of the combined function magnet is to focus or defocus the particle beam as it travels around the path. The radiofrequency (RF) cavity is a ferrite loaded cavity adapted for high speed frequency swings for rapid cycling acceleration of the particles.

Multi- and Unisensory Decoding of Words and Nonwords Result in Differential Brain Responses in Dyslexic and Nondyslexic Adults

ERIC Educational Resources Information Center

Kast, Monika; Bezzola, Ladina; Jancke, Lutz; Meyer, Martin

2011-01-01

The present functional magnetic resonance imaging (fMRI) study was designed, in order to investigate the neural substrates involved in the audiovisual processing of disyllabic German words and pseudowords. Twelve dyslexic and 13 nondyslexic adults performed a lexical decision task while stimuli were presented unimodally (either aurally or…

A Coupled 2 × 2D Babcock-Leighton Solar Dynamo Model. II. Reference Dynamo Solutions

NASA Astrophysics Data System (ADS)

Lemerle, Alexandre; Charbonneau, Paul

2017-01-01

In this paper we complete the presentation of a new hybrid 2 × 2D flux transport dynamo (FTD) model of the solar cycle based on the Babcock-Leighton mechanism of poloidal magnetic field regeneration via the surface decay of bipolar magnetic regions (BMRs). This hybrid model is constructed by allowing the surface flux transport (SFT) simulation described in Lemerle et al. to provide the poloidal source term to an axisymmetric FTD simulation defined in a meridional plane, which in turn generates the BMRs required by the SFT. A key aspect of this coupling is the definition of an emergence function describing the probability of BMR emergence as a function of the spatial distribution of the internal axisymmetric magnetic field. We use a genetic algorithm to calibrate this function, together with other model parameters, against observed cycle 21 emergence data. We present a reference dynamo solution reproducing many solar cycle characteristics, including good hemispheric coupling, phase relationship between the surface dipole and the BMR-generating internal field, and correlation between dipole strength at cycle maximum and peak amplitude of the next cycle. The saturation of the cycle amplitude takes place through the quenching of the BMR tilt as a function of the internal field. The observed statistical scatter about the mean BMR tilt, built into the model, acts as a source of stochasticity which dominates amplitude fluctuations. The model thus can produce Dalton-like epochs of strongly suppressed cycle amplitude lasting a few cycles and can even shut off entirely following an unfavorable sequence of emergence events.

Dependence of Brownian and Néel relaxation times on magnetic field strength

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

Deissler, Robert J., E-mail: rjd42@case.edu; Wu, Yong; Martens, Michael A.

2014-01-15

Purpose: In magnetic particle imaging (MPI) and magnetic particle spectroscopy (MPS) the relaxation time of the magnetization in response to externally applied magnetic fields is determined by the Brownian and Néel relaxation mechanisms. Here the authors investigate the dependence of the relaxation times on the magnetic field strength and the implications for MPI and MPS. Methods: The Fokker–Planck equation with Brownian relaxation and the Fokker–Planck equation with Néel relaxation are solved numerically for a time-varying externally applied magnetic field, including a step-function, a sinusoidally varying, and a linearly ramped magnetic field. For magnetic fields that are applied as a stepmore » function, an eigenvalue approach is used to directly calculate both the Brownian and Néel relaxation times for a range of magnetic field strengths. For Néel relaxation, the eigenvalue calculations are compared to Brown's high-barrier approximation formula. Results: The relaxation times due to the Brownian or Néel mechanisms depend on the magnitude of the applied magnetic field. In particular, the Néel relaxation time is sensitive to the magnetic field strength, and varies by many orders of magnitude for nanoparticle properties and magnetic field strengths relevant for MPI and MPS. Therefore, the well-known zero-field relaxation times underestimate the actual relaxation times and, in particular, can underestimate the Néel relaxation time by many orders of magnitude. When only Néel relaxation is present—if the particles are embedded in a solid for instance—the authors found that there can be a strong magnetization response to a sinusoidal driving field, even if the period is much less than the zero-field relaxation time. For a ferrofluid in which both Brownian and Néel relaxation are present, only one relaxation mechanism may dominate depending on the magnetic field strength, the driving frequency (or ramp time), and the phase of the magnetization relative to the applied magnetic field. Conclusions: A simple treatment of Néel relaxation using the common zero-field relaxation time overestimates the relaxation time of the magnetization in situations relevant for MPI and MPS. For sinusoidally driven (or ramped) systems, whether or not a particular relaxation mechanism dominates or is even relevant depends on the magnetic field strength, the frequency (or ramp time), and the phase of the magnetization relative to the applied magnetic field.« less

Corticospinal control of the thumb-index grip depends on precision of force control: a transcranial magnetic stimulation and functional magnetic resonance imagery study in humans.

PubMed

Bonnard, M; Galléa, C; De Graaf, J B; Pailhous, J

2007-02-01

The corticospinal system (CS) is well known to be of major importance for controlling the thumb-index grip, in particular for force grading. However, for a given force level, the way in which the involvement of this system could vary with increasing demands on precise force control is not well-known. Using transcranial magnetic stimulation and functional magnetic resonance imagery, the present experiments investigated whether increasing the precision demands while keeping the averaged force level similar during an isometric dynamic low-force control task, involving the thumb-index grip, does affect the corticospinal excitability to the thumb-index muscles and the activation of the motor cortices, primary and non-primary (supplementary motor area, dorsal and ventral premotor and in the contralateral area), at the origin of the CS. With transcranial magnetic stimulation, we showed that, when precision demands increased, the CS excitability increased to either the first dorsal interosseus or the opponens pollicis, and never to both, for similar ongoing electromyographic activation patterns of these muscles. With functional magnetic resonance imagery, we demonstrated that, for the same averaged force level, the amplitude of blood oxygen level-dependent signal increased in relation to the precision demands in the hand area of the contralateral primary motor cortex in the contralateral supplementary motor area, ventral and dorsal premotor area. Together these results show that, during the course of force generation, the CS integrates online top-down information to precisely fit the motor output to the task's constraints and that its multiple cortical origins are involved in this process, with the ventral premotor area appearing to have a special role.

A Method to Measure the Transverse Magnetic Field and Orient the Rotational Axis of Stars

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

Leone, Francesco; Scalia, Cesare; Gangi, Manuele

Direct measurements of stellar magnetic fields are based on the splitting of spectral lines into polarized Zeeman components. With a few exceptions, Zeeman signatures are hidden in data noise, and a number of methods have been developed to measure the average, over the visible stellar disk, of longitudinal components of the magnetic field. At present, faint stars are only observable via low-resolution spectropolarimetry, which is a method based on the regression of the Stokes V signal against the first derivative of Stokes I . Here, we present an extension of this method to obtain a direct measurement of the transversemore » component of stellar magnetic fields by the regression of high-resolution Stokes Q and U as a function of the second derivative of Stokes I . We also show that it is possible to determine the orientation in the sky of the rotation axis of a star on the basis of the periodic variability of the transverse component due to its rotation. The method is applied to data, obtained with the Catania Astrophysical Observatory Spectropolarimeter along the rotational period of the well known magnetic star β CrB.« less

Short-Term Forecasting of Radiation Belt and Ring Current

NASA Technical Reports Server (NTRS)

Fok, Mei-Ching

2007-01-01

A computer program implements a mathematical model of the radiation-belt and ring-current plasmas resulting from interactions between the solar wind and the Earth s magnetic field, for the purpose of predicting fluxes of energetic electrons (10 keV to 5 MeV) and protons (10 keV to 1 MeV), which are hazardous to humans and spacecraft. Given solar-wind and interplanetary-magnetic-field data as inputs, the program solves the convection-diffusion equations of plasma distribution functions in the range of 2 to 10 Earth radii. Phenomena represented in the model include particle drifts resulting from the gradient and curvature of the magnetic field; electric fields associated with the rotation of the Earth, convection, and temporal variation of the magnetic field; and losses along particle-drift paths. The model can readily accommodate new magnetic- and electric-field submodels and new information regarding physical processes that drive the radiation-belt and ring-current plasmas. Despite the complexity of the model, the program can be run in real time on ordinary computers. At present, the program can calculate present electron and proton fluxes; after further development, it should be able to predict the fluxes 24 hours in advance

Electronic and magnetic properties of double perovskite Sr2CoUO6: Heisenberg model

NASA Astrophysics Data System (ADS)

Nid-bahami, A.; Ahmed, S. Sidi; Ait-Tamerd, M.; Zaari, H.; El Kenz, A.; Benyoussef, A.

2018-01-01

This work will be focused on the electronic and magnetic properties of Sr2CoUO6 (SCUO) using ab-initio calculations and Monte Carlo Simulation (MCS). Firstly, we calculate the exchange coupling and the crystal field, then, the electronic and magnetic properties will be studied, using the full-potential linearized augmented plane wave (FP-LAPW) method, as implemented in the Wien2k code. This method employing the generalized gradient approximation (GGA) for exchange-correlation term. The half-metallic ferromagnetic nature implies a potential application of this new compound in spintronics devices. Also, we have presented the results of the band structures and densities of states for the two up and down spin polarizations. The exchange coupling and the crystal field calculated are J = 0 . 567 meV and δ = 0 . 559meV, and total spin magnetic moments is 2.96 μB closed to experimental values 3 μB. Secondly, we have presented the results for the magnetization and the susceptibility as a function of temperature. Finally, we obtain the critical temperature T = 9 . 20 K by MCS in good agreement with the experimental value.

Vortex jump behavior in coupled nanomagnetic heterostructures

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

Zhang, S.; Phatak, C., E-mail: cd@anl.gov; Petford-Long, A. K.

2014-11-24

The spin configuration and magnetic behavior in patterned nanostructures can be controlled by manipulating the interplay between the competing energy terms. This in turn requires fundamental knowledge of the magnetic interactions at the local nanometer scale. Here, we report on the spin structure and magnetization behavior of patterned discs containing exchange coupled ferromagnetic layers with additional exchange bias to an antiferromagnetic layer. The magnetization reversal was explored by direct local visualization of the domain behavior using in-situ Lorentz transmission electron microscopy, from which quantitative magnetic induction maps were reconstructed. The roles of the main competing energy terms were elucidated andmore » the reversal mechanism was identified as a coupled phenomenon of incoherent rotation in the exchange-biased layer and localized vortex nucleation and discontinuous propagation in the free layer, including an anomalous jump in the trajectory. The observations were supported by micromagnetic simulations and modeled phase shift simulations. The work presented here provides fundamental insights into opportunities for macroscopic control of the energy landscape of magnetic heterostructures for functional applications.« less

Electronic Correlation and Magnetism in the Ferromagnetic Metal Fe 3GeTe 2

DOE PAGES

Zhu, Jian-Xin; Janoschek, Marc; Chaves, D. S.; ...

2016-04-05

Motivated by the search for design principles of rare-earth-free strong magnets, we present a study of electronic structure and magnetic properties of the ferromagnetic metal Fe3GeTe2 within local density approximation (LDA) of the density functional theory, and its combination with dynamical mean-field theory (DMFT). For comparison to these calculations, we have measured magnetic and thermodynamic properties as well as X-ray magnetic circular dichroism and the photoemission spectrum of single crystal Fe3GeTe2. We find that the experimentally determined Sommerfeld coefficient is enhanced by an order of magnitude with respect to the LDA value. This enhancement can be partially explained by LDA+DMFT.more » Additionally, the inclusion of dynamical electronic correlation effects provides the experimentally observed magnetic moments, and the spectral density is in better agreement with photoemission data. Lastly, these results establish the importance of electronic correlations in this ferromagnet.« less

Vortex jump behavior in coupled nanomagnetic heterostructures

NASA Astrophysics Data System (ADS)

Zhang, S.; Petford-Long, A. K.; Heinonen, O.; Phatak, C.

2014-11-01

The spin configuration and magnetic behavior in patterned nanostructures can be controlled by manipulating the interplay between the competing energy terms. This in turn requires fundamental knowledge of the magnetic interactions at the local nanometer scale. Here, we report on the spin structure and magnetization behavior of patterned discs containing exchange coupled ferromagnetic layers with additional exchange bias to an antiferromagnetic layer. The magnetization reversal was explored by direct local visualization of the domain behavior using in-situ Lorentz transmission electron microscopy, from which quantitative magnetic induction maps were reconstructed. The roles of the main competing energy terms were elucidated and the reversal mechanism was identified as a coupled phenomenon of incoherent rotation in the exchange-biased layer and localized vortex nucleation and discontinuous propagation in the free layer, including an anomalous jump in the trajectory. The observations were supported by micromagnetic simulations and modeled phase shift simulations. The work presented here provides fundamental insights into opportunities for macroscopic control of the energy landscape of magnetic heterostructures for functional applications.

Multifunctional nanoparticles for upconversion luminescence/MR multimodal imaging and magnetically targeted photothermal therapy.

PubMed

Cheng, Liang; Yang, Kai; Li, Yonggang; Zeng, Xiao; Shao, Mingwang; Lee, Shuit-Tong; Liu, Zhuang

2012-03-01

Theranostics, the combination of diagnostics and therapies, has become a new concept in the battles with various major diseases such as cancer. Herein, we develop multifunctional nanoparticles (MFNPs) with highly integrated functionalities including upconversion luminescence, superparamagnetism, and strong optical absorption in the near-infrared (NIR) region with high photostability. In vivo dual modal optical/magnetic resonance imaging of mice uncovers that by placing a magnet nearby the tumor, MFNPs tend to migrate toward the tumor after intravenous injection and show high tumor accumulation, which is ~8 folds higher than that without magnetic targeting. NIR laser irradiation is then applied to the tumors grown on MFNP-injected mice under magnetic tumor-targeting, obtaining an outstanding photothermal therapeutic efficacy with 100% of tumor elimination in a murine breast cancer model. We present here a strategy for multimodal imaging-guided, magnetically targeted physical cancer therapy and highlight the promise of using multifunctional nanostructures for cancer theranostics. Copyright © 2011 Elsevier Ltd. All rights reserved.

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

NASA Astrophysics Data System (ADS)

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

2018-06-01

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

Facile transformation of FeO/Fe3O4 core-shell nanocubes to Fe3O4 via magnetic stimulation

NASA Astrophysics Data System (ADS)

Lak, Aidin; Niculaes, Dina; Anyfantis, George C.; Bertoni, Giovanni; Barthel, Markus J.; Marras, Sergio; Cassani, Marco; Nitti, Simone; Athanassiou, Athanassia; Giannini, Cinzia; Pellegrino, Teresa

2016-09-01

Here, we propose the use of magnetic hyperthermia as a means to trigger the oxidation of Fe1-xO/Fe3-δO4 core-shell nanocubes to Fe3-δO4 phase. As a first relevant consequence, the specific absorption rate (SAR) of the initial core-shell nanocubes doubles after exposure to 25 cycles of alternating magnetic field stimulation. The improved SAR value was attributed to a gradual transformation of the Fe1-xO core to Fe3-δO4, as evidenced by structural analysis including high resolution electron microscopy and Rietveld analysis of X-ray diffraction patterns. The magnetically oxidized nanocubes, having large and coherent Fe3-δO4 domains, reveal high saturation magnetization and behave superparamagnetically at room temperature. In comparison, the treatment of the same starting core-shell nanocubes by commonly used thermal annealing process renders a transformation to γ-Fe2O3. In contrast to other thermal annealing processes, the method here presented has the advantage of promoting the oxidation at a macroscopic temperature below 37 °C. Using this soft oxidation process, we demonstrate that biotin-functionalized core-shell nanocubes can undergo a mild self-oxidation transformation without losing their functional molecular binding activity.

Kubo Resistivity of magnetic flux ropes

NASA Astrophysics Data System (ADS)

Gekelman, Walter; Dehaas, Tim; Pribyl, Pat; Vincena, Stephen; van Compernolle, Bart; Sydora, Rick; Tang, Shawn Wenjie

2017-10-01

Magnetic flux ropes are bundles of twisted magnetic fields and their associated current. They are common on the surface of the sun (and presumably all other stars) and are observed to have a large range of sizes and lifetimes. They can become unstable and resulting in coronal mass ejections that can travel to earth and indeed, have been observed by satellites. Two side by side flux ropes are generated in the LAPD device at UCLA. Using a series of novel diagnostics the following key quantities, B, u, Vp, n, Te have been measured at more than 48,000 spatial locations and 7,000 time steps. Every term in Ohm's law is also evaluated across and along the local magnetic field and the plasma resistivity derived and it is shown that Ohms law is non-local. The electron distribution function parallel and antiparallel to the background magnetic field was measured and found to be a drifting Kappa function. The Kubo AC conductivity at the flux rope rotation frequency, a 3X3 tensor, was evaluated using velocity correlations and will be presented. This yields meaningful results for the global resistivity. Frequency spectra and the presence of time domain structures may offer a clue to the enhanced resistivity. Work supported by the Department of Energy and National Science Foundation.

Structural, electronic, and magnetic properties of Y(n)O (n=2-14) clusters: Density functional study.

PubMed

Yang, Zhi; Xiong, Shi-Jie

2008-09-28

The geometries stability, electronic properties, and magnetism of Y(n)O clusters up to n=14 are systematically studied with density functional theory. In the lowest-energy structures of Y(n)O clusters, the equilibrium site of the oxygen atom gradually moves from an outer site of the cluster, via a surface site, and finally, to an interior site as the number of the Y atoms increases from 2 to 14. Starting from n=12, the O atom falls into the center of the cluster with the Y atoms forming the outer frame. The results show that clusters with n=2, 4, 8, and 12 are more stable than their respective neighbors, and that the total magnetic moments of Y(n)O clusters are all quite small except Y(12)O cluster. The lowest-energy structure of Y(12)O cluster is a perfect icosahedron with a large magnetic moment 6mu(B). In addition, we find that the total magnetic moments are quenched for n=2, 6, and 8 due to the closed-shell electronic configuration. The calculated ionization potentials and electron affinities are in good agreement with the experimental results, which imply that the present theoretical treatments are satisfactory.

Remote sensing of the magnetic moment of uranus: predictions for voyager.

PubMed

Hill, T W; Dessler, A J

1985-03-22

Power is supplied to a planet's magnetosphere from the kinetic energy of planetary spin and the energy flux of the impinging solar wind. A fraction of this power is available to drive numerous observable phenomena, such as polar auroras and planetary radio emissions. In this report our present understanding of these power transfer mechanisms is applied to Uranus to make specific predictions of the detectability of radio and auroral emissions by the planetary radio astronomy (PRA) and ultraviolet spectrometer (UVS) instruments aboard the Voyager spacecraft before its encounter with Uranus at the end of January 1986. The power available for these two phenomena is (among other factors) a function of the magnetic moment of Uranus. The date of earliest detectability also depends on whether the predominant power source for the magnetosphere is planetary spin or solar wind. The magnetic moment of Uranus is derived for each power source as a function of the date of first detection of radio emissions by the PRA instrument or auroral emissions by the UVS instrument. If we accept the interpretation of ultraviolet observations now available from the Earth-orbiting International Ultraviolet Explorer satellite, Uranus has a surface magnetic field of at least 0.6 gauss, and more probably several gauss, making it the largest or second-largest planetary magnetic field in the solar system.

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

PubMed

de Melo, Roger Duarte; Acosta-Avalos, Daniel

2017-09-01

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

Patient positioning using artificial intelligence neural networks, trained magnetic field sensors and magnetic implants.

PubMed

Lennernäs, B; Edgren, M; Nilsson, S

1999-01-01

The purpose of this study was to evaluate the precision of a sensor and to ascertain the maximum distance between the sensor and the magnet, in a magnetic positioning system for external beam radiotherapy using a trained artificial intelligence neural network for position determination. Magnetic positioning for radiotherapy, previously described by Lennernäs and Nilsson, is a functional technique, but it is time consuming. The sensors are large and the distance between the sensor and the magnetic implant is limited to short distances. This paper presents a new technique for positioning, using an artificial intelligence neural network, which was trained to position the magnetic implant with at least 0.5 mm resolution in X and Y dimensions. The possibility of using the system for determination in the Z dimension, that is the distance between the magnet and the sensor, was also investigated. After training, this system positioned the magnet with a mean error of maximum 0.15 mm in all dimensions and up to 13 mm from the sensor. Of 400 test positions, 8 determinations had an error larger than 0.5 mm, maximum 0.55 mm. A position was determined in approximately 0.01 s.

Manipulating the magnetism and resistance state of Mn:ZnO/Pb(Zr0.52Ti0.48)O3 heterostructured films through electric fields

NASA Astrophysics Data System (ADS)

Li, Yong-Chao; Wu, Jun; Pan, Hai-Yang; Wang, Jue; Wang, Guang-Hou; Liu, Jun-Ming; Wan, Jian-Guo

2018-05-01

Mn:ZnO/Pb(Zr0.52Ti0.48)O3 (PZT) heterostructured films have been prepared on Pt/Ti/SiO2/Si wafers by a sol-gel process. Nonvolatile and reversible manipulation of the magnetism and resistance by electric fields has been realized. Compared with the saturation magnetic moment (Ms) in the +3.0 V case, the modulation gain of Ms can reach 270% in the -3.0 V case at room temperature. The resistance change is attributed to the interfacial potential barrier height variation and the formation of an accumulation (or depletion) layer at the Mn:ZnO/PZT interface, which can be regulated by the ferroelectric polarization direction. The magnetism of Mn:ZnO originates from bound magnetic polarons. The mobile carrier variation in Mn:ZnO, owing to interfacial polarization coupling and the ferroelectric field effect, enables the electric manipulation of the magnetism in the Mn:ZnO/PZT heterostructured films. This work presents an effective method for modulating the magnetism of magnetic semiconductors and provides a promising avenue for multifunctional devices with both electric and magnetic functionalities.

Progressive freezing of interacting spins in isolated finite magnetic ensembles

NASA Astrophysics Data System (ADS)

Bhattacharya, Kakoli; Dupuis, Veronique; Le-Roy, Damien; Deb, Pritam

2017-02-01

Self-organization of magnetic nanoparticles into secondary nanostructures provides an innovative way for designing functional nanomaterials with novel properties, different from the constituent primary nanoparticles as well as their bulk counterparts. Collective magnetic properties of such complex closed packing of magnetic nanoparticles makes them more appealing than the individual magnetic nanoparticles in many technological applications. This work reports the collective magnetic behaviour of magnetic ensembles comprising of single domain Fe3O4 nanoparticles. The present work reveals that the ensemble formation is based on the re-orientation and attachment of the nanoparticles in an iso-oriented fashion at the mesoscale regime. Comprehensive dc magnetic measurements show the prevalence of strong interparticle interactions in the ensembles. Due to the close range organization of primary Fe3O4 nanoparticles in the ensemble, the spins of the individual nanoparticles interact through dipolar interactions as realized from remnant magnetization measurements. Signature of super spin glass like behaviour in the ensembles is observed in the memory studies carried out in field cooled conditions. Progressive freezing of spins in the ensembles is corroborated from the Vogel-Fulcher fit of the susceptibility data. Dynamic scaling of relaxation reasserted slow spin dynamics substantiating cluster spin glass like behaviour in the ensembles.

Functional Alterations of Postcentral Gyrus Modulated by Angry Facial Expressions during Intraoral Tactile Stimuli in Patients with Burning Mouth Syndrome: A Functional Magnetic Resonance Imaging Study

PubMed Central

Yoshino, Atsuo; Okamoto, Yasumasa; Doi, Mitsuru; Okada, Go; Takamura, Masahiro; Ichikawa, Naho; Yamawaki, Shigeto

2017-01-01

Previous findings suggest that negative emotions could influence abnormal sensory perception in burning mouth syndrome (BMS). However, few studies have investigated the underlying neural mechanisms associated with BMS. We examined activation of brain regions in response to intraoral tactile stimuli when modulated by angry facial expressions. We performed functional magnetic resonance imaging on a group of 27 BMS patients and 21 age-matched healthy controls. Tactile stimuli were presented during different emotional contexts, which were induced via the continuous presentation of angry or neutral pictures of human faces. BMS patients exhibited higher tactile ratings and greater activation in the postcentral gyrus during the presentation of tactile stimuli involving angry faces relative to controls. Significant positive correlations between changes in brain activation elicited by angry facial images in the postcentral gyrus and changes in tactile rating scores by angry facial images were found for both groups. For BMS patients, there was a significant positive correlation between changes in tactile-related activation of the postcentral gyrus elicited by angry facial expressions and pain intensity in daily life. Findings suggest that neural responses in the postcentral gyrus are more strongly affected by angry facial expressions in BMS patients, which may reflect one possible mechanism underlying impaired somatosensory system function in this disorder. PMID:29163243

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.

A novel configuration for a brushless DC motor with an integrated planetary gear train

NASA Astrophysics Data System (ADS)

Yan, Hong-Sen; Wu, Yi-Chang

2006-06-01

This paper presents a novel configuration of a brushless DC (BLDC) motor with an integrated planetary gear train, which provides further functional and structural integrations to overcome inherent drawbacks of traditional designs. The effects of gear teeth on the magnetic field and performance of the BLDC motor are investigated. Two standard gear profile systems integrated on the stator with feasible numbers of gear teeth are introduced to reduce the cogging torque. An equivalent magnetic circuit model and an air-gap permeance model are applied to analytically analyze the magnetic field, while the validity is verified by 2-D finite-element method (FEM). Furthermore, the motor performance is discussed and compared with an existing design. The results show that the present design has the characteristics of lower cogging torque and torque ripple than the conventional design, which is of benefit to the widely applications on accurate motion and position control for BLDC motors.

Evaporation Rate of Water as a Function of a Magnetic Field and Field Gradient

PubMed Central

Guo, Yun-Zhu; Yin, Da-Chuan; Cao, Hui-Ling; Shi, Jian-Yu; Zhang, Chen-Yan; Liu, Yong-Ming; Huang, Huan-Huan; Liu, Yue; Wang, Yan; Guo, Wei-Hong; Qian, Ai-Rong; Shang, Peng

2012-01-01

The effect of magnetic fields on water is still a highly controversial topic despite the vast amount of research devoted to this topic in past decades. Enhanced water evaporation in a magnetic field, however, is less disputed. The underlying mechanism for this phenomenon has been investigated in previous studies. In this paper, we present an investigation of the evaporation of water in a large gradient magnetic field. The evaporation of pure water at simulated gravity positions (0 gravity level (ab. g), 1 g, 1.56 g and 1.96 g) in a superconducting magnet was compared with that in the absence of the magnetic field. The results showed that the evaporation of water was indeed faster in the magnetic field than in the absence of the magnetic field. Furthermore, the amount of water evaporation differed depending on the position of the sample within the magnetic field. In particular, the evaporation at 0 g was clearly faster than that at other positions. The results are discussed from the point of view of the evaporation surface area of the water/air interface and the convection induced by the magnetization force due to the difference in the magnetic susceptibility of water vapor and the surrounding air. PMID:23443127

The Use of Magnetic Orientation as a Pinning Modality for Investigation of Photon-Magnon Interactions in Magnetic Nanoparticle Systems.

PubMed

Cuong, Giap Van; Su, Luong Van; Tue, Nguyen Anh; Khanh, Hoang Quoc; Tuan, Nguyen Anh

2018-06-01

In this work, an experimental setup to study the dependence of a visible-light transmission through a magnetic granular film on the magnetic field direction was presented. The results measured the transmission (T) of the visible light, with the wavelengths λ were in the range from 560 to 695 nm, by the magnetic nanogranular films Cox-(Al2O3)100-x system, with Co compositions are x = 10 ÷ 45 at.%, as a function of the magnetic field direction were reported. These investigations were carried out under an external magnetic field of H = 400 Oe, which directs to the normal of the sample surface by an angle varied in the range of φ = 0° ÷ 45°, to magnetize the magnetization direction of all the Co particles following this direction. Consequently, the angle φ between the magnetization direction with the incident-light direction, which sets as the optical axis of the system and always keeps fixedly to the normal of the sample surface, is established. The experimental results showed the different dependencies of T on the angle φ, the magnetic field H, the Co composition x, and the wavelength λ. These dependencies attributed to a behavior that relates to so-called photon-magnon interaction.

Evaporation rate of water as a function of a magnetic field and field gradient.

PubMed

Guo, Yun-Zhu; Yin, Da-Chuan; Cao, Hui-Ling; Shi, Jian-Yu; Zhang, Chen-Yan; Liu, Yong-Ming; Huang, Huan-Huan; Liu, Yue; Wang, Yan; Guo, Wei-Hong; Qian, Ai-Rong; Shang, Peng

2012-12-11

The effect of magnetic fields on water is still a highly controversial topic despite the vast amount of research devoted to this topic in past decades. Enhanced water evaporation in a magnetic field, however, is less disputed. The underlying mechanism for this phenomenon has been investigated in previous studies. In this paper, we present an investigation of the evaporation of water in a large gradient magnetic field. The evaporation of pure water at simulated gravity positions (0 gravity level (ab. g), 1 g, 1.56 g and 1.96 g) in a superconducting magnet was compared with that in the absence of the magnetic field. The results showed that the evaporation of water was indeed faster in the magnetic field than in the absence of the magnetic field. Furthermore, the amount of water evaporation differed depending on the position of the sample within the magnetic field. In particular, the evaporation at 0 g was clearly faster than that at other positions. The results are discussed from the point of view of the evaporation surface area of the water/air interface and the convection induced by the magnetization force due to the difference in the magnetic susceptibility of water vapor and the surrounding air.

TU-H-BRA-04: A Novel Superconducting Magnet Design for Optimized Patient Access and Minimal SSD for Use in a Linac-MR Hybrid

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

Yaghoobpour Tari, S; Wachowicz, K; Fallone, B

2016-06-15

Purpose: A prototype rotating hybrid MR imaging system and linac has been developed to allow for simultaneous imaging and radiation delivery parallel to B{sub 0}. However, the design of a compact magnet capable of rotation in a small vault with sufficient patient access and a typical clinical source-to-surface distance (SSD) is challenging. This work presents a novel superconducting magnet design that allows for a reduced SSD and ample patient access by moving the superconducting coils to the side of the yoke. The yoke and pole-plate structures are shaped to direct the magnetic flux appropriately. Methods: The surface of the polemore » plate for the magnet assembly is optimized. The magnetic field calculations required in this work are performed with the 3D finite element method software package Opera-3D. Each tentative design strategy is virtually modeled in this software package and externally controlled by MATLAB, with its key geometries defined as variables. The particle swarm optimization algorithm is used to optimize the variables subject to the minimization of a cost function. At each iteration, Opera-3D will solve the magnetic field solution over a field-of-view suitable for MR imaging and the degree of field uniformity will be assessed to calculate the value of the cost function associated with that iteration. Results: An optimized magnet assembly that generates a homogenous 0.2T magnetic field over an ellipsoid with large axis of 30 cm and small axes of 20 cm is obtained. Conclusion: The distinct features of this model are the minimal distance between the yoke’s top and the isocentre and the improved patient access. On the other hand, having homogeneity over an ellipsoid give us a larger field-of-view, essential for geometric accuracy of the MRI system. The increase of B{sub 0} from 0.2T in the present model to 0.5T is the subject of future work. Funding Sources: Alberta Innovates - Health Solutions (AIHS)| Disclosure and Conflict of Interest: B. Gino Fallone is a co-founder and CEO of MagnetTx Oncology Solutions (under discussions to license Alberta biplanar linac MR for commercialization).« less

Functional Magnetic Resonance Imaging and Pediatric Anxiety

ERIC Educational Resources Information Center

Pine, Daniel S.; Guyer, Amanda E.; Leibenluft, Ellen; Peterson, Bradley S.; Gerber, Andrew

2008-01-01

The use of functional magnetic resonance imaging in investigating pediatric anxiety disorders is studied. Functional magnetic resonance imaging can be utilized in demonstrating parallels between the neural architecture of difference in anxiety of humans and the neural architecture of attention-orienting behavior in nonhuman primates or rodents.…

Resting state fMRI: A review on methods in resting state connectivity analysis and resting state networks.

PubMed

Smitha, K A; Akhil Raja, K; Arun, K M; Rajesh, P G; Thomas, Bejoy; Kapilamoorthy, T R; Kesavadas, Chandrasekharan

2017-08-01

The inquisitiveness about what happens in the brain has been there since the beginning of humankind. Functional magnetic resonance imaging is a prominent tool which helps in the non-invasive examination, localisation as well as lateralisation of brain functions such as language, memory, etc. In recent years, there is an apparent shift in the focus of neuroscience research to studies dealing with a brain at 'resting state'. Here the spotlight is on the intrinsic activity within the brain, in the absence of any sensory or cognitive stimulus. The analyses of functional brain connectivity in the state of rest have revealed different resting state networks, which depict specific functions and varied spatial topology. However, different statistical methods have been introduced to study resting state functional magnetic resonance imaging connectivity, yet producing consistent results. In this article, we introduce the concept of resting state functional magnetic resonance imaging in detail, then discuss three most widely used methods for analysis, describe a few of the resting state networks featuring the brain regions, associated cognitive functions and clinical applications of resting state functional magnetic resonance imaging. This review aims to highlight the utility and importance of studying resting state functional magnetic resonance imaging connectivity, underlining its complementary nature to the task-based functional magnetic resonance imaging.

Identification of prominence ejecta by the proton distribution function and magnetic fine structure in interplanetary coronal mass ejections in the inner heliosphere

NASA Astrophysics Data System (ADS)

Yao, Shuo; Marsch, Eckart; Tu, Chuan-Yi; Schwenn, Rainer

2010-05-01

This work presents in situ solar wind observations of three magnetic clouds (MCs) that contain cold high-density material when Helios 2 was located at 0.3 AU on 9 May 1979, 0.5 AU on 30 March 1976, and 0.7 AU on 24 December 1978. In the cold high-density regions embedded in the interplanetary coronal mass ejections we find (1) that the number density of protons is higher than in other regions inside the magnetic cloud, (2) the possible existence of He+, (3) that the thermal velocity distribution functions are more isotropic and appear to be colder than in the other regions of the MC, and the proton temperature is lower than that of the ambient plasma, and (4) that the associated magnetic field configuration can for all three MC events be identified as a flux rope. This cold high-density region is located at the polarity inversion line in the center of the bipolar structure of the MC magnetic field (consistent with previous solar observation work that found that a prominence lies over the neutral line of the related bipolar solar magnetic field). Specifically, for the first magnetic cloud event on 8 May 1979, a coronal mass ejection (CME) was related to an eruptive prominence previously reported as a result of the observation of Solwind (P78-1). Therefore, we identify the cold and dense region in the MC as the prominence material. It is the first time that prominence ejecta were identified by both the plasma and magnetic field features inside 1 AU, and it is also the first time that the thermal ion velocity distribution functions were used to investigate the microstate of the prominence material. Moreover, from our three cases, we also found that this material tended to fall behind the magnetic cloud and become smaller as it propagated farther away from the Sun, which confirms speculations in previous work. Overall, our in situ observations are consistent with three-part CME models.

Project FOOTPRINT: Substation modeling and simulations for E1 pulses

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

Nelson, Scott D.; Larson, D. J.; Kirkendall, B. A.

This report includes a presentation with an: Introduction to CW coupling; Introduction to single-pulse coupling; Description of E1 waveforms; Structures in a substation yard --articulated (as part of the substation's defined electrical functionality)--unarticulated (not as part of the substation's defined electrical functionality); Coupling --electrical coupling (capacitive coupling) --magnetic coupling (inductive coupling); Connectivity to long-line transmission lines; Control infrastructure; Summary; and References.

Scanning microwave microscopy technique for nanoscale characterization of magnetic materials

NASA Astrophysics Data System (ADS)

Joseph, C. H.; Sardi, G. M.; Tuca, S. S.; Gramse, G.; Lucibello, A.; Proietti, E.; Kienberger, F.; Marcelli, R.

2016-12-01

In this work, microwave characterization of magnetic materials using the scanning microwave microscopy (SMM) technique is presented. The capabilities of the SMM are employed for analyzing and imaging local magnetic properties of the materials under test at the nanoscale. The analyses are performed by acquiring both amplitude and phase of the reflected microwave signal. The changes in the reflection coefficient S11 are related to the local properties of the material under investigation, and the changes in its magnetic properties have been studied as a function of an external DC magnetic bias. Yttrium iron garnet (YIG) films deposited by RF sputtering and grown by liquid phase epitaxial (LPE) on gadolinium gallium garnet (GGG) substrates and permalloy samples have been characterized. An equivalent electromagnetic transmission line model is discussed for the quantitative analysis of the local magnetic properties. We also observed the hysteretic behavior of the reflection coefficient S11 with an external bias field. The imaging and spectroscopy analysis on the experimental results are evidently indicating the possibilities of measuring local changes in the intrinsic magnetic properties on the surface of the material.

Thermal effects on ρ meson properties in an external magnetic field

NASA Astrophysics Data System (ADS)

Ghosh, Snigdha; Mukherjee, Arghya; Mandal, Mahatsab; Sarkar, Sourav; Roy, Pradip

2017-12-01

A detailed study of the analytic structure of one-loop self energy graphs for neutral and charged ρ mesons is presented at finite temperature and arbitrary magnetic field using the real time formalism of thermal field theory. The imaginary part of the self energy is obtained from the discontinuities of these graphs across the unitary and Landau cuts, which is seen to be different for ρ0 and ρ±. The magnetic field dependent vacuum contribution to the real part of the self energy, which is usually ignored, is found to be appreciable. A significant effect of temperature and magnetic field is seen in the self energy, spectral function, effective mass, and dispersion relation of ρ0 as well as of ρ± relative to its trivial Landau shift. However, for charged ρ mesons, on account of the dominance of the Landau term, the effective mass appears to be independent of temperature. The trivial coupling of the magnetic moment of ρ± with external magnetic field, when incorporated in the calculation, makes the ρ± condense at high magnetic field.

BETA (Bitter Electromagnet Testing Apparatus) Design and Testing

NASA Astrophysics Data System (ADS)

Bates, Evan; Birmingham, William; Rivera, William; Romero-Talamas, Carlos

2016-10-01

BETA is a 1T water cooled Bitter-type magnetic system that has been designed and constructed at the Dusty Plasma Laboratory of the University of Maryland, Baltimore County to serve as a prototype of a scaled 10T version. Currently the system is undergoing magnetic, thermal and mechanical testing to ensure safe operating conditions and to prove analytical design optimizations. These magnets will function as experimental tools for future dusty plasma based and collaborative experiments. An overview of design methods used for building a custom made Bitter magnet with user defined experimental constraints is reviewed. The three main design methods consist of minimizing the following: ohmic power, peak conductor temperatures, and stresses induced by Lorentz forces. We will also discuss the design of BETA which includes: the magnet core, pressure vessel, cooling system, power storage bank, high powered switching system, diagnostics with safety cutoff feedback, and data acquisition (DAQ)/magnet control Matlab code. Furthermore, we present experimental data from diagnostics for validation of our analytical preliminary design methodologies and finite element analysis calculations. BETA will contribute to the knowledge necessary to finalize the 10 T magnet design.

In-line monitoring of (MR) fluid properties

NASA Astrophysics Data System (ADS)

Kordonski, William; Gorodkin, Sergei; Behlok, Ray

2015-05-01

Proper functionality of devices and processes based on (MR) fluids greatly depends, along with other factors, on stability of fluid characteristics such as concentration of magnetic particles and magnetic properties of the particles. The concentration of magnetic particles may change due to evaporation or leakage of carrier fluid, as well as particle sedimentation. Magnetic properties may change due to temperature, corrosion of particles or irreversible aggregation. In-line noninvasive monitoring of particle concentration and magnetic properties allows, in one way or another, compensation for the impact of destabilizing factors and provides system stable output. Two novel methods of in-line measurement of MR fluid magnetic permeability or magnetic particle concentration are considered in this presentation. The first one is based on the principle of mutual inductance and is intended for monitoring MR fluid flowing in pipes or channels. In the second one, permeability is measured by a flash-mount sensor which reacts on changes in the reluctance of the MR fluid layer adjacent to the wall. The use of the methods for stabilization of the material removal rate in high precision finishing process employing aqueous MR fluid is discussed.

γ-Fe2O3 magnetic nanoparticle functionalized with carboxylated multi walled carbon nanotube: Synthesis, characterization, analytical and biomedical application

NASA Astrophysics Data System (ADS)

Kılınç, Ersin

2016-03-01

In recent years, magnetic nanoparticles attained special interest in nanobiotechnology and nanomedicine due to their uniqe properties and biocompatibilities. From this perspective, hybride nanostructure composed from γ-Fe2O3 magnetic nanoparticle and carboxylated multi walled carbon nanotube was synthesized and characterized by FT-IR, VSM, SEM, HR-TEM and ICP-OES. Microscopy images showed that magnetic nanoparticles were nearly spherical structure that arranged on the axis of carboxylated MWCNT. Particle size was found lower than 10 nm. VSM results showed that the obtained magnetic nanoparticles presented superparamagnetic properties at room temperature. The magnetic saturation value was determined as 35.2 emu/g. It was used for the adsorption and controlled release of harmane, a potent tremor-producing neurotoxin. Maximum adsorption capacity was calculated as 151.5 mg/g from Langmuir isotherm. Concentration of harmane was determined by HPLC with fluorescence detection. The antimicrobial activity of synthesized magnetic nanoparticle was investigated against gram-negative and gram-positive bacteria. However, no activity was observed.

Extreme Material Physical Properties and Measurements above 100 tesla

NASA Astrophysics Data System (ADS)

Mielke, Charles

2011-03-01

The National High Magnetic Field Laboratory (NHMFL) Pulsed Field Facility (PFF) at Los Alamos National Laboratory (LANL) offers extreme environments of ultra high magnetic fields above 100 tesla by use of the Single Turn method as well as fields approaching 100 tesla with more complex methods. The challenge of metrology in the extreme magnetic field generating devices is complicated by the millions of amperes of current and tens of thousands of volts that are required to deliver the pulsed power needed for field generation. Methods of detecting physical properties of materials are essential parts of the science that seeks to understand and eventually control the fundamental functionality of materials in extreme environments. De-coupling the signal of the sample from the electro-magnetic interference associated with the magnet system is required to make these state-of-the-art magnetic fields useful to scientists studying materials in high magnetic fields. The cutting edge methods that are being used as well as methods in development will be presented with recent results in Graphene and High-Tc superconductors along with the methods and challenges. National Science Foundation DMR-Award 0654118.

Neuropsychological assessment of language functions during functional magnetic resonance imaging: development of new tasks. Preliminary report.

PubMed

Fersten, Ewa; Jakuciński, Maciej; Kuliński, Radosław; Koziara, Henryk; Mroziak, Barbara; Nauman, Paweł

2011-01-01

Due to the complex and extended cerebral organization of language functions, the brain regions crucial for speech and language, i.e. eloquent areas, have to be affected by neurooncological surgery. One of the techniques that may be helpful in pre-operative planning of the extent of tumour removal and estimating possible complications seems to be functional magnetic resonance imaging (fMRI). The aim of the study was to develop valid procedures for neuropsychological assessment of various language functions visualisable by fMRI in healthy individuals. In this fMRI study, 10 healthy (with no CNS pathology), right-handed volunteers aged 25-35 were examined using four tasks designed to measure different language functions, and one for short-term memory assessment. A 1.5-T MRI scanner performing ultrafast functional (EPI) sequences with 4-mm slice thickness and 1-mm interslice gap was used to detect the BOLD response to stimuli present-ed in a block design (30-second alternating blocks of activity and rest). The analyses used the SPM software running in a MATLAB environment, and the obtained data were interpreted by means of colour-coded maps superimposed on structural brain scans. For each of the tasks developed for particular language functions, a different area of increased neuronal activity was found. The differential localization of function-related neuronal activity seems interesting and the research worth continuing, since verbal communication failure may result from impairment of any of various language functions, and studies reported in the literature seem to focus on verbal expression only.

Unique topological characterization of braided magnetic fields

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

Yeates, A. R.; Hornig, G.

We introduce a topological flux function to quantify the topology of magnetic braids: non-zero, line-tied magnetic fields whose field lines all connect between two boundaries. This scalar function is an ideal invariant defined on a cross-section of the magnetic field, and measures the average poloidal magnetic flux around any given field line, or the average pairwise crossing number between a given field line and all others. Moreover, its integral over the cross-section yields the relative magnetic helicity. Using the fact that the flux function is also an action in the Hamiltonian formulation of the field line equations, we prove thatmore » it uniquely characterizes the field line mapping and hence the magnetic topology.« less

[Research progress of functional magnetic resonance imaging in mechanism studies of tinnitus].

PubMed

Ji, B B; Li, M; Zhang, J N

2018-02-07

Tinnitus is a subjective symptom of phantom sound in the ear or brain without sound or electrical stimulation in the environment. The mechanism of tinnitus is complicated and mostly unclear. Recent studies suggested that the abnormal peripheral auditory input lead to neuroplasticity changes in central nervous system followed by tinnitus. More research concerned on the tinnitus central mechanism. A rapid development of functional magnetic resonance imaging (fMRI) technique made it more widely used in tinnitus central mechanism research. fMRI brought new findings but also presented some shortages in technology and cognition in tinnitus study. This article summarized the outcomes of fMRI research on tinnitus in recent years, exploring its existing problems and application prospects.

The compensation of quadrupole errors and space charge effects by using trim quadrupoles

NASA Astrophysics Data System (ADS)

An, YuWen; Wang, Sheng

2011-12-01

The China Spallation Neutron Source (CSNS) accelerators consist of an H-linac and a proton Rapid Cycling Synchrotron (RCS). RCS is designed to accumulate and accelerate proton beam from 80 MeV to 1.6 GeV with a repetition rate of 25 Hz. The main dipole and quadruple magnet will operate in AC mode. Due to the adoption of the resonant power supplies, saturation errors of magnetic field cannot be compensated by power supplies. These saturation errors will disturb the linear optics parameters, such as tunes, beta function and dispersion function. The strong space charge effects will cause emittance growth. The compensation of these effects by using trim quadruples is studied, and the corresponding results are presented.

Magnetic Resonance Imaging-derived Flow Parameters for the Analysis of Cardiovascular Diseases and Drug Development.

PubMed

Michael, Dada O; Bamidele, Awojoyogbe O; Adewale, Adesola O; Karem, Boubaker

2013-01-01

Nuclear magnetic resonance (NMR) allows for fast, accurate and noninvasive measurement of fluid flow in restricted and non-restricted media. The results of such measurements may be possible for a very small B 0 field and can be enhanced through detailed examination of generating functions that may arise from polynomial solutions of NMR flow equations in terms of Legendre polynomials and Boubaker polynomials. The generating functions of these polynomials can present an array of interesting possibilities that may be useful for understanding the basic physics of extracting relevant NMR flow information from which various hemodynamic problems can be carefully studied. Specifically, these results may be used to develop effective drugs for cardiovascular-related diseases.

Magnetic Resonance Imaging-derived Flow Parameters for the Analysis of Cardiovascular Diseases and Drug Development

PubMed Central

Michael, Dada O.; Bamidele, Awojoyogbe O.; Adewale, Adesola O.; Karem, Boubaker

2013-01-01

Nuclear magnetic resonance (NMR) allows for fast, accurate and noninvasive measurement of fluid flow in restricted and non-restricted media. The results of such measurements may be possible for a very small B0 field and can be enhanced through detailed examination of generating functions that may arise from polynomial solutions of NMR flow equations in terms of Legendre polynomials and Boubaker polynomials. The generating functions of these polynomials can present an array of interesting possibilities that may be useful for understanding the basic physics of extracting relevant NMR flow information from which various hemodynamic problems can be carefully studied. Specifically, these results may be used to develop effective drugs for cardiovascular-related diseases. PMID:25114546

Plasma Diffusion in Self-Consistent Fluctuations

NASA Technical Reports Server (NTRS)

Smets, R.; Belmont, G.; Aunai, N.

2012-01-01

The problem of particle diffusion in position space, as a consequence ofeleclromagnetic fluctuations is addressed. Numerical results obtained with a self-consistent hybrid code are presented, and a method to calculate diffusion coefficient in the direction perpendicular to the mean magnetic field is proposed. The diffusion is estimated for two different types of fluctuations. The first type (resuiting from an agyrotropic in itiai setting)is stationary, wide band white noise, and associated to Gaussian probability distribution function for the magnetic fluctuations. The second type (result ing from a Kelvin-Helmholtz instability) is non-stationary, with a power-law spectrum, and a non-Gaussian probabi lity distribution function. The results of the study allow revisiting the question of loading particles of solar wind origin in the Earth magnetosphere.

Design of Magnetic Charged Particle Lens Using Analytical Potential Formula

NASA Astrophysics Data System (ADS)

Al-Batat, A. H.; Yaseen, M. J.; Abbas, S. R.; Al-Amshani, M. S.; Hasan, H. S.

2018-05-01

In the current research was to benefit from the potential of the two cylindrical electric lenses to be used in the product a mathematical model from which, one can determine the magnetic field distribution of the charged particle objective lens. With aid of simulink in matlab environment, some simulink models have been building to determine the distribution of the target function and their related axial functions along the optical axis of the charged particle lens. The present study showed that the physical parameters (i.e., the maximum value, Bmax, and the half width W of the field distribution) and the objective properties of the charged particle lens have been affected by varying the main geometrical parameter of the lens named the bore radius R.

The evolution of gadolinium based contrast agents: from single-modality to multi-modality

NASA Astrophysics Data System (ADS)

Zhang, Li; Liu, Ruiqing; Peng, Hui; Li, Penghui; Xu, Zushun; Whittaker, Andrew K.

2016-05-01

Gadolinium-based contrast agents are extensively used as magnetic resonance imaging (MRI) contrast agents due to their outstanding signal enhancement and ease of chemical modification. However, it is increasingly recognized that information obtained from single modal molecular imaging cannot satisfy the higher requirements on the efficiency and accuracy for clinical diagnosis and medical research, due to its limitation and default rooted in single molecular imaging technique itself. To compensate for the deficiencies of single function magnetic resonance imaging contrast agents, the combination of multi-modality imaging has turned to be the research hotpot in recent years. This review presents an overview on the recent developments of the functionalization of gadolinium-based contrast agents, and their application in biomedicine applications.

A generic signature of a fluctuating magnetic field: An additional turnover prior to the Kramers' one

NASA Astrophysics Data System (ADS)

Mondal, Shrabani; Baura, Alendu; Das, Sudip; Bag, Bidhan Chandra

2018-07-01

In this paper we have presented the dynamics of a Brownian particle which is coupled to a thermal bath in the presence of a fluctuating magnetic field (FMF). By virtue of the FMF the Brownian particle experiences a time dependent damping strength for the x -direction motion even in the presence of a stationary Markovian thermal bath. There is a transition state along this direction. The time dependent damping strength leads to appear a bi-turnover phenomenon in the variation of the barrier crossing rate as a function of the thermal bath induced damping strength. It is a generic signature of the fluctuating magnetic field.

Magnetic field induced transition in superconducting LaTiO3/SrTiO3 interfaces

NASA Astrophysics Data System (ADS)

Biscaras, J.; Bergeal, N.; Hurand, S.; Feuillet-Palma, C.; Rastogi, A.; Budhani, R. C.; Grilli, M.; Caprara, S.; Lesueur, J.

2013-07-01

Superconductivity at the LaTiO3/SrTiO3 interface is studied by low temperature and high magnetic field measurements as a function of a back-gate voltage. We show that it is intimately related to the appearance of a low density (a few 1012 cm-2) of high mobility carriers, in addition to low mobility ones always present in the system. These carriers form superconducting puddles coupled by a metallic two-dimensional electron gas, as revealed by the analysis of the phase transition driven by a perpendicular magnetic field. Two critical fields are evidenced, and a quantitative comparison with a recent theoretical model is made.

BRIEF COMMUNICATION: Fast-ion redistribution due to sawtooth crash in the TEXTOR tokamak measured by collective Thomson scattering

NASA Astrophysics Data System (ADS)

Nielsen, S. K.; Bindslev, H.; Salewski, M.; Bürger, A.; Delabie, E.; Furtula, V.; Kantor, M.; Korsholm, S. B.; Leipold, F.; Meo, F.; Michelsen, P. K.; Moseev, D.; Oosterbeek, J. W.; Stejner, M.; Westerhof, E.; Woskov, P.; TEXTOR Team

2010-09-01

Here we present collective Thomson scattering measurements of 1D fast-ion velocity distribution functions in neutral beam heated TEXTOR plasmas with sawtooth oscillations. Up to 50% of the fast ions in the centre are redistributed as a consequence of a sawtooth crash. We resolve various directions to the magnetic field. The fast-ion distribution is found to be anisotropic as expected. For a resolved angle of 39° to the magnetic field we find a drop in the fast-ion distribution of 20-40%. For a resolved angle of 83° to the magnetic field the drop is no larger than 20%.

Magnetoresistance due to domain walls in an epitaxial microfabricated Fe wire

NASA Astrophysics Data System (ADS)

Rüdiger, U.; Yu, J.; Kent, A. D.; Parkin, S. S. P.

1998-08-01

The domain wall (DW) contribution to magnetoresistance has been investigated using an epitaxial microfabricated bcc (110) Fe wires of 2 μm linewidth. A strong in-plane uniaxial component to the magnetic anisotropy perpendicular to the wire axis causes a regular stripe domain pattern with closure domains. The stripe domain width in zero-applied magnetic field is strongly affected by the magnetic history and can be continuously varied from 0.45 to 1.8 μm. This enables a measurement of the resistivity as a function of DW density in a single wire. Clear evidence is presented that the resistivity is reduced in the presence of DWs at low temperatures.

Dimensionality Controlled Octahedral Symmetry-Mismatch and Functionalities in Epitaxial LaCoO₃/SrTiO₃ Heterostructures.

PubMed

Qiao, Liang; Jang, Jae Hyuck; Singh, David J; Gai, Zheng; Xiao, Haiyan; Mehta, Apurva; Vasudevan, Rama K; Tselev, Alexander; Feng, Zhenxing; Zhou, Hua; Li, Sean; Prellier, Wilfrid; Zu, Xiaotao; Liu, Zijiang; Borisevich, Albina; Baddorf, Arthur P; Biegalski, Michael D

2015-07-08

Epitaxial strain provides a powerful approach to manipulate physical properties of materials through rigid compression or extension of their chemical bonds via lattice-mismatch. Although symmetry-mismatch can lead to new physics by stabilizing novel interfacial structures, challenges in obtaining atomic-level structural information as well as lack of a suitable approach to separate it from the parasitical lattice-mismatch have limited the development of this field. Here, we present unambiguous experimental evidence that the symmetry-mismatch can be strongly controlled by dimensionality and significantly impact the collective electronic and magnetic functionalities in ultrathin perovskite LaCoO3/SrTiO3 heterojunctions. State-of-art diffraction and microscopy reveal that symmetry breaking dramatically modifies the interfacial structure of CoO6 octahedral building-blocks, resulting in expanded octahedron volume, reduced covalent screening, and stronger electron correlations. Such phenomena fundamentally alter the electronic and magnetic behaviors of LaCoO3 thin-films. We conclude that for epitaxial systems, correlation strength can be tuned by changing orbital hybridization, thus affecting the Coulomb repulsion, U, instead of by changing the band structure as the common paradigm in bulks. These results clarify the origin of magnetic ordering for epitaxial LaCoO3 and provide a route to manipulate electron correlation and magnetic functionality by orbital engineering at oxide heterojunctions.

Clinical, radiographic, and magnetic resonance imaging findings of gastrocnemius musculotendinopathy in various dog breeds.

PubMed

Kaiser, Susanne M; Harms, Oliver; Konar, Martin; Staudacher, Anne; Langer, Anna; Thiel, Cetina; Kramer, Martin; Schaub, Sebastian; von Pückler, Kerstin H

2016-11-23

To describe clinical, radiographic, and magnetic resonance imaging (MRI) findings in 16 dogs diagnosed with gastrocnemius musculotendinopathy. Retrospective evaluation of medical records, radiographs, and MRI results, as well as follow-up completed by telephone questionnaire. Most dogs had chronic hindlimb lameness with no history of trauma or athletic activities. Clinical examination revealed signs of pain on palpation without stifle joint instability. Seven dogs had radiographic signs of osteophyte formation on the lateral fabella. Magnetic resonance imaging revealed T2 hyperintensity and uptake of contrast agent in the region of the origin of the gastrocnemius muscle. Changes were found in the lateral and medial heads of the gastrocnemius. Conservative treatment resulted in return to full function in 11 dogs. Two dogs showed partial restoration of normal function, one dog showed no improvement. Two dogs were lost to follow-up. Gastrocnemius musculotendinopathy is a potential cause of chronic hindlimb lameness in medium to large breed dogs. A history of athletic activity must not necessarily be present. Magnetic resonance imaging shows signal changes and uptake of contrast agent in the region of the origin of the gastrocnemius muscle. A combination of T1 pre- and post-contrast administration and T2 weighted sequences completed by a fat-suppressed sequence in the sagittal plane are well-suited for diagnosis. Conservative treatment generally results in return to normal function.

Kinetic features and non-stationary electron trapping in paraxial magnetic nozzles

NASA Astrophysics Data System (ADS)

Sánchez-Arriaga, G.; Zhou, J.; Ahedo, E.; Martínez-Sánchez, M.; Ramos, J. J.

2018-03-01

The paraxial expansion of a collisionless plasma jet into vacuum, guided by a magnetic nozzle, is studied with an Eulerian and non-stationary Vlasov-Poisson solver. Parametric analyzes varying the magnetic field expansion rate, the size of the simulation box, and the electrostatic potential fall are presented. After choosing the potential fall leading to a zero net current beam, the steady states of the simulations exhibit a quasi-neutral region followed by a downstream sheath. The latter, an unavoidable consequence of the finite size of the computational domain, does not affect the quasi-neutral region if the box size is chosen appropriately. The steady state presents a strong decay of the perpendicular temperature of the electrons, whose profile versus the inverse of the magnetic field does not depend on the expansion rate within the quasi-neutral region. As a consequence, the electron distribution function is highly anisotropic downstream. The simulations revealed that the ions reach a higher velocity during the transient than in the steady state and their distribution functions are not far from mono-energetic. The density percentage of the population of electrons trapped during the transient, which is computed self-consistently by the code, is up to 25% of the total electron density in the quasi-neutral region. It is demonstrated that the exact amount depends on the history of the system and the steady state is not unique. Nevertheless, the amount of trapped electrons is smaller than the one assumed heuristically by kinetic stationary theories.

Capture of dengue viruses using antibody-integrated graphite-encapsulated magnetic beads produced using gas plasma technology

PubMed Central

SAKUDO, AKIKAZU; VISWAN, ANCHU; CHOU, HAN; SASAKI, TADAHIRO; IKUTA, KAZUYOSHI; NAGATSU, MASAAKI

2016-01-01

Despite significant advances in medicine, global health is threatened by emerging infectious diseases caused by a number of viruses. Dengue virus (DENV) is a mosquito-borne virus, which can be transmitted to humans via mosquito vectors. Previously, the Ministry of Health, Labour and Welfare in Japan reported the country's first domestically acquired case of dengue fever for almost 70 years. To address this issue, it is important to develop novel technologies for the sensitive detection of DENV. The present study reported on the development of plasma-functionalized, graphite-encapsulated magnetic nanoparticles (GrMNPs) conjugated with anti-DENV antibody for DENV capture. Radiofrequency wave-excited inductively-coupled Ar and ammonia gas plasmas were used to introduce amino groups onto the surface of the GrMNPs. The GrMNPs were then conjugated with an antibody against DENV, and the antibody-integrated magnetic beads were assessed for their ability to capture DENV. Beads incubated in a cell culture medium of DENV-infected mosquito cells were separated from the supernatant by applying a magnetic field and were then washed. The adsorption of DENV serotypes 1–4 onto the beads was confirmed using reverse transcription-polymerase chain reaction, which detected the presence of DENV genomic RNA on the GrMNPs. The methodology described in the present study, which employed the plasma-functionalization of GrMNPs to enable antibody-integration, represents a significant improvement in the detection of DENV. PMID:27221214

ISOLATION OF CHICKEN FOLLICULAR DENDRITIC CELLS

USDA-ARS?s Scientific Manuscript database

The aim of the present study was to isolate chicken follicular dendritic cells (FDC). A combination of methods involving panning, iodixanol density gradient centrifugation, and magnetic cell separation technology made it possible to obtain functional FDC from the cecal tonsils from chickens, which h...

Topology optimization based design of unilateral NMR for generating a remote homogeneous field.

PubMed

Wang, Qi; Gao, Renjing; Liu, Shutian

2017-06-01

This paper presents a topology optimization based design method for the design of unilateral nuclear magnetic resonance (NMR), with which a remote homogeneous field can be obtained. The topology optimization is actualized by seeking out the optimal layout of ferromagnetic materials within a given design domain. The design objective is defined as generating a sensitive magnetic field with optimal homogeneity and maximal field strength within a required region of interest (ROI). The sensitivity of the objective function with respect to the design variables is derived and the method for solving the optimization problem is presented. A design example is provided to illustrate the utility of the design method, specifically the ability to improve the quality of the magnetic field over the required ROI by determining the optimal structural topology for the ferromagnetic poles. Both in simulations and experiments, the sensitive region of the magnetic field achieves about 2 times larger than that of the reference design, validating validates the feasibility of the design method. Copyright © 2017. Published by Elsevier Inc.

2-3D nonlocal transport model in magnetized laser plasmas.

NASA Astrophysics Data System (ADS)

Nicolaï, Philippe; Feugeas, Jean-Luc; Schurtz, Guy

2004-11-01

We present a model of nonlocal transport for multidimensional radiation magneto-hydrodynamics codes. This model, based on simplified Fokker-Planck equations, aims at extending the formulae of G Schurtz,Ph.Nicolaï and M. Busquet [Phys. Plasmas,7,4238 (2000)] to magnetized plasmas.The improvements concern various points as the electric field effects on nonlocal transport or conversely the kinetic effects on E field. However the main purpose of this work is to generalize the previous model by including magnetic field effects. A complete system of nonlocal equations is derived from kinetic equations with self-consistent E and B fields. These equations are analyzed and simplified in order to be implemented into large laser fusion codes and coupled to other relevent physics. Finally, our model allows to obtain the deformation of the electron distribution function due to nonlocal effects. This deformation leads to a non-maxwellian function which could be used to compute the influence on other physical processes.

Galactic X-ray emission from pulsars

NASA Technical Reports Server (NTRS)

Harding, A. K.

1981-01-01

The contribution of pulsars to the gamma-ray flux from the galactic plane is examined using data from the most recent pulsar surveys. It is assumed that pulsar gamma-rays are produced by curvature radiation from relativistic particles above the polar cap and attenuated by pair production in the strong magnetic and electric fields. Assuming that all pulsars produce gamma-rays in this way, their luminosities can be predicted as a function of period and magnetic field strength. Using the distribution of pulsars in the galaxy as determined from data on 328 pulsars detected in three surveys, the local gamma-ray production spectrum, the longitude profile, and the latitude profile of pulsar gamma-ray flux are calculated. The largest sources of uncertainty in the size of the pulsar contribution are the value of the mean interstellar electron density, the turnover in the pulsar radio luminosity function, and the average pulsar magnetic field strength. A present estimate is that pulsars contribute from 15 to 20 % of the total flux of gamma-rays from the galactic plane.

Study of samarium modified lead zirconate titanate and nickel zinc ferrite composite system

NASA Astrophysics Data System (ADS)

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

2015-03-01

In the present work, composites of samarium substituted lead zirconate titanate and nickel zinc ferrite with compositional formula 0.95Pb1-3x/2 SmxZr0.65Ti0.35O3-0.05Ni0.8Zn0.2Fe2O4 (x=0, 0.01, 0.02 and 0.03) were prepared by the conventional solid state route. X-ray diffraction analysis was carried out to confirm the coexistence of individual phases. Microstructural study was done by using scanning electron microscope. Dielectric constant and loss were studied as a function of temperature and frequency. To study ferroelectric and magnetic properties of the composite samples, corresponding P-E and M-H hysteresis loops were recorded. Change in magnetic properties of electrically poled composite sample (x=0.02) was studied to confirm the magnetoelectric (ME) coupling. ME coefficient (dE/dH) of the samples (x=0 and 0.02) was measured as a function of DC magnetic field.

Estimating Attitude, Trajectory, and Gyro Biases in an Extended Kalman Filter using Earth Magnetic Field Data from the Rossi X-Ray Timing Explorer

NASA Technical Reports Server (NTRS)

Deutschmann, Julie; Bar-Itzhack, Itzhack

1997-01-01

Traditionally satellite attitude and trajectory have been estimated with completely separate systems, using different measurement data. The estimation of both trajectory and attitude for low earth orbit satellites has been successfully demonstrated in ground software using magnetometer and gyroscope data. Since the earth's magnetic field is a function of time and position, and since time is known quite precisely, the differences between the computed and measured magnetic field components, as measured by the magnetometers throughout the entire spacecraft orbit, are a function of both the spacecraft trajectory and attitude errors. Therefore, these errors can be used to estimate both trajectory and attitude. This work further tests the single augmented Extended Kalman Filter (EKF) which simultaneously and autonomously estimates spacecraft trajectory and attitude with data from the Rossi X-Ray Timing Explorer (RXTE) magnetometer and gyro-measured body rates. In addition, gyro biases are added to the state and the filter's ability to estimate them is presented.

Synthesis of immunotargeted magneto-plasmonic nanoclusters.

PubMed

Wu, Chun-Hsien; Sokolov, Konstantin

2014-08-22

Magnetic and plasmonic properties combined in a single nanoparticle provide a synergy that is advantageous in a number of biomedical applications including contrast enhancement in novel magnetomotive imaging modalities, simultaneous capture and detection of circulating tumor cells (CTCs), and multimodal molecular imaging combined with photothermal therapy of cancer cells. These applications have stimulated significant interest in development of protocols for synthesis of magneto-plasmonic nanoparticles with optical absorbance in the near-infrared (NIR) region and a strong magnetic moment. Here, we present a novel protocol for synthesis of such hybrid nanoparticles that is based on an oil-in-water microemulsion method. The unique feature of the protocol described herein is synthesis of magneto-plasmonic nanoparticles of various sizes from primary blocks which also have magneto-plasmonic characteristics. This approach yields nanoparticles with a high density of magnetic and plasmonic functionalities which are uniformly distributed throughout the nanoparticle volume. The hybrid nanoparticles can be easily functionalized by attaching antibodies through the Fc moiety leaving the Fab portion that is responsible for antigen binding available for targeting.

Modulated heat pulse propagation and partial transport barriers in chaotic magnetic fields

DOE PAGES

del-Castillo-Negrete, Diego; Blazevski, Daniel

2016-04-01

Direct numerical simulations of the time dependent parallel heat transport equation modeling heat pulses driven by power modulation in 3-dimensional chaotic magnetic fields are presented. The numerical method is based on the Fourier formulation of a Lagrangian-Green's function method that provides an accurate and efficient technique for the solution of the parallel heat transport equation in the presence of harmonic power modulation. The numerical results presented provide conclusive evidence that even in the absence of magnetic flux surfaces, chaotic magnetic field configurations with intermediate levels of stochasticity exhibit transport barriers to modulated heat pulse propagation. In particular, high-order islands and remnants of destroyed flux surfaces (Cantori) act as partial barriers that slow down or even stop the propagation of heat waves at places where the magnetic field connection length exhibits a strong gradient. The key parameter ismore » $$\\gamma=\\sqrt{\\omega/2 \\chi_\\parallel}$$ that determines the length scale, $$1/\\gamma$$, of the heat wave penetration along the magnetic field line. For large perturbation frequencies, $$\\omega \\gg 1$$, or small parallel thermal conductivities, $$\\chi_\\parallel \\ll 1$$, parallel heat transport is strongly damped and the magnetic field partial barriers act as robust barriers where the heat wave amplitude vanishes and its phase speed slows down to a halt. On the other hand, in the limit of small $$\\gamma$$, parallel heat transport is largely unimpeded, global transport is observed and the radial amplitude and phase speed of the heat wave remain finite. Results on modulated heat pulse propagation in fully stochastic fields and across magnetic islands are also presented. In qualitative agreement with recent experiments in LHD and DIII-D, it is shown that the elliptic (O) and hyperbolic (X) points of magnetic islands have a direct impact on the spatio-temporal dependence of the amplitude and the time delay of modulated heat pulses.« less

Calculation of nuclear spin-spin coupling constants using frozen density embedding

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

Götz, Andreas W., E-mail: agoetz@sdsc.edu; Autschbach, Jochen; Visscher, Lucas, E-mail: visscher@chem.vu.nl

2014-03-14

We present a method for a subsystem-based calculation of indirect nuclear spin-spin coupling tensors within the framework of current-spin-density-functional theory. Our approach is based on the frozen-density embedding scheme within density-functional theory and extends a previously reported subsystem-based approach for the calculation of nuclear magnetic resonance shielding tensors to magnetic fields which couple not only to orbital but also spin degrees of freedom. This leads to a formulation in which the electron density, the induced paramagnetic current, and the induced spin-magnetization density are calculated separately for the individual subsystems. This is particularly useful for the inclusion of environmental effects inmore » the calculation of nuclear spin-spin coupling constants. Neglecting the induced paramagnetic current and spin-magnetization density in the environment due to the magnetic moments of the coupled nuclei leads to a very efficient method in which the computationally expensive response calculation has to be performed only for the subsystem of interest. We show that this approach leads to very good results for the calculation of solvent-induced shifts of nuclear spin-spin coupling constants in hydrogen-bonded systems. Also for systems with stronger interactions, frozen-density embedding performs remarkably well, given the approximate nature of currently available functionals for the non-additive kinetic energy. As an example we show results for methylmercury halides which exhibit an exceptionally large shift of the one-bond coupling constants between {sup 199}Hg and {sup 13}C upon coordination of dimethylsulfoxide solvent molecules.« less

Sensitive electrochemical immunoassay for 2,4,6-trinitrotoluene based on functionalized silica nanoparticle labels

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

Wang, Jun; Liu, Guodong; Wu, Hong

2008-03-03

We present a poly(guanine)-functionalized silica nanoparticle (NP) label-based electrochemical immunoassay for sensitively detecting 2,4,6-trinitrotoluene (TNT). This immunoassay takes advantage of magnetic bead–based platform for competitive displacement immunoreactions and separation, and use electroactive nanoparticles as labels for signal amplification. For this assay, anti-TNT-coated magnetic beads interacted with TNT analog-conjugated poly(guanine)-silica NPs and formed analog-anti-TNT immunocomplexes on magnetic beads. The immunocomplexes coated magnetic beads were exposed to TNT samples, which resulted in displacing the analog conjugated poly(guanine) silica NPs into solution by TNT. In contrast, there are no guanine residues releasing into the solution in the absence of TNT. The reaction solutionmore » was then separated from the magnetic beads and transferred to the electrode surface for electrochemical measurements of guanine oxidation with Ru(bpy)32+ as mediator. The sensitivity of this TNT assay was greatly enhanced through dual signal amplifications: 1) a large amount of guanine residues on silica nanoparticles is introduced into the test solution by displacement immunoreactions and 2) a Ru(bpy)32+-induced guanine catalytic oxidation further enhances the electrochemical signal. Some experimental parameters for the nanoparticle label-based electrochemical immunoassay were studied and the performance of this assay was evaluated. The method is found to be very sensitive and the detection limit of this assay is ~ 0.1 ng mL-1 TNT. The electrochemical immunoassay based on the poly[guanine]-functionalized silica NP label offers a new approach for sensitive detection of explosives.« less

Tunable electronic and magnetic properties of two-dimensional materials and their one-dimensional derivatives.

PubMed

Zhang, Zhuhua; Liu, Xiaofei; Yu, Jin; Hang, Yang; Li, Yao; Guo, Yufeng; Xu, Ying; Sun, Xu; Zhou, Jianxin; Guo, Wanlin

2016-01-01

Low-dimensional materials exhibit many exceptional properties and functionalities which can be efficiently tuned by externally applied force or fields. Here we review the current status of research on tuning the electronic and magnetic properties of low-dimensional carbon, boron nitride, metal-dichalcogenides, phosphorene nanomaterials by applied engineering strain, external electric field and interaction with substrates, etc, with particular focus on the progress of computational methods and studies. We highlight the similarities and differences of the property modulation among one- and two-dimensional nanomaterials. Recent breakthroughs in experimental demonstration of the tunable functionalities in typical nanostructures are also presented. Finally, prospective and challenges for applying the tunable properties into functional devices are discussed. WIREs Comput Mol Sci 2016, 6:324-350. doi: 10.1002/wcms.1251 For further resources related to this article, please visit the WIREs website. The authors have declared no conflicts of interest for this article.

Computational search for rare-earth free hard-magnetic materials

NASA Astrophysics Data System (ADS)

Flores Livas, José A.; Sharma, Sangeeta; Dewhurst, John Kay; Gross, Eberhard; MagMat Team

2015-03-01

It is difficult to over state the importance of hard magnets for human life in modern times; they enter every walk of our life from medical equipments (NMR) to transport (trains, planes, cars, etc) to electronic appliances (for house hold use to computers). All the known hard magnets in use today contain rare-earth elements, extraction of which is expensive and environmentally harmful. Rare-earths are also instrumental in tipping the balance of world economy as most of them are mined in limited specific parts of the world. Hence it would be ideal to have similar characteristics as a hard magnet but without or at least with reduced amount of rare-earths. This is the main goal of our work: search for rare-earth-free magnets. To do so we employ a combination of density functional theory and crystal prediction methods. The quantities which define a hard magnet are magnetic anisotropy energy (MAE) and saturation magnetization (Ms), which are the quantities we maximize in search for an ideal magnet. In my talk I will present details of the computation search algorithm together with some potential newly discovered rare-earth free hard magnet. J.A.F.L. acknowledge financial support from EU's 7th Framework Marie-Curie scholarship program within the ``ExMaMa'' Project (329386).

The force analysis for superparamagnetic nanoparticles-based gene delivery in an oscillating magnetic field

NASA Astrophysics Data System (ADS)

Sun, Jiajia; Shi, Zongqian; Jia, Shenli; Zhang, Pengbo

2017-04-01

Due to the peculiar magnetic properties and the ability to function in cell-level biological interaction, superparamagnetic nanoparticles (SMNP) have been being the attractive carrier for gene delivery. The superparamagnetic nanoparticles with surface-bound gene vector can be attracted to the surface of cells by the Kelvin force provided by external magnetic field. In this article, the influence of the oscillating magnetic field on the characteristics of magnetofection is studied in terms of the magnetophoretic velocity. The magnetic field of a cylindrical permanent magnet is calculated by equivalent current source (ECS) method, and the Kelvin force is derived by using the effective moment method. The results show that the static magnetic field accelerates the sedimentation of the particles, and drives the particles inward towards the axis of the magnet. Based on the investigation of the magnetophoretic velocity of the particle under horizontally oscillating magnetic field, an oscillating velocity within the amplitude of the magnet oscillation is observed. Furthermore, simulation results indicate that the oscillating amplitude plays an important role in regulating the active region, where the particles may present oscillating motion. The analysis of the magnetophoretic velocity gives us an insight into the physical mechanism of the magnetofection. It's also helpful to the optimal design of the magnetofection system.

Spin Polarization and Quantum Spins in Au Nanoparticles

PubMed Central

Li, Chi-Yen; Karna, Sunil K.; Wang, Chin-Wei; Li, Wen-Hsien

2013-01-01

The present study focuses on investigating the magnetic properties and the critical particle size for developing sizable spontaneous magnetic moment of bare Au nanoparticles. Seven sets of bare Au nanoparticle assemblies, with diameters from 3.5 to 17.5 nm, were fabricated with the gas condensation method. Line profiles of the X-ray diffraction peaks were used to determine the mean particle diameters and size distributions of the nanoparticle assemblies. The magnetization curves M(Ha) reveal Langevin field profiles. Magnetic hysteresis was clearly revealed in the low field regime even at 300 K. Contributions to the magnetization from different size particles in the nanoparticle assemblies were considered when analyzing the M(Ha) curves. The results show that the maximum particle moment will appear in 2.4 nm Au particles. A similar result of the maximum saturation magnetization appearing in 2.3 nm Au particles is also concluded through analysis of the dependency of the saturation magnetization MP on particle size. The MP(d) curve departs significantly from the 1/d dependence, but can be described by a log-normal function. Magnetization can be barely detected for Au particles larger than 27 nm. Magnetic field induced Zeeman magnetization from the quantum confined Kubo gap opening appears in Au nanoparticles smaller than 9.5 nm in diameter. PMID:23989607

Anomalous skin effects in a weakly magnetized degenerate electron plasma

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

Abbas, G., E-mail: gohar.abbas@gcu.edu.pk; Sarfraz, M.; Shah, H. A.

2014-09-15

Fully relativistic analysis of anomalous skin effects for parallel propagating waves in a weakly magnetized degenerate electron plasma is presented and a graphical comparison is made with the results obtained using relativistic Maxwellian distribution function [G. Abbas, M. F. Bashir, and G. Murtaza, Phys. Plasmas 18, 102115 (2011)]. It is found that the penetration depth for R- and L-waves for degenerate case is qualitatively small in comparison with the Maxwellian plasma case. The quantitative reduction due to weak magnetic field in the skin depth in R-wave for degenerate plasma is large as compared to the non-degenerate one. By ignoring themore » ambient magnetic field, previous results for degenerate field free case are salvaged [A. F. Alexandrov, A. S. Bogdankevich, and A. A. Rukhadze, Principles of Plasma Electrodynamics (Springer-Verlag, Berlin/Heidelberg, 1984), p. 90].« less

Influence of the Size and Structural Factors on the Magnetism of Multilayer Films Based on 3 d and 4 f Metals

NASA Astrophysics Data System (ADS)

Svalov, A. V.; Vas'kovskiy, V. O.; Kurlyandskaya, G. V.

2017-12-01

This work has presented some data on the layer structuring of films of 3 d and 4 f metals and their alloys, which have potential for practical use in magnetic sensors. The decrease in the thickness of magnetic layers with this structuring entails natural worsening of the crystallinity and leads to a degradation of magnetic ordering. However, the manifestation of these tendencies depends to a great extent on the conditions of preparation, the composition, and the sequence of the deposition of the contacting layers in the multilayer structures. The combination of these factors makes it possible to realize an optimum composition and optimum structural states of the films, which in a number of cases lead to the appearance of new combinations of functional properties.

Mathematical modeling of fluxgate magnetic gradiometers

NASA Astrophysics Data System (ADS)

Milovzorov, D. G.; Yasoveev, V. Kh.

2017-07-01

Issues of designing fluxgate magnetic gradiometers are considered. The areas of application of fluxgate magnetic gradiometers are determined. The structure and layout of a two-component fluxgate magnetic gradiometer are presented. It is assumed that the fluxgates are strictly coaxial in the gradiometer body. Elements of the classical approach to the mathematical modeling of the spatial arrangement of solids are considered. The bases of the gradiometer body and their transformations during spatial displacement of the gradiometer are given. The problems of mathematical modeling of gradiometers are formulated, basic mathematical models of a two-component fluxgate gradiometer are developed, and the mathematical models are analyzed. A computer experiment was performed. Difference signals from the gradiometer fluxgates for the vertical and horizontal position of the gradiometer body are shown graphically as functions of the magnitude and direction of the geomagnetic field strength vector.

A novel design of the high-precision magnetic locator with three-dimension measurement capability applying dynamically sensing mechanism

NASA Astrophysics Data System (ADS)

Huang, Wen-Nan; Chen, Po-Shen; Chen, Mu-Ping; Teng, Ching-Cheng

2006-09-01

A novel design of the magnetic locator, for obtaining the high-precision measurement information of variety of the buried metal pipes, is presented in this paper. The concept of dynamically sensing mechanism, including the vibrating and moving devices, proposed herein is a simple and effective way to improve the precision of three-dimension location sensing for the underground utilities. Based on the primary magnetism of Lenz's law and Faraday's law, the functions of the amplifying effect for the sensing magnetic signals, as well as the distinguishing effect by the simple filtering algorithms embedded in processing programs, are achieved while the relatively strong noise exists. The verification results of these integration designs demonstrate the effectiveness both by precise locating for the buried utility, and accurate measurement for the depth.

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

NASA Technical Reports Server (NTRS)

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

1990-01-01

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

Aperiodic topological order in the domain configurations of functional materials

NASA Astrophysics Data System (ADS)

Huang, Fei-Ting; Cheong, Sang-Wook

2017-03-01

In numerous functional materials, such as steels, ferroelectrics and magnets, new functionalities can be achieved through the engineering of the domain structures, which are associated with the ordering of certain parameters within the material. The recent progress in technologies that enable imaging at atomic-scale spatial resolution has transformed our understanding of domain topology, revealing that, along with simple stripe-like or irregularly shaped domains, intriguing vortex-type topological domain configurations also exist. In this Review, we present a new classification scheme of 'Zm Zn domains with Zl vortices' for 2D macroscopic domain structures with m directional variants and n translational antiphases. This classification, together with the concepts of topological protection and topological charge conservation, can be applied to a wide range of materials, such as multiferroics, improper ferroelectrics, layered transition metal dichalcogenides and magnetic superconductors, as we discuss using selected examples. The resulting topological considerations provide a new basis for the understanding of the formation, kinetics, manipulation and property optimization of domains and domain boundaries in functional materials.

Quantum critical singularities in two-dimensional metallic XY ferromagnets

NASA Astrophysics Data System (ADS)

Varma, Chandra M.; Gannon, W. J.; Aronson, M. C.; Rodriguez-Rivera, J. A.; Qiu, Y.

2018-02-01

An important problem in contemporary physics concerns quantum-critical fluctuations in metals. A scaling function for the momentum, frequency, temperature, and magnetic field dependence of the correlation function near a 2D-ferromagnetic quantum-critical point (QCP) is constructed, and its singularities are determined by comparing to the recent calculations of the correlation functions of the dissipative quantum XY model (DQXY). The calculations are motivated by the measured properties of the metallic compound YFe2Al10 , which is a realization of the DQXY model in 2D. The frequency, temperature, and magnetic field dependence of the scaling function as well as the singularities measured in the experiments are given by the theory without adjustable exponents. The same model is applicable to the superconductor-insulator transitions, classes of metallic AFM-QCPs, and as fluctuations of the loop-current ordered state in hole-doped cuprates. The results presented here lend credence to the solution found for the 2D-DQXY model and its applications in understanding quantum-critical properties of diverse systems.

Magnetic study of the low temperature anomalies in the underdoped PrBCO compound

NASA Astrophysics Data System (ADS)

Lahoubi, Mahieddine

2018-05-01

The low temperature anomalous magnetic properties of a non-superconducting PrBCO6+x compound in an underdoped oxygen state of concentration (x = 0.44) are characterized by paraprocess magnetic susceptibility χH(T) measurements carried out as a function of temperature T under different values of a DC magnetic field H up to 110 kOe. The derivatives dχH(T)/dT curves reveal a significant reduction with increasing H in the Néel temperature TN = 9 K of the Pr antiferromagnetic (AFM) ordering for which the transition subsists at 100 kOe. The small anomaly at T2 = 6-7 K is confirmed at 20 kOe and the previous spin reorientation attributed to this transition temperature seems to be suppressed above 60 kOe. The well defined anomaly in the vicinity of the low-critical point Tcr = 4-5 K which occurs simultaneously, is still present when the strength of H is increased up to 100 kOe. Weak field induced phase transitions are observed between T2 and TN at a low transition-field (Ht<11 kOe) in the differential magnetic susceptibility dMT(H)/dH as a function of H deduced from the isothermal magnetizations MT(H) with H up to 21 kOe, whereas a weak ferromagnetic behavior of the Pr sublattice appears below Tcr. The magnetic field effects give rise to more evidence for the Pr-Cu(2) coupling with 'exchange-frustrated AFM' interactions and ascertain the main role of the Pr sublattice whereas the Cu(2) sublattice seems to be less efficient.

Reconstruction of the static magnetic field of a magnetron

NASA Astrophysics Data System (ADS)

Krüger, Dennis; Köhn, Kevin; Gallian, Sara; Brinkmann, Ralf Peter

2018-06-01

The simulation of magnetron discharges requires a quantitatively correct mathematical model of the magnetic field structure. This study presents a method to construct such a model on the basis of a spatially restricted set of experimental data and a plausible a priori assumption on the magnetic field configuration. The example in focus is that of a planar circular magnetron. The experimental data are Hall probe measurements of the magnetic flux density in an accessible region above the magnetron plane [P. D. Machura et al., Plasma Sources Sci. Technol. 23, 065043 (2014)]. The a priori assumption reflects the actual design of the device, and it takes the magnetic field emerging from a center magnet of strength m C and vertical position d C and a ring magnet of strength m R , vertical position d R , and radius R. An analytical representation of the assumed field configuration can be formulated in terms of generalized hypergeometric functions. Fitting the ansatz to the experimental data with a least square method results in a fully specified analytical field model that agrees well with the data inside the accessible region and, moreover, is physically plausible in the regions outside of it. The outcome proves superior to the result of an alternative approach which starts from a multimode solution of the vacuum field problem formulated in terms of polar Bessel functions and vertical exponentials. As a first application of the obtained field model, typical electron and ion Larmor radii and the gradient and curvature drift velocities of the electron guiding center are calculated.

Exchange Interactions on the Highest-Spin Reported Molecule: the Mixed-Valence Fe42 Complex

PubMed Central

Aravena, Daniel; Venegas-Yazigi, Diego; Ruiz, Eliseo

2016-01-01

The finding of high-spin molecules that could behave as conventional magnets has been one of the main challenges in Molecular Magnetism. Here, the exchange interactions, present in the highest-spin molecule published in the literature, Fe42, have been analysed using theoretical methods based on Density Functional Theory. The system with a total spin value S = 45 is formed by 42 iron centres containing 18 high-spin FeIII ferromagnetically coupled and 24 diamagnetic low-spin FeII ions. The bridging ligands between the two paramagnetic centres are two cyanide ligands coordinated to the diamagnetic FeII cations. Calculations were performed using either small Fe4 or Fe3 models or the whole Fe42 complex, showing the presence of two different ferromagnetic couplings between the paramagnetic FeIII centres. Finally, Quantum Monte Carlo simulations for the whole system were carried out in order to compare the experimental and simulated magnetic susceptibility curves from the calculated exchange coupling constants with the experimental one. This comparison allows for the evaluation of the accuracy of different exchange-correlation functionals to reproduce such magnetic properties. PMID:27033418

Optimal Control-Enabled Imaging and Spectroscopy using a Nanowire Magnetic Resonance Force Microscope

NASA Astrophysics Data System (ADS)

Rose, William; Haas, Holger; Chen, Angela; Cory, David; Budakian, Raffi

Magnetic resonance imaging (MRI) is a powerful non-invasive technique that has transformed our ability to study the structure and function of biological systems. Key to its success has been the unique ability to combine imaging with magnetic resonance spectroscopy. Although it remains a significant challenge, there is considerable interest in extending MRI spectroscopy to the nanometer scale because it would provide a fundamentally new route for determining the structure and function of complex biomolecules. We present data taken with a nanowire magnetic resonance force microscopy (MRFM) setup. We show how the capabilities of this very sensitive spin-detection system can be extended to include spectroscopy and nanometer-scale imaging by combining optimal control theory (OCT) techniques with magic echo sequences. We apply OCT-based dynamical-decoupling pulses to nanoscale ensembles of proton spins in polystyrene, and demonstrate a 500-fold line-narrowing of the proton spin resonance, from 30 kHz to 60 Hz. We further demonstrate 1-D imaging over a 35-nm region with an average voxel size of 2.2 nm. Funding provided by the U.S. Army Research Office, Grant No. W911NF-12-1-0341.

First principles calculation of finite temperature magnetism in Fe and Fe3C

NASA Astrophysics Data System (ADS)

Eisenbach, M.; Nicholson, D. M.; Rusanu, A.; Brown, G.

2011-04-01

Density functional calculations have proven to be a useful tool in the study of ground state properties of many materials. The investigation of finite temperature magnetism, on the other hand, has to rely usually on the usage of empirical models that allow the large number of evaluations of the systems Hamiltonian that are required to obtain the phase space sampling needed to obtain the free energy, specific heat, magnetization, susceptibility, and other quantities as function of temperature. We have demonstrated a solution to this problem that harnesses the computational power of today's large massively parallel computers by combining a classical Wang-Landau Monte-Carlo calculation [F. Wang and D. P. Landau, Phys. Rev. Lett. 86, 2050 (2001)] with our first principles multiple scattering electronic structure code [Y. Wang et al., Phys. Rev. Lett. 75, 2867 (1995)] that allows the energy calculation of constrained magnetic states [M. Eisenbach et al., Proceedings of the Conference on High Performance Computing, Networking, Storage and Analysis (ACM, New York, 2009)]. We present our calculations of finite temperature properties of Fe and Fe3C using this approach and we find the Curie temperatures to be 980 and 425K, respectively.

Magnetomotive Optical Coherence Elastography for Magnetic Hyperthermia Dosimetry Based on Dynamic Tissue Biomechanics

PubMed Central

Huang, Pin-Chieh; Pande, Paritosh; Ahmad, Adeel; Marjanovic, Marina; Spillman, Darold R.; Odintsov, Boris; Boppart, Stephen A.

2016-01-01

Magnetic nanoparticles (MNPs) have been used in many diagnostic and therapeutic biomedical applications over the past few decades to enhance imaging contrast, steer drugs to targets, and treat tumors via hyperthermia. Optical coherence tomography (OCT) is an optical biomedical imaging modality that relies on the detection of backscattered light to generate high-resolution cross-sectional images of biological tissue. MNPs have been utilized as imaging contrast and perturbative mechanical agents in OCT in techniques called magnetomotive OCT (MM-OCT) and magnetomotive elastography (MM-OCE), respectively. MNPs have also been independently used for magnetic hyperthermia treatments, enabling therapeutic functions such as killing tumor cells. It is well known that the localized tissue heating during hyperthermia treatments result in a change in the biomechanical properties of the tissue. Therefore, we propose a novel dosimetric technique for hyperthermia treatment based on the viscoelasticity change detected by MM-OCE, further enabling the theranostic function of MNPs. In this paper, we first review the basic principles and applications of MM-OCT, MM-OCE, and magnetic hyperthermia, and present new preliminary results supporting the concept of MM-OCE-based hyperthermia dosimetry. PMID:28163565

Local magnetizations in impure two-dimensional antiferromagnets

NASA Astrophysics Data System (ADS)

van Luijk, J. A.; Arts, A. F. M.; de Wijn, H. W.

1980-03-01

The local magnetizations near dilute substitutional impurities in the quadratic-layer antiferromagnet K2MnF4 are studied both experimentally and theoretically. The impurities considered are the nonmagnetic Zn and Mg, as well as Ni. The magnetizations are probed through the positions of the impurity-associated satellites in the nuclear magnetic resonance of the out-of-layer and in-layer 19F nuclei adjacent to the magnetic ions. It is discussed in which way the effects of lattice deformations can be eliminated in order to obtain the variations of the local magnetizations with temperature. The theoretical treatment is based on Green's-function techniques. The decoupling employed is within the local spin-deviation operators and accounts for correlation between nearest neighbors. It reduces the renormalized spin-wave Hamiltonian to an effective quadratic form, rendering decoupling of Green's functions unnecessary. The spectral distributions of the excitations are calculated including local modes. The theory is subsequently applied to the 13-site cluster consisting of the impurity and the first three shells of Mn around it. Good agreement is found. The magnetization is significantly modified in the first shell. The further shells are only weakly affected, however somewhat stronger than in comparable three-dimensional systems. For nonmagnetic impurities the thermal spin deviation in the first shell is about 13 larger than that of the host; in the Ni-doped system the additional deviations are within 1%. The zero-point deviation of the Ni is 0.11 units of spin, as compared to 0.17 in the host. A further experimental result is a uniform shift, increasing with concentration, of the sublattice magnetization at large distance from the impurity. It must be related to the finite density of states near the zone center in two-dimensional systems. Finally, some data are presented on the local susceptibilities.

Magnetic hyaluronic acid nanospheres via aqueous Diels-Alder chemistry to deliver dexamethasone for adipose tissue engineering.

PubMed

Jia, Yang; Fan, Ming; Chen, Huinan; Miao, Yuting; Xing, Lian; Jiang, Bohong; Cheng, Qifan; Liu, Dongwei; Bao, Weikang; Qian, Bin; Wang, Jionglu; Xing, Xiaodong; Tan, Huaping; Ling, Zhonghua; Chen, Yong

2015-11-15

Biopolymer-based nanospheres have great potential in the field of drug delivery and tissue regenerative medicine. In this work, we present a flexible way to conjugate a magnetic hyaluronic acid (HA) nanosphere system that are capable of vectoring delivery of adipogenic factor, e.g. dexamethasone, for adipose tissue engineering. Conjugation of nanospheres was established by aqueous Diels-Alder chemistry between furan and maleimide of HA derivatives. Simultaneously, a furan functionalized dexamethasone peptide, GQPGK, was synthesized and covalently immobilized into the nanospheres. The magnetic HA nanospheres were fabricated by encapsulating super-paramagnetic iron oxide nanoparticles, which exhibited quick magnetic sensitivity. The aqueous Diels-Alder chemistry made nanospheres high binding efficiency of dexamethasone, and the vectoring delivery of dexamethasone could be easily controlled by a external magnetic field. The potential application of the magnetic HA nanospheres on vectoring delivery of adipogenic factor was confirmed by co-culture of human adipose-derived stem cells (ASCs). In vitro cytotoxicity tests demonstrated that incorporation of dexamethasone into magnetic HA nanospheres showed high efficiency to promote ASCs viabilities, in particular under a magnetic field, which suggested a promising future for adipose regeneration applications. Copyright © 2015 Elsevier Inc. All rights reserved.

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

NASA Astrophysics Data System (ADS)

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

2018-05-01

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

Rhenium-phthalocyanine molecular nanojunction with high magnetic anisotropy and high spin filtering efficiency

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

Li, J.; Institute of Nanomaterial and Nanostructure, Changsha University of Science and Technology, Changsha 410114; Hu, J.

2015-07-20

Using the density functional and non-equilibrium Green's function approaches, we studied the magnetic anisotropy and spin-filtering properties of various transition metal-Phthalocyanine molecular junctions across two Au electrodes. Our important finding is that the Au-RePc-Au junction has both large spin filtering efficiency (>80%) and large magnetic anisotropy energy, which makes it suitable for device applications. To provide insights for the further experimental work, we discussed the correlation between the transport property, magnetic anisotropy, and wave function features of the RePc molecule, and we also illustrated the possibility of controlling its magnetic state.

Scanning systems for particle cancer therapy

DOEpatents

Trbojevic, Dejan

2015-08-04

A particle beam to treat malignant tissue is delivered to a patient by a gantry. The gantry includes a plurality of small magnets sequentially arranged along a beam tube to transfer the particle beam with strong focusing and a small dispersion function, whereby a beam size is very small, allowing for the small magnet size. Magnets arranged along the beam tube uses combined function magnets where the magnetic field is a combination of a bending dipole field with a focusing or defocusing quadrupole field. A triplet set of combined function magnets defines the beam size at the patient. A scanning system of magnets arranged along the beam tube after the bending system delivers the particle beam in a direction normal to the patient, to minimize healthy skin and tissue exposure to the particle beam.

Multimodal Superparamagnetic Nanoparticles with Unusually Enhanced Specific Absorption Rate for Synergetic Cancer Therapeutics and Magnetic Resonance Imaging.

PubMed

Thorat, Nanasaheb D; Bohara, Raghvendra A; Malgras, Victor; Tofail, Syed A M; Ahamad, Tansir; Alshehri, Saad M; Wu, Kevin C-W; Yamauchi, Yusuke

2016-06-15

Superparamagnetic nanoparticles (SPMNPs) used for magnetic resonance imaging (MRI) and magnetic fluid hyperthermia (MFH) cancer therapy frequently face trade off between a high magnetization saturation and their good colloidal stability, high specific absorption rate (SAR), and most importantly biological compatibility. This necessitates the development of new nanomaterials, as MFH and MRI are considered to be one of the most promising combined noninvasive treatments. In the present study, we investigated polyethylene glycol (PEG) functionalized La1-xSrxMnO3 (LSMO) SPMNPs for efficient cancer hyperthermia therapy and MRI application. The superparamagnetic nanomaterial revealed excellent colloidal stability and biocompatibility. A high SAR of 390 W/g was observed due to higher colloidal stability leading to an increased Brownian and Neel's spin relaxation. Cell viability of PEG capped nanoparticles is up to 80% on different cell lines tested rigorously using different methods. PEG coating provided excellent hemocompatibility to human red blood cells as PEG functionalized SPMNPs reduced hemolysis efficiently compared to its uncoated counterpart. Magnetic fluid hyperthermia of SPMNPs resulted in cancer cell death up to 80%. Additionally, improved MRI characteristics were also observed for the PEG capped La1-xSrxMnO3 formulation in aqueous medium compared to the bare LSMO. Taken together, PEG capped SPMNPs can be useful for diagnosis, efficient magnetic fluid hyperthermia, and multimodal cancer treatment as the amphiphilicity of PEG can easily be utilized to encapsulate hydrophobic drugs.

Simulating functional magnetic materials on supercomputers.

PubMed

Gruner, Markus Ernst; Entel, Peter

2009-07-22

The recent passing of the petaflop per second landmark by the Roadrunner project at the Los Alamos National Laboratory marks a preliminary peak of an impressive world-wide development in the high-performance scientific computing sector. Also, purely academic state-of-the-art supercomputers such as the IBM Blue Gene/P at Forschungszentrum Jülich allow us nowadays to investigate large systems of the order of 10(3) spin polarized transition metal atoms by means of density functional theory. Three applications will be presented where large-scale ab initio calculations contribute to the understanding of key properties emerging from a close interrelation between structure and magnetism. The first two examples discuss the size dependent evolution of equilibrium structural motifs in elementary iron and binary Fe-Pt and Co-Pt transition metal nanoparticles, which are currently discussed as promising candidates for ultra-high-density magnetic data storage media. However, the preference for multiply twinned morphologies at smaller cluster sizes counteracts the formation of a single-crystalline L1(0) phase, which alone provides the required hard magnetic properties. The third application is concerned with the magnetic shape memory effect in the Ni-Mn-Ga Heusler alloy, which is a technologically relevant candidate for magnetomechanical actuators and sensors. In this material strains of up to 10% can be induced by external magnetic fields due to the field induced shifting of martensitic twin boundaries, requiring an extremely high mobility of the martensitic twin boundaries, but also the selection of the appropriate martensitic structure from the rich phase diagram.

Magnetic properties of the Tb4 + ion in Li2TbF6

NASA Astrophysics Data System (ADS)

Guillot, M.; El-Ghozzi, M.; Avignant, D.; Ferey, G.

1993-05-01

Both oxygen and fluorine have a partiality towards the stabilization of high oxidation states of rare earths such as Ce, Pr, and Tb. During the study of the MF-M'F4 (M=alkaline metal; M' rare ion) the compound Li2TbF6 was found to constitute the only representative obtained under ambient pressure of a structural type, namely α-Li2ZrF6, known until now only through the high pressure form. Magnetic measurements were carried out over the 1.4-300 K temperature range in continuous magnetic fields up to 20 T produced by a Bitter magnet. At low temperature and in H higher than 15 T, the magnetization M was observed to be field independent and very close to the calculated Tb4+ free ion value, i.e., 7μB; on the other hand, the data do not present any departure from the Brillouin function of the pure 8S7/2 state. The reciprocal magnetic susceptibility obeys a Curie-Weiss law leading to an effective moment of 7.86μB. A very unusual behavior of the terbium ion which presents a 4+ oxidation state is concluded: to the best of our knowledge, it is the first observation of this form. The so-found spherical 4f7 electronic configuration is the most compatible with the high coordination number of eight. Finally, the discussion within the series Li2MIVF6 compounds to understand the influence of both electronic configuration and size effects is presented.

Dissociations between behavioural and functional magnetic resonance imaging-based evaluations of cognitive function after brain injury

PubMed Central

Bardin, Jonathan C.; Fins, Joseph J.; Katz, Douglas I.; Hersh, Jennifer; Heier, Linda A.; Tabelow, Karsten; Dyke, Jonathan P.; Ballon, Douglas J.; Schiff, Nicholas D.

2011-01-01

Functional neuroimaging methods hold promise for the identification of cognitive function and communication capacity in some severely brain-injured patients who may not retain sufficient motor function to demonstrate their abilities. We studied seven severely brain-injured patients and a control group of 14 subjects using a novel hierarchical functional magnetic resonance imaging assessment utilizing mental imagery responses. Whereas the control group showed consistent and accurate (for communication) blood-oxygen-level-dependent responses without exception, the brain-injured subjects showed a wide variation in the correlation of blood-oxygen-level-dependent responses and overt behavioural responses. Specifically, the brain-injured subjects dissociated bedside and functional magnetic resonance imaging-based command following and communication capabilities. These observations reveal significant challenges in developing validated functional magnetic resonance imaging-based methods for clinical use and raise interesting questions about underlying brain function assayed using these methods in brain-injured subjects. PMID:21354974

Mechanical Response of Elastomers to Magnetic Fields

NASA Technical Reports Server (NTRS)

Munoz, B. C.; Jolly, M. R.

1996-01-01

Elastomeric materials represent an important class of engineering materials, which are widely used to make components of structures, machinery, and devices for vibration and noise control. Elastomeric material possessing conductive or magnetic properties have been widely used in applications such as conductive and magnetic tapes, sensors, flexible permanent magnets, etc. Our interest in these materials has focussed on understanding and controlling the magnitude and directionality of their response to applied magnetic fields. The effect of magnetic fields on the mechanical properties of these materials has not been the subject of many published studies. Our interest and expertise in controllable fluids have given us the foundation to make a transition to controllable elastomers. Controllable elastomers are materials that exhibit a change in mechanical properties upon application of an external stimuli, in this case a magnetic field. Controllable elastomers promise to have more functionality than conventional elastomers and therefore could share the broad industrial application base with conventional elastomers. As such, these materials represent an attractive class of smart materials, and may well be a link that brings the applications of modern control technologies, intelligent structures and smart materials to a very broad industrial area. This presentation will cover our research work in the area of controllable elastomers at the Thomas Lord Research Center. More specifically, the presentation will discuss the control of mechanical properties and mathematical modeling of the new materials prepared in our laboratories along with experiments to achieve adaptive vibration control using the new materials.

Total and Linearly Polarized Synchrotron Emission from Overpressured Magnetized Relativistic Jets

NASA Astrophysics Data System (ADS)

Fuentes, Antonio; Gómez, José L.; Martí, José M.; Perucho, Manel

2018-06-01

We present relativistic magnetohydrodynamic (RMHD) simulations of stationary overpressured magnetized relativistic jets, which are characterized by their dominant type of energy: internal, kinetic, or magnetic. Each model is threaded by a helical magnetic field with a pitch angle of 45° and features a series of recollimation shocks produced by the initial pressure mismatch, whose strength and number varies as a function of the dominant type of energy. We perform a study of the polarization signatures from these models by integrating the radiative transfer equations for synchrotron radiation using as inputs the RMHD solutions. These simulations show a top-down emission asymmetry produced by the helical magnetic field and a progressive confinement of the emission into a jet spine as the magnetization increases and the internal energy of the non-thermal population is considered to be a constant fraction of the thermal one. Bright stationary components associated with the recollimation shocks appear, presenting a relative intensity modulated by the Doppler boosting ratio between the pre-shock and post-shock states. Small viewing angles show a roughly bimodal distribution in the polarization angle, due to the helical structure of the magnetic field, which is also responsible for the highly stratified degree of linear polarization across the jet width. In addition, small variations of the order of 26° are observed in the polarization angle of the stationary components, which can be used to identify recollimation shocks in astrophysical jets.

Physiological self-regulation of regional brain activity using real-time functional magnetic resonance imaging (fMRI): methodology and exemplary data.

PubMed

Weiskopf, Nikolaus; Veit, Ralf; Erb, Michael; Mathiak, Klaus; Grodd, Wolfgang; Goebel, Rainer; Birbaumer, Niels

2003-07-01

A brain-computer interface (BCI) based on real-time functional magnetic resonance imaging (fMRI) is presented which allows human subjects to observe and control changes of their own blood oxygen level-dependent (BOLD) response. This BCI performs data preprocessing (including linear trend removal, 3D motion correction) and statistical analysis on-line. Local BOLD signals are continuously fed back to the subject in the magnetic resonance scanner with a delay of less than 2 s from image acquisition. The mean signal of a region of interest is plotted as a time-series superimposed on color-coded stripes which indicate the task, i.e., to increase or decrease the BOLD signal. We exemplify the presented BCI with one volunteer intending to control the signal of the rostral-ventral and dorsal part of the anterior cingulate cortex (ACC). The subject achieved significant changes of local BOLD responses as revealed by region of interest analysis and statistical parametric maps. The percent signal change increased across fMRI-feedback sessions suggesting a learning effect with training. This methodology of fMRI-feedback can assess voluntary control of circumscribed brain areas. As a further extension, behavioral effects of local self-regulation become accessible as a new field of research.

Dual responsive dysprosium-doped hydroxyapatite particles and toxicity reduction after functionalization with folic and glucuronic acids.

PubMed

Sánchez Lafarga, Ana Karen; Pacheco Moisés, Fermín P; Gurinov, Andrey; Ortiz, Genaro Gabriel; Carbajal Arízaga, Gregorio Guadalupe

2015-03-01

The development of probes for biomedical applications demands materials with low toxicity levels besides fluorescence or magnetic properties to be detected by confocal microscopes or MRI resonators. Several drug delivery systems or other biomedical materials prepared with hydroxyapatite have been proposed, however, toxicity effects might arise when the size of particles is nanometric. In this study, hydroxyapatite functionalized with glucuronic or folic acids presented lower oxidative stress, measured from lipoperoxides and nitric oxide indicators in rats than pure hydroxyapatite. In separated experiments, hydroxyapatite was doped with dysprosium cations by coprecipitation producing a single crystal phase with fluorescent properties easily visualized by confocal microscopy when excited at 488nm. These particles also presented the ability to modify the proton relaxation time in T1 maps collected by magnetic resonance imaging. These modified hydroxyapatite nanoparticles could be candidates to design bimodal probes with low toxicity. Copyright © 2014 Elsevier B.V. All rights reserved.

Functional connectivity: integrating behavioral, diffusion tensor imaging, and functional magnetic resonance imaging data sets.

PubMed

Baird, Abigail A; Colvin, Mary K; Vanhorn, John D; Inati, Souheil; Gazzaniga, Michael S

2005-04-01

In the present study, we combined 2 types of magnetic resonance technology to explore individual differences on a task that required the recognition of objects presented from unusual viewpoints. This task was chosen based on previous work that has established the necessity of information transfer from the right parietal cortex to the left inferior cortex for its successful completion. We used reaction times (RTs) to localize regions of cortical activity in the superior parietal and inferior frontal regions (blood oxygen level-dependent [BOLD] response) that were more active with longer response times. These regions were then sampled, and their signal change used to predict individual differences in structural integrity of white matter in the corpus callosum (using diffusion tensor imaging). Results show that shorter RTs (and associated increases in BOLD response) are associated with increased organization in the splenium of the corpus callosum, whereas longer RTs are associated with increased organization in the genu.

Graphene-based organic-inorganic hybrids with optoelectronic and magneto-optic functions (Conference Presentation)

NASA Astrophysics Data System (ADS)

Lee, Kwang-Sup; Kim, Sung-Hyun; Jung, Juhyoung; Teng, Xue-Cheng; Prabhakaran, Prem

2017-02-01

Groups around the world are pursuing optoelctronic and magneto-optic properties of graphene-based materials since they hold a lot of promise for future technologies. Quantum dot (QD) decorated graphenic nanohybrids can be candidates for demonstrating energy transfer, while magnetic nanoparticles (MNPs) on graphene give rise to interesting electronic phenomena like magneto-optical effects. Graphene containing MNPs are also good candidates for exploring quantum-hall effect. In medicine these materials have demonstrated applications in bioimaging, drug delivery, photothermal treatment and magnetic resonance imaging. A majority of groups working on QD or MNPs have focused on chemical functionalization methods for making graphene-MNP nanohybrids. We have developed a set of small molecule as well as polymeric ligands for noncovalent self-assembly of nanoparticles on graphene. The ligands contain pyrene as an anchor group for graphene and also thiol or dipamine as anchor groups for QD or MNPs. In this presentation we discuss the synthesis and characterization of these materials and outline some early results regarding exploratory device fabrication involving these materials.

The Electron Diffusion Region: Forces and Currents

NASA Technical Reports Server (NTRS)

Hesse, Michael

2008-01-01

The dissipation mechanism of magnetic reconnection remains a subject of intense scientific interest. On one hand, one set of recent studies have shown that particle inertia-based processes, which include thermal and bulk inertial effects, provide the reconnection electric field in the diffusion region. On the other hand, a second set of studies emphasizes the role of wave-particle interactions in providing anomalous resistivity in the diffusion region. In this presentation, we present analytical theory results, as well as PIC simulations of guide-field magnetic reconnection. We will show that the thermal electron inertia-based dissipation mechanism, expressed through nongyrotropic electron pressure tensors, remains viable in three dimensions. We will demonstrate the thermal inertia effect through studies of electron distribution functions. Furthermore, we will show that the reconnection electric field provides a transient acceleration on particles traversing the inner reconnection region. This inertia1 effect can be described as a diffusion-like term of the current density, which matches key features of electron distribution functions.

The Electron Diffusion Region: Forces and Currents

NASA Technical Reports Server (NTRS)

Hesse, Michael

2009-01-01

The dissipation mechanism of magnetic reconnection remains a subject of intense scientific interest. On one hand, one set of recent studies have shown that particle inertia-based processes, which include thermal and bulk inertial effects, provide the reconnection electric field in the diffusion region. On the other hand, a second set of studies emphasizes the role of wave-particle interactions in providing anomalous resistivity in the diffusion region. In this presentation, we present analytical theory results, as well as PIC simulations of guide-field magnetic reconnection. We will show that the thermal electron inertia-based dissipation mechanism, expressed through nongyrotropic electron pressure tensors, remains viable in three dimensions. We will demonstrate the thermal inertia effect through studies of electron distribution functions. Furthermore, we will show that the reconnection electric field provides a transient acceleration on particles traversing the inner reconnection region. This inertial effect can be described as a diffusion-like term of the current density, which matches key features of electron distribution functions.

Inflationary magnetogenesis and non-local actions: the conformal anomaly

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

El-Menoufi, Basem Kamal, E-mail: bmahmoud@physics.umass.edu

2016-02-01

We discuss the possibility of successful magnetogenesis during inflation by employing the one-loop effective action of massless QED. The action is strictly non-local and results from the long distance fluctuations of massless charged particles present at the inflationary scale. Most importantly, it encodes the conformal anomaly of QED which is crucial to avoid the vacuum preservation in classical electromagnetism. In particular, we find a blue spectrum for the magnetic field with spectral index n{sub B} ≅ 2 − α{sub e} where α{sub e} depends on both the number of e-folds during inflation as well as the coefficient of the one-loop beta function. In particular,more » the sign of the beta function has important bearing on the final result. A low reheating temperature is required for the present day magnetic field to be consistent with the lower bound inferred on the field in the intergalactic medium.« less

Ontogenetic development of magnetic compass orientation in domestic chickens (Gallus gallus).

PubMed

Denzau, Susanne; Nießner, Christine; Rogers, Lesley J; Wiltschko, Wolfgang

2013-08-15

Domestic chickens (Gallus gallus) can be trained to search for a social stimulus in a specific magnetic direction, and cryptochrome 1a, found in the retina, has been proposed as a receptor molecule mediating magnetic directions. The present study combines immuno-histochemical and behavioural data to analyse the ontogenetic development of this ability. Newly hatched chicks already have a small amount of cryptochrome 1a in their violet cones; on day 5, the amount of cryptochrome 1a reached the same level as in adult chickens, suggesting that the physical basis for magnetoreception is present. In behavioural tests, however, young chicks 5 to 7 days old failed to show a preference of the training direction; on days 8, 9 and 12, they could be successfully trained to search along a specific magnetic axis. Trained and tested again 1 week later, the chicks that had not shown a directional preference on days 5 to 7 continued to search randomly, while the chicks tested from day 8 onward preferred the correct magnetic axis when tested 1 week later. The observation that the magnetic compass is not functional before day 8 suggests that certain maturation processes in the magnetosensitive system in the brain are not yet complete before that day. The reasons why chicks that have been trained before that day fail to learn the task later remain unclear.

Longitudinal wave function control in single quantum dots with an applied magnetic field

PubMed Central

Cao, Shuo; Tang, Jing; Gao, Yunan; Sun, Yue; Qiu, Kangsheng; Zhao, Yanhui; He, Min; Shi, Jin-An; Gu, Lin; Williams, David A.; Sheng, Weidong; Jin, Kuijuan; Xu, Xiulai

2015-01-01

Controlling single-particle wave functions in single semiconductor quantum dots is in demand to implement solid-state quantum information processing and spintronics. Normally, particle wave functions can be tuned transversely by an perpendicular magnetic field. We report a longitudinal wave function control in single quantum dots with a magnetic field. For a pure InAs quantum dot with a shape of pyramid or truncated pyramid, the hole wave function always occupies the base because of the less confinement at base, which induces a permanent dipole oriented from base to apex. With applying magnetic field along the base-apex direction, the hole wave function shrinks in the base plane. Because of the linear changing of the confinement for hole wave function from base to apex, the center of effective mass moves up during shrinking process. Due to the uniform confine potential for electrons, the center of effective mass of electrons does not move much, which results in a permanent dipole moment change and an inverted electron-hole alignment along the magnetic field direction. Manipulating the wave function longitudinally not only provides an alternative way to control the charge distribution with magnetic field but also a new method to tune electron-hole interaction in single quantum dots. PMID:25624018

Longitudinal wave function control in single quantum dots with an applied magnetic field.

PubMed

Cao, Shuo; Tang, Jing; Gao, Yunan; Sun, Yue; Qiu, Kangsheng; Zhao, Yanhui; He, Min; Shi, Jin-An; Gu, Lin; Williams, David A; Sheng, Weidong; Jin, Kuijuan; Xu, Xiulai

2015-01-27

Controlling single-particle wave functions in single semiconductor quantum dots is in demand to implement solid-state quantum information processing and spintronics. Normally, particle wave functions can be tuned transversely by an perpendicular magnetic field. We report a longitudinal wave function control in single quantum dots with a magnetic field. For a pure InAs quantum dot with a shape of pyramid or truncated pyramid, the hole wave function always occupies the base because of the less confinement at base, which induces a permanent dipole oriented from base to apex. With applying magnetic field along the base-apex direction, the hole wave function shrinks in the base plane. Because of the linear changing of the confinement for hole wave function from base to apex, the center of effective mass moves up during shrinking process. Due to the uniform confine potential for electrons, the center of effective mass of electrons does not move much, which results in a permanent dipole moment change and an inverted electron-hole alignment along the magnetic field direction. Manipulating the wave function longitudinally not only provides an alternative way to control the charge distribution with magnetic field but also a new method to tune electron-hole interaction in single quantum dots.

Effects of magnets on pigeon homing

NASA Technical Reports Server (NTRS)

Keeton, W. T.

1972-01-01

The function of magnets in the navigation system of homing pigeons is investigated. Only experienced pigeons with magnets or brass bars were studied. Data show that on sunny days, pigeons with the magnets had some difficulty in orientation while those with brass bars had no problems. The same experiment was repeated on cloudy days. These results show that the magnets did not interfere with orientation. This difference suggests that sun and magnetic cues are used interchangeably, but that both together seldom function.

Long-term follow-up of nutritional status, pancreatic function, and morphological changes of the pancreatic remnant after pancreatic tumor resection in children.

PubMed

Sugito, Kiminobu; Furuya, Takeshi; Kaneda, Hide; Masuko, Takayuki; Ohashi, Kensuke; Inoue, Mikiya; Ikeda, Taro; Koshinaga, Tsugumichi; Tomita, Ryouichi; Maebayashi, Toshiya

2012-05-01

The objectives of the present study were to determine nutritional status, pancreatic function, and morphological changes of the pancreatic remnant after pancreatic tumor resection in children. The nutritional status was evaluated by the patterns of growth. Pancreatic function was evaluated by using a questionnaire, the Bristol stool form chart, the serum levels of fasting blood glucose, and hemoglobin A1c (HbA1c). Morphological changes of the pancreatic remnant were evaluated by computed tomography, magnetic resonance image, or magnetic resonance cholangiopancreatography. The present study consisted of 6 patients with pancreatic tumor (5 solid pseudopapillary tumors of the pancreas and 1 pancreatoblastoma) who underwent the following operations: tumor enucleation (3), distal pancreatectomy with splenectomy (1), and pylorus-preserving pancreatoduodenectomy (PPPD [2]). The serum levels of HbA1c have been gradually elevated in 2 patients with PPPD. A significant decrease in pancreatic parenchymal thickness and dilatation of the main pancreatic duct were observed in 2 patients with PPPD. Endocrine pancreatic insufficiency after PPPD may be explainable by obstructive pancreatitis after operation. Taking together the results of pancreatic endocrine function and morphological changes of pancreatic remnant after PPPD, tumor enucleation should be considered as surgical approach in children with pancreas head tumor whenever possible.

Computer-controlled stimulation for functional magnetic resonance imaging studies of the neonatal olfactory system

PubMed Central

Arichi, T; Gordon-Williams, R; Allievi, A; Groves, AM; Burdet, E; Edwards, AD

2013-01-01

Aim Olfactory sensation is highly functional early in human neonatal life, with studies suggesting that odours can influence behaviour and infant–mother bonding. Due to its good spatial properties, blood oxygen level–dependent (BOLD) contrast functional magnetic resonance imaging (fMRI) has the potential to rapidly advance our understanding of the neural activity which underlies the development of olfactory perception in this key period. We aimed to design an ‘olfactometer’ specifically for use with neonatal subjects for fMRI studies of odour perception. Methods We describe a fully automated and programmable, fMRI compatible system capable of presenting odorant liquids. To prevent contamination of the system and minimize between-subject infective risk, the majority of the olfactometer is constructed from single-use, readily available clinical equipment. The system was used to present the odour of infant formula milk in a validation group of seven neonatal subjects at term equivalent postmenstrual age (median age 40 weeks). Results A safe, reliable and reproducible pattern of stimulation was delivered leading to well-localized positive BOLD functional responses in the piriform cortex, amygdala, thalamus, insular cortex and cerebellum. Conclusions The described system is therefore suitable for detailed studies of the ontology of olfactory sensation and perception during early human brain development. PMID:23789919

Decreased mental time travel to the past correlates with default-mode network disintegration under lysergic acid diethylamide.

PubMed

Speth, Jana; Speth, Clemens; Kaelen, Mendel; Schloerscheidt, Astrid M; Feilding, Amanda; Nutt, David J; Carhart-Harris, Robin L

2016-04-01

This paper reports on the effects of LSD on mental time travel during spontaneous mentation. Twenty healthy volunteers participated in a placebo-controlled crossover study, incorporating intravenous administration of LSD (75 μg) and placebo (saline) prior to functional magnetic resonance imaging (fMRI). Six independent, blind judges analysed mentation reports acquired during structured interviews performed shortly after the functional magnetic resonance imaging (fMRI) scans (approximately 2.5 h post-administration). Within each report, specific linguistic references to mental spaces for the past, present and future were identified. Results revealed significantly fewer mental spaces for the past under LSD and this effect correlated with the general intensity of the drug's subjective effects. No differences in the number of mental spaces for the present or future were observed. Consistent with the previously proposed role of the default-mode network (DMN) in autobiographical memory recollection and ruminative thought, decreased resting-state functional connectivity (RSFC) within the DMN correlated with decreased mental time travel to the past. These results are discussed in relation to potential therapeutic applications of LSD and related psychedelics, e.g. in the treatment of depression, for which excessive reflection on one's past, likely mediated by DMN functioning, is symptomatic. © The Author(s) 2016.

Enzymes immobilization on Fe 3O 4-gold nanoparticles

NASA Astrophysics Data System (ADS)

Kalska-Szostko, B.; Rogowska, M.; Dubis, A.; Szymański, K.

2012-01-01

In the present study Fe3O4 magnetic nanoparticles were synthesized by coprecipitation of Fe2+ and Fe3+ from chlorides. In the next step magnetite-gold core-shell nanoparticles were synthesized from HAuCl4 using an ethanol as a reducing agent. Finally, magnetic nanoparticles were functionalized by hexadecanethiol. The immobilization of biological molecules (trypsin and glucose oxidase) to the thiol-modified and unmodified magnetite-gold nanoparticles surface was tested. The resulting nanoparticles were characterized by infrared spectroscopy, differential scanning calorimetry, Mössbauer spectroscopy and transmission electron microscopy.

Process for making diamonds

NASA Technical Reports Server (NTRS)

Rasquin, J. R.; Estes, M. F. (Inventor)

1973-01-01

A description is given of a device and process for making industrial diamonds. The device is composed of an exponential horn tapering from a large end to a small end, with a copper plate against the large end. A magnetic hammer abuts the copper plate. The copper plate and magnetic hammer function together to create a shock wave at the large end of the horn. As the wave propagates to the small end, the extreme pressure and temperature caused by the wave transforms the graphite, present in an anvil pocket at the small end, into diamonds.

The electronic and magnetic properties of quaternary Heusler alloy CoFeMnGe

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

Seema, K.

2016-05-23

We present study of quaternary Heusler alloy CoFeMnGe using density functional theory. The compound is half-metallic with half-metallic gap of 0.13 eV. The total magnetic moment of this compound is 3.96 μ{sub B} which is in close agreement with Slater-Pauling rule. The effect of lattice compression and expansion shows the robustness of half-metallicity. A large value of half-metallic gap and 100% spin-polarization makes this material interesting for spin dependent applications.

Composite magnetorheological elastomers as dielectrics for plane capacitors: Effects of magnetic field intensity

NASA Astrophysics Data System (ADS)

Balasoiu, Maria; Bica, Ioan

The fabrication of composite magnetorheological elastomers (MRECs) based on silicone rubber, carbonyl iron microparticles (10% vol.) and polyurethane elastomer doped with 0%, 10% and 20% volume concentration TiO2 microparticles is presented. The obtained MRECs have the shape of thin foils and are used as dielectric materials for manufacturing plane capacitors. Using the plane capacitor method and expression of capacitance as a function of magnetic field intensity, combined with linear elasticity theory, the static magnetoelastic model of the composite is obtained and analyzed.

Theoretical study of the magnetic behavior of hexanuclear Cu(II) and Ni(II) polysiloxanolato complexes.

PubMed

Ruiz, Eliseo; Cano, Joan; Alvarez, Santiago; Caneschi, Andrea; Gatteschi, Dante

2003-06-04

A theoretical density functional study of the exchange coupling in hexanuclear polysiloxanolato-bridged complexes of Cu(II) and Ni(II) is presented. By calculating the energies of three different spin configurations, we can obtain estimates of the first-, second-, and third-neighbor exchange coupling constants. The study has been carried out for the complete structures of the Cu pristine cluster and of the chloroenclathrated Ni complex as well as for the hypotethical pristine Ni compound and for magnetically dinuclear analogues M(2)Zn(4) (M = Cu, Ni).

Development of a highly-sensitive Penning ionization electron spectrometer using the magnetic bottle effect

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

Ota, Masahiro; Ishiguro, Yuki; Nakajima, Yutaro

2016-02-01

This paper reports on a highly-sensitive retarding-type electron spectrometer for a continuous source of electrons, in which the electron collection efficiency is increased by utilizing the magnetic bottle effect. This study demonstrates an application to Penning ionization electron spectroscopy using collisional ionization with metastable He*(2{sup 3}S) atoms. Technical details and performances of the instrument are presented. This spectrometer can be used for studies of functional molecules and assemblies, and exterior electron densities are expected to be selectively observed by the Penning ionization.

Energy density and energy flow of surface waves in a strongly magnetized graphene

NASA Astrophysics Data System (ADS)

Moradi, Afshin

2018-01-01

General expressions for the energy density and energy flow of plasmonic waves in a two-dimensional massless electron gas (as a simple model of graphene) are obtained by means of the linearized magneto-hydrodynamic model and classical electromagnetic theory when a strong external magnetic field perpendicular to the system is present. Also, analytical expressions for the energy velocity, wave polarization, wave impedance, transverse and longitudinal field strength functions, and attenuation length of surface magneto-plasmon-polariton waves are derived, and numerical results are prepared.

A COUPLED 2 × 2D BABCOCK–LEIGHTON SOLAR DYNAMO MODEL. II. REFERENCE DYNAMO SOLUTIONS

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

Lemerle, Alexandre; Charbonneau, Paul, E-mail: lemerle@astro.umontreal.ca, E-mail: paulchar@astro.umontreal.ca

In this paper we complete the presentation of a new hybrid 2 × 2D flux transport dynamo (FTD) model of the solar cycle based on the Babcock–Leighton mechanism of poloidal magnetic field regeneration via the surface decay of bipolar magnetic regions (BMRs). This hybrid model is constructed by allowing the surface flux transport (SFT) simulation described in Lemerle et al. to provide the poloidal source term to an axisymmetric FTD simulation defined in a meridional plane, which in turn generates the BMRs required by the SFT. A key aspect of this coupling is the definition of an emergence function describing the probabilitymore » of BMR emergence as a function of the spatial distribution of the internal axisymmetric magnetic field. We use a genetic algorithm to calibrate this function, together with other model parameters, against observed cycle 21 emergence data. We present a reference dynamo solution reproducing many solar cycle characteristics, including good hemispheric coupling, phase relationship between the surface dipole and the BMR-generating internal field, and correlation between dipole strength at cycle maximum and peak amplitude of the next cycle. The saturation of the cycle amplitude takes place through the quenching of the BMR tilt as a function of the internal field. The observed statistical scatter about the mean BMR tilt, built into the model, acts as a source of stochasticity which dominates amplitude fluctuations. The model thus can produce Dalton-like epochs of strongly suppressed cycle amplitude lasting a few cycles and can even shut off entirely following an unfavorable sequence of emergence events.« less

Isolating magnetic moments from individual grains within a magnetic assemblage

NASA Astrophysics Data System (ADS)

Béguin, A.; Fabian, K.; Jansen, C.; Lascu, I.; Harrison, R.; Barnhoorn, A.; de Groot, L. V.

2017-12-01

Methods to derive paleodirections or paleointensities from rocks currently rely on measurements of bulk samples (typically 10 cc). The process of recording and storing magnetizations as function of temperature, however, differs for grains of various sizes and chemical compositions. Most rocks, by their mere nature, consist of assemblages of grains varying in size, shape, and chemistry. Unraveling the behavior of individual grains is a holy grail in fundamental rock magnetism. Recently, we showed that it is possible to obtain plausible magnetic moments for individual grains in a synthetic sample by a micromagnetic tomography (MMT) technique. We use a least-squares inversion to obtain these magnetic moments based on the physical locations and dimensions of the grains obtained from a MicroCT scanner and a magnetic flux density map of the surface of the sample. The sample used for this proof of concept, however, was optimized for success: it had a low dispersion of the grains, and the grains were large enough so they were easily detected by the MicroCT scanner. Natural lavas are much more complex than the synthetic sample analyzed so far: the dispersion of the magnetic markers is one order of magnitude higher, the grains differ more in composition and size, and many small (submicron) magnetic markers may be present that go undetected by the MicroCT scanner. Here we present the first results derived from a natural volcanic sample from the 1907-flow at Hawaii. To analyze the magnetic flux at the surface of the sample at room temperature, we used the Magnetic Tunneling Junction (MTJ) technique. We were able to successfully obtain MicroCT and MTJ scans from the sample and isolate plausible magnetic moments for individual grains in the top 70 µm of the sample. We discuss the potential of the MMT technique applied to natural samples and compare the MTJ and SSM methods in terms of work flow and quality of the results.

Mössbauer Magnetic Scan experiments

NASA Astrophysics Data System (ADS)

Pasquevich, G. A.; Mendoza Zélis, P.; Lencina, A.; Veiga, A.; Fernández van Raap, M. B.; Sánchez, F. H.

2014-06-01

We report an application of the Mössbauer Effect designed to retrieve specific information on the magnetic response of iron-containing materials. It consists in the measurement of the nuclear absorption of gamma-rays as a function of an external magnetic field for a specific nuclear transition between magnetically-split nuclear levels. The experiments, here termed Mössbauer Magnetic Scan experiments, were carried out recording the absorption of 57Fe 14.4 keV gamma-ray in α-Fe at constant Doppler energies coincident with some of the spectral lines of the magnetically split Mössbauer spectrum. Due to the dependence of the transition probabilities on the relative orientation between the nuclear magnetic moment and the gamma-ray direction, the present application results in a useful method to study the magnetic-field evolution of the distribution of atomic-magnetic-moment orientations. The proposed technique inherit from the Mössbauer Spectroscopy the chemical-element selectiveness as well as the ability to differentiate responses from iron atoms located at inequivalent site or at different phases. In this work, we show that the data analysis for these experiments depends on the sample thickness that the gamma-ray has to cross. For thin samples (i.e.samples with Mössbauer effective thicknesses lower than one) the magnetic-field dependence of the second-order-moment of the orientation distribution in the direction of the gamma ray is obtained. On the other hand, for thicker samples, although the data analysis is more complex, the dependences of the three second-order-moments of the orientation distribution are obtained. The experiments were performed on two α-Fe foils of different Mössbauer effective thicknesses. They were chosen to represent the cases of thin and thick Mössbauer absorbers. The magnetic evolution of the orientations distribution is compared with results obtained from magnetometric measurements showing a good agreement as well indicating the complementarity of both techniques. A complete description of the experimental set up and the formalism for Mössbauer Magnetic Scan data analysis are presented.

Altered brain network topology in left-behind children: A resting-state functional magnetic resonance imaging study.

PubMed

Zhao, Youjin; Du, Meimei; Gao, Xin; Xiao, Yuan; Shah, Chandan; Sun, Huaiqiang; Chen, Fuqin; Yang, Lili; Yan, Zhihan; Fu, Yuchuan; Lui, Su

2016-12-01

Whether a lack of direct parental care affects brain function in children is an important question, particularly in developing countries where hundreds of millions of children are left behind when their parents migrate for economic or political reasons. In this study, we investigated changes in the topological architectures of brain functional networks in left-behind children (LBC). Resting-state functional magnetic resonance imaging data were obtained from 26 LBC and 21 children living within their nuclear family (non-LBC). LBC showed a significant increase in the normalized characteristic path length (λ), suggesting a decrease in efficiency in information access, and altered nodal centralities in the fronto-limbic regions and motor and sensory systems. Moreover, a decreased nodal degree and the nodal betweenness of the right rectus gyrus were positively correlated with annual family income. The present study provides the first empirical evidence that suggests that a lack of direct parental care could affect brain functional development in children, particularly involving emotional networks. Copyright © 2016 Elsevier Ltd. All rights reserved.

Visual cortex in dementia with Lewy bodies: magnetic resonance imaging study

PubMed Central

Taylor, John-Paul; Firbank, Michael J.; He, Jiabao; Barnett, Nicola; Pearce, Sarah; Livingstone, Anthea; Vuong, Quoc; McKeith, Ian G.; O’Brien, John T.

2012-01-01

Background Visual hallucinations and visuoperceptual deficits are common in dementia with Lewy bodies, suggesting that cortical visual function may be abnormal. Aims To investigate: (1) cortical visual function using functional magnetic resonance imaging (fMRI); and (2) the nature and severity of perfusion deficits in visual areas using arterial spin labelling (ASL)-MRI. Method In total, 17 participants with dementia with Lewy bodies (DLB group) and 19 similarly aged controls were presented with simple visual stimuli (checkerboard, moving dots, and objects) during fMRI and subsequently underwent ASL-MRI (DLB group n = 15, control group n = 19). Results Functional activations were evident in visual areas in both the DLB and control groups in response to checkerboard and objects stimuli but reduced visual area V5/MT (middle temporal) activation occurred in the DLB group in response to motion stimuli. Posterior cortical perfusion deficits occurred in the DLB group, particularly in higher visual areas. Conclusions Higher visual areas, particularly occipito-parietal, appear abnormal in dementia with Lewy bodies, while there is a preservation of function in lower visual areas (V1 and V2/3). PMID:22500014

Evolution of ground-state wave function in CeCoIn5 upon Cd or Sn doping

NASA Astrophysics Data System (ADS)

Chen, K.; Strigari, F.; Sundermann, M.; Hu, Z.; Fisk, Z.; Bauer, E. D.; Rosa, P. F. S.; Sarrao, J. L.; Thompson, J. D.; Herrero-Martin, J.; Pellegrin, E.; Betto, D.; Kummer, K.; Tanaka, A.; Wirth, S.; Severing, A.

2018-01-01

We present linear polarization-dependent soft-x-ray absorption spectroscopy data at the Ce M4 ,5 edges of Cd- and Sn-doped CeCoIn5. The 4 f ground-state wave functions have been determined for their superconducting, antiferromagnetic, and paramagnetic ground states. The absence of changes in the wave functions in CeCo (In1-xCdx) 5 suggests that the 4 f -conduction-electron (c f ) hybridization is not affected by global Cd doping, thus supporting the interpretation of magnetic droplets nucleating long-range magnetic order. This is contrasted by changes in the wave function due to Sn substitution. Increasing Sn in CeCo (In1-ySny) 5 compresses the 4 f orbitals into the tetragonal plane of these materials, suggesting enhanced c f hybridization with the in-plane In(1) atoms and a homogeneous altering of the electronic structure. As these experiments show, the 4 f wave functions are a very sensitive probe of small changes in the hybridization of 4 f and conduction electrons, even conveying information about direction dependencies.

One-step ligand exchange reaction as an efficient way for functionalization of magnetic nanoparticles

NASA Astrophysics Data System (ADS)

Mrówczyński, Radosław; Rednic, Lidia; Turcu, Rodica; Liebscher, Jürgen

2012-07-01

Novel magnetic Fe3O4 nanoparticles (NPs) covered by one layer of functionalized fatty acids, bearing entities (Hayashi catalyst, biotin, quinine, proline, and galactose) of high interest for practical application in nanomedicine or organocatalysis, were synthesized. The functionalized fatty acids were obtained by Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) of azido fatty acids with alkynes. All the magnetic NPs show superparamagnetic behavior with high values of magnetization and high colloidal stability in DCM solution.

Functional Magnetic Resonance Imaging and Spectroscopic Imaging of the Brain: Application of fMRI and fMRS to Reading Disabilities and Education.

ERIC Educational Resources Information Center

Richards, Todd L.

2001-01-01

This tutorial/review covers functional brain-imaging methods and results used to study language and reading disabilities. Although the emphasis is on magnetic resonance imaging and functional magnetic resonance spectroscopy, other imaging techniques are also discussed including positron emission tomography, electroencephalography,…

Search for the elusive magnetic state of hexagonal iron: The antiferromagnetic Fe71Ru29 hcp alloy

NASA Astrophysics Data System (ADS)

Petrillo, C.; Postorino, P.; Orecchini, A.; Sacchetti, F.

2018-03-01

The magnetic states of iron and their dependence on crystal structure represent an important case study for the physics of magnetism and its role in fundamental and applied science, including geophysical sciences. hcp iron is the most elusive structure as it exists only at high pressure but, at the same time, it is expected to be stable up to very high temperature. Exploring the magnetic state of pure Fe at high pressure is difficult and no conclusive results have been obtained. Simple binary alloys where the hexagonal phase of Fe is stabilized, offer a more controllable alternative to investigate iron magnetism. We carried out a neutron diffraction experiment on hcp Fe71Ru29 disordered alloy as a function of temperature. Fe in the hexagonal lattice of this specific alloy results to be antiferromagnetically aligned with a rather complex structure and a small magnetic moment. The temperature dependence suggests a Néel temperature TN = 124 ± 10 K, a value consistent with the low magnetic moment of 1.04 ± 0.10 μB obtained from the diffraction data that also suggest a non-commensurate magnetic structure with magnetic moments probably aligned along the c axis. The present data provide evidence for magnetic ordering in hcp Fe and support the theoretical description of magnetism of pure Fe at high pressure.

Magnetic Frequency Response of HL-LHC Beam Screens

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

Morrone, M.; Martino, M.; De Maria, R.

Magnetic fields used to control particle beams in accelerators are usually controlled by regulating the electrical current of the power converters. In order to minimize lifetime degradation and ultimately luminosity loss in circular colliders, current-noise is a highly critical figure of merit of power converters, in particular for magnets located in areas with high beta-function, like the High Luminosity Large Hadron Collider (HL-LHC) insertions. However, what is directly acting upon the beam is the magnetic field and not the current of the power converter, which undergoes several frequency-dependent transformations until the desired magnetic field, seen by the beam, is obtained.more » Beam screens are very rarely considered when assessing or specifying the noise figure of merit, but their magnetic frequency response is such that they realize relatively effective low pass filtering of the magnetic field produced by the system magnet-power converter. This work aims at filling this gap by quantifying the expected impact of different beam screen layouts for the most relevant HL-LHC insertion magnets. A welldefined post-processing technique is used to derive the frequency response of the different multipoles from multi-physics Finite Element Method (FEM) simulation results. In addition, a well approximated analytical formula for the low-frequency range of multi-layered beam screens is presented.« less

Design, Fabrication, Characterization and Modeling of Integrated Functional Materials

DTIC Science & Technology

2011-10-01

the integration of multiple functionalities with desirable properties (thermal, electrical, magnetic, mechanical , optical, etc.), the connection to...mediated magnetic interactions in the nanocomposites. Our systematic studies on the underlying mechanism of magnetic interactions between graphene...or 3- nanocrystalline phases have been seen simultaneously within an amorphous matrix. The mechanism for induced magnetic anisotropy in these alloys

Magnetic helicity generation in the frame of Kazantsev model

NASA Astrophysics Data System (ADS)

Yushkov, Egor V.; Lukin, Alexander S.

2017-11-01

Using a magnetic dynamo model, suggested by Kazantsev (J. Exp. Theor. Phys. 1968, vol. 26, p. 1031), we study the small-scale helicity generation in a turbulent electrically conducting fluid. We obtain the asymptotic dependencies of dynamo growth rate and magnetic correlation functions on magnetic Reynolds numbers. Special attention is devoted to the comparison of a longitudinal correlation function and a function of magnetic helicity for various conditions of asymmetric turbulent flows. We compare the analytical solutions on small scales with numerical results, calculated by an iterative algorithm on non-uniform grids. We show that the exponential growth of current helicity is simultaneous with the magnetic energy for Reynolds numbers larger than some critical value and estimate this value for various types of asymmetry.

Landau levels and SdH-oscillations of the quasi two-dimensional electron gas at grain boundaries and near heterojunctions

NASA Astrophysics Data System (ADS)

Paasch, G.; Gobsch, G.; Schulze, D.; Handschack, S.

1989-04-01

For the quasi two-dimensional (Q2D) electron gas important experimental information is obtained from magnetotransport measurements with a perpendicular magnetic field. The energy spectrum consists of series of Landau levels for each electric subband. There still exist several open questions if two or more electric Subbands are populated. Results are presented here for this situation. The usual procedure for interpreting Shubnikov-de Haas (SdH) measurements for the case of several populated subbands is analyzed (connection with the saw-tooth like Fermi energy as a function of the magnetic field). The transverse magnetoresistance is calculated for the Q2D electron gas in InSb-bicrystals and at InGaAs-InP heterojunctions. All details of the experimental curves can be explained including an anomalous behaviour of the quantum Hall effect (QHE) in the second system. Basic assumptions of the theory are the broadening of the Landau levels and in addition a background of localized states in the second case. The dependence of the electronic structure on the perpendicular magnetic field is discussed qualitatively. First results of magnetic field dependent self-consistent calculations for inversion layers are presented. It is shown for the first time that this magnetic field dependence causes qualitative changes of the Landau level spectrum.

A highly sensitive electron spectrometer for crossed-beam collisional ionization: A retarding-type magnetic bottle analyzer and its application to collision-energy resolved Penning ionization electron spectroscopy

NASA Astrophysics Data System (ADS)

Yamakita, Yoshihiro; Tanaka, Hideyasu; Maruyama, Ryo; Yamakado, Hideo; Misaizu, Fuminori; Ohno, Koichi

2000-08-01

A highly sensitive electron energy analyzer which utilizes a "magnetic bottle" combined with a retarding electrostatic field has been developed for Penning ionization electron spectroscopy. A beam of metastable rare-gas atoms is crossed with a continuous supersonic sample beam in the source region of the analyzer. The emitted electrons are collected by an inhomogeneous magnetic field (the magnetic bottle effect) with a high efficiency of nearly 4π solid angle, which is more than 103 times higher than that of a conventional hemispherical analyzer. The kinetic energy of electrons is analyzed by scanning the retarding field in a flight tube of the analyzer in the presence of a weak magnetic field. The velocity of the metastable atoms can also be resolved by a time-of-flight method in the present instrument. Examples of Penning ionization electron energy spectra as a function of collision energy are presented for Ar and N2 with metastable He*(2 3S) atoms. This instrument has opened the possibility for extensive studies of Penning ionization electron spectroscopy for low-density species, such as clusters, ions, electronically excited species, unstable or transient species, and large molecules with low volatility.

Aerial radiometric and magnetic survey: Aztec National Topographic Map, New Mexico

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

Not Available

1979-01-01

The results of analyses of the airborne gamma radiation and total magnetic field survey flown for the region identified as the Aztec National Topographic Map NJ13-10 are presented. The airborne data gathered are reduced by ground computer facilities to yield profile plots of the basic uranium, thorium and potassium equivalent gamma radiation intensities, ratios of these intensities, aircraft altitude above the earth's surface, total gamma ray and earth's magnetic field intensity, correlated as a function of geologic units. The distribution of data within each geologic unit, for all surveyed map lines and tie lines, has been calculated and is included.more » Two sets of profiled data for each line are included, with one set displaying the above-cited data. The second set includes only flight line magnetic field, temperature, pressure, altitude data plus magnetic field data as measured at a base station. A general description of the area, including descriptions of the various geologic units and the corresponding airborne data, is included also.« less

Magnetohydrodynamic simulations of hypersonic flow over a cylinder using axial- and transverse-oriented magnetic dipoles.

PubMed

Guarendi, Andrew N; Chandy, Abhilash J

2013-01-01

Numerical simulations of magnetohydrodynamic (MHD) hypersonic flow over a cylinder are presented for axial- and transverse-oriented dipoles with different strengths. ANSYS CFX is used to carry out calculations for steady, laminar flows at a Mach number of 6.1, with a model for electrical conductivity as a function of temperature and pressure. The low magnetic Reynolds number (<1) calculated based on the velocity and length scales in this problem justifies the quasistatic approximation, which assumes negligible effect of velocity on magnetic fields. Therefore, the governing equations employed in the simulations are the compressible Navier-Stokes and the energy equations with MHD-related source terms such as Lorentz force and Joule dissipation. The results demonstrate the ability of the magnetic field to affect the flowfield around the cylinder, which results in an increase in shock stand-off distance and reduction in overall temperature. Also, it is observed that there is a noticeable decrease in drag with the addition of the magnetic field.

Magnetohydrodynamic Simulations of Hypersonic Flow over a Cylinder Using Axial- and Transverse-Oriented Magnetic Dipoles

PubMed Central

Guarendi, Andrew N.; Chandy, Abhilash J.

2013-01-01

Numerical simulations of magnetohydrodynamic (MHD) hypersonic flow over a cylinder are presented for axial- and transverse-oriented dipoles with different strengths. ANSYS CFX is used to carry out calculations for steady, laminar flows at a Mach number of 6.1, with a model for electrical conductivity as a function of temperature and pressure. The low magnetic Reynolds number (≪1) calculated based on the velocity and length scales in this problem justifies the quasistatic approximation, which assumes negligible effect of velocity on magnetic fields. Therefore, the governing equations employed in the simulations are the compressible Navier-Stokes and the energy equations with MHD-related source terms such as Lorentz force and Joule dissipation. The results demonstrate the ability of the magnetic field to affect the flowfield around the cylinder, which results in an increase in shock stand-off distance and reduction in overall temperature. Also, it is observed that there is a noticeable decrease in drag with the addition of the magnetic field. PMID:24307870

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

Gorai, Prashun; Toberer, Eric S.; Stevanović, Vladan

Here, at room temperature and above, most magnetic materials adopt a spin-disordered (paramagnetic) state whose electronic properties can differ significantly from their low-temperature, spin-ordered counterparts. Yet computational searches for new functional materials usually assume some type of magnetic order. In the present work, we demonstrate a methodology to incorporate spin disorder in computational searches and predict the electronic properties of the paramagnetic phase. We implement this method in a high-throughput framework to assess the potential for thermoelectric performance of 1350 transition-metal sulfides and find that all magnetic systems we identify as promising in the spin-ordered ground state cease to bemore » promising in the paramagnetic phase due to disorder-induced deterioration of the charge carrier transport properties. We also identify promising non-magnetic candidates that do not suffer from these spin disorder effects. In addition to identifying promising materials, our results offer insights into the apparent scarcity of magnetic systems among known thermoelectrics and highlight the importance of including spin disorder in computational searches.« less

Bipolar magnetic semiconductor in silicene nanoribbons

NASA Astrophysics Data System (ADS)

Farghadan, Rouhollah

2017-08-01

A theoretical study was presented on generation of spin polarization in silicene nanoribbons using the single-band tight-binding approximation and the non-equilibrium Green's function formalism. We focused on the effect of electric and exchange magnetic fields on the spin-filter capabilities of zigzag-edge silicene nanoribbons in the presence of the intrinsic spin-orbit interaction. The results show that a robust bipolar magnetic semiconductor with controllable spin-flip and spin-conserved gaps can be obtained when exchange magnetic and electric field strengths are both larger than the intrinsic spin-orbit interaction. Therefore, zigzag silicene nanoribbons could act as bipolar and perfect spin filter devices with a large spin-polarized current and a reversible spin polarization in the vicinity of the Fermi energy. We also investigated the effect of edge roughness and found that the bipolar magnetic semiconductor features are robust against edge disorder in silicene nanoribbon junctions. These results may be useful in multifunctional spin devices based on silicene nanoribbons.

Gold and gold-iron oxide magnetic glyconanoparticles: synthesis, characterization and magnetic properties.

PubMed

de la Fuente, Jesús M; Alcántara, David; Eaton, Peter; Crespo, Patricia; Rojas, Teresa C; Fernandez, Asunción; Hernando, Antonio; Penadés, Soledad

2006-07-06

The preparation, characterization and the magnetic properties of gold and gold-iron oxide glyconanoparticles (GNPs) are described. Glyconanoparticles were prepared in a single step procedure in the presence of aqueous solution of thiol functionalized neoglycoconjugates and either gold salts or both gold and iron salts. Neoglycoconjugates of lactose and maltose disaccharides with different linkers were used. Iron-free gold or gold-iron oxide GNPs with controlled gold-iron ratios were obtained. The average core-size diameters are in the range of 1.5-2.5 nm. The GNPs are fully characterized by (1)H NMR spectrometry, transmission electron microscopy (TEM), and UV-vis and X-ray absorption (XAS) spectroscopies. Inductive plasma-atomic emission spectrometry (ICP) and elemental analysis gave the average number of neoglycoconjugates per cluster. The magnetic properties were measured in a SQUID magnetometer. The most remarkable results was the observation of a permanent magnetism up to room temperature in the iron-free gold GNPs, that was not present in the corresponding gold-iron oxide GNPs.