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Sample records for magnetic potential barriers

  1. Electron transmission through a periodically driven graphene magnetic barrier

    Energy Technology Data Exchange (ETDEWEB)

    Biswas, R., E-mail: rbiswas.pkc@gmail.com [Department of Physics, P. K. College, Contai, Purba Medinipur, West Bengal – 721401 (India); Maiti, S. [Ajodhya Hills G.S.A.T High School, Ajodhya, Purulia, West Bengal – 723152 (India); Mukhopadhyay, S. [Purulia Zilla School, Dulmi Nadiha, Purulia, West Bengal – 723102 (India); Sinha, C. [Department of Physics, P. K. College, Contai, Purba Medinipur, West Bengal – 721401 (India); Department of Theoretical Physics, Indian Association for the Cultivation of Science, Jadavpur – 700032 (India)

    2017-05-10

    Electronic transport through graphene magnetic barriers is studied theoretically in presence of an external time harmonic scalar potential in the framework of non-perturbative Landau–Floquet Formalism. The oscillating field mostly suppresses the transmission for rectangular magnetic barrier structure and exhibits the Fano resonance for multiphoton processes due to the presence of bound state inside the barrier. While, for a pair of delta function barriers of larger separation, the oscillating potential suppresses the usual Fabry–Perot oscillations in the transmission and a new type of asymmetric Fano resonance is noted for smaller separation, occurring due to extended states between the barriers. - Highlights: • Tunnelling of the Dirac Fermions through oscillating pure magnetic barriers is reported for the first time. • The high energy transmission through a graphene magnetic barrier is suppressed by the application of time periodic modulation. • Suppression of the Fabry Perot transmission is noted due to the application of an external time harmonic potential. • Two kinds of the Fano resonances are noted in transmission through a pair of modulated δ-function magnetic barriers.

  2. Electron optics with magnetic vector potential barriers in graphene

    International Nuclear Information System (INIS)

    Ghosh, Sankalpa; Sharma, Manish

    2009-01-01

    An analysis of electron transport in graphene in the presence of various arrangements of delta-function like magnetic barriers is presented. The motion through one such barrier gives an unusual non-specular refraction leading to asymmetric transmission. The symmetry is restored by putting two such barriers in opposite directions side by side. Periodic arrangements of such barriers can be used as Bragg reflectors whose reflectivity has been calculated using a transfer matrix formalism. Such Bragg reflectors can be used to make resonant cavities. We also analyze the associated band structure for the case of infinite periodic structures. (fast track communication)

  3. Magnetic properties and potential barrier between crystallites model of MgGa2-xFexO4 ceramics

    Directory of Open Access Journals (Sweden)

    V. A. dos S. Ribeiro

    Full Text Available Abstract The aim of this work was to investigate the magnetic properties and the electrical conductivity temperature dependence associated to the potential barrier between the crystallites model. Gallium and magnesium containing spinel ceramic has low magnetic coercivity and high electrical resistivity. MgGa2-xFexO4 samples (x= 0.01, 0.05, 0.15, 0.25, 0.35 were prepared by solid-state method and sintered at 800 °C for 8 h. X-ray diffraction analysis confirmed the formation of a single phase with compact cubic spinel structure. The magnetic measurements show that the saturation magnetization and remanence of all samples increased with increasing iron concentration. The coercive field decreased up to the concentration x= 0.15, and above x= 0.25 it was observed an increase in the coercive field. Through electrical characterization it was found that the samples presented highly insulating behavior for x= 0.01, and further increase in x above 0.15 gives a semiconductor behavior compatible with the potential barrier between the crystallites model, i.e. fulfills the condition L/2 > LD (crystallite size L in comparison with the Debye length LD, and the conduction is limited by potential barriers between the crystallites.

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

    Science.gov (United States)

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

    2018-05-01

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

  5. Magnetic properties and potential barrier between crystallites model of MgGa{sub 2-x}Fe{sub x}O{sub 4} ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Ribeiro, V.A. dos S.; Rubinger, R.M.; Oliveira, A.F.; Mendonca, C.S.P.; Silva, M.R. da, E-mail: vanderalkmin@gmail.com, E-mail: rero@unifei.edu.br, E-mail: adhimarflavio@unifei.edu.br, E-mail: sales.claudiney21@gmail.com, E-mail: mrsilva@unifei.edu.br [Universidade Federal de Itajuba (UNIFEI), MG (Brazil). Instituto de Fisica e Quimica

    2016-10-15

    The aim of this work was to investigate the magnetic properties and the electrical conductivity temperature dependence associated to the potential barrier between the crystallites model. Gallium and magnesium containing spinel ceramic has low magnetic coercivity and high electrical resistivity. MgGa{sub 2-x}Fe{sub x}O{sub 4} samples (x= 0.01, 0.05, 0.15, 0.25, 0.35) were prepared by solid-state method and sintered at 800 °C for 8 h. X-ray diffraction analysis confirmed the formation of a single phase with compact cubic spinel structure. The magnetic measurements show that the saturation magnetization and remanence of all samples increased with increasing iron concentration. The coercive field decreased up to the concentration x= 0.15, and above x= 0.25 it was observed an increase in the coercive field. Through electrical characterization it was found that the samples presented highly insulating behavior for x= 0.01, and further increase in x above 0.15 gives a semiconductor behavior compatible with the potential barrier between the crystallites model, i.e. fulfills the condition L/2 > L{sub D} (crystallite size L in comparison with the Debye length L{sub D}), and the conduction is limited by potential barriers between the crystallites. (author)

  6. Magnetized advective accretion flows: formation of magnetic barriers in magnetically arrested discs

    Science.gov (United States)

    Mondal, Tushar; Mukhopadhyay, Banibrata

    2018-05-01

    We discuss the importance of large-scale strong magnetic field in the removal of angular momentum outward, as well as the possible origin of different kinds of magnetic barrier in advective, geometrically thick, sub-Keplerian accretion flows around black holes. The origin of this large-scale strong magnetic field near the event horizon is due to the advection of the magnetic flux by the accreting gas from the environment, say, the interstellar medium or a companion star, because of flux freezing. In this simplest vertically averaged, 1.5-dimensional disc model, we choose the maximum upper limit of the magnetic field, which the disc around a black hole can sustain. In this so called magnetically arrested disc model, the accreting gas either decelerates or faces the magnetic barrier near the event horizon by the accumulated magnetic field depending on the geometry. The magnetic barrier may knock the matter to infinity. We suggest that these types of flow are the building block to produce jets and outflows in the accreting system. We also find that in some cases, when matter is trying to go back to infinity after knocking the barrier, matter is prevented being escaped by the cumulative action of strong gravity and the magnetic tension, hence by another barrier. In this way, magnetic field can lock the matter in between these two barriers and it might be a possible explanation for the formation of episodic jet.

  7. Double Barriers and Magnetic Field in Bilayer Graphene

    Science.gov (United States)

    Redouani, Ilham; Jellal, Ahmed; Bahlouli, Hocine

    2015-12-01

    We study the transmission probability in an AB-stacked bilayer graphene of Dirac fermions scattered by a double-barrier structure in the presence of a magnetic field. We take into account the full four bands structure of the energy spectrum and use the suitable boundary conditions to determine the transmission probability. Our numerical results show that for energies higher than the interlayer coupling, four ways for transmission are possible while for energies less than the height of the barrier, Dirac fermions exhibit transmission resonances and only one transmission channel is available. We show that, for AB-stacked bilayer graphene, there is no Klein tunneling at normal incidence. We find that the transmission displays sharp peaks inside the transmission gap around the Dirac point within the barrier regions while they are absent around the Dirac point in the well region. The effect of the magnetic field, interlayer electrostatic potential, and various barrier geometry parameters on the transmission probabilities is also discussed.

  8. Self-consistent potential variations in magnetic wells

    International Nuclear Information System (INIS)

    Kesner, J.; Knorr, G.; Nicholson, D.R.

    1981-01-01

    Self-consistent electrostatic potential variations are considered in a spatial region of weak magnetic field, as in the proposed tandem mirror thermal barriers (with no trapped ions). For some conditions, equivalent to ion distributions with a sufficiently high net drift speed along the magnetic field, the desired potential depressions are found. When the net drift speed is not high enough, potential depressions are found only in combination with strong electric fields on the boundaries of the system. These potential depressions are not directly related to the magnetic field depression. (author)

  9. Magnetic Nanoparticles Cross the Blood-Brain Barrier: When Physics Rises to a Challenge

    Directory of Open Access Journals (Sweden)

    Maria Antònia Busquets

    2015-12-01

    Full Text Available The blood-brain barrier is a physical and physiological barrier that protects the brain from toxic substances within the bloodstream and helps maintain brain homeostasis. It also represents the main obstacle in the treatment of many diseases of the central nervous system. Among the different approaches employed to overcome this barrier, the use of nanoparticles as a tool to enhance delivery of therapeutic molecules to the brain is particularly promising. There is special interest in the use of magnetic nanoparticles, as their physical characteristics endow them with additional potentially useful properties. Following systemic administration, a magnetic field applied externally can mediate the capacity of magnetic nanoparticles to permeate the blood-brain barrier. Meanwhile, thermal energy released by magnetic nanoparticles under the influence of radiofrequency radiation can modulate blood-brain barrier integrity, increasing its permeability. In this review, we present the strategies that use magnetic nanoparticles, specifically iron oxide nanoparticles, to enhance drug delivery to the brain.

  10. Enhanced voltage-controlled magnetic anisotropy in magnetic tunnel junctions with an MgO/PZT/MgO tunnel barrier

    Science.gov (United States)

    Chien, Diana; Li, Xiang; Wong, Kin; Zurbuchen, Mark A.; Robbennolt, Shauna; Yu, Guoqiang; Tolbert, Sarah; Kioussis, Nicholas; Khalili Amiri, Pedram; Wang, Kang L.; Chang, Jane P.

    2016-03-01

    Compared with current-controlled magnetization switching in a perpendicular magnetic tunnel junction (MTJ), electric field- or voltage-induced magnetization switching reduces the writing energy of the memory cell, which also results in increased memory density. In this work, an ultra-thin PZT film with high dielectric constant was integrated into the tunneling oxide layer to enhance the voltage-controlled magnetic anisotropy (VCMA) effect. The growth of MTJ stacks with an MgO/PZT/MgO tunnel barrier was performed using a combination of sputtering and atomic layer deposition techniques. The fabricated MTJs with the MgO/PZT/MgO barrier demonstrate a VCMA coefficient, which is ˜40% higher (19.8 ± 1.3 fJ/V m) than the control sample MTJs with an MgO barrier (14.3 ± 2.7 fJ/V m). The MTJs with the MgO/PZT/MgO barrier also possess a sizeable tunneling magnetoresistance (TMR) of more than 50% at room temperature, comparable to the control MTJs with an MgO barrier. The TMR and enhanced VCMA effect demonstrated simultaneously in this work make the MgO/PZT/MgO barrier-based MTJs potential candidates for future voltage-controlled, ultralow-power, and high-density magnetic random access memory devices.

  11. Tunable delay time and Hartman effect in graphene magnetic barriers

    International Nuclear Information System (INIS)

    Ban, Yue; Wang, Lin-Jun; Chen, Xi

    2015-01-01

    Tunable group delay and Hartman effect have been investigated for massless Dirac electrons in graphene magnetic barriers. In the presence of magnetic field, dwell time is found to be equal to net group delay plus the group delay contributing from the lateral shifts. The group delay times are discussed in both cases of normal and oblique incidence, to clarify the nature of Hartman effect. In addition, the group delay in transmission can be modulated from subluminality to superluminality by adjusting the magnetic field, which may also lead to potential applications in graphene-based microelectronics

  12. Noble magnetic barriers in the ASDEX UG tokamak

    Science.gov (United States)

    Ali, Halima; Punjabi, Alkesh; Vazquez, Justin

    2010-02-01

    The second-order perturbation method of creating invariant tori inside chaos in Hamiltonian systems (Ali, H.; Punjabi, A. Plasma Phys. Contr. F. 2007, 49, 1565-1582) is applied to the axially symmetric divertor experiment upgrade (ASDEX UG) tokamak to build noble irrational magnetic barriers inside chaos created by resonant magnetic perturbations (m, n)=(3, 2)+(4, 3), with m and n the poloidal and toroidal mode numbers of the Fourier expansion of the magnetic perturbation. The radial dependence of the Fourier modes is ignored. The modes are considered to be locked and have the same amplitude δ. A symplectic mathematical mapping in magnetic coordinates is used to integrate magnetic field line trajectories in the ASDEX UG. Tori with noble irrational rotational transform are the last ones to be destroyed by perturbation in Hamiltonian systems. For this reason, noble irrational magnetic barriers are built inside chaos, and the strongest noble irrational barrier is identified. Three candidate locations for the strongest noble barrier in ASDEX UG are selected. All three candidate locations are chosen to be roughly midway between the resonant rational surfaces ψ32 and ψ43. ψ is the magnetic coordinate of the flux surface. The three candidate surfaces are the noble irrational surfaces close to the surface with q value that is a mediant of q=3/2 and 4/3, q value of the physical midpoint of the two resonant surfaces, and the q value of the surface where the islands of the two perturbing modes just overlap. These q values of the candidate surfaces are denoted by q MED, q MID, and q OVERLAP. The strongest noble barrier close to q MED has the continued fraction representation (CFR) [1;2,2,1∞] and exists for δ≤2.6599×10-4; the strongest noble barrier close to q MID has CFR [1;2,2,2,1∞] and exists for δ≤4.6311×10-4; and the strongest noble barrier close to q OVERLAP has CFR [1;2,2,6,2,1∞] and exists for δ≤1.367770×10-4. From these results, the strongest

  13. Electric-field effects on electronic tunneling transport in magnetic barrier structures

    International Nuclear Information System (INIS)

    Guo Yong; Wang Hao; Gu Binglin; Kawazoe, Yoshiyuki

    2000-01-01

    Electronic transport properties in magnetic barrier structures under the influence of an electric field have been investigated. The results indicate that the characteristics of transmission resonance are determined not only by the structure and the incident wave vector but also strongly by the electric field. It is shown that the transmission coefficient at resonance in the low-energy range is suppressed by applying the electric field for electron tunneling through the magnetic barrier structure, arranged with identical magnetic barriers and wells. It is also shown that the transmission resonance is first enhanced up to optimal resonance, and then suppressed with further increased electric field for electron tunneling through the magnetic barrier structure, arranged with unidentical building blocks. Strong suppression of the current density is also found in the magnetic barrier structure, arranged with two different building blocks

  14. Conditions for plasmoid penetration across abrupt magnetic barriers

    International Nuclear Information System (INIS)

    Brenning, Nils; Hurtig, Tomas; Raadu, Michael A.

    2005-01-01

    The penetration of plasma clouds, or plasmoids, across abrupt magnetic barriers (of the scale less than a few ion gyro radii, using the plasmoid directed velocity) is studied. The insight gained earlier, from detailed experimental and computer simulation investigations of a case study, is generalized into other parameter regimes. It is concluded for what parameters a plasmoid should be expected to penetrate the magnetic barrier through self-polarization, penetrate through magnetic expulsion, or be rejected from the barrier. The scaling parameters are n e , v 0 , B perpendicular , m i , T i , and the width w of the plasmoid. The scaling is based on a model for strongly driven, nonlinear magnetic field diffusion into a plasma which is a generalization of the earlier laboratory findings. The results are applied to experiments earlier reported in the literature, and also to the proposed application of impulsive penetration of plasmoids from the solar wind into the Earth's magnetosphere

  15. Monitoring long-term evolution of engineered barrier systems using magnets: Magnetic response.

    Science.gov (United States)

    Rigonat, N; Isnard, O; Harley, S L; Butler, I B

    2018-01-05

    Remote and non-destructive monitoring of the stability and performance of Engineered Barrier Systems for Geological Disposal Facility of is gaining considerable importance in establishing the safety cases for Higher Activity Wastes disposal. This study offers an innovative use of mineral magnetism for monitoring groundwater saturation of the barrier. Four mixtures of permanent magnets (Nd-Fe-B, coated and uncoated; SmCo and AlNiCo) and bentonite were reacted for 4, 8 and 12 months with mildly-saline, high-pH leachates, representing the fluids saturating a time-evolved engineered barrier. Coupled hysteresis and thermomagnetic analyses demonstrate how Nd-Fe-B feature a time-dependent transition from square-like ferromagnetic to superparamagnetic loop via pot-bellied and wasp-waist loops, whereas SmCo and AlNiCo do not show so extensive corrosion-related variations of the intrinsic and extrinsic magnetic properties. This study allowed to identify magnetic materials suitable for shorter- (Nd-Fe-B) and longer-term (SmCo and AlNiCo) monitoring purposes. Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.

  16. Magnetic Transport Barriers in the DIII-D Tokamak

    Science.gov (United States)

    Kessler, J.; Volpe, F.; Evans, T. E.; Ali, H.; Punjabi, A.

    2009-11-01

    Large overlapping magnetic islands generate chaotic fields. However, a previous work [1] showed that second or third order perturbations of special topology and strength can also generate magnetic diffusion ``barriers" in the middle of stochastic regions. In the present study, we numerically assess their experimental feasibility at DIII-D. For this, realistic I- and C-coils perturbations are superimposed on the equilibrium field and puncture plots are generated with a field-line tracer. A criterion is defined for the automatic recognition of barriers and successfully tested on earlier symplectic maps in magnetic coordinates. The criterion is systematically applied to the new puncture plots in search for dependencies, e.g. upon the edge safety factor q95, which might be relevant to edge localized mode (ELM) stability, as well as to assess the robustness of barriers against fluctuations of the plasma parameters and coil currents. 8pt [1] H. Ali and A. Punjabi, Plasma Phys. Control. Fusion 49, 1565 (2007).

  17. Numerical evaluation of energy barriers and magnetic relaxation in interacting nanostructured magnetic systems

    International Nuclear Information System (INIS)

    Chubykalo-Fesenko, Oksana A.; Chantrell, Roy W.

    2004-01-01

    We discuss a model to quantify long-time thermally induced magnetization reversal in magnetic systems with distributed properties. Two algorithms, based on kinetic and Metropolis Monte Carlo are introduced. While the former requires the constant recalculation of all energy barriers and is useful when the interactions are weak, the latter uses the Metropolis Monte Carlo to estimate the magnetization trajectory and, consequently, only the most probable transition rates are evaluated. The ridge optimization method is used to evaluate the energy barriers in a multidimensional energy landscape. The algorithms are applied to a granular system modeled by means of Voronoi polyhedra and having random in-plane anisotropy

  18. Magnetic barriers and their q95 dependence at DIII-D

    Science.gov (United States)

    Volpe, F. A.; Kessler, J.; Ali, H.; Evans, T. E.; Punjabi, A.

    2012-05-01

    It is well known that externally generated resonant magnetic perturbations (RMPs) can form islands in the plasma edge. In turn, large overlapping islands generate stochastic fields, which are believed to play a role in the avoidance and suppression of edge localized modes (ELMs) at DIII-D. However, large coalescing islands can also generate, in the middle of these stochastic regions, KAM surfaces effectively acting as ‘barriers’ against field-line dispersion and, indirectly, particle diffusion. It was predicted in Ali and Punjabi (2007 Plasma Phys. Control. Fusion 49 1565-82) that such magnetic barriers can form in piecewise analytic DIII-D plasma equilibria. In this work, the formation of magnetic barriers at DIII-D is corroborated by field-line tracing calculations using experimentally constrained EFIT (Lao et al 1985 Nucl. Fusion 25 1611) DIII-D equilibria perturbed to include the vacuum field from the internal coils utilized in the experiments. According to these calculations, the occurrence and location of magnetic barriers depend on the edge safety factor q95. It was thus suggested that magnetic barriers might contribute to narrowing the edge stochastic layer and play an indirect role in the RMPs failing to control ELMs for certain values of q95. The analysis of DIII-D discharges where q95 was varied, however, does not show anti-correlation between barrier formation and ELM suppression.

  19. Magnetic barriers and their q95 dependence at DIII-D

    International Nuclear Information System (INIS)

    Volpe, F.A.; Kessler, J.; Ali, H.; Punjabi, A.; Evans, T.E.

    2012-01-01

    It is well known that externally generated resonant magnetic perturbations (RMPs) can form islands in the plasma edge. In turn, large overlapping islands generate stochastic fields, which are believed to play a role in the avoidance and suppression of edge localized modes (ELMs) at DIII-D. However, large coalescing islands can also generate, in the middle of these stochastic regions, KAM surfaces effectively acting as ‘barriers’ against field-line dispersion and, indirectly, particle diffusion. It was predicted in Ali and Punjabi (2007 Plasma Phys. Control. Fusion 49 1565–82) that such magnetic barriers can form in piecewise analytic DIII-D plasma equilibria. In this work, the formation of magnetic barriers at DIII-D is corroborated by field-line tracing calculations using experimentally constrained EFIT (Lao et al 1985 Nucl. Fusion 25 1611) DIII-D equilibria perturbed to include the vacuum field from the internal coils utilized in the experiments. According to these calculations, the occurrence and location of magnetic barriers depend on the edge safety factor q 95 . It was thus suggested that magnetic barriers might contribute to narrowing the edge stochastic layer and play an indirect role in the RMPs failing to control ELMs for certain values of q 95 . The analysis of DIII-D discharges where q 95 was varied, however, does not show anti-correlation between barrier formation and ELM suppression. (paper)

  20. Magnetization reversal processes of single nanomagnets and their energy barrier

    International Nuclear Information System (INIS)

    Krone, P.; Makarov, D.; Albrecht, M.; Schrefl, T.; Suess, D.

    2010-01-01

    Micromagnetic simulations were performed to investigate the influence of geometry and magnetic anisotropy constant on energy barrier and magnetization reversal mechanism of individual bits important for the bit patterned media concept in magnetic data storage. It is shown that dependency of the energy barrier on magnetic and geometric properties of bits can be described by an analytical approach in the case of quasi-coherent magnetization rotation process. However, when the bit size exceeds a critical size, for which an incoherent magnetization reversal is preferred, the analytical approach becomes invalid and no self-consistent theory is available. By systematically investigating the influence of bit size on the magnetization reversal mode, it was found that the transition from quasi-coherent to incoherent magnetization reversal mode can still be described analytically if an activation volume is considered instead of the bit volume. In this case, the nucleation volume is an important parameter determining thermal stability of the bit. If the volume of the bit is larger than twice the activation volume, the energy barrier stays nearly constant; with further increase in bit size, no gain in thermal stability can be achieved.

  1. Tunnel superpenetrability of potential barriers

    International Nuclear Information System (INIS)

    Zakhariev, B N.

    1982-01-01

    The transmission of two particles through the same barrier is considered. The limiting cases are compared when the particles are joined together in a single particle with double mass-energy and potential and when they pass the barrier independently. As an intermediate case a pair of particles bound in a quasideuteron of a finite size is considered. It is shown that long-range collective correlations of particles (of the superfluidity type and others) simplify very much for them passing through high potential barriers. This happens due to the transfer of the additional energy from the particles outside the barriers to those inside it

  2. A Stable Pentagonal Bipyramidal Dy(III) Single-Ion Magnet with a Record Magnetization Reversal Barrier over 1000 K.

    Science.gov (United States)

    Liu, Jiang; Chen, Yan-Cong; Liu, Jun-Liang; Vieru, Veacheslav; Ungur, Liviu; Jia, Jian-Hua; Chibotaru, Liviu F; Lan, Yanhua; Wernsdorfer, Wolfgang; Gao, Song; Chen, Xiao-Ming; Tong, Ming-Liang

    2016-04-27

    Single-molecule magnets (SMMs) with a large spin reversal barrier have been recognized to exhibit slow magnetic relaxation that can lead to a magnetic hysteresis loop. Synthesis of highly stable SMMs with both large energy barriers and significantly slow relaxation times is challenging. Here, we report two highly stable and neutral Dy(III) classical coordination compounds with pentagonal bipyramidal local geometry that exhibit SMM behavior. Weak intermolecular interactions in the undiluted single crystals are first observed for mononuclear lanthanide SMMs by micro-SQUID measurements. The investigation of magnetic relaxation reveals the thermally activated quantum tunneling of magnetization through the third excited Kramers doublet, owing to the increased axial magnetic anisotropy and weaker transverse magnetic anisotropy. As a result, pronounced magnetic hysteresis loops up to 14 K are observed, and the effective energy barrier (Ueff = 1025 K) for relaxation of magnetization reached a breakthrough among the SMMs.

  3. Potential barrier classification by short-time measurement

    International Nuclear Information System (INIS)

    Granot, Er'el; Marchewka, Avi

    2006-01-01

    We investigate the short-time dynamics of a delta-function potential barrier on an initially confined wave packet. There are mainly two conclusions: (A) At short times the probability density of the first particles that passed through the barrier is unaffected by it. (B) When the barrier is absorptive (i.e., its potential is imaginary) it affects the transmitted wave function at shorter times than a real potential barrier. Therefore, it is possible to distinguish between an imaginary and a real potential barrier by measuring its effect at short times only on the transmitting wave function

  4. Potential barrier classification by short-time measurement

    Science.gov (United States)

    Granot, Er'El; Marchewka, Avi

    2006-03-01

    We investigate the short-time dynamics of a delta-function potential barrier on an initially confined wave packet. There are mainly two conclusions: (A) At short times the probability density of the first particles that passed through the barrier is unaffected by it. (B) When the barrier is absorptive (i.e., its potential is imaginary) it affects the transmitted wave function at shorter times than a real potential barrier. Therefore, it is possible to distinguish between an imaginary and a real potential barrier by measuring its effect at short times only on the transmitting wave function.

  5. One-way Ponderomotive Barrier in a Uniform Magnetic Field

    International Nuclear Information System (INIS)

    Dodin, I.Y.; Fisch, N.J.

    2005-01-01

    The possibility of an asymmetric ponderomotive barrier in a nonuniform dc magnetic field by high-frequency radiation near the cyclotron resonance for selected plasma species was contemplated in Physics of Plasmas 11 (November 2004) 5046-5064. Here we show that a similar one-way barrier, which reflects particles incident from one side while transmitting those incident from the opposite side, can be produced also in a uniform magnetic field, entirely due to inhomogeneity of high-frequency drive

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

    Science.gov (United States)

    Esmailpour, Mohammad

    2018-04-01

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

  7. Magnetic tunnel junctions with AlN and AlNxOy barriers

    International Nuclear Information System (INIS)

    Schwickert, M. M.; Childress, J. R.; Fontana, R. E.; Kellock, A. J.; Rice, P. M.; Ho, M. K.; Thompson, T. J.; Gurney, B. A.

    2001-01-01

    Nonoxide tunnel barriers such as AlN are of interest for magnetic tunnel junctions to avoid the oxidation of the magnetic electrodes. We have investigated the fabrication and properties of thin AlN-based barriers for use in low resistance magnetic tunnel junctions. Electronic, magnetic and structural data of tunnel valves of the form Ta (100 Aa)/PtMn (300 Aa)/CoFe 20 (20 Aa - 25 Aa)/barrier/CoFe 20 (10 - 20 Aa)/NiFe 16 (35 - 40 Aa)/Ta (100 Aa) are presented, where the barrier consists of AlN, AlN x O y or AlN/AlO x with total thicknesses between 8 and 15 Aa. The tunnel junctions were sputter deposited and then lithographically patterned down to 2 x 2μm 2 devices. AlN was deposited by reactive sputtering from an Al target with 20% - 35% N 2 in the Ar sputter gas at room temperature, resulting in stoichiometric growth of AlN x (x=0.50±0.05), as determined by RBS. TEM analysis shows that the as-deposited AlN barrier is crystalline. For AlN barriers and AlN followed by natural O 2 oxidation, we obtain tunnel magnetoresistance >10% with specific junction resistance R j down to 60Ωμm 2 . [copyright] 2001 American Institute of Physics

  8. Proton nuclear magnetic resonance study on the barrier function of pig corneal epithelium and endothelium

    International Nuclear Information System (INIS)

    Yokoi, Norihiko; Kinoshita, Shigeru; Morimoto, Taketoshi; Yoshizaki, Kazuo.

    1995-01-01

    Using gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA) as a tracer, the barrier function of the corneal epithelium and endothelium was evaluated by proton nuclear magnetic resonance. Whole pig eyes and cornea excised with scleral rim, which had been incubated in dextran-added Gd-DTPA solution, were subjected to T 1 relaxation measurement and magnetic resonance imaging (MRI). After incubation, the T 1 relaxation rate (1/T 1 ) of the excised cornea increased to a steady value, whereas that of the cornea from the whole eye increased only slightly. These results indicated that the increase in the T 1 relaxation rate of the excised cornea was attributable to Gd-DTPA penetration from the corneal endothelium and that the corneal epithelium exhibited a strong barrier function against Gd-DTPA entry. The MRI study also confirmed the strong barrier, enhanced signals being detected within the aqueous fluid in the T 1 -weighted image only when the corneal epithelium was abraded. Since Gd-DTPA scarcely penetrates the intact corneal epithelium, Gd-DTPA-enhanced MRI shows potential as a quantitative tracer in evaluating epithelial barrier disruption. (author)

  9. Gate-tunable valley-spin filtering in silicene with magnetic barrier

    Energy Technology Data Exchange (ETDEWEB)

    Wu, X. Q., E-mail: xianqiangzhe@126.com [National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093 (China); Meng, H. [School of Physics and Telecommunication Engineering, Shanxi University of Technology, Hanzhong 723001 (China)

    2015-05-28

    We theoretically study the valley- and spin-resolved scattering through magnetic barrier in a one layer thick silicene, using the mode-matching method for the Dirac equation. We show that the spin-valley filtering effect can be achieved and can also be tuned completely through both a top and bottom gate. Moreover, when reversing the sign of the staggered potential, we find the direction of the valley polarization is switched while the direction of spin polarization is unchanged. These results can provide some meaningful information to design valley valve residing on silicene.

  10. Noble internal transport barriers and radial subdiffusion of toroidal magnetic lines

    Energy Technology Data Exchange (ETDEWEB)

    Misguich, J.H.; Reuss, J.D. [Association Euratom-CEA sur la Fusion, CEA/DSM/DRFC, 13 - Saint Paul lez Durance (France); Constantinescu, D.; Steinbrecher, G. [Association Euratom-N.A.S.T.I., Dept. of Physics, University of Craiova (Romania); Vlad, M.; Spineanu, F. [Association Euratom-N.A.S.T.I., National Institute of Laser, Plasma and Radiation Physics, Bucharest (Romania); Weyssow, B.; Balescu, R. [Association Euratom-Etat Belge sur la Fusion, Universite Libre de Bruxelles (Belgium)

    2002-02-01

    Internal transport barriers (ITB's) observed in tokamaks are described by a purely magnetic approach. Magnetic line motion in toroidal geometry with broken magnetic surfaces is studied from a previously derived Hamiltonian map in situation of incomplete chaos. This appears to reproduce in a realistic way the main features of a tokamak, for a given safety factor profile and in terms of a single parameter L representing the amplitude of the magnetic perturbation. New results are given concerning the Shafranov shift as function of L. For small values of L, closed magnetic surfaces exist (KAM tori) and island chains begin to appear on rational surfaces for higher values of L, with chaotic zones around hyperbolic points, as expected. Single trajectories of magnetic line motion indicate the persistence of a central protected plasma core, surrounded by a chaotic shell enclosed in a double-sided transport barrier. Magnetic lines which succeed to escape across this barrier begin to wander in a wide chaotic sea extending up to a very robust barrier (as long as L{<=}1). For values of L{>=}1, above the escape threshold, most magnetic lines succeed to escape out of the external barrier which has become a permeable Cantorus. Statistical analysis of a large number of trajectories, representing the evolution of a bunch of magnetic lines, indicate that the flux variable {psi} asymptotically grows in a diffuse manner as (L{sup 2}t) with a L{sup 2} scaling as expected, but that the average radial position r{sub m}(t) asymptotically grows as (L{sup 2}t){sup 1/4} while the mean square displacement around this average radius asymptotically grows in a sub-diffusive manner as (L{sup 2}t){sup 1/2}. This result shows the slower dispersion in the present incomplete chaotic regime, which is different from the usual quasilinear diffusion in completely chaotic situations. For physical times t{sub {phi}} of the order of the escape time defined by x{sub m}(t{sub {phi}}) {approx}1, the motion

  11. Noble internal transport barriers and radial subdiffusion of toroidal magnetic lines

    International Nuclear Information System (INIS)

    Misguich, J.H.; Reuss, J.D.; Constantinescu, D.; Steinbrecher, G.; Vlad, M.; Spineanu, F.; Weyssow, B.; Balescu, R.

    2002-02-01

    Internal transport barriers (ITB's) observed in tokamaks are described by a purely magnetic approach. Magnetic line motion in toroidal geometry with broken magnetic surfaces is studied from a previously derived Hamiltonian map in situation of incomplete chaos. This appears to reproduce in a realistic way the main features of a tokamak, for a given safety factor profile and in terms of a single parameter L representing the amplitude of the magnetic perturbation. New results are given concerning the Shafranov shift as function of L. For small values of L, closed magnetic surfaces exist (KAM tori) and island chains begin to appear on rational surfaces for higher values of L, with chaotic zones around hyperbolic points, as expected. Single trajectories of magnetic line motion indicate the persistence of a central protected plasma core, surrounded by a chaotic shell enclosed in a double-sided transport barrier. Magnetic lines which succeed to escape across this barrier begin to wander in a wide chaotic sea extending up to a very robust barrier (as long as L≤1). For values of L≥1, above the escape threshold, most magnetic lines succeed to escape out of the external barrier which has become a permeable Cantorus. Statistical analysis of a large number of trajectories, representing the evolution of a bunch of magnetic lines, indicate that the flux variable ψ asymptotically grows in a diffuse manner as (L 2 t) with a L 2 scaling as expected, but that the average radial position r m (t) asymptotically grows as (L 2 t) 1/4 while the mean square displacement around this average radius asymptotically grows in a sub-diffusive manner as (L 2 t) 1/2 . This result shows the slower dispersion in the present incomplete chaotic regime, which is different from the usual quasilinear diffusion in completely chaotic situations. For physical times t φ of the order of the escape time defined by x m (t φ ) ∼1, the motion appears to be super-diffusive, however, but less dangerous than

  12. The Insulation Vacuum Barrier for the Large Hadron Collider (LHC) Magnet Cryostats

    CERN Document Server

    Castoldi, M; Parma, Vittorio; Skoczen, Blazej; Trilhe, P

    2000-01-01

    The sectorisation of the insulation vacuum of the LHC magnet cryostats, housing the superconducting magnets, which operate in a 1.9 K superfluid helium bath, is achieved by means of vacuum barriers. Each vacuum barrier is a leak-tight austenitic stainless steel thin-wall structure, mainly composed of large diameter (between 0.6 m and 0.9 m) bellows and concentric corrugated cylinders. It is mounted in the Short Straight Section (SSS) [1], between the magnet helium enclosure and the vacuum vessel. This paper presents the design of the vacuum barrier, concentrating mostly on its expected thermal performance, to fulfil the tight LHC heat in-leak budgets. Pressure and leak test results, confirming the mechanical design of two prototypes manufactured in industry, and the preparation of one of these vacuum barriers for cryogenic testing in an SSS prototype, are also mentioned.

  13. Magneto-transport in CdTe/CdMnTe dilute magnetic semiconductor single barrier structures

    International Nuclear Information System (INIS)

    Lyons, V.R.

    1999-03-01

    This thesis presents work done on electrical transport through dilute magnetic semiconductor (DMS) single barriers in both zero and non-zero magnetic fields. The fields are applied either perpendicular or parallel to the DMS layers. The main samples under investigation consist of 100 A and 200 A CdTe/Cd 0.8 Mn 0.2 Te/CdTe single barrier heterostructures. In addition electrical characterisation of the non magnetic layers is performed. Current through the barrier is measured as a function of voltage, magnetic field and temperature. A theoretical model is derived in order to calculate the current as a function of barrier height, barrier width, emitting layer carrier concentration, applied bias and temperature. These variables are then treated as fitting parameters and comparisons are made between the calculated and the experimental currents. The barriers are shown to produce non-Ohmic transport. The roles of quantum mechanical tunnelling and thermal activation across the barrier are investigated and shown to be highly mixed. An unexpectedly high degree of tunnelling is found to occur at high temperatures, within the region previously assumed to be dominated by thermal activation. Moreover the barrier height is found to be lower and the width greater than expected. These observations suggest that a high level of Mn diffusion occurs, possibly due to In dopant related effects. This suggestion is validated by the high emitting layer carrier concentration suggested by the fitting. At low temperatures and voltages the thicker barrier sample is shown to contain a parasitic leak path which short-circuits the barrier. This leak may exist in both samples but only becomes dominant where the barriers are sufficiently opaque to the incident carriers. Changes in a magnetic field are expected to be due to sp-d exchange induced giant Zeeman splitting in the barrier and either normal spin splitting or sp-d exchange effects in the emitter regions. The application of a magnetic field is

  14. Virtual-anode formation by an intense pulsed ion beam incident upon a magnetic barrier

    International Nuclear Information System (INIS)

    Robertson, S.; Wessel, F.

    1980-01-01

    An intense, pulsed, initially space-charge-neutral ion beam (100 kV, 1 kA, 600 nsec) has been propagated into a transversely oriented magnetic barrier. When the magnetic field is adjusted so that (rho/sub i/rho/sub e/)/sup 1/2/ very-much-less-than a < rho/sub i/, a virtual anode is formed whose potential oscillates at approx.ω/sub p/i about a value near the ion accelerating potential, where a is the transverse beam dimension, ω/sub tsp/i is the ion plasma frequency, and rho/sub e/ and rho/sub i/ are the electron and ion gyroradii. This behavior is similar to that predicted by Poukey and Rostoker for virtual cathodes

  15. Electron cooling and finite potential drop in a magnetized plasma expansion

    Energy Technology Data Exchange (ETDEWEB)

    Martinez-Sanchez, M. [Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139 (United States); Navarro-Cavallé, J. [Escuela Técnica Superior de Ingeniería Aeronáutica y del Espacio, Universidad Politécnica de Madrid, Plaza Cardenal Cisneros 3, Madrid 28040 (Spain); Ahedo, E. [Departamento de Bioingeniería e Ingeniería Aeroespacial, Universidad Carlos III de Madrid, Avda. Universidad 30, Leganés 28911, Madrid (Spain)

    2015-05-15

    The steady, collisionless, slender flow of a magnetized plasma into a surrounding vacuum is considered. The ion component is modeled as mono-energetic, while electrons are assumed Maxwellian upstream. The magnetic field has a convergent-divergent geometry, and attention is restricted to its paraxial region, so that 2D and drift effects are ignored. By using the conservation of energy and magnetic moment of particles and the quasi-neutrality condition, the ambipolar electric field and the distribution functions of both species are calculated self-consistently, paying attention to the existence of effective potential barriers associated to magnetic mirroring. The solution is used to find the total potential drop for a set of upstream conditions, plus the axial evolution of various moments of interest (density, temperatures, and heat fluxes). The results illuminate the behavior of magnetic nozzles, plasma jets, and other configurations of interest, showing, in particular, in the divergent plasma the collisionless cooling of electrons, and the generation of collisionless electron heat fluxes.

  16. Pulsed Magnetic Field Improves the Transport of Iron Oxide Nanoparticles through Cell Barriers

    Science.gov (United States)

    Min, Kyoung Ah; Shin, Meong Cheol; Yu, Faquan; Yang, Meizhu; David, Allan E.; Yang, Victor C.; Rosania, Gus R.

    2013-01-01

    Understanding how a magnetic field affects the interaction of magnetic nanoparticles (MNPs) with cells is fundamental to any potential downstream applications of MNPs as gene and drug delivery vehicles. Here, we present a quantitative analysis of how a pulsed magnetic field influences the manner in which MNPs interact with, and penetrate across a cell monolayer. Relative to a constant magnetic field, the rate of MNP uptake and transport across cell monolayers was enhanced by a pulsed magnetic field. MNP transport across cells was significantly inhibited at low temperature under both constant and pulsed magnetic field conditions, consistent with an active mechanism (i.e. endocytosis) mediating MNP transport. Microscopic observations and biochemical analysis indicated that, in a constant magnetic field, transport of MNPs across the cells was inhibited due to the formation of large (>2 μm) magnetically-induced MNP aggregates, which exceeded the size of endocytic vesicles. Thus, a pulsed magnetic field enhances the cellular uptake and transport of MNPs across cell barriers relative to a constant magnetic field by promoting accumulation while minimizing magnetically-induced MNP aggregates at the cell surface. PMID:23373613

  17. Tunnel magnetoresistance in alumina, magnesia and composite tunnel barrier magnetic tunnel junctions

    International Nuclear Information System (INIS)

    Schebaum, Oliver; Drewello, Volker; Auge, Alexander; Reiss, Guenter; Muenzenberg, Markus; Schuhmann, Henning; Seibt, Michael; Thomas, Andy

    2011-01-01

    Using magnetron sputtering, we have prepared Co-Fe-B/tunnel barrier/Co-Fe-B magnetic tunnel junctions with tunnel barriers consisting of alumina, magnesia, and magnesia-alumina bilayer systems. The highest tunnel magnetoresistance ratios we found were 73% for alumina and 323% for magnesia-based tunnel junctions. Additionally, tunnel junctions with a unified layer stack were prepared for the three different barriers. In these systems, the tunnel magnetoresistance ratios at optimum annealing temperatures were found to be 65% for alumina, 173% for magnesia, and 78% for the composite tunnel barriers. The similar tunnel magnetoresistance ratios of the tunnel junctions containing alumina provide evidence that coherent tunneling is suppressed by the alumina layer in the composite tunnel barrier. - Research highlights: → Transport properties of Co-Fe-B/tunnel barrier/Co-Fe-B magnetic tunnel junctions. → Tunnel barrier consists of MgO, Al-Ox, or MgO/Al-Ox bilayer systems. → Limitation of TMR-ratio in composite barrier tunnel junctions to Al-Ox values. → Limitation indicates that Al-Ox layer is causing incoherent tunneling.

  18. Temperature dependence of interlayer coupling in perpendicular magnetic tunnel junctions with GdOX barriers

    Science.gov (United States)

    Newhouse-Illige, T.; Xu, Y. H.; Liu, Y. H.; Huang, S.; Kato, H.; Bi, C.; Xu, M.; LeRoy, B. J.; Wang, W. G.

    2018-02-01

    Perpendicular magnetic tunnel junctions with GdOX tunneling barriers have shown a unique voltage controllable interlayer magnetic coupling effect. Here, we investigate the quality of the GdOX barrier and the coupling mechanism in these junctions by examining the temperature dependence of the tunneling magnetoresistance and the interlayer coupling from room temperature down to 11 K. The barrier is shown to be of good quality with the spin independent conductance only contributing a small portion, 14%, to the total room temperature conductance, similar to AlOX and MgO barriers. The interlayer coupling, however, shows an anomalously strong temperature dependence including sign changes below 80 K. This non-trivial temperature dependence is not described by previous models of interlayer coupling and may be due to the large induced magnetic moment of the Gd ions in the barrier.

  19. Resonant tunneling via spin-polarized barrier states in a magnetic tunnel junction

    NARCIS (Netherlands)

    Jansen, R.; Lodder, J.C.

    2000-01-01

    Resonant tunneling through states in the barrier of a magnetic tunnel junction has been analyzed theoretically for the case of a spin-polarized density of barrier states. It is shown that for highly spin-polarized barrier states, the magnetoresistance due to resonant tunneling is enhanced compared

  20. Magnet system for a thermal barrier Tandem Mirror Reactor

    International Nuclear Information System (INIS)

    Kim, N.S.; Conn, R.W.

    1981-01-01

    The magnet system for a thermal barrier D-D tandem mirror reactor has been studied as part of the UCLA tandem mirror reactor design study SATYR. Three main considerations in designing the SATYR magnet system are to obtain the desired field strength variation throughout the system, to have proper space for plasma and neutron shielding, and to satisfy the MHD stability to achieve maximum central cell /beta/. Due to the importance and the complexity, the 'internal' field reversal magnet is the main concern in the entire magnet system for SATYR. Two different magnet designs, a non-uniform current density solenoid and a higher-order solenoid, are discussed. Coil levitation for the internal field reversal magnet has been analyzed

  1. Tunnel magnetoresistance in asymmetric double-barrier magnetic tunnel junctions

    International Nuclear Information System (INIS)

    Useinov, N.Kh.; Petukhov, D.A.; Tagirov, L.R.

    2015-01-01

    The spin-polarized tunnel conductance and tunnel magnetoresistance (TMR) through a planar asymmetric double-barrier magnetic tunnel junction (DBMTJ) have been calculated using quasi-classical model. In DBMTJ nanostructure the magnetization of middle ferromagnetic metal layer can be aligned parallel or antiparallel with respect to the fixed magnetizations of the top and bottom ferromagnetic electrodes. The transmission coefficients of an electron to pass through the barriers have been calculated in terms of quantum mechanics. The dependencies of tunnel conductance and TMR on the applied voltage have been calculated in case of non-resonant transmission. Estimated in the framework of our model, the difference between the spin-channels conductances at low voltages was found relatively large. This gives rise to very high magnitude of TMR. - Highlights: • The spin-polarized conductance through the junction is calculated. • Dependencies of the tunnel conductance vs applied bias are shown. • Bias voltage dependence of tunnel magnetoresistance for the structure is shown

  2. Study of the dynamical potential barriers in heavy ion collisions

    International Nuclear Information System (INIS)

    Zhu, Long; Su, Jun; Xie, Wen-Jie; Zhang, Feng-Shou

    2013-01-01

    The nucleus–nucleus interaction potentials for the fusion reactions 16 O + 208 Pb, 64 Ni + 64 Ni, 58 Ni + 58 Ni and 16 O + 154 Sm are extracted from the improved isospin-dependent quantum molecular dynamics model. The shell correction effects are discussed. The negative shell correction energies lower potential barriers of a certain reaction. The incident energy dependence of the potential barrier is investigated for each system. A complex phenomenon of energy dependence is observed. It is also found that incident energy dependence of the barrier radius and barrier height shows opposite behaviors. The Coulomb potential shows weak energy dependence when distance of two colliding nuclei is lower than the touching distance. The isospin effects of the potential barrier are investigated. The orientation effects of the potential barrier is also discussed for the system 16 O + 154 Sm. The fusion cross sections that correspond to the equatorial orientation of 154 Sm are very low in sub-barrier region because of the high fusion barriers and the shallow potential pockets

  3. Electronic and transport properties of noncollinear magnetic monatomic Mn chains: Fano resonances in the superlattice of noncollinear magnetic barriers and magnetic anisotropic bands

    International Nuclear Information System (INIS)

    Dai, C.J.; Yan, X.H.; Xiao, Y.; Guo, Y.D.

    2015-01-01

    By means of the density functional theory combined with non-equilibrium Green's function method, ballistic transport properties of one-dimensional noncollinear magnetic monatomic chains were investigated using the single-atomic Mn chains as a model system. Fano resonances are found to exist in the monatomic Mn chains with spin-spiral structure. Furthermore, in the monatomic Mn chains with magnetic soliton lattice, Fano resonances are enhanced and cause the conductance splitting in the transmission spectra. The Fano resonances in the noncollinear magnetic single-atomic Mn chains are arising from the coupling of the localized d-states and the extended states of the quantum channels. By constructing a theoretical model and calculating its conductance, it is found that the phenomena of Fano resonances and the accompanying conductance splitting exist universally in the superlattice of one-dimensional noncollinear magnetic barriers, due to the interference of the incident waves and reflected waves by the interfaces between the neighboring barriers. Moreover, the band structures of the ferromagnetic and spin-spiral monatomic Mn chains exhibit a strong dependence on the spatial arrangement of the magnetic moments of Mn atoms when spin–orbit coupling is considered. - Highlights: • Transport properties of noncollinear magnetic monatomic Mn chains are studied. • Fano resonances are found in the noncollinear magnetic monatomic Mn chains. • Magnetic soliton lattice leads to conductance splitting in the transmission curve. • Fano resonances exist in the superlattice of noncollinear magnetic barriers. • Effect of SOC on the band structure of FM and spin-spiral Mn chains are studied

  4. Anisotropy barrier reduction in fast-relaxing Mn12 single-molecule magnets

    Science.gov (United States)

    Hill, Stephen; Murugesu, Muralee; Christou, George

    2009-11-01

    An angle-swept high-frequency electron paramagnetic resonance (HFEPR) technique is described that facilitates efficient in situ alignment of single-crystal samples containing low-symmetry magnetic species such as single-molecule magnets (SMMs). This cavity-based technique involves recording HFEPR spectra at fixed frequency and field, while sweeping the applied field orientation. The method is applied to the study of a low-symmetry Jahn-Teller variant of the extensively studied spin S=10 Mn12 SMMs (e.g., Mn12 -acetate). The low-symmetry complex also exhibits SMM behavior, but with a significantly reduced effective barrier to magnetization reversal (Ueff≈43K) and, hence, faster relaxation at low temperature in comparison with the higher-symmetry species. Mn12 complexes that crystallize in lower symmetry structures exhibit a tendency for one or more of the Jahn-Teller axes associated with the MnIII atoms to be abnormally oriented, which is believed to be the cause of the faster relaxation. An extensive multi-high-frequency angle-swept and field-swept electron paramagnetic resonance study of [Mn12O12(O2CCH2But)16(H2O)4]ṡCH2Cl2ṡMeNO2 is presented in order to examine the influence of the abnormally oriented Jahn-Teller axis on the effective barrier to magnetization reversal. The reduction in the axial anisotropy, D , is found to be insufficient to account for the nearly 40% reduction in Ueff . However, the reduced symmetry of the Mn12 core gives rise to a very significant second-order transverse (rhombic) zero-field-splitting anisotropy, E≈D/6 . This, in turn, causes a significant mixing of spin projection states well below the top of the classical anisotropy barrier. Thus, magnetic quantum tunneling is the dominant factor contributing to the effective barrier reduction in fast relaxing Mn12 SMMs.

  5. Role of E x B Shear and Magnetic Shear in the Formation of Transport Barriers in DIII-D

    International Nuclear Information System (INIS)

    Burrell, K.H.

    2005-01-01

    Development of the E x B shear stabilization model to explain the formation of transport barriers in magnetic confinement devices is a major achievement of fusion research. This concept has the universality needed to explain the H-mode edge transport barriers seen in limiter and divertor tokamaks, stellarators, and mirror machines; the broader edge transport barrier seen in VH-mode plasmas; and the core transport barriers formed in tokamaks with low or negative magnetic shear. These examples of confinement improvement are of considerable physical interest; it is not often that a system self-organizes to reduce transport when an additional source of free energy is applied to it. The transport decrease associated with E x B velocity shear is also of great practical benefit to fusion research. The fundamental physics involved in transport reduction is the effect of E x B shear on the growth, radial extent, and phase correlation of turbulent eddies in the plasma. The same basic transport reduction process can be operational in various portions of the plasma because there are a number of ways to change the radial electric field E r . An important theme in this area is the synergistic effect of E x B velocity shear and magnetic shear. Although the E x B velocity shear appears to have an effect on broader classes of microturbulence, magnetic shear can mitigate some potentially harmful effects of E x B velocity shear and facilitate turbulence stabilization. The experimental results on DIII-D and other devices are generally consistent with the basic theoretical models

  6. Asymmetric voltage behavior of the tunnel magnetoresistance in double barrier magnetic tunnel junctions

    KAUST Repository

    Useinov, Arthur

    2012-06-01

    In this paper, we study the value of the tunnel magnetoresistance (TMR) as a function of the applied voltage in double barrier magnetic tunnel junctions (DMTJs) with the left and right ferromagnetic (FM) layers being pinned and numerically estimate the possible difference of the TMR curves for negative and positive voltages in the homojunctions (equal barriers and electrodes). DMTJs are modeled as two single barrier junctions connected in series with consecutive tunneling (CST). We investigated the asymmetric voltage behavior of the TMR for the CST in the range of a general theoretical model. Significant asymmetries of the experimental curves, which arise due to different annealing regimes, are mostly explained by different heights of the tunnel barriers and asymmetries of spin polarizations in magnetic layers. © (2012) Trans Tech Publications.

  7. Asymmetric voltage behavior of the tunnel magnetoresistance in double barrier magnetic tunnel junctions

    KAUST Repository

    Useinov, Arthur; Gooneratne, Chinthaka Pasan; Kosel, Jü rgen

    2012-01-01

    In this paper, we study the value of the tunnel magnetoresistance (TMR) as a function of the applied voltage in double barrier magnetic tunnel junctions (DMTJs) with the left and right ferromagnetic (FM) layers being pinned and numerically estimate the possible difference of the TMR curves for negative and positive voltages in the homojunctions (equal barriers and electrodes). DMTJs are modeled as two single barrier junctions connected in series with consecutive tunneling (CST). We investigated the asymmetric voltage behavior of the TMR for the CST in the range of a general theoretical model. Significant asymmetries of the experimental curves, which arise due to different annealing regimes, are mostly explained by different heights of the tunnel barriers and asymmetries of spin polarizations in magnetic layers. © (2012) Trans Tech Publications.

  8. Magnetic Materials: Novel Monitors of Long-Term Evolution of Engineered Barrier Systems

    Directory of Open Access Journals (Sweden)

    Simon L. Harley

    2016-12-01

    Full Text Available Most safety cases for the deep geological disposal of radioactive waste are reliant on the swelling of bentonite in the engineered barrier system as it saturates with groundwater. Assurance of safety therefore requires effective monitoring of bentonite saturation. The time- and fluid-dependent corrosion of synthetic magnets embedded in bentonite is demonstrated here to provide a novel and passive means of monitoring saturation. Experiments have been conducted at 70 °C in which neo magnets, AlNiCo magnets, and ferrite magnets have been reacted with saline (NaCl, KCl, CaCl2 solutions and alkaline fluids (NaOH, KOH, Ca(OH2 solutions; pH = 12 in the presence of bentonite. Nd-Fe-B magnets undergo extensive corrosion that results in a dramatic change from ferromagnetic to superparamagnetic behaviour concomitant with bentonite saturation. AlNiCo magnets in saline solutions show corrosion but only limited decreases in their magnetic intensities, and ferrite magnets are essentially unreactive on the experimental timescales, retaining their initial magnetic properties. For all magnets the impact of their corrosion on bentonite swelling is negligible; alteration of bentonite is essentially governed by the applied fluid composition. In principle, synthetic magnet arrays can, with further development, be designed and embedded in bentonite to monitor its fluid saturation without compromising the integrity of the engineered barrier system itself.

  9. Ballistic transport through graphene nanostructures of velocity and potential barriers

    International Nuclear Information System (INIS)

    Krstajic, P M; Vasilopoulos, P

    2011-01-01

    We investigate the electronic properties of graphene nanostructures when the Fermi velocity and the electrostatic potential vary in space. First, we consider the transmission T and conductance G through single and double barriers. We show that G for velocity barriers differs markedly from that for potential barriers for energies below the height of the latter and it exhibits periodic oscillations as a function of the energy for strong velocity modulation. Special attention is given to superlattices (SLs). It is shown that an applied bias can efficiently widen or shrink the allowed minibands of velocity-modulated SLs. The spectrum in the Kronig-Penney limit is periodic in the strength of the barriers. Collimation of an electron beam incident on an SL with velocity and potential barriers is present but it disappears when the potential barriers are absent. The number of additional Dirac points may change considerably if barriers and wells have sufficiently different Fermi velocities.

  10. Flexible MgO Barrier Magnetic Tunnel Junctions.

    Science.gov (United States)

    Loong, Li Ming; Lee, Wonho; Qiu, Xuepeng; Yang, Ping; Kawai, Hiroyo; Saeys, Mark; Ahn, Jong-Hyun; Yang, Hyunsoo

    2016-07-01

    Flexible MgO barrier magnetic tunnel junction (MTJ) devices are fabricated using a transfer printing process. The flexible MTJ devices yield significantly enhanced tunneling magnetoresistance of ≈300% and improved abruptness of switching, as residual strain in the MTJ structure is released during the transfer process. This approach could be useful for flexible electronic systems that require high-performance memory components. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Electronic transport in armchair graphene nanoribbon under double magnetic barrier modulation

    Science.gov (United States)

    Wang, Haiyan; Wu, Chao; Xie, Fang; Zhang, Xiaojiao; Zhou, Guanghui

    2018-03-01

    We present a theoretical investigation of the transport properties and the magnetoresistance effect in armchair graphene nanoribbons (AGNRs) under modulation by two magnetic barriers. The energy levels are found to be degenerate for a metallic AGNR but are not degenerate for a semiconducting AGNR. However, the conductance characteristics show quantized plateaus in both the metallic and semiconducting cases. When the magnetization directions of the barriers change from parallel to antiparallel, the conductance plateau in the metallic AGNR shows a degenerate feature due to matching between the transport modes in different regions. As the barrier height increases, the conductance shows more oscillatory behavior with sharp peaks and troughs. Specifically, the initial position of nonzero conductance for the metallic AGNR system moves towards a higher energy regime, which indicates that an energy gap has been opened. In addition, the magnetoresistance ratio also shows plateau structures in certain specific energy regions. These results may be useful in the design of electron devices based on AGNR nanostructures.

  12. Control of Internal Transport Barriers in Magnetically Confined Fusion Plasmas

    Science.gov (United States)

    Panta, Soma; Newman, David; Sanchez, Raul; Terry, Paul

    2016-10-01

    In magnetic confinement fusion devices the best performance often involves some sort of transport barriers to reduce the energy and particle flow from core to edge. Those barriers create gradients in the temperature and density profiles. If gradients in the profiles are too steep that can lead to instabilities and the system collapses. Control of these barriers is therefore an important challenge for fusion devices (burning plasmas). In this work we focus on the dynamics of internal transport barriers. Using a simple 7 field transport model, extensively used for barrier dynamics and control studies, we explore the use of RF heating to control the local gradients and therefore the growth rates and shearing rates for barrier initiation and control in self-heated fusion plasmas. Ion channel barriers can be formed in self-heated plasmas with some NBI heating but electron channel barriers are very sensitive. They can be formed in self-heated plasmas with additional auxiliary heating i.e. NBI and radio-frequency(RF). Using RF heating on both electrons and ions at proper locations, electron channel barriers along with ion channel barriers can be formed and removed demonstrating a control technique. Investigating the role of pellet injection in controlling the barriers is our next goal. Work supported by DOE Grant DE-FG02-04ER54741.

  13. Manufacture and test of prototype water pipe chase barrier in ITER Magnet Feeder system

    Energy Technology Data Exchange (ETDEWEB)

    Lu, Kun, E-mail: lukun@ipp.ac.cn [Institute of Plasma Physics, Shushan Hu Road 350, Hefei, Anhui (China); Wen, Xinjie; Liu, Chen; Song, Yuntao [Institute of Plasma Physics, Shushan Hu Road 350, Hefei, Anhui (China); Niu, Erwu [ITER China, 15B Fuxing Road, Beijing 100862 (China); Gung, Chenyu; Su, Man [ITER Organization, Route de Vinon-sur-Verdon – CS 90046, 13067 St Paul-lez-Durance Cedex (France)

    2016-11-01

    The Magnet Feeder system in the International Thermonuclear Experimental Reactor (ITER) deploys electrical currents and supercritical helium to the superconducting magnets and the magnet diagnostic signals to the operators. In the current design, the feeders located in the upper L3 level of the Tokamak gallery penetrate the Tokamak coolant water system vault, the biological shield and the cryostat. As a secondary confinement to contain the activated coolant water in the vault in the case of water pipe burst accident, a water barrier is welded between the penetration in the water pipe chase outer wall and the mid-plane of the vacuum jacket of the Feeder Coil Terminal Box (CTB). A thin-wall stainless steel diaphragm with an omega shape profile is welded around the CTB as the water barrier to endure 2 bar hydraulic pressure. In addition, the barrier is designed as a flexible compensator to withstand a maximum of 15 mm of axial displacement of the CTB in case of helium leak accident without failure. This paper presents the detail configuration, the manufacturing and assembly processes of the water barrier. Test results of the prototype water barrier under simulated accident conditions are also reported. Successful qualification of the design and manufacturing process of the water barrier lays a good foundation for the series production of this subsystem.

  14. Transport properties of Dirac electrons in graphene based double velocity-barrier structures in electric and magnetic fields

    International Nuclear Information System (INIS)

    Liu, Lei; Li, Yu-Xian; Liu, Jian-Jun

    2012-01-01

    Using transfer matrix method, transport properties in graphene based double velocity-barrier structures under magnetic and electric fields are numerically studied. It is found that velocity barriers for the velocity ratio (the Fermi velocity inside the barrier to that outside the barrier) less than one (or for the velocity ratio greater than one) have properties similar to electrostatic wells (or barriers). The velocity barriers for the velocity ratio greater than one significantly enlarge the resonant tunneling region of electrostatic barriers. In the presence of magnetic field, the plateau width of the Fano factor with a Poissonian value shortens (or broadens) for the case of the velocity ratio less than one (or greater than one). When the Fermi energy is equal to the electrostatic barrier height, for different values of the velocity ratio, both the conductivities and the Fano factors remain fixed. -- Highlights: ► We model graphene based velocity-barrier structures in electric and magnetic fields. ► Velocity barrier for ξ 1) have property similar to electrostatic well (barrier). ► Velocity barrier for ξ>1 enlarge the resonant tunneling region of electrostatic barrier. ► The plateau width of Fano factor shortens (or broadens) for the case of ξ 1). ► The conductivity remains fixed at the point of E F =U 0 for different values of ξ.

  15. Statistical analysis of internal transport barriers in JET

    Energy Technology Data Exchange (ETDEWEB)

    Maget, P [Association Euratom-CEA, Cadarache, F-13108 St Paul-lez-Durance (France); Esposito, B [Associazione Euratom-ENEA sulla Fusione, C.R. Frascati, Frascati (Italy); Joffrin, E [Association Euratom-CEA, Cadarache, F-13108 St Paul-lez-Durance (France); Hawkes, N [Euratom-UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxon OX14 3DB (United Kingdom); Mazon, D [Association Euratom-CEA, Cadarache, F-13108 St Paul-lez-Durance (France); Baranov, Y [Euratom-UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxon OX14 3DB (United Kingdom); Fourment, C [Association Euratom-CEA, Cadarache, F-13108 St Paul-lez-Durance (France); Hoang, G T [Association Euratom-CEA, Cadarache, F-13108 St Paul-lez-Durance (France)

    2003-08-01

    The potential role of magnetic shear, rational safety factor surfaces and shearing rate on the confinement is investigated on the basis of a database analysis of JET internal transport barriers (ITBs). The ITB is quantified using the JET ITB criterion (Tresset G et al 2002 Nucl. Fusion 42 520). The relation between the shearing rate and the magnetic shear, already established for positive magnetic shear barrier (Tala T J J et al 2001 Plasma Phys. Control. Fusion 43 507), is investigated at low and negative magnetic shear, where the threshold in shearing rate is found to be lower than for positive magnetic shear barriers. Defining the ITB from the departure from profile stiffness is found to be consistent with the database results, and the critical gradient length is found to be minimum at low magnetic shear. Finally, ITBs are found to be localized in the vicinity of integer safety factor surfaces in positive magnetic shear plasmas, whereas no correlation is found with integer values when the barrier is localized in negative magnetic shear regions.

  16. The strongest magnetic barrier in the DIII-D tokamak and comparison with the ASDEX UG

    Science.gov (United States)

    Ali, Halima; Punjabi, Alkesh

    2013-05-01

    Magnetic perturbations in tokamaks lead to the formation of magnetic islands, chaotic field lines, and the destruction of flux surfaces. Controlling or reducing transport along chaotic field lines is a key challenge in magnetically confined fusion plasmas. A local control method was proposed by Chandre et al. [Nucl. Fusion 46, 33-45 (2006)] to build barriers to magnetic field line diffusion by addition of a small second-order control term localized in the phase space to the field line Hamiltonian. Formation and existence of such magnetic barriers in Ohmically heated tokamaks (OHT), ASDEX UG and piecewise analytic DIII-D [Luxon, J.L.; Davis, L.E., Fusion Technol. 8, 441 (1985)] plasma equilibria was predicted by the authors [Ali, H.; Punjabi, A., Plasma Phys. Control. Fusion 49, 1565-1582 (2007)]. Very recently, this prediction for the DIII-D has been corroborated [Volpe, F.A., et al., Nucl. Fusion 52, 054017 (2012)] by field-line tracing calculations, using experimentally constrained Equilibrium Fit (EFIT) [Lao, et al., Nucl. Fusion 25, 1611 (1985)] DIII-D equilibria perturbed to include the vacuum field from the internal coils utilized in the experiments. This second-order approach is applied to the DIII-D tokamak to build noble irrational magnetic barriers inside the chaos created by the locked resonant magnetic perturbations (RMPs) (m, n)=(3, 1)+(4, 1), with m and n the poloidal and toroidal mode numbers of the Fourier expansion of the magnetic perturbation with amplitude δ. A piecewise, analytic, accurate, axisymmetric generating function for the trajectories of magnetic field lines in the DIII-D is constructed in magnetic coordinates from the experimental EFIT Grad-Shafranov solver [Lao, L, et al., Fusion Sci. Technol. 48, 968 (2005)] for the shot 115,467 at 3000 ms in the DIII-D. A symplectic mathematical map is used to integrate field lines in the DIII-D. A numerical algorithm [Ali, H., et al., Radiat. Eff. Def. Solids Inc. Plasma Sc. Plasma Tech. 165, 83

  17. Electron tunneling across a tunable potential barrier

    International Nuclear Information System (INIS)

    Mangin, A; Anthore, A; Rocca, M L Della; Boulat, E; Lafarge, P

    2009-01-01

    We present an experiment where the elementary quantum electron tunneling process should be affected by an independent gate voltage parameter. We have realized nanotransistors where the source and drain electrodes are created by electromigration inducing a nanometer sized gap acting as a tunnel barrier. The barrier potential shape is in first approximation considered trapezoidal. The application of a voltage to the gate electrode close to the barrier region can in principle affect the barrier shape. Simulations of the source drain tunnel current as a function of the gate voltage predict modulations as large as one hundred percent. The difficulty of observing the predicted behaviour in our samples might be due to the peculiar geometry of the realized tunnel junction.

  18. Reflectionlessness, kurtosis and top curvature of potential barriers

    International Nuclear Information System (INIS)

    Ahmed, Zafar

    2006-01-01

    Apart from the rectangular barrier, other barriers having a single maximum generally display reflectivity, R(E), as a smoothly decreasing function of energy. We conjecture that symmetric potential barriers with a single maximum entail zeros or sharp minima in R(E) provided they have either their coefficient of kurtosis lying in the range (1.8, 3.0), or their top curvature as zero, or both

  19. Estimates for diffusion barriers and atomic potentials in MGO

    International Nuclear Information System (INIS)

    Skala, L.; Kenkre, V.M.

    1991-01-01

    In this paper, as part of a program of investigation of microwave sintering, self-consistent CNDO/2 calculations are presented for diffusion barriers and potentials for the motion of interstitial atoms and vacancies in MgO. Clusters of 30 atoms are used in the calculations. Activation energies, diffusion barriers, shape of the potentials and electron densities are obtained

  20. A Hybrid Excited Machine with Flux Barriers and Magnetic Bridges

    Directory of Open Access Journals (Sweden)

    Marcin Wardach

    2018-03-01

    Full Text Available In this paper, an U-shape flux barrier rotor concept for a hybrid excited synchronous machine with flux magnetic bridges fixed on the rotor is presented. Using 3D finite element analysis, the influence of axial flux bridges on the field-weakening and -strengthening characteristics, electromagnetic torque, no-load magnetic flux linkage, rotor iron losses and back electromotive force is shown. Three different rotor designs are analyzed. Furthermore, the field control characteristics depending on additional DC control coil currents are shown.

  1. Comparative studies for different proximity potentials applied to sub-barrier fusion reactions

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, G.L. [Beihang University, School of Physics and Nuclear Energy Engineering, Beijing (China); Beihang University, Key Laboratory of Micro-Nano Measurement-Manipulation and Physics (Ministry of Education), Beijing (China); Qu, W.W. [Medical College of Soochow University, School of Radiation Medicine and Protection, Soochow (China); Guo, M.F.; Qian, J.Q. [Beihang University, School of Physics and Nuclear Energy Engineering, Beijing (China); Zhang, H.Q. [China Institute of Atomic Energy, Beijing (China); Wolski, R. [Henryk Niewodniczanski Institute of Nuclear Physics PAS, Cracow (Poland)

    2016-02-15

    Coulomb barrier heights calculated by using 14 different versions of proximity potentials are studied and applied for experimental data of fusion in terms of a recently proposed energy scaling approach. The results show that the descriptions of proximity potentials 77 and 88 for the barrier heights seem to be closest to the values required by the systematics. On the basis of proximity potential 77, the parameterized formulas of the barrier height and radius are obtained. These formulas can calculate the barrier positions and barrier heights reasonably well within the error, respectively. Thus it provides a simple and direct way to calculate the barrier positions and barrier heights for heavy-ion fusion reactions. (orig.)

  2. Optimization of a tunneling barrier in magnetic tunneling junction by tilted-plasma oxidation

    International Nuclear Information System (INIS)

    Nam, C.H.; Shim, Heejae; Kim, K.S.; Cho, B.K.

    2004-01-01

    Oxidation of an AlO x insulating barrier in a magnetic tunneling junction (MTJ) was carried out by a tilted-plasma oxidation method. It was found that the tilted-plasma oxidation induced a gradual change in the extent of oxidation of an insulating layer, which consequently led to a gradual change in the tunneling magnetoresistance (TMR) and specific junction resistance (RA) of the MTJ. We found a linear relation in the TMR versus RA curve with positive and negative slopes for less- and overoxidized junctions, respectively, and a parabolic relation for optimally oxidized junctions. The crossover in the TMR versus RA curves provides an effective and useful way to optimize (and monitor) the oxidation condition of a tunneling barrier in MTJs especially of a tunneling barrier less than 10 A thick. The tunneling junctions were also investigated after thermal annealing at various temperatures. The observations after thermal annealing were found to be consistent with transmission electrons microscopy images and a scenario of the partial formation of an additional ultrathin tunneling barrier at the top surface of the bottom magnetic layer

  3. Giant magnetoresistance effect in nanostructures consisting of magnetic-electric barriers

    International Nuclear Information System (INIS)

    Tang, Wei-Hua; Li, Chun-Shu; Kong, Yong-Hong; Zhang, Gui-Lian

    2007-01-01

    The GMR effect in magnetic-electric barrier nanostructure, which can be realized experimentally by depositing two parallel metallic ferromagnetic strips with an applied voltage on the top of heterostructure, is investigated theoretically. It is shown that a considerable GMR effect can be achieved in such nanosystems due to the significant transmission difference for electrons tunneling through parallel and antiparallel magnetization configurations. It is also shown that the magnetoresistance ratio is strongly dependent upon the applied voltage to metallic ferromagnetic strips in nanosystems, thus may leading to voltage-tunable GMR devices

  4. Renewable energy costs, potentials, barriers: Conceptual issues

    International Nuclear Information System (INIS)

    Verbruggen, Aviel; Fischedick, Manfred; Moomaw, William; Weir, Tony; Nadai, Alain; Nilsson, Lars J.; Nyboer, John; Sathaye, Jayant

    2010-01-01

    Renewable energy can become the major energy supply option in low-carbon energy economies. Disruptive transformations in all energy systems are necessary for tapping widely available renewable energy resources. Organizing the energy transition from non-sustainable to renewable energy is often described as the major challenge of the first half of the 21st century. Technological innovation, the economy (costs and prices) and policies have to be aligned to achieve full renewable energy potentials, and barriers impeding that growth need to be removed. These issues are also covered by IPCC's special report on renewable energy and climate change to be completed in 2010. This article focuses on the interrelations among the drivers. It clarifies definitions of costs and prices, and of barriers. After reviewing how the third and fourth assessment reports of IPCC cover mitigation potentials and commenting on definitions of renewable energy potentials in the literature, we propose a consistent set of potentials of renewable energy supplies.

  5. Temperature dependence of shot noise in double barrier magnetic tunnel junctions

    Science.gov (United States)

    Niu, Jiasen; Liu, Liang; Feng, J. F.; Han, X. F.; Coey, J. M. D.; Zhang, X.-G.; Wei, Jian

    2018-03-01

    Shot noise reveals spin dependent transport properties in a magnetic tunnel junction. We report measurement of shot noise in CoFeB/MgO/CoFeB/MgO/CoFeB double barrier magnetic tunnel junctions, which shows a strong temperature dependence. The Fano factor used to characterize shot noise increases with decreasing temperature. A sequential tunneling model can be used to account for these results, in which a larger Fano factor results from larger spin relaxation length at lower temperatures.

  6. Determination of the thickness of Al2O3 barriers in magnetic tunnel junctions

    International Nuclear Information System (INIS)

    Buchanan, J.D.R.; Hase, T.P.A.; Tanner, B.K.; Hughes, N.D.; Hicken, R.J.

    2002-01-01

    The barrier thickness in magnetic spin-dependent tunnel junctions with Al 2 O 3 barriers has been measured using grazing incidence x-ray reflectivity and by fitting the tunneling current to the Simmons model. We have studied the effect of glow discharge oxidation time on the barrier structure, revealing a substantial increase in Al 2 O 3 thickness with oxidation. The greater thickness of barrier measured using grazing incidence x-ray reflectivity compared with that obtained by fitting current density-voltage to the Simmons electron tunneling model suggests that electron tunneling is localized to specific regions across the barrier, where the thickness is reduced by fluctuations due to nonconformal roughness

  7. Tunnel barrier and noncollinear magnetization effects on shot noise in ferromagnetic/semiconductor/ferromagnetic heterojunctions

    International Nuclear Information System (INIS)

    An Xingtao; Liu Jianjun

    2008-01-01

    Based on the scattering approach, we investigate transport properties of electrons in a one-dimensional waveguide that contains a ferromagnetic/semiconductor/ferromagnetic heterojunction and tunnel barriers in the presence of Rashba and Dresselhaus spin-orbit interactions. We simultaneously consider significant quantum size effects, quantum coherence, Rashba and Dresselhaus spin-orbit interactions and noncollinear magnetizations. It is found that the tunnel barrier plays a decisive role in the transmission coefficient and shot noise of the ballistic spin electron transport through the heterojunction. When the small tunnel barriers are considered, the transport properties of electrons are quite different from those without tunnel barriers

  8. Thermally assisted interlayer magnetic coupling through Ba_0_._0_5Sr_0_._9_5TiO_3 barriers

    International Nuclear Information System (INIS)

    Carreira, Santiago J.; Steren, Laura B.; Avilés Félix, Luis; Alejandro, Gabriela; Sirena, Martín

    2016-01-01

    We report on the interlayer exchange coupling across insulating barriers observed on Ni_8_0Fe_2_0/Ba_0_._0_5Sr_0_._9_5TiO_3/La_0_._6_6Sr_0_._3_3MnO_3 (Py/BST_0_._0_5/LSMO) trilayers. The coupling mechanism has been analyzed in terms of the barrier thickness, samples' substrate, and temperature. We examined the effect of MgO (MGO) and SrTiO_3 (STO) (001) single-crystalline substrates on the magnetic coupling and also on the magnetic anisotropies of the samples in order to get a deeper understanding of the magnetism of the structures. We measured a weak coupling mediated by spin-dependent tunneling phenomena whose sign and strength depend on barrier thickness and substrate. An antiferromagnetic (AF) exchange prevails for most of the samples and smoothly increases with the barrier thicknesses as a consequence of the screening effects of the BST_0_._0_5. The coupling monotonically increases with temperature in all the samples and this behavior is attributed to thermally assisted mechanisms. The magnetic anisotropy of both magnetic components has a cubic symmetry that in the case of permalloy is added to a small uniaxial component.

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

    Science.gov (United States)

    Clément, P.-Y.; Baraduc, C.; Ducruet, C.; Vila, L.; Chshiev, M.; Diény, B.

    2015-09-01

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

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

    International Nuclear Information System (INIS)

    Clément, P.-Y.; Baraduc, C.; Chshiev, M.; Diény, B.; Ducruet, C.; Vila, L.

    2015-01-01

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

  11. 7Li breakup polarization potential at near barrier energies

    International Nuclear Information System (INIS)

    Lubian, J. . E-mail lubian@if.uff.br; Correa, T.; Paes, B.; Figueira, J.M.; Abriola, D.; Fernandez Niello, J.O.; Arazi, A.; Capurro, O.A.; de Barbara, E.; Marti, G.V.; Martinez Heinmann, D.; Negri, A.E.; Pacheco, A.J.; Padron, I.; Gomes, P.R.S.

    2007-01-01

    Inelastic and one neutron transfer cross sections at energies around the Coulomb barrier were used to derive dynamic polarization potential (DPP) for the 7 Li + 27 Al system. The DPP due to breakup, obtained in a simple way, indicates that its real part is repulsive at near barrier energies

  12. Influence of the potential well and the potential barrier on the density distribution of confined-model fluids

    CERN Document Server

    Lee, B H; Lee, C H; Seong Baek Seok

    2000-01-01

    A density functional perturbative approximation, which is based on the density functional expansion of the one-particle direct correlation function of model fluids with respect to the bulk density, has been employed to investigate the influence of the potential well and the potential barrier on the density behavior of confined-model fluids. The mean spherical approximation has been used to calculate the two-particle direct correlation function of the model fluids. At lower densities, the density distributions are strongly affected by the barrier height and the well depth of the model potential, the contribution from the short-range repulsive part being especially important. However, the effects of the barrier height and the well depth of the model potential decrease with increasing bulk density. The calculated results also show that in the region where the effect of the wall-fluid interaction is relatively weak, the square-barrier part of the model potential leads to a nonuniformity in the density distributio...

  13. Universal potential-barrier penetration by initially confined wave packets

    International Nuclear Information System (INIS)

    Granot, Er'el; Marchewka, Avi

    2007-01-01

    The dynamics of an initially sharp-boundary wave packet in the presence of an arbitrary potential barrier is investigated. It is shown that the penetration through the barrier is universal in the sense that it depends only on the values of the wave function and its derivatives at the boundary. The dependence on the derivatives vanishes at long distances from the barrier, where the dynamics is governed solely by the initial value of the wave function at the boundary

  14. Universal potential-barrier penetration by initially confined wave packets

    Science.gov (United States)

    Granot, Er'El; Marchewka, Avi

    2007-07-01

    The dynamics of an initially sharp-boundary wave packet in the presence of an arbitrary potential barrier is investigated. It is shown that the penetration through the barrier is universal in the sense that it depends only on the values of the wave function and its derivatives at the boundary. The dependence on the derivatives vanishes at long distances from the barrier, where the dynamics is governed solely by the initial value of the wave function at the boundary.

  15. Resonant tunnel magnetoresistance in double-barrier planar magnetic tunnel junctions

    KAUST Repository

    Useinov, A. N.

    2011-08-24

    We present a theoretical approach to calculate the spin-dependent current and tunnel magnetoresistance (TMR) in a double-barrier magnetic tunnel junction (DMTJ), in which the magnetization of the middle ferromagnetic metal layer can be aligned parallel or antiparallel in relation to the fixed magnetizations of the left and right ferromagnetic electrodes. The electron transport through the DMTJ is considered as a three-dimensional problem, taking into account all transmitting electron trajectories as well as the spin-dependent momentum conservation law. The dependence of the transmission coefficient and spin-polarized currents on the applied voltage is derived as an exact solution to the quantum-mechanical problem for the spin-polarized transport. In the range of the developed physical model, the resonant tunneling, nonresonant tunneling, and enhanced spin filtering can be explained; the simulation results are in good agreement with experimental data.

  16. Resonant tunnel magnetoresistance in double-barrier planar magnetic tunnel junctions

    KAUST Repository

    Useinov, A. N.; Kosel, Jü rgen; Useinov, N. Kh.; Tagirov, L. R.

    2011-01-01

    We present a theoretical approach to calculate the spin-dependent current and tunnel magnetoresistance (TMR) in a double-barrier magnetic tunnel junction (DMTJ), in which the magnetization of the middle ferromagnetic metal layer can be aligned parallel or antiparallel in relation to the fixed magnetizations of the left and right ferromagnetic electrodes. The electron transport through the DMTJ is considered as a three-dimensional problem, taking into account all transmitting electron trajectories as well as the spin-dependent momentum conservation law. The dependence of the transmission coefficient and spin-polarized currents on the applied voltage is derived as an exact solution to the quantum-mechanical problem for the spin-polarized transport. In the range of the developed physical model, the resonant tunneling, nonresonant tunneling, and enhanced spin filtering can be explained; the simulation results are in good agreement with experimental data.

  17. Discontinuity model for internal transport barrier formation in reversed magnetic shear plasmas

    International Nuclear Information System (INIS)

    Kishimoto, Y.; Kim, J-Y.; Horton, W.; Tajima, T.; LeBrun, M.J.

    2001-01-01

    To aid in understanding the internal transport barrier (ITB) being formed in reversed magnetic shear experiments, in addition to the well known shear flow effect, we point out an important nonlocal effect and/or finite size effect which comes from the complex behavior of the nonlocal mode over a finite radial region around the minimum q(safety factor)-surface. The nonlocal mode changes its structure depending on the sign of the magnetic shear and due to this fact, the nonlocal modes are weakly excited across the q min -surface. This leads to a discontinuity or gap which disconnects the phase relation in the global wave structure across the q min -surface. Once such a discontinuity (or gap) is formed, transport suppression occurs and therefore a transport barrier can be expected near the q min -surface. We confirm the existence of this discontinuity using a toroidal particle simulation. (author)

  18. Reliability enhancement due to in-situ post-oxidation of sputtered MgO barrier in double MgO barrier magnetic tunnel junction

    Directory of Open Access Journals (Sweden)

    Chikako Yoshida

    2017-06-01

    Full Text Available We have investigated the effects of in-situ post-oxidation (PO of a sputtered MgO barrier in a double-MgO-barrier magnetic tunnel junction (MTJ and found that the short error rate was significantly reduced, the magnetoresistance (MR ratio was increased approximately 18%, and the endurance lifetime was extend. In addition, we found that the distribution of breakdown number (a measure of endurance exhibits trimodal characteristics, which indicates competition between extrinsic and intrinsic failures. This improvement in reliability might be related to the suppression of Fe and Co diffusion to the MgO barrier, as revealed by electron energy-loss spectroscopy (EELS analysis.

  19. Anisotropic sensor and memory device with a ferromagnetic tunnel barrier as the only magnetic element.

    Science.gov (United States)

    Lόpez-Mir, L; Frontera, C; Aramberri, H; Bouzehouane, K; Cisneros-Fernández, J; Bozzo, B; Balcells, L; Martínez, B

    2018-01-16

    Multiple spin functionalities are probed on Pt/La 2 Co 0.8 Mn 1.2 O 6 /Nb:SrTiO 3 , a device composed by a ferromagnetic insulating barrier sandwiched between non-magnetic electrodes. Uniquely, La 2 Co 0.8 Mn 1.2 O 6 thin films present strong perpendicular magnetic anisotropy of magnetocrystalline origin, property of major interest for spintronics. The junction has an estimated spin-filtering efficiency of 99.7% and tunneling anisotropic magnetoresistance (TAMR) values up to 30% at low temperatures. This remarkable angular dependence of the magnetoresistance is associated with the magnetic anisotropy whose origin lies in the large spin-orbit interaction of Co 2+ which is additionally tuned by the strain of the crystal lattice. Furthermore, we found that the junction can operate as an electrically readable magnetic memory device. The findings of this work demonstrate that a single ferromagnetic insulating barrier with strong magnetocrystalline anisotropy is sufficient for realizing sensor and memory functionalities in a tunneling device based on TAMR.

  20. Ballistic charge carrier transmission through graphene multi-barrier structures in uniform magnetic field

    International Nuclear Information System (INIS)

    Zubarev, A; Dragoman, D

    2014-01-01

    We investigate charge carrier transport in graphene multi-barrier structures placed in a uniform magnetic field. The transmission coefficient is found analytically by generalizing the transfer matrix method for the case of graphene regions subjected to a uniform magnetic field. The transmission coefficient through the structure can be modulated by varying the gate voltages, the magnetic field and/or the width of the gated regions. Such a configuration could be used in multiple-valued logic circuits, since it has several output states with discrete and easily selectable transmission/current values. (paper)

  1. Spin-related tunneling through a nanostructured electric-magnetic barrier on the surface of a topological insulator.

    Science.gov (United States)

    Wu, Zhenhua; Li, Jun

    2012-01-27

    We investigate quantum tunneling through a single electric and/or magnetic barrier on the surface of a three-dimensional topological insulator. We found that (1) the propagating behavior of electrons in such system exhibits a strong dependence on the direction of the incident electron wavevector and incident energy, giving the possibility to construct a wave vector and/or energy filter; (2) the spin orientation can be tuned by changing the magnetic barrier structure as well as the incident angles and energies.PACS numbers: 72.25.Dc; 73.20.-r; 73.23.-b; 75.70.-i.

  2. Large magnetocurrents in double-barrier tunneling transistors

    International Nuclear Information System (INIS)

    Lee, J.H.; Jun, K.-I.; Shin, K.-H.; Park, S.Y.; Hong, J.K.; Rhie, K.; Lee, B.C.

    2005-01-01

    Magnetic tunneling transistors (MTT) with double tunneling barriers are fabricated. The structure of the transistor is AFM/FM/I/FM/I/FM/AFM, and ferromagnetic layers serve as the emitter, base and collector. This double-barrier tunneling transistor (DBTT) has an advantage of controlling the potential between the base and collector, compared to the Schottky-barrier-based base and collector of MTT. We found that the collector current density of DBTT is at least 10 3 times larger than that of conventional MTT, since tunneling through AlO x barrier provides much larger current density than that through Schottky barrier

  3. Thermally assisted interlayer magnetic coupling through Ba{sub 0.05}Sr{sub 0.95}TiO{sub 3} barriers

    Energy Technology Data Exchange (ETDEWEB)

    Carreira, Santiago J.; Steren, Laura B. [Centro Atómico Constituyentes, San Martín, Buenos Aires 1650 (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas, Ciudad Autonoma de Buenos Aires C1425FQB (Argentina); Avilés Félix, Luis; Alejandro, Gabriela [Consejo Nacional de Investigaciones Científicas y Técnicas, Ciudad Autonoma de Buenos Aires C1425FQB (Argentina); Centro Atómico Bariloche, Bariloche, Rio Negro 8400 (Argentina); Sirena, Martín [Consejo Nacional de Investigaciones Científicas y Técnicas, Ciudad Autonoma de Buenos Aires C1425FQB (Argentina); Centro Atómico Bariloche, Bariloche, Rio Negro 8400 (Argentina); Instituto Balseiro-CNEA & Univ. Nac. de Cuyo, Bariloche, Rio Negro 8400 (Argentina)

    2016-08-08

    We report on the interlayer exchange coupling across insulating barriers observed on Ni{sub 80}Fe{sub 20}/Ba{sub 0.05}Sr{sub 0.95}TiO{sub 3}/La{sub 0.66}Sr{sub 0.33}MnO{sub 3} (Py/BST{sub 0.05}/LSMO) trilayers. The coupling mechanism has been analyzed in terms of the barrier thickness, samples' substrate, and temperature. We examined the effect of MgO (MGO) and SrTiO{sub 3} (STO) (001) single-crystalline substrates on the magnetic coupling and also on the magnetic anisotropies of the samples in order to get a deeper understanding of the magnetism of the structures. We measured a weak coupling mediated by spin-dependent tunneling phenomena whose sign and strength depend on barrier thickness and substrate. An antiferromagnetic (AF) exchange prevails for most of the samples and smoothly increases with the barrier thicknesses as a consequence of the screening effects of the BST{sub 0.05}. The coupling monotonically increases with temperature in all the samples and this behavior is attributed to thermally assisted mechanisms. The magnetic anisotropy of both magnetic components has a cubic symmetry that in the case of permalloy is added to a small uniaxial component.

  4. Output voltage calculations in double barrier magnetic tunnel junctions with asymmetric voltage behavior

    KAUST Repository

    Useinov, Arthur; Mryasov, Oleg; Kosel, Jü rgen

    2011-01-01

    In this paper we study the asymmetric voltage behavior (AVB) of the tunnel magnetoresistance (TMR) for single and double barrier magnetic tunnel junctions (MTJs) in range of a quasi-classical free electron model. Numerical calculations of the TMR

  5. Study on fusion potential barrier in heavy ion reactions based on the dynamical model

    International Nuclear Information System (INIS)

    Tian Junlong; Wu Xizhen; Li Zhuxia; Wang Ning; Liu Fuhu

    2004-01-01

    Based on an improved quantum molecular dynamics model the static and dynamic potential in the entrance channel of synthesis of superheavy nuclei are studied. The dependence of the static potential (and driving potential) on mass-asymmetry is obtained. From this study authors find out that the mass-symmetric system seems to be difficult to fuse and the fusing system with the largest driving potential could be the optimal choice of the projectile-target combination. By comparing the static potential barrier with the dynamic one authors find that the latter one is lower than former one obviously, and that the dynamical potential barrier is entrance energy dependent. The maximum and minimum of dynamic potential barriers approach to the diabatic (sudden approximation) and the adiabatic static potential barriers, respectively

  6. Electron transport and noise spectroscopy in organic magnetic tunnel junctions with PTCDA and Alq3 barriers

    Science.gov (United States)

    Martinez, Isidoro; Cascales, Juan Pedro; Hong, Jhen-Yong; Lin, Minn-Tsong; Prezioso, Mirko; Riminucci, Alberto; Dediu, Valentin A.; Aliev, Farkhad G.

    2016-10-01

    The possible influence of internal barrier dynamics on spin, charge transport and their fluctuations in organic spintronics remains poorly understood. Here we present investigation of the electron transport and low frequency noise at temperatures down to 0.3K in magnetic tunnel junctions with an organic PTCDA barriers with thickness up to 5 nm in the tunneling regime and with 200 nm thick Alq3 barrier in the hopping regime. We observed high tunneling magneto-resistance at low temperatures (15-40%) and spin dependent super-poissonian shot noise in organic magnetic tunnel junctions (OMTJs) with PTCDA. The Fano factor exceeds 1.5-2 values which could be caused by interfacial states controlled by spin dependent bunching in the tunneling events through the molecules.1 The bias dependence of the low frequency noise in OMTJs with PTCDA barriers which includes both 1/f and random telegraph noise activated at specific biases will also be discussed. On the other hand, the organic junctions with ferromagnetic electrodes and thick Alq3 barriers present sub-poissonian shot noise which depends on the temperature, indicative of variable range hopping.

  7. Transport in a magnetic field modulated graphene superlattice.

    Science.gov (United States)

    Li, Yu-Xian

    2010-01-13

    Using the transfer matrix method, we study the transport properties through a magnetic field modulated graphene superlattice. It is found that the electrostatic barrier, the magnetic vector potential, and the number of wells in a superlattice modify the transmission remarkably. The angular dependent transmission is blocked by the magnetic vector potential because of the appearance of the evanescent states at certain incident angles, and the region of Klein tunneling shifts to the left. The angularly averaged conductivities exhibit oscillatory behavior. The magnitude and period of oscillation depend sensitively on the height of the electrostatic barrier, the number of wells, and the strength of the modulated magnetic field.

  8. Suppressing electron turbulence and triggering internal transport barriers with reversed magnetic shear in the National Spherical Torus Experiment

    Energy Technology Data Exchange (ETDEWEB)

    Peterson, J. L. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Bell, R.; Guttenfelder, W.; Hammett, G. W.; Kaye, S. M.; LeBlanc, B.; Mikkelsen, D. R. [Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States); Candy, J. [General Atomics, San Diego, California 92186 (United States); Smith, D. R. [Department of Engineering Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); Yuh, H. Y. [Nova Photonics Inc., Princeton, New Jersey 08540 (United States)

    2012-05-15

    The National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 40, 557 (2000)] can achieve high electron plasma confinement regimes that are super-critically unstable to the electron temperature gradient driven (ETG) instability. These plasmas, dubbed electron internal transport barriers (e-ITBs), occur when the magnetic shear becomes strongly negative. Using the gyrokinetic code GYRO [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)], the first nonlinear ETG simulations of NSTX e-ITB plasmas reinforce this observation. Local simulations identify a strongly upshifted nonlinear critical gradient for thermal transport that depends on magnetic shear. Global simulations show e-ITB formation can occur when the magnetic shear becomes strongly negative. While the ETG-driven thermal flux at the outer edge of the barrier is large enough to be experimentally relevant, the turbulence cannot propagate past the barrier into the plasma interior.

  9. Equivalent magnetic vector potential model for low-frequency magnetic exposure assessment

    Science.gov (United States)

    Diao, Y. L.; Sun, W. N.; He, Y. Q.; Leung, S. W.; Siu, Y. M.

    2017-10-01

    In this paper, a novel source model based on a magnetic vector potential for the assessment of induced electric field strength in a human body exposed to the low-frequency (LF) magnetic field of an electrical appliance is presented. The construction of the vector potential model requires only a single-component magnetic field to be measured close to the appliance under test, hence relieving considerable practical measurement effort—the radial basis functions (RBFs) are adopted for the interpolation of discrete measurements; the magnetic vector potential model can then be directly constructed by summing a set of simple algebraic functions of RBF parameters. The vector potentials are then incorporated into numerical calculations as the equivalent source for evaluations of the induced electric field in the human body model. The accuracy and effectiveness of the proposed model are demonstrated by comparing the induced electric field in a human model to that of the full-wave simulation. This study presents a simple and effective approach for modelling the LF magnetic source. The result of this study could simplify the compliance test procedure for assessing an electrical appliance regarding LF magnetic exposure.

  10. Potential and barrier study. Energy efficiency in Norwegian vocational buildings; Potensial- og barrierestudie. Energieffektivisering i norske yrkesbygg

    Energy Technology Data Exchange (ETDEWEB)

    Boehn, Trond Ivar; Palm, Linn Therese; Bakken, Line; Nossum, Aase; Jordell, Hanne

    2012-07-01

    On behalf of Enova SF, Multiconsult AS and Analyse og Strategi AS conducted an analysis to identify potential and barriers related to commercial buildings energy performance. The aim of this study was to determine what is the potential for energy efficiency for Norwegian vocational buildings that distinguishes between theoretical, technical, financial and real potential. Technical potential is the percentage of the theoretical potential that is technically feasible. Economic potential is the proportion of technical potential that is economically profitable to implement. Economic potential varies with the energy price. Build a small part of the total potential in 2020. In the calculation of the real potential is taken into account induced potential in terms of that, each year, a percentage actually implementing energy conservation measures (energy efficiency ratio 2%), a percentage rehabilitating / upgrading existing buildings (rehab rate 1.5%), and that a proportion of new buildings built better than regulatory requirements (rate 10%). In real potential for energy efficiency is the proportion of the economic potential that is not natural triggered but which is limited by various barriers. In real potential also varies with energy price. Respondents in our study is particularly concerned with the economic barriers, and least concerned the technical barriers. Attitudes and knowledge barriers are also very important. Lack of knowledge the effects and benefits of energy efficiency means that negative attitudes persist and that myths about the lack of profitability continues to exist. Many believe this is due to lack the knowledge and can be the cause of other types of barriers such as economic barriers. It has been analyzed which part of the real potential bounded by the barriers, and which type of institutions in society that can reduce these barriers with various categories of instrument. Main barriers for existing buildings practical barriers, economic barriers and

  11. Load management for refrigeration systems: Potentials and barriers

    Energy Technology Data Exchange (ETDEWEB)

    Grein, Arne, E-mail: a.grein@tu-berlin.de [University of Technology Berlin, Institute for Energy Technology, Department of Energy Systems, Einsteinufer 25 (TA8), 10587 Berlin (Germany); Pehnt, Martin [Institute for Energy and Environmental Research Heidelberg (ifeu), Wilckensstr. 3, 69120 Heidelberg (Germany)

    2011-09-15

    As a strategy to deal with the increasing intermittent input of renewable energy sources in Germany, the adaptation of power consumption is complementary to power-plant regulation, grid expansion and physical energy storage. One demand sector that promises strong returns for load management efforts is cooling and refrigeration. In these processes, thermal inertia provides a temporal buffer for shifting and adjusting the power consumption of cooling systems. We have conducted an empirical investigation to obtain a detailed and time-resolved bottom-up analysis of load management for refrigeration systems in the city of Mannheim, Germany. We have extrapolated our results to general conditions in Germany. Several barriers inhibit the rapid adoption of load management strategies for cooling systems, including informational barriers, strict compliance with legal cooling requirements, liability issues, lack of technical experience, an inadequate rate of return and organizational barriers. Small commercial applications of refrigeration in the food-retailing and cold storage in hotels and restaurants are particularly promising starting points for intelligent load management. When our results are applied to Germany, suitable sectors for load management have theoretical and achievable potential values of 4.2 and 2.8 GW, respectively, amounting to about 4-6% of the maximum power demand in Germany. - Highlights: > Potential and barriers for implementation of load shifting for refrigeration. > Empirical investigation for time-resolved bottom-up analysis in Mannheim, Germany. > Suitable sectors and further recommendations for introducing load management.> Extrapolation of results from local to national level.

  12. Load management for refrigeration systems: Potentials and barriers

    International Nuclear Information System (INIS)

    Grein, Arne; Pehnt, Martin

    2011-01-01

    As a strategy to deal with the increasing intermittent input of renewable energy sources in Germany, the adaptation of power consumption is complementary to power-plant regulation, grid expansion and physical energy storage. One demand sector that promises strong returns for load management efforts is cooling and refrigeration. In these processes, thermal inertia provides a temporal buffer for shifting and adjusting the power consumption of cooling systems. We have conducted an empirical investigation to obtain a detailed and time-resolved bottom-up analysis of load management for refrigeration systems in the city of Mannheim, Germany. We have extrapolated our results to general conditions in Germany. Several barriers inhibit the rapid adoption of load management strategies for cooling systems, including informational barriers, strict compliance with legal cooling requirements, liability issues, lack of technical experience, an inadequate rate of return and organizational barriers. Small commercial applications of refrigeration in the food-retailing and cold storage in hotels and restaurants are particularly promising starting points for intelligent load management. When our results are applied to Germany, suitable sectors for load management have theoretical and achievable potential values of 4.2 and 2.8 GW, respectively, amounting to about 4-6% of the maximum power demand in Germany. - Highlights: → Potential and barriers for implementation of load shifting for refrigeration. → Empirical investigation for time-resolved bottom-up analysis in Mannheim, Germany. → Suitable sectors and further recommendations for introducing load management.→ Extrapolation of results from local to national level.

  13. Cold atoms near surfaces: designing potentials by sculpturing wires

    International Nuclear Information System (INIS)

    Della Pietra, Leonardo; Aigner, Simon; Hagen, Christoph vom; Lezec, Henri J; Schmiedmayer, Joerg

    2005-01-01

    The magnetic trapping potentials for atoms on atom chips are determined by the current flow pattern in the chip wires. By modifying the wire shape using focused ion beam nano-machining we can design specialized current flow patterns and therefore micro-design the magnetic trapping potentials. We give designs for a barrier, a quantum dot, and a double well or double barrier and show preliminary experiments with ultra cold atoms in these designed potentials

  14. Review of potential subsurface permeable barrier emplacement and monitoring technologies

    International Nuclear Information System (INIS)

    Riggsbee, W.H.; Treat, R.L.; Stansfield, H.J.; Schwarz, R.M.; Cantrell, K.J.; Phillips, S.J.

    1994-02-01

    This report focuses on subsurface permeable barrier technologies potentially applicable to existing waste disposal sites. This report describes candidate subsurface permeable barriers, methods for emplacing these barriers, and methods used to monitor the barrier performance. Two types of subsurface barrier systems are described: those that apply to contamination.in the unsaturated zone, and those that apply to groundwater and to mobile contamination near the groundwater table. These barriers may be emplaced either horizontally or vertically depending on waste and site characteristics. Materials for creating permeable subsurface barriers are emplaced using one of three basic methods: injection, in situ mechanical mixing, or excavation-insertion. Injection is the emplacement of dissolved reagents or colloidal suspensions into the soil at elevated pressures. In situ mechanical mixing is the physical blending of the soil and the barrier material underground. Excavation-insertion is the removal of a soil volume and adding barrier materials to the space created. Major vertical barrier emplacement technologies include trenching-backfilling; slurry trenching; and vertical drilling and injection, including boring (earth augering), cable tool drilling, rotary drilling, sonic drilling, jetting methods, injection-mixing in drilled holes, and deep soil mixing. Major horizontal barrier emplacement technologies include horizontal drilling, microtunneling, compaction boring, horizontal emplacement, longwall mining, hydraulic fracturing, and jetting methods

  15. Knowledge Exchange and Management Research: Barriers and Potentials

    DEFF Research Database (Denmark)

    Bager, Torben

    2018-01-01

    Purpose: The growing involvement of management researchers in knowledge exchange activities and collaborative research does not seem to be reflected in a growing academic output. The purpose of this paper is to explore barriers for academic output from these activities as well as the potential...... for ‘interesting’ papers. Design/methodology/approach: The paper uses secondary data and statistics as well as an illustrative case study to trace knowledge exchange activities and barriers for academic output based on these activities. Findings: The paper identifies a number of barriers for the turning of data...... derived from knowledge exchange activities and Mode 2 research into academic papers such as low priority of case study research in leading management journals, a growing practice orientation in the research funding systems, methodological challenges due to limited researcher control, and disincentives...

  16. Quasibound states in graphene quantum-dot nanostructures generated by concentric potential barrier rings

    International Nuclear Information System (INIS)

    Jiang Zhao-Tan; Yu Cheng-Long; Dong Quan-Li

    2012-01-01

    We study the quasibound states in a graphene quantum-dot structure generated by the single-, double-, and triple-barrier electrostatic potentials. It is shown that the strongest quasibound states are mainly determined by the innermost barrier. Specifically, the positions of the quasibound states are determined by the barrier height, the number of the quasibound states is determined by the quantum-dot radius and the angular momentum, and the localization degree of the quasibound states is influenced by the width of the innermost barrier, as well as the outside barriers. Furthermore, according to the study on the double- and triple-barrier quantum dots, we find that an effective way to generate more quasibound states with even larger energy level spacings is to design a quantum dot defined by many concentric barriers with larger barrier-height differences. Last, we extend our results into the quantum dot of many barriers, which gives a complete picture about the formation of the quasibound states in the kind of graphene quantum dot created by many concentric potential barrier rings. (rapid communication)

  17. Transport barriers with and without shear flows in a magnetized plasma

    International Nuclear Information System (INIS)

    Martinell, Julio J.

    2014-01-01

    Different ways of producing a transport barrier in a toroidal magnetized plasma are discussed and the properties of the barriers are analyzed. The first mechanism is associated with the presence of a sheared plasma flow that is present in a limited region of the plasma, which creates a zonal flow. In contrast to the usual paradigm stating that the sheared flow reduces the turbulence correlation length and leads to suppression of the fluctuation driven transport in the region of highest shear, it is shown that from the perspective of chaotic transport of plasma particles in the fluctuation fields, the transport barrier is formed in the region of zero shear and it can be destroyed when the fluctuation level is high enough. It is also shown that finite gyroradius effects modify the dynamics and introduces new conditions for barrier formation. The second mechanism considers a method in which radio-frequency waves injected into the plasma can stabilize the drift waves and therefore the anomalous transport is reduced, creating a barrier. This process does not involve the presence of sheared flows and depends only on the effect of the RF wave field on the drift waves. The stabilizing effect in this case is due to the nonlinear ponderomotive force which acts in a way that offsets the pressure gradient destabilization. Finally, a mechanism based on the ponderomotive force of RF waves is described which produces poloidal plasma rotation around the resonant surface due to the asymmetry of induced transport; it creates a transport barrier by shear flow stabilization of turbulence

  18. l-dependent potential barriers and superdeformed states

    International Nuclear Information System (INIS)

    Gherghescu, R.A.; Royer, G.

    1999-01-01

    The macroscopic-microscopic energy of rotating nuclei moving in the fusion-like deformation valley has been determined within a generalized liquid drop model including the nuclear proximity energy, the two-center shell model and the Strutinsky method. The l-dependent potential barriers of the 84 Zr, 132 Ce, 152 Dy and 192 Hg nuclei have been determined. A first minimum having a pure microscopic origin and lodging the normally deformed states, progressively disappears with increasing angular momenta. The microscopic and macroscopic energies contribute to generate a second minimum where superdeformed states may survive. It becomes progressively the lowest one at intermediate spins. At still higher angular momenta, the minimum moves towards the foot of the external fission barrier leading to macroscopic hyper-deformed quasi-molecular states. (authors)

  19. Alpha-induced instabilities in tandem thermal barriers

    Energy Technology Data Exchange (ETDEWEB)

    Kammash, T.; Galbraith, D.L.

    1987-01-01

    A major premise in the operation of Tandem Mirror reactors is that the fusion reactions take place in the central cell only. The alpha particles generated by the Deuterium-Tritium (DT) fusions, along with other ions, will however pass from the central cell to the thermal barriers and return to the central cell as a result of reflection by the potential hills that exist by the plugs' side of these barriers. This streaming motion gives rise to electrostatic and electomagnetic instabilities which could detract from the barrier's function as a thermal insulator. The number density and streaming velocity of these passing particles are dictated by the electrostatic potential variation and the magnetic field structure in these regions. It is shown that, in the absence of alphas, barriers with deep potential depression are less susceptible to electrostatic instabilities while particularly vulnerable to unstable electromagnetic modes. In the presence of alphas, especially the fast alphas whose mean energy is significantly larger than the barrier potentials they see, (which is twice as high as that seen by the ions) both types of modes become unstable.

  20. Aptamer nanomedicine for cancer therapeutics: barriers and potential for translation.

    Science.gov (United States)

    Lao, Yeh-Hsing; Phua, Kyle K L; Leong, Kam W

    2015-03-24

    Aptamer nanomedicine, including therapeutic aptamers and aptamer nanocomplexes, is beginning to fulfill its potential in both clinical trials and preclinical studies. Especially in oncology, aptamer nanomedicine may perform better than conventional or antibody-based chemotherapeutics due to specificity compared to the former and stability compared to the latter. Many proof-of-concept studies on applying aptamers to drug delivery, gene therapy, and cancer imaging have shown promising efficacy and impressive safety in vivo toward translation. Yet, there remains ample room for improvement and critical barriers to be addressed. In this review, we will first introduce the recent progress in clinical trials of aptamer nanomedicine, followed by a discussion of the barriers at the design and in vivo application stages. We will then highlight recent advances and engineering strategies proposed to tackle these barriers. Aptamer cancer nanomedicine has the potential to address one of the most important healthcare issues of the society.

  1. Crossing the Barriers: An Analysis of Land Access Barriers to Geothermal Development and Potential Improvement Scenarios

    Energy Technology Data Exchange (ETDEWEB)

    Levine, Aaron L [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Young, Katherine R [National Renewable Energy Laboratory (NREL), Golden, CO (United States)

    2017-10-04

    Developers have identified many non-technical barriers to geothermal power development, including access to land. Activities required for accessing land, such as environmental review and private and public leasing can take a considerable amount of time and can delay or prevent project development. This paper discusses the impacts to available geothermal resources and deployment caused by land access challenges, including tribal and cultural resources, environmentally sensitive areas, biological resources, land ownership, federal and state lease queues, and proximity to military installations. In this analysis, we identified challenges that have the potential to prevent development of identified and undiscovered hydrothermal geothermal resources. We found that an estimated 400 MW of identified geothermal resource potential and 4,000 MW of undiscovered geothermal resource potential were either unallowed for development or contained one or more significant barriers that could prevent development at the site. Potential improvement scenarios that could be employed to overcome these barriers include (1) providing continuous funding to the U.S. Forest Service (USFS) for processing geothermal leases and permit applications and (2) the creation of advanced environmental mitigation measures. The model results forecast that continuous funding to the USFS could result in deployment of an additional 80 MW of geothermal capacity by 2030 and 124 MW of geothermal capacity by 2050 when compared to the business-as-usual scenario. The creation of advanced environmental mitigation measures coupled with continuous funding to the USFS could result in deployment of an additional 97 MW of geothermal capacity by 2030 and 152 MW of geothermal capacity by 2050 when compared to the business-as-usual scenario. The small impact on potential deployment in these improvement scenarios suggests that these 4,400 MW have other barriers to development in addition to land access. In other words, simply

  2. On the (DE-) stabilization of quantum mechanical binding by potential barriers

    International Nuclear Information System (INIS)

    Hogreve, H.

    1994-04-01

    Stabilization and destabilization effects caused by adding or rising a potential barrier are studied for a simple one-dimensional quantum system. Calculating the motion of the corresponding S-matrix poles for varying barrier width and height, this reveals the scenario for the transition between bound, virtual and resonance states. Our results show that the presence of a barrier leads to nonanalyticity of the ground state with respect to the involved coupling constants. Furthermore, for increasing barrier width the size of the virtual regime shrinks drastically, so that it might be hardly detectable in many practical situations. (author). 15 refs, 5 figs

  3. Magnetic resonance imaging-guided focused ultrasound to increase localized blood-spinal cord barrier permeability.

    Science.gov (United States)

    Payne, Allison H; Hawryluk, Gregory W; Anzai, Yoshimi; Odéen, Henrik; Ostlie, Megan A; Reichert, Ethan C; Stump, Amanda J; Minoshima, Satoshi; Cross, Donna J

    2017-12-01

    Spinal cord injury (SCI) affects thousands of people every year in the USA, and most patients are left with some permanent paralysis. Therapeutic options are limited and only modestly affect outcome. To address this issue, we used magnetic resonance imaging-guided focused ultrasound (MRgFUS) as a non-invasive approach to increase permeability in the blood-spinal cord barrier (BSCB). We hypothesize that localized, controlled sonoporation of the BSCB by MRgFUS will aid delivery of therapeutics to the injury. Here, we report our preliminary findings for the ability of MRgFUS to increase BSCB permeability in the thoracic spinal cord of a normal rat model. First, an excised portion of normal rat spinal column was used to characterize the acoustic field and to estimate the insertion losses that could be expected in an MRgFUS blood spinal cord barrier opening. Then, in normal rats, MRgFUS was applied in combination with intravenously administered microbubbles to the spinal cord region. Permeability of the BSCB was indicated as signal enhancement by contrast administered prior to T1-weighted magnetic resonance imaging and verified by Evans blue dye. Neurological testing using the Basso, Beattie, and Breshnahan scale and the ladder walk was normal in 8 of 10 rats tested. Two rats showed minor impairment indicating need for further refinement of parameters. No gross tissue damage was evident by histology. In this study, we have opened successfully the blood spinal cord barrier in the thoracic region of the normal rat spine using magnetic resonance-guided focused ultrasound combined with microbubbles.

  4. Barrier breakdown mechanism in nano-scale perpendicular magnetic tunnel junctions with ultrathin MgO barrier

    Science.gov (United States)

    Lv, Hua; Leitao, Diana C.; Hou, Zhiwei; Freitas, Paulo P.; Cardoso, Susana; Kämpfe, Thomas; Müller, Johannes; Langer, Juergen; Wrona, Jerzy

    2018-05-01

    Recently, the perpendicular magnetic tunnel junctions (p-MTJs) arouse great interest because of its unique features in the application of spin-transfer-torque magnetoresistive random access memory (STT-MRAM), such as low switching current density, good thermal stability and high access speed. In this paper, we investigated current induced switching (CIS) in ultrathin MgO barrier p-MTJs with dimension down to 50 nm. We obtained a CIS perpendicular tunnel magnetoresistance (p-TMR) of 123.9% and 7.0 Ω.μm2 resistance area product (RA) with a critical switching density of 1.4×1010 A/m2 in a 300 nm diameter junction. We observe that the extrinsic breakdown mechanism dominates, since the resistance of our p-MTJs decreases gradually with the increasing current. From the statistical analysis of differently sized p-MTJs, we observe that the breakdown voltage (Vb) of 1.4 V is 2 times the switching voltage (Vs) of 0.7 V and the breakdown process exhibits two different breakdown states, unsteady and steady state. Using Simmons' model, we find that the steady state is related with the barrier height of the MgO layer. Furthermore, our study suggests a more efficient method to evaluate the MTJ stability under high bias rather than measuring Vb. In conclusion, we developed well performant p-MTJs for the use in STT-MRAM and demonstrate the mechanism and control of breakdown in nano-scale ultrathin MgO barrier p-MTJs.

  5. Creation of second order magnetic barrier inside chaos created by NTMs in the ASDEX UG

    Science.gov (United States)

    Ali, Halima; Punjabi, Alkesh

    2012-10-01

    Understanding and stabilization of neoclassical tearing modes (NTM) in tokamaks is an important problem. For low temperature plasmas, tearing modes are believed to be mainly driven by current density gradient. For collisionless plasmas, even when plasma is stable to classical tearing modes, helical reduction in bootstrap current in O-point of an island can destabilize NTMs when an initial island is seeded by other global MHD instabilities or when microturbulence triggers the transition from a linear to nonlinear instability. The onset of NTMs leads to the most serious beta limit in ASDEX UG tokamak [O. Gubner et al 2005 NF 39 1321]. The important NTMs in the ASDDEX UG are (m,n)=(3,2)+(4,3)+(1,1). Realistic parameterization of these NTMs and the safety factor in ASDEX UG are given in [O. Dumbrajs et al 2005 POP 12 1107004]. We use a symplectic map in magnetic coordinates for the ASDEX UG to integrate field lines in presence of the NTMs. We add a second order control term [H. Ali and A. Punjabi 2007 PPCF 49 1565] to this ASDEX UG field line Hamiltonian to create an invariant magnetic surface inside the chaos generated by the NTMs. The relative strength, robustness, and resilience of this barrier are studied to ascertain the most desirable noble barrier in the ASDEX UG with NTMs. We present preliminary results of this work, and discuss its implications with regard to magnetic transport barriers for increasing strength of magnetic perturbations. This work is supported by the grants DE-FG02-01ER54624 and DE-FG02-04ER54793.

  6. The escape of brownian particle over potential barriers

    International Nuclear Information System (INIS)

    Zhong Yunxiao

    1985-01-01

    A convenient method is introduced to calculate the rate of escape of Brownian particle over potential barriers by exact solution of Smoluchowskian equation. This method is applied to calculate the nuclear fission probabilities. The results for four different cases are compared with the results of other theories

  7. Generalized magnetic Rosenbluth potentials

    International Nuclear Information System (INIS)

    Hassan, M.H.A.

    1977-12-01

    It is shown that the coefficients of friction and diffusion of the magnetized Balescu-Lenard equation describing the interaction of ion test particles with electron field particles can be derived from two scalar potentials, which reduce to the potentials derived previously when wave effects are neglected. The parts of the potentials describing ''wave effects'' are evaluated explicitly in the case of Maxwellian electrons and the results are compared with the unmagnetized Rosenbluth potentials. The correction is dominant when eta=Ωsub(e)/ωsub(e)(>)1

  8. Fabrication of magnetic tunnel junctions with a single-crystalline LiF tunnel barrier

    Science.gov (United States)

    Krishna Narayananellore, Sai; Doko, Naoki; Matsuo, Norihiro; Saito, Hidekazu; Yuasa, Shinji

    2018-04-01

    We fabricated Fe/LiF/Fe magnetic tunnel junctions (MTJs) by molecular beam epitaxy on a MgO(001) substrate, where LiF is an insulating tunnel barrier with the same crystal structure as MgO (rock-salt type). Crystallographical studies such as transmission electron microscopy and nanobeam electron diffraction observations revealed that the LiF tunnel barrier is single-crystalline and has a LiF(001)[100] ∥ bottom Fe(001)[110] crystal orientation, which is constructed in the same manner as MgO(001) on Fe(001). Also, the in-plane lattice mismatch between the LiF tunnel barrier and the Fe bottom electrode was estimated to be small (about 0.5%). Despite such advantages for the tunnel barrier of the MTJ, the observed tunnel magnetoresistance (MR) ratio was low (˜6% at 20 K) and showed a significant decrease with increasing temperature (˜1% at room temperature). The results imply that indirect tunneling and/or thermally excited carriers in the LiF tunnel barrier, in which the current basically is not spin-polarized, play a major role in electrical transport in the MTJ.

  9. Revival of cloaking effect in a driven bilayer graphene vector barrier

    Science.gov (United States)

    Maiti, S.; Panigrahi, A.; Biswas, R.; Sinha, C.

    2018-05-01

    Transmission profiles in bilayer graphene are studied theoretically through a rectangular vector potential (magnetic) barrier with and without the presence of an oscillatory potential. Unlike the electrostatic barrier, the Fano resonances (FR) are noted in the transmission spectra both for normal and glancing incidences due to non-conservation of chirality for a static vector barrier. The results for normal incidence indicate that the cloaking effect is a manifestation of the chirality conservation in charge transport through bilayer graphene scalar barriers. It is also noted that the aforesaid FR for a static vector barrier might disappear (photon induced electronic cloaking effect) due to the predominant photon exchange processes in presence of an external oscillating potential. The study of Fano resonances in transmission spectrum is in high demand in respect of localization of charge carriers in graphene nano structures for its potential applications in digital device fabrications.

  10. Electron internal transport barriers and magnetic topology in the stellarator TJ-II

    International Nuclear Information System (INIS)

    Estrada, T.; Alonso, A.; Castejon, F.; Hidalgo, C.; Pablos, J.L. de; Tereshin, V.; Krupnik, L.; Chmyga, A.A.; Dreval, N.; Khrebtov, S.M.; Komarov, A.D.; Kozachok, A.S.; Eliseev, L.; Melnikov, A.V.

    2005-01-01

    Electron Internal Transport Barriers (e-ITBs) are frequently observed in helical systems. e-ITBs are characterized by an increase in core electron temperature and plasma potential as well as an improvement in core electron heat confinement. A comparative study of transport barriers in different helical devices will be presented by Yokoyama et al at this conference. In most helical systems, and in particular in TJ-II stellarator, the formation of e-ITBs is observed in Electron Cyclotron Heated plasmas with high heating power density. In TJ-II, e-ITBs are also formed in magnetic configurations having a low order rational surface close to the plasma core where the ECH power is deposited. In such configurations the key element to improve heat confinement, i.e. the strong radial electric field, results from a synergistic effect between enhanced electron heat fluxes through the low order rational surface and pump-out mechanisms in the heat deposition zone. Recent experiments show a quasi-coherent mode associated with a rational surface that triggers the formation of the e-ITB. This quasi-coherent mode is observed by both ECE and HIBP diagnostics. The mode is found to be localized within the radial range ρ: 0.0 - 0.4, with a maximum amplitude around ρ: 0.25 - 0.35, close to the foot of the e- ITB. The quasi-coherent mode evolves during the formation/annihilation of the e-ITB and vanishes as the barrier is fully developed. These observations indicate that the quasi-coherent modes are modified by the radial electric fields that develop at the transitions, thereby showing the importance of ExB flows in the evolution of MHD instabilities linked to low-order rational surfaces. Further studies are in progress to investigate the influence of the order of the low rational surfaces (3/2, 5/3,...) in triggering core transitions. (author)

  11. Ultrafast spin injection from Cd1-x Mn x Te magnetic barriers into a CdTe quantum well studied by pump-probe spectroscopy

    International Nuclear Information System (INIS)

    Aoshima, I.; Nishibayashi, K.; Souma, I.; Murayama, A.; Oka, Y.

    2006-01-01

    Spin injection from diluted magnetic semiconductor (DMS) barriers of Cd 1- x Mn x Te into a quantum well (QW) of CdTe is studied, by means of pump-probe absorption spectroscopy in magnetic fields. Fast decay characteristics of circularly polarized differential absorbances of spin-polarized excitons in the DMS barrier show the exciton injection time of 6 ps from the barriers into the QW. In accordance with the fast relaxation of the spin-polarized excitons from the barrier, we observe the rise of circular polarization degree for the differential absorption of the CdTe QW in magnetic fields, evidently indicating the spin injection. In addition, the circular polarization degree up to 0.3 is developed in the well immediately after pumping, originating from the fast relaxation of a heavy hole (hh) spin less than 0.2 ps, due to the giant Zeeman effect caused by the penetration of the hh wave function into the DMS barriers

  12. Li breakup polarization potential at near barrier energies

    International Nuclear Information System (INIS)

    Lubian, F. J.; Correa, T.; Gomes, P.R.S.; Paes, B; Figueira, J. M.; Abriola, D.; Fernandez, J. O.; Capurro, O. A.; Marti, G.V.; Martinez, D.; Heimann; Negri, A.; Pacheco, A. J.; Padron, I.

    2007-01-01

    Inelastic and one neutron transfer cross sections at energies around the Coulomb barrier were used to derive dynamic polarization potential (DPP) for the 7 Li + 27 Al system. The DPP due to breakup, obtained in a simple way, indicates that its real part is repulsive at nearbarrier energies. (Author)

  13. Perpendicular magnetic tunnel junction with tunneling magnetoresistance ratio of 64% using MgO (100) barrier layer prepared at room temperature

    International Nuclear Information System (INIS)

    Ohmori, Hideto; Hatori, Tomoya; Nakagawa, Shigeki

    2008-01-01

    MgO (100) textured films can be prepared by reactive facing targets sputtering at room temperature without postdeposition annealing process when they were deposited on (100) oriented Fe buffer layers. This method allows fabrication of perpendicular magnetic tunnel junction (p-MTJ) with MgO (100) tunneling barrier layer and rare-earth transition metal (RE-TM) alloy thin films as perpendicularly magnetized free and pinned layers. The 3-nm-thick MgO tunneling barrier layer in p-MTJ multilayer prepared on glass substrate revealed (100) crystalline orientation. Extraordinary Hall effect measurement clarified that the perpendicular magnetic components of 3-nm-thick Fe buffer layers on the two ends of MgO tunneling barrier layer were increased by exchange coupling with RE-TM alloy layers. The RA of 35 kΩ μm 2 and tunneling magnetoresistance ratio of 64% was observed in the multilayered p-MTJ element by current-in-plane-tunneling

  14. Surface Treatment of Polypropylene Films Using Dielectric Barrier Discharge with Magnetic Field

    International Nuclear Information System (INIS)

    Wang Changquan; Zhang Guixin; Wang Xinxin; Chen Zhiyu

    2012-01-01

    Atmospheric pressure non-thermal plasma is of interest for industrial applications. In this study, polypropylene (PP) films are modified by a dielectric barrier discharge (DBD) with a non-uniform magnetic field in air at atmospheric pressure. The surface properties of the PP films before and after a DBD treatment are studied by using contact angle measurement, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The effect of treatment time on the surface modification with and without a magnetic field is investigated. It is found that the hydrophilic improvement depends on the treatment time and magnetic field. It is also found that surface roughness and oxygen-containing groups are introduced onto the PP film surface after the DBD treatment. Surface roughness and oxygen-containing polar functional groups of the PP films increase with the magnetic induction density. The functional groups are identified as C-O, C=O and O-C=O by using XPS analysis. It is concluded that the hydrophilic improvement of PP films treated with a magnetic field is due to a greater surface roughness and more oxygen-containing groups. (plasma technology)

  15. Tunneling effect on double potential barriers GaAs and PbS

    Science.gov (United States)

    Prastowo, S. H. B.; Supriadi, B.; Ridlo, Z. R.; Prihandono, T.

    2018-04-01

    A simple model of transport phenomenon tunnelling effect through double barrier structure was developed. In this research we concentrate on the variation of electron energy which entering double potential barriers to transmission coefficient. The barriers using semiconductor materials GaAs (Galium Arsenide) with band-gap energy 1.424 eV, distance of lattice 0.565 nm, and PbS (Lead Sulphide) with band gap energy 0.41 eV distance of lattice is 18 nm. The Analysisof tunnelling effect on double potentials GaAs and PbS using Schrodinger’s equation, continuity, and matrix propagation to get transmission coefficient. The maximum energy of electron that we use is 1.0 eV, and observable from 0.0025 eV- 1.0 eV. The shows the highest transmission coefficient is0.9982 from electron energy 0.5123eV means electron can pass the barriers with probability 99.82%. Semiconductor from materials GaAs and PbS is one of selected material to design semiconductor device because of transmission coefficient directly proportional to bias the voltage of semiconductor device. Application of the theoretical analysis of resonant tunnelling effect on double barriers was used to design and develop new structure and combination of materials for semiconductor device (diode, transistor, and integrated circuit).

  16. Double-well magnetic trap for Bose-Einstein condensates

    International Nuclear Information System (INIS)

    Thomas, N.R.; Wilson, A.C.; Foot, C.J.

    2002-01-01

    We present a magnetic trapping scheme for neutral atoms based on a hybrid of Ioffe-Pritchard and time-averaged orbiting potential traps. The resulting double-well magnetic potential has readily controllable barrier height and well separation. This offers a new tool for studying the behavior of Bose condensates in double-well potentials, and in particular for atom optics and interferometry. We formulate a description for the potential of this magnetic trap and discuss practical issues such as loading with atoms, evaporative cooling and manipulating the potential

  17. Probing the energy barriers and magnetization reversal processes of nanoperforated membrane based percolated media

    International Nuclear Information System (INIS)

    Neu, V; Schultz, L; Schulze, C; Makarov, D; Albrecht, M; Faustini, M; Grosso, D; Lee, J; Kim, S-K; Suess, D

    2013-01-01

    Magnetization reversal processes in Co/Pt multilayers prepared on nanoperforated templates are probed by magnetization relaxation measurements. The signature of pinning controlled domain wall movement as expected for percolated media is identified. This contrasts with the nucleation-type reversal mechanism of a Co/Pt reference film prepared on a smooth substrate. A zero field energy barrier of 93k B T is determined by fluctuation field measurements and is elucidated by micromagnetic calculations using the nudged elastic band method. This value is sufficiently large to qualify the material as a promising percolated medium. (paper)

  18. Spin-dependent scattering by a potential barrier on a nanotube

    International Nuclear Information System (INIS)

    Abranyos, Yonatan; Gumbs, Godfrey; Fekete, Paula

    2010-01-01

    The electron spin effects on the surface of a nanotube have been considered through the spin-orbit interaction (SOI), arising from the electron confinement on the surface of the nanotube. This is of the same nature as the Rashba-Bychkov SOI at a semiconductor heterojunction. We estimate the effect of disorder within a potential barrier on the transmission probability. Using a continuum model, we obtain analytic expressions for the spin-split energy bands for electrons on the surface of nanotubes in the presence of SOI. First we calculate analytically the amplitudes of scattering from a potential barrier located around the axis of the nanotube into spin-dependent states. The effect of disorder on the scattering process is included phenomenologically and induces a reduction in the transition probability. We analyze the relative role of SOI and disorder in the transmission probability which depends on the angular and linear momentum of the incoming particle, and its spin orientation. Finally we demonstrate that in the presence of disorder, perfect transmission may not be achieved for finite barrier heights.

  19. Magnetic fields, special relativity and potential theory elementary electromagnetic theory

    CERN Document Server

    Chirgwin, B H; Kilmister, C W

    1972-01-01

    Magnetic Fields, Special Relativity and Potential Theory is an introduction to electromagnetism, special relativity, and potential theory, with emphasis on the magnetic field of steady currents (magnetostatics). Topics covered range from the origin of the magnetic field and the magnetostatic scalar potential to magnetization, electromagnetic induction and magnetic energy, and the displacement current and Maxwell's equations. This volume is comprised of five chapters and begins with an overview of magnetostatics, followed by a chapter on the methods of solving potential problems drawn from elec

  20. Exact analytical modeling of magnetic vector potential in surface inset permanent magnet DC machines considering magnet segmentation

    Science.gov (United States)

    Jabbari, Ali

    2018-01-01

    Surface inset permanent magnet DC machine can be used as an alternative in automation systems due to their high efficiency and robustness. Magnet segmentation is a common technique in order to mitigate pulsating torque components in permanent magnet machines. An accurate computation of air-gap magnetic field distribution is necessary in order to calculate machine performance. An exact analytical method for magnetic vector potential calculation in surface inset permanent magnet machines considering magnet segmentation has been proposed in this paper. The analytical method is based on the resolution of Laplace and Poisson equations as well as Maxwell equation in polar coordinate by using sub-domain method. One of the main contributions of the paper is to derive an expression for the magnetic vector potential in the segmented PM region by using hyperbolic functions. The developed method is applied on the performance computation of two prototype surface inset magnet segmented motors with open circuit and on load conditions. The results of these models are validated through FEM method.

  1. Effect of sample container morphology on agglomeration dynamics of magnetic nanoparticles under magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Jin, Dae Seong; Kim, Hack Jin [Dept. of Chemistry, Chungnam National University, Daejeon (Korea, Republic of)

    2016-12-15

    The superparamagnetic magnetite nanoparticles have been used extensively in medical and biological applications, and agglomeration of magnetic nanoparticles is employed in the purification of water and proteins. The magnetic weight can be measured with a conventional electronic balance. Details of the experimental setup have been previously reported. That is, complex energy landscape involved in the agglomeration is changing with progress. Simulation of colloidal magnetic particles under magnetic field shows that the chain of particles is energetically more favorable than the ring and that the transition barrier between the chain and the ring is very low. The energy barriers among entangled nanoparticles of the agglomerate seem to be much more complicated than those among colloidal particles. The energy barrier distributions at 1000 min are similar for the two containers; however, the trend of blue shift and broadening is much more evident in the case of conical tube. These results indicate that the potential energy surface for agglomeration is modified more significantly in the conical tube which makes the agglomerate denser.

  2. Output voltage calculations in double barrier magnetic tunnel junctions with asymmetric voltage behavior

    KAUST Repository

    Useinov, Arthur

    2011-10-22

    In this paper we study the asymmetric voltage behavior (AVB) of the tunnel magnetoresistance (TMR) for single and double barrier magnetic tunnel junctions (MTJs) in range of a quasi-classical free electron model. Numerical calculations of the TMR-V curves, output voltages and I-V characteristics for negative and positive values of applied voltages were carried out using MTJs with CoFeB/MgO interfaces as an example. Asymmetry of the experimental TMR-V curves is explained by different values of the minority and majority Fermi wave vectors for the left and right sides of the tunnel barrier, which arises due to different annealing regimes. Electron tunneling in DMTJs was simulated in two ways: (i) Coherent tunneling, where the DMTJ is modeled as one tunnel system and (ii) consecutive tunneling, where the DMTJ is modeled by two single barrier junctions connected in series. © 2012 Elsevier B.V. All rights reserved.

  3. Reflection at a complex potential barrier in the semiclassical theory of scattering

    International Nuclear Information System (INIS)

    Avishai, Y.; Knoll, J.

    1976-01-01

    The reflection of spherical waves at a complex potential barrier is discussed in the semiclassical approximation. We study the complex WKB method and the Uniform Approximation in the special case of weakly absorptive barriers, typical of surface transparent optical potentials used in heavy-ion reactions. It is found that the complex WKB results lead to a very accurate cross-section despite their inaccuracy in the most important phase shifts. Thereby, the amazing stamina of the WKB has been confirmed once more. (orig.) [de

  4. Heavy-ion optical potential for sub-barrier fusion deduced from a dispersion relation

    International Nuclear Information System (INIS)

    Kim, B.T.; Kim, H.C.; Park, K.E.

    1988-01-01

    The heavy-ion energy-dependent optical potentials for the 16 O+ 208 Pb system are deduced from a dispersion relation. These potentials are used to analyze the elastic scattering, fusion, and spin distributions of compound nuclei for the system in a unified way based on the direct reaction theory. It turns out that the energy dependence of the optical potential is essential in explaining the data at near- and sub-barrier energies. The real part of the energy-dependent optical potential deduced was also used in calculating the elastic and fusion cross sections by the conventional barrier penetration model using an incoming wave boundary condition. The predictions of the elastic scattering, fusion cross sections, and the spin distributions of compound nuclei are not satisfactory compared with those from the direct reaction approach. It seems to originate from the fact that this model neglects absorption around the Coulomb barrier region

  5. Barrier potential design criteria in multiple-quantum-well-based solar-cell structures

    Science.gov (United States)

    Mohaidat, Jihad M.; Shum, Kai; Wang, W. B.; Alfano, R. R.

    1994-01-01

    The barrier potential design criteria in multiple-quantum-well (MQW)-based solar-cell structures is reported for the purpose of achieving maximum efficiency. The time-dependent short-circuit current density at the collector side of various MQW solar-cell structures under resonant condition was numerically calculated using the time-dependent Schroedinger equation. The energy efficiency of solar cells based on the InAs/Ga(y)In(1-y)As and GaAs/Al(x)Ga(1-x)As MQW structues were compared when carriers are excited at a particular solar-energy band. Using InAs/Ga(y)In(1-y)As MQW structures it is found that a maximum energy efficiency can be achieved if the structure is designed with barrier potential of about 450 meV. The efficiency is found to decline linearly as the barrier potential increases for GaAs/Al(x)Ga(1-x)As MQW-structure-based solar cells.

  6. Tests of potential functional barriers for laminated multilayer food packages. Part I: Low molecular weight permeants.

    Science.gov (United States)

    Simal-Gándara, J; Sarria-Vidal, M; Koorevaar, A; Rijk, R

    2000-08-01

    The advent of the functional barrier concept in food packaging has brought with it a requirement for fast tests of permeation through potential barrier materials. In such tests it would be convenient for both foodstuffs and materials below the functional barrier (sub-barrier materials) to be represented by standard simulants. By means of inverse gas chromatography, liquid paraffin spiked with appropriate permeants was considered as a potential simulant of sub-barrier materials based on polypropylene (PP) or similar polyolefins. Experiments were performed to characterize the kinetics of the permeation of low molecular weight model permeants (octene, toluene and isopropanol) from liquid paraffin, through a surrogate potential functional barrier (25 microns-thick oriented PP) into the food stimulants olive oil and 3% (w/v) acetic acid. These permeation results were interpreted in terms of three permeation kinetic models regarding the solubility of a particular model permeant in the post-barrier medium (i.e. the food simulant). The results obtained justify the development and evaluation of liquid sub-barrier simulants that would allow flexible yet rigorous testing of new laminated multilayer packaging materials.

  7. Transport barriers in plasmas

    International Nuclear Information System (INIS)

    Caldas, I L; Szezech, J D Jr; Kroetz, T; Marcus, F A; Roberto, M; Viana, R L; Lopes, S R

    2012-01-01

    We discuss the creation of transport barriers in magnetically confined plasmas with non monotonic equilibrium radial profiles. These barriers reduce the transport in the shearless region (i.e., where the twist condition does not hold). For the chaotic motion of particles in an equilibrium electric field with a nonmonotonic radial profile, perturbed by electrostatic waves, we show that a nontwist transport barrier can be created in the plasma by modifying the electric field radial profile. We also show non twist barriers in chaotic magnetic field line transport in the plasma near to the tokamak wall with resonant modes due to electric currents in external coils.

  8. Experimental investigation on the repetitively nanosecond pulsed dielectric barrier discharge with the parallel magnetic field

    Science.gov (United States)

    Liu, Yidi; Yan, Huijie; Guo, Hongfei; Fan, Zhihui; Wang, Yuying; Ren, Chunsheng

    2018-02-01

    The effects of a parallel magnetic field on the unipolar positive nanosecond pulsed dielectric barrier discharge are experimentally investigated through electrical and spectral measurements. The discharge is produced between two parallel-plate electrodes in the ambient air with a parallel magnetic field of 1.4 T. Experimental results show that both the discharge intensity and uniformity are improved in the discharge with the parallel magnetic field. The intensity ratio of the spectrum at 371.1 nm and 380.5 nm, which describes the average electron density, is increased by the parallel magnetic field. Meanwhile, the intensity ratio of the spectrum at 391.4 nm and 337.1 nm, which describes the electron temperature, is also increased. It is speculated that both the average electron density and the electron temperature are increased by the parallel magnetic field. The aforementioned phenomena have been explained by the confinement effect of the parallel magnetic field on the electrons.

  9. Parametric enhancement of the tunneling transmission through a potential barrier

    International Nuclear Information System (INIS)

    Tanaka, Masatoshi; Iwata, Giiti.

    1992-01-01

    A possibility of indicated of enhancing the tunneling transmission of particle incident on a potential barrier with the aid of an auxiliary potential parametrically in resonance with incident particles. For a simple auxiliary potential, a train of two-step square wells, examples are presented in which the ratio of the transmission coefficients with and without the auxiliary potential can be very large, e.g. (2n + 1) 2L , where n is the positive integer and L the number of the period of the auxiliary potential. (author)

  10. Effect of a two-dimensional potential on the rate of thermally induced escape over the potential barrier

    International Nuclear Information System (INIS)

    Han, S.; Lapointe, J.; Lukens, J.E.

    1992-01-01

    The thermally induced escape rate of a particle trapped in a two-dimensional (2D) potential well has been investigated through experiment and numerical simulations. The measurements were performed on a special type of superconducting quantum interference device (SQUID) which has 2 degrees of freedom. The energies associated with the motion perpendicular to (transverse) and along (longitudinal) the escape direction are quite different: the ratio between the transverse and longitudinal small oscillation frequencies is ω t /ω l ∼7. The SQUID's parameters, which were used to determine the potential shape and energy scales were all independently determined. All data were obtained under conditions for which the 2D thermal activation (TA) model is expected to be valid. The results were found in good agreement with the theoretical prediction. The measured thermal activation energy is found to be the same as the barrier height calculated from the independently determined potential parameters. No evidence of apparent potential barrier enhancement recently reported in a similar system was found. In addition, the results of our numerical simulations suggest that the region in which the 2D thermal activation model is applicable may be extended to barriers as low as ΔU∼k BT

  11. Radio-frequency shot-noise measurement in a magnetic tunnel junction with a MgO barrier

    International Nuclear Information System (INIS)

    Rehman, Mushtaq; Park, Junghwan; Song, Woon; Chong, Yonuk; Lee, Yeonsub; Min, Byoungchul; Shin, Kyungho; Ryu, Sangwan; Khim, Zheong

    2010-01-01

    We measured the noise power of a magnetic tunnel junction in the frequency range of 710 ∼ 1200 MHz. A low-noise cryogenic HEMT amplifier was used to measure the small noise signal at a high frequency with wide bandwidth. The MgO-barrier tunnel junction showed large tunnel magnetoresistance ratio of 215% at low temperature, which indicates electronic transport through the tunnel barrier without any significant spin-flip scattering. In the bias-dependent noise measurement, however, the zero-bias shot noise was enhanced compared to the value expected from a perfect tunnel barrier or the value observed from a good Al-AlO x -Al tunnel junction. We assume that this enhanced noise comes from inelastic tunneling processes through the barrier, which may be related to the observed zero-bias anomaly in the differential resistance of the tunnel junctions. We present a simple phenomenological model for how the inelastic scattering process can enhance the zero-bias noise in a tunnel junction.

  12. Plane and hemispherical potential structures in magnetically expanding plasmas

    International Nuclear Information System (INIS)

    Takahashi, Kazunori; Igarashi, Yuichi; Fujiwara, Tamiya

    2010-01-01

    Two-dimensional potential structures are measured for different gas pressure in expanding argon plasma using permanent magnets, where the magnetic field is about 100 G in the source and several gauss in the diffusion chamber. The plane potential drop is observed near the source exit for 0.35 mTorr, while the potential structure becomes hemispherical when increasing up to 1 mTorr; the hemispherical structure results in the radial divergence of the ion beam. It is found that the trajectories of the accelerated ions and the electrons overcoming the potential drop are dominated by the potential structure and magnetic-field lines, respectively.

  13. Barrier bucket experiment at the AGS

    Directory of Open Access Journals (Sweden)

    M. Fujieda

    1999-12-01

    Full Text Available A barrier bucket experiment with two dedicated barrier cavities was performed at the Brookhaven AGS. One of the barrier cavities was a magnetic alloy (MA–loaded cavity and the other was a ferrite-loaded cavity. They generated a single sine wave with a peak voltage of 40 kV at a repetition rate of 351 kHz. A barrier rf system was established with these cavities and five bunches from the AGS booster were accumulated. A total of 3×10^{13} protons were stored without beam loss, and were successfully rebunched and accelerated. The longitudinal emittance growth was observed during accumulation by the barrier bucket, the blowup factor of which was about 3. The longitudinal mismatch between the rf bucket and the beam bunch was the main reason for the emittance growth. The potential distortions by beam loading of the ferrite cavity and the overshooting voltage of the MA cavity disturbed the smooth debunching.

  14. Voltage-driven magnetization control in topological insulator/magnetic insulator heterostructures

    Directory of Open Access Journals (Sweden)

    Michael E. Flatté

    2017-05-01

    Full Text Available A major barrier to the development of spin-based electronics is the transition from current-driven spin torque, or magnetic-field-driven magnetization reversal, to a more scalable voltage-driven magnetization reversal. To achieve this, multiferroic materials appear attractive, however the effects in current materials occur at very large voltages or at low temperatures. Here the potential of a new class of hybrid multiferroic materials is described, consisting of a topological insulator adjacent to a magnetic insulator, for which an applied electric field reorients the magnetization. As these materials lack conducting states at the chemical potential in their bulk, no dissipative charge currents flow in the bulk. Surface states at the interface, if present, produce effects similar to surface recombination currents in bipolar devices, but can be passivated using magnetic doping. Even without conducting states at the chemical potential, for a topological insulator there is a finite spin Hall conductivity provided by filled bands below the chemical potential. Spin accumulation at the interface with the magnetic insulator provides a torque on the magnetization. Properly timed voltage pulses can thus reorient the magnetic moment with only the flow of charge current required in the leads to establish the voltage. If the topological insulator is sufficiently thick the resulting low capacitance requires little charge current.

  15. Internal transport barrier triggering by rational magnetic flux surfaces in tokamaks

    International Nuclear Information System (INIS)

    Joffrin, E.; Challis, C.D.; Conway, G.D.

    2003-01-01

    The formation of Internal Transport Barriers (ITBs) has been experimentally associated with the presence of rational q-surfaces in both JET and ASDEX Upgrade. The triggering mechanisms are related to the occurrence of magneto-hydrodynamic (MHD) instabilities such as mode coupling or fishbone activity. These events could locally modify the poloidal velocity and increase transiently the shearing rate to values comparable to the linear growth rate of ITG modes. For JET reversed magnetic shear scenarios, ITB emergence occurs preferentially when the minimum q reaches an integer value. In this case, transport effects localised in the vicinity of zero magnetic shear and close to rational q values may also contribute to the formation of ITBs.The role of rational q surfaces on ITB triggering stresses the importance of q profile control for advanced tokamak scenario and could contribute to lower substantially the access power to these scenarios in next step facilities. (author)

  16. Internal Transport Barrier triggering by rational magnetic flux surfaces in tokamaks

    International Nuclear Information System (INIS)

    Joffrin, E.H.

    2002-01-01

    The formation of Internal Transport Barriers (ITBs) has been experimentally associated with the presence of rational q-surfaces in both JET and ASDEX Upgrade. The triggering mechanisms are related to the occurrence of magneto-hydrodynamic (MHD) instabilities such as mode coupling or fishbone activity. These events could locally modify the poloidal velocity and increase transiently the shearing rate to values comparable to the linear growth rate of ITG modes. For reversed magnetic shear scenario, ITB emergence occurs preferentially when the minimum q reaches an integer value. In this case, transport effects localised in the vicinity of zero magnetic shear and close to rational q values may also contribute to the formation of ITBs. The role of rational q surfaces on ITB triggering stresses the importance of q profile control for advanced tokamak scenario and could contribute to lower substantially the access power to these scenarios in next step facilities. (author)

  17. Magnetic resonance imaging of blood brain/nerve barrier dysfunction and leukocyte infiltration: closely related or discordant?

    Directory of Open Access Journals (Sweden)

    Gesa eWeise

    2012-12-01

    Full Text Available Unlike other organs the nervous system is secluded from the rest of the organism by the blood brain (BBB or blood nerve barrier (BNB preventing passive influx of fluids from the circulation. Similarly, leukocyte entry to the nervous system is tightly controlled. Breakdown of these barriers and cellular inflammation are hallmarks of inflammatory as well as ischemic neurological diseases and thus represent potential therapeutic targets. The spatiotemporal relationship between BBB/BNB disruption and leukocyte infiltration has been a matter of debate. We here review contrast-enhanced magnetic resonance imaging (MRI as a non-invasive tool to depict barrier dysfunction and its relation to macrophage infiltration in the central and peripheral nervous system under pathological conditions. Novel experimental contrast agents like Gadofluorine M (Gf allow more sensitive assessment of BBB dysfunction than conventional Gadolinium (Gd-DTPA-enhanced MRI. In addition, Gf facilitates visualization of functional and transient alterations of the BBB remote from lesions. Cellular contrast agents such as superparamagnetic iron oxide particles (SPIO and perfluorocarbons (PFC enable assessment of leukocyte (mainly macrophage infiltration by MR technology. Combined use of these MR contrast agents disclosed that leukocytes can enter the nervous system independent from a disturbance of the BBB, and vice versa, a dysfunctional BBB/BNB by itself is not sufficient to attract inflammatory cells from the circulation. We will illustrate these basic imaging findings in animal models of multiple sclerosis (MS, cerebral ischemia and traumatic nerve injury and review corresponding findings in patients.

  18. Magnetic tunnel junctions with monolayer hexagonal boron nitride tunnel barriers

    Energy Technology Data Exchange (ETDEWEB)

    Piquemal-Banci, M.; Galceran, R.; Bouzehouane, K.; Anane, A.; Petroff, F.; Fert, A.; Dlubak, B.; Seneor, P. [Unité Mixte de Physique, CNRS, Thales, Univ. Paris-Sud, Université Paris-Saclay, Palaiseau 91767 (France); Caneva, S.; Martin, M.-B.; Weatherup, R. S.; Kidambi, P. R.; Robertson, J.; Hofmann, S. [Department of Engineering, University of Cambridge, Cambridge CB21PZ (United Kingdom); Xavier, S. [Thales Research and Technology, 1 avenue Augustin Fresnel, Palaiseau 91767 (France)

    2016-03-07

    We report on the integration of atomically thin 2D insulating hexagonal boron nitride (h-BN) tunnel barriers into Co/h-BN/Fe magnetic tunnel junctions (MTJs). The h-BN monolayer is directly grown by chemical vapor deposition on Fe. The Conductive Tip Atomic Force Microscopy (CT-AFM) measurements reveal the homogeneity of the tunnel behavior of our h-BN layers. As expected for tunneling, the resistance depends exponentially on the number of h-BN layers. The h-BN monolayer properties are also characterized through integration into complete MTJ devices. A Tunnel Magnetoresistance of up to 6% is observed for a MTJ based on a single atomically thin h-BN layer.

  19. Electronic band structure of magnetic bilayer graphene superlattices

    International Nuclear Information System (INIS)

    Pham, C. Huy; Nguyen, T. Thuong; Nguyen, V. Lien

    2014-01-01

    Electronic band structure of the bilayer graphene superlattices with δ-function magnetic barriers and zero average magnetic flux is studied within the four-band continuum model, using the transfer matrix method. The periodic magnetic potential effects on the zero-energy touching point between the lowest conduction and the highest valence minibands of pristine bilayer graphene are exactly analyzed. Magnetic potential is shown also to generate the finite-energy touching points between higher minibands at the edges of Brillouin zone. The positions of these points and the related dispersions are determined in the case of symmetric potentials.

  20. Discontinuity model for internal transport barrier formation in reversed magnetic shear plasmas

    International Nuclear Information System (INIS)

    Kishimoto, Y.; Dettrick, S.A.; Li, J.Q.; Shirai, S.; Kim, J.Y.; Horton, W.; Tajima, T.; LeBrun, M.J.

    2000-01-01

    It is becoming clear that tokamak anomalous transport is dominated by radially extended non-local modes which originate from strong toroidal coupling of rational surfaces in non-uniform plasmas. To aid in understanding the internal transport barrier (ITB) formed in reversed magnetic shear experiments, in addition to the well known shear flow effect, the article points out an important non-local effect and/or finite size effect which comes from the complex behaviour of the mode over a finite radial region around the minimum q (safety factor) surface. The non-local mode, which is characterized by its radial extent and the degree of tilting in the poloidal direction (Δr, θ 0 ), changes its structure depending on the sign of the magnetic shear, and as a result such modes are weakly excited across the q min surface. This leads to a discontinuity or gap which disconnects the phase relation in the global wave structure across the q min surface. Once such a discontinuity (or gap) is formed, transport suppression occurs and therefore a transport barrier can be expected near the q min surface. The existence of this discontinuity is confirmed through use of a toroidal particle simulation. It is also shown that whether such a discontinuity is efficiently established depends on the presence of the radial electric field and the related plasma shear flow. (author)

  1. Spin asymmetry calculations of the TMR-V curves in single and double-barrier magnetic tunnel junctions

    KAUST Repository

    Useinov, Arthur; Kosel, Jü rgen

    2011-01-01

    in the single as well as double barrier magnetic tunnel junctions (SMTJ & DMTJ, which are constructed from CoFeB/MgO interfaces) and numerically estimate the possible difference of the TMR-V a curves for negative and positive voltages in the homojunctions

  2. Resonant tunneling through double-barrier structures on graphene

    International Nuclear Information System (INIS)

    Deng Wei-Yin; Zhu Rui; Deng Wen-Ji; Xiao Yun-Chang

    2014-01-01

    Quantum resonant tunneling behaviors of double-barrier structures on graphene are investigated under the tight-binding approximation. The Klein tunneling and resonant tunneling are demonstrated for the quasiparticles with energy close to the Dirac points. The Klein tunneling vanishes by increasing the height of the potential barriers to more than 300 meV. The Dirac transport properties continuously change to the Schrödinger ones. It is found that the peaks of resonant tunneling approximate to the eigen-levels of graphene nanoribbons under appropriate boundary conditions. A comparison between the zigzag- and armchair-edge barriers is given. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  3. Toroidal equilibrium states with reversed magnetic shear and parallel flow in connection with the formation of Internal Transport Barriers

    Science.gov (United States)

    Kuiroukidis, Ap.; Throumoulopoulos, G. N.

    2015-08-01

    We construct nonlinear toroidal equilibria of fixed diverted boundary shaping with reversed magnetic shear and flows parallel to the magnetic field. The equilibria have hole-like current density and the reversed magnetic shear increases as the equilibrium nonlinearity becomes stronger. Also, application of a sufficient condition for linear stability implies that the stability is improved as the equilibrium nonlinearity correlated to the reversed magnetic shear gets stronger with a weaker stabilizing contribution from the flow. These results indicate synergetic stabilizing effects of reversed magnetic shear, equilibrium nonlinearity and flow in the establishment of Internal Transport Barriers (ITBs).

  4. Potential barriers to the use of health services among ethnic minorities : a review

    NARCIS (Netherlands)

    Scheppers, E.; van Dongen, E.; Dekker, J.; Geertzen, J.; Dekker, J.

    Background. Ethnic minority patients seem to be confronted with barriers when using health services. Yet, care providers are often oblivious to these barriers, although they may share to some extent the burden of responsibility for them. In order to enlighten care providers, as to the potential

  5. Generalization of Kramer's formula: Fission over a multidimensional potential barrier

    International Nuclear Information System (INIS)

    Jing-Shang, Z.; Weidenmueller, H.A.

    1983-01-01

    We generalize Kramers's rate expression for diffusion over a potential barrier to the case of a diffusion problem for n degrees of freedom. These can be thought of as the shape degrees of freedom of a fissioning nucleus. We present our formula for the fission width and discuss its dependence on the parameters: the mass tensor, the friction tensor, and the shape of the potential landscape

  6. Electronic transport for armchair graphene nanoribbons with a potential barrier

    International Nuclear Information System (INIS)

    Ben-Hu, Zhou; Ben-Liang, Zhou; Guang-Hui, Zhou; Zi-Gang, Duan

    2010-01-01

    This paper studies the electronic transport property through a square potential barrier in armchair-edge graphene nanoribbon (AGNR). Using the Dirac equation with the continuity condition for wave functions at the interfaces between regions with and without a barrier, we calculate the mode-dependent transmission probability for both semiconducting and metallic AGNRs, respectively. It is shown that, by some numerical examples, the transmission probability is generally an oscillating function of the height and range of the barrier for both types of AGNRs. The main difference between the two types of systems is that the magnitude of oscillation for the semiconducting AGNR is larger than that for the metallic one. This fact implies that the electronic transport property for AGNRs depends sensitively on their widths and edge details due to the Dirac nature of fermions in the system

  7. Internal transport barrier triggering by rational magnetic flux surfaces in tokamaks

    International Nuclear Information System (INIS)

    Joffrin, E.; Challis, C.D.; Conway, G.D.

    2003-01-01

    The formation of internal transport barriers (ITBs) has been experimentally associated with the presence of rational q surfaces in both JET and ASDEX Upgrade. The triggering mechanisms are related to the occurrence of magneto-hydrodynamic (MHD) instabilities such as mode coupling and fishbone activity. These events could locally modify the poloidal velocity and increase transiently the shearing rate to values comparable with the linear growth rate of ion temperature gradient modes. For JET reversed magnetic shear scenarios, ITB emergence occurs preferentially when the minimum q reaches an integral value. In this case, transport effects localized in the vicinity of zero magnetic shear and close to rational q values may be at the origin of ITB formation. The role of rational q surfaces in ITB triggering stresses the importance of q profile control for an advanced tokamak scenario and could assist in substantially lowering the access power to these scenarios in next step facilities. (author)

  8. Electronic transport for armchair graphene nanoribbons with a potential barrier

    International Nuclear Information System (INIS)

    Zhou Benliang; Zhou Benhu; Liao Wenhu; Zhou Guanghui

    2010-01-01

    We theoretically investigate the electronic transport properties through a rectangular potential barrier embedded in armchair-edge graphene nanoribbons (AGNRs) of various widths. Using the Landauer formula and Dirac equation with the continuity conditions for all segments of wave functions at the interfaces between regions inside and outside the barrier, we calculate analytically the conductance and Fano factor for the both metallic and semiconducting AGNRs, respectively. It is shown that, by some numerical examples, at Dirac point the both types of AGNRs own a minimum conductance associated with the maximum Fano factor. The results are discussed and compared with the previous relevant works.

  9. Spin asymmetry calculations of the TMR-V curves in single and double-barrier magnetic tunnel junctions

    KAUST Repository

    Useinov, Arthur

    2011-10-01

    Spin-polarization asymmetry is the key parameter in asymmetric voltage behavior (AVB) of the tunnel magnetoresistance (TMR) in magnetic tunnel junctions. In this paper, we study the value of the TMR as a function of the applied voltage Va in the single as well as double barrier magnetic tunnel junctions (SMTJ & DMTJ, which are constructed from CoFeB/MgO interfaces) and numerically estimate the possible difference of the TMR-V a curves for negative and positive voltages in the homojunctions. As a result, we found that AVB may help to determine the exact values of Fermi wave vectors for minority and majority conducting spin sub-bands. Moreover, significant asymmetry of the experimental TMR-Va curves, which arises due to different annealing regimes, is explained by different heights of the tunnel barriers and values of the spin asymmetry. The numerical TMR-V a data are in good agreement with experimental ones. © 2011 IEEE.

  10. Spatial characterization of the edge barrier in wide superconducting films

    Science.gov (United States)

    Sivakov, A. G.; Turutanov, O. G.; Kolinko, A. E.; Pokhila, A. S.

    2018-03-01

    The current-induced destruction of superconductivity is discussed in wide superconducting thin films, whose width is greater than the magnetic field penetration depth, in weak magnetic fields. Particular attention is paid to the role of the boundary potential barrier (the Bin-Livingston barrier) in critical state formation and detection of the edge responsible for this critical state with different mutual orientations of external perpendicular magnetic field and transport current. Critical and resistive states of the film were visualized using the space-resolving low-temperature laser scanning microscopy (LTLSM) method, which enables detection of critical current-determining areas on the film edges. Based on these observations, a simple technique was developed for investigation of the critical state separately at each film edge, and for the estimation of residual magnetic fields in cryostats. The proposed method only requires recording of the current-voltage characteristics of the film in a weak magnetic field, thus circumventing the need for complex LTLSM techniques. Information thus obtained is particularly important for interpretation of studies of superconducting film single-photon light emission detectors.

  11. Chaotic motion of a harmonically bound charged particle in a magnetic field, in the presence of a half-plane barrier

    NARCIS (Netherlands)

    Geurts, Bernardus J.; Wiegel, F.W.; Creswick, Richard J.

    1991-01-01

    The motion in the plane of an harmonically bound charged particle interacting with a magnetic field and a half-plane barrier along the positive x-axis is studied. The magnetic field is perpendicular to the plane in which the particle moves. This motion is integrable in between collisions of the

  12. MAGNETIC CIRCUIT EQUIVALENT OF THE SYNCHRONOUS MOTOR WITH INCORPORATED MAGNETS

    Directory of Open Access Journals (Sweden)

    Fyong Le Ngo

    2015-01-01

    Full Text Available Magnetic circuitry computation is one of the central stages of designing a synchronous motor with incorporated magnets, which can be performed by means of a simplified method of the magnetic-circuits equivalent modeling. The article studies the magnetic circuit of the motor with the rotor-incorporated magnets, which includes four sectors: constant magnets with the field pole extension made of magnetically soft steel, magniflux dispersion sections containing air barriers and steel bridges; the air gap; the stator grooves, cogs and the frame yoke. The authors introduce an equivalent model of the magnetic circuit. High-energy magnets with a linear demagnetization curve are employed in the capacity of constant magnets. Two magnets create the magnetic flux for one pole. The decline of magnetic potential in the steel of the pole is negligible consequent on the admission that the poles magnetic inductivity µ = ∞. The rotor design provides for the air barriers and the steel bridges that close leakage flux. The induction-permeability curve linearization serves for the bridges magnetic saturation accountability and presents a polygonal line consisting of two linear sections. The estimation of the magnet circuit section including the cogs and the frame yoke is executed with account of the steel saturation, their magnetic conductivities thereat being dependent on the saturation rate. Relying on the equivalent model of the magnetic circuit, the authors deduce a system of two equations written from the first and the second Kirchhoff laws of the magnetic circuits. These equations allow solving two problems: specifying dimensions of the magnets by the preset value of the magnetic flow in the clearance and determining the clearance magnetic flow at the preset motor rotor-and-stator design.

  13. Reversible rectification of vortex motion in magnetic and non-magnetic asymmetric pinning potentials

    International Nuclear Information System (INIS)

    Gonzalez, E.M.; Gonzalez, M.P.; Nunez, N.O.; Villegas, J.E.; Anguita, J.V.; Jaafa, M.; Asenjo, A.; Vicent, J.L.

    2006-01-01

    Nb films have been grown on arrays of asymmetric pinning centers. The lattice vortex dynamics could be modified, almost at will, by periodic pinning potentials. In the case of asymmetric pinning potentials a vortex ratchet effect occurs: the vortex lattice motion is rectified. That is, an injected ac current yields an output dc voltage, which polarity could be tuned. The output signal polarity could be switched with the applied magnetic field and the ac current strength. Ratchet effect occurs when asymmetric potentials induce outward particles flow under external fluctuations in the lack of driven direct outward forces. The output signal is similar using magnetic or non-magnetic submicrometric array of pinning centers. This device works as an adiabatic rocking ratchet. This superconducting ratchet could be a model to study biological motors

  14. Low frequency noise in asymmetric double barrier magnetic tunnel junctions with a top thin MgO layer

    International Nuclear Information System (INIS)

    Guo Hui-Qiang; Tang Wei-Yue; Liu Liang; Wei Jian; Li Da-Lai; Feng Jia-Feng; Han Xiu-Feng

    2015-01-01

    Low frequency noise has been investigated at room temperature for asymmetric double barrier magnetic tunnel junctions (DBMTJs), where the coupling between the top and middle CoFeB layers is antiferromagnetic with a 0.8-nm thin top MgO barrier of the CoFeB/MgO/CoFe/CoFeB/MgO/CoFeB DBMTJ. At enough large bias, 1/f noise dominates the voltage noise power spectra in the low frequency region, and is conventionally characterized by the Hooge parameter α mag . With increasing external field, the top and bottom ferromagnetic layers are aligned by the field, and then the middle free layer rotates from antiparallel state (antiferromagnetic coupling between top and middle ferromagnetic layers) to parallel state. In this rotation process α mag and magnetoresistance-sensitivity-product show a linear dependence, consistent with the fluctuation dissipation relation. With the magnetic field applied at different angles (θ) to the easy axis of the free layer, the linear dependence persists while the intercept of the linear fit satisfies a cos(θ) dependence, similar to that for the magnetoresistance, suggesting intrinsic relation between magnetic losses and magnetoresistance. (rapid communication)

  15. Modified Debye screening potential in a magnetized quantum plasma

    International Nuclear Information System (INIS)

    Salimullah, M.; Hussain, A.; Sara, I.; Murtaza, G.; Shah, H.A.

    2009-01-01

    The effects of quantum mechanical influence and uniform static magnetic field on the Shukla-Nambu-Salimullah potential in an ultracold homogeneous electron-ion Fermi plasma have been examined in detail. It is noticed that the strong quantum effect arising through the Bohm potential and the ion polarization effect can give rise to a new oscillatory behavior of the screening potential beyond the shielding cloud which could explain a new type of possible robust ordered structure formation in the quantum magnetoplasma. However, the magnetic field enhances the Debye length perpendicular to the magnetic field in the weak quantum limit of the quantum plasma.

  16. Experimental research on electric field jump in low magnetic fields: Detection of damage in new ex-situ MgB{sub 2} barriers in MgB{sub 2} wires

    Energy Technology Data Exchange (ETDEWEB)

    Gajda, D., E-mail: dangajda@op.pl [International Laboratory of High Magnetic Fields and Low Temperatures, Gajowicka 95, 53-421 Wroclaw (Poland); Morawski, A. [Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warszawa (Poland); Zaleski, A. [Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Okólna 2, 50-422 Wroclaw (Poland); Hossain, M.S.A. [Institute for Superconducting and Electronic Materials, AIIM, University of Wollongong, North Wollongong, NSW 2519 (Australia); Rindfleisch, M. [Hyper Tech Research, Inc, 1275 Kinnear Road, Columbus, OH 43212 (United States); Cetner, T. [Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warszawa (Poland)

    2015-10-25

    We explored the incorporation of field sweep (constant current and rapidly increasing magnetic field) into the four-probe method as a new technique to detect defects in barrier layers in superconducting MgB{sub 2} wires. This method allows us to observe jumps in the electric field in low magnetic fields. The scanning electron microscopy results indicate that such a jump originates from cracks in Nb barriers and ex-situ MgB{sub 2} barriers. Our research indicates that the field sweep allows us to detect damage to barriers that are made of superconducting materials. This method can be the basis for an industrial method for detecting damages in MgB{sub 2} wires. These defects reduce the critical current of MgB{sub 2} wire. Detection and removal of these defects will allow us to produce MgB{sub 2} wires with ex-situ MgB{sub 2} and Nb barriers that will have improved critical current density. Manufacturing of MgB{sub 2} wires with new ex-situ MgB{sub 2} barriers is a new technological concept. This type of barrier is cheaper and easier to manufacture, leading to cheaper MgB{sub 2} wires. Moreover, we show that critical current can be measured by two methods: current sweep (constant magnetic field and quickly increasing current) and field sweep. - Graphical abstract: Our results indicate that the jump electric field low magnetic fields. This jump indicates damage in Nb and ex situ MgB{sub 2} barrier. Detection and removal of defects will increase J{sub c} in MgB{sub 2} wires and will increase the applicability of MgB{sub 2} wire. - Highlights: • Jump electric field in the 1 T indicates damage to the Nb barrier. • Jump resistance at 9 K indicates damage to the Nb barrier. • Jump electric field in low magnetic field indicates damage to ex situ MgB{sub 2} barrier. • Damage Nb and ex situ MgB{sub 2} barrier significantly reduces the critical current density in the MgB{sub 2} wire.

  17. Electrically tunable tunneling rectification magnetoresistance in magnetic tunneling junctions with asymmetric barriers.

    Science.gov (United States)

    Wang, Jing; Huang, Qikun; Shi, Peng; Zhang, Kun; Tian, Yufeng; Yan, Shishen; Chen, Yanxue; Liu, Guolei; Kang, Shishou; Mei, Liangmo

    2017-10-26

    The development of multifunctional spintronic devices requires simultaneous control of multiple degrees of freedom of electrons, such as charge, spin and orbit, and especially a new physical functionality can be realized by combining two or more different physical mechanisms in one specific device. Here, we report the realization of novel tunneling rectification magnetoresistance (TRMR), where the charge-related rectification and spin-dependent tunneling magnetoresistance are integrated in Co/CoO-ZnO/Co magnetic tunneling junctions with asymmetric tunneling barriers. Moreover, by simultaneously applying direct current and alternating current to the devices, the TRMR has been remarkably tuned in the range from -300% to 2200% at low temperature. This proof-of-concept investigation provides an unexplored avenue towards electrical and magnetic control of charge and spin, which may apply to other heterojunctions to give rise to more fascinating emergent functionalities for future spintronics applications.

  18. Degradation of magnetic tunnel junctions with thin AlOx barrier

    Directory of Open Access Journals (Sweden)

    Tadashi Mihara, Yoshinari Kamakura, Masato Morifuji and Kenji Taniguchi

    2007-01-01

    Full Text Available The degradation of magnetic tunnel junctions (MTJs with AlOx barrier was experimentally investigated. Constant voltage stress (CVS measurement was carried out to monitor the time evolution of the conductance and tunneling magnetoresistance (TMR of MTJs. The gradual increase of the stress-induced leakage current (SILC was observed prior to the breakdown, following a power law function of stress time with an exponent of about 0.2–0.4, which is similar to the case of the ultrathin gate oxide films in MOSFETs. The measured TMR for SILC suggests that the spin-dependent current component would be involved in the early stage of degradation, while spin-independent conduction becomes dominant before the breakdown resulting in a decrease of TMR.

  19. [Effect of pulse magnetic field on distribution of neuronal action potential].

    Science.gov (United States)

    Zheng, Yu; Cai, Di; Wang, Jin-Hai; Li, Gang; Lin, Ling

    2014-08-25

    The biological effect on the organism generated by magnetic field is widely studied. The present study was aimed to observe the change of sodium channel under magnetic field in neurons. Cortical neurons of Kunming mice were isolated, subjected to 15 Hz, 1 mT pulse magnetic stimulation, and then the currents of neurons were recorded by whole-cell patch clamp. The results showed that, under magnetic stimulation, the activation process of Na(+) channel was delayed, and the inactivation process was accelerated. Given the classic three-layer model, the polarization diagram of cell membrane potential distribution under pulse magnetic field was simulated, and it was found that the membrane potential induced was associated with the frequency and intensity of magnetic field. Also the effect of magnetic field-induced current on action potential was simulated by Hodgkin-Huxley (H-H) model. The result showed that the generation of action potential was delayed, and frequency and the amplitudes were decreased when working current was between -1.32 μA and 0 μA. When the working current was higher than 0 μA, the generation frequency of action potential was increased, and the change of amplitudes was not obvious, and when the working current was lower than -1.32 μA, the time of rising edge and amplitudes of action potential were decreased drastically, and the action potential was unable to generate. These results suggest that the magnetic field simulation can affect the distribution frequency and amplitude of action potential of neuron via sodium channel mediation.

  20. Effect of the δ-potential on spin-dependent electron tunneling in double barrier semiconductor heterostructure

    Science.gov (United States)

    Chandrasekar, L. Bruno; Gnanasekar, K.; Karunakaran, M.

    2018-06-01

    The effect of δ-potential was studied in GaAs/Ga0.6Al0·4As double barrier heterostructure with Dresselhaus spin-orbit interaction. The role of barrier height and position of the δ- potential in the well region was analysed on spin-dependent electron tunneling using transfer matrix method. The spin-separation between spin-resonances on energy scale depends on both height and position of the δ- potential, whereas the tunneling life time of electrons highly influenced by the position of the δ- potential and not on the height. These results might be helpful for the fabrication of spin-filters.

  1. Directed Magnetic Particle Transport above Artificial Magnetic Domains Due to Dynamic Magnetic Potential Energy Landscape Transformation.

    Science.gov (United States)

    Holzinger, Dennis; Koch, Iris; Burgard, Stefan; Ehresmann, Arno

    2015-07-28

    An approach for a remotely controllable transport of magnetic micro- and/or nanoparticles above a topographically flat exchange-bias (EB) thin film system, magnetically patterned into parallel stripe domains, is presented where the particle manipulation is achieved by sub-mT external magnetic field pulses. Superparamagnetic core-shell particles are moved stepwise by the dynamic transformation of the particles' magnetic potential energy landscape due to the external magnetic field pulses without affecting the magnetic state of the thin film system. The magnetic particle velocity is adjustable in the range of 1-100 μm/s by the design of the substrate's magnetic field landscape (MFL), the particle-substrate distance, and the magnitude of the applied external magnetic field pulses. The agglomeration of magnetic particles is avoided by the intrinsic magnetostatic repulsion of particles due to the parallel alignment of the particles' magnetic moments perpendicular to the transport direction and parallel to the surface normal of the substrate during the particle motion. The transport mechanism is modeled by a quantitative theory based on the precise knowledge of the sample's MFL and the particle-substrate distance.

  2. A Novel Magnetic Actuation Scheme to Disaggregate Nanoparticles and Enhance Passage across the Blood–Brain Barrier

    Directory of Open Access Journals (Sweden)

    Ali Kafash Hoshiar

    2017-12-01

    Full Text Available The blood–brain barrier (BBB hinders drug delivery to the brain. Despite various efforts to develop preprogramed actuation schemes for magnetic drug delivery, the unmodeled aggregation phenomenon limits drug delivery performance. This paper proposes a novel scheme with an aggregation model for a feed-forward magnetic actuation design. A simulation platform for aggregated particle delivery is developed and an actuation scheme is proposed to deliver aggregated magnetic nanoparticles (MNPs using a discontinuous asymmetrical magnetic actuation. The experimental results with a Y-shaped channel indicated the success of the proposed scheme in steering and disaggregation. The delivery performance of the developed scheme was examined using a realistic, three-dimensional (3D vessel simulation. Furthermore, the proposed scheme enhanced the transport and uptake of MNPs across the BBB in mice. The scheme presented here facilitates the passage of particles across the BBB to the brain using an electromagnetic actuation scheme.

  3. Photospheric Driving of Non-Potential Coronal Magnetic Field Simulations

    Science.gov (United States)

    2016-09-19

    synthesize observable emission . In future, the computational speed of the MF model makes it a potential avenue for near- real time and/or ensemble...AFRL-AFOSR-UK-TR-2016-0030 PHOTOSPHERIC DRIVING OF NON-POTENTIAL CORONAL MAGNETIC FIELD SIMULATIONS Anthony Yeates UNIVERSITY OF DURHAM Final Report...Final 3. DATES COVERED (From - To)  15 Sep 2014 to 14 Sep 2017 4. TITLE AND SUBTITLE PHOTOSPHERIC DRIVING OF NON-POTENTIAL CORONAL MAGNETIC FIELD

  4. Potential and barrier study. Energy efficiency of Norwegian homes; Potensial- og barrierestudie. Energieffektivisering av norske boliger

    Energy Technology Data Exchange (ETDEWEB)

    Mjoenes, Christian; Pettersen, Folke Vogn Haug; Kristoffersen, Bjoerge Sandberg; Birkeland, Bjoern Mangor; Essen, Jan von; Haarberg; Karl Johan

    2012-01-15

    On behalf of Enova SF, Prognosesenteret AS and Entelligens AS carried out a potential and barrier study of energy efficiency of the Norwegian housing stock. The study made use of newer and known studies of the Norwegian housing stock, known and documented barriers to energy efficiency, and new and extensive studies of several topics which have only been partially or never explored before. Through unique analysis and a case-based approach, it revealed a real energy efficiency potential in Norwegian homes with known technology and revealed representativeness, relevance, strength and extent of the barriers that prevent that one can realize most of the technical energy efficiency potential in the Norwegian housing stock. (eb)

  5. Investigation of the potential barrier lowering for quasi-ballistic transport in short channel MOSFETs

    International Nuclear Information System (INIS)

    Lee, Jaehong; Kwon, Yongmin; Ji, Junghwan; Shin, Hyungcheol

    2011-01-01

    In this paper, the quasi-ballistic carrier transport in short channel MOSFETs is investigated from the point of potential barrier lowering. To investigate the ballistic characteristic of transistors, we extracted the channel backscattering coefficient and the ballistic ratio from experimental data obtained by RF C-V and DC I-V measurements. Two factors that modulate the potential barrier height, besides the gate bias, are considered in this work: the drain bias (V DS ) and the channel doping concentration (N A ). We extract the critical length by calculating the potential drop in the channel region and conclude that the drain bias and the channel doping concentration affect the quasi-ballistic carrier transport.

  6. Electronic tunneling through a potential barrier on the surface of a topological insulator

    Science.gov (United States)

    Zhou, Benliang; Zhou, Benhu; Zhou, Guanghui

    2016-12-01

    We investigate the tunneling transport for electrons on the surface of a topological insulator (TI) through an electrostatic potential barrier. By using the Dirac equation with the continuity conditions for all segments of wave functions at the interfaces between regions inside and outside the barrier, we calculate analytically the transmission probability and conductance for the system. It is demonstrated that, the Klein paradox can also been observed in the system same as in graphene system. Interestingly, the conductance reaches the minimum value when the incident electron energy is equal to the barrier strength. Moreover, with increasing barrier width, the conductance turns up some tunneling oscillation peaks, and larger barrier strength can cause lower conductance, shorter period but larger oscillation amplitude. The oscillation amplitude decreases as the barrier width increases, which is similar as that of the system consisting of the compressive uniaxial strain applied on a TI, but somewhat different from that of graphene system where the oscillation amplitude is a constant. The findings here imply that an electrostatic barrier can greatly influence the electron tunneling transport of the system, and may provide a new way to realize directional filtering of electrons.

  7. Effects of periodic scattering potential on Landau quantization and ballistic transport of electrons in graphene

    Energy Technology Data Exchange (ETDEWEB)

    Gumbs, Godfrey [Department of Physics and Astronomy, Hunter College, CUNY, 695 Park Avenue, New York, NY 10065, USA and Donostia International Physics Center (DIPC), P de Manuel Lardizabal, 4, 20018 San Sebastian, Basque Country (Spain); Iurov, Andrii [Department of Physics and Astronomy, Hunter College of the City University of New York, 695 Park Avenue, New York, NY 10065 (United States); Huang, Danhong [Air Force Research Laboratory, Space Vehicles Directorate, Kirtland Air Force Base, NM 87117 (United States); Fekete, Paula [West Point Military Academy, West Point, NY (United States); Zhemchuzhna, Liubov [Department of Physics, North Carolina Central University, Durham, North Carolina 27707 (United States)

    2014-03-31

    A two-dimensional periodic array of scatterers has been introduced to a single layer of graphene in the presence of an external magnetic field perpendicular to the graphene layer. The eigenvalue equation for such a system has been solved numerically to display the structure of split Landau subbands as functions of both wave number and magnetic flux. The effects of pseudo-spin coupling and Landau subbands mixing by a strong scattering potential have been demonstrated. Additionally, we investigated the square barrier tunneling problem when magnetic field is present, as well as demonstrate the crucial difference in the modulated band structure between graphene and the two-dimensional electron gas. The low-magnetic field regime is particularly interesting for Dirac fermions and has been discussed. Tunneling of Dirac electrons through a magnetic potential barrier has been investigated to complement the reported results on electrostatic potential scattering in the presence of an ambient magnetic field.

  8. Effects of periodic scattering potential on Landau quantization and ballistic transport of electrons in graphene

    International Nuclear Information System (INIS)

    Gumbs, Godfrey; Iurov, Andrii; Huang, Danhong; Fekete, Paula; Zhemchuzhna, Liubov

    2014-01-01

    A two-dimensional periodic array of scatterers has been introduced to a single layer of graphene in the presence of an external magnetic field perpendicular to the graphene layer. The eigenvalue equation for such a system has been solved numerically to display the structure of split Landau subbands as functions of both wave number and magnetic flux. The effects of pseudo-spin coupling and Landau subbands mixing by a strong scattering potential have been demonstrated. Additionally, we investigated the square barrier tunneling problem when magnetic field is present, as well as demonstrate the crucial difference in the modulated band structure between graphene and the two-dimensional electron gas. The low-magnetic field regime is particularly interesting for Dirac fermions and has been discussed. Tunneling of Dirac electrons through a magnetic potential barrier has been investigated to complement the reported results on electrostatic potential scattering in the presence of an ambient magnetic field

  9. Healthcare Access for Iraqi Refugee Children in Texas: Persistent Barriers, Potential Solutions, and Policy Implications.

    Science.gov (United States)

    Vermette, David; Shetgiri, Rashmi; Al Zuheiri, Haidar; Flores, Glenn

    2015-10-01

    To identify access barriers to healthcare and potential interventions to improve access for Iraqi refugee children. Four focus groups were conducted using consecutive sampling of Iraqi refugee parents residing in the US for 8 months to 5 years. Eight key-informant interviews also were conducted with employees of organizations serving Iraqi refugee families, recruited using snowball sampling. Focus groups and interviews were audiotaped, transcribed, and analyzed using margin coding and grounded theory. Iraqi refugees identified provider availability, Medicaid maintenance and renewal, language issues, and inadequate recognition of post-traumatic stress disorder as barriers to care for their children. Interviewees cited loss of case-management services and difficulties in understanding the Medicaid renewal process as barriers. Potential interventions to improve access include community-oriented efforts to educate parents on Medicaid renewal, obtaining services, and accessing specialists. Given the enduring nature of language and Medicaid renewal barriers, policies addressing eligibility alone are insufficient.

  10. A regularization method for extrapolation of solar potential magnetic fields

    Science.gov (United States)

    Gary, G. A.; Musielak, Z. E.

    1992-01-01

    The mathematical basis of a Tikhonov regularization method for extrapolating the chromospheric-coronal magnetic field using photospheric vector magnetograms is discussed. The basic techniques show that the Cauchy initial value problem can be formulated for potential magnetic fields. The potential field analysis considers a set of linear, elliptic partial differential equations. It is found that, by introducing an appropriate smoothing of the initial data of the Cauchy potential problem, an approximate Fourier integral solution is found, and an upper bound to the error in the solution is derived. This specific regularization technique, which is a function of magnetograph measurement sensitivities, provides a method to extrapolate the potential magnetic field above an active region into the chromosphere and low corona.

  11. Gyrofluid potential vorticity equation and turbulent equipartion states

    DEFF Research Database (Denmark)

    Madsen, Jens; Juul Rasmussen, Jens; Naulin, Volker

    2015-01-01

    . The equation is relevant for transport barriers in magnetically confined plasmas because particle density, ion temperature and the radial electric field are mutually coupled through the potential vorticity. The potential vorticity equation is derived from an energy conserving, four-field, electrostatic, full......An equation governing potential vorticity in a magnetized plasmas is derived. The equation is analogous to Ertel's theorem. In the long wave-length limit the potential vorticity equals the ratio of the gyro-frequency plus the E × B- and diamagnetic polarization densities to the particle density...

  12. The potential around a test charge in magnetized dusty plasmas

    International Nuclear Information System (INIS)

    Shukla, P.K.; Salimullah, M.

    1996-01-01

    The potential of a test dust particle in a magnetized dusty plasma is calculated, taking into account the dielectric constant associated with electrostatic ion-cyclotron waves. Besides the well-known Debye-Hueckel screening potential, an oscillatory potential distribution around a test dust particle is found, which strongly depends on the strength of the external magnetic field. copyright 1996 American Institute of Physics

  13. Magnetic field induced suppression of the forward bias current in Bi2Se3/Si Schottky barrier diodes

    Science.gov (United States)

    Jin, Haoming; Hebard, Arthur

    Schottky diodes formed by van der Waals bonding between freshly cleaved flakes of the topological insulator Bi2Se3 and doped silicon substrates show electrical characteristics in good agreement with thermionic emission theory. The motivation is to use magnetic fields to modulate the conductance of the topologically protected conducting surface state. This surface state in close proximity to the semiconductor surface may play an important role in determining the nature of the Schottky barrier. Current-voltage (I-V) and capacitance-voltage (C-V) characteristics were obtained for temperatures in the range 50-300 K and magnetic fields, both perpendicular and parallel to the interface, as high as 7 T. The I-V curve shows more than 6 decades linearity on semi-logarithmic plots, allowing extraction of parameters such as ideality (η), zero-voltage Schottky barrier height (SBH), and series resistance (Rs). In forward bias we observe a field-induced decrease in current which becomes increasingly more pronounced at higher voltages and lower temperature, and is found to be correlated with changes in Rs rather than other barrier parameters. A comparison of changes in Rs in both field direction will be made with magnetoresistance in Bi2Se3 transport measurement. The work is supported by NSF through DMR 1305783.

  14. Double-well potential in annular Josephson junction

    International Nuclear Information System (INIS)

    Shaju, P.D.; Kuriakose, V.C.

    2004-01-01

    A double-well potential suitable for quantum-coherent vortex tunnelling can be created in an annular Josephson junction by inserting a microshort in the junction and by applying an in-plane dc magnetic field. Analysis shows that the intensity of the magnetic field determines the depth of the potential well and the strength of the microshort controls the potential barrier height while a dc bias across the junction tilts the potential well. At milli-Kelvin temperatures, the system is expected to behave as a quantum two-level system and may be useful in designing vortex qubits

  15. The effect of magnetic field on chiral transmission in p-n-p graphene junctions

    Science.gov (United States)

    Li, Yuan; Wan, Qi; Peng, Yingzi; Wang, Guanqing; Qian, Zhenghong; Zhou, Guanghui; Jalil, Mansoor B. A.

    2015-12-01

    We investigate Klein tunneling in graphene heterojunctions under the influence of a perpendicular magnetic field via the non-equilibrium Green’s function method. We find that the angular dependence of electron transmission is deflected sideways, resulting in the suppression of normally incident electrons and overall decrease in conductance. The off-normal symmetry axis of the transmission profile was analytically derived. Overall tunneling conductance decreases to almost zero regardless of the potential barrier height when the magnetic field (B-field) exceeds a critical value, thus achieving effective confinement of Dirac fermions. The critical field occurs when the width of the magnetic field region matches the diameter of the cyclotron orbit. The potential barrier also induces distinct Fabry-Pérot fringe patterns, with a “constriction region” of low transmission when is close to the Fermi energy. Application of B-field deflects the Fabry-Pérot interference pattern to an off-normal angle. Thus, the conductance of the graphene heterojunctions can be sharply modulated by adjusting the B-field strength and the potential barrier height relative to the Fermi energy.

  16. The effect of magnetic field on chiral transmission in p-n-p graphene junctions.

    Science.gov (United States)

    Li, Yuan; Wan, Qi; Peng, Yingzi; Wang, Guanqing; Qian, Zhenghong; Zhou, Guanghui; Jalil, Mansoor B A

    2015-12-18

    We investigate Klein tunneling in graphene heterojunctions under the influence of a perpendicular magnetic field via the non-equilibrium Green's function method. We find that the angular dependence of electron transmission is deflected sideways, resulting in the suppression of normally incident electrons and overall decrease in conductance. The off-normal symmetry axis of the transmission profile was analytically derived. Overall tunneling conductance decreases to almost zero regardless of the potential barrier height V0 when the magnetic field (B-field) exceeds a critical value, thus achieving effective confinement of Dirac fermions. The critical field occurs when the width of the magnetic field region matches the diameter of the cyclotron orbit. The potential barrier also induces distinct Fabry-Pérot fringe patterns, with a "constriction region" of low transmission when V0 is close to the Fermi energy. Application of B-field deflects the Fabry-Pérot interference pattern to an off-normal angle. Thus, the conductance of the graphene heterojunctions can be sharply modulated by adjusting the B-field strength and the potential barrier height relative to the Fermi energy.

  17. Tunable magnetic vortex resonance in a potential well

    Science.gov (United States)

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

    2017-11-01

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

  18. Scattering of a two skyrmion configuration on potential holes or barriers in a model Landau-Lifshitz equation

    International Nuclear Information System (INIS)

    Collins, J C; Zakrzewski, W J

    2009-01-01

    The dynamics of a baby-skyrmion configuration, in a model Landau-Lifshitz equation, was studied in the presence of various potential obstructions. The baby-skyrmion configuration was constructed from two Q = 1 hedgehog solutions to the baby-skyrme model in (2+1) dimensions. The potential obstructions were created by introducing a new term into the Lagrangian which resulted in a localized inhomogeneity in the potential terms' coefficient. In the barrier system, the normal circular path was deformed as the skyrmions traversed the barrier. During the same period, it was seen that the skyrmions sped up as they went over the barrier. For critical values of the barrier height and width, the skyrmions were no longer bound and were free to separate. In the case of a potential hole, the baby skyrmions no longer formed a bound state and moved asymptotically along the axis of the hole. It is shown how to modify the definition of the angular momentum to include the effects of the obstructions, so that it is conserved

  19. Thickness-, Composition-, and Magnetic-Field-Dependent Complex Impedance Spectroscopy of Granular-Type-Barrier Co/Co-Al2O3/Co MTJs

    Science.gov (United States)

    Tuan, Nguyen Anh; Anh, Nguyen Tuan; Nga, Nguyen Tuyet; Tue, Nguyen Anh; Van Cuong, Giap

    2016-06-01

    The alternating-current (ac) electrical properties of granular-type-barrier magnetic tunnel junctions (GBMTJs) based on Co/Co x (Al2O3)1- x ( t)/Co trilayer structures have been studied using complex impedance spectroscopy (CIS). Their CIS characteristics were investigated in external magnetic fields varying from 0 kOe to 3 kOe as a function of Co composition x at 10 at.%, 25 at.%, and 35 at.%, with barrier layer thickness t of 20 nm to 90 nm. The influence of these factors on the behaviors of the ac impedance response of the GBMTJs was deeply investigated and attributed to the dielectric or conducting nature of the Co-Al2O3 barrier layer. The most remarkable typical phenomena observed in these behaviors, even appearing paradoxical, include lower impedance for thicker t for each given x, a declining trend of Z with increasing x, a clear decrease of Z with H, and especially a partition of Z into zones according to the H value. All these effects are analyzed and discussed to demonstrate that diffusion-type and mass-transfer-type phenomena can be inferred from processes such as spin tunneling and Coulomb or spin blockade in the Co-Al2O3 barrier layer.

  20. Electrostatic and magnetic fields in bilayer graphene

    Science.gov (United States)

    Jellal, Ahmed; Redouani, Ilham; Bahlouli, Hocine

    2015-08-01

    We compute the transmission probability through rectangular potential barriers and p-n junctions in the presence of a magnetic and electric fields in bilayer graphene taking into account contributions from the full four bands of the energy spectrum. For energy E higher than the interlayer coupling γ1 (E >γ1) two propagation modes are available for transport giving rise to four possible ways for transmission and reflection coefficients. However, when the energy is less than the height of the barrier the Dirac fermions exhibit transmission resonances and only one mode of propagation is available for transport. We study the effect of the interlayer electrostatic potential denoted by δ and variations of different barrier geometry parameters on the transmission probability.

  1. Potential and barrier study. Passive house and near-zero energy buildings; Potensial- og barrierestudie. Passivhus og naer nullenergibygninger

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2012-07-01

    The main conclusion from the analysis is that the barriers to realize both passive and near zero-energy buildings are significant. In addition to being a mere economic assessment indicates that 30-70% of the technical potential is not profitable depending on energy price levels, the barriers is reducing the economic potential with approximately another half as a realistic market potential.(eb)

  2. Superluminal tunneling of a relativistic half-integer spin particle through a potential barrier

    Directory of Open Access Journals (Sweden)

    Nanni Luca

    2017-11-01

    Full Text Available This paper investigates the problem of a relativistic Dirac half-integer spin free particle tunneling through a rectangular quantum-mechanical barrier. If the energy difference between the barrier and the particle is positive, and the barrier width is large enough, there is proof that the tunneling may be superluminal. For first spinor components of particle and antiparticle states, the tunneling is always superluminal regardless the barrier width. Conversely, the second spinor components of particle and antiparticle states may be either subluminal or superluminal depending on the barrier width. These results derive from studying the tunneling time in terms of phase time. For the first spinor components of particle and antiparticle states, it is always negative while for the second spinor components of particle and antiparticle states, it is always positive, whatever the height and width of the barrier. In total, the tunneling time always remains positive for particle states while it becomes negative for antiparticle ones. Furthermore, the phase time tends to zero, increasing the potential barrier both for particle and antiparticle states. This agrees with the interpretation of quantum tunneling that the Heisenberg uncertainty principle provides. This study’s results are innovative with respect to those available in the literature. Moreover, they show that the superluminal behaviour of particles occurs in those processes with high-energy confinement.

  3. A stochastic model for magnetic dynamics in single-molecule magnets

    Energy Technology Data Exchange (ETDEWEB)

    López-Ruiz, R., E-mail: rlruiz@ifi.unicamp.br [Instituto de Física Gleb Wataghin - Universidade Estadual de Campinas, 13083-859 Campinas (SP) (Brazil); Almeida, P.T. [Instituto de Física Gleb Wataghin - Universidade Estadual de Campinas, 13083-859 Campinas (SP) (Brazil); Vaz, M.G.F. [Instituto de Química, Universidade Federal Fluminense, 24020-150 Niterói (RJ) (Brazil); Novak, M.A. [Instituto de Física - Universidade Federal do Rio de Janeiro, 21941-972 Rio de Janeiro (RJ) (Brazil); Béron, F.; Pirota, K.R. [Instituto de Física Gleb Wataghin - Universidade Estadual de Campinas, 13083-859 Campinas (SP) (Brazil)

    2016-04-01

    Hysteresis and magnetic relaxation curves were performed on double well potential systems with quantum tunneling possibility via stochastic simulations. Simulation results are compared with experimental ones using the Mn{sub 12} single-molecule magnet, allowing us to introduce time dependence in the model. Despite being a simple simulation model, it adequately reproduces the phenomenology of a thermally activated quantum tunneling and can be extended to other systems with different parameters. Assuming competition between the reversal modes, thermal (over) and tunneling (across) the anisotropy barrier, a separation of classical and quantum contributions to relaxation time can be obtained. - Highlights: • Single-molecule magnets are modeled using a simple stochastic approach. • Simulation reproduces thermally-activated tunnelling magnetization reversal features. • The time is introduced in hysteresis and relaxation simulations. • We can separate the quantum and classical contributions to decay time.

  4. Transport barriers in bootstrap-driven tokamaks

    Science.gov (United States)

    Staebler, G. M.; Garofalo, A. M.; Pan, C.; McClenaghan, J.; Van Zeeland, M. A.; Lao, L. L.

    2018-05-01

    Experiments have demonstrated improved energy confinement due to the spontaneous formation of an internal transport barrier in high bootstrap fraction discharges. Gyrokinetic analysis, and quasilinear predictive modeling, demonstrates that the observed transport barrier is caused by the suppression of turbulence primarily from the large Shafranov shift. It is shown that the Shafranov shift can produce a bifurcation to improved confinement in regions of positive magnetic shear or a continuous reduction in transport for weak or negative magnetic shear. Operation at high safety factor lowers the pressure gradient threshold for the Shafranov shift-driven barrier formation. Two self-organized states of the internal and edge transport barrier are observed. It is shown that these two states are controlled by the interaction of the bootstrap current with magnetic shear, and the kinetic ballooning mode instability boundary. Election scale energy transport is predicted to be dominant in the inner 60% of the profile. Evidence is presented that energetic particle-driven instabilities could be playing a role in the thermal energy transport in this region.

  5. Filament shape versus coronal potential magnetic field structure

    Science.gov (United States)

    Filippov, B.

    2016-01-01

    Solar filament shape in projection on disc depends on the structure of the coronal magnetic field. We calculate the position of polarity inversion lines (PILs) of coronal potential magnetic field at different heights above the photosphere, which compose the magnetic neutral surface, and compare with them the distribution of the filament material in Hα chromospheric images. We found that the most of the filament material is enclosed between two PILs, one at a lower height close to the chromosphere and one at a higher level, which can be considered as a height of the filament spine. Observations of the same filament on the limb by the Solar Terrestrial Relations Observatory spacecraft confirm that the height of the spine is really very close to the value obtained from the PIL and filament border matching. Such matching can be used for filament height estimations in on-disc observations. Filament barbs are housed within protruding sections of the low-level PIL. On the base of simple model, we show that the similarity of the neutral surfaces in potential and non-potential fields with the same sub-photospheric sources is the reason for the found tendency for the filament material to gather near the potential-field neutral surface.

  6. Breaching Biological Barriers: Protein Translocation Domains as Tools for Molecular Imaging and Therapy

    Directory of Open Access Journals (Sweden)

    Benjamin L. Franc

    2003-10-01

    Full Text Available The lipid bilayer of a cell presents a significant barrier for the delivery of many molecular imaging reagents into cells at target sites in the body. Protein translocation domains (PTDs are peptides that breach this barrier. Conjugation of PTDs to imaging agents can be utilized to facilitate the delivery of these agents through the cell wall, and in some cases, into the cell nucleus, and have potential for in vitro and in vivo applications. PTD imaging conjugates have included small molecules, peptides, proteins, DNA, metal chelates, and magnetic nanoparticles. The full potential of the use of PTDs in novel in vivo molecular probes is currently under investigation. Cells have been labeled in culture using magnetic nanoparticles derivatized with a PTD and monitored in vivo to assess trafficking patterns relative to cells expressing a target antigen. In vivo imaging of PTD-mediated gene transfer to cells of the skin has been demonstrated in living animals. Here we review several natural and synthetic PTDs that have evolved in the quest for easier translocation across biological barriers and the application of these peptide domains to in vivo delivery of imaging agents.

  7. Triode for magnetic flux quanta.

    Science.gov (United States)

    Vlasko-Vlasov, Vitalii; Colauto, Fabiano; Benseman, Timothy; Rosenmann, Daniel; Kwok, Wai-Kwong

    We designed a magnetic vortex triode using an array of closely spaced soft magnetic Py strips on top of a Nb superconducting film. The strips act similar to the grid electrode in an electronic triode, where the electron flow is regulated by the grid potential. In our case, we tune the vortex motion by the magnetic charge potential of the strip edges, using a small magnetic field rotating in the film plane. The magnetic charges emerging at the stripe edges and proportional to the magnetization component perpendicular to the edge direction, form linear potential barriers or valleys for vortex motion in the superconducting layer. We directly imaged the normal flux penetration into the Py/Nb films and observed retarded or accelerated entry of the normal vortices depending on the in-plane magnetization direction in the stripes. The observed flux behavior is explained by interactions between magnetically charged lines and magnetic monopoles of vortices similar to those between electrically charged strings and point charges. We discuss the possibility of using our design for manipulation of individual vortices in high-speed, low-power superconducting electronic circuits. This work was supported by the U.S. DOE, Office of Science, Materials Sciences and Engineering Division, and Office of BES (contract DE-AC02-06CH11357). F. Colauto thanks the Sao Paulo Research Foundation FAPESP (Grant No. 2015/06.085-3).

  8. Magnetic materials in Japan research, applications and potential

    CERN Document Server

    2013-01-01

    Please note this is a Short Discount publication. This, the third report in Elsevier's Materials Technology in Japan series, concentrates on magnetic materials as a topic gaining worldwide attention, and each chapter looks not only at current research, but also describes the technology as it is being applied and its future potential. Magnetic-related research is the second largest field of research in Japan after semiconductors, with the estimated number of researchers and engineers engaged in magnetics-related activities currently at 20,000. This research report serves as both a review of

  9. The Fuel Efficiency of Maritime Transport. Potential for improvement and analysis of barriers

    Energy Technology Data Exchange (ETDEWEB)

    Faber, J.; Nelissen, D.; Smit, M. [CE Delft, Delft (Netherlands); Behrends, B. [Marena Ltd., s.l. (United Kingdom); Lee, D.S. [Manchester Metropolitan University, Machester (United Kingdom)

    2012-02-15

    There is significant potential to improve the fuel efficiency of ships and thus contribute to reducing greenhouse gas emissions from maritime transport. It has long been recognised that this potential is not being fully exploited, owing to the existence of non-market barriers. This report analyses the barriers to implementing fuel efficiency improvements, and concludes that the most important of these are the split incentive between ship owners and operators, a lack of trusted data on new technologies, and transaction costs associated with evaluating measures. As a result, in practice about a quarter of the cost-effective abatement potential is unavailable. There are several ways to overcome these barriers. The split incentive can - to some extent - be overcome by providing more detailed information on the fuel efficiency of vessels, making due allowance for operational profiles. This would allow fuel consumption to be more accurately projected and a larger share of efficiency benefits to accrue to ship owners, thus increasing the return on investment in fuel-saving technologies. This would also require changes to standard charter parties. The credibility of information on new technologies can be improved through intensive collaboration between suppliers of new technologies and shipping companies. In order to overcome risk, government subsidies could provide an incentive. This could have the additional benefit that governments could require publication of results.

  10. Potential barrier heights at metal on oxygen-terminated diamond interfaces

    Energy Technology Data Exchange (ETDEWEB)

    Muret, P., E-mail: pierre.muret@neel.cnrs.fr; Traoré, A.; Maréchal, A.; Eon, D. [Inst. NEEL, Univ. Grenoble Alpes, F-38042 Grenoble, France and CNRS, Inst. NEEL, F-38042 Grenoble (France); Pernot, J. [Univ. Grenoble Alpes, Inst. NEEL, F-38042 Grenoble, (France); CNRS, Inst. NEEL, F-38042 Grenoble, (France); Institut Universitaire de France, 103 Boulevard Saint-Michel, F-75005 Paris (France); Pinero, J. C.; Villar, M. P.; Araujo, D., E-mail: daniel.araujo@uca.es [Dpto. Ciencias de los Materiales, Universidad de Cádiz, 11510 Puerto Real (Cádiz) (Spain)

    2015-11-28

    Electrical properties of metal-semiconductor (M/SC) and metal/oxide/SC structures built with Zr or ZrO{sub 2} deposited on oxygen-terminated surfaces of (001)-oriented diamond films, comprised of a stack of lightly p-doped diamond on a heavily doped layer itself homoepitaxially grown on an Ib substrate, are investigated experimentally and compared to different models. In Schottky barrier diodes, the interfacial oxide layer evidenced by high resolution transmission electron microscopy and electron energy losses spectroscopy before and after annealing, and barrier height inhomogeneities accounts for the measured electrical characteristics until flat bands are reached, in accordance with a model which generalizes that by Tung [Phys. Rev. B 45, 13509 (1992)] and permits to extract physically meaningful parameters of the three kinds of interface: (a) unannealed ones, (b) annealed at 350 °C, (c) annealed at 450 °C with the characteristic barrier heights of 2.2–2.5 V in case (a) while as low as 0.96 V in case (c). Possible models of potential barriers for several metals deposited on well defined oxygen-terminated diamond surfaces are discussed and compared to experimental data. It is concluded that interface dipoles of several kinds present at these compound interfaces and their chemical evolution due to annealing are the suitable ingredients that are able to account for the Mott-Schottky behavior when the effect of the metal work function is ignored, and to justify the reverted slope observed regarding metal work function, in contrast to the trend always reported for all other metal-semiconductor interfaces.

  11. Heavy quark potential in a static and strong homogeneous magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Hasan, Mujeeb; Chatterjee, Bhaswar; Patra, Binoy Krishna [Indian Institute of Technology Roorkee, Department of Physics, Roorkee (India)

    2017-11-15

    We have investigated the properties of quarkonia in a thermal QCD medium in the background of strong magnetic field. For that purpose, we employ the Schwinger proper-time quark propagator in the lowest Landau level to calculate the one-loop gluon self-energy, which in the sequel gives the effective gluon propagator. As an artifact of strong magnetic field approximation (eB >> T{sup 2} and eB >> m{sup 2}), the Debye mass for massless flavors is found to depend only on the magnetic field which is the dominant scale in comparison to the scales prevalent in the thermal medium. However, for physical quark masses, it depends on both magnetic field and temperature in a low temperature and high magnetic field but the temperature dependence is very meager and becomes independent of the temperature beyond a certain temperature and magnetic field. With the above mentioned ingredients, the potential between heavy quark (Q) and anti-quark (anti Q) is obtained in a hot QCD medium in the presence of a strong magnetic field by correcting both short- and long-range components of the potential in the real-time formalism. It is found that the long-range part of the quarkonium potential is affected much more by magnetic field as compared to the short-range part. This observation facilitates us to estimate the magnetic field beyond which the potential will be too weak to bind Q anti Q together. For example, the J/ψ is dissociated at eB ∝ 10 m{sub π}{sup 2} and Υ is dissociated at eB ∝ 100 m{sub π}{sup 2} whereas its excited states, ψ{sup '} and Υ{sup '} are dissociated at smaller magnetic field eB = m{sub π}{sup 2}, 13 m{sub π}{sup 2}, respectively. (orig.)

  12. Calculation of the magnetic vector potential in the TJ-II

    International Nuclear Information System (INIS)

    Lopez Fraguas, A.; Lopez Bruna, D.; Romero, J. A.

    2005-01-01

    The properties of the vector magnetic potential and its usefulness to calculate magnetic fluxes in both stationary and time-dependent conditions are p revised in this report. We have adapted to the TJ-II Flexible Heliac efficient numerical expressions to calculate the vector potential, calculating in addition the magnetic flux with this formalism in circumstances whose complexity makes very convenient the use of the vector potential. The result on induced voltages offer theoretical support to the measurements of induced voltage due to the OH coils in the plasma, like the measurements provided by the loop voltage diagnostic installed in the TJ-II, as well as to the cylindrical approximation of the plasma often used to interpret experimental data. (Author) 11 refs

  13. Core density fluctuations in reverse magnetic shear plasmas with internal transport barrier on JT-60U

    International Nuclear Information System (INIS)

    Nazikian, R.; Shinohara, K.; Yoshino, R.; Fujita, T.; Shirai, H.; Kramer, G.T.

    1999-01-01

    First measurements of the radial correlation length of density fluctuations in JT-60U plasmas with internal transport barrier (ITB) is reported. The measurements are obtained using a newly installed correlation reflectometer operating in the upper X-mode. Before transport barrier formation in the low beam power current ramp-up phase of the discharge, reflectometer measurements indicate density fluctuation levels n-tilde/n∼0.1-0.2% and radial correlation lengths 2-3 cm (k r p i ≤0.5) in the central plasma region (r/a r p i ∼3. However, fluctuation levels are considerably higher than measured near the magnetic axis. Reflectometer measurements obtained at the foot of the ITB also indicate high fluctuation levels compared to measurements in the central region of the discharge. (author)

  14. Energy shift and conduction-to-valence band transition mediated by a time-dependent potential barrier in graphene

    Science.gov (United States)

    Chaves, Andrey; da Costa, D. R.; de Sousa, G. O.; Pereira, J. M.; Farias, G. A.

    2015-09-01

    We investigate the scattering of a wave packet describing low-energy electrons in graphene by a time-dependent finite-step potential barrier. Our results demonstrate that, after Klein tunneling through the barrier, the electron acquires an extra energy which depends on the rate of change of the barrier height with time. If this rate is negative, the electron loses energy and ends up as a valence band state after leaving the barrier, which effectively behaves as a positively charged quasiparticle.

  15. Effects of ExB velocity shear and magnetic shear on turbulence and transport in magnetic confinement devices

    International Nuclear Information System (INIS)

    Burrell, K.H.

    1996-11-01

    One of the scientific success stories of fusion research over the past decade is the development of the ExB shear stabilization model to explain the formation of transport barriers in magnetic confinement devices. This model was originally developed to explain the transport barrier formed at the plasma edge in tokamaks after the L (low) to H (high) transition. This concept has the universality needed to explain the edge transport barriers seen in limiter and divertor tokamaks, stellarators, and mirror machines. More recently, this model has been applied to explain the further confinement improvement from H (high)-mode to VH (very high)-mode seen in some tokamaks, where the edge transport barrier becomes wider. Most recently, this paradigm has been applied to the core transport barriers formed in plasmas with negative or low magnetic shear in the plasma core. These examples of confinement improvement are of considerable physical interest; it is not often that a system self-organizes to a higher energy state with reduced turbulence and transport when an additional source of free energy is applied to it. The transport decrease that is associated with ExB velocity shear effects also has significant practical consequences for fusion research. The fundamental physics involved in transport reduction is the effect of ExB shear on the growth, radial extent and phase correlation of turbulent eddies in the plasma. The same fundamental transport reduction process can be operational in various portions of the plasma because there are a number ways to change the radial electric field Er. An important theme in this area is the synergistic effect of ExB velocity shear and magnetic shear. Although the ExB velocity shear appears to have an effect on broader classes of microturbulence, magnetic shear can mitigate some potentially harmful effects of ExB velocity shear and facilitate turbulence stabilization

  16. Surface barrier and bulk pinning in MgB$_2$ superconductor

    OpenAIRE

    Pissas, M.; Moraitakis, E.; Stamopoulos, D.; Papavassiliou, G.; Psycharis, V.; Koutandos, S.

    2001-01-01

    We present a modified method of preparation of the new superconductor MgB$_2$. The polycrystalline samples were characterized using x-ray and magnetic measurements. The surface barriers control the isothermal magnetization loops in powder samples. In bulk as prepared samples we always observed symmetric magnetization loops indicative of the presence of a bulk pinning mechanism. Magnetic relaxation measurements in the bulk sample reveal a crossover of surface barrier to bulk pinning.

  17. Evaluating Zeta Potential and the Calcite/Aragonite Ratio as Potential Success Indicators for Magnetic Water Treatment

    National Research Council Canada - National Science Library

    Lambert, Kevin

    1999-01-01

    The potential benefits of anti-scale magnetic treatment (AMT) are not realized or reliably predicted because the factors measuring performance of magnetic treatment have either not been identified or are poorly defined...

  18. Complex energy eigenvalues of a linear potential with a parabolical barrier

    International Nuclear Information System (INIS)

    Malherbe, J.B.

    1978-01-01

    The physical meaning and restrictions of complex energy eigenvalues are briefly discussed. It is indicated that a quasi-stationary phase describes an idealised disintegration system. Approximate resonance-eigenvalues of the one dimensional Schrodinger equation with a linear potential and parabolic barrier are calculated by means of Connor's semiclassical method. This method is based on the generalized WKB-method of Miller and Good. The results obtained confirm the correctness of a model representation which explains the unusual distribution of eigenvalues by certain other linear potentials in a complex energy level [af

  19. Electric control of wave vector filtering in a hybrid magnetic-electric-barrier nanostructure

    Science.gov (United States)

    Kong, Yong-Hong; Lu, Ke-Yu; He, Ya-Ping; Liu, Xu-Hui; Fu, Xi; Li, Ai-Hua

    2018-06-01

    We theoretically investigate how to manipulate the wave vector filtering effect by a traverse electric field for electrons across a hybrid magnetic-electric-barrier nanostructure, which can be experimentally realized by depositing a ferromagnetic stripe and a Schottky-metal stripe on top and bottom of a GaAs/Al x Ga1- x As heterostructure, respectively. The wave vector filtering effect is found to be related closely to the applied electric field. Moreover, the wave vector filtering efficiency can be manipulated by changing direction or adjusting strength of the traverse electric field. Therefore, such a nanostructure can be employed as an electrically controllable electron-momentum filter for nanoelectronics applications.

  20. Effect of magnetic field on the impurity binding energy of the excited ...

    Indian Academy of Sciences (India)

    The effect of external magnetic field on the excited state energies in a spherical quantum dot was studied. The impurity energy and binding energy were calculated using the variational method within the effective mass approximation and finite barrier potential. The results showed that by increasing the magnetic field, the ...

  1. Effect of magnetic field on the impurity binding energy of the excited ...

    Indian Academy of Sciences (India)

    Abstract. The effect of external magnetic field on the excited state energies in a spher- ical quantum dot was studied. The impurity energy and binding energy were calculated using the variational method within the effective mass approximation and finite barrier potential. The results showed that by increasing the magnetic ...

  2. Electric-field control of magnetic domain-wall velocity in ultrathin cobalt with perpendicular magnetization.

    Science.gov (United States)

    Chiba, D; Kawaguchi, M; Fukami, S; Ishiwata, N; Shimamura, K; Kobayashi, K; Ono, T

    2012-06-06

    Controlling the displacement of a magnetic domain wall is potentially useful for information processing in magnetic non-volatile memories and logic devices. A magnetic domain wall can be moved by applying an external magnetic field and/or electric current, and its velocity depends on their magnitudes. Here we show that the applying an electric field can change the velocity of a magnetic domain wall significantly. A field-effect device, consisting of a top-gate electrode, a dielectric insulator layer, and a wire-shaped ferromagnetic Co/Pt thin layer with perpendicular anisotropy, was used to observe it in a finite magnetic field. We found that the application of the electric fields in the range of ± 2-3 MV cm(-1) can change the magnetic domain wall velocity in its creep regime (10(6)-10(3) m s(-1)) by more than an order of magnitude. This significant change is due to electrical modulation of the energy barrier for the magnetic domain wall motion.

  3. Dirac and non-Dirac conditions in the two-potential theory of magnetic charge

    Science.gov (United States)

    Scott, John; Evans, Timothy J.; Singleton, Douglas; Dzhunushaliev, Vladimir; Folomeev, Vladimir

    2018-05-01

    We investigate the Cabbibo-Ferrari, two-potential approach to magnetic charge coupled to two different complex scalar fields, Φ _1 and Φ _2, each having different electric and magnetic charges. The scalar field, Φ _1, is assumed to have a spontaneous symmetry breaking self-interaction potential which gives a mass to the "magnetic" gauge potential and "magnetic" photon, while the other "electric" gauge potential and "electric" photon remain massless. The magnetic photon is hidden until one reaches energies of the order of the magnetic photon rest mass. The second scalar field, Φ _2, is required in order to make the theory non-trivial. With only one field one can always use a duality rotation to rotate away either the electric or magnetic charge, and thus decouple either the associated electric or magnetic photon. In analyzing this system of two scalar fields in the Cabbibo-Ferrari approach we perform several duality and gauge transformations, which require introducing non-Dirac conditions on the initial electric and magnetic charges. We also find that due to the symmetry breaking the usual Dirac condition is altered to include the mass of the magnetic photon. We discuss the implications of these various conditions on the charges.

  4. Co2FeAl based magnetic tunnel junctions with BaO and MgO/BaO barriers

    Directory of Open Access Journals (Sweden)

    J. Rogge

    2015-07-01

    Full Text Available We succeed to integrate BaO as a tunneling barrier into Co2FeAl based magnetic tunnel junctions (MTJs. By means of Auger electron spectroscopy it could be proven that the applied annealing temperatures during BaO deposition and afterwards do not cause any diffusion of Ba neither into the lower Heusler compound lead nor into the upper Fe counter electrode. Nevertheless, a negative tunnel magnetoresistance (TMR ratio of -10% is found for Co2FeAl (24 nm / BaO (5 nm / Fe (7 nm MTJs, which can be attributed to the preparation procedure and can be explained by the formation of Co- and Fe-oxides at the interfaces between the Heusler and the crystalline BaO barrier by comparing with theory. Although an amorphous structure of the BaO barrier seems to be confirmed by high-resolution transmission electron microscopy (TEM, it cannot entirely be ruled out that this is an artifact of TEM sample preparation due to the sensitivity of BaO to moisture. By replacing the BaO tunneling barrier with an MgO/BaO double layer barrier, the electric stability could effectively be increased by a factor of five. The resulting TMR effect is found to be about +20% at room temperature, although a fully antiparallel state has not been realized.

  5. Potentials of surfaces in space

    International Nuclear Information System (INIS)

    Whipple, E.C.

    1981-01-01

    The potential of a body in space is determined by a balance between various charging currents such as the transfer of charge from plasma particles, photoemission, and secondary electron emission. These processes are evaluated for bodies in the solar system and in interstellar space under the headings; an overview of charging, survey of early work on charging, charging processes, effects of non-isotropic plasmas and magnetic and electric fields, calculation of surface potentials, differential charging, potential barriers and discharge processes, measurements of potential, potential modification and control on spacecraft, and astrophysical applications. (U.K.)

  6. Axisymmetric pumping scheme for the thermal barrier in a tandem mirror

    International Nuclear Information System (INIS)

    Li, X.Z.

    1985-09-01

    An axisymmetric pumping scheme is proposed to pump the particles that trap in a thermal barrier without invoking the neutral beam or geodesic curvature. In this scheme a magnetic scraper is moved uni-directionally on the barrier peak to push the barely trapped particles into the central cell. We utilize a potential jump that forms at the peak field for sufficiently strong pumping. The non-collisional catching effect has to be limited by setting an upper limit on the scraping frequency of the magnetic bump. On the other hand, the dynamic stability of the pumping scheme sets a lower limit on the scraping frequency. Using the variational method, we are able to estimate the window between these two limits, which seems feasible for the Tara reactor parameter set. A primary calculation shows that the magnetic bump, ΔB/B is about 10 -4 and the scraping frequency, nu/sub sc/, is about 10 +5 sec -1 , which are similar to the parameters required for those for drift pumping

  7. A combined vector potential-scalar potential method for FE computation of 3D magnetic fields in electrical devices with iron cores

    Science.gov (United States)

    Wang, R.; Demerdash, N. A.

    1991-01-01

    A method of combined use of magnetic vector potential based finite-element (FE) formulations and magnetic scalar potential (MSP) based formulations for computation of three-dimensional magnetostatic fields is introduced. In this method, the curl-component of the magnetic field intensity is computed by a reduced magnetic vector potential. This field intensity forms the basic of a forcing function for a global magnetic scalar potential solution over the entire volume of the region. This method allows one to include iron portions sandwiched in between conductors within partitioned current-carrying subregions. The method is most suited for large-scale global-type 3-D magnetostatic field computations in electrical devices, and in particular rotating electric machinery.

  8. Scattering and pair production by a potential barrier

    International Nuclear Information System (INIS)

    Nikishov, A.I.

    2004-01-01

    Scattering and electron-positron pair production by a one-dimensional electric barrier is considered in the framework of the S-matrix formalism. The solution of the Dirac equation are classified according to frequency sign. The Bogolyubov transformations relating the in- and out-states are given. It is shown that the norm of a solution of the wave equation is determined by the largest amplitude of its asymptotic form when x 3 → ±∞. For the Sauter-type potential we give the explicit expressions for the complete in- and out-sets of orthonormalized wave functions. It is noted that in principle virtual vacuum processes in external field influence the phase of the wave function of the scattered particle [ru

  9. Quantum mechanical streamlines. I - Square potential barrier

    Science.gov (United States)

    Hirschfelder, J. O.; Christoph, A. C.; Palke, W. E.

    1974-01-01

    Exact numerical calculations are made for scattering of quantum mechanical particles hitting a square two-dimensional potential barrier (an exact analog of the Goos-Haenchen optical experiments). Quantum mechanical streamlines are plotted and found to be smooth and continuous, to have continuous first derivatives even through the classical forbidden region, and to form quantized vortices around each of the nodal points. A comparison is made between the present numerical calculations and the stationary wave approximation, and good agreement is found between both the Goos-Haenchen shifts and the reflection coefficients. The time-independent Schroedinger equation for real wavefunctions is reduced to solving a nonlinear first-order partial differential equation, leading to a generalization of the Prager-Hirschfelder perturbation scheme. Implications of the hydrodynamical formulation of quantum mechanics are discussed, and cases are cited where quantum and classical mechanical motions are identical.

  10. Resonant tunneling of spin-wave packets via quantized states in potential wells.

    Science.gov (United States)

    Hansen, Ulf-Hendrik; Gatzen, Marius; Demidov, Vladislav E; Demokritov, Sergej O

    2007-09-21

    We have studied the tunneling of spin-wave pulses through a system of two closely situated potential barriers. The barriers represent two areas of inhomogeneity of the static magnetic field, where the existence of spin waves is forbidden. We show that for certain values of the spin-wave frequency corresponding to the quantized spin-wave states existing in the well formed between the barriers, the tunneling has a resonant character. As a result, transmission of spin-wave packets through the double-barrier structure is much more efficient than the sequent tunneling through two single barriers.

  11. Single-molecule magnets on a polymeric thin film as magnetic quantum bits

    Science.gov (United States)

    Ruiz-Molina, Daniel; Gomez, Jordi; Mas-Torrent, Marta; Balana, Ana Isabel; Domingo, Nues; Tejada, Javier; Martinez, Maria Teresa; Rovira, Concepcio; Veciana, Jaume

    2003-04-01

    Single-molecule magnets (SMM) have a large-spin ground state with appreciable magnetic anisotropy, resulting in a barrier for the spin reversal As a consequence, interesting magnetic properties such as out-of-phase ac magnetic susceptibility signals and stepwise magnetization hysteresis loops are observed. In addition to resonant magnetization tunnelling, during the last few years several other interesting phenomena have also been reported. The origin of the slow magnetization relaxation rates as well as of other phenomena are due to individual molecules rather than to long-range ordering; as confirmed by magnetization relaxation and heat capacity studies. Therefore, SMM represent nanoscale magnetic particles of a sharply defined size that offer the potential access to the ultimate high-density information storage devices as well as for quantum computing applications. However, if a truly molecular computational device based on SMM is to be achieved, new systematic studies that allow us to find a proper way to address properly oriented individual molecules or molecular aggregates onto the surface of a thin film, where each molecule or molecular aggregate can be used as a bit of information, are highly required. Here we report a new soft, reliable and simple methodology to address individual Mn12 molecules onto a film surface, as revealed by Atomic Force Microscopy (AFM) and Magnetic Force Microscopy (MFM) images. Moreover, the advantageous properties of polymeric matrices, such as flexibility, transparency and low density, make this type of materials very interesting for potential applications.

  12. Effect of parallel magnetic field on repetitively unipolar nanosecond pulsed dielectric barrier discharge under different pulse repetition frequencies

    Science.gov (United States)

    Liu, Yidi; Yan, Huijie; Guo, Hongfei; Fan, Zhihui; Wang, Yuying; Wu, Yun; Ren, Chunsheng

    2018-03-01

    A magnetic field, with the direction parallel to the electric field, is applied to the repetitively unipolar positive nanosecond pulsed dielectric barrier discharge. The effect of the parallel magnetic field on the plasma generated between two parallel-plate electrodes in quiescent air is experimentally studied under different pulse repetition frequencies (PRFs). It is indicated that only the current pulse in the rising front of the voltage pulse occurs, and the value of the current is increased by the parallel magnetic field under different PRFs. The discharge uniformity is improved with the decrease in PRF, and this phenomenon is also observed in the discharge with the parallel magnetic field. By using the line-ratio technique of optical emission spectra, it is found that the average electron density and electron temperature under the considered PRFs are both increased when the parallel magnetic field is applied. The incremental degree of average electron density is basically the same under the considered PRFs, while the incremental degree of electron temperature under the higher-PRFs is larger than that under the lower-PRFs. All the above phenomena are explained by the effect of parallel magnetic field on diffusion and dissipation of electrons.

  13. Quantum tunneling through a very narrow triangular potential barrier exact and WKB solution

    International Nuclear Information System (INIS)

    Ballo, P.; Harmatha, L.

    2011-01-01

    We have investigated the quantum-mechanical transmission of an electron in narrow potential barrier. It has been shown that application of WKB approximation could give enormous error if the slope of potential is rapid. Edification of this work is that unreasonable application of numerical approximations without the deep knowledge of theory should give wrong result. This we should remember every second, every day. (authors)

  14. Effect of nanodimensional polyethylenimine layer on surface potential barriers of hybrid structures based on silicon single crystal

    Science.gov (United States)

    Malyar, Ivan V.; Gorin, Dmitry A.; Stetsyura, Svetlana V.

    2013-01-01

    In this report we present the analysis of I-V curves for MIS-structures like silicon substrate / nanodimensional polyelectrolyte layer / metal probe (contact) which is promising for biosensors, microfluidic chips, different devices of molecular electronics, such as OLEDs, solar cells, where polyelectrolyte layers can be used to modify semiconductor surface. The research is directed to investigate the contact phenomena which influence the resulting signal of devices mentioned above. The comparison of I-V characteristics of such structures measured by scanning tunnel microscopy (contactless technique) and using contact areas deposited by thermal evaporation onto the organic layer (the contact one) was carried out. The photoassisted I-V measurements and complex analysis based on Simmons and Schottky models allow one to extract the potential barriers and to observe the changes of charge transport in MIS-structures under illumination and after polyelectrolyte adsorption. The direct correlation between the thickness of the deposited polyelectrolyte layer and both equilibrium tunnel barrier and Schottky barrier height was observed for hybrid structures with polyethylenimine. The possibility of control over the I-V curves of hybrid structure and the height of the potential barriers (for different charge transports) by illumination was confirmed. Based on experimental data and complex analysis the band diagrams were plotted which illustrate the changes of potential barriers for MIS-structures due to the polyelectrolyte adsorption and under the illumination.

  15. Formation of an internal transport barrier and magnetohydrodynamic activity in experiments with the controlled density of rational magnetic surfaces in the T-10 Tokamak

    International Nuclear Information System (INIS)

    Razumova, K. A.; Andreev, V. F.; Bel’bas, I. S.; Gorshkov, A. V.; Dnestrovskij, A. Yu.; Dyabilin, K. S.; Kislov, A. Ya.; Lysenko, S. E.; Notkin, G. E.; Timchenko, N. N.; Chudnovskiy, A. N.; Shelukhin, D. A.

    2013-01-01

    Results are presented from experiments on the formation of an internal electron transport barrier near the q = 1.5 rational surface in the T-10 tokamak. The experiments were carried out in the regime with off-axis electron cyclotron resonance (ECR) heating followed by a fast plasma current ramp-up. After suppressing sawtooth oscillations by off-axis ECR heating, an internal transport barrier began to form near the q = 1.5 rational surface. In the phase of the current ramp-up, the quality of the transport barrier improved; as a result, the plasma energy confinement time increased 2–2.5 times. The intentionally produced flattening of the profile of the safety factor q(r) insignificantly affected magnetohydrodynamic activity in the plasma column in spite of the theoretical possibility of formation of substantial m/n = 3/2 and 2/1 magnetic islands. Conditions are discussed under which the flattening of the profile of the safety factor q near low-order rational surfaces leads to the formation of either an internal transport barrier or the development of an island magnetic structure induced by tearing modes

  16. ICTs for rural development: potential applications and barriers involved

    Directory of Open Access Journals (Sweden)

    Anastasia Stratigea

    2013-03-01

    Full Text Available Rural policy nowadays is at the heart of the policy discussion in many countries all over the world, in the effort to address and effectively support the specific needs and opportunities of rural places and their population in the new era. Along these lines, the focus of the present paper is twofold: on the one hand it attempts to shed light on the role of ICTs and their applications as enabling tools empowering rural development; while on the other hand it explores the barriers appearing towards the adoption and use of ICTs in rural regions. In such a context, it firstly places emphasis on the evolving new rural development paradigm. Then, the range and potential of ICTs applications is explored, that can serve the implementation of the new policy paradigm in rural regions. It follows a discussion on the steps that are needed in order to develop value-added ICTs applications in rural regions and the barriers appearing in the adoption and use of ICTs in these regions. Finally, are presented some issues of policy concern in respect to the adoption and use of ICTs in a rural development perspective.

  17. Anomalous magnetic viscosity in α-Fe(Co)/(Nd,Pr)2Fe14B exchange-spring magnet

    International Nuclear Information System (INIS)

    Hai, Nguyen Hoang; Chau, Nguyen; Ngo, Duc-The; Gam, Duong Thi Hong

    2011-01-01

    This article presents an anomalous magnetic viscosity in α-Fe(Co)/(Nd,Pr) 2 Fe 14 B exchange-spring magnet. A similar effect has been observed in non-interacting or weakly interacting systems but not in a strong interacting magnetic systems. We reported a new procedure to measure magnetic relaxation under various magnetic fields. Changing the applied magnetic field by different field protocols during the reversal process, we found that a memory effect of the magnetization appeared if the field change is large enough. The mechanism of the phenomenon can be explained in the model of conventional magnetic reversal in strong ferromagnetic systems with an energy barrier distribution. The study of such magnetic relaxations can provide some information related to the energy barrier distribution function. - Highlights: → The memory effect was observed in a strong magnetically interacting system. → The memory effect on hard magnets can be explained by conventional reversal mechanism. → And it provides some information of the energy barrier for the reversal of magnetic moments.

  18. Origin of methyl torsional potential barrier – An overview

    Indian Academy of Sciences (India)

    Unknown

    The effect of skeletal flexing on the picture of barrier .... views to explain the origin of the barrier to this rotation have been proposed, but none of .... molecule, a model is always advantageous to predict the barrier and its cause in a given.

  19. A magnetic vector potential corresponding to a centrally conservative current element force

    International Nuclear Information System (INIS)

    Minteer, Timothy M

    2015-01-01

    The magnetic vector potential (Coulomb gauge) is commonly introduced in magnetostatic chapters of electromagnetism textbooks. However, what is not typically presented are the infinite subsets of the Coulomb gauge associated with differential current elements. This work provides a comparison of various differential magnetic vector potentials, differential magnetostatic potential energies, as well as differential current element forces as a collective work not available elsewhere. The differential magnetic vector potential highlighted in this work is the Coulomb–Ampère gauge corresponding to the centrally conservative Ampère current element force. The centrally conservative force is modeled as a mean valued continual exchange of energy carrier mediators accounting for both the differential magnetostatic potential energy and Ampère current element force of two differential current elements. (paper)

  20. Quantum size effects on spin-transfer torque in a double barrier magnetic tunnel junction with a nonmagnetic-metal (semiconductor) spacer

    International Nuclear Information System (INIS)

    Daqiq, Reza; Ghobadi, Nader

    2016-01-01

    We study the quantum size effects of an MgO-based double barrier magnetic tunnel junction with a nonmagnetic-metal (DBMTJ-NM) (semiconductor (DBMTJ-SC)) spacer on the charge current and the spin-transfer torque (STT) components using non-equilibrium Green's function (NEGF) formalism. The results show oscillatory behavior due to the resonant tunneling effect depending on the structure parameters. We find that the charge current and the STT components in the DBMTJ-SC demonstrate the magnitude enhancement in comparison with the DBMTJ-NM. The bias dependence of the STT components in a DBMTJ-NM shows different behavior in comparison with spin valves and conventional MTJs. Therefore, by choosing a specific SC spacer with suitable thickness in a DBMTJ the charge current and the STT components significantly increase so that one can design a device with high STT and faster magnetization switching. - Highlights: • The quantum size effects are studied in double barrier magnetic tunnel junctions. • Spin torque (ST) components oscillate for increasing of middle spacer thicknesses. • Due to the resonant tunneling in the quantum well, oscillations have appeared. • By replacement a metal spacer with a semiconductor (ZnO) ST has increased. • The ST components vs. bias show gradually decreasing unlike spin valves or MTJs.

  1. Quantum size effects on spin-transfer torque in a double barrier magnetic tunnel junction with a nonmagnetic-metal (semiconductor) spacer

    Energy Technology Data Exchange (ETDEWEB)

    Daqiq, Reza; Ghobadi, Nader

    2016-07-15

    We study the quantum size effects of an MgO-based double barrier magnetic tunnel junction with a nonmagnetic-metal (DBMTJ-NM) (semiconductor (DBMTJ-SC)) spacer on the charge current and the spin-transfer torque (STT) components using non-equilibrium Green's function (NEGF) formalism. The results show oscillatory behavior due to the resonant tunneling effect depending on the structure parameters. We find that the charge current and the STT components in the DBMTJ-SC demonstrate the magnitude enhancement in comparison with the DBMTJ-NM. The bias dependence of the STT components in a DBMTJ-NM shows different behavior in comparison with spin valves and conventional MTJs. Therefore, by choosing a specific SC spacer with suitable thickness in a DBMTJ the charge current and the STT components significantly increase so that one can design a device with high STT and faster magnetization switching. - Highlights: • The quantum size effects are studied in double barrier magnetic tunnel junctions. • Spin torque (ST) components oscillate for increasing of middle spacer thicknesses. • Due to the resonant tunneling in the quantum well, oscillations have appeared. • By replacement a metal spacer with a semiconductor (ZnO) ST has increased. • The ST components vs. bias show gradually decreasing unlike spin valves or MTJs.

  2. Controlling the spin-torque efficiency with ferroelectric barriers

    KAUST Repository

    Useinov, A.; Chshiev, M.; Manchon, Aurelien

    2015-01-01

    Nonequilibrium spin-dependent transport in magnetic tunnel junctions comprising a ferroelectric barrier is theoretically investigated. The exact solutions of the free electron Schrödinger equation for electron tunneling in the presence of interfacial screening are obtained by combining Bessel and Airy functions. We demonstrate that the spin transfer torque efficiency, and more generally the bias dependence of tunneling magneto- and electroresistance, can be controlled by switching the ferroelectric polarization of the barrier. In particular, the critical voltage at which the in-plane torque changes sign can be strongly enhanced or reduced depending on the direction of the ferroelectric polarization of the barrier. This effect provides a supplementary way to electrically control the current-driven dynamic states of the magnetization and related magnetic noise in spin transfer devices.

  3. Controlling the spin-torque efficiency with ferroelectric barriers

    KAUST Repository

    Useinov, A.

    2015-02-11

    Nonequilibrium spin-dependent transport in magnetic tunnel junctions comprising a ferroelectric barrier is theoretically investigated. The exact solutions of the free electron Schrödinger equation for electron tunneling in the presence of interfacial screening are obtained by combining Bessel and Airy functions. We demonstrate that the spin transfer torque efficiency, and more generally the bias dependence of tunneling magneto- and electroresistance, can be controlled by switching the ferroelectric polarization of the barrier. In particular, the critical voltage at which the in-plane torque changes sign can be strongly enhanced or reduced depending on the direction of the ferroelectric polarization of the barrier. This effect provides a supplementary way to electrically control the current-driven dynamic states of the magnetization and related magnetic noise in spin transfer devices.

  4. Oscillations in magnetoresistance and interlayer coupling in magnetic sandwich structures

    International Nuclear Information System (INIS)

    Barnas, J.; Bulka, B.

    1997-01-01

    Kubo formalism is used to calculate the magnetoresistance due to magnetization rotation in a structure consisting two magnetic films separated by nonmagnetic layer. In the approximation of an uniform relaxation time of each layer, the oscillatory term in magnetoresistance corresponds to the oscillation period which depends on the potential barriers at the interfaces. This period is longer than the oscillation period observed in the coupling parameter. (author)

  5. Targeted drug delivery to the brain using magnetic nanoparticles.

    Science.gov (United States)

    Thomsen, Louiza Bohn; Thomsen, Maj Schneider; Moos, Torben

    2015-01-01

    Brain capillary endothelial cells denote the blood-brain barrier (BBB), and conjugation of nanoparticles with antibodies that target molecules expressed by these endothelial cells may facilitate their uptake and transport into the brain. Magnetic nanoparticles can be encapsulated in liposomes and carry large molecules with therapeutic potential, for example, siRNA, cDNA and polypeptides. An additional approach to enhance the transport of magnetic nanoparticles across the BBB is the application of extracranially applied magnetic force. Stepwise targeting of magnetic nanoparticles to brain capillary endothelial cells followed by transport through the BBB using magnetic force may prove a novel mechanism for targeted therapy of macromolecules to the brain.

  6. Tuning anisotropy barriers in a family of tetrairon(III) single-molecule magnets with an S = 5 ground state.

    Science.gov (United States)

    Accorsi, Stefania; Barra, Anne-Laure; Caneschi, Andrea; Chastanet, Guillaume; Cornia, Andrea; Fabretti, Antonio C; Gatteschi, Dante; Mortalo, Cecilia; Olivieri, Emiliano; Parenti, Francesca; Rosa, Patrick; Sessoli, Roberta; Sorace, Lorenzo; Wernsdorfer, Wolfgang; Zobbi, Laura

    2006-04-12

    Tetrairon(III) Single-Molecule Magnets (SMMs) with a propeller-like structure exhibit tuneable magnetic anisotropy barriers in both height and shape. The clusters [Fe4(L1)2(dpm)6] (1), [Fe4(L2)2(dpm)6] (2), [Fe4(L3)2(dpm)6].Et2O (3.Et2O), and [Fe4(OEt)3(L4)(dpm)6] (4) have been prepared by reaction of [Fe4(OMe)6(dpm)6] (5) with tripodal ligands R-C(CH2OH)3 (H3L1, R = Me; H3L2, R = CH2Br; H3L3, R = Ph; H3L4, R = tBu; Hdpm = dipivaloylmethane). The iron(III) ions exhibit a centered-triangular topology and are linked by six alkoxo bridges, which propagate antiferromagnetic interactions resulting in an S = 5 ground spin state. Single crystals of 4 reproducibly contain at least two geometric isomers. From high-frequency EPR studies, the axial zero-field splitting parameter (D) is invariably negative, as found in 5 (D = -0.21 cm(-1)) and amounts to -0.445 cm(-1) in 1, -0.432 cm(-1) in 2, -0.42 cm(-1) in 3.Et2O, and -0.27 cm(-1) in 4 (dominant isomer). The anisotropy barrier Ueff determined by AC magnetic susceptibility measurements is Ueff/kB = 17.0 K in 1, 16.6 K in 2, 15.6 K in 3.Et2O, 5.95 K in 4, and 3.5 K in 5. Both |D| and U(eff) are found to increase with increasing helical pitch of the Fe(O2Fe)3 core. The fourth-order longitudinal anisotropy parameter B4(0), which affects the shape of the anisotropy barrier, concomitantly changes from positive in 1 ("compressed parabola") to negative in 5 ("stretched parabola"). With the aid of spin Hamiltonian calculations the observed trends have been attributed to fine modulation of single-ion anisotropies induced by a change of helical pitch.

  7. Description of the Magnetic Field and Divergence of Multisolenoid Aharonov-Bohm Potential

    Directory of Open Access Journals (Sweden)

    Araz R. Aliev

    2016-01-01

    Full Text Available Explicit formulas for the magnetic field and divergence of multisolenoid Aharonov-Bohm potential are obtained; the mathematical essence of this potential is explained. It is shown that the magnetic field and divergence of this potential are very singular generalized functions concentrated at a finite number of thin solenoids. Deficiency index is found for the minimal operator generated by the Aharonov-Bohm differential expression.

  8. The influence of magnetic field strength in ionization stage on ion transport between two stages of a double stage Hall thruster

    International Nuclear Information System (INIS)

    Yu Daren; Song Maojiang; Li Hong; Liu Hui; Han Ke

    2012-01-01

    It is futile for a double stage Hall thruster to design a special ionization stage if the ionized ions cannot enter the acceleration stage. Based on this viewpoint, the ion transport under different magnetic field strengths in the ionization stage is investigated, and the physical mechanisms affecting the ion transport are analyzed in this paper. With a combined experimental and particle-in-cell simulation study, it is found that the ion transport between two stages is chiefly affected by the potential well, the potential barrier, and the potential drop at the bottom of potential well. With the increase of magnetic field strength in the ionization stage, there is larger plasma density caused by larger potential well. Furthermore, the potential barrier near the intermediate electrode declines first and then rises up while the potential drop at the bottom of potential well rises up first and then declines as the magnetic field strength increases in the ionization stage. Consequently, both the ion current entering the acceleration stage and the total ion current ejected from the thruster rise up first and then decline as the magnetic field strength increases in the ionization stage. Therefore, there is an optimal magnetic field strength in the ionization stage to guide the ion transport between two stages.

  9. Field-aligned plasma-potential structure formed by local electron cyclotron resonance

    International Nuclear Information System (INIS)

    Hatakeyama, Rikizo; Kaneko, Toshiro; Sato, Noriyoshi

    2001-01-01

    The significance of basic experiments on field-aligned plasma-potential structure formed by local electron cyclotron resonance (ECR) is claimed based on the historical development of the investigation on electric double layer and electrostatic potential confinement of open-ended fusion-oriented plasmas. In the presence of a single ECR point in simple mirror-type configurations of magnetic field, a potential dip (thermal barrier) appears around this point, being followed by a subsequent potential hump (plug potential) along a collisionless plasma flow. The observed phenomenon gives a clear-cut physics to the formation of field-aligned plug potential with thermal barrier, which is closely related to the double layer formation triggered by a negative dip. (author)

  10. Fabrication of Mg-X-O (X = Fe, Co, Ni, Cr, Mn, Ti, V, and Zn) barriers for magnetic tunnel junctions

    Science.gov (United States)

    Yakushiji, K.; Kitagawa, E.; Ochiai, T.; Kubota, H.; Shimomura, N.; Ito, J.; Yoda, H.; Yuasa, S.

    2018-05-01

    We fabricated magnetic tunnel junctions with a 3d-transition material(X)-doped MgO (Mg-X-O) barrier, and evaluated the effect of the doping on magnetoresistance (MR) and microstructure. Among the variations of X (X = Fe, Co, Ni, Cr, Mn, Ti, V, and Zn), X = Fe and Mn showed a high MR ratio of more than 100%, even at a low resistance-area product of 3 Ωμm2. The microstructure analysis revealed that (001) textured orientation formed for X = Fe and Mn despite substantial doping (about 10 at%). The elemental mappings indicated that Fe atoms in the Mg-Fe-O barrier were segregated at the interfaces, while Mn atoms were evenly involved in the Mg-Mn-O barrier. This suggests that MgO has high adaptability for Fe and Mn dopants in terms of high MR ratio.

  11. Potential facilitators and barriers to adopting standard treatment guidelines in clinical practice.

    Science.gov (United States)

    Sharma, Sangeeta; Pandit, Ajay; Tabassum, Fauzia

    2017-04-18

    Purpose The purpose of this paper is to assess medicines information sources accessed by clinicians, if sources differed in theory and practice and to find out the barriers and facilitators to effective guideline adoption. Design/methodology/approach In all, 183 doctors were surveyed. Barriers and facilitators were classified as: communication; potential adopters; innovation; organization characteristics and environmental/social/economic context. Findings Most of the clinicians accessed multiple information sources including standard treatment guidelines, but also consulted seniors/colleagues in practice. The top three factors influencing clinical practice guideline adoption were innovation characteristics, environmental context and individual characteristics. The respondents differed in the following areas: concerns about flexibility offered by the guideline; denying patients' individuality; professional autonomy; insights into gaps in current practice and evidence-based practice; changing practices with little or no benefit. Barriers included negative staff attitudes/beliefs, guideline integration into organizational structures/processes, time/resource constraints. Fearing third parties (government and insurance companies) restricting medicines reimbursement and poor liability protection offered by the guidelines emerged as the barriers. Facilitators include aligning organizational structures/processes with the innovation; providing leadership support to guide diffusion; increasing awareness and enabling early innovation during pre/in-service training, with regular feedback on outcomes and use. Practical implications Guideline adoption in clinical practice is partly within doctors' control. There are other key prevailing factors in the local context such as environmental, social context, professional and organizational culture affecting its adoption. Organizational policy and accreditation standards necessitating adherence can serve as a driver. Originality

  12. JET internal transport barriers: experiment vs theory

    Energy Technology Data Exchange (ETDEWEB)

    Esposito, B [Associazione Euratom - ENEA sulla Fusione, C.R. Frascati, CP 65, I-00040, Frascati, Rome (Italy); Crisanti, F [Associazione Euratom - ENEA sulla Fusione, C.R. Frascati, CP 65, I-00040, Frascati, Rome (Italy); Parail, V [Euratom/UKAEA Fusion Association, Cuhlam Science Centre, Abingdon, Oxon OX14 3DB (United Kingdom); Maget, P [Association Euratom - CEA pour la Fusion, CEA Cadarache, F-13108 Saint Paul-lez-Durance Cedex (France); Baranov, Y [Euratom/UKAEA Fusion Association, Cuhlam Science Centre, Abingdon, Oxon OX14 3DB (United Kingdom); Becoulet, A [Association Euratom - CEA pour la Fusion, CEA Cadarache, F-13108 Saint Paul-lez-Durance Cedex (France); Castaldo, C [Associazione Euratom - ENEA sulla Fusione, C.R. Frascati, CP 65, I-00040, Frascati, Rome (Italy); Challis, C D [Euratom/UKAEA Fusion Association, Cuhlam Science Centre, Abingdon, Oxon OX14 3DB (United Kingdom); Angelis, R De [Associazione Euratom - ENEA sulla Fusione, C.R. Frascati, CP 65, I-00040, Frascati, Rome (Italy); Garbet, X [Association Euratom - CEA pour la Fusion, CEA Cadarache, F-13108 Saint Paul-lez-Durance Cedex (France); Giroud, C [Association Euratom - CEA pour la Fusion, CEA Cadarache, F-13108 Saint Paul-lez-Durance Cedex (France); Hawkes, N [Euratom/UKAEA Fusion Association, Cuhlam Science Centre, Abingdon, Oxon OX14 3DB (United Kingdom); Joffrin, E [Association Euratom - CEA pour la Fusion, CEA Cadarache, F-13108 Saint Paul-lez-Durance Cedex (France); Litaudon, X [Association Euratom - CEA pour la Fusion, CEA Cadarache, F-13108 Saint Paul-lez-Durance Cedex (France); Mazon, D [Association Euratom - CEA pour la Fusion, CEA Cadarache, F-13108 Saint Paul-lez-Durance Cedex (France); Riva, M [Associazione Euratom - ENEA sulla Fusione, C.R. Frascati, CP 65, I-00040, Frascati, Rome (Italy); Zastrow, K D [Euratom/UKAEA Fusion Association, Cuhlam Science Centre, Abingdon, Oxon OX14 3DB (United Kingdom)

    2003-06-01

    A large variety of JET discharges with internal transport barriers (ITBs) has been analysed in order to determine the main features which characterize turbulence stabilization at the barrier. It is found that the location of barriers is well correlated with regions where the ExB flow shearing rate exceeds the linear growth rate of the ion temperature gradient mode instability ({gamma}{sub {eta}{sub i}}). A key point is the dependence of {gamma}{sub {eta}{sub i}} on the magnetic shear: in the discharges of this database the reduction of {gamma}{sub {eta}{sub i}} associated to very low or null magnetic shear favours the formation of an ITB. After the ITB formation a positive feedback occurs in which the ExB flow shear mechanism has the leading role and the position of the barrier may be no longer linked to the low shear region.

  13. 2D Analytical Modeling of Magnetic Vector Potential in Surface Mounted and Surface Inset Permanent Magnet Machines

    Directory of Open Access Journals (Sweden)

    A. Jabbari

    2017-12-01

    Full Text Available A 2D analytical method for magnetic vector potential calculation in inner rotor surface mounted and surface inset permanent magnet machines considering slotting effects, magnetization orientation and winding layout has been proposed in this paper. The analytical method is based on the resolution of Laplace and Poisson equations as well as Maxwell equation in quasi- Cartesian coordinate by using sub-domain method and hyperbolic functions. The developed method is applied on the performance computation of two prototypes surface mounted permanent magnet motors and two prototypes surface inset permanent magnet motors. A radial and a parallel magnetization orientation is considered for each type of motor. The results of these models are validated through FEM method.

  14. Anti-collimation of ballistic electrons by a potential barrier

    Science.gov (United States)

    Coleridge, P. T.; Taylor, R. P.; Sachrajda, A. S.; Adams, J. A.

    1994-03-01

    A pair of Quantum Point Contacts separated by a continuous barrier have been fabricated using the surface gate technique. Transport measurements for each component of this system and for various combinations have shown both additive and non-additive behaviour. The results are explained by a combination of reflection by the barrier of electrons collimated by the Quantum Point Contacts and transport by diffusion across the barrier.

  15. High and tunable spin current induced by magnetic-electric fields in a single-mode spintronic device

    International Nuclear Information System (INIS)

    Bala Kumar, S; Jalil, M B A; Tan, S G; Liang, G-C

    2009-01-01

    We proposed that a viable form of spin current transistor is one to be made from a single-mode device which passes electrons through a series of magnetic-electric barriers built into the device. The barriers assume a wavy spatial profile across the conduction path due to the inevitable broadening of the magnetic fields. Field broadening results in a linearly increasing vector potential across the conduction channel, which increases spin polarization. We have identified that the important factors for generating high spin polarization and conductance modulation are the low source-drain bias, the broadened magnetic fields, and the high number of FM gates within a fixed channel length.

  16. A Rising Female Empire? : Exploring the potential barriers women face in achieving leadership positions in the humanitarian sector

    OpenAIRE

    Eriksson, Lina Elisabeth

    2015-01-01

    This research aims to explore how women and men view and perceive potential barriers to women achieving leadership positions in the humanitarian sector. Female leadership is so far an under-researched area within the humanitarian sector, so it is unknown whether females encounter any barriers in accessing and attaining leadership positions. Three categories were identified; identity, perception and challenges through which the views and barriers are explored. Semi-structured interviews were c...

  17. A new barrier potential and alpha-decay half-lives of even–even nuclei in the 82⩽Z⩽92 regime

    Energy Technology Data Exchange (ETDEWEB)

    Hassanabadi, Hasan [Physics Department, Shahrood University of Technology, Shahrood (Iran, Islamic Republic of); Javadimanesh, ELham, E-mail: elham_javadimanesh89@yahoo.com [Department of Basic Sciences, Shahrood Branch, Islamic Azad University, Shahrood (Iran, Islamic Republic of); Zarrinkamar, Saber [Department of Basic Sciences, Garmsar Branch, Islamic Azad University, Garmsar (Iran, Islamic Republic of)

    2013-05-15

    The alpha-decay half-life in a nuclear reaction is mainly affected by the penetration probability, which itself depends on the choice of the barrier potential. Here, we propose a new barrier potential to investigate the alpha-decay half-lives in the even–even nuclei from {sup 178}Po to {sup 238}U. The obtained results are motivating.

  18. An educational path for the magnetic vector potential and its physical implications

    International Nuclear Information System (INIS)

    Barbieri, S; Cavinato, M; Giliberti, M

    2013-01-01

    We present an educational path for the magnetic vector potential A aimed at undergraduate students and pre-service physics teachers. Starting from the generalized Ampère–Laplace law, in the framework of a slowly varying time-dependent field approximation, the magnetic vector potential is written in terms of its empirical references, i.e. the conduction currents. Therefore, once the currents are known, our approach allows for a clear and univocal physical determination of A, overcoming the mathematical indeterminacy due to the gauge transformations. We have no need to fix a gauge, since for slowly varying time-dependent electric and magnetic fields, the ‘natural’ gauge for A is the Coulomb one. We stress the difference between our approach and those usually presented in the literature. Finally, a physical interpretation of the magnetic vector potential is discussed and some examples of the calculation of A are analysed. (paper)

  19. Electron holography study on the microstructure of magnetic tunnelling junctions

    International Nuclear Information System (INIS)

    Xu, Q.Y.; Wang, Y.G.; You, B.; Du, J.; Hu, A.; Zhang, Z.

    2004-01-01

    Electron holography was applied to study the microstructure evolution of magnetic tunnelling junctions (MTJs) CoFe/AlO x /Co annealed at different temperatures. A mean inner potential barrier was observed in the as-deposited MTJ sample, while it was changed to a potential well after a 200 deg. C or a 400 deg. C annealing. It is suggested that the oxygen atoms were redistributed during the annealing, which left metallic atoms acting as acceptors to confine the electrons, leading to the decrease of the potential of the AlO x barrier layer. The results suggest that the electron holography may be a useful tool for the study of the microstructure of amorphous materials

  20. Magnetic microstructure of candidates for epitaxial dual Heusler magnetic tunnel junctions

    International Nuclear Information System (INIS)

    Kaiser, A.; Banerjee, D.; Rata, A.D.; Wiemann, C.; Cramm, S.; Schneider, C.M.

    2009-01-01

    Heusler alloys are considered as interesting ferromagnetic electrode materials for magnetic tunnel junctions, because of their high spin polarization. We, therefore, investigated the micromagnetic properties in a prototypical thin film system comprising two different Heusler phases Co 2 MnSi (CMS) and Co 2 FeSi (CFS) separated by a MgO barrier. The magnetic microstructure was investigated by X-ray photoemission electron microscopy (XPEEM). We find a strong influence of the Heusler phase formation process on the magnetic domain patterns. SiO 2 /V/CMS/MgO/CFS and SiO 2 /V/CFS/MgO/CMS trilayer structures exhibit a strikingly different magnetic behavior, which is due to pinhole coupling through the MgO barrier and a strong thickness dependence of the magnetic ordering in Co 2 MnSi

  1. Scattering matrix for magnetic potentials with Coulomb decay at infinity

    CERN Document Server

    Yafaev, D

    2003-01-01

    We consider the Schr\\"odinger operator $H$ in the space $L_2({\\R}^d)$ with a magnetic potential $A(x)$ decaying as $|x|^{-1}$ at infinity and satisfying the transversal gauge condition $ =0$. Such potentials correspond, for example, to magnetic fields $B(x)$ with compact support and hence are quite general. Our goal is to study properties of the scattering matrix $S(\\lambda)$ associated to the operator $H$. In particular, we find the essential spectrum $\\sigma_{ess}$ of $S(\\lambda)$ in terms of the behaviour of $A(x)$ at infinity. It turns out that $\\sigma_{ess}(S(\\lambda))$ is normally a rich subset of the unit circle ${\\Bbb T}$ or even coincides with ${\\Bbb T}$. We find also the diagonal singularity of the scattering amplitude (of the kernel of $S(\\lambda)$ regarded as an integral operator). In general, $S(\\lambda)$ is a sum of a multiplication operator and of a singular integral operator. However, if the magnetic field decreases faster than $ |x|^{-2}$ for $d\\geq 3$ (and the total magnetic flux is an integ...

  2. Effects of continuous feedback on households’ electricity consumption: Potentials and barriers

    International Nuclear Information System (INIS)

    Nilsson, Andreas; Bergstad, Cecilia Jakobsson; Thuvander, Liane; Andersson, David; Andersson, Kristin; Meiling, Pär

    2014-01-01

    Highlights: • Two studies on conservation behaviours using in home-displays are presented. • No significant effects on electricity consumption were found. • Display feedback does not necessarily contribute to lower electricity use. • Interviews conclude that different types of feedback techniques should be combined. • Two important barriers are difficulties to understand the display and a lack of interest. - Abstract: Two field experiments were carried out to study (a) the effects on energy savings of continuous visual feedback via in-home displays, and (b) the motives for responding or not. In study 1, 40 participants living in separate or semi-detached houses in two different towns participated. All participants received a questionnaire and a list of possible energy saving measures. Households were then randomly assigned to an experimental condition (display) or a control condition (no display). In study 2, 32 households in rented apartments participated. No significant differences between the conditions were found for either of the studies. In study 2, semi-structured interviews were conducted among nine of the households. Through an analysis of interview transcripts barriers were identified explaining why the feedback intervention was not sufficient to change behaviour and reduce consumption. The barriers experienced indicate that there is a risk of overconfidence in IHDs. For the development of energy policies and more wide-scale implementation, it is important to be aware of the potential obstacles to success

  3. Self-regulation of turbulence bursts and transport barriers

    International Nuclear Information System (INIS)

    Floriani, E; Ciraolo, G; Ghendrih, Ph; Sarazin, Y; Lima, R

    2013-01-01

    The interplay between turbulent bursts and transport barriers is analyzed with a simplified model of interchange turbulence in magnetically confined plasmas. The turbulent bursts spread into the transport barriers and, depending on the competing magnitude of the burst and stopping capability of the barrier, can burn through. Simulations of two models of transport barriers are presented: a hard barrier where interchange turbulence modes are stable in a prescribed region and a soft barrier with external plasma biasing. The response of the transport barriers to the non-linear perturbations of the turbulent bursts, addressed in a predator–prey approach, indicates that the barriers monitor an amplification factor of the turbulent bursts, with amplification smaller than one for most bursts and, in some cases, amplification factors that can significantly exceed unity. The weak barriers in corrugated profiles and magnetic structures, as well as the standard barriers, are characterized by these transmission properties, which then regulate the turbulent burst transport properties. The interplays of barriers and turbulent bursts are modeled as competing stochastic processes. For different classes of the probability density function (PDF) of these processes, one can predict the heavy tail properties of the bursts downstream from the barrier, either exponential for a leaky barrier, or with power laws for a tight barrier. The intrinsic probing of the transport barriers by the turbulent bursts thus gives access to the properties of the barriers. The main stochastic variables are the barrier width and the spreading distance of the turbulent bursts within the barrier, together with their level of correlation. One finds that in the case of a barrier with volumetric losses, such as radiation or particle losses as addressed in our present simulations, the stochastic model predicts a leaky behavior with an exponential PDF of escaping turbulent bursts in agreement with the simulation

  4. Strong exchange and magnetic blocking in N₂³⁻-radical-bridged lanthanide complexes.

    Science.gov (United States)

    Rinehart, Jeffrey D; Fang, Ming; Evans, William J; Long, Jeffrey R

    2011-05-22

    Single-molecule magnets approach the ultimate size limit for spin-based devices. These complexes can retain spin information over long periods of time at low temperature, suggesting possible applications in high-density information storage, quantum computing and spintronics. Notably, the success of most such applications hinges upon raising the inherent molecular spin-inversion barrier. Although recent advances have shown the viability of lanthanide-containing complexes in generating large barriers, weak or non-existent magnetic exchange coupling allows fast relaxation pathways that mitigate the full potential of these species. Here, we show that the diffuse spin of an N(2)(3-) radical bridge can lead to exceptionally strong magnetic exchange in dinuclear Ln(III) (Ln = Gd, Dy) complexes. The Gd(III) congener exhibits the strongest magnetic coupling yet observed for that ion, while incorporation of the high-anisotropy Dy(III) ion gives rise to a molecule with a record magnetic blocking temperature of 8.3 K at a sweep rate of 0.08 T s(-1).

  5. Binding of higher alcohols onto Mn(12) single-molecule magnets (SMMs): access to the highest barrier Mn(12) SMM.

    Science.gov (United States)

    Lampropoulos, Christos; Redler, Gage; Data, Saiti; Abboud, Khalil A; Hill, Stephen; Christou, George

    2010-02-15

    Two new members of the Mn(12) family of single-molecule magnets (SMMs), [Mn(12)O(12)(O(2)CCH(2)Bu(t))(16)(Bu(t)OH)(H(2)O)(3)].2Bu(t)OH (3.2Bu(t)OH) and [Mn(12)O(12)(O(2)CCH(2)Bu(t))(16)(C(5)H(11)OH)(4)] (4) (C(5)H(11)OH is 1-pentanol), are reported. They were synthesized from [Mn(12)O(12)(O(2)CMe)(16)(H(2)O)(4)].2MeCO(2)H.4H(2)O (1) by carboxylate substitution and crystallization from the appropriate alcohol-containing solvent. Complexes 3 and 4 are new members of the recently established [Mn(12)O(12)(O(2)CCH(2)Bu(t))(16)(solv)(4)] (solv = H(2)O, alcohols) family of SMMs. Only one bulky Bu(t)OH can be accommodated into 3, and even this causes significant distortion of the [Mn(12)O(12)] core. Variable-temperature, solid-state alternating current (AC) magnetization studies were carried out on complexes 3 and 4, and they established that both possess an S = 10 ground state spin and are SMMs. However, the magnetic behavior of the two compounds was found to be significantly different, with 4 showing out-of-phase AC peaks at higher temperatures than 3. High-frequency electron paramagnetic resonance (HFEPR) studies were carried out on single crystals of 3.2Bu(t)OH and 4, and these revealed that the axial zero-field splitting constant, D, is very different for the two compounds. Furthermore, it was established that 4 is the Mn(12) SMM with the highest kinetic barrier (U(eff)) to date. The results reveal alcohol substitution as an additional and convenient means to affect the magnetization relaxation barrier of the Mn(12) SMMs without major change to the ligation or oxidation state.

  6. Exponential dependence of potential barrier height on biased voltages of inorganic/organic static induction transistor

    International Nuclear Information System (INIS)

    Zhang Yong; Yang Jianhong; Cai Xueyuan; Wang Zaixing

    2010-01-01

    The exponential dependence of the potential barrier height φ c on the biased voltages of the inorganic/organic static induction transistor (SIT/OSIT) through a normalized approach in the low-current regime is presented. It shows a more accurate description than the linear expression of the potential barrier height. Through the verification of the numerical calculated and experimental results, the exponential dependence of φ c on the applied biases can be used to derive the I-V characteristics. For both SIT and OSIT, the calculated results, using the presented relationship, are agreeable with the experimental results. Compared to the previous linear relationship, the exponential description of φ c can contribute effectively to reduce the error between the theoretical and experimental results of the I-V characteristics. (semiconductor devices)

  7. Josephson-like currents in graphene for arbitrary time-dependent potential barriers

    OpenAIRE

    Savel'ev, Sergey E.; Hausler, Wolfgang; Hanggi, Peter

    2011-01-01

    From the exact solution of the Dirac-Weyl equation we find unusual currents j_y running in y-direction parallel to a time-dependent scalar potential barrier W(x,t) placed upon a monolayer of graphene, even for vanishing momentum component p_y. In their sine-like dependence on the phase difference of wave functions, describing left and right moving Dirac fermions, these currents resemble Josephson currents in superconductors, including the occurance of Shapiro steps at certain frequencies of p...

  8. Dielectric and magnetic characterizations of capacitor structures with an ionic liquid/MgO barrier and a ferromagnetic Pt electrode

    Directory of Open Access Journals (Sweden)

    D. Hayakawa

    2016-11-01

    Full Text Available The dielectric and magnetic properties of electric double layer (EDL capacitor structures with a perpendicularly magnetized Pt/Co/Pt electrode and an insulating cap layer (MgO are investigated. An electric field is applied through a mixed ionic liquid/MgO barrier to the surface of the top Pt layer, at which the magnetic moment is induced by the ferromagnetic proximity effect. The basic dielectric properties of the EDL capacitor are studied by varying the thickness of the MgO cap layer. The results indicate that the capacitance, i.e., the accumulated charge density at the Pt surface, is reduced with increasing the MgO thickness. From the MgO thickness dependence of the capacitance value, the effective dielectric constant of the ionic liquid is evaluated. Almost no electric field effect on the magnetic moment, the coercivity, or the Curie temperature is confirmed in the top Pt layer with the thickness of 1.3 nm, regardless of the presence or absence of the MgO cap layer, whereas the a clear change in the magnetic moment is observed when the top Pt layer is replaced by a Pd layer of 1.7 nm.

  9. Electron internal transport barrier formation and dynamics in the plasma core of the TJ-II stellarator

    Energy Technology Data Exchange (ETDEWEB)

    Estrada, T [Laboratorio Nacional de Fusion por Confinamiento Magnetico, Asociacion Euratom-CIEMAT, 28040 Madrid (Spain); Krupnik, L [Institute of Plasma Physics, NSC ' KIPT' , Kharkov (Ukraine); Dreval, N [Institute of Plasma Physics, NSC ' KIPT' , Kharkov (Ukraine); Melnikov, A [Institute of Nuclear Fusion, RRC ' Kurchatov Institute' , Moscow, Russia (Russian Federation); Khrebtov, S M [Institute of Plasma Physics, NSC ' KIPT' , Kharkov (Ukraine); Hidalgo, C [Laboratorio Nacional de Fusion por Confinamiento Magnetico, Asociacion Euratom-CIEMAT, 28040 Madrid (Spain); Milligen, B van [Laboratorio Nacional de Fusion por Confinamiento Magnetico, Asociacion Euratom-CIEMAT, 28040 Madrid (Spain); Castejon, F [Laboratorio Nacional de Fusion por Confinamiento Magnetico, Asociacion Euratom-CIEMAT, 28040 Madrid (Spain); AscasIbar, E [Laboratorio Nacional de Fusion por Confinamiento Magnetico, Asociacion Euratom-CIEMAT, 28040 Madrid (Spain); Eliseev, L [Institute of Nuclear Fusion, RRC ' Kurchatov Institute' , Moscow, Russia (Russian Federation); Chmyga, A A [Institute of Plasma Physics, NSC ' KIPT' , Kharkov (Ukraine); Komarov, A D [Institute of Plasma Physics, NSC ' KIPT' , Kharkov (Ukraine); Kozachok, A S [Institute of Plasma Physics, NSC ' KIPT' , Kharkov (Ukraine); Tereshin, V [Institute of Plasma Physics, NSC ' KIPT' , Kharkov (Ukraine)

    2004-01-01

    The influence of magnetic topology on the formation of electron internal transport barriers (e-ITBs) has been studied experimentally in electron cyclotron heated plasmas in the stellarator TJ-II. e-ITB formation is characterized by an increase in core electron temperature and plasma potential. The positive radial electric field increases by a factor of 3 in the central plasma region when an e-ITB forms. The experiments reported demonstrate that the formation of an e-ITB depends on the magnetic configuration. Calculations of the modification of the rotational transform due to plasma current lead to the interpretation that the formation of an e-ITB can be triggered by positioning a low order rational surface close to the plasma core region. In configurations without any central low order rational, no barrier is formed for any accessible value of heating power. Different mechanisms associated with neoclassical/turbulent bifurcations and kinetic effects are put forward to explain the impact of magnetic topology on radial electric fields and confinement.

  10. Thermopower in double planar tunnel junctions with ferromagnetic barriers and nonmagnetic electrodes

    Energy Technology Data Exchange (ETDEWEB)

    Wilczyński, M., E-mail: wilczyns@if.pw.edu.pl

    2017-01-01

    The Seebeck effect is investigated in double planar tunnel junctions consisting of nonmagnetic electrodes and the central layer separated by ferromagnetic barriers. Calculations are performed in the linear response theory using the free-electron model. The thermopower is analyzed as a function of the thickness of the central layer, temperature of the junctions and the relative orientation of magnetic moments of the barriers. It has been found that the thermopower can be significantly enhanced in the junction with special central layer thickness due to electron tunneling by resonant states. The thickness of the central layer for which the thermopower is enhanced depends not only on the temperature of the junction but also on the orientation of magnetic moments in the barriers. - Highlights: • Thermopower in the double planar junctions with magnetic barriers is analyzed. • Thermopower can be enhanced due to the resonant tunneling. • Thermopower depends on the magnetic configuration of the junction.

  11. Evaluation of the potential of PV noise barrier technology for electricity production and market share. Final report

    International Nuclear Information System (INIS)

    Goetzberger, A.; Kleiss, G.; Castello, S.; Hille, G.; Reise, C.; Wiemken, E.; Betcke, J.W.H.; Van Dijk, V.A.P.; Pearsall, N.; Hynes, K.; Gaidddon, B.; Nordmann, T.; Froelich, A.

    1999-06-01

    The analysis of existing and planned noise barriers along rails and roads has been carried out by the national partners together with national authorities, which are experts and responsible for the required data. The methodical approach of this study includes the set-up of a grid along longitude and latitudes with 1 by 1 degrees for Germany, Italy, France, United Kingdom and 0.5 by 0.5 degrees for the Netherlands and Switzerland. For each degree the length and orientation of rails and roads, the existing and planned noise barriers are registered and grouped according to their orientations. The solar radiation is based on data of a METEONORM data set. This includes the solar radiation on horizontal orientation as well as various inclination angles for all possible orientations. Moreover, possible shading has been considered. The technical specifications of noise barriers (PVNB) are based on the comprehensive knowledge of TNC GmbH and TNC AG with various plants realised. Technologies have been considered for both state-of-the-art and innovative concepts such as bifacial PVNB. In bifacial PVNB the PV-module is mounted vertically on both sides and is used at the same time as noise reflecting material. Installed PV power and produced electricity have been calculated for: 1. theoretical potential 2. technical potential 3. short-term resp. European extrapolated potential 4. anticipated potential 5. EU-member assessment The result of this study confirms the current activities to implement PV on noise barriers as an important share in the PV market.The report is subdivided into two volumes: Volume 1 contains the main topics and results, and Volume 2 contains additional information on the solar radiation, typical concepts as an excerpt of the various potentials and all country maps with the required explanations. 95 refs

  12. Spherical Magnetic Vortex in an External Potential Field: A Dissipative Contraction

    Science.gov (United States)

    Solov'ev, A. A.

    2013-09-01

    We consider the dissipative evolution of a spherical magnetic vortex with a force-free internal structure, located in a resistive medium and held in equilibrium by the potential external field. The magnetic field inside the sphere is force-free (the model of Chandrasekhar in Proc. Natl. Acad. Sci. 42, 1, 1956). Topologically, it is a set of magnetic toroids enclosed in spherical layers. A new exact MHD solution has been derived, describing a slow, uniform, radial compression of a magnetic spheroid under the pressure of an ambient field, when the plasma density and pressure are growing inside it. There is no dissipation in the potential field outside the sphere, but inside the sphere, where the current density can be high enough, the magnetic energy is continuously converted into heat. Joule dissipation lowers the magnetic pressure inside the sphere, which balances the pressure of the ambient field. This results in radial contraction of the magnetic sphere with a speed defined by the conductivity of the plasma and the characteristic spatial scale of the magnetic field inside the sphere. Formally, the sphere shrinks to zero within a finite time interval (magnetic collapse). The time of compression can be relatively small, within a day, even for a sphere with a radius of about 1 Mm, if the magnetic helicity trapped initially in the sphere (which is proportional to the number of magnetic toroids in the sphere) is quite large. The magnetic system is open along its axis of symmetry. On this axis, the magnetic and electric fields are strictly radial and sign-variable along the radius, so the plasma will be ejected along the axis of magnetic sphere outwards in both directions (as jets) at a rate much higher than the diffusive one, and the charged particles will be accelerated unevenly, in spurts, creating quasi-regular X-ray spikes. The applications of the solution to solar flares are discussed.

  13. Quantum tunneling time of a Bose-Einstein condensate traversing through a laser-induced potential barrier

    International Nuclear Information System (INIS)

    Duan Zhenglu; Fan Bixuan; Yuan Chunhua; Zhang Weiping; Cheng Jing; Zhu Shiyao

    2010-01-01

    We theoretically study the effect of atomic nonlinearity on the tunneling time in the case of an atomic Bose-Einstein condensate (BEC) traversing the laser-induced potential barrier. The atomic nonlinearity is controlled to appear only in the region of the barrier by employing the Feshbach resonance technique to tune interatomic interaction in the tunneling process. Numerical simulation shows that the atomic nonlinear effect dramatically changes the tunneling behavior of the BEC matter wave packet and results in the violation of the Hartman effect and the occurrence of negative tunneling time.

  14. HfO2 and SiO2 as barriers in magnetic tunneling junctions

    Science.gov (United States)

    Shukla, Gokaran; Archer, Thomas; Sanvito, Stefano

    2017-05-01

    SiO2 and HfO2 are both high-k, wide-gap semiconductors, currently used in the microelectronic industry as gate barriers. Here we investigate whether the same materials can be employed to make magnetic tunnel junctions, which in principle can be amenable for integration in conventional Si technology. By using a combination of density functional theory and the nonequilibrium Green's functions method for quantum transport we have studied the transport properties of Co [0001 ] /SiO2[001 ] /Co [0001 ] and Fe [001 ] /HfO2[001 ] /Fe [001 ] junctions. In both cases we found a quite large magnetoresistance, which is explained through the analysis of the real band structure of the magnets and the complex one of the insulator. We find that there is no symmetry spin filtering for the Co-based junction since the high transmission Δ2' band crosses the Fermi level, EF, for both spin directions. However, the fact that Co is a strong ferromagnet makes the orbital contribution to the two Δ2' spin subbands different, yielding magnetoresistance. In contrast for the Fe-based junction symmetry filtering is active for an energy window spanning between the Fermi level and 1 eV below EF, with Δ1 symmetry contributing to the transmission.

  15. Zero field reversal probability in thermally assisted magnetization reversal

    Science.gov (United States)

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

    2017-11-01

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

  16. The strain effect on the Dirac electrons tunneling through the time-periodic scalar and vector barriers

    Energy Technology Data Exchange (ETDEWEB)

    Yan, Weixian, E-mail: wxyansxu@gmail.com

    2017-01-01

    The tunneling of the massless and massive Dirac particle through the strained barriers driven by the time-periodic scalar potentials and the static vector potentials is investigated, where the interrelationships among the strain, the incidence angle, the dynamic scalar potential, the magnetic field and the transmission of the Dirac particle have been discussed. In either massless or massive case, the intersection angle between the obliquely incident Dirac particle and strain determines the extent of deviation of the tunneling profiles from the strainless case. The time-periodic scalar potentials can enhance the capability of the Dirac particle to surmount the energy gap induced by the mass, reflecting quantum nature of the photon-assisted tunneling. When the magnetic field is switched on, the transmission overall presents a remarkably different profile, and decreases with the increase of the magnetic fields due to the conservation of the transverse momentum, which reduces the number of the side-band channels for tunneling.

  17. Imaging and modification of the tumor vascular barrier for improvement in magnetic nanoparticle uptake and hyperthermia treatment efficacy

    Science.gov (United States)

    Hoopes, P. Jack; Petryk, Alicia A.; Tate, Jennifer A.; Savellano, Mark S.; Strawbridge, Rendall R.; Giustini, Andrew J.; Stan, Radu V.; Gimi, Barjor; Garwood, Michael

    2013-02-01

    The predicted success of nanoparticle based cancer therapy is due in part to the presence of the inherent leakiness of the tumor vascular barrier, the so called enhanced permeability and retention (EPR) effect. Although the EPR effect is present in varying degrees in many tumors, it has not resulted in the consistent level of nanoparticle-tumor uptake enhancement that was initially predicted. Magnetic/iron oxide nanoparticles (mNPs) have many positive qualities, including their inert/nontoxic nature, the ability to be produced in various sizes, the ability to be activated by a deeply penetrating and nontoxic magnetic field resulting in cell-specific cytotoxic heating, and the ability to be successfully coated with a wide variety of functional coatings. However, at this time, the delivery of adequate numbers of nanoparticles to the tumor site via systemic administration remains challenging. Ionizing radiation, cisplatinum chemotherapy, external static magnetic fields and vascular disrupting agents are being used to modify the tumor environment/vasculature barrier to improve mNP uptake in tumors and subsequently tumor treatment. Preliminary studies suggest use of these modalities, individually, can result in mNP uptake improvements in the 3-10 fold range. Ongoing studies show promise of even greater tumor uptake enhancement when these methods are combined. The level and location of mNP/Fe in blood and normal/tumor tissue is assessed via histopathological methods (confocal, light and electron microscopy, histochemical iron staining, fluorescent labeling, TEM) and ICP-MS. In order to accurately plan and assess mNP-based therapies in clinical patients, a noninvasive and quantitative imaging technique for the assessment of mNP uptake and biodistribution will be necessary. To address this issue, we examined the use of computed tomography (CT), magnetic resonance imaging (MRI), and Sweep Imaging With Fourier Transformation (SWIFT), an MRI technique which provides a

  18. Tuning magnetization avalanches in Mn12-acetate

    Science.gov (United States)

    Wen, Bo; McHugh, S.; Ma, Xiang; Sarachik, M. P.; Myasoedov, Y.; Shtrikman, H.; Zeldov, E.; Bagai, R.; Christou, G.

    2009-03-01

    We report the results of a systematic study of magnetic avalanches (abrupt magnetization reversals) in the molecular magnet Mn12-acetate using a micron-sized Hall sensor array. Measurements were taken for: (a) fixed magnetic field (constant barrier against spin reversal); and (b) fixed energy release obtained by adjusting the barrier and δM. A detailed comparison with the theory of magnetic deflagration of Garanin and Chudnovsky [1] will be presented and discussed. [1] D. A. Garanin and E. M. Chudnovsky, Phys. Rev. B 76, 054410 (2007)

  19. Low-resistance magnetic tunnel junctions prepared by partial remote plasma oxidation of 0.9 nm Al barriers

    International Nuclear Information System (INIS)

    Ferreira, Ricardo; Freitas, Paulo P.; MacKenzie, Maureen; Chapman, John N.

    2005-01-01

    Current perpendicular to the plane read-head elements suitable for high-density magnetic storage require low resistance while maintaining a reasonable magnetoresistive (MR) signal (RxA 2 and MR>20% for areal densities >200 Gb/in 2 ). This letter shows that competitive low RxA junctions can be produced using underoxidized barriers starting from 0.9 nm thick Al layers. For as-deposited junctions, tunneling magnetoresistance (TMR) ∼20% for RxA∼2-15 Ω μm 2 is obtained, while in the RxA∼60-150 Ω μm 2 range, TMR values between 40% to 45% are achieved. A limited number of junctions exhibits considerably lower RxA values with respect to the average, while keeping a similar MR (down to 0.44 Ω μm 2 with TMR of 20% and down to 2.2 Ω μm 2 with TMR of 52%). Experimental data suggest that current confinement to small regions (barrier defects/hot spots) may explain these results

  20. Magnetic nanoparticles as potential candidates for biomedical and biological applications.

    Science.gov (United States)

    Zeinali Sehrig, Fatemeh; Majidi, Sima; Nikzamir, Nasrin; Nikzamir, Nasim; Nikzamir, Mohammad; Akbarzadeh, Abolfazl

    2016-05-01

    Magnetic iron oxide nanoparticles have become the main candidates for biomedical and biological applications, and the application of small iron oxide nanoparticles in in vitro diagnostics has been practiced for about half a century. Magnetic nanoparticles (MNPs), in combination with an external magnetic field and/or magnetizable grafts, allow the delivery of particles to the chosen target area, fix them at the local site while the medication is released, and act locally. In this review, we focus mostly on the potential use of MNPs for biomedical and biotechnological applications, and the improvements made in using these nanoparticles (NPs) in biological applications.

  1. Magnetophoretic potential at the movement of cluster products of electrochemical reactions in an inhomogeneous magnetic field

    International Nuclear Information System (INIS)

    Gorobets, O. Yu.; Gorobets, Yu. I.; Rospotniuk, V. P.

    2015-01-01

    An electric field arises from the influence of a nonuniform static magnetic field on charged colloid particles with magnetic susceptibility different from that of the surrounding liquid. It arises, for example, under the influence of a nonuniform static magnetic field in clusters of electrochemical reaction products created during metal etching, deposition, and corrosion processes without an external electric current passing through an electrolyte near a magnetized electrode surface. The corresponding potential consists of a Nernst potential of inhomogeneous distribution of concentration of colloid particles and a magnetophoretic potential (MPP). This potential has been calculated using a thermodynamic approach based on the equations of thermodynamics of nonequilibrium systems and the Onsager relations for a mass flow of correlated magnetic clusters under a gradient magnetic force in the electrolyte. The conditions under which the MPP contribution to the total electric potential may be significant are discussed with a reference to the example of a corroding spherical ferromagnetic steel electrode

  2. Magnetophoretic potential at the movement of cluster products of electrochemical reactions in an inhomogeneous magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Gorobets, O. Yu., E-mail: pitbm@ukr.net; Gorobets, Yu. I., E-mail: Gorobets@imag.kiev.ua [National Technical University of Ukraine “KPI”, Peremogy Avenue 37, Kyiv 03056 (Ukraine); Institute of Magnetism NAS of Ukraine and National Academy of Sciences of Ukraine, Vernadsky Avenue, 36-b, Kyiv 03142 (Ukraine); Rospotniuk, V. P. [National Technical University of Ukraine “KPI”, Peremogy Avenue 37, Kyiv 03056 (Ukraine)

    2015-08-21

    An electric field arises from the influence of a nonuniform static magnetic field on charged colloid particles with magnetic susceptibility different from that of the surrounding liquid. It arises, for example, under the influence of a nonuniform static magnetic field in clusters of electrochemical reaction products created during metal etching, deposition, and corrosion processes without an external electric current passing through an electrolyte near a magnetized electrode surface. The corresponding potential consists of a Nernst potential of inhomogeneous distribution of concentration of colloid particles and a magnetophoretic potential (MPP). This potential has been calculated using a thermodynamic approach based on the equations of thermodynamics of nonequilibrium systems and the Onsager relations for a mass flow of correlated magnetic clusters under a gradient magnetic force in the electrolyte. The conditions under which the MPP contribution to the total electric potential may be significant are discussed with a reference to the example of a corroding spherical ferromagnetic steel electrode.

  3. Magnetic coupling at perovskite and rock-salt structured interfaces

    Energy Technology Data Exchange (ETDEWEB)

    Matvejeff, M., E-mail: mikko.matvejeff@picosun.com [Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, 277-8581 Chiba (Japan); Department of Chemistry, Aalto University, Kemistintie 1, 02150 Espoo (Finland); Ahvenniemi, E. [Department of Chemistry, Aalto University, Kemistintie 1, 02150 Espoo (Finland); Takahashi, R.; Lippmaa, M. [Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, 277-8581 Chiba (Japan)

    2015-10-05

    We study magnetic coupling between hole-doped manganite layers separated by either a perovskite or a rock-salt barrier of variable thickness. Both the type and the quality of the interface have a strong impact on the minimum critical barrier thickness where the manganite layers become magnetically decoupled. A rock-salt barrier layer only 1 unit cell (0.5 nm) thick remains insulating and is able to magnetically de-couple the electrode layers. The technique can therefore be used for developing high-performance planar oxide electronic devices such as magnetic tunnel junctions and quantum well structures that depend on magnetically and electronically sharp heterointerfaces.

  4. Fusion barriers in heavy ion collisions

    International Nuclear Information System (INIS)

    Zhu Long; Su Jun; Xie Wenjie; Guo Chenchen; Zhang Donghong; Zhang Fengshou

    2014-01-01

    Study of fusion barrier is very important for people to better understand fusion reactions. In this paper the Improved Isospin-dependent Quantum Molecular Dynamics (ImIQMD) model is introduced firstly. Then the shell correction effects, energy dependence, isospin effects and orientation effects of fusion barrier are studied. The fusion barriers for the fusion reactions "4"0Ca + "4"0Ca, "4"8Ca + "2"0"8Pb, "4"8Ca + "2"0"4Pb and "1"6O + "1"5"4Sm are extracted. The negative shell correction energies lower potential barriers of a certain reaction. A complex phenomenon of energy dependence is observed. It is also found that incident energy dependence of the barrier radius and barrier height shows opposite behaviors. The Coulomb potential shows weak energy dependence when distance of two colliding nuclei is lower than the touching distance. The isospin effects of the potential barrier are investigated. The orientation effects of the potential barrier are also discussed for the system "1"6O + "1"5"4Sm. (authors)

  5. Fabrication of fully epitaxial magnetic tunnel junctions with a Co2MnSi thin film and a MgO tunnel barrier

    International Nuclear Information System (INIS)

    Kijima, H.; Ishikawa, T.; Marukame, T.; Matsuda, K.-I.; Uemura, T.; Yamamoto, M.

    2007-01-01

    Fully epitaxial magnetic tunnel junctions (MTJs) were fabricated with a Co-based full-Heusler alloy Co 2 MnSi (CMS) thin film having the ordered L2 1 structure as a lower electrode, a MgO tunnel barrier, and a Co 50 Fe 50 upper electrode. Reflection high-energy electron diffraction patterns observed in situ for each layer in the MTJ layer structure during fabrication clearly indicated that all layers of the CMS lower electrode, MgO tunnel barrier, and Co 50 Fe 50 upper electrode grew epitaxially. The microfabricated fully epitaxial CMS/MgO/Co 50 Fe 50 MTJs demonstrated relatively high tunnel magnetoresistance ratios of 90% at room temperature and 192% at 4.2 K

  6. Double internal transport barrier triggering mechanism in tokamak plasmas

    International Nuclear Information System (INIS)

    Dong, Jiaqi; Mou, Zongze; Long, Yongxing; Mahajan, Swadesh M.

    2004-01-01

    Sheared flow layers created by energy released in magnetic reconnection processes are studied with the magneto hydrodynamics (MHD), aimed at internal transport barrier (ITB) dynamics. The double tearing mode induced by electron viscosity is investigated and proposed as a triggering mechanism for double internal transport barrier (DITB) observed in tokamak plasmas with non-monotonic safety factor profiles. The quasi-linear development of the mode is simulated and the emphasis is placed on the structure of sheared poloidal flow layers formed in the vicinity of the magnetic islands. For viscosity double tearing modes, it is shown that the sheared flows induced by the mode may reach the level required by the condition for ITB formation. Especially, the flow layers are found to form just outside the magnetic islands. The scaling of the generated velocity with plasma parameters is given. Possible explanation for the experimental observations that the preferential formation of transport barriers in the proximity of low order rational surface is discussed. (author)

  7. Calculation of multidimensional potential energy surfaces for even-even transuranium nuclei: systematic investigation of the triaxiality effect on the fission barrier

    Science.gov (United States)

    Chai, Qing-Zhen; Zhao, Wei-Juan; Liu, Min-Liang; Wang, Hua-Lei

    2018-05-01

    Static fission barriers for 95 even-even transuranium nuclei with charge number Z = 94–118 have been systematically investigated by means of pairing self-consistent Woods-Saxon-Strutinsky calculations using the potential energy surface approach in multidimensional (β 2, γ, β 4) deformation space. Taking the heavier 252Cf nucleus (with the available fission barrier from experiment) as an example, the formation of the fission barrier and the influence of macroscopic, shell and pairing correction energies on it are analyzed. The results of the present calculated β 2 values and barrier heights are compared with previous calculations and available experiments. The role of triaxiality in the region of the first saddle is discussed. It is found that the second fission barrier is also considerably affected by the triaxial deformation degree of freedom in some nuclei (e.g., the Z=112–118 isotopes). Based on the potential energy curves, general trends of the evolution of the fission barrier heights and widths as a function of the nucleon numbers are investigated. In addition, the effects of Woods-Saxon potential parameter modifications (e.g., the strength of the spin-orbit coupling and the nuclear surface diffuseness) on the fission barrier are briefly discussed. Supported by National Natural Science Foundation of China (11675148, 11505157), the Project of Youth Backbone Teachers of Colleges and Universities of Henan Province (2017GGJS008), the Foundation and Advanced Technology Research Program of Henan Province (162300410222), the Outstanding Young Talent Research Fund of Zhengzhou University (1521317002) and the Physics Research and Development Program of Zhengzhou University (32410017)

  8. Evidence-based dentistry for planning restorative treatments: barriers and potential solutions.

    Science.gov (United States)

    Afrashtehfar, K I; Eimar, H; Yassine, R; Abi-Nader, S; Tamimi, F

    2017-11-01

    Evidence-based dentistry (EBD) can help provide the best treatment option for every patient, however, its implementation in restorative dentistry is very limited. This study aimed at assessing the barriers preventing the implementation of EBD among dental undergraduate and graduate students in Montreal, and explore possible solutions to overcome these barriers. A cross-sectional survey was conducted by means of a paper format self-administrated questionnaire distributed among dental students. The survey assessed the barriers and potential solutions for implementation of an evidence-based practice. Sixty-one students completed the questionnaire. Forty-one percent of respondents found evidence-based literature to be the most reliable source of information for restorative treatment planning, however, only 16% used it. They considered that finding reliable information was difficult and they sometimes encountered conflicting information when consulting different sources. Dental students had positive attitudes towards the need for better access to evidence-based literature to assist learning and decision making in restorative treatment planning and to improve treatment outcomes. Even for dentists trained in EBD, online searching takes too much time, and even though it can provide information of better quality than personal intuition, it might not be enough to identify the best available evidence. Even though dental students are aware of the importance of EBD in restorative dentistry they rarely apply the concept, mainly due to time constraints. For this reason, implementation of EBD would probably require faster access to evidence-based knowledge. © 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  9. Creation of a magnetic barrier at a noble q close to physical midpoint between two resonant surfaces in the ASDEX UG tokamak

    Science.gov (United States)

    Vazquez, Justin; Ali, Halima; Punjabi, Alkesh

    2009-11-01

    Ciraolo, Vittot and Chandre method of building invariant manifolds inside chaos in Hamiltonian systems [Ali H. and Punjabi A, Plasma Phys. Control. Fusion, 49, 1565--1582 (2007)] is used in the ASDEX UG tokamak. In this method, a second order perturbation is added to the perturbed Hamiltonian [op cit]. It creates an invariant torus inside the chaos, and reduces the plasma transport. The perturbation that is added to the equilibrium Hamiltonian is at least an order of magnitude smaller than the perturbation that causes chaos. This additional term has a finite, limited number of Fourier modes. Resonant magnetic perturbations (m,n) = (3,2)+(4,3) are added to the field line Hamiltonian for the ASDEX UG. An area-preserving map for the field line trajectories in the ASDEX UG is used. The common amplitude δ of these modes that gives complete chaos between the resonant surfaces ψ43 and ψ32 is determined. A magnetic barrier is built at a surface with noble q that is very nearly equals to the q at the physical midpoint between the two resonant surfaces. The maximum amplitude of magnetic perturbation for which this barrier can be sustained is determined. This work is supported by US Department of Energy grants DE-FG02-07ER54937, DE-FG02-01ER54624 and DE-FG02-04ER54793.

  10. Transport barrier in Helical system

    International Nuclear Information System (INIS)

    Ida, Katsumi

    1998-01-01

    Experiments on the transport barrier in Helical plasmas are reviewed. There are two mechanisms of transport improvement, that results in the formation of the transport barrier. One is the improvement of neoclassical transport by reducing the ripple loss with radial electric field, which exist only in helical plasma. The other is the improvement of anomalous transport due to the suppression of fluctuations associated with a radial electric field shear both in tokamak and helical plasma. The formation of the transport barrier can be triggered by the radial electric field shear associated with the transition of the radial electric field (L/H transition or ion-electron root transition) or the peaked density or the optimization of magnetic field shear. The mechanisms of transport barrier formation are also discussed. (author). 60 refs

  11. Magnetic moments of octet baryons in a chiral potential model

    International Nuclear Information System (INIS)

    Barik, N.

    1986-01-01

    Incorporating the lowest-order pionic correction, the magnetic moments of the nucleon octet have been calculated in a chiral potential model. The potential, representing phenomenologically the nonperturbative gluon self-couplings, is chosen with equally mixed scalar and vector parts in a power-law form. The results are in reasonable agreement with experiment. (author)

  12. Potential and barriers for biogas production in Denmark at widely expanded organic farming with focus on the soil carbon content; Potentiale og barrierer for biogasproduktion i Danmark ved omfattende oekologisk jordbrug med fokus paa dyrkningsjordens kulstofforhold

    Energy Technology Data Exchange (ETDEWEB)

    Buch Salomonsen, K.

    2000-06-01

    The Ph.D. thesis describes the influence from continued expansion of organic farming systems to the potential for energy production from biogas in Denmark. The project analyses the consequence from three categories of barriers: 1) Practical barriers, 2) The attitude of organic farmers, and 3) Agricultural biological problems. Economic and political barriers are not examined. When the barriers can be quantified, they are included in the calculation of the maximum biogas potential. When not, the implications of barriers are expressed qualitatively. It has been a particular goal to provide new information on whether agricultural biological problems are a barrier to biogas production in organic farming systems. One important question in this connection is whether biogas production has a negative influence on the soil carbon content compared to composting. This question is investigated by an experiment. The project is based on technical and natural science disciplines, with an interdisciplinary basis ranging over energy planning, agricultural science, microbiology, and crop, and animal operation. (au)

  13. Structure of chaotic magnetic field lines in IR-T1 tokamak due to ergodic magnetic limiter

    Science.gov (United States)

    Ahmadi, S.; Salar Elahi, A.; Ghorannevis, M.

    2018-03-01

    In this paper we have studied an Ergodic Magnetic Limiter (EML) based chaotic magnetic field for transport control in the edge plasma of IR-T1 tokamak. The resonance created by the EML causes perturbation of the equilibrium field line in tokamak and as a result, the field lines are chaotic in the vicinity of the dimerized island chains. Transport barriers are formed in the chaotic field line and actually observe in tokamak with reverse magnetic shear. We used area-preserving non-twist (and twist) Poincaré maps to describe the formation of transport barriers, which are actually features of Hamiltonian systems. This transport barrier is useful in reducing radial diffusion of the field line and thus improving the plasma confinement.

  14. Structure of chaotic magnetic field lines in IR-T1 tokamak due to ergodic magnetic limiter

    Directory of Open Access Journals (Sweden)

    S. Ahmadi

    2018-03-01

    Full Text Available In this paper we have studied an Ergodic Magnetic Limiter (EML based chaotic magnetic field for transport control in the edge plasma of IR-T1 tokamak. The resonance created by the EML causes perturbation of the equilibrium field line in tokamak and as a result, the field lines are chaotic in the vicinity of the dimerized island chains. Transport barriers are formed in the chaotic field line and actually observe in tokamak with reverse magnetic shear. We used area-preserving non-twist (and twist Poincaré maps to describe the formation of transport barriers, which are actually features of Hamiltonian systems. This transport barrier is useful in reducing radial diffusion of the field line and thus improving the plasma confinement.

  15. Quantum damped oscillator II: Bateman's Hamiltonian vs. 2D parabolic potential barrier

    International Nuclear Information System (INIS)

    Chruscinski, Dariusz

    2006-01-01

    We show that quantum Bateman's system which arises in the quantization of a damped harmonic oscillator is equivalent to a quantum problem with 2D parabolic potential barrier known also as 2D inverted isotropic oscillator. It turns out that this system displays the family of complex eigenvalues corresponding to the poles of analytical continuation of the resolvent operator to the complex energy plane. It is shown that this representation is more suitable than the hyperbolic one used recently by Blasone and Jizba

  16. Identification of potential biomarkers for gut barrier failure in broiler chickens

    Directory of Open Access Journals (Sweden)

    Juxing eChen

    2015-05-01

    Full Text Available The objective of the present study was to identify potential biomarkers for gut barrier failure in chickens. A total of 144 day-of-hatch Ross 308 male broiler chickens were housed in 24 battery cages with 6 chicks per cage. Cages were randomly assigned to either a control group (CON or gut barrier failure (GBF group. During the first 13 d, birds in CON or GBF groups were fed a common corn-soy starter diet. On d 14, CON chickens were switched to a corn grower diet and GBF chickens were switched to rye-wheat-barley grower diet. In addition, on d 21, GBF chickens were orally challenged with a coccidiosis vaccine. At d 21 and d 28, birds were weighed by cage and feed intake was recorded to calculate feed conversion ratio. At d 28, one chicken from each cage was euthanized to collect intestinal samples for morphometric analysis, blood for serum, and intestinal mucosa scrapings for gene expression. Overall performance and feed efficiency was severely affected (P < 0.05 by a GBF model when compared with CON group at d 21 and d 28. Duodenum of GBF birds had wider villi, longer crypt depth, and higher crypt depth/villi height ratio than CON birds. Similarly, GBF birds had longer crypt depth in jejunum and ileum when compared with CON birds. An increase (P <0.05 in serum endotoxin, α1-acid glycoprotein (AGP, as well as interleukin (IL-8, IL-1β, transforming growth factor (TGF-β4 and fatty-acid-binding protein (FABP 6 mRNA levels were increased in GBF birds compared to CON; however, FABP2 mRNA levels were decreased (P <0.05 in GBF birds compared to CON. Occludin was numerically reduced by 24% (P = 0.107 and mucin 2 (MUC2 was reduced by 29 % (P = 0.088 in GBF birds compared to CON birds. The results from the present study suggest that serum endotoxin and AGP, as well as, gene expression of FABP2, FABP6, IL-8, IL-1β and TGF-β4 in mucosa may work as potential biomarkers for gut barrier health in chickens.

  17. Dynamical Monte Carlo investigation of spin reversal and nonequilibrium magnetization of single-molecule magnets

    Science.gov (United States)

    Liu, Gui-Bin; Liu, Bang-Gui

    2010-10-01

    In this paper, we combine thermal effects with Landau-Zener (LZ) quantum tunneling effects in a dynamical Monte Carlo (DMC) framework to produce satisfactory magnetization curves of single-molecule magnet (SMM) systems. We use the giant spin approximation for SMM spins and consider regular lattices of SMMs with magnetic dipolar interactions (MDIs). We calculate spin-reversal probabilities from thermal-activated barrier hurdling, direct LZ tunneling, and thermal-assisted LZ tunnelings in the presence of sweeping magnetic fields. We do systematical DMC simulations for Mn12 systems with various temperatures and sweeping rates. Our simulations produce clear step structures in low-temperature magnetization curves, and our results show that the thermally activated barrier hurdling becomes dominating at high temperature near 3 K and the thermal-assisted tunnelings play important roles at intermediate temperature. These are consistent with corresponding experimental results on good Mn12 samples (with less disorders) in the presence of little misalignments between the easy axis and applied magnetic fields, and therefore our magnetization curves are satisfactory. Furthermore, our DMC results show that the MDI, with the thermal effects, have important effects on the LZ tunneling processes, but both the MDI and the LZ tunneling give place to the thermal-activated barrier hurdling effect in determining the magnetization curves when the temperature is near 3 K. This DMC approach can be applicable to other SMM systems and could be used to study other properties of SMM systems.

  18. Renewable energy in South Africa: Potentials, barriers and options for support

    International Nuclear Information System (INIS)

    Pegels, Anna

    2010-01-01

    The challenge of transforming entire economies is enormous; even more so if a country is as fossil fuel based and emission intensive as South Africa. However, in an increasingly carbon constrained world and already now facing climate change impacts South Africa has to reduce greenhouse gas emissions intensity soon and decidedly. The South African electricity sector is a vital part of the economy and at the same time contributes most to the emissions problem. First steps have been taken by the South African government to enhance energy efficiency and promote renewable energy, however, they fail to show large-scale effects. This paper seeks to identify the relevant barriers to renewable energy investments and, based on experience from other countries, provide policy recommendations. The major barrier identified in the paper is based on the economics of renewable energy technologies, i.e. their cost and risk structures, two main factors in investment planning. As a solution, the South African government introduced several renewable energy support measures, such as a feed-in tariff. The paper discusses the potential and possible shortcomings of this and other existing support schemes and identifies complementing measures on a national scale.

  19. Renewable energy in South Africa. Potentials, barriers and options for support

    Energy Technology Data Exchange (ETDEWEB)

    Pegels, Anna [German Development Institute/Deutsches Institut fuer Entwicklungspolitik, Tulpenfeld 6, 53113 Bonn (Germany)

    2010-09-15

    The challenge of transforming entire economies is enormous; even more so if a country is as fossil fuel based and emission intensive as South Africa. However, in an increasingly carbon constrained world and already now facing climate change impacts South Africa has to reduce greenhouse gas emissions intensity soon and decidedly. The South African electricity sector is a vital part of the economy and at the same time contributes most to the emissions problem. First steps have been taken by the South African government to enhance energy efficiency and promote renewable energy, however, they fail to show large-scale effects. This paper seeks to identify the relevant barriers to renewable energy investments and, based on experience from other countries, provide policy recommendations. The major barrier identified in the paper is based on the economics of renewable energy technologies, i.e. their cost and risk structures, two main factors in investment planning. As a solution, the South African government introduced several renewable energy support measures, such as a feed-in tariff. The paper discusses the potential and possible shortcomings of this and other existing support schemes and identifies complementing measures on a national scale. (author)

  20. Renewable energy in South Africa: Potentials, barriers and options for support

    Energy Technology Data Exchange (ETDEWEB)

    Pegels, Anna, E-mail: anna.pegels@die-gdi.d [German Development Institute/Deutsches Institut fuer Entwicklungspolitik, Tulpenfeld 6, 53113 Bonn (Germany)

    2010-09-15

    The challenge of transforming entire economies is enormous; even more so if a country is as fossil fuel based and emission intensive as South Africa. However, in an increasingly carbon constrained world and already now facing climate change impacts South Africa has to reduce greenhouse gas emissions intensity soon and decidedly. The South African electricity sector is a vital part of the economy and at the same time contributes most to the emissions problem. First steps have been taken by the South African government to enhance energy efficiency and promote renewable energy, however, they fail to show large-scale effects. This paper seeks to identify the relevant barriers to renewable energy investments and, based on experience from other countries, provide policy recommendations. The major barrier identified in the paper is based on the economics of renewable energy technologies, i.e. their cost and risk structures, two main factors in investment planning. As a solution, the South African government introduced several renewable energy support measures, such as a feed-in tariff. The paper discusses the potential and possible shortcomings of this and other existing support schemes and identifies complementing measures on a national scale.

  1. Alloy Dependence of Electron-Phonon Interactions in Double Barrier Structures

    National Research Council Canada - National Science Library

    Wallis, Corinne

    1996-01-01

    ...)As double barrier structures as a function of the alloy concentration in the barrier. We have measured current-voltage and conductance-voltage curves associated with phonon-assisted tunneling with magnetic fields from 0 to 6.8 Tesla...

  2. Magnetic moments of octet baryons in a chiral potential model

    Energy Technology Data Exchange (ETDEWEB)

    Barik, N; Das, M

    1986-12-01

    Incorporating the lowest-order pionic correction, the magnetic moments of the nucleon octet have been calculated in a chiral potential model. The potential, representing phenomenologically the nonperturbative gluon self-couplings, is chosen with equally mixed scalar and vector parts in a power-law form. The results are in reasonable agreement with experiment. 32 refs., 2 tables.

  3. Linear and nonlinear absorption coefficients of spherical quantum dot inside external magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Çakır, Bekir, E-mail: bcakir@selcuk.edu.tr [Physics Department, Faculty of Science, Selcuk University, Campus, 42075 Konya (Turkey); Yakar, Yusuf, E-mail: yuyakar@yahoo.com [Physics Department, Faculty of Arts and Science, Aksaray University, Campus, 68100 Aksaray (Turkey); Özmen, Ayhan [Physics Department, Faculty of Science, Selcuk University, Campus, 42075 Konya (Turkey)

    2017-04-01

    We have calculated the wavefunctions and energy eigenvalues of spherical quantum dot with infinite potential barrier inside uniform magnetic field. In addition, we have investigated the magnetic field effect on optical transitions between Zeeman energy states. The results are expressed as a function of dot radius, incident photon energy and magnetic field strength. The results present that, in large dot radii, the external magnetic field affects strongly the optical transitions between Zeeman states. In the strong spatial confinement case, energy level is relatively insensitive to the magnetic field, and electron spatial confinement prevails over magnetic confinement. Also, while m varies from −1 to +1, the peak positions of the optical transitions shift toward higher energy (blueshift).

  4. Non-potential Field Formation in the X-shaped Quadrupole Magnetic Field Configuration

    Energy Technology Data Exchange (ETDEWEB)

    Kawabata, Y.; Shimizu, T. [Department of Earth and Planetary Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Inoue, S., E-mail: kawabata.yusuke@ac.jaxa.jp [Max-Planck-Institute for Solar System Research, Justus-von-Liebig-Weg 3 D-37077 Göttingen (Germany)

    2017-06-20

    Some types of solar flares are observed in X-shaped quadrupolar field configuration. To understand the magnetic energy storage in such a region, we studied non-potential field formation in an X-shaped quadrupolar field region formed in the active region NOAA 11967, which produced three X-shaped M-class flares on 2014 February 2. Nonlinear force-free field modeling was applied to a time series of vector magnetic field maps from the Solar Optical Telescope on board Hinode and the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory . Our analysis of the temporal three-dimensional magnetic field evolution shows that the sufficient free energy had already been stored more than 10 hr before the occurrence of the first M-class flare and that the storage was observed in a localized region. In this localized region, quasi-separatrix layers (QSLs) started to develop gradually from 9 hr before the first M-class flare. One of the flare ribbons that appeared in the first M-class flare was co-spatial with the location of the QSLs, suggesting that the formation of the QSLs is important in the process of energy release. These QSLs do not appear in the potential field calculation, indicating that they were created by the non-potential field. The formation of the QSLs was associated with the transverse photospheric motion of the pre-emerged flux and the emergence of a new flux. This observation indicates that the occurrence of the flares requires the formation of QSLs in the non-potential field in which free magnetic energy is stored in advance.

  5. Potential formation in axisymmetrized tandem mirror GAMMA 10

    International Nuclear Information System (INIS)

    Cho, T.; Ichimura, M.; Inutake, M.

    1985-01-01

    The paper reports experimental results on potential formation and end plugging in the axisymmetrized tandem mirror GAMMA 10. The plugging at both ends has been achieved by a combination of neutral beams and gyrotrons. The presence of a plug potential with a thermal barrier in an axisymmetric mirror has been confirmed by direct measurement of the axial potential profile. Enhancement of axial particle confinement has been observed during the end plugging. Non-ambipolar radial transport has been greatly reduced in the axisymmetrized magnetic configuration. The potentials measured by beam probes and end loss analysers are 0.7, 0.4 and 1.1 kV in the central, barrier and plug regions, respectively. Strong end plugging is observed when the central-cell density is higher than the densities in the plug and the barrier, and the plug density remains higher than the barrier density. The plug electron temperature is higher than the central temperature. Hot electrons forming a football-shaped profile have been stably produced in the axisymmetric mirror. The beta value and the fraction of the hot electrons reach up to 5% and 0.8, respectively. Central-cell ion-cyclotron resonance heating can sustain a stable plasma with higher density and ion temperature when resonance surfaces exist in both the anchor and the central cells. (author)

  6. What do patients choose to tell their doctors? Qualitative analysis of potential barriers to reattributing medically unexplained symptoms.

    Science.gov (United States)

    Peters, Sarah; Rogers, Anne; Salmon, Peter; Gask, Linda; Dowrick, Chris; Towey, Maria; Clifford, Rebecca; Morriss, Richard

    2009-04-01

    Despite both parties often expressing dissatisfaction with consultations, patients with medically unexplained symptoms (MUS) prefer to consult their general practitioners (GPs) rather than any other health professional. Training GPs to explain how symptoms can relate to psychosocial problems (reattribution) improves the quality of doctor-patient communication, though not necessarily patient health. To examine patient experiences of GPs' attempts to reattribute MUS in order to identify potential barriers to primary care management of MUS and improvement in outcome. Qualitative study. Patients consulting with MUS whose GPs had been trained in reattribution. A secondary sample of patients of control GPs was also interviewed to ascertain if barriers identified were specific to reattribution or common to consultations about MUS in general. Thematic analysis of in-depth interviews. Potential barriers include the complexity of patients' problems and patients' judgements about how to manage their presentation of this complexity. Many did not trust doctors with discussion of emotional aspects of their problems and chose not to present them. The same barriers were seen amongst patients whose GPs were not trained, suggesting the barriers are not particular to reattribution. Improving GP explanation of unexplained symptoms is insufficient to reduce patients' concerns. GPs need to (1) help patients to make sense of the complex nature of their presenting problems, (2) communicate that attention to psychosocial factors will not preclude vigilance to physical disease and (3) ensure a quality of doctor-patient relationship in which patients can perceive psychosocial enquiry as appropriate.

  7. Potential corridors and barriers for plague spread in central Asia

    Science.gov (United States)

    2013-01-01

    Background Plague (Yersinia pestis infection) is a vector-borne disease which caused millions of human deaths in the Middle Ages. The hosts of plague are mostly rodents, and the disease is spread by the fleas that feed on them. Currently, the disease still circulates amongst sylvatic rodent populations all over the world, including great gerbil (Rhombomys opimus) populations in Central Asia. Great gerbils are social desert rodents that live in family groups in burrows, which are visible on satellite images. In great gerbil populations an abundance threshold exists, above which plague can spread causing epizootics. The spatial distribution of the host species is thought to influence the plague dynamics, such as the direction of plague spread, however no detailed analysis exists on the possible functional or structural corridors and barriers that are present in this population and landscape. This study aims to fill that gap. Methods Three 20 by 20 km areas with known great gerbil burrow distributions were used to analyse the spatial distribution of the burrows. Object-based image analysis was used to map the landscape at several scales, and was linked to the burrow maps. A novel object-based method was developed – the mean neighbour absolute burrow density difference (MNABDD) – to identify the optimal scale and evaluate the efficacy of using landscape objects as opposed to square cells. Multiple regression using raster maps was used to identify the landscape-ecological variables that explain burrow density best. Functional corridors and barriers were mapped using burrow density thresholds. Cumulative resistance of the burrow distribution to potential disease spread was evaluated using cost distance analysis. A 46-year plague surveillance dataset was used to evaluate whether plague spread was radially symmetric. Results The burrow distribution was found to be non-random and negatively correlated with Greenness, especially in the floodplain areas. Corridors and

  8. Transmission through a potential barrier in Luttinger liquids with a topological spin gap

    Science.gov (United States)

    Kainaris, Nikolaos; Carr, Sam T.; Mirlin, Alexander D.

    2018-03-01

    We study theoretically the transport of the one-dimensional single-channel interacting electron gas through a strong potential barrier in the parameter regime where the spin sector of the low-energy theory is gapped by interaction (Luther-Emery liquid). There are two distinct phases of this nature, of which one is of particular interest as it exhibits nontrivial interaction-induced topological properties. Focusing on this phase and using bosonization and an expansion in the tunneling strength we calculate the conductance through the barrier as a function of the temperature as well as the local density of states (LDOS) at the barrier. Our main result concerns the mechanism of bound-state-mediated tunneling. The characteristic feature of the topological phase is the emergence of protected zero-energy bound states with fractional spin located at the impurity position. By flipping this fractional spin, single electrons can tunnel across the impurity even though the bulk spectrum for spin excitations is gapped. This results in a finite LDOS below the bulk gap and in a nonmonotonic behavior of the conductance. The system represents an important physical example of an interacting symmetry-protected topological phase, which combines features of a topological spin insulator and a topological charge metal, in which the topology can be probed by measuring transport properties.

  9. Dipolar-Biased Tunneling of Magnetization in Crystals of Single Molecule Magnets

    Science.gov (United States)

    Awaga, Kunio

    2007-03-01

    The molecular cluster Mn12 has attracted much interest as a single-molecule magnet (SMM) and as a multi-redox system. It has a high-spin ground state of S=10 and a strong uniaxial magnetic anisotropy, and the combination of the two natures makes an effective potential barrier between the up and down spin states. At low temperatures, the magnetization curve exhibited a hysteresis loop and the quantum tunneling of magnetization (QTM). In the present work, we studied the structure and magnetic properties of the mixed-metal SMM, Mn11Cr, through the analysis of Mn11Cr/Mn12 mixed crystal. High-frequency EPR spectra were well explained by assuming that Mn11Cr was in a ground spin-state of S=19/2 with nearly the same EPR parameter set as for Mn12. QTM in Mn11Cr was observed with the same field interval as for Mn12. The magnetization of Mn11Cr and Mn12 in the mixed crystal can be independently manipulated by utilizing the difference between their coercive fields. The resonance fields of QTM in Mn11Cr are significantly affected by the magnetization direction of Mn12, suggesting the effect of dipolar-biased tunneling. Besides SMM, we would also like to report the unusual magnetic properties of spherical hollow nanomagnets, the electrical properties of heterocyclic thiazyl radicals, and their possible applications in spintronics and organic electronics.

  10. Magnetic proximity control of spin currents and giant spin accumulation in graphene

    Science.gov (United States)

    Singh, Simranjeet

    Two dimensional (2D) materials provide a unique platform to explore the full potential of magnetic proximity driven phenomena. We will present the experimental study showing the strong modulation of spin currents in graphene layers by controlling the direction of the exchange field due to the ferromagnetic-insulator (FMI) magnetization in graphene/FMI heterostructures. Owing to clean interfaces, a strong magnetic exchange coupling leads to the experimental observation of complete spin modulation at low externally applied magnetic fields in short graphene channels. We also discover that the graphene spin current can be fully dephased by randomly fluctuating exchange fields. This is manifested as an unusually strong temperature dependence of the non-local spin signals in graphene, which is due to spin relaxation by thermally-induced transverse fluctuations of the FMI magnetization. Additionally, it has been a challenge to grow a smooth, robust and pin-hole free tunnel barriers on graphene, which can withstand large current densities for efficient electrical spin injection. We have experimentally demonstrated giant spin accumulation in graphene lateral spin valves employing SrO tunnel barriers. Nonlocal spin signals, as large as 2 mV, are observed in graphene lateral spin valves at room temperature. This high spin accumulations observed using SrO tunnel barriers puts graphene on the roadmap for exploring the possibility of achieving a non-local magnetization switching due to the spin torque from electrically injected spins. Financial support from ONR (No. N00014-14-1-0350), NSF (No. DMR-1310661), and C-SPIN, one of the six SRC STARnet Centers, sponsored by MARCO and DARPA.

  11. Energy consumption and CO2 emissions of industrial process technologies. Saving potentials, barriers and instruments

    International Nuclear Information System (INIS)

    Fleiter, Tobias; Schlomann, Barbara; Eichhammer, Wolfgang

    2013-01-01

    Which contribution can the increase of energy efficiency achieve in the industry energy for the energy transition in Germany? To answer this question a model-based analysis of existing energy efficiency potentials of the energy-intensive industries is performed, which account for about 70% of the total energy demand of the industry. Based on this industry for each sector are instruments proposed for the implementation of the calculated potential and to overcome the existing barriers. [de

  12. Study of the interplay between magnetic shear and resonances using Hamiltonian models for the magnetic field lines

    Science.gov (United States)

    Firpo, M.-C.; Constantinescu, D.

    2011-03-01

    The issue of magnetic confinement in magnetic fusion devices is addressed within a purely magnetic approach. Using some Hamiltonian models for the magnetic field lines, the dual impact of low magnetic shear is shown in a unified way. Away from resonances, it induces a drastic enhancement of magnetic confinement that favors robust internal transport barriers (ITBs) and stochastic transport reduction. When low shear occurs for values of the winding of the magnetic field lines close to low-order rationals, the amplitude thresholds of the resonant modes that break internal transport barriers by allowing a radial stochastic transport of the magnetic field lines may be quite low. The approach can be applied to assess the robustness versus magnetic perturbations of general (almost) integrable magnetic steady states, including nonaxisymmetric ones such as the important single-helicity steady states. This analysis puts a constraint on the tolerable mode amplitudes compatible with ITBs and may be proposed as a possible explanation of diverse experimental and numerical signatures of their collapses.

  13. Deactivation of SCR catalysts by potassium: A study of potential alkali barrier materials

    DEFF Research Database (Denmark)

    Olsen, Brian Kjærgaard; Kügler, Frauke; Castellino, Francesco

    2017-01-01

    The use of coatings in order to protect vanadia based SCR catalysts against potassium poisoning has been studied by lab- and pilot-scale experiments. Three-layer pellets, consisting of a layer ofa potential coating material situated between layers of fresh and potassium poisoned SCR catalyst, were...... the coating process. Potassium had to some extent penetrated the MgO coat, and SEM analysis revealed it to be rather thick and fragile. Despite these observations, the coating did protect the SCR catalyst against potassium poisoning to some degree, leaving promise of further optimization....... used to test the ability of the barrier layer to block the diffusion of potassium across the pellet. Of MgO, sepiolite and Hollandite manganese oxide, MgO was the most effective potassium barrier, and no potassium was detected in the MgO layer upon exposure to SCR conditions for 7 days. Two monoliths...

  14. Preparation of magnetic nanoparticles and their application to magnetic targeting drug delivery

    International Nuclear Information System (INIS)

    Li Guiping; Wang Yongxian

    2006-01-01

    Magnetic nanoparticles barrier is a novel kind of drug delivery system for magnetic targeting drugs, which can effectively deliver the drug to a tumor target site and increase therapeutic benefit, with the side effects minimized. This article summarizes the most outstanding papers on the of magnetic nanoparticles used as the targeting drug's delivery systems. (authors)

  15. On the generalized Hartman effect for symmetric double-barrier point potentials

    International Nuclear Information System (INIS)

    Lee, Molly A; Manzoni, Luiz A; Nyquist, Erik A; Lunardi, José T

    2015-01-01

    We consider the scattering of a non-relativistic particle by a symmetrical arrangement of two identical barriers in one-dimension, with the barriers given by the well-known four-parameter family of point interactions. We calculate the phase time and the stationary Salecker-Wigner-Peres clock time for the particular cases of a double δ and a double δ' barrier and investigate the off-resonance behavior of these time scales in the limit of opaque barriers, addressing the question of emergence of the generalized Hartman effect

  16. Magnetic nanoparticles for theragnostics

    Science.gov (United States)

    Shubayev, Veronica I.; Pisanic, Thomas R.; Jin, Sungho

    2009-01-01

    Engineered magnetic nanoparticles (MNPs) represent a cutting-edge tool in medicine because they can be simultaneously functionalized and guided by a magnetic field. Use of MNPs has advanced magnetic resonance imaging (MRI), guided drug and gene delivery, magnetic hyperthermia cancer therapy, tissue engineering, cell tracking and bioseparation. Integrative therapeutic and diagnostic (i.e., theragnostic) applications have emerged with MNP use, such as MRI-guided cell replacement therapy or MRI-based imaging of cancer-specific gene delivery. However, mounting evidence suggests that certain properties of nanoparticles (e.g., enhanced reactive area, ability to cross cell and tissue barriers, resistance to biodegradation) amplify their cytotoxic potential relative to molecular or bulk counterparts. Oxidative stress, a 3-tier paradigm of nanotoxicity, manifests in activation of reactive oxygen species (ROS) (tier I), followed by a pro-inflammatory response (tier II) and DNA damage leading to cellular apoptosis and mutagenesis (tier III). In vivo administered MNPs are quickly challenged by macrophages of the reticuloendothelial system (RES), resulting in not only neutralization of potential MNP toxicity but also reduced circulation time necessary for MNP efficacy. We discuss the role of MNP size, composition and surface chemistry in their intracellular uptake, biodistribution, macrophage recognition and cytotoxicity, and review current studies on MNP toxicity, caveats of nanotoxicity assessments and engineering strategies to optimize MNPs for biomedical use. PMID:19389434

  17. Electron internal transport barrier in the core of TJ-II ECH plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Estrada, T.; Hidalgo, C. [Laboratorio Nacional de Fusion por Confinamiento Magnetico. Asociacion EURATOM CIEMAT, Madrid (Spain); Dreval, N. [and others

    2003-07-01

    The influence of the magnetic topology on the formation of electron internal transport barriers (e-ITB) has been experimentally studied in the stellarator TJ-II. The formation of e-ITBs in electron cyclotron heated plasmas can be triggered by positioning a low order rational surface close to the plasma core region, while in configurations without any low order rational there are no indications of barrier formation within the available heating power. The e-ITB formation is characterized by an increase in the core electron temperature and plasma potential. Positive radial electric field increases in a factor of three in the plasma central region when the e-ITB forms. The results demonstrate that low order rational surfaces modify radial electric fields and electron heat transport. (orig.)

  18. CORONAL MAGNETIC FIELDS DERIVED FROM SIMULTANEOUS MICROWAVE AND EUV OBSERVATIONS AND COMPARISON WITH THE POTENTIAL FIELD MODEL

    Energy Technology Data Exchange (ETDEWEB)

    Miyawaki, Shun; Nozawa, Satoshi [Department of Science, Ibaraki University, Mito, Ibaraki 310-8512 (Japan); Iwai, Kazumasa; Shibasaki, Kiyoto [Nobeyama Solar Radio Observatory, National Astronomical Observatory of Japan, Minamimaki, Nagano 384-1305 (Japan); Shiota, Daikou, E-mail: shunmi089@gmail.com [Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya, Aichi 464-8601 (Japan)

    2016-02-10

    We estimated the accuracy of coronal magnetic fields derived from radio observations by comparing them to potential field calculations and the differential emission measure measurements using EUV observations. We derived line-of-sight components of the coronal magnetic field from polarization observations of the thermal bremsstrahlung in the NOAA active region 11150, observed around 3:00 UT on 2011 February 3 using the Nobeyama Radioheliograph at 17 GHz. Because the thermal bremsstrahlung intensity at 17 GHz includes both chromospheric and coronal components, we extracted only the coronal component by measuring the coronal emission measure in EUV observations. In addition, we derived only the radio polarization component of the corona by selecting the region of coronal loops and weak magnetic field strength in the chromosphere along the line of sight. The upper limits of the coronal longitudinal magnetic fields were determined as 100–210 G. We also calculated the coronal longitudinal magnetic fields from the potential field extrapolation using the photospheric magnetic field obtained from the Helioseismic and Magnetic Imager. However, the calculated potential fields were certainly smaller than the observed coronal longitudinal magnetic field. This discrepancy between the potential and the observed magnetic field strengths can be explained consistently by two reasons: (1) the underestimation of the coronal emission measure resulting from the limitation of the temperature range of the EUV observations, and (2) the underestimation of the coronal magnetic field resulting from the potential field assumption.

  19. Animal Study Registries: Results from a Stakeholder Analysis on Potential Strengths, Weaknesses, Facilitators, and Barriers.

    Science.gov (United States)

    Wieschowski, Susanne; Silva, Diego S; Strech, Daniel

    2016-11-01

    Publication bias in animal research, its extent, its predictors, and its potential countermeasures are increasingly discussed. Recent reports and conferences highlight the potential strengths of animal study registries (ASRs) in this regard. Others have warned that prospective registration of animal studies could diminish creativity, add administrative burdens, and complicate intellectual property issues in translational research. A literature review and 21 international key-informant interviews were conducted and thematically analyzed to develop a comprehensive matrix of main- and subcategories for potential ASR-related strengths, weaknesses, facilitators, and barriers (SWFBs). We identified 130 potential SWFBs. All stakeholder groups agreed that ASRs could in various ways improve the quality and refinement of animal studies while allowing their number to be reduced, as well as supporting meta-research on animal studies. However, all stakeholder groups also highlighted the potential for theft of ideas, higher administrative burdens, and reduced creativity and serendipity in animal studies. Much more detailed reasoning was captured in the interviews than is currently found in the literature, providing a comprehensive account of the issues and arguments around ASRs. All stakeholder groups highlighted compelling potential strengths of ASRs. Although substantial weaknesses and implementation barriers were highlighted as well, different governance measures might help to minimize or even eliminate their impact. Such measures might include confidentiality time frames for accessing prospectively registered protocols, harmonized reporting requirements across ASRs, ethics reviews, lab notebooks, and journal submissions. The comprehensive information gathered in this study could help to guide a more evidence-based debate and to design pilot tests for ASRs.

  20. Animal Study Registries: Results from a Stakeholder Analysis on Potential Strengths, Weaknesses, Facilitators, and Barriers.

    Directory of Open Access Journals (Sweden)

    Susanne Wieschowski

    2016-11-01

    Full Text Available Publication bias in animal research, its extent, its predictors, and its potential countermeasures are increasingly discussed. Recent reports and conferences highlight the potential strengths of animal study registries (ASRs in this regard. Others have warned that prospective registration of animal studies could diminish creativity, add administrative burdens, and complicate intellectual property issues in translational research. A literature review and 21 international key-informant interviews were conducted and thematically analyzed to develop a comprehensive matrix of main- and subcategories for potential ASR-related strengths, weaknesses, facilitators, and barriers (SWFBs. We identified 130 potential SWFBs. All stakeholder groups agreed that ASRs could in various ways improve the quality and refinement of animal studies while allowing their number to be reduced, as well as supporting meta-research on animal studies. However, all stakeholder groups also highlighted the potential for theft of ideas, higher administrative burdens, and reduced creativity and serendipity in animal studies. Much more detailed reasoning was captured in the interviews than is currently found in the literature, providing a comprehensive account of the issues and arguments around ASRs. All stakeholder groups highlighted compelling potential strengths of ASRs. Although substantial weaknesses and implementation barriers were highlighted as well, different governance measures might help to minimize or even eliminate their impact. Such measures might include confidentiality time frames for accessing prospectively registered protocols, harmonized reporting requirements across ASRs, ethics reviews, lab notebooks, and journal submissions. The comprehensive information gathered in this study could help to guide a more evidence-based debate and to design pilot tests for ASRs.

  1. Potential of the test particle in the magnetic field. I

    International Nuclear Information System (INIS)

    Sestak, B.

    1980-01-01

    The problem of the test particle potential in an external homogeneous magnetic field is solved in an unmagnetized plasma. It is shown that for the case when the parallel velocity component of the test particle is greater than the thermal velocity of the background particles, the potential is of a Coulomb character while for the case where the parallel velocity component is less than the thermal velocity the potential is of a Debye character. The Larmor radius of the test particle appears as an additional parameter in these potentials. (author)

  2. [On Atomic Nuclear Fusion Processes at Low-Temperatures. An Enhancement of the Probability of Transition through a Potential Barrier Due to the So-Called Barrier Anti-Zeno Effect].

    Science.gov (United States)

    Namiot, V A

    2016-01-01

    It is known that in quantum mechanics the act of observing the experiment can affect the experimental findings in some cases. In particular, it happens under the so-called Zeno effect. In this work it is shown that in contrast to the "standard" Zeno-effect where the act of observing a process reduces the probability of its reality, an inverse situation when a particle transmits through a potential barrier (a so-called barrier anti-Zeno effect) can be observed, the observation of the particle essentially increases the probability of its transmission through the barrier. The possibility of using the barrier anti-Zeno effect is discussed to explain paradoxical results of experiments on "cold nuclear fusion" observed in various systems including biological ones. (According to the observers who performed the observations, the energy generation, which could not be explained by any chemical processes, as well as the change in the isotope and even element composition of the studied object may occur in these systems.

  3. Suppression of Magnetic Quantum Tunneling in a Chiral Single-Molecule Magnet by Ferromagnetic Interactions.

    Science.gov (United States)

    Lippert, Kai-Alexander; Mukherjee, Chandan; Broschinski, Jan-Philipp; Lippert, Yvonne; Walleck, Stephan; Stammler, Anja; Bögge, Hartmut; Schnack, Jürgen; Glaser, Thorsten

    2017-12-18

    Single-molecule magnets (SMMs) retain a magnetization without applied magnetic field for a decent time due to an energy barrier U for spin-reversal. Despite the success to increase U, the difficult to control magnetic quantum tunneling often leads to a decreased effective barrier U eff and a fast relaxation. Here, we demonstrate the influence of the exchange coupling on the tunneling probability in two heptanuclear SMMs hosting the same spin-system with the same high spin ground state S t = 21/2. A chirality-induced symmetry reduction leads to a switch of the Mn III -Mn III exchange from antiferromagnetic in the achiral SMM [Mn III 6 Cr III ] 3+ to ferromagnetic in the new chiral SMM RR [Mn III 6 Cr III ] 3+ . Multispin Hamiltonian analysis by full-matrix diagonalization demonstrates that the ferromagnetic interactions in RR [Mn III 6 Cr III ] 3+ enforce a well-defined S t = 21/2 ground state with substantially less mixing of M S substates in contrast to [Mn III 6 Cr III ] 3+ and no tunneling pathways below the top of the energy barrier. This is experimentally verified as U eff is smaller than the calculated energy barrier U in [Mn III 6 Cr III ] 3+ due to tunneling pathways, whereas U eff equals U in RR [Mn III 6 Cr III ] 3+ demonstrating the absence of quantum tunneling.

  4. Magnetic Switching of a Single Molecular Magnet due to Spin-Polarized Current

    OpenAIRE

    Misiorny, Maciej; Barnas, Józef

    2006-01-01

    Magnetic switching of a single molecular magnet (SMM) due to spin-polarized current flowing between ferromagnetic metallic electrodes is investigated theoretically. Magnetic moments of the electrodes are assumed to be collinear and parallel to the magnetic easy axis of the molecule. Electrons tunneling through a barrier between magnetic leads are coupled to the SMM via exchange interaction. The current flowing through the system as well as the spin relaxation times of the SMM are calculated f...

  5. Barrier cell sheath formation

    International Nuclear Information System (INIS)

    Kesner, J.

    1980-04-01

    The solution for electrostatic potential within a simply modeled tandem mirror thermal barrier is seen to exhibit a sheath at each edge of the cell. The formation of the sheath requires ion collisionality and the analysis assmes that the collisional trapping rate into the barrier is considerably slower than the barrier pump rate

  6. Magnetic Thermometer: Thermal effect on the Agglomeration of Magnetic Nanoparticles by Magnetic field

    Science.gov (United States)

    Jin, Daeseong; Kim, Hackjin

    2018-03-01

    We have investigated the agglomeration of magnetite nanoparticles in the aqueous solution under magnetic field by measuring temporal change of magnetic weight. The magnetic weight corresponds to the force due to the magnetization of magnetic materials. Superparamagnetic magnetite nanoparticles are synthesized and used in this work. When the aqueous solution of magnetite nanoparticle is placed under magnetic field, the magnetic weight of the sample jumps instantaneously by Neel and Brown mechanisms and thereafter increases steadily following a stretched exponential function as the nanoparticles agglomerate, which results from the distribution of energy barriers involved in the dynamics. Thermal motions of nanoparticles in the agglomerate perturb the ordered structure of the agglomerate to reduce the magnetic weight. Fluctuation of the structural order of the agglomerate by temperature change is much faster than the formation of agglomerate and explained well with the Boltzmann distribution, which suggests that the magnetic weight of the agglomerate works as a magnetic thermometer.

  7. Developing leadership as a trainee- opportunities, barriers and potential improvements.

    Science.gov (United States)

    Doherty, Rachel; Lawson, Sara; Mc Laughlin, Laura; Donaghy, Grainne; Courtney, Julia; Gardiner, Keith

    2018-05-01

    The General Medical Council explicitly state that doctors completing training should demonstrate capabilities in leadership and teamwork. 1 However, most trainees receive little formal training in leadership. In March 2017, at the Faculty of Medical Leadership and Management (FMLM) Northern Ireland Regional Conference, a workshop on developing leadership skills as a trainee was hosted and the views of doctors in training regarding current opportunities, potential barriers and improvements were sought. In Northern Ireland presently there are a number of opportunities available for trainees to gain experience in leadership - both by learning through observation and learning through experience. These range from informal activities which do not require significant time commitment to focused, immersive leadership experiences such as ADEPT (Achieve Develop Explore Programme for Trainees) 2 , and the Royal College of Physicians' Chief Registrar scheme. 3 Several barriers to developing leadership have been identified, including limited understanding of what constitutes leadership, a lack of senior support and little formal recognition for trainees leading teams. Time pressures, frequently rotating jobs, limited resources and difficulty upscaling can also undermine the sustainability of improvement and other leadership projects. Incorporating awareness of and training in leadership skills, as well as greater engagement with senior leaders and managers, at an early stage in training could promote understanding and encourage trainees. Formalising leadership roles within training posts may improve experience. Deaneries and Trusts can also enable leadership opportunities by facilitating study leave, raising awareness amongst supervisors, and providing career enhancing incentives for interested trainees.

  8. Benefits and drawbacks of low magnetic shears on the confinement in magnetic fusion toroidal devices

    Science.gov (United States)

    Firpo, Marie-Christine; Constantinescu, Dana

    2012-10-01

    The issue of confinement in magnetic fusion devices is addressed within a purely magnetic approach. As it is well known, the magnetic field being divergence-free, the equations of its field lines can be cast in Hamiltonian form. Using then some Hamiltonian models for the magnetic field lines, the dual impact of low magnetic shear is demonstrated. Away from resonances, it induces a drastic enhancement of magnetic confinement that favors robust internal transport barriers (ITBs) and turbulence reduction. However, when low-shear occurs for values of the winding of the magnetic field lines close to low-order rationals, the amplitude thresholds of the resonant modes that break internal transport barriers by allowing a radial stochastic transport of the magnetic field lines may be much lower than the ones obtained for strong shear profiles. The approach can be applied to assess the robustness versus magnetic perturbations of general almost-integrable magnetic steady states, including non-axisymmetric ones such as the important single helicity steady states. This analysis puts a constraint on the tolerable mode amplitudes compatible with ITBs and may be proposed as a possible explanation of diverse experimental and numerical signatures of their collapses.

  9. Thermal relaxation of magnetic clusters in amorphous Hf57Fe43 alloy

    International Nuclear Information System (INIS)

    Pajic, Damir; Zadro, Kreso; Ristic, Ramir; Zivkovic, Ivica; Skoko, Zeljko; Babic, Emil

    2007-01-01

    The magnetization processes in binary magnetic/non-magnetic amorphous alloy Hf 57 Fe 43 are investigated by the detailed measurement of magnetic hysteresis loops, temperature dependence of magnetization, relaxation of magnetization and magnetic ac susceptibility, including a nonlinear term. Blocking of magnetic moments at lower temperatures is accompanied by the slow relaxation of magnetization and magnetic hysteresis loops. All of the observed properties are explained by the superparamagnetic behaviour of the single domain magnetic clusters inside the non-magnetic host, their blocking by the anisotropy barriers and thermal fluctuation over the barriers accompanied by relaxation of magnetization. From magnetic viscosity analysis based on thermal relaxation over the anisotropy barriers it is found that magnetic clusters occupy the characteristic volume from 25 up to 200 nm 3 . The validity of the superparamagnetic model of Hf 57 Fe 43 is based on the concentration of iron in the Hf 100-x Fe x system that is just below the threshold for long range magnetic ordering. This work also throws more light on the magnetic behaviour of other amorphous alloys

  10. Low-field EPR studies of levels near the top of the barrier in Mn 12-acetate reveal a new magnetization relaxation pathway

    Science.gov (United States)

    Rakvin, Boris; Žilić, Dijana; Dalal, Naresh S.; Harter, Andrew; Sanakis, Yiannis

    2006-07-01

    We show that X-band electron paramagnetic resonance (EPR) measurements using a dual-mode resonance cavity can directly probe the levels near the top of the magnetization reversal barrier in the single-molecule magnet (SMM) Mn 12-acetate. The observed transitions are much sharper than those reported in high-field EPR studies. The observed temperature dependence of the line positions points to the presence of a spin-diffusional mode. The correlation time for such fluctuations is of the order of 6×10 -8 s at 10 K, and follows an Arrhenius activation energy of 35-40 K. These results open a new avenue for understanding the mechanism of tunneling and spin-lattice relaxations in these SMMs.

  11. The stability of internal transport barriers to MHD ballooning modes and drift waves: A formalism for low magnetic shear and for velocity shear

    International Nuclear Information System (INIS)

    Connor, J.W.; Hastie, R.J.; Webster, A.J.; Wilson, H.R.

    2005-01-01

    Tokamak discharges with internal transport barriers (ITBs) provide improved confinement, so it is important to understand their stability properties. The stability to an important class of modes with high wave-numbers perpendicular to the magnetic field, is usually studied with the standard ballooning transformation and eikonal approach. However, ITBs are often characterised by radial q profiles that have regions of negative or low magnetic shear and by radially sheared electric fields. Both these features affect the validity of the standard method. A new approach to calculating stability in these circumstances is developed and applied to ideal MHD ballooning modes and to micro-instabilities responsible for anomalous transport. (author)

  12. Exploring the efficiency potential for an active magnetic regenerator

    DEFF Research Database (Denmark)

    Eriksen, Dan; Engelbrecht, Kurt; Haffenden Bahl, Christian Robert

    2016-01-01

    A novel rotary state of the art active magnetic regenerator refrigeration prototype was used in an experimental investigation with special focus on efficiency. Based on an applied cooling load, measured shaft power, and pumping power applied to the active magnetic regenerator, a maximum second-la...... and replacing the packed spheres with a theoretical parallel plate regenerator. Furthermore, significant potential efficiency improvements through optimized regenerator geometries are estimated and discussed......., especially for the pressure drop, significant improvements can be made to the machine. However, a large part of the losses may be attributed to regenerator irreversibilities. Considering these unchanged, an estimated upper limit to the second-law efficiency of 30% is given by eliminating parasitic losses...

  13. The magnetic universe through vector potential SPMHD simulations

    Science.gov (United States)

    Stasyszyn, F. A.

    2017-10-01

    The use of Smoothed Particle Magneto Hydrodynamics (SPMHD) is getting nowadays more and more common in Astrophysics. From galaxy clusters to neutron starts, there are multiple applications already existing in the literature. I will review some of the common methods used and highlight the successful approach of using vector potentials to describe the evolution of the magnetic fields. The latter have some interesting advantages, and their results challenge previous findings, being the magnetic divergence problem naturally vanished. We select a few examples to discuss some areas of interest. First, we show some Galaxy Clusters from the MUSIC project. These cosmological simulations are done with the usual sub-grid recipes, as radiative cooling and star formation, being the first ones obtained with an SPH code in a self consistent way. This demonstrates the robustness of the new method in a variety of astrophysical scenarios.

  14. Edible moisture barriers: how to assess of their potential and limits in food products shelf-life extension?

    Science.gov (United States)

    Bourlieu, C; Guillard, V; Vallès-Pamiès, B; Guilbert, S; Gontard, N

    2009-05-01

    Control of moisture transfer inside composite food products or between food and its environment remains today a major challenge in food preservation. A wide rage of film-forming compounds is now available and facilitates tailoring moisture barriers with optimized functional properties. Despite these huge potentials, a realistic assessment of the film or coating efficacy is still critical. Due to nonlinear water sorption isotherms, water-dependent diffusivities, and variations of physical state, modelling transport phenomena through edible barriers is complex. Water vapor permeability can hardly be considered as an inherent property of films and only gives a relative indication of the barrier efficacy. The formal or mechanistic models reported in literature that describe the influence of testing conditions on the barrier properties of edible films are reviewed and discussed. Most of these models have been validated on a narrow range of conditions. Conversely, few original predictive models based on Fick's Second Law have been developed to assess shelf-life extension of food products including barriers. These models, assuming complex and realistic hypothesis, have been validated in various model foods. The development of nondestructive methods of moisture content measurement should speed up model validation and allow a better comprehension of moisture transfer through edible films.

  15. Magnetic qubits as hardware for quantum computers

    International Nuclear Information System (INIS)

    Tejada, J.; Chudnovsky, E.; Barco, E. del

    2000-01-01

    We propose two potential realisations for quantum bits based on nanometre scale magnetic particles of large spin S and high anisotropy molecular clusters. In case (1) the bit-value basis states vertical bar-0> and vertical bar-1> are the ground and first excited spin states S z = S and S-1, separated by an energy gap given by the ferromagnetic resonance (FMR) frequency. In case (2), when there is significant tunnelling through the anisotropy barrier, the qubit states correspond to the symmetric, vertical bar-0>, and antisymmetric, vertical bar-1>, combinations of the two-fold degenerate ground state S z = ± S. In each case the temperature of operation must be low compared to the energy gap, Δ, between the states vertical bar-0> and vertical bar-1>. The gap Δ in case (2) can be controlled with an external magnetic field perpendicular to the easy axis of the molecular cluster. The states of different molecular clusters and magnetic particles may be entangled by connecting them by superconducting lines with Josephson switches, leading to the potential for quantum computing hardware. (author)

  16. Magnetic qubits as hardware for quantum computers

    Energy Technology Data Exchange (ETDEWEB)

    Tejada, J.; Chudnovsky, E.; Barco, E. del [and others

    2000-07-01

    We propose two potential realisations for quantum bits based on nanometre scale magnetic particles of large spin S and high anisotropy molecular clusters. In case (1) the bit-value basis states vertical bar-0> and vertical bar-1> are the ground and first excited spin states S{sub z} = S and S-1, separated by an energy gap given by the ferromagnetic resonance (FMR) frequency. In case (2), when there is significant tunnelling through the anisotropy barrier, the qubit states correspond to the symmetric, vertical bar-0>, and antisymmetric, vertical bar-1>, combinations of the two-fold degenerate ground state S{sub z} = {+-} S. In each case the temperature of operation must be low compared to the energy gap, {delta}, between the states vertical bar-0> and vertical bar-1>. The gap {delta} in case (2) can be controlled with an external magnetic field perpendicular to the easy axis of the molecular cluster. The states of different molecular clusters and magnetic particles may be entangled by connecting them by superconducting lines with Josephson switches, leading to the potential for quantum computing hardware. (author)

  17. Conductance oscillations of core-shell nanowires in transversal magnetic fields

    Science.gov (United States)

    Manolescu, Andrei; Nemnes, George Alexandru; Sitek, Anna; Rosdahl, Tomas Orn; Erlingsson, Sigurdur Ingi; Gudmundsson, Vidar

    2016-05-01

    We analyze theoretically electronic transport through a core-shell nanowire in the presence of a transversal magnetic field. We calculate the conductance for a variable coupling between the nanowire and the attached leads and show how the snaking states, which are low-energy states localized along the lines of the vanishing radial component of the magnetic field, manifest their existence. In the strong-coupling regime they induce flux periodic, Aharonov-Bohm-like, conductance oscillations, which, by decreasing the coupling to the leads, evolve into well-resolved peaks. The flux periodic oscillations arise due to interference of the snaking states, which is a consequence of backscattering at either the contacts with leads or magnetic or potential barriers in the wire.

  18. Bias voltage dependence of magnetic tunnel junctions comprising amorphous ferromagnetic CoFeSiB layer with double barriers

    International Nuclear Information System (INIS)

    Yim, H.I.; Lee, S.Y.; Hwang, J.Y.; Rhee, J.R.; Chun, B.S.; Wang, K.L.; Kim, Y.K.; Kim, T.W.; Lee, S.S.; Hwang, D.G.

    2008-01-01

    Double-barrier magnetic tunnel junctions (DMTJs) with and without an amorphous ferromagnetic material such as CoFeSiB 10, CoFe 5/CoFeSiB 5, and CoFe 10 (nm) were prepared and compared to investigate the bias voltage dependence of the tunneling magnetoresistance (TMR) ratio. Typical DMTJ structures were Ta 45/Ru 9.5/IrMn 10/CoFe 7/AlO x /free layer 10/AlO x /CoFe 7/IrMn 10/Ru 60 (in nanometers). The interlayer coupling field and the normalized TMR ratios at the applied voltages of +0.4 and -0.4 V of the amorphous CoFeSiB free-layer DMTJ offer lower and higher values than that of the polycrystalline CoFe free-layer DMTJ, respectively. An amorphous ferromagnetic CoFeSiB layer improves the interface roughness of the free layer/tunnel barrier and, as a result, the interlayer coupling field and bias voltage dependence of the TMR ratio are suppressed at a given voltage. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  19. Current limitation and formation of plasma double layers in a non-uniform magnetic field

    International Nuclear Information System (INIS)

    Plamondon, R.; Teichmann, J.; Torven, S.

    1986-07-01

    Formation of strong double layers has been observed experimentally in a magnetised plasma column maintained by a plasma source. The magnetic field is approximately axially homogenous except in a region at the anode where the electric current flows into a magnetic mirror. The double layer has a stationary position only in the region of non-uniform magnetic field or at the aperture separating the source and the plasma column. It is characterized by a negative differential resistance in the current-voltage characteristic of the device. The parameter space,where the double layer exists, has been studied as well as the corresponding potential profiles and fluctuation spectra. The electric current and the axial electric field are oppositely directed between the plasma source and a potential minimum which is formed in the region of inhomogeneous magnetic field. Electron reflection by the resulting potential barrier is found to be an important current limitation mechanism. (authors)

  20. Potential interference of small neodymium magnets with cardiac pacemakers and implantable cardioverter-defibrillators.

    Science.gov (United States)

    Wolber, Thomas; Ryf, Salome; Binggeli, Christian; Holzmeister, Johannes; Brunckhorst, Corinna; Luechinger, Roger; Duru, Firat

    2007-01-01

    Magnetic fields may interfere with the function of cardiac pacemakers and implantable cardioverter-defibrillators (ICDs). Neodymium-iron-boron (NdFeB) magnets, which are small in size but produce strong magnetic fields, have become widely available in recent years. Therefore, NdFeB magnets may be associated with an emerging risk of device interference. We conducted a clinical study to evaluate the potential of small NdFeB magnets to interfere with cardiac pacemakers and ICDs. The effect of four NdFeB magnets (two spherical magnets 8 and 10 mm in diameter, a necklace made of 45 spherical magnets, and a magnetic name tag) was tested in forty-one ambulatory patients with a pacemaker and 29 patients with an ICD. The maximum distance at which the magnetic switch of a device was influenced was observed. Magnetic interference was observed in all patients. The maximum distance resulting in device interference was 3 cm. No significant differences were found with respect to device manufacturer and device types. Small NdFeB magnets may cause interference with cardiac pacemakers and ICDs. Patients should be cautioned about the interference risk associated with NdFeB magnets during daily life.

  1. Tandem mirror reactor with thermal barriers

    International Nuclear Information System (INIS)

    Carlson, G.A.; Arfin, B.; Barr, W.L.; Boghosian, B.M.; Erickson, J.L.; Fink, J.H.; Hamilton, G.W.; Logan, B.G.; Myall, J.O.; Neef, W.S. Jr.

    1979-01-01

    This report gives detailed information in the form of the following chapters: (1) overview, (2) plasma physics, (3) magnets, (4) end-plug neutral beams, (5) barrier pump neutral beams, (6) ecr heating, (7) plasma direct converter, and (8) central cell

  2. Understanding electron magnetic circular dichroism in a transition potential approach

    Science.gov (United States)

    Barthel, J.; Mayer, J.; Rusz, J.; Ho, P.-L.; Zhong, X. Y.; Lentzen, M.; Dunin-Borkowski, R. E.; Urban, K. W.; Brown, H. G.; Findlay, S. D.; Allen, L. J.

    2018-04-01

    This paper introduces an approach based on transition potentials for inelastic scattering to understand the underlying physics of electron magnetic circular dichroism (EMCD). The transition potentials are sufficiently localized to permit atomic-scale EMCD. Two-beam and three-beam systematic row cases are discussed in detail in terms of transition potentials for conventional transmission electron microscopy, and the basic symmetries which arise in the three-beam case are confirmed experimentally. Atomic-scale EMCD in scanning transmission electron microscopy (STEM), using both a standard STEM probe and vortex beams, is discussed.

  3. Barriers for realisation of energy savings in buildings; Barrierer for realisering af energibesparelser i bygninger

    Energy Technology Data Exchange (ETDEWEB)

    Jensen, O.M.

    2004-07-01

    Many years' efforts within the energy labelling area have shown large saving potentials in heating and use of electricity in buildings. At the same time it has been proved that these saving potentials, even when economically advantageous, only are cashed to a limited extent. The reason to this is ascribed to barriers that meet the individual building owner who wants to start saving energy. Most barriers are known and a lot of these have been sought overcome for some time. The questions are how many barriers still exist, have new barriers arisen and the character of these barriers. On this background the objective of this survey has been to concretize and study the barriers, which are blocking reasonable energy savings. Focus has especially been on barriers for realisation of heating savings, but through a general evaluation of energy savings of barriers other forms of energy saving methods have been taken into consideration. Special interest has been directed towards houses, typically one family houses, which are affected by the Energy Labelling Scheme. The concept barriers include all kinds of barriers, also barriers that not are acknowledged as barriers by the individual house owner, or that on closer inspection turn out to be something else than actual barriers. This note suggests an alternative inertia model, in order to create an idea of the inertness characteristic of the many house owners who understand the message but fail to act on it. (BA)

  4. Effect of contact barrier on electron transport in graphene.

    Science.gov (United States)

    Zhou, Yang-Bo; Han, Bing-Hong; Liao, Zhi-Min; Zhao, Qing; Xu, Jun; Yu, Da-Peng

    2010-01-14

    The influence of the barrier between metal electrodes and graphene on the electrical properties was studied on a two-electrode device. A classical barrier model was used to analyze the current-voltage characteristics. Primary parameters including barrier height and effective resistance were achieved. The electron transport properties under magnetic field were further investigated. An abnormal peak-valley-peak shape of voltage-magnetoresistance curve was observed. The underlying mechanisms were discussed under the consideration of the important influence of the contact barrier. Our results indicate electrical properties of graphene based devices are sensitive to the contact interface.

  5. Potential and barrier study. Energy efficiency of Norwegian homes; Potensial- og barrierestudie. Energieffektivisering av norske boliger

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2012-07-01

    Enova has identified potentials and barriers for energy efficiency in Norwegian buildings. This report summarizes the results of this work. Efficient energy in buildings is important to ensure that future economic activity and growth can occur in a way that reduces the possibilities for an environmentally and economically sound development. (eb)

  6. Electron Emission by N6+ Ions Scattered at a Magnetized Iron Surface

    International Nuclear Information System (INIS)

    Solleder, B.; Lemell, C.; Burgdoerfer, J.; Tokesi, K.

    2006-01-01

    Complete text of publication follows. Magnetized materials are of considerable interest in the electronics industry (hard discs, spintronics, etc.). A detailed understanding of the properties of magnetized surfaces is therefore important to optimize technical applications. In the last decades, different experimental techniques have been developed to probe spin effects in magnetized materials. In this work the spin polarization of electrons emitted during the impact of N 6+ ions on a magnetized Fe surface is investigated. We study potential emission (PE) of electrons as well as secondary electron (SE) production and transport in the target with the help of Monte Carlo (MC) simulations. Spin dependence of electron transfer processes and of transport in the solid are included. Fig. 1 shows the results of our simulation for the energy distribution and spin polarization of emitted electrons in comparison with experimental data of Pfandzelter et al. [1] for the interaction of N 6+ ions with magnetized Fe. Electrons with energies higher than 200 eV are predominantly PE electrons, emitted close to the surface via autoionization (AI), Auger capture (AC) and Auger deexcitation (AD) channels. Low energy electrons are dominated by promoted, autoionized, and secondary electrons. The polarization of above surface electrons is determined by the high of the potential barrier separating projectile and target. At large distances, the barrier drops only slightly below the Fermi edge and enables transitions of electrons from this part of the band structure which has about 50% polarization. These electrons are transferred to high n states feeding promotion and AI processes between high lying states. Electrons emitted by these processes therefore reflect the polarization near the Fermi edge. Close to the surface, the barrier is low enough to allow for electron capture from the entire conduction band. K-Auger electrons are emitted in immediate vicinity of the surface and therefore mirror

  7. Quantum damped oscillator II: Bateman’s Hamiltonian vs. 2D parabolic potential barrier

    Science.gov (United States)

    Chruściński, Dariusz

    2006-04-01

    We show that quantum Bateman’s system which arises in the quantization of a damped harmonic oscillator is equivalent to a quantum problem with 2D parabolic potential barrier known also as 2D inverted isotropic oscillator. It turns out that this system displays the family of complex eigenvalues corresponding to the poles of analytical continuation of the resolvent operator to the complex energy plane. It is shown that this representation is more suitable than the hyperbolic one used recently by Blasone and Jizba.

  8. Transport properties of electrons in fractal magnetic-barrier structures

    Science.gov (United States)

    Sun, Lifeng; Fang, Chao; Guo, Yong

    2010-09-01

    Quantum transport properties in fractal magnetically modulated structures are studied by the transfer-matrix method. It is found that the transmission spectra depend sensitively not only on the incident energy and the direction of the wave vector but also on the stage of the fractal structures. Resonance splitting, enhancement, and position shift of the resonance peaks under different magnetic modulation are observed at four different fractal stages, and the relationship between the conductance in the fractal structure and magnetic modulation is also revealed. The results indicate the spectra of the transmission can be considered as fingerprints for the fractal structures, which show the subtle correspondence between magnetic structures and transport behaviors.

  9. Recent results from TMX-U thermal barrier experiments

    International Nuclear Information System (INIS)

    Molvik, A.W.; Allen, S.; Barter, J.

    1984-01-01

    The Tandem Mirror Experiment-Upgrade (TMX-U) device was designed to study plasma confinement in a tandem mirror with thermal barriers. Previously the author reported improved axial confinement with high end-plug potentials, consistent with thermal barrier operation. Now, the existence of thermal barriers in TMX-U confirmed by measuring the axial potential profile. Specifically, measured the change in energy of a 5-keV deuterium neutral beam that is injected nearly parallel to the axis and is ionized between the barrier and the central cell. The authors found that the barrier potential is lower than the central cell potential, as required for a thermal barrier. The peak potential is at least 2.4 keV, as determined from the minimum energy of end loss ions. In addition, radial transport is reduced by the use of floating and electrodes that map to concentric cylinders in the central cell. Sloshing ions continue to be microstable

  10. Effect of magnetic field on energy spectrum and localization of electron in CdS/HgS/CdS/HgS/CdS multilayered spherical nanostructure

    Energy Technology Data Exchange (ETDEWEB)

    Holovatsky, V.A., E-mail: ktf@chnu.edu.ua; Bernik, I.B.; Yakhnevych, M. Ya.

    2017-03-01

    The theoretical investigation of magnetic field effect on energy spectrum and localization of the electron and oscillator strengths of intraband quantum transitions in the nanostructure CdS/HgS/CdS/HgS/CdS is performed. The calculations are made in the framework of effective mass approximation and rectangular potential barriers model using the method of the expansion of quasi-particle wave functions over the complete basis of functions obtained as the exact solutions of the Schrodinger equation for the electron in the nanostructure without the magnetic field. It is shown that the magnetic field violates the spherical symmetry of the system and takes off the degeneration of energy spectrum with respect to the magnetic quantum number. The energy of the electron in the states with m≥0 increases when magnetic field enhances; for the states with m<0 these dependences are non-monotonous (decreasing at first and then increasing). Moreover, the ground state of electron is formed alternately by the states with m=0, −1, −2, …. Magnetic field influences on the distribution of quasi-particle density. It is shown that the electron significantly changes its localization in the nanostructure with two potential wells tunneling through the potential barrier under the effect of magnetic field, changing the oscillator strengths of intraband quantum transitions.

  11. Experimental study of neutron-optical potential with absorption using Fabry-Perot magnetic resonator

    International Nuclear Information System (INIS)

    Hino, M.; Tasaki, S.; Ebisawa, T.; Kawai, T.; Achiwa, N.; Yamazaki, D.

    1999-01-01

    Complete text of publication follows. Recently spin precession angles of neutrons tunneling and non-tunneling through [Permalloy45(PA)-germanium(Ge)]-PA Fabry-Perot magnetic resonator have been observed [1]. The spin precession angle is well reproduced by the theoretical phase difference of up and down spin neutron wave function based on one-dimensional Schroedinger equation using optical potential model [2]. Spin precession angle and transmission probability of neutron through PA-(Ge/Gd)-PA Fabry-Perot magnetic resonator are presented, where the gap(Ge/Gd) layer consists of germanium and gadolinium atoms, and the optical potential model for magnetic multilayer system with absorption is discussed. (author) [1] M. Hino, et al., Physica B 241-243, 1083 (1998).; [2] S. Yamada, et al., Annu. Rep. Res. Reactor Inst. Kyoto Univ. 11, 8 (1978)

  12. Apparatus and method for transfer of information by means of a curl-free magnetic vector potential field

    International Nuclear Information System (INIS)

    Gelinas, R.C.

    1984-01-01

    A system for transmission of information using a curl-free magnetic vector potential radiation field. The system includes current-carrying apparatus for generating a magnetic vector potential field with a curl-free component coupled to apparatus for modulating the current applied to the field generating apparatus. Receiving apparatus includes a detector with observable properties that vary with the application of an applied curl-free magnetic vector potential field. Analyzing apparatus for determining the information content of modulation imposed on the curl-free vector potential field can be established in materials that are not capable of transmitting more common electromagnetic radiation

  13. Effects of dust grain charge fluctuation on obliquely propagating dust-acoustic potential in magnetized dusty plasmas

    International Nuclear Information System (INIS)

    Mamun, A.A.; Hassan, M.H.A.

    1999-05-01

    Effects of dust grain charge fluctuation, obliqueness and external magnetic field on finite amplitude dust-acoustic solitary potential in a magnetized dusty plasma, consisting of electrons, ions and charge fluctuating dust grains, have been investigated by the reductive perturbation method. It has been shown that such a magnetized dusty plasma system may support dust-acoustic solitary potential on a very slow time scale involving the motion of dust grains, whose charge is self-consistently determined by local electron and ion currents. The effects of dust grain charge fluctuation, external magnetic field and obliqueness are found to modify the properties of this dust-acoustic solitary potential significantly. The implications of these results to some space and astrophysical dusty plasma systems, especially to planetary ring-systems and cometary tails, are briefly mentioned. (author)

  14. Superconducting pipes and levitating magnets.

    Science.gov (United States)

    Levin, Yan; Rizzato, Felipe B

    2006-12-01

    Motivated by a beautiful demonstration of the Faraday and the Lenz laws in which a small neodymium magnet falls slowly through a conducting nonferromagnetic tube, we consider the dynamics of a magnet falling coaxially through a superconducting pipe. Unlike the case of normal conducting pipes, in which the magnet quickly reaches the terminal velocity, inside a superconducting tube the magnet falls freely. On the other hand, to enter the pipe the magnet must overcome a large electromagnetic energy barrier. For sufficiently strong magnets, the barrier is so large that the magnet will not be able to penetrate it and will be levitated over the mouth of the pipe. We calculate the work that must done to force the magnet to enter a superconducting tube. The calculations show that superconducting pipes are very efficient at screening magnetic fields. For example, the magnetic field of a dipole at the center of a short pipe of radius a and length L approximately > a decays, in the axial direction, with a characteristic length xi approximately 0.26a. The efficient screening of the magnetic field might be useful for shielding highly sensitive superconducting quantum interference devices. Finally, the motion of the magnet through a superconducting pipe is compared and contrasted to the flow of ions through a trans-membrane channel.

  15. Failure Analysis in Magnetic Tunnel Junction Nanopillar with Interfacial Perpendicular Magnetic Anisotropy

    Directory of Open Access Journals (Sweden)

    Weisheng Zhao

    2016-01-01

    Full Text Available Magnetic tunnel junction nanopillar with interfacial perpendicular magnetic anisotropy (PMA-MTJ becomes a promising candidate to build up spin transfer torque magnetic random access memory (STT-MRAM for the next generation of non-volatile memory as it features low spin transfer switching current, fast speed, high scalability, and easy integration into conventional complementary metal oxide semiconductor (CMOS circuits. However, this device suffers from a number of failure issues, such as large process variation and tunneling barrier breakdown. The large process variation is an intrinsic issue for PMA-MTJ as it is based on the interfacial effects between ultra-thin films with few layers of atoms; the tunneling barrier breakdown is due to the requirement of an ultra-thin tunneling barrier (e.g., <1 nm to reduce the resistance area for the spin transfer torque switching in the nanopillar. These failure issues limit the research and development of STT-MRAM to widely achieve commercial products. In this paper, we give a full analysis of failure mechanisms for PMA-MTJ and present some eventual solutions from device fabrication to system level integration to optimize the failure issues.

  16. THE POSSIBLE IMPACT OF L5 MAGNETOGRAMS ON NON-POTENTIAL SOLAR CORONAL MAGNETIC FIELD SIMULATIONS

    Energy Technology Data Exchange (ETDEWEB)

    Weinzierl, Marion; Yeates, Anthony R. [Department of Mathematical Sciences, Durham University South Road, Durham DH1 3LE (United Kingdom); Mackay, Duncan H. [School of Mathematics and Statistics, University of St. Andrews North Haugh, St. Andrews, Fife KY16 9SS (United Kingdom); Pevtsov, Alexei A., E-mail: marion.weinzierl@durham.ac.uk [National Solar Observatory 3010 Coronal Loop, sunspot NM 88349 (United States)

    2016-09-10

    The proposed Carrington-L5 mission would bring instruments to the L5 Lagrange point to provide us with crucial data for space weather prediction. To assess the importance of including a magnetograph, we consider the possible differences in non-potential solar coronal magnetic field simulations when magnetograph observations are available from the L5 point, compared with an L1-based field of view (FOV). A timeseries of synoptic radial magnetic field maps is constructed to capture the emergence of two active regions from the L5 FOV. These regions are initially absent in the L1 magnetic field maps, but are included once they rotate into the L1 FOV. Non-potential simulations for these two sets of input data are compared in detail. Within the bipolar active regions themselves, differences in the magnetic field structure can exist between the two simulations once the active regions are included in both. These differences tend to reduce within 5 days of the active region being included in L1. The delayed emergence in L1 can, however, lead to significant persistent differences in long-range connectivity between the active regions and the surrounding fields, and also in the global magnetic energy. In particular, the open magnetic flux and the location of open magnetic footpoints, are sensitive to capturing the real-time of emergence. These results suggest that a magnetograph at L5 could significantly improve predictions of the non-potential corona, the interplanetary magnetic field, and of solar wind source regions on the Sun.

  17. Mode suppression of a two-dimensional potential relaxation instability in a weakly magnetized discharge plasma

    Science.gov (United States)

    Gyergyek, T.; Čerček, M.; Jelić, N.; Stanojević, M.

    1993-05-01

    A potential relaxation instability (PRI) is modulated by an external signal using an additional grid to modulate the radial plasma potential profile in a magnetized plasma column in a linear magnetized discharge plasma device. It is observed that the electrode current oscillations follow the van der Pol equation with an external forcing term, and the linear growth rate of the instability is measured.

  18. Investigation of the tunnel magnetoresistance in junctions with a strontium stannate barrier

    Science.gov (United States)

    Althammer, Matthias; Mishra, Rohan; Borisevich, Albina J.; Singh, Amit Vikam; Keshavarz, Sahar; Yurtisigi, Mehmet Kenan; Leclair, Patrick; Gupta, Arunava

    We experimentally investigate the structural, magnetic and electrical transport properties of La0.67Sr0.33MnO3 based magnetic tunnel junctions with a SrSnO3 barrier. Our results show that despite the high density of defects in the strontium stannate barrier the observed tunnel magnetoresistance is comparable to tunnel junctions with a better lattice matched SrTiO3 barrier, reaching values of up to 350 % at T = 5 K . Further analysis of the current-voltage characteristics of the junction and the bias voltage dependence of the observed tunnel magnetoresistance show a decrease of the TMR with increasing bias voltage. Our results suggest that by reducing the structural defects in the strontium stannate barrier, even larger TMR ratios might be possible in the future. We gratefully acknowledge financial support via NSF-ECCS Grant No. 1509875.

  19. Physics of strong internal transport barriers in JT-60U reversed-magnetic-shear plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Hayashi, N; Takizuka, T; Sakamoto, Y; Fujita, T; Kamada, Y; Ide, S; Koide, Y [Japan Atomic Energy Agency, 801-1 Mukouyama, Naka, Ibaraki 311-0193 (Japan)

    2006-05-15

    The physics of strong internal transport barriers (ITBs) in JT-60U reversed-magnetic-shear (RS) plasmas has been studied through the modelling on the 1.5 dimensional transport simulation. The key physics to produce two scalings on the basis of the JT-60U box-type ITB database are identified. As for the scaling for the narrow ITB width proportional to the ion poloidal gyroradius, the following three physics are important: (1) the sharp reduction of the anomalous transport below the neoclassical level in the RS region, (2) the autonomous formation of pressure and current profiles through the neoclassical transport and the bootstrap current and (3) the large difference between the neoclassical transport and the anomalous transport in the normal-shear region. As for the scaling for the energy confinement inside ITB ({epsilon}{sub f}{beta}{sub p,core} {approx} 0.25, where {epsilon}{sub f} is the inverse aspect ratio at the ITB foot and {beta}{sub p,core} is the core poloidal beta value), the value of 0.25 is found to be a saturation value due to the MHD equilibrium. The value of {epsilon}{sub f}{beta}{sub p,core} reaches the saturation value, when the box-type ITB is formed in the strong RS plasma with a large asymmetry of the poloidal magnetic field, regardless of the details of the transport and the non-inductively driven current.

  20. Potential solver for sloshing-ion thermal barriers

    International Nuclear Information System (INIS)

    Boghosian, B.M.; Campbell, R.B.; Gilmore, J.M.

    1981-01-01

    The quasineutrality equations at points (a) and (b) in a sloshing-ion thermal barrier are derived and an algorithm for their solution is given. The solution technique is sufficiently reliable and efficient to be used in a fluid code where it must be invoked at each time step. Circumstances under which the equations admit multiple solutions are noted and discussed

  1. Potential Magnetic Field around a Helical Flux-rope Current Structure in the Solar Corona

    OpenAIRE

    Petrie, G. J. D.

    2007-01-01

    We consider the potential magnetic field associated with a helical electric line current flow, idealizing the near-potential coronal field within which a highly localized twisted current structure is embedded. It is found that this field has a significant axial component off the helical magnetic axis where there is no current flow, such that the flux winds around the axis. The helical line current field, in including the effects of flux rope writhe, is therefore more topologically complex tha...

  2. Speeding up the first-passage for subdiffusion by introducing a finite potential barrier

    International Nuclear Information System (INIS)

    Palyulin, Vladimir V; Metzler, Ralf

    2014-01-01

    We show that for a subdiffusive continuous time random walk with scale-free waiting time distribution the first-passage dynamics on a finite interval can be optimized by introduction of a piecewise linear potential barrier. Analytical results for the survival probability and first-passage density based on the fractional Fokker–Planck equation are shown to agree well with Monte Carlo simulations results. As an application we discuss an improved design for efficient translocation of gradient copolymers compared to homopolymer translocation in a quasi-equilibrium approximation. (fast track communications)

  3. Nature of potential barrier in (Ca 1/4,Cu 3/4)TiO 3 polycrystalline perovskite

    Science.gov (United States)

    Marques, V. P. B.; Bueno, P. R.; Simões, A. Z.; Cilense, M.; Varela, J. A.; Longo, E.; Leite, E. R.

    2006-04-01

    The nonohmic electrical features of (Ca 1/4,Cu 3/4)TiO 3 perovskite ceramics, which have very strong gigantic dielectric is believed originate from potential barriers at the grain boundaries. In the present study, we used the admittance and impedance spectroscopy technique to investigate (Ca 1/4,Cu 3/4)TiO 3 perovskite ceramics with low nonohmic electrical properties. The study was conducted under two different conditions: on as-sintered ceramics and on ceramics thermally treated in an oxygen-rich atmosphere. The results confirm that thermal treatment in oxygen-rich atmospheres influence the nonohmic properties. Annealing at oxygen-rich atmospheres improve the nonohmic behavior and annealing at oxygen-poor atmospheres decrease the nonohmic properties, a behavior already reported for common metal oxide nonohmic devices and here firstly evidenced for the (Ca 1/4,Cu 3/4)TiO 3 perovskite related materials. The results show that oxygen also influences the capacitance values at low frequencies, a behavior that is indicative of the Schottky-type nature of the potential barrier.

  4. Shaping magnetic fields to direct therapy to ears and eyes.

    Science.gov (United States)

    Shapiro, B; Kulkarni, S; Nacev, A; Sarwar, A; Preciado, D; Depireux, D A

    2014-07-11

    Magnetic fields have the potential to noninvasively direct and focus therapy to disease targets. External magnets can apply forces on drug-coated magnetic nanoparticles, or on living cells that contain particles, and can be used to manipulate them in vivo. Significant progress has been made in developing and testing safe and therapeutic magnetic constructs that can be manipulated by magnetic fields. However, we do not yet have the magnet systems that can then direct those constructs to the right places, in vivo, over human patient distances. We do not yet know where to put the external magnets, how to shape them, or when to turn them on and off to direct particles or magnetized cells-in blood, through tissue, and across barriers-to disease locations. In this article, we consider ear and eye disease targets. Ear and eye targets are too deep and complex to be targeted by a single external magnet, but they are shallow enough that a combination of magnets may be able to direct therapy to them. We focus on how magnetic fields should be shaped (in space and time) to direct magnetic constructs to ear and eye targets.

  5. Permeability of the blood-brain barrier predicts conversion from optic neuritis to multiple sclerosis

    DEFF Research Database (Denmark)

    Cramer, Stig P; Modvig, Signe; Simonsen, Helle Juhl

    2015-01-01

    in the permeability of the blood-brain barrier in normal-appearing white matter of patients with multiple sclerosis and here, for the first time, we present a study on the capability of blood-brain barrier permeability in predicting conversion from optic neuritis to multiple sclerosis and a direct comparison...... with cerebrospinal fluid markers of inflammation, cellular trafficking and blood-brain barrier breakdown. To this end, we applied dynamic contrast-enhanced magnetic resonance imaging at 3 T to measure blood-brain barrier permeability in 39 patients with monosymptomatic optic neuritis, all referred for imaging...... fluid as well as levels of CXCL10 and MMP9 in the cerebrospinal fluid. These findings suggest that blood-brain barrier permeability, as measured by magnetic resonance imaging, may provide novel pathological information as a marker of neuroinflammation related to multiple sclerosis, to some extent...

  6. Thermally activated magnetization reversal in magnetic tunnel junctions

    International Nuclear Information System (INIS)

    Guang-Hong, Zhou; Yin-Gang, Wang; Xian-Jin, Qi; Zi-Quan, Li; Jian-Kang, Chen

    2009-01-01

    In this paper, the magnetization reversal of the ferromagnetic layers in the IrMn/CoFe/AlO x /CoFe magnetic tunnel junction has been investigated using bulk magnetometry. The films exhibit very complex magnetization processes and reversal mechanism. Thermal activation phenomena such as the training effect, the asymmetry of reversal, the loop broadening and the decrease of exchange field while holding the film at negative saturation have been observed on the hysteresis loops of the pinned ferromagnetic layer while not on those of the free ferromagnetic layer. The thermal activation phenomena observed can be explained by the model of two energy barrier distributions with different time constants. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  7. Magnetization reversal in single molecule magnets

    Science.gov (United States)

    Bokacheva, Louisa

    2002-09-01

    I have studied the magnetization reversal in single molecule magnets (SMMs). SMMs are Van der Waals crystals, consisting of identical molecules containing transition metal ions, with high spin and large uniaxial magnetic anisotropy. They can be considered as ensembles of identical, iso-oriented nanomagnets. At high temperature, these materials behave as superparamagnets and their magnetization reversal occurs by thermal activation. At low temperature they become blocked, and their magnetic relaxation occurs via thermally assisted tunneling or pure quantum tunneling through the anisotropy barrier. We have conducted detailed experimental studies of the magnetization reversal in SMM material Mn12-acetate (Mn12) with S = 10. Low temperature measurements were conducted using micro-Hall effect magnetometry. We performed hysteresis and relaxation studies as a function of temperature, transverse field, and magnetization state of the sample. We identified magnetic sublevels that dominate the tunneling at a given field, temperature and magnetization. We observed a crossover between thermally assisted and pure quantum tunneling. The form of this crossover depends on the magnitude and direction of the applied field. This crossover is abrupt (first-order) and occurs in a narrow temperature interval (tunneling mechanisms in Mn12.

  8. Interfacial mixing in double-barrier magnetic tunnel junctions with amorphous NiFeSiB layers

    International Nuclear Information System (INIS)

    Chun, B.S.; Ko, S.P.; Hwang, J.Y.; Rhee, J.R.; Kim, T.W.; Kim, Y.K.

    2007-01-01

    Double-barrier magnetic tunnel junctions (DMTJs) comprising Ta 45/Ru 9.5/IrMn 10/CoFe 7/AlO x /free layer (CoFe 4/NiFeSiB 2/CoFe 4, CoFe 10, or NiFeSiB 10)/AlO x /CoFe 7/IrMn 10/Ru 60 (nm) have been examined with an emphasis given on understanding the interfacial mixing effects. The DMTJ, consisted of NiFeSiB, shows low switching field and low bias voltage dependence because the amorphous NiFeSiB has lower M S (=800 emu/cm 3 ) and offers smoother interfaces than polycrystalline CoFe. An interesting feature observed in the CoFe/NiFeSiB/CoFe sandwich free layered DMTJ is the presence of a wavy MR transfer curve at high-resistance region. Because the polycrystalline CoFe usually grows into a columnar structure, diamagnetic CoSi, paramagnetic FeSi, and/or diamagnetic CoB might have been formed during the sputter-deposition process. By employing electron energy loss spectrometry (EELS) and Auger electron spectroscopy (AES), we were able to confirm that Si and B atoms were arranged evenly in the top and bottom portions of AlO x /CoFe interfaces. This means that the interfacial mixing resulted in a distorted magnetization reversal process

  9. Studies on polyaspartamide gadolinium complexes as potential magnetic resonance imaging contrast agents

    International Nuclear Information System (INIS)

    Yan Guoping; Liu Maili; Li Liyun

    2005-01-01

    Purpose: A series of polyaspartamide gadolinium complexes containing pyridoxamine groups were studied as the potential magnetic resonance imaging (MRI) contrast agents for liver enhancement. Methods: These polyaspartamide gadolinium complexes were prepared and evaluated by relaxivity, acute toxicity studies and magnetic resonance imaging of the liver in rats. Results: These polyaspartamide gadolinium complexes have higher relaxation effectiveness than that of the clinically used gadolinium diethylenetriaminepentaacetic acid and possess the low intravenous acute toxicities to Institute for Cancer Research (ICR) mice. Magnetic resonance imaging of the liver in rats indicated that they greatly enhance the contrast of magnetic resonance images and provide prolonged intravascular duration in the liver. Conclusion: These results indicated that the polyaspartamide gadolinium complexes containing pyridoxamine groups could be considered as the appropriate MRI contrast agents for liver enhancement

  10. Potential of kaolin-based particle film barriers for Formosan subterranean termite (Isoptera: Rhinotermitidae) control

    Science.gov (United States)

    Wiltz, B.A.; Woodson, W.D.; Puterka, G.J.

    2010-01-01

    Effects of three particle film products on Formosan subterranean termites, Coptotermes formosanus Shiraki, were evaluated in feeding, tunneling, and contact assays. The particle films, hydrophobic M96-018 and hydrophilic Surround and Surround WP are based on the inert clay mineral kaolin. In 2-week long no-choice feeding tests, significant mortality occurred only with M96-018-coated wood. When a choice was provided, M96-018 and Surround were consumed at higher rates than untreated wood. Surround WP did not differ from controls in either test. In the tunneling assay termites were given the option of crossing a kaolin-sand mixture to reach an alternate food source. After 3-weeks, rates of 1% and 5% M96-018 provided an effective barrier to Formosan termite tunneling, while termites were not stopped by rates as high as 20% Surround and Surround WP. Dust treatments of all three formulations caused significant increases in mortality within 24 h, with mortality rates ranging from 72.0 - 97.3% within 72 h of treatment. The particle films were most effective when moisture levels were low, suggesting that desiccation was the mechanism for mortality. All particle films showed potential for use in above ground applications while hydrophobic M06-018 has the most potential as a soil barrier to subterranean termites.

  11. Heavy-ion fusion: Channel-coupling effects, the barrier penetration model, and the threshold anomaly for heavy-ion potentials

    International Nuclear Information System (INIS)

    Satchler, G.R.; Nagarajan, M.A.; Lilley, J.S.; Thompson, I.J.

    1987-01-01

    We study the formal structure of the influence of channel coupling on near- and sub-barrier fusion. The reduction to a one-channel description is studied, with emphasis on the channel-coupling effects being manifest primarily as an energy dependence (the ''threshold anomaly'') of the real nuclear potential. The relation to the barrier penetration model is examined critically. The results of large-scale coupled-channel calculations are used as ''data'' to illustrate the discussion. Particular emphasis is placed on the importance of reproducing correctly the partial-wave (or ''spin'') distributions. The simple barrier penetration model is found to be adequate to exhibit the strong enhancements due to channel couplings when the threshold anomaly is taken into account, although there may be important corrections due to the long-ranged peripheral absorption, especially from Coulomb excitation. copyright 1987 Academic Press, Inc

  12. Single-electron tunneling in double-barrier nanostructures

    International Nuclear Information System (INIS)

    Goldman, V.J.; Su, B.; Cunningham, J.E.

    1992-01-01

    In this paper, the authors review experimental study of charge transport in nanometer double-barrier resonant tunneling devices. Heterostructure material is asymmetric: one barrier is substantially less transparent than the other. Resonant tunneling through size-quantized well states and single-electron charging of the well are thus largely separated in the two bias polarities. When the emitter barrier is more transparent than the collector barrier, electrons accumulate in the well; incremental electron occupation of the well is accompanied by Coulomb blockade leading to sharp steps of the tunneling current. When the emitter barrier is less transparent, the current reflects resonant tunneling of just one electron at a time through size-quantized well states; the current peaks and/or steps (depending on experimental parameters) appear in current-voltage characteristics. Magnetic field and temperature effects are also reviewed. Good agreement is achieved in comparison of many features of experimental data with simple theoretical models

  13. Numerical methods for finding periodic points in discrete maps. High order islands chains and noble barriers in a toroidal magnetic configuration

    Energy Technology Data Exchange (ETDEWEB)

    Steinbrecher, G. [Association Euratom-Nasti Romania, Dept. of Theoretical Physics, Physics Faculty, University of Craiova (Romania); Reuss, J.D.; Misguich, J.H. [Association Euratom-CEA Cadarache, 13 - Saint-Paul-lez-Durance (France). Dept. de Recherches sur la Fusion Controlee

    2001-11-01

    We first remind usual physical and mathematical concepts involved in the dynamics of Hamiltonian systems, and namely in chaotic systems described by discrete 2D maps (representing the intersection points of toroidal magnetic lines in a poloidal plane in situations of incomplete magnetic chaos in Tokamaks). Finding the periodic points characterizing chains of magnetic islands is an essential step not only to determine the skeleton of the phase space picture, but also to determine the flux of magnetic lines across semi-permeable barriers like Cantori. We discuss here several computational methods used to determine periodic points in N dimensions, which amounts to solve a set of N nonlinear coupled equations: Newton method, minimization techniques, Laplace or steepest descend method, conjugated direction method and Fletcher-Reeves method. We have succeeded to improve this last method in an important way, without modifying its useful double-exponential convergence. This improved method has been tested and applied to finding periodic points of high order m in the 2D 'Tokamap' mapping, for values of m along rational chains of winding number n/m converging towards a noble value where a Cantorus exists. Such precise positions of periodic points have been used in the calculation of the flux across this Cantorus. (authors)

  14. A consistent derivation of the real and imaginary parts of the heavy ion potential below and above the Coulomb barrier

    International Nuclear Information System (INIS)

    Vinh Mau, N.

    1987-03-01

    In a model including approximately a large set of non elastic channels, the real and imaginary potentials are consistently derived. The anomaly of the real potential which sharply increases in the vicinity of the Coulomb barrier where the imaginary potential is strongly reduced is studied in 16 0+ 40 Ca and 16 O+ 208 Pb systems. The results on the imaginary potential are discussed and compared to our previous calculation

  15. Microscopic calculation of sub-barrier fusion cross section and barrier distribution using M3Y-type forces

    International Nuclear Information System (INIS)

    Ismail, M.; Ramadan, Kh.A.

    2000-01-01

    The heavy-ion (HI) potential between spherical and deformed nuclei is derived using an M3Y-type nucleon-nucleon (NN) interaction. The calculation of the exchange part of the HI potential was improved by using a finite-range NN exchange force instead of the zero-range pseudo-potential which is usually used in deriving the potential between deformed nuclei. We consider an 154 Sm- 16 O nuclear pair as an example to show the effect of finite range on the nucleus-nucleus potential for different deformation parameters and at different orientation angles of the deformed target nucleus. We calculated the fusion cross section and the barrier distribution in the WKB approximation and studied their dependence on the orientation and deformation of the target nucleus. The variations found due to improving the exchange part enhance the fusion cross section below the Coulomb barrier by a factor of about four. It has been found that both the cross section and the barrier distribution are very sensitive to the deformation parameters at energies below the Coulomb barrier. (author)

  16. Microscopic calculation of sub-barrier fusion cross section and barrier distribution using M3Y-type forces

    Energy Technology Data Exchange (ETDEWEB)

    Ismail, M.; Ramadan, Kh.A. [Physics Department, Faculty of Science, Cairo University, Giza (Egypt)

    2000-10-01

    The heavy-ion (HI) potential between spherical and deformed nuclei is derived using an M3Y-type nucleon-nucleon (NN) interaction. The calculation of the exchange part of the HI potential was improved by using a finite-range NN exchange force instead of the zero-range pseudo-potential which is usually used in deriving the potential between deformed nuclei. We consider an {sup 154}Sm-{sup 16}O nuclear pair as an example to show the effect of finite range on the nucleus-nucleus potential for different deformation parameters and at different orientation angles of the deformed target nucleus. We calculated the fusion cross section and the barrier distribution in the WKB approximation and studied their dependence on the orientation and deformation of the target nucleus. The variations found due to improving the exchange part enhance the fusion cross section below the Coulomb barrier by a factor of about four. It has been found that both the cross section and the barrier distribution are very sensitive to the deformation parameters at energies below the Coulomb barrier. (author)

  17. Electron internal transport barriers and magnetic topology in the stellarator TJ-II

    Energy Technology Data Exchange (ETDEWEB)

    Estrada, T.; Lopez-Bruna, D.; Alosno, A.; Ascasibar, E.; Baciero, A.; Cappa, A.; Castejon, F.; Fernandez, A.; Herranz, J.; Hidalgo, C.; Pablos, J. L. de; Pastor, I.; Sanchez, E.; Sanchez, J.

    2005-07-01

    In most helical systems electron Internal Transport Barriers (e-ITB) are observed in Electron Cyclotron Heated (ECH) plasmas with high heating power density. In the stellarator TJ-II, e- ITBs are easily achievable by positioning a low order rational surface close to the plasma core, because this increases the density range in which the e-ITB can form. Experiments with different low order rationals show a dependence of the threshold density and barrier quality on the order of the rational (3/2, 4/2, 5/3, ...). In addition, during the formation of e-ITB quasicoherent modes are frequently observed in the plasma core region. The mode can exist before or after the e-ITB phenomenon at the radial location of the transport barrier foot but vanishes as the barrier is fully developed. (Author)

  18. Improved ring potential of QED at finite temperature and in the presence of weak and strong magnetic fields

    International Nuclear Information System (INIS)

    Sadooghi, N.; Anaraki, K. Sohrabi

    2008-01-01

    Using the general structure of the vacuum polarization tensor Π μν (k 0 ,k) in the infrared (IR) limit, k 0 →0, the ring contribution to the QED effective potential at finite temperature and the nonzero magnetic field is determined beyond the static limit, (k 0 →0, k→0). The resulting ring potential is then studied in weak and strong magnetic field limits. In the weak magnetic field limit, at high temperature and for α→0, the improved ring potential consists of a term proportional to T 4 α 5/2 , in addition to the expected T 4 α 3/2 term arising from the static limit. Here, α is the fine structure constant. In the limit of the strong magnetic field, where QED dynamics is dominated by the lowest Landau level, the ring potential includes a novel term consisting of dilogarithmic function (eB)Li 2 (-(2α/π)(eB/m 2 )). Using the ring improved (one-loop) effective potential including the one-loop effective potential and ring potential in the IR limit, the dynamical chiral symmetry breaking of QED is studied at finite temperature and in the presence of the strong magnetic field. The gap equation, the dynamical mass and the critical temperature of QED in the regime of the lowest Landau level dominance are determined in the improved IR as well as in the static limit. For a given value of the magnetic field, the improved ring potential is shown to be more efficient in decreasing the critical temperature arising from the one-loop effective potential.

  19. Potential Pathways for CNS Drug Delivery Across the Blood-Cerebrospinal Fluid Barrier

    OpenAIRE

    Strazielle, Nathalie; Ghersi-Egea, Jean-Fran?ois

    2016-01-01

    The blood-brain interfaces restrict the cerebral bioavailability of pharmacological compounds. Various drug delivery strategies have been developed to improve drug penetration into the brain. Most strategies target the microvascular endothelium forming the blood-brain barrier proper. Targeting the blood-cerebrospinal fluid (CSF) barrier formed by the epithelium of the choroid plexuses in addition to the blood-brain barrier may offer added-value for the treatment of central nervous system dise...

  20. Contaminant containment using polymer gel barriers

    NARCIS (Netherlands)

    Darwish, M.I.M.; Rowe, R.K.; Maarel, van der J.R.C.; Pel, L.; Huinink, H.P.; Zitha, P.L.J.

    2004-01-01

    Polymer gels are well known in the oil industry, but their potential for use as barriers to contaminant transport has not previously received significant study. As a first step, this paper examines the potential for a polyelectrolyte gel to serve as a barrier to the migration of sodium chloride. Two

  1. Magnetic avalanches in manganese-acetate, "magnetic deflagration"

    Science.gov (United States)

    Suzuki, Yoko

    Mn12-acetate, first synthesized in 1980 by Lis, is one example of a class of many molecules called single molecule magnets (SMMs) or molecular nanomagnets. These molecules have several atomic spins strongly coupled together within each molecule. They exhibit interesting quantum mechanical phenomena at low temperatures such as quantum tunneling of magnetization, which was first found with Mn12-acetate in 1996 by Friedman, et al. , and Berry phase oscillations which were measured in Fe8 (another SMM) in 1999 by Wernsdorfer, et al. In addition to possible application as memory storage and qubits for quantum computers, these systems provide the means for studies of mesoscopic physics as well as the interactions of the molecules with their environment, such as phonon, photon, nuclear spin, intermolecular dipole, and exchange interactions. Mn12-acetate has twelve Mn ions magnetically coupled in the center of the molecule yielding a giant spin of S = 10 at low temperature. It also has a large uniaxial anisotropy of 65 K. Below 3 K, magnetization curves show strong hysteresis due to the anisotropy barrier. At thesis temperatures, the spin relaxes through the barrier by quantum tunneling of magnetization, which produces regularly-spaced multiple resonant steps in the hysteresis curve. Magnetic avalanches, first detected by Paulsen et al., also occur for some samples only at low temperature, leading to a very fast single-step reversal of the full magnetization, which clearly differs from relaxation by tunneling. In this thesis, I present the results of detailed experimental studies of two aspects of magnetic avalanche phenomenon: "conditions for the triggering of avalanches" and "propagation of the avalanche front". In the first study, we find the magnetic fields at which avalanches occur are stochastically distributed in a particular range of fields. For the second study, we conducted local time-resolved measurements. The results indicate the magnetization avalanches spread

  2. Magnetism of hexagonal close-packed nickel calculated by full-potential linearized augmented plane wave method

    International Nuclear Information System (INIS)

    Tian, F.; Tian, H.; Whitmore, L.; Ye, L.Y.

    2015-01-01

    The energy dependent on volume of hexagonal close-packed (hcp) nickel with different magnetism is calculated by full-potential linearized augmented plane wave method. Based on the calculation ferromagnetic state is found to be the most stable state. The magnetic moment of hcp Ni is calculated and compared to those calculated by different pseudo-potential methods. Furthermore, it is also compared to that of face-centered cubic (fcc) one with the reason discussed

  3. Quantum tunneling of magnetization in solids

    International Nuclear Information System (INIS)

    Stamp, P.C.E.; Barbara, B.

    1992-01-01

    Magnetic solids should, under certain circumstances, show macroscopic quantum behavior, in which coherence exists between completely distinct magnetization states, each involving a very large number of spins (∼10 12 spins). This article reviews the recent work in this field, concentrating particularly on macroscopic quantum tunneling (MQT) of magnetization. The two main phenomena discussed are the tunneling of magnetization in single-domain particles or grains (in which some 10 3 - 10 4 spins rotate together through an energy barrier), and the tunneling of domain walls in films or in bulk magnets; where walls containing ∼10 10 spins may tunnel off a pinning potential, or from one pinning center to another. Some attention is also given to the quantum nucleation of magnetization reversal in a bulk magnet, and to the quantum motion of other magnetic solitons (such as vortices). After a thorough analysis of the basic grain and wall tunneling phenomena, the authors continue on to a discussion of the various dissipative or decoherence mechanisms, which destroy the phase correlations involved in tunneling. The coupling of grain magnetization to phonons, photons, and electrons is shown to have little consequence for weakly-conducting or insulating grains. Domain walls couple to these and also to magnons and impurities or defects; the 3rd order coupling to magnons can have serious effects, but if one uses pure insulators at low temperatures, these can also be ignored

  4. Role of the current density profile on drift wave stability in internal transport barrier reversed magnetic shear experiments at JET and Tore Supra

    Energy Technology Data Exchange (ETDEWEB)

    Fourment, C; Hoang, G T; Eriksson, L-G; Garbet, X; Litaudon, X; Tresset, G [EURATOM-CEA Association, CEA/DSM/DRFC, CEA Cadarache, 13108 St Paul-lez-Durance (France)

    2003-03-01

    The role of the current density profile on drift wave stability is investigated using a linear electrostatic gyro-kinetic code. The growth rates are shown to have a linear dependence on the normalized temperature gradients above a certain threshold. A parametric study of the threshold shows a dramatic stabilizing effect of negative magnetic shear, especially for large scale instabilities. A set of handy formulae fitting the threshold as a function of the magnetic shear and the safety factor is proposed. Analysis of reversed magnetic shear discharges with internal transport barrier (ITB) in JET shows that ion ITBs can be triggered by the negative magnetic shear in the core of the plasma. Subsequently, the increase of the ExB shearing rate allows for the expansion of the ITB, despite the increase of the linear growth rates due to the temperature gradient peaking. In the case of the electron ITB obtained in the Tore Supra LHEP mode, the central increase of the confinement is associated with the stabilization of large scale trapped electron modes by the negative magnetic shear effect, whereas the steep electron temperature gradient destabilizes the small scale electron temperature gradient modes, which prevent the electron heat transport to reach neoclassical levels.

  5. Observation of ion confining potential enhancement due to thermal barrier potential formation and its scaling law in the tandem mirror GAMMA 10

    International Nuclear Information System (INIS)

    Cho, Teruji; Nakashima, Yousuke; Foote, J.H.

    1987-01-01

    In the tandem mirror GAMMA 10, (i) the enhancement of the ion confining potential, φ c , only during the period of the thermal barrier potential φ b -formation, has been observed first by using not only end-loss-analysers (ELA's) of GAMMA 10 but an end-loss-ion-spectrometer (ELIS) installed from TMX-U. This results in strong end-loss-ion plugging with increased central cell density. (ii) The first experimental observation of the φ c vs φ b -scaling law is obtained, where φ c increases with φ b . This scaling law is consistently interpreted by Cohen's theories of the weak-ECH and the strong-ECH in the plug region. (iii) Good agreement of the plug potential measured with the ELA's and the ELIS is achieved. (author)

  6. Magnetic field effects on the open circuit potential of ferromagnetic electrodes in corroding solutions.

    Science.gov (United States)

    Dass, Amala; Counsil, Joseph A; Gao, Xuerong; Leventis, Nicholas

    2005-06-02

    Magnetic fields shift the open circuit potential (OCP) of ferromagnetic electrodes (Fe, Co, and Ni) in corroding solutions. The OCP changes we observe (a) follow the series Fe>Co>Ni; (b) increase with the magnetic flux density; (c) reach a maximum with disk electrodes approximately 1 mm in diameter; and (d) depend on the orientation of the electrode. We report that when the surface of the electrode is oriented parallel (theta = 90 degrees) or perpendicular (theta = 0 degrees) to the magnetic field, the open circuit potential moves in opposite directions (positive and negative, respectively) with the largest changes occurring when the electrode surface is parallel to the magnetic field. Nonconvective sleeve electrodes produce the same behavior. The overall experimental evidence suggests that the magnetic field changes the OCP by modifying the surface concentrations of the paramagnetic participants in the corrosion process of the ferromagnetic electrode by species in solution; this in turn is accomplished by imposing a field-gradient driven mode of mass transfer upon paramagnetic species in solution (magnetophoresis). Simulations of the magnetic field around the ferromagnetic electrode at the two extreme orientations considered here show that in one case (theta = 90 degrees) field gradients actually repel, while in the other case (theta = 0 degrees) they attract paramagnetic species in the vicinity of the electrode.

  7. Magnetic switching of a single molecular magnet due to spin-polarized current

    Science.gov (United States)

    Misiorny, Maciej; Barnaś, Józef

    2007-04-01

    Magnetic switching of a single molecular magnet (SMM) due to spin-polarized current flowing between ferromagnetic metallic leads (electrodes) is investigated theoretically. Magnetic moments of the leads are assumed to be collinear and parallel to the magnetic easy axis of the molecule. Electrons tunneling through the barrier between magnetic leads are coupled to the SMM via exchange interaction. The current flowing through the system, as well as the spin relaxation times of the SMM, are calculated from the Fermi golden rule. It is shown that spin of the SMM can be reversed by applying a certain voltage between the two magnetic electrodes. Moreover, the switching may be visible in the corresponding current-voltage characteristics.

  8. Tunnel junctions with multiferroic barriers

    Science.gov (United States)

    Gajek, Martin; Bibes, Manuel; Fusil, Stéphane; Bouzehouane, Karim; Fontcuberta, Josep; Barthélémy, Agnès; Fert, Albert

    2007-04-01

    Multiferroics are singular materials that can exhibit simultaneously electric and magnetic orders. Some are ferroelectric and ferromagnetic and provide the opportunity to encode information in electric polarization and magnetization to obtain four logic states. However, such materials are rare and schemes allowing a simple electrical readout of these states have not been demonstrated in the same device. Here, we show that films of La0.1Bi0.9MnO3 (LBMO) are ferromagnetic and ferroelectric, and retain both ferroic properties down to a thickness of 2nm. We have integrated such ultrathin multiferroic films as barriers in spin-filter-type tunnel junctions that exploit the magnetic and ferroelectric degrees of freedom of LBMO. Whereas ferromagnetism permits read operations reminiscent of magnetic random access memories (MRAM), the electrical switching evokes a ferroelectric RAM write operation. Significantly, our device does not require the destructive ferroelectric readout, and therefore represents an advance over the original four-state memory concept based on multiferroics.

  9. Reactor potential for magnetized target fusion

    International Nuclear Information System (INIS)

    Dahlin, J.E.

    2001-06-01

    Magnetized Target Fusion (MTF) is a possible pathway to thermonuclear fusion different from both magnetic fusion and inertial confinement fusion. An imploding cylindrical metal liner compresses a preheated and magnetized plasma configuration until thermonuclear conditions are achieved. In this report the Magnetized Target Fusion concept is evaluated and a zero-dimensional computer model of the plasma, liner and circuit as a connected system is designed. The results of running this code are that thermonuclear conditions are achieved indeed, but only during a very short time. At peak compression the pressure from the compressed plasma and magnetic field is so large reversing the liner implosion into an explosion. The time period of liner motion reversal is termed the dwell time and is crucial to the performance of the fusion system. Parameters as liner thickness and plasma density are certainly of significant importance to the dwell time, but it seems like a reactor based on the MTF principle hardly can become economic if not innovative solutions are introduced. In the report two such solutions are presented as well

  10. Reactor potential for magnetized target fusion

    Energy Technology Data Exchange (ETDEWEB)

    Dahlin, J.E

    2001-06-01

    Magnetized Target Fusion (MTF) is a possible pathway to thermonuclear fusion different from both magnetic fusion and inertial confinement fusion. An imploding cylindrical metal liner compresses a preheated and magnetized plasma configuration until thermonuclear conditions are achieved. In this report the Magnetized Target Fusion concept is evaluated and a zero-dimensional computer model of the plasma, liner and circuit as a connected system is designed. The results of running this code are that thermonuclear conditions are achieved indeed, but only during a very short time. At peak compression the pressure from the compressed plasma and magnetic field is so large reversing the liner implosion into an explosion. The time period of liner motion reversal is termed the dwell time and is crucial to the performance of the fusion system. Parameters as liner thickness and plasma density are certainly of significant importance to the dwell time, but it seems like a reactor based on the MTF principle hardly can become economic if not innovative solutions are introduced. In the report two such solutions are presented as well.

  11. Three dimensional magnetic fields in extra high speed modified Lundell alternators computed by a combined vector-scalar magnetic potential finite element method

    Science.gov (United States)

    Demerdash, N. A.; Wang, R.; Secunde, R.

    1992-01-01

    A 3D finite element (FE) approach was developed and implemented for computation of global magnetic fields in a 14.3 kVA modified Lundell alternator. The essence of the new method is the combined use of magnetic vector and scalar potential formulations in 3D FEs. This approach makes it practical, using state of the art supercomputer resources, to globally analyze magnetic fields and operating performances of rotating machines which have truly 3D magnetic flux patterns. The 3D FE-computed fields and machine inductances as well as various machine performance simulations of the 14.3 kVA machine are presented in this paper and its two companion papers.

  12. Magnetic quantum tunneling: insights from simple molecule-based magnets.

    Science.gov (United States)

    Hill, Stephen; Datta, Saiti; Liu, Junjie; Inglis, Ross; Milios, Constantinos J; Feng, Patrick L; Henderson, John J; del Barco, Enrique; Brechin, Euan K; Hendrickson, David N

    2010-05-28

    This perspectives article takes a broad view of the current understanding of magnetic bistability and magnetic quantum tunneling in single-molecule magnets (SMMs), focusing on three families of relatively simple, low-nuclearity transition metal clusters: spin S = 4 Ni(II)(4), Mn(III)(3) (S = 2 and 6) and Mn(III)(6) (S = 4 and 12). The Mn(III) complexes are related by the fact that they contain triangular Mn(III)(3) units in which the exchange may be switched from antiferromagnetic to ferromagnetic without significantly altering the coordination around the Mn(III) centers, thereby leaving the single-ion physics more-or-less unaltered. This allows for a detailed and systematic study of the way in which the individual-ion anisotropies project onto the molecular spin ground state in otherwise identical low- and high-spin molecules, thus providing unique insights into the key factors that control the quantum dynamics of SMMs, namely: (i) the height of the kinetic barrier to magnetization relaxation; and (ii) the transverse interactions that cause tunneling through this barrier. Numerical calculations are supported by an unprecedented experimental data set (17 different compounds), including very detailed spectroscopic information obtained from high-frequency electron paramagnetic resonance and low-temperature hysteresis measurements. Comparisons are made between the giant spin and multi-spin phenomenologies. The giant spin approach assumes the ground state spin, S, to be exact, enabling implementation of simple anisotropy projection techniques. This methodology provides a basic understanding of the concept of anisotropy dilution whereby the cluster anisotropy decreases as the total spin increases, resulting in a barrier that depends weakly on S. This partly explains why the record barrier for a SMM (86 K for Mn(6)) has barely increased in the 15 years since the first studies of Mn(12)-acetate, and why the tiny Mn(3) molecule can have a barrier approaching 60% of this

  13. Observation of potential barriers on barium strontium titanate PTCR ceramics by electrostatic force microscopy

    International Nuclear Information System (INIS)

    Manfredini, J.P.; Paulin Filho, P.I.; Gheno, S.M.

    2011-01-01

    A composition of PTCR ceramic based in barium titanate with isovalent replacement of part of barium by strontium using lanthanum and manganese as additives was investigated. The transition temperature, typical of these materials, was shifted below the room temperature by the presence of strontium, whose behavior was detected by tests of DC resistivity and impedance spectroscopy. The observation of potential barriers at grain boundaries was possible through the technique of electrostatic force microscopy (EFM). The results also showed the presence of space charges in regions inside grains, possibly at subgrain boundaries. (author)

  14. Domain wall motion in magnetically frustrated nanorings

    Science.gov (United States)

    Lubarda, M. V.; Escobar, M. A.; Li, S.; Chang, R.; Fullerton, E. E.; Lomakin, V.

    2012-06-01

    We describe a magnetically frustrated nanoring (MFNR) configuration which is formed by introducing antiferromagnetic coupling across an interface orthogonal to the ring's circumferential direction. Such structures have the unique characteristic that only one itinerant domain wall (DW) can exist in the ring, which does not need to be nucleated or injected into the structure and can never escape making it analogous to a magnetic Möbius strip. Numerical simulations show that the DW in a MFNR can be driven consecutively around the ring with a prescribed cyclicity, and that the frequency of revolutions can be controlled by the applied field. The energy landscapes can be controlled to be flat allowing for low fields of operation or to have a barrier for thermal stability. Potential logic and memory applications of MFNRs are considered and discussed.

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

    Directory of Open Access Journals (Sweden)

    Wan Haliza Abd Majid

    2012-03-01

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

  16. RELATIVE CONTRIBUTION OF THE MAGNETIC FIELD BARRIER AND SOLAR WIND SPEED IN ICME-ASSOCIATED FORBUSH DECREASES

    International Nuclear Information System (INIS)

    Bhaskar, Ankush; Vichare, Geeta; Subramanian, Prasad

    2016-01-01

    We study 50 cosmic-ray Forbush decreases (FDs) from the Oulu neutron monitor data during 1997–2005 that were associated with Earth-directed interplanetary coronal mass ejections (ICMEs). Such events are generally thought to arise due to the shielding of cosmic rays by a propagating diffusive barrier. The main processes at work are the diffusion of cosmic rays across the large-scale magnetic fields carried by the ICME and their advection by the solar wind. In an attempt to better understand the relative importance of these effects, we analyze the relationship between the FD profiles and those of the interplanetary magnetic field (B) and the solar wind speed (V sw ). Over the entire duration of a given FD, we find that the FD profile is generally (anti)correlated with the B and V sw profiles. This trend holds separately for the FD main and recovery phases too. For the recovery phases, however, the FD profile is highly anti-correlated with the V sw profile, but not with the B profile. While the total duration of the FD profile is similar to that of the V sw profile, it is significantly longer than that of the B profile. Using the convection–diffusion model, a significant contribution of advection by solar wind is found during the recovery phases of the FD.

  17. RELATIVE CONTRIBUTION OF THE MAGNETIC FIELD BARRIER AND SOLAR WIND SPEED IN ICME-ASSOCIATED FORBUSH DECREASES

    Energy Technology Data Exchange (ETDEWEB)

    Bhaskar, Ankush; Vichare, Geeta [Indian Institute of Geomagnetism, Kalamboli Highway, New Panvel, Navi Mumbai 410218 (India); Subramanian, Prasad, E-mail: ankushbhaskar@gmail.com [Indian Institute of Science Education and Research, Dr. Homi Bhabha Road, Pashan, Pune 411008 (India)

    2016-09-10

    We study 50 cosmic-ray Forbush decreases (FDs) from the Oulu neutron monitor data during 1997–2005 that were associated with Earth-directed interplanetary coronal mass ejections (ICMEs). Such events are generally thought to arise due to the shielding of cosmic rays by a propagating diffusive barrier. The main processes at work are the diffusion of cosmic rays across the large-scale magnetic fields carried by the ICME and their advection by the solar wind. In an attempt to better understand the relative importance of these effects, we analyze the relationship between the FD profiles and those of the interplanetary magnetic field (B) and the solar wind speed (V {sub sw}). Over the entire duration of a given FD, we find that the FD profile is generally (anti)correlated with the B and V {sub sw} profiles. This trend holds separately for the FD main and recovery phases too. For the recovery phases, however, the FD profile is highly anti-correlated with the V {sub sw} profile, but not with the B profile. While the total duration of the FD profile is similar to that of the V {sub sw} profile, it is significantly longer than that of the B profile. Using the convection–diffusion model, a significant contribution of advection by solar wind is found during the recovery phases of the FD.

  18. Geometric approach to inverse scattering for the Schroedinger equation with magnetic and electric potentials

    International Nuclear Information System (INIS)

    Arians, S.

    1997-01-01

    We consider the Hamiltonian H=(p-A(x)) 2 /(2m)+V(x) of a quantum particle in a magnetic field B=rotA and a potential V in space dimensions ν≥2. If V is of short range, then the high-velocity limit of the scattering operator uniquely determines the magnetic field B and the potential V. If, in addition, long-range potentials V l are present, some knowledge of (the far out tail of) V l is needed to define a modified Dollard wave operator and a scattering operator S D . Again its high- velocity limit uniquely determines B and V=V s +V l . Moreover, we give explicit error bounds which are inverse proportional to the velocity. copyright 1997 American Institute of Physics

  19. Dynamical Monte Carlo investigation of spin reversals and nonequilibrium magnetization of single-molecule magnets

    OpenAIRE

    Liu, Gui-Bin; Liu, Bang-Gui

    2010-01-01

    In this paper, we combine thermal effects with Landau-Zener (LZ) quantum tunneling effects in a dynamical Monte Carlo (DMC) framework to produce satisfactory magnetization curves of single-molecule magnet (SMM) systems. We use the giant spin approximation for SMM spins and consider regular lattices of SMMs with magnetic dipolar interactions (MDI). We calculate spin reversal probabilities from thermal-activated barrier hurdling, direct LZ tunneling, and thermal-assisted LZ tunnelings in the pr...

  20. Comparative measurements of plasma potential with ball-pen and Langmuir probe in low-temperature magnetized plasma

    Science.gov (United States)

    Zanáška, M.; Adámek, J.; Peterka, M.; Kudrna, P.; Tichý, M.

    2015-03-01

    The ball-pen probe (BPP) is used for direct plasma potential measurements in magnetized plasma. The probe can adjust the ratio of the electron and ion saturation currents Isat-/Isat+ to be close to one and therefore its I-V characteristic becomes nearly symmetric. If this is achieved, the floating potential of the BPP is close to the plasma potential. Because of its rather simple construction, it offers an attractive probe for measurements in magnetized plasma. Comparative measurements of plasma potential by BPPs of different dimensions as well as one Langmuir probe (LP) in an argon discharge plasma of a cylindrical magnetron were performed at various experimental conditions. An additional comparison by an emissive probe was also performed. All these types of probes provide similar values of plasma potential in a wide range of plasma parameters. Our results for three different BPP dimensions indicate that the BPP can be operated in a cylindrical magnetron DC argon discharge if the value of the ratio of the magnetic field and neutral gas pressure, B/p, is greater than approximately 10 mT/Pa.

  1. Spin tunneling in magnetic molecules: Quantitative estimates for Fe8 clusters

    Science.gov (United States)

    Galetti, D.; Silva, Evandro C.

    2007-12-01

    Spin tunneling in the particular case of the magnetic molecular cluster octanuclear iron(III), Fe8, is treated by an effective Hamiltonian that allows for an angle-based description of the process. The presence of an external magnetic field along the easy axis is also taken into account in this description. Analytic expressions for the energy levels and barriers are obtained from a harmonic approximation of the potential function which give results in good agreement with the experimental results. The energy splittings due to spin tunneling is treated in an adapted WKB approach and it is shown that the present description can give results to a reliable degree of accuracy.

  2. AC losses in Ag-sheathed Bi2223 tapes with Ca2CuO3 as interfilamentary resistive barriers

    International Nuclear Information System (INIS)

    Inada, R.; Iwata, Y.; Tateyama, K.; Nakamura, Y.; Oota, A.; Zhang, P.X.

    2006-01-01

    In this study, we prepared the Bi2223 multifilamentary tapes with Ca 2 CuO 3 as interfilamentary resistive barriers and evaluated their AC magnetization loss properties at 77 K. The Bi2223 tapes with thin barrier layers of Ca 2 CuO 3 around the filaments were prepared by using a standard powder-in-tube (PIT) method. To fabricate the Ca 2 CuO 3 layers around each filament, the outside surface of monocore Ag-sheathed wires was coated by Ca 2 CuO 3 with the slurry. After the heat treatment to decompose and evaporate the organic binder in the slurry, the several coated monocore wires were stacked and packed into another Ag-tube. Then, the packed tube was drawn and rolled into tape shape. The tape was subsequently sintered to form Bi2223 phase inside filaments. The AC magnetization losses in an AC transverse magnetic field were measured by a pick-up coil method. The loss properties in the barrier tape were compared with those in the tape without barriers. The results indicated that introducing Ca 2 CuO 3 barriers is very effective to suppress the electromagnetic coupling among the filaments and also to reduce the magnetization losses under parallel transverse field

  3. Beyond Magnet® Designation: Perspectives From Nurse Managers on Factors of Sustainability and High-Performance Programming.

    Science.gov (United States)

    Hayden, Margaret A; Wolf, Gail A; Zedreck-Gonzalez, Judith F

    2016-10-01

    The aim of this study was to identify patterns of high-performing behaviors and nurse manager perceptions of the factors of Magnet® sustainability at a multidesignated Magnet organization. The Magnet program recognizes exemplary professional nursing practice and is challenging to achieve and sustain. Only 10% (n = 42) of Magnet hospitals sustained designation for 12 years or longer. This study explored the perspectives of Magnet nurse managers regarding high-performing teams and the sustainability of Magnet designation. A qualitative study of nurse managers was conducted at 1 multidesignated Magnet organization (n = 13). Interview responses were analyzed using pattern recognition of Magnet model domains and characteristics of high-performing teams and then related to factors of Magnet sustainability. Transformational leadership is both an essential factor for sustainability and a potential barrier to sustainability of Magnet designation. Transformational nursing leaders lead high-performing teams and should be in place at all levels as an essential factor in sustaining Magnet redesignation.

  4. Current-current correlation function in presence of chemical potential and external magnetic field

    International Nuclear Information System (INIS)

    Apresyan, E.A.

    2017-01-01

    The (2+1)-dimensional electron system was observed, where relation between the Green functions and conductivity was used. The current-current correlation function Π_μ_ν(B) for the fermion system was calculated in presence of non-quantizing magnetic field B, chemical potential η and gap m. From this function it is possible to obtain the equation for polarization operator calculated without the magnetic field. The result is also applicable for graphene

  5. A Conditionally Integrable Bi-confluent Heun Potential Involving Inverse Square Root and Centrifugal Barrier Terms

    Science.gov (United States)

    Ishkhanyan, Tigran A.; Krainov, Vladimir P.; Ishkhanyan, Artur M.

    2018-05-01

    We present a conditionally integrable potential, belonging to the bi-confluent Heun class, for which the Schrödinger equation is solved in terms of the confluent hypergeometric functions. The potential involves an attractive inverse square root term x-1/2 with arbitrary strength and a repulsive centrifugal barrier core x-2 with the strength fixed to a constant. This is a potential well defined on the half-axis. Each of the fundamental solutions composing the general solution of the Schrödinger equation is written as an irreducible linear combination, with non-constant coefficients, of two confluent hypergeometric functions. We present the explicit solution in terms of the non-integer order Hermite functions of scaled and shifted argument and discuss the bound states supported by the potential. We derive the exact equation for the energy spectrum and approximate that by a highly accurate transcendental equation involving trigonometric functions. Finally, we construct an accurate approximation for the bound-state energy levels.

  6. Numerical simulations of a sounding rocket in ionospheric plasma: Effects of magnetic field on the wake formation and rocket potential

    Science.gov (United States)

    Darian, D.; Marholm, S.; Paulsson, J. J. P.; Miyake, Y.; Usui, H.; Mortensen, M.; Miloch, W. J.

    2017-09-01

    The charging of a sounding rocket in subsonic and supersonic plasma flows with external magnetic field is studied with numerical particle-in-cell (PIC) simulations. A weakly magnetized plasma regime is considered that corresponds to the ionospheric F2 layer, with electrons being strongly magnetized, while the magnetization of ions is weak. It is demonstrated that the magnetic field orientation influences the floating potential of the rocket and that with increasing angle between the rocket axis and the magnetic field direction the rocket potential becomes less negative. External magnetic field gives rise to asymmetric wake downstream of the rocket. The simulated wake in the potential and density may extend as far as 30 electron Debye lengths; thus, it is important to account for these plasma perturbations when analyzing in situ measurements. A qualitative agreement between simulation results and the actual measurements with a sounding rocket is also shown.

  7. Finite-size, chemical-potential and magnetic effects on the phase transition in a four-fermion interacting model

    Energy Technology Data Exchange (ETDEWEB)

    Correa, E.B.S. [Universidade Federal do Sul e Sudeste do Para, Instituto de Ciencias Exatas, Maraba (Brazil); Centro Brasileiro de Pesquisas Fisicas-CBPF/MCTI, Rio de Janeiro (Brazil); Linhares, C.A. [Universidade do Estado do Rio de Janeiro, Instituto de Fisica, Rio de Janeiro (Brazil); Malbouisson, A.P.C. [Centro Brasileiro de Pesquisas Fisicas-CBPF/MCTI, Rio de Janeiro (Brazil); Malbouisson, J.M.C. [Universidade Federal da Bahia, Instituto de Fisica, Salvador (Brazil); Santana, A.E. [Universidade de Brasilia, Instituto de Fisica, Brasilia, DF (Brazil)

    2017-04-15

    We study effects coming from finite size, chemical potential and from a magnetic background on a massive version of a four-fermion interacting model. This is performed in four dimensions as an application of recent developments for dealing with field theories defined on toroidal spaces. We study effects of the magnetic field and chemical potential on the size-dependent phase structure of the model, in particular, how the applied magnetic field affects the size-dependent critical temperature. A connection with some aspects of the hadronic phase transition is established. (orig.)

  8. Reactor potential of the magnetically insulated inertial fusion (MICF) system

    International Nuclear Information System (INIS)

    Kammash, T.; Galbraith, D.L.

    1987-01-01

    The Magnetically Insulated Inertial Confinement Fusion (MICF) scheme is examined with regard to its potential as a power-producing reactor. This approach combines the favorable aspects of both magnetic and inertial fusions in that physical containment of the plasma is provided by a metallic shell while thermal insulation of its energy is provided by a strong, self-generated magnetic field. The plasma is created at the core of the target as a result of irradiation of the fuel-coated inner surface by a laser beam that enters through a hole in the spherical shell. The instantaneous magnetic field is generated by the current loops formed by the laser-heated, laser-ablated electrons, and preliminary experimental results at Osaka University have confirmed the presence of such a field. These same experiments have also yielded a Lawson parameter of about 5x10 12 cm -3 sec, and because of these unique properties, the plasma lifetimes in MICF have been shown to be about two orders of magnitude longer than conventional, pusher type inertial fusion schemes. In this paper a quasi one dimensional, time dependent set of particle and energy balance equations for the thermal species, namely, electrons, ions and thermal alphas which also allows for an appropriate set of fast alpha groups is utilized to assess the reactor prospects of a DT-burning MICF system. (author) [pt

  9. Potential Strategies to Address the Major Clinical Barriers Facing Stem Cell Regenerative Therapy for Cardiovascular Disease: A Review.

    Science.gov (United States)

    Nguyen, Patricia K; Neofytou, Evgenios; Rhee, June-Wha; Wu, Joseph C

    2016-11-01

    Although progress continues to be made in the field of stem cell regenerative medicine for the treatment of cardiovascular disease, significant barriers to clinical implementation still exist. To summarize the current barriers to the clinical implementation of stem cell therapy in patients with cardiovascular disease and to discuss potential strategies to overcome them. Information for this review was obtained through a search of PubMed and the Cochrane database for English-language studies published between January 1, 2000, and July 25, 2016. Ten randomized clinical trials and 8 systematic reviews were included. One of the major clinical barriers facing the routine implementation of stem cell therapy in patients with cardiovascular disease is the limited and inconsistent benefit observed thus far. Reasons for this finding are unclear but may be owing to poor cell retention and survival, as suggested by numerous preclinical studies and a small number of human studies incorporating imaging to determine cell fate. Additional studies in humans using imaging to determine cell fate are needed to understand how these factors contribute to the limited efficacy of stem cell therapy. Treatment strategies to address poor cell retention and survival are under investigation and include the following: coadministration of immunosuppressive and prosurvival agents, delivery of cardioprotective factors packaged in exosomes rather than the cells themselves, and use of tissue-engineering strategies to provide structural support for cells. If larger grafts are achieved using these strategies, it will be imperative to carefully monitor for the potential risks of tumorigenicity, immunogenicity, and arrhythmogenicity. Despite important achievements to date, stem cell therapy is not yet ready for routine clinical implementation. Significant research is still needed to address the clinical barriers outlined herein before the next wave of large clinical trials is under way.

  10. Effect of Low-Frequency AC Magnetic Susceptibility and Magnetic Properties of CoFeB/MgO/CoFeB Magnetic Tunnel Junctions

    Directory of Open Access Journals (Sweden)

    Yuan-Tsung Chen

    2014-01-01

    Full Text Available In this investigation, the low-frequency alternate-current (AC magnetic susceptibility (χac and hysteresis loop of various MgO thickness in CoFeB/MgO/CoFeB magnetic tunneling junction (MTJ determined coercivity (Hc and magnetization (Ms and correlated that with χac maxima. The multilayer films were sputtered onto glass substrates and the thickness of intermediate barrier MgO layer was varied from 6 to 15 Å. An experiment was also performed to examine the variation of the highest χac and maximum phase angle (θmax at the optimal resonance frequency (fres, at which the spin sensitivity is maximal. The results reveal that χac falls as the frequency increases due to the relationship between magnetization and thickness of the barrier layer. The maximum χac is at 10 Hz that is related to the maximal spin sensitivity and that this corresponds to a MgO layer of 11 Å. This result also suggests that the spin sensitivity is related to both highest χac and maximum phase angle. The corresponding maximum of χac is related to high exchange coupling. High coercivity and saturation magnetization contribute to high exchange-coupling χac strength.

  11. Potential Pathways for CNS Drug Delivery Across the Blood-Cerebrospinal Fluid Barrier

    Science.gov (United States)

    Strazielle, Nathalie; Ghersi-Egea, Jean-François

    2016-01-01

    The blood-brain interfaces restrict the cerebral bioavailability of pharmacological compounds. Various drug delivery strategies have been developed to improve drug penetration into the brain. Most strategies target the microvascular endothelium forming the blood-brain barrier proper. Targeting the blood-cerebrospinal fluid (CSF) barrier formed by the epithelium of the choroid plexuses in addition to the blood-brain barrier may offer added-value for the treatment of central nervous system diseases. For instance, targeting the CSF spaces, adjacent tissue, or the choroid plexuses themselves is of interest for the treatment of neuroinflammatory and infectious diseases, cerebral amyloid angiopathy, selected brain tumors, hydrocephalus or neurohumoral dysregulation. Selected CSF-borne materials seem to reach deep cerebral structures by mechanisms that need to be understood in the context of chronic CSF delivery. Drug delivery through both barriers can reduce CSF sink action towards parenchymal drugs. Finally, targeting the choroid plexus-CSF system can be especially relevant in the context of neonatal and pediatric diseases of the central nervous system. Transcytosis appears the most promising mechanism to target in order to improve drug delivery through brain barriers. The choroid plexus epithelium displays strong vesicular trafficking and secretory activities that deserve to be explored in the context of cerebral drug delivery. Folate transport and exosome release into the CSF, plasma protein transport, and various receptor-mediated endocytosis pathways may prove useful mechanisms to exploit for efficient drug delivery into the CSF. This calls for a clear evaluation of transcytosis mechanisms at the blood-CSF barrier, and a thorough evaluation of CSF drug delivery rates. PMID:27464721

  12. On the analysis of magnetization and Moessbauer data for ferritin

    International Nuclear Information System (INIS)

    Madsen, D E; Moerup, S; Hansen, M F; Bendix, J

    2008-01-01

    Experimental data for antiferromagnetic nanoparticles are often analyzed as if the particles were ferromagnetic. However, due to the volume dependence of the magnetization resulting from uncompensated spins, such analysis will yield erroneous results. This is demonstrated as we analyze ac and dc magnetization data as well as Moessbauer spectra obtained for ferritin. The values of the median energy barrier obtained from the different data are in very close agreement when a distribution of volumes and a volume dependence of the magnetization are taken into account. However, when the volume dependence of the magnetization is neglected, erroneous values of the anisotropy energy barrier and the attempt time τ 0 are obtained

  13. Theory of the time orbiting potential (TOP) quadrupole magnetic trap for cold atoms

    Energy Technology Data Exchange (ETDEWEB)

    Minogin, V.G.; Richmond, J.A.; Opat, G.I.

    1997-12-31

    An analytical theory of the time orbiting potential (TOP) quadrupole magnetic trap for cold atoms is developed. It is shown that the rotating magnetic filed used to create the time-average harmonic potential is responsible for the formation of quasi-energy states of an atom in the trap. It is found that the motion of an atom near the origin of the trap can be represented as consisting of slow motion in the effective potential and fast oscillations with small amplitude. Dipole, quadrupole and higher order atomic transitions between quasi-energy states are shown to be responsible for an additional effective potential for slow atomic motion which is proportional to the fourth power of the atomic co-ordinate. Eigenstates and eigenfunctions are used to calculate the co-ordinate distribution for a single atom. It is concluded that at low temperature the quantum statistical co-ordinate distribution for a single atom exhibits a narrow central peak due to the ground state population, together with relatively broad wings due to the excited state population. (authors). 20 refs., 1 tab., 6 figs.

  14. Families' perceived benefits of home visits for managing paediatric obesity outweigh the potential costs and barriers.

    Science.gov (United States)

    Gehring, Nicole D; Ball, Geoff D C; Perez, Arnaldo; Holt, Nicholas L; Neuman, Daniel; Spence, Nicholas; Mercier, Laura; Jetha, Mary

    2018-02-01

    Home visits have successfully been used to deliver various health services, but what role could they play in paediatric weight management? Low treatment initiation and high attrition prompted our multidisciplinary paediatric weight management clinic to investigate how families perceived the benefits and barriers of home visits. We focused on children with obesity aged 2-17 who were enrolled in our tertiary-level clinic in Alberta, Canada. None had received a home visit. The families were interviewed face-to-face from October 2015 to October 2016, and we used a qualitative description methodological framework and manifest content analysis. The parents were the main interviewees. Of the 56 families, 89% were interested in a home visit, 82% wanted support from a dietician and 54% from an exercise specialist. The perceived benefits of home visits included comprehensive assessment (95%), convenience (86%), tailored care (29%) and family involvement (13%), while the costs and barriers included clinicians' potential judgmental attitudes (30%), loss of privacy (19%) and distractions (10%). Some thought clinicians would find home visits inconvenient (25%), with bureaucratic challenges (14%) and sustainability issues (5%). Families felt home visits were a convenient option for managing paediatric obesity and identified important benefits and barriers that could guide such interventions. ©2017 Foundation Acta Paediatrica. Published by John Wiley & Sons Ltd.

  15. Thermally activated magnetization reversal in monatomic magnetic chains on surfaces studied by classical atomistic spin-dynamics simulations

    International Nuclear Information System (INIS)

    Bauer, David S G; Mavropoulos, Phivos; Bluegel, Stefan; Lounis, Samir

    2011-01-01

    We analyse the spontaneous magnetization reversal of supported monatomic chains of finite length due to thermal fluctuations via atomistic spin-dynamics simulations. Our approach is based on the integration of the Landau-Lifshitz equation of motion of a classical spin Hamiltonian in the presence of stochastic forces. The associated magnetization lifetime is found to obey an Arrhenius law with an activation barrier equal to the domain wall energy in the chain. For chains longer than one domain wall width, the reversal is initiated by nucleation of a reversed magnetization domain primarily at the chain edge followed by a subsequent propagation of the domain wall to the other edge in a random-walk fashion. This results in a linear dependence of the lifetime on the chain length, if the magnetization correlation length is not exceeded. We studied chains of uniaxial and triaxial anisotropy and found that a triaxial anisotropy leads to a reduction of the magnetization lifetime due to a higher reversal attempt rate, even though the activation barrier is not changed.

  16. Blood-brain barrier leakage after status epilepticus in rapamycin-treated rats I: Magnetic resonance imaging.

    Science.gov (United States)

    van Vliet, Erwin A; Otte, Willem M; Wadman, Wytse J; Aronica, Eleonora; Kooij, Gijs; de Vries, Helga E; Dijkhuizen, Rick M; Gorter, Jan A

    2016-01-01

    The mammalian target of rapamycin (mTOR) pathway has received increasing attention as a potential antiepileptogenic target. Treatment with the mTOR inhibitor rapamycin after status epilepticus reduces the development of epilepsy in a rat model. To study whether rapamycin mediates this effect via restoration of blood-brain barrier (BBB) dysfunction, contrast-enhanced magnetic resonance imaging (CE-MRI) was used to determine BBB permeability throughout epileptogenesis. Imaging was repeatedly performed until 6 weeks after kainic acid-induced status epilepticus in rapamycin (6 mg/kg for 6 weeks starting 4 h after SE) and vehicle-treated rats, using gadobutrol as contrast agent. Seizures were detected using video monitoring in the week following the last imaging session. Gadobutrol leakage was widespread and extensive in both rapamycin and vehicle-treated epileptic rats during the acute phase, with the piriform cortex and amygdala as the most affected regions. Gadobutrol leakage was higher in rapamycin-treated rats 4 and 8 days after status epilepticus compared to vehicle-treated rats. However, during the chronic epileptic phase, gadobutrol leakage was lower in rapamycin-treated epileptic rats along with a decreased seizure frequency. This was confirmed by local fluorescein staining in the brains of the same rats. Total brain volume was reduced by this rapamycin treatment regimen. The initial slow recovery of BBB function in rapamycin-treated epileptic rats indicates that rapamycin does not reduce seizure activity by a gradual recovery of BBB integrity. The reduced BBB leakage during the chronic phase, however, could contribute to the decreased seizure frequency in post-status epilepticus rats treated with rapamycin. Furthermore, the data show that CE-MRI (using step-down infusion with gadobutrol) can be used as biomarker for monitoring the effect of drug therapy in rats. Wiley Periodicals, Inc. © 2015 International League Against Epilepsy.

  17. Transport Barriers in Bootstrap Driven Tokamaks

    Science.gov (United States)

    Staebler, Gary

    2017-10-01

    Maximizing the bootstrap current in a tokamak, so that it drives a high fraction of the total current, reduces the external power required to drive current by other means. Improved energy confinement, relative to empirical scaling laws, enables a reactor to more fully take advantage of the bootstrap driven tokamak. Experiments have demonstrated improved energy confinement due to the spontaneous formation of an internal transport barrier in high bootstrap fraction discharges. Gyrokinetic analysis, and quasilinear predictive modeling, demonstrates that the observed transport barrier is due to the suppression of turbulence primarily due to the large Shafranov shift. ExB velocity shear does not play a significant role in the transport barrier due to the high safety factor. It will be shown, that the Shafranov shift can produce a bifurcation to improved confinement in regions of positive magnetic shear or a continuous reduction in transport for weak or negative magnetic shear. Operation at high safety factor lowers the pressure gradient threshold for the Shafranov shift driven barrier formation. The ion energy transport is reduced to neoclassical and electron energy and particle transport is reduced, but still turbulent, within the barrier. Deeper into the plasma, very large levels of electron transport are observed. The observed electron temperature profile is shown to be close to the threshold for the electron temperature gradient (ETG) mode. A large ETG driven energy transport is qualitatively consistent with recent multi-scale gyrokinetic simulations showing that reducing the ion scale turbulence can lead to large increase in the electron scale transport. A new saturation model for the quasilinear TGLF transport code, that fits these multi-scale gyrokinetic simulations, can match the data if the impact of zonal flow mixing on the ETG modes is reduced at high safety factor. This work was supported by the U.S. Department of Energy under DE-FG02-95ER54309 and DE-FC02

  18. Conductance and refraction across a Barrier in Phosphorene

    Science.gov (United States)

    Dahal, Dipendra; Gumbs, Godfrey

    The transmission coefficient and ballistic conductance for monolayer black phosphorene is calculated when a potential step or square barrier is present. The Landauer-B¨uttiker formalism is employed in our calculations of the conductance. We obtain the refractive index for the step potential barrier when an incident beam of electron travel along different paths so as to observe what role the anisotropy of the energy bands plays. Numerical results are presented for various potential heights and barrier widths and these are compared with those for gapless and gapped graphene.

  19. Origin of methyl torsional potential barrier – An overview

    Indian Academy of Sciences (India)

    Unknown

    This paper presents the evolution of views on methyl internal rotation ... recognized in the early years of quantum theory.1 Since then, detailed experimental and ..... C−C bond in the methyl conjugated molecules is an important factor for barrier.

  20. Fabrication and properties of Ag-Bi2223 tapes with resistive barriers for filament decoupling

    International Nuclear Information System (INIS)

    Inada, Ryoji; Fukumoto, Yohei; Yasunami, Taeko; Nakamura, Yuichi; Oota, Akio; Li Chengshang; Zhang Pingxiang

    2007-01-01

    In this paper, we prepared the Bi2223 multifilamentary tapes with Ca 2 CuO 3 + Bi2212 as interfilamentary resistive barriers to suppress the electromagnetic coupling among the filaments under AC external magnetic field. The tapes with thin barrier layers of Ca 2 CuO 3 + 30 wt% Bi2212 around the filaments were prepared by using a standard powder-in-tube (PIT) method. The outside surface of monocore Ag-sheathed rods was coated by barrier materials. Then, the several coated monocore wires were stacked and packed into another Ag or Ag-Mg alloy tube. The packed tube was drawn and rolled into tape shape. The tape was subsequently sintered to form Bi2223 phase inside filaments. For the characterization of tapes, X-ray diffraction measurements were performed to investigate the phase formation inside the filaments. The uniformity of transport properties (J c ) for barrier tapes were evaluated on the order of several metre lengths and compared with the result for the tapes without barriers. Finally, AC loss characteristics under AC parallel transverse magnetic field were investigated to examine the effect of introducing the barriers on the filament decoupling

  1. Study and comparison of some methods for calculating the transmission factor of a potential barrier in quantum mechanics (1963); Etude et comparaison de quelques methodes de calcul du facteur de transmission d'une barriere de potentiel en mecanique quantique (1963)

    Energy Technology Data Exchange (ETDEWEB)

    Jamet, P [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

    1964-07-01

    The author formulates two accurate methods for the calculation of the transmission coefficient of a one-dimensional potential barrier. The principles of these methods are. expressed in a symmetrical form with respect to the two sides of the potential barrier; this constitutes a proof of the fact that the transmission coefficient is path direction independent. The numerical application is carried out on several examples and the results are compared to those provided by the WKB method. (author) [French] L'auteur formule deux methodes exactes pour calculer le coefficient de transmission d'une barriere de potentiel unidimensionnelle. Les principes de ces methodes s'enoncent sous forme symetrique par rapport aux deux cotes de la barriere de potentiel, ce qui constitue une demonstration du fait que le coefficient de transmission est independant du sens de parcours. L'application numerique est faite sur quelques exemples et les resultats sont compares a ceux fournis par la methode B KW. (auteur)

  2. Spin-polarized inelastic tunneling through insulating barriers.

    Science.gov (United States)

    Lu, Y; Tran, M; Jaffrès, H; Seneor, P; Deranlot, C; Petroff, F; George, J-M; Lépine, B; Ababou, S; Jézéquel, G

    2009-05-01

    Spin-conserving hopping transport through chains of localized states has been evidenced by taking benefit of the high degree of spin-polarization of CoFeB-MgO-CoFeB magnetic tunnel junctions. In particular, our data show that relatively thick MgO barriers doped with boron favor the activation of spin-conserving inelastic channels through a chain of three localized states and leading to reduced magnetoresistance effects. We propose an extension of the Glazman-Matveev theory to the case of ferromagnetic reservoirs to account for spin-polarized inelastic tunneling through nonmagnetic localized states embedded in an insulating barrier.

  3. Recording visual evoked potentials and auditory evoked P300 at 9.4T static magnetic field.

    Science.gov (United States)

    Arrubla, Jorge; Neuner, Irene; Hahn, David; Boers, Frank; Shah, N Jon

    2013-01-01

    Simultaneous recording of electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) has shown a number of advantages that make this multimodal technique superior to fMRI alone. The feasibility of recording EEG at ultra-high static magnetic field up to 9.4 T was recently demonstrated and promises to be implemented soon in fMRI studies at ultra high magnetic fields. Recording visual evoked potentials are expected to be amongst the most simple for simultaneous EEG/fMRI at ultra-high magnetic field due to the easy assessment of the visual cortex. Auditory evoked P300 measurements are of interest since it is believed that they represent the earliest stage of cognitive processing. In this study, we investigate the feasibility of recording visual evoked potentials and auditory evoked P300 in a 9.4 T static magnetic field. For this purpose, EEG data were recorded from 26 healthy volunteers inside a 9.4 T MR scanner using a 32-channel MR compatible EEG system. Visual stimulation and auditory oddball paradigm were presented in order to elicit evoked related potentials (ERP). Recordings made outside the scanner were performed using the same stimuli and EEG system for comparison purposes. We were able to retrieve visual P100 and auditory P300 evoked potentials at 9.4 T static magnetic field after correction of the ballistocardiogram artefact using independent component analysis. The latencies of the ERPs recorded at 9.4 T were not different from those recorded at 0 T. The amplitudes of ERPs were higher at 9.4 T when compared to recordings at 0 T. Nevertheless, it seems that the increased amplitudes of the ERPs are due to the effect of the ultra-high field on the EEG recording system rather than alteration in the intrinsic processes that generate the electrophysiological responses.

  4. The critical role of the barrier thickness in spin filter tunneling

    International Nuclear Information System (INIS)

    Miller, Casey W.

    2009-01-01

    Spin filter tunneling is considered in the low bias limit as functions of the temperature dependent barrier parameters. We demonstrate the generation of spin polarized tunneling currents in relation to the magnetic order parameter, and discuss how an interfacially suppressed order parameter leads to a temperature dependent tunneling current asymmetry. Analyzing the full parameter space reveals that the often overlooked barrier thickness plays a critical role in spin filter tunneling. With all else fixed, thicker barriers yield higher spin polarization, and allow a given polarization to be achieved at higher temperatures. This insight may open the door for new materials to serve as spin filter barriers.

  5. Superconducting spin valves controlled by spiral re-orientation in B20-family magnets

    Science.gov (United States)

    Pugach, N. G.; Safonchik, M.; Champel, T.; Zhitomirsky, M. E.; Lähderanta, E.; Eschrig, M.; Lacroix, C.

    2017-10-01

    We propose a superconducting spin-triplet valve, which consists of a superconductor and an itinerant magnetic material, with the magnet showing an intrinsic non-collinear order characterized by a wave vector that may be aligned in a few equivalent preferred directions under the control of a weak external magnetic field. Re-orienting the spiral direction allows one to controllably modify long-range spin-triplet superconducting correlations, leading to spin-valve switching behavior. Our results indicate that the spin-valve effect may be noticeable. This bilayer may be used as a magnetic memory element for cryogenic nanoelectronics. It has the following advantages in comparison to superconducting spin valves proposed previously: (i) it contains only one magnetic layer, which may be more easily fabricated and controlled; (ii) its ground states are separated by a potential barrier, which solves the "half-select" problem of the addressed switch of memory elements.

  6. Effects of inhomogeneity on the Shukla-Nambu-Salimullah potential in a magnetized plasma

    International Nuclear Information System (INIS)

    Salimullah, M.; Shah, H.A.; Murtaza, G.; Nitta, H.; Tessarotto, M.

    2007-01-01

    Detailed properties of the electrostatic Shukla-Nambu-Salimullah potential in an inhomogeneous magnetoplasma in the presence of ion streaming due to diamagnetic drift as in a laboratory discharge plasma have been examined analytically. The potential becomes a sensitive function of the external static magnetic field, the scalelength of inhomogeneity, and the diamagnetic ion streaming velocity. For a decreasing ion density gradient, there is a limit of existence of this static modified shielding potential

  7. Creation and dynamical co-evolution of electron and ion channel transport barriers

    International Nuclear Information System (INIS)

    Newman, D.E.

    2002-01-01

    A wide variety of magnetic confinement devices have found transitions to an enhanced confinement regime. Simple dynamical models have been able to capture much of the dynamics of these barriers however an open question has been the disconnected nature of the electron thermal transport channel sometimes observed in the presence of a standard ('ion channel' barrier. By adding to simple barrier model an evolution equation for electron fluctuations we can investigate the interaction between the formation of the standard ion channel barrier and the somewhat less common electron channel barrier. Barrier formation in the electron channel is even more sensitive to the alignment of the various gradients making up the sheared radial electric field than the ion barrier is. Electron channel heat transport is found to significantly increase after the formation of the ion channel barrier but before the electron channel barrier is formed. This increased transport is important in the barrier evolution. (author)

  8. Magnetic detection of ferrofluid injection zones

    Energy Technology Data Exchange (ETDEWEB)

    Borglin, S.; Moridis, G.; Becker, A.

    1998-03-01

    Ferrofluids are stable colloidal suspensions of magnetic particles that can be stabilized in various carrier liquids. In this study the authors investigate the potential of ferrofluids to trace the movement and position of liquids injected in the subsurface using geophysical methods. An ability to track and monitor the movement and position of injected liquids is essential in assessing the effectiveness of the delivery system and the success of the process. Ferrofluids can also provide a significant detection and verification tool in containment technologies, where they can be injected with the barrier liquids to provide a strong signature allowing determination of the barrier geometry, extent, continuity and integrity. Finally, ferrofluids may have unique properties as tracers for detecting preferential flow features (such as fractures) in the subsurface, and thus allow the design of more effective remediation systems. In this report the authors review the results of the investigation of the potential of ferrofluids to trace the movement and position of liquids injected in the subsurface using geophysical methods. They demonstrate the feasibility of using conventional magnetometry for detecting subsurface zones of injected ferrofluids used to trace liquids injected for remediation or barrier formation. The geometrical shapes considered were a sphere, a thin disk, a rectangular horizontal slab, and a cylinder. Simple calculations based on the principles of magnetometry are made to determine the detection depths of FTs. Experiments involving spherical, cylindrical and horizontal slabs show a very good agreement between predictions and measurements.

  9. Uses and evaluation methods of potential hydrogen permeation barriers for nuclear reactor materials

    International Nuclear Information System (INIS)

    Noga, J.O.; Piercy, G.R.; Bowker, J.T.

    1985-07-01

    This report summarizes results on the use of coatings as hydrogen permeation barriers on nuclear reactor component materials. Two classes of base materials were considered, exothermic hydrogen absorbers and endothermic hydrogen absorbers. The results of the tests indicate that substantial reductions in the amount of hydrogen absorbed by a metal can be achieved through the use of hydrogen permeation barrier coatings. Gold was determined to provide an effective hydrogen permeation barrier on Zr-2-1/2 Nb pressure tube material. Tin was determined to be a suitable hydrogen permeation barrier when applied on AISI 410 stainless steel and iron. Both gas phase and electrochemical permeation techniques were used to determine hydrogen permeabilities through coatings and base materials

  10. Phase-dependent dynamic potential of magnetically coupled two-degree-of-freedom bistable energy harvester.

    Science.gov (United States)

    Kim, Pilkee; Nguyen, Minh Sang; Kwon, Ojin; Kim, Young-Jin; Yoon, Yong-Jin

    2016-09-28

    A system of magnetically coupled oscillators has been recently considered as a promising compact structure to integrate multiple bistable energy harvesters (BEHs), but its design is not straightforward owing to its varying potential energy pattern, which has not been understood completely yet. This study introduces the concept of phase-dependent dynamic potential in a magnetically coupled BEH system with two degrees of freedom (DOFs) to explain the underlying principle of the complicated dynamics of the system. Through theoretical simulations and analyses, two distinct dynamic regimes, called the out-of-phase and in-phase mode regimes in this report, are found to exist in the frequency regions of the 1 st and 2 nd primary intrawell resonances. For the out-of-phase mode regime, the frequency displacement (and output power) responses of the 2-DOF BEH system exhibit typical double-well dynamics, whereas for the in-phase mode regime, only single-well dynamics is observed though the system is statically bistable. These dynamic regimes are also revealed to be caused by the difference in the dynamic potential energy trajectories propagating on a high-dimensional potential energy surface. The present approach to the dynamics of the 2-DOF BEH system can be extended and applied to higher-DOF systems, which sheds light on compact and efficient designs of magnetically coupled BEH chain structures.

  11. Observability of the effects of curl-free magnetic vector potential on ...

    Indian Academy of Sciences (India)

    We discuss here the prediction, based on a formalism by the author, on the observable effects of a curl-free magnetic vector potential on the macroscale as against the microscale of the Aharonov–Bohm effect. A new quantum concept – the 'transition amplitude wave' – postulated in the formalism has already been shown to ...

  12. Influence of magnetic topology on transport and stability in stellarators

    Energy Technology Data Exchange (ETDEWEB)

    Castejon, F [Laboratorio Nacional de Fusion. Asociacion Euratom/Ciemat, 28040-Madrid (Spain); Fujisawa, A [National Institute for Fusion Science Oroshi-cho, Toki-shi, Gifu, 509-5292 (Japan); Ida, K [National Institute for Fusion Science Oroshi-cho, Toki-shi, Gifu, 509-5292 (Japan); Talmadge, J N [University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); Estrada, T [Laboratorio Nacional de Fusion. Asociacion Euratom/Ciemat, 28040-Madrid (Spain); Lopez-Bruna, D [Laboratorio Nacional de Fusion. Asociacion Euratom/Ciemat, 28040-Madrid (Spain); Hidalgo, C [Laboratorio Nacional de Fusion. Asociacion Euratom/Ciemat, 28040-Madrid (Spain); Krupnik, L [Institute of Plasma Physics, NSC ' KIPT' , Kharkov (Ukraine); Melnikov, A [Institute of Nuclear Fusion, RRC ' Kurchatov Institute' , Moscow (Russian Federation)

    2005-12-15

    The influence of the magnetic topology on transport and stability has been investigated in four stellarators: an almost shearless medium size flexible heliac (TJ-II), a medium size and a large heliotron (CHS and LHD) with shear, and a quasihelically symmetric device (HSX) with moderate shear. All of these have variable rotational transform profiles and magnetic ripples. Using these capabilities, bifurcated states can appear and plasma can jump from one to another with subsequent changes in the transport properties. Low rational values of {iota}/2{pi} can create transport barriers in LHD and TJ-II when they are located close to the plasma core or at the edge. The key ingredient for transport barriers is a positive and sheared electric field. Internal transport barriers also appear in CHS, but the role of rationals is not clear yet in this device. The time evolution of the electric field shows the onset of a bifurcation triggered either by the rational or by the presence of the ion and electron roots. The electric potential inside ITBs follows the ECE-temperature profile in a fast time scale. The plasma stability properties and its effect on the viscosity are also studied in the HSX, and the influence of the dynamics of rational surface is studied in the LHD and TJ-II stellarators.

  13. Influence of magnetic topology on transport and stability in stellarators

    International Nuclear Information System (INIS)

    Castejon, F; Fujisawa, A; Ida, K; Talmadge, J N; Estrada, T; Lopez-Bruna, D; Hidalgo, C; Krupnik, L; Melnikov, A

    2005-01-01

    The influence of the magnetic topology on transport and stability has been investigated in four stellarators: an almost shearless medium size flexible heliac (TJ-II), a medium size and a large heliotron (CHS and LHD) with shear, and a quasihelically symmetric device (HSX) with moderate shear. All of these have variable rotational transform profiles and magnetic ripples. Using these capabilities, bifurcated states can appear and plasma can jump from one to another with subsequent changes in the transport properties. Low rational values of ι/2π can create transport barriers in LHD and TJ-II when they are located close to the plasma core or at the edge. The key ingredient for transport barriers is a positive and sheared electric field. Internal transport barriers also appear in CHS, but the role of rationals is not clear yet in this device. The time evolution of the electric field shows the onset of a bifurcation triggered either by the rational or by the presence of the ion and electron roots. The electric potential inside ITBs follows the ECE-temperature profile in a fast time scale. The plasma stability properties and its effect on the viscosity are also studied in the HSX, and the influence of the dynamics of rational surface is studied in the LHD and TJ-II stellarators

  14. Comparative measurements of plasma potential with ball-pen and Langmuir probe in low-temperature magnetized plasma

    International Nuclear Information System (INIS)

    Zanáška, M.; Kudrna, P.; Tichý, M.; Adámek, J.; Peterka, M.

    2015-01-01

    The ball-pen probe (BPP) is used for direct plasma potential measurements in magnetized plasma. The probe can adjust the ratio of the electron and ion saturation currents I sat − /I sat + to be close to one and therefore its I-V characteristic becomes nearly symmetric. If this is achieved, the floating potential of the BPP is close to the plasma potential. Because of its rather simple construction, it offers an attractive probe for measurements in magnetized plasma. Comparative measurements of plasma potential by BPPs of different dimensions as well as one Langmuir probe (LP) in an argon discharge plasma of a cylindrical magnetron were performed at various experimental conditions. An additional comparison by an emissive probe was also performed. All these types of probes provide similar values of plasma potential in a wide range of plasma parameters. Our results for three different BPP dimensions indicate that the BPP can be operated in a cylindrical magnetron DC argon discharge if the value of the ratio of the magnetic field and neutral gas pressure, B/p, is greater than approximately 10 mT/Pa

  15. Comparative measurements of plasma potential with ball-pen and Langmuir probe in low-temperature magnetized plasma

    Energy Technology Data Exchange (ETDEWEB)

    Zanáška, M.; Kudrna, P.; Tichý, M. [Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 3, 12116 Prague 2 (Czech Republic); Adámek, J. [Institute of Plasma Physics AS CR, v.v.i., Za Slovankou 3, 18200 Prague 8 (Czech Republic); Peterka, M. [Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 3, 12116 Prague 2 (Czech Republic); Institute of Plasma Physics AS CR, v.v.i., Za Slovankou 3, 18200 Prague 8 (Czech Republic)

    2015-03-15

    The ball-pen probe (BPP) is used for direct plasma potential measurements in magnetized plasma. The probe can adjust the ratio of the electron and ion saturation currents I{sub sat}{sup −}/I{sub sat}{sup +} to be close to one and therefore its I-V characteristic becomes nearly symmetric. If this is achieved, the floating potential of the BPP is close to the plasma potential. Because of its rather simple construction, it offers an attractive probe for measurements in magnetized plasma. Comparative measurements of plasma potential by BPPs of different dimensions as well as one Langmuir probe (LP) in an argon discharge plasma of a cylindrical magnetron were performed at various experimental conditions. An additional comparison by an emissive probe was also performed. All these types of probes provide similar values of plasma potential in a wide range of plasma parameters. Our results for three different BPP dimensions indicate that the BPP can be operated in a cylindrical magnetron DC argon discharge if the value of the ratio of the magnetic field and neutral gas pressure, B/p, is greater than approximately 10 mT/Pa.

  16. Magnetic edge states and magnetotransport in graphene antidot barriers

    DEFF Research Database (Denmark)

    Thomsen, M. R.; Power, Stephen; Jauho, Antti-Pekka

    2016-01-01

    Magnetic fields are often used for characterizing transport in nanoscale materials. Recent magnetotransport experiments have demonstrated that ballistic transport is possible in graphene antidot lattices (GALs). These experiments have inspired the present theoretical study of GALs in a perpendicu......Magnetic fields are often used for characterizing transport in nanoscale materials. Recent magnetotransport experiments have demonstrated that ballistic transport is possible in graphene antidot lattices (GALs). These experiments have inspired the present theoretical study of GALs...

  17. Caspase-14 Expression Impairs Retinal Pigment Epithelium Barrier Function: Potential Role in Diabetic Macular Edema

    Directory of Open Access Journals (Sweden)

    Selina Beasley

    2014-01-01

    Full Text Available We recently showed that caspase-14 is a novel molecule in retina with potential role in accelerated vascular cell death during diabetic retinopathy (DR. Here, we evaluated whether caspase-14 is implicated in retinal pigment epithelial cells (RPE dysfunction under hyperglycemia. The impact of high glucose (HG, 30 mM D-glucose on caspase-14 expression in human RPE (ARPE-19 cells was tested, which showed significant increase in caspase-14 expression compared with normal glucose (5 mM D-glucose + 25 mM L-glucose. We also evaluated the impact of modulating caspase-14 expression on RPE cells barrier function, phagocytosis, and activation of other caspases using ARPE-19 cells transfected with caspase-14 plasmid or caspase-14 siRNA. We used FITC-dextran flux assay and electric cell substrate impedance sensing (ECIS to test the changes in RPE cell barrier function. Similar to HG, caspase-14 expression in ARPE-19 cells increased FITC-dextran leakage through the confluent monolayer and decreased the transcellular electrical resistance (TER. These effects of HG were prevented by caspase-14 knockdown. Furthermore, caspase-14 knockdown prevented the HG-induced activation of caspase-1 and caspase-9, the only activated caspases by HG. Phagocytic activity was unaffected by caspase-14 expression. Our results suggest that caspase-14 contributes to RPE cell barrier disruption under hyperglycemic conditions and thus plays a role in the development of diabetic macular edema.

  18. Mucus as a Barrier to Drug Delivery

    DEFF Research Database (Denmark)

    Bøgh, Marie; Nielsen, Hanne Mørck

    2015-01-01

    Viscoelastic mucus lines all mucosal surfaces of the body and forms a potential barrier to mucosal drug delivery. Mucus is mainly composed of water and mucins; high-molecular weight glycoproteins forming an entangled network. Consequently, mucus forms a steric barrier and due to its negative charge...... barrier to drug delivery. Current knowledge of mucus characteristics and barrier properties, as achieved by state-of-the-art methodologies, is the topic of this MiniReview emphasizing the gastrointestinal mucus and an overall focus on oral drug delivery. Cell culture-based in vitro models are well......, studies of peptide and protein drug diffusion in and through mucus and studies of mucus-penetrating nanoparticles are included to illustrate the mucus as a potentially important barrier to obtain sufficient bioavailability of orally administered drugs, and thus an important parameter to address...

  19. Spin current and electrical polarization in GaN double-barrier structures

    OpenAIRE

    Litvinov, V. I.

    2007-01-01

    Tunnel spin polarization in a piezoelectric AlGaN/GaN double barrier structure is calculated. It is shown that the piezoelectric field and the spontaneous electrical polarization increase an efficiency of the tunnel spin injection. The relation between the electrical polarization and the spin orientation allows engineering a zero magnetic field spin injection manipulating the lattice-mismatch strain with an Al-content in the barriers.

  20. Geophysical characterization of subsurface barriers

    International Nuclear Information System (INIS)

    Borns, D.J.

    1995-08-01

    An option for controlling contaminant migration from plumes and buried waste sites is to construct a subsurface barrier of a low-permeability material. The successful application of subsurface barriers requires processes to verify the emplacement and effectiveness of barrier and to monitor the performance of a barrier after emplacement. Non destructive and remote sensing techniques, such as geophysical methods, are possible technologies to address these needs. The changes in mechanical, hydrologic and chemical properties associated with the emplacement of an engineered barrier will affect geophysical properties such a seismic velocity, electrical conductivity, and dielectric constant. Also, the barrier, once emplaced and interacting with the in situ geologic system, may affect the paths along which electrical current flows in the subsurface. These changes in properties and processes facilitate the detection and monitoring of the barrier. The approaches to characterizing and monitoring engineered barriers can be divided between (1) methods that directly image the barrier using the contrasts in physical properties between the barrier and the host soil or rock and (2) methods that reflect flow processes around or through the barrier. For example, seismic methods that delineate the changes in density and stiffness associated with the barrier represents a direct imaging method. Electrical self potential methods and flow probes based on heat flow methods represent techniques that can delineate the flow path or flow processes around and through a barrier

  1. RF Current Drive in Internal Transport Barrier

    Energy Technology Data Exchange (ETDEWEB)

    Peysson, Y.; Basiuk, V.; Huysmans, G. [Association EURATOM-CEA, CEA/DSM/DRFC, CEA-Cadarache, 13 - St Paul-lez-Durance (France); Decker, J.; Bers, A.; Ram, A.K. [Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA (United States)

    2005-07-01

    The current drive problem in regimes with internal transport barrier is addressed using a fast solver of the electron drift kinetic equation which may be used for arbitrary tokamak plasma magnetic equilibrium and any type of electron radio-frequency wave. Parametric studies are performed for the Lower Hybrid and Electron Cyclotron waves. (authors)

  2. The outflows accelerated by the magnetic fields and radiation force of accretion disks

    Energy Technology Data Exchange (ETDEWEB)

    Cao, Xinwu, E-mail: cxw@shao.ac.cn [Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai, 200030 (China)

    2014-03-01

    The inner region of a luminous accretion disk is radiation-pressure-dominated. We estimate the surface temperature of a radiation-pressure-dominated accretion disk, Θ=c{sub s}{sup 2}/r{sup 2}Ω{sub K}{sup 2}≪(H/r){sup 2}, which is significantly lower than that of a gas-pressure-dominated disk, Θ ∼ (H/r){sup 2}. This means that the outflow can be launched magnetically from the photosphere of the radiation-pressure-dominated disk only if the effective potential barrier along the magnetic field line is extremely shallow or no potential barrier is present. For the latter case, the slow sonic point in the outflow will probably be in the disk, which leads to a slow circular dense flow above the disk. This implies that hot gas (probably in the corona) is necessary for launching an outflow from the radiation-pressure-dominated disk, which provides a natural explanation for the observational evidence that the relativistic jets are related to hot plasma in some X-ray binaries and active galactic nuclei. We investigate the outflows accelerated from the hot corona above the disk by the magnetic field and radiation force of the accretion disk. We find that with the help of the radiation force, the mass loss rate in the outflow is high, which leads to a slow outflow. This may be why the jets in radio-loud narrow-line Seyfert galaxies are in general mildly relativistic compared with those in blazars.

  3. Anomalous Tunnel Magnetoresistance and Spin Transfer Torque in Magnetic Tunnel Junctions with Embedded Nanoparticles

    Science.gov (United States)

    Useinov, Arthur; Ye, Lin-Xiu; Useinov, Niazbeck; Wu, Te-Ho; Lai, Chih-Huang

    2015-01-01

    The tunnel magnetoresistance (TMR) in the magnetic tunnel junction (MTJ) with embedded nanoparticles (NPs) was calculated in range of the quantum-ballistic model. The simulation was performed for electron tunneling through the insulating layer with embedded magnetic and non-magnetic NPs within the approach of the double barrier subsystem connected in parallel to the single barrier one. This model can be applied for both MTJs with in-plane magnetization and perpendicular one. We also calculated the in-plane component of the spin transfer torque (STT) versus the applied voltage in MTJs with magnetic NPs and determined that its value can be much larger than in single barrier system (SBS) for the same tunneling thickness. The reported simulation reproduces experimental data of the TMR suppression and peak-like TMR anomalies at low voltages available in leterature. PMID:26681336

  4. Instantaneous Tunneling Flight Time for Wavepacket Transmission through Asymmetric Barriers.

    Science.gov (United States)

    Petersen, Jakob; Pollak, Eli

    2018-04-12

    The time it takes a particle to tunnel through the asymmetric Eckart barrier potential is investigated using Gaussian wavepackets, where the barrier serves as a model for the potential along a chemical reaction coordinate. We have previously shown that the, in principle experimentally measurable, tunneling flight time, which determines the time taken by the transmitted particle to traverse the barrier, vanishes for symmetric potentials like the Eckart and square barrier [ Petersen , J. ; Pollak , E. J. Phys. Chem. Lett. 2017 , 9 , 4017 ]. Here we show that the same result is obtained for the asymmetric Eckart barrier potential, and therefore, the zero tunneling flight time seems to be a general result for one-dimensional time-independent potentials. The wavepacket dynamics is simulated using both an exact quantum mechanical method and a classical Wigner prescription. The excellent agreement between the two methods shows that quantum coherences are not important in pure one-dimensional tunneling and reinforces the conclusion that the tunneling flight time vanishes.

  5. Potential uses of high gradient magnetic filtration for high-temperature water purification in boiling water reactors

    International Nuclear Information System (INIS)

    Elliott, H.H.; Holloway, J.H.; Abbott, D.G.

    1979-01-01

    Studies of various high-temperature filter devices indicate a potentially positive impact for high gradient magnetic filtration on boiling water reactor radiation level reduction. Test results on in-plant water composition and impurity crystallography are presented for several typical boiling water reactors (BWRs) on plant streams where high-temperature filtration may be particularly beneficial. An experimental model on the removal of red iron oxide (hematite) from simulated reactor water with a high gradient magnetic filter is presented, as well as the scale-up parameters used to predict the filtration efficiency on various high temperature, in-plant streams. Numerical examples are given to illustrate the crud removal potential of high gradient magnetic filters installed at alternative stream locations under typical, steady-state, plant operating conditions

  6. Magnetic and thermal properties of amorphous TbFeCo alloy films

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Ke, E-mail: K.Wang@hqu.edu.cn; Dong, Shuo; Huang, Ya; Qiu, Yuzhen

    2017-07-15

    Highlights: • Significant increase in magnetization is observed in TbFeCo upon crystallization. • The crystallization temperature is determined in the range between 400 and 450 °C. • The activation barriers for structural changes are obtained successfully. • Better thermal stability against crystallization and oxidation is demonstrated in FeCo-rich sample than Tb-rich type. - Abstract: Amorphous TbFeCo material with perpendicular magnetic anisotropy is currently attracting more attention for potential applications in spintronic devices and logic memories. We systematically investigate magnetic, structural, thermal, optical and electrical properties of TbFeCo alloy films. It shows out-of-plane easy axis of the films turns into in-plane orientation after annealing. Significant increase in saturation magnetization in the temperature range between 400 and 450 °C is revealed by thermomagnetic measurements. The occurrence of crystallization and oxidation at high temperatures is confirmed by X-ray diffraction measurements. Pronounced changes in optical reflectance and sheet resistance are observed with temperature, in line with structural relaxation and change. The activation barriers for crystallization and oxidation are determined to be 1.01 eV and 0.83 eV, respectively, for FeCo-rich and Tb-rich samples. Better thermal stability against crystallization and oxidation is demonstrated in the FeCo-rich sample than the Tb-rich type. Our results provide some useful information for the alloy used in device fabrication.

  7. Commercial tandem mirror reactor design with thermal barriers: WITAMIR-I

    International Nuclear Information System (INIS)

    Kulcinski, G.L.; Emmert, G.A.; Maynard, C.W.

    1980-10-01

    A conceptual design of a near term commercial tandem mirror power reactor is presented. The basic configuration utilizes yin-yang minimum-B plugs with inboard thermal barriers. The maximum magnetic fields are 6.1 T, 8.1 T, and 15 T in the central cell, yin-yang, and thermal barrier magnets, respectively. The blanket utilizes Pb 83 Li 17 as the coolant and HT-9 as the structural material. This yields a high energy multiplication (1.37), a sufficient tritium breeding ratio (1.07) and has a major advantage with respect to maintenance. The plasma Q is 28 at a fusion power level of 3000 MW(t); the net electrical output is 1530 MW(e); and the overall efficiency is 39%. Cost estimates indicate that WITAMIR-I is competitive with recent tokamak power reactor designs

  8. Permeability Barrier Generation in the Martian Lithosphere

    Science.gov (United States)

    Schools, Joe; Montési, Laurent

    2015-11-01

    Permeability barriers develop when a magma produced in the interior of a planet rises into the cooler lithosphere and crystallizes more rapidly than the lithosphere can deform (Sparks and Parmentier, 1991). Crystallization products may then clog the porous network in which melt is propagating, reducing the permeability to almost zero, i.e., forming a permeability barrier. Subsequent melts cannot cross the barrier. Permeability barriers have been useful to explain variations in crustal thickness at mid-ocean ridges on Earth (Magde et al., 1997; Hebert and Montési, 2011; Montési et al., 2011). We explore here under what conditions permeability barriers may form on Mars.We use the MELTS thermodynamic calculator (Ghiorso and Sack, 1995; Ghiorso et al., 2002; Asimow et al., 2004) in conjunction with estimated Martian mantle compositions (Morgan and Anders, 1979; Wänke and Dreibus, 1994; Lodders and Fegley, 1997; Sanloup et al., 1999; Taylor 2013) to model the formation of permeability barriers in the lithosphere of Mars. In order to represent potential past and present conditions of Mars, we vary the lithospheric thickness, mantle potential temperature (heat flux), oxygen fugacity, and water content.Our results show that permeability layers can develop in the thermal boundary layer of the simulated Martian lithosphere if the mantle potential temperature is higher than ~1500°C. The various Martian mantle compositions yield barriers in the same locations, under matching variable conditions. There is no significant difference in barrier location over the range of accepted Martian oxygen fugacity values. Water content is the most significant influence on barrier development as it reduces the temperature of crystallization, allowing melt to rise further into the lithosphere. Our lower temperature and thicker lithosphere model runs, which are likely the most similar to modern Mars, show no permeability barrier generation. Losing the possibility of having a permeability

  9. Magnetic flux dynamics in superconducting materials

    International Nuclear Information System (INIS)

    Hernandez Nieves, Alexander

    2004-01-01

    The magnetization curves, the Bean-Livingston barrier in type I and type II superconductors, the ac magnetic response, the effects of thermal fluctuations on the magnetic behavior and the different dissipation mechanism at microwave frequencies are investigated in mesoscopic superconductors.For small mesoscopic samples we study the peaks and discontinuous jumps found in the magnetization as a function of magnetic field.To interpret these jumps we consider that vortices located inside the sample induce a reinforcement of the Bean- Livingston surface barrier at fields greater than the first penetration field Hp1.This leads to multiple penetration fields Hpi Hp1;Hp2;Hp3;... for vortex entrance in mesoscopic samples.For low-T c mesoscopic superconductors we found that the meta-stable states due to the surface barrier have a large half-life time, which leads to the hysteresis in the magnetization curves as observed experimentally.A very different behavior appears for high-T c mesoscopic superconductors where thermally activated vortex entrance/exit through surface barriers is frequent.This leads to a reduction of the magnetization and a non-integer average number of flux quanta penetrating the superconductor.At microwave frequencies we found that each vortex penetration event produces a significant suppression of the ac losses since the imaginary part of the ac susceptibility X ( H d c) as a function of the magnetic field (Hdc) increases before the penetration of vortices and then it decreases abruptly after vortices have entered into the sample.We show that nascent vortices (vortices that are partly inside the sample and nucleated at the surface) play an important role in the dynamic behavior of mesoscopic samples. In type I macroscopic superconductors with first-principles simulations of the TDGL equations we have been able to reproduce several features of the intermediate state observed in experiments.Particularly, droplet and striped patterns are obtained depending

  10. Photopatternable Magnetic Hollowbots by Nd-Fe-B Nanocomposite for Potential Targeted Drug Delivery Applications

    Directory of Open Access Journals (Sweden)

    Hui Li

    2018-04-01

    Full Text Available In contrast to traditional drug administration, targeted drug delivery can prolong, localize, target and have a protected drug interaction with the diseased tissue. Drug delivery carriers, such as polymeric micelles, liposomes, dendrimers, nanotubes, and so on, are hard to scale-up, costly, and have short shelf life. Here we show the novel fabrication and characterization of photopatternable magnetic hollow microrobots that can potentially be utilized in microfluidics and drug delivery applications. These magnetic hollowbots can be fabricated using standard ultraviolet (UV lithography with low cost and easily accessible equipment, which results in them being easy to scale up, and inexpensive to fabricate. Contact-free actuation of freestanding magnetic hollowbots were demonstrated by using an applied 900 G external magnetic field to achieve the movement control in an aqueous environment. According to the movement clip, the average speed of the magnetic hollowbots was estimated to be 1.9 mm/s.

  11. Dynamic effects of dipolar interactions on the magnetic behavior of magnetite nanoparticles

    Science.gov (United States)

    Allia, Paolo; Tiberto, Paola

    2011-12-01

    Isothermal magnetization and initial dc susceptibility of spheroidal, nearly monodisperse magnetite nanoparticles (typical diameter: 8 nm) prepared by a standard thermo-chemical route have been measured between 10 and 300 K. The samples contained magnetite nanoparticles in the form of either a dried powder (each nanoparticle being surrounded by a stable oleic acid shell as a result of the preparation procedure) or a solid dispersion in PEGDA-600 polymer; different nanoparticle (NP) concentrations in the polymer were studied. In all samples the NPs were not tightly agglomerated nor their ferromagnetic cores were directly touching. The high-temperature inverse magnetic susceptibility is always found to follow a linear law as a function of T, crossing the horizontal axis at negative temperatures ranging from 175 to about 1,000 K. The deviation from the standard superparamagnetic behavior is related to dipolar interaction among NPs; however, a careful analysis makes it hard to conclude that such a behavior originates from a dominant antiferromagnetic character of the interaction. The results are well explained considering that the studied samples are in the interacting superparamagnetic (ISP) regime. The ISP model is basically a mean field theory which allows one to straightforwardly account for the role of magnetic dipolar interaction in a NP system. The model predicts the existence of specific scaling laws for the reduced magnetization which have been confirmed in all studied samples. The interaction of each magnetic dipole moment with the local, random dipolar field produced by the other dipoles results in the presence of a large fluctuating energy term whose magnitude is comparable to the static barrier for magnetization reversal/rotation related to magnetic anisotropy. On the basis of the existing theories on thermal crossing of a barrier whose height randomly fluctuates in time it is predicted that the rate of barrier crossing is substantially driven by the rate

  12. Chirality dependent pinning and depinning of magnetic vortex domain walls at nano-constrictions

    Energy Technology Data Exchange (ETDEWEB)

    Mohanan P, Vineeth; Kumar, P.S. Anil, E-mail: anil@physics.iisc.ernet.in

    2017-01-15

    The implementation of magnetic domain wall (DW) based memory and logic devices critically depend on the control over DW assisted magnetization reversal processes. Here we investigate the magnetization reversal by DW injection, pinning and depinning at a geometrical constriction in permalloy nanowire (NW) driven by external in-plane magnetic field, using local electrical probes. The observations of two distinct depinning field values are identified with the help of micromagnetic simulations, as being due to vortex DWs of different chiralities. Statistical analysis gave an estimate of chirality dependent pinning probability of DWs at this constriction. The stochastic nature of the DW based reversal driven by magnetic field is revealed here. The asymmetry in the depinning field of the DWs to move to either side of constriction indicates the asymmetric nature of the barrier potential seen by the DWs. The results demonstrate the difficulties in achieving deterministic switching behavior of DW assisted reversal, and provide a platform to understand the main bottlenecks in the technological implementation of DWs.

  13. Hyperpolarized Porous Silicon Nanoparticles: Potential Theragnostic Material for ²⁹Si Magnetic Resonance Imaging.

    Science.gov (United States)

    Seo, Hyeonglim; Choi, Ikjang; Whiting, Nicholas; Hu, Jingzhe; Luu, Quy Son; Pudakalakatti, Shivanand; McCowan, Caitlin; Kim, Yaewon; Zacharias, Niki; Lee, Seunghyun; Bhattacharya, Pratip; Lee, Youngbok

    2018-05-20

    Porous silicon nanoparticles have recently garnered attention as potentially-promising biomedical platforms for drug delivery and medical diagnostics. Here, we demonstrate porous silicon nanoparticles as contrast agents for ²⁹Si magnetic resonance imaging. Size-controlled porous silicon nanoparticles were synthesized by magnesiothermic reduction of silica nanoparticles and were surface activated for further functionalization. Particles were hyperpolarized via dynamic nuclear polarization to enhance their ²⁹Si MR signals; the particles demonstrated long ²⁹Si spin-lattice relaxation (T₁) times (~ 25 mins), which suggests potential applicability for medical imaging. Furthermore, ²⁹Si hyperpolarization levels were sufficient to allow ²⁹Si MRI in phantoms. These results underscore the potential of porous silicon nanoparticles that, when combined with hyperpolarized magnetic resonance imaging, can be a powerful theragnostic deep tissue imaging platform to interrogate various biomolecular processes in vivo. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. MgO magnetic tunnel junctions of enduring F-type upon annealing

    International Nuclear Information System (INIS)

    Schleicher, F; Halisdemir, U; Urbain, E; Gallart, M; Boukari, S; Beaurepaire, E; Gilliot, P; Bowen, M; Lacour, D; Montaigne, F; Hehn, M

    2015-01-01

    The authors performed magnetotransport experiments to determine whether annealing alters the oxygen vacancy-mediated tunnelling potential landscape of the central portion of a MgO ultrathin film within sputtered CoFeB/MgO/CoFeB magnetic tunnel junctions. Using the Î rel method reveals a temperature-dependent tunnelling barrier height for a non-annealed barrier that arises from single oxygen vacancies (F centres) and is qualitatively identical to that found for its partly and fully annealed counterparts. Thus these MTJs with F centres remain of F-type upon annealing. This explicitly confirms that the large tunnel-magnetoresistance (TMR) increase upon annealing results mainly from structural modifications of MgO and CoFeB and not from vacancy pairing within the barrier. Photoluminescence spectra performed on both annealed and non-annealed thin MgO films grown on CoFeB electrodes support this conclusion. This work should promote renewed scrutiny over the precise impact of annealing on tunnelling magnetotransport across MgO. (paper)

  15. Investigating the Potential Barrier Function of Nanostructured Materials Formed in Engineered Barrier Systems (EBS) Designed for Nuclear Waste Isolation.

    Science.gov (United States)

    Cuevas, Jaime; Ruiz, Ana Isabel; Fernández, Raúl

    2018-02-21

    Clay and cement are known nano-colloids originating from natural processes or traditional materials technology. Currently, they are used together as part of the engineered barrier system (EBS) to isolate high-level nuclear waste (HLW) metallic containers in deep geological repositories (DGR). The EBS should prevent radionuclide (RN) migration into the biosphere until the canisters fail, which is not expected for approximately 10 3  years. The interactions of cementitious materials with bentonite swelling clay have been the scope of our research team at the Autonomous University of Madrid (UAM) with participation in several European Union (EU) projects from 1998 up to now. Here, we describe the mineral and chemical nature and microstructure of the alteration rim generated by the contact between concrete and bentonite. Its ability to buffer the surrounding chemical environment may have potential for further protection against RN migration. © 2018 The Chemical Society of Japan & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Adjunctive role of preoperative liver magnetic resonance imaging for potentially resectable pancreatic cancer.

    Science.gov (United States)

    Kim, Hyoung Woo; Lee, Jong-Chan; Paik, Kyu-Hyun; Kang, Jingu; Kim, Young Hoon; Yoon, Yoo-Seok; Han, Ho-Seong; Kim, Jaihwan; Hwang, Jin-Hyeok

    2017-06-01

    The adjunctive role of magnetic resonance imaging of the liver before pancreatic ductal adenocarcinoma has been unclear. We evaluated whether the combination of hepatic magnetic resonance imaging with multidetector computed tomography using a pancreatic protocol (pCT) could help surgeons select appropriate candidates and decrease the risk of early recurrence. We retrospectively enrolled 167 patients in whom complete resection was achieved without grossly visible residual tumor; 102 patients underwent pCT alone (CT group) and 65 underwent both hepatic magnetic resonance imaging and pCT (magnetic resonance imaging group). By adding hepatic magnetic resonance imaging during preoperative evaluation, hepatic metastases were newly discovered in 3 of 58 patients (5%) without hepatic lesions on pCT and 17 of 53 patients (32%) with indeterminate hepatic lesions on pCT. Patients with borderline resectability, a tumor size >3 cm, or preoperative carbohydrate antigen 19-9 level >1,000 U/mL had a greater rate of hepatic metastasis on subsequent hepatic magnetic resonance imaging. Among 167 patients in whom R0/R1 resection was achieved, the median overall survival was 18.2 vs 24.7 months (P = .020) and the disease-free survival was 8.5 vs 10.0 months (P = .016) in the CT and magnetic resonance imaging groups, respectively (median follow-up, 18.3 months). Recurrence developed in 82 (80%) and 43 (66%) patients in the CT and magnetic resonance imaging groups, respectively. The cumulative hepatic recurrence rate was greater in the CT group than in the magnetic resonance imaging group (P magnetic resonance imaging should be considered in patients with potentially resectable pancreatic ductal adenocarcinoma, especially those with high tumor burden. Copyright © 2017 Elsevier Inc. All rights reserved.

  17. Edge-shape barrier irreversibility and decomposition of vortices in Bi 2Sr 2CaCu 2O 8

    Science.gov (United States)

    Indenbom, M. V.; D'Anna, G.; André, M.-O.; Kabanov, V. V.; Benoit, W.

    1994-12-01

    Magnetic flux dynamics is studied in Bi 2Sr 2CaCu 2O 8 single crystals by means of magneto-optical technique. It is clearly demonstrated that the magnetic irreversibility of these crystals in a magnetic field perpendicular to the basal plane at temperatures higher than approximately 35 K is governed by an edge-shape barrier and its disappearance determines the high temperature part of the magnetic irreversibility line which is commonly associated in the literature with vortex lattice melting. We argue that this barrier exists because of the non ellipsoidal shape of the samples and can disappear only when the flux lines lose their rigidity decomposing into pancakes, which is the only true magnetic phase transition on the B-T diagram for Bi 2Sr 2CaCu 2O 8.

  18. Material Barriers to Diffusive Mixing

    Science.gov (United States)

    Haller, George; Karrasch, Daniel

    2017-11-01

    Transport barriers, as zero-flux surfaces, are ill-defined in purely advective mixing in which the flux of any passive scalar is zero through all material surfaces. For this reason, Lagrangian Coherent Structures (LCSs) have been argued to play the role of mixing barriers as most repelling, attracting or shearing material lines. These three kinematic concepts, however, can also be defined in different ways, both within rigorous mathematical treatments and within the realm of heuristic diagnostics. This has lead to a an ever-growing number of different LCS methods, each generally identifying different objects as transport barriers. In this talk, we examine which of these methods have actual relevance for diffusive transport barriers. The latter barriers are arguably the practically relevant inhibitors in the mixing of physically relevant tracers, such as temperature, salinity, vorticity or potential vorticity. We demonstrate the role of the most effective diffusion barriers in analytical examples and observational data. Supported in part by the DFG Priority Program on Turbulent Superstructures.

  19. Prescriber barriers and enablers to minimising potentially inappropriate medications in adults: a systematic review and thematic synthesis.

    Science.gov (United States)

    Anderson, Kristen; Stowasser, Danielle; Freeman, Christopher; Scott, Ian

    2014-12-08

    To synthesise qualitative studies that explore prescribers' perceived barriers and enablers to minimising potentially inappropriate medications (PIMs) chronically prescribed in adults. A qualitative systematic review was undertaken by searching PubMed, EMBASE, Scopus, PsycINFO, CINAHL and INFORMIT from inception to March 2014, combined with an extensive manual search of reference lists and related citations. A quality checklist was used to assess the transparency of the reporting of included studies and the potential for bias. Thematic synthesis identified common subthemes and descriptive themes across studies from which an analytical construct was developed. Study characteristics were examined to explain differences in findings. All healthcare settings. Medical and non-medical prescribers of medicines to adults. Prescribers' perspectives on factors which shape their behaviour towards continuing or discontinuing PIMs in adults. 21 studies were included; most explored primary care physicians' perspectives on managing older, community-based adults. Barriers and enablers to minimising PIMs emerged within four analytical themes: problem awareness; inertia secondary to lower perceived value proposition for ceasing versus continuing PIMs; self-efficacy in regard to personal ability to alter prescribing; and feasibility of altering prescribing in routine care environments given external constraints. The first three themes are intrinsic to the prescriber (eg, beliefs, attitudes, knowledge, skills, behaviour) and the fourth is extrinsic (eg, patient, work setting, health system and cultural factors). The PIMs examined and practice setting influenced the themes reported. A multitude of highly interdependent factors shape prescribers' behaviour towards continuing or discontinuing PIMs. A full understanding of prescriber barriers and enablers to changing prescribing behaviour is critical to the development of targeted interventions aimed at deprescribing PIMs and reducing the

  20. Sustaining the pivotal organizational outcome: magnet recognition.

    Science.gov (United States)

    Parsons, Mickey L; Cornett, Patricia A

    2011-03-01

    To identify the facilitators and barriers for health-care organizations to sustain Magnet Recognition, the exemplar of a professional practice environment and quality care. Recognition as a Magnet Hospital is the gold standard for acknowledging excellence in nursing. However, limited evidence exists to inform nursing management practices for sustainability. This qualitative study was conducted using a national convenience sample of 15 Chief Nursing Officers of Magnet Recognized hospitals in the USA. Key macrosystem facilitators included executive management and leadership themes about quality, people, education, and the nurse executive's commitment and intent. Barriers were executive management turnover and financial challenges. Infrastructure supports and resources for empowerment and quality and unit leadership practices were found to be essential for quality outcomes. The key theme at the microsystem level was moving nursing practice to managing outcomes from tasks; barriers were challenges with unit management turnover and development. Multiple factors at system levels were found to contribute to sustainability. Further research is needed on the concept of sustainability. The findings contribute to executives' armamentarium to inform management practice for the design of evidenced based organizational systems and programs for nursing excellence. © 2011 The Authors. Journal compilation © 2011 Blackwell Publishing Ltd.

  1. Magnon spin transport driven by the magnon chemical potential in a magnetic insulator

    NARCIS (Netherlands)

    Cornelissen, L J; Peters, K J H; Bauer, G. E. W.; Duine, R A; van Wees, B J

    2016-01-01

    We develop a linear-response transport theory of diffusive spin and heat transport by magnons in magnetic insulators with metallic contacts. The magnons are described by a position-dependent temperature and chemical potential that are governed by diffusion equations with characteristic relaxation

  2. Magnon spin transport driven by the magnon chemical potential in a magnetic insulator

    NARCIS (Netherlands)

    Cornelissen, L.J.; Peters, K. J H; Bauer, G.E.; Duine, R. A.; Van Wees, B. J.

    2016-01-01

    We develop a linear-response transport theory of diffusive spin and heat transport by magnons in magnetic insulators with metallic contacts. The magnons are described by a position-dependent temperature and chemical potential that are governed by diffusion equations with characteristic relaxation

  3. Magnon spin transport driven by the magnon chemical potential in a magnetic insulator

    NARCIS (Netherlands)

    Cornelissen, Ludo J.; Peters, Kevin J. H.; Duine, Rembert A.|info:eu-repo/dai/nl/304830127; Bauer, Gerrit E. W.; Wees, Bart J. van

    2016-01-01

    We develop a linear-response transport theory of diffusive spin and heat transport by magnons in magnetic insulators with metallic contacts. The magnons are described by a position dependent temperature and chemical potential that are governed by diffusion equations with characteristic relaxation

  4. Magnetized retarding field energy analyzer measuring the particle flux and ion energy distribution of both positive and negative ions

    International Nuclear Information System (INIS)

    Rafalskyi, Dmytro; Aanesland, Ane; Dudin, Stanislav

    2015-01-01

    This paper presents the development of a magnetized retarding field energy analyzer (MRFEA) used for positive and negative ion analysis. The two-stage analyzer combines a magnetic electron barrier and an electrostatic ion energy barrier allowing both positive and negative ions to be analyzed without the influence of electrons (co-extracted or created downstream). An optimal design of the MRFEA for ion-ion beams has been achieved by a comparative study of three different MRFEA configurations, and from this, scaling laws of an optimal magnetic field strength and topology have been deduced. The optimal design consists of a uniform magnetic field barrier created in a rectangular channel and an electrostatic barrier consisting of a single grid and a collector placed behind the magnetic field. The magnetic barrier alone provides an electron suppression ratio inside the analyzer of up to 6000, while keeping the ion energy resolution below 5 eV. The effective ion transparency combining the magnetic and electrostatic sections of the MRFEA is measured as a function of the ion energy. It is found that the ion transparency of the magnetic barrier increases almost linearly with increasing ion energy in the low-energy range (below 200 eV) and saturates at high ion energies. The ion transparency of the electrostatic section is almost constant and close to the optical transparency of the entrance grid. We show here that the MRFEA can provide both accurate ion flux and ion energy distribution measurements in various experimental setups with ion beams or plasmas run at low pressure and with ion energies above 10 eV

  5. Engineered barrier system and waste package design concepts for a potential geologic repository at Yucca Mountain

    International Nuclear Information System (INIS)

    Short, D.W.; Ruffner, D.J.; Jardine, L.J.

    1991-10-01

    We are using an iterative process to develop preliminary concept descriptions for the Engineered Barrier System and waste-package components for the potential geologic repository at Yucca Mountain. The process allows multiple design concepts to be developed subject to major constraints, requirements, and assumptions. Involved in the highly interactive and interdependent steps of the process are technical specialists in engineering, metallic and nonmetallic materials, chemistry, geomechanics, hydrology, and geochemistry. We have developed preliminary design concepts that satisfy both technical and nontechnical (e.g., programmatic or policy) requirements

  6. Bound magnetic polaron in a semimagnetic double quantum well

    Science.gov (United States)

    Kalpana, P.; Jayakumar, K.

    2017-09-01

    The effect of different combinations of the concentration of Mn2+ ion in the Quantum well Cd1-xinMnxin Te and the barrier Cd1-xoutMnxout Te on the Bound Magnetic Polaron (BMP) in a Diluted Magnetic Semiconductors (DMS) Double Quantum Well (DQW) has been investigated. The Schrodinger equation is solved variationally in the effective mass approximation through which the Spin Polaronic Shift (SPS) due to the formation of BMP has been estimated for various locations of the donor impurity in the DQW. The results show that the effect of the increase of Mn2+ ion composition with different combinations on SPS is predominant for On Centre Well (OCW) impurity when compared to all other impurity locations when there is no application of magnetic field (γ = 0), γ being a dimensionless parameter for the magnetic field, and the same is predominant for On Centre Barrier (OCB) impurity with the application of external magnetic field (γ = 0.15).

  7. Effect of Rashba and Dresselhaus Spin-Orbit Couplings on Electron Spin Polarization in a Hybrid Magnetic-Electric Barrier Nanostructure

    Science.gov (United States)

    Yang, Shi-Peng; Lu, Mao-Wang; Huang, Xin-Hong; Tang, Qiang; Zhou, Yong-Long

    2017-04-01

    A theoretical study has been carried out on the spin-dependent electron transport in a hybrid magnetic-electric barrier nanostructure with both Rashba and Dresselhaus spin-orbit couplings, which can be experimentally realized by depositing a ferromagnetic strip and a Schottky metal strip on top of a semiconductor heterostructure. The spin-orbit coupling-dependent transmission coefficient, conductance, and spin polarization are calculated by solving the Schrödinger equation exactly with the help of the transfer-matrix method. We find that both the magnitude and sign of the electron spin polarization vary strongly with the spin-orbit coupling strength. Thus, the degree of electron spin polarization can be manipulated by properly adjusting the spin-orbit coupling strength, and such a nanosystem can be employed as a controllable spin filter for spintronics applications.

  8. Non-monotonic probability of thermal reversal in thin-film biaxial nanomagnets with small energy barriers

    Directory of Open Access Journals (Sweden)

    N. Kani

    2017-05-01

    Full Text Available The goal of this paper is to investigate the short time-scale, thermally-induced probability of magnetization reversal for an biaxial nanomagnet that is characterized with a biaxial magnetic anisotropy. For the first time, we clearly show that for a given energy barrier of the nanomagnet, the magnetization reversal probability of an biaxial nanomagnet exhibits a non-monotonic dependence on its saturation magnetization. Specifically, there are two reasons for this non-monotonic behavior in rectangular thin-film nanomagnets that have a large perpendicular magnetic anisotropy. First, a large perpendicular anisotropy lowers the precessional period of the magnetization making it more likely to precess across the x^=0 plane if the magnetization energy exceeds the energy barrier. Second, the thermal-field torque at a particular energy increases as the magnitude of the perpendicular anisotropy increases during the magnetization precession. This non-monotonic behavior is most noticeable when analyzing the magnetization reversals on time-scales up to several tens of ns. In light of the several proposals of spintronic devices that require data retention on time-scales up to 10’s of ns, understanding the probability of magnetization reversal on the short time-scales is important. As such, the results presented in this paper will be helpful in quantifying the reliability and noise sensitivity of spintronic devices in which thermal noise is inevitably present.

  9. The gastro-esophageal reflux barrier: biophysical analysis on 3D models of anatomy from magnetic resonance imaging.

    Science.gov (United States)

    Roy, S; Fox, M R; Curcic, J; Schwizer, W; Pal, A

    2012-07-01

    The function and structure of the gastro-esophageal junction (GEJ) determine its efficacy as a reflux barrier. This study presents a novel methodology for the quantitative assessment of GEJ and proximal gastric morphology from magnetic resonance (MR) imaging. Based on this data we propose a new conceptualization of the hypothesis that a flap valve mechanism contributes to reflux protection. 3D models of the GEJ and proximal stomach were reconstructed from MR images in 12 healthy volunteers during respiration and on eating a test meal to maximum satiation. A rotating plane analysis measured the gastro-esophageal insertion angle and span of contact. An ellipsoid fit provided quantitative assessment of gastric shape and orientation relative to a fixed anatomical reference point. Position of the esophageal insertion on the 'gastric ellipse' was noted. An ellipsoid-cylinder model was designed to analyze the relationships among parameters describing the GEJ morphology. The insertion angle became more acute on expiration, but did not change with meal ingestion. In contrast the span of contact did not vary with respiration, but increased with gastric filling. Changes in gastric morphology with distension further augmented the span of gastro-esophageal contact in almost 70% of the studies. Novel MR imaging and biophysical analysis of the GEJ and proximal stomach provide a quantitative description of structures contributing to the reflux barrier. Changes in these parameters during respiration and on eating support the hypothesis that structural components of a functional 'flap valve' like mechanism contribute to reflux protection. © 2012 Blackwell Publishing Ltd.

  10. Imaging blood-brain barrier dysfunction as a biomarker for epileptogenesis.

    Science.gov (United States)

    Bar-Klein, Guy; Lublinsky, Svetlana; Kamintsky, Lyn; Noyman, Iris; Veksler, Ronel; Dalipaj, Hotjensa; Senatorov, Vladimir V; Swissa, Evyatar; Rosenbach, Dror; Elazary, Netta; Milikovsky, Dan Z; Milk, Nadav; Kassirer, Michael; Rosman, Yossi; Serlin, Yonatan; Eisenkraft, Arik; Chassidim, Yoash; Parmet, Yisrael; Kaufer, Daniela; Friedman, Alon

    2017-06-01

    A biomarker that will enable the identification of patients at high-risk for developing post-injury epilepsy is critically required. Microvascular pathology and related blood-brain barrier dysfunction and neuroinflammation were shown to be associated with epileptogenesis after injury. Here we used prospective, longitudinal magnetic resonance imaging to quantitatively follow blood-brain barrier pathology in rats following status epilepticus, late electrocorticography to identify epileptic animals and post-mortem immunohistochemistry to confirm blood-brain barrier dysfunction and neuroinflammation. Finally, to test the pharmacodynamic relevance of the proposed biomarker, two anti-epileptogenic interventions were used; isoflurane anaesthesia and losartan. Our results show that early blood-brain barrier pathology in the piriform network is a sensitive and specific predictor (area under the curve of 0.96, P brain barrier pathology as a clinically relevant predictive, diagnostic and pharmaco!dynamics biomarker for acquired epilepsy. © The Author (2017). Published by Oxford University Press on behalf of the Guarantors of Brain. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

  11. Fabrication of magnetic tunnel junctions with epitaxial and textured ferromagnetic layers

    Science.gov (United States)

    Chang, Y. Austin; Yang, Jianhua Joshua

    2008-11-11

    This invention relates to magnetic tunnel junctions and methods for making the magnetic tunnel junctions. The magnetic tunnel junctions include a tunnel barrier oxide layer sandwiched between two ferromagnetic layers both of which are epitaxial or textured with respect to the underlying substrate upon which the magnetic tunnel junctions are grown. The magnetic tunnel junctions provide improved magnetic properties, sharper interfaces and few defects.

  12. Transferrin-conjugated magnetic dextran-spermine nanoparticles for targeted drug transport across blood-brain barrier.

    Science.gov (United States)

    Ghadiri, Maryam; Vasheghani-Farahani, Ebrahim; Atyabi, Fatemeh; Kobarfard, Farzad; Mohamadyar-Toupkanlou, Farzaneh; Hosseinkhani, Hossein

    2017-10-01

    Application of many vital hydrophilic medicines have been restricted by blood-brain barrier (BBB) for treatment of brain diseases. In this study, a targeted drug delivery system based on dextran-spermine biopolymer was developed for drug transport across BBB. Drug loaded magnetic dextran-spermine nanoparticles (DS-NPs) were prepared via ionic gelation followed by transferrin (Tf) conjugation as targeting moiety. The characteristics of Tf conjugated nanoparticles (TDS-NPs) were analyzed by different methods and their cytotoxicity effects on U87MG cells were tested. The superparamagnetic characteristic of TDS-NPs was verified by vibration simple magnetometer. Capecitabine loaded TDS-NPs exhibited pH-sensitive release behavior with enhanced cytotoxicity against U87MG cells, compared to DS-NPs and free capecitabine. Prussian-blue staining and TEM-imaging showed the significant cellular uptake of TDS-NPs. Furthermore, a remarkable increase of Fe concentrations in brain was observed following their biodistribution and histological studies in vivo, after 1 and 7 days of post-injection. Enhanced drug transport across BBB and pH-triggered cellular uptake of TDS-NPs indicated that these theranostic nanocarriers are promising candidate for the brain malignance treatment. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2851-2864, 2017. © 2017 Wiley Periodicals, Inc.

  13. Suppressing Electron Turbulence and Triggering Internal Transport Barriers with Reversed Magnetic Shear in the National Spherical Torus Experiment

    Science.gov (United States)

    Peterson, Jayson Luc

    2011-10-01

    Observations in the National Spherical Torus Experiment (NSTX) have found electron temperature gradients that greatly exceed the linear threshold for the onset for electron temperature gradient-driven (ETG) turbulence. These discharges, deemed electron internal transport barriers (e-ITBs), coincide with a reversal in the shear of the magnetic field and with a reduction in electron-scale density fluctuations, qualitatively consistent with earlier gyrokinetic predictions. To investigate this phenomenon further, we numerically model electron turbulence in NSTX reversed-shear plasmas using the gyrokinetic turbulence code GYRO. These first-of-a-kind nonlinear gyrokinetic simulations of NSTX e-ITBs confirm that reversing the magnetic shear can allow the plasma to reach electron temperature gradients well beyond the critical gradient for the linear onset of instability. This effect is very strong, with the nonlinear threshold for significant transport approaching three times the linear critical gradient in some cases, in contrast with moderate shear cases, which can drive significant ETG turbulence at much lower gradients. In addition to the experimental implications of this upshifted nonlinear critical gradient, we explore the behavior of ETG turbulence during reversed shear discharges. This work is supported by the SciDAC Center for the Study of Plasma Microturbulence, DOE Contract DE-AC02-09CH11466, and used the resources of NCCS at ORNL and NERSC at LBNL. M. Ono et al., Nucl. Fusion 40, 557 (2000).

  14. Atoms confined in a penetrable potential: effect of the atom position on the electric and magnetic responses

    International Nuclear Information System (INIS)

    Acosta Coden, Diego S; Gomez, Sergio S; Romero, Rodolfo H

    2011-01-01

    We report results of the calculation of polarizability and the nuclear magnetic shielding tensors of two-electron atoms confined within an attractive Gaussian potential well. The electric and magnetic responses are obtained within the random phase approximation (RPA) of the polarization propagator. The influence of the depth and range of the potential on the electronic structure is also studied. The dependence of the parallel (along the displacement) and perpendicular components of the polarizability and shielding tensors on the distance of the atom to the centre of the well is calculated and rationalized as a dissociation-type process of the artificial diatomic molecule formed between the Coulomb and the well potentials.

  15. Atoms confined in a penetrable potential: effect of the atom position on the electric and magnetic responses

    Energy Technology Data Exchange (ETDEWEB)

    Acosta Coden, Diego S; Gomez, Sergio S; Romero, Rodolfo H, E-mail: rhromero@exa.unne.edu.ar [Instituto de Modelado e Innovacion Tecnologica, CONICET and Facultad de Ciencias Exactas y Naturales y Agrimensura, Universidad Nacional del Nordeste, Avenida Libertad 5500 (3400) Corrientes (Argentina)

    2011-02-14

    We report results of the calculation of polarizability and the nuclear magnetic shielding tensors of two-electron atoms confined within an attractive Gaussian potential well. The electric and magnetic responses are obtained within the random phase approximation (RPA) of the polarization propagator. The influence of the depth and range of the potential on the electronic structure is also studied. The dependence of the parallel (along the displacement) and perpendicular components of the polarizability and shielding tensors on the distance of the atom to the centre of the well is calculated and rationalized as a dissociation-type process of the artificial diatomic molecule formed between the Coulomb and the well potentials.

  16. Decoupling of magnetic fields in collapsing protostellar envelopes and disc formation and fragmentation

    Science.gov (United States)

    Zhao, Bo; Caselli, Paola; Li, Zhi-Yun; Krasnopolsky, Ruben

    2018-02-01

    Efficient magnetic braking is a formidable obstacle to the formation of rotationally supported discs (RSDs) around protostars in magnetized dense cores. We have previously shown, through 2D (axisymmetric) non-ideal magnetohydrodynamic simulations, that removing very small grains (VSGs: ∼10 Å to few 100 Å) can greatly enhance ambipolar diffusion and enable the formation of RSDs. Here, we extend the simulations of disc formation enabled by VSG removal to 3D. We find that the key to this scenario of disc formation is that the drift velocity of the magnetic field almost cancels out the infall velocity of the neutrals in the 102-103 au scale 'pseudo-disc' where the field lines are most severely pinched and most of protostellar envelope mass infall occurs. As a result, the bulk neutral envelope matter can collapse without dragging much magnetic flux into the disc-forming region, which lowers the magnetic braking efficiency. We find that the initial discs enabled by VSG removal tend to be Toomre-unstable, which leads to the formation of prominent spiral structures that function as centrifugal barriers. The piling-up of infall material near the centrifugal barrier often produces dense fragments of tens of Jupiter masses, especially in cores that are not too strongly magnetized. Some fragments accrete on to the central stellar object, producing bursts in mass accretion rate. Others are longer lived, although whether they can survive for a long term to produce multiple systems remains to be ascertained. Our results highlight the importance of dust grain evolution in determining the formation and properties of protostellar discs and potentially multiple systems.

  17. Richards Barrier LA Reference Design Feature Evaluation

    International Nuclear Information System (INIS)

    N.E. Kramer

    1999-01-01

    The Richards Barrier is one of the design features of the repository to be considered for the License Application (LA), Richards was a soil scientist who first described the diversion of moisture between two materials with different hydrologic properties. In this report, a Richards Barrier is a special type of backfill with a fine-grained material (such as sand) overlaying a coarse-grained material (such as gravel). Water that enters an emplacement drift will first encounter the fine-grained material and be transported around the coarse-grained material covering the waste package, thus protecting the waste package from contact with most of the groundwater. The objective of this report is to discuss the benefits and liabilities to the repository by the inclusion of a Richards Barrier type backfill in emplacement drifts. The Richards Barrier can act as a barrier to water flow, can reduce the waste package material dissolution rate, limit mobilization of the radionuclides, and can provide structural protection for the waste package. The scope of this report is to: (1) Analyze the behavior of barrier materials following the intrusion of groundwater for influxes of 1 to 300 mm per year. The report will demonstrate diversion of groundwater intrusions into the barrier over an extended time period when seismic activity and consolidation may cause the potential for liquefaction and settlement of the Richards Barrier. (2) Review the thermal effects of the Richards Barrier on material behavior. (3) Analyze the effect of rockfall on the performance of the Richards Barrier and the depth of the barrier required to protect waste packages under the barrier. (4) Review radiological and heating conditions on placement of multiple layers of the barrier. Subsurface Nuclear Safety personnel will perform calculations to determine the radiation reduction-time relationship and shielding capacity of the barrier. (5) Evaluate the effects of ventilation on cooling of emplacement drifts and

  18. Potential formation in a collisionless plasma produced in an open magnetic field in presence of volume negative ion source

    International Nuclear Information System (INIS)

    Phukan, Ananya; Goswami, K. S.; Bhuyan, P. J.

    2014-01-01

    The electric potential near a wall for a multi-species plasma with volume produced negative ions in presence of axially varying magnetic field is studied following an analytical-numerical approach. A constant negative ion source is assumed throughout the plasma volume, along with finite temperature positive ions and Boltzmann electrons. The particles are assumed to be guided by an open magnetic field that has its maximum at the centre, and field strength decreasing towards the walls. The one dimensional (1D) Poisson equation is derived using an analytical approach, and then solved numerically to study the potential profiles. Effect of (a) negative ion production rate, (b) magnetic field profile, and (c) negative ion temperature on the potential profile has been investigated. A potential peak appears near the wall when the negative ion temperature and density are sufficiently high. Also, the presence of negative ions further decreases the potential in the plasma region for a finite Debye Length (λ D )

  19. Controlled fabrication of nano-scale double barrier magnetic tunnel junctions using focused ion beam milling method

    International Nuclear Information System (INIS)

    Wei, H.X.; Wang, T.X.; Zeng, Z.M.; Zhang, X.Q.; Zhao, J.; Han, X.F.

    2006-01-01

    The controlled fabrication method for nano-scale double barrier magnetic tunnel junctions (DBMTJs) with the layer structure of Ta(5)/Cu(10)/Ni 79 Fe 21 (5)/Ir 22 Mn 78 (12)/Co 6 Fe 2 B 2 (4)/Al(1) -oxide/Co 6 Fe 2 B 2 (6)/Al (1)-oxide/Co 6 Fe 2 B 2 (4)/Ir 22 Mn 78 (12)/Ni 79 Fe 21 (5)/Ta(5) (thickness unit: nm) was used. This method involved depositing thin multi-layer stacks by sputtering system, and depositing a Pt nano-pillar using a focused ion beam which acted both as a top contact and as an etching mask. The advantages of this process over the traditional process using e-beam and optical lithography in that it involve only few processing steps, e.g. it does not involve any lift-off steps. In order to evaluate the nanofabrication techniques, the DBMTJs with the dimensions of 200 nmx400 nm, 200 nmx200 nm nano-scale were prepared and their R-H, I-V characteristics were measured.

  20. Increasing the applicability of density functional theory. IV. Consequences of ionization-potential improved exchange-correlation potentials.

    Science.gov (United States)

    Verma, Prakash; Bartlett, Rodney J

    2014-05-14

    This paper's objective is to create a "consistent" mean-field based Kohn-Sham (KS) density functional theory (DFT) meaning the functional should not only provide good total energy properties, but also the corresponding KS eigenvalues should be accurate approximations to the vertical ionization potentials (VIPs) of the molecule, as the latter condition attests to the viability of the exchange-correlation potential (VXC). None of the prominently used DFT approaches show these properties: the optimized effective potential VXC based ab initio dft does. A local, range-separated hybrid potential cam-QTP-00 is introduced as the basis for a "consistent" KS DFT approach. The computed VIPs as the negative of KS eigenvalue have a mean absolute error of 0.8 eV for an extensive set of molecule's electron ionizations, including the core. Barrier heights, equilibrium geometries, and magnetic properties obtained from the potential are in good agreement with experiment. A similar accuracy with less computational efforts can be achieved by using a non-variational global hybrid variant of the QTP-00 approach.

  1. Formation and collapse of internal transport barrier

    International Nuclear Information System (INIS)

    Fukuyama, A.; Itoh, K.; Itoh, S.I.; Yagi, M.

    1999-01-01

    A theoretical model of internal transport barrier (ITB) is developed. The transport model based on the self-sustained turbulence theory of the current-diffusive ballooning mode is extended to include the effects of ExB rotation shear. Delayed formation of ITB is observed in transport simulations. The influence of finite gyroradius is also discussed. Simulation of the current ramp-up experiment successfully described the radial profile of density, temperature and safety factor. A model of ITB collapse due to magnetic braiding is proposed. Sudden enhancement of transport triggered by overlapping of magnetic islands terminates ITB. The possibility of destabilizing global low-n modes is also discussed. (author)

  2. Formation and collapse of internal transport barrier

    International Nuclear Information System (INIS)

    Fukuyama, A.; Itoh, K.; Itoh, S.-I.; Yagi, M.

    2001-01-01

    A theoretical model of internal transport barrier (ITB) is developed. The transport model based on the self-sustained turbulence theory of the current-diffusive ballooning mode is extended to include the effects of ExB rotation shear. Delayed formation of ITB is observed in transport simulations. The influence of finite gyroradius is also discussed. Simulation of the current ramp-up experiment successfully described the radial profile of density, temperature and safety factor. A model of ITB collapse due to magnetic braiding is proposed. Sudden enhancement of transport triggered by overlaping of magnetic islands terminates ITB. The possibility of destabilizing global low-n modes is also discussed. (author)

  3. Plasma potential in a magnetic mirror with electron-cyclotron-resonance heating

    International Nuclear Information System (INIS)

    Smith, P.K.

    1983-01-01

    Experimental and theoretical studies of the ECRH plasma in the University of Wisconsin DE Machine magnetic mirror have been undertaken. Typical plasma parameters in these experiments were T/sub e/ - 10 to 30 eV, T/sub i/ - 4 eV, V/sub po/ (plasma potential at midplane) - 20 to 50 V, midplane plasma density n 0 - 10 16 m - 3 , B 0 (magnetic field strength on axis at midplane) - .005 to .01 T, mirror ratio R - 5 to 20. The principal experimental findings were the appearance of strong density peaks (approx. 2 x background) and notable V/sub f/ dips (approx. kT/sub e//e) in a narrow (approx. 1 cm) region near the axial positions of cyclotron resonance. The properties of these dips do not change greatly over the range of operating parameters, but are narrower at higher pressures

  4. Calculation of the magnetic vector potential in the TJ-II; Calculo del Potencial Magnetico Vector en el TJ-II

    Energy Technology Data Exchange (ETDEWEB)

    Lopez Fraguas, A.; Lopez Bruna, D.; Romero, J. A.

    2005-07-01

    The properties of the vector magnetic potential and its usefulness to calculate magnetic fluxes in both stationary and time-dependent conditions are p revised in this report. We have adapted to the TJ-II Flexible Heliac efficient numerical expressions to calculate the vector potential, calculating in addition the magnetic flux with this formalism in circumstances whose complexity makes very convenient the use of the vector potential. The result on induced voltages offer theoretical support to the measurements of induced voltage due to the OH coils in the plasma, like the measurements provided by the loop voltage diagnostic installed in the TJ-II, as well as to the cylindrical approximation of the plasma often used to interpret experimental data. (Author) 11 refs.

  5. Analytic expression for the giant fieldlike spin torque in spin-filter magnetic tunnel junctions

    Science.gov (United States)

    Tang, Y.-H.; Huang, Z.-W.; Huang, B.-H.

    2017-08-01

    We propose analytic expressions for fieldlike, T⊥, and spin-transfer, T∥, spin torque components in the spin-filter-based magnetic tunnel junction (SFMTJ), by using the single-band tight-binding model with the nonequilibrium Keldysh formalism. In consideration of multireflection processes between noncollinear magnetization of the spin-filter (SF) barrier and the ferromagnetic (FM) electrode, the central spin-selective SF barrier plays an active role in the striking discovery T⊥≫T∥ , which can be further identified by the unusual barrier thickness dependence of giant T⊥. Our general expressions reveal the sinusoidal angular dependence of both spin torque components, even in the presence of the SF barrier.

  6. Effects of magnetic pre-alignment of nano-powders on formation of high textured barium hexa-ferrite quasi-single crystals via a magnetic forming and liquid participation sintering route

    International Nuclear Information System (INIS)

    Liu, Junliang; Zeng, Yanwei; Zhang, Xingkai; Zhang, Ming

    2015-01-01

    Highly textured barium hexa-ferrite quasi-single crystal with narrow ferromagnetic resonance line-width is believed to be a potential gyromagnetic material for self-biased microwave devices. To fabricate barium hexa-ferrite quasi-single crystal with a high grain orientation degree, a magnetic forming and liquid participation sintering route has been developed. In this paper, the effects of the pre-alignment of the starting nano-powders on the formation of barium quasi-single crystal structures have been investigated. The results indicated that: the crystallites with large sizes and small specific surfaces were easily aligned for they got higher driving forces and lower resistances during magnetic forming. The average restricting magnetic field was about 4.647 kOe to overcome the average friction barrier between crystallites. The pre-aligned crystallites in magnetic forming acted as the “crystal seeds” for oriented growth of the un-aligned crystallites during liquid participation sintering to achieve a high grain orientation. To effectively promote the grain orientation degrees of the sintered pellets, the grain orientation degrees of the green compacts must be higher than a limited value of 15.0%. Barium hexa-ferrite quasi-single crystal with a high grain orientation degree of 98.6% was successfully fabricated after sintering the green compact with its grain orientation degree of 51.1%. - Highlights: • Aligned particles acted as “crystal seeds” for un-aligned ones' oriented growth. • Magnetic field of 4.647 kOe was needed to overcome crystallites' friction barrier. • GOD dramatically increased after sintering if starting GOD exceeded to 15.0%. • Quasi-single crystal was prepared by sintering green compact with GOD of 51.1%

  7. Effects of magnetic pre-alignment of nano-powders on formation of high textured barium hexa-ferrite quasi-single crystals via a magnetic forming and liquid participation sintering route

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Junliang, E-mail: liujunliang@yzu.edu.cn [Key Laboratory of Environmental Materials and Engineering of Jiangsu Province, School of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou 225002 (China); Zeng, Yanwei [State Key Laboratory of Materials-Oriented Chemical Engineering, School of Materials Science and Engineering, Nanjing Tech University, Nanjing 210009 (China); Zhang, Xingkai [Key Laboratory of Environmental Materials and Engineering of Jiangsu Province, School of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou 225002 (China); Zhang, Ming [Key Laboratory of Environmental Materials and Engineering of Jiangsu Province, School of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou 225002 (China); Testing Center of Yangzhou University, Yangzhou 225002 (China)

    2015-05-15

    Highly textured barium hexa-ferrite quasi-single crystal with narrow ferromagnetic resonance line-width is believed to be a potential gyromagnetic material for self-biased microwave devices. To fabricate barium hexa-ferrite quasi-single crystal with a high grain orientation degree, a magnetic forming and liquid participation sintering route has been developed. In this paper, the effects of the pre-alignment of the starting nano-powders on the formation of barium quasi-single crystal structures have been investigated. The results indicated that: the crystallites with large sizes and small specific surfaces were easily aligned for they got higher driving forces and lower resistances during magnetic forming. The average restricting magnetic field was about 4.647 kOe to overcome the average friction barrier between crystallites. The pre-aligned crystallites in magnetic forming acted as the “crystal seeds” for oriented growth of the un-aligned crystallites during liquid participation sintering to achieve a high grain orientation. To effectively promote the grain orientation degrees of the sintered pellets, the grain orientation degrees of the green compacts must be higher than a limited value of 15.0%. Barium hexa-ferrite quasi-single crystal with a high grain orientation degree of 98.6% was successfully fabricated after sintering the green compact with its grain orientation degree of 51.1%. - Highlights: • Aligned particles acted as “crystal seeds” for un-aligned ones' oriented growth. • Magnetic field of 4.647 kOe was needed to overcome crystallites' friction barrier. • GOD dramatically increased after sintering if starting GOD exceeded to 15.0%. • Quasi-single crystal was prepared by sintering green compact with GOD of 51.1%.

  8. Influence of time-periodic potentials on electronic transport in double-well structure

    International Nuclear Information System (INIS)

    Chun-Lei, Li; Yan, Xu

    2010-01-01

    Within the framework of the Floquet theorem, we have investigated single-electron photon-assisted tunneling in a double-well system using the transfer matrix technique. The transmission probability displays satellite peaks on both sides of the main resonance peaks and these satellite peaks originate from emission or absorption photons. The single-electron resonance tunneling can be controlled through changing the applied harmonically potential positions, such as driven potential in wells, in barriers, or in whole double-well systems. This advantage should be useful in the optimization of the parameters of a transmission device. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  9. Barrier inhomogeneities limited current and 1/f noise transport in GaN based nanoscale Schottky barrier diodes

    Science.gov (United States)

    Kumar, Ashutosh; Heilmann, M.; Latzel, Michael; Kapoor, Raman; Sharma, Intu; Göbelt, M.; Christiansen, Silke H.; Kumar, Vikram; Singh, Rajendra

    2016-01-01

    The electrical behaviour of Schottky barrier diodes realized on vertically standing individual GaN nanorods and array of nanorods is investigated. The Schottky diodes on individual nanorod show highest barrier height in comparison with large area diodes on nanorods array and epitaxial film which is in contrast with previously published work. The discrepancy between the electrical behaviour of nanoscale Schottky diodes and large area diodes is explained using cathodoluminescence measurements, surface potential analysis using Kelvin probe force microscopy and 1ow frequency noise measurements. The noise measurements on large area diodes on nanorods array and epitaxial film suggest the presence of barrier inhomogeneities at the metal/semiconductor interface which deviate the noise spectra from Lorentzian to 1/f type. These barrier inhomogeneities in large area diodes resulted in reduced barrier height whereas due to the limited role of barrier inhomogeneities in individual nanorod based Schottky diode, a higher barrier height is obtained. PMID:27282258

  10. Through-barrier electromagnetic imaging with an atomic magnetometer.

    Science.gov (United States)

    Deans, Cameron; Marmugi, Luca; Renzoni, Ferruccio

    2017-07-24

    We demonstrate the penetration of thick metallic and ferromagnetic barriers for imaging of conductive targets underneath. Our system is based on an 85 Rb radio-frequency atomic magnetometer operating in electromagnetic induction imaging modality in an unshielded environment. Detrimental effects, including unpredictable magnetic signatures from ferromagnetic screens and variations in the magnetic background, are automatically compensated by active compensation coils controlled by servo loops. We exploit the tunability and low-frequency sensitivity of the atomic magnetometer to directly image multiple conductive targets concealed by a 2.5 mm ferromagnetic steel shield and/or a 2.0 mm aluminium shield, in a single scan. The performance of the atomic magnetometer allows imaging without any prior knowledge of the barriers or the targets, and without the need of background subtraction. A dedicated edge detection algorithm allows automatic estimation of the targets' size within 3.3 mm and of their position within 2.4 mm. Our results prove the feasibility of a compact, sensitive and automated sensing platform for imaging of concealed objects in a range of applications, from security screening to search and rescue.

  11. Non-Potential Magnetic Fields and Magnetic Reconnection In Low Collisional Plasmas-Discovery of Solar EUV Mini-Sigmoids and Development of Novel In-Space Propulsion Systems

    Science.gov (United States)

    Chesny, David

    Magnetic reconnection is the source of many of the most powerful explosions of astrophysical plasmas in the universe. Blazars, magnetars, stellar atmospheres, and planetary magnetic fields have all been shown to be primary sites of strong reconnection events. For studying the fundamental physics behind this process, the solar atmosphere is our most accessible laboratory setting. Magnetic reconnection resulting from non-potential fields leads to plasma heating and particle acceleration, often in the form of explosive activity, contributing to coronal heating and the solar wind. Large-scale non-potential (sigmoid) fields in the solar atmosphere are poorly understood due to their crowded neighborhoods. For the first time, small-scale, non-potential loop structures have been observed in quiet Sun EUV observations. Fourteen unique mini-sigmoid events and three diffuse non-potential loops have been discovered, suggesting a multi-scaled self-similarity in the sigmoid formation process. These events are on the order of 10 arcseconds in length and do not appear in X-ray emissions, where large-scale sigmoids are well documented. We have discovered the first evidence of sigmoidal structuring in EUV bright point phenomena, which are prolific events in the solar atmosphere. Observations of these mini-sigmoids suggest that they are being formed via tether-cutting reconnection, a process observed to occur at active region scales. Thus, tether-cutting is suggested to be ubiquitous throughout the solar atmosphere. These dynamics are shown to be a function of the free magnetic energy in the quiet Sun network. Recently, the reconnection process has been reproduced in Earth-based laboratory tokamaks. Easily achievable magnetic field configurations can induce reconnection and result in ion acceleration. Here, magnetic reconnection is utilized as the plasma acceleration mechanism for a theoretical propulsion system. The theory of torsional spine reconnection is shown to result in ion

  12. Design of tandem mirror reactors with thermal barriers

    International Nuclear Information System (INIS)

    Carlson, G.A.

    1980-01-01

    End-plug technologies for tandem mirror reactors include high-field superconducting magnets, neutral beam injectors, and gyrotrons for electron cyclotron resonant heating (ECRH). In addition to their normal use for sustenance of the end-plug plasmas, neutral beam injectors are used for ''pumping'' trapped ions from the thermal barrier regions by charge exchange. An extra function of the axially directed pump beams is the removal of thermalized alpha particles from the reactor. The principles of tandem mirror operation with thermal barriers will be demonstrated in the upgrade of the Tandem Mirror Experiment (TMX-U) in 1981 and the tandem configuration of the Mirror fusion Test Facility (MFTF-B) in 1984

  13. Barriers to healthcare for transgender individuals.

    Science.gov (United States)

    Safer, Joshua D; Coleman, Eli; Feldman, Jamie; Garofalo, Robert; Hembree, Wylie; Radix, Asa; Sevelius, Jae

    2016-04-01

    Transgender persons suffer significant health disparities and may require medical intervention as part of their care. The purpose of this manuscript is to briefly review the literature characterizing barriers to healthcare for transgender individuals and to propose research priorities to understand mechanisms of those barriers and interventions to overcome them. Current research emphasizes sexual minorities' self-report of barriers, rather than using direct methods. The biggest barrier to healthcare reported by transgender individuals is lack of access because of lack of providers who are sufficiently knowledgeable on the topic. Other barriers include: financial barriers, discrimination, lack of cultural competence by providers, health systems barriers, and socioeconomic barriers. National research priorities should include rigorous determination of the capacity of the US healthcare system to provide adequate care for transgender individuals. Studies should determine knowledge and biases of the medical workforce across the spectrum of medical training with regard to transgender medical care; adequacy of sufficient providers for the care required, larger social structural barriers, and status of a framework to pay for appropriate care. As well, studies should propose and validate potential solutions to address identified gaps.

  14. Adding remnant magnetization and anisotropic exchange to propeller-like single-molecule magnets through chemical design.

    Science.gov (United States)

    Westrup, Kátia Cristina M; Boulon, Marie-Emmanuelle; Totaro, Pasquale; Nunes, Giovana G; Back, Davi F; Barison, Andersson; Jackson, Martin; Paulsen, Carley; Gatteschi, Dante; Sorace, Lorenzo; Cornia, Andrea; Soares, Jaísa F; Sessoli, Roberta

    2014-10-13

    The selective replacement of the central iron(III) ion with vanadium(III) in a tetrairon(III) propeller-shaped single-molecule magnet has allowed us to increase the ground spin state from S=5 to S=13/2. As a consequence of the pronounced anisotropy of vanadium(III), the blocking temperature for the magnetization has doubled. Moreover, a significant remnant magnetization, practically absent in the parent homometallic molecule, has been achieved owing to the suppression of zero-field tunneling of the magnetization for the half-integer molecular spin. Interestingly, the contribution of vanadium(III) to the magnetic anisotropy barrier occurs through the anisotropic exchange interaction with iron(III) spins and not through single ion anisotropy as in most single-molecule magnets. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Demand-side mitigation options of the agricultural sector: potential, barriers and ways forward

    Directory of Open Access Journals (Sweden)

    Brunelle Thierry

    2017-01-01

    Full Text Available This paper reviews the potential and barriers of demand-side mitigation options in the agricultural sector based on the recent academic literature and on a survey conducted on a sample of 788 respondents living in France. The mitigation potential of such measures as reducing losses in the food supply chain and shifting diets toward less animal products is estimated to be particularly high, higher, in particular, than supply-side mitigation options. However, to ensure that these measures do not entail a reduction in protein intake, these estimations should consider both caloric and protein units, and take into account the digestibility differentials between protein sources. Our survey shows that people are relatively reluctant to eat more sustainably, preferring to reduce their emissions in other areas such as housing or equipment. This relative reluctance is mainly due to individual perceptions linked to health concerns, taste or habits. Some obstacles could easily be overcome through well-designed policies aiming to, for example, advertise a lower consumption of red meat for health benefits. National governments are, however, rather inactive on this topic, leaving the initiative to the civil society.

  16. The blood-tendon barrier: identification and characterisation of a novel tissue barrier in tendon blood vessels

    Directory of Open Access Journals (Sweden)

    C Lehner

    2016-05-01

    Full Text Available Tissue barriers function as “gate keepers” between different compartments (usually blood and tissue and are formed by specialised membrane-associated proteins, localising to the apicolateral plasma membrane domain of epithelial and endothelial cells. By sealing the paracellular space, the free diffusion of solutes and molecules across epithelia and endothelia is impeded. Thereby, tissue barriers contribute to the establishment and maintenance of a distinct internal and external environment, which is crucial during organ development and allows maintenance of an organ-specific homeostatic milieu. So far, various epithelial and endothelial tissue barriers have been described, including the blood-brain barrier, the blood-retina barrier, the blood-testis barrier, the blood-placenta barrier, and the cerebrospinal fluid (CSF-brain barrier, which are vital for physiological function and any disturbance of these barriers can result in severe organ damage or even death. Here, we describe the identification of a novel barrier, located in the vascular bed of tendons, which we term the blood-tendon barrier (BTB. By using immunohistochemistry, transmission electron microscopy, and tracer studies we demonstrate the presence of a functional endothelial barrier within tendons restricting the passage of large blood-borne molecules into the surrounding tendon tissue. We further provide in vitro evidence that the BTB potentially contributes to the creation of a distinct internal tissue environment impacting upon the proliferation and differentiation of tendon-resident cells, effects which might be fundamental for the onset of tendon pathologies.

  17. Piezotronically modified double Schottky barriers in ZnO varistors.

    Science.gov (United States)

    Raidl, Nadine; Supancic, Peter; Danzer, Robert; Hofstätter, Michael

    2015-03-25

    Double Schottky barriers in ZnO are modified piezotronically by the application of mechanical stresses. New effects such as the enhancement of the potential barrier height and the increase or decrease of the natural barrier asymmetry are presented. Also, an extended model for the piezotronic modification of double Schottky barriers is given. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Influence of Pt thickness on magnetization reversal processes in (Pt/Co)3 multilayers with perpendicular anisotropy

    International Nuclear Information System (INIS)

    Belhi, R.; Adanlété Adjanoh, A.; Vogel, J.

    2012-01-01

    We present a detailed study of the magnetization reversal in perpendicularly magnetized (Pt/Co) 3 multilayers with different values of the platinum interlayer thickness t Pt . To study the magnetization reversal in our samples we combined measurements of relaxation curves with the direct visualization of domain structures. Magnetization reversal was dominated by domain wall propagation for t Pt =1 nm and by domain nucleation for t Pt =0.2 nm, while a mixed process was observed for t Pt =0.8 nm. We interpret our results within the framework of a model of thermally activated reversal where a distribution of activation energy barriers is taken into account. The reversal process was correlated with the energy barrier distribution. - Highlights: ► We show that the coercivity decreases with the Pt interlayer thickness. ► The reversal process is sensitively dependent on platinum interlayer thickness. ► We interpreted the results by taking into account of an energy barrier distribution. ► The reversal process was correlated with the energy barrier distribution width. ► The energy barrier distribution width varies linearly with the applied field.

  19. Influence of Guest Exchange on the Magnetization Dynamics of Dilanthanide Single-Molecule-Magnet Nodes within a Metal-Organic Framework.

    Science.gov (United States)

    Zhang, Xuejing; Vieru, Veacheslav; Feng, Xiaowen; Liu, Jun-Liang; Zhang, Zhenjie; Na, Bo; Shi, Wei; Wang, Bing-Wu; Powell, Annie K; Chibotaru, Liviu F; Gao, Song; Cheng, Peng; Long, Jeffrey R

    2015-08-17

    Multitopic organic linkers can provide a means to organize metal cluster nodes in a regular three-dimensional array. Herein, we show that isonicotinic acid N-oxide (HINO) serves as the linker in the formation of a metal-organic framework featuring Dy2 single-molecule magnets as nodes. Importantly, guest solvent exchange induces a reversible single-crystal to single-crystal transformation between the phases Dy2(INO)4(NO3)2⋅2 solvent (solvent=DMF (Dy2-DMF), CH3CN (Dy2-CH3CN)), thereby switching the effective magnetic relaxation barrier (determined by ac magnetic susceptibility measurements) between a negligible value for Dy2-DMF and 76 cm(-1) for Dy2-CH3CN. Ab initio calculations indicate that this difference arises not from a significant change in the intrinsic relaxation barrier of the Dy2 nodes, but rather from a slowing of the relaxation rate of incoherent quantum tunneling of the magnetization by two orders of magnitude. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Collisional effects on interaction potential in complex plasma in presence of magnetic field

    International Nuclear Information System (INIS)

    Bezbaruah, Pratikshya; Das, Nilakshi

    2016-01-01

    Interaction potential in complex plasma with streaming ions is derived analytically in presence of ion-neutral collision and magnetic field. The linear dielectric response function obtained describes the behavior of charged micron sized dust particles in strong collisional limit. A new type of repulsive potential is found to be operative among the dust grains apart from the normal Debye–Hückel potential. The amplitude and shielding length involved in the potential are substantially affected by the parameters describing ion cyclotron frequency, collision frequency among ions and neutrals, and ion streaming. It is also observed that the usual mechanism of ion focusing surrounding the grain is inhibited due to collision. As a result, the attractive wake potential structure is destroyed in the ion flow direction. The horizontal interaction involves only Debye–Hückel potential.

  1. Collisional effects on interaction potential in complex plasma in presence of magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Bezbaruah, Pratikshya, E-mail: pratphd@tezu.ernet.in; Das, Nilakshi [Department of Physics, Tezpur University, Tezpur, Assam 784028 (India)

    2016-04-15

    Interaction potential in complex plasma with streaming ions is derived analytically in presence of ion-neutral collision and magnetic field. The linear dielectric response function obtained describes the behavior of charged micron sized dust particles in strong collisional limit. A new type of repulsive potential is found to be operative among the dust grains apart from the normal Debye–Hückel potential. The amplitude and shielding length involved in the potential are substantially affected by the parameters describing ion cyclotron frequency, collision frequency among ions and neutrals, and ion streaming. It is also observed that the usual mechanism of ion focusing surrounding the grain is inhibited due to collision. As a result, the attractive wake potential structure is destroyed in the ion flow direction. The horizontal interaction involves only Debye–Hückel potential.

  2. Spin-Polarization in Quasi-Magnetic Tunnel Junctions

    Science.gov (United States)

    Xie, Zheng-Wei; Li, Ling

    2017-05-01

    Spin polarization in ferromagnetic metal/insulator/spin-filter barrier/nonmagnetic metal, referred to as quasi-magnetic tunnel junctions, is studied within the free-electron model. Our results show that large positive or negative spin-polarization can be obtained at high bias in quasi-magnetic tunnel junctions, and within large bias variation regions, the degree of spin-polarization can be linearly tuned by bias. These linear variation regions of spin-polarization with bias are influenced by the barrier thicknesses, barrier heights and molecular fields in the spin-filter (SF) layer. Among them, the variations of thickness and heights of the insulating and SF barrier layers have influence on the value of spin-polarization and the linear variation regions of spin-polarization with bias. However, the variations of molecular field in the SF layer only have influence on the values of the spin-polarization and the influences on the linear variation regions of spin-polarization with bias are slight. Supported by the Key Natural Science Fund of Sichuan Province Education Department under Grant Nos 13ZA0149 and 16ZA0047, and the Construction Plan for Scientific Research Innovation Team of Universities in Sichuan Province under Grant No 12TD008.

  3. [The potential of general magnetic therapy for the treatment and rehabilitation (a review)].

    Science.gov (United States)

    Kulikov, A G; Voronina, D D

    2016-01-01

    This paper was designed to describe the main characteristics of general magnetic therapy and the mechanisms underlying its biological and therapeutic action. Special attention is given to the extensive application of this method in the routine clinical practice. The publications in the current scientific literature are reviewed in order to evaluate the potential of general magnetic therapy as a component of the combined treatment of various somatic pathologies, rehabilitation of the patients after surgical intervention with special reference to the management of the patients presenting with the oncological problems. The data suggesting good tolerability and high therapeutic effectiveness of the physiotherapeutic method under consideration.

  4. Pressure effects on single chain magnets

    Energy Technology Data Exchange (ETDEWEB)

    Mito, M. E-mail: mitoh@elcs.kyutech.ac.jp; Shindo, N.; Tajiri, T.; Deguchi, H.; Takagi, S.; Miyasaka, H.; Yamashita, M.; Clerac, R.; Coulon, C

    2004-05-01

    Pressure effects on a single chain magnet [Mn{sub 2}(saltmen){sub 2}Ni(pao){sub 2}(py){sub 2}](ClO{sub 4}){sub 2} (saltmen{sup 2-}=N,N'-(1,1,2,2-tetramethylethylene)bis(salicylideneiminate), and pao{sup -}=pyridine-2-aldoximate) have been investigated through AC magnetic measurements under pressure (P). The slow relaxation of the magnetization depends on pressure. Both the blocking temperature (T{sub B}) and energy barrier ({delta}) increase by pressurization, and those enhancements saturate at around P=7 kbar.

  5. Elucidating the Function of Penetratin and a Static Magnetic Field in Cellular Uptake of Magnetic Nanoparticles

    Directory of Open Access Journals (Sweden)

    David Stirling

    2013-02-01

    Full Text Available Nanotechnology plays an increasingly important role in the biomedical arena. In particular, magnetic nanoparticles (mNPs have become important tools in molecular diagnostics, in vivo imaging and improved treatment of disease, with the ultimate aim of producing a more theranostic approach. Due to their small sizes, the nanoparticles can cross most of the biological barriers such as the blood vessels and the blood brain barrier, thus providing ubiquitous access to most tissues. In all biomedical applications maximum nanoparticle uptake into cells is required. Two promising methods employed to this end include functionalization of mNPs with cell-penetrating peptides to promote efficient translocation of cargo into the cell and the use of external magnetic fields for enhanced delivery. This study aimed to compare the effect of both penetratin and a static magnetic field with regards to the cellular uptake of 200 nm magnetic NPs and determine the route of uptake by both methods. Results demonstrated that both techniques increased particle uptake, with penetratin proving more cell specific. Clathrin- medicated endocytosis appeared to be responsible for uptake as shown via PCR and western blot, with Pitstop 2 (known to selectively block clathrin formation blocking particle uptake. Interestingly, it was further shown that a magnetic field was able to reverse or overcome the blocking, suggesting an alternative route of uptake.

  6. Integrated control of the wastewater system – potentials and barriers

    DEFF Research Database (Denmark)

    Mollerup, Ane Loft; Grum, Morten; Muschalla, Dirk

    2013-01-01

    Applying integrated control to a sewer system and wastewater treatment plant often leads to additional benefits for both systems when compared to controlling them independently. However, barriers such as a lack of incentive for utilities to put this type of control in place mean that in practice...

  7. Observation of spin superfluidity: YIG magnetic films and beyond

    Science.gov (United States)

    Sonin, Edouard

    2018-03-01

    From topology of the order parameter of the magnon condensate observed in yttrium-iron-garnet (YIG) magnetic films one must not expect energetic barriers making spin supercurrents metastable. But we show that some barriers of dynamical origin are possible nevertheless until the gradient of the phase (angle of spin precession) does not exceed the critical value (analog of the Landau critical velocity in superfluids). On the other hand, recently published claims of experimental detection of spin superfluidity in YIG films and antiferromagnets are not justified, and spin superfluidity in magnetically ordered solids has not yet been experimentally confirmed.

  8. Projecting the range of potential future climate change as an aid in the assessment of the effectiveness of the Hanford Site Permanent Isolation Barrier

    Energy Technology Data Exchange (ETDEWEB)

    Petersen, K.L.

    1993-10-01

    The Hanford Site Permanent Isolation Barrier Development Program was organized to develop an in-place disposal capability for low-level nuclear waste for the US Department of Energy at the Hanford Site in south-eastern Washington. Layered earthen and engineered barriers are being developed by Westinghouse Hanford Company and the Pacific Northwest Laboratory that will function in what is presently a semiarid environment (annual precipitation 150 mm) for at least 1,000 yr by limiting the infiltration of water through the waste. The Long-Term Climate Change Task is one of several key barrier tasks. Based on the recommendation of a panel of internationally recognized climate and modeling experts, climatic data for this task is being acquired in a step-wise and multi-disciplinary manner. The specific research strategy includes literature review and specialized studies to obtain pollen-derived climatic reconstruction, documented historic weather patterns, and Global Circulation Model output of potential future climate changes related to both the greenhouse effect and the cycling into the next ice age. The specific goals of the task are to: (1) obtain defensible probabilistic projections of the long-term climate variability in the Hanford Site region at many different time scales into the future, (2) develop several test case climate scenarios that bracket the range of potential future climate, and (3) use the climate scenarios both to test and to model protective barrier performance.

  9. Transverse magnetic field effects on the relaxation time of the magnetization in Mn12 measured by 55Mn-NMR

    International Nuclear Information System (INIS)

    Furukawa, Y.; Watanabe, K.; Kumagai, K.; Borsa, F.; Gatteschi, D.

    2003-01-01

    The longitudinal (H Z ) and transverse (H T ) magnetic field dependence of the relaxation time of the magnetization in Mn12 in its S=10 ground state was measured by NMR. The minima in the relaxation time at the fields for level crossing are due to the quantum tunneling of the magnetization. The shortening of the relaxation time under the application of H T is shown to be due mainly to the reduction of the energy barrier

  10. Dependences of the Tunnel Magnetoresistance and Spin Transfer Torque on the Sizes and Concentration of Nanoparticles in Magnetic Tunnel Junctions

    Science.gov (United States)

    Esmaeili, A. M.; Useinov, A. N.; Useinov, N. Kh.

    2018-01-01

    Dependences of the tunnel magnetoresistance and in-plane component of the spin transfer torque on the applied voltage in a magnetic tunnel junction have been calculated in the approximation of ballistic transport of conduction electrons through an insulating layer with embedded magnetic or nonmagnetic nanoparticles. A single-barrier magnetic tunnel junction with a nanoparticle embedded in an insulator forms a double-barrier magnetic tunnel junction. It has been shown that the in-plane component of the spin transfer torque in the double-barrier magnetic tunnel junction can be higher than that in the single-barrier one at the same thickness of the insulating layer. The calculations show that nanoparticles embedded in the tunnel junction increase the probability of tunneling of electrons, create resonance conditions, and ensure the quantization of the conductance in contrast to the tunnel junction without nanoparticles. The calculated dependences of the tunnel magnetoresistance correspond to experimental data demonstrating peak anomalies and suppression of the maximum magnetoresistances at low voltages.

  11. Barriers to medication error reporting among hospital nurses.

    Science.gov (United States)

    Rutledge, Dana N; Retrosi, Tina; Ostrowski, Gary

    2018-03-01

    The study purpose was to report medication error reporting barriers among hospital nurses, and to determine validity and reliability of an existing medication error reporting barriers questionnaire. Hospital medication errors typically occur between ordering of a medication to its receipt by the patient with subsequent staff monitoring. To decrease medication errors, factors surrounding medication errors must be understood; this requires reporting by employees. Under-reporting can compromise patient safety by disabling improvement efforts. This 2017 descriptive study was part of a larger workforce engagement study at a faith-based Magnet ® -accredited community hospital in California (United States). Registered nurses (~1,000) were invited to participate in the online survey via email. Reported here are sample demographics (n = 357) and responses to the 20-item medication error reporting barriers questionnaire. Using factor analysis, four factors that accounted for 67.5% of the variance were extracted. These factors (subscales) were labelled Fear, Cultural Barriers, Lack of Knowledge/Feedback and Practical/Utility Barriers; each demonstrated excellent internal consistency. The medication error reporting barriers questionnaire, originally developed in long-term care, demonstrated good validity and excellent reliability among hospital nurses. Substantial proportions of American hospital nurses (11%-48%) considered specific factors as likely reporting barriers. Average scores on most barrier items were categorised "somewhat unlikely." The highest six included two barriers concerning the time-consuming nature of medication error reporting and four related to nurses' fear of repercussions. Hospitals need to determine the presence of perceived barriers among nurses using questionnaires such as the medication error reporting barriers and work to encourage better reporting. Barriers to medication error reporting make it less likely that nurses will report medication

  12. Magnetic-Field-Tunable Superconducting Rectifier

    Science.gov (United States)

    Sadleir, John E.

    2009-01-01

    Superconducting electronic components have been developed that provide current rectification that is tunable by design and with an externally applied magnetic field to the circuit component. The superconducting material used in the device is relatively free of pinning sites with its critical current determined by a geometric energy barrier to vortex entry. The ability of the vortices to move freely inside the device means this innovation does not suffer from magnetic hysteresis effects changing the state of the superconductor. The invention requires a superconductor geometry with opposite edges along the direction of current flow. In order for the critical current asymmetry effect to occur, the device must have different vortex nucleation conditions at opposite edges. Alternative embodiments producing the necessary conditions include edges being held at different temperatures, at different local magnetic fields, with different current-injection geometries, and structural differences between opposite edges causing changes in the size of the geometric energy barrier. An edge fabricated with indentations of the order of the coherence length will significantly lower the geometric energy barrier to vortex entry, meaning vortex passage across the device at lower currents causing resistive dissipation. The existing prototype is a two-terminal device consisting of a thin-film su - perconducting strip operating at a temperature below its superconducting transition temperature (Tc). Opposite ends of the strip are connected to electrical leads made of a higher Tc superconductor. The thin-film lithographic process provides an easy means to alter edge-structures, current-injection geo - metries, and magnetic-field conditions at the edges. The edge-field conditions can be altered by using local field(s) generated from dedicated higher Tc leads or even using the device s own higher Tc superconducting leads.

  13. Exact diagonalization of cubic lattice models in commensurate Abelian magnetic fluxes and translational invariant non-Abelian potentials

    DEFF Research Database (Denmark)

    Burrello, M.; Fulga, Ion Cosma; Lepori, L.

    2017-01-01

    of a translational invariant non-Abelian coupling for multi-component spinors does not affect the dimension of the minimal Hamiltonian blocks, nor the dimension of the magnetic Brillouin zone. General formulas are presented for the U(2) case and explicit examples are investigated involving π and 2π/3 magnetic fluxes......We present a general analytical formalism to determine the energy spectrum of a quantum particle in a cubic lattice subject to translationally invariant commensurate magnetic fluxes and in the presence of a general spaceindependent non-Abelian gauge potential. We first review and analyze the case...... of purely Abelian potentials, showing also that the so-called Hasegawa gauge yields a decomposition of the Hamiltonian into sub-matrices having minimal dimension. Explicit expressions for such matrices are derived, also for general anisotropic fluxes. Later on, we show that the introduction...

  14. Metal-oxo containing polymer nanobeads as potential contrast agents for magnetic resonance imaging

    Science.gov (United States)

    Pablico, Michele Huelar

    Magnetic resonance imaging (MRI) has greatly revolutionized the way diseases are detected and treated, as it is a non-invasive imaging modality solely based on the interaction of radiowaves and hydrogen nuclei in the presence of an external magnetic field. It is widely used today for the diagnosis of diseases as it offers an efficient method of mapping structure and function of soft tissues in the body. Most MRI examinations utilize paramagnetic materials known as contrast agents, which enhance the MR signal by decreasing the longitudinal (T1) and transverse (T2) relaxation times of the surrounding water protons in biological systems. This results into increased signal intensity differences thereby allowing better interpretation and analysis of pathological tissues. Contrast agents function by lowering the T1 or lowering the T2, resulting into bright and dark contrasts, respectively. The most common MRI contrast agents that are in clinical use today are gadolinium chelates and superparamagnetic iron oxide nanoparticles, both of which have their own advantages in terms of contrast enhancement properties. In the past few years, however, there has been interest in utilizing metal-containing clusters for MRI contrast enhancement as these materials bridge the gap between the constrained structure and magnetic properties of the gadolinium chelates with the superparamagnetic behavior of the iron oxide nanoparticles. Recently, metallic clusters containing Mn and Fe metal centers have received increased attention mainly because of their potential for high spin states and benign nature. In the quest to further develop novel imaging agents, this research has focused on investigating the use of metal-oxo clusters as potential contrast agents for MRI. The primary goal of this project is to identify clusters that meet the following criteria: high paramagnetic susceptibility, water-soluble, stable, cheap, contain environmentally benign metals, and easily derivatized. This work is

  15. The interaction of a flowing plasma with a dipole magnetic field: measurements and modelling of a diamagnetic cavity relevant to spacecraft protection

    International Nuclear Information System (INIS)

    Bamford, R; Bradford, J; Bingham, R; Gargate, L; Hapgood, M; Stamper, R; Gibson, K J; Thornton, A J; Silva, L O; Fonseca, R A; Norberg, C; Todd, T

    2008-01-01

    Here we describe a new experiment to test the shielding concept of a dipole-like magnetic field and plasma, surrounding a spacecraft forming a 'mini magnetosphere'. Initial laboratory experiments have been conducted to determine the effectiveness of a magnetized plasma barrier to be able to expel an impacting, low beta, supersonic flowing energetic plasma representing the solar wind. Optical and Langmuir probe data of the plasma density, the plasma flow velocity and the intensity of the dipole field clearly show the creation of a narrow transport barrier region and diamagnetic cavity virtually devoid of energetic plasma particles. This demonstrates the potential viability of being able to create a small 'hole' in a solar wind plasma, of the order of the ion Larmor orbit width, in which an inhabited spacecraft could reside in relative safety. The experimental results have been quantitatively compared with a 3D particle-in-cell 'hybrid' code simulation that uses kinetic ions and fluid electrons, showing good qualitative agreement and excellent quantitative agreement. Together the results demonstrate the pivotal role of particle kinetics in determining generic plasma transport barriers.

  16. Ferumoxytol-enhanced magnetic resonance angiography for the assessment of potential kidney transplant recipients

    Energy Technology Data Exchange (ETDEWEB)

    Stoumpos, Sokratis; Mark, Patrick B. [Queen Elizabeth University Hospital, Renal and Transplant Unit, Glasgow (United Kingdom); University of Glasgow, Institute of Cardiovascular and Medical Sciences, BHF Glasgow Cardiovascular Research Centre, Glasgow (United Kingdom); Hennessy, Martin; Kasthuri, Ram; Roditi, Giles [Queen Elizabeth University Hospital, Department of Radiology, Glasgow (United Kingdom); Vesey, Alex T.; Kingsmore, David B. [Queen Elizabeth University Hospital, Renal and Transplant Unit, Glasgow (United Kingdom); Radjenovic, Aleksandra [University of Glasgow, Institute of Cardiovascular and Medical Sciences, BHF Glasgow Cardiovascular Research Centre, Glasgow (United Kingdom)

    2018-01-15

    Traditional contrast-enhanced methods for scanning blood vessels using magnetic resonance imaging (MRI) or CT carry potential risks for patients with advanced kidney disease. Ferumoxytol is a superparamagnetic iron oxide nanoparticle preparation that has potential as an MRI contrast agent in assessing the vasculature. Twenty patients with advanced kidney disease requiring aorto-iliac vascular imaging as part of pre-operative kidney transplant candidacy assessment underwent ferumoxytol-enhanced magnetic resonance angiography (FeMRA) between December 2015 and August 2016. All scans were performed for clinical indications where standard imaging techniques were deemed potentially harmful or inconclusive. Image quality was evaluated for both arterial and venous compartments. First-pass and steady-state FeMRA using incremental doses of up to 4 mg/kg body weight of ferumoxytol as intravenous contrast agent for vascular enhancement was performed. Good arterial and venous enhancements were achieved, and FeMRA was not limited by calcification in assessing the arterial lumen. The scans were diagnostic and all patients completed their studies without adverse events. Our preliminary experience supports the feasibility and utility of FeMRA for vascular imaging in patients with advanced kidney disease due for transplant listing, which has the advantages of obtaining both arteriography and venography using a single test without nephrotoxicity. (orig.)

  17. [Implementing daily physical education in primary school - potentials and barriers from the involved actor's point of view].

    Science.gov (United States)

    Sterdt, E; Liersch, S; Henze, V; Röbl, M; Suermann, T; Krauth, C; Walter, U

    2015-04-01

    The objective was to determine to what extent daily physical education can be implemented in primary schools, what barriers exist and how to overcome the mentioned barriers. Moreover, it was analysed to what extent daily physical education is accepted by teachers, external trainers, parents and students. Semi-structured interviews with parents (n=7), teachers (n=5) and external trainers (n=6) of the intervention schools. The intervention students (n=44) were surveyed within focus groups. All surveyed groups appraised the implementation of daily school sports as successful. The cooperation between the schools and the sports club should be maintained during a comprehensive implementation of daily physical education. Besides an improved lessons quality teachers and external trainers reported an improved social behaviour of the children. Parents perceived positive effects on the child development. All groups believe that daily physical education increases the enjoyment of children in sports. As a certain barrier a lack of resources (e. g., facilities, equipment, financial resources) in the schools were mentioned. The cooperation between the schools and the sports club proved to be an applicable model to implement daily physical education. The combination of teachers and external trainers can contribute to a higher lesson quality. Considering the perceived potentials of daily physical education by all surveyed groups, a comprehensive implementation of systematic daily physical activity promotion in the primary school setting should be tapped more strongly in future. © Georg Thieme Verlag KG Stuttgart · New York.

  18. Advanced house air-barrier systems

    Energy Technology Data Exchange (ETDEWEB)

    Lee, R.K. [Natural Resources Canada, Ottawa, ON (Canada)

    1996-08-01

    Air barrier systems used in modern Canadian airtight homes were discussed. The Advanced Houses Program sets its airtightness requirements at 1.5 air changes per hour at 50 Pascals pressure difference (ACH{sub 5}0). In recent tests of 10 houses, it was suggested that a better airtightness level was attainable with average airtightness of about 1.0 ACH{sub 5}0. Six of the homes tested did not use the traditional polyethylene approach. Two of the houses used the airtight drywall approach, one used a foam system, and three used exterior air barriers. The advantages and disadvantages of each system was described, including cost effectiveness, cost reduction, performance and installation advantages. The confusion between an air barrier and a vapour diffusion retarder was explained. Exterior air barriers showed the greatest potential for meeting airtightness requirements at reasonable cost. 5 refs., 3 tabs.

  19. Multiple-decker phthalocyaninato dinuclear lanthanoid(III) single-molecule magnets with dual-magnetic relaxation processes.

    Science.gov (United States)

    Katoh, Keiichi; Horii, Yoji; Yasuda, Nobuhiro; Wernsdorfer, Wolfgang; Toriumi, Koshiro; Breedlove, Brian K; Yamashita, Masahiro

    2012-11-28

    The SMM behaviour of dinuclear Ln(III)-Pc multiple-decker complexes (Ln = Tb(3+) and Dy(3+)) with energy barriers and slow-relaxation behaviour were explained by using X-ray crystallography and static and dynamic susceptibility measurements. In particular, interactions among the 4f electrons of several dinuclear Ln(III)-Pc type SMMs have never been discussed on the basis of the crystal structure. For dinuclear Tb(III)-Pc complexes, a dual magnetic relaxation process was observed. The relaxation processes are due to the anisotropic centres. Our results clearly show that the two Tb(3+) ion sites are equivalent and are consistent with the crystal structure. On the other hand, the mononuclear Tb(III)-Pc complex exhibited only a single magnetic relaxation process. This is clear evidence that the magnetic relaxation mechanism depends heavily on the dipole-dipole (f-f) interactions between the Tb(3+) ions in the dinuclear systems. Furthermore, the SMM behaviour of dinuclear Dy(III)-Pc type SMMs with smaller energy barriers compared with that of Tb(III)-Pc and slow-relaxation behaviour was explained. Dinuclear Dy(III)-Pc SMMs exhibited single-component magnetic relaxation behaviour. The results indicate that the magnetic relaxation properties of dinuclear Ln(III)-Pc multiple-decker complexes are affected by the local molecular symmetry and are extremely sensitive to tiny distortions in the coordination geometry. In other words, the spatial arrangement of the Ln(3+) ions (f-f interactions) in the crystal is important. Our work shows that the SMM properties can be fine-tuned by introducing weak intermolecular magnetic interactions in a controlled SMM spatial arrangement.

  20. Barriers to Seizure Management in Schools: Perceptions of School Nurses.

    Science.gov (United States)

    Terry, Debbie; Patel, Anup D; Cohen, Daniel M; Scherzer, Daniel; Kline, Jennifer

    2016-12-01

    The purpose of this study was to assess school nurses' perceptions of barriers to optimal management of seizures in schools. Eighty-three school nurses completed an electronic survey. Most agreed they felt confident they could identify a seizure (97.6%), give rectal diazepam (83.8%), and handle cluster seizures (67.1%), but fewer were confident they could give intranasal midazolam (63.3%), had specific information about a student's seizures (56.6%), or could swipe a vagus nerve stimulator magnet (47.4%). Nurses were more likely to be available at the time of a seizure in rural (17/20) (85%) versus suburban (21/34) (62%) or urban (8/25) (32%) schools (P = .001). School nurses are comfortable managing seizures in the school setting. However, a specific seizure plan for each child and education on intranasal midazolam and vagus nerve stimulator magnet use are needed. A barrier in urban schools is decreased availability of a nurse to identify seizures and administer treatment. © The Author(s) 2016.