WorldWideScience

Sample records for polar cap magnetic

  1. An Index (PC) Aimed at Monitoring the (P)olar (C)ap for Magnetic Activity

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — PC is an index for magnetic activity in the (P)olar (C)ap. It is based on data from a single nearpole station, and aimed to monitor the polar cap magnetic activity...

  2. Central polar cap convection response to short duration southward Interplanetary Magnetic Field

    Directory of Open Access Journals (Sweden)

    P. T. Jayachandran

    2000-08-01

    Full Text Available Central polar cap convection changes associated with southward turnings of the Interplanetary Magnetic Field (IMF are studied using a chain of Canadian Advanced Digital Ionosondes (CADI in the northern polar cap. A study of 32 short duration (~1 h southward IMF transition events found a three stage response: (1 initial response to a southward transition is near simultaneous for the entire polar cap; (2 the peak of the convection speed (attributed to the maximum merging electric field propagates poleward from the ionospheric footprint of the merging region; and (3 if the change in IMF is rapid enough, then a step in convection appears to start at the cusp and then propagates antisunward over the polar cap with the velocity of the maximum convection. On the nightside, a substorm onset is observed at about the time when the step increase in convection (associated with the rapid transition of IMF arrives at the polar cap boundary.Key words: Ionosphere (plasma convection; polar ionosphere - Magnetospheric physics (solar wind - magnetosphere interaction

  3. Central polar cap convection response to short duration southward Interplanetary Magnetic Field

    Directory of Open Access Journals (Sweden)

    P. T. Jayachandran

    Full Text Available Central polar cap convection changes associated with southward turnings of the Interplanetary Magnetic Field (IMF are studied using a chain of Canadian Advanced Digital Ionosondes (CADI in the northern polar cap. A study of 32 short duration (~1 h southward IMF transition events found a three stage response: (1 initial response to a southward transition is near simultaneous for the entire polar cap; (2 the peak of the convection speed (attributed to the maximum merging electric field propagates poleward from the ionospheric footprint of the merging region; and (3 if the change in IMF is rapid enough, then a step in convection appears to start at the cusp and then propagates antisunward over the polar cap with the velocity of the maximum convection. On the nightside, a substorm onset is observed at about the time when the step increase in convection (associated with the rapid transition of IMF arrives at the polar cap boundary.

    Key words: Ionosphere (plasma convection; polar ionosphere - Magnetospheric physics (solar wind - magnetosphere interaction

  4. Polar cap patches observed during the magnetic storm of November 2003: observations and modeling

    Directory of Open Access Journals (Sweden)

    C. E. Valladares

    2015-09-01

    Full Text Available We present multi-instrumented measurements and multi-technique analysis of polar cap patches observed early during the recovery phase of the major magnetic storm of 20 November 2003 to investigate the origin of the polar cap patches. During this event, the Qaanaaq imager observed elongated polar cap patches, some of which containing variable brightness; the Qaanaaq digisonde detected abrupt NmF2 fluctuations; the Sondrestrom incoherent scatter radar (ISR measured patches placed close to but poleward of the auroral oval–polar cap boundary; and the DMSP-F13 satellite intersected topside density enhancements, corroborating the presence of the patches seen by the imager, the digisonde, and the Sondrestrom ISR. A 2-D cross-correlation analysis was applied to series of two consecutive red-line images, indicating that the magnitude and direction of the patch velocities were in good agreement with the SuperDARN convection patterns. We applied a back-tracing analysis to the patch locations and found that most of the patches seen between 20:41 and 21:29 UT were likely transiting the throat region near 19:41 UT. Inspection of the SuperDARN velocities at this time indicates spatial and temporal collocation of a gap region between patches and large (1.7 km s−1 line-of-sight velocities. The variable airglow brightness of the patches observed between 20:33 and 20:43 UT was investigated using the numerical Global Theoretical Ionospheric Model (GTIM driven by the SuperDARN convection patterns and a variable upward/downward neutral wind. Our numerical results indicate that variations in the airglow intensity up to 265 R can be produced by a constant 70 m s−1 downward vertical wind.

  5. On a distribution of electric fields caused by the northern component of the interplanetary magnetic field in the absence of longitudinal currents in the winter polar cap

    International Nuclear Information System (INIS)

    Uvarov, V.M.

    1984-01-01

    Data on the distribution of electric fields, conditioned by the northern component of the interplanetary magnetic field Bsub(z), have been discussed. The problem of electric field excitation is reduced to the solution of equations of continuity for the current in three regions: northern and southern polar caps and region beyond the caps. At the values Bsub(z)>0 in the ranqe of latitudes phi >= 80 deg the localization of convection conversion effect is obtained in calculations for summer cap and it agrees with the data of direct measurements

  6. Evidence that polar cap arcs occur on open field lines

    International Nuclear Information System (INIS)

    Gussenhoven, M.S.; Hardy, D.A.; Rich, F.J.; Mullen, E.G.; Redus, R.H.

    1990-01-01

    The characteristics of polar cap arc occurrence are reviewed to show that the assumption of a closed magnetospheric magnetic field topology at very high latitudes when the IMF B z is strongly northward is difficult to reconcile with a wide variety of observational and theoretical considerations. In particular, we consider the implications of observations of particle entry for high and low energy electrons, magnetic flux conservation between the near and far tail, the time sequencing in polar cap arcs events, and the hemispherical differences in polar cap arc observations. These points can be explained either by excluding the need for a major topological magnetic field change from explanations of polar cap arc dynamics, or by assuming a long-tailed magnetosphere for all IMF orientations in which magnetic field lines eventually merge with solar wind field lines in either a smooth or a patchy fashion. (author)

  7. Polar cap magnetic field reversals during solar grand minima: could pores play a role?

    Czech Academy of Sciences Publication Activity Database

    Švanda, Michal; Brun, A.S.; Roudier, T.; Jouve, L.

    2016-01-01

    Roč. 586, February (2016), A123/1-A123/11 ISSN 0004-6361 R&D Projects: GA ČR(CZ) GA14-04338S Institutional support: RVO:67985815 Keywords : dynamo * Sun * magnetic fields Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.378, year: 2014

  8. Edge of polar cap patches

    Science.gov (United States)

    Hosokawa, K.; Taguchi, S.; Ogawa, Y.

    2016-04-01

    On the night of 4 December 2013, a sequence of polar cap patches was captured by an all-sky airglow imager (ASI) in Longyearbyen, Norway (78.1°N, 15.5°E). The 630.0 nm airglow images from the ASI of 4 second exposure time, oversampled the emission of natural lifetime (with quenching) of at least ˜30 sec, introduce no observational blurring effects. By using such high-quality ASI images, we succeeded in visualizing an asymmetry in the gradients between the leading/trailing edges of the patches in a 2-D fashion. The gradient in the leading edge was found to be 2-3 times steeper than that in the trailing edge. We also identified fingerlike structures, appearing only along the trailing edge of the patches, whose horizontal scale size ranged from 55 to 210 km. These fingers are considered to be manifestations of plasma structuring through the gradient-drift instability (GDI), which is known to occur only along the trailing edge of patches. That is, the current 2-D observations visualized, for the first time, how GDI stirs the patch plasma and such a mixing process makes the trailing edge more gradual. This result strongly implies a close connection between the GDI-driven plasma stirring and the asymmetry in the large-scale shape of patches and then suggests that the fingerlike structures can be used as markers to estimate the fine-scale structure in the plasma flow within patches.

  9. Planck intermediate results: XLIV. Structure of the Galactic magnetic field from dust polarization maps of the southern Galactic cap

    DEFF Research Database (Denmark)

    Aghanim, N.; Alves, M. I R; Arzoumanian, D.

    2016-01-01

    Using data from the Planck satellite, we study the statistical properties of interstellar dust polarization at high Galactic latitudes around the south pole (b < −60°). Our aim is to advance the understanding of the magnetized interstellar medium (ISM), and to provide a modelling framework of the...... is an important step towards a model that can be used to assess the accuracy of component-separation methods in present and future CMB experiments designed to search the B mode CMB polarization from primordial gravity waves....

  10. Polar cap deflation during magnetospheric substorms

    Science.gov (United States)

    Moses, J. J.; Siscoe, G. L.; Heelis, R. A.; Winningham, J. D.

    1989-01-01

    The expanding/contracting polar cap model has been used to simulate DE-2 ion drift data during substorms as determined using the AL index. Of the 39 cases modeled, 57 percent required the opening of a nightside gap which maps to where reconnection occurs in the tail; 75 percent of the 16 recovery phase cases required a nightside gap, while only 29 percent of the 17 expansion phase cases required a nightside gap. On the basis of this result, it is concluded that if a nightside gap implies tail reconnection, then reconnection probably occurs after expansion phase onset and continues throughout most of the recovery phase of a substorm.

  11. GPS scintillations associated with cusp dynamics and polar cap patches

    Directory of Open Access Journals (Sweden)

    Jin Yaqi

    2017-01-01

    Full Text Available This paper investigates the relative scintillation level associated with cusp dynamics (including precipitation, flow shears, etc. with and without the formation of polar cap patches around the cusp inflow region by the EISCAT Svalbard radar (ESR and two GPS scintillation receivers. A series of polar cap patches were observed by the ESR between 8:40 and 10:20 UT on December 3, 2011. The polar cap patches combined with the auroral dynamics were associated with a significantly higher GPS phase scintillation level (up to 0.6 rad than those observed for the other two alternatives, i.e., cusp dynamics without polar cap patches, and polar cap patches without cusp aurora. The cusp auroral dynamics without plasma patches were indeed related to GPS phase scintillations at a moderate level (up to 0.3 rad. The polar cap patches away from the active cusp were associated with sporadic and moderate GPS phase scintillations (up to 0.2 rad. The main conclusion is that the worst global navigation satellite system space weather events on the dayside occur when polar cap patches enter the polar cap and are subject to particle precipitation and flow shears, which is analogous to the nightside when polar cap patches exit the polar cap and enter the auroral oval.

  12. GPS scintillations associated with cusp dynamics and polar cap patches

    Science.gov (United States)

    Jin, Yaqi; Moen, Jøran I.; Oksavik, Kjellmar; Spicher, Andres; Clausen, Lasse B. N.; Miloch, Wojciech J.

    2017-10-01

    This paper investigates the relative scintillation level associated with cusp dynamics (including precipitation, flow shears, etc.) with and without the formation of polar cap patches around the cusp inflow region by the EISCAT Svalbard radar (ESR) and two GPS scintillation receivers. A series of polar cap patches were observed by the ESR between 8:40 and 10:20 UT on December 3, 2011. The polar cap patches combined with the auroral dynamics were associated with a significantly higher GPS phase scintillation level (up to 0.6 rad) than those observed for the other two alternatives, i.e., cusp dynamics without polar cap patches, and polar cap patches without cusp aurora. The cusp auroral dynamics without plasma patches were indeed related to GPS phase scintillations at a moderate level (up to 0.3 rad). The polar cap patches away from the active cusp were associated with sporadic and moderate GPS phase scintillations (up to 0.2 rad). The main conclusion is that the worst global navigation satellite system space weather events on the dayside occur when polar cap patches enter the polar cap and are subject to particle precipitation and flow shears, which is analogous to the nightside when polar cap patches exit the polar cap and enter the auroral oval.

  13. The interplanetary magnetic field By-dependent field-aligned current in the dayside polar cap under quiet conditions

    International Nuclear Information System (INIS)

    Yamauchi, M.; Araki, T.

    1989-01-01

    Spatial distribution and temporal variation of the interplanetary magnetic field (IMF) B y -dependent cusp region field-aligned currents (FACs) during quiet periods were studied by use of magnetic data observed by Magsat. The analysis was made for 11 events (each event lasts more than one and a half days) when the IMF B y component was steadily large and B x was relatively small (|B z | y |). Results of the analysis of total 62 half-day periods for the IMF B y -dependent cusp region FAC are summarized as follows: (1) the IMF B y -dependent cusp region FAC is located at around 86 degree-87 degree invariant latitude local noon, which is more poleward than the location of the IMF B z -dependent cusp region FAC; (2) the current density of this FAC is greater than previous studies (≥ 4 μA/m 2 for IMF B y = 6 nT); (3) there are two time scales for the IMF B y -dependent cusp region FAC to appear: the initial rise of the current is on a short time scale, ∼ 10 min, and it is followed by a gradual increase on a time scale of several hours to a half day; (4) the seasonal change of this FAC is greater than that of the nightside region 1 or region 2 FACs; (5) the IMF B z -dependent cusp region FAC is not well observed around the cusp when the IMF B y -dependent cusp region FAC is intense

  14. Inclined Pulsar Magnetospheres in General Relativity: Polar Caps for the Dipole, Quadrudipole, and Beyond

    Science.gov (United States)

    Gralla, Samuel E.; Lupsasca, Alexandru; Philippov, Alexander

    2017-12-01

    In the canonical model of a pulsar, rotational energy is transmitted through the surrounding plasma via two electrical circuits, each connecting to the star over a small region known as a “polar cap.” For a dipole-magnetized star, the polar caps coincide with the magnetic poles (hence the name), but in general, they can occur at any place and take any shape. In light of their crucial importance to most models of pulsar emission (from radio to X-ray to wind), we develop a general technique for determining polar cap properties. We consider a perfectly conducting star surrounded by a force-free magnetosphere and include the effects of general relativity. Using a combined numerical-analytical technique that leverages the rotation rate as a small parameter, we derive a general analytic formula for the polar cap shape and charge-current distribution as a function of the stellar mass, radius, rotation rate, moment of inertia, and magnetic field. We present results for dipole and quadrudipole fields (superposed dipole and quadrupole) inclined relative to the axis of rotation. The inclined dipole polar cap results are the first to include general relativity, and they confirm its essential role in the pulsar problem. The quadrudipole pulsar illustrates the phenomenon of thin annular polar caps. More generally, our method lays a foundation for detailed modeling of pulsar emission with realistic magnetic fields.

  15. Fourier analysis of polar cap electric field and current distributions

    Science.gov (United States)

    Barbosa, D. D.

    1984-01-01

    A theoretical study of high-latitude electric fields and currents, using analytic Fourier analysis methods, is conducted. A two-dimensional planar model of the ionosphere with an enhanced conductivity auroral belt and field-aligned currents at the edges is employed. Two separate topics are treated. A field-aligned current element near the cusp region of the polar cap is included to investigate the modifications to the convection pattern by the east-west component of the interplanetary magnetic field. It is shown that a sizable one-cell structure is induced near the cusp which diverts equipotential contours to the dawnside or duskside, depending on the sign of the cusp current. This produces characteristic dawn-dusk asymmetries to the electric field that have been previously observed over the polar cap. The second topic is concerned with the electric field configuration obtained in the limit of perfect shielding, where the field is totally excluded equatorward of the auroral oval. When realistic field-aligned current distributions are used, the result is to produce severely distorted, crescent-shaped equipotential contours over the cap. Exact, analytic formulae applicable to this case are also provided.

  16. A simplified model of polar cap electric fields

    International Nuclear Information System (INIS)

    D'Angelo, N.

    1977-01-01

    A simple-minded 'model' is used in order to visualize the gross features of polar cap electric fields, in particular the 'diode' effect which had emerged already from earlier observations and the asymmetry between the electric fields observed on the dawn and dusk sides of the polar cap, which depends on Bsub(y)

  17. Substorms and polar cap convection: the 10 January 2004 interplanetary CME case

    Directory of Open Access Journals (Sweden)

    Y. Andalsvik

    2012-01-01

    Full Text Available The expansion-contraction model of Dungey cell plasma convection has two different convection sources, i.e. reconnections at the magnetopause and in the magnetotail. The spatial-temporal structure of the nightside source is not yet well understood. In this study we shall identify temporal variations in the winter polar cap convection structure during substorm activity under steady interplanetary conditions. Substorm activity (electrojets and particle precipitations is monitored by excellent ground-satellite DMSP F15 conjunctions in the dusk-premidnight sector. We take advantage of the wide latitudinal coverage of the IMAGE chain of ground magnetometers in Svalbard – Scandinavia – Russia for the purpose of monitoring magnetic deflections associated with polar cap convection and substorm electrojets. These are augmented by direct observations of polar cap convection derived from SuperDARN radars and cross-track ion drift observations during traversals of polar cap along the dusk-dawn meridian by spacecraft DMSP F13. The interval we study is characterized by moderate, stable forcing of the magnetosphere-ionosphere system (EKL = 4.0–4.5 mV m−1; cross polar cap potential (CPCP, Φ (Boyle = 115 kV during Earth passage of an interplanetary CME (ICME, choosing an 4-h interval where the magnetic field pointed continuously south-west (Bz By By polarity of the ICME magnetic field, a clear indication of a nightside source.

  18. Gamma-Ray Pulsar Light Curves in Offset Polar Cap Geometry

    Science.gov (United States)

    Harding, Alice K.; DeCesar, Megan; Miller, M. Coleman

    2011-01-01

    Recent studies have shown that gamma-ray pulsar light curves are very sensitive to the geometry of the pulsar magnetic field. Pulsar magnetic field geometries, such as the retarded vacuum dipole and force-free magnetospheres, used to model high-energy light curves have distorted polar caps that are offset from the magnetic axis in the direction opposite to rotation. Since this effect is due to the sweepback of field lines near the light cylinder, offset polar caps are a generic property of pulsar magnetospheres and their effects should be included in gamma-ray pulsar light curve modeling. In slot gap models (having two-pole caustic geometry), the offset polar caps cause a strong azimuthal asymmetry of the particle acceleration around the magnetic axis. We have studied the effect of the offset polar caps in both retarded vacuum dipole and force-free geometry on the model high-energy pulse profile. We find that. corn pared to the profile:-; derived from :-;ymmetric caps, the flux in the pulse peaks, which are caustics formed along the trailing magnetic field lines. increases significantly relative to the off-peak emission. formed along leading field lines. The enhanced contrast produces greatly improved slot gap model fits to Fermi pulsar light curves like Vela, which show very little off-peak emIssIon.

  19. Occurrence Locations, Dipole Tilt Angle Effects, and Plasma Cloud Drift Paths of Polar Cap Neutral Density Anomalies

    Science.gov (United States)

    Lin, C. S.; Sutton, E. K.; Huang, C. Y.; Cooke, D. L.

    2018-02-01

    Polar cap neutral density anomaly (PCNDA) with large mass density enhancements over the background has been frequently observed in the polar cap during magnetic storms. By tracing field lines to the magnetosphere from the polar ionosphere, we divide the polar cap into two regions, an open field line (OFL) region with field lines connecting to the magnetopause boundary and a distant tail field line (TFL) region threaded with magnetotail lobe field lines. A statistical study of neutral density observed by the Challenging Minisatellite Payload satellite during major magnetic storms with Dst atmospheric disturbance could be generated in the nightside polar cap. From the PCNDA size and speed of sound at 400 km, we derive an initial energy deposition duration for producing traveling atmospheric disturbance in the range from 0.5 to 2.5 hr.

  20. Water Ice Albedo Variations on the Martian Northern Polar Cap

    Science.gov (United States)

    Hale, A. S.; Bass, D. S.; Tamppari, L. K.

    2003-01-01

    The Viking Orbiters determined that the surface of Mars northern residual cap is water ice. Many researchers have related observed atmospheric water vapor abundances to seasonal exchange between reservoirs such as the polar caps, but the extent to which the exchange between the surface and the atmosphere remains uncertain. Early studies of the ice coverage and albedo of the northern residual Martian polar cap using Mariner 9 and Viking images reported that there were substantial internannual differences in ice deposition on the polar cap, a result which suggested a highly variable Martian climate. However, some of the data used in these studies were obtained at differing values of heliocentric solar longitude (L(sub s)). Reevaluation of this dataset indicated that the residual cap undergoes seasonal brightening throughout the summer, and indicated that this process repeats from year to year. In this study we continue to compare Mariner 9 and Viking Orbiter imaging observations and thermal data of the north residual polar cap to data acquired with Mars Global Surveyor s Mars Orbiter Camera (MOC) instrument. In the current study, our goal is to examine all released data from MGS MOC in the northern summer season, along with applicable TES data in order to better understand the albedo variations in the northern summer and their implications on water transport. To date, work has focused primarily on the MOC dataset. In 1999, data acquisition of the northern polar regions began at L(sub s) = 107, although there was little north polar data acquired from L(sub s)= 107 to L(sub s) = 109. We examined a total of 409 images from L(sub s) = 107 to L(sub s)=148. We have also examined data from 2000 from L(sub s)= 93 to L(sub s)= 110; additional progress is ongoing. Here we present a progress report of our observations, and continue to determine their implications for the Martian water cycle.

  1. The Effect of an Offset Polar Cap Dipolar Magnetic Field on the Modeling of the Vela Pulsar’s γ-Ray Light Curves

    Science.gov (United States)

    Barnard, M.; Venter, C.; Harding, A. K.

    2016-12-01

    We performed geometric pulsar light curve modeling using static, retarded vacuum, and offset polar cap (PC) dipole B-fields (the latter is characterized by a parameter ɛ), in conjunction with standard two-pole caustic (TPC) and outer gap (OG) emission geometries. The offset-PC dipole B-field mimics deviations from the static dipole (which corresponds to ɛ =0). In addition to constant-emissivity geometric models, we also considered a slot gap (SG) E-field associated with the offset-PC dipole B-field and found that its inclusion leads to qualitatively different light curves. Solving the particle transport equation shows that the particle energy only becomes large enough to yield significant curvature radiation at large altitudes above the stellar surface, given this relatively low E-field. Therefore, particles do not always attain the radiation-reaction limit. Our overall optimal light curve fit is for the retarded vacuum dipole field and OG model, at an inclination angle α ={78}-1+{1^\\circ } and observer angle \\zeta ={69}-1+{2^\\circ }. For this B-field, the TPC model is statistically disfavored compared to the OG model. For the static dipole field, neither model is significantly preferred. We found that smaller values of ɛ are favored for the offset-PC dipole field when assuming constant emissivity, and larger ɛ values favored for variable emissivity, but not significantly so. When multiplying the SG E-field by a factor of 100, we found improved light curve fits, with α and ζ being closer to best fits from independent studies, as well as curvature radiation reaction at lower altitudes.

  2. The Effect of an Offset Polar Cap Dipolar Magnetic Field on the Modeling of the Vela Pulsar's Gamma-Ray Light Curves

    Science.gov (United States)

    Barnard, M.; Venter, C.; Harding, A. K.

    2016-01-01

    We performed geometric pulsar light curve modeling using static, retarded vacuum, and offset polar cap (PC) dipole B-fields (the latter is characterized by a parameter epsilon), in conjunction with standard two-pole caustic (TPC) and outer gap (OG) emission geometries. The offset-PC dipole B-field mimics deviations from the static dipole (which corresponds to epsilon equals 0). In addition to constant-emissivity geometric models, we also considered a slot gap (SG) E-field associated with the offset-PC dipole B-field and found that its inclusion leads to qualitatively different light curves. Solving the particle transport equation shows that the particle energy only becomes large enough to yield significant curvature radiation at large altitudes above the stellar surface, given this relatively low E-field. Therefore, particles do not always attain the radiation-reaction limit. Our overall optimal light curve fit is for the retarded vacuum dipole field and OG model, at an inclination angle alpha equals 78 plus or minus 1 degree and observer angle zeta equals 69 plus 2 degrees or minus 1 degree. For this B-field, the TPC model is statistically disfavored compared to the OG model. For the static dipole field, neither model is significantly preferred. We found that smaller values of epsilon are favored for the offset-PC dipole field when assuming constant emissivity, and larger epsilon values favored for variable emissivity, but not significantly so. When multiplying the SG E-field by a factor of 100, we found improved light curve fits, with alpha and zeta being closer to best fits from independent studies, as well as curvature radiation reaction at lower altitudes.

  3. Polar cap index as a proxy for hemispheric Joule heating

    DEFF Research Database (Denmark)

    Chun, F.K.; Knipp, D.J.; McHarg, M.G.

    1999-01-01

    input into the polar cap, we propose to use PC as a proxy for the hemispheric Joule heat production rate (JH). In this study, JH is estimated from the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure. We fit hourly PC values to hourly averages of JH. Using a data base approximately...... is as equally accurate. Thus the single station PC index appears to provide a quick estimate of, and is an appropriate proxy for, the hemispheric Joule heating rate....

  4. The thermospheric effects of a rapid polar cap expansion

    Directory of Open Access Journals (Sweden)

    D. W. Idenden

    Full Text Available In a previous publication we used results from a coupled thermosphere-ionosphere-plasmasphere model to illustrate a new mechanism for the formation of a large-scale patch of ionisation arising from a rapid polar cap expansion. Here we describe the thermospheric response to that polar cap expansion, and to the ionospheric structure produced. The response is dominated by the energy and momentum input at the dayside throat during the expansion phase itself. These inputs give rise to a large-scale travelling atmospheric disturbance (TAD that propagates both antisunward across the polar cap and equatorward at speeds much greater than both the ion drifts and the neutral winds. We concentrate only on the initially poleward travelling disturbance. The disturbance is manifested in the neutral temperature and wind fields, the height of the pressure level surfaces and in the neutral density at fixed heights. The thermospheric effects caused by the ionospheric structure produced during the expansion are hard to discern due to the dominating effects of the TAD.

    Key words. Ionosphere (ionosphere · atmosphere interaction; modeling and forecasting; plasma convection.

  5. The thermospheric effects of a rapid polar cap expansion

    Directory of Open Access Journals (Sweden)

    D. W. Idenden

    1998-10-01

    Full Text Available In a previous publication we used results from a coupled thermosphere-ionosphere-plasmasphere model to illustrate a new mechanism for the formation of a large-scale patch of ionisation arising from a rapid polar cap expansion. Here we describe the thermospheric response to that polar cap expansion, and to the ionospheric structure produced. The response is dominated by the energy and momentum input at the dayside throat during the expansion phase itself. These inputs give rise to a large-scale travelling atmospheric disturbance (TAD that propagates both antisunward across the polar cap and equatorward at speeds much greater than both the ion drifts and the neutral winds. We concentrate only on the initially poleward travelling disturbance. The disturbance is manifested in the neutral temperature and wind fields, the height of the pressure level surfaces and in the neutral density at fixed heights. The thermospheric effects caused by the ionospheric structure produced during the expansion are hard to discern due to the dominating effects of the TAD.Key words. Ionosphere (ionosphere · atmosphere interaction; modeling and forecasting; plasma convection.

  6. Polar cap hot patches: Enhanced density structures different from the classical patches in the ionosphere

    Science.gov (United States)

    Zhang, Q.-H.; Ma, Y.-Z.; Jayachandran, P. T.; Moen, J.; Lockwood, M.; Zhang, Y.-L.; Foster, J. C.; Zhang, S.-R.; Wang, Y.; Themens, D. R.; Zhang, B.-C.; Xing, Z. Y.

    2017-08-01

    Based on in situ and ground-based observations, a new type of "polar cap hot patch" has been identified that is different from the classical polar cap enhanced density structure (cold patches). Comparing with the classical polar cap patches, which are transported from the dayside sunlit region with dense and cold plasma, the polar cap hot patches are associated with particle precipitations (therefore field-aligned currents), ion upflows, and flow shears. The hot patches may have the same order of density enhancement as classical patches in the topside ionosphere, suggesting that the hot patches may be produced by transported photoionization plasma into flow channels. Within the flow channels, the hot patches have low-energy particle precipitation and/or ion upflows associated with field-aligned currents and flow shears. Corresponding Global Navigation Satellite System (GNSS) signal scintillation measurements indicate that hot patches may produce slightly stronger radio signal scintillation in the polar cap region than classical patches. A new type of polar cap patches, "polar cap hot patches," is identified to differentiate enhanced density structures from classical patches. Hot patches are associated with particle precipitations, ion upflows, field-aligned currents, and shear flows in the polar cap. Hot patches may lead to slightly stronger ionospheric scintillations of GNSS signals in the polar cap region than classical patches.

  7. A multi-satellite study of accelerated ionospheric ion beams above the polar cap

    Directory of Open Access Journals (Sweden)

    R. Maggiolo

    2006-07-01

    Full Text Available This paper presents a study of nearly field-aligned outflowing ion beams observed on the Cluster satellites over the polar cap. Data are taken at geocentric radial distances of the order of 5–9 RE. The distinction is made between ion beams originating from the polar cusp/cleft and beams accelerated almost along the magnetic field line passing by the spacecraft. Polar cusp beams are characterized by nearly field-aligned proton and oxygen ions with an energy ratio EO+ / EH+, of the order of 3 to 4, due to the ion energy repartition inside the source and to the latitudinal extension of the source. Rapid variations in the outflowing ion energy are linked with pulses/modifications of the convection electric field. Cluster data allow one to show that these perturbations of the convection velocity and the associated ion structures propagate at the convection velocity. In contrast, polar cap local ion beams are characterized by field-aligned proton and oxygen ions with similar energies. These beams show the typical inverted V structures usually observed in the auroral zone and are associated with a quasi-static converging electric field indicative of a field-aligned electric field. The field-aligned potential drop fits well the ion energy profile. The simultaneous observation of precipitating electrons and upflowing ions of similar energies at the Cluster orbit indicates that the spacecraft are crossing the mid-altitude part of the acceleration region. In the polar cap, the parallel electric field can thus extend to altitudes higher than 5 Earth radii. A detailed analysis of the distribution functions shows that the ions are heated during their parallel acceleration and that energy is exchanged between H+ and O+. Furthermore, intense electrostatic waves are observed simultaneously. These observations could be due to an ion-ion two-stream instability.

  8. Capped bit patterned media for high density magnetic recording

    Science.gov (United States)

    Li, Shaojing; Livshitz, Boris; Bertram, H. Neal; Inomata, Akihiro; Fullerton, Eric E.; Lomakin, Vitaliy

    2009-04-01

    A capped composite patterned medium design is described which comprises an array of hard elements exchange coupled to a continuous cap layer. The role of the cap layer is to lower the write field of the individual hard element and introduce ferromagnetic exchange interactions between hard elements to compensate the magnetostatic interactions. Modeling results show significant reduction in the reversal field distributions caused by the magnetization states in the array which is important to prevent bit errors and increase achievable recording densities.

  9. Preparing an ATLAS toroid magnet end-cap for lowering

    CERN Multimedia

    Claudia Marcelloni

    2007-01-01

    One of the two 13-m high toroid magnet end-caps for the ATLAS experiment being transported from the construction hall to the experimental area. The end-cap will be lowered into the ATLAS cavern and attached to an end of the detector.

  10. Polar cap arcs from the magnetosphere to the ionosphere: kinetic modelling and observations by Cluster and TIMED

    Directory of Open Access Journals (Sweden)

    R. Maggiolo

    2012-02-01

    Full Text Available On 1 April 2004 the GUVI imager onboard the TIMED spacecraft spots an isolated and elongated polar cap arc. About 20 min later, the Cluster satellites detect an isolated upflowing ion beam above the polar cap. Cluster observations show that the ions are accelerated upward by a quasi-stationary electric field. The field-aligned potential drop is estimated to about 700 V and the upflowing ions are accompanied by a tenuous population of isotropic protons with a temperature of about 500 eV. The magnetic footpoints of the ion outflows observed by Cluster are situated in the prolongation of the polar cap arc observed by TIMED GUVI. The upflowing ion beam and the polar cap arc may be different signatures of the same phenomenon, as suggested by a recent statistical study of polar cap ion beams using Cluster data. We use Cluster observations at high altitude as input to a quasi-stationary magnetosphere-ionosphere (MI coupling model. Using a Knight-type current-voltage relationship and the current continuity at the topside ionosphere, the model computes the energy spectrum of precipitating electrons at the top of the ionosphere corresponding to the generator electric field observed by Cluster. The MI coupling model provides a field-aligned potential drop in agreement with Cluster observations of upflowing ions and a spatial scale of the polar cap arc consistent with the optical observations by TIMED. The computed energy spectrum of the precipitating electrons is used as input to the Trans4 ionospheric transport code. This 1-D model, based on Boltzmann's kinetic formalism, takes into account ionospheric processes such as photoionization and electron/proton precipitation, and computes the optical and UV emissions due to precipitating electrons. The emission rates provided by the Trans4 code are compared to the optical observations by TIMED. They are similar in size and intensity. Data and modelling results are consistent with the scenario of quasi

  11. Magnetospheric convection and current system in the dayside polar cap

    International Nuclear Information System (INIS)

    Nishida, A.; Mukai, T.; Tsuruda, K.; Hayakawa, H.

    1992-01-01

    Field and particle observations on EXOS-D (Akebono) have yielded new information on convection and current system in the dayside polar cap. Convection patterns are distinctly different depending upon whether IMF B z is northward or southward. The number of convection cells is two when B z is southward but four when B z is northward. Lobe cells in which plasma flows sunward in the region of open field lines are observed as a pair (of which one is in the dawn and the other in the dusk sector) for any polarity of IMF B y and B z . Ions in the keV range precipitate not only in the dayside cusp region but also along the sunward directed streamlines of the dawn and dusk lobe cells. These observations require reconsideration on the position and the extent of the reconnection region on the magnetopause. They also suggest that the magnetotail plays a vital role in some phenomena which have been ascribed to dayside magnetopause processes. We have not been able to find evidence to prove the presence of the viscous cell under southward IMF

  12. Diurnal Albedo Variations of the Martian North Polar Water Ice Cap

    Science.gov (United States)

    Troy, R. F.; Bass, D.

    2002-01-01

    Presentation of findings regarding diurnal variations in the north polar water ice cap of Mars as part of a larger study of the interannual and seasonal variations of the Martian north polar water ice cap. Additional information is contained in the original extended abstract.

  13. The influence of the positronium photoionization rate on the polar cap X-ray luminosity of radio pulsars

    Science.gov (United States)

    Barsukov, D. P.; Vorontsov, M. V.

    2017-12-01

    The influence of the positronium photoionization rate on the polar cap X-ray luminosity of old radio pulsars is considered. It is assumed that the polar cap is heated only by reverse positrons accelerated in the pulsar diode. It is supposed that the pulsar diode is in a stationary state with the lower plate located near the star surface (polar cap model) occupies all the pulsar tube cross section and operates in the regime of steady space charge by the limited electron flow. The influence of a small-scale magnetic field on the electric field inside the pulsar diode is taken into account. The reverse positron current is calculated in the framework of two models: rapid and gradual screening. To calculate the production rate of electron-positron pairs we take into account only the curvature radiation of primary electrons and its absorption in the magnetic field. It is assumed that some fraction of electron-positron pairs is created in a bound state (positronium). Later, such positroniums are photoionized by thermal photons from the polar cap.

  14. A study of the relationship between interplanetary parameters and large displacements of the nightside polar cap boundary

    International Nuclear Information System (INIS)

    Lester, M.; Freeman, M.P.; Southwood, D.J.; Waldock, J.A.; Singer, H.J.

    1990-01-01

    On July 14, 1982 the Sweden and Britain Radar-Aurora Experiment (SABRE) observed the ionospheric flow reversal boundary at ∼ 0400 MLT to move equatorward across the radar field of view and then later to return poleward. The polar cap appeared to be considerably inflated at this time. Concurrent observations by ISEE-3 at the L1 libration point of the solar wind speed and density, and of the interplanetary magnetic field (IMF) indicated that the solar wind conditions were unusual throughout the interval under consideration. A mapping of the solar wind parameters from the L1 point to the subsolar magnetopause and thence to the SABRE local time sector indicates that the equatorward motion of the polar cap boundary was controlled by a southward turning of the IMF. The inference of a concomitant increase in open magnetic flux is supported by a comparison of the magnetopause location observed by ISEE-1 on an inbound pass in the 2,100 MLT sector with a magnetopause model based upon the solar wind measurements made by ISEE-3. Some 20 minutes after the expansion of the polar cap boundary was first seen by SABRE, there was a rapid contraction of the boundary, the casue of which was independent of the INF and solar wind parameters, and which had a poleward velocity component in excess of 1,900 m s -1 . the boundary as it moved across the radar field of view was highly structured and oriented at a large angle to the ionospheric footprints of the magnetic L shells. Observations in the premidnight sector by the Air Force Geophysics Laboratory (AFGL) magnetometer array indicate that the polar cap contraction is caused by substorm draining of the polar cap flux and occurs without a clearly associated trigger in the interplanetary medium. The response time in the early morning local time sector to the substorm onset switch is approximately 20 minutes, equivalent to an ionospheric azimuthal phase velocity of some 5 km s -1

  15. Pulsar bi-drifting: implications for polar cap geometry

    Science.gov (United States)

    Wright, Geoff; Weltevrede, Patrick

    2017-01-01

    For many years it has been considered puzzling how pulsar radio emission, supposedly created by a circulating carousel of sub-beams, can produce the drift bands demonstrated by PSR J0815+0939, and more recently PSR B1839-04, which simultaneously drifts in opposing directions. Here, we suggest that the carousels of these pulsars, and hence their beams, are not circular but elliptical with axes tilted with respect to the fiducial plane. We show that certain relatively unusual lines of sight can cause bi-drifting to be observed, and a simulation of the two known exemplars is presented. Although bi-drifting is rare, non-circular beams may be common among pulsars and reveal themselves by having profile centroids displaced from the fiducial plane identified by polarization position angle swings. They may also result in profiles with asymmetric- and frequency-dependent component evolution. It is further suggested that the carousels may change their tilt by specific amounts and later reverse them. This may occur suddenly, accompanying a mode change (e.g. PSR B0943+10), or more gradually and short lived as in `flare' pulsars (e.g. PSR B1859+07). A range of pulsar behaviour (e.g. the shifting drift patterns of PSRs B0818-41 and B0826-34) may also be the result of non-circular carousels with varying orientation. The underlying nature of these carousels - whether they are exclusively generated by polar cap physics or driven by magnetospheric effects - is briefly discussed.

  16. Dayside and nightside contributions to cross-polar cap potential variations: the 20 March 2001 ICME case

    Directory of Open Access Journals (Sweden)

    Y. L. Andalsvik

    2011-11-01

    Full Text Available We investigate the association between temporal-spatial structure of polar cap convection and auroral electrojet intensifications during a 5-h-long interval of strong forcing of the magnetosphere by an ICME/Magnetic cloud on 20 March 2001. We use data from coordinated ground-satellite observations in the 15:00–20:00 MLT sector. We take advantage of the good latitudinal coverage in the polar cap and in the auroral zone of the IMAGE chain of ground magnetometers in Svalbard – Scandinavia – Russia and the stable magnetic field conditions in ICMEs. The electrojet events are characterized by a sequence of 10 min-long AL excursions to −1000/−1500 nT followed by poleward expansions and auroral streamers. These events are superimposed on a high disturbance level when the AL index remains around −500 nT for several hours. These signatures are different from those appearing in classical substorms, most notably the absence of a complete recovery phase when AL usually reaches above −100 nT. We concentrate on polar cap convection in both hemispheres (DMSP F13 data in relation to the ICME By conditions, electrojet intensifications, and the global UV auroral configuration obtained from the IMAGE spacecraft. The temporal evolution of convection properties such as the cross-polar cap potential (CPCP drop and flow channels at the dawn/dusk polar cap (PC boundaries around the time of the electrojet events are investigated. This approach allows us to distinguish between dayside (magnetopause reconnection and nightside (magnetotail reconnection sources of the PC convection events within the context of the expanding-contracting model of high-latitude convection in the Dungey cycle. Inter-hemispheric symmetries/asymmetries in the presence of newly-discovered convection channels at the dawn or dusk side PC boundaries are determined.

  17. The response of ionospheric convection in the polar cap to substorm activity

    Directory of Open Access Journals (Sweden)

    M. Lester

    Full Text Available We report multi-instrument observations during an isolated substorm on 17 October 1989. The EISCAT radar operated in the SP-UK-POLI mode measuring ionospheric convection at latitudes 71°λ-78°λ. SAMNET and the EISCAT Magnetometer Cross provide information on the timing of substorm expansion phase onset and subsequent intensifications, as well as the location of the field aligned and ionospheric currents associated with the substorm current wedge. IMP-8 magnetic field data are also included. Evidence of a substorm growth phase is provided by the equatorward motion of a flow reversal boundary across the EISCAT radar field of view at 2130 MLT, following a southward turning of the interplanetary magnetic field (IMF. We infer that the polar cap expanded as a result of the addition of open magnetic flux to the tail lobes during this interval. The flow reversal boundary, which is a lower limit to the polar cap boundary, reached an invariant latitude equatorward of 71°λ by the time of the expansion phase onset. A westward electrojet, centred at 65.4°λ, occurred at the onset of the expansion phase. This electrojet subsequently moved poleward to a maximum of 68.1°λ at 2000 UT and also widened. During the expansion phase, there is evidence of bursts of plasma flow which are spatially localised at longitudes within the substorm current wedge and which occurred well poleward of the westward electrojet. We conclude that the substorm onset region in the ionosphere, defined by the westward electrojet, mapped to a part of the tail radially earthward of the boundary between open and closed magnetic flux, the "distant" neutral line. Thus the substorm was not initiated at the distant neutral line, although there is evidence that it remained active during the expansion phase. It is not obvious whether the electrojet mapped to a near-Earth neutral line, but at its most poleward, the expanded electrojet does not reach the estimated latitude of the polar cap

  18. Dayside and nightside contributions to the cross polar cap potential: placing an upper limit on a viscous-like interaction

    Directory of Open Access Journals (Sweden)

    S. E. Milan

    2004-11-01

    Full Text Available Observations of changes in size of the ionospheric polar cap allow the dayside and nightside reconnection rates to be quantified. From these it is straightforward to estimate the rate of antisunward transport of magnetic flux across the polar regions, quantified by the cross polar cap potential ΦPC. When correlated with upstream measurements of the north-south component of the IMF, ΦPC is found to increase for more negative Bz, as expected. However, we also find that ΦPC does not, on average, decrease to zero, even for strongly northward IMF. In the past this has been interpreted as evidence for a viscous interaction between the magnetosheath flow and the outer boundaries of the magnetosphere. In contrast, we show that this is the consequence of flows excited by tail reconnection, which is inherently uncorrelated with IMF Bz.

  19. Dayside and nightside contributions to the cross polar cap potential: placing an upper limit on a viscous-like interaction

    Directory of Open Access Journals (Sweden)

    S. E. Milan

    2004-11-01

    Full Text Available Observations of changes in size of the ionospheric polar cap allow the dayside and nightside reconnection rates to be quantified. From these it is straightforward to estimate the rate of antisunward transport of magnetic flux across the polar regions, quantified by the cross polar cap potential ΦPC. When correlated with upstream measurements of the north-south component of the IMF, ΦPC is found to increase for more negative Bz, as expected. However, we also find that ΦPC does not, on average, decrease to zero, even for strongly northward IMF. In the past this has been interpreted as evidence for a viscous interaction between the magnetosheath flow and the outer boundaries of the magnetosphere. In contrast, we show that this is the consequence of flows excited by tail reconnection, which is inherently uncorrelated with IMF Bz.

  20. Multi-instrument observation of two different types of polar cap aurora occurring simultaneously during northward IMF

    Science.gov (United States)

    Reidy, J. A.; Fear, R. C.; Lanchester, B. S.; Whiter, D. K.; Kavanagh, A. J.; Paxton, L. J.; Zhang, Y.

    2016-12-01

    Polar cap aurora are a phenomena associated with periods of northwards IMF. By studying their appearance and formation, we can gain valuable information on the configuration of Earth's magnetosphere during the less understood `quiet' periods that occur approximately half of the time. Observations of high latitude aurora from multiple instruments on 19 January 2008 are presented, including almost simultaneous observations of the northern and southern auroral regions from the Special Sensor Ultra-violet Spectrographic Imager (SSUSI) instruments on board Defence Meteorological Satellite Programme (DMSP) spacecraft F16 and F17. SuperDARN flows are also explored in both hemispheres during the event. In the northern hemisphere, two high latitude structures were seen on opposite sides of the polar cap during the same interval. The energies of the precipitating electrons above the structure on the duskside was estimated to vary between 2-11 keV using the Auroral Structure and Kinetics (ASK) instrument in conjunction with the Southampton ion chemistry model. Further analysis of this structure revealed it to be formed on closed field lines that had protruded into the polar cap, consistent with the mechanism proposed for transpolar arcs. However this structure did not cross the entire polar cap but remained, in the northern hemisphere, at approximately 80° magnetic latitude for at least 40 minutes. This protrusion is hence suggested to be an example of a `failed transpolar arc'. The structure seen on the dawnside of the northern polar cap was analysed using DMSP particle spectrograph data. It was found to be associated with electron precipitation energies lower than 1 keV and no ion signature were present. Hence it is suggested that this sun-aligned structure is consistent with the common low intensity arcs formed by accelerated polar rain. The study shows there are at least two types of high latitude aurora occurring simultaneously during northwards IMF.

  1. Dynamical changes of the polar cap potential structure: an information theory approach

    Directory of Open Access Journals (Sweden)

    I. Coco

    2011-10-01

    Full Text Available Some features, such as vortex structures often observed through a wide spread of spatial scales, suggest that ionospheric convection is turbulent and complex in nature. Here, applying concepts from information theory and complex system physics, we firstly evaluate a pseudo Shannon entropy, H, associated with the polar cap potential obtained from the Super Dual Auroral Radar Network (SuperDARN and, then, estimate the degree of disorder and the degree of complexity of ionospheric convection under different Interplanetary Magnetic Field (IMF conditions. The aforementioned quantities are computed starting from time series of the coefficients of the 4th order spherical harmonics expansion of the polar cap potential for three periods, characterised by: (i steady IMF Bz > 0, (ii steady IMF Bz < 0 and (iii a double rotation from negative to positive and then positive to negative Bz. A neat dynamical topological transition is observed when the IMF Bz turns from negative to positive and vice versa, pointing toward the possible occurrence of an order/disorder phase transition, which is the counterpart of the large scale convection rearrangement and of the increase of the global coherence. This result has been confirmed by applying the same analysis to a larger data base of about twenty days of SuperDARN data, allowing to investigate the role of IMF By too.

  2. A multi-satellite study of accelerated ionospheric ion beams above the polar cap

    Directory of Open Access Journals (Sweden)

    R. Maggiolo

    2006-07-01

    Full Text Available This paper presents a study of nearly field-aligned outflowing ion beams observed on the Cluster satellites over the polar cap. Data are taken at geocentric radial distances of the order of 5–9 RE. The distinction is made between ion beams originating from the polar cusp/cleft and beams accelerated almost along the magnetic field line passing by the spacecraft. Polar cusp beams are characterized by nearly field-aligned proton and oxygen ions with an energy ratio EO+ / EH+, of the order of 3 to 4, due to the ion energy repartition inside the source and to the latitudinal extension of the source. Rapid variations in the outflowing ion energy are linked with pulses/modifications of the convection electric field. Cluster data allow one to show that these perturbations of the convection velocity and the associated ion structures propagate at the convection velocity.

    In contrast, polar cap local ion beams are characterized by field-aligned proton and oxygen ions with similar energies. These beams show the typical inverted V structures usually observed in the auroral zone and are associated with a quasi-static converging electric field indicative of a field-aligned electric field. The field-aligned potential drop fits well the ion energy profile. The simultaneous observation of precipitating electrons and upflowing ions of similar energies at the Cluster orbit indicates that the spacecraft are crossing the mid-altitude part of the acceleration region. In the polar cap, the parallel electric field can thus extend to altitudes higher than 5 Earth radii. A detailed analysis of the distribution functions shows that the ions are heated during their parallel acceleration and that energy is exchanged between H+ and O+. Furthermore, intense electrostatic waves are observed simultaneously. These observations could be due to an ion-ion two-stream instability.

  3. South polar permanent CO2 ice cap presentation in the Global Mars Multiscale Model

    Science.gov (United States)

    Fazel-Rastgar, Farahnaz

    2018-02-01

    The atmospheric influence caused by the Martian permanent south CO2 ice cap is examined to improve the Global Mars Multiscale Model (GM3) to see if it can significantly improve the representation of south polar meteorology. However, the seasonal carbon dioxide ice in the polar regions is presented in the surface ice simulation by the Global Mars Multiscale Model but the model does not produce a permanent south CO2 ice cap, and the physics code must modify to capture the realistic physical such as ice process detail; probably makes a bias in terms of total CO2 ice and meteorological processes in the model aside from ice formation. The permanent south CO2 ice cap in the model can significantly improve the representation of south polar meteorology for example in predicted surface temperatures, surface pressures, horizontal and zonal winds over the south cap and possible initiation of dust storms at south polar region during the southern summer period.

  4. The Mars water cycle at other epochs - Recent history of the polar caps and layered terrain

    Science.gov (United States)

    Jakosky, Bruce M.; Henderson, Bradley G.; Mellon, Michael T.

    1993-01-01

    A numerical model is presented of the integrated role of seasonal water cycle on the evolution of polar deposits on Mars over the last 10 million years. From the model, it is concluded that the only major difference between the polar caps which affects their long-term behavior is ultimately the difference in their elevations. Because of that difference, there is a preference for CO2 frost to stay longer on the northern polar cap. The average difference in sublimation at the caps results in a net south-to-north transport of water ice over long time scales. Superimposed on any long-term behavior is a transfer of water ice between the caps on the 10 exp 5 - 10 exp 6 yr time scales. The amount of water exchanged is small compared to the total ice content of the polar deposits.

  5. The Mars water cycle at other epochs: History of the polar caps and layered terrain

    Science.gov (United States)

    Jakosky, Bruce M.; Henderson, Bradley G.; Mellon, Michael T.

    1992-01-01

    The atmospheric water cycle at the present epoch involves summertime sublimation of water from the north polar cap, transport of water through the atmosphere, and condensation on one or both winter CO2 caps. Exchange with the regolith is important seasonally, but the water content of the atmosphere appears to be controlled by the polar caps. The net annual transport through the atmosphere, integrated over long timescales, must be the driving force behind the long-term evolution of the polar caps; clearly, this feeds back into the evolution of the layered terrain. We have investigated the behavior of the seasonal water cycle and the net integrated behavior at the pole for the last 10 exp 7 years. Our model of the water cycle includes the solar input, CO2 condensation and sublimation, and summertime water sublimation through the seasonal cycles, and incorporates the long-term variations in the orbital elements describing the Martian orbit.

  6. Arrays of magnetic nanoparticles capped with alkylamines

    Indian Academy of Sciences (India)

    While there has been reasonable success in preparing arrays of metal and semiconducting chalcoginide nanoparticles, arrays of metal oxides are relatively unknown. [12,13]. We considered it important to prepare arrays of metal oxide particles with use- ful magnetic properties, particularly in view of their stability under ...

  7. GPS scintillation effects associated with polar cap patches and substorm auroral activity: direct comparison

    Directory of Open Access Journals (Sweden)

    Jin Yaqi

    2014-01-01

    Full Text Available We directly compare the relative GPS scintillation levels associated with regions of enhanced plasma irregularities called auroral arcs, polar cap patches, and auroral blobs that frequently occur in the polar ionosphere. On January 13, 2013 from Ny-Ålesund, several polar cap patches were observed to exit the polar cap into the auroral oval, and were then termed auroral blobs. This gave us an unprecedented opportunity to compare the relative scintillation levels associated with these three phenomena. The blobs were associated with the strongest phase scintillation (σϕ, followed by patches and arcs, with σϕ up to 0.6, 0.5, and 0.1 rad, respectively. Our observations indicate that most patches in the nightside polar cap have produced significant scintillations, but not all of them. Since the blobs are formed after patches merged into auroral regions, in space weather predictions of GPS scintillations, it will be important to enable predictions of patches exiting the polar cap.

  8. Influence of geomagnetic energy inputs in the polar cap on the upper atmosphere during geomagnetic storms

    Science.gov (United States)

    Deng, Y.; Sheng, C.; Huang, Y.; Maute, A. I.; Lu, Y.

    2016-12-01

    Large Poynting flux has been observed in the polar cap by Defense Meteorological Satellite Program (DMSP) satellites during the main phase of the August 5, 2011 storm, the magnitude of which is comparable to that in the auroral zone. In order to understand the mechanisms for the observed large Poynting flux in the polar cap, the particle precipitation and small-scale electric field variability along DMSP satellite trajectory has been studied. Meanwhile, the global ionosphere-thermosphere model (GITM) has been run to examine the relative contribution of convection pattern and conductance to the polar cap Poynting flux enhancement. The influence of energy inputs in the polar cap including Joule heating related to both large-scale and small-scale electric field and soft particle precipitation on the thermosphere has been examined through the analysis of the GRACE neutral density observations and GITM simulations with different forcings. This study will help to illustrate the mechanisms and impacts of the polar cap energy inputs.

  9. Superconducting polarizing magnet for a movable polarized target

    International Nuclear Information System (INIS)

    Anishchenko, N.G.; Bartenev, V.D.; Blinov, N.A.

    1998-01-01

    The superconducting polarizing magnet was constructed for the JINR (Dubna) movable polarized target (MPT) with working volume 200 mm long and 30 mm in diameter. The magnet provides a polarizing magnetic field up to 6 T in the centre with the uniformity of 4.5 x 10 -4 in the working volume of the target. The magnet contains a main solenoidal winding 558 mm long and 206/144 mm in diameters, and compensating and correcting winding placed at its ends. The windings are made of a NbTi wire, impregnated with the epoxy resin and placed in the horizontal cryostat. The diameter of the 'warm' aperture of the magnet cryostat is 96 mm. The design and technology of the magnet winding are described. Results of the magnetic field map measurements, using a NMR-magnetometer are given. A similar magnet constructed at DAPNIA, CEA/Saclay (France), represented a model for the present development. The MPT array is installed in the beam line of polarized neutrons produced by break-up of polarized deuterons extracted from the synchrophasotron of the Laboratory of High Energies (LHE), JINR (Dubna)

  10. Magnetic actuation and transition shapes of a bistable spherical cap

    Directory of Open Access Journals (Sweden)

    E.G. Loukaides

    2014-10-01

    Full Text Available Multistable shells have been proposed for a variety of applications; however, their actuation is almost exclusively addressed through embedded piezoelectric patches. Additional actuation techniques are needed for applications requiring high strains or where remote actuation is desirable. Part of the reason for the lack of research in this area is the absence of appropriate models describing the detailed deformation and energetics of such shells. This work presents a bistable spherical cap made of iron carbonyl-infused polydimethylsiloxane. The magnetizable structure can be actuated remotely through permanent magnets while the transition is recorded with a high-speed camera. Moreover, the experiment is reproduced in a finite element (FE dynamic model for comparison with the physical observations. High-speed footage of the physical cap inversion together with the FE modeling gives valuable insight on preferable intermediate geometries. Both methods return similar values for the magnetic field strength required for the snap-through. High-strain multistable spherical cap transformation is demonstrated, based on informed material selection. We discover that non-axisymmetric transition shapes are preferred in intermediate geometries by bistable spherical caps. We develop the methods for design and analysis of such actuators, including the feasibility of remote actuation methods for multistable shells.

  11. Self-assembly of colloids with magnetic caps

    Energy Technology Data Exchange (ETDEWEB)

    Novak, E.V., E-mail: ekaterina.novak@urfu.ru [Ural Federal University, Lenin Av. 51, Ekaterinburg (Russian Federation); Kantorovich, S.S. [Ural Federal University, Lenin Av. 51, Ekaterinburg (Russian Federation); University of Vienna, Sensengasse 8, Vienna (Austria)

    2017-06-01

    In our earlier work (Steinbach et al., 2016 ) we investigated a homogeneous system of magnetically capped colloidal particles that self-assembled via two structural patterns of different symmetry. The particles could form a compact, equilateral triangle with a three-fold rotational symmetry and zero dipole moment and a staggered chain with mirror symmetry with a net magnetisation perpendicular to the chain. The system exhibited a bistability already in clusters of three particles. Based on observations of a real magnetic particles system, analytical calculations and molecular dynamics simulations, it has been shown that the bistability is a result of an anisotropic magnetisation distribution with rotational symmetry inside the particles. The present study is a logical extension of the above research and forms a preparatory stage for the study of a self-assembly of such magnetic particles under the influence of an external magnetic field. Since the magnetic field is only an additive contribution to the total ground state energy, we can study the interparticle interaction energies of candidate ground state structures based on the field-free terms. - Highlights: • Analytical calculations of the energies of ground state candidates for colloids with magnetic caps. • Computer simulations confirmed the theoretical model. • The structural transition between ground states was found.

  12. Perennial water ice identified in the south polar cap of Mars.

    Science.gov (United States)

    Bibring, Jean-Pierre; Langevin, Yves; Poulet, François; Gendrin, Aline; Gondet, Brigitte; Berthé, Michel; Soufflot, Alain; Drossart, Pierre; Combes, Michel; Bellucci, Giancarlo; Moroz, Vassili; Mangold, Nicolas; Schmitt, Bernard

    2004-04-08

    The inventory of water and carbon dioxide reservoirs on Mars are important clues for understanding the geological, climatic and potentially exobiological evolution of the planet. From the early mapping observation of the permanent ice caps on the martian poles, the northern cap was believed to be mainly composed of water ice, whereas the southern cap was thought to be constituted of carbon dioxide ice. However, recent missions (NASA missions Mars Global Surveyor and Odyssey) have revealed surface structures, altimetry profiles, underlying buried hydrogen, and temperatures of the south polar regions that are thermodynamically consistent with a mixture of surface water ice and carbon dioxide. Here we present the first direct identification and mapping of both carbon dioxide and water ice in the martian high southern latitudes, at a resolution of 2 km, during the local summer, when the extent of the polar ice is at its minimum. We observe that this south polar cap contains perennial water ice in extended areas: as a small admixture to carbon dioxide in the bright regions; associated with dust, without carbon dioxide, at the edges of this bright cap; and, unexpectedly, in large areas tens of kilometres away from the bright cap.

  13. Probing lateral magnetic nanostructures by polarized GISANS

    International Nuclear Information System (INIS)

    Kentzinger, E.; Frielinghaus, H.; Ruecker, U.; Ioffe, A.; Richter, D.; Brueckel, Th.

    2007-01-01

    While structural and magnetic lateral correlations in thin film materials can be investigated at the μm length scale by neutron off-specular scattering (OSS) with polarization analysis, they can also be investigated at the nm length scale by grazing incidence small-angle scattering of polarized neutrons (polarized GISANS). We exemplify this issue showing a combined OSS and GISANS study of the lateral correlations in a remanent polarizing supermirror

  14. Probing lateral magnetic nanostructures by polarized GISANS

    Science.gov (United States)

    Kentzinger, E.; Frielinghaus, H.; Rücker, U.; Ioffe, A.; Richter, D.; Brückel, Th.

    2007-07-01

    While structural and magnetic lateral correlations in thin film materials can be investigated at the μm length scale by neutron off-specular scattering (OSS) with polarization analysis, they can also be investigated at the nm length scale by grazing incidence small-angle scattering of polarized neutrons (polarized GISANS). We exemplify this issue showing a combined OSS and GISANS study of the lateral correlations in a remanent polarizing supermirror.

  15. Magnetic properties of TOAB-capped CuO nanoparticles.

    Science.gov (United States)

    Seehra, M.; Punnoose, A.; Mahamuni, S.

    2002-03-01

    Synthesis of CuO nanoparticles (NP) capped with TOAB (tetraoctylammonium bromide) and their structural properties were reported recently [1]. Here we report on the magnetic properties of the TOAB-capped CuO-NP of size 4, 6 and 10 nm and compare these properties with those of uncapped CuO-NP in the size range of 6.6-37 nm described in the above abstract [2] and in a recent publication [3]. Temperature (5 K 350 K) and magnetic field (up to 55 kOe) variations of magnetization M, coercivity H_c, exchange bias He (field-cooled in 55 kOe) and the Neel temperature TN (where He goes to zero) were measured. The TOAB-capped NP have higher magnitudes of Ms (the weak ferromagnetic component of M) and lower He values, confirming the 1/Ms variation of He observed in uncapped CuO-NP for size Magnone, Seehra & Bonevich, Phys. Rev. B64, 174420 (2001).

  16. The Mars water cycle at other epochs: Recent history of the polar caps and layered terrain

    Science.gov (United States)

    Jakosky, Bruce M.; Henderson, Bradley G.; Mellon, Michael T.

    1992-01-01

    The Martian polar caps and layered terrain presumably evolves by the deposition and removal of small amounts of water and dust each year, the current cap attributes therefore represent the incremental transport during a single year as integrated over long periods of time. The role was studied of condensation and sublimation of water ice in this process by examining the seasonal water cycle during the last 10(exp 7) yr. In the model, axial obliquity, eccentricity, and L sub s of perihelion vary according to dynamical models. At each epoch, the seasonal variations in temperature are calculated at the two poles, keeping track of the seasonal CO2 cap and the summertime sublimation of water vapor into the atmosphere; net exchange of water between the two caps is calculated based on the difference in the summertime sublimation between the two caps (or on the sublimation from one cap if the other is covered with CO2 frost all year). Results from the model can help to explain (1) the apparent inconsistency between the timescales inferred for layer formation and the much older crater retention age of the cap and (2) the difference in sizes of the two residual caps, with the south being smaller than the north.

  17. IR SPECTRAL MAPPING OF THE MARTIAN SOUTH POLAR RESIDUAL CAP USING CRISM

    Directory of Open Access Journals (Sweden)

    J. Campbell

    2016-06-01

    Full Text Available Polycyclic aromatic hydrocarbons (PAHs are considered to be important in theories of abiogenesis (Allamandola, 2011 . There is evidence that PAHs have been detected on two icy Saturnian satellites using the Visual and Infrared Mapping Spectrometer (VIMS on the Cassini spacecraft (Cruikshank et al., 2007. The hypothesised presence of PAHs in Mars south polar cap has not been systematically examined even though the Mars south polar cap may allow the preservation of organic molecules that are typically destroyed at the Martian surface by UV radiation (Dartnell et al. 2012. This hypothesis is supported by recent analyses of South Polar Residual Cap (SPRC structural evolution (Thomas et al., 2009 that suggest the possibility that seasonal and long term sublimation may excavate dust particles from within the polar ice. Periodic sublimation is believed to be responsible for the formation of so-called “Swiss Cheese Terrain”, a unique surface feature found only in the Martian south polar residual cap consisting of flat floored, circular depressions (Byrne, 2009. We show the first examples of work towards the detection of PAHs in Swiss Cheese Terrain, using data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM, on board NASA’s Mars Reconnaissance Orbiter (MRO. CRISM is designed to search for mineralogical indications of past and present water, thus providing extensive coverage of the south polar cap. In this work, we discuss whether CRISM infrared spectra can be used to detect PAHs in Swiss Cheese Terrain and demonstrate a number of maps showing shifts in spectral profiles over the SPRC.

  18. Mars seasonal polar caps as a test of the equivalence principle

    International Nuclear Information System (INIS)

    Rubincam, David Parry

    2011-01-01

    The seasonal polar caps of Mars can be used to test the equivalence principle in general relativity. The north and south caps, which are composed of carbon dioxide, wax and wane with the seasons. If the ratio of the inertial (passive) to gravitational (active) masses of the caps differs from the same ratio for the rest of Mars, then the equivalence principle fails, Newton's third law fails, and the caps will pull Mars one way and then the other with a force aligned with the planet's spin axis. This leads to a secular change in Mars's along-track position in its orbit about the Sun, and to a secular change in the orbit's semimajor axis. The caps are a poor Eoetvoes test of the equivalence principle, being 4 orders-of-magnitude weaker than laboratory tests and 7 orders-of-magnitude weaker than that found by lunar laser ranging; the reason is the small mass of the caps compared to Mars as a whole. The principal virtue of using Mars is that the caps contain carbon, an element not normally considered in such experiments. The Earth with its seasonal snow cover can also be used for a similar test.

  19. Mars Seasonal Polar Caps as a Test of the Equivalence Principle

    Science.gov (United States)

    Rubincam, Daivd Parry

    2011-01-01

    The seasonal polar caps of Mars can be used to test the equivalence principle in general relativity. The north and south caps, which are composed of carbon dioxide, wax and wane with the seasons. If the ratio of the inertial to gravitational masses of the caps differs from the same ratio for the rest of Mars, then the equivalence principle fails, Newton's third law fails, and the caps will pull Mars one way and then the other with a force aligned with the planet's spin axis. This leads to a secular change in Mars's along-track position in its orbit about the Sun, and to a secular change in the orbit's semimajor axis. The caps are a poor E6tv6s test of the equivalence principle, being 4 orders-of-magnitude weaker than laboratory tests and 7 orders-of-magnitude weaker than that found by lunar laser ranging; the reason is the small mass of the caps compared to Mars as a whole. The principal virtue of using Mars is that the caps contain carbon, an element not normally considered in such experiments. The Earth with its seasonal snow cover can also be used for a similar test.

  20. Method to locate the polar cap boundary in the nightside ionosphere and application to a substorm event

    Directory of Open Access Journals (Sweden)

    A. T. Aikio

    2006-08-01

    Full Text Available In this paper we describe a new method to be used for the polar cap boundary (PCB determination in the nightside ionosphere by using the EISCAT Svalbard radar (ESR field-aligned measurements by the 42-m antenna and southward directed low-elevation measurements by the ESR 32 m antenna or northward directed low-elevation measurements by the EISCAT VHF radar at Tromsø. The method is based on increased electron temperature (Te caused by precipitating particles on closed field lines. Since the Svalbard field-aligned measurement provides the reference polar cap Te height profile, the method can be utilised only when the PCB is located between Svalbard and the mainland. Comparison with the Polar UVI images shows that the radar-based method is generally in agreement with the PAE (poleward auroral emission boundary from Polar UVI. The new technique to map the polar cap boundary was applied to a substorm event on 6 November 2002. Simultaneous measurements by the MIRACLE magnetometers enabled us to put the PCB location in the framework of ionospheric electrojets. During the substorm growth phase, the polar cap expands and the region of the westward electrojet shifts gradually more apart from the PCB. The substorm onset takes place deep within the region of closed magnetic field region, separated by about 6–7° in latitude from the PCB in the ionosphere. We interpret the observations in the framework of the near-Earth neutral line (NENL model of substorms. After the substorm onset, the reconnection at the NENL reaches within 3 min the open-closed field line boundary and then the PCB moves poleward together with the poleward boundary of the substorm current wedge. The poleward expansion occurs in the form of individual bursts, which are separated by 2–10 min, indicating that the reconnection in the magnetotail neutral line is impulsive. The poleward expansions of the PCB are followed by latitude dispersed intensifications in the westward electrojet

  1. Magnetic polarization and two-phonon states

    International Nuclear Information System (INIS)

    Tsoneva, N.; Stoyanov, Ch.; Grinberg, M.; Vdovin, A.

    1997-01-01

    Influence of magnetic core polarization on properties of 2 - member of two-phonon quintet of states 2 1 + x 3 1 - is analyzed. Like for recently identified lowest 1 - member of this quintet, an excitation probability of 2 - state is strongly affected by polarization of the nucleus

  2. Commissioning Test of ATLAS End-Cap Toroidal Magnets

    CERN Document Server

    Dudarev, A; Foussat, A; Benoit, P; Jeckel, M; Olyunin, A; Kopeykin, N; Stepanov, V; Deront, L; Olesen, G; Ponts, X; Ravat, S; Sbrissa, K; Barth, J; Bremer, J; Delruelle, J; Metselaar, J; Pengo, R; Pirotte, O; Buskop, J; Baynham, D E; Carr, F S; Holtom, E

    2009-01-01

    The system of superconducting toroids in the ATLAS experiment at CERN consists of three magnets. The Barrel Toroid was assembled and successfully tested in 2006. Next, two End-Cap Toroids have been tested on surface at 77 K and installed in the cavern, 100-m underground. The End Cap Toroids are based on Al stabilized Nb-Ti/Cu Rutherford cables, arranged in double pancake coils and conduction cooled at 4.6 K. The nominal current is 20.5 kA at 4.1 T peak field in the windings and the stored energy is 250 MJ per toroid. Prior to final testing of the entire ATLAS Toroidal system, each End Cap Toroid passed a commissioning test up to 21 kA to guarantee a reliable performance in the final assembly. In this paper the test results are described. It includes the stages of test preparation, isolation vacuum pumping and leak testing, cooling down, step-by-step charging to full current, training quenches and quench recovery. By fast discharges the quench detection and protection system was checked to demonstrate a safe e...

  3. Case-study of the evolution of polar-cap currents and auroral electrojets during polar geomagnetic disturbances with IMS magnetometer data

    Energy Technology Data Exchange (ETDEWEB)

    Iijima, T.; Kim, J.S. (State Univ. of New York, Albany (USA). Atmospheric Sciences Research Center); Sugiura, M. (National Aeronautics and Space Administration, Greenbelt, MD (USA). Goddard Space Flight Center)

    1984-06-01

    By using 1 min average data from the US-Canada IMS network stations (Alaska, east-west and Fort Churchill chains) and also standard magnetograms from stations in the polar-cap region and in the auroral zone, we have examined the development of polar-cap currents and the relationship of their development to the evolution of auroral electrojets during individual polar geomagnetic disturbances. Characteristics that have been determined are reported and discussed.

  4. Black carbon aerosols and the third polar ice cap

    Energy Technology Data Exchange (ETDEWEB)

    Menon, Surabi; Koch, Dorothy; Beig, Gufran; Sahu, Saroj; Fasullo, John; Orlikowski, Daniel

    2010-04-15

    Recent thinning of glaciers over the Himalayas (sometimes referred to as the third polar region) have raised concern on future water supplies since these glaciers supply water to large river systems that support millions of people inhabiting the surrounding areas. Black carbon (BC) aerosols, released from incomplete combustion, have been increasingly implicated as causing large changes in the hydrology and radiative forcing over Asia and its deposition on snow is thought to increase snow melt. In India BC emissions from biofuel combustion is highly prevalent and compared to other regions, BC aerosol amounts are high. Here, we quantify the impact of BC aerosols on snow cover and precipitation from 1990 to 2010 over the Indian subcontinental region using two different BC emission inventories. New estimates indicate that Indian BC emissions from coal and biofuel are large and transport is expected to expand rapidly in coming years. We show that over the Himalayas, from 1990 to 2000, simulated snow/ice cover decreases by {approx}0.9% due to aerosols. The contribution of the enhanced Indian BC to this decline is {approx}36%, similar to that simulated for 2000 to 2010. Spatial patterns of modeled changes in snow cover and precipitation are similar to observations (from 1990 to 2000), and are mainly obtained with the newer BC estimates.

  5. Polarized neutron reflectometry of magnetic nanostructures

    Science.gov (United States)

    Toperverg, B. P.

    2015-12-01

    Among a number of methods employed to characterize various types of magnetic nano-structures Polarized Neutron Reflectometry (PNR) is shown to be a unique tool providing a scope of quantitative information on magnetization arrangement over relevant scales. Deeply penetrating into materials neutron spins are able to resolve vectorial profile of magnetic induction with accuracy of a fraction of Oersted over a fraction of nano-meters. This property is exploited in measurements of specular PNR which hence constitutes the method of depth resolved vector magnetometry widely used to examine magnetic states in exchange coupled magnetic superlattices, exchange bias systems, spin valves, exchange springs, superconducting/ferromagnetic heterostructure, etc. Off-specular polarized neutron scattering (OS-PNS) measures the in-plane magnetization distribution over scales from hundreds of nanoto hundreds of micrometers providing, in combination with specular PNR, access to lateral long range fluctuations of the magnetization vector and magnetic domains in these systems. OSPNS is especially useful in studies of co-operative magnetization reversal processes in various films and multilayers laterally patterned into periodic arrays of stripes, or islands of various dimentions, shapes, internal structures, etc., representing an interest for e.g. spintronics. Smaller sizes of 10?100 nm are accessed with the method of Polarized Neutrons Grazing Incidence Small Angle Scattering (PN-GISAS), which in a combination with specular PNR and OS-PNS is used to study self-assembling of magnetic nano-particles on flat surfaces, while Polarized Neutron Grazing Incidence Diffraction (PN-GID) complete the scope of magnetic information over wide range of scales in 3D space. The review of recent results obtained employing the methods listed above is preceded by the detailed theoretical consideration and exemplified by new developments addressing with PNR fast magnetic kinetics in nano-systems.

  6. Imaging of fast moving electron-density structures in the polar cap

    Directory of Open Access Journals (Sweden)

    C. N. Mitchell

    2007-06-01

    Full Text Available The imaging of fast-moving electron-density structures in the polar cap presents a unique set of challenges that are not encountered in other ionospheric imaging problems. GPS observations of total electron content in the polar cap are sparse compared to other regions in the Northern Hemisphere. Furthermore, the slow relative motion of the satellites across the sky complicates the problem since the velocity of the plasma can be large in comparison and traditional approaches could result in image blurring. This paper presents a Kalman-filter based method that incorporates a forward projection of the solution based on a model plasma drift velocity field. This is the first time that the plasma motion, rather than just integrations of electron density, has been used in an ionospheric imaging algorithm. The motion is derived from the Weimer model of the electric field. It is shown that this novel approach to the implementation of a Kalman filter provides a detailed view of the polar cap ionosphere under severe storm conditions. A case study is given for the October 2003 Halloween storm where verification is provided by incoherent scatter radars.

  7. Layered magnets: polarized neutron reflection studies

    Energy Technology Data Exchange (ETDEWEB)

    Zabel, H.; Schreyer, A. [Ruhr-Univ. Bochum, Lehrstuhl fuer Experimentalphysik/Festkoerperphysik, Bochum (Germany)

    1996-11-01

    Neutron reflectivity measurements from extended surfaces, thin films and superlattices provide information on the chemical profile parallel to the film normal, including film thicknesses, average composition and interfacial roughness parameters. Reflectivity measurements with polarized neutrons are particularly powerful for analyzing the magnetic density profiles in thin films and superlattices in addition to chemical profiles. The basic theory of polarized neutron reflectivity is provided, followed by some examples and more recent applications concerning polarized neutron reflectivity studies from exchange coupled Fe/Cr superlattices. (author) 5 figs., 13 refs.

  8. On determining the noon polar cap boundary from SuperDARN HF radar backscatter characteristics

    Directory of Open Access Journals (Sweden)

    M. Pinnock

    Full Text Available Previous work has shown that ionospheric HF radar backscatter in the noon sector can be used to locate the footprint of the magnetospheric cusp particle precipitation. This has enabled the radar data to be used as a proxy for the location of the polar cap boundary, and hence measure the flow of plasma across it to derive the reconnection electric field in the ionosphere. This work used only single radar data sets with a field of view limited to ~2 h of local time. In this case study using four of the SuperDARN radars, we examine the boundary determined over 6 h of magnetic local time around the noon sector and its relationship to the convection pattern. The variation with longitude of the latitude of the radar scatter with cusp characteristics shows a bay-like feature. It is shown that this feature is shaped by the variation with longitude of the poleward flow component of the ionospheric plasma and may be understood in terms of cusp ion time-of-flight effects. Using this interpretation, we derive the time-of-flight of the cusp ions and find that it is consistent with approximately 1 keV ions injected from a subsolar reconnection site. A method for deriving a more accurate estimate of the location of the open-closed field line boundary from HF radar data is described.

    Key words: Ionosphere (ionosphere–magnetosphere interactions; plasma convection · Magnetospheric physics (magnetopause · cusp · and boundary layers

  9. Estimation of Polar Cap Potential and the Role of PC Index

    Directory of Open Access Journals (Sweden)

    Ga-Hee Moon

    2012-09-01

    Full Text Available Polar cap potential has long been considered as an indicator for the amount of energy flowing in the magnetosphere-ionosphere system. Thus, the estimation of polar cap potential is important to understand the physical process of the magnetosphere. To estimate the polar cap potential in the Northern Hemisphere, merging electric field by Kan & Lee (1979 is adopted. Relationships between the PC index and calculated merging electric field (E* are examined during full-time and storm-time periods separately. For this purpose Dst, AL, and PC indices and solar wind data are utilized during the period from 1996-2003. From this linear relationship, polar cap potential (Φ* is estimated using the formula by Doyle & Burke (1983. The values are represented as 58.1 ± 26.9 kV for the full-time period and 123.7 ± 84.1 kV for a storm-time period separately. Considering that the average value of polar cap potential of Doyle & Burke (1983 is about 47 kV during moderately quiet intervals with the S3-2 measurements, these results are similar to such. The monthly averaged variation of Dst, AL, and PC indices are then compared. The Dst and AL indices show distinct characteristics with peaks during equinoctial season whereas the average PC index according to the month shows higher values in autumn than in spring. The monthly variations of the linear correlation coefficients between solar wind parameters and geomagnetic indices are also examined. The PC-AL linear correlation coefficient is highest, being 0.82 with peaks during the equinoctial season. As with the AL index, the PC index may also prove useful for predicting the intensity of an auroral substorm. Generally, the linear correlation coefficients are shown low in summer due to conductance differences and other factors. To assess the role of the PC index during the recovery phase of a storm, the relation between the cumulative PC index and the duration is examined. Although the correlation coefficient lowers

  10. Spin-polarized deuterium in magnetic traps

    International Nuclear Information System (INIS)

    Koelman, J.M.V.A.; Stoof, H.T.C.; Verhaar, B.J.; Walraven, J.T.M.

    1987-01-01

    We have calculated the spin-exchange two-body rate constants associated with the population dynamics of the hyperfine levels of atomic deuterium as a function of magnetic field in the Boltzmann zero-temperature limit. Results indicate that a gas of low-field--seeking deuterium atoms trapped in a static magnetic field minimum decays rapidly into an ultrastable gas of doubly spin-polarized deuterium. We also discuss the temperature dependence of various effects

  11. Mars Water Ice and Carbon Dioxide Seasonal Polar Caps: GCM Modeling and Comparison with Mars Express Omega Observations

    Science.gov (United States)

    Forget, F.; Levrard, B.; Montmessin, F.; Schmitt, B.; Doute, S.; Langevin, Y.; Bibring, J. P.

    2005-01-01

    To better understand the behavior of the Mars CO2 ice seasonal polar caps, and in particular interpret the the Mars Express Omega observations of the recession of the northern seasonal cap, we present some simulations of the Martian Climate/CO2 cycle/ water cycle as modeled by the Laboratoire de Meteorologie Dynamique (LMD) global climate model.

  12. A new method to reconstruct the ionospheric convection patterns in the polar cap

    Directory of Open Access Journals (Sweden)

    P. L. Israelevich

    1999-06-01

    Full Text Available A new method to reconstruct the instantaneous convection pattern in the Earth's polar ionosphere is suggested. Plasma convection in the polar cap ionosphere is described as a hydrodynamic incompressible flow. This description is valid in the region where the electric currents are field aligned (and hence, the Lorentz body force vanishes. The problem becomes two-dimensional, and may be described by means of stream function. The flow pattern may be found as a solution of the boundary value problem for stream function. Boundary conditions should be provided by measurements of the electric field or plasma velocity vectors along the satellite orbits. It is shown that the convection pattern may be reconstructed with a reasonable accuracy by means of this method, by using only the minimum number of satellite crossings of the polar cap. The method enables us to obtain a reasonable estimate of the convection pattern without knowledge of the ionospheric conductivity.Key words. Ionosphere (modelling and forecasting; plasma convection; polar ionosphere

  13. A new method to reconstruct the ionospheric convection patterns in the polar cap

    Directory of Open Access Journals (Sweden)

    P. L. Israelevich

    Full Text Available A new method to reconstruct the instantaneous convection pattern in the Earth's polar ionosphere is suggested. Plasma convection in the polar cap ionosphere is described as a hydrodynamic incompressible flow. This description is valid in the region where the electric currents are field aligned (and hence, the Lorentz body force vanishes. The problem becomes two-dimensional, and may be described by means of stream function. The flow pattern may be found as a solution of the boundary value problem for stream function. Boundary conditions should be provided by measurements of the electric field or plasma velocity vectors along the satellite orbits. It is shown that the convection pattern may be reconstructed with a reasonable accuracy by means of this method, by using only the minimum number of satellite crossings of the polar cap. The method enables us to obtain a reasonable estimate of the convection pattern without knowledge of the ionospheric conductivity.

    Key words. Ionosphere (modelling and forecasting; plasma convection; polar ionosphere

  14. Motion of the dayside polar cap boundary during substorm cycles: II. Generation of poleward-moving events and polar cap patches by pulses in the magnetopause reconnection rate

    Directory of Open Access Journals (Sweden)

    M. Lockwood

    2005-12-01

    Full Text Available Using data from the EISCAT (European Incoherent Scatter VHF and CUTLASS (Co-operative UK Twin-Located Auroral Sounding System HF radars, we study the formation of ionospheric polar cap patches and their relationship to the magnetopause reconnection pulses identified in the companion paper by Lockwood et al. (2005. It is shown that the poleward-moving, high-concentration plasma patches observed in the ionosphere by EISCAT on 23 November 1999, as reported by Davies et al. (2002, were often associated with corresponding reconnection rate pulses. However, not all such pulses generated a patch and only within a limited MLT range (11:00-12:00 MLT did a patch result from a reconnection pulse. Three proposed mechanisms for the production of patches, and of the concentration minima that separate them, are analysed and evaluated: (1 concentration enhancement within the patches by cusp/cleft precipitation; (2 plasma depletion in the minima between the patches by fast plasma flows; and (3 intermittent injection of photoionisation-enhanced plasma into the polar cap. We devise a test to distinguish between the effects of these mechanisms. Some of the events repeat too frequently to apply the test. Others have sufficiently long repeat periods and mechanism (3 is shown to be the only explanation of three of the longer-lived patches seen on this day. However, effect (2 also appears to contribute to some events. We conclude that plasma concentration gradients on the edges of the larger patches arise mainly from local time variations in the subauroral plasma, via the mechanism proposed by Lockwood et al. (2000.

  15. Identifications of the polar cap boundary and the auroral belt in the high-altitude magnetosphere: a model for field-aligned currents

    International Nuclear Information System (INIS)

    Sugiura, M.

    1975-01-01

    By means of the Ogo 5 Goddard Space Flight Center fluxgate magnetometer data the polar cap boundary is identified in the high-altitude magnetosphere by a sudden transition from a dipolar field to a more taillike configuration. It is inferred that there exists a field-aligned-current layer at the polar cap boundary. In the night side magnetosphere the polar cap boundary is identified as the high-latitude boundary of the plasma sheet. The field-aligned current flows downward to the ionosphere on the morning side of the magnetosphere and upward from the ionosphere on the afternoon side. The basic pattern of the magnetic field variations observed during the satellite's traversal of the auroral belt is presented. Currents flow in opposite directions in the two field-aligned-current layers. The current directions in these layers as observed by Ogo 5 in the high-altitude magnetosphere are the same as those observed at low altitudes by the polar-orbiting Triad satellite (Armstrong and Zmuda, 1973). The magnetic field in the region where the lower-latitude field-aligned-current layer is situated is essentially meridional. A model is presented in which two field-aligned-current systems, one at the polar cap boundary and the other on the low-latitude part of the auroral belt, are main []y connected by ionospheric currents flowing across the auroral belt. The existence of field-aligned currents deduced from the Ogo 5 observations is a permanent feature of the magnetosphere. Intensifications of the field-aligned currents and occurrences of multiple pairs of field-aligned-current layers characterize the disturbed conditions of these regions

  16. Polarized radiation in magnetic white dwarfs

    International Nuclear Information System (INIS)

    Rosi, L.A.; Zimmerman, R.L.; Kemp, J.C.

    1976-01-01

    A model for magnetic white dwarfs is proposed which attributes the partially polarized light to synchrotron radiation. The source of the radiation is relativistic electrons trapped in the magnetosphere of a white dwarf. The white dwarf's magnetic field is assumed to be dipolar. The Stokes parameters for the synchrotron radiation are tabulated as a function of frequency, observer's orientation, and energy and spatial distribution of the relativistic electrons. The results of the synchrotron calculations are applied to the polarization observations of Grw+70degree8247 and DQ Herculis. This model can account for the major features of the polarized radiation coming from these two magnetic white dwarfs. The calculations predict for Grw+70degree8247 that the surface magnetic field is B/sub s/approximately-less-than4 x 10 6 gauss, that the incident viewing angle is 45degreeapproximately-less-thantheta 0 approximately-less-than75degree, and that the electrons are trapped with nearly an isotropic distribution about the white dwarf. For DQ Herculis the surface magnetic field is B/sub s/approximately-less-than7 x 10 6 gauss and the trapped electrons are confined to a dislike region about the white dwarf. For both cases the density of electrons in the magnetosphere falls in the range of 10 5 approximately-less-thannapproximately-less-than10 7 cm -3 with energies of about 4--35 MeV

  17. Drifting field-aligned density structures in the night-side polar cap

    Czech Academy of Sciences Publication Activity Database

    Santolík, Ondřej; Persoon, A. M.; Gurnett, D. A.; Décréau, P. M. E.; Pickett, J. S.; Maršálek, O.; Maksimovic, M.; Cornilleau-Wehrlin, N.

    2005-01-01

    Roč. 32, - (2005), L06106-1 ISSN 0094-8276 R&D Projects: GA ČR(CZ) GA202/03/0832; GA MŠk ME 650; GA MŠk 1P05ME811 Grant - others: NASA (US) NAG5-9974; NASA (US) NNG04GB98G; NSF(US) 0307319; ESA PECS(XE) 98025 Institutional research plan: CEZ:AV0Z30420517 Keywords : Magnetospheric Physics * Plasma convection * Plasma waves and instabilities * Polar cap phenomena * Magnetospheric configuration and dynamics Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 2.491, year: 2005

  18. The Polar BEAR magnetic field experiment

    Science.gov (United States)

    Bythrow, P. F.; Potemra, T. A.; Zanetti, L. J.; Mobley, F. F.; Scheer, L.; Radford, W. E.

    1987-09-01

    The objectives and the instrumentation of the Polar BEAR magnetic field experiment are described along with the preliminary results from simultaneous measurements of Birkeland currents and UV auroral emissions. The experiment consists of an integrated sensor head, analog electronics, and digital electronics. The sensor head is a single unit containing sensor windings for each of the three orthogonal axes, oriented parrallel to the spacecraft coordinates; to minimize interference from spacecraft-generated magnetic fields, the sensor unit is located at the end of the +y solar panel. The digital electronics package is essentially identical to that flown on HILAT. A signal processor digitizes the analog outputs of the three orthogonal axes of the flux-gate magnetometer to a 13-bit resolution, yielding a magnetic field range of + or - 63,000 nT and a resolution of 15.2 nT. The full-resolution magnetic field values are recovered by data processing techniques on the ground.

  19. The 1997 Spring Regression of the Martian South Polar Cap: Mars Orbiter Camera Observations

    Science.gov (United States)

    James, P.B.; Cantor, B.A.; Malin, M.C.; Edgett, K.; Carr, M.H.; Danielson, G.E.; Ingersoll, A.P.; Davies, M.E.; Hartmann, W.K.; McEwen, A.S.; Soderblom, L.A.; Thomas, P.C.; Veverka, J.

    2000-01-01

    The Mars Orbiter cameras (MOC) on Mars Global Surveyor observed the south polar cap of Mars during its spring recession in 1997. The images acquired by the wide angle cameras reveal a pattern of recession that is qualitatively similar to that observed by Viking in 1977 but that does differ in at least two respects. The 1977 recession in the 0o to 120o longitude sector was accelerated relative to the 1997 observations after LS = 240o; the Mountains of Mitchel also detached from the main cap earlier in 1997. Comparison of the MOC images with Mars Orbiter Laser Altimeter data shows that the Mountains of Mitchel feature is controlled by local topography. Relatively dark, low albedo regions well within the boundaries of the seasonal cap were observed to have red-to-violet ratios that characterize them as frost units rather than unfrosted or partially frosted ground; this suggests the possibility of regions covered by CO2 frost having different grain sizes.

  20. Automated identification and tracking of polar-cap plasma patches at solar minimum

    Directory of Open Access Journals (Sweden)

    R. Burston

    2014-03-01

    Full Text Available A method of automatically identifying and tracking polar-cap plasma patches, utilising data inversion and feature-tracking methods, is presented. A well-established and widely used 4-D ionospheric imaging algorithm, the Multi-Instrument Data Assimilation System (MIDAS, inverts slant total electron content (TEC data from ground-based Global Navigation Satellite System (GNSS receivers to produce images of the free electron distribution in the polar-cap ionosphere. These are integrated to form vertical TEC maps. A flexible feature-tracking algorithm, TRACK, previously used extensively in meteorological storm-tracking studies is used to identify and track maxima in the resulting 2-D data fields. Various criteria are used to discriminate between genuine patches and "false-positive" maxima such as the continuously moving day-side maximum, which results from the Earth's rotation rather than plasma motion. Results for a 12-month period at solar minimum, when extensive validation data are available, are presented. The method identifies 71 separate structures consistent with patch motion during this time. The limitations of solar minimum and the consequent small number of patches make climatological inferences difficult, but the feasibility of the method for patches larger than approximately 500 km in scale is demonstrated and a larger study incorporating other parts of the solar cycle is warranted. Possible further optimisation of discrimination criteria, particularly regarding the definition of a patch in terms of its plasma concentration enhancement over the surrounding background, may improve results.

  1. Plasma Irregularities on the Leading and Trailing Edges of Polar Cap Patches

    Science.gov (United States)

    Lamarche, L. J.; Varney, R. H.; Gillies, R.; Chartier, A.; Mitchell, C. N.

    2017-12-01

    Plasma irregularities in the polar cap have often been attributed to the gradient drift instability (GDI). Traditional fluid theories of GDI predicts irregularity growth only on the trailing edge of polar patches, where the plasma density gradient is parallel to the plasma drift velocity, however many observations show irregularities also form on the leading edge of patches. We consider decameter-scale irregularities detected by polar-latitude SuperDARN (Super Dual Auroral Radar Network) radars with any relationship between the background density gradients and drift velocity. Global electron density from the Multi-Instrument Data Analysis System (MIDAS), a GPS tomography routine, is used to provide context for where irregularities are observed relative to polar patches and finer-scale background density gradients are found from 3D imaging from both the North and Canada faces of the Resolute Bay Incoherent Scatter Radars (RISR-N and RISR-C) jointly. Shear-based instabilities are considered as mechanisms by which plasma irregularities could form on the leading edge of patches. Theoretical predictions of instability growth from both GDI and shear instabilities are compared with irregularity observations for the October 13, 2016 storm.

  2. Spherical cap modelling of Orsted magnetic field vectors over southern Africa

    CSIR Research Space (South Africa)

    Kotze, PB

    2001-01-01

    Full Text Available Vector magnetic field observations by the Orsted satellite during geomagnetic quiet conditions around January 1, 2000, have been employed to derive a spherical cap harmonic model (Haines, 1985) over the southern African region between 10 degrees...

  3. 24/7 Solar Minimum Polar Cap and Auroral Ion Temperature Observations

    Science.gov (United States)

    Sojka, Jan J.; Nicolls, Michael; van Eyken, Anthony; Heinselman, Craig; Bilitza, Dieter

    2011-01-01

    During the International Polar Year (IPY) two Incoherent Scatter Radars (ISRs) achieved close to 24/7 continuous observations. This presentation describes their data sets and specifically how they can provide the International Reference Ionosphere (IRI) a fiduciary E- and F-region ionosphere description for solar minimum conditions in both the auroral and polar cap regions. The ionospheric description being electron density, ion temperature and electron temperature profiles from as low as 90 km extending to several scale heights above the F-layer peak. The auroral location is Poker Flat in Alaska at 65.1 N latitude, 212.5 E longitude where the NSF s new Poker Flat Incoherent Scatter Radar (PFISR) is located. This location during solar minimum conditions is in the auroral region for most of the day but is at midlatitudes, equator ward of the cusp, for about 4-8 h per day dependent upon geomagnetic activity. In contrast the polar location is Svalbard, at 78.2 N latitude, 16.0 E longitude where the EISCAT Svalbard Radar (ESR) is located. For most of the day the ESR is in the Northern Polar Cap with a noon sector passage often through the dayside cusp. Of unique relevance to IRI is that these extended observations have enabled the ionospheric morphology to be distinguished between quiet and disturbed geomagnetic conditions. During the IPY year, 1 March 2007 - 29 February 2008, about 50 solar wind Corotating Interaction Regions (CIRs) impacted geospace. Each CIR has a two to five day geomagnetic disturbance that is observed in the ESR and PFISR observations. Hence, this data set also enables the quiet-background ionospheric climatology to be established as a function of season and local time. These two separate climatologies for the ion temperature at an altitude of 300 km are presented and compared with IRI ion temperatures. The IRI ion temperatures are about 200-300 K hotter than the observed values. However, the MSIS neutral temperature at 300 km compares favorably

  4. Plasma drifts associated with a system of sun-aligned arcs in the polar cap

    International Nuclear Information System (INIS)

    Mende, S.B.; Doolittle, J.H.; Robinson, R.M.; Vondrak, R.R.; Rich, F.J.

    1988-01-01

    A series of four sun-aligned arcs passed over Sondre Stromfjord, Greenland, on the night of the 17th and 18th of February, 1985. Observations of these arcs were made using the Sondrestrom incoherent scatter radar and an intensified all-sky imaging TV system that was operated at the radar site. The first of the four arcs crossed the Sondre Stromfjord meridian just before local midnight moving westward, and the other three arcs followed at approximately half-hour intervals. When we account for the earth's rotation, the arc drift in an inertial frame was eastward, or dusk to dawn. The half-hour interval between meridian crossings of the arcs implies that the mean spacing between the arcs was 180 km. A Defense Meteorological Satellite Program (DMSP) F6 satellite pass at 0110 UT revealed the presence of highly structured electron and ion precipitation throughout the polar cap. The DMSP visible imager detected a single, sun-aligned arc associated with the largest peak in precipitating electron flux. This arc was also observed at Thule, Greenland, with an intensified film camera. These observations suggest that at least one of the arcs that were observed at Sondre Stromfjord extended across a large part of the polar cap. The radar at Sondre Stromfjord measured electron density and ion drift velocities associated with the four arcs. The radar drift measurements were superimposed on the all-sky video images to determine the location of the measurements relative to the arcs. Plasma drifts outside the arcs were found to be both sunward and antisunward, while within the arcs the drifts were predominantly antisunward. The variability of the drifts in the direction parallel to the arcs indicates that the electric fields were highly structured even though the configuration and motion of the arcs were well behaved

  5. Influence of physicochemical interactions of capping agent on magnetic properties of magnetite nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Sathish, S.; Balakumar, S., E-mail: balasuga@yahoo.com

    2016-04-15

    The properties of nanoparticles can be significantly altered by surface modification. In this present work the effect of surface inorganic–organic interactions on magnetic properties of magnetite nanoparticles have been investigated. Hence the mercaptopropionic acid (MPA) and ethylene diamine (EDA) capped magnetite nanoparticles have been prepared by polyol method. The magnetic study signifies that all the samples prepared by this method possess superparamagnetic behavior. The as-prepared, calcinated and EDA capped nanoparticles exhibit non saturation behavior, the MPA capped sample approach the saturation state and exhibit high value of magnetization whereas its calcinated sample shows complete saturation. The XRD results reveal that all the particles have nearly similar grain size so it is believed that the significant differences in magnetic properties are caused by the different interactions between the surface iron atoms and organic molecules. The XPS analysis indicates that sulfur atoms present in the MPA are chemically bonded with the surface iron atoms on the other hand, the EDA is physically adsorbed on iron oxide nanoparticles. Herein, we analyze and propose the possible interactions that could occur between the surface iron atoms and capping agent thereby influencing the magnetic properties of the nanoparticles. - Graphical abstract: The part of the MPA capping agent is chemically attached on the surface of iron atom through sulfur atom and part of them are attached via carboxylate group. - Highlights: • Organic capped magnetite nanoparticles have been prepared by polyol method. • The crystal structure and morphological analysis were studied by XRD, FESEM. • Ethylene diamine (EDA) capped nanoparticles exhibit non saturation behavior. • Mercaptopropionic acid (MPA) capped nanoparticles approaching the saturation state. • Sulfur atom present in the MPA is chemically bonded with surface iron atom.

  6. Origin of interfacial perpendicular magnetic anisotropy in MgO/CoFe/metallic capping layer structures

    Science.gov (United States)

    Peng, Shouzhong; Wang, Mengxing; Yang, Hongxin; Zeng, Lang; Nan, Jiang; Zhou, Jiaqi; Zhang, Youguang; Hallal, Ali; Chshiev, Mairbek; Wang, Kang L.; Zhang, Qianfan; Zhao, Weisheng

    2015-12-01

    Spin-transfer-torque magnetic random access memory (STT-MRAM) attracts extensive attentions due to its non-volatility, high density and low power consumption. The core device in STT-MRAM is CoFeB/MgO-based magnetic tunnel junction (MTJ), which possesses a high tunnel magnetoresistance ratio as well as a large value of perpendicular magnetic anisotropy (PMA). It has been experimentally proven that a capping layer coating on CoFeB layer is essential to obtain a strong PMA. However, the physical mechanism of such effect remains unclear. In this paper, we investigate the origin of the PMA in MgO/CoFe/metallic capping layer structures by using a first-principles computation scheme. The trend of PMA variation with different capping materials agrees well with experimental results. We find that interfacial PMA in the three-layer structures comes from both the MgO/CoFe and CoFe/capping layer interfaces, which can be analyzed separately. Furthermore, the PMAs in the CoFe/capping layer interfaces are analyzed through resolving the magnetic anisotropy energy by layer and orbital. The variation of PMA with different capping materials is attributed to the different hybridizations of both d and p orbitals via spin-orbit coupling. This work can significantly benefit the research and development of nanoscale STT-MRAM.

  7. Controlling vortex chirality and polarity by geometry in magnetic nanodots

    OpenAIRE

    Agramunt Puig, Sebastià

    2014-01-01

    The independent control of both vortex chirality and polarity is a significant challenge in magnetic devices based on nano-sized magnetic vortex structures. By micromagnetic simulations here, we show that in soft ferromagnetic nanodots with an adequate modulated thickness, the desired combination of chirality and polarity can be achieved just by changing the direction of the in-plane applied magnetic field. Despite the complex behavior, the vortex chirality and polarity control can be summari...

  8. IDENTIFYING SURFACE CHANGES ON HRSC IMAGES OF THE MARS SOUTH POLAR RESIDUAL CAP (SPRC

    Directory of Open Access Journals (Sweden)

    A. R. D. Putri

    2016-06-01

    Full Text Available The surface of Mars has been an object of interest for planetary research since the launch of Mariner 4 in 1964. Since then different cameras such as the Viking Visual Imaging Subsystem (VIS, Mars Global Surveyor (MGS Mars Orbiter Camera (MOC, and Mars Reconnaissance Orbiter (MRO Context Camera (CTX and High Resolution Imaging Science Experiment (HiRISE have been imaging its surface at ever higher resolution. The High Resolution Stereo Camera (HRSC on board of the European Space Agency (ESA Mars Express, has been imaging the Martian surface, since 25th December 2003 until the present-day. HRSC has covered 100 % of the surface of Mars, about 70 % of the surface with panchromatic images at 10-20 m/pixel, and about 98 % at better than 100 m/pixel (Neukum et. al., 2004, including the polar regions of Mars. The Mars polar regions have been studied intensively recently by analysing images taken by the Mars Express and MRO missions (Plaut et al., 2007. The South Polar Residual Cap (SPRC does not change very much in volume overall but there are numerous examples of dynamic phenomena associated with seasonal changes in the atmosphere. In particular, we can examine the time variation of layers of solid carbon dioxide and water ice with dust deposition (Bibring, 2004, spider-like channels (Piqueux et al., 2003 and so-called Swiss Cheese Terrain (Titus et al., 2004. Because of seasonal changes each Martian year, due to the sublimation and deposition of water and CO2 ice on the Martian south polar region, clearly identifiable surface changes occur in otherwise permanently icy region. In this research, good quality HRSC images of the Mars South Polar region are processed based on previous identification as the optimal coverage of clear surfaces (Campbell et al., 2015. HRSC images of the Martian South Pole are categorized in terms of quality, time, and location to find overlapping areas, processed into high quality Digital Terrain Models (DTMs and

  9. Multi-station basis for Polar Cap (PC) indices: ensuring credibility and operational reliability

    Science.gov (United States)

    Stauning, Peter

    2018-02-01

    The Polar Cap (PC) indices, PCN (North) and PCS (South) are based on polar geomagnetic observations from Qaanaaq (Thule) and Vostok, respectively, processed to measure the transpolar plasma convection that may seriously affect space weather conditions. To establish reliable space weather forecasts based on PC indices, and also to ensure credibility of their use for scientific analyses of solar wind-magnetosphere interactions, additional sources of data for the PC indices are investigated. In the search for alternative index sources, objective quality criteria are established here to be used for the selection among potential candidates. These criteria are applied to existing PC index series to establish a quality scale. In the Canadian region, the data from Resolute Bay magnetometer are shown to provide alternative PCN indices of adequate quality. In Antarctica, the data from Concordia Dome-C observatory are shown to provide basis for alternative PCS indices. In examples to document the usefulness of these alternative index sources it is shown that PCN indices in a real-time version based on magnetometer data from Resolute Bay could have given 6 h of early warning, of which the last 2 h were "red alert", up to the onset of the strong substorm event on 13 March 1989 that caused power outage in Quebec. The alternative PCS indices based on data from Dome-C have helped to disclose that presently available Vostok-based PCS index values are corrupted throughout most of 2011.

  10. Multi-station basis for Polar Cap (PC indices: ensuring credibility and operational reliability

    Directory of Open Access Journals (Sweden)

    Stauning Peter

    2018-01-01

    Full Text Available The Polar Cap (PC indices, PCN (North and PCS (South are based on polar geomagnetic observations from Qaanaaq (Thule and Vostok, respectively, processed to measure the transpolar plasma convection that may seriously affect space weather conditions. To establish reliable space weather forecasts based on PC indices, and also to ensure credibility of their use for scientific analyses of solar wind-magnetosphere interactions, additional sources of data for the PC indices are investigated. In the search for alternative index sources, objective quality criteria are established here to be used for the selection among potential candidates. These criteria are applied to existing PC index series to establish a quality scale. In the Canadian region, the data from Resolute Bay magnetometer are shown to provide alternative PCN indices of adequate quality. In Antarctica, the data from Concordia Dome-C observatory are shown to provide basis for alternative PCS indices. In examples to document the usefulness of these alternative index sources it is shown that PCN indices in a real-time version based on magnetometer data from Resolute Bay could have given 6 h of early warning, of which the last 2 h were “red alert”, up to the onset of the strong substorm event on 13 March 1989 that caused power outage in Quebec. The alternative PCS indices based on data from Dome-C have helped to disclose that presently available Vostok-based PCS index values are corrupted throughout most of 2011.

  11. Non-covalent synthesis of calix[4]arene-capped porphyrins in polar solvents via ionic interactions

    NARCIS (Netherlands)

    Fiammengo, R.; Timmerman, P.; Huskens, Jurriaan; Versluis, Kees; Heck, Albert J.R.; Reinhoudt, David

    2002-01-01

    Non-covalent synthesis of calix[4]arene capped porphyrins can be achieved in polar solvents (up to 45% molar fraction of water) via ionic interaction. Thus tetracationic meso-tetrakis(N-alkylpyridinium-3-yl) porphyrins 1a–d and tetra anionic 25,26,27,28-tetrakis(2-ethoxyethoxy)-calix[4]arene

  12. An unusual giant spiral arc in the polar cap region during the northward phase of a Coronal Mass Ejection

    Directory of Open Access Journals (Sweden)

    L. Rosenqvist

    2007-03-01

    Full Text Available The shock arrival of an Interplanetary Coronal Mass Ejection (ICME at ~09:50 UT on 22 November 1997 resulted in the development of an intense (Dst<−100 nT geomagnetic storm at Earth. In the early, quiet phase of the storm, in the sheath region of the ICME, an unusual large spiral structure (diameter of ~1000 km was observed at very high latitudes by the Polar UVI instrument. The evolution of this structure started as a polewardly displaced auroral bulge which further developed into the spiral structure spreading across a large part of the polar cap. This study attempts to examine the cause of the chain of events that resulted in the giant auroral spiral. During this period the interplanetary magnetic field (IMF was dominantly northward (Bz>25 nT with a strong duskward component (By>15 nT resulting in a highly twisted tail plasma sheet. Geotail was located at the equatorial dawnside magnetotail flank and observed accelerated plasma flows exceeding the solar wind bulk velocity by almost 60%. These flows are observed on the magnetosheath side of the magnetopause and the acceleration mechanism is proposed to be typical for strongly northward IMF. Identified candidates to the cause of the spiral structure include a By induced twisted magnetotail configuration, the development of magnetopause surface waves due to the enhanced pressure related to the accelerated magnetosheath flows aswell as the formation of additional magnetopause deformations due to external solar wind pressure changes. The uniqeness of the event indicate that most probably a combination of the above effects resulted in a very extreme tail topology. However, the data coverage is insufficient to fully investigate the physical mechanism behind the observations.

  13. Polarization transfer in relativistic magnetized plasmas

    Science.gov (United States)

    Heyvaerts, Jean; Pichon, Christophe; Prunet, Simon; Thiébaut, Jérôme

    2013-04-01

    The polarization transfer coefficients of a relativistic magnetized plasma are derived. These results apply to any momentum distribution function of the particles, isotropic or anisotropic. Particles interact with the radiation either in a non-resonant mode when the frequency of the radiation exceeds their characteristic synchrotron emission frequency or quasi-resonantly otherwise. These two classes of particles contribute differently to the polarization transfer coefficients. For a given frequency, this dichotomy corresponds to a regime change in the dependence of the transfer coefficients on the parameters of the particle's population, since these parameters control the relative weight of the contribution of each class of particles. Our results apply to either regimes as well as the intermediate one. The derivation of the transfer coefficients involves an exact expression of the conductivity tensor of the relativistic magnetized plasma that has not been used hitherto in this context. Suitable expansions valid at frequencies much larger than the cyclotron frequency allow us to analytically perform the summation over all resonances at high harmonics of the relativistic gyrofrequency. The transfer coefficients are represented in the form of two-variable integrals that can be conveniently computed for any set of parameters by using Olver's expansion of high-order Bessel functions. We particularize our results to a number of distribution functions, isotropic, thermal or power law, with different multipolar anisotropies of low order, or strongly beamed. Specifically, earlier exact results for thermal distributions are recovered. For isotropic distributions, the Faraday coefficients are expressed in the form of a one-variable quadrature over energy, for which we provide the kernels in the high-frequency limit and in the asymptotic low-frequency limit. An interpolation formula extending over the full energy range is proposed for these kernels. A similar reduction to a

  14. The temporal and spatial variations of low frequency geomagnetic pulsations at polar cusp and cap latitudes

    Directory of Open Access Journals (Sweden)

    J. Bitterly

    1999-06-01

    Full Text Available Geomagnetic field measurements at two Antarctic stations are compared during two weeks in the local summer (January 1-15, 1992. Low frequency (0.6-6 mHz pulsations are observed at each station near local magnetic noon. The same wave packets appear in some cases also at the other station, although with a significant attenuation, more clearly in the morning sector; the waves show a near noon reversal of the polarization sense from counter-clockwise in the morning to clockwise in the afternoon indicating a westward and an eastward propagation, respectively.

  15. Synthesis, Characterization, and Magnetic Properties of Pure and EDTA-Capped NiO Nanosized Particles

    Directory of Open Access Journals (Sweden)

    H. T. Rahal

    2017-01-01

    Full Text Available The effect of ethylenediaminetetraacetic acid (EDTA as a capping agent on the structure, morphology, optical, and magnetic properties of nickel oxide (NiO nanosized particles, synthesized by coprecipitation method, was investigated. Nickel chloride hexahydrate and sodium hydroxide (NaOH were used as precursors. The resultant nanoparticles were characterized by X-ray diffraction (XRD, transmission electron microscopy (TEM, and scanning electron microscopy (SEM. XRD patterns showed that NiO have a face-centered cubic (FCC structure. The crystallite size, estimated by Scherrer formula, has been found in the range of 28–33 nm. It is noticed that EDTA-capped NiO nanoparticles have a smaller size than pure nanoparticles. Thus, the addition of 0.1 M capping agent EDTA can form a nucleation point for nanoparticles growth. The optical and magnetic properties were investigated by Fourier transform infrared spectroscopy (FTIR and UV-vis absorption spectroscopy (UV as well as electron paramagnetic resonance (EPR and magnetization measurements. FTIR spectra indicated the presence of absorption bands in the range of 402–425 cm−1, which is a common feature of NiO. EPR for NiO nanosized particles was measured at room temperature. An EPR line with g factor ≈1.9–2 is detected for NiO nanoparticles, corresponding to Ni2+ ions. The magnetic hysteresis of NiO nanoparticles showed that EDTA capping recovers the surface magnetization of the nanoparticles.

  16. A polar cap absorption event observed using the Southern Hemisphere SuperDARN radar network.

    Science.gov (United States)

    Breed, A.; Morris, R.; Parkinson, M.; Duldig, M.; Dyson, P.

    A large X5 class solar flare and coronal mass ejection were observed emanating from the sun on July 14, 2000. Approximately 10 minutes later a large cosmic ray ground level enhancement was observed using neutron monitors located at Mawson station (70.5°S CGM), Antarctica; Large increases in proton flux were also observed using satellites during this time. This marked the start of a large polar cap absorption event with cosmic noise absorption peaking at 30 dB, as measured by a 30 MHz riometer located at Casey station (80.4°S CGM), Antarctica. The spatial evolution of this event and its subsequent recovery were studied using the Southern Hemisphere SuperDARN radar network, including the relatively low latitude observation provided by the Tasman International Geospace Environment Radar (TIGER) located on Bruny Island (54.6°S GGM), Tasmania. When the bulk of the CME arrived at the Earth two days later it triggered an intense geomagnetic storm. This paper presents observations of the dramatic sequence of events.

  17. Hyperspectral characterisation of the Martian south polar residual cap using CRISM

    Science.gov (United States)

    Campbell, J. D.; Sidiropoulos, P.; Muller, J.-P.

    2017-09-01

    We present our research on hyperspectral characterization of the Martian South Polar Residual Cap (SPRC), with a focus on the detection of organic signatures within the dust content of the ice. The SPRC exhibits unique CO2 ice sublimation features known colloquially as 'Swiss Cheese Terrain' (SCT). These flat floored, circular depressions are highly dynamic, and may expose dust particles previously trapped within the ice in the depression walls and partially on the floors. Here we identify suitable regions for potential dust exposure on the SPRC, and utilise data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on board NASA's Mars Reconnaissance Orbiter (MRO) satellite to examine infrared spectra of dark regions to establish their mineral composition, to eliminate the effects of ices on sub-pixel dusty features, and to assess whether ther might be signatures indicative of Polycyclic Aromatic Hydrocarbons (PAHs). Spectral mapping has identified compositional differences between depression rims and the majority of the SPRC and CRISM spectra have been corrected to minimise the influence of CO2 and H2O ice. Whilst no conclusive evidence for PAHs has been found, depression rims are shown to have higher water content than regions of featureless ice, and there are indications of magnesium carbonate within the dark, dusty regions.

  18. Low-frequency electrostatic turbulence in the polar cap E region

    International Nuclear Information System (INIS)

    Pecseli, H.L.; Primdahl, F.; Bahnsen, A.

    1989-01-01

    Electrostatic turbulent fluctuations in a broad frequency band were observed in the polar cap E region over Greenland by an instrumented rocket payload. The fluctuations were detected by potential-difference measurements on two sets of boom-mounted spherical probes. The direction and magnitude of the phase velocity of the fluctuations are determined by standard correlation techniques. The driving mechanism for the turbulence is identified as the Farley-Buneman instability. A characteristic velocity close to the sound speed is deduced while the direction of propagation deviates slightly from the E 0 x B 0 direction. A correlation time of 20-150 ms along the rocket trajectory is determined, indicating that the fluctuations are essentially statistically independent for altitude separations of >50 m. A conditional analysis of the signals indicates that to a good approximation they can be described by Gaussian statistics. The data exclude the possibility of wave steepening as a saturation mechanism for the linear instability. It is thus unlikely that wave energy is cascaded toward short wavelengths to be dissipated there

  19. Assessment of HRSC Digital Terrain Models Produced for the South Polar Residual Cap

    Science.gov (United States)

    Putri, Alfiah Rizky Diana; Sidiropoulos, Panagiotis; Muller, Jan-Peter

    2017-04-01

    The current Digital Terrain Models available for Mars consist of NASA MOLA (Mars Orbital Laser Altimeter) Digital Terrain Models with an average resolution of 112 m/ pixel (512 pixels/degree) for the polar region. The ESA/DLR High Resolution Stereo Camera is currently orbiting Mars and mapping its surface, 98% with resolution of ≤100 m/pixel and better and 100% at lower resolution [1]. It is possible to produce Digital Terrain Models from HRSC images using various methods. In this study, the method developed on Kim and Muller [2] which uses the VICAR open source program together with photogrammetry sofrware from DLR (Deutschen Zentrums für Luft- und Raumfahrt) with image matching based on the GOTCHA (Gruen-Otto-Chau) algorithm [3]. Digital Terrain Models have been processed over the South Pole with emphasis on areas around South Polar Residual Cap from High Resolution Stereo Camera images [4]. Digital Terrain Models have been produced for 31 orbits out of 149 polar orbits available. This study analyses the quality of the DTMs including an assessment of accuracy of elevations using the MOLA MEGDR (Mission Experiment Gridded Data Records) which has roughly 42 million MOLA PEDR (Precision Experiment Data Records) points between latitudes of 78 o -90 o S. The issues encountered in the production of Digital Terrain Models will be described and the statistical results and assessment method will be presented. The resultant DTMs will be accessible via http://i-Mars.eu/web-GIS References: [1] Neukum, G. et. al, 2004. Mars Express: The Scientific Payload pp. 17-35. [2] Kim, J.-R. and J.-P. Muller. 2009. PSS vol. 57, pp. 2095-2112. [3] Shin, D. and J.-P. Muller. 2012. Pattern Recognition, 45(10), 3795 -3809. [4] Putri, A.R. D., et al., Int. Arch. Photogramm. Remote Sens. Spatial Inf. Sci., XLI-B4, 463-469 Acknowledgements: The research leading to these results has received partial funding from the STFC "MSSL Consolidated Grant" ST/K000977/1 and partial support from the

  20. Magnetic properties of ultrathin Ni81Fe19 films with Ta and Ru capping layers.

    Science.gov (United States)

    Kezilebieke, S; Ali, M; Shadeke, B; Gunnella, R

    2013-11-27

    Magnetic properties of Ni81Fe19 (permalloy) ultrathin films with Ru and Ta capping layers (CLs) were investigated for applications to magnetic random access memory units (MRAM). The sample structure, which simulated an MRAM free layer, is Si- sub./SiO2/Ni81Fe19/Ru(Ta). The Ni81Fe19 thin films less than 3 nm thick with Ru CL show low coercive fields compared with the Ta capping layer. Both systems showed loss of momentum equivalent to magnetically dead layers of thickness (δ) ~0.6 nm for Ru cap layer and ~1.4 nm for Ta cap layer, respectively. Moreover, after annealing the thicknesses are slightly increased to an equivalent magnetic dead layer thickness of δ ~0:84 nm and ~1.80 nm for Ru and Ta CL, respectively. Our calculations showed that the presence of only 11% Ta concentration at the interface reduced the Ni momentum to zero, with the Ni–Ta coupling being anti-ferromagnetic; while 50% Ru intermixing at the interface reduced the Ni momentum to zero with the coupling between Ru and Ni being ferromagnetic. To find out more about the intermixing at the interface, the composition and chemical states were characterized by the x-ray photoelectron spectroscopy and peak decomposition technique. The result showed that the peak positions were different from the pure metallic case at the interface region, mainly because of the intermixing between two layers. In conclusion, the Ru capping layer might be important for MRAM use in terms of low coercive field and small δ layer thickness if compared with the Ta capping layer.

  1. Permanent magnetism in phosphine- and chlorine-capped gold: from clusters to nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Munoz-Marquez, Miguel A., E-mail: miguel.angel@icmse.csic.es; Guerrero, Estefania; Fernandez, Asuncion [Instituto de Ciencia de Materiales de Sevilla (CSIC-US) (Spain); Crespo, Patricia; Hernando, Antonio [Instituto de Magnetismo Aplicado (UCM-ADIF-CSIC) (Spain); Lucena, Raquel; Conesa, Jose C. [Instituto de Catalisis y Petroleoquimica (CSIC) (Spain)

    2010-05-15

    Magnetometry results have shown that gold NPs ({approx}2 nm in size) protected with phosphine and chlorine ligands exhibit permanent magnetism. When the NPs size decreases down to the subnanometric size range, e.g. undecagold atom clusters, the permanent magnetism disappears. The near edge structure of the X-ray absorption spectroscopy data points out that charge transfer between gold and the capping system occurs in both cases. These results strongly suggest that nearly metallic Au bonds are also required for the induction of a magnetic response. Electron paramagnetic resonance observations indicate that the contribution to magnetism from eventual iron impurities can be disregarded.

  2. Giant interfacial perpendicular magnetic anisotropy in MgO/CoFe/capping layer structures

    Science.gov (United States)

    Peng, Shouzhong; Zhao, Weisheng; Qiao, Junfeng; Su, Li; Zhou, Jiaqi; Yang, Hongxin; Zhang, Qianfan; Zhang, Youguang; Grezes, Cecile; Amiri, Pedram Khalili; Wang, Kang L.

    2017-02-01

    Magnetic tunnel junction based on the CoFeB/MgO/CoFeB structures is of great interest due to its application in the spin-transfer-torque magnetic random access memory (STT-MRAM). Large interfacial perpendicular magnetic anisotropy (PMA) is required to achieve high thermal stability. Here, we use the first-principles calculations to investigate the magnetic anisotropy energy (MAE) of the MgO/CoFe/capping layer structures, where the capping materials include 5d metals Hf, Ta, Re, Os, Ir, Pt, and Au and 6p metals Tl, Pb, and Bi. We demonstrate that it is feasible to enhance PMA by using proper capping materials. Relatively large PMA is found in the structures with the capping materials of Hf, Ta, Os, Ir, and Pb. More importantly, the MgO/CoFe/Bi structure gives rise to giant PMA (6.09 mJ/m2), which is about three times larger than that of the MgO/CoFe/Ta structure. The origin of the MAE is elucidated by examining the contributions to MAE from each atomic layer and orbital. These findings provide a comprehensive understanding of the PMA and point towards the possibility to achieve the advanced-node STT-MRAM with high thermal stability.

  3. Stabilization of atmospheric pressure and seasonal variations of polar caps in the model of chemically inhomogeneous atmosphere of Mars

    International Nuclear Information System (INIS)

    Aleshin, V.I.

    1985-01-01

    It is shownthat in the model Martian atmosphere, consisting of pure carbon dioxide, the pressure falls to 1 mBar, due to gradual freezing of CO 2 . A small admixture of noncondensing gases alters the situation considerably. The mean atmospheric pressure is thereby stabilized at the level close to 6 mBar. At the end of the winter, a snow bank is formed at the edge of the polar cap. The temperature near the poles in winter falls down to 120 K. As a result of the condensation of carbon dioxide, in polar regions enrichment of the air by noncondensing components occurs

  4. Spin-Polarized Semiconductor Induced by Magnetic Impurities in Graphene

    OpenAIRE

    Daghofer, Maria; Zheng, Nan; Moreo, Adriana

    2010-01-01

    Magnetic impurities adsorbed on graphene are coupled magnetically via the itinerant electrons. This interaction opens a gap in the band structure of graphene. The result strongly depends on how the magnetic impurities are distributed. While random doping produces a semiconductor, if all or most impurities are located in the same sublattice, the spin degeneracy is removed and a spin-polarized semiconductor arises.

  5. Polar cap absorption events of November 2001 at Terra Nova Bay, Antarctica

    Directory of Open Access Journals (Sweden)

    L. Perrone

    2004-04-01

    Full Text Available Polar cap absorption (PCA events recorded during November 2001 are investigated by observations of ionospheric absorption of a 30MHz riometer installed at Terra Nova Bay (Antarctica, and of solar proton flux, monitored by the NOAA-GOES8 satellite in geo-synchronous orbit. During this period three solar proton events (SPE on 4, 19 and 23 November occurred. Two of these are among the dozen most intense events since 1954 and during the current solar cycle (23rd, the event of 4 November shows the greatest proton flux at energies >10MeV. Many factors contribute to the peak intensity of the two SPE biggest events, one is the Coronal Mass Ejection (CME speed, other factors are the ambient population of SPE and the shock front due to the CME. During these events absorption peaks of several dB (~20dB are observed at Terra Nova Bay, tens of minutes after the impact of fast halo CMEs on the geomagnetic field.

    Results of a cross-correlation analysis show that the first hour of absorption is mainly produced by 84–500MeV protons in the case of the 4 November event and by 15–44MeV protons for the event of 23 November, whereas in the entire event the contribution to the absorption is due chiefly to 4.2–82MeV (4 November and by 4.2–14.5MeV (23 November. Good agreement is generally obtained between observed and calculated absorption by the empirical flux-absorption relationship for threshold energy E0=10MeV. From the residuals one can argue that other factors (e.g. X-ray increases and geomagnetic disturbances can contribute to the ionospheric absorption.

    Key words. Ionosphere (Polar Ionosphere, Particle precipitation – Solar physics (Flares and mass ejections

  6. Resolving 3D magnetism in nanoparticles using polarization analyzed SANS

    Science.gov (United States)

    Krycka, K. L.; Booth, R.; Borchers, J. A.; Chen, W. C.; Conlon, C.; Gentile, T. R.; Hogg, C.; Ijiri, Y.; Laver, M.; Maranville, B. B.; Majetich, S. A.; Rhyne, J. J.; Watson, S. M.

    2009-09-01

    Utilizing a polarized 3He cell as an analyzer we were able to perform a full polarization analysis on small-angle neutron scattering (SANS) data from an ensemble of 7 nm magnetite nanoparticles. The results led to clear separation of magnetic and nuclear scattering plus a 3D vectorial decomposition of the magnetism observed. At remanence variation in long-range magnetic correlation length was found to be highly dependent on temperature from 50 to 300 K. Additionally, we were able to compare the magnetic scattering from moments along and perpendicular to an applied field at saturation and in remanence.

  7. Plasma Irregularity Production in the Polar Cap F-Region Ionosphere

    Science.gov (United States)

    Lamarche, Leslie

    Plasma in the Earth's ionosphere is highly irregular on scales ranging between a few centimeters and hundreds of kilometers. Small-scale irregularities or plasma waves can scatter radio waves resulting in a loss of signal for navigation and communication networks. The polar region is particularly susceptible to strong disturbances due to its direct connection with the Sun's magnetic field and energetic particles. In this thesis, factors that contribute to the production of decameter-scale plasma irregularities in the polar F region ionosphere are investigated. Both global and local control of irregularity production are studied, i.e. we consider global solar control through solar illumination and solar wind as well as much more local control by plasma density gradients and convection electric field. In the first experimental study, solar control of irregularity production is investigated using the Super Dual Auroral Radar Network (SuperDARN) radar at McMurdo, Antarctica. The occurrence trends for irregularities are analyzed statistically and a model is developed that describes the location of radar echoes within the radar's field-of-view. The trends are explained through variations in background plasma density with solar illumination affecting radar beam propagation. However, it is found that the irregularity occurrence during the night is higher than expected from ray tracing simulations based on a standard ionospheric density model. The high occurrence at night implies an additional source of plasma density and it is proposed that large-scale density enhancements called polar patches may be the source of this density. Additionally, occurrence maximizes around the terminator due to different competing irregularity production processes that favor a more or less sunlit ionosphere. The second study is concerned with modeling irregularity characteristics near a large-scale density gradient reversal, such as those expected near polar patches, with a particular focus on

  8. Spin polarization of electrons in a magnetic impurity doped ...

    Indian Academy of Sciences (India)

    Abstract. A theoretical model is presented in this paper for degree of spin polarization in a light emitting diode (LED) whose epitaxial region contains quantum dots doped with magnetic impurity. The model is then used to investigate the effect of electron–phonon interaction on degree of spin polarization at different ...

  9. Spin polarization of electrons in a magnetic impurity doped ...

    Indian Academy of Sciences (India)

    A theoretical model is presented in this paper for degree of spin polarization in alight emitting diode (LED) whose epitaxial region contains quantum dots doped with magnetic impurity. The model is then used to investigate the effect of electron–phonon interaction on degree of spin polarization at different temperatures and ...

  10. Polarized SANS for probing magnetic nanostructures

    Science.gov (United States)

    Wiedenmann, Albrecht

    2005-02-01

    Cross-sections for small angle neutron scattering, using non-polarised and polarised neutrons, with and without polarisation analysis, are derived for single-domain ferromagnetic particles when inter-particle correlations are taken into account. The potential for magnetic contrast variation is demonstrated by investigations of poly disperse magnetic colloids. Size distributions, compositions and magnetic moments of magnetic composites and magnetic aggregates were determined precisely independently from that of non-magnetic micelles and free surfactants of similar sizes. Nuclear and magnetic inter-particle correlations have been extracted from the scattering signals by using polarisation analysis via a 3He filter cell.

  11. Polarized SANS for probing magnetic nanostructures

    International Nuclear Information System (INIS)

    Wiedenmann, Albrecht

    2005-01-01

    Cross-sections for small angle neutron scattering, using non-polarised and polarised neutrons, with and without polarisation analysis, are derived for single-domain ferromagnetic particles when inter-particle correlations are taken into account. The potential for magnetic contrast variation is demonstrated by investigations of poly disperse magnetic colloids. Size distributions, compositions and magnetic moments of magnetic composites and magnetic aggregates were determined precisely independently from that of non-magnetic micelles and free surfactants of similar sizes. Nuclear and magnetic inter-particle correlations have been extracted from the scattering signals by using polarisation analysis via a 3 He filter cell

  12. Investigating the polar electrojet using Swarm satellite magnetic data

    DEFF Research Database (Denmark)

    Aakjær, Cecilie Drost; Olsen, Nils; Finlay, Chris

    The aim of this study is to investigate the magnetic perturbations caused by the polar electrojets, which are described by means of a model consisting of a series of infinite line currents placed at the height of the ionosphere along QD latitudes. The method is applied to Swarm magnetic scalar...... of the polar electrojets as well as their temporal evolution. In addition, applying the method to data taken by the Swarm satellites Alpha and Beta allows investigating longitudinal differences of the electrojets....

  13. Polarized neutron reflectivity and scattering studies of magnetic heterostructures

    Science.gov (United States)

    Zabel, H.; Theis-Bröhl, K.

    2003-02-01

    The current interest in the magnetism of ultrathin films and multilayers is driven by their manifold applications in the magneto-and spin-electronic areas, for instance as magnetic field sensors or as information storage devices. In this regard, there is a large interest in exploring spin structures and spin disorder at the interface of magnetic heterostructures, to investigate magnetic domains in thin films and superlattices, and to understand remagnetization processes of various laterally shaped magnetic nanostructures. Traditionally neutron scattering has played a dominant role in the determination of spin structures, phase transitions and magnetic excitations in bulk materials. Today, its potential for the investigation of thin magnetic films has to be redefined. Polarized neutron reflectivity (PNR) at small wavevectors can provide precise information on the magnetic field distribution parallel to the film plane and on layer resolved magnetization vectors. In addition, PNR is not only sensitive to structural interface roughness but also to the magnetic roughness. Furthermore, magnetic hysteresis measurements from polarized small angle Bragg reflections allows us to filter out correlation effects during magnetization reversals of magnetic stripes and islands. An overview is provided on most recent PNR investigations of magnetic heterostructures.

  14. Polarized neutron reflectivity and scattering studies of magnetic heterostructures

    International Nuclear Information System (INIS)

    Zabel, H; Theis-Broehl, K

    2003-01-01

    The current interest in the magnetism of ultrathin films and multilayers is driven by their manifold applications in the magneto-and spin-electronic areas, for instance as magnetic field sensors or as information storage devices. In this regard, there is a large interest in exploring spin structures and spin disorder at the interface of magnetic heterostructures, to investigate magnetic domains in thin films and superlattices, and to understand remagnetization processes of various laterally shaped magnetic nanostructures. Traditionally neutron scattering has played a dominant role in the determination of spin structures, phase transitions and magnetic excitations in bulk materials. Today, its potential for the investigation of thin magnetic films has to be redefined. Polarized neutron reflectivity (PNR) at small wavevectors can provide precise information on the magnetic field distribution parallel to the film plane and on layer resolved magnetization vectors. In addition, PNR is not only sensitive to structural interface roughness but also to the magnetic roughness. Furthermore, magnetic hysteresis measurements from polarized small angle Bragg reflections allows us to filter out correlation effects during magnetization reversals of magnetic stripes and islands. An overview is provided on most recent PNR investigations of magnetic heterostructures

  15. Revisiting magnetism of capped Au and ZnO nanoparticles: Surface band structure and atomic orbital with giant magnetic moment

    Energy Technology Data Exchange (ETDEWEB)

    Hernando, Antonio; Crespo, Patricia [Instituto de Magnetismo Aplicado, UCM-CSIC-ADIF, Las Rozas. P.O. Box 155, 28230 Madrid (Spain); Dept. Fisica de Materiales, Universidad Complutense, Madrid (Spain); Garcia, Miguel Angel [Instituto de Ceramica y Vidrio, CSIC, C/ Kelsen, 5, Madrid 28049 (Spain); Coey, Michael [Trinity College Dublin, Dublin (Ireland); Ayuela, Andres; Echenique, Pedro Miguel [Centro de Fisica de Materiales, CFM-MPC CSIC-UPV/EHU, Donostia International Physics Center (DIPC), 20018 San Sebastian (Spain); Departamento de Fisica de Materiales, Fac. de Quimicas, Universidad del Pais Vasco UPV-EHU, 20018 San Sebastian (Spain)

    2011-10-15

    In this article we review the exotic magnetism of nanoparticles (NPs) formed by substances that are not magnetic in bulk as described with generality in Section 1. In particular, the intrinsic character of the magnetism observed on capped Au and ZnO NPs is analysed. X-ray magnetic circular dichroism (XMCD) analysis has shown that the magnetic moments are intrinsic and lie in the Au and Zn atoms, respectively, as analysed in Section 2, where the general theoretical ideas are also revisited. Since impurity atoms bonded to the surface act as donor or acceptor of electrons that occupy the surface states, the anomalous magnetic response is analysed in terms of the surface band in Section 3. Finally, Section 4 summarizes our last theoretical proposal. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  16. Assessing Zones of Low Radar Reflectivity Across the South Polar Cap of Mars

    Science.gov (United States)

    Putzig, N. E.; Smith, I. B.; Whitten, J. L.; Campbell, B. A.

    2017-12-01

    The Mars Reconnaissance Orbiter Shallow Radar (SHARAD) revealed near-surface zones of low radar reflectivity (reflection-free zones, RFZs) in many areas of Planum Australe (Phillips et al., 2011, Science 332). The most poleward, RFZ3, corresponds geographically to geologic unit AA3 (Tanaka et al., 2007, 7th Int'l Mars Conf. abs. 3276) that exhibits sublimation features. Geometric considerations demonstrated that RFZ3 consists of three distinct layers of CO2 ice, preserved from earlier periods of atmospheric collapse (Bierson et al., 2016, GRL 43). However, the nature of other RFZs at lower latitudes remains undetermined, with none of the SHARAD observations examined to date providing definitive geometric constraints on their composition. While CO2-ice composition has not been ruled out, these RFZs differ in important ways from RFZ3. Surface imagery in the vicinity of the outlying RFZs does not generally exhibit sublimation features similar to those seen in AA3, SHARAD reflectivity exhibits a lower contrast with surrounding materials relative to RFZ3, and there are no indications of distinct layering within the outlying RFZs as there are in RFZ3. In addition, climate modeling of atmospheric collapse episodes (Wood et al., 2016, LPSC abs. 3074) suggests that CO2 accumulation is highly concentrated at the highest latitudes. An alternative explanation for the outlying RFZs is that they consist of nearly pure water ice deposited during times when atmospheric dust was nearly absent. Such conditions may occur coeval with eras of CO2 accumulation at the higher latitudes. To test these possibilities, we are working to constrain the composition of the outlying RFZs, using the recently produced 3-D SHARAD data volume that encompasses the entire Martian south polar ice cap (Foss et al., 2017, The Leading Edge, 36). Work is ongoing, but we expect that the geometric corrections and improvements to the overall signal-to-noise ratio provided by the 3-D radar imaging processing may

  17. High magnetic field uniformity superconducting magnet for a movable polarized target

    International Nuclear Information System (INIS)

    Anishchenko, N.G.; Bartenev, V.D.; Blinov, N.A.

    1998-01-01

    The superconducting polarizing magnet was constructed for movable polarized target (MPT) with working volume 200 mm long and 30 mm in diameter. The magnet provides a polarizing magnetic field up to 6 T with the uniformity of 4.5 x 10 -4 in the working volume of the target. The magnet windings are made of a NbTi wire, impregnated with the epoxy resin and placed in the horizontal cryostat with 'warm' aperture diameter of 96 mm. The design and technology of the magnet winding are described. Results of the magnetic field map measurements using a NMR-magnetometer are given. The MPT set-up is installed in the beam line of polarized neutrons produced by break-up of polarized deuterons extracted from the Synchrophasotron of the Laboratory of High Energies (LHE), JINR, Dubna

  18. Magnetic resonance imaging of convection in laser-polarized xenon

    Science.gov (United States)

    Mair, R. W.; Tseng, C. H.; Wong, G. P.; Cory, D. G.; Walsworth, R. L.

    2000-01-01

    We demonstrate nuclear magnetic resonance (NMR) imaging of the flow and diffusion of laser-polarized xenon (129Xe) gas undergoing convection above evaporating laser-polarized liquid xenon. The large xenon NMR signal provided by the laser-polarization technique allows more rapid imaging than one can achieve with thermally polarized gas-liquid systems, permitting shorter time-scale events such as rapid gas flow and gas-liquid dynamics to be observed. Two-dimensional velocity-encoded imaging shows convective gas flow above the evaporating liquid xenon, and also permits the measurement of enhanced gas diffusion near regions of large velocity variation.

  19. Engineering status of the superconducting end cap toroid magnets for the ATLAS experiment at LHC

    CERN Document Server

    Baynham, D Elwyn; Carr, F S; Courthold, M J D; Cragg, D A; Densham, C J; Evans, D; Holtom, E; Rochford, J; Sole, D; Towndrow, Edwin F; Warner, G P

    2000-01-01

    The ATLAS experiment at LHC, CERN will utilise a large, superconducting, air-cored toroid magnet system for precision muon measurements. The magnet system will consist of a long barrel and two end-cap toroids. Each end-cap toroid will contain eight racetrack coils mounted as a single cold mass in cryostat vessel of ~10 m diameter. The project has now moved from the design/specification stage into the fabrication phase. This paper presents the engineering status of the cold masses and vacuum vessels that are under fabrication in industry. Final designs of cold mass supports, cryogenic systems and control/protection systems are presented. Planning for toroid integration, test and installation is described. (3 refs).

  20. Designing magnetic droplet soliton nucleation employing spin polarizer

    Science.gov (United States)

    Mohseni, Morteza; Mohseni, Majid

    2018-04-01

    We show by means of micromagnetic simulations that spin polarizer in nano-contact (NC) spin torque oscillators as the representative of the fixed layer in an orthogonal pseudo-spin valve can be employed to design and to control magnetic droplet soliton nucleation and dynamics. We found that using a tilted spin polarizer layer decreases the droplet nucleation time which is more suitable for high speed applications. However, a tilted spin polarizer increases the nucleation current and decreases the frequency stability of the droplet. Additionally, by driving the magnetization inhomogenously at the NC region, it is found that a tilted spin polarizer reduces the precession angle of the droplet and through an interplay with the Oersted field of the DC current, it breaks the spatial symmetry of the droplet profile. Our findings explore fundamental insight into nano-scale magnetic droplet soliton dynamics with potential tunability parameters for future microwave electronics.

  1. Mechanism of Cyclically Polarity Reversing Solar Magnetic Cycle as ...

    Indian Academy of Sciences (India)

    2016-01-27

    Jan 27, 2016 ... We briefly describe historical development of the concept of solar dynamo mechanism that generates electric current and magnetic field by plasma ... The dynamo is the driver of the cyclically polarity reversing solar magnetic cycle. ... Department of Astronomy, University of Tokyo, Tokyo, Japan 113-0033.

  2. Helical dipole magnets for polarized protons in RHIC

    International Nuclear Information System (INIS)

    Syphers, M.; Courant, E.; Fischer, W.

    1997-01-01

    Superconducting helical dipole magnets will be used in the Brookhaven Relativistic Heavy Ion Collider (RHIC) to maintain polarization of proton beams and to perform localized spin rotations at the two major experimental detector regions. Requirements for the helical dipole system are discussed, and magnet prototype work is reported

  3. Characterization of a magnetic trap by polarization dependent Zeeman spectroscopy

    DEFF Research Database (Denmark)

    Nielsen, Carsten Vandel; Lyngsøe, Jens Kristian; Thorseth, Anders

    2008-01-01

    This paper demonstrates a detailed experimental study of our cloverleaf magnetic trap for sodium atoms. By using polarization dependent Zeeman spectroscopy of our atomic beam, passing the magnetic trap region, we have determined important trap parameters such as gradients, their curvatures...

  4. Polar Magnetic Field Reversals of the Sun in Maunder Minimum

    Indian Academy of Sciences (India)

    tribpo

    The data on polar migration of solar magnetic fields were obtained on the basis of. Η alpha magnetic synoptic charts for 1880 1991 using Kodaikanal, Kislovodsk and Italian observations, and Atlas of Η alpha charts (Mclntosh 1979; Makarov &. Fatianov 1980; Makarov & Sivaraman 1989; Makarov 1994). The Wolf numbers ...

  5. On the possible role of cusp/cleft precipitation in the formation of polar-cap patches

    Directory of Open Access Journals (Sweden)

    I. K. Walker

    1999-10-01

    Full Text Available The work describes experimental observations of enhancements in the electron density of the ionospheric F-region created by cusp/cleft particle precipitation at the dayside entry to the polar-cap convection flow. Measurements by meridian scanning photometer and all-sky camera of optical red-line emissions from aurora are used to identify latitudinally narrow bands of soft-particle precipitation responsible for structured enhancements in electron density determined from images obtained by radio tomography. Two examples are discussed in which the electron density features with size scales and magnitudes commensurate with those of patches are shown to be formed by precipitation at the entry region to the anti-sunward flow. In one case the spectrum of the incoming particles results in ionisation being created, for the most part below 250 km, so that the patch will persist only for minutes after convecting away from the auroral source region. However in a second example, at a time when the plasma density of the solar wind was particularly high, a substantial part of the particle-induced enhancement formed above 250 km. It is suggested that, with the reduced recombination loss in the upper F-region, this structure will retain form as a patch during passage in the anti-sunward flow across the polar cap.Key words. Ionosphere (ionospheric irregularities; particle precipitation; polar ionosphere

  6. The role of polarization current in magnetic island evolution

    International Nuclear Information System (INIS)

    Connor, J.W.; Waelbroeck, F.L.; Wilson, H.R.

    2001-01-01

    The polarization current plays an important role in the evolution of magnetic islands with a width comparable to the characteristic ion orbit width. Understanding the evolution of such small magnetic islands is important for two reasons: (1) to investigate the threshold mechanisms for growth of large-scale islands (e.g., neoclassical tearing modes), and (2) to describe the drive mechanisms for small-scale magnetic turbulence and consequent transport. This article presents a two-fluid, cold ion, collisional analysis of the role of the polarization current in magnetic island evolution in slab geometry. It focuses on the role played by the conjunction of parallel electron dynamics and perpendicular transport (particle diffusion and viscosity) in determining the island rotation frequency and the distribution of the polarization current within the island

  7. Simultaneously improving optical absorption of both transverse-electric polarized and transverse-magnetic polarized light for organic solar cells with Ag grating used as transparent electrode

    Directory of Open Access Journals (Sweden)

    Yongbing Long

    2014-08-01

    Full Text Available Theoretical simulations are performed to investigate optical performance of organic solar cells with Ag grating electrode. It is demonstrated that optical absorption for both transverse-electric (TE polarized and transverse-magnetic(TM polarized light is simultaneously improved when compared with that for the device without the Ag grating. The improvement is respectively attributed to the resonance and the surface plasmon polaritons within the device. After an additional WO3 layer is capped on the Ag grating, absorption of TE-polarized light is further improved due to resonance of double microcavities within the device, and absorption of TM-polarized light is improved by the combined effects of the microcavity resonance and the surface plasmon polaritons. Correspondingly, the short current density for randomly polarized light is improved by 18.1% from that of the device without the Ag grating. Finally, it is demonstrated that high transmission may not be an essential prerequisite for metallic gratings when they are used as transparent electrode since absorption loss caused by low transmission can be compensated by using a capping layer to optimize optical resonance of the WMC structure within the device.

  8. Magnetic imaging with polarized soft x-rays

    Science.gov (United States)

    Fischer, Peter

    2017-08-01

    Properties, behavior, and functionalities of magnetic materials are largely determined by microscopic spin textures, particularly their formation into domains, their coupling mechanisms and their dynamic behavior. Advanced characterization tools are prerequisite to fundamentally understand magnetic materials and control spins for novel magnetic applications. Magnetic microscopies allow us to image directly the static and dynamic features of the relevant microscopic magnetization structures in advanced magnetic materials and thus provide detailed and direct insight into underlying physical phenomena. A large variety of magnetic imaging techniques has become available with particular strengths but also certain limitations. Essential features of magnetic microscopies are a high spatial resolution down into the nanometer regime, as this is the fundamental length scale of magnetic exchange interaction and the ultimate length scale in advanced magnetic technologies; magnetic and elemental sensitivity with quantitative capabilities, as the properties of advanced magnetic materials can be tailored by combining various magnetic elements and their magnetic moments; high temporal resolution from the ns to the fs regime to understand the associated spin dynamic processes and the functionality in magnetic devices; tomographic capabilities with nm resolution as new directions in nanoscience and technologies are moving into 3 dim arrangements of spin structures; and interfacial sensitivity as novel ways to control spins harness either the coupling across interfaces in multilayered structures or utilize non-collinear spin arrangements, which often occur from symmetry breaking at surfaces and interfaces. The unique properties of polarized soft x-rays, their abundancy and specific interaction with magnetic materials in form of dichroism effects have triggered the development of various magnetic x-ray imaging techniques. This review will provide an overview of the current state

  9. Half of one of the end-cap magnet vacuum vessels passing through Gex on its way to CERN.

    CERN Multimedia

    Maximilien Brice

    2002-01-01

    More large pieces of the ATLAS detector arrived recently at CERN. The trailer seen here carries the vacuum vessel for one half of the toroid magnet that will form one of the end-caps of the complete detector.

  10. 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.

  11. Local magnetic structure determination using polarized neutron holography

    Science.gov (United States)

    Szakál, Alex; Markó, Márton; Cser, László

    2015-05-01

    A unique and important property of the neutron is that it possesses magnetic moment. This property is widely used for determination of magnetic structure of crystalline samples observing the magnetic components of the diffraction peaks. Investigations of diffraction patterns give information only about the averaged structure of a crystal but for discovering of local spin arrangement around a specific (e.g., impurity) nucleus remains still a challenging problem. Neutron holography is a useful tool to investigate the local structure around a specific nucleus embedded in a crystal lattice. The method has been successfully applied experimentally in several cases using non-magnetic short range interaction of the neutron and the nucleus. A mathematical model of the hologram using interaction between magnetic moment of the atom and the neutron spin for polarized neutron holography is provided. Validity of a polarized neutron holographic experiment is demonstrated by applying the proposed method on model systems.

  12. Local magnetic structure determination using polarized neutron holography

    International Nuclear Information System (INIS)

    Szakál, Alex; Markó, Márton; Cser, László

    2015-01-01

    A unique and important property of the neutron is that it possesses magnetic moment. This property is widely used for determination of magnetic structure of crystalline samples observing the magnetic components of the diffraction peaks. Investigations of diffraction patterns give information only about the averaged structure of a crystal but for discovering of local spin arrangement around a specific (e.g., impurity) nucleus remains still a challenging problem. Neutron holography is a useful tool to investigate the local structure around a specific nucleus embedded in a crystal lattice. The method has been successfully applied experimentally in several cases using non-magnetic short range interaction of the neutron and the nucleus. A mathematical model of the hologram using interaction between magnetic moment of the atom and the neutron spin for polarized neutron holography is provided. Validity of a polarized neutron holographic experiment is demonstrated by applying the proposed method on model systems

  13. Interannual and seasonal changes in the south seasonal polar cap of Mars: Observations from MY 28-31 using MARCI

    Science.gov (United States)

    Calvin, W. M.; Cantor, B. A.; James, P. B.

    2017-08-01

    The Mars Color Imager (MARCI) camera on the Mars Reconnaissance Orbiter provides daily synoptic coverage that allows monitoring of seasonal cap retreat and interannual changes that occur between Mars Years (MY) and over the southern summer. We present the first analysis of this data for the southern seasonal cap evolution observed in MY 28, 29, 30 and 31 (2/2007 to 07/2013). Observation over multiple Mars years allows us to compare changes between years as well as longer-term evolution of the high albedo deposits at the poles. Seasonal cap retreat is similar in all years and to retreats observed in other years by both optical and thermal instruments. The cryptic terrain has a fairly consistent boundary in each year, but numerous small-scale variations occur in each MY observed. Additionally, numerous small dark deposits are identified outside the classically identified cyptic region, including Inca City and other locations not previously noted. The large water ice outlier is observed to retain seasonal frost the longest (outside the polar dome) and is also highly variable in each MY. The development of the cryptic/anti-cryptic hemispheres is inferred to occur due to albedo variations that develop after dust venting starts and may be caused by recondensation of CO2 ice on the brightest and coldest regions controlled by topographic winds. Ground ice may play a role in which regions develop cryptic terrain, as there is no elevation control on either cryptic terrain or the late season brightest deposits.

  14. 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...

  15. Circular polarization in a non-magnetic resonant tunneling device

    Directory of Open Access Journals (Sweden)

    Airey Robert

    2011-01-01

    Full Text Available Abstract We have investigated the polarization-resolved photoluminescence (PL in an asymmetric n-type GaAs/AlAs/GaAlAs resonant tunneling diode under magnetic field parallel to the tunnel current. The quantum well (QW PL presents strong circular polarization (values up to -70% at 19 T. The optical emission from GaAs contact layers shows evidence of highly spin-polarized two-dimensional electron and hole gases which affects the spin polarization of carriers in the QW. However, the circular polarization degree in the QW also depends on various other parameters, including the g-factors of the different layers, the density of carriers along the structure, and the Zeeman and Rashba effects.

  16. Nonlinear Magnetic Phenomena in Highly Polarized Target Materials

    CERN Document Server

    Kiselev, Yu F

    2007-01-01

    The report introduces and surveys nonlinear magnetic phenomena which have been observed at high nuclear polarizations in polarized targets of the SMC and of the COMPASS collaborations at CERN. Some of these phenomena, namely the frequency modulation eect and the distortion of the NMR line shape, promote the development of the polarized target technique. Others, as the spin-spin cross-relaxation between spin subsystems can be used for the development of quantum statistical physics. New findings bear on an electromagnetic noise and the spectrally resolved radiation from LiD with negatively polarized nuclei detected by low temperature bolometers. These nonlinear phenomena need to be taken into account for achieving the ultimate polarizations.

  17. A polarity-induced defect mechanism for conductivity and magnetism at polar-nonpolar oxide interfaces.

    Science.gov (United States)

    Yu, Liping; Zunger, Alex

    2014-10-13

    The discovery of conductivity and magnetism at the polar-nonpolar interfaces of insulating nonmagnetic oxides such as LaAlO3 and SrTiO3 has raised prospects for attaining interfacial functionalities absent in the component materials. Yet, the microscopic origin of such emergent phenomena remains unclear, posing obstacles to design of improved functionalities. Here we present first principles calculations of electronic and defect properties of LaAlO3/SrTiO3 interfaces and reveal a unifying mechanism for the origins of both conductivity and magnetism. We demonstrate that the polar discontinuity across the interface triggers thermodynamically the spontaneous formation of certain defects that in turn cancel the polar field induced by the polar discontinuity. The ionization of the spontaneously formed surface oxygen vacancy defects leads to interface conductivity, whereas the unionized Ti-on-Al antisite defects lead to interface magnetism. The proposed mechanism suggests practical design principles for inducing and controlling both conductivity and magnetism at general polar-nonpolar interfaces.

  18. Polarization measurement and vertical aperture optimization for obtaining circularly polarized bend-magnet radiation

    Energy Technology Data Exchange (ETDEWEB)

    Kortright, J.B.; Rice, M.; Hussain, Z. [Lawrence Berkeley National Lab., CA (United States)] [and others

    1997-04-01

    Growing interest in utilizing circular polarization prompted the design of bend-magnet beamline 9.3.2 at the Advanced Light Source, covering the 30-1500 eV spectral region, to include vertical aperturing capabilities for optimizing the collection of circular polarization above and below the orbit plane. After commissioning and early use of the beamline, a multilayer polarimeter was used to characterize the polarization state of the beam as a function of vertical aperture position. This report partially summarizes the polarimetry measurements and compares results with theoretical calculations intended to simulate experimental conditions.

  19. ON THE ROTATION OF SUNSPOTS AND THEIR MAGNETIC POLARITY

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, Jianchuan; Yang, Zhiliang; Guo, Kaiming [Department of Astronomy, Beijing Normal University, Beijing 100875 (China); Wang, Haimin; Wang, Shuo, E-mail: zlyang@bnu.edu.cn [Space Weather Research Laboratory, New Jersey Institute of Technology, University Heights, Newark, NJ 07102-1982 (United States)

    2016-07-20

    The rotation of sunspots of 2 yr in two different solar cycles is studied with the data from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory and the Michelson Doppler Imager instrument on board the Solar and Heliospheric Observataory . We choose the α sunspot groups and the relatively large and stable sunspots of complex active regions in our sample. In the year of 2003, the α sunspot groups and the preceding sunspots tend to rotate counterclockwise and have positive magnetic polarity in the northern hemisphere. In the southern hemisphere, the magnetic polarity and rotational tendency of the α sunspot groups and the preceding sunspots are opposite to the northern hemisphere. The average rotational speed of these sunspots in 2003 is about 0.°65 hr{sup 1}. From 2014 January to 2015 February, the α sunspot groups and the preceding sunspots tend to rotate clockwise and have negative magnetic polarity in the northern hemisphere. The patterns of rotation and magnetic polarity of the southern hemisphere are also opposite to those of the northern hemisphere. The average rotational speed of these sunspots in 2014/2015 is about 1.°49 hr{sup 1}. The rotation of the relatively large and stable preceding sunspots and that of the α sunspot groups located in the same hemisphere have opposite rotational direction in 2003 and 2014/2015.

  20. Frontiers in imaging magnetism with polarized x-rays

    Directory of Open Access Journals (Sweden)

    Peter eFischer

    2015-01-01

    Full Text Available Although magnetic imaging with polarized x-rays is a rather young scientific discipline, the various types of established x-ray microscopes have already taken an important role in state-of-the-art characterization of the properties and behavior of spin textures in advanced materials. The opportunities ahead will be to obtain in a unique way indispensable multidimensional information of the structure, dynamics and composition of scientifically interesting and technologically relevant magnetic materials.

  1. Structural, optical, XPS and magnetic properties of Zn particles capped by ZnO nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Morozov, Iu.G., E-mail: yugmor@hotmail.com [Institute of Structural Macrokinetics and Materials Science, Russian Academy of Sciences, Academician Osipyan Street 8, Chernogolovka, Moscow Region 142432 (Russian Federation); Belousova, O.V. [Institute of Structural Macrokinetics and Materials Science, Russian Academy of Sciences, Academician Osipyan Street 8, Chernogolovka, Moscow Region 142432 (Russian Federation); Ortega, D., E-mail: daniel.ortega@imdea.org [Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA-Nanociencia), Cantoblanco 28049, Madrid (Spain); Mafina, M.-K., E-mail: m.k.mafina@qmul.ac.uk [School of Engineering and Materials Science, Queen Mary University of London, Mile End, Eng, 231, London E1 4NS (United Kingdom); Kuznetcov, M.V., E-mail: maxim1968@mail.ru [Department of Chemistry, Materials Chemistry Research Centre, University College London, 20 Gordon Street, London WC1H 0AJ (United Kingdom)

    2015-06-05

    Highlights: • Levitation-jet aerosol synthesis of Zn particles capped by ZnO nanoparticles (NPs). • TEM, XRD, UV–vis, FT-IR, Raman, XPS and magnetic characterization of the NPs. • Correlation between unit-cell volume of crystal lattice and maximum magnetization. - Abstract: Spherical zinc particles ranging from 42 to 760 nm in average size and capped with plate-like zinc oxide particles of 10–30 nm in sizes have been prepared by levitation-jet aerosol synthesis through condensation of zinc vapor in an inert/oxidizer gas flow. The nanoparticles have been characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), BET measurements, ultra violet visible (UV–vis) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, X-ray electron spectroscopy (XPS), superconducting quantum interference device (SQUID), and vibrating-sample magnetometer (VSM). Magnetic and XRD data indicate that the observed ferromagnetic ordering related to the changes in unit-cell volume of Zn in the Zn/ZnO interface of the nanoparticles. These results are in good correlation with the optical measurements data.

  2. The common cryogenic test facility for the ATLAS barrel and end-cap toroid magnets

    CERN Document Server

    Delruelle, N; Junker, S; Passardi, Giorgio; Pengo, R; Pirotte, O

    2004-01-01

    The large ATLAS toroidal superconducting magnet made of the Barrel and two End-Caps needs extensive testing at the surface of the individual components prior to their final assembly into the underground cavern of LHC. A cryogenic test facility specifically designed for cooling sequentially the eight coils making the Barrel Toroid (BT) has been fully commissioned and is now ready for final acceptance of these magnets. This facility, originally designed for testing individually the 46 tons BT coils, will be upgraded to allow the acceptance tests of the two End-Caps, each of them having 160 tons cold mass. The integrated system mainly comprises a 1.2 kW@4.5 K refrigerator, a 10 kW liquid-nitrogen precooler, two cryostats housing liquid helium centrifugal pumps of respectively 80 g/s and 600 g/s nominal flow and specific instrumentation to measure the thermal performances of the magnets. This paper describes the overall facility with particular emphasis to the cryogenic features adopted to match the specific requ...

  3. The Common Cryogenic Test Facility for the Atlas Barrel and End-Cap Toroid Magnet

    CERN Document Server

    Delruelle, N; Junker, S; Passardi, Giorgio; Pengo, R; Pirotte, O

    2004-01-01

    The large ATLAS toroidal superconducting magnet made of the Barrel and two End-Caps needs extensive testing at the surface of the individual components prior to their final assembly into the underground cavern of LHC. A cryogenic test facility specifically designed for cooling sequentially the eight coils making the Barrel Toroid (BT) has been fully commissioned and is now ready for final acceptance of these magnets. This facility, originally designed for testing individually the 46 tons BT coils, will be upgraded to allow the acceptance tests of the two End-Caps, each of them having a 160 tons cold mass. The integrated system mainly comprises a 1.2 kW@4.5 K refrigerator, a 10 kW liquid-nitrogen precooler, two cryostats housing liquid helium centrifugal pumps of respectively 80 g/s and 600 g/s nominal flow and specific instrumentation to measure the thermal performances of the magnets. This paper describes the overall facility with particular emphasis to the cryogenic features adopted to match the specific re...

  4. Modulation of UK lightning by heliospheric magnetic field polarity

    Science.gov (United States)

    Owens, M. J.; Scott, C. J.; Lockwood, M.; Barnard, L.; Harrison, R. G.; Nicoll, K.; Watt, C.; Bennett, A. J.

    2014-11-01

    Observational studies have reported solar magnetic modulation of terrestrial lightning on a range of time scales, from days to decades. The proposed mechanism is two-step: lightning rates vary with galactic cosmic ray (GCR) flux incident on Earth, either via changes in atmospheric conductivity and/or direct triggering of lightning. GCR flux is, in turn, primarily controlled by the heliospheric magnetic field (HMF) intensity. Consequently, global changes in lightning rates are expected. This study instead considers HMF polarity, which doesn't greatly affect total GCR flux. Opposing HMF polarities are, however, associated with a 40-60% difference in observed UK lightning and thunder rates. As HMF polarity skews the terrestrial magnetosphere from its nominal position, this perturbs local ionospheric potential at high latitudes and local exposure to energetic charged particles from the magnetosphere. We speculate as to the mechanism(s) by which this may, in turn, redistribute the global location and/or intensity of thunderstorm activity.

  5. THE MAGNETIC FIELD IN TAURUS PROBED BY INFRARED POLARIZATION

    International Nuclear Information System (INIS)

    Chapman, Nicholas L.; Goldsmith, Paul F.; Pineda, Jorge L.; Li Di; Clemens, D. P.; Krco, Marko

    2011-01-01

    We present maps of the plane-of-sky magnetic field within two regions of the Taurus molecular cloud: one in the dense core L1495/B213 filament and the other in a diffuse region to the west. The field is measured from the polarization of background starlight seen through the cloud. In total, we measured 287 high-quality near-infrared polarization vectors in these regions. In L1495/B213, the percent polarization increases with column density up to A V ∼ 9 mag, the limits of our data. The radiative torques model for grain alignment can explain this behavior, but models that invoke turbulence are inconsistent with the data. We also combine our data with published optical and near-infrared polarization measurements in Taurus. Using this large sample, we estimate the strength of the plane-of-sky component of the magnetic field in nine subregions. This estimation is done with two different techniques that use the observed dispersion in polarization angles. Our values range from 5 to 82 μG and tend to be higher in denser regions. In all subregions, the critical index of the mass-to-magnetic flux ratio is sub-unity, implying that Taurus is magnetically supported on large scales (∼2 pc). Within the region observed, the B213 filament takes a sharp turn to the north and the direction of the magnetic field also takes a sharp turn, switching from being perpendicular to the filament to becoming parallel. This behavior can be understood if we are observing the rim of a bubble. We argue that it has resulted from a supernova remnant associated with a recently discovered nearby gamma-ray pulsar.

  6. Pleistocene reduction of polar ice caps: Evidence from Cariaco Basin marine sediments

    Science.gov (United States)

    Poore, R.Z.; Dowsett, H.J.

    2001-01-01

    Sea level is projected to rise between 13 and 94 cm over the next 100 yr due to continued climate warming. The sea-level projections assume that polar ice sheets will remain stable or even increase on time scales of centuries, but controversial geologic evidence suggests that current polar ice sheets have been eliminated or greatly reduced during previous Pleistocene interglacials indicating that modern polar ice sheets have become unstable within the natural range of interglacial climates. Sea level may have been more than 20 m higher than today during a presumably very warm interglacial about 400 ka during marine isotope stage 11. Because of the implications for future sea level rise, additional study of the conflicting evidence for warmer conditions and higher sea level during marine isotope stage 11 is needed. Here we present microfossil and isotopic data from marine sediments of the Cariaco Basin supporting the interpretation that global sea level was 10-20 m higher than today during marine isotope stage 11. The increased sea level requires reduction in modern polar ice sheets and is consistent with the interpretation that the West Antarctic ice sheet and the Greenland ice sheet were absent or greatly reduced during marine isotope stage 11. Our results show a warm marine isotope stage 11 interglacial climate with sea level as high as or above modern sea level that lasted for 25 to 30 k.y. Variations in Earth's orbit around the sun (Milankovitch cycles) are considered to be a primary external force driving glacial-interglacial cycles. Current and marine isotope stage 11 Milankovitch forcing are very similar, suggesting that the present interglacial (Holocene) that began ca. 10 ka will continue for another 15 to 20 k.y. Therefore any anthropogenic climate warming will accelerate the natural process toward reduction in polar ice sheets. The potential for increased rates of sea level rise related to polar ice sheet decay should be considered as a potential natural

  7. Synthesis and characterization of magnetic Co nanoparticles: A comparison study of three different capping surfactants

    International Nuclear Information System (INIS)

    Lu Yu; Lu Xianmao; Mayers, Brian T.; Herricks, Thurston; Xia Younan

    2008-01-01

    This paper compares the performance of three long-chain acids-oleic and elaidic (both olefinic) and stearic (aliphatic)-as a capping agent in the synthesis of magnetic Co nanoparticles. The particles were formed through thermal decomposition of dicobalt octacarbonyl in toluene in the presence of the long-chain acid, and characterized by TEM, high-resolution TEM, and SQUID measurements. Infrared spectra revealed that some of the added olefinic acid was transformed from cis- to trans-configuration (for oleic acid) or from trans- to cis- (for elaidic acid) to facilitate the formation of a densely packed monolayer on the surface of Co nanoparticles. As compared to aliphatic acids, olefinic acids are advantageous for dense packing on small particles with high surface curvatures due to a bent shape of the cis-isomer. The presence of an olefinic acid is able to control particle growth, stabilize the colloidal suspension, and prevent the final product from oxidation by air. Our results indicate that oleic acid, elaidic acid, and a mixture of oleic/stearic acids or elaidic/stearic acids have roughly the same performance in serving as a capping agent for the synthesis of Co nanoparticles with a spherical shape and narrow size distribution. - Graphical abstract: Magnetic Co nanoparticles were synthesized in the presence of different capping agents and the effect of their molecular structures on the morphology of Co nanoparticles was analyzed. The transformation between cis- and trans-isomers of olefinic acids was critical to the formation of a densely packed monolayer on the surface of small nanoparticles characterized by high curvatures

  8. Spherical cap harmonic analysis of regional magnetic anomalies based on CHAMP satellite data

    Science.gov (United States)

    Feng, Yan; Jiang, Yong; Jiang, Yi; Liu, Bao-Jia; Jiang, Jin; Liu, Zhong-Wei; Ye, Mei-Chen; Wang, Hong-Shen; Li, Xiu-Ming

    2016-09-01

    We used CHAMP satellite vector data and the latest IGRF12 model to investigate the regional magnetic anomalies over mainland China. We assumed satellite points on the same surface (307.69 km) and constructed a spherical cap harmonic model of the satellite magnetic anomalies for elements X, Y, Z, and F over Chinese mainland for 2010.0 (SCH2010) based on selected 498 points. We removed the external field by using the CM4 model. The pole of the spherical cap is 36N° and 104°E, and its half-angle is 30°. After checking and comparing the root mean square (RMS) error of Δ X, Δ Y, and Δ Z and X, Y, and Z, we established the truncation level at K max = 9. The results suggest that the created China Geomagnetic Referenced Field at the satellite level (CGRF2010) is consistent with the CM4 model. We compared the SCH2010 with other models and found that the intensities and distributions are consistent. In view of the variation of F at different altitudes, the SCH2010 model results obey the basics of the geomagnetic field. Moreover, the change rate of X, Y, and Z for SCH2010 and CM4 are consistent. The proposed model can successfully reproduce the geomagnetic data, as other data-fitting models, but the inherent sources of error have to be considered as well.

  9. Spin polarization and magnetic effects in radical reactions

    International Nuclear Information System (INIS)

    Salikhov, K.M.; Molin, Yu.N.; Sagdeev, R.Z.; Buchachenko, A.L.

    1984-01-01

    Studies on the effects of chemically induced dynamic nuclear and electron polarizations (CIDNP and CIDEP), and magnetic effects in radical reactions, have given rise to a new rapidly-progressing field of chemical physics. It came into being about ten years ago and has been attracting the ever-growing attention of researchers in related areas. The present book is a fairly all-embracing review of the state of affairs in this field. The book presents the physical background (both theoretical and experimental) of CIDNP and CIDEP, of the effects of an external magnetic field and magnetic nuclear moment (magnetic isotope effects) on radical reactions in solutions. Great attention has been paid to the application of chemical spin polarization and magnetic effects to solving various problems of chemical kinetics, structural chemistry, molecular physics, magnetobiology, and radiospectroscopy. The book will be useful for physicists, chemists and biologists employing CIDNP, CIDEP and magnetic effects in their investigations, as well as for researchers in related fields of chemical physics. The book can be also recommended for postgraduates and senior undergraduate students. (Auth.)

  10. Spin polarized auger electron spectroscopy (SPAES): An element specific local magnetization probe of magnetic materials

    Science.gov (United States)

    Anilturk, Onder S.

    Spin Polarized Auger Electron Spectroscopy (SPAES) is found to have application for investigating fundamental properties as well as element specific local magnetization information on magnetic materials. By using the uniqueness of the UTA-SEMPA tool, one can obtain the surface magnetic domain microstructure and also perform SPAES studies by probing a single domain at the surface. In the current study, knowing the probed domain, spin polarization of electrons from super Coster-Kronig MVV Auger emissions on 3%Si-Fe sheets have been investigated. It is observed that on both sides of 180° domains, separated by a domain wall with an out-of-plane component of magnetization, the spin polarized Auger spectra exhibit similar distributions with high polarization structures, which are consistent with the published data. The element specificity of the system is applied to Gd-Co composite system. Details of 4d core hole initiated Auger transitions showed that the 5d states have enhanced spin polarization, confirming the coupling of moments in the composite system via 5d states of Gd. It is also unambiguously observed that Co magnetic moments are indeed aligned antiparallel to the Gd ones via 4f-5d positive exchange and 3d-5d hybridization.

  11. Multi-site observations of the association between aurora and plasma convection in the cusp/polar cap during a southeastward(By ~ |Bz| IMF orientation

    Directory of Open Access Journals (Sweden)

    P. E. Sandholt

    2003-02-01

    Full Text Available In a case study we demonstrate the spatiotemporal structure of aurora and plasma convection in the cusp/polar cap when the interplanetary magnetic field (IMF Bz < 0 and By ~ | Bz | (clock angle in GSM Y - Z plane: ~ 135°. This IMF orientation elicited a response different from that corresponding to strongly northward and southward IMF. Our study of this "intermediate state" is based on a combination of ground observations of optical auroral emissions and ionospheric plasma convection. Utilizing all-sky cameras at NyAlesund, Svalbard and Heiss Island (Russian arctic, we are able to monitor the high-latitude auroral activity within the ~10:00–15:00 MLT sector. Information on plasma convection is obtained from the SuperDARN radars, with emphasis placed on line of sight observations from the radar situated in Hankasalmi, Finland (Cutlass. A central feature of the auroral observations in the cusp/polar cap region is a ~ 30-min long sequence of four brightening events, some of which consists of latitudinally and longitudinally separated forms, which are found to be associated with pulsed ionospheric flows in merging and lobe convection cells. The auroral/convection events may be separated into different forms/cells and phases, reflecting a spatiotem-poral evolution of the reconnection process on the dayside magnetopause. The initial phase consists of a brightening in the postnoon sector (~ 12:00–14:00 MLT at ~ 73° MLAT, accompanied by a pulse of enhanced westward convection in the postnoon merging cell. Thereafter, the event evolution comprises two phenomena which occur almost simultaneously: (1 westward expansion of the auroral brightening (equatorward boundary intensification across noon, into the ~ 10:00–12:00 MLT sector, where the plasma convection subsequently turns almost due north, in the convection throat, and where classical poleward moving auroral forms (PMAFs are observed; and (2 auroral brightening at slightly higher latitudes

  12. Effect of magnetic polarity on surface roughness during magnetic field assisted EDM of tool steel

    Science.gov (United States)

    Efendee, A. M.; Saifuldin, M.; Gebremariam, MA; Azhari, A.

    2018-04-01

    Electrical discharge machining (EDM) is one of the non-traditional machining techniques where the process offers wide range of parameters manipulation and machining applications. However, surface roughness, material removal rate, electrode wear and operation costs were among the topmost issue within this technique. Alteration of magnetic device around machining area offers exciting output to be investigated and the effects of magnetic polarity on EDM remain unacquainted. The aim of this research is to investigate the effect of magnetic polarity on surface roughness during magnetic field assisted electrical discharge machining (MFAEDM) on tool steel material (AISI 420 mod.) using graphite electrode. A Magnet with a force of 18 Tesla was applied to the EDM process at selected parameters. The sparks under magnetic field assisted EDM produced better surface finish than the normal conventional EDM process. At the presence of high magnetic field, the spark produced was squeezed and discharge craters generated on the machined surface was tiny and shallow. Correct magnetic polarity combination of MFAEDM process is highly useful to attain a high efficiency machining and improved quality of surface finish to meet the demand of modern industrial applications.

  13. A technique for accurately determining the cusp-region polar cap boundary using SuperDARN HF radar measurements

    Directory of Open Access Journals (Sweden)

    G. Chisham

    Full Text Available Accurately measuring the location and motion of the polar cap boundary (PCB in the high-latitude ionosphere can be crucial for studies concerned with the dynamics of the polar cap, e.g. the measurement of reconnection rates. The Doppler spectral width characteristics of backscatter received by the SuperDARN HF radars have been previously used for locating and tracking the PCB in the cusp region. The boundary is generally observed in meridional beams of the SuperDARN radars and appears as a distinct change between low spectral width values observed equatorward of the cusp region, and high, but variable spectral width values observed within the cusp region. To identify the spectral width boundary (SWB between these two regions, a simple algorithm employing a spectral width threshold has often been applied to the data. However, there is not, as yet, a standard algorithm, or spectral width threshold, which is universally applied. Nor has there been any rigorous assessment of the accuracy of this method of boundary determination. This study applies a series of threshold algorithms to a simulated cusp-region spectral width data set, to assess the accuracy of different algorithms. This shows that simple threshold algorithms correctly identify the boundary location in, at the most, 50% of the cases and that the average boundary error is at least ~ 1–2 range gates (~ 1° latitude. It transpires that spatial and temporal smoothing of the spectral width data (e.g. by median filtering, before application of a threshold algorithm can increase the boundary determination accuracy to over 95% and the average boundary error to much less than a range gate. However, this is sometimes at the cost of temporal resolution in the motion of the boundary location. The algorithms are also applied to a year’s worth of spectral width data from the cusp ionosphere, measured by the Halley SuperDARN radar in Antarctica. This analysis highlights the increased accuracy of

  14. A technique for accurately determining the cusp-region polar cap boundary using SuperDARN HF radar measurements

    Directory of Open Access Journals (Sweden)

    G. Chisham

    2003-04-01

    Full Text Available Accurately measuring the location and motion of the polar cap boundary (PCB in the high-latitude ionosphere can be crucial for studies concerned with the dynamics of the polar cap, e.g. the measurement of reconnection rates. The Doppler spectral width characteristics of backscatter received by the SuperDARN HF radars have been previously used for locating and tracking the PCB in the cusp region. The boundary is generally observed in meridional beams of the SuperDARN radars and appears as a distinct change between low spectral width values observed equatorward of the cusp region, and high, but variable spectral width values observed within the cusp region. To identify the spectral width boundary (SWB between these two regions, a simple algorithm employing a spectral width threshold has often been applied to the data. However, there is not, as yet, a standard algorithm, or spectral width threshold, which is universally applied. Nor has there been any rigorous assessment of the accuracy of this method of boundary determination. This study applies a series of threshold algorithms to a simulated cusp-region spectral width data set, to assess the accuracy of different algorithms. This shows that simple threshold algorithms correctly identify the boundary location in, at the most, 50% of the cases and that the average boundary error is at least ~ 1–2 range gates (~ 1° latitude. It transpires that spatial and temporal smoothing of the spectral width data (e.g. by median filtering, before application of a threshold algorithm can increase the boundary determination accuracy to over 95% and the average boundary error to much less than a range gate. However, this is sometimes at the cost of temporal resolution in the motion of the boundary location. The algorithms are also applied to a year’s worth of spectral width data from the cusp ionosphere, measured by the Halley SuperDARN radar in Antarctica. This analysis highlights the increased accuracy of

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

    Science.gov (United States)

    de Melo, Roger Duarte; Acosta-Avalos, Daniel

    2017-09-01

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

  16. Reversing the polarity of a cochlear implant magnet after magnetic resonance imaging.

    Science.gov (United States)

    Jeon, Ju Hyun; Bae, Mi Ran; Chang, Jae Won; Choi, Jae Young

    2012-08-01

    The number of patients with cochlear implant (CI) has been rapidly increasing in recent years, and these patients show a growing need of examination by magnetic resonance imaging (MRI). However, the use of MRI on patients with CI is restricted by the internal magnet of the CI. Many studies have investigated the safety of performing 1.5T MRI on patients with CI, which is now being practiced in a clinical setting. We experienced a case in which the polarity of the cochlear implant magnet was reversed after the patient was examined using 1.5T MRI. The external device was attached to the internal device oppositely. We could not find displacement of the internal device, magnet, or electrode upon radiological evaluation. We came up with two possible mechanisms by which the polarity of the magnet reversed. The first possibility was that the magnetic field of MRI reversed the polarity of the magnet. The second was that the internal magnet was physically realigned while interacting with the MRI. We believe the second hypothesis to be more reliable. A removable magnet and a loose magnet boundary of a CI device may have allowed for physical reorientation of the internal magnet. Therefore, in order to avoid these complications, first, the internal magnet must not be aligned anti-parallel with the magnetic polarity of MRI. In the Siemens MRI, the vector of the magnetic field is downward, so implant site should be placed in facing upwards to minimize demagnetization. In the GE Medical Systems MRI, the vector of the magnetic field is upward, so the implant site should be placed facing downwards. Second, wearing of a commercial mold which is fixed to the internal device before performing MRI can be helpful. In addition, any removable internal magnets in a CI device should be removed before MRI, especially in the trunk. However, to ultimately solve this problem, the pocket of the internal magnet should be redesigned for safety. Copyright © 2011. Published by Elsevier Ireland Ltd.

  17. X-ray magnetic circular dichroism and small angle neutron scattering studies of thiol capped gold nanoparticles

    International Nuclear Information System (INIS)

    de la Venta, J.; Bouzas, V.; Pucci, A.; Laguna-Marco, M.A.; Haskel, D.; te Velthuis, S.G.E; Hoffmann, A.; Lal, J.; Bleuel, M.; Ruggeri, G.; de Julian Fernandez, C.; Garcia, M.A.

    2009-01-01

    X-ray magnetic circular dichroism (XMCD) and Small Angle Neutron Scattering (SANS) measurements were performed on thiol capped Au nanoparticles (NPs) embedded into polyethylene. An XMCD signal of 0.8 · 10 -4 was found at the Au L 3 edge of thiol capped Au NPs embedded in a polyethylene matrix for which Superconducting Quantum Interference Device (SQUID) magnetometry yielded a saturation magnetization, M s , of 0.06 emu/g Au . SANS measurements showed that the 3.2 nm average-diameter nanoparticles are 28% polydispersed, but no detectable SANS magnetic signal was found with the resolution and sensitivity accessible with the neutron experiment. A comparison with previous experiments carried out on Au NPs and multilayers, yield to different values between XMCD signals and magnetization measured by SQUID magnetometer. We discuss the origin of those differences

  18. X-ray magnetic circular dichroism and small angle neutron scattering studies of thiol capped gold nanoparticles.

    Science.gov (United States)

    de la Venta, J; Bouzas, V; Pucci, A; Laguna-Marco, M A; Haskel, D; te Velthuis, S G E; Hoffmann, A; Lal, J; Bleuel, M; Ruggeri, G; de Julián Fernández, C; García, M A

    2009-11-01

    X-ray magnetic circular dichroism (XMCD) and Small Angle Neutron Scattering (SANS) measurements were performed on thiol capped Au nanoparticles (NPs) embedded into polyethylene. An XMCD signal of 0.8 x 10(-4) was found at the Au L3 edge of thiol capped Au NPs embedded in a polyethylene matrix for which Superconducting Quantum Interference Device (SQUID) magnetometry yielded a saturation magnetization, M(S), of 0.06 emu/g(Au). SANS measurements showed that the 3.2 nm average-diameter nanoparticles are 28% polydispersed, but no detectable SANS magnetic signal was found with the resolution and sensitivity accessible with the neutron experiment. A comparison with previous experiments carried out on Au NPs and multilayers, yield to different values between XMCD signals and magnetization measured by SQUID magnetometer. We discuss the origin of those differences.

  19. X-ray magnetic circular dichroism and small angle neutron scattering studies of thiol capped gold nanoparticles.

    Energy Technology Data Exchange (ETDEWEB)

    de la Venta, J.; Bouzas, V.; Pucci, A.; Laguna-Marco, M. A.; Haskel, D.; te Velthuis, S. G. E; Hoffmann, A.; Lal, J.; Bleuel, M.; Ruggeri, G.; de Julian Fernandez, C.; Garcia, M. A.; Univ.Complutense de Madrid; Inst. de Magnetismo Aplicado; Univ. of Pisa; Lab. di Magnetismo Molecolare

    2009-01-01

    X-ray magnetic circular dichroism (XMCD) and Small Angle Neutron Scattering (SANS) measurements were performed on thiol capped Au nanoparticles (NPs) embedded into polyethylene. An XMCD signal of 0.8 {center_dot} 10{sup -4} was found at the Au L{sub 3} edge of thiol capped Au NPs embedded in a polyethylene matrix for which Superconducting Quantum Interference Device (SQUID) magnetometry yielded a saturation magnetization, M{sub s}, of 0.06 emu/g{sub Au}. SANS measurements showed that the 3.2 nm average-diameter nanoparticles are 28% polydispersed, but no detectable SANS magnetic signal was found with the resolution and sensitivity accessible with the neutron experiment. A comparison with previous experiments carried out on Au NPs and multilayers, yield to different values between XMCD signals and magnetization measured by SQUID magnetometer. We discuss the origin of those differences.

  20. X-ray magnetic circular dichroism and small angle neutron scattering study of thiol capped gold nanoparticles.

    Energy Technology Data Exchange (ETDEWEB)

    de la Venta, J.; Bouzas, V.; Pucci, A.; Laguna-Marco, M. A.; Haskel, D.; Pinel, E. F.; te Velthuis, S. G. E.; Hoffmann, A.; Lal, J.; Bleuel, M.; Ruggeri, G.; de Julian, C.; Garcia, M. A.; Univ. Complutense de Madrid; Inst. de Magnetismo Aplicado UCM; Univ. Pisa; Univ. di Padova

    2009-11-01

    X-ray magnetic circular dichroism (XMCD) and Small Angle Neutron Scattering (SANS) measurements were performed on thiol capped Au nanoparticles (NPs) embedded into polyethylene. An XMCD signal of 0.8 {center_dot} 10{sup -4} was found at the Au L{sub 3} edge of thiol capped Au NPs embedded in a polyethylene matrix for which Superconducting Quantum Interference Device (SQUID) magnetometry yielded a saturation magnetization, M{sub s}, of 0.06 emu/g{sub Au}. SANS measurements showed that the 3.2 nm average-diameter nanoparticles are 28% polydispersed, but no detectable SANS magnetic signal was found with the resolution and sensitivity accessible with the neutron experiment. A comparison with previous experiments carried out on Au NPs and multilayers, yield to different values between XMCD signals and magnetization measured by SQUID magnetometer. We discuss the origin of those differences.

  1. Magnetized boxes for housing polarized spins in homogeneous fields.

    Science.gov (United States)

    Hiebel, S; Grossmann, T; Kiselev, D; Schmiedeskamp, J; Gusev, Y; Heil, W; Karpuk, S; Krimmer, J; Otten, E W; Salhi, Z

    2010-05-01

    We present novel types of permanently magnetized as well as current powered boxes built from soft-ferromagnetic materials. They provide shielded magnetic fields which are homogeneous within a large fraction of the enclosed volume, thus minimizing size, weight, and costs. For the permanently magnetized solutions, homogenization is achieved either by an optimized distribution of the permanent field sources or by jacketing the field with a soft-ferromagnetic cylindrical shell which is magnetized in parallel to the enclosed field. The latter principle may be applied up to fields of about 0.1T. With fields of about 1mT, such boxes are being used for shipping spin-polarized (3)He worldwide for MRI purposes. For current powered boxes, we present concepts and realizations of uniaxial and tri-axial shielded magnetic fields which are homogeneous on the level of 10(-4) within the entire shielded volume. This is achieved by inserting tightly fitting solenoids into a box from soft-magnetic material. The flexible tri-axial solution suits in particular laboratory applications, e.g. for establishing a spin quantization axis. Copyright 2010 Elsevier Inc. All rights reserved.

  2. Checking the Polarity of Superconducting Multipole LHC Magnets

    CERN Document Server

    Buzio, M; Brun, G; Fievez, G; Galbraith, P; García-Pérez, J; López, R; Masi, A; Russenschuck, Stephan; Smirnov, N; Tikhov, A

    2006-01-01

    This paper describes the design and operation of the â€ワPolarity Checker”, a scanning probe designed to check multipole field order, type and polarity of superconducting LHC magnets. First we introduce the measurement method, based on the harmonic analysis of the radial field component picked up by a rotating Hall sensor at different current levels. Then we describe the hardware and the software of the system, which features automatic powering, data acquisition and treatment, discussing the achieved sensitivity and performance. Finally we provide a summary of the test results on the first 505 cryoassemblies, showing how the system was usefully employed to detect some potentially harmful connection errors.

  3. Electrical polarization and orbital magnetization: the modern theories

    International Nuclear Information System (INIS)

    Resta, Raffaele

    2010-01-01

    Macroscopic polarization P and magnetization M are the most fundamental concepts in any phenomenological description of condensed media. They are intensive vector quantities that intuitively carry the meaning of dipole per unit volume. But for many years both P and the orbital term in M evaded even a precise microscopic definition, and severely challenged quantum-mechanical calculations. If one reasons in terms of a finite sample, the electric (magnetic) dipole is affected in an extensive way by charges (currents) at the sample boundary, due to the presence of the unbounded position operator in the dipole definitions. Therefore P and the orbital term in M-phenomenologically known as bulk properties-apparently behave as surface properties; only spin magnetization is problemless. The field has undergone a genuine revolution since the early 1990s. Contrary to a widespread incorrect belief, P has nothing to do with the periodic charge distribution of the polarized crystal: the former is essentially a property of the phase of the electronic wavefunction, while the latter is a property of its modulus. Analogously, the orbital term in M has nothing to do with the periodic current distribution in the magnetized crystal. The modern theory of polarization, based on a Berry phase, started in the early 1990s and is now implemented in most first-principle electronic structure codes. The analogous theory for orbital magnetization started in 2005 and is partly work in progress. In the electrical case, calculations have concerned various phenomena (ferroelectricity, piezoelectricity, and lattice dynamics) in several materials, and are in spectacular agreement with experiments; they have provided thorough understanding of the behaviour of ferroelectric and piezoelectric materials. In the magnetic case the very first calculations are appearing at the time of writing (2010). Here I review both theories on a uniform ground in a density functional theory (DFT) framework, pointing out

  4. Sensing Noncollinear Magnetism at the Atomic Scale Combining Magnetic Exchange and Spin-Polarized Imaging.

    Science.gov (United States)

    Hauptmann, Nadine; Gerritsen, Jan W; Wegner, Daniel; Khajetoorians, Alexander A

    2017-09-13

    Storing and accessing information in atomic-scale magnets requires magnetic imaging techniques with single-atom resolution. Here, we show simultaneous detection of the spin-polarization and exchange force with or without the flow of current with a new method, which combines scanning tunneling microscopy and noncontact atomic force microscopy. To demonstrate the application of this new method, we characterize the prototypical nanoskyrmion lattice formed on a monolayer of Fe/Ir(111). We resolve the square magnetic lattice by employing magnetic exchange force microscopy, demonstrating its applicability to noncollinear magnetic structures for the first time. Utilizing distance-dependent force and current spectroscopy, we quantify the exchange forces in comparison to the spin-polarization. For strongly spin-polarized tips, we distinguish different signs of the exchange force that we suggest arises from a change in exchange mechanisms between the probe and a skyrmion. This new approach may enable both nonperturbative readout combined with writing by current-driven reversal of atomic-scale magnets.

  5. 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.

  6. Candidate magnetic dust structures for star light polarization

    Science.gov (United States)

    Papoular, R.

    2017-11-01

    Rotation damping and alignment are discussed as prerequisites for polarization. An expression is derived from first principles, for the damping time of the rotation of a particle in a magnetic field, under the Faraday braking torque, provided its electrical properties are known. This makes it possible to describe mathematically, in great detail, the motion of the particle and determine its ultimate state of motion, if a steady state is possible at all. This work defines, first, the necessary condition for the Faraday braking to be effective: (a) the net electronic charge distribution should not be uniform throughout and (b) the number of vibration modes should exceed a few tens. Resonance of rotation frequency with any of these modes is not a requirement. For alignment to be possible, the ratio of gyroscopic and conservative magnetic to non-conservative (retarding) magnetic torques must be low. Either dia-, para- or ferromagnetism can do, and a small susceptibility is enough and even preferable. This opens up a wide spectrum of possible candidates. A few examples are given.

  7. Method for forming permanent magnets with different polarities for use in microelectromechanical devices

    Science.gov (United States)

    Roesler, Alexander W [Tijeras, NM; Christenson, Todd R [Albuquerque, NM

    2007-04-24

    Methods are provided for forming a plurality of permanent magnets with two different north-south magnetic pole alignments for use in microelectromechanical (MEM) devices. These methods are based on initially magnetizing the permanent magnets all in the same direction, and then utilizing a combination of heating and a magnetic field to switch the polarity of a portion of the permanent magnets while not switching the remaining permanent magnets. The permanent magnets, in some instances, can all have the same rare-earth composition (e.g. NdFeB) or can be formed of two different rare-earth materials (e.g. NdFeB and SmCo). The methods can be used to form a plurality of permanent magnets side-by-side on or within a substrate with an alternating polarity, or to form a two-dimensional array of permanent magnets in which the polarity of every other row of the array is alternated.

  8. Applications of circularly polarized photons at the ALS with a bend magnet source

    Energy Technology Data Exchange (ETDEWEB)

    1992-02-01

    The purpose of this workshop is to focus attention on, and to stimulate the scientific exploitation of, the natural polarization properties of bend-magnet synchrotron radiation at the ALS -- for research in biology, materials science, physics, and chemistry. The topics include: The Advanced Light Source; Magnetic Circular Dichroism and Differential Scattering on Biomolecules; Tests of Fundamental Symmetries; High {Tc} Superconductivity; Photoemission from Magnetic and Non-magnetic Solids; Studies of Highly Correlated Systems; and Instrumentation for Photon Transport and Polarization Measurements.

  9. Far-from-Equilibrium Quantum Magnetism with Ultracold Polar Molecules

    Science.gov (United States)

    Hazzard, Kaden R. A.; Manmana, Salvatore R.; Foss-Feig, Michael; Rey, Ana Maria

    2013-02-01

    Recent theory has indicated how to emulate tunable models of quantum magnetism with ultracold polar molecules. Here we show that present molecule optical lattice experiments can accomplish three crucial goals for quantum emulation, despite currently being well below unit filling and not quantum degenerate. The first is to verify and benchmark the models proposed to describe these systems. The second is to prepare correlated and possibly useful states in well-understood regimes. The third is to explore many-body physics inaccessible to existing theoretical techniques. Our proposal relies on a nonequilibrium protocol that can be viewed either as Ramsey spectroscopy or an interaction quench. The proposal uses only routine experimental tools available in any ultracold molecule experiment. To obtain a global understanding of the behavior, we treat short times pertubatively, develop analytic techniques to treat the Ising interaction limit, and apply a time-dependent density matrix renormalization group to disordered systems with long range interactions.

  10. Intermediate polars as low-field magnetic cataclysmic variables

    International Nuclear Information System (INIS)

    Wickramasinghe, D.T.; Kinwah Wu; Ferrario, Lilia

    1991-01-01

    We present the first detailed calculations of the polarization properties of extended accretion shocks on the surface of a magnetic white dwarf where allowance is made both for field spread and for the change in shock height as a function of specific accretion rate. These results are used to show conclusively that the null detection of circular polarization in most IPs imply fields of less than 5 MG. We suggest that the X-ray properties of MCVs depends critically on the fractional area of the white-dwarf surface over which accretion occurs, and on the type of accretion (smooth or clumpy). We argue that in the known IPs, accretion occurs via a disc. The accretion flow is smooth and a strong shock forms making them a powerful source of hard X-rays. We propose that there is a new class of MCV distinct from the IPs, where the white dwarf is asynchronous and accretes without a disc in which the accretion is clumpy and the radiation is mainly in the EUV region. (author)

  11. Trim Magnet Polarities, Dispersion, and Response Data in Sector 23

    CERN Document Server

    Butterworth, A; Fuchsberger, K; Kain, V; Lamont, M; Ponce, L; Tomás, R; Venturnini-Delsolaro, W; Wenninger, J; Zimmermann, F

    2008-01-01

    During the first LHC injection test, on 10 August 2008, the horizontal dispersion measured with beam 1 at the end of Sector 23 differed from the model prediction close to point 3. Beam-based polarity checks performed during the same period indicated an inversion of the trim quadrupole QTL11.R2. Combined with other evidence, like electrical drawings and earlier Hall-probe measurements of warm magnets, this gave rise to the hypothesis of a systematic error. Indeed a model inversion of all trim quadrupoles (QT or QTL) attached to a defocusing main quadrupole (actually the odd-numbered trim quadrupoles in Sector 23) reproduced the dispersion measurement. An analysis of kick-response measurements independently revealed an optics error left of point 3, and confirmed the inversion of the odd-numbered trim quadrupoles in this sector. After changing the polarity of the suspected set of quadrupoles prior to the second injection test on August 24, the measured dispersion nicely traced the model prediction.

  12. Polarized light modulates light-dependent magnetic compass orientation in birds

    Science.gov (United States)

    Muheim, Rachel; Sjöberg, Sissel; Pinzon-Rodriguez, Atticus

    2016-01-01

    Magnetoreception of the light-dependent magnetic compass in birds is suggested to be mediated by a radical-pair mechanism taking place in the avian retina. Biophysical models on magnetic field effects on radical pairs generally assume that the light activating the magnetoreceptor molecules is nondirectional and unpolarized, and that light absorption is isotropic. However, natural skylight enters the avian retina unidirectionally, through the cornea and the lens, and is often partially polarized. In addition, cryptochromes, the putative magnetoreceptor molecules, absorb light anisotropically, i.e., they preferentially absorb light of a specific direction and polarization, implying that the light-dependent magnetic compass is intrinsically polarization sensitive. To test putative interactions between the avian magnetic compass and polarized light, we developed a spatial orientation assay and trained zebra finches to magnetic and/or overhead polarized light cues in a four-arm “plus” maze. The birds did not use overhead polarized light near the zenith for sky compass orientation. Instead, overhead polarized light modulated light-dependent magnetic compass orientation, i.e., how the birds perceive the magnetic field. Birds were well oriented when tested with the polarized light axis aligned parallel to the magnetic field. When the polarized light axis was aligned perpendicular to the magnetic field, the birds became disoriented. These findings are the first behavioral evidence to our knowledge for a direct interaction between polarized light and the light-dependent magnetic compass in an animal. They reveal a fundamentally new property of the radical pair-based magnetoreceptor with key implications for how birds and other animals perceive the Earth’s magnetic field. PMID:26811473

  13. Spin-polarized semiconductor induced by magnetic impurities in graphene

    Science.gov (United States)

    Daghofer, Maria

    2011-03-01

    Magnetic impurities adsorbed on graphene sheets are coupled antiferromangetically via the itinerant electrons in the graphene. We study this interaction and its impact on the electrons' spectral density by use of unbiased Monte-Carlo simulations. The antiferromagnetic order breaks the symmetry between the sublattices, and a gap for the itinerant electrons opens. Our simulations show that the itinerant states below and above the gap are not dispersionless states trapped by the impurities, but are instead mobile states with a large dispersion. We compare various scenarios for the impurity distribution and find that random doping produces a standard semiconductor. If, on the other hand, all or most of the impurities are localized in the same sublattice, the spin degeneracy is lifted and the conduction band becomes spin-polarized. We also discuss the properties of edge states at edges or magnetic domain boundaries. M.~Daghofer, N.~Zheng, A.~Moreo; Phys.~Rev.~B 82, 121405(R) (2010) Supported by the DFG under the Emmy-Noether Program, and the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, U.S. DOE.

  14. Spin-polarized magnetic tunnelling magnetoresistive effects in various junctions

    Science.gov (United States)

    Miyazaki, T.; Tezuka, N.; Kumagai, S.; Ando, Y.; Kubota, H.; Murai, J.; Watabe, T.; Yokota, M.

    1998-03-01

    Recent progress concerning spin-polarized magnetic tunnelling effects for (i) trilayer standard ferromagnet (F)/insulator (I)/ferromagnet (F) junctions, (ii) spin-valve-type junctions, (iii) trilayer or multilayer ferromagnet/granular/ferromagnet junctions and (iv) F/I/F junction with a `wedge-geometry' insulator is reviewed. Special emphasis is placed on the dependence of the tunnel magnetoresistance ratio on temperature and also the intensity of the applied voltage. It was found that the resistance for the saturation magnetization state, 0022-3727/31/6/009/img1, and the tunnelling magnetoresistance ratio, TMR, of an 0022-3727/31/6/009/img2 junction decreased rapidly with increasing temperature, whereas those of a 0022-3727/31/6/009/img3 junction were insensitive to temperature. Concerning the bias voltage dependence of 0022-3727/31/6/009/img1 and TMR, the same tendency with temperature was observed for 0022-3727/31/6/009/img2 and 0022-3727/31/6/009/img3 junctions. Spin-valve-type junction exchange biased by a FeMn layer exhibits a relatively large TMR ratio up to about 400 K.

  15. Nanoscale switch for vortex polarization mediated by Bloch core formation in magnetic hybrid systems

    Science.gov (United States)

    Wohlhüter, Phillip; Bryan, Matthew Thomas; Warnicke, Peter; Gliga, Sebastian; Stevenson, Stephanie Elizabeth; Heldt, Georg; Saharan, Lalita; Suszka, Anna Kinga; Moutafis, Christoforos; Chopdekar, Rajesh Vilas; Raabe, Jörg; Thomson, Thomas; Hrkac, Gino; Heyderman, Laura Jane

    2015-01-01

    Vortices are fundamental magnetic topological structures characterized by a curling magnetization around a highly stable nanometric core. The control of the polarization of this core and its gyration is key to the utilization of vortices in technological applications. So far polarization control has been achieved in single-material structures using magnetic fields, spin-polarized currents or spin waves. Here we demonstrate local control of the vortex core orientation in hybrid structures where the vortex in an in-plane Permalloy film coexists with out-of-plane maze domains in a Co/Pd multilayer. The vortex core reverses its polarization on crossing a maze domain boundary. This reversal is mediated by a pair of magnetic singularities, known as Bloch points, and leads to the transient formation of a three-dimensional magnetization structure: a Bloch core. The interaction between vortex and domain wall thus acts as a nanoscale switch for the vortex core polarization. PMID:26238042

  16. Pre-polarization enhancement by dynamic nuclear polarization in SQUID-based ultra-low-field nuclear magnetic resonance

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Seong-Joo; Kim, Kiwoong; Kang, Chan Seok; Hwang, Seong-min; Lee, Yong-Ho, E-mail: kwkim@kriss.re.k [Brain and Cognition Measurement Laboratory, Korea Research Institute of Standards and Science (KRISS), Doryong-dong, Yuseong-gu, Daejeon 305-340 (Korea, Republic of)

    2010-11-15

    We achieved enhanced pre-polarization in a superconducting quantum interference device (SQUID)-based microtesla nuclear magnetic resonance (NMR) experiment by using dynamic nuclear polarization (DNP). The pre-polarization field is necessary to provide enough signal to noise to perform SQUID-based ultra-low-field (ULF) NMR/magnetic resonance imaging (MRI) experiments. However, it is quite tricky to deal with the strong transient magnetic field when operating the SQUID in a magnetically shielded room (MSR); besides the direct interference with the sensitive SQUID sensor, the strong magnetic field and its abrupt change generate magnetization in local areas in the MSR and eddy currents along the wall, which makes the NMR measurement difficult. The enhanced {sup 1}H NMR signals of water in TEMPOL and TEMPO solutions were obtained with a relatively weak radio-frequency (rf) field and double-relaxation oscillation SQUIDs (DROS) at a few mT pre-polarization fields. In our experimental condition, the enhancement factor was near ten in spite of the rf power far below the saturation in both samples.

  17. Pre-polarization enhancement by dynamic nuclear polarization in SQUID-based ultra-low-field nuclear magnetic resonance

    Science.gov (United States)

    Lee, Seong-Joo; Kim, Kiwoong; Kang, Chan Seok; Hwang, Seong-min; Lee, Yong-Ho

    2010-11-01

    We achieved enhanced pre-polarization in a superconducting quantum interference device (SQUID)-based microtesla nuclear magnetic resonance (NMR) experiment by using dynamic nuclear polarization (DNP). The pre-polarization field is necessary to provide enough signal to noise to perform SQUID-based ultra-low-field (ULF) NMR/magnetic resonance imaging (MRI) experiments. However, it is quite tricky to deal with the strong transient magnetic field when operating the SQUID in a magnetically shielded room (MSR); besides the direct interference with the sensitive SQUID sensor, the strong magnetic field and its abrupt change generate magnetization in local areas in the MSR and eddy currents along the wall, which makes the NMR measurement difficult. The enhanced 1H NMR signals of water in TEMPOL and TEMPO solutions were obtained with a relatively weak radio-frequency (rf) field and double-relaxation oscillation SQUIDs (DROS) at a few mT pre-polarization fields. In our experimental condition, the enhancement factor was near ten in spite of the rf power far below the saturation in both samples.

  18. Evolution of the microstructure, chemical composition and magnetic behaviour during the synthesis of alkanethiol-capped gold nanoparticles

    International Nuclear Information System (INIS)

    Guerrero, E.; Rojas, T.C.; Multigner, M.; Crespo, P.; Munoz-Marquez, M.A.; Garcia, M.A.; Hernando, A.; Fernandez, A.

    2007-01-01

    In the present paper, we show an exhaustive microstructural characterization of thiol-capped gold nanoparticles (NPs) with two different average particle sizes. These samples are compared with the polymer-like Au(I) phase formed as a precursor during the synthesis of the thiol-capped gold NPs. The set of analysed samples shows different microstructures at the nanoscale with different proportions of Au atoms bonded either to S or to Au atoms. It has been experimentally shown that the presence of a ferromagnetic-like behaviour is associated to the formation of NPs with simultaneous presence of Au-Au and Au-S bonds. In order to explain such magnetic behaviour a possible model is proposed based on the spin-orbit coupling so that localized charges and/or spins (Au-S bonds) can trap conduction electrons (Au-Au bonds) in orbits

  19. Independent control of the vortex chirality and polarity in a pair of magnetic nanodots

    Energy Technology Data Exchange (ETDEWEB)

    Li, Junqin; Wang, Yong, E-mail: wangyong@sinap.ac.cn; Cao, Jiefeng; Meng, Xiangyu; Zhu, Fangyuan; Wu, Yanqing; Tai, Renzhong

    2017-08-01

    Independent control of the vortex chirality and polarity is realized by changing the in-plane magnetic field direction in nanodot pair through Object Oriented Micromagnetic Framework (OOMMF) simulation. The two magnetic circles are close to each other and have magnetic interaction. The two circles always have the same polarity and opposite chirality at every remanent state. There are totally four predictable magnetic states in the nanodot pair which can be obtained in the remanent state relaxed from the saturation state along all possible directions. An explanation on the formation of vortex states is given by vortex dynamics. The vortex states are stable in large out-of-plane magnetic field which is in a direction opposite to the vortex polarity. The geometry of the nanodot pair gives a way to easily realize a vortex state with specific polarity and chirality.

  20. Magnetic nanostructures studied by polarized small angle neutron scattering

    International Nuclear Information System (INIS)

    Wiedenmann, Albrecht; Kammel, Martin; Heinemann, Andre

    2005-01-01

    Small Angle Neutron Scattering using polarised neutrons is introduced as a contrast variation technique for magnetic systems. The potential of this technique is illustrated on diluted Ferrofluids. Composition, magnetization and size distributions of magnetic core-shell composite particles and magnetic aggregates could be precisely evaluated beside non-magnetic micelles and free surfactants of similar sizes. Structure factors have been extracted which revealed a local pseudo-crystalline ordering of the magnetic particles induced by magnetic fields

  1. VISIONS: Remote Observations of a Spatially-Structured Filamentary Source of Energetic Neutral Atoms near the Polar Cap Boundary During an Auroral Substorm

    Science.gov (United States)

    Collier, Michael R.; Chornay, D.; Clemmons, J.; Keller, J. W.; Klenzing, J.; Kujawski, J.; McLain, J.; Pfaff, R.; Rowland, D.; Zettergren, M.

    2015-01-01

    We report initial results from the VISualizing Ion Outflow via Neutral atom imaging during a Substorm (VISIONS) rocket that flew through and near several regions of enhanced auroral activity and also sensed regions of ion outflow both remotely and directly. The observed neutral atom fluxes were largest at the lower energies and generally higher in the auroral zone than in the polar cap. In this paper, we focus on data from the latter half of the VISIONS trajectory when the rocket traversed the polar cap region. During this period, many of the energetic neutral atom spectra show a peak at 100 electronvolts. Spectra with peaks around 100 electronvolts are also observed in the Electrostatic Ion Analyzer (EIA) data consistent with these ions comprising the source population for the energetic neutral atoms. The EIA observations of this low energy population extend only over a few tens of kilometers. Furthermore, the directionality of the arriving energetic neutral atoms is consistent with either this spatially localized source of energetic ions extending from as low as about 300 kilometers up to above 600 kilometers or a larger source of energetic ions to the southwest.

  2. Polar cap mesosphere wind observations: comparisons of simultaneous measurements with a Fabry-Perot interferometer and a field-widened Michelson interferometer.

    Science.gov (United States)

    Fisher, G M; Killeen, T L; Wu, Q; Reeves, J M; Hays, P B; Gault, W A; Brown, S; Shepherd, G G

    2000-08-20

    Polar cap mesospheric winds observed with a Fabry-Perot interferometer with a circle-to-line interferometer optical (FPI/CLIO) system have been compared with measurements from a field-widened Michelson interferometer optimized for E-region winds (ERWIN). Both instruments observed the Meinel OH emission emanating from the mesopause region (approximately 86 km) at Resolute Bay, Canada (74.9 degrees N, 94.9 degrees W). This is the first time, to our knowledge, that winds measured simultaneously from a ground-based Fabry-Perot interferometer and a ground-based Michelson interferometer have been compared at the same location. The FPI/CLIO and ERWIN instruments both have a capability for high temporal resolution (less than 10 min for a full scan in the four cardinal directions and the zenith). Statistical comparisons of hourly mean winds for both instruments by scatterplots show excellent agreement, indicating that the two optical techniques provide equivalent observations of mesopause winds. Small deviations in the measured wind can be ascribed to the different zenith angles used by the two instruments. The combined measurements illustrate the dominance of the 12-h wave in the mesopause winds at Resolute Bay, with additional evidence for strong gravity wave activity with much shorter periods (tens of minutes). Future operations of the two instruments will focus on observation of complementary emissions, providing a unique passive optical capability for the determination of neutral winds in the geomagnetic polar cap at various altitudes near the mesopause.

  3. Valley polarization in magnetically doped single-layer transition-metal dichalcogenides

    KAUST Repository

    Cheng, Yingchun

    2014-04-28

    We demonstrate that valley polarization can be induced and controlled in semiconducting single-layer transition-metal dichalcogenides by magnetic doping, which is important for spintronics, valleytronics, and photonics devices. As an example, we investigate Mn-doped MoS2 by first-principles calculations. We study how the valley polarization depends on the strength of the spin orbit coupling and the exchange interaction and discuss how it can be controlled by magnetic doping. Valley polarization by magnetic doping is also expected for other honeycomb materials with strong spin orbit coupling and the absence of inversion symmetry.

  4. Magnetization-dependent viscosity in brute-force-polarized liquid 3He

    DEFF Research Database (Denmark)

    Vermeulen, G.A.; Schuhl, A.; Joffrin, J.

    1988-01-01

    A new method to measure the magnetization dependence of the viscosity in polarized liquid He3 is presented. The magnetization is obtained by "brute-force polarization" at 45 mK in magnetic fields up to 11 T; it is subsequently destroyed by saturation of the NMR signal. Our result, a relative...... increase of the viscosity of (31.5)×10-3 at 3.9% polarization and a pressure of 30 bars, disagrees with a prediction based on the "nearly metamagnetic" model....

  5. Effective Area and Various Variations of The Northern Polar Cap Magnetic Activity Index (pcn)

    Science.gov (United States)

    Gromova, L.; Papitashvili, O.; Popov, V.; Rasmussen, O.

    We investigated the effective area and various variations (universal time, seasonal, and solar cycle) from the PCN time series available since 1975 and derived from cor- relation analyses of ground geomagnetic observations at Qaanaaq (Thule, Greenland) with the "merging" interplanetary electric field. We analyzed solar cycle variations in the normalization coefficients (slope and intercept) and preferred direction of the transpolar ionospheric current (all used for routine calculations of PCN) from 1964 to 1999 combining data monthly for three consecutive years and using a 3-year box- car sliding window. The obtained results show that the solar cycle effect is clearly seen in the studied parameters amounting to 25% of the magnitude change during winter and equinox but increasing to 40% during summer. We calculated similar sets of coefficients and the index for all high-latitude Greenlandic stations, Nord and Resolute Bay stations using data from 1991 to 1999 by the 3-year sliding window. It is concluded that (even a set of normalization coefficients is obtained for a specific station) the "station-based" PC-indices are almost identical only for two most north- ern observatories Thule (THL) and Savissivik (SVS) through an entire UT day; other stations located at lower latitudes produce the index similar to THL and SVS only during few nighttime hours. Thus, we firmly justified that the area where the Northern PC index stably preserves a value is located within 7 distance from the northern geomagnetic pole.

  6. Highly polarized light emission by isotropic quantum dots integrated with magnetically aligned segmented nanowires

    International Nuclear Information System (INIS)

    Uran, Can; Erdem, Talha; Guzelturk, Burak; Perkgöz, Nihan Kosku; Jun, Shinae; Jang, Eunjoo; Demir, Hilmi Volkan

    2014-01-01

    In this work, we demonstrate a proof-of-concept system for generating highly polarized light from colloidal quantum dots (QDs) coupled with magnetically aligned segmented Au/Ni/Au nanowires (NWs). Optical characterizations reveal that the optimized QD-NW coupled structures emit highly polarized light with an s-to p-polarization (s/p) contrast as high as 15:1 corresponding to a degree of polarization of 0.88. These experimental results are supported by the finite-difference time-domain simulations, which demonstrate the interplay between the inter-NW distance and the degree of polarization.

  7. Dynamic Nuclear Polarization at low temperature and high magnetic eld for biomedical applications in Magnetic Resonance Spectroscopic Imaging

    International Nuclear Information System (INIS)

    Goutailler, Florent

    2011-01-01

    The aim of this thesis work was to design, build and optimize a large volume multi-samples DNP (Dynamic Nuclear Polarization) polarizer dedicated to Magnetic Resonance Spectroscopic Imaging applications. The experimental system is made up of a high magnetic field magnet (3,35 T) in which takes place a cryogenic system with a pumped bath of liquid helium ( 4 He) allowing temperatures lower than 1,2 K. A set of inserts is used for the different steps of DNP: irradiation of the sample by a microwave field (f=94 GHz and P=50 mW), polarization measurement by Nuclear Magnetic Resonance... With this system, up to three samples of 1 mL volume can be polarized to a rate of few per-cents. The system has a long autonomy of four hours, so it can be used for polarizing molecules with a long time constant of polarization. Finally, the possibility to get quasi-simultaneously, after dissolution, several samples with a high rate of polarization opens the way of new applications in biomedical imaging. (author) [fr

  8. Interplay between magnetism and conductivity derived from spin-polarized donor radicals.

    Science.gov (United States)

    Sugawara, Tadashi; Komatsu, Hideji; Suzuki, Kentaro

    2011-06-01

    Tutorial review: to achieve molecule-based spintronic devices, an organic conducting magnet that exhibits both conductivity and magnetism in a cooperative manner must be constructed. As a building block for such new materials, a spin-polarized donor radical, which serves as a molecular "spin-filter" in its singly oxidized state, was designed and synthesized. The resistivity of ion radical salts of selenium-substituted, tetrathiafulvalene-based spin-polarized donor radicals decreased substantially in the presence of a magnetic field, thus indicating cooperative conductivity and magnetism.

  9. The impact of structural relaxation on spin polarization and magnetization reversal of individual nano structures studied by spin-polarized scanning tunneling microscopy.

    Science.gov (United States)

    Sander, Dirk; Phark, Soo-Hyon; Corbetta, Marco; Fischer, Jeison A; Oka, Hirofumi; Kirschner, Jürgen

    2014-10-01

    The application of low temperature spin-polarized scanning tunneling microscopy and spectroscopy in magnetic fields for the quantitative characterization of spin polarization, magnetization reversal and magnetic anisotropy of individual nano structures is reviewed. We find that structural relaxation, spin polarization and magnetic anisotropy vary on the nm scale near the border of a bilayer Co island on Cu(1 1 1). This relaxation is lifted by perimetric decoration with Fe. We discuss the role of spatial variations of the spin-dependent electronic properties within and at the edge of a single nano structure for its magnetic properties.

  10. 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

  11. Polar Magnetic Field Reversals of the Sun in Maunder Minimum

    Indian Academy of Sciences (India)

    Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately.

  12. POLAR NETWORK INDEX AS A MAGNETIC PROXY FOR THE SOLAR CYCLE STUDIES

    International Nuclear Information System (INIS)

    Priyal, Muthu; Banerjee, Dipankar; Ravindra, B.; Singh, Jagdev; Karak, Bidya Binay; Muñoz-Jaramillo, Andrés; Choudhuri, Arnab Rai

    2014-01-01

    The Sun has a polar magnetic field which oscillates with the 11 yr sunspot cycle. This polar magnetic field is an important component of the dynamo process which operates in the solar convection zone and produces the sunspot cycle. We have direct systematic measurements of the Sun's polar magnetic field only from about the mid-1970s. There are, however, indirect proxies which give us information about this field at earlier times. The Ca-K spectroheliograms taken at the Kodaikanal Solar Observatory during 1904-2007 have now been digitized with 4k × 4k CCD and have higher resolution (∼0.86 arcsec) than the other available historical data sets. From these Ca-K spectroheliograms, we have developed a completely new proxy (polar network index, hereafter PNI) for the Sun's polar magnetic field. We calculate PNI from the digitized images using an automated algorithm and calibrate our measured PNI against the polar field as measured by the Wilcox Solar Observatory for the period 1976-1990. This calibration allows us to estimate the polar fields for the earlier period up to 1904. The dynamo calculations performed with this proxy as input data reproduce reasonably well the Sun's magnetic behavior for the past century

  13. Untangling inconsistent magnetic polarity records through an integrated rock magnetic analysis: A case study on Neogene sections in East Timor

    Science.gov (United States)

    Aben, F. M.; Dekkers, M. J.; Bakker, R. R.; van Hinsbergen, D. J. J.; Zachariasse, W. J.; Tate, G. W.; McQuarrie, N.; Harris, R.; Duffy, B.

    2014-06-01

    Inconsistent polarity patterns in sediments are a common problem in magnetostratigraphic and paleomagnetic research. Multiple magnetic mineral generations result in such remanence "haystacks." Here we test whether end-member modeling of isothermal remanent magnetization acquisition curves as a basis for an integrated rock magnetic and microscopic analysis is capable of isolating original magnetic polarity patterns. Uppermost Miocene-Pliocene deep-marine siliciclastics and limestones in East Timor, originally sampled to constrain the uplift history of the young Timor orogeny, serve as case study. An apparently straightforward polarity record was obtained that, however, proved impossible to reconcile with the associated biostratigraphy. Our analysis distinguished two magnetic end-members for each section, which result from various greigite suites and a detrital magnetite suite. The latter yields largely viscous remanence signals and is deemed unsuited. The greigite suites are late diagenetic in the Cailaco River section and early diagenetic, thus reliable, in the Viqueque Type section. By selecting reliable sample levels based on a quality index, a revised polarity pattern of the latter section is obtained: consistent with the biostratigraphy and unequivocally correlatable to the Geomagnetic Polarity Time Scale. Although the Cailaco River section lacks a reliable magnetostratigraphy, it does record a significant postremagnetization tectonic rotation. Our results shows that the application of well-designed rock magnetic research, based on the end-member model and integrated with microscopy and paleomagnetic data, can unravel complex and seemingly inconsistent polarity patterns. We recommend this approach to assess the veracity of the polarity of strata with complex magnetic mineralogy.

  14. High resolution spectroscopy of the Martian atmosphere - Study of seasonal variations of CO, O3, H2O, and T on the north polar cap and a search for SO2, H2O2, and H2CO

    Science.gov (United States)

    Krasnopolsky, V. A.; Chakrabarti, S.; Larson, H.; Sandel, B. R.

    1992-01-01

    An overview is presented of an observational campaign which will measure (1) the seasonal variations of the CO mixing ratio on the Martian polar cap due to accumulation and depletion of CO during the condensation and evaporation of CO2, as well as (2) the early spring ozone and water vapor of the Martian north polar cap, and (3) the presence of H2CO, H2O2, and SO2. The lines of these compounds will be measured by a combined 4-m telescope and Fourier-transform spectrometer 27097.

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

    Science.gov (United States)

    Kolen'ko, Yury V; Bañobre-López, Manuel; Rodríguez-Abreu, Carlos; Carbó-Argibay, Enrique; Deepak, Francis Leonard; Petrovykh, Dmitri Y; Cerqueira, M Fátima; Kamali, Saeed; Kovnir, Kirill; Shtansky, Dmitry V; Lebedev, Oleg I; Rivas, Jose

    2014-12-04

    To investigate magnetostructural relationships in colloidal magnetite (Fe 3 O 4 ) nanoparticles (NPs) at high temperature (300-900 K), we measured the temperature dependence of magnetization ( M ) of oleate-capped magnetite NPs ca. 20 nm in size. Magnetometry revealed an unusual irreversible high-temperature dependence of M for these NPs, with dip and loop features observed during heating-cooling cycles. Detailed characterizations of as-synthesized and annealed Fe 3 O 4 NPs as well as reference ligand-free Fe 3 O 4 NPs indicate that both types of features in M ( T ) are related to thermal decomposition of the capping ligands. The ligand decomposition upon the initial heating induces a reduction of Fe 3+ to Fe 2+ and the associated dip in M , leading to more structurally and compositionally uniform magnetite NPs. Having lost the protective ligands, the NPs continually sinter during subsequent heating cycles, resulting in divergent M curves featuring loops. The increase in M with sintering proceeds not only through elimination of a magnetically dead layer on the particle surface, as a result of a decrease in specific surface area with increasing size, but also through an uncommonly invoked effect resulting from a significant change in Fe 3+ /Fe 2+ ratio with heat treatment. The interpretation of irreversible features in M ( T ) indicates that reversible M ( T ) behavior, conversely, can be expected only for ligand-free, structurally and compositionally uniform magnetite NPs, suggesting a general applicability of high-temperature M ( T ) measurements as an analytical method for probing the structure and composition of magnetic nanomaterials.

  16. Micromagnetic investigation of the dynamics of magnetization switching induced by a spin polarized current

    Science.gov (United States)

    Lee, Kyung-Jin; Dieny, Bernard

    2006-03-01

    Using micromagnetic modeling, we tested a prediction of single-domain spin-torque theory which switching current density depends only weakly on magnetic cell size. The switching time and current density are strongly affected by the cell size for low spin polarization. Larger samples with a small length-to-width ratio and small spin polarization can exhibit a nonmonotonous dependence of switching time on current. Excitation of incoherent spin waves caused by the circular Oersted field due to the current is responsible for this nonmonotonous dependence. However, the magnetic dynamics recovers a single-domain-like behavior when the spin polarization is high and/or the cell size is small.

  17. Circularly polarized light emission in scanning tunneling microscopy of magnetic systems

    International Nuclear Information System (INIS)

    Apell, S.P.; Penn, D.R.; Johansson, P.

    2000-01-01

    Light is produced when a scanning tunneling microscope is used to probe a metal surface. Recent experiments on cobalt utilizing a tungsten tip found that the light is circularly polarized; the sense of circular polarization depends on the direction of the sample magnetization, and the degree of polarization is of order 10%. This raises the possibility of constructing a magnetic microscope with very good spatial resolution. We present a theory of this effect for iron and cobalt and find a degree of polarization of order 0.1%. This is in disagreement with the experiments on cobalt as well as previous theoretical work which found order of magnitude agreement with the experimental results. However, a recent experiment on iron showed 0.0±2%. We predict that the use of a silver tip would increase the degree of circular polarization for a range of photon energies

  18. Polarization analysis for magnetic field imaging at RADEN in J-PARC/MLF

    Science.gov (United States)

    Shinohara, Takenao; Hiroi, Kosuke; Su, Yuhua; Kai, Tetsuya; Nakatani, Takeshi; Oikawa, Kenichi; Segawa, Mariko; Hayashida, Hirotoshi; Parker, Joseph D.; Matsumoto, Yoshihiro; Zhang, Shuoyuan; Kiyanagi, Yoshiaki

    2017-06-01

    Polarized neutron imaging is an attractive method for visualizing magnetic fields in a bulk object or in free space. In this technique polarization of neutrons transmitted through a sample is analyzed position by position to produce an image of the polarization distribution. In particular, the combination of three-dimensional spin analysis and the use of a pulsed neutron beam is very effective for the quantitative evaluation of both field strength and direction by means of the analysis of the wavelength dependent polarization vector. Recently a new imaging instrument “RADEN” has been constructed at the beam line of BL22 of the Materials and Life Science Experimental Facility (MLF) at J-PARC, which is dedicated to energy-resolved neutron imaging experiments. We have designed a polarization analysis apparatus for magnetic field imaging at the RADEN instrument and have evaluated its performance.

  19. Polarization properties of low frequency electromagnetic cyclotron waves associated with magnetic clouds

    Science.gov (United States)

    Zhao, G. Q.; Feng, H. Q.; Wu, D. J.; Huang, J.

    2018-03-01

    Recent studies have revealed that there are a large number of low frequency electromagnetic cyclotron waves (ECWs) occurring in and around magnetic clouds (MCs) that are common magnetic structures in interplanetary space. Using magnetic field data from the STEREO spacecraft, this paper investigates polarization properties of ECWs associated with 120 MCs. Results show that the ECWs are highly transverse, strongly polarized waves with large ellipticities. Specifically, almost all of the waves take place with the ratios of transverse power to total power higher than 0.94, polarization degrees greater than 0.85, and ellipticities larger than 0.5. The mean values of these quantities can be up to 0.99, 0.96, 0.85, respectively. In particular, there is a tendency of ellipticities decreasing with respect to the wave normal angles for ECWs with left handed polarization. The decreasing tendency is consistent with the recent theory and simulation results.

  20. Off-specular polarized neutron reflectometry study of magnetic dots with a strong shape anisotropy

    CERN Document Server

    Temst, K; Moshchalkov, V V; Bruynseraede, Y; Fritzsche, H; Jonckheere, R

    2002-01-01

    We have measured the off-specular polarized neutron reflectivity of a regular array of rectangular magnetic polycrystalline Co dots, which were prepared by a combination of electron-beam lithography, molecular beam deposition, and lift-off processes. The dots have a length-to-width ratio of 4:1 imposing a strong shape anisotropy. The intensity of the off-specular satellite reflection was monitored as a function of the magnetic field applied parallel to the rows of dots and in the plane of the sample, allowing us to analyze the magnetization-reversal process using the four spin-polarized cross sections. (orig.)

  1. Extinction of polarized light in ferrofluids with different magnetic particle concentrations

    International Nuclear Information System (INIS)

    Socoliuc, V.; Popescu, L.B.

    2012-01-01

    The magnetic field intensity and nanoparticle concentration dependence of the polarized light extinction in a ferrofluid made of magnetite particles stabilized with technical grade oleic acid dispersed in transformer oil was experimentally investigated. The magnetically induced optical anisotropy, i.e. the dichroism divided by concentration, was found to decrease with increasing sample concentration from 2% to 8%. The magnetically induced change in the optical extinction of light polarized at 54.74 o with respect to the magnetic field direction was found to be positive for the less concentrated sample (2%) and negative for the samples with 4% and 8% magnetic nanoparticle concentrations, the more negative the higher the concentration and field intensity. Based on the theoretically proven fact that the particle orientation mechanism has no effect on the extinction of light polarized at 54.74 o with respect to the field direction, we analyzed the experimental findings in the frames of the agglomeration and long-range pair correlations theories for the magnetically induced optical anisotropy in ferrofluids. We developed a theoretical model in the approximation of single scattering for the optical extinction coefficient of a ferrofluid with magnetically induced particle agglomeration. The model predicts the existence of a polarization independent component of the optical extinction coefficient that is experimentally measurable at 54.74 o polarization angle. The change in the optical extinction of light polarized at 54.74 o is positive if only the formation of straight n-particle chains is considered and may become negative in the hypothesis that the longer chains degenerate to more isotropic structures (polymer-like coils, globules or bundles of chains). The model for the influence on the light absorption of the long-range pair correlations, published elsewhere, predicts that the change in the optical extinction of light polarized at 54.74 o is always negative, the more

  2. Solar polar magnetic field dependency of geomagnetic activity semiannual variation indicated in the Aa index

    Science.gov (United States)

    Oh, Suyeon; Yi, Yu

    2018-01-01

    Three major hypotheses have been proposed to explain the well-known semiannual variation of geomagnetic activity, maxima at equinoxes and minima at solstices. This study examined whether the seasonal variation of equinoctial geomagnetic activity is different in periods of opposite solar magnetic polarity in order to understand the contribution of the interplanetary magnetic field (IMF) in the Sun-Earth connection. Solar magnetic polarity is parallel to the Earth's polarity in solar minimum years of odd/even cycles but antiparallel in solar minimum years of even/odd cycles. The daily mean of the aa, Aa indices during each solar minimum was compared for periods when the solar magnetic polarity remained in opposite dipole conditions. The Aa index values were used for each of the three years surrounding the solar minimum years of the 14 solar cycles recorded since 1856. The Aa index reflects seasonal variation in geomagnetic activity, which is greater at the equinoxes than at the solstices. The Aa index reveals solar magnetic polarity dependency in which the geomagnetic activity is stronger in the antiparallel solar magnetic polarity condition than in the parallel one. The periodicity in semiannual variation of the Aa index is stronger in the antiparallel solar polar magnetic field period than in the parallel period. Additionally, we suggest the favorable IMF condition of the semiannual variation in geomagnetic activity. The orientation of IMF toward the Sun in spring and away from the Sun in fall mainly contributes to the semiannual variation of geomagnetic activity in both antiparallel and parallel solar minimum years.

  3. Switching Magnetism and Superconductivity with Spin-Polarized Current in Iron-Based Superconductor

    Science.gov (United States)

    Choi, Seokhwan; Choi, Hyoung Joon; Ok, Jong Mok; Lee, Yeonghoon; Jang, Won-Jun; Lee, Alex Taekyung; Kuk, Young; Lee, SungBin; Heinrich, Andreas J.; Cheong, Sang-Wook; Bang, Yunkyu; Johnston, Steven; Kim, Jun Sung; Lee, Jhinhwan

    2017-12-01

    We explore a new mechanism for switching magnetism and superconductivity in a magnetically frustrated iron-based superconductor using spin-polarized scanning tunneling microscopy (SPSTM). Our SPSTM study on single-crystal Sr2VO3FeAs shows that a spin-polarized tunneling current can switch the Fe-layer magnetism into a nontrivial C4 (2 ×2 ) order, which cannot be achieved by thermal excitation with an unpolarized current. Our tunneling spectroscopy study shows that the induced C4 (2 ×2 ) order has characteristics of plaquette antiferromagnetic order in the Fe layer and strongly suppresses superconductivity. Also, thermal agitation beyond the bulk Fe spin ordering temperature erases the C4 state. These results suggest a new possibility of switching local superconductivity by changing the symmetry of magnetic order with spin-polarized and unpolarized tunneling currents in iron-based superconductors.

  4. Switching Magnetism and Superconductivity with Spin-Polarized Current in Iron-Based Superconductor.

    Science.gov (United States)

    Choi, Seokhwan; Choi, Hyoung Joon; Ok, Jong Mok; Lee, Yeonghoon; Jang, Won-Jun; Lee, Alex Taekyung; Kuk, Young; Lee, SungBin; Heinrich, Andreas J; Cheong, Sang-Wook; Bang, Yunkyu; Johnston, Steven; Kim, Jun Sung; Lee, Jhinhwan

    2017-12-01

    We explore a new mechanism for switching magnetism and superconductivity in a magnetically frustrated iron-based superconductor using spin-polarized scanning tunneling microscopy (SPSTM). Our SPSTM study on single-crystal Sr_{2}VO_{3}FeAs shows that a spin-polarized tunneling current can switch the Fe-layer magnetism into a nontrivial C_{4} (2×2) order, which cannot be achieved by thermal excitation with an unpolarized current. Our tunneling spectroscopy study shows that the induced C_{4} (2×2) order has characteristics of plaquette antiferromagnetic order in the Fe layer and strongly suppresses superconductivity. Also, thermal agitation beyond the bulk Fe spin ordering temperature erases the C_{4} state. These results suggest a new possibility of switching local superconductivity by changing the symmetry of magnetic order with spin-polarized and unpolarized tunneling currents in iron-based superconductors.

  5. Light-free magnetic resonance force microscopy for studies of electron spin polarized systems

    International Nuclear Information System (INIS)

    Pelekhov, Denis V.; Selcu, Camelia; Banerjee, Palash; Chung Fong, Kin; Chris Hammel, P.; Bhaskaran, Harish; Schwab, Keith

    2005-01-01

    Magnetic resonance force microscopy is a scanned probe technique capable of three-dimensional magnetic resonance imaging. Its excellent sensitivity opens the possibility for magnetic resonance studies of spin accumulation resulting from the injection of spin polarized currents into a para-magnetic collector. The method is based on mechanical detection of magnetic resonance which requires low noise detection of cantilever displacement; so far, this has been accomplished using optical interferometry. This is undesirable for experiments on doped silicon, where the presence of light is known to enhance spin relaxation rates. We report a non-optical displacement detection scheme based on sensitive microwave capacitive readout

  6. Coulombian Model for 3D Analytical Calculation of the Torque Exerted on Cuboidal Permanent Magnets with Arbitrarly Oriented Polarizations

    OpenAIRE

    Allag , Hicham; Yonnet , Jean-Paul; Latreche , Mohamed E. H.; Bouchekara , Houssem

    2011-01-01

    International audience; The paper proposes improved analytical expressions of the torque on cuboidal permanent magnets. Expressions are valid for any relative magnet position and for any polarization direction. The analytical calculation is made by replacing polarizations by distributions of magnetic charges on the magnet poles (Coulombian approach). The torque exerted on the second magnet is calculated by Lorentz force formulas for any arbitrary position. The three components of the torque a...

  7. The effect of colloidal stabilization upon ferrimagnetic resonance in magnetic fluids in the presence of a polarizing magnetic field

    CERN Document Server

    Fannin, P C; Socoliuc, V; Istratuca, G M; Giannitsis, A T

    2003-01-01

    The complex magnetic susceptibility of two magnetic fluids, with different degrees of colloidal stabilization, has been measured over the frequency range 100 MHz to 6 GHz. The colloidal stabilization of the magnetic fluids has been investigated using magneto-optical measurements. Based on complex magnetic susceptibility measurements, chi(omega) chi'(omega)-i chi''(omega), the dependence of the maximum absorption frequency at resonance, f sub m sub a sub x , and of line width, DELTA f, on an external magnetic polarizing field, H, over the range 0-1.45 kOe, has been examined for both magnetic fluids. The experimental results have been interpreted in terms of magnetic interparticle interactions and particle agglomeration.

  8. Magnetic materials. Tilt engineering of spontaneous polarization and magnetization above 300 K in a bulk layered perovskite.

    Science.gov (United States)

    Pitcher, Michael J; Mandal, Pranab; Dyer, Matthew S; Alaria, Jonathan; Borisov, Pavel; Niu, Hongjun; Claridge, John B; Rosseinsky, Matthew J

    2015-01-23

    Crystalline materials that combine electrical polarization and magnetization could be advantageous in applications such as information storage, but these properties are usually considered to have incompatible chemical bonding and electronic requirements. Recent theoretical work on perovskite materials suggested a route for combining both properties. We used crystal chemistry to engineer specific atomic displacements in a layered perovskite, (Ca(y)Sr(1- y))(1.15)Tb(1.85)Fe2O7, that change its symmetry and simultaneously generate electrical polarization and magnetization above room temperature. The two resulting properties are magnetoelectrically coupled as they arise from the same displacements. Copyright © 2015, American Association for the Advancement of Science.

  9. Polarized x-ray absorption spectroscopy for the study of superconductors and magnetic materials

    Science.gov (United States)

    Ramanathan, Mohan; Alp, Esen E.; Mini, Susan M.; Salem-Sugui, S.; Bommannavar, A.

    1991-11-01

    Synchrotron radiation is a good source of polarized radiation in the x-ray regime. The radiation obtained from a bending magnet source is linearly polarized in the bending plane and has a varying degree of circular polarization away from the bending plane. This feature of synchrotron radiation can be taken advantage of with proper optics to selectively use the type of polarized radiation required for the experiment in question. Linear polarized radiation is used to study the anisotropic nature of electronic and atomic structure by x-ray absorption techniques from single crystal and oriented powder samples. We will give a specific example of the use of linearly polarized x-ray absorption spectroscopy measurements for the study of the magnetically oriented layered copper oxide superconductors. While such linear dichroism measurements help identify the symmetry of the empty electronic states, circular dichroism measurements in magnetic systems help in determining the spin contribution to the absorption process. We will discuss magnetic circular dichroism measurements of the ordered-disordered invar alloy Fe(subscript 3)Pt.

  10. Polar Magnetic Field Reversals of the Sun in Maunder Minimum

    Indian Academy of Sciences (India)

    tribpo

    tions shows that the pattern of the large scale magnetic fields can be derived with greater accuracy than can be inferred from magnetograms (Duval et al 1977; Makarov. & Tlatov 1999). Thus, Η alpha charts represent data for investigation of global proper ties of large scale magnetic fields during many solar cycles when ...

  11. Account of magnetic field effects of polarized proton target on charged particle trajectories in experiments with magnetic spectrometers

    International Nuclear Information System (INIS)

    Telegin, Yu.N.; Ranyuk, Yu.N.; Karnaukhov, I.M.; Lukhanin, A.A.; Sporov, E.A.

    1980-01-01

    Some effects of the influence of magnetic field of a polarized proton target (PPT) on trajectories of secondary particles in experiments using magnetic spectrometers are considered. It is shown that these effects can be eliminated by the target shift relatively to the spectrometer rotation axis and variation of the spectrometer installation angle. Numerical calculations of the correction values were performed for emitted particle momenta of 100-800 MeB/s and working intensity of the H 0 magnetic field H 0 =27 kG. The influence of the PPT magnetic field on the functions of angular and energy resolution in the γp→π + n experiment is investigated. The results obtained can be used in experiments with a polarized proton target

  12. The effect of reducing agents on the electronic, magnetic and electrocatalytic properties of thiol-capped Pt/Co and Pt/Ni nanoparticles

    CSIR Research Space (South Africa)

    Mathe, NR

    2015-05-01

    Full Text Available The electronic, magnetic and electrocatalytic properties of bimetallic thiol-capped Pt/Co and Pt/Ni nanoparticles were synthesised using two reducing agents, NaBH(sub4) and N(sub2)H(sub4). X-ray diffraction analysis of the nanoparticles showed Pt...

  13. Magnetization distribution in paramagnetic CoO: a polarized neutron diffraction study

    CERN Document Server

    Kernavanois, N; Brown, P J; Henry, J Y; Lelievre-Berna, E

    2003-01-01

    Unpolarized and polarized neutron diffraction by a single crystal have been used to study the magnetization distribution in the paramagnetic phase of cobalt oxide CoO. Highly accurate magnetic structure factors have been measured using the classical polarized beam method. A detailed description of the magnetization distribution is presented. The magnetization around the cobalt site has a radial distribution which is contracted by approx = 5% with respect to that of the free ion and a symmetry which approximates more closely to e sub g than to the form t sub 2 sub g sup 5 /e sub g sup 2 expected for the Co sup 2 sup + 3d sup 7 configuration. A significant magnetization, corresponding to some 8% of the total moment, is found at the oxygen site.

  14. Some problems associated with the inversion of polar magnetic substorm data recorded at the Earth's surface

    International Nuclear Information System (INIS)

    Mareschal, M.

    1975-01-01

    The major thrust of this dissertation was to test an original method for resolving the current system associated with polar magnetic substorms from ground based magnetic observations. This method is based on a general technique of inversion reviewed by Wiggins in 1972 and appears to give quite satisfactory results, at least, when the current system considered is simulated by a three-dimensional current system consisting of field-aligned currents flowing down to the ionosphere, westward in the ionosphere, and back up again to the magnetosphere. Conclusions suggest that, for the purpose of inverting polar magnetic substorm data with the use of the three-dimensional model of current, the Earth's induction effects can be simulated by introducing a perfectly conducting layer inside the Earth. However, the depth of this equivalent conductor should be allowed to vary with the source frequency as the substorm develops with time. To determine how satisfactorily each model parameter could be expected to be resolved during the process of inversion, a study of the magnetic disturbance variations under specific parameter variations was then performed. The results of that study were encouraging enough to foster the inversion of an actual polar magnetic substorm data, the event of June 15, 1970. Despite the success of the enterprise, it seems reasonable to suggest that the technique of inversion should be further tested before being systematically used to resolve polar magnetic substorms

  15. Spontaneous electric polarization in the B-site magnetic spinel GeCu2O4

    Science.gov (United States)

    Yanda, Premakumar; Ghara, Somnath; Sundaresan, A.

    2018-04-01

    We report the observation of a spontaneous electric polarization at the antiferromagnetic ordering temperature (TN ∼ 33 K) of Cu2+ ions in the B-site magnetic spinel GeCu2O4, synthesized at high pressure and high temperature. This compound is known to crystallize in a tetragonal structure (space group I41/amd) due to Jahn-Teller distortion of Cu2+ ions and exhibit a collinear up-up-down-down (↑↑↓↓) antiferromagnetic spin configuration below TN. We found a clear dielectric anomaly at TN, where an electric polarization appears in the absence of applied magnetic field. The electric polarization is suppressed by applied magnetic fields, which demonstrates that the compound GeCu2O4 is a type-II multiferroic.

  16. A method of measuring magnetic texture with polarized neutrons

    International Nuclear Information System (INIS)

    Akselrod, L.A.; Gordeev, G.P.; Lazebnick, J.M.; Lebedev, V.I.

    1979-01-01

    A new method of qualitative and quantitative magnetic texture investigation is described. The description of the equipment used and results of measurements on three different samples are presented. (Auth.)

  17. Search for Magnetic Monopoles in Polar Volcanic Rocks

    DEFF Research Database (Denmark)

    Bendtz, K.; Milstead, D.; Hächler, H. -P.

    2013-01-01

    For a broad range of values of magnetic monopole mass and charge, the abundance of monopoles trapped inside Earth would be expected to be enhanced in the mantle beneath the geomagnetic poles. A search for magnetic monopoles was conducted using the signature of an induced persistent current...... 10(-5)/g is set on the monopole density in the search samples. DOI:10.1103/PhysRevLett.110.121803...

  18. Statistics of Joule heating in the auroral zone and polar cap using Astrid-2 satellite Poynting flux

    Directory of Open Access Journals (Sweden)

    A. Olsson

    2004-12-01

    Full Text Available We make a statistical study of ionospheric Joule heating with the Poynting flux method using six months of Astrid-2/EMMA electric and magnetic field data during 1999 (solar maximum year. For the background magnetic field we use the IGRF model. Our results are in agreement with earlier statistical satellite studies using both the ΣPE2 method and the Poynting flux method. We present a rather comprehensive set of fitted Joule heating formulas expressing the Joule heating in given magnetic local time (MLT and invariant latitude (ILAT range under given solar illumination conditions as a function of the Kp index, the AE index, the Akasofu epsilon parameter and the solar wind kinetic energy flux. The study thus provides improved and more detailed estimates of the statistical Joule heating. Such estimates are necessary building blocks for future quantitative studies of the power budget in the magnetosphere and in the nightside auroral region. Key words. Ionosphere (electric fields and currents; ionosphere-magnetosphere interactions – Magnetospheric physics (magnetospheric configuration and dynamics

  19. Observations Of Polarized Dust Emission In Protostars: How To Reconstruct Magnetic Field Properties?

    Science.gov (United States)

    Maury, Anaëlle; Galametz, M.; Girart; Guillet; Hennebelle, P.; Houde; Rao; Valdivia, V.; Zhang, Q.

    2017-10-01

    I will present our ALMA Cycle 2 polarized dust continuum data towards the Class 0 protostar B335 where the absence of detected rotational motions in the inner envelope might suggest an efficient magnetic braking at work to inhibit the formation of a large disk. The Band 6 data we obtained shows an intriguing polarized vectors topology, which could either suggest (i) at least two different grain alignment mechanisms at work in B335 to produce the observed polarization pattern, or (ii) an interferometric bias leading to filtering of the polarized signal that is different from the filtering of Stokes I. I will discuss both options, proposing multi-wavelength and multi observatory (ALMA Band3 data in Cycle 5, NIKA2Pol camera on the IRAM-30m) strategies to lift the degeneracy when using polarization observations as a proxy of magnetic fields in dense astrophysical environments. This observational effort in the framework of the MagneticYSOs project, is also supported by our development of an end-to-end chain of ALMA synthetic observations of the polarization from non-ideal MHD simulations of protostellar collapse (see complementary contributions by V. Valdivia and M. Galametz).

  20. Small-angle neutron scattering investigations of magnetic nanostructures and interfaces using polarized neutrons

    Science.gov (United States)

    Wiedenmann, Albrecht

    2001-03-01

    Using polarized neutrons, the relative contrasts for small-angle scattering are strongly modified which allows a precise evaluation of magnetization, density and composition profiles at surfaces and interfaces of nanoscaled materials. In Co ferrofluids, the magnetic core behaves as a non-interacting single domain. The core is encapsulated by a shell of surfactant molecules which was found to be impenetrable for the solvent. In soft magnetic Fe-Si-B-(Nb,Cu) and Fe-Nb-B alloys, the presence of a weak magnetic interface between ferromagnetic nanocrystals and amorphous matrix has been demonstrated which breaks the exchange interactions.

  1. Solar Coronal Loops Associated with Small-scale Mixed Polarity Surface Magnetic Fields

    International Nuclear Information System (INIS)

    Chitta, L. P.; Peter, H.; Solanki, S. K.; Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Riethmüller, T. L.; Noort, M. van; Rodríguez, J. Blanco; Iniesta, J. C. Del Toro; Suárez, D. Orozco; Schmidt, W.; Pillet, V. Martínez; Knölker, M.

    2017-01-01

    How and where are coronal loops rooted in the solar lower atmosphere? The details of the magnetic environment and its evolution at the footpoints of coronal loops are crucial to understanding the processes of mass and energy supply to the solar corona. To address the above question, we use high-resolution line-of-sight magnetic field data from the Imaging Magnetograph eXperiment instrument on the Sunrise balloon-borne observatory and coronal observations from the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory of an emerging active region. We find that the coronal loops are often rooted at the locations with minor small-scale but persistent opposite-polarity magnetic elements very close to the larger dominant polarity. These opposite-polarity small-scale elements continually interact with the dominant polarity underlying the coronal loop through flux cancellation. At these locations we detect small inverse Y-shaped jets in chromospheric Ca ii H images obtained from the Sunrise Filter Imager during the flux cancellation. Our results indicate that magnetic flux cancellation and reconnection at the base of coronal loops due to mixed polarity fields might be a crucial feature for the supply of mass and energy into the corona.

  2. Solar Coronal Loops Associated with Small-scale Mixed Polarity Surface Magnetic Fields

    Energy Technology Data Exchange (ETDEWEB)

    Chitta, L. P.; Peter, H.; Solanki, S. K.; Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Riethmüller, T. L.; Noort, M. van [Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, D-37077 Göttingen (Germany); Rodríguez, J. Blanco [Grupo de Astronomía y Ciencias del Espacio, Universidad de Valencia, E-46980 Paterna, Valencia (Spain); Iniesta, J. C. Del Toro; Suárez, D. Orozco [Instituto de Astrofísica de Andalucía (CSIC), Apartado de Correos 3004, E-18080 Granada (Spain); Schmidt, W. [Kiepenheuer-Institut für Sonnenphysik, Schöneckstr. 6, D-79104 Freiburg (Germany); Pillet, V. Martínez [National Solar Observatory, 3665 Discovery Drive, Boulder, CO 80303 (United States); Knölker, M., E-mail: chitta@mps.mpg.de [High Altitude Observatory, National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307-3000 (United States)

    2017-03-01

    How and where are coronal loops rooted in the solar lower atmosphere? The details of the magnetic environment and its evolution at the footpoints of coronal loops are crucial to understanding the processes of mass and energy supply to the solar corona. To address the above question, we use high-resolution line-of-sight magnetic field data from the Imaging Magnetograph eXperiment instrument on the Sunrise balloon-borne observatory and coronal observations from the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory of an emerging active region. We find that the coronal loops are often rooted at the locations with minor small-scale but persistent opposite-polarity magnetic elements very close to the larger dominant polarity. These opposite-polarity small-scale elements continually interact with the dominant polarity underlying the coronal loop through flux cancellation. At these locations we detect small inverse Y-shaped jets in chromospheric Ca ii H images obtained from the Sunrise Filter Imager during the flux cancellation. Our results indicate that magnetic flux cancellation and reconnection at the base of coronal loops due to mixed polarity fields might be a crucial feature for the supply of mass and energy into the corona.

  3. Magnetization reversal of ferromagnetic nanoparticles induced by a stream of polarized electrons

    Energy Technology Data Exchange (ETDEWEB)

    Kozhushner, M.A.; Gatin, A.K.; Grishin, M.V.; Shub, B.R. [Semenov Institute of Chemical Physics of RAS, 4, Kosygin Street, Moscow 119991 (Russian Federation); Kim, V.P.; Khomutov, G.B. [Faculty of Physics, Lomonosov Moscow State University, Lenin Gory 1-2, Moscow 119991 (Russian Federation); Ilegbusi, O.J. [University of Central Florida, 4000 Central Florida Boulevard, Orlando, FL 32816-2450 (United States); Trakhtenberg, L.I. [Semenov Institute of Chemical Physics of RAS, 4, Kosygin Street, Moscow 119991 (Russian Federation)

    2016-09-15

    The remagnetization of ferromagnetic Fe{sub 3}O{sub 4} nanoparticles of several thousand cubic nanometers by spin-polarized current is investigated. For this purpose, magnetite nanoparticles are synthesized and deposited on a conductive nonmagnetic substrate. The remagnetization is conducted in high-vacuum scanning tunneling microscope (STM). The STM tip from magnetized iron wire constitutes one electrode while the ferromagnetic nanoparticle on the graphite surface represents the second electrode. The measured threshold value of remagnetization current (I{sub thresh}=9 nA) is the lowest value of current at which remagnetization occurs. The change in nanoparticle magnetization is detected by the effect of giant magnetic resistance, specifically, the dependence of the weak polarized current (Imagnetization of the electrodes. The results indicate essential difference with available literature data on the influence of polarized current on magnetic moment of small ferromagnetic nanoclusters. The peculiarities of size dependence of the observed effects are explained. - Highlights: • Ferromagnetic nanoparticle in STM with ferromagnetic tip. • Change of the direction of nanoparticle magnetization by current I>I{sub cr}=9 nA. • GMR effect used to control change of magnetization.

  4. Magnetic Field Generation through Angular Momentum Exchange between Circularly Polarized Radiation and Charged Particles

    CERN Document Server

    Shvets, G

    2002-01-01

    The interaction between circularly polarized (CP) radiation and charged particles can lead to generation of magnetic field through an inverse Faraday effect. The spin of the circularly polarized electromagnetic wave can be converted into the angular momentum of the charged particles so long as there is dissipation. We demonstrate this by considering two mechanisms of angular momentum absorption relevant for laser-plasma interactions: electron-ion collisions and ionization. The precise dissipative mechanism, however, plays a role in determining the efficiency of the magnetic field generation.

  5. Magnetic Field Generation through Angular Momentum Exchange between Circularly Polarized Radiation and Charged Particles

    International Nuclear Information System (INIS)

    G. Shvets; N.J. Fisch; J.-M. Rax

    2002-01-01

    The interaction between circularly polarized (CP) radiation and charged particles can lead to generation of magnetic field through an inverse Faraday effect. The spin of the circularly polarized electromagnetic wave can be converted into the angular momentum of the charged particles so long as there is dissipation. We demonstrate this by considering two mechanisms of angular momentum absorption relevant for laser-plasma interactions: electron-ion collisions and ionization. The precise dissipative mechanism, however, plays a role in determining the efficiency of the magnetic field generation

  6. Bright circularly polarized soft X-ray high harmonics for X-ray magnetic circular dichroism.

    Science.gov (United States)

    Fan, Tingting; Grychtol, Patrik; Knut, Ronny; Hernández-García, Carlos; Hickstein, Daniel D; Zusin, Dmitriy; Gentry, Christian; Dollar, Franklin J; Mancuso, Christopher A; Hogle, Craig W; Kfir, Ofer; Legut, Dominik; Carva, Karel; Ellis, Jennifer L; Dorney, Kevin M; Chen, Cong; Shpyrko, Oleg G; Fullerton, Eric E; Cohen, Oren; Oppeneer, Peter M; Milošević, Dejan B; Becker, Andreas; Jaroń-Becker, Agnieszka A; Popmintchev, Tenio; Murnane, Margaret M; Kapteyn, Henry C

    2015-11-17

    We demonstrate, to our knowledge, the first bright circularly polarized high-harmonic beams in the soft X-ray region of the electromagnetic spectrum, and use them to implement X-ray magnetic circular dichroism measurements in a tabletop-scale setup. Using counterrotating circularly polarized laser fields at 1.3 and 0.79 µm, we generate circularly polarized harmonics with photon energies exceeding 160 eV. The harmonic spectra emerge as a sequence of closely spaced pairs of left and right circularly polarized peaks, with energies determined by conservation of energy and spin angular momentum. We explain the single-atom and macroscopic physics by identifying the dominant electron quantum trajectories and optimal phase-matching conditions. The first advanced phase-matched propagation simulations for circularly polarized harmonics reveal the influence of the finite phase-matching temporal window on the spectrum, as well as the unique polarization-shaped attosecond pulse train. Finally, we use, to our knowledge, the first tabletop X-ray magnetic circular dichroism measurements at the N4,5 absorption edges of Gd to validate the high degree of circularity, brightness, and stability of this light source. These results demonstrate the feasibility of manipulating the polarization, spectrum, and temporal shape of high harmonics in the soft X-ray region by manipulating the driving laser waveform.

  7. Core Polarization and Tensor Coupling Effects on Magnetic Moments of Hypernuclei

    International Nuclear Information System (INIS)

    Jiang-Ming, Yao; Jie, Meng; Hong-Feng, Lü; Greg, Hillhouse

    2008-01-01

    Effects of core polarization and tensor coupling on the magnetic moments in Λ 13 C, Λ 17 O, and Λ 41 Ca Λ-hypernuclei are studied by employing the Dirac equation with scalar, vector and tensor potentials. It is found that the effect of core polarization on the magnetic moments is suppressed by Λ tensor coupling. The Λ tensor potential reduces the spin-orbit splitting of p Λ states considerably. However, almost the same magnetic moments are obtained using the hyperon wavefunction obtained via the Dirac equation either with or without the A tensor potential in the electromagnetic current vertex. The deviations of magnetic moments for p Λ states from the Schmidt values are found to increase with nuclear mass number. (nuclear physics)

  8. Nuclear magnetic resonance of laser-polarized noble gases in molecules, materials and organisms

    Energy Technology Data Exchange (ETDEWEB)

    Goodson, Boyd McLean [Univ. of California, Berkeley, CA (United States)

    1999-12-01

    Conventional nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) are fundamentally challenged by the insensitivity that stems from the ordinarily low spin polarization achievable in even the strongest NMR magnets. However, by transferring angular momentum from laser light to electronic and nuclear spins, optical pumping methods can increase the nuclear spin polarization of noble gases by several orders of magnitude, thereby greatly enhancing their NMR sensitivity. This dissertation is primarily concerned with the principles and practice of optically pumped nuclear magnetic resonance (OPNMR). The enormous sensitivity enhancement afforded by optical pumping noble gases can be exploited to permit a variety of novel NMR experiments across many disciplines. Many such experiments are reviewed, including the void-space imaging of organisms and materials, NMR and MRI of living tissues, probing structure and dynamics of molecules in solution and on surfaces, and zero-field NMR and MRI.

  9. Nuclear magnetic resonance of laser-polarized noble gases in molecules, materials and organisms

    International Nuclear Information System (INIS)

    Goodson, Boyd M.

    1999-01-01

    Conventional nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) are fundamentally challenged by the insensitivity that stems from the ordinarily low spin polarization achievable in even the strongest NMR magnets. However, by transferring angular momentum from laser light to electronic and nuclear spins, optical pumping methods can increase the nuclear spin polarization of noble gases by several orders of magnitude, thereby greatly enhancing their NMR sensitivity. This dissertation is primarily concerned with the principles and practice of optically pumped nuclear magnetic resonance (OPNMR). The enormous sensitivity enhancement afforded by optical pumping noble gases can be exploited to permit a variety of novel NMR experiments across many disciplines. Many such experiments are reviewed, including the void-space imaging of organisms and materials, NMR and MRI of living tissues, probing structure and dynamics of molecules in solution and on surfaces, and zero-field NMR and MRI

  10. The Hanle effect in a random magnetic field. Dependence of the polarization on statistical properties of the magnetic field

    Science.gov (United States)

    Frisch, H.; Anusha, L. S.; Sampoorna, M.; Nagendra, K. N.

    2009-07-01

    Context: The Hanle effect is used to determine weak turbulent magnetic fields in the solar atmosphere, usually assuming that the angular distribution is isotropic, the magnetic field strength constant, and that micro-turbulence holds, i.e. that the magnetic field correlation length is much less than a photon mean free path. Aims: To examine the sensitivity of turbulent magnetic field measurements to these assumptions, we study the dependence of Hanle effect on the magnetic field correlation length, its angular, and strength distributions. Methods: We introduce a fairly general random magnetic field model characterized by a correlation length and a magnetic field vector distribution. Micro-turbulence is recovered when the correlation length goes to zero and macro-turbulence when it goes to infinity. Radiative transfer equations are established for the calculation of the mean Stokes parameters and they are solved numerically by a polarized approximate lambda iteration method. Results: We show that optically thin spectral lines and optically very thick ones are insensitive to the correlation length of the magnetic field, while spectral lines with intermediate optical depths (around 10-100) show some sensitivity to this parameter. The result is interpreted in terms of the mean number of scattering events needed to create the surface polarization. It is shown that the single-scattering approximation holds good for thin and thick lines but may fail for lines with intermediate thickness. The dependence of the polarization on the magnetic field vector probability density function (PDF) is examined in the micro-turbulent limit. A few PDFs with different angular and strength distributions, but equal mean value of the magnetic field, are considered. It is found that the polarization is in general quite sensitive to the shape of the magnetic field strength PDF and somewhat to the angular distribution. Conclusions: The mean field derived from Hanle effect analysis of

  11. Onset of the Magnetic Explosion in Solar Polar Coronal X-Ray Jets

    Science.gov (United States)

    Moore, Ronald L.; Sterling, Alphonse C.; Panesar, Navdeep

    2017-08-01

    We examine the onset of the driving magnetic explosion in 15 random polar coronal X-ray jets. Each eruption is observed in a coronal X-ray movie from Hinode and in a coronal EUV movie from Solar Dynamics Observatory. Contrary to the Sterling et al (2015, Nature, 523, 437) scenario for minifilament eruptions that drive polar coronal jets, these observations indicate: (1) in most polar coronal jets (a) the runaway internal tether-cutting reconnection under the erupting minifilament flux rope starts after the spire-producing breakout reconnection starts, not before it, and (b) aleady at eruption onset, there is a current sheet between the explosive closed magnetic field and ambient open field; and (2) the minifilament-eruption magnetic explosion often starts with the breakout reconnection of the outside of the magnetic arcade that carries the minifilament in its core. On the other hand, the diversity of the observed sequences of occurrence of events in the jet eruptions gives further credence to the Sterlling et al (2015, Nature, 523, 437) idea that the magnetic explosions that make a polar X-ray jet work the same way as the much larger magnetic explosions that make and flare and CME. We point out that this idea, and recent observations indicating that magnetic flux cancelation is the fundamental process that builds the field in and around pre-jet minifilaments and triggers the jet-driving magnetic explosion, together imply that usually flux cancelation inside the arcade that explodes in a flare/CME eruption is the fundamental process that builds the explosive field and triggers the explosion.This work was funded by the Heliophysics Division of NASA's Science Mission Directorate through its Living With a Star Targeted Research and Technology Program, its Heliophsyics Guest Investigators Program, and the Hinode Project.

  12. Spin-polarized deuterium : stabilization in magnetic traps

    NARCIS (Netherlands)

    Koelman, J.M.V.A.; Stoof, H.T.C.; Verhaar, B.J.; Walraven, J.T.M.

    1987-01-01

    We report on a calculation of the spin-exchange two-body rate constants associated with the population dynamics of the hyperfine levels of atomic deuterium as a function of magnetic field in the Boltzmann zero temperature limit. We find that a gas of low field seeking deuterium atoms trapped in a

  13. Mechanism of Cyclically Polarity Reversing Solar Magnetic Cycle as ...

    Indian Academy of Sciences (India)

    tribpo

    solar dynamo mechanism that generates electric current and magnetic field by plasma flows inside the .... on the flow which makes the flow pattern twist and propagate to drive the dynamo must be strong enough to .... drive electric current in cosmos, Elsassar, a friend of Einstein, proposed that non- axisymmetric flows could ...

  14. Imaging nanoscale magnetic structures with polarized soft x-ray photons

    Energy Technology Data Exchange (ETDEWEB)

    Fischer, P.; Im, M.-Y.

    2010-01-18

    Imaging nanoscale magnetic structures and their fast dynamics is scientifically interesting and technologically of highest relevance. The combination of circularly polarized soft X-ray photons which provide a strong X-ray magnetic circular dichroism effect at characteristic X-ray absorption edges, with a high resolution soft X-ray microscope utilizing Fresnel zone plate optics allows to study in a unique way the stochastical behavior in the magnetization reversal process of thin films and the ultrafast dynamics of magnetic vortices and domain walls in confined ferromagnetic structures. Future sources of fsec short and high intense soft X-ray photon pulses hold the promise of magnetic imaging down to fundamental magnetic length and time scales.

  15. Theory of magnetic-field-induced polarization flop in spin-spiral multiferroics

    Science.gov (United States)

    Mochizuki, Masahito

    2015-12-01

    The magnetic-field-induced 90∘ flop of ferroelectric polarization P in a spin-spiral multiferroic material TbMnO3 is theoretically studied based on a microscopic spin model. I find that the direction of the P flop or the choice of +Pa or -Pa after the flop is governed by magnetic torques produced by the applied magnetic field H acting on the Mn spins and thus is selected in a deterministic way, in contradistinction to the naively anticipated probabilistic flop. This mechanism resolves a puzzle of the previously reported memory effect in the P direction depending on the history of the magnetic-field sweep, and enables controlled switching of multiferroic domains by externally applied magnetic fields. My Monte-Carlo analysis also uncovers that the magnetic structure in the P ∥a phase under H ∥b is not a previously anticipated simple a b -plane spin cycloid but a conical spin structure.

  16. Experimental evidence for lamellar magnetism in hemo-ilmenite by polarized neutron scattering

    DEFF Research Database (Denmark)

    Brok, Erik; Sales, Morten; Lefmann, Kim

    2014-01-01

    Large local anomalies in the Earth's magnetic field have been observed in Norway, Sweden, and Canada. These anomalies have been attributed to the unusual magnetic properties of naturally occurring hemo-ilmenite, consisting of a paramagnetic ilmenite host (alpha-Fe2O3-bearing FeTiO3) with exsolution...... lamellae (approximate to 3 μm m thick) of canted antiferromagnetic hematite (FeTiO3-bearing α-Fe2O3) and the mutual exsolutions of the same phases on the micron to nanometer scale. The origin of stable natural remanent magnetization (NRM) in this system has been proposed to be uncompensated magnetic...... moments in the contact layers between the exsolution lamellae. This lamellar magnetism hypothesis is tested here by using polarized neutron diffraction to measure the orientation of hematite spins as a function of an applied magnetic field in a natural single crystal of hemo-ilmenite from South Rogaland...

  17. On the relations between proton influx and D-region electron densities during the polar-cap absorption event of 28-29 October 2003

    Directory of Open Access Journals (Sweden)

    J. K. Hargreaves

    2005-11-01

    Full Text Available Observations by incoherent-scatter radar have been applied to explore relationships between the fluxes of incident protons and the resulting D-region electron densities during a polar-cap radio-absorption event. Using proton flux data from a GOES geosynchronous satellite, the energy band having the greatest influence at a selected height is estimated by a process of trial and error, and empirical relationships are defined. The height profiles of the effective recombination coefficient are determined for day and night, and the transition over the evening twilight is investigated for the height range 60-70 km.

    The results show that the day-night change is confined to heights below 80 km, night-time values at the lower levels being consistent with a balance between negative ions and electrons controlled by 3-body attachment and collisional detachment. The daytime results confirm that, contrary to the prediction of some chemical models, a square-law continuity equation may be strictly applied. It is confirmed that, as previously reported, the timing of the sunset change varies with altitude.

  18. On the relations between proton influx and D-region electron densities during the polar-cap absorption event of 28-29 October 2003

    Directory of Open Access Journals (Sweden)

    J. K. Hargreaves

    2005-11-01

    Full Text Available Observations by incoherent-scatter radar have been applied to explore relationships between the fluxes of incident protons and the resulting D-region electron densities during a polar-cap radio-absorption event. Using proton flux data from a GOES geosynchronous satellite, the energy band having the greatest influence at a selected height is estimated by a process of trial and error, and empirical relationships are defined. The height profiles of the effective recombination coefficient are determined for day and night, and the transition over the evening twilight is investigated for the height range 60-70 km. The results show that the day-night change is confined to heights below 80 km, night-time values at the lower levels being consistent with a balance between negative ions and electrons controlled by 3-body attachment and collisional detachment. The daytime results confirm that, contrary to the prediction of some chemical models, a square-law continuity equation may be strictly applied. It is confirmed that, as previously reported, the timing of the sunset change varies with altitude.

  19. Impact of spin-zero particle-photon interactions on light polarization in external magnetic fields

    International Nuclear Information System (INIS)

    Liao Yi

    2007-01-01

    If the recent PVLAS results on polarization changes of a linearly polarized laser beam passing through a magnetic field are interpreted by an axion-like particle, it is almost certain that it is not a standard QCD axion. Considering this, we study the general effective interactions of photons with spin-zero particles without restricting the latter to be a pseudo-scalar or a scalar, i.e., a parity eigenstate. At the lowest order in effective field theory, there are two dimension-5 interactions, each of which has previously been treated separately for a pseudo-scalar or a scalar particle. By following the evolution in an external magnetic field of the system of spin-zero particles and photons, we compute the changes in light polarization and the transition probability for two experimental set-ups: one-way propagation and round-trip propagation. While the first may be relevant for astrophysical sources of spin-zero particles, the second applies to laboratory optical experiments like PVLAS. In the one-way propagation, interesting phenomena can occur for special configurations of polarization where, for instance, transition occurs but light polarization does not change. For the round-trip propagation, however, the standard results of polarization changes for a pseudoscalar or a scalar are only modified by a factor that depends on the relative strength of the two interactions

  20. Variations in Solar Parameters and Cosmic Rays with Solar Magnetic Polarity

    Energy Technology Data Exchange (ETDEWEB)

    Oh, S. [Department of Earth Science Education, Chonnam National University, Gwangju, 61186 (Korea, Republic of); Yi, Y., E-mail: suyeonoh@jnu.ac.kr [Department of Astronomy, Space Science and Geology, Chungnam National University, Daejeon, 34134 (Korea, Republic of)

    2017-05-01

    The sunspot number varies with the 11-year Schwabe cycle, and the solar magnetic polarity reverses every 11 years approximately at the solar maximum. Because of polarity reversal, the difference between odd and even solar cycles is seen in solar activity. In this study, we create the mean solar cycle expressed by phase using the monthly sunspot number for all solar cycles 1–23. We also generate the mean solar cycle for sunspot area, solar radio flux, and cosmic ray flux within the allowance of observational range. The mean solar cycle has one large peak at solar maximum for odd solar cycles and two small peaks for most even solar cycles. The odd and even solar cycles have the statistical difference in value and shape at a confidence level of at least 98%. For solar cycles 19–23, the second peak in the even solar cycle is larger than the first peak. This result is consistent with the frequent solar events during the declining phase after the solar maximum. The difference between odd and even solar cycles can be explained by a combined model of polarity reversal and solar rotation. In the positive/negative polarity, the polar magnetic field introduces angular momentum in the same/opposite direction as/to the solar rotation. Thus the addition/subtraction of angular momentum can increase/decrease the motion of plasma to support the formation of sunspots. Since the polarity reverses at the solar maximum, the opposite phenomenon occurs in the declining phase.

  1. Resonant magnetic scattering of polarized soft x rays

    Energy Technology Data Exchange (ETDEWEB)

    Sacchi, M. [Centre Universitaire Paris-Sud, Orsay (France); Hague, C.F. [Universite Pierre et Marie Curie, Paris (France); Gullikson, E.M.; Underwood, J. [Ernest Orlando Lawrence Berkeley National Lab., CA (United States)

    1997-04-01

    Magnetic effects on X-ray scattering (Bragg diffraction, specular reflectivity or diffuse scattering) are a well known phenomenon, and they also represent a powerful tool for investigating magnetic materials since it was shown that they are strongly enhanced when the photon energy is tuned across an absorption edge (resonant process). The resonant enhancement of the magnetic scattering has mainly been investigated at high photon energies, in order to match the Bragg law for the typical lattice spacings of crystals. In the soft X-ray range, even larger effects are expected, working for instance at the 2p edges of transition metals of the first row or at the 3d edges of rare earths (300-1500 eV), but the corresponding long wavelengths prevent the use of single crystals. Two approaches have been recently adopted in this energy range: (i) the study of the Bragg diffraction from artificial structures of appropriate 2d spacing; (ii) the analysis of the specular reflectivity, which contains analogous information but has no constraints related to the lattice spacing. Both approaches have their own specific advantages: for instance, working under Bragg conditions provides information about the (magnetic) periodicity in ordered structures, while resonant reflectivity can easily be related to electronic properties and absorption spectra. An important aspect common to all the resonant X-ray scattering techniques is the element selectivity inherent to the fact of working at a specific absorption edge: under these conditions, X-ray scattering becomes in fact a spectroscopy. Results are presented for films of iron and cobalt.

  2. Spin polarization of electrons in a magnetic impurity doped ...

    Indian Academy of Sciences (India)

    The spin of electrons in semiconductors strongly couple with electric and magnetic fields due to ... where ckμ and d−kμ are annihilation operators for electron with momentum k and spin μ and hole with momentum −k ... kμ and ekμ are annihilation and creation operators for impurity electrons. Qkμ and Qkμ are the coefficient ...

  3. Inverse beta decay of arbitrarily polarized neutrons in a magnetic field

    Indian Academy of Sciences (India)

    Home; Journals; Pramana – Journal of Physics; Volume 62; Issue 5. Inverse beta decay of arbitrarily polarized neutrons in a magnetic field. Kaushik Bhattacharya Palash B Pal. Research Articles Volume 62 Issue 5 May 2004 pp 1041-1058. Fulltext. Click here to view fulltext PDF. Permanent link:

  4. Probing spin-polarized tunneling at high bias and temperature with a magnetic tunnel transistor

    NARCIS (Netherlands)

    Park, B.G.; Banerjee, T.; Min, B.C.; Sanderink, Johannes G.M.; Lodder, J.C.; Jansen, R.

    2005-01-01

    The magnetic tunnel transistor (MTT) is a three terminal hybrid device that consists of a tunnel emitter, a ferromagnetic (FM) base, and a semiconductor collector. In the MTT with a FM emitter and a single FM base, spin-polarized hot electrons are injected into the base by tunneling. After

  5. Auroral and magnetic variations in the polar cusp and cleft. Signatures of magnetopause boundary layer dynamics

    International Nuclear Information System (INIS)

    Sandholt, P.E.; Egeland, A.

    1987-10-01

    By combining continous ground-based observations of polar cleft/cusp auroras and local magnetic variations with electromagnetic parameters obtained from satellites in polar orbit (low-altitude cleft/cusp) and in the magnetosheath/interplanetary space, different electrodynamic processes in the polar cleft/cusp have been investigated. One of the more controversial questions in this field is related to the observed shifts in latitude of cleft/cusp auroras and the relationships with the interplanetary magnetic field (IMF) orientation, local magnetic disturbances (DP2 and DPY modes) and magnetospheric substorms. A new approach which may contribute to clarifying these complicated relationships, simultaneous groundbased observations of the midday and evening-midnight sectors of the auroral oval, is illustrated. A related topic is the spatial relationship between the cleft/cusp auroras and the ionospheric convection currents. A characteristic feature of the polar cusp and cleft regions during negative IMF B z is repeated occurrence of certain short-lived auroral structures moving in accordance with the local convection pattern. Satellite measurements of particle precipitation, magnetic field and ion drift components permit detailed investigations of the electrodynamics of these cusp/cleft structures. Information on electric field components, Birkeland currents, Poynting flux, height-integrated Pedersen conductivity and Joule heat dissipation rate has been derived. These observations are discussed in relation to existing models of temporal plasma injections from the magnetosheath

  6. COLLISION-INDUCED MAGNETIC RECONNECTION AND A UNIFIED INTERPRETATION OF POLARIZATION PROPERTIES OF GRBs AND BLAZARS

    Energy Technology Data Exchange (ETDEWEB)

    Deng, Wei; Zhang, Bing [Department of Physics and Astronomy, University of Nevada Las Vegas, Las Vegas, NV 89154 (United States); Zhang, Haocheng; Li, Hui, E-mail: deng@physics.unlv.edu, E-mail: zhang@physics.unlv.edu, E-mail: hli@lanl.gov, E-mail: hz193909@ohio.edu [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

    2016-04-10

    The jet composition and energy dissipation mechanism of gamma-ray bursts (GRBs) and blazars are fundamental questions that remain not fully understood. One plausible model is to interpret the γ-ray emission of GRBs and optical emission of blazars as synchrotron radiation of electrons accelerated from the collision-induced magnetic dissipation regions in Poynting-flux-dominated jets. The polarization observation is an important and independent information to test this model. Based on our recent 3D relativistic MHD simulations of collision-induced magnetic dissipation of magnetically dominated blobs, here we perform calculations of the polarization properties of the emission in the dissipation region and apply the results to model the polarization observational data of GRB prompt emission and blazar optical emission. We show that the same numerical model with different input parameters can reproduce well the observational data of both GRBs and blazars, especially the 90° polarization angle (PA) change in GRB 100826A and the 180° PA swing in blazar 3C279. This supports a unified model for GRB and blazar jets, suggesting that collision-induced magnetic reconnection is a common physical mechanism to power the relativistic jet emission from events with very different black hole masses.

  7. Determining polar ionospheric electrojet currents from Swarm satellite constellation magnetic data

    DEFF Research Database (Denmark)

    Aakjær, Cecilie Drost; Olsen, Nils; Finlay, Chris

    2016-01-01

    We determine the strength and location of the ionospheric currents responsible for the polar electrojets from magnetic data collected by the Swarm satellite constellation on an orbit-by-orbit basis. The ionospheric currents are modelled using a simple, yet robust, method by a series of line...

  8. Magnetic field induced strong valley polarization in the three-dimensional topological semimetal LaBi

    Science.gov (United States)

    Kumar, Nitesh; Shekhar, Chandra; Klotz, J.; Wosnitza, J.; Felser, Claudia

    2017-10-01

    LaBi is a three-dimensional rocksalt-type material with a surprisingly quasi-two-dimensional electronic structure. It exhibits excellent electronic properties such as the existence of nontrivial Dirac cones, extremely large magnetoresistance, and high charge-carrier mobility. The cigar-shaped electron valleys make the charge transport highly anisotropic when the magnetic field is varied from one crystallographic axis to another. We show that the electrons can be polarized effectively in these electron valleys under a rotating magnetic field. We achieved a polarization of 60% at 2 K despite the coexistence of three-dimensional hole pockets. The valley polarization in LaBi is compared to the sister compound LaSb where it is found to be smaller. The performance of LaBi is comparable to the highly efficient bismuth.

  9. Modulation of UK lightning and the atmospheric electric circuit by heliospheric magnetic field polarity

    Science.gov (United States)

    Owens, Mathew; Scott, Chris; Lockwood, Mike; Barnard, Luke; Harrison, Giles; Nicoll, Keri; Watt, Clare; Bennett, Alec

    2015-04-01

    Observational studies have reported solar magnetic modulation of terrestrial lightning on a range of time scales, from days to decades. The proposed mechanism is two-step: lightning rates vary with galactic cosmic ray (GCR) flux incident on Earth, either via changes in atmospheric conductivity and/or direct triggering of lightning. GCR flux is, in turn, primarily controlled by the heliospheric magnetic field (HMF) intensity. Consequently, global changes in lightning rates are expected. This study instead considers HMF polarity, which doesn't greatly affect total GCR flux. Opposing HMF polarities are, however, associated with a 40 to 60% difference in observed UK lightning and thunder rates. As HMF polarity skews the terrestrial magnetosphere from its nominal position, this perturbs local ionospheric potential at high latitudes and local exposure to energetic charged particles from the magnetosphere. We speculate as to the mechanism(s) by which this may, in turn, redistribute the global location and/or intensity of thunderstorm activity.

  10. Magnetic field and electric currents in the vicinity of polar cusps as inferred from Polar and Cluster data

    Directory of Open Access Journals (Sweden)

    N. A. Tsyganenko

    2009-04-01

    Full Text Available A detailed statistical study of the magnetic structure of the dayside polar cusps is presented, based on multi-year sets of magnetometer data of Polar and Cluster spacecraft, taken in 1996–2006 and 2001–2007, respectively. Thanks to the dense data coverage in both Northern and Southern Hemispheres, the analysis spanned nearly the entire length of the cusps, from low altitudes to the cusp "throat" and the magnetosheath. Subsets of data falling inside the polar cusp "funnels" were selected with the help of TS05 and IGRF magnetic field models, taking into account the dipole tilt and the solar wind/IMF conditions. The selection funnels were shifted within ±10° of SM latitude around the model cusp location, and linear regression parameters were calculated for each sliding subset, further divided into 10 bins of distance in the range 2≤R≤12 RE, with the following results. (1 Diamagnetic depression, caused by the penetrated magnetosheath plasma, becomes first visible at R~4–5 RE, rapidly deepens with growing R, peaks at R~6–9 RE, and then partially subsides and widens in latitude at the cusp's outer end. (2 The depression peak is systematically shifted poleward (by ~2° of the footpoint latitude with respect to the model cusp field line, passing through the min{|B|} point at the magnetopause. (3 At all radial distances, clear and distinct peaks of the correlation between the local By and By(IMF and of the corresponding proportionality coefficient are observed. A remarkably regular variation of that coefficient with R quantitatively confirms the field-aligned geometry of the cusp currents associated with the IMF By, found in earlier observations.

  11. Raman backscattering of circularly polarized electromagnetic waves propagating along a magnetic field

    International Nuclear Information System (INIS)

    Maraghechi, B.; Willett, J.e.

    1979-01-01

    The stimulated Raman backscattering of an intense electromagnetic wave propagating in the extraordinary mode along a uniform, static magnetic field is considered. The dispersion relation for a homogeneous magnetized plasma in the presence of the circularly polarized pump waves is developed in the cold-plasma approximation with the pump frequency above the plasma frequency. Formulas are derived for the threshold νsub(OT) of the parametric instability and for the growth rate γ of the backscattered extraordinary wave and Langmuir wave. The effects of the magnetic field parallel to the direction of propagation on νsub(0T) and γ are studied numerically. (author)

  12. Magnetic moment of $^{17}$Ne using beta -NMR and tilted foil polarization

    CERN Document Server

    Baby, L T; Hass, M; Haas, H; Weissman, L; Brown, B A

    2004-01-01

    We report on the measurement of the magnetic moment of the ground state of /sup 17/Ne. Radioactive /sup 17/Ne nuclei were delivered from the high resolution mass separator at ISOLDE onto a high voltage platform at -200 kV and were polarized using the tilted foil polarization method. The polarized nuclei were implanted into a Pt stopper situated in a liquid-helium cooled beta -NMR apparatus and the asymmetry destruction of the ensuing beta rays was monitored as a function of the rf frequency applied to the polarized nuclei. The measured value of mu = 0.74 +or- 0.03 affirms the nu p/sub 1/2//sup - / nature of the ground state of /sup 17/Ne and is compared to shell model calculations. (10 refs).

  13. SEARCH FOR A MAGNETIC FIELD VIA CIRCULAR POLARIZATION IN THE WOLF-RAYET STAR EZ CMa

    International Nuclear Information System (INIS)

    De la Chevrotière, A.; St-Louis, N.; Moffat, A. F. J.

    2013-01-01

    We report on the first deep, direct search for a magnetic field via the circular polarization of Zeeman splitting in a Wolf-Rayet (W-R) star. Using the highly efficient ESPaDOnS spectropolarimeter at the Canada-France-Hawaii Telescope, we observed at three different epochs one of the best W-R candidates in the sky expected to harbor a magnetic field, the bright, highly variable WN4 star EZ CMa = WR6 = HD 50896. We looked for the characteristic circular polarization (Stokes V) pattern in strong emission lines that would arise as a consequence of a global, rotating magnetic field with a split monopole configuration. We also obtained nearly simultaneous linear polarization spectra (Stokes Q and U), which are dominated by electron scattering, most likely from a flattened wind with large-scale corotating structures. As the star rotates with a period of 3.766 days, our view of the wind changes, which in turn affects the value of the linear polarization in lines versus continuum at the ∼0.2% level. Depending on the epoch of observation, our Stokes V data were affected by significant crosstalk from Stokes Q and U to V. We removed this spurious signal from the circular polarization data and experimented with various levels of spectral binning to increase the signal-to-noise ratio of our data. In the end, no magnetic field is unambiguously detected in EZ CMa. Assuming that the star is intrinsically magnetic and harbors a split monopole configuration, we find an upper limit of B ∼ 100 G for the intensity of its field in the line-forming regions of the stellar wind.

  14. Photometry and Multipolar Magnetic Field Modeling of Polars: BY Camelopardalis and FL Ceti

    Directory of Open Access Journals (Sweden)

    P. A. Mason

    2015-02-01

    Full Text Available We present new broad band optical photometry of two magnetic cataclysmic variable stars, the asynchronous polar BY Camelopardalis and the short period polar FL Ceti. Observations were obtained at the 2.1-m Otto Struve Telescope of McDonald Observatory with 3s and 1s integration times respectively. In an attempt to understand the observed complex changes in accretion flow geometry observed in BY Cam, we performed full 3D MHD simulations assuming a variety of white dwarf magnetic field structures. We investigate fields with increasing complexity including both aligned and non-aligned dipole plus quadrupole field components. We compare model predictions with photometry at various phases of the beat cycle and find that synthetic light curves derived from a multipolar field structure are broadly consistent with optical photometry. FL Ceti is observed to have two very small accretion regions at the foot-points of the white dwarf’s magnetic field. Both accretion regions are visible at the same time in the high state and are about 100 degrees apart. MHD modeling using a dipole plus quadrupole field structure yields quite similar accretion regions as those observed in FL Ceti. We conclude that accretion flows calculated from MHD modeling of multi-polar magnetic fields produce synthetic light curves consistent with photometry of these magnetic cataclysmic variables.

  15. Magnetically regulated collapse in the B335 protostar? I. ALMA observations of the polarized dust emission

    Science.gov (United States)

    Maury, A. J.; Girart, J. M.; Zhang, Q.; Hennebelle, P.; Keto, E.; Rao, R.; Lai, S.-P.; Ohashi, N.; Galametz, M.

    2018-03-01

    The role of the magnetic field during protostellar collapse is poorly constrained from an observational point of view, although it could be significant if we believe state-of-the-art models of protostellar formation. We present polarimetric observations of the 233 GHz thermal dust continuum emission obtained with ALMA in the B335 Class 0 protostar. Linearly polarized dust emission arising from the circumstellar material in the envelope of B335 is detected at all scales probed by our observations, from radii of 50 to 1000 au. The magnetic field structure producing the dust polarization has a very ordered topology in the inner envelope, with a transition from a large-scale poloidal magnetic field, in the outflow direction, to strongly pinched in the equatorial direction. This is probably due to magnetic field lines being dragged along the dominating infall direction since B335 does not exhibit prominent rotation. Our data and their qualitative comparison to a family of magnetized protostellar collapse models show that, during the magnetized collapse in B335, the magnetic field is maintaining a high level of organization from scales 1000 au to 50 au: this suggests the field is dynamically relevant and capable of influencing the typical outcome of protostellar collapse, such as regulating the disk size in B335.

  16. Magnetic field induced polarization enhancement in monolayers of tungsten dichalcogenides: effects of temperature

    Science.gov (United States)

    Smoleński, T.; Kazimierczuk, T.; Goryca, M.; Molas, M. R.; Nogajewski, K.; Faugeras, C.; Potemski, M.; Kossacki, P.

    2018-01-01

    Optical orientation of localized/bound excitons is shown to be effectively enhanced by the application of magnetic fields as low as 20 mT in monolayer WS2. At low temperatures, the evolution of the polarization degree of different emission lines of monolayer WS2 with increasing magnetic fields is analyzed and compared to similar results obtained on a WSe2 monolayer. We study the temperature dependence of this effect up to T=60 K for both materials, focusing on the dynamics of the valley pseudospin relaxation. A rate equation model is used to analyze our data and from the analysis of the width of the polarization dip in magnetic field we conclude that the competition between the dark exciton pseudospin relaxation and the decay of the dark exciton population into the localized states are rather different in these two materials which are representative of the two extreme cases for the ratio of relaxation rate and depolarization rate.

  17. Folic acid-capped PEGylated magnetic nanoparticles enter cancer cells mostly via clathrin-dependent endocytosis.

    Science.gov (United States)

    Allard-Vannier, Emilie; Hervé-Aubert, Katel; Kaaki, Karine; Blondy, Thibaut; Shebanova, Anastasia; Shaitan, Konstantin V; Ignatova, Anastasia A; Saboungi, Marie-Louise; Feofanov, Alexey V; Chourpa, Igor

    2017-06-01

    This work is focused on mechanisms of uptake in cancer cells of rationally designed, covalently assembled nanoparticles, made of superparamagnetic iron oxide nanoparticles (SPIONs), fluorophores (doxorubicin or Nile Blue), polyethylene glycol (PEG) and folic acid (FA), referred hereinafter as SFP-FA. SFP-FA were characterized by DLS, zetametry and fluorescence spectroscopy. The SFP-FA uptake in cancer cells was monitored using fluorescence-based methods like fluorescence-assisted cell sorting, CLSM with single-photon and two-photon excitation. The SFP-FA endocytosis was also analyzed with electron microscopy approaches: TEM, HAADF-STEM and EELS. The SFP-FA have zeta potential below -6mW and stable hydrodynamic diameter close to 100nm in aqueous suspensions of pH range from 5 to 8. They contain ca. 109 PEG-FA, 480 PEG-OCH 3 and 22-27 fluorophore molecules per SPION. The fluorophores protected under the PEG shell allows a reliable detection of intracellular NPs. SFP-FA readily enter into all the cancer cell lines studied and accumulate in lysosomes, mostly via clathrin-dependent endocytosis, whatever the FR status on the cells. The present study highlights the advantages of rational design of nanosystems as well as the possible involvement of direct molecular interactions of PEG and FA with cellular membranes, not limited to FA-FR recognition, in the mechanisms of their endocytosis. Composition, magnetic and optical properties of the SFP-FA as well their ability to enter cancer cells are promising for their applications in cancer theranosis. Combination of complementary analytical approaches is relevant to understand the nanoparticles behavior in suspension and in contact with cells. Copyright © 2016 Elsevier B.V. All rights reserved.

  18. Spin-polarized transport in a δ-doped magnetic-barrier nanostructure

    Energy Technology Data Exchange (ETDEWEB)

    Li, Shuai; Lu, Mao-Wang, E-mail: maowanglu@126.com; Jiang, Ya-Qing; Chen, Sai-Yan

    2014-09-05

    We theoretically investigate the electron spin transport properties through a δ-doped magnetic-barrier nanostructure, which can be realized experimentally by depositing two identical ferromagnetic stripes with the opposite in-plane magnetization on the top of a semiconductor heterostructure in parallel configuration and by using atomic layer doping technique. The δ-doping dependent transmission, conductance and spin polarization are calculated exactly by analytically solving Schrödinger equation of the spin electron. It is found that the electronic spin-polarized behavior in this device can be manipulated by changing the weight and/or the position of the δ-doping. Therefore, such a device can be used as a controllable spin filter, which may be helpful for spintronics applications. - Highlights: • Spin-polarized transport in a δ-doped magnetic-barrier nanostructure is explored. • Both magnitude and sign of spin polarization depend on the δ-doping. • A controllable spin filter can be achieved for spintronics applications.

  19. Rare Low State of DO Dra, the Magnetic Dwarf Nova=Outbursting Intermediate Polar

    Science.gov (United States)

    Breus, Vitalii V.; Andronov, Ivan L.; Yoon, Joh-Na; Dubovský, Pavol

    2017-06-01

    DO Dra is an exotic cataclysmic variable which shows properties either of the intermediate polars, or dwarf novae. It may represent a new subclass of "magnetic Dwarf Nova=outbursting intermediate polar". Very rare low luminosity state (of =16.095±0.007) was detected on June 8/9, 2017. The light curve shows a double-humped shape with a phase of the orbital period, with two unequal maxima, arguing not only for an ellipticity effect, but for a bright spot as well. Totally, we have detected 3 lows states.

  20. Calculation of the Hadronic Vacuum Polarization Disconnected Contribution to the Muon Anomalous Magnetic Moment.

    Science.gov (United States)

    Blum, T; Boyle, P A; Izubuchi, T; Jin, L; Jüttner, A; Lehner, C; Maltman, K; Marinkovic, M; Portelli, A; Spraggs, M

    2016-06-10

    We report the first lattice QCD calculation of the hadronic vacuum polarization (HVP) disconnected contribution to the muon anomalous magnetic moment at physical pion mass. The calculation uses a refined noise-reduction technique that enables the control of statistical uncertainties at the desired level with modest computational effort. Measurements were performed on the 48^{3}×96 physical-pion-mass lattice generated by the RBC and UKQCD Collaborations. We find the leading-order hadronic vacuum polarization a_{μ}^{HVP(LO)disc}=-9.6(3.3)(2.3)×10^{-10}, where the first error is statistical and the second systematic.

  1. DIRECT OBSERVATION OF SOLAR CORONAL MAGNETIC FIELDS BY VECTOR TOMOGRAPHY OF THE CORONAL EMISSION LINE POLARIZATIONS

    International Nuclear Information System (INIS)

    Kramar, M.; Lin, H.; Tomczyk, S.

    2016-01-01

    We present the first direct “observation” of the global-scale, 3D coronal magnetic fields of Carrington Rotation (CR) Cycle 2112 using vector tomographic inversion techniques. The vector tomographic inversion uses measurements of the Fe xiii 10747 Å Hanle effect polarization signals by the Coronal Multichannel Polarimeter (CoMP) and 3D coronal density and temperature derived from scalar tomographic inversion of Solar Terrestrial Relations Observatory (STEREO)/Extreme Ultraviolet Imager (EUVI) coronal emission lines (CELs) intensity images as inputs to derive a coronal magnetic field model that best reproduces the observed polarization signals. While independent verifications of the vector tomography results cannot be performed, we compared the tomography inverted coronal magnetic fields with those constructed by magnetohydrodynamic (MHD) simulations based on observed photospheric magnetic fields of CR 2112 and 2113. We found that the MHD model for CR 2112 is qualitatively consistent with the tomography inverted result for most of the reconstruction domain except for several regions. Particularly, for one of the most noticeable regions, we found that the MHD simulation for CR 2113 predicted a model that more closely resembles the vector tomography inverted magnetic fields. In another case, our tomographic reconstruction predicted an open magnetic field at a region where a coronal hole can be seen directly from a STEREO-B/EUVI image. We discuss the utilities and limitations of the tomographic inversion technique, and present ideas for future developments

  2. Periodic magnetic field as a polarized and focusing thermal neutron spectrometer and monochromator

    International Nuclear Information System (INIS)

    Cremer, J. T.; Williams, D. L.; Fuller, M. J.; Gary, C. K.; Piestrup, M. A.; Pantell, R. H.; Feinstein, J.; Flocchini, R. G.; Boussoufi, M.; Egbert, H. P.; Kloh, M. D.; Walker, R. B.

    2010-01-01

    A novel periodic magnetic field (PMF) optic is shown to act as a prism, lens, and polarizer for neutrons and particles with a magnetic dipole moment. The PMF has a two-dimensional field in the axial direction of neutron propagation. The PMF alternating magnetic field polarity provides strong gradients that cause separation of neutrons by wavelength axially and by spin state transversely. The spin-up neutrons exit the PMF with their magnetic spins aligned parallel to the PMF magnetic field, and are deflected upward and line focus at a fixed vertical height, proportional to the PMF period, at a downstream focal distance that increases with neutron energy. The PMF has no attenuation by absorption or scatter, as with material prisms or crystal monochromators. Embodiments of the PMF include neutron spectrometer or monochromator, and applications include neutron small angle scattering, crystallography, residual stress analysis, cross section measurements, and reflectometry. Presented are theory, experimental results, computer simulation, applications of the PMF, and comparison of its performance to Stern-Gerlach gradient devices and compound material and magnetic refractive prisms.

  3. Influence of an Fe cap layer on the structural and magnetic properties of Fe49Pt51/Fe bi-layers

    International Nuclear Information System (INIS)

    Chao-Yang, Duan; Bin, Ma; Zong-Zhi, Zhang; Qing-Yuan, Jin; Fu-Lin, Wei

    2009-01-01

    The influences of an Fe cap layer on the structural and magnetic properties of FePt/Fe bi-layers are investigated. Compared with single FePt alloy films, a thin Fe layer can affect the crystalline orientation and improve the chemical ordering of L1 0 FePt films. Moreover, the coercivity increases when a thin Fe layer covers the FePt layer. Beyond a critical thickness, however, the Fe cover layer quickens the magnetization reversal of Fe 49 Pt 51 /Fe bi-layers by their exchange coupling

  4. Room-Temperature Magnetic Switching of the Electric Polarization in Ferroelectric Nanopillars.

    Science.gov (United States)

    Poddar, Shashi; de Sa, Pedro; Cai, Ronggang; Delannay, Laurent; Nysten, Bernard; Piraux, Luc; Jonas, Alain M

    2018-01-23

    Magnetoelectric layers with a strong coupling between ferroelectricity and ferromagnetism offer attractive opportunities for the design of new device architectures such as dual-channel memory and multiresponsive sensors and actuators. However, materials in which a magnetic field can switch an electric polarization are extremely rare, work most often only at very low temperatures, and/or comprise complex materials difficult to integrate. Here, we show that magnetostriction and flexoelectricity can be harnessed to strongly couple electric polarization and magnetism in a regularly nanopatterned magnetic metal/ferroelectric polymer layer, to the point that full reversal of the electric polarization can occur at room temperature by the sole application of a magnetic field. Experiments supported by finite element simulations demonstrate that magnetostriction produces large strain gradients at the base of the ferroelectric nanopillars in the magnetoelectric hybrid layer, translating by flexoelectricity into equivalent electric fields larger than the coercive field of the ferroelectric polymer. Our study shows that flexoelectricity can be advantageously used to create a very strong magnetoelectric coupling in a nanopatterned hybrid layer.

  5. COMPARISONS OF THE INTERSTELLAR MAGNETIC FIELD DIRECTIONS OBTAINED FROM THE IBEX RIBBON AND INTERSTELLAR POLARIZATIONS

    International Nuclear Information System (INIS)

    Frisch, Priscilla C.; Andersson, B-G; Berdyugin, Andrei; Piirola, Vilppu; Funsten, Herbert O.; Magalhaes, Antonio M.; McComas, David J.; Schwadron, Nathan A.; Slavin, Jonathan D.; Wiktorowicz, Sloane J.

    2010-01-01

    Variations in the spatial configuration of the interstellar magnetic field (ISMF) near the Sun can be constrained by comparing the ISMF direction at the heliosphere found from the Interstellar Boundary Explorer (IBEX) spacecraft observations of a 'Ribbon' of energetic neutral atoms (ENAs), with the ISMF direction derived from optical polarization data for stars within ∼40 pc. Using interstellar polarization observations toward ∼30 nearby stars within ∼90 0 of the heliosphere nose, we find that the best fits to the polarization position angles are obtained for a magnetic pole directed toward ecliptic coordinates of λ, β ∼ 263 0 , 37 0 (or galactic coordinates of l, b ∼ 38 0 , 23 0 ), with uncertainties of ±35 0 based on the broad minimum of the best fits and the range of data quality. This magnetic pole is 33 0 from the magnetic pole that is defined by the center of the arc of the ENA Ribbon. The IBEX ENA ribbon is seen in sight lines that are perpendicular to the ISMF as it drapes over the heliosphere. The similarity of the polarization and Ribbon directions for the local ISMF suggests that the local field is coherent over scale sizes of tens of parsecs. The ISMF vector direction is nearly perpendicular to the flow of local interstellar material (ISM) through the local standard of rest, supporting a possible local ISM origin related to an evolved expanding magnetized shell. The local ISMF direction is found to have a curious geometry with respect to the cosmic microwave background dipole moment.

  6. Circularly polarized microwaves for magnetic resonance study in the GHz range: Application to nitrogen-vacancy in diamonds

    Energy Technology Data Exchange (ETDEWEB)

    Mrózek, M., E-mail: mariusz.mrozek@uj.edu.pl; Rudnicki, D. S.; Gawlik, W. [Institute of Physics, Jagiellonian University, Lojasiewicza 11, 30-348 Krakow (Poland); Mlynarczyk, J. [Department of Electronics, AGH University of Science and Technology, Mickiewicza 30, 30-059 Krakow (Poland)

    2015-07-06

    The ability to create time-dependent magnetic fields of controlled polarization is essential for many experiments with magnetic resonance. We describe a microstrip circuit that allows us to generate strong magnetic field at microwave frequencies with arbitrary adjusted polarization. The circuit performance is demonstrated by applying it to an optically detected magnetic resonance and Rabi nutation experiments in nitrogen-vacancy color centers in diamond. Thanks to high efficiency of the proposed microstrip circuit and degree of circular polarization of 85%; it is possible to address the specific spin states of a diamond sample using a low power microwave generator. The circuit may be applied to a wide range of magnetic resonance experiments with a well-controlled polarization of microwaves.

  7. Diurnal and seasonal occurrence of polar patches

    Directory of Open Access Journals (Sweden)

    A. S. Rodger

    1996-05-01

    Full Text Available Analysis of the diurnal and seasonal variation of polar patches, as identified in two years of HF-radar data from Halley, Antarctica during a period near sunspot maximum, shows that there is a broad maximum in occurrence centred about magnetic noon, not local noon. There are minima in occurrence near midsummer and midwinter, with maxima in occurrence between equinox and winter. There are no significant correlations between the occurrence of polar patches and the corresponding hourly averages of the solar wind and IMF parameters, except that patches usually occur when the interplanetary magnetic field has a southward component. The results can be understood in terms of UT and seasonal differences in the plasma concentration being convected from the dayside ionosphere into the polar cap. In summer and winter the electron concentrations in the polar cap are high and low, respectively, but relatively unstructured. About equinox, a tongue of enhanced ionisation is convected into the polar cap; this tongue is then structured by the effects of the interplanetary magnetic field, but these Halley data cannot be used to separate the various competing mechanisms for patch formation. The observed diurnal and seasonal variation in the occurrence of polar patches are largely consistent with predictions of Sojka et al. (1994 when their results are translated into the southern hemisphere. However, the ionospheric effects of flux transfer events are still considered essential in their formation, a feature not yet included in the Sojka et al. model.

  8. Neutron spin filter based on optically polarized sup 3 He in a near-zero magnetic field

    CERN Document Server

    Skoy, V R; Sorokin, V N; Kolachevsky, N N; Sobelman, I I; Sermyagin, A V

    2003-01-01

    A test of polarization of sup 3 He nuclei via spin-exchange collisions with optically pumped rubidium atoms in an extremely low applied magnetic field was carried out. Permalloy magnetic shields were used to prevent a fast relaxation of sup 3 He polarization owing to the inhomogeneity of a surrounding magnetic field. The whole installation was placed at the neutron beam line of the IBR-30 facility, and used as a neutron spin filter. Thus, a prototype of new design of neutron polarizer was introduced. We intend to apply this experience for the full-scale KaTRIn facility to test the time reversal violation in neutron-nuclear reactions.

  9. Spin-polarized scanning tunneling microscopy with quantitative insights into magnetic probes.

    Science.gov (United States)

    Phark, Soo-Hyon; Sander, Dirk

    2017-01-01

    Spin-polarized scanning tunneling microscopy and spectroscopy (spin-STM/S) have been successfully applied to magnetic characterizations of individual nanostructures. Spin-STM/S is often performed in magnetic fields of up to some Tesla, which may strongly influence the tip state. In spite of the pivotal role of the tip in spin-STM/S, the contribution of the tip to the differential conductance d I /d V signal in an external field has rarely been investigated in detail. In this review, an advanced analysis of spin-STM/S data measured on magnetic nanoislands, which relies on a quantitative magnetic characterization of tips, is discussed. Taking advantage of the uniaxial out-of-plane magnetic anisotropy of Co bilayer nanoisland on Cu(111), in-field spin-STM on this system has enabled a quantitative determination, and thereby, a categorization of the magnetic states of the tips. The resulting in-depth and conclusive analysis of magnetic characterization of the tip opens new venues for a clear-cut sub-nanometer scale spin ordering and spin-dependent electronic structure of the non-collinear magnetic state in bilayer high Fe nanoislands on Cu(111).

  10. Solid state nuclear magnetic resonance studies of cross polarization from quadrupolar nuclei

    Energy Technology Data Exchange (ETDEWEB)

    De Paul, Susan M. [Univ. of California, Berkeley, CA (United States)

    1997-08-01

    The development of solid-state Nuclear Magnetic Resonance (NMR) has, to a large extent, focused on using spin-1/2 nuclei as probes to investigate molecular structure and dynamics. For such nuclei, the technique of cross polarization is well-established as a method for sensitivity enhancement. However, over two-thirds of the nuclei in the periodic table have a spin-quantum number greater than one-half and are known as quadrupolar nuclei. Such nuclei are fundamental constituents of many inorganic materials including minerals, zeolites, glasses, and gels. It is, therefore, of interest to explore the extent to which polarization can be transferred from quadrupolar nuclei. In this dissertation, solid-state NMR experiments involving cross polarization from quadrupolar nuclei to spin-1/2 nuclei under magic-angle spinning (MAS) conditions are investigated in detail.

  11. Enabling surface nuclear magnetic resonance at high-noise environments using a pre-polarization pulse

    Science.gov (United States)

    Lin, Tingting; Yang, Yujing; Teng, Fei; Müller-Petke, Mike

    2018-02-01

    The technique of surface nuclear magnetic resonance (SNMR) has been widely used for hydrological investigations in recent years. Unfortunately, the detected SNMR signals are limited to tens of nanovolts and are thus susceptible to environmental noise. While pre-polarization pulses to enhance the detected signal amplitudes are common in laboratory applications, SNMR field testing has only utilized excitation pulses until now. In conducting measurements in China, we demonstrate that adding a pre-polarization field to the SNMR pulse sequence is feasible and allows for the reliable detection of SNMR signals in noisy scenarios that otherwise prohibit signal detection. We introduce a forward modelling for pre-polarization using SNMR and present a three-layer model obtained from inverse modelling that satisfies the observed data from the field experiment. We expect this development to open up new applications for SNMR technology, especially in high-noise level places, such as active mines.

  12. Unidirectional evanescent-wave coupling from circularly polarized electric and magnetic dipoles: An angular spectrum approach

    Science.gov (United States)

    Picardi, Michela F.; Manjavacas, Alejandro; Zayats, Anatoly V.; Rodríguez-Fortuño, Francisco J.

    2017-06-01

    Unidirectional evanescent-wave coupling from circularly polarized dipole sources is one of the most striking types of evidence of spin-orbit interactions of light and an inherent property of circularly polarized dipoles. Polarization handedness self-determines propagation direction of guided modes. In this paper, we compare two different approaches currently used to describe this phenomenon: the first requires the evaluation of the coupling amplitude between dipole and waveguide modes, while the second is based on the calculation of the angular spectrum of the dipole. We present an analytical expression of the angular spectrum of dipole radiation, unifying the description for both electric and magnetic dipoles. The symmetries unraveled by the implemented formalism show the existence of specific terms in the dipole spectrum which can be recognized as being directly responsible for directional evanescent-wave coupling. This provides a versatile tool for both a comprehensive understanding of the phenomenon and a fully controllable engineering of directionality of guided modes.

  13. Polarization-preserving confocal microscope for optical experiments in a dilution refrigerator with high magnetic field.

    Science.gov (United States)

    Sladkov, Maksym; Bakker, M P; Chaubal, A U; Reuter, D; Wieck, A D; van der Wal, C H

    2011-04-01

    We present the design and operation of a fiber-based cryogenic confocal microscope. It is designed as a compact cold-finger that fits inside the bore of a superconducting magnet, and which is a modular unit that can be easily swapped between use in a dilution refrigerator and other cryostats. We aimed at application in quantum optical experiments with electron spins in semiconductors and the design has been optimized for driving with and detection of optical fields with well-defined polarizations. This was implemented with optical access via a polarization maintaining fiber together with Voigt geometry at the cold finger, which circumvents Faraday rotations in the optical components in high magnetic fields. Our unit is versatile for use in experiments that measure photoluminescence, reflection, or transmission, as we demonstrate with a quantum optical experiment with an ensemble of donor-bound electrons in a thin GaAs film. © 2011 American Institute of Physics

  14. Spin polarization and magnetic dichroism in core-level photoemission from ferromagnets

    Energy Technology Data Exchange (ETDEWEB)

    Menchero, Jose Gabriel [Univ. of California, Berkeley, CA (United States). Dept. of Physics

    1997-05-01

    In this thesis we present a theoretical investigation of angle- and spin-resolved core-level photoemission from ferromagnetic Fe and Ni. We also consider magneto-dichroic effects due to reversal of the photon helicity or reversal of the sample magnetization direction. In chapter 1, we provide a brief outline of the history of photoemission, and show how it has played an important role in the development of modern physics. We then review the basic elements of the theory of core-level photoemission, and discuss the validity of the some of the commonly-used approximations. In chapter 2, we present a one-electron theory to calculate spin- and angle-resolved photoemission spectra for an arbitrary photon polarization. The Hamiltonian includes both spin-orbit and exchange interactions. As test cases for the theory, we calculate the spin polarization and magnetic dichroism for the Fe 2p core level, and find that agreement with experiment is very good.

  15. Collection of ions in a plasma by magnetic field acceleration with selective polarization

    International Nuclear Information System (INIS)

    1974-01-01

    A system is shown for selectively ionizing particles of one isotope type in an environment of mixed isotope types and for separating the particles through the interaction of a polarized magnetic field upon ion motion in the environment. In particular application to the enrichment of the 235 U isotope of uranium, the present invention operates in a system wherein uranium metal is vaporized to provide an expanding vapor flow into the region of a magnetic field gradient where the application of laser radiation produces selective ionization of 235 U. The selectivity is enhanced substantially by limiting Zeeman splitting in the uranium absorption lines under the influence of the magnetic field. This reduction is achieved by maintaining a predetermined polarization between the laser beam and magnetic field. The electrons released by ionization of the 235 U particles generally maintain the same temperature as the ions and other particles of the environment. At least the electrons are accelerated by the magnetic gradient field toward the weaker field point. Because of charge neutrality requirements of the plasma, the accelerated electrons will drag the 235 U ions with them. By providing collection plates in the path of the accelerated electrons and ions, the 235 U particles may be collected

  16. Squids, snakes, and polarimeters: A new technique for measuring the magnetic moments of polarized beams

    International Nuclear Information System (INIS)

    Cameron, P.R.; Luccio, A.U.; Shea, T.J.; Tsoupas, N.; Goldberg, D.A.

    1997-01-01

    Effective polarimetry at high energies in hadron and lepton synchrotrons has been a long-standing and difficult problem. In synchrotrons with polarized beams it is possible to cause the direction of the polarization vector of a given bunch to alternate at a frequency which is some subharmonic of the rotation frequency. This can result in the presence of lines in the beam spectrum which are due only to the magnetic moment of the beam and which are well removed from the various lines due to the charge of the beam. The magnitude of these lines can be calculated from first principles. They are many orders of magnitude weaker than the Schottky signals. Measurement of the magnitude of one of these lines would be an absolute measurement of beam polarization. For measuring magnetic field, the Superconducting Quantum Interference Device, or squid, is about five orders of magnitude more sensitive than any other transducer. Using a squid, such a measurement might be accomplished with the proper combination of shielding, pickup loop design, and filtering. The resulting instrument would be fast, non-destructive, and comparatively cheap. In addition, techniques developed in the creation of such an instrument could be used to measure the Schottky spectrum in unprecedented detail. We present specifics of a polarimeter design for the Relativistic Heavy Ion Collider (RHIC) and briefly discuss the possibility of using this technique to measure polarization at high-energy electron machines like LEP and HERA. copyright 1997 American Institute of Physics

  17. NEAR-INFRARED IMAGING POLARIMETRY OF GGD 27: CIRCULAR POLARIZATION AND MAGNETIC FIELD STRUCTURES

    Energy Technology Data Exchange (ETDEWEB)

    Kwon, Jungmi; Tamura, Motohide [Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Hough, James H. [University of Hertfordshire, Hatfield, Herts AL10 9AB (United Kingdom); Nagata, Tetsuya [Kyoto University, Sakyo-ku, Kyoto 606-8502 (Japan); Kusakabe, Nobuhiko [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Saito, Hiro, E-mail: jungmi.kwon@astron.s.u-tokyo.ac.jp [Department of Astronomy and Earth Sciences, Tokyo Gakugei University, Koganei, Tokyo 184-8501 (Japan)

    2016-06-20

    Near-infrared imaging polarimetry in the J , H , and K{sub s} bands was carried out for GGD 27 in the dark cloud Lynds 291. Details of an infrared reflection nebula associated with the optical nebulosity GGD 27 and the infrared nebula GGD 27 IRS are presented. Aperture photometry of 1263 point-like sources, detected in all three bands, was used to classify them based on a color–color diagram, and the linear polarization of several hundred sources was determined, with the latter used to map the magnetic field structure around GGD 27. This field, around GGD 27 IRS, appears to be associated with the extended CO outflow of IRAS 18162–2048; however, there are partly distorted or bent components in the field. The Chandrasekhar–Fermi method gives an estimate of the magnetic field strength as ∼90 μ G. A region associated with GGD 27 IRS is discovered to have a circular polarization in the range of ∼2%–11% in the K{sub s} band. The circular polarization has an asymmetric positive/negative pattern and extends out to ∼ 120″ or 1.0 pc. The circular and linear polarization patterns are explained as resulting from a combination of dense inner and fainter outer lobes, suggesting episodic outflow.

  18. A simple circular-polarized antenna: Circular waveguide horn coated with lossy magnetic material

    Science.gov (United States)

    Lee, Choon S.; Justice, D. W.; Lee, Shung-Wu

    1988-01-01

    It is shown that a circular waveguide horn coated with a lossy material in its interior wall can be used as an alternative to a corrugated waveguide for radiating a circularly polarized (CP) field. To achieve good CP radiation, the diameter of the structure must be larger than the free-space wavelength, and the coating material must be sufficiently lossy and magnetic. The device is cheaper and lighter in weight than the corrugated one.

  19. Heliospheric magnetic field polarity inversions driven by radial velocity field structures

    Czech Academy of Sciences Publication Activity Database

    Landi, S.; Hellinger, Petr; Velli, M.

    2006-01-01

    Roč. 33, č. 14 (2006), L14101/1-L14101/5 ISSN 0094-8276 Grant - others:European Commission(XE) HRPN-CT-2001-00310 Institutional research plan: CEZ:AV0Z30420517 Keywords : solar wind * magnetic field polarity inversions * microstreams * turbulence Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 2.602, year: 2006

  20. Highly polarized light from stable ordered magnetic fields in GRB 120308A.

    Science.gov (United States)

    Mundell, C G; Kopač, D; Arnold, D M; Steele, I A; Gomboc, A; Kobayashi, S; Harrison, R M; Smith, R J; Guidorzi, C; Virgili, F J; Melandri, A; Japelj, J

    2013-12-05

    After the initial burst of γ-rays that defines a γ-ray burst (GRB), expanding ejecta collide with the circumburst medium and begin to decelerate at the onset of the afterglow, during which a forward shock travels outwards and a reverse shock propagates backwards into the oncoming collimated flow, or 'jet'. Light from the reverse shock should be highly polarized if the jet's magnetic field is globally ordered and advected from the central engine, with a position angle that is predicted to remain stable in magnetized baryonic jet models or vary randomly with time if the field is produced locally by plasma or magnetohydrodynamic instabilities. Degrees of linear polarization of P ≈ 10 per cent in the optical band have previously been detected in the early afterglow, but the lack of temporal measurements prevented definitive tests of competing jet models. Hours to days after the γ-ray burst, polarization levels are low (P GRBs contain magnetized baryonic jets with large-scale uniform fields that can survive long after the initial explosion.

  1. Magnetism in grain-boundary phase of a NdFeB sintered magnet studied by spin-polarized scanning electron microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Kohashi, Teruo, E-mail: teruo.kohashi.fc@hitachi.com; Motai, Kumi [Central Research Laboratory, Hitachi, Ltd., Hatoyama, Saitama 350-0395 (Japan); Nishiuchi, Takeshi; Hirosawa, Satoshi [Magnetic Materials Research Laboratory, Hitachi Metals Ltd., Osaka 618-0013 (Japan)

    2014-06-09

    The magnetism in the grain-boundary phase of a NdFeB sintered magnet was measured by spin-polarized scanning electron microscopy (spin SEM). A sample magnet was fractured in the ultra-high-vacuum chamber to avoid oxidation, and its magnetizations in the exposed grain-boundary phase on the fracture surface were evaluated through the spin polarization of secondary electrons. Spin-SEM images were taken as the fracture surface was milled gradually by argon ions, and the magnetization in the grain-boundary phase was quantitatively obtained separately from that of the Nd{sub 2}Fe{sub 14}B phase. The obtained magnetization shows that the grain-boundary phase of this magnet has substantial magnetization, which was confirmed to be ferromagnetic.

  2. Measurement of cell wall depolarization of polarized hydrogen gas targets in a weak magnetic field

    International Nuclear Information System (INIS)

    Price, J.S.; Haeberli, W.

    1994-01-01

    Polarized gas targets using windowless storage cells are being developed for use as internal targets in medium and high energy particle storage rings. Tests were conducted to evaluate wall depolarization for different cell wall materials. Measurements of the target polarization were made on polarized vector H 0 gas targets in a weak magnetic field. Fifteen materials were tested in geometries corresponding to different average number of wall collisions, N 0 , from 40 to 380 collisions, for wall temperatures, T, from 20 K to 300 K. A method was developed to measure the polarization of a vector H 0 target in a 0.5 mT field: a beam of 50 keV D + picks up electrons from the target gas and the vector D 0 acquires a tensor polarization, p zz , which is measured by means of the 3 H( vector d, n) 4 He reaction. A simple model for depolarization at surfaces is proposed. Comparison to the data shows fair agreement, but the model is unrealistic in that it does not include the effects of the recombination of atoms on the surface to form molecules. ((orig.))

  3. Modeling of polarization phenomena due to RF sheaths and electron beams in magnetized plasma

    International Nuclear Information System (INIS)

    Faudot, E.

    2005-01-01

    This work investigates the problematic of hot spots induced by accelerated particle fluxes in tokamaks. It is shown that the polarization due to sheaths in the edge plasma in which an electron beam at a high level of energy is injected, can reach several hundreds volts and thus extend the deposition area. The notion of obstructed sheath is introduced and explains the acceleration of energy deposition by the decreasing of the sheath potential. Then, a 2-dimensional fluid modeling of flux tubes in front of ICRF antennae allows us to calculate the rectified potentials taking into account RF polarization currents transverse to magnetic field lines. The 2-dimensional fluid code designed validates the analytical results which show that the DC rectified potential is 50% greater with polarization currents than without. Finally, the simultaneous application of an electron beam and a RF potential reveals that the potentials due to each phenomenon are additives when RF potential is much greater than beam polarization. The density depletion of polarized flux tubes in 2-dimensional PIC (particles in cells) simulations is characterized but not yet explained. (author)

  4. Study of magnetic thin films by polarized neutron reflectivity. Off-specular diffusion on periodical structures

    International Nuclear Information System (INIS)

    Ott, F.

    1998-01-01

    Theoretical (Zeeman energy effects) and experimental (beam polarisation problems) progress have been made in the understanding of polarized neutron reflectivity with polarisation analysis. It has been shown that modelization and numerical simulations makes it possible to avoid to have to systematically measure a full set of reflectivity curves for each field and temperature condition. It has been possible to determine a magnetic profile as a function of the field in a magnetic bilayer system by using only a few points in the reciprocal space. This technique allows to considerable reduce the experiment time. In single nickel layer systems, we have shown that it is possible to induce magnetic rotation inhomogeneities when these systems are subjects to deformation strains. The effect are related to magneto-elastic constants gradients. In trilayer systems, with a ME constant modulation, we have been able to induce large magnetic rotation gradients. A new magneto-optic technique to measure the magnetization direction without rotating the magnetic field has been developed. The field of neutron reflectivity has been extended to off-specular studies. It has been possible to account quantitatively of the off-specular diffusion on 2-D model systems (prepared by optical lithography). This new technique should make it possible in the future to determine magnetic structures with a in-depth as well as lateral resolution. (author)

  5. Magnetized Reverse Shock: Density-fluctuation-induced Field Distortion, Polarization Degree Reduction, and Application to GRBs

    Energy Technology Data Exchange (ETDEWEB)

    Deng Wei; Zhang Bing [Department of Physics and Astronomy, University of Nevada Las Vegas, Las Vegas, NV 89154 (United States); Li Hui [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Stone, James M., E-mail: deng@physics.unlv.edu, E-mail: zhang@physics.unlv.edu, E-mail: hli@lanl.gov, E-mail: jstone@astro.princeton.edu [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544-1001 (United States)

    2017-08-10

    The early optical afterglow emission of several gamma-ray bursts (GRBs) shows a high linear polarization degree (PD) of tens of percent, suggesting an ordered magnetic field in the emission region. The light curves are consistent with being of a reverse shock (RS) origin. However, the magnetization parameter, σ , of the outflow is unknown. If σ is too small, an ordered field in the RS may be quickly randomized due to turbulence driven by various perturbations so that the PD may not be as high as observed. Here we use the “Athena++” relativistic MHD code to simulate a relativistic jet with an ordered magnetic field propagating into a clumpy ambient medium, with a focus on how density fluctuations may distort the ordered magnetic field and reduce PD in the RS emission for different σ values. For a given density fluctuation, we discover a clear power-law relationship between the relative PD reduction and the σ value of the outflow. Such a relation may be applied to estimate σ of the GRB outflows using the polarization data of early afterglows.

  6. Superior magnetic properties of Ni ferrite nanoparticles synthesized by capping agent-free one-step coprecipitation route at different pH values

    Science.gov (United States)

    Iranmanesh, P.; Tabatabai Yazdi, Sh.; Mehran, M.; Saeednia, S.

    2018-03-01

    In this work, well-dispersed nanoparticles of NiFe2O4 with diameters less than 10 nm and good crystallinity and excellent magnetic properties were synthesized via a simple one-step capping agent-free coprecipitation route from metal chlorides. The ammonia was used as the precipitating agent and also the solution basicity controller. The effect of pH value during the coprecipitation process was investigated by details through microstructural, optical and magnetic characterizations of the synthesized particles using X-ray diffraction, transmission electron microscopy, Fourier transform infrared and UV-vis spectroscopy, and vibrating sample magnetometer. The results showed that the particle size, departure from the inverse spinel structure, the band gap value and the magnetization of Ni ferrite samples increase with pH value from 9 to 11 indicating the more pronounced surface effects in the smaller nanoparticles.

  7. Theoretical consideration of spin-polarized resonant tunneling in magnetic tunnel junctions

    International Nuclear Information System (INIS)

    Mu Haifeng; Zhu Zhengang; Zheng Qingrong; Jin Biao; Wang Zhengchuan; Su Gang

    2004-01-01

    A recent elegant experimental realization [S. Yuasa et al., Science 297 (2002) 234] of the spin-polarized resonant tunneling in magnetic tunnel junctions is interpreted in terms of a two-band model. It is shown that the tunnel magnetoresistance (TMR) decays oscillatorily with the thickness of the normal metal (NM) layer, being fairly in agreement with the experimental observation. The tunnel conductance is found to decay with slight oscillations with the increase of the NM layer thickness, which is also well consistent with the experiment. In addition, when the magnetizations of both ferromagnet electrodes are not collinearly aligned, TMR is found to exhibit sharp resonant peaks at some particular thickness of the NM layer. The peaked TMR obeys nicely a Gaussian distribution against the relative orientation of the magnetizations

  8. Magnetic field sensor based on the Ampere's force using dual-polarization DBR fiber laser

    Science.gov (United States)

    Yao, Shuang; Zhang, Yang; Guan, Baiou

    2015-08-01

    A novel magnetic field sensor using distributed Bragg reflector (DBR) fiber laser by Ampere's force effect is proposed and experimentally demonstrated. The key sensing element, that is the dual-polarization DBR fiber laser, is fixed on the middle part of two copper plates which carry the current. Ampere's force is applied onto the coppers due to an external magnetic field generated by a DC solenoid. Thus, the lateral force from the coppers is converted to a corresponding beat frequency signal shift produced by the DBR laser. The electric current sensing is also realized by the same configuration and same principle simultaneously in an intuitive manner. Good agreement between the theory calculation and the experimental results is obtained, which shows a good linearity. This sensor's sensitivity to the magnetic field and to the electric current finally reaches ~258.92 kHz/mT and ~1.08727 MHz/A, respectively.

  9. Orientation and thickness dependence of magnetization at the interfacesof highly spin-polarized manganite thin films

    Energy Technology Data Exchange (ETDEWEB)

    Chopdekar, Rajesh V.; Arenholz, Elke; Suzuki, Y.

    2008-08-18

    We have probed the nature of magnetism at the surface of (001), (110) and (111)-oriented La{sub 0.7}Sr{sub 0.3}MnO{sub 3} thin films. The spin polarization of La{sub 0.7}Sr{sub 0.3}MnO{sub 3} thin films is not intrinsically suppressed at all surfaces and interfaces but is highly sensitive to both the epitaxial strain state as well as the substrate orientation. Through the use of soft x-ray spectroscopy, the magnetic properties of (001), (110) and (111)-oriented La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/SrTiO{sub 3} interfaces have been investigated and compared to bulk magnetometry and resistivity measurements. The magnetization of (110) and (111)-oriented La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/SrTiO{sub 3} interfaces are more bulk-like as a function of thickness whereas the magnetization at the (001)-oriented La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/SrTiO{sub 3} interface is suppressed significantly below a layer thickness of 20 nm. Such findings are correlated with the biaxial strain state of the La{sub 0.7}Sr{sub 0.3}MnO{sub 3} films; for a given film thickness it is the tetragonal distortion of (001) La{sub 0.7}Sr{sub 0.3}MnO{sub 3} that severely impacts the magnetization, whereas the trigonal distortion for (111)-oriented films and monoclinic distortion for (110)-oriented films have less of an impact. These observations provide evidence that surface magnetization and thus spin polarization depends strongly on the crystal surface orientation as well as epitaxial strain.

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

    Science.gov (United States)

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

    2018-02-01

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

  11. Inverse Dipolar Magnetic Anomaly Over the Volcanic Cone Linked to Reverse Polarity Magnetizations in Lavas and Tuffs - Implications for the Conduit System

    Science.gov (United States)

    Fucugauchi, J. U.; Perez-Cruz, L. L.; Trigo-Huesca, A.

    2012-12-01

    A combined magnetics and paleomagnetic study of Toluquilla monogenetic volcano and associated lavas and tuffs from Valsequillo basin in Central Mexico provides evidence on a magnetic link between lavas, ash tuffs and the underground volcanic conduit system. Paleomagnetic analyses show that lavas and ash tuffs carry reverse polarity magnetizations, which correlate with the inversely polarized dipolar magnetic anomaly over the volcano. The magnetizations in the lava and tuff show similar southward declinations and upward inclinations, supporting petrological inferences that the tuff was emplaced while still hot and indicating a temporal correlation for lava and tuff emplacement. Conduit geometry is one of the important controlling factors in eruptive dynamics of basaltic volcanoes. However volcanic conduits are often not, or only partly, exposed. Modeling of the dipolar anomaly gives a reverse polarity source magnetization associated with a vertical prismatic body with southward declination and upward inclination, which correlates with the reverse polarity magnetizations in the lava and tuff. The study documents a direct correlation of the paleomagnetic records with the underground magmatic conduit system of the monogenetic volcano. Time scale for cooling of the volcanic plumbing system involves a longer period than the one for the tuff and lava, suggesting that magnetization for the source of dipolar anomaly may represent a long time average as compared to the spot readings in the lava and tuff. The reverse polarity magnetizations in lava and tuff and in the underground source body for the magnetic anomaly are interpreted in terms of eruptive activity of Toluquilla volcano at about 1.3 Ma during the Matuyama reverse polarity C1r.2r chron.

  12. Overhauser Geomagnetic Sensor Based on the Dynamic Nuclear Polarization Effect for Magnetic Prospecting

    Science.gov (United States)

    Ge, Jian; Dong, Haobin; Liu, Huan; Yuan, Zhiwen; Dong, He; Zhao, Zhizhuo; Liu, Yonghua; Zhu, Jun; Zhang, Haiyang

    2016-01-01

    Based on the dynamic nuclear polarization (DNP) effect, an alternative design of an Overhauser geomagnetic sensor is presented that enhances the proton polarization and increases the amplitude of the free induction decay (FID) signal. The short-pulse method is adopted to rotate the enhanced proton magnetization into the plane of precession to create an FID signal. To reduce the negative effect of the powerful electromagnetic interference, the design of the anti-interference of the pick-up coil is studied. Furthermore, the radio frequency polarization method based on the capacitive-loaded coaxial cavity is proposed to improve the quality factor of the resonant circuit. In addition, a special test instrument is designed that enables the simultaneous testing of the classical proton precession and the Overhauser sensor. Overall, comparison experiments with and without the free radical of the Overhauser sensors show that the DNP effect does effectively improve the amplitude and quality of the FID signal, and the magnetic sensitivity, resolution and range reach to 10 pT/Hz1/2@1 Hz, 0.0023 nT and 20–100 μT, respectively. PMID:27258283

  13. Overhauser Geomagnetic Sensor Based on the Dynamic Nuclear Polarization Effect for Magnetic Prospecting

    Directory of Open Access Journals (Sweden)

    Jian Ge

    2016-06-01

    Full Text Available Based on the dynamic nuclear polarization (DNP effect, an alternative design of an Overhauser geomagnetic sensor is presented that enhances the proton polarization and increases the amplitude of the free induction decay (FID signal. The short-pulse method is adopted to rotate the enhanced proton magnetization into the plane of precession to create an FID signal. To reduce the negative effect of the powerful electromagnetic interference, the design of the anti-interference of the pick-up coil is studied. Furthermore, the radio frequency polarization method based on the capacitive-loaded coaxial cavity is proposed to improve the quality factor of the resonant circuit. In addition, a special test instrument is designed that enables the simultaneous testing of the classical proton precession and the Overhauser sensor. Overall, comparison experiments with and without the free radical of the Overhauser sensors show that the DNP effect does effectively improve the amplitude and quality of the FID signal, and the magnetic sensitivity, resolution and range reach to 10 pT/Hz 1 / 2 @1 Hz, 0.0023 nT and 20–100 μ T, respectively.

  14. MAGNETIC FIELD COMPONENTS ANALYSIS OF THE SCUPOL 850 μm POLARIZATION DATA CATALOG

    Energy Technology Data Exchange (ETDEWEB)

    Poidevin, Frédérick [Department of Physics and Astronomy, University College London, Kathleen Lonsdale Building, Gower Place, London WC1E 6BT (United Kingdom); Falceta-Gonçalves, Diego [SUPA, School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews, Fife KY16 9SS (United Kingdom); Kowal, Grzegorz [Universidade de São Paulo, Escola de Artes, Ciências e Humanidades Rua Arlindo Béttio, No. 1000, Ermelino Matarazzo, São Paulo, SP 03828-000 (Brazil); De Gouveia Dal Pino, Elisabete; Magalhães, Antonio Mário, E-mail: poidevin@star.ucl.ac.uk, E-mail: dfalceta@usp.br, E-mail: kowal@astro.iag.usp.br, E-mail: dalpino@astro.iag.usp.br, E-mail: mario@astro.iag.usp.br [Universidade de São Paulo, Instituto de Astronomia, Geofísica e Cîenças Atmosféricas, Rua do Matão 1226, Butantã, São Paulo, SP 05508-900 (Brazil)

    2013-11-10

    We present an extensive analysis of the 850 μm polarization maps of the SCUBA Polarimeter Legacy (SCUPOL) Catalogue produced by Matthews et al., focusing exclusively on the molecular clouds and star-forming regions. For the sufficiently sampled regions, we characterize the depolarization properties and the turbulent-to-mean magnetic field ratio of each region. Similar sets of parameters are calculated from two-dimensional synthetic maps of dust-emission polarization produced with three-dimensional magnetohydrodynamics (MHD) numerical simulations scaled to the S106, OMC-2/3, W49, and DR21 molecular cloud polarization maps. For these specific regions, the turbulent MHD regimes retrieved from the simulations, as described by the turbulent Alfvén and Sonic Mach numbers, are consistent within a factor one to two with the values of the same turbulent regimes estimated from the analysis of Zeeman measurements data provided by Crutcher. Constraints on the values of the inclination angle α of the mean magnetic field with respect to the line of sight are also given. The values obtained from the comparison of the simulations with the SCUPOL data are consistent with the estimates made by using two observational methods provided by other authors. Our main conclusion is that simple, ideal, isothermal, and non-self-gravitating MHD simulations are sufficient in order to describe the large-scale observed physical properties of the envelopes of this set of regions.

  15. Cervical Cap

    Science.gov (United States)

    ... p020041. Accessed Nov. 11, 2014. Cervical cap About Advertisement Mayo Clinic does not endorse companies or products. ... a Job Site Map About This Site Twitter Facebook Google YouTube Pinterest Mayo Clinic is a not- ...

  16. Cervical Cap

    Science.gov (United States)

    ... Things That Help Feelings Expert Answers Q&A Movies & More for Teens Teens site Sitio para adolescentes ... Because the cap has to be placed properly, women who use one should be comfortable feeling for ...

  17. Cervical Cap

    Science.gov (United States)

    ... weeks after delivery Can be inserted hours before sex and remain in place for up to 48 hours Doesn't require a partner's cooperation Poses few if any side effects The cervical cap isn't appropriate for everyone, ...

  18. Vibrational characteristics of a superconducting magnetic bearing employed for a prototype polarization modulator

    Science.gov (United States)

    Sakurai, Yuki; Matsumura, Tomotake; Sugai, Hajime; Katayama, Nobuhiko; Ohsaki, Hiroyuki; Terao, Yutaka; Terachi, Yusuke; Kataza, Hirokazu; Utsunomiya, Shin; Yamamoto, Ryo

    2017-07-01

    We present the vibrational characteristics of a levitating rotor in a superconducting magnetic bearing (SMB) system operating at below 10 K. We develop a polarization modulator that requires a continuously rotating optical element, called half-wave plate (HWP), for a cosmic microwave background polarization experiment. The HWP has to operate at the temperature below 10 K, and thus an SMB provides a smooth rotation of the HWP at the cryogenic temperature of about 10 K with minimal heat dissipation. In order to understand the potential interference to the cosmological observations due to the vibration of the HWP, it is essential to characterize the vibrational properties of the levitating rotor of the SMB. We constructed a prototype model that consists of an SMB with an array of high temperature superconductors, YBCO, and a permanent magnet ring, NdFeB. The rotor position is monitored by a laser displacement gauge, and a cryogenic Hall sensor via the magnetic field. In this presentation, we present the measurement results of the vibration characteristics using our prototype SMB system. We characterize the vibrational properties as the spring constant and the damping, and discuss the projected performance of this technology toward the use in future space missions.

  19. Connection between zero chromaticity and long in-plane polarization lifetime in a magnetic storage ring

    Science.gov (United States)

    Guidoboni, G.; Stephenson, E. J.; Wrońska, A.; Bagdasarian, Z.; Bsaisou, J.; Chekmenev, S.; Ciullo, G.; Dymov, S.; Eversmann, D.; Gaisser, M.; Gebel, R.; Hejny, V.; Hempelmann, N.; Hinder, F.; Kacharava, A.; Keshelashvili, I.; Kulessa, P.; Lenisa, P.; Lehrach, A.; Lorentz, B.; Maanen, P.; Maier, R.; Mchedlishvili, D.; Mey, S.; Nass, A.; Pesce, A.; Orlov, Y.; Pretz, J.; Prasuhn, D.; Rathmann, F.; Rosenthal, M.; Saleev, A.; Semertzidis, Y. K.; Senichev, Y.; Shmakova, V.; Stockhorst, H.; Ströher, H.; Talman, R.; Thörngren Engblom, P.; Trinkel, F.; Valdau, Yu.; Weidemann, C.; Wüstner, P.; Żurek, M.; Zyuzin, D.; JEDI Collaboration

    2018-02-01

    In this paper, we demonstrate the connection between a magnetic storage ring with additional sextupole fields set so that the x and y chromaticities vanish and the maximizing of the lifetime of in-plane polarization (IPP) for a 0.97 -GeV /c deuteron beam. The IPP magnitude was measured by continuously monitoring the down-up scattering asymmetry (sensitive to sideways polarization) in an in-beam, carbon-target polarimeter and unfolding the precession of the IPP due to the magnetic anomaly of the deuteron. The optimum operating conditions for a long IPP lifetime were made by scanning the field of the storage ring sextupole magnet families while observing the rate of IPP loss during storage of the beam. The beam was bunched and electron cooled. The IPP losses appear to arise from the change of the orbit circumference, and consequently the particle speed and spin tune, due to the transverse betatron oscillations of individual particles in the beam. The effects of these changes are canceled by an appropriate sextupole field setting.

  20. Magnetic adatoms in two and four terminal graphene nanoribbons: A comparison between their spin polarized transport

    Science.gov (United States)

    Ganguly, Sudin; Basu, Saurabh

    2018-04-01

    We study the charge and spin transport in two and four terminal graphene nanoribbons (GNR) decorated with random distribution of magnetic adatoms. The inclusion of the magnetic adatoms generates only the z-component of the spin polarized conductance via an exchange bias in the absence of Rashba spin-orbit interaction (SOI), while in presence of Rashba SOI, one is able to create all the three (x, y and z) components. This has important consequences for possible spintronic applications. The charge conductance shows interesting behaviour near the zero of the Fermi energy. Where in presence of magnetic adatoms the familiar plateau at 2e2 / h vanishes, thereby transforming a quantum spin Hall insulating phase to an ordinary insulator. The local charge current and the local spin current provide an intuitive idea on the conductance features of the system. We found that, the local charge current is independent of Rashba SOI, while the three components of the local spin currents are sensitive to Rashba SOI. Moreover the fluctuations of the spin polarized conductance are found to be useful quantities as they show specific trends, that is, they enhance with increasing adatom densities. A two terminal GNR device seems to be better suited for possible spintronic applications.

  1. Lift, drag, and guidance forces on alternating polarity magnets, using loop guideways

    International Nuclear Information System (INIS)

    Lindenbaum, S.D.; Lee, M.S.

    1975-01-01

    Exact solutions of track current, lift force, and drag force, together with their velocity dependence, have been computed for a vehicle carrying a finite number of fixed current alternating polarity superconducting magnets, suspended at various heights over structured track guideways of the single- and double-loop (''null'') types. Results for the double-loop case are compared with those of a previously reported approximate analysis. The analytical method is then applied to a study of a low-drag guidance loop guideway which is integrable with lift loop guideways utilizing a common set of vehicle magnets. Solutions are obtained for guidance track restoring forces, lateral destabilization forces, and lift force degradation as functions of lateral displacement from symmetry. The dependence of lift, drag, and lift-to-drag on track loop parameters is studied and the linear dependence of lift-to-drag on loop time constant confirmed. The contribution to the forces made by successive addition of alternating polarity magnets is calculated and the marked reduction in lift force pulsation noted

  2. Reverse polarity magnetized melt rocks from the Chicxulub impact structure, Yucatan Peninsula, Mexico

    Science.gov (United States)

    Urrutia-Fucugauchi, Jaime; Marin, Luis E.; Sharpton, Virgil L.; Quezada, Juan Manuel

    1993-03-01

    Further paleomagnetic data for core samples of melt rock recovered in the Petroleos Mexicanos (PEMEX) exploratory wells within the Chicxulub structure, northern Yucatan peninsula, Mexico are reported. A previous report by Sharpton showed that the rocks studied contain high iridium levels and shocked breccia clasts, and an Ar-40/Ar-39 age of 65.2 plus or minus 0.4 Ma. The geomagnetic polarity determined for two samples is reverse (R) and was correlated with chron 29R that includes the K/T boundary. Our present analysis is based on two samples from each of three clasts of the melt rock from PEMEX well Y6-N17 (1295 to 1299 m b.s.l.). This study concentrates on the vectorial nature and stability of the remanence (NRM), the magnetic mineralogy and remanence carriers (i.e., the reliability and origin of the record), and on the implications (correlation with expected paleolatitude and polarity). The relative orientation of the drill core samples with respect to the horizontal is known. Samples were stable under alternating field (AF) and thermal treatments, and after removal of a small component they exhibited single-vectorial behavior. The characteristic remanence inclinations show small dispersion and a mean value (-43 deg) in close agreement with the expected inclination and paleolatitude (derived from the North American apparent polar wander path). Isothermal remenence (IRM) acquisition experiments, Lowrie-Fuller tests, coercivity and unblocking temperature spectra of NRM and saturation IRM, susceptibility and Q-coefficient analyses, and the single-component nature indicate a dominant mineralogy of iron-rich titanomagnetites with single or pseduo-single domain states. The stable characteristic magnetization may be interpreted as a result of shock heating of the rock at the time of formation of the inpact structure and its polarity, age, and paleolatitude are consistent with a time about the K/T boundary.

  3. Rubber Composites Based on Polar Elastomers with Incorporated Modified and Unmodified Magnetic Filler

    Directory of Open Access Journals (Sweden)

    Ján Kruželák

    2016-01-01

    Full Text Available Rubber magnetic composites were prepared by incorporation of unmodified and surface modified strontium ferrite into rubber matrices based on NBR and NBR/PVC. Strontium ferrite was dosed to the rubber matrices in concentration scale ranging from 0 to 100 phr. The main goal was to investigate the influence of the type of ferrite on the curing process, physical-mechanical and magnetic properties of composites. The mutual interactions between the filler and rubber matrices were investigated by determination of cross-link density and SEM analysis. The incorporation of magnetic fillers leads to the increase of cross-link density and remanent magnetic induction of composites. Moreover, the improvement of physical-mechanical properties was achieved in dependence on the content of magnetic fillers. Surface modification of ferrite contributed to the enhancement of adhesion on the interphase filler-rubber. It can be stated that ferrite exhibits reinforcing effect in the composite materials and this reinforcing behavior was emphasized with the increase in polarity of the rubber matrix.

  4. Design of magnetic system to produce intense beam of polarized molecules of H2 and D2

    Science.gov (United States)

    Yurchenko, A. V.; Nikolenko, D. M.; Rachek, I. A.; Shestakov, Yu V.; Toporkov, D. K.; Zorin, A. V.

    2017-12-01

    A magnetic-separating system is designed to produce polarized molecular high-density beams of H2/D2. The distribution of the magnetic field inside the aperture of the multipole magnet was calculated using the Mermaid software package. The calculation showed that the characteristic value of the magnetic field is 40 kGs, the field gradient is about 60 kGs/cm. A numerical calculation of the trajectories of the motion of molecules with different spin projections in this magnetic system is performed. The article discusses the possibility of using the magnetic system designed for the creation of a high-intensity source of polarized molecules. The expected intensity of this source is calculated. The expected flux of molecules focused in the receiver tube is 3.5·1016 mol/s for the hydrogen molecule and 2.0·1015 mol/s for the deuterium molecule.

  5. The QED vacuum polarization function at four loops and the anomalous magnetic moment at five loops

    International Nuclear Information System (INIS)

    Baikov, P.

    2013-07-01

    The anomalous moment of the muon is one of the most fundamental observables. It has been measured experimentally with a very high precision and on theory side the contributions from perturbative QED have been calculated up to five-loop level by numerical methods. Contributions to the muon anomalous magnetic moment from certain diagram classes are also accessible by alternative methods. In this paper we present the evaluation of contributions to the QCD corrections due to insertions of the vacuum polarization function at five-loop level.

  6. Zero-field spin transfer oscillators based on magnetic tunnel junction having perpendicular polarizer and planar free layer

    Directory of Open Access Journals (Sweden)

    Bin Fang

    2016-12-01

    Full Text Available We experimentally studied spin-transfer-torque induced magnetization oscillations in an asymmetric MgO-based magnetic tunnel junction device consisting of an in-plane magnetized free layer and an out-of-plane magnetized polarizer. A steady auto-oscillation was achieved at zero magnetic field and room temperature, with an oscillation frequency that was strongly dependent on bias currents, with a large frequency tunability of 1.39 GHz/mA. Our results suggest that this new structure has a high potential for new microwave device designs.

  7. Amplified voltammetric detection of miRNA from serum samples of glioma patients via combination of conducting magnetic microbeads and ferrocene-capped gold nanoparticle/streptavidin conjugates.

    Science.gov (United States)

    Lu, Zhixuan; Tang, Hailin; Wu, Daohong; Xia, Yonghong; Wu, Minghua; Yi, Xinyao; Li, Hengfeng; Wang, Jianxiu

    2016-12-15

    MicroRNA (miRNA) plays a key regulatory role in many biological processes, emerging as an important biomarker for a large variety of cancer diseases. Employing gold nanoparticle (AuNP)-coated magnetic microbeads (AuNP-MMBs) as an immobilization matrix for higher loading density of hairpin-structured DNA probes and then ferrocene (Fc)-capped gold nanoparticle/streptavidin conjugates, amplified electrochemical assay of miRNA has been performed. In the presence of target miRNA, a novel assembly was formed via linking biotinylated hairpin DNA probe-covered AuNP-MMBs with Fc-capped gold nanoparticle/streptavidin conjugates and then collected by magnetic electrodes for voltammetric detection. The enlarged surface area, good conductivity of AuNP-MMBs and the multiple Fc tags on the electrode surface ensure high sensitivity of the method. The oxidation peak current of Fc tags is proportional to the concentrations of miRNA ranging from 5 fM to 100 fM, and a detection limit of 0.14 fM was achieved. The proposed assay is highly selective and reproducible, serving as a viable alternative for the detection of miRNA-182 from serum samples of glioma patients. Copyright © 2016 Elsevier B.V. All rights reserved.

  8. Dynamic nuclear polarization for magnetic resonance imaging. An in-bore approach

    Energy Technology Data Exchange (ETDEWEB)

    Krummenacker, Jan G.

    2012-07-01

    In this thesis, the development of an in-bore liquid state DNP polarizer for MRI applications operating in flow through mode at a magnetic field strength of 1.5 T was described. After an introductory chapter 1 and a chapter 2 on the theoretical background, chapter 3 dealt chiefly with the challenge of performing liquid state DNP at a high magnetic field of 9.2 T. The feasibility of performing liquid state DNP at this field was demonstrated for various solvents, as well as for metabolites in solution. Chapter 4 then moved to the aim of this work, the application of liquid state DNP for MRI experiments. It introduced the rationale of our approach, the hardware that was developed and demonstrated its performance in a clinical MRI tomograph.

  9. Low-angle polarized neutron and X-ray scattering from magnetic nanolayers and nanostructures

    CERN Document Server

    Paul, Amitesh

    2017-01-01

    This research monograph presents the latest results related to the characterization of low dimensional systems. Low-angle polarized neutron scattering and X-ray scattering at grazing incidence are used as the two main techniques to explore various physical phenomena of these systems. Special focus is put on systems like thin film transition metal and rare-earth layers, oxide heterostructures, hybrid systems, self-assembled nanostructures and self-diffusion.  Readers will gain in-depth knowledge about the usage of specular scattering and off-specular scattering techniques. Investigation of in-plane and out-of-plane structures and magnetism with vector magnetometric information is illustrated comprehensively. The book caters to a wide audience working in the field of nano-dimensional magnetic systems and the neutron and X-ray reflectometry community in particular.

  10. Dynamic nuclear polarization for magnetic resonance imaging. An in-bore approach

    International Nuclear Information System (INIS)

    Krummenacker, Jan G.

    2012-01-01

    In this thesis, the development of an in-bore liquid state DNP polarizer for MRI applications operating in flow through mode at a magnetic field strength of 1.5 T was described. After an introductory chapter 1 and a chapter 2 on the theoretical background, chapter 3 dealt chiefly with the challenge of performing liquid state DNP at a high magnetic field of 9.2 T. The feasibility of performing liquid state DNP at this field was demonstrated for various solvents, as well as for metabolites in solution. Chapter 4 then moved to the aim of this work, the application of liquid state DNP for MRI experiments. It introduced the rationale of our approach, the hardware that was developed and demonstrated its performance in a clinical MRI tomograph.

  11. Problem of simulating the Earth's induction effects in modeling polar magnetic substorms

    International Nuclear Information System (INIS)

    Mareschal, M.

    1976-01-01

    A major problem encountered in trying to model the current system associated with a polar magnetic substorm from ground-based magnetic observations is the difficulty of adequately evaluating the earth's induction effects. Two methods for simulating these effects are reviewed here. Method 1 simply reduces the earth to a perfect conductor and leads to very simple field equations. Method 2 considers the earth as a ''horizontally'' layered body of finite conductivity but requires a large amount of computational time. The performances of both methods are compared when the substorm current system can be approximated by an infinitely long electrojet flowing over a flat earth. In this case it appears that for most substorm modeling problems it is sufficient to treat the earth as a perfect conductor. The depth of this perfect conductor below the earth's surface should be selected in function of the source frequency content

  12. Spin-filter scanning tunneling microscopy : a novel technique for the analysis of spin polarization on magnetic surfaces and spintronic devices

    NARCIS (Netherlands)

    Vera Marun, I.J.

    2010-01-01

    This thesis deals with the development of a versatile technique to measure spin polarization with atomic resolution. A microscopy technique that can measure electronic spin polarization is relevant for characterization of magnetic nanostructures and spintronic devices. Scanning tunneling microscopy

  13. Measurement of local, internal magnetic fluctuations via cross-polarization scattering in the DIII-D tokamak (invited)

    Energy Technology Data Exchange (ETDEWEB)

    Barada, K., E-mail: kshitish@ucla.edu; Rhodes, T. L.; Crocker, N. A.; Peebles, W. A. [University of California-Los Angeles, P.O. Box 957099, Los Angeles, California 90095 (United States)

    2016-11-15

    We present new measurements of internal magnetic fluctuations obtained with a novel eight channel cross polarization scattering (CPS) system installed on the DIII-D tokamak. Measurements of internal, localized magnetic fluctuations provide a window on an important physics quantity that we heretofore have had little information on. Importantly, these measurements provide a new ability to challenge and test linear and nonlinear simulations and basic theory. The CPS method, based upon the scattering of an incident microwave beam into the opposite polarization by magnetic fluctuations, has been significantly extended and improved over the method as originally developed on the Tore Supra tokamak. A new scattering geometry, provided by a unique probe beam, is utilized to improve the spatial localization and wavenumber range. Remotely controllable polarizer and mirror angles allow polarization matching and wavenumber selection for a range of plasma conditions. The quasi-optical system design, its advantages and challenges, as well as important physics validation tests are presented and discussed. Effect of plasma beta (ratio of kinetic to magnetic pressure) on both density and magnetic fluctuations is studied and it is observed that internal magnetic fluctuations increase with beta. During certain quiescent high confinement operational regimes, coherent low frequency modes not detected by magnetic probes are detected locally by CPS diagnostics.

  14. The underlying magnetic field direction in Ulysses observations of the southern polar heliosphere

    Science.gov (United States)

    Forsyth, R. J.; Balogh, A.; Smith, E. J.; Murphy, N.; McComas, D. J.

    1995-01-01

    Between May 1993 and January 1995, the Ulysses spacecraft has probed the southern polar heliosphere at latitudes greater than 30 deg S, reaching a maximum latitude of 80.2 deg S in September 1994. Using hourly averages of the data obtained by the magnetometer experiment on Ulysses we have studied the underlying direction of the magnetic field threading this region of the heliosphere, away from the influence of the magnetic sector structure which complicates similar analyses in the ecliptic plane. We have constructed histograms of the measured magnetic field direction using the simple Parker spiral model field direction as a reference. We find that throughout this region the meridional angle between the field vector and the Parker model direction has a distribution which is symmetric and has a most probable value consistent with the model. At latitudes below about 60 deg S the azimuthal angle distribution also has a most probable value consistent with the model but this distribution is highly asymmetric with a greater number of observations of field lines less tightly wound than the expected spiral direction. At latitudes greater than 60 deg S the most probable value of the azimuthal angle is found to have become nearly 30 more tightly wound than the expected direction, but due to the asymmetric distribution still with a greater number of observations less tightly wound than expected. We consider possible causes of both the asymmetry in the distributions and the shift in the most probable value at the highest latitudes, one of which may be the presence of large amplitude, long period Alfven waves in the magnetic field originating from the Sun's southern polar coronal hole.

  15. Miniature magnetic bottle confined by circularly polarized laser light and measurements of the inverse Faraday effect in plasmas

    International Nuclear Information System (INIS)

    Eliezer, S.; Paiss, Y.; Horovitz, Y.; Henis, Z.

    1997-01-01

    A new concept of hot plasma confinement in a miniature magnetic bottle induced by circularly polarized laser light is suggested. Magnetic fields generated by circularly polarized laser light may be of the order of megagauss, depending on the laser intensity. In this configuration the circularly polarized light is used to obtain confinement of a plasma contained in a good conductor vessel. The confinement in this scheme is supported by the magnetic forces. The Lawson criterion for a DT plasma might be achieved for number density n = 5*10 21 cm -3 and confinement time τ= 20 ns. The laser and plasma parameters required to obtain an energetic gain are calculated. Experiments and preliminary calculations were performed to study the feasibility of the above scheme. Measurements of the axial magnetic field induced by circularly polarized laser light, the so called inverse Faraday effect, and of the absorption of circularly polarized laser light in plasma, are reported. The experiments were performed with a circularly polarized Nd:YAG laser, having a wavelength of 1.06 τm and a pulse duration of 7 ns, in a range of irradiances from 10 9 to 10 14 W/cm 2 . Axial magnetic fields from 500 Gauss to 2 megagauss were measured. Up to 5*10 13 W/cm 3 the results are in agreement with a nonlinear model of the inverse Faraday effect dominated by the ponderomotive force. For the laser irradiance studied here, 9*10 13 - 2.5*10 14 W/cm 2 , the absorption of circularly polarized light was 14% higher relative to the absorption of linear polarized light

  16. The evolution of the englacial temperature distribution in the superimposed ice zone of a polar ice cap during a summer season

    NARCIS (Netherlands)

    Greuell, W.; Oerlemans, J.

    1989-01-01

    The aim of the present investigation was to provide more insight into the processes affecting the evolution of the englacial temperature distribution at a non-temperate location on a glacier. Measurements were made in the top 10 m of the ice at the summit of Laika Ice Cap (Canadian Arctic)

  17. Electrically tunable dynamic nuclear spin polarization in GaAs quantum dots at zero magnetic field

    Science.gov (United States)

    Manca, M.; Wang, G.; Kuroda, T.; Shree, S.; Balocchi, A.; Renucci, P.; Marie, X.; Durnev, M. V.; Glazov, M. M.; Sakoda, K.; Mano, T.; Amand, T.; Urbaszek, B.

    2018-04-01

    In III-V semiconductor nano-structures, the electron and nuclear spin dynamics are strongly coupled. Both spin systems can be controlled optically. The nuclear spin dynamics are widely studied, but little is known about the initialization mechanisms. Here, we investigate optical pumping of carrier and nuclear spins in charge tunable GaAs dots grown on 111A substrates. We demonstrate dynamic nuclear polarization (DNP) at zero magnetic field in a single quantum dot for the positively charged exciton X+ state transition. We tune the DNP in both amplitude and sign by variation of an applied bias voltage Vg. Variation of ΔVg on the order of 100 mV changes the Overhauser splitting (nuclear spin polarization) from -30 μeV (-22%) to +10 μeV (+7%) although the X+ photoluminescence polarization does not change sign over this voltage range. This indicates that absorption in the structure and energy relaxation towards the X+ ground state might provide favourable scenarios for efficient electron-nuclear spin flip-flops, generating DNP during the first tens of ps of the X+ lifetime which is on the order of hundreds of ps. Voltage control of DNP is further confirmed in Hanle experiments.

  18. Nonlinear waves in viscoelastic magnetized complex astroplasmas with polarized dust-charge variations

    Directory of Open Access Journals (Sweden)

    Papari Das

    2018-01-01

    Full Text Available A nonextensive nonthermal magnetized viscoelastic astrofluid, compositionally containing nonthermal electrons and ions together with massive polarized dust micro-spherical grains of variable electric charge, is allowed to endure weakly nonlinear perturbation around its equilibrium. The nonextensivity originating from the large-scale non-local effects is included via the Tsallis thermo-statistical distribution laws describing the lighter species. Assuming the equilibrium as a homogeneous hydrostatic one, the dust polarization effects are incorporated via the conventional homogeneous polarization force law. The perturbed fluid model evolves as a unique conjugate pair of coupled extended Korteweg-de Vries (e-KdV equations. A constructed numerical tapestry shows the collective excitations of a new pair of distinct classes of nonlinear mode structures in new parametric space. The first family indicates periodic electrostatic compressive eigenmodes in the form of soliton-chains. Likewise, the second one reveals gravitational rarefactive solitary patterns. Their microphysical multi-parametric dependencies of the eigen-patterns are illustratively analyzed and bolstered. The paper ends up with some promising implications and applications in the astro-cosmo-plasmic context of wave-induced accretive triggering processes responsible for gravitationally bounded (gravito-condensed astro-structure formation, such as stellesimals, planetsimals, etc.

  19. Nonlinear waves in viscoelastic magnetized complex astroplasmas with polarized dust-charge variations

    Science.gov (United States)

    Das, Papari; Karmakar, Pralay Kumar

    2018-01-01

    A nonextensive nonthermal magnetized viscoelastic astrofluid, compositionally containing nonthermal electrons and ions together with massive polarized dust micro-spherical grains of variable electric charge, is allowed to endure weakly nonlinear perturbation around its equilibrium. The nonextensivity originating from the large-scale non-local effects is included via the Tsallis thermo-statistical distribution laws describing the lighter species. Assuming the equilibrium as a homogeneous hydrostatic one, the dust polarization effects are incorporated via the conventional homogeneous polarization force law. The perturbed fluid model evolves as a unique conjugate pair of coupled extended Korteweg-de Vries (e-KdV) equations. A constructed numerical tapestry shows the collective excitations of a new pair of distinct classes of nonlinear mode structures in new parametric space. The first family indicates periodic electrostatic compressive eigenmodes in the form of soliton-chains. Likewise, the second one reveals gravitational rarefactive solitary patterns. Their microphysical multi-parametric dependencies of the eigen-patterns are illustratively analyzed and bolstered. The paper ends up with some promising implications and applications in the astro-cosmo-plasmic context of wave-induced accretive triggering processes responsible for gravitationally bounded (gravito-condensed) astro-structure formation, such as stellesimals, planetsimals, etc.

  20. Accretion dynamics and polarized x-ray emission of magnetized neutron stars

    International Nuclear Information System (INIS)

    Arons, J.

    1991-01-01

    The basic ideas of accretion onto magnetized neutron stars are outlined. These are applied to a simple model of the structure of the plasma mound sitting at the magnetic poles of such as star, in which upward diffusion of photons is balanced by their downward advection. This steady flow model of the plasma's dynamical state is used to compute the emission of polarized X-rays from the optically thick, birefringent medium. The linear polarization of the continuum radiation emerging from the quasi-static mound is found to be as much as 40% at some rotation phases, but is insensitive to the geometry of the accretion flow. The role of the accretion shock, whose detailed polarimetric and spectral characteristics have yet to be calculated, is emphasized as the final determinant of the properties of the emerging X-rays. Some results describing the fully time dependent dynamics of the flow are also presented. In particular, steady flow onto a neutron star is shown to exhibit formation of ''photon bubbles,'' regions of greatly reduced plasma density filled with radiation which form and rise on millisecond time scales. The possible role of these complex structures in the flow for the formation of the emergent spectrum is briefly outlined

  1. Distribution and dynamics of laser-polarized (129)Xe magnetization in vivo.

    Science.gov (United States)

    Swanson, S D; Rosen, M S; Coulter, K P; Welsh, R C; Chupp, T E

    1999-12-01

    The first magnetic resonance imaging studies of laser-polarized (129)Xe, dissolved in the blood and tissue of the lungs and the heart of Sprague-Dawley rats, are described. (129)Xe resonances at 0, 192, 199, and 210 ppm were observed and assigned to xenon in gas, fat, tissue, and blood, respectively. One-dimensional chemical-shift imaging (CSI) reveals xenon magnetization in the brain, kidney, and lungs. Coronal and axial two-dimensional CSI show (129)Xe dissolved in blood and tissue in the thorax. Images of the blood resonance show xenon in the lungs and the heart ventricle. Images of the tissue resonance reveal xenon in lung parenchyma and myocardium. The (129)Xe spectrum from a voxel located in the heart ventricle shows a single blood resonance. Time-resolved spectroscopy shows that the dynamics of the blood resonance match the dynamics of the gas resonance and demonstrates efficient diffusion of xenon gas to the lung parenchyma and then to pulmonary blood. These observations demonstrate the utility of laser-polarized (129)Xe to detect exchange across the gas-blood barrier in the lungs and perfusion into myocardial tissue. Applications to measurement of lung function, kidney perfusion, myocardial perfusion, and regional cerebral blood flow are discussed. Magn Reson Med 42:1137-1145, 1999. Copyright 1999 Wiley-Liss, Inc.

  2. Ionic magnetic fluids in polar solvents with tuned counter-ions

    Energy Technology Data Exchange (ETDEWEB)

    Lopes Filomeno, C. [Sorbonne Universités, UPMC Univ Paris 06, CNRS, Lab. PHENIX, Paris (France); Grupo de Fluidos Complexos Inst. de Quimica, Univ. de Brasília, Brasília (DF) (Brazil); Kouyaté, M. [Sorbonne Universités, UPMC Univ Paris 06, CNRS, Lab. PHENIX, Paris (France); Cousin, F. [Lab. Léon Brillouin – CE-Saclay, Gif-sur-Yvette (France); Demouchy, G. [Sorbonne Universités, UPMC Univ Paris 06, CNRS, Lab. PHENIX, Paris (France); Dpt de physique, Univ. de Cergy Pontoise, Cergy-Pontoise (France); Dubois, E.; Michot, L.; Mériguet, G. [Sorbonne Universités, UPMC Univ Paris 06, CNRS, Lab. PHENIX, Paris (France); Perzynski, R., E-mail: regine.perzynski@upmc.fr [Sorbonne Universités, UPMC Univ Paris 06, CNRS, Lab. PHENIX, Paris (France); Peyre, V.; Sirieix-Plénet, J. [Sorbonne Universités, UPMC Univ Paris 06, CNRS, Lab. PHENIX, Paris (France); Tourinho, F.A. [Grupo de Fluidos Complexos Inst. de Quimica, Univ. de Brasília, Brasília (DF) (Brazil)

    2017-06-01

    The aim of the present study is to propose a new reproducible method for preparing colloidal dispersions of electrostatically charged nanoparticles (NPs) in polar solvents with different kinds of counter-ions. Maghemite NPs are here dispersed in solvents of different dielectric constant, namely water, dimethylsulfoxide (DMSO) and an ionic liquid, ethylammonium nitrate (EAN). If the existence of a NP superficial charge happens to be necessary for the colloidal stability of the dispersions in these three solvents, the standard DLVO theory cannot be used any more to describe the colloidal stability in EAN. The structure of the dispersions and the strength of the interparticle repulsion are investigated by small angle X-ray scattering measurements, in association with Ludwig–Soret coefficient determinations. Specificities, associated to the nature of the counter-ions are identified in this work on the colloidal stability, on the interparticle repulsion and on the Ludwig–Soret coefficient. - Highlights: • A controlled synthesis of ionic magnetic fluids in three polar solvents is proposed. • Colloidal repulsion in the magnetic fluids depends on the counter-ion nature. • Soret coefficient of citrate-coated maghemite nanoparticles is probed in water-pH7. • Thermophilicity of nanoparticles depends on the nature of their counter-ions. • Nanoparticles dressed with same counter-ions have solvent-dependent thermoproperties.

  3. Quantitative spatial magnetization distribution in iron oxide nanocubes and nanospheres by polarized small-angle neutron scattering

    International Nuclear Information System (INIS)

    Disch, S; Hermann, R P; Brückel, Th; Wetterskog, E; Salazar-Alvarez, G; Bergström, L; Wiedenmann, A; Vainio, U

    2012-01-01

    By means of polarized small-angle neutron scattering, we have resolved the long-standing challenge of determining the magnetization distribution in magnetic nanoparticles in absolute units. The reduced magnetization, localized in non-interacting nanoparticles, indicates strongly particle shape- dependent surface spin canting with a 0.3(1) and 0.5(1) nm thick surface shell of reduced magnetization found for ∼9 nm nanospheres and ∼8.5 nm nanocubes, respectively. Further, the reduced macroscopic magnetization in nanoparticles results not only from surface spin canting, but also from drastically reduced magnetization inside the uniformly magnetized core as compared to the bulk material. Our microscopic results explain the low macroscopic magnetization commonly found in nanoparticles. (paper)

  4. Effect of annealing temperature on the structural and magnetic properties of CTAB-capped SrFe{sub 12}O{sub 19} platelets

    Energy Technology Data Exchange (ETDEWEB)

    Harikrishnan, V. [Materials Research Laboratory, Crystal Growth and Crystallography Division, School of Advanced Sciences, VIT University, Vellore 632014 (India); Saravanan, P. [Defence Metallurgical Research Laboratory, Hyderabad 500058 (India); Ezhil Vizhi, R., E-mail: rezhilvizhi@vit.ac.in [Materials Research Laboratory, Crystal Growth and Crystallography Division, School of Advanced Sciences, VIT University, Vellore 632014 (India); Babu, D. Rajan [Materials Research Laboratory, Crystal Growth and Crystallography Division, School of Advanced Sciences, VIT University, Vellore 632014 (India); Vinod, V.T.P.; Kejzlar, Pavel; Černík, Miroslav [Institute for Nanomaterials, Advanced Technologies and Innovation, Department of Natural Sciences, Technical University of Liberec, Studentská 1402/2, Liberec 1 461 17 (Czech Republic)

    2016-03-01

    The use of surfactant such as cetyl-trimethyl ammonium bromide (CTAB) in producing highly coercive SrFe{sub 12}O{sub 19} platelets is presented in this study. The synthesis of SrFe{sub 12}O{sub 19} was accomplished by co-precipitation in presence of 1 wt% CTAB. The CTAB-coated precipitant thus obtained was subjected to annealing at different temperatures: 700, 800, 900 and 1000 °C. The annealed counterparts were characterized with respect to their structural and magnetic properties and the results are compared with that of those processed without CTAB. Thermogravimetry analysis was employed to study the thermo-chemical behavior for the SrFe{sub 12}O{sub 19} samples. The evolution of crystalline phases as a function of annealing temperature was studied using x-ray diffraction. For the SrFe{sub 12}O{sub 19} samples without CTAB, formation of α-Fe{sub 2}O{sub 3} secondary phases are noticed at annealing temperatures of 700 and 800 °C; while such a secondary phase formation is not evident for the CTAB-capped SrFe{sub 12}O{sub 19}. Fourier transform infrared spectroscopy of the samples annealed at 1000 °C showed deformation in the structure due to the splitting of the bands. Both morphology and composition of the samples were examined by a field-emission scanning electron microscope attached with energy dispersive x-ray analysis. The morphology of CTAB-capped SrFe{sub 12}O{sub 19} samples showed the presence of hexagonal platelets at higher annealing temperatures. The magnetic parameters such as saturation magnetization, M{sub S} and coercivity, H{sub C} were evaluated from the magnetic hysteresis loops obtained by vibrating sample magnetometer. Maximum values of H{sub C} (6.3 kOe) and M{sub S} (42.7 emu/g) were obtained for the CTAB-capped SrFe{sub 12}O{sub 19} samples annealed at 900 °C. The possible mechanism on the formation of M-type hexagonal phase with platelet morphology using minimal amount of CTAB (1 wt%) in achieving high the H{sub C} values for the Sr

  5. The effect of varying the capping agent of magnetic/luminescent Fe3O4–InP/ZnSe core–shell nanocomposite

    International Nuclear Information System (INIS)

    Paulsen, Zuraan; Onani, Martin O.; Allard, Garvin R.J.; Kiplagat, Ayabei; Okil, Joseph O.; Dejene, Francis B.; Mahanga, Geoffrey M.

    2016-01-01

    Magnetic–luminescent nanoparticles have shown great promise in various biomedical applications namely: contrast agents for magnetic resonance imaging, multifunctional drug carrier system, magnetic separation of cells, cell tracking, immunoassay, and magnetic bioseparation. This experiment describes the synthesis of a nanocomposite material, which is composed of an iron oxide (Fe 3 O 4 ) superparamagnetic core and an indium phosphide/zinc selenide (InP/ZnSe) quantum dot shell. The magnetic nanoparticles (MNP’s) and quantum dots (QD’s) were synthesized separately before allowing them to conjugate. The MNP’s were functionalized with a thiol-group allowing the QD shell to bind to the surface of the MNP by the formation of a thiol–metal bond. The nanocomposite was capped with 3-mercaptopropionic acid, oleylamine, β-cyclodextrin and their influence on the photoluminescence investigated. The synthesized nanocomposite was characterized with high- resolution transmission electron microscopy (HR-TEM), energy-dispersive spectroscopy (EDS), selective electron area diffraction (SAED), scanning electron microscopy (SEM), superconducting quantum interference device (SQUID), and photoluminescence. These techniques yielded particle size, morphology, dispersion, and chemical composition including luminescence and florescence.

  6. Confinement effect on hole polarization in (Ga,Mn)As/AlAs diluted magnetic semiconductor multiple quantum wells

    Science.gov (United States)

    Dimitriev, G. S.; Sapega, V. F.; Averkiev, N. S.; Panaiotti, I. E.; Ploog, K. H.

    2017-11-01

    The influence of quantum confinement on the spin polarization of holes in ferromagnetic multiple quantum wells based on (Ga,Mn)As diluted magnetic semiconductor has been investigated. It is shown that the spin polarization of holes in the impurity band is more likely determined by the magnetic properties of GaMnAs rather than the quantum-confinement effect. The model of Mn acceptor in a QW, describing the polarization characteristics of photoluminescence in GaAs: Mn/AlAs QWs, has been developed. Experimental data and theoretical analysis show that the spin polarization of holes in (Ga, Mn)As/AlAs QWs can be explained within a model, which suggests that holes are localized in the impurity band.

  7. Thermal cracking of CO2 slab ice as the main driving force for albedo increase of the martian seasonal polar caps

    Science.gov (United States)

    Philippe, S.; Schmitt, B.; Beck, P.; Brissaud, O.

    2015-10-01

    Understanding the microphysical processes occuring on the Martian seasonal cap is critical since their radiative properties can affect the martian climate. A well documented phenomenom is the albedo increase of the Martian seasonal caps during spring, Fig.1. There are a lot of hypotheses that have been proposed as an explanation for this observation : the decrease of the CO2 grain size [2], a cleaning process of the CO2 slab that would imply either the sinking or the ejection of the dust contained in its volume ([1], [2], [5]), a water-layer accumulation on the top of the slab [5], the role played by aerosols [2] etc ... So far, no experimental simulations have been realized to discriminate between these processes. We designed an experiment to investigate the hypothesis of CO2 ice grain size decrease through thermal cracking as well as that of dust segregation as the possible reasons for albedo increase.

  8. Constraining the regular Galactic magnetic field with the 5-year WMAP polarization measurements at 22 GHz

    Science.gov (United States)

    Ruiz-Granados, B.; Rubiño-Martín, J. A.; Battaner, E.

    2010-11-01

    Context. The knowledge of the regular (large scale) component of the Galactic magnetic field gives important information about the structure and dynamics of the Milky Way, and also constitutes a basic tool to determine cosmic ray trajectories. It can also provide clear windows where primordial magnetic fields could be detected. Aims: We aim to obtain the regular (large scale) pattern of the magnetic field distribution of the Milky Way that better fits the polarized synchrotron emission as seen by the WMAP satellite in the 5 years data at 22 GHz. Methods: We have done a systematic study of a number of Galactic magnetic field models: axisymmetric (with and without radial dependence on the field strength), bisymmetric (with and without radial dependence), logarithmic spiral arms, concentric circular rings with reversals and bi-toroidal. We have explored the parameter space defining each of these models using a grid-based approach. In total, more than one million models were computed. The model selection was done using a Bayesian approach. For each model, the posterior distributions were obtained and marginalized over the unwanted parameters to obtain the marginal (one-parameter) probability distribution functions. Results: In general, axisymmetric models provide a better description of the halo component, although with regard to their goodness-of-fit, the other models cannot be rejected. In the case of the disk component, the analysis is not very sensitive for obtaining the disk large-scale structure, because of the effective available area (less than 8% of the whole map and less than 40% of the disk). Nevertheless, within a given family of models, the best-fit parameters are compatible with those found in the literature. Conclusions: The family of models that better describes the polarized synchrotron halo emission is the axisymmetric one, with magnetic spiral arms with a pitch angle of ≈24°, and a strong vertical field of 1 μG at z ≈ 1 kpc. When a radial

  9. A polarized neutron study of the magnetization distribution in Co2FeSi

    International Nuclear Information System (INIS)

    Brown, P J; Kainuma, R; Kanomata, T; Okubo, A; Neumann, K-U; Umetsu, R Y; Ziebeck, K R A

    2013-01-01

    The magnetization distribution in Co 2 FeSi which has the largest moment per formula unit ∼6 μ B of all Heusler alloys, has been determined using polarized neutron diffraction. The experimentally determined magnetization has been integrated over spheres centred on the three sites of the L1 2 structure giving μ Fe = 3.10(3) μ B and μ Co = 1.43(2) μ B , results which are slightly lower than the moments in atomic spheres of similar radii obtained in recent LDA + U band structure calculations (Li et al 2010 Chin. Phys. B 19 097102). Approximately 50% of the magnetic carriers at the Fe sites were found to be in orbitals with e g symmetry. This was higher, ≃65%, at the Co sites. Both Fe and Co were found to have orbital moments that are larger than those predicted. Comparison with similar results obtained for related alloys suggests that there must be a finite density of states in both spin bands at the Fermi energy indicating that Co 2 FeSi is not a perfect half-metallic ferromagnet. (paper)

  10. Magnetic field calculation of variably polarizing undulator (APPLE-type) for SX beamline in the SPring-8

    International Nuclear Information System (INIS)

    Kobayashi, Hideki; Sasaki, Shigemi; Shimada, Taihei; Takao, Masaru; Yokoya, Akinori; Miyahara, Yoshikazu

    1996-03-01

    This paper describes the design of a variably polarizing undulator (APPLE-type) to be installed in soft X-ray beamline in the SPring-8 facility. The magnetic field distribution and radiation spectrum expected from this undulator were calculated. The magnetic field strength is varied by changing the gap distance of upper and lower jaws, so it changes the photon energy in soft X-ray range. By moving the relative position of pairs of magnet rows (phase shift), the polarization of radiation is varied circularly, elliptically and linearly in the horizontal and vertical direction. We expect that right and left handed circular polarizations are obtained alternately at a rate of 1 Hz by high speed phase shifting. The repulsive and attractive magnetic force working on the magnet rows were calculated which interfere in phase shifting at high speed. The magnetic force changes with gap distance and phase shift position, and the magnetic force working on a row in the direction of phase shift becomes up to 500 kgf. The construction of this undulator is started in 1996, that will be inserted in the storage ring in 1997. (author)

  11. Magnetic field calculation of variably polarizing undulator (APPLE-type) for SX beamline in the SPring-8

    Energy Technology Data Exchange (ETDEWEB)

    Kobayashi, Hideki; Sasaki, Shigemi; Shimada, Taihei; Takao, Masaru; Yokoya, Akinori; Miyahara, Yoshikazu [Japan Atomic Energy Research Inst., Kamigori, Hyogo (Japan). Kansai Research Establishment

    1996-03-01

    This paper describes the design of a variably polarizing undulator (APPLE-type) to be installed in soft X-ray beamline in the SPring-8 facility. The magnetic field distribution and radiation spectrum expected from this undulator were calculated. The magnetic field strength is varied by changing the gap distance of upper and lower jaws, so it changes the photon energy in soft X-ray range. By moving the relative position of pairs of magnet rows (phase shift), the polarization of radiation is varied circularly, elliptically and linearly in the horizontal and vertical direction. We expect that right and left handed circular polarizations are obtained alternately at a rate of 1 Hz by high speed phase shifting. The repulsive and attractive magnetic force working on the magnet rows were calculated which interfere in phase shifting at high speed. The magnetic force changes with gap distance and phase shift position, and the magnetic force working on a row in the direction of phase shift becomes up to 500 kgf. The construction of this undulator is started in 1996, that will be inserted in the storage ring in 1997. (author).

  12. Unidirectional transmission based on polarization conversion and excitation of magnetic or surface polaritons

    Directory of Open Access Journals (Sweden)

    Xiaohu Wu

    2017-07-01

    Full Text Available We propose in this work combing a uniaxial crystal slab with a one-dimensional grating to realize unidirectional transmission (UDT. The physical mechanism for the UDT is attributed to polarization conversion with uniaxial crystal slab and excitation of magnetic polaritons (MPs or surface plasmon polaritons (SPPs in the grating region. Numerical simulations were performed by taking hexagonal boron nitride as the uniaxial crystal. The results reveal that UDT can be achieved for both TE and TM waves in the mid-infrared and the optical regions if the grating material is respectively selected as silicon carbide (SiC and silver (Ag with properly chosen values of the structure’s geometric parameters. This work may provide important guidelines for design of novel unidirectional transmission devices.

  13. Polarization study of non-resonant X-ray magnetic scattering from spin-density-wave modulation in chromium

    International Nuclear Information System (INIS)

    Ohsumi, Hiroyuki; Takata, Masaki

    2007-01-01

    We present a polarization study of non-resonant X-ray magnetic scattering in pure chromium. Satellite reflections are observed at +/-Q and +/-2Q, where Q is the modulation wave vector of an itinerant spin-density-wave. The first and second harmonics are confirmed to have magnetic and charge origin, respectively, by means of polarimetry without using an analyzer crystal. This alternative technique eliminates intolerable intensity loss at an analyzer by utilizing the sample crystal also as an analyzer crystal

  14. Spin-polarized transport in manganite-based magnetic nano structures

    International Nuclear Information System (INIS)

    Granada, Mara

    2007-01-01

    Giant magnetoresistance (G M R) and tunnel magnetoresistance are spin polarized transport phenomena which are observed in magnetic multilayers.They consist in a large variation of the electrical resistivity of the system depending on whether the magnetizations of the magnetic layers are aligned parallel or anti-parallel to each other. In order to be able to align the magnetic layers by means of an external magnetic field, they must not be strongly ferromagnetically coupled.The extrinsic magnetoresistance effects in magnetic multilayers, either G M R in the case of a metallic spacer, or T M R in the case of an insulating spacer, are observed at low magnetic fields, which makes these phenomena interesting for technological applications.We studied the possibility of using the ferromagnetic manganite La 0 ,75Sr 0 ,25MnO 3 (L S M O) in magneto resistive devices, with different materials as a spacer layer.As the main result of this work, we report G M R and T M R measurements in L S M O/LaNiO 3 /L S M O and L S M O/CaMnO 3 /L S M O tri layers, respectively, observed for the first time in these systems.This work included the deposition of films and multilayers by sputtering, the structural characterization of the samples and the study of their magnetic and electric transport properties.Our main interest was the study of G M R in L S M O/LaNiO 3 /L S M O tri layers.It was necessary to firstly characterize the magnetic coupling of L S M O layers through the L N O spacer. After that, we performed electric transport measurements with the current in the plane of the samples.We measured a G M R contribution of ∼ 0,55 % at T = 83 K.We designed a procedure for patterning the samples by e-beam lithography for electric transport measurements with the current perpendicular to the plane. We also performed the study of L S M O/CaMnO 3 /L S M O tri layers with an insulating spacer.We studied the magnetic coupling, as in the previous case.Then we fabricated a tunnel junction for

  15. PHOTOSPHERIC FLOW FIELD RELATED TO THE EVOLUTION OF THE SUN'S POLAR MAGNETIC PATCHES OBSERVED BY HINODE SOLAR OPTICAL TELESCOPE

    Energy Technology Data Exchange (ETDEWEB)

    Kaithakkal, Anjali John; Suematsu, Y.; Kubo, M. [Department of Astronomical Science, Graduate University for Advanced Studies (SOKENDAI), Mitaka, Tokyo 181-8588 (Japan); Iida, Y.; Tsuneta, S. [Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), Sagamihara, Kanagawa 252-5210 (Japan); Shiota, D., E-mail: anjali.johnk@nao.ac.jp [Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya 464-8601 (Japan)

    2015-02-01

    We investigated the role of photospheric plasma motions in the formation and evolution of polar magnetic patches using time-sequence observations with high spatial resolution. The observations were obtained with the spectropolarimeter on board the Hinode satellite. From the statistical analysis using 75 magnetic patches, we found that they are surrounded by strong converging, supergranulation associated flows during their apparent lifetime and that the converging flow around the patch boundary is better observed in the Doppler velocity profile in the deeper photosphere. Based on our analysis, we suggest that the like-polarity magnetic fragments in the polar region are advected and clustered by photospheric converging flows, thereby resulting in the formation of polar magnetic patches. Our observations show that, in addition to direct cancellation, magnetic patches decay by fragmentation followed by unipolar disappearance or unipolar disappearance without fragmentation. It is possible that the magnetic patches of existing polarity fragment or diffuse away into smaller elements and eventually cancel out with opposite polarity fragments that reach the polar region around the solar cycle maximum. This could be one of the possible mechanisms by which the existing polarity decays during the reversal of the polar magnetic field.

  16. Variation of Magnetic Field (By , Bz Polarity and Statistical Analysis of Solar Wind Parameters during the Magnetic Storm Period

    Directory of Open Access Journals (Sweden)

    Ga-Hee Moon

    2011-06-01

    Full Text Available It is generally believed that the occurrence of a magnetic storm depends upon the solar wind conditions, particularly the southward interplanetary magnetic field (IMF component. To understand the relationship between solar wind parameters and magnetic storms, variations in magnetic field polarity and solar wind parameters during magnetic storms are examined. A total of 156 storms during the period of 1997~2003 are used. According to the interplanetary driver, magnetic storms are divided into three types, which are coronal mass ejection (CME-driven storms, co-rotating interaction region (CIR-driven storms, and complicated type storms. Complicated types were not included in this study. For this purpose, the manner in which the direction change of IMF By and Bz components (in geocentric solar magnetospheric coordinate system coordinate during the main phase is related with the development of the storm is examined. The time-integrated solar wind parameters are compared with the time-integrated disturbance storm time (Dst index during the main phase of each magnetic storm. The time lag with the storm size is also investigated. Some results are worth noting: CME-driven storms, under steady conditions of Bz < 0, represent more than half of the storms in number. That is, it is found that the average number of storms for negative sign of IMF Bz (T1~T4 is high, at 56.4%, 53.0%, and 63.7% in each storm category, respectively. However, for the CIR-driven storms, the percentage of moderate storms is only 29.2%, while the number of intense storms is more than half (60.0% under the Bz < 0 condition. It is found that the correlation is highest between the time-integrated IMF Bz and the time-integrated Dst index for the CME-driven storms. On the other hand, for the CIR-driven storms, a high correlation is found, with the correlation coefficient being 0.93, between time-integrated Dst index and time-integrated solar wind speed, while a low correlation, 0.51, is

  17. Polarized Line Formation in Arbitrary Strength Magnetic Fields Angle-averaged and Angle-dependent Partial Frequency Redistribution

    Energy Technology Data Exchange (ETDEWEB)

    Sampoorna, M.; Nagendra, K. N. [Indian Institute of Astrophysics, Koramangala, Bengaluru 560 034 (India); Stenflo, J. O., E-mail: sampoorna@iiap.res.in, E-mail: knn@iiap.res.in, E-mail: stenflo@astro.phys.ethz.ch [Institute of Astronomy, ETH Zurich, CH-8093 Zurich (Switzerland)

    2017-08-01

    Magnetic fields in the solar atmosphere leave their fingerprints in the polarized spectrum of the Sun via the Hanle and Zeeman effects. While the Hanle and Zeeman effects dominate, respectively, in the weak and strong field regimes, both these effects jointly operate in the intermediate field strength regime. Therefore, it is necessary to solve the polarized line transfer equation, including the combined influence of Hanle and Zeeman effects. Furthermore, it is required to take into account the effects of partial frequency redistribution (PRD) in scattering when dealing with strong chromospheric lines with broad damping wings. In this paper, we present a numerical method to solve the problem of polarized PRD line formation in magnetic fields of arbitrary strength and orientation. This numerical method is based on the concept of operator perturbation. For our studies, we consider a two-level atom model without hyperfine structure and lower-level polarization. We compare the PRD idealization of angle-averaged Hanle–Zeeman redistribution matrices with the full treatment of angle-dependent PRD, to indicate when the idealized treatment is inadequate and what kind of polarization effects are specific to angle-dependent PRD. Because the angle-dependent treatment is presently computationally prohibitive when applied to realistic model atmospheres, we present the computed emergent Stokes profiles for a range of magnetic fields, with the assumption of an isothermal one-dimensional medium.

  18. Experimental and theoretical study of magnetic ordering and local atomic polarization in Ru-substituted Lu2Fe17

    Science.gov (United States)

    Tereshina, E. A.; Isnard, O.; Smekhova, A.; Andreev, A. V.; Rogalev, A.; Khmelevskyi, S.

    2014-03-01

    The distribution of magnetic moments in the iron-rich intermetallic compound Lu2Fe17 with Fe partly substituted by Ru has been investigated on Lu2Fe16.5Ru0.5 by using several techniques. The crystal structure and temperature evolution of the magnetic structure was studied using high resolution and high flux neutron powder diffractometers. In contrast to the parent Lu2Fe17, which transforms on cooling from an antiferromagnetic to a ferromagnetic state, Lu2Fe16.5Ru0.5 is an antiferromagnet (Néel temperature TN = 208 K) down to the lowest temperatures. The magnetic polarization at the lutetium L2,3 absorption edges, iron K and ruthenium L2 edges was studied by x-ray magnetic circular dichroism (XMCD) on a single crystal of Lu2Fe16.5Ru0.5 in a magnetic field of 3 T, i.e., above the field-induced metamagnetic transition. The Ru XMCD signal proves the existence of induced magnetic polarization parallel to the dominant Fe sublattice magnetization. A corresponding theoretical analysis in the framework of the local spin density formalism is provided in order to discern the structural disorder effects and magnetism in the system.

  19. Scattering Polarization of Hydrogen Lines in Weakly Magnetized Stellar Atmospheres. I. Formulation and Application to Isothermal Models

    Czech Academy of Sciences Publication Activity Database

    Štěpán, Jiří; Trujillo Bueno, J.

    2011-01-01

    Roč. 732, č. 2 (2011), 80/1-80/20 ISSN 0004-637X Institutional research plan: CEZ:AV0Z10030501 Keywords : magnetic fields * polarization * radiative transfer Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 6.024, year: 2011

  20. Laser polarization dependent and magnetically control of group velocity in a dielectric medium doped with nanodiamond nitrogen vacancy centers

    Energy Technology Data Exchange (ETDEWEB)

    Asadpour, Seyyed Hossein; Rahimpour Soleimani, H., E-mail: Rahimpour@guilan.ac.ir

    2014-03-01

    In this paper, group velocity control of Gaussian beam in a dielectric medium doped with nanodiamond nitrogen vacancy (NV) centers under optical excitation is discussed. The shape of transmitted and reflected pulses from dielectric can be tuned by changing the intensity of magnetic field and polarization of the control beam. The effect of intensity of control beam on group velocity is also investigated.

  1. Potentiodynamic polarization assays on magnetic materials for new medical micro-devices

    Energy Technology Data Exchange (ETDEWEB)

    Pouponneau, P. [Ecole Polytechnique de Montreal, PQ (Canada). Nanorobotics Lab; Ecole Polytechnique de Montreal, PQ (Canada). Biomedical Engineering Inst., Laboratory for the Innovation and Analysis of Bioperformance; Savadogo, O.; Napporn, T. [Ecole Polytechnique de Montreal, Montreal, PQ (Canada). Laboratoire de nouveaux materiaux pour l' energie et l' electrochimie; Yahia, L' H. [Ecole Polytechnique de Montreal, PQ (Canada). Biomedical Engineering Inst., Laboratory for the Innovation and Analysis of Bioperformance; Martel, S. [Ecole Polytechnique de Montreal, PQ (Canada). Nanorobotics Lab

    2008-07-01

    This study investigated the corrosion behaviour of a terbium (Tb0.27Dy0.73Fe1.95) alloy and single crystal nickel (Ni-Mn-Ga) alloy smart magnetic materials (SMM), and Vacoflux 17 and Permendur iron-cobalt alloys. Previous studies have shown that the materials demonstrate a high potential for use in wireless medical microdevices controlled by magnetic fields. However, the Tb0.27Dy0.73Fe1.95 alloy has poor corrosion properties due to its high corrosion potential and corrosion current. Corrosion behaviour was investigated using potentiodynamic polarization measurements and scanning electron microscopy. The study showed that the surface of the alloy was impaired by cracks and holes. The single crystal Ni-Mn Ga alloy demonstrated higher corrosion resistance. The SMM were then embedded into a bio-compatible matrix to form composite with the Vacoflux 17 and Permendur alloys. The study showed that while the Vacoflux 17 surface was degraded by cracks and pits, the Permendur surface was uniformly corroded without pitting. The uniform corrosion was attributed to the formation of a stable passive layer. 4 refs., 3 figs.

  2. Plasma and magnetic field characteristics of the distant polar cusp near local noon: The entry layer

    International Nuclear Information System (INIS)

    Paschmann, G.; Haerendel, G.; Sckopke, N.; Rosenbauer, H.; Hedgecock, P.C.

    1976-01-01

    Heos 2 plasma and magnetic field measurements in the distant polar cusp region reveal the existence of a plasma layer on day side field lines just inside the magnetopause. Density and temperature in this layer are nearly the same as they are in the adjacent magnetosheath, but the flow lacks the order existing both in the magnetosheath and in the plasma mantle. Flow directions toward and away from the sun but, in general, parallel to the field lines have been found. The magnetopause (as defined by a sudden rotation of the magnetic field vector) mostly coincides with the transition to ordered magnetosheath flow. The inner boundary of the layer is located just within the outer boundary of the hot ring current plasma. In the region of overlap the hot electrons have the signature of trapped particles, though often at reduced intensity. The magnetic field is strongly fluctuating in magnitude, while its orientation is more stable, consistent with a connection to the earth, but is systematically distorted out of the meridian plane. The layer is thought to be a consequence of the entry of magnetosheath plasma, which does not appear to be unobstructed, as has been claimed in the concept of a magnetospheric cleft. The magnetopause has a cusplike indentation which is elongated in local time. The existence of field-aligned currents (total strength approx. =10 6 A) and their location of flow in the inner part of the entry layer (into the ionosphere before noon and out of it after noon) are inferred from the systematic bending of field lines. It is proposed that the dynamo of the related current system is provided by the transfer of perpendicular momentum resulting from the plasma entry into the layer. The essential features of the entry layer might be compatible with the model of plasma flow through the magnetopause of Levy et al. (1964) if a 'dam' effect caused by the cusp geometry were added

  3. Micromagnetism in (001) magnetite by spin-polarized low-energy electron microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Figuera, Juan de la, E-mail: juan.delafiguera@iqfr.csic.es [Instituto de Química-Física “Rocasolano”, CSIC, Madrid 28006 (Spain); Vergara, Lucía [Instituto de Química-Física “Rocasolano”, CSIC, Madrid 28006 (Spain); N' Diaye, Alpha T. [Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Quesada, Adrian [Instituto de Cerámica y Vidrio, CSIC, Calle Kelsen 5, 28049, Madrid (Spain); Schmid, Andreas K. [Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States)

    2013-07-15

    Spin-polarized low-energy electron microscopy was used to image a magnetite crystal with (001) surface orientation. Sets of spin-dependent images of magnetic domain patterns observed in this surface were used to map the direction of the magnetization vector with high spatial and angular resolution. We find that domains are magnetized along the surface <110> directions, and domain wall structures include 90° and 180° walls. A type of unusually curved domain walls are interpreted as Néel-capped surface terminations of 180° Bloch walls. - Highlights: ► The (001) surface of magnetite is imaged by spin-polarized low-energy electron microscopy. ► The magnetic domain microstructure is resolved. ► Magnetic easy axes in this surface are found to be along <110> directions. ► Magnetic domain wall structures include wide Néel-caps.

  4. Probing the Magnetic Field Structure in Sgr A* on Black Hole Horizon Scales with Polarized Radiative Transfer Simulations

    Energy Technology Data Exchange (ETDEWEB)

    Gold, Roman; McKinney, Jonathan C. [Department of Physics and Joint Space-Science Institute, University of Maryland, College Park, MD 20742 (United States); Johnson, Michael D.; Doeleman, Sheperd S. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

    2017-03-10

    Magnetic fields are believed to drive accretion and relativistic jets in black hole accretion systems, but the magnetic field structure that controls these phenomena remains uncertain. We perform general relativistic (GR) polarized radiative transfer of time-dependent three-dimensional GR magnetohydrodynamical simulations to model thermal synchrotron emission from the Galactic Center source Sagittarius A* (Sgr A*). We compare our results to new polarimetry measurements by the Event Horizon Telescope (EHT) and show how polarization in the visibility (Fourier) domain distinguishes and constrains accretion flow models with different magnetic field structures. These include models with small-scale fields in disks driven by the magnetorotational instability as well as models with large-scale ordered fields in magnetically arrested disks. We also consider different electron temperature and jet mass-loading prescriptions that control the brightness of the disk, funnel-wall jet, and Blandford–Znajek-driven funnel jet. Our comparisons between the simulations and observations favor models with ordered magnetic fields near the black hole event horizon in Sgr A*, though both disk- and jet-dominated emission can satisfactorily explain most of the current EHT data. We also discuss how the black hole shadow can be filled-in by jet emission or mimicked by the absence of funnel jet emission. We show that stronger model constraints should be possible with upcoming circular polarization and higher frequency (349 GHz) measurements.

  5. Probing the Magnetic Field Structure in Sgr A* on Black Hole Horizon Scales with Polarized Radiative Transfer Simulations

    International Nuclear Information System (INIS)

    Gold, Roman; McKinney, Jonathan C.; Johnson, Michael D.; Doeleman, Sheperd S.

    2017-01-01

    Magnetic fields are believed to drive accretion and relativistic jets in black hole accretion systems, but the magnetic field structure that controls these phenomena remains uncertain. We perform general relativistic (GR) polarized radiative transfer of time-dependent three-dimensional GR magnetohydrodynamical simulations to model thermal synchrotron emission from the Galactic Center source Sagittarius A* (Sgr A*). We compare our results to new polarimetry measurements by the Event Horizon Telescope (EHT) and show how polarization in the visibility (Fourier) domain distinguishes and constrains accretion flow models with different magnetic field structures. These include models with small-scale fields in disks driven by the magnetorotational instability as well as models with large-scale ordered fields in magnetically arrested disks. We also consider different electron temperature and jet mass-loading prescriptions that control the brightness of the disk, funnel-wall jet, and Blandford–Znajek-driven funnel jet. Our comparisons between the simulations and observations favor models with ordered magnetic fields near the black hole event horizon in Sgr A*, though both disk- and jet-dominated emission can satisfactorily explain most of the current EHT data. We also discuss how the black hole shadow can be filled-in by jet emission or mimicked by the absence of funnel jet emission. We show that stronger model constraints should be possible with upcoming circular polarization and higher frequency (349 GHz) measurements.

  6. Polarization enhancement and ferroelectric switching enabled by interacting magnetic structures in DyMnO3 thin films

    KAUST Repository

    Lu, Chengliang

    2013-12-02

    The mutual controls of ferroelectricity and magnetism are stepping towards practical applications proposed for quite a few promising devices in which multiferroic thin films are involved. Although ferroelectricity stemming from specific spiral spin ordering has been reported in highly distorted bulk perovskite manganites, the existence of magnetically induced ferroelectricity in the corresponding thin films remains an unresolved issue, which unfortunately halts this step. In this work, we report magnetically induced electric polarization and its remarkable response to magnetic field (an enhancement of ?800% upon a field of 2 Tesla at 2 K) in DyMnO3 thin films grown on Nb-SrTiO3 substrates. Accompanying with the large polarization enhancement, the ferroelectric coercivity corresponding to the magnetic chirality switching field is significantly increased. A picture based on coupled multicomponent magnetic structures is proposed to understand these features. Moreover, different magnetic anisotropy related to strain-suppressed GdFeO 3-type distortion and Jahn-Teller effect is identified in the films.

  7. The Polarization Signature of Photospheric Magnetic Fields in 3D MHD Simulations and Observations at Disk Center

    Energy Technology Data Exchange (ETDEWEB)

    Beck, C. [National Solar Observatory, 3665 Discovery Drive, Boulder, CO 80303 (United States); Fabbian, D. [Max-Planck-Institut für Sonnensytemforschung, Justus-von-Liebig-Weg 3, D-37077 Göttingen (Germany); Rezaei, R. [Instituto de Astrofísica de Canarias, C/Vía Láctea S/N, E-38205 La Laguna, Tenerife (Spain); Puschmann, K. G., E-mail: cbeck@nso.edu [Alzenau (Germany)

    2017-06-10

    Before using three-dimensional (3D) magnetohydrodynamical (MHD) simulations of the solar photosphere in the determination of elemental abundances, one has to ensure that the correct amount of magnetic flux is present in the simulations. The presence of magnetic flux modifies the thermal structure of the solar photosphere, which affects abundance determinations and the solar spectral irradiance. The amount of magnetic flux in the solar photosphere also constrains any possible heating in the outer solar atmosphere through magnetic reconnection. We compare the polarization signals in disk-center observations of the solar photosphere in quiet-Sun regions with those in Stokes spectra computed on the basis of 3D MHD simulations having average magnetic flux densities of about 20, 56, 112, and 224 G. This approach allows us to find the simulation run that best matches the observations. The observations were taken with the Hinode SpectroPolarimeter (SP), the Tenerife Infrared Polarimeter (TIP), the Polarimetric Littrow Spectrograph (POLIS), and the GREGOR Fabry–Pèrot Interferometer (GFPI), respectively. We determine characteristic quantities of full Stokes profiles in a few photospheric spectral lines in the visible (630 nm) and near-infrared (1083 and 1565 nm). We find that the appearance of abnormal granulation in intensity maps of degraded simulations can be traced back to an initially regular granulation pattern with numerous bright points in the intergranular lanes before the spatial degradation. The linear polarization signals in the simulations are almost exclusively related to canopies of strong magnetic flux concentrations and not to transient events of magnetic flux emergence. We find that the average vertical magnetic flux density in the simulation should be less than 50 G to reproduce the observed polarization signals in the quiet-Sun internetwork. A value of about 35 G gives the best match across the SP, TIP, POLIS, and GFPI observations.

  8. Polarized light transmission in ferrofluids loaded with carbon nanotubes in the presence of a uniform magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Vales-Pinzón, C., E-mail: cvales@mda.cinvestav.mx [Applied Physics Department, CINVESTAV-Unidad Mérida, Antigua carretera a Progreso km 6, A.P. 73, Cordemex, Mérida Yucatán 97310 (Mexico); Alvarado-Gil, J.J. [Applied Physics Department, CINVESTAV-Unidad Mérida, Antigua carretera a Progreso km 6, A.P. 73, Cordemex, Mérida Yucatán 97310 (Mexico); Medina-Esquivel, R. [Facultad de Ingeniería-UADY, Av. Industrias no Contaminantes por Periférico Norte, A.P. 150, Cordemex, Mérida, Yucatán (Mexico); Martínez-Torres, P. [Department of Mechanical Engineering, University of California, Riverside, 900 University Ave., Riverside, CA 92521 (United States)

    2014-11-15

    Magneto-optic phenomena in ferrofluids have been shown to be related to the formation of chain structures, due to the arrangement of the ferromagnetic particles, induced by an applied magnetic field. In this work, the effects on transmission of polarized light due to anisotropic effects induced by an external magnetic field in ferrofluids with carbon nanotubes are studied. The time response of the system presents two well defined stages, in the first one, which is very short, the fluid behaves as a polarizer. In contrast in the second stage, the effects of light transmission dominate. In this stage the transmitted light intensity grows with time and after a long time reaches a constant stable value. It is shown that these phenomena depend on the carbon nanotubes concentration as well as on the strength of the applied magnetic field. Using a simple model that considers a chain-like structure formation, it is possible to determine the rate of agglomeration of the formed structures and the attenuation coefficient of the transmitted light. The formation of nanostructures leads to variation in the transmitted light, depending on the polarization of the incident light. These magnetic nanostructures can find numerous applications in nanotechnology, optical devices and medicine. - Highlights: • Carbon nanotubes in ferrofluids favor the formation of chain-like structures. • In the presence of a magnetic field ferrofluids loaded with CNT behaves as a polarizer. • Transmitted light increases when samples are under a magnetic field then stabilizes. • Attenuation time for transmitted light and agglomeration parameters were studied.

  9. Enhanced polarization, magnetic response and pronounced antibacterial activity of bismuth ferrite nanorods

    Energy Technology Data Exchange (ETDEWEB)

    Biswas, Kunal [Department of Biotechnology, Maulana Abul Kalam Azad University of Technology, West Bengal, Kolkata-64 (India); De, Debashis, E-mail: dr.debashis.de@ieee.org [Department of Computer Science and Engineering, Maulana Abul Kalam Azad University of Technology, West Bengal, Kolkata-64 (India); Bandyopadhyay, Jaya [Department of Biotechnology, Maulana Abul Kalam Azad University of Technology, West Bengal, Kolkata-64 (India); Dutta, Nabanita; Rana, Subhasis; Sen, Pintu [Variable Energy Cyclotron Centre, 1/AF, Bidhan Nagar, Kolkata, 700 064 (India); Bandyopadhyay, Sujit Kumar, E-mail: drsujitkumar@gmail.com [Meghnad Saha Institute of Technology, Nazirabad Rd, Uchhepota, Kolkata, West Bengal, 700150 (India); Chakraborty, P.K. [Department of Physics, Burdwan University, Burdwan, 713104 (India)

    2017-07-01

    The present work reports on the physical and biophysical characterization of bismuth ferrite (BFO) nanorods fabricated on porous anodized alumina (AAO) templates. The diameter of the nanorods was quite large, which vary in the range of 20–100 nm. The BFO nanorods exhibited enhanced polarization and significant magnetic susceptibility. Moreover, an enhanced magnetoelectric coupling was evident from magnetocapacitance measurements, which exhibited a power law. Upon analyzing through optical, petri-plate and electron microscopy imaging, we observed that, the asymmetric structure of the nanorods gave rise to augmented antibacterial response against the chosen bacteria (Staphylococcus aureus). The x-ray photoelectron spectra (XPS) data have exhibited significant peak shifts upon interaction with bacterial cells owing to a change of Bi oxidation state from one to another. Thus potential redox reaction, which might take place at the material-bio interface, is ascertained for bacterial death. Apart from physical insights, understanding the interaction between the bacteria and the nanorods of BFO could pave the way in exploring the antibacterial potentiality of such anisotropic nanoscale systems. - Highlights: • AAO supported BiFeO3 (BFO) nanorods have been investigated. • The polarization of BFO nanorods was observed to be remarkably high (∼0.04 μC/cm{sup 2}). • Strong antibacterial activity of nanorods was witnessed against Staphylococcus aureus. • The deskinned area on cytoskeletal parts as revealed through TEM imaging, suggest strong cidal activity of the nanorods. • XPS data justifies shifting of the peak due to biophysical interaction at the interface releasing reactive oxygen species.

  10. Beamline 9.3.2 - a high-resolution, bend-magnet beamline with circular polarization capability

    Energy Technology Data Exchange (ETDEWEB)

    Moler, E.J.; Hussain, Z.; Howells, M.R. [Lawrence Berkeley National Lab., CA (United States)] [and others

    1997-04-01

    Beamline 9.3.2 is a high resolution, SGM beamline on an ALS bending magnet with access to photon energies from 30-1500 eV. Features include circular polarization capability, a rotating chamber platform that allows switching between experiments without breaking vacuum, an active feedback system that keeps the beam centered on the entrance slit of the monochromator, and a bendable refocusing mirror. The beamline optics consist of horizontally and vertically focussing mirrors, a Spherical Grating Monochromator (SGM) with movable entrance and exit slits, and a bendable refocussing mirror. In addition, a movable aperature has been installed just upstream of the vertically focussing mirror which can select the x-rays above or below the plane of the synchrotron storage ring, allowing the user to select circularly or linearly polarized light. Circularly polarized x-rays are used to study the magnetic properties of materials. Beamline 9.3.2 can supply left and right circularly polarized x-rays by a computer controlled aperture which may be placed above or below the plane of the synchrotron storage ring. The degree of linear and circular polarization has been measured and calibrated.

  11. Magnetic coupling between 3He and nuclei in a substrate A possible way to polarize bulk 3He

    Science.gov (United States)

    van den Brandt, B.; Bunyatova, E. I.; Hautle, P.; Konter, J. A.; Kovalev, A. I.; Mango, S.

    1995-02-01

    We have developed an apparatus which allows us to study the interaction of 3He with powder substrates at temperatures down to 50 mK. A Stycast cell has been filled with liquid or solid 3He, at pressures up to 65 bar, confined by fine powder that can be polarized in situ by dynamic nuclear polarization at 2.5 Tesla. A fast and accurate NMR/AFP system has been used to determine relaxation times. Different substrates have been investigated in search for polarizability and a strong enough surface interaction to eventually transmit their magnetization to bulk 3He.

  12. Magnetic coupling between {sup 3}He and nuclei in a substrate. A possible way to polarize bulk {sup 3}He

    Energy Technology Data Exchange (ETDEWEB)

    Brandt, B. van den [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Bunyatova, E.I. [Joint Institute for Nuclear Research, Dubna, Head P.O. Box 79, 101000 Moscow (Russian Federation); Hautle, P. [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Konter, J.A. [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Kovalev, A.I. [St. Petersburg Nuclear Physics Institute, 188350 Gatchina (Russian Federation); Mango, S. [Paul Scherrer Inst. (PSI), Villigen (Switzerland)

    1995-03-01

    We have developed an apparatus which allows us to study the interaction of {sup 3}He with powder substrates at temperatures down to 50 mK. A Stycast cell has been filled with liquid or solid {sup 3}He, at pressures up to 65 bar, confined by fine powder that can be polarized in situ by dynamic nuclear polarization at 2.5 Tesla. A fast and accurate NMR/AFP system has been used to determine relaxation times. Different substrates have been investigated in search for polarizability and a strong enough surface interaction to eventually transmit their magnetization to bulk {sup 3}He. ((orig.))

  13. A Comparative Study of Magnetic Fields in the Solar Photosphere and Chromosphere at Equatorial and Polar Latitudes

    Science.gov (United States)

    Petrie, G. J. D.; Patrikeeva, I.

    2009-07-01

    Besides their own intrinsic interest, correct interpretation of solar surface magnetic field observations is crucial to our ability to describe the global magnetic structure of the solar atmosphere. Photospheric magnetograms are often used as lower boundary conditions in models of the corona, but not data from the nearly force-free chromosphere. National Solar Observatory's (NSO) Synoptic Optical Long-term Investigations of the Sun VSM (Vector Spectromagnetograph) produces full-disk line-of-sight magnetic flux images deriving from both photospheric and chromospheric layers on a daily basis. In this paper, we investigate key properties of the magnetic field in these two layers using more than five years of VSM data. We find from near-equatorial measurements that the east-west inclination angle of most photospheric fields is less than about 12°, while chromospheric fields expand in all directions to a significant degree. Using a simple stereoscopic inversion, we find evidence that photospheric polar fields are also nearly radial but that during 2008 the chromospheric field in the south pole was expanding superradially. We obtain a spatially resolved polar photospheric flux distribution up to 80° latitude whose strength increases poleward approximately as cosine(colatitude) to the power 9-10. This distribution would give a polar field strength of 5-6 G. We briefly discuss implications for future synoptic map construction and modeling.

  14. A new perspective on turbulent Galactic magnetic fields through comparison of linear polarization decomposition techniques

    Science.gov (United States)

    Robitaille, J.-F.; Scaife, A. M. M.; Carretti, E.; Gaensler, B. M.; McEwen, J. D.; Leistedt, B.; Haverkorn, M.; Bernardi, G.; Kesteven, M. J.; Poppi, S.; Staveley-Smith, L.

    2017-07-01

    We compare two rotationally invariant decomposition techniques on linear polarization data: the spin-2 spherical harmonic decomposition in two opposite parities, the E- and B-mode, and the multiscale analysis of the gradient of linear polarization, |\

  15. Proton magnetic resonance with parahydrogen induced polarization. Imaging strategies and continuous generation

    Energy Technology Data Exchange (ETDEWEB)

    Dechent, Jan Falk Frederik

    2012-12-17

    A major challenge in imaging is the detection of small amounts of molecules of interest. In the case of magnetic resonance imaging (MRI) their signals are typically concealed by the large background signal of e.g. the tissue of the body. This problem can be tackled by hyperpolarization which increases the NMR signals up to several orders of magnitude. However, this strategy is limited for {sup 1}H, the most widely used nucleus in NMR and MRI, because the enormous number of protons in the body screen the small amount of hyperpolarized ones. Here, I describe a method giving rise to high {sup 1}H MRI contrast for hyperpolarized molecules against a large background signal. The contrast is based on the J-coupling induced rephasing of the NMR signal of molecules hyperpolarized via parahydrogen induce polarization (PHIP) and it can easily be implemented in common pulse sequences. Hyperpolarization methods typically require expensive technical equipment (e.g. lasers or microwaves) and most techniques work only in batch mode, thus the limited lifetime of the hyperpolarization is limiting its applications. Therefore, the second part of my thesis deals with the simple and efficient generation of an hyperpolarization. These two achievements open up alternative opportunities to use the standard MRI nucleus {sup 1}H for e.g. metabolic imaging in the future.

  16. Spin-polarized transport through single-molecule magnet Mn6 complexes

    KAUST Repository

    Cremades, Eduard

    2013-01-01

    The coherent transport properties of a device, constructed by sandwiching a Mn6 single-molecule magnet between two gold surfaces, are studied theoretically by using the non-equilibrium Green\\'s function approach combined with density functional theory. Two spin states of such Mn6 complexes are explored, namely the ferromagnetically coupled configuration of the six MnIII cations, leading to the S = 12 ground state, and the low S = 4 spin state. For voltages up to 1 volt the S = 12 ground state shows a current one order of magnitude larger than that of the S = 4 state. Furthermore this is almost completely spin-polarized, since the Mn6 frontier molecular orbitals for S = 12 belong to the same spin manifold. As such the high-anisotropy Mn6 molecule appears as a promising candidate for implementing, at the single molecular level, both spin-switches and low-temperature spin-valves. © 2013 The Royal Society of Chemistry.

  17. Universal spin-polarization fluctuations in one-dimensional wires with magnetic impurities

    DEFF Research Database (Denmark)

    Mortensen, Asger; Egues, J.C.

    2002-01-01

    -flip suppresses conductance fluctuations while enhancing spin-polarization fluctuations. More importantly, spin-polarization fluctuations attain a universal value 1/3 for large enough spin-flip strengths. This intrinsic spin-polarization fluctuation may pose a severe limiting factor to the realization of steady...

  18. The behavior of a type-II superconductor Nb in a magnetic field as investigated in polarized-neutron transmission experiments

    International Nuclear Information System (INIS)

    Aksenov, V.L.; Dokukin, E.B.; Kozhevnikov, S.V.; Nikitenko, Yu.V.; Petrenko, A.V.

    1995-01-01

    The type-II superconducting polycrystal Nb was investigated on the SPN-1 polarized-neutron spectrometer at the high-intensity pulsed reactor IBR-2 at Dubna. In polarized-neutron transmission experiments the magnetic-field dependence of the neutron beam polarization was measured. Experiments were performed over a wide magnetic-field range from 0 to H c2 at a temperature of 4.8 K. A quasiperiodic variation of the neutron depolarization as a function of magnetic-field strength was observed. (orig.)

  19. Excitation of Self-Localized Spin-Wave Bullets by Spin-Polarized Current in In-Plane Magnetized Magnetic Nano-Contacts: A Micromagnetic Study

    Science.gov (United States)

    2007-10-08

    excitation of microwave spin waves.3,10,11 The analytical theory of spin-wave excitation in magnetic nanocontacts by spin-polarized current performed...linear theory ,3 the propagating spin- wave mode excited at the threshold is a cylindrical spin- wave with the wave vector kL=1.2/Rc and frequency L... Oersted magnetic field, and/or by any other small interaction, neglected in the micromagnetic model. To make the excitation of subcritical modes12,15

  20. The new magnetic white dwarf PG 1031 + 234 - Polarization and field structure at more than 500 milion Gauss

    Science.gov (United States)

    Schmidt, Gary D.; West, Steven C.; Liebert, James; Green, Richard F.; Stockman, H. S.

    1986-01-01

    The discovery and study of a PG white dwarf which shows strong linear and circular polarization modulated with a rotation period of 3 hr 24 min is reported. The new star, PG 1031 + 234, is more highly magnetic than even Grw +70 deg 8247, with absorption components of hydrogen in its optical and UV spectra corresponding to fields from 200 to more than 500 MG. An asymmetric dependence of polarization on rotational phase shows that the surface field structure on the star is more complex than a simple centered dipole. The basic observational features can be well reproduced by a rotating star containing an oblique centered dipole punctuated near its magnetic equator by a high-field spot containing primarily radial field lines.

  1. Spin-polarized relativistic linear-muffin-tin-orbital method: Volume-dependent electronic structure and magnetic moment of plutonium

    International Nuclear Information System (INIS)

    Solovyev, I.V.; Liechtenstein, A.I.; Gubanov, V.A.; Antropov, V.P.; Andersen, O.K.

    1991-01-01

    The linear-muffin-tin-orbital method is generalized to the case of relativistic and spin-polarized self-consistent band calculations. Our formalism is analogous to the standard orthogonal--linear-muffin-tin-orbital formalism, except that the potential functions and the potential parameters are now matrices. The method is used to perform density-functional calculations for fcc plutonium with different atomic volumes. The formation of spin and orbital magnetic moments, as well as the changes in the energy bands for volume changes corresponding to the α-δ transition, are investigated. The calculated magnetic moments agree quite well with the experimental ones

  2. Effect of Stabilization Heat Treatment on Time-Dependent Polarization Losses in Sintered Nd-Fe-B Permanent Magnets

    Directory of Open Access Journals (Sweden)

    Tuominen S.

    2013-01-01

    Full Text Available Some companies in the motor and generator industry utilizing sintered NdFeB magnets have adopted pre-ageing heat treatment in order to improve the stability of the magnets. The parameters of this stabilization heat treatment are based mainly on assumptions rather than on any published research results. In this work, the effects of pre-ageing treatment on the time-dependent polarization losses of two different types of commercial sintered NdFeB magnets were studied. The material showing the squarer J(H curve did not benefit from the pre-ageing treatment, since it seems to be stable under a certain critical temperature. In contrast, a stabilizing effect was observed in the material showing rounder J(H curve. After the stabilization heat treatment, the polarization of the magnets was found to be at lower level, but unchanged over a certain period of time. The length of this period depends on the temperature and the duration of the pre-ageing treatment. In addition, our analysis reveals that the stabilization heat treatment performed in an open circuit condition does not stabilize the magnet uniformly.

  3. Modified structural and magnetic properties of nanocrystalline MnFe{sub 2}O{sub 4} by pH in capping agent free co-precipitation method

    Energy Technology Data Exchange (ETDEWEB)

    Iranmanesh, P., E-mail: p.iranmanesh@vru.ac.ir [Department of Physics, Vali-e-Asr University of Rafsanjan, 77139-36417 Rafsanjan (Iran, Islamic Republic of); Saeednia, S. [Department of Chemistry, Vali-e-Asr University of Rafsanjan, 77139-36417 Rafsanjan (Iran, Islamic Republic of); Mehran, M.; Dafeh, S. Rashidi [Department of Physics, Vali-e-Asr University of Rafsanjan, 77139-36417 Rafsanjan (Iran, Islamic Republic of)

    2017-03-01

    Nano-sized manganese ferrite (MnFe{sub 2}O{sub 4}) particles were prepared using co-precipitation method in two different pH (9 and 11). The structural, morphological, optical and magnetic properties of as-synthesized nanoparticles were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–vis absorption and vibrating sample magnetometer (VSM). The FTIR spectra revealed two strong peaks at about 600 and 400 cm{sup −1} that can be attributed to the vibration mode of octahedral and tetrahedral sites of spinel structure of MnFe{sub 2}O{sub 4}, respectively. The XRD results showed that the nanocrystalline MnFe{sub 2}O{sub 4} has pure cubic spinel crystal structure with average crystallite size of 11 nm. The cation distribution of these nanoparticles was estimated by X-ray analysis data. The blue shift was observed in the band gap when compared with bulk sample which is due to the quantum size effect. The absence of hysteresis for MnFe{sub 2}O{sub 4} nanoparticles indicated the superparamagnetic behaviour, as expected for single domain nanoparticles. The obtained value for saturation magnetization being less than its value of bulk ones and larger pH is due to surface effects. The calculated magnetic particle size was smaller than crystallite size estimated from the XRD results; which indicate the presence of dead layer on particle surface. - Highlights: • We study effect of pH on the size and magnetic properties of MnFe{sub 2}O{sub 4} nanoparticles. • MnFe{sub 2}O{sub 4} were synthesized by co-precipitation method without any capping agent. • The physical properties are affected by cation contribution and surface effects. • The smaller nanoparticles with larger pH show a red shift in the band gap energy. • The M{sub s} is less than its value of bulk ones due to surface effects.

  4. Modulation of Jahn-Teller effect on magnetization and spontaneous electric polarization of CuFeO2

    Science.gov (United States)

    Xiao, Guiling; Xia, Zhengcai; Wei, Meng; Huang, Sha; Shi, Liran; Zhang, Xiaoxing; Wu, Huan; Yang, Feng; Song, Yujie; Ouyang, Zhongwen

    2018-03-01

    CuFe0.99Mn0.01O2 and CuFe0.99Co0.01O2 single crystal samples are grown by a floating zone technique and their magnetization and spontaneous electric polarization have been investigated. Similarly with pure CuFeO2, an obviously anisotropic magnetization and spontaneous electric polarization were observed in the both doped samples, and their phase transition critical fields and temperatures are directly doping ion dependent. Considering the different d-shell configuration and ionic size between Mn3+, Co3+ and Fe3+ ions, in which the Mn3+ ion with Jahn-Teller (J-T) effect has different distortion on the geometry frustration from both of Fe3+ and Co3+ ion. Since for Mn3+ ion, the orbital splitting results from the low-symmetry J-T distortion in a crystal-field environment leads to a distorted MnO6 octahedron, which different from undistorted FeO6 and CoO6 octahedrons. The strain between distorted and undistorted octahedrons produces different effects on the spin reorientation transition and spontaneous electric polarization. Although the pure CuFeO2 has a very strong and robust frustration, the presence of the strain due to the random distribution of distorted MnO6 octahedron and undistorted CoO6 (FeO6) octahedrons leads to its spin reorientation transitions and spontaneous electric polarization different from CuFeO2.

  5. Measuring absolute spin polarization in dissolution-DNP by Spin PolarimetrY Magnetic Resonance (SPY-MR).

    Science.gov (United States)

    Vuichoud, Basile; Milani, Jonas; Chappuis, Quentin; Bornet, Aurélien; Bodenhausen, Geoffrey; Jannin, Sami

    2015-11-01

    Dynamic nuclear polarization at 1.2 K and 6.7 T allows one to achieve spin temperatures on the order of a few millikelvin, so that the high-temperature approximation (ΔEPolarimetrY Magnetic Resonance (SPY-MR), is illustrated for various pairs of (13)C spins (I, S) in acetate and pyruvate. Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.

  6. Cradle Cap (For Parents)

    Science.gov (United States)

    ... for Educators Search English Español Cradle Cap (Infantile Seborrheic Dermatitis) KidsHealth / For Parents / Cradle Cap (Infantile Seborrheic Dermatitis) What's in this article? About Cradle Cap Causes ...

  7. Greigite-related complex magnetic polarity records unraveled through an integrated rock magnetic analysis: A case study on Neogene sections in East Timor

    Science.gov (United States)

    Aben, F. M.; Bakker, R. R.; Dekkers, M. J.; Van Hinsbergen, D. J.; Harris, R. A.; Zachariasse, J.; Duffy, B. G.

    2013-12-01

    Inconsistent polarity patterns in greigite-bearing (marine) sediments are a common problem in magnetostratigraphic and paleomagnetic research. Prolonged diagenesis can result in multiple generations of greigite being present in a sedimentary record. The associated remanence ';haystack' can be filtered to some extent by paleomagnetic field tests but not all rock records are suitable for such an approach. Here, we test whether end-member modeling of IRM-acquisition curves as a basis for an integrated rock magnetic and (electron) microscopic research approach can be used to identify all magnetic mineral suites, to evaluate the nature of the magnetic remanences, and to use the acquired knowledge to isolate the ChRM from such complex magnetic records. To this end, a case study was performed on uppermost Miocene to Pliocene deep-marine clastic and chalk bearing Viqueque Type section in East Timor. This section was originally sampled to establish a bio- and magnetostratigraphic age model dating the uplift history of the young Timor-orogen. An in principle straightforward polarity record was obtained, which, however, was impossible to reconcile with the biostratigraphy of the section. Among the dominant magnetic carriers was greigite. Two magnetic end-members were distinguished in the Viqueque Type section, which were analyzed further for rock magnetic properties. With microscopy, three magnetic mineral suites are shown to result in the two end-members. The first suite occurs in all lithologies and consists of detrital magnetite with a viscous NRM, caused by partial reductive dissolution of detrital magnetite grains after deposition. This mineral suite therefore is unreliable for magnetostratigraphic use. The second and third suite both consist of interacting single domain greigite grains with a chemical remanent magnetization. The second suite is present in almost all clay levels of the Viqueque Type section and is characterized by early diagenetic framboidal greigite

  8. Tenth-Order Lepton Anomalous Magnetic Moment--Sixth-Order Vertices Containing Vacuum-Polarization Subdiagrams

    International Nuclear Information System (INIS)

    Aoyama, Tatsumi; Hayakawa, Masashi; Kinoshita, Toichiro; Nio, Makiko

    2011-01-01

    This paper reports the values of contributions to the electron g-2 from 300 Feynman diagrams of the gauge-invariant Set III(a) and 450 Feynman diagrams of the gauge-invariant Set III(b). The evaluation is carried out in two versions. Version A is to start from the sixth-order magnetic anomaly M 6 obtained in the previous work. The mass-independent contributions of Set III(a) and Set III(b) are 2.1275(2) and 3.3271(6) in units of (α/π) 5 , respectively. Version B is based on the recently developed automatic code generation scheme. This method yields 2.1271(3) and 3.3271(8) in units of (α/π) 5 , respectively. They are in excellent agreement with the results of the first method within the uncertainties of numerical integration. Combining these results as statistically independent we obtain the best values, 2.1273(2), and 3.3271(5) times (α/π) 5 , for the mass-independent contributions of the Set III(a) and Set III(b), respectively. We have also evaluated mass-dependent contributions of diagrams containing muon and/or tau-particle loop. Including them the total contribution of Set III(a) is 2.1349(2) and that of Set III(b) is 3.3299(5) in units of (α/π) 5 . The total contributions to the muon g-2 of various leptonic vacuum-polarization loops of Set III(a) and Set III(b) are 112.418(32) and 15.407(5) in units of (α/π) 5 , respectively.

  9. Asymmetric bistable reflection and polarization switching in a magnetic nonlinear multilayer structure

    DEFF Research Database (Denmark)

    Tuz, Vladimir R.; Novitsky, Denis V.; Prosvirnin, Sergey L.

    2014-01-01

    , while light reflected from the other side has its polarization unchanged. Using the nonlinear transfer matrix calculations in the frequency domain, it is demonstrated that defect resonances in the nonlinear reflection spectra undergo bending, resulting in polarization bistability of reflected light....... This bistability is shown to result in abrupt switching between linear polarization of the output reflected light when the input intensity is varied. This switching is confirmed in finite-difference time-domain simulations, and its hysteresis character is established....

  10. Polarized neutron study of the magnetic mesostructure in (Pd{sub 1-x}Fe{sub x}){sub 1-y}Mn{sub y}

    Energy Technology Data Exchange (ETDEWEB)

    Gordeev, G.P.; Axelrod, L.A.; Lazebnik, I.M.; Zabenkin, V.N. [Petersburg Nuclear Physics Institute, 188300, Gatchina (Russian Federation); Wagner, V. [Physikalisch-Technische Bundesanstalt, 38116, Braunschweig (Germany)

    2002-07-01

    In PdFeMn alloys with different Fe-atom concentrations, the behaviour of both mean magnetization and neutron depolarization in the magnetization/demagnetization process was observed by three-dimensional analysis of neutron-beam polarization. Both magnetization and depolarization have a hysteresis loop for the same values of an applied field. Depolarization loops are sharply distinguished for different alloys. This gives evidence of different magnetic mesostructures in these alloys. (orig.)

  11. Polarized neutron study of the magnetic mesostructure in (Pd sub 1 sub - sub x Fe sub x) sub 1 sub - sub y Mn sub y

    CERN Document Server

    Gordeev, G P; Lazebnik, I M; Zabenkin, V N; Wagner, V

    2002-01-01

    In PdFeMn alloys with different Fe-atom concentrations, the behaviour of both mean magnetization and neutron depolarization in the magnetization/demagnetization process was observed by three-dimensional analysis of neutron-beam polarization. Both magnetization and depolarization have a hysteresis loop for the same values of an applied field. Depolarization loops are sharply distinguished for different alloys. This gives evidence of different magnetic mesostructures in these alloys. (orig.)

  12. Aurora and open magnetic flux during isolated substorms, sawteeth, and SMC events

    Directory of Open Access Journals (Sweden)

    A. D. DeJong

    2007-08-01

    Full Text Available Using Polar UVI LBHl and IMAGE FUV WIC data, we have compared the auroral signatures and polar cap open flux for isolated substorms, sawteeth oscillations, and steady magnetospheric convection (SMC events. First, a case study of each event type is performed, comparing auroral signatures and open magnetic fluxes to one another. The latitude location of the auroral oval is similar during isolated substorms and SMC events. The auroral intensity during SMC events is similar to that observed during the expansion phase of an isolated substorm. Examination of an individual sawtooth shows that the auroral intensity is much greater than the SMC or isolated substorm events and the auroral oval is displaced equatorward making a larger polar cap. The temporal variations observed during the individual sawtooth are similar to that observed during the isolated substorm, and while the change in polar cap flux measured during the sawtooth is larger, the percent change in flux is similar to that measured during the isolated substorm. These results are confirmed by a statistical analysis of events within these three classes. The results show that the auroral oval measured during individual sawteeth contains a polar cap with, on average, 150% more magnetic flux than the oval measured during isolated substorms or during SMC events. However, both isolated substorms and sawteeth show a 30% decrease in polar cap magnetic flux during the dipolarization (expansion phase.

  13. Theory and compensation method of axial magnetic error induced by axial magnetic field in a polarization-maintaining fiber optic gyro

    Science.gov (United States)

    Zhou, Yanru; Zhao, Yuxiang; Tian, Hui; Zhang, Dengwei; Huang, Tengchao; Miao, Lijun; Shu, Xiaowu; Che, Shuangliang; Liu, Cheng

    2016-12-01

    In an axial magnetic field (AMF), which is vertical to the plane of the fiber coil, a polarization-maintaining fiber optic gyro (PM-FOG) appears as an axial magnetic error. This error is linearly related to the intensity of an AMF, the radius of the fiber coil, and the light wavelength, and also influenced by the distribution of fiber twist. When a PM-FOG is manufactured completely, this error only appears a linear correlation with the AMF. A real-time compensation model is established to eliminate the error, and the experimental results show that the axial magnetic error of the PM-FOG is decreased from 5.83 to 0.09 deg/h in 12G AMF with 18-dB suppression.

  14. The tunneling magnetoresistance and spin-polarized optoelectronic properties of graphyne-based molecular magnetic tunnel junctions

    International Nuclear Information System (INIS)

    Yang, Zhi; Ouyang, Bin; Lan, Guoqing; Xu, Li-Chun; Liu, Ruiping; Liu, Xuguang

    2017-01-01

    Using density functional theory and the non-equilibrium Green’s function method, we investigate the spin-dependent transport and optoelectronic properties of the graphyne-based molecular magnetic tunnel junctions (MMTJs). We find that these MMTJs exhibit an outstanding tunneling magnetoresistance (TMR) effect. The TMR value is as high as 10 6 %. When the magnetization directions of two electrodes are antiparallel under positive or negative bias voltages, two kinds of pure spin currents can be obtained in the systems. Furthermore, under the irradiation of infrared, visible or ultraviolet light, spin-polarized photocurrents can be generated in the MMTJs, but the corresponding microscopic mechanisms are different. More importantly, if the magnetization directions of two electrodes are antiparallel, the photocurrents with different spins are spatially separated, appearing at different electrodes. This phenomenon provides a new way to simultaneously generate two spin currents. (paper)

  15. Anomalously strong relaxation of the polarization of muons in the magnetically ordered and paramagnetic states of the TbMnO3 multiferroic

    Science.gov (United States)

    Andrievskii, D. S.; Vorob'ev, S. I.; Getalov, A. L.; Golovenchits, E. I.; Komarov, E. N.; Kotov, S. A.; Sanina, V. A.; Shcherbakov, G. V.

    2017-09-01

    An anomalously strong relaxation of the muon polarization in a magnetically ordered state in the TbMnO3 multiferroic has been revealed by the method below the μ SR Néel temperature (42 K). Such a relaxation is due to the muon channel of relaxation of the polarization and the interaction of the magnetic moment of the muon with inhomogeneities of the internal magnetic field of an ordered state in the form of a cycloid. Above the Néel temperature, beginning with temperatures depending on the applied magnetic field, a two-phase state has been revealed where one phase has an anomalously strong relaxation of the muon polarization for a paramagnetic state. These features of the paramagnetic state are due to short-range magnetic order domains that appear in strongly frustrated TbMnO3. A true paramagnetic state has been observed only at T ≥ 150 K.

  16. A Comparative Study of Magnetic Fields in the Solar Photosphere and Chromosphere at Low and Polar Latitudes

    Science.gov (United States)

    Patrikeeva, Irina; Petrie, G.

    2009-05-01

    The SOLIS Vector-Spectromagnetograph produces full-disk line-of-sight (LOS) magnetic flux images deriving from both photospheric and chromospheric layers on a daily basis. We investigate key properties of the magnetic field in these two layers using more than five years of VSM data. We find from near-equatorial measurements that the East-West inclination angle of most photospheric fields is about 12°, while chromospheric fields expand in all directions to a significant degree. Using a simple stereoscopic inversion we find evidence that photospheric polar fields are also nearly radial, but that during 2008 the chromospheric field in the south pole was expanding super-radially. We obtain a spatially-resolved polar photospheric flux distribution up to 80° latitude whose strength increases poleward approximately as cosine(colatitude) to the power 9-10. This distribution would give a polar field strength of 5-6 G. These results have implications for future synoptic map construction and global modeling. This work is carried out through the National Solar Observatory Research Experiences for Undergraduate (REU) site program, which is co-funded by the Department of Defense in partnership with the National Science Foundation REU Program.

  17. Electronic Structures of Magnetic Iron and Cobalt Thin Films on TUNGSTEN(001): a Spin-Polarized Inverse Photoemission Study

    Science.gov (United States)

    Cai, Qing

    Electronic structure is a central question in metallic magnetism as well as in magnetic materials research. The electronic properties in a two-dimensional system such as thin films of a few atomic layers is an important issue in surface science. The epitaxial thin film preparation and morphology are of special technological interests. In this thesis, these questions are addressed. Spin-polarized inverse photoemission spectroscopy is used to study the unoccupied electron band states in magnetic thin film magnets of Fe and Co epitaxially grown on W(001) surface. The clean W(001) surface was studied by angle -resolved inverse photoemission spectroscopy and the bulk band dispersion was determined. Ultrathin Fe overlayers on W(001) show a square lateral crystal structure similar to the bcc-Fe(001) surface. The electronic structure develops into a structure that is close to that of bulk Fe at about four atomic layers. In the normal-incidence spin polarized inverse photoemission spectra, direct transitions to the majority and minority final states near the H^'_ {25} point are identified in good agreement with the theoretical calculations. One Fe monolayer, or multilayers less than four, showed behavior corresponding to a gradually reduced Curie temperature. When the film thickness is reduced, the spin-resolved spectral behavior show that the majority spin signal peak moves from near the Fermi energy to about 1.3 eV while the minority peak stays at about the same position near 1.3 eV. The results are used to examine the spatial correlation of the spin fluctuations in the system in comparison with a theoretical spectral calculation, and favors the disordered-local-moment picture in the contemporary theory of itinerant magnetism. The Co overlayer shows an overlayer structure that consists of equivalent, mutually rotated domains of distorted hexagonal lateral structure. For one atomic layer of Co in that structure, which has a nominal lateral atomic density twice that of the

  18. Precessing deuteron polarization

    International Nuclear Information System (INIS)

    Sitnik, I.M.; Volkov, V.I.; Kirillov, D.A.; Piskunov, N.M.; Plis, Yu.A.

    2002-01-01

    The feasibility of the acceleration in the Nuclotron of deuterons polarized in the horizontal plane is considered. This horizontal polarization is named precessing polarization. The effects of the main magnetic field and synchrotron oscillations are included. The precessing polarization is supposed to be used in studying the polarization parameters of the elastic dp back-scattering and other experiments

  19. CMS end-cap yoke at the detector's assembly site.

    CERN Multimedia

    Patrice Loïez

    2002-01-01

    The magnetic flux generated by the superconducting coil in the CMS detector is returned via an iron yoke comprising three end-cap discs at each end (end-cap yoke) and five concentric cylinders (barrel yoke). This picture shows the first of three end-cap discs (red) seen through the outer cylinder of the vacuum tank which will house the superconducting coil.

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

    Energy Technology Data Exchange (ETDEWEB)

    Rhodes, T. L., E-mail: trhodes@ucla.edu; Peebles, W. A.; Crocker, N. A.; Nguyen, X. [Physics and Astronomy Department, University of California, Los Angeles, California 90098 (United States)

    2014-11-15

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

  1. Calculated Hanle transmission and absorption spectra of the 87Rb D1 line with residual magnetic field for arbitrarily polarized light

    International Nuclear Information System (INIS)

    Noh, Heung-Ryoul; Moon, Han Seb

    2010-01-01

    This paper reports a theoretical study on the transmission spectra of an arbitrarily polarized laser beam through a rubidium cell with or without a buffer gas in Hanle-type coherent population trapping (CPT). This study examined how laser polarization, transverse magnetic field, and collisions with buffer gas affects the spectrum. The transmission spectrum due to CPT and the absorption spectrum due to the level crossing absorption (LCA) were calculated according to the laser polarization. The results show that the LCA is strongly dependent on the transverse magnetic field and interaction time of the atoms with a laser light via collisions with the buffer gas. In addition, the spectral shape of the calculated Hanle spectrum is closely related to the direction between the (stray) transverse magnetic field and polarization of the laser.

  2. Cross polarization, magic-angle spinning /sup 13/C nuclear magnetic resonance spectroscopy of soil humic fractions

    Energy Technology Data Exchange (ETDEWEB)

    Saiz-Jimenez, C.; Hawkins, B.L.; Maciel, G.E.

    1986-01-01

    Cross polarization, magic-angle spinning /sup 13/C nuclear magnetic resonance spectroscopy was used to characterize humic fractions isolated from different soils. The humic acid fractions are more aromatic than the humin fractions, probably due to the higher polysaccharide content of humins. However, fulvic acid fractions are more aromatic than the corresponding humic acid and humin fractions. These results can be interpreted in terms of the isolation procedure, because the high affinity of Polyclar AT for phenols results in higher aromaticities as compared with other isolation methods (e.g. charcoal).

  3. Propagation of the three-dimensional dust acoustic solitons in magnetized quantum plasmas with dust polarity effect

    Science.gov (United States)

    Sadiq, M.; Ali, S.; Sabry, R.

    2009-01-01

    The quantum hydrodynamical model is employed to investigate the nonlinear properties of the quantum dust acoustic waves in a magnetized dusty plasma composed of inertialess electrons, ions, and mobile positive/negative charged dust particles. For this purpose, a quantum Zakharov-Kuznetsov equation is derived and the basic features of the electrostatic excitations are investigated by applying the direct method. It is found that positive and negative bell-shaped solitary pulses become explosive pulses depending mainly upon the angles of propagation and dust polarity. Furthermore, the effects due to nondimensional quantum parameter and the external magnetic field are examined on the width of the quantum dust acoustic solitary pulses. The relevance of the present results to semiconductor quantum wells is mentioned.

  4. BNL alternating gradient synchrotron with four helical magnets to minimize the losses of the polarized proton beam

    Directory of Open Access Journals (Sweden)

    N. Tsoupas

    2013-04-01

    Full Text Available The principle of using multiple partial helical magnets to preserve the polarization of the proton beam during its acceleration was applied successfully to the alternating gradient synchrotron (AGS which currently operates with two partial helical magnets. In this paper we further explore this idea by using four partial helical magnets placed symmetrically in the AGS ring. This provides many advantages over the present setup of the AGS, which uses two partial helical magnets. First, the symmetric placement of the four helical magnets and their relatively lower field of operation allows for better control of the AGS optics with reduced values of the beta functions especially near beam injection and allows both the vertical and horizontal tunes to be placed within the “spin tune gap,” therefore eliminating the horizontal and vertical intrinsic spin resonances of the AGS during the acceleration cycle. Second, it provides a wider spin tune gap. Third, the vertical spin direction during beam injection and extraction is closer to vertical. Although the spin tune gap, which is created with four partial helices, can also be created with a single or two partial helices, the high field strength of a single helical magnet which is required to generate such a spin tune gap makes the use of the single helical magnet impractical, and that of the two helical magnets rather difficult. In this paper we will provide results on the spin tune and on the optics of the AGS with four partial helical magnets, and compare them with those from the present setup of the AGS that uses two partial helical magnets. Although in this paper we specifically discuss the effect of the four partial helices on the AGS, this method which can eliminate simultaneously the vertical and horizontal intrinsic spin resonances is a general method and can be applied to any medium energy synchrotron which operates in similar energy range like the AGS and provides the required space to

  5. Magnetic Field Perturbations from Currents in the Dark Polar Regions During Quiet Geomagnetic Conditions

    DEFF Research Database (Denmark)

    Friis-Christensen, Eigil; Finlay, Chris; Hesse, M.

    2017-01-01

    In the day-side sunlit polar ionosphere the varying and IMF dependent convection creates strong ionospheric currents even during quiet geomagnetic conditions. Observations during such times are often excluded when using satellite data to model the internal geomagneticmain field. Observations from...... the night-side or local winter during quiet conditions are, however, also influenced by variations in the IMF. In this paper we briefly review the large scale features of the ionospheric currents in the polar regions with emphasis on the current distribution during undisturbed conditions. We examine...

  6. Inverse beta decay of arbitrarily polarized neutrons in a magnetic field

    Indian Academy of Sciences (India)

    on the states in the presence of a magnetic field. section 4 contains the calculation of the cross-section for a ... convention, is the positive unit of charge, taken as usual to be equal to the proton charge. For stationary ...... However, it should be borne in mind that magnetic fields should have magnitudes. С2 or higher in order ...

  7. Magnetic properties of the SiO2(Co)/GaAs interface: Polarized neutron reflectometry and SQUID magnetometry

    Science.gov (United States)

    Ukleev, V. A.; Grigoryeva, N. A.; Dyadkina, E. A.; Vorobiev, A. A.; Lott, D.; Lutsev, L. V.; Stognij, A. I.; Novitskiy, N. N.; Mistonov, A. A.; Menzel, D.; Grigoriev, S. V.

    2012-10-01

    The effect of giant injection magnetoresistance (GIMR) was recently observed in a granular SiO2/(54-75 at. % Co) film on a semiconductor GaAs substrate in a temperature range near T=300 K. The magnetoresistance coefficient reaches a value of 105% in a magnetic field of 1.9 T and at a voltage of 90 V. A structural model of the film was proposed based on the results of the grazing-incidence small-angle scattering (GISAXS) and x-ray reflectivity, which showed a specific interface layer 70-75 Å thick separating bulk SiO2(Co) granular film from the semiconductor substrate. This layer is formed by a monolayer of flattened Co particles which are laterally spaced apart much further than the particles in the bulk film. In the present work, using polarized neutron reflectometry (PNR), we study both the structural and magnetic properties of SiO2(Co) film separately in the bulk and in the interface layer, which is possible due to the depth resolution of the method. Temperature-dependent PNR and magnetization measurements performed by Superconducting Quantum Interference Device (SQUID) revealed the occurrence of two types of magnetic nanoparticles with different blocking temperatures and magnetization. The magnetization hysteresis curve demonstrated specific two-loop structure in fields 0.5-2 T. Thus our self-consistent results of PNR, GISAXS, and SQUID measurements emphasize the role of the interface features in the SiO2(Co)/GaAs heterostructures and show a direction for further development of the GIMR theory.

  8. Eigenanalysis and Graph Theory Combined to Determine the Seasonal and Solar-Cycle Variations of Polar Magnetic Fields

    Science.gov (United States)

    Shore, R. M.; Freeman, M. P.; Gjerloev, J. W.

    2017-12-01

    We apply the meteorological analysis method of Empirical Orthogonal Functions (EOF) to ground magnetometer measurements, and subsequently use graph theory to classify the results. The EOF method is used to characterise and separate contributions to the variability of the Earth's external magnetic field (EMF) in the northern polar region. EOFs decompose the noisy EMF data into a small number of independent spatio-temporal basis functions, which collectively describe the majority of the magnetic field variance. We use these basis functions (computed monthly) to infill where data are missing, providing a self-consistent description of the EMF at 5-minute resolution spanning 1997-2009 (solar cycle 23). The EOF basis functions are calculated independently for each of the 144 months (i.e. 1997-2009) analysed. Since (by definition) the basis vectors are ranked by their contribution to the total variance, their rank will change from month to month. We use graph theory to find clusters of quantifiably-similar spatial basis functions, and thereby track similar patterns throughout the span of 144 months. We find that the discovered clusters can be associated with well-known individual Disturbance Polar (DP)-type equivalent current systems (e.g. DP2, DP1, DPY, NBZ), or with the motion of these systems. Via this method, we thus describe the varying behaviour of these current systems over solar cycle 23. We present their seasonal and solar cycle variations and examine the response of each current system to solar wind driving.

  9. On the sensitivity of the Halpha scattering polarization to chromospheric magnetism

    Czech Academy of Sciences Publication Activity Database

    Štěpán, Jiří; Trujillo Bueno, J.

    2010-01-01

    Roč. 81, č. 2 (2010), s. 810-813 ISSN 0037-8720. [Chromospheric structure and dynamics: From old wisdom to new insights. Sunspot ,, 31.08.2009-4.09.2009] Institutional research plan: CEZ:AV0Z10030501 Keywords : polarization * radiative transfer * scattering Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

  10. Polarized Kink Waves in Magnetic Elements: Evidence for Chromospheric Helical Waves

    Energy Technology Data Exchange (ETDEWEB)

    Stangalini, M.; Giannattasio, F. [INAF-OAR National Institute for Astrophysics, Via Frascati 33, I-00078 Monte Porzio Catone (RM) (Italy); Erdélyi, R. [Solar Physics and Space Plasma Research Centre (SP2RC), School of Mathematics and Statistics, University of Sheffield, Sheffield S3 7RH (United Kingdom); Jafarzadeh, S. [Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029 Blindern, NO-0315 Oslo (Norway); Consolini, G.; Ermolli, I. [INAF-IAPS National Institute for Astrophysics, Via del Fosso del Cavaliere, 100, I-00133 Rome (Italy); Criscuoli, S. [NSO, National Solar Observatory, Boulder, CO 80303 (United States); Guglielmino, S. L.; Zuccarello, F., E-mail: marco.stangalini@inaf.it [Department of Physics and Astronomy, University of Catania, Via S. Sofia 78, I-95125 Catania (Italy)

    2017-05-01

    In recent years, new high spatial resolution observations of the Sun's atmosphere have revealed the presence of a plethora of small-scale magnetic elements down to the resolution limit of the current cohort of solar telescopes (∼100–120 km on the solar photosphere). These small magnetic field concentrations, due to the granular buffeting, can support and guide several magnetohydrodynamic wave modes that would eventually contribute to the energy budget of the upper layers of the atmosphere. In this work, exploiting the high spatial and temporal resolution chromospheric data acquired with the Swedish 1 m Solar Telescope, and applying the empirical mode decomposition technique to the tracking of the solar magnetic features, we analyze the perturbations of the horizontal velocity vector of a set of chromospheric magnetic elements. We find observational evidence that suggests a phase relation between the two components of the velocity vector itself, resulting in its helical motion.

  11. Magnetic polyethyleneimine functionalized reduced graphene oxide as a novel magnetic solid-phase extraction adsorbent for the determination of polar acidic herbicides in rice

    Energy Technology Data Exchange (ETDEWEB)

    Li, Na [Key Laboratory of Chemistry of Northwestern Plant Resources of the CAS and Key Laboratory for Natural Medicine of Gansu Province, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou, 730000 (China); University of Chinese Academy of Sciences, Beijing, 100039 (China); Chen, Juan, E-mail: chenjuan@licp.cas.cn [Key Laboratory of Chemistry of Northwestern Plant Resources of the CAS and Key Laboratory for Natural Medicine of Gansu Province, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou, 730000 (China); Shi, Yan-Ping, E-mail: shiyp@licp.cas.cn [Key Laboratory of Chemistry of Northwestern Plant Resources of the CAS and Key Laboratory for Natural Medicine of Gansu Province, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou, 730000 (China)

    2017-01-01

    A novel magnetic polyethyleneimine modified reduced graphene oxide (Fe{sub 3}O{sub 4}@PEI-RGO) had been fabricated based on a self-assemble approach between positive charged magnetic polyethyleneimine (Fe{sub 3}O{sub 4}@PEI) and negative charged GO sheets via electrostatic interaction followed by chemical reduction of GO to RGO. The as-prepared Fe{sub 3}O{sub 4}@PEI-RGO was characterized by transmission electron microscopy (TEM), Fourier transform infrared spectrometry (FT-IR), X-ray diffraction (XRD), thermal gravimetric analyzer (TGA), vibrating sample magnetometer (VSM) and zeta potential analysis, and then was successfully applied to determine four phenoxy acid herbicides and dicamba in rice coupled with high performance liquid chromatography (HPLC). As a surface modifier of RGO, PEI not only effectually affected the surface property of RGO (e.g. zeta potential), but also changed the polarity of RGO and offered anion exchange groups to polar acidic herbicides, which would directly influence the type of adsorbed analytes. Compared with Fe{sub 3}O{sub 4}@PEI, Fe{sub 3}O{sub 4}/RGO and Fe{sub 3}O{sub 4}@PEI-GO, the as-prepared Fe{sub 3}O{sub 4}@PEI-RGO, integrating the superiority of PEI and RGO, showed higher extraction efficiency for polar acidic herbicides. Besides, the adsorption mechanism was investigated as well. It turned out that electrostatic interaction and π-π interaction were considered to be two major driving force for the adsorption process. Response surface methodology (RSM), a multivariate experimental design technique, was used to optimize experimental parameters affecting the extraction efficiency in detail. Under the optimal conditions, a satisfactory performance was obtained. The calibration curves were linear over the concentration ranging from 2 to 300 ng g{sup −1} with correlation coefficients (r) between 0.9985 and 0.9994. The limits of detection (LODs) were in the range of 0.67–2 ng g{sup −1}. The recoveries ranged from 87

  12. An Empirical Orthogonal Function Reanalysis of the Northern Polar External and Induced Magnetic Field During Solar Cycle 23

    Science.gov (United States)

    Shore, R. M.; Freeman, M. P.; Gjerloev, J. W.

    2018-01-01

    We apply the method of data-interpolating empirical orthogonal functions (EOFs) to ground-based magnetic vector data from the SuperMAG archive to produce a series of month length reanalyses of the surface external and induced magnetic field (SEIMF) in 110,000 km2 equal-area bins over the entire northern polar region at 5 min cadence over solar cycle 23, from 1997.0 to 2009.0. Each EOF reanalysis also decomposes the measured SEIMF variation into a hierarchy of spatiotemporal patterns which are ordered by their contribution to the monthly magnetic field variance. We find that the leading EOF patterns can each be (subjectively) interpreted as well-known SEIMF systems or their equivalent current systems. The relationship of the equivalent currents to the true current flow is not investigated. We track the leading SEIMF or equivalent current systems of similar type by intermonthly spatial correlation and apply graph theory to (objectively) group their appearance and relative importance throughout a solar cycle, revealing seasonal and solar cycle variation. In this way, we identify the spatiotemporal patterns that maximally contribute to SEIMF variability over a solar cycle. We propose this combination of EOF and graph theory as a powerful method for objectively defining and investigating the structure and variability of the SEIMF or their equivalent ionospheric currents for use in both geomagnetism and space weather applications. It is demonstrated here on solar cycle 23 but is extendable to any epoch with sufficient data coverage.

  13. Polarized single crystal neutron diffraction study of the zero-magnetization ferromagnet Sm1 -xGdxAl2 (x =0.024 )

    Science.gov (United States)

    Chatterji, T.; Stunault, A.; Brown, P. J.

    2018-02-01

    We have determined the temperature evolution of the spin and orbital moments in the zero-magnetization ferromagnet Sm1 -xGdxAl2 (x = 0.024) by combining polarized and unpolarized single crystal neutron diffraction data. The sensitivity of the polarized neutron technique has allowed the moment values to be determined with a precision of ≈0.1 μB . Our results clearly demonstrate that, when magnetized by a field of 8 T, the spin and orbital moments in Sm1 -xGdxAl2 are oppositely directed, so that the net magnetization is very small. Below 60 K the contributions from spin and orbital motions are both about 2 μB , with that due to orbital motion being slightly larger than that due to spin. Between 60 and 65 K the contributions of each to the magnetization fall rapidly and change sign at Tcomp ≈67 K , above which the aligned moments recover but with the orbital magnetization still slightly higher than the spin one. These results imply that above Tcomp the small resultant magnetization of the Sm3 + ion is oppositely directed to the magnetizing field. It is suggested that this anomaly is due to polarization of conduction electron spin associated with the doping Gd3 + ions.

  14. The polarized neutron reflectivity and X-ray reflectivity studies of the magnetic profiles of epitaxial Ni80Fe20/Ru multilayers

    International Nuclear Information System (INIS)

    Su, H.-C.; Peir, J.-J.; Lee, C.-H.; Lin, M.-Z.; Wu, P.-T.; Huang, J.C.A.; Tun Zin

    2005-01-01

    The depth profiles of the epitaxial Ni 80 Fe 20 (1 1 1)/Ru(0 0 0 1) multilayers were studied by polarized neutron reflectivity and X-ray reflectivity. At the Ru thickness that the anti-ferromagnetic coupling was found, the magnetic moments between two Ni 80 Fe 20 interlayers show a biquadratic coupling effect with a double unit cell at low applied fields. A magnetic dead layer of about 0.3 nm was also found at the interface boundaries. The maximal polarization effect applied to the Ru layer is less than 0.03μ B

  15. Spin polarization in high density quark matter under a strong external magnetic field

    DEFF Research Database (Denmark)

    Tsue, Yasuhiko; Da Providência, João; Providência, Constança

    2016-01-01

    In high density quark matter under a strong external magnetic field, possible phases are investigated by using the two-flavor Nambu-Jona-Lasinio (NJL) model with tensor-type four-point interaction between quarks, as well as the axial-vector-type four-point interaction. In the tensor-type interact......In high density quark matter under a strong external magnetic field, possible phases are investigated by using the two-flavor Nambu-Jona-Lasinio (NJL) model with tensor-type four-point interaction between quarks, as well as the axial-vector-type four-point interaction. In the tensor...... phase appears in the wide range of the quark chemical potential. In both the interactions, the quark mass in zero and small chemical potential regions increases which indicates that the chiral symmetry breaking is enhanced, namely the magnetic catalysis occurs....

  16. Effect of lattice distortion on uranium magnetic moments in U4Ru7Ge6 studied by polarized neutron diffraction

    Science.gov (United States)

    Vališka, Michal; Klicpera, Milan; Doležal, Petr; Fabelo, Oscar; Stunault, Anne; Diviš, Martin; Sechovský, Vladimír

    2018-03-01

    In a cubic ferromagnet, small spontaneous lattice distortions are expected below the Curie temperature, but the phenomenon is usually neglected. This study focuses on such an effect in the U4Ru7Ge6 compound. Based on DFT calculations, we propose a lattice distortion from the cubic I m -3 m space group to a lower, rhombohedral, symmetry described by the R -3 m space group. The strong spin-orbit coupling of the uranium ions plays an essential role in lowering the symmetry, giving rise to two different U sites (U1 and U2). Using polarized neutron diffraction in applied magnetic fields of 1 and 9 T in the ordered state (1.9 K ) and in the paramagnetic state (20 K ), we bring convincing experimental evidence of this splitting of the U sites, with different magnetic moments. The data have been analyzed both by maximum entropy calculations and by a direct fit in the dipolar approximation. In the ordered phase, the μL/μS ratio of the orbital and spin moments on the U2 site is remarkably lower than for the free U3 + or U4 + ion, which points to a strong hybridization of the U 5 f wave functions with the 4 d wave functions of the surrounding Ru. On the U1 site, the μL/μS ratio exhibits an unexpectedly low value: the orbital moment is almost quenched, like in metallic α -uranium. As a further evidence of the 5 f -4 d hybridization in the U4Ru7Ge6 system, we observe the absence of a magnetic moment on the Ru1 site, but a rather large induced moment on the Ru2 site, which is in closer coordination with both U positions. Very similar results are obtained at 20 K in the ferromagnetic regime induced by the magnetic field of 9 T . This shows that applying a strong magnetic field above the Curie temperature also leads to the splitting of the uranium sites, which further demonstrates the intimate coupling of the magnetic ordering and structural distortion. We propose that the difference between the magnetic moment on the U1 and U2 sites results from the strong spin

  17. Cyclostratigraphic calibration of cretaceous magnetic polarity events (Cismon, Southern Alps, Italy)

    Science.gov (United States)

    Mayer, H.

    1994-01-01

    In an introductory section the problems of constructing a geologic time scale and the role of magnetic reversals and Milankovitch cycles in geochronology are outlined. Results of a detailed cyclostratigraphic and magnetostratigraphic study of the Valanginian/Hauterivian part of the pelagic limestone section at Cismon in the Southern Alps are presented and used in conjunction to estimate the duration of magnetic subchrons between CM10N and CM8. The new estimates are shorter than in most published time scales by a factor of two to three. More research along these lines may make a revision of the Early Cretaceous time scale necessary. ?? 1994 International Association for Mathematical Geology.

  18. Amorphous soft-magnetic ribbons studied by ultra-small-angle polarized neutron scattering

    International Nuclear Information System (INIS)

    Badurek, G; Jericha, E; Groessinger, R; Sato-Turtelli, R

    2010-01-01

    When we investigated the magnetic structure of a variety of soft-magnetic amorphous ribbons by means of ultra-small-angle neutron scattering (USANSPOL) we were confronted with one particularly interesting Fe 65.7 Co 18 Si 0.8 B 15.5 ribbon, provided by VAC Hanau. Due to a special thermal treatment during production a field- and stress-induced transverse domain texture was expected. Although the USANSPOL technique encountered its resolution limits during the investigation of this specific sample ribbon, such a texture could indeed be verified.

  19. Inverse beta decay of arbitrarily polarized neutrons in a magnetic field

    Indian Academy of Sciences (India)

    star. some calculations of this process exist in the literature. Roulet [6], as well as Lai and Qian [7] performed the calculation by assuming that the magnetic field .... (2.8). The solution is obtained by using the dimensionless variable. = Ф. |Й| Э +. ФЬ. Й. (2.12) which transforms eq. (2.11) to the form. Pramana - J. Phys., Vol.

  20. Field-induced magnetic phases and electric polarization in LiNiPO4

    DEFF Research Database (Denmark)

    Jensen, Thomas Bagger Stibius; Christensen, Niels Bech; Kenzelmann, M.

    2009-01-01

    Neutron diffraction is used to probe the (H,T) phase diagram of magnetoelectric (ME) LiNiPO4 for magnetic fields along the c axis. At zero field the Ni spins order in two antiferromagnetic phases. One has commensurate (C) structures and general ordering vectors k(C)=(0,0,0); the other one...

  1. Zeeman- and electric-field control of spin- and valley-polarized transport through biased magnetic junctions on WSe2

    Science.gov (United States)

    Tahir, M.; Krstajić, P. M.; Vasilopoulos, P.

    2017-04-01

    The electronic properties of WSe2 comprise a huge spin-orbit coupling, a wide direct band gap, and especially a strong anisotropic lifting of the degeneracy of the valley degree of freedom in a magnetic field. We study ballistic electron transport through single or double junctions on monolayer WSe2 in the presence of spin M s and valley M v Zeeman fields and of an electric potential U. The conductance vs. the field M s or M v decreases in a fluctuating manner. For a single junction the spin P s and valley P v polarizations rise with M=M_v=2Ms , reach a value of more than 70%, and become perfect above U≈ 90 \\text{meV} while for a double junction this change can occur for U≈ 50 \\text{meV} and M≥ 10 \\text{meV} . P v increases with U and both polarizations oscillate with the junction width. The results may render WSe2 a promising candidate for new spintronic and valleytronic devices.

  2. Magnetic and electric control of spin- and valley-polarized transport across tunnel junctions on monolayer WSe2

    Science.gov (United States)

    Tahir, M.; Krstajić, P. M.; Vasilopoulos, P.

    2017-06-01

    The recent experimental realization of high-quality WSe2 leads to the possibility of an efficient manipulation of its spin and valley degrees of freedom. Its electronic properties comprise a huge spin-orbit coupling, a direct band gap, and a strong anisotropic lifting of the degeneracy of the valley degree of freedom in a magnetic field. We evaluate its band structure and study ballistic electron transport through single and double junctions (or barriers) on monolayer WSe2 in the presence of spin Ms and valley Mv Zeeman fields and of an electric potential U . The conductance versus the field Ms or Mv decreases in a fluctuating manner. For a single junction, the spin Ps and valley Pv polarizations rise with M =Mv=2 Ms , reach a value of more than 55 % , and become perfect above U ≈45 meV while for a double junction this change can occur for U ≥50 meV and M ≥5 meV. In certain regions of the (M ,U ) plane Pv becomes perfect. The conductance gc, its spin-up and spin-down components, and both polarizations oscillate with the barrier width d . The ability to isolate various carrier degrees of freedom in WSe2 may render it a promising candidate for new spintronic and valleytronic devices.

  3. A non-local-thermodynamic equilibrium formulation of the transport equation for polarized light in the presence of weak magnetic fields. Doctoral thesis

    International Nuclear Information System (INIS)

    McNamara, D.J.

    1977-01-01

    The present work is motivated by the desire to better understand solar magnetism. Just as stellar astrophysics and radiative transfer have been coupled in the history of research in physics, so too has the study of radiative transfer of polarized light in magnetic fields and solar magnetism been a history of mutual growth. The Stokes parameters characterize the state of polarization of a beam of radiation. The author considers the changes in polarization, and therefore in the Stokes parameters, due to the transport of a beam through an optically thick medium in a weak magnetic field. The transport equation is derived from a general density matrix equation of motion. This allows the possibility of interference effects arising from the mixing of atomic sublevels in a weak magnetic field to be taken into account. The statistical equilibrium equations are similarly derived. Finally, the coupled system of equations is presented, and the order of magnitude of the interference effects, shown. Collisional effects are not considered. The magnitude of the interference effects in magnetic field measurements of the sun may be evaluated

  4. Earth’s field effect on magnetic performance of horizontally and vertically polarizing undulators

    Directory of Open Access Journals (Sweden)

    N. O. Strelnikov

    2014-06-01

    Full Text Available Effects of the interaction of the Earth’s magnetic field with different types of insertion devices (IDs were studied at the Advanced Photon Source (APS at Argonne National Laboratory (Argonne according to the improvement of high-precision field measurements and field correction techniques that should meet the tight requirements for next-generation x-ray sources. The magnetic measurements of two Advanced Photon Source hybrid-type IDs with periods of 33 and 27 mm have been performed. The impact of different design elements was considered. It was demonstrated that the specified limits for IDs can be exceeded if the effect of the Earth’s field is not taken into account for various orientations of the IDs in the storage ring. Numerical simulations were done to better interpret experimental results for both devices and to estimate the effect for novel ID with the horizontal main field, which is now under development.

  5. Spectral time-domain induced polarization and magnetic surveying – an efficient tool for characterization of solid waste deposits in developing countries

    DEFF Research Database (Denmark)

    Wemegah, David Dotse; Fiandaca, Gianluca; Auken, Esben

    Time-domain induced polarization (IP) and magnetic data were acquired to map and characterize the decommissioned, un-engineered, municipal solid waste deposit site of the Kwame Nkrumah University of Science and Technology (KNUST), located in the Kumasi Metropolis of Ghana. Thirteen induced...

  6. Generation of circularly polarized radiation from a compact plasma-based extreme ultraviolet light source for tabletop X-ray magnetic circular dichroism studies

    Energy Technology Data Exchange (ETDEWEB)

    Wilson, Daniel; Rudolf, Denis, E-mail: d.rudolf@fz-juelich.de; Juschkin, Larissa [RWTH Aachen University, Experimental Physics of EUV, Steinbachstraße 15, 52074 Aachen (Germany); Forschungszentrum Jülich GmbH, Peter Grünberg Institut (PGI-9), JARA-FIT, 52425 Jülich (Germany); Weier, Christian; Adam, Roman; Schneider, Claus M. [Forschungszentrum Jülich GmbH, Peter Grünberg Institut (PGI-6), JARA-FIT, 52425 Jülich (Germany); Winkler, Gerrit; Frömter, Robert [Institut für Angewandte Physik, Universität Hamburg, Jungiusstraße 11, 20355 Hamburg (Germany); Danylyuk, Serhiy [RWTH Aachen University, Chair for Technology of Optical Systems, JARA-FIT, Steinbachstraße 15, 52074 Aachen (Germany); Bergmann, Klaus [Fraunhofer Institute for Laser Technology, Steinbachstrasse 15, 52074 Aachen (Germany); Grützmacher, Detlev [Forschungszentrum Jülich GmbH, Peter Grünberg Institut (PGI-9), JARA-FIT, 52425 Jülich (Germany)

    2014-10-15

    Generation of circularly polarized light in the extreme ultraviolet (EUV) spectral region (about 25 eV–250 eV) is highly desirable for applications in spectroscopy and microscopy but very challenging to achieve in a small-scale laboratory. We present a compact apparatus for generation of linearly and circularly polarized EUV radiation from a gas-discharge plasma light source between 50 eV and 70 eV photon energy. In this spectral range, the 3p absorption edges of Fe (54 eV), Co (60 eV), and Ni (67 eV) offer a high magnetic contrast often employed for magneto-optical and electron spectroscopy as well as for magnetic imaging. We simulated and designed an instrument for generation of linearly and circularly polarized EUV radiation and performed polarimetric measurements of the degree of linear and circular polarization. Furthermore, we demonstrate first measurements of the X-ray magnetic circular dichroism at the Co 3p absorption edge with a plasma-based EUV light source. Our approach opens the door for laboratory-based, element-selective spectroscopy of magnetic materials and spectro-microscopy of ferromagnetic domains.

  7. Interstitial Iron Effects on Magnetic Excitations in Parent Phases Fe1+xTe from Polarized and Inelastic Neutron Scattering

    Science.gov (United States)

    Rodriguez, Efrain

    2012-02-01

    One of the simplest systems of the iron-based superconducting family, Fe1+xCh (where Ch = S, Se, or Te) presents ample opportunity to study the relationship between antiferromagnetism and superconductivity. Several studies have demonstrated how the makeup of the Ch anions changes the electronic properties drastically, but the effect of excess interstitial iron, the x in Fe1+xCh, is not as well understood. Our previous diffraction experiments on samples varying x from 4 % to 16 % demonstrated how the magnetic ordering changes from collinear antiferromagnetic to helical incommensurate via a spin-density wave state at the special composition of x 12%. We present inelastic neutron scattering measurements of the phases Fe1+xTe for two amounts of interstitial iron in the lattice, 5% and 14 %. We have combined data from cold neutron triple-axis, thermal neutron triple-axis, and spallation source time-of-flight to provide a full picture of the magnetic excitations in Fe1+xTe for x=14 % from 0.5 meV to 150 meV. In addition, we present polarized inelastic studies on this particular composition to investigate the nature of the spin waves, i.e. longitudinal vs. transverse. The results are compared with those found in the phase with low amounts of interstitial iron ( 5 %), in order to understand the nature of the exchange interactions in this important parent compound.

  8. Magnetization switching of a metallic nanomagnet via current-induced surface spin-polarization of an underlying topological insulator

    International Nuclear Information System (INIS)

    Roy, Urmimala; Dey, Rik; Pramanik, Tanmoy; Ghosh, Bahniman; Register, Leonard F.; Banerjee, Sanjay K.

    2015-01-01

    We consider a thermally stable, metallic nanoscale ferromagnet (FM) subject to spin-polarized current injection and exchange coupling from the spin-helically locked surface states of a topological insulator (TI) to evaluate possible non-volatile memory applications. We consider parallel transport in the TI and the metallic FM, and focus on the efficiency of magnetization switching as a function of transport between the TI and the FM. Transport is modeled as diffusive in the TI beneath the FM, consistent with the mobility in the TI at room temperature, and in the FM, which essentially serves as a constant potential region albeit spin-dependent except in the low conductivity, diffusive limit. Thus, it can be captured by drift-diffusion simulation, which allows for ready interpretation of the results. We calculate switching time and energy consumed per write operation using self-consistent transport, spin-transfer-torque (STT), and magnetization dynamics calculations. Calculated switching energies and times compare favorably to conventional spin-torque memory schemes for substantial interlayer conductivity. Nevertheless, we find that shunting of current from the TI to a metallic nanomagnet can substantially limit efficiency. Exacerbating the problem, STT from the TI effectively increases the TI resistivity. We show that for optimum performance, the sheet resistivity of the FM layer should be comparable to or larger than that of the TI surface layer. Thus, the effective conductivity of the FM layer becomes a critical design consideration for TI-based non-volatile memory

  9. The effect of capped layer thickness on switching behavior in perpendicular CoCrPt based coupled granular/continuous media

    International Nuclear Information System (INIS)

    Li, W.M.; Lim, W.K.; Shi, J.Z.; Ding, J.

    2013-01-01

    A systematic investigation of magnetic switching behavior of CoCrPt based capped media (perpendicularly coupled granular/continuous (CGC) media consisting of granular CoCrPt:SiO 2 TiO 2 Ta 2 O 5 /capped CoCrPt(B)) is performed by varying the thickness of the capped layer from 0 to 9 nm. The microscopic structures of CGC media with different thickness of capped layer are examined by transmission electron microscope. We find out that CoCrPt magnetic grains are separated by nonmagnetic oxide grain boundaries. Grain size and grain boundary are about 8.9 nm and 2 nm, respectively. The nonmagnetic oxide grain boundaries in the granular layer do not disappear immediately at the interface between the granular and capped layers. The amorphous grain boundary phase in the granular layer propagates to the top surface of the capped layer. After capping with the CoCrPt(B) layer, the grain size at the surface of CGC structure increases and the grain boundary decreases. Both coercivity and intergranular exchange coupling of the CGC media are investigated by Polar magneto-optic Kerr effect magnetometer and alternating gradient force magnetometer. Although H c apparently decreases at thicker capped layer, no obvious variation of macroscopic switching field distribution (SFD/H c ) is observed. We separate intrinsic switching field distribution from intergranular interactions. The investigation of reduced intrinsic SFD/H c and increased hysteresis loop slope at coercivity, suggests that improvement of absolute switching field distribution (SFD) is caused by both strong intergranular exchange coupling and uniform grain size. Micromagnetic simulation results further verify our conclusion that the capped layer in CGC media is not uniformly continuous but has some granular nature. However, grains in the CoCrPt(B) capped layer is not absolutely isolated, strong exchange coupling exists between grains. - Highlights: • In CGC media, CoCrPt magnetic grains are separated by nonmagnetic oxide

  10. The effect of varying the capping agent of magnetic/luminescent Fe{sub 3}O{sub 4}–InP/ZnSe core–shell nanocomposite

    Energy Technology Data Exchange (ETDEWEB)

    Paulsen, Zuraan [Department of Chemistry, University of the Western Cape, Private Bag X17, Bellville (South Africa); Onani, Martin O., E-mail: monani@uwc.ac.za [Department of Chemistry, University of the Western Cape, Private Bag X17, Bellville (South Africa); Allard, Garvin R.J.; Kiplagat, Ayabei [Department of Chemistry, University of the Western Cape, Private Bag X17, Bellville (South Africa); Okil, Joseph O. [532 Winchester Avenue, Union, NJ 07083 (United States); Dejene, Francis B. [Department of Physics, University of the Free State, QwaQwa Campus, Private bag X13, Phuthaditjhaba 9866 (South Africa); Mahanga, Geoffrey M. [Department of Physical Sciences, Jaramogi Oginga Odinga University of Science and Technology, P.O. Box 210, 40601 Bondo (Kenya)

    2016-01-01

    Magnetic–luminescent nanoparticles have shown great promise in various biomedical applications namely: contrast agents for magnetic resonance imaging, multifunctional drug carrier system, magnetic separation of cells, cell tracking, immunoassay, and magnetic bioseparation. This experiment describes the synthesis of a nanocomposite material, which is composed of an iron oxide (Fe{sub 3}O{sub 4}) superparamagnetic core and an indium phosphide/zinc selenide (InP/ZnSe) quantum dot shell. The magnetic nanoparticles (MNP’s) and quantum dots (QD’s) were synthesized separately before allowing them to conjugate. The MNP’s were functionalized with a thiol-group allowing the QD shell to bind to the surface of the MNP by the formation of a thiol–metal bond. The nanocomposite was capped with 3-mercaptopropionic acid, oleylamine, β-cyclodextrin and their influence on the photoluminescence investigated. The synthesized nanocomposite was characterized with high- resolution transmission electron microscopy (HR-TEM), energy-dispersive spectroscopy (EDS), selective electron area diffraction (SAED), scanning electron microscopy (SEM), superconducting quantum interference device (SQUID), and photoluminescence. These techniques yielded particle size, morphology, dispersion, and chemical composition including luminescence and florescence.

  11. BICEP2 / Keck Array IX: New bounds on anisotropies of CMB polarization rotation and implications for axionlike particles and primordial magnetic fields

    Science.gov (United States)

    BICEP2 Collaboration; Keck Array Collaboration; Ade, P. A. R.; Ahmed, Z.; Aikin, R. W.; Alexander, K. D.; Barkats, D.; Benton, S. J.; Bischoff, C. A.; Bock, J. J.; Bowens-Rubin, R.; Brevik, J. A.; Buder, I.; Bullock, E.; Buza, V.; Connors, J.; Crill, B. P.; Duband, L.; Dvorkin, C.; Filippini, J. P.; Fliescher, S.; Germaine, T. St.; Ghosh, T.; Grayson, J.; Harrison, S.; Hildebrandt, S. R.; Hilton, G. C.; Hui, H.; Irwin, K. D.; Kang, J.; Karkare, K. S.; Karpel, E.; Kaufman, J. P.; Keating, B. G.; Kefeli, S.; Kernasovskiy, S. A.; Kovac, J. M.; Kuo, C. L.; Larson, N.; Leitch, E. M.; Megerian, K. G.; Moncelsi, L.; Namikawa, T.; Netterfield, C. B.; Nguyen, H. T.; O'Brient, R.; Ogburn, R. W.; Pryke, C.; Richter, S.; Schillaci, A.; Schwarz, R.; Sheehy, C. D.; Staniszewski, Z. K.; Steinbach, B.; Sudiwala, R. V.; Teply, G. P.; Thompson, K. L.; Tolan, J. E.; Tucker, C.; Turner, A. D.; Vieregg, A. G.; Weber, A. C.; Wiebe, D. V.; Willmert, J.; Wong, C. L.; Wu, W. L. K.; Yoon, K. W.

    2017-11-01

    We present the strongest constraints to date on anisotropies of cosmic microwave background (CMB) polarization rotation derived from 150 GHz data taken by the BICEP2 & Keck Array CMB experiments up to and including the 2014 observing season (BK14). The definition of the polarization angle in BK14 maps has gone through self-calibration in which the overall angle is adjusted to minimize the observed T B and E B power spectra. After this procedure, the Q U maps lose sensitivity to a uniform polarization rotation but are still sensitive to anisotropies of polarization rotation. This analysis places constraints on the anisotropies of polarization rotation, which could be generated by CMB photons interacting with axionlike pseudoscalar fields or Faraday rotation induced by primordial magnetic fields. The sensitivity of BK14 maps (˜3 μ K -arc min ) makes it possible to reconstruct anisotropies of the polarization rotation angle and measure their angular power spectrum much more precisely than previous attempts. Our data are found to be consistent with no polarization rotation anisotropies, improving the upper bound on the amplitude of the rotation angle spectrum by roughly an order of magnitude compared to the previous best constraints. Our results lead to an order of magnitude better constraint on the coupling constant of the Chern-Simons electromagnetic term ga γ≤7.2 ×10-2/HI (95% confidence) than the constraint derived from the B -mode spectrum, where HI is the inflationary Hubble scale. This constraint leads to a limit on the decay constant of 10-6≲fa/Mpl at mass range of 10-33≤ma≤10-28 eV for r =0.01 , assuming ga γ˜α /(2 π fa) with α denoting the fine structure constant. The upper bound on the amplitude of the primordial magnetic fields is 30 nG (95% confidence) from the polarization rotation anisotropies.

  12. Polar-core spin vortex of quasi-2D ferromagnetic spin-1 condensate in a flat-bottomed optical trap with a weak magnetic field

    Science.gov (United States)

    Zheng, Gong-Ping; Li, Pin; Li, Ting; Xue, Ya-Jie

    2018-02-01

    Motivated by the recent experiments realized in a flat-bottomed optical trap (Navon et al., 2015; Chomaz et al., 2015), we study the ground state of polar-core spin vortex of quasi-2D ferromagnetic spin-1 condensate in a finite-size homogeneous trap with a weak magnetic field. The exact spatial distribution of local spin is obtained with a variational method. Unlike the fully-magnetized planar spin texture with a zero-spin core, which was schematically demonstrated in previous studies for the ideal polar-core spin vortex in a homogeneous trap with infinitely large boundary, some plateaus and two-cores structure emerge in the distribution curves of spin magnitude in the polar-core spin vortex we obtained for the larger effective spin-dependent interaction. More importantly, the spin values of the plateaus are not 1 as expected in the fully-magnetized spin texture, except for the sufficiently large spin-dependent interaction and the weak-magnetic-field limit. We attribute the decrease of spin value to the effect of finite size of the system. The spin values of the plateaus can be controlled by the quadratic Zeeman energy q of the weak magnetic field, which decreases with the increase of q.

  13. Microtubule's conformational cap

    DEFF Research Database (Denmark)

    Flyvbjerg, H.

    1999-01-01

    The molecular mechanisms that allow elongation of the unstable microtubule lattice remain unclear. It is usually thought that the GDP-liganded tubulin lattice is capped by a small layer of GTP- or GDP-P(i)-liganded molecules, the so called "GTP-cap". Here, we point-out that the elastic properties...

  14. Influence of an absorbing sublayer on polarizing property of magnetic neutron mirrors

    International Nuclear Information System (INIS)

    Korneev, D.A.; Pasyuk, V.V.; Petrenko, A.V.

    1991-01-01

    Measurements of the neutron reflectivity profile from absorbing thin film mirrors deposited onto glass substrates are presented and the results compared with theoretical predictions. The spectral dependence of the scattering length of natural Gd and GdTi alloy has been determined for the first time for the thermal neutron energy range. The unstable behavior of the neutron scattering length of Gd and consequently the principle impossibility of its compensation in a wide interval of neutron wavelengths is the reason of the strong decreasing of the polarizing properties of neutron guides with ferromagnetic mirrors. The possibility is discussed of producing a new absorbing sublayers with an important decrease of reflection in the neutron wavelength range from 1 to 10 A. The neutron reflectivity was analyzed for absorbing thin BTi, BV and CdV alloys on glass substrates. The calculated reflectivity as a function of neutron wavelength was optimized for concentration and layer thickness. Fist experimental data have been performed at the Laboratory of Neutron Physics (Joint Institute for Nuclear Research, Dubna) and are presented. (author). 7 refs, 7 figs

  15. Anisotropic magnetoresistance of spin-orbit coupledcarriers scattered from polarized magnetic impurities

    Czech Academy of Sciences Publication Activity Database

    Trushin, M.; Výborný, Karel; Moraczewski, P.; Kovalev, A.A.; Schliemann, J.; Jungwirth, Tomáš

    2009-01-01

    Roč. 80, č. 13 (2009), 134405/1-134405/14 ISSN 1098-0121 R&D Projects: GA AV ČR KJB100100802; GA AV ČR KAN400100652; GA ČR GEFON/06/E002 EU Projects: European Commission(XE) 215368 - SemiSpinNet; European Commission(XE) 214499 - NAMASTE Grant - others:AV ČR(CZ) AP0801 Program:Akademická prémie - Praemium Academiae Institutional research plan: CEZ:AV0Z10100521 Keywords : Boltzmann equation * conduction bands * enhanced magnetoresistance * Fermi surface * ferromagnetic materials * gallium compounds * III-V semiconductors Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.475, year: 2009 http://link.aps.org/doi/10.1103/PhysRevB.80.134405

  16. Vortex polarity in 2-D magnetic dots by Langevin dynamics simulations

    International Nuclear Information System (INIS)

    Depondt, Ph.; Levy, J.-C.S.; Mertens, F.G.

    2011-01-01

    Two-dimensional magnetic plots of finite size were simulated by integrating the Landau-Lifshitz equation for the isotropic Heisenberg model with a systematic exploration of the effect of dipole-dipole interactions of various strengths d, at a low temperature. Structures with or without vortices are observed, and in the cases in which vortices are present, out-of-plane contributions show only for relatively weak dipolar strengths: the integrated intensity of the out-of-plane component decreases roughly as 1/d with increasing dipolar strength while the vortex core width decreases as d -1/2 . The coexistence of several vortices with an out-of-plane component seems limited to a narrow d-range, at least for the sample sizes studied. The size limit below which the vortices disappear decreases roughly as 1/d.

  17. Magnetic storms and variations in hormone levels among residents of North Polar area - Svalbard

    Science.gov (United States)

    Breus, Tamara; Zenchenko, Tatiana; Boiko, Evgeni

    It was previously shown that magnetic storms lead to an increase in the level of cortisol and noradrenalin in healthy and sick people with cardiovascular diseases [Breus Rapoport. 2003]. However, in the healthy group in the cited study was only 4 people and it seemed that these results need to be checked. In the present work the 4 examinations (January, March, June, October) of large groups of healthy inhabitants of high latitudes (Svalbard, the most northerly in the world year-round inhabited settlements) on the blood levels of adrenal hormones (cortisol) and thyroid hormones (triiodothyronine (T3 ) and thyroxine T4) have been done. The aim was to study the possible sensitivity of these biochemical parameters in three independent groups of people living in this region (men working underground (364 samples), the men working on the ground (274 samples) and women (280 samples)) to variations in external natural factors of high latitudes. For the analysis we used the following parameters of space and terrestrial weather :index of intensity of solar radio emission at a wavelength 10.7sm (RF10.7), planetary geomagnetic activity index - daily Kp index ( Kp) , the daily average Ap index ( Ap) , the maximum per every 3 -hour Kp index ) as well as the daily average indicators of flow rate of galactic cosmic rays neutron component (N), atmospheric pressure ( RATM ) and its rate of change ( the difference between the Ratm today and yesterday ) according to the geophysical station Oulu (Finland , http://cosmicrays.oulu.fi/). The obtained data indicate that the most expressed dependence of the level of studied three hormones is from the level of geomagnetic activity (GMA)-Kp, Ap, Kpmax - 3h. For two of the four seasons (June and October) with increasing levels of GMA a significant (p stress reaction in reply on GMA disturbance. 1. Breus T.K. and Rapoport S.I. Magnetic storms. Medico- biological aspects (in Russian), Publ.Co Soviet Sport,.Moscow, 2003, 271p.

  18. ATLAS end-caps 
on the move

    CERN Document Server

    2007-01-01

    Two delicate and spectacular transport operations have been performed for ATLAS in recent weeks: the first end-cap tracker was installed in its final position, and one of the huge end-caps of the toroid magnet was moved to the top of the experiment’s shaft.

  19. Measuring surface-area-to-volume ratios in soft porous materials using laser-polarized xenon interphase exchange nuclear magnetic resonance

    Science.gov (United States)

    Butler, J. P.; Mair, R. W.; Hoffmann, D.; Hrovat, M. I.; Rogers, R. A.; Topulos, G. P.; Walsworth, R. L.; Patz, S.

    2002-01-01

    We demonstrate a minimally invasive nuclear magnetic resonance (NMR) technique that enables determination of the surface-area-to-volume ratio (S/V) of soft porous materials from measurements of the diffusive exchange of laser-polarized 129Xe between gas in the pore space and 129Xe dissolved in the solid phase. We apply this NMR technique to porous polymer samples and find approximate agreement with destructive stereological measurements of S/V obtained with optical confocal microscopy. Potential applications of laser-polarized xenon interphase exchange NMR include measurements of in vivo lung function in humans and characterization of gas chromatography columns.

  20. ATLAS End-cap Part II

    CERN Multimedia

    2007-01-01

    The epic journey of the ATLAS magnets is drawing to an end. On Thursday 12 July, the second end-cap of the ATLAS toroid magnet was lowered into the cavern of the experiment with the same degree of precision as the first (see Bulletin No. 26/2007). This spectacular descent of the 240-tonne component, is one of the last transport to be completed for ATLAS.

  1. Verification of antiferromagnetic exchange coupling at room temperature using polar magneto-optic Kerr effect in thin EuS/Co multilayers with perpendicular magnetic anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Goschew, A., E-mail: alexander.goschew@fu-berlin.de; Scott, M.; Fumagalli, P. [Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin (Germany)

    2016-08-08

    We report on magneto-optic Kerr measurements in polar geometry carried out on a series of thin Co/EuS multilayers on suitable Co/Pd-multilayer substrates. Thin Co/EuS multilayers of a few nanometers individual layer thickness usually have their magnetization in plane. Co/Pd multilayers introduce a perpendicular magnetic anisotropy in the Co/EuS layers deposited on top, thus making it possible to measure magneto-optic signals in the polar geometry in remanence in order to study exchange coupling. Magneto-optic Kerr-effect spectra and hysteresis loops were recorded in the visible and ultraviolet photon-energy range at room temperature. The EuS contribution to the magneto-optic signal is extracted at 4.1 eV by combining hysteresis loops measured at different photon energies with polar magneto-optic Kerr-effect spectra recorded in remanence and in an applied magnetic field of 2.2 T. The extracted EuS signal shows clear signs of antiferromagnetic coupling of the Eu magnetic moments to the Co layers. This implies that the ordering temperature of at least a fraction of the EuS layers is above room temperature proving that magneto-optic Kerr-effect spectroscopy can be used here as a quasi-element-specific method.

  2. Polarized Moessbauer transitions

    International Nuclear Information System (INIS)

    Barb, D.

    1975-01-01

    Theoretical aspects of the emission, absorption and scattering of polarized gamma rays are reviewed for a general case of combined magnetic and electric hyperfine interactions; various possibilities of obtaining polarized gamma sources are described and examples are given of the applications of Moessbauer spectroscopy with polarized gamma rays in solving problems of solid state physics. (A.K.)

  3. Ion diode performance on a positive polarity inductive voltage adder with layered magnetically insulated transmission line flow

    International Nuclear Information System (INIS)

    Hinshelwood, D. D.; Schumer, J. W.; Allen, R. J.; Commisso, R. J.; Jackson, S. L.; Murphy, D. P.; Phipps, D.; Swanekamp, S. B.; Weber, B. V.; Ottinger, P. F.; Apruzese, J. P.; Cooperstein, G.; Young, F. C.

    2011-01-01

    A pinch-reflex ion diode is fielded on the pulsed-power machine Mercury (R. J. Allen, et al., 15th IEEE Intl. Pulsed Power Conf., Monterey, CA, 2005, p. 339), which has an inductive voltage adder (IVA) architecture and a magnetically insulated transmission line (MITL). Mercury is operated in positive polarity resulting in layered MITL flow as emitted electrons are born at a different potential in each of the adder cavities. The usual method for estimating the voltage by measuring the bound current in the cathode and anode of the MITL is not accurate with layered flow, and the interaction of the MITL flow with a pinched-beam ion diode load has not been studied previously. Other methods for determining the diode voltage are applied, ion diode performance is experimentally characterized and evaluated, and circuit and particle-in-cell (PIC) simulations are performed. Results indicate that the ion diode couples efficiently to the machine operating at a diode voltage of about 3.5 MV and a total current of about 325 kA, with an ion current of about 70 kA of which about 60 kA is proton current. It is also found that the layered flow impedance of the MITL is about half the vacuum impedance.

  4. Self-Focusing and de-Focusing of Intense Left- and Right-Hand Polarized Laser Pulse in Hot Magnetized Plasma in the Presence of an External Non-Uniform Magnetized Field

    Science.gov (United States)

    Abedi-Varaki, Mehdi; Jafari, Saed

    2017-10-01

    In this paper, self-focusing of an intense circularly polarized laser beam in the presence of a non-uniform positive guide magnetic field with slope constant parameter δ in hot magnetized plasma, using Maxwell's equations and relativistic fluid momentum equation is investigated. An envelope equation governing the spot-size of laser beam for both of left- and right-hand polarizations has been derived, and the effects of the plasma temperature and magnetic field on the electron density distribution of hot plasma with respect to variation of normalized laser spot-size has been studied. Numerical results show that self-focusing is better increased in the presence of an external non-uniform magnetic field. Moreover, in plasma density profile, self-focusing of the laser pulse improves in comparison with no non-uniform magnetic field. Also, with increasing slope of constant parameter of the non-uniform magnetic field, the self-focusing increases, and subsequently, the spot-size of laser pulse propagated through the hot magnetized plasma decreases.

  5. Development of Efficient and Robust Heteronuclear Cross-Polarization Techniques for Biological Solid-State Nuclear Magnetic Resonance Spectroscopy

    DEFF Research Database (Denmark)

    Jain, Sheetal Kumar

    2014-01-01

    →13C polarization transfer to facilitate 2-dimensional experiments detecting 14N in the indirect dimension are shown. Finally, to test the polarization transfer efficiency with very large chemical shift anisotropies, 19F→13C polarization transfer experiments for Poly Tetra Fluoro Ethylene (PTFE...

  6. Commissioning and modification of the low temperature scanning polarization microscope (TTSPM) and imaging of the local magnetic flux density distribution in superconducting niobium samples

    International Nuclear Information System (INIS)

    Gruenzweig, Matthias Sebastian Peter

    2014-01-01

    The dissertation is separated into two different parts, which will be presented in the following. Part I of the dissertation is about the commissioning and the modification of the ''low-temperature scanning polarization microscope'' which was designed in a previous dissertation of Stefan Guenon [1]. A scanning polarization microscope has certain advantages compared to conventional polarization microscopes. With a scanning polarization microscope it is easily possible to achieve a high illumination intensity, which is important to realize a high signal-to-noise ratio. Moreover, the confocal design of the scanning polarization microscope improves the resolution of the microscope by a factor of 1.4. Normally, it is not necessary to post-process the images by means of differential frame method to eliminate the contrast of non-magnetic origin. In contrast to conventional polarization microscopes the low-temperature scanning polarization microscope is able to image electronic transport properties via beam-induced voltage variation in addition to the magneto-optical effects. In this dissertation, it was possible to demonstrate the performance capability of the scanning polarization microscope at room temperature as well as at low temperatures. The investigation of the polar Kerr-effect has been carried out with a BaFe 12 O 19 -test sample whereas the measurements of the longitudinal Kerr-effect have been carried out with an in-plane magnetized acceleration sensor. Furthermore, an independent room temperature construction for out-of-plane measurements in a magnetic field up to 1 Tesla has been designed and implemented within the framework of a diploma thesis, supervised by the author of this dissertation. Using this construction, it was possible to gain experimental results regarding the interlayer exchange coupling between iron-terbium alloys (Fe 1-x Tb x ) and cobalt-platinum multilayers (vertical stroke Co/Pt vertical stroke n ). Indeed, it has been

  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. Applications of pulsed nuclear magnetic resonance to chemistry: multiple-pulse NMR, cross polarization, magic-angle spinning annd instrumental design

    Energy Technology Data Exchange (ETDEWEB)

    Murphy, P.D.

    1979-07-01

    Pulsed Nuclear Magnetic Resonance (NMR) has been applied to: (1) Measurements of the prinicpal components of the proton shielding tensors of the hydrides of zirconium chloride and zirconium bromide. Multiple-Pulse techniques have been used to remove static homonuclear dipolar coupling. The anisotropies and isotropic shifts of these tensors have been used to infer the possible locations of the hydrogen within the sandwich-like layers of these unusual compounds. (2) Studies of the oscillatory transfer of magnetic polarization between /sup 1/H and /sup 29/Si in substituted silanes. The technique of J Cross Polarization has been used to enhance sensitivity. The /sup 29/Si NMR shifts of -Si-O- model compounds have been investigated as a possible probe for future studies of the environment of bound oxygen in coal-derived liquids. (3) Measurements of the aromatic fraction of /sup 13/C in whole coals. The techniques of /sup 1/H-/sup 13/C Cross Polarization and Magic-Angle Spinning have been used to enhance sensitivity and remove shift anisotropy. Additional topics described are: (4) Calculation and properties of the broadened lineshape of the shileding Powder Pattern. (5) Calculation of the oscillatory transfer of magnetic polarization for an I-S system. (6) Numerical convolution and its uses. (7) The technique of digital filtering applied in the frequency domain. (8) The designs and properties of four NMR probe-circuits. (9) The design of a single-coil double-resonance probe for combined Magic-Angle Spinning and Cross Polarization. (10) The designs of low Q and high Q rf power amplifiers with emphasis on the rf matching circuitry.

  9. Nonlinear dynamics of circularly polarized laser pulse propagating in a magnetized plasma with superthermal ions and mixed nonthermal high-energy tail electrons distributions

    Energy Technology Data Exchange (ETDEWEB)

    Etemadpour, R.; Dorranian, D., E-mail: doran@srbiau.ac.ir [Laser Laboratory, Plasma Physics Research Center, Science and Research Branch, Islamic Azad University, Tehran (Iran, Islamic Republic of); Sepehri Javan, N. [Department of Physics, University of Mohaghegh Ardabili, P.O. Box 179, Ardabil (Iran, Islamic Republic of)

    2016-05-15

    The nonlinear dynamics of a circularly polarized laser pulse propagating in the magnetized plasmas whose constituents are superthermal ions and mixed nonthermal high-energy tail electrons is studied theoretically. A nonlinear equation which describes the dynamics of the slowly varying amplitude is obtained using a relativistic two-fluid model. Based on this nonlinear equation and taking into account some nonlinear phenomena such as modulational instability, self-focusing and soliton formation are investigated. Effect of the magnetized plasma with superthermal ions and mixed nonthermal high-energy tail electrons on these phenomena is considered. It is shown that the nonthermality and superthermality of particles can substantially change the nonlinearity of medium.

  10. Comparison between two alternative approaches for the analysis of polarization evolution of EM waves in a nonuniform, fully anisotropic medium. A magnetized plasma

    International Nuclear Information System (INIS)

    Segre, S. E.

    2001-01-01

    A comparison is made between two alternative approaches for the analysis of polarization evolution of em waves in a magnetized plasma. The two approaches are the Coupled Wave-Equation Formalism (CWF) and the Stokes Vector Formalism (SVF). After brief descriptions of the two formalisms the correspondence between them is spelled out. The two formalisms are then compared and their relative advantages and limitations are discussed [it

  11. Electric and magnetic polarization saturations for a thermally loaded penny-shaped crack in a magneto-electro-thermo-elastic medium

    Science.gov (United States)

    Li, P.-D.; Li, X.-Y.; Kang, G.-Z.; Müller, R.

    2017-09-01

    This paper is devoted to investigating the thermal-induced electric and magnetic polarization saturations (PS) at the tip of a penny-shaped crack embedded in an infinite space of magneto-electro-thermo-elastic medium. In view of the symmetry with respect to the cracked plane, this crack problem is formulated by a mixed boundary value problem. By virtue of the solution to the Abel type integral equation, the governing equations corresponding to the present problem are analytically solved and the generalized crack surface displacement and field intensity factors are obtained in closed-forms. Applying the hypothesis of the electric and magnetic PS model to the analytical results, the sizes of the electric and magnetic yielding zones are determined. Numerical calculations are carried out to reveal the influences of the thermal load and the electric and magnetic yielding strengths on the results, and to show the distributions of the electric and magnetic potentials on the crack surfaces. It is found that the sizes of electric and magnetic yielding zones are mainly dependent on the electric and magnetic yielding strengths, respectively. Since the multi-ferroic media are widely used in various complex thermal environments, the present work could serve as a reference for the designs of various magneto-electric composite structures.

  12. Magnetic/NIR-responsive drug carrier, multicolor cell imaging, and enhanced photothermal therapy of gold capped magnetite-fluorescent carbon hybrid nanoparticles.

    Science.gov (United States)

    Wang, Hui; Cao, Guixin; Gai, Zheng; Hong, Kunlun; Banerjee, Probal; Zhou, Shuiqin

    2015-05-07

    This paper reports a type of multifunctional hybrid nanoparticle (NP) composed of gold nanocrystals coated on and/or embedded in a magnetite-fluorescent porous carbon core-shell NP template (Fe3O4@PC-CDs-Au) for biomedical applications, including magnetic/NIR-responsive drug release, multicolor cell imaging, and enhanced photothermal therapy. The synthesis of the Fe3O4@PC-CDs-Au NPs firstly involves the preparation of core-shell template NPs with magnetite nanocrystals clustered in the cores and fluorescent carbon dots (CDs) embedded in a porous carbon shell, followed by an in situ reduction of silver ions (Ag(+)) loaded in the porous carbon shell and a subsequent replacement of Ag NPs with Au NPs through a galvanic replacement reaction using HAuCl4 as a precursor. The Fe3O4@PC-CDs-Au NPs can enter the intracellular region and light up mouse melanoma B16F10 cells in multicolor mode. The porous carbon shell, anchored with hydrophilic hydroxyl/carboxyl groups, endows the Fe3O4@PC-CDs-Au NPs with excellent stability in the aqueous phase and a high loading capacity (719 mg g(-1)) for the anti-cancer drug doxorubicin (DOX). The superparamagnetic Fe3O4@PC-CDs-Au NPs with a saturation magnetization of 23.26 emu g(-1) produce localized heat under an alternating magnetic field, which triggers the release of the loaded drug. The combined photothermal effects of the Au nanocrystals and the CDs on/in the carbon shell can not only regulate the release rate of the loaded drug, but also efficiently kill tumor cells under NIR irradiation. Benefitting from their excellent optical properties, their magnetic field and NIR light-responsive drug release capabilities and their enhanced photothermal effect, such nanostructured Fe3O4@PC-CDs-Au hybrid NPs are very promising for simultaneous imaging diagnostics and high efficacy therapy.

  13. Planck intermediate results XXXIII. Signature of the magnetic field geometry of interstellar filaments in dust polarization maps

    DEFF Research Database (Denmark)

    Ade, P. A. R.; Aghanim, N.; Alves, M. I. R.

    2016-01-01

    Planck observations at 353 GHz provide the first fully sampled maps of the polarized dust emission towards interstellar filaments and their backgrounds (i.e., the emission observed in the surroundings of the filaments). The data allow us to determine the intrinsic polarization properties of the f......Planck observations at 353 GHz provide the first fully sampled maps of the polarized dust emission towards interstellar filaments and their backgrounds (i.e., the emission observed in the surroundings of the filaments). The data allow us to determine the intrinsic polarization properties...

  14. RADIO POLARIZATION OBSERVATIONS OF THE SNAIL: A CRUSHED PULSAR WIND NEBULA IN G327.1–1.1 WITH A HIGHLY ORDERED MAGNETIC FIELD

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Y. K.; Ng, C.-Y. [Department of Physics, The University of Hong Kong, Pokfulam Road (Hong Kong); Bucciantini, N. [INAF—Osservatorio Astrofisico di Arcetri, L.go E. Fermi 5, I-50125 Firenze (Italy); Slane, P. O. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Gaensler, B. M. [Dunlap Institute for Astronomy and Astrophysics, The University of Toronto, Toronto, ON M5S 3H4 (Canada); Temim, T., E-mail: ncy@bohr.physics.hku.hk [Observational Cosmology Lab, Code 665, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

    2016-04-01

    Pulsar wind nebulae (PWNe) are suggested to be acceleration sites of cosmic rays in the Galaxy. While the magnetic field plays an important role in the acceleration process, previous observations of magnetic field configurations of PWNe are rare, particularly for evolved systems. We present a radio polarization study of the “Snail” PWN inside the supernova remnant G327.1−1.1 using the Australia Telescope Compact Array. This PWN is believed to have been recently crushed by the supernova (SN) reverse shock. The radio morphology is composed of a main circular body with a finger-like protrusion. We detected a strong linear polarization signal from the emission, which reflects a highly ordered magnetic field in the PWN and is in contrast to the turbulent environment with a tangled magnetic field generally expected from hydrodynamical simulations. This could suggest that the characteristic turbulence scale is larger than the radio beam size. We built a toy model to explore this possibility, and found that a simulated PWN with a turbulence scale of about one-eighth to one-sixth of the nebula radius and a pulsar wind filling factor of 50%–75% provides the best match to observations. This implies substantial mixing between the SN ejecta and pulsar wind material in this system.

  15. What are the mesoscopic magnetic inhomogeneities in the dilute PdFeMn alloy? Polarized neutron study

    Energy Technology Data Exchange (ETDEWEB)

    Gordeev, G.; Axelrod, L.; Zabenkin, V.; Lazebnik, I.; Grigoriev, S.; Wagner, V.; Eckerlebe, H

    2003-07-01

    The 3D analysis of neutron depolarization was carried out for different thermomagnetic treatment of the dilute PdFeMn alloy versus temperature and magnetic field applied in magnetizing/demagnetizing cycles. Both the macroscopic magnetization and the mean fluctuation of local magnetization behavior were subtracted from experimental data. A complicated behavior of the latter was observed. The hysteresis of local magnetization fluctuations is found out but that of macroscopic magnetization is practically absent. The effort to apply the simple model for the description of magnetic inhomogeneities was made in order to understand the mesostructure of this alloy.

  16. A nanoparticle catalyst for heterogeneous phase para-hydrogen-induced polarization in water.

    Science.gov (United States)

    Glöggler, Stefan; Grunfeld, Alexander M; Ertas, Yavuz N; McCormick, Jeffrey; Wagner, Shawn; Schleker, P Philipp M; Bouchard, Louis-S

    2015-02-16

    Para-hydrogen-induced polarization (PHIP) is a technique capable of producing spin polarization at a magnitude far greater than state-of-the-art magnets. A significant application of PHIP is to generate contrast agents for biomedical imaging. Clinically viable and effective contrast agents not only require high levels of polarization but heterogeneous catalysts that can be used in water to eliminate the toxicity impact. Herein, we demonstrate the use of Pt nanoparticles capped with glutathione to induce heterogeneous PHIP in water. The ligand-inhibited surface diffusion on the nanoparticles resulted in a (1) H polarization of P=0.25% for hydroxyethyl propionate, a known contrast agent for magnetic resonance angiography. Transferring the (1) H polarization to a (13) C nucleus using a para-hydrogen polarizer yielded a polarization of 0.013%. The nuclear-spin polarizations achieved in these experiments are the first reported to date involving heterogeneous reactions in water. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Spin-polarized scanning tunneling microscopy experiments on the rough surface of a polycrystalline NiFe film with a fine magnetic tip sensitive to a well-defined magnetization component

    Directory of Open Access Journals (Sweden)

    H. Matsuyama

    2016-03-01

    Full Text Available We developed a micrometer-sized magnetic tip integrated onto the write head of a hard disk drive for spin-polarized scanning tunneling microscopy (SP-STM in the modulated tip magnetization mode. Using SP-STM, we measured a well-defined in-plane spin-component of the tunneling current of the rough surface of a polycrystalline NiFe film. The spin asymmetry of the NiFe film was about 1.3% within the bias voltage range of -3 to 1 V. We obtained the local spin component image of the sample surface, switching the magnetic field of the sample to reverse the sample magnetization during scanning. We also obtained a spin image of the rough surface of a polycrystalline NiFe film evaporated on the recording medium of a hard disk drive.

  18. Dual Recognition Strategy for Specific and Sensitive Detection of Bacteria Using Aptamer-Coated Magnetic Beads and Antibiotic-Capped Gold Nanoclusters.

    Science.gov (United States)

    Cheng, Dan; Yu, Mengqun; Fu, Fei; Han, Weiye; Li, Gan; Xie, Jianping; Song, Yang; Swihart, Mark T; Song, Erqun

    2016-01-05

    Food poisoning and infectious diseases caused by pathogenic bacteria such as Staphylococcus aureus (SA) are serious public health concerns. A method of specific, sensitive, and rapid detection of such bacteria is essential and important. This study presents a strategy that combines aptamer and antibiotic-based dual recognition units with magnetic enrichment and fluorescent detection to achieve specific and sensitive quantification of SA in authentic specimens and in the presence of much higher concentrations of other bacteria. Aptamer-coated magnetic beads (Apt-MB) were employed for specific capture of SA. Vancomycin-stabilized fluorescent gold nanoclusters (AuNCs@Van) were prepared by a simple one-step process and used for sensitive quantification of SA in the range of 32-10(8) cfu/mL with the detection limit of 16 cfu/mL via a fluorescence intensity measurement. And using this strategy, about 70 cfu/mL of SA in complex samples (containing 3 × 10(8) cfu/mL of other different contaminated bacteria) could be successfully detected. In comparison to prior studies, the developed strategy here not only simplifies the preparation procedure of the fluorescent probes (AuNCs@Van) to a great extent but also could sensitively quantify SA in the presence of much higher concentrations of other bacteria directly with good accuracy. Moreover, the aptamer and antibiotic used in this strategy are much less expensive and widely available compared to common-used antibodies, making it cost-effective. This general aptamer- and antibiotic-based dual recognition strategy, combined with magnetic enrichment and fluorescent detection of trace bacteria, shows great potential application in monitoring bacterial food contamination and infectious diseases.

  19. Gd-doped GaN studied with element specificity: Very small polarization of Ga, paramagnetism of Gd and the formation of magnetic clusters

    Energy Technology Data Exchange (ETDEWEB)

    Ney, A., E-mail: ney@maglomat.d [Fachbereich Physik and Center for Nanointegration Duisburg-Essen (CeNIDE), Universitaet Duisburg-Essen, Lotharstr. 1, D-47057 Duisburg (Germany); Kammermeier, T.; Ollefs, K.; Ney, V.; Ye, S. [Fachbereich Physik and Center for Nanointegration Duisburg-Essen (CeNIDE), Universitaet Duisburg-Essen, Lotharstr. 1, D-47057 Duisburg (Germany); Dhar, S. [Fachbereich Physik and Center for Nanointegration Duisburg-Essen (CeNIDE), Universitaet Duisburg-Essen, Lotharstr. 1, D-47057 Duisburg (Germany); Paul-Drude-Institut fuer Festkoerperelektronik, Hausvogteiplatz 5-7, D-10117 Berlin (Germany); Ploog, K.H. [Paul-Drude-Institut fuer Festkoerperelektronik, Hausvogteiplatz 5-7, D-10117 Berlin (Germany); Roever, M.; Malindretos, J.; Rizzi, A. [IV. Physikalisches Institut and Virtual Institute of Spinelectronics (VISel), Georg August Universitaet Goettingen, D-37077 Goettingen (Germany); Wilhelm, F.; Rogalev, A. [European Synchrotron Radiation Facility (ESRF), 6 Rue Jules Horowitz, BP 220, 38043 Grenoble Cedex (France)

    2010-05-15

    Element specific X-ray linear dichroism (XLD), X-ray magnetic circular dichroism (XMCD) at the Ga K- and Ga and Gd L{sub 3}-edges and magnetic resonance measurements have been carried out on Gd:GaN grown by molecular beam epitaxy with different Gd concentrations. XMCD studies at the Ga K-edge reveal only a very weak magnetic polarization, which is too small to account for the colossal moments reported before by SQUID. In the dilute limit we can show by XLD that the majority of the Gd dopant atoms go to substitutional Ga sites. XMCD studies demonstrate that the Gd sublattice behaves paramagnetic which is in contrast to integral SQUID measurements. The absence of ferromagnetic order at room temperature is corroborated by magnetic resonance studies. First signatures of phase separation are visible. At higher Gd concentrations phase separation is found by XLD. In such samples ferromagnetic-like order is consistently found by SQUID, XMCD and magnetic resonance which is characteristic for a blocked superparamagnetic ensemble. In turn, phase separated ferromagnetic Gd/GdN clusters cannot account for magnetic order observed at and above 300 K by SQUID.

  20. A THEORETICAL STUDY OF THE BUILD-UP OF THE SUN’S POLAR MAGNETIC FIELD BY USING A 3D KINEMATIC DYNAMO MODEL

    Energy Technology Data Exchange (ETDEWEB)

    Hazra, Gopal; Choudhuri, Arnab Rai [Department of Physics, Indian Institute of Science, Bangalore, 560012 (India); Miesch, Mark S., E-mail: ghazra@physics.iisc.ernet.in, E-mail: arnab@physics.iisc.ernet.in, E-mail: miesch@ucar.edu [High Altitude Observatory, National Center for Atmospheric Research, Boulder, CO 80301 (United States)

    2017-01-20

    We develop a three-dimensional kinematic self-sustaining model of the solar dynamo in which the poloidal field generation is from tilted bipolar sunspot pairs placed on the solar surface above regions of strong toroidal field by using the SpotMaker algorithm, and then the transport of this poloidal field to the tachocline is primarily caused by turbulent diffusion. We obtain a dipolar solution within a certain range of parameters. We use this model to study the build-up of the polar magnetic field and show that some insights obtained from surface flux transport models have to be revised. We present results obtained by putting a single bipolar sunspot pair in a hemisphere and two symmetrical sunspot pairs in two hemispheres. We find that the polar fields produced by them disappear due to the upward advection of poloidal flux at low latitudes, which emerges as oppositely signed radial flux and which is then advected poleward by the meridional flow. We also study the effect that a large sunspot pair, violating Hale’s polarity law, would have on the polar field. We find that there would be some effect—especially if the anti-Hale pair appears at high latitudes in the mid-phase of the cycle—though the effect is not very dramatic.

  1. Low frequency geomagnetic field fluctuations at cap and low latitude during October 29-31, 2003

    Directory of Open Access Journals (Sweden)

    L. Santarelli

    2007-06-01

    Full Text Available On October-November 2003 complex interplanetary structures, originated by a series of solar eruptions, hit the Earth, triggering violent Sun-Earth connection events. In this paper we analyze the low frequency geomagnetic field fluctuations detected on the ground during Oct. 29-31, 2003, a time period characterized by extremely high solar wind speed values and by out-of-ecliptic interplanetary magnetic field orientation for intervals of several hours. We analyze geomagnetic field measurements at four high latitude stations located in the polar cap, three in the southern and one in the northern hemisphere. From a comparison with simultaneous measurements at low latitude, we address the question of the global character of the observed phenomena. The results show, for selected time intervals, the occurrence of simultaneous fluctuations at all the stations, with high coherence even between high and low latitude; it is interesting that these fluctuations are detected during open magnetospheric conditions, when the high latitude stations are situated well within the polar cap, i.e. far from closed field lines.

  2. The properties of photonic band gap and surface plasmon modes in the three-dimensional magnetized photonic crystals as the mixed polarized modes considered

    Science.gov (United States)

    Zhang, Hai-Feng; Liu, Shao-Bin; Jiang, Yu-Chi

    2015-04-01

    In this paper, the properties of photonic band gap (PBG) and surface plasmon modes in the three-dimensional (3D) magnetized plasma photonic crystals (MPPCs) with face-centered-cubic (fcc) lattices are theoretically investigated based on the plane wave expansion (PWE) method, in which the homogeneous magnetized plasma spheres are immersed in the homogeneous dielectric background, as the Voigt effects of magnetized plasma are considered (the incidence electromagnetic wave vector is perpendicular to the external magnetic field at any time). The dispersive properties of all of the EM modes are studied because the PBG is not only for the extraordinary and ordinary modes but also for the mixed polarized modes. The equations for PBGs also are theoretically deduced. The numerical results show that the PBG and a flatbands region can be observed. The effects of the dielectric constant of dielectric background, filling factor, plasma frequency and plasma cyclotron frequency (the external magnetic field) on the dispersive properties of all of the EM modes in such 3D MPPCs are investigated in detail, respectively. Theoretical simulations show that the PBG can be manipulated by the parameters as mentioned above. Compared to the conventional dielectric-air PCs with similar structure, the larger PBG can be obtained in such 3D MPPCs. It is also shown that the upper edge of flatbands region cannot be tuned by the filling factor and dielectric constant of dielectric background, but it can be manipulated by the plasma frequency and plasma cyclotron frequency.

  3. One-step synthesis of robust amine- and vinyl-capped magnetic iron oxide nanoparticles for polymer grafting, dye adsorption, and catalysis.

    Science.gov (United States)

    Zhou, Li; He, Benzhao; Huang, Jiachang

    2013-09-11

    Magnetic iron oxide nanoparticles (MIONs) bearing amine and vinyl groups are fabricated straightforwardly using vinyl-based tertiary amine molecules as both alkaline source and ligands based on the coprecipitation of iron ions in aqueous solution. The as-prepared MIONs present amphiphilic performance that can be well-dispersed both in aqueous solution and common organic solvents (e.g., ethanol, dichloromethane and tetrahydrofuran). Transmission electron microscopy (TEM), X-ray diffraction (XRD), and vibrating sample magnetometer (VSM) measurements reveal that the MIONs are superparamagnetic Fe3O4 nanoparticles with a mean diameter below 10 nm. The presence of ligands on the surface of MIONs was confirmed by thermogravimetric analysis (TGA), Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS) characterizations. Benefiting from the surface vinyl groups, the MIONs are able to graft polyvinyl-based polymers by in situ polymerization of the corresponding vinyl monomers as confirmed by grafting poly(methyl methacrylate) (PMMA) in this paper. On the basis of their surface amine groups, the MIONs show high adsorption capacity (ca. 0.42 mmol/g) for congo red dye and excellent performance for in situ growth of Pt nanocatalyst. Moreover, the MIONs possess high stability and can be reused several times without obvious decrease of their adsorption capacity and catalytic efficiency. Considering the facile fabrication process and versatile performance of the obtained MIONs, this work may open up new opportunities for the large-scale applications of MIONs.

  4. Working on an LHC dipole end-cap

    CERN Multimedia

    Laurent Guiraud

    1999-01-01

    A metal worker constructs an end-cap for an LHC dipole magnet. These magnets will be used to bend the proton beams around the LHC, which is due to start up in 2008. The handmade prototype seen here will be used to make a mold from which the final set of components will be made for the accelerator.

  5. Polarized neutron reflectometry study on BiFeO3/Co0.9Fe0.1 heterostructures: enhanced magnetization in BiFeO3 and strong magnetic coupling at interface

    Science.gov (United States)

    Wang, Qiang; Gao, Ya; Ramesh, Ramamoorthy; Fitzsimmons, Michael

    2015-03-01

    Polarized neutron reflectometry (PNR) quantified the uncompensated magnetization occurring throughout the thickness of a BiFeO3 (BFO)/ Co0.9Fe0.1 (CoFe) heterostructures. The net uncompensated magnetization (1.0 μB/Fe) within BFO layer is much larger than that which has been theoretically predicted (0.1 μB/Fe) due to the Dzyaloshinskii-Moriya (DM) type interaction. The field dependent study indicates strong interfacial coupling between BFO and CoFe which extends into CoFe layer within about 1 nm interfacial region. The study also suggests the uncompensated magnetization in the BFO layer has relatively small anisotropy.

  6. Imaging with Polarized Neutrons

    Directory of Open Access Journals (Sweden)

    Nikolay Kardjilov

    2018-01-01

    Full Text Available Owing to their zero charge, neutrons are able to pass through thick layers of matter (typically several centimeters while being sensitive to magnetic fields due to their intrinsic magnetic moment. Therefore, in addition to the conventional attenuation contrast image, the magnetic field inside and around a sample can be visualized by detecting changes of polarization in a transmitted beam. The method is based on the spatially resolved measurement of the cumulative precession angles of a collimated, polarized, monochromatic neutron beam that traverses a magnetic field or sample.

  7. Real-space observation of a right-rotating inhomogeneous cycloidal spin spiral by spin-polarized scanning tunneling microscopy in a triple axes vector magnet.

    Science.gov (United States)

    Meckler, S; Mikuszeit, N; Pressler, A; Vedmedenko, E Y; Pietzsch, O; Wiesendanger, R

    2009-10-09

    Using spin-polarized scanning tunneling microscopy performed in a triple axes vector magnet, we show that the magnetic structure of the Fe double layer on W(110) is an inhomogeneous right-rotating cycloidal spin spiral. The magnitude of the Dzyaloshinskii-Moriya vector is extracted from the experimental data using micromagnetic calculations. The result is confirmed by comparison of the measured saturation field along the easy axis to the respective value as obtained from Monte Carlo simulations. We find that the Dzyaloshinskii-Moriya interaction is too weak to destabilize the single domain state. However, it can define the sense of rotation and the cycloidal spiral type once the single domain state is destabilized by dipolar interaction.

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

    Science.gov (United States)

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

    1985-01-01

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

  9. Dark Polar Dunes

    Science.gov (United States)

    2005-01-01

    20 January 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image, acquired during northern summer in December 2004, shows dark, windblown sand dunes in the north polar region of Mars. A vast sea of sand dunes nearly surrounds the north polar cap. These landforms are located near 80.3oN, 144.1oW. Light-toned features in the image are exposures of the substrate that underlies the dune field. The image covers an area about 3 km (1.9 mi) wide and is illuminated by sunlight from the lower left.

  10. Measuring the spin polarization of alkali-metal atoms using nuclear magnetic resonance frequency shifts of noble gases

    Directory of Open Access Journals (Sweden)

    X. H. Liu

    2015-10-01

    Full Text Available We report a novel method of measuring the spin polarization of alkali-metal atoms by detecting the NMR frequency shifts of noble gases. We calculated the profile of 87Rb D1 line absorption cross sections. We then measured the absorption profile of the sample cell, from which we calculated the 87Rb number densities at different temperatures. Then we measured the frequency shifts resulted from the spin polarization of the 87Rb atoms and calculated its polarization degrees at different temperatures. The behavior of frequency shifts versus temperature in experiment was consistent with theoretical calculation, which may be used as compensative signal for the NMRG closed-loop control system.

  11. The interaction of a magnetic cloud with the Earth: Ionospheric convection in the Northern and Southern Hemispheres for a wide range of quasi-steady interplanetary magnetic field conditions

    International Nuclear Information System (INIS)

    Freeman, M.P.; Farrugia, C.J.; Burlaga, L.F.; Lepping, R.P.; Hairston, M.R.; Greenspan, M.E.; Ruohoniemi, J.M.

    1993-01-01

    This is the second of three papers which study a large interplanetary magnetic cloud, and its interaction with the earth's magnetosphere. Here the authors study flows within the ionosphere during the passage of the magnetic cloud on Jan 13-15, 1988. This is the first study of ionospheric convections during prolonged periods of stable and different IMF orientations, which result from the stable, but spatially varying field structure within the magnetic cloud. Data from IMP-8 and DMSP-F8 are analyzed for this work. This observation gave information on ionospheric responses to greater than 10 hour period of northward and southward IMF, with a gradual change from one to the other. Issues studied included strengths of peak flows for north and south IMF; changes in cross polar cap potential with IMF B z ; types and variations of convective patterns vs IMF; variations in size of the polar cap; etc

  12. A modular designed ultra-high-vacuum spin-polarized scanning tunneling microscope with controllable magnetic fields for investigating epitaxial thin films.

    Science.gov (United States)

    Wang, Kangkang; Lin, Wenzhi; Chinchore, Abhijit V; Liu, Yinghao; Smith, Arthur R

    2011-05-01

    A room-temperature ultra-high-vacuum scanning tunneling microscope for in situ scanning freshly grown epitaxial films has been developed. The core unit of the microscope, which consists of critical components including scanner and approach motors, is modular designed. This enables easy adaptation of the same microscope units to new growth systems with different sample-transfer geometries. Furthermore the core unit is designed to be fully compatible with cryogenic temperatures and high magnetic field operations. A double-stage spring suspension system with eddy current damping has been implemented to achieve ≤5 pm z stability in a noisy environment and in the presence of an interconnected growth chamber. Both tips and samples can be quickly exchanged in situ; also a tunable external magnetic field can be introduced using a transferable permanent magnet shuttle. This allows spin-polarized tunneling with magnetically coated tips. The performance of this microscope is demonstrated by atomic-resolution imaging of surface reconstructions on wide band-gap GaN surfaces and spin-resolved experiments on antiferromagnetic Mn(3)N(2)(010) surfaces.

  13. Field-cycled dynamic nuclear polarization (FC-DNP) of {sup 14}N and {sup 15}N nitroxide radicals at low magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Polyon, C [Department of Physics, Faculty of Science, Khon Kaen University, Khon Kaen 40002 (Thailand); Lurie, D J [Bio-Medical Physics, School of Medical Sciences, College of Life Sciences and Medicine, University of Aberdeen, Foresterhill, Aberdeen, AB25 2ZD (United Kingdom); Youngdee, W [Department of Physics, Faculty of Science, Khon Kaen University, Khon Kaen 40002 (Thailand); Thomas, C [Department of Physics, Faculty of Science, Khon Kaen University, Khon Kaen 40002 (Thailand); Thomas, I [Department of Physics, Faculty of Science, Khon Kaen University, Khon Kaen 40002 (Thailand)

    2007-09-21

    Theoretical Overhauser-detected EPR spectra of {sup 14}N and {sup 15}N nitroxide systems in low magnetic field by field-cycled dynamic nuclear polarization (FC-DNP) were described by a combination of DNP theory and a model of FC-DNP. Spectra were simulated at magnetic fields between 0 and 8 mT. The simulations were able to predict both the EPR peak positions and their amplitudes, corresponding to those from FC-DNP experiments with {sup 14}N and {sup 15}N TEMPOL solutions. EPR irradiation was in the 45-133 MHz range while NMR signal detection occurred at a field of 59 mT. At this frequency range, four {pi} transitions of a {sup 14}N system and three {pi} transitions of a {sup 15}N system were observed. The simulation programmes were also used to predict the spectral amplitudes of the FC-DNP with EPR irradiation power in the 1-15 W range. Theoretical FC-DNP systems were in good agreement with experimental results; however, at low magnetic fields the inhomogeneity of our magnet system resulted in the EPR peaks being left-shifted and somewhat broader than those from the theoretical prediction.

  14. Saltstone Clean Cap Formulation

    Energy Technology Data Exchange (ETDEWEB)

    Langton, C

    2005-04-22

    The current operation strategy for using Saltstone Vault 4 to receive 0.2 Ci/gallon salt solution waste involves pouring a clean grout layer over the radioactive grout prior to initiating pour into another cell. This will minimize the radiating surface area and reduce the dose rate at the vault and surrounding area. The Clean Cap will be used to shield about four feet of Saltstone poured into a Z-Area vault cell prior to moving to another cell. The minimum thickness of the Clean Cap layer will be determined by the cesium concentration and resulting dose levels and it is expected to be about one foot thick based on current calculations for 0.1 Ci Saltstone that is produced in the Saltstone process by stabilization of 0.2 Ci salt solution. This report documents experiments performed to identify a formulation for the Clean Cap. Thermal transient calculations, adiabatic temperature rise measurements, pour height, time between pour calculations and shielding calculations were beyond the scope and time limitations of this study. However, data required for shielding calculations (composition and specific gravity) are provided for shielding calculations. The approach used to design a Clean Cap formulation was to produce a slurry from the reference premix (10/45/45 weight percent cement/slag/fly ash) and domestic water that resembled as closely as possible the properties of the Saltstone slurry. In addition, options were investigated that may offer advantages such as less bleed water and less heat generation. The options with less bleed water required addition of dispersants. The options with lower heat contained more fly ash and less slag. A mix containing 10/45/45 weight percent cement/slag/fly ash with a water to premix ratio of 0.60 is recommended for the Clean Cap. Although this mix may generate more than 3 volume percent standing water (bleed water), it has rheological, mixing and flow properties that are similar to previously processed Saltstone. The recommended

  15. Saltstone Clean Cap Formulation

    International Nuclear Information System (INIS)

    Langton, C

    2005-01-01

    The current operation strategy for using Saltstone Vault 4 to receive 0.2 Ci/gallon salt solution waste involves pouring a clean grout layer over the radioactive grout prior to initiating pour into another cell. This will minimize the radiating surface area and reduce the dose rate at the vault and surrounding area. The Clean Cap will be used to shield about four feet of Saltstone poured into a Z-Area vault cell prior to moving to another cell. The minimum thickness of the Clean Cap layer will be determined by the cesium concentration and resulting dose levels and it is expected to be about one foot thick based on current calculations for 0.1 Ci Saltstone that is produced in the Saltstone process by stabilization of 0.2 Ci salt solution. This report documents experiments performed to identify a formulation for the Clean Cap. Thermal transient calculations, adiabatic temperature rise measurements, pour height, time between pour calculations and shielding calculations were beyond the scope and time limitations of this study. However, data required for shielding calculations (composition and specific gravity) are provided for shielding calculations. The approach used to design a Clean Cap formulation was to produce a slurry from the reference premix (10/45/45 weight percent cement/slag/fly ash) and domestic water that resembled as closely as possible the properties of the Saltstone slurry. In addition, options were investigated that may offer advantages such as less bleed water and less heat generation. The options with less bleed water required addition of dispersants. The options with lower heat contained more fly ash and less slag. A mix containing 10/45/45 weight percent cement/slag/fly ash with a water to premix ratio of 0.60 is recommended for the Clean Cap. Although this mix may generate more than 3 volume percent standing water (bleed water), it has rheological, mixing and flow properties that are similar to previously processed Saltstone. The recommended

  16. Application of polarization ellipse technique for analysis of ULF magnetic fields from two distant stations in Koyna-Warna seismoactive region, West India

    Directory of Open Access Journals (Sweden)

    F. Dudkin

    2010-07-01

    Full Text Available A new approach is developed to find the source azimuth of the ultra low frequency (ULF electromagnetic (EM signals believed to be emanating from well defined seismic zone. The method is test applied on magnetic data procured from the seismoactive region of Koyna-Warna, known for prolonged reservoir triggered seismicity. Extremely low-noise, high-sensitivity LEMI-30 search coil magnetometers were used to measure simultaneously the vector magnetic field in the frequency range 0.001–32 Hz at two stations, the one located within and another ~100 km away from the seismic active zone. During the observation campaign extending from 15 March to 30 June 2006 two earthquakes (EQs of magnitude (ML>4 occurred, which are searched for the presence of precursory EM signals.

    Comparison of polarization ellipses (PE parameters formed by the magnetic field components at the measurement stations, in select frequency bands, allows discrimination of seismo-EM signals from the natural background ULF signals of magnetospheric/ionospheric origin. The magnetic field components corresponding to spectral bands dominated by seismo-EM fields define the PE plane which at any instant contains the source of the EM fields. Intersection lines of such defined PE planes for distant observation stations clutter in to the source region. Approximating the magnetic-dipole configuration for the source, the magnetic field components along the intersection lines suggest that azimuth of the EM source align in the NNW-SSE direction. This direction well coincides with the orientation of nodal plane of normal fault plane mechanism for the two largest EQs recorded during the campaign. More significantly the correspondence of this direction with the tectonic controlled trend in local seismicity, it has been surmised that high pressure fluid flow along the fault that facilitate EQs in the region may also be the source mechanism for EM fields by electrokinetic effect.

  17. FARADAY TOMOGRAPHY OF THE NORTH POLAR SPUR: CONSTRAINTS ON THE DISTANCE TO THE SPUR AND ON THE MAGNETIC FIELD OF THE GALAXY

    Energy Technology Data Exchange (ETDEWEB)

    Sun, X. H.; Gaensler, B. M. [Sydney Institute for Astronomy, School of Physics, The University of Sydney, NSW 2006 (Australia); Landecker, T. L.; Wolleben, M.; Douglas, K. A.; Gray, A. D. [National Research Council Canada, Herzberg Program in Astronomy and Astrophysics, Dominion Radio Astrophysical Observatory, P.O. Box 248, Penticton, British Columbia, V2A 6J9 (Canada); Carretti, E. [CSIRO Astronomy and Space Science, P.O. Box 76, Epping, New South Wales 1710 (Australia); Reich, W. [Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany); Leahy, J. P. [Jodrell Bank Centre for Astrophysics, Alan Turing Building, School of Physics and Astronomy, The University of Manchester, Oxford Road, Manchester M13 9PL (United Kingdom); McClure-Griffiths, N. M.; Crocker, R. M. [Research School of Astronomy and Astrophysics, Australia National University, Cotter Road, Weston Creek, ACT 2611 (Australia); Haverkorn, M., E-mail: X.Sun@physics.usyd.edu.au, E-mail: Tom.Landecker@nrc-cnrc.gc.ca [Department of Astrophysics/IMAPP, Radboud University Nijmegen, P.O. Box 9010, NL-6500 GL Nijmegen (Netherlands)

    2015-09-20

    We present radio continuum and polarization images of the North Polar Spur (NPS) from the Global Magneto-ionic Medium Survey conducted with the Dominion Radio Astrophysical Observatory 26 m Telescope. We fit polarization angle versus wavelength squared over 2048 frequency channels from 1280 to 1750 MHz to obtain a Faraday rotation measure (RM) map of the NPS. Combining this RM map with a published Faraday depth (FD) map of the entire Galaxy in this direction, we derive the FD introduced by the NPS and the Galactic interstellar medium (ISM) in front of and behind the NPS. The FD contributed by the NPS is close to zero, indicating that the NPS is an emitting only feature. The FD caused by the ISM in front of the NPS is consistent with zero at b > 50°, implying that this part of the NPS is local at a distance of approximately several hundred parsecs. The FD contributed by the ISM behind the NPS gradually increases with Galactic latitude up to b = 44°, and decreases at higher Galactic latitudes. This implies that either the part of the NPS at b < 44° is distant or the NPS is local but there is a sign change of the large-scale magnetic field. If the NPS is local, there is then no evidence for a large-scale anti-symmetry pattern in the FD of the Milky Way. The FD introduced by the ISM behind the NPS at latitudes b > 50° can be explained by including a coherent vertical magnetic field.

  18. Spin-polarized structural, elastic, electronic and magnetic properties of half-metallic ferromagnetism in V-doped ZnSe

    Energy Technology Data Exchange (ETDEWEB)

    Monir, M. El Amine.; Baltache, H. [Laboratoire de Physique Quantique de la Matière et de la Modélisation Mathématique (LPQ3M), Faculté des Sciences, Université de Mascara, Mascara 29000 (Algeria); Murtaza, G., E-mail: murtaza@icp.edu.pk [Materials Modeling Lab, Department of Physics, Islamia College University, Peshawar (Pakistan); Khenata, R., E-mail: khenata_rabah@yahoo.fr [Laboratoire de Physique Quantique de la Matière et de la Modélisation Mathématique (LPQ3M), Faculté des Sciences, Université de Mascara, Mascara 29000 (Algeria); Ahmed, Waleed K. [ERU, Faculty of Engineering, United Arab Emirates University, Al Ain (United Arab Emirates); Bouhemadou, A. [Laboratory for Developing New Materials and their Characterization, Department of Physics, Faculty of Science, University of Setif, 19000 Setif (Algeria); Omran, S. Bin [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Seddik, T. [Laboratoire de Physique Quantique de la Matière et de la Modélisation Mathématique (LPQ3M), Faculté des Sciences, Université de Mascara, Mascara 29000 (Algeria)

    2015-01-15

    Based on first principles spin-polarized density functional theory, the structural, elastic electronic and magnetic properties of Zn{sub 1−x}V{sub x}Se (for x=0.25, 0.50, 0.75) in zinc blende structure have been studied. The investigation was done using the full-potential augmented plane wave method as implemented in WIEN2k code. The exchange-correlation potential was treated with the generalized gradient approximation PBE-GGA for the structural and elastic properties. Moreover, the PBE-GGA+U approximation (where U is the Hubbard correlation terms) is employed to treat the “d” electrons properly. A comparative study between the band structures, electronic structures, total and partial densities of states and local moments calculated within both GGA and GGA+U schemes is presented. The analysis of spin-polarized band structure and density of states shows the half-metallic ferromagnetic character and are also used to determine s(p)-d exchange constants N{sub 0}α (conduction band ) and N{sub 0}β (valence band) due to Se(4p)–V(3d) hybridization. It has been clearly evidence that the magnetic moment of V is reduced from its free space change value of 3 µ{sub B} and the minor atomic magnetic moment on Zn and Se are generated. - Highlights: • Half metallicity origins by doping V in ZnSe. • PBE-GGA+U approximation is employed to treat the “d” electrons properly. • s(p)-d Exchange constants N{sub 0}α (conduction band ) and N{sub 0}β (valence band) are due to Se(4p)-V(3d) hybridization.

  19. Polarization Optics

    OpenAIRE

    Fressengeas, Nicolas

    2010-01-01

    The physics of polarization optics *Polarized light propagation *Partially polarized light; DEA; After a brief introduction to polarization optics, this lecture reviews the basic formalisms for dealing with it: Jones Calculus for totally polarized light and Stokes parameters associated to Mueller Calculus for partially polarized light.

  20. Determination of the orientation of the white dwarf's magnetic axis from X-ray orbital light curves

    International Nuclear Information System (INIS)

    Andronov, I.L.

    1986-01-01

    The directional pattern of soft X-ray radiation produced in a ''polar cap'' on the white dwarf's surface is calculated taking into account the absorption in the axially symmetrical accretion column, homogeneous along its height. An algorithm for the determination of orientation of the magnetic axis of a compact star from orbital curves of soft X-ray flux, is suggested. The values of the orbital inclination i (51 deg <=i<64 deg) and the angle between the rotational and magnetic axes σ (30 deg <=σ<=34 deg) were calculated for the polar AM Herculis for different values of model parameters

  1. Optically polarized 3He

    Science.gov (United States)

    Gentile, T. R.; Nacher, P. J.; Saam, B.; Walker, T. G.

    2018-01-01

    This article reviews the physics and technology of producing large quantities of highly spin-polarized 3He nuclei using spin-exchange (SEOP) and metastability-exchange (MEOP) optical pumping. Both technical developments and deeper understanding of the physical processes involved have led to substantial improvements in the capabilities of both methods. For SEOP, the use of spectrally narrowed lasers and K-Rb mixtures has substantially increased the achievable polarization and polarizing rate. For MEOP nearly lossless compression allows for rapid production of polarized 3He and operation in high magnetic fields has likewise significantly increased the pressure at which this method can be performed, and revealed new phenomena. Both methods have benefitted from development of storage methods that allow for spin-relaxation times of hundreds of hours, and specialized precision methods for polarimetry. SEOP and MEOP are now widely applied for spin-polarized targets, neutron spin filters, magnetic resonance imaging, and precision measurements. PMID:29503479

  2. Optically polarized 3He

    Science.gov (United States)

    Gentile, T. R.; Nacher, P. J.; Saam, B.; Walker, T. G.

    2017-10-01

    This article reviews the physics and technology of producing large quantities of highly spin-polarized 3He nuclei using spin-exchange (SEOP) and metastability-exchange (MEOP) optical pumping. Both technical developments and deeper understanding of the physical processes involved have led to substantial improvements in the capabilities of both methods. For SEOP, the use of spectrally narrowed lasers and K-Rb mixtures has substantially increased the achievable polarization and polarizing rate. For MEOP nearly lossless compression allows for rapid production of polarized 3He and operation in high magnetic fields has likewise significantly increased the pressure at which this method can be performed, and revealed new phenomena. Both methods have benefitted from development of storage methods that allow for spin-relaxation times of hundreds of hours, and specialized precision methods for polarimetry. SEOP and MEOP are now widely applied for spin-polarized targets, neutron spin filters, magnetic resonance imaging, and precision measurements.

  3. Method for removing strongly adsorbed surfactants and capping agents from metal to facilitate their catalytic applications

    Science.gov (United States)

    Adzic, Radoslav R.; Gong, Kuanping; Cai, Yun; Wong, Stanislaus; Koenigsmann, Christopher

    2016-11-08

    A method of synthesizing activated electrocatalyst, preferably having a morphology of a nanostructure, is disclosed. The method includes safely and efficiently removing surfactants and capping agents from the surface of the metal structures. With regard to metal nanoparticles, the method includes synthesis of nanoparticle(s) in polar or non-polar solution with surfactants or capping agents and subsequent activation by CO-adsorption-induced surfactant/capping agent desorption and electrochemical oxidation. The method produces activated macroparticle or nanoparticle electrocatalysts without damaging the surface of the electrocatalyst that includes breaking, increasing particle thickness or increasing the number of low coordination sites.

  4. Electron - polar acoustical phonon interactions in nitride based diluted magnetic semiconductor quantum well via hot electron magnetotransport

    International Nuclear Information System (INIS)

    Pandya, Ankur; Shinde, Satyam; Jha, Prafulla K.

    2015-01-01

    In this paper the hot electron transport properties like carrier energy and momentum scattering rates and electron energy loss rates are calculated via interactions of electrons with polar acoustical phonons for Mn doped BN quantum well in BN nanosheets via piezoelectric scattering and deformation potential mechanisms at low temperatures with high electric field. Electron energy loss rate increases with the electric field. It is observed that at low temperatures and for low electric field the phonon absorption is taking place whereas, for sufficient large electric field, phonon emission takes place. Under the piezoelectric (polar acoustical phonon) scattering mechanism, the carrier scattering rate decreases with the reduction of electric field at low temperatures wherein, the scattering rate variation with electric field is limited by a specific temperature beyond which there is no any impact of electric field on such scattering

  5. Polarization dependence of the magnetic fluctuations in the weak itinerant ferromagnet MnSi below T{sub c}

    Energy Technology Data Exchange (ETDEWEB)

    Boeni, P.; Tixier, S. [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Endoh, Y. [Tohoku Univ., Sendai (Japan); Roessli, B. [Institut Max von Laue - Paul Langevin, 75 - Paris (France); Shirane, G. [Brookhaven (United States)

    1997-09-01

    The dispersion of the spin-flip and non-spin-flip excitations in the weak itinerant ferromagnet MnSi have been measured in the ferromagnetic phase using inelastic polarized neutron scattering. Spin wave excitations are well defined at energy transfers as large as 7 meV. The cross section of the non-spin-flip excitations is compatible with a quasielastic response function. (author) 2 figs., 3 refs.

  6. Comprehensive analysis of polar and apolar constituents of butter and margarine by nuclear magnetic resonance, reflecting quality and production processes.

    Science.gov (United States)

    Schripsema, Jan

    2008-04-23

    The separation of butter or margarine into polar (soluble in water) and apolar fractions (soluble in chloroform) and subsequent analysis of these fractions by (1)H NMR permits a comprehensive analysis of its constituents. In the polar fraction the preservatives benzoic and sorbic acid, the organic acids citric, lactic, butyric, acetic, and formic acid, and, furthermore, the carbohydrate lactose were quantified. In the apolar fraction the conjugated linoleic acid (CLA) rumenic acid, diglycerides, and linoleic acid were quantified. Rumenic acid is a characteristic component of ruminant fats and was found in all butter samples. The levels varied between 0.50 and 1.08%. Ten brands of Brazilian butter were investigated as was one brand from Norway. Also, two brands of margarine were investigated for comparison. A large variation in especially polar constituents was found between the butter samples, revealing the presence of preservatives in five brands of butter from Brazil, remarkable because these additives are legally not allowed. Furthermore, the levels of organic acids and lactose permitted conclusions about the production process and quality; for example, the presence of higher levels of free butyric acid indicate lipolysis, leading to a lower quality, and low levels of lactose indicate that after churning the residual milk fluids have been removed by an additional washing step in the production process.

  7. [Review] Polarization and Polarimetry

    Science.gov (United States)

    Trippe, Sascha

    2014-02-01

    Polarization is a basic property of light and is fundamentally linked to the internal geometry of a source of radiation. Polarimetry complements photometric, spectroscopic, and imaging analyses of sources of radiation and has made possible multiple astrophysical discoveries. In this article I review (i) the physical basics of polarization: electromagnetic waves, photons, and parameterizations; (ii) astrophysical sources of polarization: scattering, synchrotron radiation, active media, and the Zeeman, Goldreich-Kylafis, and Hanle effects, as well as interactions between polarization and matter (like birefringence, Faraday rotation, or the Chandrasekhar-Fermi effect); (iii) observational methodology: on-sky geometry, influence of atmosphere and instrumental polarization, polarization statistics, and observational techniques for radio, optical, and X/γ wavelengths; and (iv) science cases for astronomical polarimetry: solar and stellar physics, planetary system bodies, interstellar matter, astrobiology, astronomical masers, pulsars, galactic magnetic fields, gamma-ray bursts, active galactic nuclei, and cosmic microwave background radiation.

  8. Electron's anomalous magnetic-moment effects on electron-hydrogen elastic collisions in the presence of a circularly polarized laser field

    International Nuclear Information System (INIS)

    Elhandi, S.; Taj, S.; Attaourti, Y.; Manaut, B.; Oufni, L.

    2010-01-01

    The effect of the electron's anomalous magnetic moment on the relativistic electronic dressing for the process of electron-hydrogen atom elastic collisions is investigated. We consider a laser field with circular polarization and various electric field strengths. The Dirac-Volkov states taking into account this anomaly are used to describe the process in the first order of perturbation theory. The correlation between the terms coming from this anomaly and the electric field strength gives rise to the strong dependence of the spinor part of the differential cross section (DCS) with respect to these terms. A detailed study has been devoted to the nonrelativistic regime as well as the moderate relativistic regime. Some aspects of this dependence as well as the dynamical behavior of the DCS in the relativistic regime have been addressed.

  9. Selectable spontaneous polarization direction and magnetic anisotropy in BiFeO3-CoFe2O4 epitaxial nanostructures.

    Science.gov (United States)

    Dix, Nico; Muralidharan, Rajaram; Rebled, Jose-Manuel; Estradé, Sonia; Peiró, Francesca; Varela, Manuel; Fontcuberta, Josep; Sánchez, Florencio

    2010-08-24

    We demonstrate that epitaxial strain engineering is an efficient method to manipulate the ferromagnetic and ferroelectric properties in BiFeO(3)-CoFe(2)O(4) columnar nanocomposites. On one hand, the magnetic anisotropy of CoFe(2)O(4) is totally tunable from parallel to perpendicular controlling the CoFe(2)O(4) strain with proper combinations of substrate and ferroelectric phase. On the other hand, the selection of the used substrate allows the growth of the rhombohedral bulk phase of BiFeO(3) or the metastable nearly tetragonal one, which implies a rotation of the ferroelectric polar axis from [111] to close to the [001] direction. Remarkably, epitaxy is preserved and interfaces are semicoherent even when lattice mismatch is above 10%. The broad range of sustainable mismatch suggests new opportunities to assemble epitaxial nanostructures combining highly dissimilar materials with distinct functionalities.

  10. Facility for low-temperature spin-polarized-scanning tunneling microscopy studies of magnetic/spintronic materials prepared in situ by nitride molecular beam epitaxy.

    Science.gov (United States)

    Lin, Wenzhi; Foley, Andrew; Alam, Khan; Wang, Kangkang; Liu, Yinghao; Chen, Tianjiao; Pak, Jeongihm; Smith, Arthur R

    2014-04-01

    Based on the interest in, as well as exciting outlook for, nitride semiconductor based structures with regard to electronic, optoelectronic, and spintronic applications, it is compelling to investigate these systems using the powerful technique of spin-polarized scanning tunneling microscopy (STM), a technique capable of achieving magnetic resolution down to the atomic scale. However, the delicate surfaces of these materials are easily corrupted by in-air transfers, making it unfeasible to study them in stand-alone ultra-high vacuum STM facilities. Therefore, we have carried out the development of a hybrid system including a nitrogen plasma assisted molecular beam epitaxy/pulsed laser epitaxy facility for sample growth combined with a low-temperature, spin-polarized scanning tunneling microscope system. The custom-designed molecular beam epitaxy growth system supports up to eight sources, including up to seven effusion cells plus a radio frequency nitrogen plasma source, for epitaxially growing a variety of materials, such as nitride semiconductors, magnetic materials, and their hetero-structures, and also incorporating in situ reflection high energy electron diffraction. The growth system also enables integration of pulsed laser epitaxy. The STM unit has a modular design, consisting of an upper body and a lower body. The upper body contains the coarse approach mechanism and the scanner unit, while the lower body accepts molecular beam epitaxy grown samples using compression springs and sample skis. The design of the system employs two stages of vibration isolation as well as a layer of acoustic noise isolation in order to reduce noise during STM measurements. This isolation allows the system to effectively acquire STM data in a typical lab space, which during its construction had no special and highly costly elements included, (such as isolated slabs) which would lower the environmental noise. The design further enables tip exchange and tip coating without

  11. Facility for low-temperature spin-polarized-scanning tunneling microscopy studies of magnetic/spintronic materials prepared in situ by nitride molecular beam epitaxy

    International Nuclear Information System (INIS)

    Lin, Wenzhi; Foley, Andrew; Alam, Khan; Wang, Kangkang; Liu, Yinghao; Chen, Tianjiao; Pak, Jeongihm; Smith, Arthur R.

    2014-01-01

    Based on the interest in, as well as exciting outlook for, nitride semiconductor based structures with regard to electronic, optoelectronic, and spintronic applications, it is compelling to investigate these systems using the powerful technique of spin-polarized scanning tunneling microscopy (STM), a technique capable of achieving magnetic resolution down to the atomic scale. However, the delicate surfaces of these materials are easily corrupted by in-air transfers, making it unfeasible to study them in stand-alone ultra-high vacuum STM facilities. Therefore, we have carried out the development of a hybrid system including a nitrogen plasma assisted molecular beam epitaxy/pulsed laser epitaxy facility for sample growth combined with a low-temperature, spin-polarized scanning tunneling microscope system. The custom-designed molecular beam epitaxy growth system supports up to eight sources, including up to seven effusion cells plus a radio frequency nitrogen plasma source, for epitaxially growing a variety of materials, such as nitride semiconductors, magnetic materials, and their hetero-structures, and also incorporating in situ reflection high energy electron diffraction. The growth system also enables integration of pulsed laser epitaxy. The STM unit has a modular design, consisting of an upper body and a lower body. The upper body contains the coarse approach mechanism and the scanner unit, while the lower body accepts molecular beam epitaxy grown samples using compression springs and sample skis. The design of the system employs two stages of vibration isolation as well as a layer of acoustic noise isolation in order to reduce noise during STM measurements. This isolation allows the system to effectively acquire STM data in a typical lab space, which during its construction had no special and highly costly elements included, (such as isolated slabs) which would lower the environmental noise. The design further enables tip exchange and tip coating without

  12. True Polar Wander and Hotspot Fixity: A Paleomagnetic Investigation of the Skewness of Magnetic Anomaly 12r (32 Ma B.P.) on the Pacific Plate

    Science.gov (United States)

    Gordon, R. G.; Horner-Johnson, B. C.

    2010-12-01

    Prior studies have shown that Pacific hotspots and Indo-Atlantic hotspots have moved in approximate unison relative to the spin axis since 65 Ma B.P. [Morgan, 1981; Gordon and Cape, 1981; Gordon, 1982] and since 56 Ma B.P. [Petronotis et al., 1994], which is most simply interpreted as true polar wander. In contrast, Pacific hotspots and Indo-Atlantic hotspots give conflicting results for 72 Ma B.P. and for 81 Ma B.P., which may indicate motion between Pacific hotspots and Indo-Atlantic hotspots [Tarduno and Cottrell, 1997; Petronotis et al., 1999; Tarduno et al., 2003]. Thus it is important to estimate Pacific plate apparent polar wander (APW) for more time intervals. From such estimates the APW of Pacific hotspots can be inferred and compared with that of Indo-Atlantic hotspots [e.g., Besse and Courtillot 2002]. Here we present a study of the skewness of anomaly 12r between the Galapagos and Clipperton and between the Clipperton and Clarion fracture zones. We chose this region for several reasons: First, numerical experiments, like those conducted by Acton and Gordon [1991], indicate that magnetic profiles between the Galapagos and Clarion fracture zones should contain the most information about the Pacific plate paleomagnetic pole for chron C12r (32 Ma B.P.). Second, in these two spreading rate corridors, spreading half rates range from 72 to 86 mm/a and therefore have negligible anomalous skewness, given that they exceed ≈50 mm/a [Roest et al., 1992; Dyment et al. 1994]. Third, vector aeromagnetic profiles are available for analysis. One of the challenges to interpreting magnetic anomalies in low latitudes where the anomalies strike nearly north-south is the very low amplitude of the signal relative to the noise, the latter of which can be especially intense near the present magnetic equator due to the amplification of diurnal variation by the equatorial electrojet. Previously we showed that vector aeromagnetic profiles record low-latitude Pacific plate

  13. Magnets

    International Nuclear Information System (INIS)

    Young, I.R.

    1984-01-01

    A magnet pole piece for an NMR imaging magnet is made of a plurality of magnetic wires with one end of each wire held in a non-magnetic spacer, the other ends of the wires being brought to a pinch, and connected to a magnetic core. The wires may be embedded in a synthetic resin and the magnetisation and uniformity thereof can be varied by adjusting the density of the wires at the spacer which forms the pole piece. (author)

  14. Polarized radial magnetic fields and outward plasma fluxes during shallow-reversal discharges in the ZT-40M reversed-field pinch

    International Nuclear Information System (INIS)

    Jacobson, A.R.; Rusbridge, M.G.; Burkhardt, L.C.

    1984-01-01

    The characteristics of edge-region electromagnetic disturbances and of pulsed radial fluxes of plasma to the liner as well as the detailed interrelationship among these processes have been studied on the ZT-40M reversed-field pinch in its normal, shallow-reversal operating regime. The dominant magnetic disturbances are spiky (pulsewidth approx.5--10 μs) low-amplitude (Vertical BarB/sub r//B/sub theta/Vertical Bar -2 )= poloidally symmetric radial-field structures intersecting the vacuum wall and precessing toroidally in the anti-I/sub phi/ sense. The effect of even slight toroidal-field reversal (Vertical BarB/sub phi/(a)Vertical Barroughly-equalB/sub theta/(a)/10) is to polarize these radial-field spikes preferentially positive (i.e., B/sub r/>0) and to increase the speed of the minority (B/sub r/ 0) spikes. Synchronous with the polarized B/sub r/ spikes are intense radially outward fluxes of plasma (instantaneously > or approx. =10 22 m -2 s -1 ) leading to recurrent, large amplitude (Vertical BarΔn/n> or approx. =25%) depletion of the density in the outer quarter of minor radius. The resulting time-averaged global loss-rate per particle is significant (approx.10 3 s -1 )

  15. Spherical polar co-ordinate calculations of induced fields in the retina and head for applied magnetic fields at 50 Hz

    Energy Technology Data Exchange (ETDEWEB)

    Dimbylow, Peter, E-mail: peter.dimbylow@hpa.org.uk [Health Protection Agency, Chilton, Didcot, Oxon OX11 0RQ (United Kingdom)

    2011-07-21

    This paper sets out to explore the effects of voxel resolution, from 2 mm down to 0.1 mm for Cartesian co-ordinates and the differences between Cartesian and spherical polar co-ordinates for a standardized test-bed model of the eye. This model was taken from the work of Yoriyaz et al (2005 Radiat. Prot. Dosim. 115 316-9) who have developed a detailed geometric description of the eye including choroid, retina, sclera, lens, cornea, anterior chamber, vitreous humour and optic nerve for ophthalmic brachytherapy. The spherical co-ordinate model has radial and angular steplengths of 0.1 mm and 0.25{sup 0}, respectively. The current density averaged over 1 cm{sup 2} and the 99th percentile value of the induced electric field have been calculated in the retina and central nervous system for uniform magnetic fields. The Cartesian co-ordinate calculations proceed in a sequence of grids at 2, 1, 0.5, 0.2 and 0.1 mm resolution with the potentials from the previous calculation at a coarser grid providing the boundary conditions on the finer grid. The 0.2 mm grid provides the boundary conditions for the spherical polar calculations. Comparisons are made with the International Commission on Non-Ionizing Radiation Protection reference levels.

  16. Spherical polar co-ordinate calculations of induced fields in the retina and head for applied magnetic fields at 50 Hz.

    Science.gov (United States)

    Dimbylow, Peter

    2011-07-21

    This paper sets out to explore the effects of voxel resolution, from 2 mm down to 0.1 mm for Cartesian co-ordinates and the differences between Cartesian and spherical polar co-ordinates for a standardized test-bed model of the eye. This model was taken from the work of Yoriyaz et al (2005 Radiat. Prot. Dosim. 115 316-9) who have developed a detailed geometric description of the eye including choroid, retina, sclera, lens, cornea, anterior chamber, vitreous humour and optic nerve for ophthalmic brachytherapy. The spherical co-ordinate model has radial and angular steplengths of 0.1 mm and 0.25°, respectively. The current density averaged over 1 cm(2) and the 99th percentile value of the induced electric field have been calculated in the retina and central nervous system for uniform magnetic fields. The Cartesian co-ordinate calculations proceed in a sequence of grids at 2, 1, 0.5, 0.2 and 0.1 mm resolution with the potentials from the previous calculation at a coarser grid providing the boundary conditions on the finer grid. The 0.2 mm grid provides the boundary conditions for the spherical polar calculations. Comparisons are made with the International Commission on Non-Ionizing Radiation Protection reference levels.

  17. Spherical polar co-ordinate calculations of induced fields in the retina and head for applied magnetic fields at 50 Hz

    International Nuclear Information System (INIS)

    Dimbylow, Peter

    2011-01-01

    This paper sets out to explore the effects of voxel resolution, from 2 mm down to 0.1 mm for Cartesian co-ordinates and the differences between Cartesian and spherical polar co-ordinates for a standardized test-bed model of the eye. This model was taken from the work of Yoriyaz et al (2005 Radiat. Prot. Dosim. 115 316-9) who have developed a detailed geometric description of the eye including choroid, retina, sclera, lens, cornea, anterior chamber, vitreous humour and optic nerve for ophthalmic brachytherapy. The spherical co-ordinate model has radial and angular steplengths of 0.1 mm and 0.25 0 , respectively. The current density averaged over 1 cm 2 and the 99th percentile value of the induced electric field have been calculated in the retina and central nervous system for uniform magnetic fields. The Cartesian co-ordinate calculations proceed in a sequence of grids at 2, 1, 0.5, 0.2 and 0.1 mm resolution with the potentials from the previous calculation at a coarser grid providing the boundary conditions on the finer grid. The 0.2 mm grid provides the boundary conditions for the spherical polar calculations. Comparisons are made with the International Commission on Non-Ionizing Radiation Protection reference levels.

  18. Dynamics of a quasiparticle in the α-T3 model: Role of pseudospin polarization and transverse magnetic field on zitterbewegung.

    Science.gov (United States)

    Biswas, Tutul; Ghosh, Tarun Kanti

    2018-01-09

    We consider the $\\alpha$-$T_3$ model which provides a smooth crossover between the honeycomb lattice with pseudospin $1/2$ and the dice lattice with pseudospin $1$ through the variation of a parameter $\\alpha$. We study the dynamics of a wave packet representing a quasiparticle in the $\\alpha$-T$_3$ model with zero and finite transverse magnetic field. For zero field, it is shown that the wave packet undergoes a transient $zitterbewegung$ (ZB). Various features of ZB depending on the initial pseudospin polarization of the wave packet have been revealed. For an intermediate value of the parameter $\\alpha$ i.e. for $0<\\alpha<1$ the resulting ZB consists of two distinct frequencies when the wave packet was located initially in $rim$ site. However, the wave packet exhibits single frequency ZB for $\\alpha=0$ and $\\alpha=1$. It is also unveiled that the frequency of ZB corresponding to $\\alpha=1$ gets exactly half of that corresponding to the $\\alpha=0$ case. On the other hand, when the initial wave packet was in $hub$ site, the ZB consists of only one frequency for all values of $\\alpha$. Using stationary phase approximation we find analytical expression of velocity average which can be used to extract the associated timescale over which the transient nature of ZB persists. On the contrary the wave packet undergoes permanent ZB in presence of a transverse magnetic field. Due to the presence of large number of Landau energy levels the oscillations in ZB appear to be much more complicated. The oscillation pattern depends significantly on the initial pseudospin polarization of the wave packet. Furthermore, it is revealed that the number of the frequency components involved in ZB depends on the parameter $\\alpha$. © 2018 IOP Publishing Ltd.

  19. ATLAS end-cap detector

    CERN Multimedia

    Maximilien Brice

    2003-01-01

    Three scientists from the Institute of Nuclear Phyiscs at Novossibirsk with one of the end-caps of the ATLAS detector. The end-caps will be used to detect particles produced in the proton-proton collisions at the heart of the ATLAS experiment that are travelling close to the axis of the two beams.

  20. Cu–Ni core–shell nanoparticles: structure, stability, electronic, and magnetic properties: a spin-polarized density functional study

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Qiang, E-mail: wangqiang@njtech.edu.cn; Wang, Xinyan; Liu, Jianlan; Yang, Yanhui [Nanjing Tech University, School of Chemistry and Molecular Engineering, Institute of Advanced Synthesis (IAS) (China)

    2017-02-15

    Bimetallic core–shell nanoparticles (CSNPs) have attracted great interest not only because of their superior stability, selectivity, and catalytic activity but also due to their tunable properties achieved by changing the morphology, sequence, and sizes of both core and shell. In this study, the structure, stability, charge transfer, electronic, and magnetic properties of 13-atom and 55-atom Cu and Cu–Ni CSNPs were investigated using the density functional theory (DFT) calculations. The results show that Ni@Cu CSNPs with a Cu surface shell are more energetically favorable than Cu@Ni CSNPs with a Ni surface shell. Interestingly, three-shell Ni@Cu{sub 12}@Ni{sub 42} is more stable than two-shell Cu{sub 13}@Ni{sub 42}, while two-shell Ni{sub 13}@Cu{sub 42} is more stable than three-shell Cu@Ni{sub 12}@Cu{sub 42}. Analysis of Bader charge illustrates that the charge transfer increases from Cu core to Ni shell in Cu@Ni NPs, while it decreases from Ni core to Cu shell in Ni@Cu NPs. Furthermore, the charge transfer results that d-band states have larger shift toward the Fermi level for the Ni@Cu CSNPs with Cu surface shell, while the Cu@Ni CSNPs with Ni surface shell have similar d-band state curves and d-band centers with the monometallic Ni NPs. In addition, the Cu–Ni CSNPs possess higher magnetic moment when the Ni atoms aggregated at core region of CSNPs, while having lower magnetic moment when the Ni atoms segregate on surface region. The change of the Cu atom location in CSNPs has a weak effect on the total magnetic moment. Our findings provide useful insights for the design of bimetallic core–shell catalysts.

  1. Investigation of magnetic mesostructure of (Pd{sub 0.984}Fe{sub 0.016}){sub 0.95}Mn{sub 0.05} alloy by polarized neutrons

    Energy Technology Data Exchange (ETDEWEB)

    Gordeev, G. [Petersburg Nuclear Physics Institute RAS, 188300 Gatchina, St. Petersburg (Russian Federation)]. E-mail: ggordev@pnpi.spb.ru; Zabenkin, V. [Petersburg Nuclear Physics Institute RAS, 188300 Gatchina, St. Petersburg (Russian Federation); Axelrod, L. [Petersburg Nuclear Physics Institute RAS, 188300 Gatchina, St. Petersburg (Russian Federation); Lazebnik, I. [Petersburg Nuclear Physics Institute RAS, 188300 Gatchina, St. Petersburg (Russian Federation); Wagner, V. [Physikalish-Technishe Bundesanstalt D-38116, Braunschweig (Germany); Eckerlebe, H. [Forschung Zentrum GKSS, Geesthacht (Germany)

    2007-07-15

    Neutron depolarization measurements and a simple model for depolarization were used to determine the geometrical sizes of magnetic inhomogeneities in the (Pd{sub 0.984}Fe{sub 0.016}){sub 0.95}Mn{sub 0.05} alloy. Polarized small angle scattering shows an asymmetric part, which should be attributed to a chiral ordering of the spins.

  2. Hyperfine fields in a Ag/Fe magnetic multilayer probed with low energy spin polarized {sup 8}Li

    Energy Technology Data Exchange (ETDEWEB)

    Keeler, T.A. [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada); Salman, Z. [TRIUMF, 4004 Wesbrook Mall, Vancouver, V6T 2A3 (Canada); Chow, K.H. [Department of Physics, University of Alberta, Edmonton, AB, T6G 2J1 (Canada); Heinrich, B. [Department of Physics, Simon Fraser University, Vancouver, BC (Canada); Hossain, M.D. [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada); Kardasz, B. [Department of Physics, Simon Fraser University, Vancouver, BC (Canada); Kiefl, R.F. [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada)]. E-mail: kiefl@triumf.ca; Kreitzman, S.R. [TRIUMF, 4004 Wesbrook Mall, Vancouver, V6T 2A3 (Canada); MacFarlane, W.A. [Department of Chemistry, University of British Columbia, Vancouver, V6T 1Z1 (Canada); Mosendz, O. [Department of Physics, Simon Fraser University, Vancouver, BC (Canada); Parolin, T.J. [Department of Chemistry, University of British Columbia, Vancouver, V6T 1Z1 (Canada); Wang, D. [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada)

    2006-03-31

    A beam of low energy Li8 has been used to probe the hyperfine field distribution in a magnetic multilayer composed of Au(4nm)/Ag(80nm)/Fe(2nm) grown on a GaAs substrate. The {beta}-NMR frequency spectrum is shown to be a strong function of the implantation energy reflecting the depth dependence of the local hyperfine fields. Correlating the spectra with TRIM.SP implantation profiles allows us to identify signals from the GaAs, Ag and Au layers. The frequency spectrum in Ag is a strong function of energy. A very narrow line, and corresponding distribution of hyperfine fields, is observed when the beam in centered well away from the Fe whereas a much broader distribution is observed when the Li stops close to the Fe. These results demonstrate that low energy {beta}-NMR can act as a sensitive probe of the induced magnetism in the otherwise non-magnetic Ag spacer layers.

  3. Dispersive changes in magnetic background noise polarization at 0.1 to 6Hz during sunset and sunrise at L=1.3

    Directory of Open Access Journals (Sweden)

    T. Bösinger

    2004-06-01

    Full Text Available Polarization properties of the magnetic background noise (MBN and the spectral resonance structure (SRS of the ionospheric Alfvén resonator (IAR below the first Schumann resonance but above 0.1 Hz are measured by a sensitive pulsation magnetometer at the island of Crete (L=1.3 and analyzed using the existing SRS theory by Belyaev et al. (1989b. The focus of the paper is on the systematic changes in the MBN and SRS properties associated with the transition from a sunlit to a dark ionosphere (sunset and vice versa (sunrise. We are able to pinpoint in observations an E-region and F-region terminator effect and to simulate it by means of a simple ionosphere model, implying the formalism given by Belyaev et al. (1989b. The E-region terminator effect is associated with an apparent control for the SRS presence or absence with no clear frequency dispersion in polarization properties, whereas the F-region terminator effect exhibits strong frequency dispersion, especially in the low frequency range. This yields a change in the ellipticity of MBN, starting as early as 2 to 3h ahead of the "zero-line" of the terminator. In a 24h presentation of the ellipticity versus frequency and time, the sunrise/sunset effect produces a sharp, dispersive boundary between night and day (day and night. Only inside this boundary, during the night hours, is SRS observed, at times accompanied by a large quasi-periodic long period modulation in the azimuthal angle of the major axis of the polarization ellipse. Attention is also paid to peculiarities in the low frequency range (~0.1Hz, where especially large changes in the polarization properties occur in association with the passage of the terminator. The F-region effect is very distinct and well reproduced by our simple model. Changes in the azimuth associated with the E-region terminator effect are of the order of 20°.

  4. Dispersive changes in magnetic background noise polarization at 0.1 to 6Hz during sunset and sunrise at L=1.3

    Directory of Open Access Journals (Sweden)

    T. Bösinger

    2004-06-01

    Full Text Available Polarization properties of the magnetic background noise (MBN and the spectral resonance structure (SRS of the ionospheric Alfvén resonator (IAR below the first Schumann resonance but above 0.1 Hz are measured by a sensitive pulsation magnetometer at the island of Crete (L=1.3 and analyzed using the existing SRS theory by Belyaev et al. (1989b. The focus of the paper is on the systematic changes in the MBN and SRS properties associated with the transition from a sunlit to a dark ionosphere (sunset and vice versa (sunrise. We are able to pinpoint in observations an E-region and F-region terminator effect and to simulate it by means of a simple ionosphere model, implying the formalism given by Belyaev et al. (1989b. The E-region terminator effect is associated with an apparent control for the SRS presence or absence with no clear frequency dispersion in polarization properties, whereas the F-region terminator effect exhibits strong frequency dispersion, especially in the low frequency range. This yields a change in the ellipticity of MBN, starting as early as 2 to 3h ahead of the "zero-line" of the terminator. In a 24h presentation of the ellipticity versus frequency and time, the sunrise/sunset effect produces a sharp, dispersive boundary between night and day (day and night. Only inside this boundary, during the night hours, is SRS observed, at times accompanied by a large quasi-periodic long period modulation in the azimuthal angle of the major axis of the polarization ellipse. Attention is also paid to peculiarities in the low frequency range (~0.1Hz, where especially large changes in the polarization properties occur in association with the passage of the terminator. The F-region effect is very distinct and well reproduced by our simple model. Changes in the azimuth associated with the E-region terminator effect are of the order of 20°.

  5. Spin dynamics and magnetic field induced polarization of excitons in ultrathin GaAs/AlAs quantum wells with indirect band gap and type-II band alignment

    Science.gov (United States)

    Shamirzaev, T. S.; Rautert, J.; Yakovlev, D. R.; Debus, J.; Gornov, A. Yu.; Glazov, M. M.; Ivchenko, E. L.; Bayer, M.

    2017-07-01

    The exciton spin dynamics are investigated both experimentally and theoretically in two-monolayer-thick GaAs/AlAs quantum wells with an indirect band gap and a type-II band alignment. The magnetic field induced circular polarization of photoluminescence Pc is studied as function of the magnetic field strength and direction as well as sample temperature. The observed nonmonotonic behavior of these functions is provided by the interplay of bright and dark exciton states contributing to the emission. To interpret the experiment, we have developed a kinetic master equation model which accounts for the dynamics of the spin states in this exciton quartet, radiative and nonradiative recombination processes, and redistribution of excitons between these states as result of spin relaxation. The model offers quantitative agreement with experiment and allows us to evaluate, for the studied structure, the heavy-hole g factor, gh h=+3.5 , and the spin relaxation times of electron, τs e=33 μ s , and hole, τs h=3 μ s , bound in the exciton.

  6. Good Regulatory Lags for Price Cap and Rolling Cap contracts

    OpenAIRE

    Jose Luis Lima R; Andres Gomez Lobo

    2004-01-01

    Price caps are a popular form of monopoly price regulation. One of its disadvantages is the perverse incentives that regulated firms might have to scamp on cost reducing effort during the last years before a price review. In order to avoid this problem a “rolling cap†contract was introduced in the United Kingdom that overcomes this last problem. In spite of their popularity, there is scant research on the optimal regulatory lag (number of years between price reviews) of a price cap or rol...

  7. Adsorption and magnetism of bilayer graphene on the MnO polar surface with oxygen vacancies in the interface: First principles study

    Science.gov (United States)

    Ilyasov, Victor V.; Ershov, Igor V.; Popova, Inna G.; Pham, Khang D.; Nguyen, Chuong V.

    2018-05-01

    In this paper, we investigate systematically the structural, electronic, magnetic and adsorption properties of Bernal-stacked bilayer graphene on MnO(111) surface terminated by an oxygen atom, as a function of nonstoichiometric composition of the BLG/MnOx(111) interface. For additional functionalization of the BLG/MnOx(111) system, we also studied the adsorption properties of oxygen adsorbed on the BLG/MnOx(111) interface. Our results showed that the BLG is bound to the MnOx(111) substrate by the weak interaction for both spin-up and spin-down. Furthermore, we found that BLG adsorbed on the MnOx(111) substrate with a reduced oxygen symmetry in the interface is accompanied with a downshift of the Fermi level, which identifies the band structure of BLG as a p-type semiconductor. Upon interaction between BLG and MnOx(111) substrate, a forbidden gap of about 350 meV was opened between its bonding and antibonding π bands. A forbidden gap and the local magnetic moments in bilayer graphene can be controlled by changing the oxygen nonstoichometry or by oxygen adsorption. Additionally, magnetism has been predicted in the bilayer graphene adsorbed on the polar MnOx(111) surface with oxygen vacancies in the BLG/MnOx(111) interface, and its nature has also been discussed in this work. These results showed that the adsorption of bilayer graphene on the MnO(111) substrate can be used for developing novel generation of electronic and spintronic devices.

  8. Physics of polarized targets

    CERN Document Server

    Niinikoski, Tapio

    2014-01-01

    For developing, building and operating solid polarized targets we need to understand several fields of physics that have seen sub stantial advances during the last 50 years. W e shall briefly review a selection of those that are important today. These are: 1) quantum statistical methods to describe saturation and relaxation in magnetic resonance; 2) equal spin temperature model for dy namic nuclear polarization; 3 ) weak saturation during NMR polarization measurement; 4 ) refrigeration using the quantum fluid properties of helium isotopes. These, combined with superconducting magnet technologies, permit today to reach nearly complete pola rization of almost any nuclear spins. Targets can be operated in frozen spin mode in rather low and inhomogeneous field of any orientation, and in DNP mode in beams of high intensity. Beyond such experiments of nuclear and particle physics, applications a re also emerging in macromolecular chemistry and in magnetic resonance imaging. This talk is a tribute to Michel Borghini...

  9. 3D inversion of magnetic and electrical resistivity-induced polarization data for an epithermal Au-Ag and underlying porphyry deposit: A case study from British Columbia, Canada

    Science.gov (United States)

    Abbassi, B.; Huebert, J.; Liu, L.; Lee, B.; Cheng, L.; Richards, J. P.; Unsworth, M. J.; Oldenburg, D.

    2013-12-01

    The Newton property is an epithermal Au-Ag deposit containing precious metals in association with disseminated sulfide minerals such as pyrite. This type of deposit often shows variable geological patterns, so it is important to find fast and cost-efficient methods for their exploration. Aeromagnetic surveys and ground electrical resistivity-induced polarization methods were applied over the Newton property. From preliminary 3D inversion of ZTEM and aeromagnetic data, and joint 3D inversion of electrical resistivity-induced polarization data, we show that low-resistivity and high-chargeability regions are signatures of disseminated sulfide mineralization. Potassic alteration, characterized by hydrothermal biotite (now mostly chloritized) and magnetite is also present locally, and may be related to underlying porphyry-type mineralization. This type of alteration can be identified from its magnetic signature, but the occurrence of other magnetic formations in the deposit area made interpretations of magnetic data difficult. We show that filtering geological noises related to background magnetic anomalies is an essential step in focusing on potassic alteration zones. We used electrical resistivity and induced polarization chargeability models to remove the signals of barren magnetic zones to focus on the susceptibilities pertaining to deep potassic alterations. In order to test the credibility of these interpretations, extensive petrophysical measurements (magnetic susceptibility, electrical resistivity, and gamma ray spectra) were collected on drill-core samples. We show that potassic alteration can also be characterized accurately from high levels of potassium to thorium ratio (K/Th) in gamma ray spectrometric measurements, and that this correlation is stronger than the magnetic signal (likely because hydrothermal magnetite is variable in abundance). Therefore, we focused on magnetic susceptibility values correlated with high K/Th ratios in order to reduce the

  10. Polarization at the SLC

    Energy Technology Data Exchange (ETDEWEB)

    Moffeit, K.C.

    1988-10-01

    The Stanford Linear collider was designed to accommodate polarized electron beams. Longitudinally polarized electrons colliding with unpolarized positrons at a center of mass energy near the Z/sup 0/ mass can be used as novel and sensitive probes of the electroweak process. A gallium arsenide based photon emission source will provide a beam of longitudinally polarized electrons of about 45 percent polarization. A system of bend magnets and a superconducting solenoid will be used to rotate the spins so that the polarization is preserved while the 1.21 GeV electrons are stored in the damping ring. Another set of bend magnets and two superconducting solenoids orient the spin vectors so that longitudinal polarization of the electrons is achieved at the collision point with the unpolarized positrons. A system to monitor the polarization based on Moller and Compton scattering will be used. Nearly all major components have been fabricated and tested. Subsystems of the source and polarimeters have been installed, and studies are in progress. The installation and commissioning of the entire system will take place during available machine shutdown periods as the commissioning of SLC progresses. 8 refs., 16 figs., 1 tab.

  11. Investigating the Development of Abnormal Subauroral Ion Drift (ASAID) and Abnormal Subauroral Polarization Stream (ASAPS) During the Magnetically Active Times of September 2003

    Science.gov (United States)

    Horvath, Ildiko; Lovell, Brian C.

    2018-02-01

    This study investigates two recently reported subauroral phenomena: the abnormal subauroral ion drift (ASAID) appearing as an inverted SAID and the shielding-E—SAID structure depicting a SAID feature on the poleward side of a small eastward or antisunward flow channel that is the shielding electric (E) field's signature. We have analyzed polar cross sections, constructed with multi-instrument Defense Meteorological Satellite Program data, for the development of these subauroral phenomena. New results show the features of abnormal subauroral polarization stream (ASAPS) and ASAID-ASAPS comprised by a narrow ASAID embedded in a wider ASAPS. We have identified undershielding, perfect shielding, and overshielding events. Our observational results demonstrate SAPS development during undershielding, the absence of subauroral flow channel during perfect shielding, and ASAID/ASAPS and shielding-E—SAID/SAPS development during overshielding. The appearance of an ASAID-ASAPS structure together with a pair of dayside-nightside eastward auroral flow channels implies the intensification of region 2 field-aligned currents via the westward traveling surge and thus the strengthening of overshielding conditions. From the observational results presented we conclude for the magnetically active time period studied that (i) the shielding E field drove the wider ASAPS flow channel, (ii) the ASAID-ASAPS structure's narrow antisunward flow channel developed due to the injections of hot ring current ions in a short-circuited system wherein the hot ring current plasma was closer to the Earth than the cold plasmaspheric plasma, and (iii) overshielding created this hot-cold plasma configuration via the development of a plasmaspheric shoulder.

  12. The North Zealand CAP Monitor

    DEFF Research Database (Denmark)

    Nielsen, Minna; Ravn, Pernille; Notander Clausen, Lise

    Contect We describe how we developed a monitoring system for community acquired pneumonia (CAP) at North Zealand Regional hospital. We serve 310.000 inhabitants and annually around 3200 patients with CAP are admitted. As part of a program of clinical pathways for common conditions, a pathway...... nurses and two senior doctors. Direct observations of the clinical processes revealed problems of coordination, complex disease trajectories that did not fit with the pneumonia pathway, unclear guidelines and variation in their interpretation. Intervention We designed a measurement system to monitor...... with CAP. We started with 34 audit variables. Through repeated cycles of testing, feedback and discussions, we reduced the number of indicators to 22 and time per audit from 20 to 10 minutes. Strategy for change To link the monitoring system with our patient pathway for CAP we established an improvement...

  13. Silicon photonic thermometer operating on multiple polarizations

    DEFF Research Database (Denmark)

    Guan, Xiaowei; Wang, Xiaoyan; Frandsen, Lars Hagedorn

    2016-01-01

    A silicon photonics optical thermometer simultaneously operating on the multiple polarizations is designed and experimentally demonstrated. Measured sensitivities are 86pm/°C and 48pm/°C for the transverse-electric and transverse-magnetic polarizations, respectively.......A silicon photonics optical thermometer simultaneously operating on the multiple polarizations is designed and experimentally demonstrated. Measured sensitivities are 86pm/°C and 48pm/°C for the transverse-electric and transverse-magnetic polarizations, respectively....

  14. Polarized electron beams at SLAC

    International Nuclear Information System (INIS)

    Moffeit, K.C.

    1992-11-01

    SLAC has successfully accelerated high energy polarized electrons for the Stanford Linear Collider and fixed polarized nuclear target experiments. The polarized electron beams at SLAC use a gallium arsenide (GaAlAs for E-142) photon emission source to provide the beam of polarized electrons with polarization of approximately 28% (41% for E-142). While the beam emittance is reduced in the damping ring for SLC operation a system of bend magnets and superconducting solenoids preserve and orient the spin direction for maximum longitudinal polarization at the collision point. The electron polarization is monitored with a Compton scattering polarimeter, and was typically 22% at the e+e- collision point for the 1992 run. Improvements are discussed to increase the source polarization and to reduce the depolarization effects between the source and the collision point

  15. Rocket Measurements Within a Polar Cap Arc: Ionospheric Modelling,

    Science.gov (United States)

    1987-11-19

    References Aarons, Jules , Global morphology of ionospheric scintillations, Proc. IEEE, 70, 360, 1982. Banks, P.M., Chapell, C.R., and A.F. Nagy, A new model...penetration of soft electrons into the ionosphere, Planet. Space Sci., 24, 409, 1975. Mantas, George P., Carlson, Herbert C. Jr., and Caesar H. LaHoz

  16. Spin-polarized electron tunneling in bcc FeCo/MgO/FeCo(001) magnetic tunnel junctions.

    Science.gov (United States)

    Bonell, F; Hauet, T; Andrieu, S; Bertran, F; Le Fèvre, P; Calmels, L; Tejeda, A; Montaigne, F; Warot-Fonrose, B; Belhadji, B; Nicolaou, A; Taleb-Ibrahimi, A

    2012-04-27

    In combining spin- and symmetry-resolved photoemission, magnetotransport measurements and ab initio calculations we detangled the electronic states involved in the electronic transport in Fe(1-x)Co(x)(001)/MgO/Fe(1-x)Co(x)(001) magnetic tunnel junctions. Contrary to previous theoretical predictions, we observe a large reduction in TMR (from 530 to 200% at 20 K) for Co content above 25 atomic% as well as anomalies in the conductance curves. We demonstrate that these unexpected behaviors originate from a minority spin state with Δ(1) symmetry that exists below the Fermi level for high Co concentration. Using angle-resolved photoemission, this state is shown to be a two-dimensional state that occurs at both Fe(1-x)Co(x)(001) free surface, and more importantly at the interface with MgO. The combination of this interface state with the peculiar density of empty states due to chemical disorder allows us to describe in details the complex conduction behavior in this system.

  17. Magnetic field reversal of electric polarization and magnetoelectric phase diagram of the hexaferrite Ba{sub 1.3}Sr{sub 0.7}Co{sub 0.9}Zn{sub 1.1}Fe{sub 10.8}Al{sub 1.2}O{sub 22}

    Energy Technology Data Exchange (ETDEWEB)

    Shen, Shipeng; Yan, Liqin; Chai, Yisheng; Cong, Junzhuang; Sun, Young, E-mail: youngsun@iphy.ac.cn [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China)

    2014-01-20

    Low magnetic field reversal of electric polarization has been demonstrated in the multiferroic Y-type hexaferrite Ba{sub 1.3}Sr{sub 0.7}Co{sub 0.9}Zn{sub 1.1}Fe{sub 10.8}Al{sub 1.2}O{sub 22} single crystal. The maximum magnetoelectric coefficient at 200 K reaches 1065 ps/m near zero magnetic field. By a systematic investigation of magnetic field dependence of magnetic and dielectric responses at various temperatures, we obtained the magnetoelectric phase diagram describing the detailed evolution of the spin-induced ferroelectric phases with temperature and magnetic field. Below 225 K, the transverse spin cone can be stabilized at zero magnetic field, which is responsible for the reversal behavior of electric polarization. Our study reveals how to eventually achieve magnetic field reversal of electric polarization in hexaferrites at room temperature.

  18. NATURE MANAGEMENT, LANDSCAPE AND THE CAP

    OpenAIRE

    Brouwer, Floor M.; Godeschalk, Frans E.

    2004-01-01

    The integration of nature management, landscape and environmental concerns into the Common Agricultural Policy (CAP) has gained momentum with the CAP reforms adopted in June 2003. The report explores instruments and approaches that contribute to the inte-gration of nature conservation and landscape concerns into the CAP. A broader use of the CAP instruments might help to achieve nature types in the Netherlands.

  19. MAGNET

    CERN Multimedia

    by B. Curé

    2011-01-01

    The magnet operation was very satisfactory till the technical stop at the end of the year 2010. The field was ramped down on 5th December 2010, following the successful regeneration test of the turbine filters at full field on 3rd December 2010. This will limit in the future the quantity of magnet cycles, as it is no longer necessary to ramp down the magnet for this type of intervention. This is made possible by the use of the spare liquid Helium volume to cool the magnet while turbines 1 and 2 are stopped, leaving only the third turbine in operation. This obviously requires full availability of the operators to supervise the operation, as it is not automated. The cryogenics was stopped on 6th December 2010 and the magnet was left without cooling until 18th January 2011, when the cryoplant operation resumed. The magnet temperature reached 93 K. The maintenance of the vacuum pumping was done immediately after the magnet stop, when the magnet was still at very low temperature. Only the vacuum pumping of the ma...

  20. Polarization in electron and proton beams

    International Nuclear Information System (INIS)

    Buon, J.

    1986-03-01

    One first introduces the concept of polarization for spin 1/2 particle beams and discusses properties of spin kinetics in a stationary magnetic field. Then the acceleration of polarized protons in synchrotrons is studied with emphasis on depolarization when resonances are crossed and on the cures for reducing it. Finally, transverse polarization of electrons in storage rings is discussed as an equilibrium between polarizing and depolarizing effects of synchrotron radiation. Means for obtaining longitudinal polarization are also treated