549 research outputs found

    Specific loss power of magnetic nanoparticles: A machine learning approach

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    A machine learning approach has been applied to the prediction of magnetic hysteresis properties (coercive field, magnetic remanence, and hysteresis loop area) of magnetic nanoparticles for hyperthermia applications. Trained on a dataset compiled from numerical simulations, a neural network and a random forest were used to predict power losses of nanoparticles as a function of their intrinsic properties (saturation, anisotropy, and size) and mutual magnetic interactions, as well as of application conditions (temperature, frequency, and applied field magnitude), for values of the parameters not represented in the database. The predictive ability of the studied machine learning approaches can provide a valuable tool toward the application of magnetic hyperthermia as a precision medicine therapy tailored to the patient's needs. (C) 2022 Author(s)

    Magnetic hysteresis in granular CuCo alloys

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    Room-temperature hysteresis loops of granular Cu100-xCox alloys (5 less than or equal to x less than or equal to 15) obtained by planar flow casting in air and submitted to proper annealing treatments have been measured up to a field of 10 kOe by means of a vibrating sample magnetometer. In major loops (\H-vert\ = 10 kOe), the reduced remanence-to-saturation ratio m(r) = M-r/M-s and the coercivity H-c measured on all studied materials appear to be related by an almost linear law of the type m(r) approximate to 1/3 (mu H-c/kT), mu being the average magnetic moment on Co particles. A similar relation is also observed on minor symmetrical loops (100 Oe less than or equal to\H-vert\ less than or equal to 9 kOe). The observed results are accounted for by a model which considers the hysteresis as originating by magnetic interactions among nearly superparamagnetic Co particles. (C) 1999 American Institute of Physics. [S0021-8979(99)51408-4]

    Ionospheric and magnetic signatures of a high speed solar wind in low latitudes on 13 October 2012

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    International audienceThis paper presents the impact of a fast solar wind on the ionosphere, in low latitudes, on 13 October 2012. On that day, the high speed solar wind reached the Earth around 16:00UT, during the recovery phase of a geomagnetic storm which started around 00:00UT. The solar wind speed was determined to be 580km/s, on the same day, around 17:00UT. Its impact was observed in low and equatorial latitudes, in Africa and in Eastern South America, on the F layer and on the geomagnetic field variations. Through the analysis of magnetic indices, ionosonde characteristics and the horizontal component of the geomagnetic field, we found that the 13 October 2012 event exhibited a local impact, affecting the observatories situated in a longitude sector between 315°E and 45°E. Particularly, the F layer in Africa (observed by the ionosonde at Ascension Island) did not present any lift, and there was a delay for approximately two hours of the ascent of the F layer in America (the ionosonde at Fortaleza). In this case, there was an evident inhibition on the development of spread F at the time of the Pre Reversal Enhancement (PRE) in Africa and Eastern America, while the ionograms of the days before and after presented clear spread F traces. The disturbances of the ionospheric equivalent electric current (Diono) deduced from the variations of the geomagnetic field at M'Bour near Dakar (Africa) and at Kourou (Eastern America) exhibited on the dayside, an anti Sq current which is signature of the influence of the Disturbance Dynamo Electric Field (DDEF)

    Thermally evaporated Cu-Co top spin valve with random exchange bias

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    A cobalt-copper top spin valve was prepared by thermal evaporation of a stack of ferromagnetic thin films separated by thin layers of the diamagnetic metal, with a cap layer containing an antiferromagnetic AFM exchange-biasing material. A nonconventional top AFM layer was used, in order to optimize the multilayer roughness and to avoid electrical interference with metallic layers; it consists of a composite material easily processed by means of optical lithography, basically a polymeric matrix composite with a dispersion of nickel oxide microparticles. Magnetization and magnetoresistance measurements were performed from 4 to 300 K. The measurements of both quantities indicate random pinning action of the top AFM layer, resulting in a small exchange-bias field and in asymmetric magnetization and magnetoresistance curves. A simple model explains the observed physical effect

    A method to ingest GPS-TEC into the NeQuick ionospheric model

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    This paper presents a method to ingest Total Electron Content measurements from ground-based GPS receivers into the empirical NeQuick model. The method here presented relies upon optimizing the parameter that primarily drives the NeQuick profile, i.e., the electron density of the F2 peak, NmF2. The effectiveness of the method is assessed in a rather benevolent ionospheric scenario: a midlatitude region and quiet geomagnetic days that cover solstices and equinoxes conditions during a medium-high solar activity year. Thus, the procedure demonstrated to be capable of improving the climatological value of NmF2 computed from the Radioscience Section of the International Telecommunication Union (ITU-R) database. This capability was assessed by comparing the ITU-R value and the corrected value produced by our method to the value measured with a Digisonde. The result of this comparison was an overall reduction of the error of the NmF2 parameter to approximately half of its original value.Facultad de Ciencias AstronĂłmicas y GeofĂ­sica