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Gough, D. I. "The Interpretation of Magnetometer Array Studies". Geophysical Journal of the Royal Astronomical Society 35, nr 1-3 (15.09.2009): 83–98. http://dx.doi.org/10.1111/j.1365-246x.1973.tb02416.x.
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Gough, D. Ian. "Magnetometer array studies, Earth structure, and tectonic processes". Reviews of Geophysics 27, nr 1 (1989): 141. http://dx.doi.org/10.1029/rg027i001p00141.
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Untiedt, J., i W. Baumjohann. "Studies of polar current systems using the IMS Scandinavian magnetometer array". Space Science Reviews 63, nr 3-4 (1993): 245–390. http://dx.doi.org/10.1007/bf00750770.
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Arora, B. R. "Magnetometer array studies in India: Present status, data interpretation and assessment of numerical modelling results". Journal of Earth System Science 99, nr 4 (grudzień 1990): 693–716. http://dx.doi.org/10.1007/bf02840323.
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Engebretson, M. J., W. J. Hughes, J. L. Alford, E. Zesta, L. J. Cahill, R. L. Arnoldy i G. D. Reeves. "Magnetometer array for cusp and cleft studies observations of the spatial extent of broadband ULF magnetic pulsations at cusp/cleft latitudes". Journal of Geophysical Research 100, A10 (1995): 19371. http://dx.doi.org/10.1029/95ja00768.
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Ahlers, Malte T., Christoph T. Block, Michael Winklhofer i Martin Greschner. "Integration and evaluation of magnetic stimulation in physiology setups". PLOS ONE 17, nr 7 (22.07.2022): e0271765. http://dx.doi.org/10.1371/journal.pone.0271765.
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A large number of behavioral experiments have demonstrated the existence of a magnetic sense in many animal species. Further, studies with immediate gene expression markers have identified putative brain regions involved in magnetic information processing. In contrast, very little is known about the physiology of the magnetic sense and how the magnetic field is neuronally encoded. In vivo electrophysiological studies reporting neuronal correlates of the magnetic sense either have turned out to be irreproducible for lack of appropriate artifact controls or still await independent replication. Thus far, the research field of magnetoreception has little exploited the power of ex vivo physiological studies, which hold great promise for enabling stringent controls. However, tight space constraints in a recording setup and the presence of magnetizable materials in setup components and microscope objectives make it demanding to generate well-defined magnetic stimuli at the location of the biological specimen. Here, we present a solution based on a miniature vector magnetometer, a coil driver, and a calibration routine for the coil system to compensate for magnetic distortions in the setup. The magnetometer fits in common physiology recording chambers and has a sufficiently small spatial integration area to allow for probing spatial inhomogeneities. The coil-driver allows for the generation of defined non-stationary fast changing magnetic stimuli. Our ex vivo multielectrode array recordings from avian retinal ganglion cells show that artifacts induced by rapid magnetic stimulus changes can mimic the waveform of biological spikes on single electrodes. However, induction artifacts can be separated clearly from biological responses if the spatio-temporal characteristics of the artifact on multiple electrodes is taken into account. We provide the complete hardware design data and software resources for the integrated magnetic stimulation system.
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Janhunen, P., A. Olsson, J. Hanasz, C. T. Russell, H. Laakso i J. C. Samson. "Different Alfvén wave acceleration processes of electrons in substorms at ~4-5 <i>R<sub>E</sub></i> and 2-3 <i>R<sub>E</sub></i> radial distance". Annales Geophysicae 22, nr 6 (14.06.2004): 2213–27. http://dx.doi.org/10.5194/angeo-22-2213-2004.
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Abstract. Recent statistical studies show the existence of an island of cavities and enhanced electric field structures at 4-5RE radial distance in the evening and midnight magnetic local time (MLT) sectors in the auroral region during disturbed conditions, as well as ion beam occurrence frequency changes at the same altitude. We study the possibility that the mechanism involved is electron Landau resonance with incoming Alfvén waves and study the feasibility of the idea further with Polar electric field, magnetic field, spacecraft potential and electron data in an event where Polar maps to a substorm over the CANOPUS magnetometer array. Recently, a new type of auroral kilometric radiation (AKR) emission originating from ~2-3RE radial distance, the so-called dot-AKR emission, has been reported to occur during substorm onsets and suggested to also be an effect of Alfvénic wave acceleration in a pre-existing auroral cavity. We improve the analysis of the dot-AKR, giving it a unified theoretical handling with the high-altitude Landau resonance phenomena. The purpose of the paper is to study the two types of Alfvénic electron acceleration, acknowledging that they have different physical mechanisms, altitudes and roles in substorm-related auroral processes.
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Murphy, K. R., I. J. Rae, I. R. Mann, A. P. Walsh, D. K. Milling i A. Kale. "The dependence of Pi2 waveforms on periodic velocity enhancements within bursty bulk flows". Annales Geophysicae 29, nr 3 (10.03.2011): 493–509. http://dx.doi.org/10.5194/angeo-29-493-2011.
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Abstract. Pi2s are a category of Ultra Low Frequency (ULF) waves associated with the onset of magnetic substorms. Recent work has suggested that the deceleration of bulk plasma flows in the central plasmasheet, known as bursty bulk flows (BBFs), are able to directly-drive Pi2 oscillations. Some of these studies have further shown evidence that there is a one-to-one correlation between Pi2 magnetic waveforms observed on the ground and periodic peaks in flow velocity within the BBF, known as flow bursts. Utilising a favourable conjunction between the Geotail spacecraft and the Canadian Array for Real-time Investigations of Magnetic Activity (CARISMA) magnetometer array on 31 May 1998, we examine the causality of the link between BBF flow bursts and Pi2 waveforms. Using a series of analytical tests in both the time and frequency domains, we find that while the Pi2 and BBF waveforms are very similar, the ground response for this event occurs prior to the observed flow enhancements in the magnetotail. We conclude that during this specific case study the temporal variations of the flow bursts within the BBF are not directly-driving the observed ground-based Pi2 waveforms, despite the fact that a visual inspection of both time-series might initially suggest that there is a causal relationship. We postulate that rather than there being a direct causal relation, the similar waveforms observed in both Pi2s and BBFs may result from temporal variations in a common source for both the BBFs and the Pi2s, such as magnetic reconnection in the tail, this source modulating both the Pi2 and BBF at the same frequency.
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SUKHAREV, A., M. ORLYUK, M. RYABOV, L. SOBITNIAK, V. BEZRUKOVS, S. PANISHKO i A. ROMENETS. "Results of comparison of fast variations of geomagnetic field and ionospheric scintillations of 3C 144 radio source in the area of Odessa geomagnetic anomaly". Astronomical and Astrophysical Transactions, Volume 33, Numéro 1 (1.07.2022): 67–88. http://dx.doi.org/10.17184/eac.6481.
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From November 2017 to May 2019 at the Astronomical Observatory of Odessa I.I. Mechnikov National University, the variational component of the geomagnetic field was monitored to study short-periodic geomagnetic variations in the central part of the Odessa regional magnetic anomaly. The measurements were carried out using a LEMI-008 precision fluxgate magnetometer with a sampling rate of 1 Hz. The aim of this work is to compare the manifestation of short-periodic geomagnetic oscillations (which in some cases coincided with periods of geomagnetic pulsations) and ionospheric scintillations of the 3C 144 radio source (Taurus A) according to the data of URAN-4 low-frequency phased antenna array at frequencies of 20 and 25 MHz. The data obtained were processed on a daily basis using the method of continuous wavelet transform, as well as band-pass filtering based on Fourier transform, to select individual frequency bands containing irregular and quasi-harmonic variations in the geomagnetic field and radio flux density. The analysis of results of the observations, during geomagnetic disturbances, storms and in calm conditions, is carried out. The data from long-term monitoring of variational component of the geomagnetic field in the most interesting, central part of the Odessa magnetic anomaly, where such studies have not been conducted before, have been obtained. Observations of various manifestations of ionospheric scintillations were carried out both during magnetic storms and during a calm geomagnetic field. It is shown that during storms, main scintillation time scale of the 3C 144 radio source is 1–3 minutes. Ionospheric scintillations occasionally show a quasiperiodic structure.
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YEH, W. J., BO CHENG i KUN YANG. "FABRICATION OF UNIFORM ARRAY OF NANO-DOTS AND ITS APPLICATIONS". International Journal of Modern Physics B 19, nr 01n03 (30.01.2005): 675–77. http://dx.doi.org/10.1142/s0217979205029304.
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We have developed a novel technique to fabricate extremely uniform arrays of nano-sized dots. Regular arrays of nanometer-sized metallic dots are obtianed by magnetron sputtering deposition through a nanochannel glass replica mask. The platinum replica masks are fabricated using thin film deposition on an etched nanochannel glass and contain hexagonally patterned uniform voids with diameters as small as 50 nanometers. The metallic dot density can be as high as 5×1011 per square centimeter. The magnetic properties of Ni and Co dot arrays have been studied by a Alternating Gradient Magnetometer. The magnetic dot array can be used as pinning centers for superconductors and also can be used as the discrete magnetic media for magnetic recording.
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Xu, Lei, Ning Zhang, Liqing Fang, Huadong Chen, Pengfei Lin i Chunsheng Lin. "Simulation Analysis of Magnetic Gradient Full-Tensor Measurement System". Mathematical Problems in Engineering 2021 (19.03.2021): 1–13. http://dx.doi.org/10.1155/2021/6688364.
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The magnetic gradient full-tensor measurement system is diverse, and the magnetometer array structure is complex. Aimed at the problem, seven magnetic gradient full-tensor measurement system models are studied in detail. The full-tensor measurement theories of the tensor measurement arrays are analyzed. Under the same baseline distance, the magnetic dipole model is used to simulate the measurement system. Based on different measurement systems, the paper quantitatively compares and analyzes the error of the structure. A more optimized magnetic gradient full-tensor measurement system is suggested. The simulation results show that the measurement accuracy of the planar measurement system is slightly higher than that of the stereo measurement system. Among them, the cross-shaped and square measurement systems have relatively smaller structural errors and higher measurement accuracy.
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Черкасов, Д. А., Д. Л. Загорский, Р. И. Хайбуллин, А. Э. Муслимов i И. М. Долуденко. "Структура и магнитные свойства слоевых нанопроволок из 3d-металлов, полученных методом матричного синтеза". Физика твердого тела 62, nr 9 (2020): 1531. http://dx.doi.org/10.21883/ftt.2020.09.49782.28h.
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Arrays of layered nanowires (NWs) with a diameter of 100 nm consisting of alternating layers of Ni/Cu and Co/Cu were obtained by matrix synthesis based on polyethylene terephthalate track etched membranes. The process of galvanic deposition was studied and the regimes of obtaining of layered nanowires with different thicknesses of magnetic (Ni or Co) and non-magnetic (Cu) components of layers were determined. Electron microscopic investigation was performed to verify regimes of obtaining of layered nanowires and to refine the geometric properties of alternating layers. Using vibration magnetometer, the magnetization curves of the obtained arrays of layered NWs was measured at room temperature for two limiting orientations of the scanning magnetic field: parallel and perpendicular to the growth axis of the NW. It is shown that the magnetic anisotropy of the NW array is determined not only by the chemical composition, but also by the thickness and period of alternating magnetic layers in the NW. Numerical calculations of the dependence of the magnetostatic energy and the magnitude of the demagnetizing field in the synthesized layered NWs on the factor of their filling with a magnetic metal are carried out, which are qualitatively consistent with experimental observations.
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Zagorsky D. L., Doludenko I. M., Khaibullin R. I., Chuprakov S. A., Gippius A. A., Zhurenko S. V., Tkachev A. V. i in. "Synthesis features, structure, magnetometry and NMR spectroscopy of nanowires of various types". Physics of the Solid State 64, nr 9 (2022): 1158. http://dx.doi.org/10.21883/pss.2022.09.54144.25hh.
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Various types of nanowires obtained by matrix synthesis --- homogeneous (from iron) and heterogeneous (layered) --- have been studied. A technique for obtaining arrays of layered nanowires with alternating thin layers of magnetic and non-magnetic metals (Co/Cu, Ni/Cu) has been developed and described. Microscopy methods (SEM and TEM with elemental analysis) have been used to study the topography of the resulting structures, the diameters of nanowires and the thicknesses of individual layers, and the features of interlayer interfaces. Methods of synthesis of nanowires with thin layers and clear boundaries are proposed --- dilution of the electrolyte, use of a reference electrode, control of the leaked charge. Layered nanowires have been studied by magnetometry methods and it has been shown that the magnetic properties of an array of layered nanowires (in particular, the direction of the axis of light magnetization in the Co/Cu-NP array) depend not only on the aspect ratio of the magnetic layer, but also on the ratio of the thickness of the magnetic metal layer to the thickness of a non-magnetic spacer (copper layer). The nuclear magnetic resonance (NMR) method was used to study two types of nanowires. The NMR method (on 59-Co nuclei) studied the layer structures of Co/Cu: it is shown that in nanowires with layers of smaller thickness (and, accordingly, with a large contribution of interfaces), a large proportion of Co atoms coordinated by Cu atoms is observed. The high proportion of atoms coordinated by copper suggests that an admixture of copper enters the cobalt layers. Homogeneous iron nanowires (NMR on 57-Fe nuclei) were compared with bulk iron samples. A shift of the line towards high frequencies (by 0.3 MHz) was detected, indicating an increase in the field by about 0.2 T. A significant broadening of the line and a decrease in the spin-lattice relaxation time may indicate a significant variation in the local magnetic field values. Keywords: nanowires, matrix synthesis, microscopy, elemental analysis, magnetic properties, NMR.
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Pilipenko, V., O. Kozyreva, V. Belakhovsky, M. J. Engebretson i S. Samsonov. "Generation of magnetic and particle Pc5 pulsations during the recovery phase of strong magnetic storms". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 466, nr 2123 (26.05.2010): 3363–90. http://dx.doi.org/10.1098/rspa.2010.0079.
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The dynamics of intense ultra-low-frequency (ULF) activity during three successive strong magnetic storms during 29–31 October 2003 are considered in detail. The spatial structure of Pc5 waves during the recovery phases of these storms is considered not only from the perspective of possible physical mechanisms, but as an important parameter of the ULF driver of relativistic electrons. The global structure of these disturbances is studied using data from a worldwide array of magnetometers and riometers augmented with data from particle detectors and magnetometers on board magnetospheric satellites (GOES, LANL). The local spatial structure is examined using the IMAGE magnetometers and Finnish riometer array. Though a general similarity between the quasi-periodic magnetic and riometer variations is observed, their local propagation patterns turn out to be different. To interpret the observations, we suggest a hypothesis of coupling between two oscillatory systems—a magnetospheric magnetohydrodynamic (MHD) waveguide/resonator and a system consisting of turbulence + electrons. We propose that the observed Pc5 oscillations are the result of MHD waveguide excitation along the dawn and dusk flanks of the magnetosphere. The magnetospheric waveguide turns out to be in a meta-stable state under high solar wind velocities, and quasi-periodic fluctuations of the solar wind plasma density stimulate the waveguide excitation.
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Sander, Tilmann H., Urban Marhl i Vojko Jazbinšek. "Avoiding non-linearity of optically pumped magnetometer MEG within an actively shielded two-layer mu-metal room". Current Directions in Biomedical Engineering 7, nr 2 (1.10.2021): 543–46. http://dx.doi.org/10.1515/cdbme-2021-2138.
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Abstract Some optically pumped magnetometer (OPM) sensors available for biomagnetic investigations have a linear range limited to +- 1 nT due to the specific properties of their open loop operation. In a two-layer magnetically shielded room of type Ak3b/Vacoshield Advanced with an external active compensation we studied how much sensor movement is allowed until amplitudes exceed the linearity range. Intentional movements were performed by a subject wearing an OPM-MEG sensor array. It was found that movements of 8 cm did yield non-linear amplitudes, but a reduction of the movement in half already preserves linearity. Despite movements, the heartbeat was found to generate a periodic signal, although the generating mechanism could not be identified so far.
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Chisham, G., D. Orr, T. K. Yeoman, D. K. Milling, M. Lester i J. A. Davies. "The polarization of Pc5 ULF waves around dawn: A possible ionospheric conductivity gradient effect". Annales Geophysicae 13, nr 2 (28.02.1995): 159–67. http://dx.doi.org/10.1007/s00585-995-0159-z.
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Abstract. In this study over 100 Pc5 events observed on the SAMNET magnetometer array have been catalogued. The ground horizontal polarization of these waves has been investigated and it has been shown that there are large differences between the polarization azimuth distributions on either side of noon. In the morning the azimuth distributions are spread evenly across all possible orientations whereas in the afternoon they are predominantly in a North-South orientation. The difference appears to be the result of a specific polarization pattern that occurred across the SAMNET array for 31 of the Pc5 events. These 31 Pc5 events all occurred in the morning sector, close to the dawn terminator. It is suggested that this special polarization pattern is a consequence of ionospheric conductivity gradients that occur at around dawn. This theory is reinforced by the comparison of the local times of these polarization variations with the local time of sunrise. By employing ionospheric conductivity data from the EISCAT radar for two of these Pc5 events, this connection has been studied in more detail.
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Belyaev, Victor K., Dmitry Murzin, Jose C. Martínez-García, Montserrat Rivas, Nikolay V. Andreev, Aleksei G. Kozlov, Aleksei Yu Samardak, Alexey V. Ognev, Alexander S. Samardak i Valeria Rodionova. "FORC-Diagram Analysis for a Step-like Magnetization Reversal in Nanopatterned Stripe Array". Materials 14, nr 24 (8.12.2021): 7523. http://dx.doi.org/10.3390/ma14247523.
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The fabrication approach of a magnonic crystal with a step-like hysteresis behavior based on a uniform non-monotonous iron layer made by shadow deposition on a preconfigured substrate is reported. The origin of the step-like hysteresis loop behavior is studied with local and integral magnetometry methods, including First-Order Reversal Curves (FORC) diagram analysis, accompanied with magnetic microstructure dynamics measurements. The results are validated with macroscopic magnetic properties and micromagnetic simulations using the intrinsic switching field distribution model. The proposed fabrication method can be used to produce magnonic structures with the controllable hysteresis plateau region’s field position and width that can be used to control the magnonic crystal’s band structure by changing of an external magnetic field.
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Thiem, Luu Van. "ANGULAR DEPENDENCE OF MAGNETIC PROPERTIES IN Co NANOWIRE ARRAYS". Vietnam Journal of Science and Technology 56, nr 1A (4.05.2018): 65. http://dx.doi.org/10.15625/2525-2518/56/1a/12505.
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The Co nanowire arrays were fabricated by electrodeposition method by using the porous polycarbonate template. Study on crystallographic structure, micro structure, and the element composition confirmed the quality of the fabricated Co nanowires. SEM image shows the wires with an average diameter of 200 nm and the average length of 9 mm. The magnetic properties, measured at room temperature using vibrating sample magnetometry (VSM), displays that the nanowires have anisotropic property. The angular dependence of coercivity of Co nanowires has been studied. The decrease of the coercivity, when the angular changed from 0 o to 90 o, will be discussed.
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Menk, F. W., T. K. Yeoman, D. M. Wright, M. Lester i F. Honary. "High-latitude observations of impulse-driven ULF pulsations in the ionosphere and on the ground". Annales Geophysicae 21, nr 2 (28.02.2003): 559–76. http://dx.doi.org/10.5194/angeo-21-559-2003.
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Abstract. We report the simultaneous observation of 1.6–1.7 mHz pulsations in the ionospheric F-region with the CUTLASS bistatic HF radar and an HF Doppler sounder, on the ground with the IMAGE and SAMNET magnetometer arrays, and in the upstream solar wind. CUTLASS was at the time being operated in a special mode optimized for high resolution studies of ULF waves. A novel use is made of the ground returns to detect the ionospheric signature of ULF waves. The pulsations were initiated by a strong, sharp decrease in solar wind dynamic pressure near 09:28 UT on 23 February 1996, and persisted for some hours. They were observed with the magnetometers over 20° in latitude, coupling to a field line resonance near 72° magnetic latitude. The magnetic pulsations had azimuthal m numbers ~ -2, consistent with propagation away from the noon sector. The radars show transient high velocity flows in the cusp and auroral zones, poleward of the field line resonance, and small amplitude 1.6–1.7 mHz F-region oscillations across widely spaced regions at lower latitudes. The latter were detected in the radar ground scatter returns and also with the vertical incidence Doppler sounder. Their amplitude is of the order of ± 10 ms-1. A similar perturbation frequency was present in the solar wind pressure recorded by the WIND spacecraft. The initial solar wind pressure decrease was also associated with a decrease in cosmic noise absorption on an imaging riometer near 66° magnetic latitude. The observations suggest that perturbations in the solar wind pressure or IMF result in fast compressional mode waves that propagate through the magnetosphere and drive forced and resonant oscillations of geomagnetic field lines. The compressional wave field may also stimulate ionospheric perturbations. The observations demonstrate that HF radar ground scatter may contain important information on small-amplitude features, extending the scope and capability of these radars to track features in the ionosphere.Key words. Ionosphere (Ionosphere-magnetosphere interactions; ionospheric disturbances) – Magnetospheric physics (MHD waves and instabilities)
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Spanswick, E., E. Donovan i G. Baker. "Pc5 modulation of high energy electron precipitation: particle interaction regions and scattering efficiency". Annales Geophysicae 23, nr 5 (27.07.2005): 1533–42. http://dx.doi.org/10.5194/angeo-23-1533-2005.
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Abstract. Using the NORSTAR riometer and CANOPUS magnetometer arrays we have investigated the modulation of high energy electron precipitation by ULF waves in the Pc5 frequency band. We conducted two separate studies of Pc5 activity in the riometers. The first is an independent survey of three riometer stations in the Churchill line (one at each sub-auroral, auroral, and typical polar cap boundary latitudes) in which we identified all riometer Pc5-band pulsations over 11 years. All had a corresponding magnetometer pulsation implying that a magnetic pulsation, is a necessary condition for a riometer pulsation (in the Pc5 Band). We find seasonal and latitude dependencies in the occurrence of riometer pulsations. By a factor of two, there are more riometer pulsations occurring in the fall-winter than the spring-summer. At higher latitudes there is a tendency towards noon pulsations during the spring-summer, suggesting that the criteria for riometer pulsations is affected by the dipole tilt. Our second study was based on the previous magnetometer study of Baker et al. (2003). Using the database of Pc5 activity from that study we were able to select the riometer Pc5 pulsations which adhere to the strict Pc5 definition in the magnetometer. We find that roughly 95% of the riometer pulsations occurred in the morning sector compared to 70% in the magnetometer. Given a magnetometer pulsation at Gillam in the morning sector, there is a 70% chance of there being a corresponding riometer pulsation. The morning sector probabilities at Rankin (geomagnetic (PACE) latitude 74°) and Pinawa (61°) are 3% and 5%, respectively. These statistics suggest there is a localized region in the pre-noon magnetosphere where Pc5 band ULF activity can modulate high energy electron precipitation. We also find that riometer pulsations display a Kp selection towards mid (i.e. 3–4) activity levels which mimics the product of the Kp dependence of high-energy electron fluxes on the dawn side (from CRRES) and all magnetic Pc5 activity. A superposed epoch analysis revealed that the elevated electron flux needed to produce a riometer pulsation is most likely provided by substorm injections on the nightside. We also find that the amplitude of modulated precipitation correlates well with the product of the background absorption and the magnetic pulsation amplitude, again leading to the idea that a riometer pulsation needs both favorable magnetospheric electron flux conditions and large enough magnetic Pc5 wave activity. We further separate our pulsations into field line resonances (FLRs), and non-field line resonances (non-FLRs), as identified in the Baker et al. (2003) survey. We find that FLRs are more efficient at modulating particle precipitation, and non-FLRs display an amplitude cutoff below which they do not interact with the high energy electron population. We conclude that the high energy electron precipitation associated with Pc5 pulsations is caused by pitch angle scattering (diffusion) rather than parallel acceleration. We suggest two future studies that are natural extensions of this one. Keywords. Energetic Particles/Precipitating; Wave-Particle Interactions; Auroral Phenomena
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Confalonieri, Giovanni A. Badini, Philipp Szary, Durgamadhab Mishra, Maria J. Benitez, Mathias Feyen, An Hui Lu, Leonardo Agudo, Gunther Eggeler, Oleg Petracic i Hartmut Zabel. "Magnetic coupling mechanisms in particle/thin film composite systems". Beilstein Journal of Nanotechnology 1 (1.12.2010): 101–7. http://dx.doi.org/10.3762/bjnano.1.12.
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Magnetic γ-Fe2O3 nanoparticles with a mean diameter of 20 nm and size distribution of 7% were chemically synthesized and spin-coated on top of a Si-substrate. As a result, the particles self-assembled into a monolayer with hexagonal close-packed order. Subsequently, the nanoparticle array was coated with a Co layer of 20 nm thickness. The magnetic properties of this composite nanoparticle/thin film system were investigated by magnetometry and related to high-resolution transmission electron microscopy studies. Herein three systems were compared: i.e. a reference sample with only the particle monolayer, a composite system where the particle array was ion-milled prior to the deposition of a thin Co film on top, and a similar composite system but without ion-milling. The nanoparticle array showed a collective super-spin behavior due to dipolar interparticle coupling. In the composite system, we observed a decoupling into two nanoparticle subsystems. In the ion-milled system, the nanoparticle layer served as a magnetic flux guide as observed by magnetic force microscopy. Moreover, an exchange bias effect was found, which is likely to be due to oxygen exchange between the iron oxide and the Co layer, and thus forming of an antiferromagnetic CoO layer at the γ-Fe2O3/Co interface.
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Загорский, Д. Л., К. В. Фролов, С. А. Бедин, И. В. Перунов, М. А. Чуев, А. А. Ломов i И. М. Долуденко. "Структура и магнитные свойства нанопроволок из маталлов группы железа, полученных методом матричного синтеза". Физика твердого тела 60, nr 11 (2018): 2075. http://dx.doi.org/10.21883/ftt.2018.11.46642.08nn.
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Abstract —Samples of arrays of nanowires are produced from iron, iron–cobalt and iron–nickel alloys via matrix synthesis based on polymer track membranes with pore diameters ranging from 30 to 300 nm. The influence of stress and pore diameter on the galvanic process and structure of nanowires is studied. The arrays of nanowires are examined by microscopy and X-ray diffraction. The magnetic properties are inspected via magnetometry and Mössbauer spectroscopy. The angular dependences of hysteresis loop shape are obtained and comprehensively discussed. As shown, decreasing the growth stress and/or increasing the pore diameter make the Mössbauer spectra of nanowires similar to those of bulk materials. Furthermore, the higher the growth stress is, the larger is the coercive force of nanowires. For the studied species of nanomaterials, the ability to control the magnetic properties during the synthesis is shown, as well.
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Graf, M. J., C. P. Opeil i T. E. Huber. "Magnetic Anisotropy and de Haas–van Alphen Oscillations in a Bi Microwire Array Studied via Cantilever Magnetometry at Low Temperatures". Journal of Low Temperature Physics 134, nr 5/6 (styczeń 2004): 1055–68. http://dx.doi.org/10.1023/b:jolt.0000016729.99257.25.
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KERK, W. T., J. M. LI, W. S. CHIN i A. C. H. HUAN. "SYNTHESIS AND CHARACTERIZATION OF COBALT FERRITES MAGNETIC NANOPARTICLES IN ALKANETHIOL SOLUTION". International Journal of Nanoscience 03, nr 04n05 (sierpień 2004): 639–48. http://dx.doi.org/10.1142/s0219581x04002474.
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Magnetic nanoparticles of cobalt ferrite have been synthesized in a homogeneous solution containing dodecanethiol at room temperature. The alkanethiol molecules have provided a mean to control the particle size distribution. The uniformed size distribution, crystallinity and morphology of these nanoparticles are characterized with X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). The stoichiometry of the cobalt ferrite is confirmed by both elemental analysis and Energy Dispersive X-ray (EDX). Fabrication of assembled arrays of these nanoparticles on Si (100) have been achieved by slow evaporation of the solution and studied by Atomic Force Microscopy (AFM). Magnetic properties of the nanoparticles are determined by Vibrating Sample Magnetometer (VSM) and show a magnetization (Ms) of 75.3 emu/g and a coercivity (Hc) of 1500 Oe at room temperature.
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Загорский, Д. Л., И. М. Долуденко, К. В. Фролов, И. В. Перунов, М. А. Чуев, Н. К. Чумаков, И. В. Калачикова, В. В. Артёмов, Т. В. Цыганова i С. С. Кругликов. "Особенности получения методом матричного синтеза, структура и магнитные свойства нанопроводов из железа". Физика твердого тела 65, nr 6 (2023): 973. http://dx.doi.org/10.21883/ftt.2023.06.55653.11h.
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Nanowires from iron were investigated. Samples in the form of arrays of parallel threads (wires) were obtained by matrix synthesis using track membranes. Matrices with parallel pores of 100 nm were used, and the growth voltage was varied - 0.8 V, 1 V and 1.2 V. Electron microscopic studies of the growth matrix and samples were carried out. The obtained data of Mössbauer spectroscopy and magnetometry correlate well. Thus, a comparison of the results obtained by these methods showed that with an increase in the deposition potential during the synthesis of nanowires, the misorientation angle of the magnetic moments of domains increases. It is also shown that as the deposition potential increases, the coercive force decreases.
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Zagorskiy D. L., Doludenko I. M., Frolov K. V., Perunov I. V., Chuev M. A., Chumakov N. K., Kalachikova I. V., Artemov V. V., Tziganova T. V. i Kruglikov S. S. "Features of obtaining by the method of matrix synthesis, structure and magnetic properties of iron nanowires". Physics of the Solid State 65, nr 6 (2023): 932. http://dx.doi.org/10.21883/pss.2023.06.56104.11h.
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Nanowires from iron were investigated. Samples in the form of arrays of parallel threads (wires) were obtained by matrix synthesis using track membranes. Matrices with parallel pores of 100 nm were used, and the growth voltage was varied --- 0.8 V, 1 V and 1.2 V. Electron microscopic studies of the growth matrix and samples were carried out. The obtained data of Mossbauer spectroscopy and magnetometry correlate well. Thus, a comparison of the results obtained by these methods showed that with an increase in the deposition potential during the synthesis of nanowires, the misorientation angle of the magnetic moments of domains increases. It is also shown that as the deposition potential increases, the coercive force decreases. Keywords: magnetic nanowires, matrix synthesis, structure, Mossbauer spectroscopy, magnetic properties.
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Wanliss, J. "Substorm onset location and dipole tilt angle". Annales Geophysicae 24, nr 2 (23.03.2006): 577–88. http://dx.doi.org/10.5194/angeo-24-577-2006.
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Abstract. From an initial data set of over 200 substorms we have studied a subset of 30 magnetospheric substorms close to magnetic midnight to investigate, in a statistical fashion, the source region of the auroral arc that brightens at the onset of expansive phase. This arc is usually identified as the ionospheric signature of the expansive phase onset that occurs in the magnetotail. All the substorm onsets were identified via ground-based magnetometer and photometer data from the CANOPUS array. Various Tsyganenko global magnetic field models were used to map magnetic field lines from the location of the onset arc out to its greatest radial distance in the magnetotail. The results appear to favour the current disruption model of substorms since the average onset location has an average of 14.1 Earth radii (RE) and is therefore more consistent with theories that place the onset location in the inner magnetotail. For the narrow range of tilts available our modeling indicates the parameter that appears to strongly influence the location of the substorm onset is the dipole tilt angle; as tilt becomes less negative onsets occur further downtail.
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Хайретдинова, Д. Р., И. М. Долуденко, Л. В. Панина i Д. Л. Загорский. "Нанопроволоки из двух- и трехкомпонентных сплавов: корреляция структурных и магнитных свойств". Физика твердого тела 64, nr 9 (2022): 1144. http://dx.doi.org/10.21883/ftt.2022.09.52798.24hh.
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Several types of nanowires (NWs) made of alloys of various compositions obtained by the method of matrix synthesis based on track membranes have been studied. Electrolytes were selected to obtain NWs of the desired composition. The control of electrodeposition by chronoamperograms made it possible to systematically change the geometric parameters and morphology. The topographies of the resulting NW arrays and their elemental composition were studied using electron microscopy with an X-ray spectral analyzer. The magnetic properties of the samples were studied on a vibrating magnetometer. The structures of binary alloys were studied: for NWs of FeCo alloys, the dependence of the coercive force on the composition was studied. The obtained dependence has two maxima - at an equiatomic composition and at a cobalt content of about 90%. For Fe0.3Co0.7 NWs, a sharp increase in the coercive force with decreasing diameter is shown. It is assumed that this effect is due to the formation of single-domain crystallites, the processes of magnetization reversal of which are associated with a uniform rotation of the magnetization. For NWs made of FeNi alloys, the influence of the aspect ratio on the coercive force has been proved. Ternary alloys of the FeCoCu system have been studied: it has been shown that the addition of copper significantly increases the coercive force, which reaches a maximum at a copper content of about 5%. The obtained X-ray data suggest that the effect of an increase in the coercive force is associated with the formation of fine-grained inclusions based on copper, which lead to effective deceleration of the domain walls. The data obtained expand the range of possibilities for controlling the magnetic properties of NW arrays obtained by the method of matrix synthesis. Keywords: nanowires, matrix synthesis, microscopy, elemental analysis, magnetic properties, coercive force.
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Khayretdinova D. R., Doludenko I. M., Panina L. V. i Zagorsky D. L. "Two- and three-component alloys nanowires: correlation of structural and magnetic properties". Physics of the Solid State 64, nr 9 (2022): 1150. http://dx.doi.org/10.21883/pss.2022.09.54143.24hh.
Pełny tekst źródłaStreszczenie:
Several types of nanowires (NWs) made of alloys of various compositions obtained by the method of matrix synthesis based on track membranes have been studied. Electrolytes were selected to obtain NWs of the desired composition. The control of electrodeposition by chronoamperograms made it possible to systematically change the geometric parameters and morphology. The topographies of the resulting NW arrays and their elemental composition were studied using electron microscopy with an X-ray spectral analyzer. The magnetic properties of the samples were studied on a vibrating magnetometer. The structures of binary alloys were studied: for NWs of FeCo alloys, the dependence of the coercive force on the composition was studied. The obtained dependence has two maxima --- at an equiatomic composition and at a cobalt content of about 90%. For Fe0.3Co0.7 NWs, a sharp increase in the coercive force with decreasing diameter is shown. It is assumed that this effect is due to the formation of single-domain crystallites, the processes of magnetization reversal of which are associated with a uniform rotation of the magnetization. For NWs made of FeNi alloys, the influence of the aspect ratio on the coercive force has been proved. Ternary alloys of the FeCoCu system have been studied: it has been shown that the addition of copper significantly increases the coercive force, which reaches a maximum at a copper content of about 5%. The obtained X-ray data suggest that the effect of an increase in the coercive force is associated with the formation of fine-grained inclusions based on copper, which lead to effective deceleration of the domain walls. The data obtained expand the range of possibilities for controlling the magnetic properties of NW arrays obtained by the method of matrix synthesis. Keywords: nanowires, matrix synthesis, microscopy, elemental analysis, magnetic properties, coercive force. Keywords: nanowires, matrix synthesis, microscopy, elemental analysis, magnetic properties, coercive force.
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Thiem, Luu Van, Le Tuan Tu i Pham Duc Thang. "Influence of Bath Composition on the Electrodeposited \(\text{Co-Ni-P}\) Nanowires". Communications in Physics 24, nr 3S1 (10.11.2014): 90–94. http://dx.doi.org/10.15625/0868-3166/24/3s1/5232.
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CoNiP nanowire arrays were fabricated by electrodeposition method into polycarbonate (PC) templates at different pH values. It is obvious that the crystal structure of the CoNiP nanowires depends on the pH values of electrolyte. The XRD results show that crystal structure of the CoNiP nanowires is hcp structure and the intensity of the hcp (002) increased enhances as solution pH =5. Magnetic measurements indicate a dependence of the squareness and the coercivity of the magnetization hysteresis loop on pH values with a maximum coercivity of 1425 Oe. The morphological properties of CoNiP nanowires were studied by transmission electron microscopy (TEM). The chemical composition was determined by examination of the energy dispersive X-ray (EDS) spectra and the magnetic properties were measured by vibrating sample magnetometry (VSM).
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Ritter, P., H. Lühr, A. Viljanen, O. Amm, A. Pulkkinen i I. Sillanpää. "Ionospheric currents estimated simultaneously from CHAMP satelliteand IMAGE ground-based magnetic field measurements: a statisticalstudy at auroral latitudes". Annales Geophysicae 22, nr 2 (1.01.2004): 417–30. http://dx.doi.org/10.5194/angeo-22-417-2004.
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Abstract. One important contribution to the magnetic field measured at satellite altitude and at ground level comes from the external currents. We used the total field data sampled by the Overhauser Magnetometer on CHAMP and the horizontal magnetic field measurements of the IMAGE ground-based magnetometer network to study the ionospheric Hall current system in the auroral regions. For the CHAMP data a current model consisting of a series of lines and placed at a height of 110km is fitted to the magnetic field signature sampled on the passage across the polar region. The derived current distributions depend, among others, on season and on the local time of the satellite track. At dawn/dusk the auroral electrojets can be detected most clearly in the auroral regions. Their intensity and location are evidently correlated with the A E activity index. For a period of almost two years the results obtained from space and the currents determined from ground-based observations are studied. For the full IMAGE station array a newly-developed method of spherical elementary current systems (SECS) is employed to compute the 2-D equivalent current distribution, which gives a detailed picture of an area covering latitudes 60° – 80° N and 10° – 30° E in the auroral region. Generally, the current estimates from satellite and ground are in good agreement. The results of this survey clearly show the average dependence of the auroral electrojet on season and local time. This is particularly true during periods of increased auroral activity. The correlation coefficient of the results is close to one in the region of sizeable ionospheric current densities. Also the ratio of the current densities, as determined from above and below the ionosphere, is close to unity. It is the first time that the method of Hall current estimate from a satellite has been validated quantitatively by ground-based observations. Among others, this result is of interest for magnetic main field modelling, since it demonstrates that ground-based observations can be used to predict electrojet signatures in satellite magnetic field scalar data. Key words. Ionosphere (auroral Ionosphere; electric fields and currents; ionosphere-magnetosphere interactions)
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Prikryl, P., R. Ghoddousi-Fard, E. G. Thomas, J. M. Ruohoniemi, S. G. Shepherd, P. T. Jayachandran, D. W. Danskin i in. "GPS phase scintillation at high latitudes during geomagnetic storms of 7–17 March 2012 – Part 1: The North American sector". Annales Geophysicae 33, nr 6 (2.06.2015): 637–56. http://dx.doi.org/10.5194/angeo-33-637-2015.
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Abstract. The interval of geomagnetic storms of 7–17 March 2012 was selected at the Climate and Weather of the Sun-Earth System (CAWSES) II Workshop for group study of space weather effects during the ascending phase of solar cycle 24 (Tsurutani et al., 2014). The high-latitude ionospheric response to a series of storms is studied using arrays of GPS receivers, HF radars, ionosondes, riometers, magnetometers, and auroral imagers focusing on GPS phase scintillation. Four geomagnetic storms showed varied responses to solar wind conditions characterized by the interplanetary magnetic field (IMF) and solar wind dynamic pressure. As a function of magnetic latitude and magnetic local time, regions of enhanced scintillation are identified in the context of coupling processes between the solar wind and the magnetosphere–ionosphere system. Large southward IMF and high solar wind dynamic pressure resulted in the strongest scintillation in the nightside auroral oval. Scintillation occurrence was correlated with ground magnetic field perturbations and riometer absorption enhancements, and collocated with mapped auroral emission. During periods of southward IMF, scintillation was also collocated with ionospheric convection in the expanded dawn and dusk cells, with the antisunward convection in the polar cap and with a tongue of ionization fractured into patches. In contrast, large northward IMF combined with a strong solar wind dynamic pressure pulse was followed by scintillation caused by transpolar arcs in the polar cap.
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Yeoman, T. K., J. A. Davies, N. M. Wade, G. Provan i S. E. Milan. "Combined CUTLASS, EISCAT and ESR observations of ionospheric plasma flows at the onset of an isolated substorm". Annales Geophysicae 18, nr 9 (30.09.2000): 1073–87. http://dx.doi.org/10.1007/s00585-000-1073-z.
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Abstract. On August 21st 1998, a sharp southward turning of the IMF, following on from a 20 h period of northward directed magnetic field, resulted in an isolated substorm over northern Scandinavia and Svalbard. A combination of high time resolution and large spatial scale measurements from an array of coherent scatter and incoherent scatter ionospheric radars, ground magnetometers and the Polar UVI imager has allowed the electrodynamics of the impulsive substorm electrojet region during its first few minutes of evolution at the expansion phase onset to be studied in great detail. At the expansion phase onset the substorm onset region is characterised by a strong enhancement of the electron temperature and UV aurora. This poleward expanding auroral structure moves initially at 0.9 km s-1 poleward, finally reaching a latitude of 72.5°. The optical signature expands rapidly westwards at ~6 km s-1, whilst the eastward edge also expands eastward at ~0.6 km s-1. Typical flows of 600 m s-1 and conductances of 2 S were measured before the auroral activation, which rapidly changed to ~100 m s-1 and 10-20 S respectively at activation. The initial flow response to the substorm expansion phase onset is a flow suppression, observed up to some 300 km poleward of the initial region of auroral luminosity, imposed over a time scale of less than 10 s. The high conductivity region of the electrojet acts as an obstacle to the flow, resulting in a region of low-electric field, but also low conductivity poleward of the high-conductivity region. Rapid flows are observed at the edge of the high-conductivity region, and subsequently the high flow region develops, flowing around the expanding auroral feature in a direction determined by the flow pattern prevailing before the substorm intensification. The enhanced electron temperatures associated with the substorm-disturbed region extended some 2° further poleward than the UV auroral signature associated with it.Key words: Ionosphere (auroral ionosphere) - Magnetospheric physics (magnetosphere - ionosphere interactions; storms and substorms)
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Zesta, E. "A statistical study of traveling convection vortices using the Magnetometer Array for Cusp and Cleft Studies". Journal of Geophysical Research 107, A10 (2002). http://dx.doi.org/10.1029/1999ja000386.
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Galindo, Arturo, José Luis Reyes-Rodríguez, Miriam Carolina Mendoza-Ramirez, Mario Moreno, Netzahualcoyotl Carlos i Arturo Ponce. "Magnetic saturation enhancement of gold-capped nickel nanorods". Applied Physics Letters 123, nr 4 (24.07.2023). http://dx.doi.org/10.1063/5.0150500.
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Nickel nanorods (NRs) capped with gold (Au/Ni) were grown into porous anodic aluminum oxide templates and subsequently transferred onto Au/Si (100) substrates. A high dense 2D array of Ni and Au/Ni nanorods was analyzed by vibrating sample magnetometry; it was found that an increase in 14.8% of the magnetic moment following the deposition of Au caps. In order to further investigate this phenomenon, the magnetic distribution of Au/Ni nanorods was studied by off-axis electron holography. The magnetization and induction strengths were evaluated to be 4.7 × 105 A/m and 0.62 T, respectively, which is equivalent to magnetometry measurements of the Ni NR arrays. Remarkably, a vortex state configuration was imaged in the Au segment by the retrieved magnetic phase of the electron holograms under free lens conditions of the transmission electron microscope column. It was concluded that the magnetic distribution in the Au segment is associated with a ferromagnetic coupling with Ni and correlated with the magnetometry measurements.
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Fabricant, Anne, Geoffrey Z. Iwata, Sönke Scherzer, Lykourgos Bougas, Katharina Rolfs, Anna Jodko-Władzińska, Jens Voigt, Rainer Hedrich i Dmitry Budker. "Action potentials induce biomagnetic fields in carnivorous Venus flytrap plants". Scientific Reports 11, nr 1 (14.01.2021). http://dx.doi.org/10.1038/s41598-021-81114-w.
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AbstractUpon stimulation, plants elicit electrical signals that can travel within a cellular network analogous to the animal nervous system. It is well-known that in the human brain, voltage changes in certain regions result from concerted electrical activity which, in the form of action potentials (APs), travels within nerve-cell arrays. Electro- and magnetophysiological techniques like electroencephalography, magnetoencephalography, and magnetic resonance imaging are used to record this activity and to diagnose disorders. Here we demonstrate that APs in a multicellular plant system produce measurable magnetic fields. Using atomic optically pumped magnetometers, biomagnetism associated with electrical activity in the carnivorous Venus flytrap, Dionaea muscipula, was recorded. Action potentials were induced by heat stimulation and detected both electrically and magnetically. Furthermore, the thermal properties of ion channels underlying the AP were studied. Beyond proof of principle, our findings pave the way to understanding the molecular basis of biomagnetism in living plants. In the future, magnetometry may be used to study long-distance electrical signaling in a variety of plant species, and to develop noninvasive diagnostics of plant stress and disease.
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Cheng, Bo, Kun Yang, B. L. Justus i W. J. Yeh. "Regular Array of Magnetic Nano-Dots Prepared by Nanochannel Glass Replica Masks". MRS Proceedings 721 (2002). http://dx.doi.org/10.1557/proc-721-e5.6.
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AbstractIn magnetic recording technology, barriers based on fundamental physical limits on the data density are being approached for the current longitudinal recording modes. However, demands for higher data storage density have escalated in recent years. Discrete perpendicular recording is a viable method to achieve 100 Gb per square inch and beyond. We report on the development of a novel technique to fabricate uniform arrays of nano-sized magnetic dots. Uniform arrays of nanometer-sized magnetic dots are obtained by magnetron sputtering deposition through a nanochannel glass replica mask. The platinum replica masks are fabricated using thin film deposition on etched nanochannel glass and contain uniform hexagonally patterned voids with diameters as small as 50 nanometers. The magnetic dot density can be as high as 1011 per square inch. Our method provides a simple yet effective way to create regularly arranged discrete magnetic media that can be used for perpendicular magnetic recording. The magnetic properties of the dots are studied with a vibrating sample magnetometer.
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Alissandrakis, Costas E., T. S. Bastian i Roman Brajša. "The quiet sun at mm wavelengths as seen by ALMA". Frontiers in Astronomy and Space Sciences 9 (11.10.2022). http://dx.doi.org/10.3389/fspas.2022.981320.
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Solar observations at sub-mm, mm and cm wavelengths offer a straightforward diagnostic of physical conditions in the solar atmosphere because they yield measurement of brightness temperature which, for optically thick features, equals intrinsic temperature - much unlike solar diagnostics in other spectral ranges. The Atacama Large Millimeter and sub-millimeter Array (ALMA) has therefore opened a new, hitherto underexplored, spectral window for studying the enigmatic solar chromosphere. In this review we discuss initial ALMA studies of the quiet chromosphere that used both single-dish and compact-array interferometric observing modes. We present results on the temperature structure of the chromosphere, comparison with classic empirical models of the chromosphere, and observations of the chromospheric network and spicules. Furthermore, we discuss what may be expected in the future, since the ALMA capabilities continuously expand and improve towards higher angular resolution, wavelength coverage, and polarization measurement for magnetometry.
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Welipitiya, D., C. N. Borca, P. A. Dowben, I. Gobulukoglu, Hong Jiang, B. W. Robertson i Jiandi Zhang. "Fabrication of Micron Scale Magnetic Nickel Features by Selective Area Organometallic Chemical Vapor Deposition". MRS Proceedings 475 (1997). http://dx.doi.org/10.1557/proc-475-257.
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AbstractWe demonstrate that it is possible to deposit a wide range of magnetic features, using photoassisted and electron radiation induced selective area organometallic chemical vapor deposition. Large arrays of identical micron to nano scale Ni features were deposited by these methods. Their magnetic properties were studied by alternating gradient force magnetometry as well as magnetic force microscopy. Our morphological and magnetic measurements show that the structures are spatially well defined, and the magnetic properties are related to the structural shapes of the features.
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Alem, Orang, K. Jeramy Hughes, Isabelle Buard, Teresa P. Cheung, Tyler Maydew, Andreas Griesshammer, Kendall Holloway i in. "An integrated full-head OPM-MEG system based on 128 zero-field sensors". Frontiers in Neuroscience 17 (14.06.2023). http://dx.doi.org/10.3389/fnins.2023.1190310.
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Compact optically-pumped magnetometers (OPMs) are now commercially available with noise floors reaching 10 fT/Hz1/2. However, to be used effectively for magnetoencephalography (MEG), dense arrays of these sensors are required to operate as an integrated turn-key system. In this study, we present the HEDscan, a 128-sensor OPM MEG system by FieldLine Medical, and evaluate its sensor performance with regard to bandwidth, linearity, and crosstalk. We report results from cross-validation studies with conventional cryogenic MEG, the Magnes 3,600 WH Biomagnetometer by 4-D Neuroimaging. Our results show high signal amplitudes captured by the OPM-MEG system during a standard auditory paradigm, where short tones at 1000 Hz were presented to the left ear of six healthy adult volunteers. We validate these findings through an event-related beamformer analysis, which is in line with existing literature results.
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Tiberto, Paola, Luca Boarino, Federica Celegato, Gabriele Barrera, Marco Coisson, Natascia De Leo i Franco Vinai. "Large-area patterned magnetic nanostructures by self-assembling of polystyrene nanospheres". MRS Proceedings 1411 (2012). http://dx.doi.org/10.1557/opl.2012.731.
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ABSTRACTIn this work, dot and anti-dot structures in Co, Ni, Ni80Fe20, Fe50Pd50, Fe73.5Cu1Nb3Si13.5B9 and Fe78B13Si9 thin films have been produced by means of nanosphere lithography. Two multi-step processes have been followed and will be here described. The first one directly exploits polystyrene nanosheres (PN) as a mask to fabricate arrays of magnetic nanoholes and dots. In the second case, the nanospheres are used to design a polymeric mask of a photoresist subsequently used to pattern a magnetic nanostructure on a film. Advantages and disadvantages of the two lithographical techniques will be here highlighted. In both processes, the dimension and mutual distance of the patterns are dependent on the starting PN diameter (in the interval 500-800 nm). Samples microstructure has been studied by means of SEM and AFM microscopy. Room-temperature hysteresis loops have been measured by an AGFM (Alternating Gradient Field Magnetometer). MFM microscopy has been exploited to study the magnetic domain pattern. All produced systems have been observed to display tunable microstructure and, consequently, various magnetic properties for application.
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Vanhamäki, Heikki, Astrid Maute, Patrick Alken i Huixin Liu. "Dipolar elementary current systems for ionospheric current reconstruction at low and middle latitudes". Earth, Planets and Space 72, nr 1 (15.10.2020). http://dx.doi.org/10.1186/s40623-020-01284-1.
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Abstract The technique of spherical elementary current systems (SECS) is a powerful way to determine ionospheric and field-aligned currents (FAC) from magnetic field measurements made by low-Earth-orbiting satellites, possibly in combination with magnetometer arrays on the ground. The SECS method consists of two sets of basis functions for the ionospheric currents: divergence-free (DF) and curl-free (CF) components, which produce poloidal and toroidal magnetic fields, respectively. The original CF SECS are only applicable at high latitudes, as they build on the assumption that the FAC flow radially into or out of the ionosphere. The FAC at low and middle latitudes are far from radial, which renders the method inapplicable at these latitudes. In this study, we modify the original CF SECS by including FAC that flow along dipolar field lines. This allows the method to be applied at all latitudes. We name this method dipolar elementary current systems (DECS). Application of the DECS to synthetic data, as well as Swarm satellite measurements are carried out, demonstrating the good performance of this method, and its applicability to studies of ionospheric current systems at low and middle latitudes.
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Porro, Jose M., Sophie A. Morley, Diego Alba Venero, Rair Macêdo, Mark C. Rosamond, Edmund H. Linfield, Robert L. Stamps, Christopher H. Marrows i Sean Langridge. "Magnetization dynamics of weakly interacting sub-100 nm square artificial spin ices". Scientific Reports 9, nr 1 (grudzień 2019). http://dx.doi.org/10.1038/s41598-019-56219-y.
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AbstractArtificial Spin Ice (ASI), consisting of a two dimensional array of nanoscale magnetic elements, provides a fascinating opportunity to observe the physics of out-of-equilibrium systems. Initial studies concentrated on the static, frozen state, whilst more recent studies have accessed the out-of-equilibrium dynamic, fluctuating state. This opens up exciting possibilities such as the observation of systems exploring their energy landscape through monopole quasiparticle creation, potentially leading to ASI magnetricity, and to directly observe unconventional phase transitions. In this work we have measured and analysed the magnetic relaxation of thermally active ASI systems by means of SQUID magnetometry. We have investigated the effect of the interaction strength on the magnetization dynamics at different temperatures in the range where the nanomagnets are thermally active. We have observed that they follow an Arrhenius-type Néel-Brown behaviour. An unexpected negative correlation of the average blocking temperature with the interaction strength is also observed, which is supported by Monte Carlo simulations. The magnetization relaxation measurements show faster relaxation for more strongly coupled nanoelements with similar dimensions. The analysis of the stretching exponents obtained from the measurements suggest 1-D chain-like magnetization dynamics. This indicates that the nature of the interactions between nanoelements lowers the dimensionality of the ASI from 2-D to 1-D. Finally, we present a way to quantify the effective interaction energy of a square ASI system, and compare it to the interaction energy computed with micromagnetic simulations.
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Lobo Guerrero, Azdrubal, Armando Encinas, Elsie Araujo Palomo, Luc Piraux i Joaquín de la Torre Medina. "Crystalline texture of arrays of cobalt nanowires probed by the switching field distribution and FORC diagrams". Journal of Physics D: Applied Physics, 3.01.2023. http://dx.doi.org/10.1088/1361-6463/acaf8c.
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Abstract The crystalline texture of arrays of low diameter Co nanowires (NWs) synthesized by electrodeposition using electrolytes with different acidities (pH in the range 2.0 to 6.6) was studied by the switching field distribution (SFD) and first order reversal curve (FORC) diagrams. Particularly, the SFD determined as the derivative dM/dH of the descending part of the major hysteresis loop (MHL) has proven to be a reliable and powerful method for the identification of different crystalline textures in the NWs and the quantification of their corresponding texture percentages. The presence of the fcc-like texture at low pH values and hcp textures with the c-axis perpendicular and parallel to the NWs axis at higher pH values have been identified by performing multiple Gaussian fits to the SFD by virtue of their different magnetic behavior observed during reversal of the magnetization. The field position and size of each curve in the multiple Gaussian fit provide information about the corresponding magnetic contribution and volumetric texture percentage of each crystalline texture in the NWs, respectively. The analysis of the SFD has been complemented and validated with FORC diagram measurements, showing that the width of the coercive field distribution (CFD) is in good agreement with the width of the SFD. Also, it has been found that the different branches observed in the FORC diagrams along the interaction axis provide further insight on the interaction between magnetocrystalline fields. This work provides a novel methodology for the use of magnetometry as a reliable technique for the study of the interplay between the microstructure and magnetic behavior of arrays of NWs.