Search Results (204)

This paper presents a comprehensive statistical analysis of extremely/very low-frequency (ELF/VLF) whistler-mode waves observed within magnetic ducts (B-ducts) using data from NASA’s Magnetospheric Multiscale (MMS) mission. A total of 687 events were analyzed, comprising 504 occurrences on the dawn-side flank of the magnetosphere and 183 in the nightside magnetotail, to investigate the spatial distribution and underlying mechanisms of wave–particle interactions. We identify distinct differences between these regions by examining key parameters such as event width, frequency, plasma density, and magnetic field extrema within B-ducts. Using an independent two-sample t-test, we assess the statistical significance of variations in these parameters between different observation periods. This study provides valuable insights into the magnetospheric conditions influencing B-duct formation and wave propagation, offering a framework for understanding ELF/VLF wave dynamics in Earth’s space environment. Full article

Measuring the small tree trunk variations during the day–night cycle, seasonal cycles, as well as those caused by the plant’s growth and health regime is a very important action in horticulture or forestry because by analyzing the collected data, assessments can be made on the health of the trees, but also on the climatic conditions and changes in a certain region. This can be performed with devices called dendrometers. This paper presents a new type of approach to these measurement types in which the trunk volume changes are highly sensitively converted into the axial stress on sensitive elements made of magnetic materials in wire form in which the giant stress impedance effect occurs. Finally, by electronic processing of the signals provided by the sensitive elements, digital words with a decimal value proportional to the diameter variations are obtained. This paper presents the operating principle, the constructive details and the experimental results obtained by testing the device in the laboratory and in-field. The proposed dendrometer, compared to those available commercially, has the advantage of good resolution and sensitivity, good immunity to temperature variations, the possibility of transmitting the result remotely, robustness and low price. Some metrological parameters obtained from the experimental testing are the following: resolution 1.6 µm, linearity 1.4%, measurement range 0 to 5 mm, temperature coefficient 0.012%/°C. Full article

In order to break through the difficulties with a very-low-frequency (VLF) miniaturized antenna with small power capacity and low radiation efficiency, this paper proposes a high-radiation-field-strength magnetic loop antenna based on a nanocrystalline alloy magnetic core. A high-permeability nanocrystalline toroidal core (μ_r = 50,000, B_s = 1.2 T) is used to optimize the thickness-to-diameter ratio (t = 0.08) and increase the effective permeability to 11,000. The Leeds wires, characterized by their substantial carrying capacity, are manufactured through a toroidal winding process. This method results in a 68% reduction in leakage compared to traditional radial winding techniques and enhances magnetic induction strength by a factor of 1.5. Additionally, this approach effectively minimizes losses, thereby facilitating support for kilowatt-level power inputs. A cascaded LC resonant network (resonant capacitance 2.3 μF) and ferrite balun transformer (power capacity 3.37 kW) realize a 20-times amplification of the input current. A series connection of a high-voltage isolation capacitor blocks DC bias noise, guaranteeing the stable transmission of 1200 W power, which is 6 times higher than the power capacity of traditional ring antenna. At 7.8 kHz frequency, the magnetic field strength at 120 m reaches 47.32 dBμA/m, and, if 0.16 pT is used as the threshold, the communication distance can reach 1446 m, which is significantly better than the traditional solution. This design marks the first instance of achieving kilowatt-class VLF effective radiation in a compact 51 cm-diameter magnetic loop antenna, offering a highly efficient solution for applications such as mine communication and geological exploration. Full article

Belle II is a particle physics experiment working at an high luminosity collider within a hard irradiation environment. The Time-Of-Propagation detector, aimed at the charged particle identification, surrounds the Belle II tracking detector on the barrel part. This detector is composed by 16 modules, each module contains a finely fused silica bar, coupled to microchannel plate photomultiplier tube (MCP-PMT) photo-detectors and readout by high-speed electronics. The MCP-PMT lifetime at the nominal collider luminosity is about one year, this is due to the high photon background degrading the quantum efficiency of the photocathode. An alternative to these MCP-PMTs is multi-pixel photon counters (MPPC), known as silicon photomultipliers (SiPM). The SiPMs, in comparison to MCP-PMTs, have a lower cost, higher photon detection efficiency and are unaffected by the presence of a magnetic field, but also have a higher dark count rate that rapidly increases with the integrated neutron flux. The dark count rate can be mitigated by annealing the damaged devices and/or operating them at low temperatures. We tested SiPMs, with different dimensions and pixel sizes from different producers, to study their time resolution (the main constraint that has to satisfy the photon detector) and to understand their behavior and tolerance to radiation. For these studies we irradiated the devices to radiation up to $5\times {10}^{11}1$ MeV neutrons equivalent (neq) per cm² fluences; we also started studying the effect of annealing on dark count rates. We performed several measurements on these devices, on top of the dark count rate, at different conditions in terms of overvoltage and temperatures. These measurements are: IV-curves, amplitude spectra, time resolution. For the last two measurements we illuminated the devices with a picosecond pulsed laser at very low intensities (with a number of detected photons up to about twenty). We present results mainly on two types of SiPMs. A new SiPM prototype developed in collaboration with FBK with the aim of improving radiation hardness, is expected to be delivered in September 2025. Full article

Stem-cell-based therapies rely on the transplantation of stem cells or stem-cell-derived organotypic cells into injured tissues in order to improve or restore tissue function that has been impaired by various diseases. The potential of induced pluripotent stem cells has created many applications in the field of cell therapy, for example. Some applications, for example, those in cardiac cell therapy, suffer from low or very low efficiencies of cell engraftment. Therefore, magnetic cell targeting can be discussed as a method for capturing superparamagnetic nanoparticle-labelled cells in the tissue. Here, we employ superparamagnetic iron oxide nanoparticles (SPIONs) for the intracellular magnetic loading of mesenchymal stem cells (MSCs). In addition, we test a novel strategy of labelling MSCs with ferromagnetic particles. The adhesion assays demonstrate a faster adhesion kinetic of SPIONs-loaded MSC spheroids when a magnetic field was applied, resulting in >50% spheroid adhesion after 30 min. Clustering of cells inside the magnetic field is a second potential mechanism of magnetic cell retention and >80% of cells were found to be aggregated in clusters when placed in a magnetic field for 10 min. SPIONs-loaded and ferromagnetic-particle-loaded cells performed equally in the cell clustering assay. In conclusion, the clustering of SPION-labelled cells explains the observation that magnetic targeting reaches maximal efficiency in vivo after only 10 min of magnetic field application. This has significant implications for magnetic-targeting-assisted stem cell and cell replacement therapies. Full article

Manganese oxides (manganites) are among the most studied materials in condensed matter physics due to the famous colossal magnetoresistance and very rich phase diagrams characterized by strong competition between ferromagnetic (FM) metallic and antiferromagnetic (AFM) insulating phases. One of the key questions that remains open even after more than thirty years of intensive research is the exact conductivity mechanism in insulating as well as in metallic phases and its relation to the corresponding magnetic structure. In order to shed more light on this problem, here, we report magnetotransport measurements on sintered nanocrystalline samples of the very poorly explored manganites ${\mathrm{Ca}}_{1-x}{\mathrm{Gd}}_x{\mathrm{MnO}}_3$ with $x=0.05$ and $x=0.10$, in the temperature range 2–300 K, and in magnetic fields up to 16 T. Our results indicate that both compounds at low temperatures exhibit metallic behavior with a peculiar resistivity upturn and a large negative magnetoresistance. We argue that such behavior is consistent with a Kondo-like scattering on Gd impurities coupled with the percolation of FM metallic regions within insulating AFM matrix. Full article

The simulation of the transport properties of confined, low-dimensional fluids can be performed efficiently by means of multi-particle collision (MPC) dynamics with suitable thermal-wall boundary conditions. We illustrate the effectiveness of the method by studying the dimensionality effects and size-dependence of thermal conduction, since these properties are of crucial importance for understanding heat transfer at the micro–nanoscale. We provide a sound numerical evidence that the simple MPC fluid displays the features previously predicted from hydrodynamics of lattice systems: (1) in 1D, the thermal conductivity $\kappa$ diverges with the system size L as $\kappa \sim L^{1/3}$ and its total heat current autocorrelation function $C\left(t\right)$ decays with the time t as $C\left(t\right)\sim t^{-2/3}$; (2) in 2D, $\kappa$ diverges with L as $\kappa \sim \ln \left(L\right)$ and its $C\left(t\right)$ decays with t as $C\left(t\right)\sim t^{-1}$; (3) in 3D, its $\kappa$ is independent with L and its $C\left(t\right)$ decays with t as $C\left(t\right)\sim t^{-3/2}$. For weak interaction (the nearly integrable case) in 1D and 2D, there exists an intermediate regime of sizes where kinetic effects dominate and transport is diffusive before crossing over to the expected anomalous regime. The crossover can be studied by decomposing the heat current in two contributions, which allows for a very accurate test of the predictions. In addition, we also show that, upon increasing the aspect ratio of the system, there exists a dimensional crossover from 2D or 3D dimensional behavior to the 1D one. Finally, we show that an applied magnetic field renders the transport normal, indicating that pseudomomentum conservation is not sufficient for the anomalous heat conduction behavior to occur. Full article

Energy harvesting from ambient vibrations has received significant attention as an alternative renewable, clean energy source for microelectronic devices in diverse applications such as wearables and environmental monitoring. However, typical vibrations in remote environments exhibit ultra-low frequencies with variations and uncertainty leading to operation away from resonance and severe underperformance in terms of power output. Pendulum-based energy harvesters offer a promising solution to these issues, particularly when designed for parametric resonant response to driven displacement of the pendulum pivot. Parametric excitation has been shown to trigger fast rotational motion of the pendulum VEH that is beneficial for energy generation and the necessary space utilization. Nevertheless, low-frequency ambient vibrations typically come at very weak amplitudes, a fact that establishes significant design barriers when traditional gravitational pendula are used for rotary energy harvesting. In this paper, we propose a novel concept that utilizes permanent magnet arrays to establish pendulum dynamics. Extensive investigation of the restoring torque of the proposed magnetic pendulum concept is conducted with analytical tools and FEA verification. The resulting oscillator exhibits frequency tuning that is decoupled from gravity and adjustable via the circularly arranged magnetic fields, leading to increased flexibility in the concurrently necessary amplitude tuning. Numerical integration of the nondimensional equation of motion is performed in the system’s parameter space to identify the impact on the regions triggering rotational response to parametric excitation. Finally, a theoretical case study is numerically investigated with the device space constrained within 20 cm³, showing a multi-fold improvement in the achieved power density of over 600 μW/cm³/g²/Hz over a broad range of frequencies and driving amplitudes as low as 1.1 Hz at 0.2 g. Full article

The so-call SQUIDs (abbreviated from superconducting quantum interference device) are very sensitive apparatuses especially built for metering very low magnetic fields. These systems have applications in various practical fields—biology, geology, medicine, different engineering areas, etc. Their features are mainly based on superconductors and the Josephson effect. They can be differentiated into two main groups—direct current (DC) and radio frequency (RF) SQUIDs. Both of them were constructed in the 1960s at Ford Research Labs. The main difference between them is that the second ones use only one superconducting tunnel junction. This reduces their sensitivity, but makes them significantly cheaper. We investigate namely the rf-SQUIDs in the present work. A number of authors devote their research to the rf-SQUIDs driven by an oscillating external flux. We aim to enlarge the theoretical base of these systems by adding new factors in their dynamics. Several particular cases are explored and simulated. We demonstrate also some specialized modules for investigating the proposed model. One application for possible control over oscillations is also discussed. It is based on the Fourier transform and, as a consequence, on the characteristic function of some probability distributions. Full article

Understanding the hydration kinetics of cement paste is essential for adjusting the early-age performance of concrete. Low-field nuclear magnetic resonance (LF-NMR) has emerged as an innovative technique to evaluate cement hydration progress by analyzing the evolution of transverse relaxation time (T₂) signals. This study provides insights into the influence of a super-absorbent polymer (SAP) as an internal curing agent and calcium oxide (CaO) as an expansive agent (EA) on LF-NMR spectroscopy of cement paste for the first time. The chemical compositions of the cement and CaO-based EA were determined by X-ray fluorescence, while the morphological characterizations of the cement, SAP and CaO-based EA materials were characterized by scanning electron microscopy. Based on the extreme points in the first-order derivatives of the T₂ signal maximum amplitude curve, the hydration progress was analyzed and identified with four stages in detail. The results showed that the use of the SAP with a higher content retarded the hydration kinetics more evidently at a very early age, thus prolonging the duration of the induction and acceleration stages. The use of the CaO-based EA shortened the induction, acceleration and deceleration stages, which verified its promotion of hydration kinetics in the presence of the SAP. The combination of 3 wt% SAP and 2 wt% CaO consumed more water content synergistically in the first 100 h by hydration reactions. These findings revealed the roles of SAP and CaO-based EA (commonly adopted for low-shrinkage concrete) in adjusting hydration parameters and the microstructure evolution of cement-based materials, which would further offer fundamental knowledge for the early-age cracking control of concrete structures. Full article

In the modern world, gas sensors play a crucial role in sectors such as high-tech industries, medicine, and environmental monitoring. Among these fields, oxygen sensors are the most important. There are several types of oxygen sensors, including optical, magnetic, Schottky diode, and resistive (or chemoresistive) ones. Currently, most oxygen-resistive sensors (ORSs) described in the literature are fabricated as thick layers, typically deposited via screen printing, and they operate at high temperatures, often exceeding 700 °C. This work presents a novel approach utilizing atomic layer deposition (ALD) to create very thin layers. Combined with appropriate doping, this method aims to reduce the energy consumption of the sensors by lowering both the mass requiring heating and the operating temperature. The device fabricated using the proposed process demonstrates a response of 88.21 at a relatively low temperature of 450 °C, highlighting its potential in ORS applications based on doped ALD thin films. Full article

The simulations presented here are based on the observational data of lightning electric currents associated with the eruption of the Hunga Tonga volcano in January 2022. The response of the lithosphere (Earth)–atmosphere–ionosphere–magnetosphere system to unprecedented lightning currents is theoretically investigated at low frequencies, including ultra low frequency (ULF), extremely low frequency (ELF), and very low frequency (VLF) ranges. The electric current source due to lightning near the location of the Hunga Tonga volcano eruption has a wide-band frequency spectrum determined in this paper based on a data-driven approach. The spectrum is monotonous in the VLF range but has many significant details at the lower frequencies (ULF, ELF). The decreasing amplitude tendency is maintained at frequencies exceeding 0.1 Hz. The density of effective lightning current in the ULF range reaches the value of the order of 10⁻⁷ A/m². A combined dynamic/quasi-stationary method has been developed to simulate ULF penetration through the lithosphere (Earth)–atmosphere–ionosphere–magnetosphere system. This method is suitable for the ULF range down to 10⁻⁴ Hz. The electromagnetic field is determined from the dynamics in the ionosphere and from a quasi-stationary approach in the atmosphere, considering not only the electric component but also the magnetic one. An analytical/numerical method has been developed to investigate the excitation of the global Schumann resonator and the eigenmodes of the coupled Schumann and ionospheric Alfvén resonators in the ELF range and the eigenmodes of the Earth–ionosphere waveguide in the VLF range. A complex dispersion equation for the corresponding disturbances is derived. It is shown that oscillations at the first resonance frequency in the Schumann resonator can simultaneously cause noticeable excitation of the local ionospheric Alfvén resonator, whose parameters depend on the angle between the geomagnetic field and the vertical direction. VLF propagation is possible over distances of 3000–10,000 km in the waveguide Earth–ionosphere. The results of simulations are compared with the published experimental data. Full article

The hybrid FEM-DBCI numerical method is proposed for the computation of coupling factors between time-harmonic magnetic fields and human bodies. Characteristics are highlighted which make FEM-DBCI very suitable to perform such computations. Several coil geometries are considered (circular coils) at low frequency. A simplified model of the human body is assumed as suggested by IEC standards. Details of the method are highlighted, and numerical results are also provided. Full article

The EASL diagnostic algorithm for hepatocellular carcinoma, currently in use, dates back to 2018. While awaiting its update, numerous advancements have emerged in the field of hepatocellular carcinoma imaging. These innovations impact every step of the diagnostic algorithm, from surveillance protocols to diagnostic processes, encompassing aspects preceding a patient’s inclusion in surveillance programs as well as the potential applications of imaging after the hepatocellular carcinoma diagnosis. Notably, these diagnostic advancements are particularly evident in the domain of magnetic resonance imaging. For example, the sensitivity of ultrasound in diagnosing very early-stage and early-stage hepatocellular carcinoma during the surveillance phase is very low (less than 50%) and a potential improvement in this sensitivity value could be achieved by using abbreviated protocols in magnetic resonance imaging. The aim of this review is to explore the 2024 updates in magnetic resonance imaging for hepatocellular carcinoma, with a focus on its role in surveillance, nodular size assessment, post-diagnosis imaging applications, and its potential role before the initiation of surveillance. Full article

Ionized metal physical vapor deposition (IMPVD), which is operated at a very low pressure to take advantage of the metal sputtering effect on the target surface, has unique properties compared with conventional DC magnetron sputtering. In this study, we investigated the effect of the rotating magnetic field on the plasma formation of IMPVD to enhance the deposition uniformity. This was accomplished through a multi-step simulation, which enabled plasma analysis, sputtered particle and chemical reaction analysis, and deposition profile analysis. A two-dimensional particle-in-cell Monte Carlo simulation utilizes the exact cross-section data of the Cu ion collisions and calculates the particle trajectories under specific magnetic field profiles. This new methodology gives guidance for the design of the magnetic field profiles of IMPVD and an understanding of the physical mechanism. Full article