Search Results (66)

The novel sub-stoichiometric copper oxide CuO_0.75 was prepared via the slow oxidation of Cu₂O. This compound retains the original crystallographic structure of tenorite CuO, despite the considerable presence of disordered oxygen vacancies. CuO_0.75 resembles the mixed valence oxide Cu²⁺/Cu¹⁺, while the unit cell contains one oxygen vacancy. Performance-wise, the electric resistivity and magnetic susceptibility data follow the Anderson–Mott localization theories. The exponential localization decay length was found to be α⁻¹ = 2.1 nm, in line with modern scaling research. Via cooling, magnetic double-exchange interaction, mediated by oxygen, results in Zener conductivity at T~122 K, which is followed by antiferromagnetic transition at T~51 K. The obtained results indicate that the CuO_0.75 compound can be perceived as a showcase material for the demonstration of a new class of high-performance magnetic materials. Full article

The macroscopic magnetic properties of magnetorheological elastomers (MREs) are influenced by their microstructure, yet limited investigations has been conducted on this subject to date. In this paper, a microstructure-based model is proposed to investigate the magnetization response of MREs. The dipole theory is employed to compute the local magnetic field, and a fitting equation derived from finite element analysis is used to correct the magnetic field. The Fröhlich–Kennelly equation is applied to describe the nonlinear magnetic properties of the particle material. Based on experimental observations, a body-centered tetragonal (BCT) model is established to describe the magnetization properties of anisotropic MREs. The proposed model is validated by comparison with experimental data and can be utilized to predict the effective susceptibility of MREs. The effects of particle volume fraction, the direction of the external magnetic field, and the shape of the MRE samples can also be analyzed using this model. Full article

A mononuclear complex [Dy(phenN₆)(HL′)₂]PF₆·CH₂Cl₂ (H₂L′ = R/S-1,1′-binaphthyl-2,2′-diphenol) with local D_6h symmetry was synthesized. Structural determination shows that Dy³⁺ was encapsulated within the coordination cavity of the neutral hexaaza macrocyclic ligand phenN₆, forming a non-planar coordination environment. The axial positions are occupied by two phenoxy groups of binaphthol in the trans form. The local geometry of Dy³⁺ closely resembles a regular hexagonal bipyramid D_6h configuration. The axial Dy-O_phenoxy distances are 2.189(5) and 2.145(5) Å, respectively, while the Dy-N bond lengths in the equatorial plane are in the range of 2.524(7)–2.717(5) Å. The axial O_phthalmoxy-Dy-O_phthalmoxy bond angle is 162.91(17)°, which deviates from the ideal linearity. Under the excitation at 320 nm, the complex exhibits a characteristic emission peak at 360 nm, corresponding to the naphthalene ring. The AC susceptibility measurements under an applied DC field of 1800 Oe show distinct temperature-dependent and frequency-dependent AC magnetic susceptibility, typical of single-molecule magnetic behavior. The Cole–Cole plot in the temperature range of 6.0–28.0 K was fitted using a model incorporating Orbach and Raman relaxation mechanisms, giving an effective energy barrier of U_eff = 300.2 K. Theoretical calculations on complex 1 reveal that the magnetization relaxation proceeds through the first excited Kramers doublets with a calculated magnetization blocking barrier of 404.1 cm⁻¹ (581.4 K). Full article

Susceptibility-weighted imaging (SWI) is a magnetic resonance imaging (MRI) sequence sensitive to substances that alter the local magnetic field, such as calcium and iron, allowing phase information to distinguish between them. SWI is a 3D gradient–echo sequence with high spatial resolution that leverages both phase and magnitude effects. The interaction of paramagnetic (such as hemosiderin and deoxyhemoglobin), diamagnetic (including calcifications and minerals), and ferromagnetic substances with the local magnetic field distorts it, leading to signal changes. Neurodegenerative diseases are typically characterized by the progressive loss of neurons and their supporting cells within the neurovascular unit. This cellular decline is associated with a corresponding deterioration of both cognitive and motor abilities. Many neurodegenerative disorders are associated with increased iron accumulation or microhemorrhages in various brain regions, making SWI a valuable diagnostic tool in clinical practice. Suggestive SWI findings are known in Parkinson’s disease, Lewy body dementia, atypical parkinsonian syndromes, multiple sclerosis, cerebral amyloid angiopathy, amyotrophic lateral sclerosis, hereditary ataxias, Huntington’s disease, neurodegeneration with brain iron accumulation, and chronic traumatic encephalopathy. This review will assist radiologists in understanding the technical framework of SWI sequences for a correct interpretation of currently established MRI findings and for its potential future clinical applications. Full article

A fundamental limitation of fMRI based on the BOLD effect is its limited spatial specificity. This is because the BOLD signal reflects neurovascular coupling, leading to macrovascular changes that are not strictly limited to areas of increased neural activity. However, neuronal activation also induces microstructural changes within the brain parenchyma by modifying the diffusion of extracellular biological water. Therefore, diffusion-weighted imaging (DWI) has been applied in fMRI to overcome BOLD limits and better explain the mechanisms of functional activation, but the results obtained so far are not clear. This is because a DWI signal depends on many experimental variables: instrumental, physiological, and microstructural. Here, we hypothesize that the γ parameter of the fractional diffusion representation could be of particular interest for DW-fMRI applications, due to its proven dependence on local magnetic susceptibility and diffusion multi-compartmentalization. BOLD fMRI and DW-fMRI experiments were performed at 3T using an exemplar application to task-based activation of the human visual cortex. The results, corroborated by simulation, highlight that γ provides complementary information to conventional diffusion fMRI and γ can quantify cellular morphology changes and neurovascular regulation during neuronal activation with higher sensitivity and specificity than conventional BOLD fMRI and DW-fMRI. Full article

Inducing magnetic hyperthermia (MHT) involves locally raising the temperature to 39–45 °C, which increases the susceptibility of tumor cells to therapeutic agents without damaging healthy tissues. Recent studies on trapezoidal pulsed alternating magnetic fields (TP-AMFs) have proven their considerable efficacy in increasing the temperature of magnetic nanoparticles (MNPs) compared to sinusoidal fields. Thermal therapies have been known to incorporate multiple combinations of therapeutic approaches to optimize the medical procedure for healing cancer patients such as chemotherapy and radiotherapy. The combination of MHT with chemotherapy aims to enhance the therapeutic effects against cancer due to the synergistic interaction in tumor cells. In this study, we aim to exploit the synergistic effects of combining MHT produced by TP-AMFs with a low concentration of 5-Fluorouracil (5-FU) to optimize the therapeutic outcomes in comparison to TP-AMFs MHT alone. Hence, we exposed a glioblastoma cell line (CT2A) incubated with iron oxide nanoparticles at 1 mg/mL to two cycles of MHT employing a trapezoidal-square waveform at 200 kHz and 2 mT for 30 min for each cycle, separated by a 45 min break, both as a single treatment and in combination with 0.1 μg/mL of 5-FU. Our findings demonstrated the efficacy of the synergistic effect between MHT treatment via TP-AMFs and the 5-FU, increasing the cell death to 58.9 ± 2%, compared to 31.4 ± 3% with MHT treatment alone. Cell death was primarily driven by the necrosis pathway (47.3 ± 2%) compared to apoptosis (11.6 ± 2). The addition of 5-FU enhanced the cytotoxic effect of MHT on CT2A cells, increasing the calreticulin (CRT) positive cells to 17 ± 1% compared to 10 ± 1% as produced by MHT treatment alone. Furthermore, this combination suggests that the employed treatment approach can promote immune system activation due to the exposure of CRT in the treated cells. Full article

Circuit breakers are effectively utilized for the controlled switching technique to mitigate inrush current when energizing an unloaded transformer. The core of the controlled switching technique is to obtain the appropriate closing angle based on the residual flux after opening. For the prediction of residual flux, the voltage integration method faces the difficult problem of determining the integration upper limit, while the Jiles- Atherton (J-A) model has the advantages of clear physical meaning of parameters, accurate calculation, and the ability to iteratively solve residual magnetism. It has low dependence on the initial conditions and greatly avoids the influence of DC offset and noise on measurement results. Firstly, an improved particle-swarm optimization algorithm is proposed in this paper to address the problem of slow convergence speed and susceptibility to local optima in current particle-swarm optimization algorithms for extracting J-A model parameters. The problem of slow convergence speed and susceptibility to local optima in traditional particle-swarm optimization algorithms is solved by optimizing the velocity and position-update formulas of particles in this algorithm. This new algorithm not only accelerates convergence speed, but also balances the overall and local search capabilities. Then, based on the J-A model, residual flux prediction of the transformer is carried out, and a transformer no-load energization experimental platform is built. A simulation model combining the J-A model and classical transformer is constructed using PSCAD/EMTDC to predict the residual flux of the transformer at different closing angles. Finally, by combining simulation with actual experimental waveform data, the accuracy of residual flux prediction was verified by comparing the peak values of the inrush current. Full article

The thermodynamic and magnetic properties of weakly interacting electron gas localized in a CdSe cylindrical core–shell quantum dot in the presence of axial magnetic field are investigated. The entropy, mean energy, and heat capacity of such a gas are determined, and its magnetic properties (magnetization and diamagnetic susceptibility) are studied. The possibilities of controlling thermodynamic parameters by changing the geometric parameters of quantum dots are shown. Calculations show that this gas has diamagnetic properties. These results provide insights into the features of physical processes occurring in thin core–shell quantum systems, which have potential applications in opto- and nanoelectronics. Full article

Parameter identification of a permanent magnet synchronous wind generator (PMSWG) is of great significance for condition monitoring, fault diagnosis, and robust control. However, the conventional multi-parameter identification approach for a PMSWG is plagued by deficiencies, including its sluggish identification speed, subpar accuracy, and susceptibility to local optimization. In light of these challenges, this paper proposes a distributed parameter identification framework based on intelligent algorithms. The proposed approach involves the deployment of SSA, DBO, and PSO algorithms, leveraging golden sine ratio and Gaussian variation strategies for multi-parameter optimization and performance enhancement. Second, the optimal solutions of each intelligent algorithm are aggregated to achieve overall optimization performance enhancement. The efficacy of the proposed method is substantiated by a 6 MW PMSWG parameter identification practice simulation result, which demonstrates its superiority. The proposed method was shown to identify parameters more quickly and effectively than the underlying algorithms, which is of great significance for condition monitoring, fault diagnosis, and robust control of the PMSWG. Full article

Permanent Magnet Synchronous Motors (PMSMs) are nonlinear, multi-parameter systems that exhibit structural symmetry but are susceptible to parameter variations and external disturbances. These challenges can disrupt the inherent symmetrical characteristics of PMSM dynamics during real-world operations, posing difficulties for achieving efficient control. To address this issue, this paper proposes a Model-Free Generalized Super-Twisting Algorithm Fast Terminal Sliding Mode Control (MFFTSMC-GSTA) method. First, a novel ultra-local model incorporating PMSM uncertainties is established, and the MFFTSMC-GSTA controller is designed to address the system’s complex dynamic behavior. By integrating the generalized super-twisting algorithm with the nonsingular fast terminal sliding mode algorithm, the proposed controller ensures finite-time convergence and effectively mitigates chattering. Second, an extended sliding mode disturbance observer is developed to estimate the unknown components of the ultra-local model and provide feedforward compensation, further enhancing system robustness and dynamic performance. The experimental results show that the total harmonic distortion (THD) value of the proposed control method is 1.38%, demonstrating significant improvements in response speed and robustness for motor speed control, and verifying the algorithm’s superior performance under complex operating conditions. Full article

In this paper, we focus on the properties of local energy minima and energy barriers in immobilized dense clusters of magnetic nanoparticles. Understanding of these features is highly interesting both for the fundamental physics of disordered systems with long-range interparticle interaction and for numerous applications of modern ferrofluids consisting of such clusters. In particular, it is needed to predict the ac-susceptibility of these systems and their magnetization relaxation after a sudden change in the external field, because both processes occur via magnetization jumps over energy barriers that separate the energy minima. Due to the exponential increase in the corresponding jump time with barrier height ($t_{\mathrm{sw}}\sim \exp (\Delta E/kT)$), direct Langevin dynamics simulations of this process are not feasible. For this reason, we have developed efficient numerical methods both for finding as many energy minima as possible and for the reliable evaluation of energy barriers between them. Our results for the distribution of overlaps between the local energy minima imply that there is no spin-glass state in such clusters even when they consist of particles with a small anisotropy. Further, we show that the distributions of energy barrier heights are qualitatively different for clusters of particles with small, intermediate, and large anisotropies, which has important consequences for the magnetization dynamics of these systems. Full article

Spin Hamiltonians, like the Heisenberg model, are used to describe the magnetic properties of exchange-coupled molecules and solids. For finite clusters, physical quantities, such as heat capacities, magnetic susceptibilities or neutron-scattering spectra, can be calculated based on energies and eigenstates obtained by exact diagonalization (ED). Utilizing spin-rotational symmetry SU(2) to factor the Hamiltonian with respect to total spin S facilitates ED, but the conventional approach to spin-adapting the basis is more intricate than selecting states with a given magnetic quantum number M (the spin z-component), as it relies on irreducible tensor-operator techniques and spin-coupling coefficients. Here, we present a simpler technique based on applying a spin projector to uncoupled basis states. As an alternative to Löwdin’s projection operator, we consider a group-theoretical formulation of the projector, which can be evaluated either exactly or approximately using an integration grid. An important aspect is the choice of uncoupled basis states. We present an extension of Löwdin’s theorem for $s=\frac{1}{2}$ to arbitrary local spin quantum numbers s, which allows for the direct selection of configurations that span a complete, linearly independent basis in an S sector upon the spin projection. We illustrate the procedure with a few examples. Full article

Existing magnetic tracer detection systems primarily rely on fundamental wave signal acquisition using non-differential sensor configurations. These sensors are highly susceptible to external interference and lack tomographic localization capabilities, hindering their clinical application. To address these limitations, this paper presents a novel method for achieving the deep spatial localization of tracers. The method exploits second harmonic signal detection at non-zero field points. By considering the combined nonlinear characteristics of the coil’s axial spatial magnetic field distribution and the Langevin function, a correlation model linking the signal peak and bias field is established. This model enables the determination of the tracer’s precise spatial location. Building on this framework, a handheld device for localizing magnetic nanoparticle tracers was developed. The device harnesses the second harmonic response generated by coupling an AC excitation field with a DC bias field. Our findings demonstrate that under conditions of reduced coil turns and weak excitation fields, the DC bias field exhibits exclusive dependence on the axial distance of the detection point, independent of particle concentration. This implies that the saturated DC bias field corresponding to the second harmonic signal can be used to determine the magnetic nanoparticle sample detection depth. The experimental results validated the method’s high accuracy, with axial detection distance and concentration reduction errors of only 4.8% and 4.1%, respectively. This research paves the way for handheld probes capable of tomographic tracer detection, offering a novel approach for advancing magnetically sensitive biomedical detection technologies. Full article

We synthesized some SWCNTs films under different magnetic fields and temperatures in a magnetic field-assisted FC-CVD and obtained Raman spectra of the films. By analyzing the Raman spectra, it was concluded that the SWCNTs films had defects, and the relative content of m-SWCNTs in the SWCNTs films was obtained. The trajectory of m-SWCNTs was obtained by analyzing the motion behavior of m-SWCNTs flow in the field-assisted system, and a model was built to describe the relationship between the relative content of m-SWCNTs and magnetic fields. The axial magnetic susceptibility of m-SWCNTs as a parameter was obtained by fitting the experimental results and the model. This is the first time that the axial magnetic susceptibility of m-SWCNTs has been obtained. The result obtained at 1273 K is at least two orders of magnitude greater than the magnetic susceptibilities and anisotropies of purified m-SWCNTs at 300 K, indicating that the defects increase the Curie temperature and Curie constant of m-SWCNTs. This is consistent with the spin-polarized density functional theory, which predicts that m-SWCNTs with vacancies have local magnetic moments around the vacancies and exhibit ferro- or ferrimagnetism. Full article

Currently, magnetic gradient tensor-based localization methods face challenges such as significant errors in geomagnetic field estimation, susceptibility to local optima in optimization algorithms, and inefficient performance. In addressing these issues, this article propose a two-point localization method under the constraint of overlaying geometric invariants. This method initially establishes the relationship between the target position and the magnetic gradient tensor by substituting an intermediate variable for the magnetic moment. Exploiting the property of the eigenvector corresponding to the minimum absolute eigenvalue being perpendicular to the target position vector, this constraint is superimposed to formulate a nonlinear system of equations of the target’s position. In the process of determining the target position, the Nara method is employed for obtaining the initial values, followed by the utilization of the Levenberg–Marquardt algorithm to derive a precise solution. Experimental validation through both simulations and experiments confirms the effectiveness of the proposed method. The results demonstrate its capability to overcome the challenges faced by a single-point localization method in the presence of some errors in geomagnetic field estimation. In comparison to traditional two-point localization methods, the proposed method exhibits the highest precision. The localization outcomes under different noise conditions underscore the robust noise resistance and resilience of the proposed method. Full article