Dipole Clusters Research Articles

Influence of synergistic effect on the structure and dielectric property of La2(TiZrSnHfGe)2O7 high entropy oxides

In this study, La2(TiZrSnHfGe)2O7 high entropy oxides were firstly prepared by solid state reaction method. The effects of different sintering temperatures on the structure, morphology and dielectric properties were studied. When the pre-calcination temperature is 1300 °C, the powder exhibits a single pyrochlore phase instead of defective fluorite phase. The existence of high entropy affects the changes in the crystal structure of A2B2O7 type oxides, resulting in lattice distortion. The dielectric results showed that the ceramics have certain frequency dispersion, and the dielectric properties are affected by temperature and frequency. Due to the high entropy effect, the La2(TiZrSnHfGe)2O7 ceramic exhibits good dielectric stability at both high and low frequencies. The formation of defect dipole clusters in the system results in the increase of dielectric constant. It is feasible to change the dielectric properties of ceramics by designing high entropy oxides, which showed the potential value in microelectronics field.

Polarization loss in rutile TiO2 doped with acceptor ions for microwave absorption

With an increase in electromagnetic (EM) pollution, inducing polarization loss using lattice defects has become one of the main strategies for the design and optimization of a new generation of microwave absorbers. In this study, point defects in TiO2 absorbers are designed and controlled using a sol–gel method. The influences of the electronegativity difference and the ionic valence states of the dopant ions on the microwave absorption (MA) performance of rutile TiO2 composites are investigated. The results show that the defects such as oxygen vacancy (VO∙∙) and Ti3+ can be adjusted continuously at a high-temperature sintering process. Cu2+, which has a larger electronegativity than Ti4+ (Cu2+χ = 1.90 > Ti4+χ = 1.54) promotes the localization of electrons. Furthermore, compared with Ag+, which has a similar electronegativity (Ag+χ = 1.93 ≈ Cu2+χ = 1.90), polyvalent copper ions (Cu2++e→Cu+) enhance the electron-hopping process. The formed electron-pinning defect dipole clusters (TiTi′, VO∙∙, CuTi″, CuTi″′, Ti3+→VO∙∙←Ti3+, Ti3+→VO∙∙←Cu2++e, Cu2++e→Cu+, Ti4++e→Ti3+) produce a stronger polarization relaxation process, which regulates the MA performance of TiO2 absorbers. Therefore, this study provides an essential reference for refining the EM wave attenuation performance of simple oxide absorbers.

Slow and non-equilibrium dynamics due to electronic ferroelectricity in a strongly-correlated molecular conductor

Ferroelectricity, where electronic degrees of freedom determine the polar order—thereby enabling fast switching and phase control—is an important research field in current condensed-matter physics. Using a combination of resistance noise and dielectric spectroscopy we investigate the nature of relaxor-type electronic ferroelectricity in the organic conductor κ-(BETS)2Mn[N(CN)2]3, a system that represents a wider class of materials of correlated electron systems for which functionalities for organic spintronics recently have been discussed. The two complementary spectroscopies reveal a distinct low-frequency dynamics on different length scales, namely (i) an intrinsic relaxation that is typical for relaxor ferroelectrics which classifies the system as a possible new multiferroic, and (ii) two-level processes which we identify as fluctuating polar nanoregions (PNR), i.e., clusters of quantum electric dipoles that fluctuate collectively. The PNR preform above the metal insulator (MI) transition. Upon cooling through TMI, a drastic increase of the low-frequency 1/f-type fluctuations and slowing down of the charge carrier dynamics is accompanied by the onset of strong non-equilibrium dynamics indicating a glassy transition of interacting dipolar clusters. The freezing of PNR and non-equilibrium dynamics is suggested to be a common feature of organic relaxor-type electronic ferroelectrics.

Colossal permittivity with ultra-wide temperature stability in Bi + Ca co-doped BaTiO3

The poor temperature stability of the BaTiO3 ceramic has always been the main problem limiting their application. This situation has been improved but sacrifices the intrinsic polarization, which significantly reduces the dielectric constant. In this work, the mechanism of multiple polarization was creatively introduced, and the temperature stability and dielectric properties of BaTiO3-based ceramics are simultaneously enhanced. In particular, the Ba0.9925Bi0.005Ti0.995Ca0.005O2.995 (BBTC0.5) ceramic sample achieved excellent temperature stability (−14.8% to 8.85%) over an ultra-wide temperature range (−47 to 400 °C) and exhibited colossal permittivity (27,125, 25 °C, 1 kHz) and low dielectric loss (0.07, 25 °C, 1 kHz). The dielectric properties, complex impedance spectra combined with XPS results indicate that the defective dipole clusters (Ti3+-VO..-Ti3+, BiBa. and CaTi″-VO..) along with surface effects lead to colossal permittivity effect. More importantly, SEM images show the presence of the second phase at grain boundaries, which prevent the carriers within the grains from accumulating at the grain boundaries. As a result, the dielectric loss was reduced and the temperature stability was further extended. This strategy breaks the traditional limitation of single/noncomprehensive enhancement by single-polarization mechanism, and is of great theoretical and practical significance to promote the research and application of high-performance BaTiO3-based ceramic materials.

Colossal permittivity and low dielectric loss of Ta5+ and Al3+ co-doped strontium titanate ceramics sintered in N2 atmosphere

In this work, the ceramics of Sr(Ta1/2Al1/2)xTi1-xO3 (x = 0 %, 0.5 %, 1 %, 2 %, 3 %, 4 %, and 5 %) were produced through the solid-state reaction and sintered under N2 atmosphere. The frequency coefficient of permittivity and dielectric loss for the sample with x = 4 % is blow |24%| and |26%|, respectively, within the frequency of 1 kHz to 1 MHz. This demonstrates favorable frequency stability in the dielectric properties. The sample with x = 4 % exhibits remarkable permittivity (εr ∼ 125,000 @ 1 kHz, εr ∼ 95,000 @ 1 MHz) and low dielectric loss (tanδ ∼ 0.054 @ 1 kHz, tanδ ∼ 0.044 @ 1 MHz) were achieved at room temperature. Through the analysis of HAADF-STEM, XPS, it is concluded that and dielectric relaxation, the colossal permittivity effect is primarily attributed to defect clusters associated with oxygen vacancies such as Ti3+−VO••− Ti3+. The clusters of defect dipoles exert a pinning effect on freedom electrons, constraining their long-range transition and improving the dielectric properties. This study lays the foundation for advancing the electronic components, making a significant milestone in technological advancements.

Research on electromagnetic scattering characteristics of dipole clusters

AbstractThis paper equates chaff clouds to dipole clusters and studies the electromagnetic scattering problem of dipole clusters based on the linear method of moment (LMM) that solve the electric field Integral equation with the pulse basis function. Firstly, the radar cross section (RCS) of three dipole elements is calculated. The dipole element is divided into 11 segment line units using pulse basis functions. The actual chaff clouds are modeled as two nearest dipole cluster models, which are cubic dipole cluster with uniform distribution formed and spherical dipole cluster with Gaussian distribution formed. The total RCS and total E‐Field magnitude of two dipole cluster models were calculated. Finally, two physical models are constructed based on the simulation models and an experiment is designed. The electromagnetic scattering characteristics of the two models are measured, which verifies the accuracy of the simulation results and the operability of the experiment.

The role of magnetoencephalography in preoperative localization and postoperative outcome prediction in patients with posterior cortical epilepsy.

We aimed to explore the value of magnetoencephalography in the presurgical evaluation of patients with posterior cortex epilepsy. A total of 39 patients with posterior cortex epilepsy (PCE) and intact magnetoencephalography (MEG) images were reviewed from August 2019 to July 2022. MEG dipole clusters were classified into single clusters, multiple clusters, and scatter dipoles based on tightness criteria. The association of the surgical outcome with MEG dipole classifications was evaluated using Fisher's exact tests. Among the 39 cases, there were 24 cases of single clusters (61.5%), nine cases of multiple clusters (23.1%), and six cases of scattered dipoles (15.4%). Patients with single dipole clusters were more likely to become seizure-free. Among single dipole cluster cases (n = 24), complete MEG dipole resection yielded a more favorable surgical outcome than incomplete resection (83.3% vs. 16.7%, p = 0.007). Patients with concordant MRI and MEG findings achieved a significantly more favorable surgical outcome than discordant patients (66.7% vs. 33.3%, p = 0.044), especially in single dipole cluster patients (87.5% vs. 25.0%, p = 0.005). MEG can provide additional valuable information regarding surgical candidate selection, epileptogenic zone localization, electrode implantation schedule, and final surgical planning in patients with posterior cortex epilepsy.

Association Between Magnetoencephalography-Localized Epileptogenic Zone, Surgical Resection Volume, and Postsurgical Seizure Outcome.

Surgical resection of magnetoencephalography (MEG) dipole clusters, reconstructed from interictal epileptiform discharges, is associated with favorable seizure outcomes. However, the relation of MEG cluster resection to the surgical resection volume is not known nor is it clear whether this association is direct and causal, or it may be mediated by the resection volume or other predictive factors. This study aims to clarify these open questions and assess the diagnostic accuracy of MEG in our center. We performed a retrospective cohort study of 68 patients with drug-resistant epilepsy who underwent MEG followed by resective epilepsy surgery and had at least 12 months of postsurgical follow-up. Good seizure outcomes were associated with monofocal localization (χ2 = 6.94, P = 0.001; diagnostic odds ratio = 10.2) and complete resection of MEG clusters (χ2 = 22.1, P < 0.001; diagnostic odds ratio = 42.5). Resection volumes in patients with and without removal of MEG clusters were not significantly different (t = 0.18, P = 0.86; removed: M = 20,118 mm3, SD = 10,257; not removed: M = 19,566 mm3, SD = 10,703). Logistic regression showed that removal of MEG clusters predicts seizure-free outcome independent of the resection volume and other prognostic factors (P < 0.001). Complete resection of MEG clusters leads to favorable seizure outcomes without affecting the volume of surgical resection and independent of other prognostic factors. MEG can localize the epileptogenic zone with high accuracy. MEG interictal epileptiform discharges mapping should be used whenever feasible to improve postsurgical seizure outcomes.

Origin of high comprehensive electromechanical properties of novel donor and acceptor–codoped PMN–30PT ceramics

Donor and acceptor–codoped PMN–30PT ceramics with 1–3 mol% Sm and 1 mol% Mn were fabricated via a two-step solid-state reaction. The crystal structure and electrical properties were investigated in detail. Donor Sm and acceptor Mn codoping substantially enhances the electromechanical, piezoelectric, and dielectric properties with a high piezoelectric coefficient d33 = 483–680 pC/N, a high mechanical quality factor Qm = 518–642, a high field-induced strain = 0.20%–0.24 %, and a low dielectric loss tan δ = 0.54%–0.69 %. X-ray diffraction and Raman spectra reveal the coexisting triple phase composition of the rhombohedral phase, tetragonal phase, and monoclinic polar nanoregions. Thermally stimulated depolarization current verifies the formation of various defect dipole clusters such as (MnTi″–VO··)×. With enhanced local structure heterogeneity induced by Sm, the phase composition and defect chemistry are regarded as the origin of such high comprehensive performance.

Extended source analysis of movement related potentials (MRPs) for self-paced hand and foot movements demonstrates opposing cerebral and cerebellar laterality: a preliminary study

The cerebellum is known to have extensive reciprocal connectivity with the cerebral cortex, including with prefrontal and posterior parietal cortex, which play an important role on the planning and execution of voluntary movement. In the present article we report an exploratory non-invasive electrophysiological study of the activity of the cerebellum and cerebrum during voluntary finger and foot movements. In a sample of five healthy adult subjects, we recorded EEG and the electro-cerebellogram (ECeG) with a 10% cerebellar extension montage during voluntary left and right index finger and foot movements. EMG was recorded from finger extensors and flexors and from the tibialis anterior and soleus muscles and was used to generate triggers for movement related averaging (−2000 to +2000 ms). Source analysis was conducted over five epochs defined relative to EMG onset: whole epoch (−1000 to +1000 ms), pre-move 1000 (−1000 to 0 ms), pre-move 500 (−500 to 0 ms), post-move 500 (0 to +500 ms) and post-move 1000 (0 to +1000 ms). This yielded a total of 123 cerebral and 65 cerebellar dipole clusters from across all epochs, including the pre-movement epochs, which were then subject to statistical analysis. These demonstrated predominantly contralateral dominance for the cerebral clusters, but predominantly ipsilateral dominance for the cerebellar clusters. In addition, both cerebral and cerebellar clusters showed evidence of a somatotopic gradient, medially (X-axis) for the cerebral clusters, and medially and dorso-ventrally (Z-axis) for the cerebellar clusters. These findings support the value of recording cerebellar ECeG and demonstrate its potential to contribute to understanding cerebellar function.

Effect of different defects on the polarization mechanism of (Nb,Ga) codoped TiO2 single crystals

Various defects have a profound impact on the dielectric properties and polarization mechanisms of (Nb,Ga) codoped TiO2 crystals. However, the research conducted in this area remains limited. To address this, we grew (Nb,Ga) codoped TiO2 crystals via the Verneuil method and investigated their dielectric properties under various atmospheric annealing conditions. Annealing in oxygen reduces the number of defects. In this case, the point defects associated with oxygen vacancies is unable to fully form the ideal complex defect clusters which can form effective pegging of free electrons. On the other hand, the defects are mainly in the form of simple defect clusters that causes hopping polarization. Annealing under mixed gas (Ar:H2 = 95%:5%) increases the number of defects and contains more free carriers, which migrate to the interface between the sample and the electrode, leading to interfacial polarization. Both hopping polarization and interfacial polarization are slow polarization, resulting in an increase in dielectric loss and a decrease in frequency stability. Annealing in air or nitrogen atmospheres forms ideal defect dipole clusters, where the electron-pinned defect dipoles (EPDD) are predominantly polarized, resulting in superior dielectric properties. It has been clarified that EPDD as the main polarization form can yield better dielectric properties. By focusing on single crystals as the research subject, we effectively eliminate the influence of grain boundaries, enabling a more accurate assessment of the effects of various crystal defects on dielectric properties. This study holds substantial implications for the advancement of TiO2-based dielectric materials, offering valuable insights into their performance optimization.

Electromagnetic source imaging predicts surgical outcome in children with focal cortical dysplasia

ObjectiveTo evaluate the diagnostic accuracy of electromagnetic source imaging (EMSI) in localizing spikes and predict surgical outcome in children with drug resistant epilepsy (DRE) due to focal cortical dysplasia (FCD). MethodsWe retrospectively analyzed magnetoencephalography (MEG) and high-density (HD-EEG) data from 23 children with FCD-associated DRE who underwent intracranial EEG and surgery. We localized spikes using equivalent current dipole (ECD) fitting, dipole clustering, and dynamical statistical parametric mapping (dSPM) on EMSI, electric source imaging (ESI), and magnetic source imaging (MSI). We calculated the distance from the seizure onset zone (DSOZ) and resection (DRES). We estimated receiver operating characteristic (ROC) curves with Youden’s index (J) to predict outcome. ResultsEMSI presented shorter DSOZ (15.18 ± 9.06 mm) and DRES (8.56 ± 6.24 mm) compared to ESI (DSOZ: 25.04 ± 16.20 mm, p < 0.009; DRES: 18.88 ± 17.30 mm, p < 0.03) and MSI (DSOZ: 23.37 ± 8.98 mm, p < 0.03; DRES: 15.51 ± 10.11 mm, p < 0.02) for clustering in patients with good outcome. Clustering showed shorter DSOZ and DRES compared to ECD fitting and dSPM (p < 0.05). EMSI had higher performance as outcome predictor (J = 70.63%) compared to ESI (J = 41.27%) and MSI (J = 33.33%) for clustering. ConclusionsEMSI provides superior localization and improved predictive performance than individual modalities. SignificanceEMSI can help the surgical planning and facilitate the localization of epileptogenic foci.

The Clustering Properties of AGNs/Quasars in CatWISE2020 Catalog

We study the clustering properties of 1,307,530 AGNs/quasars in the CatWISE2020 catalog prepared using the Wide-field Infrared Survey Explorer and Near-Earth Object Wide-field Infrared Survey Explorer survey data. For angular moments ℓ ⪆ 10 (⪅18°) down to nonlinear scales, the results are in agreement with the standard ΛCDM cosmology, with a galaxy bias roughly matching that of the NRAO VLA Sky Survey (NVSS) AGNs. We further explore the redshift dependence of the fraction of infrared-bright AGNs on stellar mass, , and find , ruling out a nonevolution hypothesis at a ≈4.6σ confidence level. The results are consistent with the measurements obtained with NVSS AGNs, though considerably more precise thanks to the significantly higher number density of objects in CatWISE2020. The excess dipole and high clustering signal above angular scale ≈18° remains anomalous.

Supression of Alpha- and Beta-Oscillations during Virtual Social Interactions

The aim was to study the oscillatory dynamics accompanying the processes of interaction with the virtual character and the localization of the revealed effects. 42 subjects (of which 25 are women) aged 18 to 41 years took part in the study. During the EEG recording, the subjects had to interact with the virtual character by choosing one of three options (“offer friendship”, “attack” or “avoid contact”). Faces with 5 types of emotional expressions (angry, happy, frightened, sad and neutral) were used. An analysis of equivalent dipoles revealed that the choice of active interaction (to attack or offer friendship), compared with the avoidance of interaction, was accompanied by a large decrease in α- and β-rhythms, which may be associated with the processes of understanding the virtual character’s intentions. The choice of friendship versus avoidance of interaction was accompanied by an increase in δ-rhythm, which may indicate the presence of a motivational component. The revealed effects were found in clusters of equivalent dipoles, the localization of which coincides with the structures of the mentalization network and the network of mirror neurons involved in the processes of people’s intent assessment.

Dipole dynamics in the point vortex model

At the very heart of turbulent fluid flows are many interacting vortices that produce a chaotic and seemingly unpredictable velocity field. Gaining new insight into the complex motion of vortices and how they can lead to topological changes of flows is of fundamental importance in our strive to understand turbulence. Our aim is form an understanding of vortex interactions by investigating the dynamics of point vortex dipoles interacting with a hierarchy of vortex structures using the idealized point vortex model. Motivated by its close analogy to the dynamics of quantum vortices in Bose–Einstein condensates, we present new results on dipole size evolution, stability properties of vortex clusters, and the role of dipole–cluster interactions in turbulent mixing in 2D quantum turbulence. In particular, we discover a mechanism of rapid cluster disintegration analogous to a time-reversed self-similar vortex collapse solution.

Normal-mode oscillations for the circular and dipolar states of a filled hexagonal magnetic dipole cluster.

We analyze the rotational dynamics of six magnetic dipoles of identical strength at the vertices of a regular hexagon with a variable-strength dipole in the center. The seven dipoles spin freely about fixed axes that are perpendicular to the plane of the hexagon, with their dipole moments directed parallel to the plane. Equilibrium dipole orientations are calculated as a function of the relative strength of the central dipole. Small-amplitude perturbations about these equilibrium states are calculated in the absence of friction and are compared with analytical results in the limit of zero and infinite central dipole strength. Normal modes and frequencies are presented. Bifurcations are seen at two critical values of the central dipole strength, with bistability between these values.

Magnetoencephalography: at the forefront of optimizing epilepsy surgery

Magnetoencephalography: at the forefront of optimizing epilepsy surgery

Utility of magnetoencephalography combined with stereo-electroencephalography in resective epilepsy surgery: A 2-year follow-up.

Precise and accurate implantation of stereo-electroencephalography (SEEG) electrodes is critical for the localization of the seizure onset zone (SOZ), which plays a leading role in the prognosis of resective epilepsy surgery. Magnetoencephalography (MEG) is a noninvasive technique which can delineate the epilepsy focus by visualizing interictal spikes into dipole clusters. MEG may provide supporting information for guiding SEEG electrode implantation and improve the long-term outcomes of epilepsy surgery. In this study, we evaluated the accuracy of MEG in determining the SOZ. We retrospectively analyzed patients with refractory epilepsy who underwent MEG examination and SEEG implantation before resective epilepsy surgery in the Shanghai Ruijin Hospital. The SEEG plan was designed according to the dipole clusters and the resections were operated according to the SEEG recordings. We investigated the relationships of the pattern of MEG dipole clusters and SEEG sampling to the final resective surgery prognosis. We included 42 patients with a postoperative follow-up of at least 2 years (mean 34.1 months). Eighteen (42%) patients who showed concordant localization between MEG and SEEG evaluation had a higher probability of seizure-free outcome (p=0.046, χ2=4.835, odds ratio=5.00, 95% CI=1.12-22.30). Complete sampling of MEG dipole clusters by SEEG electrodes was found in 23 (54%) patients, who had higher probability of seizure-free outcome that those with incomplete sampling (p<0.001, odds ratio=16.67, 95% CI=3.11-89.28). MEG results showing a single, tight cluster or stable orientation were associated to better seizure outcomes after resective surgery. MEG dipole cluster helps SEEG implantation in localizing the SOZ for better long-term epilepsy surgery outcome. The MEG results can play a role as prognostic predictors of epilepsy surgery.

Colossal permittivity and ultralow dielectric loss in SrTi1-xNbxO3 ceramics sintered at different atmospheres via defect chemistry improvement

SrTiO3 is recognized as one of the most promising candidate materials for colossal permittivity. However, the origin of colossal permittivity is still not well understood. In this work, SrTi0.998Nb0.002O3 ceramics (SNT) were synthesized via typical solid-state reaction process and sintered in air, N2, and N2–H2 atmospheres (labelled as SNT-Air, SNT-N2 and SNT-H2). The SNT-H2 ceramic achieves a colossal permittivity of 89254 and a dielectric loss of 0.013 at 1 kHz and maintains a colossal permittivity (∼8 × 104) with a low dielectric loss (<0.1) throughout a wide temperature (50 °C–300 °C) and frequency (100 Hz-1 MHz) range. The mechanism of the outstanding properties of SNT-H2 ceramics was investigated by X-ray photoelectron spectroscopy (XPS), impedance spectrum and activation energy analysis. The TiTi′−VO⋅⋅−TiTi′ defect dipole and VO⋅⋅−3TiTi′−NbTi⋅ defect dipole clusters exist in SNT ceramics by sintering in the reducing atmosphere of H2. Otherwise, the grain is semi-conducting, and the grain boundary is insulating in SNT-H2 ceramics by impedance spectrum analysis. In conclusion, the defect dipole and clusters localized in the grain could be the fundamental cause for the ultra-dielectric properties. As a result, The SNT-H2 ceramic exhibits the colossal permittivity with low dielectric loss, as well as good temperature and frequency stability, potentially aiding in the development of colossal materials.

Hysteretic transition between states of a filled hexagonal magnetic dipole cluster

By minimizing the magnetostatic potential energy and by finding zeros in the sum of the squares of the torques, we find the equilibrium states of six dipoles of identical strength at the vertices of a regular hexagon and a variable-strength dipole at the center. The seven dipoles spin freely about fixed axes that are perpendicular to the plane of the hexagon, with their dipole moments directed parallel to the plane. When the central dipole is weak compared with the perimeter dipoles, a “circular” state applies in which the perimeter dipole moments circle around the central dipole, which points toward a perimeter dipole. When the central dipole is strong, a more symmetric “dipolar” state applies in which the perimeter dipole moments align approximately with the field of the central dipole. Over an intermediate range of dipole strengths bounded by two critical values, both states are locally stable and the state of the system depends upon its history. Iron filings are used to observe both states in experiments on small spherical neodymium magnets. A “misaligned” state that is barely unstable theoretically is also observed experimentally; this state resembles the circular state except that the central dipole moment points toward a point of contact between two perimeter magnets.