Electric Field Levels Research Articles

Influence of crystalline electric field on the magnetic properties of CeCd3X3(X=P,As)

CeCd$_3$P$_3$ and CeCd$_3$As$_3$ compounds adopt the hexagonal ScAl$_3$C$_3$-type structure, where magnetic Ce ions on a triangular lattice order antiferromagnetically below $T_\text{N} \sim$0.42~K. Their crystalline electric field (CEF) level scheme has been determined by fitting magnetic susceptibility curves, magnetization isotherms, and Schottky anomalies in specific heat. The calculated results, incorporating the CEF excitation, Zeeman splitting, and molecular field, are in good agreement with the experimental data. The CEF model, with Ce$^{3+}$ ions in a trigonal symmetry, explains the strong easy-plane magnetic anisotropy that has been observed in this family of materials. A detailed examination of the CEF parameters suggests that the fourth order CEF parameter $B_{4}^{3}$ is responsible for the strong CEF induced magnetocrystalline anisotropy, with a large $ab$-plane moment and a small $c$-axis moment. The reliability of our CEF analysis is assessed by comparing the current study with earlier reports of CeCd$_{3}$As$_{3}$. For both CeCd$_{3}X_{3}$ ($X$ = P and As) compounds, less than 40 \% of $R\ln(2)$ magnetic entropy is recovered by $T_\text{N}$ and full $R\ln(2)$ entropy is achieved at the Weiss temperature $\theta_{p}$. Although the observed magnetic entropy is reminiscent of delocalized 4$f$-electron magnetism with significant Kondo screening, the electrical resistivity of these compounds follows a typical metallic behavior. Measurements of thermoelectric power further validate the absence of Kondo contribution in CeCd$_{3}X_{3}$.

Stimuli-responsive dynamic hydrogels: design, properties and tissue engineering applications.

The field of tissue engineering and regenerative medicine has been evolving at a rapid pace with numerous novel and interesting biomaterials being reported. Hydrogels have come a long way in this regard and have been proven to be an excellent choice for tissue regeneration. This could be due to their innate properties such as water retention, and ability to carry and deliver a multitude of therapeutic and regenerative elements to aid in better outcomes. Over the past few decades, hydrogels have been developed into an active and attractive system that can respond to various stimuli, thereby presenting a wider control over the delivery of the therapeutic agents to the intended site in a spatiotemporal manner. Researchers have developed hydrogels that respond dynamically to a multitude of external as well as internal stimuli such as mechanics, thermal energy, light, electric field, ultrasonics, tissue pH, and enzyme levels, to name a few. This review gives a brief overview of the recent developments in such hydrogel systems which respond dynamically to various stimuli, some of the interesting fabrication strategies, and their application in cardiac, bone, and neural tissue engineering.

Electric field-driven fabrication of anisotropic hydrogels from plant proteins: Microstructure, gel performance and formation mechanism

Soy protein isolate (SPI) hydrogels with anisotropic structures were fabricated under a low voltage electric field (1.5 V/cm) and different levels of NaCl (100–500 mmol/L). Under the weak direct-current electric field, the negatively charged protein molecules orderly arranged and accumulated around the positive electrode, where the surface charges of the amino acids were screened by the local H+ and added ions. Meanwhile, the random coil in the protein secondary structure disappeared to form ordered structures (α-helix and β-turn), and the protein exposed more hydrophobic and sulfhydryl groups. Intermolecular interactions, including disulfide bonds, hydrogen bonds and hydrophobic interactions facilitated the cross-linking of protein molecules to form hydrogels. All the hydrogels showed anisotropic networks, and the fraction of SPI attached to the gel phase (36.80% ∼ 62.17%) was found to increase with the rise of NaCl level in the protein solution. Moreover, the hardness (96.13–210.54 g), springiness (33.88% ∼ 68.30%), chewiness (121.59–292.12 g⋅s) and swelling resistance (142.79% ∼ 54.20%) of electrogels were all enhanced with increased NaCl level. Conversely, a higher ionic strength compromised the water holding stability (99.62% ∼ 66.75%) of electrogels, which could be attributed to the increased pore size within their networks that allowed moisture to be transferred. These findings may provide a novel insight for design and fabrication of plant protein hydrogels with desirable structures and characters through a green and sustainable approach.

Spin dynamics and exchange interaction in orthoferrite TbFeO3 with non-Kramers rare-earth ion

The low-temperature spin dynamics of the orthorhombic TbFeO$_3$ perovskite has been studied. It has been found that the inelastic neutron scattering (INS) spectrum contains two modes corresponding to different sublattices in the compound. The iron subsystem orders antiferromagnetically at T$_N$ = 632 K and exhibits the high-energy magnon dispersion. Magnetic dynamics of this subsystem has been described using the linear spin wave theory and our solution yields sizable anisotropy between in-plane and out-of-plane exchange interactions. This approach was previously used to describe the magnon dispersion in the TmFeO$_3$ compound. Three non-dispersive crystal electric field levels corresponding to Tb$^{3+}$ ions have been established in the region below 40 meV at about 17, 26, and 35 meV. Study of diffuse scattering at different temperatures has elucidated the behavior of the magnetic correlation length. The behavior of the Tb$^{3+}$ ion subsystem has been numerically described in the framework of the point charge model. The numerical data agree satisfactorily with the experiment and with the general concept of the single-ion approximation applied to the rare-earth subsystem of orthorhombic perovskites.

A polyconvex transversely-isotropic invariant-based formulation for electro-mechanics: Stability, minimisers and computational implementation

The use of Electro-Active Polymers (EAPs) for the fabrication of evermore sophisticated miniaturised soft robotic actuators has seen an impressive development in recent years. The incorporation of crystallographic anisotropic micro-architectures, within an otherwise nearly uniform isotropic soft polymer matrix, has shown great potential in terms of advanced three-dimensional actuation (i.e. stretching, bending, twisting), especially at large strains, that is, beyond the onset of geometrical pull-in instabilities. From the computational point of view, the design of accurate and robust albeit efficient constitutive models is a very active area of research. This paper introduces a novel polyconvex phenomenological invariant-based transversely isotropic formulation (and relevant computational frameworks) for the simulation of transversely isotropic EAPs at large strains, where the ab initio satisfaction of polyconvexity is exploited to ensure the robustness of numerical results for any range of deformations and applied electric fields. The paper also presents key important results both in terms of the existence of minimisers and material stability of coupled electro-mechanics, enhancing previous works in the area of large strain elasticity. In addition, a comprehensive series of selected numerical examples is included in order to demonstrate the effect that the anisotropic orientation and the contrast of material properties, as well as the level of deformation and electric field, have upon the response of the EAP when subjected to large three-dimensional stretching, bending and torsion, including the possible development of wrinkling and the potential loss of ellipticity in ill-posed constitutive models.

Intensification of the Extraction Yield of Eucalyptus globulus Phenolic Compounds with Pulsed Electric Field

Eucalyptus extract-based pharmaceutical products are widely used because of their medicinal properties and their rich content of secondary metabolites, mainly phenolic compounds. This study aimed to maximise the extraction yield of these compounds and reduce the extraction duration by using a pulsed electric field (PEF) level of 6 kV/cm. The pulse width (T), number of pulses (n), and solvent concentration [C] were analysed. Several ethanolic extracts were obtained from the leaves of Eucalyptus globulus, and the content of total phenols, total flavonoids, and condensed tannins was measured through spectrophotometry. The results, obtained immediately after PEF treatment, revealed that for optimal values of the analysed factors, the total phenol content doubled and the flavonoid content increased significantly. However, PEF pre-treatment had no effect on the tannin yield. Moreover, optimisation was performed using the design of experiments methodology for identifying optimal values of the analysed factors.

High-time resolution search for compact objects using fast radio burst gravitational lens interferometry with CHIME/FRB

The gravitational field of compact objects, such as primordial black holes, can create multiple images of background sources. For transients such as fast radio bursts (FRBs), these multiple images can be resolved in the time domain. Under certain circumstances, these images not only have similar burst morphologies but are also phase-coherent at the electric field level. With a novel dechannelization algorithm and a matched filtering technique, we search for repeated copies of the same electric field waveform in observations of FRBs detected by the FRB backend of the Canadian Hydrogen Mapping Intensity Experiment (CHIME). An interference fringe from a coherent gravitational lensing signal will appear in the time-lag domain as a statistically significant peak in the time-lag autocorrelation function. We calibrate our statistical significance using telescope data containing no FRB signal. Our dataset consists of ∼100-ms long recordings of voltage data from 172 FRB events, dechannelized to 1.25-ns time resolution. This coherent search algorithm allows us to search for gravitational lensing signatures from compact objects in the mass range of 10−4–104 M⊙. After ruling out an anomalous candidate due to diffractive scintillation, we find no significant detections of gravitational lensing in the 172 FRB events that have been analyzed. In a companion work [C. Leung and Z. Kader, Phys. Rev. D 106, 043017 (2022).], we interpret the constraints on dark matter from this search.6 MoreReceived 14 April 2022Accepted 15 June 2022DOI:https://doi.org/10.1103/PhysRevD.106.043016© 2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasGravitational lensesMassive compact halo objectsRadio, microwave, & sub-mm astronomyTransient & explosive astronomical phenomenaGravitation, Cosmology & Astrophysics

Electronic and structural properties of RbCeX2 (X2: O2, S2, SeS, Se2, TeSe, Te2)

Triangular lattice delafossite compounds built from magnetic lanthanide ions are a topic of recent interest due to their frustrated magnetism and realization of quantum disordered magnetic ground states. Here we report the evolution of the structure and electronic ground states of $\mathrm{RbCe}{X}_{2}$ compounds, built from a triangular lattice of ${\mathrm{Ce}}^{3+}$ ions, upon varying their anion character $({X}_{2}={\mathrm{O}}_{2}$, ${\mathrm{S}}_{2}, \mathrm{SeS}, {\mathrm{Se}}_{2}, \mathrm{TeSe}, {\mathrm{Te}}_{2})$. This includes the discovery of a new member of this series, ${\mathrm{RbCeO}}_{2}$, that potentially realizes a quantum disordered ground state analogous to ${\mathrm{NaYbO}}_{2}$. Magnetization and susceptibility measurements reveal that all compounds manifest mean-field antiferromagnetic interactions and, with the exception of the oxide, possess signatures of magnetic correlations onset below 1 K. The crystalline electric field level scheme is explored via neutron scattering and ab initio calculations in order to model the intramultiplet splitting of the $J=5/2$ multiplet. In addition to the two excited doublets expected within the $J=5/2$ manifold, we observe one extra local mode present across the sample series. This added mode shifts downward in energy with increasing anion mass and decreasing crystal field strength, suggesting a long-lived anomalous mode endemic to anion motion about the ${\mathrm{Ce}}^{3+}$ sites.

Second order Zeeman interaction and ferroquadrupolar order in TmVO4

TmVO4 exhibits ferroquadrupolar order of the Tm 4f electronic orbitals at low temperatures, and is a model system for Ising nematicity. A magnetic field oriented along the c-axis constitutes a transverse effective field for the quadrupolar order parameter, continuously tuning the system to a quantum phase transition as the field is increased from zero. In contrast, in-plane magnetic fields couple to the order parameter only at second order, such that orienting along the primary axes of the quadrupole order results in an effective longitudinal field, whereas orienting at 45 degrees results in a second effective transverse field. Not only do in-plane fields engender a marked in-plane anisotropy of the critical magnetic and quadrupole fluctuations above the ferroquadrupolar ordering temperature, but in-plane transverse fields initially enhance the ferroquadrupolar order, before eventually suppressing it, an effect that we attribute to admixing of the higher crystalline electric field levels.

A combined experimental and modeling study of Microwave-assisted methane dehydroaromatization process

The challenges in direct methane conversion to higher-value chemicals include rapid catalyst deactivation and comparatively low single-pass conversion. The most important step in direct methane conversion is the activation of strong C–H bonds. In this paper, we integrated microwave irradiation with heterogeneous catalysis to enable a higher methane conversion to C2 and aromatics at low temperature. The results showed that the methane conversion can reach 18% at 550 °C under microwave irradiation, while a temperature higher than 800 °C was required to achieve the same level of methane conversion in a traditional fixed-bed reactor. The microwave irradiation may facilitate this heterogeneous catalysis process both thermally and non-thermally. Thermal effect, as known as “hot spots”, can be characterized experimentally. The results indicated the “hot spot” temperature can reach as high as 800 °C while the bulk temperature stayed at 550 °C. However, the non-thermal effect is difficult to characterize due to the limitations of existing in-situ instrumentations. Finite-element modeling can be a powerful engineering tool to simulate and understand complex physic fields. The simulation results show that between spherical catalyst particles the electric field on the catalyst bed was at a level of 104 V/m and the non-uniform electric field distribution on the catalyst bed. Under this level of external electric field, methane activation on the catalyst surface was possible. These field distributions can explain the non-thermal effects of microwave-assisted catalytic chemical reactions, supported by the observation of benzene hydrogenolysis side reaction. With the thermal and non-thermal effects from microwave irradiation, microwave-assisted heterogeneous catalytic process can be an attractive solution to activate stable feedstock molecules and can be applied to direct methane conversion process.

Microwave breakdown of sub-atmospheric argon gas in the vicinity of a microgap

The microwave electric field at breakdown for argon gas in a microgap (generally, gap size <1 mm) over a wide range of pressures and gap sizes was found to exhibit two behavioral pressure regimes. A high microwave electric field was established in the gap of a re-entrant mode resonator. By slowly raising the microwave electric field level, a breakdown level is reached where impact ionization induces low pressure argon gas to breakdown preferentially outside of the gap. At high pressure, breakdown is found to occur preferentially inside the gap, but only after the pressure is high enough for impact ionization to produce breakdown there. Impact ionization has a lower threshold electric field than the boundary-controlled processes, such as secondary electron emission, that would eventually produce breakdown inside the microgap if impact ionization did not occur first. Thus, the lower pressure regime is characterized by breakdown outside of the gap, while in the high-pressure regime, breakdown occurs inside the gap, in both cases by impact ionization. The transition pressure PT between these two pressure regimes depends on the gap size dgap, roughly as PT ∝ dgap−2. Consistent with the model developed here, this corresponds to the full-amplitude of electron oscillation in the gap field being commensurate with the gap size.

Thermal Expansion in a diluted Ce system La1–x Ce x Cu6

The thermal expansion of a diluted Ce system La1-x Ce x Cu6 for (0.6 ≤ x ≤ 1) has been measured between 10 and 150 K to reveal the change from the coherent heavy Fermion state (0.9 ≤ x ≤ 1) to the incoherent Kondo state (0 < x ≤ 0.73). The large Ce concentration x dependence of the linear thermal expansion coefficient along b-axis αb (T) suggests that the coupling between the 4f 1 electron and the lattice strain is the largest along the b-axis in the three crystallographic axes. The maximum of the magnetic contribution to the volume thermal expansion coefficient β m(T) at T = 50 K is retained in the x range of 0.6 ≤ x ≤ 1, suggesting the crystalline electric field (CEF) level for x = 1 doesn’t change by the substitution. Furthermore, the upturn in β m(T) below 25 K, which should be a precursor of the maximum at T = 2.5 K reported for x = 1, is retained when we decrease x from 1 to 0.6. Because the ground state for x = 0.6 is the incoherent Kondo state, the robustness of the maximum at T = 50 K and upturn in the current x value implies that β m(T) in 10 ≤ T ≤ 150 K is attributed to the CEF and Kondo effects rather than the formation of the heavy Fermion state.

EMI radiation of power transmission lines in Malaysia

Background: There has been rising concern amongst the public regarding their home's proximity to high tension power transmission lines. The primary cause of fear is the impact of the electromagnetic interference (EMI) radiation on the nearby occupants' health. Despite the presence of national permissible limits of EMI radiation, there is still lack of information with regards to the EMI radiation of the types of power lines configuration in Malaysia. Methods: The electric and magnetic fields of several selected power transmission lines were simulated using the EMFACDC software program from the recommendation ITU-T K.90. Five types of power transmission lines available in Malaysia are considered. Results: It was found that the simulated electric and magnetic field levels at all the power lines' right of way (ROW) boundary complies with the prescribed exposure limit. However, the electromagnetic fields (EMF) level increases significantly as the separation distance is reduced from 30m. For a more conservative approach, the ROW can be set at 30m across all transmission voltage level and corridor area condition. Conclusion: It can be concluded that Malaysia's power transmission lines are within the prescribed exposure limits. To further minimize the electric and magnetic field level, it is recommended that the residential building should be built at least 30 meters away from the power transmission lines, especially for the 275kV double circuit, 275/132kV quadruple circuit, and 500kV double circuit lines.

EMI radiation of power transmission lines in Malaysia

Background: There has been rising concern amongst the public regarding their home's proximity to high tension power transmission lines. The primary cause of fear is the impact of the electromagnetic interference (EMI) radiation on the nearby occupants' health. Despite the presence of national permissible limits of EMI radiation, there is still lack of information with regards to the EMI radiation of the types of power lines configuration in Malaysia. Methods: The electric and magnetic fields of several selected power transmission lines were simulated using the EMFACDC software program from the recommendation ITU-T K.90. Five types of power transmission lines available in Malaysia are considered. Results: It was found that the simulated electric and magnetic field levels at all the power lines' right of way (ROW) boundary complies with the prescribed exposure limit. However, the electromagnetic fields (EMF) level increases significantly as the separation distance is reduced from 30m. For a more conservative approach, the ROW can be set at 30m across all transmission voltage level and corridor area condition. Conclusion: It can be concluded that Malaysia's power transmission lines are within the prescribed exposure limits. To further minimize the electric and magnetic field level, it is recommended that the residential building should be built at least 30 meters away from the power transmission lines, especially for the 275kV double circuit, 275/132kV quadruple circuit, and 500kV double circuit lines.

The Dynamics of the Radiated Field Near a Mobile Phone Connected to a 4G or 5G Network

Characterizing the time variations of signals emitted by mobile terminals provides complementary information to health authorities, especially with the increase of frequency and energy of radiation towards millimeter waves. This experimental work aimed to quantify and classify the time variability of the electric field level measured at 10cm from a mobile phone connected sequentially to a 4th and 5th generation mobile network. Statistic analysis was performed on data from real-time spectrum analyzers, while self-similarity was computed by first recurrence plots of the radiated emissions, corresponding to five different types of mobile applications. Moreover, specificities to the communication standard and the type of application were identified.

Classification of Partial Discharges Originating From Multilevel PWM Using Machine Learning

A partial discharge (PD) is a small, localized breakdown which often appears in high-voltage insulation systems. PDs can be initiated within material defects such as voids or cracks when exposed to sufficiently high electric field levels. In this research work, we study and propose a machine learning (ML) approach to detect and classify PDs originating from multilevel pulsewidth modulation (PWM) waveforms as utilized in power electronic devices, such as inverters and variable frequency drives. Due to the increased use of power conversion units, new types of higher magnitude PDs have been observed to increase insulation degradation. By creating a cavity placed at different locations within the test object and exposing it to PWM voltage waveforms with two different rise times, a total of 345 660 PD events are recorded and organized into ten different classes. The maximum PD amplitude, duration, the time distance between consecutive PDs, and the area under the PD are used as features for PD classification. A unique way of concatenating a sequence of the extracted features to capture the temporal dependence of consecutive PDs is also presented. It is observed that when creating a sequence of information from consecutive observed PDs, a significant increase in classification accuracy can be obtained. Trained classifiers based on ensemble bagged decision trees (DTs) and long short-term memory (LSTM) architecture resulted in 95.3% and 98.5% average classification accuracy on test data respectively.

Измерительные цепи сдвоенных электроиндукционных сферических датчиков напряженности электрического поля замкнутой конфигурации

To control the levels of electric fields, electric field strength sensors are required. Currently, for these purposes, the most promising are dual electric induction sensors, which are a constructive combination of two double sensors into one whole. There are two types of dual sensors with overhead, composite and separate sensing elements. The output signals of such sensors are electrical parameters such as charge, current and voltage. Studies have shown that electrical charge has the greatest advantage. To remove the charge from the sensor, it is recommended to use a current integrator (charge amplifier) as the primary measuring circuit. Secondary measuring circuits of the dual sensors considered in this work are used for averaging the signals of double sensors in order to reduce the error from the inhomogeneity of the electric field and form an output signal proportional to the field strength. It has been established in the work that sensors with overhead and composite sensitive elements allow to perceive the intensity of an inhomogeneous electric field with an error not exceeding +4,6 % in the spatial measurement range 0a1. The work also determined the sensitivities of two types of dual sensors of the electric field strength.

Analysis of SAR reduction to human head with plasma photonic crystals shield using ICCG-SFDTD method

A novel and effective biological electromagnetic method using plasma photonic crystals shield to protect the human head from electromagnetic radiation of an ultra-high-field magnetic resonance imaging (MRI) frequency is explored. An improved incomplete Cholesky conjugate gradient (ICCG)-based symplectic finite-difference time-domain (ICCG-SFDTD) method, which maintains the property of the Hamilton system and ensures energy conservation numerically with high precision, is applied to a bioelectromagnetic simulation of human head models without shield, with plasma shield and with plasma photonic crystals shield. Results show that plasma photonic crystals shield is superior to plasma shield with the same thickness in reducing the specific absorption rate (SAR) and electric field levels of the human head. In addition, the relationship of SAR and electric field in the human head models with the parameters of plasma photonic crystals, such as the plasma frequency, plasma collision frequency and dielectric constant of the medium is studied in order to provide a guidance to design plasma photonic crystals protective layer for biological tissue.

Aging Assessment of Corona-Exposed HTV-SiR/EPDM Blends Loaded With Nanofillers

Exposure of insulating systems to strong electric field and other environmental stresses may cause loss of their desired properties. In high-voltage applications, phenomena, such as corona discharges and unexpected flashovers, may deteriorate the surface as well as bulk conditions of an insulating material and thereby affect its lifetime. In this article, several types of corona-exposed HTV-SiR/ethylene propylene diene monomer (EPDM) blends filled with different concentrations of nano-sized boron nitride and silicon carbide particles are evaluated and the induced modifications of their properties are presented and discussed. The diagnosis is based on measured data of surface partial discharge (PD) and volume current. For the latter, experiments were performed at different levels of electric field between 0.5 and 4 kV/mm and ambient temperature ranging from 22 °C to 70 °C. Results of the conducted experiments revealed the degradation of surface properties through an increase in the PD magnitude. It was also observed that corona aging of the samples decreases the threshold electric field particularly at elevated temperatures, above which space charge effect in the materials may become significant. Moreover, it was observed that the blend compositions loaded with nanofillers retard surface PD and bulk deterioration.

Preparation of Novel ZnO/Cu2O Heterojunctions Composite Film by Codeposition Method and Their Enhanced Photocatalytic Performance Analysis

Refractory organic pollutants have caused widespread concern about their pollution of water environments. Photocatalytic oxidation technology is an effective way to remove organic pollutants. Photocatalyst is the components core of photocatalytic oxidation technology. The development of visible light responsive catalysts with high catalytic activity is of great significance for the removal of organic pollutants using sunlight as a light source. In this paper, a codeposition method is used to prepare ZnO/Cu2O composite film with a heterojunction structure in one step. The microstructure and photoelectric properties of the prepared ZnO/Cu2O composite film are characterized and analyzed, and its photocatalytic performance is evaluated. Compared with pure the Cu2O film, the composite film exposes more (111) crystal planes, and has a smaller impedance and a larger photocurrent and open circuit voltage value. These findings indicate that the ZnO/Cu2O composite film exhibits excellent photogenerated carrier separation and migration efficiencies. Among the prepared samples, M2 demonstrates the highest photocatalytic and recycling performance. The calculation of the band position shows that the Fermi level of the composite film exhibits a significant shift compared to that of the pure Cu2O film. The analysis shows that the decrease in the recombination probability of photogenerated carriers caused by the shift of the Fermi level and formation of an internal electric field is the main factor for the significant enhancement in the Cu2O photocatalytic performance. This article provides a novel method and idea to realize the efficient removal of organic dye pollutants in sewage.