Part Of Constant Research Articles

Transport and dielectric properties of MIS structure with embedded Si QDs (AuPd/SiO2:Si QDs/n-Si) grown by MBE

This study focuses on the growth of silicon quantum dots (Si QDs) on insulator substrates via solid-state dewetting of ultrathin silicon films deposited by molecular beam epitaxy (MBE). The resulting Si QDs exhibit well-defined spherical shapes, low size dispersion with an average diameter of 6 nm, and a high density (1012/cm2), making them ideal for microelectronic applications. Current-voltage spectroscopy and impedance spectroscopy were employed to investigate the electrical transport and dielectric properties of Si QDs integrated into a metal-insulator-semiconductor (MIS) structure (AuPd/SiO2: Si QDs/n-Si). Current-voltage measurements reveal that the insertion of Si QDs into the MIS structure improves the electrical transport by introducing new conduction mechanisms. Impedance measurements demonstrate the influence of Si QDs on the frequency dependence of the real part of the dielectric constant (ε′) and the loss tangent (tan δ). Furthermore, Si QDs impact both the real (M′) and imaginary (M″) parts of the electric modulus. Despite slight deviations in dielectric properties, the MIS structure retains its fundamental nature. These investigations affirm the high electrical quality of Si QDs grown via solid-state dewetting and offer valuable insights for researchers engaged in the development of Si QD-based devices, such as non-volatile memories and MIS photodetectors.

Parental Involvement in Assisting the Student in the Social Domain: The Educators' Perspective

Abstract Parental involvement is one of the key issues in education that remains a constant part of the public and academic agenda, but little is known about the perspective of educators on parental involvement in assisting the student in the social domain. It is essential to throw light on this perspective in order to construct an effective parent-educator partnership in this domain. This qualitative study focuses on educators' perspectives (perceptions and strategies). It is based on analyses of 10 case studies perceived by educators as successful and 16 statements by educators, which were not connected to a specific case study, but expressed their views about parents generally. It was found that the educators' perceptions include positive and negative aspects. Three types of effective strategies have emerged from the data: creating good communication with parents, giving practical advice to parents, and driving positive change in the relations between the child and their parents. The conclusions point to aspects that should be emphasized in teacher education, particularly professional training in how to develop social competence in students.

Effect of glass powder on mechanical properties and electromagnetic transmission properties of high alumina cement paste

The mechanical properties and electromagnetic transmission properties of high alumina cement (HAC) paste with different glass powder (GP) contents were investigated in this paper. The effects of hydration phase, unhydrated phase, GP phase and pore phase on the dielectric properties of HAC paste were quantitatively analyzed. The results show that the strength, fluidity and setting time of HAC paste decrease with the increase of GP replacement rate. The real part, imaginary part and loss angle tangent of dielectric constant decrease. The addition of GP leads to a reduction in reflectivity and absorptivity of electromagnetic waves in the paste, while increasing transmittivity.Furthermore, the real part of the dielectric constant of each phase in the HAC paste follows the order: hydration product phase > unhydrated phase > GP phase > pore phase. With an increase in GP content, the real part of the dielectric constant of the hydration product phase increases. Finally, based on the results of vector network analysis (VNA), mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM), the reasons for the changes of mechanical properties and electromagnetic properties of HAC paste under different GP replacement rates were analyzed from the aspects of phase composition, pore distribution and microstructure.

Detection of fat concentration milk using TMDC-based surface plasmon resonance sensor

In this paper, a TMDC-based surface plasmon resonance (SPR) sensor for detecting fat concentration milk, incorporating an Ag-Pt (bimetallic) layer, is presented. The Pt (Platinum) layer provides chemical stability and increases sensitivity with the TMDC layer. Compared to the conventional SPR sensor, the maximum sensitivity, detection accuracy (DA), and figure of merit (FoM) of 314∘/RIU, 0.142/degree, and FoM 44.05/RIU are achieved with the WS2 layer. The sensor’s increased sensitivity is due to the increased field intensity and depth of penetration into the sensor layer, resulting in a larger interaction volume. The presence of the WS2 layer, with its significant imaginary part of the dielectric constant, helps improve sensitivity and broadens the SPR curves. This broadening SPR curve ultimately affects the DA and FoM of the sensor. The capability of the proposed sensor to detect various biological analytes with a refractive index (1.3452–1.3657) can be demonstrated.

Electric, Dielectric, and Phonon Properties of Cu2OCl2

Investigating the multiferroic properties of , their temperature and magnetic‐field dependencies around the magnetic and ferroelectric phase transition temperatures and are analyzed using a microscopic model and Green's function technique. Near the Neel temperature , a kink in the specific heat and also in the phonon energy and damping due to strong anharmonic spin–phonon interaction is observed. The kink in disappears with increasing magnetic field h. The polarization shows also a small anomaly at and decreases with increasing magnetic field h. This behavior strongly suggests that exhibits multiferroic characteristics. A kink at can be seen in the real part of the dielectric constant , too. It should be noted that demonstrates a significant increase with increasing field strength h below , which is a pronounced magneto‐dielectric effect. These findings qualitatively agree with the experimental data.

Optoelectronic and Dielectric Properties of Tenorite CuO Thin Films Sprayed at Various Molar Concentrations

The work in hand presents the elaboration of CuO thin films using a home-made spray pyrolysis technique at room atmosphere. The films were synthesized on preheated glass substrate at 450 °C. The source solution molarity was varied from 0.025 to 0.1 mol/L. The films were characterized by employing X-Ray Diffraction technique, UV-Vis-NIR spectrophotometry, Scanning Electron Microscope imagery, Energy Dispersive Spectroscopy, and four-points probe techniques. The X-ray diffraction analysis confirmed that all films are polycrystalline with a preferred orientation along the plane (−111) of the monoclinic crystal structure phase of tenorite (CuO). The SEM images showed a homogeneous and smooth surface. Crystallinity and grain size were improved. The rise of solution concentration induced a reduction of transmittance and reflectance in the visible region. The energy gap, the absorption coefficient, the extinction coefficient, refractive index, dielectric constant (ԑr and ԑi) and loss energy were estimated from transmittance and reflectance data. The gap energy decreases from 2.72 to 2.56 eV. The film deposited for 0.025 mol/L exhibits the highest real part of the dielectric constant (ԑr ~ 17). The film resistivity which is in order of 102 Ω cm decreases with the increase of molar concentration. The estimated dielectric constant indicated that the resulting CuO thin films could be used as dielectric layers for optoelectronic devices working in Vis-NIR region of radiation. Furthermore, the relatively high band gap, high absorption coefficient and high conductivity of the film obtained at 0.075 mol/L, make them good candidates as absorption layers in solar cells applications.

ПАРАМЕТРИЧЕСКИЕ МЕТОДЫ ЦЕНООБРАЗОВАНИЯ: МЕТОДИКА И ПРАКТИКА ПРИМЕНЕНИЯ

The scientific article contains a review of economic publications presenting scientific research by domestic and foreign scientists on the problems of pricing in the agricultural sector of the economy: establishing the optimal level of purchase, wholesale and retail prices for agricultural products, ensuring the growth of financial results by increasing income from the sale of products, identifying the dynamics food market, forecasting price dynamics in agricultural production, methodology of pricing policy and price relations of agricultural organizations. A production feasibility study was conducted for the expected sales volume. The influence of sales timing (first batches or the main harvest of agricultural products) and price on the amount of demand (expected sales volume) is shown. A function has been constructed for the dependence of sales volume on the price of agricultural products, clearly showing that an increase in sales volume is possible if the price of agricultural products decreases. It is indicated that at the beginning of the season, a high price repels the consumer, this negatively affects the amount of revenue. A paired regression equation was constructed, and the expected sales volume was determined using regression analysis. The methodology for calculating the total costs of production, their classification depending on the degree of variability (the influence of the expected sales volume) is shown. It is noted that in total costs there is a constant part (fixed costs that do not depend on the expected sales volume) and a variable part (variable costs that change in direct proportion to changes in the expected sales volume). A profit generation model is described, including data from a regression analysis of the expected sales volume and calculation of the total costs of production.

Optical band structure with enhanced plasmonic effect of SiO2/rGO bilayer deposited by spray pyrolysis

Reduced graphene oxide (rGO) has been extensively studied as an alternative plasmonic material which offers activity at broad wavelength region. A bilayer film combining SiO2 and rGO was successfully deposited on a glass substrate by spray pyrolysis. For a comparative review, the rGO from commercial product (rGO-com) and from our samples (rGO-csc) derived from biomass (coconut shell) are used in this study. X-ray diffractometry (XRD), scanning electron microscopy (SEM), and X-ray photoemission spectroscopy (XPS) were used to characterize these materials. The existence of plasmonic state was clarified by investigating the real component of the dielectric function and by applying the base layer correction of optical conductivity, derived from UV–Vis spectra at wavelength of 300–1000 nm. The real part of the dielectric constant was approximately −20 and −10 for SiO2/rGO-csc and SiO2/rGO-com films respectively. Meanwhile, the optical conductivity for both samples has confirmed a peak of around ∼3.5 eV, indicating the presence of correlated plasmon. Broadly speaking, the rGO can be employed to generate the plasmon effect in term of either conventional or correlated plasmons. This result also offers the groundwork for the development of potentially far-reaching discipline of graphene plasmonics, where the usage of biomass-derived rGO-like compounds leading to increasing optical characteristics is interestingly superior to that of the commercial rGO.

A Theoretical Investigation of the Electrical and Dielectric Properties of PDMS‐CNT

AbstractIn the present study, the dielectric and electrical properties of the carbon nanotube/polydimethylsiloxane (CNT/PDMS) composite are theoretically analyzed for various doping concentrations. For both single‐walled and multiwalled CNTs (SCNTs and MCNTs), the work is done between 75 and 750 THz. The behavior of the dielectric constant, loss factor, and conductivity are analyzed as functions of frequency. It is observed that there is no appreciable change in the real part of the dielectric constant at high frequencies in single‐walled CNT. The loss tangent is high at lower frequencies, and the loss peak is observed at a particular frequency. The Cole–Cole plot is used to interpret the static‐ and high‐frequency dielectric constants and relaxation time of the composite. With increasing concentrations of SCNT and MCNT, the conductivity at the obtained peak maximum shifts to a lower frequency.

Dielectric and magnetic response of Cu-Co-Sm ferrite impregnated with graphene nanoplatelets for high-frequency device applications

This work studied a composite of graphene nanoplatelets (GNPs) impregnated copper-cobalt-samarium ferrites Cu0.5Co0.5Fe1.97Sm0.03O4/GNPs synthesized via sol-gel auto-combustion route. The structural, electrical, dielectric, and optical properties of the as-prepared composites were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), EDX, I-V characteristics, impedance measurement, raman spectroscopy, scanning electron microscopy (SEM), vibrating sample magnetometry (VSM) analysis, and UV–visible spectroscopy. XRD confirmed that the spinel ferrites had a crystalline single-phase FCC structure with the lattice constant of around 8.33 Å, and the crystallite size range from 54.10 nm to 51.85 nm. SEM analysis confirmed the homogenous dispersion of spinel ferrites in graphene sheets, and EDX confirmed the presence of all elements in ferrite composites with GNPs. Furthermore, the spinel matrix was confirmed by the Raman and UV-visible analysis. A minimum particle size of 21.73 nm was determined using TEM, and the minimum value of activation energy (0.01 eV) was obtained from IV characteristics for ferrite composite with 2.5% GNPs. Further, our ferrite composites with GNPs demonstrated improved electroconductive properties, with conductivity ranging from 5.88×10−8S/cm to 1.04×10−6S/cm at 673 K. The real & imaginary part of permittivity, dielectric constant (ε’), and impedance (Z) were also improved with the addition of GNPs. At low frequencies, a permeability loss value of 0.81 was obtained for the ferrite composite with 5% GNPs. VSM analysis confirmed that the saturation magnetization decreased in ferrite composites with graphene nanoplatelets. The minimum value of skin depth of 1.03 mm was observed at 1.25 % GNPs. Our ferrite composites with GNPs exhibited minimal eddy current at high frequencies, making them promising candidates for high-frequency device applications.

Stabilization under unknown control directions and disturbed measurements via a time‐delay approach to extremum seeking

AbstractWe study stabilization of linear uncertain systems under unknown control directions using a bounded extremum seeking controller in the presence of a small time‐varying measurement delay. We assume that the measurements are subject to discontinuous disturbances. The main novelty is that these disturbances possess not only the constant part as in the existing results, but also small discontinuous part that may appear due to quantization. We consider two types of measurements: the state measurements and the state quadratic norm ones. In the latter case the constant part of the disturbances may be arbitrary large. By using the recently proposed time‐delay approach to Lie‐brackets‐based averaging, we transform the closed‐loop system to a time‐delay (neutral type) one with no terms depending on the disturbance derivative, which has a form of perturbed Lie brackets system. The input‐to‐state stability (ISS) of the time‐delay system guarantees the same for the original one. We further transform the neutral system to an ordinary differential equation (ODE) with delayed perturbations and employ variation of constants formula leading to explicit conditions in terms of simple inequalities with less conservative results in the most of numerical examples. Two numerical examples are provided to illustrate the efficiency of the method.

Structural, Morphological, Spectroscopic, and Dielectric Properties of Ca-Mg Nanoferrites for High-frequency Applications

Introduction:: Ca-Mg nanoferrites of composition Ca0.5Mg0.5Fe2O4 were synthesized by wet chemical citrate precursor approach. Methods:: The prepared nanoparticles were characterized by an “X-ray diffractometer, Scanning electron microscopy, Diffused reflectance spectroscopy, and Impedance analyzer”. In the XRD pattern, the most intense reflection was observed from the (311) peak that corresponds to the cubic spinel phase of the prepared ferrite. Results:: The average size of all crystallites was calculated to be 19 nm. The sample's porosity was found to be 61%. In the SEM micrograph, uniformity in the size of the particles was detected with some agglomeration. The calculated energy band gap (1.91eV) reveals the semiconducting nature of the prepared material. Conclusion:: The high value of the real part of the dielectric constant (290) and the low value of loss tangent (0.17) reveals that the synthesized material can be useful in magnetic cores, microwave components, and other high-frequency applications.

Magnetic and dielectric properties of Nd-Sn-Cu co-doped yttrium iron garnet ferrite

Ion doping to regulate the magnetic and dielectric properties of yttrium iron garnet ferrites is highly desirable for microwave devices. This study successfully fabricated Y3-xNdxFe4.8Cu0.1Sn0.1O12 (x = 0, 0.5, 1.0, 1.5) ceramics, controlling their magnetic and dielectric properties via Nd ion doping. The results indicate that the introduction of Nd ions into the YIG lattice, occupying dodecahedral sites and replacing Y3+ ions, leads to an increase in the lattice parameter. The hysteresis loops demonstrate that as the concentration of Nd ion doping increases, the saturation magnetization initially decreases and then increases. Additionally, the complex impedance and dielectric spectrum analysis reveal that the resistivity and dielectric constant of the material increase with the increasing concentration of Nd ion doping. The real part of the dielectric constant reaches its maximum value, 29.5@200 kHz, at x = 1.5. Consequently, Nd doping concentration effectively controls the crystal structure, microstructure, magnetic, and dielectric properties of garnet ferrite, enhancing its magnetic and dielectric properties and potential application in microwave devices.

Coexistence of doping and strain to tune electronic and optical properties of monolayer graphene

We performed first-principles calculations to study the structural, electronic and optical properties of monolayers graphene through strain and Al atoms doping with different concentrations. The results show that band gap of pristine graphene and graphene doped with 3.at% of Al consistently increases with strain, whereas the band gap of graphene doped with 6 at%, 9 at%, and 12 at% of Al initially increases and subsequently decreases as strain is introduced, and the band gap characteristics change from direct to indirect.Notably, a flat band phenomenon was found when the strain of 6.at%Al doped graphene reached 10 %. Furthermore, the study of optical properties reveals that the increase of Al doping concentration leads to a redshift of the peak in the imaginary part of the dielectric constant of graphene. This not only reduces reflectance to ultraviolet light but also enhances absorption of visible light while decreasing transmittance within the infrared and visible light ranges. Additionally, strain further induces a redshift in the imaginary part of the dielectric constant of Al-doped graphene.

Free energy curves for the Volmer reaction obtained from molecular dynamics simulation based on quantum chemistry

Hydrogen desorption from Au(111) at a constant electrode charge has been studied by a DFT-based tight binding theory (DFTB). Free energy curves have been obtained from molecular dynamics with umbrella sampling. The activation energy increases linearly with the applied negative charge and decreases with temperature, so that the Butler-Volmer law does not hold in its strict form. The activation energy is determined by the reorganization of the accepting water molecule and its surroundings, which becomes more facile with temperature. A separation of the free energy curves into a constant chemical part and an electrostatic part, which varies with the charge, does not hold. Because of its speed DFTB is very suitable for the investigation of electrochemical reactions, but is presently hampered by a lack of sets of interaction parameters.

Structural characterization and dielectric properties of ternary polyaniline/berlin blue/ruthenium dioxide nanocomposite

ABSTRACT A ternary nanocomposite composed of polyaniline/berlin blue/ruthenium dioxide, i.e. PANI/BB/RuO2 was synthesized through a one-pot process using ammonium persulfate as a strong oxidizing agent in H2SO4 medium. The structure, morphology, thermal and optical properties of unary PANI, BB, RuO2, and ternary PANI/BB/RuO2 nanomaterials were analyzed through FTIR, XRD, FESEM, TGA, and UV-Vis techniques. The FTIR and XRD studies confirmed the formation of ternary nanocomposite. FESEM analysis revealed the homogenous structure with uniform distribution of PANI, BB, and RuO2 nanoparticles in the ternary nanocomposite. From UV-Vis studies, a low optical band gap value was obtained for PANI/BB/RuO2 nanocomposite in comparison to PANI nanoparticles. Further, the dielectric behavior of the unary and ternary nanomaterials was analyzed through various parameters such as dielectric constant, dielectric loss, real and imaginary parts of electric modulus in the frequency range of 10 Hz−1 MHz by varying the temperature. It was found that ternary PANI/BB/RuO2 nanocomposite exhibits high dielectric constant and electric modulus (150°C) compared to unary nanoparticles. Hence, PANI/BB/RuO2 can serve as a suitable dielectric material for energy storage devices such as in solid-state capacitors.

Two step model for crosslinking polymerization with account of diffusion

The proposed model includes two parallel reactions, initiation and propagation that respectively follow the reaction order and autocatalytic kinetics. The effect of diffusion is accounted for in both steps by introducing a term that depends linearly on conversion. The term is introduced into the exponential part of the rate constants. Determining the magnitude of this term allows for estimating the diffusion effect on the overall activation energy in the final stages of crosslinking polymerization. The model is tested on five previously published datasets. It appears to fit all data very well and yield physically meaningful fit parameters. Algorithms for successful fitting of the model are suggested. It is also demonstrated that disregarding the effect of diffusion gives rise to markedly inferior results. The model is quite general and expected to be applicable to any polymerization complicated by diffusion or other processes that involve the interplay between the reaction and diffusion kinetics.

Effect of Gravity Modulation on the Onset of Heat Transfer by Buoyancy Induced Convection in Boussinesq- Stokes Suspension with Temperature

The current paper considers the Boussinesq-Stokes suspensions and the temperature-dependent viscosity with the influence of gravity modulation to analyze a weak non-linear stability problem of Rayleigh Benard magnetoconvection. In the study of convective instability problems, the impact of time-periodic body force also known as gravity modulation or g-gitter is essential. In the problem of gravity modulation, the gravity field has two components: one is the constant part and another an externally imposed time periodic part, which can be produced by oscillating the fluid layer. The effect of varying frequency of gravitational oscillation on convection is examined. The truncated form of the Fourier series is used in the non-linear analysis. The effects of numerous factors on the onset of convection have been discussed in this paper. The thermal Nusselt number is computed and shown for slow time periods using non-linear theory. The impacts of gravity modulation frequency and amplitude have been investigated in order to study heat transport in the system, as well as other aspects that exist in the problem.

Structural and electrical characterization of iron and lithium co-doped barium strontium titanate composite

This communication reports the effect of Iron (Fe) and Lithium (Li) co-doping on the structural, dielectric and electrical properties of Ba0.8Sr0.2TiO3; i.e. (Fe0.5Li0.5)0.1Ba0.7Sr0.2TiO3 (FLBST). The FLBST composite was synthesized by the solid-state mixed oxide method at 1400 °C for 12h. The crystalline phase formation has been confirmed by the X-ray diffraction technique and analyzed through the Rietveld Analysis using X’Pert Highscore plus software. From the XRD analysis, lattice parameters and the average crystallite size was calculated. The electrical properties of sintered (at 1450 °C for 2h) pellets were carried out in the temperature range of 30 °C–350 °C using impedance spectroscopy. Based on the real and imaginary part of the dielectric constant, i) the dipolar contribution which is dominant in 30 °C–150 °C is characterized by Curie-Weiss law and ii) contribution from defects and oxygen vacancies seen beyond 150 °C is described by Arrhenius equation.

Biological Effects of Magnetic Storms and ELF Magnetic Fields.

Magnetic fields are a constant and essential part of our environment. The main components of ambient magnetic fields are the constant part of the geomagnetic field, its fluctuations caused by magnetic storms, and man-made magnetic fields. These fields refer to extremely-low-frequency (<1 kHz) magnetic fields (ELF-MFs). Since the 1980s, a huge amount of data has been accumulated on the biological effects of magnetic fields, in particular ELF-MFs. However, a unified picture of the patterns of action of magnetic fields has not been formed. Even though a unified mechanism has not yet been generally accepted, several theories have been proposed. In this review, we attempted to take a new approach to analyzing the quantitative data on the effects of ELF-MFs to identify new potential areas for research. This review provides general descriptions of the main effects of magnetic storms and anthropogenic fields on living organisms (molecular-cellular level and whole organism) and a brief description of the main mechanisms of magnetic field effects on living organisms. This review may be of interest to specialists in the fields of biology, physics, medicine, and other interdisciplinary areas.