Showing papers in "European Physical Journal-applied Physics in 2018"
••
TL;DR: In this paper, an analytical model for the stress-dependent magnetostriction strain of ferromagnetic materials is proposed based on a simplified energetic description of magneto-elastic behaviour.
Abstract: Magnetostriction is the magnetisation-induced strain in ferromagnetic materials. It highly depends on mechanical stress. Stress state in electromagnetic devices is usually multiaxial and its effect on magnetostrictive properties is not easily predicted. In this paper, an original three-parameter analytical model for the stress-dependent magnetostriction strain of ferromagnetic materials is proposed. It is based on a simplified energetic description of magneto-elastic behaviour. It follows a similar method previously adopted for the description of the effect of stress on the magnetic permeability of magnetic materials. It is applied for the first time to the magnetostriction behaviour and results in a simple formula to express the effect of multiaxial magneto-mechanical loadings on the magnetostriction strain. The approach also naturally includes the description of the so-called ΔE effect. The analytical formula is derived in the paper. It shows very satisfying agreement with experimental results on iron–cobalt alloy and pure iron specimen.
25 citations
••
TL;DR: In this article, the effect of different parameters such as charge carriers mobility, electrodes work function, energy gap, series as well as shunt resistances on the performances of an organic photovoltaic cell based on polymer/fullerene P3HT: PCBM was investigated.
Abstract: This paper reports a study on the effect of different parameters such as charge carriers mobility, electrodes work function, energy gap, series as well as shunt resistances on the performances of an organic photovoltaic cell based on polymer/fullerene P3HT: PCBM. Thus, numerical simulations have been investigated on ITO/PEDOT:PSS/P3HT: PCBM/LiF/Al structure with Analysis of Microelectronic and Photonic Structures the simulation one dimension (AMPS-1D) and General-Purpose Photovoltaic Device Model (GPVDM) softwares. The results show that the optimum efficiency is obtained for electron and hole motility values of 10−4 cm2 V−1 s−1 and 2 × 10−4 cm2 V−1 s−1 , respectively. Moreover, we reported that the ohmic contact for both anode and cathode electrodes of the investigated device remains very important to get the maximum efficiency. Furthermore, when the gap energy increases, the efficiency is considerably improved, and reach's a value of about 5.421%. In addition, in this present work, the complimentary between the both softwares AMPS and GPVDM is also well illustrated as an original modeling approach to investigate the performances of organic photovoltaic cells.
16 citations
••
TL;DR: In this paper, an oxidized liquid metal droplet-based energy harvester that converts acoustic energy into electrical energy by modulating an electrical double layer that originates from the deformation of the oxidized Liquid Metal droplet was reported.
Abstract: We report an oxidized liquid metal droplet-based energy harvester that converts acoustic energy into electrical energy by modulating an electrical double layer that originates from the deformation of the oxidized liquid metal droplet. Gallium-based liquid metal alloy has been developed for various applications owing to the outstanding material properties, such as its high electrical conductivity (metallic property) and unlimited deformability (liquid property). In this study, we demonstrated energy harvesting using an electrical double layer between the acoustic wave-modulated liquid metal droplet and two electrodes. The proposed energy harvester consisted of top and bottom electrodes covered with the dielectric layer and a Gallium-based liquid metal droplet placed between the electrodes. When we applied an external bias voltage and acoustic wave to the proposed device, the contact area between the liquid metal droplet and the electrodes changed, leading to the variation of the capacitance in the electrical double layer and the generation of electrical output current. Using the proposed energy harvester, the maximum output current of 41.2 nA was generated with an applied acoustic wave of 30 Hz. In addition, we studied the relationships between the maximum output current and a variety of factors, such as the size of the liquid metal droplet, the thickness of the hydrophobic layer, and the distance between the top and bottom electrode plates.
14 citations
••
TL;DR: In this paper, the H -polarized electromagnetic wave by multilayer graphene grating in the THz range is considered, and the scattering and absorption characteristics as functions of frequency and distance between layers are studied.
Abstract: Diffraction of the H -polarized electromagnetic wave by multilayer graphene grating in the THz range is considered. The scattered field is represented in the spectral domain via unknown spectral functions. The mathematical model is based on the graphene surface impedance and the method of singular integral equations. The numerical solution is obtained by the Nystrom-type method of discrete singularities. The scattering and absorption characteristics as functions of frequency and distance between layers are studied.
13 citations
••
TL;DR: In this paper, the melting of a phase change material (PCM) in a square cavity with a single fin attached at the center of the heated wall is studied numerically employing the enthalpy-porosity method.
Abstract: In this study, melting of a phase change material (PCM) in a square cavity with a single fin attached at the center of the heated wall is studied numerically employing the enthalpy-porosity method The opposite wall to the heated wall in the square cavity is cold The other two adjacent walls are thermally insulated Paraffin wax is chosen as a PCM due to its demonstrable favorable properties The thermophysical properties of the paraffin wax are assumed to be a dual function of temperature and phase The influence of the fin length on the melting process of the paraffin wax is examined Moreover, the orientation of the square cavity on the melting process is scrutinized The numerical results elucidate that the melting rates increase significantly by embedding the fin into the paraffin wax As the fin length is incremented, the melting rate intensifies considerably during the early stages of melting However, the effect of the fin length on the melting rate diminishes after a long period of heating has happened It is also observed that the melting rate can be augmented significantly by changing the orientation of the heated wall in the square cavity
13 citations
••
TL;DR: In this paper, a pulsed magnetic reconnection thruster consisting of two parallel-connected slit coaxial tubes was constructed and operated in argon plasma produced by RF energy at 13.56 MHz.
Abstract: Plasma thrusters propel spacecraft by the application of Lorentz forces to ionized propellants. Despite evidence that Lorentz forces resulting from magnetic reconnection in solar flares and Earth's magnetopause produce jets of energetic particles, magnetic reconnection has only recently been considered as a means of accelerating plasma in a thruster. Based on theoretical principles, a pulsed magnetic reconnection thruster consisting of two parallel-connected slit coaxial tubes was constructed. The thruster was operated in argon plasma produced by RF energy at 13.56 MHz. A 1.0 ms current pulse of up to 1500 A was applied to the tubes. Three results provide evidence for magnetic reconnection. (1) The production of high-energy electrons resembling the outflow that is observed in the reconnection of field lines in solar flares and in laboratory experiments. (2) The high-energy electron current coincided with the rise of the magnetic field in the thruster and was followed by a large ion current. (3) In accordance with known physics of magnetic reconnection, ion currents were found to increase as the plasma became less collisional. The Alfven speed of the outflowing ions was calculated to be 8.48 × 103 m s− 1 corresponding to an Isp of 860 s.
12 citations
••
TL;DR: In this article, the authors explore the physics underlying the interparticle charge diffusion, which remains not well understood, by means of numerical simulations and propose a time-scale for its characterization for particular systems.
Abstract: Dispersed solid particles in wall-bounded flows may get electrified during particle-wall collisions due to triboelectric effects. Subsequently, the electrostatic charge migrates from the near-wall regions to the bulk of the flow through the dynamics of the particles ( particle-bound charge transport ) and charge transfer during collisions between particles ( inter-particle charge diffusion ). In this paper, we explore the physics underlying the mechanism of inter-particle charge diffusion, which remains not well understood, by means of numerical simulations. We investigated the efficiency of the charge transport within the particulate phase via this mechanism and propose a time-scale for its characterization for particular systems. The considered parameters of these systems included the particle number density and charge as well as their mechanical and electrical properties. It was found that both an increase of the material density of the particles or of their number density results in an enhanced inter-particle charge diffusion and, thus, a reduction of its time scale. Moreover, if only the number density is high but the material density is kept low, then inter-particle charge diffusion may even become the dominant wall-normal charge transport mechanism. Further, in case some particles carry a high charge they are accelerated towards uncharged particles through electrostatic forces which leads to an efficient charge redistribution.
11 citations
••
TL;DR: In this article, the effects of temperature and nanoparticle size on viscosity using molecular dynamics simulations (MD) were investigated for CO2-Al2O3 interaction. But the authors did not consider the effect of Brownian motion and its contribution to changes in viscosities.
Abstract: High-viscosity CO2 is of interest to the oil and gas industry in enhanced oil recovery and well-fracturing applications. Dispersing nanoparticles in CO2 is one way of achieving increased viscosity. However, parametric studies on viscosity estimation of CO2 nanofluids is not found in the open literature. A comparison of various interatomic potentials for their accuracy in predicting viscosity is also missing. In this work, we studied Al2 O3 nanoparticles in CO2 base fluid. We screened the inter-molecular interaction potential models available for CO2 –CO2 interactions and found that the TraPPE-flexible model (with MORSE potential) to be most suitable for conditions used in this work. We estimated the CO2 –Al2 O3 interaction potential using quantum mechanical simulations. Using this combination for CO2 –CO2 and CO2 –Al2 O3 interactions, we explored the effects of temperature and nanoparticle size on viscosity using molecular dynamics simulations (MD). We predicted that the viscosity would increase with increase in temperature and particle size. We also calculated the base fluid self-diffusion coefficient to investigate the effect of Brownian motion and its contribution to changes in viscosity. We found that it decreases with increase in particle size and temperature, thereby indicating that Brownian motion does not contribute to the increased viscosity. Further, the nanolayer formed at the Al2 O3 –CO2 interface is studied through density distributions around the nanoparticle; the thickness of this nanolayer is found to increase with nanoparticle diameter. Finally, we examined the structures of CO2 fluid in presence of nanoparticles at different thermodynamic states through radial distribution functions. The current work sheds light on the viscosity enhancement by the addition of nanoparticles; it is hoped that such studies will lead to tools that help tailor fluid properties to specific requirements.
11 citations
••
TL;DR: In this article, the effects of dielectric barrier discharge (DBD) exposure on the physico-chemical and tribo-electric properties of polymers were quantified by means of an optical profilometer, a fourier transform infrared (FTIR) spectrometer and an electric charge measurement system.
Abstract: The aim of this paper is to quantify the effects of dielectric barrier discharge (DBD) exposure on the physico-chemical and tribo-electric properties of polymers. The study was conducted in atmospheric air on polypropylene, polyethylene and polyvinyl-chloride. These three types of polymers are widely used in industry. The polymers were characterized by means of an optical profilometer, a fourier-transform infrared (FTIR) spectrometer and an electric charge measurement system. The latter is composed of a Faraday pail connected to an electrometer. The profilometer analyses showed that the DBD plasma treatment has increased the surface roughness of the three polymers. FTIR revealed that oxygen atoms and polar groups were grafted on their surfaces, thereby conferring them a hydrophilic character. The short (2 sec) DBD plasma treatment has considerably improved the electrostatic charge acquired by the polymers during electrostatic tribo-charging, while longer exposures conferred the polymer anti-static properties and decreased its tribo-charging capability. The correlation between the results of the physico-chemical analyses and the tribo-electric behavior has been discussed.
11 citations
••
TL;DR: In this article, a cylindrical coordinate system was applied, wherein the solution domain was truncated in the radial direction, and the final formulas for the change of the coil impedance with regard to the air space, and also pertaining to the test object without a flaw.
Abstract: The paper examines the problem of an axially symmetric I-cored coil located above a three-layered plate with a hole in the middle layer. A cylindrical coordinate system was applied, wherein the solution domain was truncated in the radial direction. The employment of the truncated region eigenfunction expansion (TREE) method resulted in deriving the final formulas for the change of the coil impedance with regard to the air space, and also pertaining to the test object without a flaw. Formulas for various configurations of the test object, among others for a surface hole, a subsurface hole and a through hole, have been presented. For the purpose of defectoscopy, the influence of the hole in the plate on the impedance components was investigated. The calculations were made in Matlab for frequencies from 100 Hz to 50 kHz. The obtained results were verified using the finite element method (FEM) in Comsol Multiphysics package. A very good agreement was observed in the case of both the resistance and reactance.
9 citations
••
TL;DR: In this paper, the authors studied the dielectric behavior of a quaternary composite made from a mixture of barium titanate (BT), manganese dioxide (MnO 2 ) and calcium oxide (CaO) in the same epoxy resin matrix (RE) maintained at 70% by volume fraction.
Abstract: The main objective of this paper is to study the dielectric behavior of a quaternary composite, made from a mixture of barium titanate (BT), manganese dioxide (MnO 2 ) and calcium oxide (CaO) in the same epoxy resin matrix (RE) maintained at 70% by volume fraction, while those of the other constituents are variable and completing each other in a way to achieve the remaining proportion, i.e. 30%. Random mixtures are made at room temperature and under atmospheric pressure. A dielectric characterization of this mixture type was performed by time-domain spectroscopy (TDS) over a frequency wide band (DC–2 GHz). This has been carried out to illustrate the effect of two oxides (MnO 2 and CaO) simultaneously at low frequency (500 MHz), in the presence of (BT), on the composite dielectric behavior. This has led consequently to make a comparison between the present acquired results and those of the ternary composite, where (MnO 2 ) and (CaO) act separately. The results obtained so far in this study allowed us to check the validity of the modified Lichtenecker law (MLL)-based predictive model in the quaternary composite case. The interest of this study lies on applications of these materials in microelectronics circuits and absorber materials in telecommunication domain.
••
TL;DR: In this article, a contactless method for the identification of the electrical conductivity tensor of a carbon fiber composite materials plate using a rotating magnetic field and multi-coil eddy current sensor is proposed.
Abstract: This paper proposes a contactless method for the identification of the electrical conductivity tensor of a carbon fiber composite materials plate using a rotating magnetic field and multi-coil eddy current sensor. This sensor consists of identical rectangular multi-coil, excited by two-phase sinusoidal current source in order to generate a rotating magnetic field and to avoid the mechanical rotation of the sensor. The fibers orientations, the longitudinal and transverse conductivities in each ply of carbon fiber composite material plate were directly determined with analysis of the impedance variation of each coil as function of its angular position. The inversion process is based on the use of artificial neural networks. The direct calculation associated with artificial neural networks makes use of 3D time-harmonic finite element method based on the A , V–A formulation.
••
TL;DR: In this paper, a dielectric barrier discharge plasma based atmospheric pressure plasma jet has been generated in a floating helix and floating end ring electrode configuration using mixture of argon and nitrogen gases.
Abstract: In this paper, a dielectric barrier discharge plasma based atmospheric pressure plasma jet has been generated in a floating helix and floating end ring electrode configuration using mixture of argon and nitrogen gases (50:50 ratio) This configuration is subjected to a range of supply frequencies (10–25 kHz) and supply voltages (65–95 kV) at a fixed rate of gas flow rate (ie, 1 l/min) The electrical characterization of the plasma jet has been carried out using a high voltage probe and current transformer The current–voltage characteristics have been analyzed, and the power consumed by the device has been estimated at different applied combinations of supply frequency and voltages for optimum power consumption and maximum jet length A comparative analysis of the results of the above experiments has shown that maximum power consumed by the device in helix electrode configuration with end ring is 19 W for (Ar+N2 ) mixture as compared to only 12 mW and 77 mW for Ar and He gas respectively (With end ring), this may be due to the main ionization mechanisms which are different depending on the working gas Furthermore, maximum jet length of 42 mm has been obtained for He gas at 6 kV/25 kHz due to penning ionization process in comparison to jet lengths of only 32 mm for Ar gas and jet length of only 26 mm for Ar+N2 mixture The obtained average power consumed and maximum jet length for mixture of (Ar+N2 ) gases are 65 W and 26 mm
••
TL;DR: In this article, a surface plasmons resonance (SPR) biosensor based on optical fiber was applied for the detection of pathogenic bacteria (Escherichia coli), in order to overcome the stresses caused by the massive prism and to obtain a reliable and efficient miniature device.
Abstract: In the present work, we have investigated the surface plasmons resonance (SPR) biosensor based on optical fiber applied for the detection of pathogenic bacteria (Escherichia coli), in order to overcome the stresses caused by the massive prism and to obtain a reliable and efficient miniature device. The modeling procedure is based on a matrix formalism developed for the optical studies of multilayer media. We have tested the response of the fiber optic biosensor based on a golden substrate functionalized with thiol acid. The results show that the SPR biosensor sensitivity is improved by treating the gold electrode with thiol. An improved SPR biosensor with a high resolution is obtained.
••
TL;DR: In this article, the minimum sheet resistance of 6'Ω/square was achieved with 70% of transmission in the visible wavelength region by carefully optimizing the thickness of the metal layer.
Abstract: Silver (Ag) incorporated aluminium doped zinc oxide (AZO) based multilayer films were fabricated for transparent conducting electrode applications. AZO and Ag thin film layers were deposited using direct current magnetron sputtering system without breaking the vacuum. By carefully optimizing the thickness of the metal layer, the minimum sheet resistance of 6 Ω/square was achieved with 70% of transmission in the visible wavelength region. The surface morphology of the film was studied with atomic force microscope mapping in 5 µm × 5 µm area of the multilayer structure. The significance of the Ag layer thickness in determining the electrical and optical properties of the multilayer film was investigated.
••
TL;DR: In this article, the first harmonic of an acousto-optically Q-Switched Nd:YAG laser is utilized at 13, 18 and 23 J/cm2 laser fluences.
Abstract: Here in this paper, synthesis of WO3 nanoparticles (NPs) by laser ablation of a pure tungsten plate immersed in water is reported. For this purpose, the first harmonic of an acousto-optically Q-Switched Nd:YAG laser is utilized at 13, 18 and 23 J/cm2 laser fluences. X-ray diffraction (XRD) and transmission electron microscopy (TEM) associated with dynamic light scattering (DLS) techniques show that while the laser fluence increases from 13 to 23 J/cm2 , the crystallinity, length of particle chains and average particle size of the products increase, respectively. UV–Vis spectra indicate a red shift on the absorption edge towards the visible region for the samples produced at higher laser fluences attributed to the particle size increment and energy band gap decrement, subsequently. Also other linear optical parameters including Urbach energy, refractive index dispersion, relaxation time, complex dielectric and conductivity functions are derived and discussed. Z-scan analysis is carried out to determine the nonlinear refraction index, nonlinear absorption coefficient and third-order nonlinear susceptibility. It is found that WO3 NPs can be considered for optical limiting performance because of the high nonlinear absorption. Furthermore, the specimens prepared at higher laser fluences are more applicable due to the larger particle size and higher nonlinear absorption, consequently.
••
TL;DR: In this paper, the effect of shape and deformation on the drag coefficient of a free-falling liquid gallium droplet in water in a terminal state is investigated experimentally.
Abstract: In this article, the effect of shape and deformation on the drag coefficient of a free-falling liquid gallium droplet in water in a terminal state is investigated experimentally. The temperature of the dispersed and continuous liquid was varied in order to examine the effect on the liquid–metal droplets. The falling droplets were imaged using a high-speed camera, and a simple model was developed to predict drag coefficient over a Reynolds number range of 103 . The drag coefficients of the deformed liquid gallium droplets were found to be larger than that associated with a solid sphere and the associated Weber number was below 4.5. It was found that the shape of all droplets in our experiment were oblate spheroid. A correlation has been established to predict the aspect ratio of a liquid gallium droplet moving in quiescent water. The deformation is highly dependent on interfacial surface tension and inertial force, while the viscosity ratio and pressure distribution have negligible effect.
••
TL;DR: In this article, a layered parity-time (PT)-symmetric structure including resonators was designed to achieve enhanced transmittance of parity time (PT) systems, and the authors used the scatter matrix method to study the optical properties of the designed structure under the modulation of resonators.
Abstract: In order to achieve enhanced transmittance of parity-time (PT)-symmetric system, we design a layered PT-symmetric structure including resonators. We use the scatter matrix method to study the optical properties of the designed structure under the modulation of resonators. The structure system takes on a singular pole effect, i.e., the huge reflectance and transmittance occur at a special wavelength and period number. The field distribution reveals that the singular pole results from the coupling resonance of single cavity and the whole structure. Because of the coupling resonance, the total gain in layer A is much larger than the total loss in layer C. The reflectance and transmittance at the singular pole take on a high sensitivity on the refraction index of the resonators.
••
TL;DR: In this paper, the evaporation of a saline solution from a heterogeneous porous medium formed by the assembly of a coarse medium column and a fine medium column is studied numerically.
Abstract: The evaporation of a saline solution from a heterogeneous porous medium formed by the assembly of a coarse medium column and a fine medium column is studied numerically. We concentrate on the locus of the formation of first crystals on the evaporative surface from the computation of the ion mass fraction distribution at the surface prior to the efflorescence development. Two basic situations considered in previous works, namely the evaporation–wicking situation and the drying situation are considered. The study makes clear that each situation leads to a markedly different locus of the efflorescence formation, except, however, for very high initial salt concentrations. The study emphasizes the key-role of the velocity field induced in the porous domain in the case of the evaporation–wicking situation. In the case of the drying situation, a key aspect lies in the local increase in the ion mass fraction due to the local desaturation, i.e. the local shrinking of the liquid volume containing the ions.
••
TL;DR: In this article, the phase structure, optical properties, size and morphology of thin PbO films were investigated by scanning electron microscopy, X-ray diffraction and UV-vis spectroscopy.
Abstract: Effect of the annealing oxidation time of electrodeposited lead (Pb) on the phase formation of lead oxide (PbO) films is reported. The phase structure, optical properties, size and morphology of the films were investigated by scanning electron microscopy, X-ray diffraction and UV-vis spectroscopy. The relationship between structur and photoelectrochemical properties was investigated. Thin films of PbO produced via air annealing of electrodeposited lead consist of a mixture of two phases, orthorhombic (o -PbO) and tetragonal (t -PbO), that determine the material properties and effectiveness as absorber layer in a photoelectrochemical device. The proportion of tetragonal t -PbO increases for longer heat treatments. After 40 h, the sample consists mainly of tetragonal t -PbO. The p-type semiconducting behavior of lead oxide was studied by photocurrent measurements. Different heat treatments yield variations in the ratio of tetragonal to orthorhombic lead oxide that effect on device performances, where devices with a higher content of tetragonal t -PbO show higher photocurrent than with the orthorhombic phase.
••
TL;DR: In this paper, a sol-gel chemistry is explored to deposit CuO using cupric chloride dihydrate (CuCl2 · 2H2 O) with 5, 10 and 15% concentration of EDTA (capping agent) using low-cost dip-coating and annealed at 400 °C.
Abstract: Copper oxide is a compound that has been considered significant owing to its many advantages such as easy availability of copper in huge quantity, its non-toxic nature and the good electrical and optical properties. It is p-type with bandgap range of 1.21–1.51 eV and has potential of absorption of solar spectrum. In this work, sol–gel chemistry is explored to deposit CuO using cupric chloride dihydrate (CuCl2 · 2H2 O) with 5, 10 and 15% concentration of EDTA (capping agent) using low-cost dip-coating and annealed at 400 °C. The bandgap of the CuO films was found to be in the range of 1.3–1.8 eV, which is comparable with the reported values and also suggests quantum shift in these nanostructures. These investigations suggest suitability of these layers as absorber for photovoltaic applications. SEM investigation suggests the uniform growth of layers by dip-coating techniques. Capping also appears to control the grain growth as observed by electron microscopy. Sol–gel dip-coating technique is presented in this study for deposition of flat layers.
••
TL;DR: A combination of two powerful techniques, namely, charge deep level transient spectroscopy and spectroscopic ellipsometry is employed on atomic layer deposited Si-metal oxide semiconductor capacitors (MOSCAPs) to investigate the energy efficiency of the physical process as mentioned in this paper.
Abstract: A combination of two powerful techniques, namely, charge deep level transient spectroscopy and spectroscopic ellipsometry is employed on atomic layer deposited Si-metal oxide semiconductor capacitors (MOSCAPs) to investigate the energy efficiency of the physical process. Ultra-thin TiN/HfSiO acted as gate-dielectric stack on Si substrate was carefully subjected to rapid thermal processing and subsequent spectroscopic measurements to determine the transient behaviour of charges and electro-optical characteristics. Some key parameters such as trap concentration, activation energy required to surmount the traps, capture cross section, refractive index and extinction coefficient are found to play an important role in order to assess the energy efficiency of the devices both in terms of post-process quality of the retained surface and residual efficiency of the process by virtue of dynamics at atomistic scales. The results may provide a useful insight to the Si manufacturing protocols at ever decreasing nodes with desirable energy efficiency.
••
TL;DR: In this article, physical mechanisms related to the creeping discharges propagation growing over insulators subjected to perpendicular electric field and positive lightning impulse voltage were discussed, and the developed discussion attempts to answer some observations especially noticed for main discharges feature namely (i) the discharges morphology, (ii) their velocity and (iii) the space charges effects on electric field computation.
Abstract: In many high voltage equipment, partial discharges are regarded as one of the most widespread pathology whose ignition conditions and effects are studied by scientists and manufacturers to avoid major failures. Actually, those electrical gaseous phenomena generally occur under several constraints such as the electrostatic field level, the nature of insulating surface being polluted or not, and switching or lightning transients. The present paper discusses physical mechanisms related to the creeping discharges propagation growing over insulators subjected to perpendicular electric field and positive lightning impulse voltage. More precisely, the developed discussion attempts to answer some observations especially noticed for main discharges feature namely (i) the discharges morphology, (ii) their velocity and (iii) the space charges effects on electric field computation. Several factors like (i) the influence of the type of a material’s interface, its electric conductivity, permittivity and discharges mobility, (ii) the relationship between the applied electrostatic field, the space charges, the velocity, the propelling pressure and discharges temperature are among numerous parameters that have been addressed in this study which discusses lightning impulse transients phenomena.
••
TL;DR: In this paper, the amplitude of a given Fourier component can strongly depend on both the nature of the windowing (either flat, Hahn or Blackman window) and, since oscillations are obtained within a finite field range, the window width.
Abstract: Quantum oscillation amplitudes of multiband metals, such as high-Tc superconductors in the normal state, heavy fermions or organic conductors, are generally determined through Fourier analysis of the data even though the oscillatory part of the signal is field dependent. It is demonstrated that the amplitude of a given Fourier component can strongly depend on both the nature of the windowing (either flat, Hahn or Blackman window) and, since oscillations are obtained within a finite field range, the window width. Consequences on the determination of the Fourier amplitudes, hence of the effective masses, are examined in order to determine the conditions for reliable data analysis.
••
TL;DR: In this article, the authors extracted curcuminoids from turmeric (Curcuma longa L.) by means of three methods, comprising the normal method, use of Soxhlet apparatus and by combining the normal methods with the Syshlet extraction approach.
Abstract: In this study, curcuminoids were extracted from turmeric (Curcuma longa L.) by means of three methods, comprising the normal method, use of Soxhlet apparatus and by combining the normal method with the Soxhlet extraction approach. The limitation of stickiness in the use of curcuminoids was resolved by mixing it with silica gel. The curcuminoids used light down-conversion of UV light (390 nm) for the white light-emitting diode (WLED). The characteristics of the white light chromaticity were controlled by changing the current and concentration of the curcuminoids. The chromaticity coordinates (CIE) and correlated color temperature (CCT) were measured for different applied currents (20, 60 and 100 mA) and weights (25, 35 and 50 mg) of curcuminoids. It was observed from the concentration of phosphor that the combination of the normal and Soxhlet apparatus methods is most effective extraction approach. The results showed that increasing the concentration of phosphor significantly and remarkably increased the value of CCT when different values of current were applied. The stress test showed that the prolongation of dye degradation can be improved using air gap and glass slid, with air gap being more effective. An optimum color rendering index (CRI) value of 61.2 is obtained. The white phosphor exhibited CIE values of 0.333, 0.3151 and color temperature (CCT) of 5405 K.
••
TL;DR: In this paper, the theoretical investigations on the concept of new active radiation shields based on graphene are discussed and the cross section of the gamma and X radiation interaction with a charged graphene layer is presented and used to calculate the linear attenuation coefficient of the proposed shield.
Abstract: The theoretical investigations on the concept of new active radiation shields based on graphene are discussed. The cross section of the gamma and X radiation interaction with a charged graphene layer is presented and used to calculate the linear attenuation coefficient of the proposed shield. Finally, the technical concept and potential applications of the graphene shield, as well as some potential difficulties, are discussed.
••
TL;DR: In this article, two intrinsic p-type contacts of graphene-GeC/GeS and further tune them from p-Type to n-type by external electric fields are presented.
Abstract: n-Type contact of Schottky barriers at two-dimensional (2D) materials/metal interfaces is a usual formalization in the modern FETs applications. It is common to modulate it from n- to p-type through some specific methods. In this work, we came up with two new intrinsic p-type contacts of graphene-GeC/GeS and further tune them from p-type to n-type by external electric fields. It proved that the electronic properties of graphene and GeC/GeS can be roughly preserved for the weak van der Waals (vdW) interaction. p-Type contacts with relatively small barriers are formed at g-GeC/GeS heterointerfaces. After external electric field applied, the Schottky barrier can be effectively tuned by different external electric and the p-type contact further turns into n-type. Variation of the Schottky barriers indicated a partial pinning for interfaces of g-GeC/GeS. This is because the interfacial states between graphene and GeC/GeS hardly exists. The barrier height of g-GeC/GeS and the corresponding contact type can be flexibly tuned, which is of great importance in the design of novel transistors-based 2D materials. Searching for novel nanoscale electronic equipment based on 2D materials is a hot topic in the current study. This work would provide meaningful guidelines for nanoscale devices.
••
TL;DR: In this article, the chemical changes on polymethyl methacrylate (PMMA) surface are analyzed by Fourier transform infrared spectroscopy and a chemical degradation mechanism is proposed.
Abstract: In high-voltage applications, insulators may be exposed to corona discharges during long periods. In this experimental work, corona discharge tests of different durations are carried out in air at atmospheric pressure on polymethyl methacrylate (PMMA) samples. The resulting surface degradation is studied with several techniques. The surface damages are observed with environmental scanning electron microscope and atomic force microscopy. The results show that electrical trees occur on the surface of material and their distribution depends on the corona discharge duration. The chemical changes on PMMA surface are analyzed by Fourier transform infrared spectroscopy and a chemical degradation mechanism is proposed. Evolution of surface resistivity with corona aging is also implemented by using a classical I (V ) method. In addition, to study the dielectric behavior of PMMA, the monitoring of kinetics of the trapped charge under electron irradiation in a scanning electron microscope is performed. The charging ability of PMMA under electron irradiation and its time constant of charging decrease with electrical aging.
••
TL;DR: In this paper, the authors used a finite element method (FEM) simulation to understand the composite behavior on the microscopic scale, and an estimation of the harvested voltage was modeled according to the grains size.
Abstract: Recent trends in electromechanical conversion using alternative materials, have demonstrated the advantages of using piezoelectric composites for energy generation. There have been several papers on ceramic/polymer composites in which the fillers have high piezoelectric constant. Basically, the energy harvested depends on the proportion of the piezoelectric properties of composite. The fillers size within the composites is also an important criterion of the composites properties. Thus, in this paper 0–3 composites, made of lead zirconate titanate (PZT) ceramic powder and polyurethane (PU) were prepared. Different sizes of ceramic grains were used: grains with average size of 10 μm, size under 80 μm and size under 100 μm. Sizes of the PZT grains was determined according to the homogenization efficiency of the composite. Piezoelectric (piezoelectric coefficient d 33 ) and dielectric properties (dielectric constant) were investigated. They have shown an interesting improvement with the increasing grains size up to 20 pC/N and 100, respectively. In order to understand the composite behavior on the microscopic scale, a simulation was carried out by mean of a finite element method (FEM) software. Finally, an estimation of the harvested voltage was modeled according to the grains size.
••
TL;DR: The room temperature electrical characteristics of the organic Au/mTPP/p-Si device fabricated by spin coating method were investigated with I-V and C-V measurements.
Abstract: The room temperature electrical characteristics of the organic Au/mTPP/p-Si device fabricated by spin coating method were investigated with I – V and C – V measurements. It has been determined that the device has a high rectification coefficient and current transport is dominated by the thermionic emission. The serial resistance value is calculated at 92 ohms with two different approaches. Serial resistance effects were also found to be effective in C – V and G – V measurements. The different barrier heights from the I – V and C – V measurements indicate possible interface and trap states or barrier inhomogeneities.