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Thermodynamic properties of cellulose insulation paper are vital factors affecting the life of a transformer; in order to obtain cellulose insulation paper with better thermodynamic properties, three types of silane coupling agents—3-aminopropyltriethoxy silane (KH550), 3-glycidoxypropyltrimethoxy silane (KH560), and 3-methacryloyloxypropyltrimethoxy silane (KH570)—were grafted on the surface of nano-SiO2, and thermodynamic properties of cellulose modified with nano-SiO2 were explored. The molecular dynamics method was used to establish a composite model of nano-SiO2/cellulose. Also, different silane coupling agent grafted nano-SiO2/cellulose models were established to explore the effect of mechanical properties, interaction energy, free volume, and hydrogen bonds on thermodynamic properties. The results showed that KH550 was the best modification of the nano-SiO2/cellulose system among the three grafted silane coupling agents because KH550 grafted on the surface of nano-SiO2 formed more hydrogen bonds in the cellulose system. The interfacial bonding strength between the nano-SiO2 and the cellulose chains can effectively improve the thermal stability of the cellulose insulating paper.

In order to improve the thermal stability of insulation paper cellulose in micro-water environment, the molecular simulation was used to compare and analyze the thermal stability of polysiloxane-grafted cellulose with 3% micro-water content in the present study. The static mechanics, glass transition temperature and number of hydrogen bonds are used to characterize the thermal stability of insulating paper cellulose in this paper. First, analysis of the mechanical properties of the model demonstrated that the value of the elastic moduli (E) and bulk moduli (K) of the grafted model were greater than those of the ungrafted model at each temperature. Second, the glass transition temperature of the grafted model was 60 K higher than that of the ungrafted model. Finally, the analysis of the radial distribution function (RDF) and hydrogen bonding showed that polysiloxane-grafted insulation paper cellulose can reduce the number of hydrogen bonds formed between the water molecules and the cellulose chains, which can reduce the damage caused to the cellulose chains by the water molecules. Therefore, the present study shows that the polysiloxane-grafted insulation paper cellulose can improve its thermal stability in micro-water environment.

Accurate monitoring of insulation aging of oil-paper insulation power equipment such as oil-immersed transformers is a key and difficult point in the field of high voltage research. In this paper, a method based on Raman spectroscopy to diagnose the aging degree of oil-paper insulation is discussed. Raman detections of the samples were carried out on a self-built Raman detection platform. The partial least squares method was used to extract and analyze the spectral features. The aging time of the sample was used to supervise the feature extraction of oil-paper insulation Raman data, and the intrinsic mathematical relationship between the Raman features of oil-paper insulation and the aging was excavated. Finally, a quantitative aging diagnostic model based on Raman spectral features of oil-paper insulation to predict its aging state was built with the assistance of the support vector regression method. The results of aging time prediction for 30 test samples show that the mean square error is 0.0123 and the square of correlation coefficient is 0.987. The proposed method provides a new idea for Raman aging diagnosis of oil-paper insulation.

In this study, we composite coated silica nanoparticles with functional groups on paper to form a double-size surface roughness, then hexafluorobutyl methacrylate was polymerized with 3-trimethoxymethylsilyl propyl methacrylate (TSPM), a one-step method is used to prepare a hydrophobic polymer with low surface energy (PHFMA-co-TSPM), and the superhydrophobic surface was prepared by hydrophobic treatment of the paper with a low surface energy polymer. Further tests show that the superhydrophobic paper prepared by this method not only exhibits extremely strong hydrophobicity, but also has strong stability, transparency, and self-cleaning properties.

The accuracy of insulation defect diagnosis based on the dielectric spectrum response is severely influenced by temperature for oil-impregnated paper bushing. The dielectric loss (tan δ) mathematical model with a temperature–frequency factor to restrict the application of the frequency domain dielectric spectrum (FDS) for insulation diagnosis is not clear. In this paper, five temperatures are selected to study the frequency temperature characteristic of the FDS and polarization current for oil-impregnated paper bushing. The experimental results show that the temperature has different effects on the lower frequency (0.001 Hz–1 Hz) and higher frequency (1000 Hz–10 kHz) of FDS. With the increasing temperature, the lower frequency tan δ of 1 mHz–1 Hz shows a better pattern of exponential growth, while the higher frequency tan δ at 1 kHz–10 kHz shows the declining law with the rising temperature. With the increasing temperature, the polarization current shows a better pattern of exponential growth, while resistance obviously shows the declining law of the exponential pattern. The FDS curve of oil-impregnated paper bushings can be amended by the mathematical model of tan δ for the dielectric response on site for accuracy diagnosis.

A study of plasma treatment of clay-coated paper is presented. The wettability of the paper surface before and after the plasma treatment was determined by measuring the water contact angle and surface free energy. The appearance of the surface-functional groups was determined by using high-resolution X-ray photoelectron spectroscopy, while changes in the surface morphology were monitored by scanning electron microscopy. Already after 0.25 s of the plasma treatment, the paper surface improved its wettability. The X-ray photoelectron spectroscopy analyses showed a gradual increase of oxygen-rich functional groups on the surface while scanning electron microscopy analyses did not show a significant modification of the morphology and no alternation of the surface structure after the plasma treatment.

Cantilevers are one of the most utilized mechanical elements for acoustic sensing. In comparison to the edge clamped diaphragms of different shapes, a single edge clamped cantilever makes an acoustic sensor mechanically sensitive for detection of lower pressure. The aspect ratio of cantilevers is one of the most important parameters which affect sensitivity. Herein, we present a mathematical, finite element method and experimental analysis to determine the effect of the aspect ratio on the resonant frequency, response time, mechanical sensitivity, and capacitive sensitivity of a cantilever-based acoustic pressure sensor. Three cantilevers of different aspect ratios (0.67, 1, and 1.5) have been chosen for sound pressure application to detect capacitance change. The cantilever with the smallest aspect ratio (0.67) has the highest response time (206 ms), mechanical sensitivity, and capacitive sensitivity (22 fF), which reduce after increasing the aspect ratio. The resonant frequency of the cantilever was also analyzed by applying sweep in sound frequency. It was found to be minimum for the cantilever with the smallest aspect ratio (510 Hz) and increases with an increase in the aspect ratio. We have applied the garage fabrication process using low cost, recyclable, and easily available materials such as metal coated polymer sheets, mounting tapes and glass slides as alternative materials for expensive materials.

We presented a distance-based detection method for visual quantification of mercury ions on a microfluidic paper-based analytical device (μPAD). Dithizone in NaOH solution was used as chromogenic reagent and deposited onto paper channel delimited by hydrophobic wax barrier. Reactions happened between mercury ions and dithizone to form an insoluble colored complex, producing colored precipitate on the paper channel. The length of colored precipitate could be readily measured using the printed ruler along each device. The length of precipitate increase linearly with the mercury concentrations, mercury in sample solution could be quantified by measuring the length of the colored precipitate. Being free of any electronic instruments, this method has the advantages of portability, ease of use, low cost and disposability. This presented method was used to detect mercury ions in a synthetic sample, demonstrating its potential in on-site and real time analysis.

The effect of silica nanoparticle (Nano-SiO2) dopants on insulation paper cellulose, and the interaction between them, was investigated using molecular dynamics simulations. The mechanical properties, interactions, and cellulose-Nano-SiO2 compatibility of composite models of cellulose doped with Nano-SiO2 were studied. An increase in Nano-SiO2 size leads to a decrease in the mechanical properties, and a decrease in the anti-deformation ability of the composite model. The binding energies and bond energies per surface area of the composite models indicate that the bonding interaction between spherical Nano-SiO2 and cellulose is the strongest among the four different Nano-SiO2 shapes that are investigated. The solubilities of the four composite models decrease with increasing Nano-SiO2 size, and the difference between the solubility of pure cellulose and those of the composite models increases with increasing Nano-SiO2 size. Good doping effects with the highest cellulose-Nano-SiO2 compatibility are achieved for the cellulose model doped with spherical Nano-SiO2 of 10 A in diameter. These findings provide a method for modifying the mechanical properties of cellulose by doping, perhaps for improving insulation dielectrics.

Paper-based batteries represent a new frontier in battery technology. However, low-flexibility and poor ionic conductivity of solid electrolytes have been major impediments in achieving practical mechanically flexible batteries. This work discuss new highly ionic conductive polymer gel electrolytes for paper-based battery applications. In this paper, we present a poly(vinylidene fluoride-hexafluoropropylene) (PVDH-HFP) porous membrane electrolyte enhanced with lithium bis(trifluoromethane sulphone)imide (LiTFSI) and lithium aluminum titanium phosphate (LATP), with an ionic conductivity of 2.1 × 10−3 S cm−1. Combining ceramic (LATP) with the gel structure of PVDF-HFP and LiTFSI ionic liquid harnesses benefits of ceramic and gel electrolytes in providing flexible electrolytes with a high ionic conductivity. In a flexibility test experiment, bending the polymer electrolyte at 90° for 20 times resulted in 14% decrease in ionic conductivity. Efforts to further improving the flexibility of the presented electrolyte are ongoing. Using this electrolyte, full-cell batteries with lithium titanium oxide (LTO) and lithium cobalt oxide (LCO) electrodes and (i) standard metallic current collectors and (ii) paper-based current collectors were fabricated and tested. The achieved specific capacities were (i) 123 mAh g−1 for standard metallic current collectors and (ii) 99.5 mAh g−1 for paper-based current collectors. Thus, the presented electrolyte has potential to become a viable candidate in paper-based and flexible battery applications. Fabrication methods, experimental procedures, and test results for the polymer gel electrolyte and batteries are presented and discussed.

The composite of nano-metal materials and wood to prepare multifunctional metallized wood is of great significance for increasing the added value of wood and expanding the field of wood applications. In this paper, the veneer of Pinus sylvestris L. var. mongholica Litv was used as the research object and the wood veneer was treated by simple physical methods. A copper thin film was grown on the surface of the wood veneer by the magnetron sputtering method to realize the preparation of “environmentally friendly” metalized wood. The preparation method of “environmentally friendly” metallized wood was explored, and the mechanical properties, electrical conductivity, and fluorescent effect of metallized wood were studied. The nano-indenter, square resistance tester, and fluorescence microscope were used to characterize the mechanical properties, electrical conductivity, and fluorescent effect of the “environmentally friendly” metallized wood surface. The results show that as the sputtering time increases, the load–displacement curve shifts gradually and the elastic modulus and hardness of the metallized wood veneers also gradually increase. The loading displacement of magnetron sputtered samples for 15 min (200 °C) is 269.9 nm. The loading displacement decreases by more than 60%, the average elastic modulus increases by 6.7 times, and the average hardness increases by 6.6 times. The transverse grain square resistance on the surface of metallized wood is about 2–3 times the parallel grain square resistance. As the sputtering time increases, the natural fluorescence intensity of the metallized wood surface gradually decreases and the wood surface is completely covered by the copper film.

As a new environmentally friendly liquid dielectric material, vegetable insulating oil has been widely used in oil-filled power equipment. In oil-filled power equipment, ageing, faults of overheating and discharge cause the decomposition of insulating oil and insulating paper, resulting in dissolved gases in oils. The diffusion behavior of dissolved gases in oils is helpful for evaluation of health state of oil-filled power equipment. In this study, the molecular dynamics simulation based on polymer consistent force field (PCFF) is adopted to analyze diffusion processes of dissolved gases in camellia insulating oils. The diffusion coefficients and free volume of dissolved gases including hydrocarbons, carbon oxides and hydrogen are calculated. The diffusion trajectory of dissolved gases in oils are also given. In addition, impacts of gas species and temperature on molecular diffusion coefficients of oils were also studied. Results quantitatively describe the diffusion behavior of gases with different molecular weight in the oils under various temperatures. The research provides theoretic support for further application of vegetable insulating oils in power equipment.As a new environmentally friendly liquid dielectric material, vegetable insulating oil has been widely used in oil-filled power equipment. In oil-filled power equipment, ageing, faults of overheating and discharge cause the decomposition of insulating oil and insulating paper, resulting in dissolved gases in oils. The diffusion behavior of dissolved gases in oils is helpful for evaluation of health state of oil-filled power equipment. In this study, the molecular dynamics simulation based on polymer consistent force field (PCFF) is adopted to analyze diffusion processes of dissolved gases in camellia insulating oils. The diffusion coefficients and free volume of dissolved gases including hydrocarbons, carbon oxides and hydrogen are calculated. The diffusion trajectory of dissolved gases in oils are also given. In addition, impacts of gas species and temperature on molecular diffusion coefficients of oils were also studied. Results quantitatively describe the diffusion behavior of gases with different mole...

Electrical breakdown behaviors of nanopaper prepared from nanofibrillated cellulose (NFC) were investigated. Compared to conventional insulating paper made from micro softwood fibers, nanopaper has a dramatically enhanced breakdown strength. Breakdown field of nanopaper is 67.7 kV/mm, whereas that of conventional paper is only 20 kV/mm. Air voids in the surface of conventional paper are observed by scanning electron microscope (SEM). Further analyses using mercury intrusion show that pore diameter of conventional paper is around 1.7 μm, while that of nanopaper is below 3 nm. Specific pore size of nanopaper is determined to be approximately 2.8 nm by the gas adsorption technique. In addition, theoretical breakdown strengths of nanopaper and conventional paper are also calculated to evaluate the effect of pore size. It turns out that theoretical values agree well with experimental data, indicating that the improved strength in nanopaper is mainly attributed to the decreased pore size. Due to its outstanding breakdown strength, this study indicates the suitability of nanopaper for electrical insulation in ultra-high voltage convert transformers and other electrical devices.

Aiming at the ultra high speed permanent magnet synchronous motor (PMSM) supported by gas foil bearings (GFBs), this paper calculates the transient line starting of the motor. Firstly, the start effect of the rotor composed of cylindrical PM and stainless steel sleeve is studied. Then, in order to enhance the start torque, copper ring, nickel ring and copper squirrel-cage are introduced in the rotor and their start effect are analysed, respectively. It can be found that the rotor including nickel ring can be accelerated to set speed, but all the other rotors are failed due to the higher PM and braking torques. It can be concluded that some material owning slight large relative permeability can be applied in the rotor to reduce the PM field and contribute to start by using the line-start method.

This paper proposes a novel permanent magnet (PM) motor for high torque performance, in which hybrid PM material and asymmetric rotor design are applied. The hybrid PM material is adopted to reduce the consumption of rare-earth PM because ferrite PM is assisted to enhance the torque production. Meanwhile, the rotor structure is designed to be asymmetric by shifting the surface-insert PM (SPM), which is used to improve the torque performance, including average torque and torque ripple. Moreover, the reasons for improvement of the torque performance are explained by evaluation and analysis of the performances of the proposed motor. Compared with SPM motor and V-type motor, the merit of high utilization ratio of rare-earth PM is also confirmed, showing that the proposed motor can offer higher torque density and lower torque ripple simultaneously with less consumption of rare-earth PM.

Magnetic nanostructures of different size, shape, and composition possess a great potential to improve current technologies like data storage and electromagnetic sensing. In thin ferromagnetic nanowires, their magnetization behavior is dominated by the competition between magnetocrystalline anisotropy (related to the crystalline structure) and shape anisotropy. In this way electron diffraction methods like precession electron diffraction (PED) can be used to link the magnetic behavior observed by Electron Holography (EH) with its crystallinity. Using off-axis electron holography under Lorentz conditions, we can experimentally determine the magnetization distribution over neighboring nanostructures and their diamagnetic matrix. In the case of a single row of nickel nanowires within the alumina template, the thin TEM samples showed a dominant antiferromagnetic arrangement demonstrating long-range magnetostatic interactions playing a major role.

In this research, reduced graphene oxide was incorporated into the ZnO seed layer to modulate the rod diameter of ZnO nanorods (NRs) during solgel/hydrothermal growth. To characterize the reduced graphene oxide incorporated ZnO NRs, multiple material analysis techniques including field-emission scanning electron microscopy, surface contact angle measurements, X-ray diffraction, and photoluminescence were used to explore distinct properties of these size modulatable NRs. Results indicate ZnO NRs with smaller diameters could be observed with more reduced graphene oxide added into the ZnO seed layer. Furthermore, better crystallinity, higher hydrophobicity and lower defect concentration could be obtained with more amount of reduced graphene oxide added into the ZnO seed layer. The modulatable reduced graphene oxide-incorporated ZnO NRs growth is promising for future ZnO NRs based nanodevice applications.

Deep vein thrombosis, the development of blood clots in the peripheral veins, is a very serious, life threatening condition that is prevalent in the elderly. To deliver proper treatment that enhances the survival rate, it is very important to detect thrombi early and at the point of care. We explored the ability of magnetic particle spectroscopy (MSB) to detect thrombus via specific binding of aptamer functionalized magnetic nanoparticles with the blood clot. MSB uses the harmonics produced by nanoparticles in an alternating magnetic field to measure the rotational freedom and, therefore, the bound state of the nanoparticles. The nanoparticles' relaxation time for Brownian rotation increases when bound [A.M. Rauwerdink and J. B. Weaver, Appl. Phys. Lett. 96, 1 (2010)]. The relaxation time can therefore be used to characterize the nanoparticle binding to thrombin in the blood clot. For longer relaxation times, the approach to saturation is more gradual reducing the higher harmonics and the harmonic ratio. The harmonic ratios of nanoparticles conjugated with anti-thrombin aptamers (ATP) decrease significantly over time with blood clot present in the sample medium, compared with nanoparticles without ATP. Moreover, the blood clot removed from the sample medium produced a significant MSB signal, indicating the nanoparticles are immobilized on the clot. Our results show that MSB could be a very useful non-invasive, quick tool to detect blood clots at the point of care so proper treatment can be used to reduce the risks inherent in deep vein thrombosis.

The design and validation of a magnetic particle spectrometer (MPS) system used to study the linear and nonlinear behavior of magnetic nanoparticle suspensions is presented. The MPS characterizes the suspension dynamic response, both due to relaxation and saturation effects, which depends on the magnetic particles and their environment. The system applies sinusoidal excitation magnetic fields varying in amplitude and frequency and can be configured for linear measurements (1 mT at up to 120 kHz) and nonlinear measurements (50 mT at up to 24 kHz). Time-resolved data acquisition at up to 4 MS/s combined with hardware and software-based signal processing allows for wide-band measurements up to 50 harmonics in nonlinear mode. By cross-calibrating the instrument with a known sample, the instantaneous sample magnetization can be quantitatively reconstructed. Validation of the two MPS modes are performed for iron oxide and cobalt ferrite suspensions, exhibiting Neel and Brownian relaxation, respectively.

Graphene has attracted much attention at various research fields due to its unique optical, electronic and mechanical properties. Up to now, graphene has not been widely used in optoelectronic fields due to the lack of large-area uniform doped graphene (n-doped and p-doped) with smooth surface. Therefore, it is rather desired to develop some effective doping methods to extend graphene to optoelectronics. Here we developed a novel doping method to prepare large-area (> centimeter scale) uniform doped graphene film with a nanoscale roughness(RMS roughness ∼1.4 nm), the method (nano-metal film doping method) is simple but effective. Using this method electron doping (electron-injection) may be easily realized by the simple thermal deposition of Ag nano-film on a transferred CVD graphene. The doping effectiveness has been proved by Raman spectroscopy and spectroscopic ellipsometry. Importantly, our method sheds light on some potential applications of graphene in optoelectronic devices such as photodetectors, LEDs, phototransistors, solar cells, lasers etc.

Despite the fact that there have been many studies of graphite exfoliation, none really addresses the issue of starting form of graphite. To address this issue various graphite forms (solid, powder and sooth) and graphite oxide (powder) are exfoliated in acetonitrile and studied via ultraviolet-visible (UV-Vis) spectroscopy. In different graphite forms two major absorbance peaks are observed at 223 nm and 273 nm corresponding to graphene oxide and graphene dispersions, respectively. The intensity change of the peaks refers to the layer number change. The intensity ratios of these peaks give information about the concentration of the exfoliation products. We observed that graphite oxide sample has the thinnest graphene dispersions among the compared samples, whereas graphite rod has the thickest. It appears that few layer graphene oxide dispersions exist more in graphite sooth and graphite oxide samples. Graphite oxide UV-Vis spectrum reveals two new absorbance peaks at 312 nm and 361 nm in addition to the graphene oxide and graphene dispersion peaks. To our knowledge these peaks were not observed before. We think that these new peaks are formed due to conjugated polyenes that affect π → π* plasmon peak.

Permalloy nanoparticles containing bacterial cellulose hydrogel obtained after reduction was compressed into a xerogel flexible sheet by hot pressing at 60 ° C at different pressures. The permalloy nanoparticles with an ordered structure have a bimodal size distribution centered around 25 nm and 190 nm. The smaller nanoparticles are superparamagnetic while the larger particles are ferromagnetic at room temperature. The sheets have a room temperature magnetisation of 20 emug-1 and a coercivity of 32 Oe. The electrical conductivity of the flexible sheets increases with hot pressing pressure from 7 Scm-1 to 40 Scm-1 at room temperature.

In this paper, the physical phenomena of gallium (Ga+) ion impacting monolayer graphene in the nanosculpting process are investigated experimentally, and the mechanisms are explained by using Monte Carlo (MC) and molecular dynamics (MD) simulations. Firstly, the MC method is employed to clarify the phenomena happened to the monolayer graphene target under Ga+ ion irradiation. It is found that substrate has strong influence on the damage mode of graphene. The mean sputtering yield of graphene under 30 keV Ga+ ion irradiation is 1.77 and the least ion dose to completely remove carbon atoms in graphene is 21.6 ion/nm2. Afterwards, the focused ion beam over 21.6 ion/nm2 is used for the irradiation on a monolayer graphene supported by SiO2 experimentally, resulting in the nanostructures, i.e., nanodot and nanowire array on the graphene. The performances of the nanostructures are characterized by atomic force microscopy and Raman spectrum. A plasma plume shielding model is put forward to explain the nanosculpting results of graphene under different irradiation parameters. In addition, two damage mechanisms are found existing in the fabrication process of the nanostructures by using empirical MD simulations. The results can help us open the possibilities for better control of nanocarbon devices.

The role of B on the microstructure and magnetism of Zr16Co82.5-xMo1.5Bx ribbons prepared by arc melting and melt spinning is investigated. Microstructure analysis show that the ribbons consist of a hard-magnetic rhombohedral Zr2Co11 phase and a minor amount of soft-magnetic Co. We show that the addition of B increases the amount of hard-magnetic phase, reduces the amount of soft-magnetic Co and coarsens the grain size from about 35 nm to 110 nm. There is a monotonic increase in the volume of the rhombohedral Zr2Co11 unit cell with increasing B concentration. This is consistent with a previous theoretical prediction that B may occupy a special type of large interstitial sites, called interruption sites. The optimum magnetic properties, obtained for x = 1, are a saturation magnetization of 7.8 kG, a coercivity of 5.4 kOe, and a maximum energy product of 4.1 MGOe.

Selective growth of either monolayer or bilayer graphene is of great importance. We developed a method to readily tune large area graphene growth from complete monolayer to complete bilayer. In an ambient pressure chemical vapor deposition process, we used the sample temperature at which to start the H2 flow as the control parameter and realized the change from monolayer to bilayer growth of graphene on Cu foil. When the H2 starting temperature was above 700°C, continuous monolayer graphene films were obtained. When the H2 starting temperature was below 350°C, continuous bilayer films were obtained. Detailed characterization of the samples treated under various conditions revealed that heating without the H2 flow caused Cu oxidation. The more the Cu substrate oxidized, the less graphene bilayer could form.

Integrating carbon nanotubes (CNTs) and graphene into hybrid structures provides a novel approach to three dimensional (3D) materials with advantageous properties. Here we present a water-processing method to create integrated CNT/graphene hybrids and test their field emission properties. With an optimized mass ratio of CNTs to graphene, the hybrid shows a significantly enhanced field emission performance, such as turn-on electric field of 0.79 V/μm, threshold electric field of 1.05 V/μm, maximum current density of 0.1 mA/cm2, and field enhancement factor of ∼1.3 × 104. The optimized mass ratio for field emission emphasizes the importance of both CNTs and graphene in the hybrid. We also hypothesize a possible mechanism for this enhanced field emission performance from the CNT/graphene hybrid. During the solution treatment, graphene oxide behaves as surfactant sheets for CNTs to form a well dispersed solution, which leads to a better organized 3D structure with more conducting channels for electron transport.

Here, we report the synthesis of high quality monolayer graphene on the pre-treated copper (Cu) foil by chemical vapor deposition method. The pre-treatment process, which consists of pre-annealing in a hydrogen ambient, followed by diluted nitric acid etching of Cu foil, helps in removing impurities. These impurities include native copper oxide and rolling lines that act as a nucleation center for multilayer graphene. Raman mapping of our graphene grown on pre-treated Cu foil primarily consisted of similar to 98% a monolayer graphene with as compared to 75 % for the graphene grown on untreated Cu foil. A high hydrogen flow rate during the pre-annealing process resulted in an increased I-2D/IG ratio of graphene up to 3.55. Uniform monolayer graphene was obtained with a I2D/IG ratio and sheet resistance varying from 1.84-3.39 and 1110-1290 Omega/square, respectively. (C) 2014 Author(s).

Growth of thin cobalt film with perpendicular magnetic anisotropy has been investigated on pristine graphene for spin logic and memory applications. By reduction of the kinetic energy of the sputtered atoms using indirect sputtered deposition, deposition induced defects in the graphene layer have been controlled. Cobalt film on graphene with perpendicular magnetic anisotropy has been developed. Raman spectroscopy of the graphene surface shows very little disorder induced in the graphene by the sputtering process. In addition, upon increasing the cobalt film thickness, the disorder density increases on the graphene and saturates for thicknesses of Co layers above 1 nm. The AFM image indicates a surface roughness of about 0.86 nm. In addition, the deposited film forms a granular structure with a grain size of about 40 nm.

In the present work, we demonstrated a new method of graphene films transferring applying a marker-frame instead of polymer-like films as a support. This method is an alternative that is much faster, cheaper and freely available to all. Our technique guarantees cleaner graphene surface and no polymer residues on it. Consequently, it significantly increases the applicability of graphene. For instance, one can think of using graphene as a component of nanocomposites or coupling it with other nanomaterials. As an example we showed graphene films suspended on GaN nanowires. The characterization of the properties of graphene transferred following the enhanced frame method was performed by Raman spectroscopy, as well as by carrying out SEM imaging and conducting TEM investigations.

Many oilfields report that the viscosity of polymers in high-salinity reservoirs will decrease significantly. In this paper, molecular dynamics simulations were conducted to investigate the molecular configuration and network of hydrolyzed polyacrylamide (HPAM) molecules in high-salinity formation-water and the viscosity changes from the microscopic dense to dilute phase. In addition, the viscosity of HPAM/formation-water solution was measured to verify and compare with simulation results. Simulation and experimental results show that the molecular network of the microscopic dense phase is essential for the apparent viscosity. The calculated apparent viscosity could decrease 37% as the net-shape molecular network of the microscopic dense phase is broken by calcium ions, which is similar to our experimental results. This paper improved our understanding of the mechanisms of polymer viscosity alteration in high-salinity formation-water and provided insights that can be used to improve the strategy of enhanced polymer flooding and the novel polymer gel formula.

In this paper, we take advantage of the high sensitivity of two-dimensional electron gas concentration in the heterojunction channel of a GaN high electron mobility transistor (HEMT) to device surface states and gate voltages. By integrating a HEMT with ferroelectric materials with photovoltaic effects, a photo-sensitive gate HEMT photodetector based on ferroelectric integration is obtained. By exploring the ferroelectric and composite film sputtering growth epitaxial atmosphere, a high-performance PZT/ZnO composite ferroelectric film grown in an oxygen-containing atmosphere is obtained. Comparing the PZT and LiNbO3 (LN) ferroelectric thin films prepared with or without the buffer layer, the following conclusions are obtained. The quantum efficiency of the PZT/ZnO film increases by 240% and 596% at the peak of 300–400 nm, reaching 14.55%; the residual polarization of the PZT film obtained in an oxygen-containing atmosphere reaches 52.31 μC/cm2; the PZT/ZnO composite film has better fatigue characteristics. The GaN HEMT detector prepared by using magnetron sputtered PZT/ZnO as the sensing gate under the oxygen atmosphere has a photocurrent increment of 11.51 mA under ultraviolet light and a responsivity of 111A/W at 365 nm. At the same time, the device has τr = 0.12 s and τf = 8.3 s transient response. The research in this paper shows that a new structure photodetector based on a GaN HEMT has excellent ultraviolet light response, which provides a new research direction for the light detection mechanism.

This paper presents a methodology to simulate the nonlinear free surface flow around an advancing ship. This methodology is based on the Moving Particle Semi-implicit (MPS) method, which is widely used to simulate the incompressible fluid flow. In this paper, the original MPS method is modified in order to analyze effectively the nonlinear free surface flow around an advancing ship. Several treatment techniques are newly proposed, and the original MPS method is modified by combining these techniques with other previous research studies. The proposed techniques include the Laplacian compensation model in the region near the body boundary, the collision model between fluid particles and wall particles, and some treatments for the opened boundary. The accuracy of the modified MPS method is verified through the numerical simulations on two benchmark problems for the performance evaluation of the particle methods and on the flows around both the wedged body and model ship. The numerical results demonstrate that the modified MPS method can be effectively applied to the simulation of nonlinear free surface flow around an advancing ship in marine engineering.

The present paper is concerned with the implementation of the optimal homotopy asymptotic method to find the approximate solutions of two-dimensional fractional order Volterra integro-differential equations. The technique’s applicability and validity are tested through some numerical examples. The fractional order derivatives are calculated using Caputo’s sense. Results obtained by the proposed technique are compared with the Legendre wavelet method. The proposed method provides us with efficient and more accurate solutions than the other existing methods in the literature. Error analysis and convergence of the proposed method are also provided in the paper.

To examine mechanisms of the high speed and efficiency of propulsion of aquatic animals and to apply the findings to the design of underwater vehicles, this study uses dolphins as an example. The motion of aquatic animals is divided into three stages for the convenience of analysis of bio-propulsion: the oscillation of one-third of the rear body, the oscillation of the caudal fin, and the deformation of the caudal fin. We call the case multi-stage propulsion when all the stages are contained in a bio-propulsion. We investigate the effects of the phase difference between oscillations of the first and second stages φ on hydrodynamic performance and the chordwise deformation factor δc0 on hydrodynamic performance. The results show that when the phase difference was 90°, the propulsion efficiency was the highest and an appropriate caudal chordwise deformation could increase the propulsion efficiency, which was consistent with the result of previous studies. The key part of this paper is the comparative study between different propulsion modes in terms of fluid mechanism from multiple perspectives, such as the force generated by the oscillating motion, the shedding frequency of the wake vortex, and the spacings of vortices induced by different propulsion modes. The aim of this paper is to understand the mechanism supporting a larger thrust and higher efficiency of multi-stage propulsion and provide reference for the improvement and optimization of bionic propulsion in the future.

Due to its rich variety of electromagnetic properties, such as a colossal magnetoresistance, charge and orbital ordering, and metal-insulator transition, the magnetic behavior in La0.5Ba0.5MnO3 double perovskite compounds has been investigated by several techniques, however more experimental data, especially from atomic resolution techniques, are still necessary to understand such complex behavior. In this paper, we have used a nuclear and short-range technique, the Perturbed Angular Correlation (PAC) spectroscopy, to investigate the magnetic hyperfine interaction at the 140Ce and 111Cd probe nuclei as impurities occupying La sites. This double perovskite samples were synthesized by Sol-Gel route. The crystal structure was determined by X-ray diffraction and the analyses showed that this method produced perovskite oxides with cubic structure in Pm-3m space group and the homogeneity was determined by Transmission Electron Microscopy (TEM). The local properties investigated by PAC spectroscopy revealed a ferromagnetic transition temperature above 300 K and a pure antiferromagnetic interaction below 100 K. Moreover, it also indicates an anomalous behavior of the temperature dependence of magnetic hyperfine field at La sites measured with 140Ce probe nuclei, which can be ascribed to the contribution of 4f band of Ce to Magnetic Hyperfine Field (Bhf) at low temperatures due to the increase in its localized character.Due to its rich variety of electromagnetic properties, such as a colossal magnetoresistance, charge and orbital ordering, and metal-insulator transition, the magnetic behavior in La0.5Ba0.5MnO3 double perovskite compounds has been investigated by several techniques, however more experimental data, especially from atomic resolution techniques, are still necessary to understand such complex behavior. In this paper, we have used a nuclear and short-range technique, the Perturbed Angular Correlation (PAC) spectroscopy, to investigate the magnetic hyperfine interaction at the 140Ce and 111Cd probe nuclei as impurities occupying La sites. This double perovskite samples were synthesized by Sol-Gel route. The crystal structure was determined by X-ray diffraction and the analyses showed that this method produced perovskite oxides with cubic structure in Pm-3m space group and the homogeneity was determined by Transmission Electron Microscopy (TEM). The local properties investigated by PAC spectroscopy revealed a fe...

Superhydrophobic coatings have been applied in various fields. The materials used in the preparation of superhydrophobic coatings have attracted the attention of scholars. Due to the harm of fluorine-containing substances with low surface energy to the environment, fluorine-free superhydrophobic coatings have become a hotspot in the research field. Herein, a fluorine-free superhydrophobic coating with oil/water separation was made by a solution immersion way. The fluorine-free copolymer and polydimethylsiloxane (PDMS)/SiO2 nanoparticles (NPs) were mixed to prepare a composite solution, and the superhydrophobic surface was obtained on the paper by a dipping method. The scanning electron microscope, x-ray photoelectron spectrometer, 1H nuclear magnetic resonance, and Fourier transform infrared were used to study the surface characteristics and structural composition of the superhydrophobic material. The research proved that the copolymer and PDMS/SiO2 NPs were successfully coated on the paper surface, and the rough structure of the superhydrophobic surface was also attributed to the introduction of the copolymer and PDMS/SiO2 NPs. The evaluation of the coating has proved its excellent hydrophobicity, oil/water separation performance, and self-cleaning performance. The coating is a sustainable and environmentally friendly superhydrophobic material that can be used in packaging, construction, petrochemical, and other industries.

This paper investigates the analytical solutions of the perturbed nonlinear Schrodinger equation through the modified Khater method. This method is considered one of the most recent accurate analytical schemes in nonlinear evolution equations where it obtained many distinct forms of solutions of the considered model. The investigated model in this paper is an icon in quantum fields where it describes the wave function or state function of a quantum-mechanical system. The physical characterization of some obtained solutions in our study is explained through sketching them in two- and three-dimensional contour plots. The novelty of our study is clear by showing the matching between our solutions and those that have been constructed in previously published papers.

In this paper, we study the optical filtering properties of plasma-dielectric photonic crystals based on Thue–Morse multilayers. The method of generating the Thue–Morse sequence used in the current paper is different from that used in the available literature. We fix the total multi-material system length and use two, three, and four alternative layers of materials with different refractive indices to study the optical transmission properties of a few proposed structures. We also use plasma layers to have more tunable bandgaps. We employ the transfer matrix method to do our numerical calculations. We change the geometrical parameters, the number of layers, the arrangement of the layers, material refractive indices, and plasma properties and extract their effects on the bandgap behavior. We determine the tunability of the proposed structures to facilitate the selection of the one with desired filtering properties. However, understanding the tunability of our systems can facilitate the devising of optical devices such as an optical filter.

There is no doubt that the accurate assessment of local magnetization in three-dimensional objects exhibiting hysteresis is crucial to accurate performance estimation of a variety of electromagnetic devices. Recently, it has been demonstrated that a Stoner-Wohlfarth-like elementary hysteresis operator may be constructed using two-node Hopfield neural network (HNN) having internal positive feedback. Based upon the previously mentioned approach, this paper presents a methodology using which local magnetization in 3D objects exhibiting hysteresis may be assessed. The approach utilizes a four-node tetrahedron-shaped HNN with activation functions constructed using a weighted superposition of a step and sigmoidal functions in accordance with the M − H curve of the material under consideration. In this approach, the internal feedback factors between the different nodes for any tetrahedron are dependent on its geometrical configuration. Hence, shape configuration effects on the magnetization patterns of any three-dimensional object approximated by an ensemble of tetrahedra are implicitly taken into consideration. To demonstrate the applicability of the proposed approach, computations were carried out for different three-dimensional magnetized bodies having different M − H curves. Theoretical and computational details of the approach are given in the paper.

This paper investigated the influence of gas humidity (1%, 3%, 8%, 10%, and 12%) on the characteristics of a microwave-induced atmospheric plasma jet. The plasma discharge was generated by a microwave solid-state source with a H2O–Ar mixture gas flow of 8.1 L/min. The variation in energy efficiency, O and OH concentrations, rotational temperature of heavy species, shapes of plasma plumes with different humidities, and microwave input powers were recorded and analyzed. The results showed that the concentrations of O and OH increase monotonously with gas humidity at higher input powers while they fluctuate with gas humidity at lower input powers. With an increase in the H2O/Ar ratio from 1% to 12%, the energy efficiency of the plasma generator decreases, and the plasma plumes become shorter and thinner. The rotational temperature of plasma at the nozzle also showed positive correlation with increasing humidity. Adding more input power would make all the values of these parameters increase. This paper is supposed to be helpful for the research of the interaction mechanism of mix gas plasma and microwave power and for improving the effect of plasma treating biomedical materials.

This paper identifies different methodologies used to design suitable magnetic field generators (MFG) with adjustable characteristics. Variations in parameters, such as pulse frequency and amplitude elicit distinct responses. Assessing the differences between design parameters and experimental observations of magnetic field generators is essential for various applications. The use of magnetic field generator-based techniques is first studied in applications related to optical transmission, transcranial magnetic stimulation devices and magnetic resonance. Decades of research and technological advancement are associated with these methods. The associated nomenclature for describing and characterizing these methods are introduced and discussed. Finally, the paper presents possible future framework and design considerations in functionality where new MFGs are expected to play a key role in the future.

High efficiency and short saturation time have great significance on the practical work of high power microwave devices. A dual-band Cerenkov microwave generator with high-efficiency based on electrical tuning is presented in this paper. Two-segment slow wave structures for the C-band and X-band separately are adopted, which are isolated by a drift cavity. The collimating hole is replaced by a resonant reflector, which can effectively shorten the saturation time. Moreover, in order to realize dual-band microwave output, the electrical tuning method is used in this paper. In particle-in-cell simulation, when the guiding magnetic field is 0.7 T, the output microwaves at the X-band can be obtained with an efficiency of 38% and saturation time for nearly 20 ns; when the guiding magnetic field is 1.5 T, the output microwaves at the C-band can be obtained with an efficiency of 32% and saturation time for nearly 20 ns. Thus, microwaves at the X-band and C-band can be generated separately by modulating the guiding magnetic field, which can be realized just by altering the current in the magnetic coil. It should be mentioned that such a modulating method is much more convenient than mechanical modulation.

Aiming at the position sensorless control system of permanent magnet synchronous motor (PMSM), an improved high-frequency square wave (HFSW) signal injection scheme considering nonlinear inductance variation in d-q axis is proposed and implemented in this paper. Compared with the existing model, the modified scheme can take the dynamic variation of d-q axis inductance under different operation conditions into consideration by offsetting the resulting high-frequency incremental (HFI) current harmonic components, thus effectively suppressing the estimation error of the rotor position. The experimental results verify that the improved scheme proposed in this paper can not only improve the estimation accuracy of rotor position impaired by the non-linear variations of d-q axis inductance but also maintain the good steady-state and dynamic performance of traditional schemes.

This paper proposes a possible theoretical model to analyze the impacts of light illumination on the post-illumination transient current of sputter-deposited non-doped ZnO films. Although the authors have already demonstrated experimentally the impact of wavelength on the resistance of such films (various light-emitting diodes were used), the influence of ambient gas on their resistance, and the influence of temperature on resistance in detail, no significant theoretical basis was provided. In this paper, the physical images of the phenomena are theoretically reconsidered and a theoretical model is developed based on the experimental results. The mathematical formulation provided involves the time-dependent diffusion current model, and the continuity equation is solved to achieve a plausible solution of the time constant of the transient process. The theoretical solution strongly suggests that oxygen vacancy levels and/or traps around the grain boundaries and inside the grains contribute to the post-illumination transient behavior of dc-biased current. The non-linear effect on the transient process is also discussed for directing future research.

The key to preparing nano-films by DC (Direct Current) sputtering is to prepare the film materials into targets. Organic small molecule fluorescent materials (such as 1, 4-Bis(2-cyanostyryl) benzene, to be noted as ER-I) are usually not conductive, and it is not possible to make the elements as targets. Therefore, there are some difficulties in preparing the organic materials into films by DC sputtering. In this paper, we fabricated ER-I nano-films by using the DC sputtering method, and their fluorescence properties are significantly different from those of powder materials. The fluorescence emission spectra of the films prepared by the DC sputtering method have an apparent bimodal morphology. Compared with the ER-I powder material, the fluorescence emission peak has a blue shift of 5 nm and 22 nm. To study the luminescence mechanism of the films, we further investigated the fluorescence properties of the films after thermal treatment and analyzed the structure and surface morphology of the films by XRD and SEM. This paper provides a new idea and method for the preparation of organic nano-films and has a potential application value in the preparation of organic light-emitting films and soft optics devices.

In a previous paper, a calculation system for a high-accuracy, high-speed calculation of a one-dimensional (1D) Poisson equation based on the interpolation finite difference method was shown. Spatial high-order finite difference (FD) schemes, including a usual second-order accurate centered space FD scheme, are instantaneously derived on the equally spaced/unequally spaced grid points based on the definition of the Lagrange polynomial function. The upper limit of the higher order FD scheme is not theoretically limited but is studied up to the tenth order, following the previous paper. In the numerical analyses of the 1D Poisson equation published in the previous paper, the FD scheme setting method, SAPI (m), m = 2, 4, …, 10, was defined. Due to specifying the value of m, the setting of FD schemes is uniquely defined. This concept is extended to the numerical analysis of two-dimensional Poisson equations. In this paper, we focus on Poiseuille flows passing through arbitrary cross sections as numerical calculation examples. Over regular and irregular domains, three types of FD methods—(i) forward time explicit method, (ii) time marching successive displacement method, and (iii) alternative direction implicit method—are formulated, and their characteristics of convergence and numerical calculation errors are investigated. The numerical calculation system of the 2D Poisson equation formulated in this paper enables high-accuracy and high-speed calculation by the high-order difference in an arbitrary domain. Especially in the alternative direction implicit method using the band diagonal matrix algorithm, convergence is remarkably accelerated, and high-speed calculation becomes possible.

In this paper, the vorticity-stream function method is proposed to study the incompressible oscillating flow in the channel of Stirling regenerators. The vorticity field and velocity field in the channels of the parallel-plate regenerator are investigated. The plate spacing and oscillating frequency and kinematic viscosity of the working medium are unified as a dimensionless number e. The results showed that when e is ∼7, the “velocity overshoot” phenomenon occurs in the flow field, and this phenomenon becomes more evident with the increase of e and it gradually approaches the wall of the channel. The phase relationship between the pressure drop and the flow rate was obtained; the results showed that the phase of the flow rate lags behind the pressure drop, and the phase difference is influenced by spacing, frequency, and kinematic viscosity, with the maximal phase difference being 90°. The viscous dissipation loss in the channel was obtained based on the characteristic relationship between the cumulative flow and the pressure drop, and the wasted power of helium crossing a single channel was calculated to be less than 50 W when the frequency is no more than 100 Hz and the plate spacing is greater than 0.5 mm (given a swept volume of 500 ml). The results obtained in this paper verified the application of the vorticity-stream function method in oscillating flows, and the advantage of low resistance of helium over nitrogen was theoretically demonstrated in the relatively high frequency range.

Generation of spontaneous magnetic fields (SMFs) is one of the most interesting phenomena accompanying an intense laser–matter interaction. One method of credible SMFs measurements is based on the magneto-optical Faraday effect, which requires simultaneous measurements of an angle of polarization plane rotation of a probe wave and plasma electron density. In classical polaro-interferometry, these values are provided independently by polarimetric and interferometric images. Complex interferometry is an innovative approach in SMF measurement, obtaining information on SMF directly from a phase–amplitude analysis of an image called a complex interferogram. Although the theoretical basis of complex interferometry has been well known for many years, this approach has not been effectively employed in laser plasma research until recently; this approach has been successfully implemented in SMF measurement at the Prague Asterix Laser System (PALS). In this paper, proprietary construction solutions of polaro-interferometers are presented; they allow us to register high-quality complex interferograms in practical experiments, which undergo quantitative analysis (with an original software) to obtain information on the electron density and SMFs distributions in an examined plasma. The theoretical foundations of polaro-interferometric measurement, in particular, complex-interferometry, are presented. The main part of the paper details the methodology of the amplitude–phase analysis of complex interferograms. This includes software testing and examples of the electron density and SMF distribution of a laser ablative plasma generated by irradiating Cu thick planar targets with an iodine PALS laser at an intensity above about 1016 W/cm2.

The self-excitation of asymmetric modes is one of the main factors limiting the long-pulse operation of the relativistic triaxial klystron amplifier (TKA). Research studies have revealed that the asymmetric TM modes with negative beam loading conductance (Ge/G0) in the bunching cavities are the main culprits of self-excitation. The existing studies focus on passively destroying the growth of asymmetric TM modes, but we attempt to actively suppress their self-excitation in this paper. Investigation results demonstrate that the employment of single-gap bunching cavities can significantly reduce the risk of self-excitation of asymmetric TM modes, as the Ge/G0 of asymmetric TMn11 modes in single period structures are positive. The current modulation capacity of a single-gap bunching cavity, however, is not sufficient, so a cascade structure consisting of two groups of bunching cavities is employed to compensate for this deficiency. Based on the above conclusions, an X-band TKA device with four single-gap beam–wave interaction cavities is proposed and investigated in this paper. The three-dimensional particle-in-cell simulation results demonstrate that there is no self-excitation of asymmetric modes in the proposed X-band TKA device.

This paper studies the sparsity prior to compressed video reconstruction algorithms. An effective non-convex 3DTPV regularization (0 < p < 1) is proposed for sparsity promotion. Based on the augmented Lagrangian reconstruction algorithm, this paper analyzes and compares three non-convex proximity operators for the lp-norm function, and numerous simulation results confirmed that the 3DTPV regularization can gain higher video reconstruction quality than the existing convex regularization and is more competitive than the existing video reconstruction algorithms.