3,475 results
Search Results
2. Molecular simulation of different types of polysilsesquioxane doped cellulose insulating paper: A guide for special cellulose insulating paper.
- Author
-
Zeng, Zhenglin, Tan, Weimin, Deng, Yanhe, Cheng, Quan, Fu, Liuyue, and Tang, Chao
- Subjects
- *
CELLULOSE fibers , *CELLULOSE , *GLASS transition temperature , *MODULUS of rigidity , *BULK modulus , *ELASTIC modulus , *DIELECTRIC properties - Abstract
To develop special insulating paper is of great significance to promote the service life of transformers. Using molecular simulation to guide the development of special insulating paper can greatly reduce the trial-and-error rate and waste of resources in traditional experiments. The effect of different types of polysilsesquioxane (POSS) on cellulose insulating paper was investigated by using molecular simulation. This paper investigated the thermal stability and mechanical properties and electrical characteristics of caged POSS, semi-caged POSS, and ladder-like POSS doped cellulose insulating paper. The results show that POSS with all types can enhance the performance of cellulose insulating paper, and ladder-like POSS possess the best modification effect. The glass transition temperature was increased by 58 K, and the bulk modulus, shear modulus, and elastic modulus of cellulose insulating paper doped with ladder-like POSS can improve up to 27.07%, 45.67%, and 41.28%, respectively. Meanwhile, the dielectric properties of ladder-like POSS modified insulating paper are also significantly improved. The findings of this paper propose a method for the preparation of ladder-like POSS modified insulating paper, which provides theoretical guidance for the experimental preparation of special insulating paper. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
3. Fabrication of negative magnetostrictive Japanese traditional paper (washi) with cobalt ferrite particles.
- Author
-
Kurita, Hiroki, Rova, Lovisa, Keino, Takumi, and Narita, Fumio
- Subjects
- *
MAGNETOSTRICTION , *FERRITES , *COBALT , *JAPANESE language , *WOOD-pulp , *CELLULOSE fibers , *MAGNETIC particles - Abstract
The cellulose fibers that form washi are longer than those of regular paper made from wood pulp. Hence, the mechanical properties of washi can be higher than those of conventional paper. This study evaluated the magnetic, magnetostrictive, and tensile properties of negative magnetostrictive cobalt ferrite (CoFe2O4) particle dispersed handmade washi (washi−CoFe2O4). The CoFe2O4 additives magnetized the washi, which displayed negative magnetostriction with the fiber direction perpendicular to the magnetic field and in the parallel fiber direction. Concerning the mechanical properties, the washi−CoFe2O4 displayed an elongation of up to 77% after yielding. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
4. Mechanism study of the conductivity characteristics of cellulose electrical insulation influenced by moisture.
- Author
-
Zhao, Haoxiang, Mu, Haibao, Zhang, Daning, Baumeier, Björn, Yao, Huanmin, Guo, Guangzhi, and Zhang, Guanjun
- Subjects
ELECTRIC insulators & insulation ,FRONTIER orbitals ,MOLECULAR dynamics ,CELLULOSE ,ELECTRIC distortion ,MOISTURE ,CELLULOSE synthase ,SILICONE rubber - Abstract
Cellulose insulating paper is widely used in the power industry for its good electrical insulating properties. Moisture sharply increases its conductivity, which directly leads to the weakening of insulation performance and greatly increases the risk of subsequent electric field distortion and insulation breakdown. This paper focuses on the microscopic mechanism of moisture changing the characteristics of charge transport in cellulose insulation and attempts to reveal the related conductivity mechanism. To achieve this purpose, microscopic and macroscopic perspectives are integrated and several simulation and experimental methods are utilized comprehensively. The molecular dynamics simulation results showed that most water molecules in damped cellulose were individually and uniformly adsorbed on the hydroxyl groups by hydrogen bond, and the quantum chemistry computation results showed that the lowest unoccupied molecular orbital more appeared on the water molecule and the corresponding density of state increased. Then, experimentally, it was confirmed that the trap energy level decreased by the thermally stimulated current method. On this basis, the promotion effect of moisture on charge transport is predicted and verified by polarization and depolarization current methods. As the moisture content increased, more charge carriers escaped from the trap by hopping and participated in long-range continuous charge motion. Therefore, after dampness, the current of cellulose insulating paper increased exponentially with the increase in electric field strength, which was consistent with the hopping conductivity mechanism. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
5. Development of a differential photoacoustic system for the determination of the effective water diffusion and water vapor permeability coefficients in thin films.
- Author
-
Martinez-Munoz, P. E., Martinez-Hernandez, H. D., Rojas-Beltran, C. F., Perez-Ospina, J. L., and Rodriguez-Garcia, M. E.
- Subjects
THIN films ,PERMEABILITY ,WATER vapor ,HUMIDITY ,ELECTRONIC noise ,DIFFUSION coefficients ,RESERVOIRS - Abstract
This paper focused on developing a methodology and metrology using a differential photoacoustic (PA) system to determine the effective water vapor diffusion coefficient (D e f f ) and the effective permeability coefficient (Π) in thin films as a piece of paper and standard polystyrene for a controlled relative humidity. The methodology proposes a new differential photoacoustic system, including the water reservoir, relative humidity, and temperature detectors. Two cells, reference/sample, were used to obtain the instrumental function to reduce the electronic and environmental noises. A method based on the study of ln [ 1 − (S − S 0) / Δ S ] = t / τ D and the behaviors of R
2 as a function of the number of data was proposed to assess the region in which the photoacoustic signal should be processed to determine each effective coefficient. S is the amplitude of the PA signal, S 0 is the initial amplitude value, Δ S is the change, t (time), and τ D is the water vapor diffusion time. The effective water diffusion coefficient (D e f f ) for water and polystyrene was 1.90 × 10−11 m2 /s and 3.09 × 10−11 m2 /s, respectively. The permeability coefficient value for the piece of paper was 4.18 × 10−9 mol kg−1 cm−2 s−1 Pa−1 , while for polystyrene, it was 6.80 × 10−9 mol kg−1 cm−2 s−1 Pa−1 for 70% of relative humidity. This methodology can be extended by changing the moisture content on the chamber to obtain the dependence of D e f f as a function of relative humidity. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
6. Microwave driven atmospheric water harvesting with common sorbents.
- Author
-
Nepal, Suman, Shahrokhian, Aida, and King, Hunter
- Subjects
WATER harvesting ,SORBENTS ,MASS transfer ,MICROWAVES ,HUMIDITY ,MICROWAVE heating ,SORPTION - Abstract
Using sorbent materials to separate and concentrate ambient humidity is a promising option for atmospheric water harvesting in the face of impending worldwide freshwater scarcity. The method of cycled sorption and forced release can facilitate efficient condensation, but performance strongly depends on device-scale issues of heat and mass transfer. We examine the potential of using microwave radiation to liberate sorbed vapor, in proof-of-concept experiments with hygroscopic salt-infused paper towel as simple sorbents. We quantify performance as a function of tunable system parameters and ambient humidity. Our results demonstrate promising aspects: both rapid desorption and regeneration, owing to water-tuned dielectric heating and directing flow through fibrous sorbent, respectively; substantial efficiency of moisture separation toward very low (∼ 25 %) relative humidity; and robust repeatability over many cycles, due to the targeted energy input and retention of hygroscopic salt within the paper scaffold. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
7. Understanding ac losses in CORC cables of YBCO superconducting tapes by numerical simulations.
- Author
-
Nguyen, Linh N., Shields, Nathaniel, Ashworth, Stephen, and Nguyen, Doan N.
- Subjects
SUPERCONDUCTING coils ,SUPERCONDUCTING cables ,HIGH temperature superconductors ,CABLES ,FINITE element method ,COMPUTER simulation ,ADHESIVE tape ,CURRENT distribution - Abstract
Alternating current (ac) losses in conductor-on-rounded-core (CORC) cables of YBCO high-temperature superconducting (HTS) tapes are a significant challenge in HTS power applications. This study employs two finite element analysis (FEA) models to investigate the contributions from different ac loss components and provide approaches for reducing ac losses in cables. An FEA model based on the T-A formulation treats the cross section of thin superconducting layers as 1D lines and, therefore, only can predict the ac loss generated by the perpendicular magnetic field. In contrast, the model based on H-formulation can be performed on the actual 2D rectangular cross section HTS tapes to provide the total ac losses generated by magnetic fluxes penetrating from both the edges and surfaces of HTS tapes, although this model requires more computing time and memory. The 1D and 2D simulation models were validated by cross comparing the results from both models and by comparing sub-section and full cross section models. Subsequently, two models relate cable design and operational parameters to the surface and edge losses of a two-layer CORC cable by considering the (1) relative contributions of edge and surface losses to the overall ac losses; (2) effect of the current distribution between inner and outer HTS layers on ac losses; (3) impact of the tape alignment on ac losses in each HTS layer; (4) influence of the thickness of HTS layers on ac losses; (5) effect of size and number of inter-tape gaps on ac losses; and (6) contribution frequency on the ac losses. The research results given in this paper are therefore not only valuable to suggest strategies for reducing ac loss in multi-layer cables but also for developing more accurate and effective methods to calculate ac loss in CORC HTS cables. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
8. Multi-scale modeling of shock initiation of a pressed energetic material III: Effect of Arrhenius chemical kinetic rates on macro-scale shock sensitivity.
- Author
-
Parepalli, P., Nguyen, Yen T., Sen, O., Hardin, D. B., Molek, C. D., Welle, E. J., and Udaykumar, H. S.
- Subjects
MULTISCALE modeling ,CHEMICAL kinetics ,CHEMICAL models ,PREDICTION models - Abstract
Multi-scale predictive models for the shock sensitivity of energetic materials connect energy localization ("hotspots") in the microstructure to macro-scale detonation phenomena. Calculations of hotspot ignition and growth rely on models for chemical reaction rates expressed in Arrhenius forms; these chemical kinetic models, therefore, are foundational to the construction of physics-based, simulation-derived meso-informed closure (reactive burn) models. However, even for commonly used energetic materials (e.g., HMX in this paper) there are a wide variety of reaction rate models available. These available reaction rate models produce reaction time scales that vary by several orders of magnitude. From a multi-scale modeling standpoint, it is important to determine which model best represents the reactive response of the material. In this paper, we examine three global Arrhenius-form rate models that span the range of reaction time scales, namely, the Tarver 3-equation, the Henson 1-equation, and the Menikoff 1-equation models. They are employed in a meso-informed ignition and growth model which allows for connecting meso-scale hotspot dynamics to macro-scale shock-to-detonation transition. The ability of the three reaction models to reproduce experimentally observed sensitivity is assessed by comparing the predicted criticality envelope (Walker–Wasley curve) with experimental data for pressed HMX Class V microstructures. The results provide a guideline for model developers on the plausible range of time-to-ignition that are produced by physically correct Arrhenius rate models for HMX. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
9. A compensation method of carrier magnetic interference under pathological conditions for geomagnetic navigation.
- Author
-
Ji, Caijuan, Song, Chengying, Li, Sheng, Gao, Yang, and Chen, Qingwei
- Subjects
LEAST squares ,MEASUREMENT errors ,GEOMAGNETISM ,ELECTRONIC equipment ,MAGNETOMETERS ,NAVIGATION - Abstract
Geomagnetic navigation has become a hot spot in current research because of its characteristics of passiveness and good concealment. However, the magnetic interference from various ferromagnetic substances, electronic equipment, etc., of the carrier will be superimposed on the geomagnetic field, causing magnetometer measurement errors, thus affecting navigation accuracy. In practice, due to the limited maneuverability of the carrier, sufficient geomagnetic observation data cannot be obtained, resulting in the observation equation used for carrier magnetic interference compensation to be seriously pathological. To achieve the compensation of carrier magnetic interference, this paper proposes the total least squares method based on the ridge regression using the L curve to solve ridge parameters. This method can effectively suppress the measurement noise that exists on both sides of the observation equation, and is suitable for alleviating the pathological effects of carrier magnetic interference compensation. Experimental results show that the compensated magnetometer measurement error is reduced to 3% of the carrier magnetic interference by using the method proposed in this paper, which obtains more stable and accurate parameter estimates. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
10. Piezoelectric energy harvester with outstanding output performance at low frequency vibration based on concentrating force on the piezoelectric element by parallel springs.
- Author
-
Hao, Yifan, Luo, Hongzhi, Lu, Xinyue, Huang, Jiawei, Chen, Hang, and Yang, Tongqing
- Subjects
FREQUENCIES of oscillating systems ,PIEZOELECTRIC ceramics ,STAINLESS steel ,LEAD titanate ,LEAD zirconate titanate - Abstract
This paper proposes a piezoelectric energy harvester that concentrates force on the piezoelectric element by parallel springs. When vibrating, the force exerted by the mass is released at three equal points on the surface of the brass substrate through three parallel springs. This concentrated release of energy through the spring amplification effect facilitates large deformation of the piezoelectric ceramic sheet, resulting in a higher charge output. The results show that under the combined action of a 14 g annular hollow mass and a 0.3 mm wire diameter stainless steel spring, the energy harvester based on the lead zirconate titanate ceramic exhibited an outstanding output power of 1.0–32.1 mW at a low resonance frequency with acceleration amplitudes of 0.5–3 g (1 g = 9.8 m/s
2 ). More importantly, to match the vibration frequency of the actual environment, this paper optimized the structure of the harvester and proposed that the harvester can be designed by selecting the weight of the mass block, the parameters and number of springs, and the shape of the brass substrate. The energy harvester designed in this study is expected to capture energy from low-frequency natural environments and exhibit outstanding output performance, which can provide guidelines for future efforts in this direction. [ABSTRACT FROM AUTHOR]- Published
- 2024
- Full Text
- View/download PDF
11. High-volume biological sample processing using microwaves.
- Author
-
Wilson-Garner, S., Alzeer, S., Baillie, L., and Porch, A.
- Subjects
SAMPLING (Process) ,BACTERIAL DNA ,MICROWAVES ,DNA probes ,CAVITY resonators - Abstract
This paper describes the design and optimization of a 10 ml cartridge for patient sample processing using a 3.5 GHz (empty resonant frequency) TM
010 cylindrical microwave cavity. The cartridge has been designed to augment a novel approach for the rapid diagnosis of M. tuberculosis (the causative agent of Ttuberculosis), which uses the direct application of microwaves to a bacteria-containing sample to release pathogen-specific DNA. The target bacterial DNA is then captured and recovered using magnetic nanoparticles coated with pathogen-specific DNA probes. Excitation parameters were optimized using three surrogates for M. tuberculosis, namely, M. smegmatis, M. abscessus, and M. bovis suspended in water and simulated sputum. The paper also explores the mechanism of microwave-mediated DNA release from bacteria using scanning electron microscopy. Examination of bacteria exposed to microwaves at power levels known to mediate the release of DNA reveals no obvious signs of permanent cell disruption, suggesting that a more subtle interaction is taking place. Finally, the presence of microwave-liberated M. bovis DNA was able to be detected at a level of sensitivity comparable to that achieved using microscopy. [ABSTRACT FROM AUTHOR]- Published
- 2024
- Full Text
- View/download PDF
12. Study of electric-field induced ionic migration on all-inorganic perovskite CsPbBr3 single crystal nuclear radiation detector.
- Author
-
Zhang, Mingzhi, Xia, Guotu, Huang, Chentao, Liu, Juan, Deng, Wenjuan, Tian, Fang, Zou, Jijun, and Tang, Bin
- Subjects
NUCLEAR counters ,SINGLE crystals ,PEROVSKITE ,HYSTERESIS ,ACTIVATION energy ,ELECTRIC fields ,PHOTOELECTRICITY - Abstract
As one of the promising room temperature nuclear radiation detection materials, the all-inorganic perovskite CsPbBr
3 single crystal has been receiving much attention in recent years. Even though the performance of the CsPbBr3 detector is improving continuously, the disadvantages of detection instability have not been solved fundamentally, and this instability is mainly caused by ionic migration in the CsPbBr3 single crystal itself. In this paper, a reasonable ionic migration model is proposed based on an in-depth study of the current hysteresis phenomenon and ionic migration mechanism in the Ti/CsPbBr3 /Ti detector. The model shows that the ions migrate to the anode or cathode under an external electric field, and the accumulated ions subsequently form an inverted internal electric field inside the crystal and carrier transport barriers at the metal–semiconductor interface simultaneously. The photoelectric characteristic and ionic migration activation energy (E a i o n) fitting results also prove the rationality of the ionic migration model. Furthermore, the ionic migration model can also be used to explain the left-shift of the energy response peak and the decrease in the normalized charge collection efficiency in the Ti/CsPbBr3 /Ti detector. This paper systematically investigates the intrinsic origin of migrated ions and the influence of ionic migration on detection stability, which will provide a potential solution to improve detection stability by suppressing ionic migration in the near future. [ABSTRACT FROM AUTHOR]- Published
- 2024
- Full Text
- View/download PDF
13. 2D Quantum materials: Magnetism and superconductivity.
- Author
-
Milošević, M. V. and Mandrus, D.
- Subjects
MAGNETISM ,SUPERCONDUCTIVITY ,INELASTIC neutron scattering ,MAGNETIC impurities ,MAGNETIC materials ,MAGNETIC traps ,CUPRATES - Abstract
Although the study of quasi-2D magnetism is well-established in bulk materials, the study of literal 2D magnets - consisting of a single layer of magnetic ions - is quite limited. Four of the contributed papers report experimental work on nanostructures: three of these involve superconductivity and one is on magnetism. Proximity effects in superconductors have been known for nearly 90 years,[13] but until recently proximity effects in magnets have been harder to study due to the much smaller range of the proximity effect in magnets compared to superconductors. One of the most exciting recent developments in quantum materials is the discovery and characterization of magnetism and superconductivity in exfoliated single-layer materials. [Extracted from the article]
- Published
- 2021
- Full Text
- View/download PDF
14. Research on the encounter motion of super-cavitating vehicles.
- Author
-
Zhou, Feng, Fan, Chunyong, Tian, Ying, Wang, Min, and Luan, Hengxuan
- Subjects
CAVITATION ,MOTION - Abstract
In this paper, the super-cavitating phenomenon under the effect of two vehicles' encounter motion processes is numerically studied. Particular attention is given to the influence of the vertical gaps between the vehicle, the cavitation number, and the slenderness ratio on the cavity profile and radial force of the object. Several numerical models are built to study the cavity evolution process and the force acting on the vehicle to explore the influence mechanism of two vehicles' encounter motion on supercavitating flow. The study shows that the cavity around the vehicle is primarily affected by the vertical gaps and cavitation number, but is relatively weakly affected by the slenderness ratio. Several impact laws are acquired in the paper. The relationship between cavity fracture time and vertical gaps is approximately a power function and obeys the law of t = 5.433h
0.3688 . The concept of the time of the maximum radial force occurrence and the cavitation number follows the formula of t = 4.86e0.3688σ . The relationship between the maximum radial force occurrence position and the cavitation number is a function of Ln and consistent with the law n = −0.799ln(σ) + 8.427. [ABSTRACT FROM AUTHOR]- Published
- 2023
- Full Text
- View/download PDF
15. Quantifying uncertainty in analysis of shockless dynamic compression experiments on platinum. II. Bayesian model calibration.
- Author
-
Brown, Justin L., Davis, Jean-Paul, Tucker, J. Derek, Huerta, Gabriel, and Shuler, Kurtis W.
- Subjects
PLATINUM ,CALIBRATION ,LOW temperatures - Abstract
Dynamic shockless compression experiments provide the ability to explore material behavior at extreme pressures but relatively low temperatures. Typically, the data from these types of experiments are interpreted through an analytic method called Lagrangian analysis. In this work, alternative analysis methods are explored using modern statistical methods. Specifically, Bayesian model calibration is applied to a new set of platinum data shocklessly compressed to 570 GPa. Several platinum equation-of-state models are evaluated, including traditional parametric forms as well as a novel non-parametric model concept. The results are compared to those in Paper I obtained by inverse Lagrangian analysis. The comparisons suggest that Bayesian calibration is not only a viable framework for precise quantification of the compression path, but also reveals insights pertaining to trade-offs surrounding model form selection, sensitivities of the relevant experimental uncertainties, and assumptions and limitations within Lagrangian analysis. The non-parametric model method, in particular, is found to give precise unbiased results and is expected to be useful over a wide range of applications. The calibration results in estimates of the platinum principal isentrope over the full range of experimental pressures to a standard error of 1.6%, which extends the results from Paper I while maintaining the high precision required for the platinum pressure standard. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
16. Realization of an ultra-thin absorber with fragmented magnetic structure at L-, S-, and partial C-bands.
- Author
-
E, Liujia, Liu, Zhongqing, Zhang, Jingwei, Xu, Zhaoxuan, Yuan, Zhenliang, Mei, Zhonglei, and Niu, Tiaoming
- Subjects
MAGNETIC structure ,RADAR cross sections ,METAMATERIALS ,EVOLUTIONARY algorithms ,COPPER plating ,MAGNETIC materials ,POLARIZATION (Nuclear physics) - Abstract
In this paper, an ultra-thin absorber with a total thickness of 9.2 mm is designed and verified at the frequency band of 1–5.34 GHz. The absorber is composed of a layer of metasurface, multi-layered magnetic substrate, a layer of fragmented magnetic structure obtained by improved MOEA/D-GO (Multi-Objective Evolutionary Algorithm based on Decomposition combined with Enhanced Genetic Operators), and a copper back plate. The absorber is achieved by two steps. First, we designed and measured an ultra-thin absorber at 0.78–2.04 GHz by adding a layer metasurface onto the top of a basic multi-layer absorber composed of magnetic materials. The fractional bandwidth (FBW) of the absorber is 89.4%, and the electrical thickness is only 0.024 λ 0 at the lowest operating frequency. Second, to broaden the bandwidth, we use an improved MOEA/D-GO to optimize one magnetic layer of the absorber. The working frequency band of the optimized absorber is 1–5.34 GHz, covering L- (1–2 GHz), S- (2–4 GHz), and partial C-bands (4–8 GHz). Furthermore, we modified the structure of the metasurface to make the absorber polarization-independent. The FBW of the final absorber is 136.4%, and the electrical thickness is 0.031 λ 0 at the lowest operating frequency. The prototype of the absorber is measured, and the experimental results agree well with the simulated performance. The results show that the improved MOEA/D-GO can be used to design and optimize sophisticated electromagnetic (EM) structures with the predesigned properties, and the absorber with ultrathin thickness and light weight verified in this paper have great application potentials in EM compatibility, EM shielding, and radar cross section reduction at the low bands of the microwave spectrum. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
17. Self-consistent model and numerical approach for laser-induced non-equilibrium plasma.
- Author
-
Pokharel, S. and Tropina, A. A.
- Subjects
NONEQUILIBRIUM plasmas ,LASER plasmas ,LASER-induced breakdown spectroscopy ,PLASMA production ,ATMOSPHERIC nitrogen ,FEMTOSECOND pulses - Abstract
This paper presents a self-consistent multi-dimensional mathematical model and a numerical approach for simulating the low-temperature plasma induced by the femtosecond laser filament. Addressing limitations in current models, we analyze key aspects of the laser plasma behavior, including plasma generation, detailed chemical kinetics, energy exchange channels, total energy balance, and hydrodynamics. The developed model and LOTASFOAM code are applied to study the temporal and spatial decay of the plasma produced by a femtosecond laser pulse in pure nitrogen at atmospheric pressure. The paper also includes a discussion on the spatial and temporal dynamics of electronically excited states of nitrogen in the decaying laser plasma. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
18. Dynamic deformation behavior and constitutive model of a Zr–W alloy.
- Author
-
Ma, Yue, Wang, Chuanting, Guo, Zhiping, Chen, Ying, Gao, Hongyin, Meng, Yuanpei, Yang, Yansong, He, Yuan, Guo, Lei, and He, Yong
- Subjects
MECHANICAL behavior of materials ,HOPKINSON bars (Testing) ,MATERIAL plasticity ,DEFORMATIONS (Mechanics) ,ALLOYS - Abstract
In this paper, a Zr–5W alloy was fabricated via casting. In order to obtain the mechanical properties of the material, quasi-static compression tests at room temperature and split Hopkinson pressure bar tests at various temperatures were carried out. The x-ray diffraction result showed that the main components of the alloy were αZr and W
2 Zr, where αZr is the matrix and W2 Zr is the reinforcement. The metallographic characterization results showed that there were two main forms of W2 Zr in the material, namely, large particle boundary and small diffuse submicrometer precipitates. The reinforcements of both distributions have the effect of increasing the strength of the material, but the small submicrometer W2 Zr precipitates would cause microcrack nucleation during the late plastic deformation stage, resulting in damage softening. In order to make theoretical calculations of the mechanical properties of materials, the Johnson–Cook (JC) constitutive model and Zerilli–Armstrong (ZAM) constitutive model of the material were obtained. It was found that the JC constitutive model had poor consistency in describing material properties. Although the consistency of the ZAM constitutive model was higher than that of the JC constitutive model, it still had obvious shortcomings. Combined with the deformation mechanism of the alloy, a modified constitutive relation was established by adding damage softening terms based on the hexagonal close-packed metal constitutive model inferred by the kinetics of heat-activated dislocations. The relative error results of all working conditions show that the correlation consistency of the improved constitutive model in this paper is significantly better than that of JC constitutive and ZAM constitutive. [ABSTRACT FROM AUTHOR]- Published
- 2023
- Full Text
- View/download PDF
19. Phase field study on electrical treeing under combined AC/DC voltage based on bipolar barrier transfer model.
- Author
-
Shang, Gaoyi, Sun, Yingman, Chen, Ming, Shao, Yuhang, Li, Minjie, Tang, Hao, Li, Xining, and Liu, Xuandong
- Subjects
TREES (Electricity) ,SPACE charge ,VOLTAGE ,INSULATING materials ,ELECTRONIC equipment ,DIELECTRIC breakdown ,PARTIAL discharges - Abstract
The study of insulation degradation processes is crucial for the reliable operation of power equipment and electronic devices. The phase field method has been widely used in recent years to simulate the degradation process of insulation materials. However, the effect of space charge was ignored. In this paper, a novel phase field method based on the bipolar carrier transfer model is suggested. This model can simulate degradation under different temperatures and DC or combined AC/DC voltage. The cases under AC and combined AC/DC voltage at different temperatures are simulated by COMSOL. Methods to ensure model convergence are proposed. The results show that the field strength distribution under a combined AC/DC field is more uniform, especially for negative polarity. For the same voltage form, temperature and breakdown time show an exponential relationship. The results are consistent with those of previous experimental studies, proving the usability of the model. In addition, the processes of initiation, growth, and breakdown stage of the dielectric degradation process, as well as the stagnation period, are explored theoretically. The stagnation time at low temperatures under combined AC/negative DC voltage is long. The research in this paper is useful for insulation optimization design, condition assessment, and longevity prediction. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
20. Toward new scaling laws for wrinkling in biologically relevant fiber-reinforced bilayers.
- Author
-
Mirandola, A., Cutolo, A., Carotenuto, A. R., Nguyen, N., Pocivavsek, L., Fraldi, M., and Deseri, L.
- Subjects
WRINKLE patterns ,THICK films ,THIN films ,FINITE element method ,PHENOMENOLOGICAL biology - Abstract
Wrinkling, creasing, and folding are frequent phenomena encountered in biological and man-made bilayers made by thin films bonded to thicker and softer substrates often containing fibers. Paradigmatic examples of the latter are the skin, the brain, and arterial walls, for which wiggly cross sections are detected. Although experimental investigations on corrugation of these and analog bilayers would greatly benefit from scaling laws for prompt comparison of the wrinkling features, neither are they available nor have systematic approaches yielding to such laws ever been provided before. This gap is filled in this paper, where a uniaxially compressed bilayer formed by a thin elastic film bonded on a hyperelastic fiber-reinforced substrate is considered. The force balance at the film–substrate interface is here analytically and numerically investigated for highly mismatched film–substrates. The onset of wrinkling is then characterized in terms of both the critical strain and its corresponding wavenumber. Inspired by the asymptotic laws available for neo-Hookean bilayers, the paper then provides a systematic way to achieve novel scaling laws for the wrinkling features for fiber-reinforced highly mismatched hyperelastic bilayers. Such novel scaling laws shed light on the key contributions defining the response of the bilayer, as it is characterized by a fiber-induced complex anisotropy. Results are compared with finite element analyses and also with outcomes of both existing linear models and available ad hoc scalings. Furthermore, the amplitude, the global maximum and minimum of ruga occurring under increasing compression spanning the wrinkling, period doubling, and folding regimes are also obtained. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
21. Plasma propulsion modeling with particle-based algorithms.
- Author
-
Taccogna, F., Cichocki, F., Eremin, D., Fubiani, G., and Garrigues, L.
- Subjects
PLASMA chemistry ,CYCLOTRON resonance ,PLASMA-wall interactions ,PROPELLANTS ,ELECTROMAGNETIC devices ,PLASMA interactions ,ELECTRIC arc - Abstract
This Perspective paper deals with an overview of particle-in-cell/Monte Carlo collision models applied to different plasma-propulsion configurations and scenarios, from electrostatic (E × B and pulsed arc) devices to electromagnetic (RF inductive, helicon, electron cyclotron resonance) thrusters, as well as plasma plumes and their interaction with the satellite. The most important items related to the modeling of plasma–wall interaction are also presented. Finally, the paper reports new progress in the particle-in-cell computational methodology, in particular, regarding accelerating computational techniques for multi-dimensional simulations and plasma chemistry Monte Carlo modules for molecular and alternative propellants. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
22. Phase shifting profilometry based on Hilbert transform: An efficient phase unwrapping algorithm.
- Author
-
Meng, Xianglin, Wang, Fei, Liu, Junyan, Chen, Mingjun, and Wang, Yang
- Subjects
HILBERT transform ,SHAPE measurement ,PHASE coding ,ALGORITHMS ,COMPUTATIONAL complexity ,TIME measurements - Abstract
Digital fringe projection profilometry based on phase-shifting technology is a reliable method for complex shape measurement, and the phase is one of the most important factors affecting measurement accuracy. The calculation of the absolute phase depends on the calculation of the wrapped phase and encoding technology. In this paper, a technique of obtaining the absolute phase of multi-frequency heterodyne fringe images using the Hilbert transform is presented. Since the wrapped phase can be calculated from only one fringe image of each frequency, the method does not need phase-shifting. The absolute phase can be obtained from the wrapped phase by applying the heterodyne method. The measurement time and computational complexity are dramatically reduced, the measurement efficiency is greatly improved, and this benefit from the number of images is greatly reduced. The experimental results show that the method presented in this paper performs well in the application, and the accuracy is no different from that of the phase-shifting method while the efficiency is greatly improved. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
23. The criterion of planar instability in alloy solidification under varying conditions: A viewpoint from free energy.
- Author
-
Yu, Fengyi
- Subjects
SOLIDIFICATION ,ALLOYS - Abstract
In alloy solidification, the transport processes of heat and solute result in morphological instability of the interface, forming different patterns of the solidification structure and determining the mechanical properties of components. As the first observable phenomenon of morphological instabilities, planar instability influences the subsequent stages significantly, deserving in-depth investigations. In this paper, the planar instability in alloy solidification under varying conditions is studied. First, the dynamical evolution of the planar instability is performed by the theoretical model and the phase-field model, respectively. Second, to represent the history-dependence of solidification, varying parameters are adopted in the simulations. Then, the criterion of planar instability under varying conditions is discussed. This paper considers that the critical parameters of planar instability are the excess free energy at the interface and the corresponding interfacial energy. Finally, to validate the criterion, comparisons between the phase-field and theoretical models are carried out, showing good consistency. Moreover, solidification processes with different preferred crystallographic orientations are performed, demonstrating the effect mechanism of the excess free energy and interfacial energy on planar instability. The idea of the interfacial energy influencing the planar instability could be applied to investigating other patterns induced by interfacial instability. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
24. Topological optimization of a composite square lattice structure for bandgap property based on an improved multi-parameter genetic algorithm.
- Author
-
Wang, Xueqi and Li, Dong
- Subjects
PHONONIC crystals ,GENETIC algorithms ,FINITE element method ,ENERGY bands ,COMPOSITE structures ,THEORY of wave motion - Abstract
This paper proposed a two-dimensional composite square lattice structure containing two kinds of inclusions (polymethylmethacrylate and T2 copper). To maximize the relative widths of the gaps between the adjacent energy bands of the phononic crystals (PnCs), an improved multi-parameter genetic algorithm was adopted in this paper. The material distribution and ligament sizes were considered simultaneously by ternary encoding and binary encoding. The propagation wave behaviors of the composite lattice structures were studied by the finite element method. The effects of different lattice shapes and other relevant influencing parameters on the bandgaps were discussed. The results showed that the lattice shape, ligament width, and material density affect the width and the location of the bandgaps, and the effectiveness of the proposed method was demonstrated by a transmission spectrum experiment. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
25. An improved hybrid quantum-classical convolutional neural network for multi-class brain tumor MRI classification.
- Author
-
Dong, Yumin, Fu, Yanying, Liu, Hengrui, Che, Xuanxuan, Sun, Lina, and Luo, Yi
- Subjects
CONVOLUTIONAL neural networks ,BRAIN tumors ,TUMOR classification ,MAGNETIC resonance imaging ,QUANTUM computing - Abstract
The efficiency of quantum computing has recently been extended to machine learning, which has made a significant impact on quantum machine learning. The hybrid structure of quantum and classical ones has developed into the most successful application mode currently due to noisy intermediate scale quantum limitations. In this paper, an improved hybrid quantum-classic convolutional neural network (HQC-CNN) with fast training speed, lightweight, and high performance is proposed. Its convolution layer realizes feature mapping through parameterized quantum circuit, while other layers keep classic operation and finally complete the task of four classifications of brain tumors. The experiment in this paper is based on kaggle brain tumor magnetic resonance imaging public dataset. The final experimental results show that HQC-CNN can effectively classify meningioma, glioma, pituitary, and no tumor with a classification accuracy of 97.8%. When compared to numerous well-known landmark models, HQC-CNN has obvious advantages. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
26. Flexoelectric aging effect in ferroelectric materials.
- Author
-
Zhang, Zhen, Wen, Zhaokuan, Li, Ting, Wang, Zhiguo, Liu, Zhiyong, Liao, Xiaxia, Ke, Shanming, and Shu, Longlong
- Subjects
FERROELECTRICITY ,FERROELECTRIC materials ,FLEXOELECTRICITY ,STRAINS & stresses (Mechanics) ,PERMITTIVITY ,CERAMICS - Abstract
In spite of the flexoelectric effect being a universal phenomenon in the ferroelectric perovskites, the current understanding of flexoelectric aging in ferroelectrics is, actually, rather incomplete. In this paper, we have fabricated a series of Mn-doped BaTiO
3 perovskite ceramics (BaTi1–x Mnx O3 , x = 0.1% and 1%, BTMO) to systematically investigate the corresponding flexoelectric aging behavior by controlling the concentration of Mn. We found that the variation of Mn dopant significantly effects the Curie temperature, dielectric constant, flexoelectric aging, and flexoelectric coefficient of the BTMO ceramics. Especially for the BTMO (0.1%) ceramics, obvious ferroelectric aging and flexoelectric aging phenomenon are observed at room temperature. The main reason for aging of BTMO ceramics is that the doping of Mn introduces oxygen vacancies, which tend to be stable under the action of strain gradient and electric field. Therefore, the results presented in this paper verify that the flexoelectric aging in Mn-doped BTO ceramics is closely related to ferroelectric fatigue. [ABSTRACT FROM AUTHOR]- Published
- 2023
- Full Text
- View/download PDF
27. Magnetization mechanism of a hybrid high temperature superconducting trapped field magnet.
- Author
-
Liao, Hengpei, Yuan, Weijia, Zhang, Zhiwei, and Zhang, Min
- Subjects
HIGH temperature superconductors ,MAGNETIZATION ,ELECTROMAGNETIC interactions ,SUPERCONDUCTING magnets ,MAGNETS - Abstract
This paper studies the magnetization mechanism of a hybrid high temperature superconducting (HTS) trapped field magnet. To address the size limitation of traditional HTS bulk materials, hybridization between HTS-stacked ring magnets and HTS bulks is proposed here. A jointless HTS-stacked ring magnet is used to increase the trapped field area for HTS bulks. A hybrid HTS magnet with 90 mm in length and 60 mm in width was tested to provide a trapped field of 7.35 T in a field cooling magnetization. The paper focuses mainly on understanding the novel magnetization mechanism of this hybrid HTS trapped field magnet. A numerical model based on homogenized H formulation was used to compare with experimental results, and a good match was found. Our experimental and numerical study of the electromagnetic interaction between the HTS-stacked ring magnet and the HTS bulks reveals that there are two magnetization stages, and the magnetization speed differs in these two stages by a sing criterion: whether the HTS-stacked ring magnet is fully penetrated or not. This study confirms that hybridization helps to build large HTS trapped field magnets. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
28. Impact of thermal annealing on deep levels in nitrogen-implanted β-Ga2O3 Schottky barrier diodes.
- Author
-
Fregolent, Manuel, De Santi, Carlo, Buffolo, Matteo, Higashiwaki, Masataka, Meneghesso, Gaudenzio, Zanoni, Enrico, and Meneghini, Matteo
- Subjects
SCHOTTKY barrier diodes ,ELECTRON traps ,ACTIVATION energy ,CURRENT-voltage characteristics ,GALLIUM nitride films ,BASE isolation system - Abstract
Understanding the properties of N-implanted β-Ga
2 O3 is fundamental for the optimization of doping and isolation structures based on gallium oxide. This paper reports an extensive analysis of the impact of thermal annealing on the concentration and properties of deep levels in N-implanted β-Ga2 O3 Schottky barrier diodes by means of capacitance isothermal transient spectroscopy. Samples with annealing temperatures from 800 to 1200 °C were considered. The original results presented in this paper demonstrate the following: (a) The instability of current–voltage characteristics detected for all the samples under test can be attributed to the presence of three electron traps with activation energies of 0.6, 0.7, and 1 eV, consistent with previous reports in β-Ga2 O3 . (b) The detected traps are not the nitrogen level but intrinsic defects whose concentration is increased by the implantation process. (c) The concentration of deep levels decreases as the annealing temperature increases, demonstrating that the annealing process can effectively restore the quality of the material while keeping the conductivity decrease related to the presence of the nitrogen. Finally, (d) we demonstrate that the residual leakage and the turn-on voltage shift are correlated with the Arrhenius signature of the detected deep levels. An interpretation is proposed to explain the measurement results. [ABSTRACT FROM AUTHOR]- Published
- 2021
- Full Text
- View/download PDF
29. Simulation method of magneto-acousto-electrical tomography for improving computational efficiency.
- Author
-
Li, Cailian, Wu, Sanxi, Bu, Shuaiyu, Li, Yuanyuan, and Liu, Guoqiang
- Subjects
COMPUTER simulation ,TOMOGRAPHY ,COMPUTERS ,TISSUES ,DEGREES of freedom ,DISCRETE Fourier transforms - Abstract
In this paper, a frequency domain simulation method of magneto-acousto-electrical tomography (MAET) was proposed. This method is based on discrete Fourier transform. With this approach, the solving degrees of freedom of the simulation model can be significantly reduced. It can greatly reduce the requirements of computer hardware and improve efficiency. At the same time, the interaction between fluid and biological tissues was considered, which makes the simulation model closer to the real model. In this paper, an MAET simulation model of acoustic–solid–electromagnetic multi-physical field coupling corresponding to the actual physical world was established. It is more reasonable to adopt the fully coupled method. However, the fully coupled method needs more computational memory. To further study the memory and time required for calculation, the segregated method was used to calculate the simulation model without affecting the accuracy and tolerance in this paper. The results show that using the segregated method can significantly reduce the memory requirement of the MAET model, but the solution time will increase accordingly. Therefore, the appropriate solution method can be selected according to the simulation computer configuration and the desired solution time. We, finally, built an experimental platform to conduct MAET experiments and verified the theoretical and simulation analyses. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
30. Calculation of tunneling current across trapezoidal potential barrier in a scanning tunneling microscope.
- Author
-
Dessai, Malati and Kulkarni, Arun V.
- Subjects
SCANNING tunneling microscopy ,QUANTUM tunneling ,POTENTIAL barrier ,TUNNEL design & construction ,AIRY functions ,FERMI level - Abstract
Accurate calculation of the tunneling currents in a scanning tunneling microscope (STM) is needed for developing image processing algorithms that convert raw data of the STM into surface topographic images. In this paper, an accurate calculation of the tunneling current for several tip–sample distances, bias voltages, and tips of a hyperboloidal shape with several radii of curvature is carried out. The main features of this calculation are the following. Non-WKB exact solutions to the trapezoidal (linear) potential in the barrier region are used to calculate the tunneling probabilities. Pauli blocking effects on both forward and reverse current densities are introduced. Finite temperature (viz. 300 K) calculation in which electrons belonging to a narrow band of energy about the Fermi level contribute to tunneling is carried out. Integration over a field line method is used to obtain tunneling currents for the nonplanar hyperboloidal shaped tips, using the expressions obtained in the paper, for planar model current densities. An estimate of the lateral resolution is introduced. Earlier works do not consider all these aspects together in a single calculation. Tunneling currents are found to increase rapidly with increasing bias voltage and decrease exponentially with increasing tip–sample distances. Airy function determined currents are a more accurate function of a tip–sample distance than the WKB determined currents. Pauli effects are found to not always reduce currents from their non-Pauli values. The lateral resolution is found to be degraded for blunter tips, larger bias voltages, and larger tip–sample distances. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
31. CNT/Cu composite cathode: A new approach to long lifetime for explosive emission cathode.
- Author
-
Wu, Ping, Yang, Wenshu, Sun, Jun, and Wu, Gaohui
- Subjects
CARBON nanotubes ,CATHODES ,MICROWAVE generation ,MICROSCOPY - Abstract
Carbon nanotube (CNT) cathodes have attracted much attention in recent years due to the advantages of large field enhancement factor and low emission threshold. However, the severe ablation under intense emission makes the lifetime short and therefore limits the application in the field such as high power microwave generation. To resolve this problem, this paper proposes to mix CNTs with metals, and a novel CNT/Cu composite cathode is manufactured. The lifetime experiments under voltage of 940 kV and repetition frequency of 20 Hz demonstrate that the lifetime of the CNT/Cu composite cathode is over 3 × 10
5 pulses, which is much longer than that of the normal copper cathode by at least one order of magnitude. The microscopic morphology analysis reveals that the CNT micro-protrusions and whiskers should be vital for the good emission property of the new cathode. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
32. Mode conversion of Lamb waves in a composite phononic crystal plate: Numerical analysis and experimental validation.
- Author
-
Ding, Taotao, Song, Ailing, Sun, Chaoyu, Xiang, Yanxun, and Xuan, Fu-Zhen
- Subjects
LAMB waves ,PHONONIC crystals ,NUMERICAL analysis ,COMPOSITE plates ,POLYVINYLIDENE fluoride - Abstract
The mode manipulation of Lamb waves plays an important role in damage detection and identification of damage types, location, and size. In this paper, we propose a composite phononic crystal (PC) plate with antisymmetric and symmetric PCs for realizing mode conversion from A0 to S0 mode of Lamb waves. The theoretical analysis, numerical simulations, and experimental validation are introduced and the mode conversion mechanism of the composite PC plate is systematically investigated. The effect of geometrical parameters on band structures of antisymmetric and symmetric PCs is first discussed. Then multi-physics field simulation models are developed and in-plane displacement fields are obtained in numerical simulations, which shows that the mode conversion is enhanced when the period number of the antisymmetric PC decreases and that of symmetric the PC increases. The composite PC plate specimens are fabricated with precision wire cutting technology for experimental measurements and the self-designed polyvinylidene fluoride (PVDF) comb transducer is used to stimulate the Lamb waves. The experimental results are consistent with the numerical simulations, which demonstrate that the proposed composite PC plate can achieve the mode conversion from A0 to S0 mode of Lamb waves. Our proposed structures have applicable values for the mode manipulation of Lamb waves in damage detection. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
33. Cavity magnonics for large and small amplitude precession.
- Author
-
Iyaro, J. and Stamps, R. L.
- Subjects
MAGNONS ,NONLINEAR dynamical systems ,MICROMAGNETICS ,MAGNETICS ,SEMICLASSICAL limits - Abstract
Excitations that may appear in cavity magnonics experiments are examined with numerical micromagnetics using a recently developed semi-classical cavity magnonics theory. The theory is generally applicable to linear and nonlinear dynamic systems. In this paper, example applications of the theory for magnetic systems are presented where the dynamics is described using numerical micromagnetics for field driven ferromagnets. Examples of large amplitude driving are studied as a function of drive field amplitude and frequency. We comment also on large amplitude dynamics under elliptically polarized driving fields. The main conclusion is that when implemented together with micromagnetics, the theory can be used to describe cavity photon–magnon coupling for a wide variety of linear and nonlinear magnetic dynamics, thereby providing a useful technique for cavity magnonics. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
34. Origins of observational errors in field sweep DC measurements for unidirectional magnetoresistance.
- Author
-
Fan, Yihong, Saha, Renata, Yang, Yifei, and Wang, Jian-Ping
- Subjects
ENHANCED magnetoresistance ,MAGNETORESISTANCE ,MEASUREMENT errors - Abstract
Understanding the mechanisms of unidirectional magnetoresistance (UMR) has become an important topic for its potential application of a two-terminal spin–orbit torque device. Field sweep DC measurements have been proposed and adopted to measure the value of UMR instead of second harmonic measurements. In this paper, potential measurement errors in conventional DC measurements are investigated. Oersted field and field-like torque usually do not influence the measurement, but a large field-like torque was found to lead to an anisotropic magnetoresistance difference when the sample is not perfectly aligned with the external field. The existence of ordinary magnetoresistance was also found to contribute to a large background. In this paper, an alternative measurement method for UMR was proposed and demonstrated to address those issues related to previous DC measurements. Our work may broaden the understanding of the error sources of UMR measurements and provide a reliable DC measurement method for the characterization of UMR. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
35. An efficient analytical model and experiments of 3D electromagnetic force of permanent magnet electrodynamic suspension system.
- Author
-
Wu, Chuan, Li, Guanchun, Wang, Dong, and Xu, Jie
- Subjects
ELECTROMAGNETIC forces ,PERMANENT magnets ,MOTOR vehicle springs & suspension ,COMPUTATIONAL electromagnetics ,MAGNETIC fields ,REQUIREMENTS engineering - Abstract
Electrodynamic suspension (EDS) with a linear permanent magnet Halbach array, which can be used in ultrahigh-speed maglev systems, has gained increasing attention in recent years. However, inefficient calculation methods of electromagnetic forces restrict the stability research of EDS systems. Hence, an efficient 3D analytical model of the electromagnetic force is established in the paper based on an improved analytical model of the source magnetic field excited by the Halbach array, and then the application conditions of the model are studied. Finally, the analytical results are compared with the experimental results, which are provided by the experiments carried out on a high-speed rotating experiment platform with a flywheel. The results show that the proposed model can shorten the computation time of electromagnetic force to less than 10 ms and the relative errors of analytical results are around 5% under the conditions ① w p / τ ≥ 2.5 , w d / w p ≥ 1.5 or ② w p / τ ≥ 4 , w d / w p ≥ 1 (τ is the pole pitch of the Halbach array, w p is the width of the permanent magnet, w d is the width of the conducting plate). The analytical model meets the engineering requirements and can provide a reference for further stability research and experiments on EDS systems. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
36. On the origin of twist in 3D nucleation islands of tetrahedrally coordinated semiconductors heteroepitaxially grown along hexagonal orientations.
- Author
-
Vennéguès, P., Largeau, L., Brändli, V., Damilano, B., Tavernier, K., Bernard, R., Courville, A., Rennesson, S., Semond, F., Feuillet, G., and Cornet, C.
- Subjects
NUCLEATION ,SEMICONDUCTORS ,ISLANDS ,DISLOCATION density ,BORON nitride - Abstract
In the first part of this paper, we present a model that explains and determines quantitatively the twists between nucleation islands in the case of a Volmer–Weber heteroepitaxial growth of tetrahedrally coordinated semiconductors along hexagonal orientations. These twists are caused by the network of the screw components of the 60° misfit dislocations. The orientations of the screw components are distributed randomly, and the maximum twist is obtained when all the screw components have the same orientation. The maximum twists are related to the density of misfit dislocations and, therefore, increase with the mismatch between the deposited materials and their substrate. In the second part of the paper, we study five systems having a large distribution of mismatches from 4% to 19%. For the four systems fulfilling the conditions necessary for the application of the model (plastic relaxation of grown islands), the measured maximum twists fit with the calculated values, thereby validating the model. The twists of nucleation islands are related to the mismatch and are, therefore, intrinsic to the material systems. The defects created at the coalescence of twisted islands determine the initial microstructure/defect distribution of the nucleation layer. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
37. Computational study of the effect of grain boundary and nano-porosity on xenon behavior in UO2.
- Author
-
Zamzamian, Seyed Mehrdad, Kowsar, Zahra, and Zolfaghari, Ahmadreza
- Subjects
CRYSTAL grain boundaries ,XENON ,WOOD pellets ,FISSION products ,DIFFUSION coefficients ,GRAIN - Abstract
Since xenon (Xe) production is always an unavoidable part of the fission products in fuel pellets, the challenges of its presence have always been the subject of many papers. In line with these goals, in the present paper, the effect of the presence of grain boundaries (GBs) with misorientations (θ G B ) of 36 ° , 39 ° , 52 ° , 53 ° , 71 ° , and 129 ° in 10%Xe-UO
2 (uranium dioxide in which 10% of its uranium atoms have been replaced by xenon atoms) on the behavior of xenon (diffusion, nucleation, and formation of clusters) was investigated by performing molecular dynamics (MD) simulations. The results showed that xenon atoms aggregate in the GB with misorientations of 36 ° and 53 ° and form larger clusters relative to other GBs. This was interpreted due to the low formation energy of these two GBs in comparison with other misorientations. A decrease in the number of xenon atoms was also observed at a slight distance from these two GB regions, indicating their sink efficiency. The calculation of diffusion coefficients also indicated that the presence of these two GBs increases the coefficients (xenon, oxygen, and uranium). All of these demonstrate the effective role of θ G B = 36 ° and θ G B = 53 ° in swelling. To reduce the destructive effect of xenon atoms on the fuel pellet, a conceptual design in the form of nanoporous was proposed. The results of the MD simulation of such a design showed that the presence of nano-porosity significantly reduces xenon clusters. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
38. Layer-by-layer acoustic travel time approximation using ray theory for total focusing method imaging in carbon fiber reinforced polymer.
- Author
-
Cao, Ziyi, Shi, Fangfang, and Zhang, Bixing
- Subjects
CARBON fibers ,MONOMOLECULAR films ,FINITE element method ,TIME management ,POLYMERS - Abstract
This paper proposes a layer-by-layer acoustic travel time approximation method based on ray theory for total focusing method (TFM) imaging in carbon fiber reinforced polymer (CFRP) laminates. The method considers the anisotropy in every monolayer and heterogeneity of CFRP, which approximates the path of propagation as straight in the whole material. The application of this method to TFM imaging is called TravelTimeAppro-TFM. In comparison to isotropic-TFM and Dijkstra-TFM, the experimental results indicated that TravelTimeAppro-TFM outperforms isotropic-TFM in terms of imaging amplitude gain with a maximum gain of 4.67 dB. On the other hand, this approach reduces the computational work compared to Dijkstra-TFM. The proposed method demonstrates significant improvements in both focusing performance and the speed of calculation. This paper also investigates the effective angular range of the layer-by-layer acoustic travel time approximation method through experimental and finite element simulation analysis. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
39. High-precision wave height detection of triboelectric nanogenerator by using voltage waveforms and artificial neural network.
- Author
-
Lai, Yuming, Ma, Jiahua, Wen, Honggui, Yao, Huilu, Wei, Wenjuan, Wan, Lingyu, and Yang, Xiaodong
- Subjects
TRIBOELECTRICITY ,WATER waves ,VOLTAGE - Abstract
As we known waves contain important information, however, to realizing high-precision quantification for ocean exploitation and utilization is challenging. In this paper, we proposed a neural network for wave height detection by training the voltage waveform of a triboelectric nanogenerator (TENG). First, we analyzed the voltage signal obtained using a TENG. Second, we proposed a lightweight artificial neural network model that achieves a minimal monitoring error of 0.049% at low amplitudes and yields better monitoring results than the linear model. The findings presented in this paper enable the measurement of water surface waves and eliminate the influence of external factors on sensor performance. Wave parameters can be obtained using neural networks, and this work provides a new strategy for computational and intelligent applications by using wave data. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
40. Second harmonic generation in centrosymmetric multilayered structures: Theoretical approach for nonlinear boundary conditions.
- Author
-
Obeid, B., Ionica, I., Vitrant, G., Damianos, D., and Bastard, L.
- Subjects
SECOND harmonic generation ,NONLINEAR optics ,OPTOELECTRONIC devices - Abstract
Second harmonic generation (SHG) is used to characterize the interfaces of centrosymmetric materials typically used in microelectronic/optoelectronic devices. For such applications, the materials are actually multi-layer stacks, and in this case, the SHG can be difficult to interpret and model. This paper presents the theory of the second harmonic light generated from multilayer structures. The focus is on describing the nonlinear boundary conditions at the interfaces between two different materials, taking into account the distinct contributions of bulk and interface regions. Using these conditions, it is possible to calculate the second harmonic signal from any stack of materials. In this paper, we address stacks containing silicon (100) because it is a material with numerous applications. The nonlinear polarization expressions of the surface and bulk of Si(100), according to Sipe et al. [Phys. Rev. B 35, 1129 (1987)], were integrated into nonlinear boundary conditions in order to determine transmitted and reflected second harmonic waves. An analytical validation was performed on the simple case of an air–silicon interface. For multilayered stacks, the model was compared with experimental results obtained on samples corresponding to pragmatic substrates widely used in microelectronic and optoelectronic applications. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
41. On the polytropic coefficient of negative ions for modeling the sheath and presheath of electronegative plasmas.
- Author
-
Schiesko, L., Lishev, St., Revel, A., Carbone, E., and Minea, T.
- Subjects
ANIONS ,LOW temperature plasmas ,PLASMA chemistry ,CATIONS ,PLASMA sheaths - Abstract
The fluid description is widely used for the multi-dimensional modeling of low temperature plasmas with complex chemistries due to their relative low computational cost. It relies, however, on a series of simplifying assumptions and some truncation of the moment equations for describing the non-equilibrium between the electrons, positive ions, negative ions, and the neutrals. In this paper, the classical assumption of isothermal negative ions is revisited for electronegative plasmas and, more particularly, for the fluid modeling of the transition between the plasma and its sheath. To do so, and in contrast to previous studies, the energy balance equation for the negative ions is also computed, and it allows us to derive the polytropic coefficient γ of the negative ions in addition to one of the positive ions. Strong variations in the sheath and presheath of the negative ions temperature and their polytropic coefficient are observed. The polytropic coefficient is shown to be a strongly varying function of space having for consequence that the negative ions are isothermal only in a very narrow extension of the presheath. For the case considered in this paper, both positive and negative ion flows are nearly adiabatic at the sheath-edge and become adiabatic inside the sheath. This paper shows that classical fluid modeling assumptions need to be verified for each system under consideration, most particularly while modeling the transition from plasma to a wall. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
42. Ab initio calculations of structural stability, thermodynamic and elastic properties of Ni, Pd, Rh, and Ir at high pressures.
- Author
-
Smirnov, N. A.
- Subjects
THERMODYNAMICS ,AB-initio calculations ,ELASTICITY ,STRUCTURAL stability ,BODY centered cubic structure - Abstract
This paper presents results of a comprehensive study from first principles into the properties of Ni, Pd, Rh, and Ir crystals under pressure. We calculated elastic constants, phonon spectra, isotherms, Hugoniots, sound velocities, relative structural stability, and phase diagrams. It is shown that in nickel and palladium under high pressures (>0.14 TPa) and temperatures (>4 kK), the body-centered cubic structure is thermodynamically most stable than of the face-centered cubic one. Calculated results suggest that nickel under Earth-core conditions (P ∼ 0.3 TPa, T ∼ 6 kK) have a bcc structure. No structural changes were found to occur in Rh and Ir under pressures to 1 TPa at least. This paper also provides estimations for the pressure and temperature at which the metals of interest begin to melt under shock compression. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
43. Construct Schottky interface containing energy-filtering effect: An efficient strategy to decouple thermopower and conductivity.
- Author
-
Lin, Zizhen, Ping, Xiaofan, Zhao, Dongming, Wang, Lichuang, Li, Menglei, Cai, Zihe, Zhang, Yun, Li, Xinlian, and Zhang, Xuankai
- Subjects
THERMOELECTRIC power ,THERMOELECTRIC materials ,IMPURITY centers ,ELECTRIC conductivity ,CHARGE carriers ,SEEBECK coefficient ,FILTERS & filtration - Abstract
Organic/inorganic thermoelectric hybrids demonstrate great potential for wearable applications. However, their scalability is hindered by an inferior power factor (S 2 σ). Nowadays, achieving deep optimization of S 2 σ necessitates a strategy to decouple the Seebeck coefficient (S) and electrical conductivity (σ). In this work, we propose a strategy to break the coupling between S and σ by constructing a Schottky interface that exhibits an energy-filtering effect. We validate the feasibility of this approach using a PANI/TiN–TiO
2 /carbon paper. The results demonstrate a 1.16-fold increase in σ and a 1.08-fold increase in S in PANI/TiN–TiO2 /carbon paper achieved through the construction of a Schottky-type TiN/TiO2 interface. The separation of hole/electron at the TiN/TiO2 interface serves as the scattering center for ionized impurity scattering and facilitates the transport pathway for charge carriers. These factors are crucial in determining the simultaneous optimization of S and σ , respectively. Additionally, the energy-filtering effect of the TiN/TiO2 interface plays a positive role in the ionized impurity scattering mechanism by selectively filtering out low-energy carriers. This further strengthens decoupling of the thermoelectric properties. The 14.9% PANI/11.2% TiN–14.5% TiO2 /59.44% carbon paper displays the highest S 2 σ and achieves a high ZT value of 223.6 μVm−1 K−2 and 0.31 at 300 K, highlighting the advantages of PANI-based thermoelectric hybrids. This work provides valuable guidance for the design of thermoelectric hybrids incorporating multi-interface morphology. [ABSTRACT FROM AUTHOR]- Published
- 2023
- Full Text
- View/download PDF
44. Erratum: "Understanding the response of aluminosilicate and aluminoborate glasses to sharp contact loading using molecular dynamics simulation" [J. Appl. Phys. 128, 035106 (2020)].
- Author
-
Liu, Haidong, Deng, Binghui, Sundararaman, Siddharth, Shi, Yunfeng, and Huang, Liping
- Subjects
MOLECULAR dynamics ,GLASS ,RADIAL distribution function - Abstract
Figures 5-8 show density and Si/Al coordination change during the compression-decompression cycle with and without a shear stress component using the two sets of parameters. In the original paper, the short-range interaction parameters for the Si-Li pair in the SHIK potential[1] were used by mistake for the Si-Na pair in the sodium aluminosilicate (NAS) glass. Si and Al coordination changes during the compression-decompression cycle in NAS without [(a) and (b)] and with shear [(c) and (d)] using the two sets of short-range interaction parameters. [Extracted from the article]
- Published
- 2021
- Full Text
- View/download PDF
45. Respiratory droplet resuspension near surfaces: Modeling and analysis.
- Author
-
Nikfar, Mehdi, Paul, Ratul, Islam, Khayrul, Razizadeh, Meghdad, Jagota, Anand, and Liu, Yaling
- Subjects
SURFACE analysis ,CONTACT angle ,HYDROPHOBIC surfaces ,SURFACE energy ,MEDICAL personnel ,SURGICAL gloves - Abstract
Knowing the environmental spreading pathway of COVID-19 is crucial for improving safety practices, particularly for health care workers who are more susceptible to exposure. This paper focuses on the possible secondary transmission due to resuspension of virus-laden droplets from common surfaces, which several studies have shown to be possible under external disturbances. Such disturbances could be body motion during walking, running, clothes removal, or airflow in the environment. In this paper, a three-dimensional two-phase model is utilized to study respiratory droplet resuspension dynamics on various surfaces due to sudden agitation. The velocity range and variation during walking, surgical glove removal, and dropping an object are studied experimentally. A parametric study is performed to characterize the effects of droplet size and surface wettability on the minimum initial droplet velocity required for detachment from surfaces. The results are reported as average droplet velocity during the detachment process, total detachment time, and detached droplet volume. The obtained results indicate that respiratory droplets larger than 200 μm can detach from typical surfaces due to normal daily activities. Droplets are partially separated from hydrophilic surfaces with contact angle ≤ 90 ° , while the entire droplet is detached from hydrophobic surfaces with contact angle > --> 90 °. Furthermore, the minimum initial droplet velocity to induce the resuspension depends on the droplet size. Droplet velocity immediately after detachment is a function of droplet size, initial droplet velocity, and surface wettability. Bigger droplets have larger detached volume percentage as well as higher velocity after detachment compared to smaller droplets. Finally, a higher initial velocity is needed to separate droplets from hydrophilic surfaces as compared to hydrophobic surfaces. In accordance with the results, the droplet minimum initial velocity to cause detachment is 2 m s
−1 , while our experiments show that surface velocity can reach up to 3 m s−1 during normal human activities. We also develop an analytical model to predict the required kinetic energy to detach droplets from different surfaces, which is in good agreement with numerical results. The mechanism of droplet detachment is dictated by a competition between droplet kinetic energy induced by surface motion and surface energy due to droplet–surface interaction as well as droplet–vapor and surface–vapor interactions. We believe that the results of this fundamental study can potentially be used to suggest proper surface wettability and safe motion that reduce respiratory droplet resuspension from various surfaces. [ABSTRACT FROM AUTHOR]- Published
- 2021
- Full Text
- View/download PDF
46. Variational algorithm of quantum neural network based on quantum particle swarm.
- Author
-
Dong, Yumin, Xie, Jianshe, Hu, Wanbin, Liu, Cheng, and Luo, Yi
- Subjects
PARTICLE swarm optimization ,ARTIFICIAL neural networks ,QUANTUM superposition ,ALGORITHMS - Abstract
Most models of quantum neural networks are optimized based on gradient descent, and like classical neural networks, gradient descent suffers from the barren plateau phenomenon, which reduces the effectiveness of optimization. Therefore, this paper establishes a new QNN model, the optimization process adopts efficient quantum particle swarm optimization, and tentatively adds a quantum activation circuit to our QNN model. Our model will inherit the superposition property of quantum and the random search property of quantum particle swarm. Simulation experiments on some classification data show that the model proposed in this paper has higher classification performance than the gradient descent-based QNN. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
47. Surface plasmon resonance enhanced self-powered graphene/Al2O3/InGaAs near-infrared photodetector.
- Author
-
Zhang, Yinglu and Chen, Jun
- Subjects
PHOTODETECTORS ,SPIN coating ,SILVER nanoparticles ,INDIUM gallium arsenide ,LIGHT absorption ,SURFACE plasmons ,SURFACE plasmon resonance - Abstract
In recent years, there has been extensive research on improving the performance of photodetectors. In this paper, the performance of a graphene/Al
2 O3 /InGaAs photodetector is studied. In order to reduce the dark current of this device and improve the photocurrent, the structure of the device is optimized to improve the responsivity of the device. A 2 nm thick Al2 O3 layer is inserted as the passivation layer. The InP layer between the SiNx layer and the InGaAs layer is retained. It is speculated that the InP layer could reduce the defects and interface states between layers. A layer of silver nanoparticles (Ag NPs) was spin coated on the surface of the single-layer graphene, and the surface plasmon resonance of Ag NPs could enhance the local electric field of InGaAs interface and increase the light absorption of graphene, which can promote carrier generation and transmission in graphene and, thus, effectively enhance the photocurrent of device. The improved device achieves a high responsivity of 265.41 mA/W at 1064 nm and a detection rate of 4.06 × 1011 cm Hz1/2 W−1 . At −1.25 V, the responsivity of the device is improved to 1618.8 mA/W. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
48. Unified creeping model identifying the critical state of granular materials.
- Author
-
Tong, L. H., Wu, B. N., Lei, Z. X., and Xu, C. J.
- Subjects
GRANULAR materials ,CRITICAL velocity ,MECHANICAL behavior of materials ,CREEP (Materials) ,FRICTION velocity ,DEAD loads (Mechanics) - Abstract
The mechanical properties of granular materials at a low shear rate are frequently viewed as rate-independent, and a rate-independent constitutive relation is used to describe the mechanical behaviors of the granular material. However, time-dependent behaviors (or creeping behaviors) become significant in the long run. In this paper, we conduct triaxial experiments to observe the creep of granular materials under both dynamic and static loading conditions. Three typical creeping behaviors, aging, transitional, and fluidic, have been observed. To describe the time-dependent behaviors, an internal state variable characterizing the fluidity of the granular system is introduced to propose a rate-dependent constitutive relation which we call in this paper, a state evolution model. A characteristic strain is also introduced into the model to account for the influences of historic strain on the current state. The experiments are analyzed using the proposed model and it has been found that our model can well discern the observed three creeping behaviors. A criterion to identify the stability of a granular system is also given out based on the proposed model. Two key factors dominating the stability of the granular system are recognized – shear wave velocity and critical velocity. Our laboratory experiments in combination with the proposed criterion offer a physical explanation of the intrinsic triggering mechanism of system evolution from a stable to fluidic state: decrease in wave velocity or/and critical velocity. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
49. Segmentation and accurate identification of large carious lesions on high quality x-ray images based on Attentional U-Net model. A proof of concept study.
- Author
-
Li, Wei, Zhu, Xueyan, Wang, Xiaochun, Wang, Fei, Liu, Junyan, Chen, Mingjun, Wang, Yang, and Yue, Honghao
- Subjects
DEEP learning ,X-ray imaging ,DENTAL caries ,PROOF of concept ,IMAGE segmentation ,IMAGE recognition (Computer vision) ,X-rays - Abstract
Dental caries is a bacterial infectious disease that destroys the structure of teeth. It is one of the main diseases that endanger human health [R. H. Selwitz, A. I. Ismail, and N. B. Pitts, Lancet 369(9555), 51–59 (2007)]. At present, dentists use both visual exams and radiographs for the detection of caries. Affected by the patient's dental health and the degree of caries demineralization, it is sometimes difficult to accurately identify some dental caries in x-ray images with the naked eye. Therefore, dentists need an intelligent and accurate dental caries recognition system to assist diagnosis, reduce the influence of doctors' subjective factors, and improve the efficiency of dental caries diagnosis. Therefore, this paper combines the U-Net model verified in the field of biomedical image segmentation with the convolution block attention module, designs an Attention U-Net model for caries image segmentation, and discusses the feasibility of deep learning technology in caries image recognition so as to prepare for the next clinical verification. After testing, the Dice similarity coefficient, mean pixel accuracy, mean intersection over union, and frequency-weighted intersection over the union of teeth segmentation with Attention U-Net are 95.30%, 94.46%, 93.10%, and 93.54%, respectively. The Dice similarity coefficient, mean pixel accuracy, mean intersection over union, and frequency-weighted intersection over the union of dental caries segmentation with Attention U-Net are 85.36%, 91.84%, 82.22%, and 97.08%, respectively. As a proof of concept study, this study was an initial evaluation of technology to assist dentists in the detection of caries. There is still more work needed before this can be used clinically. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
50. Understanding the factors affecting contact resistance in nanowire field effect transistors (NWFETs) to improve nanoscale contacts for future scaling.
- Author
-
Ramesh, S., Ivanov, Ts., Sibaja-Hernandez, A., Alian, A., Camerotto, E., Milenin, A., Pinna, N., El Kazzi, S., Lin, D., Lagrain, P., Favia, P., Bender, H., Collaert, N., and De Meyer, K.
- Subjects
FIELD-effect transistors ,NANOWIRES ,PLASMA etching ,SURFACE states ,LOW temperatures ,OHMIC contacts - Abstract
In this paper, dry etched vertical nanowires (VNWs) are used in transmission line/transfer length analysis to study the contacts of gate-all-around devices for future technology nodes. VNW resistors with Mo and Pd based metal stack contacts to p-InGaAs show Schottky behavior, unlike the planar counterpart. The resistance for Mo contact is higher than Pd, however, Pd was found to form an alloy with InGaAs at temperatures as low as 190 °C, and the length of Pd diffusion into the InGaAs increased at smaller NW dimensions, hindering future scalability. The minimum extracted specific contact resistivity (ρ
C ) values are 1.6 × 10−5 Ω cm2 (Mo) and 4.2 × 10−6 Ω cm2 (Pd) for a doping level of 1 × 1019 cm−3 . An apparent dependence of ρC on the NW diameter was also observed. This has been attributed to the surface states under the un-gated region of NW devices and found to dominate at smaller diameters. An analytical model to account for such geometrical effects has also been developed and validated with technology computer-aided design simulations. The analysis presented in this paper effectively captures the 3D aspects of an NW contact at nanoscale dimensions and can be applied irrespective of the semiconductor and contact metal used. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.