bluuebunny/crossref_metadata_2025 huggingface dataset:
Theoretical and numerical analysis of layered cylindrical pentamode acoustic cloak
Authors: Zhang Xiang-Dong  , Chen Hong  , Wang Lei  , Zhao Zhi-Gao  , Zhao Ai-Guo  ,   Wuhan Second Ship Design and Research Institute, Wuhan 430205, China
Published: December 2020

As a newly-developed method, acoustic cloak made of pentamode materials is on its speedway to the promising potential application. However, physical fabrication of pentamode cloak with continuously varying material parameters can be a tough work, if not totally impossible. Layering is a natural compromise to bypass this quandary. Researches on layering effects of inertial cloak are ample. However, researches on layering pentamode acoustic cloak are relatively limited. Among these researches Scandrett extends the effective bandwidth through optimization of material parameters[2010 J. Acoust. Soc. Am. 127 2856, 2011 Wave Motion. 48 505].#br#The present work concerns the layering effects of pentamode acoustic cloak. By comparing with precedent results, the present paper has two major innovations: Firstly, cylinder is chosen to be the basic geometry. This is of obvious advantage since cylinder is the basic geometry of acoustic cloak's important potential host. Secondly, effects of layers' number and thickness distribution on the stealth effect are analyzed. The two are key parameters to be determined in the layering process. This paper is organized as follows: Firstly, analytical expression of the scattering pressure field of layered cloak is deduced by means of variables separation. In this process Fourier expansion plays a key role. And the harmonic assumption of the incident acoustic wave is made. Secondly, typical cases are calculated to verify the validation of the theoretical analysis. First let material parameters tend towards that of water, and compare the scattering field with that of the bare rigid object when the cloak is replaced by water. Second let the layering number goes to infinity, and compare the scattering field with that of the continuous cloak. Phenomena conforming with basic physical laws are observed. And validity of the theory and codes is confirmed. Thirdly, effects of layers' number and thickness distribution on the stealth character are theoretically and numerically analyzed. One can easily see from the computational results that a critical number N exists. When layers' number exceeds N, improvement of the stealth effect becomes less efficient by further adding layers' number. One can also see from the computational results that a wise distributional strategy that helps improve the stealth effect indeed exists. And the optimization iteration can be utilized to further improve it.#br#As a summary, the present paper concerns the layering process of cloaking. Qualitatively and quantitatively, several significant results are obtained. This paper offers a useful reference for future fabrication of realistic acoustic pentamode cloak.
Lateral pressure distribution and steering coefficient in two-dimensional lattice pile of granular material
Authors: Yang Lin  , Hu Lin  , Zhang Xing-Gang  ,   Department of Physics, Guizhou University, Guiyang 550025, China
Published: December 2020

Granular material is a kind of soft condensed matter, which gathers up a large number of particles, and the relation between its microstructure and macroscopic mechanical properties is very complex. In this paper, the lateral stress distribution of the two-dimensional vertically stacked lattice of granular material under a pressure in the vertical direction has been investigated experimentally. The steering behavior of the vertical pressure in a granular system is discussed and analyzed in detail based on the experimental results. Results show that in the process of slow compression, the vertical pressure increases slowly in a nonlinear form at first and gradually transforms into a linear increase. This phenomenon corresponds to the dynamic processes of friction-slip-extrusion. This kind of behavior is more significant in the particle system of the same size. In the initial stage of pressing, the vertical force of the stepping motor is mainly used to overcome the friction between the particles and the sliding friction between the particle and the wall. As the friction in the granular system is related to the geometry of the particulate deposits, the material of particles, the roughness of the wall surface, and other relevant factors, the front-end of vertical pressure displays nonlinear characteristics. Continuing the squeeze and push forward, a force chain is formed among particles through self-organization. The vertical force is mainly used to overcome the elastic pressing force between the particles and the force to the wall, so later on the vertical pressure performs linear growth. For the system of particles with an established packed structure, the vertical pressure applied in the vertical direction steers along the force chain between the particles, and the value of horizontal pressure is different at different stacking heights. That is, the pressure in the middle is greater than that at the top and the bottom. The saturated value of steering coefficient k decreases with the stacking angle θ. As the stacking angle increases, the vertical component of the stress becomes more pronounced than its horizontal component. The expression of steering coefficients against stacking angle has been obtained through careful analysis of the geometrical structure and the force distribution of the granular pile, and the theoretical value fit well with the experimental results.
Theoretical analysis of high flow conductivity of a fracture induced in HiWay fracturing
Authors: Yan Xia  , Huang Zhao-Qin  , Xin Yan-Ping  , Yao Jun  , Li Yang  , Gong Liang  ,   School of Petroleum Engineering, China University of Petroleum, Qingdao 266580, China;,   School of Oil&Gas Engineering, ShengLi College, China University of Petroleum, Dongying 257061, China;,   Department of Oilfield Exploration & Development, Sinopec, Beijing 100029, China;,   College of Pipeline and Civil Engineering, China University of Petroleum, Qingdao 266580, China
Published: December 2020

HiWay (or channel) fracturing has been a new technology for development of unconventional oil and gas resources in recent years. It has been carried out more than 4000 times worldwide, and obtained good performance in oil and gas recovery. HiWay fracturing improves the flow conductivity of fractures by constructing inhomogeneous distributions of proppant and stable, open flow channel in hydraulic fractures. However, the mechanism and impact factors of high flow conductivity of HiWay fractures are not very clear. To the best of our knowledge, there are no relevant research reports available for such analysis. In this paper, it is first assumed that the fluid flow in proppant clusters follows the Darcy's law and the flow in the channels with proppant clusters is laminar viscous flow, which can be described using Stokes equation. However, the coupling of Darcy-Stokes equations is difficult, and some untrivial interface conditions at the interface between the porous and free-flow regions should be introduced, this will increase greater complexity in numerical computation. As an alternative approach, the Darcy-Brinkman equation is often used for this coupling flow problem, which provides a unified equation with continuous variable coefficients in the two different flow regions. Therefore, there is not necessary to introduce specific interface conditions any more. In this work, we first applied the Darcy-Brinkman equation to model the fluid flow in hydraulic fractures, and then the upscaling of Darcy-Brinkman equation is conducted to evaluate the equivalent permeability of a fracture by using homogenization theory and finite element numerical simulation. Finally, various impact factors of flow conductivity of a hydraulic fracture, such as the cluster shape, cluster distribution, cluster size, etc., are analyzed based on the equivalent permeability. Results show that the permeability of a hydraulic fracture is considerably greater than thst of proppant cluster when the free-flow region is well connected in the fracture, and the geometric properties of proppant clusters are also the key influencing factors for the flow conductivity. Therefore, in HiWay fracturing process, how to construct the well-connected free-flow region in hydraulic fractures is most important, and the flow conductivity of proppant cluster is not the keypoint. However, the surface roughness and stress sensitivity of the hydraulic fractures have not been considered in this work, it will be considered in the future work.
Experimental study of heat transfer from droplet impact on a heated surface
Authors: Shen Sheng-Qiang  , Zhang Jie-Shan  , Liang Gang-Tao  ,   School of Energy and Power Engineering, Dalian University of Technology, Key Laboratory for Desalination, Liaoning Province, Dalian 116024, China
Published: December 2020

Droplets impact on surfaces exist widely in industrial equipments, such as spraying cooling, ink jet printing, oil drops impact on walls in combustion chamber, brine droplets impact on heat transfer tubes in horizontal-tube falling film evaporators etc. In particular, for the droplets impinging on heated surfaces, the contact scale and the heat transfer flux affect the cooling of the hot surfaces greatly. In this work, evaporation processes of water and ethanol droplets impact on a heated surface are observed using a high-speed digital camera with a capacity of 106 frames per second. The corresponding evaporation parameters including the contact diameter, the droplet height, the contact angle, and heat flux are analyzed. The initial liquid temperature keeps constant at 20 ℃, and the initial surface temperature varies in the range of 68-126 ℃. Diameters of single water droplets and ethanol droplets are 2.07 and 1.64 mm, respectively. The impact Weber number of water droplets ranges from 2 to 44 while that of ethanol droplets ranges from 3 to 88. The present results show that due to the coupled effects of gravity, surface tension, fluid flow and evaporation processes, the height of water droplets reduces continuously while the contact diameter almost does not change during the most part of evaporation time. In the later stage of evaporation, the contact diameter, height and contact angle of water droplets oscillate, mainly because of droplet retraction. The critical contact angle for water droplets retraction is in the range of 4-8. The contact angle of ethanol droplets first reduces and then remains constant, while the contact diameter and the height decrease continuously. The droplet evaporation time depends on liquid properties and the surface temperature, and the Weber number effect is minor. The evaporation time decreases with the increase in the surface temperature. At the same time, with increasing surface temperature, the ratio between the sensible heat and the total heat increases, and this part of heat cannot be neglected from the total heat transfer calculation. Based on the present experimental conditions, the average heat flux for the water droplets ranges from 0.014 to 0.110 Wmm-2 in this work.
Experiment and numerical study on the characteristics of self-propellant Janus microspheres near the wall
Authors: Cui Hai-Hang  , Tan Xiao-Jun  , Zhang Hong-Yan  , Chen Li  ,   School of Environment and Municipal Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, China
Published: December 2020

Self-propellant Janus microsphere is a special class of active particles with a regular shape and irregular surface characteristic. With the self-propulsion of 2 μm diameter Pt-SiO2 Janus microsphere near the wall, we have measured the relationship of self-propellant velocity VJanus versus the observed time Δtobs. A diffusiophoretic force-dominated motion, which can be deemed as a quasi-1 D motion with the characteristics of both force free and torque free, is distinguished from the entire motion process. At the same time, it is also observed that the Janus microsphere is deflected about the vertical direction with an angle ψ. The deflection angle ψ is found to decrease with the increase of H2O2 concentration in the solution. For the 2.5%-10% H2O2 solution in this experiment, the angle ψ ranges from 20° to 7° approximately. A numerical model, involving viscous force, diffusiophoretic force and the effective gravity, is created with a reference frame, this quasi-1 D self-propellant motion can be solved to satisfy the conditions of the force and torque balance simultaneously. We have studied the changes of angle ψ and separation distance δ of the microsphere from the substrate under different conditions, including the concentrations of H2O2 solution, the material density, and the diameter of the microsphere. For the self-propulsion velocity VJanus and the deflection angle ψ, numerical results show good agreement with the published experimental observation results. Moreover, it is found that the lower density or the smaller diameter of the microsphere will generate the smaller distance δ, while the higher concentration of H2O2 in the solution will result in a larger distance δ. The predicted δ is 2-8 μm. With the obtained data, we further discuss the effect of near wall on the characteristic time τR of rotational diffusion of the Janus microsphere. Because the predicted values of δ are relative high, the near wall effect can be neglected, indicating that this effect should not be a significant factor to cause a big discrepancy of τR in different references. The present work will be beneficial to the understanding of the mechanism of self-propulsion and the development in its potential applications.
Investigation on the viscoelastic behavior of an Fe-base bulk amorphous alloys based on the fractional order rheological model
Authors: Liao Guang-Kai  , Long Zhi-Lin  , Xu Fu  , Liu Wei  , Zhang Zhi-Yang  , Yang Miao  ,   College of Civil Engineering and Mechanics, Xiangtan University, Xiangtan 411005, China
Published: December 2020

Combined with the microstructure evolution in amorphous alloys under the external load, a fractional order viscoelastic constitutive model is first derived by replacing a Newtonian dashpot in the classical Zener model with the fractional derivative Abel dashpot. Based on the Hertzian theory and the fractional order viscoelastic constitutive model, a relationship between displacement and load (or time) for an instrumental nanoindentation test with a spherical indenter is then proposed. Finally, a series of nanoindentation test data for an Fe-base bulk amorphous alloy are employed to verify the derived model, and its viscoelastic behavior in the apparent elastic region is analyzed in detail. Results show that the fractional order rheological model has higher fitting accuracy than that of the integer order model, and the fitting parameters of the proposed model are more suitable to reflect the effect of the loading rate on the viscoelastic behavior in the alloy studied. Variation of the above-mentioned fitting parameters exhibits a strong correlation with the microstructure evolution during the loading of this Fe-base amorphous alloy.
Single event transients in a 0.18 m partially-depleted silicon-on-insulator complementary metal oxide semiconductor circuit
Authors: Zhao Xing  , Mei Bo  , Bi Jin-Shun  , Zheng Zhong-Shan  , Gao Lin-Chun  , Zeng Chuan-Bin  , Luo Jia-Jun  , Yu Fang  , Han Zheng-Sheng  ,   Institute of Microelectronics of Chinese Academy of Sciences, Beijing 100029, China
Published: December 2020

Single event transients (SETs) in a 100 series 0.18 m partially- depleted silicon-on-insulator (PDSOI) complementary metal oxide semiconductor (CMOS) inverter chain are studied by using pulsed laser. In this paper, effects of struck transistor type and struck locations on the threshold laser energy and the pulse width of SETs are investigated. Results show that the threshold laser energies at different locations are similar, but the threshold laser energies of n-channel metal-oxide-semiconductor (NMOS) transistors are much smaller than that of p-channel metal-oxide-semiconductor (PMOS) transistors. The SET pulse width of n-channel metal-oxide-semiconductor field-effect transistor (NMOSFET) is 427.5 ps as measured at the output terminal when the 2nd stage is irradiated, and 287.4 ps when the 100th stage is irradiated; the SET pulse width of p-channel metal-oxide-semiconductor field-effect transistor (PMOSFET) is 295.9 ps as measured at the output terminal when the 1st stage is irradiated, and 150.5 ps when the 99th stage is irradiated. Both broadening rates are about 1.4 ps/stage. When the struck locations are close to the output terminal of the chain, the SET pulse is narrowed; however, when the struck nodes are close to the input terminal, the SET pulse is broadened. SET pulses are progressively broadened up when propagating is along inverter chains. A similar broadening rate in neither NMOSFET nor PMOSFET, indicates that the SET pulse broadening effect is caused by propagation, independent of the type of struck transistors. Through analysis, the charge of floating body-induced threshold voltage hysteresis in PDSOI transistors is the main cause of pulse broadening. The positive SET pulse observed on the oscilloscope, contrary to the expectation, is due to charging and discharging of the output node capacitor. Also, the observed sub-rail-to-rail swings of the SET pulses are due to the voltage division between the internal resistance of the oscilloscope and the resistance of the PMOS transistor.
Quantitative separation of radiation induced charges for NPN bipolar junction transistors based on 1/f noise model
Authors: Zhao Qi-Feng  , Zhuang Yi-Qi  , Bao Jun-Lin  , Hu Wei  ,   School of Microelectronics, Xidian University, Xi'an 710071, China;,   School of Electro-mechanical Engineering, Xidian University, Xi'an 710071, China
Published: December 2020

Ionizing-radiation-induced oxide-trapped charges and interface states cause the current and 1/f noise degradation in bipolar junction transistors. In order to better understand these two degradation mechanisms and develop hardening approaches for a specific process technology, it is necessary to measure the effect of each mechanism separately. In recent years, several techniques have been developed, but no charge-separation approach based on 1/f noise for NPN bipolar junction transistors is available. In this paper, the effects of ionizing-radiation-induced oxide trapped charges and interface states on base current and 1/f noise in NPN bipolar junction transistors are studied in detail. Firstly, a new model of base surface current of NPN bipolar junction transistors is presented with some approximations, based on an available model for the base surface current under certain conditions; this model can identify the physical mechanism responsible for the current degradation. Secondly, combining the theory of carrier number fluctuation and the new model of base surface current another model is developed which can well explain the 1/f noise degradation. This model suggests that the induced oxide-trapped charges would make more carriers, involving the dynamic trapping-detrapping, which leads to the 1/f noise to increase; and the induced oxide-trapped charges and interface states can also bring about an increase in base surface current which can also cause the l/f noise increase. These two models suggest that the current and1/f noise degradations can be attributed to the same physical origin, and these two kinds of degradations are the result of accumulation of oxide-trapped charges and interface states. According to these two models, simple approaches for quantifying the effects of oxide-trapped charges and interface states are proposed. The base surface current can be extracted from the base current using the available method. The oxide-trapped charge density is estimated using the amplitude of 1/f noise (10-100 Hz) and the base surface current. Given the estimated oxide-trapped charge density, the interface state density can be estimated using the base surface current. These methods are simple to implement and can provide insight into the mechanisms and magnitudes of the radiation-induced damage in NPN bipolar junction transistors.
Effect of 170 keV proton irradiation on structure and electrical conductivity of multi-walled carbon nanotubes film
Authors: Yang Jian-Qun  , Li Xing-Ji  , Ma Guo-Liang  , Liu Chao-Ming  , Zou Meng-Nan  ,   School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China
Published: December 2020

Due to their unusual electrical conductivity, carbon nanotubes as the ideal candidates for making future electronic components have extensive application potentiality. In order to meet the requirements in space electronic components for carbon nanotubes, effect of 170 keV proton irradiation on structure and electrical conductivity of multi-walled carbon nanotubes (MWCNTs) film is investigated in this paper. Surface morphologies and microstructure of the carbon nanotube films are examined by scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) spectroscopy, respectively. Electrical conductivities of the carbon nanotube films before and after 170 keV proton irradiation are measured using four-point probe technique. SEM analysis reveals that when proton irradiation fluence is greater than 51015 p/cm2, the surface of the carbon nanotube film becomes rough and loose, and obvious bending, shrinkage, and entanglement of nanotubes are observed. Moreover, the shrinkage phenomenon of MWCNTs caused by proton irradiation is found the first time so far as we know. Based on Raman and XPS analyses, it is confirmed that 170 keV protons can improve the ordered structure of the MWCNTs, and irradiation fluence plays a key role in reducing the disorder in the MWCNTs. Improvement of the irradiated MWCNTs by 170 keV protons can be attributed to restructuring of defect sites induced by knock-on atom displacements. On the other hand, carbon impurities on surface of the MWCNT film are reduced due to the effect of sputtering by the 170 keV proton irradiation, which is also helpful to the improvement of the structure of carbon nanotubes. EPR spectra show that the electrons delocalized over carbon nanotubes decrease with increasing irradiation fluence, implying that the carbon nanotube film is not sensitive to ionizing radiation induced by the 170 keV protons, and the electrical conductivities of the MWCNTs films may be decreased. Four-point probe technical analysis shows that with increasing irradiation fluence, electrical properties of the carbon nanotubes film deteriorate, which can be attributed to the changes in electronic properties and morphology of the MWCNT films induced by 170 keV protons. Acquired results could be beneficial to tailoring of structure and properties for the carbon nanotubes film irradiated by protons to develop nanoelectronics of radiation-resistant systems.
Permeability of cracked porous solids through percolation approach
Authors: Li Le  , Li Ke-Fei  ,   Key Laboratory of Structure Safety and Durability of China Education Ministry; Department of Civil Engineering, Tsinghua University, Beijing 100084, China
Published: December 2020

This paper investigates the permeability of microcracked porous solids incorporating random crack networks in terms of continuum percolation theory. Main factors of permeability include the geometry of crack networks, permeability of porous matrix, and crack opening. For the two-dimensional random crack networks, a new connectivity factor is defined to take into consideration the spanning cluster of cracks, fractal dimension of networks, and the size of a finite domain. For an infinite domain, the connectivity factor around a percolation threshold observes the scaling law, so this definition of connectivity is proved to be consistent with the percolation concepts. Geometric analysis reveals that the local clustering will not necessarily contribute to the global connectivity of networks. It is also found that too strong a local clustering of cracks will decrease the probability of the global percolation, and this adverse aspect of the local clustering effect has never been reported in the literature. The percolation threshold changes with the crack pattern of networks and the scaling exponents of percolation are not constant but depend on the fractal dimension of the crack networks. On the basis of connectivity and tortuosity of crack networks, the scaling law for permeability is established, K=K0(Km,b)(-c), taking into consideration the geometris characteristics through (-c), the permeability of porous matrix Km, and the crack opening aperture b. Then the permeability of a solid incorporating random crack networks is solved by finite element methods: all the cracks are idealized as 2-node elements and the matrix is divided into 6-node triangle elements. The fluid is assumed to be incompressible and Newtonian. With these assumptions the effective permeability of numerical samples is evaluated through Darcy's law. The scaling exponents of the permeability obtained numerically are very near to the theoretical values, and the impact of crack opening is less important as the crack density is far below the percolation threshold and the effect of crack opening becomes significant only as the crack density approaches the percolation threshold. Influence of crack opening on the permeability is strongly dependent on the opening aperture of the cracks. Finite element simulation results show that K0 depends on b through a power law near the percolation threshold and this dependence disappears as the ratio between the local permeability of crack and the matrix permeability exceeds 106.
A technique for extracting the density of states of the linear region in an amorphous InGaZnO thin film transistor
Authors: Xu Piao-Rong  , Qiang Lei  , Yao Ruo-He  ,   School of Electronic and Information Engineering, South China University of Technology, Guangzhou 510640, China
Published: December 2020

Defects and weak bonds generated in the fabricating process of amorphous InGaZnO(a-IGZO) films distribute non-uniformly in the band gap of the a-IGZO film in the form of traps. These traps would capture the charges induced by gate voltage, and affect the linear region mobility, channel carrier density and so on, then the electrical properties in the linear region of a-IGZO thin film transistor. The model used is based on the mobility in linear region which is in direct proportion to the ratio of the free charge to the total induced charge in the channel, and then the free charge and the trapped charge are separated. From the ratio of the density of free carriers to that of the trapped, a direct relationship with the derivative of the free charge with respect to surface potential, and the derivative of the trapped charge with respect to surface potential is calculated by bringing in the gate voltage that serves as an intermediate variable between the linear region mobility and the total induced charge. In this way, the free carrier density and the trapped carrier density can be separated by using the transfer characteristic and capacitor-voltage characteristic. Poisson's equation and Gauss theorem are applied to the interface between the channel layer and the insulating layer. In consideration of the non-uniform characteristic between the surface potential and the gate voltage, the relationship between the free carrier density and the surface potential, the trapped carrier density and the surface potential are obtained. Finally, the density of states in the linear region could be gained by differentiating the trapped carrier density with respect to surface potential.
Preparation and gas-sensing properties of the silver nanoparticles/porous silicon composite
Authors: Yan Da-Li  , Li Shen-Yu  , Liu Shi-Yu  , Zhu Yun  ,   College of Physics and Materials Science, Tianjin Normal University, Tianjin 300387, China;,   School of Marine Science and Engineering, Hebei University of Technology, Tianjin 300401, China
Published: December 2020

The p-type porous silicon layer with the aperture about 1.5 microns and hole depth about 15-20 microns is prepared by electrochemical etching of a p-type monocrystalline silicon wafer with a resistivity 10-15 Ω·cm and along [100] orientation in a double-tank cell which consists of the electrolyte (volume ratio HF: DMF=1:2). Silver nanoparticles film with different thickness has been deposited on porous silicon by the electroless deposition for different deposition times. Morphology and microstructure of the silver nanoparticles/porous silicon composite are studied by scanning electron microscope and X ray diffracmeter. Result indicates that the silver nanoparticles are uniformly distributed on the surface of porous silicon and the deposition time has an important influence on the morphology of the composite. The gas-sensing properties of the silver nanoparticles/porous silicon composite to NH3 are tested at room temperature by the static volumetric method. Results show that the deposition time has a significant impact on the gas-sensing properties of the silver nanoparticles/porous silicon. In a short deposition time, the composite with an appropriate amount of silver nanoparticles doped on the porous silicon shows good gas-sensing properties to NH3 with high sensitivity, fast response-recovery characteristic due to the high specific surface area and special microstructure. At room temperature, the gas sensor has a sensitivity of about 5.8 to 50 ppm NH3.
Compressive behavior of nanocrystalline nickel at various temperatures and strain rates
Authors: Yang Jian-Qun  , Ma Guo-Liang  , Li Xing-Ji  , Liu Chao-Ming  , Liu Hai  ,   School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China
Published: December 2020

In this paper, compressive behavior of electrodeposited nano-crystalline (nc) Ni at various temperatures and strain rates is studied using a low temperature mechanic test system. Plastic deformation mechanisms of nc Ni caused by compression are characterized by the strain rate sensitivity index, the activation volume, and examined by scanning electron microscopy and high resolution transmission electron microscopic analysis. Results show that at low temperatures, the plastic deformation of nc Ni is mainly dominated by grain boundary accommodated dislocations. In other words, during plastic deformation of nc Ni at low temperatures, the intrinsic dislocation at the grain boundary bends up and expands without obstacles to the opposite grain boundary in the inner grain dislocation-free zone, until the occurrence of similar cutting forest-dislocation behavior appearing at opposite grain boundary. Moreover, the residual dislocations in the grain boundary bending out during plastic deformation could increase the strain compatibility and decrease the stress concentration. At room temperature, the plastic deformation mechanism of nc Ni is controlled by the deformation of grain boundary accommodated dislocations and grain slipping/rotating. Based on the above analyses, differences in compressive behavior of nc Ni at various temperatures and strain rates can be revealed by the correlation of deformation mechanisms of grain boundary accommodated dislocations and residual dislocation movement, temperature and defects in nc Ni.
Preparation and gas-sensing properties of the silver nanoparticles/porous silicon composite
Authors: Yan Da-Li  , Li Shen-Yu  , Liu Shi-Yu  , Zhu Yun  ,   College of Physics and Materials Science, Tianjin Normal University, Tianjin 300387, China;,   School of Marine Science and Engineering, Hebei University of Technology, Tianjin 300130, China
Published: December 2020

The p-type porous silicon layer with the aperture about 1.5 microns and hole depth about 15 microns is prepared by electrochemical etching of a p-type monocrystalline silicon wafer with a resistivity 10-15 cm and along [100] orientation in a double-tank cell which consists of the electrolyte (volume ratio HF: DMF=1:2). Silver nanoparticles film with different thickness has been deposited on porous silicon by the electroless deposition for different deposition times. Morphology and microstructure of the silver nanoparticles/porous silicon composite and ere studied by scanning electron microscope and X ray diffracmeter. Result indicates that the silver nanoparticles are uniformly distributed on the surface of porous silicon and the deposition time has an important influence on the morphology of the composite. The gas-sensing properties of the silver nanoparticles/porous silicon composite to NH3 are tested at room temperature by the static volumetric method. Results show that the deposition time has a significant impact on the gas-sensing properties of the silver nanoparticles/porous silicon. In a short deposition time, the composite with an appropriate amount of silver nanoparticles doped on the porous silicon shows good gas-sensing properties to NH3 with high sensitivity, fast response-recovery characteristic due to the high specific surface area and special microstructure. At room temperature, the gas sensor has a sensitivity of about 5.8 to 50 ppm NH3.
Stability of magnetization states in a ferromagnet/heavy metal bilayer structure
Authors: Wang Ri-Xing  , He Peng-Bin  , Xiao Yun-Chang  , Li Jian-Ying  ,   College of Electrical and Information Engineering, Hunan University of Arts and Science, Changde 415000, China;,   School of Physics and Electronics, Hunan University, Changsha 410082, China
Published: December 2020

The influence of spin Hall effect on magnetization dynamics is one of the hottest topics in spintronics. In this paper, the magnetization dynamics driven by the spin Hall effect-induced torque in a ferromagnet /heavy metal bilayer structure has been investigated theoretically. By linearizing the Landau-Lifshitz-Gilbert equation which includes the spin Hall effect torque term, and taking stability analysis, the phase diagrams in the plane defined by the current density and external magnetic field have been obtained. Under the control of the current density and external magnetic field, several magnetic states, such as in-plane stable state, in-plane precession and bistable states can be realized. With the external magnetic field oriented within a certain range, the magnetization reversal and precession can be realized through adjusting the current density. In addition, the dynamic evolutions of these magnetic states are demonstrated by solving the temporal evolutive equations numerically.
Application of semiconductor quantum dots to white-light-emitting diodes
Authors: Gao Xiao-Qin  , Zhuo Ning-Ze  , Wang Hai-Bo  , Cui Yi-Ping  , Zhang Jia-Yu  ,   School of Electronic Science and Engineering, Advanced Photonics Center, Southeast University, Nanjing 210096, China;,   Research Institute of Electric Light Source Materials, Nanjing University of Technology, Nanjing 210015, China
Published: December 2020

Based on the electro-optical energy transfer process, the pseudo-spectral-luminous efficiency function (QD) of quantum dots (QDs) is introduced, the equations of chromaticity coordinates, luminous efficiency, and the QDs' mass of the white-light-emitting devices with CdSe, CuInS2 or CdS:Mn QDs are obtained, and the calculated results are in agreement with the experimental data. For a certain luminescent peak wavelength, when the full width at half maximum of the QD's photoluminescence becomes larger, the QD value becomes smaller while the chromaticity coordinates become more different from those of the corresponding monochromatic light. It is indicated that the color rendering index (CRI) of the devices is strongly dependent on the photoluminescent position and width of the QDs, and the CRI value can be increased towards 98 when a certain kind of CdS:Mn QDs is added into the traditional white-light LEDs.
Calculation of coherent X-ray diffraction from bent Cu nanowires
Authors: Gao Feng-Ju  ,   Department of Mathematics and Physics, Shijiazhuang TieDao University, Shijiazhuang 050043, China;,   Institute of Applied Physics, Shijiazhuang TieDao University, Shijiazhuang 050043, China
Published: December 2020

A method of calculating coherent X-ray diffraction from a bent nanowire, simulated by the molecular dynamics technique under the bent periodic boundary condition, is reported. The segment of nanowire under the X-ray beam consists of the central box and 2N image boxes. X-ray diffraction from this segment of nanowire is obtained from a single calculation of the amplitude of diffraction from the atoms in the central box according to the kinematic theory. Contributions from the image boxes are then obtained by rotations of this amplitude in the reciprocal space and additional phase factors to take into account the position of the image boxes with respect to the central box. This method will be called rotation in the reciprocal space (RRS). Comparison between the RRS and the full calculation of the diffracted amplitude from all the atoms in the central box and the 2N image boxes (full kinematic sum) is done in the Cu nanowire case. The bending of an FCC Cu nanowire oriented along a direction with an equilibrium shape made up of {100} and {111} facets is calculated by using the SMA (The second-moment approximation of the density of states in the tight-binding formalism) potential. The Cartesian x, y, and z axes correspond, respectively, to [112], [111] and [110] directions. The bending occurs in the y-z plane. The calculation time of the RRS method is about 1/(2N+1) times that obtained by doing the full kinematic sum, the RRS method being more efficient when the number of image boxes N is a bigger one. A very small difference in the calculated intensity between the RRS and the full kinematic sum comes from the interpolation in the reciprocal space. So the RRS method is more accurate, when there are more points calculated in the reciprocal space. Similarly, the RRS method can be applied to tension, compression and torsion of the nanowires, When using the molecular dynamics simulation under periodic boundary conditions. In the cases of tension and compression, it is simpler as only the phase factors have to be considered. Results are also reported in this paper.
Analysis of epitaxial morphology evolution due to stress and diffusion
Authors: Chen Zhen-Fei  , Feng Lu  , Zhao Yang  , Qi Hong-Rui  ,   Tianjin Key Laboratory of Modern Engineering Mechanics, Tianjin 300072, China;,   Department of Mechanics, Tianjin University, Tianjin 300072, China
Published: December 2020

In this paper, a new phase-field model based on diffusion interface is put forward to describe the epitaxial growth including island nucleation, growth, and ripening. Thermodynamics and kinetics play an important role in epitaxial morphology evolution. This model includes combined effects of the following processes, such as elastic field, surface energy, deposition, diffusion, desorption, and energy barrier etc. We use the classical BCF model to describe the atomic diffusion and nucleation processes, and use a new free energy function, including elastic strain energy, to obtain a phase-field equation that can describe the growth of dynamic multi-island by variation method. This model can effectively simulates the complex morphology in epitaxial growth. The nonlinear coupled equations can be solved by finite difference scheme. Numerical result shows that this model can reproduce the real multilayer epitaxial growth structure, and the simulation results are consistent with the experimental results. At the same time we also simulate the complex growth stress with morphology evolution. Results show that, accompanied with the epitaxial growth, a complex stress distribution is produced, and the stress reaches a local maximum on the boundaries of the island, which is consistent with the experimental results. Most importantly, the stress significantly affects the atomic diffusion process. While the stress exists, the epitaxial structure will change faster. These results can make a significance effect on the research of physical mechanism in epitaxial growth.
Structure and optical property of Cr-O films deposited by pulsed bias arc ion plating
Authors: Liu Hai-Yong  , Zhang Min  , Lin Guo-Qiang  , Han Ke-Chang  , Zhang Lin  ,   Key Laboratory of Materials Modification by Laser, Ion and Electron Beams, Dalian University of Technology, Minstry of Education, Dalian 116085, China;,   Liaoning Normal University, School of Physics and Electronic Technology, Dalian 116029, China
Published: December 2020

A series of uniform and transparent Cr-O films were synthesized on the silicon and quartz glass substrates at different bias voltages by pulsed bias arc ion plating. Effects of bias voltage on surface morphology, phase structure, composition, chemical valence states, hardness and optical property of the films were investigated by field emission scanning electron microscopy, grazing incident X-ray diffraction, X-ray photoelectron spectroscopy, nanoindentation and ultraviolet-visible spectrophotometer, respectively. Results indicate that the bias voltage can improve the quality of the films significantly and plays an important role in the film properties. Macroparticles and holes are observed on the surface of the films if without application of bias voltage, while the films prepared with bias voltage are uniform and smooth. The crystalline phase of the film is of amorphous structure if without bias voltage. While the bias voltage applies and increases from -100 V to -500 V, the Cr2O3 phase appears and changes into CrO phase. The crystal plane (104), (116) of the Cr2O3 phase and (200) of the Cr phase are observed in the film at the bias voltage of -100 V. When the bias voltage is above -200 V, the crystal planes (311) and (400) of the CrO phase can be observed. In order to further obtain the structure information, a detailed XPS study is performed. Chromium in the films shows different valence states, namely metallic Cr, Cr2+, Cr3+ and Cr6+. Thereby, the main components of the polycrystalline films are Cr2O3 and CrO phases, meanwhile, and the films also contain a small amount of CrO3 and metal Cr phases. The films under different bias voltage show good mechanical properties and the hardness of all the films is above 19 GPa. With the increase of bias voltage the hardness first increases and then decreases, reaching a maximum value of 24.4 GPa at the bias voltage of -300 V. The films show good optical transmittance and its highest value can be up to 72%. As the bias voltage rises, it is observed first the red shift and then blue shift of the absorption edge. And the optical band gap reaches the maximum value of 1.88 eV when the bias voltage is -200 V. Therefore, Cr-O functional films can be synthesized by pulsed bias arc ion plating and the phase structure and properties can be effectively adjusted.
Channel allocation game algorithm based on lifetime model in wireless sensor network
Authors: Hao Xiao-Chen  , Yao Ning  , Ru Xiao-Yue  , Liu Wei-Jing  , Xin Min-Jie  ,   School of Electrical Engineering, Yanshan University, Qinhuangdao 066004, China
Published: December 2020

In wireless sensor network, the lager interference makes the data transmission failed, thus leading to data retransmission of nodes. This situation exacerbates the energy consumption of retransmission. As a result, some nodes will prematurely fail to work, thus reducing the network lifetime. In order to deal with the above issue, this paper takes full advantage of the topology and route information to design a novel load model of nodes. Then, a lifetime model of each node is constructed based on the load model. Subsequently, the path gain, intersecting interference and node lifetime are integrated into a utility function to construct a channel allocation game model called channel allocation based-game (CABG) by taking advantage of the game theory. The theoretical analysis proves the existence of the Nash Equilibrium of CABG. And then, using the best response dynamics, a channel allocation game algorithm for anti-interference and lifetime optimization (CAGLO) is established based on CABG. This algorithm CAGLO makes nodes avoid selecting the same channel as the large intersecting interference nodes and shorter-lifetime nodes in the process of channel selection, thus realizing the channel selection with less interference, less and balanced energy consumption. The theoretical analysis and simulation results show that the algorithm CAGLO could converge to the Nash Equilibrium with a good convergence speed finally. And the algorithm CAGLO has less message complexity. As a result, the algorithm itself has less energy consumption of communication. At the same time, it has good characteristics of anti-interference, energy consumption equilibrium and channel equalization. The algorithm CAGLO proved in this paper prolongs the network lifetime effectively.
Thermodynamic properties of harmonic oscillator system in noncommutative phase space
Authors: Aili Mieralimujiang  , Mamat Mamatrishat  , Ghupur Yasenjan  ,   School of Physics Science and Technology, Xinjiang University, Urumqi 830046, China
Published: December 2020

In the last 15 years, noncommutative effects have received much attention and have been extensively studied in the fields of quantum mechanics, field theory, condensed matter physics, and astrophysics. The aim of this paper is to investigate the thermodynamic properties of a harmonic oscillator system in noncommutative phase space. For an example, the effects of noncommutativity between positions and that between momenta in the phase space on thermodynamic properties of two- and three-dimensional harmonic oscillator system are studied by a statistical method. First, in the commutative phase space, the thermodynamic state functions are obtained from the partition functions of the harmonic oscillator system which satisfies Boltzmann statistics. Then, in the noncomummutative phase space, both noncommutative positions and noncommutative momenta are represented in terms of the commutative positions and momenta of the usual quantum mechanics by linear transformation method. Meanwhile, the other physical quantities such as the volume element, the number of microstates, and partition function in the noncommutative phase space are represented in terms of commutative positions and momenta. Finally, the thermodynamic and statistical state functions for the system in the noncommutative phase space are derived from the partition function, and the thermodynamic state functions in noncummutative and commutative phase spaces are compared with each other. The results show that the noncommutative effect changes the values of microscopic functions such as the partition function and entropy with the correction terms including noncummutative parameters. As the noncommutative parameters vanishes, i.e., reaches the commutative limit, the partition and entropy functions of the system coincide with the results of usual thermodynamics and statistical physics. Moreover, the macroscopic state functions such as the internal energy and heat capacity, remain constant. The results imply that the correction terms in the partition function and entropy may result from the corrections of the number of microstates and potential energy of the system by noncommutativity of the position and momentum. In conclusion, the method used in the paper is corresponding to the classical system that satisfies Boltzmann statistics, and the results derived here can provide a starting point for further studying the quantum system that satisfies Fermi-Dirac and Bose-Einstein statistics.