bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermodynamic analysis of lubrication considering solid-liquid interface interaction
Authors: Jing Hao-Da  , Zhang Xiang-Jun  , Tian Yu  , Meng Yong-Gang  ,   State Key Laboratory of Tribology, Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China
Published: December 2020

Friction or lubrication process is a typical process of the energy dissipation. It can be reasonably described and speculated by using the entropy increase and dissipative structure theory of the non-equilibrium thermodynamics. In this paper, we model and analyze the typical thin-film lubrication mechanism based on the theory of thermodynamics, by using the interfacial disjoining pressure to characterize the dominant role of the solid-lubricant interaction on a microscale and establishing the lubrication Stribeck curve based on thermodynamic concepts. The concept of entropy production is adopted to describe the lubrication system, which is defined as the sum of multiplications of the thermodynamic forces and flows. Then the variations and the competing relations between the pairs of thermodynamic forces and flows could be used to reveal the different factors dominated in the lubrication system, such as the solid-liquid interaction, the sliding velocity, and the normal load. In this paper, we assume that all the dissipated energy caused by the viscous resistance of lubricant is converted into heat, then the total entropy increase per surface area at the frictional interface is considered, affected by interfacial disjoining pressure and the one-dimensional heat flow. With the entropy increasing analysis of lubrication process, we find that when the entropy production in the steady state becomes minimum, the total energy dissipation due to friction also becomes minimum, which directly indicates the lowest friction coefficient point at the lubrication Stribeck curve. Moreover, when a lubrication system loses its stability slightly from the equilibrium state, self-organization may occur at the solid-lubricant interface, thus resulting in partially ordering interfacial structures, which may indicate the interfacial structures when tribosystem turns from hydrodynamic lubrication phase into thin-film lubrication phase. In the experimental aspect, the location of the lowest friction coefficient point at the Stribeck curve has a very good correspondence to the minimum entropy point predicted by our thermodynamic model, and the lubrication transition process from hydrodynamic phase to thin-film phase can be explained quite well by the theory of dissipative structures when the system loses its stability. Furthermore, a calculation model of the friction coefficient for thin-film lubrication is obtained when considering the dominant contribution of the solid-lubricant interfacial interaction through an equivalent force method. The calculation data correspond well to the experimental results. In summary, thermodynamic model could effectively characterize the lubrication process in mechanism by revealing the involved multi-scale effect, multi-physical effect and nonlinear coupling effect.
Principal component analysis of terahertz spectrum on hemagglutinin protein and its antibody
Authors: Sun Yi-Wen  , Zhong Jun-Lan  , Zuo Jian  , Zhang Cun-Lin  , Dan Guo  ,   National-Regional Key Technology Engineering Laboratory for Medical Ultrasound, Guangdong Key Laboratory for Biomedical Measurements and Ultrasound Imaging, Department of Biomedical Engineering, School of Medicine, Shenzhen University, Shenzhen 518060, China;,   Department of Physics, Capital Normal University, Beijing 100048, China
Published: December 2020

One has proved that the collective structural vibrational modes of proteins are in the terahertz (THz) frequency range. These frequencies relate to the polypeptide backbone and are thought to be essential for conformational dynamics necessary for protein function. Hemagglutinin (HA) is the main surface glycoprotein of the influenza A virus. The H9N2 subtype influenza A virus is recognized as the most possible pandemic strain as it crosses the species barrier, infects swine and humans. In this paper we use principal component analysis (PCA) to study the 7 different concentrations dependent terahertz spectra of hemagglutinin proteins, and detect the binding interaction of HA with the broadly neutralizing monoclonal antibody F10 in liquid phase. Spectrum pretreatment and band selection play a vital role in the THz spectroscopic analysis due to the fact that the original spectrum contains a large amount of interference information. In order to compress variables and extract useful information, we use a variety of pretreatment methods, such as second derivative, multiplicative scatter correction (MSC), least square polynomial fitting derivation, standard normalization, smoothing, moving window median filtering before PCA analysis. We even consider MSC + smoothing + SG second derivative + median filtering as the optimized pretreatment method finally. THz spectrum parameters including refractive index, absorption coefficient, reduced absorption cross-section and dielectric loss angle tangent are calculated in a frequency range of 0.1-1.4 THz for comparison. The results indicate that the reduced absorption cross-section presents the highest correlation response to the concentration variation of HA protein, and the dielectric loss angle tangent appears to be more appropriate for qualitative analysis of HA-antibody binding interaction. PCA method provides a feasible and effective way to find the sensitive parameters for further analyzing the function of protein and the antigen-antibody interaction using terahertz spectrum, whereas an appropriate pretreatment method is required.
Plastic deformation in nanoporous aluminum subjected to high-rate uniaxial compression
Authors: Diwu Min-Jie  , Hu Xiao-Mian  ,   Graduate School, China Academy of Engineering Physics, Beijing 100088, China;,   National Lab of Computational Physics, Beijing Institute of Applied Physics and Computational Mathematics, Beijing 100088, China
Published: December 2020

The mechanical behavior of nanoporous monocrystal aluminum subjected to uniaxial compressive loading at a rate of 2109 s- 1 along [110] crystallographic orientation is studied using molecular dynamics simulations. Subjected to such a loading, nanovoids act as the effective sources of dislocation nucleation and emission, four of the twelve {111}110 slip systems may be activated. With the same strain of 3.8%, dislocation nucleation will occur in both the sample of multiple voids and that with a single void. The configuration of multiple voids decreases the required stress for the onset of dislocation nucleation and emission in comparison with the sample with an isolated void of the same size. Because of the emission of trial partials, the accumulation of dislocation density can be changed into a piecewise linear process by the dislocation density propagation rate dd/d: in the initial stage of plastic deformation we obtain dd/d1.071018 m-2, but this changes to dd/d5.361018 m-2 at higher deformation. The velocity of dislocation is calculated to be subsonic and is a variable value during the plastic deformation. Dislocation loop pairs emit from the same void, glide and approach to each other, leading to the reduction of dislocation velocity. Then one loop of each pair continues to glide to intersect mutually and finally interact with the loops emitted from other voids, causing a strain hardening to reach the peak flow stress of 4.3 GPa. There is a post-yield softening corresponding to the onset of rapid dislocation density proliferation at higher dislocation densities. With the temperature evolution of the sample with multiple voids during plastic deformation, the density of mobile dislocations is calculated to be one magnitude lower than the total dislocation density. There is a decrease of mobile dislocation densities at large strains, showing that the mobile dislocation are diminished by the formation of dislocation forest and junctions. At the onset of their nucleation, the dislocations are all Shockley partials, however, when dislocation intersection happens, the majority are still Shockley partials, while the rest consists of Frank partials, perfect fcc dislocations and other dislocation ingredients. Voids collapse at the strain of 11.8%. No twins are found in the present simulation due to the high stacking-fault energy of aluminum. Prismatic dislocation loop emission is observed in this simulation.
Inverse problem of Mei symmetry for a general holonomic system
Authors: Huang Wei-Li  ,   College of Communication and Electronic Engineering, Hunan City University, Yiyang 413000, China
Published: December 2020

Inverse problems in dynamics are the basic problems in astronautics, rocket dynamics, and motion planning theory, etc. Mei symmetry is a kind of new symmetry where the dynamical function in differential equations of motion still satisfies the equation's primary form under infinitesimal transformations of the group. Mei symmetry and its inverse problem of dynamics for a general holonomic system in generalized coordinates are studied. Firstly, the direct problem of dynamics of the system is proposed and solved. Introducing a one-parameter infinitesimal transformation group with respect to time and coordinates, the infinitesimal generator vector and its first prolonged vector are obtained. Based on the discussion of the differential equations of motion for a general holonomic system determined by n generalized coordinates, their Lagrangian and non-potential generalized forces are made to have an infinitesimal transformation, the definition of Mei symmetry about differential equation of motion for the system is then provided. Ignoring the high-order terms in the infinitesimal transformation, the determining equation of Mei symmetry is given. With the aid of a structure equation which the gauge function satisfies, the system's corresponding conserved quantities are derived. Secondly, the inverse problem for the Mei symmetry of the system is studied. The formulation of the inverse problem of Mei symmetry is that we use the known conserved quantity to seek the corresponding Mei symmetry. The method is: considering a given integral as a Noether conserved quantity obtained by Mei symmetry, the generators of the infinitesimal transformations can be obtained by the inverse Noether theorem. Then the question whether the obtained generators are Mei symmetrical or not is verified by the determining equation, and the effect of generators' changes on the symmetries is discussed. It has been shown from the studies that the changes of the generators have no effect on the Noether and Lie symmetries, but have effects on the Mei symmetry. However, under certain conditions, while adjusting the gauge function, changes of generators can also have no effect on the Mei symmetry. In the end of the paper, an example for the system is provided to illustrate the application of the result.
Study on composite electromagnetic scattering from the double rectangular cross-section columns above rough sea surface using hybrid method
Authors: Tian Wei  , Ren Xin-Cheng  , Guo Li-Xin  ,   School of Physics and Electronic Information, Yan'an University, Yan'an 716000, China;,   School of Physics and Optoelectronic Engineering, Xidian University, Xi'an 710071, China
Published: December 2020

The actual rough sea surface is described by Pierson-Moscowitz (PM) spectrum and Monte Carlo method; the composite electromagnetic scattering from the double rectangular crosssection conductor columns above the rough sea surface is investigated using the hybrid methodthe Method of Moment with the Kirchhoff approximation. Angular distribution curves of composite scattering coefficient are obtained; and this coefficient that varies with the parameter of sea surface, rectangular cross-section conductor columns and incident waves is calculated in detail. The characteristics of the composite scattering coefficient from the double rectangular cross-section conductor columns above the rough sea surface are also obtained. Results show that the hybrid methodthe Method of Moment with the Kirchhoff approximation, compared to the traditional Method of Moment, can obtain higher accuracy. Moreover, the hybrid method can effectively reduce the computation time and memory footprint, and the performance becomes more favorable with the increase of the sizes of rough surface.
A diode pumped passively Q-switched Nd:LuYAG laser emitting at 1123 nm
Authors: Liu Yang  , Liu Zhao-Jun  , Cong Zhen-Hua  , Xu Xiao-Dong  , Xu Jun  , Men Shao-Jie  , Xia Jin-Bao  , Zhang Sa-Sa  ,   School of Information Science & Engineering and Shandong Provincial Key Laboratory of Laser Technology and Application, Shandong University, Jinan 250100, China;,   Key Laboratory of Transparent and Opto-functional Inorganic Materials, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China
Published: December 2020

A diode pumped passively Q-switched 1123 nm laser is reported in this paper; and a mixed crystal Nd:LuYAG is selected as the gain medium. A large number of excellent properties from Nd:YAG are obtained, and the mixed crystal Nd:LuYAG has been used widely in all-solid-state lasers. Besides, compared with Nd:YAG, the Nd:LuYAG has some other wonderful advantages. For example, both the absorption bands and the fluorescence line are broadened, resulting from the crystal strong inhomogeneity. Their wide absorption makes the Nd:LuYAG lasers' pump source not rigorous in their temperature control. And the broadened fluorescence line can generally improve the laser performance in Q-switched regimes. In this paper, a concave-plane configuration cavity with its length as long as 35 mm is designed to achieve high-efficiency laser output. The rear mirror is a concave mirror with a curvature radius of 300 mm, and the output coupler is a flat mirror with a transmission of 2% at 1123 nm, 5% at 1112 nm, 4% at 1116 nm, and has high transmissions at 1064, 1319 and 1444 nm respectively. A Cr4+:YAG crystal, with its initial transmission of 97%, is used as the saturable absorber. In the continuous wave operation, the maximum average output power can reach 2.77 W, with the corresponding optical-to-optical conversion efficiency of 29.53%. In Q-switched operation, the maximum average output power is 0.94 W at 9.38 W absorbed pump power. The repetition rate is 9.40 kHz, with the corresponding single pulse energy being 100 J. The high single-pulse energy explains that the Nd:LuYAG mixed crystal is better than Nd:YAG in high energy storage. Only one wavelength can be observed in our experiment. The center wavelength is 1122.7 nm and the line width is 0.03 nm. To the best of our knowledge, this is the first time to report the Nd:LuYAG mixed crystal laser emitting at 1123 nm.
Coherently controlled fourth harmonic generation in gases induced by a two-color field
Authors: Lü Zhi-Zhong  , Zhang Tian-Qi  , Zhong Gong-Xiang  ,   College of Mechatronic Engineering, Southwest Petroleum University, Chengdu 610050, China;,   Science college, National University of Defense Technology, Changsha 410073, China
Published: December 2020

Induced by the harmonically related two-color pulse, the fourth harmonic wave in the vacuum ultraviolet range has been observed in gases. The process of the fourth harmonic generation is studied. In the case of non-ionized gas, the intensity dependence on the pump pulse reveals that the fourth harmonic generation is a third-order parametric process of 2ω+ω+ω→4ω. In the case of ionized gas, the intensity of the fourth harmonic wave can be coherently controlled by the relative phase of the pump. Employing synchronous measurements of the fourth-order harmonic and terahertz emissions, the optimized relative phases of the two emissions have been studied and compared with each other experimentally. Results agree well with those of the time-dependent Schrödinger equation (TDSE). According to the reported optimized phase for the terahertz generation, the fourth harmonic generation involves two parametric processes: 2ω+2ω±ΩTHz→4ω and 2ω+ω+ω→4ω. The modulation of the fourth harmonic wave can be understood as the interference of the two channels.
Dispersion properties of plasma-filled metallic photonic crystal slow-wave structure
Authors: Fu Tao  , Yang Zi-Qiang  , Ouyang Zheng-Biao  ,   Shenzhen University, College of Electronic Science and Technology, THz Technical Research Center of Shenzhen University, Shenzhen Key Laboratory of Micro-Nano Photon Information Technology, Shenzhen 518060, China;,   School of Physical Electronics, University of Electronic and Technology of China, Chengdu 610054, China
Published: December 2020

Plasma-filled slow-wave devices provide a new way to develop high efficiency and high power vacuum-electron microwave sources, but their theoretical analysis and simulation is difficult. This paper introduces the wheel spoke antenna to excite signals for analyzing the dispersion characteristics of resonant cavity with plasma-filled metallic photonic crystal slow-wave structure (SWS). Influences of parameters of the SWS and plasma density on dispersion characteristics of the SWS are studied. Results show that there is little difference in dispersion characteristics obtained by wheel spoke antenna excitation of signals and other methods without plasma filling. When plasma fills in the SWS, the frequency of zero mode is consistent with the previous results obtained by other methods. Hence, both the results with and without plasma filling demonstrate that the wheel spoke antenna signal-excitation method is effective. Moreover, decreasing the thickness of wheel spoke antenna properly and the distance between the antenna and reflection surface of the metal plate can reduce the wheel spoke antenna influence on the cavity resonance frequency. Furthermore, thicker antenna can excite the slow wave field easily, while thinner antenna can excite the resonant mode easily. Besides, the outer radius and thickness of the SWS plate have little influence on the dispersion characteristics, while the period length and the inner radius of the SWS plate have greater influence on the dispersion characteristics. In addition, the dispersion curves of frequency and phase velocity will move to higher frequency regions with the increase of plasma density. Further, the influence of plasma filling on low-order modes is greater than that on higher order modes. It is also found that the higher-order mode operation can reduce the size of cavity and the velocity of the electron beam.
Numerical simulation on the motion characteristics of freely rising bubbles using smoothed particle hydrodynamics method
Authors: Sun Peng-Nan  , Li Yun-Bo  , Ming Fu-Ren  ,   College of Shipbuilding Engineering, Harbin Engineering University, Harbin 150001, China;,   CNR-INSEAN, Marine Technology Research Institute, Rome 00128, Italy
Published: December 2020

Based on the principle of virtual works, a multiphase smoothed particle hydrodynamics (SPH) model is further developed from the foundation of Hu X Y et al. (2006) and Grenier N et al. (2009). In the present model, the surface tension force implementation suitable for the multiphase flows with a large density ratio is applied, and this allows a good continuity at the multiphase interface. Artificial displacement correction is applied to keep the particles distributing uniformly in the whole flow field, and therefore any artificial viscous term is never needed; this is very important in the numerical simulation of viscous flows since the introduction of artificial viscosity changes the Reynolds number. Background pressure and interface sharpness force are added in the equation of state and the equation of momentum respectively to ensure the multiphase interface stability and smoothness; this is essential in the simulation of multiphase flows with large density difference at the multiphase interface. Two types of viscosity expressions suitable for multiphase flows are introduced and analyzed; the conclusion is that the formula proposed by Morris et al. (1997) and its similarly derived forms can give more accurate results. In the numerical validations, an oscillating droplet test is applied first to confirm the accuracy of the surface tension model and good results are achieved. This demonstrates that the artificial displacement and the interface sharp force will make negligible effects to the surface tension implementation. After that, two classic quantitative benchmarks of rising bubbles are simulated and the results of SPH agree well with the reference data. Moreover, in the two numerical benchmarks, the effect of the artificial displacement, the choice of the viscosity expression, and the type of the kernel function are compared and finally an optimal combination of these numerical aspects is recommended. Based on the above numerical investigations, the splitting process of an initially circular bubble is simulated and the numerical results agree well with the experimental data. In the last numerical case, the process of chasing and merging between two rising bubbles in vertical direction is simulated, based on which the mechanisms of these interesting interactions between two rising bubbles are analyzed. It is demonstrated in the present work that further improved multiphase SPH model may provide a potential method for the research of bubble dynamics.
Theoretical study on the microwave air breakdown threshold
Authors: Zhou Qian-Hong  , Sun Hui-Fang  , Dong Zhi-Wei  , Zhou Hai-Jing  ,   Institute of Applied Physics and Computational Mathematics, Beijing 100088, China
Published: December 2020

By analyzing the breakdown threshold obtained from effective magnitude or RMS (root mean square) of microwave field, it is pointed out that the assumption of threshold is not suitable for microwave air breakdown. Variations of effective electron temperature and breakdown threshold in microwave fields, which are studied theoretically and numerically by fluid-based plasma equations coupled with the Maxwell equations, are compared with those in static fields. It is found that the effective electron temperature varies greatly with the microwave field at high pressures (electron energy transfer frequency is much larger than microwave frequency) due to its high energy transfer frequency. This causes the microwave air breakdown threshold to be smaller than that obtained from the RMS of field at high pressures because the ionization frequency varies faster than electron energy loss at an effective electron temperature. On the other hand, the effective electron temperature variation with the microwave field is insignificant at low pressures (electron energy transfer frequency is much smaller than microwave frequency) due to the negligible electron energy loss in a microwave period. In this case, the microwave air breakdown threshold is approximately equal to that obtained from the RMS one of the field. The fit formula of microwave air breakdown threshold is obtained by numerical and theoretical analysis.
Analysis of heavy metals in poplar leaves by femtosecond filament-induced breakdown spectroscopy
Authors: Zhang Ya-Wei  , Gao Xun  , Zhang Yuan  , Song Chao  , Lin Jing-Quan  ,   Changchun University of Science and Technology, Changchun 130022, China;,   School of chemistry and environmental engineering, Changchun university of science and technology, Changchun 130022, China
Published: December 2020

Femtosecond filament-induced breakdown spectroscopy (FIBS) is employed to qualitatively analyze the heavy metal elements (Ca, Fe and Cr) in poplar leaves, at the same age, from four representative locations in Changchun City, i.e. Changchun First Automobile Factory, Railway Station, Jingyue National Forest Park, and Changchun University of Science and Technology (CUST) in the same season. The stem and mesophyll from the same leaf are investigated as samples by the FIBS technique. Experimental results demonstrate that the concentration of Ca and Fe elements in the leaf stem are higher than those in the leaf mesophyll through comparing the spectral intensities of Ca Ⅱ 393.37 nm and Fe Ⅰ 422.87 nm. Based on the analysis of the FIBS spectral intensity of heavy metals mentioned above in the poplar leaves from the four different locations, the heavy metal elements Ca, Fe and Cr in the poplar leaves gathered from the Automobile factory area have the highest concentration among the four locations, and those from Jingyue National Forest Park are the lowest. The FIBS technique can obtain stable plasma spectrum for the poplar leaves with irregular surfaces because of the optical intensity clamping effect inside the femtosecond filament. This experiment demonstrates that FIBS can be utilized to find new applications in the environmental pollution on-site detection.
Distribution and evolution of thermal field induced by intense pulsed ion beam on thin metal target
Authors: Yu Xiao  , Shen Jie  , Zhong Hao-Wen  , Qu Miao  , Zhang Jie  , Zhang Gao-Long  , Zhang Xiao-Fu  , Yan Sha  , Le Xiao-Yun  ,   School of Physics and Nuclear Energy Engineering, Beihang University, Beijing 100191, China;,   Institute of Heavy Ion Physics, Peking University, Beijing 100871, China
Published: December 2020

In this paper, combined with the latest development in relevant diagnostic and modeling techniques, the intense-pulsed ion beam (IPIB) energy deposition model in solid targets is established. The power density distribution induced by IPIB is simulated by Monte Carlo method on the basis of energy balance. By taking the power density as the source term, the thermal field distribution and evolution on a 100 μm stainless steel target irradiated by IPIB are simulated using the finite element method (FEM) in a time scale of several ms. Results reveal that in a time scale of several μups after IPIB irradiation, the main feature in the induced thermal field is a thermal shock within the depth of several times of the ion range. In the time scale of ms, thermal equilibrium can be established between the front and rear surfaces of the target, and the cross-sectional temperature field profile has a similar profile to the cross-sectional energy density distribution of the ion beam. This proves that by the infrared imaging diagnostic method, high resolution cross-sectional energy density diagnostics of IPIB can be achieved with a shooting time delay in ms scale.
Effects of thermal stress induced by mulitiple through silicon vias on mobility and keep out zone
Authors: Dong Gang  , Liu Dang  , Shi Tao  , Yang Yin-Tang  ,   Key Laboratory of Ministry of Education for Wide Band-Gap Semiconductor Materials and Devices, Microelectronics Institute, Xidian University, Xi'an 710071, China
Published: December 2020

Effects of thermal stress induced by multiple through silicon vias (TSVs) on mobility and keep out zone (KOZ) are mainly discussed in this paper. It is found that the angle and pitch between TSVs have a great effect on the carrier mobility and KOZ. In this paper, the device channel direction is set along [100]. And two types of KOZ are presented, namely the variations of electron mobility are 5% and 10% respectively. As for the two TSVs, their KOZ sizes change significantly with the angles between TSVs which change from zero to π/4, and the area of a KOZ is the minimum when the angle is π/4. But the zone for device placement is irregular, which is difficult for agreement. The area of a KOZ is the maximum when the angle is zero, and it is easy to make arrangement as the space for device distribution is regular. Based on these analyses, the effects of pitch between TSVs are presented. When the angle is zero, the area of KOZ decreases as the pitch increases and tends to be the same as that of a single TSV. For example, the KOZ, in which the variations of electron mobility are 5% and 10%, will reduce to 8.4 μm and 5.1 μm as the pitch increases to 20 μm, which is close to that of the single TSV. But when the angle is π/4, the KOZ with an electron mobility 5% increases from 5.2 to 6.4 μm as the pitch increases and tends to be the same as that of a single TSV at last. The KOZ with an electron mobility 10% will increase from 4.2 to 4.5 μm. In addition, the above analyses can be extended to the KOE of four TSVs, a more representative pattern. And two kinds of TSV displacement style including “square” and "diamond" TSV patterns are also discussed, the impact of pitch for these two patterns are also given in this paper. For the “square” TSV pattern, the KOZ decreases as the pitch increases. Under this condition, the devices can only be placed in a small square region surrounded by TSVs, but the region is regular, which is beneficial for device arranging. While for the "diamond" TSV pattern, the KOZ increases as the pitch increases. Under this condition, the area for device placement is larger than the “square” TSV pattern, but the region is irregular as it is divided into long narrow parts, which is hard for device placement.
Piezoelectric property of cross-linked polypropylene piezoelectret and its application in vibration energy harvester
Authors: Wu Li-Ming  , Zhang Xiao-Qing  ,   Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology & School of Physics Science and Engineering, Tongji University, Shanghai 200092, China
Published: December 2020

Piezoelectrets, also known as ferroelectrets, are space-charge electrets based polymer foams with strong piezoelectric effect. The piezoelectric effect in piezoelectrets originates from the regularly arranged dipolar space charges in the polymer matrix, achieved by properly charging the specific foam structure. The large figure of merit (FOM, d33·g33) in piezoelectrets implies that such kinds of materials are promising candidates in energy harvesters. In this article, the electron-irradiated cross-linked polypropylene (IXPP) foam sheets are rendered piezoelectric (i.e. to become piezoelectrets) by modification of the microstructure using hot-pressing process and polarization using corona charging at room temperature. The electromechanical properties of the fabricated IXPP piezoelectrets are investigated by measurements of quasi- and dynamic piezoelectric d33 coefficients, dielectric resonance spectrum, and isothermal decay at elevated temperatures. The energy harvesting from vibrations by using the IXPP piezoelectret films, at various vibration frequencies, load resistances, and seismic masses, are also studied. Results indicate that the quasi-static piezoelectric d33 coefficients of IXPP films up to 620 pC/N can be achieved. The variation of quasi-static piezoelectric d33 coefficient is dependent on the applied pressures, from 0.1 to 1.3 kPa, while it shows good linearity at larger pressures from 1.3 to 15 kPa. The typical values of Young's modulus in the thickness direction and the figure of merit (FOM) are 0.7 MPa and 11.2 GPa-1, respectively. The d33 coefficients will drop to 54%, 43%, 29% of the initial values after annealing the samples for 24 h at 50, 70, 90℃, respectively. At an exciting frequency of 820 Hz, the normalized output power of 65 μW/g2 is obtained from an IXPP film with an area of 3.14 cm2 and a seismic mass of 25.6 g around the optimum load resistance. Such thin, light and flexible IXPP piezoelectret films may be applied in vibration energy harvesters for powering low-power electronic devices.
Theoretical analysis on ferroelectricity critical dimension of BaTiO3 nanoparticles
Authors: Liu Yong-Guang  , Kang Ai-Guo  , Zhang Shao-Fei  , Hou Zhi-Wen  , Liu Wen-Bin  ,   Taiyuan University of Technology, School of Physics and Optical Engineering, Taiyuan 030024, China
Published: December 2020

The expression of the total polarization intensity of BaTiO3 nanoparticles based on Euler-Lagrange equation for ferroelectric particles and the form of the series solution of Bessel function are obtained, the influences of coefficient on the total polarization intensity are analyzed. According to the expression for the total polarization intensity, the ferroelectricity of BaTiO3 nanoparticles with different size below 100 nm is simulated and analyzed by MATLAB. Based on experimental data, the effect of grain size on the ferroelectricity is discussed by searching for the numerical value of the solution, and the critical grain size of BaTiO3 nanoparticles with ferroelectricity is predicted to be 6 nm subsequently; or, more specifically, based on the Euler-Lagrange equation of ferroelectric particle's total free energy, and according to the boundary condition, the equation is given in spherical coordinates, and the transformed equation has the form and characteristics of the Bessel equation, Therefore, it can be discussed according to the characteri-stics of the Bessel equation. It is considered that it has the series solution, and according to the form of deduced series solution, at the same time, under reasonable conditions, the change of polarization is simulated. By combining with the boundary conditions, the total expression of polarization of nanoparticles may be obtained. It contains some factors, first of all, it is analyzed on the whole, and the effect the factors have on the total expression of polarization of the nanoparticles is analyzed. The factors that directly affect, or indirectly affect the polarization intensity, and thus influence the trend of polarization intensity change is analyzed and identified. Then, the effect of each factor on the dielectric constant is simulated by adjusting the factors, and the numerical solution obtained is consistent with the experimental data, so the predictive value can be obtained.
Study on photoluminescence properties of 1.05 eV InGaAsP layers grown by molecular beam epitaxy
Authors: Yang Wen-Xian  , Ji Lian  , Dai Pan  , Tan Ming  , Wu Yuan-Yuan  , Lu Jian-Ya  , Li Bao-Ji  , Gu Jun  , Lu Shu-Long  , Ma Zhong-Quan  ,   SHU-SOLARE R&D JOINT LAB, College of Science, Shanghai University, Shanghai 200444, China;,   Key Lab of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences (CAS), Suzhou 215123, China
Published: December 2020

The photoluminescence properties of InGaAsP films with a bandgap energy of 1.05 eV for quadruple-junction solar cells grown by molecular beam epitaxy (MBE) are investigated. We make the excitation intensity and temperature dependence of continuous-wave photoluminescence (cw-PL) measurements. The PL peak position is 1.1 eV at 10 K, and almost independent of the excitation power, but the integrated intensity of the PL emission peaks is roughly proportional to the excitation power. The shift of peak position with temperature follows the band gap shrinking predicted by the well-known Varshni's empirical formula. These results indicate that the intrinsic transition dominates the light emission of the InGaAsP material. In addition, we also make the time-resolved photoluminescence (TRPL) measurements to determine the carrier luminescence relaxation time in InGaAsP. PL spectra suggest that the relaxation time is 10.4 ns at room temperature and increases with increasing excitation power, which demonstrates the high quality of the InGaAsP material. However, the relaxation time shows an S-shape variation with increasing temperature: it increases at temperatures lower than 50 K, and then decreases between 50–150 K, and increases again when temperature is over 150 K. According to the effect of temperature and the non-radiative recombination center concentration on the carrier relaxation time, the recombination mechanism of S-shape variation can be explained by the carrier relaxation dynamics.
Color-tunableness of Er3+/Eu3+ co-doped BiOCl phosphors for near ultraviolet excitation
Authors: Li Yong-Jin  , Huang Yang-Bin  , Liu Qun  , Qiu Jian-Bei  , Yin Zhao-Yi  , Song Zhi-Guo  ,   Yunnan Technology and Business University, Kunming 651700, China;,   School of Materials Science and Engineering, Kunming University of Science and Technology, Kunming 650093, China
Published: December 2020

In this paper, Er3+/Eu3+ co-doped BiOCl phosphors are synthesized by the conventional solid state method at 500℃, which are characterized by XRD, SEM, absorption spectra, excitation spectra and emission spectra. XRD analysis indicates that the samples exhibit pure tetragonal phase BiOCl. In SEM pictures, the samples exhibit smooth plate-like particles. The absorption spectra indicate that Er3+/Eu3+ ion dopants result in an impurity energy level, and the excitation spectra show that the sample has excellent broadband near ultraviolet (NUV)-exciting ability, which is due to the electronic transitions of the BiOCl bandgap. Under at 380 nm excitation, the emission bands located at 410 nm (2H9/2→4I15/2), 525 nm (2H11/2→4I15/2), 554 nm (4S3/2→4I15/2), 673 nm (4F9/2→4I15/2) of Er3+ ions, and 581 nm (5D0→7F0), 594 nm (5D0→7F1), 622 nm (5D0→7F2), 653 nm (5D0→7F3), 699 nm (5D0→7F4) of Eu3+ ions can be observed, respectively. Moreover, contrary to most of the Er3+/Eu3+-activated phosphors, the Er3+/Eu3+ co-doped BiOCl phosphor shows the unique and effective emission of the violet (Er3+) and far-red (Eu3+), which results from the particular structure of BiOCl crystals. The tunability in color of emitted radiation has been visualized by using chromaticity diagram on changing the doping concentration. Results show that the Er3+/Eu3+ co-doped BiOCl is a promising phosphor for near UV white LEDs.
Changes of stress and luminescence properties in GaN-based LED films before and after transferring the films to a flexible layer on a submount from the silicon epitaxial substrate
Authors: Huang Bin-Bin  , Xiong Chuan-Bing  , Tang Ying-Wen  , Zhang Chao-Yu  , Huang Ji-Feng  , Wang Guang-Xu  , Liu Jun-Lin  , Jiang Feng-Yi  ,   National Engineering Technology Research Center for LED on Si Substrate, Nanchang University, Nanchang 330047, China;,   LED Light Source and Lighting Research Center, Minnan Normal University, Zhangzhou 363000, China
Published: December 2020

Due to the lack of GaN substrates, hetero-epitaxial growth of GaN thin films is usually carried out on a foreign substrate. There are three kinds of substrate for GaN: sapphire, silicon carbide, and silicon; the sapphire substrate is the chief one, currently. Due to the availability of large scale and low cost of Si substrates, in recent years, extensive research has been devoted to the development of gallium nitride (GaN) optoelectronic devices on silicon substrates. Because of the large lattice mismatch and thermal-expansion cofficient difference between Si and GaN, it is difficult to grow thick enough crack-free GaN LED film on Si substrates. The two main kinds of methods for overcoming the crack problem are using the patterned Si substate and the thick AlGaN buffer layer. Although the two techniques could solve the problem of crack by cooling after growth, they will lead to an increase in tensile stress for GaN on Si. When making vertical-structured LED devices by transferring the GaN-based LED thin films from Si substrate to a new submount, this tensile stress will be partially released; but few researches have been made about the stress change before and after the transfer of the film, although the stress in GaN is an important factor that alters the energy band structure and may influence the vibrational properties. In this paper, we grow the crack-free GaN-based LED films on patterned Si(111), then light-emitting diode (LED) thin films are successfully transferred from the original Si (111) substrate to the submount with a flexible layer, and then the LED films without the influence of the submount and substrate are fabricated. In the following experiments, the strain-stress variation of the LED film is determined by using nondestructive high resolution X-ray diffraction (HRXRD) in detail, and the variation of photoluminescence (PL) properties of the film is studied too. Results obtained are as follows: 1) When the LED film is transferred to the flexible submount, the huge tensile stress will turn into compressive stress, and the latter in the InGaN layers will increase. 2) The In concentration in the (InGaN/GaN) MQW (multi-quantum well) systems can be evaluated with the help of reciprocal space maps (RSM) around the symmetric (0002) and asymmetric (1015) Bragg reflections. The In concentration in (InGaN/GaN) MQW will reduce when the GaN-based LED film is transferred to the flexible submount. 3) The PL spectra of the LED films will obviously appear red shift, after they are transferred to the flexible submount.
Magnetic coupling properties of Gd-doped ZnO nanowires studied by first-principles calculations
Authors: Zhang Yan-Ru  , Zhang Lin  , Ren Jun-Feng  , Yuan Xiao-Bo  , Hu Gui-Chao  ,   College of Physics and Electronics, Shandong Normal University, Jinan 250014, China
Published: December 2020

Magnetic coupling properties of Gd-doped ZnO nanowires are studied theoretically by using first-principles calculations. Several positions of Zn atoms that may be substituted by Gd atoms in ZnO nanowires are discussed. Numerical results show that the magnetic coupling is ferromagnetic when the two Gd atoms doped in ZnO nanowires are near each other. Injection of suitable amount of electrons can enforce these ferromagnetic properties in Gd-doped ZnO nanowires. It is also found that s-f coupling becomes remarkable when the Gd atoms are doped in ZnO nanowires, making the ferromagnetic coupling state more stable than the anti-ferromagnetic coupling state, and this is also the mechanism to elucidate the origination of ferromagnetic state in Gd-doped ZnO nanowires in experiments. These results will give a theoretical support for those who found experimentally that Gd-doped ZnO nanowires show ferromagnetic properties.
Application of nonlinear dynamical methods in abrupt climate change detection
Authors: Liu Qun-Qun  , He Wen-Ping  , Gu Bin  ,   College of Physics, Nanjing University of Information Science and Technology, Nanjing 210044, China;,   Institute of Space Weather, Nanjing University of Information Science and Technology, Nanjing 210044, China;,   National Climate Center, China Meteorological Administration, Beijing 100081, China;,   The Key Laboratory for Aerosol-Cloud-Precipitation of CMA-NUIST, Nanjing 210044, China
Published: December 2020

The research of abrupt climate change is an important field in the climate change. The rapid and accurate detection of the abrupt climate change has important practical significance and major economic-social costs, which will help us understand climate change and forecast the future evolutionary trend of the climate system. The detection results of most traditional abrupt climate change depend on the selection of the time scale concerned, which may result in the fact that we cannot identify an abrupt climate change until the event has been past for a long time. Moreover, these detection methods cannot extract the dynamical changes from the observational data of the climate system. As the rapid development in nonlinear science, the abrupt climate change detection technology has also been improved gradually. This article briefly reviews several new progresses in abrupt dynamical detection methods developed on the basis of recent nonlinear technologies, and some applications in the real observational data. These new methods mainly contain the technologies based on the long-range correlation of climate systems, such as moving detrended fluctuation analysis, moving cut data-detrended fluctuation analysis, moving cut data-R/S analysis, degenerate fingerprinting, and red noise. Moreover, some abrupt dynamical detection methods developed by the complexity of the time series, namely, entropy, such as approximate entropy, moving cutting data-approximate entropy, Fisher information, and wavelet Fisher's information measure. Furthermore, there are some other abrupt dynamical detection methods based on the theory of phase space, such as the dynamics exponent Q. Climate system is a complex dynamical system with nonlinear and interactive nature, which has long-range persistence in spatio-temporal variation, thus the abrupt detection method on spatial field change is pointed out to be a promising direction for further research in future. Because the spatial field contains abundance of information about the evolution of climate system which is much more than that in a time series in single meteorological station, the detecting methods on spatial field will greatly help us detect an abrupt climate change as soon as possible. And then we will have enough time to take action and make preparations for the new challenges due to the abrupt climate change.
Higgs mode near superfluid-to-Mott-insulatortransition studied by the quantum Monte Carlo method
Authors: Chen Kun  , Deng You-Jin  ,   National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China;,   University of Massachusetts at Amherst, MA 01002, USA
Published: December 2020

In additional to the phonon (massless Goldstone mode) in Galilean invariant superfluid, there is another type of mode known as the Higgs amplitude mode in superfluid with emergent Lorentz invariance. In two dimensions, due to the strong decay into phonons, whether this Higgs mode is a detectable excitation with sharp linear response has been controversial for decades. Recent progress gives a positive answer to this question. Here, we review a series of numerical studies of the linear response of a two-dimensional Lorentz invariant superfluid near the superfluid-Mott insulator quantum critical point (SF-MI QCP). Particularly, we introduce a numerical procedure to unbiasedly calculate the linear response properties of strongly correlated systems. The numerical procedure contains two crucial steps, i.e., one is to use a highly efficient quantum Monte Carlo method, the worm algorithm in the imaginary-time path-integral representation, to calculate the imaginary time correlation functions for the system in equilibrium; and then, the other is, based on the imaginary time correlation functions, to use the numerical analytical continuation method for obtaining the real-time (real-frequency) linear response function. Applying this numerical procedure to the two-dimensional Bose Hubbard model near SF-MI QCP, it is found that despite strong damping, the Higgs boson survives as a prominent resonance peak in the kinetic energy response function. Further investigations also suggest a similar but less prominent resonance peak near SF-MI QCP on the MI side, and even on the normal liquid side. Since SF-MI quantum criticality can be realized by ultracold aotms in optical lattice, the Higgs resonance peak can be directly observed in experiment. In addition, we point out that the same Higgs resonance peak exists in all quantum critical systems with the same universality, namely (2 + 1)-dimensional relativistic U(1) criticality, as SF-MI QCP.