bluuebunny/crossref_metadata_2025 huggingface dataset:
First-principles study of electronic structures and electrochemical properties for Al, Fe and Mg doped Li2MnSiO4
Authors: Jia Ming-Zhen  , Wang Hong-Yan  , Chen Yuan-Zheng  , Ma Cun-Liang  , Wang Hui  ,   School of Physical Science and Technology, Southwest Jiaotong University, Chengdu 610031, China;,   Key Laboratory of Advanced Technologies of Materials, Ministry of Education, Southwest Jiaotong University, Chengdu 610031, China
Published: December 2020

Li2MnSiO4 is one of the potential cathode materials for lithium batteries due to its high capacities, but the poor conductivity hinders its further development. The cycling performance and electrochemical property of Li2MnSiO4 cathode material can be improved by doping metal cation. Twelve structures LixMn1-yMySiO4 (x=2, 1, 0; y=0.5, 1; M= Al, Fe, Mg) by doping Al, Fe and Mg are constructed in this paper, and their structures, electronic properties and delithiation process are studied by using the density functional theory of first principles within the GGA+U scheme. The best doping site and delithiated structure are found by comparing their energies. The results show that Al-doping is the best way to improve the conductivity and cyclability of the cathode material Li2MnSiO4. The pure Li2MnSiO4 has a low conductivity because of its large band gap (3.41 eV), while Al-doping Li2MnSiO4 crystal has metallic characteristics due to its electron densities of state with up-spin and down-spin cross through the Fermi level. The band gap is also reduced when it is Fe-doped, which improves the conductivity of Li2MnSiO4. Among the delithiated structures LixMnSiO4 (x=1, 0), Al-doping enhances the structural stability because of the lowest formation energy and its cyclability is improved by reducing the volume change. Within the lithium ion extraction from the Li2MnSiO4 and Li2Mn0.5M0.5SiO4 (M=Al, Fe, Mg), the Mn-O and M-O bonding have much more ionic features, while the covalent bonding feature between Si and O is almost unchanged. And the fully delithiated MnSiO4 and Mn0.5M0.5SiO4 show semic-metallic properties depending on the density of states of configuration. The delithiated voltages for the first Li extraction process decrease when Al and Fe are doped. Therefore the Al-doping in the Li2MnSiO4 is expected to be an effective way to improve the cycling performance and electrochemical property for Li-ion battery cathode material.
Charge distribution of Li-doped few-layer MoS2 and comparison to graphene and BN
Authors: Chen Xin  , Yan Xiao-Hong  , Xiao Yang  ,   Department of Applied Physics, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
Published: December 2020

According to first-principles calculation, we study the charge distribution of Li-doped few-layer (1-3 layers) MoS2 and compare it with the results of graphene and BN. It is found that the stable adsorption sites of Li are the top (Mo) site for MoS2 layer, and the hexagonal center for graphene and BN layers. Band structures of pristine MoS2 show that single-layer MoS2 is a direct band gap semiconductor while few-layer MoS2 is an indirect one. As MoS2 is doped, the Fermi level will shift to the conduction band, indicating a charge transfer between Li and MoS2. The charge transfer takes place mostly between Li and the topmost MoS2 layer, which is very similar to that happening between graphene and BN. However, the second and third layer of MoS2, which are far from Li, can acquire about 10% of transferred charges. In contrast, the second and third layer obtain no more than 2% of charges for graphene and BN. Based on the electrostatic theory, we derive for both double and triple layers the formulas of electrostatic energy, which show clearly that only charge transfer between Li and the topmost layer will give the lowest electrostatic energy. Moreover, we calculate the work functions of pristine MoS2, graphene and BN, and find that, despite similar work functions of MoS2 and BN, the larger band gap of BN will make charge transfer between Li and BN harder. The analyses of electrostatic energy and work function show that the charge distribution is dominated by both interlayer electrostatic interaction and work function of material. It is expected that the above results could be helpful for doping layered structures and designing devices.
Electric field controlled energy gap and Landau levels in silicene
Authors: Ji Qing-Shan  , Hao Hong-Yan  , Zhang Cun-Xi  , Wang Rui  ,   Department of Donghai Science and Engineering, Zhejiang Ocean University, Zhoushan 316000, China;,   Department of Electronic Information Science and Engineering, Zhejiang Ocean University, Zhoushan 316022, China
Published: December 2020

We investigate the electric field controlled energy gap and the Landau levels in silicene in detail. The energy gap at different Dirac points has different closing and reopening conditions and the 2-fold degeneracy induced by the K-K' symmetry is resolved. An externally applied electric field gives rise to two Rashba spin-orbit-couplings between the nearest neighbour and the next nearest neighbour in silicene. Both these couplings can resolve the spin degeneracy at some isolated values of the electric field, where the crossover of the successive Landau levels become anti-crossover. Except some special values of the electric field, the 4-fold degeneracy of energy levels associated with the K-K' symmetry and spin symmetry is completely resolved in silicene, each level has a definite spin polarization, which correspond to the quantum Hall plateaux with filling factor ν=0, ±1, ±2,….
Directed transport of fractional Brownian motor driven by a temporal asymmetry force
Authors: Ren Rui-Bin  , Liu De-Hao  , Wang Chuan-Yi  , Luo Mao-Kang  ,   Department of Mathematics, Sichuan University, Chengdu 610064, China
Published: December 2020

The directed transport of a Brownian particle in a spatially periodic symmetric field under a temporal asymmetric force is studied. Based on the Caputo’s fractional derivatives theory, we establish a differential aquation for an overdamped fractional Brownian motor as the system’s mathematic model, where the external force is zero-mean and the fractional order is used to describe the inhomogeneity of the real environment. Using the fractional differential algorithm, we analyze the relationships between transport velocity and model parameters. It is worth mentioning that the impact of fractional order is discussed in detail. According to the reflearch we find that a temporal asymmetric force can induce a net current without the application of a ratchet potential, even a noise. We also find that the velocity of the current increases monotonically with the increase in fractional order. Moreover with certain fractional orders, a generalized resonance phenomenon is reflealed since the velocity of the current varies non-monotonically with the system parameters, such as the height of the potential barrier and the noise strength etc. Research shows that the fractional system is a generalization of the traditional dynamic systems, which could probably give a more reasonable explanation of the directed transport as a consequence.
Design and verification of a two-dimensional wide band phase-gradient metasurface
Authors: Li Yong-Feng  , Zhang Jie-Qiu  , Qu Shao-Bo  , Wang Jia-Fu  , Wu Xiang  , Xu Zhuo  , Zhang An-Xue  ,   College of Science, Air Force Engineering University, Xi’an 710051, China;,   Key Laboratory of Electronic Materials Research of Ministry of Education, Xi’an Jiaotong University, Xi’an 710049, China;,   School of Electronics & Information Engineering, Xi’an Jiaotong University, Xi’an 710049, China
Published: December 2020

For dealing with circularly polarized waves, a high-efficient two-dimensional dispersionless phase-gradient metasurface is devised and achieved by spatially arranging co-polarized reflective metasurface unit cells. The phase of the co-polarized reflection can be freely modulated via a rotating metallic wire of the co-polarized reflective metasurface unit cell in-plane. The achieved phase gradient metasurface can produce opposite-sign phase gradient for left-and right-handed circularly polarized incident waves. During linearly polarized wave incidence, the reflected waves will decompose into two counter-directionally propagating circularly polarized waves. Reflective power density spectra for the linearly polarized wave in normal incidence are simulated, which are well consistent with the theoretically designed anomalous reflection direction. A 2 mm thick sample is fabricated and the mirror reflectivity curve is measured. Experimental results show that for linearly polarized wave normal incidence, the mirror reflectivity is reduced to below -5 dB in a wide band from 9.5 to 17.0 GHz.
Simulation of radiation transfer properties of polarized light in non-spherical aerosol using Monte Carlo method
Authors: Hu Shuai  , Gao Tai-Chang  , Liu Lei  , Yi Hong-Liang  , Ben Xun  ,   College of Meteorology and Oceanography, PLA University of Science and Technology, Nanjing 211101 China;,   School of Energy Science and Engineering, Harbin Institute of Technology, 92 West Dazhi Street, Harbin 150001, China
Published: December 2020

The shape of atmospheric aerosol is an important factor that influences radiation transfer. In this paper, a vector radiation transfer model based on Monte Carlo method is systematically introduced, and its accuracy is validated against the published results. and the sensitivity of Stokes vectors of transmitted and reflected light to aerosol shape is discussed when polarized light incidents. In addition, the influence of the particle shape on the depolarization ratio, transmission rate and the reflection rate is analyzed for incident light with different polarization states. Simulation results show that for the incident light in different polarization states, the sensitivity of the Stokes vectors of the diffuse light to different aerosol shapes is not the same in different viewing directions, and the Q, U, V elements of Stokes vector are all insensitive to the change of particle shape near the direction of the zenith angle 0°. It is evident that the aerosol shapes have a stronger influence on the depolarization ratio for reflected diffuse light compared with that for transmitted diffuse light, and there are also remarkable differences between the degree of depolarization of the diffuse light when the polarization states of the incident light are different. Results also show that the aerosol shape has a significant influence on the whole transmission rate and the reflection rate, and with the increasing of propagation distance, the influence also becomes more remarkable. Compared with particle shape, the influence of polarization states of incident light is relatively small, the transmission rate of horizontally-polarized light is slightly larger than that of unpolarized light, while for perpendicularly-polarized light, its results is opposite. For circularly polarized light, the results is almost the same as that of unpolarized light.
Mecanism and applications of the nonlinear dynamic response to ultrasound contrast agent microbubbles
Authors: Yu Jie  , Guo Xia-Sheng  , Tu Juan  , Zhang Dong  ,   Institute of Acoustics, Key Laboratory of Modern Acoustics (MOE), School of Physics, Nanjing University, Nanjing 210093, China;,   Jiangsu Province Hospital of TCM, Nanjing 210029, China
Published: December 2020

Ultrasound contrast agent (UCA) reflers to the agent that has specific acoustic properties to enhance the contrast in ultrasound imaging by composition of gas-filled microbubbles with micrometer-diameters. In a diagnostic ultrasound field, microbubbles in fluid create an acoustic impedance mismatch between fluid and surrounding tissue to increase the reflection of sound and achieve a better contrast. Ongoing developments improve diagnostic possibilities of UCA remarkably, whereas their potential therapeutic applications have also been investigated for a couple of decades. The nonlinear response of UCA microbubbles has clinical reflevance from both diagnostic and therapeutic perspectives. The aim of this review is to introduce the latest reflearch progress of our group regarding the mechanism and applications of the nonlinear dynamic response to UCA, which include (1) an all-in-one solution characterizing coated bubble parameters with the help of the light scattering technique and flow cytometry, which makes it possible to quickly integrate the size distribution with dynamic motions of thousands of microbubbles and easily verify the validities of different shelled bubble dynamic models; (2) the development of a new bubble dynamics model that takes into account both nonlinear shell elasticity and viscosity, which can not only be capable of simulating the “compression-only” behavior of microbubbles excited by large amplitude ultrasound but also eliminate the dependence of bubble shell parameters on bubble size; (3) the estimation of UCA inertial cavitation thresholds of two types of commercial UCA microbubbles (viz., SonoVue microbubbles coated with lipid shells and KangRun microbubbles coated with albumin shells) and the evaluation of the relationship between microbubble inertial cavitation thresholds and their shell parameters; and (4) the reflearches of DNA transfection efficiency and the reduction of cytotoxicity in gene delivery facilitated by UCA excited by 1-MHz focused ultrasound pulses, and the results indicate that the measured DNA transfection efficiency and sonoporation pore size generally increase with the enhancement of inertial cavitation dose, while the cell viability decreases linearly with the increase of International Classification of Diseases (ICD). These studies are of significance for better understanding the mechanism of ultrasound-induced microbubble nonlinear dynamics and investigating the effective quantification technique for microbubble cavitation activity, which are important for further optimizing therapeutic ultrasound effects and avoiding the side-effects.
A new boundary treatment method in smoothed particle hydrodynamics
Authors: Liu Hu  , Qiang Hong-Fu  , Chen Fu-Zhen  , Han Ya-Wei  , Fan Shu-Jia  ,   Department of Power Engineering, The Second Artillery Engineering University, Xi’an 710025, China;,   151 Unit of The Second Artillery, Luoyang 471000, China
Published: December 2020

As the smoothed particle hydrodynamics (SPH) is a truly Lagrangian meshfree method, the implementation of solid boundary condition has been one of the key problems that hinder SPH from applying to lots of engineering problems. In order to treat the boundary conditions efficiently, based on the boundary-fluid interaction principles, a new boundary treatment method is proposed. In this method, the solid boundary is repreflented implicitly by several layers of dummy particles along the boundary line. During the simulation, the dummy particles are treated as an extension of the fluid phase. The densities of dummy particles are kept constant, and the pressures and velocities are interpolated from the nearby fluid particles at each time step. Dummy particles can be involved in the calculation of the continuity equation conditionally and exert influences on the density/pressure field of the fluid phase. Then, for the fluid particles that approach the solid boundary, local pressure gradients are used to repreflent the dummy-fluid particle pair’s interaction strength and act as the boundary force term implicitly, which is tuned to be repulsive only and normal to the boundary. Thus, large pressure gradients mean strong boundary-fluid interaction strength, and the boundary force from the dummy particles should also be large enough to preflent the fluid particles from penetrating the solid boundary; and on the contrary, small pressure gradients mean weak boundary-fluid interaction strength and the boundary force becomes soft and little disturbs the flow field. Results of numerical tests demonstrate that, compared with the existing boundary treatment methods, the new method is in better accordance with the physical principles of the fluid-boundary interaction, and is able to treat arbitrary solid boundaries with limited modeling and computational costs. With the help of this new boundary treatment method, the stable flow field, well-ordered particle distribution, smooth velocity and pressure fields could be obtained. Theoretically, this new boundary treatment method could be directly used in three-dimensional multi-phase problems. Further tests are planned to be carried out; meanwhile, expanding the new boundary treatment method to rigid-fluid interaction problems is also a work in the future.
Characteristics of acoustic-controlled arc in ultrasonic wave-assisted arc
Authors: Xie Wei-Feng  , Fan Cheng-Lei  , Yang Chun-Li  , Lin San-Bao  , Zhang Yu-Qi  ,   State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001, China
Published: December 2020

As a new welding method, ultrasound has been successfully introduced into the pool during ultrasonic wave-assisted arc welding process. However, the interaction mechanism between the ultrasound and the arc plasma is not clear, thus preflenting the new technique from engineering applications. In this paper, the characteristic of arc regulation by external ultrasonic field is investigated based on the experimental data and the corresponding theory. In order to figure out the characteristics of arc, the arc images obtained by high-speed camera are processed. Compared with the conventional welding arc, ultrasonic wave-assisted arc is more contracted and becomes brighter, the high-temperature region in an arc column greatly expands, and there are internal particle agglomerations shaking up and down at a constant frequency. The arc shape varies with ultrasound excitation current and the height of ultrasonic radiator. In the vicinity of the resonance point, the straight-degree of the arc is the strongest and the ripple frequency is also the largest. Results show that the purpose of using external ultrasound field to regulate the thermal plasma has basically achieved. Analyzing the acoustic pressure wave equation for the neutral component shows that the spatial distribution of acoustic wave can be generated in the arc and its intensity is proportional to the local amplitude of acoustic waves. Acoustic pressure field can be calculated based on the dependence of the electron temperature and density on time and space. In addition to the action of acoustic field within the arc, the arc plasma is also controlled by the acoustic field structure. A two-cylinder model incorporating boundary element method is developed, establishing a relationship between the binding capability and the geometric parameters of an ultrasonic radiator with reflerence to wavelength. This model is successful in predicting resonant modes of the acoustic field and explaining the influences of the ultrasonic radiator height on welding arc. Variation of arc shape is the result of the combined effect of axial and radial acoustic radiation forces on particles (electron, ion and neutral). The thermal efficiency will be significantly enhanced since the particle density increases in the ultrasonic wave-assisted arc. The acoustic propagation in the arc is the interacting process between acoustic and thermal plasmas. The mechanism of ultrasound acting on the arc can be reasonably explained in this study. And the results may provide a reflerence for plasma engineering applications. However, it also needs further reflearch on the impact of an arc on the acoustic field.
Electronic transport properties of graphene pn junctions with spin-orbit coupling
Authors: Chen Dong-Hai  , Yang Mou  , Duan Hou-Jian  , Wang Rui-Qiang  ,   Laboratory of Quantum Engineering and Quantum Materials, School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou 510006, China
Published: December 2020

We have investigated the electronic transport properties of graphene pn junction with spin-orbit coupling. If the incident energy lies between the potentials of the two ends of the pn junction, a particle can penetrate the graphene pn junction by tunneling accompanied by the electron-hole transition. The curve of conductance versus Fermi energy shows steps and reaches its maximum when the Fermi energy lies at the middle of the potentials of the p and n areas. As the length of graphene pn junction increases, the conductance decays exponentially. The spin-orbit coupling leads to a bulk energy gap and edge states; the gap reduces the conductance dramatically and the edge states result in an almost perfect conductance plateau. When the pn region is influenced by randomly doped impurities, the conductance curves are no longer symmetrical in the case of weak doping, while in the strong doping case, the step structures are destroyed but the conductance plateau contributed by the edge states survives well.
Multi-parameter photoacoustic imaging and its application in biomedicine
Authors: Yin Jie  , Tao Chao  , Liu Xiao-Jun  ,   MOE Key Laboratory of Modern Acoustics, Institute of Acoustics, Physical School, Nanjing University, Nanjing 210093, China
Published: December 2020

Photoacoustic imaging is a hybrid imaging technique based on the photoacoustic effect. As a non-invasive and non-ionizing modality, photoacoustic imaging takes the both merits of the conventional acoustic imaging and optical imaging. Firstly, the contrast of photoacoustic imaging primarily depends on the optical absorption. The unique optical spectra of atoms and molecules makes optical methods to be a widely used modality to probe the molecular and chemical information of biological tissue. Therefore, photoacoustic imaging has its inherent advantage in high-contrast functional and physiological imaging of biological tissue, as well as the optical imaging method. Secondly, photoacoustic imaging has the high spatial resolution in deep tissue in comparison with the pure optical imaging method. Since the strongly optical scattering in biological tissue, pure optical imaging method is difficult to obtain the high-resolution image in the tissue deeper than ～1 mm. Whereas, acoustic wave suffers much less from scattering than optical wave, the acoustic scattering coefficient is about 2-3 orders of magnitude less than the optical scattering coefficient. Photoacoustic imaging can achieve a fine resolution in deep tissue, which equivalent to 1/200 of the imaging depth. Thirdly, non-ionizing radiation used for photoacoustic imaging is much safer than X-ray. Moreover, the low-temperature rises make photoacoustic imaging be safely used in live tissue. A laser-induced temperature rise of 1 mK yields an initial pressure of ～800 Pa in soft tissue. Such a sound pressure level has reached the sensitivities of typical ultrasonic transducers. Fourthly, photoacoustic imaging has the ability of extracting multiple contrasts, including biochemical parameter, biomechanical parameter, blood velocity distribution, tissue temperature, and microstructure information. Photoacoustic imaging can capture more specific and reliable information about the tissue structure, function, metabolism, molecule, and gene. As a result, photoacoustic imaging has become one of the fastest growing biomedical imaging techniques in the past decade.#br#In this review, we will explain photoacoustic effect and the principle of photoacoustic imaging. Then, we introduce the two classical photoacoustic imaging schemes, including photoacoustic tomography and photoacoustic microscopy. Their main specifications, such as resolution, are also preflents. We review the ability of photoacoustic imaging in extracting multiple contrasts and discuss their biomedicine applications. In addition, we also introduce the remarkable breakthroughs in super-resolution photoacoustic imaging. Finally, we look the further development and the limitations of photoacoustic imaging.
Gain characteristics of grapheme plasmain terahertz range
Authors: Li Dan  , Liu Yong  , Wang Huai-Xing  , Xiao Long-Sheng  , Ling Fu-Ri  , Yao Jian-Quan  ,   Department of Applied Physics, Hubei University of Education, Wuhan 430205, China;,   College of Optoelectronic Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China;,   College of Precision Instrument and Opto-electronics Engineering, Tianjin University, Tianjin 300072, China
Published: December 2020

Graphene is a single atomic layer of carbon atoms forming a dense honeycomb crystal lattice. Now tremendous results of two dimensional (2D) graphene have been obtained recently in the electronic properties both experimentally and theoretically due to the massless energy dispersion relation of electrons and holes with zero (or close to zero) bandgap. In addition, through the process of stimulated emission in population inverted graphene layers, the coupling of the plasmons to interband electron-hole transitions can lead to plasmon amplification. Recently, research results have also shown that at moderate carrier densities (109-1011/cm2), the frequencies of plasma waves in graphene are in the terahertz range.In this paper, based on the Maxwell's equations and material constitutive equation, the gain characteristics of the surface plasmon in graphene are theoretically studied in the terahertz range. In the simulations process we assume a nonequilibrium situation in graphene, where the densities of the electron and the hole are equal. And the gain characteristics for different carrier concentrations, graphene temperature and the momentum relaxation time are calculated. The calculated results show that the peak gain positions shift towards the higher frequencies with the increase of the quasi Fermi level of electron and hole associated with electron-hole concentrations. The reason may be that the change rate of the electron quasi Fermi level is higher than the hole's and thus the distributions of electrons and holes in energy are broader, resulting in the peak gain frequency shifting towards higher frequencies. However, the results also indicate that the temperature of the graphene has little effect on both the peak gain value and the peak gain position of the plasmon. It is maybe because in the simulation process the temperature is taken to be less than 50 K, which is corresponding to the energy of the 1 THz. However the calculated results show that the frequencies of the gain peak positions are all larger than 1 THz, hence, the effects of the temperature on the peak gain value and peak position both could be neglected. Moreover, it is obviously seen that the peak gain value is a function of momentum relaxation time in graphene. This is because when the momentum relaxation time increases, more electrons will be excited, and this will increase the plasmon gain probability in graphene. However, the momentum relaxation time has no effect on the position of the gain peak. It is maybe because the momentum relaxation time has little effect on radiation frequency in the whole momentum relaxation period.
Analyses of droplet spreading and the movement of wetting line on a solid surface
Authors: Jiao Yun-Long  , Liu Xiao-Jun  , Pang Ming-Hua  , Liu Kun  ,   Institute of Tribology, Hefei University of Technology, Hefei 230009, China
Published: December 2020

Droplet spreading behavior on a substrate is closely bound up with the wettability of the substrate, and plays a critical role in many industrial applications, such as lubrication, painting, coating, and mineral flotation. In this paper, a dynamical model of droplet spreading on a smooth substrate is established through a mechanical analysis. According to the lubrication approximation theory and Navier-Stokes equation, a general nonlinear evolution equation or equations are derived, including the momentum equation, the continuity equation, and the evolution equation of film thickness. We adopt numerical methods to solve these equations, and also quantitatively analyze the relation among film thickness, spreading radius, speed of wetting contact line and time in detail. The results show that the droplet spreading process is mainly divided into two phases, namely expansion phase and contraction phase. Moreover, the spreading process is along with mutual transformation among surface energy, kinetic energy, and different kinds of potential energies. In addition, the final spreading radius Rf of droplet is determined by the inherent wettability of solid surface, and the collapse effect, which emerges at t=0.006 s in the spreading process, is related to Laplace pressure difference of curved liquid surface. Finally, by controlling the droplet size, we obtain the scaling law of droplet spreading radius with time, which approximately meets R ～ t1/7. The scaling law is validated both experimentally and numerically. The results of this study are expected to enhance our knowledge of the movement of wetting contact line and also provide some guidance for the wetting theory.
Double ellipsoid model for conductivity effective mass along [110] orientation in (100) Si-based strained p-channel metal-oxide-semiconductor
Authors: Song Jian-Jun  , Bao Wen-Tao  , Zhang Jing  , Tang Zhao-Huan  , Tan Kai-Zhou  , Cui Wei  , Hu Hui-Yong  , Zhang He-Ming  ,   Key Lab of Wide Band-Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi'an 710071, China;,   National Key Laboratory of Analog Integrated Circuitry, No. 24 Research Institute of CETC, Chongqing 400060, China
Published: December 2020

The performance of a Si metal-oxide-semiconductor field-effect transistor can be enhanced effectively by the strain technology and the orientation engineering. For example, the [110] direction is usually used as the channel direction in the Si p-channel metal-oxide-semiconductor (PMOS) on 100 oriented substrate. While SunEdison company rotates the channel direction 45 degrees to the [100] direction, its hole mobility is 1.15 times larger than the hole mobility of the former.The orientation engineering is based on the anisotropy of the hole effective mass along different directions. The enhancement of carrier mobility naturally occurs when we choose the direction with the smaller carrier effective mass as the channel direction.However, according to the reported results in the literature, the hole effective mass values along the [110] and [100] orientation are about 0.6m0 and 0.29m0, respectively. The former is twice larger than the latter, which cannot explain that the experimental result increases 1.15 times.We find that the effective mass values along both the long axis and the short axis should be taken into consideration, and the value of 0.6m0 can only represent the long axis term by observing the equivalent energy diagram of the first sub-band in Si PMOS.In view of this, the double ellipsoid model is given for the conductivity effective mass along the [110] direction in (100) Si PMOS, which explains the reason why the hole mobility along the [100] direction is 1.15 times larger than that along the [110] direction in Si PMOS. And then, based on the E-k relation of the inversion layer in Si-based strained PMOS, we study the conductivity effective mass along the [110] direction in (100) Si-based strained PMOS by the above method.The results show that 1) the [110] oriented hole conductivity effective mass of biaxially strained Si PMOS can be calculated directly by its spherical equivalent energy diagram; 2) in the case of biaxially strained Si1-xGex PMOS, its conductivity effective mass needs to be calculated by the double ellipsoid method; 3) the [110] oriented hole conductivity effective mass of uniaxially strained Si PMOS should be solved approximately by two different sizes of ellipsoid.Our valid models can provide the valuable references for studying and designing the Si-based strained PMOS device.
Tridiagonal representation with pseudospin symmetry for a noncentral electric dipole and a ring-shaped anharmonic oscillator potential
Authors: Gao Jie  , Zhang Min-Cang  ,   College of Physics and Information Technology, Shaanxi Normal University, Xi'an 710119, China
Published: December 2020

The concepts of pseudospin symmetry in atomic nuclei and spin symmetry in anti-nucleon are reviewed. The exploration for understanding the origin of pseudospin symmetry and its breaking mechanism, and the empirical data supporting the pseudospin symmetry are introduced. A noncentral anharmonic oscillatory potential model is proposed, in which a noncentral electric dipole and a double ring-shaped component are included. The pseudospin symmetry for this potential model is investigated by working on a complete square integrable basis that supports a tridiagonal matrix representation of the Dirac wave operator. Then, solving the Dirac equation is translated into finding solutions of the recursion relation for the expansion coefficients of the wavefunction. The angular/radial wavefunction is written in terms of the Jacobi/Laguerre polynomials. The discrete spectrum of the bound states is obtained by diagonalization of the radial recursion relation, and the property of energy equation is discussed for showing the exact pseudospin symmetry. Several particular cases obtained by setting the parameters of the potential model to appropriate values are analyzed, and the energy equations are reduced to that of the anharmonic oscillator and that of the ring-shaped non-spherical harmonic oscillator, respectively. Finally, it is pointed out that the exact spin symmetry exists also in this potential model.
Study of downstream light intensity modulation induced by mitigated damage pits of fused silica using numerical simulation and experimental measurements
Authors: Bai Yang  , Zhang Li-Juan  , Liao Wei  , Zhou Hai  , Zhang Chuan-Chao  , Chen Jing  , Ye Ya-Yun  , Jiang Yi-Lan  , Wang Hai-Jun  , Luan Xiao-Yu  , Yuan Xiao-Dong  , Zheng Wan-Guo  ,   Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China;,   Graduate School of China Academy of Engneering Physics, Beijing 100088, China
Published: December 2020

For high-power UV laser facilities, one of the key problems limiting the maximum light influence and safe routine operation is that the UV laser induces damage to fused silica optics. The most effective mitigation protocol of the damaged optics is the CO2 laser processing that leads to make locally melt or evaporate the damage. While the mitigated damage sites possess particular morphology, which may modulate the passing laser beam and induce the downstream intensification that will ruin the neighbor optics. In this work, the morphology features of the mitigated damage pits of fused silica optics are systematically investigated. According to the measured morphology features, a 3D grid model of mitigated pit is built, and the downstream light intensity distribution of the mitigated pit model under incident 351 nm laser is studied by scalar diffraction theory and fast fourier transform (FFT) methods. Results indicate that there are two kinds of downstream intensification: off-axis and on-axis intensifications. In the former intensification, the maximum intensity is located near the output surface of the optics and comes mainly from the depth of the mitigated pit; it increases with the depth. In the alter intensification, the maximum intensity is located far from the output surface of the optics and is mainly dependent on the height of the rim structure at the fringe of the mitigated damage pit; so it increase with increasing height. In addition, it is found that the location of the maximum off-axis or on-axis intensity can approach the output surface of the optics with increasing maximum intensity. For comparison, experimental measurements of downstream intensification induced by the mitigated pits are carried out, and the experimental results are almost consistent with the numerical simulation, implying the validity of the numerical simulation of the mitigated pit model. Results of this research indicate that the downstream intensification of mitigated pits can be suppressed by controlling the morphology features of mitigated pits. this is significant for the development and improvement of the mitigated techniques of damage optics.
Research on the interaction of Airy pulse and soliton in the anomalous dispersion region
Authors: Zhu Kun-Zhan  , Jia Wei-Guo  , Zhang Kui  , Yu Yu  , Zhang Jun-Ping  , Ke Neimule  ,   School of Physical Science and Technology, Inner Mongolia University, Hohhot 010021, China
Published: December 2020

Based on the split step Fourier method, the interaction between soliton and Airy pulse is studied in the anomalous dispersion region. And after that the strength, time-domain, and time-shift are simulated by the software of MATLAB, respectively. Results show that cross phase modulation (XPM) builds up when soliton and Airy pulse begin to overlap, which affects the properties of the two pulses. The soliton keeps its original shape but the direction of propagation is deflected by the influence of Airy pulse's self-acceleration. Airy pulse converts to soliton and the direction of propagation changes due to XPM. Therefore, the properties of Airy pulse and soliton are interacted with each other because of XPM. The time-domain of the two pulses is also influenced by XPM and their different shapes will change so as to contain a main and a secondary peaks whose structures are similar and the location and pulse width of the main and the secondary peaks are also roughly the same, which is the basis for Airy pulse to convert to soliton. In addition, the change of Airy pulse and soliton is simulated for different input intensity value of r. Simulation shows that the time-shifts of Airy pulse and soliton increase with increasing input intensity r and their variation trends are the same.
High-bandwidth control of piezoelectric steering mirror for suppression of laser beam jitter
Authors: Fan Mu-Wen  , Huang Lin-Hai  , Li Mei  , Rao Chang-Hui  ,   Key Laboratory on Adaptive Optics, Chinese Academy of Sciences, Chengdu 610209, China;,   Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Laser beam steering or pointing, which stabilizes the beam direction, is critical in many areas, such as optical communication systems, astronomy and directed-energy systems etc. However, the disturbances including atmospheric turbulence and mechanical jitter on platform may degrade the pointing accuracy. A proportional-integral (PI) feedback control commonly has been used in the track loop with a fast steering mirror. To compensate dynamic disturbance effectively, the laser beam steering control system must have a larger bandwidth than the disturbance bandwidth. But the control bandwidth is limited by the noise of the sensor, computing latency, and the light energy. So, a simple proportional-integral (PI) feedback controller of a piezoelectric fast steering mirror (PFSM) can only compensate the broadband disturbance of the atmospheric turbulence, but cannot effectively compensate a larger amplitude narrowband jitter because of the low control bandwidth. Moreover, when the control bandwidth is tuned to high, the mechanical resonance of the PFSM can cause the instability of the system. An improved dual two-order filter assisted high-bandwidth control algorithm to improve the pointing accuracy and error attenuation capability is proposed. This method can control a PFSM for suppression of laser beam jitter. The influence of filter parameters on frequency characteristics is analyzed, and then, a practical design method is proposed. The dual two-order filter can combine the characteristics of traditional notch filter and two-order low-pass filter, and can also obtain any desired amplitude in the interesting frequency ragion with little influence on the others. The principle of the proposed filter for suppressing the mechanical resonance of the PFSM and the narrowband disturbance is elaborated. And then, the different dual two-order filters are designed according to the frequency content of the PFSM and the narrowband disturbance. Finally, the proposed dual two-order filter assisted PI control algorithm and classic PI control algorithm are compared with each other. Experimental results show that, in the same conditions, the pointing accuracy of the proposed two-order filter assisted PI control algorithm is nearly 5 times better than that of the classic PI control algorithm, and the error attenuation bandwidth is one time higher. It also indicates that the proposed algorithm does not need an additional sensor; it is simple and effective for the suppression of the mechanical resonance of a PFSM and that of the narrowband disturbance, hence it improves the system error attenuation bandwidth and the beam pointing accuracy.
Loading characteristics and dynamic behaviors of the plane tin flying layer driven by detonation collision
Authors: Chen Da-Wei  , Wang Pei  , Sun Hai-Quan  , Yu Xi-Jun  ,   National Key Laboratory of Computational Physics, Institute of Applied Physics and Computational Mathematics, Beijing 100094, China
Published: December 2020

Under strong impact loading, metal materials will produce deformation and show ejecta behaviors. The mixing phenomenon, due to the detached matters entering into the background fluid, has a direct influence on the compression properties. According to the researches of ejecta, the damage and mixing are closely related with the loading state and the dynamic process. Up to now, many results have already been obtained under the condition of the directive impact of detonation. Further study on the metal materials response driven by detonation collision is needed. Previous studies have focused on the macro characteristics, such as the collision uplift and destruction. In this paper, we aim at the wave system's interaction process, in order to obtain the physical detail and to reveal the mechanisms of dynamic behaviors in the collision region. Investigations are carried out by means of both the numerical simulation and the shock polar theory analysis. Planer tin flying layer calculation model is designed for numerical simulation, so the sliding wave systems and shock conditions are obtained effectively. Based on the numerical results in the plane tin flying layer, the shock polar theory forecasts that the Mach reflection will occur, and the images of wave interactions given by numerical simulation also display the three-wave structure, which is the typical structure of the Mach reflection. Quantitative comparisons between the numerical results and theoretical analysis of the shock polar are in good agreement with each other. Furthermore, the critical conditions of Mach reflection in the cases of different shock conditions are given. Meanwhile typical characteristics of the histories of free surface velocity in the collision zone are analyzed. From the numerical and theoretical analyses, the shock dynamical model in the collision zone is proposed to reveal the mechanisms, and the model is very important for investigating the collision zone problem deeply in decomposition way. The results illustrate that in the collision zone there exist multiple kinds of shock loading ways, including one-dimensional once plane impact region, two-dimensional once oblique impact region, and two-dimensional twice oblique impacts region. The complex loading dynamic processes coupling with the unsteady flow field lead to the distributions of the peak pressure at different positions in the collision zone. The corresponding destroyed behaviors are shown, and thus we can establish the relationship between the reflection wave structure and the fracture morphology of the collision zone. This research results will provide an important theoretical support for the understanding and interpretation of the physical phenomena of material deformation, damage and mixing in the collision zone.
Study on discharge phenomena of short-air-gap in needle-plate electrode based on fractal theory
Authors: Zheng Dian-Chun  , Ding Ning  , Shen Xiang-Dong  , Zhao Da-Wei  , Zheng Qiu-Ping  , Wei Hong-Qing  ,   Key Laboratory of Engineering Dielectrics and Its Application, Ministry of Education, Harbin University of Science and Technology, Harbin 150080, China;,   Instrumentation Technology & Economy Institute, Beijing 100055, China
Published: December 2020

The process of gas discharge is very complicated and experimental observations indicate that streamers in short gap under non-uniform electric fields always exhibit irregularity and self-similarity, so a dielectric breakdown model, which is the combination of the random fractal method and the traditional streamer theory, can simulate this phenomenon.In this paper, a stochastic model with the growth probability index at any point proportional to the power of the electric field is utilized to quantify the channel tortuosity, and the space charge effect is taken into account as well. The potential distribution is solved by the Poisson's equation which is calculated iteratively by finite difference method; and the box counting method is used to characterize the channel tortuosity and estimate the fractal dimensions of the discharge channels. Based on this, an idea is proposed that the analysis of the experimental results, which in turn provide the appropriate parameters for the model, can better elucidate this phenomenon.The growth probability index can always get from the previous data, but the range of the will change under different experimental condition and there will exist differences in simulation results on fractal dimensions for different , so the limitation of the previous studies is its possible lack of generalizability. In order to define the range of the growth probability index in this model, the bifurcation phenomenon of plasma channels generated by the discharge, affected by HVDC (high-voltage direct current) of short-air-gap in a needle-plate electrode, is captured by ICCD. Before estimating the fractal dimensions of discharge channels, experimental images are saved as a binarized (black and white) image, and the gray-level transformation and boundary identification algorithm will be conducted to remove the apparent thickness of the discharge channel caused by the magnitude of the flowing currents through different branches. Experimental results show that the range of fractal dimensions in the box counting method for the discharge channel is 1.40-1.55. Under the same condition that other factors remain the same but the adjusted growth probability index in this simulation model should accord with the experimental results, all the facts demonstrate that the value of must lie between 0.04 and 0.05.