Table of contents

A tiny fraction of influential individuals play a critical role in the dynamics on complex systems. Identifying the influential nodes in complex networks has theoretical and practical significance. Considering the uncertainties of network scale and topology, and the timeliness of dynamic behaviors in real networks, we propose a rapid identifying method (RIM) to find the fraction of high-influential nodes. Instead of ranking all nodes, our method only aims at ranking a small number of nodes in network. We set the high-influential nodes as initial spreaders, and evaluate the performance of RIM by the susceptible–infected–recovered (SIR) model. The simulations show that in different networks, RIM performs well on rapid identifying high-influential nodes, which is verified by typical ranking methods, such as degree, closeness, betweenness, and eigenvector centrality methods.

In this article, the fractional derivatives are described in the modified Riemann–Liouville sense. We propose a new approach, namely an ansatz method, for solving fractional differential equations (FDEs) based on a fractional complex transform and apply it to solve nonlinear space–time fractional equations. As a result, the non-topological as well as the singular soliton solutions are obtained. This method can be suitable and more powerful for solving other kinds of nonlinear fractional FDEs arising in mathematical physics.

In this paper, based on the conjugate of the complex basis function, a new complex variable moving least-squares approximation is discussed. Then using the new approximation to obtain the shape function, an improved complex variable element-free Galerkin (ICVEFG) method is presented for two-dimensional (2D) elastoplasticity problems. Compared with the previous complex variable moving least-squares approximation, the new approximation has greater computational precision and efficiency. Using the penalty method to apply the essential boundary conditions, and using the constrained Galerkin weak form of 2D elastoplasticity to obtain the system equations, we obtain the corresponding formulae of the ICVEFG method for 2D elastoplasticity. Three selected numerical examples are presented using the ICVEFG method to show that the ICVEFG method has the advantages such as greater precision and computational efficiency over the conventional meshless methods.

We propose a new scheme for simulation of a high-order nonlinear Schrödinger equation with a trapped term by using the mid-point rule and Fourier pseudospectral method to approximate time and space derivatives, respectively. The method is proved to be both charge- and energy-conserved. Various numerical experiments for the equation in different cases are conducted. From the numerical evidence, we see the present method provides an accurate solution and conserves the discrete charge and energy invariants to machine accuracy which are consistent with the theoretical analysis.

We present a novel efficient approach in calculating induced transmembrane voltage (ITV) on cells based on transformation optics. As cell membrane is much thinner than the dimension of a typical cell, discretizing the membrane needs numerous meshes. Using an anisotropic medium based on transformation optics, the thickness of the membrane can be exaggerated by at least one order, which eliminates rigorous mesh refinement and reduces unknowns greatly. The accuracy and efficiency of the proposed method are verified by a cylindrical cell model. Moreover, the influence on ITV with bound water (BW) layers is also studied. The results show that when cells are exposed to nanosecond electric field, BW layers should be rigorously considered in calculating ITV.

The characteristic of group delay is analyzed based on an electronic circuit, and its time-domain nature is studied with time-domain simulation and experiment. The time-domain simulations and experimental results show that group delay is the delay of the energy center of the amplitude-modulated pulse, rather than the propagation delay of the electromagnetic field. As group velocity originates from the definition of group delay and group delay is different from the propagation delay, the superluminality or negativity of group velocity does not mean the superluminal or negative propagation of the electromagnetic field.

By virtue of the operator Hermite polynomial method and the technique of integration within the ordered product of operators we derive a new kind of special function, which is closely related to one- and two-variable Hermite polynomials. Its application in deriving the normalization for some quantum optical states is presented.

The Shannon information entropy for the Schrödinger equation with a nonuniform solitonic mass is evaluated for a hyperbolic-type potential. The number of nodes of the wave functions in the transformed space z are broken when recovered to original space x. The position S_x and momentum S_p information entropies for six low-lying states are calculated. We notice that the S_x decreases with the increasing mass barrier width a and becomes negative beyond a particular width a, while the S_p first increases with a and then decreases with it. The negative S_x exists for the probability densities that are highly localized. We find that the probability density ρ(x) for n = 1, 3, 5 are greater than 1 at position x = 0. Some interesting features of the information entropy densities ρ_s(x) and ρ_s(p) are demonstrated. The Bialynicki–Birula–Mycielski (BBM) inequality is also tested for these states and found to hold.

In the analysis of quantum discord, the minimization of average entropy traditionally involved over orthogonal projective measurements may be attained at more optimal decompositions by using the positive-operator-valued measure (POVM) measurements. Taking advantage of the quantum steering ellipsoid in combination with three-element POVM optimization, we show that, for a family of two-qubit X states locally interacting with Markovian non-dissipative environments, the decay rates of quantum discord show smooth dynamical evolutions without any sudden change. This is in contrast to two-element orthogonal projective measurements, in which case the sudden change of the decay rates of quantum and classical decoherences may be a common phenomenon. Notwithstanding this, we find that a subset of X states (including the Bell diagonal states) involving POVM optimization can still preserve the sudden change character as usual.

We study the non-Markovianity of the single qubit system coupled with an isotropic Lipkin–Meshkov–Glick (LMG) model by an effective method proposed by Breuer et al. (Breuer H P and Piilo J 2009 Europhys. Lett.85 5004). It is discovered that the non-Markovianity is concerned with the quantum phase transitions (QPTs). In the open system, we present that the strong coupling inside the bath and the strong interaction between the system and bath can enhance the degree of non-Markovianity. Moreover, the non-Markovianity is stronger and more sensitive for the bath in the symmetric phase than the symmetry broken phase.

We propose a scheme for purification of a general mixed entangled state. In this scheme, we start from a large number of general mixed entangled states and end up, after local operation and classical communication, with a smaller number of Bell diagonal states with higher entanglement. In particular, the scheme can purify one maximally entangled state from two entangled pairs prepared in a class of mixed entangled state. Furthermore we propose a linear optical implementation of the present scheme with polarization beam splitters and photon detectors.

In this paper, two novel schemes for deterministic joint remote state preparation (JRSP) of arbitrary single- and two-qubit states are proposed. A set of ingenious four-particle partially entangled states are constructed to serve as the quantum channels. In our schemes, two senders and one receiver are involved. Participants collaborate with each other and perform projective measurements on their own particles under an elaborate measurement basis. Based on their measurement results, the receiver can reestablish the target state by means of appropriate local unitary operations deterministically. Unit success probability can be achieved independent of the channel's entanglement degree.

Perturbation imposed on a chaos system is an effective way to maintain its chaotic features. A novel parameter perturbation method for the tent map based on the Lyapunov exponent is proposed in this paper. The pseudo-random sequence generated by the tent map is sent to another chaos function — the Chebyshev map for the post processing. If the output value of the Chebyshev map falls into a certain range, it will be sent back to replace the parameter of the tent map. As a result, the parameter of the tent map keeps changing dynamically. The statistical analysis and experimental results prove that the disturbed tent map has a highly random distribution and achieves good cryptographic properties of a pseudo-random sequence. As a result, it weakens the phenomenon of strong correlation caused by the finite precision and effectively compensates for the digital chaos system dynamics degradation.

A novel adaptive–impulsive scheme is proposed for synchronizing fractional-order chaotic systems without the necessity of knowing the attractors' bounds in priori. The nonlinear functions in these systems are supposed to satisfy local Lipschitz conditions but which are estimated with adaptive laws. The novelty is that the combination of adaptive control and impulsive control offers a control strategy gathering the advantages of both. In order to guarantee the convergence is no less than an expected exponential rate, a combined feedback strength design is created such that the symmetric axis can shift freely according to the updated transient feedback strength. All of the unknown Lipschitz constants are also updated exponentially in the meantime of achieving synchronization. Two different fractional-order chaotic systems are employed to demonstrate the effectiveness of the novel adaptive–impulsive control scheme.

In this paper, we consider the synchronization of chaotic Hindmarsh Rose (HR) neurons via a scalar control input. Chaotic HR neurons coupled with a gap junction are taken into consideration, and an active compensation mechanism-based adaptive control is employed to realize the synchronization of two HR neurons. As such an adaptive control is utilized, an accurate model of the system is of no necessity. Asymptotical synchronization of two HR neurons is guaranteed by theoretical results. Numerical results are also provided to confirm the proposed synchronization approach.

The discrete iterative map model of peak current-mode controlled buck converter with constant current load (CCL), containing the output voltage feedback and ramp compensation, is established in this paper. Based on this model the complex dynamics of this converter is investigated by analyzing bifurcation diagrams and the Lyapunov exponent spectrum. The effects of ramp compensation and output voltage feedback on the stability of the converter are investigated. Experimental results verify the simulation and theoretical analysis. The stability boundary and chaos boundary are obtained under the theoretical conditions of period-doubling bifurcation and border collision. It is found that there are four operation regions in the peak current-mode controlled buck converter with CCL due to period-doubling bifurcation and border-collision bifurcation. Research results indicate that ramp compensation can extend the stable operation range and transfer the operating mode, and output voltage feedback can eventually eliminate the coexisting fast-slow scale instability.

Wavelength-dependent AC Stark shifts and magic wavelengths of the terahertz clock transitions between the metastable triplet states 6s5d ³D₁ and 6s5d ³D₂ are investigated with considering the optical lattice trapping of barium atoms with the linearly polarized laser. The trap depths and the slopes of light shift difference with distinct magic wavelengths of the optical lattices are also discussed in detail. Several potentially suitable working points for the optical lattice trapping laser are recommended and selected from these magic wavelengths.

Energy levels, radiative rates, oscillator strengths and line strengths are reported for transitions among the lowest 97 levels of the (1s²2s²2p⁶) 3s²3p², 3s²3p3d, 3s3p³, 3p⁴, 3s3p²3d, and 3s²3d² configurations of Rb XXIV. A multiconfiguration Dirac–Fock (MCDF) method is adopted for the calculations. Radiative rates, oscillator strengths, and line strengths are provided for all electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2), and magnetic quadrupole (M2) transitions from the ground level to all 97 levels, although calculations are performed for a much larger number of levels. To achieve the accuracy of the data, comparisons are provided with similar data obtained from the Flexible Atomic Code (FAC) and also with the available theoretical and experimental results. Our energy levels are found to be accurate to better than 1.2%. Wavelengths calculated are found to lie in EUV (extreme ultraviolet) and x-ray regions. Additionally, lifetimes for all 97 levels are obtained for the first time.

We investigate the target and intensity dependence of plateau in high-order above threshold ionization (HATI) by simulating the two-dimensional (2D) momentum distributions and the energy spectra of photoelectrons in HATI of rare gas atoms through using the quantitative rescattering model. The simulated results are compared with the existing experimental measurements. It is found that the slope of the plateau in the HATI photoelectron energy spectrum highly depends on the structure of elastic scattering differential cross section (DCS) of laser-induced returning electron with its parent ion. The investigations of the long- and short-range potential effects in the DCSs reveal that the short-range potential, which reflects the structure of the target, plays an essential role in generating the HATI photoelectron spectra.

The combination of a velocity mapping imaging technique and mathematical transformation is adopted to study the angular distribution of electrons ejected from the Eu 4f⁷6p_1/26d autoionizing states, which are excited with a three-step excitation scheme via different Eu 4f⁷6s6d ⁸D_J (J = 5/2, 7/2, and 9/2) intermediate states. In order to determine the energy dependence of angular distribution of the ejected electrons, the anisotropic parameters are measured in the spectral profile of the 6p_1/26d autoionizing states by tuning the wavelength of the third-step laser across the ionic resonance lines of the Eu 6s⁺ → 6p⁺. The configuration interaction is discussed by comparing the angular distributions of ejected electrons from the different states. The present study reveals the profound variations of anisotropic parameters in the entire region of autoionization resonance, highlighting the complicated nature of the autoionization process for the lowest member of 6p_1/26d autoionization series.

The resonant charge transfer process for Li⁺−Li(2s) collision is investigated by the quantum-mechanical molecular orbital close-coupling (QMOCC) method and the two-center atomic-orbital close-coupling (AOCC) method in an energy range of 1.0 eV/u–10⁴ eV/u. Accurate molecular structure data and charge transfer cross sections are given. Both the all-electron model (AEM) and one-electron model (OEM) are used in the QMOCC calculations, and the discrepancies between the two models are analyzed. The OEM calculation can also give a reliable prediction of the cross sections for energies below 1 keV/u.

The site preferences of the rare earth intermetallics Nd₆Fe_13−xT_xSi (T = Co, Ni) are investigated by using interatomic pair potentials which are converted from a lattice-inversion method. Calculation shows that the order of the site preference of Co is 4d, 16k, 16l₁, and 16l₂ and that of Ni is 16l₂, 16l₁, 16k, and 4d in Nd₆Fe_13−xT_xSi. Calculated lattice and positional parameters are found to agree with those reported in the literature. Furthermore, the phonon density of states for Nd₆Fe_13−xT_xSi is also evaluated, and a qualitative analysis featuring the coordination and the relevant potentials is carried out.

A four-body distorted wave approximation is presented for theoretical investigations of the single ionization of ground-state helium atoms by fully stripped carbon ions at impact energies of 2 MeV/amu and 100 MeV/amu. The nine-dimensional integrals for the partial quantum-mechanical transition amplitudes of the specified reaction are reduced to some analytical expressions or one-dimensional integrals over real variables. Fully differential cross sections (FDCSs) are calculated and compared with their experimental values as well as the results obtained from other theories. Despite the simplicity and quickness of the proposed quadrature, the comparison shows that the obtained results are in reasonable agreement with the experiment and are compatible with those of other complicated theories.

The molecular dynamics method is used to investigate the interaction between one–six nitrate anions and water clusters absorbing six ozone molecules. The infrared (IR) absorption and reflection spectra are reshaped significantly, and new peaks appear at Raman spectra due to the addition of ozone and nitrate anions to the disperse water system. After ozone and nitrate anions are captured, the average (in frequency) IR reflection coefficient of the water disperse system increased drastically and the absorption coefficient fell.

According to the reciprocity principle, we propose an efficient model to compute the shielding effectiveness of a rectangular cavity with apertures covered by conductive sheet against an external incident electromagnetic wave. This problem is converted into another problem of solving the electromagnetic field leakage from the cavity when the cavity is excited by an electric dipole placed within it. By the combination of the unperturbed cavity field and the transfer impedance of the sheet, the tangential electric field distribution on the outer surface of the sheet is obtained. Then, the field distribution is regarded as an equivalent surface magnetic current source responsible for the leakage field. The validation of this model is verified by a comparison with the circuital model and the full-wave simulations. This time-saving model can deal with arbitrary aperture shape, various wave propagation and polarization directions, and the near-field effect.

The linearity of the traveling-wave tube is a very important characteristic for a modern communication system. To improve the linearity of the traveling-wave tube at no expense of the saturated output power and overall efficiency, a modified pitch profile combined with a small adjustment of operating parameters is proposed. The optimal design of the helix circuit is evaluated theoretically by a large signal analysis, and the experimental test is also carried out to make a comparison of performance between the novel and original designed traveling-wave tubes. The experiments show that the saturated output powers and efficiencies of these two tubes are close to each other, while the linearity of the traveling-wave tube is obviously improved. The total phase shift and AM/PM conversion at saturation of the novel tube, averaged over the operating band, are only 30.6°/dB and 2.5°/dB, respectively, which are 20.1°/dB and 1.6°/dB lower than those of the original tube, respectively. Moreover, the third-order intermodulation of the novel tube is up to 2.2 dBc lower than that of the original tube.

We numerically investigate the electromagnetic properties of tellurium dielectric resonator metamaterial at the infrared wavelengths. The transmission spectra, effective permittivity and permeability of the periodic tellurium metamaterial structure are investigated in detail. The linewidth of the structure in the direction of magnetic field W_x has effects on the position and strength of the electric resonance and magnetic resonance modes. With appropriately optimizing the geometric dimensions of the designed structure, the proposed tellurium metamaterial structure can provide electric resonance mode and high order magnetic resonance mode in the same frequency band. This would be helpful to analyze and design low-loss negative refraction index metamaterials at the infrared wavelengths.

A lossy high-impedance surface comprised of two layers of resistive frequency selective surfaces is employed to design a tunable electromagnetic absorber. The tunability is realized through changing the composite unit cell by moving the top layer mechanically. To explain the absorbing mechanism, an equivalent circuit model with an interacting coefficient is proposed. Then, simulations and measurements are carried out and agree well with each other. Results show that the complex structure with a thickness less than λ₀/4 is able to achieve a wideband absorption in a frequency range from 5.90 GHz to 19.73 GHz. Moreover, it is tunable in the operation frequency band.

Light absorption enhancement is very important for improving the power conversion efficiency of a thin film a-Si solar cell. In this paper, a thin-film a-Si solar cell model with double-sided SiO₂ particle layers is designed, and then the underlying mechanism of absorption enhancement is investigated by finite difference time domain (FDTD) simulation; finally the feasible experimental scheme for preparing the SiO₂ particle layer is discussed. It is found that the top and bottom SiO₂ particle layers play an important role in anti-reflection and light trapping, respectively. The light absorption of the cell with double-sided SiO₂ layers greatly increases in a wavelength range of 300 nm–800 nm, and the ultimate efficiency increases more than 22% compared with that of the flat device. The cell model with double-sided SiO₂ particle layers reported here can be used in varieties of thin film solar cells to further improve their performances.

We present a narrow band forward scattering optical antenna which is based on the excitation of distinctive whispering gallery modes (WGMs). The antenna is composed of three coaxial cylinder layers: a dielectric layer is sandwiched between a metallic core and cladding. Owing to the destructive interference between the scattering of the outer metallic cladding and the WGM in the backward direction, the power flow in the forward direction is increased. Simulation and analysis show that in proper geometry conditions, the cavity can be tuned into a superscattering state. At this state, both the zeroth and the first order of WGM are excited and contribute to the total scattering. It is shown that the power ratio (power towards backward divided by power towards forward) can be enhanced to about 27 times larger than that for a non-resonant position by the superscattering. Owing to the confinement of the cladding to WGMs, the wavelength range of effective forward scattering is considerably narrow (about 15 nm).

We present a scheme that is able to achieve the ghost imaging with broad distance. The physical nature of our scheme is that the different wavelength beams are separated in free space by an optical media according to the slow light or dispersion principle. Meanwhile, the equality of the optical distance of the two light arms is not violated. The photon correlation is achieved by the rotating ground glass plate (RGGP) and spatial light modulator (SLM), respectively. Our work shows that a monochromic ghost image can be obtained in the case of RGGP. More importantly, the position (or distance) of the object can be ascertained by the color of the image. Thus, the imaging and ranging processes are combined as one process for the first time to the best of our knowledge. In the case of SLM, we can obtain a colored image regardless of where the object is.

In order to improve the reconstruction performance for ill-posed emission tomographic problems with limited projections, a generalized interpolation method is proposed in this paper, in which the virtual lines of projection are fabricated from, but not linearly dependent on, the measured projections. The method is called the virtual projection (VP) method. Also, an iterative correction method for the integral lengths is proposed to reduce the error brought about by the virtual lines of projection. The combination of the two methods is called the iterative virtual projection (IVP) method. Based on a scheme of equilateral triangle plane meshes and a six asymmetrically arranged detection system, numerical simulations and experimental verification are conducted. Simulation results obtained by using a non-negative linear least squares method, without any other constraints or regularization, demonstrate that the VP method can gradually reduce the reconstruction error and converges to the desired one by fabricating additional effective projections. When the mean square deviation of normal error superimposed on the simulated measured projections is smaller than 0.03, i.e., the signal-to-noise ratio (SNR) for the measured projections is higher than 30.4, the IVP method can further reduce the reconstruction error reached by the VP method apparently. In addition, as the regularization matrix in the Tikhonov regularization method is updated by an iterative correction process similar to the IVP method presented in this paper, or the Tikhonov regularization method is used in the IVP method, good improvement is achieved.

We propose a scheme to coherently control the field-free orientation of NO molecule whose rotational temperature is above 0 K. It is found that the maximum molecular orientation is affected by two factors: one is the sum of the population of M = 0 rotational states and the other is their distribution, however, their distribution plays a much more significant role in molecular orientation than the sum of their population. By adopting a series of linearly polarized pulses resonant with the rotational states, the distribution of M = 0 rotational states is well rearranged. Though the number of pulses used is small, a relatively high orientation degree can be obtained. This scheme provides a promising approach to the achievement of a good orientation effect.

We study the two coupling two-level single molecules driven by an external field as a photon pair source. The probability of emitting two photons, P₂, is employed to describe the photon pair source quality in a short time, and the correlation coefficient R_AB is employed to describe the photon pair source quality in a long time limit. The results demonstrate that the coupling single quantum emitters can be considered as a stable photon pair source.

We show experimentally that when an unfocused continuous wave (CW) laser beam is obliquely incident onto the surface of a millimeter-sized mineral oil drop on sucrose solution, it will exert a pushing force on the oil drop, making it move forwards along the surface of the sucrose solution. However, after a period of time, the oil drop stops moving. This can be explained as the phenomenon caused by the change of Abraham momentum, the optical gradient force, and friction together.

We theoretically investigate the entanglement properties in a hybrid system consisting of an optical cavity–array coupled to a mechanical resonator. We show that the steady state of the system presents bipartite continuous variable entanglement in an experimentally accessible parameter regime. The effects of the cavity–cavity coupling strength on the bipartite entanglements in the field–mirror subsystem and in the field–field subsystem are studied. We further find that the entanglement between the adjacent cavity and the movable mirror can be entirely transferred to the distant cavity and mirror by properly choosing the cavity detunings and the coupling strength in the two-cavity case. Surprisingly, such a remote macroscopic entanglement tends to be stable in the large coupling regime and persists for environment temperatures at above 25 K in the three-cavity case. Such optomechanical systems can be used for the realization of continuous variable quantum information interfaces and networks.

The lattice structure image of a plasma standing wave in a Purcell cavity of silicon is observed. The plasma wave produced by the pulsed laser could be used to fabricate the micro-nanostructure of silicon. The plasma lattice structures induced by the nanosecond pulsed laser in the cavity may be similar to the Wigner crystal structure. It is interesting that the beautiful diffraction pattern could be observed in the plasma lattice structure. The radiation lifetime could be shortened to the nanosecond range throughout the entire spectral range and the relaxation time could be lengthened for higher emission efficiency in the Purcell cavity, which results in the fact that the plasmonic emission is stronger and its threshold is lower.

The steady-state gain distribution in cladding pumped thulium-doped fiber laser (TDFL) is analytically and numerically solved based on the rate equations including loss coefficients and cross relaxation effect. With the gain curve, a problem, which is named optical feedback inhibition (OFI) and always occurs in tandem TDFL-Ho:YAG laser system, is analyzed quantitatively. The actual characteristics of output spectra and power basically prove the conclusion of theoretical analysis. Then a simple mirror-deflected L-shaped cavity is employed to restrain the external feedback and simplify the structure of fiber-bulk Ho:YAG laser. Finally, 25 W of 2097-nm laser power and 51.2% of optical-to-optical conversion efficiency are obtained, and the beam quality factor is less than 1.43 obtained by knife-edge method.

We report a robust method of directly stabilizing a grating feedback diode laser to an arbitrary frequency in a large range. The error signal, induced from the difference between the frequency measured by a wavelength meter and the preset target frequency, is fed back to the piezoelectric transducer module of the diode laser via a sound card in the computer. A visual Labview procedure is developed to realize a feedback system. In our experiment the frequency drift of the diode laser is reduced to 8 MHz within 25 min. The robust scheme can be adapted to realize the arbitrary frequency stabilization for many other kinds of lasers.

A wide wavelength tuning range swept external-cavity laser using an InAs/GaAs quantum-dot superluminescent diode as a gain device is demonstrated. The tunable filter consists of a polygon scanner and a grating in Littrow telescope-less configuration. The swept laser generates greater than 54-mW peak output power and up to 33-kHz sweep rate with a sweep range of 150 nm centered at 1155 nm. The effects of injection current and sweep rate on the sweep performance of the swept laser are studied.

Environmental vibration causes mechanical deformation in optical fibers, which induces excess frequency noise in fiber-stabilized lasers. In order to solve such a problem, we propose an ultralow acceleration sensitivity fiber spool with symmetrically mounted structure. By numerical analysis with the finite element method, we obtain the optimal geometry parameters of the spool with which the horizontal and vertical acceleration sensitivity can be reduced to 3.25 × 10⁻¹²/g and 5.38 × 10⁻¹²/g respectively. Moreover, the structure features the insensitivity to the variation of geometry parameters, which will minimize the influence from numerical simulation error and manufacture tolerance.

A novel three-dimensional (3D) imaging lidar system which is based on a virtual instrument technique is introduced in this paper. The main characteristics of the system include: the capability of modeling a 3D object in accordance with the actual one by connecting to a geographic information system (GIS), and building the scene for the lidar experiment including the simulation environment. The simulation environment consists of four parts: laser pulse, atmospheric transport, target interaction, and receiving unit. Besides, the system provides an interface for the on-site experiment. In order to process the full waveform, we adopt the combination of pulse accumulation and wavelet denoising for signal enhancement. We also propose an optimized algorithm for data decomposition: the V–L decomposition method, which combines Vondrak smoothing and laser-template based fitting. Compared with conventional Gaussian decomposition, the new method brings an improvement in both precision and resolution of data decomposition. After applying V–L decomposition to the lidar system, we present the 3D reconstructed model to demonstrate the decomposition method.

Soft-stamped nanoimprint lithography (NIL) is considered as one of the most effective processes of nanoscale patterning because of its low cost and high throughput. In this work, this method is used to emboss the poly (9, 9-dioctylfluorene) film. By reducing the linewidth of the nanogratings on the stamp, the orientations of nanocrystals are confined along the grating vector in the nanoimprint process, where the confinement linewidth is comparable to the geometrical size of the nanocrystal. When the linewidth is about 400 nm, the poly (9, 9-dioctylfluorene) (PFO) nanocrystals could be orderly arranged in the nanogratings, so that both pattern transfer and well-aligned nanocrystal arrangement could be achieved in a single step by the soft-stamped NIL. The relevant mechanism of the nanocrystalline alignment in these nanogratings is fully discussed. The modulation of nanocrystal alignment is of benefit to the charge mobilities and other performances of PFO-based devices for the future applications.

The experiment setup of a reflecting combination device, which has more advantages than a transmitting combination device, is designed in this study. To achieve angular spectrum selectivity, only one type of reflective component is needed, so difficulties of design and preparation are reduced. A dielectric multilayer film is applied to the reflective component, and the long wave-pass coating stacks of the structure are designed. To achieve high stopband transmittance and reduce electric field intensity at a wavelength of 1053 nm, an objective function is proposed for designing an optimized coating. The final optimized coating has good spectral characteristics and a high laser-induced damage threshold. A dielectric multilayer film with high reflectance plays an important role in preparing and applying a dielectric multilayer film reflecting cutoff filter-combination device.

In order to design a sonochemical reactor with high reaction efficiency, it is important to clarify the size and intensity of the sonochemical reaction field. In this study, the reaction field in a sonochemical reactor is estimated from the distribution of pressure above the threshold for cavitation. The quantitation of hydroxide radical in a sonochemical reactor is obtained from the calculation of bubble dynamics and reaction equations. The distribution of the reaction field of the numerical simulation is consistent with that of the sonochemical luminescence. The sound absorption coefficient of liquid in the sonochemical reactor is much larger than that attributed to classical contributions which are heat conduction and shear viscosity. Under the dual irradiation, the reaction field becomes extensive and intensive because the acoustic pressure amplitude is intensified by the interference of two ultrasonic waves.

We design a planar metasurface to modulate the wavefront of a water surface wave (WSW) on a deep sub-wavelength scale. The metasurface is composed of an array of coiling-up-space units with specially designed parameters, and can take on the work of steering the wavefront when it is pierced into water. Like their acoustic counterparts, the modulation of WSW is ascribed to the gradient phase shift of the coiling-up-space units, which can be perfectly tuned by changing the coiling plate length and channel number inside the units. According to the generalized Snell's law, negative refraction and 'driven' surface mode of WSW are also demonstrated at certain incidences. Specially, the transmitted WSW could be efficiently guided out by linking a symmetrically-corrugated channel in 'driven' surface mode. This work may have potential applications in water wave energy extraction and coastal protection.

Hyperthermia is a promising method to enhance chemo and radiation therapy of breast cancer. In the process of hyperthermia, temperature monitoring is of great importance to assure the effectiveness of treatment. The transmission speed of ultrasound in biomedical tissue changes with temperature. However, when mapping the speed of sound directly to temperature in each pixel as desired for using all speeds of ultrasound data, temperature bipolar edge enhancement artifacts occur near the boundary of two tissues with different speeds of ultrasound. After the analysis of the reasons for causing these artifacts, an optimized method is introduced to rebuild the temperature field image by using the continuity constraint as the judgment criterion. The significant smoothness of the rebuilding image in the transitional area shows that our proposed method can build a more precise temperature image for controlling the medical thermal treatment.

In the present work, we investigate the nonlinear parametrically excited vibration and active control of a gear pair system involving backlash, time-varying meshing stiffness and static transmission error. Firstly, a gear pair model is established in a strongly nonlinear form, and its nonlinear vibration characteristics are systematically investigated through different approaches. Several complicated phenomena such as period doubling bifurcation, anti period doubling bifurcation and chaos can be observed under the internal parametric excitation. Then, an active compensation controller is designed to suppress the vibration, including the chaos. Finally, the effectiveness of the proposed controller is verified numerically.

The skew-gradient representation of a generalized Birkhoffian system is studied. A condition under which the generalized Birkhoffian system can be considered as a skew-gradient system is obtained. The properties of the skew-gradient system are used to study the properties, especially the stability, of the generalized Birkhoffian system. Some examples are given to illustrate the application of the result.

A series of direct numerical simulations of the fully developed plane Couette flow at a Reynolds number of 6000 (based on the relative wall speed and half the channel height h) with different streamwise and spanwise lengths are conducted to investigate the effects of the computational box sizes on the secondary flow (SF). Our focuses are the number of counter-rotating vortex pairs and its relationship to the statistics of the mean flow and the SF in the small and moderate computational box sizes. Our results show that the number of vortex pairs is sensitive to the computational box size, and so are the slope parameter, the rate of the turbulent kinetic energy contributed by the SF, and the ratio of the kinetic energy of the SF to the total kinetic energy. However, the averaged spanwise width of each counter-rotating vortex pair in the plane Couette flow is found, for the first time, within 4(1 ± 0.25)h despite the domain sizes.

The phase transition between a massive dense phase and a diluted superparamagnetic phase has been studied by means of a direct molecular dynamics simulation. The equilibrium structures of the ferrofluid aggregate nucleus are obtained for different values of a temperature and an external magnetic field magnitude. An approximate match of experiment and simulation has been shown for the ferrofluid phase diagram coordinates "field–temperature". The provided phase coexistence curve has an opposite trend comparing to some of known theoretical results. This contradiction has been discussed. For given experimental parameters, it has been concluded that the present results describe more precisely the transition from linear chains to a dense globes phase. The theoretical concepts which provide the opposite binodal curve dependency trend match other experimental conditions: a diluted ferrofluid, a high particle coating rate, a high temperature, and/or a less particles coupling constant value.

Dynamic mechanical properties of nanocomposite films with different ratios of single walled carbon nanotubes/polymethyl methacrylate (SWCNTs/PMMA) are studied. Nanocomposite films of different ratios (0, 0.5, 1.0, and 2.0 weight percent (wt%)) of SWCNTs/PMMA are fabricated by using a casting technique. The morphological and structural properties of both SWCNT powder and SWCNTs/PMMA nanocomposite films are investigated by using a high resolution transmission electron microscope and x-ray diffractometer respectively. The mechanical properties including the storage modulus, loss modulus, loss factor (tan δ) and stiffness of the nanocomposite film as a function of temperature are recorded by using a dynamic mechanical analyzer at a frequency of 1 Hz. Compared with pure PMMA film, the nanocomposite films with different ratios of SWCNTs/PMMA are observed to have enhanced storage moduli, loss moduli and high stiffness, each of which is a function of temperature. The intensity of the tan δ peak for pure PMMA film is larger than those of the nanocomposite films. The glass transition temperature (T_g) of SWCNTs/PMMA nanocomposite film shifts towards the higher temperature side with respect to pure PMMA film from 91.2 °C to 99.5 °C as the ratio of SWCNTs/PMMA increases from 0 to 2.0 wt%.

Microwave breakdown at atmospheric pressure causes the formation of a discrete plasma structure. The one-dimensional fluid model coupling Maxwell equations with plasma fluid equations is used to study the effect of the microwave frequency on the formation of air plasma. Simulation results show that, the filamentary plasma array propagating toward the microwave source is formed at different microwave frequencies. As the microwave frequency decreases, the ratio of the distance between two adjacent plasma filaments to the corresponding wavelength remains almost unchanged (on the order of 1/4), while the plasma front propagates more slowly due to the increase in the formation time of the new plasma filament.

An AlGaN/GaN high electron mobility transistor (HEMT) device is prepared by using a semiconductor nanofabrication process. A reflective radio-frequency (RF) readout circuit is designed and the HEMT device is assembled in an RF circuit through a coplanar waveguide transmission line. A gate capacitor of the HEMT and a surface-mounted inductor on the transmission line are formed to generate LC resonance. By tuning the gate voltage V_g, the variations of gate capacitance and conductance of the HEMT are reflected sensitively from the resonance frequency and the magnitude of the RF reflection signal. The aim of the designed RF readout setup is to develop a highly sensitive HEMT-based detector.

Bond valence method illustrates the relation between valence and length of a particular bond type. This theory has been used to predict structure information, but the effect is very limited. In this paper, two indexes, i.e., global instability index (GII) and bond strain index (BSI), are adopted as a judgment of a search-match program for prediction. The results show that with GII and BSI combined as judgment, the predicted atom positions are very close to real ones. The mechanism and validity of this searching program are also discussed. The GII & BSI distribution contour map reveals that the predicted function is a reflection of exponential feature of bond valence formula. This combined searching method may be integrated with other structure-determination method, and may be helpful in refining and testifying light atom positions.

The physical effects on surface and flexoelectric polarization in a weak anchoring nematic liquid crystal cell are investigated systematically. We derive the analytic expressions of two effective anchoring energies for lower and upper substrates respectively as well as their effective anchoring strengths and corresponding tilt angles of effective easy direction. All of these quantities are relevant to the magnitudes of both two polarizations and the applied voltage U. Based on these expressions, the variations of effective anchoring strength and the tilt angle with the applied voltage are calculated for the fixed values of two polarizations. For an original weak anchoring hybrid aligned nematic cell, it may be equivalent to a planar cell for a small value of U and has a threshold voltage. The variation of reduced threshold voltage with reduced surface polarization strength is also calculated. The role of surface polarization is important without the adsorptive ions considered.

This work is devoted to the experimental determination of the electrostatic properties of the molecular 4-methyl-7-(salicylidene amino) coumarin (C₁₇H₁₃NC₃) using high resolution x-ray diffraction data. The experimental results are compared with those obtained theoretically from calculation type ab initio. The experimental investigation is carried out using the molecular electron charge density distribution based on the multipolar model of Hansen and Coppens. However the theoretical calculations are conducted by using the molecular orbital B3LYP method and the Hartree–Fock (HF) approximation with the basis set 6-31G (d,p) implemented in the Gaussian program. In addition to the structural analysis, the thermal agitation is also analyzed in terms of rigid blocks to ensure a better precision of the results. Subsequently, the electrostatic atomic and molecular properties such as the net charges, the molecular dipolar moment to highlight the nature of charge transfer existing within the molecule studied are derived. Moreover, the obtained electrostatic potential enables the localization of the electropositive and the electronegative parts of the investigated molecule. The present work reports in detail the obtained electrostatic properties of this biologically important molecule.

By combining first-principles calculations with the particle swarm optimization algorithm, we predicted a hexagonal structure for TcB, which is energetically more favorable than the previously reported WC-type and Cmcm structures. The new phase is mechanically and dynamically stable, as confirmed by its phonon and elastic constants calculations. The calculated mechanical properties show that it is an ultra-incompressible and hard material. Meanwhile, the elastic anisotropy is investigated by the shear anisotropic factors and ratio of the directional bulk modulus. Density of states analysis reveals that the strong covalent bonding between Tc and B atoms plays a leading role in forming a hard material. Additionally, the compressibility, bulk modulus, Debye temperature, Grüneisen parameter, specific heat, and thermal expansion coefficient of TcB are also successfully obtained by using the quasi-harmonic Debye model.

Our calculations demonstrate that the concentration of neutral oxygen vacancies can affect the geometrical structrue, electronic structure, and optical properties of α-quartz. Moreover, the distribution of the neutral oxygen divacancy can also exert some influence on the properties of α-quartz. The dissimilarity and similarities are presented in the corresponding density of state (DOS) and absorption spectrum. In addition, when a higher defect concentration is involved in α-quartz, the influence of center on the geometry of α-quartz becomes more significant. However, the introduction of an center barely results in any improvement compared with the influence produced by the corresponding neutral defect.

Functional failure mode of commercial deep sub-micron static random access memory (SRAM) induced by total dose irradiation is experimentally analyzed and verified by circuit simulation. We extensively characterize the functional failure mode of the device by testing its electrical parameters and function with test patterns covering different functional failure modes. Experimental results reveal that the functional failure mode of the device is a temporary function interruption caused by peripheral circuits being sensitive to the standby current rising. By including radiation-induced threshold shift and off-state leakage current in memory cell transistors, we simulate the influence of radiation on the functionality of the memory cell. Simulation results reveal that the memory cell is tolerant to irradiation due to its high stability, which agrees with our experimental result.

In this study we investigate the dynamic recovery effects in IRF9520 commercial p-channel power vertical double diffused metal–oxide semiconductor field-effect transistors (VDMOSFETs) subjected to negative bias temperature (NBT) stressing under the particular pulsed bias. Particular values of the pulsed stress voltage frequency and duty cycle are chosen in order to analyze the recoverable and permanent components of stress-induced threshold voltage shift in detail. The results are discussed in terms of the mechanisms responsible for buildup of oxide charge and interface traps. The partial recovery during the low level of pulsed gate voltage is ascribed to the removal of recoverable component of degradation, i.e., to passivation/neutralization of shallow oxide traps that are not transformed into the deeper traps (permanent component). Considering the value of characteristic time constant associated with complete removal of the recoverable component of degradation, it is shown that by selecting an appropriate combination of the frequency and duty cycle, the threshold voltage shifts induced under the pulsed negative bias temperature stress conditions can be significantly reduced, which may be utilized for improving the device lifetime in real application circuits.

Hydrogenated amorphous silicon nitride films (SiN_x:H) are deposited at low temperature by high-frequency plasma-enhanced chemical vapor deposition (HF PECVD). The main effort is to investigate the roles of plasma frequency and plasma power density in determining the film properties particularly in stress. Information about chemical bonds in the films is obtained by Fourier transform infrared spectroscopy (FTIR). The stresses in the SiN_x:H film are determined from substrate curvature measurements. It is shown that plasma frequency plays an important role in controlling the stresses in SiN_x:H films. For silicon nitride layers grown at plasma frequency 40.68 MHz initial tensile stresses are observed to be in a range of 400 MPa–700 MPa. Measurements of the intrinsic stresses of silicon nitride films show that the stress quantity is sufficient for film applications in strained silicon photonics.

We calculated the structural, elastic, and electronic properties of alkali metal Na atoms doped type-I silicon–clathrate compound (Na₈Si₄₆) under pressure using first-principles methods. The obtained dependencies of bond lengths and bond angles on pressure show heterogeneous behaviors which may bring out a structural transition. By using the elastic stability criteria from the calculated elastic constants, we confirm that the Na₈Si₄₆ is elastically unstable under high pressure. Some of the mechanical and thermal quantities include bulk modulus, shear modulus, Young's modulus, Debye temperature, sound velocity, melting point, and hardness, which are also derived from the elastic constants. The calculated total and partial electron densities of states of Na₈Si₄₆ indicate a weak interaction between the encapsulated Na atoms and the silicon framework. Moreover, the effect of pressure on its electronic structure is also investigated, which suggests that pressure is not a good choice to enhance the thermoelectricity performance of Na₈Si₄₆.

An oxide p–n heterojunction composed of a 150-nm La_0.67Ca_0.33MnO₃ (LCMO) film, 0.05 wt% Nb doped SrTiO₃ substrate (STON), and sandwiched 5-nm LaAlO₃ (LAO) thin film is fabricated with the pulsed laser deposition technique and the interfacial transport properties are experimentally studied. The rectifying behavior of the junction is in agreement with Newman's equation, indicating that tunneling is the dominant process for the carriers to pass through the interface while thermal emission is the dominant transport model of an LCMO/STON heterojunction with no LAO buffer layer.

The Pr and Ta separately doped FTO (10 at.% F incorporated SnO₂) films are fabricated via spray pyrolysis. The microstructural, topographic, optical, and electrical features of fluorine-doped TO (FTO) films are investigated as functions of Pr and Ta dopant concentrations. The x-ray diffraction (XRD) measurements reveal that all deposited films show polycrystalline tin oxide crystal property. FTO film has (200) preferential orientation, but this orientation changes to (211) direction with Pr and Ta doping ratio increasing. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) analyses show that all films have uniform and homogenous nanoparticle distributions. Furthermore, morphologies of the films depend on the ratio between Pr and Ta dopants. From ultraviolet-visible (UV-Vis) spectrophotometer measurements, it is shown that the transmittance value of FTO film decreases with Pr and Ta doping elements increasing. The band gap value of FTO film increases only at 1 at.% Ta doping level, it drops off with Pr and Ta doping ratio increasing at other doped FTO films. The electrical measurements indicate that the sheet resistance value of FTO film initially decreases with Pr and Ta doping ratio decreasing and then it increases with Pr and Ta doping ratio increasing. The highest value of figure of merit is obtained for 1 at.% Ta- and Pr-doped FTO film. These results suggest that Pr- and Ta-doped FTO films may be appealing candidates for TCO applications.

In this paper, we report a Schottky ultraviolet photodetector based on poly (3,4-ethylenedioxy-thiophene) poly(styrenesulfonate) (PEDOT:PSS) transparent electrode contacts to Mg_0.1Zn_0.9O. The I–V characteristic curves of the device are measured in the dark condition and under the illumination of a 340-nm UV light. The device shows a typical rectifying behavior with a current rectification ratio of 10³ at ±2 V, which exhibits a good Schottky behavior. The photo-to-dark current ratio is high, which is 1×10³ at −4 V. A peak response of 0.156 A/W at 340 nm is observed. The device also exhibits a wide response from 250 nm to 340 nm, with a response larger than 0.1 A/W. It covers the UV-B region (280 nm–320 nm), which makes the device very suitable for the detection of UV-B light.

The Pt/Si/Ta/Ti multilayer metal contacts on 4H–SiC are annealed in Ar atmosphere at 600 °C–1100 °C by a rapid thermal processor (RTP). The long-term thermal stability is evaluated by aging the annealed contact at 600 °C in air. The contact's properties are determined by current–voltage measurement, and the specific contact resistance is calculated based on the transmission line model (TLM). Transmission electron microscope (TEM) and energy-dispersive x-ray spectrometry (EDX) are used to characterize the interface morphology, thickness, and composition. The results reveal that a higher annealing temperature is favorable for the formation of an Ohmic contact with a lower specific contact resistance, and causes the rapid degradation of the Ohmic contact in the aging process.

A GaN/Si nanoheterojunction is prepared through growing GaN nanocrystallites (nc-GaN) on a silicon nanoporous pillar array (Si-NPA) by a chemical vapor deposition (CVD) technique at a relatively low temperature. The average size of nc-GaN is determined to be ∼10 nm. The spectral measurements disclose that the photoluminescence (PL) from GaN/Si-NPA is composed of an ultraviolet (UV) band and a broad band spanned from UV to red region, with the feature that the latter band is similar to that of electroluminescence (EL). The electron transition from the energy levels of conduction band and, or, shallow donors to that of deep acceptors of GaN is indicated to be responsible for both the broad-band PL and the EL luminescence. A study of the I–V characteristic shows that at a low forward bias, the current across the heterojunction is contact-limited while at a high forward bias it is bulk-limited, which follows the thermionic emission model and space-charge-limited current (SCLC) model, respectively. The bandgap offset analysis indicates that the carrier transport is dominated by electron injection from n-GaN into the p-Si-NPA, and the EL starts to appear only when holes begin to be injected from Si-NPA into GaN with biases higher than a threshold voltage.

A C-band high efficiency and high gain two-stage power amplifier based on AlGaN/GaN high electron mobility transistor (HEMT) is designed and measured in this paper. The input and output impedances for the optimum power-added efficiency (PAE) are determined at the fundamental and 2nd harmonic frequency (f₀ and 2f₀). The harmonic manipulation networks are designed both in the driver stage and the power stage which manipulate the second harmonic to a very low level within the operating frequency band. Then the inter-stage matching network and the output power combining network are calculated to achieve a low insertion loss. So the PAE and the power gain is greatly improved. In an operation frequency range of 5.4 GHz–5.8 GHz in CW mode, the amplifier delivers a maximum output power of 18.62 W, with a PAE of 55.15% and an associated power gain of 28.7 dB, which is an outstanding performance.

The dependences of Fermi-level pinning on interface state densities for the metal–dielectric, ploycrystalline silicon–dielectric, and metal silicide–dielectric interfaces are investigated by calculating their effective work functions and their pinning factors. The Fermi-level pinning factors and effective work functions of the metal–dielectric interface are observed to be more susceptible to the increasing interface state densities, differing significantly from that of the ploycrystalline silicon–dielectric interface and the metal silicide–dielectric interface. The calculation results indicate that metal silicide gates with high-temperature resistance and low resistivity are a more promising choice for the design of gate materials in metal-oxide semiconductor (MOS) technology.

Lateral resistance of silicon-based p-type and n-type Schottky junctions is investigated. After one electrode on a metallic film is irradiated, the differential lateral resistance of the system is dependent on the direction of the bias current: it keeps constant in one direction and decreases in the opposite direction. By systematically investigating the electrical potential changes in silicon and the junction, we propose a new mechanism based on light-controlled leak current. Our work provides an insight into the nature of this phenomenon and will facilitate the advanced design of switchable devices.

Magnetic behaviors of the Ising system with bilayer honeycomb lattice (BHL) structure are studied by using the effective-field theory (EFT) with correlations. The effects of the interaction parameters on the magnetic properties of the system such as the hysteresis and compensation behaviors as well as phase diagrams are investigated. Moreover, when the hysteresis behaviors of the system are examined, single and double hysteresis loops are observed for various values of the interaction parameters. We obtain the L-, Q-, P-, and S-type compensation behaviors in the system. We also observe that the phase diagrams only exhibit the second-order phase transition. Hence, the system does not show the tricritical point (TCP).

We propose an integrable spin-1/2 Heisenberg model where the exchange couplings and Dzyloshinky–Moriya interactions are dependent on the sites. By employing the quantum inverse scattering method, we obtain the eigenvalues and the Bethe ansatz equation of the system with the periodic boundary condition. Furthermore, we obtain the exact solution and study the boundary effect of the system with the anti-periodic boundary condition via the off-diagonal Bethe ansatz. The operator identities of the transfer matrix at the inhomogeneous points are proved at the operator level. We construct the T–Q relation based on them. From which, we obtain the energy spectrum of the system. The corresponding eigenstates are also constructed. We find an interesting coherence state that is induced by the topological boundary.

The effects of oxidation of DyH₃ with respect to dysprosium addition to Nd–Fe–B sintered magnets are examined. Samples sintered with the addition of freshly milled dysprosium hydride, dysprosium hydride exposed to air at room temperature for 15 min and dysprosium hydride exposed to air at 100 °C for 3.5 hours are studied from the aspects of magnetic properties, microstructures, and their degradation, respectively. It is found that some oxidized dysprosium is distributed in the Nd-rich phase; hence, the decrease of remanence occurred. The degradation results indicate that pre-oxidised dysprosium can be a major factor in increasing the corrosion rate. The microstructures and corrosion acceleration test suggested that the oxidation is detrimental to remanence.

We investigate the low-temperature magnetic properties of intermetallic compounds Tb_{1 − x}Pr_x(Fe_0.4Co_0.6)_1.88C_0.05 (x = 0, 0.8, and 1) by detailed magnetization measurements. Obvious temperature- and field-induced irreversibilities suggest the coexistence of multiple magnetic phases. Sharp magnetization jumps across the antiferromagnetic to ferromagnetic transition are observed only in the Pr-containing samples, indicating that the behavior of the avalanche-like growth of ferromagnetic clusters is mainly related to the light lanthanide Pr ions. In addition, the time relaxation, field sweep rate, and cooling field dependence of magnetization jumps in the sample with x = 1 are consistent with those in the martensitic scenario.

CoPt₃/Co multilayered nanowire (NW) arrays are synthesized by pulsed electrodeposition into nanoporous anodic aluminum oxide (AAO) templates. The electrochemistry deposition parameters are determined by cyclic voltammetry to realize the well control of the ratio of Co to Pt and the length of every segment. The x-ray diffraction (XRD) patterns show that both Co and CoPt₃ NWs exhibit face-centered cubic (fcc) structures. In the UV-visible absorption spectra, CoPt₃/Co NW arrays show a red-shift with respect to pure CoPt₃NWs. Compared with the pure Co nanowire arrays, the CoPt₃/Co multilayered nanowire arrays show a weak shape anisotropy and well-modulated magnetic properties. CoPt₃/Co multilayered nanowires are highly encouraging that new families of bimetallic nanosystems may be developed to meet the needs of nanomaterials in emerging multifunctional nanotechnologies.

A lumped-equivalent circuit model of a novel magnetoelectric tunable bandpass filter, which is realized in the form of multi-stage cascading between a plurality of magnetoelectric laminates, is established in this paper for convenient analysis. The multi-stage cascaded filter is degraded to the coupling microstrip filter with only one magnetoelectric laminate and then compared with the existing experiment results. The comparison reveals that the insertion loss curves predicted by the degraded circuit model are in good agreement with the experiment results and the predicted results of the electromagnetic field simulation, thus the validity of the model is verified. The model is then degraded to the two-stage cascaded magnetoelectric filter with two magnetoelectric laminates. It is revealed that if the applied external bias magnetic or electric fields on the two magnetoelectric laminates are identical, then the passband of the filter will drift under the changed external field; that is to say, the filter has the characteristics of external magnetic field tunability and electric field tunability. If the applied external bias magnetic or electric fields on two magnetoelectric laminates are different, then the passband will disappear so that the switching characteristic is achieved. When the same magnetic fields are applied to the laminates, the passband bandwidth of the two-stage cascaded magnetoelectric filter with two magnetoelectric laminates becomes nearly doubled in comparison with the passband filter which contains only one magnetoelectric laminate. The bandpass effect is also improved obviously. This research will provide a theoretical basis for the design, preparation, and application of a new high performance magnetoelectric tunable microwave device.

The 0.9Pb(Sc_0.5Ta_0.5)O₃–0.1PbTiO₃/0.55Pb(Sc_0.5Ta_0.5)O₃–0.45PbTiO₃ multilayer thin films ((PSTT10/45)_n, n = 1–6, 10) are deposited on SiO₂/Si(100) substrates by radio frequency magnetron sputtering technique with LaNiO₃ buffer and electrode layer, and the films are subsequently annealed by a two-step rapid thermal approach. It is found that the interfacial density of the film has an important influence on the electric property of the film. The electric property of the film increases and reaches its critical point with the increase of interface density, and then decreases with the further increase of the interface density. With an interfacial density of 16 μm⁻¹, the film shows an optimized dielectric property (high dielectric constant, ε_r = 765, lowest dielectric loss, tanδ = 0.041, at 1 kHz) and ferroelectric property (highest remnant polarization, 2P_r = 36.9 μC/cm², low coercive field, 2E_c = 71.9 kV/cm). The possible reason for the electric behavior of the film is the competition of the interface stress with the interface defect.

The switching process of ferroelectric thin films in electronic devices is one of the most important requirements for their application. Especially for the different external fields acting on the film surface, the mechanism of domain switching is more complicated. Here we observe the nanoscale domain switchings of Bi_3.15Eu_0.85Ti₃O₁₂ thin film under different mechanical forces at a fast scan rate. As the force increases from initial state to 247.5 nN, the original bright or grey contrasts within the selected grains are all changed into dark contrasts corresponding to the polarization vectors reversed from the up state to the down state, except for the clusters. As the mechanical force increases to 495 nN, the color contrasts in all of the selected grains further turn into grey contrasts and some are even changed into grey contrasts completely showing the typical 90° domain switching. When another stronger loading force 742.5 nN is applied, the phase image becomes unclear and it indicates that the piezoelectric signal can be suppressed under a sufficiently high force, which is coincident with previous experimental results. Furthermore, we adopt the domain switching criterion from the perspective of equilibrium state free energy of ferroelectric nanodomain to explain the mechanisms of force-generated domain switchings.

The ultraviolet (UV) photoresponses of ZnO nanorods directly grown on and between two micro Au-electrodes by using electric-field-assisted wet chemical method are measured comprehensively under different conditions, including ambient environment, applied bias voltage, gate voltage and temperature. Experimental results indicate that the photoresponses of the ZnO nanorods can be modulated by surface oxygen adsorptions, applied voltages, as well as temperatures. A model taking into account both surface adsorbed oxygen and electron-hole activities inside ZnO nanorods is proposed. The enhancement effect of the bias voltage on photoresponse is also analyzed. Experimental results shows that the UV response time (to 63%) of ZnO nanorods in air and at 59 °C could be shortened from 34.8 s to 0.24 s with a bias of 4 V applied between anode and cathode.

Infrared absorption local vibration mode (LVM) spectroscopy is used to study hydrogen related defects in n-type ZnO single crystal grown by a closed chemical vapor transport (CVT) method under Zn-rich growth conditions, in which carbon is used as a transport agent. Two C–H complex related absorption peaks at 2850 cm⁻¹ and 2919 cm⁻¹ are detected in the sample. The formation of the C–H complex implies an effect of carbon donor passivation and formation suppression of H donor in ZnO. The influence of the complex defects on the electrical property of the CVT-ZnO is discussed based on Hall measurement results and residual impurity analysis.

We investigate the resistive switching and ferroelectric polarization properties of high-quality epitaxial BiFeO₃ thin films in various temperature ranges. The room temperature current–voltage (I–V) curve exhibits a well-established polarization-modulated memristor behavior. At low temperatures (< 253 K), the I–V curve shows an open circuit voltage (OCV), which possibly originates from the dielectric relaxation effects, accompanied with a current hump due to the polarization reversal displacement current. While at relative higher temperatures (> 253 K), the I–V behaviors are governed by both space-charge-limited conduction (SCLC) and Ohmic behavior. The polarization reversal is able to trigger the conduction switching from Ohmic to SCLC behavior, leading to the observed ferroelectric resistive switching. At a temperature of > 298 K, there occurs a new resistive switching hysteresis at high bias voltages, which may be related to defect-mediated effects.

A multifunctional surface plasmon polariton disk device coupled by two metal–insulator–metal (MIM) waveguides is proposed and investigated numerically with finite-difference time-domain simulation. It can be used as optical switch and temperature sensor by filling disk with liquid crystal and ethanol, respectively. The simulation results demonstrate that the transmission characteristics of an optical switch can be manipulated by adjusting the radius of disk and the slit width between disk and MIM waveguides. The transmittance and modulation depth of optical switch at 1550 nm are up to 64.82% and 17.70 dB, respectively. As a temperature sensor, its figure of merit can reach 30.46. In this paper, an optical switch with better efficiency and a temperature sensor with better sensitivity can be achieved.

A dual-band terahertz (THz) filter consisting of two different cross slots is designed and fabricated in a single molybdenum layer. Experimental verification by THz time-domain spectroscopy indicates good agreement with the simulation results. Owing to the weak coupling between the two neighboring cross slots in the unit cell, good selectivity performance can be easily achieved, both in the lower and higher bands, by tuning the dimensions of the two crosses. The physical mechanisms of the dual-band resonant are clarified by using three differently configured filters and electric field distribution diagrams. Owing to the rotational symmetry of the cross-shaped filter, the radiation at normal incidence is insensitive to polarization. Compared with the THz dual-band filters that were reported earlier, these filters also have the advantages of easy fabrication and low cost, which would find applications in dual-band sensors, THz communication systems, and emerging THz technologies.

For the proper interpretation of the experimental data produced in slow positron beam technique, the positron implantation properties are studied carefully using the latest Geant4 code. The simulated backscattering coefficients, the implantation profiles, and the median implantation depths for mono-energetic positrons with energy range from 1 keV to 50 keV normally incident on different crystals are reported. Compared with the previous experimental results, our simulation backscattering coefficients are in reasonable agreement, and we think that the accuracy may be related to the structures of the host materials in the Geant4 code. Based on the reasonable simulated backscattering coefficients, the adjustable parameters of the implantation profiles which are dependent on materials and implantation energies are obtained. The most important point is that we calculate the positron backscattering coefficients and median implantation depths in amorphous polymers for the first time and our simulations are in fairly good agreement with the previous experimental results.

We make a gradient correction to a new local density approximation form of positron–electron correlation. The positron lifetimes and affinities are then probed by using these two approximation forms based on three electronic-structure calculation methods, including the full-potential linearized augmented plane wave (FLAPW) plus local orbitals approach, the atomic superposition (ATSUP) approach, and the projector augmented wave (PAW) approach. The differences between calculated lifetimes using the FLAPW and ATSUP methods are clearly interpreted in the view of positron and electron transfers. We further find that a well-implemented PAW method can give near-perfect agreement on both the positron lifetimes and affinities with the FLAPW method, and the competitiveness of the ATSUP method against the FLAPW/PAW method is reduced within the best calculations. By comparing with the experimental data, the new introduced gradient corrected correlation form is proved to be competitive for positron lifetime and affinity calculations.

In this paper, the temperature-dependent photoluminescence (PL) properties of GaN grown on Si (111) substrate are studied. The main emission peaks of GaN films grown on Si (111) are investigated and compared with those grown on sapphire substrates. The positions of free and bound exciton luminescence peaks, i.e., FX_A and D⁰X peaks, of GaN films grown on Si (111) substrates undergo red shifts compared with those grown on sapphire. This is attributed to the fact that the GaN films grown on sapphire are under the action of compressive stress, while those grown on Si (111) substrate are subjected to tensile stress. Furthermore, the positions of these peaks may be additionally shifted due to different stress conditions in the real sample growth. The emission peaks due to stacking faults are found in GaN films grown on Si (111) and an S-shaped temperature dependence of PL spectra can be observed, owing to the influence of the quantum well (QW) emission by the localized states near the conduction band gap edge and the temperature-dependent distribution of the photo-generated carriers.

By using the plasma enhanced chemical vapor deposition (PECVD) technique, amorphous silicon oxide films containing nanocrystalline silicon grain (nc-SiO_x:H) are deposited, and the bonding configurations and optical absorption properties of the films are investigated. The grain size can be well controlled by varying the hydrogen and oxygen content, and the largest size is obtained when the hydrogen dilution ratio R is 33. The results show that the crystallinity and the grain size of the film first increased and then decreased as R increased. The highest degree of crystallinity is obtained at R = 30. The analyses of bonding characteristics and light absorption characteristics show that the incorporation of hydrogen leads to an increase of overall bonding oxygen content in the film, and the film porosity first increases and then decreases. When R = 30, the film can be more compact, the optical absorption edge of the film is blue shifted, and the film has a lower activation energy.

Porous graphene has a high mechanical strength and an atomic-layer thickness that makes it a promising material for material separation and biomolecule sensing. Electrostatic interactions between charges in aqueous solutions are a type of strong long-range interaction that may greatly influence fluid transport through nanopores. In this study, molecular dynamic simulations were conducted to investigate ion and water transport through 1.05-nm diameter monolayer graphene nanopores, with their edges charge-modified. Our results indicated that these nanopores are selective to counterions when they are charged. As the charge amount increases, the total ionic currents show an increase–decrease profile while the co-ion currents monotonically decrease. The co-ion rejection can reach 76.5% and 90.2% when the nanopores are negatively and positively charged, respectively. The Cl^– ion current increases and reaches a plateau, and the Na⁺ current decreases as the charge amount increases in systems in which Na⁺ ions act as counterions. In addition, charge modification can enhance water transport through nanopores. This is mainly due to the ion selectivity of the nanopores. Notably, positive charges on the pore edges facilitate water transport much more strongly than negative charges.

In this work, we study the influences of current density on surface morphology and electrochemical characterization of electrodeposited Ni–Mo. The Ni–Mo composite coatings are deposited on pretreated copper substrates by electrolytic deposition. The Ni–Mo solution is taken from nickel sulfate fluid and ammonium heptamolybdate with 10 g/l. The Ni–Mo composite coatings are deposited at a temperature of 303 K with an applied current density of j_dep = 10 A/dm²–30 A/dm². We find that the corrosion resistance is improved by incorporating Mo particles into Ni matrix in 0.6-M NaCl solution. From the potentiodynamic polarization curve of electrodeposited Ni–Mo it is confirmed that the corrosion resistance decreases with increasing applied current density. The x-ray diffraction (XRD) analyses of Ni–Mo coatings indicate three phases of MoNi₄, Mo_1.24Ni_0.76, and Ni₃Mo phases crystallites of nickel and molybdenum. The scanning electronic microscopy (SEM) tests indicate that Ni–Mo coatings present cracks and pores.

Efficient calculation of the electrostatic interactions including repulsive force between charged molecules in a biomolecule system or charged particles in a colloidal system is necessary for the molecular scale or particle scale mechanical analyses of these systems. The electrostatic repulsive force depends on the mid-plane potential between two charged particles. Previous analytical solutions of the mid-plane potential, including those based on simplified assumptions and modern mathematic methods, are reviewed. It is shown that none of these solutions applies to wide ranges of inter-particle distance from 0 to 10 and surface potential from 1 to 10. Three previous analytical solutions are chosen to develop a semi-analytical solution which is proven to have more extensive applications. Furthermore, an empirical closed-form expression of mid-plane potential is proposed based on plenty of numerical solutions. This empirical solution has extensive applications, as well as high computational efficiency.

In this paper, we present a compact low-temperature co-fired ceramic (LTCC) dual-band antenna by using the electromagnetic coupling effect concept for global positioning system (GPS) and universal mobile telecommunication system (UMTS) applications. The overall dimension of the antenna is 8.6 mm × 13.0 mm × 1.1 mm. It consists of double meander lines and a via hole line. The top meander line operates at the upper band, and the bottom radiating patch is designed for the lower band. The via-hole line is employed to connect the double meander lines. Because of the effect of the coupled line, total dimension of the proposed antenna is greatly reduced. With the 2.5: voltage standing wave ratio (VSWR) impedance bandwidth definition, the lower and upper bands have the bandwidths of 110 MHz and 150 MHz, respectively. The proposed antenna is successfully designed, simulated, and analyzed by a high frequency structure simulator (HFSS). And the antenna is manufactured by using the 0.95Zn₂SiO₄-0.05CaTiO₃ ceramics (ε_r = 7.1, tanδ = 0.00038) that is prepared by ourselves. The results show that the antenna is compact, efficient, and of near omnidirectional radiation pattern.

The charge and spin-dependent thermoelectric properties of different lengths of polythiophene in a molecular junction are investigated using the Büttiker probe method within Green function formalism in linear response regime. The coupling of the molecular chain to three-dimensional ferromagnetic electrodes is described by a tight-binding model for both parallel and antiparallel spin configurations. The decrease of height of transmission probability peaks and thermoelectric coefficients are observed in the presence of the Büttiker probes. The reduction is more intensive in the strong dephased chains. Results show that the spin magnetothermopower is bigger than the charge magnetothermopower due to the larger difference between the spin thermopowers with respect to the charge ones. In addition, we observed that the kind of carriers participating in the thermoelectric transport depends on the number of the thiophene rings.

We use the method of device simulation to study the losses and influences of geminate and bimolecular recombinations on the performances and properties of the bulk heterojunction organic solar cells. We find that a fraction of electrons (holes) in the device are collected by anode (cathode). The direction of the corresponding current is opposite to the direction of photocurrent. And the current density increases with the bias increasing but decreases as bimolecular recombination (BR) or geminate recombination (GR) intensity increases. The maximum power, short circuit current, and fill factor display a stronger dependence on GR than on BR. While the influences of GR and BR on open circuit voltage are about the same. Our studies shed a new light on the loss mechanism and may provide a new way of improving the efficiency of bulk heterojunction organic solar cells.

Developing an electrostatic discharge (ESD) protection device with a better latch-up immunity has been a challenging issue for the nanometer complementary metal-oxide semiconductor (CMOS) technology. In this work, an improved grounded-gate N-channel metal-oxide semiconductor (GGNMOS) transistor triggered silicon-controlled rectifier (SCR) structure, named GGSCR, is proposed for high holding voltage ESD protection applications. The GGSCR demonstrates a double snapback behavior as a result of progressive trigger-on of the GGNMOS and SCR. The double snapback makes the holding voltage increase from 3.43 V to 6.25 V as compared with the conventional low-voltage SCR. The TCAD simulations are carried out to verify the modes of operation of the device.

A novel diode string-triggered gated-PiN junction device, which is fabricated in a standard 65-nm complementary metal-oxide semiconductor (CMOS) technology, is proposed in this paper. An embedded gated-PiN junction structure is employed to reduce the diode string leakage current to 13 nA/μm in a temperature range from 25 °C to 85 °C. To provide the effective electrostatic discharge (ESD) protection in multi-voltage power supply, the triggering voltage of the novel device can be adjusted through redistributing parasitic resistance instead of changing the stacked diode number.

Strontium-zinc-oxide (SrZnO) films forming the semiconductor layers of thin-film transistors (TFTs) are deposited by using ion-assisted electron beam evaporation. Using strontium-oxide-doped semiconductors, the off-state current can be dramatically reduced by three orders of magnitude. This dramatic improvement is attributed to the incorporation of strontium, which suppresses carrier generation, thereby improving the TFT. Additionally, the presence of strontium inhibits the formation of zinc oxide (ZnO) with the hexagonal wurtzite phase and permits the formation of an unusual phase of ZnO, thus significantly changing the surface morphology of ZnO and effectively reducing the trap density of the channel.

In this paper, a surface potential based threshold voltage model of fully-depleted (FD) recessed-source/drain (Re-S/D) silicon-on-insulator (SOI) metal-oxide semiconductor field-effect transistor (MOSFET) is presented while considering the effects of high-k gate-dielectric material induced fringing-field. The two-dimensional (2D) Poisson's equation is solved in a channel region in order to obtain the surface potential under the assumption of the parabolic potential profile in the transverse direction of the channel with appropriate boundary conditions. The accuracy of the model is verified by comparing the model's results with the 2D simulation results from ATLAS over a wide range of channel lengths and other parameters, including the dielectric constant of gate-dielectric material.

A top-illuminated circular mesa uni-traveling-carrier photodetector (UTC-PD) is proposed in this paper. By employing Gaussian graded doping in InGaAs absorption layer and InP depleted layer, the responsivity and high speed response characteristics of the device are optimized simultaneously. The responsivity up to 1.071 A/W (the external quantum efficiency of 86%) is obtained at 1550 nm with a 40-μm diameter device under 10-V reverse bias condition. Meanwhile, the dark current of 7.874 nA and the 3-dB bandwidth of 11 GHz are obtained with the same device at a reverse bias voltage of 3 V.

Ultrashort multi-keV x-ray pulses are generated by electron plasma produced by the irradiation of femtosecond pulses on metals. These sub-picosecond x-ray pulses have extended the field of x-ray spectroscopy into the femtosecond time domain. However, pulse-to-pulse instability and long data acquisition time restrict the application of ultrashort x-ray systems operating at low repetition rates. Here we report on the performance of a femtosecond laser plasma-induced hard x-ray source that operates at 1-kHz repetition rate, and provides a flux of 2.0 × 10¹⁰ photons/s of Cu K_α radiation. Using this system for time-resolved x-ray diffraction experiments, we record in real time, the transient processes and structural changes induced by the interaction of 400-nm femtosecond pulse with the surface of a 200-nm thick Au (111) single crystal.

The relationship between noise variance and spatial resolution in grating-based x-ray phase computed tomography (PCT) imaging is investigated with reverse projection extraction method, and the noise variances of the reconstructed absorption coefficient and refractive index decrement are compared. For the differential phase contrast method, the noise variance in the differential projection images follows the same inverse-square law with spatial resolution as in conventional absorption-based x-ray imaging projections. However, both theoretical analysis and simulations demonstrate that in PCT the noise variance of the reconstructed refractive index decrement scales with spatial resolution follows an inverse linear relationship at fixed slice thickness, while the noise variance of the reconstructed absorption coefficient conforms with the inverse cubic law. The results indicate that, for the same noise variance level, PCT imaging may enable higher spatial resolution than conventional absorption computed tomography (ACT), while ACT benefits more from degraded spatial resolution. This could be a useful guidance in imaging the inner structure of the sample in higher spatial resolution.

In many ultrafast imaging applications, the reduced field-of-view (rFOV) technique is often used to enhance the spatial resolution and field inhomogeneity immunity of the images. The stationary-phase characteristic of the spatiotemporally-encoded (SPEN) method offers an inherent applicability to rFOV imaging. In this study, a flexible rFOV imaging method is presented and the superiority of the SPEN approach in rFOV imaging is demonstrated. The proposed method is validated with phantom and in vivo rat experiments, including cardiac imaging and contrast-enhanced perfusion imaging. For comparison, the echo planar imaging (EPI) experiments with orthogonal RF excitation are also performed. The results show that the signal-to-noise ratios of the images acquired by the proposed method can be higher than those obtained with the rFOV EPI. Moreover, the proposed method shows better performance in the cardiac imaging and perfusion imaging of rat kidney, and it can scan one or more regions of interest (ROIs) with high spatial resolution in a single shot. It might be a favorable solution to ultrafast imaging applications in cases with severe susceptibility heterogeneities, such as cardiac imaging and perfusion imaging. Furthermore, it might be promising in applications with separate ROIs, such as mammary and limb imaging.

The n-type silicon integrated-back contact (IBC) solar cell has attracted much attention due to its high efficiency, whereas its performance is very sensitive to the wafer of low quality or the contamination during high temperature fabrication processing, which leads to low bulk lifetime τ_bulk. In order to clarify the influence of bulk lifetime on cell characteristics, two-dimensional (2D) TCAD simulation, combined with our experimental data, is used to simulate the cell performances, with the wafer thickness scaled down under various τ_bulk conditions. The modeling results show that for the IBC solar cell with high τ_bulk, (such as 1 ms–2 ms), its open-circuit voltage V_oc almost remains unchanged, and the short-circuit current density J_sc monotonically decreases as the wafer thickness scales down. In comparison, for the solar cell with low τ_bulk (for instance, < 500 μs) wafer or the wafer contaminated during device processing, the V_oc increases monotonically but the J_sc first increases to a maximum value and then drops off as the wafer's thickness decreases. A model combing the light absorption and the minority carrier diffusion is used to explain this phenomenon. The research results show that for the wafer with thinner thickness and high bulk lifetime, the good light trapping technology must be developed to offset the decrease in J_sc.

We report a GaInP/GaAs tandem solar cell with a novel GaAs tunnel junction (TJ) with using tellurium (Te) and magnesium (Mg) as n- and p-type dopants via dual-filament low temperature effusion cells grown by molecular beam epitaxy (MBE) at low temperature. The test Te/Mg-doped GaAs TJ shows a peak current density of 21 A/cm². The tandem solar cell by the Te/Mg TJ shows a short-circuit current density of 12 mA/cm², but a low open-circuit voltage range of 1.4 V∼1.71 V under AM1.5 illumination. The secondary ion mass spectroscopy (SIMS) analysis reveals that the Te doping is unexpectedly high and its doping profile extends to the Mg doping region, thus possibly resulting in a less abrupt junction with no tunneling carriers effectively. Furthermore, the tunneling interface shifts from the intended GaAs n⁺⁺/p⁺⁺ junction to the AlGaInP/GaAs junction with a higher bandgap AlGaInP tunneling layers, thereby reducing the tunneling peak. The Te concentration of ∼ 2.5 × 10²⁰ in GaAs could cause a lattice strain of 10⁻³ in magnitude and thus a surface roughening, which also negatively influences the subsequent growth of the top subcell and the GaAs contacting layers. The doping features of Te and Mg are discussed to understand the photovoltaic response of the studied tandem cell.

Routing and path selection are crucial for many communication and logistic applications. We study the interaction between nodes and packets and establish a simple model for describing the attraction of the node to the packet in transmission process by using the gravitational field theory, considering the real and potential congestion of the nodes. On the basis of this model, we propose a gravitational field routing strategy that considers the attractions of all of the nodes on the travel path to the packet. In order to illustrate the efficiency of proposed routing algorithm, we introduce the order parameter to measure the throughput of the network by the critical value of phase transition from a free flow phase to a congested phase, and study the distribution of betweenness centrality and traffic jam. Simulations show that, compared with the shortest path routing strategy, the gravitational field routing strategy considerably enhances the throughput of the network and balances the traffic load, and nearly all of the nodes are used efficiently.

Based on an objective identification technique for regional low temperature event (OITRLTE), the daily minimum temperature in China has been detected from 1960 to 2013. During this period, there were 60 regional extreme low temperature events (ERLTEs), which are included in the 690 regional low temperature events (RLTEs). The 60 ERLTEs are analyzed in this paper. The results show that in the last 50 years, the intensity of the ERLTEs has become weak; the number of lasted days has decreased; and, the affected area has become small. However, that situation has changed in this century. In terms of spatial distribution, the high intensity regions are mainly in Northern China while the high frequency regions concentrate in Central and Eastern China. According to the affected area of each event, the 60 ERLTEs are classified into six types. The atmospheric circulation background fields which correspond to these types are also analyzed. The results show that, influenced by stronger blocking highs of Ural and Lake Baikal, as well as stronger southward polar vortex and East Asia major trough at 500-hPa geopotential height, cold air from high latitudes is guided to move southward and abnormal northerly winds at 850 hPa makes the cold air blow into China along diverse paths, thereby forming different types of regional extreme low temperatures in winter.