Vol. 63, No. 9 (2014)
A new type of conserved quantity deduced from conformal invariance in nonholonomic mechanical system
2014, 63 (9): 090201. doi: 10.7498/aps.63.090201
Conformal invariance and a new type of conserved quantity in nonholonomic mechanical system are studied. The definition and determining equation of conformal invariance for the nonholonomic mechanical system are provided; and the necessary and sufficient conditions that the conformal invariance for a nonholonomic mechanical system should be of Lie symmetry are deduced. With the aid of a new structure equation that the gauge function satisfies, the system's corresponding new conserved quantity is obtained. Finally an example is given to illustrate the application of the results.
Conserved quantities and approximate solutions of a two-dimensional charged coupled oscillator system
2014, 63 (9): 090202. doi: 10.7498/aps.63.090202
Coupled terms are present in the Lagrangian and the corresponding differential equations of a two-dimensional charged oscillator system are nonlinearly coupled. Firstly, the coupled terms in the Lagrangian are eliminated by transformation of coordinates; secondly, the conserved quantities in new coordinates are obtained by direct integral method, and the approximate solutions are obtained by Abdomina decomposition method. Finally, the conserved quantities and the approximate solutions can be expressed in original coordinates by using the inverse transform of the coordinates. The discussion of the approximate solutions is also given in this paper.
2014, 63 (9): 090203. doi: 10.7498/aps.63.090203
Based on the second order delay inertia neural network model, this paper puts forward the bifurcation control method: delay feedback control method. Applying the theory of delay differential equations, we give some stability and Hopf bifurcation conditions for the feedback control system. Examples are given to validate that the feedback controller can control the occurrence of bifurcation effectively, expand the stability domain, and change the convergence speed of the network as well.
The traveling wave approximation method for solving solitary wave in Schrödinger disturbed coupled system
2014, 63 (9): 090204. doi: 10.7498/aps.63.090204
A class of the Schrödinger nonlinear disturbed coupled system is studied, using the specific technique to relate the exact and approximate solutions. Firstly, the corresponding non-disturbed coupled system is considered. The exact solitary wave solution is obtained by using the projection method. Then, the traveling wave approximation solution to the Schrödinger disturbed coupled system is found by using a functional mapping method.
Using time delay compensation scheme in dynamic output feedback controller for networked control systems
2014, 63 (9): 090205. doi: 10.7498/aps.63.090205
This paper proposes a new method to design the dynamic output feedback controller for networked control systems (NCS) with communication delay in both forward and feedback channels. In order to remove the effects of the communication delay according to one's will, two different network delay compensation schemes are provided in two cases: the controlled plant whose state vectors can be measured and the one whose state vectors cannot be measured. Furthermore, another key part of this paper is to analyse the stability of the closed-loop networked control system. Finally, numerical simulation results show the effectiveness of the proposed method.
2014, 63 (9): 090206. doi: 10.7498/aps.63.090206
Large-scale geographic environmental monitoring and physical infrastructure for transferring and processing data cannot maintain the same growth rate with the monitoring scale, thus make the data gathering and processing under unreliable links, showing a kind of saturation flow state; and the ability of wireless sensor network (WSN) seemingly cannot be stabilized. On the other hand, though the calculation results from ideal network model are accurate enough, they deviate from the practical application greatly, hence the network users cannot adequately analyze and utilize the sensed data from industrial field network, and also cannot analyze the influence of network size and performance on data fusaggregation. Because of these, we will present the‘transitional region phenomenon'to be one of assumptions for industrial field simulation, and propose a data fusaggregation algorithm for the practical application on this basis, i.e. data fusaggregation algorithm based on reliability (R algorithm). When designing the R algorithm, as an example of sum operator, the lower limit η of reliability of appreciate aggregation sum result will be calculated by analyzing and synthesizing the result automatically. Then the aggregation sum result and the value of η will be sent to users together. In addition to providing the summary information from the monitored area to users, R algorithm also provides the parameter η as the judgment of information reliability to facilitate users to do further handling of aggregation results and improve the WSN sensing performance. Simulation results describe the changing rule of reliability η caused by unreliable links from the signal-to-noise ratio in transitional region, and discuss the network influence of size and performance on reliability η, with the increase of network operation cycles and network scale, when the value of reliability η becomes gradually close to 0. And this provides theoretical foundations and empirical formulas for WSNs from theoretical model to practical industrial application.
This paper proposes a unified model for hypernetworks and complex networks, and studies the evolution mechanisms of scale-free hypernetworks and the topological properties of the hypernetwork. We have analyzed the proposed model and calculated the stationary average hyperdegree distribution of the hypernetwork by using a Poisson process theory and a continuous technique. The analytical result agrees well with the simulation. It is shown that the hyperdegree distribution of the dynamic model follows a scale-free law. This paper not only integrates the hypernetwork model, in which one new node forms an edge with some old nodes, and the hypernetwork model, in which some new nodes form an edge with one old node, but also integrates the scale-free model in complex networks.
Studies on vibration response and energy harvesting of elastic-supported bistable piezoelectric cantilever beams
2014, 63 (9): 090501. doi: 10.7498/aps.63.090501
Based on the results of study on conventional rigid support nonlinear energy harvesters, in this paper, we conceive a kind of structure with an elastic-supported external magnet, for keeping the system in a state of bistable oscillation due to low-intensity excitations. Thus, an efficient electromechanical energy conversion can be accomplished. Studies show that the elastic-supported nonlinear energy harvesting systems do not need real-time adjustment of magnet spacings to meet varying-intensity random excitation vibrations. This structure helps to better satisfy the variable-intensity random excitation source, consequently it achieves efficiently electromechanical energy conversion.
2014, 63 (9): 090502. doi: 10.7498/aps.63.090502
To investigate the control problem of chaotic motion in spacecraft system caused by the coupled effect of liquid fuel sloshing and small periodic disturbance inside or outside spacecraft, the H∞ control strategy based on neural network disturbance observer is presented, which makes liquid spacecraft disengage chaos and liquid fuel sloshing which are inhibited. Disturbance observer is designed to track and compensate the coupled disturbance caused by liquid sloshing, parameter uncertainty, and external disturbance based on the nonlinear approximation capability of neural network. Taking into account the problems of observation error and model inaccuracy, the H∞ control strategy can be applied to improve the robustness of the control system. Compared with the existing common control algorithm, the proposed strategy proves to be valid and better at adaptability and robustness by simulations.
Study on the scale-free topology model with strong intrusion-tolerance ability in wireless sensor networks
2014, 63 (9): 090503. doi: 10.7498/aps.63.090503
Considering that the scale-free topology in wireless sensor networks has poor ability of intrusion-tolerance, we use the Poisson network model with node batch arrival to construct a new scale-free topology model with intrusion-tolerance optimization. Additionally, the two adjustment factors about the residual energy and the node degree are introduced in the construction of the topology model. Then the scale-free topology whose power-law exponent can be adjusted in the range of (1, + ∞) is obtained. Finally, the power-law exponent is optimized by the network structure entropy, and its optimal value is derived. Results show that the new topology has a strong fault-tolerance. And it also can enhance the network intrusion-tolerance and has good energy-saving advantages.
2014, 63 (9): 090504. doi: 10.7498/aps.63.090504
To improve the image scrambling and encryption effect in traditional two-dimensional discrete Arnold transform, a new nonlinear transform for image scrambling is proposed which improves the classical discrete Arnold transform with quasi-affine properties, and can be applied in image scrambling and encryption researching. This method first makes good use of the construction thought in classical discrete standard map, and embeds the nonlinear expressions of output results of one congruence equation for classical two-dimensional discrete Arnold transform into the input item of the other congruence equation for two-dimensional discrete Arnold transform. Then a new transform with good nonlinear characteristics is constructed on the basis of classical two-dimensional discrete Arnold transform in order to quickly improve the scrambling effect of the gray image. In the end, through mathematical proof it is shown that the proposed transform no longer has the quasi-affine invariance properties in the existing two-dimensional discrete Arnold transform, but it is still a reversible mapping with periodic properties; and when it is applied in image scrambling encryption, the original image can be restored from the scrambling and encryption in gray image for its periodic properties or inverse transform. Some experimental results show that the proposed nonlinear transform is effective, and can obtain better scrambling and encryption quality than the existing discrete two-dimensional Arnold transform, meanwhile it is more practical than the standard Arnold transform in view of security.
Risk analysis on long inclined-shaft construction in coalmine by TBM techniques based on multiple variables chaotic time series
2014, 63 (9): 090505. doi: 10.7498/aps.63.090505
Multi-variable chaotic time series are used to predict the long inclined-shaft construction in coalmine construction by TBM techniques, and principal component analysis (PCA) is used to determine the main factors that impact risk (shield) of the long inclined-shaft construction in coalmine by TBM techniques. Phase space of risk time series for construction by TBM are reconstructed; time delay and embedding dimension are determined. Maximum Lyapunov indexes of risk are obtained by using small data quantity method; it is found that the time series have characteristics of chaos. Prediction model is established using the combination of first-order local method and double hidden layer neural network. Simulation experiments show that the combined model has a strong ability of prediction and achieves better effect. As a result, it provides a new way for long inclined-shaft construction in coalmine by TBM techniques.
2014, 63 (9): 090601. doi: 10.7498/aps.63.090601
We have investigated the vibrational sensitivity of a horizontal-mounted spherical reference cavity, which can be applied to develop an ultra-stable laser. Effects of different magnitudes of height and area as well as acceleration of the cavity support points on the length variation of the cavity are studied. When the cavity support points are totally constrained, the vibration sensitivity can be reduced to below 3.0×10-10/g. After performing extensive numerical simulations, we can find the optimal support position. According to the obtained results we present the mounting scheme of the spherical cavity. Taking into consideration the machining errors, near-horizontal mounting, and unsymmetrical mounting of the cavity, we can describe quantitatively the length variation of the cavity caused by these three factors. We also discuss the contribution of the second order effect to the length variation of the cavity.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
Collimated electrons generated by intense laser pulse interaction with cone-structured targets using particle simulation
2014, 63 (9): 094101. doi: 10.7498/aps.63.094101
Generation and propagation of fast electron bunches from interaction of short, ultra intense laser with cone-sandwich target are investigated by PIC (particle-in-cell) simulation. Results are compared with those in the interaction of the same laser parameters with cone-channel target, cone-wire target and cone target. Fast electrons generated by the interaction of intense laser with cone-sandwich target can be effectively collimated and propagated by the quasi-static strong magnetic field generated by the material surface of different densities. Compared with the other three cone-structured target, the more number and the higher energy of the fast electrons are generated by cone-sandwich target. This can well improve the energy conversion efficiency of the laser to fast electrons and the quality of fast electron bunches, which are favorable for the fast ignition energy deposition.
2014, 63 (9): 094201. doi: 10.7498/aps.63.094201
Based on the coherent superposition principle of direct-transmited light with the Gaussian speckle field, and also with the Kirchhoff approximation, the speckle in the deep Fresnel diffraction region is investigated. Expressions of speckle field in the deep Fresnel diffraction region, and the probability density of intensity, and contrast are obtained. In the deep Fresnel diffraction region of different scattering distance the variation of speckles is simulated with the height distribution data of random scattering surface measured by atomic force microscopy, and the curves of these two statistic functions are drawn. Combining the theory with the simulation, characteristics of these two statistic functions, the effect of the fraction of the direct transmit light intensity as well as their variations with the scattering distance are discussed.
2014, 63 (9): 094202. doi: 10.7498/aps.63.094202
Theoretical analysis on the far-field diffraction of the coherent beam combination (CBC) is presented. An introduction is given to the definitions of filling factor and evaluation parameter of CBC. Based on the theoretical mode and definition, the influence of filling factor on far-field intensity distribution and the relationship between evaluation parameter and filling factor are theoretically described in detail. It is found that the filling factor influences far-field intensity distribution through space modulation factor. Results also indicate that SR is a constant which has not connection with the filling factor, and CR is of a linear relation with filling factor, and NACL has little connections with filling factor, and RCL varies approximately linearly with the square of filling factor, and PIB decreases when filling factor increases in general. If we make the filling factor larger than √2/2, more than half of the best values of RCL and PIB may be obtained.
2014, 63 (9): 094203. doi: 10.7498/aps.63.094203
A method of generating cylindrical vector beams based on metasurface is presented in this paper. The metasurface is a fused silica with a space-variant non-periodic grating which is written by laser. The non-periodic grating induces a space-variant effective birefringence that modulates the space distribution of polarization state. It is shown that an incident linearly polarized light can be converted to a cylindrical vector beam by the method of Jones matrix. We can obtain an arbitrary cylindrical vector beam on the equator of the higher-order Poincaré sphere. A simple and efficient experimental system is established with a metasurface. Experimental results are in agreement with the theoretical analysis.
2014, 63 (9): 094204. doi: 10.7498/aps.63.094204
Method of target detection and tracking is one of the hot topics in image processing and computer vision field, which is significant not only in military such as imaging guidance and military target tracking, but also for civil use such as security and monitoring and the intelligent man-machine interaction. Treating the feature matching problem as a more general equinoctial classification question, can turn the intractable high-dimensional problem to a classification problem and deplete computer complexity. This method is based on the law of large numbers and Bayes rule. In this paper we propose a non-hierarchy structure classifier, for which the equation for calculation is theoretically derived, and apply 1bitBP feature to the classifier; and for further reducing the amount of calculation, we use integral image and square integral image to variance classifier as preprocessor, and then use non-hierarchy classifier to handle the patches which meet the variance demand and use the nearest neighbor to further improve the accuracy, and finally realize target detection and tracking based on cascade classifier. Our experimental results show that the method proposed is far superior in calculation amount and processing precision, and is robust to scale changing and rotation, so the method proposed in this paper is of high practical value.
Spontaneous emission from a two-level atom in a dynamic photonic crystal with an isotropic disoersion relation
2014, 63 (9): 094205. doi: 10.7498/aps.63.094205
The spontaneous emission of a two-level atom, located in an isotropic photonic crystal with dynamically modulated photonic band edge, has been studied. When the photonic band edge is modulated with step functions or triangle functions, the evolution of atomic population on the upper level has been discussed. When the photonic band edge is modulated with step functions, the dynamics of atomic population depends not only on the detuning value of the atomic transition frequency from the band edge, but also on the time point of stepping. With the different time point of stepping, the dynamics of atomic population after stepping is different. When the photonic band edge is modulated with triangle functions, the atomic population oscillates quasi-periodically while decaying in general. The oscillation frequency, peak and valley values, and the decaying rate of oscillation can be modulated by choosing the frequency and initial phase of triangle functions.
2014, 63 (9): 094206. doi: 10.7498/aps.63.094206
We have studied the steady-state properties of a hybrid optomechanical system, where a Y-type four-level atomic ensemble is confined in a microcavity with an oscillating mirror in one end. We find that the hybrid system will have multistability for the oscillating mirror and the confined atoms as the elastic coefficient of the spring decreases. When the elastic coefficient is very large, the oscillating mirror hardly affects the optomechanical system, therefore the system and the atomic ensemble have a single steady-state solution. However, when the elastic coefficient is small enough, the multiequilibrium positions of the oscillating mirror will be found, and the steady-state behaviors of the atomic ensemble confined in the microcavity may be affected. As a result, the susceptibility of the atomic ensemble will have multiple steady-state solutions and the probe absorption and dispersion will be changed as well. It has also been found that the number of steady-state solutions of the entire system could be controlled by changing the value of the elastic coefficient. These results may have potential applications in the area of high-precision quantum measurement and quantum information processing.
2014, 63 (9): 094207. doi: 10.7498/aps.63.094207
A cross bus single microring electro-optical switch model is proposed based on the theory of coupling modes, electro-optical modulation, and transfer matrix. Simulation is carried out for the 1561 nm wavelength light signal. Result shows that the switch voltage is about 400 V, the interrupt is less than -30 dB and the insertion loss is less than 4 dB. The response time is only 5.4 ps, in which the rise and fall time on the microring is only 0.32 ps. Besides, since the electro-optical switch is controlled by a single-pole double-throw switch, the three states of the latter can be realized through adding driving voltage on microring and U bend waveguide. Unlike the tranditional microring switch, the above-mentioned one not only can realize the selection of light signal pathway, but also can let the two output ports have light signal sent out.
2014, 63 (9): 094208. doi: 10.7498/aps.63.094208
The coupled nonlinear Schrödinger (CNLS) equation including Raman gain has been utilized for birefringence fiber. Evolution process of the optical soliton pulse has been simulated by the fractional Fourier method when the optical soliton pulse transmission in a birefringence fiber has a different nature. Results show that the drift of soliton caused by nonlinear coupling effect can be suppressed by Raman gain, at the same time, the soliton pulse peak in the transmission is enhanced. The interaction between optical solitons can be effectively restrained by Raman gain in the birefringence fiber.
Generation of broadband multicolor femtosecond laser pulses by using cascading four-wave mixing in a CaF2 plate
2014, 63 (9): 094209. doi: 10.7498/aps.63.094209
Femtosecond laser pulses with new properties have been required for the great progress of femtosecond laser spectroscopy experiments. For example, simultaneous multiple ultrashort femtosecond laser pulses with different frequencies are needed in multicolor pump-probe experiments. Here, we have designed a much more simple and compact system for multicolor femtosecond pulse generation by using cascaded four-wave mixing in a 0.5 mm thick CaF2 plate. Multicolor femtosecond pulses with a sub-10 fs Fourier transform limit pulse width have been obtained by using two oppositely chirped incident pulses. These ultrashort multicolor femtosecond pulses will be used as a new laser source in femtosecond laser spectroscopy.
2014, 63 (9): 094301. doi: 10.7498/aps.63.094301
Atmospheric temperature is an important parameter for studying the process of atmospheric dynamics and photochemistry, and is a significant sign of the atmospheric vertical stratification structure. It is a challenge in atmospheric science research to obtain temperature profiles with high space-time resolution all the time. MST (mesosphere-stratosphere-troposphere) radar, which is the modern large-scale ground-based radio remote sensing equipment, can measure 3D atmospheric winds with high space-time resolution and unattended 24 hours a day. This paper uses the time series of vertical wind observed by MST radar to make spectral analysis and calculate B-V (Brunt-Väisälä) frequency. Then this paper builds the discrete model of temperature inversion based on the relationship between B-V frequency and temperature. Compared with actual measurement of temperature from radiosondes, the agreement between the radiosonde profile and the profile from MST radar data is quite good. Furthermore, the Richardson number can also be obtained by using the B-V frequency and horizontal winds, which can judge the atmospheric stability, quantize many of the dynamic characteristics, and explain the wave phenomenon. So the acquisition of B-V frequency is MST radar's another outstanding contribution to atmospheric dynamics research. It can accurately calculate the atmospheric temperature profiles and attain dynamic stability parameters.
2014, 63 (9): 094401. doi: 10.7498/aps.63.094401
According to the characteristics of dredging thermal protection system (DTPS) of hypersonic vehicle leading edge, both the structure of embedded high conductivity materials and that of integrative plate of heat pipe are designed to complete the two kinds of comparative experiments so as to prove the feasibility of the DTPS. As a source of radiation heating, the spherical short arc xenon lamp is simulated for aerodynamic heating. The pure steel leading edge, the embedded copper leading edge, the plate pure steel leading edge, and the integrative plate for heat pipe leading edge are heated respectively. Temperature variations of stagnation point region and tail fins are measured. Experimental results show that DTPS of the embedded high conductivity materials can reduce the temperature of stagnation point region and increase the temperature of the tail fins. It also can achieve the aim of thermal protection of leading edge. The DTPS of integrative plate heat pipe whose working fluid is pure water also can protect the leading edge under the condition of low heat flux. At the huge pressure of vapor, DTPS of the integrative plate of heat pipe may be broken at high heat flux. It is shown that the working fluid of heat pipe can play a key role in the application range for the thermal protection effect.
2014, 63 (9): 094501. doi: 10.7498/aps.63.094501
A set of experimental schemes of pedestrian evacuation from a room having two exits is proposed and applied to experiments. Some quantitative results of evacuation time varying with the number of pedestrians in different circumstances are obtained from the video recordings. The concept of attraction domain of a two-exit room is established. It is proved that the boundary curve of attraction domain of the smaller exit is always a circular arch, by which the mechanism of arch formation near an exit can be illustrated. Compared with the passenger evacuation procedure in a subway waiting hall, we have established a quadratic function model of evacuation time which can fit the measured data well for various cases. The evacuation time increases linearly with the number of people without waiting, and increases as a quadratic function of the number of people after the formation of a waiting region. It is also found that the expression is affected by the width of exit more sensitively than in other well-known models.
A cellular automaton model for the road in front of elementary and middle school gates during students going to school
2014, 63 (9): 094502. doi: 10.7498/aps.63.094502
Based on the studies on traffic bottleneck of road, interference area, and mixed traffic flow, a cellular automaton model for the roads in front of elementary and middle school gates during students going to school is established. Characteristics of traffic flow are discussed via the simulation experiment. Effects of the traffic flow and the traffic volume are analyzed including the proportion of student driving private cars, the proportion of school buses, and the command giving by traffic policeman on the scene. Results of examples given in this paper show that traffic safety can be ensured, the traffic jams can be suppressed, and the goal of achieving largest traffic flow and decreasing the passing time of vehicles can be realized by decreasing the proportion of student driving private cars, increasing the proportion of school buses, and assisting the traffic policeman to command on the scene.
An analytical solution for the interaction of two-dimensional currents and gravity short-crest waves
2014, 63 (9): 094701. doi: 10.7498/aps.63.094701
Short-crest wave and current coexist widely in the ocean environments. However, the interaction between them has been studied recently and the method of velocity potential function was generally applied. Unlike the previous study, this article considers that location variable‘x'and time variable‘t'are independent of each other and it does not take into account the capillary effect, thus leading to an addition of a first-order time item in the second-order velocity potential function. Based on the perturbation technique, a second-order analytical solution is derived. Comparisons between the result in this article, where variables‘x'and‘t'are dependent on each other and the capillary effect is considered, and Huang's solutions show the difference. The difference between wave profile and wave pressure on mudline will become apparent with the increase of wave height, indicating that the solutions obtained in this article will be much suitable for ocean conditions with larger wave height.
2014, 63 (9): 094702. doi: 10.7498/aps.63.094702
A coupled level set and volume of fluid (CLS-VOF) method is applied to simulate the process of double droplets which continuously impact on a hot liquid film on a wall of constant temperature, and the evolution processes after the double droplets impinge on the hot flat liquid film are studied. Influences of vertical spacing between the two droplets, impact velocity, film thickness and droplet diameter on the flow and heat transfer characteristics are discussed. It is found that the average heat flux density of the wall increases with the rise of impact velocity. The influences of vertical spacing between the two droplets, droplet diameter, and liquid film thickness on the average heat flux density are small, but they have an important effect on the distribution of heat flow density in the impact area and the border area.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2014, 63 (9): 095201. doi: 10.7498/aps.63.095201
According to the experimental results of spectrum diagnosis made on Qiang-Guang-I generator, we report a method to separate and diagnose Z-pinch plasma radiation spectrum. Spectral lines and different continuums are separated from experimental results and electron temperatures can be acquired. Results show that continuums are superposed by radiation of high electron temperature plasma at the centre field (Te=290.7 eV ± 1.2 eV) and radiation of lower electron temperature plasma at shell region (Te=95.3 eV ± 8.3 eV). Spectral lines reflect the information of high electron temperature plasma at the centre field. According to the calculation by using NLTE model, the electron temperature of such a plasma is in the range of 299–313 eV. The diagnose result by spectral lines is identical with the continuum's results.
2014, 63 (9): 095202. doi: 10.7498/aps.63.095202
Research of interactions between high-power microwave and plasma is of importance for both microwave discharge and electromagnetic compatibility. Based on wave equations, fluid equations, and Boltzmann equations of plasma interactively, a theoretical model of interactions between high-power microwave and plasma was established. Combined with characteristic parameters of plasma, the model was solved numerically by the method of finite difference in time domain to analyze variations of plasma electron density and transmission property of high-power microwave. Results show that heating of electrons by incident high-power microwave makes nonlinear effects become obvious in the plasma, and gas breakdown increases plasma electron density which results in the enhancement of reflection of microwave and the of decrease transitivity. The model mentioned above and results related are instructive for protecting against high-power microwave and electromagnetic pulse.
2014, 63 (9): 095203. doi: 10.7498/aps.63.095203
In this paper, the element content detection of heavy metal Cr in soil is investigated experimentally by femtosecond filament induced breakdown spectroscopy (FIBS). The plasma filament length is measured using the fluorescence method, and the spatial distribution of Cr 425.5 nm spectral intensity is obtained at lens focal lengths 150 mm and 1000 mm. A calibration curve of the heavy metal element Cr in the soil is obtained based on experimental results. Results demonstrate that the relative deviation of the quantitative analytic result from the standard value is smaller than 5%, and the detection limit of Cr in soil is 7.85 ppm at the laser repetition rate 1 kHz. The femtosecond laser filaments induced breakdown spectroscopy is entirely feasible for quantitative detection of heavy metal element Cr in the soil.
2014, 63 (9): 095204. doi: 10.7498/aps.63.095204
In order to meet the requirement for uniform irradiation on the target in inertial confinement fusion, a schemie is proposed for achieving the depolarized superposition of multi-beams and further improving the uniformity of the focus spot by using complementary polarization control plates to change the polarization state of the beam. A physical model of multi-beam transformation by complementary polarization control plates is built up, and the mechanism how complementary polarization control plates affect the polarization characteristics of the focus spot is analyzed theoretically. The polarization properties and uniformity of the focus spot are compared for the two cases: viz the complementary polarization control plates and the un-complementary polarization control plates. Furthermore, the selection of elements of polarization control plates is discussed. Results show that after beams propagating through the complementary polarization control plates, the focal spot is not completely polarized but mixed randomly with various kinds of partially polarized states. Compared with the un-complementary polarization control plates, the complementary polarization control plates can achieve better depolarization effect on focus plane, resulting in the degree of polarization dropping to below 0.2, and thus achieving the effective improvement of intensity uniformity. When the complementary polarization control plates are utilized, the number of elements of polarization control plates has little effect on the polarization characteristics of the spot, but it can influence the intensity uniformity to some extent. Consequently, the number of elements of polarization control plates should be chosen appropriately in practical application.
Particle-in-cell simulation on surface-wave discharge process influenced by gas pressure and negative-biased voltage along ion sheath layer
2014, 63 (9): 095205. doi: 10.7498/aps.63.095205
Due to surface electromagnetic waves propagating along the dielectric-plasma interface, the application of surface-wave plasma (SWP) is limited in view of the fact that it is very difficult to realize metal sputtering by using negative-biased voltage in traditional SWP sources. Recently, this problem is overcome by a type of SWP source based on the guided wave in ion sheath layer driven by negative-biased voltage. And the plasma heating mechanism is originated from gas discharges excited by the local-enhanced electric field of surface plasmon polariton (SPP). However, the best discharge condition is not obtained because the influence factors affecting the discharge process studied is not clear. In this paper, the discharge mechanism of SWP ionization process influenced by gas pressure and negative-biased voltage along the ion sheath layer is investigated. The simulation method is by means of combining particle-in-cell (PIC) with Monte Carlo collision (MCC). Simulated results suggest that the values of negative-biased voltage and gas pressure can influence the thickness of ion sheath layer, the excitation of SPP, and the spatio-temporal conversion of wave mode, which further induces the different discharge performances. Moreover, the discussed analysis states that a better discharge performance can be obtained when approximately a negative-biased voltage of -200 V and a gas pressure of 40 Pa applied.
Simulation on similarity law of glow discharge in scale-down gaps of rod-plane electrode configuration
2014, 63 (9): 095206. doi: 10.7498/aps.63.095206
A fluid model of direct-current (DC) discharge in argon atmosphere between the gaps of rod-plane electrode configuration was established, and the discharge models of two geometrically similar gaps were solved using the finite-element method, respectively. The dimension ratio of the gaps was set as 10:1, and the gas pressure was ～133.3 Pa for the prototype and ～133 Pa for the scale-down gap; to the gaps the same DC voltages were applied. Voltage-current characteristics, as well as the physical discharge parameters (such as electric potential, electric field, electron density, ion density, and electron temperature) were obtained. Relations between parameters of the two gaps were investigated according to the theoretical relations derived by similarity law. Simulation results show that the discharge type in the two similar gaps is verified as a normal glow discharge; the parameter relations are in good agreement with the similarity law, and the working points of discharges are identical in similar gaps with the same applied DC voltage. This study could offer theoretical instruction in extrapolating the discharge properties for similar gaps.
2014, 63 (9): 095207. doi: 10.7498/aps.63.095207
Kerr effect is defined as an electro-optical physical phenomenon, in which the testing laser can change its polarization state as passing through a Kerr medium stressed by applied field. In this work, an on-line measurement system based on Kerr effect is established to investigate the surface electric field of insulator stressed by nanosecond HV pulse in vacuum which include a HV pulse source, YAG laser, synchronous controlling apparatus, Kerr cell & insulator sample, optical phase shift detecting subsystem. According to comparison experiments, the distortion of insulator surface electric field caused by surface charging is observed. And a time-resolution measurement on this field distortion is also performed.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Study on the excited states of zinc porphyrinogen and anisotropy of 2, 2, 6, 6-tetramethylpiperidinooxy by the technology of electron paramagnetic resonance
2014, 63 (9): 097201. doi: 10.7498/aps.63.097201
To investigate the energy transfer and electron transfer of the photo-induced excited state in porphyrin sensitizers, we built the “zinc porphyrin-2, 2, 6, 6-tetramethylpiperidinooxy-xylene” experimental system. Zinc porphyrin's UV-visible spectrum shows that the characteristic absorption line of zinc porphyrin consists of bands B and Q, which are generated by the transition of elections from the ground state to the excited state in molecules of zinc porphyrin. The electron paramagnetic resonance spectrum of the experimental system is produced under the UV-visible light irradiation, at a temperature of 143 K; and we have detected the enhanced electron paramagnetic resonance spectrum of 2, 2, 6, 6-tetramethylpiperidinooxy. Based on the theory of the molecular excited states, and the photophysical and photochemical theory as well as the theory of the chemical-induced electron spin polarization, we also analyze the experimental results. Our conclusion is that the enhanced electron paramagnetic resonance spectrum of 2, 2, 6, 6-tetramethylpiperidinooxy is caused by the energy transfer and electron transfer of the photo-induced excited state in the porphyrin sensitizers. The anisotropic characteristics of the phenomenon of electron paramagnetic resonance spectrum of 2, 2, 6, 6-tetramethylpiperidinooxy at low temperatures are due to the anisotropic hyperfine interaction between nitroxide electrons and nitrogen nuclear.
2014, 63 (9): 097301. doi: 10.7498/aps.63.097301
Enhancement effect of surface plasmon in the metal nano-particle is a hot topic in nano-material field. A system is investigated where a spherical metal nano-particle is placed near a dye molecule. Under the optical excitation of a polarized electric field the subsequent charge transfer dynamics for different relative positions are simulated by density matrix theory approach, where the Coulomb interaction of molecule and metal nano-particle is calculated in the framework of the dipole-dipole approximation. It is found that the enhancement effect is closely related to the relative distance between the molecule and metal nano-particle. Effect of enhancement due to the surface plasmon is discussed in detail for various coupling interactions, polarization of field, lifetime of plasmon, and non-resonant excitation; and the physical essence in the molecule-metal nano-particle coupled system is analysed.
2014, 63 (9): 097302. doi: 10.7498/aps.63.097302
Multilayer electroluminescent devices with a system in which red-emitting quantum dots doped PVK serves as the active layer is fabricated through non-treatment process, the device structure being ITO/PVK:QDs/Alq3/Al. Measuring the emission spectra and electrical characteristics of the devices we study the effect of different QDs doping concentration (mass fraction), and propose some possible solutions to optimize the PVK:QDs system after taking pure QDs for comparison. Experimental results show that changing QDs doping concentration would bring significant impact on the electroluminescence (EL) spectra, current density, brightness, and the stability of devices. When QDs doping concentration is low, we will mainly see the light of Alq3; when QDs doping concentration is 20%, saturated pure red light emission is observed and it is brighter than other devices. However, when the doping concentration is high, a slight red shift occurs in the EL spectra, and the performance of the device gets worse. With a suitable doping concentration, the PVK:QDs may increase the stability of devices.
First-principles study on phonon properties of iron-based fluoride superconductors SrFe1-xCoxAsF (x=0, 0.125)
2014, 63 (9): 097401. doi: 10.7498/aps.63.097401
Using plane-wave pseudopotential method based on first-principles, we calculate the phonon spectra (including phonon dispersion curves and phonon density of states) and electron-phonon coupling constants of SrFe1-xCoxAsF (x=0, 0.125) in tetragonal nonmagnetic (NM) and orthorhombic striped antiferromagnetic (SAF) states. Results show that under striped antiferromagetic interaction the spin-phonon coupling is stronger than the electron-phonon coupling, leading to the decrease of phonon spectra width; and the increased effective phonon quality due to spin effects makes the frequencies of coupling vibration between Fe and As atoms reduced. In addition, doping and spin effects are two effective methods to enhance the electron-phonon coupling, however, the calculated superconducting transition temperature is far lower than the experimental measurement, which rules out the simple electron-coupling superconducting pairing mechanism in SrFe1-xCoxAsF.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2014, 63 (9): 098101. doi: 10.7498/aps.63.098101
Al-Cu-Ge alloy system, a typical ternary eutectic alloy system, has been used widely in the industries. Our research is helpful for better understanding its thermophysical properties and improving its structural performance. In this paper, the specific heat values and thermal expansion coefficients of Al55Cu10Ge35, Al70Cu10Ge20 and Al80Cu10Ge10 alloys are investigated. The microstructural characteristics and the solidification paths of these alloys under near-equilibrium solidification and rapid solidification conditions are studied comparatively. Their specific heat values increase as Al content increases and Ge content decreases. The softening temperature is 666 K, and the thermal expansion coefficient fluctuates around 1.5×10-5 K-1 in the temperature range of 370–650 K. Under a near-equilibrium solidification condition, the last formation microstructure is (Al)+(Ge) pseudobinary eutectic instead of ternary eutectic. This means that (Al), (Ge), and CuAl2 phases are difficult to nucleate simultaneously or grow cooperatively. In comparison, during rapid solidification, the nucleation of primary phase is depressed, pseudobinary eutectic and ternary eutectic are much easier to form in these alloys.
2014, 63 (9): 098102. doi: 10.7498/aps.63.098102
In this paper, a novel fabrication process of the nanocrystalline Sm3Co alloys and their fundamental properties were studied. The polycrystalline Sm3Co bulk material was prepared by the vacuum melting method. By using the polycrystalline Sm3Co bulk metal, the nanocrystalline Sm3Co alloys with an average grain size of about 8 nm was prepared by combined ball milling and spark plasma sintering. The crystal structure model was constructed and the magnetic and mechanical properties of the polycrystalline and nanocrystalline Sm3Co alloys were characterized and compared with each other in detail. Results show that the nanocrystalline alloys exhibit magnetic properties and high mechanical properties. Microhardness and elastic modulus of the nanocrystalline Sm3Co alloys are 4.87 GPa and 63.7 GPa, respectively, which are increased by 8.7% and 13.3% as compared with the polycrystalline alloys.
Influence of external magnetic field on properties of aluminum-doped zinc oxide films prepared by RF magnetron sputtering
2014, 63 (9): 098103. doi: 10.7498/aps.63.098103
Al-doped ZnO (AZO) transparent conductive oxide films were prepared by RF magnetic sputtering. An external magnetic field was applied to the traditional magnetron sputtering system. The influence of the external magnetic field on the crystalline structure, surface topography and photoelectric properties of the AZO transparent conductive film have been studied. XRD diffraction patterns show that under the same processing condition, the intensity of (002) diffraction peak is significantly increased with the external magnetic field, suggesting a higher degree of c-axis preferred orientation. Scanning electron microscope shows that the external magnetic field can enlarge the grain size and density of films; the surface topography of the AZO films deposited without an external magnetic field is wormlike. Deposition rate and square resistance test results show that in an external magnetic field, the deposition rate will increase from 13.04 nm/min to 19.93 nm/min, and the sheet resistance reduce to 12.88 Ω /□ from 30.74 Ω /□ at a sputtering time of 90 min. Optical transmittance spectra shows that the average transmittance of all the films in visible light spectrum is over 85% when the sputtering time is not more than 60 min, while the external magnetic field has little effect on the transmittance of the films, but making a larger blue shift of the absorption edge. Ansys software is used to simulate the two-dimensional magnetic field distribution above the target. Results show that the intensity of the horizontal magnetic field and the uniformity of it are improved by the external magnetic field, the secondary electrons near the target are tightly bound, leading to a much larger target current intensity. So the deposition rate, surface topography and photoelectric properties of the AZO films are improved.
2014, 63 (9): 098104. doi: 10.7498/aps.63.098104
Size-controlled Si nanopore array with a pore size less than 100 nm is fabricated on Si (100) substrates by using monolayer self-assembled and KOH anisotropic wet etching technique. Morphology and structure of the pores are characterized by SEM and AFM. Results show that a large area of defect-free polystyrene (PS) monolayer film can be obtained when the volume ratio of PS solution to methanol solution is 9:11. A larger volume ratio or a smaller volume ratio will induce similar bilayer structure and defects (point and line) in the PS film, respectively. The lateral size and depth of the nanopore will increase with the etching time, and its morphology will change from circular to inverted pyramid type gradually. But the orderly arranged structure will be destroyed as the etching time is over 10 min. On the other hand, ordered Ge/Si nanoislands and nanorings will be grown on nanopore-patterned Si (100) substrates (inverted pyramid and circular nanopores, respectively) by ion beam sputtering. In addition, reasonable interpretations have been proposed for the formation mechanism of the ordered Ge/Si nanostructure.
2014, 63 (9): 098105. doi: 10.7498/aps.63.098105
The solid phase transition in crystals prepared from molecular energetic materials under extreme conditions is important for understanding the detonation mechanisms. By applying the first principles density functional calculations, a detailed theoretical study of the lattice parameters and molecular structures, equations of state, densities of state for solid nitromethane is reported. By analyzing the pressure dependence of lattice parameters, a sudden change of the lattice parameters occurs between 10-12 GPa, implying that a transition has taken place. It is also found that the maximum dihedral angle of H-C-N-O has increased from 155.3° to 177.5°, indicating that a rotation of the methyl group from a staggered to an eclipsed conformation occurs in the pressure range 11–12 GPa. Before the phase transition, the intramolecular O … H–C interactions are mainly of hydrogen bonds. After the phase transition, the intramolecular and intermolecular O … H interactions are mainly of the hydrogen bonds. Phase transition also affects the reduced ratio of band gap and the density of state near the Fermi level.
2014, 63 (9): 098106. doi: 10.7498/aps.63.098106
The two-mode phase-field-crystal (PFC) method is used to calculate two-dimensional phase diagram and to simulate the process of multistage microstructural evolution in the transformation from hexagonal phase to square phase, which is induced by deformation. And the effect of misorientation and deformation on dislocation, grain boundary, crystal structure and morphology of the new phase is carefully analyzed. Simulation results show that both the nucleation site and growth direction of the square phase are affected by the direction of deformation. Under a tensile deformation, the nucleation of the square phase occurs preferentially in the deformation zone; while under compression deformation, the nucleation of the square phase may begin at dislocations and grain boundary. Moreover, the new phase grows towards the direction along which the degree of atomic mismatch decreases, i.e. the vertical direction of tensile deformation and the parallel direction of compressive deformation. Besides, the free energy varies with misorientation. In small misorientation, the dislocation climbing, slipping and annihilating will result in an energy peak; while in a big misorientation, the dislocation annihilates in several stages and thus offsetting the energy caused by deformation. Furthermore, the process of phase transformation is complex: It is not a pure phase transformation but a composite change of phase transformation and dynamic recrystallization.
2014, 63 (9): 098201. doi: 10.7498/aps.63.098201
When the granular matter is being pushed a certain point can be found, before arriving at which the force increases linearly, and after that it increases exponentially. The granular matter is a large assemblage of solid grains, which are fundamentally different from any other type of matters, such as solid blue and liquids; they have different physical properties. The meso-scale of force chain bridges single particles and granular matter, and leads to unique properties and behaviours of granular matters, thus acts as the key issue in the study of granular matter. In this work, we first find the variation of different forces by simulation. We then propose a discrete element model based on rigorous Hertzian contact law and Mindlin-Deresiewicz contact theory for normal and tangential contact forces, respectively, and then point out that the change of force chain is the key to the granular dynamics. The force distribution and the force chain length distribution are calculated and analyzed to show the change rule and the origin of the drag force.
2014, 63 (9): 098401. doi: 10.7498/aps.63.098401
Pulse train (PT) control technique is a novel discrete control technique for switching converter operating in discontinuous conduction mode (DCM). When the inductive energy storage is not zero, the low-frequency oscillation phenomenon may occur in PT controlled switching converters operating in continuous conduction mode (CCM). The low-frequency oscillation phenomenon will seriously affect the steady and transient performances of switching converters. In order to solve this problem, valley current mode pulse train (VCM-PT) control technique, which extends the application range from DCM to CCM, is proposed in this paper. The energy model of VCM-PT controlled switching converter is derived and compared with the energy model of PT controlled switching converter. Result indicates that the VCM-PT controlled CCM switching converter has the same energy transfer mode as the traditional PT controlled DCM switching converter and can eliminate fundamentally the low-frequency oscillation phenomenon.
2014, 63 (9): 098402. doi: 10.7498/aps.63.098402
Nano-scaled titanium oxide memristors exhibit unstable conductive characteristics under the same test condition: restricting the possibility to have accurate reading and control of the transient resistance of the device. Moreover, the reliability and stability of memristor-based circuits cannot be guaranteed. Coexistence of dopant drift and tunnel barrier is one of possible origins which causes undesirable instability, and the ambient temperature has a close relationship with dopant drift. However, there have been no detailed researches which may improve the stability of memristors by controlling temperatures. Based on the coexistence of dopant drift and tunnel barrier, the connections between temperature and memristor conductive characteristics are analyzed, and the influences of changes of active area width and initially doped layer width on the critical temperature are studied. Simulations are performed in SPICE and the results are given in this paper. In conclusion, methods are proposed for enhancing the conductive stability of memristors, which include increasing the active area width, decreasing the initially doped layer width, keeping the temperature to be under the critical value, and stability. Our work may provide a basis for manufacturing memristors with stable performance and promoting the practical circuit in applications.
Circuit parameter calculation based on characteristic parameters and pseudo-impedance of damped oscillation signal
2014, 63 (9): 098403. doi: 10.7498/aps.63.098403
This paper mainly studied the circuit parameter calculation theory and the methods based on damped oscillations in transient signals. The methods can be used for the location and origin of faults by calculating the circuit parameters of transient fault signals' path when the fault occurs in the power system transmission lines. It is important in theoretical and practical engineering to locate faults in powerlines by calculating circuit parameters based on damped oscillations which are the main component of the transient signals. In R-L and R-C circuits, relations of the characteristic parameters in damped oscillation voltage and current in time domain, with the circuit parameters as well as the component parameters are deduced. And the impedance characteristic of the circuit under damped oscillation is analyzed, which is defined as a pseudo-impedance based on the definition that impedance is steady and sinusoidal. Relations between the pseudo-impedance and circuit parameters are also found. Relations between component parameter and pseudo-impedance in series or parallel are also analyzed. So methods for circuit parameter calculation are proposed separately based on the characteristic parameters and pseudo-impedance, each of which is a kind of characteristic of the damped oscillation signal. Specific calculation methods are also proposed combining with the state-of-the-art signal analysis for damped oscillation signal. Analyses in this paper may lay an important foundation for practical engineering application. The proposed theory and methods are verified based on simulation of fault signals produced by MATLAB. The equivalent circuit of an actual distribution system is simulated by using PSCAD/EMTDC. Actual fault signals reappear in the simulation. Location of single-line-to-ground fault using damped oscillation signal proposed in the paper is proved feasible.
According to HP memristor model, a grounded memristor emulator is proposed in this paper. Based on the proposed memristor emulator, a universal emulator of mem-elements is implemented with common off-the-shelf components. This universal emulator can transform the grounded memristor into a floating memristor, or a floating meminductor, or a floating memcapacitor by connecting different components to it. Because the universal emulator is floating, it is not confined to be grounded and can be connected between any two voltages. In order to verify theoretical presumptions about the universal emulator, Pspice simulations are conducted on this circuit.
Ag-ZnO-Ag X-ray detectors based on ZnO film and nanowires are both fabricated in this paper. Results of continuous X-ray radiation measurement show that the two detectors have high responsivity: the responsivity of the ZnO film device is about 0.12 μC/Gy under a 100 V bias voltage, and that of the ZnO nanowires device is about 0.15 μC/Gy under a 50 V bias voltage. Surface effect due to the absorption and desorption of oxygen on the ZnO surface, which makes the carrier lifetime increase, is decisive to the high responsivity. ZnO film and nanowires have their potential applications in the X-ray dose rate measurement.
2014, 63 (9): 098503. doi: 10.7498/aps.63.098503
Properties of low-frequency noise in the amorphous InZnO thin film transistors have been investigated in this paper. Due to the emission and trapping processes of carriers between trapping states located in the interface between the IZO layer and gate insulator, the drain current spectral density shows a 1/fγ(γ =0.75) low-frequency noise behavior. In addition, the normalized drain current spectral density is decreased linearly with the increase of gate length and width. This property confirms that the low-frequency noise in the IZO TFTs is due to the flicker noise in the channel, the contribution of source/drain contact and parasitic resistances can be ignored. Finally, based on the number fluctuation theory and the mobility fluctuation theory, the γ and average Hooge's parameters have been extracted to estimate the quality of devices and materials.
2014, 63 (9): 098701. doi: 10.7498/aps.63.098701
Removing baseline drift is an important step in preprocessing ECG signal. The traditional methods have disadvantages of large computation and poor results. This paper utilizes the morphology theory combined with the characteristics of ECG signal to propose a morphological method for removing the baseline drift, which uses different shapes and sizes to design a two-stage morphological filter and perform cascaded combination operations of closing-opening and opening-closing respectively. The proposed method is verified that it can maintain the morphological specificity, improve the SNR, reduce the MSE, and remove the noise efficiently.
High voltage direct current additional reduced-order controller design based on improved projective control
2014, 63 (9): 098801. doi: 10.7498/aps.63.098801
A new reduced-order controller design method based on improved projective control is introduced. And the low-frequency oscillations can be suppressed by high voltage direct current additional controller through this method. The system reduced mode and relative oscillation frequencies are obtained through TLS-ESPRIT algorithm. Then the controller is designed by improved projective control, after the pole-placement method is applied to obtain a state-feedback matrix. The traditional pole-placement controller based on observer is compared with the projective controller at the same time. The advantages of lower order, stronger robustness and better control effect have been proved through simulation.
2014, 63 (9): 098901. doi: 10.7498/aps.63.098901
This paper proposes a quantum mechanical state equation for describing evolution of projects of financial investment, while the parameters of this equation well simulate the fundamental elements of financial market, including investment (input), assets loss (assets decrease), assets increase and income (output), the quantum mechanics operators involved in this equation also can reflect the dynamic process and characteristics of the project, so the equation can be taken as the evolution model of a kind of financial investment projects in the market. The entangled state representation is introduced to solve this equation and its solution is obtained in an infinite operator-sum form, which exhibits the link between the initial state and final state, i.e., the dynamic process of the financial investment project. As an example, we derive the evolution law of a pure investment project in financial market, which conforms with the evolution trend of the market. In solving the equation we also find a new state which we name it as the binomial-negative binomial entangled state. Throughout the discussions we make full use of Dirac's symbolic method and the technique of integration within an ordered product (IWOP) of operators.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2014, 63 (9): 099101. doi: 10.7498/aps.63.099101
Global static gravitational field determined by GOCE satellite data has become a hotspot in current research of geodesy. In this paper, a global static gravity field model entitled SWJTU-GO01S up to the degree and order 210 is recovered based on 12 months of GOCE orbit and gradient data from 2011-02-28 to 2012-03-05 with direct approach. GOCE gradient data are filtered by the zero phase finite impulse band-pass digital filter, and then a gradient observation equation is founded directly in gradiometer coordinates, which avoids high-accuracy gradient component loss in accuracy in the conversion process, while the orbit data is processed with short-arc integral approach. The optimal weight of combination result based on SST and SGG data is determined by variance component estimation and the polar gaps is dealt with the Kuala regularization method. Comparison of internal and external precision of SWJTU-GO01S with EGM2008 and with GPS leveling data of North America, shows that the geoid error and cumulative error of the SWJTU-GO01S model with the degree and order 210 are 2.1 cm and 13.7 cm respectively. Compared with the second generation models released by ESA and ITG-GRACE2010S, the accuracy of the model SWJTU-GO01S is higher than that of the model ITG-GRACE2010S and ESA official time-wise and space-wise model in the above degree and order 150. This study provides a reference to further joint multi-class satellite observation data to recover gravity field models.
Spatial distribution and seasonal variation characteristics of global atmospheric moisture recycling
2014, 63 (9): 099201. doi: 10.7498/aps.63.099201
This paper makes use of new definitions of moisture recycling to study the complete process of global moisture feedback. An accounting procedure based on ERA-Interim reanalysis data is used to calculate moisture recycling ratios. Furthermore, the spatial distribution and seasonal variation characteristics of global moisture recycling are analyzed. Results indicate that: a) Precipitation recycling ratio in different regions show distinct patterns. It is indicated that the dependences of precipitation in different regions on moisture transport are different. b) Spatial distribution of precipitation recycling ratio and evaporation recycling ratio are in good agreement over the lands, but show significant difference over the oceans. c) Seasonal variation characteristics of global moisture recycling ratio are significant, which are stronger in the Northern Hemisphere than in the Southern Hemisphere. d) Main oceanic sources are dominant over continental moisture recycling, and most of the evaporation is transported to other regions by advection. e) Regional moisture recycling ratio not only depends on the factors such as time, location, and shapes of the regions, but also the regional horizontal scale. The moisture recycling ratio curve rises as the regional horizontal scale increases. It is computed that, on the average, precipitation recycling ratio and evaporation recycling ratio of Chinese mainland are respectively about 32.6% and 44.9%; the main source of rainfall in China is moisture evaporated over the South China Sea, the Bay of Bengal, the Arabian Sea and the Western Australia Ocean. The atmospheric moisture recycling model in this paper is based on the atmospheric water balance equation, in terms of good mathematical and physical theory, hence the results are credible.
Characteristics of forecast errors in the National Climate Center atmospheric general circulation model in winter
2014, 63 (9): 099202. doi: 10.7498/aps.63.099202
By using the National Climate Center atmospheric general circulation model (BCC_AGCM) for the second generation monthly dynamic extended range system and the NCEP/NCAR reanalysis data accumulated during 1982-2010, the model forecast errors in winter temperature prediction and their relationship with external forcing factors are analyzed. Result indicates that the model can well reproduce the variation trends of winter temperature over Eurasia region, and the main interannual variability pattern of winter temperature over East Asian monsoon domain can be successfully presented. It reveals that the model has acceptable performances in winter temperature prediction over East Asian monsoon domain, while the forecast errors are still considerable. In spatial distribution, the forecast errors over lands are larger than those over oceans. Meanwhile, the errors at high latitudes are larger than at low latitudes, and they are also closely related to altitude. The principal components of forecast errors have significant association with the sea surface temperature and the sea ice concentration over some key regions, it is shown that the response capability to external forcings is insufficient. This may provide a valuable reference for improving the prediction skill of winter temperature for East Asian monsoon domain, in combination with the model response to external forcings.
Influence of the observation distance on the lightning channel temperature studied by means of spectroscopic diagnosis
2014, 63 (9): 099203. doi: 10.7498/aps.63.099203
The spectra for first return strokes of cloud-to-ground lightning discharge were obtained by a slit-less spectrograph at the Qinghai plateau of China. In this paper, the effect of the observation distance on diagnosis results of channel temperature was calculated and discussed by applying the Beer-Lambert law and considering the attenuation of spectral line intensity in transmission. Results show that there is some difference in channel temperature obtained at different observation distances. The observation distance is further enlarged, then the temperature obtained will be lower. Furthermore, at further increased distance we take observation, the bigger the error will be. So the correction for the temperature is more important for longer observation distance. According to our calculation and analysis, a semi-empirical formula has been obtained, which shows a relationship between the lightning channel temperature and the observation distance. The influence of the observation distance on lightning channel temperature could be eliminated by using the semi-empirical formula.