Showing papers in "Acta Physica Sinica in 2015"

Quantum secure direct communication

Abstract: Quantum secure direct communication (QSDC) is one of the most important branches of quantum communication. In contrast to the quantum key distribution (QKD) which distributes a secure key between distant parties, QSDC directly transmits secret message instead of sharing key in advance. To establish a secure QSDC protocol, on the one hand, the security of the quantum channel should be confirmed before the exchange of the secret message. On the other hand, the quantum state should be transmitted in a quantum data block since the security of QSDC is based on the error rate analysis in the theories on statistics. Compared with the deterministic quantum key distribution (DQKD) which can also be used to transmit deterministic information, QSDC schemes do not need extra classical bits to read the secret message except for public discussion. In this article, we introduce the basic principles of QSDC and review the development in this field by introducing typical QSDC protocols chronologically. The first QSDC protocol was proposed by Long and Liu, which can be used to establish a common key between distant parties. In their scheme, the method for transmitting quantum states in a block by block way and in multiple steps was proposed and the information leakage before eavesdropping detection was solved. Subsequently, Deng et al. presented two pioneering QSDC schemes, an entangled-state-based two-step QSDC scheme and a single-photon-state-based quantum one-time pad scheme, in which the basic principle and criteria for QSDC were pointed out. From then on, many interesting QSDC schemes have been proposed, including the high-dimension QSDC scheme based on quantum superdense coding, multi-step QSDC scheme based on Greenberger-Horne-Zeilinger states, QSDC scheme based on quantum encryption with practical non-maximally entangled quantum channel, and so on. We also introduce the anti-noise QSDC schemes which were designed for coping with the collective-dephasing noise and the collective-rotation noise, respectively. In 2011, Wang et al. presented the first QSDC which exploited the hyperentangled state as the information carrier and several QSDC schemes based on the spatial degree of freedom (DOF) of photon, single-photon multi-DOF state and hyperentanglement were proposed subsequently. In addition to the point-to-point QSDC schemes, we also review the QSDC networks. Finally, a perspective of QSDC research is given in the last section.

Leveraging neighborhood “structural holes” to identifying key spreaders in social networks

Abstract: The identifying of influential nodes in large-scale complex networks is an important issue in optimizing network structure and enhancing robustness of a system. To measure the role of nodes, classic methods can help identify influential nodes, but they have some limitations to social networks. Local metric is simple but it can only take into account the neighbor size, and the topological connections among the neighbors are neglected, so it can not reflect the interaction between the nodes. The global metrics is difficult to use in large social networks because of the high computational complexity. Meanwhile, in the classic methods, the unique community characteristics of the social networks are not considered. To make a trade off between affections and efficiency, a local structural centrality measure is proposed which is based on nodes' a nd their ‘neighbors’ structural holes. Both the node degree and “bridge” property are reflected in computing node constraint index. SIR (Susceptible-Infected-Recovered) model is used to evaluate the ability to spread nodes. Simulations of four real networks show that our method can rank the capability of spreading nodes more accurately than other metrics. This algorithm has strong robustness when the network is subjected to sybil attacks.

Ranking key nodes in complex networks by considering structural holes

Abstract: Structural hole nodes in complex networks play important roles in the network information diffusion. Unfortunately, most of the existing methods of ranking key nodes do not integrate structural hole nodes and other key nodes. According to the relevant research on structural hole theory as well as the key node ranking methods, network constraint coefficient, betweenness centrality, hierarchy, efficiently, network size, PageRank and clustering coefficient, 7 metrics are selected to rank the key nodes. Based on the 7 metrics, a ranking learning method based on ListNet is introduced to solve ranking key nodes by multi metrics. Comprehensive experiments are conducted based on different artificial networks and real complex networks. Experimental results with manual annotation show that the ranking method can comprehensively consider the structural hole nodes and other nodes with different important features. The ranking results on different networks are highly consistent with the manual ranking results. The spreading experiment results using signed to interference ratio propagation model show that SIR model can reach a maximum propagating ratio in a shorter propagating time initiated by TOP-K key nodes selected by our method than TOP-K key nodes selected by other methods.

Joint for time of arrival and direction of arrival estimation algorithm based on the subspace of extended hadamard product

Abstract: In the joint estimation for time of arrival (TOA) and direction of arrival (DOA) in the narrow-band orthogonal frequency division multiplexing (OFDM) system with antenna arrays, the estimation accuracy is not high in the situation of few numbers of arrays. Especially, DOA cannot be estimated if the number of multiple paths is more than that of the arrays. For these problems, a joint estimation algorithm for TOA and DOA based on the subspace of the extended hadamard product is proposed. First of all, the algorithm constructs an extended channel response in frequency domain via channel estimation for each array in the frequency domain. Then, auto-correlation matrix of extended channel response in the frequency domain is estimated by sampling many times. This estimation method of channel response in the frequency domain can use the fast Fourier transform algorithm. And the hadamard product in the extended noise subspace is obtained by eigenvalue decomposition. Finally, the pseudo-spectral function is constructed and used to search for spectrum peaks, so as to realize the joint estimation of TOA and DOA. The proposed algorithm requires no parameter paring but needs a two-dimensional searching. Monte Carlo algorithm can be used to reduce computational complexity. Simulation results show that the root mean square error of the joint TOA and DOA estimation which can be matched automatically is closer to the Cramer-Rao bound than that using present algorithms. And the proposed algorithm can be still applied when the number of multiple paths is more than number of arrays.

Dynamic response and stochastic resonance of a tri-stable system

Abstract: Stochastic resonance (SR) describes a nonlinear phenomenon in nature, of which the essential ingredients are a nonlinear system, a weak signal, and a source of noise. Using the nonlinear system, the signal-to-noise ratio (SNR) of the output signal of the system will peak at a certain value of noise intensity under a synergistic action of input signal and noise. Besides the traditional Langevin equation, the new SR models such as monostable oscillators, chaotic systems, time-delay systems and bistable Duffing systems, can also produce SR phenomena. In this paper, a normalized symmetrical tri-stable potential function is constructed by using equilibrium parameters p and q, and a tri-stable system model simultaneously driven by weak signal and noise is further proposed. The tri-stable system model can be understood through a cantilever beam structure with three magnets, and deduced from the Brownian motion equation. We study in-depth and summarize the influences of parameters p and q on the potential barrier heights ΔU1, ΔU2 and their difference value. By analyzing the steady-state solution of the tri-stable system under invariable input, the concept of system steady-state solution curve (SSS curve) is proposed, and is used to further study the system dynamic response under low-frequency harmonic signal input. In these situations, the system response can be obtained by combining the steady-state solutions of the system following time t under a group of tempolabile inputs. Moreover, with the noise injection, the tri-stable system can realize SR under appropriate parameter condition, which can be demonstrated by the output amplitude curve and also the output SNR curve of the system against noise intensity. The mechanism of noise-induced SR of tri-stable system can be analyzed from the perspective of SSS curve. Finally, we further study the influence of tri-stable SR against system parameters. The value of damping ratio k affects the value of damping force acting on the Brownian particle, thus the tri-stable system needs noise with larger intensity to produce SR under a larger k. The values of equilibrium parameters p and q both affect the shape of the SSS curve, a larger p or a smaller q may result in larger-intensity noise for the system to produce SR.

Progess of discrete Boltzmann modeling and simulation of combustion system

Abstract: Detonation is a kind of self-propagating supersonic combustion where the chemical reaction is rapid and violent under an extreme condition. The leading part of a detonation front is pre-shocked by a strong shock wave propagating into the explosive and triggering chemical reaction. The combustion system can be regarded as a kind of chemical reactive flow system. Therefore, the fluid modeling plays an important role in the studies on combustion and detonation phenomena. The discrete Boltzmann method (DBM) is a kind of new fluid modeling having quickly developed in recent thirty years. In this paper we review the progress of discrete Boltzmann modeling and simulation of combustion phenomena. Roughly speaking, the discrete Boltzmann models can be further classified into two categories. In the first category the DBM is regarded as a kind of new scheme to numerically solve partial differential equations, such as the Navier-Stokes equations, etc. In the second category the DBM works as a kind of novel mesoscopic and coarse-grained kinetic model for complex fluids. The second kind of DBM aims to probe the trans-and supercritical fluid behaviors or to study simultaneously the hydrodynamic non-equilibrium (HNE) and thermodynamic non-equilibrium (TNE) behaviors. It has brought significant new physical insights into the systems and promoted the development of new methods in the fields. For example, new observations on fine structures of shock and detonation waves have been obtained; The intensity of TNE has been used as a physical criterion to discriminate the two stages, spinodal decomposition and domain growth, in phase separation; Based on the feature of TNE, some new front-tracking schemes have been designed. Since the goals are different, the criteria used to formulate the two kinds of models are significantly different, even though there may be considerable overlaps between them. Correspondingly, works in discrete Boltzmann modeling and simulation of combustion systems can also be classified into two categories in terms of the two kinds of models. Up to now, most of existing works belong to the first category where the DBM is used as a kind of alternative numerical scheme. The first DBM for detonation [Yan, et al. 2013 Front. Phys. 8 94] appeared in 2013. It is also the first work aiming to investigate both the HNE and TNE in the combustion system via DBM. In this review we focus mainly on the development of the second kind of DBM for combustion, especially for detonation. A DBM for combustion in polar-coordinates [Lin, et al. 2014 Commun. Theor. Phys. 62 737] was designed in 2014. It aims to investigate the nonequilibrium behaviors in implosion and explosion processes. Recently, the multiple-relaxation-time version of DBM for combustion [Xu, et al. 2015 Phys. Rev. E 91 043306] was developed. As an initial application, various non-equilibrium behaviors around the detonation wave in one-dimensional detonation process were preliminarily probed. The following TNE behaviors, exchanges of internal kinetic energy between different displacement degrees of freedom and between displacement and internal degrees of freedom of molecules, have been observed. It was found that the system viscosity (or heat conductivity) decreases the local TNE, but increases the global TNE around the detonation wave. Even locally, the system viscosity (or heat conductivity) results in two competing trends, i. e. to increase and decrease the TNE effects. The physical reason is that the viscosity (or heat conductivity) takes part in both the thermodynamic and hydrodynamic responses to the corresponding driving forces. The ideas to formulate DBM with the smallest number of discrete velocities and DBM with flexible discrete velocity model are presented. As a kind of new modeling of combustion system, mathematically, the second kind of DBM is composed of the discrete Boltzmann equation(s) and a phenomenological reactive function; physically, it is equivalent to a hydrodynamic model supplemented by a coarse-grained model of the TNE behaviors. Being able to capture various non-equilibrium effects and being easy to parallelize are two features of the second kind of DBM. Some more realistic DBMs for combustion are in progress. Combustion process has an intrinsic multi-scale nature. Typical time scales cover a wide range from 10(-13) to 10(-3) second, and typical spatial scales cover a range from 10(-10) to 1 meter. The hydrodynamic modeling and microscopic molecular dynamics have seen great achievements in combustion simulations. But for problems relevant to the mesoscopic scales, where the hydrodynamic modeling is not enough to capture the nonequilibrium behaviors and the molecular dynamics simulation is not affordable, the modeling and simulation are still keeping challenging. Roughly speaking, there are two research directions in accessing the mesoscopic behaviors. One direction is to start from the macroscopic scale to smaller ones, the other direction is to start from the microscopic scale to larger ones. The idea of second kind of DBM belongs to that of the first direction. It will contribute more to the studies on the nonequilibrium behaviors in combustion phenomena.

Simulation of electric activity of neuron by setting up a reliable neuronal circuit driven by electric autapse

Abstract: Transition of electric activity of neuron can be induced by electric autapse, and its action potential is much sensitive to the stimuli from the electric autapse. Generally, the effect of electric autapse on membrane potential of neuron is often described by using time-delayed feedback in closed loop. Based on Pspice software, a class of electric circuit is designed with the electric autapse being taken into consideration, and a time-delayed circuit is used to detect the adjusting action of electric autapse on the action potential. Results are found as follows: (1) The neuronal electric circuit can produce quiescent state, spiking, bursting state under an external force besides the electric autapse circuit. (2) The transition of electric activity occurs between four different atates (quiescent, spiking, bursting state) by imposing a time-varying forcing current; its potential mechanism is that the electric circuit is associated with the memory, and the neuron can give different types of response to the same external forcing current. (3)When a strong external force is imposed, the outputs can show different type of electric activities due to an electric autapse, that is to say, self-adaption of gain in the autapse is useful for the neuron and thus different type of electric activities occurs, whose potential mechanism may be due to the effective feedback in the loop; so it is helpful to understand the synaptic plasticity.

Adaptive fuzzy synchronization for uncertain fractional-order chaotic systems with unknown non-symmetrical control gain

Abstract: In this paper the synchronization problem for the uncertain fractional-order chaotic systems with unknown non-symmetrical control gain matrices is investigated by means of adaptive fuzzy control. Fuzzy logic systems are employed to approximate the unknown nonlinear functions. We decompose the control gain matrix into a positive definite matrix, a unity upper triangular matrix, and a diagonal matrix with diagonal entries +1 or -1. The positive matrix is used to construct the Lyapunov function; the diagonal matrix is employed to design the controller. Based on the fractional Lyapunov stability theorem, an adaptive fuzzy controller, which is accompanied by fractional adaptation laws, is established. The proposed methods can guarantee the boundedness of the involved signals as well as the asymptotical convergence of the synchronization errors. It should be pointed out that the methods for using quadratic Lyapunov function in the stability analysis of the fractional-order chaotic systems are developed in this paper. Based on the results of this paper, many control methods which are valid for integer-order nonlinear systems can be extended to control fractional-order nonlinear systems. Finally, the effectiveness of the proposed methods is shown by simulation studies.

A review of the perovskite solar cells

Abstract: The efficiency of solar cells based on organic-inorganic hybrid perovskite materials has a rapid growth from 3.8% in 2009 to 19.3%. The perovskite material (CH3NH3PbX3) exhibits advantages of high absorbing coefficient, low cost, and easily synthesised, which achieved extremely rapid development in recent years and gains great concern from the academic circle. As we know, perovskite materials not only serve as light absorption layer, but also can be used as either electron or hole transport layer. Consequently, various structures are designed based on the function of the perovskite, such as the solid-state mesoscopic heterojunction, meso-superstructured planar-heterojunction, HTM-free and the organic structured layers. Besides, it is also attractive for its versatility in fabrication techniques: one-step precursor solution deposition, two-step sequential deposition, dual-source vapor deposition, and vapor-assisted solution processing etc. This review mainly introduces the development and mechanism of the perovskite solar cells performance and the fabrication methods of peroskite films, briefly describes the specific function and improvement of each layer, and finally discusses the challenges we are facing and the development prospects, in order to have a further understanding of perovskite solar cells and lay a solid foundation for the preparation of new structures of the perovskite solar cells.

乘性色噪声激励下三稳态van der Pol-Duffing振子随机P-分岔

Abstract: 研究了乘性色噪声作用下三稳态van der Pol-Duffing振子的随机P-分岔问题. 首先应用随机平均法得到系统振动幅值稳态概率密度函数的表达式, 进而应用奇异性理论, 得到刻画随机P-分岔发生的临界参数条件的转迁集以及系统存在的典型稳态概率密度曲线, 并通过Monte-Carlo数值模拟进行了验证. 以此为基础讨论了噪声强度、相关时间、系统线性阻尼系数对随机P-分岔和系统稳态响应行为的影响.

Study on 0.34 THz overmoded surface wave oscillator

Abstract: The simulation design and preliminary experiment on a 0.34 THz large-power overmoded surface wave oscillator are presented in this paper. For the slow wave structure (SWS) with large overmoded ratio (D/λ ≈ 6.8), a small signal theory is derived for appropriate dimensions of SWS and gap between electron beam and SWS, and makes the device oscillate near the π point of surface wave at TM01 mode. PIC (particle in cell) simulation results show that this SWO (small wave oscillation) can genetate the terahertz wave with frequency and output power of 0.34 THz and 22.8 MW, respectively. SWS with stainless steel is integrally and precisely fabricated by employing mirco-EDM technology, and the experimental setup is built based on a miniaturized pulse power driving source. Results of preliminary experiment and diagnostics show that a terahertz pulse is radiated at a frequency range of 0.319–0.349 THz, a power of no less than 250 kW, and a pulse duration of about 2 ns at beam voltage of about 420 kV and beam current of about 3.1 kA. Finally, the reason for discrepancy between the measured power and the simulation result is analyzed and discussed, laying the foundation for the performance improvement of terahertz surface wave oscillator.

Internet public opinion chaotic prediction based on chaos theory and the improved radial basis function in neural networks

Abstract: The information of Internet public opinion was influenced by many netizens and net medias, the characteristics of this information are no rules, stochastic chaotic and are a nonlinear complex evolution system. The corresponding model is difficult to establish and effectively predict by the traditional methods based on statistical and machine learning. The characteristics of internet public opinion are chaotic, so the chaos theory was introduced to research firstly, the information of internet public opinion having chaotic characteristic was proved by the lyapunov index. Then the model to predict the development trend of internet public opinion was established by the phase space reconstruction theory. At last, the hybrid algorithm EMPSO-RBF which was based on EM algorithm and the RBF neural network optimized by the improved PSO algorithm was proposed to solve the model. The hybrid algorithm fully took the advantage of the EM clustering algorithm and improved PSO, the RBF neural network was improved by initializing the network structure in the early stage and optimizing the network parameters in the late. Firstly, the EM clustering algorithm was adopted to obtain the center value and variance and the radial basis function was improved with the combination of traditional Gauss model. Then the relevant network parameters were obtained by the improved PSO algorithm which was based on error optimizing constantly the network parameters. The model algorithm can be accurately simulated the time series of chaotic information by the experiments which were validated by different chaotic time series information, and it can better describe the development trend of different information of internet public opinion. The prediction results are made for government to monitor and guide the information of internet public opinion and benefit the social harmony and stability.

Recent advances in planar heterojunction organic-inorganic hybrid perovskite solar cells

Abstract: The development of highly efficient and low-cost solar cells is the key to large-scale application of solar photovoltaic technology In recent years, the solution-processed organic-inorganic perovskite solar cells attracted considerable attention because of their advantages of high energy conversion efficiency, low cost, and ease of processing The ambipolar semiconducting characteristic of perovskite enables the construction of planar heterojunction architecture to be possible in perovskite-based solar cells This kind of architecture avoids the use of mesoporous metal oxide film, which simplifies the processing route and makes it easier to fabricate flexible and tandem perovskite-based solar cells Planar heterojunction perovskite solar cells can be divided into n-i-p type and p-i-n type according to the charge flow direction Two interfaces are formed between perovskite film and hole/electron transport layer, where efficient charge separation can be realized Hole and electron transport layers can form separated continuous paths for the transport of holes and electrons, thus beneficial to improving exciton separation, charge transportation, and collection efficiency In addition, this planar architecture avoids the use of high temperature sintered mesoporous metal oxide framework; this is beneficial to expanding the choice of the charge transport materials In this paper, we review the recent progress on the planar heterojunction perovskite solar cells First, we introduce the material properties of perovskite, the evolution of device architecture, and the working principle of p-i-n type and n-i-p type planar heterojunction perovskite solar cells Then, we review the recent progress and optimization of planar heterojunction perovskite solar cells from every aspect of perovskite preparation and the selection of electron/hole transport materials Finally, we would like to give a perspective view on and address the concerns about perovskite solar cells

Phenomenological modeling of nanosecond pulsed surface dielectric barrier discharge plasma actuation for flow control

Abstract: One-zone inhomogeneous phenomenological nanosecond dielectric barrier discharge (NS-DBD) actuation model used for flow control simulation is established to investigate the flow control mechanisms, based on experiments and theoretical analysis. When the inhomogeneous phenomenological model is applied to a plate, the formation of spanwise vorticity is analyzed through the vorticity transport equation, and the spanwise vorticity is mainly engendered due to the baroclinicity of pressure gradient and density gradient, also due to the vorticity transfer by the flow convection in the vicinity of the actuation region. Agreement of the simulation with experiments on a column shows that the inhomogeneous phenomenological NS-DBD actuation model is reasonable. Separation control over NACA 0015 airfoil at high angle of attack indicates that the spanwise vortices induced by plasma actuation make the separated shear layer instable, promote interaction between shear layers, and downstream the separation point. Different excitation frequency has different effect on the lift, with the optimum reduced frequency F+ ≈ 6 in current simulation.

Recognition of epilepsy electroencephalography based on AdaBoost algorithm

Abstract: Automatic recognition of epilepsy electroencephalography (EEG) signal has become a research focus because of its high efficiency, and many algorithms have been put forward to achieve it. As one of the classic algorithms of boosting algorithm, AdaBoost algorithm has been widely used in face detection and target tracking fields, but the algorithm also has a disadvantage that is its degradation. In order to solve this problem, this paper puts forward three measures to optimize the algorithm by filtering the weak classifiers whose recognition rates are low, introducing the smoothing factor and a weighted correction function. In order to verify the robustness of optimized algorithm, we choose three main parameters, i.e., the number of weak classifier, which is denoted by T; the base of logarithmic function, which is denoted by α; the threshold of weight, which is denoted by β. The experimental results of optimized AdaBoost show that it has good robustness and high recognition rate. #br#In this paper, we divide the whole process into three steps. The first step is to use the Butterworth digital low-pass filter in which the cutoff frequency of pass band is 40 Hz to filter noise whose frequency is above 40 Hz. The second step is to do feature extraction with the help of wavelet packet decomposition. The third step is to compute the sum of absolute value which are the wavelet packet coefficients of fourth layer, the wavelet package entropy and the sum of signal amplitude square and combine them together to form the feature vector of each EEG. Because the wavelet package entropy is far less than the sum of absolute value and the sum of signal amplitude square, in order to make sure that the entropy reacts in the third step, we use one thousandth of the sum of absolute wavelet packet coefficients, one hundredth of the sum of signal amplitude square and the wavelet package entropy as the weighted feature vector. Finally, we succeed in distinguishing EEGs between epilepsy and normal by using the optimized AdaBoost whose input is the weighted feature vector. The result shows that the presented method has a high recognition rate, it can identify 96.11% epilepsy EEGs and 99.51% normal EEGs, thus it provides an effective solution for the correct diagnosis of epilepsy.

D-shaped photonic crystal fiber refractive index and temperature sensor based on surface plasmon resonance and directional coupling

Abstract: The photonic crystal fiber has received the widespread attention in the sensing field because of its flexible structure and unique features. A refractive index and temperature sensor based on the D-shaped photonic crystal fiber is designed and analyzed. In the side section of the D-shaped photonic crystal fiber, a coat with a gold film is used as a surface plasmon resonance (SPR) sensing channel for measuring the refractive index of liquid determinand. Temperature sensitive liquid-toluene is filled in an air hole A as a directional coupling sensing channel to realize the temperature measurement. When the SPR mode and guided mode satisfy the phase matching condition, the SPR effect is produced. Most of the core energy is transferred to the metal film layer in the surface, and then the loss of guided mode in the fiber core will grow. Therefore, the shift of the SPR peak position can be used to measure the refractive index of the determinand indirectly. When the wave mode in the thermosensitive liquid-toluene can achieve phase matching with the guided mode, the directional coupling effect occurs, and then the wavelength of the absorption peak position can be used to measure the change of temperature indirectly. Based on further numerical simulation, the peak position of directional coupling is not changed by the refractive index of the determinand, and the SPR peak position is not shifted by the temperature change either. As these two sensing mechanisms can be distinguished easily, the refractive index and temperature sensing are simultaneously realized. The characteristics of the sensor are simulated numerically by using a full vector finite element method under the boundary condition of anisotropic perfectly matched layer. From the analysis of the D-shaped photonic crystal fiber structure parameters, we find that the diameter d of air hole plays an important role in the directional coupling absorption peak position and temperature sensitivity. For the SPR peak, its position is only affected by the thickness t of gold film, and its relative intensity is changed with the diameter d of air hole and grinding depth d1. The results show that when the temperature ranges from -10 ℃ to 80 ℃, the temperature sensitivity reaches 11.6 nm/℃, and when the refractive index is in a range from 1.32 to 1.44, its sensitivity reaches 26000 nm/RIU.

For the first time fengyun3 C satellite-global navigation satellite system occultation sounder achieved spaceborne Bei Dou system radio occultation

Abstract: The radio occultation (RO) technique using signals from the global navigation satellite system, is widely used to observe the atmosphere for applications such as numerical weather prediction (NWP) and global climate monitoring. Since 1995, there have been turborogue sounder on board global positioning system/meteorology, black jack sounder on board challenging minisatellite payload and gravity recovery and climate experiment, IGOR sounder on board constellation observing system for meteorology, ionosphere and climate, GRAS on board meteorological operational, which have been recieving a large number of RO data, but their observed signals come only from global positioning system (GPS). These RO data have been wildly used in NWP and climate monitoring, however they cannot meet the requirements for high accuracy and real time atmosphere observation, in this case compatible RO sounder to obtain more RO observations is significant. Global navigation satellite system occultation sounder (GNOS) on board the fengyun3 C (FY3 C) satellite, which is the first Bei Dou system (BDS)/GPS compatible RO sounder in the world, was launched on 23 September 2013. Up to now, lots of RO observations have been obtained. In this study, the components of GNOS are introduced; one-day GNOS RO events and their global distribution are analyzed; compared with the GPS RO observations, the accuracy and consistency of BDS real-time positioning results and BDS RO products are analyzed. The preliminary results show that the BDS can enhance the number of RO events by 33.3%; the average deviation and standard deviation of BDS real time positioning results are 6 m and 7 m, respectively; the BDS/GPS difference standard deviation of refrectivity, temperature, humidity, pressure and ionospheric electron density are lower than 2%, 2 K, 1.5 g/kg, 2%, and 15.6%, respectively. The BDS observations/products are consistent with those of GPS, therefore BDS RO products can bring benefit to numerical wheather prediction and global chlimate change analysis.

Real-time polarization difference underwater imaging based on Stokes vector

Abstract: Polarization difference imaging technique can effectively solve the underwater image deterioration problem that is caused by the interaction between light and water. Therefore, it has a significant application value in detecting and recognizing underwater target. In a traditional polarization difference imaging system, the object image is carried out by the common-mode rejection of background scattering light. However, the polarization state of the background scattering light is unknown, so the polarization difference imaging is realized by the irregular mechanical rotation of the optical polarization analyzer with two orthogonal polarization orientations. Therefore, it needs more time to determine the optimum detection angle of the polarization analyzer and cannot perform real-time underwater imaging, which restricts the rapid detecting function in the process of underwater imaging. In this paper, the detection principle of underwater polarization difference imaging is considered to exploit the difference in the polarization angle between background scattering light and target light. According to Marius's law, the physical model of polarization difference imaging is that the common-mode rejection of background scattering light will be achieved when the angles between the vibration direction of background and the two orthogonal polarization orientations are 45. Because the Stokes vector can be used to express the polarization angle of light, we propose the principle and construction of a computational polarization difference imaging system for real-time underwater imaging by incorporating the Stokes vector into the established model. It replaces the mechanical rotation of the polarization analyzer in a traditional polarization difference imaging system with the information processing of the Stokes vector. The experimental results show that the proposed method not only has the same effective performance as the conventional polarization difference imaging compared with the regular imaging, but also can improve the blurred imaging performance caused by an underwater scattering effect as well as increase the underwater detection distance. This method realizes rapid underwater target detection and recognition because it saves a large amount of time compared with the traditional one. Further, if we combine this method with the current polarization imaging instruments that capture the Stokes vector instantaneously, then a real-time automatic underwater polarization imaging can improve the efficiency of the underwater target detection and recognition. These findings are helpful for designing and developing the underwater polarization difference imaging systems.

Chaos synchronization of coronary artery system based on higher order sliding mode adaptive control

Abstract: Many biomedical engineering fields are studied by combining with nonlinear science which has major advances in theoretical curing related diseases. The coronary artery system is chosen as a muscular blood vessel model. With the change of vessel diameter, some chaotic behaviors will occur which may cause complex diseases such as myocardial infarction.#br#In order to avoid the undesired chaotic motion, this paper investigates the finite-time chaos synchronization problem for a coronary artery system by utilizting high-order sliding mode adaptive control method. First, the error chaos synchronization system is obtained using the master and slave systems. Second, the error chaos synchronization system can be transformed into an integrator chain system by coordinate transformation, which is equivalent to an error chaos synchronization system. Considering that the sliding mode control has main obstacle (the control high activity and chattering phenomenon), a high-order sliding mode adaptive controller is designed for a coronary artery system with unknown disturbances at geometric homogeneity and integral sliding mode surface. The proposed method shows that the drive and response systems are synchronized and the states of the response system track the states of the drive system in finite-time. This approach does not require any information about the bound of disturbances in advance. Theoretic analysis based on Lyapunov theory proves that the systems with the proposed controller could be stabilized in finite-time. The convergence time of the system states is estimated. In order to alleviate the chattering effect, we use tanh(·) function in place of sign(·) function to design an improved high-order sliding mode adaptive controller. Simulation results show that the proposed adaptive sliding mode controller can achieve better robustness and adaptation against disturbances, which offer the theoretic basis for curing myocardial infarction.

Improvement and adaptability evaluation of standardized precipitation evapotranspiration index

Abstract: In view of the question about larger estimate error in arid areas by using the Thornthwaite method of estimating potential evaporation in the process of calculating standardized precipitation evapotranspiration index, we use the FAO Penman-Monteith method instead of Thornthwaite method to improve the method of calculating the standardized precipitation evapotranspiration index. Based on the 1961-2013 daily meteorological data offered by 541 stations of Meteorology Bureau, the distribution of test and standardized rainfall index, Palmer drought severity index and soil moisture are used to analyze the consistency with standardized rainfall evaporation index when used to evaluate drought in the applicability of area and season. Result shows that the improvement on the method of evaporation capacity calculation can significantly expand the application of standardized precipitation evapotranspiration index in area and season, making standardized precipitation evapotranspiration index applied to national drought assessment well, making up the shortcomings in the applicability of standardized precipitation evapotranspiration index in winter at a short time scale level in arid region. In addition, both yearly time scale and monthly time scale of drought assessment ability about modified standardized precipitation evapotranspiration index are improved, meeting the demand for drought assessment in our country, which is given priority to seasonal drought.

Optical properties of graphene plasmons and their potential applications

Abstract: Graphene plasmons have aroused a great deal of research interest in recent years due to their unique features such as electrical tunability, ultra-strong field confinement and relatively low intrinsic damping. In this review paper, we summarize the fundamental optical properties of localized and propagating plasmons supported by graphene, and the experimental techniques for excitation and detection of them, with focusing on their dispersion relations and plasmon-phonon coupling mechanism. In general, the dispersion of graphene plasmons is affected by the Fermi level of graphene and the dielectric environment. The graphene plasmons can exist in a broad spectrum range from mid-infrared to terahertz. This has been experimentally verified for both the localized and propagation plasmons in graphene. On the one hand, the excitation frequency and confinement of localized plasmons supported by graphene micro/nano-structures are constrained by the structural geometry. Additionally, influenced from the tunability of the optical conductivity of graphene, the excitation frequency of graphene plasmons can be tuned by electrostatic or chemical doping. On the other hand, propagating plasmons have been launched and detected by using scattering-type scanning near-field optical microscopy. This technique provides the real-space imaging of the electromagnetic fields of plasmons, thereby directly confirming the existence of the graphene plasmons and verifying their properties predicted theoretically. In a similar regime, the launching and controlling of the propagating plasmons have also been demonstrated by using resonant metal antennas. Compared to metal plasmons, graphene plasmons are much more easily affected by the surroundings due to their scattering from impurity charges and coupling with substrate phonons. In particular, graphene plasmons can hybridize strongly with substrate phonons and there are a series of effects on plasmon properties such as resonance frequency, intensity and plasmon lifetime. The designing of the dielectric surrounding can effectively manipulate the graphene plasmons. Finally, we review the emerging applications of graphene plasmon in the mid-infrared and terahertz, such as electro-optical modulators and enhanced mid-infrared spectroscopy.

Characteristics of the geometrical scattering waves from underwater target in fractional Fourier transform domain

Abstract: The components of the underwater target scattering waves alias together in time domain and frequency domain realistically. They are affected by the incident angle, and show great differences under different angles. It is necessary to build an analytical model of scattering waves under all-direction incident angles theoretically. The analytical expressions of geometrical scattering components changing with the incident angle in fractional Fourier transform domain are deduced in this paper. The all-direction model in optimal fractional Fourier transform domain of the scattering waves is built. Based on this, the geometrical feature of underwater target echo is provided. In addition, the relationships between the resolution and the bandwidth of transmitted signal, and between the calculation accuracy and the length of observational signal are given. By processing experimental data, it is indicated that the model in fractional Fourier transform domain is in accordance with the characteristics of underwater target. It can provide a theoretical basis for target recognition under unknown incident angle.

Dynamic behavior in firing rhythm transitions of neurons under electromagnetic radiation

Abstract: This paper presents the mathematical model of membrane current of neuron resulting from electromagnetic radiation based on the foundation of neuronal energy theory; and the effect of electromagnetic radiation on the dynamic behaviors of single neuron and the firing activities of two neurons coupled with gap connection are investigated. Results show that the neuronal firing rate is lowered as the radiation intensity increases, and finally reaches a stable value. As the radiation intensity increases, the periodical spiking of neuron is transformed into bursting firing, which is well explained based on the dynamic bifurcation theory. It turns out that the bursting firing induced by the electromagnetic radiation could spread out in neuronal network through an electrical gap junction.