Vol. 55, No. 8 (2006)
2006-04-20
GENERAL
2006, 55 (8): 3799-3804.
doi: 10.7498/aps.55.3799
Abstract +
In software engineering, class diagrams are generally used to describe the relationship of classes. Software systems as networks are studied in this paper. By the demonstration and analysis of the large-scale software systems provided by Sun and IBM, it is found that the degree distribution of software systems written in Java is characterized by the scale-free distribution, and its scaling exponent γ is about 2.5. In the evolving process of software systems, in addition to addition of nodes, there are some other local events as follows: addition of edges, random removal of edges and rewiring edges. The evolving model of software systems is established consequently. As for the network generated by this model, its degree distribution follows the power-law distribution. The actual application and numerical simulations validate this model.
2006, 55 (8): 3805-3812.
doi: 10.7498/aps.55.3805
Abstract +
In this paper, the general variable coefficient nonlinear Schrdinger equation for the optical fiber is investigated based on the extended cubic nonlinear Klein-Gordon equation. The soliton solutions under non-chirp case are discussed, and some new exact solutions, including the bright soliton, the dark soliton and the soliton-like solution are obtained. The standard nonlinear Schrdinger equation and four kinds of the variable coefficient nonlinear Schrdinger equation are all corresponding special cases. In addition, some interesting results for the optical fiber system with periodic gain or loss are also obtained.
2006, 55 (8): 3813-3816.
doi: 10.7498/aps.55.3813
Abstract +
In this paper, the Lie symmetrical non-Noether conserved quantity of variable mass Birkhoffian system under the infinitesimal transformations is studied. First, variable mass Birkhoffian equations are established; second, Lie symmetry determining equations are given. Then the non-Noether conserved quantity is obtained. An example is given to illustrate the application of the result.
2006, 55 (8): 3817-3820.
doi: 10.7498/aps.55.3817
Abstract +
In this paper, a new symmetry, i.e., Noether-Lie symmetry and its conserved quantities of the non-holonomic mechanical system is studied. The definition and the criterion of the Noether-Lie symmetry for the system are given. A theorem asserting that the Noether-Lie symmetry for the system leads to both the Noether conserved quantity and the general Hojman conserved quantity is presented. An example is given to illustrate the application of the result. The Hojman conserved quantity of the system is a special case of the general Hojman conserved quantity obtained in this paper.
2006, 55 (8): 3821-3824.
doi: 10.7498/aps.55.3821
Abstract +
In this paper, a new kind of symmetry and its conserved quantities of a mechanical system in the phase space are studied. The definition of this new symmetry, i.e., the Lie-Mei symmetry is presented, and the criterion of this new symmetry is also given. The generalized Hojman and the Mei conserved quantities of the Lie-Mei symmetry of the system are obtained. An example is given to illustrative the application of the result.
2006, 55 (8): 3825-3828.
doi: 10.7498/aps.55.3825
Abstract +
This paper presents two ways of comprehending the Noether symmetry for the Lagrange system.One is based on invariance of the Lagrangian, the other is based on invariance of the action. This paper proves that these two comprehensions are different from each other. We give the condition under which the invariance of the Lagrangian can become the invariance of the action,and the condition under which the invariance of the action can become the invariance of the Lagrangian is obtained. It is suitable that the Noether symmetry is comprehended as the invariance of the action.
2006, 55 (8): 3829-3832.
doi: 10.7498/aps.55.3829
Abstract +
The definition and the criterion of Mei symmetry of generalized Hamilton systems with additional terms is studied in this paper. A necessary and sufficient condition for Mei symmetry of systems to be Lie symmetry is given. The Hojman conserved quantity for the differential equation of motion of generalized Hamilton system with additional terms being Mei symmetry can be deduced indirectly by Lie symmetry. An example is given to show the application of this result.
2006, 55 (8): 3833-3837.
doi: 10.7498/aps.55.3833
Abstract +
The perturbation of symmetries and adiabatic invariants for Birkhoffian system are studied. The exact invariants in the form of Hojman conserved quantities introduced by the Lie symmetries of Birkhoffian system without perturbations are given. Based on the definition of high-order adiabatic invariants of a mechanical system, the perturbation of Lie symmetries for Birkhoffian system under the action of small disturbance is investigated, and a new type of adiabatic invariants of the system are obtained. An example is given to illustrate the application of the results.
2006, 55 (8): 3838-3844.
doi: 10.7498/aps.55.3838
Abstract +
For general nonholonomically constrained systems, variation identity is used to define three kinds of unfree variations, i.e., nonholonomic variations: the vakonomic, the Hlder and the Suslov by means of vector fields on the extended configuration manifold. The relations among the three kinds variations are discussed and a necessary and sufficient condition for the variations to become free ones is obtained. The nonholonomic variations and the corresponding integral variational principles are utilized to derive the two kinds of dynamical equations: vakonomic equations and Routh's equations or Chaplygins equations. By comparing vakonomic equations with Rouths equations and Chaplygins equations respectively, two necessary and sufficient conditions for the two kinds of equations to have common solutions are obtained, which are not integrable conditions of the constraints.
2006, 55 (8): 3845-3851.
doi: 10.7498/aps.55.3845
Abstract +
A cross section of the rod is taken as object of investigation. The freedom of the section in free or constraint case is analyzed and the definition of virtual displacement of the section is given, which can be expressed by a variational operation. Assuming the variational and partial differential operations has commutativity, based on the hypothesis about surface constraint subjected to the rod, the freedom of the section on constraint surface is discussed and the equations satisfied by virtual displacements of the section are given. Combining D'Alembert principle and the principle of virtual work, D'Alembert-Lagrange principle is established. When constitutive equation of material of the rod is linear, the principle can be transformed to Euler-Lagrange form. From the principle, a dynamical equation in various forms such as Kirchhoff, Lagrange, Nielsen and Appell equation can be derived. For the case when a rod is subjected to a surface or a nonholonomic constraint, Lagrange equation with undetermined multipliers is obtained. Integral variational principle of dynamics of a super-thin elastic rod is also established, from which Hamilton principle formulation is obtained when the material of the rod is linear. Finally, canonical variables to describe the state of the section and Hamilton function are defined, and Hamilton canonical equation is derived. The analytical methods of dynamical modeling of a super-thin elastic rod have been constructed, which can serve as a theoretical framework of analytical dynamics of a super-thin elastic rod with two independent variables.
2006, 55 (8): 3852-3857.
doi: 10.7498/aps.55.3852
Abstract +
For solving stability of motion in a nonlinear relative rotation shafting, a sort of periodic variable coefficient linear ordinary differential equations was studied. Movement stabilization criterion of nonlinear relative rotation system was obtained by transferring the fundamental matrix of the solution of the ordinary differential equation to Jordan canonical. Using the Lyapunov function method, the stabile balance position of relative rotation motion of driving system in a variety of mechanical equipments was studied, and the analytic expression of the stable region was obtained. The method supplies theoretical laws, similarity analog criterion and technique means of selecting working parameter of stable working interval of a type of mechanical driving systems. The result of the research can be used for analysis and evaluation of the torsional vibration stability of the main driving system of heavy and complex rotary machines.
2006, 55 (8): 3858-3863.
doi: 10.7498/aps.55.3858
Abstract +
A modified double Jacobian elliptic function expansion method under a general function transform, which is more general than the Jacobian elliptic function expansion method under a travelling wave transform, is proposed to construct the exact solutions of nonlinear evolution equations. Some new exact periodic solutions are obtained by this method which include previous solutions, replenishing the known results of the equations.
2006, 55 (8): 3864-3868.
doi: 10.7498/aps.55.3864
Abstract +
Symmetry analysis is an important method used in almost all fields of natural science. In this paper, by means of the symmetry analysis, a new model, namely the coupled Burgers equations, which can be used to describe two-layer fluids is studied in detail. The Lie point symmetries of the model are obtained. By using the symmetries, four types of symmetry reductions are found. Some special types of exact solutions such as the rational solutions, travelling soliton solutions and non-travelling soliton solutions are explicitly given by solving the reduction equations.
2006, 55 (8): 3869-3874.
doi: 10.7498/aps.55.3869
Abstract +
In this article an obvious expression of concurrence of the mixed state of two non-orthogonal pure states in two qubits is derived. The result reveals that the expression of concurrence of the mixed state of two orthogonal states can be directly generalized to the case of the mixed state of two non-orthogonal states. Then the maximally entangled states mixed by two pure states and the concurrences in some important special cases are discussed.
2006, 55 (8): 3875-3879.
doi: 10.7498/aps.55.3875
Abstract +
The exact solutions of bound states of Klein-Gordon equation and Dirac equation with Coulomb potential plus a new ring-shaped potentials are studied on the assumption that the scalar potential is equal to the vector potential. The exact energy expressions and the normalized wave functions for Klein-Gordon equation are presented. The exact energy expressions and the normalized spinor wave functions for Dirac equation are given.
2006, 55 (8): 3880-3884.
doi: 10.7498/aps.55.3880
Abstract +
On the linear spin-wave frame, the XYZ antiferromagnetic Heisenberg model in an external magnetic field is proposed to have an so(3,2) algebraic structure. The energy eigenvalues and the squeezed state solutions are obtained by making use of algebraic diagonalization. Some properties of the energy eigenvalues are investigated. The connection with the model of the special two-mode harmonic oscillators is also established.
2006, 55 (8): 3885-3891.
doi: 10.7498/aps.55.3885
Abstract +
For the nonlinear Schrdinger model with an integrable open boundary, the scalar products of Bethe eigenstates and form factors of operators at the boundary are calculated. The results are represented as determinants of usual functions with parameters of the model.
2006, 55 (8): 3892-3897.
doi: 10.7498/aps.55.3892
Abstract +
The multi-mode Bose quadratic polynomial system (MBQPS) is studied. The normal, anti-normal, Wigner characteristic functions, P-representation and Q-representation of MBQPS are presented by utilizing the general theory of linear quantum transformation of multi-mode Bose system. And as a example, its quantum squeezed characteristics are studied.
2006, 55 (8): 3898-3901.
doi: 10.7498/aps.55.3898
Abstract +
When we take the black hole as a canonical ensemble composed of a naked black hole and the two-dimensional thermodynamic surface (horizon of the black hole), using the quantum statistical method, we derive the energy spectrum of the black hole Hawking radiation. The relation between the radiation temperature of the black hole and the entropy is obtained. This gives an insight into the process of the black hole Hawking radiation.
2006, 55 (8): 3902-3905.
doi: 10.7498/aps.55.3902
Abstract +
Using the quantum statistical method, we directly obtain the partition function of Bose field and Fermi field on the background of Schwarzschild spacetime. The integral expression is obtained. According to the latest research results, Hawking radiation process of the black hole is a tunnel effect. During the creation of tunnel effect, the energy of the black hole changes. The lower limit of integral is the location of the black hole horizon. Therefore, the leading term of the black hole entropy is a quarter of the horizon area. In our calculation, there are no cutoffs. We obtain that the energy of the black hole radiation particle is proportional to the radiation temperature. This provides an insight into the thermodynamics and quantum property of the black hole.
2006, 55 (8): 3906-3911.
doi: 10.7498/aps.55.3906
Abstract +
Complex network is adopted to describe the Chinese railway system, and two different ways are used to construct the networks. One of ways is that the stations are viewed as “nodes” and rails are regarded as “links”, thus a railway geographic network is generated. The geographic network has approximately zero average clustering coefficient, thus this network is a tree-form network. The other way is that by viewing stations as “nodes”, an arbitrary pair of stations is considered to be connected by a “link” when at least one train stops at both stations. Thereby, a railway traffic network is generated. The traffic network has comparatively large average clustering coefficient (〈C〉=0.83) and small average path length(〈d〉=3.27), and the degrees of most nodes of the traffic one follow a scale-free degree distribution. Consequently, the traffic network is a small world network with scale-free property.
2006, 55 (8): 3912-3915.
doi: 10.7498/aps.55.3912
Abstract +
Using the equation of free energy for a weakly interacting Fermi gas, the stability of a weakly interacting Fermi gas in the absence of external potential is studied by means of thermodynamics. The instability arising from the weakly attractive interacting of a Fermi gas is pointed out. The particle density criterion and the temperature criterion of instability for the imperfect Fermi gas with weakly attractive interaction are given, and the dependance of the critical density of particles on the temperature and the mass of particle and the attractive interaction is discussed.
2006, 55 (8): 3916-3921.
doi: 10.7498/aps.55.3916
Abstract +
Basing on the property of supply-chain networks, this paper proposes a randomly growing directional model whose node-arrival process is a renewal process and the number of new edges is a random variable with Bernoulli distribution. We calculate the degree distributions and stationary average degree distributions of the network model by using the renewal process theory and the continuum theory. The paper shows that the supply chain networks have bilateral power-law distributions.
2006, 55 (8): 3922-3927.
doi: 10.7498/aps.55.3922
Abstract +
In this paper, we study the fractional order the critical chaotic system and design an electronic circuit to realization the fractional order. The chaotic dynamic behavior of the fractional order of the critical system is verified by computer simulation and circuit experiment.
2006, 55 (8): 3928-3932.
doi: 10.7498/aps.55.3928
Abstract +
This paper investigates the synchronization of a class of uncertain chaotic systems based on reduced-order observer. Without any prerequisite on the nature of the perturbation, a reduced-order observer-based response system is designed for synchronization with the drive system. Numerical simulation shows the effectiveness of the proposed method.
2006, 55 (8): 3933-3937.
doi: 10.7498/aps.55.3933
Abstract +
In this paper a new chaotic system is presented. Some basic dynamical properties are investigated. The oscillator circuit of a new chaotic system realized is simulated using EWB.
2006, 55 (8): 3938-3944.
doi: 10.7498/aps.55.3938
Abstract +
A novel circuit design approach for Chua's non-dimension state equation is proposed in this paper. First, variable-scale reduction, differential to integral conversion and time yardstick transformation are made on the Chua's non-dimension state equation. Then each module circuit based on the state equation is designed and linked with the other circuits by corresponding relationships between state variables. The circuit consists of inverted adder, integrator and inverter, and has symmetric structure. Compared with the other existing chaotic circuits, the circuit has three main characters: (1) It proposes a circuit modularization design, giving a more general design principle for a family of chaos circuits which and can be applied to circuit design of other non-dimensional state equations. (2) The circuit parameters are independent and adjustable by using inverted adder, and convenient for circuit implementation. (3) The chaotic signal spectrum can be regulated by adjusting integral resistors or capacitances, convenient for practical applications. According to this method, a novel Chua's circuit which can generate three scrolls using polynomial is designed, and corresponding hardware experiments are performed. The computer simulations are in good agreement with hardware experiment results. This confirms the feasibility of our method.
2006, 55 (8): 3945-3949.
doi: 10.7498/aps.55.3945
Abstract +
We describe the problem of chaos synchronization with rigorous mathematical theory, and convert it to the analysis of stability of the differential equations. Chen's system, which belongs to the Lorenz's group, has been introduced as a typical system for discussing the stability of the linear coupled chaotic systems. A theorem on the sufficient conditions for attaining the chaotic synchronization has been proposed and a detailed proot is given. Using the conditions discussed above, a method of identifying the coupled parameter is also developed. Eventually, the results of simulation prove the validity of the theorem, and demonstrate the synchronization phenomenon of coupled systems in different ways and for different systems.
2006, 55 (8): 3950-3955.
doi: 10.7498/aps.55.3950
Abstract +
Using state observers theory, the drive and response systems are constructed, and then synchronization control of a new piecewise-linear chaotic system is achieved. The sufficient condition is deduced for synchronizing two chaotic systems with different initial values. Theoretical analysis shows that the algorithm has no special requests for the original systems, nor needs the Lyapunov functions to be solved, which makes it adequate to control piecewise chaotic systems. Satisfactory results of simulation experiments verified the validity of this algorithm. The method can quickly synchronize two systems at different initial values. This algorithm should be feasible for synchronization control of a class of piecewise chaotic systems.
2006, 55 (8): 3956-3963.
doi: 10.7498/aps.55.3956
Abstract +
This paper reports a new three-dimensional continuous autonomous chaotic system, which is different from the Lorenz, Chen and Lü systems. The new system contains two quadratic cross-product terms and four system parameters. Basic dynamic properties of the new system are studied by means of theoretical analysis, numerical simulation, Lyapunov exponent spectrum, bifurcation diagrams and Poincaré section diagrams. The different dynamic behaviors of the new system are analyzed when each system parameter is changed.
2006, 55 (8): 3964-3968.
doi: 10.7498/aps.55.3964
Abstract +
A novel pseudo-random number generator based on z-logistic map is proposed. The observed binary sequence of the chaotic orbit which is realized exactly under finite computing precision mostly retains the statistical characteristics and the randomness of the chaos-based information source which is defined on real domain, so the cryptographic properties of this novel chaos-based pseudo-random number generator (CPRNG) can be supported theoretically. Moreover, the period of this CPRNG is predicable and the weak keys can be excluded using a simple algorithm. This CPRNG overcomes the disadvantage of the traditional CPRNG whose existing weak keys are difficult to be excluded. Theoretical analysis and simulation results demonstrate that the cryptographic properties of the novel CPRNG are good, so it has potential application prospect in many areas including data encryption.
2006, 55 (8): 3969-3973.
doi: 10.7498/aps.55.3969
Abstract +
The bifurcation diagram of a wavelet function is discussed in the paper. The chaotic property of the map is changed with the variations of the constant k. Its μ-y diagram shows specially that there are bifurcations not only from period-2n to chaotic state but also from the chaotic state to period-2n when the parameter μ increases. The Lyapunov exponent diagram of the maps and one of the graphical iteration plot for the map are drawn. The wavelet function is also expanded with polynomial approximation in order to analyze the chaotic process.
2006, 55 (8): 3974-3978.
doi: 10.7498/aps.55.3974
Abstract +
A method of chaotic control based on improving the space correlation is presented. As examples, the Hénon discrete chaotic system and the four-order Chua's circuit is studied numerically. The results show that by improving the space correlation between chaotic signals, the chaotic dynamic systems can be controlled to converge rapidly to its equilibrium point or to the multi-periodic orbits.
2006, 55 (8): 3979-3984.
doi: 10.7498/aps.55.3979
Abstract +
This paper reports five different features in piecewise continuous and noninvertible system described by two conservative maps or one conservative map and another dissipative map. The features are as follows: the stochastic web bounded by images of discontinuous borderline is the only chaotic trajectory; phase collapse is caused by the irreversibility which makes some points to have two pre-images; fat fractal forbidden web induced by irreversibility; riddled-like attraction basin in stochastic web and forbidden web, when there are different attractors coexisting; and the impossibility to tell to which attractor an initial condition will approach. In an integrate-and-fire circuit, we find that the features still exist in the circuit system described by two dissipative maps, so they are common features in discontinuous and noninvertible maps.
2006, 55 (8): 3985-3991.
doi: 10.7498/aps.55.3985
Abstract +
Adopting the model of fractional Brownian motion, this paper presents the method of deducing Hurst exponent based on the observed sea clutter of S-band radar. Secondly the prediction technology of chaotic time series is studied based on memory-based predictor. Furthermore, adopting the method of support vector machine classifiers of the improved radial basis kernel function, this paper proposes a novel method of target detection based on the sea clutter. Thirdly, on the basis of observed sea clutter of S-band radar, the fractal dimension and the largest Lyapunov exponent are obtained, which proves its chaos and fractal characteristic. Finally, the computer simulation is carried out and the results prove the effective detection performance and noise tolerance.
2006, 55 (8): 3992-3996.
doi: 10.7498/aps.55.3992
Abstract +
A tracking control method is proposed for chaotic synchronization with diverse structures. When the controlled system satisfies Lipchitz condition, it's proved by means of Lyapunov function that this method can make the controlled chaotic system approach to any desired smooth orbit at an exponenting rate. The model of a designed controller has unique structure for different chaotic systems, and synchronization between any chaotic systems can be achieved. Computer simulations are given to illustrate the effectiveness of the proposed method.
2006, 55 (8): 3997-4004.
doi: 10.7498/aps.55.3997
Abstract +
In this paper two different methods——active control synchronization method and adaptive synchronization method are presented to study hyperchaotic Chen system and hyperchaotic Rssler system with different structure. Two different controllers are designed for synchronizing response system and drive system. When the parameters are known in advance, active control synchronization is adopted, the method is simple without constructing Lyapunov function and the time which realizes synchronization is short, when the parameters are fully unknown, the analytical expression of synchronization controller and adaptive law of parameters is given based on Lyapunov stability theory, which makes the different systems reach to synchronization and identifies the unknown parameters. Numerical simulation shows the effectiveness and feasibility of these two methods.
2006, 55 (8): 4005-4012.
doi: 10.7498/aps.55.4005
Abstract +
Center manifold theory presented an approach that the order of a system can be reduced. This paper investigates the basic characteristic of a new chaotic system by the approach. A flow equation on the center manifold is obtained and the pitchfork bifurcation is analyzed for the new chaotic system. An analog electronic circuit is designed to implement the new system, so the chaotic attractor are verified. We explain the significant distinction of application due to different frequencies used in numerical simulation and circuit implementation. Finally, the synchronization of the new chaotic system is realized by using the single variable coupling feedback, and the circuit of synchronization is presented.
2006, 55 (8): 4013-4019.
doi: 10.7498/aps.55.4013
Abstract +
Laguerre polynomial approximation method is applied to study the period-doubling bifurcation and chaos behavior in double-well Duffing system with a random parameter subjected to harmonic excitation. Firstly the stochastic system is reduced to its equivalent deterministic counterpart, through which the response of the stochastic system can be obtained by numerical methods. Then bifurcation and chaos in the stochastic double-well Duffing system is explored. Numerical simulations show that the nonlinear dynamical behavior is similar to their counterpart in deterministic nonlinear system such as period-doubling bifurcation, but in some local areas they are shown to have their specific features.
2006, 55 (8): 4020-4025.
doi: 10.7498/aps.55.4020
Abstract +
Based on the two-dimensional neural map, we use the Gaussian white noise to imitate the noisy environments of neurons. We investigate the impacts of Gaussian white noise on the phase diagram of parameters. It is found that adding the noise leads to an enhancement of excitability of the system. We also study the coherence resonance (CR) by numerical simulation, and the parameter condition of the CR phenomenon is discussed. Only when the parameters of the system are chosen in the regime of silence and near the dividing line between spiking and silence can we get the CR phenomenon.
2006, 55 (8): 4026-4031.
doi: 10.7498/aps.55.4026
Abstract +
An improved two-lane traffic flow lattice model is proposed. The model introduces a new function to govern the flow shift between two lanes, and then eliminates the flaws of vehicle backward movement which may appear in existing lattice models. The sufficient and necessary conditions for keeping the model’s linear stability are derived. Numerical simulations which correctly reproduce the lane changing behavior induced by small disturbances are presented.
2006, 55 (8): 4032-4038.
doi: 10.7498/aps.55.4032
Abstract +
Intelligent decision-making based on the information feedback in a two-route traffic flow model is studied. Compared to the mechanical decision-making which induces an oscillation and low efficiency of system, intelligent decision-making will improveme the efficiency. Our results suggest that one should not only devote to obtaining optimal information feedback, but also make an intelligent decision based on information feedback at hand.
2006, 55 (8): 4039-4045.
doi: 10.7498/aps.55.4039
Abstract +
We introduce in the diffusion-limited aggregation model an internal degree of freedom, i.e., a spin taking two states (up and down) with power-law Ising interaction. The fractal aggregation of magnetic particles with different ranges of interaction is investigated by Monte Carlo simulation. The simulation shows that for the antiferromagnetic coupling, the spins of the particles in the aggregates tend to be oriented alternately. For the ferromagnetic coupling, however, the spin orientation distribution of the aggregates depends on the interaction range: for the short-range interaction, domains with different sizes are observed in the aggregates, i.e., the aggregates exhibit ferromagnetic structure; for the long-range interaction, during the earlier stage of the growth process, the aggregates exhibit approximately antiferromagnetic structure, then, in subsequent growth of the outer part of the aggregates, the spin states of all particles are similar. The morphology and magnetization of the magnetic fractal aggregates as well as their evolutions with different ranges of interaction are also studied.
2006, 55 (8): 4046-4050.
doi: 10.7498/aps.55.4046
Abstract +
The interacting herding model only includes the affects of the last activity and ignores all the activities before. In real market, agents have a long-range time memory about the past activities which affects actually the current one. But, due to oblivion, the past activities have different influences on the current one depending on the time line. In the paper, a long-range memory is introduced to the interacting herding model in which the past activities affect the current one with exponential decay which reflects the fact that agents have a long-range time memory and mislay along with time about the past activities. The numerical calculation shows that its dynamics behaviors exhibit some characteristics more close to the real markets and can include the previous model as a limit case.
EDITOR'S SUGGESTION
2006, 55 (8): 4051-4057.
doi: 10.7498/aps.55.4051
Abstract +
Inspired by the observation that some real-life networks' sizes grow as a geometric series, a growing complex network model with acceleratingly increasing number of nodes is proposed. At each time step, the number of newly added nodes is proportional to the size of the network. This network shows scale-free property when the growing rate r is not large, and its power-law exponent is tunable from 2 to 3 through r. The average path length decreases and clustering coefficient increases with r respectively. In addition, we also give an analytical solution about power-law exponent versus r that agrees well with the simulation result.
2006, 55 (8): 4058-4064.
doi: 10.7498/aps.55.4058
Abstract +
Based on the weighted scale-free network model proposed by Barrat, Barthélemy and Vespignani (BBV), we propose a generalized BBV (GBBV) model with large-scale tunable clustering coefficient. Theoretical analysis and numerical simulations show that the GBBV model retains many properties of the BBV model, such as power-law distributions of node degree, node strength and edge weight. However, the GBBV model overcomes the drawback of the BBV model that the clustering coefficient can only be tuned in a small interval, and therefore the GBBV model can be used for modeling networks with large clustering coefficients.
2006, 55 (8): 4065-4069.
doi: 10.7498/aps.55.4065
Abstract +
Based on the unique advantages of high intensity, high resolution and good collimation of synchrotron radiation X-ray, the nondestructive synchrotron radiation computed-tomography technique is widely used in many fields. In this paper, the contrast error of this technique is studied, and four basic error-forms are discussed. The numerical simulation results confirmed the analysis.
ATOMIC AND MOLECULAR PHYSICS
2006, 55 (8): 4070-4077.
doi: 10.7498/aps.55.4070
Abstract +
Extensive analysis of fine-structure energy levels of configurations 4s24p3(4S3/2,2P1/2,3/2, 2D1/2,3/2)and 4s24p25s(4P1/2，3/2，5/2,2P1/2,3/2, 2D3/2,5/2，2S1/2) are made for arsenic isoelectronic sequence of ions from YⅦ to AgⅩⅤ by Hartree-Fock method with relativistic corrections (HFR) using the Cowan code. The Slater parameters of fine-structure level are obtained by least-square-fit for ions mentioned above with the available experimental data, and the unknown parameters are calculated by the generalized-least-square-fit with the extra-(inter)polation method. With these new parameter values, the fine-structure energy levels of 4s24p3, 4s24p25s are computed. All of the 35 electronic-dipole transition wavelengths and its associated oscillator strengths between configurations 4s24p3 and 4s24p25s are calculated for Rh，Pd and AgⅩⅤ. The wavelength uncertainties with the available experimental values for Rh are mostly within 0.003nm. All results of Pd and AgⅩⅤ are predicted values currently anavailable in experiment.
2006, 55 (8): 4078-4085.
doi: 10.7498/aps.55.4078
Abstract +
Solving time-dependent Schrdinger equation numerically, we investigate the high-order harmonic generation and ionization probability of one-dimensional, two-dimensional and three-dimensional hydrogen atom exposed to intense laser field. Our results show that high-order harmonic generations and the ionization probabilities of the model atoms and real hydrogen atom are similar both in the multi-photon ionization regime and in the over-barrier ionization regime; in the tunneling ionization regime, the plateau feature and cut-off position of high order harmonic generations of the model atoms and real hydrogen atom are almost the same, and the trend of change of the ionization probabilities with time is similar, but the values of ionization probabilities for the model atoms are different from those for real hydrogen atom. We discuss the reason for the difference of ionization probabilities between the model atoms and the real hydrogen atom according to the classical three-step model.
2006, 55 (8): 4086-4090.
doi: 10.7498/aps.55.4086
Abstract +
Laser collimation of Cr atomic beam using a transverse Doppler cooling scheme is studied. The frequency of laser is stabilized at 5±0.26MHz below the 7S3→7PO452Cr transition. The shortest size of the laser cooling beam is computed theoretically to be 13.7mm. Accordingly a Cr beam was collimated using a transverse Doppler cooling scheme. We obtained that the transverse distribution of Cr beam is less than 1/3 of the uncooled beam.
2006, 55 (8): 4091-4095.
doi: 10.7498/aps.55.4091
Abstract +
Terahertz time-domain spectroscopy has been used to measure the spectral properties of polycrystalline asparagines at room temperature. The absorption spectra and the indexes of refraction are obtained. This result shows the sample has the spectral response in terahertz spectral range and the fact demonstrates the terahertz spectra of asparagine could be used to study the molecular structure and vibration of sample. Two absorption peaks, the broad band ranged from 1.642 to 1.758THz and the narrow one located at 2.266THz, are observed in the frequency range 0.5—2.4THz. The assignments of vibrational modes in this spectral region are made using density functional theory at the level of B3LYP/6-31+G(d,p). The theoretical results agree well with the experimental data.
2006, 55 (8): 4096-4102.
doi: 10.7498/aps.55.4096
Abstract +
Taking into consideration the overlapping effect of electron clouds between two atoms in a molecule, a modification method is presented which can be used to calculate the total cross sections for electron scattering from numerous molecules at medium and high energies. The modified complex optical potential composed of static, exchange, polarization plus absorption is directly employed to calculate the total cross sections for electron scattering from isoelectronic molecules (HCl, H2S, PH3 and SiH4) over the energy range 30—5000eV using the additivity rule model at Hartree-Fock level. The obtained quantitative molecular total cross sections are compared with those obtained by experiments and other theories wherever available, and good agreement is obtained. It is shown that the additivity rule model together with the modified complex optical potential can give much better results than the unmodified one. So, the modification potential method presented here can improve the accuracy of the total cross section calculations of electron scattering from molecules.
2006, 55 (8): 4103-4110.
doi: 10.7498/aps.55.4103
Abstract +
The energy and normal force of self-adatom on Pt(110) surface have been calculated by the modified analytical embedded atom method. The most stable position for a Pt adatom on Pt(110) surface is 0.11 nm above the hollow of the first layer atoms, and the best path for a Pt adatom migrating from a hollow to neighbor hollow is along the close-packed direction. On leaving the surface, the adatom will go through the repulsive, transitional and attractive regions, successively. In the repulsive and transitional regions, due to stronger pair interaction potential between adatom and the first layer atoms, the contour maps of the energy and normal force could be seen simply as a duplicate of the Pt(110) surface. This is consistent with the results of pair potential theory and embedded atom method. The complicated contour maps of the energy and normal force were obtained in the attractive region due to relatively increasing effects of the many-body interactions and nonspherical distribution of the electrons of the atoms in the crystal.
2006, 55 (8): 4111-4116.
doi: 10.7498/aps.55.4111
Abstract +
A new method based on micro-cantilever sensors was presented and used to investigate conformation transition of macromolecules. Poly(N-isopropylacrylamide)(PNIPAM)were grafted onto one surface of a micro-cantilever by self assemble monolayer method. Then the micro-cantilever was immersed into distilled water in which the temperature can be adjusted in the range of 20—40℃. The deflection of the micro-cantilever induced by conformation transition of PNIPAM chains was measured using optical lever technique. The results show that the micro-cantilever deflects upon heating and opposite deflection occurs upon cooling, which indicates that the surface stress of the micro-cantilever changes when the conformation of PNIPAM changes upon heating and cooling. The surface stress changes continuously over the range of 20—40℃. However, a sharp change appears around the low critical solution temperature (～32℃), at which a coil-globule transition occurs in free aqueous solution of PNIPAM. The whole process is irreversible and shows a clear hysteresis, which can be attributed to hydrogen bonding and the possible chain entanglement formed during the collapse process.
CLASSICAL AREA OF PHENOMENOLOGY
2006, 55 (8): 4117-4122.
doi: 10.7498/aps.55.4117
Abstract +
Using the theory of waveguide excited, the full three-dimensional self-consistent working equations of interaction between slow electromagnetic traveling wave and electronic beam have are obtained in traveling-wave tubes, considering multi-signal inputs and relativistic effect. The equations include excited equation, motion equations, energy conversion equation, phase evolving equation etc., which can be applied to simulate most of nonlinear interactions between slow electromagnetic traveling wave and electronic beam in traveling wave tubes (TWT). The crossmodulation in a wide-band helix TWT is simulated using this theory, and is compared with the experimentation results to confirm the theory. The nonlinear beam-wave interaction processes in a relativistic disk-loaded waveguide TWT are also been simulated using the theory.
2006, 55 (8): 4123-4131.
doi: 10.7498/aps.55.4123
Abstract +
Based on the time dependent theory of random lasers, which was established via combining Maxwell equations with the rate equations of a four-level atomic system, the output intensity of lasing modes varying with the pump rate and area as well as the medium's size and shape is simulated for two-dimensional random media by use of the finite difference time domain method. Results show that the pump-rate dependence of the output intensity presents not only a threshold property, but also a saturation property, just like that of the lasing modes in conventional lasers. Based on the dependence of mode property on the medium's and pump's parameters, the mode-selection approaches are proposed for two-dimensional random lasers, which are quite different from those performed in conventional lasers.
2006, 55 (8): 4132-4138.
doi: 10.7498/aps.55.4132
Abstract +
High density digital video disc (HD-DVD) is one of the high density optical data storage technologies to meet the demand of high definition TV. The knife-edge method for focus error detection in HD-DVD driver is proposed in this paper. The calculation model for optical intensity distribution on photo detector under different defocusing amount is deduced on the basis of Fresnel formula and scalar diffraction theory.The S curve obtained theoretically showing how the focus error intensity varies with defocusing amount is in agreement with the experimental one for HD-DVD driver,which validates the calculation model.Furthermore, the focusing noise caused by pit-modulation in HD-DVD driver is analyzed and indicated to be less than 4.5%. It is concluded that a satisfactory focus range of linearity is realized in HD-DVD driver with knife-edge method which has high sensitivity and low focusing noise.
2006, 55 (8): 4139-4144.
doi: 10.7498/aps.55.4139
Abstract +
A novel kind of fiber amplifier——quantum dot doped fiber amplifier (QDFA) is presented. Using semiconductor nanocrystal PbSe as a dopant, the gain bandwidths of the PbSe-QDFA are simulated by solving the rate equation and the light propagation equation in a two-level system, applying a genetic algorithm combined with an “inversing method”. Comparing with conventional erbium-doped fiber amplifiers available, there is evidence to show that characteristics of the PbSe-QDFA are obviously advantageous in respect of bandwidth and noise, especially on long-waelength band. Furthermore, the ideal emission-absorption cross-sections of the quantum dot are determined by utilizing the genetic algorithm. Under such ideal cross-sections, the QDFA possesses with the performance of ultra-bandwidth and low noise figure near a quantum limit.
2006, 55 (8): 4145-4149.
doi: 10.7498/aps.55.4145
Abstract +
A four-level atomic system is employed as an example, in which three transitions are in N configuration and the middle transition is used as a probe transition. We show that electromagnetically induced absorption and electromagnetically induced transparency can appear in the four-level N-type atomic system, which are dependent not only on the spontaneous transfer of atomic coherence, but also on the relaxation of the fourth level, the Rabi frequency of the coupling and the control field.
2006, 55 (8): 4150-4155.
doi: 10.7498/aps.55.4150
Abstract +
A novel scheme for all-optical logic AND and NOR gates is proposed based on the same structure, and the principle of operation is the cross-gain modulation in cascaded single-port-coupled semiconductor optical amplifiers (SOAs). By using the dynamic models of single-port-coupled SOA, two kinds of logic operations are demonstrated successfully at 20Gb/s. A good agreement is shown between the numerical simulation and the experimental results.
2006, 55 (8): 4156-4160.
doi: 10.7498/aps.55.4156
Abstract +
This paper presented the results of experimental studies on transient soft X-ray laser using a picosecond pulsed laser facility.A rather intensive Ni-like Ag X-ray laser at 13.9nm with output energy of about 5—10nJ was obtained by irradiating the solid flat targets with a several hundred picosecond long laser pulse in combination with an 1ps ultra-short laser pulse.
2006, 55 (8): 4161-4165.
doi: 10.7498/aps.55.4161
Abstract +
The scheme for synchronizing Ti:sapphire femtosecond laser and Nd:YVO4 picosecond laser is discribed. Sub-ps jitter is obtained, based on which broad-band femtosecond blue-light laser of 460nm is generated through mixing two laser pulses in the BBO crystal. The technique not only shows a general way of synchronizing lasers of completely different wavelength and pulse width, but also demonstrates a new scheme for generating ultra-short laser with new wavelength through nonlinear frequency mixing.
2006, 55 (8): 4166-4169.
doi: 10.7498/aps.55.4166
Abstract +
Transparent polycrystalline Cr:Al2O3 ceramics were synthesized by conventional pressureless synthesis processing. The absorption and emission spectra of Cr:Al2O3 ceramics specimens before and after annealing were measured at room temperature. It was discovered that the emission spectra of Cr4+ in Al2O3 octahedral coordination site is in infrared wavelength range of 1100—1600nm. The emission peak of Cr4+ is centered at 1223nm, which is similar to that of Cr4+ in tetrahedral site. Al2O3 has smaller lattice constant, resulting in the larger crystal field strength, so there is a blue shift in the peak of Cr4+:Al2O3 ceramics compared to those of other Cr4+-doped crystals. And the emission band is much narrower with full width at half maximum Δλ 37nm.
2006, 55 (8): 4170-4175.
doi: 10.7498/aps.55.4170
Abstract +
On the laser driver “Shenguang Ⅱ”, eight fundamental beams have realized power balance. By changing detuning values of parameters of the frequency tripling systems, the output pulse shapes of the output beams are mutually compared. The experiment results indicate that for the type Ⅱ-type Ⅱ polarization-mismatch frequency tripling system, when the input intensity is about 1GW/cm2, of the three parameters that influence the freguency tripling efficiency, polarization detuning angle Δθp has the most important effect on the pulse shape. When all three parameters of tripling system are at the optimized values, the full width at half maximum of pulse shape τ reaches minimum. This work describes the method of crystal adjustment to actualize the power balance of the eight frequency tripling beams.
2006, 55 (8): 4176-4180.
doi: 10.7498/aps.55.4176
Abstract +
A compensated compact microstrip resonant cell (C-CMRC) with photonic band-gap (PBG) performance is presented in this paper. Two open microstrip stub-lines are added at the center of the compact microstrip resonant cell (CMRC) to compensate for the unbalanced change of inductance and capacitance in low pass band. It can significantly improve the return loss and insertion loss. Furthermore, the C-CMRC with capacitive loading leads to a stronger slow-wave and enlarged stop-band bandwidth. A low pass filter with 3 C-CMRC resonators in series has been designed according to the PBG performance. The period is only 0.15λg due to the slow-wave effect. Comparison with the general PBG period of 0.5λg, the circuit size is reduced effectively. The original CMRC and the C-CMRC with open stub lines are designed, fabricated and measured to validate the improved performance. A low pass filter with 3 C-CMRC resonators is also designed with 1.26dB insertion loss below 1.8GHz and more than 25dB stop-band from 2.6 to 9GHz.
2006, 55 (8): 4181-4187.
doi: 10.7498/aps.55.4181
Abstract +
Adopting basic-differential equations for self-simulating motion of one-dimensional nonstable flow in ideal gas, the self-simulating characteristics of wave-rear gas in spherical strong shock wave have been analyzed in detail. Additionally, the general form of propagation formula for the spherical strong shock wave,owning self-simulating motion characteristics, is deduced out. Study indicates that the self-simulating motion mode of spherical strong shock wave need not start from a point having irregularity, and the initial shock velocity and self-simulating temperature function, generally, do not exist the problem of driving to infinite. And, Taylor’s self-simulating mode of the shock wave from point explosion is a special case of the general self-simulating mode with the assumption that the whole energy of the self-simulating motion is a definite value.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2006, 55 (8): 4188-4192.
doi: 10.7498/aps.55.4188
Abstract +
Based on the results of the X-ray diffraction experiment, we implement the fractal concept to study the liquid structure of In-80wt% Sn at 300℃. Partially-overlapping multirange fractals in the melt In-80wt%Sn are observed. According to the characteristic of the partially-overlapping multirange fractals, a model of multirange fractals in liquid structure is proposed and the simulated results agree with the experimental data, where the relative error is less than 1.5%. From the fractal analysis, the whole structure of liquid is clearly revealed, and the range of the transition region between the fractals is speculated to be related closely with the properties of the liquid alloys，and the changes of the transition region may disclose the changes of the liquid alloy characteristics.
2006, 55 (8): 4193-4196.
doi: 10.7498/aps.55.4193
Abstract +
We report the Young's modulus of a series single-wall carbon nanotubes(armchair type and zigzag type)and BN zigzag type nanotubes on the basis of ab initio theory. According to the calculations, the relation between Young's modulus and the diameter of nanotubes is presented. We have also discussed how the strain energy of rolling effect of all kinds of nanotubes and how the balance basis set a of nanotubes varies with the type of nanotubes.
2006, 55 (8): 4197-4201.
doi: 10.7498/aps.55.4197
Abstract +
Multiwalled carbon nanotube bundles have been investigated with the near-edge X-ray absorption fine structure (NEXAFS) spectra. In the angle-dependent NEXAFS spectra of multiwalled carbon nanotube bundles, a change of the intensity of the C—H σ* with the synchrotron radiation light incident angle has been observed. The presence of the C—H bond at room temperature and ambient pressure may be related to the defects in the carbon nanotubes. Neither the C—C π* nor the C—C σ* is similar to the C—H σ*, which strongly suggests that the hydrogen atoms are adsorbed on the defects on the interior surface of the wall of carbon nanotubes at room temperature and ambient pressure. These results indicate that NEXAFS spectrum is a powerful tool for the investigation of multiwalled carbon nanotube bundles.
2006, 55 (8): 4202-4207.
doi: 10.7498/aps.55.4202
Abstract +
A velocity interferometer system for use with an arbitrary reflector was used to measure the free surface velocity history of LY12 aluminum alloy in a wide range of pre-heating from the room temperature approaching to the melting point, and the dependences of dynamic yield strength and spall strength on the initial sample temperature have been investigated. Experimental results indicate that the dynamic yield strength decreases rapidly with the heating temperature, and only 15% of the initial strength at room temperature is retained when heated up to 847K (86K lower than the melting temperature). The measured yield strength has been compared with the Zerilli-Armstrong (ZA) model and Steinberg-Cochran-Guinan (SCG) model calculation, which points out that the ZA model could describe the dependence of the yield strength on temperature well and the SCG model has overestimated the dynamic yield strength at high temperature significantly. Decrease of the spall strength with the increase of heating temperature for LY12 aluminum alloy was observed also, and nearly 80% loss of spall strength was determined in the present experimental temperature range of 296—847 K. An empirical formula has been proposed to normalize the dependence of spall strength on the heating temperature, and it gives a fairly good fitting for a number of aluminum based materials, including pure aluminum, aluminum alloy and single crystal aluminum, measured in this work and by others in the literature.
2006, 55 (8): 4208-4213.
doi: 10.7498/aps.55.4208
Abstract +
First-principle calculations based on the plane-wave pseudopotential method have been used to study the surface energy and structure of anatase TiO2(101) surface.There are six different structures of the anatase TiO2(101) crystal surface because different atoms are terminated on the surface layers. The calculation result shows that anatase TiO2(101) crystal surface structure which the outermost and second layer respectively terminated by twofold coordinated oxygen atoms and fivefold coordinated titanium atoms is much more stable than the other five structures. By investigating the effect of variable vacuum layer thickness and slab thickness on the surface energy and surface atomic displacements, we find that slab thicknesses of at least 12 atom layers and vacuum layer thickness of more 0.4nm are sufficient to converge the surface energy to within 0.01 J/m2. At last, we obtained the result that the twofold coordinated oxygen atoms have an inward relaxation of 0.0012nm, and fivefold coordinated titanium atoms have an outward relaxation of 0.0155nm,while the length of Ti—O bonds and quantity of electric charge of titanium and oxygen atoms are changed, making the structure more stable.
2006, 55 (8): 4214-4220.
doi: 10.7498/aps.55.4214
Abstract +
Based on the atomic interaction potential with the embedded atom, molecular dynamics simulation was used to study the variation of Cu(001) surface caused by a Cu adatom and the hopping barriers of another Cu adatom in its vicinity. The results show that the Cu adatom may distort the positions of Cu atoms in the substrate to the extent of 2 lattice constants and the influence is as deep as 10 layers. Due to the interaction of the stress field between two adatoms, the hopping diffusion barriers of the adatoms are decreased and the adatoms are more active in diffusion than a single adatom. By comparing the difference of hopping barriers to and fro along the same diffusion path, the migrating behavior of the adatoms can be divided into two kinds of diffusion, depending on the distance between the two adatoms. If they are at a distance longer than the effective distance of the atomic interaction potentials, the diffusion of adatoms is affected only by the interaction of the stress field between two adatoms. If they are at a distance shorter than the effective distance of the atomic interaction potentials, the two adatoms should be considered as an ad-dimer in different states.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2006, 55 (8): 4221-4225.
doi: 10.7498/aps.55.4221
Abstract +
We have studied silica single and double chain based on two-membered ring and nanotubes based on three-membered ring using the density-functional theory at 6-31G(d) level. The average binding energy, electronic structure and vibration frequency were calculated. Our calculations show that the average binding energy and energy gap monotonically change with increasing SiO2 units. Infrared spectrum indicated that the frequency and intensity of radial and tangential vibration shift obviously. Radial vibration frequency shifts to high frequency while tangential vibration frequency shifts to low frequency showing the existence of quantum size effect and anisotropic property of vibration in SiO2 nanomaterial.
2006, 55 (8): 4226-4231.
doi: 10.7498/aps.55.4226
Abstract +
The La0.67Pb0.33MnO3 (LPMO) thin films doped with Ag on vicinal-cut LaAlO3 substrates were prepared using standard pulsed laser deposition technique, in which laser induced thermoelectric voltage (LITV) effect was found. With Ag doping level x (x is defined as,x=massAg/massLPMO) increasing from 0.00 to 0.10, the response time of LITV signals in LPMO thin films firstly decreases (reaching minimum at 0.06), and then increases (still less than that with zero Ag doping). Further, an optimal film thickness was found, at which the peak voltage and response time of LITV signals to reaches maximum and minimum, respectively. The response time of LITV in the LPMO thin films are substantially smaller than that of La0.67Ca0.33MnO3 thin films at the same Ag doping level.
2006, 55 (8): 4232-4237.
doi: 10.7498/aps.55.4232
Abstract +
Using on-line measurement of plasma emission spectra during reactive magnetron sputtering, the growth of ZnO films was studied with the variation of O2 flow and deposition temperature, ranging from room temperature to 750℃. With the structural characterization and measurement of optical properties, we revealed the role of growth temperature and O2 flow in the growth of ZnO film. The results showed that O2 flow was important in determining the sputtering yield of Zn target. When the flow ratio of O2 to Ar+O2 (R)>0.75%, the sputtering yield of Zn decreased linearly with increasing O2 flow. When R was in the 10%—50% range, the concentration of oxygen varied slowly, which may be useful for the control of film growth. The intensity of emission spectrum of atomic Zn at 481.3 nm varied with increasing deposition temperature T. When T550℃, the intensity increased sharply with increasing deposition temperature. By controlling the deposition temperature, a high-quality film with the composition close to stoichiometric ZnO was fabricated on Si(001) substrate at 750℃ and ultraviolet photoluminescence was detected at room temperature.
2006, 55 (8): 4238-4246.
doi: 10.7498/aps.55.4238
Abstract +
Chemical species in the low-pressure inductively coupled plasma for cubic boron nitride (cBN) film deposition using B2H6, N2, He and Ar as reactant gases were investigated by quadrupole mass spectrometry. B2H6 was found to be ionized totally, while N2 was only partially ionized. The species in plasma were Ar, He, N2 molecules and Ar+, He+, N+, N+2, B+, BxH+y, H+ and H+2 ions, no H and N radical was detected by appearance potential mass spectrometry. The introduction of H2 and N2 gases into the deposition system was found to produce a large mount of H radicals and excited N*2 molecules, which suppressed the cBN formation by reacting with the growth surface. The etching and sputtering of cBN and turbostraotic boron nitrde (tBN) by H2 and Ar plasmas were also evaluated, and we did not find that the tBN is selectively etched or sputtered. Moreover, high-resolution transmission electron microscopy of as-deposited cBN on the edge of ultrathin silicon flake substrate showed that the surface of as-deposited cBN film was composed of cBN {111} nanofacets, and no thin sp2-bonded boron nitride surface layer was observed. Our results suggest that cBN nucleates and then grows on the top surface in chemical vapor deposition systems, and the processes of cBN surface nucleation and growth in the present system was also discussed simply.
2006, 55 (8): 4247-4252.
doi: 10.7498/aps.55.4247
Abstract +
The electronic structure and photoresponse of p-type quantum well infrared photodetector (QWIP) are calculated by self-consistent method. The effect of distribution of holes in the momentum-space on the photoresponse of the device is studied. The calculation results show that the contribution of holes to the photocurrent depends on the distribution of holes in the momentum-space, so the density of holes and the temperature influence the photoresponse of the p-type QWIP. The theoretical results agree well in the change of photoresponse of device with doping concentration and temperature in the experiment.
2006, 55 (8): 4253-4258.
doi: 10.7498/aps.55.4253
Abstract +
The relationship between the equivalent barrier height of ZnO-Bi2O3 based varistor ceramics and normalized applied voltage was studied and it was found that the equivalent barrier height is influenced by normalized voltage greatly. With the increase of normalized voltage the equivalent barrier height increases firstly, then changes little and finally decreases quickly. Because the Schottky barrier height at the reverse-biased side is higher than that at the forward-biased side, the equivalent barrier height is determined by the former. The changing trend of the equivalent barrier height with normalized voltage indicates three steps of conduction. Firstly, in low normalized voltage range the velocity of electron injection from the forward-biased barrier area into the amorphous layer at grain-boundary is lower than that of ejection from traps in the amorphous layer into the reverse-biased barrier area. Thus the equivalent barrier height increases with the growth of normalized voltage. Secondly, in medium normalized voltage range, the injection velocity and the ejection velocity of electron is equal and the equivalent barrier height reaches its maximum value. Finally, in high normalized voltage range the injection velocity of electron is quicker than the ejection velocity of electron and the equivalent barrier decreases with the increase of the normalized voltage. In the end the Schottky barrier will break electrically. At the same time the relationship between the equivalent barrier height and the leakage current was analyzed and it was found that the leakage current is determined by an exponential function of the difference between the equivalent barrier heights when normalized voltage is 1 and 0.75.
2006, 55 (8): 4259-4264.
doi: 10.7498/aps.55.4259
Abstract +
Phases and core-levels of Sm-intercalated C60 thin films are researched with X-ray photoemission spectroscopy. The solid solution phase dominates until the stoichiometry of Sm0.5C60. Below the intercalation level of Sm2.75C60, the sample is phase-separated into the solid solution phase and Sm2.75C60, while the sample is not the mixture of Sm2.75C60 and Sm6C60 with the Sm concentration higher than Sm2.75C60. Experimental data of Sm 4f and 4d clearly reveal the valence state of Sm is divalent for Sm fullerides. Two subpeaks of divalent Sm 3d5/2 level are found.
2006, 55 (8): 4265-4270.
doi: 10.7498/aps.55.4265
Abstract +
Valence band structure of Sm-intercalated C60 thin films is researched with ultraviolet photoelectron spectroscopy and synchrotron-radiation photoemission spectroscopy. Most valence electrons of Sm transfer to C60，and the bonding nature is mainly ionic. No Fermi edge is observed for all stoichiometries. Thus the superconducting Sm fulleride has semiconducting property at room temperature. Density of states near the Fermi level is obtained for single phase of Sm2.75C60. Photoemission of the solid solution phase differs apparently from that of Sm2.75C60. SmxC60 (2.752.75C60 and Sm6C60, which indicates that another phase exists or Sm doping proceeds smoothly through the LUMO+1 band. The interfaces between different phases are unstable above 130 ℃.
2006, 55 (8): 4271-4275.
doi: 10.7498/aps.55.4271
Abstract +
This paper demonstrates a technique on heat-assisted magnetic probe recording. The recording medium is a CoNi/Pt multilayered film, suitable for perpendicular recording. Scanning tunneling microscopy(STM) current was introduced to heat the medium locally. Pulse voltages of 2—9V, 500ns in width and 100ns in risetime were used to write marks. Marking was achieved at bias voltages higher than the threshold value 4V in the shape of circular dots with an average size of 170nm. Below the threshold, no marks were observed. A simple model qualitatively explains the experiment.
2006, 55 (8): 4276-4281.
doi: 10.7498/aps.55.4276
Abstract +
In order to obtain the two dimensional distribution of the refractive index changes due to the domain inversion in the RuO2:LiNbO3 crystal, we make use of the Mach-Zehnder interferometer and 4f optical lens system to record holograms, with the object light transmitting through the poled RuO2:LiNbO3 crystal, and then filter the spectrum in the frequency domain to get the object light spectrum for numerically reconstructing the object wavefront. The results confirm that the electro-chromic effect region well coincides with the domain inversion region in RuO2:LiNbO3 crystal. Digital holographic interferometry has the merits of being nondestructive and it provides a prospective way to in-situ visualization, monitoring and analysis of the domain inversion in LiNbO3 crystal.
2006, 55 (8): 4282-4286.
doi: 10.7498/aps.55.4282
Abstract +
One to ten Fe monatomic layers (ML) with wedge-shape were deposited on the NiO(001) substrate by molecular beam epitaxy (MBE) and pulsed laser deposition (PLD), respectively. The analysis in situ of surface magneto-optic Kerr effect indicates that the Fe layer gives rise to an about 2ML thick magnetic dead layer at the interface of Fe/NiO by MBE deposition. The magnetic dead layer is about 3ML for the method of PLD. X-ray photoelectron spectroscopy indicates that both ways of deposition can lead to interfacial chemical reactions.
2006, 55 (8): 4287-4291.
doi: 10.7498/aps.55.4287
Abstract +
We theoretically study the properties of the magnetic polarization currents (MPC) in parallel-coupled double-quantum-dot devices by means of the two-impurity Anderson Hamiltonian and Green functions. It is shown that at zero temperature, the Kondo effect of the system becomes weaker with the increase of the coupling strength. At low temperature, by varying some conditions such as temperature and bias voltage, the direction and magnitude of MPC can be changed, which implies that the magnetic states of the device can be mode up-, non- or down-polarized.
2006, 55 (8): 4292-4297.
doi: 10.7498/aps.55.4292
Abstract +
The equivalent electrical model of 0-3 piezoelectric composite was proposed to analyze the effect of polymer conductance on the polarization properties of the composite. The relationship between the polarization properties in polyaniline-doped 0-3 lead zirconate titanate/pelyvinylidene fluoride composite and the polymer conductance was studied. Both the theoretical and experimental results show that the polarization of the composite increases with the polymer conductance.
2006, 55 (8): 4298-4303.
doi: 10.7498/aps.55.4298
Abstract +
This paper reports on the influence of energy acceptors Ce3+ ions on the upconversion and 1.5μm emission properties of fluorophosphate glasses codoped with Er3+/Yb3+. The energy transfer mechanism has been discussed based on the energy matching and the energy level. The Ce3+ ions are excited from the 2F5/2 level to the 2F7/2 level due to the non-radiatively energy transfer process of the Er3+ ions from the 4I11/2 level to the 4I13/2 level. The upconversion luminescence intensities of the Er3+ are decreased quite significantly owing to this energy transfer process. Meanwhile, the luminescence intensities, peak stimulated emission cross sections, and lifetimes of the 4I13/2 level of Er3+/Yb3+-codoped fluorophosphate glasses increase largely with the introduction of the Ce3+ ions at the proper concentration of 1.11×1020cm-3.
2006, 55 (8): 4304-4309.
doi: 10.7498/aps.55.4304
Abstract +
In this paper, Tm3+/Yb3+-codoped bismuth tellurite glasses with high refractive index have been synthesized. The refractive index of Tm3+/Yb3+-codoped bismuth tellurite glasses were measured by Metricon 2010 prism coupler at two wavelengths, and the values n1=2.0365 at 632.8nm and n2=1.9795 at 1550nm were obtained. The absorption spectra, fluorescence spectra and infrared transmittance spectra of this glass were measured and analyzed. Based on Judd-Ofelt theory, and intensity parameters Ωt(t=2，4 and 6) were obtained to be 3.90×10-20, 2.03×10-20 and 9.03×10-21cm2, respectively. Then the radiative transition probabilities, radiative lifetimes and fluorescence branching ratio were calculated. Intense blue three-photon upconversion fluorescence and near-infrared two-photon upconversion fluorescence were investigated under the excitation of 980nm diode laser at room temperature. Wide infrared transmission window, high refractive index and strong blue three-photon upconversion emission of Tm3+ indicate that Tm3+/Yb3+-codoped LKBBT glasses are promising upconversion optical and laser materials.
2006, 55 (8): 4310-4314.
doi: 10.7498/aps.55.4310
Abstract +
BaZr(BO3)2:Eu phosphor was successfully prepared by thermal decomposition of the corresponding nitrates. The luminescence properties of BaZr(BO3)2:Eu were investigated under 254 and 147nm excitation. In the emission spectrum of BaZr(BO3)2:Eu excited by 254nm, the main peak is located at about 612nm, which is due to the electric dipole transition of 5D0—7F2 of Eu3+. But in the emission spectrum excited by 147nm, the main peak is located at about 592nm, which is due to the magnetic dipole transition of 5D0—7F1 of Eu3+. Analysis of the excitation spectra indicated that Eu3+ occupying the non-centrosymmetric site Ba2+ can be excited preferentially by 254nm light, but under 147nm excitation, Eu3+ occupying centrosymmetric site Zr4+ can be excited preferentially. It shows that BaZr(BO3)2:Eu is not a suitable red phosphor for plasma display panel.
2006, 55 (8): 4315-4320.
doi: 10.7498/aps.55.4315
Abstract +
Yb-doped borate-silicate glasses with various Yb2O3 concentrations were fabricated by means of high-temperature solid-state reaction. The absorption and the photoluminescence, as well as the Raman spectra, were measured and analyzed. The absorption and emission cross-section around 980nm is calculated based on the absorption measurement. The dependence of radiative lifetime of Yb3+-2F5/2 on Yb2O3 concentration is also presented. The relationship between up-conversion photon and the infrared emission, together with the assistant phonon, is described according to the up-conversion photoluminescence and Raman spectra analysis.
2006, 55 (8): 4321-4326.
doi: 10.7498/aps.55.4321
Abstract +
0.5at% and 1.0at% Er/Y co-doped silicate glasses with different Y2O3 concen trations were fabricated by means of high-temperature solid-state reaction, with the Y concentration varying from 0.0at%—2.5at% and 0.0at%—5.0at%, respectively. By measuring the absorption spectra, the photoluminescence (PL) and PL decay, we studied the dependence of absorption and emission cross-section at 1530nm and the lifetime and PL features on Y concentration. The results showed that Y co-doping enabled the absorption peak to widen and enhanced the absorption. The lifetime was prolonged considerably, especially for the highly Er-doped silicate glasses. However, considerable enhancement of PL intensity was not detected when the glasses were excited by a 980nm laser.
2006, 55 (8): 4327-4331.
doi: 10.7498/aps.55.4327
Abstract +
We studied the low temperature (15K) photoluminescence properties of un-doped GaAs(110) quantum wells modulated by surface acoustic waves (SAW) by photoluminescence (PL) spectroscopy technique. Under the influence of the SAW, the decreasing of PL intensity and the splitting of the PL lines were observed. The magnitude of the splitting can be up to 10meV when the power applied to the transducers is 20dBm. Furthermore, the spin injection in GaAs(110) quantum wells generated by circular polarization light under the influence of SAW was also discussed.
2006, 55 (8): 4332-4336.
doi: 10.7498/aps.55.4332
Abstract +
Er3+, Yb3+ codoped ZrO2 nanocrystalline powders were prepared by chemical co-precipitation. We determined the crystal structures and the room temperature upconversion emission properties of samples with different doping concentrations of Yb3+ and at different sintering temperatures, respectively. It is shown that the monoclinic phase increases with the sintering temperature and the tetragonal phase increases with the increasing of Yb3+ concentration. We found that the green emission intensity and the red emission intensity of the samples sintered at 800℃ were enhanced with the increasing of Yb3+ concentration, but the red emission intensity increased much more. The quadratic dependence of the green and the red emissions on excitation power indicates that a two-photon absorption process occurs under 976nm excitation. The infrared emission properties were also discussed in the present paper.
2006, 55 (8): 4337-4341.
doi: 10.7498/aps.55.4337
Abstract +
In this paper, the one-dimensional band structures of poly (para-phenylene) (PPP) and its alkoxyl derivatives are calculated by an extended Hückel method (BICON-CEDiT code). The results of the band gaps Eg of these materials are in agreement with the available experimental data. In addition, we found the band gaps of PPP's alkoxyl derivatives become wider as the carbon atoms increase in alkoxyl side chain. The calculation indicates that the heteroatom and side groups have an obvious effect on the band structure of polymer, which is also consistent with the experimental results. The results are useful for synthesizing PPP with different emitting wavelength.
2006, 55 (8): 4342-4346.
doi: 10.7498/aps.55.4342
Abstract +
Nanocomposite films composed of Ag particles embedded in BaTiO3 matrix were grown on MgO(100) substrates by pulsed laser deposition. The structures of the films were determined by X-ray diffraction. The size and shape of the Ag particles were observed by transmission electron microscopy. The X-ray photoelectron spectroscopy results showed that Ag is in the metallic state. The optical absorption properties were measured from 300 to 800nm, and the absorption peaks due to the surface plasmon resonance of Ag particles were observed. With increasing annealing temperature and Ag concentration, the peak absorption increased and shifted to longer wavelength (red-shift).
2006, 55 (8): 4347-4352.
doi: 10.7498/aps.55.4347
Abstract +
Nitrogen-doped Ge2Sb2Te5 (N-GST) film for phase change memory was prepared by reactive sputtering. Testing results show that doped nitrogen combines with Ge to form GeN, which not only restrains crystal grain growth but also increases the crystallization temperature and phase transformation temperature of Ge2Sb2Te5 (GST). Phase change memory (PCM) with N-GST can realize three-state storage in one PCM cell by using the resistivity difference between the amorphous state, the face centered cubic phase and the hexagonal phase of GST.
2006, 55 (8): 4353-4357.
doi: 10.7498/aps.55.4353
Abstract +
ZnO single crystals were implanted with He ions of energy of 20—100keV. The total implantation dose was 4.4×1015cm-2. Doppler broadening of positron annihilation spectra were measured using a slow positron beam to study the implantation-induced defects. The results suggest that after implantation, divacancies or larger vacancy clusters are produced. After annealing below 400℃, He impurity begins to occupy the vacancy clusters. Upon further annealing above 400℃, the vacancy clusters grow in size. At annealing temperature of above 800℃, He atom is released from the vacancy clusters, and the vacancies begin to recover and are annealed out at 1000℃.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2006, 55 (8): 4358-4364.
doi: 10.7498/aps.55.4358
Abstract +
Yb：Y3Al5O12(Yb:YAG) single crystals with Yb3+ doping level of 5.4at%, 16.3at%, 27.1at%, 53.6at%, and 100at% were grown by the Czochralski method. The effects of different Yb3+ doping level on the absorption spectra and fluorescence spectra were studied. The results showed that the real absorption coefficient of the absorption peaks increases linearly with the increasing of Yb3+ doping level in Yb:YAG crystals. Absorption band oscillator strengths of Yb：YAG crystals were calculated with Smakula formula and the effects of different Yb3+ doping level on the oscillator strengths were also studied. The concentration quenching of fluorescence was observed when the Yb3+ doping level reached 27.1at% in Yb:YAG crystals. The shape of fluorescence spectra of Yb:YAG could be significantly influenced when the Yb3+ doping level is higher than 53.6at%.
2006, 55 (8): 4365-4370.
doi: 10.7498/aps.55.4365
Abstract +
Photoacoustic tomography is a new type of medical imaging technology based on the measurement of laser-induced ultrasonic waves. It can detect the light absorption distribution of the target hidden inside optically turbid or opaque tissues. When a short laser pulse illuminates the scattering medium, such as biological tissue, the scattering media will generate ultrasound signals which are linearly proportional to the optical absorption of the media. The ultrasound signals are imaged with an acoustic lens. According to the imaging principle of lens, the photoacoustic signals from a plane in scattering media require the same delay time to reach the image plane, and the signals from different planes require different delay time to reach the same detecting plane. A BOXCAR was used to hold on the same delay-time, and a 64-element linear transducer array was one-dimensionally scanned on an imaging plane to acquire the acoustic pressure distribution, and the signals were recorded and reconstructed by a computer. By scanning the sampling gate of BOXCAR, the photoacoustic images of different planes in the media can be obtained. We experimentally obtained photoacoustic tomography images on different planes of the scattering media successfully. The images are vivid and contrast clearly with the background. This method directly provides images of absorbing structures without the need of computational reconstruction.
2006, 55 (8): 4371-4382.
doi: 10.7498/aps.55.4371
Abstract +
A series of ZrO2 and polymer doped-ZrO2 sols have been synthesized by the controlled hydrolysis of zirconium n-propoxide. Acetic acid was used as the chelating agent. Poly(ethylene glycol)(PEG) 200 and polyvinylpyrrolidone(PVP) were introduced to produce the hybrid sols. ZrO2 and the polymer doped-ZrO2 optical thin films were then prepared by spin-coating the stable sols on K9 glass substrates. Effects of various synthetic parameters were studied, on the sol stability, the microstructure of colloidal system, the structural and optical properties of the films, as well as the laser damage resistance. In our reaction systems, both hydrolysis and chelation coexist. The preference for any of the two reactions strongly depends on the system composition and ultimately determines the stability and microstructure of the colloidal system. Besides, the addition of a proper amount of PEG200 and PVP, which probably acts as the competitive ligands, particle surface protective polymers and structure directive agents, can modify the hydrolysis-condensation process, thus producing more stable, uniform sols with mass fractal structure (fm=2.33—2.46) and average particle diameter of 19.1—23.7nm. Benefiting from the precursor sol structure, the polymer doped-films exhibit excellent surface planarity and uniform inner structure, which endows the films with good optical property and excellent laser damage resistance. For instance, the hybrid film with 10% PEG200 and 15% PVP (mass fractions) showed a high laser damage threshold of 24.5J/cm2 (for 1ns pulse duration) and a reflectivity increase of about 2% than that of the substrate at wavelength of about 1000nm.
2006, 55 (8): 4383-4387.
doi: 10.7498/aps.55.4383
Abstract +
This paper reports the systematic study of supporting forces and moving track of the ferromagnetic drug particulates in target therapy is performed using the electromagnetic theory. We have obtained the rules of action and effect of magnetic fields and blood stream and the walls of blood vessel on the ferromagnetic drug particulates. At the same time, we also give out the new method of magnetic drug targeting, namely, we make use of the magnetic navigating device located outside human body to produce the variable magnetic fields to realize magnetic drug targeting. The result of our research gives the conditions of carrying out magnetic medication target treatment.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2006, 55 (8): 4388-4396.
doi: 10.7498/aps.55.4388
Abstract +
A new method named multi-reference-state updating (MRSU) pertaining to the dynamical analogue prediction, is developed on the basis of previous studies on analogue-dynamical models, in order to further effectively utilize the available information of historical observation data. In this scheme, according to a new idea of “updating", it is required that multi-reference states are renewedly selected on the period of analogue updating in the process of the analogue-dynamical model integration, and optimal forecast vectors are estimated from multi-forecasts produced by analogue-dynamical model by employing the hyperplane approximation method. Such “selection-estimation" cycles are repeatedly operated until the whole forecasts are completed. Furthermore, the simplified MRSU is applied to the T63 global spectral model, and the results of monthly forecast experiments show that for the daily and monthly mean circulation, the MRSU can effectively reduce forecast errors and improve forecast skill compared with the control forecasts.
