Vol. 63, No. 8 (2014)
2014, 63 (8): 080201. doi: 10.7498/aps.63.080201
Gyro-TWT is one of the most promising candidates for the transmitter microwave source of the next generation imaging radar; meanwhile, it plays an important role in national security. Gyro-TWT with helical waveguide is capable of generating broad-bandwidth radiation and highly stable. In this paper, we derive the dispersion equation of helical waveguide and the non-linear theory for calculating the beam-wave interaction. Numerical stimulations basically accord with the experimental results. We design a W-band Gyro-TWT operating with a 80 keV, 5 A electron beam, producing an output power of 142 kW with 3 dB bandwidth 4.5%, central frequency 95 GHz, and saturation gain 52 dB. In the end, we calculate the effects of the changes of voltage, current and input power on the output performance of Gyro-TWT.
2014, 63 (8): 080202. doi: 10.7498/aps.63.080202
By the self-consistent solution of the Schrödinger and poisson equations, the effects of GaN channel layer, AlGaN back barrier layer with and without Si doping and AlN interlayer on two-dimensional electron gas in N-polar GaN/AlGaN heterostructure are systematically studied. The results indicate that the increases of the thickness values of GaN channel layer and AlGaN back barrier layer and Al content value can improve the density of 2DEG to a certain degree, and the influences of different Si doping forms on 2DEG sheet density are not the same, also the confinement of 2DEG could be strengthened by increasing Al content value and thickness value of the AlGaN barrier layer. The AlN interlayer is a comparatively outstanding one in improving the performance of the 2DEG such as the 2DEG sheet density and confinement. When GaN channel layer thickness is less than 5 nm, there is no 2DEG in the simulation, when it exceeds 20 nm the 2DEG sheet density tends to be saturated. 2DEG has a tendency to be saturated when the thickness value of AlGaN back barrier is more than 40 nm. 2DEG sheet densities with uniform doping and delta doping in AlGaN back barrier are saturated when the doping concentration is more than 5×1019 cm-3. The 2DEG sheet density could be increased from 0.93×1013 cm-2 without AlN interlayer to 1.17×1013 cm-2 with 2 nm AlN interlayer.
2014, 63 (8): 080501. doi: 10.7498/aps.63.080501
A three-dimensional grid multi-scroll chaotic system is presented by simplifying a generalized Jerk system. The analog circuit system is designed and realized by using positive-type second generation current conveyers. Compared with the chaotic circuit realized by traditional op amp, the chaotic circuit based on current conveyers can generate grid multi-scroll attractors at high frequency, and also has the advantages of simple circuit structure, and few components. Finally, the grid multi-scroll chaotic attractor are observed through using an oscilloscope, and the physical realizability of chaotic circuit is verified by circuit experiment. The results of circuit experiments and numerical simulations are accordant.
2014, 63 (8): 080502. doi: 10.7498/aps.63.080502
Recently, there has been a growing interest in chaotic memristive circuits. However, four-dimensional (4D) memristive system often can only exhibit common chaos with only one positive Lyapunov exponent. By replacing the resistor of Chua’s circuit with a memristor, we propose a new simple 4D memristive circuit in this paper. A major difference between our proposed system and the known chaotic or hyperchaotic system is that our modified system has infinitely many stable and unstable equilibria. We show that the system can exhibit rich complex dynamic behaviors, such as limit cycles, chaos and hyperchaos. Further numerical study and circuit simulation verify the existence of a hyperchaotic attractor in the memristive circuit, which gives a positive answer about whether there exists hyperchaos in 4D memristive systems.
2014, 63 (8): 080503. doi: 10.7498/aps.63.080503
By simulating biological synapses with memristors according to the function and principle of biological visual system and by combining the memory characteristic of memristor with high-efficient processing ability in spiking neural network, a three-layer spiking neural network model for image edge extraction is constructed, in which the image edge information is represented by the variation of the memristor conductance. The edge extraction result obtained with this approach has the characteristics of continuity, smoothness, low false leak detection and edge positioning accuracy. Since the processing mechanism of this neural network conforms to the biological counterpart, it offers a new idea for the bionic implementation of biological visual system.
2014, 63 (8): 080504. doi: 10.7498/aps.63.080504
In this paper, we introduce a type of chaotic synchronization, where two chaotic systems are synchronized based on a function matrix. In particular, each drive system state synchronizes with a certain combination of response system states. Based on linear system theory and the pole placement technique, the scheme is given and illustrated with hyperchaotic Lorenz system and Lorenz chaotic system. Numerical simulations are carried out to verify the effectiveness of the proposed scheme.
2014, 63 (8): 080505. doi: 10.7498/aps.63.080505
A novel method is presented generating multi-wing butterfly chaotic attractors in this paper. Based on Liu chaotic system, a multi-wing butterfly chaotic system is constructed via designing a new piecewise linear function. The equilibrium point, Lyapunov exponent spectra, bifurcation diagram, phase diagram, frequency spectrum and Poincaré mapping of the system are studied. Furthermore, an electronic circuit is designed to implement the system. The experimental results are in agreement with numerical simulation results, which verify the feasibility and availability of this method.
2014, 63 (8): 080506. doi: 10.7498/aps.63.080506
With the help of the symbolic computation system Maple and Riccati equation (ξ’=a0+a1ξ+a2ξ2) expansion method and a variable separation method, some complex wave solutions with q=C1x+C2y+C3t+R(x,y,t) of the (2+1)-dimensional Korteweg-de Vries system is derived. Based on the derived solitary wave solution, some novel complex wave localized excitations such as complex wave fusion and complex wave annihilation are investigated.
2014, 63 (8): 080507. doi: 10.7498/aps.63.080507
In order to effectively depict the evacuation process in three-dimensional space, combining with the ladder factors, a novel three-dimensional cellular automata model is proposed. Based on the position attraction and collision possibility, the model presents a formula for calculating the transition probability, and expounds the evacuation strategy through defining the cellular evolutionary process. Meanwhile, experiments are conducted using the simulation platform to study the relationships between evacuation time, exit flow rate, exit width, original pedestrian density and system average velocity. The results show that evacuation time and exit flow rate have a positive correlation with original pedestrian density, and a negative correlation with exit width; in addition, concerning the optimum evacuation time, there exists a desirable threshold value for system average velocity and exit width.
ATOMIC AND MOLECULAR PHYSICS
2014, 63 (8): 083101. doi: 10.7498/aps.63.083101
The formation model of hydroxyl group in silica glass is studied by first-principles calculations combined with coupling plane wave pseudo-potential method. The electronic structures and optical properties of silica glass with and without hydroxyl group are systematically calculated, including electronic densities of states, charge difference densities, Bader charge, etc. And optical transition models are analyzed. Our results show that three-fold coordinated silicon in silica glass induces two defect energy levels in forbidden gap, which are at 7.8 eV and 8.8 eV, respectively. Also, we find that H atom can interact with five-fold coordinated Si and forms hydroxyl group, and causes the three-fold coordinated silicon atom to change from sp2 hybridization to sp3 hybridization. Such a kind of hydroxyl group influences the electronic structure and optical properties of silica glass, by forming a half-occupied electronic state at Fermi level, and also by generating an optical transition, of which the excitation energy is 6.2 eV.
2014, 63 (8): 083102. doi: 10.7498/aps.63.083102
Potential energy curves (PECs) for the ground state and the second excited state (a3Π and A1Π) of SnO molecule are calculated by using the multi-reference configuration interaction method (MRCI) and also considering Davidson correction’ multi-reference configuration interaction method with aug-cc-pvTZ basis for O atom, aug-cc-pvTZ-PP basis for Sn atom, respectively. On the basis of the PECs, the Re, ωe, ωeχe, Be, Te and De are obtained. The symmetries and dissociation limits for these electronic states are determined by group theory. The results show that three electronic states are dissociated along the same channel, Sn (3P)+O (3P). And then the PECs are fitted by using level program. The spectroscopic constants are determined according to fitted results, which shows that MRCI results are in good agreement with the experimental values. By solving the radial Schrödinger equation of nuclear motion, the vibration levels can be obtained, molecular constant (Bv and Dv) are reported for the first time at J=0.
2014, 63 (8): 083103. doi: 10.7498/aps.63.083103
Molecular dynamic simulation is performed to investigate the thermal properties of U1-xPuxO2 (x=0.07, 0.15, 0.25, 0.5) using the potential of partially ionic model at temperatures ranging from 300 to 3000 K and pressures in a range of 0-1.5 GPa. The results indicate that the lattice parameters decrease linearly with Pu ratio increasing under different temperatures. The linear expansion coefficient increases with Pu ratio increasing. The isothermal compressibility decreases with Pu ratio decreasing. In addition, the experience functions of lattice parameter and linear expansion coefficient are also derived.
Theoretical and experimental study of measuring gas temperature in vacuum environment using tunable diode laser absorption spectroscopy
2014, 63 (8): 083301. doi: 10.7498/aps.63.083301
Measuring the temperature in vacuum environment is more complex than in atmospheric environment. For example, high vacuum will cause the thermocouple sensor surface desorption, and the mechanism of heat transfer is also different. Therefore, there are some uncertainties if the thermocouple is used to measure the gas temperature in vacuum condition. In the present paper, tunable diode laser absorption spectroscopy (TDLAS) is employed to measure the gas temperature and also explore the application prospect of TDLAS temperature measurement technology in vacuum environment. During the thermal vacuum experiments, the vacuum gas cell is immersed in the thermostatic bath, and the gas temperature is determined by TDLAS. Meanwhile, a standard Pt-resistance is used to measure the thermostatic bath temperature. The results show that the temperatures of the gas and thermostatic bath are highly consistent with each other, and the difference between the two temperatures is less than 0.2 ℃ when the thermostatic bath is stable.
2014, 63 (8): 083302. doi: 10.7498/aps.63.083302
The rapid measuring of the underwater temperature on a large scale is very important for marine monitoring, and it has vital significances in the civilian and military fields. In this paper, a new coherent Rayleigh scattering method to measure underwater temperature is presented. A wide-band photodetector is used to receive the heterodyne signal combined by the local oscillator laser and water Rayleigh backscattering light, and the water Rayleigh scattering spectrum can be acquired by transform analysis, then the water temperature can be obtained. Firstly, theoretical study and simulation are made on the basic principles of measuring underwater temperature based on Rayleigh scattering. Secondly, theoretical analysis and simulation are made on how to measure water Rayleigh scattering spectrum using coherent detection. Finally, the water temperature measurement accuracy based on Rayleigh scattering is analyzed, showing that for 1 MHz measurement accuracy of Rayleigh scattering spectrum half-width, about 0.35 K temperature measurement accuracy can be achieved.
2014, 63 (8): 083401. doi: 10.7498/aps.63.083401
Using non-equilibrium molecular dynamics method, we study the transient kinetics of graphene bombarded by fullerene through controlling the temperature and velocity. Our results show that fullerene (C60) with low velocity cannot pass through graphene at any temperature. However C60 with high velocity can pass through graphene at any temperature. Between low velocity and high velocity, we find that the probability of C60 passing through graphene increases with temperature, the reason is that the probability of destroying carbon-carbon bond at high temperature is higher than at low temperature. In this paper, we also discuss the potential applications in the surface cleaning of graphene and the production of nanopore.
Study of dielectronic recombination and resonance transfer and excitation with X-ray emission for Fe24++H2 collision
2014, 63 (8): 083402. doi: 10.7498/aps.63.083402
Based on the theory of Hartree-Fock with relativistic correction, the theoretical study is carried out on the resonance strength of dielectronic recombination (DR) of the resonance double-excited states (i.e., KLL, KLM, KLN, KLO, KLP) of Fe24+. The resonance strength and colliding cross section of KLL are investigated. By using the experimental results of Compton profiles for H2, the resonance transfer and excitation with X-ray emission cross sections during collision between Fe24+ and target molecule H2 in an energy range of 300-800 MeV are studied. Our results are compared with the recent experimental and theoretical studies. It is found that for the double-excited states of Fe24+, the Kα decay tunnel is the major decay tunnel, and the wavelengths of X-ray in this process range from 1.850 to 1.880 Å. For other decay tunnels, the wavelengths of decay wave range from 1.460 to 1.601 Å. There is no overlap between the wavelengths for two cases. Our results are in reasonable agreement with the experimental results within an estimated uncertainty.
2014, 63 (8): 083701. doi: 10.7498/aps.63.083701
A new scheme for generating a vector hollow beam is proposed by using π phase plates, in which two linearly polarized light beams with perpendicular polarizations pass through two π phase plates respectively, and then an elliptical hollow beam is generated by the superposition of two diffracted waves. The eccentricity of the ellipse can be adjusted by varying the geometric size of phase plates with rectangular diaphragm. And the conversion from the radial vector beam into the angular vector beam can be realized by adjusting directions of phase plates. The feasibility and potential applications in atom optics are analysed and discussed showing that our scheme has a good potential application in atom optics.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2014, 63 (8): 084101. doi: 10.7498/aps.63.084101
A novel elliptical complementary invisible cloak is designed based on the transformation optics and the complementary media theory. The constitutive parameter tensor expressions have been obtained. The results of full-wave simulations by using finite-element software confirm the validity of the constitutive parameter tensor expressions. This invisible cloak can not only hide the objects inside the cloak, but also permit the electromagnetic wave penetrate into the cloak and communicate with the outside world.
Research on the single-frequency super-resolution focusing of micro-structured antenna based on time reversal electromagnetic wave
2014, 63 (8): 084102. doi: 10.7498/aps.63.084102
The idea that single-frequency electromagnetically excited signal can possess the property of super-resolution focusing under time reversal technique is proposed in this paper. The feasibility of the idea is investigated from the channel theory. A micro-structured model with inter-element spacing of 1/4 wavelength is proposed based on the traditional coaxial probe antenna. Simulated results verify that in combination with time reversal technique, the model shows super-resolution focusing characteristics under single-frequency and broadband input signal excitation. The theoretical analysis and simulated results have great guiding significance for the super-resolution research of the single-frequency and multi-band antennas.
Design and experimental verification of a two-dimensional phase gradient metasurface used for radar cross section reduction
2014, 63 (8): 084103. doi: 10.7498/aps.63.084103
Dealing with potential applications of phase gradient metasurfaces in stealth technologies, we propose to realize wide-band radar cross section (RCS) reduction by combining the two mechanisms of surface wave generation and anomalous reflection. A two-dimensional phase gradient based metasurface is designed using split-ring resonators. Around the designed central frequency f=10 GHz, the incident waves are coupled into surface waves propagating along the metasurface. While at the frequency band f>11 GHz, anomalous reflection and diffuse reflection occur. In this way, wide-band RCS reduction can be realized. A test sample with a total thickness of 2 mm is fabricated and its reflection and backward RCS are measured and compared with those of bare metallic plate with the same size. The comparison shows that the metasurface achieves more than 10 dB reduction in the measured wide range (9.5-17.0 GHz). The metasurface is a polarization independent, electrically thin, light-weight and wide-band, so it is of great application values in novel stealth technologies and materials.
2014, 63 (8): 084104. doi: 10.7498/aps.63.084104
Searching for new light source, especially short wave-length coherence light source has attracted extensive attention. The using of the crystalline undulator radiation as a short wave-length coherence light source is most likely to be one of the options. From the viewpoints of potential and field, the centrifugal force generated by periodic bent crystal is regarded as centrifugal potential, the particle motion equation is reduced to Mathieu equation with Duffing-type, and from the energy viewpoint the stability of the system is discussed. The behaviors of particles in the vicinity of the resonance are analyzed by perturbation method; the jump phenomena and instable behavior are revealed. The results show that the stability of the system is related to its parameters, and only properly adjusting these parameters, the bifurcation and instability for the system can be avoided in principle.
The influences of detuning on the duperfluid-nsulator phase transition in coupled dissipative cavity arrays
2014, 63 (8): 084201. doi: 10.7498/aps.63.084201
In this paper, based on the effective Jaynes-Cummings-Hubbard model Hamiltonian in the presence of detuning, we use the mean-field and the perturbation theory to figure out the superfluid order parameter of the system. By which we find that detuning from resonance allows one to drive the system from the superfluid into the insulator state of the polaritons and the reverse. In addition, combining with the properties of transportation of coupled dissipative cavity arrays with detuning, we discuss the influence of detuning on the number of superfluid polaritons and the lifetime of superfluid states. It suggests that the number of the superfluid polaritons will increase to its maximum and then reduce again along the negative part of detuning, which is similar to the spectrum of the transmission.
Experimental studies of multiple pulses in a passively ytterbium-doped fiber laser based on graphene-oxide saturable absorber
2014, 63 (8): 084202. doi: 10.7498/aps.63.084202
The different multiple pulse phenomena are experimentally studied in a passively mode-locked ytterbium-doped fiber laser based on graphene-oxide saturable absorber (GOSA) with net normal dispersion cavity. At the same pump power with different polarization orientations, we observe the multiple pulse phenomena, including harmonic mode-locking of rectangular pulses, dissipative solitons, quasi-harmonic mode-locking, periodical peak modulation, multipulse bunches, multipulse cluster, and chaotic multipulse. The inserted 2 nm narrow bandwidth filter is important for limiting the gain bandwidth and shaping pulses. Adjusting the polarization controller is equivalent to changing the gain in the laser cavity, which is the main reason for the formation of different multiple pulses states. This is the first time that different multiple pulses states have been observed in an-normal-dispersion Yb-doped fiber laser with graphene-oxide saturable absorber. These results could extend the understanding of multiple pulse dynamics in GOSA mode-locked fiber lasers.
Coherence properties of supercontinuum generated by a picosecond pulse in normal dispersion region of highly nonlinear fiber
2014, 63 (8): 084203. doi: 10.7498/aps.63.084203
The coherence properties of the supercontinuum generated by a picosecond pulse in normal dispersion region of highly nonlinear fiber are numerically calculated and analyzed at different input noise powers by introducing the definition of the complex degree of mutual coherence. The results show that the coherence of the generated supercontinuum is affected by the noise ratio of the picosecond pulse. The coherence of the spectrum sidelobes generated by optical wave breaking is lower than that of the center part of the spectrum. The chirp of pulse and shape of pulse do not have an obvious effect on the coherence of the broaden spectrum. Low noise power input is required to obtain high coherent supercontinuum, and the pump power and waveshape should be optimized to obtain the wide bandwidth and high coherent supercontinuum.
The human colorectal cancer tissue in vitro experimental study based on photoacoustic endoscopic system
2014, 63 (8): 084204. doi: 10.7498/aps.63.084204
This paper developed a 4 array transducers photoacoustic endoscopic probe, and based on this, a photoacoustic endoscopic imaging system was build. Phantom experimental imaging was carried out, and the capability of location for endoscopic probe was demonstrated via analyzing the absorption of the light on the 4 sensors position. The in vitro human normal tissues and early colorectal cancer tissues was imaged using photoacoustic endoscopic system. The statistical analysis of the light absorbtion intensity distribution on different position proved that the photoacoustic endoscopic system has the ability to distinguish human normal tissues and early colorectal cancer tissues. This technology is expected to improve the accuracy of early diagnosis of colorectal cancer and has the potential clinical application.
Capability of single optical buffer loop implementing all-optical time slot interchange based on nonlinear polarization rotation in semiconductor optical amplifier
2014, 63 (8): 084205. doi: 10.7498/aps.63.084205
Based on nonlinear polarization rotation (NPR) in semiconductor optical amplifier (SOA), a single optical buffer loop theoretically and experimentally demonstrates its switch capability to realize all-optical time slot interchange (TSI) on multiple optical packets (MOPs). Firstly, a series of prerequisites is theoretically deduced with a single optical buffer loop performing all-optical TSI on MOPs. And the corresponding equations which experimental parameters should satisfy are derived from these prerequisites for different cases of all-optical TSI. Accounting to the theoretical results, a single optical buffer loop based on NPR in SOA experimentally realizes all-optical TSI on three packets and four packets at data rate of 10 Gb/s. Experimental results are in accordance with those expected theoretically. These results will be very helpful to make all-optical TSI system more compact and more highly efficient, and have less expensive elements such as SOA, and also significant for developing the all-optical TSI technology.
2014, 63 (8): 084301. doi: 10.7498/aps.63.084301
Non-intrusive polynomial chaos expansion (NPCE) method is a fast algorithm with the best performances for an uncertain acoustic filed currently, in which the selection of collocation points is an important factor for the computational accuracy, and some special processing methods such as piecewise probabilistic collocation method, should be adopted when the outputs of acoustic field vary severely with uncertain ocean environmental parameters. A new fast algorithm for uncertain acoustic filed in shallow-water is proposed based on Kriging model. The theoretical description of the new algorithm is given, and numerical simulations are conducted to verify the performances of the proposed algorithm. The physical interpretations are given in detail. The results demonstrate that the proposed algorithm is more accurate than the NPCE method under the same conditions, and any special processing method does not need to be adopted when the outputs of acoustic field vary severely with the uncertain ocean environmental parameters. The weakness of NPCE method can be overcome by the proposed algorithm, which is that the computational cost increases with the stochastic polynomial expanding to a higher order for enhancing the computational accuracy. The selection of sample point of the proposed algorithm is simpler and easier than that of NPCE method, and the calculation errors can be given directly. Thus, the proposed algorithm is more universal than NPCE method.
2014, 63 (8): 084302. doi: 10.7498/aps.63.084302
Aiming at the disadvantages of current methods to estimate sediment geoacoustic parameters, a geoacoustic estimation scheme is presented, in which used are the bottom back reflection signals from multiple angles sampled with a multi-beam parametric array sub-bottom profiler. Firstly, the sediment thickness and sound speed are estimated with difference frequency backscatter signals separately from upper and lower sediment surfaces with vertical and outboard direction. Then, the sediment attenuation coefficient is estimated by use of the two backscatter signals with different difference frequencies from upper and lower sediment surfaces with vertical direction. Finally, the sediment property impedance is estimated with primary frequency backscatter signals from upper sediment surface with vertical direction and followed by the computation of the sediment density, thereby solving its coupling with sound speed. The efficiency is tested through pool experiment.
2014, 63 (8): 084601. doi: 10.7498/aps.63.084601
A gas-liquid two-phase model for the simulation of viscoelastic fluid mold filling process with the consideration of phase change is proposed, in which the governing equations for the melt and air in the cavity, including the mass conservation, momentum conservation and energy conservation equations, are unified into one system of equations. A revised enthalpy method, which can be used for both the melt and air in the mold cavity, is proposed to describe the phase change during the mold filling. Finite volume method on non-staggered grid is used to solve the system. The level set method is used to capture the interface evolution in the mold filling process. The distributions of physical quantities such as velocity, pressure and temperature and so on are given. The "frozen skin" layers under different temperatures and velocities are discussed in detail. Numerical results show that increasing the temperatures of the melt and cavity is a better way to get rid of the "frozen skin" layer than increasing the injection velocity.
2014, 63 (8): 084701. doi: 10.7498/aps.63.084701
The dynamics of a drop on a mesoscopic scale is investigated by using the many-body dissipative particle dynamic (MDPD) method. The formation of liquid-vapor coexistence interface in the MDPD system is explored. The simulations of the pressure inside/outside the drop and the surface tension are carried out, and it is verified that Laplace’s law is satisfied in our simulation. Different contact angles are obtained by changing conservative interaction parameters between particles. The relationship between MDPD paremeters and contact angles is discussed. Based on the results, the flow behaviors of a drop moving in grooved microcannels are simulated. The results in this paper are useful in studying the fluid with free surfaces flow behavior on rough surface.
2014, 63 (8): 084702. doi: 10.7498/aps.63.084702
Unsteady transient phenomena in flow over impulsively started circular cylinder, such as the generation of separation, burst of separation bubble, vortex shedding, etc., are studied from Lagrangian viewpoint. The transient flow is solved numerically by using characteristic-based split scheme with dual time stepping. Then Lagrangian coherent structures (LCSs) are extracted to study the transport and mixing of these transient phenomena. Results show that the variation of drag is closely related to the evolutions of separation bubbles and vortex shedding. The evolutions of the symmetric bubbles in streamwise induce high pressure distribution at rear of cylinder and result in drag reduction of the circular cylinder. As separation bubbles become asymmetric, the transport between separation bubbles and main flow is enhanced and thus can reduce the separation region and suppress flow separation as well. The results also show that the shedding vortices are induced by the transpor between separation bubble and main flow. Compared with streamline patterns, LCSs have huge advantages in describing the dynamic features of the unsteady phenomena.
Experimental investigation of interactions between laminar or turbulent boundary layer and shock wave
2014, 63 (8): 084703. doi: 10.7498/aps.63.084703
Investigation on the interactions between laminar or turbulent layer and shock wave is performed in a Mach 3.4 supersonic wind tunnel, based on nanoparticle-tracer based planar laser scattering (NPLS) system and supersonic particle image velocimetry (PIV) system. The model geometry in this experiment is composed of two flats with different positions in the test section which can provide the flat with different kinds of boundary layer, and a shock wave generator–a 12° wedge. Boundary layer separation/attachment, induced suppression waves, induced shock wave and expansion fan were clearly presented by NPLS images, velocity field and vorticity field were given by PIV results. Instantaneous flow structures and temporal evolution of two different flow conditions were analysised and compared according to both NPLS and PIV results. The experimental results show that: the separation zone in the turbulent boundary layer is long and narrow, but it’s quite different in the turbulent boundary layer where it is oval-shaped; upstream of the oblique shock wave, a serious of suppression waves can be observed outside of the laminar boundary layer and they will focus into a unsteady induced shock wave, but in contrast, only a focused shock wave can be found outside of the turbulent boundary layer and it’s quite stable; the expansion fan downstream of the oblique shock wave is small in the laminar boundary layer, leading to a sufficient acceleration of the flow, and the attachment shock wave behind the expansion fan is extremely weak, however it is a totally different condition in the turbulent boundary layer with a wide expansion fan and a strong attachment shock wave.
2014, 63 (8): 084704. doi: 10.7498/aps.63.084704
We design two types of 8-fold quasi-period short groove structures which are arranged in single row and three rows respectively The flow field in the turbulent boundary layer and the total stress over these groove surfaces are numerically simulated by using Reynolds average Navier-Stokes equation and turbulence model. It is shown that the 8-fold quasi-periodic structure has good drag reduction effect compared with the periodic and disorder structures, especially for structure arranged in three rows. The results are also confirmed by the sheer stress measurements which are performed on substrates with the designed structures. By analyzing the distribution of flow field, we find that the quasi-periodic structure effectively inhibits the intensity of vortex, reduces the turbulent dissipation rate, and keeps the stripe phase stable. Furthermore, by using the two-dimensional grating model, it is found that the 8-fold quasi-periodic structure can reduce spectrum intensity in the large angle direction, revealing that the inhibition of the extension of coherence disturbance waves is responsible for the drag reduction effect, which is also confirmed by the flow field analysis.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Effects of Ba-doping and process conditions on the structure and magnetic properties of BiFeO3 ceramics
2014, 63 (8): 085101. doi: 10.7498/aps.63.085101
Multiferroic Bi1-xBaxFeO3 (named as BBFO-x, x=0, 0.05, 0.15) are prepared by the sol-gel method through rapid thermal process. The effects of Ba-doping and process conditions on the structures and magnetic properties of the samples are investigated. The experimental results indicate that the process requirements of the pure BBFO-x samples are rigorous. The samples annealed at 800 ℃ for 450 s possess the best structures and magnetic properties. X-ray diffraction results show that Ba-doping causes lattice deformations, but does not change the macroscopic lattice structures of the samples, which is further proved by the Raman spectra of the samples. Besides, Ba-doping is beneficial to enhancing the magnetization of the sample, which is attributed to both the destruction of long-rang antiferromagnetic spiral magnetic structure and the possible spin coupling resulting from the valent state change of the Fe ions. These achievements provide experimental foundation for further studying the microstructure and magnetoelectric coupling effect in such single phase multiferroics.
2014, 63 (8): 085201. doi: 10.7498/aps.63.085201
Because the boundary layer of the plasma sheath formed around the hypersonic vehicle flying in atmosphere is turbulent, the parameters of plasma sheath, such as the electron density, become time-varying. Both the amplitude and phase of electromagnetic (EM) signal are modulated by the time-varying plasma. By using a large volume uniform plasma generator, an experimental system for the propagation of EM signals in the time-varying plasma is built. The propagation experiment of the monochromatic signals and binary phase shift keying signals in S band of plasma is conducted. The modulations of the amplitude and phase of EM signal are proved, and the rotation of constellation of the multiple phase shift keying (MPSK) signal is observed. The experimental and simulation results demonstrate that the frequency of parasitic modulation is the same as that of time-varying plasma and the parasitical modulation intensity varies in proportion to the ratio of the electron density profile to the carrier frequency. Even if the carrier frequency is higher than the plasma frequency, the parasitical modulation will make the constellation of the MPSK signals circumvolve, and the bit error rate higher.
Experimental study on mode instability in high power all-fiber master oscillator power amplifer fiber lasers
2014, 63 (8): 085202. doi: 10.7498/aps.63.085202
Mode instability (MI) is an abrupt mode change when the average output power increases above a certain threshold power, which results in degrading beam quality and restricting the enhancement of power output for diffraction-limited high power fiber laser. The experimental study on MI in all-fiberized master oscillator power amplifer (MOPA) is presented in detail for the first time. It is revealed that MI in all-fiberized MOPA results in reducing the slope efficiency. The theoretical threshold power of MI for 20/400 step-index large-mode-area double-cladding Yb-doped fiber is about 1 kW and MI is rooted mainly from the thermal effect.
Theoretical analysis of effects of viscosity, surface tension, and magnetic field on the bubble evolution of Rayleigh-Taylor instability
2014, 63 (8): 085203. doi: 10.7498/aps.63.085203
The evolution of bubble in Rayleigh-Taylor (RT) instability for non-ideal hydromagnetic fluid is investigated theoretically in this study. In a plane perpendicular to the magnetic field, the general governing equation describing the bubble evolution is derived by considering the influences of viscousity, surface tension and magnetic field. The numerical and asymptotic solutions of the bubble velocity in two-dimensional planar geometry are obtained under different conditions and the effects of fluid viscosity, surface tension and magnetic field on the bubble growth are then analyzed in detail. It is found that the bubble velocity is reduced by viscosity and surface tension, which indicates that viscosity and surface tension can suppress the RT instability. It is also observed that the influence of magnetic field on the RT instability is caused by its nonlinear part, and whether the RT instability can be suppressed or enhanced depends on the direction of the nonlinear part of magnetic field.
2014, 63 (8): 085204. doi: 10.7498/aps.63.085204
Hall thruster plasma discharge channels interact with wall forming sheath, and different secondary electron emission coefficients of wall material can considerably affect sheath characteristics. In this paper, we establish a two-dimensional physical model in wall sheath area to study the secondary electron emission characteristics of three different wall materials which are boron nitride (BN), silicon carbide (SiC) and aluminium oxide (Al2O3), and SiC material secondary electron emission model is improved. On the basis of improved secondary electron emission model, the relationship between the wall secondary electron emission coefficient and both electron temperature and magnetic field intensity is discussed by the particle in cell simulation method, and the different sheath properties of three materials (BN, SiC and Al2O3), are also investigated. The results show that fitting curve is consistent with the experimental results; at the same electron temperature, the values of secondary electron emission coefficient and electron density of three materials (BN, SiC and Al2O3) increase but the values of sheath electric field and sheath potential drop decrease in their sequence. The BN material has the appropriate secondary electron radiation coefficient, which makes the thruster work steadily under low current condition.
Richtmyer-Meshkov instability induced by the interaction between shock wave and SF6 isosceles trapezoid cylinders
2014, 63 (8): 085205. doi: 10.7498/aps.63.085205
Based on the large eddy simulation, combined with the 5th order weighted essentially non-oscillatory scheme and the immersed boundary method, the interaction between planar shock wave and two isosceles trapezoid SF6 cylinders is numerically simulated. Our numerical results clearly show that the deformations of isosceles trapezoid cylinders are induced by the Richtmyer-Meshkov instability due to the interaction of shock wave with them. The reflecting, refracting and diffracting process of incident shock are discussed in detail, and the complex wave structures induced during these processes are revealed. In addition, the mixing mechanism of SF6 gas and air is expatiated. Furthermore, the efforts are made to understand the difference in the evolution of the interface between these two isosceles trapezoid cylinders by analyzing the variation of four characteristic scales.
2014, 63 (8): 085206. doi: 10.7498/aps.63.085206
In this paper, the train of thought and contents of studying the polar drive for SG-Ⅲ prototype facility are teased out, and the beam approximation principle regarding the illumination uniformity on the target is proposed. Based on such a principle, the increase-by-degrees design method is developed and numerically simulated as well. The required laser parameters of target symmetrical illumination are optimally designed under various conditions. The investigation results are experimentally demonstrated on SG-Ⅲ prototype facility, showing that they are in excellent agreement with the designed illumination uniformity on the target. The obtained conclusions can give powerful guidance for the theoretical and experimental study of polar drive in the future.
2014, 63 (8): 085207. doi: 10.7498/aps.63.085207
Stimulated Raman scatting (SRS), which is one of the parametric processes of laser-plasma interactions, is examined by an explicit, electromagnetic, relativistic kinetic particle-in-cell code in one dimension. The code algorithm and implementation details are discussed. It is found that kinetic effects are important to SRS instability. Time-averaged reflectivity onsets at threshold intensity, and saturates at higher intensity. Backward SRS bursts in sub-picosecond, periodically. Kinetic ions initially delay the growth of SRS. Electron trapping results in the SRS bursts. The saturation of SRS results from the nonlinear frequency shift of Langmuir wave. Work is underway to add binary Coulomb collision to parallelize it, and to extend the code to 2D3V.
2014, 63 (8): 085208. doi: 10.7498/aps.63.085208
Conventional discharge (Townsend and streamer mechanisms) theories are not able to well explain the phenomenon in nanosecond-pulse discharges. Recently, much attention has been paid to the runaway breakdown due to high-energy electrons in nanosecond-pulse discharges, and some experimental data confirm that high-energy runaway electron beam is an important characteristic parameter for nanosecond-pulse discharges. In this paper, two designed collectors are used for detecting runaway electron beams in nanosecond-pulse discharges. These collectors are used to measure the runaway electron beams in discharges driven by a nanosecond-pulse generator with a pulse width of 3-5 ns and a rise time of 1.2-1.6 ns. The measuring principle of both two collectors is similar to that of Faraday cup, where high-energy electrons are collected by a metal cone, and converted into an electric signal that can be recorded by an oscilloscope. Furthermore, optimal designs of collectors are conducted in order to improve the impedance matching characteristics and to obtain better recording data. Using the above two collectors, characteristics of runaway electron beams are investigated. Experimental results show that runaway electron beams can be effectively measured by the collectors, and the optimized collector has a shorter time resolution and higher amplitude of the runaway electron beam current. When the applied voltage is 80 kV, the electron beam current can be measured with an amplitude of 160 mA and a full width at half maximum of less than 1 ns. In addition, experimental results with pulse sequences prove that the collectors have excellent reliability, and both the transient response and the time resolution are stable.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2014, 63 (8): 086101. doi: 10.7498/aps.63.086101
In this paper, for the study of static random access memory (SRAM), the online-test and offline-test are carried out on the total dose radiation damages. The differences between the two kinds of test methods and physical mechanisms are investigated. The results show that SRAM present multiple failure mode, the online-test only includes one fixed failure mode and the offline-test includes multiple failure mode. Due to the restrictions on signal integrity at test frequency, the online dynamic current test value is significantly less than offline test value. Since the existence of imprinting effect, the online-test static current is significantly less than offline-test value when the device-stored data are opposite to irradiation data. The parameters that cannot be detected online, may lapse prior to the data that could be detected online. The results are significantly important for studying the total dose radiation effect and the experimental evaluation of SRAM under radiation environment.
2014, 63 (8): 086102. doi: 10.7498/aps.63.086102
Using the classical molecular dynamics simulations, we have investigated the thermally-excited ripples of the multilayer graphenes at different temperatures, and compared them with those of the single- and doublelayer graphene. It is found that: 1) the ripples in multilayer graphene are intrinsic with a characteristic size of about 100 at room tempe- rature, increasing with increase of temperature; at the same time, the ripples height also increases with the temperature; 2) the ripples intralayer height-height correlation functions for the multilayer graphene follow a power-law behavior, Gh(q) q-; the scaling exponent decreases as temperature increases. Moreover, the scaling exponents are different for different types of multilayer graphene even at the same temperature. All these phenomena result from the anharmonic effects which are induced by the temperature and the interlayer interactions.
2014, 63 (8): 086401. doi: 10.7498/aps.63.086401
In this study we have investigated the thermite reaction of Al/SiO2 layered structure by classical molecular dynamics simulation in combination with the reactive force field function. Under the adiabatic conditions, we simulate the structural changes and energetic properties of the system at six different initial temperatures (600, 700, 800, 900, 1000 and 1100 K). These results show that the thermite reaction of Al/SiO2 is the self-heating reduction-oxidation (redox) reaction. When the initial temperatures are 900 and 1000 K, the Al layers change into liquid-like structure under melting points. The thermite reaction happens with a much faster rate. At other initial temperatures such as 600, 700, 800 and 1100 K, the thin Al-O layer at the interface is quite weak for the higher initial temperature. The adiabatic reaction temperature increases and the effective reaction time decreases with the increasing of the initial temperature. the reaction self-heating rates are 3.4, 3.5, 4.7 and 5.4 K/ps for the initial temperatures of 600, 700, 800 and 1100 K, respectively. The results reveal that the thermite reaction self-heating rates depend on the thickness of interfacial diffusion barrier in the nanoparticle. In addition, the thermite reaction of the Al/SiO2 system leaves the Si, which accord well with the experimental result.
A theoretical study on coalescence-induced jumping of partially wetted condensed droplets on nano-textured surfaces
2014, 63 (8): 086801. doi: 10.7498/aps.63.086801
Partially wetted (PW) droplets specially exist on textured surfaces with proper nano-structural parameters. Such tiny drops can depart from surfaces by coalescence-induced jumping, and become the main medium for dropwise condensation heat transfer. Therefore, it is of great importance to study the relationship between nano-structural parameters and PW drop post-merging jumping. In this study, the principle of minimum energy increasing during condensed droplets growth was used to judge if a condensed drop is in PW state. The initial shape of a coalesced droplet was determined based on the conservation of PW drop interface free energy and viscous dissipation energy before and after two or more PW condensed droplets merge. The dynamic equation describing the shape conversion of the post-coalescence droplet was then solved. Whether jumping or not of a merged drop was determined by whether the base radius of the droplet can reduce to 0 and if existing a up moving speed of drop gravity center at this moment. The calculation results show that PW droplets can form only on the textured-surfaces with certain nano-pillar height and relatively larger ratio between pillar diameter and pitch, dn/s, while completely wetted droplets easily form on the surfaces with low pillar height and dn/s less than 0.1. Meanwhile, post-coalescence jumping of PW droplets closely relates to nano-structural parameters. Not all PW drops can jump after merging. Instead, self-propelled jumping of PW drops takes place only on the surfaces with relatively higher nano-pillar height and suitable dn/s. Moreover, PW drop size and the scale ratio between two PW droplets to merge also have significant effect on the coalescence-induced jumping. It is difficult for a merged drop to jump spontaneously if the size of PW drops is too large or too small, or the scale ratio of two PW drops is too small. Finally, post-coalescence jumping of multi-droplets is easier than that of two drops since more surplus interface free energy exists in the former case. The calculation results of this model are well consistent with the experimental observations in literatures for whether the post-coalescence condensed drops jump on nano-textured surfaces, with accuracy of 95%. In conclusion, coalescence-induced jumping takes place only when PW droplets with suitable size on the textured surfaces with proper nano-structural parameters.
Effect of magnetic field assisted heat-treatment on field emission properties of metalized multi-walled carbon nanotubes cathodes
2014, 63 (8): 086802. doi: 10.7498/aps.63.086802
The effect of magnetic field assisted heat-treatment on the field emission properties of metalized multi-walled carbon nanotubes (MWNTs) is investigated. The metalized MWNTs are prepared via an electroless plating method, and then the MWNTs/Ni cathodes are fabricated by screen printing. The morphology and composition of MWNTs/Ni were studied by transmission electron microscopy and energy dispersive X-ray detector, and the difference between MWNTs/Ni cathodes heat-treated with or without magnetic field was observed by scanning electron microscopy. The force of a single MWNT coated with Ni was simulated, and the results demonstrate that the magnetic field force could induce the rotation of MWNTs/Ni during magnetic field assisted heat-treatment. The field emission characteristics show that the MWNTs/Ni cathodes heat-treated with magnetic field has a low turn-on field of 0.80 Vm-1 and high field enhancement factor of 16068, which are attributed to the embossment of MWNTs/Ni from substrates under the magnetic field.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Effect on the electronic structures and optical bandgaps of Ga-doped wurtzite TM0.125Zn0.875O(TM=Be, Mg)
2014, 63 (8): 087101. doi: 10.7498/aps.63.087101
The optimized structure parameters, electron density of states, energy band structures and optical bandgaps of the TM0.125Zn0.875O (TM=Be, Mg) alloys and Ga-doped TM0.125Zn0.875O are calculated and analyzed by using the ultra-soft pseudopotential approach of the plane-wave based upon density functional theory. The theoretical results show the Ga-doped TM0.125Zn0.875O materials are easily obtained and their structures are more stable. The Ga-doped TM0.125Zn0.875O are good n-type materials and their energy bandgaps are determined by Ga 4s states of the conduction band minimum and O 2p states of the valence band maximum. Compared with the TM0.125Zn0.875O alloys, the optical bandgaps of Ga-doped TM0.125Zn0.875O become wider due to the Burstein-Moss shift and many-body effects, which is consistent with previous experimental data. The Ga-doped TM0.125Zn0.875O materials are suitable as TCO films for the UV and deep UV optoelectronic device.
2014, 63 (8): 087102. doi: 10.7498/aps.63.087102
For Mo doped with the transition metals W, Ti, Cu and Fe with the molar percentages of 2.08% and 4.17%, the generalized-stacking-fault energies and the cleavage energies along the direction  in (110) plane are calculated by the first principles method based on the density functional theory, and the shear information and the brittle-ductile influences of the transition metals on the Mo material are investigated. It is found that doping W and Ti atoms can make the shear deformation difficult to happen and the brittleness of Mo enhanced, however, doping Cu and Fe atoms can make the shear deformation easy to happen and the ductility of Mo enhanced. Moreover, with the increase of doping concentration, the influences of W and Fe atoms are more obvious. Doping W atoms can make the shear deformation more difficult to happen and the brittleness of Mo stronger. Doping Fe atoms can make the shear deformation easier to happen and the ductility of Mo stronger.
Models on threshold voltage/subthreshold swing and structural design of high-k gate dielectric GeOI MOSFET
2014, 63 (8): 087301. doi: 10.7498/aps.63.087301
An analytical model on threshold voltage and subthreshold swing for high-k gate dielectric GeOI MOSFET (metal-oxide-semiconductor field-effect transistor) is established by considering the two-dimensional effects in both channel and buried-oxide layers and solving two-dimensional Poisson’s equation. The influences of the main structural parameters of the device on threshold voltage and subthreshold swing, and the short-channel effects, drain induction barrier lower effect and substrate-biased effect are investigated using the model, and the design principles and value range of the structural parameters are presented to optimize the electrical performances of the device. The simulated results are in good agreement with the TCAD simulated data, confirming the validity of the model.
The Co82-xZr18Crx (x=0, 2, 3, 4) alloys are produced by melt-spinning. It is found that a proper addition of Cr can improve the coercivity significantly and a maximum coercivity of 6.5 kOe is obtained in the Co79Zr18Cr3 ribbon after having been annealed at 600 ℃. X-ray diffraction and thermomagnetic analysis are employed to determine its phase composition. It is found that the sample is comprised of the single Co11Zr2 and the Cr atoms enter into its lattice. A significant enhancement in the magnetocrystalline anisotropy field of Co11Zr2 is observed. SEM investigations show a microstructure consisting of equiaxed grains whose average size is about 400-500 nm. The coercivity enhancement in the Co79Zr18Cr3 alloy is ascribed to the increase in Ha.
2014, 63 (8): 087502. doi: 10.7498/aps.63.087502
Magnetic ground state of perovskite structure quantum paraelectric EuTiO3 has been known to have a planar anisotropic G-type antiferromagnet structure according to the experimental study. In this paper, based on density functional theory, first-principles computations are performed to investigate the magnetic properties and spin-exchange interaction of EuTiO3 in both of the quantum paraelectric phase and ferroelectric tetragonal phase under stress. By analyzing the energies of different magnetic structures and paths of spin exchange coupling as well as the effect of stress on the magnetic exchange paths change, it is found that when the system of EuTiO3 is free, it has a G-type antiferromagnetic structure with uniaxial anisotropic spin along  direction. Furthermore, in this structure, Eu 4f electron spin achieves antiferromagnetic super-exchange coupling via O 2p state at face-centered position. However, in the ferroelectric tetragonal phase structure induced by applied stress field, Eu 4f electron spin achieves ferromagnetic exchange coupling in  direction due to the variation of Eu-O-Eu bond angle in spin exchange path.
2014, 63 (8): 087503. doi: 10.7498/aps.63.087503
Perovskite manganites with nominal composition La2/3Sr1/3FexMn1-xO3 (x=0, 0.1, 0.2, 0.3, 0.5) are prepared by the sol-gel method. The samples are treated three times at 773 K, 873 K and 1073 K, separately, in which processes the temperature is slowly increased. The X-ray diffraction patterns indicate that the samples have a single phase and perovskite structure each. The dimensions of the crystalline particles, lattice constants, cell volumes of the samples are calculated using the XPert HighScore Plus software. The magnetic properties are measured using a Quantum Design Physical Property Measurement System. The magnetic moments of the samples at 10 K decrease with the increase of Fe doping level x. The decreasing process can be divided to two ranges: one is from x=0 to x=0.2, in which range the average magnetic moment per formula decreases rapidly from 2.72 B to 0.33 B, while the Curie temperature decreases rapidly from 327 K to 95 K, i.e., it is reduced by 232 K; the other is from x=0.2 to x=0.5, in which range, however, the average magnetic moment per formula decreases slowly from 0.33 B to 0.05 B, while the Curie temperature decreases slowly from 95 K to 46 K, i.e., it is reduced only by 49 K. The experimental result that the magnetic moments of the samples decrease with the increase of Fe doping level may be explained as the fact that the magnetic moment direction of the Fe cations is opposite to those of Mn cations.
2014, 63 (8): 087801. doi: 10.7498/aps.63.087801
The ion-doped ceramic crystal is different from the single crystal in the respect of theoretical calculation method, because of the presence of grain boundaries. The populations at the active levels in both CW and pulsed regimes each as a function of the concentration of active impurities are deduced by means of the luminescence decay curve. Taking the Nd3+:YAG laser ceramic for example, we calculate the optimal doping concentration and compare our calculated results with reported experimental data, showing that our theoretical calculation is in line with the trend of the experimental data, and also we compare our results with the Nd3+:YAG single crystal theoretical data. showing that the ceramic crystal is superior to the laser doped laser crystal in the respect of population.
Experimental and theoretical study of tris-(8-hydroxyquinoline) aluminum (Alq3) photoluminescence enhanced by self-assembled silver films
2014, 63 (8): 087802. doi: 10.7498/aps.63.087802
Alq3 photoluminescences (PL) enhanced by self-assembled silver films are investigated experimentally and theoretically. The experimental results show that both the apparent enhancement factor (AEF) and the emission enhancement factor (EEF) of Alq3 PL increase with the increase of density of average 70 nm diameter silver nanoparticles on the substrate. The maxima of AEF and EEF are about 3.2 and 13, respectively. Based on the optical antenna theory, the theoretical maxima of both quantum efficiency enhancement factor and EEF of Alq3 PL are about 1.4 and 15, respectively. By comparing of the experimental results with the theoretical results, we can conclude that the near-field enhancement of silver nanoparticles makes a major contribution to Alq3 PL emission enhancement, and the emission enhancement is dependent on the Alq3-silver nanoparticle distance and the area coverage ratio of silver nanoparticles to substrate.
Upconversion luminescence properties in Er3+/Yb3+ codoped TiO2 films prepared by magnetron sputtering
2014, 63 (8): 087803. doi: 10.7498/aps.63.087803
The Er3+/Yb3+ codoped TiO2 films prepared by magnetron sputtering can emit the green light at 490 nm and the red light at 670 nm by using a 980 nm diode laser irradiation. The emission intensity of upconversion is influenced by ErxYb2-xTi2O7 crystal and concentration of Er3+/Yb3+. The experiment shows that an appropriate codoping proportion of Er3+/Yb3+ brings a notable enhancement of upconversion luminescence intensity. Er3+ plays a main role in the upconversion luminescence, and the sensitized ion Yb3+can greatly improve the efficiency of upconversion. The TiO2 film prepared by magnetron sputtering has a small density of phonon states, thus it inhibits the process of non-radiative transitions, which leads to the formation of green light at 490 nm and the intensity of red light being greater than green light.
2014, 63 (8): 087804. doi: 10.7498/aps.63.087804
A weighted real-coded genetic algorithm is proposed in this paper, in allusion to the characteristics of optimizing designs of metamaterials, which have many parameters and parameters of different powers in metamaterial structure. The algorithm utilizing allele or double gene to change the power of one gene, develops the idea of weighted encoded binary coding. Compared with common real-coded based genetic algorithm, the weighted real-coded genetic algorithm adds artificial selection in it, it can not only accelerate the speed of convergence, but also improve the solution quality, especially for the design of large-scale and long computation time. In this paper, the algorithm is verified by optimizing a metamaterial absorber.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2014, 63 (8): 088801. doi: 10.7498/aps.63.088801
In this paper, we propose a cooperative decoupling method and a cross-layer joint method for multi-layer resource allocation in multi-hop cognitive radio networks. In cooperative decoupling method, the task of path choosing is accomplished independently, and then the game of channel and power allocations is implemented. In cross-layer joint method, the three-layer resource of path, channel and power is allocated simultaneously by process of game. The heuristic principles of network layer, media access control layer and physical layer are employed synthetically in two methods. The degree of receiving interference and the degree of sending interference are adopted to assist path choosing. The Boltzmann exploration based on the width of permitting power is designed to select the channel and power. The means of replacement and elimination of long link or bottleneck link are proposed to further enhance network performance. The sequential game process instead of simultaneous game process is chosen because the former has better convergence property in current scenario, and the concrete process of game is provided. Moreover, the Nash equilibrium of the games and the complexity of the algorithms are analyzed and discussed. Simulation results show that the cooperative decoupling method and the cross-layer joint method have better performances in the number of success flows, the achievable data transmission rate and power consumption than the cooperative link game and the local flow game with simple decoupling.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2014, 63 (8): 089101. doi: 10.7498/aps.63.089101
To solve the problems of basic gravity aided matching algorithm, i.e., time consuming, low precision and inefficiency when the inertial navigation system (INS) has a large initial error, a real algorithm on adaptive chaotic ant colony optimization-RD is proposed by using modified ant colony algorithm in continuous space to approach an optimizing model. The search efficiency, noise immunity and matching probability are improved by adaptively adjusting pheromone, chaos adaptive manage of ant colony algorithm search strategy, parameter and local pheromone. Experiment shows that it is more robust to INS initial error, matching efficient and good real-time calculation.
2014, 63 (8): 089201. doi: 10.7498/aps.63.089201
Land-surface albedo reflects the ability that land surface reflects solar radiation and plays a very important role in surface energy balance. By picking 10 different underlying surfaces including bare soil, cropland and grassland, the differences in the diurnal variation of land surface radiation and energy processes over North China are investigated using the data measured during July and September, 2008, provided by the Experimental Co-observation and Integral Research in Semi-arid and Arid Regions over North China, the characteristic of land-surface albedo and the response to precipitation are analyzed, and the relationships between land-surface albedo and solar altitude angle and soil humidity are studied. According to the average albedo, the sequence of albedo over all the underlying surfaces are arid meadow in the northeast of China>alpine meadow in the northwest of China>oasis farmland in the northwest>natural vegetation on the Loess Plateau>semi-arid meadow in the northeast of China>farmland in the northeast of China>fruit bearing forest in the northeast of China. And the albedo is smaller when the precipitation is much while it is bigger when the precipitation is less on the whole. The diurnal variation curves of albedo have three types: symmetric type, bigger in the morning and smaller in the noon and afternoon, biggest in the afternoon and smallest in the morning. In the selected 6 stations, the valley of albedo basically occurs on rainy days and the peak occurs on days which are not rainy but have strong solar radiation. The land-surface albedo decreases with the solar altitude angle increasing and tends to remain when the solar altitude angle is bigger than 40°. The land-surface albedo decreases obviously with soil moisture increasing in Yuzhong and farmland of Tongyu, then the grassland of Tongyu. And the land-surface albedos of Maqu, Miyun, Jinzhou have no significant change with the soil moisture.