Vol. 61, No. 3 (2012)
2012-02-05
GENERAL
2012, 61 (3): 030201.
doi: 10.7498/aps.61.030201
Abstract +
For a nonholonomic system of Chetaev's type, the conformal invariance and the conserved quantity are studied. By the infinitesimal one-parameter transformation group and the infinitesimal generator vector, the definition of conformal invariance of Mei symmetry and the determining equation for the holonomic system which corresponds to a nonholonomic system are provided, and the relationship between the system conformal invariance and Mei symmetry is discussed. Using the restriction equations and the additional restriction equations, the conformal invariances of weak and strong Mei symmetrys for the system are given. With the aid of a structure equation that gauge function satisfies, the system corresponding conserved quantity is derived. Finally, an example is given to illustrate the application of the result.
2012, 61 (3): 030202.
doi: 10.7498/aps.61.030202
Abstract +
A class of generalized phase tracks of canard system is obtained. Firstly, the solutions to the generalized Lienard system are considered. Then the possessed head canard solutions are constructed, and illustrated the examples to construct the canard. Using this same method, we may construct also more extensive canards.
2012, 61 (3): 030203.
doi: 10.7498/aps.61.030203
Abstract +
A air-sea coupled dynamical system describing the oscillating physical mechanism of ENSO is studied. Using the modified variational iteration method (MVIM), the approximate expansions of the solution for corresponding problem are obtained effectively. And the numerical results show that the approximate solutions from the MVIM method are highly accurate by comparson with the exact solution of the model in a special case.
2012, 61 (3): 030204.
doi: 10.7498/aps.61.030204
Abstract +
A new control technique, current referenced pulse train (CR-PT), applied to switching dc-dc converter is proposed and analyzed in this paper. By sensing and comparing the output voltage and the load current at each switching cycle, an appropriate pulse is selected from among several preset pulses as an active control signal of converter. A buck converter is taken as an example to illustrate the principle, the application, the regulation, the steady state performance and the transient performance of CR-PT control scheme. The study results show that the CR-PT control enjoys the fast transient response, the convenient implementation and the stability, and the steady state performance of CR-PT control is much better than that of pulse train control.
2012, 61 (3): 030301.
doi: 10.7498/aps.61.030301
Abstract +
We study the entanglement dynamics of the system composed of a Λ-type atom and a V-type atom resonantly interacting with two coupled cavities. The evolution of the state vector of the system is given. We investigate the evolutions of atom-atom entanglement, cavity-cavity entanglement, and atom-cavity entanglement by Negativity. The influences of cavity-cavity coupling coefficient on the entanglements are discussed. The results obtained by the numerical method show that the atom-atom entanglement is strengthened and the cavity-cavity entanglement is weakened with the increase of the cavity-cavity coupling coefficient.
2012, 61 (3): 030302.
doi: 10.7498/aps.61.030302
Abstract +
By virtue of the properties of thermal entanglement, we succeed to obtain the solution to the representative phase diffusion master equation and give the operator sum representation of density operator. After analyzing the time evolution process of density operator at different initial state, we find out density operators keep invariable with the initial state being Fock state or thermal state. But the system always maintains coherence with phase diffusion when the initial state is coherent state.
2012, 61 (3): 030303.
doi: 10.7498/aps.61.030303
Abstract +
The topic about how to realize quantum computation has aroused great interest of many people. The small quantum device including Josephson junction (SQUID, e.g.) is a very promising physical system to realize quantum computation. In this paper, through the discussion about the Cooper-pair number-phase quantization scheme of the circuit system coupled by SQUID and mesoscopic LC resonator, and through the rational modulation of the parameter, we derive the J-C model of this coupled circuit under the condition of two-level approximation. According to on this model, we propose a protocol which can realize the transfer of quantum information. According to this protocol, we can carry out the transfer of the charge qubits between the two SQUIDs by utilizing the mesoscopic LC resonator as the data bus.
2012, 61 (3): 030304.
doi: 10.7498/aps.61.030304
Abstract +
A cuprate superconductor model based on the analogy with atomic nuclei was presented to have an su(3) algebraic structure by Iachello. Our previous work showed that the mean-field approximation Hamiltonian can be expressed as a linear function of the generator of su(3) algebra. Through the realization of the algebra generator, an sus(1,1) ⊕ sud(1,1) algebraic structure is shown. By using the unitary transformation of the coherent operator U(θ,φ), the gap equations and the eigenvalues of the reduced Hamiltonian are obtained. The analysis of the physical model through different algebraic structures leads to different particular results.
2012, 61 (3): 030501.
doi: 10.7498/aps.61.030501
Abstract +
We investigated the stochastic resonance of the time-delayed mono-stable system modulated by periodic rectangular signal and Gaussian white noises. The expression of signal-to-noise ratio (SNR) is obtained, and the stochastic resonance phenomenon is found in this system. The study shows that the effects of multiplicative and white noise intensity on the SNR are different. In the SNR-D plot, the phenomenon of resonance and suppression exists together. When the value of the bias of system |r| is bigger or the ratio of multiplicative and white noise intensity D/ is less than 1, the stochastic resonance phenomena in the SNR- plots disappear.
2012, 61 (3): 030502.
doi: 10.7498/aps.61.030502
Abstract +
Traditional encryption schemes are not suitable for the Wireless sensor networks (WSNS) due to some intrinsic features of nodes in WSNS such as low energy, limited computation ability and storage resources. This paper presented a novel block encryption scheme based on hybrid chaotic maps dynamically and proposed an integer digital random method, and the Feistel network structure, which is a kind of fast, secure, low resource consumption and suitable for WSNS nodes encryption scheme. The experimental tests show the new encryption scheme has follows prefect performance: the large key space, very good diffusion and disrupt performance, strict avalanche effect, excellent statistical balance and fast encryption speed of the new scheme, and the encryption scheme passes the SP800-22 test; meanwhile, the analysis and testing of speed, time and storage space on the simulator platform shows this new encryption scheme is well able to hide the data information the node in WSNS.
2012, 61 (3): 030503.
doi: 10.7498/aps.61.030503
Abstract +
This paper designs an adaptive and robustness backstepping control law to realize the control of Rossler-like systems of uncertainties. First, a wavelet network is used for the identification the nonlinear part of the system to change it into parametric model with parametric and structural uncertainties; Then, for the parameter uncertainties, an adaptive control law is designed to online estimate the unknown parameters; for the structural uncertainties, a robust control law is designed to make the system robustness. Finally, The effective of this methodology is illustrated by the simulation results.
2012, 61 (3): 030504.
doi: 10.7498/aps.61.030504
Abstract +
In this paper, a novel three-dimensional autonomous chaotic system is reported. The dynamic properties of the new system are investigated via Lyapunov dimension, numerical simulation, Poincare diagrams, Lyapunov exponent spectrum and bifurcation diagrams. The different dynamic behaviors of the system are analyzed especially when each system parameter is changed. Finally, the circuit of this new chaotic system is designed and realized by Multisim software. The simulation results confirm that the chaotic system is different from the exisiting chaotic systems and is a novel chaotic system.
2012, 61 (3): 030505.
doi: 10.7498/aps.61.030505
Abstract +
A passivity-based adaptive control law is presented, which transforms the permanent magnet synchronous motor (PMSM) with v/f controller into an equivalent passive system. It is proved that the equivalent system can be asymptotically stabilized at different equilibrium points without any influence of undeterministic parameters. Simulation results show the proposed control law is very effective and robust against the uncertainty in system parameters.
2012, 61 (3): 030506.
doi: 10.7498/aps.61.030506
Abstract +
We propose an improved visibility graph method, i.e., limited penetrable visibility graph, for establishing complex network from time series. Through evaluating the degree distributions of three visibility algorithms(visibility graph, horizontal visibility graph, limited penetrable visibility graph), we find that the horizontal visibility graph cannot distinguish signals from periodic, fractal, and chaotic systems; for fractal signal, the degree distributions obtained from visibility graph and limited penetrable visibility both can be well fitted to a power-law(scale-free distribution), but the anti-noise ability is not good; for periodic and chaotic signals, the limited penetrable visibility graph shows better anti-noise ability than visibility graph. In this regard, we use the limited penetrable visibility graph to extract the network degree distribution parameters from conductance fluctuating signals measured from oil-gas-water three-phase flow test. The results indicate that combination parameters of network degree distribution can be used to classify typical three phase flow patterns, e.g., oil-in-water bubble flow, bubble-slug transitional flow and slug flow.
2012, 61 (3): 030507.
doi: 10.7498/aps.61.030507
Abstract +
The entropy production is expressed as the product of the generalized force (driving force) and generalized flux, which plays a central role in classical non-equilibrium thermodynamics. This expression has shortcomings in two aspects: first, the decomposition into generalized fluxes and forces is arbitrary to some extent; more importantly, the entropy production is negative value calculated in heat wave propagation, which breaks the second law. In this paper, we carry out analyses based on the thermomass theory and show that the entropy production is induced by the dissipation of thermomass energy during heat condution. The generalized force of entropy production is not driving force but resistive force, having a unit of force in Newton’s mechanics. The modified expression for entropy production not only guarantees its positiveness in propagation of heat waves consistent with the extended irreversible thermodynamics, but also avoids the arbitrariness of decomposition.
2012, 61 (3): 030508.
doi: 10.7498/aps.61.030508
Abstract +
The characteristics of stability diagram of several typical flow patterns are studied, and the signals of flow patterns under 47 kinds of flowing conditions are identified with stochastic subspace parameter identification. The results show that the characteristic of a stability diagram can reflect the internal characteristics of complex time series, the characteristics of time series can be quantified by extracted straightness characteristics and the differences of characteristics of stability diagrams of three typical flow patterns. The characteristics of stability diagrams of bubble flow are the most confused and followed by Mist flows'. Slug flows' are the most regular. The extraction and recognition for characteristics of gray fluctuation sequence of gas-liquid two-phase images and the accurate classification for flow pattern samples provide a new path for the classification of multi-phase flow patterns. At the same time, the stability diagram analysis method provides a useful exploration for the further revelation of flowing mechanism of multi-phase flows.
2012, 61 (3): 030701.
doi: 10.7498/aps.61.030701
Abstract +
Molecular dynamics simulations are carried out to investigate the effect of low energy CH radical on the growth of hydrogenated carbon film. The results show that the adsorption rate of CH on clear diamond(111) is about 98%, while on hydrogenated diamond (111) the adsorption rate is lower than 1%. It indicates that the selective adsorption of low energy CH radical at the unsaturated surface C site is the dominated mechanism of the hydrogenated carbon film growth in PECVD.
2012, 61 (3): 030702.
doi: 10.7498/aps.61.030702
Abstract +
In the process of wind retrieval for Rayleigh Doppler lidar, besides atmospheric temperature and pressure, the accuracy of the wind retrieval result is also affected by Mie signal. When the Mie scattering sigal is large, especially in the cases such as high altitude clouds or volcanic ash and so on, the wind retrieval result will largely deviate from the ture value if the aerosol signal is ignored due to temperature uncertainty and Mie signal contamination. A nonlinear iterative algorithm is proposed, which can retrieve both wind and atmospheric temperature by using the mesured signal with outgoing laser pointing to the zenith. The initial operating point of laser is optimized. Simulation results show that the proposed algorithm can retrieve scattering ratio effectively, and by combination with the nonlinear iterative algorithm of wind retrieval, this algorithm can eliminate the effect of aerosol backscattering signal and then improve the atmopheric wind speed and the temperature retrieval accuracy effectively.
2012, 61 (3): 030703.
doi: 10.7498/aps.61.030703
Abstract +
MgO nano-particles are prepared by ultrasonic cavitate, and-Fe2O3 nano-particles are prepared by chemical precipitation method, then MgO and-Fe2O3 are mixed in a beaker. After the ultrasonic dispersion for 2 h, MgO/-Fe2O3 admixture is calcined at 400℃ to synthesize MgFe2O4 nano-particles. TEM and XRD tests show that MgFe2O4 takes on a spinel structure and the particles sizes range from 20 to 30 nm. The theoretieal analysis indicates that the ultrasonic cavitate effect enhances the reaction activity of raw material, augmentes specific surface area and the contact area of reactant, which can promote reaction rate, reduce reaction temperature, and make possible the chemical reaction that is difficult to complete in common condition.
ATOMIC AND MOLECULAR PHYSICS
2012, 61 (3): 033101.
doi: 10.7498/aps.61.033101
Abstract +
Potential energy curves (PECs)for the ground state and several low-lying electronic excited states of BeCl molecule are calculated using the multi-reference configuration interaction (MRCI)method with the basis set of aug-cc-pVTZ where the Davidson correction is considered as an approximation to full CI. The symmetries and dissociation limits for these electronic states are determined through group theory. The PECs of ground state(X2+)and first excited state(A2)are fitted to the Murrell-Sorbie (MS)potential function, and from the fitting parameters the spectroscopic constants are determined to be De=3.74 eV, Re=0.18173 nm(0.17970), we=857.4 cm-1(847.2), wexe=5.03 cm-1(5.14), Be=0.7103 cm-1(0.7285), and e =0.0059 cm-1(0.0069)(where the values in parentheses are the cited experimental results)for X2+ state and De=3.02 eV, Re=0.18369 nm(0.18211), we=832.7 cm-1(822.1), wexe=5.93 cm-1(5.24), Be=0.6953 cm-1(0.7094), and e=0.0065 cm-1(0.0068)for A2 state of BeCl. All the calculation results are in good agreement with the experimental values. In addition, we use the Level program to calculate the radial Schrdinger equation of nuclear motion to obtain the vibrational levels for the X2+ and A2 states.
2012, 61 (3): 033201.
doi: 10.7498/aps.61.033201
Abstract +
Spectra of even-parity highly excited states of the Sm atom have been systematically studied with two color three-step excitation and photoionization detection method. With two different excitation paths, the atom is resonantly excited to given bound states where it is detected by photoionization. The wavelength of the first laser is fixed at 627.50 nm or 624.41 nm so that the Sm atom can be excited to the two different intermediate states with the 4f66s6p configuration. Then the wavelength of the second laser is scanned from 440-700 nm to further excite the atom, so that the highly excited states in the 30040-38065 cm-1energy region can be populated. Based on precise calibration of wavelength and the selection rules, the level energies of 136 even-parity states and their relative line intensities are determined with a unique assignment of the J momentum. Except for the level energies of 71 even-parity states are confirmed by the present work, all information mention above has not been reported previously.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
EDITOR'S SUGGESTION
2012, 61 (3): 034201.
doi: 10.7498/aps.61.034201
Abstract +
Luminescent solar concentrator (LSC) photovoltaic system can cut down the cost of photovoltaic electricity generation by reducing the consumption of solar cells. Compared with the single-layer LSC, the cascaded LSC can make use of the solar spectrum effectively and obtain high photoelectric conversion efficiency. In this paper, the physical processes of the single-layer and cascaded LSC are analyzed and the corresponding mathematical models are established. Based on the models, the simulation software is developed to calculate the photoelectric conversion efficiencies of the LSC and the cascaded LSC. The effects of the size of the optical waveguide and the bandgap of solar cells on the total conversion efficiency are investigated.
2012, 61 (3): 034202.
doi: 10.7498/aps.61.034202
Abstract +
Based on P3 approximate spatially-resolved diffuse reflectance theory for semi-infinite biological tissue, the simplified expression SP3 function for highly absorbing medium close to source is studied. The research result shows that function SP3 can better describe the spatially-resolved diffuse reflectance close to source for higher absorption; the inversion of the optical parameters of highly absorbing medium with function SP3 shows the existence of extreme values of the curves fitted with diffuse reflectance data for different start distances, and the inversion results near the extreme values are the most closest to the optical parameters of real tissues.
2012, 61 (3): 034203.
doi: 10.7498/aps.61.034203
Abstract +
Based on the wave coupling theory of linear electrooptic effect in quasi-phase- matched periodical poled LiNbO3(PPLN), the control of the vector chaotic polarization of VCSEL output with external optical feedback by electro-optic modulation is numerically investigated. The investigation results show that the polarization state of VCSEL output switching periodically with the applied external electronic field or the length of the crystal. The original chaotic polarized state of its output caused by different parameters of VCSEL can be conversed into the other arbitrary chaotic polarized state. In particular, by controlling a certain applied external electronic field or the length of the crystal, any chaotic polarization model of VCSEL output can be conversed into two complete identical linear chaotic polarization model(x and ŷ polarization). In the case, this indicates that the energy of two linear chaotic polarization model can be steadily realized balanced status.
2012, 61 (3): 034204.
doi: 10.7498/aps.61.034204
Abstract +
A kind of target-in-the-loop (TIL)technique which promises the coherent combination of multi-element laser beams in far field is experimentally demonstrated. The physical model of coherent beam combination (CBC)based on TIL is established. A kind of adaptive fiber optics collimator (AFOC)correcting optical path and tip/tilt errors simultaneously is employed to compensate phase errors between beamlets. The CBC of a 3-element fiber array based on TIL is successfully achieved and a perfect effect of CBC is captured. In this paper, we present a reference for long-distance transmission of multi-element coherent beams in real atmospheric environment.
2012, 61 (3): 034205.
doi: 10.7498/aps.61.034205
Abstract +
When generating a bottle beam by using an axicon-lens system, diffraction factors often cause a bright spot in the center of bottle beam. This central bright spot is unfavorable for the using of bottle beam in constructing hollow optical tweezers system. In the article, we propose a new method of phase modulation, by adding a spiral phase plate (SPP) to optical path to make the bottle beam center have phase singularity,thereby eliminating the bright spot well. Theoretical analysis and numerical stimulation are shown to agree with the experimental results.
2012, 61 (3): 034206.
doi: 10.7498/aps.61.034206
Abstract +
For a system composed of a three-mode cavity field interacting with a movable mirror, the time evolution operator of the system and its transformation are given, and the time evolution of the system state is obtained by means of quantum theory. The result shows that the state of the three-mode cavity field is in an entangled coherent state when the mirror returns to its original state, and the preparations of different entangled coherent states can be controlled. Nine different three-mode entangled coherent states are given, and the different phase factors of these states indicate the different reactions between the field and the movable mirror, which provides an important theoretical basis for the experimental preparations of controllable entangled coherent states.
2012, 61 (3): 034207.
doi: 10.7498/aps.61.034207
Abstract +
The measuring accuracy of self-heterodyne coherent measuring system can be deteriorated by the tuning nonlinearity of the diode laser with injection current. The tuning characteristics of a DFB laser were analyzed, and a mathematical model for compensating Mach-Zehnder interferometer based self-heterodyne system was presented. The dynamic frequency modulation coefficient of the model was built by prior beat frequency of foregone optical path difference. The relative error of predicted beat frequency is reduced about 3%. This method could simplify the setup of the system, and is especially suited for online tunable laser measurement system.
2012, 61 (3): 034208.
doi: 10.7498/aps.61.034208
Abstract +
Considering that the power spectral density of 1/f noise signal varies inversely with frequency and sparse decomposition is able to create dictionaries according to signals' own features, in this paper we propose a new method to estimate the parameter of 1/f noise of high power semiconductor laser diode based on sparse decomposition, and create a dictionary whose feature is similar to 1/f noise. Sparse decomposition of white noise and 1/f noise aliased signal is implemented by Matching-Pursuit(MP)algorithm. The experimenat results indicate that sparse decomposition could effectively estimate the parameter of 1/f noise signal covering white noise and the estimated parameter is in accordance with the measured result of spectrum analyzer. Finally, the superiority of the dictionary created in this paper is illustrated by comparing with a different dictionary.
2012, 61 (3): 034209.
doi: 10.7498/aps.61.034209
Abstract +
A new double-heterostructure photonic crystal L3 microcavity is designed, under the condition of gentle confinement, the quality factor of the cavity is optimized to reach as high as 2.8105 by comparing the simulated mode distribution calculated by finite difference time domain algorithm with the ideal Gaussian distribution, while the mode volume remains small, Veff=0.1813(/n)3. This is the best result at present. Additionally, an energy correlation coefficient is introduced to qualitatively describe the optimization level of a photonic crystal microcavity, which improves the speed and the accuracy of optimization.
2012, 61 (3): 034210.
doi: 10.7498/aps.61.034210
Abstract +
We report on a frequency-tunable terahertz pulse train generated from a rectangular GaP waveguide emitter pumped by a pulse width tunable femtosecond photonic crystal fiber amplifier. The THz frequency can be tuned by varying the pump pulse duration. The dispersion of the emitter can be controlled via the geometry of the waveguide, and the coherent buildup length can be increased to scale up the output power. Waveguides with different cross sections can be used to tune the THz spectrum. Combined with the pump pulse duration tuning technique, THz pulses with a precisely tunable frequency can be obtained. In the experiment, tunable THz radiation is obtained from a GaP waveguide emitter with a cross section of 1 mm0.7 mm. Finally, a GaP emitter array is designed to achieve a wider tuning range.
2012, 61 (3): 034211.
doi: 10.7498/aps.61.034211
Abstract +
Optical-feedback laser diodes have been widely applied in chaotic optical communication, because it can simply generate wideband and high-dimension chaos and its external-cavity length is often regarded as an additional key. In this paper, it is experimentally demonstrated that the time delay signature of a chaotic laser diode with optical feedback can be identificated. Through locally enlarging the power spectral of chaotic light and observing its fine structure, the external-cavity key can be directly extracted by the spectrum analyzer, regardless of the laser diode with single or dual optical feedback of different external cavity length ratio.
2012, 61 (3): 034212.
doi: 10.7498/aps.61.034212
Abstract +
In this paper, we report on a novel photocatalytic reactor having 547 pieces of TiO2-nanofilm-modified capillaries, which is derived from a microstructured polymer optical fiber(MPOF) preform. TiO2-film-modified MPOF preform is obtained by directly inhaling P25-doped TiO2 sol into array holes of MPOF and forming TiO2 film on their side walls. The MPOF perform acts as not only a light-transmitting media(rolling-up thin film waveguide, collecting and transmitting light into the TiO2thin film), but also a TiO2supporting and waste-water pipe to supply for photocatalytic degradation of toxic organic solute. Methylene blue(MB) is chosen as a model contaminant in water. The effects of loading quantity of TiO2, pH of MB and initial concentration of MB on photocatalytic degradation are investigated. The photocatalytic reactor has so large surface area for TiO2 loading that photodegradation efficiency is enhanced. As far as we know, the photocatalytic reactor with functions of collecting and transmitting light, conveying matter and loading catalyst has not been reported before.
2012, 61 (3): 034213.
doi: 10.7498/aps.61.034213
Abstract +
A spacecraft running in the space environment would be irradiated by the proton, and the irradiation effects on the most important parts of the optical fiber gyroscope in the spacecraft -the optical fiber ring is the most. In order to investigate the irradiation damage induced by proton irradiation on the Capsule type polarization-maintaining optical fibers made in china, the variation of the transportation power at 1310 nm wavelength is measured by means of situ measurement for the 5 MeV and 10 MeV environments protons irradiation on the Capsule type polarization-maintaining optical fibers made in china. The irradiation induced loss is calculated by us. The Stopping and Range of Ions in Matter (SRIM) software was used to simulate the ionic and displacement damage of 5 MeV and 10 MeV energy protons irradiation on the optical fibers. The O 1s and Si 2p analytic spectrum of the before and after irradiation were obtained by means of X ray photoelectron spectroscopy (XPS). Using the Fourier transform infrared spectrometer (FTIR), we analyzed the before and after irradiation spectrum. The results show that at the 1310 nm wavelength, the rradiation induced loss of the of optical fibers increase with the increasing of the protons fluence due to the increase of the SiOH concentration in optical fiber core. The 5 MeV proton irradiation induced loss is worse than that of the 10 MeV mainly because the more worse displacement and the ironic damage induced by 5 MeV proton at the position of the optical fiber core than that of 10 MeV, i.e., the more amount of SiOH generation.
2012, 61 (3): 034214.
doi: 10.7498/aps.61.034214
Abstract +
Based on the laser Doppler effect, real-time and on-line measurements of velocity in high-speed flows can be realized using tunable diode laser absorption spectra (TDLAS). The fundamental theory and the method to measure the velocity are presented. A dual-beam system used in the experiments is described. The water vapor absorption feature at 1398 nm is utilized to detect the flows generated within a wind tunnel. The DFB laser is quickly tuned at a rate of 10 kHz to obtain the spectra of the transient flows by using scanned-wavelength direct absorption spectroscopy. The ways to calibrate the frequency and calculate the Doppler shift (DS) are also introduced. The measured velocity is compared with the calculated velocity, and they are in good agreement with each other, which proves that the way combining DS with TDLAS to measure the velocity in high-speed flows is reasonable. The system capability and possible factors to induce measurement deviations are analyzed to improve the system performance in the future.
2012, 61 (3): 034215.
doi: 10.7498/aps.61.034215
Abstract +
A thermal-optical tunable filter based on the Venier effect of cascade microring resonator, which can expand the Free-Spectrum-Range (FSR) and the tuning range, is designed and simulated. The FSR of the filter with a radius of 48 m for the first order and 50 m for the second order microring can be expanded to 76.5 nm, which is at present the largest FSR to our best knowledge. A tuning range covering all of the above mentioned FSR can be reached under 103.1 mW heating power, which is also the largest one for silicon based thermal-optic tunable microring resonator filers. The response time, calculated by finite-element-method, of the designed tunable filter with 50 m radius ring is 3.5 s for the rise edge and 0.8 s for the fall edge.
2012, 61 (3): 034301.
doi: 10.7498/aps.61.034301
Abstract +
The flexural vibration behavior of elastic wave across a slender beam with locally resonant multi-oscillators structure is studied by using the transfer-matrix method and the finite element method. A simplified model is proposed, and the formulas of start and end frequencies of band gap are deduced. The more abundant and wider flexural elastic wave band gaps are found in this locally resonant multi-oscillator beam than in one oscillator beam, which can be used in the reduction of multiple-frequency vibration and noise. The frequency response of vibration in the band gap frequency range has obvious attenuation. The results of simplified model are in good agreement with results from the theory model. The research project will provide a new way for vibration reduction of beam structure.
2012, 61 (3): 034701.
doi: 10.7498/aps.61.034701
Abstract +
In this paperan improved dissipative particle dynamics(DPD) method was applied to simulate droplet motion in a grooved microchannel. The improved DPD method adopted a recently proposed combination of short-range repulsive and long-range attractive interaction, which can simulate fluid flows with free surfaces, such as droplet motions. The static contact angle between the droplet and the solid wall was simulated with the new potential function, andstatic contactangle～awf/af curve was obtained by Polynomial fit of the 2nd order. The influences ofwall wettability, flow field force, droplet temperature on the flow pattern of droplet in the grooved microchannel were investigated. The results showed that wall wettability and flow field force have large affectson the flow pattern of the droplet, whiledroplet temperature have little affectson it. This article is helpful to understand the fluid flow behavior with free surfaces on rough surfaces.
EDITOR'S SUGGESTION
2012, 61 (3): 034702.
doi: 10.7498/aps.61.034702
Abstract +
A third-order Lagrangian solutions is found directly by the full Lagrangian parametric governing equations, with the parameters of identifying each water particle which is obtained in mass conservation from taking the wavelength-averaged level of the vertical displacement of water particles along the direction of the wave propagation and is just the position of particle in the original still water, for the irrotational free surface progressive gravity waves propagating on uniform current in the three dimension. It is found that the effect of wave-current interaction is occurred in Lagrangian velocity potential, so that the pressure is not affected by the uniform current in the wave-current field. The drift velocity, Lagrangian mean level of particle and its motion period longer than the wave period which are exponentially decreasing with the depth of particle's level and the pathlines of particle and the streakline are then all presented, these are to be excluded in Eulerian solution. Furthermore, the forms of the helical pathlines of particles varying with the direction and speed of the uniform current are appeared to be turned from the wave velocity and current velocity component in co-direction to in anti-direction, even become into a closed orbit. The special case when the wave-current field is at the steady motion is also interpreted its consequential charateristics. The present solution can be reduced to that of the pure progressive waves as no current exists.
2012, 61 (3): 034703.
doi: 10.7498/aps.61.034703
Abstract +
The quantitative experiments are made to measure the motional characteristics of water particles in the progressive gravity waves propagating on following and reversing uniform currents. The theoretical results of the third-order Lagrangian solution in Part 1[1] are shown good agreements with those measured by the experiments for the wave-form, the velocity distribution, the mass transport velocity, the particle trajectory, particle's motion period and Lagrangian mean level. It is also verified that identifying parameters of each particle is equal to the coordinates of its position in a still water. Consequentially, the wavelengths of the wave-forms constituted by the particles in the field are all equal to that of the progressive waves and their propagating speeds are the sum of the velocities of the progressive waves and the uniform current as the so-called Doppler effect is proved, but the motion periods and the Lagrangian mean levels of particles are the same as those in the progressive waves. The variations of the orbital forms of particles in the field are also revealed that the orbits like the prolate trochiod, the cycloid and the curtate trochoid are presented in the case of following uniform current as the horizontal velocity components of particles at the section of wave trough are, respectively, negative, zero and positive in the direction of the progressive waves, and that the orbits like the prolate trochoid and the ellipse are occurred in the case of reversing uniform current as the mass transport velocities of particles are, respectively, positive and zero in the direction of the progressive waves, and that the orbits like the turned prolate trochoid, the turned cycloid and the turned curtate trochiod are appeared in the case of reversing uniform current when the mass transport velocities of particles are negative and the horizontal velocity components of particles at the section of wave crest are, respectively, positive, zero and negative in the direction of the progressive waves.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2012, 61 (3): 035201.
doi: 10.7498/aps.61.035201
Abstract +
The Bohm criterion for an electronegative magnetized plasma sheath is investigated with a fluid model. It is shown that the existence of negative ions has an effect on the Bohm criterion. And the numerical value of the ion Mach number depends on the magnetic field and the incidence status of the ions.
2012, 61 (3): 035202.
doi: 10.7498/aps.61.035202
Abstract +
Research on the characteristics of X-ray emission in repetitive pulsed discharge is associated with the behavior of runaway electrons and the mechanism of nanosecond pulsed discharge. In the experiments, X-ray emission in the repetitive pulsed discharge with a rise time of ～15 ns and an FWHM of 30-40 ns in atmospheric air is directly measured by a detection system consisting of NaI scintillator and a photomultiplier tube, and the energy range of the X-ray detector is demonstrated to be between 10 and 130 keV. Results show that main part of the energy of X-ray is from 20 keV to 90 keV, and a little X-ray with an the energy of less than 20 keV or more than 90 keV is detected. X-ray emission increases with the increase of pulse repetition frequency, and it has a peak value with the variation of air gap spacing. There is a maximum value of X-ray emission when the nanosecond discharge appears in a diffuse mode.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2012, 61 (3): 036101.
doi: 10.7498/aps.61.036101
Abstract +
Different from the previous experimental and simulating methods, ab initio molecular dynamics simulations are performed to investigate the partial structures of liquid Ga, In and Ga-In alloys. In liquid Ga-In alloys, the positions of first peaks in gGaGa(r) and gInIn(r) are close to those of the pure Ga and In, respectively, and the position of first peak in gGaIn(r) is larger than the average value of pure Ga and In, indicating that inhomogeneous atoms are prone to be repulsed and Ga-Ga and In-In clusters are easy to emerge in the system. The most popular 1311 pair bonds existing in liquid pure Ga and In are dominant in liquid alloys, proving that Ga-Ga and In-In clusters coexist in liquid Ga-In alloy. Through the Voronoi analysis, with In increasing, in the Ga100-xInx (30 ≤x≤50 at.%) region, the main coordination number around Ga atoms abruptly decrease from 12 to 10, proving that Ga-Ga and In-In clusters are prone to be separated. These results are different from those obtained from the micro-inhomogeneous model and reveal the mechanism of cluster separation in liquid Ga-In alloy.
2012, 61 (3): 036102.
doi: 10.7498/aps.61.036102
Abstract +
Ag nanoparticles with 2-dimensional (2D) array structure were fabricated via nanosphere lithography. The influence of Cr interlayer position and metal deposition direction on the array structure was systematically studied. It was found that the structure of the 2D Ag nanoparticle array with Cr interlayer was better than that without interlayers. When the Cr interlayer was deposited on the PS mask, the tips of the acquired triangle nanoparticles were much sharper, and the area of the nanoparticle array was much larger than the other cases. Moreover, the achieved nanoparticle array has a better uniformity and compactness in structure, and higher binding ability to the substrate when Cr and Ag deposition direction was perpendicular to the surface of the substrate. Further absorption spectrum experiment proved the improvement of the structure and feature of the 2D Ag nanoparticle array. All these are very crucial for the future modification and fabrication of biochemical sensors with the 2D Ag nanoparticle array.
2012, 61 (3): 036103.
doi: 10.7498/aps.61.036103
Abstract +
The effect of an n-type AlGaN layer on the physical properties of dual-wavelength light-emitting diode (LED) is investigated numerically. The simulation results show that compared with the conventional p-type AlGaN electron-blocking layer (EBL), the n-type AlGaN layer can improve the distribution of electrons and holes more uniformly and realize the radiation balance between electrons and holes in the quantum wells, and further reduce the efficiency dro of dual-blue wavelength LED at high current. In addition, the spontaneous emission rate of two kinds of quantum wells can be adjusted through the control of Al composition. It can be found from the results that the emission spectrum of dual-blue wavelength LED is more stable at low current with an Al composition of 0.16, while the emission spectrum is more stable at high current with an Al composition of 0.12.
2012, 61 (3): 036104.
doi: 10.7498/aps.61.036104
Abstract +
Aluminum-doped zinc oxide (AZO) films have potential applications in photoconducting and piezo-electric devices, and gas and piezo sensors. Although the film structure and optical properties are intensively studied, the effect of gas flow ratio of O2 to Ar (GFR) on the film structure and optical properties has not been reported in terms of macrostress and lattice strain. In this paper, a series of AZO films is deposited on glass substrates by direct-current pulse magnetron reactive sputtering under different GFRs. The influence of the GFR on the crystalline structure, the surface topography, and the optical properties of the film is systematically studied in terms of macrostress and lattice strain by using X-ray diffractometry, scanning electron microscopy and spectrophotometry, respectively. The as-deposited AZO films are polycrystalline and (103) oriented, which can be attributed to the change in crystalline face energy during the accompanied thermal annealing for 3 h. The film tensile stress first increases to a maximum value, and then decreases gradually with GFR values increasing. It is noted that the transition from tensile to compressive stress occurs with GFR increasing. This result is different form that of lattice strain. The film transmissivity in the visible region first decreases and then increases with GFR increasing, which is attributed mainly to the scattering of grain boundary induced by the grain size.
First principles calculation of electronic structures and optical properties for -CuX(X = Cl, Br, I)
2012, 61 (3): 036105.
doi: 10.7498/aps.61.036105
Abstract +
We use first-principles calculation with pseudo-potential and plane wave method to study the bulk meduli, electronic structures and optical properties of copper halides CuX (X = Cl, Br, I). A comparison of the calculation results with the available experimental results show that it is more suitable using the generalized gradient approximation to study these properties than using the local density approximation. The results show that valence bands of CuXX(X = Cl, Br, I) are dominated by the d bands of Cu. Conduction bands are mainly from s bands of Cu and halide atoms, as well as from p bands of halide atoms. The calculated refractive indices of CuX(X = Cl, Br, I) are 1.887, 2.015, and 2.199, respectively. These results are in good agreement with the those calculated from the Gladstone-Dale relationship.
2012, 61 (3): 036201.
doi: 10.7498/aps.61.036201
Abstract +
By taking the pressure effect into account in the free volume evolution, the yield asymmetry between tension and compression of metallic glasses under different temperatures is investigated. The yield strength in MGs with a (T/Tg)1/2 temperature dependence is obtained for both tension and compression. The pressure - sensitive factor is derived to be a constant ～ 0.1 within a broad range of temperatures. Furthermore, it is revealed that, the declining effect of pressure on the free volume evolution causes a weaker tension - compression asymmetry with increasing temperature. The significant structural relaxation at high temperature slows down the free volume evolution and hinders the sharp yield. These results improve our understanding of the underlying mechanisms of the yielding and its asymmetry between tension and compression in MGs.
2012, 61 (3): 036202.
doi: 10.7498/aps.61.036202
Abstract +
Tensile-strained germanium is one of the promsing materials for Si-based photonic devices due to its quasi-direct band and compatiblility with silicon technology. The band structure of tensile-strained germanium is investigated based on the theory of van de Walle deformed potential. The carrier distributions in the conduction bands at Γ and L vallies under the strain, and the n-type doping concentratoin in germanium are analyzed. Considering the competition between radiative recombinations at Γ and L vallies and Auger recombination, as well as dislocation induced non-radiative recombination, internal quantum efficiency and optical gain for direct band transition in n-type Ge are calculated. It is shown that 74.6% internal quantum efficiency can be obtained in the 1.5% tensile-strained n-type doped Ge under carrier injection and a strong optical gain is predicted, which is comparable to those of III-V materials.
2012, 61 (3): 036203.
doi: 10.7498/aps.61.036203
Abstract +
Order to get a new type carbon foam material, AlN/C composite foam was successfully synthesized by using AlN as an additive and hollow microspheres/reticulated carbon foam as a basement thought the annealing high-temperature heated process. The prepared samples were characterized by Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM). The results of test indicated that AlN whiskers with diameter of 50nm, length large than 10 um and larger length-diameter ratio were prepared by amorphous AlN recrystallization at the surface of carbon microspheres. Diffraction peaks of XRD demonstrated that the sample was characterized as graphitization and AlN whiskers were hexagonal structure. XPS test showed that there was an obvious peak of CN bond on 287.5 eV, which revealed that AlN and carbon foam through CN bond combined on their interfaces. Meanwhile, it was showed that AlN/C foam material's compression strength was 40.27 MPa through the analysis of the stress-strain of mechanical performance, which increased nearly one order of magnitude compared with the carbon foam material. The results of test showed that compressive strength of carbon foam was obvious reinforced by AlN whisker. And this new composite foam has infinite applications value in various kinds of resist compression and absorbing aeronautical materials.
2012, 61 (3): 036401.
doi: 10.7498/aps.61.036401
Abstract +
The nanoinstability of single-wall carbon nanotubes(SWCNT) under electron beam irradiation is systematically investigated by in-situ transmission electron microscopie observation at room temperature. Under the same irradiation condition, it is found that with the increasre irradiation time(or electron dose), the SWCNT whose two ends are fixed at ropes of nanotubes shrinks in its radial direction with an increasingly faster rate; the curved SWCNT is more instable than the straight one with a the same diameter; the SWCNT with a free capped end but the other end fixed at a rope of nanotubes shrinks in the axial direction but almost keeps its diameter unchanged. All experimental phenomena could be well accounted for by new concepts of vaporing and diffusing of carbon atoms as strongly driven by the nanocurvature of SWCNT as well as by the electron beam-induced athermal activation.
2012, 61 (3): 036402.
doi: 10.7498/aps.61.036402
Abstract +
Ideal metallic glasses are the metallic glasses that satisfy electronic structure stability. Previously we have developed a so-calledcluster-plus-glue-atom modeland more recently acluster-resonance modelfor the ideal metallic glasses. Good metallic glass forming compositions always satisfy simple cluster formulas [cluster] (glue atoms), with x denoting the number of glue atoms matching one cluster. In this paper we present an electrochemical potential equilibrium criterion based on these models to obtain the number of glue atoms. By examples of Cu-Zr and Co-B bulk metallic glasses, it is confirmed that the experimentally determined good BMG-forming compositions well agree with the calculated composition formulas.
2012, 61 (3): 036701.
doi: 10.7498/aps.61.036701
Abstract +
Nonpolar Zn(Mn, Na)O thin films with orientation (a-plane) have been successfully grown on r-plane sapphire substrates by pulsed laser deposition (PLD) through a Mn-Na codoping route. The X-ray diffraction(XRD), field-emission on scanning electron micorscope(FE-SEM), Hall-effect and X-ray photoelectron spectroscopy(XPS) measurements show that substrate temperature and work pressure have a significant influence on the nonpolar growth of Zn(Mn,Na)O thin films. The films prepared under a work pressure of 0.02Pa and substrate temperature of 600 ℃ could achieve a high quality crystallite with fine optical and electrical properties through Mn-Na codoping. Moreover, the influence of the growth orientation on room temperature ferromagnetism (RTFM) of the thin films is investigated by superconducting quantum interference device(SQUID), and the possible mechanism involving the origin of RTFM in the Zn(Mn,Na)O films is discussed as well.
2012, 61 (3): 036801.
doi: 10.7498/aps.61.036801
Abstract +
The antiperovskite Mn3CuNx thin films are successfully deposited on single crystal Si (100) substrates using facing target magnetron sputtering. The effects of nitrogen content on the structures and physical properties of the Mn3CuNx thin films are investigated. The crystal structure, composition, surface morphology and the temperature dependence of resistivity and magnetization are characterized by X-ray diffraction, Auger electron spectroscopy, atomic force microscope, X-ray photoelectron spectroscopy, physical property measurement systems and superconducting quantum interference device. It is found that the thin film has an antiperovskite structure and a preferred orientation along (200) plane. The surface roughness and particle size increase with N content increasing. N content has little influence on the electronic transport behavior of the film. All the films display semiconductor-like behaviors, i.e. their resistivities monotonically decrease considerably, which is different from the bulk counterpart. The film undergoes a magnetic transition from ferrimagnetic to paramagnetic with the increase of temperature. Moreover, the Curie temperature (TC) increases as the N content decreases, owing to the effect of N deficiency on the interaction of Mn6N octahedron.
Real time and ex situ spectroscopic ellipsometry analysis microcrystalline silicon thin films growth
2012, 61 (3): 036802.
doi: 10.7498/aps.61.036802
Abstract +
Microcrystalline silicon thin films with and without a seed layer were deposited using very high frequency plasma enhanced chemical vapor deposition method at a high growth rate. The influence of the seed-layer method on the film growth and structure were investigated using spectroscopic ellipsometry(SE), Raman spectrum and X-ray diffraction. The results show that the seed-layer can not only increase the growth rate, but also promote crystalline nucleation at the initial growth stage. The deposition processes were monitored by real time spectroscopic ellipsometry(RTSE). The film was also measured by ex situ SE in the air. The differences between the RTSE and ex situ SE have been studied in testsing the microcrystalline silicon thin films. Results show that for the thin films the total thickness obtained by RTSE is smaller than that by ex situ SE, while for the thick films the measured total thicknesses by two methods are almost the same. However, the surface roughness thickness detected by RTSE is larger than that by ex situ SE. The reason for this is due to oxidation of the thin film exposed to the air which smoothed the film surface.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2012, 61 (3): 037101.
doi: 10.7498/aps.61.037101
Abstract +
Using density functional calculations within the generalized gradient approximation and Hubbard U framework, the electronic and the magnetic properties of SrCoO3 are investigated. The result shows that the spin-up t2g and eg states of Co shift toward the lower energy with the increase of the U value, whereas the spin-down t2g and eg states of Co shift toward the higher energy. The O 2p state almost does not shift with the increase of U value. The electronic structure of SrCoO3 changes from metal state into half-metal state around U of 7-8 eV. The magnetic moment of Co ions increases linearly with U increasing for U 7.0 eV, and almost does not change for U 8.0 eV. Compared with the experimental results, U = 8.0 eV is thought to be suited for the study of SrCoO3. The result shows that with U = 8.0 eV, the magnetic moment on Co site is 3.19 B and SrCoO3 has the half-metallic nature.
2012, 61 (3): 037102.
doi: 10.7498/aps.61.037102
Abstract +
The electronic, the magnetic and the orbital structures of KCrF3 are studied by first principles in its recently identified crystallographic phases (tetragonal and cubic) [Margadonna and Karotsis 2006 J. Am. Chem. Soc. 128 16436]. In tetragonal phase, both generalized gradient approximation (GGA) and GGA+U calculations show that the ground state is the A-type antiferromagnetic (A-AFM) configuration with G-type orbital ordering pattern. Our calculations show that the orbital structures and the magnetic configurations can be measured by the optical conductivity. In the cubic state, the GGA calculations show that the ground state is ferromagnetic half metal state, while the GGA+U(Ueff = 3.0 eV) calculations show that the A-AFM insulator phase is the ground state. Our calculations indicate that the electron-electron interactions rather than the electron-phonon interactions are the driving forces behind the orbital order.
2012, 61 (3): 037103.
doi: 10.7498/aps.61.037103
Abstract +
In the paper, we study how the geometry structure and the growing ambience and the Fermi level of several intrinsic point defects effect the defect formation energy of the rutile and anatase TiO2, which type of point defect will be formed, and how to predict the experimental condition of point defect from theory. The key problem is how to calculat the defect formation energy with charge, and correcte the calculation results. The results show the defect type and the defect concentration are related to the nonequilibrium growth condition. In general, under the O-rich condition, VTi will form spontaneously, and under the Ti-rich condition, Ti4+ and VO easily appear in Schottky defects.
2012, 61 (3): 037301.
doi: 10.7498/aps.61.037301
Abstract +
The localized surface plasmon resonance (LSPR) properties of bimetallic gold and silver three-layered nanotubes such as SiO2-Ag-Au and SiO2-Au-Ag nanotubes have been investigated with the variations of Au or Ag shell thickness and size of the core by means of Finite Difference Time Domain (FDTD) method. With increase in the core size, it is found that the LSPR peaks show red-shift. We also observe with increasing the thickness of the Au or Ag shell that the LSPR peaks show blue-shift. Furthermore, the modulation of LSPR due to Ag shell is more significant compared with that due to Au shell. We have ascribed the variations of the LSPR peaks to the plasmon hybridization and the competition between the changes of conduction and oscillation electrons.
2012, 61 (3): 037302.
doi: 10.7498/aps.61.037302
Abstract +
Graphene thin films are grown on Si substrates covered by SiO2 layers (SiO2/Si) with the method of directly depositing carbon atoms in the molecular beam epitaxy (MBE) equipment. The structural properties of the samples produced at different substrate temperatures (500℃, 600℃, 900℃, 1100℃, 1200℃) are investigated by Raman spectroscopy (Raman) and near-edge x-ray absorption fine structure (NEXAFS). The results indicate that the thin films grown at lower temperatures are amorphous carbon thin films. While the thin films grown above 700℃ exhibi the characteristics of graphene. As the substrate temperature increases, the crystalline quality of graphene is improved. However, very high temperature can reduce the quality of grapheme. The best graphene films are obtained at a substrate temperature of 1100℃. When the substrate temperature is low, the activity of the carbon atoms is not enough to form the ordered six member rings of C-sp2. While the substrate temperature is too high, the decomposition of some SiO2 induces the deposited carbon atoms to bond with decomposed oxygen atoms or silicon atoms, resulting in the defects on the surface, which leads to the poor crystalline quality of graphene films.
2012, 61 (3): 037801.
doi: 10.7498/aps.61.037801
Abstract +
Current-induced Kerr rotation spectra and reflectivity spectra of (Ga,Mn)As and p-GaAs were measured in the absence of the magnetic field via magneto-optic Kerr effect around the energy gap. The dependence of the Kerr rotation and the reflectivity on the laser wavelength show Lorentzian profile. The Kerr rotation depends linearly on the current and the reflectivity depends linearly on the square of the current. The Kerr rotation of P-GaAs is much weaker than that of the (Ga,Mn)As which indicate that the doping of Mn enhance the current-induced spin polarization . The dependence of the Kerr rotation and the reflectivity on the temperature was also measured, both showing red shift of their Lorentzian peaks, a familiar behavior as the absorption edge of GaAs. In addition, we observed the dependence of the Kerr signal on the polarizational direction of the incident beam.
2012, 61 (3): 037802.
doi: 10.7498/aps.61.037802
Abstract +
Fermi resonance (FR) plays an important role in the spectral line identification and assignment in spectral analysis. It contains a wealth of physical laws which are urgently needed for research. In the present paper, we propose a new method of varying the refractive index of the solution to study the FR, which is based on the model of Onsager. The basic principle of this method is to use Raman scattering intensity (Raman scattering coefficient) changing with the refractive index of solution to study the FR. With this method we not only can give the relationship between the FR parameters and the refractive index of solution, but also find new spectrum phenomena (including the asymmetric shift of Fermi doublet and the FR tuned fundamental freguency of the overtone). In this article we provide a new research method to study the FR.
2012, 61 (3): 037803.
doi: 10.7498/aps.61.037803
Abstract +
One transmission-mode extended blue GaAs photocathode is prepared by MOCVD , whose integral sensitivity is 1980 A/lm. Its spectral curve is compared with the spectral curve of ITT photocathode for analyzing optical structure. The comparison indicates that the differences lie in the thickness and the Al mole value of the Ga1-xAlxAs window layer, electron diffusion length, and back-interface recombination velocity, which make the photocathode in this experiment inferior to that of ITT in extended blue performance. However our surface electron-escape probability and the thickness of the GaAs active layer are in accordance with those of ITT, which leads their difference in the long waveband part to be less than in the short one. In addition, our absorptivity in the whole response waveband is smaller than that of ITT photocathode, which leads the spectral response and integral sensitivity of the domestic transmission-mode extended blue GaAs photocathode to be inferior to the exotic one.
EDITOR'S SUGGESTION
2012, 61 (3): 037804.
doi: 10.7498/aps.61.037804
Abstract +
The infrared quantum cutting phenomena, which is an international hot research field, of Er1.0P5O14 noncrystalline glass are studied by the present paper for the first time. The 1537.0nm infrared fluorescence of Er1.0P5O14 noncrystalline glass is confirmed to be the multi-photon quantum cutting fluorescence by computation and comparison between absorption and excitation spectra. It is found that the 4I13/2→4I15/2 quantum cutting fluorescence is very strong, induced by the excited 2H11/2, 4G11/2, and 4G9/2 energy levels. Its mechanism is thoroughly analyzed based on the calculation of spontaneous emission rates, nonradiative multiphonon relaxation rates and energy transfer rates. It is found the strong downconversion energy transfers {2H11/2→4I9/2,4I15/2→4I13/2},{4G11/2→4I13/2, 4I15/2→2H11/2},{4G9/2→4F7/2,4I15/2→4I13/2} 和 {4G9/2→4I13/2, 4I15/2→2H11/2} are responsible for the strong infrared three-photon and four-photon quantum cutting fluorescence of Er1.0P5O14 noncrystalline glass. The present research is significant for enhancing solar cell efficiency.
2012, 61 (3): 037805.
doi: 10.7498/aps.61.037805
Abstract +
The change ofQ-band fluorescence lifetime of tetraphenyl porphyrins(TPP) adsorbed on the surface of silver nanoparticles is reported. The lifetime was extended when the surface plasmon resonant peak of silver nanoparticles was adjusted to resonant with theQ- absorption band. Silver nanoparticles bring large surface plasmon resonant enhancement effect to the surface light field, and the excited TPP molecules have higher polarity. The enhanced light field will stabilize the TPP molecules of high polarity, which causes the extendedQ-band fluorescence lifetime. It has an important significance in photodynamic therapy using porphyrins as photosensitizer.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2012, 61 (3): 038101.
doi: 10.7498/aps.61.038101
Abstract +
Persistent photoconductivity(PPC) is a deterring factor for the time response of ultraviolet photo-detectors made of polycrystalline diamond films. The existence of PPC can greatly prolong the response time of photo-detectors. In this paper, ultraviolet photo-detectors with interdigital electrode spacings of 20 μm and 30 μm(denoted as "device A" and "device B", respectively) are fabricated on microcrystalline diamond films, and the influences of grain boundary on time response of diamond ultraviolet photo-detectors are discussed. Results show that performances of PPC and photoconductive gain are present in the two photo-detectors, and the PPC is longer and the photoconductive gain is higher in device B than in device A. It is suggested that grain boundaries may induce a shallow level in the bandgap and act as minority carrier trapping centers, leading to PPC and high gain. There are more grain boundaries between the electrodes in device B than in device A, which hence explains the higher photoconductive gain and responsivity as well as more significant PPC in device B than in device A.
2012, 61 (3): 038102.
doi: 10.7498/aps.61.038102
Abstract +
Cr,Mg:GSGG crystals are successfully grown by the Czochralski method. The influences of reducing- and oxidizing- annealing treatments on the absorption spectra of Cr,Mg:GSGG crystals are investigated. From the changes of their absorption spectra, it can be inferred that the Cr4+ ions are initially generated at octahedrally coordinated sites, and then exchange positions with tetrahedral Ga3+ ions in neighboring sites under heat exciting. Differences between absorption spectra also suggest that Mg2+ ions can improve the concentration of tetrahedral Cr4+ ions.
2012, 61 (3): 038210.
doi: 10.7498/aps.61.038210
Abstract +
The mechanism of Li insertion into Sn3InSb4 alloy is investigated by means of the first-principle plane-wave pseudo-potential method. The lithium intercalation formation, the theoretical capacity, the volume expansion ratio and the electronic structures are calculated. In the intercalation process, lithium atoms firstly fill the interstitial sites, and then lithium atoms continue to replace the metal atoms. Large expansion ratio from 11.74% to 43.40% would lead to the bad cycle stability for Sn3InSb4 alloy as the lithium battery electrode material. The conduct electricity is improved with lithium content increasing, then the conduct electricity decreases with interstitial sites being filled with lithium atoms and Sn-replacement reaction occurring.
2012, 61 (3): 038401.
doi: 10.7498/aps.61.038401
Abstract +
The relativistic magnetron with axial extraction, also known as magnetron with diffraction output (MDO), is an important device for the miniaturization and compaetification of magnetron. It is also promising to be one of the most compact narrow band high power microwave sources. Based on the manners and traits of the MDO directly radiating the quasi-TE11 mode in axial direction, the investigation of the power combination of double MDOs with a horn antenna is carried out. After discussing the combination ways and results, a modified configuration is proposed for improving the radiation directivity. Finally, the results show that when the adjacent double MDOs have an open angle of 7 and the common horn antenna has the parameters of h = 600 mm and r = 340 mm, the mode reflection coefficient of the power combination system is 0.31, the maximum gain is 21.5 dB, the radiation mode is TE11.
2012, 61 (3): 038701.
doi: 10.7498/aps.61.038701
Abstract +
The experimential evidences confirm that spiral waves are observed in the disinhibited mammalian neocortex. The scheme of ceullar networks is used to simulate the formation and the evolution of spiral wave in the neocortical slices. The regular networks of neurons are constructed in the two-dimensional space, the dynamical properties of thermosensitive neurons is described by temperature factor, and the effect of membrane temperature on the evolution of spiral wave is investigated in detail. A statistical factor of synchronization is defined to measure the critical condition inducing phase transition of spiral wave (death or breakup) by the factor of temperature of membrane. It is confirmed that spiral wave is removed and the whole networks become homogeneous and synchronous completely when the membrane temperature exceeds a certain threshold; the breakup of spiral wave is induced in the presence of weak channel noise being considered. Furthermore, it is suggested that the mechanism of temporary heat stupor could be the blocking of spiral wave propagation in some functional domain.
2012, 61 (3): 038702.
doi: 10.7498/aps.61.038702
Abstract +
Graphene has received great interest because of its peculiar band structure and excellent physical properties. But today, the development of graphene is limited to its size and quality. In this paper, single- and multilayer graphene films were synthesized on copper foils by chemical vapor deposition(CVD) using methane at ambient pressure. Experiment results find the high temperature, low concentration of methane gas, shorter growth time and suitable gas flow are the key to get high-quality and large-scale graphene films. Raman spectra, scanning electron microscope(SEM) and transmission electron microscope(TEM) characterization indicate the graphene films are mostly single-layer, only with rare area having multilayer around copper boundaries. Further electrical tests show the graphene films grown by CVD method represent semiconductor behaviors under low temperature and the sheet resistance of graphene films is decreasing with the external magnetic field increasing.
2012, 61 (3): 038801.
doi: 10.7498/aps.61.038801
Abstract +
The optical characteristic of the nanohole array film is analyzed by using rigorous coupled wave, and the nanohole array film is proposed to serve as photovoltaic device anti-reflection film to improve the device absorption and efficiency. According to theoretical analysis, nanohole array anti-reflection film has a better anti-reflection effect than the monofilm and can better enhance the photovoltaic device's efficiency, especially in a speetral range of 400 nm600 nm; the optimal period of the nanohole array is 500 nm, the optimal filling factor of the nanohole array is 0.2 and the optimal thickness of the nanohole array is 110 nm. In order to testify the optical effect of nanohole array, the nanohole arrays of different sizes are made by the micro-nano processing technology in the anti-reflection film of the 200 m Si Detector, and a relevant experimental system is set up. With the optimized nanohole arrays, the short circuit currents of the experimental sample are increased ～6% in a 4001100 nm spectral range, especially, increased ～15% in a 400 nm-600 nm spectral range.
2012, 61 (3): 038802.
doi: 10.7498/aps.61.038802
Abstract +
Compared with single-layer contact, optimized two-layer contact of front side could diminish power losses distinctly and improve the electrical performance of crystalline silicon solar cell. In this paper, the optimized analysis and experimental study for two-layer contact of crystalline silicon solar cell are carried out. The model of two-layer contact is established by abstracting the cross-section of two-layer contact into semi-elliptical shape closer to the realistic situation according to the SEM observation . The electrical losses and the optical losses of two-layer contact are analyzed in theory. In combination with experimental screen-printed contact thickened by light-induced electroplating solar cell, the relationship between the optimum thickening contact thickness by light-induced electroplating and the screen-printed contact width is achieved in theory and experiment. The corresponding theory and experimental results are in good agreement with each other. Due to involving no concrete technology of contact preparation, the theoretical model of two-layer contact is generally appticable for many types of two-layer contact structurs in consequence.
2012, 61 (3): 038901.
doi: 10.7498/aps.61.038901
Abstract +
In this paper, we find the decreasing law of maximum eigenvalue of the principal sub-matrix for coupling matrix, propose a method of calculating quickly pinning nodes in complex networks, and reveal the relation between the pinning strategy and the number pinning nodes. Numerical simulations show the trends of evolution under the conditions of three pinning strategies in a scale-free network and a small world, and the effectiveness of the pinning synchronization by selecting pining nodes randomly in a scale-free network.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2012, 61 (3): 039201.
doi: 10.7498/aps.61.039201
Abstract +
For a stable dynamic system, probability density distribution (PDD) of a system variable is relatively stable, and if there is a change in dynamic structure of a system, the PDD of the system variable will have some change correspondingly. According to this characteristic of PDD of a dynamic system, in this paper we present two new methods, namely, skewness index and kurtosis index, to detect an abrupt change in a time series by means of identifying some small changes in PDD. Tests on model time series indicate that skewness index and kurtosis index can be used to identify an abrupt change, such as abrupt change in parameter of an equation and abrupt dynamic change. Thus, we provide a new approach to detecting abrupt change in time series based on PDD. Further studies show that the detected results of the skewness index and kurtosis index are almost independence of the length of a subseries.
2012, 61 (3): 039202.
doi: 10.7498/aps.61.039202
Abstract +
Sea surface freshwater flux(FWF, evaporation minus precipitation) plays an important role in understanding and modeling atmosphere and ocean processes, but there exists strong disagreement different freshwater flux estimates. In this study, a weekly sea surface FWF product is reconstructed for the period from 2002 through 2008 based on the mixed layer salinity balance model for the first time, by combining the Argo data with OSCAR current data. Compared with the other precipitation and evaporation data from satellite product and TAO observations, the reconstructed FWF can capture not only the seasonal cycle of freshwater flux, but also some high-frequency features of freshwater flux. The FWF product provides a useful tool for studying the climate variation over the ocean.
2012, 61 (3): 039203.
doi: 10.7498/aps.61.039203
Abstract +
Propagating properties of a upward positive leader are analyzed by using the data from the artificially triggered lightning experiment in Shandong 2009, including the high-speed camera records and simultaneous surface electric field fast change measurements at 30 m, 60 m and 480 m from the channel. The tip of the leader is brighter, and the leader's 2-D partial propagating speed along its channel irregularly changes in a wide range. This indicates that the upward positive leader exhibits obviously stepped characteristics. The average speed is 9.8×104 m/s from 340 m to 705 m at the beginning stage of the leader propagating. The upward positive leader is initiated at a speed of 3.8×104 m/s. The partial speed shows an increasing tendency with height increasing. The electric field change waveform of upward positive leaders has a regularly stepped shape. The step interval of 28 steps recorded ranges from 14 μs to 39 μs with a geometrical mean value of 25.1 μs. The induced step length varies from 0.9 m to 3.7 m with a geometrical mean value of 1.7m. The electric field change of upward positive leaders includes the slowly stepped change and pulsed change. The high-speed camera records and electric field measurements show that the channel of the leader tip bending can eliminate or weaken the stepped property of the electric field change. The positive step leader has a similar propagating mechanism to that the negative leader has, that is a step of leader originates from a bi-directional streamer front end of the leader tip.
2012, 61 (3): 039204.
doi: 10.7498/aps.61.039204
Abstract +
Total mass conservation is a basic property of advection-diffusion differential equation. While since the difference schemes is not positive-definite, total mass is not conserved, caused by negative mass in numerical integration. Aiming at this problem, a new positive-definite renormalization scheme is proposed based on the physical meaning of negative mass. Experiments of point-source advection-diffusion show that the new renormalization scheme not only solves the positive-definite problem of advection-diffusion differential equation, but also keeps the property of total mass conservation. Compared with the renormalization scheme in the WRF model, the new positive-definite renormalization scheme has virtues of clear physical meaning and easier mannpulation.
2012, 61 (3): 039501.
doi: 10.7498/aps.61.039501
Abstract +
For the sparse-optical-synthetic-aperture telescope system, the co-phasing detection plays an important role for the realization of system's high resolution in solving out piston errors between sub-apertures. In this paper, the relationship between piston error and system's far-field intensity was analyzed based on physical principles, then the impact of piston error on system's far-field images was clarified theoretically. Furthermore, an innovative co-phasing detecting method based on the far-field images' similarity was approved for the bi-sub-aperture systems, with its feasibility, detecting deviation and dynamic range were researched by simulation. The results proved that, with this method, the piston error between the system's two sub-apertures can be soundly detected principally while immune from the problems of 2 ambiguity and direction decision that might exist within some other co-phasing detecting methods. Plus its dynamic range shown from these results, this new co-phasing detecting method provides effective references for deeper research of co-phasing detecting techniques.
2012, 61 (3): 039601.
doi: 10.7498/aps.61.039601
Abstract +
It may cause generation of plasma and induce the ESD phenomenon when the super-hypervelocity space small debris impact on the charged spacecraft surface. This is a important factor may cause spacecraft abnormity. In this article, a kind of charged material is impacted on the plasma driven accelerator and the discharging signal induced by impact is collected. The effect of the simulating test is obvious. By theoretical analysis, we verified initiatively the hidden trouble of ESD induced by space debris impacting on the charged materials.
