Vol. 62, No. 18 (2013)
2013, 62 (18): 183301. doi: 10.7498/aps.62.183301
In this paper, high-resolution vib-rotational spectrum of ultracold cesium molecule in its first excited state of 6S1/2+6P3/2 with dissociation limit 0g- long range state is obtained by cold atom fluorescence frequency modulation method. The rotation constants of different vibration energy levels of cesium molecule for vibrational quantum number from 0 to 51 are achieved. The results are in good agreement with the theoretical results given by Daniel.
2013, 62 (18): 184209. doi: 10.7498/aps.62.184209
In stimulated Raman gain and loss spectra with the D1 line of an Rb85 atomic vapor system we observe experimentally that as the detuning of the pump field becomes larger, a probe beam can exhibit a sharp transition from gain to loss. We use the dressed-state model to explain this phenomenon as the consequence of polarization interference between atoms of different velocities, which have competing contributions to the probe beam.
2013, 62 (18): 184214. doi: 10.7498/aps.62.184214
Silicon-based photonic integrated chips recently have attracted great attention and actively intervened in many applications such as optical communications, optical interconnects, and optical sensing for relevant research institutions. Photonic integrated circuits are the key block to build information infrastructures. Among of them, grating couplers play an important role in silicon photonics, due to high efficient optical coupling on/off photonic chips. Also, they have many advantages in high density photonic packaging and on-wafer testing, such as large alignment tolerances and no requirements for wafer scribing or chip polishing. This review focuses on the principles and performances of grating couplers on silicon-on-insulator substrates. In this article, we also discuss the state-of-art and the trends in the near future, with a summary of our achievements over the last few years.
2013, 62 (18): 180201. doi: 10.7498/aps.62.180201
Liu and Barabasi applied the modern control theory to the network controllability of linear dynamical systems and proposed a method to calculate the minimal set of driver node which controls the states of all nodes in a linear time invariant complex network with any topology. The network controllability model solves the computable problems of the network controllability. Facing the problem of node overloaded failure in real networks, in the paper we investigate the model of network controllability based on node overloaded failure. Through the simulation of betweenness and Weibull failure model, the results demonstrate that the difficulty in maintaining the controllability of SF network is significantly greater than that of ER network. In the target failure mechanism, even if the failure signals input rarely to the networks, they can greatly increase the difficulty of network controllability. Besides, the node failure based high betweenness centrality is more efficient than failure based high degree on damaging network controllability, which indicates the nodes with high betweenness centrality play an important role in maintaining the network controllability. Furthermore, taking the reasonable measures for different load failure model can prevent the networks from inducing a step uncontrollable phenomenon.
2013, 62 (18): 180202. doi: 10.7498/aps.62.180202
A class of isothermal throttling process with generalized mass transfer law is investigated, and the optimality condition for the minimum mass entransy dissipation of the process is obtained by applying optimal control theory. The results for special cases with mass transfer laws [g∝(Δp)m] and [g∝Δ(μ)] are further obtained based on the general optimization result, and the obtained results are also compared with other mass transfer strategies of the minimum entropy generation, constant pressure ratio and constant pressure difference. Numerical examples for the cases with the mass transfer laws [g∝(Δp)1/2], [g∝Δ(p)] and [g∝Δ(μ)] are also provided. The results obtained herein can provide some theoretical guidelines for the optimal design and operation of real throttling processes and devices.
An instrument based on Fourier transform infrared spectrometer is developed, which is capable of simultaneously measuring carbon dioxide (CO2) and 13CO2 in a single air sample with higher precision. The temperature and pressure effect on the values of CO2 and 13CO2 are investigated. Both the standard gas and air sample gas are continuously measured using this method. Precision and accuracy are improved by comparing with the measurements of standard gas after correction using the law of temperature and pressure effect on the values of CO2 and 13CO2.
2013, 62 (18): 180301. doi: 10.7498/aps.62.180301
By exactly solving the model of two two-level atoms with dipole-dipole interaction, interacting with a common environment, quantum entanglement and quantum discord of two atoms are obtained. In this paper, the influences of the non-Markovian effect of environment, the dipole-dipole interaction of two atoms and the detunings of the central frequency of the cavity and the transition frequency of the atoms on quantum entanglement and quantum discord dynamics of two atoms are comprehensively considered. The study shows that in the non-Markovian regime and the resonant case, if two atoms are initially in the entangled state, the damping of quantum entanglement and quantum discord will be remarkably suppressed. More specially, in the off-resonant case, the disentanglement time of the two atoms can be considerably prolonged. On the other hand, if two atoms are initially in the separable state, the dipole-dipole interaction can enhance the amplitude of oscillations of quantum entanglement and quantum discord in a short time, but the steady values of quantum entanglement and quantum discord cannot be changed by the dipole-dipole interaction in the long-time limit. Finally, the different influences of the dipole-dipole interaction on quantum entanglement and quantum discord also are discussed.
2013, 62 (18): 180302. doi: 10.7498/aps.62.180302
The performance of active decoy-state quantum key distribution (QKD) system with an untrusted source is compared with that of passive decoy-state QKD. The key generation rate with the change of the secure transmission distance is shown under the condition of active decoy-state (or passive decoy-state) QKD where we pick the data size to be N=1012. The security characteristics of the passive scheme are studied with statistical fluctuation of the counting rate and the intensity of the practical source. At communication wavelength 1310 nm or 1550 nm, The security range of communication distance is [73.2 km, 96.5 km] or [104.5 km, 137.9 km] respectively. This analysis will provide important theoretical parameters for practical QKD experiment.
2013, 62 (18): 180501. doi: 10.7498/aps.62.180501
In this paper, the unstable state evolution problem of the non-linear dynamical system driven by Gaussian white and colored noise is investigated. Using the eigenvalue and eigenvector theory, the expression of the approximate time-dependent solution (ρ(x, t)) is derived. The effects of parameters on ρ(x, t), mean and normalized variance are also analyzed. Numerical simulations show that 1) ρ(x, t) is a monotonic function of t and x under the certain limits of t, which increases with τ increasing, but decreases with α increasing; it is very remarkable for large τ and large α; 2) the mean of the state variable x is positive, which increases with τ increasing, but decreases with α increasing; the normalized variance of the state variable x is a non-monotonic function of the α and τ. Therefore, a phase transition phenomenon is found in this system.
2013, 62 (18): 180502. doi: 10.7498/aps.62.180502
Chaotic detection method can be used to pick out the weak sinusoidal signal submerged in noise. Three types of detection properties of this method are proposed in this paper, i.e., sharp change ability of phase diagram, maintenance zone of chaos, and the sufferance with noise of the chaos critical point. After analyzing the factors influencing these three properties, two different chaotic systems are compared according to the three properties.
2013, 62 (18): 180503. doi: 10.7498/aps.62.180503
The pitchfork bifurcation and vibrational resonance are investigated in this paper. Based on the method of separating slow motion from fast motion, the equivalent equation to the slow motion is obtained. Then, the pitchfork bifurcation is studied. The results show that the amplitude of the high-frequency signal can induce the subcritical pitchfork bifurcation, while both the frequency of the high-frequency signal and the value of the fractional-order can induce supercritical pitchfork bifurcation. The pattern of the vibrational resonance depends on the pitchfork bifurcation. The vibrational resonance presents double-resonance pattern when the pitchfork bifurcation occurs. Or else, the vibrational resonance presents single-resonance pattern. The analytical predications are in good agreement with the numerical calculation results, which verifies the validity of the theoretical results.
Finite-time stability control of permanent magnet synchronous motor chaotic system with parameters uncertain
2013, 62 (18): 180504. doi: 10.7498/aps.62.180504
A novel active finite-time stability controller is presented for permanent magnet synchronous motor chaotic system considering parameters uncertain. The controller combines with active control and finite-time stability theory. Adjusting the parameters of terminal attractor, this controller has not only strong robustness but also good responsiveness. Simulation results show that the proposed controller has superior performance than traditional one.
Modified function projective synchronization for a class of partially linear fractional order chaotic systems
2013, 62 (18): 180505. doi: 10.7498/aps.62.180505
In this paper, a method of modified function projective synchronization for a class of partially linear fractional order chaotic systems is proposed. This kind of system can be constructed by single variable coupling response system. The modified function projective synchronization controller is designed by Routh-Hurwitz conditions. Theoretical analyses and numerical simulations of two chaotic systems verify the effectiveness of the proposed method.
Gamma-distributed maximum a posteriori despeckling algorithm of high-resolution synthetic aperture radar images
2013, 62 (18): 180701. doi: 10.7498/aps.62.180701
In order to solve the problem that the traditional Gamma-distributed maximum a posteriori despeckling algorithm cannot effectively preserve the point target in the homogeneous region, nor effectively keep the weak edge, and nor efficiently suppress the speckle in the strong edge region, the Gamma-distributed maximum a posteriori despeckling algorithm with prior parameter estimation based on second-kind statistics is proposed for high-resolution synthetic aperture radar images. Using the Mellin convolution and the multiplicative model of speckle, the parameters of the Gamma prior distribution are accurately estimated from the first two log-cumulants of the observed image. The proposed algorithm has the analytical filtering output, and it is easy to implement. Despeckling experiments on high-resolution synthetic aperture radar images of agricultural field and urban region demonstrate that compared with the traditional Gamma-distributed maximum a posteriori despeckling algorithm, the proposed one can effectively preserve the point target in the homogenous region, effectively retain the weak edge, and efficiently suppress the speckle in the strong edge region.
Multi-scale analysis of nanoscale contact process between spherical indenter and single crystal aluminium
2013, 62 (18): 180702. doi: 10.7498/aps.62.180702
Based on the quasicontinuum method and repulsive force-field approach, a muti-scale modeling of nano-contact process between rigid spherical indenter and surface of single crystal aluminium is established. The corresponding load-depth, graph of atomic state, and moire pattern of displacement are obtained, from which the arrangement of atoms and the effects of the shape of indenter on the nucleation and emission of dislocations in the contact process are studied. Therefore micro-mechanisms of deformation are analyzed. The result shows that due to the fact that the direction of force on atoms that contact the indenter is constantly changing with the increase of contact depth, the corresponding load-depth shows that step increases which is different from that of the square indenter with the response of the underlying crystal. Due to the indenter geometry, the close packed planes under both sides of indenter slip partially lead to Shockley partial dislocations. In the process of disengagement, the elastic recovery is accomplished as the atoms move up with indenter. The residual depth is 0.3 nm, which is close to the magnitude of the Burgers vector, 0.285 nm.
Calibration of pressure to 35 GPa for the cubic press using the diamond-cemented carbide compound anvil
2013, 62 (18): 180703. doi: 10.7498/aps.62.180703
In the present study, we analyse the mechanical structure for the two-stage anvil cell, and design the two-stage high pressure cell using diamond-cemented carbide compound as anvil-material. The diamond-cemented carbide compound material is synthesized using the 6×2500 ton cubic press in our laboratory. We sinter diamond/Co layer (Φ30 mm×10 mm) on a WC-cobalt substrate (Φ30 mm×13 mm) at high pressures and temperatures, then, we obtain the cubic anvils from the sintered cylindrical chunks by wire-electrode cutting. The diamond-cemented carbide compound anvil has three advantages over the traditional sintered diamond anvil: first, a scaled-up version of the sintered diamond anvil could be obtained by sintering the diamond/Co layer on a WC-cobalt substrate; second, the diamond-cemented carbide compound anvil is machined easily compared with the sintered diamond anvil; and third, the experimental cost using the diamond-cemented carbide compound anvils is much lower than using the sintered diamond anvil. Using the diamond-cemented carbide compound anvil, we design the two-stage 5.5/1.5 (octahedral edge-length/anvil truncation edge-length, in millimetre) assemble. Pressure calibration at room temperature is performed for the 5.5/1.5 assemble using the phase transitions of Zr (α-ω, 7.96 GPa; ω-β, 34.5 GPa) under high pressures. The pressure range of the two-stage apparatus besed on hinge-type cubic press is extended from 20 GPa to about 35 GPa using the 5.5/1.5 assemble. The pressure calibration for the two-stage apparatus using diamond-cemented carbide compound anvil is ongoing in our laboratory. We believe that the pressures above 50 GPa could be achieved using these anvils.
2013, 62 (18): 180704. doi: 10.7498/aps.62.180704
Electron spin is very important for investigating magnetic properties of nano-structure surface on the atomic scale. Magnetic exchange force microscope (MExFM) which is a significant method of measuring exchange force of electron spin, is adopted. However, the external magnetic field is necessary for the MExFM, which will damage the structure of the sample surface; further, cross-talk between topography and spin information becomes serious for separating the two signals in MExFM measurement. These shortcomings will restrict the application of MExFM. In order to solve these problems, we develop a new method to separate the topography from the spin information using ferromagnetic resonance by microwave radiation combined MExFM and atomic force microscopy. We demonstrate that the topography and spin information can be completely separated from each other using this method theoretically and experimentally. MExFM using ferromagnetic resonance effect is very useful for developing spintronic devices and new-generation magnetic materials.
Retrieving vertical profile of aerosol extinction by multi-axis differential optical absorption spectroscopy
2013, 62 (18): 180705. doi: 10.7498/aps.62.180705
Using the oxygen dimer (O4 information measured by multi-axis differential optical absorption spectroscopy (MAX-DOAS)), an inversion method of vertical profile of aerosol extinction based on nonlinear optimal estimation algorithm is developed. At first we study how to calculate some parameters (weighting function, the covariance matrices of measurement and a priori) of the algorithm and design nonlinear iteration strategy suited to Chinese region where aerosol usually shows rapid variation and high load. Then this inversion method is verified by computer simulation combined with discussion about error source in three typical cases of low, high and elevated aerosol. After that a continuous observation is reported in the city of Hefei. The aerosol optical depth (AOD) derived from MAX-DOAS is compared with that of CE318 sun photometer and the correlation coefficient is 0.94. The total relative error of AOD is about 20%. In addition the aerosol extinction in the lowest altitude (0-0.3 km) is compared with that of visibility meter and the correlation coefficient is about 0.65. The total relative error of surface-near aerosol extinction is about 25%. Both of simulation verification and comparison experiment indicate that the inversion method can well rebuild the vertical profile of aerosol extinction in the troposphere.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
Based on the Regge phenomenology, we first study the mass relations for six mesons involving three flavors in one spin-parity multiplet. Using the examined mass relation, mass of the unobserved vector doubly heavy charm-bottom Bc*(13S1) is calculated. Masses of the unobserved radial excited vector (23S1) mesons and the orbital excited 13G5 meson nonet are given. Our predictions are discussed. We suggest searching Bc* near 6355 MeV. D(2600) and Ds1(2700) can be considered as candidates for nc(23S1 and sc(23S1) dominated states, respectively. We suggest searching B*(2S), Bs*(2S) and Bc*(2S) near 5812, 5917 and 6896 MeV, respectively. We suggest restudying 5(2350) near 2259 MeV, searching 5(13G5) near 2438 MeV and identifying 5(2250) as isoscalar member of 13G5 nonet. The results may be profoundly useful for the JP assignment of related states and the discovery of the unobserved excited mesons.
2013, 62 (18): 182801. doi: 10.7498/aps.62.182801
A quantitative phase-field model is developed to study the evolution of vacancy cluster in Fe. Total energy of the system is constructed based on the assumption of ideal gas state equation, and an approach to linking the computational parameters in the phase-field model to the experimental properties of Fe is provided. Such a phase filed model is employed to quantitatively investigate the nucleations, growths, and coalescences of voids in single and polycrystalline Fe. The effects of grain boundary on voids evolution are also investigated. These results provide a way of further studying the evolution behaviors of both H/He gas atoms and voids in Fe.
ATOMIC AND MOLECULAR PHYSICS
2013, 62 (18): 183101. doi: 10.7498/aps.62.183101
According to Einstein’s equation and Marcus charge transport model, the structures and charge transport rates of six truxene derivative molecules are calculated using the density functional theory at B3LYP/6-31g** theoretical level. The results show that the hole and electron transport rates of the six truxene derivative molecules are 0.018-0.062 and 0.055-0.070 cm2·V-1·s-1, respectively, and the truxene derivative molecule with 3, 8, 13-three octyloxy chains can be designed into dual polarity transport materials. In truxene derivative molecules with three alkoxy chains, introduction of three methoxyl or hydroxyl group could reduce hole and electron transport rate. The introduction of electron-donating groups or conjugated groups would reduce the energy gap of truxene derivative molecules, which meet the requirements for the organic semiconductor.
Influence of Ξ-type three-level atomic Bose-Einstein condensate on the squeezing properties of light field
2013, 62 (18): 183201. doi: 10.7498/aps.62.183201
The Hamiltonian operator of a system of Ξ-type three-level atomic Bose-Einstein condensate interacting with single-mode squeezed coherent light field is improved in terms of the lattice-liquid model, and the squeezing properties of light field in this system are studied. The results show that two quadrature components of light can be squeezed periodically. The maximum depth of squeezing is determined by the interaction intensity between light field and atoms and the initial squeezing factor of light, and squeezing period is correlated with the frequency of the light field.
2013, 62 (18): 183302. doi: 10.7498/aps.62.183302
The pure CaWO4 and 1%Eu3+ doped CaWO4 phosphors are successfully prepared by the conventional solid state reaction method. The photoluminescence (PL) spectra, decay cures, and time-resolved PL spectra are measured at depend on different temperatures. Fluorescence spectra at room temperature (300 K) and low temperature (10 K) show that these two samples each have a broad band at about 430 nm, originating from the WO42- groups under 240 nm excitation, while the CaWO4:Eu3+sample exhibits the characteristic emission of Eu3+ corresponding to 5D0→7F1, 2, 3,4 transitions due to the absorbed energy transfer from WO42- groups to Eu3+ ions. And the red light at 616 nm of CaWO4: Eu3+ can be excited efficiently by UV (395 nm) and blue (465 nm) light. The decay curves at 300 K illustrate that the lifetime of WO42- group in pure CaWO4 is about 8.85 s but is shortened to 6.27 μs after Eu3+ions have been doped, which is a further good evidence for demonstrating the existence of WO42-–Eu3+ energy transfer process. The energy transfer efficiency (ηET)) and rate (ωET) between WO42- and Eu3+in CaWO4: 1%Eu3+ are 29.2% and 4:65×104 s-1 respectively, when T = 300 K. The energy transfer process is studied in detail by the time-resolved PL spectra, and the lifetime for the appearance of Eu3+ emission in CaWO4 decreases monotonically as temperature increases from 10 K to 300 K. The temperature dependence of luminescence decay time is performed and the results indicated that the lifetime of Eu3+ increases in a temperature range of 10-50 K, when the temperature is more than 50 K, thermal quenching of Eu3+ begins and the lifetime is shortened. However, the lifetime of WO42- reduces constantly with the increase of temperature.
Triple differential cross section for the ionization of Ar(3p) by low-energy electron impact in the coplanar asymmetric geometry
2013, 62 (18): 183401. doi: 10.7498/aps.62.183401
(e, 2e) triple differential cross sections for the ionization of Ar (3p) by 70.8 eV electron impact are calculated in the coplanar asymmetric geometry using the modified distorted-wave Born approximation, and compared with the recent experimental data of Ren et al. [Ren et al. 2012 Phys. Rev. A 85 032702]. The results show that electron exchange effect and post-collision interaction play an important role in the (e, 2e) process of low-energy electron impact.
Influence of screening effect on double differential cross section and single differential cross section for (e, 2e) process of helium
2013, 62 (18): 183402. doi: 10.7498/aps.62.183402
The double differential cross sections for electron impact single ionization of helium at incident energies of 32.5, 36.5 and 40.7 eV are calculated by using the DS3C model. The calculated results are compared with the experimental date. The exchange effects are discussed. The single differential cross section for electron impact single ionization of helium is obtained by integrating the double differential cross sections over the angle of the ejected electron. The single differential cross sections of helium at incident energies of 32.5, 36.5, 40.7 and 50 eV are calculated by using the 3C model and the DS3C model. The calculated results are compared with the experimental date. The structure of the cross section is analysed and the contribution of exchange effect to the corss section is discussed.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
Ray optics calculation of axial force exerted by a highly focused Gaussian beam on a left-handed material sphere
2013, 62 (18): 184201. doi: 10.7498/aps.62.184201
Theoretical expressions and numerical calculations of axial forces for a left-handed material sphere, exerted by a highly focused Gaussian beam, in the ray optics regime are presented. Comparison is made between a dielectric sphere and a left-handed material sphere. The position at which the maximal magnitude of the axis force occurs is determined by the beam and the sphere parameters. A very strong axial force can be obtained from a low refractivity of a left-handed material sphere, exerted by a highly focused Gaussian beam, which is hundred times larger than that of a dielectric sphere.
2013, 62 (18): 184202. doi: 10.7498/aps.62.184202
Using the generalized nonlinear Schrödinger equation, we present a numerical study of trapping of dispersive waves by solitons during femtosecond pumped supercontinuum generation in photonic crystal fiber with single or double zero dispersive wavelength. Numerical simulation results show that the generated supercontinuum in photonic crystal fiber with two zero dispersive wavelengths includes both blue-shifted dispersive wave (B-DW) and red-shifted dispersive wave (R-DW) while the generated supercontinuum in photonic crystal fiber with single zero dispersive wavelength has only blue-shifted dispersive wave. We find a novel phenomenon that not only B-DW but also R-DW can be trapped by solitions via four-wave mixing when the group-velocity matching between the soliton and the dispersive wave is satisfied, thus leading to the generation of new spectral components. In order to clearly display the evolution of soliton trapping of dispersive waves, the spectrogram of output pulses is observed using cross-correlation frequency-resolved optical gating technique.
2013, 62 (18): 184203. doi: 10.7498/aps.62.184203
Based on theoretical analysis, in this paper studied are the low pass and band stop filter effects of the μ-negative materials/double positive materials/μ-negative materials (MNG-DPS-MNG) surface plasmon polaritons waveguide with branch defect. The research results show that the defect is equivalent to a sub wavelength resonator. The central frequency of the band stop filter is determined by the resonator length and it is independent of the position where the resonator is located in the MNG region. The transmission dips of the waveguide are closely related to the coupling distance. So the filter characteristics of the surface plasmon polariton waveguide can be adjusted by changing the resonator length and number and the coupling distance. The experimental results are in good agreement with simulation results. These properties will have potential application value in the tunable single channel or multi-channel band stop filters.
2013, 62 (18): 184204. doi: 10.7498/aps.62.184204
A single shot PIE (ptychographic imaging engine) imaging method is proposed to overcome the disadvantages of common PIE algorithm. In this proposed method, a multiple beam illumination obtained with a cross grating is used to illuminate the object studied, and a CCD camera is adopted to record the diffraction pattern array of all the illumination beams simultaneously. The phase and the modulus images of the object can be faithfully reconstructed with stand PIE computation algorithm from the recorded data.
2013, 62 (18): 184205. doi: 10.7498/aps.62.184205
The quality of the image in ghost imaging with thermal light is of great importance in practical applications. Through theoretical analysis and simulation, we find that the intensity fluctuations of the field can greatly influence the visibility of thermal ghost imaging. According to this, we suggest a new scheme to improve the visibility by appropriately scaling the intensity and variance of the incident thermal field. The influence of this method on the signal-to-noise ratio is also studied. In addition, comparison is made with the high-order correlation ghost imaging, another means adopted in recent years to increase the visibility. Our analysis should help promote our understanding of thermal ghost imaging.
2013, 62 (18): 184206. doi: 10.7498/aps.62.184206
A different method of laser Doppler shift measurement is proposed. By using the sinusoidal phase-modulation, the plus and minus one-order sidebands beside the original frequency component in signal light are generated. And a beat frequency signal with fixed-frequency is present when the amplitude and phase of the modulated light are turned with Fabry-Perot interferometer. The characteristic of the amplitude of this beat frequency signal changing with the frequency is used to measure the Doppler shift. By theoretically analyzing, it can be concluded that this method can possess the advantages of both the normal coherent and non-coherent methods and also has the merits of high measuring accuracy and easy fabrication. The validity and feasibility of this method are verified experimentally, and its measurement accuracy is found experimentally to be one order of magnitude higher than that of the normal non-coherent method.
Application of machine vision to the measurement of the effective d31 coefficient in laser interferometry
2013, 62 (18): 184207. doi: 10.7498/aps.62.184207
A novel method based on machine vision is proposed for measuring the effective d31 coefficient. Based on the best estimation of gray scale of interference pattern, the sensitivity of the twin-beam interferometry is significantly improved in comparison with previously reported system. Firstly, the interference pattern grabbed by machine vision system is extracted using the algorithm developed in this work. Secondly, using gray-scale pattern with 256 gray-levels the measurement accuracy of the interferometric optical path difference of the interferometer can reach 1/1024 of the wavelength of the laser theoretically. So the experimental results of a PZT pipe in the method are greatly accurate.
2013, 62 (18): 184208. doi: 10.7498/aps.62.184208
All-optical tunable slow light technology has promising applications in all-optical network and optical information process. Tunable slow light based on stimulated Brillouin scattering is experimentally investigated, using highly nonlinear microstructured fiber which is designed and drawn by ourselves. The experiment setup is composed of single pump and a single-stage delay. When the pump power reaches 162.6 mW, a maximum delay of 76 ns, equal to 0.76 pulse width, is achieved in the highly nonlinear microstructured fiber of 120 m in length. In addition, by adjusting the pump power, the tunable slow light can be realized. This scheme of slow light has advantages such as large delay, being all-optical tunable and compatible with optical communications systems.
2013, 62 (18): 184210. doi: 10.7498/aps.62.184210
Evolutions of ultrashort pulse in time and frequency domain are modeled based on the nonlinear schrödinger equation by predictor-corrector split-step flourier method when the pulse travels in an all normal dispersion photonic crystal fiber. And the influences of the pulse duration and energy on generated continuum are also investigated. It is shown that a single pulse is maintained in the time domain and that a larger spectrum broadening is achieved with higher peak power. When the fiber is pumped by an unchirped Gaussian pulse centred at 1060 nm with duration about 50 fs and energy 1.5 nJ, good continuum is available after only 12 cm traveling distance with fine continuity and coherence. And a perfect continuum is achieved with duration about 15 fs and spectrum about 700 nm after pulse compression by a pair of prisms.
2013, 62 (18): 184211. doi: 10.7498/aps.62.184211
Knowledge of crystallization behavior and kinetics mechanism is essential to achieve the controllable crystallization. Surface crystallization of 20GeS2·80Sb2S3 chalcogenide glass is realized using differential scanning calorimeter technique and heat treatment method. An about 40 μm thick Sb2S3 crystal layer is precipitated after heat treatment at 268℃ (Tg+30℃) for 60 h. Then, non-isothermal method is employed to theoretically analyze the crystallization kinetics of this glass sample. Crystallization activation energy Ec is calculated to be (223.6±24.1) kJ·mol-1, and crystallization rate constant K at 268℃ was obtained to be 1.23×10-4 s-1, indicating that the crystallization of 20GeS2·80Sb2S3 glass is more difficult than that of other chalcogenide glass system, such as GeS2-Ga2S3. The crystal growth index, m and crystal growth dimensionality, n both are equal to 2, which suggests that the crystallization of Sb2S3 glass phase is of 2D growth process. This work would contribute to the fabrication of Sb2S3 crystallites embedded chalcogenide glass-ceramics.
Effect of uniaxial stress on photon localization of one-dimensional photonic crystal with a mirror symmetry
2013, 62 (18): 184212. doi: 10.7498/aps.62.184212
In this paper, the transfer matrix method is used to study the characteristics of the photon localization in the mirror heterogeneous structure which has three periods and one-dimensional photonic crystal in uniaxial stress change. In a mirror structure triply-periodic photonic crystal system, its mirror structure destroys the orderliness of the photonic crystal and produces a defect state, so the transmission peaks of a photon localization appear in the photonic band gap wider center. The study shows that when a uniaxial stress is exerted on the mirror structure with three-periodic photonic crystal, the photon localization transmittance peak dramatically changes with the stress. When a weak external mechanical stress is applied to the photonic crystal, photonic crystal forms a tensile strain which induces the change in the photonic crystal structure and significantly affects the rate of the transmittance peak transmittance of photon localization. The results show that the transmission peak transmittance is significantly influenced by the uniaxial stress. These features provide a theoretical reference for the design of ultra-high-sensitivity pressure sensor with the photonic crystal structure.
2013, 62 (18): 184213. doi: 10.7498/aps.62.184213
Lateral coupled-mode theory of optical waveguide includes orthogonal coupled-mode theory and nonorthogonal coupled-mode theory. However, the two kinds of coupled-mode theories do not have unified analytical solutions. And they both do not deal with the asymmetric coupling power of unmatched-coupled waveguides deeply. On the one hand, a new kind of nonorthogonal coupled-mode equation is derived from the Helmholtz wave equation in this paper. And both of the orthogonal coupled-mode equations and the nonorthogonal coupled-mode equations are processed and solved uniformly. As a result, a unified solution is obtained. On the other hand, the asymmetric coupling power of unmatched-coupled waveguides is studied in detail, based on the obtained solution. The calculated results show that both of the maximum mutual-coupling power and the minimum self-coupling power can be approximated by the unified solution.
2013, 62 (18): 184215. doi: 10.7498/aps.62.184215
A novel bend-resistant large-mode-area photonic crystal fiber with a triangular-core is proposed in this paper. In this structure, the circle air holes with uniform size are used to reduce the difficulty in fabrication. At a wavelength of 1.064 μm, mode field area of the fundamental mode is 1386 μm2 in a straight state, and it is 1153 μm2 at a bending radius of 30 cm. The decrement of mode field area in a bent state is only 16.85% compared with that in a straight state. When a bending radius is 30 cm, bending loss of the fundamental mode is 0.087 dB/m while bending loss of the second order mode is higher than 1.5 dB/m. The bending loss difference between fundamental mode and second order mode is large enough to ensure that the fiber conforms to the single mode operation conditions. Furthermore, when the fiber is bent with a bending radius of 30 cm, the bending orientation angle can be extended to ±180°, breaking the limit of the bending orientation. The fiber with large mode area, small decrement in mode field area, low bending loss and low sensitivity of bending orientation makes a great contribution to the miniaturization of high power fiber laser and fiber amplifier.
A selective mapping peak-to-average power ratio reduction algorithm without side information for underwater acoustic multiple-input multiple-output orthogonal frequency division multiplexing communication
2013, 62 (18): 184301. doi: 10.7498/aps.62.184301
To overcome the disadvantage of side information transmission, an improved selective mapping algorithm is proposed for peak-to-average power ratio reduction of multiple-input multiple-output orthogonal frequency division multiplexing communication via underwater acoustic channels. The scrambling patterns are carried by comb pilot with different distributions. And taking advantage of neritic channel sparse characteristics, the scrambling patterns can be distinguished without side information. The results of experiment performed with numerical simulation and tank demonstrate that the proposed algorithm can distinguish between scrambling patterns without degrading the performance, abate the burst noise effect, and significantly enhance the quality of the system.
2013, 62 (18): 184302. doi: 10.7498/aps.62.184302
The performance of Capon beamformer degrades sharply in the presence of array steering vector mismatch. To solve this problem, a robust beamforming algorithm based on semi-definite programming and rank-one decomposition is proposed, which improves the robustness of the adaptive beamforming by estimating an actual steering vector. The constraints for estimating the steering vector are deduced under the requirement that the estimate does not weaken the ability to suppress interference and noise, and the analysis shows that the approach to formulating constraint using matrix pre-filter is reasonable. The optimization problem is constructed and converted into a semi-definite relaxation problem, and rank-one decomposition technique is adopted in order to obtain the optimal solution. The simulation results demonstrate that compared with the existing algorithms, the proposed algorithm offers high SINR (signal to interference plus noise power ratio) and accuracy of power estimation, with the sole prior information about the angular vector in which the actual signal lies.
Solution and analysis of non-Fourier heat conduction in a plane slab under arbitrary periodic surface thermal disturbance
2013, 62 (18): 184401. doi: 10.7498/aps.62.184401
In this paper, the non-Fourier heat conduction in a plane slab under arbitrary periodic surface thermal disturbance is solved analytically. Hyperbolic heat conduction equation is employed to describe this problem involving high-rate change of temperature. Firstly, when the plane slab surface is subjected to a sudden heat flux change or a harmonic heat flux change, the analytic solution of this problem is found by using the separation of variables method and Duhamel’s principle. On this basis, when the plane slab surface is subjected to an arbitrary periodic heat flux change, the analytic solution of temperature field is obtained by using the Fourier series and the principle of superposition. Using the obtained analytical solution, the temperature profiles of the plane slab are analyzed, and the differences between the temperature response obtained by using non-Fourier heat conduction model and that obtained by using Fourier model are discussed. This solution can be applied to more realistic periodic boundary conditions in technology.
2013, 62 (18): 184501. doi: 10.7498/aps.62.184501
In this paper, the multi-disperse systems composed of 2048 frictionless particles with different size polydispersities are simulated by using the distinct element method, and effects of size polydispersity on mechanical and geometrical properties of these systems are studied under isotropic confining. The result shows that changing polydispersity can qualitatively affect the coordination number, shear modulus, static structure factor and orientational order correlation function, but it does not influence the cumulative force distribution. At small wave number k, static structure factor of mono-disperse systems shows the power scaling law S(k)∝0.2k-4/3. Moreover, the peak of orientational order correlation function exhibits an exponent scaling law g6 (r)∝ae-r/ξ6, and the scaling exponent ξ6 decreases with polydispersity increasing.
2013, 62 (18): 184701. doi: 10.7498/aps.62.184701
Using dimensional analysis and experimental technique, the aero-optical effect for a compressible mixing layer around optical side window is investigated. According to the theoretical analysis, we find that time-averaged boresight error increases with the increase of convective Mach number (Mc). Moreover, we also present the relations between time-averaged boresight error (BSE) and Reynolds number, shear stress at interface between mixing layer and free stream, free stream velocity ratio and density ratio. The experimental results from a thin beam light passing through compressible mixing layer verify the theoretical result between time-averaged BSE and Mc.
Experimental investigations on structures of supersonic laminar/turbulent flow over a compression ramp
2013, 62 (18): 184702. doi: 10.7498/aps.62.184702
Experimental investigations of supersonic laminar/turbulent flow over a compression ramp are carried out in a Mach 3.0 wind tunnel, the angles of ramp are 25 degrees and 28 degrees. Fine structures of holistic flow field and local regions are visualized via nanoparticle-tracer based planar laser scattering (NPLS) technique, some typical flow structures such as boundary layer, shear layer, separation shock, recirculation zone and reattachment shock are visible clearly, and the wall pressure coefficient of laminar flow is measured. The angle of separation shock and reattachment shock, the development of boundary layer after reattachment are measured by time-averaged flow field structures. The analyses of time-relevant NPLS images reveal the spatio temporal evolution characteristics of flow field. The experimental results indicate that when the ramp angle is 25 degrees, a typical separation appearing in the supersonic laminar flow with boundary layer increases and is converted into turbulence quickly, at the same time, a shock is induced by developing boundary layer; K-H vortexes, shear layer and compression waves arise in the flow field. But the supersonic turbulent flow does not show separation, and the turbulent boundary layer always adhers to the wall. When the ramp angle is 28 degrees, the range of recirculation zone expanded obviously in supersonic laminar flow which is separated further, induces shock and separation shock moves upstream, reattachment shock moves downstream. Therefore the structures of separated region is complicated. By comparison with laminar flow, the range of recirculation zone in supersonic turbulent flow is obviously small, boundary layer increases slowly, and there are not any induced shock, K-H vortexes, compression waves in the flow field. The structures of separated region is simple, but the strength of separation shock is much stronger.
2013, 62 (18): 184703. doi: 10.7498/aps.62.184703
The phenomenon of liquid drop impact on wetted spherical surfaces with low impact velocity is observed using a high speed digital camera at 10000 frames per second. Drop rebound, partial rebound and spreading are observed and analyzed, considering the effect of viscosity. Influences of the sphere diameter, impact velocity and viscosity on the spreading characteristic parameter are discussed quantitatively. The experimental observations show that the drop rebound and partial rebound phenomena may occur at large viscosity and low impact velocity, which cannot be observed at small viscosity. The spreading area can be increased by increasing impact velocity. The results also reveal that the spreading factor increases with viscosity decreasing. At the sphere diameters ranging from 4 mm to 20 mm, it is found that with the increase of the sphere diameter, the spreading factor will be increased.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2013, 62 (18): 186101. doi: 10.7498/aps.62.186101
Molecular dynamics simulations are performed on nano clusters with 500 nickle atoms (Ni500) to determine the structure and dynamics in the isothermal crystallization using embed atom model potentials. Through the study of nano Ni cluster dynamic behavior, we find that multi-step crystallization process of Ni500 is at temperatures far below the melting temperature (Tm), whereas one-step crystallization process is at the temperatures just below Tm. Multi metastable states are observed before Ni500 becomes fully crystallized in multi-step crystallization process. We find that atom rearrangements take not only string-like cooperative motion manner but also other collective motion manner.
2013, 62 (18): 186102. doi: 10.7498/aps.62.186102
The electron transport properties of the system consisting of the zigzag graphene nanoflake doped with nitrogen and boron atoms connected to two Au electrodes through S-Au bonds are investigated theoretically. The results show that a nanoflake doped with nitrogen and boron atoms at edges has poor rectifying performance. While the system consisting of two pieces of graphene flakes doped by boron and nitrogen atoms, respectively, and linked with an alkane chain, shows good performance. And the significant effects of the doped sites on the current-voltage characteristics are observed. The mechanisms for these phenomena are explained by the different shifts of transmission spectra, the different spatial distributions of the molecular projected self-consistent Hamiltonian eigenstates. The negative differential resistance behavior results from the biase induced shifts of the energy level and change of the resonance transmission spectra, and the suppression of the relevant channels at some bias voltages.
Monte Carlo simulations of microstructure and texture evolution during annealing of a two-phase titanium alloy
2013, 62 (18): 186103. doi: 10.7498/aps.62.186103
Nucleation and grain growth are important phenomena during static recrystallization of metallic materials and both processes have significant influences on the material properties. The Monte Carlo (MC) method has been widely used to simulate static recrystallization behavior during annealing of metallic materials. In this study, an MC model for static recrystallization of two-phase alloys is proposed by extending an existing MC model, through the introduction of the nucleation stage to account for the grain growth by both consuming deformed grains and competing with other recrystallized grains. The two-phase MC model is used to simulate the evolution of microstructure and texture during annealing of a TC11 (Ti-6.5Al-3.5Mo-1.5Zr-0.3Si) titanium alloy, accounting for initial grain morphology, phase compositions, crystallographic orientations, and relative values of strain stored energy determined by electron back-scattered diffraction. The results show that the model can reproduce satisfactorily the recrystallization and grain growth behavior in annealing. Compared with the β phase, the α phase depicts a lower recrystallization rate but a higher grain growth rate: the former difference can be mainly attributed to the lower strain stored energy in the α phase before annealing, whereas the latter suggests that the grain growth in the system is significantly influenced by the grain morphology, distribution of grains, and relative volume fractions of the two phases in the initial condition. Due to the influence of heterogeneous nucleation accounted for in the model, the simulated recrystallization rate deviates considerably from that described by the Johnson-Mehl-Avrami-Kolmogorov equation. The simulation also indicates that for both phases the textures strengthen with little changes in their basic features during annealing.
2013, 62 (18): 186201. doi: 10.7498/aps.62.186201
In the NiTi shape memory alloys (SMAs), the macro-mechanical deformations and the microstructural evolutions at different strain-rates (0.001-1200 s-1) are investigated. It is found that the detwinning stress of martensitic twin increases with strain-rate increasing, which indicates that the detwinning stress has the positive strain-rate dependence. A large number of detwinning regions are found in the NiTi specimen which is deformed at the strain-rate of 10 s-1 under tension. However, with the strain-rate further increasing up to 100 s-1 and 1200 s-1, no detwinning region is observed and many twins still exist. It is shown that the detwinning rates of martensitic twin in NiTi SMAs are in a range of 10-100 s-1. Simultaneously, thermally-induced austenite is detected in the NiTi specimens deformed at high strain-rates (≥qslant10 s-1). It is ascribed to the fact that there is a change from the isothermal process to the adiabatic process when the tensile strain-rate goes up to a critical value. Additionally, a small shoulder peak is detected in differential scanning calorimeter peak of 1200 s-1 strain-rate specimen, indicating that the two-stage phase transformation occurs.
2013, 62 (18): 186202. doi: 10.7498/aps.62.186202
Molecular dynamics simulations of polyimide/copper-nanoparticle composites are implemented to calculate the morphological structures, thermodynamic and mechanical properties, and to investigate their relationships with the nanoparticle dimension and simulation temperature. The results demonstrate that polyimide/copper-nanoparticle composites are of isotropic amorphous structures, in which the copper nanoparticles combine with polyimide matrix due to van der Waals effect and multi-layers of atoms on nanoparticle surface change into amorphous configurations, forming interface layers between them. The interface regions shrink and expand respectively with increased nanoparticle dimension and temperature. The polyimide/copper-nanoparticle composites exhibit the explicit increase of isometric heat capacity with larger nanoparticle dimension in moderated temperature dependence, resulting in lower heat capacities at relatively low temperature for nanocomposites with relatively small nanoparticle size, compared with polyimide system. The thermal pressure coefficients of polyimide/copper-nanoparticle composites are distinctly higher than those of polyimide system, and increase substantially with enlarged nanoparticle dimension and reduce slightly with elevated temperature. The thermodynamic properties of polyimide/copper-nanoparticle composites manifest obvious scale-effect and distinctly higher temperature stability than polyimide system. The mechanical properties of polyimide/copper-nanoparticle composites represent isotropic elastic constant tensors with distinctly lower Young modulus and Poisson ratio than those of polyimide system, which decrease and increase respectively with increasing simulation temperature, exactly contrary to polyimide system and with substantially higher temperature stability of Young modulus. The composites with larger nanoparticle dimension exhibit considerably higher Poisson ratio with slight change of Young modulus, indicating the remarkably different mechanical properties of new nanocomposites with Cu nanoparticle filler.
The first-principles technique is employed to determine the adsorption system of the CO monolayer on Cu(100) surface under the coverages of 1.00 ML, 0.50 ML and 0.25 ML. The calculation shows that the CO dimer is not stable enough. The atomic structures of CO monolayer on virtual Cu(100) surface and in the adsorption system on Cu(100) surface are proposed. In the CO/Cu(100) adsorption system, under the coverage of 1.00 ML the top and bridge sites are both stable, but the hollow site is not stable enough; under the coverages of 0.50 and 0.25 ML three adsorption sites are all stable. A comparison of the structure of the CO monolayer between before and after adsorption on Cu(100) surfrace shows that the interaction between the CO molecule and Cu(100) is clearly stronger than that between the CO monolayers.
2013, 62 (18): 186302. doi: 10.7498/aps.62.186302
Anharmonic lattice dynamics method is employed to investigate the phonon frequency and relaxation time without any fitting parameters. The phonon relaxation time is used in Boltzmann transport equation to predict the lattice thermal conductivity of solid argon between 10 K and 80 K, and the results agree very well with experimental data. The effects of calculation parameters on the prediction accuracy are also analyzed, including mesh size of the reciprocal lattice points, and the broadening factor of delta function. The contribution of each individual phonon mode to the thermal conductivity is investigated. It is found that higher frequency phonons contribute more to the thermal conductivity at higher temperature, which is consistent with previous theoretical results.
2013, 62 (18): 186501. doi: 10.7498/aps.62.186501
The contributions of phonon and electron transport to the thermal conductivities of Cu and Ag nanowires are studied theoretically. The effects of surface and grain boundary scatterings are involved. The embeded atom method is employed to express the interatomic potential of nanowires. While the molecular dynamic simulation and Green-Kubo formulation are used to obtain the lattice thermal conductivity, a model derived from Boltzmann transport equation and the Wiedemann-Franz relation are used to calculate electronic thermal conductivity. In addition, diffuse mismatch model is used to calculate thermal resistance of grain boundary to modify the lattice thermal conductivity, meanwhile, Mayadas-Shatzkes model is used to consider the influence of grain boundary scattering on the electronic thermal conductivity. By coupling the lattice and electronic thermal conductivity, the effective thermal conductivity of nanowire is obtained. On this base, the influences of size and temperature are analyzed. It turns out that Cu and Ag nanowires have a similar tendency in the thermal conductivity. The contribution of electron transport to the thermal conductivity of nanowire is dominated, but the contribution of phonon transport cannot be ignored on the nanoscale. The thermal conductivity of nanowire decreases due to the grain boundary scattering. And it decreases with temperature increasing or size decreasing. The contribution of phonon transport becomes more important in the case of smaller size.
2013, 62 (18): 186801. doi: 10.7498/aps.62.186801
In this paper, ZrN/TaN nano-multilayers are fabricated in mixing atmosphere by radio frequency magnetron sputtering. The phase structures, He-related defects, helium content and cross-section morphologies of ZrN/TaN nano-multilayers are characterized by X-ray diffraction, slow positron beam analysis, enhanced proton backscattering spectrome and scanning electron microscope, respectively. The results show that the interface of ZrN/TaN nano-multilayer with 30 nm modulation period is stable and could resist the damage of helium even annealed at 600℃. The He retention rate of ZrN/TaN nano-multilayer with 30 nm modulation period can reach up to 45.6%.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
First-principles calculations on electronic structures of Zn adsorbed on the anatase TiO2 (101) surface having oxygen vacancy and hydroxyl groups
2013, 62 (18): 187101. doi: 10.7498/aps.62.187101
The energies, atomic Mulliken charges, and electronic structures of Zn adsorbed on the pure surface, and on the surfaces with an oxygen vacancy (Zn-TiO2-VO) and one hydroxyl group (Zn-TiO2-VO-OH) are investigated by density functional theory, plane-wave pseudo-potential method, and the most stable surface structures (namely model (c), model (aI), and model (aII) are found. The results indicate that firstly, Zn interacts mainly with the surface oxygen by Zn–O covalent bond; secondly, when Zn atoms are adsorbed on the defective surface, the adsorption energy is reduced down to -1.75 eV, showing that Zn atoms are prone to being adsorbed on the oxygen vacancy surface. Finally, although no impurity states are introduced in to the gap when the Zn atoms are adsorbed to the surface with hydroxyl group, the band gap is reduced down to a minimum (1.85 eV), which is expected to improve the photocatalytic activity of TiO2.
2013, 62 (18): 187102. doi: 10.7498/aps.62.187102
According to density functional theory of first-principles calculations theory, we systematically study the electronic structures, magnetisms and stabilities of transition metal (TM = V, Cr, Mn) doped MoS2 single-layers. The results show that V-and Mn-monodoped systems each have magnetism and the magnetic moment mainly concentrates on the transition metal dopant atom, but Cr-doped MoS2 does not display magnetism. Further study on the magnetic coupling of double atoms doped MoS2 shows that the stable ferromagnetic state at room temperature is observed in the Mn-doped MoS2. However, the system shows a non-spin polarization state due to doping with V. The calculated formation energy indicates that the Mn-doped MoS2 is the most stable system. Therefore, Mn-doped single-layer MoS2 maybe have potential applications in the spin electronic devices due to its good ferromagnetism and reliable stability.
Effect of double substitution of Ba and Ag on thermal transport of Ca3Co4O9-based thermoelectric oxide
2013, 62 (18): 187201. doi: 10.7498/aps.62.187201
The Ba and Ag co-doped BaxAgyCa2.8Co4O9 thermoelectric bulk materials are fabricated by acid sol-gel and spark plasma sintering method. The phase compositions, microstructures and thermal transport properties of the resulting bulk materials are analyzed by X-ray diffraction, scanning electron microscopy and the thermal transport constant measurement apparatus. The results show that the thermal conduction behavior for the titled system can be effectively tuned by Ba and Ag co-doping, and the thermal conductivity could be reduced by increasing the Ba doping content. The analysis results show that the total thermal conduction suppressing comes from the lattice thermal conduction confinement. The Ba0.1Ag0.1Ca2.8Co4O9 bulk material is found to have the lowest thermal conductivity with total thermal conductivity and lattice thermal conductivity reaching 1.43 W/mK and 1.10 W/mK at 973 K, respectively.
2013, 62 (18): 187301. doi: 10.7498/aps.62.187301
We theoretically simulate one-photon and two-photon absorption spectra for monolayer and bilayer graphene employing the second-order perturbation theory of the electron-photon interaction. The tight-binding model is used to describe the band structure of graphene. The results show that one-photon absorption coefficient of monolayer graphene is a constant about 6.8×107 m-1, demonstrating that the absorptivity of incident light in monolayer graphene approximates to 2.3%. The one-photon absorption coefficient of bilayer graphene changes sectionally with the wavelength and is greater than that of monolayer graphene. The two-photon absorption coefficient of monolayer graphene is proportional to λ4. The two-photon absorption coefficient of bilayer graphene exhibits a giant resonance absorption peak in the infrared (～ 3100 nm) region. Our results will provide theoretical guidance for the application of graphene in the research field of optoelectronic devices.
2013, 62 (18): 187302. doi: 10.7498/aps.62.187302
ZnO nanobelts are synthesized using chemical vapors deposition method on silica substrate. The average width of the nanobelts is ～1 μm and the length is dozens of micron. Single ZnO nanobelt device is assembled using the micro-grid template method. The current-voltage characteristics are linear and the resistance and resistivity of the ZnO nanobelt are calculated to be ～3 MΩ and ～0.4 Ω·cm at room temperature, respectively. It is found that there are two different conduction mechanisms through the single ZnO nanobelt, according to the temperature dependence of the resistance of the single ZnO nanobelt at 20-280 K. In the higher temperature range (130-280 K) the thermally activated conduction is dominant. However, as the temperature comes down (<130 K), the nearest-neighbor hopping conduction mechanism instead of the thermally activated conduction turns into the dominant conduction mechanism through the single ZnO nanobelt.
2013, 62 (18): 187801. doi: 10.7498/aps.62.187801
SiO2 is one of important low refractive index materials, and SiO2 films are prepared by both ion-beam sputtering (IBS) and electron-beam evaporating (EB) technology. Dielectric constants of SiO2 films are calculated by infrared spectrum inversion technique in a wavenumber range from 400 cm-1 to 1500 cm-1. Through analyzing dielectric energy loss function, the oscillation frequency and the Si–O–Si angle of two types of SiO2 films are obtained in the transverse optics and longitudinal optics oscillating mode. The research results indicate that the attended modes of SiO4 are main coesite-like structure, three-plane folding ring structure, and keatite-like structure in the range of short-range order for EB-SiO2 films, but the attended modes of SiO4 are main coesite-like structure, three-plane folding ring structure, four-plane folding ring structure, and keatite-like structure in the range of short-range order for IBS-SiO2 films.
2013, 62 (18): 187802. doi: 10.7498/aps.62.187802
The uv-vis absorption and resonance Raman spectra of all-trans-β-carotene in polar solvent 1, 2-dichloroethane with iodine are measured at 293 K. The results indicate that the absorption peak of all-trans-β-carotene in the complex disappears at 460 nm and instead a new peak of the complex formed by all-trans-β-carotene and iodine is found at 1000 nm, so that the all-trans-β-carotene within the complex cannot produce the resonance Raman spectrum by 514.5 nm excitation laser. The Raman scattering cross section of CC bonds of all-trans-β-carotene taht does not form in complex decreases, its full bandwidth broadens and electron-phonon parameter increases with the increase of concentration of the complex, because when the concentration of the complex increases, the disorder increases in the solution and the molecular structural order decreases. These phenomena are analyzed using the coherent weakly damped electron-lattice vibration mode, the effective conjugation length mode as well as the theory of amplitude mode in this work.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2013, 62 (18): 188101. doi: 10.7498/aps.62.188101
A great number of point defects are created in diamond by electron irradiation, most of which are charged. In this paper, we come up with an interesting thought to determine the charge states of these defects in diamond. The irradiated regions are exposed by high-energy electrons with a scanning electron microscopy (SEM), and then are characterized by the low temperature micro-photoluminescence (PL) technology. Some evidences to determine the charge states of defects are obtained by comparing the PL spectra between the cases with and without SEM exposure.
Synthesis and magnetic properties of three-dimensional self-assembly Eu3+-graphene composite material
2013, 62 (18): 188102. doi: 10.7498/aps.62.188102
The three-dimensional self-assembly Eu3+-graphene composite materials are synthesized through a one-pot hydrothermal reaction under 180 ℃. The obtained samples are analyzed through powder X-ray diffraction, scanning electron microscope, and transmission electron microscopy. The results show that each sample has porous structure and no independent Eu3+ agglomerates. Raman spectrum and Fourier transform infrared spectrum analyses indicate Eu3+ is well complexed with graphene through oxygen-containing groups. The magnetic properties are measured using vibrating sample magnetometer. The magnetic hysteresis loop shows the corresponding coercivity Hc ≈ 39.61 Oe (1 Oe=79.5775 A/m) and the magnetization saturation Ms ≈ 0.08 emu/g that indicates that the sample presents weak ferromagnetism and good soft magnetic properties compared with graphene.
Synthesis of gem diamond crystals by multiseed method using China-type cubic high-pressure apparatus
2013, 62 (18): 188103. doi: 10.7498/aps.62.188103
In this paper, gem diamond synthesis is systematically studied using the multiseed method in China-type cubic high-pressure apparatus. High-quality Ib diamond crystals are synthesized in a growth cell with 3-5 diamond seeds, by adjusting the growth cell assembly and investigating the pressure and temperature regions of diamond synthesis. Because of several diamond seeds embedded in a growth cell, the synthesized diamond crystals possess the same morphology and quality. At the same time, the whole growth rate increases apparently. Using the multiseed method of diamond synthesis the growth cell volume can be effectively utilized, the efficiency of diamond synthesis can be enhanced, and the problem of low utilization rate is solved. Meanwhile, those also provide an effective support for the gem diamond industrialization synthesis.
2013, 62 (18): 188104. doi: 10.7498/aps.62.188104
We use nanosphere lithography and thermal evaporation techniques to fabricate multilayer metal-dielectric cone nanoparticle arrays. Scanning electron microscope measurements reveal that the ordered nanoparticles are of triangular shapes. Optical transmittance measurements show that there is a transmittance dip for each sample, and the transmittance dip is caused by the localized surface plasmon resonance of the metal/dielectric particles. With the increase of the number of the metal/dielectric layers of a sample, the position of the transmittance dip of the sample shows a blue-shift. Moreover, the transmittance spectrum and the electric field distribution of the metal/dielectric nanoparticles are simulated by HFSS, and the electric field distribution is used to explain the blue-shift phenomenon.
2013, 62 (18): 188105. doi: 10.7498/aps.62.188105
As a novel development of semiconductor process, direct metallic patterning has the advantages of simple steps, low cost, etc. However, almost all transfer media are Newtonian fluids in traditional nanoimprint lithography. Newtonian fluid viscosity is constant. Too high a viscosity is adverse to filling the small space, and if viscosity is too low, it is harmful to solidify graphics. So an appropriate viscosity range that can both realize a high filling degree and benefit solidification is difficult to determine. Pseudoplastic fluid viscosity decreases with the increase of shear rate. The problem would be solved well when pseudoplastic fluid is used as a transfer medium. Synthesizing the advantages of direct metallic patterning and pseudoplastic fluid feature, a novel idea is put forward. The pseudoplastic metal nanofluids, which would be fabricated with metal nanoprticals, can take the place of transfer medium in nanoimprint lithography. Based on the finite element method, COMSOL software is used to compute the filling degree of pseudoplastic fluid, and the results are compared with those of Newtonian fluid under the same conditions. Factors, such as viscosity, imprinting speed, pressure, etc., which would affect filling degree, can be obtained from simulation results. These parameters provide a theoretical basis for designing technological process and fabricating pseudoplastic fluids in future work.
2013, 62 (18): 188106. doi: 10.7498/aps.62.188106
Based on the several solute redistribution models, a more reasonable solute redistribution model is presented. The cellular states on the solid/liquid interface and the states of its neighboring cells possibly occurring during the grain growth are fully considered in the model, and different formulas are built for different cases. Firstly, the simulation result shows that the disadvantage of the original cellular automation (CA) model (its grain growth is controlled by solute distribution), in which the cells on the grain boundary are kept unsolidified all the time, is eliminated. Then, in order to verify the reliability of the new model, the new model is introduced into the CA model in which grain growth is controlled by Kurz-Giovanola-Trivedi model. The microstructure of the Al-4.7 wt%Cu ingot is calculated. The simulation results are in good accordance with experimental results in two aspects of microstructure morphology and concentration distribution.
Study on transmission characteristics of matching transformer in DC superconducting quantum interference device readout
2013, 62 (18): 188501. doi: 10.7498/aps.62.188501
In a magnetic flux modulated DC superconducting quantum interference device (SQUID) readout, the matching transformer could realize the function of signal amplification and impedance matching, which is the key element of a low noise SQUID readout. We use a simulated DC SQUID readout to test the characteristics of matching transformer, study the transmission characteristics of transformer with different turns, and confirm its best turn ratio. In the coupling network that the transformer picks up voltage signals of SQUID, We also study the transmission characteristics of transformers with different matching capacitances, realize the matching of the parameters and the optimization in the transformer coupling network. At room temperature, for the matching transformer with a turn ratio of 1:20, when matching capacitance is 1 μF, the gain of output voltage source could reach 21.2 and its bandwidth could reach 210 kHz. Finally, in magnetic flux modulation DC SQUID readout, we evaluate the performance of the matching transformer.
Simulation study of the influence of ionizing irradiation on the single event upset vulnerability of static random access memory
2013, 62 (18): 188502. doi: 10.7498/aps.62.188502
Single event upset vulnerabilities of static random access memory (SRAM) cells on the micron scale and deep sub-micron scale are characterized and analyzed under ionizing irradiation. Meanwhile, by means of three-dimentional simulation, electrical responses of 6-T SRAM cell with feature size 0.18 μm are calculated when ions are injected into the different central single transistors under the irradiotion with different deposited doses. The simulation results are consistent with the analysis conclusion: the single event upset vulnerability would increase only when the SRAM cell stores the same state as the one stored in the irradiation period.
Characteristics of gate-modulated generation current under the reverse substrate bias in nano-nMOSFET
2013, 62 (18): 188503. doi: 10.7498/aps.62.188503
The characteristics of gate-modulated generation (GMG) current IGMG in nano-scale LDD nMOSFET under the reverse substrate bias VB are investigated. It is found that the rising and falling edges of IGMG curve shift rightwards as |VB| increases. On the basis of experimental and theoretical analysis, the physical mechanism behind this shift phenomenon is attained. The shift phenomenon is ascribed from the fact that VB modulates the proportion of surface potential φs in the gate bias VG. φs decreases with |VB| increasing under a certain VG, and consequently the maximum generation factor of the rising edge (gr) diminishes and that of the falling edge (gf) augments. Further, it is found that the transconductance peaks of the rising edge (GMR) and falling edge (GMF) increase with |VB| increasing. Moreover, GMR and GMF both have the linear relationship with VB in log coordinate. Due to the different roles of drain bias VD on the rising and falling edge of IGMG curve, GMR keeps constant but GMF varies under different values of VD. Increasing VD can enhance the change of gf with VG, there by increasing GMF under a given VB. Also, this results in the fact that the trend of GMF increasing with |VB| increasing slows down under a larger VD: the slop of GMF-VB curve decreases from 0.09 to 0.03 as VD increases from 0.2 to 0.6 V.
2013, 62 (18): 188701. doi: 10.7498/aps.62.188701
An auto-regressive (AR) model is established by analysing the characteristic of the particle motion in an optical trap. In this paper, a new method based on the AR model is investigated to simulate the Brownian motion of the particle in an optical trap. When optical stiffness values are 10, 20, 50 pN/μm respectively, the displacement signals of 1 μm diameter particle in these optical traps are simulated with this method. Their simulative autocorrelation function of the motion of the particle accords with their theoretical autocorrelation function. In order to further clarify the validity of the model, the particle signals are respectively simulated with the AR model method and the Monte-Carlo method, then the stiffness values are calibrated with power spectrum density method. The results show that the stiffness value based auto-regressive simulation can have the same precision as that based the Monte-Carlo simulation, therefore, the AR method can simulate effectively the motion of the particle in the optical trap.
2013, 62 (18): 188702. doi: 10.7498/aps.62.188702
It is well known that the dynamics of the chaotic system is very sensitive to the initial conditions of the state, and the synchronization of two identical chaotic systems is only obtained, in general, with the high gain control law once their initial conditions are in a certain large deviation. Furthermore, the initial conditions are commonly unknown in practice, which causes difficulty in synchronizing two chaotic systems. This paper deals with the synchronization of two unified chaotic systems with input constraint. First, the scalar sign function is utilized to approximate the constrained non-smooth input function so that a continuous smooth nonlinear input function and an approximated nonlinear synchronized error system are obtained. Then, an optimal linear quadratic regulator (LQR) continuous-time control law is designed based on the optimal linear model, which is constructed at the sampled operating point of the afore-mentioned approximated nonlinear synchronized error system. To reduce the high magnitude of the obtained control law, the continuous-time control law is digitally redesigned for the implementation and an iterative procedure is proposed to adjust the weighting matrices in the LQR performance index so as to avoid input saturation occurs. Finally, three illustrative examples of the Lorenz, the Chen and the L chaotic systems decomposed from the unified chaotic system are given to demonstrate the effectiveness of the proposed method.
Analysis of electrical property parameters of CdS/CdTe solar cells fabricated by close space-sublimation
2013, 62 (18): 188801. doi: 10.7498/aps.62.188801
CdS/CdTe Thin film solar cells are grown in a homemade close-space sublimation system where the cell fabrication of p-n junction is carried out in a continuous, in-line process. The best efficiency achieved is about 11% (AM1.5). Another cell is prepared with the same procedure except for the n-CdS layer coated by sputtering(SP), achieving an efficiency of about 10% (AM1.5). Current density-voltage and external quantum efficiency measurements are analyzed and the solar cell performances are characterized. By the comparison between the practical fitted data and theoretical calculations, the method of improving CdS/CdTe solar cell efficiency, i.e., increasing the open-circuit voltage (Voc), short circuit current (Jsc), and fill factor (FF), is proposed.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2013, 62 (18): 189201. doi: 10.7498/aps.62.189201
Now, it is difficult to consider the typhoon rainfall in the short-term climate prediction. This is mainly because the typhoon is a strong synoptic scale system and it does not match the scale of the short-term climate forcast. It is a factor restricting the great improvement of forecast. By using station precipitation data in eastern China from 1960 to 2011 and CMA-STI Best track dataset for tropical cyclones over the western north pacific, we analyse the strength variation of typhoon influence from month and quarter scale in summer by determining the typhoon influence index, then discuss the contribution of typhoon rainfull to summer rainfall in eastern China. 1) On average, the typhoon is enhanced from June to August, it is weakest in June, and strongest in August. 2) From the distribution of typhoon rainfall and its proportion of the total precipitation in eastern China, totally, the tyhoon rainfall is higher in eastern region than in the western region on the same latitude, and it is higher in southern region than in the northern region on the same longitude. The ratio of typhoon rainfall to the total precipitation could reach up to 10% in the South of the Yangtze river region. The typhoon rainfall can also reach up to 100 mm in the southeast coastal area in July and August, which can amount to 40% of the total precipitation during the month. 3) The correlation of the typhoon influence index with summer precipitation shows that the typhoon’s influences on the precipitation in eastern China are different spatiotemporally. The results indicate that the negative correlation is in southern part of China in June, the positive correlation is the southeast coastal area in July, the positive correlation is in the south China in August, and the negative correlation is in the middle and lower reaches of the Yangtze river region, which are mainly due to the typhoon, summer moonsoon, and high pressure in the north-east pacific subtripics respectively.
The multi-parameter observation of lightning M changes in northeastern part of the Qinghai-Tibet Plateau
2013, 62 (18): 189202. doi: 10.7498/aps.62.189202
The M change characteristics in continuing current process of negative cloud-to-ground lightning discharge and artificially triggering lightning discharge are comparatively analyzed using the synchronous data of optical channel high-speed video camera pictures, electric field changes on ground and the peak very high frequency radiation. The results indicate that M process could be identified accurately from synchronous data of optical channel luminance and electric field changes on ground. There are lots of rapid changes of electric field (MP) prior to and during classic M change. And the M changes caused by lots of MP changes. There is mostly no difference in waveform characteristics between M changes and K changes and their generated physical mechanisms are similar. MP change is a rapid change of electric field corresponding to the rapid flow of charge caused by the breakdown process in the stage of continuous current process and accompanied with channel sudden brightening and high intensity radiation. Most of the M changes are unipolar, positive or negative and a few are irregular and last within 0.1 ms. Only M change in close lightning discharge exhibits a classic U-shaped structure because of its waveform mostly caused by static electric field, and its duration is about from 0.2 to 0.8 ms. MP and K changes are all caused by the breakdown. The difference between MP and K changes is that the electric charges flow into the original return stroke channel in the process of MP change, but not in the process of K change.
Research on the implementation of GPS radio occultation one-dimensional bending angle operator in four-dimensional variational data assimilation system
2013, 62 (18): 189203. doi: 10.7498/aps.62.189203
GPS radio occultation data are implemented in the numerical weather prediction as a kind of very important observation data because of its excellent characteristics, which makes a remarkable positive effect in the system. In this article, we design an implement method and a quality control strategy of one-dimensional bending angle operator in four-dimensional variational data assimilation system, and we also describe the steps of implementing one-dimensional bending angle forward operator and its linear and adjoint operators in four-dimensional variational data assimilation system. The author chose Reger’s three term expression and its best average coefficients are chosen to calculate refractivity values. In this article, we introduce an observation error model of one-dimensional bending angle operator through the statistics of GPS radio occultation observation data of August, 2012. A comparison of experiment of the analysis field between in the cases with and without GPS radio occultation data is made. It is concluded that GPS radio occultation data plays a positive role in the global areas, especially in the low and middle latitude areas higher than 10 km. This conclusion is the foundation of the following-up GPS radio occultation data assimilation verification experiments.
2013, 62 (18): 189204. doi: 10.7498/aps.62.189204
The dynamics structure of many complex system there often happens a suddenly change due to the effect of outside force in nature. This abrupt change is closely related to human life. In order to make an accurate prediction of abrupt change and take corresponding measures, abrupt change should be detected effectively. Fisher information (FI) can keenly catch and characterize a small change in probability density distribution (PDD) of a system variable. While there is a change in dynamic structure of a system, the PDD of the system variable will have some changes correspondingly. In view of this, in this paper we describe in detail that FI is used to detect and recognize the abrupt change of system dynamics structure, and it is a new method to solve the detection of abrupt change in dynamic structure of a system. First of all, this method is used to present the ability to detect abrupt change lying in ideal datasets of different types of ideal signals. Next, this method is used to analyze daily datasets of ground climate from national meteorological information center of China meteorological administration between 1960 and 2008 in Lanzhou meteorological observation station in Northwest area. The results show that the daily datasets are consistent with historical records, which further verifies that the method is effective and practical.