Vol. 62, No. 4 (2013)
Asymptotic solution of thermal-solutal capillary convection in a slowly rotating shallow annular pool of two components solution
2013, 62 (4): 040201. doi: 10.7498/aps.62.040201
In order to understand the characteristics of the coupled thermal and solutal capillary convection with the radial temperature gradient in a slowly rotating shallow annular pool with the free surface, the asymptotic solution is obtained in the core region using asymptotical analysis in the limit as the aspect ratio, which is defined as the ratio of the layer thickness to the gap width, goes to zero. The influences of the rotating, Soret effect, solute diffusion coefficient, buoyant force and geometric parameters on fluid flow are analyzed. The results show that when the rotating and the solutal capillary force and the buoyancy induced by the ununiform distribution of solute concentration are not considered, the asymptotic solution is the same as that of the previous work. The influences of the rotating, the buoyancy, solute diffusion coefficient and the geometric parameters on the fluid flow are all small and the coupled thermal and solutal capillary forces play a dominant role in the convection. When the coupled forces are in the same direction, the flow is reinforced, otherwise, the flow is suppressed.
2013, 62 (4): 040202. doi: 10.7498/aps.62.040202
A direct and effective linear-controller is employed to exactly control the locations of bifurcation points, both the symmetry-breaking bifurcation and the period-doubling bifurcation, in a cubic symmetry discrete system. Moreover, both the sensibility and the symmetry to the initial values of the system are analyzed. The lack of the solution branches due to the symmetry-breaking bifurcation can be reinstated temporarily by selecting the corresponding basins of attraction. The effectiveness of the controller is verified by numerical simulations.
Solution of a class of rotational relativistic rotation dynamic equation using the generalized variational iteration theory
2013, 62 (4): 040203. doi: 10.7498/aps.62.040203
A class of relational relativistic rotation nonlinear disturbed dynamical equations possessing nonlinear damping force and forcing periodic force is investigated. Firstly, by using the variational principle, the generalized variational iteration is constructed. Then the initial approximate solution is determined. Finally, by using the iteration, the approximation to an arbitray degree for corresponding equation is found.
2013, 62 (4): 040301. doi: 10.7498/aps.62.040301
A hybrid stream cipher scheme is proposed based on the novel interacting neural networks and the multiple chaotic systems. At first, random sequences generated by 3 independent logistics functions respectively are taken as dynamic inputs to 3 hidden layers of the interacting neural networks model. Then two inner weights of the two structures of neural networks will be synchronized through some steps of interacting learning, and the random key stream can be finally identified by combining the random sequence extracted from the aforementioned synchronized weight and 3 Logistics sequences. The comparison shows that the generated key stream performs the better randomness than others. As a good example, the proposed novel chaos-based stream cipher works perfectly on digital image encryption.
2013, 62 (4): 040501. doi: 10.7498/aps.62.040501
In this paper, we first discuss the physical meaning of the fractional Frenkel-Kontorova model and depict the transport phenomenon of elastically coupled particles in a memorable medium, then give the effects of various parameters on the motion of coupled particles. According to the numerical value, the memory effect of system has a significant influence on the motion of coupled particles, in addition, the current reversal which does not exist in a non-memorable system appears, this is an abnormal phenomenon. What is more in this research we find that there appears the generalized resonance in the system mean velocity as the spring constant and the fractional order are varied, and the generalized stochastic resonance will appear with noise intensity changing.
2013, 62 (4): 040502. doi: 10.7498/aps.62.040502
A partial oscillation phenomenon in a digital-controlled three-phase inverter system, which is controlled by proportional controller in synchronous rotating reference frame, is analyzed in this paper. First, the discrete-time model of the system is derived. Then, a dynamics analysis scheme for this type of system is proposed. In addition, the underlying mechanism of the partial oscillation phenomenon occurring in this system is analyzed. The factors, which will cause the partial oscillation, are exactly predicted by analytical expressions. Finally, the theoretical results are verified by both simulations and experiments. These conclusions can provide an insight into the dynamics of the system.
2013, 62 (4): 040503. doi: 10.7498/aps.62.040503
This paper deals with the synchronization of complex networks with random nodes. Sufficient conditions for the synchronization of complex networks are derived by using the Lyapunov functional method and linear matrix inequality technique, and the obtained criteria depend on not only the size of the delay, but also the probability distribution of random nodes. A simulation example is exploited in order to illustrate the effectiveness of the proposed method.
2013, 62 (4): 040504. doi: 10.7498/aps.62.040504
The propagation and interaction properties of optical vortex solitons in a self-defocusing Kerr-type nonlocal medium are investigated by the numerical simulation method. It is indicated that the singly charged vortices are stable and the multicharged vortices are topologically unstable in both the nonlocal and local cases. And in the nonlocal and local cases the point vortices model is applicable for describing the interactions of vortices provided that the interval distances between vortices are much larger than the size of the core of the vortices. However, vortices interact differently in short distance, depending on the nonlocality, and the larger the characteristic nonlocal respond length, the larger the rotating period of two singly charged vortices.
Influence of the strong beam impedance on injection and bunching features of the relativistic klystron amplifier
2013, 62 (4): 040701. doi: 10.7498/aps.62.040701
With numerical calculation and particle simulation program, the influences of the intense electron beam impedance, voltage and current characteristics on the beam modulation and bunching characteristics in relativistic klystron amplifier (RKA) are analyzed. Within the particle-in-cell simulation program, the beam emission method is used to accurately control the impedance of the electron beam. The results show that the electron beam of low-impedance can reduce the bunching distance and shorten the overall length of the RKA devices but degrade the injected modulation of the electron beam. Electron beam of high impedance is just opposite. When the electron beam impedance is constant, the increase of the electron beam accelerating voltage is similar to the increase of the impedance of the electron beam. In addition, with the particle simulation method, the beam loaded conductance of a specific input cavity loaded by a different impedance of the electron beam is determined, thereby meeting the demand of the power level of the seed, and the requirements for the externally loaded quality factor of the input cavity.
2013, 62 (4): 040702. doi: 10.7498/aps.62.040702
A new algorithm for infrared image segmentation is proposed based on clustering combined with sparse coding and spatial constraints. The clustering algorithm is fused on the basis of sparse coding. The traditional image segmentation method based on K-means clustering is extended. The clustering algorithm combined with sparse coding can fuse the local information of image. The inner relationships between pixels are used. However, the problem of over-segmentation and difficulty in pixels classification for segmentation arise. The clustering method is introduced for atoms into dictionary learning. The class number of atoms in dictionary is reduced in order to avoid over-segmentation. The spatial class property information is also introduced by considering the property of the pixel, and the pixels in the neighbor region should have class coherent constraints. An alternate optimization algorithm is proposed to learn the dictionary, sparse coefficients, cluster center and degrees of membership jointly. Then the classes of pixels are estimated by constructing pixel ownership degrees, combining the sparse coefficients and the degrees of membership with the atoms to cluster center. The experimental results show that the important area can be separated well, and the proposed method has good robustness.
ATOMIC AND MOLECULAR PHYSICS
MRCI+Q study on spectroscopic parameters and molecular constants of X1Σ+ and A1Π electronic states of the SiSe molecule
2013, 62 (4): 043101. doi: 10.7498/aps.62.043101
The potential energy curves (PECs) of X1Σ+ and A1Π electronic states of the SiSe molecule are calculated using the internally contracted multireference configuration interaction approach with the Davidson modification (MRCI+Q) with the correlation-consistent basis sets, aug-cc-pV5Z and aug-cc-pVQZ. In order to improve the quality of the PEC, the PEC is extrapolated to the complete basis set limit by the two-point total-energy extrapolation scheme; and the scalar relativistic correction is included. Scalar relativistic correction calculations are carried out using the third-order Douglas-Kroll Hamiltonian approximation at the level of a cc-pV5Z basis set. The spectroscopic parameters (Te, De, Re, ωe, ωexe, ωeye, Be and αe) of two states are calculated. The spectroscopic results are compared in detail with those reported in the previous literature. Excellent agreement is found between the present spectroscopic results and the experimental ones. Using the PECs obtained by the MRCI+Q/Q5+DK calculations, the Bυ and Dυ are calculated for each vibrational state of each electronic state, and their values of the first 30 vibrational states are reported for X1Σ+ and A1Π states of 28Si80Se molecule when J=0. Comparison with the measurements demonstrates that the present vibrational manifolds are both reliable and accurate. They should be good predictions for the future experimental or theoretical research.
2013, 62 (4): 043102. doi: 10.7498/aps.62.043102
The lattice parameters, charge populations, band structures, density of states and absorption spectra of P-doped anatase TiO2 are calculated using the first-principles based on the density functional theory. The results indicate that when the Ti atom is substituted for P atom, the volume of TiO2 decreases. When P atom substitutes for O atom or exists as interstitial atom, the volume of TiO2 increases. The substitutional P at Ti site and interstitial P are oxidized to different degrees, and the substitutional P at O site is reduced a little. The different three sites of P doping result in the increase of anatase TiO2 forbidden gap width and the introduction of local doping energy levels. The band gap increasing of P-doped anatase TiO2 is in the following sequence: interstitial P>substitutional P at Ti site>substitutional P at O site. The absorption spectra indicate that the substitutional P at Ti site cannot enhance the visible light absorption ability of the anatase TiO2, whereas the interstitial P strongly enhances the visible light absorption ability of the anatase TiO2. The interstitial P is probably an important reason for the experimental enhancement of the photocatalytic activity of P-doped anatase TiO2.
On the basis of the theoretical imaging method, we study the photodetachment of H- near a deform sphere. We deduce the formula of the detached electron flux. Then we calculate the detached electron flux distribution and the photodetachment cross-section. The calculation results suggest that the influence of the plane on the photodetachment of negative hydrogen ion is only within a certain range. In the region close to the z axis, the spherical effect dominates and the electron flux and photodetachment cross section are the same as those that exist only on the sphere surface. While in the region far from the z axis, both the plane and sphere surface have significant effect and the electron flux and photodetachment cross section become much complicated. If we fix the radius of sphere and the distance between the deform sphere and the negative hydrogen ion, the oscillating amplitude in the electron flux fist increases and then decreases with the increase of the photon energy. Finally it increases slowly. But the oscillating frequency becomes complicated at all times. If we fix the distance between the deform sphere and the negative hydrogen ion, the detached electron flux distribution becomes more like that in the sphere case as the radius of the sphere increases. Hence, we can control the photodetachment of H- near the deform sphere by changing the incident photon energy or the radius of the sphere. Our results will provide some reference values for the photodetachment of H- near the curved surface and the experimental research of microscopy photodetachment.
2013, 62 (4): 043401. doi: 10.7498/aps.62.043401
The spectrum range from 300 to 600 nm is measured with low energy (V≈0.01 VBohr) highly charged Krq+ ions (q=8, 10, 13, 15, 17) impacted on Al surface. The results show that the spectral lines are induced by the impact of low-energy ions on Al surface, and that these lines belong to the sputtered atoms, ions, and the incident ions which are neutralized. The intensity of emission line increases with the projectile potential. The electron of Al can be efficiently excited to the 4s state by the higher potential energy compared with the excited state of 3d.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
Semi-analytical recursive convolution algorithm in the finite-difference time domain analysis of anisotropic dispersive medium
2013, 62 (4): 044101. doi: 10.7498/aps.62.044101
The polarizability tensor of magnetized plasma in frequency domain in laboratory coordinate system is gained by using the transfer matrix between the principal and the laboratory system, and then its exponential function form in time domain is derived by inverse Fourier transform. Combined with the semi-analytical recursive convolution (SARC) algorithm in digital signal process techniques, the SARC-finite-difference time-domain method applied to magnetized plasma subjected to an arbitrary direction of external dc magnetic field is derived. The co-polarized and cross-polarized backward radar scattering cross-section for a magnetized plasma sphere are obtained by the presented algorithm. The computed results indicate the correctness and feasibility of the method.
Theory and measurement for mutual coupling effect of ultra high frequency radio-frequency identification in dense environments
2013, 62 (4): 044102. doi: 10.7498/aps.62.044102
The close displacement of ultra high frequency radio-frequency identification (UHF RFID) tags can be considered as an electromagnetically interconnected system which causes the mutual coupling effect among antennas of tags, thereby resulting in change in impedance matching condition. Based on the principles of RFID technology and Friis propagation equation, a link budget model of UHF RFID is provided which consists of one reader and one tag. Expressions of mutual impedance in dense environments are derived by using a two-port network. Utilizing the parameters of power transmission coefficient and modulation factor, the variation of system performance is discussed in theory and tested by three experiments which are conducted in open indoor environment. The measurement results show that the change rate of minimum power transmitted by the reader antenna is in a range from -7% to 11.6% for two-tag scene and from -10% to 12.5% for two-plane arrangement.
Design of an ultrathin and wideband metamaterial absorber based on resistance film and fractal frequency selective surface
2013, 62 (4): 044103. doi: 10.7498/aps.62.044103
An ultrathin, wideband, polarization-insensitive and wide-angle metamaterial absorber is presented, which is based on one order Minkowski fractal double square loop (MFDSL) electric resonator structure and resistance film. The unit cell of this absorber consists of MFDSL, square resistance film, dielectric substrate and metal ground plane. The simulations and analyses of electromagnetic absorbing properties of this composite structure absorber are performed by the finite-difference time-domain method. The simulated reflection and absorption indicate that the absorption of the composed structure absorber is greater than 90% in a frequency range of 7.5-42 GHz. The simulated absorptions under different polarization conditions and incident angles indicate that this composite structure absorber is polarization-insensitive and of wide-angle. The further numerical simulation results indicate that the absorption of this absorber originates mainly from the absorbing mechanism of electromagnetic resonance and circuit resonance, the operation frequency range can also be adjusted by the design of the square resistance.
2013, 62 (4): 044104. doi: 10.7498/aps.62.044104
We present the tunable resonance behavior of laminated metal mesh metamaterial embedded by barium strontium titanate (BST) thin film. The electromagnetic frequency response shows a redshift when the dielectric constant of BST thin film increases, and the tunability is about 22.6%. For the tunable metamaterial proposed in this paper, the structural unit of metal graphics is used as electrodes to apply the electric potential, which simplifies the preparation and application of tunable THz metamaterials greatly. It has potential application in the THz media modulators.
2013, 62 (4): 044105. doi: 10.7498/aps.62.044105
Ultra-wideband (UWB) microwave imaging technology can be used as an effective method of detecting early breast cancer, which is based on the difference of the electrical characteristic between normal breast tissues and tumor. The method can provide both the sufficient resolution and the adequate penetration depth in the breast. In this paper, the finite difference time domain method is employed to simulate the microwave propagation in three-dimensional breast tissue. The single pole Debye model is used to approximate the real electrical properties of the breast organism. The antenna arrays made up of 8 emitters and 9 detectors are performed for the detection. The confocal imaging algorithm is employed for the reconstruction of the breast tissue and location. The tumor information displayed in the reconstructed breast image verifies the correctness of the confocal imaging algorithm and the effectiveness of the UWB microwave imaging technique applied to the early breast cancer detection.
Magnetic properties of permanent magnet for cryogenic undulator of permanent Shanghai synchrotron radiation facility
2013, 62 (4): 044106. doi: 10.7498/aps.62.044106
M-H and M-T curve at cryogenic (10-300 K) of domestic Nd2Fe14B (N50M) permanent magnet are tested by physical property measurement system (PPMS). Br-T and Hci-T figure under the cryogenic condition for N50M are obtained. The orientation degree and three-dimensional magnetization are also analyzed and researched under the cryogenic conditon. The results show that N50M has a strong spin reorientation effect(SRT) between 80 and 150 K, Br shows a peak between 120 and 130 K and Hci increases linearly with temperature decresing. At 130 K, Br increases 15.6% and Hci increases 220% compared with at room temperature (300 K), reaching 1.65 T and 3638 kA/m respectively. Between 150 and 300 K, with temperature declining, the macroscopic orientation degree uniformity and the external magnetic field uniformity of N50M are improved gradually. Between 80 and 235 K, the micro-external magnetic field uniformity shows a deterioration phenomenon. The experimental research also indicates that near 235 K the N50M perpendicular to orientation direction presents a “remanent magnetization jump” phenomenon. The experimental results provide a reference for the physical design of cryogenic undulator for Shanghai Synchrotron Radiation Facility II and other high-precision cryogenic permanent magnet instruments and equipment.
2013, 62 (4): 044201. doi: 10.7498/aps.62.044201
A novel bend-resistant large-mode-area silica photonic crystal fiber (PCF) is proposed and fabricated. With the advantage of flexible design on the PCF configuration, the properties of large-mode-area, single mode propagation and low bend loss can be simultaneously achieved by intentionally designing the position of defect and the size of air holes. Modal properties and bending loss of the actual PCF can be evaluated with previous model for assessing the properties of the actual fiber. Numerical results demonstrate that this fiber has an extremely large mode area of 2812 μm2, low confine loss of 0.00024 dB/m of the fundamental mode and high confine loss of over 1.248 dB/m of higher order mode at a wavelength of 1064 nm when the optical fibre is kept straight. The large difference in propagation loss levels between fundamental mode and higher order modes ensures the efficient single-mode propagation in the fiber core. Furthermore, the effects of bend radius and bend direction angle on bend loss are investigated when the fiber is bent. Even if bend radius is as small as 5 cm, bend loss of this fiber is still below 10-3 dB/m. It is found that the proposed fiber has the negligible bending loss at a bending radius of 30 cm with the bending angle ranging from -60° to 60°. These results illustrate that the fabricated fiber possesses the better bend resistant properties and can overcome the sensitivity to bend direction angle caused by the asymmetric structure. The fabricated fiber will play an important role in developing high power fiber laser, fiber amplifier and high power delivery application.
2013, 62 (4): 044202. doi: 10.7498/aps.62.044202
The simulation of nonlinear self-focusing phenomenon using ray-tracing method can macroscopically provide an intuitive picture of the propagation of light in a self-focusing material, without adopting paraxial approximation or self-similar hypothesis. In this paper, propagation of light is sampled by discrete slices along a certain direction. Thus nonlinear propagation is turned into the combination of optical modulation of the refractive index on separate slices and linear propagation between each two adjacent slices. On each slice, after calculating the flux, we use a novel algorithm to suppress the quantized errors. For the linear propagating process, Adams method is adopted to solve the ray equations, which solve the problem that the widely used Runge-Kutta method cannot be used in simulation of light in nonlinear materials. The simulation results reveal that there are several foci along the propagating axis and the location of the first focus becomes closer to the incident plane as the power of light goes up. Furthermore, because the program traces real rays, it is possible to reach the non-paraxial region and reveal the phenomenon of ring-structure flux distributions caused by self-focusing. This is significant for the safety of high-power laser systems. Some commercial optical design and simulation software are also based on ray-tracing methods. Thus the systems including both nonlinear and linear materials are possible to simulate, which can guide people to set up the corresponding experimental systems.
The aperture averaging effect of scintillation of pseudo-partially Gaussian-Schell model beam propagation in turbulent atmosphere
2013, 62 (4): 044203. doi: 10.7498/aps.62.044203
By using numerical simulation, the propagation of pseudo-partially coherent Gaussian-Schell model beam in atmospheric turbulence is simulated. The properties of intensity fluctuation of different receiving aperture and aperture averaging factors are statistically analyzed. And the influence of relative changing frequency of the modulating phase which models the partial coherence of beam source on scintillation index is also discussed. The simulation results of pseudo-partially coherent beam are compared with those of the well-developed partially coherent beam and fully coherent Gaussian beam. It is found that the reduction of coherence degree may cause scintillation index to decrease. However, the aperture averaging effect is weakened at the same time. At the same receiving aperture diameter, the aperture averaging factor of pseudo-partially coherent beam is greater than that of the fully coherent beam. The increase of relative changing frequency of modulating phase may cause a reduction of scintillation index to some degree. And with the increase of relative changing frequency, the scintillation index of pseudo-partially coherent beam tends to be coincident with that of the partially coherent beam.
2013, 62 (4): 044204. doi: 10.7498/aps.62.044204
An inversion method for electromagnetic scattering echo data from large-scale layered medium is presented to simultaneously retrieve the electromagnetic property parameters of the medium. Firstly, the inversion is converted into an optimization problem. Then the simulating annealing algorithm is adopted to find the optimal solution by taking full advantage of the algorithm global optimization. Besides, the search control strategy of the algorithm is optimized so that the algorithm can adaptively adjust the search step in the optimal solution search process. The search efficiency of the algorithm is improved by these optimizations. Results show that the proposed method can achieve an accurate result in the inversion of the characteristic parameters of large-scale layered media as well as a strong anti-noise ability. The inversion method presented can be applied to the Mars/lunar radar echo data inversion and analysis of underground layered medium.
2013, 62 (4): 044205. doi: 10.7498/aps.62.044205
In 1979, Berry and Balazs [M V Berry and N L Balazs 1979 Am. J. Phys. 47 264] obtained a strict solution of the Schrödinger equation with Airy function used as the initial condition, and described the wave function represented by such solution as the Airy wave-packets. They discovered that infinite Airy wave-packet has unique properties such as non-spreading and free acceleration, proving that it is the only nontrivial non-spreading solution of the time-dependent Schrödinger equation in one dimension. However, the observing of the finite Airy beam seems to be more meaningful since wave-packets in reality is inevitably band limited. A certain form of finite Airy beam was investigated by Siviloglou et al. in 2007 [Siviloglou G A, Broky J, Dogariu A, Christodoulides D N 2007 Phys. Rev. Lett. 99 213901; Siviloglou G A, Christodoulides D N 2007 Opt. Lett. 32 979]. They noted that the Airy wave packet still exhibits its most exotic feature, i.e., its trend toward free acceleration. While in the present paper we discuss the properties of Airy beam in a few steps further and propose several conclusions. On the one hand, a theoretic explanation is given to solve the matter of the centre of mass of infinite Airy beam. On the other hand, deeper research is conducted on the unique properties of finite Airy beam. Another form of finite Airy beam is discussed by reduction to absurdity, and its field distribution is put forward by numerical simulation. We find that the trajectory of the centroid holds its position, which means that the beam cannot accelerate freely as a whole. Ultimately, we have the conclusion that finite Airy beam can neither freely accelerate nor be non-diffractive.
2013, 62 (4): 044206. doi: 10.7498/aps.62.044206
Spectral imaging and polarimetric imaging are both advanced optical detection techniques. Owing to their wide potential in military and civil communities, these techniques have rapidly developed within the past two decades and become well-recognized tools in remote sensing. In recent years, these two techniques presented a new trend toward merging into the imaging spectropolarimetry, and make the optical remote sensing tend to multi-dimensional and multi-information fusion. However, in conventional imaging spectropolarimeters, rotating polarization elements, electrically controllable components, and microretarder or micropolarizer arrays are typically required. These apparatuses generally suffer from vibration, electrical noise, heat generation, and alignment difficulty. Consequently, the incorporation of mechanical components typically increases the complexity and reduces the reliability of the measurement system. To overcome these drawbacks, we propose a novel method of real-time measuring the spectrum, polarization and imaging of scenes with static birefringent crystal elements in 2010. In this paper, the concept and theory of a sensor based on the method are given. With specially aligned static birefringent retarders, different phase factors are modulated into the Stokes vector of incidence light. After passing through a static birefringent interferometer, the spectrally dependent Stokes parameters are distributed into several separated interferogram channels. With corresponding Fourier-transform demodulation, the wavelength-dependent polarization, spectral and 1-D spatial imaging of objects can be completely obtained with a single snapshot. The simulated and experimental demonstration of the sensor are also presented. This research gives a new way for spectropolarimetric imaging measurement, and provides theoretical and practical support for the development of new space remote sensors.
2013, 62 (4): 044207. doi: 10.7498/aps.62.044207
The interaction between two edge dislocations in the presence of a tilted lens is studied. It is shown that for the interaction between two off-axis edge dislocations, the edge dislocations vanish, and one or two noncanonical vortices appear under certain conditions. A noncanonical vortex appears for the interaction between the on-axis edge dislocation and off-axis edge dislocation. However, one or two edge dislocations may take place when two edge dislocations are perpendicular or parallel to each other in the initial plane. The variation of the tilt coefficient does not affect the type and number of phase singularities, but the relation between the transverse position of phase singularities and the tilt coefficient is linear. The three-dimensional trajectories of vortices are nonlinear while the center of the pair of vortices propagates along a line during propagation.
2013, 62 (4): 044208. doi: 10.7498/aps.62.044208
Based on holographic lithography, layered dye-doped photonic crystals are fabricated in dichromated gelatin emulsions. Under pumping of 532 nm pulse laser, fluorescence spectrums of samples show up remarkable band gaps, and lasing is achieved at the edge of fluorescence band gap with pumping energy increasing. Furthermore, the effects on lasing of matching between the edge of band gap and the peak of fluorescence are studied. Lasing threshold becomes lower as the edge of band gap is closer to the peak of fluorescence. Otherwise, it is difficult for lasing. The study provides new idea and method for the development of super low-threshold photonic crystal laser.
Correlated imaging offers great potentiality, with respect to standard imaging, to obtain the imaging of objects located in optically harsh or noisy environment. It can solve the problems which are difficult to solve by conventional imaging techniques. Recently, it has become one of the hot topics in quantum optics. In this paper, we propose a new scheme of correlated imaging with differential correlated imaging based on compressive sensing, named differential compressive correlated imaging. The new scheme takes advantage of the high signal-to-noise ratio of the differential correlated imaging and low-imaging sampling frequency of the compressed sensing technique. In the scheme, we utilize the intensity of the thermal light, which is in line with the Gaussian distribution, as the measurement matrix of compressive sensing. We extract the differential object information as the image object information which could be recovered via orthogonal matching pursuit algorithm with high quality. By numerical simulations, we verify the proposed scheme. Here, we select the two gray-scale images, such as double-slit and NUPT, as well as the two multi-grayscale images (Lena and Boats) as the object. We take sampling 350 times in differential compressive correlated imaging for measurement. The numerical simulation results show that for the above image objects, the average mean-square error (MSE) over 10 times for the differential compressive correlated imaging scheme is reduced by 97.7%, 93.9%, 92.5% and 71.4% respectively with respect to that of the differential correlated imaging scheme. Moreover, compared with the compressive ghost imaging, the MSE value of the same double-slit in CDGI, as well as Lena and Boats under the same conditions, is reduced by 50.4%, 72.9% and 66.8% separately, which indicates that the compressive differential correlated imaging scheme can greatly improve the signal-to-noise ratio of the imaging, and significantly reduce the imaging time.
2013, 62 (4): 044210. doi: 10.7498/aps.62.044210
We show experimentally that a tandem-pumped Yb-doped fiber amplifier with high power and low quantum-defect can be reached. And a high power 21 W output power at 1018 nm is demonstrated finally. We use this 1018 nm fiber laser as a pumping source of the 1080 nm fiber laser to demonstrate the tandem-pumped double-cladding Yb-doped fiber amplifier, and obtain an output power of 18.6 W at 1080 nm with a slope efficiency of 90.86%.
Quantitative analysis of cadmium in navel orange by laser-induced breakdown spectroscopy combined with partial least squares
2013, 62 (4): 044211. doi: 10.7498/aps.62.044211
The navel orange is analysed quantitatively for cadmium by laser-induced breakdown spectroscopy. The laser-induced breakdown spectroscopy is used to obtain the characteristic spectrum of Cd in sample. The concentration of sample is detected as a reference concentration by atomic absorption spectrophotometer. The partial least squares method is applied to the data of 39 samples which are preprocessed by combining the five smoothing formula and centerization method to establish quantitative analysis of cadmium model. Other 13 samples are used to be compared with the results from the quantitative analysis model. In this model, the correlation coefficient of fitting curve is 0.9806 and the relative error of 12 samples is 10.94 percent. The research results show that laser-induced breakdown spectroscopy can nondestructively and accurately detect heavy metals in agricultural products without preparing any sample and provides a technology for the safety of agricultural products.
2013, 62 (4): 044212. doi: 10.7498/aps.62.044212
In this paper, we report on a distributed sensing system of phase-sensitive optical time-domain reflectometer (Φ-OTDR) based on bi-directional Raman amplification. With the bi-directional Raman amplification, the transmission loss of the optical fiber can be compensated efficiently. The experimental characterization of evenly detected signals along the whole sensing distance of 74 km with 20 m spatial resolution is successfully demonstrated, resulting in the longest distributed sensing system based phase-sensitive optical time-domain reflectometer reported so far, to the best of our knowledge. The influences of different incident powers and pump powers on Φ-OTDR are studied experimentally.
Intensity distribution of the flat-topped beam propagating through the thick nonlinear medium with defects
2013, 62 (4): 044213. doi: 10.7498/aps.62.044213
Based on the nonlinear Schrödinger equation and Fourier transformation, the intensity distributions of the high power flat-topped beam propagating in the nonlinear medium and the free space are studied. The influences of the defects on medium surface on the intensity evolution of flat-topped light beam in the medium and the free space are analyzed. The results show that the larger the beam order, the poorer the beam self-focusing property is, and the closer to the back surface of the medium the position related to the maximal intensity point is a stronger initial intensity, a thicker medium or a higher nonlinear coefficient will lead to a stronger self-focusing property. The defects on the surface of medium will produce a relatively large intensity, closer to the back surface of medium. The effect of the phase modulated defect on the intensity evolution is greater than that of amplitude modulated defect.
2013, 62 (4): 044214. doi: 10.7498/aps.62.044214
Due to its future use in communication area, nonlocal spatial optical soliton has been a hot research topic recently. However, because of its special border condition, little research has been done on spatial dark solitons especially on its linear stability. In this paper, a method to analyze linear stability of nonlocal spatial dark soliton is put forward, moreover a numerical simulation and analysis is done on the linear stability of (1+1)-dimensional fundamental and second-order dark soliton in thermal nonlinear medium. Numerical results show that (1+1)-dimensional fundamental nonlocal dark solitons are always stable in their entire existence domain, while second-order dark solitons are oscillatorily unstable and the width of unstable domain depends on propagation constant and nonlocality degree of thermal nonlinear medium. The propagation graphs of initial input with noise addition confirms the correctness of linear stability analysis results.
Raman effect on parametric amplification gain spectra of different frequency propagation regimes in polarization maintaining fibers
2013, 62 (4): 044215. doi: 10.7498/aps.62.044215
The expression of gain is derived from nonlinear Schrödinger equation with consideration of raman effect when two laser pulses with different wavelengths are emitted into birefringence fiber along two polarization axes. The gain characteristic input laser pulses of different frequencies are revealed by comparing the laser pulses of identical frequency. The result show that the gain spectra will apparently differ when input laser pulses have different frequencies in normal dispersion regime and anomalous dispersion regime. The intensities of outboard gain peak about stokes part and anti-stokes part increase and frequency deviates from central frequency as group velocity mismatch increases. Therefore, the THz pulse can be extracted. The gain spectrum will be apparently different from that with no Raman effect taken into account, when the two polarization modes, are in different dispersion regimes. The symmetry of gain spectrum will be damaged. The intensity of gain peak of stokes is apparently stronger than the peak of anti-stoke.
2013, 62 (4): 044216. doi: 10.7498/aps.62.044216
The multi-axis differential optical absorption spectroscopy (MAX-DOAS) technique, in which solar scattered light beams of different elevation angles are used and the spatial distribution of various trace gases is derived, has been widely used for monitoring the NO2 slant column density. Due to the lack of information in a detectable horizontal range of the MAX-DOAS instrument, the concentration of trace gases including NO2 is unable to yield directly. In this work, the relationship between extinction coefficient and light path length of MAX-DOAS observation is analyzed, and a retrieval algorithm to convert the horizontal NO2 differential slant column density into the volume mixing ratio with the information of visibility is described. This algorithm has been used in the MAX-DOAS observation at Hefei, and volume NO2 mixing ratio is derived from MAX-DOAS measurement combining the data of visibility. The NO2 concentration measured with MAX-DOAS shows that it is in good agreement with the result obtained with long path differential optical absorption spectroscopy, proving the feasibility of the retrieval method. This research presents a simple and effective monitoring method of volume NO2 mixing ratio with MAX-DOAS, there by expanding the application scope of MAX-DOAS technique.
2013, 62 (4): 044217. doi: 10.7498/aps.62.044217
The higher-order intensity moments of optical beams propagating through atmospheric turbulence are studied in the paper. The method to derive higher-order intensity moments in atmospheric turbulence is proposed, and the simple expressions for intensity moments up to the fourth-order are derived. The results obtained in this paper are general, which can reduce to higher-order intensity moments of an arbitrary optical beam propagating in both free space and turbulence. Taking the Gaussian beam for example, the propagation of the kurtosis parameter in atmospheric turbulence is studied. It is shown that the kurtosis parameter of Gaussian beams is not a propagation invariant in atmospheric turbulence, which depends on propagation distance, waist width, inner and outer scales of turbulence and refraction index structure constant. This result is different from that obtained by using the quadratic approximation of Rytov’s phase structure function or the strong fluctuation condition of turbulence. The reasonable explanations for the differences are given in this paper.
2013, 62 (4): 044218. doi: 10.7498/aps.62.044218
Extracting the equivalent parameters of the weak-coupling and strong-coupling fishnet structure metamaterial based on the traditional retrieval algorithm and the improved algorithm of Kramers-Kronig relations are proposed, respectively. A comparative analysis of the effectiveness and applicability of the two algorithms are also included. The theoretical analysis and numerical results show that the traditional retrieval algorithm can retrieve the equivalent parameters of the weak-coupling and strong-coupling cases of electromagnetic metamaterials accurately, but with high computational complexity. While the improved algorithm based on the Kramers-Kronig relations can reduce the computational complexity and extract the equivalent parameters only for the weak-coupling case of electromagnetic metamaterials. However, it is not suitable for the strong-coupling case which may disobey the continuity requirement of the Kramers-Kronig relations. The presented results may extend the equivalent medium theory and provide a theoretical reference for the design of new metamaterials.
2013, 62 (4): 044219. doi: 10.7498/aps.62.044219
The wedge cell of cholesteric liquid crystal device is designed and fabricated, and doping PM580 (exciton) in the cholesteric liquid crystal, the laser emission action is studied. There appear a series of parallel wedge edges of dislocation lines and different shapes of domain in the wedge cell. The planar state of alignment is confirmed. A second harmonic Nd:YAG 532 nm laser is adopted as a pump light beam, and then one-dimensional tunable laser radiation is obtained and its wavelength interval is approximately 1 nm and tuning range is about 17 nm. In the processs of interaction between the torques of LC and the surface anchoring of direction film, the pitch elongation takes place. The positon of photonic band gap is changed, so the laser radiation wavelength can be tuned in the band edge.
2013, 62 (4): 044220. doi: 10.7498/aps.62.044220
According to the nonlinear Kerr effect of photonic crystal, we design a simple structure with arbitrary proportion of energy output, which can be controlled by the pump intensity. At the same time, the structure can also realize the dynamic control of optical switch function, and has low insertion loss, crosstalk, two states of the signal light on/off. Therefore the light switch is of high efficiency.
2013, 62 (4): 044221. doi: 10.7498/aps.62.044221
We perform the finite-difference time-domain (FDTD) simulations and analyze a dual-beam-reflection phenomenon for a Gaussian beam illuminating a Kretschmann configuration composed of a lossless dielectric waveguide between a photonic-crystal-made prism and air. One reflection beam has a small positive shift and the other has a large negative shift in the dual-beam-reflection phenomenon. The FDTD shows that the specific phenomenon takes place just when the corresponding leaky surface mode supported in the Kretschmann configuration is excited. Field profile of the surface mode demonstrates a strong localized stationary field in the dielectric waveguide. We find that the maximum negative lateral shift is -23.23a, corresponding to 4.99 times of the incident wavelength, which is 1.1615 times of the beam waist.
Effects of structure parameters on the dispersion properties of dispersion compensation photonic crystal fiber
2013, 62 (4): 044222. doi: 10.7498/aps.62.044222
Photonic crystal fiber has great potential applications such as dispersion compensation due to its adjustable and flexible dispersion characteristics. In this paper, we design a dispersion compensation photonic crystal fiber, simulate the dispersion characteristics by the finite-difference frequency-domain method, and analyse the effects of the structure parameters air hole spacing Λ and air-filling fraction d/Λ on the dispersion of photonic crystal fiber theoretically. And we also fabricate three photonic crystal fibers with different structural parameters. Through the comparison and analysis of their dispersion curves, we have the following conclusions: the dispersion coefficient increases with air hole spacing Λ and air-filling fraction d/Λ increasing when the air hole spacing of photonic crystal fiber is about 1 μm, but the dispersion is more sensitive to the change of air hole spacing Λ than to air-filling fraction d/Λ, and the effect of air hole spacing on the dispersion coefficient decreases with the increase of air hole spacing. One of the photonic crystal fibers realizes the designed structure: its dispersion coefficient is 241.5 ps·nm-1·km-1, relative dispersion slope is 0.0018 at 1550 nm, it has good ability in dispersion compensation.
2013, 62 (4): 044223. doi: 10.7498/aps.62.044223
In this paper ferrofluid is infiltrated in the index-guiding microstructured optical fiber (MOF) by the well-known capillary force and air pressure. The influences of the length and concentration of filled fiber on its guidance property are analyzed. Based on the response of fluid refractive index to temperature, the temperature sensitivities of filled MOF with different lengths are investigated without applying any external magnetic field. The results show that the short-wavelength edge of the absorption spectrum near 1460 nm remains unchanged, while the long-wavelength profile is sensitive to the temperature and the transmission power of the filled MOF decreases with the increase of temperature. There is a linear relationship between temperature and transmission power of the filled MOF. For the device with a length of 10 cm, its temperature sensitivity reaches 0.06 dB/℃. Combining the excellent thermo-optic effect of ferrofluid with MOF, the single edge of the device could be tuned by the temperature. It is potential to be used as a thermo-optic modulator, filter, and other adjustable photonics device. Considering a large number of magnetically tunable ferrofluids available and the high degree of freedom in MOF design, ferrofluid-filled MOF shows still a great promise and underexplored possibilities for both basic and applied research, opening new perspectives in optical telecommunication, all-optical switching and fiber-optic sensing applications, such as magnetic field sensors. The present study can offer an effective method for the novel technique and structure of all-in-fiber photonic devices.
2013, 62 (4): 044224. doi: 10.7498/aps.62.044224
A novel double air hole multi-core dual-mode large-mode-area optical fiber is proposed. The characteristics of mode field distribution, effective area of fundamental mode, and bending loss are analyzed. And the effects of all structure parameters on the effective refractive index and effective area are discussed. This structure makes TE01 and TM01 mode cut off, and it is of dual-mode transmission in the fiber. Besides, this structure can increase the effective area. The effective area of fundamental mode is approximately 1044 μm2. It is even able to achieve single-mode operation by adjusting the structure parameters. The fabrication of the structure is simple, and design is flexible. Therefore, it is suitable for the high-speed and large-capacity passive fibers as well as for active fibers. The effective area can reach or even exceed 3512 μm2 by adjusting the structure parameters, in order to satisfy the practical demands of large-capacity high-power fiber transmission in the optical communications.
Resonance theory of SH wave total reflection tunnel effect in 1D solid-solid infinite cycle phononic crystal
2013, 62 (4): 044301. doi: 10.7498/aps.62.044301
Using the boundary conditions the SH wave transfer matrix is derived in one-dimensional (1D) solid-solid photonic crystal, and the dispersion relation of the SH wave is obtained. The resonator model 1D infinite cycle photonic crystal is established, and the wavelength formula of SH wave total reflection tunnel effect is investigated using the resonance condition of resonator. The physical mechanism of SH wave total reflection tunnel effect in the 1D solid-solid infinite cycle phononic crystal is explained.
2013, 62 (4): 044501. doi: 10.7498/aps.62.044501
The rigid-flexible coupling dynamic properties of an internal cantilever beam attached to a rotating hub are studied in this paper. Based on the accurate description of non-linear deformation of the flexible beam, the first-order approximation coupling model is derived from Hamilton theory and assumed mode method, taking into account the second-order coupling quantity of axial displacement caused by transverse displacement of the beam. The simplified first-order approximation coupling model which neglects the effect of axial deformation of a beam is presented. The simplified model is transformed into dimensionless form in which dimensionless parameters are identified. Firstly, the dynamic response of an internal cantilever beam is compared with that of an external cantilever beam, which are both in non-inertia system. Then, the stability of an internal cantilever beam is analyzed. Finally, the convergence of critical rotating speed of an internal cantilever beam is analyzed. Generally, it is pointed that an internal cantilever beam has a dynamic softening phenomenon, which is different from the dynamic stiffening phenomenon of an external cantilever beam. The critical ratio of the internal radius to the length of the beam for unconditional stability and the critical rotating speed of conditional stability of an internal cantilever beam are derived. When the first natural frequency decreases as the rotating speed increases, the dynamic system of the internal cantilever beam is conditionally stable. As the number of modes increases, the critical rotating speed of an internal cantilever beam decreases, and it has a convergent value.
2013, 62 (4): 044601. doi: 10.7498/aps.62.044601
Thin elastic rod mechanics with background of a kind of single molecule such as DNA and other engineering object has entered into a new developing stage. In this paper the vector method of exact Cosserat elastic rod dynamics is transformed into the form of analytical mechanics with the arc length and time as its independent variables, whose aims are to find new tools for studying rod mechanics and to develop the area of applications of classical analytical mechanics. Based on the plane cross-section assumption, a cross-section of the rod is taken as an object. Basic formulas on deformation and motion of the section are given. After defining virtual displacement of a cross-section and its equivalent variation rule, a differential variational principle such as d’Alembert-Lagrange one is established, from which dynamical equations of thin elastic rod are expressed as Lagrange equations or Nielsen equations under the condition of linear elasticity of the rod. For the rod statics when there exist conserved quantities, Lagrange equation which makes use of these quantities is derived and its first integral is discussed. Finally integral variational principle is derived from differential one, and expressed as Hamilton principle under the condition of linear elasticity. Hamilton canonical equations in phase space with 3×6 dimensions are also derived. All of the results have formed the method of analytical mechanics of dynamics of an exact Cosserat elastic rod, so that the further problems such as symmetry and conserved quantities, and numerical simulation of the rod dynamics may be further studied.
2013, 62 (4): 044701. doi: 10.7498/aps.62.044701
The capillary flow in a circular tube under microgravity environment is investigated by the homotopy analysis method (HAM), and the approximate analytical solution in the form of series solution is obtained. Different from other analytical approximate methods, the HAM is totally independent of small physical parameters, and thus it is suitable for most nonlinear problems. The HAM provides us a great freedom to choose basis functions of solution series, so that a nonlinear problem can be approximated more effectively, and it adjusts and controls the convergence region and the convergence rate of the series solution through introducing auxiliary parameter and the auxiliary function. The HAM hews out a new approach to the analytical approximate solutions of capillary flow in a circular tube. Through the specific example and comparing homotopy approximate analytical solution with the numerical solution which is obtained by the fourth-order Runge-Kutta method, the computed result indicate that this method has the good computational accuracy.
2013, 62 (4): 044702. doi: 10.7498/aps.62.044702
Compared with traditional mesh method the smoothed particle hydrodynamics (SPH) is unable to directly implement the solid boundary conditions, which hinders its further application to engineering. Therefore, a new repulsive model is deduced based on the Galerkin method of weighted residuals and traditional repulsive methods. Compared with traditional repulsive models, this model does not include unknown parameters; it can avoid fluid particles penetrating wall surface effectively without reducing the size of boundary particle, and also it avoids the oscillation of fluid particles around the boundary in speed and pressure. The new method is examined and compared with traditional methods using four numerical examples including static dam on a fixed boundary, a dam-break flow on a fixed boundary because of gravity, fluid still gradually in a tank because of gravity, dam-break. It is demonstrated that SPH with this new method overcomes the disadvantages in traditional methods, and that this method is an effective method for solid boundary condition.
2013, 62 (4): 044703. doi: 10.7498/aps.62.044703
The solition wave in Bose-Einstein condensate with disk-shaped trap is investigated in this paper. Beyond the mean field, a two-dimensional nonlinear Schrödinger equation is obtained. The modulational instability for this system is studied analytically, and the growth rate for it is given.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2013, 62 (4): 045201. doi: 10.7498/aps.62.045201
The spectra of N2 plasma induced by a femtosecond pulsed laser are studied experimentally at sub-atmospheric pressure. The results show that the spectra of laser-induced plasmas for all sample pressures are composed of continuous spectra and line spectra. As the sample pressure is reduced the intensities of continuous spectra undergo the transition from slow increase to rapid decrease; on the other hand, the intensities of N+ spectra increase significantly with the decrease of pressure. The spectra of N++ species are observed when the pressure is lower than 0.3 atm. The behaviors of the femtosecond laser propagation and energy absorption in N2 plasma at sub-atmospheric pressure are also given and the feature of the laser-induced plasma channel is briefly discussed. These results are helpful for better understanding the laser-induced plasma characteristics, especially provide the clue to the experimental measurement conditions for different charged species, which is useful for the future corresponding experimental research.
2013, 62 (4): 045202. doi: 10.7498/aps.62.045202
The heavy metal elements contained in soil samples which are collected from Changchun train station, CUST campus, South Lake and Jingyue Lake park are separately analyzed by using the orthogonal dual laser pulses induced breakdown spectroscopy (DP-LIBS). The elements Mn, Cr, Cu and Pb are qualitatively analyzed according to the LIBS spectral intensity. It is shown that the intensity of the spectrum is greatly enhanced by using the DP-LIBS and the enhancement is closely related to the delay time between the double pulses. Enhancement variation with delay time presents double-peak changing when 532 nm and 1064 nm laser pulse energies are 70 mJ and 100 mJ respectively. The enhancement of Mn I 406.4 nm is 2.75 at a delay time of 20 s and it is 2.4 at a delay time of 30 s when the second peak appears. The enhancement mechanism of orthogonal pre-ablation DP-LIBS is further discussed.
2013, 62 (4): 045203. doi: 10.7498/aps.62.045203
A new type of pinhole-assisted point backlighter developed and optimized based on experimental research performed on Shenguang-Ⅲ proto-type facility is presented. High quality images of tungsten micro wires and capsule are acquired with a 4.75 keV X-ray point source produced by 1600 J/1 ns/351 nm laser interaction with 3 μm Ti target. Detailed parameters of this backlighter are also obtained using a multiple diagnostic device. The results indicate that pinhole-assisted point-projection backlighter has advantages of high intensity and high spatial resolution, and can be widely used in high energy density physics research.
In order to obtain the dynamic evolution image of tungsten array for foam padding, and to research the form of interaction between tungsten plasma and foam column, a shadow imaging system of four-frame ultraviolet probe laser (266 nm) is designed on 1 MA pulse power device. The time resolution of the system is 2.5 ns, and static space resolution is superior to 70 μm. The radial shadowgraphy image reveals the whole process from the melting and expansion of solid wire to the interaction between the precursor plasma and the foam, from the pinch to rebound inflation. The image shows the continuous interaction between tungsten plasma and foam in the form of Raining within a time of about 50 ns, the plasma shell structure is not found in the whole period of pinch. The quantitative analysis indicates that the minimum pinching speed of the foam column is 1.0×106 cm/s, and maximum pinching speed is 6.0×106 cm/s, and the axial stagnation diameter is about 1 mm. Shadowgram mainly shows the inverse bremsstrunlung effect of interaction between laser and plasma through simulation calculating, and main tungsten plasma interacting with foam column image is shown through synchronizing radial power profile.
Based on microchannel plate (MCP) X-ray optics, a transmission soft X-ray band-pass approach is presented. X-ray transmission band-pass characteristics are given through three structures of MCP channel. Calibration results from a square hole MCP and filter on Beijing Synchrotron Radiation Facility show that MCP transmission spectrum is of a wide range of band-pass options and high efficiency, and can achieve multi-point design of 100 eV bandwidth at lower than 1 keV with different filters.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
First-principles calculations of structural thermodynamic and mechanical properties of 5d transitional metal diborides
2013, 62 (4): 046201. doi: 10.7498/aps.62.046201
The structural, thermodynamic, mechanical and electronic properties of 5d transitional metal diborides TMB2 (TM=Hf-Au) are systematically investigated by first-principles within density functional theory. For each diboride, three structures are considered, i.e., AlB2, ReB2 and WB2 structure. The calculated lattice parameters are in good agreement with previous theoretical and experimental results. From the calculated formation enthalpy, thermodynamic stability of compounds is predicted and the formation enthalpy increases from HfB2 to AuB2. Among the considered structures, AlB2 structure is the most stable for HfB2 and TaB2; ReB2 structure is the most stable for WB2, ReB2, OsB2, IrB2 and AuB2; WB2 structure is the most stable for PtB2. The ReB2 in ReB2 structure has the largest shear modulus (295 GPa), and is the hardest compound, which is in agreement with previous theoretical and experimental results. The calculated density of states shows that they are all metallic. Their variation trends are discussed.
2013, 62 (4): 046202. doi: 10.7498/aps.62.046202
The structure, elastic constant, Debey temperature and electron distribution of α-Ti2Zr under high pressure are presented by using first-principles pseudopotential method based on density functional theory in this paper. The calculated structural parameters at zero pressure are in agreement with experimental values. The elastic constants and their pressure dependence are calculated using the static finite strain technique. We obtain the bulk modulus, Young’s modulus and Poisson’s ratio for α-Ti2Zr. The G and B at zero pressure are 101.2 and 35.6 GPa, respectively. The G/B value is relatively small and decreases with pressure increasing, showing that the α-Ti2Zr is rather ductile. The Debye temperature Θ=321.7 K is obtained by the average sound velocity based on elastic constants. We investigate anisotropies of the compressional wave and two shear waves. The acoustic velocities are obtained from elastic constants by solving Christoffel equation. The results indicate the strong anisotropy for α-Ti2Zr. Moreover, the pressure dependence of s→d electron transfer indicates that β-Ti2Zr will occur under high pressure.
Numerical simulations of the phase transition property of the explosive percolation model on Erds Rnyi random network
2013, 62 (4): 046401. doi: 10.7498/aps.62.046401
Based on the modified Newman and Ziff algorithm combined with the finite-size scaling theory, in this present work we analytically study the phase transition property of the explosive percolation model induced by Achlioptas process on the Erds Rnyi random network via numerical simulations for the basic percolation quantities including the order parameter, the average cluster size, the moments, the standard deviation and the cluster heterogeneity. It is explicitly shown that all these relevant quantities display a typical power-law scaling behavior, which is the characteristic of continuous phase transition at the percolation threshold despite the fact that the order parameter presents a certain feature of discontinuous transition at the same time. Strictly, the explosive percolation transition during the Erds Rnyi random network is a singular transition, which means that it is neither a standard discontinuous phase transition nor the continuous transition in the regular random percolation model.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2013, 62 (4): 047101. doi: 10.7498/aps.62.047101
In this paper we use first-principles full potential linearized augmented plane wave method to investigate the band structure, density of states as well as the optical properties of ZnO, intrinsic and doped separately with Er and Gd. We find that dut to the carriers contributed by the introduced impurity atoms of rare earth (RE), the electrical conductivity of the system is improved and the Fermi level has an upward shift to the conduction band. The data show that due to the doping of RE, there appear the new electron occupied states around the Fermi level. This is formed by the states of Er-4f and Gd-4f. Meanwhile, intrinsic ZnO and doped structures are obviously different. For the optical properties, the absorption coefficient and reflectivity of rare earth doped ZnO are higher than those of intrinsic ZnO in visible region and the energy loss spectra of RE doped ZnO structure present red-shift.
Theoretical investigation on the spin-Hamiltonian parameters for Gd3+-doped molybdates AMoO4 (A=Ca, Sr, Ba, Pb)
2013, 62 (4): 047102. doi: 10.7498/aps.62.047102
In this paper the spin-Hamiltonian parameters, g factors g//, g⊥ and zero-field splittings b20, b40, b44, b60, b64, for Gd3+ ion in molybdates AMoO4 (A=Ca, Sr, Ba, Pb) are calculated by a diagonalization (of energy matrix) method based on one-electron crystal field mechanism. The crystal field parameters in the matrix are calculated from the superposition model. The results indicate that seven calculated spin-Hamiltonian parameters are in good agreement with the experimental values by using only three reasonable adjustable parameters (i.e., the intrinsic parameters Ak (R0), where k=2, 4, 6, in the superposition model). It is shown that the diagonalization method can be used to calculate and explain the spin-Hamiltonian parameters of Gd3+ ion in crystals. The results are discussed.
2013, 62 (4): 047201. doi: 10.7498/aps.62.047201
Vanadium oxide thin films are deposited on Cu/Ti/SiO2/Si by reactive sputtering at room temperature. The crystal structure, component and surface morphology of VOx film are characterized by X ray diffraction, X-ray photoelectron spectroscopy and atomic force microscopy, respectively. These investigations reveal that there is no obvious crystal orientation except weak V2O5 (101) and V2O3 (110) peaks, and the film contains VO2, V2O5, V2O3 and VO mixture phase. The surface particle size of the film is uniform with a root mean square roughness of 1 nm. The resistive switching properties of VOx thin film are tested by semiconductor device analyzer (Agilent B1500A). The I-V characteristics of the VOx memory cell reveal that the cell has low switch voltage (VSetVResetIReset) increases with current compliance increasing. The double-logarithmic plots of the I-V curve for the high and low resistance state show high configuration slope >1 and low resistance state slope=1. It is confirmed that the copper ion diffusion and the formation of conduction filaments may be the resistance switching mechanism of the VOx/Cu structure.
Temperature dependence of electrical resistivity for Sr-doped perovskite-type oxide Y1-xSrxCoO3 prepared by sol-gel process
2013, 62 (4): 047202. doi: 10.7498/aps.62.047202
The temperature dependences of electrical resistivity for Sr-substituted compounds Y1-xSrxCoO3 (x=0, 0.01, 0.05, 0.10, 0.15, 0.20), prepared successfully by sol-gel process, are investigated in a temperature range from 20 to 720 K. The results indicate that with the increase of doping content of Sr the resistivity of Y1-xSrxCoO3 decreases remarkably, which is found to be caused by the increase of carrier concentration. In a temperature range below 330 and 260 K for the sample x=0 and 0.01, the relationship of resistivity versus temperature processes exponential relationship lnρ∝1/T, with conduction activation energy 0.2950 and 0.1461 eV for the sample x=0 and 0.01 respectively. Moreover, experiments show that the relationship lnρ∝1/T exists only in high-temperature regime for the heavily doped samples; at low temperatures Mott’s law lnρ∝T-1/4 is observed, indicating that heavy doping produces strong potential, which leads to the formation of considerable localized state. By fitting the experimental data to Mott’s T-1/4 law, the density of localized states N(EF) at Fermi level is estimated, which is found to increase with doping content increasing.
A compact model of substrate resistance for deep sub-micron gate grounded NMOS electrostatic discharge protection device
2013, 62 (4): 047203. doi: 10.7498/aps.62.047203
The current controlled voltage source model of substrate parasitic resistance of deep sub-micron electrostatic discharge protection device is optimized by considering the effect of conductance modulation. A compact macro-model of substrate resistance is presented according to the characteristics of lightly doped bulk substrate and heavily doped substrate with a lightly doped epitaxial layer, which is scalable with the layout dimension. The experimental model parameters of devices with various spaces between source and substrate diffusion can be extracted by device simulation. The breakdown behavior of gate grounded negative-channel metal oxide semiconductor shows the effectiveness of this method. In the meantime, the simulation time-consuming of the compact model is only 7% that of the device simulation software.
2013, 62 (4): 047301. doi: 10.7498/aps.62.047301
Flexible organic field-effect transistors (OFETs) have revealed wide prospect in their applications to the flexible display, flexible sensor, flexible radio frequency tag and flexible integrated circuit due to their advantages such as foldability, light weight of device and low-cost fabrication process. On the basis of the introduction of advancement in the study of flexible OFETs in this paper, a broad overview about device structures of flexible OFETs, substrate materials, gate insulating layer materials, active layer materials and electrode materials used for flexible OFETs is given, the fabricating process of flexible OFETs is explained, and the effect of bending pattern on the performance of flexible OFETs is discussed. Finally, the application areas of flexible OFETs are summarized and prospected.
Josephson effect in ferromagnetic d-wave superconductor/ferromagnet/ferromagnetic d-wave superconductor junctions
2013, 62 (4): 047401. doi: 10.7498/aps.62.047401
By solving a self-consistent equation for the ferromagnetic d-wave superconducting gap and the exchange energy, we study the Josephson current in the ferromagnetic d-wave superconductor/ferromagnet/ferromagnetic d-wave superconductor junctions. In the Josephson critical current, there are two oscillation components with different periods. It is found that the short-period component can be separated from the long-period one by increasing the exchange energy in ferromagnet and the barrier strength at the ferromagnet/ferromagnetic d-wave superconductor interface, and vice versa. Under a certain thickness for the ferromagnet, exchange energy for the ferromagnetic d-wave superconductor may increase the critical current in the case of a parallel alignment of the magnetization in the ferromagnetic d-wave superconductor.
Preparation and magnetoelectric characteristics of K0.5Na0.5NbO3-LiSbO3-BiFeO3/CuFe2O4 composite ceramics
2013, 62 (4): 047501. doi: 10.7498/aps.62.047501
The (1-x)(K0.5Na0.5NbO3-LiSbO3-BiFeO3)-xCuFe2O4 (x=0.1, 0.2, 0.3 and 0.4) magnetoelectric composite ceramics are prepared by the conventional solid-state reaction method. The microstructures and properties of the composite ceramics are characterized by X-ray diffractometer, scanning electron microscope and magnetoelectric coupling coefficient meter. The weak ionic interdiffusions between the phases K0.5Na0.5NbO3-LiSbO3-BiFeO3 and CuFe2O4 are observed and their particle sizes are well matched between each other. With the increase of CuFe2O4 content, the piezoelectric coefficient (d33) of the composite ceramics decreases from 130 pC/N to 30 pC/N and the magnetostriction coefficient (-λ) increases from 4.5×10-6 to 12.4×10-6. The magnetoelectric coupling coefficient (αE) of the composite ceramics first increases and then decreases with the CuFe2O4 content increasing. When the composition x=0.3, a maximum value of αE=9.4 mV·cm-1·Oe-1 is achieved.
2013, 62 (4): 047801. doi: 10.7498/aps.62.047801
Quantum dot (QD) samples studied in the experiment are grown by molecular-beam epitaxy on semi-insulating GaAs substrates. The photoluminescences (PLs) of the excitons in a single QD are measured at 5 K. The PL spectra of the excitons, biexcitons and charged excitons are identified by measuring and analyzing both PL peaks of the circular and linear polarization and power-dependent PL properties. The charged exciton emissions can be tuned by applying a bias voltage, i.e., negatively charged excitons are changed into positively charged excitons by changing the voltage from 1.0 to -1.0 V. It is shown that the electron-spin will slowly relax compared with that of the hole when they relax from wetting layer into the QD.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2013, 62 (4): 048101. doi: 10.7498/aps.62.048101
Metal rubber (MR) is a new-type damping material with special raw material and manufacturing process. The helix wire is considered as the geometric unit of MR. The thermal expansion model of the MR is established based on the thermal expansion analyses of micro-springs in different contact states with the Schapery model. Thermal experiments are conducted to analyze the effects of relative density and temperature on the thermal expansion property of metal rubber. The heat transfer process of the MR and the heat transfer model of helix wires are obtained based on MR microstructure. Under certain conditions, the heat transfer can be simplified into the single thermal conductions. Based on the Fourier law, thermal conduction of MR microstructure is analyzed using the thermoelectric analogy method. Combined with the equivalent coefficient law of the thermal conduction, the thermal conduction model of MR is established. The formula of the thermal conduction coefficient is derived. The accuracy of the theoretical model is verified by the experimental results. The theoretical and experimental results of the thermal expansion and heat transfer provide strong theoretical and calculative analytical foundation for the application of the MR in the heat insulation material field at high temperature.
2013, 62 (4): 048102. doi: 10.7498/aps.62.048102
The rapid solidification of ternary NiAl-Mo eutectic alloy is investigated by using melt-spinning technique, and the conventional casting is also carried out for a comparison study. The phase constitutions of the alloy samples obtained from different experiments each include both B2-NiAl intermetallic and bcc-Mo solid solution, which are both presented in the 〈110〉priority growth direction. The growth orientation relationship of the coupled two eutectic phases are obtained to be (110)NiAl//(110)Mo. The cast alloy is composed mainly of two regular eutectic phases in structure and exhibits daisy-like eutectic cells. However, the melt-spinning ribbons show the microstructures of the columnar grain near the roller surface zone and the equiaxed grain near the air zone. With the wheel speed increasing from 10 m/s to 50 m/s, the cooling rate of the alloy ribbons increases from 1.01×107 K/s to 2.46×107 K/s, while the thickness of alloy ribbons decreases from 49.4 μm to 22 μm. Meanwhile, the volume fraction of columnar grain zone increases gradually, and the grains are refined obviously. The cooling rate in the melt-spinning experiment for alloy ribbon is obviously higher than that in the conventional casting test, which leads to a significant difference in solidification microstructure between two techniques.
2013, 62 (4): 048401. doi: 10.7498/aps.62.048401
In the presence of Se, Cu(In0.7Ga0.3)Se2 (CIGS) thin films are prepared by the sequential evaporation of Ga, In, Cu at a constant substrate temperature between 250 ℃ and 550 ℃ on the Mo/soda lime glass substrates. The thickness values of films are about 0.7 μm. The structural and phase properties of CIGS films are studied by an X-ray diffractometer, the morphology and crystalline quality are characterized by a scanning electron microscope, the depth profiles of elements are measured by a secondary ion mass spectroscopy, the surface compositions are analyzed by a Raman spectrometer, and the optical properties of CIGS films are measured by a spectrophotometer with an integrating sphere. It is found that the films prepared at substrate temperature above 450 ℃ each exhibite a single Cu(In0.7Ga0.3)Se2 phase, and the homogenization of Ga/(Ga+In) distribution in the Ga-In-Se precursor is achieved by the diffusion of In atoms through grain boundaries. As the substrate temperature is less than 400 ℃, a serious Ga phase separation is observed and the high content of Ga phase mainly exists at the top and bottom of CIGS films. Below 300 ℃, a serious deterioration of crystalline quality is found, and Ga atoms cannot effectively enter into the CIS lattice position to form CIGS. The films prepared at the substrate temperature less than 400 ℃ are covered with lots of Cu(In0.5Ga0.5)Se2 small grains, which results in the enhancement of the surface roughness and the formation of a light trapping structure at the interface of Cd/CIGS. Thus, the light absorption of solar cell is improved. In addition, the smaller gap value of the low Ga content phase also facilitats the light absorption, then the short-circuit current density of thinned solar cell is greatly improved. The analysis shows that the short-circuit current density is the main factor affecting the conversion efficiency of thinned solar cell prepared between 550 ℃-350 ℃. However, when the substrate temperature is below 350 ℃, the reduction of VOC and FF has become the main reason for the deterioration of solar cell. In conclusion, the efficiency of solar cell with 0.7 μm CIGS absorber prepared at substrate temperature of 350 ℃ reaches 10.3% due to the improvement of short-circuit current density.
3D simulation of heavy ion induced charge collection of single event effects in SiGe heterojunction bipolar transistor
2013, 62 (4): 048501. doi: 10.7498/aps.62.048501
In this paper, we establish a three-dimensional numerical simulation model for SiGe heterojunction bipolar transistor by the technology computer aided design simulations. In the simulation we investigate the charge collection mechanism by heavy ion radiation in SiGe HBT technology. The results show that the charge collected by the terminals is a strong function of the ion striking position. The sensitive area of charge collection for each terminal is identified based on the analyses of the device structure and simulation results. For a normal strike within and around the area of the collector/substrate junction, most of the electrons and holes are collected by the collector and substrate terminals, respectively. For an ion strike between the shallow trench edges surrounding the emitter, the base collects a large quantity of charge, while the emitter collects a negligible quantity of charge.
2013, 62 (4): 048701. doi: 10.7498/aps.62.048701
Dielectric properties of aqueous NaCl solution, which are dependent on temperature (293-353 K), with a concentration in a range of 0.001-0.5 mol/L at microwave frequencies ranging from 200 MHz to 6.25 GHz are studied experimentally. The results indicate that imaginary part decreases with frequency increasing, and tetrahedral structure of H2O and hydrogen bond of aqueous NaCl solution is broken by high temperature, leading to the decreasing of real part of dielectric. The loss angle tangent in solution obviously decreases in a low frequency zone at 353 K compared with that in pure water. Temperature window effect that complex dielectric increases or decreases with temperature varying at 2.45 GHz and 5.8 GHz, thereby leading to the oscillation of dissipation power in microwave heating process and the nonequilibrium distribution of temperature is also confirmed.
A new fast magnetic resonance imaging method based on variabledensity spiral data acquisition and Bregman iterative reconstruction
2013, 62 (4): 048702. doi: 10.7498/aps.62.048702
Data acquisition time is a bottle neck for increasing imaging speed of magnetic resonance imaging. To solve the problem, a new fast magnetic resonance imaging method based on variable-density spiral acquisition and Bregman iterative reconstruction is proposed in this paper, under the framework of compressed sensing. The proposed method increases the acquisition speed by data undersampling. The resulting undersampling aliasing artifact is removed by utilizing the intrinsic property of variable-density spiral and Bregman iterative recosntruction. The proposed method is validated by both phantom experiemnt and in vivo experiment. The experimental results demonstrate that the proposed method can effectively remove aliasing artifact from data undersampling, and achieve an image with well-preserved image structure information. Therefore this method can be used for reducing data acquisition time.
2013, 62 (4): 048801. doi: 10.7498/aps.62.048801
Ga2+xO3-x thin films grown on sapphire substrates by metal-organic chemical vapor deposition under different conditions (temperature pressure) are studied by rutherford backscattering spectrometry/channeling. The structural information and crystalline quality are further investigated by high resolution X-ray diffraction (HR-XRD). The results suggest that at the same growth-temperature the crystalline quality is improved with pressure decreasing, while χmin reaches a minimum 14.5% when the pressure decreases to 15 Torr (1 Torr=133.322 Pa). Then if the pressure is kept at 15 Torr, all films present similar crystalline qualities, which hints that the temperature is not a chief factor. Moreover, films prepared under the same condition are annealed at different temperatures: 700, 800 and 900 ℃. At first the crystalline quality is improved by increasing the annealing temperature and reaches a best χmin of 11.1%. Nevertheless, as the annealing temperature is further increased, the samples become decomposed. XRD spectra of annealed samples each reveal a strong peak of Ga2O3 (402), indicating that the epitaxial layer has a preferred orientation (402).
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Effect of substitution Fe2+ on physical properties of MgSiO3 perovskite at high temperature and high pressure
2013, 62 (4): 049101. doi: 10.7498/aps.62.049101
(Mg, Fe)SiO3-perovskite is currently considered to be the most abundant mineral in the earth’s lower mantle. Its behavior at high temperature and high pressure is crucial for interpreting conditions at the deep level of the mantle, variations of seismic waves, and so on. Equilibrium crystal structures and mechanics properties of MgSiO3 and (Mg0.75, Fe0.25)SiO3 are determined using first-principles calculations in a series of hydrostatic pressures up to 140 GPa. Seismic wave velocity as a function of pressure is derived from the Voigt-Reuss-Hill scheme. Their thermodynamic quantities under the conditions of the lower mantle’s pressures and temperatures are computed by means of the Debye model within the quasi-harmonic approximation. The substitution effect of Fe2+ on the thermoelastic property for silicate perovskite is discussed. Substitution of Fe2+ for Mg2+ can provoke softening wave velocity phenomenon arising from the minerals containing Mg element located in the earth interior. The present theoretical results are useful for interpreting seismic wave velocity softened in certain areas of the mantle.
Influence of thermal decomposition temperature of zinc acetate on the structural and the optical properties of ZnO nanorods
2013, 62 (4): 049102. doi: 10.7498/aps.62.049102
ZnO nanorods are fabricated by hydrothermal method on glass substrates that are covered with a ZnO seed layer by the thermal decomposition of zinc acetate. The influences of the thermal decomposition temperature on the structural and the optical properties of the obtained ZnO nanorods are carefully studied by using X-ray diffractometry, scanning electron microscopy and spectrophotometry. It is found that the crystalline quality, head-face dimension, macro stress, and transmissivity are found to be dependent on the thermal decomposition temperature. The 〈002〉c-axis-preferred orientation of the obtained ZnO nanorod is first enhanced and then weakened; the macro tensile stress first decreases and then increases; the average transmissivity first increases and then decreases as thermal decomposition temperature increases. When the thermal decomposition temperature reaches 350 ℃, the c-axis preferred orientation is strongest; the tensile stress is smallest; the average transmissivity in the visible region is maximal for the obtained ZnO nanorod. The surface scattering induced by the head-face dimension is the key mechanism of the average transmissivity of the obtained ZnO nanorod in the visible region.
Gradient calculation based ensemble variational method and its application to the inversion of the turbulent coefficient in atmospheric Ekman layer
2013, 62 (4): 049201. doi: 10.7498/aps.62.049201
The accurate value of the turbulent coefficient in Ekman layer of atmosphere is quite important for the numerical weather prediction and pollutant diffusion calculation. In the paper, based on ensemble method and variational method, the ensemble variational retrieval method is proposed, and the gradient of objective function is calculated with the method. Two calculation procedures are also given based on the linear condition of forward model. The inversion numerical experiments of the turbulent coefficient using ensemble variational method and two calculation flow process are carried out, and the results show that the method has the simple and convenient characteristics, and the turbulent coefficient can be retrieved accurately by observational data.