2012, Vol.61 No.12: 124203. doi: 10.7498/aps.61.124203
In this paper, we numerically study the soliton trapping of supercontinuum in photonic crystal fiber by solving generalized nolinear Schrödinger equation. Using the cross-correlation frequency resolved optical gating (X-FROG) technique, the propagation of the supercontinuum is recorded along the fiber and the evolution of soliton trapping is observed. When the phase-matching condition is met, new frequency of the pulse trapping is generated from four-wave mixing of soliton with nonsolitonic radiation, and is continuously blueshifted while the soliton is redshifted. Higher pump-power shows the strong interaction between soliton and nonsolitonic radiation. Provided in the paper is a theoretical basis for tunable ultra-short laser pulses and supercontinuum researches.
2013, Vol.62 No.8: 084704. doi: 10.7498/aps.62.084704
The deflecting oscillation of planar opposed jets is experimentally studied and numerically simulated by large-eddy simulation (LES) at 25 ≤ Re ≤ 10000 (Re= U0hρ/μ, where U0 is the bulk velocity of the jet at the nozzle exit, h is the height of the slit of the planar nozzle, and ρ and μ are the density and dynamic viscosity of fluid, respectively) and 4h≤ L ≤ 40h, where L is the nozzle separation. The numerical results are validated by comparing with the experimental results of planar opposed jets. Maps of parameter space describing the deflecting oscillation of planar opposed jets at various nozzle separations and exit Reynolds numbers are presented. And the variation features of deflecting oscillation periods and velocity-pressure of turbulent planar opposed jets are primarily investigated. The results of the study show that the LES can effectively predict the deflecting oscillation of planar opposed jets. The velocity and pressure at specific points vary periodically while the deflecting oscillation of planar opposed jets happens. Furthermore, the variation periods of velocity and pressure are in accordance with the periods of the deflecting oscillation. In essence, the deflecting oscillation of planar opposed jets is caused by periodical variation and transformation of the velocity and pressure.
Effect of concentration of heavy oxygen vacancy in rutile and anatase (TiO2) on electric conductivity performance studied by simulation and calculation
2013, Vol.62 No.23: 237101. doi: 10.7498/aps.62.237101
The pure and heavy oxygen vacancy for both rutile and anatase supercell models of TiO1.9375 were structured by using first-principles plane-wave ultrasoft pseudopotential method based on the density functional theory, the geometry optimizations, band structures, and density of states of these models were calculated. Results show that the volumes become greater for both heavy oxygen vacancy rutile and anatase, meanwhile, all of the stability, mobility, and conductivity of anatase supercell model of TiO1.9375 ore greater than the rutile supercell model, which are in agreement with the experimental results.
2012, Vol.61 No.13: 137103. doi: 10.7498/aps.61.137103
Quasiparticle band structures of 3C-SiC and 2H-SiC were calculated using ab initio many body perturbation theory with GW approximation. Quasiparticle energies along high symmetry lines in the first Brillouin zone were evaluated using quasiparitcle self-consistent GW (QPscGW) method and the Maximally-localized Wannier Function interpolation. Both 3C-SiC and 2H-SiC have an indirect band gap with valence band maximum locating at point. The conduction band maximum of 3C-SiC is at X point. As a comparison, band gaps of 3C-SiC calculated by DFT-LDA, one-shot G0W0 and QPscGW are 1.30 eV, 2.23 eV and 2.88 eV respectively. The conduction band minimum of 2H-SiC locates at K point with a band gap of 2.12 eV, 3.12 eV and 3.75 eV predicted by DFT-LDA, one-shot G0W0 and QPscGW respectively. Lattice parameters calculated by DFT-LDA were used in this work. The QPscGW calculations are based on pseudopotential method, predicting slightly larger bandgaps for both 3C-SiC and 2H-SiC comparing with experiments.
Proximity-effect-induced superconductivity by granular Pb film on the surface of Bi2Te3 topological insulator
2013, Vol.62 No.16: 167401. doi: 10.7498/aps.62.167401
The appearance of topological insulators provides us with a chance of finding topological superconductors and Majorana fermions. To pursue these findings one might need to induce large areas of proximity superconductivity on the surface of Bi2Te3 by depositing granular and discrete Pb film. In this experiment, a superconducting state over a distance of 9.5 rm is observed below 0.25 K on a Bi2Te3 crystal whose surface is deposited with Pb grains with a thickness of less than 20 nm and separated at a distance of 20-30 nm.
Research on the bidirectional reflectance of typical urban surface types measured by the directional polarimetric camera
2012, Vol.61 No.7: 077801. doi: 10.7498/aps.61.077801
This paper deals with the retrieving of the bidirectional reflectance distribution functions (BRDFs) of the distinct urban cover in the Pearl River Delta (PRD) region employing the high-spatial-resolution multi-angle polarized measurements made by the directional polarimetric camera (DPC). The results show that three BRDF models (RPV, Ross-Roujean and Ross-Li) describe the DPC measurements well. Forest is best fitted by Ross-Li and bare soil is best fitted by Ross-Roujean. Urban and shrub are best fitted by RPV. The results demonstrate that the reflectances of different types of surfaces are different and increase with the increase of scattering angle. The basic theory of investigating surface properties using multi-angle measurements is proposed.
2014, Vol.63 No.1: 010508. doi: 10.7498/aps.63.010508
In this paper, right-turning vehicle and straight-going bicycle are regarded as the objects for studying the mixed traffic flow characteristics at the intersection. Based on vehicle-bicycle interference characteristics, and the coupling between the vehicle cellular automaton model and the bicycle cellular automaton model, a kind of cellular automaton model (NS-BCA) is presented to analyze the mixed traffic flow of intersection, in which the delay rules of bicycle through vehicle, the gap rules of vehicle through bicycle, and the disposal rules of the occupied conflict zone are taken into consideration. The mixed traffic flow of the right-turning vehicle and the straight-going bicycle is simulated, and the vehicle-non vehicle interference mechanism in mixed traffic flow at the intersection is investigated according to the relationship between traffic volume and arriving rate, transformation of traffic flow phases, the relationship among traffic flow phase, arriving rate and state of mixed traffic flow.
2014, Vol.63 No.10: 104217. doi: 10.7498/aps.63.104217
Based on power spectral density method, the uniform sampling leading to the leakage of low frequency in atmosphere phase screens is analyzed. A new method - non-uniform sampling is proposed. The non-uniform sampling is modeled. The covered sampling frequency regions and the powers of single sampling region by the two sampling methods are discussed and compared. The new method proves to be effective and feasible. For the Kolmogorov spectrum of atmospheric turbulence, the numerical simulation phase screens are generated by the two sampling methods. The simulation results show that the random phase screens generated by the non-uniform sampling method under the condition of increasing neither sampling number nor computation burden, possesses rich high and low frequency information.
INVESTIGATION ON THE MODE OF GROWTH UNIT FOR HYDROTHERMAL SYNTHESIS OF BARIUM TITANATE CRYSTALLITES(Ⅱ)——CALCULATION FOR THE STABILITY ENERGY OF THE GROWTH UNITS-AND THE FORMATION OF THE BARIUM TITANATE CRYSTALLITES-UNDER HYDROTHERMAL CONDITIONS
1997, Vol.46 No.1: 1-11. doi: 10.7498/aps.46.1
The calculation results of the stability energy of the growth unit for hydrothermal barium titanate crystallites are reported and the nucleation as well as the growth of the crystallites under hydrothermal conditions are discussed.
2015, Vol.64 No.13: 137104. doi: 10.7498/aps.64.137104
The p-type porous silicon layer with the aperture about 1.5 microns and hole depth about 15 microns is prepared by electrochemical etching of a p-type monocrystalline silicon wafer with a resistivity 10-15 cm and along  orientation in a double-tank cell which consists of the electrolyte (volume ratio HF: DMF=1:2). Silver nanoparticles film with different thickness has been deposited on porous silicon by the electroless deposition for different deposition times. Morphology and microstructure of the silver nanoparticles/porous silicon composite and ere studied by scanning electron microscope and X ray diffracmeter. Result indicates that the silver nanoparticles are uniformly distributed on the surface of porous silicon and the deposition time has an important influence on the morphology of the composite. The gas-sensing properties of the silver nanoparticles/porous silicon composite to NH3 are tested at room temperature by the static volumetric method. Results show that the deposition time has a significant impact on the gas-sensing properties of the silver nanoparticles/porous silicon. In a short deposition time, the composite with an appropriate amount of silver nanoparticles doped on the porous silicon shows good gas-sensing properties to NH3 with high sensitivity, fast response-recovery characteristic due to the high specific surface area and special microstructure. At room temperature, the gas sensor has a sensitivity of about 5.8 to 50 ppm NH3.
Two-dimensional numerical simulation of laser-ablation of aluminum material by nanosecond laser pulse
2010, Vol.59 No.10: 7120-7128. doi: 10.7498/aps.59.7120
To investigate the interaction between high-power pulsed laser and metal materials,we established a two-dimensional numerical model. The laser-induced two-dimensional temperature distribution was simulated using a finite difference method. From comparison of temperature evolution under different pulse time,spot sizes and energies,it can be seen that the rise of temperature in the initial period is faster than that in the later periods. Isothermal diagram shows that the temperature rising rate is fastest in the center of laser irradiating zone and that the ablation depth is in the range of 1—5 μm. As the laser pulse duration becomes longer,the ablation zone becomes narrower and deeper. As the laser spot diameter increases,the ablation zone becomes wider and shallower. The present numerical results indicate that: (1) the ablation shape and depth sensitively depend on the laser shape,pulse duration and power density, (2) with laser power density in the order of 109 W/cm2,the ablation area is roughly of the orgc of the laser spot. These results are helpful for designing relevant laser parameters in experiments.
Experimental investigations on structures of supersonic laminar/turbulent flow over a compression ramp
2013, Vol.62 No.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.
A cellular automaton model for the road in front of elementary and middle school gates during students going to school
2014, Vol.63 No.9: 094502. doi: 10.7498/aps.63.094502
Based on the studies on traffic bottleneck of road, interference area, and mixed traffic flow, a cellular automaton model for the roads in front of elementary and middle school gates during students going to school is established. Characteristics of traffic flow are discussed via the simulation experiment. Effects of the traffic flow and the traffic volume are analyzed including the proportion of student driving private cars, the proportion of school buses, and the command giving by traffic policeman on the scene. Results of examples given in this paper show that traffic safety can be ensured, the traffic jams can be suppressed, and the goal of achieving largest traffic flow and decreasing the passing time of vehicles can be realized by decreasing the proportion of student driving private cars, increasing the proportion of school buses, and assisting the traffic policeman to command on the scene.
2013, Vol.62 No.16: 167701. doi: 10.7498/aps.62.167701
The formation energies and ionization energies of Ag-N dual-doped ZnO and interstitial N and H monodoped ZnO:(Ag,N) are investigated from the firstprinciples pseudo-potential approach based on density functional theory. It is found that AgZn-NO accepter pair has lower formation energy and ionization energy than Ag-N related to acceptor clusters, which demonstrates that the p-type conductivity of Ag-N dual-doped ZnO system is mainly attributed to the formation of the accepter pairs. Moreover, when ZnO:(Ag,N) system has additional N atoms in some interstitial sites of ZnO crystal, interstitial N atom and AgZn-NO accepter pair prefer to bind together to form AgZn-(N2)O donor complex which lowers doping efficiency, which is not conducive to p-type conductivity. For H doping in the ZnO:(Ag,N) system, the interstitial H atoms also prefer to bind to the AgZn-NO accepter pair, forming acceptor-donor-acceptor (AgZn-H#em/em#-NO) triplet, which not only enhances the incorporation of acceptors (AgZn-NO) but also gives rise to a shallower acceptor level in the band gap in p-type ZnO crystal. Thus, it is suggested that H-assisted Ag-N codoping is an effective method of p-type doping in ZnO.
The human colorectal cancer tissue in vitro experimental study based on photoacoustic endoscopic system
2014, Vol.63 No.8: 084204. doi: 10.7498/aps.63.084204
This paper developed a 4 array transducers photoacoustic endoscopic probe, and based on this, a photoacoustic endoscopic imaging system was build. Phantom experimental imaging was carried out, and the capability of location for endoscopic probe was demonstrated via analyzing the absorption of the light on the 4 sensors position. The in vitro human normal tissues and early colorectal cancer tissues was imaged using photoacoustic endoscopic system. The statistical analysis of the light absorbtion intensity distribution on different position proved that the photoacoustic endoscopic system has the ability to distinguish human normal tissues and early colorectal cancer tissues. This technology is expected to improve the accuracy of early diagnosis of colorectal cancer and has the potential clinical application.
2013, Vol.62 No.3: 039205. doi: 10.7498/aps.62.039205
The global distribution of the second lapse-rate tropopause (LRT2) is investigated with the radio occultation measurements from the constellation observing system for meteorology, ionosphere and climate (COSMIC) covering December 2006-November 2008 Comparisons between COSMIC and radiosonde in terms of the tropopause are examined in three stations to check the difference. The research results are as follows. 1) In the winter, occurrence frequency for LRT2 in the northern hemisphere (NH) is of 50%-70% and in the southers hemisphere is of 20%-40%. 2) The second tropopause over the equatorial zone with 20%-26% occurrence seems to be related to the equatorial jet stream and subvisual cirrus above the first tropopause. 3) In the tropic, the difference in altitude and occurrence between the first and second tropopause decrease with latitude. In the extratropic zone, the difference increases with latitude and reaches a maximum of 7-8 km in the winter of the NH. 4) The second tropopause occurs frequently over the subtropical jet stream region, in which the first tropopause temperature is almost higher than the second one. 5) The more intense the single station daily variations of tropopause height, the bigger the difference between COSMIC and radiosonde is.
Lithium intercalation properties of SnSb/C composite in carbonthermal reduction as the anode material for lithium ion battery
2014, Vol.63 No.16: 168201. doi: 10.7498/aps.63.168201
The SnSb/C composite material is prepared by using the carbonthermal reduction to deal with the mixture of SnO2 and SbO3, respectively with different carbon reductant-glucose and mesocarbon microbead (MCMB). The morphologies and electrochemical properties of two kinds of structures of SnSb/C composite are compared. To characterize the phase and morphology of the composite material, X-ray diffraction, Raman spectra and scanning electron microscope are used. The current charge and discharge, cyclic voltammograms and AC impedancetests are also used to test the electrochemical performance of SnSb/C. The experimental results show that a kind of core-shell structure, of which the alloy particle serves as the core and the pyrolytic carbon as the outside shell, is formed when the glucose is used as the reducing agent. The first discharge specific capacity is 793.379 mA·h/g and it is still kept at 449.987 mA·h/g after 50 cycles. However, when the MCMB is used as the reducing agent, there are only a few of alloy particles attaching to the surface of MCMB, and it is not a kind of core-shell structure but a mixture of alloy particles and MCMB spheres. Its initial discharge specific capacity is 1164.938 mA·h/g, and after 50 cycles it is only 290.807 mA·h/g.
2015, Vol.64 No.13: 134701. doi: 10.7498/aps.64.134701
Precondition for simulating low-speed turbulence is studied in this paper. Against the stiffness of the time-dependent scheme applied to low-speed turbulence, the precondition based on conservative variables is developed, which adopts an implicit iterative method for solving main control equations coupled with turbulence transport equations. In order to ensure the iterative solution stable, a reference Mach number, the dual-time stepping no-matrix scheme, and the method for processing implicitly the source terms of turbulence equations etc. have been developed reasonably, making the software platform unified for all-speed turbulence. Reference Mach number is defined in terms of global and local velocity by a single parameter, and the parameter can be used to control stability, numerical result accuracy, and switch of the precondition. The dual-time stepping LU-SGS method based on conservative variable precondition is developed, realizing no-matrix iterative solution for unsteady flow problems. Against the stiffness in solving the main control equations coupled with turbulence transport equations, the dissipation term of the turbulence equations is processed implicitly, which can enhance main diagonal dominance of the turbulence equations and make the iteration with greater stability. In simulating the turbulence in a nozzle and around a square cylinder or an airfoil, the precondition depicts correctly the structural character of the flowfield; and the computational results are in good agreement with those of theory and experiment etc., and its iterative convergence and numerical accuracy is excellent. It is shown that the precondition in this paper for low-speed turbulence is very effective.
2008, Vol.57 No.6: 3440-3445. doi: 10.7498/aps.57.3440
The line intensities of 100000-000000 transition of asymptotic asymmetric-top molecule H122C16O at several temperatures were calculated by directly calculating the partition functions and regarding the rotationless transition dipole moment squared as a constant. Results showed that the calculated line intensity data at 500 and 3000K are in excellent agreement with the data in HITRAN database，which provide a strong support for the calculations of partition function and line intensity at high temperature. Thereby，the line intensities and spectral simulations of 100000-000000 transition band at the higher temperature 4000 and 5000K were presented. The results are of significance for studying the high-temperature molecular spectrum by experimental measurement and theoretical calculation.
2011, Vol.60 No.4: 040304. doi: 10.7498/aps.60.040304.2
The principle of the quantum switch is introduced by means of entanglement swapping. With the help of quantum switch operating entanglement swapping one by one, quantum correlations between Alice and Bob can be established. Adding entangled particle generator into conventional interconnection equipments, such as switch, and keeping quantum correlations between adjacent devices in the network leisure time, one can upgrade the classic internet to quantum teleportation internet. In quantum teleportation internet, the routing is selected also by utilizing the routing algorithm of classical internet. The routing selection can be synchronized with the establishment of quantum channel in static routing strategy. When the dynamic routing strategy is selected, quantum switch first selects a route to generate a router sequence table and then operates entanglement swapping one by one according to the table to establish the quantum correlations between Alice and Bob.