Vol. 61, No. 9 (2012)
2012, 61 (9): 090201. doi: 10.7498/aps.61.090201
Al ultra-fine grains are prepared by dry roller vibration milling at room temperature. After the ultrasonic hydrolyzing, the Al powders are milled for 2 h, 4 h and 8 h, separately, becoming the colloidal Al(OH)3. After the hydrolyzing production are dried, grinded, calcined, the flaky -Al2O3 nano-particles are obtained, and the particles sizes are in the range from 30 to 50 nm. By X ray diffraction (XRD) analysis method and transmission electron microscope (TEM), we analyze the energy conversion of solid particles in the vibration milling, and study the relation between the structure evolvement of solid particles and mechano-chemical reaction, in order to ascertain ideal milling time. The research results indicate that the solid particles under the action of mechanical force generate a mass of deformation and dislocation flaws and the material is in metastable high-energy state, which is favorable for inducing mechano-chemical reaction. In certain conditions, the surface energy of crystalloid, strain and dislocation energy could be mutually converted. The odds of lattice distortion and dislocation are maximal for the 2 h-milled Al powders, so the material shows a higher chemical reaction activation. On the ultrasonic agitation, the energy is fully released from the material interior, then Al(OH)3 nano-particles are prepared in a short time.
Study on a model of topology evolution of wireless sensor networks among cluster heads and its immunization
2012, 61 (9): 090202. doi: 10.7498/aps.61.090202
A new evolving network model based on complex network theory among the cluster heads is proposed to study the influence of node failure on the performance of wireless sensor network. According to the proposed model, we discuss the virus immunization strategies, and present a new immune mechanism. Theoretical analysis shows that such an evolving network not only has strong fault tolerance, but also can effectively avoid node premature death caused by the rapid energy depletion. It is also found that if the global network information is unknown, the proposed immunization strategies in this paper can obtain better immune effect than the random immunization and acquaintance immunization strategies. The theoretical analysis is verified by numerical simulations.
2012, 61 (9): 090301. doi: 10.7498/aps.61.090301
We present a theoretical scheme for conversion from ultracold atoms to heteronuclear tetrameric molecule A3B via Efimov resonace-assisted stimulated Raman adiabatic passage (ER-STIRAP). The dark state solutions of the system are obtianed for two different pathways. For the first pathway, the intermediate state is populated by homonuclear Efimov trimer A3, and the second one by heteronuclear Efimov trimer A2B. The feasibility and the effectiveness of the scheme are also verified. Meanwhile, we investigate the effects of external field parameters, including the intensity of associated laser pulses, its width, magnetic coupling strength and its detuning, on the fomation of heteronuclear tetrameric molecules. By comparison, it is found that the ultimate yield of the tetrameric molecules for the second pathway is less than ones for the first pathway. In addition, the effects of the intrinsic nolinearity of the system and the spontaneous decay in the intermediate state on the tetramer formation are discussed.
2012, 61 (9): 090501. doi: 10.7498/aps.61.090501
Considering the multiformity in the PWM modulation principle, the diversity in the structures of filter and load, and the limitation of the method based on state transition matrix in the analysis of digital controlled single-phase full-bridge inverter, we present a new method based on analytic expression of the elements in the state transition matrix. This method can analytically express the relationship between the parameters and the dynamic motion of a system named N-M digitally controlled single-phase full-bridge inverter, which has N state variables and structure changing M times within one switching cycle. As an example, the discriminant of Hopf bifurcation, the analytic expressions of the stability boundary and the oscillation frequency of a 3-3 digitally controlled single-phase full-bridge inverter are derived. Finally, the theoretical results are verified by simulations and circuit experiments.
2012, 61 (9): 090502. doi: 10.7498/aps.61.090502
To realize the synchronization of nonlinear dynamical system, the general control method is unidirectional linear coupling. Research on function coupling of chaos synchronization is not enough, so there arises a question: for nonlinear dynamical system, if chaos synchronization is realized by linear coupling, whether can any type of function coupling always make the system go to chaos synchronization? In this paper, a class of nonlinear dynamical system is considered and the relation between linear coupling and function coupling is investigated. It is proved that if linear coupling can make chaos synchronization, then any function satisfying some conditions can do so too. The condition is given and proved. Finally for Duffing system, three coupling functions are used to prove the analytical result. The simulation results show that the conclusion is correct.
2012, 61 (9): 090503. doi: 10.7498/aps.61.090503
In this paper, a novel impulsive control method based on comparison system is proposed to realize complete synchronization of a class of fractional order chaotic systems. By constructing the suitable response system, the original fractional order error system can be converted into the integral order one. Based on the theory of Lyapunov stability and impulsive differential equations, some effective sufficient conditions are derived to guarantee the asymptotical stability of synchronization error system. In particular, some simpler and more convenient conditions are derived by taking the same impulsive distances and control gains. Compared with the existing results, the main results in this paper are more practical and rigorous. Simulation results for fractional order Chen system show the effectiveness and the feasibility of the proposed impulsive control method.
2012, 61 (9): 090504. doi: 10.7498/aps.61.090504
Anti-synchronization of complex network is investigated in which nodes are discrete spatiotemporal chaos systems with diverse structures. The form of the coupling functions connecting nodes in the complex network and the control gain are obtained through constructing an appropriate Lyapunov function. The spatially extended system of laser phase conjugate wave having spatiotemporal chaos behavior in physics, Gibbs electrical-optical spatiotemporal chaos model, Bragg acousto-optical spatiotemporal chaos model and the one-dimensional discrete convective equation are all taken as nodes of the complex network. Artificial results show that a stable anti-synchronization is obtained in the whole network.
Research of fluorescent properties of photo-induced electron transfer of 5(6)-carboxyfluorescein dye-sensitized TiO2 nanoparticles
2012, 61 (9): 090505. doi: 10.7498/aps.61.090505
Anatased TiO2 nanoparticles were prepared by controlling hydrolysis of the TiCl4. Time-resolved fluorescence experiments were carried out to study the photo-induced electron transfer dynamics in the system of the 5(6)CFL dye-sensitized TiO2 nanoparticles. For the aboved system, the formation of the charge transfer complex is attributed to the coupling interaction between the wave functions of the excited electronic state of the dye ((D*)) and the charge separated state ((D++e-)). On excitation of 5(6)CFL dye-sensitized TiO2 nanoparticle system. The injection of electrons into the conduction band of TiO2 nanoparticles takes place in two different ways: through the excited state of the 5(6)CFL dye and through direct injection from the charge transfer complex. The time-resolved fluorescence experimental results indicate that the free 5(6)CFL dye in water has double-exponential decay with lifetimes1=41 ps (74.4%) and2=3.22 ns (25.6%). However, 5(6)CFL dye-sensitized TiO2 nanoparticles have triple-exponential decay with lifetimes of1=44 ps (90.4%),2=478 ps (8.6%) and3=2.41 ns (1.0%). Our research will provide a valuable reference for the mechanism of dye-sensitized solar cell.
2012, 61 (9): 090506. doi: 10.7498/aps.61.090506
This paper presents the day-to-day dynamic evolution of network traffic flow in a simple two-route network. Firstly, a day-to-day dynamical assignment model is formulated, which can depict the evolution of network traffic flow. We have proved that the fixed point of the dynamical system, which is the stochastic user equilibrium solution, exists and is unique. Secondly, based on nonlinear dynamics theory, an equilibrium stability condition for the network is derived. Moreover, the evolution of network traffic flow is investigated through numerical experiments. Meanwhile, periodic and chaotic flows are discovered under certain conditions. Finally, a chaotic control method is derived considering OD demand as control variable.
2012, 61 (9): 090701. doi: 10.7498/aps.61.090701
Spatiotemporally modulated polarization interference imaging spectrometer(TSMPIIS)is static, miniature, stable instrument for remote sensing polarization detecting, which can be used to obtain the spectral and the polarized information about the target. It has been approved that TSMPIIS can obtain the target information by circumrotating its polarizer. However this method destroys the structure of TSMPIIS and reduces the measurement accuracy. According to the detecting theory of TSMPIIS, in this paper, we derive the basic equations for TSMPIIS detecting by analyzing and calculating its Mueller matrix, and authenticate the feasibility and the veracity of TSMPIIS for polarization detecting in full field of view. This work is very helpful for TSMPIIS remote sensing detecting and the retrieval of Stokes parameters.
2012, 61 (9): 092501. doi: 10.7498/aps.61.092501
The coherence parameters of partially chaotic pion sources in relativistic heavy-ion collisions for two statistical ensembles are given.
Finite element analysis and experimental studies on fracture splitting processing by Nd: YAG laser ablation
2012, 61 (9): 092801. doi: 10.7498/aps.61.092801
Laser fracture splitting technology significantly improves the processing quality and efficiency of engine crankcase main bearing block. In order to research the splitting mechanism of ductile iron material fracture notch cauterized by Nd: YAG Laser, the FEAmodel of fracture splitting processing of engine crankcase main bearing block has been developed successfully. The splitting parameters of ductile iron material (QT500-7) main bearing block is analyzed. The numerical simulation results indicate that: among all the key parameters affecting the quality of fracture splitting, the effect of notch depth on fracture splitting load is more obvious than that of the notch opening angle and radius. The value of splitting load decreases rapidly with the increasing notch depth, while the splitting load increases with the increasing notch angle and radius. The optimum value of the notch depth, angle, and radius should be respectively at 0.5 mm, 60 o, and 0.2 mm. The results have been proved by experiments. The optimum parameters obtained from the ABAQUS simulation and experiments provide a numerical reference for significantly reducing the splitting load and optimizing the fracture splitting process, help to achieve the rapid development of engine block process and promote the green manufacture of automobile industry.
The fabrication process of micro-bulk micromegas is introduced. The energy resolution of the 55Fe X-ray is compared with the result of nylon line micromegas. Furthermore, the detailed effect of electric field is discussed.
ATOMIC AND MOLECULAR PHYSICS
The calculation of excitation cross-sections of collisions between Ne isotope atoms with HF molecule
2012, 61 (9): 093101. doi: 10.7498/aps.61.093101
In this paper, we use the Huxley potential function to fit the interaction energy data, which have been calculated at the theoretical level of the QCISD(T)/aug-cc-pVTZ. Differential and partial cross-sections of 16Ne, 20Ne, 34Ne atoms and HF molecule collisions are calculated by the accurate close-coupling approximation method when the incident energy is 100meV. We study the changing tendencies of Ne-HF collisional cross-sections with Ne isotopic substitution.
2012, 61 (9): 093102. doi: 10.7498/aps.61.093102
In this paper,the ab initio method of quantum mechanics is used to optimize the geometric structure of the ground state of LiF molecule with the DFT B3LYP method and 6-311basis in electric fields ranging from -0.015 to 0.015 a.u. The effects of external electric fields on the system energy, bond distance, dipole moment,energy levels, HOMO-LUMO gaps, charge distribution and the infrared spectrum are studied. The results show that the molecular bond distance, dipole moment, HOMO-LUMO gaps and the total atomic charges gradually increase with the increase of the external electric field along the molecular axis Z. At the same time, the total energy of the molecule, frequency and IR intensity decrease and the energy of dissociation becomes smaller with the increase of the external electric field.
2012, 61 (9): 093103. doi: 10.7498/aps.61.093103
The equilibrium geometries, vibrational frequencies of VOxH2O (x= 15) and interactions between H2O with VOx(x= 15) are studied by using the density functional theory B3LYP/DZP method. The results show that ground states for VOxH2O (x= 15) belong to C1 point group symmetry,their electronic state is 2A, and in ground state of VOxH2O (x= 1, 4, 5) water molecule H2O is dissociated; H2O molecule is absorbed easily in VOx(x= 15) and VOxH2O(x= 15) are formed; In VOxH2O(x=15), chemical activations of VOxH2O (x= 1, 4, 5) are lower than those of VOxH2O (x= 2, 3); the sequence of interaction strength between H2O and VOx(x= 15) is VO4H2O VO5H2O VOH2O VO3H2O VO2H2O; there is possibility that OH segment and H atom are dissociated easily from VOH2O and VO5H2O, respectively by visible light exposure. Criterion that H2O molecule is dissociated in VOxH2O(x= 15) is obtained by analyzing frequency spectrum.
2012, 61 (9): 093104. doi: 10.7498/aps.61.093104
bct-C4 carbon allotrope has been attracted great interest because its excellent mechanical properties. In this paper, we study the elastic properties and the strength properties of bct-C4 carbon by first-principles method. Our results show that bct-C4 presents a super uniaxial compressive strength of 524.3GPa, which is 6.9% more than the corresponding value of diamond. The high compressive strength originates from the high compressive rate of chemical bond deviating from compressive direction. Our work suggests that bct -C4 carbon can be widely used in the area of high pressure research.
2012, 61 (9): 093105. doi: 10.7498/aps.61.093105
The potential energy curves (PECs) of the X1+ and a3 electronic states of the BF radical are studied by employing the ab initio quantum chemical method. The calculations are performed by using the complete active space self-consistent field (CASSCF) method followed by the valence internally contracted multireference configuration interaction (MRCI) approach in combination with the basis set, aug-cc-pV6Z, for internuclear separations from 0.095 to 1.33 nm. The effects of the Davidson modification and core-valence correlation and relativistic corrections on the PECs are included. The way to consider the relativistic correction is to employ the second-order DouglasKroll Hamiltonian approximation. The relativistic correction is carried out at the level of cc-pV5Z basis set. And the core-valence correlation correction is made by using the cc-pCV5Z basis set. With the PECs obtained here, the spectroscopic parameters (De, Re, e, exe, eye, Be and e) are determined and compared with those reported in the literature. With the PECs obtained by the MRCI+Q/aug-cc-pV6Z+CV+DK calculations, the complete vibrational states are computed for each electronic state when J = 0. And the vibrational levels, the inertial rotation constants and the centrifugal distortion constants of the first 20 vibrational states of each electronic state are reported. On the whole, as expected, the spectroscopic parameters and molecular constants closest to the experimental data are determined by the MRCI+Q/ aug-cc-pV6Z+DK+CV calculations for the two electronic states.
2012, 61 (9): 093106. doi: 10.7498/aps.61.093106
The transition energies, probabilities, and oscillator strengths for the electric dipole (E1) transitions between all levels of the ground state and the low-lying excited states of 1s2nl (n=24, l= s, p, d, f) configurations of Li atom and Li-like ions(Be+, C3+, O5+, Ne7+, Ar15+, Fe23 +, Mo39+, W71+, U89+) have been calculated, using the relativistic atomic computational code GRASP2K, which based on the Multi-configuration Dirac-Hartree-Fock (MCDHF) method. The norelativistic results for all of those transitions have been also obtained for comparative purposes by performing the similar calculations in the non-relativistic limit. The effects of relativity on the E1 transition energies and oscillator strengths of Li-like isoelectronic sequence are discussed with a particular emphasis, and some important conclusions are drawn. Comparison of the present results with other available data is also made, good agreement is obtained.
2012, 61 (9): 093301. doi: 10.7498/aps.61.093301
Based on the physical energy expression of diatomic molecule, an analytical formula is developed by taking multiple differences to predict the R-branch rovibrational transition spectral lines of diatomic system. Only 15 accurate experimental transition lines, and two rotational constants Bv, Bv corresponding to transition band (v, v) are needed when the new formula is used. The new formula is used to study the transition lines of (3, 7) and (4, 8) bands of the A2uX2g system of Cl2+ ion. Not only the experimental transition lines are reproduced, but also the lost ones, especially the high-lying transitions ones are obtained.
2012, 61 (9): 093302. doi: 10.7498/aps.61.093302
Rovibrational population transfer is controlled by a two-overlapping- pulse scheme in which the frequency ratio of the two pulses is 1:3. The calculated results show that nearly 100% of the population can be transferred from initial state |0,0to target state |3,1. The probability of population transfer can be controlled by pulse phase. When 1 =1.68 , the two pulses can be increased mutually and the probability of population transfer is also increased. When 1 =0.64 , the two pulses can be offset mutually and the probability of population transfer is reduced. The intensity of the second pulse has a significant effect on the population transfer.
Dependence of nonsequential double ionization of He on intensity ratio of orthogonal two-color field
2012, 61 (9): 093303. doi: 10.7498/aps.61.093303
Using classical ensemble model, the dependence of nonsequential double ionization of He on intensity ratio of orthogonal two-color field is investigated. It is shown that this dependence is related to the relative phase() of two-color pulse. When =0.25, with intensity ratio increasing, correlated momentum distribution along the polarization of long wavelength field changes from correlation to anticorrelation pattern; when =0.35, 0.45, correlated momenta are mainly distributed in the first and third quadrants, correlation pattern is nearly unchanged with the variation of intensity ratio. Back analyses of recollision time, recollision angle, recollision momentum of double ionization trajectories are responsible for the above results, and reveal the control of recollision time and the recollision angle in NSDI by orthogonally polarized two-color field.
Accurate calculation of elastic scattering properties of potassium and cesium atoms at ultracold temperatures
2012, 61 (9): 093401. doi: 10.7498/aps.61.093401
In this paper, we calculate the scattering parameters for collision between potassium and cesium atoms at ultracold temperatures, such as s-wave scattering length, effective range and p-wave scattering length, by the quantum method and semiclassical method, respectively. The singlet and the triplet elastic scattering cross sections between 39K and Cs atoms at ultracold temperatures are dominated by s-wave scattering, and shape resonance occurs with the increase of collision energy. There exist pronounced g-wave and d-wave shape resonances for the singlet and the triplet cross sections, respectively. In addition, s-wave scattering lengths are calculated by using the degenerate internet state approximation for selected hyperfine states of 41KCs.
Triply differential cross-sections for single ionization of sodium by electron impact in doubly symmetric geometry
2012, 61 (9): 093402. doi: 10.7498/aps.61.093402
Dynamically screened three-Coulomb-wave model (DS3C) is used to study the single ionization of the 3S orbital of sodium by electron impact. Triply differential cross-sections (TDCSs) are calculated in doubly symmetric geometry at excess energies of 6, 10, 15, 20, 30, 40, 50 and 60 eV using a parameterized optimized effective potential. Comparisons are made between recently experimental data and theoretical predictions of the three-Coulomb wave function (3C) approach and distorted-wave Born approximation (DWBA). The angular distribution of the present TDCS is found to qualitatively reproduce the reported experimental data. It is shown that dynamically screened effects are important in this geometry.
2012, 61 (9): 093601. doi: 10.7498/aps.61.093601
In this paper, using the plane waves ultrasoft pseudopotential method which is base on the first principles of DFT, we study the effects of C, Si, Ge, Sn and Pb alloying on the electronic structure and dehydrogenation properties of VH2. The calculated results show that the electron density of Ef fermi level is higher than that of pure VH2 alloy, exhibiting that the structural stability becomes weakened thus the hydrogen desorption property of VH2 can be improved. Moreover, the computed results of electron density of V-H bond also demonstrate that the interaction between V and H atoms decreases, also showing that the hydrogen desorption property of VH2 is improved. At the same time, it is found from the calculated results that the Mulliken population of V-s orbital increases whereas that of V-d orbital decreases, which is related to the enhanced dehydrogenation property alloyed by La, Ce and Pr.
Molecular dynamics simulation of the influence of Cu(010) substrate on the melting of supported Co-Cu bimetallic clusters
2012, 61 (9): 093602. doi: 10.7498/aps.61.093602
Structural evolution and thermal stability of nanoclusters supported on the substrate play a key role in their applications. In this paper, we study the melting of the mixed Co281Cu280 bimetallic cluster with the icosahedral configuration by using molecular dynamics simulation with a general embedded atom method. The influence of the free or fixed Cu(010) substrate on the melting of the supported cluster is explored. It is found that the melting is strongly related to the substrate condition. There is a sharp increase in the temperature-energy curve for the cluster on the free substrate. The melting point (1320 K) is much lower than that (1630 K) of the cluster on the fixed substrate. The icosahedral configuration is converted into epitaxial cluster along the (010) of the substrate. Premelting occurs for the epitaxial cluster with the increase of temperature. The premelted atoms diffuse to the surface of the substrate and form surface layer until the cluster melt. The variation of the atomic spreading for the cluster on the free substrate is different from the case on the fixed substrate due to the atomic embedding into the substrate.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2012, 61 (9): 094101. doi: 10.7498/aps.61.094101
A novel higher order mode depressed L-band magnetically insulated transmission line oscillator (MILO) device is put forward by destroying the-mode oscillating condition of HEM11 mode. High frequency analysis and PIC simulation are carried out. The simulation results reveal that the novel MILO device oscillates in TM00 mode and successfully suppresses the higher order HEM11 mode generation. Contrastive experiments are carried out. Purified 1.3 GHz microwave obtains a corresponding fundamental mode oscillation in higher order depressed MILO in contrast with original MILO which obtains a 1.42 GHz microwave output.
Study on the interaction between a sheet electron beam and the slow-wave structure for dielectric-loaded rectangular Cerenkov maser
2012, 61 (9): 094102. doi: 10.7498/aps.61.094102
A three-dimensional model for the interaction between a sheet electron beam and the slow-wave structure of dielectric-loaded rectangular Cerenkov maser is proposed. Based on this model, the hybrid-mode dispersion equation and its analytical solution are derived by using the field-match method and the Borgnis function method. Through numerical calculations, the effects of dielectric layer thickness, beam voltage, current density, bean thickness and beam-dielectric layer gap on the linear growth rate are analyzed.
2012, 61 (9): 094201. doi: 10.7498/aps.61.094201
We propose an novel optical element-liquid axicon-to generate self-imaged bottle beams in this paper. From the diffraction theory combined with geometrical optics the light field behind the liquid axicon is analyzed, and the result shows that when the refractive index of infused liquid is smaller than that of the axicon material, it can produce self-imaged optical bottle beams. Through simulation with software MathCAD, we obtain the conversion process of a complete self-imaged optical bottle beam cycle and the evolution process of the bottle beam. We find that the coherent length of self-imaged bottle beams generated by liquid axicon is adjustable. In this paper, we analyze how to use self-imaged bottle beams to capture the particles, and the advantages of capturing multilayer particles using self-imaged bottle beams are also discussed.
2012, 61 (9): 094202. doi: 10.7498/aps.61.094202
In this paper, we present an improved technology of making multi-mode polysiloxane waveguides. Through this kind of improvement, we can solve these problems such as reducing the number of air bubbles, demoulding, uncuring of the core layer, the chemical reaction between the core layer and the cover layer,etc. Finally, more than 80% of waveguides made by us can be successful, but before the improvement of the technology we can only have less than 40% successful waveguides. The longest waveguides can be 22.5 cm in length, compared with the 21 cm of previous ones. The propagation loss of the waveguides is 0.21 dB/cm (850 nm) by cutting back method, but before the improvement we can only have a loss of 0.3 dB/cm (850 nm). So the improvement of the technology is important in optical waveguides making.
Study on measurement and simulation of manipulating electromagnetic wave polarization by metamaterials
2012, 61 (9): 094203. doi: 10.7498/aps.61.094203
The polarization properties of electromagnetic wave have been gradually applied to the fields of communications, navigation and radar. In order to effectively control the polarization state of electromagnetic waves, a kind of metamaterial based on split-ring resonators(SRRs) is designed in this paper. The metamaterial is composed of SRRs, dielectric substrate and metal backplane, and it can completely convert incident linear-polarized waves into circular-polarized waves, elliptic-polarized waves and linear-polarized waves whose polarization is perpendicular to the incident wave. Our design is demonstrated by microwave experiments and simulations,and the experimental result and the simulation result are in good agreement with each other.
Slowdown of group velocity of light pulse in erbium-doped optical fiber amplifier under no absorption loss at a room temperature
2012, 61 (9): 094204. doi: 10.7498/aps.61.094204
Because of the absorption of erbium-doped optical fiber, the group velocity of the optical pulse propagation is slowed down and the intensity of signal is reduced, which brings more difficulties to the actual measurement of slow light and its application in communications, such as the distortion and the low measurement.Therefore only after the group velocity slowdown of light pulse in erbium-doped optical fiber under no absorption loss is realized, can the slow light technology really have the practical application. We investigate the erbium-doped optical fiber amplifier deeply and develop a technology, in which the different pump powers and fiber lengths are used to reduce the signal loss through theoretical calculation and realize the group velocity slowdown of light pulse. The results show that no absorption loss is realized at a pump power of 3.5 mW, and we realize the slow light with a fiber length of 0.1 m when the pump power is zero.
2012, 61 (9): 094205. doi: 10.7498/aps.61.094205
A radio-over-fiber(ROF) downlink system based on a new polarization-stable millimeter-wave generator is proposed to reduce costs, increase transmission distance and improve system performance. Compared with traditional system, the system uses two polarization-stable laser signals produced by selecting the frequency of the polarization maintaining fiber Bragg grating(PMFBG) to generate millimeter-wave by beating frequency. It is easy to be implemented and the influence of power noise on the system is reduced. The effects of laser power, linewidth and reflectance spectrum of PMFBG on the performance of millimeter-wave are analyzed; Simulation shows that the frequency of millimeter-wave is affected by the group delay, the length, the dispersion of the polarization-maintaining fiber(PMF) and the width, the chirp coefficient of laser's pulse profile. After optimizing parameters of PMF, millimeter-wave of 60GHz is generated, and the ROF downlink system is analyzed. The results of the study show that the eye diagrams demodulated in the mobile station are excellent when the optical carrier which is modulated by the millimeter-wave serving as sub-carrier transmits over 80 kilometers from center station to base station. The excellent performance of the system is verified.
2012, 61 (9): 094206. doi: 10.7498/aps.61.094206
Beam quality M2 factor of the single-aperture coherent laser beam synthesis system is a major problem to be solved. Based on the definition of second-order moment, beam quality M2 factors of the coherently combined beam supposed by the basic model TEM00, TEM01and TEM10 are presented by some analytical expressions in this paper. And, the effects produced by the beam waist width, the propagation distance, the ratio of the two amplitudes and the distance between the two coherent sources on the beam quality M2 factor are numerically analyzed. Some results show that the beam quality M2 factor of the coherently combined beam is unchanged when the propagation distance parameter d1100. And the experiment is carried to verify some theories of the two TEM00 coherently combined beam.
Infrared thermal wave imaging for inspecting the insulation layer of superconducting busbar in thermonuclear experimental reactor
2012, 61 (9): 094207. doi: 10.7498/aps.61.094207
This work aims at developing a thermal wave imaging method for testing the insulation layer of superconducting busbar in thermonuclear experimental reactor. In the paper, a film bag filled with hot water is used to heat the sample surface. The approximate theoretical model of transient heat conduction under an instantaneous cylindrical surface source in cylindrical structure is given. Through simulation and analysis of the theoretical model, it is found that differential processing of the thermal cooling signals can improve the signal contrast between defects and non-defects areas. Compared with the flash pulse excitation method, the contact excitation method can detect deep defects.
Study on anisotropic diffraction properties of holographic dispersed liquid crystal transmission grating
2012, 61 (9): 094208. doi: 10.7498/aps.61.094208
In this paper, we study the anisotropic diffraction properties of transmission grating based on scaffolding morphology holographic dispersed liquid crystal. Due to the absence of liquid crystal droplet formation within the grating, a simple model is proposed and combined with the anisotropic coupled-wave theory to investigate the diffractive properties. The detailed comparison between experiment and theory indicates that the alignment of liquid crystal molecules in the LC-rich region is along the grating vector.
Optical generation of high-quality millimeter-wave based on an optically injected VCSEL subject to polarization-rotated external optical feedback
2012, 61 (9): 094209. doi: 10.7498/aps.61.094209
A scheme of optical generation of high-quality millimeter-wave based on the optically injected vertical-cavity- surface-emitting laser (VCSEL) subject to polarization-rotated optical feedback is proposed in this paper. Based on the spin-flip model (SFM), wich external disturbances taken into account, the performances of the millimeter-wave generated by this scheme are numerically investigated. The results show that under suitable operation conditions, a slave VCSEL (S-VCSEL) injected by a master VCSEL (M-VCSEL) will operate in a period-one (P1) oscillation state and the output optical intensity of S-VCSEL looks like being modulated by a microwave signal. By adjusting the injection strength iand the frequency detuning between S-VCSEL and M-VCSEL, a millimeter-wave, whose frequency can be continuously adjusted in a large range from 30 GHz to 60 GHz, is obtained. After introducing polarization-rotated optical feedback, the linewidth of millimeter-wave can be obviously narrowed by adjusting the feedback strength i and the feedback delay time . For a millimeter-wave with a linewidth of 5.509 MHz, generated by the optically injected VCSEL, its linewidth can be reduced to 230.2 kHz under optimum feedback parameters. The results obtained in this paper are helpful for acquiring high-quality millimeter-wave used in high speed Radio-over-Fiber (RoF) system.
Novel flux concentrator with a single CSRR surrounded by a resonator for radio frequency superconducting quantum interference device
2012, 61 (9): 094210. doi: 10.7498/aps.61.094210
A novel flux concentrator surrounded by a resonator is proposed in this paper. A complementary single split ring resonator (single CSRR) is introduced for the flux concentrator, while the resonator surrounding the flux concentrator employs a third-order stepped-impedance hairpin resonator (SIR). High frequency structure simulation software ANSYS HFSSv.11 is used to simulate the proposed flux concentrator and resonator. Moreover, the single CSRR is analyzed theoretically. Simulation and theoretical results shows that the novel flux concentrator surrounded by a resonator introduces a single CSRR, which improves the flux focus effect of the concentrator significantly, and so enhances the performance of coupling between the RF SQUID and the flux concentrator (the coupling coefficient ksc is improved 2 times) and increases the effective area to 1.227 mm2.
Fabrication of nanoporous metal by selective electrochemical dealloying from laser cladding Cu-Mn alloys
2012, 61 (9): 094211. doi: 10.7498/aps.61.094211
The nanoporous metal is fabricated by means of hybrid laser processing in combination with electrochemical dealloying. Cu-Mn alloy coatings with fine shape, low dilute ratio and refined microstructure are fabricated on medium carbon steel by means of laser processing. Polarization curve indicates that the Cu-Mn alloy shows selective dissolution characteristics for different electrolytes. Nanoporous Cu and nanoporous Mn are fabricated with optimal electrochemically dealloying parameters. Nanoporous Cu has pore sizes rangeing from 30 to 50 nm, while the surface morphology of the porous Mn shows a ribbon-like structure with ultrahigh roughness factor up to 900. Finally, the potential-pH diagram is used to explain the mechanism of the dealloying.
2012, 61 (9): 094212. doi: 10.7498/aps.61.094212
The degree of coherence of the supercontinuum(SC) directly determine the resolution and the precision in many optical apparatus, so how to achieve highly coherent SC is one of the focuses in nonlinear optics. It is shown that modulation instability (MI) is the key element that influences the coherence of SC. Therefore an effective way of achieving coherent SC is to avoid MI and to use other nonlinear effects such as self-phase modulation (SPM). We design a kind of photonic crystal fiber (PCF) which has an all-normal group velocity dispersion (GVD) profile. After numerical investigation on the generation of SC in the PCF we obtain the degrees of the SC in different lengths. Results indicate that for the generated SC by pumping 50 cm of this PCF with TFWHM=400 fs unchirped pulse Gaussian pulse can realize high coherence in the entire broadening area on condition that relative power is larger than -80 dB.
2012, 61 (9): 094213. doi: 10.7498/aps.61.094213
Multifunctional photonic differentiation is robust in optical computing and optical signal processing. We theoretically propose a multifunctional optical differentiator based on phase modulation and linear filtering. We also experimentally demonstrate two kinds of differentiators by using a phase modulator cascaded a fiber delay interferometer (DI) whose transmission spectrum is approximately linear. Difference between the two differentiators relies on whether the differentiated signals are formed by the optical intensity or the optical field of the output signal, which in turn depends on the relative shift between the signal wavelength and the closest notches of a linear filter. We also show the average errors of all kinds of differentiations and results show that the increase of the degree of linearity of the transmission spectrum of the DI will reduce the average error. Moreover, we demonstrate multi-channel multifunctional differentiation due to the comb spectrum of the DI.
Experimental research and application of pulse clean technique based on cross polarized wave generation
2012, 61 (9): 094214. doi: 10.7498/aps.61.094214
Cross polarized wave (XPW) generation technique is used to improve the contrast of the output pulses from a 800 nm Ti: sapphire femtosecond (fs) laser. The measured temporal contrast of the cleaned pulse is 1011 (limited by the dynamic range of the third-order auto-correlator), which is 3 orders of magnitude higher than the temporal contrast ratio of the initial pulse. The efficiency of XPW is 22%. And the bandwidth of the cleaned pulse is broadened after the XPW nonlinear process. Through the dispersion compensation using double chirped mirrors and fused silica plate, the 25 fs pulse duration is achieved. With the cleaned pulse used as the seed of a TW-level Ti: sapphire chirped-pulse amplification laser system, the 250 mJ/50 fs pulses corresponding to 5 TW peak power are obtained. And the 1011 temporal contrast is demonstrated on the time scale of hundreds of picoseconds before the main femtosecond pulse.
2012, 61 (9): 094215. doi: 10.7498/aps.61.094215
According to the wave equation used when the optical pulse propagation in the fiber, the nonlinear coupled equation is a deduced under the joint actions of Raman effect and parametric amplification in the birefringent. with Lorentzian model of parallel Raman gain spectrum, the gain is obtained by combining the Raman effect and the parametric amplification when the pump wave polarization is oriented at 45 between the birefringent fiber axes. The gain spectrum is discussed as a function of the input parameters (input power, the group velocity mismatch) in different dispersion regimes. The result shows that Stokes and anti-Stokes gain spectra are asymmetric because of Raman effect. The gain appears as primarily anti-Stokes wave in anomalous dispersion regime, and Stokes wave in normal dispersion regime.
2012, 61 (9): 094216. doi: 10.7498/aps.61.094216
For the modulation phenomenon of output light intensity in the laser gyro consisting of totally reflecting prisms during its dither bias, the effect of mechanical dither is calculated and analyzed systematically. By the numerical simulation and finite element analysis methods, an analytical expression for the output light intensity of the laser gyro is derived as a function of stress induced birefringence and deviation of photodetector. A new laser gyro type with the symmetic rectangle structure that can improve the stability of optical output is suggested for the first time. The results show that the position assembly accuracy of the photodetector and the stress induced birefringence have a significant effect on light intensity modulation. Reducing the photodetector deviation and using symmetic prisms material with a suitable refractive index, the extent of intensity modulation could be reduced by over 52.63%. The analytic study provides an important reference for improving the quality of output light and the reliability of prisms laser gyro.
2012, 61 (9): 094217. doi: 10.7498/aps.61.094217
The thermal lensing effect of solid-state lasers under the lasing condition is studied by a thermal model for designing a working cavity. We simulate variations of the stable zones for cavities with different configurations. Theoretical descriptions are verified by a Nd: YAG laser in the experiment. The control of the thermal lensing is achieved experimentally by changing the configuration of the cavity.
2012, 61 (9): 094218. doi: 10.7498/aps.61.094218
The delay theoretical analysis result of single-longitudinal-mode pulse injected in active Fabry-Perot cavity has been obtained. The gain in Fabry-Perot cavity has been calculated and the numerical simulation result of output pulse has been obtained. The results show that when the energy of the pulse decreases at a certain value, the gain produced by increased pump particle population can compensate the loss in the cavity and the delay pulse can achieve steady state. In experiment, the active Fabry-Perot cavity is a Nd: YAG laser sided pumped by laser diode. For the pulse inputed externally, we achieve 140 pulses within 2 ups. Finally, the reference light is delayed using the active Fabry-Perot cavity. And we show the heterodyne experiment of signal light whose frequency shift generated by an acousto-optic modulation (AOM), and the experiment results accord with the frequency shift of the AOM and the error is less than 4%.
2012, 61 (9): 094501. doi: 10.7498/aps.61.094501
The bifurcation and chaotic motion of some nonlinear relative rotation system with heteroclinic orbit is studied. By using dissipative system Lagrange equation, the dynamics equation of nonlinear relative rotation system under combination harmonic excitations is established. Firstly, the bifurcation response equation of relative rotation system under combination resonance is deduced with the method of multiple scales. Singularity analysis is employed to obtain the transition set of steady motion. Secondly, the Melnikov function of heteroclinic orbit is solved according to heteroclinic orbit parameter equation of relative rotation system. The critical condition of chaos about Smale commutation is given. Finally, numerical method is employed to analyze the influences of different system parameters on chaotic motion by bifurcation diagram, the maximum Lyapunov, phase trajectory and Poincare map.
Dynamic characteristics of multivariate graph centrobaric trajectory in phase space of two-phase flow
2012, 61 (9): 094701. doi: 10.7498/aps.61.094701
We propose a multivariate graph centrobaric trajectory-based method for characterizing nonlinear dynamics from high-dimensional chaotic time series. After the optimal selecting of the embedding dimension and time delay, we map the high-dimensional vector point into the two-dimensional radial plane graph, i.e., the high-dimensional vector point is transformed correspondingly to a geometric polygon. By extracting the geometric location of the polygon barycenters, we can obtain the evolving feature of the barycenter dynamical trajectory. Then we use the moment quantity of the barycenter trajectory to distinguish different chaotic time series. Finally, we apply our method to the fluctuating signals measured from gas-liquid two-phase flow experiments. The results suggest that our method can be a powerful tool for not only distinguishing the different flow patterns but also investigating the dynamical evolving mechanism of flow patterns.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
The analytic model between effective heat capacity and relaxation time in gas acoustic relaxation process
2012, 61 (9): 095101. doi: 10.7498/aps.61.095101
The acoustic relaxation is one important nature of gas, which is caused by the sound propagation in the polyatomic molecule gas. It is the basic relaxation process, which arises from the translational-vibrational degree of freedom (V-T) and the molecular energy transfer between different vibrational degrees of freedom (V-V) separately. By studying the molecule energy transition model of the basic acoustic relaxation processes of gas, we propose an analytic model reflecting the correspondence between effective specific heat capacity and relaxation time in this paper. Compared with the existing relaxation model, the analytic model provides the corresponding relationship between the vibrational specific heat capacity and the relaxation time in V-T and V-V. The solution procedure of the analytic model illustrates that the higher vibrational energy level is the determinant of the basic relaxation process. The effective heat capacity is the foundation of acoustic relaxation attenuation spectrum of gas. The relaxation attenuation spectra result from the analytic model in this paper, which is modified by fine-tuning the collision diameter of the gas molecule, are more consistent with the experiment data than with the existing theoretical value. It proves the correctness and validity of the analytic model.
Experimental study of time characteristic of optical radiation in femtosecond laser interaction with solid targets
2012, 61 (9): 095201. doi: 10.7498/aps.61.095201
In this paper, the time-integrated image pattern of spatial distribution and time-resolved image of optical radiation are measured in the normal direction from the rear side of targets by employing optical streak camera on the 100 TW femtosecond laser facility. The image pattern of spatial distribution presents a strip-shape: the region of optical radiation has a radiation angle and optical intensity distribution, and contains various components; the time-resolved image of optical radiation presents the time-resolved pattern of the optical radiation, witch further proves that the transition radiation is intense, which has short duration (ps) and correspouns to duration of TR of 85.5 ps. and other optical radiations are weak, which have very long duration (ns). The time-resolved characteristic of optical radiation can provide new evidence for discrimination and judgement of TR.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2012, 61 (9): 096101. doi: 10.7498/aps.61.096101
Extensive molecular dynamics simulations of water permeation and ion selectivity of the single-walled carbon nanotubes with the radial deformation are presented. The simulated results indicate that there is a close relationship between the minor axis of deformed carbon nanotubes and the variety, density as well as the position of functional groups. The critical minor axis of different diameter carbon nanotubes exists, and the carbon nanotube whose minor axis is less than the critical minor axis owns the selectivity of chlorine and sodium ions. Meanwhile, compared with intrinsic carbon nanotubes, the deformed nanotubes do not obviously reduce the permeation of water. The analysis of the potential of mean force reveals that the selectivity and the permeation of ions come from the pass potential barrier of carbon nanotubes with various minor axises. Furthermore, our observations of modifying functional groups may have significance for controlling the minor axis and improving the selectivity and permeation of ions in real manufacture of some large nanotubes.
NPN bipolar effect and its influence on charge sharing in a tripe well CMOS technology with n+ deep well
2012, 61 (9): 096102. doi: 10.7498/aps.61.096102
In this paper, we investigate the charge sharing collection induced by heavy ion radiation in a tripe well CMOS technology with n+ deep well though 3-D TCAD device simulation. Result shows that n+ deep well will induce the parasitical NPN bipolar transistor, and therefore enhance the charge sharing between NMOS remarkably. The enhancement factor is 24 times that in PNP bipolar in dual well technology. Furthermore, the effects of n-well contact and p-well contact on NPN bipolar are studied. The result shows that the NPN bipolar enhancement factor will decrease with the increase of p-well contact area and with the decreasing of its distance to device, while the NPN bipolar enhancement factor will increase with the increase of n-well contact area.
2012, 61 (9): 096201. doi: 10.7498/aps.61.096201
The relationship between spall strength and impact stress of AD95 ceramics which is in a one-dimensional strain state is determined by velocity profile measurement of the free surface or the sample/window interface. All fiber displacement interferometer system for any reflector is used in velocity measurement. Further the relationship between shock compressive damage degree and impact stress is discussed. The results indicate that the stress threshold of AD95 ceramics against shock compressive damage is about 3.7 GPa, which is less than its Hugoniot Elastic Limit (HEL, about 5.47 GPa). When impact stress is less than the threshold, no compressive damage occurs, and the spall strength increases with impact stress gradually. When impact stress is greater than the threshold, shock compressive damage occurs and develops rapidly which leads to the decrease of the spall strength with impact stress. The spall strength falls to zero when the impact stress increases up to about the HEL, which indicates that the material has lost the ability to resist the tensile stress and severe shock compressive damage has happened.
Simple harmonic oscillator immune optimization algorithm for solving vertical handoff decision problem in heterogeneous wireless network
2012, 61 (9): 096401. doi: 10.7498/aps.61.096401
In heterogeneous wireless network environment, wireless local area network (WLAN) are usually deployed within the coverage of a cellular network to provide users with the convenience of seamless roaming among heterogeneous wireless access networks. Vertical handoffs between the WLAN and the cellular network could occur frequently, with regard to vertical handoff performance, there is a critical need for developing algorithms for connection management and optimal resource allocation for seamless mobility. In this paper, we develop a mathematical model for vertical handoff decision problem, propose an artificial simple harmonic oscillator immune algorithm-based vertical handoff decision scheme, and perform the simulation experiments to validate proposed solution. Experimental result shows that the proposed solution, compared with literature solutions, can not only balance the overall load among all networks but also increase the collective battery lifetime of mobile terminals, and has the advantage of good application value.
2012, 61 (9): 096801. doi: 10.7498/aps.61.096801
The deposition process for Be atoms on Be substrate is studied using molecular dynamic simulations. The morphologies of the deposited films are distinctly different under different incident energies. In a specified range, the surface roughness of the film decreases with the increase of the incident energy. However, the over-high incident energy is unfavourable for reducing the surface roughness of the film. The distributions of the coordination numbers and potential energy of the single atom are used to analyze the film structure under different incident energies. With the bigger incident energy the density of the film is bigger and the distribution of the potential energy of the single atom is more continuous. At the same time, the distribution of the atomic stress is more continuous. Finally, the energy conversion process of the single atom is given, and the influence of the initial incident energy on the locally accelerated energy near the substrate is analyzed.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2012, 61 (9): 097101. doi: 10.7498/aps.61.097101
In this paper, the electronic structure and the optical properties of ZnO doped with Ta are calculated by the first-principles method based on the density function theory. The calculation results show that fermi energy levels enter into the conduction band after Ta-doped. With the increase of Ta concentration, the bandgap of ZnO is reduced and dielectric function imaginary part, absorption coefficient, the refractive index, and reflectivity are all changed significantly. The imaginary part of dielectric function and the reflectivity shift toward the higher-energy region. The absorption edge shifts to ward the red. The relationship between electronic structure and optical properties is pointed out in theory.
2012, 61 (9): 097102. doi: 10.7498/aps.61.097102
The crystal structure, electronic configuration and electronic structure of siderite FeCO3 are studied by first-principles calculations through the plane wave pseudo-potential method. The real antiferromagnetic (AFM) spin ordering state is considered. The pressure increases up to 500 GPa under hydrostatic pressure condition. FeCO3 transforms from high spin (HS) AFM state to low spin (LS) nonmagnetic (NM) state in a pressure range between 40 and 50 GPa, accompaned with a volume collapse of 10.5%. Siderite FeCO3 is insulating before and after the phase transition, but the 3d electrons of Fe2+ ions for the LS-NM state are more localized, The band gap increases with pressure increasing, and the LS-NM state moves into a more strong ionic state and no metal-insulator transition (MIT) occurs.
2012, 61 (9): 097103. doi: 10.7498/aps.61.097103
In this paper, based on the framework of kp method, the influence of uniaxial stress on the conduction band energy-band structure of bulk-Si is analysed first, the coupling of 1 and 2 bands at the X point, and the influence of that band-band coupling on the minimum of energy valley are then separately discussed under the action of shear strain. On that basis, the dispersion relation close to the minimum is obtained. Furthermore, the different valley orientations need to be taken into account. Using the coordinate transformation, the modelling for dispersion relation of each valley with arbitrary uniaxial stress is finally achieved. The proposed analytical model in this paper is also suited to the understanding of the physical properties of uniaxial strained Si material and may provide some references for the study on bandstructure and electrical properties of the inversion layer in uniaxial strained Si nMOSFETs.
2012, 61 (9): 097201. doi: 10.7498/aps.61.097201
The error of asymptotic waveform evaluation (AWE) is estimated by the error analysis of rational approximation, and an efficient bandwidth estimation approach is finally proposed, which is used to form a new adaptive frequency-sweep analysis algorithm for a given frequency band in this paper. The broadband electromagnetic scattering analysis of three-dimensional (3-D) perfectly electrically conducting (PEC) objects with different shapes is performed, and dispersive dielectric object is considered. The effectiveness of the proposed method is proved by comparing the numerical results with those obtained from the analytical solution and the direct solution.
2012, 61 (9): 097401. doi: 10.7498/aps.61.097401
High frequency coherent acoustic-phonons are excited in Fe/Si film by using femtosecond pump-probe technique. The dynamics of coherent acoustic-phonons can be fitted well to a classical damped harmonic function. The frequency and the dephasing time of the observed acoustic-phonons are 0.25 THz and 12 ps, respectively, which are independent of pumping photo-energy and fluence. Moreover, the amplitude of the coherent acoustic-phonons is linearly proportional to the fluence. The critical parameter (12e-ph/T) is calculated to be about 0.6, which indicates that the electron pressure might play a significant role in driving coherent acoustic phonons. The thickness and the mass density of the film are required to determine the out-of-plane elastic constant C～283 GPa of the Fe/Si film.
A method of determining the highest temperature attained by magnetic material in the adiabatic magnetization
2012, 61 (9): 097501. doi: 10.7498/aps.61.097501
Determining the highest temperature attained by a magnetic material in the adiabatic magnetization is important for the optimal selecting of magnetocaloric material. As an example, the Gd3Ga5O12 crystals are investigated. Under the superstrong magnetic field and at low temperature, the form of effective magnetic susceptibility is given based on the tendency-saturation law. The magnetic entropy change and the phonon entropy change as well as the magnetocaloric effect are calculated in a magnetic field range from 0 to 40 T. The calculated results are in good agreement with the measured data. A method of determining the highest temperature attained by magnetic material in the adiabatic magnetization is given by using the only intersection point between the curves of the saturation-magnetic entropy change and the phonon entropy change. The highest temperature in the adiabatic magnetization is predicted to be 64.7 K for the Gd3Ga5O12 crstal.
2012, 61 (9): 097502. doi: 10.7498/aps.61.097502
Arrays of Ni1-xMnxFe2O4 (x = 0.0, 0.25, 0.5, 0.75) nanowires with an average diameter of about 80 nm are prepared by porous anodic aluminum oxide membrane poured sol technique. X-ray diffraction analysis shows that the nickel manganese ferrites nanowires with cubic spinel structure are synthetized. Scanning electron microscopy and transmission electron microscope images indicate that the nanowire arrays are composed of prolate spheroids with different crystal orientations. Magnetic measurements show that saturation magnetization increases and then decreases with Mn increasing. The change is related to the location and the substitution of ion in spinel structure. Compared with of block material NiFe2O4, the saturation magnetization of nickel ferrite nanowire arrays is low. This is due to the fact that the noncollinear magnetic structure in nanowire arrays become predominant.
2012, 61 (9): 097503. doi: 10.7498/aps.61.097503
Magnetic quantum-dot cellular automata (MQCA) corner structure consists of both ferromagnetic coupling and anti-ferromagnetic coupling. Signal propagation of corner structure for magnetic material Fe is theoretically investigated by applying an external clocking field method. Magnetization evolution image on signal propagation of the corner is presented by micromagnetic simulation; it is shown that Fe nanomagnets can ensure stable switching of corner including two kinds of lengthy coupling. The proposed corner structure is then fabricated by electron beam lithography, thermal evaporation and lift-off technologies. Scanning electron microscopy and magnetic force microscopy measurement results demonstrate perfect pattern and correct signal propagation of two types of coupling.
2012, 61 (9): 097701. doi: 10.7498/aps.61.097701
Based on the common behavior of the Vogel-Fulcher relation followed by both dielectric dispersion of relaxor ferroelectrics in transition region and the viscosity-temperature relation for glassy liquids in supercooled state, vacancy compensation principles of donor doped barium titanate systematic ceramics are analyzed. By the introduction of the concept of configurational entropy, the temperature dependent Ti cation vacancy reaction potential is investigated, and the results show that the increase in donor content gives rise to the increase in disorder degree, the increase in Ti cation vacancy content, and the decrease in size of average polar region; on condition that configurational entropy satisfies the Vogel-Fulcher relation, Ti cation vacancy reaction regime and therefore the polar region will both increase with temperature lowing, and the variation of the regime causes dielectric dispersion of relaxor ferroelectrics. Frozen effect happens and dispersion disappears for the Ti cation vacancy reaction at a certain lower temperature.
2012, 61 (9): 097702. doi: 10.7498/aps.61.097702
Because of the strong coupling between the magnetic and dielectric properties, the study of quantum paraelectric EuTiO3 has attracted more and more attention in both theoretical and experimental research recently. In this paper, the first principles based on the density functional theory within the generalized gradient approxiamtion is used to investigate the magnetic and electronic structure of quantum paraelectric EuTiO3, and to analyze the effects of the strain on the magnetic and strutural phase transition, in turn to discuss the possible magnetoelectric coupling mechanism of this material. The calculations show that EuTiO3 with the strain-free is in a paraelectric cubic and G-type antiferromagnetic state at low temperature, while appling either compressive or tensile strain along the c-axis to it, the balance of hybridization between Ti 3d and O 2p orbit will be breaken and EuTiO3 will transite from paraelectric and G-antiferromagnetic to ferroelectric-ferromagnetic structure as the strain is increased to a certain value. All those indicate the strong spin-lattice coupling effect in EuTiO3.
2012, 61 (9): 097801. doi: 10.7498/aps.61.097801
Locating and imaging the specific pathological lesions in human thyroid are pretty helpful for reliable diagnosis and effective treatment of thyroid nodules. In this paper, we evaluate the feasibility of photoacoustic tomography (PAT) for imaging thyroid tissue in vitro. Imaging is performed based on an imaging system with a 30 MHz focused transducer. In the experiment, 350 upm transverse resolution and 74 upm axial resolution are achieved. A normal thyroid tissue and the tissue with a mimic lesion embedded are imaged in vitro, Separately. As a result, the localization and the imaging of mimic pathological lesion in human thyroid tissue are realized. We demonstrate that our imaging system is able to detect the lesion from normal thyroid tissue successfully. This technique is expected to be a potential clinical tool for increasing diagnostic accuracy and performing more effective treatment of thyroid diseases.
2012, 61 (9): 097802. doi: 10.7498/aps.61.097802
The Raman spectra of the SiC layers in TRISO particles of fuel elements of HTGRs are studied. Through the analysis of the Raman shifts, the FWHM and intensities, the crystal phases, the residual stress and densities of SiC layers and corresponding spectroscopic features are clarified. The study of the 2D correlation spectrum of first order Raman scattering of SiC layer shows that the LO mode is much more sensitive than the TO mode to the change of density of SiC layer. All these conclusions are significant for synthesising TRISO particles and fuel elements of HTGRs and estimating their qualities.
2012, 61 (9): 097803. doi: 10.7498/aps.61.097803
After electron irradiation, a large number of interstitial and vacancy-related centres are created in diamond. In this paper, We compare these irradiation-induced centres among ultra pure, nitrogen doped and boron doped crystals by using 488 nm and 325 nm lasers. Results show that some new interesting emissions are observed after the donor or acceptor atoms have been implanted into diamond, such as nitrogen-vacancy complex, DB1 centre.
Synthesis and infrared up-conversion photostimulated luminescence properties of a novel optical storage material Sr2SnO4: Tb3 +, Li+
2012, 61 (9): 097804. doi: 10.7498/aps.61.097804
The novel electron trapping material of Sr2SnO4: Tb3+, Li+ for optical storage is synthesized by the solid state method. Stimulated by 980 nm infrared laser, the material shows intense up-conversion photostimulated luminescence. The ultraviolet light at 292 nm is an optimal writing source. The material has less shallow traps, which corresponds to its weak afterglow (less than 500 s). On the other hand, this material has lots of deep traps. Thus, the Sr2SnO4:Tb3 +, Li+ is a promising optical storage material. In addition, we propose the optical storage luminescence mechanism of Sr2SnO4:Tb3 +, Li +.
2012, 61 (9): 097805. doi: 10.7498/aps.61.097805
The characteristics of scatting and extinction spectra of gold nanoshell pairs, dependent on the its geometry and physical parameters, are investigated by the Finite Element Method based on the plasmon hybridization theory. The numerical results indicate that the resonante peaks in the scattering spectra and the extinction spectra emerge from blue-shift to red-shift with the increases of the thickness of gold nanoshells, whereas they present the red-shift with the decrease of the interparticle separation or with the increases of the size and the refractive index of inner core of gold nanoshells. In the same time, for the case of decreasing the inner core size and the shell thickness or increasing the refractive index of inner core, the intensity of the scattering resonance and the extinction resonance decrease. And, with the decrease of the interparticle separation, the intensity of the scattering resonance of gold nanoshell pairs trends to first increase and then decrease, while the intensity of the extinction resonance increases gradually. All the above is in agreement with the analysis of the plasmon hybridization theory.
COMPREHENSIVE SURVEY FOR THE FRONTIER DISCIPLINES
2012, 61 (9): 097504. doi: 10.7498/aps.61.097504
The low-frequency noise is the most important influence on the low frequency resolution and sensitivity in tunnel junction magnetoresistance(TMR) sensors and giant magnetoresistance (GMR) sensor for the large noise power density. In this paper, We describe the 1/f noise characteristics, sources, theoretical models, testing methods and noise reduction measures for TMR sensors and GMR sensors, and the detailed physical model of 1/f noise in the tunnel junction magnetoresistive sensor is explained. By nano-simulation software Virtual NanoLab, Fe/MgO/Fe magnetic tunnel junctions (MTJs) with different thicknesses of MgO layer are studied. Their tunneling probabilities and TMR change rates are simulated and calculated, the conservative and the optimistic estimates of the Change rate of TMR are 98.1 % and 10324.55%.While the influence of MgO thickness on noise is studied through the MTJ model. To study the noise dependance on external magnetic field, an magnetic shielding equipment for noise measurement is set up, and the tests show that the noise in the magnetic shielding environment is significantly reduced.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Influence of active layer thickness on the performance of distyrylarylene derivative blue organic light-emitting device
2012, 61 (9): 098101. doi: 10.7498/aps.61.098101
Thickness of emissive layer in organic electroluminescent device is one of the important factors affecting the device performance. In this report, a blue electroluminescent device with an active layer of 4, 4'-bis(2, 2'-diphenylvinyl) -1, 1'- biphenyl (DPVBi) is fabricated. The device performance varies with the thickness of DPVBi. With the increase of the DPVBi thickness between 1050 nm, the device luminance and efficiency at the same current density first increase and then decrease, the device with a DPVBi thickness of 40 nm exhibits the highest luminance of 15840 cd/m2 and a maximum external quantum efficiency of 3.2%, with Commission Internationale de l'Eclairage (CIE) co-ordinates being (0.15, 0.15). The luminescent spectral red shift and the color purity deteriorate when the thickness is over 40 nm, which can be attributed to a result of microcavity effect. In the meantime, the analysis from experimental results shows that the exciton diffusion length in DPVBi is between 2030 nm.
2012, 61 (9): 098102. doi: 10.7498/aps.61.098102
The effect of grain boundary on conductivity in multicomponent polycrystalline solid electrolyte has become a bottleneck for the development of high temperature solid electrolyte materials. The corresponding relationship between the microstructure and conductivity at high temperature is difficult to obtain based on the traditional methods of grain boundaries observation. In view of this, the variable temperature AC impedance characteristics of partially stabilized zirconia (PSZ) solid electrolyte material are investigated, and their fitting to AC impedance spectrum is analyzed. It is found that the fitting equivalent circuits varies with temperature increasing. By analyzing the physical meanings of different equivalent circuits, the microstructure evolution model of PSZ electrolyte material at elevated temperature is obtained. A microstructure model of 'short-range ordered ' with the structure of 'boundary bridge' is deduced after further analysis, which could provide the reference for improving the grain boundary conductivity in PSZ electrolyte materials.
2012, 61 (9): 098103. doi: 10.7498/aps.61.098103
Real-time monitoring and control of welding process is important for laser welding quality. Therefore, the variation rule of sensing characteristics of welding process and their relations to weld quality should be known. Spatter is one of the most important phenomena in high-power laser welding process. The characteristics of spatters are related to the quality and stability of welding and the utilization of the laser power. An approach to analyze the characteristics of spatters is investigated during high-power disk laser bead-on-plate welding of Type 304 austenitic stainless steel plates at a continuous wave laser power of 10 kW. An ultraviolet and visible sensitive high-speed video camera is used to capture the dynamic images of the laser welding spatters. The number, area, and ejecting distance of spatters and the centroid height of spatter images are calculated as the characteristic parameters of spatters by using the image processing technology. The weld bead width is considered as a parameter reflecting the quality and stability of welding process. The linear and the higher order polynomial curve fitting for the data of the characteristic parameters are used to study the variation rule of the characteristic parameters of spatters. In comparison of the fluctuation of the weld bead width, the correlation between the spatter characteristics and the quality and stability of welding is studied. The experimental results of actual laser welding show that the quality and stability of a high-power disk laser welding of Type 304 austenitic stainless steel plates could be monitored and estimated by analyzing the characteristic parameters of spatters, which is the foundation for monitoring and control of welding quality in real time.
2012, 61 (9): 098104. doi: 10.7498/aps.61.098104
In this paper, cellular automata (CA) model for free dendritic growth of alloy is presented, in which the interface cell is refined by MeshTV interface reconstruction algorithm. In the present CA model, the growth kinetic for both pure material and alloy is used. The effect of interfacial energy anisotropy parameter is validated in the CA model. The dendrite tip growth velocity and tip radius are compared with those of the LGK theoretical model, when =0.02.
Direct fluorination, as one of the most effective approaches to chemical modification of polymer surfaces, has been widely developed from fundamental researches to industrial applications for about forty years in chemical industry field. However, today, its investigations and applications in adjusting and controlling the electrical properties of polymers are still deficient. The present paper attempts to briefly bring together our study results obtained in recent years and recently, related to the influence of surface fluorination on space charge behavior in polyethylene (PE), and to give a concluding discussion on the correlation between space charge accumulation in PE and its fluorinated layer properties and characteristics. The results show that a very thin fluorinated layer can yield effective charge suppression in the absence of oxygen in the reactive gas mixtures, whereas a very thick fluorinated layer with a high degree of fluorination is needed to achieve the effective charge blocking in the presence of oxygen. Among the electrical factors influencing space charge, charge transport properties of the fluorinated layer are more important than its charge trapping properties and permittivity or polarity to prevent charge injection into the bulk material, although high permittivity and deeply trapped charges in the surface layer would reduce the interface electric field and thus decrease charge injection from the electrodes. The charge transport properties of the fluorinated layer are closely related to its free volume, and oxygen in the reactive gas mixtures has a strong negative influence on the decrease of free volume and thus on the suppression of space charge.
Research on the focusing mechanism of one dimensional time reversal EM wave in sub-wavelength metal wire array
2012, 61 (9): 098401. doi: 10.7498/aps.61.098401
Based on the equivalent dielectric model of the periodic metal wire array, the analytical expression of time reversal EM wave in the metal wire array is derived using transmission line method. Then, the influence of metal wire radius, metal wire array period and the amount of layers on time reversal EM wave focusing property is discussed within the equivalent dielectric model. This structure can be used to focus time reversal EM wave in the far field, at the same time, it provides an engineering reference for time reversal technique.
2012, 61 (9): 098701. doi: 10.7498/aps.61.098701
A terahertz wireless transmission system is constructed by using a continuous wave terahertz quantum-cascade laser (THz QCL) and a spectrally-matched terahertz quantum-well photodetector (THz QWP). The transmission bandwidth of the system is measured. The transmission processes at 4.13 THz of a picture file are demonstrated by employing the above system, and the both message totally consistent with the original one are received correctly. Hence, the feasibility of wireless transmission based on THz QCL and THz QWP devices is confirmed. Finally, we analyze the transmission rate of the demonstrating system and give the improving methods.
2012, 61 (9): 098901. doi: 10.7498/aps.61.098901
To understand the spatiotemporal evolution of online public opinion and reveal its formation mechanism, we investigate the data from several popular online comments by means of statistical physics. Although the empirical results show that the heterogeneity of concerns exists in different areas, which follows a double power law, an obvious consistency of such concerns occurs during the evolution of online public opinion. Through correlation analysis, we reveal that the regional population and economy may have a significant influence on the concern about the event, and find that the consistency of concerns in different areas derives from the strong correlations among regions. On the other hand, the public opinion guide can significantly affect the concern about the event, and lead to the rapid increase of propagation velocity. By calculating the information entropy of propagation velocity, we find that the geographical distribution of online comments is relatively stable in most time, and the public opinion guide may help to maintain this consistency. Furthermore, the correlation analysis shows that the more developed areas tend to be more synchronized, which suggests the responses of these areas to the public opinion guide may be faster. Therefore, enhancing the guide of public opinion in developed areas can help our government to control the spread of the online public opinion.
2012, 61 (9): 098902. doi: 10.7498/aps.61.098902
In order to study the fluctuation of bivariate correlation which had time series characters, this paper selected International crude oil futures prices and Chinese Daqing crude oil spot prices as the sample data, using the method of statistical physics to study. The modes of fluctuation of correlation were defined by coarse graining process. Then three problems modes' statistics, law of variation and evolution mechanism were analyzed by complex network theory and analytical method. The results indicated that forms of modes showed that consecutive days of weak or strong positive correlation, and modes obeyed the power-law distribution. There were three kinds of sub-groups appearing in the network of fluctuation of bivariate correlation. These sub-groups were fluctuation of weak positive correlation, strong positive correlation and unrelated, and a core mode existed in each category of sub-groups. Transmission and evolution of fluctuation of bivariate correlation were a few modes. The fluctuation of bivariate correlation was transmitted and evolved by a few modes. The fluctuation had periodicity that the transmission among modes need average 8.74 days and a whole volatility cycle need about 18.55 days. These results not only can be the analyze method between two variables but also provides idea for researching a general law in different variables.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
The accurate measurement of local gravitational acceleration (g, normal value 9.81 m/s2) is a key approach to the exploration of the gravitational field of the earth, and it has been applied in metrology, geodesy, geodynamics, seismology, and mineral exploration. With the plan of '2000 national gravity network' and 'China crustal motion observation network', highly precision gravity measurement will be increasingly required in the long term. In order to further investigate the possible systematic error of current absolute gravity measurement, and satisfy various requirements for highly accurate gravity observation, the T-1 absolute gravimeter prototype is designed and built at Tsinghua University. The T-1 instrument adopts the classic free-fall scheme to measure the g value by tracking the trajectory of a free-fall motion in vacuum with a laser interferometer. The T-1 absolute gravimeter consists of several sub-systems: high vacuum free-fall chamber, compact laser interferometer, low-frequency vertical vibration isolation, high-speed signal acquisition system, instrument control and data processing system. The length and time standards used in g measurement are stabilized He-Ne laser and rubidium atomic clock respectively. It's well known that both of the two standards have an uncertainty of less than 1 10-9. The practical gravity measurement results of T-1 absolute gravimeter give a standard deviation of the mean of less than 1 upGal (1 up Gal = 10-8 m/s2) in a typical observation within 12 h. And the reproducibility of less than 3 upGal is verified by repeatedly measuring gravity. The T-1 absolute gravimeter is a promising instrument by which highly accurate gravity measurement at a microgal level can be realized, and it is hopefully to be used in many research and application areas.