Vol. 61, No. 15 (2012)
2012, 61 (15): 154203. doi: 10.7498/aps.61.154203
The development trend of single-order diffraction grating is introduced. The feasibility of single-order diffraction grating is theoretically demonstrated, and a novel diffractive optical element named quasi-sinusoidal reflection type single-order diffraction grating(QSRG) is proposed. It can suppress higher order diffraction, and improve the signal-noise-ratio (SNR) and accuracy. The experimental results verify this new type of dispersion component, where the higher order diffraction components are efficiently suppressed, which accords well with theoretical prediction. These results are expected to be widely used in the reflection spectrum measurement system.
2012, 61 (15): 154214. doi: 10.7498/aps.61.154214
Superconducting quantum computing is currently considered as one of the most promising options to realize a quantum computer. Superconducting qubit is the core component of the superconducting quantum computer. To increase the decoherence time of superconducting qubits as far as possible, the large-scale integration of superconducting qubits have become the main research topic of superconducting quantum computing. As a macroscopic artificial atom, lots of quantum optical phenomena can be observed in the superconducting qubits. Electromagnetically induced transparency based on superconducting qubits can provide a new method to study the superconducting qubit decoherence mechanism, and can also arouse new ideas to study the nonlinear optics, optical storage, ultra-slow optical transmission and quantum optics. In this paper, we introduce a theoretical basis of electromagnetically induced transparency, review the current research of electromagnetically induced transparency based on superconducting qubits, compare the difference between electromagnetically induced transparencies based on gas atoms and superconducting qubits, and evaluat the prospect applications for its development.
2012, 61 (15): 155203. doi: 10.7498/aps.61.155203
The aircrafts, such as space shuttle, spaceship and so on, are facing the well-known blackout problem when they reentry into the atmosphere. The plasma sheath leads electromagnetic waves to attenuation, and the communications between the aircrafts and the ground to losing, and even completely interrupte, thereby resulting in the loss of radar targets and threatening the lives of the astronauts. Therefore, it is important to study the properties of the electromagnetic wave transmission in plasma. The characteristics of electromagnetic wave transmission in plasma are studied theoretically and experimentally in this paper. The variations of the electromagnetic wave attenuation with plasma density, collision frequency and electromagnetic wave frequency are obtained. The electromagnetic wave attenuation increasean an order of magnitude with plasma density increasing an order of magnitude. The electromagnetic wave attenuation first increases and then decreases with plasma collision frequency increasing, the electromagnetic wave attenuation decreases with the increase of electromagnetic wave frequency. The electromagnetic wave transmission properties in plasma are studied experimentally with shock tube, and the experimental results accord well with the theoretical results. The results show that increasing the electromagnetic wave frequency is an effective way to solve the reentry blackout problem.
2012, 61 (15): 150201. doi: 10.7498/aps.61.150201
The infectivity of a node is determined by its actual betweenness bk in the epidemic model based on traffic-flow other than degree k which is different from the classical epidemic models. Utilizing the mean-field theory, we propose a modified SIS epidemic model based on traffic-flow. With this model, taking MIP route as an example, we re-study the relationship among spreading probability β, traffic generation rate λ, epidemic threshold βc, the stationary density of infected nodes ρ. Both theoretical analysis and experimental results show that βc is the ratio of the mean of the actual betweenness bk > to its mean square bk2 >, when network topology and route strategy are given. Moreover, the stationary density of infected notes ρ behaves as power-law exponent with the reciprocal of the product of the spreading probability β , the traffic generation rate λ and the mean of the actual betweenness bλ=1 >.
2012, 61 (15): 150202. doi: 10.7498/aps.61.150202
Consensus problems of first-order and second-order multi-agent system with communication delays and input delays are proposed based on the frequency-domain analysis and generalized Nyquist criterion. Supposing that the topology of the multi-agent system is fixed, asymmetrically interconnected digraph and owns a globally reachable node, the sufficient condition for system convergence is obtained. The results show that the condition of convergence is dependent only on system coupling strength, each agent input time delay and the adjacent weights to its neighbors, but independent of communication delay which can affect the dynamics of the system. Finally, simulations are provided to demonstrate the effectiveness of our theoretical results.
Sudden birth and control of entanglement between two atoms successively passing through a bimodal cavity
2012, 61 (15): 150301. doi: 10.7498/aps.61.150301
The dynamics of entanglement of two atoms passing through a bimodal cavity one after another are investigated by employing the concurrence. The effects of the atomic coherence of the first atom and the initial entanglement of the cavity field on the time evolution of atom-atom entanglement are analyzed. The results show that the phenomenon of sudden birth of entanglement between two atoms occurs under some conditions and the maximum for the creation of the entanglement is dependent on the initial entanglement of the cavity field. Moreover, the threshold time and maximum for the creation of the entanglement can be controlled by changing the amplitude of atom. We find that the proposal may provide us with a theoretical way to control and manipulate the entanglement.
A four-level entangled quantum refrigeration cycle working with a two-qubit entangled system is proposed in this paper. Based on the first law of quantum thermodynamics and the concept of thermal entanglement, the relation between the quantum entanglement and the several thermodynamic quantities such as the heat transfer, the input work and the coefficient of performance is analyzed. It is found that the isoline of the coefficient of performance is the loop line and it no longer monotonically changes with the ratio of entanglement; in a small exchange constant J the operation region of the refrigerator is c1>c2 and in a larger exchange constant J the operation region of the refrigerator may be c1>c2 or c1c2; the maximal coefficient of performance increases as the exchange constant increases.
2012, 61 (15): 150303. doi: 10.7498/aps.61.150303
The entanglement dynamics of the system composed of three two-level atoms resonantly interacting with three coupled cavities is investigated in this paper. The influence of coupling constant between cavities on the entanglement between atoms and that between cavities are discussed. The results obtained using the numerical method show that the entanglement between atoms has a nonlinear relation with increase of the cavity-cavity coupling coefficient. On the other hand, the entanglement between cavity A and cavity B and the entanglement between cavity B and cavity C weaken with the increase of the coupling constant between cavities, but the entanglement between cavity A and cavity C strengthens with the increase of cavity-cavity coupling coefficient.
A two-dimensional (2D) lattice Boltzmann method (LBM)-cellular automaton (CA) coupled model is developed for the simulation of dendritic growth and bubble formation during solidification. In the model, the dendritic growth is simulated by a CA approach. The driving force of dendritic growth is determined by a local solute equilibrium approach. The LBM based on the Shan-Chen multiphase flow scheme is adopted to simulate the growth and the motion of bubbles in liquid. The interaction mechanism between dendrites and bubbles is embedded in the model. Model validation is carried out by comparing the simulations with the Laplace law, and by simulating the wettability of a bubble on a smooth solid surface. The proposed model is used to study the effect of gas-liquid interaction coefficient on single bubble growth. It is found that the growth velocity and the equilibrium radius of bubble increase with the gas-liquid interaction coefficient. The simulations of the dendritic growth and bubble formation during directional solidification reproduce the physical phenomena, including dendritic competitive growth, the preferential nucleation locations of bubbles, and bubble growth, coalescence, deformation due to the squeeze of neighboring dendrites, as well as bubble motion in the liquid channels. The simulation results are compared reasonably well with the experimental results. In addition, gas pore volume fraction increases with the initial gas content. The simulations of the present LBM-CA model provide an insight into the physical mechanism of bubble nucleation, growth, and motion, as well as the interaction between the dendritic growth and bubble formation during solidification.
The effect of the relaxation oscillation frequency of chaotic semiconductor laser on the rate of random sequence
2012, 61 (15): 150502. doi: 10.7498/aps.61.150502
In this paper, chaotic light generated by semiconductor laser with optical feedback is employed as physical entropy source to generate high-speed random sequence. The relationship between autocorrelation coefficient of chaotic signal and run number of random sequence is analyzed. Based on the analysis, the changes of random sequence run number are further investigated at different ratios between laser relaxation oscillation frequency fr and random sequence generation rate fn. The results show that random sequence run can easily meet the requirement for run test of NIST SP800-22 when the ratio between fr and fn satisfies the equation of fr/fn=(2k+1)/4. When k in the equation is equal to 1, the maximal rate fn=4fr/3 of random sequence is obtained.
2012, 61 (15): 150503. doi: 10.7498/aps.61.150503
A linear single degree-of-freedom (SDOF) oscillator with two kinds of fractional-order derivatives is investigated by the averaging method, and the approximately analytical solution is obtained. The effects of the parameters on the dynamical properties, including the fractional coefficients and the fractional orders in the two kinds of fractional-order derivatives, are characterized by the equivalent linear damping coefficient and the equivalent linear stiffness, and the results is entirely different from the results given in the existing literature. A comparison of the analytical solution with the numerical results is made, and their satisfactory agreement verifies the correctness of the approximately analytical results. The following analysis of the effects of the fractional parameters on the amplitude-frequency is presented, and it is found that the fractional coefficients and the fractional orders can affect not only the resonance amplitude through the equivalent linear damping coefficient, but also the resonance frequency by the equivalent linear stiffness. Finally, the effects of the fractional coefficient in the second fractional-order derivative on resonance frequency are analyzed, and the design rule for the fractional coefficient in the second fractional-order derivative to meet the satisfactory vibration control performance is pointed out.
2012, 61 (15): 150504. doi: 10.7498/aps.61.150504
A coupled dynamos model considering two loss characteristics is proposed, which can characterize the practical situation well compared with the previous one. By numerical calculation, the Lyapunov exponential spectrum, bifurcation diagram and Poincaré mapping are given. Then the dynamic characteristics of the parameters space are analyzed. From these results, it can be found that the novel coupled dynamo model with the consideration of mechanical damping loss, has double attractors. The mechanical damping loss can suppress the chaotic occurrence and leads to more complex bifurcation characteristic appearing in the parameter space. The two kinds of the loss characteristic parameters have significant influence on the dynamic behavior of the system.
A probable explanation for bat's auditory nervous system identifying inserts in the complex surrounding
2012, 61 (15): 150505. doi: 10.7498/aps.61.150505
The high sensitivity and reliability of the biosonar have attracted many bionic scientists' attention. However, there is no convincing physical model to explain the reasons of the superior performance of biosonar. The main reason is that the neuron coding of the nervous system is still uncertain. Based on the physiological structure of the bat's auditory nervous system, a probable explanation is proposed to discuss the Doppler signal process with the principle of circle maps and symbolic dynamics. Through the computer simulation, the rationality of this method is proved. For the instability of the nervous system, using symbolic dynamics to analye the mechanism of the neural information processing has high sensitivity and robustness. It is expected that the research of this new explanation will be able to promote the understanding of the biosonar signal processing and its applications.
2012, 61 (15): 150506. doi: 10.7498/aps.61.150506
Pressure fluctuation signals at the inlet/outlet of an oxygen phase-change heat exchanger are analyzed using non-linear method. Chaotic characteristic parameters such as correlation dimension, Kolomogrov entropy and the largest singular value decomposition (SVD) for the covariance matrix of an established 10-dimensional phase space are analyzed. Results prove that the heat exchanger is a non-linear system with chaotic characteristics. Correlations between these parameters and Prantl Number are also examined for the thermal behavior of oxygen in the critical region. The strong dependence of these characteristic parameters on Pr indicates that they can be used to investigate effectively the phase change behavior of pure substance.
Design of parameter identification law and studies on projective synchronization of spatiotemporal chaotic system
2012, 61 (15): 150507. doi: 10.7498/aps.61.150507
The parameter identification and the projective synchronization between spatiotemporal chaotic systems are studied. The parameter identification law and the adaptive law of undetermined function representing the coupling strength are designed based on Lyapunov theorem. Not only the unknown parameters in responses system are identified, but also projective synchronization between spatiotemporal chaotic systems is realized. The Burgers equation with spatiotemporal chaos behavior is further taken as an example of simulation analysis.
2012, 61 (15): 150508. doi: 10.7498/aps.61.150508
The invistigations on dropwise condensation process and the mechanism of heat transfer enhancement are usually based on the droplet distribution and the movement principle of droplets on condensing surface. In the meanwhile, a single droplet is treated as a stable individual and the movement property inside the droplet is rarely considered. With infrared thermography, the surface temperature distribution of condensate droplet during steam dropwise condensation process is observed. The result shows that the temperature of droplet surface first decreases and then increases and up to a value higher than the initial one as the droplet migrates from one position to another. The droplet will roll and the surface film would be tracked when the droplet moves on the hydrophobic surface. With the convection inside the droplet, condensate near the wall moves to the surface side. The analysis of surface temperature evolution of droplet indicates that the continuous condensation on droplet surface may occur when the surface subcooling exceeds a critical value. The direct condensation on large droplet surface can be promoted by the dynamic process such as droplet coalescence or falling off, which provides a new approach to the condensation heat transfer enhancement.
2012, 61 (15): 150509. doi: 10.7498/aps.61.150509
Social network services and microblog are important application modes of Web2.0, in which opinion spread is quite different from that in other cyber-media and in traditional media. In this paper, we present an opinion-spreading model based on online social network services, to study the forms and features of the spread of public opinion in social network services. The simulation results show that the model can fit the actual data from a social network site. The speed of information spread is consistent with the conclusion of six degrees of separation theory. When an opinion with strong tendency spreads in a network in which intrinsic views obey uniform distribution, the opposite view cannot exist in the stable network. In a stable network, view distribution is related to the degree of source node and the depth of backtrack, but not related to confidence limit, which is different from Deffuant model and Hegselmann-Krause model. Meanwhile, in this paper, we the also analyze the influence of the probability of spreading will, the probability of opinion change and confidence limit on relaxation time. Finally, in the paper are shown two applications of the model: the spread of rumors and the role of opinion leaders.
Investigation of polarization-induced phase noise in interferometric optical fiber sensing system based on FRM
2012, 61 (15): 150701. doi: 10.7498/aps.61.150701
One of the key technologies of interferometric optical fiber sensing system is to overcome polarization-induced signal fading in interferometric fiber sensors. The theoretical and the experimental investigations of the residual polarization-induced phase noise (PIN) in single-mode optical fiber Michelson interferometer based on Faraday rotation mirror (FRM) are conducted in this paper. A theoretical model of the residual PIN based on Jones matrix is developed. Three leading influencing factors of the residual PIN are educed: the rotation deviation angle of FRM, the state of polarization of input light, and the birefrigent effect of the optical fiber. And three methods are proposed to overcome the residual PIN. The maximal PIN with its amplitude of 0.0815 rad possibly exists in the sensing system when the polarization modulation degree equals 1.84 rad. The correctness of the theoretical model is proved by the experimental results.
2012, 61 (15): 152401. doi: 10.7498/aps.61.152401
In order to investigate phase change and chemical stability of pyrochlore Gd2Zr2O7 used for immobilizing Pu(Ⅳ), tetravalent cerium is used as the simulacrums for plutonium with tetravalence, and Gd2Zr2-xCexO7(0≤ x≤ 2.0) series samples are successfully synthesized by high temperature solid reaction and using Gd2O3 and ZrO2 powders as starting materials. The experiments of long-term chemical stability are conducted in synthetic seawater at 40 °C and 70 °C separately. The XRD diffractive data and extraction ratio of as-gained samples are collected by the help of X-ray diffraction (XRD) instrument and inductively coupled plasma mass spectrometry. The results indicate that the phases of compounds change from pyrochlore to fluorite-type phase when the value of x is more than 0.08. Extraction ratios of Gd3+, Zr4+ and Ce4+ in waste forms increase with the increase of immersion time in synthetic seawater. The extraction ratio of waste form at 70 °C is higher than at 40 °C. The highest extraction ratios of Gd3+, Zr4+ and Ce4+ for 42 days are no more than 0.032, 0.003 and 0.032 μg·ml-1 respectively.
Systematic analysis of the fusion barrier heights and positions for projectile using the double folding model
2012, 61 (15): 152501. doi: 10.7498/aps.61.152501
The relations of fusion barrier height and position to charge number and root-mean-square radus of the interacting nucleus for projectile fusing with the different target nuclei are systematically analyzed in this paper. The nuclear potential is calculated by using the double folding model with the density-dependence nucleon-nucleon interaction(CDM3Y6). The pocket formulas are obtained for the fusion barrier height and position for projectile fusing with the different nuclei with mass in a range from 16 to 238. The parameterized formulas can reproduce the exact barrier heights and positions only for projectile within the accuracy of 1%. Moreover, the results are perfectly agreeable with the experimental data, the empirical data and the results of Royer, KNS, AW and the proximity potential.
ATOMIC AND MOLECULAR PHYSICS
2012, 61 (15): 153101. doi: 10.7498/aps.61.153101
In order to study the influence of external electrical field on molecular structure, chemical bond and electronic spectrum of environmental poison chlorophenol, the method B3LYP of the density functional theory (DFT) at 6-311++G(d, p) level is used to calculate geometrical parameters, dipole moments and total energies of the ground state of pentachlorophenol molecule under different external electric fields (from 0 to 0.025 a.u.) in this article. On this basis, the UV absorption spectra of pentachlorophenol (PCP) are studied using the time-dependent density functional theory (TDDFT) in the same fundamental group and compared with the ultraviolet absorption peak of phenol given in the literature. Finally, the rules of external electric field influencing wavelengths and oscillator strengths of the first ten excited states of a PCP molecule are studied. The results show that molecular geometry is strongly dependent on the field intensity, the molecular dipole moment is proved to be first decreasing, then increasing and the total energy first increasing then decreasing with the increase of the field intensity. Compared with the ultraviolet absorption peak of phenol, that of PCP is red-shifted. The oscillator strength of excited state of PCP is proved to be decreasing, and the ultraviolet absorption peak is also red-shifted with the increase of the field intensity.
2012, 61 (15): 153102. doi: 10.7498/aps.61.153102
First-principles calculations are employed to investigate total energies and electronic structures of the B/N doped silicon nanowires, the B/N doped silicon nanowires with and without dangling bond (DB). And the calculation indicates that the DB would lead to the doping failure. Band-structure calculations indicate that B/N doped silicon nanowires without dangling bond show regular p/n type of the charge carrier, while the dangling bond would cause signal atom doping failure, which is not due to the transfer of electrons, but results from the capturing of the electron (hole) by the defect energy level induced by the surface dangling bond. Moreover, the small molecule adsorption can reactivate impurities doping p/n characteristics. The reactivation mechanism is not the transfer of the electrons, thus it can hold the doping characteristics.
2012, 61 (15): 153103. doi: 10.7498/aps.61.153103
The electrical and dielectric properties and the microstructures of a polynary ZnO-based varistor ceramics with 14000 times impulse current aging test are measured. The relationship between defect structure and impulse current aging is mainly investigated. It is found that the electrical properties decrease rapidly with impulse aging and the dimensional effect of ZnO varistor ceramics is dominated not only by grain but also by grain boundary. Additionally, four defect relaxations are found at different temperatures by using dielectric spectra. Two defect relaxations appearing below -60 ℃ with activation energies about 0.24 eV and 0.35 eV are identified to be intrinsic defects originating from interstitial Zn L(Zni··) and vacancy oxygen L(VO·), which are not affected by impulse current aging. Other two relaxations appearing above 80 °C are suggested to be extrinsic defects originating from trap levels L(ingr) at intergranular phase and trap levels L(gb) at grain-boundary interfaces, respectively. Only L(gb) decreases from 0.84 eV to 0.76 eV due to impulse current aging while other trap levels keep unchanged. It is further proposed that L(gb) is responsible mainly for the electrical property and stability of ZnO ceramics.
2012, 61 (15): 153104. doi: 10.7498/aps.61.153104
The fine-structure intervals of Na principal series np(n=39) are calculated by the many-body perturbation theory (MBPT) within the framework of relativity. To deal with the problem that a large set of continuum states is required in the MBPT calculation, an exponential potential is employed to generate a discrete, finite and nearly complete set of numerical basis functions. The zeroth-order wavefunctions and eignvalues are obtained by solving the relativistic Hartree-Fock (RHF) equation and the RHF equation with the action of a potential barrier. The basis set used in this work contains intermediate orbitals with the angular momentum l 6 and in an appropriate energy range, and most of them are the so called contracted orbitals. Encouraging results are obtained using this technique to calculate the second-order correlation corrections, combining the Breit effects in a first-order perturbation approach. Compared with other theoretical calculations, the present results are much close to the experimental results.
A Multi-reference configuration interaction investigation of the X2+and A2 low-lying electronic states of AsO+ isotope ion
2012, 61 (15): 153105. doi: 10.7498/aps.61.153105
The potential energy curves (PECs) of AsO+(X2+) and AsO+(A2) are investigated using the full valence complete active space self-consistent field (CASSCF) method through the highly accurate valence internally contracted multireference configuration interaction approach including Davidson correction (MRCI+Q). In the present calculations, the basis sets for As and O are aug-cc-pV5Z and aug-cc-pV6Z respectively. The spectroscopic parameters of the isotopes 75As16O+ and 75As18O+ are determined. The present values of Re, e, exe, e and Be for 75As16O+ (X2+) are 0.15770 nm, 1091.07 cm-1, 5.02017 cm-1, 0.514826 cm-1 and 0.003123 cm-1, respectively; the present values of Te, Re, e, exe, e and Be for 75As16O+ (A2) are 5.248 eV, 0.16982 nm, 776.848 cm-1, 6.71941 cm-1, 0.443385 cm-1 and 0.003948 cm-1, respectively, which are compared with those reported by previous investigations in the literature. And the comparison shows that excellent agreement exists between the present results and the experimentsal ones. With the PECs of AsO+ (X2+) and AsO+ (A2) determined here, the first 20 vibrational states for each electronic state are determined when the rotational quantum number J equals zero (J =0). For each vibrational state, the vibrational level G(v ), inertial rotation constant Bv and centrifugal distortion constant Dv are evaluated when J=0, which are in good accord ance with the available experimental data.
Carotenoid is a short-chain polyene biomolecule of 9 CC conjugate double-bonds. Due to its special structure carotenoid is used not only in photoprotection and anti-cancer, but also in molecule wires, light switch, and light filter. In this paper molecule spectra of carotenoid are studied. The carotenoid has the broadband fluorescence, the broadband stimulated Raman scattering is obtained when the fluorescence of carotenoid is used to enhance stimulated Raman scattering. Electron energy gap of carotenoid becomes narrow with temperature decreasing, and absorption spectra are red-shifted. These characteristics can make the carotenoid a high-quality semiconductor component. Raman active is intensive and the 3rd order optical nonlinear coefficient is large. The Raman scattering cross section of CC bond is about 10 orders of magnitude larger than that of common molecule. The Raman scattering intensity of overtone is intensive: the ratio of overtone to basic frequency is around 0.5 at low temperature. These spectrum characteristics of carotenoid are significant for studying polyene molecule structure, property and non-biology domain.
Quasi-classical trajectory approach to the influence of the rotational excitation on the stereodynamics of the reaction O+HBrOH+Br
2012, 61 (15): 153401. doi: 10.7498/aps.61.153401
Quasi-classical trajectory method is used to investigate the influence of rotational excitation on the vector properties of the dynamics for the reaction O+HBrOH+Br based on the abinitio potential energy surface. At the collision energy 0.3 eV, we discuss the polarization-dependent differential cross sections (PDDCSs), the distribution P(r) describing k - j correlation, and the distribution P(r) describing k - k- j correlation. The calculated results suggest that the product rotational polarization becomes weaker as the rotational quantum number increases and the products are mainly forward scattered.
2012, 61 (15): 153601. doi: 10.7498/aps.61.153601
The geometrical and electronic structures of ConCm (n=15, m=1,2) clusters are investigated using spin-polarized DFT calculations. ConC (n=25) and ConC2 (n=14) clusters of their ground-state structures different. From n=3, two C atoms are located apart from each other, we think, it is an important reason for Co catalyze C in to single walled carbon nanotubes effectively. The total magnetic moment of ConC2 (n=25) are lower than those of ConC (n=25) clusters, and they both alternated with odd and even numbers. By comparing the fragmentation energies of neutral and charged ConC and ConC2 (n=15) clusters, we conclude that the single walled carbon nanotubes obtained in experiment is electropositive. This conclusion is in good agreement with that from expersimental model
2012, 61 (15): 153701. doi: 10.7498/aps.61.153701
Liquid crystal spatial light modulator (LC-SLM) can be readily used to fabricate the diffractive optical elements. However, a disadvantage of the finite resolution always exists in LC-SLM. In this paper, a new scheme of fabricating phase grating with LC-SLM is proposed to produce one-dimensional (1D) and two-dimensional (2D) array of optical traps. The advantage of the LC-SLM is fully utilized and the disadvantage is well avoided in our scheme. The phase distribution of the grating is optimized by using iterative Fourier series expansion. The grating is designed by simulation according to the LC-SLM technique parameters, and the corresponding light intensity distribution is calculated. The results show that the array has very high peak value intensity and big gradient of intensity by illuminating the grating with a large detuning and low power laser. The optical dipole potential of trapping cold atoms achieves the order of mK, and the interaction force between atom and optical field is much greater than the atom gravity.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
We demonstrate the tuning of Fano resonances in a symmetric planar metamaterial both experimentally and theoretically, on the basis of a unit cell consisting of two identical split ring resonators. The electromagnetic responses of the planar metamaterial to incident TE and TM waves are measured. By controlling the excitation of the Fano-type trapped-mode resonance via the angle of incidence, the resonance can be switched on/off and the resonance is red-shifted by up to 21%. Based on the finite element method, the field distributions are presented and a very sharp normal phase dispersion renders the response of the structure a metamaterial analog of classical electromagnetically-induced transparency (EIT). The simulated results are in good agreement with the measured ones. The switching feature of the trapped mode resonance in symmetric metamaterial can provide an easy approach to tuning the performance of metamaterial.
Broadband and low-loss left-handed metamaterial composed of oblique triangular open-loop pairs resonator
2012, 61 (15): 154102. doi: 10.7498/aps.61.154102
A method of realizing multiband and broadband left-handed metamaterials with low-loss is presented. By integrating oblique triangular open-loop pair resonator plus wire (OTOR-wire) with oblique triangular open-loop pair resonator (OTOR), the combined structure exhibits double LH passbands, which can form broad LH passband by adjusting the unit cell geometrical dimension. Simulation and experimental results and analysis demonstrate that this structure exhibits negative effective permittivity and permeability simultaneously in a frequency range from 9.3 GHz to 13.2 GHz, its relative negative refraction passband reaches 347%, and the figure of merit reaches 347.9. The idea can help us to design multiband and broadband left-handed metamaterials with low-loss
2012, 61 (15): 154201. doi: 10.7498/aps.61.154201
The complex degree of self-coherence is introduced to quantify the coherence of supercontinuum generated by the same long pulse, and experiments are performed. The coherence properties of supercontinuum generated in the photonic crystal fiber pumped by 700 ps pulse are measured using the Mach-Zehnder interferometer. The experimental results show that the coherence lengths of different wavelength parts of the supercontinuum are all longer than 40 m, and can reach 225 m in the long wavelength region. The coherence degrees of different parts of supercontinuum are not the same; however, the mean coherence degree over the supercontinuum is 0.461 which manifests good coherence property of the whole spectrum of supercontinuum. Consequently, requirements of many applications such as optical measurement and optical sensing can be satisfied.
2012, 61 (15): 154202. doi: 10.7498/aps.61.154202
In this paper, the concept of electrical potential influencing factor is proposed to describe the effect of electrical potential difference between the dust particle and background plasma on conductivity, based on which the conductivity model of dusty plasma is improved. The electrical potential influencing factor is directly proportional to the charge number, number density, radius of the dust particle, and the electron number density of the background plasma. Meanwhile, it is inversely proportional to the electron temperature of the background plasma. Taking rocket exhaust plume for example, the conductivities with and without considering potential difference are given both in the microwave and near infrared regions. In the given dusty plasma parameters condition, the influence of electrical potential difference on electrical conductivity reduces as the incident frequency increases. When the frequency increases to the near-infrared light region, the influence of electrical potential difference on the imaginary part of the conductivity can be ignored.
2012, 61 (15): 154204. doi: 10.7498/aps.61.154204
If particles are mixed with other type of particles, the light scattering characteristics will be changed. In this paper, the light scattering characteristics of water clouds mixed with black carbon are studied. Based on the Mie theory, the single scattering phase function, the single scattering albedo and the asymmetric parameters of water clouds and black carbon aerosols are computed. The Monte Carlo method for simulating the scattering of mixed particles is given, the methods of sampling particle types, sampling free path length, and the sampling scattering directions based on the Mie phase function are given. The changes of the scattering characteristics for water clouds mixed with black carbon aerosols are studied. Reflected light intensity varying with observation angle is calculated with the light normal incidence, and the plane albedo is computed as a function of incidence angle. The influences of mixing ratio and effective radius of black carbon on the scattering characteristic of mixture are discussed. The results show that the black carbon can greatly increase the absorption of the clouds, and the ratio and the size of black aerosols can greatly affect the scattering characteristics of the mixture.
Two-dimensional performance of uniform irradiation with the use of a concentricity deviation lens array and partially coherent light
2012, 61 (15): 154205. doi: 10.7498/aps.61.154205
A method of employing a lens array (LA) and partially coherent light (PCL) is presented for uniform irradiation on targets in inertial confinement fusion. Quasi-near field spots with a profile of sharp edge and flat top can be obtained with an LA, while the spatial coherence of the incidence beam is reduced by PCL. An appropriate concentricity deviation (CD) of LA results in the superposition of beamlets at the focus dislocated by a small amount each other and the CD and PCL reduce the fringe separations, thus the interference fringes become denser and the small-scale intensity non-uniformity of intensity distribution is suppressed. Based on the generalized diffraction integral theory, the intensity distribution of a Gaussian Schell Beam (GSB), point focused by an LA and a spherical lens is investigated in detail by two-dimensional simulation. And irradiation uniformity effects are compared with coherent light and partially coherent light after the LA. Numerical results indicate that using an appropriate CD and moving the target slightly from the exact focal plane of the principal focusing, a well-irradiated laser spot and great energy efficiency can be obtained.
2012, 61 (15): 154206. doi: 10.7498/aps.61.154206
By exploiting quantum teleportation, we propose a continuous-variable quantum deterministic key distribution (CVQDKD) protocol using two-mode squeezed vacuum state and coherent state. The efficiency is 100% under the homodyne detection. The security of CVQDKD is analyzed in detail from information theory, and the result shows that the proposed protocol can securely hand over the pre-deterministic key. By contrast with the quantum random key distribution, the quantum deterministic key distribution plays an irreplaceable role in the field of key management. Furthermore, the CVQDKD can obtain a higher rate and better efficiency than the quantum deterministic key distribution protocols with discrete variables, and the quantum states used in the protocol are also easy to produce and manipulate, which i suitable for long-distance transmission. Therefore, the CVQDKD protocol is more practical.
Design and optimization of a novel broadband and polarization-insensitive dual-core photonic crystal fiber coupler over the whole optical communication band
2012, 61 (15): 154207. doi: 10.7498/aps.61.154207
In this paper, a novel broadband polarization-insensitive dual-core photonic crystal fiber with elliptical central hole is proposed and the influence of its structural parameters on coupling characteristic is investigated in detail by the full-vector finite element method. Through optimizing the fiber structural parameters, broadband and polarization-insensitive characteristics are achieved over the whole optical communication band from 1.225 m to 1.675 m. The variation of coupling ratio is stabilized at 50% 1%, and the coupling ratio difference between x polarization and y polarization is less than 0.5% overall the wavelength range. Due to its relatively independent of cores and elliptical central hole and suitable structural parameters, this fiber meets the application requirements, that is, easy to fabricate, easy to splice and low splice loss. This research is freed from the current coupler limit: narrow bandwidth, wavelength dependence, polarization-sensitive, difficulty of fabricating, thereby provides the theoretical basis for the study of the large capacity high speed all-optical networks and multi-wavelength tunable fiber laser.
2012, 61 (15): 154208. doi: 10.7498/aps.61.154208
A novel slow-wave structure called V-shape folded rectangular groove waveguide is proposed. This structure evolves from a conventional rectangular groove waveguide bending the groove with V-shape along its longitudinal direction, and the gap between metal plates forms a sheet electron beam channel naturally. Compared with the traditional U-shape structure, it can increase the interaction area without changing good high-frequency properties, which can adopt the sheet electron beam with a larger area to acquire more output power. In this paper, the high-frequency properties of this structure are analyzed, the interaction circuit for the V-band TWT is designed and the PIC simulation is performed to predict the operating characteristics. From our calculations, this tube can produce average saturation output power over 1000 Watts in a frequency range from 58 GHz to 64 GHz when the cathode voltage and beam current are set to be 12.8 kV and 600 mA respectively. The corresponding saturation gain and electron efficiency can reach over 33 dB and 13.2% respectively.
2012, 61 (15): 154209. doi: 10.7498/aps.61.154209
Based on the principle of scanning filtering, a new optical scanning filtering method for improving signal-to-noise ratio(SNR) of the chirped pulse is proposed. For the scanning filtering scheme of Fabry-Perot (F-P) etalon including an electro-optic crystal, the spectral characteristics of the scanning filter are analyzed quantitatively. Furthermore, the effects of the reflectivity of the parallel-plates of F-P etalon and the types of the electro-optic crystals on the output SNR are discussed in detail, and the influence of the variation of the controlling voltage applied to the electro-optic crystal on the filtering effect is also studied. The results show that the narrower the bandwidth of scanning filter transmission window is, the better the improved SNR will be. In order to ensure the filtering effect, the reflectivity of the parallel-plates of F-P etalon should be more than 0.9. Compared with the scheme of scanning filter built-in ordinary linear electro-optic crystal, the scheme of F-P etalon including an secondary standard electro-optic crystal, i.e., KTa1-xNbxO3 crystal, requires a low voltage, and it is easy to control. The differences of KTa1-xNbxO3 crystal components have little influence on the filtering effect, whereas the variations of controlling voltage and chirp rate of the signal exhibit a greater influence on the filtering effect.
2012, 61 (15): 154210. doi: 10.7498/aps.61.154210
A stable all-normal-dispersion dissipative-soliton mode-locked laser is demonstrated with a Yb3+-doped large-mode-area double-clad gain fiber, and nonlinear polarization evolution and spectral filtering composed of a grating and an aperture are exploited to produce sufficient amplitude modulation to shape pulses of this laser. The laser generates chirped pulses at a 76.6 MHz repetition rate, with an average power of 6.3 W, and a single pulse energy of 82 nJ. Pulse duration of the direct output pulse is 1.33 ps and it can be dechirped to 377 fs after externally compressed. By adjusting the grating, the central wavelength of the output pulses can also be tuned from 1025 nm to 1078 nm.
2012, 61 (15): 154211. doi: 10.7498/aps.61.154211
In this paper, the research on the multipole surface soliton in nonlocal nonlinear medium is done. Theoretical study indicates that multipole surface soliton in nonlocal nonlinear medium can also be regarded as a half part of a bulk soliton with an antisymmetric amplitude distribution. Using this fact, we could obtain the analytical solution of multipole surface soliton easily. Secondly, comparing the numerical solution acquired by numerical computation with analytical solution, we find that analytical solution is in good agreement with numerical solution. Finally, a research is done on the stability of multipole surface soliton using our model. The result shows that the width of the instability domain of dipole surface soliton is smaller than that of quadrupole bulk soliton. In addition all higher-order multipole surface solitons are unstable.
2012, 61 (15): 154212. doi: 10.7498/aps.61.154212
Controllable precipitation of crystals is one of the key points in the fabrication of chalcogenide glass-ceramics. Glass compositions of 65GeS225Ga2S310CsI (GGC25) and 70GeS220Ga2S310CsI (GGC20) are specifically selected, and their glass-ceramic samples are obtained by careful heat treatment. The transmission spectra, grain sizes, and crystal phases of obtained samples are characterized using visible-near IR spectroscopy, SEM, XRD, and Raman scattering. Different crystallization behaviors are evidenced that GeS2 crystals are precipitated in GGC20 glass, and GGC25 samples show two crystallization mechanisms during the heat treatment, that is, Ga2S3 crystals were first precipitated and then the GeS2 ones. The compositional and the microstructural dependences of crystallization behavior are discussed, which would be a significant reference for the controllable crystallization in chalcogenide glasses.
2012, 61 (15): 154213. doi: 10.7498/aps.61.154213
According to the photon grating diffraction principle, the extraction efficiency of LED with photonic crystal can be improved. In this paper, the dielectric photonic crystal is introduced into the SiO2 layer of the red LED to improve the extraction efficiency. The theoretical analyses and experimental results show that the LED with dielectric photonic crystal can well achieve the extraction efficiency. The luminous flux of new type LED is improved by 26% compared with the normal red LED.
2012, 61 (15): 154301. doi: 10.7498/aps.61.154301
The incoherent sound field obtained by scanning measurement cannot be used directly for nearfield acoustic holography to reconstruct the sound field. And therefore, the incoherent sound field needs to be decomposed into fully coherent partial fields. In previous methods, the pressure is used as reference to obtain the partial fields. In this paper, the pressure gradient is used as the reference for the partial field decomposition. Because the pressure gradient decays faster than the pressure, the interaction of the pressure gradient between the incoherent sources is weaker than that of the pressure, which may improve the effect of the partial field decomposition. A numerical simulation and an experiment are conducted to test the feasibility of the method. And it is shown that the partial field decomposition method based on pressure gradient reference is robust and the decomposed results are better than those based on pressure references.
2012, 61 (15): 154302. doi: 10.7498/aps.61.154302
Based on the mechanical wave selective absorption principle of mass-spring microstructures by the optical vibration mode, a two-dimensional acoustic metamaterial panel consisting of lumped mass and elastic membrane is presented. The vibration characteristic simulation of the metamaterial equivalent panel representative cell is performed using the finite element method and the results indicate that the presented 2D metamaterial panel behaves just like regular mass-spring microstructures. Under the guidance of the simulation results, a square metamaterial panel is fabricated and its vibration characteristics are examined using a Polytec scanning laser vibrometer. The test results indicate that the metamaterial panel can efficiently absorb mechanical waves of about 157.5 Hz.
2012, 61 (15): 154401. doi: 10.7498/aps.61.154401
Energy shortage and environment pollution are the major and large problems presently encountered by human all over the world. It is an effective way to save energy and reduce emission of polluted gas by using the nanofluids technology. There has been not a widely recognized theory which can explain flow and heat transfer of nanofluids until now. So the mechanism of flow and heat transfer of nanofluids is not clear. Considering the Brownian motion of nanoparticles in nanofluids, a mechanism model for heat transfer by heat convection is proposed based on the fractal distribution of nanoparticle. No additional/new empirical constant is introduced. The proposed fractal model for heat flux of nanofluids is found to be a function of temperature, average nanoparticle size, concentration, fractal dimension of nanoparticles, fractal dimension of active cavities on boiling surfaces and basic fluid property in pool boiling. The model predictions are compared with the existing experimental data, and fair agreement between the model predictions and experimental data is found for the cases of different nanoparticle concentrations and different average nanoparticle diameters. The analytical model can reveal the physical principles for convection heat transfer in nanofluids.
2012, 61 (15): 154402. doi: 10.7498/aps.61.154402
Conductive polymers polyaniline (PANI) and polypyrrole (PPy) loaded mesoporous silica (SBA-15) composites are prepared and characterized. The one-dimensional reference bar method and the relevant devices to measure the thermal conductivity are introduced and established. The equivalent pore diameter is proposed to characterize the mesostructures of conductive polymers polyaniline (PANI) and polypyrrole (PPy) in PANI/SBA-15 and PPy/SBA-15 composites. The effects of the equivalent and the measurement pore diameters on thermal conductivities of PANI/SBA-15 and PPy/SBA-15 composites are analyzed. The result shows that thermal conductivities of PANI/SBA-15 and PPy/SBA-15 are higher than that of the substrate SBA-15; the thermal conductivity of PANI/SBA-15 is higher than that of PPy/SBA-15; loading of PANI and PPy in pores of PANI/SBA-15 and PPy/SBA-15 composites is more effective than loading outside of pores for improving the thermal conductivities of PANI/SBA-15 and PPy/SBA-15 composites.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2012, 61 (15): 155201. doi: 10.7498/aps.61.155201
In this paper, we present an optimal design of TE0n nonuniform ripple-wall mode converter in circular waveguide. The research work is based on the general coupled wave theory and numerical optimization method. The results of numerical calculation are in good agreement with those of simulation by HFSS. Compared with traditional TE0n mode converter of periodic waveguide perturbations, the TE0n nonuniform ripple-wall mode converter can achieve a high mode conversion efficiency with less corrugated periods. The length of the converter is shortened nearly by a half and the operating bandwidth with over 95% mode conversion is increased by 150%. The research work provides an important theoretical reference and a physics model for designing high power gyrotron mode converter with small axial size, wide operating bandwidth and high conversion efficiency.
2012, 61 (15): 155202. doi: 10.7498/aps.61.155202
A class of disturbed evolution equation is considered by a simple and valid technique. We first introduce the traveling solitary wave solution of a corresponding typical differential equation, and then use the asymptotic method to obtain the approximate solution for an original disturbed evolution equation. And we point out that the series of approximate solution is convergent and the precision of the approximate solution is discussed by using the fixed point theorem for the functional analysis.
2012, 61 (15): 155204. doi: 10.7498/aps.61.155204
The Bohm criterion for a collisinal electronegative plasma sheath in an oblique magnetic field is investigated with a fluid model. The effects of negative ions and magnetic field on the Bohm criterion are discussed. It is shown that the parameters of the negative ions affect only the lower limit for Bohm criterion, and the external magnetic field can affect the whole range of the ion Mach number values.
2012, 61 (15): 155205. doi: 10.7498/aps.61.155205
In this paper, we calculate permanent magnet theoretically for a multicusp ion source Coulomb collision between electrons is treated with the "binary collision" model and collisions between the electrons and hydrogen species are treated with the "null-collision" method. A 3D PIC-MCC simulation algorithm is developed, and based on this algorithm the electron deposition process in multicusp ion source is simulated, and the multicusp magnetic field effects on the electron energy distribution and spatial distribution are analyzed. The results show that the spatial non-uniformity of electron distribution comes from high energy electron B× ▽B drift in the filter field.
The study on adaptability and effect of mesh-inducing for plasma immersion ion implantation on non-conductor polymer
2012, 61 (15): 155206. doi: 10.7498/aps.61.155206
Plasma immersion ion implantation (PIII) of non-conductor polymer materials is inherently difficult because the voltage across the sheath is reduced by the voltage drop across the insulator due to dielectric capacitance and charge accumulation on the insulator surface. Based on the particle-in-cell (PIC) model, the secondary electron emission (SEE) coefficient is related to the instant energy of implanting ions. Statistical results can be obtained through scouting each ion in the plasma sheath. The evolution of surface potential is simulated for ion implantation on insulator materials. The effects of thickness, dielectric constant and SEE coefficient on the surface bias potential and the effect of mesh-inducing are studied. For thicker non-conductor polymer, it is difficult to achieve omni-directional implantation by self-bias. The mesh-assisted PIII can improve the equivalent surface potential, suppress the emission of secondary electrons and provide an effective way for ion implantation on insulator.
2012, 61 (15): 155207. doi: 10.7498/aps.61.155207
The transport dynamics of the ablated particles is simulated via Monte Carlo simulation. The influences of ambient gases (He, Ne, and Ar dummy gas) on velocity splitting of the ablated particles under 100 Pa are investigated. The results show that the velocity splitting appears in four types of gases. The formation times of velocity splitting of the ablated particles decrease in sequence of He, Ne, dummy gas and Ar. The influences of the mass and radius of ambient gas molecule on the velocity splitting are also investigated. The formation time of the velocity splitting decreases with mass/radius of ambient gas molecule increasing. The intensity is the smallest when the two velocity peak intensities are equal. The formation time of velocity splitting is explained by the underdamping oscillation model and the inertia fluid model. These results give a good foundation for the further study of the Si nanoparticle growth.
2012, 61 (15): 155208. doi: 10.7498/aps.61.155208
The measurement of implosion velocity is the core problem of inertial confinement fusion and it is also a key quantity of estimation of fusion ignition. A clear implosion trajectory X-ray image of hohlraum-radiative-driven CH-capsule is obtained in Sheng-GuangII laser facility with 1600 J laser energy, triple frequency and 1 ns pulse width. KB-microscope coupled with X-ray streak camera whose temporal resolution is about 10 ps is used for diagnosis. The maximal velocity of implosion is about 160 km/s which can be extracted from the experimental trajectory data. The experimental data are compared with Multi1D simulation results of velocity and both are in good agreement with each other.
Spectral response calibration of Au and CsI transmission photocathodes of X-ray streak camera in a 605500 eV photon energy region
2012, 61 (15): 155209. doi: 10.7498/aps.61.155209
A method is described of measuring absolute spectral response for Au and CsI transmission photocathodes in soft X-ray streak camera, which is of great importance for the inertial confinement fusion (ICF) diagnostics. Transmission photocathode is conventionally employed as photo-to-electron conversion accessories. To derive quantity information of X-ray spectra, the absolute response of photocathode must be calibrated in a range of interest. Here Au and CsI transmission photocathodes with slits are calibrated respectively on Beijing Synchrotron Radiation Facility (BSRF), in a photon energy range of 60 eV5500 eV. This method has an uncertainty less than 10% and good feasibility. Calibration results are in good agreement with the calculation results obtained from the Henke's photon emission model, with CH substrate effect revised.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
DFT calculations on the adsorption of component SF6 decomposed under partial discharge onto carbon nanotubes modified by -OH
2012, 61 (15): 156101. doi: 10.7498/aps.61.156101
Partial discharge (PD) in gas insulated switchgear (GIS) is one of important factors causing accidents. The PD can lead to the decomposition of SF6, generating different gas components. To detect and analyze the decomposed characteristic components of SF6 under PD is significant for fault diagnosis of GIS. However, how to detect the characteristic components from mixed gas components is a main puzzler. In this paper, the molecular dynamics simulation software of MS is used to calculate accurately the process of single-wall carbon nannobutes modified by hydroxide radical (SWNT-OH) adsorbing the main components of SF6 decomposed under PD. The main components contain SOF2, SO2F2, SO2 and CF4. By analyzing the frontier orbital of gas molecules and SWNT-OH, as well as adsorption energy, charge transfer and the electronic density of states in the adsorption process, and the values of energy gap after SWNT-OH adsorbing the gas molecules, the sensitivity and the selectivity of SWNT-OH on gas molecules are evaluated and the theoretical basis on whether the SWNTOH can be prepared as gas sensors to detect the components of SF6 decomposed under PD is presented.
2012, 61 (15): 156102. doi: 10.7498/aps.61.156102
Based on the modified Rapini-Papoular formula for surface anchoring energy, the saturation behaviour of a weak anchoring nematic liquid crystal cell is studied. The mathematical equations of solving director distribution are obtained. A parameter reflecting the characteristic of director distribution is introduced. Expressions for saturation voltage and the parameter reflecting the characteristic of director distribution are obtained for the second order transition. The methods of calculating the two quantities for the first order transition are also given. The influences of surface polarization on the two quantities are discussed in detail. The results show that whether the second or the first order transition, the position of the maximal tilt angle of director will shift towards the substrates with the increase of surface polarization. The influences of surface polarization on saturation voltage for the second and the first order are reverse. The saturation voltage will increase for the second order but decrease for the first order with the increase of surface polarization.
Effects of preparation temperature of graphite oxide on the structure of graphite and electrochemical properties of graphene-based lithium-ion batteries
2012, 61 (15): 156103. doi: 10.7498/aps.61.156103
Graphite oxide is synthesized from graphite powder by a modified Hummers method, and the oxidation temperature is controlled in high-temperature oxidation process. By treating graphite oxide powders in a commercial microwave oven, graphene materials can be readily obtained. The morphologies, microstructures, specific surface areas and other features of the graphene and graphite oxide are characterized by FESEM, XPS, XRD and BET. Electrochemical performances of the lithium-ion batteries based on graphene anodes are investigated. The results show that graphene obtained at the oxidation temperature of 90℃ in high-temperature oxidation process actually displays the most remarkable electrochemical performances, that is, the first discharge specific volume and charge capacity of graphene are as high as 1555.5 mAh/g and 1024.6 mAh/g, and after 30 cycles graphene still possess as high as a discharge capacity of 600 mAh/g.
Investigations on the thermal stability of fatigue dislocation structures in a single-slip-oriented copper single crystal
2012, 61 (15): 156201. doi: 10.7498/aps.61.156201
The fatigue dislocation structures in cyclically saturated [4 18 41] single-slip-oriented Cu single crystal at different values of plastic strain amplitude pl, as well as their thermal stabilities under annealing at different temperatures for 30 min are studied using the electron channeling contrast (ECC) technique in scanning electron microscopy (SEM). It is found that the dislocation structures, such as veins, PSB ladders, PSB cells, Labyrinths, etc. undergo an obvious process of recovery after annealing at 300 ℃. However, when the annealing temperature is higher than 500℃, those dislocation structures basically disappear, and the recrystallization takes place in all specimens, meanwhile, annealing twins form in most cases. The occurrence of the recrystallization and the formation of annealing twins are related not only to the annealing temperature and applied pl, but also closely to the accumulative cyclic plastic strain.
2012, 61 (15): 156202. doi: 10.7498/aps.61.156202
By using plate impact and laser interferometry technology, careful experiments and theoretical analysis for 100 LiF are carried out for its dynamic mechanical response and optical characteristics under shock pressures up to 40 GPa. The accurate shock Hugoniot relation and velocity correction at 1550 nm wavelength are then obtained. Moreover, the direct wave-profile measurments show that LiF keeps an obvious elastic-plastic response within 20.3 GPa, and the estimated lower limit pressure for single-wave shock response is about 2223 GPa. The strength influence of LiF window on the dynamic behavior of the sample should be taken into account in precise experiments with shock pressure lower than this range. The results above establish foundations for the design and data post-processing of shock experiments in which LiF is used as an optical window for the dynamic material properties such as elasto-plasticity, phase transition and melting.
Research on tritium and helium-3 content distributions in steel wall of spherical pressure vessel under general boundary condition
2012, 61 (15): 156601. doi: 10.7498/aps.61.156601
In order to understand the changes of mechanical properties of the wall materials and the carrying capacity of vessel which contains high pressure tritium, the spatiotemporal changes of tritium and helium-3 content in the wall should be studied during tritium storage. Taking into consideration the case that the outer surface of the vessel is with general mass transfer boundary condition and the tritium inside the vessel is van der Waals gas, and also taking into account both decay and permeation of tritium inside the vessel and decay and diffusion of tritium in the wall material, the analytical theoretical models of tritium and helium-3 content in the wall are developed and solved, and relevant theoretical formulas are deduced. Through analytical calculations, the curves of tritium and helium-3 content in the wall versus mass transfer coefficient of the outer surface, storage time and the spatial positions are plotted. Through analysis, a law called 21+2/2 time law of helium-3 content is put forward, where 1 and 2 are the coefficients which are related to van der Waals constant of tritium. The law is proposed: helium-3 content in the wall of the spherical high pressure vessel storing tritium which is in an open space rises along the radius from outer to inner, and the content radial gradient increases with storage time. If storage time is long enough, the helium-3 content at any point will approach to its final value, that is, a maximal value at a relevant point. The ratio of the maximum helium-3 content to the related initial tritium content is 21 + 2/2 at the inner surface. The obtained formulas and understandings can be used as a premise of the safety assessment of tritium stored vessel.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2012, 61 (15): 157201. doi: 10.7498/aps.61.157201
The spin-dependent transport through double quantum-dot-array coupled to a single quantum dot is studied by using the non-equilibrium Green function formalism. Due to the quantum interference and the spin-dependent phase induced by Rashba spin-orbit interaction, the spin of the electron through the device is polarized. When the energy level of quantum dot is in the bias window, the spin accumulation in the single quantum dot can maintain a large value in a wide range of energy and the quantum dot is largely spin polarized. The spin accumulations in the single quantum dot under positive bias and negative bias are absolutely different because of asymmetric quantum dot structure. These results is helpful for designing and fabricateing the practical spintronics devices.
2012, 61 (15): 157301. doi: 10.7498/aps.61.157301
By using the first-principles method, we study the relative stabilities and the thermal ionization energies of the doped Li (LiZn) in the different atomic layers for both the non-polar and polar surfaces. Our calculations indicate that the LiZn in the surface region is more stable than in the ZnO bulk, and the thermal ionization energy of the LiZn in the surface region is considerably bigger than in the ZnO bulk. So, the surface of ZnO film degrades the p-type conductivity of the Li-doped film significantly, which is important for the p-type doping in the low-dimensional ZnO system. Furthermore, we find that the observed difference in thermal ionization energy of LiZn between a surface and bulk actually stems from the different distributions of the electrostatic potentials between a surface and bulk.R66
2012, 61 (15): 157401. doi: 10.7498/aps.61.157401
Intermittent superconductivity for mesoscopic thin-film rings is investigated by the phenomenological Ginzburg-Landau theory. Phase diagram for intermittent superconductivity vs. ring dimension is given in the presence of an external applied field. The intermittent superconductivity exists only in the small ring, which is a feature for distingushing superconductive ring from superconductive disk.
2012, 61 (15): 157501. doi: 10.7498/aps.61.157501
Based on the transfer matrix method and the principle of light localization, the optical bi stability (OB) changing with magnetic field strength, incident angle and dielectric layer are investigated in an one-dimensional antiferromagnetic photonic crystal near the resonant frequencies. We find that the OBs can be observed near the two resonant frequencies at a smaller incident angle, but they disappear near the higher resonant frequencies at a bigger incident angle when the magnetic field strength is 1.0 kG. However, once the external magnetic field strength increases up to 2.0 kG, the lost OB will be induced due to the the two resonant frequencies shifting towards two sides. In addition, the dielectric layers also have a greater influence on OB near the lower resonant frequencies at a smaller incident angle.
Influence of Y addition on the glass forming ability and soft magnetic properties of Fe-Si-B amorphous alloy
2012, 61 (15): 157502. doi: 10.7498/aps.61.157502
Addition of rare earth elements can significantly improve the glass forming ability of Fe-based alloys. But the magnetic domain that most of the rare earths possess themselves always worsens soft magnetic properties of the alloys. By contrast, the rare earth element Y does not have this kind of magnetic domain itself, and is an ideal candidate to add to the Fe-based amorphous alloys as soft magnetic materials. In order to systematically study the effect of partial substitution of Fe in Fe78Si9B13 alloy with rare earth element Y on glass forming ability and soft magnetic properties, a series of wedge-shaped specimens and amorphous ribbons are prepared by copper mold suction casting and melt spinning respectively. It is found that the replacement of Fe by minor Y enhances the glass forming ability of the alloy. When 3 at.% Fe is replaced, the critical thickness and supercooled liquid region of the amorphous alloy reach their maximum values, 313 μm and 65 K, respectively. The amorphous alloys have excellent soft magnetic properties: coercive force (Hc) all bellow 200 A/m and saturation magnetic induction (Bs) all above 1.30 T. Specially, Bs reaches a maximal value, 1.67 T, when 1 at.% Fe is substituted.
2012, 61 (15): 157503. doi: 10.7498/aps.61.157503
Co doped ZnO powders and tablets are synthesized by the solid-state reaction. The X-ray diffraction experimental results indicate that Zn2+ ions are substituted by Co2+ ions. All samples are paramagnetic at room temperature. Using density functional theory (DFT+U) method, the calculated results indicate that the antiferromagnetic ground state of Co2Zn14O16 system is more stable. By calculating the electronic transfers of Co and O atoms, it is indicated that the mechanism of the magnetism tends to the indirect exchange model of Co2+O2-Co2+ bonding in CoZnO system. The direct exchange formula Jpd of Anderson model is modified. Two possible ways to achieve the intrinsic ferromagnetic oxide semiconductor are putted forward.
Fabrication of erbium-doped chalcogenide glass and study on mid-IR amplifying characteristics of its microstructured fiber
2012, 61 (15): 157701. doi: 10.7498/aps.61.157701
In order to demonstrate the characteristics of chalcogenide glass Er3+-doped microstructured optical fiber (MOF) amplifying the mid-infrared band signal, Er3+-doped Ga5Ge20Sb10S65 chalcogenide glass is prepared with high temperature melt-quenching method. The absorption spectrum and 2.7 m band fluorescence spectrum of glass sample are measured, and the spectroscopic parameters such as radiative transition probability, radiative lifetime and 2.7 m band stimulated emission cross-section of Er3+ ion are calculated and analyzed according to the Judd-Ofelt and Futchbauer-Ladenburg theories. The 2.7 m band mid-infrared signal amplifying model of Ga5Ge20Sb10S65 chalcogenide glass Er3+-doped MOF under the excitation of 980 nm is presented, and the amplifying characteristics of 2.7 m-band mid-infrared signals for chalcogenide glass Er3+-doped MOF are investigated theoretically. The results show that the chalcogenide glass Er3+-doped MOF exhibits a higher signal gain and very broad gain spectrum: its maximal gain of small signal exceeds 40 dB and amplifying bandwidth of higher than 30 dB gain reaches about 120 nm (26962816 nm) for a 100 cm long chalcogenide glass erbium-doped MOF with a pump power of 200 mW. The theoretical studies indicate that the Ga5Ge20Sb10S65 chalcogenide glass Er3+-doped MOF is an excellent gain medium which can be applied to broadband amplifiers in the mid-infrared wavelength region.
2012, 61 (15): 157801. doi: 10.7498/aps.61.157801
Silver nanoparticles are synthesized through thermal evaporation for molecular detection using surface enhanced Raman scattering microscopy. The optical properties of silver nanoparticles are obtained by ultraviolet-visible spectrometry, which show the resonance wavelength near the detecting wavelength of Raman scattering (488 nm). Using rhodamine 6G as a test molecule, the results in this paper show that the detected Raman peak intensity has a nonlinear relationship with the incident power density when surface plasmon of silver nanoparticles was excitated by incident photon. This nonlinear phenomenon of surface enhanced Raman scattering caused by "hot spot" with high electromagnetic field strength provides an effective way to obtain high scattering intensity without high incident power density, which may expand the scope of Raman scattering application.
Thermoluminescence and optically stimulated luminescence characteristics of -Al2O3:C crystal powder of different particle size
2012, 61 (15): 157802. doi: 10.7498/aps.61.157802
In this work, we first report on the radiation dose effect of -Al2O3:C crystal powder. The thermoluminescence(TL) and optically stimulated luminescence (OSL) of the powder are investigated by RisTL/OSL-DA-15. The as-grown -Al2O3:C crystal powder of same particle size shows a single TL peak and the TL intensity increases as irradiation dose increases, but no shift of the position of the TL peak is found, which is consistent with first-order recombination kinetics. And in the same radiation dose and test conditions, with the particle size of -Al2O3:C crystal powder decreasing, the TL intensity decreases after first increase and then the TL peak is gradually increases and approaches to a stable value, which shows that the -Al2O3:C crystal powder, 4060 m in diameter, has the best TL effect. The OSL decay curve of -Al2O3:C crystal powder shows the typical exponential decay characteristics, and the relationship between OSL intensity and decay rate with the particle size of -Al2O3:C crystal powder is found to be consistent with the shallow-electronic-trap theory.
The characterization of hydrogenated amorphous silicon and epitaxial silicon thin films grown on crystalline silicon substrates by using spectroscopic ellipsometry
2012, 61 (15): 157803. doi: 10.7498/aps.61.157803
Two series of silicon films on c-Si substrates with different thicknesses are deposited by radio frequency plasma enhanced chemical vapor deposition (rf-PECVD). The structures of samples are investigated by spectroscopic ellipsometry (SE) with fixed angle. The results show that the films are all amorphous for the first series of samples. In such a case an abrupt a-Si:H/c-Si heterojunction is formed which is beneficial for the passivation of the interface of HIT solar cell. For amorphous silicon films, the fitting result is acceptable by using Tauc-Lorentz Genosc model. For the second series, the films are of epitaxial Si at the initial deposition stages, the amorphous fraction increases with the increase of thickness. When the film thickness reaches a critical value of 46 nm, a transition to pure amorphous phase occurs. The epitaxial film shows excellent fitting by using the effective medium approximation (EMA) model under the assumption of the mixture of c-Si phases and a-Si:H. However, we obtain better fitting result by using a three-layer model, whose bulk layer is divided into EMA layer and a-Si layer after the transition to pure amorphous phase. This study indicates that the SE analysis, operated in different models, is effective to characterize different structures of silicon films on c-Si substrate.
Effects of thermal treatments on the formation of nanocrystalline Si embedded in Si-rich oxide films
2012, 61 (15): 157804. doi: 10.7498/aps.61.157804
Silicon oxide films containing nanocrystalline Si (nc-Si) are fabricated by magnetron sputtering method followed by one-step-annealing, two-step-annealing and rapid thermal annealing (RTA), separately. In silicon-rich oxide films containing ～ 42.63 at.% of Si, dense nc-Si in a magnitude of 1012/cm-2 are obtained in all of the samples subjected to three different thermal treatments. In the two-step-annealing sample, the density of nc-Si reachs a maximum (2.2× 1012/cm-2), and the nc-Si is well crystallized and uniform in size distribution. In the one-step-annealing sample, the density of nc-Si is silightly lower than in the two-step-annealing sample, and large deficiently crystallized nc-Si is observed in the sample. The RTA leads to the lowest density of nc-Si with the largest size distribution among the three samples. Moreover, large nc-Si formed by coalescence of small ones and twin crystals are also discovered in the RTA sample. It is believed that nucleation at the early stage of nanocrystal growth influences the density and the micostructure of nc-Si. The annealing at low temperature in the two-step-annealing facilitates the formation of new nulcei, which is beneficial to improving the quality and density of nc-Si.
2012, 61 (15): 157805. doi: 10.7498/aps.61.157805
We propose a novel tunable photonic crystal (PC) waveguide Mach-Zehnder interferometer (MZI) based on nematic liquid crystals (LCs) 5CB and investigate its interference properties numerically by using the finite-difference time-domain method. We can change the refractive index of LC by rotating the directors of the LC molecules. The line defect modes of the PC waveguide with different liquid crystal refractive indices are analyzed by using the plane wave expansion method. Owing to the slow group velocity region of the line defect mode, when the index of 5CB changes from 1.53 to 1.63, the variation of the effective index of the line defect mode arrives at 0.168. This property helps to significantly control the phase of light propagation in a PC waveguide MZI. The novel interferometer can be used as either an optically controlled on-off switch or an amplitude modulator in optical circuits.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2012, 61 (15): 158201. doi: 10.7498/aps.61.158201
In order to suppress surface charge accumulation on the epoxy resin insulation and to investigate the influence of treatment time on the charge accumulation, epoxy samples are surface fluorinated for the different times of 10 min, 30 min and 60 min in a laboratory vessel using an F2/N2 mixture. Attenuated total reflection infrared analyses and the observations of the cross section and the surface of the samples by SEM indicate the increases in degree of fluorination, thickness and compactness of the fluorinated layer, and the decrease in surface roughness, with treatment time increasing. Compared with the deep surface charge traps and stable surface charge of the unfluorinated (original) sample, as indicated by the open-circuit thermally stimulated discharge current measurement, the fluorinated surface cannot store the charge. The corona charges deposited on the sample surfaces fluorinated for 10 min, 30 min or 60 min rapidly decay to zero in about 2 min, 10 min or 15 mi at room temperature respectively, showing a slowed-down release of charge with fluorination time. The measurements of surface conductivity and contact angle and the calculation of surface energy reveal that fluorination gives rise to dramatic increases in surface conductivity, surface wettability and polarity, while they decrease with treatment time. The significant increase in surface conductivity of the fluorinated sample is attributed to a very likely substantial decrease in trap depth and the adsorbed water on the fluorinated surfac. Surface charging current measurements further show that large steady state current flows along the fluorinated surface during corona charging, in comparison with the almost zero steady state current for the original sample. This implies that the fluorinated sample has much lower surface charge accumulation in the period of charging, than the original sample.
The influence of spatiotemporal modulation on spiral tip dynamics in excitable medium and its application for spiral control
2012, 61 (15): 158202. doi: 10.7498/aps.61.158202
In this paper, the influence of spatiotemporal modulation on tip dynamics of periodic spiral wave in excitable medium is studied first. By varying spatiotemporal modulation item, the dynamics of spiral wave changes dramatically and the system undergoes periodic spiral wave, epicycloid meandering spiral wave, traveling spiral wave and hypocycloid meandering spiral wave. An order parameter is introduced to detect the critical conditions of non-equilibrium transition between different patterns. And the variation of spiral tip radius induced by spatiotemporal modulation can also be reflected by this order parameter. When spatiotemporal modulation increases to a critical value, spiral waves break up. And spiral waves will damp to homogeneous rest state if spatiotemporal modulation increases further. The mechanisms of spiral breakup and damping are explained in the paper. Finally we apply the spatiotemporal modulation method to the meandering spiral waves and can successfully control meandering spiral waves into periodic spiral waves or homogeneous rest state.
2012, 61 (15): 158203. doi: 10.7498/aps.61.158203
Calcium ion spiral wave induced by random released calcium ion sparks in single heart cell is studied using the improved discrete fire-diffuse-fire model and phase analysis method. The results show that calcium ion spiral wave can be excited in resting heart cell by calcium ion sparks at an appropriate release frequency. The key of the generation of calcium ion spiral wave is the emergence of the phase singularity caused by the calcium sparks in the different time and space sequences. The number of phase singularity is exponentially linked with calcium ion spark frequency, and has the limit in a fixed system.
2012, 61 (15): 158301. doi: 10.7498/aps.61.158301
The electrification of wind-blown sand, such as dust storms and dust devils, is known as the tribo-electric effect of sand particles and the stratification of different size particles. Combined with the grain electrification model, a new numerical method of gas-solid two-phase flow is developed for the simulation of wind-blown-sand two-phase flow, which is a hybrid method of computational fluid dynamics and discrete element method (CFD-DEM). In the developed wind-blown-sand two-phase flow of horizontal wind tunnel, the simulation results indicate that large size grains become positively charged while small size grains become negatively charged, and the critical diameter of grain with electric neutrality is about 300μm. The simulated charge-to-mass ratio and electric field intensity of the wind-blown sands in the field wind tunnel approach to the measured data, showing the rationality of this numerical method. The simulation also demonstrates that there occurs the maximum of electric field intensity over the sand bed of the field wind tunnel, which is the reason why the electric grounding of the field wind tunnel is used in experiment. The coupling of grain electrification model and gas-solid two-phase flow method provides an important tool for interpreting laboratory and field observations of wind-blown sands and insights into the physical dynamics of dust storms and dust devils as well.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
The influences of air heat storage, plant photosynthesis and soil water movement on surface energy balance over the loess plateau
2012, 61 (15): 159201. doi: 10.7498/aps.61.159201
The surface energy imbalance problem has become a challenge in the study of surface land process since it was found in the late 1980s. By using data provided by the program the Loess Plateau Land-surface Process Experiment (LOPEX) and introducing the vertical sensible heat flux into the surface energy balance equation, in the paper, we estimate the heat storage associated with change of air temperature and humidity as well as the energy stored in plants due to the photosynthesis, determine the water vertical flux in the shadow soil layer both by water conservation principle and two-level soil temperature, and investigate the influences of air and plant photosynthesis energy storages and heat transferred by the soil water movement on the surface energy budget. It is found that the diurnal variation peaks of averaged energy storages of air and plant photosynthesis reach 1.5 and 2.0 Wm-2 respectively. Additionally, the diurnal variation peak of mean heat transferred by vertical water movement is close to 8.0 Wm-2. The closure of energy balance is improved from 88.1% to 89.6% by adding the three additional energy terms to the energy balance equation. As a whole, the energy storage related to air and the plant photosynthesis, and the heat transferred by the soil water movement both promote the surface energy balance to some extent. Furthermore, the semi-arid climate and the vegetation condition of Loess Plateau essentially lead to significant differences of energy storage be tween this area and other climatic districts.
2012, 61 (15): 159202. doi: 10.7498/aps.61.159202
Neutron monitor (NM) in Yangbajing Cosmic Ray Observatory mainly detects nucleus components with energy in a range of 500 MeV20 GeV and a small number of negative muons. On the basis of synchronous data of neutron monitor and atmospheric electric field during 62 thunderstorms from 2008 to 2010, obvious changes of NM counting rate during 27 thunderstorms with significance greater than S5 are found, and among them, 13 cases with significance greater than S10 . A coincident approximate change trend is found between counting rate change percentage and atmospheric electric field amplitude for 13 cases with significance S10 . However no obvious coincident change trend is found for 14 cases with significance 5 S10 . Obvious changes of counting rate do not occur when thunderstorm is just over electric field mill, however obvious changes occur when electric field mill is not exactly below thunderclouds but in the control of bottom positive charge layer. Dorman put forward the theory that NM counting rate changes are correlated with the atmospheric electric field, thus they attributed the former to the acceleration of the electric field to negative muons inside thunderstorms. However, there is found no evident correlation between NM counting rate charge and the atmospheric electric field in this paper, so our experiment does not support Dormanetal's theory.
2012, 61 (15): 159203. doi: 10.7498/aps.61.159203
The Wen's wave spectrum model is adopted to describe the rough sea surface, and the relation between wind and ocean waves using sea wave spectrum theory is derived. The improved discrete mixed Fourier transform algorithm and the modified rader scattering coefficient model are used to calculate radio propagation loss and radar cross section respectively. On this basis, the influence of wind waves on radar echoes in the environment of atmosphere ducts is analysed by using numerical calculations. The results show that the influences of wind on propagation loss at different heights are different; wich respect to the propagation loss, rader scattering coefficient influenced by waves of factors is large, which results in large change in the radar echo power.