Vol. 61, No. 24 (2012)
2012-12-20
GENERAL
2012, 61 (24): 240201.
doi: 10.7498/aps.61.240201
Abstract +
In this article, Raman bond polarizability of trans-2,3-epoxybutane is derived from its Raman intensity, and the charge distribution of its Raman excited virtual state is obtained. The differential bond polarizability is also obtained from its Raman optical activity (ROA) intensity. The Raman chirality is explained via the coupling between the dipole moment induced by the C-H bond around the chiral center and the magnetic dipole moment which is caused by the electronic current generated in the Raman process. Further analysis shows that the differential bond polarizabilities on the two opposite sides of the C-H bond around the chiral center are of opposite sign. This demonstrates the local asymmetry of this chiral molecule. The symmetric and antisymmetric coordinates are also analyzed, and their results are explained via the irreducible representations of C2 group.
2012, 61 (24): 240202.
doi: 10.7498/aps.61.240202
Abstract +
For an inhomogeneous quantum magnetoplasma system in the atmospheric environment with density and temperature gradient, a two-dimensional nonlinear fluid dynamic perturbation equation is studied in the case where the collision frequency between ions and neutrals is small. The approximate solution of the potential in the dense astrophysical environment is obtained.
2012, 61 (24): 240301.
doi: 10.7498/aps.61.240301
Abstract +
A noncentral harmonic oscillatory ring-shaped potential is proposed, in which the noncentral electric dipole is included. The pseudospin symmetry for this potential is investigated by working in a complete square integrable basis that supports a tridiagonal matrix representation of the wave operator. The resulting three-term recursion relations for the expansion coefficients of the wavefunctions (both angular and radial) are presented. The angular/radial wavefunction is written in terms of the Jacobi/Laguerre polynomials. The discrete spectrum of the bound state is obtained by diagonalizing the radial recursion relation. The algebraic property of energy equation is also discussed, showing the exact pseudospin symmetry
2012, 61 (24): 240302.
doi: 10.7498/aps.61.240302
Abstract +
Via a system of two kicked particles that are coupled in an infinite square well, we numerically show that the interaction with a particle of very small mass is able to lead to a quantum-to-classical transition on condition that the corresponding classical dynamics is almost unaffected. With the decrease of the mass of one of the particles, its effect on the classical dynamics of the other one decreases. Such an effect is even negligible if the mass of the particle is small enough. The classically chaotic dynamics of this small particle is effective for promoting the decoherence of the heavy particle. Therefore its quantum behavior exhibits the transition from the dynamical localization to the classically chaotic diffusion with the decrease of the effective Planck's constant ħ. Under the perturbation from the small particle, the linear entropy is rapidly saturated as time passes by. With the decrease of ħ, the time-averaged linear entropy exponentially increases from zero to almost unity.
2012, 61 (24): 240303.
doi: 10.7498/aps.61.240303
Abstract +
Is this paper we mainly investigate the effects of the temperature and Josephson energy on teleportation of one qubit state in both the standard and the non-standard protocols as well as the partial teleportation of an entangled state under the standard protocol via two identical superconducting charge qubits in thermal equilibrium as the teleportation channel, and give the analytical expression of the average fidelity. Our results show that the teleportation of one qubit state in non-standard protocol and the partial teleportation of entanglement in standard protocol can be almost perfect, indicating that quantum teleportation, with using superconducting charge qubits in thermal equilibrium as a quantum channel, is feasible in theory.
2012, 61 (24): 240304.
doi: 10.7498/aps.61.240304
Abstract +
In this article, we investigate thermal entanglements of the two-site, three-site and four-site mixed spin (1/2,1) XYsystems. The entanglement versus temperature and external magnetic field is discussed. It is found that the entanglements decrease monotonically as temperature increases in the presence and absence of a weak external magnetic field. For the two-site and four-site XY systems, thermal entanglements disappear at the same temperature which is called critical temperature no matter in the ferromagnetic case or antiferromagnetic. It also shows that the critical temperature is independent of external magnetic field. For the three-site system, the corresponding critical temperature is also irrelevant to external magnetic field, while the critical temperature for the ferromagnetic case is higher than that for the antiferromagnetic case. The entanglement of XY systems can develop a few stable platform in an environment of low temperature, but the entanglement vanishes when external magnetic field exceeds some critical value. In this article, we also analyze the difference in thermal entanglement between mixed-spin system and single-spin system, and find that there exists multi-level level crossing in the mixed-spin system.
2012, 61 (24): 240305.
doi: 10.7498/aps.61.240305
Abstract +
Solid-state superconducting circuit-quantum electrodynamics (QED) system is a promising candidate for quantum information processing and an ideal platform for quantum measurement and quantum control studies. As an extension to our previous simulation for single qubit circuit-QED, in this work we simulate the quantum measurement and control of multi-qubit system. Particularly, we consider the deterministic generation of a two-qubit Bell state. In this context we examine the validity conditions of two cavity-photon-elimination scheme. On the level of quantum trajectory simulation, we find that, owing to the qubit flip caused by feedback, the advanced polaron-transformation scheme is no longer applicable if the measurement is not weak, which also makes meaningless the elegant effective measurement operator.
2012, 61 (24): 240306.
doi: 10.7498/aps.61.240306
Abstract +
A subcarrier multiplexing quantum key distribution is based on phase modulation polarization coding scheme. The key could be shared by several parallel sideband channels, and each sideband has a random and independent polarization which is synthesized by controlling the phase difference of subcarriers in two electro-optical phase modulators. The key rate could be increased multiply. The simulation result shows that the scheme works well.
2012, 61 (24): 240501.
doi: 10.7498/aps.61.240501
Abstract +
Based on the Lyapunov stability theory, the Lyapunov function in the form of exponential type is constructed. The four-variable Chen hyperchaotic model is investigated as an example. The reliability of a linear coupling-inudced synchronization of hyperchaotic system is proofed analytically. Furthermore, the modulation effect of nonlinear coupling on the synchronization induced by linear coupling is investigated. A statictical function is defined to evaulate the power consumption of controller according to the dimensionaless dynamical equations, the appropriate parameter region for synchronization due to the joint action of linear and nonlinear coupling, and the extensive numerical results confirm the correctress of the theoretical predication.
2012, 61 (24): 240502.
doi: 10.7498/aps.61.240502
Abstract +
A ball dropped on a vertically vibrating table exhibits intricate dynamical behaviors including period-doubling bifurcations and chaos. If the collision between the ball and the table is completely inelastic, the motion of the ball is always periodic, and the plateaus caused by saddle-node instability and clumping structures for periodic trajectories occur in the bifurcation diagram. Here the effect of air damping on the dynamics of the ball with zero elasticity is analyzed. The air damping is treated as linear viscous one. It is shown that a weak air damping does not change the sequence of bifurcations, but makes the bifurcation points shift to larger values and broadens the transverse dimensions of the plateaus and the clumping zones in the diagrams. However, when the air damping becomes larger, overlapping between the plateaus and clumping zones takes place. In the overlapping section, the mechanism originally leading to periodic motion is destroyed, and chaos is introduced.
2012, 61 (24): 240503.
doi: 10.7498/aps.61.240503
Abstract +
In this paper we propose a novel grid-scroll chaotic attractor generator based on the second generation current conveyor(CCII), which is used for hybrid image encryption of physical chaos encryption and advanced encryption standard (AES) encryption algorithm, because CCII has a higher speed and larger dynamic range than ordinary operational amplifier and can generate multiscroll physical chaotic signal with higher frequency and more complex dynamics properties. The hybrid encryption system of multiscroll physical chaos encryption and AES encryption based on the CCII, does not assure the relationship between plaintext and ciphertext, and the statistical characteristics of ciphertexts in this algorithm should be better than those of any other encryption system. The difference in statistical property of cipher text between the two cases is studied. One case is that the ciphertexts come from different schemes, i. e. the hybrid and the single stage ones, respectively, and the other is that the ciphertexts are generated by chaotic signals with different numbers of scrolls in the same algorithm. We design and implement the chaos circuit based on CCII, and simulat the encryption system. The results shown that they are in agreement with the theoretical analyses, and that the bigger number of scrolls chaotic system causes the weaker correlation of ciphertexts.
2012, 61 (24): 240504.
doi: 10.7498/aps.61.240504
Abstract +
A method of detecting weak signals embedded in chaotic noise by selective support vector machine ensemble based on the theory of phase space reconstruction of the complicated nonlinear system is presented. For improving the generalization ability of support vector machine ensemble, K-means algorithm is used to select the most accurate individual support vector machine from every cluster for ensembling It is established a one-step predictive model that detects the weak signal, including transient signal and period is signals, from the predictive error in the chaotic sequences. It is illustrated in the experiment which is conducted to detect weak signals from Lorenz chaotic background and IPIX Sea Clutter, that the proposed method is highly effective to detect weak signal from a chaotic background and to minimize the influence of noise on weak signals, Compared wich the RBF neural network and SVM model, the new method presents great value in predicting accuracy and detection threshold.
2012, 61 (24): 240505.
doi: 10.7498/aps.61.240505
Abstract +
The evolution of the dynamic behaviors of beating rhythms from independent states to the formation of network is studied in biological experiment on two heterogeneous cells. The beating rhythms are independent and not synchronous when there is no coupling between two cells. With the enhancement of the coupling strength, the mean and maximum of absolute value of the phase difference drastically decrease in the beating rhythms of the two cells, from non-phase synchronization to phase synchronization, eventually not to full synchronization. Some of beatings become synchronous while others not synchronous for non-synchronization states while all beatings are synchronous for the phase synchronization state. With the increase of coupling strength, the times of synchronized beatings increases for the non-phase synchronization state, and time interval between the corresponding synchronous beatings of the two cells decreases to a low but non-zero value for the phase synchronization state. The results not only provide experimental demonstration of rhythm synchronization in a biological network, but also give changing regularity in the forming process of synchronous rhythm in the heterogeneous network.
2012, 61 (24): 240506.
doi: 10.7498/aps.61.240506
Abstract +
Switching electrical circuit with switcher between different types of Jerk systems is established. Based upon the analysis of equilibrium states, stable focus as well as periodic oscillations via Hopf bifurcation can be observed in the two subsystems as parameters varies. Complicated behavior caused by the periodic switcher is investigated in detail, and the point/circle and circle/circle switching periodic oscillations as well as the mechanism are presented. In the different types of switching oscillations, the number of the switching points on the trajectory may increase doubly with the variation of the parameter, which may lead to the cascade of period-doubling bifurcation to chaos. Furthermore, the variation of the parameter may influence the amplitude of the periodic oscillation of the subsystem and therefore the structure of the attractor of the whole switching system.
2012, 61 (24): 240601.
doi: 10.7498/aps.61.240601
Abstract +
High-precision distance measurement in a long range is critical for many advanced applications, such as satellite formation flying, free space optical communication and large scale machining. A 52 m absolute distance measurement in free space based on time of flight of femtosecond laser is demonstrated. The timing offset between target-reflected and the reference pulses is precisely characterized by balanced optical cross-correlation method. The balanced cross correlation signal is used for the feedback control of the cavity length and tightly locks the distance under test to multiple of pulse separation. As a result, the time of flight of the target-reflected pulse is determined by the repetition rate of the femtosecond laser, which effectively avoids the loss of timing resolution caused by direct access of pulse time-of-flight from photo-detection. In the experiment, a Yb -doped high repetition rate mode-locked fiber laser working at 1.04 μm is used as a femtosecond laser source, and a measurement precision of 12 nm is achieved in an average time of one second.
2012, 61 (24): 240701.
doi: 10.7498/aps.61.240701
Abstract +
According to nominal composition (PrNd)xAl0.6Nb0.5Cu0.15B1.05Fe97.7-x(weight percentage), the sintered NdFeB magnets are prepared by melting processing, milling processing, moulding processing and sintering processing. Microstructures and properties of these bulk samples at different high pressures are tested. It is shown that with pressure increasing, appearance and microstructure of samples are destroyed, but their inoxidizability at high temperature is increased, although their flexure strength is badly reduced. On the other hand, there are more excellent magnetic properties of bulk NdFeB samples pressed at high pressures (1.5 GPa and 3.0 GPa) than those of this bulk samples without being pressed. For example, values of their maximum magnetic energy products are increased by 7.69 kJ·m-3 and 0.94 kJ·m-3 respectively, and values of their remanence are increased by 0.02 T and 0.01 T respectively, in addition, the values of their intrinsic coercive force are increased by 20.06 kA·m-1 and 30.33 kA·m-1 respectively. It is ind that high pressure has some effects on microstructure, mechanical and magnetic property of the bulk NdFeB alloy.
2012, 61 (24): 240702.
doi: 10.7498/aps.61.240702
Abstract +
Based on the tunable diode laser absorption spectroscopy, the combustion gas concentration and temperature distribution are reconstructed using algebraic iterative reconstruction technique (ART). Time division multiplexing technology is adopted to scan two H2O absorption transitions (7205.25 cm-1 and 7416.05 cm-1) simultaneously at 1 kHz repetition rate. The influences of projected angle and the number of beams on the temperature and concentration field reconstruction are studied. Compared with the thermocouple readings, the temperature distribution reconstruction has a well agreement except a low temperature area in the middle of the combustion field. Aiming to achieve an optimal reconstruction with a limited number of beams, a few virtual beams are added to the ART method. Through this method, the effectivenesses of temperature and concentration field reconstructions increase, but there is not an obvious improvement when a large gradient of temperature exists between two lines.
2012, 61 (24): 240703.
doi: 10.7498/aps.61.240703
Abstract +
The gate length dependence of PD SOI NMOS device on total dose irradiation is investigated, which is exposed to 60Co gamma ray at a dose rate of 50 rad(Si)/s. The result shows that the transistor with shorter gate length shows larger radiation-induced interface trap density, which leads to the maximum transconductance degradation. The local floating body effect induces the output characteristic variation of irradiated MOSFET with gate length. After irradiation, the breakdown voltage of short channel SOI device decreases. Due to the buried oxide, the radiation-induced degradation of short channel SOI device is much serious compared with that of long channel SOI device.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
2012, 61 (24): 241301.
doi: 10.7498/aps.61.241301
Abstract +
Motivated by recent measurements of the neutral Bs-meson mixing, obtained by LHCb group and the Tevatron, and the possibility to have sizable NP effects in 12s, we revisit the Bs mixing in a family non-universal Z' model. We assume that the Z' boson contributes to the off-diagonal element M12s and also to the off-diagonal element 12s via tree-level Z'-induced b scc operators. We find that, with the constraints from Mss and the indirect CP asymmetry in BdJ/KS imposed, the present measured 1 experimental ranges for afss could not be reproduced. Thus, such a specific model could not simultaneously explain the present data on Bs mixing. It is expected that with the operation of the LHCb group and the future super B experiments, more accurate measurements, especially of the flavour-specific CP asymmetries, could shed light on the issue.
2012, 61 (24): 241401.
doi: 10.7498/aps.61.241401
Abstract +
The secondary electron emission is widely used in production practice, but it is difficult to measure accurately because the measuring result is severely affected by the experimental environment and equipment. A model of secondary electron emission is proposed in this paper. The model has three sections: the generation of secondary electrons, the motions of secondary electrons inside the solid and the escape of secondary electrons from the solid surface. Based on Monte-Carlo method, the relationship between the secondary electron emission coefficient and the range of energy with the energy and angle of the incident electrons is also analyzed. Simulation results show that the model proposed in this paper is corresponding to the actual condition very well. The relation between the secondary electron emission coefficient and the range of energy with the energy and angle of the incident electron is obtained.
NUCLEAR PHYSICS
2012, 61 (24): 242801.
doi: 10.7498/aps.61.242801
Abstract +
The X-ray radiation ionization processes at different altitudes of atmosphere with high-altitude nuclear explosions are numerically simulated, and the temporal and spatial distribution curves of electrons are shown in this paper. The electron density has one maximal point with 1 kt equivalent explosion at 80 kilometers, which is near the explosion point. It is different from the explosion point above 80 kilometers, and the electron density has two maximal points in that case. One is near the explosion point, and the other is near 90 km altitude, where the ionization effect range of high-altitude nuclear explosion is widest. The X-ray of high-altitude nuclear explosion has no effect at below 70 km altitude. With the increase of radiation angle, the altitude of the second electron density maximal point increases, and the cut-off altitude of X-ray increases too.
2012, 61 (24): 242901.
doi: 10.7498/aps.61.242901
Abstract +
The fine structure spectra from very highly stripped ions of the medium and high-Z elements have important applications in plasma diagnostics and the atomic structure calculations. Therefore, on the SG-II laser facility, the X-ray emission spectra from highly stripped plasma of Molybdenum (Mo) are observed by focusing an Nd-glass frequency-tripled (0.35 m) laser beam onto the surface of the Mo target. The fine structure spectra of Mo ions in a range of 0.320.58 nm are measured by a high-resolution elliptically bent crystal spectrometer. Some of resonance transitions and inner-shell transitions of the type 42 and 32 in the C-like, O-like, F-like and Ne-like iso-electronic sequence and the lines from H-like and He-like Mo ions are identified and classified. In addition, the full widths at half maximum (FWHM) of wavelengths are also analyzed. Wavelengths are measured within an uncertainty of 0.0005 nm. A comparison shows that they are in good agreement with computational results of Hartree-Fock-Relativistic (HFR) method. This work is very helpful for enriching the spectra of Mo ions.
2012, 61 (24): 242902.
doi: 10.7498/aps.61.242902
Abstract +
Based on the basic principle of four-quadrant-based tracking sensor, the centroid detection error and the displacement sensitivity of four-quadrant detector, caused by noise or crosstalk in multiple anode photomultiplier (PMT tube), are analyzed in detail. The tracking error formula of four-quadrant-based tracking senor is given in theory and verified in experiment. The results show that when the photon-electron number per frame is constant, the tracking error of four-quadrant-based tracking senor increases as the crosstalk in multiple-anode PMT increases, and when the crosstalk in multiple-anode PMT is constant, the tracking error of four-quadrant-based tracking senor decreases as the photon-electron numbers increases.
ATOMIC AND MOLECULAR PHYSICS
2012, 61 (24): 243101.
doi: 10.7498/aps.61.243101
Abstract +
The structure evolutions and electronic properties of InAs Double-Walled tubelike clusters and nanotubes are studied by first-principles theory. Tubelike clusters, In(3pk+4p)/2As(3pk+4p)/2 (p=6, 8, 10, k=3-11), and the counterpart nanotubes, (m,n)@(2m,2n) (m=n=3,4,5), are analyzed. All geometric structures of clusters and nanotubes are optimized by using density functional theory with generalized gradient approximation, and they obey the Euler formula. The tube diameter formula is obtained. Size-dependent properties of clusters and nanotubes, such as binding energy, HOMO-LUMO gaps, density of state and energy band structures are calculated and discussed. The results show that both [6,k]@[12,k+2] and (3,3)@(6,6) possess relatively high stabilities in the corresponding systems. They also explain why the long and stable tublike clusters can be successfully obtined, and why InAs nanotubes can be synthesized experimentally. All of the double-walled tubelike clusters and nanotubes possess the characteristics of semiconductor.
2012, 61 (24): 243102.
doi: 10.7498/aps.61.243102
Abstract +
The potential energy curve (PEC) of b4Σ- electronic state of the SO+ cation is calculated using the internally contracted multireference configuration interaction approach with the Davidson modification (MRCI+Q) for internuclear separations from 0.103 to 1.083 nm. The basis set used is a correlation- consistent aug-cc-pV5Z basis set. The spin-orbit coupling effect on the spectroscopic parameters is taken into account by the state interaction approach with the full Breit-Pauli operator with all-electron basis set, aug-cc-pCVTZ. To improve the quality of PEC and spin-orbit coupling constant, core-valence correlation and relativistic corrections are included. Core-valence correlation correction is calculated using a cc-pCVTZ basis set. Relativistic corrections are included by the third-order Douglas-Kroll Hamiltonian approximation at the level of a cc-pV5Z basis set. At the MRCI+Q/aug-cc-pV5Z+CV+DK level, the spin-orbit coupling constant of the SO+ (b4Σ-1/2,3/2) is 1 cm-1 when the aug-cc-pCVTZ basis set is used for the spin-orbit coupling calculations The spectroscopic parameters are determined and compared with those reported in the literature. Excellent agreement is found between the present results and the measurements. The vibrational level G(v) inertial rotation constant Bv and centrifugal distortion constant Dv are predicted for each vibrational state of the b4Σ- electronic state by solving the ro-vibrational Schrödinger equation of nuclear motion using Numerov's method and those of the first 2 vibrational states are reported for the non-rotation SO+ cation. Comparison with the measurements demonstrates that the present vibrational manifolds are both reliable and accurate. They should be good predictions for future experimental or theoretical research.
2012, 61 (24): 243401.
doi: 10.7498/aps.61.243401
Abstract +
The impact ionization process of Be by H+ is investigated using the continuum-distorted-wave and the eikonal-initial-state (CDW-EIS) approximation in this paper. The single and double differential cross sections are calculated for the projectile energies ranging from 50keV/u to 10000 keV/u. The total cross sections are consistant well with the previous results. The ionization mechanism of soft-collision, electron captured to continuum states and binary-encounter collisions are discussed. The soft-collision ionization mechanism is the most important contributor to the total cross section. Auger process for Be(1s2s2) is under study by adopting the FAC code.
2012, 61 (24): 243701.
doi: 10.7498/aps.61.243701
Abstract +
We investigate the orientation of the CO (X1∑+) molecules in the combined electrostatic and laser fields. We analyze the adiabatic and nonadiabatic interactions of the molecules with the applied laser field. It shows that the pendular energy levels induced by the laser field form the tunneling doublets which can be coupled by the applied electrostatic field. The CO molecules in the X1∑+ state with small permanent dipoles can be greatly orientated due to the coupling interaction. If the laser field is added adiabatically, the excellent orientation is achieved even at a weak electrostatic field. While in a nonadiabatic case, the molecular orientation reoccurs periodically when the laser field is turned off. Additionally, we study the dependence of the degree of the molecular orientation on the applied laser and electrostatic intensities and the molecular temperature.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2012, 61 (24): 244101.
doi: 10.7498/aps.61.244101
Abstract +
In three-layer-parallel-medium mode, the method of secondary equivalent is proposed to derive the analytic expression of the electric field produced by a static electric dipole based on the uniqueness theorem when the source point is located in the middle layer but the field point is located in other layer. That is, the distribution of the electric field is solved when the source point and the field point are located in the same medium using the first equivalent method. Then the three-layer model is equivalent to two-layer model using the second equivalent method. Finally, the mirror image theory is used to obtain the field distribution. The expression of the scalar electric potential is proved to satisfy the boundary conditions, so the derivation results are proved to be effective. In order to prove the correctness of the expression of the scalar electric potential, a three-layer-parallel-medium mode, that is air-seawater-seabed, is simulated in laboratory, and the scalar electric potentials in the space of seawater and in the space of seabed are measured respectively. Some theoretical analyses are performed and the results of the analyses are in accordance with the experimental measurements, so the correctness of the solution is validated. The research results provide a theoretical base for the actual application such as modeling and characteristic analysis of electric field whose basic simulator is the static electric dipole.
2012, 61 (24): 244102.
doi: 10.7498/aps.61.244102
Abstract +
A mode analysis is presented for the double-grating rectangular waveguide slow-wave structure (SWS) with arbitrary longitudinal displacements between the two gratings. By matching boundary conditions along the sides of the gratings, the distribution of electromagnetic field and high frequency characteristics of the SWS are studied. The simulation results show that the dispersion curve deduced from field equations is in good agreement with that simulated by software while the interaction impedance is higher than that calculated by HFSS, but lower than by CST. It also demonstrates that the longitudinal displacement between two gratings has a great effect on the first stop-band. The upper cutoff frequency of the first mode almost overlaps the lower cutoff frequency of the second mode when the displacement is set to be strictly half period, that is to say, the first stop-band disappears. To avoid the mode degeneracy and competition, the displacement is reduced to be about 0.45 times of period, so that with the interaction impedance kept unchanged, the stop-band increases about 7.9GHz, while the pass-band declines about 2.8 GHz.
2012, 61 (24): 244103.
doi: 10.7498/aps.61.244103
Abstract +
The reading region of ultra high frequency radio-frequency identification (UHF RFID) system is affected by polarization mismatch, reader antenna height, coherent interference and so on. Based on the principles of RFID technology and ray-tracing method, a complete propagation model in real environments is derived. Utilizing recognition rate of target region (RRTR), a method of evalualing the performances of a system is presented. In order to obtain the maximization of RRTR, two solutions including tag diversity and phase switch are proposed, which combines the theories of electromagnetic propagation and coherent interference suppression. The values of RRTR under different parameters are measured in outdoor and indoor environments with a commodity hardware. The measurement results show that the values of RRTR can be enhanced by 10% and 7.6% with the two solutions respectively.
2012, 61 (24): 244104.
doi: 10.7498/aps.61.244104
Abstract +
In this paper, the self-reconstructing property of periodic bottle beam generated by the Bessel beam interfering behind obstacle is analyzed. Based on the Hankel wave theory, we analyze the principle of self-reconstruction. According to the diffraction theory, we derive the evolution of beam behind an on-axis circular obstacle. The results show that the periodic bottle beam has the self-reconstructing property and the reconstructed beam maintains the beam intensity distribution. The research results are significant for realizing the multi-plane micro-manipulation by using a periodic bottle beam.
2012, 61 (24): 244105.
doi: 10.7498/aps.61.244105
Abstract +
According to the scattering characteristics of target and rough surface in a high frequency region in the presenca a narrow beam illumination, we employ composite multiple scattering beam-tracking algorithm based on the ray tracing method and iterative method of electromagnetic to obtain a quick solution to calculate the near field composite scattering characteristics of target at low altitude and rough surface. Then we calculate the Doppler echoes of the PEC plate and sphere and compare the data with the ones from MLFMM, and find that they are in good agreement with each other. Finally we carry out testing validation of our tank, and calculation resuets are consistent with the test results.
2012, 61 (24): 244106.
doi: 10.7498/aps.61.244106
Abstract +
Based on velocity-modulating model, a nonlinear wave-beam interaction theory for folded-waveguide traveling wave tubes is developed. In this theory, the continuing beam is treated as discrete macro-particles with different initial phases. Then beam-wave interaction and energy exchange are analyzed at each crossing point between beam-tunnel and wave-tunnel. Compared with PIC result, the error of output power predicted by this model is within 10%, and the error of saturated length is within 15%. The results of this model are significant for designing folded-waveguide traveling wave tubes.
2012, 61 (24): 244201.
doi: 10.7498/aps.61.244201
Abstract +
Polarized beam coherent combination of pulsed fiber laser is studied. The self-organizing passive phase lock of multilevel high power Yb-doped fiber amplifiers is achieved with optical feed-back ring cavity. Polarized beam coherent combination and multi-channel beam coaxial output are realized by using cascade polarized combining configuration. Polarized beam coherent combination of four Yb-doped fiber amplifiers is experimentally demonstrated, The efficiency of coherent combination is up to 91.9%. Stable combination pulsed fiber laser with temporal and spatial characteristic is achieved. This approach provides a feasible technique for power scaling of high-power pulsed fiber laser.
2012, 61 (24): 244202.
doi: 10.7498/aps.61.244202
Abstract +
Based on the propagation law of partially coherent beams and Fourier transform, the analytical expressions for the spectral intensity and spectral degree of coherence of focused spatially and spectrally partially coherent Hermite-Gaussian (H-G) pulsed beams are derived and used to study the spatial correlation properties in the focal region. It is shown that the spectral degree of coherence depends on the spatial correlation length, temporal coherence length and beam order. As the temporal coherence length decreases, the spectral degree of coherence decreases, whereas the temporal coherence length does not contribute to the spatial distribution of the spectral degree of coherence. An increase of the beam order results in an oscillatory behavior of the spectral degree of coherence, which becomes more prominent with the increase of beam order or the decrease of spatial correlation length.
2012, 61 (24): 244203.
doi: 10.7498/aps.61.244203
Abstract +
Coherent diffractive imaging is a new lensless imaging technique which has important applications in optical measurements, microscopic imaging and adaptive optics. We propose a method for coherent diffractive imaging from one single Fresnel diffraction intensity pattern. In this method, a Fresnel diffraction intensity pattern of the object wave passing through a specially designed sampling array is recorded and the complex amplitude of the object wave can be extracted through some digital processing such as inverse Fresnel transform and spatial filtering to the recorded intensity pattern; and then the image of the object can be reconstructed in computer. Some theoretical analyses and digital simulations about how the diffraction parameters affect the rebuilding image are given, such as sampling aperture, diffraction distance, image sensor size, etc. We find that there exists an optimal recording distance when the pinhole size and the recording aperture are given. Some serious noise will appear if the recording distance is longer than the optimal value, while shorter recording distance will result in a worse resolution of the reconstructed image. The influence of the pinhole size on the imaging resolution power of the system is also discussed. As this method requires only a single measurement of the diffraction intensity pattern and it does not need any iterative algorithm and lens systems, it provides a practically valuable approach to real-time wavefront measuring and lensless diffractive imaging of a complex-valued object in a wide rang of wavelengths.
2012, 61 (24): 244204.
doi: 10.7498/aps.61.244204
Abstract +
Combining the techniques of double random phase encoding and phase-shifting interferometry, an information hiding system is proposed, in which the information to be hidden can be encrypted into multiple interferograms. By choosing the appropriate weighting factor, the interferograms can be embedded in the host image. The secrete information can be successfully extracted and decrypted by special phase-shifting reconstruction formula and inverse Fresnel diffraction transform. A software of information hiding system is designed by mixed programming between Visual C++ and Matlab based in the Matcom software environments. By testing the software interface, the designed software can successfully realize the main functions, such as image reading and displaying, input of basis geometrical parameters, information encrypting and embedding, information extracting, decrypting, robustness testing, etc..
2012, 61 (24): 244205.
doi: 10.7498/aps.61.244205
Abstract +
A simple and practical method of estimating reflectivity and refractive-index modulation is reported when writing fiber Bragg grating (FBG) into silica fiber core based on 800 nm femtosecond laser pulses and a phase mask. By monitoring and recording the variation of the fiber laser output power, the reflectivity and refractive-index modulation are estimated theoretically and experimentally. The reflectivity of FBG is approximate 96.4%, and the refractive-index modulation is about 1.2×10-3. When the FBG is used as a linear cavity mirror, 15.5 W of output power is obtained under an incident pump power of 51.6 W, corresponding to a slop efficiency of 37.9%. A beam factor of M2=1.4 at an output power of 15 W is measured by using the knife-edge method.
2012, 61 (24): 244206.
doi: 10.7498/aps.61.244206
Abstract +
Mid-infrared lasers are very effective for the spectroscopic measuring of the fundamental absorption lines for most gases. The quantum cascade laser (QCL), with the advantages of high power, wide tuning range and room-temperature operation, is one of the ideal mid-IR sources for trace gas detection. In this paper, the spectral characteristics of room temperature operated pulsed QCL with a cental wavelength of 1274 cm-1 is presented. By using high-bandwidth HgCdTe detector and high-speed data acquisition devices, and combining with a high-resolution etalon, the features of the spectrum in the frequency domain can be acquired. Analysis of the measured spectral data gives the information about spectral shape, tuning characteristics and resolution variation with time, also about the influences of voltage and temperature on spectrum. The effective way to improve the spectral resolution and optimize the spectral quality is obtained, and it can be used to improve the accuracy of spectrum quantitative analysis.
2012, 61 (24): 244207.
doi: 10.7498/aps.61.244207
Abstract +
In this paper, the influences of fiber core structure on photonic band gap and transmission loss for hollow-core photonic crystal fiber are investigated, and the proper fiber core structure of fiber preparation technology is obtained. First, the band gap structure of triangular lattice of hollow core photonic crystal fiber with a fixed duty ratio is calculated by using plane wave expansion method. When the transmission wavelength λ=1.55 μm, the structural parameters of the optical fiber are figured out. The value range of the core diameter is given by simulating the influences of core diameter on the band gap location and size, and the value of core wall thickness is obtained through analyzing the leak loss characteristics. Then the fiber end view drawing is designed according to the analytical results. The mode field distributions are simulated by the full-vectorial finite element method under different core diameters. Through the contrast analysis the best fiber core radius with R=1.6 Λ—1.75 Λ is obtained. The results indicate that choosing appropriate core structure not only can meet the photonic band gap and loss characteristics of hollow-core photonic crystal fiber, but also can properly reduce the difficulty in the preparation technology of fiber.
2012, 61 (24): 244208.
doi: 10.7498/aps.61.244208
Abstract +
Waveguide geodesic lenses are key basic components in guide wave optical devices. Since their focus characteristics are independent of the wavelengths and the moded of the guided waves. Geodesic lenses lend themselves extremely well to the integrated optical devices. In this paper, the effects of fabrication errors of geodesic lenses described by four improved analytical solutions are studied by numerical analysis. The relations between the changes of the focal length and the depth changes due to fabrication errors of these lenses are obtained and compared. Considering the use of geodesic lenses in integrated optical devices, the fabrication tolerances of these lenses are given.
2012, 61 (24): 244209.
doi: 10.7498/aps.61.244209
Abstract +
Considering the fact that the GaAs has the characteristics of thermal decomposition, the thermal decomposition damage to GaAs surface, induced by a 532 nm wavelength long pulse laser with a millisecond pulse width is studied by the heat conduction theoretical and semi-analytical method. First, the calculation models of two-dimensional axisymmetric transient temperature field and the surface thermal decomposition damage threshold for long pulse laser irradiation of GaAs are established, and the transient temperature fields and the thermal decomposition damage thresholds in GaAs with different absorption rates are simulated. The results show that the higher absorption rate causes the higher temperature rise on the surface of material, but the required decomposition damage energy density is lower. With the increase of laser energy density, the decomposition damage occurs more early. This paper has guiding significance and practical value for investigating the interaction between long pulse laser and GaAs and its damage mechanism.
2012, 61 (24): 244210.
doi: 10.7498/aps.61.244210
Abstract +
Directional cracking in Ti,C:sapphire crystals grown along [1120] by Vertical Bridgman method often occurs in the cutting and processing process. In this work, we discuss the characteristic and mechanism of directional cracking of Ti,C:sapphire, and find that directional cracking originates from (1100) lattice plane and spreads along [0001] orientation. Through the Crystalmaker Simulation software, we find that atomic arrangement on (1100) lattice plane is the most sparse and adjacent atomic spacing is the largest along vertical [0001] direction, so in the system (1100) [0001] of lattice has a minimum cracking strength. Irregular carbon inclusions in the cracked Ti,C:sapphire are observed with optical microscopy, scanning electron microscopy (SEM), and X-ray diffractometry. These inclusions cause great internal stress in the cooling process due to thermal expansion mismatch and cracking originating from and spreading in the weak system (1100) [0001] of lattice. As a consequence, macroscopic directional cracking is observed in the Ti,C:sapphire. The study has important theoretical and practical significance for growing high-quality Ti,C:sapphire crystal.
EDITOR'S SUGGESTION
2012, 61 (24): 244301.
doi: 10.7498/aps.61.244301
Abstract +
Considering liquid slight compressibility, the dynamical behaviors of a bubble cluster in an acoustic field are investigated by regarding water as a work medium. The effects of initial radius of gas bubble, the number of bubbles for monodisperse cluster and polysidperse cluster, acoustic frequency, acoustic pressure on bubble dynamics are numerically simulated. The effect of each parameter on bubble motion state and collapse pressure is analysed. Chaotic characteristics of bubble dynamics in monodisperse cluster are investigated. Two collapse pressure features under chaotic state are analysed. The results show that the suitable parameters are helpful for improving cavitation treatment effect.
2012, 61 (24): 244501.
doi: 10.7498/aps.61.244501
Abstract +
The method of constructing Birkhoffian and Birkhoffian funcations of mechanical system is studied. Based on the conditions of self-adjointness and integrability conditions of linear partial differential equations, a method of undetermined tensor for constructing Birkhoffian and Birkhoffian funcations of mechanical systems is given. Two examples are given to illustrate the application of the results.
2012, 61 (24): 244502.
doi: 10.7498/aps.61.244502
Abstract +
With considering the influence of relative motion of vehicles in car following behavior, safe driving conditions and lane changing rules, a two-lane cellular automaton traffic model is proposed based on car following behavior, which is able to illustrate the system's metastable state near the critical point and produce simulation results that accord with observed data. With simulation data on lane changing behavior, a study is conducted on relationship between traffic density and number of vehicles meeting lane changing conditions. Lane changing function is defined to describe lane change process under standard driving behavior. Analytical solution of the function is obtained and used to predict traffic density that stabilizes after lane change process, which contributes to further research on vehicle lane changing behavior.
2012, 61 (24): 244503.
doi: 10.7498/aps.61.244503
Abstract +
Based on symmetric two-lane Nagel-Schreckenberg (STNS) model, a cellular automaton model of variable speed limit section in freeway is established with access to real-time traffic information of intelligent transportation system (ITS). The effects are discussed about how the different speed limit values, the lengths of speed limit section, and the different traffic states affect the traffic flow and the traffic volume via the simulation experiment of dynamic speed control. The effectual condition of speed limit is analyzed. The results of the examples show that speed limit can be used solely under some traffic states as an assistant traffic management strategy. The traffic jam phenomena can be suppressed and the goal of achieving a largest traffic flow and reducing the passing time of vehicles can be realized by using the dynamic speed control method with the different speed limit values and lengths under some traffic states.
EDITOR'S SUGGESTION
2012, 61 (24): 244504.
doi: 10.7498/aps.61.244504
Abstract +
The shear behavior of granular material is not only the most important mechanical property but also the most basic technical indicator in an engineering project. Today, it is still widely used, owing to its simplicity in operation. However, unlike common solid material, granular material shows the properties of disorder and non-uniformity. This is due to the formation of complex network force chains in granular medium. This also leads to the size effect of shear stress in granular solid. In this paper, direct shear tests with various sizes of high-precision spherical glass beads and sample aspect ratio are carried out to investigate the size effect of shear stress. It is found that when the particle size of glass bead decreases, or when the number of glass beads increases, the shear stress decreases slightly, while the reduction of the sample aspect ratio will lead to similar changes. The experimental results show that when the sample length is less than 50 times the particle size or aspect ratio less than 0.5, direct shear tests shows a significant size effect. Therefore the result of this investigation suggests that the guidance for current standard direct shear test should be revised.
2012, 61 (24): 244701.
doi: 10.7498/aps.61.244701
Abstract +
In this paper, we present a modified smoothed particle hydrodynamics (SPH) method. In order to well predict the morphology change of liquid drop, the presented SPH method employs a kernel gradient correction and a coupled solid boundary treatment algorithm. An inter-particle interaction force is used to model surface tension, and an artificial stress model is used to deal with tensile instability. The process of droplet impacting on liquid film is numerically simulated by the modified SPH method, which can well predict the pressure field evolution process of the drop impacting onto the liquid film and capture the variation of the free surface at different instants. Effects of Web number and surface stress on droplet impacting are also investigated, and mechanism of droplet splashing is analyzed. It is clearly demonstrated that the modified SPH method can effectively describe the dynamics of droplet splashing and the variation of the free surface. The obtained liquid drop morphology accords well with the results from other sources.
2012, 61 (24): 244702.
doi: 10.7498/aps.61.244702
Abstract +
The vortex axial-symmetrization is an important dynamical process affecting tropical cyclone track change, and it is identified by previous work, up to now, in terms of vorticity fields rather subjectively. Two-dimensional simulations whose integration time is 48 h using a quesi-geostrophic non-divergence barotropic vorticity equation model are performed. The evolutional processes from an initial non-axial-symmetric vortex to the final axial-symmetric vortex are produced. Fractal dimension DB of the perimeter of the vortex is calculated hourly based on the model output data. The results show that fractal dimension can be used to characterize the vortex axial-symmetrization objectively. Based on DB calculated, the correction coefficients CRD and CVD are calculated to be CRD=-0.70 and CVD=-0.75. They each have a significant correction. Here CRD denotes the correction coefficient between DB and Rm being TC scale parameter, and CVD denotes the correction coefficient between DB and Vmax being tropical cyclone intensity parameter. The relation between the vortex axial-symmetrization and the tropical cyclone parameters may be characterized. The results have potential applications in tropical cyclone forecasting.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2012, 61 (24): 245201.
doi: 10.7498/aps.61.245201
Abstract +
Corona discharges are usually generated at sharp points, edges or on thin wires where the electric field is strongly concentrated. With the rapid development of extra and ultra high-voltage transmission lines, the air corona discharge becomes one of the critical problems associated with high-voltage lines, which can lead to the deterioration of insulation systems, power loss, radio noise. Corona discharge studies have been undertaken for many years, not only because of the scientific interest in the corona mechanism but also because of its practical engineering importance. Transient space charge distribution effect that is one of the important canses in the process of corona discharge, is closely related to the corona discharge mechanism and onset, self-sustaining. In this paper, we present an improved self-consistent, multi-component and two-dimensional plasma hybrid model for simulating the DC positive corona discharge under atmospheric environment. The model is based on the plasma hydrodynamics and the chemical dynamics, and it includes 12 species and 27 reactions. Besides, the photoionization effect is also considered in the proposed model. The simulation and the experiment on bar-plate electrode configuration with an inter-electrode gap of 5.0 mm at 2-5.5 kV are carried out. The discharge voltage-current characteristics and single pulse waveform are in good agreement with the experimental measurements. Based on this model, the electric field distribution, the electron temperature distribution, and the evolution of charged species distribution are investigated in detail. The results show that distributions of electron temperature and electric field have the same patterns, In the process of discharge, electron density is kept at 1019 m-3 or so. O4+ is dominant compared with the other charged heavy species, and O2+ and N2+ play the key role in secondary electron emission: the unmbers of O2- and O are the largest in negative ions and neutral particle respectively, they play a negligible role in discharge process.
2012, 61 (24): 245202.
doi: 10.7498/aps.61.245202
Abstract +
The space crafts, such as spaceship, space shuttle and so on, will face a famous blackout problem when they re-enter the earth's atmosphere at high velocity. The plasma sheath severely affects the propagation of the incident electromagnetic wave and causes severe electromagnetic wave attenuation, which results in the communication failures between the space crafts and the ground control center. It is important to study the properties of terahertz wave propagation in non-magnetized plasma, for using the terahertz wave communication is an alternative method to solve the reentry blackout problem. The terahertz wave propagation characteristics in non-magnetized plasma are studied in this paper. The variations of the terahertz wave propagation properties with the terahertz wave frequency, plasma density, plasma collision frequency and the thickness of the plasma are acquired. Some new phenomena are found i.e., there appears periodic oscillation on the reflectivity curve with the increase of terahertz wave frequency, and the period of oscillation is 0.03THz. The oscillation amplitude increases with the increase of terahertz frequency, decreases with the increase of plasma density, and increases with the increase of plasma collision frequency. The oscillation is attributed to the multiple reflections of the electromagnetic wave at the interfaces at z=0 and z=-d. The terahertz wave propagation properties in plasma are studied experimentally with the shock tube, and the experimental results match well with the theoretical ones. Both the theoretical and experimental results indicate that using terahertz wave communication is an effective way to solve the reentry blackout problem.
2012, 61 (24): 245203.
doi: 10.7498/aps.61.245203
Abstract +
Based on the relativistic Brillouin flow theory, electron current and power loss in loss-front stage of coaxial cylinder vacuum magnetically insulated transmission line (MITL) are deduced under limiting current approximation. Through the particle-in-cell (PIC) model, loss currents and loss powers under different anode voltages are simulated. Simulation and theory results show that the proportions of loss current and loss power to the total current and power decrease when cathode-anode voltage increases. Beyond 4MV, limiting current approximation fits simulation results better than minimum current approximation. At voltages higher than 10 MV, relative error from limiting approximation is under 10%, while it exceeds 50% under minimum current approximation. This work is meaningful for establishing full circuit simulation of MITL system.
2012, 61 (24): 245204.
doi: 10.7498/aps.61.245204
Abstract +
Control of the spatiotemporal pattern with time delayed feedback in a gas discharge system is studied both analytically and numerically. The time delay in the semiphenomenological model is reduced as a perturbation. Based on the linear stability analysis, the effects of the time delay on the Turing and the Hopf modes near the Turing-Hopf codimension-two phase space are investigated. Then, the relations between the parameters of feedback and the oscillatory frequency, and the critical wavelength of the system are obtained. Results show that the transition between patterns can be controlled effectively by applying appropriate feedback even when the applied voltage keeps constant. The consequence of increasing the feedback intensity or the delayed time is equivalent to increasing the applied voltage. Furthermore, the analytical results are verified by two-dimensional numerical simulation. Our work proposes a way to control the pattern formation in a gas discharge system.
2012, 61 (24): 245205.
doi: 10.7498/aps.61.245205
Abstract +
In order to investigate the mechanism of dielectric barrier glow discharge in Ar/NH3 mixture at atmospheric pressure, a multiple particles self-consistent coupled fluid model is proposed. And the finite-element method is used in the numerical calculation model, so the periodically varying waveforms of gas voltage, dielectric surface charge density and discharge current density are investigated. The spatial and temporal distributions of charged and neutral particles density and space electrical field strength are also obtained. The simulation results show that the periodic breakdown process of the gas gap is controlled by the gas voltage, and affected by dielectric surface charges. The spatiotemporal distributions of charged particle density and electrical field strength show that the discharge under conditions considered in this model is a typical atmospheric pressure glow discharge, and that in the discharge process there exist an obvious cathode fall region, a negative glow region, a Faraday dark space, and a positive column region. In the Ar/NH3 plasma, the dominant positive ions are NH3+, and the next ions are Ar2+; the dominant negative ions are NH2-; the main radical molecule products of ammonia decomposition are NH, NH2, and N2H3, but the main final stable products are N2 and H2.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2012, 61 (24): 246101.
doi: 10.7498/aps.61.246101
Abstract +
The total dose effect of 0.8 μm SOI NMOS device with H-gate is analyzed. The device is exposed to 60Co γ-ray at low dose rate. The result shows that the irradiation effect is more serious at low dose rate for the same total irradiation dose. The threshold voltage shift in on state is lower than in off state. Irradiation leads to the increased drain voltage VD of kink effect. Because the number of effective interface traps varies with gate bias, interface trap has different influences on sub-threshold slope and transconductance.
2012, 61 (24): 246102.
doi: 10.7498/aps.61.246102
Abstract +
A simulation study is performed on the effects of six different cooling rates on microstructural evolution during solidification process of liquid Ca50Zn50 alloy with larger atomic size difference by using the molecular dynamics method. The pair distribution function, Honeycutt-Andersen (HA) bond-type index method, cluster-type index method (CTIM-2) and three-dimensional visualization method are adopted to deeply analyze the microstructural evolution. The results show that there is a critical cooling rate (in a range of 11012 and 51011 K/s) for forming amorphous or crystal structure. When the cooling rate, such as 11014 K/s, 11013 K/s, 11012 K/s and 51011 K/s, is above the critical cooling rate, the amorphous structures are formed mainly to be the 1551, 1541 and 1431 bond-types or the icosahedron basic clustr (12 0 12 0 0 0); while the cooling rate is under the critical cooling rate, such as at 11012 K/s, the partial crystal structures are formed mainly to be the 1441 and 1661 bond-types or the bcc clusters (14 6 0 8 0 0) (containing part of hcp (12 0 0 0 6 6) and fcc (12 0 0 0 12 0) basic crystal clusters) in the system. In the cooling rate range of forming amorphous structure, the first peak of the pair distribution function g(r) is split obviously into three secondary peaks corresponding to the nearest neighbor as Zn-Zn, Ca-Zn and Ca-Ca, respectively, and with the decrease of cooling rate, the secondary peak formed by the like atoms is inereased and the secondary peak formed by unlike atoms is reduced. With the decrease of cooling rate, the Zn atoms can be easily segregated to form the larger clusters; the lower the cooling rate, the bigger the number of basic icosahedrons formed in the system, and the amorphous system is more stable. In the cooling rate range of forming crystal structure, a great number of Zn atoms are segregated to form the bulk bcc crystal structures and part of Ca atoms are segregated to form some hcp and fcc crystal clusters.
2012, 61 (24): 246201.
doi: 10.7498/aps.61.246201
Abstract +
The phase transitions, elastic and thermodynamic properties of MnPd are investigated using first-principles calculations. The elastic constant calculations indicate that the paramagnetic cubic structure is unstable to external strain and the softening of C11-C12 triggers the paramagnetic cubic phase transformation. The paramagnetic tetragonal structure is mechanically and dynamically stable. When considering the magnetic property, a antiferromagnetic tetragonal structure is lower in energy than the paramagnetic tetragonal structure. So we can conclude that the structural behaviors of MnPd alloys change from paramagnetic cubic to paramagnetic tetragonal, and then to antiferromagnetic tetragonal structure. Moreover, we employ quasiharmonic approximation to calculate the heat capacity and the Debye temperature.
2012, 61 (24): 246501.
doi: 10.7498/aps.61.246501
Abstract +
The response to temperature of HMX polymorph is important for understanding the sensitivity, stability, and phase transitions of energetic material. Using ReaxFF-lg with isothermal-isobaric molecular dynamics (NPT-MD) methods, the crystal and molecular structures of -, -, and -HMX crystals in a temperature range of 303-503 K and at atmospheric pressure are investigated. The calculated crystal structures and thermal expansion coefficients are in general agreements with experimental results, indicating that ReaxFF-lg potential can correctly describe the thermal expansion of HMX polymorph. The linear thermal expansion coefficients indicate that the thermal expansion of -HMX is anisotropic, the thermal expansion along c axis is slightly different from those for a and b axes for -HMX, and the thermal expansion along a, b, and c axes are almost the same for -HMX. The volume expansion coefficients for the three phases decrease in the following sequence: -HMX-HMXHMX, showing that -HMX is the most sensitive to temperature in the three crystals, which may be the reason for higher sensitivity of this phase. Sharp changes in lattice parameter and molecular conformation transformation from chair to boat-chair occur for HMX when temperature reaches 443 K. Helmholtz free energy derived from the two-phase thermodynamics (2PT) model suggests a phase transition for HMX at T=423-443 K. The , -, and -HMX crystals are stable in the temperature ranges of 303-423 K, 443-503 K, and 363-423 K, respectively.
2012, 61 (24): 246801.
doi: 10.7498/aps.61.246801
Abstract +
The stability and electronic structure of Si6H4Ph2 are investigated by a comparative study of pure silicon nanosheet Si6, hydrogen-passivated silicon nanosheet Si6H6 and phenyl-passivated silicon nanosheet Si6H4Ph2 using density functional calculations. The mechanism on the stability of Si6H4Ph2 is elucidated. In addition, by examining the electronic structures of Si6H6 and Si6H4Ph2, we find the they both behave like an indirect gap semiconductor with a quite large gap.
COMPREHENSIVE SURVEY FOR THE FRONTIER DISCIPLINES
2012, 61 (24): 246202.
doi: 10.7498/aps.61.246202
Abstract +
In the middle of last century, some scientists discovered grain-boundary anelastic relaxation (GAR) peaks by means of torsional pendulum. Later, various models about the origin of GAR peaks are established through further research. However, its micro-mechanism is still unclear. Recently, according to the results of solute grain boundary segregation or dilution caused by elastic stress, a micro-mechanism of GAR which is grain-boundary absorbing or emitting vacancies has been proposed. Then, the equilibrium equations and the kinetic equations of GAR are established, and the process of GAR is expressed analytically. Furthermore, it has successfully elaborated the intermediate temperature embrittlement peak movement which exists widely in metals. Those developments of GAR theory are reviewed in the present paper.
EDITOR'S SUGGESTION
2012, 61 (24): 248502.
doi: 10.7498/aps.61.248502
Abstract +
Graphene has rich optical and electronic properties, nincluding zero band gap, high mobility and special optical absorption properties, and it has attracted much attention. More and more investigations focus on its fundamental physical properties and electronic devices. However, many researchers believe that its true potential lies in photonics and optoelectronics, such as photodetectors, modulators and transparent conductors used in light-emitting diodes or touch screens. In this review, we summarize its applications in semiconductor photoelectric devices, mainly for telecommunications.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2012, 61 (24): 247101.
doi: 10.7498/aps.61.247101
Abstract +
Electronic and atomic structures of LiP5, Li3P7 and LiP, which are formed in the process of lithium intercalation into black phosphorus, are systematically studied and analyzed using first-principles ultrasoft pseudopotential method based on the density functional theory (DFT). By caculating the electronic strucrures of these products, we find that the three products are all of semiconductor band structure, of which band gaps are larger than those of black phosphorus, indicating that the electronic conductivity of the black phosphorus is reduced after lithium has been intercalated into it. We simulate the diffusion of lithium ions in the LiP5, Li3P7 and LiP materials using nudged elastic band (NEB) method, and the diffusion activation energy of lithium ions is obtained firstly through the theoretical calculation. Compare with the results of other electrode materials, our results show that the migration energy barriers of lithium ions in LiP5, Li3P7 and LiP are all low. The diffusion coefficient of lithium ions in LiP5 is about 10-4 m2/s and the diffusion channel is one-dimensional. The diffusion coefficient of lithium ions in Li3P7 is approximately 10-7-10-6 cm2/s and the diffusion channel is three-dimensional. The diffusion coefficient of lithium ions in LiP is approximately 10-8-10-5 cm2/s and the diffusion channel is three-dimensional.
2012, 61 (24): 247102.
doi: 10.7498/aps.61.247102
Abstract +
Based on density functional theory calculations, the electronic structure and magnetic properties of C-doped BaTiO3 are investigated. It is found that the BaTiO3 doped by a nonmagnetic 2p light element (C) is ferromagnetic. The local magnetic moment is mainly localized on doped C atoms for Csub, while ferromagnetism in Cins comes from precipitation of magnetic ions Ti3+. Our results indicate that the proposed C-doped BaTiO3 is a potential candidate for dilute magnetic semiconductor material and multiferroics material.
2012, 61 (24): 247301.
doi: 10.7498/aps.61.247301
Abstract +
We experimentally investigate the dependences of the surface plasmon polarization (SPP) in the Ag nanowires on the polarizations of the excitation light and the emission light with a wavelength of excitation light 750nm. We find that the excitation and transmission efficiency change obviously with the polarization of incident light. However, the emission light is always linearly polarized light with an unchanged polarization direction. For the nanowires synthesized using a self-seeding process, their ends are axisymmetric. When the direction of the incident light is parallel to these Ag nanowires, the excitation and transmission efficiency of SPP are high. Conversely, when the polarization direction of the incident light is perpendicular to the wire axis, it is very low. For the nanowires with asymmetric ends, when the direction of the incident light has an angle with respect to the Ag nanowires, the excitation and transmission efficiency of SPP are high. While the polarization direction of emission light is always parallel to the wire axis which means that the polarization of the emission light does not depend on the polarization direction of the incident light. The polarization characteristics of the SPP in the thin Ag nanowires can realize the nanoscale manipulation of the intensity and polarization.
2012, 61 (24): 247302.
doi: 10.7498/aps.61.247302
Abstract +
In order to optimize the surface electric field of the traditional AlGaN/GaN high electron mobility transistor and improve the breakdown voltage and reliability, a new AlGaN/GaN high electron mobility transistor is proposed with the partial fixed positive charges in the Si3N4 passivation layer in this paper. The partial fixed positive charges of the Si3N4 passivation layer do not affect the polarization effect of the AlGaN/GaN heterojunction. The surface electric field tends to the uniform distribution due to the new electric field peak formed by the partial fixed positive charges, which modulates the surface electric field by applying the electric field modulation effect. The high electric fields near the gate and drain electrode decrease due to the new electric field peak. The breakdown voltage is improved from the 296V for the traditional structure to the 650V for the new structure proposed. The reliability of the device is improved due to the uniform surface electric field. The effect of the electric field modulation is explained by the horizontal and vertical electric field distribution between the Si3N4 and AlGaN interface, which provides a scientific basis for designing the new structure with the partial fixed positive charges in the Si3N4 layer. Because of the fixed positive charge compensation, the two-dimensional electron gas concentration increases, and the on-resistance decreases. So, the output current of the new structure increases compared with that of the traditional AlGaN/GaN High Electron Mobility Transistor.
2012, 61 (24): 247303.
doi: 10.7498/aps.61.247303
Abstract +
In the paper, we mainly investigate the SOI MOSFET characteristics of high-k gate dielectric with quantum effect. Self-consistent solutions of Schrdinger and Poisson equation are solved in this paper to obtain carrier wave function in the directiong perpendicular to the SiO2/Si interface and energy level distribution. Based on Young model, the threshold voltage and short-channel effects of SOI MOSFET with high-k gate dielectric are simulated and analyzed. The carrier distribution in inversion layer deviates from the surface with the increase of longitudinal electric field, which is caused by quantum effect. It increases the thickness of effective gate oxide and fluctuation of threshold voltage. Meanwhile, high-k gate dielectric materials can reduce the threshold voltage and restrain the DIBL efficiently. The calculation results matching ISE simulation results show that the model has a high-level accuracy, and faster operation ensures the efficiency of the simulation analysis.
2012, 61 (24): 247304.
doi: 10.7498/aps.61.247304
Abstract +
The n-type Si-rich SiNx film is deposited on a p-type crystalline Si (c-Si) substrate by facing target sputtering technique, and the Si-rich SiNx/c-Si heterojunction device is finally formed. The heterojunction device shows a high rectification ratio (1.3 103 at 2 V) at room temperature. Three distinct regions of temperature-dependence J-V characteristic curve can be identified, where different current density variations are indicated. In the low voltage range the current follows Ohmic behavior. In the intermediate range of voltage the current is governed by tunneling and recombination process, while space-charge-limited current (SCLC), with an exponential distribution of trapping states, dominates the conduction mechanism in the relatively high voltage range.
2012, 61 (24): 247501.
doi: 10.7498/aps.61.247501
Abstract +
The FexZn1-xO (x=0.80, 0.86, 0.93)amorphous films were fabricated by RF sputtering method. The films each have a strong ferromagnetism at room temperature. The saturation magnetization Ms can reacl 333.29 emu/cm3 in the as-sputtered Fe0.93Zn0.07O. Magnetism is isotropic. The sample obviously exhibits an anomalous Hall effect, which is different from the polycrystalline FexZn1-xO (x≤ 20%). The samples are of n-type semiconductor, with a carrier concentration of about 1019—1020 cm-3. After being annealed, the samples each present a resistance minimum phenomenon at a low temperature (222 K). The conductive mechanism is of the spin dependent variable range hopping resistance in the low-temperature. The experimental results show that amorphous FeZnO system of high Fe composition is a potential candidate of the new spintronic device materials.
2012, 61 (24): 247701.
doi: 10.7498/aps.61.247701
Abstract +
Sb-doped ZnO thin films with various impurity content values are deposited on glass substrates by radio frequency magnetron sputtering medthods. The influences of Sb doping content on the microstructural, photoluminescence and Raman properties of ZnO film are systematically investigated by X-ray diffraction (XRD), transmission spectrum, photoluminescence (PL) spectrum and Raman scattering spectrum. The results indicate that ZnO thin film doped with Sb exhibits a hexagonal wurtzite structure with preferred c-axis orientation; The vibrational mode at 532 cm-1 induced by Sb dopant can be observed in the Raman spectrum of the Sb-doped ZnO thin film, which can be attributed to local vibrational mode (LVMSb-O) that are formed by substituting Sb for Zn substitution and bonding O in ZnO lattice. The strong violet emission peak located at 3.11 eV is observed only in Sb-doped ZnO thin film by photoluminescence. Conbining the Raman scattering spectrum with photoluminescence, it is concluded that the strong violet emission peak is relation to SbZn-O complex defect in ZnO:Sb film.
2012, 61 (24): 247801.
doi: 10.7498/aps.61.247801
Abstract +
FeSi2 is a promising environment-friendly semiconductor material. However it is difficult to obtain pure phase for such a line compound. To investigate the solubilities for a third alloying elements, in this work Fe3Si8M (M=B, Cr, Ni, Co) ternary alloys are designed based on the cluster-plus-glue-atom-model. Thin films are then prepared using magnetron sputtering. The as-deposited films are all amorphous and become crystallized after annealing at 850 for 4 h. It is shown that samples alloyed with third components Cr and B can reach single phase easily. However, the main phase is phase and the films tend to exhibit metallic characteristics while alloyed with Co. Of these films, the Fe2.7Si8.4B0.9 film presents the most prominent semiconductor performance, and it has a resistivity of 0.17 cm, a sheet carrier concentration of 2.81020 cm-3, a mobility of 0.13 cm2=Vs and a band-gap width of 0.65 eV. It is confirmed that doping a proper third component can expand the phase zone, exhibiting a similar semiconductor property to that of binary -FeSi2.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2012, 61 (24): 248101.
doi: 10.7498/aps.61.248101
Abstract +
At pressure 5.0-5.7 GPa and temperature 1250-1600 ℃, the conditions of synthesis Gem-diamond are reported using FeNiMnCo catalyst by temperature gradient method (TGM), and the P-T phase diagram is given. Temperature field and carbon concentration gradient are simulated based on finite element method (FEM). The results of simulation and experiment show that type-I temperature field is suitable for growing high-quality large sheet-shaped Gem-diamond and small tower-shaped Gem-diamond; however, choosing type-II temperature field, both large sheet-shaped Gem-diamond and large tower-shaped Gem-diamond can be synthesized (type-Ib diamond and boron-doped diamond). On this basis, the growth speed and crystal quality are found to be determined by the carbon concentration gradient, and the rule that high-quality Gem-diamond can be synthesized when temperature field is suitable for the size and shape of diamond growing is given. The pressure and temperature regions for {110} and {113} faces to exist are studied. According to the analysis of Fourier infrared spectroscopy, it is found that the nitrogen concentrations in type-Ib and boron-doped diamonds synthesized by FeNiMnCo catalyst, which are due to the influence of Fe element, are lower than that of normal diamond. The diamond with low nitrogen can be used as an optical material with better transmission characteristics.
2012, 61 (24): 248102.
doi: 10.7498/aps.61.248102
Abstract +
Atomic layer deposited (ALD) aluminum oxide (Al2O3) has been known as an almost-perfect candidate of passivation dielectric layer for PERC-type c-Si solar cell. Its passivation performance and thermal stability are key issues for industrial PERC c-Si solar cell based on screen-printed technology. In this paper, 20 nm and 30nm Al2O3 films are synthesized on the solar grade CZ-Si by thermal atomic layer deposition. The results show that the effective lifetime can reach 100 μs for CZ-Si after annealing and is kept a half after the sintering process in the industrial beltline furnace, and the materials can be used in PERC-type solar cell. The SEM image demonstrates that the blisters occur in a thicker Al2O3 film, which explains why the passivation and thermal stability of 30 nm film are inferior to those of 20 nm film.
2012, 61 (24): 248401.
doi: 10.7498/aps.61.248401
Abstract +
Compared with the conventional klystron, high power multi-beam klystron makes use of many low perveance beams, then it has a high output efficiency and low operating voltage, but it brings new problems. There fore, the multi-beam intense relativistic electron beam transmission in the multi-beam klystron is investigated by experiment and simulation. The results show that the multi-beam rotates around the center of the system due to the interaction of the multi-beam, and simultaneously the multi-beam rotates around its own center due to the space charge effect of each beam's own. All the process can result in electron beams loss.
2012, 61 (24): 248402.
doi: 10.7498/aps.61.248402
Abstract +
In order to solve the problems that engineering model of photovoltaic array has low accuracy (within 5%) and five-parameter model has more parameters which are difficult to obtain, a new method of parameters extraction is presented in this paper. This method is first to use Lambert W function to obtain the analytic expression for photovoltaic module, then to use polynomial curve fitting method to obtain the current-voltage relationship of PV module, and finally to use the subsection integral method to obtain the value of parameters for photovoltaic module. The proposed method shows that the accuracy is within 0.5%. Compared with conductivity method and pattern search method, this method not only has intuitive features but also is easy to use. Furthermore, the obtained photovoltaic module parameters possess smaller errors (within 0.1%).
2012, 61 (24): 248501.
doi: 10.7498/aps.61.248501
Abstract +
A resistometric model based on microscopic analysis of electromigration failure mechanism is built. An extraction method for failure parameters of electromigration in copper interconnects is proposed from resistometric characteristics including the slope and step height. The results show that the failure time can be considered as the time to deplete grains at the cathode line end under a given stressing current. Two dominant failure modes with resuling slit and trench voids are observed in electromigration induced failures. The resistance curve for the trench-voiding failure mode consists of two characteristic regions,i.e., a step jump and an oblique line. The grain size and the extracted critical void length are lognormally distributed with close parameters. The variation in the slop of the oblique line in resistance curve with temperature obeys an exponential law. Activation energy of approximately 0.9 eV obtained from the resisometric model is consistent with that from Black equation.
2012, 61 (24): 248701.
doi: 10.7498/aps.61.248701
Abstract +
Although a pulsed-wave (PW) Doppler system can measure blood velocity with range information, measurable velocity is limited by frequency aliasing, and signal-noise-ratio (SNR) is poor. Continuous wave (CW) Doppler system offers a higher SNR in Doppler signal and no measurable velocity limitations but does not provide ranging information. Linear frequency-modulated continuous wave (LFMCW) and sine frequency-modulating continuous wave are able to provide high SNR Doppler signals with ranging information, and low clutter power, but with a certain range ambiguity due to signal periodicity of the Doppler signal spectrum. Various efforts have been made to improve the SNR, range resolution, and velocity limitations with FMCW Doppler system. An ultrasonic doppler blood flow velocity measurement system based on chaotic FMCW is proposed which has a higher SNR with no range ambiguity because of the aperiodicity of the Doppler signal spectrum. Principle analysis and experimental simulation show that the effectiveness of the new system is verified.
2012, 61 (24): 248801.
doi: 10.7498/aps.61.248801
Abstract +
Microbial fuel cell (MFC) is a kind of device, which can transform microbial metabolic energy into electric energy and simultaneously degrade the pollutants in wastewater by electrochemical technologies. Currently, the density of output power and efficiency are low and research of MFC is still in laboratory and in developing stage. In this paper, we design a kind of novel MFC system in which the semiconductor photocatalysis cooperating with the microbial catalysis is used by connecting photovoltaic cells to the traditional MFC systems in series. Thus we achieve a "photovoltaic cells-microbial cell" new MFC system. Experiments show that open-circuit voltage, short-circuit current and maximum output power density are greatly improved in the novel MFC system when the photovoltaic cells are exposed to the illumination. Photocatalysis of the semiconductor improves the reaction rate in the cathode chamber and the anode chamber, contributes part of power to runing the novel MFC system, and provides the basis for improving the pollutant degradation rate in wastewater. It is of great significance to solve the problem of energy crisis and environmental pollution.
2012, 61 (24): 248901.
doi: 10.7498/aps.61.248901
Abstract +
Using the theory of gravitational field, we study the gravitational field induced by the node in the process of the network transmission, establish the gravitational filed equation, and define two parameters α and γ for adjusting the dependencs of transmission data on the unblocked degree of node, the transmission capacity of node and the path length. Based on the gravitational field of node, an efficient routing strategy is proposed, and the package will be transferred along the route with maximum gravitation. In order to characterize the efficiency of the method, we introduce an order parameter η to measure the throughput of the network by the critical value of phase transition from free state to jammed state, and use the node betweenness centrality B to test the transmission efficiency of network and the congestion distribution. We simulate the network transmission efficiencies under different values of α and γ. Simulation results show that compared with the traditional shortest routing strategy, our routing strategy improves the network capacity several times, and effectively balances the distribution of the betweenness centrality of nodes, and the average path length Lavg> shows a trend from ascent to descent with the increase of load amount R, and the change of the parameters α and γ nearly have no effect on the network transmission capacity, which suggests the efficiency of our routing strategy is independent of α and γ, the network capacities are approximately equal for any values of α and γ in the feasible region.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2012, 61 (24): 249201.
doi: 10.7498/aps.61.0249201
Abstract +
Multiyear (2002-2011) wind observations from TIMED Doppler Interferometer (TIDI) onboard the thermosphere ionosphere mesosphere energetics and dynamics (TIMED) satellite are used for studying the typical structures and variations of mesospheric and lower thermospheric (MLT) mean zonal wind from 80 to 105 km in 120 °E meridian. Comparisons between TIDI measurements and empirical models indicate that TIDI is in good agreement with models in the extratropic regions especially in the middle and high latitudes, but significant differences occur mainly in the tropic regions. In the altitudes of TIDI's coverage from 80 to 105 km, monthly zonal winds are always westward over the tropical regions, forming an easterly band centered at the equator. Results from multiyear observations show complicated variations in the MLT tropical easterlies. The averaged width of easterlies is 37.5 degrees and corresponding variation is about 14 degrees.
2012, 61 (24): 249202.
doi: 10.7498/aps.61.249202
Abstract +
The mainstream data assimilation system in operation will still employ four-dimensional variational data assimilation(4DVAR) method in a long time of future. We develop a new 4DVAR system, i.e., YH4DVAR, using global spectral model as a constraint to impose a dynamic balance on the assimilation. The cost function of YH4DVAR consists of four terms: background, observations, digital filter, and bias correction, respectively. YH4DVAR employs the wavelet background error convariance, the multi-resolution incremental formulation, the tangent linear and adjoint models for dynamics core and physical processes, and ATOVS radiance data assimilation. Simultaneous spatial and spectral variations of horizontal and vertical covariance are achieved by dividing the control vector into several parts, each of which corresponds to a band of total spherical wavenumbers. Using NWP consisting of YH4DVAR and global spectral model, the anomaly correlation with the verifying analysis for geopotential height 8-day forecast on the 500 hPa isobaric surface at 12-month mean is above 60%. The formulation and implementation of YH4VAR are described in detail in this paper.
