Vol. 63, No. 12 (2014)
2014-06-20
GENERAL
2014, 63 (12): 120503.
doi: 10.7498/aps.63.120503
Abstract +
Based on the fractional calculus theory, in the absence of external driving force, the fractional transport model of asymmetric coupling particle chain in symmetric periodic potential is established. Using the method of fractional difference, the model is solved numerically and the influences of the various system parameters on directional transport velocity are discussed. Numerical results show that in the case without external force and noise-driven, the fractional asymmetric coupling system can still generate directional transport, and the transport velocity increases as fractional order increases. When the fractional order is fixed, the average velocity of the particle chain varies non-monotonically with coupling strength and barrier height. In the case with noise, the generalized stochastic resonance phenomenon occurs. Besides, we can make the noise not affect the system or even promote directional transport by adjusting other parameters.
2014, 63 (12): 120504.
doi: 10.7498/aps.63.120504
Abstract +
Using the quantum statistical theory, the stability of a weakly interacting Fermi gas trapped in a strong magnetic field is investigated, the expression of stability condition is given, and the mechanisms of influences of interparticle interaction and magnetic field on the stability are analyzed. The results show that repulsive interaction will increase both the chemical potential and the space domain needed for system stability. But, the increasing of magnetic field strength will reduce the space domain needed for the system stability, and lower the stability of the particle number density distribution.
2014, 63 (12): 120507.
doi: 10.7498/aps.63.120507
Abstract +
Z-source converter can have a high voltage transmission ratio, reduce the losses of switching devices, and improve the efficiency of the system, etc., because of embedding the Z-source network into the system, which makes it find wide applications in DC conversion, inverters, etc. Nonlinear dynamics of the peak-current-mode controlled synchronous switching Z-source converter is studied for the first time so far as we know. The discrete iterated mapping model under continuous current mode is established, while the effects of the reference current on the stability of the system are analyzed by using the trajectories of eigenvalues, and the steady state operation parameter domain is schemed. Period-doubling bifurcation, border-collision bifurcation, tangent bifurcation and intermittent chaos are found in this converter based on the bifurcation diagram and the Lyapunov exponent diagram, and the evolvement and mechanism of the border-collision bifurcation and chaos are analyzed. Finally, the circuit simulation and the experimental results show that the theoretical analysis is correct. Results obtained indicate that with the increase of the reference current, the peak-current-mode controlled synchronous switching Z-source converter goes from period 1 into period 2 and period 4 through the period-doubling bifurcation, and moves into the intermittent chaos due to the border-collision bifurcation. Then the system exhibits a period-3 behaviour because of the tangent bifurcation. Finally, the converter moves into chaos due to the border-collision bifurcation again.
2014, 63 (12): 120508.
doi: 10.7498/aps.63.120508
Abstract +
In this paper, for the fault detection of a single-input single-output (SISO) system, we define a concept of matching chaotic stimulation with a measured system, establish a criterion of matching chaotic stimulation with a measured system, and propose a method of adjusting the matching of chaotic stimulation with a measured system. Finally, the improved prediction error is used to detect faults in the SISO system. The simulation results show that matched chaotic stimulation can be used to detect faults effectively, while unmatched ones can add uncertainty into the fault detection.
2014, 63 (12): 120509.
doi: 10.7498/aps.63.120509
Abstract +
Lyapunov index is one of criteria for testing whether the system is in a chaotic state, and its value represents the developed level of system chaotic state. To study the Lyapunov index characteristic of cascade chaotic system and reveal disturbance mechanism among subsystems in cascade chaotic system, the following researches are carried out. First, the disturbance model among subsystems is constructed from the viewpoint of pseudo noise disturbance, Lyapunov index difference between without and with external noise influence is investigated. Then the conclusion that disturbances among subsystems can be considered as pseudo noise influence is drawn. Second, the conclusion is proved that cascade system Lyapunov index is not the algebraic sum of each independent subsystems, but the one of each subsystems which consist of pre disturbances. Then taking the logistic representation for example, nine cascade systems are designed to prove this conclusion. And some novel characteristics and phenomena are found from the above investigations. They are (a) the phenomenon of “more is less”, that is, Lyapunov index will decrease with the increase of cascade levels, and the phenomenon of “A miss is as good as mile”; (b) even each independent subsystems is chaotic, the cascade system needs not to be chaotic; conversely, even each independent subsystems is not chaotic, the cascade system may be chaotic; (c) whether the cascade system is chaotic is associated with the order of subsystem. Finally, it is pointed out that cascade level has the influences of pros and cons on cascade system, thus revealing the latent hazard of parametric cascade chaotic system. The research result can provide important theoretic foundation for system security and the scientific evaluation of encryption keys.
2014, 63 (12): 120510.
doi: 10.7498/aps.63.120510
Abstract +
Grid-connected inverter system is recognized as a time-varying nonlinear system, and it has complex nonlinear behaviors in practice. However, the introduction of dead-time nonlinearity can make the nonlinear behaviors of the system more complex and harder to predict. In this paper, the proportional control single-phase grid-connected inverter with L-filter considering dead-time nonlinearity is investigated. The observation of current waveforms under fixed controller parameter and different dead-time parameters shows that the bifurcation phenomenon occurs with the increase of dead-time. According to the features of dead-time nonlinearity and the zero current clamping phenomenon caused by dead-time, an exact and complete discrete-time model is established by comprehensively considering the system from various aspects. And the theoretical analysis of bifurcation behaviors of system is carried out based on the proposed model. Moreover, the stability judgment has engineering significance. However, with the consideration of dead-time nonlinearity, analytical methods are difficult to use and the graphic methods do not have satisfactory accuracy. Therefore, a stability criterion based on equivalent duty ratio is proposed in this paper, which can accurately judge the stability boundary and provide reliable references for the parameter design of controller and dead-time.
2014, 63 (12): 120701.
doi: 10.7498/aps.63.120701
Abstract +
In order to reduce the number of numerical meshes and simplify aperture array modeling, an equivalent method of modeling aperture array in which the size effect of apertures is taken into account, is presented in the paper. In this method, the aperture array is replaced by a single aperture which has the same area as the original aperture array, then the scaling factor of the aperture is obtained according to the number of apertures. The empirical relations between the number of apertures and scaling factor are proposed based on theoretical derivation and curve fitting method respectively. The comparison with the commercial software HFSS indicates that the formula based on curve fitting method has a higher accuracy. The applicability of the method is verified by varying the interference source, monitoring point, total area and position of aperture array, shape of aperture and cavity size. As shown by the numerical results, the equivalent modeling approach can significantly reduce the number of meshes, which can serve as a simplified approach to numerical simulation of shielding characteristics of complex cavity.
2014, 63 (12): 120501.
doi: 10.7498/aps.63.120501
Abstract +
The calculation and simulation results show that f(x,y,z)=sin(k(x2+y2+z2)), f(x,y,z)=k(1-(x2+y2+z2))e(-(x+y+z+u)2), f(x,y,z)=k((x2+y2+z2)/3)(1-(x2+y2+z2)/3) can easily constructe a three-dimensional (3D) discrete dynamic system by combining other two polynomial functions generated randomly. Through calculating Lyapunov exponent and drawing the bifurcation diagram, the characteristics of chaos of the function are confirmed, and according to the bifurcation diagram of parameters and the Lyapunov exponent curve more chaotic mapping functions are found. Analysis shows that the cross-section geometric shape can determine the chaotic characteristics of 3D function, and the cross-sections are all the median convex or middle concave surfaces, which can constructe chaotic dynamic systems easily. In the future, the mathematical description model and some basic theorems are to be further investigated and their results will be used to solve practical problems such as turbulence.
2014, 63 (12): 120502.
doi: 10.7498/aps.63.120502
Abstract +
In this paper, we continue to study the chaotic characteristics of two curved surface mapping which forms a function in a unit area, and find that when one of the two curved surfaces is a standard curved surface and subjected to strong oscillation, and the other is randomly generate, the occurrence of chaos is more prone. Many different chaotic attractors are drawn by this method, adjusting the random surface to become subjective, the probability of chaotic attractor appearing can reach a half or more, which means that when certain conditions are meet, chaos is extremely common. Through calculating Lyapunov exponent and drawing the bifurcation diagram to analyze characteristics of chaos of the function, according to the bifurcation diagram of parameters and the Lyapunov exponent curve to look for more chaotic mapping function, a lot of chaotic attractors can be obtained. Finally a three-dimensional trigonometric function and two randomly generated three-dimensional polynomial functions are iterated, and many fancy three-dimensional attractors are obtained.
2014, 63 (12): 120505.
doi: 10.7498/aps.63.120505
Abstract +
With the development of micro electromechanical systems, many researchers focus their attention on nonlinear energy harvesting device. The stochastic equivalent linearization method is used to analyze an energy harvesting system under ambient noise. First, according to the bistability of beam axially loaded, a model of bistable nonlinear vibration energy harvester under the stochastic condition is proposed. A close-form approximation expression for the ensemble average of harvested power is derived and the numerical simulation of the system shows stochastic resonance. The results show that it is possible to optimally design system such that the harvest power is maximized for a given density or variance of random excitation.
2014, 63 (12): 120506.
doi: 10.7498/aps.63.120506
Abstract +
In this paper, (supra-threshold) stochastic resonance phenomenon of noise-enhanced information transmission is studied in detail through the numerical calculation and the computer simulation in a non-linear multilevel threshold neural networks system, which is affected by both additive noise and multiplicative noise, then the mutual information is used to characterize the phenomenon. The mutual information as a function of additive noise intensity or multiplicative noise intensity brings on convex changes under a suitable system threshold and a fixed multiplicative noise intensity or additive noise intensity, which shows that the (supra-threshold) stochastic resonance phenomenon occurs. The increases in the number of the system threshold units can enhance the effectiveness of information transmission; the increase of the system threshold can increase the signal components that are under the threshold, and thus the supra-threshold stochastic resonance takes place more easily. In addition, by changing the additive noise intensity the supra-threshold stochastic resonance occurs more easily than by changing the multiplicative noise intensity. The above results show that both the existence of the supra-threshold stochastic resonance and the effectiveness of noise-improved the signal transmission are closely related to multiplicative or additive noise intensity, the number of threshold units, and the system threshold level.
2014, 63 (12): 120511.
doi: 10.7498/aps.63.120511
Abstract +
Two linear systems are obtained by employing linearization technique in a simplified Lorenz system, and a two-scroll chaotic attractor is generated via the control method. Multi-scroll chaotic attractors are generated by extending the saddle-focus equilibrium points with index 2. Dynamic characteristics of the multi-scroll chaotic system are analyzed by observing the phase diagrams, bifurcation diagrams, Poincaré sections and calculating the largest Lyapunov exponent. A circuit for the multi-scroll attractor is designed and simulated. The numerical simulation result and the circuit simulation result are consistent with each other. To apply the multi-scroll chaotic systems to image encryption, an improved hybrid encryption algorithm is designed based on the multi-scroll chaotic system and advanced encryption standard (AES), and its encryption performances are analyzed. The results show that the improved hybrid encryption has a higher security.
2014, 63 (12): 120202.
doi: 10.7498/aps.63.120202
Abstract +
Matrix filling and equation solving are the most computationally-expensive steps in the method of moments (MoM). Based on the compressed sensing (CS) theory, an improved method of MoM is proposed in this paper. Through introducing sparse transform matrix, the unknown response can be expressed sparsely, so we can construct and optimally solving underdetermined equation under the framework of CS. Numerical examples show that the proposed method can reduce the matrix filling cost dramatically, and also can improve the efficiency of equation solving effectively.
2014, 63 (12): 120301.
doi: 10.7498/aps.63.120301
Abstract +
Multi-band excitation (MBE) algorithm in classical communication is applied to quantum communication. The corresponding relation between classical information and quantum information is proposed, and the quantum measurement of information is presented. Simulations of quantum MBE algorithm by C language programming demonstrate that the wave of synthesized speech is similar to the original one. An MOS score of 3.337 is obtained from the Perceptual Evaluation of Speech Quality software.
2014, 63 (12): 120201.
doi: 10.7498/aps.63.120201
Abstract +
The method of combining function transformations with auxiliary equation is presented to search for new infinite sequence soliton-like solutions of Camassa-Holm-r (CH-r) equation. And many new conclusions are obtained. Step one,according to some function transformations, CH-r equation is changed into the solvable ordinary differential equation. Step two, new infinite sequence soliton-like solutions of CH-r equation are constructed by applying new solutions and Bäcklund transformation of the solvable ordinary differential equation.
NUCLEAR PHYSICS
2014, 63 (12): 122801.
doi: 10.7498/aps.63.122801
Abstract +
An identification method of γ-ray fingerprints based on adaptive network-based fuzzy inference system is brought forward. By setting up model and performing simulation, the parameters of the system relevant to the γ-ray fingerprints are extracted as the identification features. The two-dimensional fuzzy set about the identification features is put forward, and the fundamental principle for identification is established. The types and the individuals of nuclear materials are identified successfully with high degree of confidence. The simulation materials as radiation sources are identified with the method, and the performance of the method is studied and discussed. The results show that the method has not only strong capabilities for identifying the types and the individuals of the radiation sources, but also strong de-noising capability and low identification limit, and it can be applied to the nuclear materials safeguard.
ATOMIC AND MOLECULAR PHYSICS
2014, 63 (12): 123101.
doi: 10.7498/aps.63.123101
Abstract +
With the further scaling down of device dimensions, charge trapping memory with high k materials HfO2 serving as capture layer shows good endurance and high storage capacity. Its relatively simple process and complete compatibility with the conventional semiconductor process furthermore make it widely studied. The oxygen vacancies in HfO2 are studied using the first-principles calculation in order to learn their influence on the storage properties of charge trapping memory. Write and erase operations of memory devices are simulated via changing the number of electrons in the super cell with defects. The results show that basically the distance between oxygen vacancies has no effect on charge trapping, but the number of oxygen vacancies does affect it. The more the number of oxygen vacancies, the stronger the electron capture ability is. Moreover, four-fold coordinated oxygen vacancy (Vo4) has lager capability for trapping charge than three-fold coordinated oxygen vacancy (Vo3). The analysis of density of states shows that Vo4 induces a large number of quantum states with deep energy levels which is little affected by distance and has large possibility of trapping charges. The results show that oxygen vacancy defects in HfO2 tetravalent coordination are conducive to improving the storage characteristics of charge trapping memory.
2014, 63 (12): 123102.
doi: 10.7498/aps.63.123102
Abstract +
The X1Σ+, a3Π and A1Π states of BCl molecule are studied using the highly accurate valence internally contracted multireference configuration interaction approach including the Davidson modification. The Dunning's correlation-consistent basis sets, aug-cc-pV6Z and aug-cc-pV5Z, are used in the study. To obtain more reliable results, the potential energy curves (PECs) of three electronic states are extrapolated to the complete basis set limit by the two-point total-energy extrapolation scheme. The effects of the core-valence correlation and relativistic corrections on the PECs are taken into account. By fitting these PECs, the spectroscopic parameters (Te, Re, ωe, ωexe, Be, αe and De) of the X1Σ+, a3Π and A1Π states of BCl are determined. These parameter values coincide with the experimental results. In addition, the whole vibrational states for X1Σ+, a3Π and A1Π states at J =0 (J is the rotational quantum number) are determined by numerically solving the radical Schrödinger equation of the nuclear motion of diatomic molecules. For each vibrational state, the vibrational level and inertial rotation constants are obtained, which are in excellent accordance with the experimental results. With the potential energy curves obtained at MRCI+Q/56+CV+DK level and the MRCI wave functions, the Franck-Condon factors, radiative lifetime of transition from a3Π and A1Π to the ground state are computed.
EDITOR'S SUGGESTION
2014, 63 (12): 123201.
doi: 10.7498/aps.63.123201
Abstract +
Systematic error caused by stray magnetic fields is often one of the major sources of the uncertainties in many precision measurements. It is necessary to accurately control the magnetic fields in these measurements. The spectrum of the fine structure of helium can be used to determine the fine structure constant, and also to test the quantum electrodynamic theory of multi-electron systems. In this work, we present a magnetic shield that can eliminate stray magnetic fields and a cosine coil that generates a uniform magnetic field. The central magnetic strength produced by the coil is measured through the spectrum of a 4He metastable atomic beam. The magnetic shield reduces the strength of the external magnetic field down to less than 0.8 mGs. The variation of the magnetic strength in the spectrum region is less than 10 mGs at a magnetic strength up to 20 Gs. In this case, the uncertainty introduced by the magnetic field will be less than in the spectrum of helium fine structure.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2014, 63 (12): 124101.
doi: 10.7498/aps.63.124101
Abstract +
A method of designing a kind of shared aperture radar absorbing material (SA-RAM) is presented, in which method the scattering problem of passive metamaterial (MTM) is converted into the radiation problem of active array. Multifunctional SA-RAM is realized by optimizing the position, amplitude, and phase of the MTM subarray composed of finite MTM structures based on the array theory. An SA-RAM with absorber and phase cancellation characteristics is fulfilled by interleaving artificial magnetic conductor (AMC) subarray and perfect metamaterial absorber (PMA) subarray. Simulation and experimental results demonstrate that the backscattering radar cross section (RCS) of SA-RAM is smaller than that of the metal plate in a frequency range of 5.5-8.3 GHz. Especially, the RCS reduction is caused by high absorbance at 5.54 GHz and by phase cancellation between AMC subarray and PMA subarray at 7.0 GHz. The idea can help to design radar absorbing material, which combines frequency stealth with space stealth function.
2014, 63 (12): 124102.
doi: 10.7498/aps.63.124102
Abstract +
In view of the need of the electromagnetic compatibility analysis in the design process of the electronic equipment, an equivalent method of modeling the characteristics of electromagnetic radiation from printed circuit board interference source is proposed by using magnetic dipole array. According to the characteristics of the electromagnetic boundary value problems, the radiating source and the structures affecting the radiation are modeled separately. At first, the actual source is modeled in detail. Then the effect of surrounding structures on the overall radiation is incorporated into the model. Moreover, the basic ideas of equivalent modeling are introduced, and the derivation of the formulas to obtain the magnetic dipole array is given. Finally, a patch antenna is used to demonstrate the validity of the method. The results show that the equivalent modeling method significantly reduces the complexity of the model, the modeling time, and the computational burden.
2014, 63 (12): 124201.
doi: 10.7498/aps.63.124201
Abstract +
The time evolutions of the entanglement between a two-level atom and its spontaneous emission field in free space, cavity, isotropic and anisotropic photonic crystal are studied by using quantum entropy. It is found that the evolution properties of the atom-field entanglement are directly related to the nature of the structured reservoir,specifically, to the distribution of the density of modes. In free space and cavity, as the density of the modes varies smoothly with frequency, the atom-field entanglement decays to zero in a finite time. However in an isotropic and anisotropic photonic crystal, the atom-field entanglement can keep steady due to the existence of a photonic band gap in the density of the modes. Thus, we can control the time evolution of the entanglement between the atom and its spontaneous emission field by changing the density of the modes of the structured reservoirs.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2014, 63 (12): 125202.
doi: 10.7498/aps.63.125202
Abstract +
In this article, the X ray special line radiation from Z-pinch Al plasma is calculated by using non-local-thermodynamic-equilibrium model (NLTE) based on digital energy level. The electron density of Z-pinch plasma at centre is obtained. The single plasma state parameter cannot well describe the special line radiation. In the next step, the Z-pinch plasma is divided into two parts: high electron temperature plasma at centre and low electron temperature plasma. The superposition of radiations from two parts is analyzed, and modified calculation result is presented. The calculation results are significantly improved after the superposition of radiations from two parts has been taken into account.
2014, 63 (12): 125203.
doi: 10.7498/aps.63.125203
Abstract +
The collisional-radiative model, that has been constructed for the helium plasma in the Sino-United Spherical Tokamak is introduced. The result of the 447.1nm (23P-43S)/492.2nm(21P-41D) and 492.2nm/504.8nm(21P-41S) line ratios is given. The line ratio method that is used for measuring electron temperature Te and density Ne parameters is described. The result from the line ratio method is consistent with the measurement of the 94 GHz interferometer. The method is also validated by comparing the relative population densities of the excited states which are deduced from the CR model and the measured intensity data of helium lines. The factors that brings errors into the diagnostic result are discussed, including the error from the measurements, and those from the uncertainties of the rate coefficients that are used in the CR model and the viewing chord integration characteristic of the optical emission measurement.
2014, 63 (12): 125205.
doi: 10.7498/aps.63.125205
Abstract +
The laser energy will be increased substantially when the Shenguang-II laser facility upgrade is completed and the petawatt picosecond laser beam will be equipped at the same time. For the fast ignition approach, direct-drive implosions have some advantages over indirect-drive ones, such as higher energy efficiency and lower mixing of cone material into fuel. Based on Shenguang-II upgraded laser facility, integrated direct-drive fast ignition experiments will be carried out and it will contribute to the further understanding of the relevant physics such as integrated coupling efficiency. The radiation hydrodynamic code Multi1D is used to design fast-ignition targets, and the optimized target parameters are achieved. The optimized target has a relatively thick wall (35 μm) and 420 μm-outer-radius CH shell, which are consistent with the scaling laws in target design. The deposition in the optimization target of the hot electrons generated by the picosecond petawatt pulse is also calculated according to the hot electrons scaling relation. The results show that the achieved areal density is high enough to stop the hot electrons.
2014, 63 (12): 125206.
doi: 10.7498/aps.63.125206
Abstract +
In order to suppress the core-corona structures commonly observed in the single-wire exploding stage of wire array Z-pinch, the laser probe diagnostic is analyzed, and the exploding characteristics of aluminum wire under negative-polarity and fast-rising current pulses (90-170 A/ns) are investigated using a picosecond laser probe. The aluminum wire with a diameter of 15 μ m and a length of 2 cm, has a peak resistive voltage of 35-50 kV and a resistivity of 30-40 μΩ·cm before the voltage collapsed. The ohmic energy deposited in the load is 1.5-2.5 eV/atom at the voltage peak time, and 2.5-4.0 eV/atom at the time when the Joule heating power drops off to half of its maximum value. A faster rising current would lead to an increase of the energy deposition rate, and enhance the breakdown voltage. In most shots, nearly all the aluminum atoms near the electrodes are in the gaseous state, and liquid drops or clusters existing at the central part of the wire. While in some shots, the load is exploded into a gaseous state homogeneously along the axis. At about 127 ns after the laser peak, 70% of the initial mass is located within a diameter of 1 mm, and all the mass is within a diameter of 2 mm.
2014, 63 (12): 125207.
doi: 10.7498/aps.63.125207
Abstract +
In order to study the transportation and conversion of the electromagnetic energy from the pulsed power driver to Z-pinch load, a circuit model for the driver is analyzed, and coupled with magneto-hydrodynamics model for the load plasma. Our simulation results are compared with those obtained from circuit software and experimental results based on the “Qiangguang-I” facility. The simulated voltage and current waveform coincide well with the experimental results. Results show that the pulse width decreases and the peak increases as the pulse transmits from the storage capacitors to the pulse transmission line. When the storage capacitors are initially charged at 35 kV, the peak of electric powers at the transfer capacitor, the pulse forming line and the pulse output line are 0.23, 0.80 and 1.46 TW, respectively, and their rise-times (10%-90%) are 550, 160 and 45 ns, respectively. The load current is 1.5 MA and the X-ray radiation power is 0.58 TW.
2014, 63 (12): 125208.
doi: 10.7498/aps.63.125208
Abstract +
The applications of Z-pinch are realized through dynamic hohlraum driven by Z-pinch, in which a uniform and symmetrical radiation field may be produced for ablating implosion of the inertial confinement fusion (ICF) capsule, and the radiation sources may also be created for heating and backlighting the samples in opacity measurement experiments. The radiation field is essentially related to driven current, hohlraum configuration and material. In physics it is determined by energy transfer in the hohlraum. For rapidly obtaining the knowledge about the primary energy transfer chracteristics in the hohlraum, and its trends of variation in the configuration, linear mass of the load, and the driven current, the simplified model is used to simulate the dynamic hohlraum implosion. The obtained implosion kinetic energy of the cylindrical foam accords well with the kinetic energy obtained from a one-dimensional magneto radiation hydrodynamics simulation of Z-pinch-driven dynamic hohlraum. In the dynamic hohlraum for ICF the kinetic energy loss is important for the radiation field formation when the imploding wire-array plasma collides with the cylindrical foam, while ones for radiation source the kinetic energy loss and for the final implosion kinetic energy of the foam are both important. The maximum implosion kinetic energy of cylindrical foam is directly proportional to the square of the peak current, while the kinetic energy loss increases with the mass of cylindrical foam increasing. The mass energy density in the foam tends to increase, and in turn the radiation power is enhanced when the rise time of the current turns longer.
2014, 63 (12): 125209.
doi: 10.7498/aps.63.125209
Abstract +
The spatial profiles of implosion core temperature and density are very important to check the theoretical simulation codes and understand the implosion physics in depth. A method is presented that the temperature and density profiles are evaluated by multi-objective optimization, where the normalized intensity profile is calculated from implosion core X-ray images. Two models, i.e., the model with considering absorption and the model without considering absorption, are studied. The results indicate that the temperature profile from the model without considering absorption is about twice that from the model with considering absorption. The density profiles evaluated by the two models are almost the same in the fuel zone, but the density from the model without considering absorption is more than ten times smaller than that from the model with considering absorption in the ablator zone.
2014, 63 (12): 125210.
doi: 10.7498/aps.63.125210
Abstract +
The diagnoses of laser-produced plasma electron density have important significance for inertial confinement fusion, plasma physics, high energy density physics and other relevant fields, especially for measuring electron density distribution information of medium and high-Z material plasma near the critical density surface. With 13.9 nm Ni-like Ag X-ray laser serving as a probe, using double frequency grating shearing interference technique, the electron density distribution of plasma produced by laser irradiating a gold planar target is measured. Clear interference fringe image is obtained. Preliminary deduction of the fringe shows that the maximum density measured is about 1.4 times the critical density. It is found that there are some discrepancies between experimental results and simulation results, which provides a useful reference to the further optimization of the simulation program. The experimental results fully demonstrate that the soft X-ray double frequency grating shearing interference technique is practical to diagnose near-critical-density plasma of medium and high-Z materials, which will have a good application value.
2014, 63 (12): 125211.
doi: 10.7498/aps.63.125211
Abstract +
Indirectly driven low-convergence-ratio implosion experiments are conducted on SGIII prototype laser facility. Neutron yield, ion temperature and bangtime, and also their variation laws with the increase of ablator thickness are measured. These results are analyzed quantitatively and qualitatively, and the difference between the measurements and the calculations is discussed. The degradation of neutron yield is attributed to the hydrodynamic instabilities and implosion asymmetries.
2014, 63 (12): 125201.
doi: 10.7498/aps.63.125201
Abstract +
In edge plasma, hydrogen molecules have considerably high density. The vibrational distribution of hydrogen can be changed via collisions with plasma. In this paper, various processes of hydrogen molecules are discussed and newest cross section data are adopted while the unavailable data are calculated by semi-classical Gryzinski method. Based on the quasi-stationary approximation and the quasi-steady collisional-radiative model, the vibratioanl distribution of hydrogen in low temperature are studied. The results show that at lower vibrational level, the distribution decreases with the increase of electron temperature when the electron temperature is less than 10 eV. On the other hand, the distribution presents an opposite trend at high vibrational level.
2014, 63 (12): 125204.
doi: 10.7498/aps.63.125204
Abstract +
A dual-polarization frequency-modulated continuous-wave (FMCW) reflectometer is established on J-TEXT for measuring density profile. The frequency of reflectometer covers both Q band and V band. In order to measure wider density range, ordinary mode polarization and extraordinary mode polarization are utilized at the same time. For the FMCW reflectometer, temporal resolution depends on sweeping rate of the microwave source. Benefited from HTO (hyperabrupt varactortuned oscillator) source, a full frequency sweep period of the reflectometer could be less than 40 μs. Electron density profile from 0-6.0×1019 m-3 can be detected, which covers the whole low field side in J-TEXT. To reconstruct the full density profile, the position of the zero density should be confirmed first, which is determined from where the intermediate frequencies change transiently. Meanwhile, we observe the propagation of left-hand extraordinary wave from data in X-mode reflectometer.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2014, 63 (12): 126101.
doi: 10.7498/aps.63.126101
Abstract +
Valence electron structure has an intrinsical influence on the physical properties of material. On the basis of empirical electron theory of solids and molecules, combining with dynamic mechanical process of calculating steel, we constructe a new model for calculating static and dynamic strengths of steel. The static (dynamic) strengths of multi-composition steel, predicted by the proposed model, accord well with the experimental values. It is the first time to introduce the valence electron structure into the model for predicting dynamic properties.
2014, 63 (12): 126201.
doi: 10.7498/aps.63.126201
Abstract +
Using shock wave loading and real time optical transmission measurements, the transmission spectra of liquid water compressed between the quartz windows under pressures in a range of 1-1.6 GPa are obtained. A discontinuity of liquid water at nearly 0.9 GPa during the shock is observed. Combining the phase diagram of water with calculation results, it is suggested that the discontinuity of liquid water is due to a possible phase transition from low density water to high density water under the experimental conditions. The method can also be used to study other transparent molecular liquids in shock compression experiments.
2014, 63 (12): 126301.
doi: 10.7498/aps.63.126301
Abstract +
The crystal structure, spontaneous polarization, contributions of electrons and phonons to the dielectric and piezoelectric responses of BaTiO3/SrTiO3 (1:1) 10-atom superlattice are calculated using first-principles. We explore the ground structure from the highest P4/mmm phase by successively freezing the unstable polar modes. We find that the ground structure possesses the Cm symmetry. The contributions of phonons to dielectric and piezoelectric tensor coming from individual atoms and individual modes are explored. Detailed analysis shows that the ε22 and e26 are mainly due to the A“phonons with ωλ=197 and 146 cm-1, while the A” phonons with ωλ=97 cm-1 also make relatively large contributions. The ε33 and e33 are mainly due to the A' phonons with ωλ=189 and 139 cm-1. The ε11 and e11 are mainly due to the A' phonons with ωλ=246 cm-1. On the other hand, the O and Ti atoms make great contributions to the lattice dielectric and piezoelectric responses.
2014, 63 (12): 126801.
doi: 10.7498/aps.63.126801
Abstract +
The low-energy bombardment on Au (111) surface by Au atoms is studied by molecular dynamics (MD) simulation. The atomic interaction potential of embedded atom method is used in the simulation. The incident-energy effects on the morphologies and the surface roughness values of the deposited films are observed and summarized. The incident energy (Ein) varies from 0.1 eV to 50 eV. The transition of incident energy dependence occurs when the energy value is about 25 eV. The incident energy of about 25 eV is the sputtering threshold of Au (111) substrate. When the incident energy is lower than 25 eV, no atoms can be implanted into the depth beyond the second layer and all atoms are in face-centered cubic (111) arrangement without dislocation. The surface roughness decreases with the increase of the incident energy. For the case of Ein≥25 eV, the deposited atoms reach the third layer. When the number of atoms deposited in a substrate layer reaches about half the total number of atoms in this layer, the deposited atoms could go throgh this laer and enter into a deeper layer in the substrate. Surface roughness increases with the increase of the incident energy, and the energetic deposition can produce defects in both substrate and film.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2014, 63 (12): 127102.
doi: 10.7498/aps.63.127102
Abstract +
The characteristics of ground state X2Πi and the first excited state A2Σ+ of HF+ under spin-orbit coupling are studied by using the multi-configuration quasi-degenerate perturbation theory. The vertical excited energy is v[2Π1/2 (v = 0)→ X2Π3/2(v = 0)] = 285.176 cm-1, and the potential energy curves of the splitting electronic states X2Π3/2, 2Π1/2 of X2Πi are obtained. The analytical potential functions of these states are derived by employing the Murrell- Sorbie function (M-S) and the least-square fitting method, and then the spectroscopic constants for X2Π3/2, 2Π1/2 and A2Σ+ are derived from the M-S function. All the spectroscopic data and the analytical potential functions for states X2Π3/2 and 2Π1/2 are given for the first time in our calculation.
2014, 63 (12): 127201.
doi: 10.7498/aps.63.127201
Abstract +
With the globally enhancing demand for the energy saving and environmental protection of electronic products, the requirement for Schottky diode which is widely used in electronic products becomes higher and higher. The trench metal-oxide-semiconductor barrier Schottky (TMBS) diode is more and more favored because of its excellent performance. The shape of the trench plays an important role in determining the electrical properties of the Schottky diode. However, there is no intensive study on this point. In this study, we propose two novel trench structures, i. e., filleted corner trench and ladder trench. By performing the simulation with Medici, it is found that compared with the traditional trench TMBS diode, the filleted corner trench TMBS diode has a breakdown voltage with 15.8% increase under the conditions of the same leakage current and the forward turn-on voltage. Also, the ladder trench TMBS diode can reduce the leakage current by 35%, while have a breakdown voltage not smaller than the right angle trench TMBS and a forward turn-on voltage only a little bit higher than the right angle trench TMBS.
2014, 63 (12): 127301.
doi: 10.7498/aps.63.127301
Abstract +
A symmetrically breaking nanostructure, equilateral triangle with triangle notch, is designed. The extinction spectrum and surface electric field distribution on the structure surface are investigated by the discrete dipole approximation method. The results show that a Fano resonance line-shape occurs in the extinction spectrum, which results from the interference between the bonding and antibonding hybridized plasmon resonance. The effects of the structural parameters of the symmetrically breaking nanostructure on resonance mode are also studied.
2014, 63 (12): 127302.
doi: 10.7498/aps.63.127302
Abstract +
The ohmic reflectivity of Ni/Ag/Ti/Au in contact with p-GaN is studied. It is found that under different thickness values of Ni, different annealing temperatures and different annealing atmospheres, the performances of Ni/Ag/Ti/Au electrode are greatly changed. The contact resistivity is measured using the transmission line model. The reflectivity of the electrode is investigated by using a spectrophotometer. The results reveal that the thinner the Ni metal layer, the higher its reflectivity is, in addition, the thickness value of Ni metal has a little influence on contact resistivity. There appears an abrupt decrease in reflectivity of electrode after annealing at a temperature higher than 400 ℃. It is noticed that the reflectivity decreases more sharply after annealing in oxygen atmosphere than in nitrogen atmosphere. However, annealing in oxygen atmosphere is more helpful to reduce the contact resistivity. The comprehensive evaluations of the contact resistivity and reflectivity indicate that the better performances of Ni (1 nm)/Ag/Ti/Au electrode after rapid annealing in oxygen atmosphere at 400 ℃ are achieved: its contact resistance reaches 5.5× 10-3 Ω·cm2 and reflectivity rises up to 85% at 450 nm. Light emitting diode (LED) of vertical structure is fabricated with an optimal electrode. The LED under an injection current of 350 mA can achieve the following working parameters: the working voltage is 3.2 V, the optical output power is 270 mW, and the electro-optical conversion efficiency is 24%.
2014, 63 (12): 127303.
doi: 10.7498/aps.63.127303
Abstract +
Plasmon resonances in C60 fullerene dimers are investigated using time-dependent density functional theory. Owing to larger separation between molecules, there exist capacitive coupling plasmon modes in fullerene dimers. With the decrease of the gap distance, low-energy capacitive coupling plasmon modes show red shift. When the gap distance further decreases, because of the electrons tunneling across the dimer junction, plasmon resonance modes of C60 fullerene dimers are significantly modified, and the charge transfer plasmon modes occur. C60 fullerene dimer is different from metallic nanostructures dimmer. As the gap distance is again reduced, the charge transfer plasmon modes are not blue-shifted, but they are further red-shifted. In the range of the visible spectrum, C60 fullerene dimmers have strong absorption peaks.
2014, 63 (12): 127501.
doi: 10.7498/aps.63.127501
Abstract +
In NaZn13 type La(Fe,Si)13 compound, the phase transition nature varies from the first order to the second order, the cell volume contracts, the saturated magnetization decreases and the Curie temperature increases with increasing Si content. In this paper, the relation between the Curie temperature and the cell volume is investigated systematically by introducing the interstitial carbon atoms, which is an efficient method to control the cell volume and the Curie temperature. It is found that the relation between the Curie temperature and the cell volume is consistent with the Jaccarino-Walker model, in which only 5% or less 3d electrons are considered as the itinerant electrons and the others are regarded as the localized ones. With the polarized itinerant electrons used as a medium, the interaction between the 3d localized electrons is similar to Ruderman-Kittel-Kasuya-Yosida interaction, whose sign and magnitude oscillate periodically with distance. The number of the itinerant electrons of the La (Fe,Si)13 increases with the increase of Si content. The Curie temperature is dependent on both the cell volume and the number of itinerant electrons.
2014, 63 (12): 127801.
doi: 10.7498/aps.63.127801
Abstract +
The InGaN/GaN multiple quantum wells are grown on a (0001)-oriented sapphire by using metalorganic chemical vapor deposition. Dependences of the photoluminescence (PL) peak energy and PL efficiency on injected carrier density and temperature are studied. The results show that the temperature-dependent behavior of the peak energy is in the manner of decrease-increase-decrease (S-shaped), and the maximum of the PL efficiency is observed at about 50 K. The former is attributed to the potential inhomogeneity and local characteristics of the carrier recombination in the InGaN matrix. The latter indicates that the traditional method that the internal quantum efficiency (IQE) is considered to be 100% at low temperature, should be corrected. Furthermore, it is found that the IQE depends on not only temperature but also injected carrier density. Based on the above discussion, an improved method of setting the IQE, i.e., measuring the dependence of PL efficiency is proposed.
EDITOR'S SUGGESTION
2014, 63 (12): 127202.
doi: 10.7498/aps.63.127202
Abstract +
Size-dependent exciton spin relaxation dynamics in CdTe colloidal quantum dots is studied at room temperature with the cross-polarized heterodyne third-order nonlinear transient grating technique The CdTe exciton spin relaxation reveals a mono-exponential decay behavior with a time constant of 0.1-0.5 ps when the pump-probe photon energy is tuned to be in resonance with the lowest exciton absorption transition (1Se-1Sh). The exciton spin relaxation in quantum dot is mainly governed by the hole spin flip process and ascribed to the transitions between bright-dark exciton fine structure states, i.e. J= 1+2. This finding suggests that the exciton spin relaxation rate in CdTe quantum dot is inversely proportional to the fourth power of quantum dot size.
2014, 63 (12): 127101.
doi: 10.7498/aps.63.127101
Abstract +
In this paper, the geometries and properties of H2S and its decomposition fragments adsorbed on Fe(111) surface are studied by means of the density functional theory based on generalized gradient approximation in wide ranges of coverage; the adsorption energy, work function, charge density difference, density of states, and charge population are calculated; the effect of coverage on surface adsorption is discussed; the adsorbability values of H2S, HS radical and S on Fe(111) are compared and analyzed. The results show that the force between absorbates and surface gradually weaken as the coverage increases, the interactions between the above-mentioned particles and Fe(111) are compared with each other: the magnitudes of their interactions are in the order of H2SxSy corrosion product films are easily formed, and the compactnesses of corrosion product films change with coverage variation. A study of the adsorbability values of various adsorbates in low index crystal plane indicates that the interactive force between adsorbates and Fe(111) surface is strongest, and that between the Fe(100) surface and Fe(110) is relatively weak, the difference in adsorption energy between them is not so much.
2014, 63 (12): 127802.
doi: 10.7498/aps.63.127802
Abstract +
We prepare Er3+/Yb3+ co-doped oxyfluoride glass ceramic samples by high temperature calcination method (41.2SiO2-29.4Al2O3-17.6Na2CO3-11.8LaF3-0.5ErF3-2.5 YbF3), and also fabricate transparent microspheres each with a handle. We propose a new method of studying the luminescent properties of Er3+/Yb3+ co-doped oxyfluoride glass ceramic with the tapered fiber-microsphere coupling system. The method has characteristics such as low excitation optical power, easy preparation and testing. We couple the 976 nm laser into the microspheres with the coupler of optical tapered fiber, then the fluorescence and laser are connected to spectrum analyzer with the optical tapered fiber. The strong up-conversion fluorescences at 522, 545 and 657 nm are obtained, and the laser oscillation spectra generated by Er3+ ions at 1562 nm are also measured. The up-conversion luminescence mechanism of Er3+, the mechanism of high luminescence efficiency in Er3+/Yb3+ co-doped oxyfluoride glass ceramic microsphere, and the mechanism of higher laser oscillation threshold in the oxyfluoride glass ceramic microsphere than in the SiO2 matrix microsphere are all analyzed.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2014, 63 (12): 128101.
doi: 10.7498/aps.63.128101
Abstract +
The phase-field crystal method is used to analysis the dislocation annihilation and grain boundary migration mechanism in the grain shrink process of the circular grain which has three different misorientations from the matrix grain. Results show that when the misorientation between the circular grain and the matrix grain is 17°, the structure of grain boundary is composed of dislocations whose cores is so near that can not find a single dislocation. This grain boundary can not be explained by the dislocation model. However the circular grain area decreases linearly with time, which is in good agreement with the classical boundary migration theory. When the misorientation is 4°, the grain boundary structure is composed of discrete dislocations. Dislocations climb along the radial dierction and the grain rotation occurs for the circular grain to adjust the space of dislocations in the process of circular grain shrinkage. Reactions may take place with the dislocatins becoming closer. For the misorientation of 10°, portion of the grain boundary is composed of discrete dislocations and portion of dislocations with cores overlapped. Dislocations climb along the radial direction and tangential motion occurs at the same time in the grain shrinkage process. The coupled motion lead to the dislocations becoming close and reacting with each other.
2014, 63 (12): 128102.
doi: 10.7498/aps.63.128102
Abstract +
The influences of technological condition on thickness and refractive index of the SiON films preprared by plasma enhanced chemical vapor deposition and the influence of SiON/SiNx stacked film on passivation performance on P-type silicon wafer are investigatied. The results show that the refractive index of SiON film varies from 1.48 to 2.1 and thickness varies from 30-60 nm by changing the gas flow of NH3 and the gas flow ratio of N2O/SiH4. The pressure and RF power mainly affect the thickness of the film. The greater the pressure, the higher the RF power, the faster the deposition rate is and the thicker the film is. The influences of temperature on the film thickness and refractive index can be ignored. The passivation shows that the passivation performance of P-type silicon film after annealing SiON/SiNx stacked films with a gas flow ratio of N2O/SiH4 20 and 30 in the absence and the presence of NH3, is best, which the implied voltages and the lifetimes of minority carriers are 652 mV, 56.7 μs and 649 mV, 50.8 μs, respectively. The passivation effect of SiON/SiNx stacked film is superior to that of the reference SiNx film.
2014, 63 (12): 128103.
doi: 10.7498/aps.63.128103
Abstract +
Adopting the Euler and the volume averaging methods, a three-phase mathematical model with parent melt as the primary phase, columnar dendrites and equiaxed grains as two different secondary phases is developed, and the coupled macroscopic mass, momentum, energy and species conservation equations are obtained separately. Taking the Al-4.7 wt% Cu binary alloy ingots for example, the flow field, temperature field, solute field, columnar-to-equiaxed-transition and grain sedimentation in two-dimension are simulated, and the simulated result of ingot and macrosegregation result are compared with their experimental values. The simulation results of temperature field, flow field and structure are basically consistent with the theoretical results, but the result of solute field shows that the simulated values is lower than the measured value on the edge, this is because the model does not take the shrinkage and forced convection into account, and the inner results is higher than the results on edge. The shrinkage and inverse segregation therefore should not be neglected. This model are still necessarily improved. Besides, based on the analysis of simulation results, the advantages and the disadvantages of the volume averaging method to simulate the solidification in a ingot are evaluated.
2014, 63 (12): 128104.
doi: 10.7498/aps.63.128104
Abstract +
The increasing of areal density of hard disk drives promotes the decreasing of the slider flying height. Lubricant transfer between slider and disk, caused by reducing slider flying height, plays an important role in affecting slider flying stability. In this study, the improved coarse-grained, bead-spring model is used to investigate the mechanism of lubricant transfer between slider and disk by molecular dynamics simulation. The effects of lubricant thickness on disk surface, lubricant type, and local temperature difference on the slider surface on lubricant transfer are studied. We observe that the amount of lubricant transferred to the slider sharply increases with the increase of lubricant thickness value on the disk surface. Increasing the number of hydroxyl groups in an individual lubricant molecule can greatly reduce the volume of the lubricant transferred to the slider. In addition, the local temperature difference on the slider surface can increase the volume of lubricant transferred to slider. What is more, the increasing of the number of hydroxyl groups contained in an individual molecule can considerably improve the influence of the local temperature difference on the lubricant transfer between slider and disk.
2014, 63 (12): 128501.
doi: 10.7498/aps.63.128501
Abstract +
By using the pulsed laser single effect facility, the single event upset and latch-up phenomenon are studied, and the bitmap of 90 nm complementary metal oxide semiconductor (CMOS) static random-access memory (SRAM) is mapped. It is shown that many multiple bit upsets occur and pulsed supply current of 20 mA amplitude is monitored. Based on the technology computer aided design (TCAD), it is found that the localized latch-up in CMOS SRAM is the main reason for the single event multiple bit upsets. Finally, by analyzing the results of the pulsed laser experiment and TCAD, it is found that the P/N well potential collapse is the key physical mechanism responsible for the spreading of the single event latch-up effect in 90 nm CMOS SRAM.
2014, 63 (12): 128502.
doi: 10.7498/aps.63.128502
Abstract +
The memristor is a novel kind of electronic device with dynamic variable resistance that is dependent on the past history of the input current or voltage. As the fourth fundamental circuit element, the memristor captures a number of unique properties that have been found to possess attractive potentials in some promising fields such as nonvolatile memory, nonlinear circuit and system, and neuromorphic system. Additionally, compared with a circuit of single memristor, series-parallel circuit of memristors possesses more abundant device characteristics which arouses increasingly extensive interest from numerous researchers. In this paper, the mathematical closed-form charge-governed and flux-governed HP memristor nonlinear models are presented with constructive procedures. In particular, these models are more realistic by taking into account the nonlinear dopant drift effect nearby the terminals and the boundary conditions, and by adding a simple and effective window function. Furthermore, based on the internal parameters and threshold of the memristor respectively, the theoretical derivation and numerical analysis of the memristor-based series-parallel connection circuits have been made comprehensively. For obtaining the characteristics of the memristor-based combinational circuits intuitively, a graphical user interface is designed based on Matlab software, which is beneficial to displaying the properties of the memristive system clearly. The results in the present paper may provide theoretical reference and reliable experimental basis for the further development of the memristor-based combinational circuits.
2014, 63 (12): 128802.
doi: 10.7498/aps.63.128802
Abstract +
In order to solve the problem of the multi-objective spectrum allocation on the joint optimization of maximal network utility and fairness of users in cognitive radio network, based on quantum bee colony theory and membrane computing, a novel multi-objective discrete combinatorial optimization algorithm, named membrane-inspired quantum bee optimization, is proposed. The global optimal solution of single objective can be searched in the elementary membranes, and Pareto front solutions which take account of network utility and fairness, can be obtained from skin membrane with the proposed method. The multi-objective optimization algorithm, which can solve both single objective and multi-objective optimization problems at the same time, is designed by the communication rules between membranes, the cooperative evolution of foraging behavior based on quantum state, and non-dominated sorting. Compared with classical color-sensitive graph coloring algorithm, genetic algorithm, quantum genetic algorithm, and particle swarm optimization under different objective functions, the proposed spectrum allocation method can search the global optimal solution of single objective as shown by the simulation results, and it is superior to classical spectrum allocation algorithms and existing intelligence spectrum allocation methods. The optimal Pareto front solutions of multi-objective spectrum allocation are also obtained.
2014, 63 (12): 128801.
doi: 10.7498/aps.63.128801
Abstract +
A new type of high-performance back reflector based on one-dimensional photonic crystal (1D PC) is introduced in this paper. The 1D PC is designed by alternately depositing a-Si and a-SiOx layers. Firstly the influences of refractive index, layer-thickness and corresponding periodicity on the band-gap of 1D PC are simulated using the finite difference time domain method. Based on the simulation results 1D PCs with different bandgaps are experimentally deposited. Just by adjusting the a-Si layer thickness, the high-reflection bandgaps in ranges of 500-750 nm and 650-1100 nm are easily achieved. The reflectivity values of 96.4% and 99% in the above-mentioned bandgaps are obtained. Comparing with the cells without a back reflector, a relative enhancement of 18.3% and 15.2% can be achieved for the short circuit current densities of a-Si:H single-junction and a-Si:H/μc-Si:H tandem solar cells, respectively, by integrating the above optimized 1D PC in the back. Also the influences of incident angles of white light, TE waves and TM waves on the reflectivity of 1D PC are studied using a software to generate spectrophotometric and ellipsometric spectra of a thin film stack. It is found that the reflectivity of 1D PC in solar cell is less affected by the changes of incident angles from air.
2014, 63 (12): 128401.
doi: 10.7498/aps.63.128401
Abstract +
Wireless sensor networks (WSNs) are widely used in various measurement fields. However, their nodes are characteristic of constrained energy supply, limited hardware resource, large number of nodes, self-organization and dynamic topology, which make networks prone to malfunction. As a result, high reliability and low fault are the basic requirements of WSNs. To prevent too many active nodes and wasting more energy in redundant routing method for WSNs, a fault-prevention technique of controlling redundant routes into sleeping based on health degree is proposed. This technique uses sink node to collect the residual energy of each node, and to calculate energy consumption degree parameter and health degree parameter, and adopts a-star algorithm to control the redundant routes into sleeping mode. The simulation results of NS2 and actual node experimental results show that the present health degree based technique can balance the networks energy consumption and prolong the network lifetime significantly.
2014, 63 (12): 128503.
doi: 10.7498/aps.63.128503
Abstract +
To maintain and improve the manufacturing yield of integrated circuit becomes a research hot spot in optimized circuit design and manufacturing technology, with the expansion of the integrated circuit scale and shrinkage of devices feature sizes. In order to reduce the yield loss caused by redundancy material defect and missing material defect, choosing a preferentially optimizing net becomes an important subject in the process of layout optimization. Layout optimization is an effective way to increase integrated circuit yield which is based on the critical area diminution. In the paper presented is a new kind of short circuit and open circuit sensitivity model, which is net-based and not only reflects the size of the short critical area between the single net and the nets around it, but also possesses open critical area. Because this model is based on single net and includes the information about the surrounding net, the short critical area between the single net and the net around it and the open critical area of its own can be reduced at the same time. In this way, the efficiency of layout optimization is enhanced. According to the experimental results, this sensitivity model can be used to choose the position for optimization.
EDITOR'S SUGGESTION
2014, 63 (12): 128701.
doi: 10.7498/aps.63.128701
Abstract +
A method of fast-neutron imaging with energy threshold is presented in this paper, which is based on an imaging plate covered with a metal foil and a hydrogen-rich foil in order to reduce the contribution from the neutrons with a lower energy such as the scattering neutrons from samples. The method is capable of effectively reducing the relative sensitivity of the imaging detector to neutrons with energies in a certain energy range. The 14 MeV neutron imaging structure with an energy threshold is designed, and it includes a TR imaging plate covered with an about 150 m Pb foil and a 500 m polyethylene foil. The calculated results show that for the present structure its sensitivity to the neutrons with smaller than 8 MeV is reduced by 30% less than that to the neutrons with 14 MeV. The fast-neutron radiography is validated experimentally on a DT neutron generator (K400). The results indicate that the neutron imaging structure with an energy threshold is available to remove the edge enhancement effect introduced by scattering neutrons from samples.
2014, 63 (12): 128402.
doi: 10.7498/aps.63.128402
Abstract +
The launcher is an important component of the gyrotron builded-in quasi optical convertor. The propagate characteristics of high order modes in volume waveguide are analyzed in this paper based on geometric optical theory. The waveguide coupling equations and the corresponding coupling coefficients of the modes in the perturbation waveguide are derived based on the mode coupling theory. The power distribution in the perturbation waveguide and the field on the wall are analyzed by the numerical calculation code which is written in MATLAB language. The 3D simulation software can be used to verity the numerical result. As an example, a Denisov launcher of 94 GHz, TE6,2 is designed, and the numerical simulation result shows that the conversion efficiency is more than 98%, The hot-test experimental results show that the profile of output field is well consistent with the numerical result.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2014, 63 (12): 129601.
doi: 10.7498/aps.63.129601
Abstract +
In the research of space debris impact induced discharge the measurements of the density and temperature of the impact plasma are very important and difficult. Spectrum analysis is the best method of measuring the density and temperature of hypervelocity impact induced plasma. This method has been successfully used for detecting the density of the plasma produced by hypervelocity particles with diameters larger than 1 mm. In this paper, we present a method of detecting the light flash that is produced by the hypervelocity impact of 200 μm particles which is the foundation for the spectrum analysis method. The characteristics of the light flash of the impact and the impact induced discharge are also discussed.
2014, 63 (12): 129201.
doi: 10.7498/aps.63.129201
Abstract +
Based on the data of daily wind and specific humidity, surface pressure from NCEP/NCAR and the data of monthly average precipitation of 160 stations in China from National Climate Center, and according to correlation filed of precipitation with water vapor transport, the water vapor transport which is perpendicular to a cross section is defined as an objective indicator of vapor transport path, and six mainly vapor transport paths are found for North China. The results show that the confluent water vapor path, the water vapor path which outputs to the east, the water vapor path which inputs from the west and the water vapor path from the South China Sea have obvious inter-decadal variation, and the inter-decadal variation is basically the same as the inter-decadal variation of summer precipitation in North China. It is found that the water vapor path which outputs to the east and the water vapor path which inputs from the west have main influence on the precipitation in North China on summer though sliding correlation analysis. It is influenced by westerly. Second, the water vapor transport of water vapor path which is from the west of North China increases, at the same time which is from the southeast of the Pacific Ocean is enhanced obviously. Then water vapor which passes through the middle and lower Yangtze river and the South China and directly transports to the North China and Northeast China, results in heavy precipitation of North China and Northeast China and slight precipitation of the south and the Yangtze river. However, the water vapor from the bay of Bengal began to influence the precipitation in North China in summer from 2000.
