Vol. 62, No. 7 (2013)
2013, 62 (7): 070201. doi: 10.7498/aps.62.070201
Since communication is often constrainted and the computational resources are limited in wireless sensor networks, it is more important for local sensors to send in compressed data. In this paper, a nonlinear coordinate compression rule is constructed based on arctangent function. Beneficial from the nonlinear feature of arctangent function, near the centroid the compression ratio is low and apart from the centroid the compression ratio becomes higher and higher. The proposed algorithm is more suitable for the signal that has a useful high frequency near centroid. And the proposed algorithm has the following features: the sampling interval is not even; the compression can be done before sampling, which is similar to a compression sensing; it has low computation amount, is simple and easy to implement in a real system.
Construction of new infinite sequence complexion soliton-like solutions of nonlinear evolution equations
2013, 62 (7): 070202. doi: 10.7498/aps.62.070202
The G'(ξ)/G(ξ) expansion method is further studied for constructing new infinite sequence complexion soliton-like solutions of nonlinear evolution equations. First, to solve a linear ordinary differential equation with constant coefficients of second order is changed into the solving of one unknown quadratic equation and Riccati equation by a function transformation. Then a nonlinear superposition formula of the solutions to Riccati equation is presented to seek new infinite sequence complexion solutions of a second order linear ordinary differential equation with constant coefficients. Based on this, the new infinite sequence complexion soliton-like solutions to (2+1)-dimensional modified dispersive water wave system and (2+1)-dimensional dispersive long-wave equation are obtained with the help of symbolic computation system Mathematica.
2013, 62 (7): 070203. doi: 10.7498/aps.62.070203
Traveling wave in a nonlinear LC circuit with dissipation have been investigated theoretically. With the aid of the extended hyperbolic function method,developed by the authors in recent works to solve nonlinear partial differential equations exactly, the fourth order nonlinear wave equation with dissipation, which models shock wave propagation in a nonlinear LC circuit, have been analytically studied. Abundant explicit and exact traveling wave solutions to the fourth order nonlinear wave equation with dissipation are obtained. These solutions include exact shock wave solutions, singular traveling wave solutions, and periodic wave solutions in a rational form of trigonometric functions.
2013, 62 (7): 070204. doi: 10.7498/aps.62.070204
The full-vectorial finite-difference method has been improved for solving mode loading problem on irregular ports, and the boundary conditions are derived. The new mode solver reduces the demand for computing resources: it can solve waveguide mode with arbitrary shape. The mode characteristics of waveguide with different shape are calculated; the results are compared to analytical solutions and those obtained from commercial software, they agree well with one another.
2013, 62 (7): 070301. doi: 10.7498/aps.62.070301
Developing quantum key distribution (QKD) protocols that can resist losses and noises is of great importance in practice. We show that the maximum transmission distance and tolerable excess noise of the no-switching CV-QKD protocol can be dramatically increased by using a noiseless linear amplifier (NLA). It is proved that an NLA with a gain g can increase the maximum transmission distance by 20 log10g/α km, where α=0.2 dB/km is the loss coefficient of the fiber channel.
2013, 62 (7): 070302. doi: 10.7498/aps.62.070302
By means of variational solution and direct numerical simulation of the Gross-Pitaevskii equation (GPE), we have studied the stability of matter-wave solitons in two-dimensional (2D) Bose-Einstein condensations (BECs), with 2D linear and nonlinear optical lattices (OLs). Using the static variational approach and Vakhitov-Kolokolov criterion necessary for stability, we obtain the stability condition for solitons in different combinations of OL's parameters. We show that the 2D linear and nonlinear optical lattices allow us to stabilize 2D solitons for both attractive and repulsive interactions. We also study the time-evolution problems of 2D BECs, using the time-dependent variational approach and numerical solution of GPE for 2D linear and nonlinear OLs. Very good agreement between the results corresponding to both treatments is observed.
2013, 62 (7): 070501. doi: 10.7498/aps.62.070501
The phenomenon of stochastic resonance (SR) and coherence resonance (CR) in a bi-stable system driven by additive and multiplicative noises has been investigated. For the case that the system has uncorrelated or correlated additive and multiplicative noises, we introduce an appropriate index that can characterize both SR and CR at the same time. Applying the first-order Euler numerical computation to study the SR and CR, We can show that for small noise density, with the increase of additive noise density, and the appearance of CR, if we add a small periodic force to the bi-stable system, SR will occur almost at the same time. However, with increasing multiplicative noise density, the above conclusion may be satisfied only for correlated additive and multiplicative noises. Moreover, the effects of other parameters on CR and SR can be shown to be the same.
2013, 62 (7): 070502. doi: 10.7498/aps.62.070502
The directed transport performance of two coupled Brownian particles in the double-well ratchet potential under the external force has been studied in this paper. Langevin equation in the overdamped regime is solved numerically. The influence of the external force, the thermal noise, and the asymmetric parameter of the potential on the transport properties of the coupled Brownian particles including the average velocity, the effective diffusion coefficient Deff , and the Pe number, is discussed in detail. It is found that the average velocity changes periodically under the external force. Meanwhile, there is an optimal value of the intensity of the thermal noise at which the current reaches the maximum. It is worthwhile to point out that the enhancement of the current can be achieved by changing the structure of the ratchet potential.
2013, 62 (7): 070503. doi: 10.7498/aps.62.070503
The stochastic resonance of cascaded bistable Duffing system (CBDS) has been studied in this paper. We have shown that with the appropriate adjustment of the parameters of the CBDS, such as the scale transformation coefficient, the damping ratio and the number of cascaded systems, the CBDS can not only achieve large or small parameter stochastic resonance, but also optimize the stochastic resonance result of a single bistable Duffing system (SBDS). That is, with the parameter adjustment, the stochastic resonance effect of the CBDS is much better than that of the SBDS. Furthermore, the CBDS has excellent filtering and smoothing characters for a square wave signal, which can be applied to the recovery of the square wave signal masked by heavy noise.
2013, 62 (7): 070504. doi: 10.7498/aps.62.070504
To improve the ability of quickly and effectively resolving the coupling of electrically large complex cavities (microwave chaotic cavities), the statistical properties of the scattering from these cavities have been studied by using a statistical electromagnetics method. Firstly, based on the antenna theory, the input impedance expression of cavities is established by using the expanded electromagnetic eigenmode expression. Secondly, the random coupling model (RCM) is introduced from wave chaos theory and statistical method about microwave chaotic cavities. It is simply to use this method to directly obtain the three-dimensional model. Lastly, the three-dimensional Sinai microwave chaotic cavity is designed, and used to carry out the numerical experiment. Their statistical properties obtained are agreed well with one-another between the numerical result and RCM one. Importantly, the RCM, which is a very good method to be able to quickly predict the sensitivity of coupling about the microwave chaotic cavities, is independent of the details of the cavities.
Retrieving dynamic forecast model of the western pacific subtropical high in abnormal years based on GA
2013, 62 (7): 070505. doi: 10.7498/aps.62.070505
On the basis of the potential field data on 500 hPa from 2000-2010 from NCEP/NCAR, introducing the ideas of EOF(empirical orthogonal function) time-space separation and the dynamic system reconstruction of time series, with the advantages of the global optimization and parallel calculation by genetic assistance, dynamic model inversion is carried out, thus a nonlinear forecast model of the subtropical high activity and aberrance is established. And a mid/long-range forecast of subtropical high activity was carried out. The results of dynamic model forecast experiment showed that the mid/long-range forecast of subtropical high pressure by our model can be very actual. Especially, the aberrance of the subtropical high pressure can be drawn and forecast. A new method of idea is presented for diagnosing and forecasting such complicated weathers as subtropical high activity.
2013, 62 (7): 070506. doi: 10.7498/aps.62.070506
This paper studies the synchronizability and the synchronization processes of three kinds of clustered networks with different inter-cluster couplings, where each clustered network is composed of two BA scale-free subnets. The clustered network is called a TWD network if the inter-cluster coupling is a two-way coupling, but it is called a BDS network if the small subnet is driven by the big one, and is called an SDB network if the big subnet is driven by the small one. The result shows that when the ratio of node number of small subnet to that of big one is larger than a critical value, the whole synchronizability of the TWD networks is better than that of the BDS networks; however, when this ratio is smaller than the critical value, the whole synchronizability of the TWD networks is weaker than that of the BDS ones, the whole synchronizability of the SDB networks is always the worst. For a one-way-driven clustered network, the synchronizability is just related to the node number of the driven subnet and the number of the inter-links, but has nothing to do with the node number of the driving subnet. The increase in the inter-links can reduce the synchronous speed of the subnet at the beginning but may enhance the synchronizability of the whole network eventually. The Kuramoto phase oscillators are taken as the network nodes to further study the synchronization process of the three-clustered networks for different cases, and the correctness of the above conclusions are evidenced.
Analysis of an innovative method for large-scale high-precision absolute distance measurement based on multi-heterodyne interference of dual optical frequency combs
2013, 62 (7): 070601. doi: 10.7498/aps.62.070601
Femtosecond optical frequency comb (FOFC) has been widely used in time-frequency technique and precision spectral measurement. The derivative technique for absolute distance measurement by FOFC, which has features of high-speed, large-scale and high-precision, has become a worldwide research hotspot and is promising to be directly applied in some precision ranging missions, such as large equipment manufacturing, satellites formation flying, laser radar and space gravitation measurement, etc. An innovative method for large-scale and high-precision absolute distance measurement based on multi-heterodyne of dual FOFCs, is proposed in this paper. This method combines the multi-heterodyne cross-correlation distance measurement of dual optical combs with the beat-frequency distance measurement based on repetition frequency of the comb, so that it achieves large-scale and high-precision absolute distance measurement without relying on the earlier judgment with time-of-flight measurement, scanning the repetition frequency or scanning the reference beam path. Based on the basic theory of FOFC and the ranging scheme, the theoretical model for large scale distance measurement chain based on dual FOFCs has been constructed; influence of the multi-heterodyne lowest spectral lines and the repetition frequency stability on the measurement results has been discussed, and lots of simulation calculations have been done. Simulation results show that the method has achieved measurement errors better than ± 50 pm on the premise of not considering the phase demodulation accuracy, and the impact caused by the deviation of the lowest multi-heterodyne spectrum is figured out to be far below the ranging resolution of the multi-heterodyne measurement, which has verified that the proposed method may be used to realize large-scale and high-precision absolute distance measurement.
Purity analysis of helium using quartz-enhanced photoacoustic spectroscopy with two non-resonant micro-tubes
2013, 62 (7): 070701. doi: 10.7498/aps.62.070701
A trace gas sensor, based on quartz-enhanced photoacoustic spectroscopy (QEPAS) with two non-resonant micro-tubes, was designed to detect the ammonia concentration in impure helium. Unlike the traditional micro-resonator, the non-resonant micro-tubes are used to confine the sound wave, but do not exhibit a well-defined resonant behavior. Such a design makes the dimension of the spectrophone much smaller than the micro-resonant configuration, which facilitates the optical alignment. Signal and noise, that were dependent on gas pressure, were also investigated to optimize sensor performance. With the optimal sensor parameters and the optimal gas pressure, the detection sensitivity was found to be 463 ppb (1 , 1 s averaging time), which corresponds to the normalized absorption sensitivity of 4.310-9cm-1W/Hz.
Closed-loop displacement control system for piezoelectric transducer based on optical frequency comb
2013, 62 (7): 070702. doi: 10.7498/aps.62.070702
A sub-nanometric closed-loop displacement control system for piezoelectric transducers has been set up based on an optical frequency comb, an external cavity diode laser and a Fabry-Perot interferometer. The external cavity diode laser is locked to the optical frequency comb, so that the optical frequency can be set precisely in the working range by tuning the repetition frequency of the optical frequency comb. As a sensor of the piezoelectric transducer, the Fabry-Perot cavity is locked to the external cavity diode laser by means of the Pound-Drever-Hall locking technique. With the aid of precisely controlling the diode laser frequency, displacements of the piezoelectric transducer can be obtained with a sub-nanometric resolution. Experimental results show that the Allan deviation of the diode laser frequency is 1.68×10-12 after locked to the optical frequency comb. The displacement range of 4.8 μm can be generated by the piezoelectric transducer through continuously and precisely tuning the diode laser frequency in the range of 30.9496 GHz. Meantime, the displacement resolution of 450 pm is achieved by scanning the repetition frequency of the optical frequency comb at a step of 3.75 Hz. Besides, the hysteresis characteristic of the piezoelectric transducer is measured using this system. Compared to those methods based on heterodyne interferometers to calibrate the displacement of piezoelectric transducers, the nonlinear errors are eliminated and the measurement results are traceable to an Rb clock.
2013, 62 (7): 070703. doi: 10.7498/aps.62.070703
The M-Z interferometer with gratings or multilayer mirrors is widely used in the X-ray laser plasma diagnoses; however, this system is difficult to adjust, and results in the low success rate in experiment. Since wavefront shearing interferometers do not need a separate reference wavefront, they have inherent advantages compared with conventional interferometers. But the absence of shearing element for soft X-ray has restrained the application of the shearing interferometry in soft X-ray measurement. In this paper, a new-structured double-frequency grating was proposed and fabricated that served as the shearing element for soft X-rays, which can promote the application of shearing interferometers in the X-ray laser plasma diagnoses. The diffraction characteristics of the double-frequency grating are analyzed and tested in the synchrotron radiation beams. It is found that the intensity ratio of the two working diffracted beams is over 75%, and the intensity ratio of the rest diffracted beam to the working beam is less than 5%. An X-ray shearing interferometer using a double-frequency grating with 1000 lines/mm and 1002.5 lines/mm gratings was set up, and a clear shear interferogram was obtained. The experimental results demonstrated that the soft X-ray shearing interferometer using double-frequency grating can be applied in the X-ray laser plasma diagnoses.
2013, 62 (7): 072301. doi: 10.7498/aps.62.072301
Based on the shell model and random phase approximation theory, and using a shell-model Monte Carlo (SMMC) method, we have investigated the electron capture (EC) for nuclides 56,57,59,60Co, and the rate of change of electron fraction (RCEF) in supernova explosive surroundings. We compared our results, which were obtained by using SMMC method, with those analyzed by using Aufderheide's method. The results show that the EC rates increase greatly, even more than 6 orders of magnitude (e. g. for 57,59,60Co at ρ7=0.43, Ye=0.48). On the other hand, with the increase in temperature and density, the RCEF decreases greatly, even by 5 orders of magnitude (e. g. for 59Co at ρ7=5.86, Ye=0.47). The discussions of error factor show that in a lower density and temperature surrounding, the error is relatively great. But it may be small in the higher density and temperature surroundings.
2013, 62 (7): 072501. doi: 10.7498/aps.62.072501
The temperature of hot electrons produced in ultra-short ultra-intense laser-plasma interactions could be measured by photonuclear diagnostic method. In this paper, the process of bremsstrahlung gamma photons generated by hot electrons interacting separately with 63Cu, 107Ag, and 12C, were simulated using the Monte Carlo N-particle transport code (MCNP). According to the different cross-sections, the activities of different samples were calculated. The activity ratios for 11C/62Cu and11C/106Ag were achieved at different electron temperatures. This method can realize the temperature diagnostic of hot electrons in laser-plasma interactions.
ATOMIC AND MOLECULAR PHYSICS
The first principle study of electronic and optical properties of defect chalcopyrite XGa2S4 (X=Zn, Cd, Hg)
2013, 62 (7): 073101. doi: 10.7498/aps.62.073101
The electronic and optical properties of the defect chalcopyrite XGa2S4 (X=Zn, Cd, Hg) compounds are studied based on the first-principle calculations. Its structural properties are consistent with the earlier experimental and theoretical results, and its electronic and optical properties are discussed in detail in this paper. The results indicate that the three compounds described hare exhibit an anisotropic behaviour in the intermediate energy range (4 eV10 eV), and an isotropic behaviour in the low(4 eV) or high(10 eV) energy range. The refractive index curves of ZnGa2S4 and HgGa2S4 have an inflection point at the plasma frequency p, and their reflectivity reaches a maximal value at p and then declines sharply. Moreover, the calculated optical properties indicate that these compounds can serve as shielding and detecting devices for ultraviolet radiation.
The ground state properties and excitation properties for the SnSe molecule under different external electric fields
2013, 62 (7): 073102. doi: 10.7498/aps.62.073102
Effects of electric field ranging from -0.04 to 0.04 a.u., on the equilibrium structure, mulliken atomic charges, the highest occupied molecular orbital(HOMO) energy level, the lowest unoccupied molecular orbital(LUMO) energy level, energy gap, fermi energy, harmonic frequency and infrared intensities of SnSe ground state molecule are investigated by employing density functional (B3LYP) method with SDB-cc-pVTZ for Sn atom and 6-311++G** basis sets for Se atom. The magnitude and direction of the external electric field have significant effects on these characteristics of SnSe molecule. The results show that the bond length is proved to be first decreasing, and then increasing with the increase of the external field, and the minimum value is 0.2317 nm when the field strength is equal to 0.03 a.u.; electric dipole moment is found to increase linearly with the increase of external field, but the HOMO energy EH, LUMO energy EL, energy gap Eg and fermi energy EF are proved to decrease with the increase of external field. The total energy and harmonic frequency are found to first increase, and then decrease, but the infrared intensities are proved to first decrease, and then increase. The wavelengths from ground state to the first ten excited states are found to increase, but the excited energies are decreasing with the increase of the external field. Meanwhile, the sequence of excited states for SnSe molecule can be changed, and some prohibited transition can be allowed under an external field.
2013, 62 (7): 073103. doi: 10.7498/aps.62.073103
Based on the equilibrium structure obtained, the ground states of ZnO molecule under external electric fields ranging from -0.05 to 0.05 a.u. were optimized using the density functional theory B3P86 at 6-311++g(d,p) level. Effects of electric fields on the bond length, total energy, charge distribution, energy levels, HOMO-LUMO gap and the infrared spectrum of the ground states of ZnO molecule have been investigated systematically. The results show that the molecular geometry and electronic properties were dependent on the magnitude and direction of the external electric field considerebly. With the increase of electric field along the molecular axis O-Zn, the equilibrium bond length first decreased and then increased, while the total energy, the harmonic frequency and infrared spectrum first increased and then decreased. But the HOMO, LUMO energy levels and the energy gap decreased monotonically, indicateing that the molecule could be excited easily by a specific electric field. We think that the present results are useful for better understanding the physical mechanism underlying the electroluminescence properties of ZnO molecule.
2013, 62 (7): 073104. doi: 10.7498/aps.62.073104
The theoretical investigations on the molecular energy levels, energy gaps, and the singlet-singlet electronic excitation properties (such as absorption spectra, excited energy, oscillator strengths) of the anthracene molecule in different external electric field were carried out by employing density functional theory (DFT) and time-dependent density functional theory (TDDFT) method with 6-311G(d, p) basis set. The stable molecular structure in ground state was optimized by DFT. The calculated results show that the absorption bands of anthracene molecule concentrate in ultraviolet region without external electric field, the absorption peak of which corresponds to the S0→S5 transitions with an excitation wavelength of 234.5 nm. The calculated absorption spectra agree well with the experimental data. Moreover, it is noticeable that the effects of the external electric field on optical properties cannot be neglected. The ultraviolet absorption spectra of anthracene molecule show a red shift into the blue-light region with the increases of electric field intensity. At the same time, the energy gaps between LUMO and HOMO for the anthracene molecule decrease with the increase of external electric field intensity. It can be shown that the anthracene molecule is promising as a useful blue-light emitting material through modulating by an electric field.
2013, 62 (7): 073105. doi: 10.7498/aps.62.073105
The detailed stereodynamics of the reaction Li+HF(v=0–3) with different collision energy and in different vibration-excited state has been carried out by using the quasi-classical trajectory (QCT) method based on a new potential energy surface constructed by Aguado and Pariagua (Aguado and Paniagua J. Chem. Phys., Vol. 119, No. 19, 2003). The correlated k-j', k-k'-j' angular distributions and the polarization-dependent differential cross sections (PDDCSs) are discussed in detail. The results indicate that the collision energy has more impact on the P(θr) distributions describing the k-j' correlation than the vibration excitation. The distributions of P(φr) describing the k-k'-j' correlation, as well as the polarization-dependent generalized differential cross-sections, are sensitive to the vibration excitation. Meanwhile, the collision energy also has more influence on them.
2013, 62 (7): 073201. doi: 10.7498/aps.62.073201
For hydrogen atom imbedded in Debye plasmas with an external magnetic field, the combined effect on bound-bound transitions has been investigated. The electron eigenenergies and wave functions are determined by non-perturbatively solving the Schrdinger equation. Both transition frequencies and oscillator strengths are presented for a wide range of plasma screening parameters and external magnetic field strengths. With increasing the plasma screening, the shielding effects on the Lyman series are shown to be decreased in its intensity and the red-shift of its frequency. After adding an external magnetic field, atomic energy levels undergo even stronger perturbation, and the line shapes become polarized. The non-perturbative effect is significant for the quantum states (n 3). Comparisons made with other theoretical calculations are shown in good agreement. The results reported here may be useful for the interpretation of spectral properties of H-like ions in laboratory and astrophysical Debye plasmas.
2013, 62 (7): 073202. doi: 10.7498/aps.62.073202
We investigate theoretically the influence of the long-range and short-range potentials on the plateau structure of the above threshold ionization. In a considerable range of laser parameter, the above threshold ionization spectra of the atoms in the long-range potential always exhibit a clear double-plateau structure; as for the atoms with a short-range potential, the boundary of the double-plateau in photoelectron spectra is no longer clear, and with the decrease of laser intensity, it transits from the double-plateau to the single-plateau gradually. The numerical simulation based on classical analysis and quantum mechanics illustrates that in different model potentials, the distinction of ionization rates as well as the difference of the electronic elastic rescattering cross-sections results in the difference of plateau structures. In addition, the influence of intensity distribution of laser pulse on the phenomenon is discussed.
2013, 62 (7): 073203. doi: 10.7498/aps.62.073203
We have investigated theoretically the high-order harmonics and attosecond pulse generation by numerically solving the one-dimensional time-dependent Schrödinger equation from a helium atom in a two-color laser field, which is synthesized by adding a 1330-nm infrared pulse with higher intensity to an 800-nm fundamental pulse with lower intensity. Our results clearly show that if the phase difference between the two pulses is selected suitably, the generation of high-order harmonics spectrum with a broadband supercontinuum characteristic can be achieved, and an isolated 38 as pulse can be realized. By the time-frequency analysis, we find that the isolated attosecond pulse comes from the contribution of the long and short quantum paths, and for these two quantum paths the change of emission time with the harmonics order is rather slow. This is different from the traditional isolated attosecond pulse generation that a single quantum path needs to be picked up to obtain an isolated attosecond pulse.
2013, 62 (7): 073301. doi: 10.7498/aps.62.073301
By means of the time-dependent density functional theory (TDDFT) (applied to valence electrons), coupled with non-adiabatically molecular dynamics of ions, the excitation and dynamics of water molecules in a laser field with different polarizations have been explored. It is found that for the same polarization, the water molecule ionization can be enhanced with increasing laser intensity, while the laser intensity keeps constant, the ionization shows a maximum when the polarization is along the molecular symmetry axis, and the ionization is suppressed maximally when the polarization is perpendicular to the symmetry axis of the water molecule. The study of the dipole moment indicates that when the molecule is in the linear response region, there is only the oscillation of Dx for the case of the polarization along the x axis, while there is only the oscillation of Dy for the case of the polarization along the y axis. The bond lengths and the bond angle of H2O molecules are enlarged, while their may ictudes decrease with increasing polarization angle. Furthermore, it is found that in different polarization cases the vibration frequency of OH bonds is almost the same as the laser frequency during the action of the laser field, and it decreases after the laser pulse is switched off; however, the vibration mode of H2O molecule is sensitive to the laser polarization.
Investigation of state-selective cross-sections for excitation processes of the collisions of He2++ H(1s) in strong magnetic fields
2013, 62 (7): 073401. doi: 10.7498/aps.62.073401
Based on the excitation cross-sections in collisions of H(1s) atoms with He2+ obtained by using the classical trajectory Monte Carlo method, the state-selective cross-sections of excitation processes for different n and m, where n and m are the principal and magnetic quantum numbers respectively, are studied with the application of strong longitudinal and transverse magnetic fields. Meanwhile, the precise energy levels for atom H in strong magnetic fields are obtained by non-perturbative quantum method. It is found that there is some strong separation of the state-selective cross-sections among different magnetic quantum states. Such behaviors are related to the variation of the energy levels and the diamagnetic terms induced by the applied magnetic fields. The diamagnetic terms in transverse magnetic fields result in the rapid increase of the cross-sections for the state of negative m at 25keV/u, which is further indicated by the trajectory in this case. In some cases the decrease of the total excitation cross-sections is found to be due to the rise of the energy levels caused by the magnetic fields. The orbital angular momentum along the direction of the magnetic field is not conserved absolutely; this phenomenon is found also in the trajectories and agrees with our analysis.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2013, 62 (7): 074101. doi: 10.7498/aps.62.074101
A structure of matematerial absorber constructed based on lumped elements is proposed, analyzed theoretically and verified experimentally. The simulated results indicate that the absorption of the proposed absorber is over 95% in the frequency range of 2.5 to 4.46 GHz, and the FWHM is 70.4%. The designed structure has a better impedance matching characteristic to the free space in a wider frequency range when loaded with lumped elements by scattering parameter retrieval calculation. It also can be found that the large loss occurs in lumped resistance, which contributes much to the low-frequency broadband absorption properties obtained by simulating the energy loss distribution of the dielectric surface. Results measured by means of the free space method agree well with the simulation. Further measured results also show that the thickness of FR4 substrate obviously has controllable effects on absorption properties of the absorber, the absorption wide band will move to lower frequency with the increase of thickness, and the optimal thickness for the structure of certain parameters also can be obtained.
2013, 62 (7): 074102. doi: 10.7498/aps.62.074102
A structure of two-dimensional incident left-handed metamaterial composed of double Σ-shaped metal strips is proposed. The structure consists of a dielectric substrate and two anti-symmetrical Σ-shaped metal strips on each side of it, and the structure presents double negative properties (εμ<0), with electromagnetic waves being incident parallel or perpendicular to the substrate. With HFSS software, the two-dimensional incident left-handed properties of the structure are analyzed and verified in X waveband by means of spectrum analysis and effective parameters extracted from S parameters. The two-dimensional incident properties of the structure widen electromagnetic wave angle and are also of reference value for developing multi-dimensional incidence of the metamaterial.
First-principle study of vacancy-induced cubic boron nitride electronic structure and optical propertiy changes
2013, 62 (7): 074201. doi: 10.7498/aps.62.074201
Influences of vacancies on the electronic and optical properties of cubic boron nitride were investigated by using first-principles ultra-soft pseudopotential approach of the plane wave, based on the density functional theory. It was found that the formation of B vacancy is stable from the view of energy. Only the nearest atom were affected by vacancy, and the bandgap decreased from 6.3 eV to 2.86 eV or to 3.43 eV, by the introduction of 4.17% B or N vacancy . In addition, the boron vacancy also induce the emergence of an absorption band in the visible region, with the increase in vacancy concentration, the absorption in the visible region increased gradually, while the absorption in the ultraviolet region decreased.
2013, 62 (7): 074202. doi: 10.7498/aps.62.074202
Considering a double J-C model with intensity-dependent coupling, we have studied the effects of the intensity-dependent coupling, the mean photon numbers and the atomic motion, on the entanglement and quantum discord between the two two-level atoms when the moving atoms are initially in a maximally entangled state and the fields are in the single-mode thermal fields. The results show that, the entanglement and quantum discord disappear and revive periodically, and can have up to their starting values after revival. A rise in cavity temperature accelerates the death of the entanglement and quantum discord. In addition, the field-mode structural parameter has a strong effect on the entanglement and quantum discord in the system. When the field-mode structural parameter takes a suitable value, the entanglement and quantum discord of the two atoms can be kept from start to finish.
Numerical simulation of different ratios of oscillator to amplifier of chemical laser with MOPA configuration
2013, 62 (7): 074203. doi: 10.7498/aps.62.074203
Master oscillator power-amplifier (MOPA) configuration was widely used in high-power laser system. In order to find the optimal ratio of oscillator to amplifier, influences of this ratio on the near-field intensity distribution and the output power were studied. Fast Fourier transform method was used to calculate the near-field intensity distribution and the powers at the ratios of 1:4, 1:1 and 2:1. The simulation results indicated that when the total volume of the gain is constant, the output power of the oscillator increases with the ratio. The results also showed that the diffraction influence increases with the length of the amplifier. It was noted that the ultimate output power of the laser system was affected by the ratio of oscillator to amplifier intensity, when the laser was run at the same gain distribution, saturable intensity, amplification of the unstable oscillator, size of the whole laser and various losses of the cavity.
2013, 62 (7): 074401. doi: 10.7498/aps.62.074401
The structure of leading edge embedded high temperature heat-pipe (HTHP) is considered as thermal protection system to prevent hypersonic vehicle's leading edge that requires sharp figure during hypersonic flying from the serious aerodynamic heating. Under the complex flow and heat transfer condition of the heat pipe, the model of leading edge embedded HTHP is established. In contrast with experimental results, the model of heat pipe which is a core component of leading edge embedded HTHP has good accuracy. Using a numerical method, we analyze the thermal protection effect of leading edge embedded HTHP under the given condition. The maximum temperature of leading edge can be decreased by 11.6% and the minimum temperature of the leading edge increases by 8%. Both high temperature areas and low temperature areas are closed in the outer zone of the leading edge. While the temperature distribution of the inner zone is almost uniform, the heat transfer from high temperature areas to low areas is achieved. Thus the thermal load in high temperature areas is reduced. The influence of contact thermal resistance on the thermal protection effect of heat-pipe cooled leading edge is also studied.
2013, 62 (7): 074701. doi: 10.7498/aps.62.074701
A one-dimensional unsteady ignition and combustion model is established for the pulverized magnesium particles in a spherical cloud. The behavior of ignition and combustion of magnesium particle cloud is numerically simulated. The result shows that the ignition of particle cloud occurs at the boundary of particle cloud first, then the initial of which bifurcates into two flames, one of which propagates into the particle cloud, and the other moves away from it. Finally, the inner flame disappears because of O2 depletion, and only the outer flame, which maintains and controls the combustion of magnesium particle cloud, exists at the outside of it. The flame propagation velocity accelerates, while the flame temperature decreases during the process of the inner flame going into the magnesium particle cloud. The effects of the interior and the environmental parameters on the ignition and combustion of the magnesium particle cloud were analyzed. With the increase in the particle concentration, the ignition delay time increases slightly, but the propagation velocity of the inner flame becomes faster, and the steady particle cloud flame sphere is enlarging. With increasing initial temperature of the particle cloud, the ignition delay time canbe reduced significantly, the propagation of inner flame speeds up, but the size of steady particle cloud flame sphere keeps almost constant. The effect of ambient temperature on ignition and combustion of particle cloud is complicated. The higher the ambient temperature, the shorter the ignition delay time, however, the propagation velocity of inner flame becomes slower, and the size of the steady particle cloud flame sphere changes very insignificantly. Both the size of particle and the temperature of radiation source have great influences on the ignition and combustion of particle cloud. The smaller the particle size or the higher the temperature of radiation source, the shorter the ignition delay time of particle cloud, the faster the propagation velocity of inner flame, and the bigger the size of steady flame sphere. The results of numerical simulation are in good agreement with experimental data published in the literature.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2013, 62 (7): 075201. doi: 10.7498/aps.62.075201
The nitrogen microhollow cathode discharge and Ti cathode sputtering, bombarded by ions (N2+, N+), have been studied using a two-dimensional PIC/MCC model. The behavior of ions (N2+, N+) and sputtered atom (Ti), and the thermalization process of the sputtered atoms in a nitrogen microhollow cathode discharge are simulated. The results show that hollow cathode effect is due to electron oscillations in the overlapping negative glow under our simulation condition. The densities of ions (N2+, N+) in the microhollow cathode discharge are two orders in magnitude greater than that in the conventional hollow cathode discharge; but the distributions and sizes of the mean energy of the ions (N2+, N+) are almost the same. The density of N2+ is fivefold as much as that of N+ in the microdischarge space; however, the maximum of mean energy of the latter is twice larger than the former. For various parameters (P, T, V), the densities of ions(N2+, N+) bombarding the cathode internal surface are almost uniformly distributed, and their mean energy are almost the same. When these atoms are 0.15 mm away from the cathode. The sputtered atoms are almost thermalized completely.
2013, 62 (7): 075202. doi: 10.7498/aps.62.075202
Nitrogen-doped and undoped diamond films grown by microwave plasma chemical vapor deposition (CVD) were etched by electron cyclotron resonance (ECR) plasma with asymmetric magnetic mirror field. The influences of nitrogen doping on the etching characteristic of CVD diamond films are studied by scanning electron microscope (SEM), X-ray photoelectron spectroscopy(XPS), and surface roughness measuring instrument; and the etching mechanism is explicated in detail by etching models. It is found that the crystal edges are dramatically etched for the nitrogen-doped diamond film, while the (111) facets are etched and crystalline grains collapse for the undoped diamond film. And after etching by ECR plasma for 4 h, the nitrogen-doped diamond film surface roughness decreases from 4.761 μm to 3.701 μm, while the surface roughness of the undoped film decreases from 3.061 μm to 1.083 μm. The results indicate that nitrogen doping has great influence on the etching characteristic of the CVD diamond films. Nitrogen-doping deteriorates the film quality and increases the defect density in the crystallites. And the defects distributed in the crystal edge lead to dramatically etching of the crystal edge. Compared with the nitrogen-doped diamond film, the defect density in undoped diamond film is relatively low and the distribution of defects is comparatively uniform, resulting in the fact that (111) facets would suffer from oxygen cyclotron ion beams bombardment and so grains of the film collapse. The reason why the surface roughness of nitrogen-doped diamond film decreases less than the undoped diamond film is that the movement of ions is affected by the electrons emitting from crystal edge, which weakens the ion bombardment on (111) facets.
2013, 62 (7): 075203. doi: 10.7498/aps.62.075203
In the laser indirect-driven inertial confinement fusion, laser light is converted into X-rays by laser-plasma interactions in the hohlraum, then at the surface of the capsule the re-emission of hohlraum inner wall would drive a symmetrical radiation source to motivate implosion. It is of great importance to improve the features of laser to X-ray conversion in the hohlraum. The influence of low density gold foam on conversion features was investigated numerically with the help of one-dimensional hydrodynamics code. The numerical simulation results show that conversion efficiency increases with the decrease in gold density under the given laser condition. In particular, it can indeed have more than 19% extra conversion efficiency relatively when solid gold is replaced by gold foam of 0.1 g/cm3 density. In addition, the percentage of M-band decreases. There is an appropriate density of gold foam, at which the movement of plasma are restrained. According to the simulation results of energy balance, we get a higher radiation energy proportion when low density gold foam is selected as the target, and this is due to the decrease of kinetic energy losses compared with solid gold. Anyway, it is an effective approach to optimize the hohlraum by using low density gold foam to improve the features of laser to X-ray conversion, and these simulations would provide a scientific basis for further attempting correlative experiments.
2013, 62 (7): 075204. doi: 10.7498/aps.62.075204
By considering the effect of high-field-side cutoff, the conventional Budden model has been extended to Triplet model. In this model, the reflection coefficient, transmission coefficient and mode conversion (MC) coefficient of the fast wave for a single evanescence region can be derived through using phase-integral method. Furthermore, numerical calculation of MC coefficient for double-ion species and three-ion species have been done. In the case of double ions, the result is consistent with Kazakov's work. In addition, as an example of three ions plasma, (H, 3He)D plasma in tokamak EAST, simulations of the dependence of the MC efficiency on the magnetic field, microwave frequency and minority concentration for different antenna phasings are carried out. The results show how to choose proper phasing to reach an optimum MC efficiency. This result may provide a reference to improve ICRF heating efficiency.
Experimental study on the thrust and the ratio of thrust to power of multi-points/grid ionic wind exciter
2013, 62 (7): 075205. doi: 10.7498/aps.62.075205
The thrust of ionic wind exciters in 19 points-grid and 31 points-grid electrodes configurations was measured in this paper by means of air suspension test platform without friction. Meanwhile, a control method was also provided for multipoint-grid ionic wind exciter. And then the study was done on the factors, e.g. the gap of point-grid electrodes, the spacing between points, the curvature radius of the point, and the voltage, current of corona discharge, all of which may affect the thrust character; so some methods for getting high thrust at low power were also proposed in order to improve the thrust and the thrust per unit power at the same time.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2013, 62 (7): 076101. doi: 10.7498/aps.62.076101
Based on the fact that helical pitch and average refractive index of a cholesteric liquid crystal is electric-tunable and temperature-tunable, we have designed dye-doped cholesteric liquid crystal (CLC) lasers. First, the effects of the concentration of chiral and the temperature on helical pitch are investigated. Next, we gain the relationship of tunable laser with temperature and electric field. When the temperature is changed from 23 to 35℃, the wavelength shift of the lasing peak vasies from 618.90 to 594.76 nm, nearly 24.14 nm in total; when the electric field is changed from 0 to 9 V, the wavelength shift of the lasing peak ehanges from 617.40 to 608.11 nm, nearly 9.29 nm in total.
2013, 62 (7): 076102. doi: 10.7498/aps.62.076102
The nonlinear optical properties of semiconductor nanowires are of vital importance in the researches of nano-optics and fabrication of nano-scale optoelectronic components. GaAs is a direct bandgap semiconductor material of wide bandgap, high electron mobility, large χ(2), high laser damage threshold and stable chemical properties, all of which make it a potential nonlinear optical material. In this report, based on the finite element method (FEM), we investigated the optical response and local field enhancement of GaAs nanowires perpendicular to the GaAs substrate surface. Under the radiation of femto-second laser pulses at different wavelengths, efficient second harmonic generation (SHG) signal was acquired from the nanowires. Furthermore, noise-free broadband SHG signal was also detected to be excitated by super-continuous femto-second pulses (1000-1300 nm). The high-efficiency SHG process could be attribated mainly to the local field enhancement effect of the nanowires. Our investigation is the first, as far as we know, demonstrate the SHG properties of GaAs nanowires, and the results suggest that GaAs nanowires are promising in the potential applications in nano-scale optical devices, integrated nanophotonic circuits, from which related nano-optics researches can benefit.
2013, 62 (7): 076103. doi: 10.7498/aps.62.076103
The precipitation behavior of copper in denuded zone (DZ) of Czochralski silicon has been systematically investigated by means of etching and optical microscopy (OM). Firstly, the samples were treated in a conventional furnace by high-low-high annealing for the formation of denuded zone. Subsequently, copper contamination was introduced at different temperatures. Finally, samples were treated with rapid thermal annealing (RTA) and conventional furnace annealing separately. It was found that, copper precipitates could be observed in DZ through OM only in the samples which experienced RTA followed by contamination in 900 ℃ and 1100 ℃. This indicates that the out-diffusion of vacancy which is produced in the process of RTA is the main cause for the copper precipitation in DZ.
2013, 62 (7): 076104. doi: 10.7498/aps.62.076104
The effects of total ionizing dose on narrow-channel N-type metal-oxide-semiconductor field-effect-transistors (NMOSFETs) in a 130 nm partially depleted silicon-on-insulator (SOI) technology are presented. The charge conservation principle is utilized to analyze the radiation-induced narrow-channel effect (RINCE). In addition, it is found for the first time, as for as we know that for the narrow-channel NMOSFETs operated in the linear region, the radiation-induced positive charges trapped in the shallow trench isolation can increase the probability of electron-electron collisions and surface roughness scattering, resulting in the degradation of the carrier mobility and transconductance of the main transistor. Finally, the RINCE as well as the degradation of the carrier mobility has been verified by our three-dimensional device simulation; and good agreement between the simulation and experimental results is obtained.
Effects of irradiation on PNP input bipolar operational amplifiers in different radiation environments and under various post-annealing treatments
2013, 62 (7): 076105. doi: 10.7498/aps.62.076105
Radiation responses and variation characteristics of PNP input bipolar operational amplifier LM837 have been studied in two different radiation environments under the 1MeV electron and 60Coγ irradiation. The parametric failure mechanism of LM837 caused by a total dose radiation for different biases has been discussed through analyzing the characteristics of LM837 which is annealed at room temperature, 100 ℃ and 125 ℃ after irradiation. The results show that the ionization damage is the primary damage for LM837 caused by 1MeV electron irradiation, and it is larger than that by 60Coγ source irradiation under forward bias condition. In the different radiation environments, bias current under forward bias condition changes larger than that with zero bias. Annealing characteristics of LM837 after irradiation are dependeut on the annealing temperatures, and this relationship is directly related to the increase of radiation-induced interface traps during irradiation.
60Coγ-radiation effects on the ideality factor of AlxGa1?xN p-i-n solar-blind detector with high content of aluminum
2013, 62 (7): 076106. doi: 10.7498/aps.62.076106
High Al content AlxGa1-xN solar-blind photodetector and Si p-i-n visible light detector were irradiated with 60Co γ-rays up to 0.1, 1, 10 Mrad(Si). With the increase of total radiation dose, the ideality factor of AlxGa1-xN p-i-n diode saw a significant rise and the ideality factor n is grater than 2 with a total dose up to 10 Mrad(Si); the ideality factor of Si p-i-n diode, however, changed only slightly even up to 10 Mrad(Si). The degradation of AlxGa1-xN p-i-n diode might be attributed to the deterioration of Ohmic contacts, however, to some extent, the slight increase of the Si p-i-n diode might be due to the degradation of the insensitive layer.
2013, 62 (7): 076107. doi: 10.7498/aps.62.076107
The thermal conductivity of carbon nanotube (CNT) Y junctions and the thermal rectification behavior in the Y junctions have been investigated by means of classical non-equilibrium molecular dynamics simulation with quantum effects considered. The results indicate that the thermal conductivity of a CNT Y junction is about 12%–85% lower than a (10,10) pristine CNT. The thermal conductivity of the Y junction in the positive direction, when the heat flux is directed from the stem to branches, is always higher than that of the reverse direction, i.e. from branches to the stem. The decline of the thermal conductivity due to the existence of Y junctions decreases with increasing temperature. The thermal rectification coefficient of the Y junction first decreases and then increases with the increase of temperature.
Effect of doping on the photoluminescence of multilayer Ge quantum dots deposited on Si(001) substrate
2013, 62 (7): 076108. doi: 10.7498/aps.62.076108
Four-bilayer Ge quantum dots (QDs) with Si spacers were epitaxially grown on Si(001) substrates by means of ultrahigh vacuum chemical vapor deposition. In two samples, Ge QDs were in situ doped with phosphorus or boron, separately. Surface morphology and room temperature photoluminescence (PL) of multilayer Ge/Si QDs wer studied. Compared with the undoped Ge QDs, phosphorus-doping did not change the morphology of Ge QDs, enhanced PL wer observed from the phosphorus-doped Ge QDs. But reduction of Ge QDs density and PL intensity wer observed from the boron-doped Ge QDs. The intensity enhancement of PL could be attributed to the sufficient supply of electrons in Ge QDs for radiative recombination.
2013, 62 (7): 076201. doi: 10.7498/aps.62.076201
Employing an embedded-atom-method potential and molecular dynamics simulations, we have simulated the microscopic process and dynamical properties of the dynamic failure of metal Al specimens under triangular wave loading. The microstructure evolution of the sample is analyzed using the central symmetry parameter, while the difference of morphology between non molten and molten states is also explained. The pressure profiles were calculated based on the virial theorem, and the results show that the tensile strength of the material is decreased considerably in its molten state. Using the simulation results for different impact velocities, we discuss the variation of morphology and density distribution, from which the change of damage depth in the process from non molten to molten states is obtained. Our simulations also suggest that: the tensile strength of material derived from acoustic approximation is distinctively higher than the peak of internal stress from virial theorem for the melted state.
2013, 62 (7): 076202. doi: 10.7498/aps.62.076202
(Zr,V)N thin films with different V contents were deposited by reactive unbalanced magnetron sputtering. Their chemical composition, microstructure, mechanical and tribological properties were investigated by EDS, XRD, XPS, nanoindentation and tribometer. The results indicated that the fcc crystal structure of ZrN has not been changed by adding vanadium added, but the preferential orientation of films change from (200) to (111). As the V contents increased, the hardness of (Zr,V)N thin films decreased slowly after increased slightly, and decreased rapidly when V contents increased over 25.8 at.%. With increasing V contents, the coefficient of friction of (Zr,V)N thin films decreased slightly. The V2O3 was firstly found in the film of (Zr,V)N at 300 ℃ and when the temperature was increased over 500 ℃, the presence of V2O5 was found. Moreover, with the increase of the temperature the content of V2O5 increased, and the coefficient of friction of films decreased with the formation of V2O5.
Application of reed-vibration mechanical spectroscopy of liquids for studying dehydration denaturation of protein hydrogel
2013, 62 (7): 076203. doi: 10.7498/aps.62.076203
Protein denaturation is not only one of the basic problems in biophysics and biochemistry, but also a practical one in applications. It is undoubtedly useful to explore new methods for detecting protein denaturation because they will surely provide some new information from new angles of view. For the first time, Sofar as we know we apply the reed-vibration mechanical spectroscopy for liquids (RMS-L) to measure the dehydration and denaturation process of egg white, one of typical protein hydrogels, in this work. The results show that there exist at least 4 remarkable processes of mechanical spectra with the reduction of water content. Based on the experiments and the analyses according to the relevant mechanical spectrum theories, the authors inferred that, with the water content reduction egg white may undergo the following 4 states successively: 1) bulk-like water protein hydrogel state; 2) bond water protein hydrogel state; 3) bond water and bonding protein mixed state; 4) bonding protein state. And the spatial configuration change of protein, namely degeneration, happens mainly in the mixed state in which the protein with bond water transforms to binding protein by losing the water. This means that the detection of dehydration and denaturation of egg white by RMS-L is effective, and we think the conclusions would also be reference materials for the deep studies of protein denaturation mechanisms and protein hydrogel states.
2013, 62 (7): 076601. doi: 10.7498/aps.62.076601
A series of La1.9Y0.1Mo2O9 bulk samples of different grain sizes were made by microwave sintering the nanocrystalline powders prepared by sol-gel methods. Phases, microstructure, grain size of the powders and bulk samples were examined by using X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM) and scanning electron microscope (SEM); and the electrical properties of the bulk samples were studied by AC impedance spectroscopy. Experimental results show that the substituent Y can stabilize the cubic β phase to room temperature; the bulk samples are dense and uniform with an average grain size from 60 nm to 4 μm; the highly dense bulk samples show enhanced ionic conduction, e.g. the conductivity of the sample with relative density 99% is 0.026 S/cm at 600 ℃, which is two times higher than that of bulk samples prepared by solid-state reaction. It can be concluded that the effect of sample density on the electrical conductivity is mainly due to the grain boundary conductivity; and the effect of sample grain size (from 60 nm to 4 μm) on the electrical properties is not so significant.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2013, 62 (7): 077101. doi: 10.7498/aps.62.077101
In contrast to the results of sulfur atom adsorption, the adsorption of hydrogen sulfide on the Fe(100) surface has been studied using first principles method, which is based on the density functional theory (DFT). The structures, electronic properties were calculated by the generalized gradient approximation (GGA) for the coverage of 0.25 monolayer (ML). The results show that the H2S adsorbed on B2 site is stable and the adsorption energy is -1.23 eV and the structure of H2S is little changed. While the density of states (DOS) for the adsorption of hydrogen sulfide in the most unstable state after the adsorption at B1 and most stable adsorption at the site of B2 are analyzed. We have compared, under same conditions, the electronic properties of the sulfur atoms of the adsorbed hydrogen sulfide and a single sulfur atom adsorbed on Fe(100) surface. The adsorption effect is very weak for sulfur atoms in adsorbed hydrogen sulfide. At the same time, the density of states for the adsorption of Fe(100) surface was studied comparatively, and we found that the sulfur atom adsorption on Fe(100) showed a series of peaks that have discrete distributions generated by ferrous sulfide. It shows that the adsorption is given by sulfur atoms instead of molecules of hydrogen sulfide.
2013, 62 (7): 077102. doi: 10.7498/aps.62.077102
Equation of state and phase transformation under high pressure of ZnS in zinc blende (ZB) and rock salt (RS) structures have been calculated by means of plane wave pseudo-potential method (PWP) with generalized gradient approximation (GGA). The electronic density of states, band structure and optical properties of change mechanism have been discussed near the point of phase transformation. The results reveal that the transition pressure of ZnS from ZB to RS phase is 18.1 GPa by the equation of state, but it is 18.0 GPa obtained with the enthalpy equal principle. The sp3 hybrid orbital has not been eliminated and the metalic behavior of RS ZnS is enhanced significantly in the structural phase transition process. By comparing RS phase with ZB one, the main peak of the dielectric constant in RS ZnS becomes higher and shifts to the lower energy direction apparently, and other dielectric peaks are also extended to lower energy direction, at the same time the electronic transitions are enhanced in the low energy region.
2013, 62 (7): 077103. doi: 10.7498/aps.62.077103
The development of strained-Si physical compact threshold voltage model is based on Poisson's equation, using the gradual channel approximation (GCA) and coherent quasi-two-dimensional (2D) analysis, as well as taking into account the effects of short channel effect (SCE), narrow channel effect (NCE), non-uniform doping effect, and drain-induced barrier lowering (DIBL) effect. Moreover, the threshold voltage parameters are extracted from the experimental results by software. Finally, the validity of our model is derived from the comparison of our simulation results. The proposed model may be useful for the design and simulation of very large scale integrated circuits (VLSI) made of strained-Si.
2013, 62 (7): 077201. doi: 10.7498/aps.62.077201
The Cu(In, Ga)Se2 (CIGS) phase transformation during the "three-stage" evaporation is the key problem for obtaining high-quality absorber. Cu(In, Ga)Se2 (CIGS) thin film has been prepared via co-evaporation "three-stage process". The phase transformation was studied by means of XRD, XRF (X-ray fluoroscopy) and SEM. And the efficiency above 15% of CIGS film solar cell was obtained succossfully.
2013, 62 (7): 077202. doi: 10.7498/aps.62.077202
In this paper, thin films of ZnO were deposited on different bottom electrodes (BEs) by DC magnetron sputtering to fabricate resistive random access memory (ReRAM) with a W/ZnO/BEs structure. The effects of different BEs on the resistive switching characteristics of the fabricated device have been investigated. The results reveal that the devices fabricated on different BEs exhibit reversible and steady unipolar resistive switching behaviors. The conduction behavior in the low resistance state has an Ohmic behavior. However, the conduction mechanism in the high resistance state fits well with the classical space charge limited conduction. Schottky barrier heights between ZnO and different BEs have great effect on the operation voltages during the resistive switching processes. The resistances in low resistance state and the reset currents of the ZnO films fabricated on different BEs were discussed based on the filamentary model.
2013, 62 (7): 077301. doi: 10.7498/aps.62.077301
The analytical I-V model of single electron transistor has been established and simulated by combining the Monte Carlo method with the Master Equation method. Effects of gate voltage, drain voltage, temperature, and tunneling junction resistance on electrical characteristics of a single electron transistor are analyzed. Simulation results indicate that for the device with symmetrical tunneling junction structure, the Coulomb staircases shift with increasing gate voltage, and the Coulomb oscillation amplitude increases with increasing drain voltage, while the Coulomb gaps decrease. The Coulomb staircases and the Coulomb oscillation disappear gradually with increasing temperature. The Coulomb blockade effects become more significant when the resistance ratio of the two asymmetrical tunneling junctions increases.
The preparation and characteristics research of high mobility amorphous indium gallium zinc oxide thin-film transistors
2013, 62 (7): 077302. doi: 10.7498/aps.62.077302
Indium gallium zinc oxide (IGZO) is widely used in thin-film transistors (TFT) as an active layer due to its high mobility and transmittance. The amorphous n-type indium gallium zinc oxide thin-film transistors (IGZO-TFT) of bottom gate with high mobility were prepared, the active layer, source and drain electrode of the TFT were prepared by using magnetron sputtering method, and a low cost mask was used to control the size of the channel. The diffraction pattern and transmittance spectrum were measured by using X-ray diffraction and ultraviolet-visible spectrophotometer, respectively. The structural and optical properties of the IGZO thin film were studied. The dependence of active layer thickness on the performance was analyzed by testing the output characteristics and transfer property of IGZO-TFT. The field effect mobility of the IGZO-TFT reaches 15.6 cm2·V-1·s-1, and the on/off ratio is higher than 107.
2013, 62 (7): 077701. doi: 10.7498/aps.62.077701
In this research, DC degradation for ZnO varistors at 3.2 kV/cm and 50 mA/cm2 for 115 hours was performed, and its effect on electrical properties and defects of ZnO varistors was investigated. It was found that the breakdown field and nonlinear coefficient drops sharply from 2845 V/cm to 51.6 V/cm and 38.3 to 1.1, respectively, when the DC degradaion time reaches 115 hours. For the degraded sample, the dielectric loss was dominated by the increase of conductivity so that some defect relaxation peaks cannot be observed is the DC degraded ZnO varistors. However, in electrical modulus plot, one relaxation peak can be observed. The conductivity in low frequency range increases greatly and the conductance activation energy drops from 0.84 to 0.083 eV. Additionally, the heat-treatment process of ZnO varistors at 800 ℃ for 24 hours was also performed. It is interesting to note that the electrical properties and the relaxation processes of ZnO varistor is restorable completely again after heat-treatment. The breakdown field and the nonlinear coefficient increase to 3085 V/cm and 50.8, respectively, and the activation energy of conductance increases to 0.88 eV. It is also found that the defect relaxation peak, which is shown in dielectric spectra corresponding to oxygen vacancy defect, is suppressed evidently by heat-retreating. Therefore, it is proposed that oxygen is likely to diffuse into the ZnO grain boundaries at the heat-treatment process, which can play an important role in restorability of the DC degraded ZnO varistor.
2013, 62 (7): 077801. doi: 10.7498/aps.62.077801
The effects of temperature on the visible absorption and Raman spectra of all-trans-β-carotene dissolved in dimethyl sulfoxide at temperatures ranging from 81 ℃ to 18 ℃ were determined. The bands of the visible absorption and Raman spectra of all-trans-β-carotene showed red blue shifts. The bandwidth of the Raman spectra becomes narrow. Raman scattering cross-section increases as the temperature decreases. The red shift of the absorption spectrum is attributed to the thermal conformational change-induced decrease in the effective conjugation length in all-trans-β-carotene chains. The molecular structural order increases and the π-electron delocalization range is extended as the temperature decreases. The red shift in all-trans-β-carotene can be also attributed to the decrease in the liquid density, and the concomitant decrease in the refractive index is shown by the Lorentz-Lorenz relation. The apparent behavior of the temperature-induced band broadening of CC bonds can be associated with the decrease of difference in C-C and C=C bond lengths, and the shorter vibrational relaxation time. The shoulder observed below 1520 cm-1 shows a red shift. The enhancement of coherent weakly-damped CC stretching vibrations may increase the Raman scattering cross-section.
2013, 62 (7): 077802. doi: 10.7498/aps.62.077802
Single conical nanopores were fabricated by etching single-ion-irradiated polymer (ethylene terephthalate) (PET) films. The etching process was monitored by measuring the transmembrane current. A series of conical nanopores with different tip sizes were obtained at different maximum etching currents, "Imax". Results showed that it was possible to control the tip diameter by terminating etching at a certain Imax. The current-voltage characteristic of the nanopores in KCl solution was investigated. Results showed also that the ionic conduction was asymmetrical, this phenomenon is called rectification. The current rectification coefficient, was influenced by the tip size and electrolyte concentration.
2013, 62 (7): 077901. doi: 10.7498/aps.62.077901
The accuracy of the model for secondary electron yield (SEY) has a remarkable influence on the simulation result of multipactor threshold. A new combined phenomenological model for SEY was proposed based on the corrected Vaughan model and Furman model. It combines virtues of the latter two models by integrating corrected Vaughan model into Furman model for its calculation of yield of true secondary electron. The new model provides high flexibility and accuracy to fit experimental data of SEY as a function. For comparison, experimental data of silver and aluminum alloys were tested with the three models. It was found that the fitting accuracy has been improved by at least 10% under the circumstances of different incident angles of the original electron.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2013, 62 (7): 078101. doi: 10.7498/aps.62.078101
The transmission and absorption spectra of the Te/TeO2-SiO2 thin film were obtained by using a spectrophotometer, with the surface plasmon rensoance (SPR) observed at 480 nm. While the dependence of the third-order nonlinear susceptibility of composite films on the Te particle was investigated by Z-scan technique with renosant wavelength (532 nm) and non-renosant wavelength (1064 nm). Optical properties of these films was analyzed using the effective medium theory, and the relationship was investigated to obtain Te particle size and nonlinear optical properties of Te/TeO2-SiO2 films. The results show that the Te particle size was smaller, the number of particles was increased, and the particle distribution tends to be uniform. The surface plasmon resonance peak was red-shifted, and the absorption intensity was enhanced; and the third-order nonlinear optical effects was enhanced, χ(3) was increased by 5.12×10-7 esu at 1064 nm to 8.11×10-7 esu at 532 nm with preparation potential increased.
2013, 62 (7): 078102. doi: 10.7498/aps.62.078102
The cellular and dendritic formations are two kinds of typical morphology in the solidification, and there are many theoretical models and experimental researches on them. Most models and researches are based on purely diffusive transport mechanism. However, convection effects are of importance in the evolution of cellular and dendritic growth. Since the metal materials are not transparency and the researches on microstructure only after quenching, it is difficult to observe the dynamic microstructure evolution in real time. In this paper, the effect of liquid flow on the cellular and dendritic growth was investigated by the in-situ observation of SCN-1.8 wt% Ace transparent alloy during the directional solidification under the liquid flow. The cellular tip splitting is found in the presence of liquid flow and the cellular microstructure is smaller after the cellular tip splitting. The cellular spacing decreases as the flow rate becomes larger, but the spacing will become steady ultimately. At high growth rate the dendritic spacing increases with the increase of the flow rate, because the upstream side branches, which are accelerated by liquid flow, will suppress adjacent branches. But, at low growth rate the dendritic spacing decreases with the increase of the flow rate, because the lateral branches will exceed the tip of dendrite to form new dendrite by liquid flow.
2013, 62 (7): 078401. doi: 10.7498/aps.62.078401
In the application of low loss beam waveguides and high performance reflector antennas, high power microwave should be converted to quasi-Gaussian HE11 mode, to decrease side lobe level and increase feed coefficient. Based on the fact that TM01 mode converts to TE11 and TM11 mode at the same time in bent overmode circular waveguide, a TM01 to HE11 mode converter was proposed in this paper, which can convert TM01 mode to HE11 mode directly using a bent circular waveguide, the converter has higher power compacity than corrugated TE11-HE11 mode converter and more compact than TE11-TM01 mode converter added with smooth wall TE11-HE11 mode converter. The geometric parameters of the convertor were analyzed and optimized by using coupled mode theory and Taguchi method, to output the target modes content, 80% TE11 and 20% TM11 modes, which are primarily composed of HE11 mode. The optimized converter was analyzed using full electro-magnetic simulation method, the scalar Gauss ratio of the output beam is higher than 99% from 9.05 GHz to 9.8 GHz, the power capacity is as high as 4.5 GW.
Antenna cross-polarization correction for spaceborne polarimetric microwave correlation radiometer (I): Derivation of the antenna temperature equation
2013, 62 (7): 078402. doi: 10.7498/aps.62.078402
Spaceborne polarimetric microwave correlation radiometer is a new type of instrument for the passive microwave remote sensing from space, which can provide an important way for remote sensing of sea surface wind vector and other ocean atmosphere environmental parameters. Antenna cross-polarization correction is an important part of the data pre-processing algorithm. In this paper, for the demand of antenna cross-polarization correction in spaceborne polarimetric microwave correlation radiometer, we have independently derived the full polarization antenna temperature equation based on the polarization coherent detection theory and the definition of Stokes parameters. The equation for the four parameters of Stokes antenna temperature introduced the cross polarization amplitude and phase between the Stokes parameters. Besides, the influence of the polarization rotation angle on the antenna pattern computation was considered. Finally, we established a geometric correspondence between the antenna scanning beam and the earth scene. The principle for determining the parameters of the antenna temperature equation was also discussed. Stokes antenna temperature equation laid the foundation for antenna cross-polarization correction for spaceborne polarimetric microwave correlation radiometer in the future.
Antenna cross-polarization correction for spaceborne polarimetric microwave correlation radiometer (II): Correction experiment
2013, 62 (7): 078403. doi: 10.7498/aps.62.078403
In this paper, we simulated the earth scene brightness temperature by creating the earth scene data sets and using polarimetric microwave radiative transfer model. On the basis of the fully polarized antenna temperature equation we have derived, the radiometer antenna temperature was also simulated by generating antenna pattern through GRASP9 software. Then by using multiple linear regression method, the M matrix was calculated and the antenna cross-polarization correction for spaceborne polarimetric microwave correlation radiometer was realized. The correction results show that the antenna temperature and earth scene brightness temperature have a linear relationship. Antenna cross-polarization influences the orthogonal channels brightness temperature seriously, especially the vertical polarization brightness temperature. The antenna cross-polarization for each channel has been effectively reduced. Residual cross-polarization is better than -23 dB and the polarization purity is greater than 99.5%. Correction of using M matrix to eliminate the antenna cross-polarization is feasible. It has been proved that this technique is most appropriate for the final correction of antenna cross-polarization for the spaceborne polarimetric microwave correlation radiometer on orbit.
2013, 62 (7): 078404. doi: 10.7498/aps.62.078404
An intensive research have been done about the W-band sheet beam klystron (WSBK) for its potential value in active denial system application. The output cavity has an important influence on the output power, efficiency, bandwidth and spectrum. In this paper, multiple types of quasi-optical (QO) output couplers are designed based on the theory of equivalent dipoles and phase superimposition, and detailed study on the cold characteristics such as R/Q, M, loaded Q and mode uniformity has been all demonstrated. Compared with other tapers, QO output coupler with parabolic taper shows more excellent performance than the linear, triangle and Chebyshev tapers. We will receive benefit from improving the beam-wave efficiency and bandwidth of WSBK. Besides, a QO-output coupler with linear taper for initial experiment is fabricated.
Swarm initialization of shuffled frog leaping algorithm for cooperative spectrum sensing in cognitive radio
2013, 62 (7): 078405. doi: 10.7498/aps.62.078405
A swarm initialization method is proposed for modified shuffled frog leaping algorithm (SFLA) for linear combination cooperative spectrum sensing in cognitive radio. The solution obtained by modified deflection coefficient optimization is included in the initial swarm of SFLA, thus improving the performance of the algorithm at the early stage of the search. Simulations show that compared with the traditional swarm initialization technique, the proposed swarm initialization can obtain expected solutions faster, which means that the proposed technique can save computation time and is more suitable for real time applications.
A novel spectrum detecting algorithm for cognitive radio based on the characteristics of authorized channel
2013, 62 (7): 078406. doi: 10.7498/aps.62.078406
In a cognitive radio (CR) network, the system throughput and the probability of collision between primary users (PUs) and CR users are directly influenced by the frequency of spectrum sensing. This paper focuses on adaptively scheduling spectrum sensing such that negative impacts to the performance of the CR network are minimized. Based on an in-depth analysis into the spectral usage patterns of PUs, an adaptive spectrum detecting algorithm is proposed. By introducing a "control factor", the proposed algorithm can adaptively schedule the spectrum sensing, while maintaining the CR system stability, so as to increase spectral utilization efficiency, as well as reducing the probability of collision between PUs and CR users. Therefore, the energy consumption of the CR system is reduced. Simulations show that the proposed algorithm can effectively increase the system throughput, with minimal interference to primary users while ensuring the system stability. Meanwhile, it is shown that the proposed algorithm has low implementation complexity for practical applications.
"Ying-Guang 1" is a multi-bank pulsed power device for investigating the formation, confinement and instability of the high temperature and high density field-reversed configuration (FRC) plasma injector for the magnetized target fusion (MTF). This paper described the physical design of the "Ying-Guang 1" device which will be constructed in 2013 at the Institute of Fluid Physics, CAEP. Theoretical results show that the peak reversed current and magnetic field of this device are 1.5 MA and 4 T respectively with the rise time of 3 μ s. Based on the semi-empirical formula developed by Tuszewski the magnetized plasma of equilibrium density 6.6×1016 cm-3 and temperature (Ti+Te) ～ 300 eV could be achieved on the "Ying-Guang 1" device when the initially filled D2 gas pressure is about 50 mTorr, and the length of the FRC separatrix is 17 cm with a radius of 2 cm. The average ratio of the thermal pressure to magnetic pressure β is about 0.95, and the magnetic field embedded in plasma is 0.5 T. From the adiabatic compression scaling laws and the corresponding ignition conditions, the formated FRC plasma target of the "Ying-Guang 1" device approaches the necessity of the MTF if the radius compression ratio of the solid metal liner were set to 10.
Influences of plasma activation Se source on selenization of electrodeposited Cu-In-Ga metallic precursors
2013, 62 (7): 078801. doi: 10.7498/aps.62.078801
In this paper, the electrodeposited Cu-In-Ga metallic precursors have been selenized by using plasma activation Se source. The power of plasma has great influence on the grain growth of Cu(In1-xGax)Se2(CIGS). The films were shown to be single phase Cu(In0.7Ga0.3)Se2 when the plasma power was 75W. And the fact that high activity Se promotes the generation of binary selenide phase at a low temperature, thus helping the growth of single phase Cu(In0.7Ga0.3)Se2, was proved by XRD analysis of the films selenized at defferent temperatures and the comparison with the films prepared by ordinary selenization. Solar cells have been prepared and found that the single phase have no influence on battery performance. The efficiency can reach 9.4% by process optimization.
2013, 62 (7): 078802. doi: 10.7498/aps.62.078802
Based on some special physical properties of solar cells prepared from quantum dots polymeric materials, which have high photoelectric conversion performance, we use MOPPV solution for obtaining controllable grain sizes, good crystallinity, with a particle size of about 3.75 nm ZnSe quantum dot polymer composite materials, and different quality ratios of the composites. We also use XRD, TEM, UV-vis absorption spectra to study the characterizstics of the materials. The result shows that MOPPV and ZnSe quantum dots have effectively combined together and photoinduced charge transfer. Through the study of MOPPV, ZnSe, and MOPPV/ZnSe composite materal solar cell performance, we found that the composites exhibit an increasing trend compared with MOPPV, ZnSe monomer material photovoltaic characteristics, and the photoelectric properties of the composites showed an increase at first and then reduced with increasing quality of ZnSe quantum dots; when the ratio of MOPPV and the quality of the ZnSe is 1:1, its conversion efficiency reaches a maximum, The Voc, Isc, FF and conversion efficiency of solar cells were 0.516 V, 2.018 mA, 25.53%, and 0.167%.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Effects of the radial temperature gradient and axial conduction of drilling fluid on the wellbore temperature distribution
2013, 62 (7): 079101. doi: 10.7498/aps.62.079101
Therefore, in this study, based on energy balance principle between wellbore and formation, a temperature model of drilling fluid layers was established under different grid units of wellbore condition. Meanwhile, the axial thermal conductivity temperature model of drilling fluid was established by introducing axial conduction items of drilling fluid, followed by using discrete and solving of implicit finite difference method to these mathematical models. The calculation results indicated that the error temperature of the radial and axial of drilling fluid wellbore temperature which was caused of radial temperature gradient were 0.15 and 0.2 ℃ respectively, whereas axis thermal conductivity of drilling fluid has little effect on wellbore temperature distribution. Therefore, the above results confirmed that it can ignore both of them to influence wellbore temperature distribution by established the wellbore-formation coupled transient heat transfer model. Moreover, it is the first proved the correctness of model assumptions from previous scholars based on the mathematical modeling methods, and then further provides the reliable theoretical basis for down-hole temperature distribution of oil and gas well and geothermal well.
The W-J equation of state proposed by Wu qiang and Jing fu-qian is a volume equation with pressure and temperature as the independent variables, which is mutually complementary to the Grneisen equation of state, and is extending and perfecting in theory of the equation of state. It is significant to determine the W-J parameters for the study and application of the equation. The W-J parameters can be educed from the Grneisen parameters and adiabatic bulk modulus, but it is difficult to take into account the uncertainty of these parameters. In this paper we explore a method of direct measurement of the W-J parameters. Temperature and pressure were recorded in situ during the rapid compression process, in which the rate of change in temperature was obtained, with pressure at midpoint pressure during the isentropic compression process, through correcting temperature and increasing substantially pressure combined with mean value theorem, and finally the W-J parameters were obtained according to equation R=(P/T) ( T/ P)S. No additional parameter was introduced in the whole process. In addition, as a comparison, the W-J parameters and their relationship with the pressure of sodium chloride were also calculated by using the equation of state, the empirical formula and known parameters. The results showed that the experimentally measured W-J parameters are increased with increasing pressure, and all the W-J parameters obtained by experiments are in good agreement with those by calculation. This suggests that the experimental method in rapid compression process is feasible and reliable for the direct measurement of the W-J parameters.
2013, 62 (7): 079201. doi: 10.7498/aps.62.079201
Under the atmospheric multipath conditions, both canonical transform (CT) and full spectrum inversion (FSI) method can solve the problem of calculating bending angle profiles within the multipath area. The atmospheric propagation of GPS signals under atmospheric multipath conditions is simulated using multiple phase screens (MPS) technique. Bending angle profiles computed by CT method are compared with corresponding solutions to Abel integral (taken as the true value). The results show that CT method is close to the true value in the multipath area. The retrieval accuracy of CT method is degraded to some extent when Gaussian noises are added to the phase of simulated signal. About 4500 COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) atmPhs profiles from DOY (day of year) 71 to DOY 73 in 2007 are retrieved by CT method. Statistical comparisons of the retrieved refractivity profiles, together with atmPrf data (retrieved by FSI method), with those from corresponding ECMWF (European Centre for Medium-Range Weather Forecasts) analysis show that CT method contains greater systematic negative bias than atmPrf data below 5 km. A possible reason is that the signal aperture is decreased for back-propagating the signal from LEO position to the back-propagation plane in CT method. The small aperture means low accuracy in the refractivity. The influence of signal truncation on both retrieval accuracy and occultation number is also discussed.
2013, 62 (7): 079202. doi: 10.7498/aps.62.079202
The traditional detection method of abrupt change may pay more attention on the "point of abrupt change" and neglect the process of its onset, development and extinction. This paper has proposed a new detection method to obtain the abrupt change process (ACP); it can extract suitable parameters from real time series by using a piecewise function which is based on a logistic model that reflects the ACP. With the help of parameters' physical meaning, we researched and analyzed the whole ACP, deepened the understanding and awareness of ACP, to lay the scientific foundation for further study on the formation mechanism, affecting factors and trends of the abrupt change. Besides, by detecting the PDO time series' ACP, we also find that the time series began to change in 1940/1942, 1977, 1987, and the duration of abrupt change is locked in some fixed values; furthesmore, the phase graph of the system showed that a normal system world have 3 basic states.
Infrared characteristic radiation under first order phase transitions–melt crystallization and vapor condensation or deposition
2013, 62 (7): 079203. doi: 10.7498/aps.62.079203
We have studied the specimens made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid residues. The sequence of amino acids in a protein is defined by a gene and encoded in the genetic code. This can happen either before the protein is used in the cell, or as part of control mechanism. This paper considers a new physical phenomenon - infrared characteristic radiation (IRCR) at first order phase transitions (melt crystallization, and vapor condensation and/or deposition). Experimental results are analyzed in terms of their correspondence to the theoretical model. This model is based on the assertion that the particle's (atom's, molecule's, or cluster's) transition from a higher energetic level in a metastable or unstable phase (vapor or liquid) to a lower level in a stable phase (liquid or crystal) can emit one or more photons. The energy of these photons depends on the latent energy of the phase transition and the character of bonds formed by the particles in the new phase. For all investigated substances, this energy falls in the infrared range. This is a reason why the radiation is named as IRCR-infrared characteristic radiation. Many sources of the infrared radiation recorded in the atmosphere seem to be a result of crystallization, condensation and/or sublimation of water during fog and cloud formation. Thus, the effect under investigation must play a very important role in atmospheric phenomena: it is one of the sources of Earth's cooling; formation of hailstorm clouds is accompanied by intensive characteristic infrared radiation that could be used for process characterization and meteorological warnings. IRCR seems to explain red color of Jupiter. It can be used for atmospheric energy accumulation, and, thus, together with wind, falling water, solar and geothermal energies, IRCR makes available the fifth source of ecologically pure energy.