Vol. 56, No. 11 (2007)
2007-06-05
GENERAL
2007, 56 (11): 6169-6172.
doi: 10.7498/aps.56.6169
Abstract +
A strong nonlinear evolution equation is studied. Using the homotopic mapping method, firstly, the corresponding homotopic mapping transform is constructed; secondly, the suitable initial approximation is selected; and thirdly, using the iteration method, the approximate solution with arbitrary degree of accuracy for the solitary wave is obtained.
2007, 56 (11): 6173-6177.
doi: 10.7498/aps.56.6173
Abstract +
The dynamic characteristics of the non-linear bistable system subject to the action of high and low frequency signals were analyzed. The analytic formulation of the relationship between the parameters of high frequency signals and the SNR, spectral power amplification (SPA) of the bistable system output was presented. The stochastic resonance control method based on vibration resonance was proposed. The theoretical analysis and numerical simulation showed that the SNR and SPA of output signal of the bistable system can be controlled effectively by adjusting the amplitude and frequency of the high frequency signal.
2007, 56 (11): 6178-6182.
doi: 10.7498/aps.56.6178
Abstract +
Based on current φ-mapping topological theory, a kind of self-dual equations in Jackiw-Pi model are studied. We first obtain explicit, self-dual solutions that satisfy Liouville equation which contains δ-function. Then we get perfect vortex solutions which reflect the system's internal topological structure, and consequently the quantization of flux.
2007, 56 (11): 6183-6187.
doi: 10.7498/aps.56.6183
Abstract +
This paper studies the perturbation to symmetries and the adiabatic invariant for nonholonomic controllable mechanical system in the phase space. The exact invariants introduced by the form invariance of the nonholonomic controllable mechanical system in phase space without perturbation are given. Based on the definition of high-order adiabatic invariants of the mechanical system, the perturbation to symmetries and the adiabatic invariant for nonholonomic controllable mechanical system in phase space under the action of small disturbance is investigated, then the form of high-order adiabatic invariants and the conditions for their existence are presented. An example is finally given to illustrate the application of the results.
2007, 56 (11): 6188-6193.
doi: 10.7498/aps.56.6188
Abstract +
Mei symmetry and Mei conserved quantity for a system with unilateral non-Chetaev nonholonomic constraints in the event space are studied. The differential equations of motion of the system are established. The definition and the criteria of Mei symmetry, weakly Mei symmetry, strongly Mei symmetry for the system are given in this paper. The existence condition and the expression of Mei conserved quantity are deduced directly from Mei symmetry. An example is given to illustrate the application of the results.
2007, 56 (11): 6194-6198.
doi: 10.7498/aps.56.6194
Abstract +
The nonlinear dynamic equation with two end faces in relativistic rotation is established, which contains a kind of nonlinear elastic force. The qualitative analysis of the relativistic rotational nonlinear autonomous equation is performed, and the stability of the equation is studied. The high-order approximate solution of the equation under forcing excitation is obtained by parameter transformation method.
2007, 56 (11): 6199-6203.
doi: 10.7498/aps.56.6199
Abstract +
Properties of geometric phase under Galilean transformation are investigated within a general framework. We found that the geometric phase in the system commonly met with in the laboratory is Galilean invariant. However, this is not always true for general non-relativistic quantum systems. The physical origins of the frame dependence of geometric phase is discussed in detail. We emphasize that the change of geometric phase caused by Galilean boosts does not destroy the results of measurement for two-state interference. It is consistent with the general constraint of Galilean invariance on a non-relativistic quantum system.
2007, 56 (11): 6204-6208.
doi: 10.7498/aps.56.6204
Abstract +
In this paper, using the exponential function transformation, the radial Schrdinger equation with the Hulthén potential is transformed into a hypergeometricdifferential equation under the condition that an effective approximation as 1/r2≈λ2e-λr/(1-e-λr)2 is used for the centrifugal term in the case of any l-states. The exact solution of s-wave scattering state and the approximate analytical solution of non-s-wave scattering states for the Schrdinger equation with the Hulthén potential are presented. The normalized wave functions expressed in terms of hypergeometric functions of scattering states on the “k/2π scale" and the calculation formula of phase shifts are given. The physical meaning of the approximate analytical solution is discussed.
2007, 56 (11): 6209-6213.
doi: 10.7498/aps.56.6209
Abstract +
The scattering matrix approach to analyze the recurrence spectra of diatomic molecules in strong external magnetic field in the energy range E=77010—77050cm-1 is investigated. A new potential model is introduced to simplify the potential of the Rydberg electron of NO in external field. Based on the calculation of semiclassical orbits for the Rydberg states with rotation quantum number N=1,3,5, the long-range scattering matrix elements are obtained, which demonstrates that the quantum resonance peaks are intimately related to the corresponding closed orbits.
2007, 56 (11): 6214-6219.
doi: 10.7498/aps.56.6214
Abstract +
A novel scheme of secure quantum addition module n+1(n≥2) is proposed, based on non-orthogonal states, which allows a number to be added to an unknown number secretly. A proposed protocol for secure n-parity quantum summation is quasisecure to Eve. The collusive attack performed by n-1 legitimate participators cannot eavesdrop all the input information of the other participator in the protocol.
2007, 56 (11): 6220-6223.
doi: 10.7498/aps.56.6220
Abstract +
For a harmonic oscillator coupled to a heat bath with harmonic velocity noise and harmonic noise, we obtain the exact average energy by resoving the corresponding generalized quantum Langevin equation. Due to the different power spectra of the two kinds of noise, the harmonic oscillator driven by external harmonic force exhibits different resonant features. This is an approach for examing the characterization of internal noise.
2007, 56 (11): 6224-6229.
doi: 10.7498/aps.56.6224
Abstract +
A novel robust terminal sliding mode control based on fast fuzzy disturbance observer is designed for a class of chaotic systems with uncertainties. To deal with the shortcoming of slow learning of traditional fuzzy disturbance observer when the approximation errors are very small, a fast fuzzy disturbance observer is designed which improves the learning speed. It is rigorously proved that the synchronization error and approximation error converge to very small values in finite time. Finally, simulation results of the Duffing-Holmes chaotic system demonstrate the effectiveness of the presented closed-loop control scheme.
2007, 56 (11): 6230-6237.
doi: 10.7498/aps.56.6230
Abstract +
In this paper a new chaotic system is presented. Some of its basic dynamical properties are studied. An electronic circuit is designed to realize the new chaotic system. Experimental chaotic behavior of the system is found to be identical to the dynamical properties predicted by theoretical analysis and numerical simulations. Based on Lyapunov stability theory, the new chaotic system is controlled by the method of adaptive backstepping. Numerical simulation shows the feasibility and effectiveness of this approach.
2007, 56 (11): 6238-6244.
doi: 10.7498/aps.56.6238
Abstract +
In this paper, the generalized projective synchronization has been observed in the coupled four_dimensional chaotic systems. The different nonlinear feedback controllers are designed by an active control method for synchronization of two chaotic systems with the same or different structures. The proposed technique allows us to arbitrarily direct the scaling factor to a desired value. Numerical simulation is provided to show the effectiveness of the theoretical analysis.
2007, 56 (11): 6245-6249.
doi: 10.7498/aps.56.6245
Abstract +
It's of vital importance to estimate the unknown parameters of chaotic systems in chaos control and synchronization. Nonlinear observer is used to investigate the problem of parameter identification for two different types of time-delay chaotic systems. The unknown parameter is regarded as the unknown state of the chaotic system. Based on the theory of nonlinear state observer, by selecting suitable nonlinear gain function in observer, which makes the closed-loop error system globally exponentially stable or approximately stable, a sufficient condition for existence of parameter estimator is presented. A numerical simulation on the well-known time-delay logistic system is conducted. Simulation results show that the proposed method is effective for parameter estimation of the time-delay chaotic system.
2007, 56 (11): 6250-6257.
doi: 10.7498/aps.56.6250
Abstract +
The problem of finite-time synchronization for chaotic system is proposed. By applying the global sliding mode control technique and selecting the exponential fast terminal sliding mode reaching law, a global sliding mode controller is designed and applied to synchronization of a class of chaotic systems. Aimed at the chaotic system with parameter uncertainties and disturbance, fuzzy basis function network is introduced to on-line estimate the parameter bound. The design scheme eliminates the reaching phase of sliding mode control. The tracking error stays on the sliding mode surface and tends to zero in finite time. To verify the feasibility and effectivness of this control strategy, the synchronization for Duffing chaotic system is illustrated.
2007, 56 (11): 6258-6262.
doi: 10.7498/aps.56.6258
Abstract +
Control of chaos in Colpitts oscillator by using Washout filter is studied. Firstly, normalization of the circuit and controlling equations are derived based on Washout filter technique. Then by adjusting the control parameters, chaos in Colpitts oscillator is controlled to stable equilibrium point or periodic state. Finally, the controlling result is analyzed simulation is done and the effectiveness of this control method is verified.
EDITOR'S SUGGESTION
2007, 56 (11): 6263-6269.
doi: 10.7498/aps.56.6263
Abstract +
The chaos tracking control problem is studied for a class of uncertain time-delay chaotic systems. Based on the principle of sliding mode control (SMC), a novel adaptive design scheme is proposed. The approach not only overcomes the drawback reported in the literature, but also removes the assumptions that the dead-zone is symmetric and the slopes are known. By theoretical analysis, it is shown that tracking error asymptotically converges to zero. Finally, simulation results of Duffing-Holmes chaotic system demonstrate the effectiveness of the proposed approach.
2007, 56 (11): 6270-6274.
doi: 10.7498/aps.56.6270
Abstract +
A delay-combining reception scheme for DCSK communications system over a multipath fading channel is proposed. BER performance of the scheme is analyzed theoretically and simulated. The results indicate that in comparison with the original DCSK communication system, the one with delay-combining reception has better BER performance. When the delays of reception paths are different, the BER performance are almost the same. When equal gain combining is adopted for the reception paths, the scheme achieves the best BER performance. The theoretical upper bound of the BER performance decreases with the increase of the number of reception paths.
2007, 56 (11): 6275-6281.
doi: 10.7498/aps.56.6275
Abstract +
The output time-delayed feedback control (TDFC) was introduced into the control prototype of the current-mode BOOST converter. Firstly, the discrete iteration model of the controlled system was set up, and its Jacobian matrix was obtained. Based on the analysis of equilibrium point variance and Jacobian matrix eigenvalue trajectory, the range of TDFC feedback gain was determined. According to the convergence of the state variable and duty ratio, the steady-state and dynamic properties of the system were discussed, and the feedback gain of TDFC was optimized. The simulation results confirm that the proposed method is valid and the theoretical analysis holds true.
2007, 56 (11): 6282-6287.
doi: 10.7498/aps.56.6282
Abstract +
A discrete orbit is seperated into m pieces, eaoh constituted of k near points. The monopolized sphere capacity of a point is the extent seperating this one from the others. Instantaneous chaometry, which represents the total capacity of the k monopolized spheres, showes the total seperating extent of a orbital piece.The k step chaometry is the mean of the instantaneous chaometries of the m orbital pieces. The convergent property of k step chaometry is proved for the asymptotic periodic orbit. Althongh the convergence of k step chaometry has not been proved mathematically for the chaotic orbit, it is verified by numerical analysis. Lorenz attractor is interpreted by the 250 step chaometry. The powerful interpreting capability is shown by the 250 step chaometry of 3_dimensional and x component of the Lorenz system. The regression equation between the 250 step chaometry and the age of the 71 normal sinus heart rate time series is y=6.4623 -0.0496x with the correlation coefficient r=-0.669, which supports the view point of Goldberger, and means that the 250 step chaometry will decrease to zero before 130 years of age.
2007, 56 (11): 6288-6293.
doi: 10.7498/aps.56.6288
Abstract +
The generalized synchronization of hyperchaos systems is investigated. Based on the Lyapunov stability theory, a new linear and nonlinear generalized synchronization approach is proposed. Theoretical analysis is provided to show its feasibility. The proposed method can realize the generalized synchronization not only of structurally equivalent systems, but also of systems of different dimensions. If the error gain matrix is suitably chosen, the generalized synchronization between drive system and response system will be obtained. Numerical simulations further demonstrate the effectiveness of the proposed scheme.
2007, 56 (11): 6294-6300.
doi: 10.7498/aps.56.6294
Abstract +
Compared with singular value decomposition, symplectic geometry spectrum is a measure preserving and nonlinear transform. So, it is more suitable for nonlinear dynamics system analysis. A new method to detect determinism in time series based on symplectic geometry spectrum (SGS) is proposed in the present work. Chaos and stochastic process could be recognized by applying the non_parameter Mann_Whitney on the SGS of original data and its surrogate data. The method is first tested on stochastic processes, the Lorenz, Rossler, Mackey_Glass and high dimensional coupling equations. Then it is applied to two data sets of Santa Fe to test its effect on experimental data. Finally, the robust ness of the method is tested on the time series with different data length and different levels of additive noise.
2007, 56 (11): 6301-6306.
doi: 10.7498/aps.56.6301
Abstract +
A novel chaotic repeater system based on the cascade synchronization in optoelectronic negative feedback chaotic lasers is proposed. The synchronization characteristics and the influence of the parameter mismatch on the synchronization have been investigated. The results show that complete synchronization can be realized with suitable system parameters, and the internal parameter mismatch of the lasers have influence on the synchronization quality. But the system has greater robustness to parameter mismatch compared with the cascade synchronization based on the optical feedback.
2007, 56 (11): 6307-6314.
doi: 10.7498/aps.56.6307
Abstract +
The model of capacitively coupled intrinsic Josephson junction array was constructed with the software PSpice. Taking advantage of this new model, we investigated the behavior of capacitively coupled intrinsic Josephson junction array driven by constant current. The time domain wave, freguency spectrum, fractal dimension and phase portrait were obtained. Compared with the uncoupled array, chaotic behaviors were found firstly in the capacitively coupled intrinsic Josephson junction array. The results are valuable for the research and application of intrinsic Josephson junction arrays.
2007, 56 (11): 6315-6320.
doi: 10.7498/aps.56.6315
Abstract +
Using stochastic simulation and chemical Langevin methods, we numerically investigated the influence of clustering of cells on the system size effects in two-dimensional coupled internal noisy cell systems. It was found that, when the system works near the Hopf bifurcation, the systems' cells assemble to a team in forming, a cell cluster. Interestingly, the teamwork in clustering may significantly raise the system's working efficiency, leading to the system obtaining the best performance under external stimulus. Furthermore, for different coupling intensities the optimal cluster size varies in robustness to external stimuli, but the signal-to-noise ratio (SNR) shows an increscent tendency with the coupling intensity increasing. These phenomena illustrate that clustering of cells may greatly enhance the sensitivity of Ca2+ signal, by which the biologic systems would probably improve their capability to respond to external stimulation.
2007, 56 (11): 6321-6325.
doi: 10.7498/aps.56.6321
Abstract +
The day-to-day route choice is a non-cooperative game process with many participants during a long time period. We use the multi-agent simulation system SeSAm to investigate two different route update rules designed for traffic information release and unrelease respectively. Simulation results on a small grid network show that the rule under information release can make route flow evolve to the logit stochastic user equilibrium faster than that under information unrelease. However, the flow pattern may be unstable if travelers put undue compliance on the released information. A stable flow pattern can also be achieved only relying on travelers' perceived experience and learning ability, but the evolution is rather slow. It is thus suggested that the traffic information should be timely released to public meanwhile utilized properly.
2007, 56 (11): 6326-6333.
doi: 10.7498/aps.56.6326
Abstract +
Using the dynamic method to evolve a weighted network, a new weighted network with accelerated attachment of newly added edges is proposed. At each time step, the number of newly added edges is proportional to the size of the network. The degree distribution of the network is discussed. The strength distribution is also obtained, and the analytical relation between the strength and the degrees of nodes is presented. The network shows scale-free property in both theoretical analysis and numerical simulations. In addition, regardless of degree preferential attachment or strength preferential attachment in the evolution process, as long as the weight of edge follows a certain probability distribution, the degree distribution always follows the power-law distribution and its exponent is not related with the attachment mechanism and the specific probability distribution.
2007, 56 (11): 6334-6339.
doi: 10.7498/aps.56.6334
Abstract +
An ensemble Monte Carlo simulation method has been employed to study the operating modes of semi-insulated GaAs (SI-GaAs) photoconductive semiconductor switches (PCSS) excited by a femtosecond laser pulse and biased in an electrical field. The results show that, under a bias field lower than the Gunn threshold field (which is 4.2kV/cm for GaAs), or the optical pulse energy is below the optical threshold, the time-resolved current in the switch operates in the linear mode. When the bias field and triggering optical energy are respectively greater than the electrical and optical thresholds, the PCSS operates in the nonlinear mode. The simulation shows that when triggered by laser pulse with higher photon energy, the switch has lower optical threshold in the nonlinear mode. The mechanism of the nonlinear mode for the switch is concluded to be due to the inter-valley scattering of the photo-generated carriers, leading to local high field in the switch.
2007, 56 (11): 6340-6344.
doi: 10.7498/aps.56.6340
Abstract +
A series of colloidal CdSe quantum dots (QDs) were synthesized, and the photoluminescence (PL) quantum yield of CdSe nanocrystals was found to increase at first and then decrease with increasing size. The chromatic coordinates of samples with different size and different size distributions were calculated to see the influence of size distribution of CdSe QDs. And white QDs sample was prepared by mixing red and blue QDs. The experimental value of chromatic coordinates of the prepared sample coincide with that estimated according to the empirical formula.
2007, 56 (11): 6345-6351.
doi: 10.7498/aps.56.6345
Abstract +
The theoretical model about energy dissipation of atomic force microscopy (AFM) in tapping-mode has great significance for the investigation of the dynamic response of AFM tip influenced by the adhesive force. Based on the Hamaker hypotheses and the Lennard-Jones potential and elastic theory, a novel elastic model is established for adhesive contact between a sphere and a plane. The model shows that the variation of the adhesive force with the distance in the loading process is different from that in the unloading process, i.e., an adhesive hysteresis, which is the indication of energy dissipation of AFM, is engendered in the tapping-mode. On the basis of the adhesive model, the dynamic model of AFM in tapping-mode is established to investigate the variations of the amplitude, phase shift and energy dissipation with the distance between AFM tip and the sample surface. The results obtained by the dynamic model are in agreement with the experimental results available.
2007, 56 (11): 6352-6357.
doi: 10.7498/aps.56.6352
Abstract +
Ternary alloy CdS0.65Se0.35 nanoribbons were successfully grown by a one-step thermal evaporation. The nanoribbons obtained have high-quality single-crystalline nature. To understand the whole picture of waveguide behavior in CdS0.65Se0.35 nanoribbons, we quantitatively studied the guided photoluminescence (PL) through individual CdS0.65Se0.35 nanoribbon by using scanning near-field optical microscopy (SNOM) at room temperature. The results show significant sustained red shift of PL spectra of the CdS0.65Se0.35 nanoribbons optical waveguide with the increase of the light propagation distance. According to our analysis, the red shift is attributed to the absorption of band-tail of states in nanoribbons. This finding may be extended to other ternary nanosyotems and be useful for fabricating new subwavelength photonic components.
ATOMIC AND MOLECULAR PHYSICS
2007, 56 (11): 6358-6366.
doi: 10.7498/aps.56.6358
Abstract +
The modulational instability (MI) of nonlinear coherent spin waves in an atomic spin chain of spinor Bose-Einstein condensates confined in an optical lattice is studied. Analytically we obtained the criteria for the MI of nonlinear coherent spin waves and its relation with the long-range nonlinear spin coupling. We analysed the MI in the case of blue-detuned and red-detuned opctical lattice respectively. It was found that the long-range nonlinear spin coupling in the optical lattice is due to light-induced and static magnetic field-induced dipole-dipole interaction.
2007, 56 (11): 6367-6372.
doi: 10.7498/aps.56.6367
Abstract +
Trapping potential of a Z-trap is calculated with analytic and numeric methods. It's found that when a trapping center is a little bit far from the chip surface (the distance is about one order of the half length of the Z-wire central part), the trapping depth is not approximately eqsual to the potential By created by a bias magnetic field, the potential energy at the trapping center should be subtracted from the potential By created by the bias field. On the other hand, if an atom cloud is compressed to a certain extent by increasing By, the trapping depth will be decreased rather than increased. The preparation of the Z-trap in an atom chip, the experimental setup, and the experimental procedure for trapping neutral 87Rb atoms is also introduced. At last we obtained 2×106 87Rb atoms trapped in the Z-trap.
2007, 56 (11): 6373-6377.
doi: 10.7498/aps.56.6373
Abstract +
A high resolution photoassociation spectrum of ultracold cesium atoms is reported in this paper. A photoassociation laser with its frequency red detuned below 6S1/2+6P3/2 dissociation limit acts on the cold cesium atoms in magnetic optical trap and the excited ultracold molecules generated in the photoassociation process are observed. In order to obtain a high signal-to-noise ratio, the trapping laser is amplitude modulated using acousto-optic modulator and the fluorescence signal is demodulated by lock-in technique. The results are discussed using the density matrix equations.
2007, 56 (11): 6378-6385.
doi: 10.7498/aps.56.6378
Abstract +
In the present work we have studied the double differential cross sections for single ionization of a helium atom by electron impact at low energies. The double differential cross sections of the secondary ejected electron have been obtained by integrating the triple differential cross sections over the entire angular range of the primary scattered electron. The double differential cross sections for electron impact ionization of helium at incident energies of 26.3，28.3，30.3，32.5，34.3，36.5 and 40.7eV have been calculated in the BBK and DS3C model. The present DS3C results are compared with the absolute measurements，and reasonably good agreement has generally been found except for low incident energies (e.g.，26.3eV) and low ejected angles. In addition，the direct and exchange amplitudes are also considered. It has also been shown how the exchange effects contribute to the cross sections.
2007, 56 (11): 6386-6392.
doi: 10.7498/aps.56.6386
Abstract +
We have performed an experiment on near threshold double ionization of helium by 106eV electron impact with an improved reaction microscope. In this experiment the momenta of three particles after ionization were measured, and the information on correlation of emitted electrons was obtained. Detailed descriptions of the experimental setup and the methods of reconstruction of electron momentum were given. We focused on the analysis of momentum and energy distributions and the angular correlation of the emitted electrons. The experimental results were compared with Wannier's prediction, and it was found that the experimental results showed some characteristic features predicted by Wannier theory.
CLASSICAL AREA OF PHENOMENOLOGY
2007, 56 (11): 6393-6397.
doi: 10.7498/aps.56.6393
Abstract +
Application of ridged rectangular and circular waveguides has been found in many areas. In this paper，with the Rayleigh-Ritz method and polynomial representation，the wave propagation characteristics in the ridged elliptical waveguide are analyzed. The numerical results are in good agreement with calculation using electromagnetic field simulation software. The variation of bandwidth with physical dimensions has been studied. It is helpful for optimizing this kind of structure.
2007, 56 (11): 6398-6402.
doi: 10.7498/aps.56.6398
Abstract +
Based on the electromagnetic theory，the Manly-Rowe relations for nonlinear left-handed metamaterials are studied. Energy conversion process and spatial distribution of forward-propagating wave of fundamental frequency and backward-propagating second harmonic wave under phase-matching condition are investigated. That a surface of nonlinear left-handed metamaterials operates as an effective mirror which reflects the energy in the form of second harmonics is demonstrated. Numerical results of field intensity distribution of a finite thickness metamaterial slab is given. Finally，the importance of phase-matching condition to the investigation of nonlinear left-handed metamaterials is illustrated from the viewpoint of phase-mismatching. This work provides a basis for studying nonlinear left-handed metamaterials.
2007, 56 (11): 6403-6407.
doi: 10.7498/aps.56.6403
Abstract +
The far-field focusing properties of two dimensional rod-type honeycomb lattice photonic crystals are investigated by using finite difference time domain method，and it was found that it explicitly follows the wave-beam negative refraction law with relative refractive index of -1. But the image qualities are limited by low transmission at large incident angles. The image qualities can be improved by modifying the radius of rods near the surface of photonic crystals slab.
2007, 56 (11): 6408-6412.
doi: 10.7498/aps.56.6408
Abstract +
Optical feedback characteristics of frequency modulated microchip Nd：YAG lasers are investigated. Without optical feedback，the output intensity changes by one fringe with the laser frequency changing by one longitudinal mode spacing. With optical feedback，the modulation frequency of output intensity is proportional to the ratio of external cavity length to internal cavity length. The theoretical analysis based on three-cavity-mirror equivalent model is in good agreement with experimental results. The potential applications of this phenomenon in precision measurement are also discussed.
2007, 56 (11): 6413-6419.
doi: 10.7498/aps.56.6413
Abstract +
Based on radiometry，electromagnetism and polarization theories and the Fourier transform spectroscopy，an in-depth study is conducted on the SNR of the self-developed ultra-compact static polarization interference imaging spectrometer (USPIIS) theoretically and experimentally. The theoretical equations of its SNR are deduced. Under paraxial approximation，the curve of the SNR changing with incidence angle is given via computer simulation. How the polarizing directions affect the SNR of USPIIS，which is a particular feature of the polarization interference imaging spectrometer，is deeply studied. When modulation depth equals 0.6，0.7，0.8，0.9 and 1.0，the curves of the SNR changing with polarizing directions are given respectively; after which the optimum value is recommended. Under optimum conditions，the changing laws of SNR with the elements of detector are obtained，which turned out the same as the prediction of the theory. The theoretical and experimental results both indicate that the novel imaging spectrometer has the properties of high throughput and high SNR under the condition of high modulation depth，which is suitable for aviation，remote sensing，weak signal testing applications. The work can provide theoretical basis and guidance for the design，development and engineering of polarizer，interferometer and polarization imaging interferometer.
2007, 56 (11): 6420-6426.
doi: 10.7498/aps.56.6420
Abstract +
Using the complete quantum theory，the process of M two-level atoms interacting with M multi-mode light fields with intensity-dependent coupling is studied. It is found that quantum entanglement information can be transferred back and forth or be preserved between the cavity fields and atoms under certain time conditions. The entanglement states of the atoms or the cavities can be transferred when t=π/(2λ). The results are verified by numerically computing the entanglement degree. And it was shown that the entanglement states of the atoms or the cavities can be preserved when t=π/λ.
2007, 56 (11): 6427-6433.
doi: 10.7498/aps.56.6427
Abstract +
A quantum key distribution scheme using two-mode squeezed states is proposed in this paper. The security of the proposed scheme against beam splitter attack is analyzed using Shannon information theory. The analytical expression of the secret information rate is given in terms of squeezed factor and channel parameters. The mode-mode correlation of two-mode squeezed states guarantees the security of the proposed scheme.
2007, 56 (11): 6434-6440.
doi: 10.7498/aps.56.6434
Abstract +
An improved DPS-QKD scheme is proposed and demonstrated in this paper. At Alice's site，we use a M-Z interferometer to produce two coherent pulses. At Bob's site，a Faraday-mirrors-based Michelson interferometer is used instead of a M-Z interferometer to auto-compensate for the phase drifts and polarization mode dispersions in the fiber. It enhances the security of the whole system to use the two quantum cryptography protocols (namely the two pulse DPS-QKD scheme associated with the BB84 scheme). It is shown in our experiment that such a system features perfect stability with a quantum bit error rate less than 5% and high key generation rate. This scheme has been implemented successfully during the 80km fiber transmission.
2007, 56 (11): 6441-6445.
doi: 10.7498/aps.56.6441
Abstract +
In this paper，we report the effects of vacuum-induced coherence in a laser-driven four-level atom consisting of three near-degenerate upper levels having an additional coherence term due to interaction with the vacuum of the radiation field. We show that such coherence preserves the electromagnetically induced transparency and optical bistability phenomena. The dynamical behavior of the population distribution via vacuum-induced coherence was also analyzed numerically.
2007, 56 (11): 6446-6450.
doi: 10.7498/aps.56.6446
Abstract +
Three-dimensional Casimir force between two negative-refractive-material slabs is calculated. For the negative-refractive material characterized by dispersive permittivity and permeability of Drude-Lorentz type，the structure of negative refraction frequency band is determined by characteristic frequencies. The different width and depth of the negative refraction frequency bands correspond to reflection properties of different medium，and thus influences the magnitude of Casimir effect between the slabs.
2007, 56 (11): 6451-6456.
doi: 10.7498/aps.56.6451
Abstract +
Based on the semi-classical theory，the pulsed-laser pumped D2O gas tera-Hz laser was theoretically analyzed，the relation between the intensity of pumping laser and the output tera-Hz laser light was studied and numerically calculated. According to the result of calculation，the intensity of the output tera-Hz laser light increased approximately linearly with that of the input laser in a certain range，but gradually decreased because of the bottleneck effect when the intensity of the input laser exceeded a fixed value，and for given gas pressure，cavity length and operating temperature，an optimal intensity of pumping laser exists. A frequency tuning range of the output signal occurred when the intensity of the input laser was strong enough.
2007, 56 (11): 6457-6462.
doi: 10.7498/aps.56.6457
Abstract +
Based on the ray tracing method，the implicit expression of the output spectrum of the extremely short external cavity semiconductor laser (ESECSL) has been deduced for the first time. As a result，the output spectrum and P-I characteristic of ESECSL have been investigated. The results show that: when the length of external cavity changes by an amount of the order of wavelength，the P-I characteristic of ESECSL will change obviously. The lasing wavelength of ESECSL will hop periodically in the range of 10nm with the variation of the length of external cavity. Especially，the hopping range of the lasing wavelength will reach the maximum for the external cavity length varying within the range of 40—70μm. The simulations are well in accordance with the experimental reports.
2007, 56 (11): 6463-6467.
doi: 10.7498/aps.56.6463
Abstract +
We observed the characteristics of high energy nanosecond chirped pulse by spectral-resolved streak camera，which works well with energetic chirped pulse of nanosecond pulse duration. At the same time，it can monitor the alignment of grating compressor. The measurement results show that the pulse generated by PW demonstration facility is linearly chirped，verifying the compressibility of amplified nanosecond pulse.
2007, 56 (11): 6468-6472.
doi: 10.7498/aps.56.6468
Abstract +
Based on the nonlinear coupling equations，the relation between group-velocities of 1ω，2ω and 3ω waves in the mixing process of broadband third-harmonic generation (THG) is investigated theoretically. The formula of three-wave group-velocity-matching (GVM) is derived. The THG mixing process of ultrashort pulses in Type-Ⅱ KDP crystals is simulated. Obtained results show that both the THG conversion efficiency and the bandwidth reach maximum when the formula is satisfied (i.e., at zero group-velocity mismatch)，and drop down rapidly when it's not satisfied. The three-wave GVM formula presented is useful for finding proper nonlinear crystals and choosing effective GVM methods.
2007, 56 (11): 6473-6479.
doi: 10.7498/aps.56.6473
Abstract +
We use an extended Tanh-function expansion method to solve the nonlinear equation for ultrashort pulse propagation in matamaterial，and obtain dark solitary solutions in various cases. Further，we study the influence of the controllable self-steepening effect and the second-order nonlinear dispersion on the formation and propagation of dark solitons in metamaterials. It is found that the negative self-steepening effect in metamaterial makes the soliton center move to the leading side，opposite to the moving direction of soliton in ordinary materials in which the self-steepening effect is always positive. Most importantly，due to the role of the second-order nonlinear dispersion，dark solitons can be formed in the medium without linear dispersion or with an anomalous linear dispersion.
2007, 56 (11): 6480-6485.
doi: 10.7498/aps.56.6480
Abstract +
The transmission properties of one-dimension metamaterials characterized by resonance were studied. With theoretic analysis it is shown that the transmission coefficient S21 has either one left-handed passband or two left-handed passbands under certain conditions. The experimental verification of the transmission properties has been realized by the composite right/left-handed transmission line used as a leaky-wave antenna.
2007, 56 (11): 6486-6489.
doi: 10.7498/aps.56.6486
Abstract +
According to the heat conduction theory，different sections of the cladding of microstructured fibres (MSF) have different temperature in the high temperature zone during drawing MSF. The temperature decreases gradually from the surface to the central in MSF preform，and the temperature gradient will increase with either the increase of feed speed of MSF preform or decrease of the air-filling fraction. Because both the surface tension and the coefficient of viscosity are functions of temperature，when the MSF preform is thinned to MSF，the actual structure of MSF is not a simple down-sealing of the perform. The shrink size of the air holes will increase as the temperature rises. In order to obtain the MSF as expected，we must design the size of air holes of the MSF preform to vary corectly with the temperature variations，so as to effectively eliminate the effects of uneven heating temperature on the air holes in the cladding of MSF.
2007, 56 (11): 6490-6495.
doi: 10.7498/aps.56.6490
Abstract +
Within the range from 0 to 1，the transmissivity of fused tapered fiber reflector as a conic function of the departure of the coupling-ratio from 50∶50 was examined theoretically and experimentally. Bending the fiber in loop-cavity causes no obvious change. However，twist and the radial pressure change the transmissivity，obviously，producing birefringence in the fiber core. Temperature changes the transmissivity through the induced departure of the coupling-ratio. Constructed with a broad-band 3dB fused tapered fiber coupler，the reflector shows total reflection. A pulse was observed at the beginning of the formation of the transmitted beam. Increasing the input intensity causes，the rise-time and the fall-time of the pulse to decrease, while the width of the pulse and the steady state value of the transmitted power to increase.
2007, 56 (11): 6496-6502.
doi: 10.7498/aps.56.6496
Abstract +
A new method based on the Fourier-Bessel series is applied in KZK equation to calculate the second harmonic component of a zero-order Bessel ultrasonic field in viscous medium. An analytical solution of a series form is obtained and a new conclusion is drawn. Assuming the source sound pressure to be J0(α0r)，the second harmonic sound pressure has a radial distribution of J20(α0r) function profile in the near field. This conclusion explains the experimental results reported in literature appropriately and indicates that the second harmonic field has different radial distributions in the near and far field，thus solves the problem of radial distribution of the second harmonic in the nearfield of Bessel ultrasonic field. Moreover，the conclusion implies that the second harmonic field has similar limited diffraction property as the fundamental. A numerical computation and simulation example is given subsequently.
2007, 56 (11): 6503-6507.
doi: 10.7498/aps.56.6503
Abstract +
The horizontal convection at high Rayleigh number (Ra) in a rectangle cavity with aspect ratio of 1∶10 is numerically simulated. The horizontal convection is an important model to understand the ocean circulation and the power laws of the flow are the most concerned. According to the results within the regime of 104Ra11, three continuous regimes are obtained: the linear regime (104Ra6), the transition regime (106Ra8) and the 1/5-power law regime (108Ra11). For the flow strength, a 1/3-power law of Ra is fitted when Ra is not high enough (107Ra8). However, a 1/5-power law is obtained when Ra is high enough (108Ra11). The 1/5-power law confirms the analysis of Rossby and implies that 1/3-power law of Ra for Nusselt number by Siggers et al. is an over estimation.
2007, 56 (11): 6508-6513.
doi: 10.7498/aps.56.6508
Abstract +
A novel force sensor based on optical beam deflection was developed to investigate the mechanical effects during the pulsed laser ablation of a metal in liquids with different viscosities. The experimental results show that the targets in viscous liquids are affected by laser-generated ablation force and high- speed liquid-jet impulse induced by bubble collapse. In the same liquid, the amplitudes of the three kinds of forces increase with the increase of laser energy. With the increase in viscosity, the amplitudes of all three forces decrease, and the cavitation erosion is reduced. Larger viscosities make the bubble expand or contract more slowly, and bubble life-time becomes larger. Besides, the Rayleigh equation was revised, and the results are in good agreement with the experimental data.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2007, 56 (11): 6514-6520.
doi: 10.7498/aps.56.6514
Abstract +
Cd0.9Zn0.1Te wafers grown by vertical Bridgman method were annealed in cadmium vapor at different temperatures. The formerly established model correlating resistivity and conduction type of CdZnTe with the main diffusion parameter-diffusion coefficient is used in combination with the analysis of our experimental data (DCd=1.464×10-10, 1.085×10-11 and 4.167×10-13cm2/s), and the values of Cd self-diffusion coefficient in Cd0.9Zn0.1Te at 1073K, 973K and 873K have been obtained, which coincide closely with the Cd self-diffusion coefficient in CdTe provided by different authors. With the data, the effect of annealing time on the resistivity and change of conduction type of Cd0.9Zn0.1 Te wafers annealed in saturated Cd vapor at 1073K, 973K and 873K were simulated, and good agreement was found.
2007, 56 (11): 6521-6525.
doi: 10.7498/aps.56.6521
Abstract +
In situ energy dispersive X-ray diffraction measurements with synchrotron radiation source have been performed on nanocrystalline Ge with particle sizes 13, 49 and 100 nm by using diamond anvil cell. Whereas the percentage volume collapse at the transition is almost constant, the values of the bulk modulus and transition pressure increase with decreasing particle size. Models are suggested to describe the grain-size dependences of bulk modulus and transition pressure. The trend of the predicted results is consistent with the experimental results while the absolute values are still different from experimental ones.
2007, 56 (11): 6526-6530.
doi: 10.7498/aps.56.6526
Abstract +
The electronic transport sensitivity depending on the coupling interface between a phenalenyl molecule and atomic chain lead in three-electrode single-molecular device is theoretically modeled and studied using self-consistent tight-binding method. Electronic transmission probabilities are obtained by changing the hopping integral on the interface. The result shows that the electron transmission probability lowers as the coupling strength becomes weak. Not only the transmission probability shows high peaks, but also the transmission energy bands become wider as the coupling strength increases. A novel property of the symmetrical three-electrode phenalenyl molecule device acting as a good plus-minus energy switch without source is discovered.
2007, 56 (11): 6531-6536.
doi: 10.7498/aps.56.6531
Abstract +
Using Sn and SnO powder as source material, SnO2 one-dimensional nanostructures (nanowires, nanorods, nanobelt and nanoneedles) with controllable diameters were successfully prepared by chemical vapor deposition. The nanostructure and morphology of the products depend strongly on the proportion of oxygen in the growth chamber, which can be altered by adjusting the proportion of SnO in the source material or the proportion of oxygen in the carrier gas. It is crucial to adjust the relative contents of Sn and O atoms in the region of high temperature growth of the Si wafer during controlled preparation of SnO2 one-dimensional nanostructures. We will also discuss the growth mechanism of SnO2 one-dimensional nanostructures under different growth conditions.
2007, 56 (11): 6537-6542.
doi: 10.7498/aps.56.6537
Abstract +
The variation of electrical parameters during microarc oxidation (MAO) of titanium alloys at constant voltage has been studied by means of a laboratory-made data acquisition system. Experimental results show that the variation of the cathodic and anodic current amplitudes and effective working current in an electrical loop with the duration of treatment show obviously four stages, and the variation of the coating thickness with the treating time has obviously three stages, and the variations of dynamic forward and backward resistance as well as resistance rate of coatings also show different stages. During MAO process, the dynamic forward resistance is always different from the backward resistance, and the former is generally greater than the latter. Scanning electron microscopy shows that the surface morphology of MAO coatings is porous and varies with treatment time in steps.
2007, 56 (11): 6543-6546.
doi: 10.7498/aps.56.6543
Abstract +
The effect of Zr-ion implantation into zircaloy-4 and the defect recovery was investigated by slow positron beam. Specimens were implanted by zirconium ions with doses ranging from 1×1015 to 1×1017 ions/cm2 using a MEVVA source at an extract voltage of 50 kV. It was found that defects in the samples irradiated with a dose above 1×1016 ions/cm2 has been recovered during the implantation process, and the thickness of oxide layer increases as indicated by auger electron spectroscopy (AES) measurements. Meanwhile, the defects in the sample implanted with a dose of 1×1015ions/cm2 turns out to be recovered after annealing at 300℃ in high vacuum for 1 hour, showing the corresponding the recovery energy of defects is very low. We propose the method of keeping the material at an appropriate temperature during implantation to improve the corrosion resistance of Zr-4 alloy, according to the relationship between the defect concentration and the corrosion resistance.
2007, 56 (11): 6547-6551.
doi: 10.7498/aps.56.6547
Abstract +
Dimethyl phthalate, diethyl phthalate, dibutyl phthalate, and dioctyl phthalate series samples were measured by the reed-vibration mechanical spectroscopy for liquids recently invented. The results indicate that the processes of dynamical glass transition, crystallization of the supercooled liquid, crystal-liquid phase transition, and gasification take place successively for the dimethyl phthalate sample in the measured temperature range on heating, but only the glass transition and the gasification appear in the other 3 samples. The above measurements and corresponding analysis show that the reed-vibration mechanical spectroscopy for liquids is a reliable and effective method for the investigation of physical processes in liquid state, so that it could provide physical information of soft condensed matter.
2007, 56 (11): 6552-6556.
doi: 10.7498/aps.56.6552
Abstract +
The phase transformation and the structure change of the silicon surface are investigated by molecular dynamics simulation of the incidence and recoil of a nanoparticle at the monocrystlline silicon surface. The simulation shows that during the collision process, the impacted region on the silicon surface transforms from diamond structure to a molten state, then goes through the state of supercooled liquid, and finally solidifies into an amorphous phase. Furthermore, the temperature of solidification transformation calculated from the simulation is very close to the glass transition temperature of silicon. The structure changes taking place during the nanoparticles recoiling process are also revealed. Beginning with an instantaneous, highly disordered, and badly depressed supercooled state, the impacted region evolves along the direction to a more ordered and lessdepressed state. These evolutional tendencies are determined by the cooling andunloading process the impacted region undergoes. The amorphous silicon formed after the collision has the average coordination of 5.27, and the fivefold and sixfold coordinated atoms accounts for 61.5% of the whole atoms in the impacted region.
2007, 56 (11): 6557-6564.
doi: 10.7498/aps.56.6557
Abstract +
High-pressure phase-transition behaviors of z-cut lithium tantalate single-crystal have been studied by Hugoniot measurements at our two-stage light-gas gun and DFT-PWP calculations. A distinct discontinuity was discovered on the D-u (shock-wave velocity versus particle velocity) relation. An elastic-plastic two-wave structure was observed from the VISAR measured particle velocity profiles at low pressures (25.9 GPa and 32.6 GPa), while three-wave structure appeared in the measured particle velocity profiles at the final pressure of 42.9 GPa and 53.0 GPa. Both facts indicate a shock-induced phase transition of LiTaO3 samples occurred with an onset pressure of 37.9GPa. The theoretically calculated 0K pressure versus compression ratio (P-V/V0) curve for the rhombohedral phase (R3c space group) is in good agreement with the low-pressure experimental data, while that for orthorhombic phase (Pbnm space group) is in accord with the results by deducing thermal pressure contribution from the measured shock-compression data at high pressures. This suggests that the high-pressure phase has orthorhombic symmetry. High-pressure phase transformation behaviors including the transition pressure and structures, which are unclear in current literature, have been clarified in this paper by our new shock-wave data and ab-initio calculations. These behaviors were demonstrated to be in close similarity with that of its isomorphous crystal LiNbO3. The present work is significant for the investigations of shock-induced phase-transition of similar single-crystal materials.
2007, 56 (11): 6565-6571.
doi: 10.7498/aps.56.6565
Abstract +
Based on the classical electrostatic theory, the model of dipole-dipole interaction of rod-like amphiphilic molecules in Y-type Langmuir-Blodgett (LB) film is presented in the paper. The relations between the structure and spectral absorption peak of LB films were obtained by using this model. For Y-type films, the relationship of molecular aggregation state and the structure parameters, i.e. molecular separation distance a, separation d between two adjacent layers, molecular tilt angle θ, and layer number g, were studied using our model. Then we compared the similarities and differences of aggregation behavior between Y-type and Z-type films. The theoretical results agree well with experimental data.
2007, 56 (11): 6572-6579.
doi: 10.7498/aps.56.6572
Abstract +
Diamond film was deposited in CO and H2 gas mixture by microwave plasma assisted chemical vapor deposition (MPCVD). Bias enhanced nucleation and two-step growth method were employed. Scanning electron microscopy (SEM), Raman spectroscopy and transmission electron microscopy (TEM) were used to characterize the film. It was found that twins and stacking faults were mainly produced at the stages of nucleation and growth. In the second growth stage, the production of defects in the film was reduced considerably, resulting in the final smooth-faceted diamond grains with five-fold symmetry or parallel twins with a small amount of stacking faults. At the edge of the sample, there was a region with low nucleation density, which might be the result of non-uniform plasma existing there. Meanwhile, a non-diamond structure of carbon was found in the edge region.
2007, 56 (11): 6580-6587.
doi: 10.7498/aps.56.6580
Abstract +
Molecular dynamics simulation was used to study the strain relaxation and evolution of Ag/Cu(111) and Au/Cu(111) heteroepitaxial systems with embedded atom method. By comparing the evolution behaviors of the two systems, the atomistic mechanism leading to the formation of Moir structure in Ag/Cu(111) epitaxial layer is studied and is related to the physical properties of the components in the heteroepitaxial system. It is found that the adhesion between epilayer and substrate is one of the important factors that affect the formation of Moir structure. Positive solution heat of the alloy enables the adhesion of heteroepitaxial system to be weak and is helpful for the formation of Moir structure. The relaxing ability of atoms in epilayer is also important in the formation of Moir structure, which can be related to the bulk modulus of epilayer. The larger the bulk modulus of epilayer, the easier the formation of Moir structure. On the other hand, the formation of Moir structure is related to the island size, which is caused by the boundary atoms confining the relaxation of interior atoms in the island.
2007, 56 (11): 6588-6591.
doi: 10.7498/aps.56.6588
Abstract +
Electric field modeling of nodular defects is performed to investigate the interaction between defective multilayer coatings and Gaussian profile laser beam. Light intensity is significantly enhanced as large as 6 times within the nodular defects. Different geometries of defects irradiated by laser beams at 0 to 40 deg incident laser angles are analyzed. Nodules with large but shallow seeds, or irradiation of 40 deg p-polarized laser beam, tends to produce the greatest enhancement effect.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2007, 56 (11): 6592-6599.
doi: 10.7498/aps.56.6592
Abstract +
The geometry, electronic structure and optical properties of pure and 3d transition metals-doped anatase-phase TiO2 were studied by using the plane-wave ultrasoft pseudopotential method based on the density functional theory. The calculations show that the formation of impurity energy level is mainly contributed by 3d orbital of the transition metal doped in TiO2, and the position of impurity energy levels in the band gap is the dominating factor that decides whether the absorption threshold wavelength has a red-shift or not. The doping of Cr, Mn, Fe, Ni, Co and Cu causes the absorption wavelength to red-shift, and the absorption coefficient in the visible light region is increased; whereas the doping of Sc, Zn causes the absorption wavelength to blue-shift, but leads to higher absorption coefficients in the visible region. The doping of V not only causes the absorption wavelength to red-shift and strengthens the absorption in the ultraviolet light region, but also gives rise to extremely big absorption coefficient in the visible region.
2007, 56 (11): 6600-6607.
doi: 10.7498/aps.56.6600
Abstract +
Using a transfer matrix method, we study the characteristics of the localized interface phonon polariton modes in two coupled superlattices (SLs) with a defect layer. Comparing different structure defects of SL where the dielectric characteristics of defect layers are different, we find that there are certain differences in the distribution and number of the localized interface phonon polariton modes in the Reststrahlen regions ［ωTO，ωLO］ and there are different characteristics for anti-symmetric modes in the above structures. The structuraly defective SL of which the dielectric constant of defect layer is independent of frequency was emphatically investigated. We found that the localized interface phonon polariton modes in such structure are sensitive to the thicknesses and order of the constituent layers, the thickness of the defect layer as well as the transverse wavenumber q∥.
2007, 56 (11): 6608-6615.
doi: 10.7498/aps.56.6608
Abstract +
The 252 rank completely diagonalized Hamiltonian matrix of the 3d5 configuration with trigonal symmetry have been established by group theory, crystal field theory and irreducible tensor operator method. The spectral fine structure, zero-field splitting parameters, and Jahn-Teller effect, as well s the influence of spin doublet state and spin quartet state on the ground-state energy levels in LiNbO3∶Fe3+ crystals were studied with this matrix. The results show that the contribution of spin quartet state on the ground- state energy levels is the most important, the contribution of spin doublet state is weak but can not be neglected. The calculated results are in good agreement with the experiments. On their basis, the influence of spin-orbit interaction and spin-spin interaction on the spectra fine structure and zero-field splitting parameters were further studied, and we found that the influence of spin-orbit interaction is dominant, but the influence of spin-spin interaction can not be neglected. The research shows this substance has J-T effect in the spectral structure of spin quartet state. The reason is the combined action of spin-orbit interaction and trigonal distortion.
2007, 56 (11): 6616-6622.
doi: 10.7498/aps.56.6616
Abstract +
The field enhancement is one of the important factors that indicate the performance of field emission cold cathode devices. It is intimately related to the field emission current density and the threshold voltage of the device. In our paper, the field enhancement factor of a normal-gated field emission nanowire cold cathode model was analytically deduced on the basis of classical electrostatic theory, and it is given by the equation. β=k1{N2·(L-d1)2+［1/k1+(L-d1)］2}1/2. The effect of geometrical parameters of the device on the field enhancement factor was explored. The theoretical analysis showed that the larger the length (L-d1) of nanowire above the gate and the gate hole radius, the larger the enhancement factor is; but the larger the nanowire radius, the smaller the enhancement factor is. When the L is much larger thand1, the enhancement factor satisfies the relation. β∝Ｌ／r0, for which N=N1(k1r0)/N0(k1r0), N0(k1r0) and N1(k1r0) are both Neumann functions and k1=0.8936/R. R, L, r0 and d1 are the gate hole radius, the nanowire length, the nanowire radius and the gate-cathode distance, respectively.
2007, 56 (11): 6623-6628.
doi: 10.7498/aps.56.6623
Abstract +
The time-frequency properties of the high-order harmonic generation in the presence of a static electric field are investigated. It is found that an attosecond pulse train with one burst per optical cycle can be extracted by superposing the harmonics near the cutoff. This characteristic can be used to generate isolated attosecond pulse in multi-cycle regime. When the ratio of the laser field to the static field is 0.39, the harmonic spectrum is extended to Ip＋9.1Up, and the harmonics above Ip＋0.7Up are emitted almost in phase. The phase-locked harmonics covering a broad bandwidth are produced, and then a regular attosecond pulse train with the pulse duration less than 100 as is generated.
2007, 56 (11): 6629-6633.
doi: 10.7498/aps.56.6629
Abstract +
Hall measurement with Van der Pauw method and the Capacitance-Voltage(C-V) characteristics method are performed on AlGaN/GaN heterostructures with different Al contents grown on sapphire substrates by metalorganic chemical vapor deposition. It is found that the value of sheet carrier density obtained from Hall measurement is larger than that deduced from C-V carrier density profile, and both values, as well as the difference between them increase with increasing Al content. This result is ascribed to two reasons. On the one hand, Ni/Au Schottky contact deposited on AlGaN/GaN heterostructure changes the surface states of the AlGaN barrier layer. Some electrons in the two-dimensional electron gas (2DEG) are extracted to the void surface donor states, and consequently the 2DEG sheet carrier concentration is reduced. And with the Al content increasing, the more the surface states of the AlGaN layer, the more the electrons are extracted to the void surface donor states. On the other hand, the precision of C-V measurement is influenced by the series resistance, which causes underestimation of the magnitude of the depletion-layer capacitance and hence the carrier concentration.
2007, 56 (11): 6634-6641.
doi: 10.7498/aps.56.6634
Abstract +
Retention characteristics of SONOS non-volatile memory (NVM) device is expected to be improved by doping silicon nitride to change the type and number of defects which traps charge. Firstly, cluster models of defects in amorphous silicon nitride with and without doping special element, such as oxygen, sulfur, phosphorus, fluorine or chlorine, are built. By density functional theory (DFT) of first-principles, positions of all atoms of the cluster are optimized, and energiesof these clusters are calculated. Energy changes of charge capturing processes for various defects are obtained. The calculational data can provide references for investigating discharge mechanism and improving charge retention on nonvolatile memory device. The capability of capturing electrons for all defects is usually better than capability of capturing holes. The electron discharge process should be sensitive to temperature, but the hole discharge process may be mainly controlled by tunneling mechanism. Like silicon oxynitride, silicon nitride doped with sulfur or phosphorus is promising for improving charge retention characteristics of SONOS device, due to more defects having better capability of capturing electrons.
2007, 56 (11): 6642-6647.
doi: 10.7498/aps.56.6642
Abstract +
By introducing a new term into the traditional Rose-Fowler-Vaisberg model, The exponential relationship between radiation induced conductivity and dose rate is explained. The evolution of radiation induced conductivity under different radiation conditions are also analyzed. The result indicates that dose rate mainly changes the magnitude of radiation induced conductivity while the long-time decay of radiation induced conductivity is determined by carrier recombination rate of the material.
2007, 56 (11): 6648-6653.
doi: 10.7498/aps.56.6648
Abstract +
A two-dimensional (2D) metal (Copper) sphere array is designed for the optical coupling of 9.5μm long-wavelength quantum well infrared photodetectors (LW-QWIPs). The optical coupling is studied based on Huygens' principle. It was shown that a metal sphere array with 3μm period and 0.9μm radius can reach optimal optical coupling for the 9.5μm LW-QWIPs. The maximal quantum efficiency hits 66%, which is highly superior to the conventional 45° angle coupling. The theoretical results provide detailed guidelines for 2D metal sphere array optical coupling for 9.5μm LW-QWIPs.
2007, 56 (11): 6654-6659.
doi: 10.7498/aps.56.6654
Abstract +
This paper presents a comprehensive study of the effect of heavy B doping and strain in Si1-xGex strained layers. On the one hand, bandgap narrowing (BGN) will be generated due to the heavy doping, on the other hand, the dopant boron causes shrinkage in the lattice constant of SiGe materials, thus will compensate for part of the strain. Taking the strain compensation of B into account for the first time and uesing the with semi-empirical method, the Jain-Roulston model is modified. And the real BGN distributed between the conduction and valence bands is calculated, which is important for the accurate design of SiGe HBTs.
2007, 56 (11): 6660-6665.
doi: 10.7498/aps.56.6660
Abstract +
An analytical model for the surface electrical field distributions of double RESURF devices with Gaussian-doped P-top region is presented. Based on solvisng the 2-D Poisson equation, the model gives the closed form solutions of the surface potential and electrical field distribution as functions of the structure parameters and drain bias. The dependence of breakdown voltage on drift region length and thickness is calculated. An effectual way to get the optimum high-voltage devices is also proposed. All analytical results are well verified by simulation results obtained by MEDICI and previous experimental data, showing the validity of the presented model.
2007, 56 (11): 6666-6673.
doi: 10.7498/aps.56.6666
Abstract +
Na+-doped and compositional graded doped Ba0.25Sr0.75TiO3 thin films were grown on Pt/Ti/SiO2/Si substrates by Sol-Gel technique. The dielectric properties of thin films were investigated as a function of Na+ doping level. It is revealed that with the increase of Na+ concentrations both the dielectric constant and the loss decrease continuously while the leakage current initially decreases (Na+< 2.5mol%) and then increases. The increase of leakage current may be caused by the formation of porous structure which was confirmed by field emission scanning microscopy (FE-SEM). The improvement of overall dielectric properties were achieved by using the compositional graded doping which results in a better microstructure in the film.
2007, 56 (11): 6674-6679.
doi: 10.7498/aps.56.6674
Abstract +
Based on fractal theory , through the fractal dimension of electro-diffusion, the dimensions of noise time series and grain boundary are corelated. The change of noise dimension is shown to be useful for studying the damage mechanism and determining the parameters for electromigration. The picture of grain boundary becomes complicated in the early period of electromigration, but after the voids are informed, it becomes more regular. So the fractal dimension of time series increases during the early stage of electromigration and goes down after the voids are informed. The theoretical analysis is confirmed by experiment, the dimension of noise time series may be a new characteristic parameter for metallic interconnection electromigration.
2007, 56 (11): 6680-6684.
doi: 10.7498/aps.56.6680
Abstract +
Appling the in situ powder-in-tube method, 11 meter long Fe-sheath MgB2 superconducting wires with outer diameter 1.75mm were fabricated, using 99.5% Mg powder and 99.9% amorphous boron powder doped with 30 nm SiC powder as starting materials. This procedure begins with ball-milling of the mixture powder immersed in acetone solution in a jar and subsequently drying in vacuum. Then the iron tube loaded with the powder mixture was grooved, swaged and drawn to the final wire size. The transition temperature, microstructure, lattice constant and chemical element distribution were evaluated by SQUID, XRD, SEM and EDS, respectively. It was found that TC(onset) and ΔTC are 35.1K and 5.3K, respectively. All samples containing a small amount of MgO, exhibit rather uniform microstructure. Besides, by nano-SiC doping, the MgB2 lattice distortion due to substitution of boron by carbon, results in forming effective flux pining centers, which significantly improves the critical current, and the C element was uniformly distributed in the MgB2 matrix. The standard four_probe measurement shows that all the 10 sample points, which were evenly cut at 1 meter intervals of the 11 meter length wire, have good superconducting homogeneity with critical current values fluctuating within 10% under the applied fields vavying from 10 to 18 Tesla, and all Jc values are above 104A/cm2, with the highest value reaching 1.2×104A/cm2 at 4.2K and 10T.
2007, 56 (11): 6685-6690.
doi: 10.7498/aps.56.6685
Abstract +
The photoluminescent and electroluminescent characteristics of a blend polymer system consisting of a novel fluorene-carbazole copolymer (PFC) and poly(vinylcarbazole) (PVK) were investigated. Three OLED devices with the structures of indium-tin-oxide (ITO)/PVK:PFC/bathocuproine(BCP)/tris-(8-hydroxylquinoline)-aluminum (Alq3)/Mg∶Ag, indium-tin-oxide(ITO)/PFC/bathocuproine(BCP)/Alq3/Mg∶Ag and indium-tin-oxide(ITO)/PVK/ bathocuproine(BCP)/Alq3/Mg∶Ag respectively, were fabricated. The optoelectronic properties of the devices were measured. The results demonstrated that PVK in the blend system effectively restrained the formation of PFC excimers in solid films. Light emission of the device with blend system shifted with the variation of applied electric field, and variable color ranging from green to blue could be obtained. The luminance of blue light reached 1650cd/m2 when the drive voltage was higher than 7V. It was inferred that an energy transfer process from PVK to PFC might have occurred in this blend system.
2007, 56 (11): 6691-6694.
doi: 10.7498/aps.56.6691
Abstract +
Plasma enhanced chemical vapor deposition (PECVD) was used to prepare a-Si:H/SiO2 multilayers. Two-step thermal annealing was then used to transform them into nc-Si/SiO2 multilayers. The size of formed nc-Si (about 4nm) can be controlled and room temperature visible photoluminescence was observed from the annealed samples with the peak located at 750nm. Moreover, we found that annealing in hydrogen can enhance the PL intensity of the materials. The electron paramagnetism resonance (EPR) suggested that annealing in hydrogen atmospheye effectively reduces the nonradiative recombination sites existing in the nc-Si and results in the enhancement of the luminescence efficiency.
EDITOR'S SUGGESTION
2007, 56 (11): 6695-6700.
doi: 10.7498/aps.56.6695
Abstract +
Superposed-neutral-atom model and the finite-difference method (SNA-FD) is used to calculate the positron annihilation lifetime in single-walled carbon nanotube bundles with different diameters in a large range. We find that in single-walled carbon nanotube bundles，the main area where positron annihilation takes place，the main object that positron annihilates with, as well as the positron annihilation lifetime change regularly as the diameter of single-walled carbon nanotube bundles changes. The positron annihilation lifetime in single-walled carbon nanotube bundles with diameter between 0.8—1.6nm is calculated to be 332—470ps. It agrees well with the experimental result of 394ps.
2007, 56 (11): 6701-6704.
doi: 10.7498/aps.56.6701
Abstract +
Carbon nanotube field emission display has been regarded as one of the most promising flat panel displays due to its unique advantages. The morphology of the cathode material composed of the nanotubes will directly affect the field emission display properties. In this paper, we used single-walled carbon nanotubes synthesized by arc discharge method as the cathode material. This material was printed onto the conducting surface of the cathode plate using a screen-printing process. We studied the field emission properties of the cathode and the brightness of the green phosphor also screen printed on the anode. The display unit exhibited good field emission properties. The single-walled nanotube cathode was shown to have low turn-on voltage and high field emission current density.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2007, 56 (11): 6705-6711.
doi: 10.7498/aps.56.6705
Abstract +
Carbon nanotubes/nanofibers (CNTs) were grown on sodalime glass by low temperature chemical vapor deposition. The catalytic films were pre-patterned using screen-printing method, combined with filtered cathodic vacuum arc or ion beam sputtering. The effect of different catalysts on the CNT growth and field emission were investigated. For samples catalyzed with a-C:Co, Ni-Cu or Cu, no CNTs are formed, and they show no field emission below the applied field of 4.4V/μm. For samples catalyzed with Ni-Fe or Ni-Cr, large amounts of entangled CNTs are successfully obtained and exhibit good electron emission, having a turn-on field as low as 2.5V/μm. The process, due to its simplicity and relatively low growth temperature, is promising for practical application in field emission display.
2007, 56 (11): 6712-6716.
doi: 10.7498/aps.56.6712
Abstract +
Highly ordered metal Sn nanodot arrays were prepared by vacuum electron beam evaporation using porous anodic alumina (PAA) membrane as the substrate. They were characterized by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). SEM images indicated that the Sn nanodot arrays are highly ordered and coincid with the contours of porous anodic alumina. The shape of Sn nanodot is spherical and the diameter approximates the pore diameter of the PAA membrane. XRD showed that crystallographic structures of Sn nanodot arrays are the same as the bulk Sn. The forming process and mechanism of the Sn nanodot array was discussed.
2007, 56 (11): 6717-6721.
doi: 10.7498/aps.56.6717
Abstract +
High quality AlGaN materials used in the DBR structure of ultraviolet detector are grown under different growth conditions. The structure, composition and photographic characteristics are determined by XRD, SEM and AFM. The influence of the growth conditions on the characteristics of the AlGaN materials are discussed.The good performance of the DBR structure of ultraviolet detector is obtained.
2007, 56 (11): 6722-6726.
doi: 10.7498/aps.56.6722
Abstract +
In this paper, a new in situ method was developed for characterizing the kinetics of the oxidation process of copper thin films by using sheet resistance. Copper thin films were prepared on glass substrate by vacuum deposition. The oxidation kinetics of the copper thin films was studied via sheet resistance which increased during the process. The results suggested that this new method can be applied to the characterization of the reaction kinetics of copper thin film.
2007, 56 (11): 6727-6735.
doi: 10.7498/aps.56.6727
Abstract +
The characteristics of methane hydrate dissociation in the presence of thermal stimulation, chemical injection, and thermal stimulation in conjunction with chemical injection method were investigated by molecular dynamics simulation. The effect of the injection of liquid water (WTR) and 30wt% ethylene glycol (EG) solution at 277K and 340K on methane hydrate dissociation was studied. The results showed the hydrogen bonds between WTR molecules and the water molecules on the hydrate surface were formed，which destroyed the original hydrogen bond balance of the hydrate. Therefore, the clathrate structure of hydrate collapsed, and the hydrate dissociated. The hydrogen bonds was formed obviously between hydroxyl groups of EG molecules and the water molecules on the hydrate surface; this caused the original stable clathrate structure of the hydrate to be destroyed and collapse, and, furthermore, promoted the dissociation of the methane hydrate and the release of methane gas. Compared with the effects of injecting WTR and 30wt% EG solution at 277K and 340K on the dissociation of methane hydrate, the effectivences was found to be: EG(340K)> WTR(340K)>EG(277K)>WTR(277K). The thermal stimulation in conjunction with chemical injection method can more effectively promote the dissociation of hydrate.
2007, 56 (11): 6736-6741.
doi: 10.7498/aps.56.6736
Abstract +
A fractal shape model was used to simulate the morphology of fire smoke particles, as the aggregated spherical particles have intrinsical fractal structures. The shape model, whose parameters, including the total number of primary spherical particles in an aggregate, the fractal dimension and the radius of the primary particles, were obtained from a sequence of SEM images, was considered to be compatible with the smoke particle shape. The shape model was then used to compute the light scattering of smoke particles, and the results showed that, compared with the spherical particle with the same volume and other optical parameters, the fractal-like aggregate has smaller forward scattering and larger backward scattering.
2007, 56 (11): 6742-6748.
doi: 10.7498/aps.56.6742
Abstract +
Three-dimensional flame temperature distribution reconstruction in furnace according to the flame radiative energy images captured by CCD cameras was studied. Temperature reconstruction matrix equation is an ill-posed linear system of equations and the reconstruction problem is an ill-posed problem. Truncated singular value decomposition method (TSVD) was introduced to deal with the ill-posed matrix equation and L-curve method was adopted to choose regularization parameter. Singular value decomposition (SVD) and discrete Picard condition were used to analyze the ill-posed characteristics of the reconstruction problem carefully. The results show that reasonable solutions can be obtained by TSVD and the reconstructed temperature distribution can reproduce the feature of the assumed temperature distribution.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2007, 56 (11): 6749-6753.
doi: 10.7498/aps.56.6749
Abstract +
Physical model was established to describe the broadband pulsed laser amplification processes. In this model, Cross relaxation was introduced to study the transformation of homogeneous and inhomogeneous population inversion after laser passage. Hybrid-widened linewidth, homogeneity and inhomogeneity were emphatically considered, which were had not been take into account in other models. Based on the physical model, computer simulation software CPAP for broadband pulse laser amplification process was developed. At last, we discussed the possibility that this broadband physical model can be transfered to the narrow_band physical model under certain conditions.
2007, 56 (11): 6754-6759.
doi: 10.7498/aps.56.6754
Abstract +
Based on the extended Huygens-Fresnel principle, the propagation formulas for Bessel-correlated partially coherent hollow beams in a turbulent atmosphere has been derived, then the propagation properties of such beams in the turbulent atmosphere have been investigated in great detail. The results indicate that the turbulent atmosphere, the spatial coherence and the beam width play important roles in the beam propagation.
2007, 56 (11): 6760-6766.
doi: 10.7498/aps.56.6760
Abstract +
One of the basic capabilities of cognitive radio is to adapt the radio parameters according to the changing environment and user needs. A cognitive radio decision engine based on quantum genetic algorithm is proposed, in which the radio parameters are adapted and optimized by quantum genetic algorithm. The multiple objective functions are designed and multi-carrier system is used for performance analysis. Experimental results show that the proposed method has better convergence, precision and stability than the classic genetic algorithm, and the good performance of the proposed method in small population size illustrates that it is suitable for hardware implementation. Simulation results under different weighting scenarios illustrate the trade-off between multiple objective functions and that the adapted parameter configuration is consistent with the weights of the objective functions.
2007, 56 (11): 6767-6771.
doi: 10.7498/aps.56.6767
Abstract +
Considering a Gibbons-Maeda dilaton black hole and a Garfinkle-Horowitz-Strominger dilaton black hole, the effect of space noncommutativity on black hole thermodynamics is investigated. By comparing the Gibbons-Maeda dilaton black hole in commutative space with the Garfinkle-Horowitz-Strominger dilaton black hole in noncommutative space, it has been concluded that the noncommutativity of the space has an effect on Garfinkle-Horowitz-Strominger dilaton black hole similar as has the electric or magnetic charge in Gibbons-Maeda dilaton black hole.
2007, 56 (11): 6772-6776.
doi: 10.7498/aps.56.6772
Abstract +
Using the Tortoise coordinate transformation and the Dirac field equation near the event horizon, the Hawking temperature of Kinnersley black hole is obtained. Meanwhile, adopting thin film brick-wall model, the entropy of Kinnersley black hole is calculated. The entropy near the event horizon is shown to be the entropy of black hole by regulating the cut-off parameter and the thin film's thickness properly. The results show that the entropy of the black hole is proportional to the area of the event horizon.
