Vol. 63, No. 19 (2014)
2014-10-05
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2014, 63 (19): 194209.
doi: 10.7498/aps.63.194209
Abstract +
Based on the fact that Bragg reflection grating (BRG) is a special case of one-dimensional photonic crystal, we may apply the one-dimensional photonic crystal band gap theory to design the BRG. OptiFDTD is used to simulate both the width error and tilt angle error in BRG. It turns out that the diffraction efficiency will stay high at the 10% width error or the 10° tilt angle error of the Bragg grating. These indicate that the BRG has a high fabrication tolerance. One model of a Bragg diffraction double-grating in the Rowland circle structure is proposed based on the one-dimensional photonic crystal band gap theory for achieving the two-band spectral diffraction. Result shows that the diffraction efficiency of the two incident bands can be as high as 70% when the first set of Bragg grating periods is 6 layers while the second is 10. It is significantly higher than the traditional deeply etched diffraction grating. This is the foundation of a new type of EDG-WDMer with its advantages being of small size and high diffraction efficiency. It may have great potentiality for developing high diffraction efficiency dense wavelength division multiplexer in the future.
2014, 63 (19): 194704.
doi: 10.7498/aps.63.194704
Abstract +
Bionic micro-fluidic driving model is built in this paper based on the velocity source immersed boundary-lattice Boltzmann method. In order to avoid the transformation between the velocity and the force, this method introduces an immersed boundary into the lattice Boltzmann equation as the velocity source, which can reduce the computational expense. Firstly, the effects of the traveling waves produced by the elastic filament on the velocity and pressure of the flow field are studied. Secondly, the paper focuses on the influences of parameters on the flow rate. Results show that the flow rate increases with increasing frequency, wave amplitude, and filament length. Relationships between the flow rate and the other parameters of the model, such as the position of filament, wavelength, and kinematic viscosity of the fluid, are shown to be nonlinear and complicated.
2014, 63 (19): 194702.
doi: 10.7498/aps.63.194702
Abstract +
Performance of a two-electrode plasma synthetic jet actuator has been experimentally studied by discharge measurements with high-speed shadowgraphy technology. Results show that the breakdown voltage and the peak discharge current of the actuator may be decreased by decreasing the ambient pressure and increasing the discharge frequency. The discharge developed in the actuator cavity is a spark-arc discharge. In the actuator could be created a strong “precursor shock” and a high kinetic energy jet. During the development of the plasma synthetic jet, the speed of the “precursor shock” is invariable and the jet propagates with an approximately local sonic velocity (350 m/s). But with decreasing jet exit diameter and ambient pressure, the increase of the cavity volume and the discharge frequency could lead to decreasing strength of the “precursor shock”. Heating efficiency of the gas in the cavity will decrease with the increase of the cavity volume and discharge frequency, and the jet velocity is decreased as well. The jet exit diameter and the ambient pressure can have their optimal values for affecting the velocity of the jet. Under all the working conditions we have studied, the plasma actuator may create a strong “precursor shock” and a high-speed jet, and also may have the potential to be used in high-speed active flow control.
2014, 63 (19): 194204.
doi: 10.7498/aps.63.194204
Abstract +
Considering a gain-noise model for two-mode laser system driven by a periodic signal and two-color cross-correlation noises, we calculate the power spectrum and signal-to-noise ratio (SNR) of an output signal by means of linear approximation method, and discuss the influence of the system coefficients on SNR. Results show that under a certain condition satisfied by the coefficients of the system and input signals, the stochastic resonance phenomenon may be detected in the evolution of SNR, and also at certain intensities of noise, saturation coefficient c2, cross coupling coefficient b, and input signal frequency Ω.
2014, 63 (19): 194203.
doi: 10.7498/aps.63.194203
Abstract +
The intensity noise in a 1560 nm single frequency fiber laser after passing through an optical mode cleaner is analyzed both theoretically and experimentally. Experimental measurement shows that in addition to the evident suppression of intensity noise by the mode cleaner, there exist induced observable periodic fluctuations in the analyzing frequency range of 2 to 12 MHz, as well as the amplification of the intensity noise at low frequencies. The above results cannot be explained by the present mode cleaner model for noise suppression. In this paper, we propose a new theoretical model, in which the mode cleaner is considered equivalent to a delay line and through it the phase-noise of the fiber laser is partially converted to the intensity noise. The phase-induced relative intensity noise (RIN) amplitude is jointly determined by the laser linewidth, the mode cleaner linewidth, and the analyzing frequency. The theoretical analysis shows a very good agreement with the experimental results. The noise suppression effect of the acoustic optical modulator is further analyzed by inserting it into the setup and providing a frequency modulation for it. We have observed an evident improvement of the mode cleaner locking, while the bandwidth of the laser is slightly suppressed from 26 to 16kHz, and the degradation of the measured intensity noise after the mode cleaner is also moderate. The theoretical analysis according to our proposed model fits well with this result. This result further confirms that the phase-induced intensity noise has no direct connection to the mode cleaner locking quality. Through the above analysis, a complete theoretical mode for analyzing the noise suppression by a mode cleaner is built.
EDITOR'S SUGGESTION
2014, 63 (19): 194208.
doi: 10.7498/aps.63.194208
Abstract +
Supercontinuum generation has received extensive attention because of the innovation of high nonlinear fiber, which makes the supercontinuum system more simple, compact, and efficient. Nonlinear effects are enhanced greatly during the strong interaction between the light and matter in high nonlinear fiber, and the spectrum will be broadened effectively. In this paper, we demonstrate the supercontinuum generation in a photonic crystal fiber and a conventional tapered single-mode fiber pumped by the mode-locked Yb fiber laser. Through the experimental comparison of the supercontinuum spectrum between two kinds of the high nonlinear fibers, the spectral flatness, Raman perturbation, and dispersion wave radiation are discussed for studying the characteristics of supercontinuum generation. Finally, the octave supercontinuum-based both kinds of high nonlinear fibers could be achieved. In particular, the employment of tapered single-mode fiber is proven to be an appropriate candidate for supercontinuum generation and further application.
2014, 63 (19): 194301.
doi: 10.7498/aps.63.194301
Abstract +
By taking into account the macroscale nonlinear effect, quadratic and cubic microscale nonlinear effects, and microscale dispersion effect, a new model capable to describe the longitudinal wave propagation in one-dimensional microstructured solid is established based on the Mindlin theory. Using the qualitative analysis theory in the planar dynamical systems, we have analyzed the existence conditions and geometrical characteristics of solitary waves, and proved that the faces under the influence of quadratic microscale nonlinear effect, can form an asymmetric solitary wave in the microstructured solid; and under the influence of cubic microscale nonlinear effect, they can form a symmetric solitary wave in the microstructured solid, when the medium parameters and the propagation speeds of solitary waves satisfy certain appropriate conditions. Finally, the above results are further verified using a numerical method.
2014, 63 (19): 194201.
doi: 10.7498/aps.63.194201
Abstract +
For the needs of online nondestructive testing method in glass industry, we have presented a large-range line-field parallel spectral domain optical coherence tomography system. Based on fast area scan CMOS camera, the whole cross-sectional image can be acquired by a single shot. Depth-resolved image at different lateral positions can be acquired simultaneously, without the lateral scanning mechanism. The axial resolution is 17.9 μm, the lateral resolutions in parallel direction and scanning direction are 55.7 μm and 24.8 μm, respectively. The system measurement range is 32 mm in lateral direction and 6 mm in axial direction. At 1 mm axial position, the system sensitivity can reach 62 dB at a rate of 128 000 A-scan/s. By using the present system, application in glass defect inspection has been investigated.
2014, 63 (19): 194305.
doi: 10.7498/aps.63.194305
Abstract +
In order to reconstruct the sound field of target sources in non-free sound field, a method of sound field separation and reconstruction is presented based on spatial resampling with single layer microphone array. In this method, the spherical harmonics are taken as the basis functions, and the spherical harmonics of different orders are added to describe the mathematical model of the sound field. On the basis of the nearfield acoustic holography, the coefficients of the basis functions can be obtained with two groups' sound pressures resampled from the microphone array, then the sound fields generated by the sound sources on both sides of the microphone array are separated. The mathematical model is validated against the benchmark values. A non-free sound field with a radially oscillating sphere and a transversely oscillating rigid sphere is built, and the impact of various parameters such as the signal to noise ratio, the geometric shape and area of the microphone array, location of target sound source, and frequency of signals on the accuracy of separation is examined. Finally, some suggestions are given for the industrial application of the above method.
2014, 63 (19): 194402.
doi: 10.7498/aps.63.194402
Abstract +
How to control and manipulate the heat flow in a flexible way is a hotspot of current research. Based on Laplace's equation, we propose a method to design thermal cloak of arbitrary shape. For a thermal cloak of regular shape, the thermal conductivity expression is derived by analytically solving the Laplace's equation under certain boundary conditions; for a thermal cloak of irregular shape, the distribution of thermal conductivity can also be obtained based on the numerical solution of Laplace's equation. Results of full wave simulation show that no heat fluxes emerge in the internal stealth area both for two-dimensional and three-dimensional thermal cloak of arbitrary shape. Meanwhile, the heat fluxes return to their original pathways, resulting in a perfect thermal invisible effect. This research provides a feasible method to design a thermal cloak of non-conformal cross section and has a guiding significance for the design and manufacturing of thermal cloak.
2014, 63 (19): 194302.
doi: 10.7498/aps.63.194302
Abstract +
In this paper, PM (Preisach-Mayergoyz) model in one dimension is extended to two dimensions. Hysteretic stress-strain relation could be obtained when hysteretic mesoscopic elastic unit (HMEU) is considered.The sound field is calculated using a first-order finite difference equation, and the high-odd-order harmonic waves can be found apparently in the sound field. Then, the received full waves are filtered,amplified, time-reversed, and re-emitted through corresponding receiving transducers. The high-order harmonic waves focus on the micro-damage zone. So this method can be used to detect the micro-damages by nonlinear high-order harmony waves. Furthermore, it also provides a method of the early detection of fatigue damages.
2014, 63 (19): 194202.
doi: 10.7498/aps.63.194202
Abstract +
We have made a low scattering holographic polymer dispersed liquid crystal (HPDLC) transmission grating with polymer scaffolding morphology, which was fabricated under the condition of low curing intensity and no liquid crystal droplet. We studied the amplified spontaneous emission (ASE) thresholds and relative intensities of PM567(4, 4-difluoro-1, 3, 5, 7, 8-pentamethyl-2, 6-diethyl-4-bora-3a, 4a-diaza-s-indacene), DCM (4-Dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran), and DCJTI(4-dicyanomethylene)-2-isopropyl-6-(1, 1, 7, 7-tetramethylzulolidyl-9-enyl)-4H-pyran). It is shown that the dye DCJTI has the best properties of ASE, the lowest threshold and the highest relative intensity among the three dyes. Results suggest that DCJIT is a promising material for low threshold, high slope efficiency lasers. Each dye was doped in HPDLC grating with polymer scaffolding morphology individually, and lasers with different wavelengths can be obtained by changing the period of the gratings. The excellent laser property is obtained from the DCJIT-doped laser. A spectral linewidth of 0.3 nm is observed at pump energy threshold 0.65 J/pulse and a conversion efficiency of 1.6% is achieved at the operating wavelength 635 nm. The laser performance is improved in some aspects such as threshold energy, conversion efficiency, and linewidth to some extent as compared with those reported previously.
2014, 63 (19): 194303.
doi: 10.7498/aps.63.194303
Abstract +
To explain the change of the waveguide invariant β caused by the internal wave, the waveguide invariant is expressed as a stochastic distribution and the time-varying characteristics of β are analyzed; then the cause and principle of variation of β are discussed in terms of the normal modes theory of the acoustic field. It turns out that the waveguide invariant shows great frequency-dependent characteristics. And in the internal wave environment, when the sound is propagated parallel to the internal wave front, the sound field's composition of normal modes remains unchanged, but the turbulence in the group slowness and phase slowness of the main normal modes in the sound field may also change the distribution of β; when the sound is propagated perpendicular to the internal wave front, the coupling between acoustic normal modes might also cause obvious changes in the values of β.
2014, 63 (19): 194206.
doi: 10.7498/aps.63.194206
Abstract +
The frequency entangled biphoton source generated via spontaneous parametric down-conversion (SPDC) process has found important applications in the fields of quantum clock synchronization, quantum communication, quantum information processing, etc. As quantum technologies evolve, quantitative characterization of the frequency entanglement becomes necessary and has been implemented by measuring the spectral properties of the biphoton state. However, due to the high dark rate and low quantum efficiency of the InGaAs single-photon detectors, direct measurement of the spectral properties of the biphoton state at optical communication wavelength is hard to implement. In this paper, we report the measurement of the spectral properties of a biphoton state at optical communication wavelength which is generated from periodically poled potassium titanyl phosphate (PPKTP) pumped by an ultra-short pulsed optical source at 787 nm. Based on the coincidence measurement setup together with two infrared spectrometers, the spectra of the signal and idler photons are obtained with their center wavelengths being 1574.4 nm and 1574.9 nm, while their 3-dB bandwidths being 35.3 nm and 37.6 nm respectively. The joint spectrum of the photon pair is observed as well and shows a coincident-frequency entanglement and a joint spectrum bandwidth of 3 nm. According to the ratio of the single-photon spectral bandwidth to the joint spectral bandwidth of the photon pairs, the degree of frequency entanglement is quantified to be 12, denoting a relatively high quality of the entanglement.
2014, 63 (19): 194703.
doi: 10.7498/aps.63.194703
Abstract +
A strong coupling effect between the bubble and water occurs when an explosive bubble expands and contracts near the water surface, leading to the complex changes of the flow field and various shapes of water plumes. An experimental system for small equivalent of charge RDX is designed to investigate the relations between the shapes of water plumes and the changes of the flow field. Two synchronized high speed cameras are used to record the changing process of the shapes of bubbles and water plume. Three typical shapes of bubble and six typical shapes of water plumes are observed. By theoretical analysis and direct observation of flow field changes among the bubble, the water surface, and the air, the evolution rule and formation mechanism of the six shapes of water plumes are allready revealed. Experimental results are also compared with that from the experiment of bubbles formed by electric spark. Through statistical analysis of bubble radius, expansion time, pulsation period, and bubble boundary movement, the dynamic process of bubble formation in near water surface explosion is clarified.
2014, 63 (19): 194102.
doi: 10.7498/aps.63.194102
Abstract +
An ultra-wideband (UWB) microwave robust Capon beamforming imaging system is presented based on a self-designed compact UWB antenna for early breast cancer detection. Simulation results show that the proposed detection system is sensitive to tumor response. Simulated tumor detection experiments are carried out in both simple planar breast model and magnetic resonance imagining (MRI)-derived model using the antenna array. Robust Capon beamforming algorithm is employed to reconstruct the breast image. Successful detection of 3-mm-diameter tumor is achieved in the planar model and the same detection result of 4-mm-diameter tumor is achieved in the MRI-derived model. The right information of the tumor can be obtained from the imaging results, which demonstrates the feasibility of the proposed system in early breast cancer detection.
2014, 63 (19): 194401.
doi: 10.7498/aps.63.194401
Abstract +
In this paper, based on the hyperbolic equation of heat conduction, utilizing the image method and the wave function expansion method, the temperature distributions on the surface of a functionally graded material(FGM) containing a cylindrical inclusion are investigated. According to the model of thermal waves, a general solution of scattered fields of thermal waves is obtained. Effects of different physical parameters (such as the depth of buried inclusion, the thermal conductivity, the thermal diffusion length, the thermal diffusivity, and the thermal relaxation time) on the distribution of temperature are analyzed. The thermal waves are excited on the surface of the FGM by a periodically modulated laser. A cylindrical defect is taken as an inclusion under a thermal conduction condition. Results are expected to provide calculation methods and reference data for infrared thermal wave nondestructive evaluation of an FGM and the inverse problems in mathematical physics.
2014, 63 (19): 194103.
doi: 10.7498/aps.63.194103
Abstract +
Due to its attractive features such as compact size, simple to align and wide working range of photon energy, the X-ray compound refractive lens (CRL) has gradually become one of the standard accessories to focus the X-ray beams from the synchrotron radiation light source. In this paper, a cascaded planar parabolic CRL is designed and fabricated. The novel CRL is composed of type Ⅰ and type Ⅱ refractive elements in order to achieve a small spot size while maintaining the transmission. In type I refractive element, the parabolic geometry aperture (R0) is large, while, in type Ⅱ refractive element, the radius of curvature (R) at the parabolic vertex is small. So N1 numbers of type I and N2 numbers of type Ⅱ refractive elements are cascaded to form a single-chip CRL. A cascaded X-ray planar parabolic CRL is constructed using PMMA material by means of LIGA techniques. The main structural parameters of type Ⅰ refractive elements are: N1=15, R1=200 μm, 2R01=564 μm. The main structural parameters of type Ⅱ refractive elements are: N2=20, R2=50 μm, 2R02=140 μm. The cascaded planar parabolic CRL is tested on the beam line whose original incident X-ray spot is 200 μm×100 μm at Shanghai synchrotron radiation facility. The measured lateral focusing spot size is 24.9 μm@8 keV, the transmission rate is 2.19% and the focal length is 1.052 m.
2014, 63 (19): 194101.
doi: 10.7498/aps.63.194101
Abstract +
This paper has built the one-dimensional model of the time-varying un-magnetized plasma, and the finite different time domain (FDTD) algorithm is used to calculate the reflection and transmission coefficients, as well as the absorption rate of terahertz (THz) electromagnetic waves in time-varying plasma. The relation between the frequency of the THz wave and the propagation characteristic influenced by rise time, electron density, temperature, and depth of time-varying plasma plate is analyzed. Results demonstrate that the reflection coefficient is mainly influenced by plasma rise time and electron density. The absorption rate increases with decreasing rise time, increasing depth and electron density. Furthermore, the THz electromagnetic wave is an effective tool for the communication of reentry vehicle and high density plasma diagnosis because of its strong penetrability in high density plasma.
2014, 63 (19): 194701.
doi: 10.7498/aps.63.194701
Abstract +
To research the effect of pulsation flow on anti-thrombosis, the plasma is treated as water, and the red blood cells are regarded as suspended rigid particles having the same density as water. First, an appropriate embolism is formed in a tapered pipe under a certain hematocrit and differential pressure, and then a pulsating flow is exerted on the inlet of the tapered pipe to study the positive effect on anti-thrombosis of the pulsating flow.
2014, 63 (19): 194304.
doi: 10.7498/aps.63.194304
Abstract +
Single-carrier frequency domain equalization (SC-FDE) has drawn increasing researches because of its lower computational complexity and better performance of mitigating intersymbol interference (ISI) as compared with the time domain equalization. The practical SC-FDE systems, however, require the knowledge of the channel frequency domain response and the noise power to calculate filter coefficients of the frequency domain equalizer. Improper channel and noise estimations have been shown to result in error floor at high signal-to-noise ratio (SNR), which may impede the utilization of SC-FDE in the high-rate underwater acoustic (UWA) communications. In this paper, we discuss the possible influence of inaccurate noise estimation on the error floor at high SNR, and propose a joint estimation scheme for the channel time domain and frequency domain responses and also the noise power based on Chu sequence. The channel energy concentration region is determined by the threshold and the sparse channel impulse response (CIR) of UWA channels, used in denoising process of the CIR and the noise power computation. The bite error ratio performance of the SC-FDE variation versus the threshold is simulated via the UWA models, and accurate noise power estimation is shown to be desirable to improve the SC-FDE performance. Numerical examples also indicate that our joint estimation scheme can eliminate the error floor and improve the performance of SC-FDE at high SNR.
2014, 63 (19): 194205.
doi: 10.7498/aps.63.194205
Abstract +
In order to study the thermal and stress fields in the multilayered structure of silicon-based positive-intrinsic-negative(PIN) photodiode irradiated by millisecond(ms)-pulsed laser, we use the thermal elasto-plastic constitutive theory and the equivalent specific heat method, to deal with the phase change latent heat. The multiple-heat-source, especially the influence of reflection from bottom-aluminum-electrode, and the effect of the nonlinearity of material parameters are taken into consideration. A 2-D simulation model is built by means of the finite element simulation software of COMSOL Multiphysics. The surface and the internal each layer showing changes of the transient distribution and evolution of the thermal and stress fields with space and time can be obtained. Because of taking account of the reflection of the aluminum electrode, the temperature of the aluminum electrode rises slightly. On this basis, we analyze the hard failure mechanism of ms-pulsed laser irradiated silicon-based PIN, and the mechanical damage before melting that leads to a malfunction of silicon-based PIN detector.
2014, 63 (19): 194207.
doi: 10.7498/aps.63.194207
Abstract +
To improve the phase accuracy of the reconstructed image of the digital hologram, we investigate the theory and method of the phase reconstruction based on the Hilbert transform, then, verify it by the image plane digital holographic experiment, and finally, compare it with the conventional digital holographic reconstruction method. Results show that Hilbert transform itself posseses the effect of eliminating DC term, therefore the effect of the zero-order frequency spectrum of the hologram which is filtered by frequency domain can be completely eliminated by Hilbert transform. Compared with the conventional Fourier reconstruction mehtod, the accuracy of the phase image can be improved by the reconstruction method based on Hilbert transform, and the standard deviation of the phase image is reduced by 14% in the experiment of red blood cell. This result has an important guiding significance to improve the accuracy of the digital holographic phase reconstruction.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2014, 63 (19): 198801.
doi: 10.7498/aps.63.198801
Abstract +
In this paper, the influence of different front and back grating period ratio on the optical absorption property of a dual-grating structured thin film solar cell is analyzed using finite difference time domain method. Grating height, fill factor, and thickness of silicon layer are optimized, and the resonance modes that contribute to the absorption enhancement are studied. Results show that light leakage effect exists in the conformal grating structure with grating period ratio of 1:1, the structure with grating period ratio deviating from 1:1 suppresses the light leakage from the silicon active layer. The effective excitation and propagation of waveguide modes in the silicon active layer play an important role in the absorption enhancement of the structure with the front grating period smaller than the back grating period, while the excitation and propagation of the plasmonic modes in the active layer dominate the absorption enhancement of the structure with the front grating period larger than the back grating period. The light leakage effect also exists in the structure with grating period ratio of 1:2 and 1:3 when the silicon active layer is thick. As a result, the structure with the best absorption property deviates from the structures with these grating period ratios.
2014, 63 (19): 198502.
doi: 10.7498/aps.63.198502
Abstract +
Influences of InGaAs/GaAsP quantum wells on the quantum efficiency of GaAs solar cells are investigated. In addion of extending the absorption spectrum from 890 nm to 1000 nm, introduction of quantum wells has important effects on the quantum efficiency below 890 nm. In the range of shorter wavelengths(<680 nm), the GaAs control cells have higher quantum efficiencies, while in the longer wavelengths (680-890 nm), the quantum well solar cells have higher quantum efficiencies. This phenomenon can be explained by the difference in the absorption coefficients of quantum well structure and GaAs materials.
2014, 63 (19): 198802.
doi: 10.7498/aps.63.198802
Abstract +
In this paper, we design a type of light trapping structure with an anodic aluminum oxide (AAO) nanograting on the surface and the backside of thin Si solar cells. Simulation of the influence of AAO's period, hole thickness, and duty cycle on thin Si solar cell's short current density are carried out by finite difference time domain method. Simulation results show that the optimum size for surface AAO is 0.5 for duty cycle, 75 nm for thickness, 440nm for period, and the optimum AAO size for rear AAO is 0.75 for duty cycle, 90nm for thickness, 380nm for period. The double AAO light trapping structure can increase the light absorption in the wavelength range from 280 to 1100nm，the absorption relative enhancement is 74.44%.
2014, 63 (19): 198101.
doi: 10.7498/aps.63.198101
Abstract +
In this paper, by choosing catalyst of FeNiMnCo alloy, boron-doped diamond single crystals are synthesized under 5.1–5.6 GPa and 1230–1600℃; the temperature field is studied by finite element method (FEM). First, the P-T phase diagram for diamond single crystal growth, in the synthesis system of FeNiMnCo-C-B, is obtained, and the lowest synthesis conditions of 5.1 GPa and 1230℃ is found in the studies. By simulation with FEM, it is found that the content of boron element should be less and less in the growth of diamond single crystal in the {111} sector, and the reason is that the growth speed is reduced in the sectors. By growing diamond crystals with {111} faces, it is also found that the content of boron element in {111} secondary sector is greater than that in {111} primary sector, which is duo to the rapid growth of {111} secondary sector. Compared with the synthesis of diamond single crystal by film growth method, the diamond crystals thus obtained has no pits, the doping content of boron can be greater, and the diamond can be synthesized by temperature gradient method.
2014, 63 (19): 198404.
doi: 10.7498/aps.63.198404
Abstract +
The missile-borne synthetic aperture radar (SAR) often use nonlinear scaling algorithm to improve the focusing effect. However, the nonlinear scaling algorithm cannot be used in missile-borne spotlight SAR because of its own limitations. Aiming at this problem, this paper first puts forward a new method named “sub-band compensation” and combineds it to the missile-borne SAR spotlight imaging algorithm. This new algorithm does not introduce the three phases of operation, so the Doppler frequency rate can be effectively compensated under low PRF. Simulation results and analysis show that compared with the nonlinear chirp scaling algorithm, the proposed one has advantages in computation, results obtained, and applicability.
2014, 63 (19): 198202.
doi: 10.7498/aps.63.198202
Abstract +
The dissociation dynamics of hydrogen molecular ions in intense fields has been investigated by using an accurate three-dimensional (3D) time-dependent wave packet approach. Its dissociation mechanism and intensity dependence can be studied by analyzing the dissociation probability and kinetic energy resolved (KER) spectra of H2+. It is found that the dissociation of H2+ comes from ν=5–9 states at the laser intensity of I1= 5.0×1013 W/cm2. The dissociation process includes bond softening (BS), bond hardening (BH), and below threshold dissociation (BTD). As the laser intensity increases to I2=1.0×1014 W/cm2, the above threshold dissociation (ATD) from ν=3 and 4 states is predominant, and the contributions from the bond softening and bond hardening are reduced during the dissociation process. The above conclusions may provide scientific prediction and theoretical guidance for the experiment in the future.
Low-frequency oscillation of continuous conduction mode buck converter with pulse skipped modulation
2014, 63 (19): 198401.
doi: 10.7498/aps.63.198401
Abstract +
Low-frequency oscillation phenomenon in pulse skipped modulation (PSM) buck converter operating in continuous conduction mode (CCM) is reported in this paper. Energy transfer difference between the PSM-controlled buck converter operating in discontinuous conduction mode (DCM) and that in CCM is studied. The mechanism of low-frequency phenomenon in PSM-controlled CCM buck converter is revealed, and a discrete-time model of PSM-controlled buck converter operating in CCM is established. Based on this model, the border collision bifurcation with variations of the ESR is studied; meanwhile, the inhibition effect of output capacitor equivalent series resistance (ESR) on low-frequency oscillation is presented. Based on the above analysis, a capacitor current pulse skipped modulation (CC-PSM) technology is proposed; the energy transfer principle of CC-PSM controlled buck converter is analyzed. The control pulse of CC-PSM is generated by the comparison between the sampled capacitor current and preset peak reference current, and thus the range of inductor current ripple is limited. Results show that CC-PSM effectively eliminates the low-frequency oscillation in CCM buck converter under classical PSM when the ESR is low. Finally, the experimental results validate the correctness of theory and simulation analysis
2014, 63 (19): 198402.
doi: 10.7498/aps.63.198402
Abstract +
Construction of a compressive measurement matrix is one of the key technologies of compressive sensing. A circulant matrix corresponds to the discrete convolutions with a high-speed algorithm, which has been widely used in compressive sensing. This paper combines the advantages of chaotic sequence with circulant matrix to propose a circulant compressive measurement matrix based on the chaotic sequence. The elements of a chaotic circulant measurement matrix are generated by taking advantage of the chaotic internal certainty, i.e. the independent identically distributed randomness sequence can be produced by the chaotic mapping formula using the initial value and a certain sampling distance. At the same time, the external randomness of chaotic sequence can satisfy the stochastic requirements of compressive measurement matrix. This paper presents the method of constructing chaotic circulant measurement matrix using a Cat chaotic map and the test method for RIPless property of the matrix. Measurement results of one-dimensional and two-dimensional signals using the chaotic circulant measurement matrix are studied and are compared with the results of conventional circulant measurement matrix. It can be shown that the chaotic circulant measurement matrix has good recovery results for both one-dimensional and two-dimensional signals. Moreover, it may get better results than the traditional matrix for the two-dimensional signal. From the point of view of phase diagram, the essential reason of chaotic circulant measurement matrix outperforms the conventional one is its integration of internal certainty with the external randomness of the chaotic sequence.
EDITOR'S SUGGESTION
2014, 63 (19): 198501.
doi: 10.7498/aps.63.198501
Abstract +
System and methods for wireless communication that could go through hydrous rocks, seawater, and even soil are investigated. The key components of the system are the high sensitive receivers of commercial HighTcSQUID and high-speed signal acquisition and processing systems. Within the frequency band of 30 Hz to 100 kHZ, the intrinsic noise spectral density of commercial HTcSQUID could be as good as 100 fT/Hz1/2, so that with commercial software, signals could be accurately modulated, collected,demodulated and processed. In the low frequency end, with the features of long penetration depth of electromagnetic wave and high sensitive, small size of HTcSQUID magnetometer, the feasibility of the implementation of portable low-frequency wireless communication system which could be used both under ground and water is discussed preliminarily. Using a 1 m2 square coil as test signal transmitting antenna, with the HTcSQUID magnetometer receiving sensor placed in an electromagnetic shielding cavity which could provide considerable electromagnetic attenuation, the 99 Hz AM signal emitted by the transmitting antenna is successfully collected. The result proves that with the technology of HTcSQUID, practical wireless communications can be realized between the earth's surface and a depth of hundreds of meters underground.
2014, 63 (19): 198701.
doi: 10.7498/aps.63.198701
Abstract +
The quantum computation method has been used to investigate the atomic charge and electrostatic interaction of five models: four of which are composed of two mirror-symmetrical long-chain organic molecules (CH3 (CH2)5–R (R=COOH, CH3, OH) and CH3(CH2)4COOH); and one is composed of two parallel CH3 (CH2)5 COOH molecules. Results show that: (1)The charge of the C atoms of the methylenes(–CH2–) in the molecules is different from each other; (2) the atomic charge is mainly determined by the chain-length and the functional group; meanwhile, it may change when the distance between molecules changes or the arrangement of the molecules changes. The atomic charge in the bimolecular models changes more than in the single molecule models; (3)the electrostatic interaction is mainly determined by the tail function groups: the interaction strength is –COOH>–OH>–CH3; while the other atoms have little contribution. Electrostatic interaction will decrease when the atomic charge of the tail functional groups decreases, which is caused by the increased chain-length.
2014, 63 (19): 198703.
doi: 10.7498/aps.63.198703
Abstract +
Heart rate variability(HRV) signals can provide the important information about the active state of heart. To set up a reversed sleep model, then, we analyze the 24-hours HRV signals modulated by the reversed sleep state using the power spectrum and base-scale entropy method, and study the effect of the interaction of autonomic nerve system and the chaotic intensity of HRV signals in the case of reversed sleep. Results show that because of the reversed sleep state, the activity rhythm of autonomic nerve is contrary to that in normal state. The variational trend of base-scale entropy is corresponding to that reversed in day and night. This means that the chaotic intensity of HRV signals is closely related to the reaction of autonomic nerve system. In further researches, it is found that the chaotic intensity of HRV signals is in positive correlation with the modulation intensity of sympathetic nerve, but in negative correlation with the modulation intensity of vagus.
2014, 63 (19): 198702.
doi: 10.7498/aps.63.198702
Abstract +
Array beam field is a necessary condition for high frame rate(HFR) ultrasonic imaging system according to the non-diffraction wave theory. However, the sine function characteristic of array beam waves makes it more difficult to weight the ultrasonic wave transmission signal so the transmission system is very complex. To solve this problem, this paper proposes an effective solution. Based on Fourier transform theory, the energy component of the square wave focuses mainly on the fundamental wave. In this paper a kind of square wave with a single value is utilized to weight the transmitted signals from an ultrasonic transducer. Thus only one power signal source and a very simple electronic switch system can be used to achieve this kind of transmission circuit in the HFR system. Experiments show that such an option has little impact on the image quality of the HFR, however it greatly simplifies the HFR ultrasound imaging system.
2014, 63 (19): 198201.
doi: 10.7498/aps.63.198201
Abstract +
Co2SnO4/graphene composite has been prepared by multi-step synthetic process. Firstly, the formation of Co2SnO4 and the reduction of graphene oxide (GO) occur simultaneously during the hydrothermal process and the Co2SnO4 particles are uniformly embedded in the film-like graphene to form a mosaic structure. To characterize the phase and morphology of the composite material, X-ray diffraction (XRD), scanning electron microscope (SEM) are used. The constant current charge and discharge (CC), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) are also used to test the electrochemical performance of Co2SnO4/graphene composite. Results show that graphene can effectively improve the electrochemical performance of Co2SnO4/graphene composite by its good dispersibility and high electrical conductivity. The composite material exhibits a first discharge specific capacity of 1415.2 mA·h/g with the specific capacity still higher than 469.7 mA·h/g after 50 cycles.
2014, 63 (19): 198403.
doi: 10.7498/aps.63.198403
Abstract +
Frequency estimation based on the reconstruction algorithm of the Chinese remainder theorem(CRT) is one of the frontier focuses in the fields of signal processing, electromagnetism, and optics etc. Howerver, the existing studies can only realize a rough frequency estimation of complex exponential signals. Hence this paper generalizes the CRT-based frequency reconstruction from a rough frequency estimation of complex exponential signals to the accurate frequency estimation of sinusoidal signals. The procedure of the proposed estimation scheme is as follows: (1) Detect zero crossing point on the original high-frequency sinusoidal waveform so as to determine the ideal phase information; (2) implement fast Fourier transform(FFT) to each path's undersampled signal, and then use Candan estimator to correct the frequencies at the peak FFT spectral bins so that the frequency biases can be extracted to realize phase correction; (3) use the proposed classification method based on phase features to screen the corrected remainders; (4)substitute the filtered frequency remainders into the closed-form robust Chinese remainder theorem to obtain the high-accuracy frequency estimation of the original signal. Additionally, this paper also deduces the theoretic expressions of the frequency estimation variance, which is also verified through numerical simulation. And the experimental results also reflect that the proposed scheme possesses high precision and high robustness to noise.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2014, 63 (19): 197103.
doi: 10.7498/aps.63.197103
Abstract +
Hot carrier gate current is one of the factors that influence the power and reliability of metal-oxide-semiconductor field effect transistor (MOSFET). Based on the physical process of generation of the hot carrier effect, a model of hot carrier gate current for uniaxially strained Si NMOSFET is developed. With that model, the simulation results of hot carrier gate current against stress intensity, gate-source bias, channel doping concentration, and drain-source bias are obtained and analyzed. The relationship between life time of time-dependent dielectric break down (TDDB) and gate-source bias is simulated and analyzed. Results show that the uniaxially strained Si MOSFET not only has smaller hot carrier gate current, but also has more stable reliability as compared with the strainless bulk device. Meanwhile, the simulation results match the experimental results very well, which validates the accuracy of the model.
2014, 63 (19): 197301.
doi: 10.7498/aps.63.197301
Abstract +
One-dimensional (1D) graphene superlattices were formed on a prototypical high index surface-Cu(410)-O. Atomic hydrogen adsorption on the superlattice was studied by using Raman spectroscopy, low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). Selective H adsorption due to the 1D modulation from the Cu substrate was observed in defect-free graphene area. Most H adatoms occupy the same positions in the 1D graphene superlattice stripes, as revealed by STM. This opens the possibility for further graphene property tuning through 1D superlattices. In addition to H monomers and dimers, a new type of trimer configuration was also observed.
2014, 63 (19): 197801.
doi: 10.7498/aps.63.197801
Abstract +
A nitrogen-contained solid solution Ca2Si(O4-xNx):Eu2+ green phosphors was successfully synthesized using the method of mixing Ca-Si-O xerogel precursor with Si3N4 powders in a non-reducing atmosphere (pure nitrogen). The structure, morphology, and luminescent properties of the phosphors are characterized by X-ray diffraction (XRD), \text {scanning} electron microscopy (SEM) and photoluminescence (PL) spectra. Results show that the Ca2Si(O4-xNx):Eu2+ is obtained and especially the reduction of Eu3+ to Eu2+ occurs when the mixture of Si3N4 and precursor is calcined at 1100℃ in pure nitrogen atmosphere. XRD results show that the crystalline structure of N-contained solid solution Ca2Si(O4-xNx):Eu2+ is consistent with that of βup -Ca2SiO4 phase. The phosphors can be efficiently excited at a wavelength of 270–400 nm and shows a single intense broadband emission (450–600 nm). Significantly, the red-shift (501 nm to 504 nm) of emission peak occurs and the luminescent intensity is improved significantly with increasing N concentration. With increasing Eu2+ concentration, luminescent intensity of the phosphors increases continuously and reaches a maximum value at the concentration of 0.25 mol% Eu2+. Then the luminescent intensity decreases significantly and the concentration quenching effect appears when Eu2+ concentration is above 0.25 mol%.
2014, 63 (19): 197901.
doi: 10.7498/aps.63.197901
Abstract +
By applying a femtosecond electric pump pulse to a poly(p-phenylene vinylene) (PPV) molecule, we theoretically investigate the dynamical processes for its stimulated absorption and emission. The simulations are performed within the framework of an extended version of one-dimensional Su-Schrieffer-Heeger tight-binding model combined with a nonadiabatic evolution method. Firstly, we set the molecule initially lying in the ground state, by which we give the relation between different stimulated transition modes and the photoexciting pulse. Analysis of the final states shows that we can only obtain some electron-hole binding states by an external photoexcitation for the molecule, which includes exciton, biexciton, and high-energy exciton. We have calculated their yields and find that they are determined by the photoexciting energy. In addition, based on the experimental observations, we separately investigate the effect of the photoexciting intensity on the yields of biexciton and high-energy exciton. The calculated results are consistent with the corresponding experimental speculations. Finally, by setting the molecule lying in an exciton or a biexciton, we focus on the stimulated emission process between their generated intragap states. Effects of the photoexciting energy and intensity on them are separately analyzed. These results might be of great importance for further improving the optical applications of polymers, especially for optimizing the polymer photovoltaic and laser properties.
2014, 63 (19): 197201.
doi: 10.7498/aps.63.197201
Abstract +
This paper presents an improved model of thermoelectric power generation, taking into consideration the effect of air heat transfer in a closed cavity between the thermoelectric couples. We have used the ANSYS software, under the condition of different numbers of thermoelectric couples and different models, to simulate numerically and analyze the temperature field and, the voltage field of thermoelectric power generation. Results show that the energy conversion efficiency of 127 pairs of thermoelectric couples increases rapidly as the temperature gradient between the hot and cold ends increases as compared with 1 pair of thermoelectric units; it is enhanced from 0.39% to 5.16% at an average of 3.02% while the temperature gradient varies from 20℃ to 220℃. The output voltage of the chip, power, and energy conversion efficiency would increase as the cross-sectional area increases while the cold junction temperature stays at 305℃, and the cold arm galvanic greater the temperature difference across the greater the increase rate, and thermoelectric power generation chip resistance, along with the cross-sectional area of the galvanic arm decreases. The output power can be up to 28.9W as the temperature difference is 220℃.
2014, 63 (19): 197302.
doi: 10.7498/aps.63.197302
Abstract +
Back-gate field effect transistors based on In-doped ZnO individual nanobelts have been fabricated using the low-cost microgrid template method. The output (Ids-Vds) and transfer (Ids-Vgs) characteristic curves for the transistors are measured, and the mobility is derived to be 622 cm2· V-1· s-1. This value is obviously superior to those for most of materials including pure ZnO in the literature, and possible influence factors have also been discussed.
2014, 63 (19): 197501.
doi: 10.7498/aps.63.197501
Abstract +
We have studied systematically the effects of temperature, time, and pressure on the process of hydrogen absorption in LaFe11.5Si1.5 compound. Results show that hydrogen absorption can increase the lattice parameter of the compound without changing its crystal structure. The LaFe11.5Si1.5H1.6 compound can be prepared at a hydrogen pressure of 0.0987 MPa at 423 K with uniform distribution of hydrogen. Hydrogen absorption can also increase the Curie temperature obviously, decrease the thermal hysteresis and maintain the magnetic entropy change at a high standard. With prolonged exposure time in air, the variation of the Curie temperature and magnetic entropy change of LaFe11.5Si1.5H1.6 compound are very small, implying that the magnetic thermal performance of hydride alloy has a good time stability.
2014, 63 (19): 197101.
doi: 10.7498/aps.63.197101
Abstract +
Variations of electronic properties of bulk α-Fe(C) due to the addition of Cr, Mo, Ni are studied using the first principles method, which is based on the density functional theory (DFT). Lattice distortion, cohesive energy, density of states, Mulliken charge population, overlap population and charge density differences are calculated by the generalized gradient approximation (GGA)-PW91, and the occupancy, bonding characters and alloying effect of α-Fe(C) after mixing with alloy atoms are explained. Results show that Cr occupies perferentially the corner of α-Fe(C) unit cell, but Mo and Ni occupy the body-center position of the cell perferentially. The mixing with Cr produces the biggest cohesive energe, and that with Ni and Mo in turn produces lower cohensive energy. There coexist the metallic bond, covalent bond, and weaker ionic bond in the unit cell. The bonding orbitals are created by Cr3d with Fe3d, Mo4d with Fe3d, and Ni3d with Fe3d and C2p; the bonding force between Cr and other atoms in the bulk is powerful, and the stability of cell is good, so it helps improve the mechanical strength of steels. The bonding force between Ni and other atoms in the bulk is weaker, but it can also maintain the stability of the cell. Though the bonding force between Mo and other atoms in the bulk is powerful, but the antibonding is so strong, that the statility of the cell reduced greatly. This is harmful to the mechanical strength of steels.
2014, 63 (19): 197102.
doi: 10.7498/aps.63.197102
Abstract +
Nowadays, in the reports of V-heavy-doped ZnO, when the doping moles of V in the range of 0.03125 to 0.04167, there is a current controversy between the two experimental results, i.e. the conductivity may be increased or decreased as the doping content increases. To solve this contradiction, the undoped and the two different concentrations of heavy-doped V atoms in Zn1-xVxO(x=0.03125, 0.04167) compounds have been set up based on the first-principles plane wave ultra-soft pseudo potential method of density functional theory in this paper, then all three compunds are geometrically optimized, and on this basis the GGA+U method is adopted to calculate the band structures, density of states, and the absorption spectrum. Results reveal that when the doping mole of V is in the range of 0.03125 to 0.04167, the volume doped system of the is increased as the total energy decreases; as the doping mole of V increases, the formation energy is reduced, the doping system is more stable, and the relative electronic concentration decreases, the migration rate and the conductivity are reduced; as the optical band gap is enlarged, the absorption spectrum blue shift is more significant. There are in agreement with the experimental results.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2014, 63 (19): 199202.
doi: 10.7498/aps.63.199202
Abstract +
Low-frequency rainfall over the lower reaches of Yangtze river valley (LYRV) and the principal component of the global 850 hPa meridional wind anomalies are adopted to construct an extended complex autoregressive (ECAR) model, which can be applied to the daily forecasting of the low-frequency rainfall component over LYRV in 2013 for the extended range forecast. Results show that this model for the forecasting of the 2030-day rainfalls over LYRV has a good predictive skill up to 43 days, which is able to well predict the nonlinear enhancement processes of low-frequency rainfall component associated with heavy rainstorm process. And the correlation skill of the extended range forecast produced form the ECAR model is superior to the autoregressive model (AR) forecast. This method, in which the complex autoregressive (CAR) models are set up via constructing the extended complex matrix (ECM) for the principal low-frequency time series, provides a new description for the emerging dynamic processes of the interactions between components in climate systems. Based on the development and evolution of the principal 2030-day oscillations of the global circulation, it is help for better forecast the process of heavy rainfall in the early October of 2013 over LYRV for times ahead of about 27 days. In these low-frequency variabilities, the 2030-day oscillation in extratropics over the Southern Hemisphere is one of the main factors causing the changes of the heavy rainfall over LYRV for the extended range during the summer and fall in 2013.
2014, 63 (19): 199201.
doi: 10.7498/aps.63.199201
Abstract +
In order to obtain the microphysical features of snowflakes under the natural conditions by using the self-developed sensor, precipitation microphysical characteristics, capture probability, and space distribution retrieve algorithm based on the velocity of snowflakes are discussed; and the shape, size, velocity, axial ratio, orientation and the space distribution of snowflakes are investigated by the field observation. Results show that the snowlakes may take needles, flakes, and oblate ellipsoids shapes; the falling velocity of snowflakes will increase slightly with inereasing diameter, their axial ratio may increase linearly with the diameter, and their orientations are easily influenced by the wind; the canting angle may be 0.9° and tends to be nearly symmetric with a standard deviation around 13.2°. Empirical equations of velocity and diameter, and of axial ratio and diameter are fitted by nonlinear fitting and linear fitting of observed data respectively. Compared with previous model proposed by authors abroad, this paper further provides the microphysical characteristics of snowflakes with localization features. The above conclusions can be of significance for the research on cloud precipitation physics, ground validation of weather radar, assessment of precipitation-induced microwave attenuation, etc.
GENERAL
2014, 63 (19): 190502.
doi: 10.7498/aps.63.190502
Abstract +
We have studied the dynamic behavior of bright-bright solitons in two-species Bose-Einstein condensates trapped in an optical lattice. It is shown that the directions of motion and oscillations of the bright-bright solitons can be effectively controlled by adjusting the lattice spacing and height, respectively. Especially, two separated solitons can be localized in the optical lattice, and the fission of each localized soliton is newly observed due to the increase of the lattice height.
2014, 63 (19): 190202.
doi: 10.7498/aps.63.190202
Abstract +
Using Mawhin's continuation theorem, the existence of periodic solution for a class of nonlinear problem is discussed, and then by using it, the problem of periodic solution of drift motion of the guidance center in earth's magnetosphere electromagnetic field is investigated. A result on the existence of periodic solution to the model is obtained, and the feasibility of our result is explained.
2014, 63 (19): 190302.
doi: 10.7498/aps.63.190302
Abstract +
In the previous studies and literatures, quantum mechanics representations are a pure state representation, while in this paper beginning with reasonable ordering of operators in quantum mechanics and the normal distribution thought in probability statistics, we propose the concept of quantum mechanics mixed state representation firstly,and prove its completeness and orthogonality. The advantages of mixed state representation is that it can reflect a variety of expression of quantum mechanics operators and the corresponding operators ordering rules.
2014, 63 (19): 190301.
doi: 10.7498/aps.63.190301
Abstract +
This paper gives a general n-order character functional, and uses the quantitative causal principle to derive the general variational principle; furthermore the Euler-Lagrange equation and conservative quantities for a general n-order character functional are derived, and the link between the principle of relativity and the quantitative causal principle is revealed. Newton's first, second, and third laws are then derived, but the third laws is also regarded as a new law: it is a theorem that force is zero in translational invariance, and its general physical meaning in classic mechanics is revealed. The results obtained have been successful applied to the galaxy gravitational potential correction, molecular potential, quark confinement potential, etc., and the results are consistent with the physical experiments.
2014, 63 (19): 190503.
doi: 10.7498/aps.63.190503
Abstract +
In this paper noise-induced intermittency phenomenon in Hénon map is studied. Through numerical simulation and global analysis the mechanism of noise-induced intermittency in Hénon map is revealed. By using stochastic sensitivity function method to detect whether there will be collisions between confidence ellipse of periodic attractor and chaotic saddle, a method to estimate the critical strength of noise is proposed. Results show that the noise-induced intermittency in Hénon map is caused by interactions between cycle attractor and unstable manifold of chaotic saddle, whereas the stochastic sensitivity function method can estimate the critical noise strength in intermittency phenomenon accurately.
2014, 63 (19): 190504.
doi: 10.7498/aps.63.190504
Abstract +
Due to the energy limitation in nodes in the wireless sensor networks, the problem whether the node energy consumption is balanced becomes a primary one in the design of networks. Through building the node lifetime model, we conclude that the node lifetime is affected by the node residual energy and the communication distance. Additionally, both ends of the node lifetime are introduced as the influencing factors on edge weights. And then through the edge weight the node weight is controlled, so that the weighted scale-free topology with energy consumption balanced characteristics is obtained. Finally, theoretical proof shows that the distribution of the node weight, the edge weight, and the node degree all obey the power-law distribution. Simulation results show that this model has the good fault tolerance characteristics that the scale-free topology can have. And it also has obvious advantages in balancing the network energy consumption and prolonging the network lifetime.
2014, 63 (19): 190201.
doi: 10.7498/aps.63.190201
Abstract +
In order to study the structural characteristic and node centrality of a structure composed of two related heterogeneous networks, in this paper, interlacing layered complex networks are defined as networks which are composed of two subnets having the partially same nodes and similar links. Also the definitions of the node interlacing coefficient, path interlacing coefficient and networks interlacing coefficient are given, so the intimacy level of two subnets can be measured definitely. Based on the definitions above, a node centrality algorithm of degree and betweenness is studied and redefined, while a new node centrality measuring index is given, which can be used to measure the supporting degree of a node in one subnet to the others' connectivity and negotiability. Finally, experimental results show that the proposed method is effective.
2014, 63 (19): 190501.
doi: 10.7498/aps.63.190501
Abstract +
Applications and limitations of the entransy theory for heat-work conversion processes are analyzed and discussed in this paper. Our analyses for the Carnot cycle show that the system entransy of the Carnot cycle is in balance, but the relationship, dG=T2dS, does not exsit between the concepts of entransy and entropy. Therefore, the concept of entropy cannot be replaced by the concept of entransy. For common thermodynamic processes, the analyses show that the present entransy theory is applicable when heat is transferred into an endoreversible thermodynamic cycle to do work. In addition, in the analyses of heat-work conversion processes, the differences between the entransy theory and entropy theory are also discussed. It is shown that the viewpoints and preconditions of the two theories for the analyses and optimizations of heat-work conversion processes are different. The viewpoint of the analyses of entropy generation is the loss of exergy, while that of the analyses of entransy is the consumption of thermal potential. When the input exergy flow of the discussed system is prescribed or the input heat flow and the corresponding thermodynamic forces of the heat flows into and out of the system are prescribed, the entropy generation minimization leads to the maximum output work. For the entransy theory, the maximum entransy loss corresponds to the maximum output work when the input heat flow and the corresponding temperatures of the heat flows into and out of the system are prescribed. Meanwhile, they both have limitations. When the corresponding preconditions are not satisfied, the maximum entransy loss or the minimum entropy generation may not correspond to the maximum output work.
ATOMIC AND MOLECULAR PHYSICS
2014, 63 (19): 193601.
doi: 10.7498/aps.63.193601
Abstract +
Under ergodic condition, the analytic expressions for the fluctuations of temperature and particle number in the well of a system are obtained rigorously in particle-spilling-from-well model by means of integration approaches in phase space; the relationships among fluctuations of thermodynamic variables, the total particle numbers, and the well volume are emphasized. Results show that the less the total number of particles and the smaller the well's volume, the more remarkable the thermodynamic fluctuations effect, and the more closely the thermodynamic fluctuations related to the particle spilling from the well. There is a one to one correspondence between particle spilling from the well and the occurrence of negative specific heat, and the huge thermodynamic fluctuations,as well as, the origin of this phenomenon can be understood by the apparent energy inverse partition.
EDITOR'S SUGGESTION
2014, 63 (19): 193701.
doi: 10.7498/aps.63.193701
Abstract +
Ultracold Cs2 molecules have been formed by photoassociation. Using the multiphoton ionization technique, we measure the time-evolution of expanding process in ultracold Cs2 molecule system and obtain the decay curve of photoionization signals. Based on a simple case, where the initial distribution of atomic or molecular sample is a Gaussian function of position and of velocity, we get the sample's temperature by theoretical simulation. The result shows a reasonable agreement with the result of release-recapture method in cold atom sample. This method avoids the disadvantage of detecting the weakly fluorescence and can be widely used for measuring the temperature in cold atom or cold molecule system.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2014, 63 (19): 196101.
doi: 10.7498/aps.63.196101
Abstract +
Based on first-principles plane-wave ultrasoft pseudopotential density functional theory method,the lattice structure, formation energy, density of states and charge density of the ZnO:(Mn,N) system are calculated and studied theoretically. Results show that Mn and N co-doped ZnO system is more suitable for doping into a p-type system, for it has a lower impurity formation energy and higher chemical stability; Mn and N in a proportion of 1:2 doping system can effectively reduce the formation energy of the system and so it is more stable; when the system forms a double acceptor level defects, the p-type characteristic of the system is more obvious, for the solubility of impurities and the number of carriers in the system are increased. In addition, it is found that more impurities can go through the Fermi level density of states in the Mn-N co-doped system, while the 2p state density of N is widened and effective mass of holes is smaller and more delocalized.Moreover,compared with the Mn-N-doped system, the density of states of Mn-2N co-doped system is more dispersed near the Fermi level, and the non-localized characteristics are distinctive, thus it is expected to be a more effective means of p-type doping.
2014, 63 (19): 196102.
doi: 10.7498/aps.63.196102
Abstract +
An extraction method for single event upset cross section based on Monte Carlo code and device simulation is proposed, which can be used to calculate single event effects and sensitive regions in memories accurately. Single event upset cross sections of domestic static random access memory (SRAM) and field programmatic gate array (FPGA) devices are calculated, and results agree well with these from heavy ion test. Simulation results reveal the physical mechanism of the relationship between single event upset sensitivity and surface area of off-state NMOSFET and PMOSFET. Sensitive regions of single event upset under different linear energy transfer (LET) values are obtained. The radial ionization profiles of heavy ions with different energy, but the same LET, are also calculated using the Monte Carlo method. The track radius of high-energy ion is significantly larger than that of low-energy ion, while the charge density at the track center of low-energy ion is higher by two or three orders of magnitude. With decreasing technology scaling, the impact of these differences on single event effects will be more pronounced, and the threshold LET and saturated cross-section will not be capable of describing the single event response completely.
2014, 63 (19): 196201.
doi: 10.7498/aps.63.196201
Abstract +
Magnetically driven loading technology is to load the large pulse current to the test area through the pulsed power, which forms a smooth magnetic pressure rising over time to achieve a quasi-isentropic compression of sample and hyper-velocity flyer launch. Based on the output characteristics and parameters of PTS accelerator, two types of hyper-velocity flyer launch experiments with different load configurations, such as the load, flyer plates size, current waveform and diagnostic systems etc, are designed and tested. LY12 aluminum flyer plates with dimensions of 10 mm0.725 mm was launched by single-sided stripline load configuration to 11.5 km/s while the magnetic drive load pressure is near 0.9 10^5 MPa. Simulation and experimental results agrees well with those of in the flyer launch process and the ultimate velocity. Further simulation shows that the launch velocity of aluminum flyer plates with dimensions of 8.5 mm1 mm is expected to exceed 15 km/s under the program of optimizing the structural parameters and regulation. The design and experiment technology of hyper-velocity flyer launch based on multi-branch pulsed power generator has been mastered during the designs and experiments.
2014, 63 (19): 196202.
doi: 10.7498/aps.63.196202
Abstract +
In this paper, the rate-dependent characteristics of oxygen-free high-purity copper (OFHC) under plate-impact loading is investigated experimentally. The velocity of flyers is measured by magnetic measurement system, and the free surface velocity of targets is measured by Doppler pins system (DPS). Characteristic parameters of free surface velocity are calculated using the measured data. Results show that the spall strength of OFHC is enhanced with the increase in strain rate. It is indicated that the rate from the minima to the spall peak grows slowly at low stain rate, but steeply at high strain rate. The slope as it appears, from the minima to the spall peak is very different as the strain rate increases, The interaction of shock waves in the copper samples is systematically analysed to access the slope characteristics.
