Vol. 64, No. 5 (2015)
2015, 64 (5): 050502. doi: 10.7498/aps.64.050502
Current network security defense strategy focuses on deploying to high degree nodes where there are mainly two aspects of the problem: One is that the high-degree nodes are not the backbone nodes for the network communication in many occasions; another is that these nodes are not always the most effective ones for forwarding and propagation information. With the disadvantage of current network defense strategy deployment, this paper tends to improve the traditional diffusion model of malicious program propagation and measure the importance of network nodes by using intermediate hops, then the important node for recommended deployment technology based on betweenness center control and closeness center control model is put forward. Experimental results show that the nodes with high betweenness centrality and low closeness centrality as compared with the high degree nodes can more effectively quarantine the spreading of the worms whether in scale-free network or in small world network. Meanwhile, the clustering behavior of a network will also play a certain negative impact on the spread of malicious programs.
2015, 64 (5): 050703. doi: 10.7498/aps.64.050703
The simulation design and preliminary experiment on a 0.34 THz large-power overmoded surface wave oscillator are presented in this paper. For the slow wave structure (SWS) with large overmoded ratio (D/λ ≈ 6.8), a small signal theory is derived for appropriate dimensions of SWS and gap between electron beam and SWS, and makes the device oscillate near the π point of surface wave at TM01 mode. PIC (particle in cell) simulation results show that this SWO (small wave oscillation) can genetate the terahertz wave with frequency and output power of 0.34 THz and 22.8 MW, respectively. SWS with stainless steel is integrally and precisely fabricated by employing mirco-EDM technology, and the experimental setup is built based on a miniaturized pulse power driving source. Results of preliminary experiment and diagnostics show that a terahertz pulse is radiated at a frequency range of 0.319–0.349 THz, a power of no less than 250 kW, and a pulse duration of about 2 ns at beam voltage of about 420 kV and beam current of about 3.1 kA. Finally, the reason for discrepancy between the measured power and the simulation result is analyzed and discussed, laying the foundation for the performance improvement of terahertz surface wave oscillator.
Research on emission transition mechanisms of InGaN/GaN multiple quantum well light-emitting diodes using low-frequency current noise
2015, 64 (5): 050701. doi: 10.7498/aps.64.050701
In this paper, we measure the emission transition mechanisms in InGaN/GaN multiple quantum well (MQW) light-emitting diodes (LED) using low-frequency current noise from 0.1 to 10 mA. According to the characteristics of the low-frequency current noise and the emission mechanisms of InGaN/GaN LEDs, we study the relationships between low-frequency current noise and current flows through the LEDs. Conclusions indicate that the low-frequency current noise is increased with the increasing current from 0.1 to 10 mA. With a lower current (I10 mA) it is the 1/f noise that dominates in LEDs, so there exists an emission transition mechanism in InGaN/GaN MQW LEDs between 0.1 and 10 mA, showing that the mechanism of the carrier recombination changes from non-radiative recombination to a stable fluctuation of carrier numbers. Conclusions of this paper provide an effective method to characterize the emission transition mechanisms, optimize the design of LED so as to improve the quantum efficiency for InGaN/GaN MQW LEDs.
Robust fractional-order proportional-derivative control of unified chaotic systems with parametric uncertainties
2015, 64 (5): 050503. doi: 10.7498/aps.64.050503
In this paper, a robust fractional-order proportional-derivative (PDμ) control is designed for controling in integer-order unified chaotic systems with parametric uncertainties. Equivalent plant is obtained by transforming the controlled dynamic system, and then the PDμ controller as an equivalent controller is applied to the equivalent plant. In the uncertain controlled unified chaotic systems, one equation is certain, and the other two equations are uncertain . The equivalent controller for the certain system is then designed based on a fractional-order proportional-derivative controller, in which three specifications for phase margin, gain crossover frequency, and robustness should be met. On the other hand, the robustness of uncertain systems is achieved by an improved Monje-Vinagre tuning method, however, the pre-specified frequency band should be replaced by the gain crossover frequency in order to reduce the complexity in determining the controllers for the uncertain systems. Specifications related to phase margin for the lower bound of the phase, gain crossover frequency for the upper bound of the gain, and robustness for the lower bound of the phase constraints are satisfied by the uncertain system. Parameters of the equivalent controller are determined based on a graphical method. Origins of the unstable equilibrium can be asymptotically stabilized by the proposed strategy for the integer-order unified chaotic systems with parametric uncertainties. Numerical simulation examples for Chen system, L system, and Lorenz system, are given to show the effectiveness of the proposed method.
An integral-transformation corresponding to quantum mechanical fundamental commutative relation and its application in deriving Wigner function
2015, 64 (5): 050301. doi: 10.7498/aps.64.050301
In this paper, it can be found that there is a type of integra-transformation which corresponds to a quantum mechanical fundamental commutative relation, with its integral kernel being 1/exp[2i(q-Q)(p-P)], here denotes Weyl ordering, and Q and P are the coordinate and the momentum operator, respectively. Such a transformation is responsible for the mutual-converting among three ordering rules(P-Q ordering, Q-P ordering and Weyl ordering). We also deduce the relationship between this kernel and the Wigner operator, and in this way a new approach for deriving Wigner function in quantum states is obtained.
2015, 64 (5): 050501. doi: 10.7498/aps.64.050501
In this paper, we first introduce a mutual influence function among network nodes based on characteristics of information spreading in online social network. Then we put forward an information spreading model based on relative weight, analyze the propagation path and process of the network, and discuss the influence on different paths. Finally, the simulation experiments of the traditional SIR model and the model in this paper are conducted with six different network topologies. Results show that the two models have no significant difference in homogeneous networks, but there are significant differences in inhomogeneous networks. This result shows that the information spreading is influenced by the status of spreading nodes, and also shows that the real networks like Twitter and Sina Microblog have certain similarity in topological structure.
2015, 64 (5): 050702. doi: 10.7498/aps.64.050702
Stray radiation is an important indicator for the infrared optical systems involved in the process of designing and testing. In order to measure the internal stray radiation in infrared imaging systems, a method based on radiometric calibration is proposed, and its rationality is verified by theoretical analysis and experiments. Firstly, the model of radiometric calibration without lens, in other words the detector for absorbing the radiation flux directly from the calibration reference source, is developed to show the influence of internal factors of the detector on the system output. Then it is compared with the results of calibration of the infrared system with a lens to obtain the system output results from the optical system, namely the internal stray radiation caused by the optical system. Finally, experiments are performed to prove the correctness of the theories proposed in this paper. The proposed method has some advantages, such as simple operation, low demand for the experimental conditions, and the capability of measuring the internal stray radiation accurately. It can be used to guide the stray radiation suppression in the process of infrared system designing, to verify the stray radiation analysis results, and to test whether the stray radiation level meets the practical requirements.
2015, 64 (5): 050201. doi: 10.7498/aps.64.050201
This paper addresses the stabilization problem of a class of switched linear systems. Due to the presence of switching delay in the switching signal of the controller, the switching of the controller and the of the system are turned out to be asynchronous. By combining switching signal method with the multiple Lyapunov function method, some sufficient conditions are provided to guarantee the stability of the whole switched system by an adjacent mode-dependent average dwell time scheme. These conditions imply the relationship among the continuous dynamics, switching delay, and the average dwell time. Finally, a numerical example is presented to illustrate the effectiveness of the proposed method.
2015, 64 (5): 050704. doi: 10.7498/aps.64.050704
This paper introduces a kind of single mode-multimode-single mode intrinsic Fabry-Perot interferometer (SMS-IFPI). We optimize the sensing length of the graded-index multimode fiber (GI-MMF), insertion loss, and multiplexing capability through the analysis and simulation of the optical field distribution in the GI-MMF. Experiment proves that the insertion loss of a single sensing unit from the optimized cascade SMS-IFPI may be decreased from 4 dB to 0.83 dB. Testing the response characteristics of SMS-IFPI temperature sensors in the distribution under the condition of different temperature, the experimental results show that each SMS-IFPI can have better sensitivity and linearity.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2015, 64 (5): 054201. doi: 10.7498/aps.64.054201
A zooming optical system based on a simple lens array used for uniform irradiation by a large-aperture laser is studied; and it can be shown that the size of target spot may be flexibly adjusted by changing the separation between the lens array and the focusing lens. How the choice of optical parameters will affect the zooming ability is analyzed, and a practical system is designed. Propagation of laser beam through the optical system is simulated numerically; results show that the spots in different size are similar in intensity structure. Speckle separation, modulation contrast, rms nonuniformity, and concentration ratio of the spot are quantified, and their variations are analyzed when the target is placed in different positions relative to the focal plane of the focusing lens.
2015, 64 (5): 054204. doi: 10.7498/aps.64.054204
According to the realization principle of phase closure in coherent field imaging, a new four-phase closure (FPC) algorithm is proposed for T-array multi-beam transmitter system. A type of four-item measurement radio of closure phase is first defined, and then the validity of FPC is confirmed in cancelling out the random atmospheric phase aberrations as well as eliminating atmospheric scintillation effect on degradation of the reconstructed image. Simulations prove the effectiveness of FPC, providing a new approach in removing atmospheric aberrations for multi-beam coherence field imaging.
Design of shared aperture metamaterial and its applications for high gain and low radar cross section antenna
2015, 64 (5): 054101. doi: 10.7498/aps.64.054101
A shared aperture metamaterial (SA-MTM) with partially reflection and absorber characteristics is presented. The SA-MTM is composed of two metallic layers separated by a dielectric spacer; the top absorbing surface (AS) consists of oblique cross metallic pattern loaded with lumped resistances, and the bottom partially reflecting surface (PRS) consists of etched parallel slots in a metallic layer. An SA-MTM with partial reflection and absorption characteristics is fulfilled by making the absorbing surface and partially reflecting surface shared the same aperture in the vertical direction. The SA-MTM is applied to the waveguide slot antenna; the Fabry-Perot resonance cavity constructed by the PRS and the metallic ground layer of the waveguide slot antenna can achieve high gain, while the AS can obtain the low radar cross section (RCS) characteristic antenna by absorbing the incident wave. Simulation and experimental results demonstrate that the antenna with SA-MTM gain is enhanced above 3 dB in the operation frequency range, the backscattering RCS is obviously reduced in a frequency range of 2–9 GHz. This idea can help us design a high gain and low RCS antenna, which overcomes the conflict between scattering and radiation performance of antenna.
Shape classification of single aerosol particle using near-forward optical scattering patterns calculation
2015, 64 (5): 054202. doi: 10.7498/aps.64.054202
Particle shapes can be distinguished by the properties of near-forward optical scattering patterns of particles. The discrete dipole approximation method is used to calculate the light scattering patterns of Bacillus sphaericus, Bacillus subtilis, Burkholderia pseudomallei based on their prolate spheroid models. Shape dependence of forward angle-resolved light scattering intensity for nonspherical biological aerosol particles is discussed by simulating their light scattering response of three detectors located in different azimuthal range. Combined with sphericity index method, forward small angle (5°–20°) angle-resolved light scattering intensity has the ability to identify the elongated particles and non-elongated particles under certain orientation conditions. This study can help not only design particle morphology measurement instrument but also detect harmful biological aerosol rapidly.
Analysis on the simplified optic coma effect on spectral image inversion of coded aperture spectral imager
2015, 64 (5): 054205. doi: 10.7498/aps.64.054205
With the novel spectrum imaging technology development in recent years, the push-broom coded-aperture spectral imaging (PCASI) shows the advantages of high throughput, high SNR, high stability etc. This coded-aperture spectral imaging utilizes fixed-code templates and push-broom mode, which can realize high-precision reconstruction of spatial and spectral information. But during optical lens designing, manufacturing and debugging, there inevitably exist some minor coma errors. Even minor coma errors can reduce image quality. In this paper, we simulate the system optical coma error which influences the quality of reconstructed image, analyze the variantion of the coded aperture in different optical coma effect, and then propose an accurate curve for image quality and optic coma quality in 255× 255 coded template, which provides important references for the design and development of push-broom coded-aperture spectrometer.
Influence of Raman scattering effect and self-steepening effect on the propagation characteristic of picosecond solitons
2015, 64 (5): 054207. doi: 10.7498/aps.64.054207
By solving the higher-order nonlinear Schrödinger equation (NLSE), including Raman gain and self-steepening effect, the influence of the combined effect of Raman gain and self-steepening on the propagation characteristic of soliton pulse is simulated by the software of MATLAB. Results show that self-steepening effect can produce temporal shifts of the soliton and also can lead to the breakup of higher-order solitons through the phenomenon of soliton fission. Meanwhile, the Raman gain changes the propagation characteristic of optical soliton and inhibits the self-steepening effect, resulting in the increase in pulse width, and the decrease in pulse offset. As a result, the required propagation distance for higher-order soliton decaying into fundamental solitons is increased under the condition of Raman gain.
2015, 64 (5): 054301. doi: 10.7498/aps.64.054301
Far-field high resolution imaging is one of the research focus in the field of acoustics and optics in recent years. The greatest difficulty for high resolution imaging in the far field is the evanescent waves not being able to propagate in the medium. A kind of scatterers composed of uniformly spaced steel columns is presented in this work. Negative reflection of periodic structure can change the evanescent waves to the waves that can propagate to enhance imaging. A finite element simulation has been used to study and verify the feasibility of the scheme. Results show that with the sound wave of 3.4 mm wavelength one can obtain an imaging resolution of about 0.6 wavelength in the far field of 20 cm. We further note that by reducing the lattice constant of scatterers a higher far-field resolution imaging can be hopefully reached.
Generation of octave-spanning super-continuum in tapered single mode fibre pumped by femtosecond Yb:YCOB laser
2015, 64 (5): 054206. doi: 10.7498/aps.64.054206
It is a pivotal step in the measurement of carrier-envelope phase offset frequency in optical femtosecond frequency combs that a stable octave-spanning super-continuum spectrum is generated. In this paper, a home-made Yb:YCOB femtosecond laser pulse is led into a tapered fiber in which some nonlinear effects like self pulse modulation are generated and the four-wave mixing is made to broaden a spectrum to more than one octave-spanning. A Yb:YCOB oscillator emits 130 fs, 620 mW and 76.8 MHz laser pulses, the center wavelength at 1052 nm. Such pulses are focused into a tapered single-mode fiber, and then more than one octave-spanning supercontinuum from 550 nm to 1350 nm has been produced. The coupling efficiency can reach 52% when 323 mW SC laser pulses are detected. Based on the experimental result, a new optical comb will be built with the Yb:YCOB solid state laser as the light source.
2015, 64 (5): 054701. doi: 10.7498/aps.64.054701
Because of their ability of self-clean, superhydrophobic surfaces have received substantial attention for years especially in surface science field. In this paper, the drop's wettability on different rough surfaces is simulated by using many-body dissipative particle dynamics (MDPD) and a contrast with the Cassie-Baxter theory's predictions is made. A combination of short-range repulsive and long-range attractive forces is used as wall-fluid interaction to generate different wettability, and a simple but efficient numerical method is introduced to measure the contact angle. The simulation could capture the static and dynamic properties of drop on textured surfaces, it is also shown that the microstructured surfaces can pin the three-phase (solid-liquid-vapour) contact line and this phenomenon has also been observed by other researchers in their physical experiments, suggesting that people should be careful when using the Cassie-Baxter theory. An analysis was given about energy transformation between kinetic energy and surface energy. The simulated results also show that the low Φs can cause the drop to rebound easily under the same impact velocity.
Modulational instability of a two-dimensional Bose-Einstein condensate in an optical lattice through a variational approach
2015, 64 (5): 054702. doi: 10.7498/aps.64.054702
We investigate the modulational instability of a two-dimensional Bose-Einstein condensate in a two-dimensional optical lattice using a time-dependent variational approach. Within this framework, we derive the ordinary differential equations for time evolution of the amplitude and phase of modulational perturbations. Analyzing these equations and the Hamiltonian of the system, we obtain the modulational instability criterion.
2015, 64 (5): 054704. doi: 10.7498/aps.64.054704
A unified colored-noise approximation (UCNA) method has been widely used to solve the simple one-dimensional problem, and this paper attempts to extend this method to multi-dimensional systems. Firstly, a Fokker-Planck equation is obtained by UCNA method based on the Langevin equation for particle motion, then a two-order moment trajectory model is established on this basis. The new model can be successfully used to predict the backward-facing step two-phase flow, and the simulation results agree well with the measurements. This study shows that the UCNA method is still effective in dealing with multi-dimensional two-phase turbulent systems.
Experimental study on screech tone mode switching of supersonic jet flowing through rectangular nozzles
2015, 64 (5): 054703. doi: 10.7498/aps.64.054703
An experiment was carried out to analyse and compare the screech tone characteristics and schlieren structures of an under-expanded jet flowing through four rectangular nozzles, aspect ratios of which are different (having the same height but different widths), with the jet pressure ranging from 0.2 to 0.8 MPa. Results indicate that there exist two different screech tone modes in the noise generated by supersonic jet flowing through the rectangular nozzles with different aspect ratios, and a mode switching can be found by altering the jet pressure. Mode switching is a phenomenon that different mode dominates or disappears according to the change of jet pressure. The switching time of fundamental frequencies in the screech tone modes and the width of the domination interval would be shortened as the aspect ratio decreases. The jet flow pressure drop interval of one mode, whose aspect ratio is 2, is extremely small. This phenomenon has never been mentioned in the literature. When the aspect ratio of the rectangular nozzle is 4, there exists an interruption and skip on the fundamental frequency-jet pressure curve within the jet flow domination interval for jet pressure at 0.49 MPa. As the pressure reduces, the axes of the schlieren figures begin to shake, and the structure stability of the flow field with different aspect ratio varies with the jet pressure. When the jet pressure is within the range of 0.45 to 0.70 MPa, the density in the first shock-cell decreases as the aspect ratio reduces. Meanwhile, axial pulsation and disorder of the flow field behind the second shock-cell appear. When the jet pressure is under 0.45 MPa, the flow field structure of the shock wave becomes more stable as the aspect ratio increases. In this pressure region, the periodical shock-cell structure is weaker than those above 0.45 MPa. Analyzing the screech frequency spectrum and the schlieren figures, we can find that the second and third shock-cells also have feedback and enhancement for the sound pressure of the screech frequency.
2015, 64 (5): 054705. doi: 10.7498/aps.64.054705
Although high-speed vehicles are designed to be smooth, they tend to have some protuberances on their surfaces. Thus the aerodynamic characteristics and thermal loads are changed. Meanwhile, mounting protuberances on a flat plate is an important way of flow control, and appropriate structure and location of the protuberance can improve the performance of the scramjet inlet remarkably. The nanotracer planar laser scattering (NPLS) technique is used to test the flow field of Mach 3.0 supersonic flow over circular protuberances of different heights. In total three models are tested. And the second-order scheme and fifth-order weighted compact nonlinear scheme (WCNS-E-5) is adopted to simulate the flow field. Fine structures of supersonic flow over the circular protubernaces have been obtained and the development of boundary layer in the wake flow can be observed. By comparison, it may be concluded that the protuberance lower than the local thickness will have weak disburances on its boundary layer development, and the layer after reattachment can keep its laminar state within a long distance. During the transition many clear hairpin vortices can be distinguished. When the protuberance height is larger than the thickness of the boundary layer, and the later in the region of wake flow would develop into a turbulence quickly due to intense disturbances. The transition point observed from the experimental results lies closer to the protuberance, and this might be cansed by the noise from the walls of the wind tunnel. Intermittency analysis has been done for the boundary layer in the wake flow based on the NPLS images, and the results show that the intermittency curves of the two protuberances that are larger than the local boundary layer thickness are quite similar and fluctuations are strong.
Experimental investigation on surface heat transfer characteristics of hypersonic two-dimensional rearward-facing step flow
2015, 64 (5): 054706. doi: 10.7498/aps.64.054706
Hypersonic rearward-facing step flow is one of the basic flow problems in the design of engine for endo-atmospheric hypersonic vehicle, including thermal protection, and aero-optical correction for infrared imaging window of hypersonic interceptors, etc. To know the characteristics of hypersonic rearward-facing step flow is of vital importance in improving the performances of vehicles, and understanding the basis of the flow. This paper investigates the characteristics of a two-dimensional hypersonic rearward-facing step flow, measures the surface heat transfer coefficient and the surface static pressure downstream the step, and compares the results with the values predicted using the hypersonic boundary layer theory. And the results are demonstrated by the flow structure visualization using NPLS (nano-based planar laser scattering) technique. It is concluded that for the hypersonic two-dimensional rearward-facing step flow, the surface heat transfer distribution can be determined directly by the boundary layer edge parameters at the step; and the viscous effect dominates the flow characteristic in the separation and reattachment region; whole in the far-field region downstream the step, the heat transfer coefficient approaches an asymptotic value that may be equal to the turbulent flat plate value. Furthermore, the boundary layer structure may depend on the ratio of boundary layer thickness to the height of step. It is concluded that, when studying the problem of hypersonic rearward-facing step using CFD (computational fluid dynamics) technology, choosing an appropriate turbulent model is needed.
2015, 64 (5): 054208. doi: 10.7498/aps.64.054208
Relationship among the composition, properties, and structure of glasses are one of the long standing topics in glass science. In this paper, (100-x) GeS2-xIn2S3 (x=10, 15, 20, 25 or 30 mol%) glasses and glass-ceramics are prepared by melt-quenching and subsequent heat treatments. Their composition dependence of optical bandgap, glass transition temperature, and crystallization behavior is measured by various techniques, and the effect of Ga or In element and the related structural units on their properties is discussed with the help of the previous researches on the GeS2-Ga2S3 glass system. Results show that In has a much bigger influence than Ga on the optical bandgap and glass transition temperature of chalcogenide glasses, while the crystallization behavior of the two kinds of glasses containing Ga and In is totally different, but has a close connection with the respective phase diagram. Their structural motifs can be realized by employing polarized Raman spectra. Consequently, combined with the recognition of their phase diagrams, the composition dependence of physiochemical properties and crystallization behavior, as well as the structural motifs, the correlation between chemical and structural topology is briefly discussed, which may provide a new insight into the glass topological structure.
2015, 64 (5): 054209. doi: 10.7498/aps.64.054209
Illumination uniformity of a target is highly required to achieve central ignition in inertial confinement fusion based on direct-driven fusion. However, the shell may be compressed due to its interaction with laser beams during the laser pulse duration, and may further result in the degradation of illumination uniformity and the enhancement of the cross-beam energy transfer (CBET). Hence a novel fast zooming scheme for direct-driven laser fusion is proposed, i.e., by introducing the variable wavefront to the laser beam provided by a special-designed electro-optic crystal, thus the location and size of the focal spot could be controlled in real time, achieving the aim of improving the illumination uniformity and alleviating the CBET. This model of fast zooming has been built up, and variations of spot size and the radius of curvature of the additional spherical wavefront with time have been numerically simulated and analyzed based on the analysis of the interaction of the laser beam and the target. Results indicate that the fast zooming scheme could achieve effective and real-time control on the radius ratio between the focal spot and the target. Moreover, the fast zooming scheme has a little impact on the spatial filter capability and the third harmonic frequency conversion efficiency.
A theory for monitoring combustion of natural gas based on the maximum point in sound absorption spectrum
2015, 64 (5): 054302. doi: 10.7498/aps.64.054302
Compositions of natural gases are different between each other because of different sources, resulting in the fact that natural gases have different energy contents and monetary value. This paper presents a theory to monitor the combustion properties of natural gas by using the acoustic relaxation phenomenon in which the maximum point of acoustic spectrum varies with gas composition. The theory is developed from the frequency-dependent sound absorption spectrum which can be reconstructed from its maximum point synthesized in the acoustic measurements at two frequencies. The theory uses the relation between the two values of the maximum point (i.e. the relaxation frequency and the maximum relaxational absorption) and gas composition to quantitatively monitor the gas. Moreover, the theory has the advantages of avoiding the detection of the gas density and the variation of the ambient pressure, which is necessary in the traditional way of measuring the maximum point of sound absorption spectrum.
2015, 64 (5): 054303. doi: 10.7498/aps.64.054303
For the problem of broadband beamforming in a subregion of interest, a robust Frost beamforming algorithm is derived by reconstructing the signal subspace. The basic idea of the proposed algorithm is to extract the characteristic components of the signal of interest (SOI) from the estimated signal-plus-interference subspace by a matrix filter first, then employ these characteristic components to reconstruct the signal subspace, and finally construct a set of linearly constrained minimum variance (LCMV) constraints to protect the SOI components. Compared with some other robust Frost beamformers, the proposed algorithm has a significant advantage, i.e., its steering-angle and band are effective to match the SOI without prior information. Hence, the performance of the proposed algorithm is almost always close to the optimal value across the whole region of interest. Theoretical analysis and simulation results validate the effectiveness of the proposed algorithm.
A regular composite feature extraction method for vibration signal pattern recognition in optical fiber link system
2015, 64 (5): 054304. doi: 10.7498/aps.64.054304
Phase optical time-domain reflectometer link monitoring system is a kind of sensor system which uses optical fiber as sensing medium. It can detect, recognize and locate invasive signals. The module of pattern recognition, which is one of the important parts of the system, can intelligently and instantly distinguish dangerous intrusions from safe disturbances. This paper proposes a regular composite feature extraction method which can be used for vibrational signal pattern recognition in an optical fiber monitoring system. This method applies an improved double-threshold method to detect the start-stop positions of the valid signal segments, and then combines the maximum energy and maximum signal noise ratio to select the main invasion feature segment within a sampling period. The composite eigenvectors, which are extracted by using the last time of the feature segment and wavelet packet energy spectrum, can be used by the support vector machine to recognize the signal patterns. Experiment results show that the accuracy rate of the pattern recognition has been improved significantly based on the proposed method in this paper.
Numerical study of cooling heat transfer of supercritical carbon dioxide in a horizontal helically coiled tube
2015, 64 (5): 054401. doi: 10.7498/aps.64.054401
In the present study, cooling heat transfer of supercritical CO2 in a horizontal helically coiled-tube 4 mm in diameter, 2000 mm in length, a pitch of 10 mm and 0.1 in curvature is numerically investigated with RNG turbulence model. Influences of mass flow rate, heat flux and pressure on heat transfer of supercritical CO2 are studied. The characteristics of the flow and heat transfer are compared with those in a horizontal straight tube. Results show that the secondary flow and heat transfer coefficient in a helically coiled tube is obviously larger than in a horizontal straight tube. The heat transfer coefficient of supercritical CO2 increases with increasing mass flow rate, and the heat transfer coefficient increases slightly as the heat flux increases in the gas-like region, while the heat transfer coefficient is unaffected by heat flux in the liquid-like region. The peak of the heat transfer coefficient decreases and shifts to a higher temperature region as the pressure increases.
Constructal optimization of variable cross-section insulation layer of steel rolling reheating furnace wall based on entransy theory
2015, 64 (5): 054402. doi: 10.7498/aps.64.054402
Based on the entransy dissipation extremum principle for thermal insulation process, the constructal optimizations of a variable cross-sectional insulation layer of the steel rolling reheating furnace wall with convective and compound heat transfer (mixed convective and radiative heat transfer) boundary conditions are carried out. An optimal construct of the insulation layer with minimum entransy dissipation rate can be obtained. Results show that the global thermal insulation performance of the variable cross-sectional insulation layer at minimum entransy dissipation rate is better than that of the constant cross-sectional one. The optimal constructs of the insulation layer obtained based respectively on the minimizations of the entransy dissipation rate and heat loss rate are different. The optimal construct of the insulation layer at minimum heat loss rate leads to a reduction of the energy loss, and that at minimum entransy dissipation rate leads to an improvement of the global thermal insulation performance. The difference between the optimal constructs of the variable cross-sectional insulation layer based on the minimizations of the entransy dissipation rate and the maximum temperature gradient is small. This makes the global thermal insulation performance and thermal safety of the insulation layer improved simultaneously. The constructal optimization of the insulation layer based on entransy theory can provide some new guidelines for the optimal designs of the insulation systems.
2015, 64 (5): 054601. doi: 10.7498/aps.64.054601
Effects of peak stress on the properties of dynamic damage evolution of oxygen free high-pure copper (OFHC) are investigated. The spall fracture experiments are conducted in gas gun, and the damage evolution process is studied using the time-resolved free-surface velocity interferometry, also the post-experiment metallurgical analysis of the soft-recovered samples. It is indicated that, with the increase of peak stress, the spall strength has little changed, but distinct differences are observed in the magnitude and rate of damage at which the velocity rises to the first peak beyond the minima, and the rate of damage evolution increases remarkably. It is concluded that the peak stress is not sensitive to the nucleation of voids, but is one of the most important factors for the growth of voids.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
Theoretical investigations on the electronic modulation of diamond nanocrystals by sulfur modification
2015, 64 (5): 056102. doi: 10.7498/aps.64.056102
By stochastic search and the first-principles calculations, we have carried out a systematic investigation on the structural stabilities and electronic properties of sulfur-modified diamond nanocrystals. Among the possible catenarian, annular and cage-like candidates, we determine the stable structures as a function of hydrogen/sulfur chemical potentials according to the phase diagrams. In addition, we also study the electronic properties of sulfur-modified nanocrystals, including the gap modulation and charge distributions.
2015, 64 (5): 056101. doi: 10.7498/aps.64.056101
Quasi-elastic neutron scattering (QENS) is a novel experimental technique for studying the translational dynamics of water in cement paste. In our work, the improved empirical diffusion model has been used to the nonlinear least square fit of the QENS experimental data of cement samples cured for 7, 14 and 30 days, where an energy resolution function R (Q, E) of four Gaussian terms instead of one Gaussian term is utilized during the fitting process. Parameters of the translational dynamics of water in cement paste have been deduced: the number density of immobile water A, the free water index FWI=B1/(A+B1+B2), the full width half maximum of Lorentzian function Γ, the average residence time τ0 between jumps and the self-diffusion coefficient Dt of mobile water. Fitted QENS spectra are more accurate and the dynamics of water in cement paste can be quantitatively explained with these deduced parameters.All this provides a practical and useful method for spectral analysis of QENS on translational dynamics of water in cement.
2015, 64 (5): 056401. doi: 10.7498/aps.64.056401
Al-4 wt.%Ni (hypoeutectic), Al-5.69 wt.%Ni (eutectic) and Al-8 wt.%Ni (hypereutectic) liquid alloys are highly undercooled and rapidly solidified under free fall condition. Theoretical calculations indicate that the coupled zone of (Al+Al3 Ni) fibrous eutectic is an unclosed region in the composition range from 4.8 to 15 wt.% Ni, which is strongly skewed towards the Al3 Ni phase side. It is found that the cooling rate and undercooling of liquid alloys would increase as the droplet size decreases. Then the microstructural evolution of Al-Ni alloys will be induced by the competitive growth of (Al) dendrite, Al3 Ni dendrite, and (Al+Al3 Ni) eutectic. During the rapid solidification of Al-4 wt.%Ni hypoeutectic alloy, complete solute trapping effect occurs and then causes the formation of metastable segregationless (Al) solid solution phase. When the droplet undercooling exceeds 58 K, the structural morphology of Al-5.69 wt.%Ni eutectic alloy shows a transition from (Al+Al3 Ni) fibrous eutectic to primary phase (Al)-dominated hypoeutectic structure. As the undercooling increases further, the fibrous eutectic becomes the unique microstructure of Al-8 wt.%Ni hypereutectic alloy, and finally evolves into a kind of granular eutectic.
ATOMIC AND MOLECULAR PHYSICS
2015, 64 (5): 053201. doi: 10.7498/aps.64.053201
We report the experiment data of X-ray spectra produced by the impact of Xeq+ (q=10, 15, 20, 26) with 2.4 MeV kinetic energy on Au surface in the National Laboratory of Heavy Ion Research Facility in Lanzhou. Results show that there is different broadening of Au M X-ray owing to multiply ionized effect in the collision with heavy ions, the degree of ionization mainly depends on the distribution of the electronic states in the ions' outer shell. The yield of X-ray is calculated and compared with BEA (binary encounter approximation) model, and the effect of ion charge state on the X-ray yield is also discussed.
2015, 64 (5): 053301. doi: 10.7498/aps.64.053301
Line width is the key parameter in tunable diode laser absorption spectroscopy (TDLAS); the dominant line widths are Doppler and collisional broadenings. Under low absorbance, the ratios of 2nd to 4th harmonics at the line center monotonously decrease and intersect at a fixed point, regardless of the changes in Doppler and collisional line widths. Based on this characteristic, a method is proposed which employs the ratios to measure the line width. To validate the reliability and accuracy of the proposed method, the transition of CO2 at 6982.0678 cm-1 is selected to measure the line width, the gas partial and total pressure. Experimental results show that the proposed method can achieve high precision in actual measurements.
2015, 64 (5): 053701. doi: 10.7498/aps.64.053701
A novel scheme is proposed for a double-dark-hollow beam (DDHB) based on non-full-range phase modulation with double-period. Upon illumination by a collimated He-Ni laser beam shaped by a round hole with a radius of 1.5 mm, the DDHB with an axial length of 30 mm, a width of 0.110.14 mm for each dark hollow beam and their separated distance being 57.6 m is generated in the image space of lens with a focal length of 200 mm. The proposed scheme has the advantages of simple construction and high controllability, and the separated distance between the two light pipes is only dependent on the factor of phase modulation of p. Under the given conditions, a reversible evolution process from a DDHB to a single dark hollow beam (SDHB) can be realized. Experiments for our scheme are performed, results of which are consistent with the theoretical ones. A valuable expansion of the application of DDHB in blue-detuned optical trapping is also discussed. Double and four well hollow optical traps, even the hollow optical lattices can be obtained by using various spatial combinations of our DDHB. The proposed DDHB is expected to play an important role in the study of trapping and manipulation of cold atoms or molecules.
Study on the properties of vector beams generated by a curved wave plate in the strong-focusing regime
2015, 64 (5): 053702. doi: 10.7498/aps.64.053702
We propose a new scheme to generate the axisymmetric vector beam. A curved wave plate, designed by using the birefringence properties of a crystal, can generate two different phase distributions with respect to the o-light and e-light, and it then can transform the linearly polarized light into the radial or azimuthal vector beam with the property of rotational symmetry. The above scheme has the advantage of having a simple light path and can be adjusted conveniently. According to Richards-Wolf's model of the classical vector diffraction, we calculate the distributions of the diffracted electromagnetic field that is illuminated by a hollow Gaussian beam and focused by a lens with high numerical aperture. Results show that the hollow vector beam has a very high intensity and intensity gradient and longitudinal distribution of the electric or magnetic field even if illuminated by the laser with a power of 0.5 W. In addition, real-time adjusted distributions of the photon angular momentum can be generated. This scheme has good application prospects in the manipulations of the microscopic particles.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Experimental investigation on attenuation effects of electromagnetic waves in an unmagnetized plasma
2015, 64 (5): 055201. doi: 10.7498/aps.64.055201
Plasma stealth technology has many unique advantages, hence it has a promising application in the aviation and aerospace fields. The attenuation characteristics of vertical incidence of electromagnetic waves into unmagnetized plasmas with metal underlay are studied theoretically and experimentally in this paper. Regulations for the change of electromagnetic wave attenuation with plasma parameters are analyzed in theory using WKB method. A-large-area plasma slab is generated stably by inductively coupled discharge, and the reflectivity arch test system of plasma slab is set up. While the attenuation effects of electromagnetic wave in unmagnetized plasmas are studied experimentally. The electron density of plasma generated at different discharge powers is obtained by using the microwave phase and plasma spectrum diagnostic technique, ranging from 8.17× 109 to 7.61× 1010 cm-3. The plasma generated by inductively coupled plasma (ICP) has an effect on the attenuation of electromagnetic waves, and the experimental results accord well with the theoretical ones. Results show that increasing the plasma electron density and covering homogeneity can contribute to improving the attenuation effect of plasma on electromagnetic waves.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Gold nanowire tip-contact-related negative differential resistance twice and the rectification effects
2015, 64 (5): 057301. doi: 10.7498/aps.64.057301
Electron transport properties of molecular junctions formed by 1, 4-dithiolbenzene(DTB) coupled to [1,1,1] Au nanowires are investigated by using the method of non-equilibrium Green's functions based on first-principle density functional theory. Different S-Au contact configurations are constructed and optimized. The junction with tip-type Au electrode top binding to a thio (S) atom is illustrated by the best configuration for electron transport. Juntions with asymmetric electrode-DTB contact show excellent rectifying performance (the largest rectification ratio being 25.6). Other junctions display negative differential resistance (NDR) effect twice. Analysis shows that the rectifying effect may originate from the difference between the stabilities of S-Au contact modes at both sides. Molecular orbitals including the tip Au atoms are calculated. In low bias region, the orbitals near the Fermi energy dominate the electrons transmission; while, as the bias increases, those apart from the Fermi energy contribute to the transport, along with the DTB eigen-level. During the whole process, the locations and amplitude of transmission vary with bias voltage and I/V curves show two peaks, resulting in twice-NDR effect.
Cobalt-doped ferroferriborate ((Fe1-xCox)3BO5) nanorods (NRs) have been synthesized by using a high-temperature organic-solution-phase method, and characterized by high resolution transmission electron microscope (HRTEM) and SQUID. The aspect ratios of the NRs are tuned by reductive decomposition of Fe(acac)3 and Co(acac)2 with a predetermined ratio. HRTEM showS that the sample is polycrystalline NRs and the top view of a NR tip reveals a multiply-twined structure. Magnetization curves indicate that (Fe1-xCox)3BO5 NRs are ferromagnetic above room temperature and the antiferromagnetic component is included, the magnetic properties are dramatically modified by Co substitutional doping. The NRs are expected to be used to study the mechanical properties of biological macromolecules.
A new characteristics matrix method based on conductivity and its application in the optical properties of graphene in THz frequency range
2015, 64 (5): 057801. doi: 10.7498/aps.64.057801
A new characteristics matrix method along with the formulas based on conductivity, which can be used to calculate the optical properties of an ultra-thin conductive composite multilayer dielectric structure, is derived for the first time as faras we know based on the electromagnetic boundary conditions Maxwell's equations required. It can be used to calculate the reflection, transmission, and absorption of light, provided that the conductivity of the conductive body is known, also it can overcom the shortcoming of the traditional transfer matrix method, i.e.it is necessary to know the permittivity and permeability of the material. By using the proposed method, the optical behavior of graphene and composite multilayer structures can be obtained in the THz frequency range.
2015, 64 (5): 057401. doi: 10.7498/aps.64.057401
Taking into account the interface scattering effect on each band (in-band interaction) and the interaction between the bands (inter-band interaction), within an extended Blonder-Tinkham-Klapwijk scattering formalism, we have studied the quasi-particle transport coefficients and the tunneling spectrum for quantum wire/iron-based superconductor junction of different types of two-level system by solving the Bogoliubov-de Gennes equations. It has been shown that: 1) When the junction is in ballistic limit, the platform near zero bias of the s -wave tunneling spectroscopy will become a conductance peak as the inter-band interaction increases, while a dip occurs in s++ -wave tunneling spectroscopy, and the zero-bias conductance peak will be depressed for p-wave. 2) When the interface scattering effect is not zero, the peaks in the two energy gaps of both s -wave and s++ -wave iron-based superconductor will be depressed; as the inter-band interaction increases, the dip between the two peaks will increase, moreover, the value of zero-bias conductance peaks for p-wave will be lowered and the value of nonzero-bias conductance will be increased. 3) As the in-band interaction is increased, the self-conductance peak will become sharper, while the another conductance peak is not only lowered but also smoothed. These results will be helpful for clarifying the structure of the pair-potential in iron-based superconductor and distinguishing their types.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Study of energy partitioning and its feedback on the microclimate over different surfaces in an arid zone
2015, 64 (5): 059201. doi: 10.7498/aps.64.059201
Model simulations show that land use and land cover changes(LUCC) may alter surface energy budget and influence surface microclimate, but up to now, it still lacks of sufficient observations for explaining the mechanism of climate change brought about by LUCC. Grasslands and shrub lands are typical land covers in the mid-latitude arid zone of the northern hemisphere. The data used in this paper was collected from four sites which are related to grassland, open shrubland, savanna and closed shrubland, and all located in New Mexico, USA. The four sites are near each other and have the same background in climate and weather. Thus, the difference in surface energy partitioning over the four surfaces is induced by different land processes, which was explained in our study. The paper also analyzed the feedbacks of different land surface parameters and energy partitioning for the surface microclimate.We find that the leaf area index(LAI) and surface roughness of the four sites increases from the desert grassland to the closed shrubland. The difference in vegetation structures and functions also affects aerodynamic resistance and surface resistance to heat transfer and the resistances exhibit larger over sparse surfaces. Generally, the sites with high vegetation cover have higher net radiation, sensible and latent heat fluxes, particularly in the growing season. In addition, the contributions of impacting factors to the turbulent fluxes are diagnosed by Penman-Monteith equation and a mathematical formula combining net radiation with Bowen ratio. Compared to the desert grassland, the variations in net radiation over other three surfaces indicate positive contributions to both sensible and latent heat fluxes and govern their changes. The variations in the aerodynamic resistance and the surface resistance lead to opposite contributions. Besides, both radiative surface temperature and surface air temperature over the sparse surfaces are significantly higher than that over the closed shrubland. Larger aerodynamic resistance and Bowen ratio over the sparse vegetation dominate the warming trend accompanying the vegetation degradation and simultaneously offset the cooling effect induced by the decrease in net radiation, showing the land surface process over different surfaces factually has an evident feedback on surface micro-climate in the same climate and weather background.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Simulation of electric activity of neuron by setting up a reliable neuronal circuit driven by electric autapse
2015, 64 (5): 058702. doi: 10.7498/aps.64.058702
Transition of electric activity of neuron can be induced by electric autapse, and its action potential is much sensitive to the stimuli from the electric autapse. Generally, the effect of electric autapse on membrane potential of neuron is often described by using time-delayed feedback in closed loop. Based on Pspice software, a class of electric circuit is designed with the electric autapse being taken into consideration, and a time-delayed circuit is used to detect the adjusting action of electric autapse on the action potential. Results are found as follows: (1) The neuronal electric circuit can produce quiescent state, spiking, bursting state under an external force besides the electric autapse circuit. (2) The transition of electric activity occurs between four different atates (quiescent, spiking, bursting state) by imposing a time-varying forcing current; its potential mechanism is that the electric circuit is associated with the memory, and the neuron can give different types of response to the same external forcing current. (3)When a strong external force is imposed, the outputs can show different type of electric activities due to an electric autapse, that is to say, self-adaption of gain in the autapse is useful for the neuron and thus different type of electric activities occurs, whose potential mechanism may be due to the effective feedback in the loop; so it is helpful to understand the synaptic plasticity.
2015, 64 (5): 058501. doi: 10.7498/aps.64.058501
Limited by materials and process stability, the nano-scale IC manufacturing process is still based on the 193 nm light technology and the wavelength is larger than the feature size of layout, thus the induced interference and diffraction greatly reduce the resolution, which affect the quality of the chip. So the layout needs to be checked by the design-for-manufacturability (DfM) model before manufacturing. Traditional DfM models describe the process steps using physical models, and deduce the convolution kernels by decomposing the matrix in corresponding physical models, which are not only complicated but also hard to use; thus combined with the insufficiency of physical models, it is difficult to describe the process with thousands of parameters. This paper uses convolution form as the framework of DfM model, and deduces the relationship, represented as convolution kernels, between layout and contour by an optimization method. Every element in the convolution kernels is optimized based on the input and output data of the process and is also a dimension to describe the process. This model overcomes the disadvantages of the traditional model which needs confidential information such as process parameters, and it has more powerful capability to describe the process. Moreover, the model can contain the layout correction information, and describe the process from layout to contour. Experiment results for 65 nm process show that the model has an accuracy of 8 nm.
2015, 64 (5): 058701. doi: 10.7498/aps.64.058701
Assessment of resting-state functional connectivity (FC) has become an important tool in studying brain disease mechanisms. Conclusions from previous resting-state investigations were based upon the hypothesis which assumed that the FC was constant throughout a period of task-free time. However, emerging evidence suggests that it may change over time. Here we investigate the dynamic FC based on the 64 electrodes EEG (electroencephalogram) of 25 healthy subjects in eyes closed (EC) and eyes open (EO) resting-state. A data-driven approach based on independent component analysis, standardized low-resolution tomography analysis, sliding time window, and graph theory are employed. Dynamic changes of FC over time with EC and EO in the visual network, the default mode network etc. are discovered. And the principal component analysis is used to the concatenated dynamic FC matrixes for finding meaningful FC patterns. Our results have complemental the traditional stationary analyses, and revealed novel insights in choosing the type of resting condition in experimental design and EEG clinical research.
2015, 64 (5): 058703. doi: 10.7498/aps.64.058703
Currently, the one-dimensional signal processing method for heart-sound analysis and recognition is the mainstream in researches. In order to gain more intuitive features in manifestation, to improve the effect of classification, and to endarge the heart-sound recognition field, this paper puts forward a heart-sound texture feature extraction and recognition algoriithm, which is based on heart-sound window function and the combination of heart-sound and image processing technology. Firstly, we give a heart-sound model, a definition of heart-sound time-frequency diagram, and a heart-sound texture map; we also discuss how to utilize heart-sound window function and short-time Fourier transform to obtain a two-dimensional heart-sound time-frequency diagram. After that, in the light of the characteristics of heart-sound, we mainly study the structure principle and implementation method of a heart-sound window function Finally, the heart-sound texture feature extraction and identification are realized by the improved pulse-coupled neural network model (IPCNN). Simulation experiments show that compared with the traditional window function, the heart-sound time-frequency diagram obtained using heart-sound window function has a clearer and noise well suppressed texture. Furthermore, compared with other three kinds of typical recognition methods, IPCNN has the lower computational cost and higher recognition rate. So, we can arrive at the conclusion that the method for heart-sound feature extraction and recognition based on image processing techniques is the effective one.
A half-covered helical cone-beam reconstruction algorithm based on the Radon inversion transformation
2015, 64 (5): 058704. doi: 10.7498/aps.64.058704
Compared with the traditional helical cone-beam computed tomography (CT), the field-of-view (FOV) half-covered cone-beam CT can almost double the FOV and thus image the large object by using a smaller panel detector. However, the projections are transversely truncated, resulting in truncation errors in reconstructed images if no correction measures are taken. In this paper, a half-covered cone-beam reconstruction algorithm based on the Radon inversion transformation is developed, in which the data filtering is performed in two steps. The first step is a local operation and can be carried out correctly even when the data is truncated. This performance of local operation makes the original data closer to zero, so the continuity of data is improved. And this also can restrain the truncation errors caused by the following global operation. Numerical simulations and experimental results are presented to demonstrate the algorithm and to compare it with existing algorithms. Preliminary results indicate that the proposed algorithm can well restrain the truncation errors and improves reconstruction quality.
2015, 64 (5): 058901. doi: 10.7498/aps.64.058901
When in operation, cipher chips emit photons which can reveal important information about their operation and data. An experimental system based on single-photon counting for the detection, transmission, processing and analysis of photonic emission from CMOS semiconductor integrated circuits has been designed and constructed. Using time-correlated single-photon counting (TCSPC) technology, we have analyzed the photon emission of cipher chip AT89C52, and measured the relationship between its emission intensity and voltage. We have also analyzed in detail the relationship between the photonic emission and the operations and data processed in the chip at the instruction level. Furthermore, we have confirmed the feasibility of our TCSPC technique using an oscilloscope. Our experimental results show that cipher chip photonic emission analysis based on TCSPC technology is a relatively low cost but effective method for optical side-channel attacks, and that it poses a serious practical threat to cipher chip security.
2015, 64 (5): 058902. doi: 10.7498/aps.64.058902
Structural hole nodes in complex networks play important roles in the network information diffusion. Unfortunately, most of the existing methods of ranking key nodes do not integrate structural hole nodes and other key nodes. According to the relevant research on structural hole theory as well as the key node ranking methods, network constraint coefficient, betweenness centrality, hierarchy, efficiently, network size, PageRank and clustering coefficient, 7 metrics are selected to rank the key nodes. Based on the 7 metrics, a ranking learning method based on ListNet is introduced to solve ranking key nodes by multi metrics. Comprehensive experiments are conducted based on different artificial networks and real complex networks. Experimental results with manual annotation show that the ranking method can comprehensively consider the structural hole nodes and other nodes with different important features. The ranking results on different networks are highly consistent with the manual ranking results. The spreading experiment results using signed to interference ratio propagation model show that SIR model can reach a maximum propagating ratio in a shorter propagating time initiated by TOP-K key nodes selected by our method than TOP-K key nodes selected by other methods.
2015, 64 (5): 052801. doi: 10.7498/aps.64.052801
Because of a very non-uniform power distribution in core region, a very non-uniform distribution of relative uncertainties exists for tallies in Monte Carlo criticality calculations of pin-by-pin reactor model. To make a large part of cells obtain small enough relative uncertainties with reasonable time costs, increasing the total sample scale is not a good choice. By realizing a modified uniform-fission-site algorithm on the basis of source iteration algorithm of parallel Monte Carlo transport code JMCT, we obtain higher efficiencies for tallies in the calculations of pin-by-pin model of the Dayawang reactor plant. This work supplies a useful tool for matching the goal of simulating the benchmark pin-by-pin reactor models with a pre-described standard(the so called Kord-Smith challenge).
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER,CLASSICAL MECHANICS, AND FLUID DYNAMICS
2015, 64 (5): 054203. doi: 10.7498/aps.64.054203
In order to achieve precise extraction of the phase with a light feedback mechanism, based on empirical mode decomposition (EMD) algorithm, an adaptive phase extraction method is proposed in this paper. First of all, the EMD algorithm is acted on the self-mixing interference (SMI) mixed noise signals, then using the principle of HHT to extract the instantaneous phase information in the SMI signal in time and retrieve the true phase of the object from the wrapped phase. In this paper, the phase extraction algorithm based on EMD are simulated under different optical feedback conditions. Finally, an experimental setup based on SMI has been given for demonstration. Experimental results show that this method is correct in principle and can be used in the precise extraction and its maximum error is less than 1.6 rad. The simulation results are consistent with the experimental data, which show the effectiveness of the proposed method.
SPECIAL ISSUE — Cancer biophysics
2015, 64 (5): 058707. doi: 10.7498/aps.64.058707
Investigation of tumors from a physics perspective has attracted more and more attention since the initiation, development, and metastasis of tumors are strongly influenced by the physical interactions between the tumor cells and their microenvironments. Since tumor metastasis accounts for more than 90% of cancer-associated death, one of the focuses is to understand its underlying mechanism, especially how tumor cells polarize during their migration. Cell polarization directs tumor-cell migration in response to a spatial stimulus, e.g., the gradient of chemokine or oxygen molecules. It forms the front and back edges of cells by estiblishing asymmetric distributions of cell polarity proteins such as the Rho family GTPases and organelles such as Golgi. This paper reviews how the experimental and theoretical studies combining physics with biology reveal the underlying mechanisms of cell migration and cell polarity. Experimental results demonstrate that the physics clues including extracellular matrix's mechanical properties, dimensionality, and topography are strongly coupled with the biochemical reactions to establish and maintain the cell polarity and direct cell migration. The cell migration mode in a more physiological three-dimensional (3D) matrix is different from that in a two-dimensional(2D) system. Moreover, the membrane tension is suggested to maitain cell polarity by inhibiting polarization processes outside the front edge. On the other hand, a series of reaction diffusion models have been developed to characterize cell polarity. Representative examples inculding Turing-type model, local-excitation and global-inhibition (LEGI) model, and wave-pinning model can capture certain features of cell polarization, however none of them takes the physical factors, such as the membrane tension, into account hence fails to explain previous published experimental results about the membrane tension with cell polarization. To further improve our understanding of the mechanism of cell polarity, in the future study it is experimentally important to estiblish 3D tumor systems and study the gene regulation network that can control cell polariztion by advanced microscope; theroetically it is of importance to build mathematical models for the chemical reaction diffusion systems coupled with the mechanical factors such as membarne tension. These studies will reveal the molecular mechanism of cell polarization and cell migration under a more physiological relevant condition. They may also help us understand how the higher deformation ability of cancer stem cells provides the higher migration capability compared with the normal cancer cells. Ultimately, they will facilitate developing new therapeutic strategy against tumor metastasis by targeting the signaling of tumor cells in response of physical stimuli.
2015, 64 (5): 058201. doi: 10.7498/aps.64.058201
Mechanical interaction between cancer cells and their microenvironment plays a central role in the progression of tumors. In vitro models based on biopolymer networks have been successfully employed to simulate the 3D extracellular matrix (ECM) of tumors. In this review, we focus on type I collagen gel. We describe the hierarchical structural and mechanical properties of type I collagen ECM. We demonstrate that corresponding to the scales of adhesion sites, single cells and cell colonies, the mechanics of the ECM is dominated by single fibers, fiber clusters and rheology of the whole fiber network. In the end, we discuss the limitations of reconstituted type I collagen as in vitro ECM.
2015, 64 (5): 058705. doi: 10.7498/aps.64.058705
The major reason why cancer kills is its metastatic potentials. Metastasis is an extremely complex three-dimensional (3D) process. Currently, routine in vivo cancer research still experiences bottlenecks in observation and manipulation, while in vitro research mainly stays in petri-dish levels that limit cell environment with two-dimensional confinements. Therefore, it is in urgent needs to construct 3D in vitro models to deepen the studies in cancer invasion and metastasis. However “how to carry out” is a big question that harasses scientists for decades. In this report, we will systematically discuss several popular technologies for 3D microfabrication and their applications in bio and cancer research. Besides, we will demonstrate our efforts to construct an all-in-one 3D micro ecology simulation system (3D MESS) which highly integrates a UV bio-compatible hydrogel printer, a light-sheet imaging system, and a nano pipette operation system. This novel system will create a brand-new method to fabricate, observe and controls the 3D structures and the cells inside. We believe that these advanced technology and ambitions will definitely update the current cancer research methods and bring promising hopes for future deeper understandings and more efficient treatment of cancer.
2015, 64 (5): 058706. doi: 10.7498/aps.64.058706
Emergence of invasive and metastatic behavior in malignant tumors can often lead to fatal outcomes for patients. The collective malignant tumor behavior resulting from the complex tumor-host interactions and the interactions between the tumor cells are currently poorly understood. Progress towards such an understanding necessarily requires an interdisciplinary and collaborative effort. In this paper, we review a state-of-art simulation technique, i.e., a cellular automaton (CA) model which has been developed by the authors over the past few years to investigate microenvironment-enhanced invasive growth of avascular solid tumors. This CA model incorporates a variety of microscopic-scale tumor-host interactions, including the degradation of the extracellular matrix by the malignant cells, nutrient-driven cell migration, pressure build-up due to the deformation of the microenvironment by the growing tumor and its effect on the local tumor-host interface stability. Moreover, the effects of cell-cell adhesion on tumor growth are also explicitly taken into account. A number of bench-mark collective invasion behaviors have been successfully reproduced via the CA model, including the emergence of elongated invasion branches characterized by homotype attraction and least resistance path, development of rough tumor surface in a high-pressure confined environment, as well as reduced invasion due to strong cell-cell adhesion. Such simulated bench-mark behaviors strongly indicate the validity and predictive power of the CA model. In addition, the CA model allows one to investigate the role of various different microenvironment factors in the progression of the neoplasm, in particular, the promotion and enhancement of tumor malignancy. As an example, a “phase diagram” that summarizes the dependency of tumor invasive behavior on extracellular matrix (ECM) rigidity (density) and strength of cell-cell adhesion is constructed based on comprehensive simulations. In this simple phase diagram, a clear transition from non-invasive to invasive behaviors of the tumor can be achieved by increasing ECM rigidity and/or decreasing the strength of cell-cell adhesion. This model, when properly combined with clinical data, in principle enables one to broaden the conclusions drawn from existing medical data, suggest new experiments, test hypotheses, predict behavior in experimentally unobservable situations, be employed for early detection and prognosis, and to suggest optimized treatment strategy for individual patient.