Simulation studies on W-band traveling-wave tube with double rectangular comb slow-wave structure
Design and simulation of a single-sided left-handed material in THz regime
By retrieving the constitutive effective parameters of bifilar spiral structure, it is proved that its permittivity and permeability are negative at different frequencies. With the electromagnetic waves incidence in the direction either perpendicular or parallel to the surface of bifilar spiral structure, it is found that the causes of negative permittivity are the same. Previously the investigation of single-sided left-handed materials was limited to microwave band. Through modifying bifilar spiral metamaterials, we design a new single-sided left-handed material in the terahertz regime and the design principle is explained with an LC equivalent circuit. The left-handed material generally consists of electric and magnetic resonators etched on each side of the dielectric substrate respectively Compared with these composite structures, the new single-sided left-handed material has the advantages of low loss, simple structure and easy operating
Analysis of symmetrical, periodic negative-permeability metamaterial using interdigital capacitance loading
Fast parallel iterative calculating of the composite scattering between targets and rough surface
A new fast far field approximation algorithm is introduced to calculate the composite scattering characteristics of rough surface and the target in near field, by using the reduced-order electromagnetic current iteration method. Also we use the multi-process parallel algorithm to reduce the simulation time and analyze the influence on the results of the reduced-order electromagnetic current iteration. The calculated results by the algorithm described in the paper and the results obtained by multi-level fast multi-pole method (MLFMM) are in good agreement, so the effectiveness of the algorithm is verified. At the same time, the use of tank to carry out the measurements of near-field complex scattering between the targets and rough surfaceshows that the test results and the calculation results are very consistent.
Simulation for Space target interference imaging system distorted by atmospheric turbulence
Smoothing of small on-target spots produced by frequency-tripled beams using lens array and spectral dispersion
The performances of the smoothing of small target spots with a lens array (LA) and two-dimensional smoothing by spectral dispersion (2D SSD) in frequency-tripled high-power laser driver are numerically studied. Intensity distributions and spatial power spectra of the spots are analyzed. Simulative results show that LA can reduce the near-field nonuniformity of the beam and control the envelope of on-target intensity distribution. The 2D SSD has obvious effects in eliminating high-contrast intensity modulation, even in the case that the spots are very small. The results indicate that SSD mainly smoothes the intensity modulation at low-to-middle spatial frequency for small spots, and this would lead to the modifying of the spot profile, while for large spots, SSD sweeps the fine speckle structure to reduce nonuniformity at middle-to-high frequency. These results are valuable for choosing the suitable beam smoothing method in indirect-drive experiment.
Numerical simulation of soliton trapping of the supercontinuum in photonic crystal fiber
Study on the polarization mismatch in micro/millimeter-wave generation employing optical self-heterodyning technology
Study of the satellite line in measurement of the argon -gas-induced broadening of the barium Rydberg levels by two-photon resonant nondegenerate four-wave mixing
We study the satellite lines in measurement of the foreign-gas-induced broadening of the barium Rydberg levels by two-photon resonant nondegenerate four-wave mixing (NFWM). The NFWM spectra of the 6s2 1S0-6snd 1D2 (n=16, 22, 36) transitions at different argon pressures are measured. The plots of the center of satellite line principal quantum number and versus pressure are discussed. The contribution of satellite line to the NFWM spectral profile is analyzed. We find that the pressure-broadening rate coefficient can be corrected when the contribution of satellite line is considered.
The dynamic effect of a field with a time-varying frequency on the atom-atom entanglement in a double J-C model
The entanglement between the two atoms of two separate Jaynes-Commings models is investigated by means of the concurrence. We restrict our attention to two cases, the field frequency varying with time in the forms of sine and rectangle. When the field frequency varies with time in the form of sine, the period and the amplitude of the atom-atom concurrence will decrease as the amplitude of the sine frequency modulation increases. Not only the sine field frequency modulation but also the rectangular field frequency modulation can affect the interaction of the field with atom between resonance and off-resonance. The field frequency modulation can also affect the atom-atom entanglement. The suitable field frequency modulation is favorable for improving, enhancing and stabilizing the degree of the atom-atom entanglement. The suitable field frequency modulation can also prevent the atom-atom entanglement from entanglement sudden death and control it dynamically.
Two-site Hubbard-holstein model polaron of quantum entanglement properties
We obtain the exact solution of energy spectrum and dynamics for the two-site Hubbard-Holstein model by the coherent states orthogonal expansion method. The influences of coupling strength g, the average number of phonons n and the initial electronic state on the evolution of system entanglement and von Neumann entropy are discussed. Numerical results are as follows. (a) Entanglement evolution with time shows a good periodicity. When the other parameters are fixed, the evolution period decreases as the coupling strength g goes up but it is independent of the average number of phonons n. (b) The von Neumann entropy of the system demonstrates strict synchronia with the electronic state occupancy probability. (c) Under the weak coupling strength and low average number of phonons, the initial electronic state c2↑+ c2↓+|O>e or c1↑+ c1↓+|O>e shows larger maximum von Neumann entropy during its evolution than that of c1↑+c2↓+–c1↓+c2↑++ but they gradually approach to each other with the increase of coupling strength or average number of phonons.
Study of orbital angular momentum entangled photons entanglement in atmospheric channel
Focusing properties of the high order vector beam by a high numerical aperture lens
A study of two-dimensional hexagonal phase array optical beam splitter modulated by external electric field
In this paper, we establish a theoretical model of reciprocal-lattice vector of the two-dimensional hexagonal phase array optical beam splitter modulated by an external electric field, perform the analysis of the tunable phase-difference array optical beam splitter according to the numerical simulation, and then obtain the images of intensity distribution with different values of fractional Talbot distance and external electric field. The two-dimensional hexagonal phase array optical beam splitter is designed and fabricated by lithium niobate. An experimental study of beam splitting is also given. When the applied voltage is 0.5 kV (with electric field of 1 kV/mm), we observe the phenomenon of the beam splitting in Talbot diffraction. As the external field increases, the images of beam splitting in diffraction become clearer, the experimental results are in agreement with theoretical results.
Coherence properties of the supercontinuum generated in anomalous dispersion region of photonic crystal fibers
Experimental research of triangular optical pulse generation in normal dispersive fiber
Investigation on Doppler spectra of microwave scattering from sea surface
Based on the composite surface scattering model, the analytical formulas for Doppler shift and bandwidth of radar echoes return from time-varying sea surface are derived. In our derivations, the influences of the tilt modulation, the shadow and the curvature of large-scale undulating waves are all taken into account for achieving more reasonable results. Comparisons between the theoretical results and direct numerical simulations demonstrate that the analytical formulas can significantly improve the simulated results. And the effects of the tilt modulation, the shadow and the curvature on Doppler spectral properties are discussed in detail. From the simulated results, it is found that the predicted Doppler shifts are always larger in HH-polarization than in VV-polarization due to the tilt modulation of large-scale waves. In addition, at low-grazing angles, the shadow of large-scale waves results in a rapid increase of the predicted Doppler shift, and on the contrary maks the bandwidth narrower.
Near-field modulated simulation of repaired site contained crack or bubble in fused silica subsurface
Key technology on all-plastic optical life detection instrument
Plastic fiber image bundle with 250 μ single fiber diameter, 4096 pixels, 15 m length is fabricated. The result indicates that 25% of the input image remains after it has translated though the 15m fiber bundle, which can meet the need of eye observation or CCD image capture. Based on the key component of image bundle, the eye observation life detection instrument prototype and intelligent life detection instrument prototype connected with CCD, image capture card and portable computer are designed and produced. The effectiveness of researching and rescuing the person from danger is demonstrated. The system can be used not only for researching and rescuing the buried person, but also for video monitoring some special occasions, such as strong electromagnetic interference environment, security department and explosive places.
Full-vectorial analysis of the directional couplers in horizontal multiple-slotted silicon wires with trapezoidal cross-section
Dynamic behavior of a cavitation bubble in acoustic field and electric field
The dynamics of a cavitation bubble under acoustic field and an electric field is studied by regarding liquid as a working medium. The effects of the dimensionless frequency and strength of acoustic field and electric field on cavitation bubble dynamical behaviors by Rayleigh-Plesset equation are numerically investigated. The results show that when acoustic field and electric field are combined, chaos area range of cavitation bubble motion is larger than that when only acoustic field or single electric field exists. This is of significance not only for further research of acoustic cavitation but also for enhancing and improving the cavitation degration of organic pollutant technology.
Experimental research on cylindrical focused beamforming localization method of moving sound sources based on vector sensor array
Based on the passive synthetic aperture principle, a new cylindrically focused beamforming localization method of moving sound sources based on vector sensor array suited for both narrowband and broadband signal is proposed in this paper. By establishing the measurement model of moving sound sources, calculating the localization accuracy versus error, and analyzing the experimental results of cabin model, the performance of this new method can be verified. A comparison between the focused beamforming localization results and the shell vibration measurement results proveds that the proposed method not only can obtain the localization results, but also can reflect the relative contribution of each coherent source.
Analysis of thermal protection mechanism of leading structure embedded high directional thermal conductivity layer
The structure of embedded high thermal conductivity layer leading thermal protection is considered as thermal protection system to prevent hypersonic vehicle from the serious aerodynamic heating. By numerical method, we analyze the cooling effect of the leading thermal protection system under given conditions. The maximum outer surface temperature and the inner surface temperature are reduced by 9.1% and by 31.5% respectively. Both high temperature region and low temperature region are blocked in the external layer and the inner temperature distributions are more uniform. The transfer of heat from high temperature region to low one is achieved, the thermal load of the high temperature area is weakened, and the ability of leading thermal protection system is strengthened. The research shows that the cooling effect of leading system increases with the increases of aerodynamic flux ratio and the area ratio of radiative surfaces. The influences of structure parameters and materials properties on thermal protection are discussed, which provides some references for the design of the structure and the selection of materials.
Effect of particle density on the segregation of binary granular systems in a rotating drum
Research on convective cooling effect of leading edge platelet of airfoil
A convective cooling platelet structure is a considered as thermal protection system to prevent the leading edge of airfoil from the serious aerodynamic heating. The cooling effect parameter η is proposed in this paper. By the use of fluid structure interaction method, the cooling effect of convective cooling structure is investigated under given condition. The minimum η that is 0.25 when the coolant is water occurs on the leading edge of airfoil head. The research shows that the η increases with the increase of channel aspect radio (γ) and reaches a stable value that indicates that the cooling effect is saturated. Situation unfavorable for cooling may occur if the γ keeps increasing. And the η decreases with the radio of airfoil's head decreasing. With coolant flux increasing, the η also increases to a stable value and the pressure drop between inlet and outlet increases rapidly when the structure and the material of the convective cooling platelet structure are fixed. Considering the pressure brought to the supply system due to the increase of flux, we should choose the optimal coolant flux value in order to obtain better cooling effect. Both the inner coolant groove and the external refractory protection should be of high thermal conductivity material which can strengthen the heat transfer of structure and enhance the cooling effect.
Time periodic electroosmotic flow of the generalized Maxwell fluids between two micro-parallel plates with high Zeta potential
In this study, semi-analytical solutions are presented for the time periodic (electroosmotic flow) of linear viscoelastic fluids between micro-parallel plates. The linear viscoelastic fluids used here are described by the general Maxwell model. The solution involves analytically solving the nonlinear Poisson-Boltzmann (P-B) equation, the Cauchy momentum equation and the general Maxwell constitutive equation. By numerical computations, the influences of the dimensionless wall Zeta potentialψ0, the periodic EOF electric oscillating Reynolds number Re, and normalized relaxation times λ1ω on velocity profiles are presented. Results show that for prescribed electrokinetic width K, relaxation time λ 1ω and oscillating Reynolds number Re, higher Zeta potential ψ0 will lead to larger amplitude of EOF velocity, and the variation of velocity is restricted to a very narrow region close to the Electric double-layer. In addition, with the increase of relaxation time λ 1ω, the elasticity of the fluid becomes conspicuous and the velocity variations can be expanded to the whole flow field. For prescribed Re, longer relaxation time λ 1ω will lead to quick change of the EOF velocity profile, and the amplitude becomes larger gradually.
Wavelength tunable properties for distributed feedback lasing from dye-doped holographic polymer dispersed liquid crystal transmission grating
In this paper, we study the wavelength tunable properties for distributed-feedback lasing from 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) dye-doped holographic polymer dispersed liquid crystal grating. By preparing and pumping the DCM-doped HPDLC gratings with various grating spacings, we depict the tuning curve of the distributed-feedback lasing and confirm that only in a range from 574 nm to 685 nm, the lasing action can be observed. Then, we adjust the temperature of the sample and measure the lasing spectrum from the DCM-doped holographic polymer dispersed liquid crystal grating with a grating period of 610nm. There is an obvious 4.9 nm blueshift from 627.9 nm to 623 nm for the lasing wavelength with the temperature increasing from 20℃ to 65℃.
Growth and photoluminescence character research of aluminum nitride nanowires upon carbon foam substrate
To simplify preparation process of AlN/C composite foam, AlN nanomaterials are prepared via double decomposition reaction and then 800℃ annealing process to recrystallize hexagonal AlN (h-AlN) nanowires on carbon foam substrate. Fore the morphology characterization it follows that, h-AlN nanowires with straight cylindrical morphology grow along the direction on carbon microspheres surface and are about 50 nm in diameter and several micrometers in length. Meanwhile, the growth mechanism of nanowire is interpreted as vapor-liquid-solid(VLS) process. The photoluminescence(PL) spectrum of as-prepared sample also researched, and the results show that a sharp photoluminescence peak appears at 423 nm and shifts toward the red side with temperature increasing. The peak is attributed to the transition luminescence, owing to the substitution of C for N impurity energy level. The sample has good PL character in purple light band and is potential to be used the in photodetector field.
Analysis of Interfacial Mechanical Properties of Carbon Nanotube–Polymer Composite
In this paper, the interfacial mechanical properties of carbon nanotube-polyethylene (CNT-PE) composite are investigated by using classical molecular dynamics simulation. Basd on the simulations for the CNT pulling-out process from the PE, the influences of the CNT sliding velocity, the chain length of PE and the radius of CNT on the interfacial shear stress are explored. As the chain length of PE increases, the critical interfacial shear stress increases remarkably while the sliding shear stress increases slightly. Both the critical shear stress and the sliding shear stress increase with the radius of CNT enlarging. Moreover, the mechanism for the variation of interfacial shear stress is analyzed and discussed.
The Alloying of Ti, C, N in Bulk α -Fe and Their Effects on Bond Characters
The electronic structures and the bond characters of bulk α -Fe with Ti, C, N additions are studied using the first-principls pseudopotential plane-wave method. The total energy and the cohesive energy are calculated, and the Mulliken population, the overlap population, the density of states and the charge density are also analyzed, which can give a microscopic reason why the mechanical property is improved after the infiltration of Ti, C, N into bulk Fe. The calculated results show that with the alloying element Ti(0–12.5 at%), C(0–11.11 at%), N(0–11.11 at%) contents increasing, the cohesive energy of alloy increases slowly and the structure keeps stable. The additions of Ti, C, N into the alloy enhance the reciprocal hybridization in Fermi energy level, and the binding abilities of Ti, C, N, Fe become stronger. The pseudo-gap near the Fermi energy level means the coexistence of covalent and metallic bonds in alloy. With the contents of alloying elements increasing, the covalent bondings between C, N and Ti, Fe become stronger, and part of C and N atoms will be bound to Ti atoms and form TiC and TiN particles, thereby strengthening the dispersion.
Effective g-factor in high-mobility InGaAs/InP Quantum well
High-mobility In0.53Ga0.47As/InP quantum well is fabricated by the chemical beam epitaxy technique. Clear Shubnikov-de Hass (SdH) oscillation and beating pattern due to zero-field spin splitting are observed by magnetotransport measurements at low temperature. We use an analytical method, involving the simultaneous fitting of fast Fourier transform spectra of SdH oscillations at different tilted fields, to extract the effective g-factor.
Electronic structures and optical properties of AAl2C4 (A=Zn, Cd, Hg; C=S, Se) semiconductors
First-principles density functional calculations are performed to study the geometries, the electronic and the optical properties of AⅡAl2C4Ⅵ (A =Zn, Cd, Hg; C = S, Se) semiconductors each with a defect chalcopyrite structure. For the linear optical properties, five compounds show good transmissions of light in the IR and part of visible regions, and among them HgAl2S4 and HgAl2Se4 possess moderate birefringences. For the nonlinear optical properties, the strong second harmonic generation (SHG) response can be expected for these crystals, and the large static SHG coefficients (> 20 pm/V) are predicted in this work. The SHG response of AⅡAl2C4Ⅵ semiconductors can be attributed to the transitions from the bands near the top of valence band which are derived from S/Se p states to the unoccupied bands that are contributed by p states of Al and Hg atoms. By comparing with the optical properties of the commercialized AgGaC2 crystals, our results indicate that HgAl2S4 and HgAl2Se4 compounds are good candidates for the second-order nonlinear optical crystals in the IR region.
First-principles calculation of matal and nonmetal codoped anantase TiO2
We present a first-principles calculation study of matal and nonmetal codoped anatase TiO2. We mainly investigate C/TM and N/TM (carbon and metal codoped, nitrogen and metal codoped) codoped TiO2, are calculate their bound energies, energy band structures and densities of states. We find that the metal and the nonmetal impurities have an aggregate tendenty by calculating the bound energy of codoping structure. Positive bound energy show that the doping atom and the peripheral atom will combine into a bond, the boding-effect-produced system energy is higher than the geometric-distortion-effect produced stress energy. We analyze the energy band structure and boding of N/V and C/Cr --codoped TiO2, and further find that if we want to extend TiO2 light absorb edge and improve TiO2 photocatalysis properties by metal and nonmetal codoped TiO2, we should make codoping by the codoped joint method, namely, below the conduction band and on the top of valence band can arise impurity energy levels contributed by metal 3d and nonmetal 2p orbits respectively
Lithium-doped tris (8-hydroxyquinoline) aluminum studied by density functional theory
Research on shot noise suppression in quasi-ballistic transport nano-mOSFET
Previous studies of shot noise suppression in nano-MOSFET either ignored its suppression or emphasized only its existence but gave no deeper research. In this paper, based on the Navid model, the expressions of shot noise suppression factor (Fano) in quasi-ballistic transport nano-MOSFETs are derived with separately considering Fermi effect, Coulomb interaction and the combination of the two effects. The variations of suppression-factors with source-drain voltage, gate voltage, temperature and source-drain doping are investigated. The results we obtained with considering the combination of the two effects are consistent with those from experiments, and the theoretical explanation is given.
One-dimensional spinless fermions in a confined system
According to the exact analytical Bethe-ansatz solution of the one-dimensional spin-1/2 XXZ model, we perform a numerical study of one-dimensional spinless fermions in an optical lattice in the presence of harmonic potential by using a local density approximation. We study the density profile, and obtain the ρ-u phase diagram (here ρ=Nf√V2/t is the characteristic dimensionless density and u=V/t is the interaction strength scaled in units of the hopping parameter t). With the increases of particle density and nearest-neighbour interaction, the system undergoes five different quantum phases. Through calculating the thermodynamic stiffness Sρ, we find that it can be used as an order parameter. Its singular points can measure the quantum phase transitions in such a confined system.
Room temperature absorption spectra analysis of Er3+/Yb3+-doped Hydrothermal Epitaxial Layer on LiNbO3 and LiTaO3 Single Crystal Substrates
In this paper we introduce the undetermined parameter kNL which is related to the concentration and thickness, and perform the fitting calculation that is on the basis of the absorption spectrum about the hydrothermal epitaxial polycrystalline sample on the surfaces of LiNbO3 and LiTaO3 doped with Er3+/Yb3+ single crystalline substrates according to the J-O theory at the room temperature. It is obtained that for LiNbO3 Ω2=2.34× 10-20 cm2, Ω4=0.77× 10-20 cm2, Ω6=0.31× 10-20 cm2, and kNL=4.32× 10-2 mol·m-2. LiTaO3 Ω2=1.68× 10-20 cm2, Ω4=0.84× 10-20 cm2, Ω6=0.45× 10-20 cm2, kNL=9.17× 10-3 mol· m-2. This method can be extended to the systems in which the data of concentration and thickness such as powder or colloid are difficult to obtain. According to the up-conversion luminescence analysis and the calculation via spectrum parameters, it is confirmed that both the samples have the green up-conversion luminescence at Er3+:Yb3+=1:1, the method of reducing the energy of matrix phonon is tried to improve the quantum cutting yield of 4I13/2 to 2H11/2 and 4S3/2.
Super broadband near infrared luminescence properties in Bi-doped aluminosilicate glasses
Influences of alkaline earth oxides on super broadband near infrared luminescence properties from Bi-doped RO-Al2O3-SiO2 (R=Ca, Sr, Ba) aluminosilicate glasses are investigated. The results show that under different pumping sources, the near infrared (NIR) luminescence shows different behaviors. Under 808 nm excitation, the infrared emission located at 1300 nm with lifetime more than 600 μms is observed, whose intensity increases with the increase of ionic radius. However, under 690 nm excitation, the luminescence at 1100 nm with a full width at half maximum of 400 nm decreases with the increase of ionic radius. According to the above results, it is suggested that infrared emissions may originate from Bi+ and BiO.
Analysis of influencing factors on current spreading of flip-chip light-emitting diodes (LEDs)
Investigation of vibronic structures of optical centres in diamond by photoluminescence spectra
The vibronic spectra mainly depend on the nature of the defects in diamond. The strong sharp local vibronic modes are observed for the interstitial-related centres beyond their phonon cut-off energy (165meV), but not for the vacancy-related centres. The vibronic spectra of these vacancy-related centres show very strong and broad sidebands closely after the zero phonon lines. Further, the vibrations involving only one vacancy are due to two separate phonons or both, one has an energy of approximately 42 meV and the other has approximately 67 meV.
The luminescence properties of a novel electron trapped material Sr2SnO4:Sb3+ for optical storage
A novel electron trapped material Sr2SnO4:Sb3+ for optical storage is successfully obtained by conventional solid state method at 1300℃ It indicates that the 1S0 → 1P1 (208 nm) and 1S0 → 3P1 (265 nm) transitions of Sb3+ are the most efficient writing light source. Its emission covers 400–700 nm and can be attributed to 3P0,1 → 1S0 transition of Sb3+. We can observe yellowish white light and its color coordination is (0.341, 0.395). The thermoluminescence of Sr2SnO4:Sb3+ contains four peaks at about 39 ℃, 124 ℃, 193 ℃ and 310 ℃, respectively. The intensity of peak at 39 ℃ is low and thus it has a weak afterglow which can last only 140 s. However, even after putting it in dark for 1 day, the peak at 310 ℃ can still keep 45.6% of its original intensity and can be efficiently stimulated by 980 nm infrared laser. As a conclusion, the Sr2SnO4:Sb3+ is a promising electron trapping material for application in optical storage.
Preparation and near-infrared luminescence properties of Bi-doped BaO-B2O3 glasses
Bi-doped BaO-B2O3 glasses are prepared by the melting method. Visible and infrared luminescence spectra, fluorescence decay curve and Raman scattering spectra are measured. NIR emissions, not only one broadband emission peak but also several emission peaks, appear in Bi-doped BaO-B2O3 glass under 808 nm LD pumping. The effect of the network structure of BaO-B2O3 glass on the NIR emission is discussed, and the mechanism for the emission is investigated preliminarily.
Structural optimization of GaN blue light LED with double layers of photonic crystals
The GaN-based blue light LED with double layer photonic crystals is designed to enhance the vertical light extraction efficiency. The effective index approximation method is proposed and used to solve the distribution of the modes in the LED model. The geometrical parameters including the depth of the top photonic crystal d, the thickness of the embedded photonic crystal T, and the distance between the active layer and the embedded photonic crystal D are optimized. Compared with other numerical optimization, the mode analysis used in this work can dramatically save computation time and reduce complexity. In addition, it can provide more theoretical details about the influence of these geometrical parameters on light extraction efficiency. It can be found that when the surface photonic crystal satisfies the condition of d ≈ λ / nPhCs, high order modes localized in the structure are still not cut off but the low order modes obtain less power since they are pushed away from the active layer. Hence, the light extraction efficiency reaches its maximum. The cap layer modes can be excited by the embedded photonic crystals, when this layer satisfies 100 nm ≤ T ≤ 300 nm and 100 nm≤ D ≤ 200 nm, the cap layer modes gather much power from the active layer and interact with the surface photonic crystals more efficiently. Hence the light extraction efficiency is dramatically improved. With our optimized parameters, the light extraction efficiency can be achieved to be up 4 times that of ordinary LED. These results shows a significant promise of designing a high-efficiency GaN-based blue light LED.
Radiation degradation mechanism of pn-junction diode based on 1/f noise variation
Based on the relationship between ionizing damage effect and displacement damage effect under radiation degradation mechanism of pn-junction diode, and combined with the noise theory of radiation degradation of pn-junction diode, a change law of low frequency noise of pn-junction diode under radiation found. The inconsistency between the change laws of of two kinds of effects is found. Based on the experimental result, the relationship between two kinds of effects is judged. This relationship can explain the experimental result. This is very important for the device hardening research.
Mechanism study of a THz source using field emission array
The micro-vacuum electronic device is one of the most promising sources for the generation of high power THz-wave radiations. In this paper, the systematical theoretical analyses and computer simulations on the physical mechanism of a kind of micro-vacuum electronic THz radiation source based on the cathode of field-emission array (FEA) are carried out. The mode matching method is used to study the electromagnetic characteristics of the structure, and π-mode is confirmed to be an optimal operation mode for its field distribution. Linear theory (small signal theory) is used to analyze the beam-wave interaction of this kind of source, and the starting condition of the π-mode oscillation is derived. The premodulation of electron beam emitted from FEA and the electron transit time effect in the interaction gap are the physical cause of the electromagnetic oscillation. These results are well verified by the computer simulations.
Design and analysis of thermally tunable liquid-crystal-filled microstructured polymer optical fiber
Structure and spectral properties of Yb3+:Gd2SiO5 crystal
15at.%Yb3+:Gd2SiO5 crystal with a size of φ30 mm × 75 mm is grown by the Czochralski method, and its lattice parameters, atom coordinates and temperature factors are determined by the full-profile Rietveld refinement method. Its spectral parameters of oscillator strength, line strength, transition probability, energy lifetime and integral emission cross-section for Yb3+2F7/2↔2F5/2 transition are calculated using the absorption spectraum. And the laser performance evaluation shows that this crystal is a potential laser crystal with relatively high threshold, and could be used as a medium of tunable or ultra-fast laser pumped by high-power laser diode.
Analysis and design of X-band coaxial multi-beam relativistic klystron amplifier
Comparison of the performance for InAlAs/GaSbAs/InP DHBT and InP/GaSbAs/InP DHBT
Failure mechanism of FC-PBGA devices under external stress
Ultraviolet light-enhanced field electron emission of zinc oxide nanowires
One-dimensional nanomaterial possesses an electric field reinforcing effect, and its field emission properties have aroused much interest. In this paper, ZnO nanowire (NW) arrays are prepared by the thermal chemical vapor deposition (CVD) method, and the characteristic of field electron emission of ZnO NW arrays under the illumination of ultraviolet light is investigated. It is found that, upon ultraviolet light illumination, the turn-on voltage drops off and emission current increases. A process of field emission coupled with semiconducting properties of ZnO NWs is proposed. Ultraviolet photon-excited electron transition from valence band to conductance band and defect energy levels of ZnO NWs can lead the number of emitting electrons to increase, and the photoemission reduces the effective work function of zinc oxide emitters, which largely enhances the field emission performance. The characteristic of field emission of ZnO NWs under ultraviolet light illumination suggests an approach to tuning field emission of semiconductor emitters, which is promising for the applications in optical sensor, cold-cathode flat panel display and field electron source.
Effect of surface potential barrier on quantum efficiency decay of reflection-mode GaN photocathode
The asymptotic solving method of traveling wave solution to a class of sea-air coupled oscillator model
The tropical sea-air oscillator is a complicated natural phenomenon. In this paper, based on a sea-air oscillator model, by a new method of combining the undetermined coefficients with the perturbation theory the asymptotic traveling wave solution of the corresponding model is obtained.
A Study of the hydrodynamic behavior of cylindrical structure with double porous outer shelters
Uniform finite-time stability of discrete-time switched descriptor systems
Optimizing quantum circuits using higher-dimensional Hilbert spaces
Inspired by Lanyon (B. P. Lanyon et al. 2008 Nature Physics. 5 134) successfully simplifying the three-qubit Toffoli gate, we present a novel scheme that optimizes universal quantum logic circuits using assisted higher-dimensional Hilbert space. We construct a more efficient two-qubit circuit and a more effective three-qubit universal quantum circuit by using assisted dimension, Cosine-Sine Decomposition (CSD) and Quantum Shannon Decomposition (QSD). Meanwhile, we present the formula for the complexity of arbitrary n-qubit universal quantum gate. We propose the physical implementation of this scheme by linear optical circuits and cavity-QED. The results show that the two-qubit and three-qubit universal quantum circuits are respectively close and superior to the current optimal scheme in complexity. And with the increase of the number of qubits, the advantage of our scheme will become increasingly prominent.
Entropy exchange and entanglement in the multi-photon J-C model of a moving atom
Study on gravitational waveform from post-Newtonian orbits of spinning compact binary
Dynamical modeling and border collision bifurcation in pulse train controlled discontinuous conduction mode buck converter
According to the charge variation of output capacitor in a switching cycle, the output voltage variation in a switching cycle can be obtained, from which an approximate discrete-time model of pulse train (PT) controlled buck converter operating in discontinuous conduction mode (DCM) is established. Based on the model, the border-collision bifurcations of the PT controlled DCM buck converter with the variations of the load resistance and the input voltage are studied. By constructing the corresponding iterative map curves, the stabilities of the fixed points, formed by the orbits of period-1, period-2, period-3 and so on, are analyzed, and the mechanisms of border-collision bifurcations of the converter under different operation states are revealed. The analysis results indicate that with the variation of parameters, the PT controlled DCM buck converter always operates in different periodic states, in which the change of the operation mode with periodic state is caused by the border-collision bifurcation and the lyapunov exponent is always less than zero. By using PSIM circuit simulation software, the time domain waveforms and phase portraits under different load resistances are obtained. Experimental results are provided to verify the correctnesses of theoretical analyses and circuit simulations and the feasibility of dynamical modelling.
Investigation of blind detection mechanism for chaotic UWB system based on generalized negentrogy
Cryptanalysis and improvement of a class of hyperchaos based image encryption algorithms
Chaos synchronization of regular network based on sliding mode control
Relay node placement and addition algorithms in wireless sensor networks
The node placement is the foundation of network operation in wireless sensor networks. In many applications, the positions of gateway node and sensor node are relatively fixed. To guarantee network connectivity and reliability, some relay nodes must be reasonably placed between the gateway node and the sensor node. In the context of the above applications, we introduce many constraint conditions into the existing placement model, and adopt a hybrid placement method based on enumeration and greedy optimization algorithms to determine relay node positions from their candidate location sets, and we finally achieve the relay node initial placement and follow-up adjustment strategies, owing to new sensor nodes joining the current network. The simulation results demonstrate that our operable and optimized relay node placement algorithm can ensure multi-restricted fault-tolerant relay node placement, and the presented new evaluation standard based on the minimum distance factor can significantly improve the energy-efficiency of relay node placement algorithm.
Effect of noises on the stability of a metapopulation
The Levins model subjected to the noise is employed to study the stability of a metapopulation. The analytic expressions of the stationary probability distribution function and the mean extinction time of the metapopulation are obtained according to the Fokker-Planck Equation. The results show that for the case of no correlation between the additive noise and the multiplicative noise (λ=0, λ is the intensity of correlation between multiplicative and additive noise), the increase of the additive noise intensity α weakens the stability of a metapopulation; for the case of λ≠ 0, λ enhances the stability of a metapopulation. For -(c-e-D)2/(4c√Dα)<λ<1, λ can induce the “resonance restrain” phenomenon. Meantime, there exists a critical value of D. When D is lower than the critical value, the stability of the system is enhanced.
Steady state characteries of FitzHugh-Nagumo neural system subjected to two different kinds of colored noises
Making use of the unified colored noise approximation, the steady sate characteristics of the one-dimension of FitzHugh-Nagumo neural system with two different colored noises are investigated. The expressions of the steady state probability distribution function and the mean value are obtained. After numerical calculation, the results show that the self-correlated time of the multiplicative noise τ1, the self-correlated time of the additive noise τ2,the intensity of the additive noise α, and the intensity of the multiplicative noise D can induce the transition. The increases of α and D are conductive to the switch from the exciting state to the resting state. However, with τ1 and τ2 increasing, the switch from the resting state to the exciting state becomes obvious. The noise intensity and it self-correlated time play opposite roles.
Analysis the convergency speed of estimating the network topology based on the dynamical synchronization
Identifying convergent speed is an important but rarely discussed problem in estimating topologies of complex networks. In this paper, we discuss this problem mainly in both weakly and strongly coupled conditions. In the weakly coupled conditions, the convergent speed we defined increases linearly with coupling strength increasing. After analyzing the dynamics, we find that this relation is universal. In light of the repeatedly driving method we proposed recently, we generalize the definition of the convergent speed into the area of synchronization. In this case, there is a best length of the driving time series to maximize the convergent speed. The knowledge of convergent speed helps us understand the topological information embedded in the time series.
Sparse and dense spiral waves in heterogeneous excitable media
Dynamic behaviors of sparse and dense spirals are investigated numerically based on a Barkley model in heterogeneous excitable media. It is found that the rotating frequency of sparse spiral wave decreases rapidly with b increasing and then tends to saturation, which is different from that of dense spiral wave. The period and wavelength of dense spiral wave increase with the increase of parameter ε or the size R of localized inhomogeneity, which depends more sensitively on the size R than those of sparse sprial wave. The change of the speed of dense spiral wave tip with R is opposite to that of the sparse spiral wave tip. In addition, inhomogeneous effect gives rise to a defect point in arm of each of the two spiral waves when ε or b increases above a critical value.
Complex networks from multivariate time series for characterizing nonlinear dynamics of two-phase flow patterns
Research on the real-time measurement system based on QEPAS
A real-time measurement of gases based on QEPAS is introduced. For eliminating fluctuation of laser, a simple method, in which a digital PID algorithm and a software lock-in amplifier designed by using Lab-VIEW are employed, is utilized to lock the laser to the center of the absorption line. In order to test the system, an absorption line of water vapor near 1.396 μm is chosen by using a fiber-coupled distributed feedback (DFB) diode laser. An over-40-hours continuous measurement is implemented, and the relevant results are presented and discussed. The detection limit of the system is 1 ppm. This method can also be used to measure the trace gases and monitor the industry gases.
Design and fabrication of 1000 line/mm soft X-ray freestanding blazed transmission gratings
The performance prediction of freestanding blazed transmission grating is discussed using scalar diffraction theory, and grating design parameters are accodingly given. A freestanding transmission grating with a period of 1 μm, duty cycle of 0.1–0.2, aspect ratio of about 100, thickness of 10 μm and fractional area of 65% is successfully fabricated by holographic lithography and anisotropic wet etching. The size of a single die is 15 mm× 15 mm divided into four 5 mm× 5 mm windows. The diffraction efficiency of the fabricated grating is tested at the National Synchrotron Radiation Laboratory in a wavelength region of 5–50 nm. The wavelength scanning results show a strong blazing effect in the direction of specular reflection from mirror-like grating sidewalls, as expected. The measured and normalized diffraction efficiency is consistent with the theoretical prediction within 38%–49% due to grating structural imperfections. These experimental results prove not only the concept of blazed transmission grating but also practicability of the fabrication process.
Solving the spheroidal wave equation with s=3/2 by super-symmetric quantum mechanic
In the paper, we use the method of super-symmetric quantum mechanics to study the spin-weighted spheroidal wave equation in the case of s=3/2. We first change the equation into Schrödinger's form, then calculate and derive the first four terms concerning E and super-potential W. we summarize the general formula of super-potential Wn and use mathematical induction to prove its correctness. In turn, this completely gives all the information about the ground eigenvalue and eigenfunction.
Numerical simulation and study of three-dimensional thermal field emission
In this paper, we study the basic theory of field emission, thermionic emission and the thermal field emission, derive their current density formula, the initial distribution of the particles and their initial momentum. And then we achieve a field emission model, thermionic emission model and thermal field emission model on the basis of FDTD-PIC algorithm software. Finally, we verify its correctness using a wedge-shaped-cathode device.
Investigation on regulating the topological electronic structure of the half-Heusler compound LaPtBi
Using the full-potential linearized augmented plane-wave method based on the density functional theory, we investigate the influences of chemical substitution and uniaxial strain on the topological electronic structure of the half-Heusler compound LaPtBi. It is shown that the Γ8 band which is protected by the cubic symmetry of the C1b structure can open and form a gap by substituting Sc element for La or Pd for Pt in LaPtBi compound. However, in the case of distorting cubic lattice by using a uniaxial strain, not only the gap mentioned above appears, but also the Fermi level can be tuned regularly. Thus the LaPtBi compound becomes a real topological insulator.
Isolated intense sub-30-as pulse generation by quantum path control in the three-color laser pulse
We theoretically investigate the high-order harmonic generation from He+in the two-color laser pulse, which is composed of a multi-cycle 800 nm laser and 1600 nm laser. Compared with the case of the fundamental laser, the harmonic spectrum presents a two-plateau structure, and a broadband supercontinuum appears in the second plateau, of which the efficiency is approximately 2 orders of magnitude lower than that of the first plateau. Adding the 27th harmonic pulse to the two-color laser at a proper time, we can control the ionization mostly occurring at half the optical cycle, and the short quantum path can be picked out, the second plateau is heightened four orders of magnitude compared with the case of the two-color case. Furthermore, the supercontinuum spectrum is extended from the second plateau to the first one. An intense isolated pulse with a duration of 29 as is obtained by superposing the 190th–285th harmonics in the continuous region.
Theoretical and experimental study of emission spectrum of the second positive system of N2
The optical emission spectrum of the second positive system of N2(C3∏u→B3∏g)isanalyzed and calculated based on the energy structure of nitrogen radical triplet system. Some key parameters of the equation for the radiative transition intensity are evaluated theoretically, including the potentials of the upper and lower states obtained from diagonalizing their Hamiltonian matrices, the electronic transition moments calculated by using r-centroid approximation, and the Einstein coefficients of different vib-rotational levels. For comparing with the theoretical spectrum, we achieve the measured results from corona discharge experiments of N2 and Ar. By fitting the measured spectral intensities and the calculated ones, the vibrational and the rotational temperatures are determined approximately to be 4300 K and 800 K. The results also demonstrate that with the reduction of nitrogen concentration, the intensity of N2 radiative state first increases and then decreases due to Penning excitation from argon metastable states. The experimental results verify the correctness of the theoretical calculations on the second positive system.
SO-FDTD method of analyzing the reflection and transmission coefficient of weakly ionized dusty plasma layer
The complex permittivity of weakly ionized dusty plasma is presented as a fractional polynomial in jω. A frequency-domain constitutive relation of weakly ionized dusty plasma is given by shift operator finite-difference time-domain (SO-FDTD) method in time domain. Also the recurrence relation on the electromagnetic properties of weakly ionized dusty plasma is deduced by the SO-FDTD. The reflection and transmission coefficients of the weakly ionized dusty plasma layer are calculated, and the influences which is caused by the change of the dust particle concentration and radius on reflection and transmission coefficients are also analyzed by the SO-FDTD method. The result shows that the reflection coefficient in the presence of dust particles is smaller than in the absence of dust particles, while the transmission coefficient in the former case is larger than in the latter case. Besides, it is found that the reflection coefficient decreases as the concentration or radius of dust particle increases.
Effects of size and electric field coupling on the surface plasmon properties of gold nanoring dimer structures
The extinction spectra and the electric field distribution of the surface plasmon coupling of gold nanoring dimer in horizontal and vertical arrangements are calculated by the discrete dipole approximation method. It is found that the peaks of extinction spectra and electric field distribution of the surface plasmon coupling are sensitive to the size and the separation gap between gold nanorings. It is demonstrated that the peaks of extinction spectra will be red-shifted or blue-shifted due to the different structure parameters of gold nanorings. Because of the effect of the polarization charge coupling between adjacent gold nanoring, the local electric field distribution is found to be stronger for the gold nanoring dimer and trimer in horizontal arrangement than for the single gold nanoring. The horizontal gold nanoring trimer has stronger enhancement of local electric field than the dimer. It shows that the greater separation gap has the weaker local electric field distribution for the gold nanoring dimer and trimer in horizontal arrangement. Therefore the gold nanoring horizontal array is predicted to be an ideal surface enhanced Raman scattering substrate and is expected to have potential applications in biological and chemical detections.
Magnetotelluric joint inversion for anisotropic conductivities in layered media
The electrical anisotropy in the crust and the upper mantle is the main link among geoelectrical model, underlying structure, and tectonic model. In recent years, great attention was paid to this phenomenon, which promotes the new research towards the structure model of electrical anisotropy and inversion theory. According to the Marquardt's inversion theory, in the paper we first improve the weighting factor and apply it to the apparent resistivity and impedance phase joint inversion. Then, the detailed example analysis of them proves the corrctness of the mentioned theory. Additionally, the processing and the interpretation of the measured magnetotelluric data in northwest of china not only indicate the practicability of the theory, but also provide a new method for the future research of deep electrical structures.
Relationship between the South China Sea summer monsoon and the first-landfall tropical cyclone over mainland of China
This study investigates the relationship between the South China Sea summer monsoon and the first tropical cyclone (TC) of the season to make landfall over mainland China (in short, the first-landfall TC) using the South China Sea summer monsoon index, NCEP/NCAR reanalysis monthly average data, and best-track TC data from Joint Typhoon Warning Center (JTWC) for 1948–2009. The results show that the characteristics of the first-landfall TC are closely associated with the frequency, active stage, and strength of subsequent landfall TCs in the same year. In detail, a stronger (weaker) South China Sea summer monsoon index year corresponds to more (fewer) landfall TCs over Mainland China, a later (earlier) date of the first-landfall TC, a lower (higher)-latitude landing point of the first-landfall TC, and a stronger (weaker) monsoon trough. The anomalous wind field and the track of the first-landfall TC are also significantly related to the strength of the index. The location of the first-landfall TC has shows a gradual trend toward higher latitudes over the analysis period, and there is a decreasing trend in the variability of the South China Sea summer monsoon index.
Effect of noises on moving cut data-approximate entropy
A method for temperature inversion in middle-upper atmosphere using FPI without laser calibration and its observational data preliminary analysis
In this paper we present a method, by which the temperature inversion is carried our without the calibration of the laser under the FPI observations. On the basis of 630 nm and 557.7 nm observational data are obtained by Wuhan University FPI atmospheric temperature measurement system, using the above method. The results of temperature inversion show that the method doesnot require the calibration of the laser, and can be used for FPI temperature inversion with different wavelengths.
Modal prediction for open-loop liquid-crystal adaptive optics systems
In order to reduce the time delay of the liquid-crystal (LC) adaptive optics system (AOS) which reduces the image resolution of the observed objects, we present a new technique for the first time which is called recursive least square (RLS) modal prediction of turbulent wavefront. First, we introduce the structure of the open-loop LC AOS with RLS predictor. Second, we present the RLS modal prediction algorithm in detail. Third, an actual open-loop LC AOS is designed and built, and the RLS prediction is carried out on it. It is shown that under a pure time delay system and the turbulent condition with Greenwood frequency of 35Hz and Fried parameter of 6 cm, after prediction the residual wavefront error reduce to 0.15 wave (wave=785 nm) from 0.26 wave that is obtained through the direct open loop correction. The prediction gain reaches 42%. Finally, the images obtained by the open-loop AOS with and without prediction are demonstrated. With direct correction without prediction, the image resolution reache 25.4 cycles/mm. After the correction with RLS prediction, the image resolution reaches 32.0 cycles/mm which is equal to 0.9 of the diffraction limit resolution of the system. Therefore, with respect to correction without prediction, a relative gain of 26% in image resolution is achieved with RLS prediction. In conclusion, the RLS modal prediction can improve the image resolution of the open-loop LC AOS effectively.