Research on the coherence of partially coherent radially polarized beam during propagation
Guided filter-based blind image restoration method
Study on the relationship between coherent population beating signal and the coherence of ground-state hyperfine sublevels
Coherent population beating (CPB) phenomenon occurs in a typical three-level Λ system. When the frequency difference between two coherent pumping laser fields has a certain detuning from the ground-state hyperfine splitting, the excited state population will experience a transient oscillation before reaching equilibrium, and the oscillation frequency is equal to the detuning. The CPB phenomenon enables us to directly obtain the beat frequency between the measured radio frequency (RF) signal and the atomic transition frequency. Then we can get the standard frequency by compensating the beat frequency to the RF. We propose a scheme to implement atomic clock based on the CPB phenomenon in 2009, and the scheme has been implemented. When this effect is used to achieve an atomic clock, the frequency stability is directly related to the amplitude and SNR (signal to noise ratio) of the CPB signal. Influence of the ground-state hyperfine sublevels' coherence on CPB signal is theoretically simulated and experimentally investigated in this paper. A formula of the CPB signal is derived by using the semi-classical model of the interaction of atoms with light, and the theoretical simulation is done using the formula obtained. In the experiment two coherent pumping laser fields are used to interact with 87Rb atoms. A CPB process includes the coherence build-up and the CPB stimulation. The coherence of the ground-state hyperfine sublevels is achieved by controlling the pumping time of the coherent laser fields that are resonant to the ground-state hyperfine sublevels. With this method, the relationship between CPB signal and coherence of the ground-state hyperfine sublevels can be observed. Result shows that the amplitude of CPB signal is proportional to the ground-state hyperfine sublevels' coherence. The hign quality CPB signal can be achieved when the CPB stimulation is started with a pure coherent population trapping (CPT) state. In the CPB process, the coherence build-up rate is approximately equal to the coherence decay rate. So a 50% duty cycle square wave can be used to modulate the RF, and the period of the square wave had better be twice of the decay time of the ground-state hyperfine sublevels' coherence. To improve the SNR of CPB signal and the stability of atomic frequency standard, the ground-state hyperfine sublevels' coherence must be built up, improved, and maintained before the CPB stimulation. The feasibility of applying CPB phenomenon to the weak magnetic field measurement and other applications is also discussed in this paper.
Study on atomic localization of Λ-type quasi-four level atoms based on absorption with quantum coherent control
A narrow linewidth diode laser at 243 nm
The two-photon spectroscopy of 1S-2S transition in atomic hydrogen needs a narrow linewidth laser at the wavelength of 243 nm. In order to reduce the linewidth to several tens hertz level, a free operation CW ECDL 972 nm laser has been locked to a high fineness ultralow expansion reference cavity by using the Pound-Drever-Hall technique. And the part of 972 nm laser output is set into the tapered amplifier and the two enhanced doubling frequency stages to obtain the output of purple light at 243 nm. It is estimated that such a narrow linewidth laser system at 243 nm can be used well in the detection of the 1S-2S transition of hydrogen.
Repetition rate optimization of passively mode-locked fiber laser for high-speed linear optical sampling
Experimental research on focusing anisoplanatism of sodium guide star via synchronous pulse detection
Study of vibration propagation in periodic rib-stiffened plates using advanced statistical energy analysis
Research on the oscillation effect of near-surface metal defect based on laser-generated acoustic surface wave
Theoretical and numerical analysis of layered cylindrical pentamode acoustic cloak
Conformal invariance and conserved quantity of Mei symmetry for Appell equation in a holonomic system in relative motion
Lateral pressure distribution and steering coefficient in two-dimensional lattice pile of granular material
Energy dissipation and periodic segregation of vibrated binary granular mixtures
Mechanical properties and phase transformation of porous unpoled Pb(Zr0.95Ti0.05)O3 ferroelectric ceramics under uniaxial compression
Study of precondition for simulating low-speed turbulence
Numerical simulation on oscillation of micro-drops by means of smoothed particle hydrodynamics
Theoretical analysis of high flow conductivity of a fracture induced in HiWay fracturing
Experimental study of heat transfer from droplet impact on a heated surface
Droplets impact on surfaces exist widely in industrial equipments, such as spraying cooling, ink jet printing, oil drops impact on walls in combustion chamber, brine droplets impact on heat transfer tubes in horizontal-tube falling film evaporators etc. In particular, for the droplets impinging on heated surfaces, the contact scale and the heat transfer flux affect the cooling of the hot surfaces greatly. In this work, evaporation processes of water and ethanol droplets impact on a heated surface are observed using a high-speed digital camera with a capacity of 106 frames per second. The corresponding evaporation parameters including the contact diameter, the droplet height, the contact angle, and heat flux are analyzed. The initial liquid temperature keeps constant at 20 ℃, and the initial surface temperature varies in the range of 68-126 ℃. Diameters of single water droplets and ethanol droplets are 2.07 and 1.64 mm, respectively. The impact Weber number of water droplets ranges from 2 to 44 while that of ethanol droplets ranges from 3 to 88. The present results show that due to the coupled effects of gravity, surface tension, fluid flow and evaporation processes, the height of water droplets reduces continuously while the contact diameter almost does not change during the most part of evaporation time. In the later stage of evaporation, the contact diameter, height and contact angle of water droplets oscillate, mainly because of droplet retraction. The critical contact angle for water droplets retraction is in the range of 4°-8°. The contact angle of ethanol droplets first reduces and then remains constant, while the contact diameter and the height decrease continuously. The droplet evaporation time depends on liquid properties and the surface temperature, and the Weber number effect is minor. The evaporation time decreases with the increase in the surface temperature. At the same time, with increasing surface temperature, the ratio between the sensible heat and the total heat increases, and this part of heat cannot be neglected from the total heat transfer calculation. Based on the present experimental conditions, the average heat flux for the water droplets ranges from 0.014 to 0.110 W·mm-2 in this work.
Experiment and numerical study on the characteristics of self-propellant Janus microspheres near the wall
Investigation on the viscoelastic behavior of an Fe-base bulk amorphous alloys based on the fractional order rheological model
Single event transients in a 0.18 μm partially-depleted silicon-on-insulator complementary metal oxide semiconductor circuit
Single event transients (SETs) in a 100 series 0.18 μm partially- depleted silicon-on-insulator (PDSOI) complementary metal oxide semiconductor (CMOS) inverter chain are studied by using pulsed laser. In this paper, effects of struck transistor type and struck locations on the threshold laser energy and the pulse width of SETs are investigated. Results show that the threshold laser energies at different locations are similar, but the threshold laser energies of n-channel metal-oxide-semiconductor (NMOS) transistors are much smaller than that of p-channel metal-oxide-semiconductor (PMOS) transistors. The SET pulse width of n-channel metal-oxide-semiconductor field-effect transistor (NMOSFET) is 427.5 ps as measured at the output terminal when the 2nd stage is irradiated, and 287.4 ps when the 100th stage is irradiated; the SET pulse width of p-channel metal-oxide-semiconductor field-effect transistor (PMOSFET) is 295.9 ps as measured at the output terminal when the 1st stage is irradiated, and 150.5 ps when the 99th stage is irradiated. Both broadening rates are about 1.4 ps/stage. When the struck locations are close to the output terminal of the chain, the SET pulse is narrowed; however, when the struck nodes are close to the input terminal, the SET pulse is broadened. SET pulses are progressively broadened up when propagating is along inverter chains. A similar broadening rate in neither NMOSFET nor PMOSFET, indicates that the SET pulse broadening effect is caused by propagation, independent of the type of struck transistors. Through analysis, the charge of floating body-induced threshold voltage hysteresis in PDSOI transistors is the main cause of pulse broadening. The positive SET pulse observed on the oscilloscope, contrary to the expectation, is due to charging and discharging of the output node capacitor. Also, the observed sub-rail-to-rail swings of the SET pulses are due to the voltage division between the internal resistance of the oscilloscope and the resistance of the PMOS transistor.
Radiation damage effect and post-annealing treatments of NPN-input bipolar operational amplifier in electron radiation environment
Quantitative separation of radiation induced charges for NPN bipolar junction transistors based on 1/f noise model
Ionizing-radiation-induced oxide-trapped charges and interface states cause the current and 1/f noise degradation in bipolar junction transistors. In order to better understand these two degradation mechanisms and develop hardening approaches for a specific process technology, it is necessary to measure the effect of each mechanism separately. In recent years, several techniques have been developed, but no charge-separation approach based on 1/f noise for NPN bipolar junction transistors is available. In this paper, the effects of ionizing-radiation-induced oxide trapped charges and interface states on base current and 1/f noise in NPN bipolar junction transistors are studied in detail. Firstly, a new model of base surface current of NPN bipolar junction transistors is presented with some approximations, based on an available model for the base surface current under certain conditions; this model can identify the physical mechanism responsible for the current degradation. Secondly, combining the theory of carrier number fluctuation and the new model of base surface current another model is developed which can well explain the 1/f noise degradation. This model suggests that the induced oxide-trapped charges would make more carriers, involving the dynamic trapping-detrapping, which leads to the 1/f noise to increase; and the induced oxide-trapped charges and interface states can also bring about an increase in base surface current which can also cause the l/f noise increase. These two models suggest that the current and1/f noise degradations can be attributed to the same physical origin, and these two kinds of degradations are the result of accumulation of oxide-trapped charges and interface states. According to these two models, simple approaches for quantifying the effects of oxide-trapped charges and interface states are proposed. The base surface current can be extracted from the base current using the available method. The oxide-trapped charge density is estimated using the amplitude of 1/f noise (10-100 Hz) and the base surface current. Given the estimated oxide-trapped charge density, the interface state density can be estimated using the base surface current. These methods are simple to implement and can provide insight into the mechanisms and magnitudes of the radiation-induced damage in NPN bipolar junction transistors.
Effect of 170 keV proton irradiation on structure and electrical conductivity of multi-walled carbon nanotubes film
Due to their unusual electrical conductivity, carbon nanotubes as the ideal candidates for making future electronic components have extensive application potentiality. In order to meet the requirements in space electronic components for carbon nanotubes, effect of 170 keV proton irradiation on structure and electrical conductivity of multi-walled carbon nanotubes (MWCNTs) film is investigated in this paper. Surface morphologies and microstructure of the carbon nanotube films are examined by scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) spectroscopy, respectively. Electrical conductivities of the carbon nanotube films before and after 170 keV proton irradiation are measured using four-point probe technique. SEM analysis reveals that when proton irradiation fluence is greater than 5×1015 p/cm2, the surface of the carbon nanotube film becomes rough and loose, and obvious bending, shrinkage, and entanglement of nanotubes are observed. Moreover, the shrinkage phenomenon of MWCNTs caused by proton irradiation is found the first time so far as we know. Based on Raman and XPS analyses, it is confirmed that 170 keV protons can improve the ordered structure of the MWCNTs, and irradiation fluence plays a key role in reducing the disorder in the MWCNTs. Improvement of the irradiated MWCNTs by 170 keV protons can be attributed to restructuring of defect sites induced by knock-on atom displacements. On the other hand, carbon impurities on surface of the MWCNT film are reduced due to the effect of sputtering by the 170 keV proton irradiation, which is also helpful to the improvement of the structure of carbon nanotubes. EPR spectra show that the electrons delocalized over carbon nanotubes decrease with increasing irradiation fluence, implying that the carbon nanotube film is not sensitive to ionizing radiation induced by the 170 keV protons, and the electrical conductivities of the MWCNTs films may be decreased. Four-point probe technical analysis shows that with increasing irradiation fluence, electrical properties of the carbon nanotubes film deteriorate, which can be attributed to the changes in electronic properties and morphology of the MWCNT films induced by 170 keV protons. Acquired results could be beneficial to tailoring of structure and properties for the carbon nanotubes film irradiated by protons to develop nanoelectronics of radiation-resistant systems.
Permeability of cracked porous solids through percolation approach
This paper investigates the permeability of microcracked porous solids incorporating random crack networks in terms of continuum percolation theory. Main factors of permeability include the geometry of crack networks, permeability of porous matrix, and crack opening. For the two-dimensional random crack networks, a new connectivity factor is defined to take into consideration the spanning cluster of cracks, fractal dimension of networks, and the size of a finite domain. For an infinite domain, the connectivity factor around a percolation threshold observes the scaling law, so this definition of connectivity is proved to be consistent with the percolation concepts. Geometric analysis reveals that the local clustering will not necessarily contribute to the global connectivity of networks. It is also found that too strong a local clustering of cracks will decrease the probability of the global percolation, and this adverse aspect of the local clustering effect has never been reported in the literature. The percolation threshold changes with the crack pattern of networks and the scaling exponents of percolation are not constant but depend on the fractal dimension of the crack networks. On the basis of connectivity and tortuosity of crack networks, the scaling law for permeability is established, K=K0(Km,b)(ρ-ρc)μ, taking into consideration the geometris characteristics through (ρ-ρc)μ, the permeability of porous matrix Km, and the crack opening aperture b. Then the permeability of a solid incorporating random crack networks is solved by finite element methods: all the cracks are idealized as 2-node elements and the matrix is divided into 6-node triangle elements. The fluid is assumed to be incompressible and Newtonian. With these assumptions the effective permeability of numerical samples is evaluated through Darcy's law. The scaling exponents of the permeability μ obtained numerically are very near to the theoretical values, and the impact of crack opening is less important as the crack density is far below the percolation threshold and the effect of crack opening becomes significant only as the crack density approaches the percolation threshold. Influence of crack opening on the permeability is strongly dependent on the opening aperture of the cracks. Finite element simulation results show that K0 depends on b through a power law near the percolation threshold and this dependence disappears as the ratio between the local permeability of crack and the matrix permeability exceeds 106.
A comparative study of multifractal detrended fluctuation analysis and multifractal detrended moving average algorithm to estimate the multifractal spectrum
A technique for extracting the density of states of the linear region in an amorphous InGaZnO thin film transistor
Preparation and gas-sensing properties of the silver nanoparticles/porous silicon composite
Compressive behavior of nanocrystalline nickel at various temperatures and strain rates
In this paper, compressive behavior of electrodeposited nano-crystalline (nc) Ni at various temperatures and strain rates is studied using a low temperature mechanic test system. Plastic deformation mechanisms of nc Ni caused by compression are characterized by the strain rate sensitivity index, the activation volume, and examined by scanning electron microscopy and high resolution transmission electron microscopic analysis. Results show that at low temperatures, the plastic deformation of nc Ni is mainly dominated by grain boundary accommodated dislocations. In other words, during plastic deformation of nc Ni at low temperatures, the intrinsic dislocation at the grain boundary bends up and expands without obstacles to the opposite grain boundary in the inner grain dislocation-free zone, until the occurrence of similar cutting forest-dislocation behavior appearing at opposite grain boundary. Moreover, the residual dislocations in the grain boundary bending out during plastic deformation could increase the strain compatibility and decrease the stress concentration. At room temperature, the plastic deformation mechanism of nc Ni is controlled by the deformation of grain boundary accommodated dislocations and grain slipping/rotating. Based on the above analyses, differences in compressive behavior of nc Ni at various temperatures and strain rates can be revealed by the correlation of deformation mechanisms of grain boundary accommodated dislocations and residual dislocation movement, temperature and defects in nc Ni.
The p-type porous silicon layer with the aperture about 1.5 microns and hole depth about 15 microns is prepared by electrochemical etching of a p-type monocrystalline silicon wafer with a resistivity 10-15 Ω·cm and along  orientation in a double-tank cell which consists of the electrolyte (volume ratio HF: DMF=1:2). Silver nanoparticles film with different thickness has been deposited on porous silicon by the electroless deposition for different deposition times. Morphology and microstructure of the silver nanoparticles/porous silicon composite and ere studied by scanning electron microscope and X ray diffracmeter. Result indicates that the silver nanoparticles are uniformly distributed on the surface of porous silicon and the deposition time has an important influence on the morphology of the composite. The gas-sensing properties of the silver nanoparticles/porous silicon composite to NH3 are tested at room temperature by the static volumetric method. Results show that the deposition time has a significant impact on the gas-sensing properties of the silver nanoparticles/porous silicon. In a short deposition time, the composite with an appropriate amount of silver nanoparticles doped on the porous silicon shows good gas-sensing properties to NH3 with high sensitivity, fast response-recovery characteristic due to the high specific surface area and special microstructure. At room temperature, the gas sensor has a sensitivity of about 5.8 to 50 ppm NH3.
Stability of magnetization states in a ferromagnet/heavy metal bilayer structure
Exchange bias tuning of metal ions doped in CuO nanocomposites
Study on the photocatalytic mechanism of tio2 sensitized by zinc porphyrin
Suppression of secondary electron multipactor on dielectric surface in TM mode
Application of semiconductor quantum dots to white-light-emitting diodes
Based on the electro-optical energy transfer process, the pseudo-spectral-luminous efficiency function (ΦQD) of quantum dots (QDs) is introduced, the equations of chromaticity coordinates, luminous efficiency, and the QDs' mass of the white-light-emitting devices with CdSe, CuInS2 or CdS:Mn QDs are obtained, and the calculated results are in agreement with the experimental data. For a certain luminescent peak wavelength, when the full width at half maximum of the QD's photoluminescence becomes larger, the ΦQD value becomes smaller while the chromaticity coordinates become more different from those of the corresponding monochromatic light. It is indicated that the color rendering index (CRI) of the devices is strongly dependent on the photoluminescent position and width of the QDs, and the CRI value can be increased towards 98 when a certain kind of CdS:Mn QDs is added into the traditional white-light LEDs.
Preparation and upconversion luminescence properties of Ba5SiO4Cl6: Yb3+, Er3+, Li+ phosphors
The Ba5SiO4Cl6: Yb3+, Er3+, Li+ phosphor has been prepared by high temperature solid state reaction, and their upconversion (UC) luminescence properties and mechanisms are investigated. The UC emission bands located at 525 nm (2H11/2→4I15/2), 548 nm (4S3/2→4I15/2), and 662 nm (4F9/2→4I15/2) due to Er3+ are observed under the excitation of 980 nm. UC luminescence of Ba5SiO4Cl6: Yb3+, Er3+ phosphors is increased with increasing Er3+ and Yb3+ concentration due to the energy transfer enhancement of Er3+ and Yb3+. Based on the relations of UC luminescence intensity and excitation light power, the UC luminescence mechanisms are discussed. At a low excited power (below 0.8 W), the two-photon processes are involved in both green and red UC emission mechanisms. When the power exceeds 0.9 W, the green and red UC emission is a four-photon process. One new and interesting UC emission mechanism may occur in the Ba5SiO4Cl6: Yb3+, Er3+ phosphors. Both green and red UC emissions at a higher pumping power are generated by photon avalanche UC process. Influence of Li+ doping on the UC luminescence of Ba5SiO4Cl6: Yb3+, Er3+ phosphors is investigated. Result demonstrates that Li+ ion doping could enhance the UC luminescence of Ba5SiO4Cl6: Yb3+, Er3+, which is attributed to the distortion of the local symmetry around Er3+.
Calculation of coherent X-ray diffraction from bent Cu nanowires
Analysis of epitaxial morphology evolution due to stress and diffusion
Structure and optical property of Cr-O films deposited by pulsed bias arc ion plating
CT imaging method with varying energy based on logarithm demodulation
Numerical investigations of dynamic behaviors of the restricted solid-on-solid model for Koch fractal substrates
A new data assimilation method based on dual-number theory
Numerical modeling and research on nonlinear dynamic behaviors of two-stage photovoltaic grid-connected inverter
A novel method to identify the scaling region of correlation dimension
Finite-temperature properties of N two-level atoms in a single-mode optic cavity and phase transition
Experimental research on loading strontium bosons into the optical lattice operating at the “magic” wavelength
Design and optimization of off-beam NO2 QEPAS sensor by use of E-MOCAM with a high power blue laser diode
A highly sensitive NO2 optical sensor has been designed by means of combining the electrical modulation cancellation method (E-MOCAM) and off-beam quartz enhanced photoacoustic spectroscopy (QEPAS). A high power multimode blue laser diode emitting at around 450 nm is used as the excitation light source of the photoacoustic signal. In the E-MOCAM, the balance signal is generated from a dual-channel function generator and introduced to the pin of the quartz tuning fork (QTF) to balance out the huge background noise. The principle of the E-MOCAM is explained in detail from the perspective of equivalent circuit of QTF, and the background noise of the high power LD-based QEPAS sensor is analyzed. Results show that stray light noises coming from the LD beam and blocked by the resonator and the photoacoustic cell are dominated in all the noises. Gas flow noise of QEPAS sensor is also estimated, and excessive noise could be introduced by the gas flow even at a rate below 200 sccm. The gas flow noise is measured at different gas flow rate, from 60 to 200 sccm. Compared with the QEPAS sensor based on wavelength modulation, the sensor based on amplitude modulation, especially in the case of high power light source, is more sensitive to the gas flow. The ultimate background noise of the off-beam QEPAS sensor can be reduced by 269 times after the E-MOCAM is applied. The performance of the NO2 QEPAS sensor is evaluated in the NO2/N2 mixtures of different concentrations, ranging from ppb to ppm levels. In the case of the 2.85 ppm NO2 measurement, the SNR of 630 is achieved. A linear fitting is implemented to evaluate the response of the sensor, resulting in an R square value of 0.999. Allan plot is used to investigate the long term stability of the sensor. The original background noise produced from the off-beam QEPAS configuration is less than that from the on-beam QEPAS configuration, thus the combination of off-beam QEPAS configuration and E-MOCAM shows a better stability. A detection limit of 0.34 ppb (1σ, 46 s integration time) for NO2 in N2 at atmospheric pressure can be achieved, which corresponds to a normalized noise equivalent absorption coefficient of 2.2×10-8 cm-1·W/Hz1/2.
Constructing circulant measurement matrix through alternating optimizing amplitudes together with chaotic stochastic phases of the matrix generating elements
Influence on the recovered spectrum caused by thermal optics effect of the collimation lens used in static Fourier transform infrared spectrometer
Realisation of orbital angular momentum sorter of photons based on sagnac interferometer
Orbital angular momentum (OAM) of photons has both classical and quantum applications due to its feature of optical vortex and infinite dimension. OAM discrimination is one of the basic problems, which has been paid much attention recently. Here we present an interferometer method in which a Sagnac interferometer with a Dove prism is placed on each arm to separate the different OAM of photons into different output ports, namely, OAM sorters. We demonstrate experimentally the feasibility of OAM sorter by dividing different OAM states into different output ports. Using the cascade interferometers, we also sort the superposition state successfully. Experimental results are in good agreement with the theoretical predictions. Compared with other methods, this method is more stable and can be used to separate superposition states into single photon levels. Furthermore, this method can also be used to couple OAM modes with spatial modes, a very important method for manipulating OAM states. It is a useful method and has potential applications in high-capacity optical communication, quantum entanglement, quantum cryptography, quantum computation and quantum information.
A concentration retrieval method for incoherent broadband cavity-enhanced absorption spectroscopy based on O2-O2 absorption
Theoretical calculation of the vib-rotational interaction potential and the scattering cross section for the Ar-H2 (D2, T2) collision system
Based on the ab initio coupled-cluster CCSD(T) method in quantum mechanics, the charge distribution of Ar atom and its vib-rotational interaction with H2 molecule are calculated using augmented correlation consistent basis sets aug-cc-pV5Z and 3s3p2d1f1g Gaussian bonding function, and the basis set superposition error (BSSE) is eliminated using Boy and Bernardi's full counterpoise method. Afterwards, the analytical expression of the interaction potential of the Ar-H2 system is fitted with Tang-Toennies potential function. With this interaction potential, the scattering cross section of Ar-H2(D2, T2) collision system is calculated by using close-coupling method when the incident energy of Ar atoms is 83 meV. The calculated differential cross section of Ar-D2 collision system is consistent with the experimental results. Calculated result and analysis show that the dispersion energy plays a key role in the long-range attractive potential scattering, and the exchange energy plays an important role in the short-range repulsive potential scattering. The direction of the radial dipole of the Ar-H2 (D2, T2) collision system is turned twice in the range of impact parameters from 0.27 to 0.47 nm.
First-principles study on the minimization of over-erase phenomenon in Si3N4 trapping layer
Photoexcitation and photoionization of alkali atoms
Potentials of long-range cesium Rydberg molecule
Quantum control of the XUV photoabsorption spectrum of helium atoms via the carrier-envelope-phase of an infrared laser pulse
A study of the middle time-scale periodic behavior of light curve of BL Lac object OJ287