Investigation of electromagnetic scattering interaction between the column with rectangular cross-section and rough land surface covered with snow using finite difference time domain method
Research on spatial coherence of undulator source in Shanghai synchrotron radiation facility
A new technique for generating non-diffracting beam with long propagation distance using two axicons
Effective radius of curvature of spatially partially coherent beams propagating through non-Kolmogorov turbulence
The laser beam propagation through atmospheric turbulence is of importance for both theoretical study and practical applications. Taking the Gaussian Schell-model (GSM) beam as a typical example of spatially partially coherent beams,based on the non-Kolmogorov spectrum and generalized Huygens-Fresnel principle, the analytical expression for the effective radius of curvature of GSM beams propagating through non-Kolmogorov turbulence is derived. The effects of turbulence parameters (including generalized exponent parameterα, inner scale l0, and outer scale L0) and propagation distance z on the effective radius of curvature of GSM beams are stressed. It is shown that the effective radius of curvature of GSM beams increases with outer scale L0 decreasing for 3.6 <α < 4 and the inner scale l0 increasing, but dose not monotonically vary with the increases of exponent parameter α and propagation distance z. The results are explained physically.
Numerical simulation of leaf-shaped metamaterial absorber at infrared frequency
Quantitative infrared prediction method for defect depth in carbon fiber reinforced plastics composite
Laser without inversion in a Δ -configuration three-level system with cyclic transition
Study of air-clad large-mode-area ytterbium doped photonic crystal fiber
The Yb3+ doped double clad photonic crystal fiber (PCF) with a large core of around 90 μm in diameter is prepared from SiO2-Al2O3-P2O5 core glass of an optical fiber preform through a conventional modified chemical-vapor deposition technique, solution doping and gas doping. The double clad PCF has a mode area of about 1330 μm2. The core and inner cladding have numerical apertures of about 0.065 and 0.5, respectively. 1 m long photonic crystal fiber laser generates up to 102 W output power with a slope efficiency of 76%. Such lasers are potentially scalable to high power.
Research on the influence of impurity particles on the optical breakdown threshold value of stimulated Brillouin scattering medium
In this paper, we establish the physical model of hot damage to the stimulated Brillouin scattering (SBS) medium, and with numerical simulation method the curve of the temperature of impurity particles versus the radius is investigated. The result indicates that impurity particle has a maximal thermal effect radius and when the sizes of particles contained in the medium are near the radius, the optical breakdown phenomenon is most likely to appear, and at this point the optical breakdown threshold is lowest. We use FC-3283, GF-180 and HFE-7100 as the SBS medium in Continuum Nd: YAG laser system. The SBS medium passes through the filter with different diameters. We study the optical breakdown thresholds and energy reflectivities before and after filtration. It is demonstrated that with the filter diameter decreasing, the optical breakdown threshold increases gradually and the energy reflectivity is significantly improved through filter. In addition, a method of using He-Ne laser transmission light spot size to judge whether optical breakdown phenomenon happens, is also developed. This method is convenient and accurate, and can effectively reduce the error caused by naked eye observation.
The propagation characteristics of a Gaussian beam passing through the thick nonlinear medium with defects
The influences of Sr or Ba substitution on the structure and luminescence properties for Ca2.955Si2O7: 0.045Eu2+ phosphor
A series of Ca2.955-xMxSi2O7: 0.045Eu2+ (M= Sr, Ba, x= 0.1–0.5) phosphors is prepared by solid-state reaction method. The influences of Sr or Ba with larger radius substitution on the structure and luminescence properties for Ca2.955Si2O7: 0.045Eu2 + phosphor are investigated. The XRD results show that a small quantity of Sr or Ba substitution of Ca does not change the structure of Ca3Si2O7 host which has a monoclinic crystal structure. Before the substitution, the emission peak is at about 574 nm. If the Ca2+ ions are substituted by Sr2+ or Ba2+ ions, the emission peak is blue shifted when the Sr or Ba concentration is 0.5. In addition, for the same doping contents of Sr and Ba, the Ba doped phosphors have stronger emission intensity.
Coherent control of the Goos-Hänchen shift in four-level atomic medium
The manipulation of the Goos-Hänchen shifts in the reflected and transmitted light beam through a cavity containing four-level atomic medium is investigated by modifying the dispersion-absorption properties of the intracavity medium. Via two external coherent control fields, the Goos-Hänchen shifts of the reflected and transmitted beam can be easily controlled. It is found that around the transparent region of the medium, the Goos-Hänchen shifts are very sensitive and can be enhanced as compared with strong absorption and amplification.
Optimization of phased array ultrasonic field in multi-medium
According to the ultrasonic propagation characteristics in the multi-medium, a control method of ultrasonic focus in the multi-medium is presented through introducing the phase compensation factors and using genetic algorithm. The patterns of multi-focus ultrasonic field generated by two-dimensional phased array consisting of 16×16 elements are simulated in multi-biological tissue, and the ultrasonic fields are calculated under the various thicknesses and the various absorption coefficients of medium layer. The results show that this approach can optimize the patterns of multi-focus ultrasonic field and restrain side-lobe, which can improve the ultrasonic intensity gain and make the maximal ultrasonic intensity focus on the target area. When the thickness and the absorption coefficient of biological tissue are changed, the focus position remains unchanged, but the ultrasonic intensity of the focus area will change relatively.
Modeling bi-direction pedestrian flow by cellular automata and complex network theories
Modeling and simulation of weaving pedestrian flow in subway stations
Characteristic analyses of high birefringence and two zero dispersion points photonic crystal fiber with octagonal lattices
Aiming to the requirements of high birefringence and multiple zero dispersion points of optic-fiber sensing and communication systems, a new type of photonic crystal fiber (PCF) is proposed. The cladding is arrayed by octagonal air holes, and two big elliptical air holes are added in inner cladding to increase the birefringence. Numeral results show that this type of PCF exhibits high birefringence with a level of 10-3 when wavelength ranges from 0.8-2 μm, which fulfils the requirement of high birefringence, and two zero dispersion points are obtained after optimization. In addition, high nonlinear coefficient with a level of 10-2 m-1·W-1 is obtained, which could be used in the case where the nonlinearity is highly required.
Conformal invariance, Noether symmetry and Lie symmetry for systems with unilateral Chetaev non-holonomic constraints
Effect of Mn4+ doping on the microstructure and electrical property of BiFeO3 ceramic
Multiferroic BiFe1-xMnxO3 (x= 0, 0.05, 0.10, 0.15, 0.20) (represented as BF1-xMxO) ceramics are prepared by the conventional solid state reaction technique. The effects of Mn4+ doping on density, phase structure, morphology, dielectric and ferroelectric properties are investigated. The X-ray diffraction patterns of the samples indicate that the typical perovskite phase structure of BiFeO3 is formed, and a phase transition starts near x= 0.05, i.e., the phase structure is distorted from rhombohedral to orthorhombic by Mn4+ doping. The dielectric susceptibility of the sample is significantly increased and the dielectric loss is slightly increased with the increase of Mn4+ content. The dielectric constant εr of the BiFe0.85Mn0.15O3 ceramic at 10 kHz is as high as 1065, 22 times larger than that for pure BiFeO3. It is suggested by hysteresis loop measurements that the ferroelectric property of the BF1-xMxO ceramics is improved and the remanent polarization is increased by Mn4+ doping. This is probably because Mn4+ is more stable than Fe3+, and the B-site doping with higher valent Mn4+ could reduce the volatilization of Bi3+ and suppress the valence fluctuation of Fe3+, thereby reducing the concentration of oxygen vacancies and the leakage current in the ceramic.
Isospin-dependent nucleon-nucleon cross section and the collective flow of nucleons in heavy-ion collision at intermediate energy
Research on plasma axial velocity generated by small debris accelerator coaxial gun
The current status of surface wave plasma source development
In this paper, a flat-type surface wave plasma (SWP) source generated by microwave discharg is introduced systematically. The principle of the surface wave plasma is analyzed and the energy absorption mechanism of the surface wave plasma discharge is explored. A novel wave-mode converter composed of the single-mode resonator array, sub-wavelength diffraction grating and a new type of slot antenna array is introduced. The research findings, such as the mechanism of the generation, the realization, the characteristics of plasma parameters and the numerical simulation of the new SWP sources are beneficial to industrial applications, will promote the effectiveness of the microelectronics industry and obtain a new breakthrough.
Behaviors of ion and electron temperatures on EAST with lower hybrid current drive and lithium wall coating
It is observed that the profiles of ion and electron temperatures become broader within a region of r/a ≤ 0.6 on experimental advanced superconducting tokamak with high-power lower hybrid wave heating and lithium wall coating. It is found that the above phenomena are related to the low recycling at the first wall as a result of the lithium wall coating. The lithium wall coating affects the plasma particles coming from the plasma boundary to the first wall, thereby causing a reduction in recycling. The low recycling causes the temperature profiles to change. It is also found that the electron and ion temperatures approach to each other as a result of high collision rate between electrons and ions when the plasma density increases.
Properties and fabrication status of capsules for ignition targets in inertial confinement fusion experiments
Nonlinear evolution equation with variable coefficient G'/G expansion solution
Stable behavior of solution for the reaction-diffusion system of atmospheric nonlinear dynamics and thermodynamics
Interaction of multi-optical solitions in the three-level gaseous media
Optical solitons in gaseous atomic media display many striking features under electromagnetically induced transparency (EIT). Study of theoretical model, which describes these features of optical solitons, has important meaning in optical informational process and propagation. Two-dimensional saturated nonlinear Schrödinger equation, which describes the spatial soliton evolution in the three-level gaseous atomic EIT media, is transformed into the Hamilton system with the symplectic structure. The Hamilton system is discretizated by the symplectic method. The corresponding symplectic scheme is obtained. Evolution behaviors of two and four spatial solitons with the same amplitude in a three-level, gaseous atomic EIT media are simulated by the symplectic scheme. Numerical results further show that the phase difference and the direction of the entering gauss beams have an obvious effect on the interaction of multi-solitons. The entering Gauss beam can form the stable optical solitons in a gaseous atomic media.
Infinitesimal canonical transformation and integral for a generalized Birkhoff system
Eigen-vector expansion theorem of a class of operator matrices appearing in elasticity and applications
An algebraic approach to the generalization of n-dimensional coupled harmonic oscillators system
Using the quadratic form theory, we achieve the decoupling of systematic Hamiltonian of generalization of n-dimensional coupled harmonic oscillators and derive the diagonalized Hamiltonian by three linear transformations with keeping the commutation relations unchanged. The energy eigenvalue and the eigenfunction of the system are also obtained.
Quantum behaviors of the particles affected by the linear-damping and time-dependent external force
Study on the phase transitions of ferroelectric systems by Weiss's molecular field theory with an external field
Neural network-based backstepping design for the synchronization of cross-strict feedback hyperchaotic systems with unmatched uncertainties
Adaptive modified function projective synchronization of a class of chaotic systems with uncertainties
Study on spatiotemporal chaos network synchronization of the laser Maxwell-Bloch equation
Spatiotemporal chaos network synchronization of the laser Maxwell-Bloch equation is studied. The single-mode laser Maxwell-Bloch equation is amended. Then N single-mode laser Maxwell-Bloch equations amended are taken as nodes to constitute a complex network. Considering the fact that the parameters of the spatiotemporal chaos systems taken as nodes may have small deviations from the actual values because of some interference in the network connecting process, the system at the first node is take as a driven system to drive the rest of the N-1 systems in parallel to achieve synchronization. Furthermore, simulation is performed to verify the effectiveness of the method.
Multiple solitoff solutions and the evolution of (2+1)-dimensional breaking soliton equation
Blind detection of M-ary quaternary phase shift keying signals by a complex Hopfield neural network with amplitude-phase-type hard-multistate-activation-function
Study on chromatic dispersion of beam splitter in spatially modulated Fourier transform spectrometer
Due to the chromatic dispersion of beam splitter, the interferogram units from various wavelengths could shift by different offsets, leading to interferogram aliasing in transverse space. Simultaneously, the interferograms of different wavelengths have different offsets of optical path difference, which makes the interferogram aliasing in vertical space. According to geometric optics principles, the transverse aliasing of the interferogram reduces the area of the interferogram unit, and the vertical aliasing of the interferogram leads to a phase-frequency response which could reduce the spectral line intensity. The calculation and the analysis indicate that the transverse aliasing area is only 3.4% of the total area of the interferogram unit in our study, which could be removed in the data processing; and the phase delay from the vertical aliasing of the interferogram is proportional to the thickness difference between the beam splitter and the compensating plate. The maximal thickness difference is provided when the contrast reversion appears in the interference fringe. Finally, we correct the chromatic dispersion from the aliasing interferogram by solving linear equation set, and recover the ideal spectrum.
Incoherent broadband cavity enhanced absorption spectroscopy for measurements of HONO and NO2 with a LED optical source
An application of incoherent broadband cavity enhanced absorption spectroscopy with a near-ultraviolet LED (λpeak≈ 372 nm and FWHM is 13 nm) to simultaneously detecting HONO and NO2 is described. The light emitted from the LED is collimated and then coupled into an 70 cm long high finesse cavity formed with two high reflectivity mirrors. The spectra are respectively recorded when the cell is filled with He and then N2, and the mirror reflectivity is determined from the change in transmitted intensity due to the difference in Rayleigh scattering cross-section between He and N2. The maximum of mirror reflectivity is 0.99962 at 390 nm in a spectral region of 360-390 nm, and corresponding maximum of light path length is about 1.71 km when NO2/HONO mixture is measured. The concentrations of HONO and NO2 are obtained using least-squares fit. Detection sensitivity (1σ) of 0.6 ppbv for HONO and 1.9 ppbv for NO2 are achieved using an acquisition time of 1000 s. The experimental results demonstrate the possible application of this technology to in situ monitoring the trace gases in the atmosphere.
Measurement of a gas using none dispersive infrared technique with two analysis channels
Measurement of atmospheric water vapor using infrared differential optical absorption spectroscopy
Generation of isolated attosecond pulse from two-color pulse with duration of 60 fs
A theoretical study on electron impact ionization helium (e, 2e) reactions at 64.6 eV
Anisotropic explosions of hydrogen clusters in intense femtosecond laser field
Molecular dynamics simulation of isothermal crystallization dynamics in Cu nanocluster
Steered molecular dynamics simulation of peeling a carbon nanotube on silicon substrate
First principles investigations of the structural stability and thermal dynamical properties of metal Ba under high pressure
Phase field crystal model for the effect of colored noise on homogenerous nucleation
Dual drag reduction mechanism of water-based dispersion with hydrophobic nanoparticles in core microchannel and experimental verification
The theoretical study on CH4 adsorption in different zeolites
First-principles study of Be, O codoped p-type AlN
Effect of doping concentration on electric-pulse- induced resistance in Nd1-xSrxMnO3 ceramics
Electric-pulse-induced resistances (EPIRs) and I-V characteristics of polycrystalline Nd1-xAxMnO3 (A = Ca, Ba, Sr, x = 0-0.9) ceramics synthesized by solid state reaction are investigated. The results show that similar to Nd0.7Sr0.3MnO3, compounds Nd0.7Ba0.3MnO3 and Nd0.7Ca0.3MnO3, with the same doped concentration as that of Nd0.7Sr0.3MnO3, can also exhibit a nonlinear I-V behaviour and a stable EPIR effect at room temperature. Further studies on the Nd1-xSrxMnO3 series indicate that the stability of EPIR is closely correlated with the Sr doped concentration. Around the half doping x= 0.5, the EPIR effect can be observed stably. With Sr concentration increasing or decreasing, however, the EPIR becomes weaker gradually and disappears completely if Sr concentration further increases or decreases. The redistribution of various defects between the electrode and bulk interface with polar pulses is proposed to explain the unique transport behaviour.
Resistively detected nuclear magnetic resonance: recent developments
The resistively detected nuclear magnetic resonance (RDNMR), a high-sensitivity NMR technique developed by Klaus von Klitzing's group in 1988, is used to investigate exotic electron and nuclear spin properties in GaAs two-dimensional electron gases (2DEGs). Because the dynamic nuclear polarization (DNP) approach required for the RDNMR demonstration is strongly dependent on unique material properties of GaAs, this highly-sensitive technique has not yet been applied to 2DEGs confined in other host semiconductors. More recently, we have developed a novel DNP method for demonstration of RDNMR in a 2DEG within the typical narrow-gap semiconductor InSb. In this article, we focus on the discussion of our newly-developed DNP method, experimental details and results as well as future prospects after some preliminary remarks on the principles of RDNMR and DNP.
Enhancing photovoltaic effect of Co2-C98/Al2O3/Si heterostructures by Al2O3
Structural, magnetic, transport, and half-metallic properties of Fe2Co1-xCrxSi Heusler alloys
Preliminary investigation on the method of determining electron mobility of tris (8-hydroxyquinolinato) aluminum by space charge limited current
Effects of annealing time on the microstructural and electrochemical properties of B-doped nanocrystalline diamond films
The effects of annealing time under 1000 ℃ on the microstructural and the electrochemical properties of boron-doped nanocrystalline diamond (BDND) films are investigated by HRTEM, UV and visible Raman spectroscopy, and cyclic voltammetry measurements. The results show that the size of nano-diamond grain in the film decreases with annealing time increasing. When the annealing time is 0.5 h, the grain size decreases from about 15 nm in the unannealed sample to about 8 nm and the content of diamond phase increases. When the annealing time increases to 2.0 h, the diamond grain size decreases to 2-3 nm, and the content of diamond phase decreases with the grain boundary increasing. In the case of annealing time of 2.5 h, the grain size of nano-diamond and the content of diamond phase increase slightly. The variations of nano-diamond grain size and the content of diamond phase indicate that the transformation between the diamond phase and the amorphous carbon occurs under the annealing with different times. The visible Raman spectra show that the G-peak position and the ID/IG value exhibit similar variations with annealing time increasing, revealing that the ordering of the amorphous graphite phase is improved when sp2 carbon cluster increases in number or size. The reactions on the electrode surface are quasi-reversible when the annealing times are 0.5, 1.0, 1.5 and 2.0 h. On the contrary, the reactions are irreversible when the sample is unannealed or annealed for 2.5 h. It is observed that the annealing treatment is beneficial to the improvement of the electrode mass transfer efficiency of BDND film. When the annealing time is 0.5 h, the electrode mass transfer efficiency as well as the ability of catalytic oxidation of BDND film is best. The results suggest that the smaller size of nano-diamond grain, the higher content of diamond phase and the uniform distribution of the nanocrystalline diamond grains are conducible to the improvement of the reaction reversibility on the electrode surface and the ability of catalytic oxidation of BDND films.
Study on the optical characteristic of "black silicon" antireflection coating prepared by plasma immersion ion implantation
Surface texturing is an effective method to reduce surface reflectance and improve the efficiency of silicon solar cell. In this paper, the "black silicon" antireflection coating is fabricated by using plasma immersion ion implantation. The surface morphology and reflectance are investigated by atomic force microscope and UV-VIS-NIR spectrophotometer, respectively. Results show that mountain-like structure with a depth of 0–550 nm is fabricated on black silicon surface. Both the fractional area occupied by silicon and refractive index decrease smoothly with the increase of depth across the antireflection coating. The weighted average reflectance of black silicon is as low as 6.0% in a wavelength range of 300–1000 nm. The depression mechanism of the optical reflectance is analyzed by simulating the structure with the transfer matrix method, and the simulation result fits the measured spectrum well.
Study of characteristics of plume based on hue-saturation-intensity during high-power disk laser welding
During high-power disk laser welding, the surface of the weldment is gasified strongly by the laser irradiation. Meanwhile, the metal vapor plume is generated and changed into the plasma state. This plume can transmit through the laser beam reversely and has a significant shielding effect on the laser beam. Therefore, the laser power which should be transferred inside the weldment is decreased, the welding efficiency and welding quality are seriously affected. By studying and exploring the relation between the characteristics and variation rules of plume and the welding quality, the state of laser welding can be monitored in real-time by the plume characteristics. In the high-power disk laser bead on plate welding of a type 304 austenitic stainless steel plate at a continuous laser power of 10 kW, an extraviolet and visible sensitive high speed color camera is used to capture the metal vapor plume dynamic images. These digital images are transfered to the hue-saturation-intensity color spaces from the red-green-blue color spaces. Also, the area of metal vapor plume and the path length which the laser beam runs through the metal vapor plume are segmented and defined as the plume eigenvalues. The fluctuation of weld bead width is used to evaluate the stability of welding quality. By analyzing the statistics of the variance and mean values of plume eigenvalues, the experimental results confirm that the stability of the welding could be evaluated by the plume characteristics dynamically.
Effect of crystallographic orientation on instability behavior of planar interface in directional solidification
The instability process of planar interface in directional solidification with respect to the crystallographic orientation is studied using a transparent model alloy–succinonitrile-acetone. Three typical crystal grains which have preferred dendrite, tilted dendrite and seaweed patterns at rapid pulling velocity respectively are chosen in our experiment. The experimental results show that the preferred dendrite grain has the shortest incubation time and the smallest initial perturbation wavelength of planar interface instability, the tilted dendrite grain has the largest ones and the seaweed grain has median ones. These results accord qualitatively with previous analytical results and phase-field simulation results. It is also found that the interfacial non-steady-state evolution behaviors of the preferred dendrite grain and the tilted dendrite grain are significantly different from that of the seaweed grain, suggesting that the non-steady-state evolution behavior of planar interface instability is closely related to the crystallographic orientation.
First-principles study of lattice dynamic of IrTi alloy
The formation mechanism of the silicon nano-clusters embedded in silicon nitride
The silicon nitride films are prepared on c-Si substrates by plasma enhanced chemical deposition (PECVD) with silane as the silicon source in mixture gas (N2/NH3) as the nitrogen source. We prepare different kinds of films at different flow rates of the nitrogen with other conditions kept the same. X-ray diffraction (XRD) is employed to analyze the crystal structure, and the existence of the silicon nanoparticles embedded in the silicon nitride film is verified according to the caculation of the lattice size. Fourier transform infrared spectra are employed to probe the concentration evolutions of various chemical bonds with the flow rate of the nitrogen, with which by combining the chemical reaction process, the formation mechanism of the silicon nano-clusters embedded in silicon nitride is investigated. The results show the initial positions of silicon nanoparticles are conducible to the formation of silicon nanoparticles when the chemical reaction proceeds towards the direction in which the Si–Si bonds form. In addition, XRD analysis and photoluminescence characteristics show that the size and the concentration of the embedded nanoparticles increase with the flow rate of the nitrogen increasing.
Model and simulation of liquid rocket organic gel spray droplet evaporation
The calculation model of space-charge field based on the Galerkin series
Parameter adaptation in green cognitive radio
Ocean surface wind direction retrieval from multi-polarization airborne SAR based on wavelet
Radiometric calibration accuracy of airborne synthetic aperture radar in ocean surface wind field sounding
The application of phase contrast imaging to implosion capsule diagnose in high energy density physics environment
A first-principles study of capacity and mechanism of a single titanium atom storing hydrogen
Estimating topology of complex networks based on sparse Bayesian learning
Multi-resolution density modularity for finding community structure in complex networks
Viscoelastic relaxation attenuation property for saturated sandstones and corresponding investigation of micro-scale mechanism
The development of atmosphere-current-wave fully coupled model and its application during a typhoon process
Rain effect on C-band scatterometer wind measurement and its correction
Study of weak constraint 4dvar with model error forcing control variable
A new method of analogue–dynamical prediction of monsoon precipitation based on analogue prediction principal components of model errors
To correct the model errors in analogue-dynamical prediction, a new idea of using the analogue prediction of principal components of model errors, instead of analogue prediction of model error directly, is proposed. By decomposing the empirical orthogonal function, the principal components of the model errors are divided into two parts subjectively: predictable and unpredictable. For the predictable part, it is analogically predicted by the scheme of dynamical and optimal configuration of multiple predictors; while for the unpredictable part, it is estimated by average of the system. Based on the National Climate Center (NCC) of China operational seasonal prediction model results for the period 1983-2010 and the US National Weather Service Climate Prediction Center merged analysis of precipitation in the same period, together with the 74 circulation indices of NCC Climate System Diagnostic Division and 40 climate indices of NOAA of US during 1951-2010, the method is implemented in objective and quantitative prediction of monsoon precipitation in Northeast China. The independent sample validation shows that this technique has effectively improved the monsoon precipitation prediction skill during 2005-2010, for which the averaged anomaly correlation coefficients and the system correct of errors are 0.29 and 0.04 respectively. This study demonstrates that the analogue-dynamical approach can enhance the prediction level of NCC operational seasonal forecast model obviously.
The research on the sensitivity of climate change in China in recent 50 years based on composite index
Climate change index is one of advanced issues in climate change research. There exist many specific indices in climate change research in China and other countries, but comprehensive indexes are very rare. So in this paper, a comprehensive climate change index (CCI) is defined based on single factor of temperature and precipitation index to assess the sensitivity of climate change, and the comprehensive information about climate change is obtained. Because the index size represents the difference in frequency between before and after extreme climate events around abrupt climate change, reflecting the ability for one region to respond to climate change and the sensitivity to the climate change, the index indicates a variety of information about climate change and can provide a certain judgment basis to better deal with extreme climate events. According to the CCI, the climate change and its regional sensitivity in China in recent 50 years are discussed. The results show that Inner Mongolia, northeast central, northwest and central Yunnan have higher CCI indexes, which indicates that the extreme climate events in these regions happen more frequently after the abrupt climate change. The mean CCI is computed of all stations in each province in China, showing that South China and east part of Southwest China each have a minimal index, indicating that these areas are not sensitive to climate change; in the North and Northeast China extreme events happen frequently. Climate change is obvious in high latitude and tropical and subtropical regions, the North and Southwest China are more sensitive, while the South of the Yellow River is less sensitive. The coastal areas with relatively high CCI have strong sensitivities due to the heavy rainfall influence from monsoon and typhoon.
GPS occultation excess phase computed utilizing the updated single difference technique
The parameters retrieved from GPS occultation data can be assimilated into numerical weather prediction model. The accuracy of excess phase is affected by the noise from ionosphere and L2 frequency, especially, when L2 signal is encrypted. In order to improve the accuracy of excess phase and remove the noise by the single Difference (SD) method from reference link into occulted link, we use the updated single difference (USD) method to compute atmospheric excess phase. The combined frequency LC data from the reference link are used and smoothed in an interval time window of 2 s. The antenna phase center correction and relativity correction are estimated. The USD method is validated by utilizing COSMIC data. The case analyses of representative rising and setting occultation events indicate that the excess phases from USD and COSMIC are in good agreement. The excess phase of globally distributed 440 occultation events is also computed. The results show that USD method can obviously improve the distribution of mean bias and standard deviation of bias, which demonstrates the reliability of our USD algorithm. The USD method can be applied to the data processing for FY-3 GNOS (GNss Occultation Sounder) occultation mission which uses semi-codeless technique to track L2 signal.
Numerical method of designing nuclear magnetic resonance logging device sensor
Optimal design of nuclear magnetic resonance (NMR) logging device sensor can enhance its detection performance and improve signal-to-noise ratio, and the accuracy of results from numerical method is absolutely critical for optimal design. In this paper, an eccentric NMR logging device static field distribution and radio frequency field distribution are simulated by the electromagnetic finite element method, and the influences of model shape, model size and element shape on simulation results are analyzed. A comparison between the measurements and simulation data indicates that they are in good agreement with each other. In the design process of NMR logging device sensor, by choosing a circinal model which is similar to the shape of borehole, setting model size to be 10-15 times the sensor diameter, and adopting triangle element, the accuracy of numerical simulation can be improved and the reliability of optimization design can also be enhanced.