This paper focuses on the discussion of the heterogeneous nucleation on the substrate of three mutually perpendicular planes. According to the condition of heterogeneous nucleation, we study the critical radius of nucleation and the critical nucleation energy to form a critical nucleus, and obtain a mathematical expression of critical nucleation energy and contact angle. The result shows that the critical nucleation energy is only relevant to the contact angle and that the contact angle plays an important role in heterogeneous nucleation. The discussion on contact angles of nucleation indicates that the critical nucleation energy of heterogeneous nucleation is smaller than that of spontaneous nucleation.
We propose a pair copula-GARCH model to analyze the risk of Multi-asset portfolio. Compared to other Copula-GARCH models,our method can capture the tail dependence of different pairs of risk factors in a portfolio so that it can describe the dependence structure of the risk factors better. By using this model combined with Monte Carlo techniques, the numerical analysis of portfolio VaR is fully discussed in this paper. Finally, the empirical portfolio risk analysis is given.
With a full length cDNA of expansin, designed PaEXP1, was cloned in Phytolacca acinosa by the Homology-based cloning method. The PaEXP1 consisted of 1128 bp with an open reading frame of 759 bp that code a protein of 252 amino acids. Structural analysis showed that the eight cysteine residues and the HFD(His-Phe-Asp) sequence are near the N-terminal end, four tryptophan residues near the C-terminal end of predicted PaEXP1. The phylogenetic tree showed that PaEXP1 belonged to the α-expansion protein family. PaEXP1 was preferentially expressed in root. The expression of PaEXP1were strongly inhibited by various abiotic stress, such as the low temperature, salt, heavy metals and osmotic stress. The expression of PaEXP1 in yeast increased the average diameter of yeast, indicating PaEXP1 involved in cell wall expansion.
The paper discussed accumulation of heavy metals in the digestive glands and gills of Ruditapes philippinarum with single or combined exposure of zinc and lead and relationship between MT (metallothioneinm) induction and accumulation of heavy metals. Results indicated that the antagonistic effect of znic and lead was obvious in clam jointly exposed to zinc and lead (Zn2+ 50μg/L and Pb2+ 25μg/L). MT varied with exposure concentrations of zinc and lead and the effect of lead was significant.
The fractured rock, one of the major types of seepage media for groundwater flow, exists widely in the shallow layers of the earth. It is commonly realized that fracture networks in fractured rocks constitute the main or the unique flow path for groundwater flow and solute transport. Based on the graph theory, the fracture network transporting groundwater was conceptualized as the unconnected graph, in which the algorithms of data structures were applied to storing and organizing the data of the stochastically distributed fractures. A computer program was developed to identify the flow paths along the groundwater flow gradient in fractured rocks and remove the disconnected fractures from the network. Consequently, computation efficiency can be then significantly increased for the identification and numerical simulations of groundwater flow and solute transport become more practicable at a large field scale.
When constructing the segmented primary mirror of a maximum aperture telescope, the piston error of segmented mirrors needs testing accurately. In this paper, a dispersed fringe sensor (DFS) was simulated from physical optics, according to the principle of dispersed fringe sensoring technology. DFS interferograms were produced and signals were sampled from them to obtain the result of detection through fitting curve of light distribution. We compared sampling signals in different wavebands and put forward two methods of sampling effective signals by opening window on a CCD camera to improve measuring precision. The measurement range is as large as ±50μm, and the measurement accuracy is about several tens of nanometers.
This paper presents a new jam nulling scheme for airborne synthetic aperture radar using digital beam forming. This scheme adaptively adjusts the weight vector of each receiving channel to form the beam pattern which receives the radar echo without distortion and nulls the interference. An optimized sector nulling technique is introduced for reducing the times of weight adjusting. Further more, the performance analysis of this scheme is given. Simulation results show its efficiency and feasibility.
This paper presents a design of L band space-borne SAR digital receiver using direct RF sampling. Appropriate RF sampling frequency is selected and digital quadrature demodulation structure is improved. In order to reduce the volume of data that is stored onboard and later transmitted to ground station, a block adaptive quantization (BAQ) module with flexible compression ratio is developed. Simple electrical system design and advanced SAR system are achieved by using direct RF sampling. Feasibility and performance are verified by experimental results.
Under narrowband signal and array assumptions, the maximum likelihood estimations (MLE) for target parameters in the adaptive radar with uniform planar array (UPA)weve analyzed. The UPA model was analyzed, and then the ML estimators for target parameters and the corresponding CRB were given. By means of Jacobian matrix, the CRBs for target elevation, azimuth, velocity, and magnitude, and phase were derived. The results are an extension from 1-D ULA to 2-D UPA, which can be applied to the performance evaluation for parameter estimation of airborne moving target.
A novel dual-tone CW radar is proposed. Six-port circuit is used as a mixer to obtain the phase difference and Doppler frequency difference between the received and transmitted signals, and then the range and relative velocity of the target can be calculated. An anti-noise method is also proposed according to the measurement process and noise transfer principle. Simulation results show that this proposed radar has a higher accuracy with a simpler measure procedure.
An ultra wideband (UWB) planar balun (balanced to unbalanced transformer) is designed based on Coplanar Waveguide (CPW) and coplanar strip (CPS). The proposed balun is fabricated on a substrate with low dielectric constant. For this balun, one Chebyshev impedance transform section is inserted and the structure making the two grounds of CPW electrically equal is improved. By means of these methods, the operation bandwidth of the proposed balun is expanded, and the insertion loss becomes lower. An UWB planar balun, which can transform a 50Ω unbalanced input to the 100Ω balanced output, is designed and fabricated. The measured results indicate that the insertion loss of the balun is lower than 1.5 dB and the VSWR is lower than 2 when the match load is connected with output in the frequency range from 0.1 to 3GHz. The simulation and measurement results are in good agreement.
A new dimension-reduction method based on subarray architecture is proposed for solving problems in partially adaptive array processing. This method uses the smoothing array algorithm and divides the whole array into the overlapping subarrays to actualize dimension-reduction. This beamformer has a two hierarchical weighted structure. Based on the principle of the antenna map multiplication, this new beamformer is equivalent to the serial form of two spatial filter. Finally, simulation demonstrates the validity and superiority of the new algorithm.
In this paper, a new algorithm is proposed based on the EMD (empirical mode decomposition) speckle reduction and tophat transform. First, we use EMD to every column signal of the image to get the IMF signals, deduce the first and second IMF signals from the original signal to get a coarse-processed image, and then do the same to the row signal of the coarse-processed image. The speckle can be greatly reduced with this algorithm. Furthermore, the local background of non-homogeneity caused by waves is greatly reduced with tophat transform. The signal-to-clutter-rate of the image is greatly enhanced, which is favorable for detection. The simulation results show the effectiveness of the algorithm.
This paper describes the FPGA design and implementation of bus controller and remote terminal based on MIL-STD-1553B protocol. We implement both the bus controller and remote terminal functions on a single FPGA, and demonstrate the design principles and response workflow. The test result shows that this method is feasible.
The problem of joint routing and scheduling in 802.16j based wireless relay networks is studied to minimize the traffic time. The routing problem is solved by linear programming method, and the traffic is allocated to links. A novel link scheduling algorithm based on shifting and switching is proposed. Theoretical analysis indicates that the performance of the proposed algorithm is within a factor of 1.5 of that of any optimal algorithm in the worst case. Simulation results show that with the proposed algorithm near-optimal performance can be effectively achieved.
An approach to enforce Clark-Wilson model in the combination of RBAC and TE models is presented, namely: separation of duties is addressed by assigning different roles to different users; special domains are used for representing transformation procedures; and the constrained data items and unconstrained data items are labeled with different types. The correctness of the enforcement and certification rules is analyzed. A detailed case study of FTP integrity policy is implemented under SEBSD, and shows that the approach achieves fine-grained access control and flexible configuration.
Many existing password-based group key exchange protocols use the symmetric ciphers and Hash functions to maintain their security. An efficient and provably secure password-based group key exchange protocol, using only Hash function, is proposed. It is semantically secure against off-line dictionary attacks in the random oracle model and is more efficient than the related works.
There are a variety of techniques for estimating the parameters of the Muskingum routing model. However the robustness of these methods has to be questioned because of the tendency of outliers in data to strongly influence the outcome. A robust estimation has been presented. The robustness of this estimator has been compared with the least squares method by means of synthetic data sets, in which both Gaussian random errors and outliers have been introduced. The study demonstrates that the robust estimator has the potential to reduce estimation bias in the presence of outliers, and it has an advantage over the least squares method.
An automatic detection system of special position for photoelectric encoder was designed. First, a brief description is given on the meaning of detection of special position for photoelectric encoder and the traditional detection methods. Then the principle and the designed hardware and software of the system are described in detail. The experimental results show that the system can meet the conditions of its use and replace the traditional detection methods.
Polycyclic aromatic hydrocarbons (PAHs) are a group of persistant pollutants which are difficult to degrade and metabolize in the environment and exist widely around the world. They can accumulate in organisms and subsequently translocate, transform and be concentrated in food chain due to their lipophilicity. Some PAHs are carcinogenic and pose great risk to human health. In order to predict their potential risk, it is essential to explore the bioavailability of PAHs in soil. The uptake and acropetal translocation of 14 priority PAHs by wheat (Triticum aestivum L.) from field-contaminated soils has been investigated. The results indicate that compounds with intermediate to high hydrophobicity such as PAHs can acropetally translocate in plants. The amount of PAHs translocated from roots to aerial tissues has been quantified. Furthermore, a new type of semipermeable membrane-based passive sampler,triolein embedded cellulose acetate membrane (TECAM), was successfully applied to sample PAHs in soils. PAHs in soil sampled by TECAMs reached apparent equilibrium within 48h, significantly saving time for sampling PAHs in soil. The content of PAHs sampled by TECAMs was related to soil organic matter, dissolved organic carbon and the aging time of PAHs in soil. TECAM-accumulated PAHs correlated well with PAHs accumulated in earthworms (Eisenia andrei) and wheat roots (Triticum aestivum L.). Soil-pore water-TECAM three-compartment model was successfully used to describe the overall pro cess of PAH sampling by TECAM from field-contaminated soils. Additionally, TECAM caused minimal disturbance to soil and was easy to deploy. Therefore, TECAM is believed to be a useful tool to sampling hydrophobic organic carbons in soil and predict their bioavailability to earthworms and plants.