In this paper, representation formulas and properties for the sub-Laplacian on quaternionic Heisenberg groups are established and then some unique continuation results to solutions of sub-Laplace equations with potentials are given.
Experimental studies were conducted to investigate the interaction of water mist with flames of ethanol fuels soaked in porous beds. Effects of the nozzle jet pressure, the fire preburn time and the characteristics of porous materials on the water mist extinguishing were conducted and discussed. The experimental results show that for the same preburn time, the larger the nozzle jet pressure is, the faster the temperature in both the flame zone and porous beds changes and thus the shorter the fire extinguishing time is. While under the same nozzle jet pressure condition, the longer the preburn time is, the shorter the fire extinguishing time is. Furthermore, effects of the characteristics of porous materials on fire extinguishment by water mist were also discussed in this paper. Experimental studies were conducted to investigate the interaction of water mist with flames of ethanol fuels soaked in porous beds. Effects of the nozzle jet pressure, the fire preburn time and the characteristics of porous materials on the water mist extinguishing were conducted and discussed. The experimental results show that for the same preburn time, the larger the nozzle jet pressure is, the faster the temperature in both the flame zone and porous beds changes and thus the shorter the fire extinguishing time is. While under the same nozzle jet pressure condition, the longer the preburn time is, the shorter the fire extinguishing time is. Furthermore, effects of the characteristics of porous materials on fire extinguishment by water mist were also discussed in this paper.
The catalysts were prepared by the method of the co-precipitation. The catalytic performance for selective oxidation of isobutylene to methacrolein was studied by the pH value of solution and calcination temperature during the preparation of catalysts, the content of the vapor in the material and the pressure of reaction during the process of reaction. The physico-chemical properties of the catalysts were characterized by SEM and XPS. The experimental results indicated that: The conversion of isobutylene with the catalyst of pH=3.0 was obvious higher than that with catalyst of pH=1.0 and pH=6.0.The catalyst on calcination temperature of 400℃ had the highest conversion of isobutylene and the catalyst on calcination temperature of 500℃ had the highest selectivity of methacrolein .With the increase of the vapour content the conversion of the isobutylene and the selectivity of the methacrolein improved, enhancing the pressure increased the conversion of the isobutylene simultaneously decreased the selectivity of the methacrolein.
In this paper, asymmetric synthesis of oxidation reaction of achiral isophorone influenced by artificial centrifugal force field was studied. The reaction system was characterized by UV, Infrared (IR) and Circular dichroism (CD). The CD230 of product mixture was positive and negative in the clockwise and anticlockwise rotation,respectively, and the effect was dependent on the rotation speed. The data indicated that enantiomeric excess of isophorone oxide was able to be caused by the external centrifugal force field. It was suggested that the chiral effect was resulted from the chiral interaction between the chiral right- and left- handed helical motion and the chiral enantiomers.
Digital Elevation Model (DEM) is essential data for research on global environment change and regional sustainable development. Aiming at the topographic characteristics of undulating hills, using ARCVIEW software, the author selects typical test area and compares SRTM data with the DEM generated from 1:50000 and 1:100000 topographic maps. The result shows that SRTM data can present more detail in gentle slope area and lay out the shape of small channels. Topographic Index extracted by SRTM data is more similar with the actual land surface by giving the natural winding stream and low-lying marshes. Consequently, SRTM data contain more detail than 1:50000 topographically derived DEM.
Altitude angel can influence the echo waveform of radar altimeter severely, so it is an important parameter in altimeter tracking, and there are several approaches to estimate it. In this paper the authors describe two algorithms based on altimeter waveform tracking and carry out the accuracies of them. Afterwards, the authors implement some Monte-Carlo simulations, consider the performance of the algorithms and validate the conclusions of theoretic analysis.
Many P2P media streaming protocols assume that peers are all collaborative. They do not consider about the problem of selfish peers. We propose a score and monitoring based incentive mechanism for P2P media streaming system. In this mechanism each peer obtains contribution score in two ways: uploading data to others by itself and by its child peers. The peers with higher scores have better chances to download data. To maximize the score, peer can choose to monitor its child peers to stimulate sharing, accordingly improve the system performance. Through simulation, we verify that the proposed incentive mechanism can solve the long-term history score problem, increase the cooperative proportion and maintain higher system performance.
It’s usually considered to be practical and effective to predict the amplitude of solar cycle using statistical precursor methods based on the geomagnetic precursors, but it will appear biggish error in a certain cycle prediction by this method. Particularly, the error exceeds 30% in predicting the amplitude of the 23rd solar cycle, which we are now standing. This paper provides a synthesis prediction method based on multi-information. Computer simulation shows that the new method is more adaptive and stable, compared with the statistical precursor methods based on the geomagnetic precursors. In predicting the 23rd solar cycle amplitude, the average error is only 10%.
This paper presents a method for steganalysis of images based on principal component analysis and support vector machine. Considering that embedding information inevitably brings noise to cover images, we design and calculate eigenvectors of images after analyzing principal components of image blocks. By using eigenvectors of cover images and steg-images to train SVM, we can obtain a trained SVM to be used to blind detection. Experimental results show that the proposed scheme is effective to many steganographic methods and correct detection rate is better than the steganalysis method using image quality metrics.
This paper presents a distributed user authentication scheme in wireless sensor networks. Our scheme utilizes the self-certified keys cryptosystem (SCK) to establish pair-wise keys. Based on these keys we propose two different kinds of user authentication scheme: local user authentication and remote user authentication. Our proposed user authentication scheme imposes very light computational and communication overhead, and our analysis also shows that our scheme is feasible for the real wireless sensor networks.
A novel fragile watermarking algorithm based on binary look-up-table (LUT) and Hash value in the discrete wavelet domain is proposed to overcome the security problems of block-wise independence watermarking schemes. Since the wavelet transform has space and frequency characteristic, we embed a marking watermark in the LL sub-band with the look-up-table method for the detection and localization tampering. Choose the Hash value of the HL sub-band or LH sub-band as another watermark to embed in HH sub-band for resisting the counterfeiting attacks. The experimental results demonstrate that the algorithm has both the effectiveness in resisting possible attacks and good ability of detecting local alterations.
Since IEEE 802.11 protocol implements a limited number of retransmissions at link layer, an energy-efficient routing algorithm named ERRC is proposed for reliable communication in IEEE 802.11-based Mobile Ad Hoc networks (MANET). It can be easily applied to current MANET active routing protocols. ERRC proposes an energy consumption model based on IEEE 802.11 retransmissions and provides power control mechanism in data transmission. Packet error rate and node cost are considered during ERRC’s route selection. The simulation result shows that ERRC can significantly prolong the MANET’s lifetime and is more accurate than traditional energy efficient routing algorithms which do not consider packet error rate.
In term of the fundamentals of traditional Extended Chirp Scaling processing, a new CS Algorithm for along track mode Bistatic Synthetic Aperture Radar is presented, based on second order approximation of range history. The complexity of 2D Fourier transformation of signal impulse response, due to receiver-transmitter separation, is settled. It is a very precision image formation algorithm for along track Bistatic SAR system with small squint angles.
As a typical authentication and key exchange protocol, TLS handshake protocol could be analyzed under the framework of BR computational model. We provide computational analysis of this protocol and prove that, when implemented with pseudorandom function as message authentication algorithm and encryption scheme which satisfies IND-CCA standard, the TLS handshake protocol is indeed secure under computational model. The technicalities of our proof reveal insights regarding the relationship between formal and computational models of security protocol.
In this paper, a video stabilization technique based on Dynamic Displacement Field (DDF) model is introduced to stabilize the spatially variable distorted image sequence. Based on motion filtering technique of the spatially invariable image sequence, motion estimation and frequency filtering techniques of the spatially variable image sequence are used to stabilize the projective distorted image sequence. Experimental results show that the proposed method removes high-frequency jitter and stabilize the projective distortion after motion filtering. If we know the physical factors that create the distortion, we can correct the projective distortion while stabilize the projective distortion. It can not only be potentially applied in video stabilization system but also be applied in other practical spatially variable distortion correction fields.
The increase of FFT computing speed is the main subject in the realm of digital signal processing. Parallel computing and pipeline structure are the basic technologies to achieve high speed of large scale FFT computing. After analyzing the address of computing data in radix-2 decimation-in-time FFT algorithm, we design a two-dimension SRAM. The non-linear changing of data address, which is the bottleneck when using normal SRAM to compute an N-point FFT, can be removed. butterfly units in FFT can compute fluently in parallel. The amount of simplified data address can be decreased largely. An 8 by 8 words, 16 bits word length, two-dimension SRAM is designed and simulated, the function is verified.
This paper firstly describes some techniques of space-borne SAR raw signal simulation, including satellite-ground space geometric model, space-borne SAR raw signal mathematic model and RFPC algorithm. Based on these techniques, a method for space-borne SAR raw signal simulation is presented and the simulation flow is given in details. After the parallelizability analysis, the simulation method is parallelized with parallel programming tool OpenMP. Simulation results prove that the parallel simulation method is correct and effective.
Organic π-conjugated systems such as porphyrin, perylene bisimide, pyrene, fullerene, ferrocene have been synthesized and their self-assemble based on specific molecular interaction have been studied. The self-assemble into more complicated systems such as molecular machine and light-to-current converter have also been studied.
