Abstract:Location-based social networks, which add geo-information into traditional social networks, link people’s virtual and real world lives. As an important application of location-based social networks, location recommendation can recommend places that people may be interested in, provide choices for people’s out-going and make people’s lives much more convenient. Against this background, the relevant concepts of location recommendation, the methods it usually uses, data sets it deals with, evaluation methods for recommendation effectiveness and the problems it faces were delved and the future possible research directions were forecasted, hoping to provide more useful reference for researches in relevant fields.

Abstract:Large scale geo-raster data have been accumulated all over the world in different departments and organizations during the past decades, but quite often in a variety of data formats, resulting in geospatial data sharing as an everlasting headache. Despite of various methodologies created, geospatial data conversion has always been a fundamental and efficient way for geospatial data sharing. However, as the size of data tends to be larger and larger, the methodology which was bounded by limited disk data transfer rate and bandwidth, needs a re-write and up-grade. A parallel geo-raster data conversion engine (PGRCE) was proposed to deal with massive geo-raster data sharing efficiently by utilizing high performance computing technologies. PGRCE was designed in an extendable and flexible framework, and was capable of customizing the way of reading and writing of particular spatial data formats. An experiment, in which georaster data in the CNSDTF-DEM format (Raster spatial data defined in Chinese Geospatial Data Transfer Format Standard) were transferred using PGRCE in a parallel file system (Lustre), were conducted to validate the engine framework and its performance. Results show that PGRCE can achieve a 7.54 speedup on a Luster cluster of 8 nodes.

Abstract:Aiming at the invalid accesses and memory redundancies caused by data overlap of more than one logic map tile in the visualization process of virtual earth, an optimal retrieval method of multi-theme tiles considering the spatio-temporal semantics was proposed. On the client side, the self-adoptive retrieval of tiles considering spatio-temporal semantics automatically matches the viewpoint information with semantics of datasets like space-time range, resolution and priority, then the invalid selection was filtered and the efficiency of target tiles data hit ratio was improved. On the server side, the theme oriented data cache based on memory database was achieved to prompt the response speed of server in the second access of tiles. Finally, the experiments prove that this method can prevent stable and high hitrate of target tile affected by amount of datasets and the cache method can further improve the efficiency of tiles access. The realtime visualization performance of massive image data is significantly improved.

Abstract:According to the load balance problem of large-scale parallel vector polygon rasterization, a novel data decomposition method was proposed. Firstly, the number of polygon nodes or the number of polygons was employed to evaluate the amount of calculations of a subset. The spatial locations of decomposed lines were computed iteratively and the balanced calculations between decomposed subsets were guaranteed, so as to realize data decomposition and load balancing. Secondly, a binary-tree based fusion strategy was put forth to merge the polygons across multiple subsets. The proposed parallel algorithm was implemented under a multi-core CPU-based environment and multiple China land use datasets were employed. Experimental results show that the presented method can outperform conventional methods for different datasets and can achieve a higher speed-up ratio and good load balancing. Moreover, when dealing with a large-scale vector dataset, the number of polygonal nodes is more appropriate to be the metric to evaluate the calculation of a subset precisely.

Abstract:The camera calibration from vanishing points is easily distracted by noise in the image, leading to inaccurate results which are often inadmissible for camera calibration. To overcome the limitation, an iterative optimization approach, which makes full use of geometric constraints of vanishing points and ellipse in the image, was presented for selfcalibration from single image. According to the polepolar relationship and the orthogonality represented by it, a set of orthogonal conjugate vanishing point pairs were calculated through using the ellipse curve and the coplanar vanishing line. A nonlinear model of the principle distance and principle point was established on the basis of these vanishing point pairs. Choosing the minimum variance of principle distances as optimization criterion and setting multiple points as the initial values of the principle point, the principle distance and principle point were iteratively optimized and their optimal results were obtained. Simulated results and real data show that the approach can effectively realize camera selfcalibration from a single image. Compared with the camera calibration method using vanishing points, the approach achieves more satisfactory calibration results.

Abstract:Kriging interpolation algorithm is of great practical significance and is widely applied to various fields of geoscience. However, Kriging interpolation would inevitably encounter the performance bottleneck when the output grid or input samples increase. Implemented with OpenCL and OpenMP, the ordinary Kriging interpolation was accelerated on heterogeneous platforms: GPU and CPU. By considering the performance difference of CPU and GPU on the densities of samples, a new load balancing method of LBCPDD (Load Balancing based on Computation Performance and Data Distribution) was proposed, in which not only hardware performance but also data distribution characteristics were taken into account. Experiment results show that LBCPDD method can effectively enhance the speed of ordinary Kriging, save memory space and improve the efficiency of memory access.

Abstract:The current topology inspection methods which use serial computation method accompanied with the complicated algorithms and excessive calculation amount cannot satisfy the demands of the efficient topology inspection for massive cadastral data. On the basis of the characteristics of topology calculation between point and line, the parallel topological computing method aiming at boundary points and lines has been implemented by combining the decomposition method for boundary points data with the Q tree and R tree spatial index method for boundary lines data. The topology parallel tests using the datasets of boundary points and lines in one area was taken in this method. The results show that the parallel efficiency of the algorithm which decreased with the increased number of processes steady maintains at above 30%, and the parallel speedup ratio reaches up to 5. The computation efficiency is improved more than 30 times than that of ArcGIS. The method can be used as a tool in high performance geographic information system and achieves good application effect.

Abstract:In order to improve the computing efficiency of signal blind area for BeiDou geostationary orbit satellites, it requires more computing resources in parallel computing environment. According to the analysis on parallel characteristics of the existing resolving principle and algorithm, a novel algorithm was designed for computing signal blind area of BeiDou geostationary orbit satellites based on elevation angle related dynamic blind influence scope. Based on this algorithm, the parallel computing tasks of signal blind area was divided and arranged by raster data partition. An experiment was taken for computing the blind area in china based on 59 scene digital elevation model data and 8 processes, and spent about 5 hours. The result shows that the parallel efficiency of the algorithm decreases with the increasing process count, but stably maintains at more than 96%. The method has been integrated as a tool in high performance geographic information system and can obtain good application effect.

Abstract:Camera coverage is an important basis of camera network initial configuration, optimal deployment and so on. Its precision and efficiency are the critical influences on the results of coverage analysis, which are very important to the application of large area camera coverage analysis, but many methods do not consider them. A new method to efficiently estimate camera coverage was proposed. Firstly, the geographic space was dispersed into grids. Secondly, the statuses of the four corners of each grid were computed. If the corner was covered by the camera, the status was denoted by using 1 or 0. So the status of the gird can be presented by the code which is either 0 or 1. Consequently there are 16 statuses to represent the status of a grid. Finally, if the code of the grid was not (0000) or (1111), the gird would be divided into four isometrical sub-girds until the subgirds were small enough or their codes were (0000) or (1111). According to the levels and statues of all grids, the whole camera coverage was estimated. Experimental results show that the proposed method can obtain more precise camera and can give consideration to both efficiency and accuracy.

Abstract:Electromagnetic launcher for unmanned aerial vehicle (UAV) which utilizes linear motor to accelerate in short distance is already a new trend for launching fixed-wing UAV. To brake shuttle in shorter distance when aircraft taking off, a hybrid brake method including solid stator eddy current brake, eddy current brake based on Halbach permanent arrays and rubber damping brake was proposed and analyzed. When the speed of shuttle is above 10 m/s, it is notable for the brake by means of solid stator eddy current brake. In addition, when the speed of shuttle is below 3 m/s, the brake force induced by solid stator eddy current is decreased greatly. It can increase 30% brake force by Halbach permanent arrays eddy current brake. By model analysis and collision experiments, rubber damping brake can absorb kinetic energy to brake shuttle in short distance as the final stage brake.

Abstract:A numerical method to solve the contact kinematic problems of elastic bar or circular micro-slip dry friction damper was proposed. Firstly, the damper and the time course of external excitation were discretized in the space and time domain respectively, and the same number of contact points was attached to the discrete damper. Secondly, the determination criterion of the contact kinematic state of the contact point pairs was used to each contact pair, and the stiffness matrix of the damper was modified. Thirdly, the whole balance equation with the new stiffness matrix was solved in each time step. Differing from the way the finite element software dealing with the contact problem with friction, the iteration was avoided, thus the feasibility of the solution was guaranteed. Meanwhile, the restriction of the distribution and the time variability of the normal load was overcome, and therefore it provided a more accurate boundary condition for solving dynamic response of structure. Lastly, the response of structures constrained by the macro-slip and micro-slip damper were computed by the MHBM (Multi Harmonic Balance Method) respectively and the distinctness of the solution was analyzed. Results show that the microslip model damper can have a broader normal force range for vibration reduction.

Abstract:A power transmission mechanism of twin-rotor engine based on wobble plate and cam was proposed. The advantages of the power transmission mechanism of twin-rotor engine based on wobble plate and cam are simple structure, completely symmetrical arranged, good balance, and the movement is controllable. For analyzing its operating characteristics, the basic kinematic model was established by Euler-equation, and its trajectory and cam contour lines were obtained. Effects on volume variation of the main structural parameters, such as plate inclination angle and roller axis angle were analyzed. Main results are as follows: the closer to 90° roller axis angle is, the larger volume variation is. Plate inclination angle is proportional to volume variation. For 4-blade pistons rotor, the maximum plate inclination angle is approximately 65°. In practice, the best roller axis angle is 90°, plate inclination angle should be large enough after taking the thickness of blade piston into account.

Abstract:By using the shock wave theory, the process that PELE (Penetrator with Enhanced Lateral Efficiency) penetrated a thin metal target was analyzed. The energy loss of the PELE in the process of penetrating the target plate could be divided into the energy obtained by plug when jacket and filling impacted the target, the increased internal energy of jacket and filling, and the shear energy dissipated in the outer and inner edge on the front end of jacket in the process of penetrating the target, etc. Based on the principle of conservation of energy and the method to determine these energies, the approximate formula of the axial residual velocity of PELE was presented. Results show that the axial residual velocity and the calculated results are in good agreement with the experimental data. Compared with the energy loss in different conditions, the filling material has little effect on projectile penetrating ability, and the energy that the plug obtained is the largest while the shear dissipated energy can be neglected.

Abstract:Supercooling phenomenon of stratospheric long duration balloons means that the temperature of helium gas inside is lower than that of atmosphere outside, this will cause the loss of buoyancy and affect ascent process of the balloon as a result. Radiation and convection thermal models and the vertical dynamic model of long duration balloons were established, and the influence regularity of some important factors, including initial net buoyancy, skin thermal physical parameters, launch time and launch date, on supercooling phenomenon was analyzed. Simulation results show that the temperature difference between helium gas and outside atmosphere enlarges remarkably along with the increase of initial net buoyancy, and the temperature difference decreases when the absorptivity for visible light and infrared radiation increases. Simulation results also show that the influence of launch time and launch date on supercooling phenomenon is much smaller, while flight time from ground to designed altitude displays great difference when the launch time is different. The research results can provide theoretical reference for conceptual design and flight test.

Abstract:The autopilot is the crucial device for a unmanned aerial vehicle to implement autonomous flights and missions. Most of the existing commercial autopilots have no hardware reinforcement, which will lead to a risk in carrying out some significant tasks. The analysis reveals that the control resolver is the module which performs the greatest impact on the security and the reliability in the composing of an autopilot. With the increasing fault-tolerance requirements, 4 reinforcements were respectively designed, namely, the single resolver reset reinforcement, the dual resolver hot backup reinforcement, and the dual host systems switched by hardware and software. Several simple devices such as repositors, counters, inverters, selectors, and additional codes inside the resolvers were used to build the reinforcements. The reliabilities varying with time of the reinforcements were emphatically studied and comparatively analyzed. With the simulation of the working mechanisms, the fault-tolerance performances, such as the abnormal output durations, of the reinforcements in fault treatments were analyzed. The calculations show that all the reinforcements can obviously enhance the reliability of the autopilot, of which the dual host systems increase the most. This research provides a meaningful direction to the tradeoff of the fault-tolerance performance, complexity, and cost in high reliability autopilot designs.

Abstract:On the basis of Davenport wind speed spectrum and using M.Shinozuka method, samples of wind load were numerically simulated on the different girds of rocket core and booster under three basic wind velocities. Then a transient response analysis was made to the rocket and its launching platform by invoking the MSC.Nastran, and the displacement response of the rocket and its launching platform under different basic wind velocities was obtained. The value of the displacement increases along with the increase of height away from the ground, and the ratio of the maximal displacement approximates to the ratio of the square of basic wind velocity on a grid. Finally, a designed load-relieving structure was placed on the umbilical cord tower. Results indicate that the maximal displacement on different grids decreases conspicuously and the anti-wind capability of the rocket and its launching platform are enhanced by a large margin with the help of the load-relieving structure. The designed structure can make a reference to the engineering practice.

Abstract:A precision conversion methodology with truncated normal distribution theory assumption oriented to maximum-error specification was brought forward, and it could be taken as a reference frame for the precision conversion between maximum-error specification and other precision measurement specifications, so that the precision class of according true value measurement systems could be determined in advance. The method assumes that the conformity probability of the observation sequence is subjected to logarithmic truncated normal distribution; based on the aimed confidence level for maximum-error specification and the given sample size of target sequence, the calculation formulation of upper truncated limit, lower truncated limit, mean and standard deviation of the truncated normal distribution were proved and derived, thus the precision conversion relationships between maximum-error specification and other precision measurement specifications, such as 1σ, were turned out; through referring to the corresponding theories on precision instrument fields, the determination methodology for precision class of true value measurement systems under maximum-error specification was given. The application on related example cases proved the feasibility of the proposed method.

Abstract:Investigation of boron particle agglomeration ignition and combustion in secondary chambers is very important for increasing the capabilities of ducted rockets. By experimentally mimicking ducted rockets, boron particle agglomeration ignition and combustion in secondary chamber flow field was investigated. The ignition and combustion processes, flame constructions and size changes of boron particle agglomeration were analyzed with the image processing techniques of high speed flame and the measurement results of flow field parameters. The effects of gas temperature and oxygen content on ignition and combustion of boron particle agglomeration were acquired. The analysis result of residue indicates that the particle size changes little and the gas may get into the boron particle agglomeration and react with boron particles.

Abstract:Focusing on the deficiencies of standard-form laminate with extensionshear coupling, such as weak extension-shear coupling, the design method for free-form laminate with extension-shear coupling using the method of optimization design was proposed. Necessary and sufficient material-independent conditions were derived for extension-shear coupled laminates. The stacking sequences of 7-ply to 14-ply free-form laminates with extension-shear coupling were derived. Comparisons were made on buckling strength and robustness of extension-shear coupled laminates. The free-form laminate with extension-shear coupling was used to design structure with extension-twist coupling. Compared to the standard-form laminate, the free-form laminate with extension-shear coupling is worse in buckling strength and robustness, while it’s stronger in coupling. The results also indicate that with an increase in the number of plies, the maximum extension-shear coupling flexibility coefficient of the free-form laminate decreases.

Abstract:To solve the problems that human limitations may cause the loss of important information, thus affecting the classification results, a feature extraction method based on unsupervised feature learning techniques was proposed. Unsupervised feature learning method to learn multiple feature maps was used and concatenated together. This method can avoid the loss of important information, and also can significantly reduce the scale of unsupervised feature learning model used. To evaluate the proposed method, experiments on a public human activity recognition dataset were performed, using three commonly used unsupervised feature learning models, and finally using support vector machines to classify activities. The results show that the proposed feature extraction method achieves good results, and has certain advantages compared with other methods. 

Abstract:In order to accurately estimate the unknown parameters for chaotic systems, the artificial bee colony optimization algorithm was improved, and an adaptive artificial bee colony optimization algorithm was proposed. The proposed method formatted the problem of parameter estimation for chaotic systems to a multidimensional variable optimization problem, and used the artificial bee colony optimization algorithm to search the unknown parameters in a guided random manner. During the search process, the method adaptively adjusted the step size and the solution trial limits based on the optimum degree of the population and the quality of the solutions. The numerical simulation on the classic Lorenz chaotic system demonstrates that the proposed method is robust and can obtain accurate estimation for chaotic systems without noise or with intensive noise.

Abstract:Aiming at the difficulty in analysis of binary program vulnerabilities, an approach for software vulnerable spots localization based on taint analysis was proposed, and a corresponding tool named SwordChecker was implemented. This method is based on dynamic taint tracing. Software vulnerable spots were localized by character matching according to vulnerability patterns, and sensitive bytes which affected the vulnerable spots were localized by binary-search. Experiment results show that SwordChecker can accurately identify and localize three types of software vulnerable spots fast, has successfully analyzed the causes of multiple open vulnerabilities, and has assisted mining several undisclosed vulnerabilities.

Abstract:In the field of array signal processing, direction of arrival (DOA) estimation is a hotspot problem. Classical DOA estimation methods usually require the number of sensor should be larger than the source signals’ (which the so-called over-determined case is). However, what we encounter in practice is always the underdetermined case in which the number of source signal is larger than the sensors’. To solve the problem, a multiple signal classification (MUSIC) extension algorithm based on spatial time-frequency distribution was proposed to achieve the underdetermined DOA estimation by expanding the dimension of the spatial time-frequency distributions matrices. Compared with the existing time-frequency MUSIC, the proposed algorithm can be applied to both the over-determined and the underdetermined cases. The proposed algorithm also has advantages over the existing underdetermined DOA estimation methods for it guarantees the estimation precision, relaxes the requirements for source signal sparseness and lowers standards of the number of snapshots. Simulation results confirm the validity and high performance of the proposed algorithm.

Abstract:Aiming at the problem of exorbitant sampling rate and sensing time too long in wideband sensing, a wideband spectrum sensing method using improved multiple signal classification (MUSIC) based on modulated wideband converter (MWC) was proposed. The MWC for sub-Nyquist sampling was used, the number of signals by minimum description length (MDL) criterion was estimated, and the signals’ location using improved MUSIC was estimated. In the improved MUSIC, an adjustment factor was given, which enhanced the MUSIC spectrum at the signal’ locations and reduced others, and the noise jam was restrained. An amount of calculations was reduced, because it neither needed to recover original wave, nor calculated PSDs in the whole process. The complexity of sensing method was small, so that it increased sensing efficiency. The results show a reliable detection even in low signal noise ratio.

Abstract:With its intrinsic characteristics, circular synthetic aperture radar has lately become a particular interest to the radar community. The differences of imaging processing between the circular synthetic aperture radar and linear trajectory synthetic aperture radar were compared and analyzed. The detailed comparisons containing the size of the observed area, the properties of the point spread function, and the properties of echo spectrum were carried out. It was learnt that the difficulty of the imaging processing of single-pass circular synthetic aperture radar lies on its space dependence. To overcome this difficulty, the plane circular synthetic aperture radar and multi-base line circular synthetic aperture radar imaging models were analyzed. Simulation test was carried out and the corresponding results prove the proposed analysis is valid.

Abstract:Interference approximate method (IAM) for orthogonal frequency division multiplexing / offset quadrature amplitude modulation (OFDM/OQAM) channel estimation needs the value of preamble at the background of un-cooperative communications. Motivated by this consideration, an OQAM characteristic based-IAM (OCB-IAM) algorithm, which used IAM preamble framework and OQAM symbols’ real finite-alphabet characteristics, was introduced. OCB-IAM algorithm estimated the amplitude and phase of channel fading coefficients separately, and just needed preamble position, which was a kind of semi-blind channel estimators. OCB-IAM algorithm converted white Gaussian noise into single tone interference based on the secondorder statistics of received symbols. Then it could be proved that OCB-IAM algorithm has a better performance than IAM algorithm in medium and low SNR regime. Numerical results show the validity of theoretical analysis and the reliability of OCB-IAM algorithm.

Abstract:Multi-sensor image matching is a challenging problem in image process field. As synthetic aperture radar images and optical images have significant differences, most existing methods cannot achieve satisfied matching result. To respond to this issue, a new multi-sensor image matching method based on Gabor binary encoding was presented: the big and small input images were first convoluted respectively by a group of Gabor filters; the compressed representation was executed on the convolution result by using pooling method; the binarization of pooling results was conducted and it was transformed into binary code to create Gabor binary encoding features; the similarities of corresponding window features between real-time images and reference images were calculated by using bit manipulation and the maximum value indicated the matching result. This method describes images by binary representation, so the computation complexity is much lower than that of the traditional method, while the common characters are better revealed. Experimental results show that the proposed method has much higher matching rate and require much lower computation time than those of the existing methods.

Abstract:In order to overcome the disadvantages of the low registration accuracy and the computational complexity of traditional algorithms, a new sub-pixel registration algorithm based on combination of curved surface fitting method and gradient method was proposed. Firstly, curved surface fitting method based on 9 correlation coefficients was used to achieve the image rough registration. Secondly, subimages were extracted from the reference images according to a predefined selection method. At last, gradient method based on the rough registration was proposed to achieve the accurate sub-pixel registration. Test results among experimental images with different translational relations show that the new algorithm has the advantages of both curved surface fitting method and gradient method, and greatly improves the accuracy of image subpixel registration．The maximum absolute error of registration accuracy is reduced from 0.17 pixel to 0.02 pixel.

Abstract:Based on underwater unit short/open circuit failure modes, a method for analyzing the reliability of constant current remote power feeding system of cabled seafloor observatory network was proposed. According to system power supply and structural properties, the system was divided into different links and segments. Influence on power supply state of the links and observation equipments by unit failures in different position was studied in detail. The causes of leading system and link cannot be conducted and observation equipment cannot be operated were summarized, and the probability of different fault occurrence was analyzed, then power supply reliabilities method of system, links and observation equipments were obtained. Through example analysis，the general law of the three kinds of power supply reliability needs comprehensive considerations in system construction and design phase.

Abstract:Due to the difference between theory detection and inbattlefield detection ability of airborne IRST (Infrared Search and Track) system, the method of evaluation for detection system was put forward. Firstly, the theory aiming at operational capability of airborne infrared detection system was analyzed, especially the betterment of NEFD (Noise Equivalent Flux Density) operating range model, and the analysis of functional relationship between operating range and detection probability. According to the operation mode of IRST system, the computational formula of physical detection probability and target identification probability was deduced, and the target identification probability changing with operating range as well as speed was analyzed. Finally, the test platform of IRST system detection probability was set up and the experimental evaluation steps were made, and a simple and reliable method of evaluation and calibration was proposed. Simulation result shows that the operation range limitation of IRST system can reach 60km.Testing by semi-physical simulation，the rationality of the model is verified through the experimental conclusion.