Abstract:An overview of the literatures is presented on cellulose-silica organic-inorganic hybrid aerogels. According to the technological characteristics, cellulose-silica composite aerogels can usually be synthesized by three methods, i.e. solution impregnation method, direct mixing and layer-by-layer deposition. The dissolution or dispersion of cellulose and the introducing method of silica are discussed in detail, which are important influencing factors for compositing cellulose-silica aerogels. The characteristics of microstructures and crosslinking mechanisms of cellulose-silica aerogels are analyzed, and the properties in mechanics, thermal insulation, optics, hydrophobicity and biology are compared. Based on the physical and chemical properties of organic cellulose and inorganic silica, some of composite problems are discussed and some new ideas for further development are proposed.

Abstract:A two-branch transmit method based on the weighted-type fractional Fourier transform (WFRFT) is proposed to improve the bit error rate (BER) performance of multi-input multi-output (MIMO) systems. The signal to be transmitted is first sent into the information modulation and synthesis module of the transmitter. Then the proposed method is accomplished in a two-step manner. Specifically, the transmitter first decomposes the transmission signal into four way signals. Then, the four-way transmitting signals are combined into two-way signals by time-frequency combination and are transmitted via two independent antennas. The signal is received by single antenna at the receiver. And inverse-WFRFT is performed such that the transmission signal can be recovered reliably. Numerical results show that the proposed scheme leads to a significant performance advantage, in terms of both BER performance and robustness against doubly-dispersive fading, compared with the Alamouti space-time block coding.

Abstract:A distributed fetch structure of M5-edge is designed for the purpose of expanding the design space of EDGE architecture. The structure includes the overall function, distributed fetch unit and the interconnection network between the units. Two kinds of fetching block head are realized, including fixed fashion and round robin one. The analyses, which are made in different distributed fetch unit counts, provide the leave of reduction of distributed fetch comparing with the ideal lumped fetch model, as well as the difference between the two fashions of fetching block head. Furthermore, the effect of the processor performance by the communication latency and the cache miss rate are shown.

Abstract:In order to reduce more complexity while maintaining a good bit error rate performance, a new SM-SD algorithm is proposed. The new SM-SD algorithm employs a different real-valued equivalent transformation from existing sphere decoding algorithms, and it has a unique search tree structure, the adjacent two layers of the search tree are independent of each other. The principle and process of the new algorithm are analyzed, and the computation complexity of SM-SD algorithms is compared by the matrix analysis. Then, the bit error rate and computational complexity of SM-SD algorithms are compared by simulation in different SM systems. Theoretical analysis and simulation results show that the new SM-SD algorithm has a very close performance to Maximum-Likelihood optimum detection, with lower computational complexity than other existing SM-SD algorithms. Thus, the new SM-SD algorithm is more suitable for SM signals detection.

Abstract:In order to achieve the mass spectrum at low vacuum, the equation of ion motion with resistance is derived. Pressure effects are treated by adding a drag term to the Mathieu function which is calculated based on fifth-order Runge-Kutta in MATLAB. The effects of gas pressure on stability regions and ion motion are described. A numerical method for getting stability regions is proposed. The first, the second and the higher stability regions in the presence of the damping force are given. The results show that the damping force caused by gas pressure enlarges the stability regions. The initially separate stability zones merge together for higher pressure. In low vacuum conditions, mass analysis can be performed by altering operation mode. The pressure effects can be reduced by increasing the frequency.

Abstract:Focusing on the problem of high computation complexity of MUSIC algorithm which is used for joint polarization-DOA estimation of conical conformal array, the signal model of conical conformal array is established and is built by single polarizative elements. Through the building of same polarizative sub-array, the polarization and DOA information of steering vector is de-coupled, considering the shadow effectors of conformal array, dimension reduced MUSIC is derived by rank reduction theory, which realizes polarization-DOA estimation by less computation complexity. The method has been verified by computer simulations.

Abstract:In order to replace the traditional pretreatment process for electroless plating of chromic acid roughening and colloid palladium activation, the metal layer was prepared on the surface of nylon (PA10T) through a green method. The distribution of functional groups and the change of valence bonds on the nylon surface were characterized by Fourier transform infrared spectrometry and X ray photoelectron spectrometry, and then a model was established to illustrate the metallization process. The results show that the roughening system of sulphuric acid-ethanol can be used to achieve the effect of roughening, make the amide bond rupture and generate amino and carboxyl in PA10T. When the palladium-free activation process is adopted, the surface activation of nylon could be achieved by the coordination of Cu²⁺ with amino groups and carboxyl groups. The simple and environmentally friendly method mentioned above could get a good adhesion of the metal coating on the PA10T surface, the coating binding force reaches 537 N·cm^-2 which is tested by electronic universal material testing machine.

Abstract:In recent years, lots of fruitful results have been achieved in the aspects of simulation technology for embedded hardware and virtual testing for embedded software. However, there are some shortcomings in the previous achievements. For example, there are no overall, unified, flexible and general interfaces among the generic components, so it results that different architecture or different type of simulation processors cannot interact and integrate with simulation devices directly, and result that system-level customization capabilities are lack. Based on component, a set of general structures, standard interfaces, processing logics for virtual processors, virtual peripherals and debugger are proposed. We did some optimizations and deletions, added some new features in GDB, so that GDB can dynamically load at runtime to support multiple processor architectures. A virtual testing system is developed, by it the validity and correctness of the proposed method, structure, interfaces are verified. The proposed methods and technologies have more advantages compared with other similar technologies or projects.

Abstract:Tensile experiments on adhesively scarf-repaired composite laminate joints were conducted, for analyzing the stiffness, strength, failure modes and key positions' strain distributions of the joints with different scarf angles and extra ply numbers subjected to unidirectional tensions. A kind of carbon fiber woven reinforced composite was applied to fabricate the base laminates and repair patches, and a kind of curing modified epoxy supported film adhesive was used as adhesive layer, designing a series of specimens with one extra ply or two extra plies, of which scarf angles are equal to 1.8°, 2.6°, 3.5° and 4.4°, respectively. Tensile experiment results show that stiffness and strength of the joints are negatively related to scarf angles in the range from 1.8° to 4.4°. Adding extra plies helps enhancing the stiffness and strength of the joints. The failure modes of the joints can be summarized into four types, which are related to scarf angles and extra ply numbers. The longitudinal strain changing at the key points of the joints can be applied to reflect the failing process of the joints dynamically.

Abstract:In order to study error influence of relaying nodes decoding process in which the signal to noise ratio is low, bidirectional soft information relaying scheme based on spatially coupled low density parity check (SC-LDPC) is proposed, and a more accurate model is also presented to describe the residual noise characteristics of the soft symbol. The proposed scheme adopts a pre-computing look-up table at the node of destination, which makes the calculation of the residual noise scale factor and the soft error variance more convenient. Compared with the previous soft noise modeling techniques, the proposed scheme reduces the signaling cost. In addition, the variance correction factor is introduced to correct the equivalent noise variance at the destination node. Simulation results show that, compared with other similar schemes, the proposed scheme achieves a significant improvement in bit error rate.

Abstract:To overcome the limitations of compute capability and bandwidth in UAV (Unmanned Aerial Vehicle) video, this paper proposes a novel video compression algorithm based on hierarchical description. The video is split into background layer and object layer. Background layer is encoded with global motion estimation, while object layer is encoded with local block matching. The experimental results demonstrate that, when bandwidth is narrow e.g. 50 kbit/s, using background layer encoding can achieve higher PSNR than H.264, and the subjective quality is much more acceptable; in most cases, combining background and object layer can give more details than H.264 with the same bitrate; the consuming time is only 18% of H.264's. Additionally, alternative bitstream can be extracted for different bandwidth. Consequently, the proposed algorithm is suitable for low latency and complexity applications in UAV video due to its good performance, high efficiency and flexibility.

Abstract:Aiming at improving the performance of obtaining texture regions by directional filters and achieving better steganography security, a novel adaptive steganographic algorithm is proposed based on WOW algorithm and Gabor wavelet. Firstly, a directional filter bank is established by Gabor wavelet and then the residual weights are determined by this bank from 8 directions. Then the cost function is defined based on H?lder norm, and is updated by convolution with an average filter. Finnally, secret messages are embedded by syndrome trellis codes according to the cost function. Experimental results illustrate that the presented steganographic algorithm achieves a better performance on resisting the Spatial Rich Mode steganalysis than that of the same kind of steganographic algorithms under the same secret message payload.

Abstract:To make up for the deficiencies of existing sounding method in obtaining the seabed microtopography, a linear algorithm to obtain three-dimensional sea topography using side scan sonar image based on its high resolution features is proposed. Firstly, the incident sound direction estimation model is given according to the side scan sonar imaging mechanism, and the linear inversion algorithm is derived from the seabed lambert model. Meanwhile, the constraint model is built using the initial terrain data of the same area, and the transform from inversion topography to real topography is completed. Based on the above, the inversion process and the accuracy evaluation method are finally achieved. Lastly, experiments are carried out to test and verify the given method. Experimental results show that this method can obtain the topography whose accuracy is better than 15 cm and whose resolution is about 170 times higher than that of the initial terrain.

Abstract:For safety transmission, a security method in the physical layer is proposed based on generalized spatial modulation technique. The transmitter pretreats the signals according to the state information of the legal channel so that phases of all signals sent by different antennas are identical at the legal receiver. At the same time, different additional phase shift is imposed when different combination of the activated antennas is used, so the performance of the legitimate user is improved. However, phases of signals sent by different antennas are random at the eavesdropper, thus its performance is significantly lower than that of the legitimate user so that the information conveyed by the antenna index is protected. Artificial noise pointed to the eavesdropper is sent simultaneously at the transmitter to safeguard the information conveyed by amplitude and phase modulation symbols. Then the secrecy capacity, error performance and power assignment between signal and artificial noise are analyzed. The simulation results show that the legitimate receiver's error performance is superior to that of the eavesdropper, and a considerable secrecy capacity can be obtained.

Abstract:To improve the localization performance of the WKNN location fingerprinting algorithm when the indoor environment is complex, an improved WKNN location fingerprinting algorithm—Discrete Degree Weighted K-Nearest Neighbor (DD-WKNN) is proposed, which takes the dispersion of location fingerprints as the weight reference. The K-means clustering algorithm is used to cluster the location fingerprints when the offline location fingerprint database is established, which reduces the computational complexity of searching the location fingerprint database. K location fingerprints which are most similar to online measured RSSIs are selected from the offline location fingerprint database, and the discrepancy degrees are compared. A higher weighting coefficient is assigned to the position fingerprint with a small degree of dispersion, which reduces the error of position estimation caused by the original WKNN algorithm when the signal strength of the indoor environment changes greatly with distance. The analysis of the time complexity of DD-WKNN algorithm shows that its computational complexity is less than that of the original WKNN algorithm. The experimental results show that the DD-WKNN algorithm has a higher positioning accuracy and the positioning error fluctuates less.

Abstract:Aimed at the disadvantages of simple construction and attack mode in study of the Command Information System (CIS) cascading failure, a CIS bi-layer coupled network model is constructed. We analyze some characteristics of CIS cascading failure by setting different attack modes based on it. Firstly, the model is constructed by coupling communication network and function network of CIS architecture, and the node weightiness parameter is proposed based on the multilayer network theory. Secondly, by setting three attack modes and defining attack intensity, we analyze cascading failure mechanism of the bi-layer coupled network model. Lastly, simulation results show that the bi-layer coupled network model can reflect characteristics of CIS network structure, and based on this model, we can analyze cascading failure mechanism of CIS under conditions of setting different attack modes and attack intensities.

Abstract:For the case that the direction of the reflected signal from desired target in the presence of clutter is uncertain, a robust joint design of transmit waveform and receive filter for MIMO radar is proposed. Under the condition of the transmit power constraint for each transmit element, a Max-min optimal model about the output SINR within the uncertainty set is designed using transmit weighting matrix. On this basis, the sequential optimization method, semi-definite relaxation and Charnes-Cooper transform are used to transform the joint optimization problem, which is non-convex, into two convex sub-problems about transmit waveform and receive filter, respectively. And through iteration optimization procedure, the optimized covariance matrixes of transmit waveform and receive filter are obtained. Finally, the desired transmit weighting matrix and receive filter are synthesized via the randomization method with the optimized covariance matrixes. Theoretical analysis and demonstration about the computation complexity and the convergence of the proposed method are given. The proposed method can improve the robustness and reduce the computational burden with the same transmit power constraint of each antenna. And the efficiency and validity of the proposed method are verified by the simulation results.

Abstract:Aiming at the problem of sea surface temperature (SST) measurement in radar power prediction (RPP), a modification method of sea surface temperature is proposed based on infrared sensor. The measured deviation of infrared sensor for SST is analyzed. The infrared models of sea surface radiation and reflection are modeled. The affections of sky radiation to result of SST and RPP are analyzed by simulation. A modification method for RPP is deduced. Through experiment, the result shows that the relative error of prediction result is limited in 20% with 80% probability by this method, which greatly enhances the prediction accuracy.

Abstract:In order to further improve the resolution of direction-of-arrival (DOA) estimation of antenna array, a high resolution approach of DOA estimation is proposed based on the fourth-order multiple signal classification (FO-MUSIC) approach. First, the antenna array is extended through the fourth-order moment of the received data. Then, the antenna array is extended through the conjugate value of the received data. When the expanded steering vector and the expanded covariance matrix are used for DOA estimation instead of the original steering vector and the original covariance matrix, virtual array elements are formed and the aperture of array is extended. It is shown by simulation results that, compared to the FO-MUSIC approach, the proposed method has a higher probability of target resolution, lower root mean square error and higher resolution. Hence, more virtual array elements are formed by the proposed approach based on twice virtual extension, and the resolution of DOA estimation of antenna array is effectively improved.

Abstract:To improve the outage performance of a bidirectional amplify and forward relaying system in an asymmetric Rayleigh fading channel, a new power allocation scheme based on minimizing the outage probability is proposed. First, the asymmetry factor is introduced, and under the theoretical analysis, the closed outage probability expressions of four cases asymmetric two-way relay channel with traditional three nodes network structure is derived. Simulation results show that downlink asymmetry is the worst case. Furthermore, in order to minimize the downlink asymmetry system outage probability, a power allocation scheme based on channel state information is proposed. In this scheme, the power allocation is a piecewise function of the asymmetry factor. The node can adjust the transmission power adaptively according to the variation of the channel state. Simulation results show that the proposed power allocation scheme can improve the outage performance of the downlink asymmetric two-way relay system. Compared with the equal power allocation scheme, the smaller the asymmetry factor is, the better the effect is.

Abstract:In order to improve the efficiency of lung airway skeleton extraction, this paper introduces a new look-up-table (LUT) based thinning algorithm. This new approach consists of three major steps: the analysis and creation of the thinning model and the establishment of LUT based on above thinning model result. Thinning process by index-searching uses the LUT. Branch cutting based on the result of thinning obtains the final result. The usage of LUT index-searching during the thinning step transforms simple point judgments into LUT index search and has significantly improved the performance of the whole algorithm. Experimental results demonstrate that the new skeleton algorithm is 22.95 times faster than the existing thinning algorithm.

Abstract:To achieve the selective solid-phase extraction of Pb²⁺ and Hg²⁺ ions by microfluidic chip, the surface modification of nano-silica was carried out by using 3-chloropropyltrimethoxysilane and 5-methylbenzotriazole. And then, an integrated solid-phase extraction chip with replaceable adsorbent was designed and prepared based on the modified nano-silica. The results show that, the agglomeration of the adsorbent is improved significantly. When pH=5, the adsorption rates of Pb²⁺ and Hg²⁺ are 99.1% and 98.9% respectively, while the adsorption rates of Cr³⁺ and Mn²⁺ are only 20.4% and 13.2% respectively. In addition, the absorption rates of Pb²⁺ and Hg²⁺ are both more than 97% even when mixing with the interference ions (K⁺, Na⁺ or Mn²⁺). When the sample flow rate is no more than 1.5 mL/min, the microfluidic chip adsorption rate of Pb²⁺ or Hg²⁺ are both more than 98%; when using the hydrochloric acid (0.5 mol / L) and 2% thiourea [CS (NH₂)₂(W/W)] as eluent, the elution rate of Pb²⁺ or Hg²⁺ is both more than 92% (the flow rate is between 0.2~0.3 mL/min). The successful preparation of selective solid-phase extraction chips for Pb²⁺ and Hg²⁺ contributes to the application and popularization of microfluidic technology in heavy metal pollution monitoring.

Abstract:The strengthening mechanism during aging treatment after 84.18% cold rolling of MP35N alloy was performed in this study. Mechanical properties were tested on universal tensile testing machine and the microstructures were analyzed by OM, SEM, TEM and EDS. The results show that the maximum micro-hardness, 704.26 HV, was obtained when MP35N alloy was aged at 500 ℃ for 4 h, at which state the tensile strength was 2641.16 MPa. The two values increased by 30.44% and 37.41% over cold rolling state respectively. Tear holes which formed during cold forming healed after aging and the TEM result revealed that the thin "twin cluster" consisting of 3 to 4 fine twins which thickness about 3 nm appeared after aged at 400 ℃. When the temperature increased to 500 ℃, twin size became larger, staggered and then "twin cluster" disappeared. The EDS results shows there is no obvious concentration of Mo atom occurred in the twins. Nano flake twins formed during aging treatment play a major role in strengthening.

Abstract:In order to optimize stamping process, the effect of tensile deformation on recrystallization, precipitation behavior, bake hardenability and fracture mechanisms of a cold-rolled AA6016 sheet with T4P state were investigated. The alloy was solution heat treated in new heating treatment equipment, similar to air-cushion furnace production line, and then pre-aged immediately. After that the sheet was placed at room temperature in order to achieve T4P state. The local stamping process was simulated by uniaxial tensile. Recrystallization, fracture and dislocations were observed by optical microscopy, scanning electron microscopy and transmission electron microscopy respectively. Combined with differential scanning calorimetry (DSC) and tensile tests, precipitation behavior and mechanical property were characterized. The results indicated that local grains were elongated with the increasing of the deformation. GP zones were suppressed, and strengthening phase precipitation was promoted by deformation. Bake hardenability decreased with the increasing of the deformation. The fracture mechanisms were plastic fracture before and after bake hardening with small deformation. While the alloy tended to cleavage fracture before bake hardening, and the trend of cleavage fracture weakened after bake hardening with large deformation.

Abstract:convolutional neural network (CNN) has too many parameters to initialize, and the usual random initialization method is easy to disappear of modified gradient and the problem of premature. The unsupervised PCA learning method is used to obtain oriented initialization parameters. And the gradient descendent method with exponential flexible momentum for updating free parameters of the network is proposed on the basis of analyzing the error propagation of the network. Image detection experiments are respectively carried out on pedestrian detection, and the results show that, compared with other artificial feature detection algorithms, this method can effectively improve target detection accuracy and the detection speed of this method is 20% faster than that of classical CNN; compared with homologous updating mechanism of other momentum, our method has faster convergence and smaller oscillation, and can improve the detection accuracy by 1.6%, 1.8% and 6.19% respectively in different depth models.

Abstract:In order to solve the problems of brittleness and high curing temperature of polybenzoxazines, first, benzoxazine hydrochloride was synthesized with Bisphenol A-based Benzoxazine (BZ) monomer and hydrochloric acid. Second, Bz-MMT was prepared via ion-exchange reaction between Na-montmorillonite (Na-MMT) and benzoxazine hydrochloride, and then was characterized by FTIR, XRD and TGA. Thirdly, curing behavior of the mixture of BZ monomer and Na-MMT, or the mixture of BZ monomer and Bz-MMT, was followed by DSC. Fourthly, polybenzoxazine/montmorillonite nanocomposites PBZ/Na-MMT and PBZ/Bz-MMT were prepared by heating these mixtures of BZ monomer and MMT. Finally, TGA was used to test the thermal stability of PBZ and PBZ/Bz-MMT nanocomposites. The results show that for Bz-MMT, the basal spacing shows no obvious change, organic content increases and the onset decomposition temperture decreases as the amount of benzoxazine hydrochloride added increases. Compared with pure BZ monomer, the onset ring-opening polymerization temperature of the mixture of BZ monomer and Bz-MMT decreases obviously. Compared with PBZ, the char yeild, tensile strength and impact strength of PBZ/Bz-MMT nanocomposites all are increased.

Abstract:Aiming at the deformation controlling for compressor blades with volume damage, the birth and death finite element method was adopted to simulate the forming course of pulsed laser remanufacture. The dynamic deformation process and rules were got through the analysis. The pulsed laser forming process was optimized. The IPG optical fiber laser remanufacturing system was taken to experiment on the laser remanufacturing forming on impeller. The PowerScan Ⅱ blue light three dimensional reverse seeking measuring instrument was taken to measure the size of the remanufacturing forming deformation precisely. The conclusion of the finite element analysis was validated. The results show that, through the time increasing of the first and last two layers, the whole forming deformation is controlled within 1 mm; the deformation precision of heat-affected zone is controlled between 0.28~0.50 mm; the dimension precision after mechanical machining is within 0.02 mm; the angle precision is within 0.03°. The optimization of pulsed laser technology is verified. The process is taken reference for the remanufacturing forming of blade parts.

Abstract:To evaluate the effect of impact energy on plastic deformation of metal, repeated impact tests of YT01 were performed on the cam mechanical multi touch machine in the laboratory. The plastic deformation of YT01 was investigated by Coordinate Grid method, while the microstructure and phase were investigated by scanning electron microscope (SEM) and metalloscope in order to understand the different impact energy on the plastic deformation and microstructure. The results show that: the cumulative plastic deformation was greater with increasing impact energy and unchanged impact stress. The plastic deformation rate decreased with the increase of the impact number. The plastic deformation stopped at 6-9 mm from the top surface. After 256 000 repeated impacts, microstructure refinement and increased grain boundaries occurred. Meanwhile, transgranular cracks and holes were presented at 6-9 mm from the contact surface due to intense shear deformation in the sample. As a consequence, the plastic deformation of metallic material is not only related with impact stress but also with impact energy.

Abstract:In order to obtain the damage coefficient of Cyclic Void Growth Model (CVGM) and Degraded Significant Plastic Strain (DSPS) model for Steel Q235B widely used in China, taking four types of steel Q235B materials extracted from the hot-rolled seamless pipe and the matrix, heat affected zone as well as welded zone of cold-welding pipe respectively, twelve smooth specimens and eight notched specimens were machined. A series of low-frequency cyclic loading material tests were carried out to acquire the combined hardening parameters. The UVARM subroutines of CVGM model and DSPS model were developed in FORTRAN language and embedded in ABAQUS. The calibration of the damage degradation coefficients of CVGM model and DSPS model of four kinds of steel materials was performed. Based on the UVARM subroutine and identified damage coefficients, fracture initiation for the notched specimens can be predicted and simulation results match well with experimental results.