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The development of novel cermet composites based on porous ceramics with high porosity, interconnected pore structure and good mechanical property has attracted considerable attention in engineering application. In this work, water-based freeze casting process was employed to fabricate ZrB2-SiC porous ceramic with aligned lamellar-channels structure using PAA-NH4 as the dispersant. The results revealed that the well-dispersed suspension with best rheological behavior was obtained using 1.0 wt% PAA-NH4 at pH 9. The crack-free porous ceramic exhibited small volume shrinkage ranging from 2.59 % to 1.87 %. By varying the solid loading, the fabricated samples displayed a tailored porosity ranging from 76.12% to 59.37% and an excellent compressive strength of 7 MPa to 78 MPa. After oxidation, the samples displayed a decreased porosity and an increased compressive strength. The ZrB2­SiC porous ceramic fabricated in this work will be a promising candidate for the framework of cermet composite.

In this work, a ZrB2-SiC-Ta4HfC5/Ta4HfC5 oxidation-resistant dual-layer coating was fabricated to improve the oxidation resistance of carbon–carbon (C/C) composites. The coating was prepared by pack cementation combined with the slurry paste method. Spark plasma sintering was used in the procedure. The as-prepared dual-layer coating was approximately 110 μm, and no distinct interface was observed between the coating and the matrix. The isothermal oxidation test results showed that the dual coating effectively prevented C/C composites from oxidizing. The weight loss of the coated samples was only 3.3 and 9.5% after oxidation at 1773 K for 20 h and ten thermal shock cycles between 1773 K and room temperature in air, respectively. The pores and microcracks were the main reason for the failure of the coating.

To improve the thermal cycling resistance of ZrB 2 –SiC/SiC dual layer coating, MgO was added into the pack powders used to prepare ZrB 2 –SiC outer coating by pack cementation. The composition, microstructure and thermal cycling resistance of these coatings were studied. The results show that as-received coatings were mainly composed of SiC, ZrB 2 and Si. ZrB 2 –SiC outer coating contained 5 wt%, 7 wt%, 9 wt% MgO additive showed better thermal cycling resistance with 97.6%, 98.8% and 96.5% weight retention after 15 thermal shock cycles between 1500 °C and room temperature.

Acidic silica sol was used as precursor to prepare SiO2 aerogels using the atmospheric pressure drying technology. The influence of pH, water bath temperature and concentrations of silica sol on the structure parameters and morphology were systematically studied. SiO2 aerogel prepared with the sol concentration of 20% possessed uniform structure and the best structure parameters. Water bath temperature exhibited an obvious effect on morphology, specific surface area and porosity. Moreover, the optimal SiO2 aerogel showed a good heat resistance up to 700 °C. A lower thermal conductivity was 0.019 W/m · K at room temperature (25 °C) and 0.044 W/m · K at 600 °C.

ZrB2 grains were prepared on graphite by chemical vapor deposition using a gas mixture of ZrCl4, BCl3, H2 and Ar at 1150 °C. The microstructure and phase composition of the coating were investigated by SEM, XRD, XPS and TEM. The results indicated that ZrB2 grains were deposited and grown directly by a vapor–solid growth mechanism on graphite without intermediate phase. Granulated ZrB2 grains were composed by many sub–grains with different crystal orientation. The rod–like or pagoda–like ZrB2 grains with lamellar structures were grew on the granulated ZrB2 particles and composed of two parts: the internal part with axial stacking faults and annular part with radial stacking faults.

In order to further improve the oxidation protective ability of (ZrB 2 –SiC)/SiC coated graphite, ferrocene was introduced into the outer ZrB 2 –SiC coatings during pack cementation process. The ferrocene addition increased the porosity of the outer ZrB 2 –SiC coatings, which was favorable to thermal shock resistance of (ZrB 2 –SiC)/SiC coated specimens. The ZrB 2 –SiC coating with 3 wt% ferrocene (ZS50-3f) has optimum oxidation protective ability. Its weight retention after 15 thermal shock cycles between 1500 °C and room temperature was 96. 2%. The weight loss of ZS50-3f was only 0.2% after 19 h oxidation at 1500 °C.

The Domain Name System (DNS) is a critical Internet service, which translates easily memorized domain names to numerical IP addresses for locating computer resources and services. In this paper, we try to explore the behaviors of DNS lookup by mining DNS logs from three primary DNS servers in a large university campus network in China. Our dataset is made up of two parts, namely DNS query logs and messages received or send by DNS servers. Firstly, through analyzing these DNS query logs, we are able to understand the overall trend of users’ surfing. For dealing with huge DNS dataset, we introduce an algorithm we call DNSReduce , which can be used to dig out top 10 client IP addresses and top 10 destination domain names efficiently. Moreover, we make comparative analysis of lookup behavior between wired and wireless users. Secondly, with messages received or send by DNS servers we can find these DNS servers׳ behaviors, i.e., TTLs, equivalent answers and are able to accurately identify domain names with dynamic IP addresses. We provide different and specific visualization techniques for presenting these analysis results and show these techniques are very useful for understanding user behaviors, analyzing security events and characterizing overall tendency in campus network management.

The characterization of interfaces in woven ceramic matrix composites is one of the most challenging problems in composite application. In this investigation, a new model material consisting of the chemical vapor infiltration unidirectional C/SiC composites with PyC fiber coating were prepared and evaluated to predict the interfacial mechanic properties of woven composites. Single fiber push-out/push-back tests with the Berkovich indenter were conducted on the thin sliced specimens using nano-indentation technique. To give a detailed illustration of the interfacial crack propagation and failure mechanism, each sector during the push-out process was analyzed at length. The test results show that there is no detectable difference between testing a fiber in a direct vicinity to an already tested fiber and testing a fiber in vicinity to not-pushed fibers. Moreover, the interface debonding and fiber sliding mainly occur at the PyC coating, and both the fiber and surrounding matrix have no plastic deformation throughout the process. Obtained from the load-displacement curve, the interfacial debonding strength (IDS) and friction stress (IFS) amount to, respectively, 35 ± 5 MPa and 10 ± 1 MPa. Based on the findings, the interfacial properties with PyC fiber coating can be predicted. Furthermore, it is expected to provide a useful guideline for the design, evaluation and optimal application of CVI-C/SiC.

Inorganic coating was fabricated on the surface of the porous Si3N4 ceramic by polymer derived (PD) and spraying technology, via using vinyl-polysilazane (PSN-1) as a preceramic polymer and Si3N4 and lithium aluminosilicate (LAS) powders as fillers. The phase and microstructure of the coatings were analyzed by X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM), respectively. The effect of the coatings on mechanical property and humidity resistance of the porous Si3N4 ceramic was investigated. The experimental results showed that we successfully fabricated the uniform and dense coating which preferably combined with the substrate upon the addition of fillers. The bending strength of the porous Si3N4 ceramic sprayed the coating increased by more than 18%, and the surface hardness increased by 1.7 times. The apparent porosity of the materials reduced by an average of 97.7%, and water absorption was below 0.5%. Therefore, the prepared coating with preferable density had an obviously moisture-proof and enhanced effect on the porous Si3N4 ceramic.

Spherical array plays important role in 3D targets localization. In this paper, we develop a novel DOA estimation method for the spherical array with super resolution approach. The proposed method operates in spherical harmonic domain. Based on the atomic norm minimization, we develop a gridless L1-SVD algorithm in spherical harmonic domain and then we adopt the spherical ESPRIT method to two-dimensional DOA estimation. Compared to the previous work, the proposed method acquires better estimation performance. Numerical simulation results verify the performance of the proposed method.

A spinnable zirconium solution was obtained by heating the aqueous solution that contains ZrOCl2.8H2O, Y(NO3)3.6H2O, H2O2 and CH3COOH under a reduced pressure in a rotary evaporator. The preparation of the sol, possible structure of PZA, idealized formation process of PZA, firing schedule of the gel fiber, phase transformation of ZrO2 and characterization of the fibers were discussed in this article. The green fibers and those sintered at different temperatures were characterized by thermogravimetry-differential thermal analysis (TG-DTA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopic (SEM) techniques. After calcined at 1200oC, zirconia fibers with cubic phase were obtained by the addition of 6 mol% Y2O3. The diameters of the zirconium oxide fiber were 5-7 µm, and the grain size was about 20-30 nm. The activation energy for grain growth of zirconia fiber was estimated to be 24.18 kJ.mol–1.

Joint direction-of-arrive (DOA) and Doppler frequency estimation plays important role in radar and wireless communication. In this paper, we propose a continuous compressed sensing based joint DOA and Doppler frequency estimation method for incorporating coprime array and samplers. Atomic norm minimization is used to complete the sparse virtual aperture of the spatial-temporal co-array and recover the received signals. Then a search-free method based on unitary ESPRIT can be adopted to estimate parameters. Compared to the previous work, the proposed method does not need the discretization which may cause modeling error or increased computations due to dense grid and can fully recover and utilize the virtual aperture. Numerical simulations demonstrate superior performance of the proposed method to existing methods.

While email plays a growingly important role on the Internet, we are faced with more severe challenges brought by compromised email accounts, especially for the administrators of institutional email service providers. Inspired by the previous experience on spam filtering and compromised accounts detection, we propose several criteria, like Success Outdegree Proportion, Reverse Pagerank, Recipient Clustering Coefficient and Legitimate Recipient Proportion, for compromised email accounts detection from the perspective of graph topology in this paper. Specifically, several widely used social network analysis metrics are used and adapted according to the characteristics of mail log analysis. We evaluate our methods on a dataset constructed by mining the one month (30 days) mail log from an university with 118,617 local users and 11,460,399 mail log entries. The experimental results demonstrate that our methods achieve very positive performance, and we also prove that these methods can be efficiently applied on even larger datasets.

The functional acrylate monomer (FAM) containing an amino group was synthesized by using glycidyl methacrylate (GMA) and ammonia. FAM was then copolymerized with Vinyl acetate and other acrylate mo...

La 2 NiO 4 compounds were prepared by a modified sol–gel auto-combustion method, which is a low-temperature combustion synthesis procedure using microwave-assisted sol–gel as precursors. The high-temperature transport properties of the samples were investigated. The band structure, total density of states (DOS), and partial density of states (PDOS) of low-temperature orthorhombic (Bmab) phase and high-temperature tetragonal (I4 / mmm) phase for La 2 NiO 4 were calculated in order to study the transport properties of the as-obtained samples.

SrO(SrTiO 3 ) n ( n = 1, 2, …, ∞) powders were prepared by a modified sol–gel self-propagating combustion method and characterized by ultraviolet–visible (UV–vis) absorption spectroscopy and infrared spectra. UV–vis spectra indicate that the absorption edge of SrO(SrTiO 3 ) n ( n = 1, 2) shift to the violet with the decrease of n value, and the band gap values obtained from the UV–vis spectroscopy measurements are 3.41 and 3.26 eV, respectively. The infrared spectra show that the width of absorption band of TiO 6 octahedron stretching vibration decreases with the increasing of n value. The optical absorption of the compounds SrO(SrTiO 3 ) n ( n = 1, 2, …, ∞) were investigated by theoretical caculation using density functional theory (DFT). The interband transitions were assigned according to the partial density of states (PDOS). The calculated results are close to the experimental results.

In this paper we introduce an active-probing approach that measures the eDonkey (eDonkey 2000) network by us- ing an experimental client developed for this purpose. Our approach collects information from the eDonkey network by issuing queries for files. Based on this technique, we present our experiment and the results that evaluate the ca- pacity of the eDonkey network and characterize the distri- bution of servers, clients, and files, considering within the English/Chinese context when applicable.