压力容器环焊缝事故率高的剖析及对策

本文从压力容器设计、制造及标准三方面分析了压力容器环焊缝事故率高的原因,提出了相应的对策。希压力容器有关工程技术人员要充分重视压力容器环焊缝的质量问题,以确保压力容器的安全使用。     

Verifiable computation with access control in cloud computing

With the tremendous growth of cloud computing, verifiable computation has been firstly formalized by Gennaro et al. and then studied widely to provide integrity guarantees in the outsourced computation. However, existing verifiable computation protocols either work in the secret key setting or in the public key setting, namely, work either for single client or for all clients, which rules out some practical applications with access control policies. In this paper, we introduce and formalize the notion of verifiable computation with access control (AC-VC), in which only the computationally weak clients with necessary access control permissions can be allowed by a trusted source to apply the outsourced computation of a function to a server. We present a formal security definition and a proved secure black-box construction for AC-VC. This construction is built based on any verifiable computation in the secret key model and ciphertext-policy attribute-based encryption (CP-ABE). The access control policies that our AC-VC can realize depend on that realized in the based CP-ABE.     

Kinetics of thermal decomposition of unsaturated polyester resins with reduced flammability

In this article, the kinetics of thermal decomposition of unsaturated maleic–phthalic polyester resins, flame‐retarded with zinc hydroxystannate, was studied by thermogravimetric analysis at different heating rates. At the first stage, it was found, on the basis of isoconversional analysis by the methods of Friedman and of Ozawa–Flynn–Wall, that the value of the (apparent) activation energy (E) characteristically changes in three steps during the degradation. Further kinetic studies using nonlinear regression methods revealed the best fits for both pristine and stabilized resins. It was observed that the course of E versus the degree of conversion (α) during degradation of zinc hydroxystannate‐containing resins (α > 0.8) was characterized by higher values of E—this phenomenon can be explained in terms of the flame‐retardation action of zinc hydroxystannate, which is believed to operate primarily in the condensed phase. At the next stage, kinetic analysis by the nonregression method was performed to find the kinetic model [f(α) function] of the decomposition process; hence, for pristine resin, the best fit was found for the Avrami–Yerofeeyev model (nuclei growth), and for stabilized samples, the nth‐order function with catalysis proved to be the best approximation. The obtained kinetic parameters in the form of E, the preexponential factor A, and the model function f(α) allow a prediction of the polyester resin's thermal behavior in an extrapolated range of degree of conversion, time, and temperature. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2851–2857, 2003     

An efficient KPCA algorithm based on feature correlation evaluation

Classic kernel principal component analysis (KPCA) is less computationally efficient when extracting features from large data sets. In this paper, we propose an algorithm, that is, efficient KPCA (EKPCA), that enhances the computational efficiency of KPCA by using a linear combination of a small portion of training samples, referred to as basic patterns, to approximately express the KPCA feature extractor, that is, the eigenvector of the covariance matrix in the feature extraction. We show that the feature correlation (i.e., the correlation between different feature components) can be evaluated by the cosine distance between the kernel vectors, which are the column vectors in the kernel matrix. The proposed algorithm can be easily implemented. It first uses feature correlation evaluation to determine the basic patterns and then uses these to reconstruct the KPCA model, perform feature extraction, and classify the test samples. Since there are usually many fewer basic patterns than training samples, EKPCA feature extraction is much more computationally efficient than that of KPCA. Experimental results on several benchmark data sets show that EKPCA is much faster than KPCA while achieving similar classification performance.     

Mechanical properties and thermal stability of double‐shell thermal‐energy‐storage microcapsules

Double‐shell‐structured microcapsules encapsulating phase‐change materials (micro‐PCMs) with an average diameter of 5–10 μm were successfully fabricated with a melamine–formaldehyde resin as the coating material. The mechanical properties of the obtained piled micro‐PCMs, tested under compression, were evaluated with a pressure sensor. Typical stress–strain curves showed that both the single‐shell‐ and double‐shell‐structured microcapsules had yield points and maximum point pressures. The morphological changes in the shell surface confirmed the existence of yield points by scanning electron microscopy. When the pressure was beyond the yield point, the microcapsules showed conventional plastic behavior, and the double‐shell structure was more mechanically stable than the single‐shell one. Differential scanning calorimetry analysis results revealed that the properties of the phase‐change materials experienced no variation after coating with a single‐shell‐ or double‐shell‐structured polymer. Thermogravimetric analysis showed that the double‐shell‐structured micro‐PCMs experienced a weight loss of only about 5% from 86.3 to 232°C but did so more rapidly from 232 to 416°C. Thermoregulation was determined with periodical heating and cooling tests. The data showed that the micro‐PCMs changed temperature in a narrow range of 20–25°C with a time lag of 20 min to reach the maximum or minimum temperature in comparison with a reference temperature of 18–28°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1295–1302, 2007     

Effect of chromium aging on the structural and thermal properties of chromium polyacrylate

The effects of aging time of Cr(III) solutions on the structural, thermal, magnetic, and morphological properties of chromium polyacrylate complexes were studied. Chromium retention was found to increase with longer aging periods. IR spectra revealed the formation of polychelate structures with noticeable changes on aging. The interaction of multivalent, polynuclear Cr(III) species with the polymer backbone resulted in a decrease in thermal stability for the complexes prepared from olated chromium solutions. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 490–493, 2005     

Harnessing the Melting Peculiarities of Ultra‐High Molecular Weight Polyethylene Fibers for the Processing of Compacted Fiber Composites

Summary: Compacted fiber composites offer unique properties due to their lack of an extraneous matrix. The conditions of processing ultra‐high molecular weight polyethylene (UHMWPE) fibers were simulated in a heated pressure cell. In situ X‐ray diffraction measurements were used to follow the relevant transitions and the changes in the degree of crystallinity during melting and crystallization. The results strongly support the suggestion that the hexagonal crystal phase, in which the chain conformation is extremely mobile on the segmental level, constitutes the physical basis of compaction technologies for processing UHMWPE fibers into a single‐polymer composite. This report suggests that using a pseudo‐phase diagram outlining the occurrence of different phases during slow heating and the degree of crystallinity can provide valuable insight into the technological parameters relevant for optimal processing conditions.

Degree of crystallinity as a function of pressure and temperature in a region relevant to compaction processes.     

聚偏氟乙烯/聚丙烯酸酯复合乳液的合成与性能

在含氟表面活性剂存在下，将聚偏氟乙烯超声分散于甲基丙烯酸甲酯和丙烯酸丁酯的混合单体中进行乳液聚合，制备了聚偏氟乙烯／聚丙烯酸酯复合乳液。采用动态光散射DLS、透射电镜TEM和红外光谱FT—IR对乳液组成及乳胶粒子的形态进行了表征，并对聚合物胶膜的性能进行了测试分析。结果表明：聚偏氟乙烯的加入，使复合乳液膜的拉伸强度显著增大，吸水率减小。     

Vitamin A microencapsulation within poly(methyl methacrylate)‐g‐polyethylenimine microspheres: Localized proton buffering effect on vitamin A stability

To stabilize vitamin A in a cosmetic/dermatological formulation, we present here a new encapsulation method based on polymer microspheres having a localized “proton‐buffering” capacity. Poly(methyl methacrylate)‐g‐polyethylenimine (PMMA‐g‐PEI) was prepared by direct condensation grafting of PEI onto poly(methyl methacrylate‐co‐methyl acrylic acid). The reaction was confirmed by FT‐IR analysis showing the amide vibration at 1,550 cm^?1. Elemental analysis indicated that the weight content of the grafted PEI was 1.6% (w/w). Vitamin A was encapsulated into PMMA‐g‐PEI microspheres by using an oil‐in‐water (O/W) single emulsion method. The presence of PEI moiety dramatically improved the chemical stability of vitamin A in microspheres. Vitamin A encapsulated within PMMA‐g‐PEI microspheres maintained 91% of its initial activity after 30‐day incubation at 40°C, while only maintaining 60% within plain PMMA microspheres. This study demonstrates that proton‐buffering within hydrophobic polymer matrix is a useful strategy for stabilizing “acid‐labile” active ingredients. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 517–522, 2004     

一种多接口多信道VANET动态信道分配算法研究

为了合理地实现多接口多信道车载自组织网络（VANET）车辆节点间通信信道的动态分配,提出了一种基于通信双方车辆节点信道切换队列的动态信道分配算法。定义了车辆节点的射频接口状态,给出了信道的性能因子以及信道切换队列的生成方法,通过综合考虑通信双方车辆节点的射频接口状态和信道切换队列,快速自主地建立通信链路,从而解决了信道公平接入和分配不合理的问题。通过软件仿真比较可以看出,该算法实现了信道的动态分配,减小了平均端到端时延,增加了网络平均吞吐量,显著提高了多接口多信道VANET的网络性能。