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881.
882.
883.
RSA型加密系统(RSA加密系统及其改进系统的统称)至今仍然被广泛应用于许多注重电子数据安全的电子商务系统中.然而对现有的RSA型加密方案分析发现:(1)只有在随机谕言机模型下抗CCA2攻击的RSA型加密方案,还没有在标准模型下实现IND-CCA2安全的RSA型概率加密方案;(2)没有在标准模型下实现抗CPA且保持乘法同态性的RSA型同态加密方案,而同态性是实现安全多方计算和云计算安全服务的重要性质之一;(3)在实现密文不可区分方面,这些方案除HD-RSA外都是通过一个带hash的Feistel网络引入随机因子的,从而导致这些方案只能在随机谕言机模型下实现IND-CCA2安全.针对以上问题,本文在RSA加密系统的基础上,通过增加少量的有限域上的模指数运算,设计了一个标准模型下具有IND-CPA安全的RSA型概率同态加密方案和一个具有IND-CCA2安全的RSA型概率加密方案.这两个方案在实现密文不可区分时,都不再通过明文填充引入随机因子.此外,本文还提出一个RSA问题的变形问题(称作RSA判定性问题). 相似文献
884.
在无线光正交频分复用(FSO-OFDM)系统中,因需要加入循环前缀而消耗近20%的带宽,降低了数据传输效率。为了进一步减少带宽损耗,改善系统性能,采用小波包变换代替FSO-OFDM中的傅里叶变换,设计了一种基于小波变换的无线光正交频分复用(FSO-WOFDM)系统。该系统无需加入循环前缀,利用小波基函数的正交性来抑制子载波间的干扰。根据FSO-WOFDM系统原理,研究了信道估计方法、湍流强度、小波基对FSO-WOFDM系统误码率的影响,对比分析了FSO-WOFDM与FSO-OFDM的系统性能,并通过实验验证了FSO-WOFDM系统的可行性及其优良的抗混合噪声干扰能力。 相似文献
885.
《Ceramics International》2017,43(15):11807-11814
Since hydroxyapatite crystals are characteristically c-axis orientation on the surface of vertebrate long bone, c-axis orientation HAP biomimetic synthesized will find extensive applications in long bone growth, remodeling and fracture healing. In this paper, plate-like single-crystal HAP rods with c-axis orientation was successfully synthesized at bone mineralization conditions in vivo, with small intestinal submucosa membrane as biomineralization template. The samples were characterized by XRD, FIIR, SEM, TEM and EDS to unveil the phase structure, composition, morphology, and a plausible growth mechanism was proposed. The results showed that morphology of samples changed from flower-like to plate-like with extension reaction time from 1 day to 10 days. The plate-like HAp rods were single-crystal with c-axis orientation. A unit of plate-like HAP rods is about 70 µm and the width is 4 µm. Phase composition transformed from octocalcium phosphate and HAp biphase to HAp phase with very little octocalcium phosphate phase. Finally, biocompatibility of the samples was evaluated by CCK8. The samples without significant cytotoxicity conformed to the need for substitute materials of bone regeneration. 相似文献
886.
《Ceramics International》2017,43(17):14593-14598
During freeze casting of TiO2 porous ceramics, the porous architecture is strongly influenced by TiO2 particle size, solids loading, and cooling temperature. This work investigates the influences of particle size, freezing substrate, and cooling temperature on the TiO2 green bodies prepared by freeze casting. The results show that the lamellar channel width with 100 nm particles is larger than that of 25 nm particles, yet the ceramic wall thickness is noticeably decreased. The lamellar structure is more ordered when using a copper sheet than glass as its freezing substrate. A finer microstructure results when frozen at − 50 ℃ than − 30 ℃. Such porous materials have application potentials in a wide range of areas such as photocatalysis, solar cells, and pollutant removal and should be further studied. 相似文献
887.
《Ceramics International》2017,43(16):13541-13546
Energy storage properties of {Bi0.5[(Na0.8K0.2)1-zLiz]0.5}0.96Sr0.04(Ti1-x-yTaxNby)O3 (BNKLSTTN-x/y/z) lead-free ceramics are investigated. It is found that Ta performs better than Nb in the case of their energy storage density values, and the addition of optimum Li contents can enhance the energy storage properties by enhancing the dielectric breakdown strength (DBS). Enhanced energy storage density of 1.60 J/cm3 under a low electric field of 90 kV/cm is achieved in BNKLSTTN-0.025/0/0.10 samples, and the fatigue-free properties are also observed. In addition, the BNKLSTTN-0.025/0/0.10 samples show the enhanced temperature dependence of energy storage density. These results indicate that the BNKLSTTN-x/y/z ceramics are one of the most promising lead-free materials for energy storage applications. 相似文献
888.
《Ceramics International》2017,43(8):5881-5886
The TiO2/SiO2 monoliths with macro- and mesopore structure have been synthsized by sol-gel method. The double pore structure was developed by adding polyethylene glycol and urea in the precurser solution. The morphology, crystallinity, surface area and porosity of the TiO2/SiO2 monoliths were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), N2 adsorption/desorption and mercury intrusion techniques. The photocatalytic activity and applicablity of the monoliths were investigated by degradation of methylene blue and purificaiton of actual dyeing and finishing wastewater. The result showed the prepared TiO2/SiO2 monolith to have enhanced photocatalytic activity, reusability and easy recovery, so it may be considered a promising material for practical application in wastewater treatment. 相似文献
889.
《Ceramics International》2017,43(13):10277-10287
This work aims at obtaining aluminum titanate-based ceramics (Al2TiO5: AT) composites from industrial wastes. Al-sludge waste and rutile ore were used as rich sources of alumina and titania instead of pure materials. Sludge-(0–40 wt%) rutile mixtures were mixed, formed and fired at 1350 °C for various times. Phase composition, microstructure, densification, mechanical and thermal behaviors of the obtained AT composites have been investigated. Complete conversion of the starting materials to AT with bulk density of 3.199 g/cm3, compressive strength and modulus of rupture of 326.425 MPa and 30.84 MPa, respectively and very low CTE (−0.927*10−6 K−1) were achieved by firing the sludge-(30 wt%) rutile at 1350 °C for 4 h. These results suggest that the obtained AT-ceramics from Al-sludge waste-rutile ore are a promising and an ecofriendly route. 相似文献
890.
《Ceramics International》2017,43(9):6925-6931
TiO2 has been widely used in the fields of environmental protection, energy conversion, plastics, coatings, cosmetics, and more. However, it has a wide band gap (3.2 eV) and the easy agglomeration of TiO2 nanoparticles hinders its application. This study adopts a one-step hydrothermal method to prepare urchin-like TiO2 photocatalyst and studies the morphology of TiO2 in relation to hydrothermal time, hydrothermal temperature and hydrogen peroxide (H2O2) amount. In addition, the urchin-like TiO2 is annealed in hydrogen atmosphere to discuss the influence of oxygen vacancies on the band gap and photocatalytic performance improvement. 相似文献