Transesterification of canola oil as biodiesel over Na/Zr-SBA-15 catalysts: Effect of zirconium content

A series of mesoporous Zr-SBA-15-supported Na catalysts was prepared and applied to the heterogeneous catalysis of canola oil transesterification. The effects of Si/Zr ratio, reaction time, and percentage of Na loading on the conversion to fatty acid methyl esters (FAME) were studied. The dependence of the textural structure and chemical properties of Zr-SBA-15 supports on Zr content was investigated using small-angle X-ray diffraction, Brunauer–Emmett–Teller analysis, transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) spectroscopy. The results obtained from FTIR and TEM indicate that the incorporation of Zr atoms into the SBA-15 structure facilitated the formation of Brönsted acid sites and decreased the particle size of Na species. Catalysts with a higher Zr content enhanced the FAME yield. The optimum conditions determined were as follows: reaction temperature of 70 °C, 15 wt.% Na, reaction time of 6 h, and 12% catalyst content (wt.% oil) with a methanol/oil molar ratio of 6:1. The optimum conditions resulted in a FAME yield of up to 99%.     

A conflict-insensitive NATed roaming framework using NAToD for proxy mobile IPv4 in WLANs

Providing efficient mobility management in the current Internet is increasingly important due to the quick growth of wireless mobile users. The emerging Proxy Mobile IPv4 (PMIPv4) technique brings a possible solution for that purpose. Since NAT function is widely adopted in IPv4 environment nowadays because of lacking IPv4 addresses, the PMIPv4 interoperating with NAT must be considered. Unfortunately, owing to the possible conflict of private IP address, we encounter a problem in broadcasted point-to-multipoint wireless networks such as IEEE 802.11 networks. To address this issue, we proposed a novel Network Address Translation on Demand (NAToD) scheme, which can well interoperate with the PMIPv4 solution. With our scheme, single public IPv4 addresses can be shared by multiple mobile nodes in both home and foreign networks, low-latency handoff can be achieved, deployment cost can be reduced, and software upgrade can be avoided for mobile nodes in wireless LANs. Our work allows mobile users in WLAN to access Internet based on the advantages of both PMIPv4 and NAT.     

新型压电晶体锗酸镓锶与硅酸镓镧声表面波传播特性的研究

新型压电晶体Sr₃Ga₂Ge₄O₁₄(SGG)在声表面波传感器方面有潜在的应用前景. 根据最新的关于锗酸镓锶的特性报道, 理论计算了SGG在X切、Y切和Z切上的声表面波(SAW)传播特性(相速度、机电耦合系数、能流角). 与类质同构体LGS相比较, SGG晶体表现出了更优异的机电特性.     

一种有效处理冲突证据的组合方法

为了有效融合高度冲突的证据,提出一种新的基于证据距离的组合方法,首先引入了一个证据体距离函数,之后求出系统中各证据被其它证据所支持的程度,对支持度归一化后获得各个证据的可信度,并将可信度作为证据的权重,对系统中的证据加权平均后再利用Dempster组合规则实现信息融合,与其它方法比较,该方法在系统存在伪证据(干扰)时仍然能够有效快速地识别出目标。     

Challenge and solutions of NAT traversal for ubiquitous and pervasive applications on the Internet

Network Address Translator (NAT) has brought up many changes and opportunities to the Internet. How do the ubiquitous and pervasive applications coexist with NAT and interoperate with each other? In this article, we discuss the essence of NAT sensitive applications as well as the challenge and response for various NAT traversal solutions. All questions pointed to redesign a new NAT framework with a major change to accommodate NAT problems all at once. We introduce a novel next generation NAT (NATng) framework, which consists of a Bi-directional NAT (BNAT) and a Domain Name System Application Level Gateway (DNS_ALG) with a Border Network Address Translator Control Protocol (BNATCP) function to control all BNATs. The above components coordinate and provide bidirectional access capability between intranet and Internet, so all private hosts can be addressed via Fully Qualified Domain Name (FQDN). Logistically, NATng extends the IPv4 address space from or even more. It features high potential to solve the problems for ubiquitous and pervasive applications which may encounter IPv4 address exhaustion on the current Internet.     

神经程序修复领域数据泄露问题的实证研究

修复软件缺陷是软件工程领域一个无法回避的重要问题,而程序自动修复技术则旨在自动、准确且高效地修复存在缺陷的程序,以缓解软件缺陷所带来的问题.近年来,随着深度学习的快速发展,程序自动修复领域兴起了一种使用深度神经网络去自动捕捉缺陷程序和其补丁之间关系的方法,被称为神经程序修复.从在基准测试上被正确修复的缺陷的数量上看,神经程序修复工具的修复性能已经显著超过了非学习的程序自动修复工具.然而,近期有研究发现神经程序修复系统性能的提升可能得益于测试数据在训练数据中存在,即数据泄露.受此启发,为进一步探究神经程序修复系统数据泄露的原因及影响,更公平地评估现有的系统,本文(1)对现有神经程序修复系统进行了系统的分类和总结,根据分类结果定义了神经程序修复系统的数据泄露,并为每个类别的系统设计了数据泄露的检测方法;(2)依照上一步骤中的数据泄露检测方法对现有模型展开了大规模检测,并探究了数据泄露对模型真实性能与评估性能间差异的影响以及对模型本身的影响;(3)分析现有神经程序修复系统数据集的收集和过滤策略,加以改进和补充,在现有流行的数据集上基于改进后的策略构建了一个纯净的大规模程序修复训练数据集,并验证了该数据集避免数据泄露的有效性.实验结果发现:本次调研的10个神经程序修复系统在基准测试集上均出现了数据泄露,其中神经程序修复系统RewardRepair的数据泄露问题较为严重,在基准测试集Defects4J(v1.2.0)上的数据泄露达24处,泄露比例高达53.33%.此外,数据泄露对神经程序修复系统的鲁棒性也造成了影响,调研的5个神经程序修复系统均因数据泄露产生了鲁棒性降低的问题.由此可见,数据泄露是一个十分常见的问题,且会使神经程序修复系统得到不公平的性能评估结果,以及影响系统本身的性质.研究人员在训练神经程序修复模型时,应尽可能避免出现数据泄露,且要考虑数据泄露问题对神经程序修复系统性能评估产生的影响,尽可能更公平地评估系统.     

条件事件代数研究综述

综述了条件事件代数理论的原理、主要性质和应用．条件事件代数是一门新兴的解决不确定性、概率性和模糊性推理问题的学科,是在确保规则概率与条件概率相容的前提下,把布尔代数上的逻辑运算推广到条件事件(规则)集合中得到的代数系统,目的是为智能系统中的条件推理建立一个数学基础．该文也对比条件事件代数更一般的逻辑系统——关联事件代数理论进行了介绍．     

A fuzzy-Bayesian approach to target recognition based on multisensor fusion

The Bayesian approach is widely used in automatic target recognition (ATR) systems based on multisensor fusion technology. Problems in data fusion systems are complex by nature and can often be characterized by not only randomness but also fuzziness. However, in general, current Bayesian methods can only account for randomness. To accommodate complex natural problems with both types of uncertainties, it is profitable to improve the existing approach by incorporating fuzzy theory into classical techniques. In this paper, after representing both the individual attribute of the target in the model database and the sensor observation or report as the fuzzy membership function, a likelihood function is constructed to deal with fuzzy data collected by each sensor. A similarity measure is introduced to determine the agreement degree of each sensor. Based on the similarity measure, a consensus fusion approach (CFA) is developed to generate a global likelihood from the individual attribute likelihood for the whole sensor reports. A numerical example is illustrated to show the target recognition application of the fuzzy-Bayesian approach. The text was submitted by the authors in English.     

A cross-layer error correction scheme based on multiple-CRC in OFDM/OFDMA wireless networks

The orthogonal frequency division multiplexing access (OFDM/OFDMA) based wireless transmission technology has been widely deployed in recent years. The frame check sequence (FCS) scheme is employed to enhance the reliability of OFDM/OFDMA systems. Since the padding overhead cannot be effectively avoided in OFDM/OFDMA when medium access control frames are encapsulated, we propose a novel cyclic redundancy check based error correction scheme by utilizing the padding space to carry extra segmented FCS information as much as possible; compared with the legacy FCS scheme, our approach greatly enhance the error detection and correction upon the first retransmission (second transmission). A significant performance improvement based on the simulation results is also demonstrated.     

Determination of lutein and zeaxanthin and antioxidant capacity of supercritical carbon dioxide extract from daylily (Hemerocallis disticha)

Lutein and zeaxanthin were extracted from daylily (Hemerocallis disticha) flowers using supercritical fluid extraction-carbon dioxide (SFE-CO₂) at a temperature range of 50–95 °C and pressure range of 300–600 bar. The extracts were analysed by HPLC with a C30 column and an isocratic solvent system: methanol/methyl-tert-butyl ether = 86/14 (v/v). Moreover, the antioxidant capacities of the extracts were evaluated by a 2,2-diphenyl-2-picrylhydrazyl radical scavenging assay and a chemiluminescence assay to measure the scavenging activity of hydrogen peroxide, superoxide anion and hydroxyl radical. The optimal lutein and zeaxanthin extraction could be achieved at 80 °C and 600 bar, and the extraction pressure was the most important parameter for SFE-CO₂. In addition, the extracts had significantly higher antioxidant activities in all antioxidant assays.