Occurrence and Characteristics of Staphylococcus aureus Isolated from Dairy Products

Food, particularly milk and cheese, may be a reservoir of multi-drug resistant Staphylococcus aureus strains, which can be considered an important issue in terms of food safety. Furthermore, foods of animal origin can be a cause of staphylococcal food poisoning via the production of heat-stable enterotoxins (SE). For this reason, we investigated the prevalence of and characterized Staphylococcus aureus strains isolated from milk and fresh soft cheese obtained from farms located in Wielkopolskie and Zachodniopomorskie Provinces in Poland. Overall, 92% of S. aureus isolates were positive for at least one of the 18 enterotoxin genes identified, and 26% of the strains harbored 5 to 8 enterotoxin genes. Moreover, the S. aureus strains contained genes conferring resistance to antibiotics that are critically important in both human and veterinary medicine, i.e., β-lactams (mecA), aminoglycosides (aac(6′)/aph(2″), aph(3′)-IIIa, ant(4′)-Ia) and MLS_B (erm(A), msr(A), lun(A)). The antimicrobial susceptibility of S. aureus to 16 antibiotics representing 11 different categories showed that 74% of the strains were resistant to at least 1 antibiotic. Moreover, 28% of the strains showed multidrug resistance; in particular, two methicillin-resistant S. aureus strains (MRSA) exhibited significant antibiotic resistance. In summary, our results show that dairy products are contaminated by S. aureus strains carrying genes encoding a variety of enterotoxins as well genes conferring resistance to antibiotics. Both MRSA strains and MSSA isolates showing multidrug resistance were present in foods of animal origin.     

基于Web的图书馆管理系统访问控制策略

针对基于Web的图书馆管理系统资源访问控制的动态性问题，提出了一种基于角色的访问控制策略描述方案．通过对基于Web的图书馆管理系统访问控制管理影响因素和访问控制需求的分析，结合NIST基于角色的访问控制统一模型标准，构造了一种基于角色的访问控制元模型．并在这一元模型的基础上，提出了一种紧凑的基于角色的访问控制XML策略描述语言框架．结果表明该访问控制策略描述语言框架适合表述动态环境下对图书馆资源的访问策略，提高了基于Web的图书馆管理系统资源访问的安全性．     

Correlation between crystallinity and resistive switching behavior of sputtered WO3 thin films

The as-deposited WO₃ thin films were post-annealed at different temperatures (300 °C and 600 °C) in air to investigate a correlation between crystallinity and switching behavior of WO₃ thin films. Associating the results of XRD, FTIR, XPS and FESEM measurements, the annealing-caused crystallinity change contributes to the variation of the switching behaviors of the WO₃ thin films. The as-deposited WO₃ films with low crystalline structure are preferred for random Ag conducting path, resulting in large switching ratio but fluctuating I–V hysteresis, whereas the annealed WO₃ films with crystallized compact structure limits Ag conducting path, favoring the stable I–V hysteresis but small switching ratio. It is therefore concluded that electrochemical redox reaction-controlled resistance switching depends not only on electrode materials (inert and reactive electrodes) but also on crystallinity of host oxide.     

Molecularly Imprinted Polymers Combined with Electrochemical Sensors for Food Contaminants Analysis

Detection of relevant contaminants using screening approaches is a key issue to ensure food safety and respect for the regulatory limits established. Electrochemical sensors present several advantages such as rapidity; ease of use; possibility of on-site analysis and low cost. The lack of selectivity for electrochemical sensors working in complex samples as food may be overcome by coupling them with molecularly imprinted polymers (MIPs). MIPs are synthetic materials that mimic biological receptors and are produced by the polymerization of functional monomers in presence of a target analyte. This paper critically reviews and discusses the recent progress in MIP-based electrochemical sensors for food safety. A brief introduction on MIPs and electrochemical sensors is given; followed by a discussion of the recent achievements for various MIPs-based electrochemical sensors for food contaminants analysis. Both electropolymerization and chemical synthesis of MIP-based electrochemical sensing are discussed as well as the relevant applications of MIPs used in sample preparation and then coupled to electrochemical analysis. Future perspectives and challenges have been eventually given.     

氧分压对Ni/HfO_x/TiN阻变存储单元阻变特性的影响

采用射频磁控溅射的方法,基于不同氧分压制备的氧化铪构建了Ni/HfO_x/TiN结构阻变存储单元.研究发现,随着氧分压的增加,薄膜表面粗糙度略有降低;另一方面,阻变单元功耗降低,循环耐受性能可达10~3次,且转变电压分布的一致性得到改善.结合电流-电压曲线线性拟合结果及外加温度测试探究了器件的转变机理,得出在低阻态的传导机理为欧姆传导机理,在高阻态的传导机理为肖特基发射机理,并根据氧空位导电细丝理论,对高低阻态的阻变机理进行了详细的理论分析.     

表面增强拉曼光谱在食源性致病微生物检测中的应用研究

食源性致病微生物导致的食源性疾病已成为全球化的公共卫生问题。快速、有效地检测食源性致病微生物是实现食源性疾病预防与控制的关键环节，也是保障食品安全的技术关键。表面增强拉曼光谱(SERS)具有简单、快速、灵敏度高等优点，在食品安全、生物医学、环境监控等领域展现出良好的应用前景。介绍了近年来SERS在食源性致病微生物检测中的应用研究进展。对SERS技术概况、SERS增强理论及SERS增强基底进行了简要介绍，重点回顾了SERS在食源性致病微生物检测中的应用和发展现状。在食品安全分析方面，利用SERS与模式识别方法相结合对食品中常见食源性致病微生物能实现快速、有效鉴别，部分研究已应用于不同食品样品的分析，体现了SERS作为“指纹图谱”的分析优势；在医学诊断方面，SERS可对病理样品(如血液、尿液等)中食源性致病微生物进行快速检测，缩短了样本分析时间，使食源性疾病的快速诊断成为可能；随着微流控技术的发展，微流控平台结合SERS技术被称为“芯片实验室”应用于食源性致病微生物的检测，可提高分析的可控性，稳定性，特异性和灵敏度。通过对比分析，发现不同研究可采用不同分离方法、不同基底、不同目标捕获方式等实现了食源性致病微生物的检测，展示了不同方法间的差异性。已有研究表明了SERS在食源性致病微生物检测中应用可克服传统方法耗时等缺点，实现灵敏快速分析，为食品安全实时监控，食源性疾病即时诊断提供了有效的分析工具。同时，指出了SERS技术应用于食源性致病微生物分析依然面临很大挑战，(1)大多数研究并没有聚焦于实际样品，而标准培养液和实际样品的SERS检测存在较大差异，实际样品组分会对SERS响应产生干扰；(2)不同方法结果有较大差异，主要是由于纳米增强基底差异，吸附方式原理的差异，稳定性的差异等，因此需要更多深入研究进一步优化条件；(3)期望建立标准化的SERS方法替代传统技术，充分展示SERS作为新兴分析工具快速、灵敏、简捷的优势应用于食品安全，医学诊断等领域。将来，随着研究的深入及相关学科的发展，SERS作为极具潜力的快速分析工具，将在食品安全，生物医学等领域具有更广阔的应用前景。     

安全质量费用工期在网络计划中的系统优化研究

施工网络计划中安全、质量、费用、工期达到综合优化是工程管理决策追求的目标,在工程项目管理中对这4个指标进行全面系统分析,并且进行综合均衡优化,对于提高工程项目的综合效益至关重要.采取在网络计划所有可行的施工方案中寻求最优的方案组合,从而达到总目标的优化.并且通过一个实例来说明本方法的应用.     

基于Cu/SiO_x/Al结构的阻变存储器多值特性及机理的研究

采用氧化硅材料构建了Cu/SiOx/Al的三明治结构阻变存储器件.用半导体参数分析仪对其阻变特性进行测量,结果表明其具有明显的阻变特性,并且通过调节限制电流,得到了四个稳定的阻态,各相邻阻态的电阻比大于10,并且具有良好的数据保持能力.在不同温度条件下对各个阻态进行电学测试及拟合,明确了不同阻态的电子传输机理不尽相同:阻态1和阻态2为欧姆传导机制,阻态3为P-F(Pool-Frenkel)发射机制,阻态4为肖特基发射机制.根据电子传输机制,建立了铜细丝导电模型并对Cu/SiOx/Al阻变存储器件各个阻态的电致阻变机制进行解释.     

Multi-Class Cost-Constrained Random Coding for Correlated Sources over the Multiple-Access Channel

This paper studies a generalized version of multi-class cost-constrained random-coding ensemble with multiple auxiliary costs for the transmission of N correlated sources over an N-user multiple-access channel. For each user, the set of messages is partitioned into classes and codebooks are generated according to a distribution depending on the class index of the source message and under the constraint that the codewords satisfy a set of cost functions. Proper choices of the cost functions recover different coding schemes including message-dependent and message-independent versions of independent and identically distributed, independent conditionally distributed, constant-composition and conditional constant composition ensembles. The transmissibility region of the scheme is related to the Cover-El Gamal-Salehi region. A related family of correlated-source Gallager source exponent functions is also studied. The achievable exponents are compared for correlated and independent sources, both numerically and analytically.     

Spectrum Slicing for Multiple Access Channels with Heterogeneous Services

Wireless mobile networks from the fifth generation (5G) and beyond serve as platforms for flexible support of heterogeneous traffic types with diverse performance requirements. In particular, the broadband services aim for the traditional rate optimization, while the time-sensitive services aim for the optimization of latency and reliability, and some novel metrics such as Age of Information (AoI). In such settings, the key question is the one of spectrum slicing: how these services share the same chunk of available spectrum while meeting the heterogeneous requirements. In this work we investigated the two canonical frameworks for spectrum sharing, Orthogonal Multiple Access (OMA) and Non-Orthogonal Multiple Access (NOMA), in a simple, but insightful setup with a single time-slotted shared frequency channel, involving one broadband user, aiming to maximize throughput and using packet-level coding to protect its transmissions from noise and interference, and several intermittent users, aiming to either to improve their latency-reliability performance or to minimize their AoI. We analytically assessed the performances of Time Division Multiple Access (TDMA) and ALOHA-based schemes in both OMA and NOMA frameworks by deriving their Pareto regions and the corresponding optimal values of their parameters. Our results show that NOMA can outperform traditional OMA in latency-reliability oriented systems in most conditions, but OMA performs slightly better in age-oriented systems.