Validation of a stochastic modelling approach for Listeria monocytogenes growth in refrigerated foods

A stochastic modelling approach was developed to describe the distribution of Listeria monocytogenes contamination in foods throughout their shelf life. This model was designed to include the main sources of variability leading to a scattering of natural contaminations observed in food portions: the variability of the initial contamination, the variability of the biological parameters such as cardinal values and growth parameters, the variability of individual cell behaviours, the variability of pH and water activity of food as well as portion size, and the variability of storage temperatures. Simulated distributions of contamination were compared to observed distributions obtained on 5 day-old and 11 day-old cheese curd surfaces artificially contaminated with between 10 and 80 stressed cells and stored at 14 °C, to a distribution observed in cold smoked salmon artificially contaminated with approximately 13 stressed cells and stored at 8 °C, and to contaminations observed in naturally contaminated batches of smoked salmon processed by 10 manufacturers and stored for 10 days a 4 °C and then for 20 days at 8 °C. The variability of simulated contaminations was close to that observed for artificially and naturally contaminated foods leading to simulated statistical distributions properly describing the observed distributions. This model seems relevant to take into consideration the natural variability of processes governing the microbial behaviour in foods and is an effective approach to assess, for instance, the probability to exceed a critical threshold during the storage of foods like the limit of 100 CFU/g in the case of L. monocytogenes.     

Pressure-Thermal Kinetics of Furan Formation in Selected Fruit and Vegetable Juices

Furan, a potential carcinogenic compound, can be formed in array of processed foods. The objective of this study was to conduct kinetic studies in pineapple juice and assess the interactive effects of pressure (0.1 to 600 MPa) and temperature (30 to 120 °C) on furan formation. Additional experiments were carried out in tomato, watermelon, cantaloupe, kale, and carrot juice to understand the influence of matrix and juice pH. Furan was monitored in raw (control) and processed samples by automated headspace gas chromatography mass spectrometry, and quantified by calibration curve method with d₄-furan as internal standard. The data were modeled using zero-, first-, and second-order equations. The zero-order rate constants (k _T,P ), activation energy (E _a ), and Gibbs free energy of activation (ΔG ^?) of furan formation in thermally processed (TP; 90–120 °C) pineapple juice were found to be 0.036–0.55 μg/kg/min, 98–114 kJ/mol, and 173.9–180.5 kJ/mol, respectively. Furan concentration was negligible and close to the detection limit (0.37 μg/kg) after pressure treatment (600 MPa at 30 °C) of juice samples. For similar process temperatures, the rate constants of pressure-assisted thermally processed (PATP; 600 MPa at 105 °C) pineapple juice were lower than that of TP samples. Furan formation was influenced by juice matrix and pH. On the other hand, PATP markedly suppressed furan (0.7 to 1.6 μg/kg) in these selected juices. In conclusion, furan formation increased with process temperature and treatment time, while pressure treatment at ambient temperature did not promote its production. Furan formation in TP fruit juices was also influenced by juice matrix and pH, but these were not the significant factors for PATP-treated juices.     

NH3和N2混合等离子体预处理对锗MOS器件性能的影响

对锗衬底进行NH3和N2混合等离子体(V/(NH3)∶V/(N2)= 5∶1)原位预处理,其自然氧化层GeOx反应生成GeOyNz.XPS结果显示,随着预处理时间的延长,GeOyNz厚度稍有增加.结构为500 nm Al/20 nm Ti/10 nm HfO2/Ge的锗MOS电容样品,在1 V的偏压下,未经过原位等离子体预处理的样品的漏电流密度为10-4A/cm2量级,而120sNH3/N2混合等离子体预处理后的样品的漏电流密度减小到10-5A/cm2量级;所有等离子体预处理样品的C-V曲线不存在明显的翘曲变形,表明样品的界面陷阱电荷密度较低;通过C-V曲线计算可得,NH3/N2混合等离子体预处理60s后样品的等效电容约为17,小于理想HfO2的介电常数值,说明预处理条件下仍有不可忽略的层间电容.与其他预处理方法相比,NH3/N2混合等离子体原位预处理锗衬底可以更加有效地提高锗衬底上原子层沉积HfO2层间界面的质量,抑制Ge向HfO2的扩散,对界面的陷阱电荷有重要的限制作用.在提高锗MOS器件的性能方面,NH3和N2混合等离子体原位预处理的方法在工业生产中更具有潜在优势.     

Injectable nanocarriers for biodetoxification

Hospitals routinely treat patients suffering from overdoses of drugs or other toxic chemicals as a result of illicit drug consumption, suicide attempts or accidental exposures. However, for many life-threatening situations, specific antidotes are not available and treatment is largely based on emptying the stomach, administering activated charcoal or other general measures of intoxication support. A promising strategy for managing such overdoses is to inject nanocarriers that can extract toxic agents from intoxicated tissues. To be effective, the nanocarriers must remain in the blood long enough to sequester the toxic components and/or their metabolites, and the toxin bound complex must also remain stable until it is removed from the bloodstream. Here, we discuss the principles that govern the use of injectable nanocarriers in biodetoxification and review the pharmacological performance of a number of different approaches.     

Electrochemical fabrication of highly stable redox-active nanojunctions

Redox-gated molecular junctions were obtained starting with a relatively large gap between two electrodes, in the micrometer range, followed by electrochemical polymerization of aniline. Polyaniline (PANI) grows from the tip side until it bridges the two electrodes. The resulting junctions were characterized electrochemically by following the variation of the tip-substrate current as a function of the electrochemical gate potential for various bias voltages and by recording their I(V) characteristics. The two electrodes make contact through PANI wires, and microjunctions with conductances around 10(-3) S were obtained. On the basis of a similar setup, PANI nanojunctions with conductances between 10(-7) and 10(-8) S were made, where the current appears to be controlled by fewer than 10 oligoaniline strands. Despite the small number of strands connecting the two electrodes, the junctions are highly stable even when several successive potential sweeps are performed. Comparison of the conductance measured in the oxidized and reduced states leads to an on/off ratio of about 70-100, which is higher than that reported for a single aniline heptamer bridging two electrodes, highlighting the interest of connecting a few tens of molecules using the scanning electrochemical microscopy (SECM) configuration. In some cases, the switching of the PANI takes place in several individual conductance steps close to that obtained for a single oligoaniline. Finally, starting with a microjunction and mechanically withdrawing the tip shrinks it down to the nanometer scale and makes it possible to reach the regime where the conductance is controlled by a limited number of strands. This work presents an easy method for making redox-gated nanojunctions and for probing the conductance of a few oligoanilines despite an initially large tip-substrate gap.     

Thorium/uranium mixed oxide nanocrystals: Synthesis, structural characterization and magnetic properties

One of the primary aims of the actinide community within nanoscience is to develop a good understanding similar to what is currently the case for stable elements. As a consequence, efficient, reliable and versatile synthesis techniques dedicated to the formation of new actinide-based nano-objects （e.g., nanocrystals） are necessary. Hence, a ＂library＂ dedicated to the preparation of various actinidebased nanoscale building blocks is currently being developed. Nanoscale building blocks with tunable sizes, shapes and compositions are of prime importance. So far, the non-aqueous synthesis method in highly coordinating organic media is the only approach which has demonstrated the capability to provide size and shape control of actinide-based nanocrystals （both for thorium and uranium, and recently extended to neptunium and plutonium）. In this paper, we demonstrate that the non-aqueous approach is also well adapted to control the chemical composition of the nanocrystals obtained when mixing two different actinides. Indeed, the controlled hot co-injection of thorium acetylacetonate and uranyl acetate （together with additional capping agents） into benzyl ether can be used to synthesize thorium/uranium mixed oxide nanocrystals covering the full compositional spectrum. Additionally, we found that both size and shape are modified as a function of the thorium：uranium ratio. Finally, the magnetic properties of the different thorium/uranium mixed oxide nanocrystals were investigated. Contrary to several reports, we did not observe any ferromagnetic behavior. As a consequence, ferromagnetism cannot be described as a universal feature of nanocrystals of non-magnetic oxides as recently claimed in the literature.     

Microstructural influence on high temperature creep flow of Zr-1%NbO alloy in near-α, (α + β), and β temperature ranges in a high vacuum environment

Uniaxial tensile creep tests were carried out at 650-1100 °C in a high vacuum environment on Zr-1%NbO tubes with various microstructures. The effect of microstructure on creep flow in the (α + β) temperature range is significant (the creep rate being modified by up to three orders of magnitude) under stresses lower than 10 MPa, that is, for stress values of one order of magnitude lower than those characteristic of prototypical Loss-of-coolant-accident (LOCA) conditions. Under stresses higher than about 20 MPa, this effect is much smaller. No transformation-induced plasticity was detected from anisothermal creep tests, once the creep strain was thoroughly taken into account to process experimental strain vs. time data.     

等离子体增强原子层沉积制备压电AlN薄膜

采用等离子体增强原子层沉积(PEALD)技术在单晶硅衬底上成功制备了具有(002)晶面择优取向的氮化铝(AlN)晶态薄膜,为设计新型压电功能器件提供了思路.利用椭圆偏振光谱仪(SE)、原子力显微镜(AFM)、X射线衍射仪(XRD)、X射线光电子能谱仪(XPS)对.样品的生长速率、表面形貌、晶体结构、薄膜成分进行了表征和分析.结果 表明,在250℃沉积温度下,以N2H2和Ar的混合气体的等离子体作为共反应物,在相同工艺条件下仅增加前驱体三甲基铝(TMA)脉冲注入之后的氮气吹扫时间(tp1),制备的AlN薄膜的(002)晶面择优取向趋于显著,说明tp1的增加可以促进Al和N原子的有序排列,并促进(002)晶面择优取向形成.实验中,tp1为30 s且循环次数为1150时,PEALD制备的AlN薄膜表面平整光滑,均方根表面粗糙度为0.885 nm,(002)晶面衍射峰最明显,薄膜中氧原子数分数为11.04％,氧原子在AlN薄膜中形成氧缺陷并形成一种稳定的基于八面体配位铝的新型氧缺陷相,XPS结果证明了N-O-Al键的形成.     

SU-8光刻胶去胶工艺研究

SU-8光刻胶因具有良好的机械耐久性、聚合物水密性、介电性能、生物兼容性和抗化学腐蚀性而被广泛用于MEMS器件、生物医学和芯片封装等领域。现有制作工艺中,在不损伤器件的同时完全去除和剥离SU-8光刻胶仍是一个难题。文章研究了一种基于O₂/CF₄等离子刻蚀配合湿法刻蚀的去除方法,实现了SU-8光刻胶在硅基底、非晶无机非金属材料、电镀金属等材料上的有效去除。