熔体过热处理对Mg-5Si合金组织与性能的影响

采用质量分数为99.9％的纯镁锭和99.9％的粒度为45μm的硅粉,制备了质量分数为5%的Mg-5Si合金,研究了熔体过热温度和保温时间对Mg-5Si合金铸态组织和力学性能的影响。研究实现了Mg2Si相尺寸由处理前的27μm减小到20μm,此时初生Mg2Si相的平均尺寸最小,分布趋于均匀,形貌逐渐向树枝状转变,甚至溶解为较为圆整的颗粒,且共晶Mg2Si相层片间距较小,并采用抗拉强度、屈服强度和伸长率表征其力学性能。研究结果表明：熔体过热温度为770℃、保温时间为30min时,合金的抗拉强度、屈服强度和伸长率分别为152MPa、84 MPa和6.5%,合金的力学性能得到明显改善。     

低场MRI原位研究离子液体合成及相态变化

离子液体作为一个平台化合物已经在诸多领域得到广泛应用,但离子液体的生产成本仍然是限制其进一步工业化推广的瓶颈之一。深入研究反应动力学、反应传递耦合规律对优化离子液体合成工艺/关键设备,降低大规模离子液体制备成本至关重要。本研究用一个原位低场磁共振成像(MRI)设备实时监测ILs合成过程中的反应动力学和相态变化。通过建立双组分分析模型,即1H低场核磁共振(LF-NMR)弛豫法对反应体系中的各个组分进行定量分析,并采集MRI图像记录相位分离和倒置过程,系统考察了卤代烷烃的链长、卤素种类、搅拌速度、反应温度等对咪唑类离子液体反应动力学的影响规律。对溴丁烷、甲基咪唑合成溴代1-丁基-3-甲基咪唑类离子液体合成过程中相态变化进行了实时动态观测。本研究为检测离子液体反应过程及有机溶剂中离子液体的残余量提供一种快速、便利、无损的检测方法,有望利用低场MRI对离子液体系统中传质和反应动力学的结合研究做进一步探索。     

双束(H~+/e~-)同时辐照对12Cr-ODS钢氧化物稳定性影响

利用氢离子和电子双束(H~+/e~-)对用化学浸润法制备的新型12cr-ODS铁素体钢进行辐照,研究了辐照对12Cr-ODS钢氧化物稳定性的影响.对不同辐照剂量下原位观察辐照区内氧化物形貌的变化过程发现:辐照前和15 dpa辐照后,约10～20nm氧化物的尺寸并没有明显变化,而氧化物周围出现微小高密度空洞并没有影响氧化物的稳定性;当辐照温度升高至823 K时,大尺寸的氧化物Y_2O_3与基体的相界面变得不规则,但氧化物颗粒尺寸并不发生明显变化.实验结果表明:弥散强化相Y_2O_3尺寸稳定,无明显溶解现象.     

Occurrence and relationship of organophosphorus insecticides and their degradation products in the atmosphere in Western Canada agricultural regions

This paper presents the atmospheric occurrence and seasonal variations of the most frequently detected organophosphorus insecticides (OPs) and their OP oxon degradation products at Bratt's Lake, Saskatchewan in the Canadian Prairies (April 2003 to March 2004, January-December, 2005) and at Abbotsford in the Lower Frazer Valley (LFV) of British Columbia from May 2004 to December, 2005. During 2005 there were 10 OPs, 8 OP oxons, and 6 other OP degradation products measured. The most frequently detected OPs were chlorpyrifos, malathion, and diazinon. At Bratt's Lake the highest atmospheric concentrations were observed for chlorpyrifos, with maximum concentrations observed during July and August in 2003 showing much higher concentrations than those from 2005. This was related to its usage for grasshopper control in the province. At Abbotsford, diazinon and malathion were observed in much higher atmospheric concentrations than chlorpyrifos. Concentrations reached maximum in spring for diazinon and summer for malathion. This study is the first reported study of seasonal variations of OP oxons with their parent OP. Chlorpyrifos oxon concentrations during July were generally low, indicating strong local source contributions. The chlorpyrifos oxon/chlorpyrifos ratio and diazinon oxon/diazinon ratio showed a strong seasonal variation with increasing ratio from spring to summer which was attributed to increasing sunlight hours. Malathion oxon/mathion at both sites was similar and relatively constant throughout the year. The oxon/thion ratio represents a good indicator of age of source or contributions from local versus regional atmospheric sources.     

代谢工程在酿酒酵母茵育种中的应用研究进展

酿酒酵母(Saccharomyces cerevisiae)是传统的乙醇生产重要菌株,也是第1个完成基因组测序的真核生物。随着世界能源储备的日益枯竭,燃料乙醇作为液体可再生能源的广泛应用,利用生物技术对酿酒酵母进行遗传修饰,改变其代谢网络,构建高产乙醇的转基因酿酒酵母已成为当今酿酒酵母分子育种的热点。针对近年来利用代谢工程拓展酿酒酵母底物利用范围、降低副产物生成率、提高乙醇产量、改良细胞特性以及缩短发酵周期等方面的研究进展予以综述。     

Polydimethylsiloxane/postmodified MIL‐53 composite layer coated on asymmetric hollow fiber membrane for improving gas separation performance

Composite layer containing postmodified MIL‐53 (P‐MIL‐53) was exploited to be coated on as‐fabricated asymmetric hollow fiber membrane for improving gas separation performance. The morphology and pore size distribution of P‐MIL‐53 particles were characterized by SEM and N₂ adsorption isotherm. The EDX mapping and FTIR spectra were performed to confirm the presence of P‐MIL‐53 deposited on the outer surface of hollow fiber membranes. The results of pure gas permeation measurement indicated that incorporation of P‐MIL‐53 particles in coating layer could improve permeation properties of hollow fiber membranes. By varying coating times and P‐MIL‐53 content, the membrane coated with PDMS/15%P‐MIL‐53 composite by three times achieved best performance. Compared to pure PDMS coated membrane, CO₂ permeance was enhanced from 29.96 GPU to 40.24 GPU and ideal selectivity of CO₂/N₂ and CO₂/CH₄ also increased from 23.28 and 26.95 to 28.08 and 32.03, respectively. The gas transport through composite membrane was governed by solution‐diffusion mechanism and CO₂ preferential adsorption of P‐MIL‐53 contributed to considerable increase of CO₂ solubility resulting in accelerated permeation rate. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44999.     

Fabrication and characteristics of graphene oxide/nanocellulose fiber/poly(vinyl alcohol) film

Poly(vinyl alcohol) (PVA), PVA/nanocellulose fiber (CNF), and PVA/CNF/graphene oxide (GO) films were prepared simply by casting stable aqueous mixed solutions. FTIR investigation indicated that hydrogen bonding existed between the interface of GO and PVA‐CNF. Scanning electron microscopy and X‐ray diffraction analysis showed that GO was uniformly dispersed in PVA‐CNF matrix. Introducing CNF into PVA caused a significant improvement in tensile strength, and further incorporating GO into PVA/CNF matrix led to a further increase. The tensile strength of the neat PVA film, PVA/CNF composite, and PVA/CNF/GO film (0.6 wt % GO) was 43, 69, and 80 MPa, respectively. Moreover, when incorporating 8 wt % CNF into PVA matrix, O₂ permeability and water absorption decreased from 13.36 to 11.66 cm³/m²/day and from 164.2% to 98.8%, respectively. Further adding 0.6 wt % GO into PVA/CNF matrix resulted in a further decrease of permeability and water absorption to 3.19 cm³/m²/day and 91.2%, respectively. Furthermore, for all composite samples, the transmittance of visible light was higher than 67% at 800 nm. CNF and GO‐reinforced PVA with high mechanical and barrier properties are potential candidates for packaging industry. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45345.     

一株产抑菌物质的蜡样芽胞杆菌的鉴定及其抑菌物质性质

从酱渣中分离到一株产抑菌物质的新菌株,暂命名为菌株B。研究表明,该菌株经碱中和后的无细胞发酵液对革兰氏阳性菌、革兰氏阴性菌和真菌均有抑制作用;其发酵上清液经硫酸铵盐析和透析后,仍然有抑菌活性;双缩脲和茚三酮实验表明,抗菌活性物质为肽类物质。生理生化实验、16S rDNA序列比对及系统发育分析表明,菌株B为蜡样芽胞杆菌,其生长和抑菌最适培养基为NB培养基,在pH 7.0的NB培养液中培养40h其抑菌活性达到最大。     

芦笋老茎中芦丁的提取工艺

采用正交试验方法,对芦笋老茎中芦丁的最佳提取工艺进行了研究。结果表明:热水提取芦丁的最佳工艺条件为,加水量为原料质量的10倍,提取温度为70℃,时间2.5 h;用乙醇水溶液提取芦丁,体积分数为70%的乙醇溶液用量为原料质量的25倍,提取温度70℃,时间3 h。     

稻谷整精米率标准样品研制

参照GB/T 15000.1-15000.9<标准样品工作导则>的要求进行了稻谷整精米率标准样品的研制.研究了颗粒类物质稻谷特定参数整精米率标准样品制备的原料选择、匀质(混匀)、均匀性试验、定值试验的过程.在本试验条件下,用人工和多级分样器混匀样品,可以得到均匀度合格的样本,经由多个实验室定值,分别得到籼稻整精米率标准样品理论真值为(45.8±1.4)%,粳稻理论真值为(74.6±1.2)%的结果.标准样品的制备为实验砻谷机、实验碾米机的校验和考核以及整精米率检验的质量控制提供了参照物.