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关键词： controlled polymerization   density functional theory   diimine   nickel catalysis   poly(thiophene)  

摘要： Kumada catalyst transfer polymerization (KCTP) is currently an unparalleled catalytic method for preparing pi-conjugated materials with well-defined end-groups, targeted molecular weights, and narrow dispersity. Polymerization control is both catalyst and monomer dependent. Polymerizations using bidentate Ni(phosphine) catalysts and 3-alkylthiophene (or related) monomers lead to the highest degrees of polymerization control;however the scope of monomers that Ni(phosphines) can polymerize is quite limited. Here, two possible mechanistic limitations of Ni(diimine) catalysts are evaluated: 1) the role of spin states, and 2) the redox non-innocence of diimine ligands. Density functional theory (DFT) calculations are utilized to evaluate singlet and triplet spin states of Ni(diimine) species throughout the KCTP catalytic cycle. It is found that in the energetically favored triplet state, Ni(diimine) catalyst dissociation from polymer chains is competitive with intramolecular oxidative addition, which reduces polymerization control. The redox activity of Ni(diimine) catalysts during polymerization is investigated and it is determined that a Ni(diimine)X-2 precatalyst is converted into Ni(diimine)(2) under reductive conditions analogous to KCTP, but surprisingly this species is also active during polymerization which leads to an interesting off-cycle pathway that has not been previously considered. These insights differentiate the mechanisms of Ni(diimine) and Ni(phosphine) polymerizations, highlighting catalyst spin and redox activity as additional factors in KCTP.

关键词： Microfibers   Microplastic   Stimulated Raman scattering   SRS microscopy   Vibrational microspectroscopy  

摘要： Microfibers are reported as the most abundant microparticle type in the environment. Their small size and light weight allow easy and fast distribution, but also make it challenging to determine their chemical composition. Vibrational microspectroscopy methods as infrared and spontaneous Raman microscopy have been widely used for the identification of environmental microparticles. However, only few studies report on the identification of microfibers, mainly due to difficulties caused by their small diameter. Here we present the use of Stimulated Raman Scattering (SRS) microscopy for fast and reliable classification of microfibers from environmental samples. SRS microscopy features high sensitivity and has the potential to be faster than other vibrational microspectroscopy methods. As a proof of principle, we analyzed fibers extracted from the fish gastrointestinal (GIT) tract, deep-sea and coastal sediments, surface seawater and drinking water. Challenges were faced while measuring fibers from the fish GIT, due to the acidic degradation they undergo. However, the main vibrational peaks were still recognizable and sufficient to determine the natural or synthetic origin of the fibers. Notably, our results are in accordance to other recent studies showing that the majority of the analyzed environmental fibers has a natural origin. Our findings suggest that advanced spectroscopic methods must be used for estimation of the plastic fibers concentration in the environment. (c) 2020 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://***/licenses/by/4.0/).

关键词： Dalbergia wood   Species characterization   Geolocation   Classification  

摘要： New regulations concerning the trade in protected tropical hardwoods require a way to assess the species and the country of origin for wood samples. Rosewoods from the Dalbergia genus are heavily traded and are now one of the wood sources that are controlled. While may efforts have been reported on characterization of the species of Dalbergia samples, none has investigated the feasibility of providing probable provenance of the sample by locating the country where the tree grew. This study reports use of several well-known classifiers applied to data from an extensive elemental analysis and isotope ratio analysis of 239 curated samples of wood from the genus Dalbergia. The species and the country of origin can be identified with about 90% balanced accuracy.

关键词： 质量控制   临床免疫   免疫检验  

摘要： 探讨质量控制在临床免疫检疫中的作用。方法:本文选取在2019年1月~2020年1月期间,本院所检测的临床免疫检测报告。根据监测方法对其进行分组,分为对照组与观察组,每组均为54例检验报告,对照组不实施质量控制检验,观察组实施质量控制检验,对比两组患者检验报告结果。结果:在实施质量控制措施之后,观察组患者各项指标检查明显优于对照组患者,差异对比有统计学意义(P<0.05)。结论:实施质量控制之后开展免疫检验质量控制,能够保障检验流程更加规范,同时保障免疫结果更加具有可靠性与稳定性,在临床当中具有较大价值。

关键词： Bodily pain   mental health   musculoskeletal pain   work ability   well-being  

摘要： Construction work is physically demanding, and incidences of physical injury and work disability are high. This study explores musculoskeletal bodily pain and the impact this has on construction workers' mental health. A mixed-method approach incorporated survey and interview data. Sixty-seven construction workers completed a survey consisting of work ability and mental health measures. Eighteen workers who completed a survey participated in an interview exploring the occurrence and management of body pain, and the impact of pain on mental health. Survey findings indicated that participants whose pain had originated from work had significantly higher levels of depression, anxiety, and stress severity. Findings also revealed that depression, anxiety, and stress had a negative relationship with work ability indicators, suggesting that work ability is likely to decline when workers experience poor mental health. Key themes emerging from the interview data comprised of the expectation of pain, managing pain, impact of pain on mental health, pressure to work with pain, work ability and planning for the future, and the stigma of mental health. A conceptual model is presented which illustrates the relationship between work tasks, pain, mental health, and work ability. The model identifies that anticipated and experienced bodily pain creates harmful psychological demands for workers which impacts on their mental health.

关键词： 数字水印技术   垃圾分类   包装纸   循环经济发展   AIM   废纸  

摘要： 本刊讯(Mondi消息)全英国包装纸企Mondi与欧洲品牌协会(AIM)以及其他相关企业携手合作,致力于证明数字水印技术在大规模垃圾分类方面的可行性。几家企业和组织共同实行了“HolyGrail 2.0计划”,该计划的目标是评估这项开创性的数字技术是否能够帮助欧盟实现更好的分类,提高废纸包装回收率,从而推动循环经济发展。

关键词： 利率分层   波动特征   标度指数  

摘要： 本文以票据一、二级市场21个利率品种数据为基础,汇总分析各信用等级,各期限票据利率差异,并用Python建立趋势消解波动分析模型(DFA)研究不同承兑、直贴、期限票据业务中的利率分层及波动特征。这一研究可为当前疫情影响下央行为降低中小企业融资成本相关政策的制定提供数据支撑,并能为现实交易中的策略设计提供借鉴。

关键词： 标本溶血   骨折   生化指标检验  

摘要： 探究为骨折患者标本溶血进行生化检验其结果的价值和影响。方法:在2018.6年~2020.6年中选择120例患者展开评价和判定,根据标本溶血与否分为观察组和对照组。观察组骨折患者和对照组的骨折患者,均进行生化指标常规检验,共计17个项目,并将两组指标变化情况展开评估。结果:观察组各项生化指标检验结果较之对照组具有较为显著的差异(P<0.05)。结论:标本是否存在溶血对于骨折患者生化检验指标结果具有一定程度的影响,因此,需要加强血液采集与管理的监管力度,提高生化指标检验质量从而使得生化指标检验的结果具有较高的精确性和有效性。

关键词： 审核   考试考核   发证  

摘要： 根据国家《生猪屠宰管理条例》的有关规定,对畜禽屠宰技术和肉品品质检疫检验人员实行持证上岗制度,确保出厂(场)肉品的质量安全。

关键词： 临床生化检验   临床检验技术   加样器   血清样本   生化分析仪器   分离操作   血清分离   纤维蛋白  

摘要： 最近几年,科学技术的迅猛发展,临床检验技术随之产生,各种全新的生化分析仪器越来越多,而这些发展和进步都是为了获得更加准确的检验结果。在以往临床生化检验的过程中,所使用到的样本主要为血清样本,在对血清样本进行处理的过程中,通常需要花费大量时间来实行血清分离操作,并且,在实行分离操作的过程中,血清会产生纤维蛋白凝丝,这些凝丝的产生很有可能会对加样器或者仪器管路进行堵塞,会在一定程度上对医生的诊断和治疗带来不利影响。