基于插入损耗的噪声源阻抗修正计算方法

为了使EMI滤波器能够实现有效的插入损耗，需要考虑噪声源阻抗的频谱特性。电压插入损耗法是最简单的测试噪声源阻抗的方法。本文分析了传统的电压插入损耗法在实现过程中采用的假设条件，部分假设在数学上并不严格成立，相应的简化近似计算可能导致较大误差；甚至有些计算结果会与假设条件矛盾，进而导致计算结果无效。在不改变传统插入损耗法的测试方案的前提下，对噪声源阻抗的计算方法进行修正，推导了源阻抗幅值的精确解析表达式，进而确定源阻抗幅值的最大值和最小值。解析计算结果经过数学验证成立。在此基础上，以电动汽车用DC-DC变换器为测试对象，实现了源阻抗幅值的测试和计算，验证了该方法的有效性和适用性。通过该测试和设计实例的分析可以发现，改进的电压插入损耗法可以获得更精确的噪声源阻抗，避免滤波器的过设计，便于滤波元件的设计和选型，并为滤波器体积、重量等的优化提供帮助。     

Young drivers who continue to drive while sleepy: What are the associated sleep‐ and driving‐related factors?

Crashes due to sleepiness account for a substantial proportion of road crash incidents. The purpose of the current study was to examine several sleep‐related factors and driving‐related factors for their association with self‐reports of continuing to drive while sleepy. In total 257 young drivers aged 18–25 years completed an online survey that assessed factors such as sleep quality, sleep duration and consistency, excessive daytime sleepiness, experiences with sleepiness and their driving‐related behaviours. The results demonstrate that being older, having a perceived ability to overcome sleepiness, committing more highway code violations and having experienced a sleep‐related close call were positively associated with an increased likelihood of continuing to drive while sleepy. The obtained results highlight the acceptance of risky driving behaviours among some younger drivers. Younger drivers’ risky driving behaviour is certainly a road safety concern given the impairment associated with sleepiness and their over‐representation in road crash incidents.     

Nuclear spin singlet states as a contrast mechanism for NMR spectroscopy

Nuclear magnetic resonance (NMR) spectra of complex chemical mixtures often contain unresolved or hidden spectral components, especially when strong background signals overlap weaker peaks. In this article we demonstrate a quantum filter utilizing nuclear spin singlet states, which allows undesired NMR spectral background to be removed and target spectral peaks to be uncovered. The quantum filter is implemented by creating a nuclear spin singlet state with spin quantum numbers j = 0, m_z = 0 in a target molecule, applying a continuous RF field to both preserve the singlet state and saturate the magnetization of undesired molecules and then mapping the target molecule singlet state back into an NMR observable state so that its spectrum can be read out unambiguously. The preparation of the target singlet state can be carefully controlled with pulse sequence parameters, so that spectral contrast can be achieved between molecules with very similar structures. We name this NMR contrast mechanism ‘Suppression of Undesired Chemicals using Contrast‐Enhancing Singlet States’ (SUCCESS) and we demonstrate it in vitro for three target molecules relevant to neuroscience: aspartate, threonine and glutamine. Copyright © 2013 John Wiley & Sons, Ltd.     

Retrieval of overviews of systematic reviews in MEDLINE was improved by the development of an objectively derived and validated search strategy

ObjectivesLocating overviews of systematic reviews is difficult because of an absence of appropriate indexing terms and inconsistent terminology used to describe overviews. Our objective was to develop a validated search strategy to retrieve overviews in MEDLINE.Study Design and SettingWe derived a test set of overviews from the references of two method articles on overviews. Two population sets were used to identify discriminating terms, that is, terms that appear frequently in the test set but infrequently in two population sets of references found in MEDLINE. We used text mining to conduct a frequency analysis of terms appearing in the titles and abstracts. Candidate terms were combined and tested in MEDLINE in various permutations, and the performance of strategies measured using sensitivity and precision.ResultsTwo search strategies were developed: a sensitivity-maximizing strategy, achieving 93% sensitivity (95% confidence interval [CI]: 87, 96) and 7% precision (95% CI: 6, 8), and a sensitivity-and-precision–maximizing strategy, achieving 66% sensitivity (95% CI: 58, 74) and 21% precision (95% CI: 17, 25).ConclusionThe developed search strategies enable users to more efficiently identify overviews of reviews compared to current strategies. Consistent language in describing overviews would aid in their identification, as would a specific MEDLINE Publication Type.     

气管插管全麻术中预防气道感染的临床研究

目的观察一次性病毒/细菌过滤器在气管插管全麻术中预防气道感染的应用价值,为临床预防策略的制定提供参考。方法选择2011年3月-2013年3月接受气管插管全麻手术的患者76例,按照随机数字表法将其分为观察组和对照组各38例;观察组应用一次性病毒/细菌过滤器,而对照组则未用,分别在麻醉前和手术结束时用无菌棉签采集麻醉机呼气端、吸气端表面标本行细菌学检测;在手术结束时收集钠石灰罐底部10g钠石灰行细菌学检测,对比两组患者的检测结果和术后24h内气道感染发生率。结果两组患者在麻醉开始前麻醉机呼气端、吸气端细菌学培养结果均为阴性;手术结束时,麻醉机吸气端、呼气端和钠石灰的细菌学培养阳性率均为0,对照组分别为5.26%、42.11%和15.79%,观察组细菌培养阳性率均显著低于对照组,差异有统计学意义(P<0.05);术后24h内气道感染发生率观察组为2.63%,显著低于对照组的18.62%,差异有统计学意义(P<0.05)。结论麻醉机气管插管全麻可增加患者气道感染的机会,通过一次性病毒/细菌过滤器、及时更换钠石灰等措施,可有效预防气道感染的发生。     

评价一次性使用输血器具用尼龙血液过滤网过滤性能的新方法

建立一种使用240μm和160μm的标准粒子溶液评价尼龙血液过滤网过滤性能新方法,代替传统人体血液的评价方法。并通过试验证实,用该方法评价过滤网的过滤性能具有良好的重复性,操作简便、试验材料可得性强、避免因使用血液带来的安全隐患等优点。可用于尼龙血液过滤网和输血器生产的过程控制。