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排序方式: 共有507条查询结果,搜索用时 15 毫秒
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Blake Gardner Frederick Ling Philip K Hopke Mark W Frampton Mark J Utell Wojciech Zareba Scott J Cameron David Chalupa Cathleen Kane Suresh Kulandhaisamy Michael C Topf David Q Rich 《Particle and fibre toxicology》2014,11(1):1-11
Background
We and others have shown that increases in particulate air pollutant (PM) concentrations in the previous hours and days have been associated with increased risks of myocardial infarction, but little is known about the relationships between air pollution and specific subsets of myocardial infarction, such as ST-elevation myocardial infarction (STEMI) and non ST-elevation myocardial infarction (NSTEMI).Methods
Using data from acute coronary syndrome patients with STEMI (n?=?338) and NSTEMI (n?=?339) and case-crossover methods, we estimated the risk of STEMI and NSTEMI associated with increased ambient fine particle (<2.5 um) concentrations, ultrafine particle (10-100 nm) number concentrations, and accumulation mode particle (100-500 nm) number concentrations in the previous few hours and days.Results
We found a significant 18% increase in the risk of STEMI associated with each 7.1 μg/m3 increase in PM2.5 concentration in the previous hour prior to acute coronary syndrome onset, with smaller, non-significantly increased risks associated with increased fine particle concentrations in the previous 3, 12, and 24 hours. We found no pattern with NSTEMI. Estimates of the risk of STEMI associated with interquartile range increases in ultrafine particle and accumulation mode particle number concentrations in the previous 1 to 96 hours were all greater than 1.0, but not statistically significant. Patients with pre-existing hypertension had a significantly greater risk of STEMI associated with increased fine particle concentration in the previous hour than patients without hypertension.Conclusions
Increased fine particle concentrations in the hour prior to acute coronary syndrome onset were associated with an increased risk of STEMI, but not NSTEMI. Patients with pre-existing hypertension and other cardiovascular disease appeared particularly susceptible. Further investigation into mechanisms by which PM can preferentially trigger STEMI over NSTEMI within this rapid time scale is needed. 相似文献3.
Soft X‐ray Ptychographic Imaging and Morphological Quantification of Calcium Silicate Hydrates (C–S–H) 下载免费PDF全文
Sungchul Bae Rae Taylor David Shapiro Peter Denes John Joseph Rich Celestre Stefano Marchesini Howard Padmore Tolek Tyliszczak Tony Warwick David Kilcoyne Pierre Levitz Paulo J. M Monteiro 《Journal of the American Ceramic Society》2015,98(12):4090-4095
Morphological details of calcium silicate hydrate (C–S–H) stemming from the hydration process of Portland cement (PC) phases are crucial for understanding the PC‐based systems but are still only partially known. Here we introduce the first soft X‐ray ptychographic imaging of tricalcium silicate (C3S) hydration products. The results are compared using both scanning transmission X‐ray and electron transmission microscopy data. The evidence shows that ptychography is a powerful method to visualize the details of outer and inner product C–S–H of fully hydrated C3S, which have fibrillar and an interglobular structure with average void sizes of 20 nm, respectively. The high‐resolution ptychrography image enables us to perform morphological quantification of C–S–H, and, for the first time, to possibly distinguish the contributions of inner and outer product C–S–H to the small angle scattering of cement paste. The results indicate that the outer product C–S–H is mainly responsible for the q?3 regime, whereas the inner product C–S–H transitions to a q?2 regime. Various hypotheses are discussed to explain these regimes. 相似文献
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Jeppe Rich Carlo Giacomo PratoTove Hels Allan LyckegaardNiels Buus Kristensen 《Accident; analysis and prevention》2013
While the number of fatalities on Danish roads has decreased in the last 40 years, research has not investigated the contribution of legislation changes, enforcement measures, technological enhancements, infrastructural improvements and human factors to this reduction. In the context of a Danish car market with remarkably high registration tax that causes potential buyers to hold longer onto old cars, the relationship between technological enhancements of vehicles and severity of crashes requires particular attention. 相似文献
6.
The recently approved ANSI/CEA-2018 standard is motivated by the current usability crisis in computer-controlled electronic products. The standard facilitates a new user interface design methodology that uses a task model at runtime to guide users. 相似文献
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ABSTRACT A microcomputer-controlled dual-wavelength spectrophotometer suitable for automated phytochrome assay is described. The optomechanical unit provides for sequential irradiation of the sample by the two measuring wavelengths with intervening dark intervals and for actinic irradiation to inter-convert phytochrome between its two forms. Photomultiplier current is amplified, converted to a digital value and transferred into the computer using a custom-designed IEEE-488 bus interface. The microcomputer calculates mathematically both absorbance and absorbance difference values with dynamic correction for photomultiplier dark current. In addition, the computer controls the operating parameters of the spectrophotometer via a separate interface. These parameters include control of the durations of measuring and actinic irradiation intervals and their sequence. Because the data are processed solely within the microcomputer, except for the initial linear amplification, any output desired can be obtained, including automated determination of not only total phytochrome content, but also of the proportions present in the far-red- and red-absorbing forms. 相似文献
9.
A current model for carotenoid transport and absorption in the gut proposes an initial solubilization in the oil phase of
dietary emulsions followed by incorporation of the carotenoids in mixed bile salt micelles. To assess the relevance of the
first stage of this model to what is observed in vivo we have examined the transfer of carotene from carrot juice to olive oil. Increased acidity enhanced the transfer from both
whole juice and carotene crystals isolated from both whole juice and carotene crystals isolated from carrot chromoplasts.
The transfer was significantly slower from whole juice. By using exogenous β-carotene and measuring its transfer to oil in
the presence and absence of carrot juice we have demonstrated that the inhibition of the transfer in juice arises, at least
in part, from soluble juice factors. The inhibition is relieved by a fall in pH, which leads to lowering of the electric potential
at the oil/aqueous phase interface and aggregation of carrot tissue including crystalline carotene. Under conditions of low
pH, oil droplets adhere to the tissue aggregates, allowing carotene to pass into the oil. Our results provide an explanation
for why carotene absorption in vivo is depressed by conditions of low gastric acidity. 相似文献
10.
Crawford Eean R.; LePine Jeffery A.; Rich Bruce Louis 《Canadian Metallurgical Quarterly》2010,95(5):834
We refine and extend the job demands–resources model with theory regarding appraisal of stressors to account for inconsistencies in relationships between demands and engagement, and we test the revised theory using meta-analytic structural modeling. Results indicate support for the refined and updated theory. First, demands and burnout were positively associated, whereas resources and burnout were negatively associated. Second, whereas relationships among resources and engagement were consistently positive, relationships among demands and engagement were highly dependent on the nature of the demand. Demands that employees tend to appraise as hindrances were negatively associated with engagement, and demands that employees tend to appraise as challenges were positively associated with engagement. Implications for future research are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献