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221.
Gilbert D. Nessim Matteo Seita Desirée L. Plata Kevin P. O’Brien A. John Hart Eric R. Meshot Christopher M. Reddy Philip M. Gschwend Carl V. Thompson 《Carbon》2011,49(3):804-810
Despite significant progress in carbon nanotube (CNT) synthesis by thermal chemical vapor deposition (CVD), the factors determining the structure of the resulting carbon filaments and other graphitic nanocarbons are not well understood. Here, we demonstrate that gas chemistry influences the crystal structure of carbon filaments grown at low temperatures (500 °C). Using thermal CVD, we decoupled the thermal treatment of the gaseous precursors (C2H4/H2/Ar) and the substrate-supported catalyst. Varying the preheating temperature of the feedstock gas, we observed a striking transition between amorphous carbon nanofibers (CNFs) and crystalline CNTs. These results were confirmed using both a hot-wall CVD system and a cold-wall CVD reactor. Analysis of the exhaust gases (by ex situ gas chromatography) showed increasing concentrations of specific volatile organic compounds (VOCs) and polycyclic aromatic hydrocarbons (PAHs) that correlated with the structural transition observed (characterized using high-resolution transmission electron microscopy). This suggests that the crystallinity of carbon filaments may be controlled by the presence of specific gas phase precursor molecules (e.g., VOCs and PAHs). Thus, direct delivery of these molecules in the CVD process may enable selective CNF or CNT formation at low substrate temperatures. The inherent scalability of this approach could impact many promising applications, especially in the electronics industry. 相似文献
222.
Analyzing correlated binary data using SAS 总被引:1,自引:0,他引:1
We discuss methods for analyzing repeated binary measurements on the same individual. In spite of the fact that the repeated measurements on the same individual are correlated, the ordinary logistic regression maximum likelihood estimates (which assume that the repeated measures are independent) are consistent and asymptotically normal (K. Y. Liang and S. L. Zeger, Biometrika 73, 13 (1986]. However, the inverse of the estimated information matrix (assuming independence) can give inconsistent estimates of the asymptotic variance of estimated parameters. We describe how to obtain the logistic regression estimates, as well as a consistent estimate of their covariance matrix, in SAS, with minimal matrix manipulations. 相似文献
223.
Chen Zhiying Nash Philip Zhang Ying 《Metallurgical and Materials Transactions B》2019,50(4):1718-1728
Metallurgical and Materials Transactions B - A study of the hardenability, the microstructure and the phase transformations as a function of the cooling rate, of a marine crankshaft S34MnV steel... 相似文献
224.
The aim of this work was to assess the response of Friesian steers to road transportation at low, medium and high (ca 200, 300 and 600 kg/m(2)) stocking densities in terms of physiology, behaviour and carcass bruising. Stocking density was determined by adjusting the number of animals per pen (3 runs) or by adjusting pen size (3 runs). Plasma cortisol and glucose increased (P < 0·001) with stocking density, as did plasma CK activity (P < 0·001) and carcass bruising (P < 0·01) both of which indicate muscle damage. At constant stocking density stress increased with pen location towards the tail of the truck, as reflected by a significant increase in plasma cortisol. Stocking density influenced standing orientation within the truck. At low stocking density animal movement was unrestricted and the preferred orientation was standing parallel to the direction of travel; there was a strong bias against diagonal orientations. Losses of balance were associated with specific driving events, notably braking and cornering. Minor losses of balance were observed at all stocking densities, but major losses of balance including animals going down underfoot were associated with high density. When an animal went down at high stocking density it did so involuntarily and was sometimes trapped down, destabilizing other members of the group in a domino effect. Exploratory, sexual and aggressive behaviours were inhibited at high stocking density, with the exception of mounting and pushing, which increased in frequency with stocking density. It was concluded that the high stocking density adversely affected animal welfare and lowered carcass quality when compared with the medium and low stocking densities. 相似文献
225.
Zero Risk Does Not Exist: Lessons Learned from Microbial Risk Assessment Related to Use of Water and Safety of Fresh Produce 下载免费PDF全文
Ann De Keuckelaere Liesbeth Jacxsens Philip Amoah Gertjan Medema Peter McClure Lee‐Ann Jaykus Mieke Uyttendaele 《Comprehensive Reviews in Food Science and Food Safety》2015,14(4):387-410
Risk assessments related to use of water and safety of fresh produce originate from both water and food microbiology studies. Although the set‐up and methodology of risk assessment in these 2 disciplines may differ, analysis of the current literature reveals some common outcomes. Most of these studies from the water perspective focus on enteric virus risks, largely because of their anticipated high concentrations in untreated wastewater and their resistance to common wastewater treatments. Risk assessment studies from the food perspective, instead, focus mainly on bacterial pathogens such as Salmonella and pathogenic Escherichia coli. Few site‐specific data points were available for most of these microbial risk assessments, meaning that many assumptions were necessary, which are repeated in many studies. Specific parameters lacking hard data included rates of pathogen transfer from irrigation water to crops, pathogen penetration, and survival in or on food crops. Data on these factors have been investigated over the last decade and this should improve the reliability of future microbial risk estimates. However, the sheer number of different foodstuffs and pathogens, combined with water sources and irrigation practices, means that developing risk models that can span the breadth of fresh produce safety will be a considerable challenge. The new approach using microbial risk assessment is objective and evidence‐based and leads to more flexibility and enables more tailored risk management practices and guidelines. Drawbacks are, however, capacity and knowledge to perform the microbial risk assessment and the need for data and preferably data of the specific region. 相似文献
226.
Davis CR Heller LC Peak KK Wingfield DL Goldstein-Hart CL Bodager DW Cannons AC Amuso PT Cattanii J 《Journal of food protection》2004,67(5):1005-1008
Molecular methods have become vital epidemiological tools in the detection and characterization of bacteria associated with a foodborne outbreak. We used both culture and real-time PCR to detect a Vibrio parahaemolyticus isolate associated with a foodborne outbreak. The outbreak occurred in July 2002 in Polk County, Florida, and originated at a Chinese buffet, with one person being hospitalized. The hospital isolated V. parahaemolyticus from the patient but destroyed the sample after diagnosis. From an onsite visit of the restaurant, food samples that possibly contributed to the outbreak were collected and sent to the Florida Department of Health, Tampa Branch Laboratory. Crab legs, crabsticks, and mussel samples were homogenized and incubated according to the Food and Drug Administration Bacteriological Analytical Manual culture protocol. Three sets of primers and a TaqMan probe were designed to target the tdh, trh, and tlh genes and used for real-time PCR. This study was successful in isolating V. parahaemolyticus from a mussel sample and detecting two of its genes (tdh and tlh) in food and pure culture by real-time PCR. 相似文献
227.
访谈中菲利普·乌尔施布隆首先讨论了当前历史性面临的危机,并得出"建筑理论已失去它的自主性"的观点.他认为当代理论已不存在中心化的大师理论,而是呈现出多元化的概念,恰如米克·巴尔的"微型理论"般运作.基于巴尔关于"概念旅行"的理论,他探讨了全球化语境下建筑教育的新机遇,最后由此出发分析中国与西方国家当代建筑教育之间的相互... 相似文献
228.
The experimental investigations of the effect of contact time/temperature on initiating the cook-off using 7.62 mm calibre cartridge cases (CC) were conducted previously. These cartridges were filled with commercial off-the-shelf (COTS) double based (DB) propellant (Bulls Eye) and were loaded in a hot chamber. The thermal explosion temperature is of great significance to both weapon designers and safety inspectors as it provides the operational limit and safe operating temperature. For CC under test, it was found that the cook-off temperatures of this propellant were encountered with the heat transfer profile of the simulated gun barrel between 151.4 ℃ and 153.4 ℃, with a reaction occurring in less than 300 s after the round was chambered. Usefully, each experiment was found to be consistent and repeatable. 相似文献
229.
Philip Schulz Leah L. Kelly Paul Winget Hong Li Hyungchul Kim Paul F. Ndione Ajaya K. Sigdel Joseph J. Berry Samuel Graham Jean‐Luc Brédas Antoine Kahn Oliver L. A. Monti 《Advanced functional materials》2014,24(46):7381-7389
The interfacial electronic structure between oxide thin films and organic semiconductors remains a key parameter for optimum functionality and performance of next‐generation organic/hybrid electronics. By tailoring defect concentrations in transparent conductive ZnO films, we demonstrate the importance of controlling the electron transfer barrier at the interface with organic acceptor molecules such as C60. A combination of electron spectroscopy, density functional theory computations, and device characterization is used to determine band alignment and electron injection barriers. Extensive experimental and first principles calculations reveal the controllable formation of hybridized interface states and charge transfer between shallow donor defects in the oxide layer and the molecular adsorbate. Importantly, it is shown that removal of shallow donor intragap states causes a larger barrier for electron injection. Thus, hybrid interface states constitute an important gateway for nearly barrier‐free charge carrier injection. These findings open new avenues to understand and tailor interfaces between organic semiconductors and transparent oxides, of critical importance for novel optoelectronic devices and applications in energy‐conversion and sensor technologies. 相似文献
230.
AbstractThis article discusses how key risks from extreme weather events might affect progress towards meeting Sustainable Development Goals 6 and 11 in cities in developing countries. It outlines the magnitude of the existing shortfall in safe water and sanitation services, and how climate change will exacerbate existing problems. It argues that the performance of many governments thus far has lacked urgency and purpose. Unless governments in particular become more committed, with redoubled effort, the goals are unlikely to be achieved. 相似文献