摘要 :
A sensitive Mobile differential optical absorption spectroscopy (DOAS) system with real-time evaluation capability and HCHO detection limit of 3 ppb over 100m has been developed. The system was operated together with a Solar Occul...
展开
A sensitive Mobile differential optical absorption spectroscopy (DOAS) system with real-time evaluation capability and HCHO detection limit of 3 ppb over 100m has been developed. The system was operated together with a Solar Occultation Flux system for large-scale vertical flux measurements of HCHO, NO_2, SO_2, and VOCs in the Houston-Galveston-Brazoria area during two studies, in 2009 (Study of Houston Atmospheric Radical Precursors campaign) and in 2011 (Air Quality Research Program study). Both in 2009 and 2011, HCHO plumes from five separate local sources in Texas City, Mont Belvieu, and Houston Ship Channel (HSC) were repeatedly detected using Mobile DOAS with emissions varying between 6 and 40 kg/h. In many cases significant alkene emissions were detected simultaneously with the HCHO plumes. Furthermore, in 2011 two additional sources were observed in Texas City and in HSC, with 10 kg/h and 31 kg/h HCHO, respectively. A plume chemistrymodel was applied to 13 cases to investigatewhether the detected HCHO was emitted directly from the industries or was produced by photochemical degradation of VOCs. The model results showed that on average 90% of the detected HCHO was of primary origin and the photochemical production contributed more than 10% in only three cases. Based on the repeatability, it is likely that the most significant HCHO sources in the area are included in this study with an overall emission of 120 kg/h. On a regional scale, this emission is small compared to the secondary HCHO formed from oxidation of reactive VOCs emitted from the same industries, estimated to be an order of magnitude higher.
收起
摘要 :
Based on the results of multiyear measurements of spectral atmospheric transparency in the wave-length range of 0.37–4 μm, we discuss the regularities of daytime variations of the characteristics of aerosol optical depth (AOD) a...
展开
Based on the results of multiyear measurements of spectral atmospheric transparency in the wave-length range of 0.37–4 μm, we discuss the regularities of daytime variations of the characteristics of aerosol optical depth (AOD) and atmospheric moisture content in a typical Siberian region (Tomsk). For different atmospheric conditions (seasons, air masses), quantitative characteristics of the average daytime behavior of the spectral AOD and Angstrom parameters are presented. We suggest an empirical model for the daytime behavior of atmospheric AOD in the wavelength region of 0.37–4 μm, which is based on the use of the daily average values of the Angstrom parameters. We discuss the effect of the daytime AOD variations on the instan-taneous and daily average values of the aerosol radiative forcing at the underlying surface level and at the top of the atmosphere. The aerosol radiative effects are analyzed taking into account both the average daytime variations of the AOD as well as relatively large AOD variations during the day characteristic of a concrete situation.
收起
摘要 :
"In almost all cases when dealing with a limit of detectionor limit of determination, the primary purpose of deter-mining that limit is to stay away from it." Thus spoke the late William Horwitz (a chemist with the FDA and AOACfor...
展开
"In almost all cases when dealing with a limit of detectionor limit of determination, the primary purpose of deter-mining that limit is to stay away from it." Thus spoke the late William Horwitz (a chemist with the FDA and AOACfor many years) during a panel discussion on detection limits.~1Indeed, any analyst would prefer to report only asurementsthat have low uncertainty associated with them. The obviousnext step, then, is deciding how far away from the detectionlimit (DL) the measurement should be in order for the numberto be "reportable." Such discussions fall into the realm of whatare often called "quantitation limits" or "reporting limits." Inthe opinion of the authors of this column, such limits: 1) areless rigorously calculated and applied than are detection limitsand 2) should be abandoned in favor of reporting every measure-ment (made without extrapolation of the applicable regressioncurve) along with its prediction interval and associated confi-dence level. (See Part 26, American Laboratory, Jun/Jul 2007,for an editorial on detection limits.) Such an approach gives theuser the statistically sound data he or she needs to make a well-informed decision on the acceptability of the noise level in themeasurements. However, other protocols for reporting data aremore widely employed. The rest of this article will discuss theseprocedures and expand on one of them (i.e., the reporting of thenumber of significant digits).
收起
摘要 :
Given that bluetongue (BT) may potentially be transmitted by semen, that the disease has significantly expanded in recent years, and that millions of doses of cattle semen are annually traded throughout the world, the transmission...
展开
Given that bluetongue (BT) may potentially be transmitted by semen, that the disease has significantly expanded in recent years, and that millions of doses of cattle semen are annually traded throughout the world, the transmission of bluetongue virus (BTV) by semen could have severe consequences in the cattle industry. The hypothesis that infected bulls could excrete BTV in their semen led to restrictions on international trade of ruminant semen and the establishment of measures to prevent BTV transmission by semen. However, neither the risk of BTV transmission by semen nor the effectiveness of these measures was estimated quantitatively. The objective of the study was to assess, in case of introduction of BTV into a bovine semen collection centre (SCC), both the risk of BTV transmission by bovine semen and the risk reduction achieved by some of the preventive measures, by means of a stochastic risk assessment model. The model was applied to different scenarios, depending on for example the type of diagnostic test and the interval between the controls (testing) of donor bulls, or the rate of BTV spread within the SCC.Enzyme-linked immunosorbant assay (ELISA) controls of donor bulls every 60 days seemed to be an ineffective method for reducing the risk of BTV transmission in contrast to polymerase chain reaction (PCR) tests every 28 days. An increase in the rate of spread within the SCC resulted in a reduced risk of BTV transmission by semen. The storage of semen for 30 days prior to dispatch seemed to be an efficient way of reducing the risk of transmission by semen.The sensitivity analysis identified the probability of BTV shedding in semen as a crucial parameter in the probability of BTV transmission by semen. However, there is a great degree of uncertainty associated with this parameter, with significant differences depending on the BTV serotype
收起
摘要 :
Given that bluetongue (BT) may potentially be transmitted by semen, that the disease has significantly expanded in recent years, and that millions of doses of cattle semen are annually traded throughout the world, the transmission...
展开
Given that bluetongue (BT) may potentially be transmitted by semen, that the disease has significantly expanded in recent years, and that millions of doses of cattle semen are annually traded throughout the world, the transmission of bluetongue virus (BTV) by semen could have severe consequences in the cattle industry. The hypothesis that infected bulls could excrete BTV in their semen led to restrictions on international trade of ruminant semen and the establishment of measures to prevent BTV transmission by semen. However, neither the risk of BTV transmission by semen nor the effectiveness of these measures was estimated quantitatively. The objective of the study was to assess, in case of introduction of BTV into a bovine semen collection centre (SCC), both the risk of BTV transmission by bovine semen and the risk reduction achieved by some of the preventive measures, by means of a stochastic risk assessment model. The model was applied to different scenarios, depending on for example the type of diagnostic test and the interval between the controls (testing) of donor bulls, or the rate of BTV spread within the SCC.Enzyme-linked immunosorbant assay (ELISA) controls of donor bulls every 60 days seemed to be an ineffective method for reducing the risk of BTV transmission in contrast to polymerase chain reaction (PCR) tests every 28 days. An increase in the rate of spread within the SCC resulted in a reduced risk of BTV transmission by semen. The storage of semen for 30 days prior to dispatch seemed to be an efficient way of reducing the risk of transmission by semen.The sensitivity analysis identified the probability of BTV shedding in semen as a crucial parameter in the probability of BTV transmission by semen. However, there is a great degree of uncertainty associated with this parameter, with significant differences depending on the BTV serotype
收起
摘要 :
Objective: To investigate measurement errors and head positioning effects on radiographs made with new dental panoramic radiograph equipment that uses tomosynthesis. Materials and Methods: Radiographic images of a simulated human ...
展开
Objective: To investigate measurement errors and head positioning effects on radiographs made with new dental panoramic radiograph equipment that uses tomosynthesis. Materials and Methods: Radiographic images of a simulated human head or phantom were made at standard head positions using the new dental panoramic radiograph equipment. Measurement errors were evaluated by comparing with the true values. The phantom was also radiographed at various alternative head positions. Significant differences between measurement values at standard and alternative head positions were evaluated. Magnification ratios of the dimensions at standard and alternative head positions were calculated. Results: The measurement errors were small for all dimensions. On the measurements at 4-mm displacement positions, no dimension was significantly different from the standard value, and all dimensions were within ±5% of the standard values. At 12-mm displacement positions, the magnification ratios for tooth length and mandibular ramus height were within ±5% of the standard values, but those for dental arch width, mandibular width, and mandibular body length were beyond±5%of the standard values. Conclusions: Measurement errors on radiographs made using the new panoramic radiograph equipment were small in any direction. At 4-mm head displacement positions, no head positioning effect on the measurements was found. At 12-mm head displacement positions, the measurements for vertical dimensions were little affected by head positioning, while those for lateral and anteroposterior dimensions were strongly affected.
收起
摘要 :
Engineers and scientists are often faced with the problem of objectively comparing time histories of measured and/or simulated data. This article presents a reliable and intuitive validation metric for use in the validation proces...
展开
Engineers and scientists are often faced with the problem of objectively comparing time histories of measured and/or simulated data. This article presents a reliable and intuitive validation metric for use in the validation process. The proposed validation metric is able to quantify the agreement/disagreement between deterministic system response quantities of interest obtained from measurements on a physical system and predictions from a mathematical model. The validation metric is based on the relative error, and the challenges concerning the use of the relative error on periodic signals are addressed. The validation metric is compared to similar metrics and their advantages and limitations are discussed. The results show that the proposed validation metric gives a comprehensive error that is able to quantify the agreement between two periodic signals and is easily interpretable.
收起
摘要 :
Although measurement has been an important component of human activities for millennia, it remains remarkably difficult to provide a fully satisfactory definition of the concept. In part this is due to the fact that measurement is...
展开
Although measurement has been an important component of human activities for millennia, it remains remarkably difficult to provide a fully satisfactory definition of the concept. In part this is due to the fact that measurement is a diverse and dynamic human activity, and takes shape in a wide variety of ways depending on the nature of the subject matter, application, and context. If a definition of measurement is to pay respect to this basic fact, it cannot be so narrowly construed as to apply to only one area of scientific activity (e.g., physics); on the other hand, the definition cannot be so permissive as to trivialize the concept to the point that measurement is not recognizably superior to, for instance, guesses or statements of opinion. One issue at the heart of this tension is the relationship between the concepts of measurement, quantity, and quantification. In particular, it is sometimes argued or assumed either that quantification is a necessary condition for measurement, or that quantification is simply synonymous with measurement. To assess the validity of these positions, the concepts of measurement, quantity, and quantification should be independently defined and their relationships analyzed. In this paper we conduct such an analysis, from both historical and philosophical perspectives, and present the case that quantification is neither necessary nor sufficient for measurement. We conclude by considering how the conceptual separation of measurement and quantification serves to promote more productive and shared understandings of measurement across disciplines. (C) 2016 Elsevier Ltd. All rights reserved.
收起
摘要 :
Objectives/Hypothesis To understand: 1) how endoscopic airway measurements compare to three-dimensional (3D) CT derived measurements; 2) where each technique is potentially useful; and 3) where each has limitations. Study Design C...
展开
Objectives/Hypothesis To understand: 1) how endoscopic airway measurements compare to three-dimensional (3D) CT derived measurements; 2) where each technique is potentially useful; and 3) where each has limitations. Study Design Compare airway diameters and cross-sectional areas from endoscopic images and CT derived 3D reconstructions. Methods Videobronchoscopy was performed and recorded on an adult-sized commercially available airway mannequin. At various levels, cross-sectional areas were measured from still video frames using a referent placed via the biopsy port. A 3D reconstruction was generated from a high resolution CT of the mannequin; planar sections were cut at similar cross-sectional levels; and cross-sectional areas were obtained. Results At three levels of mechanically generated tracheal stricture, the differences between the endoscopic measurement and CT-derived cross-sectional area were 1%, 0%, and 7% (1.8, 0.8, and 14 mm2). At the vocal folds, the difference was 9% (7.8 mm2). The tip of the epiglottis and width of the epiglottis differed by 27% and 10% (18.73 mm2, 0.40mm). The airway measurements at the base of tongue, minimal cross-sectional area of the pharynx, and choana differed by 26%, 36%, and 30% (101.40 mm2, 36.67 mm 2, 122.71 mm2). Conclusions Endoscopy is an effective tool for obtaining airway measurements compared with 3D reconstructions derived from CT. Concordance is best in geometrically simple areas where the entire cross-section measured is visible within one field of view (trachea, round; vocal folds, triangular) versus geometrically complex areas that encompass more than one field of view (i.e. pharynx, choana).
收起
原文获取