1,721,206 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Combustion sources of particles: 2. Emission factors and measurement methods
No full textEmissions from the combustion of biomass and fossil fuels are a significant source of particulate matter (PM) in ambient outdoor and/or indoor air. It is important to quantify PM emissions from combustion sources for regulatory and control purposes in relation to air quality. In this paper, we review emission factors for several types of important combustion sources: road transport, industrial facilities, small household combustion devices, environmental tobacco smoke, and vegetation burning. We also review current methods for measuring particle physical characteristics (mass and number concentrations) and principles of methodologies for measuring emission factors. The emission factors can be measured on a fuel-mass basis and/or a task basis. Fuel mass based emission factors (e.g., g per kg of fuel) can be readily used for the development of emission inventories when the amount of fuels consumed are known. Task-based emission factors (g per mile driven, g per MJ generated) are more appropriate when used to conduct comparisons of air pollution potentials of different combustion devices. Finally, we discuss major shortcomings and limitations of current methods for measuring particle emissions and present recommendations for development of future measurement techniques
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
The Effects of Ozone Exposure on Cardiovascular Pathophysiology
No full textIt has been commonly accepted until recently that particulate matter (PM) is responsible for the cardiovascular toxicity of air pollution mixtures, while ozone (O3) mainly adversely affects respiratory health. However, there is increasing evidence that O3, independent of PM, is also associated with cardiovascular hospitalizations and mortality, even at levels below current regulatory standards. The mechanisms underlying these epidemiological associations between O3 and cardiovascular disease remain poorly understood. The goal of this dissertation research is to use human biomarker outcomes in real-world exposure scenarios to elucidate plausible mechanisms by which O3 affects cardiovascular health. The findings of this dissertation research are primarily based on a single longitudinal cohort study designed to assess biomarker associations with time-activity-adjusted air pollutant exposures and with indoor air purification interventions, specifically different combinations of a high efficiency particulate air (HEPA) filter and a particle-removing and O3-producing electrostatic precipitator (ESP). Eighty-nine healthy participants living on a work campus in Changsha City, China were recruited for this study conducted from December 1st, 2014 - January 31st, 2015. The unique quasi-experimental setting of participants all living and working together on a work campus allowed for better characterization of air pollutant exposure effects due to minimal variation in potential confounders. At baseline, workers had a combination of an ESP and a HEPA in the central air handling units (AHUs) of their work and living spaces. During a five-week intervention period from December 6th, 2014 to January 13th, 2015, subjects were split into two groups, both of which had the ESPs turned off and one of which also had the HEPAs removed, and after this intervention original conditions were restored. Biomarkers indicative of inflammation and oxidative stress, arterial stiffness, myocardial function, blood pressure, thrombotic factors, and spirometry were measured at four sessions, one at baseline, two at two and four weeks into the intervention period, and one two weeks after restoring baseline conditions post-intervention. Indoor and outdoor O3 and PM of less than or equal to 2.5 µm in diameter (PM2.5), along with ambient co-pollutants NO2 and SO2, were monitored throughout the study period and combined with time-activity information and filtration conditions of each residence and office. These data were used to estimate 24-hour and 2-week combined indoor and outdoor average exposure concentrations, in addition to exposures in filtered and unfiltered environments. To test the hypothesis that air pollutant exposures observed during this study would be associated with biomarker outcomes, associations between each exposure measure and biomarker were analyzed with single- and two-pollutant linear mixed models. The 24-hour mean O3 exposure concentrations during the study ranged from 1.4 to 19.4 ppb, corresponding with daily 8-hour maximum outdoor concentrations ranging from 3.6 to 60.5 ppb, with all but six days during the study period falling below the WHO 8-hour mean O3 guideline of 50 ppb6. Within this range, in models controlling for a second co-pollutant and other potential confounders, a 10 ppb increase in 24-hour O3 was associated with mean percent increases (95% CIs) of 36.3% (29.9%, 43.0%) in the platelet activation marker soluble P-selectin (sCD62P), 2.8% (0.6%, 5.1%) in diastolic blood pressure (DBP), and 18.1% (4.5%, 33.5%) and 31.0% (0.2%, 71.1%) in the pulmonary inflammation markers fractional exhaled nitric oxide (FeNO) and exhaled breath condensate nitrite and nitrate (EBCNN), respectively, as well as a -9.5% (-17.7%, -1.4%) decrease in arterial stiffness marker augmentation index (AI) and a -15.5% (-23.8%, -6.2%) decrease in the systemic oxidative stress marker urinary malondialdehyde (UMDA). A 10 ppb increase in 2-week O3 was associated with increases of 61.1% (37.8%, 88.2%) in sCD62P and 126.2% (12.1%, 356.2%) in EBCNN. In contrast, PM2.5, NO2, and SO2 exposure measures were variably and weakly associated with markers indicating increased arterial stiffness and endothelial cell dysfunction. Only the O3 associations with sCD62P are robust in two-pollutant models and multiple testing p-value correction. These results suggest that O3 exposure enhances cardiovascular disease risk through platelet activation and blood pressure increases at levels lower than those capable of affecting lung function.To examine if the removal of HEPA filtration and ESP in the indoor air purification systems were associated with changes in biomarker outcomes, Bayesian hierarchical generalized ridge regression (GRR) models accounting for subject-specific intercept random effects were used to assess associations between categorical intervention variables while controlling for cumulative pollutant exposures in unfiltered microenvironments, namely outdoors and places other than the offices and dorms. The GRR models allowed for more stable maximized likelihood estimates when model predictors were highly correlated. When factoring in time-activity patterns, subjects without HEPA filtration had total 24-hour PM2.5 exposures on average 37.9 µg/m3 (88.3%) higher than subjects with HEPA filtration, and the removal of the ESPs resulted in a small average reduction of 2.2 ppb (a 32.8% decrease as compared to the overall mean 24-hour O3 exposure) in each subject’s total 24-hour O3 exposure. Despite this large change in PM2.5 exposure, no biomarkers were associated with HEPA removal in any models, but ESP removal was associated with decreases of -17.1% (-23.1%, -11.3%) in sCD62P, -3.6% (-5.5%, -1.4%) in systolic blood pressure (SBP), and -3.3% (-5.9%, -0.7%) in DBP. In addition, though subjects spent an average of 64.5% of their time in filtered locations during each two-week period between sampling visits, cumulative air pollutant exposure in unfiltered environments was associated with increased sCD62P for O3, increased FeNO for PM2.5, and increased EBC MDA and decreased subendocardial viability ratio (SEVR, a marker of myocardial oxygen supply and demand) for SO2. This study suggests that ESP use may result in O3-associated adverse health effects, biomarkers traditionally associated with PM exposure may not show a response weeks into an intervention, and time spent in environments filtered by particulate air filters, though perhaps not ESPs, should be maximized to avoid the health effects of cumulative high exposures in unfiltered locations.These O3 associations with platelet activation and blood pressure are consistent with related results in some studies but not others, and so I hypothesized that age and sex may influence each individual’s response to O3 and account for some of this variability. I tested this hypothesis by assessing pollutant exposure by age or by sex interaction term estimates in association with biomarker outcomes in the GRR models. This statistical analysis was applied not only to the main study conducted in Changsha, but also to a subsequent study conducted in Shanghai with similar exposure and biomarker measurements that had younger study participants with more balanced sex ratio. In addition, the exposure and biomarker data between these two studies were pooled for an additional analysis checking the results from the individual study findings. In the main Changsha Study, significant age by pollutant exposure interaction terms were observed for the associations between 24-hour and 2-week O3 and sCD62P, 2-week O3 and SBP, and 2-week SO2 and PWV. In addition, the association between PWV and 2-week SO2 was significantly higher in men, and the association between PWV and 24h O3 was significantly higher in women, though the latter interaction term became nonsignificant in a sensitivity analysis assessing the independent interaction effect. No interaction terms were significant in the Shanghai Study analysis. In the pooled analysis, the 24-hour O3 exposure by age interaction term was significant for both sCD62P and SBP. Also, the pooled analysis showed that women had a significantly higher association between 24-hour O3 exposure and PWV as had been seen in the Changsha Study, but as in that case this association was not robust to the sensitivity analyses. These results indicate that older individuals are more susceptible to O3-associated effects on platelet activation and blood pressure, which is supported by literature examining age-associated changes in platelets and vascular tone.Taken together these results and the findings in previous research examining cardiovascular pathophysiologic mechanisms, a coherent, plausible mechanistic pathway emerges. In this pathway, O3-associated reaction products in the airway lead to the propagation of signals that activate platelets, which in turn enhance blood pressure and induce a procoagulant state. The findings of this dissertation contribute to the mechanistic understanding of how O3 exposure affects cardiovascular health outcomes.</p
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Panel Study in Beijing: The Effects of PM2.5 in Pre-diabetic Populations
No full textBackground - Multiple research studies have demonstrated consistent associations between particulate matter smaller than 2.5 µm in diameter (PM2.5) and relevant health endpoints of Type 2 Diabetes Mellitus (T2DM) and metabolic syndrome (MS). Patients with pre-diabetes symptoms constitute a significant population who not only have the risk of progressing to diabetes but also are susceptible to metabolic syndrome. Evidence suggests that response to acute PM2.5 exposure could be assessed by monitoring metabolic clinical indices.Method – This Beijing panel study had a total of 114 subjects divided equally into two groups: pre-diabetic and healthy groups. Inter-group differences in clinical indices (blood pressure, fasting blood glucose) responding to pre-24 hours PM2.5 exposure were assessed using mixed-effects linear regression models.Results – With a limited sample size and partial data available to the current analysis, this study reveals no significant association of PM2.5 with fasting blood glucose or blood pressure in both healthy and pre-diabetic populations.Conclusions – Our data did not provide evidence that PM2.5 exposure has significant association with blood pressure or fasting blood glucose. Moreover, no significant response differences were observed existed between the pre-diabetic population and the healthy population.</p
The Health Impact of Indoor Air Filtration in Healthy Adults and Asthmatic Children
No full textThe World Health Organization (WHO) estimated that 92% of the world’s population lived in areas with outdoor air pollution levels exceeding the WHO guidelines in 2014. Although the ultimate solution is to control emission sources, exposure reduction strategies at the individual level can address more immediate needs. As people typically spend approximately 80% of their time indoors, improvement of indoor air quality, such as using air filtration technologies, may lead to reduced total exposure. However, evidence is limited to support the effectiveness of air filtration in bringing beneficial health effects to the users. The goal of this dissertation research is to evaluate the health impact of indoor air filtration in healthy adults and asthmatic children using two randomized, double-blind, crossover trials (Aim 1 and Aim 2). Utilizing data from these two trials and other data, this dissertation also addresses two methodological questions. Aim 3 examines the relationship between free and total malondialdehyde, a biomarker of oxidative stress commonly used in air pollution research, in various types of human specimens. Aim 4 evaluates the relationship between the subjective evaluation of asthma control by childhood asthma control test (C-ACT) and objective indicators of lung pathophysiology using longitudinal measurements.In Aim 1 of this dissertation, a double-blinded, randomized, crossover study was conducted to examine the cardiorespiratory health effect of a sporadic, overnight use of indoor air filtration. Seventy healthy non-smoking adults were recruited from the medical and nursing students who were living in the same dormitory building in a suburb of Shanghai, China. The participants were aged 19 to 26 years old and included 41 (59%) females. Each participant received a true and a sham indoor air filtration session in a randomized sequence. Participants and research staff that performed health assessments were blinded to this sequence until the end of the study. Each filtration session was approximately 13 hours long. True and sham filtration sessions were separated by a two-week “washout” interval. During the study period, outdoor PM2.5 concentrations ranged from 18.6 to 106.9 µg/m3, which overlapped with levels measured in Western Europe and North America. Compared to sham filtration, true filtration on average decreased indoor PM2.5 concentration by 72.4% to 10.0 µg/m3 and particle number concentration by 59.2% to 2316/cm3. For lung function measured immediately after the end of filtration, true filtration significantly lowered airway impedance at 5 Hz (Z5) by 7.1% [95% CI: 2.4%, 11.9%], airway resistance at 5 Hz (R5) by 7.4% [95% CI: 2.4%, 12.5%], and small airway resistance (R5-R20) by 20.3% [95% CI: 0.1%, 40.5%], reflecting improved airway mechanics especially for the small airways. However, no significant improvements for spirometric indicators of lung function (FEV1, FVC) were observed. True filtration also significantly lowered von Willebrand factor (VWF) by 26.9% [95% CI: 7.3%, 46.4%] 24 hours after the end of filtration, indicating reduced risk for thrombosis. Stratified analysis in male and female participants showed that true filtration significantly decreased pulse pressure by 3.3% [95% CI: 0.8%, 7.4%] in females, and significantly reduced VWF by 42.4% [95% CI: 17.4%, 67.4%] and interleukin-6 by 22.6% [95% CI: 0.4%, 44.9%] in males. Effect modification analyses indicated that filtration effects in male and female participants were not significantly different. These findings suggest that a single overnight residential air filtration, capable of reducing indoor particle concentrations substantially, can lead to improved airway mechanics and reduced thrombosis risk.Air pollution exposure is a well-established risk factor for asthma exacerbation. In individuals with asthma, indoor air filtration has only been evaluated for allergen removal in areas with low outdoor levels of PM2.5. As asthmatic individuals may be responsive to short-term changes in air pollution levels, it is not clear whether the exposures occurring outside the home environment can override the potential health benefits of residential indoor air filtration. In Aim 2 of this dissertation, I investigated the respiratory impact of residential indoor air filtration in asthmatic children living with moderate levels of outdoor PM2.5. This double-blind, randomized crossover trial recruited 43 participants (40% females) aged 5 to 13 with mild or moderate asthma. From February to April 2017, each participant used a true filtration device and a sham filtration device, respectively in their bedrooms for two weeks. A two-week washout period separated the two sessions. During the study, the average PM2.5 concentrations for outdoor, indoor with sham filtration, and indoor with true filtration were 56.5 µg/m3, 34.1µg/m3, and 14.8 µg/m3, respectively. Compared to sham filtration, on average, true filtration reduced indoor PM2.5 concentrations by 53.3%. Concomitantly, true filtration significantly decreased fractional exhaled oxide (FeNO) by 5.1 [95% CI: 0.5, 9.6] ppb, airway impedance at 5Hz (Z5) by 14.7% [3.7%, 25.8%], respiratory resistance at 5Hz (R5) by 22.4% [9.6%, 35.2%], and small airway resistance (R5-R20) by 40.6% [10.2,% 70.9%]. Peak expiratory flow (PEF) measurements were made twice daily throughout each two-week intervention session. PEF values during true filtration were 1.5% [0.7%, 2.4%] higher than the measurements during sham filtration. True filtration also introduced a non-significant increase on FEF25-75 by 5.80% [-4.09%, 15.68%]. Stratified analyses show that the participants with blood eosinophil count ≤ 500/mm3, compared to those with blood eosinophil count > 500/mm3, had a 24.3% greater increase of FEF25-75 by true filtration; and that the participants allergic to dust mite had smaller improvements in small airway resistance (R5 and R5-R20). These findings suggest that a two-week long intervention of indoor air filtration, capable of significantly reducing indoor PM2.5 concentrations, can lead to reduced respiratory inflammation, improved lung function (PEF) and airway mechanics in asthmatic children.Oxidative stress is a core mechanism involved in the cardiorespiratory effects of air pollution. Malondialdehyde (MDA) is a well-established marker of oxidative stress. However, most of its use in existing studies were conducted by researchers in clinical medicine and epidemiology, who were unaware that MDA is present in both unconjugated and conjugated forms. Aim 3 of this dissertation examined the relationship between free MDA (unconjugated MDA) and total MDA (the sum of both unconjugated and conjugated MDA) in various types of human biospecimens. Using bio-banked samples from multiple studies, free MDA and total MDA were measured simultaneously in nasal fluid (N=158), saliva (N=158), exhaled breath condensate (N=40), serum (N=232), and urine samples (N=429). MDA quantification was performed using an HPLC-fluorescence method with high sensitivity and specificity. Due to the right-skewed distribution of free MDA and total MDA, natural-log transformation was performed before subsequent statistical analyses. The relationship between the natural log of free and total MDA was evaluated by R2 of simple linear regression. T-test was used for comparisons of means between two groups. One-way analysis of variance was used in combination with Tukey’s test to compare the natural log of the ratio of free MDA to total MDA across various types of biospecimens. For exhaled breath condensate, serum, urine, nasal fluid and saliva samples, the R2 between free and total MDA were 0.61, 0.22, 0.59, 0.47 and 0.06, respectively; the medians of the free MDA to total MDA ratio were 48.1%, 17.4%, 9.8%, 5.1% and 3.0%, respectively. The free MDA to total MDA ratio in EBC > serum > urine > nasal fluid > saliva (PThe Childhood Asthma Control Test (C-ACT) is a validated questionnaire that provides a subjective evaluation of asthma control using collective inputs from children and their caregivers. Cross-sectional studies have identified cut-points for discerning different degrees of asthma control. However, few studies have examined whether changes in the C-ACT score are reflective of changes in airway pathophysiology in longitudinal measurements from the same individuals. In Aim 4 of this dissertation, I utilized data from four clinical visits originally conducted for Aim 2. The clinical visits were scheduled bi-weekly over a period of six weeks. Thirty-seven children aged 5 to 10 with mild or moderate asthma (43% female) took the C-ACT. The scores were 24.4 ± 2.4 (mean ± standard deviation) and ranged from 16 to 27. Linear mixed-effects models were used to examine the association between C-ACT and clinical measurements from the same participants. As a change of two points in the C-ACT score is considered as the minimal clinically important difference, I reported the change in biomarkers associated with a two-point decrease in C-ACT score. Results showed that a two-point decrease was significantly associated with a 1.7% [95% CI: 0.1%, 3.3%] decrease in FEV1, a 1.6% [0.5%, 2.8%] decrease in FVC, and a 3.8% [0.0%, 7.6%] increase in airway resistance at 5 Hz (R5). For PEF measurements conducted within two weeks before the C-ACT, a two-point decrease in C-ACT score was significantly associated with a 17.3% [95%CI: 6.8%, 27.8%] increase in the coefficient of variation, while no significant association was observed with the average PEF value (P=0.12). In contrast, within-participant measurements showed no significant associations of C-ACT with respiratory inflammation (FeNO) or any of the small airway function and mechanics parameters (FEF25-75, FEF25-75, R5-R20, X5, and Fres). When examining individual questions of the C-ACT, none of the questions answered by the caregiver were significantly associated with indicators of lung function and respiratory inflammation. In contrast, three out of the four questions answered by the child demonstrated significant or marginally significant associations with FEV1, FVC, FEF25-75, R5, and R20. This suggests that in spite of the relatively young age of the participants, their perception of disease control provides important information for asthma control assessment. Overall, the findings in Aim 4 indicate that subjective evaluation of asthma control using the C-ACT was associated with objective measurements of airway obstruction, airway restriction, respiratory resistance and the variation of airflow limitations in longitudinal measurements. However, the C-ACT is not reflective of changes in respiratory inflammation and small airway mechanics, indicating that its use should be complementary to but not a substitute for these measurements.</p
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