Pore structures are one of the most important factors affecting the hydro-mechanical properties of the reservoirs. Unlike the homogeneous pore structures in sandstones, the pores in the shale formations are heterogeneous and more complex to characterize due to the diagenesis and geological processes that they experienced. The heterogeneous rock pore structures can influence not only the flow properties of the oil and gas but also the fracture initiation and propagation characteristics which can impact the hydraulic fracturing performance, a common technique to increase the total production in tight shale formations. Therefore, quantifying the heterogeneities of the pore structures in unconventional shale formations carries a great importance. In this paper, we collected the samples from Bakken formation, which is a typical unconventional oil shale reservoir in North America. We applied image analysis method to study the pore structures. After segmentation of these images, we determined the representative elementary area (REA) of the samples based on the relationships between porosity and magnification ratios. Multifractal theory and lacunarity methods were applied to analyze the pore structures. Multifractal parameters were used to describe the pore probability distributions and the lacunarity value was applied to quantify the heterogeneity of the pores. The impact of the mineral compositions on heterogeneity values is also discussed. Finally, a new REA indicator, which contains the porosity and heterogeneity information, was proposed.
Isocyanic acid (HNCO) is a known toxic species and yet the relative importance of primary and secondary sources to regional HNCO and population exposure remains unclear. Off-road diesel fuel combustion has previously been suggested to be an important regional source of HNCO, which implies that major industrial facilities such as the oil sands (OS), which consume large quantities of diesel fuel, can be sources of HNCO. The OS emissions of nontraditional toxic species such as HNCO have not been assessed. Here, airborne measurements of HNCO were used to estimate primary and secondary HNCO for the oil sands. Approximately 6.2 +/- 1.1 kg hr(-1) was emitted from off-road diesel activities within oil sands facilities, and an additional 116-186 kg hr(-1) formed from the photochemical oxidation of diesel exhaust. Together, the primary and secondary HNCO from OS operations represent a significant anthropogenic HNCO source in Canada. The secondary HNCO downwind of the OS was enhanced by up to a factor of 20 relative to its primary emission, an enhancement factor significantly greater than previously estimated from laboratory studies. Incorporating HNCO emissions and formation into a regional model demonstrated that the HNCO levels in Fort McMurray (similar to 10-70 km downwind of the OS) are controlled by OS emissions; > 50% of the monthly mean HNCO arose from the OS. While the mean HNCO levels in Fort McMurray are predicted to be below the 1000 pptv level associated with potential negative health impacts, (similar to 25 pptv in August-September), an order of magnitude increase in concentration is predicted (250600 pptv) when the town is directly impacted by OS plumes. The results here highlight the importance of obtaining at-source HNCO emission factors and advancing the understanding of secondary HNCO formation mechanisms, to assess and improve HNCO population exposure predictions.
A comprehensive field campaign was carried out in summer 2014 in Wangdu, located in the North China Plain. A month of continuous OH, HO2 and RO2 measurements was achieved. Observations of radicals by the laser-induced fluorescence (LIF) technique revealed daily maximum concentrations between (5-15) x 10(6) cm(-3), (3-14) x 10(8) cm(-3) and (3-15) x 10(8) cm 3 for OH, HO2 and RO2, respectively. Measured OH reactivities (inverse OH lifetime) were 10 to 20 s(-1) during daytime. The chemical box model RACM 2, including the Leuven isoprene mechanism (LIM), was used to interpret the observed radical concentrations. As in previous field campaigns in China, modeled and measured OH concentrations agree for NO mixing ratios higher than 1 ppbv, but systematic discrepancies are observed in the afternoon for NO mixing ratios of less than 300 pptv (the model-measurement ratio is between 1.4 and 2 in this case). If additional OH recycling equivalent to 100 pptv NO is assumed, the model is capable of reproducing the observed OH, HO2 and RO2 concentrations for conditions of high volatile organic compound (VOC) and low NOx concentrations. For HO2, good agreement is found between modeled and observed concentrations during day and night. In the case of RO2, the agreement between model calculations and measurements is good in the late afternoon when NO concentrations are below 0.3 ppbv. A significant model underprediction of RO2 by a factor of 3 to 5 is found in the morning at NO concentrations higher than 1 ppbv, which can be explained by a missing RO2 source of 2 ppbvh(-1). As a consequence, the model underpredicts the photochemical net ozone production by 20 ppbv per day, which is a significant portion of the daily integrated ozone production (110 ppbv) derived from the measured HO2 and RO2. The additional RO2 production from the photolysis of ClNO2 and missing reactivity can explain about 10% and 20% of the discrepancy, respectively. The underprediction of the photochemical ozone production at high NOx found in this study is consistent with the results from other field campaigns in urban environments, which underlines the need for better understanding of the peroxy radical chemistry for high NOx conditions.
A comprehensive field campaign was carried out in summer 2014 in Wangdu, located in the North China Plain. A month of continuous OH, HO2 and RO2 measurements was achieved. Observations of radicals by the laser-induced fluorescence (LIF) technique revealed daily maximum concentrations between (5-15) x 10(6) cm(-3), (3-14) x 10(8) cm(-3) and (3-15) x 10(8) cm 3 for OH, HO2 and RO2, respectively. Measured OH reactivities (inverse OH lifetime) were 10 to 20 s(-1) during daytime. The chemical box model RACM 2, including the Leuven isoprene mechanism (LIM), was used to interpret the observed radical concentrations. As in previous field campaigns in China, modeled and measured OH concentrations agree for NO mixing ratios higher than 1 ppbv, but systematic discrepancies are observed in the afternoon for NO mixing ratios of less than 300 pptv (the model-measurement ratio is between 1.4 and 2 in this case). If additional OH recycling equivalent to 100 pptv NO is assumed, the model is capable of reproducing the observed OH, HO2 and RO2 concentrations for conditions of high volatile organic compound (VOC) and low NOx concentrations. For HO2, good agreement is found between modeled and observed concentrations during day and night. In the case of RO2, the agreement between model calculations and measurements is good in the late afternoon when NO concentrations are below 0.3 ppbv. A significant model underprediction of RO2 by a factor of 3 to 5 is found in the morning at NO concentrations higher than 1 ppbv, which can be explained by a missing RO2 source of 2 ppbvh(-1). As a consequence, the model underpredicts the photochemical net ozone production by 20 ppbv per day, which is a significant portion of the daily integrated ozone production (110 ppbv) derived from the measured HO2 and RO2. The additional RO2 production from the photolysis of ClNO2 and missing reactivity can explain about 10% and 20% of the discrepancy, respectively. The underprediction of the photochemical ozone production at high NOx found in this study is consistent with the results from other field campaigns in urban environments, which underlines the need for better understanding of the peroxy radical chemistry for high NOx conditions.
Objective: To estimate the current prevalence, temporal incidence trends, and contribution of risk factors for stroke in China.Methods: The China National Stroke Screening Survey (CNSSS) is an ongoing nationwide population-based program. A representative sample of 1,292,010 adults over 40 years old with 31,188 identified stroke cases from the 2013 and 2014 CNSSS database was analyzed to provide descriptive statistics of the prevalence and risk factors for stroke in 2014. In addition, a retrospective evaluation of 12,526 first-ever stroke cases in 2002-2013 and stroke mortality data from the 2002-2013 China Public Health Statistical Yearbook was conducted to estimate the incidence rates.Results: In 2014, the adjusted stroke prevalence was 2.06% in adults aged 40 years and older. After full adjustments, all risk factors assessed showed significant associations with stroke (p < 0.01); the largest contributor was hypertension (population-attributable risk 53.2%), followed by family history, dyslipidemia, atrial fibrillation, diabetes, physical inactivity, smoking, and overweight/ obesity. The incidence of first-ever stroke in adults aged 40-74 years increased from 189/100,000 individuals in 2002 to 379/100,000 in 2013-an overall annual increase of 8.3%. Stroke-specific mortality in adults aged 40-74 years has remained stable, at approximately 124 deaths/100,000 individuals in both 2002 and 2013.Conclusions: In 2002-2013, the incidence of stroke in China increased rapidly. Combined with a high prevalence, a trend toward a younger age, and stable mortality, this finding suggests that additional clinical and behavioral interventions for metabolic and lifestyle risk factors are necessary to prevent stroke, particularly in certain populations.
Recurrent tuberculosis is an important indicator of the effectiveness of tuberculosis control and can occur by relapse or exogenous reinfection. We conducted a retrospective cohort study on all bacteriologically confirmed tuberculosis cases that were successfully treated between 2000 and 2012 in Shanghai, an urban area with a high number but a low prevalence rate of tuberculosis cases and a low prevalence of HIV infection. Genotyping the Mycobacterium tuberculosis from clinical isolates was used to distinguish between relapse and reinfection. In total, 5.3% (710/13,417) of successfully treated cases had a recurrence, a rate of 7.55 (95% CI 7.01-8.13) episodes per 1000 person-years, more than 18 times the rate of tuberculosis in the general population. Patients who were male, age 30-59, retreatment cases, had cavitation, diabetes, drug-resistant or multidrug-resistant tuberculosis in their initial episode of tuberculosis, were at high risk for a recurrence. Among 141 recurrent cases that had paired isolates, 59 (41.8%) had different genotypes, indicating reinfection with a different strain. Patients who completed treatment were still at high risk of another episode of tuberculosis and exogenous reinfection contributed a significant proportion of the recurrent tuberculosis cases. Targeted control strategies are needed to prevent new tuberculosis infections in this setting.
Silica aerogel, with mesoporous structure and high hydrophobicity, is a promising adsorbent for oil spill clean-up. To make it economic and environmental-friendly, hydrocarbon desorption and silica aerogel regeneration were investigated. After hydrocarbon desorption at 80°C, silica aerogel maintained its hydrophobicity. After toluene, petrol, and diesel desorption, shrinkage of mesopores (from 19.9 to 16.8, 13.5, and 13.4nm) of silica aerogels occurred, causing decreased adsorption capacities (from 12.4, 11.2, and 13.6 to 12.0, 6.5, and 2.3g/g). Low surface tension of petrol caused high stress on mesopores during its desorption, resulting in significant pore shrinkage. For diesel, its incomplete desorption and oxidation further hindered the regeneration. Therefore, diesel desorption was also conducted at 200°C. Severe diesel oxidation occurred under aerobic condition and destroyed the mesopores. Under anaerobic condition, no diesel oxidation occurred and the decreases in pore size (to 13.2nm) and adsorption efficiency (to 10.0g/g) of regenerated silica aerogels were much less, compared with under aerobic condition. This study provided new insights on silica aerogel regeneration for oil spill clean-up.
In the recent Intergovernmental Panel on Climate Change assessment, multimodel ensembles (arithmetic model averaging, AMA) were constructed with equal weights given to Earth system models, without considering the performance of each model at reproducing current conditions. Here we use Bayesian model averaging (BMA) to construct a weighted model ensemble for runoff projections. Higher weights are given to models with better performance in estimating historical decadal mean runoff. Using the BMA method, we find that by the end of this century, the increase of global runoff (9.81.5%) under Representative Concentration Pathway 8.5 is significantly lower than estimated from AMA (12.21.3%). BMA presents a less severe runoff increase than AMA at northern high latitudes and a more severe decrease in Amazonia. Runoff decrease in Amazonia is stronger than the intermodel difference. The intermodel difference in runoff changes is mainly caused not only by precipitation differences among models, but also by evapotranspiration differences at the high northern latitudes.
The fundamental problems inherent in relativistic explicit correlation are highlighted, with practical suggestions for guiding future development of relativistic explicitly correlated wave function methods.
Particulate organonitrates are formed from volatile organic compounds (VOCs) oxidation by radicals. A portion of semi-volatile gas-phase organonitrates can be incorporate into aerosol by oxidation reactions or portioning, and has been an important component of secondary organic aerosol (SOA). Particulate organonitrates study has become one of the important aspects of atmospheric chemistry. Given the large number and variability of chemical constituents, and possible chemical transformations of organonitrates, such characterization presents a key problem for research. Based on recent research progress on particulate organonitrates, this paper summarizes the formation mechanism and quantification method of particulate organonitrates. Profiting from the application of high time resolution techniques, field measurements has become the major approach of particulate organonitrates study. Thermal dissociation-laser induced fluorescence (TD-LIF) and aerosol mass spectrometers (AMS) have been used to quantify and provide the evolution processes of particulate organonirates. Meanwhile, chemical ionization mass spectrometer(CIMS)allows for the determination of molecular ion composition of organonitrates, promising to become the important direction of study of particulate organonirates in future field measurements. To have a deep insight on precursor and atmospheric chemistry processes of particulate organonirates, future research should focus on the combination of field measurement, modeling simulation and laboratory simulation, and these will also lead to a more comprehensive understanding of formation mechanism of particulate organonirates