bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nitrate-driven urban haze pollution during summertime over the North China Plain
Authors: Li Haiyan , Zhang Qiang , Zheng Bo , Chen Chunrong , Wu Nana , Guo Hongyu , Zhang Yuxuan , Zheng Yixuan , Li Xin , He Kebin 
Published: April 2018

Abstract. Compared to the severe winter haze episodes in the North China Plain (NCP),
haze pollution during summertime has drawn little public attention. In this
study, we present the highly time-resolved chemical composition of submicron
particles (PM1) measured in Beijing and Xinxiang in the NCP region
during summertime to evaluate the driving factors of aerosol pollution.
During the campaign periods (30 June to 27 July 2015, for Beijing and 8 to
25 June 2017, for Xinxiang), the average PM1 concentrations were 35.0
and 64.2 µg m−3 in Beijing and Xinxiang. Pollution episodes
characterized with largely enhanced nitrate concentrations were observed at
both sites. In contrast to the slightly decreased mass fractions of sulfate,
semivolatile oxygenated organic aerosol (SV-OOA), and low-volatility
oxygenated organic aerosol (LV-OOA) in PM1, nitrate displayed a
significantly enhanced contribution with the aggravation of aerosol
pollution, highlighting the importance of nitrate formation as the driving
force of haze evolution in summer. Rapid nitrate production mainly occurred
after midnight, with a higher formation rate than that of sulfate, SV-OOA, or
LV-OOA. Based on observation measurements and thermodynamic modeling, high
ammonia emissions in the NCP region favored the high nitrate production in
summer. Nighttime nitrate formation through heterogeneous hydrolysis of
dinitrogen pentoxide (N2O5) enhanced with the development of haze
pollution. In addition, air masses from surrounding polluted areas during
haze episodes led to more nitrate production. Finally, atmospheric
particulate nitrate data acquired by mass spectrometric techniques from
various field campaigns in Asia, Europe, and North America uncovered a higher
concentration and higher fraction of nitrate present in China. Although
measurements in Beijing during different years demonstrate a decline in the
nitrate concentration in recent years, the nitrate contribution in PM1
still remains high. To effectively alleviate particulate matter pollution in
summer, our results suggest an urgent need to initiate ammonia emission
control measures and further reduce nitrogen oxide emissions over the NCP
region.
Spatial distribution analysis of the OMI aerosol layer height: a pixel-by-pixel comparison to CALIOP observations
Authors: Chimot Julien , Veefkind J. Pepijn , Vlemmix Tim , Levelt Pieternel F. 
Published: April 2018

Abstract. A global picture of atmospheric aerosol vertical distribution with a high temporal resolution is of key importance not only for
climate, cloud formation, and air quality research studies but also for correcting scattered radiation induced by aerosols in
absorbing trace gas retrievals from passive satellite sensors. Aerosol layer height (ALH) was retrieved from the OMI 477 nm
O2−O2 band and its spatial pattern evaluated over selected cloud-free scenes. Such retrievals benefit from a synergy with
MODIS data to provide complementary information on aerosols and cloudy pixels. We used a neural network approach previously trained
and developed. Comparison with CALIOP aerosol level 2 products over urban and industrial pollution in eastern China shows consistent
spatial patterns with an uncertainty in the range of 462–648 m. In addition, we show the possibility to determine the height
of thick aerosol layers released by intensive biomass burning events in South America and Russia from OMI visible
measurements. A Saharan dust outbreak over sea is finally discussed. Complementary detailed analyses show that the assumed aerosol
properties in the forward modelling are the key factors affecting the accuracy of the results, together with potential cloud
residuals in the observation pixels. Furthermore, we demonstrate that the physical meaning of the retrieved ALH scalar corresponds to
the weighted average of the vertical aerosol extinction profile. These encouraging findings strongly suggest the potential of the OMI
ALH product, and in more general the use of the 477 nm O2−O2 band from present and future similar satellite
sensors, for climate studies as well as for future aerosol correction in air quality trace gas retrievals.
Natural ocean acidification at Papagayo upwelling system (north Pacific Costa Rica): implications for reef development
Authors: Sánchez-Noguera Celeste , Stuhldreier Ines , Cortés Jorge , Jiménez Carlos , Morales Álvaro , Wild Christian , Rixen Tim 
Published: April 2018

Abstract. Numerous experiments have shown that ocean acidification impedes coral calcification, but knowledge about in situ reef ecosystem response to ocean acidification is still scarce. Bahía Culebra, situated at the northern Pacific coast of Costa Rica, is a location naturally exposed to acidic conditions due to the Papagayo seasonal upwelling. We measured pH and pCO2 in situ during two non-upwelling seasons (June 2012, May–June 2013), with a high temporal resolution of every 15 and 30 min, respectively, using two Submersible Autonomous Moored Instruments (SAMI-pH, SAMI-CO2). These results were compared with published data from the 2009 upwelling season. Findings revealed that the carbonate system in Bahía Culebra shows a high temporal variability. Incoming offshore waters drive intra- and interseasonal changes. Lowest pH (7.8) and highest pCO2 (658.3 µatm) values measured during a cold-water intrusion event in the non-upwelling season were similar to those minimum values reported from upwelling season (pH  =  7.8, pCO2  =  643.5 µatm), unveiling that natural acidification also occurs sporadically in the non-upwelling season. This affects the interaction of photosynthesis, respiration, calcification and carbonate dissolution and the resulting diel cycle of pH and pCO2 in the reefs of Bahía Culebra. During the non-upwelling season, the aragonite saturation state (Ωa) rises to values of  >  3.3 and during the upwelling season falls below 2.5. The Ωa threshold values for coral growth were derived from the correlation between measured Ωa and coral linear extension rates which were obtained from the literature and suggest that future ocean acidification will threaten the continued growth of reefs in Bahía Culebra. These data contribute to building a better understanding of the carbonate system dynamics and coral reefs' key response (e.g., coral growth) to natural low-pH conditions, in upwelling areas in the eastern tropical Pacific and beyond.
Interannual drivers of the seasonal cycle of CO2 in the Southern Ocean
Authors: Gregor Luke , Kok Schalk , Monteiro Pedro M. S. 
Published: April 2018

Abstract. Resolving and understanding the drivers of variability of CO2 in the Southern Ocean and its potential climate feedback is one of the major scientific challenges of the ocean-climate community. Here we use a regional approach on empirical estimates of pCO2 to understand the role that seasonal variability has in long-term CO2 changes in the Southern Ocean. Machine learning has become the preferred empirical modelling tool to interpolate time- and location-restricted ship measurements of pCO2. In this study we use an ensemble of three machine-learning products: support vector regression (SVR) and random forest regression (RFR) from Gregor et al. (2017), and the self-organising-map feed-forward neural network (SOM-FFN) method from Landschützer et al. (2016). The interpolated estimates of ΔpCO2 are separated into nine regions in the Southern Ocean defined by basin (Indian, Pacific, and Atlantic) and biomes (as defined by Fay and McKinley, 2014a). The regional approach shows that, while there is good agreement in the overall trend of the products, there are periods and regions where the confidence in estimated ΔpCO2 is low due to disagreement between the products. The regional breakdown of the data highlighted the seasonal decoupling of the modes for summer and winter interannual variability. Winter interannual variability had a longer mode of variability compared to summer, which varied on a 4–6-year timescale. We separate the analysis of the ΔpCO2 and its drivers into summer and winter. We find that understanding the variability of ΔpCO2 and its drivers on shorter timescales is critical to resolving the long-term variability of ΔpCO2. Results show that ΔpCO2 is rarely driven by thermodynamics during winter, but rather by mixing and stratification due to the stronger correlation of ΔpCO2 variability with mixed layer depth. Summer pCO2 variability is consistent with chlorophyll a variability, where higher concentrations of chlorophyll a correspond with lower pCO2 concentrations. In regions of low chlorophyll a concentrations, wind stress and sea surface temperature emerged as stronger drivers of ΔpCO2. In summary we propose that sub-decadal variability is explained by summer drivers, while winter variability contributes to the long-term changes associated with the SAM. This approach is a useful framework to assess the drivers of ΔpCO2 but would greatly benefit from improved estimates of ΔpCO2 and a longer time series.
Continuous state-space representation of a bucket-type rainfall-runoff model: a case study with the GR4 model using state-space GR4 (version 1.0)
Authors: Santos Léonard , Thirel Guillaume , Perrin Charles 
Published: April 2018

Abstract. In many conceptual rainfall–runoff models, the water balance
differential equations are not explicitly formulated. These differential
equations are solved sequentially by splitting the equations into terms that
can be solved analytically with a technique called “operator splitting”. As
a result, only the solutions of the split equations are used to present the
different models. This article provides a methodology to make the governing
water balance equations of a bucket-type rainfall–runoff model explicit and
to solve them continuously. This is done by setting up a comprehensive
state-space representation of the model. By representing it in this way, the
operator splitting, which makes the structural analysis of the model more
complex, could be removed. In this state-space representation, the lag
functions (unit hydrographs), which are frequent in rainfall–runoff models
and make the resolution of the representation difficult, are first replaced
by a so-called “Nash cascade” and then solved with a robust numerical
integration technique. To illustrate this methodology, the GR4J model is
taken as an example. The substitution of the unit hydrographs with a Nash
cascade, even if it modifies the model behaviour when solved using operator
splitting, does not modify it when the state-space representation is solved
using an implicit integration technique. Indeed, the flow time series
simulated by the new representation of the model are very similar to those
simulated by the classic model. The use of a robust numerical technique that
approximates a continuous-time model also improves the lag parameter
consistency across time steps and provides a more time-consistent model with
time-independent parameters.
Next‐generation lineage discovery: A case study of tuberous Claytonia L.
Authors: Stoughton Thomas R. , Kriebel Ricardo , Jolles Diana D. , O'Quinn Robin L. 
Published: April 2018

Premise of the StudySpecies formation is an intuitive endpoint of reproductive isolation, but circumscribing taxa that arise during speciation can be difficult because of gene flow, morphological continuity, hybridization or polyploidization, and low sequence variation among newly diverged lineages. Nonetheless, species complexes are ubiquitous, and their classification is essential for understanding how diversity influences ecosystem function.MethodsWe used modern sequencing technology to identify lineages of perennial Claytonia L. and assessed correspondence between genetic lineages and morphological/ecological variation. Subsets of 18 taxa from 63 populations were used for (a) lineage discovery using network and coalescent analyses, (b) leaf shape analyses using elliptical Fourier analysis and ordination, and (c) ecological analyses (soil chemistry, climate) using ANOVA and ordination.Key ResultsSamples mainly aggregated into groups representing each of the previously recognized species in each of the genetic data sets. Compared to the double‐digest restriction‐site‐associated DNA sequencing data set, genome skimming data provided more resolution and further opportunity to probe into patterns of nuclear and chloroplast genome diversity. Morphological and ecological associations are significantly different (albeit intergrading) among the taxa investigated. A new species, Claytonia crawfordii, is described based on morphological data presented here.ConclusionsGenetic data presented in this study provide some of the first insights into phylogenetic relationships among recently diverged perennial Claytonia and are suggestive of past hybridization among caudicose and tuberous species. Given prior difficulties in understanding species boundaries among newly diverged plant lineages, this case study demonstrates the revolutionary breakthrough for systematics research that high throughput sequencing represents.
The Functionality of Surface Hydroxy Groups on the Selectivity and Activity of Carbon Dioxide Reduction over Cuprous Oxide in Aqueous Solutions
Authors: Yang Piaoping , Zhao Zhi‐Jian , Chang Xiaoxia , Mu Rentao , Zha Shenjun , Zhang Gong , Gong Jinlong 
Published: April 2018

AbstractCarbon dioxide (CO2) reduction in aqueous solutions is an attractive strategy for carbon capture and utilization. Cuprous oxide (Cu2O) is a promising catalyst for CO2 reduction as it can convert CO2 into valuable hydrocarbons and suppress the side hydrogen evolution reaction (HER). However, the nature of the active sites in Cu2O remains under debate because of the complex surface structure of Cu2O under reducing conditions, leading to limited guidance in designing improved Cu2O catalysts. This paper describes the functionality of surface‐bonded hydroxy groups on partially reduced Cu2O(111) for the CO2 reduction reaction (CO2RR) by combined density functional theory (DFT) calculations and experimental studies. We find that the surface hydroxy groups play a crucial role in the CO2RR and HER, and a moderate coverage of hydroxy groups is optimal for promotion of the CO2RR and suppression of the HER simultaneously. Electronic structure analysis indicates that the charge transfer from hydroxy groups to coordination‐unsaturated Cu (CuCUS) sites stabilizes surface‐adsorbed COOH*, which is a key intermediate during the CO2RR. Moreover, the CO2RR was evaluated over Cu2O octahedral catalysts with {111} facets and different surface coverages of hydroxy groups, which demonstrates that Cu2O octahedra with moderate coverage of hydroxy groups can indeed enhance the CO2RR and suppress the HER.
Acid‐Induced Shift of Intramolecular Hydrogen Bonding Responsible for Excited‐State Intramolecular Proton Transfer
Authors: Wang Qin , Niu Yahui , Wang Rong , Wu Haoran , Zhang Yanrong 
Published: April 2018

AbstractThe significant progress recently achieved in designing smart acid‐responsive materials based on intramolecular charge transfer inspired us to utilize excited‐state intramolecular proton transfer (ESIPT) for developing a turn‐on acid‐responsive fluorescent system with an exceedingly large Stokes shift. Two ESIPT‐active fluorophores, 2‐(2‐hydroxyphenyl)pyridine (HPP) and 2‐(2‐hydroxyphenyl)benzothiazole (HBT), were fused into a novel dye (HBT‐HPP) fluorescent only in the protonated state. Moreover, we also synthesized three structurally relevant control compounds to compare their steady‐state fluorescence spectra and optimized geometric structures in neutral and acidic media. The results suggest that the fluorescence turn‐on was caused by the acid‐induced shift of the ESIPT‐responsible intramolecular hydrogen bond from the HPP to HBT moiety. This work presents a systematic comparison of the emission efficiencies and basicity of HBT and HPP for the first time, thereby utilizing their differences to construct an acid‐responsive smart organic fluorescent material. As a practical application, red fluorescent letters can be written using the acid as an ink on polymer film.
Robust Wind Speed Estimation and Control of Variable Speed Wind Turbines
Authors: Barambones Oscar 
Published: April 2018

AbstractIn this work, a robust control scheme for variable speed wind turbine system that incorporates a doubly feed induction generator is described. The sliding mode controller is designed in order to track the optimum wind turbine speed value that produces the maximum power extraction for different wind speed values. A robust sliding mode observer for the aerodynamic torque is also proposed in order to avoid the wind speed sensors in the control scheme. The controller uses the estimated aerodynamic torque in order to calculate the reference value for the wind turbine speed. Another sliding mode control is also proposed in order to maintain the dc‐link voltage constant regardless of the direction of the rotor power flow. The stability analysis of the proposed controller under disturbances and parameter uncertainties is provided using the Lyapunov stability theory. Finally, the simulation results show that the proposed control scheme provides a high‐performance turbine speed control, in order to obtain the maximum wind power generation, and a high‐performance dc‐link regulation in the presence of system uncertainties.
Comparison of epidemiological features, clinicopathological features, and treatments between premenopausal and postmenopausal female breast cancer patients in western China: a retrospective multicenter study of 15,389 female patients
Authors: Feng Fan , Wei Yuxian , Zheng Ke , Li Yujing , Zhang Lu , Wang Tielin , Zhang Yanli , Li Hongyuan , Ren Guosheng , Li Fan 
Published: April 2018

AbstractPremenopausal and postmenopausal breast cancers are considered different types. Thus, this study aimed to explore differences in risk factors, epidemiological features, clinicopathological features, and treatment modes of premenopausal breast cancer compared to postmenopausal patients in western China. This was a hospital‐based, retrospective, multicenter epidemiological study of patients with breast cancer. Using the Western China Clinical Cooperation Group database, we obtained the records of 15,389 female breast cancers between January 2010 and April 2017. These patients were divided into premenopausal and postmenopausal groups, and their risk factors, epidemiological feature, clinicopathological features, and treatment modes were compared. Chi‐square tests, t‐test, and the multivariate logistic regression analysis were applied for statistical analysis. A total of 8395 patients were categorized as premenopausal, and 6994 patients were categorized as postmenopausal. Their risk factors, epidemiological features, clinicopathological features, and treatment modes were compared. Premenopausal patients with breast cancer had a greater tumor diameter at diagnosis (P = 0.008); higher rates of estrogen receptor (ER) expression (P < 0.0001), progesterone receptor (PR) expression (P < 0.0001), negative human epidermal growth factor receptor 2 (HER2) expression (P = 0.015), and negative P53 expression (P < 0.0001); and higher proportions of receiving breast‐conserving surgery and breast reconstruction (P < 0.0001), chemotherapy (P < 0.0001), radiotherapy (P < 0.0001), and endocrine therapy (P < 0.0001). The ethnicity, age at menarche, marital status, number of pregnancies, and number of births were the risk factors for age at diagnosis of breast cancer before or after menopause in western China. We found that the fall in the fertility rate, early menarche age, married, and less breastfeeding might have increased the possibility of premenopausal breast cancer. Significant differences exist in the tumor size, hormone receptor state, HER2 expression, epidemiological features, and treatment modes between premenopausal and postmenopausal female breast cancer patients in western China. Its further implementation requires prospective clinical testing.
Atrial remodeling and ectopic burden in recreational athletes: Implications for risk of atrial fibrillation
Authors: Elliott Adrian D. , Mahajan Rajiv , Linz Dominik , Stokes Michael , Verdicchio Christian V. , Middeldorp Melissa E. , La Gerche Andre , Lau Dennis H. , Sanders Prashanthan 
Published: April 2018

BackgroundAtrial remodeling, vagal tone, and atrial ectopic triggers are suggested to contribute to increased incidence of atrial fibrillation (AF) in endurance athletes. How these parameters change with increased lifetime training hours is debated.HypothesisAtrial remodeling occurs in proportion to total training history, thus contributing to elevated risk of AF.MethodsWe recruited 99 recreational endurance athletes, subsequently grouped according to lifetime training hours, to undergo evaluation of atrial size, autonomic modulation, and atrial ectopy. Athletes were grouped by self‐reported lifetime training hours: low (<3000 h), medium (3000–6000 h), and high (>6000 h). Left atrial (LA) volume, left ventricular (LV) dimensions, and LV systolic and diastolic function were assessed by echocardiography. We used 48‐hour ambulatory electrocardiographic monitoring to determine heart rate, heart rate variability, premature atrial contractions, and premature ventricular contractions.ResultsLA volume was significantly greater in the high (+5.1 mL/m2, 95% CI: 1.3–8.9) and medium (+4.2 mL/m2, 95% CI: 0.2–8.1) groups, compared with the low group. LA dilation was observed in 19.4%, 12.9%, and 0% of the high, medium, and low groups, respectively (P = 0.05). No differences were observed between groups for measures of LV dimensions or function. Minimum heart rate, parasympathetic tone expressed using heart rate variability indices, and premature atrial contraction and premature ventricular contraction frequencies did not differ between groups.ConclusionsIn recreational endurance athletes, increased lifetime training is associated with LA dilation in the absence of increased vagal parameters or atrial ectopy, which may promote incidence of AF in this cohort.
Whole‐exome sequencing reveals microsatellite DNA markers for response to dofetilide initiation in patients with persistent atrial fibrillation: A pilot study
Authors: Kinney Nick , Larsen Timothy R. , Kim David M. , Varghese Robin T. , Poelzing Steven , Garner Harold R. , AlMahameed Soufian T. 
Published: April 2018

BackgroundDofetilide is a class III antiarrhythmic drug effective for the treatment of atrial fibrillation (AF). Dofetilide initiation (DI) associates with corrected QT interval (QTc) prolongation. Significant QTc prolongation during DI mandates dose adjustment or discontinuation of the drug. Microsatellite DNA are novel genetic markers associated with congenital and acquired health conditions.Hypothesis.DNA microsatellite polymorphism may associate with QTc response to dofetilide initiation in patients with persistent AF.MethodsWe performed whole‐exome sequencing in a cohort of patients with persistent AF undergoing DI. Electrocardiographic variables and clinical data were assessed. We defined patients as eligible for DI when no significant QTc prolongation (>20% compared with baseline) was seen with a 500‐μg dose. We defined patients as ineligible for DI when significant QTc prolongation was seen during DI with 500 μg. We investigated polymorphisms for 11 919 DNA microsatellite loci in relation to QTc response to DI.ResultsDuring the study, 14 consecutive patients with persistent AF presenting for DI were enrolled. Whole‐exome sequencing revealed 14 different microsatellite loci in the 2 groups. All genes or proximal genes that harbor these loci are known to have expression in the human heart. Two genes, MYH6 and TRAK2, are known to have expression in the atria. TRAK2 is known to interact with KCNJ2, the inward‐rectifier potassium channel 1.ConclusionsMicrosatellite DNA polymorphisms seem to associate with QTc response to DI therapy in patients with persistent AF who are deemed otherwise eligible for dofetilide therapy.