A vast area in China is currently going through severe haze episodes with
drastically elevated concentrations of PM2.5 in winter. Nitrate and
sulfate are the main constituents of PM2.5, but their ...formations via
NO2 and SO2 oxidation are still not comprehensively understood,
especially under different pollution or atmospheric relative humidity (RH)
conditions. To elucidate formation pathways of nitrate and sulfate in
different polluted cases, hourly samples of PM2.5 were collected
continuously in Beijing during the wintertime of 2016. Three serious
pollution cases were identified reasonably during the sampling period, and
the secondary formations of nitrate and sulfate were found to make a
dominant contribution to atmospheric PM2.5 under the relatively high RH
condition. The significant correlation between NOR, NOR = NO3-/(NO3-+NO2), and NO22 × O3 during the nighttime under the RH≥60 % condition indicated
that the heterogeneous hydrolysis of N2O5 involving aerosol
liquid water was responsible for the nocturnal formation of nitrate at the
extremely high RH levels. The more often coincident trend of NOR and HONO × DR (direct radiation) × NO2 compared to its occurrence with Dust × NO2 during the daytime under the 30 % < RH < 60 % condition provided convincing evidence that the gas-phase
reaction of NO2 with OH played a pivotal role in the diurnal formation
of nitrate at moderate RH levels. The extremely high mean values of SOR, SOR = SO42-/(SO42-+SO2), during the whole day
under the RH≥60 % condition could be ascribed to the evident
contribution of SO2 aqueous-phase oxidation to the formation of sulfate
during the severe pollution episodes. Based on the parameters measured in
this study and the known sulfate production rate calculation method, the
oxidation pathway of H2O2 rather than NO2 was found to
contribute greatly to the aqueous-phase formation of sulfate.
The development of two-dimensional (2D) high-performance electrode materials is the key to new advances in the fields of energy storage and conversion. As a novel family of 2D layered materials, ...MXenes possess distinct structural, electronic and chemical properties that enable vast application potential in many fields, including batteries, supercapacitor and catalysis. However, MXene layers are easily formed by stacking together, which significantly reduces the specific surface area, hinders the transmission of ions, and restricts other functional materials on the surface, thereby reducing performance. In addition, due to the inherent defects of a single electrode material, electrodes or catalysts made of single-phase MXene may not meet specific practical application requirements. MXenes nanocomposites materials based on enhanced electrochemical performance through nano-engineering technology and surface modification for morphological control are highly sought after to solve these challenges. This review aims to present recent advances in these emerging MXene nanocomposites for energy storage and conversion applications such as batteries, supercapacitors and catalytic reactions. We also introduced some of the challenges and opportunities in this rapidly developing field.
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In this paper, we propose a new approach for heartbeat classification based on a combination of morphological and dynamic features. Wavelet transform and independent component analysis (ICA) are ...applied separately to each heartbeat to extract morphological features. In addition, RR interval information is computed to provide dynamic features. These two different types of features are concatenated and a support vector machine classifier is utilized for the classification of heartbeats into one of 16 classes. The procedure is independently applied to the data from two ECG leads and the two decisions are fused for the final classification decision. The proposed method is validated on the baseline MIT-BIH arrhythmia database and it yields an overall accuracy (i.e., the percentage of heartbeats correctly classified) of 99.3% (99.7% with 2.4% rejection) in the "class-oriented" evaluation and an accuracy of 86.4% in the "subject-oriented" evaluation, comparable to the state-of-the-art results for automatic heartbeat classification.
Microsupercapacitors (MSCs) show promise for use in wearable electronics for biomedical, consumer, and military applications. However, the development of innovative engineering technologies that ...enable high-capacity loading of active materials on the MSCs is still challenging. In this work, we report a conformal active-material loading strategy for developing high-performance planar MSCs based on stereoscopic carbon electrodes produced via direct laser writing (DLW). Oxidized laser-induced graphene (LIG-O) was prepared by combining laser-induced pyrolysis of polyimide (PI) and oxygen plasma-induced oxidation. The resultant LiG-O electrodes showed well-defined micropatterns, protuberant stereoscopic structures, high porosities, and superhydrophilicity. The combined effects enabled high-capacity loading of active materials ( e.g ., NiFe layered double hydroxide) on the stereoscopic carbon electrodes in a conformal manner, which contributed to a 10-fold improvement in the areal capacitances of the planar MSCs. In addition, the resultant flexible planar MSCs served as energy storage devices to power a flexible ink display system. This work will open new avenues for developing high-performance planar MSCs.
HONO (nitrous acid) is a crucial precursor for tropospheric OH radicals, and its sources are not well understood. In the past decade, soil was proven to be a potential source for HONO. However, more ...field measurements of soil HONO emission flux are needed to explore the mechanism and its impact on regional air quality. Here, we developed a system based on twin open-top chambers (OTCs) and wet chemical methods to measure HONO emission flux from agricultural soil in the North China Plain (NCP). The performance of the OTC system was tested under laboratory and field measurement conditions. The results showed that the system could reflect the strength (>90%) and variation of gas emission with an average residence time of 4–5 min. The greenhouse effect and chemical reaction interference in the chamber was proven to have no significant influence on the HONO flux measurement. Field measurement revealed that agricultural soil before fertilization was an important source of HONO. The emission flux showed radiation-dependent or temperature-dependent variation, with a peak of 3.21 ng m−2 s−1 at noontime that could account for approximately 67 pptv h−1 of the missing HONO source under an assumed mixing layer height of 300 m. Fertilization substantially accelerated HONO emission, which was rationally attributed to biological processes including nitrification. Considering the high fertilization rate in the NCP and other similar regions in China, HONO emission from agricultural soil likely has enormous impact on regional photochemistry and air quality, suggesting that more research should be conducted on this aspect.
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•A system based on open-top chamber method and wet chemical method to measure soil HONO emission was developed.•The performance of the OTCs system was tested in laboratory and field measurement conditions.•Soil HONO emission fluxes in NCP showed radiation-dependent or temperature-dependent variation.•Fertilization process substantially accelerated HONO emission which was rationally attributed to biological process including nitrification.
The hypoxic microenvironment is an essential characteristic of most malignant tumors. Notably, hypoxia-inducible factor-1 alpha (HIF-1α) is a key regulatory factor of cellular adaptation to hypoxia, ...and many critical pathways are correlated with the biological activity of organisms via HIF-1α. In the intra-tumoral hypoxic environment, HIF-1α is highly expressed and contributes to the malignant progression of tumors, which in turn results in a poor prognosis in patients. Recently, it has been indicated that HIF-1α is involved in various critical processes of life events and tumor development via regulating the expression of HIF-1α target genes, such as cell proliferation and apoptosis, angiogenesis, glucose metabolism, immune response, therapeutic resistance, etc. Apart from solid tumors, accumulating evidence has revealed that HIF-1α is also closely associated with the development and progression of hematological malignancies, such as leukemia, lymphoma, and multiple myeloma. Targeted inhibition of HIF-1α can facilitate an increased sensitivity of patients with malignancies to relevant therapeutic agents. In the review, we elaborated on the basic structure and biological functions of HIF-1α and summarized their current role in various malignancies. It is expected that they will have future potential for targeted therapy.
In the summer of 2018, a comprehensive field campaign, with measurements on HONO and related parameters, was conducted at the foot (150 m a.s.l.) and the summit of Mt. Tai (1534 m a.s.l.) in the ...central North China Plain (NCP). With the implementation of a 0-D box model, the HONO budget with six additional sources and its role in radical chemistry at the foot station were explored. We found that the model default source, NO + OH, could only reproduce 13 % of the observed HONO, leading to a strong unknown source strength of up to 3 ppbv h.sup.-1 . Among the additional sources, the NO.sub.2 uptake on the ground surface dominated (â¼ 70 %) nighttime HONO formation, and its photo-enhanced reaction dominated (â¼ 80 %) daytime HONO formation. Their contributions were sensitive to the mixing layer height (MLH) used for the parameterizations, highlighting the importance of a reasonable MLH for exploring ground-level HONO formation in 0-D models and the necessity of gradient measurements. A ÎHONO/ÎNO.sub.x ratio of 0.7 % for direct emissions from vehicle exhaust was inferred, and a new method to quantify its contribution to the observations was proposed and discussed. Aerosol-derived sources, including the NO.sub.2 uptake on the aerosol surface and the particulate nitrate photolysis, did not lead to significant HONO formation, with their contributions lower than NO + OH.
During haze periods in the North China Plain, extremely high NO concentrations have been observed, commonly exceeding 1 ppbv, preventing the classical gas-phase H2O2 formation through HO2 ...recombination. Surprisingly, H2O2 mixing ratios of about 1 ppbv were observed repeatedly in winter 2017. Combined field observations and chamber experiments reveal a photochemical in-particle formation of H2O2, driven by transition metal ions (TMIs) and humic-like substances (HULIS). In chamber experiments, steady-state H2O2 mixing ratios of 116 ± 83 pptv were observed upon the irradiation of TMI- and HULIS-containing particles. Correspondingly, H2O2 formation rates of about 0.2 ppbv h–1 during the initial irradiation periods are consistent with the H2O2 rates observed in the field. A novel chemical mechanism was developed explaining the in-particle H2O2 formation through a sequence of elementary photochemical reactions involving HULIS and TMIs. Dedicated box model studies of measurement periods with relative humidity >50% and PM2.5 ≥ 75 μg m–3 agree with the observed H2O2 concentrations and time courses. The modeling results suggest about 90% of the particulate sulfate to be produced from the SO2 reaction with OH and HSO3 – oxidation by H2O2. Overall, under high pollution, the H2O2-caused sulfate formation rate is above 250 ng m–3 h–1, contributing to the sulfate formation by more than 70%.
Atmospheric hydrogen peroxide (H2O2), as an important oxidant, plays a key role in atmospheric sulfate formation, affecting the global radiation budget and causing acid rain deposition. The ...disproportionation reactions of hydroperoxyl radicals (HO2) in both gas and aqueous phases have long been considered as dominant sources for atmospheric H2O2. However, these known sources cannot explain the significant formation of H2O2 in polluted areas under the conditions of high NO levels and low ambient relative humidity (RH). Here, we show that under relatively dry conditions during daytime, atmospheric fine particles directly produce abundant gas-phase H2O2. The formation of H2O2 is verified to be by a reaction between the particle surface −OH group and HO2 radicals formed by photooxidation of chromophoric dissolved organic matters (CDOMs), which is slightly influenced by the presence of high NO levels but remarkably accelerated by water vapor and O2. In contrast to aqueous-phase chemistry, transition metal ions (TMIs) are found to significantly suppress H2O2 formation from the atmospheric fine particles. The H2O2 formed from relatively dry particles can be directly involved in in situ SO2 oxidation, leading to sulfate formation. As CDOMs are ubiquitous in atmospheric fine particles, their daytime photochemistry is expected to play important roles in formation of H2O2 and sulfate worldwide.
Porous CaSiO3 ceramics were prepared via a solid-state reaction method using CaCO3 and SiO2 as raw materials and active carbon as a pore-forming agent. The results indicated that porous CaSiO3 ...ceramics could be obtained under a low sintering temperature of 1320 °C. The addition of active carbon significantly affected the volume density, microstructure, pore size distribution and mechanical strength of porous CaSiO3 ceramics. With the increase of active carbon content, the volume density decreased, meanwhile the pore size and porosity increased gradually. Besides, the three-point bending tests demonstrated that the mechanical strength was decreased with increasing active carbon content. However, all the porous ceramics still exhibited high mechanical strength. These results implied that the increase of active carbon content not only enlarged the pore size and enhanced the porosity, but also kept a remarkable mechanical strength of porous CaSiO3 ceramics. Therefore, these rationally designed CaSiO3 porous ceramics will be a highly potential material in various applications due to its high mechanical strength, low sintering temperature and narrow pore size distribution.
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