科研成果

The traditional eigen beam based localization algorithms are usually not employed on the non-spherical microphone array, for which the eigen beam is hard to be obtained. In this paper, the transfer functions are introduced to calculated the eigen beam on the non-spherical microphone array. Based on it, three localization algorithms including the eigen beam based intensity vector, eigen beam based beamforming, eigen beam based MUSIC, are employed and their performance on localization are evaluated.

Personalized recommendation has important implications in raising online shopping efficiency and increasing product sales. There has been wide interest in finding ways to provide more efficient personalized recommendations. Most existing studies focus on how to improve the accuracy of the recommendation algorithms, or are more concerned on ways to increase consumer satisfaction. Unlike these studies, our study focuses on the process of decision-making, using long tail theory as a basis, to reveal the mechanisms involved in consumers' adoption of recommendations. This paper analyzes the effect of personalized recommendations from two angles: product sales and ratings, and tries to point out differences in consumer preferences between mainstream products and niche products, high rating products and low rating products, search products and experience products. The study verifies that consumers demand diversity in the recommended content, and also provides suggestions on how to better plan and operate a personalized recommendation system. © 2019 IEEE Computer Society. All rights reserved.

Scholars commonly regard the Comintern as having played a critical role in the emergence of the communist movement in late-colonial Malaya. When discussing the Comintern’s early influence, existing scholarships often use the arrest of Joseph Ducroux — alias Serge Lefranc, a French agent of the Comintern — in Singapore in June 1931 to illustrate the Comintern-China-Malaya connection. Additionally, historians have attached special meanings to the Ducroux Case, primarily because of the more significant repercussions it caused internationally. Laurent Metzger has conducted detailed research on Ducroux’s arrest in and eventual exile from Singapore between 1931 and 1932. While such an account is useful in demonstrating the incident’s international significance, little is known as to what immediate impression it created in the cosmopolitan port city. Moreover, it is also unclear how Singapore’s general public perceived communism when communist organizations had yet firmly established themselves in the British colony. This article seeks to make sense of such issues by investigating how the Singapore press reported on the Ducroux Case.

As the common saying goes: All's well that ends well. This research was the first to explore whether the end effect could be observed in the perception of air pollution and further examined the effect of perceived difference on the end effect. In Experiment 1, participants went through a short trial of 30 severe air pollution pictures and a long trial of 45 pollution pictures containing 15 extra moderate pollution pictures at the end. The results showed preference for the long trial as well as more willingness to experience it again, which verified the end effect. In Experiment 2, the long trial was adjusted to 45 severe air pollution pictures, which caused the end effect to disappear. In Experiment 3, it was confirmed that perceived difference had an impact on the end effect, as the end effect worked when subjects cognitively focused on the variated pollution extent but disappeared when they focused on the air pollution quality. These results advance our understanding by directly demonstrating the influence of perceived difference on the end effect as well as providing a useful view to intervene in people's perception of air pollution. Further theoretical and practical implications are discussed.

© 2019 Elsevier Ltd Effective policy requires comprehensive analysis of many factors. But presently there does not exist a sufficiently comprehensive research on the interrelationship between energy input and output, carbon emissions, and water use in the oil and gas extraction process. To more comprehensively measure this phenomenon, this paper constructs an assessment model of energy return on energy, carbon, and water investment for the development of oil and gas resources using the Daqing and Shengli oilfields as practical examples. The results show that the method for evaluating energy input and output (energy return on energy invested) can be made more comprehensive for covering the resources required in the oilfield extraction process; this method ignores the environmental impacts of carbon emissions (energy return on carbon) and water use (energy return on water). However, the energy return evaluation method, which considers energy, carbon, and water inputs, is more comprehensive and practically used to evaluate the development status of oil and gas resources as well as other types of energy development processes. Policy implications for biophysical input accounting and the management of energy resource extraction are given accordingly.

Sulfur-modified zero valent iron (S-ZVI) particles have been reported to show improved reactivity and selectivity than conventional ZVI. However, current methods for ZVI sulfidation do not fully utilize the advantages of the material, and S-ZVI has not been tested for U(VI) immobilization. In this work, we synthesized a new type of FeS-modified ZVI core-shell particles (FeS@Fe0) through a facile two-step reaction approach, and then tested for reductive sequestration of U(VI) in water. X-ray diffraction, Scanning transmission electron microscopy, and physical property analyses confirmed the formation of the core-shell structure, surface compositions and magnetic properties. Batch kinetic tests showed that FeS@Fe0 with an Fe0/FeS molar ratio of 1:1 offered the highest U(VI) reduction rate, prolonged reactive life than pristine ZVI, and the reduced uranium was most resistant to re-oxidation when exposed to oxygen. The retarded first-order kinetic model was able to adequately interpret the experimental rate data. FeS@Fe0 performed well over the pH range 5.5–9.0, with higher pH more favoring the reaction. High concentrations (5–10 mg/L) of humic acid, bicarbonate (1–5 mM) and Ca2+ (1 mM) showed only modest inhibition to the U(VI) reduction. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and extraction studies indicated that U(VI) was immobilized via both direct adsorption and reductive precipitation, where Fe0 was the main electron source, with Fe0, sorbed Fe(II) and structural Fe(II) acting as the electron donors. FeS@Fe0 may serve as an improved material for efficient immobilization of U(VI) and other redox-active contaminants in water.

Current air quality models usually underestimate the concentration of ambient air sulfate, but the cause of this underestimation remains unclear. One reason for the underestimation is that the sulfate formation mechanism in the models is incomplete, and does not adequately consider the impact of the synergistic effects of high concentrations of multiple pollutants on sulfate formation. In this work, the roles of gaseous NO2, NH3 and solution ionic strength in the formation of sulfate in the aqueous phase were quantitatively investigated using a glass reactor and a 30 m(3) smog chamber, separately. The results showed that sulfate formation was enhanced to different degrees in the presence of gas-phase NO2, NH3 and their coexistence as solutes in both liquid solution and aerosol water. NH3 enhances the aqueous oxidation of SO2 by NO2 mainly by accelerating the uptake of SO2 through increased solubility. More importantly, we found that high ionic strength in aerosol water could significantly accelerate the aqueous oxidation of SO2, resulting in unexpectedly high S(VI) formation rates. We estimate that under severe haze conditions, heterogeneous oxidation of SO2 by NO2 on aerosols may be much shorter than that through gas phase oxidation by OH, aided by high ionic strengths in aerosols. Considering the existence of complex air pollution conditions with high concentrations of NO2, NH3 and aerosol water, as expected in typical urban and suburban settings, the sulfate formation mechanisms revealed in the present work should be incorporated into air quality models to improve the prediction of sulfate concentrations. (C) 2019 Elsevier Ltd. All rights reserved.

Two-dimensional (2D) metal–semiconductor transition-metal dichalcogenide (TMDC) vertical heterostructures play a crucial role in device engineering and contact tuning fields, while their direct integration still challenging. Herein, a robust epitaxial growth method is designed to construct multiple lattice-matched 2D metal–semiconductor TMDC vertical stacks (VSe2/MX2, M: Mo, W; X: S, Se) by a two-step chemical vapor deposition method. Intriguingly, the metallic VSe2 preferred to nucleate and extend from the energy-favorable edge site of the semiconducting MX2 underlayer to form VSe2/MX2 vertical heterostructures. This growth behavior was also confirmed by density functional theory calculations of the initial adsorption of VSe2 adatoms. In particular, the formation of Schottky-diode or Ohmic contact-type band alignments was detected for the stacks between VSe2 and p-type WSe2 or n-type MoSe2, respectively. This work hereby provides insights into the direct integration, band-alignment engineering, and potential applications of such 2D metal–semiconductor stacks in next-generation electronics, optoelectronic devices, and energy-related fields.

Volatile organic compounds (VOCs) pollution, which is closely linked to photochemical smog and secondary organic aerosols, has become a severe concern in China. Therefore, we compiled a new high-resolution emission inventory for the industrial non-methane Volatile organic compounds (NMVOCs) using “bottom-up” approaches throughout 2010 and 2016. In this work, the industrial sources were divided into five major categories, and 108 specific sources, as well as an emission factor database, was developed for industrial NMVOCs. Results indicated that the total NMVOCs emissions from industrial sources increased from 16.88 Tg in 2010 to 21.04 Tg in 2016 at an annual average rate of 3.7%. The five major source categories including “production of VOCs”, “storage and transportation”, “industrial processes using VOCs as raw material”, “processes using VOCs-containing products”, and “fossil fuel combustion” generated 1.92 Tg, 0.94 Tg, 6.54 Tg, 10.04 Tg, and 1.60 Tg NMVOCs, respectively, in 2016. Coke production, plastic manufacturing, raw medicine industry, and architectural decoration were the primary sources of industrial NMVOCs and emissions of these sources increased by 140 Gg, 190 Gg, 640 Gg, and 700 Gg between 2010 and 2016. The emissions displayed distinct spatial characteristics, with significantly higher emissions in the Beijing-Tianjin-Hebei region, the Pearl River Delta, the Yangtze River Delta, and the Cheng-Yu region than in other areas. Shandong, Guangdong, Jiangsu, Zhejiang, and Henan were the top five provinces with the highest NMVOCs emissions, while the emission hotspots in the county-level were mainly distributed in Guangzhou urban area, Shanghai Pudong New Area, Hangzhou urban area, and Shenzhen urban area. The emissions in Henan province, Hubei province, and Cheng-Yu region increased significantly during the study period. Instead, emissions in some counties of Zhejiang province and Hebei province decreased than in 2010.

As the major producer and consumer of hydrofluorocarbons (HFCs), China is obligated to phase-down HFCs to mitigate global warming if China ratifies the Kigali Amendment (KA) to the Montreal Protocol. Based on historical HFCs consumption in each sector, here we estimated historical HFCs emissions with a bottom-up method, and projected the consumption baseline and schedule for HFCs phase-down in China under the KA and the corresponding potential for emission reduction. Results showed that China's HFCs consumption and emissions in 2017 were 164,000 t (311 Mt CO2-eq) and 108 Mt CO2-eq, respectively. HFCs consumption baseline was projected to be (724 ± 18) Mt CO2-eq in 2024, and China should take measures to phase-down HFCs by 2029, at the latest, to meet the requirements of the KA. HFCs consumption in 2050 under KA would reach the level of 2012–2013. Cumulative reduced consumption was estimated at 10.8 (10.1–11.6) Gt CO2-eq, and cumulative reduced emissions were estimated at 5.38 (4.90–5.64) Gt CO2-eq by 2050.

Thermal maturity is an important geochemical parameter for the study of source rocks in unconventional shale plays. Using well logs to estimate thermal maturity would overcome the discontinuity of core sample analysis and can provide continuous profiles. However, estimating thermal maturity from well logs, unlike total organic carbon (TOC) content has received less attention. In this paper, we used vitrinite reflectance (Ro) to characterize thermal maturity and proposed a practical method to produce a continuous profile of thermal maturity from well logs. For this purpose, a maturity indicator (Im) regarding with kerogen element compositions and types was defined. Im was calculated for different kerogen types based on their H/C versus O/C atomic ratios. It was found that Ro decreases with the Im of all three types of kerogen monotonically, which was used as a foundation for thermal maturity predictions. Then, the Im was related to the compensated neutron log (CNL) responses of kerogen by considering the variations in elemental compositions of organic matter with maturity. Based on known CNL response of major sedimentary minerals and pore fluids, a petrophysical equation was established to obtain Im from well logs. Finally, the proposed method was applied to Chang 7 Shale of Triassic Yanchang Formation of the Ordos Basin, China and the Bakken Shale of Williston Basin, North Dakota, USA, two major source rocks with different kerogen types and maturities. The results showed an acceptable agreement between lab measurements and predictions of Ro with a good correlation coefficient, verifying the new method is effective and reliable.