Atomic insights into mechanisms of carbon coating on titania nanoparticle during flame synthesis

Carbon-metal oxide (CMO) nanocomposites have seen increasing research due to their extraordinary properties for energy storage materials and photocatalysts. Flame aerosol synthesis provides a promising route for producing CMO nanocomposites. Various CMO nanocomposites have been successfully synthesized through flame aerosol techniques in laboratories. However, a detailed understanding of the formation and growth mechanisms of such materials is lacking. Therefore, in this study, the reactive force-field molecular dynamics (ReaxFF MD) was deployed to gain atomic insights into the initial stage of carbon coating on the titania nanoparticle. We performed a large number of simulations of carbon coating with 18 typical hydrocarbon species in flames including aliphatics of C1-C4 species and polycyclic aromatic hydrocarbons (PAHs) at temperatures ranging from 400 K to 2500 K. We found that the titania nanoparticle can not only serve as a nucleus for physical adsorption of the surrounding hydrocarbons, but also can form Csingle bondTi/O bonds with them, and abstract H atoms from the surrounding hydrocarbons. The optimal temperature range for carbon coating is , because Csingle bondTi/O bonds are unstable at higher temperatures. At , hydrocarbons tend to gather to form larger carbonaceous species instead of coating onto the particle surface, as the formation of C-C bonds is promoted at high temperatures. Small aliphatics are favored to be chemically coated on the particle, while PAH molecules tend to be physically absorbed on the nanoparticle surface due to their stable electronic structure and large size. Coating tendencies of aliphatics are closely related to the number of C-C triple bonds

Dynamics and kinetics of reversible homo-molecular dimerization of polycyclic aromatic hydrocarbons

Physical dimerization of polycyclic aromatic hydrocarbons (PAHs) has been investigated via molecular dynamics (MD) simulation with the ReaxFF reactive force field that is developed to bridge the gap between the quantum mechanism and classical MD. Dynamics and kinetics of homo-molecular PAH collision under different temperatures, impact parameters, and orientations are studied at an atomic level, which is of great value to understand and model the PAH dimerization. In the collision process, the enhancement factors of homo-molecular dimerizations are quantified and found to be larger at lower temperatures or with smaller PAH instead of size independent. Within the capture radius, the lifetime of the formed PAH dimer decreases as the impact parameter increases. Temperature and PAH characteristic dependent forward and reverse rate constants of homo-molecular PAH dimerization are derived from MD simulations, on the basis of which a reversible model is developed. This model can predict the tendency of PAH dimerization as validated by pyrene dimerization experiments [H. Sabbah et al., J. Phys. Chem. Lett. 1(19), 2962 (2010)]. Results from this study indicate that the physical dimerization cannot be an important source under the typical flame temperatures and PAH concentrations, which implies a more significant role played by the chemical route

Classical and reactive molecular dynamics: Principles and applications in combustion and energy systems

Molecular dynamics (MD) has evolved into a ubiquitous, versatile and powerful computational method for fundamental research in science branches such as biology, chemistry, biomedicine and physics over the past 60 years. Powered by rapidly advanced supercomputing technologies in recent decades, MD has entered the engineering domain as a first-principle predictive method for material properties, physicochemical processes, and even as a design tool. Such developments have far-reaching consequences, and are covered for the first time in the present paper, with a focus on MD for combustion and energy systems encompassing topics like gas/liquid/solid fuel oxidation, pyrolysis, catalytic combustion, heterogeneous combustion, electrochemistry, nanoparticle synthesis, heat transfer, phase change, and fluid mechanics. First, the theoretical framework of the MD methodology is described systemically, covering both classical and reactive MD. The emphasis is on the development of the reactive force field (ReaxFF) MD, which enables chemical reactions to be simulated within the MD framework, utilizing quantum chemistry calculations and/or experimental data for the force field training. Second, details of the numerical methods, boundary conditions, post-processing and computational costs of MD simulations are provided. This is followed by a critical review of selected applications of classical and reactive MD methods in combustion and energy systems. It is demonstrated that the ReaxFF MD has been successfully deployed to gain fundamental insights into pyrolysis and/or oxidation of gas/liquid/solid fuels, revealing detailed energy changes and chemical pathways. Moreover, the complex physico-chemical dynamic processes in catalytic reactions, soot formation, and flame synthesis of nanoparticles are made plainly visible from an atomistic perspective. Flow, heat transfer and phase change phenomena are also scrutinized by MD simulations. Unprecedented details of nanoscale processes such as droplet collision, fuel droplet evaporation, and CO2 capture and storage under subcritical and supercritical conditions are examined at the atomic level. Finally, the outlook for atomistic simulations of combustion and energy systems is discussed in the context of emerging computing platforms, machine learning and multiscale modelling

Efficacy and safety of Kanglaite injection combined with chemotherapy for colorectal cancer: A protocol for systematic review and meta-analysis

Abstract Background: The incidence and mortality of colorectal cancer are high. Chemotherapy is currently the commonly used therapeutic scheme, but there are drug resistance and toxic and side effects. Kanglaite(KLT) injection is a broad-spectrum anticancer drug extracted from Semen Coicis(Yi Yi Ren), which has been widely used in the treatment of colorectal cancer. Clinical practice shows that KLT injection combined with chemotherapy has certain therapeutic advantages, but there is a lacking of evidence of evidence-based medicine. The purpose of this study is to systematically investigate the efficacy and safety of KLT injection combined with chemotherapy in the treatment of colorectal cancer. Methods: Randomized controlled trials(RCTs) of KLT injection combined with chemotherapy in the treatment of colorectal cancer were retrieved from English databases (PubMed, Embase, Web of Science, the Cochrane Library) and Chinese databases (China National Knowledge Infrastructure(CNKI), Wanfang, Chongqing VIP Chinese Science and Technology Periodical Database, Chinese Biological and Medical database (CMB)) ,as well as searching Baidu academic and Google academic manually, and the retrieval time was from their establishment to August 2020. Two researchers independently conducted data extraction and literature quality evaluation on the quality of the included literatures, and meta-analysis was conducted on the included literatures using RevMan5.3 software. Results: This study assessed the efficacy and safety of Kanglaite injection combined with chemotherapy in the treatment of colorectal cancer by effective rate, Karnofsky Performance Status (KPS), Carcinoemybryonic Angtigen (CEA) remission rate, pain remission rate and incidence of adverse reactions etc. Conclusions: This study will provide reliable evidence-based evidence for the clinical application of Kanglaite injection combined with chemotherapy in the treatment of colorectal cancer

Experimental Investigation on Asphalt Binders Ageing Behavior and Rejuvenating Feasibility in Multicycle Repeated Ageing and Recycling

Multicycle repeated utilization of reclaimed asphalt pavement (RAP) is a quite recent development of sustainable pavement materials technology. To investigate ageing rules and recycling possibility of asphalt binders in repeatedly used asphalt mixture, virgin asphalt AH-70 samples were heated by the rolling thin film oven test (RTFOT) at 163°C, respectively, for 40, 85, 180, 240, and 300 minutes to simulate different ageing degrees, and then the aged ones were rejuvenated by adding a self-made rejuvenator. This ageing and recycling process was repeated altogether for 5 cycles to simulate repeated use of RAP binders. In repeated recycling, rejuvenator contents for different cycle numbers or ageing durations were not the same, and the optimum ones were initially estimated by an empirical formula and finally obtained by comparative tests. Empirical rheological tests and the infrared spectral (IR) analysis were done before and after each cycle of recycling. Results indicate that for impact on deterioration of asphalt binders, ageing time is more important than cycle number. Meanwhile, the asphalt after multicycle repeated ageing and recycling can be restored to the empirical rheological indices level of the virgin asphalt and meet specifications requirements

A multi-criteria evaluation system for arable land resource assessment

This study proposed a multi-criteria evaluation system for arable land resources by combining the soil integrated fertility index (IFI) with a soil cleanliness index (based on heavy metals and metalloid content). A total of 16 typical arable land units in Chongming District, China, were evaluated using the proposed evaluation system based on 104 collected soil samples in 16 towns. The comprehensive soil evaluation scores of arable lands in 16 towns were in the range of 90.7 to 99.2 with a mean of 96.2, indicating that the arable land in all 16 towns was at the level of excellent (≥ 90.0). Lower cleanliness indices had a significant impact on the final evaluation score. In comparison with single-index evaluation systems (i.e., the IFI or soil cleanliness index), the proposed multi-criteria system better reflects the quality of the soil. In the practice of arable land requisition and subsidy policy, the proposed multi-criteria evaluation system not only encourages farmers to preserve arable lands during farming but also helps agricultural authorities make effective and reliable management decisions.peerReviewe

Remote sensing image mosaic technology based on SURF algorithm in agriculture

Abstract The remote sensing technology of unmanned aerial vehicle (UAV) is a low altitude remote sensing technology. The technology has been widely used in military, agricultural, medical, geographical mapping, and other fields by virtue of the advantages of fast acquisition, high resolution, low cost, and good security. But limited by the flying height of UAV and the focal length of the digital camera, the single image obtained by the UAV is difficult to form the overall cognition of the ground farmland area. In order to further expand the field of view, it is necessary to mosaic multiple single images acquired by UAV into a complete panoramic image of the farmland. In this paper, aiming at the problem of UAV low-altitude remote sensing image splicing, an image mosaic technique based on Speed Up Robust Feature (SURF) is introduced to achieve rapid image splicing. One hundred fifty ground farmland remote sensing images collected by UAV are used as experimental splicing objects, and the image splicing is completed by the global stitching strategy optimized by Levenberg-Marquardt (L-M). Experiments show that the strategy can effectively reduce the influence of cumulative errors and achieve automatic panoramic mosaic of the survey area

Do Community Home-Based Elderly Care Services Improve Life Satisfaction of Chinese Older Adults? An Empirical Analysis Based on the 2018 CLHLS Dataset

Population aging has become a major challenge for the Chinese government. Based on the Chinese Longitudinal Healthy Longevity Survey (CLHLS) in 2018, this study adopts the propensity score matching (PSM) method to assess the effect of community home-based elderly care services (CHECS) on the life satisfaction of the elderly in China. The results demonstrate that CHECS can improve their life satisfaction. Compared with life care services (LCS) and medical care services (MCS), the positive effect of spiritual and cultural services (SCS) and reconciliation and legal services (RLS) is more obvious. Moreover, the heterogeneity test demonstrates that the effect is more significant for the elderly who live with their families, whose activities of daily living are unrestricted, and whose depression levels are lower. The results obtained indicate that CHECS need precise policies for different elderly groups, attention to the positive impact of SCS and RLS on the life satisfaction of the elderly, and the substantive effectiveness of LCS and MCS