Facile synthesis of efficient pentaethylenehexamine-phosphotungstic acid heterogeneous catalysts for oxidative desulfurization

The ultra-deep desulfurization of oil needs to be solved urgently due to various problems,including environmental pollution and environmental protection requirements.Oxidative desulfurization(ODS)was considered to be the most promising technology.The facile synthesis of highly efficient and stable HPW-based heterogeneous catalysts for oxidative desulfurization is still a challenging task.In this paper,pentamethylene hexamine(PEHA)and phosphotungstic acid(HPW)were combined by a simple one-step method to prepare a heterogeneous catalyst of PEHA-HPW for the production of ultra-deep desulfurization fuel oil.The composite material exhibited excellent catalytic activity and high recyclability,which could reach a 100% dibenzothiophene(DBT)removal rate in 30 min and be recycled at least 5 times.Experiments and DFT simulations were used to better examine the ODS mechanism of PEHA-HPW.It was proved that the rich amino groups on the surface of PEHA-HPW play a crucial role.This work provides a simple and feasible way for the manufacture of efficient HPW-based catalysts.

Diagnosis of the Forcing of Inertial-gravity Waves in a Severe Convection System

The non-hydrostatic wave equation set in Cartesian coordinates is rearranged to gain insight into wave generation in a mesoscale severe convection system. The wave equation is characterized by a wave operator on the lhs, and forcing involving three terms—linear and nonlinear terms, and diabatic heating—on the rhs. The equation was applied to a case of severe convection that occurred in East China. The calculation with simulation data showed that the diabatic forcing and linear and nonlinear forcing presented large magnitude at different altitudes in the severe convection region. Further analysis revealed the diabatic forcing due to condensational latent heating had an important influence on the generation of gravity waves in the middle and lower levels. The linear forcing resulting from the Laplacian of potential-temperature linear forcing was dominant in the middle and upper levels. The nonlinear forcing was determined by the Laplacian of potential-temperature nonlinear forcing. Therefore, the forcing of gravity waves was closely associated with the thermodynamic processes in the severe convection case. The reason may be that, besides the vertical component of pressure gradient force, the vertical oscillation of atmospheric particles was dominated by the buoyancy for inertial gravity waves. The latent heating and potential-temperature linear and nonlinear forcing played an important role in the buoyancy tendency. Consequently, these thermodynamic elements influenced the evolution of inertial-gravity waves.

A New Method of Multi-Focus Image Fusion Using Laplacian Operator and Region Optimization

Considering the continuous advancement in the field of imaging sensor, a host of other new issues have emerged. A major problem is how to find focus areas more accurately for multi-focus image fusion. The multi-focus image fusion extracts the focused information from the source images to construct a global in-focus image which includes more information than any of the source images. In this paper, a novel multi-focus image fusion based on Laplacian operator and region optimization is proposed. The evaluation of image saliency based on Laplacian operator can easily distinguish the focus region and out of focus region. And the decision map obtained by Laplacian operator processing has less the residual information than other methods. For getting precise decision map, focus area and edge optimization based on regional connectivity and edge detection have been taken. Finally, the original images are fused through the decision map. Experimental results indicate that the proposed algorithm outperforms the other series of algorithms in terms of both subjective and objective evaluations.

Gravel Image Auto-Segmentation Based on an Improved Normalized Cuts Algorithm

The study of the grain-size distribution of gravels is always an important and challenging issue in stratigraphy and morphology, especially in the field of automated measurement. It largely reduces many manual processes and time consumption. Precise segmentation method plays a very important role in it. In this study, a digital image method using an improved normalized cuts algorithm is proposed for auto-segmentation of gravel image. It added grain-size estimation, and used the feature vector based on color. It has made great improvements in many respects, especially in accuracy of edge segmentation and automation. Compared with manual measurement methods and other image processing methods, the method studied in this paper is an efficient method for precisely segmenting gravel images.

Surface active agents stabilize nanodroplets and enhance haze formation

Although many organic molecules found commonly in the atmosphere are known to be surface-active in aqueous solutions, their effects on the mechanisms underlying haze formation remain unclear. In this paper, based on a simple thermodynamic analysis, we report that the adsorption of amphiphilic organics alone not only lowers the surface tension,but also unexpectedly stabilizes nanodroplets of specific size under water vapor supersaturation. Then we determine how various factors, including relative humidity, water activity effect due to dissolution of inorganic components as well as surface tension effect due to surface adsorption of organic components, cooperatively induce the stability of nanodroplets.The nanodroplet stability behaviors not captured in the current theory would change the formation mechanism of haze droplets, from the hygroscopic growth pathway to a nonclassical two-step nucleation pathway.

Wave-ice dynamical interaction:a numerical model and its application

In this paper,an ice floe inner stress caused by the wave-induced bending moment is derived to estimate the stress failure of ice floe.The strain and stress failures are combined to establish a wave-induced ice yield scheme.We added ice stress and strain failure module in the Finite-Volume Community Ocean Model(FVCOM),which already includes module of ice-induced wave attenuation.Thus a fully coupled wave-ice dynamical interaction model is established based on the ice and wave modules of FVCOM.This model is applied to reproduce the ice and wave fields of the breakup events observed during the second Sea Ice Physics and Ecosystem Experiment(SIPEX-2)voyage.The simulation results show that by adopting the combined wave-induced ice yield scheme,the model can successfully predict the ice breakup events,which the strain failure model is unable to predict.By comparing the critical significant wave height deduced from strain and stress failure schemes,it is concluded that the ice breakup is caused by the strain failure when wave periods are shorter than a threshold value,while the stress failure is the main reason for the ice breakup when wave periods are longer than the threshold value.Neglecting either of these two ice-break inducement mechanisms could overestimate the ice floe size,and thus underestimate the velocity of the ice lateral melt and increase the error of simulation of polar ice extent.

Role of substrate softness in stabilizing surface nanobubbles

The contact line pinning and supersaturation theory for the nanobubble stability has attracted extensive concerns from experimental investigators,and some experimenters argue that the contact line pinning is unnecessary.To interpret the experimental observations,we have proposed previously through molecular dynamics simulations that the deformation of soft substrates caused by surface nanobubbles may play an important role in stabilizing surface nanobubbles,while yet no quantitative theory is available for explanation of this mechanism.Here,the detailed mechanism of self-pinning-induced stability of surface nanobubbles is investigated through theoretical analysis.By manipulating substrate softness,we find that the formation of surface nanobubbles may create a deformation ridge nearby their contact lines which leads to the self-pinning effect.Theoretical analysis shows that the formation of nanobubbles on sufficiently rigid substrates or on liquid-liquid interfaces corresponds to a local free energy maximum,while that on the substrates with intermediate softness corresponds to a local minimum.Thus,the substrate softness could regulate the surface nanobubble stability.The critical condition for the self-pinning effect is determined based on contact line depinning,and the effect of gas supersaturation is explored.Finally,the approximate stability range for the surface nanobubbles is also predicted.

Analysis on Formation Reason of "0902" Blizzard in Northeast China

[Objective]The research aimed to analyze formation reason of ＂ 0902＂ blizzard in northeast China. [Method]By using timely observation data,NCEP reanalysis data and Doppler radar data at Baishan station,blizzard process in southeast part of northeast China during 12-13 February,2009 was analyzed. [Result]Snowfall zone of the blizzard process was wide,snowfall was more,snowfall gradient was big,and snowfall time relatively concentrated. These characteristics reflected that the blizzard process had significant convection characteristics. Baroclinic disturbance at high-altitude straight frontal zone and ground warm frontogenesis caused by eastward movement and northward advancement of North China low vortex at low altitude were the circulation characteristics in the process. Water vapor from the sea went northward as southwest airflow,and strongly converged in blizzard zone,which provided sufficient water vapor condition for the blizzard. Before heavy snowfall occurred,there was accumulation process of heat and energy. Conditional symmetric instability was main unstable mechanism of the blizzard. During heavy snowfall period,ascending branch of secondary vertical circulation at exit zone of high-altitude jet coupled with ascending branch of secondary vertical circulation of warm frontegenesis at low layer,inducing strong development of the vertical motion. Doppler radar intensity echo revealed that it was easy to generate blizzard in the area where echo intensity was consistently above 20 dBz. Strong wind velocity convergence zone at radical velocity field especially adverse wind zone was favorable for the generation of blizzard. [Conclusion]The research could provide reference for blizzard forecast in northeast China.

Stable bulk nanobubbles can be regarded as gaseous analogues of microemulsions

In our previous work[2022 Phys.Chem.Chem.Phys.249685],we used molecular dynamics simulations to show that bulk nanobubbles can be stabilized by forming a compressed amphiphile monolayer at bubble interfaces.This observation closely matches the origin of stability of microemulsions and inspired us to propose here that,in certain cases,stable bulk nanobubbles can be regarded as gaseous analogues of microemulsions:the nanobubble phase and the bubble-containing solution phase coexist with the external gas phase.This three-phase coexistence is then validated by molecular dynamics simulations.The stability mechanism for bulk nanobubbles is thus given:the formation of a compressed amphiphilic monolayer because of microbubble shrinking leads to a vanishing surface tension,and consequently the curvature energy of the monolayer dominates the thermodynamic stability of bulk nanobubbles.With the monolayer model,we further interpret several strange behaviors of bulk nanobubbles:gas supersaturation is not a prerequisite for nanobubble stability because of the vanishing surface tension,and the typical nanobubble size of 100 nm can be explained through the small bending constant of the monolayer.Finally,through analyzing the compressed amphiphile monolayer model we propose that bulk nanobubbles can exist ubiquitously in aqueous solutions.

Fluctuating magnetic droplets immersed in a sea of quantum spin liquid

The search of quantum spin liquid(QSL),an exotic magnetic state with strongly fluctuating and highly entangled spins down to zero temperature,is a main theme in current condensed matter physics.However,there is no smoking gun evidence for deconfined spinons in any QSL candidate so far.The disorders and competing exchange interactions may prevent the formation of an ideal QSL state on frustrated spin lattices.Here we report comprehensive and systematic measurements of the magnetic susceptibility,ultralow-temperature specific heat,muon spin relaxation(μSR),nuclear magnetic resonance(NMR),and thermal conductivity for NaYbSe2 single crystals,in which Yb3+ions with effective spin-1/2 form a perfect triangular lattice.All these complementary techniques find no evidence of long-range magnetic order down to their respective base temperatures.Instead,specific heat,μSR,and NMR measurements suggest the coexistence of quasi-static and dynamic spins in NaYbSe2.The scattering from these quasi-static spins may cause the absence of magnetic thermal conductivity.Thus,we propose a scenario of fluctuating ferrimagnetic droplets immersed in a sea of QSL.This may be quite common on the way pursuing an ideal QSL,and provides a brand new platform to study how a QSL state survives impurities and coexists with other magnetically ordered states.

慕课学习完成者的学习效率及其群体差异性研究

慕课学习者的学习效率提升是保证学习成功率的关键,但以往研究对慕课学习完成者的学习效率和群体差异性还缺乏有效考察。文章以1,388名慕课学习完成者为研究对象,通过构建9个学习投入指标和3个学习产出指标,运用Kmeans聚类算法确立了学习者集群,选用数据包络分析法(Data Envelopment Analysis),并以输出导向的CCR模型、BCC模型和超效率模型测算了学习者的学习效率及群体差异性。研究结果表明:完成慕课的学习者可以分为勤奋收获者和打卡体验者;慕课学习完成者也普遍存在学习效率不佳的问题;两类学习者在学习效率和学习投入贡献率上均存在组间差异,论坛回帖频次对学习者的学习效率的贡献率最大。文章提出了改进慕课学习者学习效率的策略建议,以期激发慕课的潜在价值,提升慕课学习者的学习效率。

The existence and stability of bulk nanobubbles:a long-standing dispute on the experimentally observed mesoscopic inhomogeneities in aqueous solutions

In theory,nanobubbles can stably exist with a lifetime of microseconds at most,but numerous experimental observations demonstrate that nanobubbles in bulk solution can be stable from hours to weeks.Although various conjectures on the stability mechanism of bulk nanobubbles,such as the contaminant mechanism,skin mechanism,surface zeta potential mechanism,are proposed,there has not yet been a unified conclusion.Since bulk nanobubbles show great potential in a wide spectrum of applications and are relevant to a number of unsolved questions on cavitation and nucleation,the debate over their stability mechanisms has been active.In the past,extensive studies have been carried out to understand the mechanism of nanobubble stability,and important insights have already been provided.This paper will provide a brief overview of our current understanding of the unexpected stability of bulk nanobubbles.

Interpreting the vulnerability of power systems in cascading failures using multi-graph convolutional networks

Analyzing the vulnerability of power systems in cascading failures is generally regarded as a challenging problem. Although existing studies can extract some critical rules, they fail to capture the complex subtleties under different operational conditions. In recent years, several deep learning methods have been applied to address this issue. However, most of the existing deep learning methods consider only the grid topology of a power system in terms of topological connections, but do not encompass a power system’s spatial information such as the electrical distance to increase the accuracy in the process of graph convolution. In this paper, we construct a novel power-weighted line graph that uses power system topology and spatial information to optimize the edge weight assignment of the line graph. Then we propose a multi-graph convolutional network(MGCN) based on a graph classification task, which preserves a power system’s spatial correlations and captures the relationships among physical components. Our model can better handle the problem with power systems that have parallel lines, where our method can maintain desirable accuracy in modeling systems with these extra topology features. To increase the interpretability of the model, we present the MGCN using layer-wise relevance propagation and quantify the contributing factors of model classification.