熔体静电纺丝纤维细化技术研究进展

聚合物熔体静电纺丝技术是纳米纤维绿色高效制备的重要途径。但受限于熔体黏度高、导电性差和射流冷却快,制备纤维的平均直径往往分布在数百纳米至几十微米,远未达到直径小于100 nm的纳米材料。熔体电纺过程涉及驱动力、表面张力、熔体黏度和射流热交换速率等多种影响成型纤维直径的因素,各因素间相互影响,这使得熔体静电纺丝的纤维细化机理极其复杂。为此,文中从熔体泰勒锥形成和射流牵伸细化2个阶段出发,归纳分析了现有熔体电纺纤维细化研究的方法、工艺及材料体系对纤维直径的影响。研究表明,通过装置设计、材料体系调控和工艺优化来缩小泰勒锥尺寸、增大驱动力、降低熔体黏度并尽量延长射流牵伸细化时间是纤维细化的关键。射流运动状态与温度变化检测系统的设计、高电导率低黏度绿色纺丝专用料的开发以及吹-吸热气流辅助纺丝系统的设计等是熔体电纺纤维细化的研究趋势。

Casein kinase-2 inhibition promotes retinal ganglion cell survival after acute intraocular pressure elevation

Intraocular pressure elevation can induce retinal ganglion cell death and is a clinically reversible risk factor for glaucoma,the leading cause of irreversible blindness.We previously demonstrated that casein kinase-2 inhibition can promote retinal ganglion cell survival and axonal regeneration in rats after optic nerve injury.To investigate the underlying mechanism,in the current study we increased the intraocular pressure of adult rats to 75 mmHg for 2 hours and then administered a casein kinase-2 inhibitor(4,5,6,7-tetrabromo-2-azabenzimidazole or 2-dimethylamino-4,5,6,7-tetrabromo-1H-benzimidazole)by intravitreal injection.We found that intravitreal injection of 4,5,6,7-tetrabromo-2-azabenzimidazole or 2-dimethylamino-4,5,6,7-tetrabromo-1H-benzimidazole promoted retinal ganglion cell survival and reduced the number of infiltrating macrophages.Transcriptomic analysis showed that the mitogen activated protein kinase signaling pathway was involved in the response to intraocular pressure elevation but was not modulated by the casein kinase-2 inhibitors.Furthermore,casein kinase-2 inhibition downregulated the expression of genes(Cck,Htrsa,Nef1,Htrlb,Prph,Chat,Slc18a3,Slc5a7,Scn1b,Crybb2,Tsga10ip,and Vstm21)involved in intraocular pressure elevation.Our data indicate that inhibition of casein kinase-2 can enhance retinal ganglion cell survival in rats after acute intraocular pressure elevation via macrophage inactivation.

Directly predicting N_(2) electroreduction reaction free energy using interpretable machine learning with non-DFT calculated features

Electrocatalytic nitrogen reduction to ammonia has garnered significant attention with the blooming of single-atom catalysts(SACs),showcasing their potential for sustainable and energy-efficient ammonia production.However,cost-effectively designing and screening efficient electrocatalysts remains a challenge.In this study,we have successfully established interpretable machine learning(ML)models to evaluate the catalytic activity of SACs by directly and accurately predicting reaction Gibbs free energy.Our models were trained using non-density functional theory(DFT)calculated features from a dataset comprising 90 graphene-supported SACs.Our results underscore the superior prediction accuracy of the gradient boosting regression(GBR)model for bothΔg(N_(2)→NNH)andΔG(NH_(2)→NH_(3)),boasting coefficient of determination(R^(2))score of 0.972 and 0.984,along with root mean square error(RMSE)of 0.051 and 0.085 eV,respectively.Moreover,feature importance analysis elucidates that the high accuracy of GBR model stems from its adept capture of characteristics pertinent to the active center and coordination environment,unveilling the significance of elementary descriptors,with the colvalent radius playing a dominant role.Additionally,Shapley additive explanations(SHAP)analysis provides global and local interpretation of the working mechanism of the GBR model.Our analysis identifies that a pyrrole-type coordination(flag=0),d-orbitals with a moderate occupation(N_(d)=5),and a moderate difference in covalent radius(r_(TM-ave)near 140 pm)are conducive to achieving high activity.Furthermore,we extend the prediction of activity to more catalysts without additional DFT calculations,validating the reliability of our feature engineering,model training,and design strategy.These findings not only highlight new opportunity for accelerating catalyst design using non-DFT calculated features,but also shed light on the working mechanism of"black box"ML model.Moreover,the model provides valuable guidance for catalytic material design in multiple proton-electron coupling reactions,particularly in driving sustainable CO_(2),O_(2),and N_(2) conversion.

Influence of the position relationship between the cathode and magnetic separatrix on the discharge process of a Hall thruster

Previous studies have shown that there is an obvious coupling relationship between the installation location of the external cathode and the magnetic separatrix in the plume region of a Hall thruster.In this paper,the particle-in-cell simulation method is used to compare the thruster discharge process under the conditions of different position relationships between the cathode and the magnetic separatrix.By comparing the distribution of electron conduction,potential,plasma density and other microscopic parameters,we try to explain the formation mechanism of the discharge difference.The simulation results show that the cathode inside and outside the magnetic separatrix has a significant effect on the distribution of potential and plasma density.When the cathode is located on the outer side of the magnetic separatrix,the potential above the plume region is relatively low,and there is a strong potential gradient above the plume region.This potential gradient is more conducive to the radial diffusion of ions above the plume,which is the main reason for the strong divergence of the plume.The distribution of ion density is also consistent with the distribution of potential.When the cathode is located on the outer side of the magnetic separatrix,the radial diffusion of ions in the plume region is enhanced.Meanwhile,by comparing the results of electron conduction,it is found that the traiectories of electrons emitted from the cathode are significantly different between the inner and outer sides of the magnetic separatrix.This is mainly because the electrons are affected by the magnetic mirror effect of the magnetic tip,which makes it difficult for the electrons to move across the magnetic separatrix.This is the main reason for the difference in potential distribution.In this paper,the simulation results of macroscopic parameters under several conditions are also compared,and they are consistent with the experimental results.The cathode is located on the inner side of the magnetic separatrix,which can effectively reduce the plume divergence angle and improve the thrust.In this paper,the cathode moves from R=50 mm to R=35 mm along the radial direction,the thrust increases by 3.6 mN and the plume divergence angle decreases by 23.77%.Combined with the comparison of the ionization region and the peak ion density,it is found that the main reason for the change in thrust is the change in the radial diffusion of ions in the plume region.

Spinal Vertebral Fracture Detection and Fracture Level Assessment Based on Deep Learning

This paper addresses the common orthopedic trauma of spinal vertebral fractures and aims to enhance doctors’diagnostic efficiency.Therefore,a deep-learning-based automated diagnostic systemwithmulti-label segmentation is proposed to recognize the condition of vertebral fractures.The whole spine Computed Tomography(CT)image is segmented into the fracture,normal,and background using U-Net,and the fracture degree of each vertebra is evaluated(Genant semi-qualitative evaluation).The main work of this paper includes:First,based on the spatial configuration network(SCN)structure,U-Net is used instead of the SCN feature extraction network.The attention mechanismandthe residual connectionbetweenthe convolutional layers are added in the local network(LN)stage.Multiple filtering is added in the global network(GN)stage,and each layer of the LN decoder feature map is filtered separately using dot product,and the filtered features are re-convolved to obtain the GN output heatmap.Second,a network model with improved SCN(M-SCN)helps automatically localize the center-of-mass position of each vertebra,and the voxels around each localized vertebra were clipped,eliminating a large amount of redundant information(e.g.,background and other interfering vertebrae)and keeping the vertebrae to be segmented in the center of the image.Multilabel segmentation of the clipped portion was subsequently performed using U-Net.This paper uses VerSe’19,VerSe’20(using only data containing vertebral fractures),and private data(provided by Guizhou Orthopedic Hospital)for model training and evaluation.Compared with the original SCN network,the M-SCN reduced the prediction error rate by 1.09%and demonstrated the effectiveness of the improvement in ablation experiments.In the vertebral segmentation experiment,the Dice Similarity Coefficient(DSC)index reached 93.50%and the Maximum Symmetry Surface Distance(MSSD)index was 4.962 mm,with accuracy and recall of 95.82%and 91.73%,respectively.Fractured vertebrae were also marked as red and normal vertebrae were marked as white in the experiment,and the semi-qualitative assessment results of Genant were provided,as well as the results of spinal localization visualization and 3D reconstructed views of the spine to analyze the actual predictive ability of the model.It provides a promising tool for vertebral fracture detection.

“核”你在一起--重庆大学学生核学会的成长

一、我们社团从哪里来,要到哪里去新中国成立至今,我们不畏艰险,矢志不移地追逐“核大国梦”:两弹一星元勋钱学森先生说过:“外国人能造出来的,我们中国人同样能造出来。”抱有赤子之心的他直面挫折,愈挫愈勇,铸就“五年惊心归国路,十年铸剑导弹成”;中苏冷战时期,我们面对苏方的挑衅和蔑视,毛泽东主席切身体会到核武器在国家安全中有着无比重要的地位,他说:“核潜艇,一万年也要搞出来”。这是主席当时对国防科研工作者下达的死命令。星光不问赶路人,岁月不负有心人,从1964年罗布泊上空爆炸的蘑菇云,到1970年“长征一号”在波涛巨浪中浮出水面,甚至不久以后即将出世的004型核动力航母,在党的第一个一百年我们取得了世界瞩目的成就。如今,站在充满巨大挑战与无限可能的拐角处,拦在我们面前的是能源危机这座大山,“鲜衣怒马少年时,不负韶华行且知”,我们--重庆大学学生核学会于2017年应运而生。

A Blockchain-Based Life-Cycle Environmental Management Framework for Hospitals in the COVID-19 Context

During the coronavirus disease 2019 (COVID-19) emergency, many hospitals were built or renovated around the world to meet the challenges posed by the rising number of infected cases. Environmental management in the hospital life cycle is vital in preventing nosocomial infection and includes many infection control procedures. In certain urgent situations, a hospital must be completed quickly, and work process approval and supervision must therefore be accelerated. Thus, many works cannot be checked in detail. This results in a lack of work liability control and increases the difficulty of ensuring the fulfillment of key infection prevention measures. This study investigates how blockchain technology can transform the work quality inspection workflow to assist in nosocomial infection control under a fast delivery requirement. A blockchain-based life-cycle environmental management framework is proposed to track the fulfillment of crucial infection control measures in the design, construction, and operation stages of hospitals. The proposed framework allows for work quality checking after the work is completed, when some work cannot be checked on time. Illustrative use cases are selected to demonstrate the capabilities of the developed solution. This study provides new insights into applying blockchain technology to address the challenge of environmental management brought by rapid delivery requirements.

Behaviour of non-ballast pre-stressed and precast track structures in high speed railway based on multiscale finite element model

In order to make further study on the mechanical property of CRTSIII type slab non-ballast track structures,which was self-designed in China,based on the method of the multiscale finite element model(FEM),the traditional FEM of slab non-ballast track structures was improved.The multiscale FEM of CRTSII type slab nonballast track structures was established based on the general finite element program ABAQUs.Then the comparative calculation was made between various FEMs,showing that the high solution precision,fast modelling speed and high solution efficiency could be obtained.Therefore,the multiscale FEM was suitable for the parametric study on mechanical behaviour of CRTSII type slab non-ballast track structures,and then the key influence factor and constructions could be optimized.

Towards electronic-photonic-converged thermo-optic feedback tuning

As Moore’s law approaching its end,electronics is hitting its power,bandwidth,and capacity limits.Photonics is able to overcome the performance limits of electronics but lacks practical photonic register and flexible control.Combining electronics and photonics provides the best of both worlds and is widely regarded as an important post-Moore’s direction.For stability and dynamic operations considerations,feedback tuning of photonic devices is required.For silicon photonics,the thermooptic effect is the most frequently used tuning mechanism due to the advantages of high efficiency and low loss.However,it brings new design requirements,creating new design challenges.Emerging applications,such as optical phased array,optical switches,and optical neural networks,employ a large number of photonic devices,making PCB tuning solutions no longer suitable.Electronic-photonic-converged solutions with compact footprints will play an important role in system scalability.In this paper,we present a unified model for thermo-optic feedback tuning that can be specialized to different applications,review its recent advances,and discuss its future trends.

低化学交联反蛋白石水凝胶的制备及多重刺激响应性

将物理交联与化学交联相结合,利用蛋白石结构光子晶体模板法制备了低化学交联的聚N-异丙基丙烯酰胺/丙烯酸(C-dots/BIS-P(NIPAm-AA))反蛋白石结构光子晶体水凝胶(IOH_(P(NIPAm-AA)))。其中,pH敏感性单体丙烯酸(AA)和温敏性单体N-异丙基丙烯酰胺(NIPAm)的引入赋予了IOH_(P(NIPAm-AA))多重刺激响应性。通过扫描电镜表征了IOH_(P(NIPAm-AA))的内部微观结构,探究了共聚单体AA含量对IOH_(P(NIPAm-AA))的影响,并基于结构色的变化来研究IOH_(P(NIPAm-AA))对外部刺激的响应行为。结果表明,低化学交联的IOH_(P(NIPAm-AA))具有规整有序的三维大孔结构。随着共聚单体AA用量从0.54 mL增大到0.9 mL,IOH_(P(NIPAm-AA))的结构色由蓝色转为蓝绿色再变为黄绿色,同时反射光谱发生了明显的红移。IOH_(P(NIPAm-AA))对pH、温度和溶剂有灵敏的响应,在这些因素刺激下,IOH_(P(NIPAm-AA))的结构色发生显著变化,其最大反射峰波长也产生了相应的移动。因温敏性单体NIPAm的存在,IOH_(P(NIPAm-AA))的结构色在近40℃呈现可逆的出现-消失。

Gold-loaded graphene oxide/PDPB composites for the synchronous removal of Cr(Ⅵ) and phenol

The construction of novel inorganic‐organic hybrid nanomaterials for synchronous photocatalyticremoval of heavy metal ions and organic pollutants has received significant attention.We successfullysynthesized gold‐loaded graphene oxide/PDPB(polymer poly(diphenylbutadiyne))composites(Au‐GO/PDPB)through a facile mechanical agitation and photoreduction method.The compositeswere characterized by XPS and TEM images,which confirmed the presence of GO and Au nanoparticleson the PDPB.The as‐prepared Au‐GO/PDPB composites displayed enhanced photocatalytic activity compared with that of pure PDPB for the synchronous photoreduction of hexavalent chromium(Cr(VI))and photo‐oxidation of phenol.We also determined the optimal loading mass of GO and Au nanoparticles on the PDPB;the Au1‐GO2/PDPB(2.0wt%GO and1.0wt%Au)composite displayed the best photocatalytic activity among all the catalysts.Our study provides a facile way to prepare inorganic‐organic composites for the synchronous photocatalytic removal of heavy metal ions and organic pollutants.?2018,Dalian Institute of Chemical Physics,Chinese Academy of Sciences.Published by Elsevier B.V.All rights reserved.

Location Privacy in Device-Dependent Location-Based Services:Challenges and Solution

With the evolution of location-based services(LBS),a new type of LBS has already gain a lot of attention and implementation,we name this kind of LBS as the Device-Dependent LBS(DLBS).In DLBS,the service provider(SP)will not only send the information according to the user’s location,more significant,he also provides a service device which will be carried by the user.DLBS has been successfully practised in some of the large cities around the world,for example,the shared bicycle in Beijing and London.In this paper,we,for the first time,blow the whistle of the new location privacy challenges caused by DLBS,since the service device is enabled to perform the localization without the permission of the user.To conquer these threats,we design a service architecture along with a credit system between DLBS provider and the user.The credit system tie together the DLBS device usability with the curious behaviour upon user’s location privacy,DLBS provider has to sacrifice their revenue in order to gain extra location information of their device.We make the simulation of our proposed scheme and the result convince its effectiveness.

Overcoming coke formation in high-temperature CO_(2)electrolysis

High-temperature CO_(2)reduction reaction(HT-CO_(2)RR)in solid oxide electrochemical cells(SOECs)features near-unity selectivity,high energy efficiency,and industrial relevant current density for the production of CO,a widely-utilized“building block”in today’s chemical industry.Thus,it offers an intriguing and promising means to radically change the way of chemical manufacturing and achieve carbon neutrality using renewable energy sources,CO_(2),and water.Albeit with the great potential of HT-CO_(2)RR,this carbon utilization approach,unfortunately,has been suffering coke formation that is seriously detrimental to its energy efficiency and operating lifetime.In recent years,much effort has been added to understanding the mechanism of coke formation,managing reaction conditions to mitigate coke formation,and devising coke-formation-free electrode materials.These investigations have substantially advanced the HT-CO_(2)RR toward a practical industrial technology,but the resulting coke formation prevention strategies compromise activity and energy efficiency.Future research may target exploiting the control over both catalyst design and system design to gain selectivity,energy efficiency,and stability synchronously.Therefore,this perspective overviews the progress of research on coke formation in HT-CO_(2)RR,and elaborates on possible future directions that may accelerate its practical implementation at a large scale.

DPIF:A Framework for Distinguishing Unintentional Quality Problems From Potential Shilling Attacks

Maliciously manufactured user profiles are often generated in batch for shilling attacks.These profiles may bring in a lot of quality problems but not worthy to be repaired.Since repairing data always be expensive,we need to scrutinize the data and pick out the data that really deserves to be repaired.In this paper,we focus on how to distinguish the unintentional data quality problems from the batch generated fake users for shilling attacks.A two-steps framework named DPIF is proposed for the distinguishment.Based on the framework,the metrics of homology and suspicious degree are proposed.The homology can be used to represent both the similarities of text and the data quality problems contained by different profiles.The suspicious degree can be used to identify potential attacks.The experiments on real-life data verified that the proposed framework and the corresponding metrics are effective.

Efficient Heavy Hitters Identification over Speed Traffic Streams

With the rapid increase of link speed and network throughput in recent years,much more attention has been paid to the work of obtaining statistics over speed traffic streams.It is a challenging problem to identify heavy hitters in high-speed and dynamically changing data streams with less memory and computational overhead with high measurement accuracy.In this paper,we combine Bloom Filter with exponential histogram to query streams in the sliding window so as to identify heavy hitters.This method is called EBF sketches.Our sketch structure allows for effective summarization of streams over time-based sliding windows with guaranteed probabilistic accuracy.It can be employed to address problems such as maintaining frequency statistics and finding heavy hitters.Our experimental results validate our theoretical claims and verifies the effectiveness of our techniques.

Theoretical and quantitative evaluation of hybrid PMLABCs for seismic wave simulation

A good artificial boundary treatment in a seismic wave grid-based numerical simulation can reduce the size of the computational region and increase the computational efficiency,which is becoming increasingly important for seismic migration and waveform inversion tasks requiring hundreds or thousands of simulations.Two artificial boundary techniques are commonly used:perfectly matched layers(PMLs),which exhibit the excellent absorption performance but impose a greater computational burden by using finite layers to gradually reduce wave amplitudes;and absorbing boundary conditions(ABCs),which have the high computational efficiency but are less effective in absorption because they employ the one-way wave equation at the exterior boundary.Naturally,PMLs have been combined with ABCs to reduce the number of PMLs,thus improving the computational efficiency;many studies have proposed such hybrid PMLs.Depending on the equations from which the ABCs are derived,there are two hybrid PML variants:the PML+unstretched ABC(UABC),in which the ABC is derived from a physical equation;or the PML+stretched ABC(SABC),in which the ABC is derived from the PML equation.Even though all the previous studies concluded that hybrid PMLs can improve the absorption performance,none of them quantified how many PMLs can be removed by combining the PML with the ABC compared with the pure PML.In this paper,we systematically study the absorption performance of the two hybrid PML variants.We develop a method to distinguish the artificial reflections from the PML-interior interface and those caused by the PML exterior boundary to accurately approximate the additional absorption achieved by using the UABC and the SABC.The reflection coefficients based on a theoretical derivation and numerical tests both show that the UABC amplifies most reflections and is not recommended in any situation;conversely,the SABC can always diminish reflections,but the additional absorption achieved by the SABC is relatively poor and cannot effectively reduce the number of PMLs.In contrast,we find that simply increasing the damping parameter improves absorption better than the PML+SABC.Our results show that the improvement in absorption achieved by combining the PML with either the SABC or the UABC is not better than that obtained by simply adjusting the damping profile of the PML;thus,combining the PML with the ABC is not recommended in practice.

Research on Real-Time High Reliable Network File Distribution Technology

The rapid development of Internet of Things(IoT)technology has made previously unavailable data available,and applications can take advantage of device data for people to visualize,explore,and build complex analyses.As the size of the network and the number of network users continue to increase,network requests tend to aggregate on a small number of network resources,which results in uneven load on network requests.Real-time,highly reliable network file distribution technology is of great importance in the Internet of Things.This paper studies real-time and highly reliable file distribution technology for large-scale networks.In response to this topic,this paper studies the current file distribution technology,proposes a file distribution model,and proposes a corresponding load balancing method based on the file distribution model.Experiments show that the system has achieved real-time and high reliability of network transmission.

风电机组支撑结构技术发展现状及趋势

发展风电是实现“双碳”目标的重要途径。与欧洲地区相比,我国风电产业起步较晚,但发展迅速。目前我国风电行业已进入平价上网阶段,并面临大型化发展趋势,对风电机组支撑结构(包括塔筒与基础)的稳定性、安全性、经济性提出了更高要求。在陆上风电机组塔筒方面,全钢结构塔筒和钢-混凝土混合结构塔筒已广泛使用,其中全钢结构塔筒目前的研究主要围绕局部屈曲和结构优化展开,钢-混凝土混合结构塔筒研究的重、难点在接缝和混凝土疲劳设计方面,当前轮毂高度超过140 m的风电机组普遍使用钢-混凝土混合结构塔筒。此外,格构式和桁架式风电机组塔架在超大容量风电机组和超高轮毂区间具有显著优势,目前已有多种不同形式的样机完成并网。在陆上风电机组基础方面,现浇式混凝土基础施工技术成熟、适应性广,已广泛得以应用,装配式混凝土基础适用于现浇混凝土施工困难的特殊环境。对于海上风电固定式基础,单桩基础结构形式简单,应用最为广泛;重力式基础、吸力筒式基础和多桩式基础也有一定的应用;导管架式基础具有刚度大、稳定性好等优势,适用于较深水域。漂浮式海上风电基础是新的发展方向,包括半潜式、张力腿式、单柱式和驳船式等形式,截至2023年底全球漂浮式风电总装机容量未超过500 MW,还有很大的发展空间。目前风电机组支撑结构仍面临设计理论不完善、具有自主知识产权的通用型设计软件缺失、技术标准体系尚未建立等问题,未来需重点开展相关工作。

数值模拟法分析压裂生产井的裂缝开度

非常规油气藏水力压裂后的数值模拟中,裂缝开度普遍采用的是均匀分布的方式。但是实验室的试验结果表明,有效应力发生变化会导致裂缝开度分布并不均匀。而在绝大多数数值模型中往往不考虑这一现象。本文调研了生产过程中压力对裂缝开度的影响作用。在数值模拟模型中,裂缝开度的作用比较明确,与此同时,考虑了闭合应力的影响。通过一个非结构化的泰森多边形网格完成离散型裂缝建模,该模型考虑了复杂的裂缝几何形状。

Experimental study on combustion characteristics of supersonic combustor based on alternating-wedge strut

Acetone Planar Lase-Induced Fluorescence(PLIF)and OH-PLIF were employed to capture the fuel distribution and OH distribution downstream for the supersonic combustor based on the alternating-wedge strut.The combustion establishment process and combustion mode in the combustor under different fuel injection methods and different equivalence ratios were analyzed.Combined with the kerosene-PLIF and OH-PLIF results in the cavity combustor,a comparative analysis was conducted to understand the combustion characteristics and combustion modes between the alternating-wedge strut-based combustor and the cavity-based combustor.The results show that the combustor is in weak combustion mode in the case of low equivalence ratio,and the combustor is in intensive combustion mode in the case of high equivalence ratio.The lower limit of the equivalence ratio of the combustor to maintain the intensive combustion mode varies based on different fuel injection methods.The OH distribution under reacting condition has a strong correlation with the fuel distribution under non-reacting condition.The OH fluorescence signal near the injector is weaker when the fuel distribution is more concentrated.The injector position located at the base of the strut rear has better mixing performance,enabling the combustor to be in intensive combustion mode at a lower equivalence ratio.The combustion reaction in the alternating-wedge strut-based combustor is not necessarily dominated by mass transfer due to the mixing enhancement and premixed zone downstream of strut,while the combustion reaction process in the cavity-based combustor is mainly influenced by mass transfer.