尾渣中砷的精细化学结构、赋存形态

本文以安徽某有色金属冶炼厂排放的尾渣为研究对象,利用扫描电镜(SEM)、X射线衍射仪(XRD)、X射线荧光光谱分析仪(XRF)和X射线光电子能谱仪(XPS)等方法对尾渣中As的精细结构进行分析,并结合Tessier提取法研究As在尾渣中的赋存形态。结果表明,尾渣中As主要与O共生以As(Ⅴ)-O金属砷酸盐形式存在,含砷矿物为砷酸铁FeAsO_(4)和拉砷铜石Cu(AsO_(4))_(2),伴有少量砷酸铝和硫化砷;总砷含量范围为0.11%—0.17%,赋存形态以残渣态为主,占90%—95%,不同形态As含量大小依次为残渣态>Fe-Mn氧化态>碳酸盐结合态>可交换态>有机结合态;pH是影响As迁移转化的重要因素之一,在环境中会积累一定水平的潜在As释放风险。

Room-temperature continuous-wave operation of GaN-based blue-violet laser diodes with a lifetime longer than 1000h

GaN-based continuous-wave operated blue-violet laser diodes(LDs) with long lifetime are demonstrated, which are grown on a c-plane GaN substrate by metal organic chemical vapor deposition with a 10 × 600 μm^2 ridge waveguide structure.The electrical and optical characteristics of a blue-violet LD are investigated under direct-current injection at room temperature(25 °C). The stimulated emission wavelength and peak optical power of the LD are around 413 nm and over 600 mW, respectively.In addition, the threshold current density and voltage are as small as 1.46 kA/cm^2 and 4.1 V, respectively. Moreover, the lifetime is longer than 1000 hours under room-temperature continuous-wave operation.

GDNF-Enhanced Axonal Regeneration and Myelination Following Spinal Cord Injury is Mediated by Primary Effects on Neurons

我们先前研究表明胶质细胞源性神经营养因子(GDNF)联合施万细胞移植能促进脊髓损伤后轴突再生和髓鞘形成。然而,GDNF介导这一过程的细胞靶点尚不清楚。在此,我们报道了GDNF可增加在体再生轴突的数目和直径,并促进体外背根神经节神经元的轴突向外生长,提示GDNF对神经元有直接作用。在施万细胞-背根神经节神经元共培养下,GDNF显著增加施万细胞生成的髓鞘数目;GDNF处理对孤立培养的施万细胞增殖无作用,但可促进已与神经轴突有突触联系的施万细胞增殖;GDNF可增加孤立施万细胞中分子量为140kDa的神经细胞黏附分子(NCAM)的表达,但对黏附分子L1表达或神经营养因子NGF、NT3及BDNF分泌没有影响。总之,这些结果支持假设:GDNF提高轴突再生和施万细胞髓鞘形成主要是通过GDNF对神经元的直接作用介导的,并且提示GDNF联合施万细胞移植可能是促进脊髓损伤后轴突再生和髓鞘形成的有效策略之一。

Effect of inhomogeneous broadening on threshold current of GaN-based green laser diodes

The inhomogeneous broadening parameter and the internal loss of green LDs are determined by experiments and theoretical fitting. It is found that the inhomogeneous broadening plays an important role on the threshold current density of green LDs. The green LD with large inhomogeneous broadening even cannot lase. Therefore, reducing inhomogeneous broadening is a key issue to improve the performance of green LDs.

Effect of microstructure of Au80Sn20 solder on the thermal resistance TO56 packaged GaN-based laser diodes

Au80Sn20 alloy is a widely used solder for laser diode packaging.In this paper,the thermal resistance of Ga N-based blue laser diodes packaged in TO56 cans were measured by the forward voltage method.The microstructures of Au80Sn20 solder were then investigated to understand the reason for the difference in thermal resistance.It was found that the microstructure with a higher content of Au-rich phase in the center of the solder and a lower content of(Au,Ni)Sn phase at the interface of the solder/heat sink resulted in lower thermal resistance.This is attributed to the lower thermal resistance of Au-rich phase and higher thermal resistance of(Au,Ni)Sn phase.

A comparative study of 85 hyperelastic constitutive models for both unfilled rubber and highly filled rubber nanocomposite material

Nonlinear finite element analysis is widely used for structural optimization of the design and the reliability analysis of complex elastomeric components.However,high-precision numerical results cannot be achieved without reliable strain energy functions(SEFs)of the rubber or rubber nanocomposite material.Although hyperelastic constitutive models have been studied for nearly 80 years,selecting one that accurately describes rubber's mechanical response is still a challenge.This work reviews 85 isotropic SEFs based on both the phenomenological theory and the micromechanical network theory proposed from the 1940s to 2019.A fitting algorithm which can realize the automatic fitting optimization and determination of the parameters of all SEFs reviewed is developed.The ability of each SEF to reproduce the experimental data of both the unfilled and highly filled rubber nanocomposite is quantitatively assessed based on a new proposed evaluation index.The top 30 SEFs for the unfilled rubber and the top 14 SEFs for the highly filled rubber nanocomposite are presented in the ranking lists.Finally,some suggestions on how to select an appropriate hyperelastic constitutive model are given,and the perspective on the future progress of constitutive models is summarized.

Hydrodynamics and mass transfer performance analysis of flow-guided trapezoid spray packing tray

Distillation is the most common separation technology utilized in the petroleum and chemistry industries.Due to the wide usage of the distillation column,even a small improvement in performance may result in significant energy cost savings.Aiming to improve the hydrodynamics and mass transfer performance,the flow-guided trapezoid spray-packing tray(FTS-PT)was designed by combining flow-guided holes and trapezoidal caps with structured packing.And the experimental measurements of the FTSPT,including pressure drop,clear liquid height,weeping,entrainment,and tray efficiency,were conducted in a 500 mm diameter plexiglass column with the air-water-oxygen system.Moreover,the performance of the FTS-PT was compared with that of new vertical sieve tray(New VST)and F1 valve tray.The results show that FTS-PT has a significant advantage in pressure drop,entrainment,and capacity.Furthermore,the calculation model of the pressure drop was derived and used for the FTS-PT with a relative deviation of less than 5%.

冻融环境下钢筋混凝土粘结性能研究现状

基于国内外关于钢筋混凝土结构在冻融循环作用下钢筋和混凝土之间粘结性能的研究进展,重点总结了在冻融条件下以及冻融和腐蚀、荷载等因素共同作用下钢筋混凝土粘结滑移性能的研究进展和现状,综合分析了现有的研究成果,在此基础上提出了一些不足和建议。

Fabrication of a High-Performance and Reusable Planar Face Mask in Response to the COVID-19 Pandemic

The coronavirus disease 2019(COVID-19)pandemic has caused a surge in demand for face masks,with the massive consumption of masks leading to an increase in resource-related and environmental con-cerns.In this work,we fabricated meltblown polypropylene(mb-PP)-based high-performance planar face masks and investigated the effects of six commonly used disinfection methods and various mask-wearing periods on the reusability of these masks.The results show that,after three cycles of treatment using hot water at 70℃ for 30 min,which is one of the most scalable,user-friendly methods for viral disinfection,the particle filtration efficiency(PFE)of the mask remained almost unchanged.After mask wearing for 24 h and subsequent disinfection using the same treatment procedures,the PFE decreased to 91.3%;the average number of bacterial and fungal colonies was assessed to be 9.2 and 51.6 colony-forming units per gram(CFU∙g^(-1)),respectively;and coliform and pyogenic bacteria were not detected.Both the PFE and the microbial indicators are well above the standard for reusable masks after disinfection.Schlieren pho-tography was then used to assess the capabilities of used and disinfected masks during use;it showed that the masks exhibit a high performance in suppressing the spread of breathed air.

Particle Filtering with Multi Proposal Distributions

Particle filtering algorithm has been applied to various fields due to its capacity to handle nonlinear/non-Gaussian dynamic problems. One crucial issue in particle filtering is the selection of the proposal distribution that generates the particles. In this paper, we give a novel strategy for selecting proposal distribution. Firstly, divide-conquer strategy is used, in which the particles used are divided into several parts. Afterward, different parts of particles are drawn from different proposal distributions. People can flexibly adjust how many of the particles drawn from specific proposal distributions according to their idiographic requirements. We provide simulation results that show its efficiency and performance.

关于散度型超抛物方程弱解的正则性

本文综述散度型有界可测系数的超抛物型方程弱解正则性方面的进展及相关的研究.首先,介绍相关方程的背景和在不同相关领域的应用;其次,重点描述De Giorgi-Nash-Moser的正则性理论在该方面研究上的发展;最后,介绍在相关问题研究上的应用.

Design and preparation of a crosslinkable,oil-resistant,and bio-based elastomer from fumarate

Poly(diethyl fumarate-co-methoxyethyl acrylate-co-vinyl chloroacetate)(PDEFMV),a novel bio-based elastomer with a saturated structure,was synthesized via redox emulsion polymerization.The glass-transition temperatures of PDEFMV,adjusted through the variation of the diethyl fumarate-to-methoxyethyl acrylate feeding ratio,ranged from-36.1 to-14.8 ℃.The number-average molecular weights of PDEFMV ranged from 384,000 to 46,000 g/mol.In designing the molecular structure,vinyl chloroacetate was used to provide active sites for subsequent vulcanization and crosslinking.The active chlorine groups within the PDEFMV chain reacted with the crosslinking agent trithiocyanuric acid under high temperature and pressure to form a nonsulfur crosslinked three-dimensional network structure.To achieve the desired properties,carbon black(CB,N330) was incorporated to reinforce PDEFMV,leading to the formation of PDEFMV/CB composites.A comprehensive study was conducted on the high-temperature oil resistance of PDEFMV/CB composites.Following immersion in IRM903 oil at temperatures of 150 and 200 ℃ for 72 h,the mass and volume changes in PDEFMV/CB were lower than those observed in commercially available acrylate rubber(AR)/CB,indicating that PDEFMV exhibited superior oil resistance.Furthermore,the aging characteristics and mechanisms of oil resistance in the PDEFMV/CB and AR/CB composites were investigated at different temperatures(150,200,and 250 ℃).The results provide insights into the operational temperature ranges suitable for PDEFMV/CB and offer valuable guidance for potential industrial applications.

C^(α)regularity of weak solutions of non-homogeneous ultraparabolic equations with drift terms

We consider a class of non-homogeneous ultraparabolic differential equations with singular drift terms arising from some physical models,and prove that weak solutions are H?lder continuous,which are sharp in some sense and also generalize the well-known De Giorgi-Nash-Moser theory to degenerate parabolic equations satisfying the H?rmander hypoellipticity condition.The new ingredients are manifested in two aspects:on the one hand,for lower-order terms,we exploit a new Sobolev inequality suitable for the Moser iteration by improving the result of Pascucci and Polidoro(2004);on the other hand,we explore the G-function from an early idea of Kruzhkov(1964)and an approximate weak Poincaréinequality for non-negative weak sub-solutions to prove the H?lder regularity.

On the steady Prandtl boundary layer expansions

In this paper,we consider the zero-viscosity limit of the 2D steady Navier-Stokes equations in(0,L)×R+with no-slip boundary conditions.By estimating the stream-function of the remainder,we justify the validity of the Prandtl boundary layer expansions.Specially,we show the global stability under the concavity condition of the Prandtl profile for an arbitrarily large constant L when the Euler flow is shear.

Research progress on sustainability of key tire materials

In recent years,countries worldwide have engaged actively in the research and development of green and sustainable materials in the face of the increasing depletion of petroleum resources,the need to reduce material waste,and the environmental pollution caused by the various types of waste.In the tire industry,the key materials for the various components of tires are mostly dependent on petroleum resources.Development of green tires and green processing technologies using sustainable materials is an important development direction for the future of the tire industry,and many tire-manufacturing companies have proposed their visions for the development of eco-friendly tires.Rubber,cord fabric,and additives are the main materials used in tire manufacturing.This article summarizes the research status of the green materials that can meet the requirements of environmental friendliness and sustainability,replace traditional materials,and reduce petroleum resource consumption in existing tire production.These materials mainly include natural rubber or bio-based synthetic rubber,green renewable cord fabrics,and green processing additives.The prospects for the application of these new green materials in tire manufacturing are also discussed.

Topological network design toward high-performance vegetable oil-based elastomers

As a kind of bio-derived feedstock,vegetable oil(VO)shows great potential to replace petroleum-based monomers to develop sustainable polymer materials because of its easy availability,low cost,bio-renewable,and environmentally friendly nature.However,due to the high cross-linking density and amorphous nature,directly cured VOs generally tend to be brittle and weak.To date,it is still difficult to adopt VOs and their derivatives as structural materials to prepare high-performance elastomers.To address this important issue,amulti-scale topology design strategy was proposed in this work.First,topology regulation and functionalization of VO-based networks were realized by managing functional groups proportion during the bulk polymerization of epoxidized soybean oil with dimer fatty acids.Furthermore,a second polymer(SN)network was introduced into the VO-based network as a protective layer via interfacial cross-links.The generated VO-based elastomers(VOEs)exhibit unprecedented comprehensive properties(VO content≥70 wt.%,T_(g)as low as−24.4℃,toughness up to 6.8 MJ/m^(3)).Besides,the VOEs also exhibit excellent reprocessability and self-healing capability.Overall,this work developed a novel kind of VOEs with significant comprehensive advantages and provided important inspiration for the preparation of high-performance elastomers throughmulti-scale topology regulation.

Recyclable thermally conductive poly(butylene adipate-co-terephthalate)composites prepared via forced infiltration

With the rapid development of electronic equipment and communication technology,the demand for polymer composites with high thermal conductivity and mechanical properties has increased significantly.However,its nondegradable polymer matrix will inevitably bring more and more serious environmental pollution.Therefore,it is urgent to develop biodegradable thermally conductive polymer composites.In this work,biodegradable poly(butylene adipate-coterephthalate)(PBAT)is used as the matrix material,and vacuum-assisted filtration technology is employed to prepare carbon nanotube(CNT)and cellulose nanocrystal(CNC)networks with high thermal conductivity.Then CNT-CNC/PBAT composites with high thermal conductivity and excellent mechanical properties are prepared by the ultrasonic-assisted forced infiltration method.Both experiment and simulation methods are used to systematically investigate the thermally conductive and dissipation performances of the CNT-CNC/PBAT composites.Above all,a simple alcoholysis reaction is applied to realize the separation of the PBAT matrix and functional fillers without destroying the conductive network skeleton,which makes it possible for the recycling of thermally conductive polymer composites.

RAFT链转移剂的选用原则及通用型RAFT链转移剂

可逆加成-断裂链转移聚合(RAFT Polymerization)是目前最为常用的活性可控自由基聚合方法之一,因其产物分子量分布较窄、适用单体范围广、反应条件温和等优势得到了不同领域科学家的广泛应用。然而,科学家们在选择RAFT链转移剂(也称RAFT试剂)时,经常会忽略RAFT链转移剂与单体活性的匹配原则,导致在制备高活单体与低活单体的嵌段共聚物方面存在产物分子量分布宽、聚合速率慢,甚至反应无法成功进行的问题。基于此,本文首先综述聚合中RAFT链转移剂的选用原则,随后介绍近几年开发的一类同时适用于高/低活性单体聚合的通用型RAFT链转移剂(Universal/Switchable RAFT agent)的作用原理及适用条件,并着重探讨了基于通用型RAFT链转移剂制备高/低活性单体的嵌段共聚物的最新进展及应用。

GaN基蓝光与绿光激光器

GaN基激光二极管(LD)将半导体LD的波长扩展到可见光谱和紫外光谱范围,因此有望被广泛用于光钟等量子技术、生物医疗仪器、激光显示、照明和材料加工等领域.尽管它们与GaN基发光二极管(LED)基于相同的Ⅲ氮化物材料,但是蓝光和绿光LD面临更大的挑战.在本文中,我们从外延生长和结构设计的角度对GaN基蓝光和绿光LD面临的挑战和进展进行了回顾总结.InN、GaN和AlN之间的晶格常数和生长条件差异很大,因此需要进行深入研究来提高蓝光,尤其是绿光LD的InGaN/GaN多量子阱(MQW)增益介质的材料质量.p型掺杂分布,生长条件和器件结构对减少内部损耗并抑制InGaN MQW的热退化至关重要.此外,空穴注入也是GaN基LD面临的关键问题.

Design and synthesis by redox polymerization of a bio-based carboxylic elastomer for green tire

Poly(dibutyl itaconate-co-isoprene-co-methacrylic acid)(PDIM) elastomer was designed and synthesized by redox emulsion polymerization under mild conditions. PDIM has high molecular weight, relatively high yield, and low glass transition temperature(Tg). The structure of PDIM was determined by FTIR and NMR, and the carboxyl content was obtained by titration in a non-proton solvent. Tensile strength and elongation at break increased with increasing carboxyl content. In addition, the interaction between PDIM and silica was elucidated by rubber process analyzer(RPA) and TEM, and the results showed that the silica-PDIM interaction was strong, but the silica-silica interaction was weak.