碳载体空位工程助力原位合成的Pt纳米枝晶促进电催化氧气还原

质子交换膜燃料电池(PEMFCs)因其高能量密度、低操作温度和环保等特性,被视为极具潜力的能量转换系统.目前,碳载铂颗粒(Pt/C)是PEMFCs阴极氧还原反应(ORR)中使用最广泛的催化剂.然而,Pt与碳载体间的电子结构差异导致Pt纳米颗粒(Pt NPs)易从碳载体上脱落,严重降低了ORR的催化活性.此外,Pt的高成本和稀缺性也限制了其广泛应用.相比之下,Pt纳米枝晶(NDs)因具有高利用率的表面活性位点而备受关注.然而,Pt NDs的合成通常需要严格控制反应条件,且其与碳基底间的弱相互作用易导致活性位点损失和性能下降.因此,开发具有强金属载体相互作用的Pt复合碳催化剂对PEMFCs的实际应用至关重要.本文通过原位Cl-介导的生长策略,结合碳本征空位工程,成功制备了分散在富含碳本征空位的中空氮掺杂碳基底上的Pt NDs催化剂(Pt@HNC-V-800).拉曼光谱和电子顺磁共振光谱结果表明,碳本征空位的形成机制源于碳基底结构中氮原子的耗散,该过程引起碳原子的重新排列,进而产生了丰富的本征缺陷位点.X射线吸收光谱和X射线光电子能谱结果表明,与无碳空位的Pt@HNC催化剂相比,富含本征碳空位的样品(Pt@HNC-V-800)表现出较低的Pt-Pt键配位数(8.64)和更强的给电子效应.得益于Pt NDs丰富的活性位点及其与本征碳空位基底之间的强电子效应,Pt@HNC-V-800的ORR半波电位高达0.947 V,质量活性和比表面活性分别为1.55 A mg^(-1) Pt和1.85 mA cm^(-2),是商用Pt/C的8.2和6.8倍(0.191 A mg^(-1)Pt和0.27 mA cm^(-2)).加速耐久性测试结果表明,经20000次电势循环后,Pt@HNC-V-800的活性无明显变化,其活性损失远低于无碳本征空位的Pt@HNC材料和商业Pt/C催化剂.因此,与无碳本征空位的Pt@HNC材料相比,Pt@HNC-V-800的ORR活性和稳定性都有较大提升,进一步证实了碳本征空位工程协同Pt NDs策略的优越性.此外,密度泛函理论计算结果表明,Pt@HNC-V的丰富空位降低了氧中间体过电势,优化了ORR中间体在Pt NDs上的吸附能,进而提高了催化剂的ORR本征活性.同时,富碳本征空位的存在增强了Pt NDs在碳载体上的结合能,使Pt NDs不易在电势循环过程中脱离碳载体,从而增强了稳定性.综上所述,本文通过Pt NDs与碳本征空位工程协同效应策略,精准调控碳负载Pt基催化剂的结构,大幅提升其在酸性条件下的ORR性能,为进一步设计高性能的ORR电催化剂提供了新思路.

电场处理对YG8硬质合金及其刀具性能的影响

为探索一种高效的硬质合金强化处理技术,研究了电场处理对YG8硬质合金显微组织及性能的影响,采用TEM、SEM等对电场处理前后的YG8硬质合金试样及其刀具进行微观组织分析,采用维氏硬度计进行力学性能测试,数控车床进行切削加工实验。结果表明:经电场处理后,YG8硬质合金试样断裂韧性有所增大,其刀具切削性能得到提升,且电场处理刀具的被加工工件表面质量明显得到提高。在脉冲电流作用下,材料会发生电塑性效应,为位错运动提供驱动力,使位错更容易进行增殖和滑移,位错密度增加,从而有利于材料性能的提高。当脉冲电流为15 A/mm^(2)时,断裂韧性达到最大值9.41 MPa·m^(1/2),相比于未使用电场处理的断裂韧性提高了近10%。经电场处理的YG8硬质合金刀具在切削过程中切削温度降低,可有效防止积屑瘤产生,改善切削过程的摩擦状态,保证了切削质量,使得被加工工件表面质量明显提高。

Residual stress modeling of mitigated fused silica damage sites with CO_(2)laser annealing

A numerical model based on measured fictive temperature distributions is explored to evaluate the residual stress fields of CO_(2)laser-annealed mitigated fused silica damage sites.The proposed model extracts the residual strain from the differences in thermoelastic contraction of fused silica with different fictive temperatures from the initial frozen-in temperatures to ambient temperature.The residual stress fields of mitigated damage sites for the CO_(2)laser-annealed case are obtained by a finite element analysis of equilibrium equations and constitutive equations.The simulated results indicate that the proposed model can accurately evaluate the residual stress fields of laser-annealed mitigated damage sites with a complex thermal history.The calculated maximum hoop stress is in good agreement with the reported experimental result.The estimated optical retardance profiles from the calculated radial and hoop stress fields are consistent with the photoelastic measurements.These results provide sufficient evidence to demonstrate the suitability of the proposed model for describing the residual stresses of mitigated fused silica damage sites after CO_(2)laser annealing.

Healthy life expectancy with cardiovascular disease among Chinese rural population based on the prospective cohort study

BACKGROUND Limited research has explored the impact of cardiovascular disease(CVD)on healthy life expectancy(HLE)especially in resource-limited areas.This study aimed to investigate the association between CVD and HLE in Chinese rural population.METHODS This study included 11,994 participants aged 45 years and older from the baseline and follow-up surveys of the Henan rural cohort study.Healthy status was measured via a Visual Analogue Scale.The multistate Markov model was applied to estimate the association between CVD and transitions in health,unhealthiness and death.Gender-specific total life expectancy,HLE and unhealthy life expectancy were calculated by the multistate life table method.RESULTS During a mean follow-up time of 3.85(3.84–3.86)years,there were 588 deaths recorded.For individuals with CVD,the risk of switching from health to unhealthiness status was increased by 71%[hazard ratio(HR)=1.71,95%CI:1.42–2.07],the chance of recovery was reduced by 30%(HR=0.70,95%CI:0.60–0.82).Men aged 45 years without CVD could gain an extra 7.08(4.15–10.01)years of HLE and lose 4.00(1.60–6.40)years of unhealthy life expectancy compared to their peers with CVD,respectively.The corresponding estimates among women were 8.62(5.55–11.68)years and 5.82(2.59–9.04)years,respectively.CONCLUSIONS This study indicated that CVD was significantly associated with poorer health status and lower HLE among Chinese rural population.It is an important public health policy to adopt targeted measures to reduce the CVD burden and enhance the quality of life and HLE in resource-limited areas.

济阳页岩油水平井套管变形影响规律研究

套管变形导致压裂工具串遇阻是胜利济阳页岩油压裂开发过程中面临的主要难题之一。压裂开采中套管载荷影响因素复杂,基于常规区块的页岩油套管变形研究理论不能有效适用于工程地质条件复杂的济阳页岩。为此,针对济阳首口页岩油井,在分析现场测井数据的基础上,采用有限元方法模拟了固井质量和压裂施工参数对套管变形的影响规律。研究结果表明:水泥环在缺失严重时(缺失角度大于50°或缺失深度大于25 mm)会使套管发生强度破坏,水泥环缺失的临界部位是最容易发生套管损坏的部位;套管的最大应力随水泥环弹性模量的增大而减小,而受泊松比影响较小;注入排量的增加与周围地应力差成正比,在排量为10~12 m^(3)/min时可获得较好的裂缝宽度,注入时间在150 s时周围地应力差最小;随压裂段间距的增加,套管周围地应力差减小,在压裂间距大于18 m后,再增大压裂间距以降低套管应力作用已不大。研究结果可为济阳页岩油水平井下一步压裂施工提供理论依据。

Who Benefits More from Physical Exercise?On the Relations between Personality,Physical Exercise,and Well-Being

Although employers believe that encouraging and supporting physical exercise activities by purchasing fitness equipment and building sports venues can improve employees’well-being,the utilization rate is rather low.Since most of the evidence of the well-being promotion in the workplace concentrated on the perspectives of organizational factors and psychosocial factors and focused on the reduction of the negative affect of well-being,it is still an open question whether physical exercise has benefits on both negative and positive affect of well-being and who benefits more from physical exercise.Thus,the purpose of this study is to investigate the impact of physical exercise on occupational well-being(job burnout and work engagement)and examine whether effectiveness depends on personality traits.Online questionnaires were distributed.The sample included 671 participants from different enterprises in China.Results showed that the effectiveness of physical exercise was also applicable to well-being in the workplace.Physical exercise was negatively correlated with job burnout and positively correlated with work engagement.The effectiveness was different among employees with different personality traits.Contrary to our expectation,individuals with neuroticism were more likely to improve their work engagement through physical exercise.Extroversion and conscientiousness weakened the benefits of physical exercise.Therefore,differences of effectiveness among different personality traits emphasize the need for a more personalized strategy in physical exercise interventions.

全自溶分段压裂滑套的研制与应用

针对常规水平井裸眼多级滑套压裂管柱不能实现压裂后管内全通径,后期储层二次改造、封堵底水、单段测试等作业受到限制等问题,开展了全自溶合金材料在分段压裂工具中的应用研究。通过球座结构优化和表面涂层强化,实现滑套入井后球座不溶解,压裂后迅速溶解的目的。经排量为6 m^3/min、压裂液砂比为30%、循环时间为32 h的冲蚀实验表明,球座仍具备承压70 MPa的能力。在杭锦旗气田的压裂井中开展了现场应用,成功实现了入井静置48 d后顺利开启,并满足了压裂施工过程中的大排量冲蚀要求,压裂后球及球座在地层环境下溶解,滑套内形成了全通径。全自溶分段压裂滑套的研制与应用为优化压裂工艺、提升施工效率提出了解决思路,具有重要的指导意义。

水平井趾端压裂关键工具设计与试验

大牛地气田和东胜气田水平井采用连续油管底封拖动或桥塞泵送压裂工艺,趾端首段压裂施工时存在封隔器解封困难、电缆射孔施工工期长和费用高等问题。为解决这些问题,结合现场压裂工艺,研究了水平井趾端滑套分段压裂技术,研制了趾端延时滑套、密封锁紧座等关键工具,以满足水平井套管柱试压需求,实现水平井趾端免射孔全通径压裂。地面性能试验结果表明,设计的水平井趾端压裂关键工具能够实现压裂滑套定压延时开启、固井碰压锁紧密封等功能,趾端延时滑套爆破阀在压力达到82.0 MPa时启动,延时29min后滑套完全打开,且滑套承压达到105.0MPa;密封锁紧座与配套胶塞可实现碰压锁紧,反向承压能力达到52.5MPa,具备现场应用可行性。水平井趾端压裂工具的成功研制,为今后替代水平井射孔作业、降低国内致密油气藏开发成本提供了技术支持。

模拟套管固井滑套工况下冲蚀实验方案设计

新研发的井下工具必须经严格实验检验才能投放现场,因此,实际工况的准确模拟显得尤为重要。针对固井滑套在压裂时具有大排量与高含砂比的特点,设计了四泵串并联方式的工况模拟实验模型。根据实验条件,先假设冲蚀实验设备连接方案为两泵并联方式,而理论计算得出泵为管路所提供的扬程需达到35.82 m,与实测单台离心泵Q H特性曲线相结合,最终确定了设备连接方案为四泵串并联方式。通过监测模拟冲蚀实验中的排量与含砂比,结果表明,所设计的实验方案能够满足模拟大排量(4.5～7.0 m3/min)、高含砂比(体积比25%)的冲蚀要求且存在较大余量;同时得出进行压裂作业时不同孔眼数的滑套对管路整体压力损耗、实验流量、泵送能力等影响明显。

石墨对TA7钛合金微弧氧化涂层组织结构及摩擦磨损行为的影响

为提高TA7钛合金耐磨损关键服役性能,在钛合金表面制备微弧氧化陶瓷涂层。通过厚度、粗糙度、显微硬度测量、X射线衍射、场发射扫描电镜观察、能谱分析、摩擦学性能检测等手段研究了石墨对微弧氧化涂层组织结构及摩擦学行为的影响机制。结果表明:基础电解液中加入石墨颗粒能够显著提高TA7钛合金微弧氧化涂层的厚度,降低微弧氧化涂层的表面粗糙度和显微硬度,且随着石墨浓度的升高,微弧氧化涂层的厚度增大,表面粗糙度和显微硬度减小;微弧氧化涂层降低了TA7钛合金的摩擦系数,显著改善了合金的耐磨性能;石墨颗粒的加入进一步降低了微弧氧化涂层的摩擦系数,当石墨浓度为3 g/L时,涂层摩擦系数保持在0.15以下,表现出良好的减摩特性。

Phylogenetic Analysis of Anaerobic Co-Digestion of Animal Manure and Corn Stover Reveals Linkages between Bacterial Communities and Digestion Performance

Over 3 million tons of manures are produced annually in the United States and pose environmental and health risks if not remediated. Anaerobic digestion is an effective method in treating organic wastes to reduce environmental impacts and produce methane as an alternative energy. Previous studies suggested that optimization of feed composition, hydraulic retention time, and other operational conditions can greatly improve total solids removal and increase methane productivity. These environmental factors improve functionality by altering the microbial community structure but explicit details of how the bacterial community shifts are poorly understood. Our investigations were conducted to investigate the relationship between environmental factors, microbial community structure and bioreactor efficiency by using metagenomic analysis of the microbial communities. Our results indicated that the bioreactor with the greatest methane production, digestion efficiency and reduced levels of E. coli/Shigella had a distinctive community structure at the genus level with unique and abundant uncultivated strains of Bacteroidetes. Moreover the same bioreactor was enriched in Aminomonas paucivorans and Clostridia populations that can utilize secondary metabolites produced during cellulose/hemicellulose degradation to generate hydrogen and acetate. Hence specific digestion conditions that enrich for these populations may provide a route to the optimization of co-digestion systems and control the variability in reactor performance.

烧结温度对Micro-FAST制备TC4钛合金的影响

采用多物理场活化烧结微成形技术(Micro-FAST)快速制备TC4微型圆柱,研究烧结温度对TC4微型圆柱的致密化过程及力学性能的影响。研究发现,Micro-FAST技术可在5 min内实现TC4的快速成形,在900～1200℃的烧结温度区间均可获得相对密度大于97%的微型圆柱件,其显微组织由条状α相和β相组成,组织分布均匀、晶粒细小。当烧结温度为1000℃时,硬度达到最大值380.3HV0.5,较传统方法制备的TC4零件硬度提高10%。随着烧结温度的提高,烧结体中出现魏氏组织,合金的韧性逐渐降低。

铝合金油管特殊螺纹接头设计及密封性能

以应用于油井特殊环境下的铝合金油管为研究对象,对其接头螺纹及密封进行了设计研究。首先根据应用环境,确定了接头的结构及密封形式,然后采用理论设计方法,对偏梯形螺纹进行等强度设计,通过建立二维轴对称有限元模型,对螺纹面、密封锥面、密封环的密封特性进行了设计研究,结果表明:螺纹面和锥面的接触应力都随着其自身过盈量的增加而增加,但内外锥面的接触应力随着螺纹面过盈量的增加而减少,螺纹面的接触应力随锥面的过盈量变化不大。端面密封环过盈量的设计要综合考虑油管及自身受力的变形,以确保在密封环的变形量在其弹性范围内,提供较好的密封性能。最后以设计的结构参数为例,分析了接头在不同工况下的强度及密封性能,结果满足应用要求,验证了设计的合理性。

聚乙醇酸材料的加工改性及其水下降解特性的研究进展

从具有广阔应用前景的聚乙醇酸(PGA)材料的物性、加工改性及应用等方面概括了PGA的基本改性原理、改性方法以及加工过程中需要注意的问题;从增韧、增强、增塑、增容等角度,阐述了不同助剂,如增容剂、扩链剂及增塑剂等对PGA材料的改性机理,比较了不同增韧材料与PGA材料相容性及界面互溶增强技术;最终总结了PGA加工性能及使用性能的调控规律。

水平井压裂装置智能趾端滑套设计

在压裂作业中,压力完整性测试阶段的高压环境将严重影响趾端滑套的使用寿命。为了解决该问题,根据压裂装置的工作原理和技术要求,创新设计了一种在压力完整性测试之后能延时开启的智能电控趾端滑套,并设计了能够控制滑套延时开启的锁定系统结构及其控制系统。根据工作环境的要求,设计了尺寸较小的PCB控制板。通过数据计算、Ansys仿真分析和模拟试验,证明设计的智能电控趾端滑套在压力完整性测试之后能够有效、精确地开启,为后续压裂作业创造了安全、高效的环境。该设计对压裂装置工作效率的提高和未来发展方向具有重要意义。

预变形对Al-4.28Cu-1.33Li-0.40Mg-0.30Ag-0.14Zr合金时效组织与性能的影响

采用室温拉伸、透射电镜观察等手段,研究了3%拉伸预变形对Al-4.28Cu-1.33Li-0.40Mg-0.30Ag-0.14Zr合金单级和双级时效组织与性能的影响。拉伸结果表明,对于190℃/(3~7)h的单级时效处理,3%拉伸预变形可以提高拉伸强度56~75 MPa,时效时间延长,预变形提高强度的效果大幅度降低。3%拉伸预变形可以使得190℃/7 h+100℃/24 h双级时效样品的强度提高81 MPa,达到748 MPa。透射电镜观察结果表明,190℃/7 h单级时效态样品对应的组织主要为T_1和θ′相,还有少量S′相;190℃/7 h+100℃/24 h双级时效态样品在190℃/7 h时效组织基础上析出了大量δ′相;而在190℃/7 h+100℃/24 h双级时效前施加3%拉伸预变形则极大地促进了T_1相和θ′相的析出,从而大幅度提高合金抗拉强度,而δ′相的析出受到抑制。

A Life-skills-based HIV/AIDS Prevention Education for Rural Students of Primary Schools in China:What Changed? What Have We Learned?

Objective To evaluate a four-hour life-skills-based HIV/AIDS prevention curriculum among 5th grade students in rural primary schools of Hainan province.Methods The study included two stages.Stage one （September 2006-May 2007） was a pre-post-quasi experimental design;a total of 2 413 students aged 9 to 14 years from fifth grade classes of nine primary schools completed a baseline survey （1 720 students were in the intervention group,693 in the control group）,and over 98% of them took part in a short survey.The experimental curriculum was provided to the intervention group.At stage two （September 2008）,a cross-sectional questionnaire was administered to 6 923 students in 7th grade classes of eight middle schools in the same study sites.There were 1 437 students in the intervention group when the curriculum was conducted.Results Students tended to score higher in areas of HIV/AIDS related knowledge and attitudes,if they were younger than average,lived in the county seat,had access to the internet,and their parents had completed higher levels of education.Path analysis showed that,after controlling for characteristics such as family and community factors,the total effects of curriculum on knowledge in the short-term model increased remarkably compared with the baseline,and maintained major contributions to knowledge in the mid-term model.The positive effect of knowledge on attitudes was significantly improved in the short-term model as well.Conclusion A life-skills based curriculum can improve HIV/AIDS related knowledge and self-perceived level of life-skills among primary school students in rural areas in a short time,and these positive effects can still be observed at least 2 years post participation in the curriculum.

Effects of protein and lignin on cellulose and xylan anaylses of lignocellulosic biomass

Interactions of lignocellulosic components during fiber analysis were investigated using the highly adopted compositional analysis procedure from the National Renewable Energy Laboratory（NREL）,USA.Synthetic feedstock samples were used to study the effects of lignin/protein,cellulose/protein,and xylan/protein interaction on carbohydrate analysis.Disregarding structural influence in the synthetic samples,lignin and protein components were the most significant（P〈0.05）factors on cellulose analysis.Measured xylan was consistent and unaffected by content variation throughout the synthetic analysis.Validation of the observed relationships from synthetic feedstocks was fulfilled using real lignocellulosic feedstocks：corn stover,poplar,and alfalfa,in which similar results have been obtained,excluding cellulose analysis of poplar under higher protein content and xylan analysis of alfalfa under higher protein content.The results elucidated that according to their protein and lignin contents of different lignocellulosic materials,accuracy of the NREL method on cellulose and xylan analyses could be improved by applying a stronger extraction step to replace water/ethanol extraction.

Effect of the end cap on the fragment velocity distribution of a cylindrical cased charge

The prediction of the fragment velocity distribution of a cylindrical cased charge with end caps is one of the key issues to assess the damage efficiency of the warhead. However, limited work has been conducted to predict the fragment velocity distributions along the axis of cylindrical cased charges with end caps. This paper presents a study of the velocity distribution of fragments caused by the explosion of a cylindrical cased charge with end caps. The fragment velocity distribution and the end cap velocity were determined by an X-ray radiography method, and the axial fragment distribution was determined by witness plates. It was found that the velocities of fragments, especially near the edge, were increased when the end caps were added, and the position of maximum velocity is closer to the non-detonation end. The fragment velocities were increased, and the fragment projection range was decreased with the increase of the thickness of the end cap. A formula for fragment velocity distributions of a cylindrical cased charge with end caps, which is based on Huang’s formula, was proposed by the theoretical analysis and data fitting and validated experimentally. The results indicate that the proposed formula is accurate in predicting the fragment velocity distribution along the axis of a cylindrical cased charge with end caps detonated at one end.

Formation mechanism of a smooth, defectfree surface of fused silica optics using rapid CO2 laser polishing

Surface defects introduced by conventional mechanical processing methods can induce irreversible damage and reduce the service life of optics applied in high-power lasers.Compared to mechanical processing,laser polishing with moving beam spot is a noncontact processing method,which is able to form a defect-free surface.This work aims to explore the mechanism of forming a smooth,defect-free fused silica surface by high-power density laser polishing with coupled multiple beams.The underlying mechanisms of laser polishing was revealed by numerical simulations and the theoretical results were verified by experiments.The simulated polishing depth and machined surface morphology were in close agreement with the experimental results.To obtain the optimized polishing quality,the effects of laser polishing parameters(e.g.overlap rate,pulse width and polishing times)on the polishing quality were experimentally investigated.It was found that the processing efficiency of fused silica materials by carbon dioxide(CO2)laser polishing could reach 8.68 mm2 s−1,and the surface roughness(Ra)was better than 25 nm.Besides,the cracks on pristine fused silica surfaces introduced by initial grinding process were completely removed by laser polishing to achieve a defect-free surface.The maximum laser polishing rate can reach 3.88μm s−1,much higher than that of the traditional mechanical polishing methods.The rapid CO2 laser polishing can effectively achieve smooth,defect-free surface,which is of great significance to improve the surface quality of fused silica optics applied in high-power laser facilities.