强降雨情景下附着式升降脚手架事故致因IFRAM-BN模型

强降雨事件频发造成附着式升降脚手架事故剧增,为提高强降雨情景下施工安全性,降低事故发生率,提出一种基于改进的功能共振分析模型(IFRAM)和贝叶斯网络(BN)相结合的事故致因分析模型。首先,从定性角度,利用IFRAM识别事故机制并深度挖掘系统功能共振情况;其次,将IFRAM映射至BN定量分析模型,并引入联系云优化计算各根节点的先验概率;最后,以西安“9·10”事故为例,进行实证研究并提出相应预防措施。结果表明:事故在安全状态为Ⅳ级时,发生的可能性最大。工人违规操作、未进行旁站等强制性监督、强降雨等是导致爬架事故的核心致因;强降雨环境→雨后架体载荷超载等致因组合是诱发爬架事故的关键。

术前血清hsTnI、Hcy及BNP检测在心脏瓣膜置换术患者术后预后中的预测作用

目的 分析术前血清高敏肌钙蛋白I(hs-TnI)、同型半胱氨酸(Hcy)及脑钠肽(BNP)检测在心脏瓣膜置换术(CVR)患者术后预后中的预测作用。方法 选取2020年1月至2023年1月间郑州市第七人民医院收治的行CVR术患者132例。术后行1年随访,分析随访情况并分组;比较无不良事件组、不良事件组血清hsTnI、Hcy及BNP水平;为识别影响CVR术患者预后的独立危险因素,首先筛选NYHA分级、LVEF、hsTnI、Hcy和BNP等潜在因素,并进行单因素分析。随后,采用逐步前进法的多因素二元Logistic回归分析,深入探讨这些因素对患者预后的独立影响。结果 132例接受CVR术治疗的患者在随访终止时,101例患者未发生不良事件(即无不良事件组),31例患者发生不良事件(即不良事件组)。不良事件组中,人工瓣膜功能衰退2例、瓣周漏1例、人工瓣膜性心内膜炎1例、再次更换瓣膜1例、出血6例、血栓栓塞3例、恶性心律失常15例、出现死亡2例,共计发生率为23.48%(31/132)。不良事件组血清hsTnI、Hcy及BNP水平均显著高于无不良事件组,差异具有统计学意义(P<0.05)。单因素二元Logistic回归分析显示,NYHA分级、LVEF、hsTnI、Hcy、BNP是影响CVR患者预后的影响因素(P<0.05)。多因素二元Logistic回归分析显示,NYHA分级为Ⅲ~Ⅳ级、LVEF<45%、术前血清hsTnI、Hcy及BNP水平升高是影响CVR患者术后不良事件发生的独立危险因素(P<0.05)。结论 术前血清hsTnI、Hcy及BNP检测在CVR术患者术后预后中具有重要的预测作用,术前上述生物标志物水平升高可能提示患者存在较高的不良事件风险。因此,在临床工作中,应加强对术前血清hsTnI、Hcy及BNP的监测和评估,以便及时发现并处理潜在的风险因素,从而提高CVR术后患者的预后质量。

基于BN和PLS-SEM的大学生网约车忠诚度研究

为分析大学生网约车乘客忠诚度及其影响因素的作用机制,将贝叶斯网络(Bayesian networks,BN)和偏最小二乘法结构方程模型(partial least squares structural equation modelling,PLS-SEM)结合,以2019年大连市大学生网约车乘客为例,分析大学生网约车乘客的负面体验、运营服务、环境满意、乘客满意度和忠诚度的关系。在BN中采用基于约束的自动学习方法学习因子间的作用关系,获得不同影响因素间相关关系的网络结构。通过PLS-SEM测试和分析BN结构,建立乘客忠诚度模型。结果表明:乘客满意度是影响忠诚度的最大因素,总效应为0.508;负面体验是影响忠诚度的最小因素,总效应为-0.146。乘客满意度是提高大学生网约车忠诚度的关键指标,网约车平台应通过优化车内环境、缩短出行时间、规范司机行为、升级应用软件等措施提升大学生的乘车体验,提高大学生网约车乘客的忠诚度。基于BN和PLS-SEM的大学生网约车忠诚度研究可丰富网约车乘客的决策行为机制与研究方法,为相关部门和网约车平台提供管理决策依据。

ZrO_(2)(AlN)/h-BN复合陶瓷性能研究及超重力凝固坩埚研制

凝固是制备材料很基本的成型技术之一,但超重力凝固时,高转速产生的离心力克服合金熔体在坩埚孔隙处产生的表面张力,极易在超重力凝固过程中发生熔体渗漏或坩埚破碎,导致实验失败。本工作采用热压烧结工艺制备ZrO_(2)/h-BN和AlN/h-BN复合陶瓷,测试其物理和力学性能,择优选材加工成坩埚。结果表明,AlN/h-BN的热导率优于ZrO_(2)/h-BN,其高温压缩强度明显高于ZrO_(2)/h-BN。基于超重力凝固时坩埚损伤的力学分析,选用低密度、高热导率、高压缩强度的AlN/h-BN制备坩埚,通过50炉超重力凝固实验,验证其性能满足超重力凝固的需要。

Synthesis of Nano-sized Yttria via a Sol-Gel Process Based on Hydrated Yttrium Nitrate and Ethylene Glycol and Its Catalytic Performance for Thermal Decomposition of NH_4ClO_4

Nano-sized yttria particles were synthesized via a non-aqueous sol-gel process based on hydrated yttrium nitrate and ethylene glycol. The effects of the molar ratio of ethylene glycol to yttrium ion and calcination temperature on crystallite size of the products were studied. The catalytic performance of the as-prepared yttria for the ammonium perchlorate （AP） decomposition was investigated by differential scanning calorimetry （DSC）. The results indicate that the nano-sized cubic yttria particles with less than 20 nm in average crystallite size can be obtained after 2 h reflux at 70℃, dried at 90 ℃, forming xerogel, and followed by annealing of xerogel for 2 h, and that the addition of the nano-sized yttria to AP incorporates two small exothermic peaks of AP in the temperature ranges of 310 - 350 ℃ and 400 - 470 ℃ into a strong exothermic peak of AP and increases the apparent decomposition heat from 515 to over 1110 J·g^- 1. It is also clear that the temperature of AP decomposition exothermic peak decreases and the apparent decomposition heat of AP increases with the increase of the amount of nano-sized yttria. The fact that the addition of the 5 % nano-sized yttria to AP decreases the temperature of AP exothermic peak to 337.7℃ by reduction of 114.6℃ and increases the apparent decomposition heat from 515 to 1240 J·g^-1, reveals that nano-sized yttria shows strong catalytic property for AP thermal decomposition.

NiMo/Al_2O_3 catalyst containing nano-sized zeolite Y for deep hydrodesulfurization and hydrodenitrogenation of diesel

Two mixed-matrix NiMo/Al2O3 catalysts containing nano-and micro-sized zeolite Y have been prepared to explore the size effect of zeolite Y particle on the hydrodesulfurization（HDS）and hydrodenitrogenation（HDN）activities of fluid catalytic cracking（FCC）diesel.They were characterized by SEM,BET,XRD,H2-TPR,NH3-TPD and HRTEM.The results show that the catalyst containing nano-sized zeolite Y possesses larger average pore diameter,higher pore volume,weaker and lesser acid sites,more easily reducible metal phases,shorter MoS2 slabs and more slab layers than the catalyst containing micro-sized zeolite Y.The catalysts were also evaluated with a high-pressure fixed-bed reactor using real FCC diesel as feed.The results display that the catalyst containing nano-sized zeolite Y bears higher HDS and HDN activities and exhibits higher relative rate constant for the removal of total sulfur or nitrogen than the one containing micro-sized zeolite.

Synthesis and Characterization of Nano-sized Boron Powder Prepared by Plasma Torch

Hydrogen thermal plasma jet was employed to prepare nano-sized boron powder with hydrogen reduction of BCI3. The maximum yield of nano-sized boron powders was about 50% with the operational conditions of H2/BCl3 of 4.5：1, total feed of 4.9 m3/h, and plasma power of 25 kW. The samples were analyzed by X-ray diffraction （XRD）, field emission scanning electron microscopy （FE-SEM）, and inductively coupled plasma - mass spectrometry （ICP-MS）, inductively coupled plasma - atomic emission spectrometry （ICP-AES）, inductive combustion infrared absorption （ICIA） and infrared thermal conductivity of oxygen and nitrogen analyzer （ITCA）. The results show that the boron powders have different crystal structures with higher dispersion and purity. The average diameter is about 50 nm, and the purity is 90.29% or so. This new technology can use simple process to produce high quality boron powders, and is feasible for industrial production.

Kinetics and Mechanism of Decomposition of Nano-sized Calcium Carbonate under Non-isothermal Condition

Experiments on thermal decomposition of nano-sized calcium carbonate were carried out in a thermo-gravimetric analyzer under non-isothermal condition of different heating rates (5 to 20K·min-1). The Coats and Redfern's equation was used to determine the apparent activation energy and the pre-exponential factors. The mechanism of thermal decomposition was evaluated using the master plots, Coats and Redfern's equation and the kinetic compensation law. It was found that the thermal decomposition property of nano-sized calcium carbonate was different from that of bulk calcite. Nano-sized calcium carbonate began to decompose at 640℃, which was 180℃lower than the reported value for calcite. The experimental results of kinetics were compatible with the mechanism of one-dimensional phase boundary movement. The apparent activation energy of nano-sized calcium carbonate was estimated to be 151kJ·mol-1 while the literature value for normal calcite was approximately 200kJ·mol-1. The order of magnitude of pre-exponential factors was estimated to be 10~9 s-1.

掺杂BN-OH纳米片的P/PEG@BN-OH同轴纳米纤维的制备及其热性能

为制备高效稳定的相变储热材料,采用同轴静电纺丝技术制备了以聚丙烯腈(PAN)为鞘、聚乙二醇(PEG)与羟基化氮化硼纳米片(BN-OH)为芯的同轴纳米纤维(P/PEG@x BN-OH),并分别通过场发射扫描电子显微镜、透射电子显微镜、差示扫描量热仪、红外热成像仪等手段分析了掺杂不同质量BN-OH纳米片对纤维形貌、热性能、循环稳定性、热能效率及热导率的影响。结果表明:纤维形成了稳定且连续的鞘-芯同轴结构,平均直径介于279~335 nm,而且PEG和BN-OH被包裹在PAN纤维内部,内径大小范围为107~188 nm;P/PEG@x BN-OH纳米纤维显示了优异的相变储热焓值(75~78 J/g)和热稳定性,经100次热循环后PEG无相变渗漏现象;掺杂质量分数为10.0%的BN-OH纳米片可将纤维的热导率提高95%,而且其相变储热和释放率分别提高了67%和154%。

基于STPA-BN的船舶航行人为风险因素分析与评估

人为因素是引发船舶事故的最主要因素之一,为了研究船舶人为风险因素的因果关系,从中国海事局发布的船舶事故报告出发,引入系统理论过程分析-贝叶斯网络(STPA-BN)模型对船舶航行人为风险因素进行分析和评估。采用系统理论过程分析(STPA)方法识别出船舶航行中存在的不安全控制行为,结合事故报告内容提取出12种人为风险因素,利用风险因素的内在因果关系和结构学习功能构建贝叶斯网络拓扑结构;将事故报告量化,并对网络进行参数学习,对模型进行验证。在此基础上,利用贝叶斯网络(BN)的推理功能得到船舶航行中7种突出的人为风险因素和3条事故核心致因链,为保障船舶安全航行与船员培训提供数据支持。

Corrosion resistance of waterborne epoxy coating pigmented by nano-sized aluminium powder on steel

A novel kind of waterborne epoxy coating pigmented by nano-sized aluminium powders on high strength steel was formulated. Several coatings with different pigment volume content (PVC) were prepared. The coating morphology was observed using scanning electron microscopy (SEM), and the electrochemical properties were investigated by electrochemical impedance spectroscopy (EIS). Immersion test and neutral salt spray test were also conducted to investigate the corrosion resistance of the coating. It is demonstrated that the critical pigment volume content (CPVC) value is between 30% and 40%. The coating with PVC of 30% exhibits good corrosion resistance in 3.5% (mass fraction) NaCl solution.

Effects of nano-sized aluminum on detonation characteristics and metal acceleration for RDX-based aluminized explosive

Nano-sized aluminum(Nano-Al)powders hold promise in enhancing the total energy of explosives and the metal acceleration ability at the same time.However,the near-detonation zone effects of reaction between Nano-Al with detonation products remain unclear.In this study,the overall reaction process of 170 nm Al with RDX explosive and its effect on detonation characteristics,detonation reaction zone,and the metal acceleration ability were comprehensively investigated through a variety of experiments such as the detonation velocity test,detonation pressure test,explosive/window interface velocity test and confined plate push test using high-resolution laser interferometry.Lithium fluoride(LiF),which has an inert behavior during the explosion,was used as a control to compare the contribution of the reaction of aluminum.A thermochemical approach that took into account the reactivity of aluminum and ensuing detonation products was adopted to calculate the additional energy release by afterburn.Combining the numerical simulations based on the calculated afterburn energy and experimental results,the parameters in the detonation equation of state describing the Nano-Al reaction characteristics were calibrated.This study found that when the 170 nm Al content is from 0%to 15%,every 5%increase of aluminum resulted in about a 1.3%decrease in detonation velocity.Manganin pressure gauge measurement showed no significant enhancement in detonation pressure.The detonation reaction time and reaction zone length of RDX/Al/wax/80/15/5 explosive is 64 ns and 0.47 mm,which is respectively 14%and 8%higher than that of RDX/wax/95/5 explosive(57 ns and 0.39 mm).Explosive/window interface velocity curves show that 170 nm Al mainly reacted with the RDX detonation products after the detonation front.For the recording time of about 10 ms throughout the plate push test duration,the maximum plate velocity and plate acceleration time accelerated by RDX/Al/wax/80/15/5 explosive is 12%and 2.9 ms higher than that of RDX/LiF/wax/80/15/5,respectively,indicating that the aluminum reaction energy significantly increased the metal acceleration time and ability of the explosive.Numerical simulations with JWLM explosive equation of state show that when the detonation products expanded to 2 times the initial volume,over 80%of the aluminum had reacted,implying very high reactivity.These results are significant in attaining a clear understanding of the reaction mechanism of Nano-Al in the development of aluminized explosives.

Effect of deep cryogenic treatment on the formation of nano-sized carbides and the wear behavior of D2 tool steel

The effect of deep cryogenic treatment on the microstructure, hardness, and wear behavior of D2 tool steel was studied by scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, X-ray diffraction （XRD）, hardness test, pin-on-disk wear test, and the reciprocating pin-on-fiat wear test. The results show that deep cryogenic treatment eliminates retained austenite, makes a better carbide distribution, and increases the carbide content. Furthermore, some new nano-sized carbides form during the deep cryogenic treatment, thereby increasing the hardness and improving the wear behavior of the samples.

Deformation behavior of explosive detonation in electroformed nickel liner of shaped charge with nano-sized grains

Nickel liner of shaped charge with nano-sized grains was prepared by electroforming technique and the ultra-highstrain-rate deformation was performed by explosive detonation.The as-electroformed and post-deformed microstructures of electroformed nickel liner of shaped charge were observed by optical metallography(OM),scanning electron microscopy(SEM) and transmission electron microscopy(TEM) and the orientation distribution of the grains was analyzed by electron backscattering pattern(EBSP) technique.Both melting phenomenon in the jet fragment and recovery and recrystallization in the slug after ultra-high-strain-rate deformation were observed.The research evidence shows that dynamic recovery and recrystallization play an important role in ultra-high-strain-rate deformation for electroformed nickel liner of shaped charge with nano-sized grain.

Comparative study of the explosion pressure characteristics of micro- and nano-sized coal dust and methane–coal dust mixtures in a pipe

Coal dust explosion accidents often cause substantial property damage and casualties and frequently involve nano-sized coal dust.In order to study the impact of nano-sized coal on coal dust and methane–coal dust explosions,a pipe test apparatus was used to analyze the explosion pressure characteristics of five types of micro-nano particle dusts(800 nm,1200 nm,45μm,60μm,and 75μm)at five concentrations(100 g/m3,250 g/m3,500 g/m3,750 g/m3,and 1000 g/m3).The explosion pressure characteristics were closely related to the coal dust particle size and concentration.The maximum explosion pressure,maximum rate of pressure rise,and deflagration index for nano-sized coal dust were larger than for its micro-sized counterpart,indicating that a nano-sized coal dust explosion is more dangerous.The highest deflagration index Kst for coal dust was 13.97 MPa/(m·s),indicating weak explosibility.When 7%methane was added to the air,the maximum deflagration index Kst for methane–coal dust was 42.62 MPa/(m·s),indicating very strong explosibility.This indicates that adding methane to the coal dust mixture substantially increased the hazard grade.

Synthesis of Neodymium-Doped Yttrium Aluminum Garnet (Nd∶YAG) Nano-Sized Powders by Low Temperature Combustion

The homogeneously dispersed, less agglomerated (Nd0.01Y0.99)3Al5O12 nano-sized powders were synthesized by the low temperature combustion (LCS), using Nd2O3, Y2O3, Al(NO3)3·9H2O, ammonia water and citric acid as starting materials. This method effectively solves the problems caused by solid-state reaction at high temperature and hard agglomerates brought by the chemical precipitation method. The powders were characterized by TG-DTA, XRD, FT-IR, TEM respectively and the photoluminescence (PL) spectra of (Nd0.01Y0.99)3Al5O12 green and sintered ceramic disks were measured. The results show that the forming temperature of YAG crystal phase is 850 ℃ and YAP crystal phase appearing during the calcinations transforms to pure YAG at 1050 ℃. The particle size of the powders synthesized by the LCS is in a range of 20～50 nm depending on the thermal treatment temperatures. The effectively induced cross section (σin) with the value 4.03×10-19 cm2 of (Nd0.01Y0.99)3Al5O12 ceramics is about 44% higher than that of single crystal.

C/SiC-BN复合材料的制备及氧化行为

C/SiC复合材料作为一种高温结构材料,在航空航天热防护领域具有广泛的应用前景。然而,该材料的中低温抗氧化性能相对较差,制约了其在更广泛领域的应用。本研究采用料浆抽滤工艺,通过调节料浆中陶瓷含量在纤维增强体中引入不同含量的抗氧化组元BN,再通过反应熔体渗透法制备C/SiC-BN复合材料。系统研究了不同BN含量对复合材料结构组成及抗氧化行为的影响,并分析相关氧化机理。研究结果表明:引入BN颗粒显著降低了C/SiC的开口孔隙率,并明显提高了C/SiC的起始氧化温度。引入质量分数3%BN时,C/SiC-BN复合材料(B3样品)的抗氧化性能最优,其在900、1200和1500℃静态氧化1 h的质量损失率分别为0.009%、–0.301%、–0.596%,显著优于C/SiC。1500℃氧化后,B3样品的强度保持率最高,达到52%。900℃氧化时,C/SiC-BN复合材料主要经历C相和BN相的氧化,以O_(2)扩散反应控制的缓慢失重为主;1200℃氧化时,C相和BN相氧化速率加快,SiC发显著氧化,生成的B_(2)O_(3)、硼硅酸盐和SiO_(2)等氧化产物减缓了O_(2)的扩散速率,减小了基体碳的损伤;1500℃氧化时,SiC氧化速率加快,生成的SiO_(2)在复合材料表面形成的连续氧化膜阻碍了O_(2)的向内扩散。B_(2)O_(3)、CO等气体产物溢出及持续生成SiO_(2)主导了整个氧化过程。

Effect of nano-sized Al2O3 reinforcing particles on uniaxial and high cycle fatigue behaviors of hot-forged AZ31B magnesium alloy

The effect of hot-forging process was investigated on microstructural and mechanical properties of AZ31 B alloy and AZ31 B/1.5 vol.%Al2 O3 nanocomposite under static and cycling loading. The as-cast alloy and composite were firstly subjected to a homogenization heat treatment at 450 ℃ and then an open-die forging at 450 ℃. The results indicated that the presence of reinforcing particles led to grain refinement and improvement of dynamic recrystallization. The forging process was more effective to eliminate the porosity in the cast alloy workpiece. Microhardness of the forged composite was increased by up to 80% and 16%, in comparison with those of the cast and forged alloy samples, respectively. Ultimate tensile strength and maximum tensile strain of the composite were improved by up to 45% and 23%, compared with those of the forged alloy in similar regions. These enhancements were respectively 50% and 37% in the compression test. The composite exhibited a fatigue life improvement in the region with low applied strain;however, a degradation was observed in the high applied strain region. Unlike AZ31 B samples, tensile, compressive and high cycle fatigue behaviors of the composite showed less sensitivity to the applied strain, which can be attributed to the amount of porosity in the samples before and after the hot-forging.

Seed-Assisted Synthesis and Catalytic Performance of Nano-sized ZSM-5 Aggregates in a One-Step Crystallization Process

Hierarchical nano-sized ZSM-5 aggregates were successfully synthesized via a seed-assisted method in the presence of cetyltrimethylammonium bromide(CTAB)through a facile one-step crystallization process.Commercial ZSM-5 zeolites with a SiO2/Al2O3 ratio comparable to that of ZSM-5 products were treated with alkali and used as the seed particles.The influences of crystallization conditions were investigated,and the possible synthesis mechanism was proposed.ZSM-5 zeolites with diff erent amounts of CTAB added were characterized using many techniques and evaluated in toluene alkylation with methanol.The results showed that a trace amount of CTAB signifi cantly promoted the crystallization of ZSM-5 zeolite,with the morphology changing from hexagonal-shape crystals to uniform spherical aggregates.CTAB may act as the structure-directing agent and assemble the primary crystallites to generate hierarchical ZSM-5 aggregates.The ZSM-5 zeolite with the smallest primary particles of 50-80 nm exhibited large specific surface area,abundant mesopores,and the greatest microporosity.The hierarchical nano-sized ZSM-5 aggregate showed higher toluene conversion and a longer lifetime without compromising the selectivity to xylene and p-xylene in toluene alkylation with methanol.

Fabrication of Fine-Grained Si_3N_4-Si_2N_2O Composites by Sintering Amorphous Nano-sized Silicon Nitride Powders

Si3N4-Si2N2O composites were fabricated with amorphous nano-sized silicon nitride powders by the liquid phase sintering （ LPS ）. The Si2 N2O phase was generated by an in-situ reaction 2 Si3 N4 （ s ） ＋ 1.5 02 （ g ） = 3 Si2 N2O （ s ） ＋ N2 （ g ） . The content of Si2 N2 O phase up to 60% in the volume was obtained at a sintering temperature of 1 650℃ and reduced when the sintering temperature increased or decreased, indicating the reaction is reversible. The mass loss, relative density and average grain size increased with increasing the sintering temperature. The average grain size was less than 500 nm when the sintering temperature was below 1 700 ℃. The sintering procedure contains a complex crystallization and a phase transition ： amorphous silicon nitride→equiaxial α- Si3 N4→ equiaxial β- Si3 N4→ rod- like Si2 N2O→ needle- like β- Si3N4 . Small round-shaped β→ Si3 N4 particles were entrapped in the Si2 N2O grains and a high density of staking faults was situated in the middle of Si2 N2O grains at a sintering temperature of 1 650 ℃. The toughness inereased from 3.5 MPa·m^1/2 at 1 600 ℃ to 7.2 MPa· m^1/2 at 1 800 ℃ . The hardness was as high as 21.5 GPa （Vickers） at 1 600 ℃ .