铀矿排风井周边地表大气氡致辐射效应的数值模拟

为了指导铀矿排风井周边地表环境的辐射防护设计,基于放射性气态流出物大气扩散的高斯烟羽模型,建立了铀矿排风井周边地表年均氡浓度以及公众个人年有效剂量的数学计算模型,研究了排风井气态流出物初始氡浓度、排风风量和源强对排风井周边地表1 km范围内年均氡浓度以及公众个人年有效剂量分布的影响.结果表明,在其他参数不变的情况下,年均氡浓度和公众个人年有效剂量的最大值随气态流出物初始氡浓度的增加而增大,随排风风量的增加而减小;最大值离井口的距离和氡致辐射的影响范围随初始氡浓度的增加而增大,随排风风量的增加而减小;相同源强下,最大值随气态流出物的初始氡浓度增加而增大,随排风风量的增大而减小;最大值离井口的距离随排风风量的增加而增大.最后,根据所得结论提出铀矿排风井周边的辐射防护建议.     

学龄前和学龄期儿童希氏束以上心动过速性心肌病高危因素分析

目的探讨学龄前和学龄期儿童希氏束以上的心动过速(室上性心动过速)与心动过速性心肌病的相关性及高危因素.方法选取室上性心动过速患儿179例,根据心动过速时心功能状态分为心肌病组23例,非心肌病组156例.分析患儿性别、年龄、发作类型、发作频率、持续时间、心室率与心功能损伤的关系和相关高危因素.结果 179例患儿中心动过速性心肌病23例,其中房室折返性、房室结折返性、无明确分类的心肌病分别为7例、10例、6例.房速所致心动过速性心肌病发生率为25.00%(8/32),明显高于阵发性室上性心动过速所致的心肌病发生率10.20%(15/147),差异具有统计学意义(P0.05).心肌病组患儿中房速所占比例、发作持续时间明显高于非心肌病组患儿,发作频率明显低于非心肌病组患儿,差异均具有统计学意义(P0.05).二元Logistic回归分析显示:发作持续时间是心动过速性心肌病的独立影响因素.结论学龄前和学龄期儿童室上性心动过速所致心动过速性心肌病的发生率为12.85%,其中房速所致的心肌病发生率明显高于阵发性室上性心动过速,发作持续时间是唯一高危因素.     

一种新型冷轧辊用钢的组织演变

本文以一种新型冷轧辊用钢为研究对象,借助金相显微镜和扫描电子显微镜分析了试验钢在正火、球化退火、淬火、回火过程中的组织演变,研究了碳化物的成分变化和溶解析出行为。结果显示,试验钢正火后得到马氏体+部分颗粒状和少量块状碳化物的显微组织;球化退火后的显微组织为铁素体基体上分布有大量颗粒状碳化物+少量块状碳化物,球化退火组织评定为为2~3级;淬火后的组织为马氏体+部分颗粒状和少量块状碳化物;三次回火后的组织为回火马氏体+部分颗粒状和少量块状碳化物。试验钢中的块状碳化物在整个热处理过程中始终存在,1100℃以下奥氏体化时只发生边缘部分的少量溶解。颗粒状碳化物主要为M23C6型,在热处理过程中存在明显的溶解和析出行为,1100℃以下奥氏体化时部分溶解。     

分级多孔纳米炭纤维的结构及电容性能

以酚醛树脂为碳源、PVP为纺丝助剂、纳米MgO颗粒为模板剂,通过静电纺丝法制得酚醛树脂基纳米炭纤维,经过炭化、KOH活化、酸洗后得到分级多孔纳米炭纤维,利用SEM、XRD、XPS、拉曼光谱仪及氮气吸脱附实验,对所制多孔纳米炭纤维的结构和形貌进行表征,并将其作为模拟电容器的电极,利用循环伏安、恒电流充放电及交流阻抗方法测试了材料的电化学性能。结果表明,KOH活化引入了数量可观的微孔,所得纳米炭纤维表现出明显的"微孔-中孔-大孔"分级孔分布的特点,其比表面积达到1058.4m~2/g,总孔容为1.64cm~3/g。电化学测试结果表明,所制分级多孔纳米炭纤维在6mol/L KOH电解液中显示出优异的电容性能,在0.2A/g的电流密度下,其放电比容量达到198F/g,在20A/g电流密度下,电容保持率达到65%。     

Improved hemimorphite flotation using xanthate as a collector with S(Ⅱ) and Pb(Ⅱ) activation

The flotation of hemimorphite using the S(Ⅱ)–Pb(Ⅱ)–xanthate process, which includes sulfidization with sodium sulfide, activation by lead cations, and subsequent flotation with xanthate, was investigated. The flotation results indicated that hemimorphite floats when the S(Ⅱ)–Pb(Ⅱ)–xanthate process is used; a maximum recovery of approximately 90% was obtained. Zeta-potential, contact-angle, scanning electron microscopy–energy-dispersive spectrometry (SEM–EDS), and diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements were used to characterize the activation products on the hemimorphite surface and their subsequent interaction with sodium butyl xanthate (SBX). The results showed that a ZnS coating formed on the hemimorphite surface after the sample was conditioned in an Na₂S solution. However, the formation of a ZnS coating on the hemimorphite surface did not improve hemimorphite flotation. With the subsequent addition of lead cations, PbS species formed on the mineral surface. The formation of the PbS species on the surface of hemimorphite significantly increased the adsorption capacity of SBX, forming lead xanthate (referred to as chemical adsorption) and leading to a substantial improvement in hemimorphite flotation. Our results indicate that the addition of lead cations is a critical step in the successful flotation of hemimorphite using the sulfidization–lead ion activation–xanthate process.     

应急资源配送中Dijkstra改进算法的研究

路径规划问题是应急资源配送中的核心问题,最短路径算法在路径规划过程中起着决定性的作用,在众多路径规划算法中最经典且最具代表性的就是Dijkstra算法。以传统的Dijkstra算法分析为基础,从存储结构和算法过程两个方面进行一定程度的改进,目的是在节点数和边数较多的情况下,提高网络模型的处理效率。以真实道路交通数据为基础进行相关实验,结果证明,改进后的Dijkstra算法可以有效减少节点的计算量,提高算法的运行效率。     

反思在服务学习中的作用研究

反思是服务学习的一个重要特质,也是实施过程中一个重要的阶段,是保证服务学习质量,提升服务效果的重要组成部分。本文主要从反思的理论基础,反思的特质以及反思的作用等方面阐述反思在服务学习中的地位和价值,有助于更好地开展服务学习,提升服务学习效果。     

Template/surfactant free and UV light irradiation assisted fabrication of Mn-Co oxides composite nanorings: Structure and synthesis mechanism

A facile, green, cost effective, and template or surfactant free strategy via a two-step route i.e. UV irradiation followed by dissolution-growth for the controlled synthesis of Mn-Co composite nanorings at room temperature was proposed. The nanorings structures and the process were systematically studied via TEM, HRTEM, EDX and XRD. Bir-MnO_2 nanosheets first formed through the direct photolysis of KMnO_4 under UV light irradiation. This was followed by a dissolution-growth process via the dissolution of Bir-MnO_2 nanosheets by the generated H~+ from the redox reaction between the added Co(NO_3)_2 and residual KMnO_4, as well as the accompanied formation of CoOOH, and Mn-Co composite nanorings. It was found that a balance between the dissolution and growth rate was needed. Suitable pH, KMnO_4 presence and the starting nanosheets like Bir-MnO_2 were the key factors for the formation of nanorings. The obtained Mn-Co nanorings/TiO_2 showed enhanced efficiency for the catalytic oxidation of HCHO. Based on the above understandings, it is believed that the developed dissolution-growth method can be adopted for the designing and preparation of other Mn-Co composite nanostructures which can be further applied for environmental pollution remediation.     

碱性与中基性粗集料影响混凝土抗冻性能对比

粗集料作为混凝土的重要组成材料,其品质直接关系到混凝土的各项性能.通过试验对比研究了碱性矿料石灰岩(ω(SiO_2)为1.01%)和中基性矿料玄武岩(ω(SiO_2)为53.5%)混凝土的抗冻性能,分析了两类试件的质量损失率和相对动弹性模量.结果表明:碱性矿料能够提高混凝土的抗冻性能,这对解决混凝土抗冻性能具有重要意义.     

肝动脉化疗栓塞术治疗肝恶性肿瘤对肝功能的影响

目的探讨肝动脉化疗栓塞术(TACE)治疗肝恶性肿瘤患者对肝功能的影响.方法选取60例肝恶性肿瘤患者作为本组观察病例,分别在术前、术后1d、7d、3周及6周时对患者进行肝功能检测,并对结果进行对比分析.结果术后1d及术后7d的ALT,TBIL,DBIL均明显高于术前,差异具有统计学意义(P0.05);术后其余各项指标与术前相比均无明显差异,无统计学意义(P0.05).结论 TACE治疗后短期内对肝恶性肿瘤患者的肝功能有较大影响,在治疗后要注意加强对患者肝功能的保护.