Enhancing surface wear resistance is critical for uranium (U) and its alloys to retard degradation of their mechanical and physical properties. Deposited nanotwinned (NT) silver (Ag), which is relatively "soft" in-plane and "hard" out-of-plane with respect to surface, may serve as wear-resistant coating. In this work, first-principles density functional theory (DFT) calculations were performed to reveal the energetics of possible Ag/alpha-U interfaces. Meanwhile, molecular statics (MS) and molecular dynamics (MD) simulations were carried out to understand the behaviors of Ag adatoms and the tribological performance of subsequent different textured Ag. The {111}(Ag)-textured coating with fine twins with small plastic zone, low delamination height and subsequent minimal coefficient of friction (COF) was designed. Furthermore, by controlling the bias voltage of magnetron sputtering from -100 to -800 V, Ag coatings with various surface roughness, grain size, and nanoscale twin density were experimentally deposited on depleted uranium (DU) for tribological performance studies. Microstructural characterizations showed that at the optimized bias voltage of -400 V, the sputter-deposited Ag coating exhibited {111}-oriented texture with high-density nanoscale twins and also well-bonded Ag/DU interface with an UO2 interlayer, thus endowing the Ag coating highly stable wear resistance with low mass wear rate of similar to 1.37 x 10(-7) g/(Ns). The present findings may shed lights on microstructural and interface design of surface anti-wear coatings on U and its alloys.

Because of various excellent properties of low density, high specific strength and stiffness, high modulus, good thermal stability and corrosion-resistant, beryllium-aluminum (Be-Al) alloys have shown great potential to be used in nuclear industries. However, Be-Al alloys suffer from the bottlenecks of low solubility between Be and Al and the lack of effective technology for fabricating large-sized products. Herein, based on Sc and Zr addition, BeAl-Sc-Zr alloys are successfully fabricated by conducting the electron beam welding (EBW) technology, and the effect of Sc and Zr addition on microstructure, mechanical property and fracture behavior of Be-Al-Sc-Zr alloys are studied. Microstructural characterizations show that both the EBWed Be-Al and Be-Al-Sc-Zr alloys exhibit two distinct zones of substrate zone (SZ) and fusion zone (FZ). Compared to grain size of the SZ and FZ in Be-Al alloys, grain sizes of these two zones in Be-Al-Sc-Zr alloys are significantly refined, thus leading to ultimate tensile strength (UTS) of the Be-Al-Sc-Zr alloys ( 176 MPa) approximately 150 % higher than that of the Be-Al alloys ( 118 MPa). Besides, a newly generated third phase (TP), which is confirmed as Be13(Scx, Zr1-x), forms within Al phase in both SZ and FZ of the Be-Al-Sc-Zr alloys. Different from fracture behavior of Be-Al alloys that preferentially fractures within Al phase or near the Be/Al interface, fracture of the Be-Al-Sc-Zr alloys is prone to occur within Be phase. As revealed by the calculation results of finite element method (FEM), the underlying mechanism for different fracture behaviors mainly ascribe to that the reinforcement of Al phase and existence of the newly formed TP can greatly increase the internal stress and even causes stress concentration within Be phase of the Be-Al-Sc-Zr alloys. The present findings may provide more insights to the micro-alloying and deformation mechanism of Be-Al alloys that with enhanced mechanical properties.

Owing to excellent mechanical properties, beryllium-aluminum (Be-Al) alloys have garnered significant attentions as advanced structural materials in the military sector. However, they also suffer from extremely low solubility between Be and Al, and a lack of effective techniques for large-scale Be-Al alloy fabrication. In this study, Be-Al-Ag-Si alloys were fabricated with significantly refined microstructures and improved micro-mechanical properties by incorporating additional Ag and Si elements and utilizing electron beam welding (EBW) technique. Micropillar compression results indicate that the yield strength (YS) of the fusion zone (FZ) in the as-welded Be-Al-Ag-Si alloys is approximately 540 MPa, which is around 135% higher than that of the substrate zone (SZ) with YS of approximately 230 MPa. The significant improvement can be mainly attributed to the grain boundary strengthening and dislocation strengthening due to the rapid heating/cooling rate and high thermal residual stress in the FZ, as revealed by microstructural analysis. Additionally, other strengthening mechanisms, such as Orowan and GP zone strengthening, could also make a contribution. These results offer further understanding towards the production of large-scale Be-Al alloys with improved flow ability and mechanical properties.

The microstructure and micropillar compression responses of thin-walled Be-Al and Be-AlSi10Mg samples, produced by laser solid forming (LSF), were investigated. Both alloys resembled typical 3-D net-shaped structures. The Be-AlSi10Mg alloy exhibited coarser Be grains embedded in the refined Al net-like matrix owing to a broader solidification region. Owing to the multi-hardening by Si and Mg alloying, the yield strength of the system significantly increased from 150 MPa to 220 MPa. In addition, the failure mode changed from plastic fracture of the Al phase in Be-Al to brittle fracture of the Be phase in Be-AlSi10Mg during microcompression. Based on the theoretical calculation of the yield strength and fracture strength, grain size refinement by the nonuniform nucleation process was dominant factor affecting the Al matrix strength increment of Be-AlSi10Mg. Meanwhile, the critical resolved shear stress of Be was smaller than the ultimate strength of the Al phase strengthened by Si and Mg in the Be-AlSi10Mg alloy. Thus, the failure preferentially occurred in the Be phase rather than the Al phase. These results suggest that improving the fracture strength of the Be phase is important for obtaining high-performance Be-Al alloys after the strengthening of the Al phase by alloying additions and artificial aging measurements.

目的 探讨家庭关联性鹦鹉热感染来源与传播途径,为制定科学、有效的防制措施提供经验.方法 收集患者资料,包括流行病学、临床表现、实验室和病原学检查结果等.采用病原体基因测序和间接免疫荧光法等检测法核实疫情.结果 该起事件为由家养鸟类引起的经接触感染的家庭关联性鹦鹉热疫情,共涉及病例3例.结论 多部门联防联控是社区鹦鹉热疫情处理的重要手段,减少与鸟类和禽类接触、交易市场的动物检疫和环境治理是预防和控制感染的重要措施.

Objective:To analyze the epidemiological characteristics and spatial and temporal clustering of incidence of influenza from 2015 to 2019 at the street/township level in Haidian district, Beijing.Methods:The incidence data of influenza in Haidian district was collected from the Infectious Disease Reporting Management System, and descriptive epidemiological method, spatial autocorrelation analysis and retrospective spatiotemporal scanning analysis were used to analyze the characteristics of reported influenza cases.Results:The average incidence rate of influenza in Haidian district was 356.94/100 000 during 2015-2019. The peak period of incidence was the 49th week to the 17th week of next year. The incidence rates of influenza among students, children in childcare, children under 10 years old and people 80 years old or above were high. The hot spots showed dynamic changes from south to north. The most likely cluster were in the midwest of Haidian district, and the time was the 1st week to the 4th week of 2019.Conclusions:Incidence rates of influenza in Haidian district varied among different groups of people, and showed temporal and spatial clustering during 2015-2019. Different prevention measures should be applied to different groups of populations, time and areas.

采用真空感应熔炼的方法制备了U-0.5％Ti、U-0.75 ％Ti和U-0.95％Ti合金试样,研究了Ti含量对合金微观组织、室温拉伸性能和耐腐蚀性能的影响.结果 表明:三种成分的U-Ti合金组织均以针状和双凸透镜状马氏体为主,物相组成主要有α'相和U2 Ti相;随着Ti含量的增加,U-Ti合金的晶粒逐渐细化,U2Ti相的含量逐渐增大.同时,随着Ti含量的增加,U-Ti合金的强度逐渐提高,而塑性逐渐降低,耐腐蚀性能也略有下降.

The microstructure and micro-mechanics around the repaired interface, and the tensile properties of laser additive repaired (LARed) Inconel 625 alloy were investigated. The results showed that the microstructure around the repaired interface was divided into three zones: the substrate zone (SZ), the heat-affected zone (HAZ), and the repaired zone (RZ). The microstructure of the SZ had a typical equiaxed crystal structure, displaying simultaneously precipitated block-shaped MC-type carbides (NbC, TiC), with bimodal sizes of approximately 10 μm and 0.5 μm and an irregularly shaped flocculent Laves phase. Recrystallization occurred in the HAZ, and led to significant grain growth; a portion of the second phase dissolved in the original grain boundaries. In the RZ, there was a columnar crystal structure, and the size increased with increasing deposition thickness. Moreover, the microstructure between the layer interface and layer interior was quite different, presenting an overlapping transition zone (OTZ), in which the dendritic structure coarsened and more Laves phase were precipitated, compared to in the layer interior. The hardness and tensile properties of the LARed samples were equivalent to those of the wrought substrate, which indicates that laser additive repairing (LAR) is a reliable repair solution for damaged and mis-machined components comprising Inconel 625 alloy.

目的 了解北京市海淀区医疗机构传染病报告填写质量,为进一步提高传染病信息报告工作质量提供科学依据.方法 按照分层抽样原则,从北京市海淀区64家医疗机构中共抽查1150张纸质(电子)传染病报告进行填写质量调查,调查内容包括完整性、准确性、一致性和正确性.结果 报告填写的完整率、准确率、一致率和正确卡率分别为92.44％,88.52％,83.04％和70.87％;不同类型医疗机构完整率差别有统计学意义(P<0.05),不同级别、类型医疗机构准确率、一致率和正确率差别有统计学意义(P<0.05).结论 应加强培训与监管,建立健全医疗机构自查工作等管理机制,完善传染病信息报告信息化建设,进一步提高传染病报卡填写质量.

目的 构建医疗机构传染病信息报告的质量评价各指标的组合权重,并对北京市海淀区医疗机构传染病信息报告质量进行综合评价.方法 采用熵权法和主成分因子分析法构建单一评价模型,利用最优方案构建组合评价模型并形成各评价指标的组合权重;利用组合权重,对不同类型医疗机构的传染病信息报告质量进行评价.结果 熵权法和主成分分析法模型评价结果差别具有一致性(w=0.956,P<0.01);组合模型赋予漏报率、迟报率、不完整比率、不准确比率、不一致比率和工作量6个指标的权重分别为0.319、0.328、0.115、0.098、0.109和0.032;各单一评价模型与组合权重模型对不同类型医疗机构的排序结果一致,即:地方二、三级医疗机构>高校医疗机构>社区卫生服务中心/站>部队医疗机构.结论 各单一评价模型对各医疗机构评价结果不尽相同,但总体趋势一致;组合权重模型对不同类型医疗机构传染病信息报告的质量评价结果与实际情况相符;不同类型医疗机构传染病信息报告质量存在差异.

采用混合元素法开展了激光增材制造W-Ni合金的成形性、组织和硬度研究.结果 表明,Ni含量大于20％的W-Ni合金可以稳定沉积,沉积层横截面宽度变化较小,成形性能较好,而当Ni含量小于10％时,经过多层沉积后横截面宽度逐渐变窄,呈现三角形形状,成形性较差.随着Ni含量的减小,W-Ni合金组织中W颗粒的密度也逐渐增加,且试样底部存在较多W颗粒相.随着Ni含量的减小,沉积区的硬度逐渐升高,且沿沉积方向,从基材到沉积区顶部显微硬度的变化呈现先降低后快速上升到缓慢上升的趋势.

目的 对2018-06-27/08-03北京市海淀区某小学肺炎支原体感染引起的流感样病例暴发疫情进行调查,分析疫情流行特征,为防控工作提供依据.方法 通过现场流行病学调查,搜索病例进行个案调查,采集病例咽拭子标本进行呼吸道多病原核酸检测,采用χ2检验进行率的比较.结果 北京市海淀区某小学共发生肺炎支原体感染临床诊断病例和实验室确诊病例26例,其中学生24例,教师2例,男性罹患率16.83％,女性罹患率10.59％,不同性别罹患率差异无统计学意义(χ2=1.496,P=0.221);指示病例1(首发病例)6月27日发病,疫情共持续37 d;病例主要集中在四年级1-4班,发病时间集中在07-16至07-22;临床症状以发热、咳嗽为主,均占100％;四年级1-4班罹患率为13.98％,其中四4班罹患率最高为39.13％,班级罹患率差异有统计学有意义(χ2=33.013,P<0.001);该起疫情结案前病例肺炎支原体核酸阳性率为68.42％,结案后为40.00％,结案后波及人群阳性率为30.00％,三者阳性率差异无统计学意义(χ2=5.112,P=0.078).结论 肺炎支原体传染性较强,在潜伏期至症状缓解数周仍有传染性,而且导致的无症状感染患者较多,使防控工作面临更严峻的考验,必须及时处置,防止扩散.

目的 通过对2017年北京市海淀区67起诺如病毒聚集性疫情的流行病学特征描述和分析,找出潜在的危害因素,为切实有效预防疫情的发生和蔓延提供参考依据.方法 采取现场流行病学方法和描述分析方法,对疫情发生单位和疑似病例个案进行详细的调查,并进行统计学分析.结果 67起疫情中聚集性疫情57起,暴发疫情10起;67起疫情中诺如病毒GⅡ型65起,GⅠ和GⅡ混合感染型2起;报告疑似病例992例,波及人数5 701人,罹患率波动范围为4.1％～73.33％,平均罹患率为17.40％,2～6、7～12、13～18和19～60岁4个年龄组的呕吐、腹泻、恶心、腹痛和发热的症状比较,差异均有统计学意义(x呕吐=38.309,x2 腹泻=114.051,x恶心=55.445,x腹痛=106.129,x2发热=10.253;均P＜0.05);采集标本755件,检出阳性标本457件,检出率60.53％,不同类型的标本阳性率比较,差异有统计学意义(x2=234.271,P＜0.01).结论 作为诺如病毒感染疫情高发的中小学校和托幼机构,防控工作至关重要,在日常传染病防控中,一定要加强疑似病例的早期发现,及时隔离,防止疫情的蔓延;规范消毒,有效阻止病毒的快速传播;加强宣传教育,提高整体防病意识.

The process parameters and microstructure of the laser forming repaired (LFR) samples of Inconel 625 alloy were investigated. The results show that a wide range of process parameters are suitable for the laser forming repairing of Inconel 625 alloy. The laser power mainly affects the width of single track LFR samples. The scanning velocity has significant effect on the size of single track LFR samples. The powder feeding rate has less effect on the size of single track LFR samples. The interface between the substrate and laser repaired zone (LRZ) shows a metallurgical bonding. The phases in the substrate mainly include the gamma(Ni-Cr) matrix, MC (NbC, TiC) carbides with bimodal sizes of about 10 mu m and 0.5 mu m, and Laves phase. In the LRZ, columnar dendrites grow epitaxially from the substrate, approx following the deposition direction. The phases in LRZ mainly consist of gamma matrix, Laves phase and a small amount of MC carbides. Due to the increase of nucleation sites, a large amount of Laves phase are precipitated in the layer interface and track interface.

目的 探讨新生儿低血糖的相关危险因素,为预防新生儿低血糖提供临床数据.方法 采取回顾性分析方法收集2012年1月—2016年12月入住北京市上地医院新生儿科的3184例新生儿及其母亲临床资料,新生儿低血糖205例,分别采用单因素分析与Logistic多元回归分析法筛选新生儿低血糖的相关危险因素.结果 新生儿低血糖发生率为6.438％.T检验结果显示,低血糖患儿体重较轻(t=5.327,P=0.000);卡方分析结果显示新生儿低血糖发病率差别有统计学意义的因素是:早产儿、小于胎龄儿、病理性黄疸、先天性心脏病、湿肺、呼吸性酸中毒、呼吸窘迫综合征、代谢性酸中毒、呼吸衰竭、妊娠合并糖尿病、子痫前期、胎儿生长受限、胎儿宫内窘迫、不良孕产史、妊娠合并子宫异常、双胎(P<0.05)(Χ2=49.191,8.657,42.495,11.315,9.450,9.493,6.515,5.365,19.634,5.753,7.551,12.793,9.560,4.194,6.336,10.816).多因素分析显示新生儿低血糖的影响因素有不良孕产史、胎儿宫内窘迫、妊娠合并糖尿病、妊娠合并子宫异常、早产儿、新生儿病理性黄疸、新生儿呼吸衰竭、新生儿先天性心脏病(P<0.05),OR值范围为1.544～2.329,其中新生儿呼吸衰竭、 胎儿宫内窘迫和新生儿先天性心脏病OR值分别为2.329、2.226和2.202.结论 应加强具有新生儿呼吸衰竭、胎儿宫内窘迫和新生儿先天性心脏病等危险因素的新生儿血糖监测,减少新生儿低血糖的发生.

目的 调查某医院住院病人腹泻暴发疫情的致病因子,找出传染源和危险因素,提出针对性的预防控制建议,有效控制疫情.方法 采用统一的调查表对病例进行流行病学调查;开展现场卫生学调查并采集便标本,采用RT-PCR对便标本进行诺如病毒核酸检测.结果 调查该病区暴露的住院患者和医务人员135名,发现22名病例,罹患率为16.30％;患者临床表现以腹泻、恶心、呕吐为主,部分患者出现发热症状;不同楼层住院老人罹患率差异无统计学意义(x2=0.82,P＞0.05);住院老人罹患率高于护工(x2=5.35,P＜0.05),不同性别住院老人发病风险相同(x2=0.18,P＞0.05);采集的14份便标本中,8份检测结果为诺如病毒核酸阳性.结论 该次急性胃肠炎暴发疫情是由诺如病毒引起,传染源可能为隐形感染者或病原携带者,病毒通过某种共用媒介传播后再以人-人传播模式进一步扩散,高危人群为住院老人;采取针对性措施后,疫情得以有效控制.

目的 分析北京市海淀区一起腺病毒53型引起的结膜炎暴发疫情流行病学特征.方法 对某中学发生的结膜炎病例进行流行病学调查,采集咽拭子和眼拭子标本进行病毒分离和鉴定.结果 病例主要集中在初一、初二和初三年级,患病率分别为11.5％、14.9％和9.8％,流行曲线为单峰分布,疫情持续59 d,由学生通过密切接触传播.平均年龄14.4岁.患者以眼部不适症状为主,无发热症状,其中单眼不适61例,占85.9％;双眼不适10例,占14.1％.其中结膜充血41例,占57.7％;畏光1例,占1.4％;眼部疼痛5例,占7.0％;眼痒7例,占9.9％;眼分泌物增多3例,占4.2％.推测最长潜伏期为35 d.经过Hep-2细胞培养分离毒株4株,采用中和试验鉴定为腺病毒53型,与PCR检测结果一致.结论 该起疫情是由腺病毒53型引起的结膜炎暴发,应加强对高危人群防控知识的宣传教育.

Objective To understand the incidence and prevalent features of epidemic hemorrhagic fever in Haidian District and provide scientific basis for the control of the disease. Methods The descriptive epidemiology method was used to analyze the monitoring conditions of epidemic hemorrhagic fever in Haidian District from 2008 to 2012. Results 12 cases of epidemic hemorrhagic fever were reported, no death case. Annual report rate was 0.04/lakh, 0.04/lakh, 0.15/lakh and 0.15/lakh, respectively.In the entire district about half of the streets had cases, which were referred as sporadic cases. But there were family clusters in the village of Shuguang Street, where cases reported mainly concentrated in urban-rural fringe zone. The disease occurred mainly in the spring. 9 cases(75%) were reported from March to May. There were more male patients. The proportion of male to female was 3: 1and no gender difference was found(P0.05). The young people composed the main patients, and 10 patients were 20-50 years old(83.3% of total patients). Most of the patients were peasants, rural laborers and unoccupied person whose education level was relatively low. Conclusion In 2008-2012, the incidences of epidemic hemorrhagic fever were scattered in Haidian District, but showing a rising trend in recent years. The deratization rat related work should be strengthened.

Objective To build various single models and combination model based on Exponentially Weighted Moving Average(EWMA for forecasting weekly-incident of Hand-foot-mouth disease(HFMD), and to verify and evaluate the goodness of fit of the models. Methods A ARIMA- Generalized Autoregressive Conditional Heteroskedasticity(GARCH) model, Vactor Autoregressive(VAR) model and Holt-Winters- Multiplicative model were built using meteorological factors and the incidence of HFMD during May 2, 2008 to May 5, 2013. The reciprocal EWMAs of the absolute percentage error(APE) of single models at different times were adopted as combined weights of single models to build combination model based on EWMA. Incidence of HFMD forecasting during May 6, 2013 to June 30, 2013 was performed by various models. Results The value of mean absolute percentage error(MAPE), root mean square error(RMSE) and Theil inequality coefficient(TIC) of single models were higher as compared to combination model.The optimal model was got when the combination model weighting factor was 0.1. Conclusion Combination model based on EWMA is superior to every single model.

The influence of Fe particle addition on MgZnCa eutectic-composition as-cast alloy was investigated. No difference was observed in the other main crystal phases, except for the Fe particles. Compared with the as-cast Mg69Zn27Ca4 ternary system, the alloy with Fe added exhibited higher strength and plasticity. The fracture stress of Mg69Zn27Ca4 with 4vol% Fe reached nearly 700MPa with 12% plasticity. The porous Fe particles increased the strength and toughness of the alloy.