氟中毒对小鼠学习记忆相关脑区突触结构的影响

用Ｙ－迷宫反应观察长期饮用不同浓度的氟化钠溶液对小鼠学习记忆行为的影响,然后用电镜和计算机图像分析仪观测小鼠脑内海马ＣＡ３区ＧｒａｙⅠ突触结构的损伤效应。结果表明：饮用高浓度氟化钠溶液能显著降低小鼠的学习能力,并能引起小鼠海马ＣＡ３区突触后致密物质厚度极显著减小,和引起突触间隙宽度极显著变大等超微结构的变化。结果提示,慢性氟中毒对小鼠的学习能力的显著影响可能与其脑内突触界面结构的病理变化有关。     

Development of a Flexible Metamaterial Film with High EM Wave Absorptivity by Numerical and Experimental Methods

The present study is intended to develop and test a cost-effective and efficient printing method for fabricating flexible metamaterial film with high electromagnetic wave absorptivity. The film can be easily applied to the surfaces with curved aspects. Firstly, numerical parametric study of the absorption characteristics of the film is performed for the range of frequency varying from 2.0 to 9.0 GHz based on commercial software package. Secondly, the flexible metamaterial films are fabricated, and experiments are conducted. The flexible metamaterial film consists of a flexible dielectric film made of polyimide (PI) and an array of split-ring resonators. The split-ring resonators of different geometric dimensions are fabricated on the PI film surface by using a silver nanoparticles ink jet printer. The performance of the flexible structure is then measured and dependence of operation frequency with higher absorptivity on the dimensions of the split-ring resonators is investigated. A comparison between the numerical and experimental data shows that the numerical predictions of the operation frequency with higher absorptivity closely agree with the experimental data.     

Experimental and Theoretical Studies on Possibility of Void Filling by Magnesium in Mg-Doped Tetrahedrites

Tetrahedrites, due to their promising thermoelectric properties, are one of the materials being investigated for use in thermoelectric generators. One problem is the lack of n-type tetrahedrites, which would be beneficial for the design of tetrahedrite thermoelectric modules. Preliminary theoretical studies have shown that elements from groups I and II can be introduced into the structural voids of tetrahedrite, acting as donor dopants, and should enable n-type conductivity. Therefore, in this work, an attempt was made to obtain and study magnesium-doped tetrahedrites. A series of samples, Mg_xCu₁₂Sb₄S₁₃, with different magnesium contents were obtained and their phase and chemical compositions were characterized. It was observed that the structural changes occurring upon doping indicate that Mg atoms are likely to be embedded in the structural voids. The experimental studies have been supported by electronic structure calculations indicating that the most likely location of Mg is in the structural voids at the 6b Wyckoff position. Seebeck coefficient and resistivity measurements showed that doping with Mg reduces the concentration of holes, which is consistent with the predicted donor character of the dopant. However, the introduction of magnesium in sufficient amounts to achieve n-type conductivity was not successful.     

The Effect of Pore Structure on Impact Behavior of Concrete Hollow Brick,Autoclaved Aerated Concrete and Foamed Concrete

Porous concrete is an energy absorption material, which has been widely used in civil engineering, traffic engineering and disaster reduction engineering. However, the effect of pore structure on the impact behavior of the porous concrete is lacked. In this study, a series of drop-weight impact tests were carried out on three typical types of porous concrete, i.e., concrete hollow brick (CHB), autoclaved aerated concrete (AAC) and foamed concrete (FC), to investigate the effect of pore structures on their impact behavior. For comparison, static load tests were also conducted as references. According to the damage to the samples, the developments of impact force, strain, contact stress–strain relationship and absorbed energy during drop-weight during the impact test were measured and analyzed. The results show that the ratio between the peak impact stress and compressive strength of CHB was 0.44, while that of AAC and FC increased to about 0.6, indicating that the small and uniform pore structure in AAC and FC had a higher resistance against impact load than the hollow cavity of CHB. In addition, the elastic recovery strain in AAC increased by about 0.2% and its strain at peak contact stress increased by about 160% for a comparison of CHB, implying that a small open pore structure could enhance ductility. Besides, the peak contact stress of FC was close to that of AAC during impact loading, while the strain at peak contact stress of FC increased by about 36% compared with AAC, revealing that the closed-pore structure could further enhance the deformation potential. Correspondingly, the energy absorption rates of CHB, AAC and FC were 85.9 kJ/s, 54.4 kJ/s and 49.7 kJ/s, respectively, where AAC decreased by about 58% compared with CHB, and FC decreased by about 10% compared with AAC.     

Thoughts on how to think (and talk) about RNA structure

Recent events have pushed RNA research into the spotlight. Continued discoveries of RNA with unexpected diverse functions in healthy and diseased cells, such as the role of RNA as both the source and countermeasure to a severe acute respiratory syndrome coronavirus 2 infection, are igniting a new passion for understanding this functionally and structurally versatile molecule. Although RNA structure is key to function, many foundational characteristics of RNA structure are misunderstood, and the default state of RNA is often thought of and depicted as a single floppy strand. The purpose of this perspective is to help adjust mental models, equipping the community to better use the fundamental aspects of RNA structural information in new mechanistic models, enhance experimental design to test these models, and refine data interpretation. We discuss six core observations focused on the inherent nature of RNA structure and how to incorporate these characteristics to better understand RNA structure. We also offer some ideas for future efforts to make validated RNA structural information available and readily used by all researchers.     

北京市出租车司机膳食结构与饮食行为调查

目的了解北京市出租车司机膳食结构与饮食行为,为改善出租车司机的营养健康状况提供科学依据。方法采用方便抽样的方法,在北京首都机场T3航站楼地下停车场候机排队的出租车中随机抽取1052人作为调查对象。采用问卷调查的方法收集司机的饮食行为、膳食结构等信息。结果 21.8%的出租车司机出车时3餐均在外就餐,郊区司机3餐进食时长低于城区司机。出租车司机不吃早餐、午餐、晚餐的比例分别是10.5%、4.4%和14.8%。出租车司机出车时午餐和晚餐的构成主要是"主食+荤菜+素菜",较少司机选择加入水果,尤其是午餐。干净卫生和能吃饱是司机们选择就餐环境时考虑的主要因素,仅有少部分司机在选择午餐(20.4%)或晚餐(27.4%)时会考虑营养因素。结论北京市出租车司机特别是郊区司机,目前仍存在饮食不规律、3餐分配及膳食结构不合理的现象。     

Application of Iron Tailings-Based Composite Supplementary Cementitious Materials (SCMs) in Green Concrete

How to treat the iron tailings of mining solid waste with high value is an urgent problem on a global scale. In recent years, the application of iron tailings in the building materials industry has attracted the attention of many scholars. The conversion of iron tailings into green building materials helps achieve carbon neutrality and high-value utilization of solid waste, and promotes sustainable development. Although iron tailings have been extensively studied as supplementary cementitious materials, the performance of concrete is not ideal due to its low activity. In this study, the hybrid supplementary cementitious materials system was prepared by iron tailings, phosphorus slag, and steel slag, and the effects of supplementary cementitious materials type, iron tailings content, iron tailings grinding time, and supplementary cementitious materials content on concrete performance were studied. The compressive properties, iron tailings properties, pore structure, interfacial transition zone, and element distribution of hydration products of concrete were tested by compressive strength tests, X-ray Diffractometer (XRD), X-ray Photoelectron Spectroscopy (XPS), Mercury Intrusion Porosimetry (MIP), Backscattering Electron Tests (BSE), and Energy Dispersive Spectrometer (EDS). The results show that further grinding improves the iron tailings activity. There is a synergistic mechanism between steel slag and phosphorus slag in the composite supplementary cementitious materials, which overcomes the low activity defect of iron tailings and produces concrete with a compressive strength exceeding 40 MPa. The composite supplementary cementitious materials can optimize the interfacial transition zone of the concrete interface and reduce the calcium–silicon ratio of the hydration products. However, it will deteriorate the pore structure of the concrete matrix, cause part of the concrete matrix to be damaged and lead to a loss of compressive strength, and the loss is acceptable. This work broadens the methods of comprehensive utilization of iron tailings and also provides a reference for a more detailed understanding of the properties of iron tailings-based concrete.     

2005年全国疾病预防控制机构人力结构现状分析

通过全国系统抽样,获取疾病预防控制机构2005年人力结构基本资料,从年龄、学历、职称和专业四个维度对疾病预防控制机构人员构成进行描述。结果显示,全国疾病预防控制机构在岗人员平均年龄为39.8岁,以大、中专学历为主,本科学历次之,职称集中在初、中级水平,专业化程度较高,并以预防医学和非预防专业的医学专业背景为主。     

新医疗服务项目及收费标准对住院费用和收费结构的影响

目的:比较新医疗服务收费标准执行前后某专科医院医疗服务费用和收费结构的变化,分析费用构成比及合理程度,初步评价新收费标准对住院费用和收费结构的影响。方法:采用回顾性调查方法,抽取2005—2006年度和2006—2007年度的5种常见病种共1000例,应用SPSS13.0软件统计分析。结果:2006—2007年度各病种治疗、检查和化验等费用和费用构成比下降;手术、护理等费用和费用构成比上升。结论:各病种收费标准和费用构成比例逐步规范、合理,仍有待进一步改进。