A simple and robust estimator for linear regression models with strictly exogenous instruments

In this paper, I investigate the estimation of linear regression models with strictly exogenous instruments under minimal identifying assumptions. I introduce a uniformly (in the data‐generating process) consistent estimator under nearly minimal identifying assumptions. The proposed estimator, called the integrated instrumental variables (IIV) estimator, is a simple weighted least‐squares estimator. It does not require the choice of a bandwidth or tuning parameter, or the selection of a finite set of instruments. Thus, the estimator is extremely simple to implement. Monte Carlo evidence supports the theoretical claims and suggests that the IIV estimator is a robust complement to optimal instrumental variables in finite samples. In an application with quarterly UK data, the IIV estimator estimates a positive and significant elasticity of intertemporal substitution and an equally sensible estimate for its reciprocal, in sharp contrast to instrumental variables methods that fail to identify these parameters.     

肝纤维化研究的热点及其展望

肝硬化严重威胁人类健康,肝纤维化阶段是大多数慢性肝病向肝硬化发展的必经阶段,目前多数研究认为肝纤维化阶段疾病尚可逆转,因此本文对肝纤维化研究的热点进行讨论,并展望其发展方向。     

过渡层弹性模量对全瓷叠层冠应力分布影响的实验研究

目的 分析过渡层弹性模量对全瓷叠层冠应力分布的影响。方法 在上颌第一磨牙叠层冠有限元模型上，对照组过渡层弹性模量与饰面瓷同为70 GPa，实验组过渡层厚度为0.6 mm，弹性模量分别为175、150、100 Gpa，进行力的加载，对模型饰瓷表面最大主应力进行计算，导出最大主应力云图及各应力集中区最大主应力值。结果 实验组随过渡层弹性模量增加，所有最大主应力集中区的高应力区面积逐渐减小，饰面瓷加载区最大主应力值无明显变化，但次主应力集中区的最大主应力值下降，并且随着弹性模量的增加，下降幅度增加。结论 设计过渡层有利于分散全瓷叠层冠饰面瓷应力，并且其弹性模量越大分散效果越好。     

不同运动步态下锁定加压钢板固定胫骨干骨折的有限元分析

背景：目前有限元分析广泛应用于人体骨折内固定模型的力学分析,但大多研究局限于静态下,动态下的骨折模型有限元分析尚未见报道。目的：通过三维有限元分析来探讨锁定加压钢板固定胫骨干不同类型骨折在不同运动步态下的应力分布情况。方法：利用CT扫描获得正常成人胫腓骨及足部的薄层扫描图像;运用相关软件建立其三维模型,在此模型上模拟出胫骨中段横行、斜行、粉碎性、螺旋形4种类型骨折,并与锁定钢板进行装配生成实验模型,各组模型加载相同的轴向压缩载荷600N。通过有限元分析软件Ansys12.0分别测定各组模型在落地相、中立相、离地相三种步态下的应力分布情况。结果与结论：在步态下,胫骨在骨折各组中的应力分布由小到大均为：落地相〈中立相〈离地相。锁定钢板在胫骨中段横行、斜行、粉碎性骨折中的应力分布由小到大均为：中立相〈落地相〈离地相;在胫骨中段螺旋形骨折中应力分布由小到大为：离地相〈中立相〈落地相;提示在运动步态中,钢板和胫骨均在离地相受力最大。钢板的应力集中在中间或边缘;而胫骨的应力分布在骨折线以上靠近近端,骨折线以下靠近骨折线。就胫骨整体而言,呈现两端集中,中间分散的状态。     

Intra-rater reliability and smallest detectable change of compression sonoelastography in quantifying the material properties of the musculoskeletal system

Musculoskeletal conditions can change tissue elasticity. Knowledge of musculoskeletal elasticity could therefore aid clinical diagnosis and management. Sonoelastography is an ultrasound-based system that examines the material properties of tissues, and it may be useful in musculoskeletal practice. Therefore, it is important to establish its clinimetric properties. This study aimed to explore the intra-rater reliability and the smallest detectable changes of sonoelastography in examining musculoskeletal structures. A quantitative reliability design was used to examine 22 healthy participants using a compression sonoelastography system that produces color-coded images. The deltoid, biceps brachii, brachioradialis, rectus femoris, gastrocnemius medius muscles, and Achilles tendon were examined twice at 1-hr intervals to assess the intra-rater reliability. The sonoelastography images were analyzed using the strain index, strain ratio, and color pixels. The intra-rater reliability and the smallest detectable changes of each outcome variable were determined. The intra-class correlation coefficient was used to quantify the repeatability of the measurements, and the smallest detectable changes were calculated to determine clinically important differences above the error of measurement. The intra-rater reliability for the strain index, strain ratio, and color pixel analysis ranged from moderate to excellent (intra-class correlation coefficients: .734–.950, .776–.921, and .754–.990, respectively), with color pixel analysis demonstrating the highest reliability. The smallest detectable changes were determined for all structures, including the Achilles tendon (0.11 for the higher boundary of the strain index, 1.80 for the strain ratio, and 2.90% for red pixels, representing soft tissues). Color pixel analysis may be more reliable for sonoelastography interpretation compared with the strain index and strain ratio. The calculated smallest detectable changes could be used to identify clinically important differences.     

急性白血病患儿父母心理弹性影响因素的调查分析

目的探讨急性白血病患儿父母心理弹性水平及影响因素。方法采用心理弹性量表(CD-RISC),对某三甲医院小儿血液科两个病区于2014年12月-2015年1月期间住院的,符合纳入标准的急性白血病患儿父母进行调查。结果急性白血病患儿父母的心理弹性处于中等水平。心理弹性各维度得分以自强维度各条目得分最高,坚韧维度各条目得分最低。不同职业的白血病患儿父母的心理弹性水平不同,职业为农民的父母心理弹性及坚韧、自强维度得分最低。患儿父母与患儿不同亲子关系的心理弹性水平存在差异,在心理弹性及坚韧、自强维度上,母亲的得分均低于父亲。结论应对不同亲子关系和不同职业的父母进行针对的心理支持和健康教育,来自农村家庭的患儿母亲为重点关注对象。     

Behavior of Plain Concrete of a High Water-Cement Ratio after Freeze-Thaw Cycles

An experimental study of plain concrete specimens of water-cement ratio 0.55, subjected to 0, 15, 25, 40, 50 and 75 cycles of freeze-thaw was completed. The dynamic modulus of elasticity (DME), weight loss, compressive strength, tensile strength, flexural strength, cleavage strength and stress-strain relationships of plain concrete specimens suffering from freeze-thaw cycles were measured. The experimental results showed that the strength decreased as the freeze-thaw cycles were repeated. A concise mathematic formula between DME, weight loss, mechanical properties and number of freeze-thaw cycles was also established. The influences of freeze-thaw cycles on the DME, weight loss and mechanical properties were analyzed. The experimental results serve as a reference for the maintenance, design and life prediction of dams, hydraulic structures, offshore structures, concrete roads and bridges in cold regions.