温度和疲劳共同作用对溴化丁基橡胶气体阻隔性能的影响

溴化丁基橡胶(BIIR)因其出色的气体阻隔性能成为轮胎内衬层首选材料,但轮胎使用过程中因摩擦生热产生的高温和滚动过程中的屈挠疲劳作用,其性能和使用寿命将会受到很大的影响,因此,探索温度和疲劳作用对BIIR气体阻隔性能的影响具有重要意义。文中对比研究了温度和屈挠疲劳单因素作用以及双因素作用下,BIIR气体阻隔性能的变化情况;通过交联密度测试、动态力学热分析及透射电镜等手段,探寻了BIIR在温度和疲劳双因素作用下其分子交联网络和填料分布情况的变化。结果表明,热老化作用使BIIR交联度增加,气体阻隔性能提高;疲劳作用对其气体阻隔性能的影响也较小;但温度和疲劳共同作用下,BIIR在较高温度下形成的交联网络又经屈挠疲劳的作用,更易发生裂解,并带动填料粒子的“移动”,导致了BIIR橡胶气体阻隔性能的大幅降低。

大学生参与MOOC学习实证研究

MOOC的学习者参与问题是影响其未来发展的重要问题.本研究以我国某师范大学386名在校学生为研究对象,进行了关于参与MOOC学习情况的问卷调查,并对其中有完整MOOC学习经历的样本进行了学习满意度影响因素分析,对没有完整MOOC学习经历的样本进行了原因分析.研究结果表明,学习MOOC所带来的高质量学习资源、优质教师以及个性化的学习方式是影响学习者学习满意度评价的三个重要因素.有用性认识不足和困难预期过高是导致目前MOOC在大学生群体内参与率和完成率不高的两类主要原因.

以氧化诱导期为性能变化指标推算三元乙丙橡胶O型密封圈的贮存寿命

商品化的橡胶制品常常由于尺寸小、异形等原因难以使用传统的力学性能作为寿命推算的性能指标,为了解决这一问题,文中首次提出将氧化诱导期(OIT)作为性能变化指标来推算三元乙丙橡胶O型密封圈的贮存寿命。分别在80℃,100℃,120℃,140℃和160℃对EPDM O型圈进行数小时至2年的热空气加速老化,测试老化前后样品的拉伸强度、断裂伸长率及氧化诱导时间。研究结果表明,随着老化时间的延长和老化温度的升高,OIT的变化趋势与拉伸强度和断裂伸长率一致;使用OIT作为性能变化指标计算出的EPDM O型圈的贮存寿命为28.6年,与以拉伸强度为性能变化指标时基本一致,充分证明了以OIT作为寿命推算指标的可行性,解决了微小或异形制品的寿命估算难的问题。

Numerical modeling of thermal breakthrough induced by geothermal production in fractured granite

It is well known that the complicated channeling of fluid flow and heat transfer is strongly related with the intricate natural fracture system.However,it is still challenging to set up the fracture network model which is strong heterogeneous.Compared with other methods(e.g.equivalent continuum model(ECM),discrete fracture model(DFM),and ECM-DFM),the fracture flow module in the COMSOL Multiphysics simulator is powerful in definition of fractures as the inner flow boundary existing in the porous media.Thus it is selected to simulate the fluid flow and heat transfer in the geothermal-developed fractured granite of Sanguliu area located at Liaodong Peninsula,Eastern China.The natural faults/fractures based on field investigation combined with the discrete fracture network(DFN)generated by the MATLAB are used to represent the two-dimensional geological model.Numerical results show that early thermal breakthrough occurs at the production well caused by quick flow of cold water along the highly connected fractures.Suitable hydraulic fracturing treatments with proper injection rates,locations,etc.can efficiently hinder the thermal breakthrough time in the natural fracture system.Large well spacing helps the long-term operation of geothermal production,but it is highly dependent on the geometrical morphology of the fracture network.The enhancement of reservoir properties at the near-well regions can also increase the geothermal production efficiency.The results in this study can provide references to achieve a sustainable geothermal exploitation in fractured granitic geothermal reservoirs or hot dry rocks at depth.

Early Age of Onset, Multiple Primary Malignancies and Poor Prognosis Are Indicative of an Inherited Predisposition to Esophageal Squamous Cell Carcinoma in Familial Rather Than Sporadic Disease- An Update Based on 14- to 23-year Follow-up

OBJECTIVE To demonstrate the effects of an inherited predisposition to familial esophageal squamous cell carcinoma （ESCC） through the comparison and analysis of the clinicopathologic differences between familial and sporadic ESCC cases. METHODS Differences in age of onset, prevalence rates of double primary ESCC, and survival rates between familial ESCC （n = 476） and sporadic ESCC cases （n = 1226） were analyzed. RESULTS Overall, familial ESCC cases showed a significantly younger age of onset （51.9±8.2 vs. 53.4 ±8.0, Pt.test = 0.00）, a significantly higher prevalence rate for double ESCC （2.73 % vs. 1.22%, adjusted with TNM：χMH2 = 4.029, P = 0.045）, and a lower survival rate than in sporadic cases （Pwald = 0.04）. The familial cases showed both a younger age of onset and poorer survival in most subgroups, and the differences were more marked in early-stage rather than in the .late-stage disease groups. CONCLUSION Theses findings confirm the existence of familial as opposed to sporadic ESCC. By the theory of the ＂two-hit＂ origin of cancer, these findings also suggest that the ＂first hit＂, a genetic predisposition, can affect the age of onset, number of primary carcinomas, and the prognosis for familial ESCC patients.

NATURAL HISTORY OBSERVATION FOR ESOPHAGEAL AND CARDIA PRECURSORS BY REPETITIVE ENDOSCOPIC SCREENING OF 301 SUBJECTS IN SHEXIAN

OBJECTIVE To investigate the natural history of fast developing esophageal and cardia precursors.METHODS Repetitive endoscopic screenings were performed among 40-69-year-olds in the high-incidence areas for esophageal cancer in Shexian. RESULTS The initial diagnosis and the lag-time for 7 subsequently identified severe dysplasia （SD） subjects were as follows： in one subject 13 months after a baseline diagnosis of normal epithelium, in another subject 7 months after a baseline diagnosis of base cell hyperplasia （BCH）, in four subjects 3, 4, 4, and 10.5 months after baseline diagnosis of mild dysplasia （mD）, and in one subject 12.5 months after a baseline diagnosis of moderate dysplasia （MD）. The initial diagnosis and the lag-time for 6 subsequently identified carcinomas in situ or intramucosal carcinoma cases were： in one case 48 months after a baseline diagnosis of mD, in 2 cases 4 and 13 months after baseline diagnoses of MD, and in the other 3 cases 3.5, 9, and 17.5 months after baseline diagnoses of SD. The initial diagnosis and lag-time for 3 subsequently identified invasive cancer cases, were： in one case 50 months after a baseline diagnosis of MD, in 2 cases 14 and 19 months after baseline diagnoses of SD. In addition, during a 4-year-follow-up of 18 subjects after endoscopic mucosa resection, 9 of them were found to have developed precursors again at other sites, and also additional findings were obtained for 11 of the 16 dysplasia cases by repetitive biopsy in less than 2 months after the initial endoscopy. CONCLUSION A 5-year screening interval for BCH and mD, and a 3-year interval for MD may be too long for the fast developing precursors. Periodic screenings with shorter intervals should be considered to control the number of interval cases due to fast development, multifocal carcinogenesis, and false negative results inherent in one-time endoscopic biopsy sampling.

Statistical analysis for genome-wide association study

In the past few years, genome-wide association study （GWAS） has made great successes in identifying genetic susceptibility loci underlying many complex diseases and traits. The findings provide important genetic insights into understanding pathogenesis of diseases. In this paper, we present an overview of widely used approaches and strategies for analysis of GWAS, offered a general consideration to deal with GWAS data. The issues regarding data quality control, population structure, association analysis, multiple comparison and visual presentation of GWAS results are discussed; other advanced topics including the issue of missing heritability, meta-analysis, setbased association analysis, copy number variation analysis and GWAS cohort analysis are also briefly introduced.

中国新诊断胶质母细胞瘤患者实际治疗方案与Stupp方案的一致性比较

目的评估中国新诊断胶质母细胞瘤(glioblastoma multiforme,GBM)患者实际接受的治疗方案与指南推荐的Stupp方案的一致性。方法纳入202例新诊断GBM患者,评估实际接受的治疗方案与Stupp方案一致的患者比例,以及不符合Stupp方案的原因。结果研究发现,仅15.8%的GBM患者接受了与Stupp方案一致的治疗。治疗方案的不一致主要是由于同步放化疗阶段替莫唑胺剂量>75 mg/m^(2)(58/120;48.3%)和治疗持续时间<42 d(84/120;70.0%),以及辅助治疗阶段替莫唑胺剂量<150 mg/m^(2)(89/101;88.1%)。接受符合Stupp方案治疗的患者的中位总生存期(27.09 vs 18.21个月)和无进展生存期(14.27 vs 12.10个月)更长。结论需要提高中国GBM患者实际接受的治疗方案与Stupp方案的一致性。

A Novel Wireless PassiveTemperature-Pressure SAW-based Sensor

A novel wireless and passive surface acoustic wave(SAW)sensor is developed for measuring temperature and pressure.The sensor has two single-port resonators on a substrate.One resonator,acting as the temperature sensor,is located at the fixed end without pressure deformation,and the other one,acting as the pressure sensor,is located at the free end to detect pressure changes due to substrate deformation.Pressure at the free end bends the cantilever,causing a relative change in the acoustic propagation characteristics of the SAW traveling along the surface of the substrate and a relative change in the resonant frequency of the resulting signal.The temperature acts on the entire substrate,affecting the propagation speed of the SAW on the substrate and directly affecting the resonant frequency characteristic parameters.The temperature and pressure performance of this new antenna-connected sensor is tested by using a network analyzer,a constant temperature heating station,and a force gauge.A temperature sensitivity of 1.5015 kHz/℃and a pressure sensitivity of 10.6 kHz/gf at the ambient temperature have been observed by wireless measurements.This work should result in practical engineering applications for high-temperature devices.

Effects of Different Doses of Stereotactic Radiotherapy on Recurrence,Metastasis and Survival of Patients with Lung Cancer

Objective:To investigate the effect of different doses of stereotactic radiotherapy(SBRT)on the recurrence,metastasis and survival of lung cancer patients.Methods:The clinical data of 13 patients with lung cancer who were treated in our hospital from May 2016 to June 2020 and were followed up for one year were retrospectively analyzed.The patients treated with low-dose SBRT were divided into the observation group(7 cases)and the patients treated with high-dose SBRT were divided into the control group(6 cases).The clinical efficacy,recurrence,metastasis,survival status and incidence of adverse reactions were compared between the two groups.Results:There were no significant differences in the clinical total effective rate,1-year recurrence rate,metastasis rate and survival rate between the two groups(P>0.05);The incidence of adverse reactions in the observation group was lower than that in the control group,the difference was statistically significant(P<0.05).Conclusion:High dose or low dose SBRT can achieve good curative effect and prognosis in patients with lung cancer,but low dose SBRT has less adverse reactions and higher safety.

Mechanism of capture section affecting an intake for atmosphere-breathing electric propulsion

Atmosphere-Breathing Electric Propulsion(ABEP)can compensate for lost momentum of spacecraft operating in Very Low Earth Orbit(VLEO)which has been widely concerned due to its excellent commercial potential.It is a key technology to improve the capture efficiency of intakes,which collect and compress the atmosphere for ABEP.In this paper,the mechanism of the capture section affecting capture efficiency is investigated by Test Particle Monte Carlo(TPMC)simulations with 3D intake models.The inner surface smoothness and average collision number are determined to be key factors affecting capture efficiency,and a negative effect growth model is accordingly established.When the inner surface smoothness is less than 0.2,the highest capture efficiency and its corresponding average collision number interval are independent of the capture section’s geometry and its mesh size.When the inner surface smoothness is higher than 0.2,the capture efficiency will decrease by installing any capture section.Based on the present results,the manufacturing process and material selection are suggested to be prioritized during the intake geometry design in engineering projects.Then,the highest capture efficiency can be achieved by adjusting the length and mesh size of the capture section.

SEMI-PROXIMAL POINT METHOD FOR NONSMOOTH CONVEX-CONCAVE MINIMAX OPTIMIZATION

Minimax optimization problems are an important class of optimization problems arising from modern machine learning and traditional research areas.While there have been many numerical algorithms for solving smooth convex-concave minimax problems,numerical algorithms for nonsmooth convex-concave minimax problems are rare.This paper aims to develop an efficient numerical algorithm for a structured nonsmooth convex-concave minimax problem.A semi-proximal point method(SPP)is proposed,in which a quadratic convex-concave function is adopted for approximating the smooth part of the objective function and semi-proximal terms are added in each subproblem.This construction enables the subproblems at each iteration are solvable and even easily solved when the semiproximal terms are cleverly chosen.We prove the global convergence of our algorithm under mild assumptions,without requiring strong convexity-concavity condition.Under the locally metrical subregularity of the solution mapping,we prove that our algorithm has the linear rate of convergence.Preliminary numerical results are reported to verify the efficiency of our algorithm.

无中和器离子推力器的发展现状、关键技术及展望

离子推力器具有高比冲和高效率等优势,是目前应用最广泛的电推力器之一,但亦存在着系统结构复杂、关键部件繁多等缺点.无中和器离子推力器可以消除对中和器的依赖,实现离子推进系统结构的简化,从而减小推力器体积和重量并提高系统可靠性.本文首先归纳了传统离子推力器的原理、优势及限制,引出了无中和器离子推力器的概念,对其基本原理、技术优势及分类进行了介绍;随后从等离子体源的束流自中和技术出发,总结了无中和器离子推力器的发展现状;结合空间应用需求以及无中和器离子推力器的工作特点,分析了无中和器离子推力器的关键技术,提出应将工质选择、等离子体机理研究、磁过滤装置和栅极系统设计以及栅极射频电压灵活调控方法这四方面作为其研究重点,同时应该发展并完善新的推力器参数测量方法,进一步明确无中和器离子推力器的工作特性.

Wellbore leakage risk management in CO_(2) geological utilization and storage: A review

CO_(2) geological utilization and storage(CGUS)is an important technology to achieve a deep cut of global CO_(2) emissions.CO_(2) leakage from the subsurface may impair the performance of CGUS projects,and the CO_(2) leakage through wellbores is the most common leakage pathway.This paper proposes a workflow for wellbore CO_(2) leakage risk management,and the workflow consists of the following steps:i)leakage risk identification;ii)leakage risk evaluation;iii)leakage risk monitoring;iv)leakage handling.Representative approaches in each step of the workflow are systematically reviewed.Key challenges of wellbore CO_(2) leakage risk management include:lack of effective detection and evaluation approaches to tackle the CO_(2) leakage risk induced by cement failure;lack of low-cost acid resistance alloys and CO_(2)-resistant cement;lack of automated monitoring systems that could enable automated shutdowns of the wellbore whenever certain warning criteria are met.

A STOCHASTIC NEWTON METHOD FOR NONLINEAR EQUATIONS

In this paper,we study a stochastic Newton method for nonlinear equations,whose exact function information is difficult to obtain while only stochastic approximations are available.At each iteration of the proposed algorithm,an inexact Newton step is first computed based on stochastic zeroth-and first-order oracles.To encourage the possible reduction of the optimality error,we then take the unit step size if it is acceptable by an inexact Armijo line search condition.Otherwise,a small step size will be taken to help induce desired good properties.Then we investigate convergence properties of the proposed algorithm and obtain the almost sure global convergence under certain conditions.We also explore the computational complexities to find an approximate solution in terms of calls to stochastic zeroth-and first-order oracles,when the proposed algorithm returns a randomly chosen output.Furthermore,we analyze the local convergence properties of the algorithm and establish the local convergence rate in high probability.At last we present preliminary numerical tests and the results demonstrate the promising performances of the proposed algorithm.

Hierarchical metal-peptide assemblies with chirality-encoded spiral architecture and catalytic activity

We report the coordination assembly of the ferrocene-diphenylalanine(Fc-FF)with divalent copper ions(Cu^(2+))into metalpeptide assemblies(MPAs)with hierarchical spiral architectures.The MPA particles are composed of helically organized nanofibers which can be correlated to the logarithmic spirals.The MPAs are hierarchically porous with abundant Fc and Cu2+active sites and show much higher catalytic activity than natural laccase toward the decolorization reaction.Moreover,a series of hierarchical structures of the MPAs can be synthesized by controlling the temperature and enantiomeric excess(ee).The peptide enantiomers with higher ee values will self-assemble into highly complex and ordered structures,which show higher surface area and porosity and thus enhanced catalytic activity compared with those assembled by peptides with lower ee values.The results provide new insights into the vital role of chirality in directing the self-assembly of biomolecules into highly ordered complex functional structures.

Convergent and Orthogonality Preserving Schemes for Approximating the Kohn-Sham Orbitals

To obtain convergent numerical approximations without using any orthogonalization operations is of great importance in electronic structure calculations.In this paper,we propose and analyze a class of iteration schemes for the discretized Kohn-Sham Density Functional Theory model,with which the iterative approximations are guaranteed to converge to the Kohn-Sham orbitals without any orthogonalization as long as the initial orbitals are orthogonal and the time step sizes are given properly.In addition,we present a feasible and efficient approach to get suitable time step sizes and report some numerical experiments to validate our theory.

充分发挥神经外科的学科特点和优势,完善中国“脑计划”战略布局和实施

脑科学与脑研究已经成为全球科技与健康领域最为关注的热点话题. 2016年8 月在全国卫生与健康大会上,习近平主席说,“把人民健康放在优先发展战略地位,努力全方位全周期保障人民健康.没有全民健康,就没有全面小康”。在《健康中国2030 规划纲要》中提到要从国家战略层面统筹解决关系健康的重大和长远问题.健康中国已经成为国家战略,没有脑健康就不能成为真正的健康,这已经为健康赋予了新的含义.

组织控制悖论:地方政府的“矫枉过正”现象——基于田野调查的组织学分析

目前的地方政府运作逐渐表现出"矫枉过正"的倾向,反映了组织控制有效性的悖论。本文基于多位点的案例研究,提炼出地方政府"矫枉过正"的若干表现,并从组织控制的角度分析了"矫枉过正"的形成机理。基于组织控制视角下"激励—成本—沟通"的分析框架,"矫枉过正"的形成机理可以从激励结构失衡、规避治理成本与组织沟通失效三个方面加以解释:结果导向的问责制度诱导了地方政府执行过程中为了结果而"不择手段"的工作方式;地方政府为规避组织中的监管成本以及协调成本而放弃政策"留口",并采取统一的政策标准;下级同上级沟通中,上级的无效回应又强化了"矫枉过正"的行为。

Formation Mechanism and Numerical Model of Quartz in Fine-Grained Organic-Rich Shales: A Case Study of Wufeng and Longmaxi Formations in Western Hubei Province, South China

The difference in quartz types in shales not only affects the porosity and permeability of the rocks,but also reflects the difference in the sedimentary environments.We established the formation mechanism and numerical model of quartz in shales of Wufeng and Longmaxi formations in the Wangjiawan Section,South China,based on thin-section studies using SEM(scanning electron microscope),SEM-CL(cathodoluminescence),XRD(X-ray diffraction)and geochemical analyses.There are two types of quartz in the shales:detrital quartz and authigenic quartz.Detrital quartz is mostly silt-size,typically ranging from 10 to 60μm in size and subangular to angular monocrystal in shape,and brighter than authigenic quartz by CL intensity;authigenic quartz is present in two phases in shape:grain overgrowths and crystallite grains.Overgrowth surfaces are subhedral.Crystallite grains are typically less than 10μm in size,euhedral or subhedral monocrystal in shape.Authigenic quartz can be subdivided into biogenic quartz and clay mineral transformed quartz according to the source of silicon.In the numerical model,the content of detrital quartz is relatively consistent(20%);the content of biogenic quartz ranges from 40%to 70%,with a sharp fall(0–30%)in the Guanyinqiao mudstone.During the Katian,a lower anoxic and dense water column make the dissolution of biogenic silica well preserved.Biogenic quartz is the major contributor to the sediment.During the early Hirnantian interval,due to the drop of sea level and the oxygenation of seafloor,the sediment is mainly composed of clay transformed quartz and detrital quartz.During the latest Hirnatian and Rhuddanian,rapid sea level rise and anoxic ocean enhance the preservation of the biogenic silica,thereby biogenic quartz re-emerges as the major contributors to the sediment.Authigenic crystallite grains and grain overgrowths have filled in primary pore space and have decreased the interparticle porosity,however,as a rigid framework,they can suppress compaction and maintain the internal pore structure.The formation of authigenic quartz results in the increase of total quartz,which fortifies the brittleness of rocks and is beneficial to the development of shale gas.