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随着人类基因组计划的完成,检测出与疾病相关的分子标靶成为可能,针对有特定疾病标靶的靶向药物开发日渐增多,靶向临床试验呈快速增长趋势。然而,以标靶检测阳性作为入组标准的靶向临床试验,由于疾病标靶诊断技术的不完善,致使入组病人中存在假阳性的现象,因而导致了靶向临床试验效应估计的偏倚。本文在分析疾病标靶的诊断性能对效应估计影响的基础上,指出常规分析方法估计效应存在的偏倚,并介绍一种基于EM算法联合参数Bootstrap抽样,实现靶向临床试验效应无偏估计的统计方法,为正确评价靶向临床试验提供了方法学支持。 相似文献
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目的: 了解剂量、疗程、病例数、组别(试验组与对照组)以及出版年份对随机对照试验疗效的影响。方法: 通过《中国医院数字图书馆》中的CNKI期刊全文库检索Meta分析文献。采用二项Logistic回归进行多因素分析。结果: 获得达标文献1篇,含有26项氨氯地平治疗高血压的临床对照试验,其中23项随机分组,9项氨氯地平作为对照药。疗程和组别均是疗效的影响因素;试验组的疗效优势是对照组疗效优势的2.445~3.690倍。结论: 在随机对照试验中,可能出现试验组的疗效被夸大和(或)对照组被贬低。在Meta分析和循证医学研究中,应注意组别偏倚的影响。 相似文献
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以某车型门把手的表面收缩痕为例,对前期模流分析收缩痕深度和后期实际塑件的收缩痕深度进行对比,利用偏倚和线性分析工具进行数据分析,找到模流分析与实际塑件收缩痕指数对应关系,并通过现场调整注射工艺参数,使成型塑件表面收缩痕控制在某个值以下,再反推到模流分析中,得到模流分析的计算值,在前期获知某种皮纹条件下,最终消除成型塑件表面的收缩痕。 相似文献
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随着铝合金在现代制造业中的应用越来越广泛,铝焊接烟尘及其危害逐渐引起了人们的关注.介绍了铝焊接烟尘的产生机理、主要排放物、影响因素及其规律、扩散规律等特性,分析了铝及其焊接烟尘对人体的危害,并提出一些降低铝焊接烟尘排放量、加强人体防护的措施. 相似文献
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《稀有金属材料与工程》2021,(6)
为了解掌握钚(Pu)及其化合物表面氧化腐蚀机理和探索能够有效缓解钚材料氧化腐蚀的环境体系,对国内外开展钚及其化合物表面化学的研究进行了综述,加深了对钚及其化合物在空气中的腐蚀行为的认识;对H2、O2、CO、CO2等活性气体和Xe等稀有气体在钚及其化合物不同表面的吸附行为进行了对比分析,得到一些有益的结论。研究表明,Pu与各种活性气体和稀有气体的相互作用中伴随着电荷的转移,作用机理主要是气体原子分子的不同杂化轨道和Pu7s、Pu6p、Pu6d、Pu5f等杂化轨道相互作用生成了新的化学键,从而导致了相关反应和现象的产生。本研究还从改善研究方法、开展不同相的钚原子的不同表面吸附行为研究和探索防护钚材料氧化腐蚀新体系3个方面对钚及其化合物表面腐蚀研究工作进行了展望。 相似文献
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意向性原则(intention to treat, ITT)是以意向性治疗(即计划的治疗方案)为基础,而不以实际给予的治疗为基础进行评价的原则,在随机对照试验(randomized controlled trial, RCT)中广泛应用。随着临床试验的不断发展和进步,对ITT原则需要重新理解和诠释。在ITT原则的标准定义中,受试者的意向性分组并未特指随机化分组,而是计划的治疗方案,非随机化临床试验中受试者同意入组某一治疗方案同样为一种意向性。在单臂临床试验及非随机化的现实世界研究(real world study, RWS)中,应用ITT原则可评价由患者/医生决定的意向性治疗方案的有效性。在实际应用过程中,应根据研究目的结合ITT原则进行分组策略的综合考虑。 相似文献
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偏压对CrTiAlN镀层组织形貌及磨损性能的影响 总被引:6,自引:0,他引:6
利用闭合场非平衡磁控溅射离子镀技术制备了耐磨CrTiAlN镀层,分析了溅射偏压对该镀层的形貌、相结构以及磨损性能的影响。研究表明:偏压对镀层的形貌、相结构以及与摩擦学性能有关的摩擦系数、硬度、结合力以及磨损率等参数都有影响。在制备CrTiAlN镀层的过程中,当偏压为-75V时镀层的耐磨损性最好,当偏压在-65V--85V变化时,镀层形貌的变化对镀层的磨损性能无明显影响,CrTiAlN镀层相结构的变化是影响磨损性能的主要原因。 相似文献
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基于一维平板鞘层模型,建立了脉冲偏压电弧离子镀(PBAIP)鞘层随时间演化的动力学模型,给出了其解析表达式,并结合PBAIP工艺中等离子体参数的测量结果,模拟分析了PBAIP鞘层的厚度和鞘层中的离子流密度随时间的演化规律及其受脉冲偏压幅度等参数的影响.结果表明:在PBAIP工艺中,稳态鞘层的厚度及形成稳态鞘层的时间均远小于已报道的等离子体源注入(PSII)等鞘层对应的值;PBAIP鞘层的扩展几乎是实时跟随脉冲偏压的变化,脉冲偏压下每一时刻的鞘层厚度与对应直流偏压下的鞘层厚度几乎相等. 相似文献
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Arka Dey Joydeep Dhar Sayantan Sil Rajkumar Jana Partha Pratim Ray 《Journal of Materials Engineering and Performance》2018,27(6):2727-2733
In this report, bias voltage-dependent dielectric and electron transport properties of ZnS nanoparticles were discussed. ZnS nanoparticles were synthesized by introducing a modified hydrothermal process. The powder XRD pattern indicates the phase purity, and field emission scanning electron microscope image demonstrates the morphology of the synthesized sample. The optical band gap energy (Eg?=?4.2 eV) from UV measurement explores semiconductor behavior of the synthesized material. The electrical properties were performed at room temperature using complex impedance spectroscopy (CIS) technique as a function of frequency (40 Hz-10 MHz) under different forward dc bias voltages (0-1 V). The CIS analysis demonstrates the contribution of bulk resistance in conduction mechanism and its dependency on forward dc bias voltages. The imaginary part of the impedance versus frequency curve exhibits the existence of relaxation peak which shifts with increasing dc forward bias voltages. The dc bias voltage-dependent ac and dc conductivity of the synthesized ZnS was studied on thin film structure. A possible hopping mechanism for electrical transport processes in the system was investigated. Finally, it is worth to mention that this analysis of bias voltage-dependent dielectric and transport properties of as-synthesized ZnS showed excellent properties for emerging energy applications. 相似文献
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Feature selection is an essential step in classification tasks with a large number of features, such as in gene expression data. Recent research has shown that particle swarm optimisation (PSO) is a promising approach to feature selection. However, it also has potential limitation to get stuck into local optima, especially for gene selection problems with a huge search space. Therefore, we developed a PSO algorithm (PSO-LSRG) with a fast “local search” combined with a gbest resetting mechanism as a way to improve the performance of PSO for feature selection. Furthermore, since many existing PSO-based feature selection approaches on the gene expression data have feature selection bias, i.e. no unseen test data is used, 2 sets of experiments on 10 gene expression datasets were designed: with and without feature selection bias. As compared to standard PSO, PSO with gbest resetting only, and PSO with local search only, PSO-LSRG obtained a substantial dimensionality reduction and a significant improvement on the classification performance in both sets of experiments. PSO-LSRG outperforms the other three algorithms when feature selection bias exists. When there is no feature selection bias, PSO-LSRG selects the smallest number of features in all cases, but the classification performance is slightly worse in a few cases, which may be caused by the overfitting problem. This shows that feature selection bias should be avoided when designing a feature selection algorithm to ensure its generalisation ability on unseen data. 相似文献
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DAVID R. SHANKS 《连接科学》1991,3(2):143-162
In two experiments subjects were required to make medical diagnoses for simulated patients on the basis of the symptoms the patients had. Each patient had one of two diseases, the common disease, which occurred on 75% of trials, or the rare disease, which occurred on 25%, and these diseases occurred with 16 different combinations of four symptoms. In the first experiment, subjects learned across a large number of trials to associate the symptoms with the diseases, and the probability of diagnosing each disease for each symptom pattern was recorded. These probabilities were well modelled by a connectionist network. In the second experiment, a stronger test of the connectionist model was attempted. The crucial feature was that the probability of the rare disease given one particular symptom was equal to the probability of the common disease given the same symptom, but the contingency between the symptom and the rare disease was greater than that between the symptom and the common disease, which meant that the symptom was a better predictor of the rare disease. Subjects in one group were more likely to diagnose the rare disease than the common disease on these trials than were subjects in a control group, thus showing a bias associated with the differing base-rates of the diseases. The bias is consistent with the predictions of the connectionist account of categorization. In fact, while the data could be comfortably accommodated by a connectionist theory, they are difficult to reconcile with a variety of alternative theories of categorization. Finally, some possible limitations of connectionist accounts of categorization are considered. 相似文献
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选择Linux2.6作为嵌入式操作系统的内核,介绍了其内核和根文件系统的定制,以及图形用户接口(GUI)的实现过程。以此为基础,设计了闸门控制系统的结构,并给出了各功能模块的实现方法。 相似文献