一类含时滞非线性传染病模型的渐近分析

本文研究了一大类具有潜伏期的传染病模型,其中潜伏期可长可短,并对模型进行无量钢化,归结为一个含小参数的方程组,运用奇摄动的边层函数法进行了渐进分析,求出了一致有效的渐进解。     

快中子在铅核上的小角弹性散射测量

用伴随粒子飞行时间方法,在1.7°至25°范围内测量了14.2MeV中子在铅核上的弹性散射微分截面.用蒙特卡罗方法对中子在样品中的注量衰减,多次散射及有限角分辨做了修正.实验结果与其它测量及球形核光学模型作了比较.     

基于YOLO-PCB的印刷电路板裸板缺陷检测

针对当前印刷电路板PCB（Printed Circuit Board）裸板缺陷检测算法对小目标检测准确率较低、误检率过高等问题,一种改进的YOLO-PCB缺陷检测算法被提出。新算法在YOLOv5s算法的基础上引入注意力机制,增强特征图的通道特征;同时引入加权双向特征金字塔网络改进特征融合层,使网络实现更高层次的特征融合;而且增加小目标检测层,提高网络对印刷电路板上小目标缺陷的检测能力。实验结果表明,相较于原YOLOv5算法,改进后的检测算法具有更强的特征提取融合能力和更高的检测精度,YOLO-PCB算法的mAP_0.5提升了4.08%,mAP0.5:0.95提升了56.69%,精确度提升了1.81%,召回率提升了6.76%。     

寒旱地区混凝土箱形渡槽湿热耦合效应

针对冬季渡槽的湿热全耦合效应问题,避免渡槽在冬季输水过程中出现裂缝现象,以寒旱地区某渡槽为工程背景,利用湿热耦合传输理论分析,实测2023年1月5至1月20日的环境温度、环境湿度及风速,采用Fluent有限元软件建立了不同环境参数的混凝土箱形渡槽温度场、湿度场、湿热耦合场有限元模型。并分析不同工况对冬季渡槽的非耦合和全耦合状态下的温度效应的影响。分析结果表明,渡槽通水时冬季最不利温差为-14.7℃,不通水时为-6.3℃;渡槽通水时冬季最不利横向温差为-10.2℃,不通水时为-6.2℃;在湿度扩散过程中,沿板厚方向湿度由内向外逐渐减小,且吸水速度随时间的增大而减小;在湿热耦合过程中,全耦合场温度值小于非耦合场温度值,湿热全耦合作用的挠度变化值小于湿热非耦合作用下的挠度变化值,湿热耦合作用的拉应力小于湿热非耦合作用下的拉应力值,因此,湿热全耦合作用对渡槽结构变形有利。     

浅谈预应力混凝土小箱梁预制施工技术

预应力小箱梁具有施工速度快、外观简捷明快、重量轻、承载力强、结构性能好等特点,目前已被广泛应用于各等级公路桥梁的上部结构。     

小动物PET 在神经科学研究中的应用

小动物PET 是动物实验中不可或缺的一种显像模式,被广泛应用于生命科学、医学等多个领域. 本文介绍了近年来小动物PET 应用于神经科学研究的进展,从代谢显像、血流显像、受体显像和基因显像等4 个方面出发,阐述了小动物PET 在这些领域的应用,以及它体现出来的优势与不足. 面对小动物PET 应用的不断拓展对其仪器性能提出的更高要求,以应用为导向、将探测器系统设计与图像重建算紧密结合的小动物PET 系统设计思路将成为未来的趋势.     

浅谈红层地区小型水库的常见地质病害

根据对自贡地区300余座小一型及小二型水库病害的分析、统计,列出红层地区小型水库的普遍性地质病害,为川南、川北以及川东地区的水库病害整治提供一点借鉴作用。     

Regulation of cell adhesion by PP2A and SV40 small tumor antigen: An important link to cell transformation

The serine/threonine protein phosphatase 2A (PP2A) represents a large family of highly conserved heterotrimeric enzymes. Their critical importance in cell homeostasis is underlined by the fact that they are targets of natural toxins like the tumor promoter okadaic acid, and of simian virus 40 small tumor antigen (SV40 small t), a viral protein known to promote cell transformation. Furthermore, mutated or lower expression levels of PP2A subunits have been found in certain cancers. One major known event in PP2A-dependent cell transformation is the alteration of key signaling pathways that control cell growth and survival. In this review, we focus on how PP2A enzymes also affect cell adhesion and cytoskeletal dynamics, the disruption of which is linked to loss of cell polarity, increased cell motility and invasiveness. We also examine how those various pathways participate in the transforming activity of SV40 small t. Received 29 June 2006; received after revision 3 August 2006; accepted 20 September 2006     

Bias in the estimation of non‐linear transformations of the integrated variance of returns

Volatility models such as GARCH, although misspecified with respect to the data‐generating process, may well generate volatility forecasts that are unconditionally unbiased. In other words, they generate variance forecasts that, on average, are equal to the integrated variance. However, many applications in finance require a measure of return volatility that is a non‐linear function of the variance of returns, rather than of the variance itself. Even if a volatility model generates forecasts of the integrated variance that are unbiased, non‐linear transformations of these forecasts will be biased estimators of the same non‐linear transformations of the integrated variance because of Jensen's inequality. In this paper, we derive an analytical approximation for the unconditional bias of estimators of non‐linear transformations of the integrated variance. This bias is a function of the volatility of the forecast variance and the volatility of the integrated variance, and depends on the concavity of the non‐linear transformation. In order to estimate the volatility of the unobserved integrated variance, we employ recent results from the realized volatility literature. As an illustration, we estimate the unconditional bias for both in‐sample and out‐of‐sample forecasts of three non‐linear transformations of the integrated standard deviation of returns for three exchange rate return series, where a GARCH(1, 1) model is used to forecast the integrated variance. Our estimation results suggest that, in practice, the bias can be substantial. Copyright © 2006 John Wiley & Sons, Ltd.     

非饱和绢云母片岩残积土动力特性试验分析

以广泛分布于大临铁路沿线的绢云母片岩残积土为研究对象,开展非饱和状态下绢云母片岩残积土的共振柱试验,研究了动剪应变γd在小应变范围内(10-6<γd<10-4)不同含水率、干密度及固结围压对动剪切模量Gd与阻尼比D的影响.试验结果表明,含水率对动剪切模量与阻尼比的影响较大,对干密度及固结围压的影响较小.Gd及D随含水率...