头痛冲剂对偏头痛模型的作用

目的 探讨头痛冲剂对偏头痛模型的作用.方法 利血平皮下注射制备偏头痛小鼠模型,用热板法测定痛阈值,用玻片法测定凝血时间,用荧光分光光度法检测脑组织5-羟色胺(5-HT)的含量.结果 头痛冲剂可延长凝血时间,提高痛阈值,但对脑组织5-HT没有明显影响.结论 头痛冲剂可在一定程度上治疗偏头痛.     

可拓检测在动态负载均衡策略中的应用研究

在DNS动态负载均衡策略中,服务器负载状态的获取是控制的关键.现有的DNS负载均衡策略在状态获取的实时性、状态表示的合理性等方面都存在不足.针对这些不足,本文提出了一种新的动态负载均衡策略,把可拓检测技术的思想和模糊数学引入到负载均衡策略中,利用可拓学的物元、关联函数,可拓检测和模糊学的隶属度等概念来构建一个集群动态负载均衡策略模型.实验证明,在该策略模型中,利用可拓检测的思想来获取负载状态,能明显提高负载均衡策略的有效性、实时性、动态性和稳定性.     

近红外快速鉴别保健品中非法添加盐酸丁二胍的方法

目的 利用近红外特征谱段相关系数法建立快速鉴别保健品中非法添加盐酸丁二胍的方法.方法 以盐酸丁二胍对照品的近红外光谱图为参照光谱,选择特征谱段,根据已知样本的近红外光谱与参照光谱的相关系数、盐酸丁二胍的有效剂量,确定阈值,建立检测模型.结果 选定7294～7402cm-1,5354～5432cm-1波数为特征谱段,设定阈值r=80%,用10批含盐酸丁二胍的样品进行验证,相关系数高于阈值的有10批,占样品总量的100%;用7批不含盐酸丁二胍的降糖类样品进行验证,相关系数低于阈值的有6批,占样品总量的85.71%.结论 该方法具有较好的预测能力,可用于保健品中非法添加盐酸丁二胍的快速检测.     

数字震动感觉阈值联合踝肱指数在诊断糖尿病患者早期并发症中的意义

目的 验证数字震动感觉阈值联合踝肱指数在诊断糖尿病早期并发症中的作用.方法 设定新确诊的100例无手足麻木、灼痛、刺痛、视物不清、头痛、头昏等感觉的2型糖尿病患者为实验组,设定该地区100名健康人作为对照组,分别分组采用数字震动感觉阈值法、踝肱指数检测法及上述两者联合使用法对此200名实验对象进行检测,并将检测结果进行比较.结果 与单独检测数字震动感觉阈值或踝肱指数相比,联合检测发展糖尿病早期并发症的概率要明显高于单独检测组.联合测量组与数字震动感觉阈值测量组间差异有统计学意义（P＜0.05）.结论 联合检测数字震动感觉阈值结合踝肱指数,可提高糖尿病早期并发症的诊断率,值得临床推广.     

P2P文件共享系统中基于访问控制的信任模型

在P2P文件共享系统中,节点之间共享彼此的文件.但是由于对等网络的匿名性和开放性,在文件共享系统中存在很多信任方面的问题,如恶意节点和自私节点的大量存在.为了孤立恶意节点和鼓励节点共享自己的文件,提出了基于访问控制的信任模型.首先,定义了一种信任机制,它引入了直接信任,推荐信任,时间衰减等因子.其次,对每个共享文件都加入了两个阈值--可信性总评价阈值和贡献量阈值来控制访问.对于每个请求者,只有当它有了对文件的访问资格后才能访问该文件.最后,通过大量的实验证明了本模型的可行性和高效性,特别是对恶意节点具有很好的孤立作用.     

多阈值故障的δ-冲击模型最优维修更换策略

将单阈值故障的δ-冲击模型推广为多阈值故障的情形,以用于处理不同的冲击间隔会导致不同程度故障的工程实际问题.在假设系统是退化的且有k个不同阈值的条件下,以降低系统的运行费用为目标,以部件故障次数N为更换策略,通过更新过程理论求得系统的平均费用率表达式.最后借助数值例子演示了本模型,并对相关参数进行了灵敏度分析.     

传染病的数学模型及其动力学特征研究

目的:探讨几类传染病的传播与流行规律.方法:利用微分方程理论建立传染病的数学模型并对模型进行动力学分析.结果:建立了传染病的几个数学模型,并获得了模型的一些动力学特征.结论:某些传染病存在区分传染病是否会流行的阈值.当有关参数值不超过该阈值时,传染病不会流行.当有关参数值大于该阈值时,传染病会流行.     

基于二维主成分分析的运动目标检测

运动目标检测是计算机视觉研究的重要领域,在视频监控和智能交通等领域应用广泛.本文提出了一种自适应的运动目标检测方法.该方法采用二维主成分分析建立背景模型,通过比较重建图像和原图像的差异来检测运动目标.为了自适应动态变化的复杂背景,该模型由增量算法在线更新.实验结果表明,提出的方法可以在复杂变化的动态背景环境下进行有效的运动目标检测.     

肠激安胶囊对腹泻性肠易激综合征模型大鼠腹痛的影响及分子机制研究

目的:研究肠激安胶囊对腹泻性肠易激综合征(IBS-D)模型大鼠腹痛的影响及降钙素基因相关肽(CGRP)与皮质酮(CORT)相关分子机制。方法:采用母乳分离联合醋酸刺激法复制IBS-D大鼠模型后,将大鼠随机分为模型(等容生理盐水)组,匹维溴铵(0.018 g/kg)组和肠激安胶囊高、中、低剂量(2.812、1.406、0.703 g/kg)组;另取SD大鼠作为正常对照(等容生理盐水)组。ig给药,每天1次,连续14 d。采用注入生理盐水法对大鼠进行腹痛敏感性测定,采用酶联免疫吸附(ELISA)法检测大鼠血清中CORT含量,采用实时荧光定量聚合酶链反应(RT-PCR)法检测大鼠下丘脑与结肠组织中CGRP m RNA的表达。结果:与正常对照组比较,模型组大鼠拱背阈值和抬腹阈值降低,血清中CORT含量增加,下丘脑与结肠组织中CGRP m RNA表达增强,差异有统计学意义(P<0.01)。与模型组比较,匹维溴铵组与肠激安胶囊高、中剂量组大鼠拱背阈值和抬腹阈值升高,血清中CORT含量减少,大鼠下丘脑及结肠组织中CGRP m RNA表达均减弱;肠激安胶囊低剂量组大鼠拱背阈值升高,差异有统计学意义(P<0.01或P<0.05)。结论:肠激安胶囊对IBS-D模型大鼠腹痛有改善作用,其作用机制可能与下调下丘脑和结肠组织中CGRP m RNA表达和降低血清中CORT含量有关。     

动态心电图监测心肌缺血与冠状动脉造影对比分析

本文报告65例冠心病患者先后进行24小时动态心电图监测并与冠状动脉造影对比分析.结果 显示72例中冠状动脉狭窄＞50%者29例,其中动态心电图监测心肌缺血阳性者22例,阴性7例,冠状动脉正常者36例,动态心电图检测心肌缺血阳性22例,阴性7例,冠状动脉正常者36例,动态心电图检测心肌缺血阳性7例,阴性29例,动态心电图检测心肌缺血的敏感性76%,特异性80%,预测准确性76%.陈旧性心肌梗死29例中动态心电图检测心肌缺血22例,真阳性20例,预测准确性76%,而36例可疑冠心病患者动态心电图检测心肌缺血阳性8例,其中真阳性2例,预测准确性仅25%.以上表明动态心电图检测心肌缺血的敏感性与准确性较高,在日常生活中应用24小时动态心电图检测是探讨早期心肌缺血变化的一个可靠及方便的方法.     

A Threshold Regression Mixture Model for Assessing Treatment Efficacy in a Multiple Myeloma Clinical Trial

A first-hitting-time (FHT) survival model postulates a health status process for a patient that gradually declines until the patient dies when the level first reaches a critical threshold. Threshold regression (TR) is a new regression methodology that incorporates the effects of covariates on the threshold and process parameters of this FHT model. In this study, we use TR to analyze data from a randomized clinical trial of treatment for multiple myeloma. The trial compares VELCADE and high-dose Dexamethasone, the former a new therapy and the latter an established therapy for this disease. Patients are switched between the two drugs based on patient response. The novel contribution of this work is the modeling of this clinical trial design using a mixture of TR models. Specifically, we propose a mixture FHT model to fit the survival distribution. The model includes a composite time scale that differentiates the rate of disease progression before and after switching. The analysis shows significant benefit from initial treatment by VELCADE. A comparison is made with a Cox proportional hazards regression analysis of the same data.     

A threshold regression mixture model for assessing treatment efficacy in a multiple myeloma clinical trial

A first-hitting-time (FHT) survival model postulates a health status process for a patient that gradually declines until the patient dies when the level first reaches a critical threshold. Threshold regression (TR) is a new regression methodology that incorporates the effects of covariates on the threshold and process parameters of this FHT model. In this study, we use TR to analyze data from a randomized clinical trial of treatment for multiple myeloma. The trial compares VELCADE and high-dose dexamethasone, the former a new therapy and the latter an established therapy for this disease. Patients are switched between the two drugs based on patient response. The novel contribution of this work is the modeling of this clinical trial design using a mixture of TR models. Specifically, we propose a mixture FHT model to fit the survival distribution. The model includes a composite time scale that differentiates the rate of disease progression before and after switching. The analysis shows significant benefit from initial treatment by VELCADE. A comparison is made with a Cox proportional hazards regression analysis of the same data.     

Are apparent findings of nonlinearity due to structural instability in economic time series?

Many modelling issues and policy debates in macroeconomics depend on whether macroeconomic time series are best characterized as linear or nonlinear. If departures from linearity exist, it is important to know whether these are endogenously generated (as in, e.g. a threshold autoregressive model) or whether they merely reflect changing structure over time. In this paper, we discuss a model comparison methodology which addresses these issues. We advocate a Bayesian approach and show how such an approach can be implemented in practice. An empirical exercise involving several macroeconomic time series shows that apparent findings of threshold type nonlinearities could be due to structural instability. JEL: C22, C11, E30     

Olfactory dysfunction in schizophrenia: a qualitative and quantitative review.

Olfactory dysfunction in patients with schizophrenia has been a topic of increasing interest, with deficits in odor identification, detection threshold sensitivity, discrimination, and memory being reported. Despite increasing knowledge, controversy has existed about possible differential deficits among olfactory tests as well as the influences of gender, smoking, and medication status on olfactory measures. To help elucidate some of this controversy, we conducted a qualitative and quantitative (meta-analytic) review of the English language literature on olfaction in schizophrenia. Moderator variables such as gender, medication status, and smoking history were also examined. Results indicated that substantial olfactory deficits, across all domains, are observed in patients with schizophrenia. No differential deficits were observed across domains of odor identification, detection threshold sensitivity, discrimination, and memory. The influences of gender, medication status, and smoking on effect sizes were not significant across studies. This supports the hypothesis of primary dysfunction in the olfactory system that is regulated by brain regions where structural and functional abnormalities have also been reported in neuroimaging studies.     

A new threshold dose-response model including random effects for data from developmental toxicity studies

Usually, in teratological dose finding studies, there are not only threshold effects but also extra variations that cannot be accounted for by the beta-binomial model alone. The beta-binomial model assumes correlation between fetuses in the same litter. The general random effect threshold (RE) model allows the additional variability that arises due to correlation and between litter variability to be modeled, in combination with threshold in the model. The goal of this research was to investigate a threshold dose-response model with random effects (RE) to model the variability that exists between litters of animals in studies of toxic agents. Data from a developmental toxicity study of a toxic agent were analysed, using the proposed RE threshold dose-response model, which is an extension of logit in form. Also, an approximate likelihood function was used to derive parameter estimates from this model, and tests were performed to determine the significance of the model parameters, in particular, the RE parameter. A simulation study was conducted to assess the performance of the RE threshold model in estimating the model parameters.     

Thresholds in a low-threshold setting: An empirical study of barriers in a centre for people with drug problems and mental health disorders

BackgroundSome services for drug users with mental health disorders can be characterised as low-threshold services. These aim at making help easily accessible for people who are not able to request help from services at higher levels. In this study we examine what kind of thresholds are experienced by clients at a low-threshold centre.MethodsEthnographic field work, including participant observation, individual interviews and focus group interviews with clients and staff in a low-threshold centre for the most vulnerable drug users in Oslo were employed.ResultsOur analyses agree with other studies in showing that the following three thresholds are significant, also in services for drug users with mental health disorders: the registration threshold, the competence threshold and the threshold of effectiveness. In addition to these, we suggest that a fourth threshold is of importance for this group: the threshold of trust. In the low-threshold centre we studied, we observed that for the clients, crossing the threshold of trust seemed to be an essential precondition for subsequently being able to cross the other thresholds in order to receive the help they need. We suggest that focus on the four thresholds can improve our understanding of clients’ access to services. We also suggest that processes of recovery may be improved if increased attention is given to the barriers that clients experience.ConclusionThe threshold of trust seems to be particularly important for people suffering from drug problems and mental health disorders. The results have implications both for practice and policy because if taken seriously into consideration, more clients could access the services they need. Services for this group may be improved by focusing on the fourth threshold: trust.     

具饱和传染率和时滞两阶段结构的传染病模型

讨论了一类具饱和传染率和时滞两阶段结构传染病模型,利用离散动力系统频闪映射理论,得到了传染病最终消除和成为地方病的阈值,当它小于1时,无病平衡点是全局渐近稳定的,此时疾病消除。当它大于1时,地方病平衡点是局部渐近稳定的,此时传染病成为地方病。     

Weighted composite quantile regression estimation of DTARCH models

In modelling volatility in financial time series, the double‐threshold autoregressive conditional heteroscedastic (DTARCH) model has been demonstrated as a useful variant of the autoregressive conditional heteroscedastic (ARCH) models. In this paper, we propose a weighted composite quantile regression method for simultaneously estimating the autoregressive parameters and the ARCH parameters in the DTARCH model. This method involves a sequence of weights and takes a data‐driven weighting scheme to maximize the asymptotic efficiency of the estimators. Under regularity conditions, we establish asymptotic distributions of the proposed estimators for a variety of heavy‐ or light‐tailed error distributions. Simulations are conducted to compare the performance of different estimators, and the proposed approach is used to analyse the daily S&P 500 Composite index, both of which endorse our theoretical results.     

Mitochondrial dysfunction in cancer chemoresistance

Mitochondrial dysfunction has been associated with cancer development and progression. Recent evidences suggest that pathogenic mutations or depletion of the mitochondrial genome can contribute to development of chemoresistance in malignant tumors. In this review we will describe the current knowledge on the role of mitochondrial dysfunction in the development of chemoresistance in cancer. We will also discuss the significance of this research topic in the context of development of more effective, targeted therapeutic modalities and diagnostic strategies for cancer patients, with a particular focus on the potential use of PARP inhibitors in cancer patients displaying mitochondrial DNA mutations. We will discuss recent studies highlighting the importance of the cross-talk between the tumor microenvironment and mitochondrial functionality in determining selective response to certain chemotherapeutic drugs. Finally, owing to the similarities between cancer and yeast cell metabolism, we will point out the use of yeast as a model system to study cancer-related genes and for anti-cancer drugs screening.     

Analyzing Receiver Operating Characteristic Curves with SAS,by M. Gönen

In infectious diseases, it is important to predict the long-term persistence of vaccine-induced antibodies and to estimate the time points where the individual titers are below the threshold value for protection. This article focuses on HPV-16/18, and uses a so-called fractional-polynomial model to this effect, derived in a data-driven fashion. Initially, model selection was done from among the second- and first-order fractional polynomials on the one hand and from the linear mixed model on the other. According to a functional selection procedure, the first-order fractional polynomial was selected. Apart from the fractional polynomial model, we also fitted a power-law model, which is a special case of the fractional polynomial model. Both models were compared using Akaike's information criterion. Over the observation period, the fractional polynomials fitted the data better than the power-law model; this, of course, does not imply that it fits best over the long run, and hence, caution ought to be used when prediction is of interest. Therefore, we point out that the persistence of the anti-HPV responses induced by these vaccines can only be ascertained empirically by long-term follow-up analysis.