The Federal Railroad Administration (FRA)’s Web Based Accident Prediction System (WBAPS) is used by federal, state and local agencies to get a preliminary idea on safety at a rail-highway grade crossing. It is an int...The Federal Railroad Administration (FRA)’s Web Based Accident Prediction System (WBAPS) is used by federal, state and local agencies to get a preliminary idea on safety at a rail-highway grade crossing. It is an interactive and user-friendly tool used to make funding decisions. WBAPS is almost three decades old and involves a three-step approach making it difficult to interpret the contribution of the variables included in the model. It also does not directly account for regional/local developments and technological advancements pertaining to signals and signs implemented at rail-highway grade crossings. Further, characteristics of a rail-highway grade crossing vary by track class which is not explicitly considered by WBAPS. This research, therefore, examines and develops a method and models to estimate crashes at rail-highway grade crossings by track class using regional/local level data. The method and models developed for each track class as well as considering all track classes together are based on data for the state of North Carolina. Linear, as well as count models based on Poisson and Negative Binomial (NB) distributions, was tested for applicability. Negative binomial models were found to be the best fit for the data used in this research. Models for each track class have better goodness of fit statistics compared to the model considering data for all track classes together. This is primarily because traffic, design, and operational characteristics at rail-highway grade crossings are different for each track class. The findings from statistical models in this research are supported by model validation.展开更多
Injection wells have been used for disposal of fluids for nearly 100 years. Design of injection well systems has advanced over the years, but environmental concerns due to the potential for migration of injected fluid...Injection wells have been used for disposal of fluids for nearly 100 years. Design of injection well systems has advanced over the years, but environmental concerns due to the potential for migration of injected fluids remain. Fluids range from hazardous materials, to mining waste to treated wastewater. This paper presents an evaluation of wells injecting treated wastewater to assess which create the greatest risk to migration potential. Prior studies have looked at the risks of Class I injection wells for wastewater disposal, but limited data were available at that time. This research involved collecting data and evaluating the differences as a means to predict the potential for fluid migration in the wells. There were four issues that might portend migration: well depth-shallower wells tended to have more migration;the tightness of the confining unit immediately above the injection zone;well age;and the use of tubing and packers. Florida is moving away from tubing and packer wells which may be an indicative of this issue. The results provide a pathway to investigate injection wells in other states.展开更多
Let R（t）=u＋ct-∑ I=1^N（t） Xi,t≥0 be the renewal risk model, with Fx（x）being the distribution function of the claim amount X. Let ψ（u） be the ruin probability with initial surplus u. Under the condition of F...Let R（t）=u＋ct-∑ I=1^N（t） Xi,t≥0 be the renewal risk model, with Fx（x）being the distribution function of the claim amount X. Let ψ（u） be the ruin probability with initial surplus u. Under the condition of Fx（x） ∈ S^＊（γ）,y ≥ 0, by the geometric sum method, we derive the local asymptotic behavior for ψ（u,u ＋ z] for every 0 （ z （ oo, On one hand, the asymptotic behavior of ψ（u） can be derived from the result obtained. On the other hand, the result of this paper can be applied to the insurance risk management of an insurance company.展开更多
目的分析轻度认知功能障碍(mild cognitive impairment,MCI)患者的简易精神状态检查(minimental state examination,MMSE)得分轨迹及阿尔兹海默病(Alzheimer's disease,AD)发病风险,分析MCI向AD转化的危险因素,为疾病干预提供参考...目的分析轻度认知功能障碍(mild cognitive impairment,MCI)患者的简易精神状态检查(minimental state examination,MMSE)得分轨迹及阿尔兹海默病(Alzheimer's disease,AD)发病风险,分析MCI向AD转化的危险因素,为疾病干预提供参考。方法基于AD神经影像学计划数据库2005—2016年的随访数据,采用联合潜在类别模型(joint latent class modle,JLCM)分析不同类别MCI患者MMSE得分变化轨迹及AD发病风险因素。结果共纳入324例患者,随访后113例转化为AD,211例为MCI,两组临床痴呆评分总和量表(clinical dementia rating scale sum of boxes,CDR-SB)得分、功能活动评估(functional activities questionnaire,FAQ)得分、MMSE得分、听觉语言学习测试(rey auditory-verbal learning test,RAVLT)得分、年龄、体质量指数(body mass index,BMI)差异有统计学意义(t=-17.14、-16.97、11.33、11.42、-2.41、2.98,P<0.05)。根据MMSE的动态变化轨迹将人群划分为高危组和低危组,JLCM分析发现,在高危组中,CDR-SB得分(HR=1.55,95%CI:1.05~2.29)和FAQ得分(HR=1.10,95%CI:1.03~1.18)越高,BMI(HR=0.91,95%CI:0.85~0.97)越低,AD发病风险越高;在低危组中,CDR-SB得分(HR=1.30,95%CI:1.03~1.65)、糖蛋白-N-乙酰(glycoproteinN-acetyl,GlycA)(HR=13.30,95%CI:3.46~51.14)和FAQ得分(HR=1.06,95%CI:1.01~1.11)越高,RAVLT得分越低(HR=0.95,95%CI:0.93~0.97),AD发病风险越高。相较于女性,男性高危组中BMI越低(HR=0.91,95%CI:0.85~0.97),AD发病风险越高;而男性低危组中GlycA越高(HR=13.32,95%CI:3.46~51.42),AD发病风险越高。结论JLCM模型能识别MCI人群中MMSE评分变化的异质性,发现不同风险MCI人群发生AD的危险因素,从而实现AD的个性化预防和干预,为AD的有效防控提供实践依据。展开更多
Under the assumption that the claim size is subexponentially distributed and the insurance surplus is totally invested in risky asset, a simple asymptotic relation of tail probability of discounted aggregate claims fo...Under the assumption that the claim size is subexponentially distributed and the insurance surplus is totally invested in risky asset, a simple asymptotic relation of tail probability of discounted aggregate claims for renewal risk model within finite horizon is obtained. The result extends the corresponding conclusions of related references.展开更多
文摘The Federal Railroad Administration (FRA)’s Web Based Accident Prediction System (WBAPS) is used by federal, state and local agencies to get a preliminary idea on safety at a rail-highway grade crossing. It is an interactive and user-friendly tool used to make funding decisions. WBAPS is almost three decades old and involves a three-step approach making it difficult to interpret the contribution of the variables included in the model. It also does not directly account for regional/local developments and technological advancements pertaining to signals and signs implemented at rail-highway grade crossings. Further, characteristics of a rail-highway grade crossing vary by track class which is not explicitly considered by WBAPS. This research, therefore, examines and develops a method and models to estimate crashes at rail-highway grade crossings by track class using regional/local level data. The method and models developed for each track class as well as considering all track classes together are based on data for the state of North Carolina. Linear, as well as count models based on Poisson and Negative Binomial (NB) distributions, was tested for applicability. Negative binomial models were found to be the best fit for the data used in this research. Models for each track class have better goodness of fit statistics compared to the model considering data for all track classes together. This is primarily because traffic, design, and operational characteristics at rail-highway grade crossings are different for each track class. The findings from statistical models in this research are supported by model validation.
文摘Injection wells have been used for disposal of fluids for nearly 100 years. Design of injection well systems has advanced over the years, but environmental concerns due to the potential for migration of injected fluids remain. Fluids range from hazardous materials, to mining waste to treated wastewater. This paper presents an evaluation of wells injecting treated wastewater to assess which create the greatest risk to migration potential. Prior studies have looked at the risks of Class I injection wells for wastewater disposal, but limited data were available at that time. This research involved collecting data and evaluating the differences as a means to predict the potential for fluid migration in the wells. There were four issues that might portend migration: well depth-shallower wells tended to have more migration;the tightness of the confining unit immediately above the injection zone;well age;and the use of tubing and packers. Florida is moving away from tubing and packer wells which may be an indicative of this issue. The results provide a pathway to investigate injection wells in other states.
文摘目的探索山东省不同性别老年人群中可改变心血管危险因素(modifiable cardiovascular risk factors,MCVRFS)的聚集模式,并评估其与脑卒中发生的关联性。方法基于齐鲁全生命周期电子健康研究型数据库(Cheeloo Lifespan Electronic Health Research Data-library,Cheeloo LEAD),纳入2015年6月1日至12月31日期间具有完整健康体检记录、电子病历记录和公共卫生建档记录的≥60岁老年人,构建包含58633名参与者的随访队列,随访期为7年,研究终点为脑卒中事件。通过潜在类别分析(latent class analysis,LCA)探索MCVRFS的聚集模式,采用Cox比例风险回归模型评估不同聚集模式与脑卒中的关联性。结果本研究通过LCA在不同性别亚群中均识别出4种MCVRFS聚集模式。男性人群低风险组、吸烟饮酒组、超重肥胖组和代谢综合征组的占比分别为39.02%、16.41%、36.34%和8.22%;女性人群中,低风险组、吸烟饮酒组、体质量及血脂异常组和代谢综合征组的占比分别为41.00%、0.44%、46.76%和11.80%。男性人群中,新发脑卒中6764例,发病密度为0.04947/人年;女性新发脑卒中8141例,发病密度为0.04273/人年。校正混杂因素后,Cox回归结果显示,男性人群中,吸烟饮酒组、超重肥胖组、代谢综合征组发生脑卒中的风险分别为低风险组的1.13倍(HR=1.13,95%CI=1.05~1.21)、1.16倍(HR=1.16,95%CI=1.09~1.23)和2.20倍(HR=2.20,95%CI=2.04~2.38);女性人群中,体质量及血脂异常组和代谢综合征组发生脑卒中的风险分别为低风险组的1.16倍(HR=1.16,95%CI=1.10~1.21)和2.39倍(HR=2.39,95%CI=2.25~2.54)。结论本研究在山东省不同性别老年人群中均识别出4种MCVRFS的聚集模式,男性人群中,超重肥胖组、吸烟饮酒组和代谢综合征组均增加脑卒中风险;女性人群中,体质量及血脂异常组和代谢综合征组均增加脑卒中发生风险。针对不同聚集模式的个体化干预策略可能有助于降低老年人脑卒中的发生率,减轻其疾病负担。
基金Supported by the National Natural Science Foundation of China (70273029)
文摘Let R（t）=u＋ct-∑ I=1^N（t） Xi,t≥0 be the renewal risk model, with Fx（x）being the distribution function of the claim amount X. Let ψ（u） be the ruin probability with initial surplus u. Under the condition of Fx（x） ∈ S^＊（γ）,y ≥ 0, by the geometric sum method, we derive the local asymptotic behavior for ψ（u,u ＋ z] for every 0 （ z （ oo, On one hand, the asymptotic behavior of ψ（u） can be derived from the result obtained. On the other hand, the result of this paper can be applied to the insurance risk management of an insurance company.
文摘目的分析轻度认知功能障碍(mild cognitive impairment,MCI)患者的简易精神状态检查(minimental state examination,MMSE)得分轨迹及阿尔兹海默病(Alzheimer's disease,AD)发病风险,分析MCI向AD转化的危险因素,为疾病干预提供参考。方法基于AD神经影像学计划数据库2005—2016年的随访数据,采用联合潜在类别模型(joint latent class modle,JLCM)分析不同类别MCI患者MMSE得分变化轨迹及AD发病风险因素。结果共纳入324例患者,随访后113例转化为AD,211例为MCI,两组临床痴呆评分总和量表(clinical dementia rating scale sum of boxes,CDR-SB)得分、功能活动评估(functional activities questionnaire,FAQ)得分、MMSE得分、听觉语言学习测试(rey auditory-verbal learning test,RAVLT)得分、年龄、体质量指数(body mass index,BMI)差异有统计学意义(t=-17.14、-16.97、11.33、11.42、-2.41、2.98,P<0.05)。根据MMSE的动态变化轨迹将人群划分为高危组和低危组,JLCM分析发现,在高危组中,CDR-SB得分(HR=1.55,95%CI:1.05~2.29)和FAQ得分(HR=1.10,95%CI:1.03~1.18)越高,BMI(HR=0.91,95%CI:0.85~0.97)越低,AD发病风险越高;在低危组中,CDR-SB得分(HR=1.30,95%CI:1.03~1.65)、糖蛋白-N-乙酰(glycoproteinN-acetyl,GlycA)(HR=13.30,95%CI:3.46~51.14)和FAQ得分(HR=1.06,95%CI:1.01~1.11)越高,RAVLT得分越低(HR=0.95,95%CI:0.93~0.97),AD发病风险越高。相较于女性,男性高危组中BMI越低(HR=0.91,95%CI:0.85~0.97),AD发病风险越高;而男性低危组中GlycA越高(HR=13.32,95%CI:3.46~51.42),AD发病风险越高。结论JLCM模型能识别MCI人群中MMSE评分变化的异质性,发现不同风险MCI人群发生AD的危险因素,从而实现AD的个性化预防和干预,为AD的有效防控提供实践依据。
基金Supported by the National Natural Science Foundation of China(70871104)the Planning Project of the National Educational Bureau of China(08JA630078)the Project of Key Research Base of Human and Social Sciences(Finance) for Colleges in Zhejiang Province(Grant No. of Academic Education of Zhejiang [2008]255)
文摘Under the assumption that the claim size is subexponentially distributed and the insurance surplus is totally invested in risky asset, a simple asymptotic relation of tail probability of discounted aggregate claims for renewal risk model within finite horizon is obtained. The result extends the corresponding conclusions of related references.
