基于PRA技术的发电厂系统状态风险管控可行性研究

以典型发电厂系统为研究对象,基于概率风险评价技术,建立发电厂系统概率风险评价模型,鉴别各类风险源及用于事故缓解的结构、系统、设备的各种状态风险,并进行"风险指引型"安全分级,提出并优化管控策略,为发电厂安全生产风险管控体系建设提供技术支撑。

Product reliability assessment based on proportional hazard degradation model

In order to evaluate the reliability of long-lifetime products with degradation data, a new proportional hazard degradation model is proposed. By the similarity between time-degradation data and stress-accelerated lifetime, and the failure rate function of degradation data which is assumed to be proportional to the time covariate, the reliability assessment based on a proportional hazard degradation model is realized. The least squares method is used to estimate the model＇s parameters. Based on the failure rate of the degradation data and the proportion function of the known time, the failure rate and the reliability function under the given time and the predetermined failure threshold can be extrapolated. A long life GaAs laser is selected as a case study and its reliability is evaluated. The results show that the proposed method can accurately describe the degradation process and it is effective for the reliability assessment of long lifetime products.

Source and hazard identification of heavy metals in soils of Changsha based on TIN model and direct exposure method

A total of 153 soil samples were collected from Changsha City, China, to analyze the contents of As, Cd, Cr, Cu, Hg, Mn, Ni, Pb and Zn. A combination of sampling data, multivariate statistical method, geostatistical analysis, direct exposure method and triangulated irregular network （TIN） model was successfully employed to discriminate sources, simulate spatial distributions and evaluate children＇s health risks of heavy metals in soils. The results show that not all sites in Changsha city may be suitable for living without remediation. About 9.0% of the study area provided a hazard index （HI）1.0, and 1.9% had an HI2.0. Most high HIs were located in the southern and western areas. The element of arsenic and the pathway of soil ingestion were the largest contribution to potential health risks for children. This study indicates that we should attach great importance to the direct soil heavy metals exposure for children＇s health.

Uniform asymptotics for finite-time ruin probability in some dependent compound risk models with constant interest rate

Consider two dependent renewal risk models with constant interest rate. By using some methods in the risk theory, uniform asymptotics for finite-time ruin probability is derived in a non-compound risk model, where claim sizes are upper tail asymptotically independent random variables with dominatedly varying tails, claim inter-arrival times follow the widely lower orthant dependent structure, and the total amount of premiums is a nonnegative stochastic process. Based on the obtained result, using the method of analysis for the tail probability of random sums, a similar result in a more complex and reasonable compound risk model is also obtained, where individual claim sizes are specialized to be extended negatively dependent and accident inter-arrival times are still widely lower orthant dependent, and both the claim sizes and the claim number have dominatedly varying tails.

Construction of Risk Assessment Application Model of Epidemic Disease in Large-scale Pig Farms

The application model of epidemic disease assessment technology for Web-based large-scale pig farm was expounded from the identification of epidemic disease risk factors, construction of risk assessment model and development of risk assessment system. The assessed pig farm uploaded the epidemic disease risk data information through on-line answering evaluating questionnaire to get the immediate evaluation report. The model could enhance the risk communication between pig farm veterinarian, manager and veterinary experts to help farm system understand and find disease risk factors, assess and report the potential high risk items of the pig farm in the three systems of engineering epidemic disease prevention technology, biological safety and immune monitoring, and promote the improvement and perfection of epidemic disease prevention and control measures.

美国员工持股制度对我国的启示

美国员工持股制度的主要特征 (一)以"福利型"为主,"风险型"为辅,构造了合理的持股类型 美国企业的员工持股是以"福利型"为主,其直接目的是为企业员工谋取福利,吸引员工和保留人才,增加企业对职工的凝聚力.其实现形式多样,总体上可分为"杠杆型"和"非杠杆型"两种,占主流的是杠杆型员工持殷,它是在公司之外成立员工持股信托基金,由公司担保,该基金出面向银行贷款购买公司股东手中的部分股票,购入的股票由信托基金掌握,并利用分得的公司利润归还银行贷款的利息和本金.

Precise large deviation result for heavy-tailed random sums and applications to risk theory

The differences between two sequences of nonnegative independent and identically distributed random variables with sub-exponential tails and the random index are studied. The random index is a strictly stationary renewal counting process generated by some negatively associated random variables. Using a revised large deviation result of partial sums, the elementary renewal theorem and the central limit theorem of negatively associated random variables, a precise large deviation result is derived for the random sums. The result is applied to the customer-arrival-based insurance risk model. Some uniform asymptotics for the ruin probabilities of an insurance company are obtained as the number of customers or the time tends to infinity.

Empirical Bayes Estimation for the Parameter of Two-dimen sional One-side Truncated Distribution Families with Linex Loss

In this paper, we construct the EB estim ation for the parameter of the two-dimensional one side truncat ed distribution fam ilies using Linex loss. The convergence rate of EB estimation is given and it is shown that the proposed empirical Bayes estimaiton can be arbitrarily close to 1 under certain conditions.

Graft-versus-host disease after liver transplantation:A comprehensive literature review

AIM： To determine the factors affecting mortality in pa- tients who developed graft-versus-host disease （GvHD） after liver transplantation （LT）. METHODS： We performed a review of studies of GvHD following LT published in the English literature and ac- cessed the PubMed, Medline, EBSCO, EMBASE, and Google Scholar databases. Using relevant search phras- es, 88 articles were identified. Of these, 62 articles con- raining most of the study parameters were considered eligible for the study. Risk factors were first examined using a univariate Kaplan-Meier model, and variables with a significant association （P 〈 0.05） were then sub- jected to multivariate analyses using a Cox proportional- hazards model. RESULTS： The 61 articles reported 87 patients, 58 male and 29 female, mean age, 40.4 ± 15.5 years （range： 8 mo to 74 years）, who met the inclusion criteria for the present study. Deaths occurred in 59 （67.8%） patients, whereas 28 （32.2%） survived after a mean follow-up period of 280.8 ± 316.2 d （range： 27-2285 d）. Among the most frequent symptoms were rash （94.2%）, fever （66.6%）, diarrhea （54%）, and pancytopenia （54%）. The average time period between LT and first symptom on- set was 60.6 ± 190.1 d （range： 2-1865 d）. The Kaplan- Meier analysis revealed that pancytopenia （42.8% vs 59.3%, P = 0.03）, diarrhea （39.2% vs 61.0%, P = 0.04）, age difference between the recipient and the donor （14.6 ± 3.1 years vs 22.6 ± 2.7 years, P 〈 0.0001）, and time From first symptom occurrence to diagnosis or treatment （13.3 ± 2.6 mo vs 15.0 ± 2.3 mo, P 〈 0.0001） were significant factors affecting mortality, whereas age, sex, presence of rash and fever, use of immunosuppressive agents, acute rejection before GvHD, etiological causes, time of onset, and donor type were not associated with mortality risk. The Cox proportional-hazards model, de- termined that an age difference between the recipient and donor was an independent risk Factor （P = 0.03; hazard ratio, 7.395, 95% confidence interval, 1.2-46.7）. CONCLUSION： This study showed that an age differ- ence between the recipient and donor is an independent risk factor for mortality in patients who develop GvHD after LT.

Prediction model of in-hospital mortality in elderly patients with acute heart failure based on retrospective study

Objectives The aim of this study was to develop a clinical risk model that is predictive of in-hospital mortality in elderly patients hos- pitalized with acute heart failure （AHF）. Methods 2486 patients who were 60 years and older from intensive care units of Cardiology De- partment in the hospital were analyzed. Independent risk factors for in-hospital mortality were obtained by binary logistic regression and then used to establish the risk prediction score system （RPSS）. The area under the curve （AUC） of receiver operator characteristic and C-statistic test were adopted to assess the performance of RPSS and to compare with previous get with the guidelines-heart failure （GWTG-HF）. Re- sults By binary logistic regression analysis, heart rate （OR： 1.043, 95% CI： 1.030-1.057, P 〈 0.001）, left ventricular ejection fraction （OR： 0.918, 95% CI： 0.833~）.966, P 〈 0.001）, pH value （OR： 0.001, 95% CI： 0.000-0.002, P 〈 0.001）, renal dysfunction （OR： 0.120, 95% CI： 0.066M）.220, P 〈 0.001） and NT-pro BNP （OR： 3.463, 95% CI： 1.870-6.413, P 〈 0.001） were independent risk factors of in-hospital mortal- ity for elderly AHF patients. Additionally, RPSS, which was composed of all the above-mentioned parameters, provided a better risk predic- tion than GWTG-THF （AUC： 0.873 vs. 0.818, P = 0.016）. Conclusions Our risk prediction model, RPSS, provided a good prediction for in-hospital mortality in elderly patients with A/IF.

Preoperative predictors of short-term survival after hepatectomy for multinodular hepatocellular carcinoma

AIM： To investigate preoperative factors associated with poor shore-term outcome after resection for multi- nodular hepatocellular carcinoma （HCC） and to assess the contraindication of patients for surgery, METHODS： We retrospectively analyzed 162 multi- nodular HCC patients with Child-Pugh A liver function who underwent surgical resection. The prognostic significance of preoperative factors was investigated by univariate analysis using the log-rank test and by multivariate analysis using the Cox proportional hazards model. Each independent risk factor was then assigned points to construct a scoring model to evaluate the in- dication for surgical intervention. A receiver operating characteristics （ROC） curve was constructed to assess the predictive ability of this system.RESULTS： The median overall survival was 38.3 mo （range： 3-80 too）, while the median disease-free sur- vival was 18.6 mo （range： 1-79 too）. The 1-year mor- tality was 14%. Independent prognostic risk factors of 1-year death included prealburnin 〈 170 rng/L [hazard ratio （HR）： 5.531, P 〈 0.001], alkaline phosphatase 〉 129 U/L （HR： 3.252, P = 0.005）, α fetoprotein 〉 20 μg/L （HR： 7.477, P = 0.011）, total tumor size 〉 8 cm （HR： 10.543; P 〈 0.001）, platelet count 〈 100×109/L （HR： 9.937, P 〈 0.001）, and y-glutamyl transpeptidase 〉 64 U/L （HR： 3.791, P 〈 0.001）. The scoring model had a strong ability to predict 1-year survival （area under ROC： 0.925, P 〈 0.001）. Patients with a score ≥5 had significantly poorer short-term outcome than those with a score 〈 5 （1-year mortality： 62% vs 5%, P 〈 0.001; 1-year recurrence rate： 86% vs 33%, P 〈 0.001）. Patients with score ≥5 had greater possibility of microvascular invasion （P 〈 0.001）, poor tumor dif- ferentiation （P = 0.003）, liver cirrhosis with small nod- ules （P 〈 0.001）, and intraoperative blood transfusion （P = 0.010）. CONCLUSION： A composite preoperative scoring model can be used as an indication of prognosis of HCC patients after surgical resection. Resection should be considered with caution in patients with a score ≥5, which indicates a contraindication for surgery.

Bilateral liver resection for bilateral intrahepatic stones

AIM: To evaluate the shortand long-term outcomes of bilateral liver resection for bilateral intrahepatic stones. METHODS: We reviewed retrospectively 101 consecutive patients with bilateral intrahepatic stones who underwent bilateral liver resection in the past 10 years. The shortand long-term outcomes of the patients were analyzed. The Cox proportional hazards model was used to identify the risk factors related to stone recurrence. RESULTS: There was no surgical mortality in this group of patients. The surgical morbidity was 28.7%. Stone clearance rate after hepatectomy was 84.2% and final clearance rate was 95.0% following postoperative choledochoscopic lithotripsy. The stone recurrence rate was 7.9% and the occurrence of postoperative cholangitis was 6.5% in a median follow-up period of 54 mo. The Cox proportional hazards model indicated that liver resection range, less than the range of stone distribution (P = 0.015, OR = 2.152) was an independent risk factor linked to stone recurrence. CONCLUSION: Bilateral liver resection is safe and its shortand long-term outcomes are satisfactory for bilateral intrahepatic stones.

Frailty and cardiovascular disease： potential role of gait speed in surgical risk stratification in older adults

Frailty is a state of late life decline and vulnerability, typified by physical weakness and decreased physiologic reserve. The epidemiology and pathophysiology of frailty share features with those of cardiovascular disease. Gait speed can be used as a measure of frailty and is a powerful predictor of mortality. Advancing age is a potent risk factor for cardiovascular disease and has been associated with an increased risk of adverse outcomes. Older adults comprise approximately half of cardiac surgery patients, and account for nearly 80% of the major complications and deaths following surgery. The ability of traditional risk models to predict mortality and major morbidity in older patients being considered for cardiac surgery may improve if frailty, as measured by gait speed, is included in their assessment. It is possible that in the future frailty assessment may assist in choosing among therapies （e.g., surgical vs. percutaneous aortic valve replacement for patients with aortic stenosis）.

Log-normal censored regression model detecting prognostic factors in gastric cancer:A study of 3018 cases

AIM:To investigate the efficiency of Cox proportional hazard model in detecting prognostic factors for gastric cancer.METHODS:We used the log-normal regression model to evaluate prognostic factors in gastric cancer and compared it with the Cox model.Three thousand and eighteen gastric cancer patients who received a gastrectomy between 1980 and 2004 were retrospectively evaluated.Clinic-pathological factors were included in a log-normal model as well as Cox model.The akaike information criterion (AIC) was employed to compare the efficiency of both models.Univariate analysis indicated that age at diagnosis,past history,cancer location,distant metastasis status,surgical curative degree,combined other organ resection,Borrmann type,Lauren's classification,pT stage,total dissected nodes and pN stage were prognostic factors in both log-normal and Cox models.RESULTS:In the final multivariate model,age at diagnosis,past history,surgical curative degree,Borrmann type,Lauren's classification,pT stage,and pN stage were significant prognostic factors in both log-normal and Cox models.However,cancer location,distant metastasis status,and histology types were found to be significant prognostic factors in log-normal results alone.According to AIC,the log-normal model performed better than the Cox proportional hazard model (AIC value:2534.72 vs 1693.56).CONCLUSION:It is suggested that the log-normal regression model can be a useful statistical model to evaluate prognostic factors instead of the Cox proportional hazard model.

Large Deviations for Random Sums on Some Kind of Heavy-tailed Classes in Risk Models

This paper is a further investigation into the large deviations for random sums of heavy-tailed,we extended and improved some results in ref. [1] and [2]. These results can applied to some questions in Insurance and Finance.

The Survival Probability in Generalized Poisson Risk Model

In this paper we generalize the aggregated premium income process from a constant rate process to a poisson process for the classical compound Poinsson risk model,then for the generalized model and the classical compound poisson risk model ,we respectively get its survival probability in finite time period in case of exponential claim amounts.

Antidiabetic therapy and increased risk of hepatocellular carcinoma in chronic liver disease

AIM： To explore the association between hepatocellular carcinoma （HCC） and type 2 diabetes mellitus, describe the temporal relations between the onset of diabetes and the development of HCC and evaluate the possible effects of antidiabetic therapy on HCC risk,METHODS： We recruited 465 HCC patients, 618 with cirrhosis and 490 control subjects. We evaluated the odds ratio （OR） for HCC by univariate and multivariate analysis. Moreover, OR for HCC in diabetic subjects treated with insulin or sulphanylureas and with metformin were calculated.RESULTS： The prevalence of diabetes mellitus was 31.2% in HCC, 233% in cirrhotic patients and 12.7% in the Control group. By univariate and multivariate analysis, the OR for HCC in diabetic patients were respectively 3.12 （CI 2.2-4.4, P 〈 0.001） and 2.2 （CI 1.2-4.4, P = 0.01）. In 84.9% of cases, type 2 diabetes mellitus was present before the diagnosis of HCC. Moreover, we report an OR for HCC of 2.99 （CI 1.34-6.65, P = 0.007） in diabetic patients treated with insulin or sulphanylureas, and an OR of 0.33 （CI 0.1-0.7, P = 0.006） in diabetic patients treated with metformin.CONCLUSION： Our study confirms that type 2 diabetes mellitus is an independent risk factor for HCC and pre-exists in the majority of HCC patients. Moreover, in male patients with type 2 diabetes meUitus, our data shows a direct association of HCC with insulin and sulphanylureas treatment and an inverse relationship with metformin therapy.

Prognostic factors for 5-year survival after local excision of rectal cancer

AIM:To evaluate the prognostic factors for 5-year survival after local excision of rectal cancer,and to examine the therapeutic efficacy and surgical indications for this procedure. METHODS:Clinical data,obtained from 106 local rectal cancer excisions performed between January 1980 and December 2005,were retrospectively analyzed.Survival analysis was performed using the Kaplan-Meier method,statistical comparisons were performed using the log-rank test,and multivariate analysis was performed using the Cox proportional hazards model. RESULTS:Transanal,transsacral,and transvaginal excisions were performed in 92,12,and 2 cases, respectively.The rate of complication,local recurrence, and 5-year survival was 6.6%,17.0%,and 86.7%, respectively.Univariate analysis showed that T stage, vascular invasion,and local recurrence were related to the prognosis of the cases(P<0.05).Multivariate analysis showed that T stage[P=0.011,95% confidence interval(CI)=1.194-3.878]and local recurrence(P=0.022,95%CI=1.194-10.160)were the major prognostic factors for 5-year survival of cases after local excision of rectal cancer. CONCLUSION:Local rectal cancer excision is associated with few complications,and suitable for stages Tis and T1 rectal cancer.Prevention of local recurrence,active postoperative follow-up,and administration of salvage therapy are the effective methods to increase the efficacy of local excision of rectal cancer.

Catastrophe theory-based risk evaluation model for water and mud inrush and its application in karst tunnels

This paper presents a risk evaluation model of water and mud inrush for tunnel excavation in karst areas.The factors affecting the probabilities of water and mud inrush in karst tunnels are investigated to define the dangerousness of this geological disaster.The losses that are caused by water and mud inrush are taken into consideration to account for its harmfulness.Then a risk evaluation model based on the dangerousness-harmfulness evaluation indicator system is constructed,which is more convincing in comparison with the traditional methods.The catastrophe theory is used to evaluate the risk level of water and mud inrush and it has great advantage in handling problems involving discontinuous catastrophe processes.To validate the proposed approach,the Qiyueshan tunnel of Yichang-Wanzhou Railway is taken as an example in which four target segments are evaluated using the risk evaluation model.Finally,the evaluation results are compared with the excavation data,which shows that the risk levels predicted by the proposed approach are in good agreements with that observed in engineering.In conclusion,the catastrophe theory-based risk evaluation model is an efficient and effective approach for water and mud inrush in karst tunnels.

Assessment on Agricultural Drought Risk Based on Variable Fuzzy Sets Model

Drought is one of the major natural disasters causing huge agricultural losses annually. Regional agricultural drought risk assessment has great significance for reducing regional disaster and agricultural drought losses. Based on the fuzzy characteristics of agricultural drought risk, variable fuzzy sets model was used for comprehensively assessing agricultural drought risk of Liaoning Province in China. A multi-layers and multi-indices assessment model was estab-lished according to variable fuzzy sets theory, and agricultural drought risk of all 14 prefecture-level cities was respec-tively estimated in terms of dangerousness, vulnerability, exposure and drought-resistibility. By calculating the combi-nation weights of four drought risk factors, agricultural drought risk grade of each city was obtained. Based on the as-sessment results, the spatial distribution maps of agricultural drought risk were drawn. The results shows that eastern cities have lower drought dangerousness than western cities in Liaoning Province totally. Most cities are located in low drought vulnerability region and high drought exposure region. Because of frequent and severe drought since 2000, most cities are located in lower drought-resistibility region. Comprehensive agricultural drought risk presents apparent spatial characteristics, escalating from the east to the west. Drought dangerousness is the most important factor influencing comprehensive agricultural drought risk. Through the spatial distribution maps of drought risk, decision makers could find out drought situation and make decisions on drought resistance conveniently.