Covariance Research Articles

Relationship between diabetic retinopathy and coronary atherosclerosis in type 2 diabetes patients

Objective To investigate the relationship between diabetic retinopathy (DR) and coronary atherosclerosis (CAS) in type 2 diabetes patients and other risk factors of DR.Methods A total of 118 patients of type 2 diabetes with DR (DR group),120 patients of type 2 diabetes without DR matched in age and sex (non-DR group),and 86 normal controls (control group) were enrolled in this study.The body mass index (BMI),blood pressure (BP),fasting blood-glucose (FPG),glycosylated haemoglobin (HbA1C),total cholesterol (TC),triglyceride (TG),high density lipoprotein cholesterol (HDL-C),low density lipoprotein cholesterin (LDL-C),creatinine,estimate glomerular filtration rate (eGFR) and urinary albumin excretion rate(UAER) in all the subjects were measured.Meanwhile,the incidence of CAS in the three groups was detected by 64-slice multidetector computed tomography angiography (MDCTA).Assume concurrent DR as dependent variable,clinical indicators and laboratory parameters as independent variable,the risk factors were determined by Logistic regression analysis.In addition,CAS as dependent variable,DR as fixed factor,analysis of covariance was used to investigate the relationship between CAS and DR.Results The incidence of CAS in DR group was higher than that in non-DR group and control group,the differences were statistically significant (x2 =26.9,35.5; P＜0.05).The results of Logistic regression analysis showed that systolic BP,BMI,CAS,myocardial infarction and UAER were key risk factors for DR [odds ratio (OR) =1.02,0.89,4.50,3.89,1.34 ; P＜0.05].There was a negative relationship between BMI and DR.The results of analysis of covariance showed that there was significant correlation between CAS and DR (OR=5.31,95％ confidence interval=2.62-10.60; P＜0.05).Conclusion CAS is independently associated with DR in type 2 diabetes patients.In addition,the other risk factors for DR include systolic BP,BMI,myocardial infarction and UAER. Key words: Diabetic retinopathy/etiology; Coronary artery disease; Diabetes mellitus, type 2/complications; Tomography, spiral computed

Corrigendum to "Four-year (2006–2009) eddy covariance measurements of CO<sub>2</sub> flux over an urban area in Beijing" published in Atmos. Chem. Phys., 12, 7881–7892, 2012

Corrigendum to "Four-year (2006–2009) eddy covariance measurements of CO<sub>2</sub> flux over an urban area in Beijing" published in Atmos. Chem. Phys., 12, 7881–7892, 2012

Performance analysis of advanced GPS receiver technique in radio frequency difficult environment

Global Positioning System (GPS) is widely used in many applications, especially on its position, velocity and timing (PVT) services. In general, a GPS receiver performs accurately and smoothly under open-sky environment. However, under urban canyon and dense foliage environments, a GPS receiver could not provide PVT services adequately due to GPS signal blockage or multipath. As a result, this paper develops and implements an advance GPS receiver technique, the Vector Tracking (VT) technique, to compare its performance with the conventional standard GPS receiver design under radio frequency difficult environments. The VT technique is based on an Extended Kalman Filter (EKF) to track all GPS satellites simultaneously and to estimate the user's position, velocity, and clock bias. The VT technique takes the advantage of the user's dynamic to predict the associated changes in the GPS signal, and it could thus facilitate the GPS receiver to bridge the temporary signal outages. Additionally, the tuning of the EKF is the key performance factor of the VT technique, and two algorithms to estimate the noise covariance, namely the correlation method and the empirical setting method, are discussed in this paper as well. Finally, this paper presents the performance gained from the developed VT technique in comparison to the conventional GPS receiver under various Radio Frequency (RF) difficult environments.

User Acceptance Factors of u-Health System - For Converged Smart Health

Lately, in accordance with the improvement of living standards and income level, concern about the health is continuously increasing and the desire is also becoming diverse. This study focused on the user's acceptance of converged smart u-health system. For the study purpose, this paper analyzed the health and technology factors influencing the user's acceptance on u-health system. Thus this study was carried out by using covariance based SEM in order to test the model fitness and path coefficient. As the results, the health management experience among HPM factors and perceived usefulness among TAM had a positive effect on attitude and the perceived usefulness had a direct effect on behavioral intention.

Efficacy of laparoscopic hepatectomy for the treatment of hepatocellular carcinoma

Objective To investigate the efficacy of laparoscopic hepatectomy for the treatment of hepatocellular carcinoma (HCC).Methods The clinical data of 30 HCC patients who were admitted to the Affiliated Cancer Hospital of Guangxi Medical University from January 2011 to December 2011 were retrospectively analyzed.All patients were divided into the laparoscopic hepatectomy (LH) group (10 patients) and open hepatectomy (OH) group (20 patients) according to the operation patterns and at the ratio of 1 ∶ 2.The degree of cirrhosis,size and location of tumor of the 2 groups were analyzed using the covariance analysis.The student t test was used for analysing the difference of the 2 groups.Results In the LH group,7 patients received laparoscopic nonanatomical liver resection,3 received anatomical resection of the left lateral lobe,no patient was converted to the hand assisted laparoscopic surgery or open surgery.In the OH group,14 patients received non-anatomical liver resection,and 6 received anatomical liver resection.The volume of blood loss of the LH group was (247 ± 235) ml,which was significantly lower than (408 ± 191)ml of the OH group (t =2.199,P ＜ 0.05).The mean postoperative fasting time,postoperative abdominal drainage time and duration of hospital stay of the LH group were (1.9 ±0.6) days,(3.2 ± 1.2) days and (8.9 ± 2.3) days,which were significantly shorter than (3.0 ± 1.6) days,(4.9±1.6)daysand (11.5±2.3)days of the OH group (t=2.149,2.917,2.921,P＜0.05).The levels of alanine aminotransferase (ALT) of the LH group at day 1,3,5 were (228 ± 100)U/L,(143 ± 51)U/L,(85 ±24) U/L,and the levels of aspartate aminotransferase (AST) of the LH group at day 1,3,5 were (196 ± 67)U/L,(90 ± 35) U/L,(46 ± 10) U/L.The levels of ALT of the OH group at day 1,3,5 were (557 ± 401) U/L,(414 ±397)U/L,(217 ± 199)U/L,and the levels of AST of the OH group at day 1,3,5 were (506 ±317)U/L,(178 ± 122) U/L,(71 ± 33) U/L.The time for hepatic function recovery of the LH group was significantly shorter than that of the OH group (t =3.675,3.001,2.073 ; 4.196,2.223,2.272,P ＜ 0.05).All the 30 patients were followed up for 3-15 months.The level of alpha fetoprotein of 1 patient in the LH group was increased at postoperative month 4,and the results of computed tomography showed multiple intrahepatic lesions.The patient was cured by intervention treatment.One patient of the OH group was diagnosed as with tumor recurrence at the resection margins and adjacent hepatic segments.The patient was cured by radiofrequency ablation,with no tumor recurrence.No tumor recurrence or metastasis was observed in the other patients.Conclusion Laparoscopic hepatectomy is a feasible,safe and minimally invasive approach for patients with HCC. Key words: Liver neoplasms ; Laparoscopy ; Hepatectomy

Effects of smoking on the concentrations of urinary 10 metabolites of polycyclic aromatic hydrocarbons in coke oven workers

To explore the effects of smoking on urinary 10 metabolites of polycyclic aromatic hydrocarbons (PAHs) in the coke oven workers. Occupational health examination was performed on 1401 coke oven workers in one coking plant, their urine were collected respectively. The concentrations of the ten monohydroxy polycyclic aromatic hydrocarbons in urine were detected by gas chromatography/mass spectrometry. The 1401 workers were divided into four groups, namely control, adjunct workplaces, bottom and side, top group according to their workplaces and the different concentrations of PAHs in the environment. The concentrations of the ten monohydroxy polycyclic aromatic hydrocarbons between smokers and nonsmokers in each workplace group were compared using analysis of covariance, respectively. The levels of concentrations of the sixteen polycyclic aromatic hydrocarbons we detected at control were significantly higher than those at other areas (P < 0.05). Comparing the ten monohydroxy polycyclic aromatic hydrocarbons levels between smokers and nonsmokers, the levels of 1-hydroxynaphthalene and 2-hydroxynaphthalene among smokers were higher than nonsmokers with statistically significance in control, adjunct workplaces, bottom and side and top groups (P < 0.05). However, the levels of 1-hydroxypyrene had no statistically significant differences between the four areas. Urinary 1-hydroxynaphthalene and 2-hydroxynaphthalene may be used as biomarkers for the impact of smoking on monohydroxy polycyclic aromatic hydrocarbons in the coke oven workers.

Impact of Resilience and Role Model Influence on Academic Achievement of Low Socio-Economic Status Adolescent Students

The impact of Resilience and Role Model among low socio economic status students was examined. Resilience connotes 'bouncing back' to normalcy after facing 'negative events': an individual's capacity to withstand stressors and not to manifest psychological dysfunction, such as mental illness or persistent negative mood in spite of difficult circumstances. Role Model influence is an immense driving force and moral support for the student's academic achievement. A role model is someone with whom, an admirer identifies and wants to be like. The sample consisted of 502 low socio economic status adolescent students. Resilience scale (Annalakshmi, 2009) and Role model influence scale (Nancy, 2009) were administered to the sample. Criterion groups representing high and low levels of Resilience and Role Model Influence were constructed using median of the distribution of scores of the sample. Analysis of covariance, which controlled the influence of covariates Intelligence and Educational Risk on Academic Achievement, revealed that there is an impact of Resilience and Role Model Influence on the Academic Achievement of low SES adolescent students.

On the effect of the near-surface layer energy closure degree on land surface process simulations

Many surface-layer observations have shown that the sum of sensible and latent heat fluxes was lower than the available energy when using the eddy covariance method. It means the observed energy was unclosed. The unclosed degree was usually 20% and even more in particular cases. The land surface models were developed based on the concept of energy balance between the atmosphere and land surface, and the parameterization scheme of the boundary layer in the land surface models were often developed from the observed turbulent heat fluxes. Thus, energy closure degree was bound to affect land surface models. Based on the data observed at SACOL site in spring, 2007, following the law of energy conservation, the residual part of the energy from its imbalance was distributed into the turbulent heat fluxes through the Bowen ratio so as to modify the direct measurement and make energy closed. Then two turbulent boundary layer parameterization schemes were developed as energy closure and unclosure schemes from the observed and modified turbulent heat fluxes. The impacts of energy unclosure and closure on land surface process simulations were investigated by using the land surface model SHAW with numerical simulation and comparing the simulations with the observation. The results suggest that the energy closure remarkably affect the land surface models. For taking using of the energy unclosure turbulent boundary layer parameterization schemes the model obviously overestimated upward longwave radiation and soil temperature. And in the case of using the schemes by modifying the measured turbulent heat flux to make the energy closed, the model is able to better simulate upward longwave radiation and soil temperature with any physical and bio-chemical properties of soil that are kept unchanged.

Planning Planning of experiments for a nonautonomous Ornstein-Uhlenbeck process

We study exact optimal designs for processes governed by mean-reversion stochastic differential equations with a time dependent volatility and known mean-reversion speed. It turns out that any mean-reversion Itō process has a product covariance structure. We prove the existence of a nondegenerate optimal sampling design for the parameter estimation and derive the information matrix corresponding to the observation of the full path. The results are demonstrated on a process with exponential volatility.

Composition of the genetic covariance between traits using high density SNP information

The authors acknowledge Mike Coffey et al. (SAC), Donagh Berry et al. (Teagasc) and Erling Strandberg (SLU) for sharing the data. The RobustMilk project is financially supported by the European Commission under the Seventh Research Framework Programme, Grant Agreement KBBE-211708. The content of this paper is the sole responsibility of the authors, and it does not necessarily represent the views of the Commission or its services. Acknowledgements Investigate the makeup and asymmetry of the genetic covariance using dense SNP markers

主成分分析法在环境评价中的应用辨析 Discrimination on Application of Principal Component Analysis in Environmental Assessment

主成分分析法在环境评价中已被广泛应用，以水环境质量评价为例，探讨该方法应用于环境评价的可行性。结果表明，在不少情形下主成分分析法在环境评价中的应用明显有误。从物理意义和操作流程两个方面分析错误原因，得出以下结论：1) 主成分分析实质主要做协方差的数值分析，综合评价则是对评价体系的价值判断，当围绕指标体系的协方差所得数值差异不构成对该体系价值判断时，强行应用主成分分析法进行环境价值评价是一种错误的做法；2) 方差贡献率只代表指标体系的方差信息，而非全部信息，仅依据方差贡献率的大小判断信息量载荷大小的观点不妥，仅根据方差贡献率的大小甄选指标可能会造成重要指标被错误剔除；不能简单拿方差贡献率作为价值高低的评价尺度，在综合评价中，将方差贡献率作为各指标的权重系数不恰当；3) 主成分分析法本身是个好的数学方法，但不能盲目引申该数学方法的物理意义，当且仅当评价指标体系中各个指标的协方差所得数值差异构成对其所评价事物的价值判断时，才可能可以采用主成分分析法进行价值评价，具体何时恰当，何时不恰当，必须具体问题具体分析，难以简单下结论。Principal component analysis (PCA) has been widely applied to environmental assessment. Taking the water environmental quality assessment as an example, whether the method can be applied to environmental quality assessment has been discussed. And the results showed that it was obviously wrong in many cases. We analyze the reasons why it was wrong in these cases from two aspects including the physical meanings and operation process of PCA, The conclusions were as follows: 1) PCA is a Mathematics method about numerical analysis of covariance essentially, but comprehensive evaluation is the judgment of the value of the evaluation system. When the numerical difference has not constituted value judgments on the comprehensive evaluation, it is wrong to apply PCA to environmental valuation forcibly. 2) The variance contribution rate only represents the variance information of the index system, not all of the information. It may cause the removal of the important index, if researchers select important indexes only according to variance contribution rate. We must consider other factors to select important index, such as, Natural and Geographical conditions, Social and Economic status and so on. So it can not be taken as a mainly yardstick to judge whether the value is high or low, and also, it is not appropriate to regard the variance contribution and the weight coefficient as the same in comprehensive evaluation. 3) PCA is a good mathematical method which has physical meaning itself, but we can’t quote its physical meaning blindly. Whether a method could be applied to environmental quality assessment or not, if and only if the numerical difference of the evaluation index system constitutes on the value differ of things being evaluated. Specifically speaking, it is difficult to get a simple conclusion of when it is appropriate or not. We must make a detail analysis according to concrete problems.

Genetic parameter estimation and model selection for hot carcass weight in matebele goat

Genetic parameter estimation for simple carcass traits has been confined to the improved goat breeds worldwide unlike in the unimproved breeds in developing countries where goats are numerous. Variance components for additive direct, additive maternal, permanent environmental maternal effects, the covariance between additive direct and maternal effects were estimated by restricted maximum likelihood, fitting five animal models from 2341 ( 1359 males; 982 females) hot carcass weight pedigree records collected over a period of 13 years (1984- 1997) of indigenous Matebele goat of Zimbabwe. All investigated models included a random direct genetic effect, but different combinations of random maternal genetic and permanent environmental maternal effects as well as direct-maternal genetic covariance. The analytical models included fixed effects of sex, age at slaughter and year of slaughter. The direct heritability (h 2 a ) ranged from 0.14 to 0.26 when the maternal genetic effects were included in the model, whereas h 2 a estimate was 0.26 when maternal effects were excluded. The maternal heritability (h 2 m ) was 0.00 when only maternal genetic effects were included in the model and were 0.05 and 0.10 when the permanent environmental effect of the dam was added. The permanent environmental effect of the dam was negligible. A positive covariances between direct and maternal genetic effects (σ 2 am ) was observed when maternal genetic effects and permanent environmental maternal effects were accounted for in the model. A simple animal model with direct additive genetic effects as the only random effects other than the residuals was the best model for genetic evaluation of hot carcass weight in indigenous Matebele goat.

Impact of maternal effects on ranking of animal models for genetic parameter estimation for birth weight in male Afrikaner cattle in Zimbabwe

Variance components for additive direct, additive maternal, permanent environmental maternal effects, the covariance between additive direct and maternal effects were estimated by restricted maximum likelihood, fitting four animal models from 1359 pedigree male birth weight records of Afrikaner cattle of Zimbabwe. All investigated models included a random direct genetic effect, but different combinations of random maternal genetic and permanent environmental effects as well as direct-maternal genetic covariance. The direct heritability (h 2 a ) ranged from 0.40 to 0.43 when the maternal genetic effects were included in the model, whereas h 2 a was highest 0.45 when maternal effects were excluded. The maternal heritability (h 2 m ) was 0.00 when only maternal genetic effects were included in the model and were 0.09 and 0.09 when the permanent environmental effect of the dam was added. The permanent environmental effect of the dam was negligible. A weak negative covariances between direct and maternal genetic effects (σ 2 am ) was observed in model which had all the random effects fitted and proved to the appropriate among the four models using the log likelihood ration test.

EDDY COVARIANCE AND SAP FLOW MEASUREMENT OF ENERGY AND MASS EXCHANGES OF WOODY CROPS IN A MEDITERRANEAN ENVIRONMENT

EDDY COVARIANCE AND SAP FLOW MEASUREMENT OF ENERGY AND MASS EXCHANGES OF WOODY CROPS IN A MEDITERRANEAN ENVIRONMENT

Bootstrapping Multilayer Neural Networks for Portfolio Construction

Despite having become firmly established as one of the major cornerstone principles of modern finance, traditional Markowitz mean-variance analysis has, nevertheless, failed to gain widespread acceptance as a practical tool for equity management. The Markowitz optimization enigma essentially centers on the severe estimation risk associated with the input parameters, as well as the resultant financially irrelevant or even false optimal portfolios and asset allocation proposals. We therefore propose a portfolio construction method in the present study which incorporates the adoption of bootstrapping neural network architecture. In specific terms, a residual bootstrapping sample, which is derived from multilayer feedforward neural networks, is incorporated into the estimation of the expected returns and the covariance matrix, which are then, in turn, integrated into the traditional Markowitz optimization procedure. The efficacy of our proposed approach is illustrated by comparing it with traditional Markowitz mean-variance analysis, as well as the James-Stein and minimum-variance estimators, with the empirical results indicating that this novel approach significantly outperforms the benchmark models, in terms of various risk-adjusted performance measures. The evidence provided in this study suggests that this new approach has significant promise with regard to the enhancement of the investment value of Markowitz mean-variance analysis.

Influence of central obesity on clustering of other risk variables on metabolic syndrome among adults with normal body mass index

To study the influence of central obesity on clustering of other metabolic syndrome (MS) risk variables among adults with normal body mass index. Through cluster multistage and random sampling methods, local people aged>35 years old with normal body mass index (BMI=18.5-24.9 kg/m2) in Lanxi country were selected. Overnight fasting blood specimens of these people were collected. Chi-square test, analysis of covariance, and logistic regression analyses were performed. (1) 1821 residents were surveyed including 844 male and 977 female subjects. The overall prevalence of MS was 8.68% and the overall prevalence of central obesity was 15.87%. Both prevalence rates of the two diseases appeared to be lower in males than in females (MS: 3.32% vs. 13.31%; center obesity: 5.57% vs. 24.77%, all P<0.001). (2) The overall positive rate of clustering on other MS risk variable was 36.02%, with 34.12% in males and 37.67% in females. Comparing the subjects who did not have central obesity, those subjects wth central obesity had higher positive rate in other MS risk variables. (3) Data from analysis of covariance showed that the level of waist circumference appeared an upward trend along with the count of other MS risk variables (all P<0.001). (4) Data from multivariable logistic regression analysis showed that central obesity was a risk factor on clustering of other MS risk variables. Control the level of waist circumference among normal body mass index was an effective method in preventing metabolic syndrome and cardiovascular disease in adults.

Identification of Terrain Cover Using the Optimum Polarimetric Classifier

A systematic approach for the identification of terrain media such as vegetation canopy, forest, and snow-covered fields is developed using the optimum polarimetric classifier. The covariance matrices for various terrain cover are computed from theoretical models of random medium by evaluating the scattering matrix elements. The optimal classification scheme makes use of a quadratic distance measure and is applied to classify a vegetation canopy consisting of both trees and grass. Experimentally measured data are used to validate the classification scheme. Analytical and Monte Carlo simulated classification errors using the fully polarimetric feature vector are compared with classification based on single features which include the phase difference between the VV and HH polarization returns. It is shown that the full polarimetric results are optimal and provide better classification performance than single feature measurements.

Body mass index and percentage of body fat determined physical performance in healthy personnel

Background: Body mass index (BMI) and percentage of body fat may be linked to physical performance. However, the nature and extent of such association is not known. In addition, it is unknown whether BMI is a good reflection of body fat. Objectives: We measured the impact of obesity on physical performance and to determine the association between BMI, body fat, and various parameters of physical performance. Therefore, we tested whether BMI could be used as a good reflection of body fat. Methods: Three hundred people (126 men and 174 women) attending Chula Medical Exposition 2008 were included in this study. All participants underwent various measurements including percentage of body fat by Lange skinfold caliper, submaximal cycle ergometer test, handgrip strength, leg and back dynamometer, and flexibility determination. They were classified by BMI Asian criteria into normal (BMI 25 kg/m2). The body fat categorized was into satisfied (body fat 16.9%). Differences in physical performance between groups were calculated by unpaired t-test and analysis of covariance using SPSS for windows version 16.0. Results: Subjects with normal BMI had significantly higher handgrip strength than overweight and obese group (p = 0.007 and p Conclusions: Increased BMI and body fat tended to inversely affect physical performance in both cardiorespiratory fitness and muscular strength. Body fat seemed to have a stronger correlation with impaired physical performance. It could not be fully replaced by BMI in determination of aerobic power and muscular strength. Keywords: Body fat, BMI, physical performance

On principal components and least square methods of factor analysis

Summary In § 2 the least square estimatcs are derived for a common factor structure. §§ 3–4 are devoted to further discussion of the estimation and test problems, while the asymptotic variances and covariances of the loading estimates are evaluated in § 5.

A survey on respiratory infectious diseases related health literacy and health behavior in Fengtai district, Beijing

This study aims to survey respiratory infectious disease related health literacy (RIDHL) and health behavior (RIDHB) among residents in Fengtai district, Beijing, analyze impact factors of RIDHL , explore the association between RIDHL and RIDHB. Multistage sampling was employed and 1100 respondents were surveyed by self-designed questionnaires, which including social-demographic characteristics and evaluation of RIDHL and RIDHB. The survey results were described, the impact factors of RIDHL and the association between RIDHL and RIDHB were analyzed by analysis of variance or covariance. A total of 998 qualified questionnaires were recollected with the effective rate of 90.7%. The respondents aged from 15 to 65, scored (71.3 +/- 19.0) points in RIDHL test. Of those respondents, 25.7% (256/998), 43.2% (432/998) and 31.1% (310/998) were evaluated as low( <60 points), medium (60 - 85 points), and high level ( > 85 points) of RIDHL, respectively. There were significant difference in RIDHL scores between registered and non-registered residents, who scored (74.1 +/- 18.9) and (68.4 +/- 18.8) points, respectively (P < 0.01). RIDHL sections were ranked as audiovisual (77.6%, 4647/5988), internet using (75.2%, 2251/2994), reading (74.6%, 3724/4990), map using (68.3%, 4090/5988) and quantitative (65.5%, 5230/7984) according to the accurate rates from high to low. Analysis of variance or covariance showed that RIDHL scores were significantly different among respondents with different ages, nationalities, educational levels, occupations, and incomes (P < 0.01), yet no significant differences among those with different genders and marital status (P > 0.05). Respondents scored (69.7 +/- 15.5) points in RIDHB test. The RIDHB scores ((64.5 +/- 15.0), (70.4 +/- 15.6), (72.5 +/- 14.9) points, respectively) increased among residents with low, medium and high level of RIDHL (P < 0.01). Residents in Fengtai district, Beijing possessed medium level of RIDHL. The non-registered residents showed lower RIDHL than registered residents. Ages, nationalities, educational levels, occupations, and incomes were impact factors of RIDHL. People with higher level of RIDHL also showed a higher level of RIDHB.