Time-variant reliability analysis (TRA) has drawn tremendous interest of engineers attributable to its ability in assessing the probability that a system performs its intended function over the time ...interval of interest. This paper proposes a new simulation method for TRA by combining moment-based Hermite polynomial model (HPM) and importance sampling (IS). By evaluating the statistical moments of limit state function (LSF) and using moment-based HPM, the LSF is transformed into a moment-based equivalent Gaussian process. Then, based on the concept of the composite limit state, the time-variant reliability problem is equivalent to solving a multi-dimensional Gaussian integral. To improve the computational efficiency, an efficient updating strategy is proposed to simultaneously construct Kriging models for both the mean value function and auto-correlation function of this process. Meanwhile, an efficient IS method is also developed to combine Expansion Optimal Linear Estimation for solving multi-dimensional Gaussian integral. The efficiency and accuracy of the proposed method is demonstrated through three numerical examples involving nonlinear LSFs and non-stationary non-Gaussian processes.
•The behavior of eccentrically loaded circular CFST stub columns with localized corrosion was investigated.•The localized corrosion at the mid-height caused more significant capacity deterioration ...than that at the column ends.•Localized corrosion with γ = 0° and 180° has more adverse effects on the capacity than that with γ = 90°.•A design model was proposed for eccentrically loaded CFST column with localized corrosion.
In this paper, 12 concrete-filled steel tube (CFST) stub columns with localized corrosion were tested under eccentric load. The effects of the depth ratio, size and location of localized corrosion, and loading eccentricity on the eccentric compression behavior of circular concrete-filled steel tube stub columns were investigated. A finite element model of circular CFST stub columns with localized corrosion under eccentric load was developed and then parameter analysis was carried out. Based on the experimental and numerical results, it was found that the load bearing capacity decreases with increasing the depth ratio and size of localized corrosion. The localized corrosion at the mid-height caused more significant capacity deterioration than that at the column ends. In addition, the localized corrosion with γ = 0° and 180° has more adverse effects on the capacity of eccentrically loaded CFST columns than that with γ = 90°. Moreover, the localized corrosion with γ = 0° (at compression side) is more harmful than that γ = 180° (at tension side) for the specimens with compression-controlled failure, and vice versa for the specimens with tension-controlled failure. Finally, a design model of eccentrically loaded CFST column with localized corrosion was proposed based on an established equivalent specimen. The results suggested that the proposed model predicted the load bearing capacities with reasonable accuracy.
Itch and pain are two distinct sensations. Although our previous study suggested that gastrin-releasing peptide receptor (GRPR) is an itch-specific gene in the spinal cord, a long-standing question ...of whether there are separate neuronal pathways for itch and pain remains unsettled. We selectively ablated lamina I neurons expressing GRPR in the spinal cord of mice. These mice showed profound scratching deficits in response to all of the itching (pruritogenic) stimuli tested, irrespective of their histamine dependence. In contrast, pain behaviors were unaffected. Our data also suggest that GRPR⁺ neurons are different from the spinothalamic tract neurons that have been the focus of the debate. Together, the present study suggests that GRPR⁺ neurons constitute a long-sought labeled line for itch sensation in the spinal cord.
•Stress paths of confined concrete in the whole-section-loaded CFT columns and corresponding stress path effects are investigated.•The influences of column parameters upon the stress paths of ...confined concrete in whole-section-loaded CFT columns are different from those in concrete-loaded CFT columns.•The confinement effects of the concrete in whole-section loaded CFT columns are generally worse than those in concrete-loaded CFT columns.•For the confinement coefficient less than about 0.2, the confinement effects of the concrete in CFT columns under the two loading conditions are nearly the same.•A compressive strength model incorporating the stress path effect was developed for the confined concrete in CFT columns under two loading conditions.
Previous study has suggested that the stress paths of confined concrete in concrete-filled steel tube (CFT) stub columns influence the compressive strengths of the concrete, which, however, is based on the test of concrete-loaded CFT columns. In this paper, to fully understand the compressive strength of confined concrete in CFT column, the stress paths of confined concrete in the whole-section-loaded CFT columns are investigated. A detailed parametric study is conducted on the stress paths and their corresponding effects on compressive strength. Test results suggest that the lateral stress of the concrete in a whole-section-loaded CFT column generally occurred in a later stage and less significant than that in a concrete-loaded CFT column. The compressive strength of confined concrete in the whole-section-loaded CFT column with a small confinement coefficient is path-dependent, and the confinement effect of the concrete is generally weaker than that in concrete-loaded CFT column. With the increase of the confinement coefficient, the compressive strengths of confined concrete in whole-section-loaded CFT columns become path-independent. Based on the test results, a compressive strength model incorporating the stress path effect is developed for confined concrete in both whole-section-loaded and the concrete-loaded CFT columns. Good agreement between the experimental results and the ones predicted by the model is found, indicating a high performance of the proposed model.
The confinement effect of external and internal steel tubes on sandwiched concrete in concrete-filled double-skin circular steel tubular (CFDST) short columns has a significant impact on the ...compressive strength and ductility of columns. Limited researches on CFDST columns have only considered the influences of a part of column parameters on the confinement effect, leading to the absence of appropriate compressive strength formulas in international standards. To comprehend the compressive behavior of circular CFDST short columns and suitably evaluate their compressive strength for practical engineering design, it is necessary to further launch the experiments on circular CFDST short columns and develop a suitable estimated formula for their compressive strength. The purpose of this paper is to develop a simple and accurate formula for predicting the compressive strength of axially loaded CFDST short circular columns with a wide range of parameters. A total of 24 specimens with outer and inner circular carbon steel tubes that withstand axial compression were tested. A new confinement coefficient reflecting the confinement effect of concrete strength in CFDST columns was proposed on the basis of the test data in the present paper and data collected from literature. Utilizing the proposed confinement coefficient, a novel strength design formula was developed to estimate the compressive strength of CFDST short circular columns. It shows that the proposed confinement coefficient can reasonably reflect the interaction effect between the sandwiched concrete and steel tubes, and the formula suggested in this paper offers better predictions of the compressive strength than current design formulas.
•Tests on 24 circular CFDST short columns were conducted.•Existing strength prediction formulas were evaluated using conducted and collected test data.•New confinement coefficient reflecting the confinement effect of concrete strength was proposed.•The influences of column parameters on the confinement effects were clarified.•Novel design formula was proposed to predict the strengths of circular CFDST short columns.
•Tests on 28 circular concrete axially loaded CFDST short columns are conducted.•The confinement effects of outer and inner to sandwiched concrete are briefly analyzed.•The tested CFDST columns show ...good ductility performance similar to that of circular STCC columns.•A enhancement coefficient reflecting the increase of concrete strength is developed using the test and numerical results.•A strength formula incorporating the enhancement coefficient is proposed and high prediction performance is achieved.
This paper aims to experimentally and numerically investigate the compressive behavior of circular concrete-filled double-skin steel tubular (CFDST) short columns, in which only the sandwiched concrete is under axial compression. In total, 28 CFDST columns were loaded axially, and their axial load-shortening curves, ultimate strength and failure modes were briefly discussed. Results suggest that the wall thickness and yield stress of outer steel tube have a significant effect on the failure modes, while the concrete strength shows an insignificant effect. The tested columns exhibited good ductility concerned by seismic resistant design. The ultimate strength of the columns using STK490 outer steel tubes was about 20–26% than that of ones with STK400 outer steel tubes. With an increase in the concrete strength and wall thickness of outer steel tube, the ultimate strength of the columns was improved by 32% and 43%, respectively. Moreover, finite element (FE) models were established and verified by comparing with the test results, and then an extensive parametric analysis was carried out to ascertain the effects of key variables on the compressive behaviour of the studied CFDST short columns. Finally, based on the numerical and test results, a novel formula was proposed to estimate the ultimate strength of CFDST columns, and high prediction performance was found in the proposed formula. The proposed formula is not only applicable for the strength prediction of CFDST columns, but also for that of steel tube confined concrete (STCC) columns.
•Develop a novel framework for simulating non-stationary non-Gaussian processes.•Transform non-stationary non-Gaussian ACF to non-stationary Gaussian ACF.•Translate underlying Gaussian processes into ...non-stationary non-Gaussian process using L-moments-based HPM.•Incompatibilities between L-moments and ACF are effectively resolved.•Demonstrate the efficiency and accuracy of the proposed method.
A novel and efficient method is proposed for simulating strongly non-Gaussian and non-stationary processes by combining Karhunen–Loève expansion with Linear-moments-based (L-moments-based) Hermite polynomial model (HPM). In this method, the complete transformation from non-stationary non-Gaussian auto-correlation function (ACF) to non-stationary Gaussian ACF is realized using L-moments-based HPM. Then, the underlying Gaussian processes is represented by Karhunen–Loève expansion and further transformed into target non-stationary non-Gaussian processes by L-moments-based HPM. Moreover, a novel approach is proposed to deal with the two kinds of incompatibilities that may occur in strongly non-Gaussian processes, including that non-stationary non-Gaussian ACF falls outside of its applicable range and non-stationary Gaussian ACF is non-positive semi-definite. It can be found from some representative numerical examples that the precision and efficiency of the proposed method are considerable.
Previous studies suggested that diabetes mellitus was associated with cancer risk and prognosis, but studies investigating the relationship between diabetes mellitus and survival in patients with ...hepatocellular carcinoma (HCC) reported inconsistent findings. To derive a more precise estimate of the prognostic role of diabetes mellitus in HCC, we systematically reviewed published studies and carried out a meta-analysis.
Eligible articles were identified in electronic databases from their inception through September 16, 2013. To evaluate the correlation between diabetes mellitus and prognosis in HCC, the pooled hazard ratios (HR) and their 95% confidence intervals (95% CI) for poorer overall and disease-free survivals were calculated by standard meta-analysis techniques with fixed-effects or random-effects models.
21 studies with a total of 9,767 HCC patients stratifying overall survival and/or disease-free survival in HCC patients by diabetes mellitus status were eligible for meta-analysis. 20 studies with a total of 9,727 HCC cases investigated the overall survival, and 10 studies with a total of 2,412 HCC patients investigated the disease-free survival. The pooled HRs for overall survival and disease-free survival were 1.46 (95% CI, 1.29 to 1.66; P<0.001) and 1.57 (95% CI, 1.21 to 2.05; P = 0.001), respectively. The adjusted HRs for overall survival and disease-free survival were 1.55 (95% CI, 1.27 to 1.91; P<0.001) and 2.15 (95% CI, 1.75 to 2.63; P<0.001), respectively. In addition, for patients receiving hepatic resection, diabetes mellitus was associated with both poorer overall survival and poorer disease-free survival, and for patients receiving non-surgical treatment or patients receiving radiofrequency ablation, diabetes mellitus was associated with poorer overall survival. There was no evidence for publication bias.
Diabetes mellitus is independently associated with both poorer overall survival and poorer disease-free survival in HCC patients.
•Extend LHPM to non-stationary non-Gaussian cross-correlated fields.•Establish transformation model from non-stationary non-Gaussian CMF to the underlying Gaussian CMF.•Represent the underlying ...Gaussian cross-correlated fields by multivariate K-L expansion.•Compute eigenvalues and eigenfunctions using Nyström method.•Develop a unified simulation framework for non-stationary non-Gaussian cross-correlated fields.
In practical engineering, cross-correlated random fields are often used to model structural materials or random loads containing multiple correlations. Effective and accurate simulation of these cross-correlation fields is an important prerequisite for subsequent reliability analysis and uncertainty quantification of complex systems. Therefore, this paper proposes a new simulation method for non-stationary non-Gaussian cross-correlated random fields to satisfy realistic engineering requirements. In this new method, L-moments-based Hermite polynomials model (LHPM) is extended to non-stationary non-Gaussian cross-correlated fields. Then, a transformation model from non-stationary non-Gaussian correlation matrix function (CMF) to the underlying Gaussian CMF is explicitly given. Multivariate K-L expansion is further used to approximate the underlying Gaussian cross-correlated fields, where the eigenvalue and eigenfunctions are estimated via the Nyström method with uniform weights. The approximation permits the application of few random variables to characterize the entire Gaussian cross-correlated fields. Ultimately, the simulated underlying Gaussian cross-correlated fields are mapped back to the target non-stationary non-Gaussian cross-correlated fields based on LHPM. Three typical examples, including exponential kernel, Wiener process kernel and spatially varying non-Gaussian and nonstationary seismic ground motions, are used to validate the effectiveness of the proposed method. The source code is readily available at: https://github.com/zhaozhao23/Simulation-of-non-stationary-and-non-Gaussian-cross-correlated-fields.
•An overview of the current status of cold chain in China has been conducted.•Current perishable food and frozen food production were summarized.•Research on technology and devices at different ...stages of cold chain were stated.•Refrigerants used in cold chain of China and its future trends are presented.•Regulations on cold chain and related standards are summarized.
An overview of the current status of the cold chain in China was conducted. First, food waste and losses in China were outlined, which is caused partly by the incomplete cold chain facilities in China. The problems relating to food preservation and safety in China were stated, in conjunction with rapid increase of China's frozen food production in recent years. Moreover, the relevant governmental policies supporting the development of cold chain are also introduced. The current status of different stages of cold chain in China were reviewed briefly. The application and development of technologies, facilities and devices along the cold chain, including pre-cooling, freezing, cold storage, refrigerated transportation, distribution, refrigerated trucks, cold warehouses, home refrigerators and freezers are discussed. Refrigerants currently utilized and future trends in cold chain were also presented. Furthermore, the quotas for refrigerants, R22 and R141b, consumed within cold chain are also presented. Additionally, regulations and standards relating to the cold chain were summarized. Some important research activities related to the cold chain conducted in recent years were introduced.
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