Search Results (10)

In order to clarify the influence of cross-section change mode of a large-span variable cross-section tunnel on the stability of the surrounding rock of a tunnel, four three-dimensional finite element models were established for four typical cross-section conversion forms: Sudden changes in the cross-section of the symmetric tunnel, Gradual changes in the cross-section of the symmetric tunnel, Sudden changes in the cross-section of the asymmetric tunnel, and Gradual changes in the cross-section of the asymmetric tunnel. The Stress characteristics and deformation laws of the surrounding rock under different cross-sectional changes were systematically analyzed. The simulation results were compared with the field monitoring results, and the construction scheme was optimized based on the results of the numerical analysis and field monitoring. The results demonstrate that the final settlement values for sudden changes in the cross-section of the symmetric tunnel and sudden changes in the cross-section of the asymmetric tunnel were 21.23 mm and 21.98 mm, respectively, representing reductions of 14.6% and 15.7% compared to gradual changes in the cross-section of the symmetric tunnel and gradual changes in the cross-section of the asymmetric tunnel. The final support stress values of sudden changes in the cross-section of the symmetric tunnel and sudden changes in the cross-section of the asymmetric tunnel were 8.59 and 7.88 MPa, respectively, representing reductions of 21.5% and 26.9% compared with gradual changes in the cross-section of the symmetric tunnel and gradual changes in the cross-section of the asymmetric tunnel. Compared with asymmetric construction, symmetrical construction is more likely to lead to a stress concentration effect on both sides of the tunnel. Considering the overall construction feasibility and economy, the asymmetric sudden-change construction scheme provides better comprehensive benefits. The research results can provide a theoretical basis and technical reference for solving engineering problems such as complex stress in a large section transition zone and difficult control of tunnel construction. Full article

This paper proposes estimating linear dynamic panels by explicitly exploiting the endogeneity of lagged dependent variables and expressing the crossmoments between the endogenous lagged dependent variables and disturbances in terms of model parameters. These moments, when recentered, form the basis for model estimation. The resulting estimator’s asymptotic properties are derived under different asymptotic regimes (large number of cross-sectional units or long time spans), stable conditions (with or without a unit root), and error characteristics (homoskedasticity or heteroskedasticity of different forms). Monte Carlo experiments show that it has very good finite-sample performance. Full article

Due to the size limitations of shaking tables, dynamic scale models of large-span space structures for engineering have small cross-sections and thin wall thicknesses. It is difficult to use the structural steels commonly used in prototypes to make dynamic scale models. In this paper, 304 stainless steel is proposed for making the scale model, and the similarity relationship between the structural-steel prototype and the 304-stainless-steel dynamic scale model was studied. Firstly, a uniaxial test was conducted to study the elastic modulus similarity and the yielding stress similarity. The test results demonstrated that the elastic modulus similarity ratio was 1:1, and the stress similarity ratios of the 304 stainless steel and the three typical structural steels were 1:1 (Q235 steel), 1:1.5 (Q355 steel) and 1:1.8 (Q420 steel). Then, the similarities of other variables were derived using the dimensional analysis method. In the end, a numerical analysis was conducted to verify the similarity relationship between the structural-steel prototype and the 304-stainless-steel dynamic scale model. In the numerical analysis, a single-layer spherical reticulated shell structure and a dynamic scale model with a length similarity ratio of 1:20 were established by using the ABAQUS 2021 software, and the node displacement, the element internal force and natural vibration characteristics were analyzed. The results show that standard deviations of the displacements, the internal forces and the natural vibration frequencies between the prototype and the scale model were within 5%. It turns out that the proposed similarity between the structural-steel prototype and the 304-stainless-steel dynamic scale model was applicable in the elastic stage. The findings provide a reference for designing a dynamic scale model of large-span space structures for engineering by using 304 stainless steel. Full article

During the excavation process of a large-span variable cross-section of a tunnel, the deformation and stress characteristics of the surrounding rock supporting the structure are complex, and construction control is difficult. Based on an actual tunnel project, the mechanical effect and deformation characteristics of the surrounding rock and support structure of a large-span variable cross-section tunnel during its excavation and support process were studied via numerical simulation. The construction method, using the bench method to excavate and set up the transition section in the variable cross-section, was proposed. Based on the numerical simulation results, two optimized excavation schemes were proposed and analyzed to address the construction method conversion problems in constructing large-span variable cross-section tunnels. The rationality of the optimized construction scheme was verified through a comparison with field monitoring data. The research results show that the three-bench temporary inverted arch method supported by the temporary vertical portal frame has good applicability in constructing the large-span variable cross-section tunnel. This scheme can effectively control the stress concentration and excessive deformation of the surrounding rock in the large-span variable cross-section tunnel. The numerical simulation results agree with the field monitoring data, which verifies the rationality of analyzing the construction mechanical effects of variable cross-section tunnels and selecting construction schemes through numerical simulation. The research results can provide reference for the construction of similar tunnel projects. Full article

Background: Identification of progressive liver disease necessitates the finding of novel non-invasive methods to identify and monitor patients in need of early intervention. Investigating patients with early-liver injury may help identify unique biomarkers. Early-liver injury is characterized by remodeling of the hepatocyte basement membrane (BM) of the extracellular matrix. Thus, we quantified biomarkers targeting two distinct neo-epitopes of the major BM collagen, type IV collagen (PRO-C4 and C4M), in patients spanning the non-alcoholic fatty liver disease (NAFLD) spectrum. Methods: We evaluated PRO-C4 and C4M in a cross-sectional study with 97 patients with NAFLD confirmed on histology. Serological levels of PRO-C4 and C4M were quantified using validated competitive enzyme-linked immunosorbent assays (ELISA). Using the fatty liver inhibition of progression (FLIP) algorithm, we stratified patients into two groups: non-alcoholic fatty liver (NAFL) and non-alcoholic steatohepatitis (NASH). Biomarker levels were investigated in the two groups in patients stratified by the NAFLD activity score (NAS). In both groups, biomarker measurements were analyzed in relation to histological scorings of steatosis, inflammation, ballooning, and fibrosis. Results: Patients had a body mass index (BMI) of 30.9 ± 5.6 kg/m², age of 53 ± 13 years and a NAS range of 1–8. Upon stratification by FLIP, the NASH patients had higher platelets, ALT, and AST levels than the NAFL group. Both PRO-C4 (p = 0.0125) and C4M (p = 0.003) increased with increasing NAS solely within the NAFL group; however, a large variability was present in the NASH group. Furthermore, both markers were significantly associated with lobular inflammation (p = 0.020 and p = 0.048) and steatosis (p = 0.004 and p = 0.015) in patients with NAFL. Conclusions: This study found that type IV collagen turnover increased with the increase in NAS in patients with NAFL; however, this was not the case in patients with NASH. These findings support the assessments of the BM turnover using biomarkers in patients with early-disease development. These biomarkers may be used to track specific processes involved in the early pathobiology of NAFL. Full article

A comparative study of composite floor systems with I-beams and corrugated web beams is performed based on non-linear programming (NLP) algorithm. The optimization is conducted to find the most economical design with minimum steel consumption considering variables associated with the cross-sectional dimensions and multiple constraints from standards, specifications and engineering practices. Various parameters of live loads ranging from 2 to 10 kN/m² and spans ranging from 20 to 100 m are considered. The optimization results reveal that composite floors with corrugated web beams have reasonable and economical cross-sections with less steel consumption, owing to the high performance of the corrugated web in shear resistance and stability. Further comparative studies show that composite floors with corrugated web beams are economically competitive for spans larger than 30 m with a steel saving of 20–60%, and composite floors with welded I-beams can be applicable for spans less than 30 m considering the simpler configuration and construction. In addition, a spatially structured cable-supported steel–concrete composite floor system is proposed and recommended for super-large-span floor structures considering the cost-effectiveness of the analyzed floor systems reduces as the span further increases. Full article

Diagnostic load testing refers to the use of the measured historical responses of the structure in the field data to better understand its dynamic and static structural behaviours. It is important and necessary to predict the health state, load capacity, and aging of the structure by updating the finite element (FE) model, which can give useful information to aid the design of retrofits and the maintenance of the existing bridge in the future. The paper presents an update of the full-scale FE model for the reinforced concrete (RC) bridge structure over the seawater river based on the experimental strains under the static load testing in which the representative FE model of the actual structure is determined from the optimisation procedures. The optimisation variables are applied, including the cross-sectional properties and concrete material calibrated through the genetic algorithm (GA) optimisation in the MATLAB software, which interfaces with the FE modelling in the scripting of the SOFISTIK TEDDY software automatically. The bending moments at the mid-span of the RC girders are determined in the FE modelling to compute stresses, which are compared with the measured stresses through optimisation scenarios with a percentage error of the objective function less than 10%. The measured data of concrete strains are recorded from reusable strain transducers installed on the mid-span girders for every bridge span, which are used to calibrate the bridge model in static load testing. The novelty of the solution is to implement innovative techniques using field data as an improved approach for calibrating automatically the analytical FE model parameters of all RC spans of the bridge until its static behaviours are very similar to those of the actual bridge. The final updated FE modelling is used to apply truck load configurations according to bridge design standards such as the AASHTO specifications, which can predict the load limits of the existing bridge structure more accurately and reliably. These proposed approaches can be applied to large bridges as well as complex structures with supporting FE analysis software and data processing software. Full article

Podded propulsors are widely used in warships and cruise ships, which have a higher requirement of vibrational and acoustic design. Therefore, studying vibration characteristics and the transmission mechanism of podded propulsor shafting is significant for reducing vibration and ensuring the safe operation of ships. This paper establishes a model of podded propulsor shafting by analytical method. The shafting is simplified to a heterogeneous variable cross-section beam, while bearings are seen as springs. The podded propulsor shafting has one radial-thrust hybrid bearing and one radial bearing. The excitations from the propeller and cabin are considered. The influences of bearing stiffness, bearing location, and excitation on vibration characteristics of shafting are analyzed. The main conclusions are as follows: Based on the analysis of the area that resonance frequency is sensitive to the change of bearing stiffness, the resonance frequencies of the shafting can be adjusted to the proper range. The large span between hybrid bearing and radial bearing leads to low stiffness of shafting and low resonances frequencies. Under radial excitations, the low vibration always occurs at the hybrid bearing, motor shafting, or propeller end of shafting. This research provides theoretical support for the design and optimization of vibration reduction of podded propulsor shafting. Full article

Background: Prader-Willi syndrome (PWS) is conventionally regarded as a model of genetic obesity carrying a metabolically healthier profile and fat compartmentalization than subjects with non-syndromic obesity. Serum uric acid (sUA) is a recognized surrogate marker of metabolic derangement. As no information is currently available on sUA levels in adults with PWS, we aimed to analyze sUA in a large cohort of adult patients with PWS in comparison to a control counterpart; secondly, we aimed to investigate the metabolic and non-metabolic determinants of sUA in PWS. Methods: A cross-sectional study was conducted on 89 consecutive adult patients with genetically confirmed PWS spanning a wide BMI range (17.2–56.7 kg/m²). As controls, 180 age-, sex- and BMI-matched healthy controls were included. sUA levels were analyzed in relation to the PWS status, metabolic variables, hormone status, body composition, and resting energy expenditure (REE). Bivariate correlation and multivariable regression studies were used to test for predictors of sUA in PWS. Results: Despite having similar BMI values, patients with PWS presented with higher FM (p < 0.0001), lower FFM (p < 0.0001) and REE values than controls (p < 0.0001). In PWS, sUA levels were non-significantly different between subjects with and without obesity (5.4 ± 1.3 vs. 4.9 ± 1.1 mg/dL, p = 0.09), and did not vary significantly in relation to genotype, sex steroid or GH replacement, as well as psychiatric treatments. Rates of hyperuricaemia (19.1% vs. 33.7%, p < 0.01) and absolute sUA levels were lower in patients with PWS compared to controls owing to significant differences between subgroups with obesity (5.5 ± 1.4 vs. 6.6 ± 1.6 mg/dL, p < 0.0001). In merged populations, sUA increased in parallel with age, BMI, FM, FFM, REE, glucolipid homeostasis, and inflammatory markers. In a separate analysis in PWS, however, sUA correlations with BMI, FM, and inflammatory markers were null. Stepwise multivariable regression analysis in the PWS group adjusted for karyotype, age, sex, FM, FFM, obesity, triglycerides, and HDL cholesterol, showed that sUA levels were independently associated with FFM (β = 0.35, p < 0.0001) and, albeit less significantly, with triglycerides (β = 0.23, p < 0.05). The introduction of height-normalized FFM (FFM index) in the regression model, however, abrogated the predictive role of FFM on sUA. Conclusions: FFM mass is a strong predictor of sUA. PWS is associated to lower sUA levels than controls likely due to genetic predisposition to different body composition and healthier metabolic phenotype. Further studies are warranted to assess purine metabolism and the clinical significance of the FFM index in PWS. Full article

This study examines variability across the age span in cognitive performance in a cross-sectional, population-based, adult lifespan cohort from the Cambridge Centre for Ageing and Neuroscience (Cam-CAN) study (n = 2680). A key question we highlight is whether using measures that are designed to detect age-related cognitive pathology may not be sensitive to, or reflective of, individual variability among younger adults. We present three issues that contribute to the debate for and against age-related increases in variability. Firstly, the need to formally define measures of central tendency and measures of variability. Secondly, in addition to the commonly addressed location-confounding (adjusting for covariates) there may exist changes in measures of variability due to confounder sub-groups. Finally, that increases in spread may be a result of floor or ceiling effects; where the measure is not sensitive enough at all ages. From the Cam-CAN study, a large population-based dataset, we demonstrate the existence of variability-confounding for the immediate episodic memory task; and show that increasing variance with age in our general cognitive measures is driven by a ceiling effect in younger age groups. Full article