• The Bulletin of The Korean Astronomical Society
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• v.46 no.1
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• pp.51.2-51.2
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• 2021

Nuclear rings are sites of intense star formation at the center of barred spiral galaxies. A straightforward but unanswered question is what controls star formation rate (SFR) in nuclear rings. To understand how the ring SFR is related to mass inflow rate, gas content, and background gravitational field, we run a series of semi-global hydrodynamic simulations of nuclear rings, adopting the TIGRESS framework to handle radiative heating and cooling as well as star formation and supernova feedback. We find: 1) when the mass inflow rate is constant, star formation proceeds in a remarkably steady fashion, without showing any burst-quench behavior suggested in the literature; 2) the steady state SFR has a simple linear relationship with the inflow rate rather than the ring gas mass; 3) the midplane pressure balances the weight of the overlying gas and the SFR surface density is linearly correlated with the midplane pressure, consistent with the self-regulated star formation theory. We suggest that the ring SFR is controlled by the mass inflow rate in the first place, while the gas mass adjusts to the resulting feedback in the course of achieving the vertical dynamical equilibrium.

• Structural Engineering and Mechanics
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• v.88 no.6
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• pp.589-598
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• 2023

This article addresses the quasi-static analysis of time-dependent honeycomb sandwich plates with various geometrical properties based on the bending analysis of elastic honeycomb sandwich plates employing a time function with three unknown coefficients. The novel point of the developed method is that the responses of viscoelastic honeycomb sandwich plates under static transversal loads are clearly formulated in the space and time domains with very low computational costs. The mechanical properties of the sandwich plates are supposed to be elastic for the faces and viscoelastic honeycomb cells for the core. The Boltzmann superposition integral with the constant bulk modulus is used for modeling the viscoelastic material. The shear effect is expressed using the first-order shear deformation theory. The displacement field is predicted by the product of a determinate geometrical function and an indeterminate time function. The simple HP cloud mesh-free method is utilized for discretizing the equations in the space domain. Two coefficients of the time function are extracted by answering the equilibrium equation at two asymptotic times. And the last coefficient is easily determined by solving the first-order linear equation. Numerical results are presented to consider the effects of geometrical properties on the displacement history of viscoelastic honeycomb sandwich plates.

• Geomechanics and Engineering
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• v.35 no.5
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• pp.475-486
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• 2023

Ballast particles have an irregular shape and are discrete in nature. Due to the discrete nature of ballast, it exhibits complex mechanical behaviour under loading conditions. The discrete element method (DEM) can model the behaviour of discrete particles under a multitude of loading conditions. DEM is used in this paper to simulate a series of three-dimensional direct shear tests in order to investigate the shear behaviour of railway ballast and its interaction at the microscopic level. Particle flow code in three dimension (PFC3D) models the irregular shape of ballast particles as clump particles. To investigate the influence of particle size distribution (PSD), real PSD of Indian railway ballast specification IRS:GE:1:2004, China high-speed rail (HSR) and French rail specifications are generated. PFC3D built-in linear contact model is used to simulate the interaction of ballast particles under various normal stresses, shearing rate and shear box sizes. The results indicate how shear resistance and volumetric changes in ballast assembly are affected by normal stress, shearing rate, PSD and shear box size. In addition to macroscopic behaviour, DEM represents the microscopic behaviour of ballast particles in the form of particle displacement at different stages of the shearing process.

• Steel and Composite Structures
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• v.49 no.6
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• pp.701-711
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• 2023

In order to fully reflect variation characteristics of composite concrete dam health state, the monitoring data is applied to diagnose composite concrete dam health state. Composite concrete dam lesion development to wreckage is a precursor, and its health status can be judged. The monitoring data are generally non-linear and unsteady time series, which contain chaotic information that cannot be characterized. Thus, it could generate huge influence for the construction of monitoring models and the formulation of corresponding health diagnostic indicators. This multi-scale diagnosis process is from point to whole. Chaotic characteristics are often contained in the monitoring data. If chaotic characteristics could be extracted for reflecting concrete dam health state and the corresponding diagnostic indicators will be formulated, the theory and method of diagnosing concrete dam health state can be huge improved. Therefore, the chaotic characteristics of monitoring data are considered. And, the extracting method of the chaotic components is studied from monitoring data based on fuzzy dynamic cross-correlation factor method. Finally, a method is proposed for formulating composite concrete dam health state indicators. This method can effectively distinguish chaotic systems from deterministic systems and reflect the health state of concrete dam in service.

• Computers and Concrete
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• v.33 no.2
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• pp.163-173
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• 2024

Fiber-reinforced polymers (FRP) have a proven strength enhancement capability when installed into Reinforced Concrete (RC) beams. The brittle failure of traditional FRP strengthening systems has attracted researchers to develop novel materials with improved strength and ductility properties. One such material is that known as polyethylene terephthalate (PET). This study presents a numerical investigation of the flexural behavior of reinforced concrete beams externally strengthened with PET-FRP systems. This material is distinguished by its large rupture strain, leading to an improvement in the ductility of the strengthened structural members compared to conventional FRPs. A three-dimensional (3-D) finite element (FE) model is developed in this study to predict the load-deflection response of a series of experimentally tested beams published in the literature. The numerical model incorporates constitutive material laws and bond-slip behavior between concrete and the strengthening system. Moreover, the validated model was applied in a parametric study to inspect the effect of concrete compressive strength, PET-FRP sheet length, and reinforcing steel bar diameter on the overall performance of concrete beams externally strengthened with PET-FRP.

• Nuclear Engineering and Technology
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• v.56 no.4
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• pp.1544-1551
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• 2024

A unique brick series based on Vietnamese clay was manufactured at 114.22 MPa pressure rate for γ-ray attenuation purposes, consisting of (x) metallic waste & (90%-x) red clay mineral & 10% (hardener mixed with epoxy resin), where (x) is equal to the values 0%, 20%, 40%, 50%, and 70%. The impacts of industrial metal waste ratio in the structure and radiation protective characteristics were evaluated experimentally. The increase in metallic waste doping concentrations from 0% to 70% was associated with an increase in the manufactured brick's density (ρ) from 2.103 to 2.256 g/cm³ while the fabricated samples' porosity (Φ) decreased from 11.7 to 1.0%, respectively. Together with a rise in fabricated brick's density and a decrease in their porosities, the manufactured bricks' γ-ray attenuation capacities improved. The measured linear attenuation coefficient (μ, cm^-1) was improved by 30.8%, 22.1%, 21.6%, and 19.7%, at E_γ equal to the values respectively 0.662, 1.173, 1.252, and 1.332 MeV, when the metallic waste concentration increased from 0% to 70%, respectively. The study demonstrates that manufactured bricks exhibit superior radiation shielding properties, with radiation protection efficiencies of 88.4%, 90.0%, 91.7%, 92.1%, and 92.4% for bricks with industrial metal waste contents of 0%, 20%, 40%, 50%, and 70%, respectively, at γ-ray energy (E_γ) of 1.332 MeV.

• Steel and Composite Structures
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• v.51 no.2
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• pp.173-183
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• 2024

This study investigates a new seismic retrofit system that utilizes rotational friction dampers and axial springs. The retrofit system involves a steel frame with rotational friction dampers (RFD) at beam-column joints and linear springs at the corners, providing energy dissipation and self-centering capabilities to existing structures. The axial spring acts as a self-centering mechanism that eliminates residual deformations, while the friction damper mitigates seismic damage. To evaluate the seismic performance of the proposed retrofit system, a series of cyclic loading tests were carried out on a steel beam-column subassembly equipped with the proposed devices. An analytical model was then developed to validate the experimental results. A performance point ratio (PPR) was presented to optimize the design parameters of the retrofit system, and a performance-based seismic design strategy was developed based on the PPR. The retrofit system's effectiveness and the presented performance-based design approach were evaluated through case study models, and the analysis results demonstrated that the developed retrofit system and the performance-based design procedure were effective in retrofitting structures for multi-level design objectives.

• Nuclear Engineering and Technology
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• v.56 no.6
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• pp.2063-2070
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• 2024

A series of ordinary concrete is casted in order to examine the influence of the manganiferous siltstone rocks on the physical, mechanical, and gamma-ray shielding properties. Thus, a partial replacement for the coarse aggregates by siltstone rocks was performed during the fabrication of the currently ordinary concrete. The test revealed that raising the siltstone concentration improved the mechanical characteristics and density of the developed concretes. The addition of siltstone rocks at concentrations ranging from 0 to 40 wt% of the coarse aggregate concentration raises the density of the concrete from 2.05 g/cm³ to 2.3 g/cm³. Furthermore, partial substitution of basalt with siltstone rocks improves gamma-ray shielding properties. The experimental results for the linear attenuation coefficient show an increase in its value from 0.146 cm1 to 0.160 cm^-1 when the siltstone concentration is increased between 0 and 40 wt% at 0.662 MeV. Furthermore, increasing the concentrations of siltstone affected the half-value thickness, which varied between 4.759 and 4.319 cm at 0.662 MeV. Therefore, the replacement presents a new alternative coarse aggregate that can enhance the mechanical and radiation shielding properties of ordinary concretes.

• Geomechanics and Engineering
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• v.39 no.1
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• pp.27-41
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• 2024

Accurately estimating the performance of tunnel boring machines (TBMs) is crucial for mitigating the substantial financial risks and complexities associated with tunnel construction. Machine learning (ML) techniques have emerged as powerful tools for predicting non-linear time series data. In this research, six advanced meta-heuristic optimization algorithms based on long short-term memory (LSTM) networks were developed to predict TBM penetration rate (TBM-PR). The study utilized 1125 datasets, partitioned into 20% for testing, 70% for training, and 10% for validation, incorporating six key input parameters influencing TBM-PR. The performances of these LSTM-based models were rigorously compared using a suite of statistical evaluation metrics. The results underscored the profound impact of optimization algorithms on prediction accuracy. Among the models tested, the LSTM optimized by the particle swarm optimization (PSO) algorithm emerged as the most robust predictor of TBM-PR. Sensitivity analysis further revealed that the orientation of discontinuities, specifically the alpha angle (α), exerted the greatest influence on the model's predictions. This research is significant in that it addresses critical concerns of TBM manufacturers and operators, offering a reliable predictive tool adaptable to varying geological conditions.

• Asia-Pacific Journal of Business
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• v.15 no.2
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• pp.223-236
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• 2024

Purpose - The purpose of the paper is to empirically investigate the asymmetric adjustment of loan and deposit interest rates among banks and non-bank depository institutions. Design/methodology/approach - We construct a VAR model using time series data comprising loan and deposit interest rates of banks and non-bank depository institutions, along with the call rate. Based on this model, we conduct impulse-response analysis and variance decomposition to investigate the dynamic relationship between the interest rates. Findings - In the case of banks and credit unions, the responses of deposit rates to the call rate are larger than the responses of loan rates, and we cannot find evidence of non-linear responses. In the case of savings banks, the responses of loan rates to the call rate are larger than the responses of deposit rates. The responses of loan rates to a positive call rate shock are statistically significant, while the responses of loan rates to a negative call rate shock are not statistically significant. Research implications or Originality - This study differs from previous research in that it examines the asymmetric response of loan and deposit rates of both banks and non-bank financial institutions to changes in the call rate. The implications for the impact of these findings on the financial system and income inequality are presented.