• Fisheries and Aquatic Sciences
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• v.26 no.4
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• pp.294-303
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• 2023

Beside that the fish species and their sub-populations are highly important as a keystone species in the coastal and marine ecosystem, there are very few studies on their presence, distribution and temporal variations within and around the lagoon ecosystems in Albania. This paper provides an updated review on the life cycle, fishery, exploitation state and management of the main species that are subject of commercial fishing in the Karavasta lagoon, southeastern Adriatic coast of Albania. Due to the fact that lagoons represent a continuum between continental and marine aquatic ecosystems they play a crucial role in species life cycles. Further on in the circumstances of rapid utilizations and environmental changes, anomalies in salinity and temperatures, accelerated anthropogenic influences their rate of vulnerability is highly increased. Following the requirements of the Water Framework Directive, transitional water, coastal lagoons and estuaries there is a need for urgent monitoring and management approaches. The commercial species include: European eel (Anguilla anguilla), species of Family Mugilidae (Mugil cephalus, Liza ramada, Liza salienes and Chelon labrosus), Seabream (Sparus aurata), Seabass (Dincentrarchus labrax), etc. Fish productivity is oscillating from maximum value of 61.95 kg/ha is recorded in period of 1975-80 and lower value of 31 kg/ha in year 2020. Our study highlights importance of fish and fishery long-term monitoring, and contributes to understand the driving factors in productivity, migration patterns and species ecology in the vital coastal ecosystems.

• Geomechanics and Engineering
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• v.28 no.2
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• pp.135-143
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• 2022

Soils are natural granular materials whose mechanical properties differ according to the size and composition of the particles, so soils exhibit an obvious scale effect. Traditional soil mechanics is based on continuum mechanics, which can not reflect the impact of particle size on soil mechanics. On that basis, a matrix-reinforcing-particle cell model is established in which the reinforcing particles are larger-diameter sand particles and the matrix comprises smaller-diameter bentonite particles. Since these two types of particles deform differently under shear stress, a new shear-strength theory under direct shear that considers the stress concentration and bypass phenomena of the matrix is established. In order to verify the rationality of this theory, a series of direct shear tests with different reinforcing particle diameter and volume fraction ratio are carried out. Theoretical analysis and experimental results showed that the interaction among particles of differing size and composition is the basic reason for the size effect of soils. Furthermore, the stress concentration and bypass phenomena of the matrix enhance the shear strength of a soil, and the volume ratio of reinforcing particles has an obvious impact on the shear strength. In addition, the newly proposed shear-strength theory agrees well with experimental values.

• Advances in Computational Design
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• v.8 no.2
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• pp.97-112
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• 2023

The Finite Element (FE) modeling of Reinforced Concrete (RC) under seismic loading has a sensitive impact in terms of getting good contribution compared to experimental results. Several idealized model types for simulating the nonlinear response have been developed based on the plasticity distribution alone the model. The Continuum Models are the most used category of modeling, to understand the seismic behavior of structural elements in terms of their components, cracking patterns, hysteretic response, and failure mechanisms. However, the material modeling, contact and nonlinear analysis strategy are highly complex due to the joint operation of concrete and steel. This paper presents a numerical simulation of a chosen RC column under monotonic and cyclic loading using the FE Abaqus, to assessthe hysteretic response and failure mechanisms in the RC columns, where the perfect bonding option is used for the contact between concrete and steel. While results of the numerical study under cyclic loading compared to experimental tests might be unsuccessful due to the lack of bond-slip modeling. The monotonic loading shows a good estimation of the envelope response and deformation components. In addition, this work further demonstrates the advantage and efficiency of the damage distributions since the obtained damage distributions fit the expected results.

• Coupled systems mechanics
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• v.12 no.2
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• pp.183-197
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• 2023

Scarce research has been published on crack propagation fracture of flywheels manufactured with carbon fiber-reinforced polymers. The present work deals with a calculation method to determine the conditions for which a crack propagates in the axial direction of the flywheel. The assumptions are: flywheels made with just a single thick ply or ply clustering laminates, oriented following the hoop direction; a single crack is analyzed in the plane defined by the hoop and axial directions; the crack starts close to one of the free edges; its axial length is initially large enough so that its tip is far away from that free edge, and the crack expands the entire circumferential perimeter and keeps its concentric position. The developed method provides information for a good design of flywheels. It is concluded that a fracture-based crack propagation criterion generally occurs at a lower speed than a stress-based criterion. Also, that the evolution of failure with thickness using the fracture criterion is exponential, demonstrating that thin flywheels are relatively not sensitive to crack propagation, whereas thick ones are very prone.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.73.2-73.2
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• 2019

The physical origin of low escape fractions of ionizing radiation derived from Lyman-break galaxies (LBGs) at z ~ 3 - 4 is a puzzle in the theory of reionization. We perform idealized disk galaxy simulations to investigate how galactic properties, such as metallicity and gas mass, affect the escape of Lyman continuum (LyC) photons using radiation-hydrodynamic code RAMSES-RT, with strong stellar feedback. We find that the luminosity-weighted escape fraction from a metal-poor (Z=0.002) galaxy embedded in a halo of mass M_h ~ 10¹¹ M_⊙ is 〈f^3D_esc〉 ~ 8%. However, when the gas metallicity is increased to Z=0.02, the escape fraction is significantly reduced to 〈f^3D_esc〉 ~ 1%, as young stars are enshrouded by their birth clouds for a longer period of time. On the other hand, increasing the gas mass by a factor of 5 leads to 〈f^3D_esc〉 ~ 4%, as LyC photons are only moderately absorbed by the thicker disk. Our experiments seem to suggest that high metallicity is primarily responsible for the low escape fractions observed from LBGs, supporting the scenario in which the escape fraction has a negative correlation with halo mass. Indeed, our simulated galaxy with the typical metallicity of LBGs (Z=0.006) shows the relative escape fraction of 8%, consistent with recent observations of galaxies with M₁₅₀₀ = -20.

• Earthquakes and Structures
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• v.24 no.6
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• pp.393-404
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• 2023

This paper presents the application of hybrid-simulation-based adapter elements for the non-linear two-scale analysis of reinforced concrete frames with masonry infills under seismic-like demands. The approach provides communication and distribution of the computations carried out by two or more remote or locally distributed numerical models connected through the OpenFresco Framework. The modeling consists of a global analysis formed by macro-elements to represent frames and walls, and to reduce global degrees of freedom, portions of the structure that require advanced analysis are substituted by experimental elements and dimensional couplings acting as interfaces with their respective sub-assemblies. The local sub-assemblies are modeled by solid finite elements where the non-linear behavior of concrete matrix and masonry infill adopt a continuum damage representation and the reinforcement steel a discrete one, the conditions at interfaces between concrete and masonry are considered through a contact model. The methodology is illustrated through the analysis of a frame-wall system subjected to lateral loads comparing the results of using macro-elements, finite element model and experimental observations. Finally, to further assess and validate the methodology proposed, the paper presents the pushover analysis of two more complex structures applying both modeling scales to obtain their corresponding capacity curves.

• Geomechanics and Engineering
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• v.34 no.5
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• pp.529-545
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• 2023

The coupled soil-pile-structure seismic response is recently in the spotlight of researchers because of its extensive applications in the different fields of engineering such as bridges, offshore platforms, wind turbines, and buildings. In this paper, a simple analytical model is developed to evaluate the dynamic performance of seismically isolated bridges considering triple interactions of soil, piles, and bridges simultaneously. Novel expressions are proposed to present the dynamic behavior of pile groups in inhomogeneous soils with various shear modulus along with depth. Both cohesive and cohesionless soil deposits can be simulated by this analytical model with a generalized function of varied shear modulus along the soil depth belonging to an inhomogeneous stratum. The methodology is discussed in detail and validated by rigorous dynamic solution of 3D continuum modeling, and time history analysis of centrifuge tests. The proposed analytical model accuracy is guaranteed by the acceptable agreement between the experimental/numerical and analytical results. A comparison of the proposed linear model results with nonlinear centrifuge tests showed that during moderate (frequent) earthquakes the relative differences in responses of the superstructure and the pile cap can be ignored. However, during strong excitations, the response calculated in the linear time history analysis is always lower than the real conditions with the nonlinear behavior of the soil-pile-bridge system. The current simple and efficient method provides the accuracy and the least computational costs in comparison to the full three-dimensional analyses.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.34.2-34.2
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• 2020

Reverberation mapping is one of the best ways to investigate the physical mechanism of broad-line regions around central supermassive black holes of active galactic nuclei (AGNs). It is usually used to estimate the masses of supermassive black holes. Although spectroscopic reverberation mapping has used to study dozens of AGN, spectroscopic monitoring campaign of large sample is expansive. Here, we present results of photometric reverberation mapping with medium-band photometry. We monitored five nearby AGN which were already studied with H-alpha emission line. Observation has been performed for ~3 months with ~3 days cadence using three medium-band filters installed in LSGT (Lee Sang Gak Telescope; 0.43m). We found 0.01-0.08 magnitude variations from differential photometry. Also time-lags between continuum light-curves and H-alpha emission line light-curves are found using JAVELIN software. The result shows that our study and previous studies are consistent within uncertainty range. In the near future, medium-band photometric reverberation mapping seems useful to study large AGN samples. We will present preliminary result of following study that report new time lag measurement of six AGNs in the similar way.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.63.2-63.2
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• 2020

FLASH is a blind neutral hydrogen (HI) absorption line survey, eventually targeting about 100,000 background radio continuum sources in the entire southern sky using the full 36-antenna of the Australian Square Kilometre Array Pathfinder (ASKAP). Our primary goal is to search for associated and intervening HI absorption lines in the intermediate redshift range 0.4 < z < 1.0. The survey aims to understand the evolution of HI gas in galaxies as well as various physical mechanisms in active galactic nuclei, such as accretion and feedback processes. In this poster, we give an overview of the FLASH survey and present the preliminary results from our first 100-hrs of pilot observations. The latest survey data covers 1,000 square degrees and is ideal for validating observation and data processing in the continuous 300MHz-width low frequency ASKAP band (700-1000MHz). One of the crucial objectives of the pilot survey is to establish the analysis methodology that will be applied to upcoming large absorption surveys in the future. We discuss our data quality validation and present some detections of associated/intervening HI absorption lines. These absorption lines allow us to trace the cold gas properties of active and normal galaxies at higher redshifts where the HI emission line is too weak to be detectable.

• Steel and Composite Structures
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• v.44 no.4
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• pp.519-529
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• 2022

Sandwich structures with the superior mechanical properties such as high stiffness and strength-to-weight ratio, good thermal insulation, and high energy absorption capacity are used today in aerospace, automotive, marine, and civil engineering industries. These structures are composed of moderately stiff, thin face sheets that withstand the majority of transverse and in-plane loads, separated by a thick, lightweight core that resists shear forces. In this research, the finite element technique is used to simulate a sandwich panel with a truss core under axial compressive stress using ABAQUS software. A review of past experimental studies shows that the bondline between the core and face sheets plays a vital role in the critical failure load. Therefore, this modeling analyzes the damage initiation modes and debonding between face sheet and core by cohesive surface contact with traction-separation model. According to the results obtained from the modeling, it can be observed that the adhesive stiffness has a significant influence on the critical failure load of the specimens. To achieve the full strength of the structure as a continuum, a lower limit is obtained for the adhesive stiffness. By providing this limit stiffness between the core and the panel face sheets, sudden failure of the structure can be prevented.