• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.53.2-53.2
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• 2011

We combine the physics of the ellipsoidal collapse model with the excursion set theory to study the shapes of dark matter halos. In particular, we develop an analytic approximation to the nonlinear evolution that is more accurate than the Zeldovich approximation; we introduce a planar representation of halo axis ratios, which allows a concise and intuitive description of the dynamics of collapsing regions and allows one to relate the final shape of a halo to its initial shape; we provide simple physical explanations for some empirical fitting formulae obtained from numerical studies. Comparison with simulations is challenging, as there is no agreement about how to define a non-spherical gravitationally bound object. Nevertheless, we find that our model matches the conditional minor-to-intermediate axis ratio distribution rather well, although it disagrees with the numerical results in reproducing the minor-to-major axis ratio distribution. In particular, the mass dependence of the minor-to-major axis distribution appears to be the opposite to what is found in many previous numerical studies, where low-mass halos are preferentially more spherical than high-mass halos. In our model, the high-mass halos are predicted to be more spherical, consistent with results based on a more recent and elaborate halo finding algorithm, and with observations of the mass dependence of the shapes of early-type galaxies. We suggest that some of the disagreement with some previous numerical studies may be alleviated if we consider only isolated halos.

• Smart Structures and Systems
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• v.20 no.6
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• pp.669-682
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• 2017

The normalised version of bispectrum, the so-called bicoherence, has often proved a reliable method of damage detection on engineering applications. Indeed, higher-order spectral analysis (HOSA) has the advantage of being able to detect non-linearity in the structural dynamic response while being insensitive to ambient vibrations. Skewness in the response may be easily spotted and related to damage conditions, as the majority of common faults and cracks shows bilinear effects. The present study tries to extend the application of HOSA to damage localisation, resorting to a neural network based classification algorithm. In order to validate the approach, a non-linear finite element model of a 4-meters-long cantilever beam has been built. This model could be seen as a first generic concept of more complex structural systems, such as aircraft wings, wind turbine blades, etc. The main aim of the study is to train a Neural Network (NN) able to classify different damage locations, when fed with bispectra. These are computed using the dynamic response of the FE nonlinear model to random noise excitation.

• Advances in aircraft and spacecraft science
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• v.3 no.1
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• pp.95-112
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• 2016

This paper presents the free vibration analysis of damaged beams by means of 1D (beam) advanced finite element models. The present 1D formulation stems from the Carrera Unified Formulation (CUF), and it leads to a Component-Wise (CW) modelling. By means of the CUF, any order 2D and 1D structural models can be developed in a unified and hierarchical manner, and they provide extremely accurate results with very low computational costs. The computational cost reduction in terms of total amount of DOFs ranges from 10 to 100 times less than shell and solid models, respectively. The CW provides a detailed physical description of the real structure since each component can be modelled with its material characteristics, that is, no homogenization techniques are required. Furthermore, although 1D models are exploited, the problem unknown variables can be placed on the physical surfaces of the real 3D model. No artificial surfaces or lines have to be defined to build the structural model. Global and local damages are introduced by decreasing the stiffness properties of the material in the damaged regions. The results show that the proposed 1D models can deal with damaged structures as accurately as a shell or a solid model, but with far lower computational costs. Furthermore, it is shown how the presence of damages can lead to shell-like modal shapes and torsional/bending coupling.

• ETRI Journal
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• v.45 no.3
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• pp.543-550
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• 2023

Electrostatic discharge (ESD) testing for human body model tests is an essential part of the reliability evaluation of electronic/electrical devices and components. However, global environmental concerns have called for the need to replace the mercury-wetted relay switches, which have been used in ESD testers. Therefore, herein, we propose an ESD tester using metal oxide semiconductor-controlled thyristor (MCT) devices with a significantly higher rising rate of anode current (di/dt) characteristics. These MCTs, which have a breakdown voltage beyond 3000 V, were developed through an in-house foundry. As a replacement for the existing mercury relays, the proposed ESD tester with the developed MCT satisfies all the requirements stipulated in the JS-001 standard for conditions at or below 2000 V. Moreover, unlike traditional relays, the proposed ESD tester does not generate resonance; therefore, no additional circuitry is required for resonant removal. To the best of our knowledge, the proposed ESD tester is the first study to meet the JS-001 specification by applying a new switch instead of an existing mercury-wetted relay.

• The Korean Journal of Physiology and Pharmacology
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• v.22 no.1
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• pp.81-89
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• 2018

This study evaluated the anti-asthmatic activities of 2,6-di-tert-butyl-4-hydroxymethylphenol (DBHP) that is a potent phenolic antioxidant in edible vegetable oil. The effects of DBHP on bronchial asthma were evaluated by determining the specific airway resistance (sRaw) and tidal volume (TV) during the immediate asthmatic response (IAR) and the late-phase asthmatic response (LAR) in guinea pigs with aerosolized ovalbumin-induced asthma. Recruitment of leukocytes and the levels of biochemical inflammatory mediators were determined in the bronchoalveolar lavage fluids (BALFs), and histopathological surveys performed in lung tissues. DBHP significantly inhibited the increased sRaw and improved the decreased TV on IAR and LAR, and also inhibited recruitment of eosinophils and neutrophils into the lung, and release of biochemical inflammatory mediators such as histamine and phospholipase $A_2$ from these infiltrated leukocytes, and improved pathological changes. However, anti-asthmatic activities of DBHP at oral doses of 12.5 to 50 mg/kg was less than those of dexamethasone (5 mg/kg, p.o.) and cromoglycate (10 mg/kg, p.o.), but more potent or similar to that of salbutamol (5 mg/kg, p.o.). These results in the present study suggest that anti-asthmatic effects of DBHP in the guinea pigs model of OVA-induced asthmatic responses principally are mediated by inhibiting the recruitments of the leukocytes and the release of biochemical inflammatory mediators from these infiltrated leukocytes.

• Journal of Environmental Science International
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• v.25 no.11
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• pp.1485-1491
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• 2016

PSf/D2EHPA/CNT beads were prepared by immobilizing di-(2-ethylhexyl)-phosphoric acid (D2EHPA) and carbon nanotubes (CNT) on polysulfone (PSf) and used to remove Cu(II) from aqueous solutions. Optimum pH was in the range of 4 to 6. The removal kinetic of Cu(II) by the prepared PSf/D2EHPA/CNT beads was mainly governed by internal diffusion, and the diffusion coefficient of Cu(II) by PSf/D2EHPA/CNT beads was found to be $2.19{\times}10^{-4}{\sim}2.64{\times}10^{-4}cm^2/s$. The Langmuir isotherm model predicted the experimented data well. The maximum removal capacity of Cu(II) obtained from this isotherm was 7.32 mg/g. Calculated thermodynamic parameters such as ${\Delta}G^o$, ${\Delta}H^o$ and ${\Delta}S^o$ showed that the adsorption of Cu(II) ions onto PSf/D2EHPA/CNT beads was feasible, spontaneous and endothermic at 293-323 K.

• Structural Engineering and Mechanics
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• v.61 no.5
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• pp.625-635
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• 2017

Sets of nonlinear formulations together with an energy-based damage index (DI) are proposed to model the behavior and quantify the damage of the confined and unconfined concretes under monotonic and cyclic loading. The proposed formulations and DI can be employed in numerical simulations to determine the stresses and the damages to the fibers or the layers within the sections of reinforced concrete (RC) components. To verify the proposed formulations, an adaptive finite element computer program was generated to simulate the RC structures subjected to monotonic and cyclic loading. By comparing the simulated and the experimental test results, on both the full-scale structural members and concrete cylindrical samples, the proposed uniaxial behavior modeling formulations for confined and unconfined concretes under monotonic and cyclic loading, based on an iterative process, were accordingly adjusted, and then validated. The proposed formulations have strong mathematical structures and can readily be adapted to achieve a higher degree of precision by improving the relevant coefficients based on more precise tests. To apply the proposed DI, the stress-strain data of concrete elements is required. It can easily be calculated by using the proposed nonlinear constitutive laws for confined and unconfined concretes in this paper.

• Advances in aircraft and spacecraft science
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• v.4 no.4
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• pp.401-419
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• 2017

This paper presents the main outcomes of the preliminary development of the Anuloid, an innovative disk-shaped VTOL aircraft. The Anuloid has three main features: lift is provided by a ducted fan powered by a turboshaft; control capabilities and anti-torque are due to a system of fixed and movable surfaces that are placed in the circular internal duct and the bottom portion of the aircraft; the Coanda effect is exploited to enable the control capabilities of such surfaces. In this paper, results from CFD analyses and wind tunnel tests are presented. Horizontal and vertical flights were considered, including accelerated flight. Particular attention was paid to the experimental analysis of the Coanda effect via a reduced scale 3D printed model. The results suggest that the Coanda effect is continuously present at the lower surface of the Anuloid and may be exploited for the control of the aircraft. Also, very complex 3D flows may develop around the aircraft.

• Advances in aircraft and spacecraft science
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• v.6 no.6
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• pp.443-461
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• 2019

This communication investigates exact and distorted similitudes and the related scaling laws for the analysis of both dynamic response and radiated power of rectangular plates. The response of a given panel in similitude from another one is determined from a generalization of the modal approach, allowing the use of mode shapes, natural frequencies and finally radiation functions in order to establish appropriate scaling laws. Analytical models of simply supported rectangular plates are used to produce both original and replica model responses under point mechanical excitation. Emphasis is then especially put on laboratory experiments which are performed on baffled simply supported aluminum panels under mechanical excitations. All the six possible scaling directions, i.e. predicting a plate vibroacoustic reponse from another plate, are reported. All obtained results show that structural response or radiated sound power of a given plate can be both recovered with satisfactory accuracy by using the related scaling laws, even if parent models are used.

• Computers and Concrete
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• v.18 no.6
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• pp.1175-1194
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• 2016

Nonlinear models, capable of taking into account all the phenomena involved in the cracking and in the failure of lightly reinforced concrete beams, are nowadays available for a rigorous calculation of the minimum reinforcement. To simplify the current approaches, a new procedure is proposed in this paper. Specifically, the ductility index, which is lower than zero for under-reinforced concrete beams in bending, is introduced. The results of a general model, as well as the data measured in several tests, reveal the existence of two linear relationships between ductility index, crack width, and the amount of steel reinforcement. The above relationships can be applied to a wide range of lightly reinforced concrete beams, regardless of the geometrical dimensions and of the mechanical properties of materials. Accordingly, if only a few tests are combined with this linear relationships, a new design-by-testing procedure can be used to calculate the minimum reinforcement, which guarantees both the control of cracking in service and the ductility at failure.