• Communications of the Korean Mathematical Society
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• v.39 no.1
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• pp.149-160
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• 2024

In this paper, we give sufficient conditions for the generalized Ornstein-Uhlenbeck operators perturbed by regular potentials and inverse square potentials A_Φ,G,V,c=∆-∇Φ·∇+G·∇-V+c|x|^-2 with a suitable domain generates a quasi-contractive, positive and analytic C₀-semigroup in L^p(ℝ^N , e^-Φ(x)dx), 1 < p < ∞. The proofs are based on an L^p-weighted Hardy inequality and perturbation techniques. The results extend and improve the generation theorems established by Metoui [7] and Metoui-Mourou [8].

• Pediatric Gastroenterology, Hepatology & Nutrition
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• v.27 no.3
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• pp.137-145
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• 2024

Stunting, a condition characterized by impaired growth and development in children, remains a major public health concern worldwide. Over the past decade, emerging evidence has shed light on the potential role of gut microbiota modulation in stunting. Gut microbiota dysbiosis has been linked to impaired nutrient absorption, chronic inflammation, altered short-chain fatty acid production, and perturbed hormonal and signaling pathways, all of which may hinder optimal growth in children. This review aims to provide a comprehensive analysis of existing research exploring the bidirectional relationship between stunting and the gut microbiota. Although stunting can alter the gut microbial community, microbiota dysbiosis may exacerbate it, forming a vicious cycle that sustains the condition. The need for effective preventive and therapeutic strategies targeting the gut microbiota to combat stunting is also discussed. Nutritional interventions, probiotics, and prebiotics are among the most promising approaches to modulate the gut microbiota and potentially ameliorate stunting outcomes. Ultimately, a better understanding of the gut microbiota-stunting nexus is vital for guiding evidence-based interventions that can improve the growth and development trajectory of children worldwide, making substantial strides toward reducing the burden of stunting in vulnerable populations.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.11
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• pp.6406-6411
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• 2014

This paper presents the analytical-FE (finite element) squeal model, which can provide the efficient simulation time and accuracy. The system geometry and the extraction of the vibration modes were constructed using the finite element method. Instead, the friction contact model was derived from theoretical contact kinematics of the rotating disc and the stationary pads. This modeling procedure was incorporated into the perturbed equations of motion based on the finite elements of the system. Throughout the analytical-FE squeal model, the accuracy of linear stability analysis and the simulation time of FE squeal analysis were improved. In addition, the sensitivity of contact stiffness on brake squeal and the mode-coupling mechanism were provided by the system parameter study.

• Fisheries and Aquatic Sciences
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• v.3 no.2
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• pp.143-150
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• 2000

Assuming that summer surface waters in the South Sea (northern East China Sea) are formed mostly by a mixing of three source water (Changjiang Discharge Water; Kuroshio Water and Yellow Sea Surface Water) we apply optimum multiparameter (OMP) analysis to calculate the mixing ratio of each source water to a given surface water. Since OMP requires more parameters than the number of water types (three in this study), we utilize two radium isotopes of dissolved $^{226}Ra\;and\;^{228}Ra$ along with temperature and salinity. Parameter values of each source water are deduced from in situ and historical data. Results with three source of waters on the surface waters are quite promising with less than $1\%$ of unanswered portions. Results not only reproduce the measured temperature and salinity faithfully but also discern the water masses of similar T and S according to their source water mixing. Extending OMP analysis to a whole water column obviously requires more parameters because more source waters are involved in the water mass formation. Original OMP routine utilized dissolved oxygen and nutrients. However, they seem to be perturbed too much by biological activities in the case of shallow waters. We discussed the use of other potential parameters. Also the benefit of parameter substitution is briefly introduced for the future OMP application on shallow waters.

• Computers and Concrete
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• v.21 no.4
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• pp.441-449
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• 2018

FE models for complex or large-scaled structures that need detailed modeling of structural components are usually constructed using commercial analysis softwares. Updating of such FE model by conventional sensitivity-based methods is difficult since repeated computation for perturbed parameters and manual calculations are needed to obtain sensitivity matrix in each iteration. In this study, an FE model updating procedure avoiding such difficulties by using response surface (RS) method and a Pareto-based multiobjective optimization (MOO) was formulated and applied to FE models constructed with a commercial analysis package. The test building is a low-rise reinforced concrete building that has been seismically retrofitted. Dynamic properties of the building were extracted from vibration tests performed before and after the seismic retrofits, respectively. The elastic modulus of concrete and masonry, and spring constants for the expansion joint were updated. Two RS functions representing the errors in the natural frequencies and mode shape, respectively, were obtained and used as the objective functions for MOO. Among the Pareto solutions, the best compromise solution was determined using the TOPSIS (Technique for Order of Preference by Similarity to Ideal Solution) procedure. A similar task was performed for retrofitted building by taking the updating parameters as the stiffness of modified or added members. Obtained parameters of the existing building were reasonably comparable with the current code provisions. However, the stiffness of added concrete shear walls and steel section jacketed members were considerably lower than expectation. Such low values are seemingly because the bond between new and existing concrete was not as good as the monolithically casted members, even though they were connected by the anchoring bars.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.2
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• pp.182-191
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• 2001

The paper describes the improvement on concurrent subspace optimization(CSSO) via automatic differentiation. CSSO is an efficient strategy to coupled multidisciplinary design optimization(MDO), wherein the original design problem is non-hierarchically decomposed into a set of smaller, more tractable subspaces. Key elements in CSSO are consisted of global sensitivity equation, subspace optimization, optimum sensitivity analysis, and coordination optimization problem that require frequent use of 1st order derivatives to obtain design sensitivity information. The current version of CSSO adopts automatic differentiation scheme to provide a robust sensitivity solution. Automatic differentiation has numerical effectiveness over finite difference schemes tat require the perturbed finite step size in design variable. ADIFOR(Automatic Differentiation In FORtran) is employed to evaluate sensitivities in the present work. The use of exact function derivatives facilitates to enhance the numerical accuracy during the iterative design process. The paper discusses how much the automatic differentiation based approach contributes design performance, compared with traditional all-in-one(non-decomposed) and finite difference based approaches.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1993.10a
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• pp.77-83
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• 1993

In this paper, the dynamics of a 2-DOF not 1:1 resonant Hamiltonian system are studied. In the first part of the work, the behaviors of special periodic orbits called normal modes are examined by means of the harmonic balance method and their approximate stability ar analyzed by using the Synge's concept named stability in the kinematico-statical sense. Secondly, the global dynamics of the system for low and high energy are studied in terms of a perturbation analysis and Poincare' maps. In this part, one can see that the unstable normal mode generates chaotic motions resulting from the transverse intersections of the stable and unstable manifolds. Although there exist analytic methods for proving the existence of infinitely many periodic orbits, chaos, they cannot be applied in our case and thus, the Poincare' maps constructed by direct numerical integrations are utilized fot detecting chaotic motions. In the last part of the work, the existence of arbitrarily many periodic orbits of the system are proved by using a subharmonic Melnikov's method. We also study the possibility of the breakdown of invariant KAM tori only when h>h$_{0}$ (h$_{0}$:bifurcating energy) and investigate the generality of the destruction phenomena of the rational tori in the systems perturbed by stiffness and inertial coupling.

• Bulletin of the Korean Chemical Society
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• v.13 no.2
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• pp.131-135
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• 1992

High-Tc superconducting materials, $HoBa_2Cu_3O_{7-x}F_y$ with $0.0{\leq}y{\leq}0.5$, were synthesized by ceramic method and studied by X-ray diffraction, thermogravimetric analysis, differential thermal analysis, scanning electron microscopy and resistivity measurement. From the X-ray diffraction data, it was found that the samples had only single phase of which lattice volumes were decreased in proportional to the amount of fluorine, which indicated that the relatively small fluorine atoms are effectively substituted for the oxygen sites. Also, an anomalous phenomenon appeared that the peak intensities of (001) planes were greatly increased as fluorine contents increased. SEM photographs revealed that the grain sizes were enlarged progressively with fluorine contents. This fact could be explained along with DTA & TGA data that the incorporation of fluorine gave rise to lowering the melting point. Tc decreased as the incorporation of fluorine content increased. This implies that the superconducting electrons are perturbed due to the substitution of electronegative fluorine atom.

• Korean Chemical Engineering Research
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• v.48 no.4
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• pp.519-533
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• 2010

Activity oefficients and solubilities of L-Alanine in aqueous solutions containing each of four electrolytes(NaCl, KCl, $NaNO_3$ and $KNO_3$) were measured at 298.15 K. The measurements of activity coefficients were carried out in the electrochemical cell coupled with two ion-selective electrodes(cation and anion), and the solubilities were measured by the gravimetric analysis of saturated solutions in equilibrium with the solid phase of L-alanine. To model the activity coefficients and solubilities of amino acid in the amino acid/electrolyte aqueous solutions, thermodynamic relations of the residual Helmholtz free energy in the amino acid/electrolyte aqueous solutions were developed based on the perturbed-chain statistical associating fluid theory(PC-SAFT) combined with the primitive mean spherical approximation(primitive-MSA). In the present model, it is assumed that the zwitterions of L-alanine are associated with each other and cross-associated with water molecules, and also cross-associated with the cation and anion dissociated from an electrolyte(inorganic salt). The activity coefficients and solubilities of L-Alanine calculated from the theoretical model proposed in this work are found to be well agreeable with experimental data.

• Journal of computational fluids engineering
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• v.6 no.2
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• pp.22-31
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• 2001

The two-dimensional unsteady incompressible viscous flow behind rectangular bluff bodies between two parallel plates was analyzed numerically. The steady state flow and the vortex flow behind rectangular bluff bodies in the channel were investigated for two regimes i.e., the laminar(Re = 100, 300, 500) and the turbulent flows(Re = 10⁴∼10/sup 6/). The vortex shedding was generated by a physical disturbance(6%) numerically imposed at the rear of the bluff bodies for a short time. It was observed that the perturbed flow became periodic after a transient period. And in the case of unsteady inflow, the sinusoidal pulsatile flow was applied as the inlet condition in the turbulent flow of Reynolds number of 1.0×10/sup 5/. FLUENT code was employed to solve the problems. The power-law scheme was used to get stable linearized equations and the PISO algorithm was applied to finding the solution of them.