• Journal of the Korean Mathematical Society
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• v.56 no.6
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• pp.1561-1597
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• 2019

In this paper we introduce the notions of topological entropy and topological pressure for non-autonomous iterated function systems (or NAIFSs for short) on countably infinite alphabets. NAIFSs differ from the usual (autonomous) iterated function systems, they are given [32] by a sequence of collections of continuous maps on a compact topological space, where maps are allowed to vary between iterations. Several basic properties of topological pressure and topological entropy of NAIFSs are provided. Especially, we generalize the classical Bowen's result to NAIFSs ensures that the topological entropy is concentrated on the set of nonwandering points. Then, we define the notion of specification property, under which, the NAIFSs have positive topological entropy and all points are entropy points. In particular, each NAIFS with the specification property is topologically chaotic. Additionally, the ${\ast}$-expansive property for NAIFSs is introduced. We will prove that the topological pressure of any continuous potential can be computed as a limit at a definite size scale whenever the NAIFS satisfies the ${\ast}$-expansive property. Finally, we study the NAIFSs induced by expanding maps. We prove that these NAIFSs having the specification and ${\ast}$-expansive properties.

• Journal of the Korean Mathematical Society
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• v.41 no.6
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• pp.1087-1099
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• 2004

We study the metrical and topological pressure for flows without fixed points on a compact metric space, and get the results as follows: (1) The metrical pressure with respect to an ergodic measure can be defined by (t, $\varepsilon$)-spanning sets. (2) The topological pressure is the supremum of metrical pressures with respect to all ergodic measures. (3) The properties that the topological pressure is zero, nonzero, finite or infinite respectively are invariant under weak equivalence.

• Communications of the Korean Mathematical Society
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• v.20 no.2
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• pp.365-379
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• 2005

The purpose of this paper is to correct erroneous proofs of theorems of He, Lu, Wang and Zheng [1] about the topological pressure of continuous flows without fixed points and to give proofs of some results which are stated in the literature without proofs and thereby to show that their theorems are still true.

• Journal of the Optical Society of Korea
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• v.20 no.1
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• pp.135-139
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• 2016

I propose a vector passive harmonic mode-locked fiber laser based on topological insulator Bi2Se3 interacting with a fiber taper with a diameter of 7 μm. The particles of topological insulator are deposited uniformly onto the fiber taper with light pressure effect. By incorporating the fabricated saturable absorber into an Er-doped fiber laser cavity, stable mode-locked fiber is obtained. Due to the intense evanescent field of the fiber taper, strong confinement of light enhances the nonlinearity of the laser cavity, and passive harmonic mode-locking is performed. I observe a maximum harmonic mode-locking of 356th, corresponding to a frequency of 3.57 GHz. The pulse duration is 824 fs, and the full width at half maximum of the spectrum is about 8.2 nm. The polarization dependent loss of the saturable absorber is ~ 2.5 dB in the wavelength range of the C band. As the cavity contains no other polarization dependent device, the mode-locked laser is functioning in the vector state. The harmonic order vs pump power is investigated. To the best of our knowledge, this report is the highest frequency mode-locked fiber laser based on Bi2Se3. Experimental results indicate that the topological insulator Bi2Se3 functioning with a thin fiber taper is effective for vector harmonic mode-locking.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.8
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• pp.573-578
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• 2010

Topological matrix which reflects characteristics of network connectivity has been widely used in efficient solving for complicated flow network. Using topological matrix, one can easily define continuity at each node of flow network and make algorithm to automatically generate continuity equation of matrix form. In order to analyze flow network completely it is required to satisfy energy conservation in closed loops of flow network. Fundamental cycle retrieving algorithm based on graph theory automatically constructs energy conservation equation in closed loops. However, it is often accompanied by NP-complete problem. In addition, it always needs fundamental cycle retrieving procedure for every structural change of flow network. This paper proposes alternative mathematical method to analyze flow network without fundamental cycle retrieving algorithm. Consequently, the new mathematical method is expected to reduce solving time and prevent error occurrence by means of simplifying flow network analysis procedure.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.4
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• pp.10-17
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• 2000

This work presents an investigation of aerodynamic characteristics of fuel spray injected from a high pressure hollow cone swirl injector into a constant volume chamber. Laser tomography visualization was used to interrogate the fuel and air mixing characteristics and the effect of chamber pressure and temperature increase was analyzed, Preliminary results on spray development showed that mixing effect tends to increase with the increase of injection pressure and chamber gas pressure yielding a decrease of spray penetration and an attenuation of well-defined vortex structure. Topological analysis of the spray structure has been performed to initiate the understanding of mixing and vaporization process. For the present experimental conditions fuel injection pressure and chamber gas pressure appear as the dominant factors which govern the transient mixing characteristics. Moreover spray atmixation characteristics are improved by increasing chamber gas temperature.

• International Journal of Naval Architecture and Ocean Engineering
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• v.3 no.4
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• pp.254-262
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• 2011

This study aims to optimize an arrangement of ship compartments with knowledge-based systems. Though great attention has been shown to the optimization of hull forms in recent years, the study on arrangement design optimization has received relatively little attention. A ship is both an engineering system and a kind of assembly of many spaces. This means that, to design an arrangement of ship compartments, it is necessary to treat not only geometric data but also knowledge on topological relations between spaces and components of a ship. In this regard, we select a suitable knowledge representation scheme for describing ship compartments and their relations, and then develop a knowledge-based system using expert system shell. This new approach is applied to create design variations for optimization on an arrangement of a pressure hull of a submerged vehicle. Finally, we explicate how our approach improves the design process.

• Journal of Multimedia Information System
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• v.5 no.2
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• pp.121-130
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• 2018

We developed multimedia esophageal catheters for use with birds to measure and record ECG and angular velocity while anesthesized, at rest, and in flight. These catheters enable estimates of blood pressure based on readings given by an angular velocity sensor and by RR intervals of ECG affected by EMG. In our experiments, the catheters had the following characteristics: 1. Esophageal catheters offer a topological advantage with 8-dB SNR improvement due to elimination of electromyography (EMG). 2. We observed a very strong correlation between blood pressure and the angular velocity of esophageal catheter axial rotation. 3. The impulse conduction pathway (Purkinje fibers) of the cardiac ventricle has a direction opposite to that of the mammalian pathway. 4. Sympathetic nerves predominate in flight, and RR interval variations are strongly suppressed. The electrophysiological data obtained by this study provided especially the state of the avian autonomic nervous system activity, so we can suspect individual's health condition. If the change of the RR interval was small, we can perform an isolation or screening from the group that prevent the pandemics of avian influenza. This catheter shall be useful to analysis an avian autonomic system, to perform a screening, and to make a positive policy against the massive infected avian influenza.

• Journal of computational fluids engineering
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• v.13 no.1
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• pp.14-20
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• 2008

The flow characteristics around a rudder in open water condition is analyzed by the computational method. Reynolds averaged Navier-Stoke's equation is utilized for the computation. The computational hydrodynamic force coefficients are verified through comparing with the experimental results. The information of these flow characteristics is necessary to predict cavitation and maneuvering performances, to estimate steering gear capacitance, and to get the bending moment which is useful for the structural analysis. The pressure distribution, the three-dimensional flow separation, and the tip vortices are investigated. The pattern of the three-dimensional flow separation is analyzed utilizing a topological rule. The tip vortices are also investigated through a visualization technique.

• Journal of Korea Water Resources Association
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• v.43 no.9
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• pp.769-780
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• 2010

Topological and hydraulic assessments to examine whether required demand and pressure are satisfied and using these assessed results as a criteria have been general methodology for reliability assessment of water distribution systems. However, many of existing studies that used nodal pressure calculated by hydraulic assessment for reliability assessment have two major issues to be solved. The one is that demand-driven analysis was used for hydraulic assessment and the other is that serviceability was not considered for reliability assessment. In addition, all of the studies used pressure-demand analysis which is suitable to hydraulic analysis for water distribution systems under abnormal operating condition considered only available nodal demand for reliability assessment. This means that advantages which can be obtained by pressure-driven analysis are not used properly and efficiently. In this study, new methodology for reliability assessment of water distribution systems using HSPDA model and distance measure method is suggested. This methodology considers both nodal pressure and nodal available demand for reliability assessment. Suggested methodology is applied to two water distribution systems to show its applicability and application results are compared with existing study.