• Earthquakes and Structures
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• v.24 no.4
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• pp.259-274
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• 2023

In this paper, mechanical properties of periodic foundation made of concrete and rubber are investigated by a parametric study using the finite element method (FEM). Periodic foundation is a special type of seismic isolation foundation used in civil engineering, which is inspired by the meso-scale structure of phononic crystals in solid-state physics. This type of foundation is capable of reducing the seismic wave propagating though the foundation, therefore providing additional protection for the structures. In the FEM analysis, layered periodic foundation is frequently modelled due to its simplicity in numerical modeling. However, the isolation effect of periodic foundation on nuclear power plant has not been fully discussed to the best knowledge of authors. In this work, we construct four numerical models of nuclear power plant with different foundations to investigate the seismic isolation effects of periodic foundations. The results show that the layered periodic foundation can increase the natural period of the nuclear power plant like traditional base isolation systems, which is beneficial to the structures. In addition, the seismic response of the nuclear power plant can also be effectively reduced in both vertical and horizontal directions when the frequencies of the incident waves fall into some specific frequency bandgaps of the periodic foundation. Furthermore, it is demonstrated that the layered periodic foundation can reduce the amplitude of the floor response spectrum, which plays an important role in the protection of the equipment.

• Annals of Clinical Neurophysiology
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• v.13 no.1
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• pp.26-30
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• 2011

Although the pathophysiologic mechanism is unknown, there has been long-running debate on whether periodic discharges such as periodic lateralized epileptiform discharges (PLEDs) and generalized periodic epileptiform discharges are an ictal or interictal EEG pattern. The goal of this review is to give evidence that such periodic discharges on EEG are not ictal phenomenon and just represent underlying acute brain damage. This review includes coma with epileptiform EEG pattern and its prognostic and therapeutic implications. Based on previous reports, rather than taking the view PLEDs represent either an underlying ictal process or an electrographic correlate of neuronal injury, it would be more reasonable that PLEDs are considered as a dynamic pathophysiological state in which unstable neurobiological processes create an ictal-interictal continuum.

• Journal of Auto-vehicle Safety Association
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• v.4 no.2
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• pp.17-21
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• 2012

The periodic technical vehicle inspection is to prevent the accident through the finding and fixing the defects of the vehicle. The periodic technical vehicle inspection in Korea was studied for assessing the adequacy of the inspection frequency. The inspection frequencies of many countries including EU, USA and Japan were compared. The average mileages by the vehicle usage and type were represented. The warranty period and recommended replacement period of parts of the domestic auto makers was studied. Currently, the inspection frequency for the periodic technical vehicle inspection in Korea is appropriate. The pass-fail rate and the cost-benefit analysis for the periodic technical inspection in Korea will be needed in the decision making process for the inspection frequency.

• Journal of Applied Reliability
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• v.6 no.3
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• pp.195-203
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• 2006

This paper deals with cost analysis model in periodic maintenance policy. The repair policy with minimal repair is considered as follow : as the occurrence of failure between minimal repair and periodic interval time, unit is replaced by a new unit before the periodic maintenance time comes. Then total expected cost per unit time is calculated according to time delta t in a view of customer's. The total expected costs are included repair and usage cost : operating, fixed, minimal repair, periodic maintenance and new unit expected cost. Numerical example is shown in which failure time of item has Normal distribution.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.41 no.5
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• pp.50-58
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• 2009

Periodic variation of local paper structure was evaluated using two-dimensional fast Fourier transform (FFT) and spectral analysis. Since the periodic variation could originate from various sources and have different magnitudes and patterns depending on the origins, a complete analysis of local paper structure properties such as local grammage, local thickness, local apparent density and surface topography was proposed in this study. For a commercial copy paper, the individual periodic patterns for each local structural property were identified by using inverse FFT spectrums of the filtered spectrum. The spectral analysis of newsprint sample provided the period of variation quantitatively, which was useful in comparing the origins of the individual periodic patterns of the local structural properties.

• Structural Engineering and Mechanics
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• v.40 no.3
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• pp.373-392
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• 2011

Periodic and quasi-periodic Timoshenko beams on Pasternak foundation are investigated using the differential quadrature method. Not only band gaps in the beams but also the dynamic response of them is analyzed. Numerical results show that vibration in periodic beams can be dramatically attenuated when the exciting frequency falls into band gaps. Different from the band structures of periodic beams without foundation, the so-called critical frequency was found because of the Pasternak foundation. Its physical meaning was explained in detail and a useful formula was given to calculate the critical frequency. Additionally, a comprehensive parameter study is conducted to highlight the influence of foundation modulus on the band gaps.

• Korean Journal of Mathematics
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• v.28 no.2
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• pp.223-240
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• 2020

The paper is concerned with periodic linear evolution equations of the form x"(t) = A(t)x(t)+f(t), where A(t) is a family of (unbounded) linear operators in a Banach space X, strongly and periodically depending on t, f is an almost (or asymptotic) almost periodic function. We study conditions for this equation to have almost periodic solutions on ℝ as well as to have asymptotic almost periodic solutions on ℝ⁺. We convert the second order equation under consideration into a first order equation to use the spectral theory of functions as well as recent methods of study. We obtain new conditions that are stated in terms of the spectrum of the monodromy operator associated with the first order equation and the frequencies of the forcing term f.

• Structural Engineering and Mechanics
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• v.18 no.5
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• pp.671-690
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• 2004

An assumed strain finite strip method(FSM) using the non-periodic B-spline for a shell is presented. In the present method, the shape function based on the non-periodic B-splines satisfies the Kronecker delta properties at the boundaries and allows to introduce interior supports in much the same way as in a conventional finite element formulation. In the formulation for a shell, the geometry of the shell is defined by non-periodic B3-splines without any tangential vectors at the ends and the penalty function method is used to incorporate the drilling degrees of freedom. In this study, new assumed strain fields using the non-periodic B-spline function are proposed to overcome the locking problems. The strip formulated in this way does not posses any spurious zero energy modes. The versatility and accuracy of the new approach are demonstrated through a series of numerical examples.

• Journal of electromagnetic engineering and science
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• v.9 no.1
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• pp.46-52
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• 2009

This paper conducts a study on the frequency-dependent filtering and blocking effects of a variety of periodic structures, dubbed frequency selective surface(FSS). The periodic structures of interest are 1D and 2D repeated patterns of metal patches or slots sitting on the interface between the two different regions in the layered media which will show the capacitive or inductive behaviors and incorporated with the electromagnetic bandgap(EBG) geometry as another stratified media. Besides the normal substances so called double positive(DPS)-type in the layered media, metamaterials of double negative(DNG) are considered as layering components on the purpose of investigating the unusual electromagnetic phenomena. Frequency responses of transmission(absorption in terms of scattering) and reflection will be calculated by a numerical analysis which can be validated by the comparison with the open literature and demonstrated for the periodic structures embedding metamaterials or not. Most importantly, numerous examples of FSS will present the useful guidelines to have absorption or reflection properties in the frequency domain.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.3
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• pp.329-339
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• 1999

LPXDA(Log-Periodic X Dipole Antenna), consisting of X dipole elements, was proposed as a Log-periodic antenna with short boom length and good Performance relative to LPDA(Log-Periodic Dipole Antenna) . LPXDA for operating frequency band of 500 MHz~l,000 MHz was designed and radiation characteristics of the designed antenna was analyzed by moment method, and compared with LPDA characteristics. The proposed LPXDA, in this paper, was found to have shorter boom length by 20% and better radiation characteristics with variations of frequency relative to the LPDA. The calculated results show good agreement with measurements.