• Journal of Power Electronics
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• v.10 no.1
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• pp.51-57
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• 2010

This paper proposes a new random switching strategy using a DSP TMS320F2812 to reduce the harmonics spectra of single phase switched reluctance motors. The proposed method combines the random turn-on/off angle technique and the random pulse width modulation technique. A harmonic spread factor (HSF) is used to evaluate the random modulation scheme. In order to confirm the effectiveness of the proposed method an experiment was conducted. The experimental results show that the harmonic intensity of the output voltage for the proposed method is better than that for conventional methods.

• Proceedings of the KIEE Conference
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• 2006.10d
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• pp.139-142
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• 2006

This paper describes a new method using random modulated strategies for switched reluctance machines. The proposed method is combined random turn-on, turn-off angle technique and random pulse width modulation technique. The purpose of this proposed method is to decrease harmonic spectrum, and thus reduce the emitted acoustical noise. A random generator is generated by linear congruential generator (LCG) using random pulse position (RPP) scheme. Simulation results show that the harmonic intensity of proposed method is better than that of conventional method.

• Current Optics and Photonics
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• v.2 no.4
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• pp.368-377
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• 2018

In this paper, we evaluate cryptographic properties of a double random phase encoding (DRPE) scheme in the discrete Gyrator domain with avalanche and bit independence criterions. DRPE in the discrete Gyrator domain is reported to have higher security than traditional DRPE in the Fourier domain because the rotation angle involved in the Gyrator transform is viewed as additional secret keys. However, our numerical experimental results demonstrate that the DRPE in the discrete Gyrator domain has an excellent bit independence feature but does not possess a good avalanche effect property and hence needs to be improved to satisfy with acceptable avalanche effect that would be robust against statistical-based cryptanalysis. We compare our results with the avalanche and bit independence criterion (BIC) performances of the conventional DRPE scheme, and improve the avalanche effect of DRPE in the discrete Gyrator domain by integrating a photon counting imaging technique. Although the Gyrator transform-based image cryptosystem has been studied, to the best of our knowledge, this is the first report on a cryptographic evaluation of discrete Gyrator transform with avalanche and bit independence criterions.

• Journal of the Earthquake Engineering Society of Korea
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• v.23 no.1
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• pp.55-70
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• 2019

The phase properties of ground acceleration records from Mw 5.5~6.5 earthquakes are analyzed. The interrelationships between phase properties and significant durations, as well as PGA, are clarified through both of theoretical and empirical approaches. The probabilistic characteristics of phase information is also discussed based on previous studies and it is shown that circular normal distribution is the most appropriate probability distribution for the phase angle and phase difference. Whereas those variates can be modeled by Gaussian random variables. From the survey results on the frequency dependency of the phase statistics, a simple model is introduced, which is possible to express the frequency dependency of phase information. It is also shown that the significant duration can be controlled by appropriately chosen standard deviation of phase difference for 4~8Hz frequency band and additional consideration of phase scattering in higher frequency band through a series of Monte Carlo simulations. The source of phase scattering effect is also pointed out and discussed.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.387-398
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• 2020

In the design stage of the very large container ships, some methodologies for the whipping effects have been developed, but most of them are based on single sea state. We developed a methodology that considers multiple sea states. Fluid-structure Interaction (FSI) analyses with one dimensional structural model were carried out to capture slamming-induced transient whipping behaviors. Because of the nature of random phases of the applied wave spectra, the required period for entire FSI analyses was determined from the convergence study where the whipping effect became stable. Low pass filtering was applied to the transient whipping responses to obtain the hull girder bending moment processes. Peak counting method for the filtered whipping responses was used to obtain collection of the vertical bending moment peaks. The whipping effect from this new method is compared with that from based on single sea state approach. The efficiency and advantage of the new methodology are presented.

• Steel and Composite Structures
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• v.36 no.1
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• pp.87-101
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• 2020

A multi-scale epoxy/CNT/fiberglass annular sector plate is studied in this paper in the view of determining nonlinear forced vibration characteristics. A 3D Mori-Tanaka model is employed for evaluating multi-scale material properties. Thus, all of glass fibers are assumed to have uni-direction alignment and CNTs have random diffusion. The geometry of annular sector plate can be described based on the open angle and the value of inner/outer radius. In order to solve governing equations and derive exact forced vibration curves for the multi-scale annular sector, Jacobi elliptic functions are used. Obtained results demonstrate the significance of CNT distribution, geometric nonlinearity, applied force, fiberglass volume, open angle and fiber directions on forced vibration characteristics of multi-scale annular sector plates.

• Macromolecular Research
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• v.17 no.10
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• pp.757-762
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• 2009

The micro domain structures and crystallization behavior of the binary blends of poly(methyl methacrylate)-b-poly(pentafluorostyrene)-b-poly(methyl methacrylate) (PMMA-PPFS-PMMA) triblock copolymer with a low molecular weight poly(vinylidene fluoride) (PVDF) were investigated by small-angle X-ray scattering (SAXS), small-angle light scattering (SALS), transmission electron microscopy (TEM), optical microscopy, and differential scanning calorimetry (DSC). A symmetric, PMMA-PPFS-PMMA triblock copolymer with a PPFS weight fraction of 33% was blended with PVDF in N,N-dimethylacetamide (DMAc). In the wide range of PVDF concentration between 10.0 and 30.0 wt%, PVDF was completely incorporated within the PMMA micro domains of PMMA-PPFS-PMMA without further phase separation on a micrometer scale. The addition of PVDF altered the phase morphology of PMMA-PPFS-PMMA from well-defined lamellar to disordered. The crystallization of PVDF significantly disturbed the domain structure of PMMA-PPFS-PMMA in the blends, resulting in a poorly-ordered morphology. PVDF displayed unique crystallization behavior as a result of the space constraints imposed by the domain structure of PMMA-PPFS-PMMA. The pre-existing microdomain structures restricted the lamellar orientation and favored a random arrangement of lamellar crystallites.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.2
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• pp.289-296
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• 2001

We propose a method to add phase-modulation to binary amplitude data pages using a twisted-nematic liquid crystal display as a dynamic phase mask. For this, the phase modulation characteristics of the display were examined both theoretically and experimentally, and an unexpected abnormal phenomenon was found experimentally in which the modulation property changed as the incident beam intensity increased. To investigate the characteristics of holographically storing the binary data images, eight pages of holograms were stored at one spot of in un-thick Dupont's photopolymer with angle multiplexing. When phase-modulation-added pages were stored at the Fourier plane, the uniformity of the signal beam at the plane was improved, and thus more holograms can be recorded with our method, compared with the conventional case of using only binary amplitude modulation under the same condition.

• Bulletin of the Korean Chemical Society
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• v.16 no.9
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• pp.873-885
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• 1995

The local structural and thermodynamical properties of blends A-B/H of a diblock copolymer A-B and a homopolymer H are studied using the polymer reference interaction site model (RISM) integral equation theory with the mean-spherical approximation closure. The random phase approximation (RPA)-like static scattering function is derived and the interaction parameter is obtained to investigate the phase transition behaviors in A-B/H blends effectively. The dependences of the microscopic interaction parameter and the macrophase-microphase separation on temperature, molecular weight, block composition and segment size ratio of the diblock copolymer, density, and concentration of the added homopolymer, are investigated numerically within the framework of Gaussian chain statistics. The numerical calculations of site-site interchain pair correlation functions are performed to see the local structures for the model blends. The calculated phase diagrams for A-B/H blends from the polymer RISM theory are compared with results by the RPA model and transmission electron microscopy (TEM). Our extended formal version shows the different feature from RPA in the microscopic phase separation behavior, but shows the consistency with TEM qualitatively. Scaling relationships of scattering peak, interaction parameter, and temperature at the microphase separation are obtained for the molecular weight of diblock copolymer. They are compared with the recent data by small-angle neutron scattering measurements.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.6.2-6.2
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• 2011

Block copolymer (BCP) self-assembly in a film geometry has recently been the focus of increased research interest due to their potential use as templates and scaffolds for the fabrication of nanostructured materials. The phase behavior in a thin film geometry that confines polymer chains to the interfaces will be influenced by the interfacial interactions at substrate/polymer and polymer/air and the commensurability between the equilibrium period (L0) of the BCP and the total film thickness. We investigated the phase transitions for the films of block copolymers (BCPs) on the modified surface, like the order-to-disorder transition (ODT) by in-situ grazing incidence small angle x-ray scattering (GISAXS) and transmission electron microscopy (TEM). The selective interactions on the surface by a PS-grafted substrate provide the preferential interactions with the PS component of the block, while a random copolymer (PS-r-PMMA) grafted substrate do the balanced interfacial interactions on the surface. The thickness dependence of order-to-disorder behavior for BCP films will be discussed in terms of the surface interactions.