• Journal of the Korean institute of surface engineering
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• v.35 no.3
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• pp.149-157
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• 2002

Spectral emissivity depends on the surface conditions of the materials. The mechanisms that affect the spectral emissivity in anodic oxide films on aluminum were investigated. The aluminum specimens were anodized in a sulfuric acid solution and the thickness of the resulting oxide film formed changed with the anodizing time. FT-IR spectrum analysis identified the anodic oxide film as boehmite ($Al_2$$O_3$.$H_2$O). Both the infrared emisivity and reflectivity of the anodized aluminum were affected by the structure of the anodic oxide film because Al-OH and Al-O-Al have a pronounced absorption band in the infrared region of the spectrum. The presence of an anodic oxide film on aluminum caused a rapid drop in the infrared reflectivity. An aluminum surface in the clean state had an emissivity of approximately 0.2. However, the infrared emissivity rapidly increased to 0.91 as the thickness of the anodic oxide film increased.

• Bulletin of the Korean Chemical Society
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• v.27 no.10
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• pp.1705-1707
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• 2006

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.1
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• pp.322-340
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• 2012

Orthogonal Frequency Division Multiplexing (OFDM) is usually regarded as a spectral efficient multicarrier modulation technique, yet it suffers from a high peak-to-average power ratio (PAPR) problem. Among all the existing PAPR reduction techniques in OFDM systems, side information based PAPR reduction techniques such as partial transmit sequence (PTS) and selective mapping (SLM) schemes, have attracted the most attention. However, the transmission of side information results in somewhat spectral loss and this does not significantly improve the bit error rate (BER) performance. Parallel combinatory (PC) OFDM yields higher spectral efficiency (SE) and better BER performance on Gaussian channels,while is a little but not obvious PAPR improvement over the ordinary OFDM system. This investigation aimed to design a 'perfect' OFDM system. We introduce the side information to rotate the subcarrier phases of our novel PC-OFDM system structure, and call this new system the SIPC(Side information based Parallel Combinatory)-OFDM system. The proposed system achieves better PAPR and SE performance. In addition, considering the tradeoff of system parameters, the proposed system also has the properties of a higher BER.

• Advances in aircraft and spacecraft science
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• v.6 no.6
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• pp.479-495
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• 2019

Periodic cellular core structures included in sandwich panels possess good stiffness while saving weight and only lately their potential to act as passive vibration filters is increasingly being studied. Classical homogeneous honeycombs show poor vibracoustic performance and only by varying certain geometrical features, a shift and/or variation in bandgap frequency range occurs. This work aims to investigate the vibration filtering properties of the AUXHEX "hybrid" core, which is a cellular structure containing cells of different shapes. Numerical simulations are carried out using two different approaches. The first technique used is the harmonic analysis with commercially available software, and the second one, which has been proved to be computationally more efficient, consists in the Wave Finite Element Method (WFEM), which still makes use of finite elements (FEM) packages, but instead of working with large models, it exploits the periodicity of the structure by analysing only the unit cell, thanks to the Floquet-Bloch theorem. Both techniques allow to produce graphs such as frequency response plots (FRF's) and dispersion curves, which are powerful tools used to identify the spectral bandgap signature of the considered structure. The hybrid cellular core pattern AUXHEX is analysed and results are discussed, focusing the investigation on the possible spectral bandgap signature heritage that a hybrid core experiences from their "parents" homogeneous cell cores.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.230.2-230.2
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• 2015

Nanoparticles of magnesium ferrite are used as a heterogeneous catalyst, humidity sensor, oxygen sensor and cure of local hyperthermia. These applications usually utilize the magnetic behavior of these nanoparticles. Moreover, magnetic properties of nanoferrites exhibit rather complex behavior compared to bulk ferrite. The magnetic properties of ferrites are complicated by spins at vortices, surface spins. Reports till date indicate strong dependency on the structural parameters, oxidation state of metal ions and their presence in octahedral and tetrahedral environment. Thus we have carried out investigation on magnesium ferrite nanoparticles in order to study coordination, oxidation state and structural distortion. For present work, magnesium ferrite nanoparticles were synthesized using nitrates of metal ions and citric acid. Fe L-edge spectra measured for these nanoparticles shows attributes of $Fe^{3+}$ in high spin state. Moreover O K-edge spectra for these nanoparticles exhibit spectral features that arises due to unoccupied states of O 2p character hybridized with metal ions. Mg K-edge spectra shows spectral features at 1304, 1307, 1311 and 1324 eV for nanoparticles obtained after annealing at 400, 500, 600, 800, 1000, and $1200^{\circ}C$. Apart from this, spectra for precursor and nanoparticles obtained at $300^{\circ}C$ exhibit a broad peak centered around 1305 eV. A shoulde rlike structure is present at 1301 eV in spectra for precursor. This feature does not appear after annealing. After annealing a small kink appear at ~1297 eV in Mg K-edge spectra for all nanoparticles. This indicates changes in local electronic structure during annealing of precursor. Observed behavior of change in local electronic structure will be discussed on the basis of existing theories.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.40.1-40.1
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• 2021

Hydrogen is the most abundant element in the universe, which is, in the cosmological context, attributed to its simplest structure consisting of a proton and an electron. Hydrogen interacts with an electromagnetic wave in astrophysical environments. Rayleigh scattering refers to elastic scattering, where the frequencies of the incident and scattered photons are the same. Rayleigh and resonance scattering is a critical role study Lyman Alpha objects in the early universe. The scattering causes the frequency and spatial diffusion of Lyα. In the case of Raman scattering, the energies of the incident and scattered photons are different. The photons near Lyβ convert to the optical photons near Hα through Raman scattering. The photon scattered by atomic hydrogen can carry both of the properties of the H I region and the emission region. I adopt a Monte Carlo approach to investigate the formation of the various spectral line features through Rayleigh and Raman scattering in highly thick media of atomic hydrogen. In this thesis, I present my works on radiative transfer involving the scattering processes between far UV photon and atomic hydrogen. I introduce scattering processes with atomic hydrogen and the spectral, spatial, and polarized information originating from the scattering.

• Macromolecular Research
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• v.12 no.5
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• pp.501-506
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• 2004

We have investigated the spectral properties of DNA, including its electric absorption, circular and linear dichroism (CD and LD), and fluorescence emission, in the DNA-linear polyethyleneimine (LPEI) and DNA-branched polyethyleneimine (BPEI) complexes at various polymer concentrations. The spectral properties of both complexes are similar. We observed a relatively moderate change in the absorption and CD spectra at low amine/DNA phosphate (NIP) ratios (< 0.5), followed by a drastic collapse within the N/P range from 0.8 and 1.0. The absorption and CD spectra recovered as the N/P ratio increased to ca. 1.2. In contrast, the LD and emission of ethidium intercalated between the DNA bases decreased almost linearly at N/P ratios between 0.0 and 1.0. These spectra never recovered at higher N/P ratios. We believe that the moderate changes in the spectrum at low N/P ratios occurred because of electrostatic interactions between DNA and BPEI, while the collapsed spectra at N/P ratios between 0.5 and 1.5 occurred because of condensation/aggregation of the DNA. Considering the structure of the polymers, we suggest that the secondary amino group of LPEI and all three amino groups of BPEI are equally involved in DNA condensation.

• Journal of the Optical Society of Korea
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• v.7 no.2
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• pp.53-58
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• 2003

We report the formation of inner cladding modes in the optical fiber having an inner cladding structure. The inner cladding layer located between the core- and the cladding- layers of a conventional fiber might have, so called, inner cladding mode(s). The brief history of the inner cladding fiber and the spectral properties of the inner cladding mode are presented. By utilizing fiber gratings, the spectral properties of the inner cladding mode formed in Dispersion Compensating Fiber (DCF) are discussed. It was observed that one resonant peak of a long-period fiber grating was not sensitive to the variation on the cladding surface. With a fiber Bragg grating, a small group of unusual resonant Peaks was observed between the main Bragg Peak and the series of usual Peaks resulted from the mode coupling to counter-propagating cladding modes. Within the DCF by using fiber gratings, it is noted, at least one mode can be coupled to the inner cladding mode and a few outer cladding modes are severely affected by the inner cladding of the fiber.

• Journal of the Korean Ceramic Society
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• v.20 no.3
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• pp.236-242
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• 1983

The purpose of present study is to find the structures physical properties and their inter-relations in the system of (60-x) PbO.xMO.$40B_2O_3$ glasses where MO represents for ZnO and CdO. The experiments such as differential thermal analysis infrared spectral analysis X-ray diffraction analysis density and thermal expansion measurements have been done. From infrared spectral analysis the structural units of glasses and the corresponding crystallized glasses were com-posed of $BO_3$ triangles and $BO_4$ tetrahedra. These basic units found in $PbO-B_2O_3$ binary glass system did not charge even though the divalent metallic oxides were substituted for PbO. The structures of these ternary glasses were more coalescenced than $PbO-B_2O_3$ binary glass system. This fact was supported bydecrease in thermal expansion coeffici-ent and molar volume with substitution of divalent metallic oxide for PbO. Crystalline phases obtained from the heat treatment of the $PbO-ZnO-B_2O_3$ glasses were 4PbO.2ZnO.$5B_2O_3$ PbO.2ZnO.$B_2O_3$ and unknown phases.

• Proceedings of the KSLP Conference
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• 1995.11a
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• pp.141-153
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• 1995

CSpeech is a software package that implements an audio waveform/speech analysis workstation on an IBM Personal Computer or hardware compatible computer. Features include digitizing audio waveforms on single or multiple channels, displaying the digitized waveforms, playing back audio waveforms from selected intervals of sing1e channels, saving and retrieving waveforms from binary format disk files, and analysing audio waveforms for their temporal and spectral properties. The distinguishing characteristics of CSpeech are its support for multiple channels, minimal restrictions on sample rate and waveform duration support fur a variety of hardware configurations, fast graphics display, and its user- extensible menu- based command structure.