• Kyungpook Mathematical Journal
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• v.60 no.4
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• pp.723-729
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• 2020

Let ℤ_n be the ring of integers modulo n and let ℤ_n[X]] be either ℤ_n[X] or ℤ_n[[X]]. Let 𝚪(Z_n[X]]) be the zero-divisor graph of ℤ_n[X]]. In this paper, we study some properties of 𝚪(ℤ_n[X]]). More precisely, we completely characterize the diameter and the girth of 𝚪(ℤ_n[X]]). We also calculate the chromatic number of 𝚪(ℤ_n[X]]).

• Bulletin of the Korean Mathematical Society
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• v.60 no.6
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• pp.1463-1475
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• 2023

In this paper, we introduce a class of rings generalizing unit regular rings and being a subclass of semipotent rings, which is called idempotent unit regular. We call a ring R an idempotent unit regular ring if for all r ∈ R - J(R), there exist a non-zero idempotent e and a unit element u in R such that er = eu, where this condition is left and right symmetric. Thus, we have also that there exist a non-zero idempotent e and a unit u such that ere = eue for all r ∈ R - J(R). Various basic characterizations and properties of this class of rings are proved and it is given the relationships between this class of rings and some well-known classes of rings such as semiperfect, clean, exchange and semipotent. Moreover, we obtain some results about when the endomorphism ring of a module in a class of left R-modules X is idempotent unit regular.

• Language and Information
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• v.20 no.1
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• pp.51-71
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• 2016

The status of the Korean morphological marker '-e ci' has been controversial whether it is a passive marker, an anticausative marker, or a passive/anticausative marker. However, the previous approaches that tried to classify '-e ci' constructions based on the syntactic verb classes (i.e. intransitive or transitive) were short of explaining the properties of the constructions. In this study, the '-e ci' constructions were distinguished based on agentivity, following Levin & Rappaport Hovav (1995) and Alexiadou et al. (2006). Moreover, how the verbal root meaning is associated with the passive/anticausative construction was investigated by means of Distributed Morphology (DM) (Embick 2010; Marantz 1997). I argued that the morphological marker '-e ci' is the instantiation of the absence of external arguments. With respect to the behavior of the Korean '-e ci' constructions with the semantics of each verbal root class, I found out that the '-e ci' constructions can form passives with the verbal roots that require the external arguments; whereas, the anticausatives cannot be formed with the roots that necessarily require the agentive arguments. However, contrary to the previous arguments that '-e ci' passives can be only formed with transitive verbs, it is discovered that non-agentive transitive roots do form anticausatives. Moreover, I argued that there are two types of the anticausatives - zero and '-e ci' anticausatives. Since the valency reduction is marked by the non-active voice morphology, the zero anticausatives appear only with the roots that do not require external arguments. The different '-e ci' constructions (passives, '-e ci', and zero anticausatives) are represented by the distinct syntactic structures. I proposed that the morphological similarity between the passives and the '-e ci' anticausatives is due to the presence of VoiceP, which introduces the external arguments. Moreover, the lack of the voice morphology in the zero anticausatives is explained by the absence of the VoiceP.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.5
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• pp.57-63
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• 2006

This paper deals with the physical properties and statistical analysis of waveform parameters of electric and magnetic folds radiated from lightning return strokes. The lightning electric and magnetic fields were detected by an plate-type electric field sensor and a loop-type magnetic field sensor respectively, and they were recorded by a data acquisition system having a resolution of 12bits, a sampling rate of 10[MS/s] and recording length of 10[ms]. As a result, a little difference between the parameters of electric and magnetic fields for positive and negative polarities was observed. The rise times of electric and magnetic fields were within the range of less than $13[{\mu}s]$ and the average values for positive and negative polarities were $4.1[{\mu}s]\;and\;4.2[{\mu}s]$, respectively. The average values of the zero-to zero crossing times were $65.2[{\mu}s]\;and\;67.0[{\mu}s]$, and the average depths of the dip to opposite polarity were 38.0[%] and 40.3[%], for positive and negative polarities, respectively.

• Korea-Australia Rheology Journal
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• v.20 no.3
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• pp.109-116
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• 2008

The effect of intermolecular aggregation induced by hydrophobic and electrostatic interactions on shear and elongational flow properties of aqueous acrylic thickener solutions is discussed. Complex shear modulus is determined at frequencies up to $10^4$ rad/s employing oscillatory squeeze flow. Extensional flow behavior is characterized using Capillary Break-up Extensional Rheometry. Aqueous solutions of poly(acrylic acid)(PAA)/poly(vinylpyrrolidone-co-vinylimidazole) (PVP-VI) mixtures exhibit unusual rheological properties described here for the first time. Zero-shear viscosity of the mixtures increases with decreasing pH and can exceed that of the pure polymers in solution by more than two orders of magnitude. This is attributed to the formation of complexes induced by electrostatic interactions in the pH range, where both polymers are oppositely charged. PAA/PVP-VI mixtures are compared to the commercial thickener Sterocoll FD (BASF SE), which is a statistical co-polymer including (meth) acrylic acid and ethylacrylate (EA) forming aggregates in solution due to "sticky" contacts among hydrophobic EA-sequences. PAA/PVP-VI complexes are less compact and more deformable than the hydrophobic Sterocoll FD aggregates. Solutions of PAA/PVP-VI exhibit a higher zero-shear viscosity even at lower molecular weight of the aggregates, but are strongly shear-thinning in contrast to the weakly shear-thinning solutions of Sterocoll FD. The higher ratio of characteristic relaxation times in shear and elongation determined for PAA/PVP-VI compared to Sterocoll FD solutions reflects, that the charge-induced complexes provide a much stronger resistance to extensional flow than the aggregates formed by hydrophobic interactions. This is most likely due to a break-up of the latter in extensional flow, while there is no evidence for a break-up of complexes for PAA/PVP-VI mixtures. These flexible aggregates are more suitable for the stabilization of thin filaments in extensional flows.

• Korean Journal of Materials Research
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• v.1 no.1
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• pp.54-61
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• 1991

YBCO films deposited on MgO(100) and Si(100) by rf-magnetron sputtering using stoichiometric single target were annealed under oxygen atmosphere at $880^{\circ}C$ for 1 hr. The microstructure and superconducting properties of YBCO thin films depended on the composition of pre-annealed thin films. Basal planesuperconducting particles grown on MgO(100) substrate had small and rod-like shade due to preferred orientation, while superconducting film grown on the basal plane-superconducting particles showed round-shape particles. If pre-annealed thin film had nonstoichiometric composition, liquid phase was formed during the heat treatment, which made it easy for particles to grow in the preferred orientation and thus to form textured structure. But the thin films with the textured structure did not show good superconducting properties, especially $T_c$, since the liquid phase transformed into second phase in the grain boundary during the cooling. The effect of the second phase on $T_{c, \;zero}$ was greater than that on $T_{c, \;on}$.

• Korean Journal of Medicinal Crop Science
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• v.25 no.5
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• pp.282-289
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• 2017

Background: To investigate the possibility of using Asarum sieboldii as an environment-friendly fumigant for protecting organic cultural heritages, the inhibitory effect of A. sieboldii extract against wood rot fungi on Hanji was examined. Methods and Results: The physical, optical, and morphological properties of Hanji inoculated with Trametes versicolor and Tyromyces palustris, and exposed to the n-hexane fraction of A. sieboldii extract, were measured. The physical properties were expressed as weight loss, zero-span tensile strength and viscosity and the optical properties were depicted by luminance and chromaticity ($L^*$, $a^*$, and $b^*$). The results showed that, the n-hexane fraction of A. sieboldii extract inhibited the growth of fungi on Hanji, and preserved its condition. At a concentration of 25 mg, the n-hexane fraction of A. sieboldii extract maintained zero-span tensile strength, increased viscosity, and restricted discoloration of Hanji. It also was confirmed that the weight of fungi infested Hanji exposed to the extract did not decrease. Scanning electron microscopic images revealed that the spores and hyphae of T. versicolor and T. palustris were not present on Hanji during treatment with > 25 mg of the n-hexane fraction of A. sieboldii extract. Conclusions: These results indicate that the n-hexane fraction of A. sieboldii extract by virtue of its antifungal effectiveness may help in preserving Korean paper cultural heritages, including Hanji.

• Journal of Korea Foundry Society
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• v.11 no.4
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• pp.323-330
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• 1991

The relationships between the microstructure changes, retained austenite volume and elevated temperature tensile properties of Mo-Ni-Cu ADI corresponding to various austempering temperatures and time were investigated, After the $250^{\circ}C$ tensile test for the test piece austempered at $270^{\circ}C$ the accicular bainite structure was observed blunted under room temperature microscope. In the case of $370^{\circ}C$ austempering, the feathery bainite lath spacing was observed broadened. But after the $450^{\circ}C$ tensile test, bainitic features could not be observed. As the testing temperature increased, retained austenite volume tested at room temperature decreased. Especially, after the $450^{\circ}C$ tensile test retained austenite volume approached nearly to zero. A little higher tensile properties appeared at $250^{\circ}C$ testing than those at room temperature.

• Journal of the Korean Ceramic Society
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• v.32 no.4
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• pp.448-454
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• 1995

The effect of WO3 addition on microwave dielectric properties of BaTiO3-3{(1-x)TiO2-xWO3} system was studied. Addition of WO3 to this system resulted in the formation of BaWO4 and Ba2Ti9O20 phases. Both the dielectric constant (K) and the temperature coefficientof resonant frequency (Tf) were decreased with the amount of WO3 addition. The value of Q$\times$f0 was increased as the amount of WO3 was increased up to x=0.0275, and then decreased when x exceeded 0.03. At x=0.0275, this ceramic showed excellent microwave proprties of K=34-35, Q$\times$f0=50,000-53,000, and near zero ppm/$^{\circ}C$ of Tf.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.31 no.5
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• pp.18-23
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• 1999

This study examined the effects of multiple recycling on deinkability and properties of recycled paper from laser computer printout(LCPO). First, alkaline paper with a 20% printed area was disintegrated by TAPPI standard disintegrator. After dewatering , the pulp was followed by flotation, handsheet making, and drying at room temperature, in order. A sequence of printing , disintegrating, flotating , handsheet making and drying was one recycling cycle and this cyclic treatment was repeateed from zero to five times. The residual ink content in recycled handsheets by SEM-EDXA and Py-GC analyseswas increased slightly as recycling number increase. After five cycles of recycling the ISO brightness of recycled handsheets dropped to about 90% of the original brightness. However, it had a gain of 10% in opacity. The most of physical properties of recycled handsheets were decreased as recycling numbers increase except of for tear strength.