• Progress in Superconductivity
• /
• v.1 no.1
• /
• pp.9-13
• /
• 1999

The influence of quenching temperature and annealing time on superconducting characteristics has been investigated for a $(Pb_{0.6}V_{0.4})Sr_2(Ca_{0.65}Er_{0.35})Cu_2O_z$ compound. From the resistivity measurements for samples annealed at $400^{\circ}C$ to $860^{\circ}C$ in oxygen and subsequently quenched, it is observed that $T_c$(zero) of the sample decreases with the increase of annealing temperature up to $600^{\circ}C$ and increases again beyond $700^{\circ}C$. Annealings of the sample at $860^{\circ}C$ show that $T_c$(zero) goes through a maximum of 62K with the increase of the annealing time. It is also found that $T_c$(zero) of the sample quenched from high temperature decreases when the sample is subjected to low temperature annealing below. $600^{\circ}C$ in oxygen. The experimental results indicate that the as-prepared samples contain excessive oxygen and removal of this excessive oxygen in as-prepared samples is a key factor in controlling the superconducting properties of the samples and are discussed in connection with thermal gravimetric measurements.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.54 no.6
• /
• pp.262-268
• /
• 2005

In this work, to obtain the detailed information about lightning electromagnetic field waveforms, the LabVIEW based-measurement system of time-changing magnetic fields was designed and constructed. The frequency bandwidth of the magnetic field measuring system ranges from 300 [Hz] to 1 [MHz], and the response sensitivity is 2.78 [mV/nT]. Data acquisition system with the resolution of 12 bits and memory capacity of 32 [Mbyte] was triggered by the magnetic field to be measured. The properties and parameters of the magnetic fields produced by cloud discharges were statistically investigated. The magnetic field waveforms radiated from cloud lighting discharges tend to be bipolar, with two or more narrow and several pulses superimposed on the initial front part. The recording length of the magnetic field measurement system is about 10 [ms]. The mean duration of cloud discharges is 1.3 [ms], and the number of outburst pulses for the period is 8 in average. The front times of the magnetic fields are 6.15 [$\mu$s] in average. The the zero-to-zero crossing times that is the initial half-cycle duration is widely dispersed and the mean value is 9.61 [$\mu$s], and the mean value of percentage depth of dip to opposite polarity is 41.1 [$\%$].

• Korean Journal of Optics and Photonics
• /
• v.4 no.3
• /
• pp.252-259
• /
• 1993

A holosymmetric four-mirror system with unit magnification is designed for use in the micro-lithography using a deep ultraviolet wavelength of $0.248 {\mu}m$(KrF excimer laser line). In the holosymmetric system all orders of coma and distortion are zero. By applying this principle to the 4-spherical mirror system, we have obtained only one exact solution for the unit magnification holosymmetric four-spherical mirror system with all zero third order aberrations. For correction of the residual higher order aberrations of the system, aspherization is introduced keeping the holosymmetric properties. We have obtained near diffraction-limited performance for the wavelength of 0.248 pm within N.A. of 0.33 and image field diameter of 7.6 mm.

• Bulletin of the Korean Mathematical Society
• /
• v.56 no.3
• /
• pp.729-743
• /
• 2019

In this paper, we introduce strongly quasi primary ideals which is an intermediate class of primary ideals and quasi primary ideals. Let R be a commutative ring with nonzero identity and Q a proper ideal of R. Then Q is called strongly quasi primary if $ab{\in}Q$ for $a,b{\in}R$ implies either $a^2{\in}Q$ or $b^n{\in}Q$ ($a^n{\in}Q$ or $b^2{\in}Q$) for some $n{\in}{\mathbb{N}}$. We give many properties of strongly quasi primary ideals and investigate the relations between strongly quasi primary ideals and other classical ideals such as primary, 2-prime and quasi primary ideals. Among other results, we give a characterization of divided rings in terms of strongly quasi primary ideals. Also, we construct a subgraph of ideal based zero divisor graph ${\Gamma}_I(R)$ and denote it by ${\Gamma}^*_I(R)$, where I is an ideal of R. We investigate the relations between ${\Gamma}^*_I(R)$ and ${\Gamma}_I(R)$. Further, we use strongly quasi primary ideals and ${\Gamma}^*_I(R)$ to characterize von Neumann regular rings.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.29 no.11A
• /
• pp.1244-1252
• /
• 2004

In this paper, we derive some properties of linear detectors (zero forcing or minimum mean square error) at spatial multiplexing systems with alamouti's space-time block code. Based on the derived properies, this paper proposes low-complexity receivers. Implementing MMSE detector adaptively, the number of weight vectors to be calculated and updated is greatly reduced with the derived properties compared to the conventional methods. In the case of recursive least square algorithm, with the proposed approach computational complexity is reduced to less than the half. We also identify that sorted QR decomposition detector, which reduces the complexity of V-Blast detector, has the same properties for unitary matrix Q and upper triangular matrix R. A complexity reduction of about 50%, for sorted QR decomposition detector, can be achieved by using those properties without the loss of performance.

• Current Optics and Photonics
• /
• v.2 no.6
• /
• pp.525-531
• /
• 2018

The effect of eccentricity on dispersion and nonlinear properties of a photonic crystal fiber having elliptical air holes is investigated using a fully vectorial effective index method. It is found that the effective refractive index increases with increase of eccentricity. The dependence of dispersion and nonlinear properties of the PCF on the eccentricity of the air hole is investigated. It is revealed that eccentricity of the air hole affects the zero dispersion wavelength. Further, the nonlinear properties such as mode field area, nonlinear coefficient and self phase modulation of the Photonic crystal fibers are analyzed. The mode field area increases and the nonlinear coefficient decreases with increase in eccentricity. The variation of the self phase modulation with elliptical air hole is also discussed.

• Honam Mathematical Journal
• /
• v.38 no.3
• /
• pp.593-611
• /
• 2016

This paper is concerned with the classifications of quadric surfaces of first and second kinds in Euclidean 3-space satisfying the Jacobi condition with respect to their curvatures, the Gaussian curvature K, the mean curvature H, second mean curvature $H_{II}$ and second Gaussian curvature $K_{II}$. Also, we study the zero and non-zero constant curvatures of these surfaces. Furthermore, we investigated the (A, B)-Weingarten, (A, B)-linear Weingarten as well as some special ($C^2$, K) and $(C^2,\;K{\sqrt{K}})$-nonlinear Weingarten quadric surfaces in $E^3$, where $A{\neq}B$, A, $B{\in}{K,H,H_{II},K_{II}}$ and $C{\in}{H,H_{II},K_{II}}$. Finally, some important new lemmas are presented.

• Kyungpook Mathematical Journal
• /
• v.60 no.2
• /
• pp.307-318
• /
• 2020

This article concerns the class of rings which satisfy the property of inserting regular elements at zero products, and rings with such property are called regular-IFP. We study the structure of regular-IFP rings in relation to various ring properties that play roles in noncommutative ring theory. We investigate conditions under which the regular-IFPness pass to polynomial rings, and equivalent conditions to the regular-IFPness.

• The Transactions of the Korean Institute of Electrical Engineers
• /
• v.37 no.7
• /
• pp.475-483
• /
• 1988

One of the advantages of the well-known PID controller is that it is a sufficiently flexible controller for many applications. But, when the plant parameters and disturbances are unknown or change with time, it is desirable to make automatic tuning of PID controller in order to achieve an acceptable level of performance of the control system. This paper presents a reformulation of the self-tuning pole-zero placement controller subject to some conditions and restrictions. It has the structure of a digital PID controller and is based on Vogel and Edgar's pole-zero placement design method. Various properties of this self-tuning PID controller are described and illustrated by simulation examples.

• Bulletin of the Korean Mathematical Society
• /
• v.22 no.2
• /
• pp.89-93
• /
• 1985

One of the most important problems in automatic continuity theory is to solve the question of continuity of an algebra homomorphism from a Banach algebra into a semisimple Banach algebra with dense range. Many results on this subject are obtained imposing some conditions on the domains or the ranges of homomorphisms. For most recent results and references in automatic continuity theory one may refer to [1], [4] and [5]. In this note we study some properties of homomorphisms from $C^{*}$-algebras into Banach algebras. It is shown that the range of an isomorphism from a $C^{*}$-algebra into a Banach algebra contains no non zero element of the radical of B. Using this result we show that the same holds for a continuous homomorphism, hence a Banach algebra which is the image of a $C^{*}$-algebra under a continuous homomorphism is necessarily semisimple. Thus if there is a homomorphism from a $C^{*}$-algebra onto a non-semisimple Banach algebra it must be discontinuous. Also it follows that every non zero homomorphism from a $C^{*}$-algebra into a radical algebra is discontinuous. Then we make a brief observation on the behavior of quasinilpotent element of noncommutative $C^{*}$-algebras in relation with continuous homomorphisms.momorphisms.