Showing papers by "Seoul National University published in 1997"
TL;DR: The hypothesis that inflammatory cytokines released during the course of intrauterine infection play a role in the genesis of brain white matter lesions is supported.
717 citations
TL;DR: In this article, a generalized phenomenological yield description is proposed to account for the behavior of the solute strengthened aluminum alloy sheets studied in this work and the experimental yield surfaces were found to be in good agreement with the polycrystal predictions for all materials and with the phenomenological predictions for most materials.
Abstract: In this work, yield surfaces were measured for binary aluminum-magnesium sheet samples which were fabricated by different processing paths to obtain different microstructures. The yielding behavior was measured using biaxial compression tests on cubic specimens made from laminated sheet samples. The yield surfaces were also predicted from a polycrystal model using crystallographic texture data as input and from a phenomenological yield function usually suitable for polycrystalline materials. The experimental yield surfaces were found to be in good agreement with the polycrystal predictions for all materials and with the phenomenological predictions for most materials. However, for samples processed with high cold rolling reduction prior to solution heat treatment, a significant difference was observed between the phenomenological and the experimental yield surfaces in the pure shear region. In this paper, a generalized phenomenological yield description is proposed to account for the behavior of the solute strengthened aluminum alloy sheets studied in this work. It is subsequently shown that this yield function is suitable for the description of the plastic behavior of any aluminum alloy sheet.
504 citations
TL;DR: In this article, the authors found that infants who develop bronchopulmonary dysplasia have higher amniotic fluid concentrations of pro-inflammatory cytokines than those who do not develop it.
444 citations
28 Aug 1997
TL;DR: In this article, the rotor flux angle was estimated from stator voltages and currents by injecting a high-frequency signal, which is not a rotating one but a fluctuating one at a reference frame rotating synchronously to the fundamental stator frequency.
Abstract: This paper describes a new scheme to find the rotor flux angle from stator voltages and currents by injecting a high-frequency signal. The signal is not a rotating one but a fluctuating one at a reference frame rotating synchronously to the fundamental stator frequency. When the estimated rotor flux angle coincides with the actual angle, the proposed method makes virtually no ripple torque, no vibration and less audible noise caused by the injected signal. The difference of impedances between the flux axis and the quadrature axis at high-frequency signal injection on the rotor flux angle is explained by the equivalent circuit equation of the induction machine. The difference is verified by experiments on test motors under various testing conditions. A sensorless field orientation algorithm is proposed and experimental results clarify the satisfactory operation of the algorithm with one hundred and fifty percent load torque at zero stator frequency.
415 citations
TL;DR: In this article, a flux-weakening scheme for the interior permanent magnet synchronous motor (IPMSM) is proposed based on the output of the synchronous PI current regulator-reference voltage to the PWM inverter.
Abstract: A novel flux-weakening scheme for the interior permanent magnet synchronous motor (IPMSM) is proposed. This is implemented based on the output of the synchronous PI current regulator-reference voltage to the PWM inverter. The onset of flux weakening and the flux level are adjusted inherently by the outer voltage regulation loop to prevent saturation of the current regulator. Attractive features of this flux weakening scheme include no dependency on the machine parameters. The guarantee of current regulation at any operating condition, and smooth and fast transition into and out of the flux weakening mode. Experimental results at various operating conditions including the case of detuned parameters are presented to verify the feasibility of the proposed control scheme.
412 citations
TL;DR: In this article, the authors investigated the relationship between the local expression of cytokines and periventricular leukomalacia, a common neonatal brain white matter lesion, and determined whether high expression of tumor necrosis factor-α, interleukin-1β, and interleuxin-6 was observed in these lesions.
346 citations
TL;DR: In this article, pitch-based active carbon fibers (ACFs) were analyzed by a FTIR micro-ATR technique by introducing a very thin KBr layer on their surfaces.
300 citations
TL;DR: The authors examined how news frames in campaign coverage affect individuals' interpretation of campaigns and found that both strategy and issue-framed and issueframed print news stories are effective in influencing campaign interpretation.
Abstract: This study examines how news frames in campaign coverage affect individuals' interpretation of campaigns. Framing effects are conceptualized in terms of the process by which textual features in news stories set limits on knowledge use in the construction of a discourse model - a mental model constructed through the interaction between news frames and the interpreter's social knowledge. Examining message structures in campaign news stories led to identifying two major frames in campaign coverage: strategy and issue. Narrative data collected from two field experiments were analyzed. The findings suggest that both strategy-framed and issue-framed print news stories are effective in influencing campaign interpretation.
271 citations
TL;DR: In this paper, a study was conducted to determine whether ascending intrauterine infection could cause brain white matter lesions in the fetal rabbit, which is a major risk factor for cerebral palsy.
269 citations
TL;DR: The addition of posterior lumbar interbody fusion to posterolateral fusion after a complete decompression and pedicle screw fixation is a recommended procedure for the treatment of spondylolytic sponylolishesis with spinal stenosis.
Abstract: STUDY DESIGN This is a retrospective study analyzing 76 patients treated by decompression, pedicle screw instrumentation, and fusion for spondylolytic spondyiolisthesis with symptomatic spinal stenosis. OBJECTIVES To verify the advantages of adding posterior lumbar interbody fusion to the usual posterolateral fusion with pedicle screw instrumentation. SUMMARY OF BACKGROUND DATA Stabilization after decompression of spondylolytic spondylolisthesis is difficult because of a lack of fusional bone bases, gap between the transverse process bases, and incompetent anterior disc support. Posterior lumbar interbody fusion offers anterior support, reduction, and a broad fusion base. METHODS Forty patients were treated with posterolateral fusion, and 36 were treated with additional posterior lumbar interbody fusion. They were compared for union, reduction of the deformity, and clinical results. RESULTS The patients were followed up for more than 2 years. Nonunion was observed in three patients who underwent posterolateral fusion (7.5%), and no cases of nonunion was found in patients who underwent posterior lumbar interbody fusion. Reduction of slippage was 28.3% in those who underwent posterolateral fusion and 41.6% in those who had posterior lumbar interbody fusion (P = 0.05). In the posterolateral fusion group, eight patients (20%) had recurrence of deformity, with loss of reduction more than 50%. Hardware failures occurred in two patients who had posterolateral fusion. There was no major neurologic complications in both groups. Both groups had satisfactory results in more than 90% of patients, with marked improvement of claudication. However, subjective improvement of back pain by Kirkaldy-Willis criteria revealed differences in the excellent results. An excellent result was reported by 45% in the posterolateral fusion group and by 75% in posterior lumbar interbody fusion group. CONCLUSIONS The addition of posterior lumbar interbody fusion to posterolateral fusion after a complete decompression and pedicle screw fixation is a recommended procedure for the treatment of spondylolytic spondylolishesis with spinal stenosis.
268 citations
TL;DR: In this paper, yield surfaces for binary aluminum-magnesium sheet samples were measured using biaxial compression tests on cubic specimens made from laminated sheet samples, and the yield surfaces were also predicted from a polycrystal model using crystallographic texture data as input and from a phenomenological yield function proposed previously.
TL;DR: The microwave dielectric properties of MNb2O6 compounds have been investigated as a function of M ions in this paper, and the temperature coefficient of the resonant frequency was found to correlate strongly with the M ions.
TL;DR: In this article, the stabilization mechanism of lifted flames in a laminar non-premixed jet has been analyzed and experimentally investigated, and an analysis on the flame response by the perturbation from the tribrachial location shows that the lifted flame is unstable for Sc
TL;DR: The microwave dielectric properties of AB2O6 compounds, where A=Ca, Mg, Mn, Co, Ni, or Zn, and B=Nb or Ta, were investigated in this article.
Abstract: The microwave dielectric properties of AB2O6 compounds, where A=Ca, Mg, Mn, Co, Ni, or Zn, and B=Nb or Ta, were investigated. All samples were prepared using the mixed oxide method. In particular, AB2O6 compounds with Mg2+ and Zn2+ revealed very good dielectric properties with respect to dielectric resonator applications. However, their temperature coefficient of resonant frequencies should be modified. It was found that the electronegativity of AB2O6 compounds is relevant to their dielectric constant. The temperature coefficient of resonant frequency was discussed in terms of volume contraction.
TL;DR: In this article, the maximum norm of the gradient of the passive scalar of the Boussinesq equation was shown to control the breakdown of smooth solutions of the problem.
Abstract: In this paper, we prove local existence and uniqueness of smooth solutions of the Boussinesq equations. We also obtain a blow-up criterion for these smooth solutions. This shows that the maximum norm of the gradient of the passive scalar controls the breakdown of smooth solutions of the Boussinesq equations. As an application of this criterion, we prove global existence of smooth solutions in the case of zero external force.
TL;DR: MAPK phosphorylation at the membrane is important for the internalization of apCAMs and, thus, may represent an early regulatory step in the growth of new synaptic connections that accompanies long-term facilitation in Aplysia.
TL;DR: An algorithm for generating a twice-differentiable curve on the rotation group SO(3) that interpolated a given ordered set of rotation matrices at their specified knot times is presented.
Abstract: We present an algorithm for generating a twice-differentiable curve on the rotation group SO(3) that interpolated a given ordered set of rotation matrices at their specified knot times. In our approach we regard SO(3) as a Lie group with a bi-invariant Riemannian metriac, and apply the coordinate-invariant methods of Riemannian geometry. The resulting rotation curve is easy to compute, invariant with respect to fixed and moving reference frames, and also approximately minimizes angular acceleration.
TL;DR: In this article, a damage detection and assessment algorithm is developed based on a parameter estimation with an adaptive parameter grouping scheme, which is characterized by a reduction in a constitutive property of a parameterized finite-element model between two time-separated inferences.
Abstract: A damage detection and assessment algorithm is developed based on a parameter estimation with an adaptive parameter grouping scheme. Damage is characterized by a reduction in a constitutive property of a parameterized finite-element model between two time-separated inferences. We assume that the baseline parameter values are known. An adaptive parameter grouping scheme is proposed to localize damage in a structural system for which the measured data are sparse. A data perturbation scheme is proposed both for the baseline structure, to establish the damage threshold above which damage can be confidently discerned from noise, and for the damaged structure, to compute the damage indices. To examine and illustrate the damage assessment algorithm, a numerical simulation study on a planar bowstring truss structure is performed.
TL;DR: Results demonstrate that G-Rg1 is a functional ligand of GR, and the growth of FT02B cells was suppressed by G- Rg1 as well as by Dex, each of whose effects were abolished by RU486.
TL;DR: By introducing the direct field-oriented (DFO) control, which is insensitive to the variation of machine parameters in the field-weakening region, the drive system can obtain robustness to parameter variations.
Abstract: In this paper, a novel field-weakening scheme for the induction machine is presented. The proposed algorithm, based on the voltage control strategy, ensures the maximum torque operation over the entire field-weakening region without using the machine parameters. Also, by introducing the direct field-oriented (DFO) control, which is insensitive to the variation of machine parameters in the field-weakening region, the drive system can obtain robustness to parameter variations. Moreover, the speed sensorless control can be achieved in the very-high-speed range, where the utilization of the speed sensor is limited. Experimental results for the laboratory induction motor drive system confirm the validity of the proposed control algorithm.
TL;DR: In this article, the authors estimate the intertemporal elasticity of substitution of non-durable consumption, which has often been estimated with the generalized methods of moments (GMM), which is not consistent in the presence of liquidity constraints, aggregation over heterogeneous consumers, unknown preference shocks, or a general form of time-nonseparability.
TL;DR: In this article, two different categories of sooting flame structures can be classified depending on the relative transport of soot particles to flames, i.e., the soot formation-oxidation flame (SFOF) and the SOOT formation flame (SSFL).
TL;DR: This paper presents some results on the robust stabilization of a class of feedback linearizable nonlinear single-input/single-output (SISO) systems exhibiting parametric uncertainty and analysis and implementation of nonlinear feedback linearizing control for an electromagnetic suspension (EMS) system.
Abstract: This paper presents some results on the robust stabilization of a class of feedback linearizable nonlinear single-input/single-output (SISO) systems exhibiting parametric uncertainty. We characterize a class of nonlinear systems with bounded uncertain parameters which can be transformed into a linear interval matrix robustness problem. We also present some analysis and implementation of nonlinear feedback linearizing control for an electromagnetic suspension (EMS) system. We show that the EMS system is nonlinear feedback linearizable and satisfies the proposed condition, and hence that the proposed nonlinear feedback controller for an EMS system is robust against mass parameter perturbation and force disturbance. Some tests are performed for making an experimental comparison between feedback linearizing control and classical state feedback control using linearization by small perturbation analysis.
TL;DR: In this paper, a new method employing the immune algorithm (IA) as the search method for the shape optimization of an electromagnetic device is presented, which is applied to the shape optimisation of a pole face of an electromagnet.
Abstract: A new method employing the immune algorithm (IA) as the search method for the shape optimization of an electromagnetic device is presented. The method is applied to the shape optimization of a pole face of an electromagnet. For the magnetic field analysis the finite element method is used. It is shown that the proposed method with the IA is very useful for the shape optimization of electromagnetic devices.
TL;DR: In this article, a mixture model of the exponential and the Erlang-2 distribution with heterogeneous frequency for shopping trip intervals was proposed to segment shoppers by their shopping trip regularity.
TL;DR: In this article, the authors study counting statistics of electric current pumped by pulses of an external field, and develop an approach that allows them to calculate all counting statistics for various driving fields, optimal and non-optimal.
Abstract: We study counting statistics of electric current pumped by pulses of an external field. The fluctuations depend on the pulse shape, and can be minimized by choosing the pulse shape properly. For an optimal pulse shape, the fluctuations are reduced to the dc level, i.e., they do not depend on the duty cycle of the signal. We develop an approach that allows us to calculate all counting statistics for various driving fields, optimal and nonoptimal. The statistics depend in an interesting way on the analytic structure of the field time dependence, and display an analogy with coherent states and instantons.
TL;DR: Chitosan, a cationic polysaccharide, was heterogeneously deacetylated with a 47% sodium hydroxide solution and followed by a homogeneous reacetylation with acetic anhydrides to control the N-acetyl content of chitosans having a similar molecular weight as mentioned in this paper.
Abstract: Chitosan, a cationic polysaccharide, was heterogeneously deacetylated with a 47% sodium hydroxide solution and followed by a homogeneous reacetylation with acetic anhydrides to control the N-acetyl content of the chitosan having a similar molecular weight. The chitosans having different degrees of N-acetylation were complexed with sodium alginate, an anionic polysaccharide, and the formation behavior of polyelectrolyte complexes (PECs) was examined by the viscometry in various pH ranges. The maximum mixing ratio (Rmax) increased with a decrease in the degree of N-acetylation of the chitosan at the same pH, and with a decrease in pH at the same degree of N-acetylation. Similarly, N-acylated chitosans were also prepared. The N-acyl chitosans scarcely affected the formation behavior of PECs with sodium alginates. For the application of the PECs produced, the microencapsulation of a drug was performed and the release property of drug was tested. The microcapsules were prepared in one step by the extrusion of a solution of guaifenesin and sodium alginate into a solution containing calcium chloride and chitosan through interpolymeric ionic interactions. The drug release during the drug-loaded microcapsules storage in saline was found to depend on the pH where the microcapsules were formed and the kind of N-acyl groups introduced to the chitosan. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 425–432, 1997
TL;DR: A novel error concealment technique based on the discrete cosine transform (DCT) coefficients recovery and its application to the MPEG-2 bit stream error, requiring much lower computational load and simpler hardware structure than existing algorithms, while providing adequate performances.
Abstract: This paper presents a novel error concealment technique based on the discrete cosine transform (DCT) coefficients recovery and its application to the MPEG-2 bit stream error. Assuming a smoothness constraint on image intensity, an object function which describes the intersample variations at the boundaries of the lost block and the adjacent blocks is defined, and the corrupted DCT coefficients are recovered by solving a linear equation. Our approach can be regarded as a special case of Wang et al.'s (1991). However, we show that the linear equation in the proposed algorithm can be decomposed into four independent subequations, requiring much lower computational load and simpler hardware structure than existing algorithms, while providing adequate performances. To develop a generic error concealment (EC) system, the blocks corrupted by the random bit errors are identified by a multistage error detection algorithm. Thus, the proposed EC system can be applied to more realistic environments, such as concealment of random bit error in MPEG-2 bit stream. Computer simulation results show that the quality of a recovered image is significantly improved even at a bit error rate as high as 10/sup -5/.
TL;DR: To their surprise, Tiller and Hanson's (1984) simple method outperforms other methods for offsetting (piecewise) quadratic curves, even though its performance is not as good for high degree curves.
Abstract: Offset curves have diverse engineering applications, spurring extensive research on various offset techniques. In a paper on offset curve approximation (Lee et al., 1996), we suggested a new approach based on approximating the offset circle instead of the offset curve itself. To demonstrate the effectiveness of this approach, we compared it extensively with previous methods. To our surprise, Tiller and Hanson's (1984) simple method outperforms other methods for offsetting (piecewise) quadratic curves, even though its performance is not as good for high degree curves. The experimental results revealed other interesting facts, too. Had these details been reported several years ago, we believe offset approximation research might have developed somewhat differently. This article is intended to fill an important gap in the literature. We conducted qualitative as well as quantitative comparisons employing various contemporary offset approximation methods for freeform curves in the plane. We measured the efficiency of the offset approximation in terms of the number of control points generated while making the approximations within a prescribed tolerance.
TL;DR: In this paper, the authors deduce far-reaching generalizations of the KKM theorem, the matching theorem, a whole intersection property, an analytic alternative, the Ky Fan minimax inequality, geometric or section properties, and others on generalized convex spaces.