• Bulletin of the Korean Mathematical Society
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• v.48 no.4
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• pp.791-812
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• 2011

This is a survey on American options. An American option allows its owner the privilege of early exercise, whereas a European option can be exercised only at expiration. Because of this early exercise privilege American option pricing involves an optimal stopping problem; the price of an American option is given as a free boundary value problem associated with a Black-Scholes type partial differential equation. Up until now there is no simple closed-form solution to the problem, but there have been a variety of approaches which contribute to the understanding of the properties of the price and the early exercise boundary. These approaches typically provide numerical or approximate analytic methods to find the price and the boundary. Topics included in this survey are early approaches(trees, finite difference schemes, and quasi-analytic methods), an analytic method of lines and randomization, a homotopy method, analytic approximation of early exercise boundaries, Monte Carlo methods, and relatively recent topics such as model uncertainty, backward stochastic differential equations, and real options. We also provide open problems whose answers are expected to contribute to American option pricing.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.1358-1365
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• 2010

Estimating condition of slope is difficult because of nonlinear time dependency and seasonal effects, which affect the displacements. Displacements and displacement patterns of landslides are highly variable in time and space, and a unique approach cannot be defined to model landslide movements. Characteristics of movements are obtained by using a statistical method called Principal Component Analysis(PCA). The PCA is a non-parametric method to separate unknown, statistically uncorrelated source processes from observed mixed processes. In the non-parametric approaches, no physical assumptions of target systems are required. Instead, since the "best" mathematical relationship is estimated for given data sets of the input and output measured from target systems. As a consequence, non-parametric approaches are advantageous in modeling systems whose geomechanical properties are unknown or difficult to be measured. Non-parametric approaches are consequently more flexible in modeling than parametric approaches. This method is expected to be a useful tool for the slope management of and alarm systems.

• Journal of Plant Biotechnology
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• v.7 no.1
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• pp.1-15
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• 2005

Salinity is one of the major limiting factors for agricultural productivity. In plants, accumulation of osmolytes plays a pivotal role in abiotic stress tolerance. Likewise, exclusion or compartmentation of $Na^+$ ions into vacuoles provides an efficient mechanism to avert deleterious effects of $Na^+$ in the cytosol. Both vacuolar and plasma membrane sodium transporters and $H^+-ATPases$ can provide the necessary ion homeostasis. A variety of crop plants were engineered with respect to the synthesis of osmoprotectants and ion-compartmentation, but there are other cellular pathways involved in the salinity responses that are still not completely explored. Genomics approaches are increasingly used to identify genes and pathway changes involved in salt-tolerance. The new knowledge may be used via guided genetic engineering of multiple genes to create crop plants with significantly increased productivity in saline soils. This review surveys how plants deal with high salt conditions and how salt tolerance can be improved by transgenic approaches.

• Smart Structures and Systems
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• v.20 no.2
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• pp.207-217
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• 2017

Because of the inevitable uncertainties such as structural parameters, external excitations and measurement noises, the effects of uncertainties should be taken into consideration in structural damage detection. In this paper, two probabilistic structural damage detection approaches are proposed to account for the underlying uncertainties in structural parameters and external excitation. The first approach adopts the statistical moment-based structural damage detection (SMBDD) algorithm together with the sensitivity analysis of the damage vector to the uncertain parameters. The approach takes the advantage of the strength SMBDD, so it is robust to measurement noise. However, it requests the number of measured responses is not less than that of unknown structural parameters. To reduce the number of measurements requested by the SMBDD algorithm, another probabilistic structural damage detection approach is proposed. It is based on the integration of structural damage detection using temporal moments in each time segment of measured response time history with the sensitivity analysis of the damage vector to the uncertain parameters. In both approaches, probability distribution of damage vector is estimated from those of uncertain parameters based on stochastic finite element model updating and probabilistic propagation. By comparing the two probability distribution characteristics for the undamaged and damaged models, probability of damage existence and damage extent at structural element level can be detected. Some numerical examples are used to demonstrate the performances of the two proposed approaches, respectively.

• Smart Structures and Systems
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• v.22 no.2
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• pp.167-174
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• 2018

Digital input and output modules are widely used to connect digital sensors and actuators to automation systems. Digital I/O modules provide flexible connectivity extension to numerous sensors and actuators and protect systems from high voltages and currents by isolation. Components in digital I/O modules are inevitably affected by operating and environmental conditions, such as high voltage, high current, high temperature, and temperature cycling. Because digital I/O modules transfer signals or isolate the systems from unexpected voltage and current transients, their failures may result in signal transmission failures and damages to sensitive circuitry leading to system malfunction and system shutdown. In this study, the lifetime of optocouplers, one of the critical components in digital I/O modules, was predicted using Bayesian tracking approaches. Accelerated degradation tests were conducted for collecting the critical performance parameter of optocouplers, current transfer ratio (CTR), during their lifetime. Bayesian tracking approaches, including extended Kalman filter and particle filter, were applied to predict the failure. The performance of each prognostic algorithm was then compared using accuracy and robustness-based performance metrics.

• Language and Information
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• v.13 no.1
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• pp.127-143
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• 2009

Tough-construction is, undoubtedly, one of the most puzzling syntactic problems in the history of transformational grammar. Various approaches have been proposed including Deletion approaches (Akmajian, 1972; Lasnik and Fiengo, 1974) and movement approaches. Among the movement approaches, Chomsky (1977; 1981) argues for movement of null Operator, and Hornstein (2001) argues for a two-step movement equipped with Sideward movement. Most recently, Schueler (2004) and Hartman (2009) each have also argued for a kind of movement approach. With the development of the Minimalist syntax (Chomsky, 1995; Chomsky, 2000; Chomsky, 2001), tough-construction, an age old problem in the description of grammar, turns into another round toward to a more satisfactory answer. By examining the most recent competing analyses of tough-constructions, this paper defends and extends Schueler's (2004) analysis, rather than Hartman's (2009) two step movement approach. Furthermore, this paper proposes that tough-subject originates from the intermediate CP internal Spec-TopicP position rather than from the iterated CP layer (Authier, 1992). This approach has more descriptive power than it was originally argued for in Schueler (2004) and is a step closer toward Minimalism insofar as the conception of government is no longer utilized.

• Korean Journal of Health Education and Promotion
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• v.28 no.5
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• pp.51-60
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• 2011

Objectives: This article intends to describe the status of and challenges for physical activity in Korean university students. Methods: National level secondary data and related articles were reviewed including KNHANES(Korea National Health and Nutrition Examination Survey) and Online Youth Health Behavior Survey. Four tables and two figures were generated from original data and related articles. Results: The proportion of Korean university students practicing regular physical activity appear to be about half of that in American students. Gender difference in physical activity practicing rate seems to be maintained in university years. The main reason for physical inactivity was that physical activity was bothersome. The trends of physical activity practice in Korean students since middle school years needs further research. Conclusions: To increase the rate of physical activity in Korean university students, evidence-based comprehensive approaches are needed including campaign and informational approaches, behavioral and social approaches and policy and environmental approaches adapted to Korean university students.

• Journal of The Korean Association For Science Education
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• v.25 no.1
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• pp.1-15
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• 2005

This study examined two students' problem solving approaches: the similarities and the differences in their problem solving approaches, and the general problem solving strategies (heuristics) the students employed were discussed. The two students represent differences not only in terms of grades earned, but also in terms of participation, motivation, attention to detail, and approaches to answering questions and problem solving. Three separate problems were selected for this study: A stoichiometry problem; a fruit salad problem; and a limiting reactant problem. Each student was asked individually on three separate occasions to contribute to this study. There are more similarities in the students' problem solving strategies than there are differences. Both students were able to correctly solve the stoichiometry and the fruit salad problems, and were unable to correctly solve the limiting reactant problem. They recognized that an algorithm could be used for both chemistry problems(a stoichiometry problem & a limiting reactant problem). Both students were unable to correctly solve the limiting reactant problem and to demonstrate a clear understanding of the Law of Conservation of Mass. Nor did they show an ability to apply it in solving the problem. However, there was a difference in each one's ability to extend what had been learned/practiced/quizzed in class, to a related but different problem situation.

• Journal of Korean Neurosurgical Society
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• v.60 no.3
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• pp.275-281
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• 2017

Treating diseases in the field of neurosurgery has progressed concomitantly with technical advances. Here, as a surgical armamentarium for the treatment of cerebral aneurysms, the history and present status of the keyhole approach and the use of neuroendoscopy are reviewed, including our clinical data. The major significance of keyhole approach is to expose an essential space toward a target, and to minimize brain exposure and retraction. Among several kinds of keyhole approaches, representative keyhole approaches for anterior circulation aneurysms include superciliary and lateral supraorbital, frontolateral, mini-pterional and mini-interhemispheric approaches. Because only a fixed and limited approach angle toward a target is permitted via the keyhole, however, specialized surgical devices and preoperative planning are very important. Neuroendoscopy has helped to widen the indications of keyhole approaches because it can supply illumination and visualization of structures beyond the straight line of microscopic view. In addition, endoscopic indocyanine green fluorescence angiography is useful to detect and correct any compromise of the perforators and parent arteries, and incomplete clipping. The authors think that keyhole approach and neuroendoscopy are just an intermediate step and robotic neurosurgery would be realized in the near future.

• Journal of Information Science Theory and Practice
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• v.1 no.3
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• pp.33-46
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• 2013

Despite limited success, today's information retrieval (IR) systems are not intelligent or reliable. IR systems return poor search results when users formulate their information needs into incomplete or ambiguous queries (i.e., weak queries). Therefore, one of the main challenges in modern IR research is to provide consistent results across all queries by improving the performance on weak queries. However, existing IR approaches such as query expansion are not overly effective because they make little effort to analyze and exploit the meanings of the queries. Furthermore, word sense disambiguation approaches, which rely on textual context, are ineffective against weak queries that are typically short. Motivated by the demand for a robust IR system that can consistently provide highly accurate results, the proposed study implemented a novel topic detection that leveraged both the language model and structural knowledge of Wikipedia and systematically evaluated the effect of query disambiguation and topic-based retrieval approaches on TREC collections. The results not only confirm the effectiveness of the proposed topic detection and topic-based retrieval approaches but also demonstrate that query disambiguation does not improve IR as expected.