Showing papers by "Yonsei University published in 2004"

A Revised Approach to Ice Microphysical Processes for the Bulk Parameterization of Clouds and Precipitation

Abstract: A revised approach to cloud microphysical processes in a commonly used bulk microphysics parameterization and the importance of correctly representing properties of cloud ice are discussed. Several modifications are introduced to more realistically simulate some of the ice microphysical processes. In addition to the assumption that ice nuclei number concentration is a function of temperature, a new and separate assumption is developed in which ice crystal number concentration is a function of ice amount. Related changes in ice microphysics are introduced, and the impact of sedimentation of ice crystals is also investigated. In an idealized thunderstorm simulation, the distribution of simulated clouds and precipitation is sensitive to the assumptions in microphysical processes, whereas the impact of the sedimentation of cloud ice is small. Overall, the modifications introduced to microphysical processes play a role in significantly reducing cloud ice and increasing snow at colder temperatures and ...

Y 2 Isochrones with an Improved Core Overshoot Treatment

Abstract: Convective core overshoot affects stellar evolution rates and the dating of stellar populations In this paper, we provide a patch to the Y2 isochrones with an improved treatment of convective core overshoot The new tracks cover the transition mass range from no convective core to a fully developed convective core We compare the improved isochrones to CMDs of a few well-observed open star clusters in the Galaxy and the Large Magellanic Cloud Finally, we discuss future prospects for improving the treatment of core overshoot with the help of asteroseismology

Group Social Capital and Group Effectiveness: The Role of Informal Socializing Ties

Abstract: This study introduces the concept of group social capital, which is the configuration of group members' social relationships within a group and in the social structure of a broader organization, an...

Emotion recognition system using short-term monitoring of physiological signals.

Abstract: A physiological signal-based emotion recognition system is reported. The system was developed to operate as a user-independent system, based on physiological signal databases obtained from multiple subjects. The input signals were electrocardiogram, skin temperature variation and electrodermal activity, all of which were acquired without much discomfort from the body surface, and can reflect the influence of emotion on the autonomic nervous system. The system consisted of preprocessing, feature extraction and pattern classification stages. Preprocessing and feature extraction methods were devised so that emotion-specific characteristics could be extracted from short-segment signals. Although the features were carefully extracted, their distribution formed a classification problem, with large overlap among clusters and large variance within clusters. A support vector machine was adopted as a pattern classifier to resolve this difficulty. Correct-classification ratios for 50 subjects were 78.4% and 61.8%, for the recognition of three and four categories, respectively.

Transition metal-catalyzed carbon–carbon bond activation

Abstract: This tutorial review deals with recent developments in the activation of C–C bonds in organic molecules that have been catalyzed by transition metal complexes. Many chemists have devised a variety of strategies for C–C bond activation and significant progress has been made in this field over the past few decades. However, there remain only a few examples of the catalytic activation of C–C bonds, in spite of the potential use in organic synthesis, and most of the previously published reviews have dwelt mainly on the stoichiometric reactions. Consequently, this review will focus mainly on the catalytic reaction of C–C bond cleavage by homogeneous transition metal catalysts. The contents include cleavage of C–C bonds in strained and unstrained molecules, and cleavage of multiple C–C bonds such as CC triple bonds in alkynes. Multiple bond metathesis and heterogeneous systems are beyond the scope of this review, though they are also fascinating areas of C–C bond activation. In this review, the strategies and tactics for C–C bond activation will be explained.

Structural Models of Corporate Bond Pricing: An Empirical Analysis

Abstract: This article empirically tests five structural models of corporate bond pricing: those of Merton (1974), Geske (1977), Longstaff and Schwartz (1995), Leland and Toft (1996), and Collin-Dufresne and Goldstein (2001). We implement the models using a sample of 182 bond prices from firms with simple capital structures during the period 1986–1997. The conventional wisdom is that structural models do not generate spreads as high as those seen in the bond market, and true to expectations, we find that the predicted spreads in our implementation of the Merton model are too low. However, most of the other structural models predict spreads that are too high on average. Nevertheless, accuracy is a problem, as the newer models tend to severely overstate the credit risk of firms with high leverage or volatility and yet suffer from a spread underprediction problem with safer bonds. The Leland and Toft model is an exception in that it overpredicts spreads on most bonds, particularly those with high coupons. More accurate structural models must avoid features that increase the credit risk on the riskier bonds while scarcely affecting the spreads of the safest bonds. The seminal work of Black and Scholes (1973) and Merton (1974) in the area of corporate bond pricing has spawned an enormous theoretical literature on risky debt pricing. One motivating factor for this burgeoning literature is the perception that the Merton model cannot generate sufficiently high-yield spreads to match those observed in the market. Thus the recent theoretical literature includes a variety of extensions and

Identified charged particle spectra and yields in Au + Au collisions at √sNN = 200 GeV

Abstract: The centrality dependence of transverse momentum distributions and yields for ${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}},{K}^{\ifmmode\pm\else\textpm\fi{}},p$, and $\overline{p}$ in $\text{Au}+\text{Au}$ collisions at $\sqrt{{s}_{NN}}=200\phantom{\rule{0.3em}{0ex}}\text{GeV}$ at midrapidity are measured by the PHENIX experiment at the Relativistic Heavy Ion Collider. We observe a clear particle mass dependence of the shapes of transverse momentum spectra in central collisions below $\ensuremath{\sim}2\phantom{\rule{0.3em}{0ex}}\text{GeV}∕c$ in ${p}_{T}$. Both mean transverse momenta and particle yields per participant pair increase from peripheral to midcentral and saturate at the most central collisions for all particle species. We also measure particle ratios of ${\ensuremath{\pi}}^{\ensuremath{-}}∕{\ensuremath{\pi}}^{+}$, ${K}^{\ensuremath{-}}∕{K}^{+}$, $\overline{p}∕p$, $K∕\ensuremath{\pi}$, $p∕\ensuremath{\pi}$, and $\overline{p}∕\ensuremath{\pi}$ as a function of ${p}_{T}$ and collision centrality. The ratios of equal mass particle yields are independent of ${p}_{T}$ and centrality within the experimental uncertainties. In central collisions at intermediate transverse momenta $\ensuremath{\sim}1.5--4.5\phantom{\rule{0.3em}{0ex}}\text{GeV}∕c$, proton and antiproton yields constitute a significant fraction of the charged hadron production and show a scaling behavior different from that of pions.

Why People Continue to Play Online Games: In Search of Critical Design Factors to Increase Customer Loyalty to Online Contents

Abstract: As people increasingly play online games, numerous new features have been proposed to increase players' log-on time at online gaming sites. However, few studies have investigated why people continue to play certain online games or which design features are most closely related to the amount of time spent by players at particular online gaming sites. This study proposes a theoretical model using the concepts of customer loyalty, flow, personal interaction, and social interaction to explain why people continue to play online network games. The study then conducts a large-scale survey to validate the model. Finally, it analyzes current online games to identify design features that are closely related to the theoretical concepts. The results indicate that people continue to play online games if they have optimal experiences while playing the games. This optimal experience can be attained if the player has effective personal interaction with the system or pleasant social interactions with other people connecte...

Normal serum aminotransferase concentration and risk of mortality from liver diseases: prospective cohort study

Abstract: Objective To examine the relation between the normal range of serum aminotransferase concentration and mortality from liver disease. Design Prospective cohort study. Setting Korea Medical Insurance Corporation study with eight years9 follow up. Participants 94 533 men and 47 522 women aged 35-59 years. Main outcome measure Mortality from liver diseases according to death certificate. Results There was a positive association between the aminotransferase concentration, even within normal range (35-40 IU/l), and mortality from liver disease. Compared with the concentration Conclusion People with slightly increased aminotransferase activity, but still within the normal range, should be closely observed and further investigated for liver diseases.

Metabolic Significance of Nonalcoholic Fatty Liver Disease in Nonobese, Nondiabetic Adults

Abstract: Background Obesity and type 2 diabetes are well-known risk factors for the development of nonalcoholic fatty liver disease (NAFLD). However, NAFLD is not rare in nonobese, nondiabetic adults. The aim of this study was to evaluate the metabolic significance of NAFLD in nonobese, nondiabetic adults. Methods This study examined 768 nonobese (body mass index [BMI] [calculated as weight in kilograms divided by the square of height in meters], ≥18.5 and Results The prevalence of NAFLD in the enrolled subjects was 23.4%. In the normal-weight (BMI, ≥18.5 and Conclusions Nonalcoholic fatty liver disease is closely associated with metabolic disorders, even in nonobese, nondiabetic subjects. Nonalcoholic fatty liver disease can be considered an early predictor of metabolic disorders, particularly in the normal-weight population.

Directly Linked Porphyrin Arrays with Tunable Excitonic Interactions

Abstract: On the basis of the Ag(I)-promoted coupling reaction of Zn(II) 5,15-diaryl porphyrin that gave a meso−meso-linked diporphyrin, we developed a variety of directly linked porphyrin arrays including linear, windmill, gridlike, cyclic, and box architectures. Electronic and excitonic interactions are thus fine tuned by placing porphyrin chromophores in well-defined arrangements. Photoexcited-state dynamics of these porphyrin arrays, as revealed by various ultrafast laser-based measurements, are pertinent to photosynthetic light-harvesting antenna in terms of very efficient excitation energy hopping over many porphyrins and lack of a defect that acts as energy sink. The conformational flexibility of a meso−meso-linked diporphyrin has also been used for the fine tuning of excitonic interactions as demonstrated by strapped meso−meso diporphyrins and reversible switching of energy transfer in a triporphyrin. Triply linked porphyrin arrays have also been explored, which exhibit an exceptionally low HOMO−LUMO gap as...

Early- and Late-onset Complications of the Ketogenic Diet for Intractable Epilepsy

Abstract: Summary: Purpose: This study was undertaken to evaluate the exact limitations of the ketogenic diet (KD) and to collect data on the prevention and management of its risks Methods: Patients (129) who were on the KD from July 1995 to October 2001 at our epilepsy center were assessed in the study Early-onset (within 4 weeks of the commencement of the KD until stabilization) and late-onset complications (occurring after 4 weeks) were reviewed Results: The most common early-onset complication was dehydration, especially in patients who started the KD with initial fasting Gastrointestinal (GI) disturbances, such as nausea/vomiting, diarrhea, and constipation, also were frequently noted, sometimes associated with gastritis and fat intolerance Other early-onset complications, in order of frequency, were hypertriglyceridemia, transient hyperuricemia, hypercholesterolemia, various infectious diseases, symptomatic hypoglycemia, hypoproteinemia, hypomagnesemia, repetitive hyponatremia, low concentrations of high-density lipoprotein, lipoid pneumonia due to aspiration, hepatitis, acute pancreatitis, and persistent metabolic acidosis Late-onset complications also included osteopenia, renal stones, cardiomyopathy, secondary hypocarnitinemia, and iron-deficiency anemia Most early- and late-onset complications were transient and successfully managed by careful follow-up and conservative strategies However, 22 (171%) patients ceased the KD because of various kinds of serious complications, and four (31%) patients died during the KD, two of sepsis, one of cardiomyopathy, and one of lipoid pneumonia Conclusions: Most complications of the KD are transient and can be managed easily with various conservative treatments However, life-threatening complications should be monitored closely during follow-up

The Reliability and Validity of Kiddie-Schedule for Affective Disorders and Schizophrenia-Present and Lifetime Version- Korean Version (K-SADS-PL-K)

Abstract: In order to develop a structured and objective diagnostic instrument, authors completed: (1) the translation and back translation of the Korean version of the Kiddie-Schedule for Affective Disorders and Schizophrenia - Present and Lifetime Version (K-SADS-PL) and (2) the examination of its validity and reliability of the K-SADS-PL-Korean version (K-SADS- PL) when used with Korean children. A total of 91 study subjects were recruited from child and adolescent psychiatry outpatient clinics. Clinical diagnoses were used as a gold standard for the examination of validity of K-SADS-PL-K. Consensual validity of threshold and sub-threshold diagnoses were good to excellent for attention-deficit/hyperactivity disorder (ADHD), fair for tic and oppositional defiant disorders, and poor to fair for anxiety and depressive disorders. Inter-rater and test-retest reliabilities were fair to excellent for ADHD and tic disorder. The significant correlations between the K-SADS-PL-K and Korean Child Behavior Checklist (K-CBCL) were found, which provided additional support for the concurrent validity of the K-SADS-PL-K. Sensitivities varied according to the diagnostic categories, but specificities remained high over all diagnoses, suggesting that the K-SADS-PL-K is a desirable confirmatory diagnostic tool. The results of this study suggest that the K-SADS-PL-K is an effective instrument for diagnosing major child psychiatric disorders, including ADHD, behavioral disorders and tic disorders in Korean children. Future studies will examine the validity and reliability of the K-SADS-PL-K in larger samples, including adolescents and community samples on a variety of child and adolescent psychiatric disorders.

Bioactive metals: preparation and properties.

Abstract: Some ceramics, such as Bioglass, sintered hydroxyapatite, and glass-ceramic A-W, spontaneously form a bone-like apatite layer on their surface in the living body, and bond to bone through the apatite layer. These materials are called bioactive ceramics, and are clinically important for use as bone-repairing materials. However, they cannot be used at high-load sites, such as is found in femoral and tibial bones, because their fracture toughness values are not as high as that of human cortical bone. Titanium metal and its alloys have high fracture toughness, and form a sodium titanate layer on its surface when soaked in a 5 M-NaOH solution at 60 degrees C for 24 h, followed by a heat treatment at 600 degrees C for 1 h. On moving toward the metal interior, the sodium titanate layer gradually changes into the pure metal within a distance of 1 microm from the surface. The mechanical strength of the titanium metal or a titanium alloy is not adversely affected by these chemical and thermal treatments. The titanium metal and its alloys resulting from the above treatment can release Na+ ions from its surface into a surrounding body fluid via an ion exchange reaction with H3O+ ions, resulting in many Ti-OH groups forming on its surface. These Ti-OH groups initially combine with Ca2+ ions to form amorphous calcium titanate in the body environment, and later the calcium titanate combines with phosphate ions to form amorphous calcium phosphate. The amorphous calcium phosphate eventually transforms into bone-like apatite, and by this process the titanium metals are soon tightly bonded to the surrounding living bone through the bone-like apatite layer. The treated metals have already been subjected to clinical trials for applications in artificial total hip joints. Metallic tantalum has also been found to bond to living bone after it has been subjected to the NaOH and heat treatment to form a sodium tantalate layer on its surface.

Initial trust and the adoption of B2C e-commerce: The case of internet banking

Abstract: A possible reason for the delayed acceptance of the Internet as a retail distribution channel may be the lack of trust consumers have in the electronic channel and in the Web merchants. Few prior studies on the adoption of business-to-consumer e-commerce have considered trust in information technology as an important determinant of adoption behavior. This research explicitly encompasses the electronic channel and the merchant as objects to be trusted in a specific e-commerce application, i.e. Internet banking.Our conceptual model posits that initial trust in the electronic channel as a banking medium and trust in bank are the major determinants of adoption behavior. Based on social network theory and trust theory, determinants of trust in the electronic channel such as propensity-to-trust, word-of-mouth (WOM) referrals, structural assurances, are included in the research model.The analyses of independent variables indicated that propensity-to-trust, structural assurances, and relational content of WOM were significant predictors of initial trust in the electronic channel. Our findings also indicated that a significant relationship exists between initial trust in the electronic channel and the adoption of Internet banking. However, further analysis revealed that trust could be a necessary but not a sufficient condition for the adoption of Internet banking.

Platelet microparticles induce angiogenesis in vitro.

Abstract: Platelet microparticles (PMP) are endogenous substances generated during the coagulation process in a hypercoagulable state. This study demonstrated that PMP promote the proliferation and survival, migration, and tube formation in human umbilical vein endothelial cells (HUVEC). Heat-treated PMP did not significantly decrease the angiogenic activity in HUVEC compared with that of the untreated PMP. Meanwhile when PMP were treated with activated charcoal, a procedure known to remove the lipid growth factors, the angiogenic activity was significantly reduced. These results suggest that the lipid component(s) of the PMP may be major active factor(s) and that protein component(s) may be minor contributor(s). PMP were also shown to augment endothelial progenitor cell differentiation in peripheral blood mononuclear cells. In addition, PMP-stimulated proliferation, chemotaxis and tube formation of the HUVEC was mediated via the Pertussis toxin-sensitive G protein, extracellular signal-regulated kinase and the phosphoinositide 3-kinase pathway. Herein, a new action of PMP was demonstrated to be a potent angiogenic stimulator. It is expected that in pathological states such as a growing tumour, PMP shed from the circulating platelets may reach adequate concentrations and that the elevated levels of PMP could contribute to florid formation of new blood vessels.

Shape evolution of single-crystalline iron oxide nanocrystals.

Abstract: Shape- and size-controlled synthesis of single-crystalline maghemite (γ-Fe2O3) nanocrystals are performed by utilizing a solution-based one-step thermolysis method. Modulating the growth parameters, such as the type and amount of capping ligands as well as the growth time, is shown to have a significant effect on the overall shape and size of the obtained nanocrystals and on the ripening process itself. The resulting shapes of the novel structures are diverse, including slightly faceted spheres, diamonds, prisms, and hexagons, all of which are in fact truncated dodecahedron structures with different degrees of truncation along the {111}, {110}, or {100} faces. Spherical nanocrystals are easily assembled into the three-dimensional superlattices, demonstrating the uniformity of these nanocrystals. The size-dependent magnetic properties are examined, and large hexagon-shaped γ-Fe2O3 nanocrystals are shown to be ferrimagnetic at room temperature.