Showing papers by "Seoul National University published in 1998"

Evidence for oscillation of atmospheric neutrinos

Abstract: We present an analysis of atmospheric neutrino data from a 33.0 kton yr (535-day) exposure of the Super-Kamiokande detector. The data exhibit a zenith angle dependent deficit of muon neutrinos which is inconsistent with expectations based on calculations of the atmospheric neutrino flux. Experimental biases and uncertainties in the prediction of neutrino fluxes and cross sections are unable to explain our observation. The data are consistent, however, with two-flavor ${\ensuremath{ u}}_{\ensuremath{\mu}}\ensuremath{\leftrightarrow}{\ensuremath{ u}}_{\ensuremath{\tau}}$ oscillations with ${sin}^{2}2\ensuremath{\theta}g0.82$ and $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}l\ensuremath{\Delta}{m}^{2}l6\ifmmode\times\else\texttimes\fi{}1{0}^{\ensuremath{-}3}\mathrm{eV}{}^{2}$ at 90% confidence level.

Gauss–Newton and full Newton methods in frequency–space seismic waveform inversion

Abstract: SUMMARY By specifying a discrete matrix formulation for the frequency^space modelling problem for linear partial diierential equations (‘FDM’ methods), it is possible to derive a matrix formalism for standard iterative non-linear inverse methods, such as the gradient (steepest descent) method, the Gauss^Newton method and the full Newton method We obtain expressions for each of these methods directly from the discrete FDM method, and we refer to this approach as frequency-domain inversion (FDI)The FDI methods are based on simple notions of matrix algebra, but are nevertheless very general The FDI methods only require that the original partial diierential equations can be expressed as a discrete boundary-value problem (that is as a matrix problem) Simple algebraic manipulation of the FDI expressions allows us to compute the gradient of the mis¢t function using only three forward modelling steps (one to compute the residuals, one to backpropagate the residuals, and a ¢nal computation to compute a step length) This result is exactly analogous to earlier backpropagation methods derived using methods of functional analysis for continuous problems Following from the simplicity of this result, we give FDI expressions for the approximate Hessian matrix used in the Gauss^Newton method, and the full Hessian matrix used in the full Newton method In a new development, we show that the additional term in the exact Hessian, ignored in the Gauss^Newton method, can be e⁄ciently computed using a backpropagation approach similar to that used to compute the gradient vector The additional term in the Hessian predicts the degradation of linearized inversions due to the presence of ¢rst-order multiples (such as free-surface multiples in seismic data) Another interpretation is that this term predicts changes in the gradient vector due to second-order non-linear eiects In a numerical test, the Gauss^Newton and full Newton methods prove eiective in helping to solve the di⁄cult non-linear problem of extracting a smooth background velocity model from surface seismic-re£ection data

Essential role of mouse telomerase in highly proliferative organs

Abstract: We have investigated the role of the enzyme telomerase in highly proliferative organs in successive generations of mice lacking telomerase RNA. Late-generation animals exhibited defective spermatogenesis, with increased programmed cell death (apoptosis) and decreased proliferation in the testis. The proliferative capacity of haematopoietic cells in the bone marrow and spleen was also compromised. These progressively adverse effects coincided with substantial erosion of telomeres (the termini of eukaryotic chromosomes) and fusion and loss of chromosomes. These findings indicate an essential role for telomerase, and hence telomeres, in the maintenance of genomic integrity and in the long-term viability of high-renewal organ systems.

Human capital, social capital, and firm dissolution

Abstract: This study examined the effect of human and social capital upon firm dissolution with data from a population of Dutch accounting firms for the period 1880–1990. Human capital was captured by firm-l...

Measurements of the solar neutrino flux from Super-Kamiokande's first 300 days

Abstract: The first results of the solar neutrino flux measurement from Super-Kamiokande are presented. The results shown here are obtained from data taken between 31 May 1996, and 23 June 1997. Using our measurement of recoil electrons with energies above 6.5 MeV, we infer the total flux of ${}^{8}\mathrm{B}$ solar neutrinos to be $2.42\ifmmode\pm\else\textpm\fi{}0.06(\mathrm{stat}{)}_{\ensuremath{-}0.07}^{+0.10}(\mathrm{syst})\ifmmode\times\else\texttimes\fi{}{10}^{6}\mathrm{cm}{}^{\ensuremath{-}2}{\mathrm{s}}^{\ensuremath{-}1}$. This result is consistent with the Kamiokande measurement and is 36% of the flux predicted by the BP95 solar model. The flux is also measured in 1.5 month subsets and shown to be consistent with a constant rate.

Biased PNG law for impact with angular constraint

Abstract: A new homing guidance law is proposed to impact a target with a desired attitude angle. It is a variation of the conventional proportional navigation guidance (PNG) law which includes a supplementary time-varying bias. The proposed guidance law does not require a time-to-go estimation and has a simpler form. Analytic conditions for fulfilling the guidance goal are also provided. Simulation results demonstrate that the proposed guidance law has wider launch envelopes than the previous one and shows a good performance even against a maneuvering target.

Numerical solutions of flow past a circular cylinder at Reynolds numbers up to 160

Abstract: Flow past a circular cylinder at Reynolds numbers up to 160 is simulated using high resolution calculations. Flow quantities at the cylinder surface are obtained and compared with those from the existing experimental and numerical studies. The present study reports the detailed information of flow quantities on the cylinder surface at low Reynolds numbers.

Self-Assembly of Molecular Brick Wall and Molecular Honeycomb from Nickel(II) Macrocycle and 1,3,5-Benzenetricarboxylate: Guest-Dependent Host Structures

Abstract: Novel multidimensional supramolecular networks with brick wall and honeycomb structures, [Ni(C12H30N6O2)]3[C6H3(COO)3]2·18H2O (1) and [Ni(C12H30N6O2)]3[C6H3(COO)3]2·14H2O·2C5H5N (2), respectively, have been constructed by the self-assembly of S = 0 Ni(II) macrocyclic complex containing hydroxyl pendent chains and 1,3,5-benzenetricarboxylate (BTC3-). The host structures assembled are greatly affected even by the partial change of the guests. X-ray crystal structures indicate that each Ni(II) macrocycle binds two BTC3- in the trans position and each BTC3- coordinates three Ni(II) macrocyclic units via C1 symmetry in 1 and C3 symmetry in 2. The simplest cyclic motif of the two-dimensional (2-D) networks in 1 and 2 is a large ring consisting of six Ni(II) macrocyclic complexes and six BTC3- anions. The rings are extended to form a 2-D layer. The layers are stacked in parallel, separated by 8.850 A in 1 and 8.973 A in 2. They are interconnected by the hydrogen-bonding interactions between the hydroxyl pendants...

Broken symmetry and pseudogaps in ropes of carbon nanotubes

Abstract: Since the discovery of carbon nanotubes1, it has been speculated that these materials should behave like nanoscale wires with unusual electronic properties and exceptional strength Recently, ‘ropes’ of close-packed single-wall nanotubes have been synthesized in high yield2 The tubes in these ropes are mainly of the (10,10) type3, which is predicted to be metallic4,5,6 Experiments on individual nanotubes and ropes7,8 indicate that these systems indeed have transport properties that qualify them to be viewed as nanoscale quantum wires at low temperature It has been expected that the close-packing of individual nanotubes into ropes does not change their electronic properties significantly Here, however, we present first-principles calculations which show that a broken symmetry of the (10,10) tube caused by interactions between tubes in a rope induces a pseudogap of about 01 eV at the Fermi level This pseudogap strongly modifies many of the fundamental electronic properties: we predict a semimetal-like temperature dependence of the electrical conductivity and a finite gap in the infrared absorption spectrum The existence of both electron and hole charge carriers will lead to qualitatively different thermopower and Hall-effect behaviours from those expected for a normal metal

Analysis of cache-related preemption delay in fixed-priority preemptive scheduling

Abstract: We propose a technique for analyzing cache-related preemption delays of tasks that cause unpredictable variation in task execution time in the context of fixed-priority preemptive scheduling. The proposed technique consists of two steps. The first step performs a per-task analysis to estimate cache-related preemption cost for each execution point in a given task. The second step computes the worst case response time of each task that includes the cache-related preemption delay using a response time equation and a linear programming technique. This step takes as its input the preemption cost information of tasks obtained in the first step. This paper also compares the proposed approach with previous approaches. The results show that the proposed approach gives a prediction of the worst case cache-related preemption delay that is up to 60 percent tighter than those obtained from the previous approaches.

Brain abscess and necrotic or cystic brain tumor: discrimination with signal intensity on diffusion-weighted MR imaging.

Abstract: OBJECTIVE: The purpose of this study was to determine the differences in signal intensity between brain abscesses and necrotic or cystic tumors on diffusion-weighted MR imaging. CONCLUSION: Five consecutive patients with proven brain abscesses and four patients with proven cystic or necrotic brain tumors were prospectively evaluated with diffusion-weighted imaging. On diffusion-weighted imaging, brain abscesses showed markedly hyperintense signal in all five patients, whereas necrotic or cystic brain tumors revealed hypointense signal in all four patients. Diffusion-weighted imaging may allow the differentiation of brain abscess from necrotic or cystic brain tumor.

Dodecanethiol-Derivatized Au/Ag Bimetallic Nanoparticles: TEM, UV/VIS, XPS, and FTIR Analysis.

Abstract: Dodecanethiol-derivatized Au/Ag bimetallic nanoparticles that can be dissolved in nonpolar solvents were prepared via a two-phase synthetic route in water/toluene mixtures. The position of the surface plasmon band was found to vary linearly between 419 and 522 nm as a function of mole fraction of Au (or Ag) content, implying ready formation of Au-Ag alloy clusters. Transmission electron microscopy images revealed that the bimetallic clusters were monodisperse with an average size of approximately 4 nm. Infrared spectral features indicate that the alkyl chains of the dodecanethiolate species take fully extended trans zigzag conformations on all alloy clusters. The most interesting finding deduced from X-ray photoelectron spectroscopy and FTIR spectroscopic measurements was that Ag atoms are enriched at the outer part of the alloy clusters when compared with the Au atoms. Copyright 1998 Academic Press.

Latecomer Strategies: Evidence From the Semiconductor Industry in Japan and Korea

Abstract: The effects of strategic order of entry on firms' performance have long been an issue in many areas of study. Past res earch efforts, however, have been concentrated mostly on first mover or early entrant advantages. To contribute to developing a theory of latecomer strategies, the authors investigate how latecomers compete successfully or even leapfrog early movers. They review previous studies on early mover advantages and disadvantages, and group the sources of such advantages or disadvantages into three areas: the firm, its market, and its competitors. The theoretical focus is how a firm converts the opportunities ste mming from entry order into performance. The authors seek to confirm and extend relevant theories by examining how late entrants have caught up with incumbent industry leaders in the global semiconductor industry. On the basis of in-depth case analysis of three Japanese and three Korean semiconductor companies, they identify and categorize successful latecomer strategies into two types: strategies for overcoming latecomer disadvantages and strategies for utilizing latecomer advantages. Focusing, thin margin or loss bearing, and volume building form the essence of strategies for overcoming disadvantages, whereas odd timing, time compression, human embodied technology transfer, benchmarking, technological leap frogging, and resource leveraging form the essence of strategies for utilizing advantages. Because many companies in Asia have had to face the reality of being latecomers, the Asian perspectives are particularly useful for studying and explicating latecomer strategies.

Chemoprotective properties of some pungent ingredients present in red pepper and ginger

Abstract: There has been a substantial body of data, supporting that dietary factors have a profound impact on prevention as well as etiology of human cancer. Capsaicin has been tested by many investigators for its effects on experimental carcinogenesis and mutagenesis. Data in the literature indicate that capsaicin has dual effects on carcinogenic and mutagenic processes. At present, there is no solid evidence that hot red and chili peppers or their principal pungent ingredient capsaicin are carcinogenic in humans although results of early investigations with experimental animals exhibit the moderate tumorigenicity of this compound. In contrast, recent studies reveal substantial antigenotoxic and anticarcinogenic effects of capsaicin, suggesting this compound as another important dietary phytochemical with a potential chemopreventive activity. Some pungent constituents present in ginger and other zingiberaceous plants have potent antioxidant and anti-inflammatory effects, and some of them exhibit anti-tumor promotional activity in experimental carcinogenesis.

REAL classification of malignant lymphomas in the Republic of Korea : Incidence of recently recognized entities and changes in clinicopathologic features

Abstract: BACKGROUND The clinicopathologic characteristics of malignant lymphomas vary according to geography. The aim of this study was to determine the clinical characteristics of malignant lymphomas and the relative frequency in the Republic of Korea of lymphomas belonging to the newly described REAL (revised European-American lymphoma) classification categories. METHODS The Hematolymphoreticular Study Group of the Korean Society of Pathologists conducted a consensus-based morphologic review of a nationwide collection of 1548 malignant lymphomas, including Hodgkin's disease (HD), diagnosed at 23 institutes over a recent 2-year period. Slides stained with hematoxylin and eosin or other immunohistochemical stains were reviewed. All cases were classified according to the histologic criteria proposed by the International Lymphoma Study Group. Clinical data, including age, gender, and site of disease involvement, were reviewed. RESULTS The Republic of Korea had lower rates of HD and follicle center lymphoma and higher rates of extranodal lymphoma, diffuse large B-cell lymphoma, and angiocentric lymphoma compared with Western countries. The most frequent subtypes of non-Hodgkin's lymphoma (NHL) were diffuse large B-cell lymphoma, extranodal marginal zone B-cell lymphoma, peripheral T-cell lymphoma, unspecified type, and angiocentric lymphoma, in decreasing order. Compared with a previous nationwide study, the rates for follicular lymphoma and NHL involving the stomach, orbit, and central nervous system were increased. The rate of T-cell NHL in the current study was much lower than that reported in a previous study for the Republic of Korea and was also lower than that reported for other Far East countries. For HD, the relative frequency of nodular sclerosis subtype was higher compared with that in the previous study, and lymphocyte predominance and lymphocyte depletion were lower. CONCLUSIONS The occurrence rates for various subtypes of malignant lymphoma in the Republic of Korea are distinct from those in Western countries and similar in many ways to those in other countries in the Far East. Compared with other Far East countries, the Republic of Korea has a higher rate of extranodal lymphoma, rare adult T-cell lymphoma, and a relatively low rate of T-cell lymphomas. It appears that over time there have been changes in the relative rates for follicular lymphoma, subtypes of Hodgkin's disease, and gastric and orbital lymphoma. The authors attribute these changes primarily to refined criteria for diagnosing new clinicopathologic entities. Cancer 1998;83:806-812. © 1998 American Cancer Society.

Prevalence of symptoms of depression in a nationwide sample of Korean adults

Abstract: The prevalence and correlates of symptoms of depression in a nationwide sample of Korean adults, collected during the National Health and Health Behavior Examination Survey, were examined. A probability sample of 3,711 respondents (a response rate of 81.3%) completed the Center for Epidemiologic Studies Depression Scale (CES-D) and a variety of sociodemographic questions. In this sample 23.1% of males and 27.4% of females had scores above the cutoff point of 16 (probable depression) on the CES-D scale, and 6.8% of males and 10.4% of females were above the cutoff point of 25 (severe, definite depression). Apart from a few reports describing Afro-American and Puerto-Rican samples, these rates were somewhat higher than those found in the US and Western countries. In this report, female gender, fewer than 13 years of education, and disrupted marriage (widowed/divorced/separated) proved to be statistically significant predictors of severe, definite symptoms of depression.

FSA-based link assignment and routing in low-earth orbit satellite networks

Abstract: We propose a new framework for the link assignment (i.e., topological design) problem that arises from the use of intersatellite links (ISL's) in low-earth orbit (LEO) satellite networks. In the proposed framework, we model an LEO satellite network as a finite state automaton (FSA), where each state corresponds to an equal-length interval in the system period of the LEO satellite network. This FSA-based framework allows the link assignment problem in LEO satellite networks to be treated as a set of link assignment problems in fixed topology networks. Within this framework, we study various link assignment and routing schemes. In particular, both regular link assignment and link assignment optimized by simulated annealing are considered. For each link assignment, both static and dynamic routing schemes are considered. Our simulation results show that the optimized link assignment combined with static routing achieves the best performance in terms of both newly initiated call blocking probability and ongoing call blocking probability. The results also show that when the link assignment is the same, static routing gives better performance than dynamic routing since the latter requires a substantial amount of time to stabilize its routing table after a state transition.

The Vestigial and Scalloped proteins act together to directly regulate wing-specific gene expression in Drosophila

Abstract: A small number of major regulatory (selector) genes have been identified in animals that control the development of particular organs or complex structures. In Drosophila, the vestigial gene is required for wing formation and is able to induce wing-like outgrowths on other structures. However, the molecular function of the nuclear Vestigial protein, which bears no informative similarities to other proteins, was unknown. Here, we show that Vestigial requires the function of the Scalloped protein, a member of the TEA family of transcriptional regulators, to directly activate the expression of genes involved in wing morphogenesis. Genetic and molecular analyses reveal that Vestigial regulates wing identity by forming a complex with the Scalloped protein that binds sequence specifically to essential sites in wing-specific enhancers. These enhancers also require the direct inputs of signaling pathways, and the response of an enhancer can be switched to another pathway through changes in signal-transducer binding sites. Combinatorial regulation by selector proteins and signal transducers is likely to be a general feature of the tissue-specific control of gene expression during organogenesis.