Showing papers by "Yonsei University published in 2002"

New Sonographic Criteria for Recommending Fine-Needle Aspiration Biopsy of Nonpalpable Solid Nodules of the Thyroid

Abstract: OBJECTIVE. The purpose of our study was to provide new sonographic criteria for fine-needle aspiration biopsy of nonpalpable solid thyroid nodules.MATERIALS AND METHODS. Sonographic scans of 155 nonpalpable thyroid nodules in 132 patients were prospectively classified as having positive or negative findings. Sonographic findings that suggested malignancy included microcalcifications, an irregular or microlobulated margin, marked hypoechogenicity, and a shape that was more tall than it was wide. If even one of these sonographic features was present, the nodule was classified as positive (malignant). If a nodule had none of the features described, it was classified as negative (benign). The final diagnosis of a lesion as benign (n = 106) or malignant (n = 49) was confirmed by fine-needle aspiration biopsy and follow-up (>6 months) in 83 benign nodules, by fine-needle aspiration biopsy and surgery in 44 malignant and 15 benign lesions, and by surgery alone in five malignant and eight benign lesions. The sens...

Recurrence following curative resection for gastric carcinoma.

Abstract: Background: The diagnosis and treatment of recurrent gastric cancer remains difficult. The aim of this study was to determine the risk factors for recurrence of gastric cancer and the prognosis for these patients. Methods: Of 2328 patients who underwent curative resection for gastric cancer from 1987 to 1995, 508 whose recurrence was confirmed by clinical examination or reoperation were studied retrospectively. The risk factors that determined the recurrence patterns and timing were investigated by univariate and multivariate analysis. Results: The mean time to recurrence was 21·8 months and peritoneal recurrence was the most frequent (45·9 per cent). Logistic regression analysis showed that serosal invasion and lymph node metastasis were risk factors for all recurrence patterns and early recurrence (at 24 months or less). In addition, independent risk factors involved in each recurrence pattern included younger age, infiltrative or diffuse type, undifferentiated tumour and total gastrectomy for peritoneal recurrence; older age and larger tumour size for disseminated, haematogenous recurrence; and older age, larger tumour size, infiltrative or diffuse type, proximally located tumour and subtotal gastrectomy for locoregional recurrence. Other risk factors for early recurrence were infiltrative or diffuse type and total gastrec-tomy. Reoperation for cure was possible in only 19 patients and the mean survival time after conservative treatment or palliative operation was less than 12 months. Conclusion: The risk factors for each recurrence pattern and timing of gastric cancer can be predicted by the clinicopathological features of the primary tumour. Since the results of treatment remain dismal, studies of perioperative adjuvant therapy in an attempt to reduce recurrence are warranted. © 2000 British Journal of Surgery Society Ltd

Structural Models of Corporate Bond Pricing: An Empirical Analysis

Abstract: This paper empirically tests five structural models of corporate bond pricing: Those of Merton (1974), Geske (1977), Leland and Toft (1996), Longstaff and Schwartz (1995), 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. The compound option approach of Geske comes much closer to the spreads observed in the market, on average, but still underpredicts spreads. In contrast, the Leland and Toft model substantially overestimates credit risk on most bonds, and especially so for high coupon bonds. The Longstaff and Schwartz model modifies Merton to incorporate a stochastic interest rate and a correlation between interest rates and firm value. While the correlation and the level of interest rates have little effect, higher interest rate volatility leads to higher predicted spreads. However, this and other features of this model result in spreads that are often too high for risky bonds and too low for safe bonds. The target leverage ratio model of Collin-Dufresne and Goldstein helps to raise the spreads on the bonds that were considered very safe by the Longstaff and Schwartz model, but overall tends toward overestimation of credit risk. We conclude that structural models do not systematically underpredict spreads, as the previous literature implies, but accuracy is a problem. Moreover, some of the simplifications made to date lead to overestimation of credit risk on the riskier bonds while scarcely affecting the spreads of the safest bonds.

The injured brain interacts reciprocally with neural stem cells supported by scaffolds to reconstitute lost tissue

Abstract: Hypoxic-ischemic injury is a prototype for insults characterized by extensive tissue loss. Seeding neural stem cells (NSCs) onto a polymer scaffold that was subsequently implanted into the infarction cavities of mouse brains injured by hypoxia-ischemia allowed us to observe the multiple reciprocal interactions that spontaneously ensue between NSCs and the extensively damaged brain: parenchymal loss was dramatically reduced, an intricate meshwork of many highly arborized neurites of both host- and donor-derived neurons emerged, and some anatomical connections appeared to be reconstituted. The NSC‐scaffold complex altered the trajectory and complexity of host cortical neurites. Reciprocally, donor-derived neurons were seemingly capable of directed, target-appropriate neurite outgrowth (extending axons to the opposite hemisphere) without specific external instruction, induction, or genetic manipulation of host brain or donor cells. These “biobridges” appeared to unveil or augment a constitutive reparative response by facilitating a series of reciprocal interactions between NSC and host, including promoting neuronal differentiation, enhancing the elaboration of neural processes, fostering the re-formation of cortical tissue, and promoting connectivity. Inflammation and scarring were also reduced, facilitating reconstitution.

Imipenem-EDTA Disk Method for Differentiation of Metallo-β-Lactamase-Producing Clinical Isolates of Pseudomonas spp. and Acinetobacter spp.

Abstract: Rapid detection of metallo-β-lactamase (MBL)-producing gram-negative bacilli is necessary to prevent their dissemination. The method using a disk with imipenem plus 750 μg of EDTA differentiated all MBL-producing pseudomonads, and the sensitivity and specificity for acinetobacters were 95.7 and 91.0%, respectively. The imipenem-EDTA disks were stable for 12 and 16 weeks at 4 and −20°C, respectively.

Single-crystalline star-shaped nanocrystals and their evolution: programming the geometry of nano-building blocks.

Abstract: We demonstrate a novel synthetic scheme that can be used to differentially guide the shape of PbS semiconductor nanocrystals. Our study first demonstrates the discovery of single-crystalline star-shaped nanocrystals as novel transient species. We then carefully probe their shape evolution toward other novel nanostructures (e.g., tadpole-, L-, T-, cross-shapes, highly faceted star shapes, truncated octahedrons and cubes, etc.) and systematically elucidate the key parameters that control these final structures. In principle, through programming these growth parameters, the desired architecture of building blocks of other kinds of nano materials can be constructed.

Observation of B̄0 → D(*)0 pp̄

Abstract: The B meson decay modes B → Dpp and B → D*pp have been studied using 29.4 fb - 1 of data collected with the Belle detector at KEKB. The B 0 → D 0 pp and B 0 → D* 0 pp decays have been observed for the first time with branching fractions B(B 0 → D 0 pp) = (1.18 ′ 0.15 ′ 0.16) X 10 - 4 and B(B 0 → D* 0 pp) = (1.20 + 0 . 3 3 - 0 . 2 9 ′ 0.21) X 10 - 4 . No signal has been found for the B + → D + pp and B + → D* + pp decay modes, and the corresponding upper limits at 90% C.L. are presented.

The Y2 Isochrones for α-Element Enhanced Mixtures

Abstract: We present a new set of isochrones in which the effect of the α-element enhancement is fully incorporated. These isochrones are an extension of the already published set of Y2 Isochrones (our Paper I), constructed for the scaled-solar mixture. As in Paper I, helium diffusion and convective core overshoot have been taken into account. The range of chemical compositions covered is 0.00001 ≤ Z ≤ 0.08. The models were evolved from the pre-main-sequence stellar birthline to the onset of helium burning in the core. The age range of the full isochrone set is 0.1-20 Gyr, while younger isochrones of age 1-80 Myr are also presented up to the main-sequence turn-off. Combining this set with that of Paper I for scaled-solar mixture isochrones, we provide a consistent set of isochrones that can be used to investigate populations of any value of α-enhancement. We confirm the earlier results of Paper I that inclusion of α-enhancement effects further reduces the age estimates of globular clusters by approximately 8% if [α/Fe]= +0.3. It is important to note the metallicity dependence of the change in age estimates (larger age reductions in lower metallicities). This reduces the age gap between the oldest metal-rich and metal-poor Galactic stellar populations and between the halo and the disk populations. We also investigate whether the effects of α-enhancement can be mimicked by increasing the total metal abundance in the manner proposed by Salaris and collaborators. We find such simple scaling formulae are valid at low metallicities but not at all at high metallicities near and above solar. Thus, it is essential to use the isochrones rigorously computed for α-enhancement when modeling metal-rich populations, such as bright galaxies. The isochrone tables, together with interpolation routines have been made available via internet.

Applications of Support Vector Machines for Pattern Recognition: A Survey

Abstract: In this paper, we present a comprehensive survey on applications of Support Vector Machines (SVMs) for pattern recognition. Since SVMs show good generalization performance on many real-life data and the approach is properly motivated theoretically, it has been applied to wide range of applications. This paper describes a brief introduction of SVMs and summarizes its numerous applications.

A Study of the Preparation of NiO x Electrode via Electrochemical Route for Supercapacitor Applications and Their Charge Storage Mechanism

Abstract: NiO x thin film electrodes were prepared for use in a supercapacitor by electrochemical precipitation of Ni(OH) 2 films followed by heat-treatment. The effect of electrodeposition conditions such as cathodic current density and concentration of Ni(NO 3 ) 2 solution on the surface morphology of NiO x were examined and found to have a significant effect on the surface morphology of the deposited films. The surface morphology of the NiO x films changed from dense to porous morphology with an increase in the deposition rate of Ni(OH) 2 films. A maximum specific capacitance of 277 F/g was obtained for a highly porous NiO x film electrode prepared by heating the Ni(OH) 2 film deposited at 4.0 mA/cm 2 in 0.1 M Ni(NO 3 ) 2 at 300°C. The charge-storage mechanism of NiO x in 1 M KOH was investigated using an electrochemical quartz crystal microbalance (EQCM) and probe beam deflection (PBD) technique. Nonmonotonic mass change was observed during redox reactions of the nickel oxide film in I M KOH. Analysis of the EQCM and PBD results showed that the electrochemical redox reaction of the NiO x is not a simple OH adsorption/desorption reaction hut rather composed of predominant H + desorption in the initial stage of oxidation and thereafter predominant OH adsorption in the latter stage of oxidation and vice versa during reduction.

Thermal stability and structural characteristics of HfO2 films on Si (100) grown by atomic-layer deposition

Abstract: The thermal stability and structural characteristics for gate stack structure of HfO2 dielectrics deposited by atomic-layer deposition (ALD) were investigated. The structural characteristics and chemical state of the HfO2 films in relation to the film thickness and postannealing temperature were examined by x-ray diffraction and x-ray photoelectron spectroscopy. An interfacial layer of hafnium silicate with an amorphous structure was grown on the oxidized Si substrate at an initial growth stage. The structural characteristics of the HfO2 films are closely affected by the interfacial layer and are depended on the thickness of the films. The 45 A thick HfO2 film with an amorphous structure was changed into a polycrystalline structure after rapid temperature annealing of 750 °C for 5 min, while thicker films were grown into a polycrystalline structure of monoclinic or tetragonal crystal structure. The silicate layer grown at the interfacial region is not stable even at 700 °C under ultrahigh vacuum condition...

Polarization-dependent optical second-harmonic imaging of a rat-tail tendon.

Abstract: Using scanning confocal microscopy, we measure the backscattered second harmonic signal generated by a 100 fs laser in rat-tail tendon collagen. Damage to the sample is avoided by using a continuous scanning technique, rather than measuring the signal at discrete points. The second harmonic signal varies by about a factor of 2 across a single cross section of the rat-tail tendon fascicle. The signal intensity depends both on the collagen organization and the backscattering efficiency. This implies that we cannot use intensity measurements alone to characterize collagen structure. However, we can infer structural information from the polarization dependence of the second harmonic signal. Axial and transverse scans for different linear polarization angles of the input beam show that second harmonic generation (SHG) in the rat-tail tendon depends strongly on the polarization of the input laser beam. We develop an analytical model for the SHG as a function of the polarization angle in the rat-tail tendon. We apply this model in determining the orientation of collagen fibrils in the fascicle and the ratio gamma between the two independent elements of the second-order nonlinear susceptibility tensor. There is a good fit between our model and the measured data.

Bifurcations and chaos in a permanent-magnet synchronous motor

Abstract: This brief studies dynamic characteristics of a permanent-magnet synchronous motor (PMSM). The mathematical model of the PMSM is first derived, which is fit for carrying out the bifurcation and chaos analysis. Then, the steady-state characteristics of the system, when subject to constant input voltage and constant external torque, are formulated. Three cases are discussed and, for each case, conditions are derived under which the dynamic characteristics of the system are either of steady-state type, limit cycles or chaotic, thus by properly adjusting some system parameters, the system can exhibit limit cycles (LCs) or chaotic behaviors at will. Finally, computer simulations are presented to verify the existence of strange attractors in the PMSM.

The Y^2 Stellar Evolutionary Tracks

Abstract: We present a database of the latest stellar models of the $Y^2$ (Yonsei-Yale) collaboration. This database contains the stellar evolutionary tracks from the pre-main-sequence birthline to the helium core flash that were used to construct the $Y^2$ isochrones. We also provide a simple interpolation routine that generates stellar tracks for given sets of parameters (metallicity, mass, and $\alpha$-enhancement).

Oxygen contribution on Li-ion intercalation-deintercalation in LiCoO2 investigated by O K-edge and Co L-edge X-ray absorption spectroscopy

Abstract: To investigate the electronic structure of the electrochemically Li-ion deintercalated Li 1 - x CoO 2 system, soft X-ray absorption spectroscopy (XAS) for the oxygen K-edge and the Co L I I , I I I -edge has been carried out intensively with compositional x value variation, compared with Co K-edge X-ray absorption near edge structure (XANES) spectroscopy. To get reasonably good XAS spectra for the electrochemically Li-ion deintercalated Li 1 - x CoO 2 system, we made a binder-free LiCoO 2 film electrode using the electrostatic spray deposition (ESD) technique. The oxygen K-edge XAS for Li 1 - x CoO 2 shows more effective spectral change with respect to Li-ion content than the Co L I I , I I I -edge XAS. The dependence of the absorption peak feature on the Li content is described in terms of the ground state of the Co and O atoms, showing the systematic variation of the hole-state site distribution between Co and oxygen atoms. From the Co L I I , I I I -edge XAS, it is found that the broad peak shift to higher energy with the Li-ion deintercalation is due to rehybridization between Co and O atoms under the local structural distortion of CoO 6 octahedra, which is also confirmed by the formation of two additional absorption peaks below the threshold energy corresponding to the oxygen 2p hole state hybridized with the 3d orbital of Co ion in the distorted CoO 6 octahedral site. In the O K-edge XAS spectra for the deintercalated Li 1 - x CoO 2 film, the shoulder absorption peak in the energy region higher than the threshold energy could be assigned to the higher oxidation state of the oxygen site on Li deintercalation. From the Co L I I , I I I -edge and O K-edge XAS results for the Li-ion deintercalated Li 1 - x CoO 2 film, it is concluded that the charge compensation for the Li-ion deintercalation process could be achieved mainly in the oxygen site and Co metal atomic site simultaneously. O K-edge and Co L I I , I I I -edge XAS results for cycled LiCoO 2 film show that the capacity fading of the LiCoO 2 system is related to the decrease of Co-O bond covalency by the local structural distortion of CoO 6 octahedra remaining in the cycled LiCoO 2 .

Native-feather degradation by Fervidobacterium islandicum AW-1, a newly isolated keratinase-producing thermophilic anaerobe

Abstract: A native-feather-degrading thermophilic anaerobe was isolated from a geothermal hot stream in Indonesia. Isolate AW-1, identified as a member of the species Fervidobacterium islandicum, was shown to degrade native feathers (0.8%, w/v) completely at 70 °C and pH 7 with a maximum specific growth rate (0.14 h–1) in Thermotoga-Fervidobacterium (TF) medium. After 24 h of culture, feather degradation led to an increase in free amino acids such as histidine, cysteine and lysine. Moreover, nutritionally essential amino acids such as tryptophan and methionine, which are rare in feather keratin, were also produced as microbial metabolites. A homomultimeric membrane-bound keratinolytic protease (>200 kDa; 97 kDa subunits) was purified from a cell extract of F. islandicum AW-1. The enzyme exhibited activity toward casein and soluble keratin optimally at 100 °C and pH 9, and had a half-life of 90 min at 100 °C. The enzyme showed higher specific activity for the keratinous substrates than other proteases and catalyzed the cleavage of peptide bonds more rapidly following the reduction of disulfide bridges in feather keratin by 10 mM dithiothreitol. Therefore, the enzyme from F. islandicum AW-1 is a novel, thermostable keratinolytic serine protease.

Highly active and stable Ni/Ce-ZrO2 catalyst for H2 production from methane

Abstract: Steam reforming of methane has been carried out aimed at the development of new and highly active catalysts for H2 production The catalytic properties of Ni catalysts supported on various supports have been investigated in connection with characterization results obtained from XRD, H2 chemisorption, TPR and CO2-TPD Among the catalysts examined, Ni/Ce–ZrO2 exhibited the best activity and stability The remarkable catalytic performance is interpreted as a combined result of high oxygen storage capacity of ceria in Ce–ZrO2, strong interaction between Ni and Ce–ZrO2, basic property of the catalyst and rather high capability of H2 uptake

Atherosclerosis in rheumatoid arthritis: morphologic evidence obtained by carotid ultrasound.

Abstract: Objective Recent studies have suggested increased cardiovascular disease among patients with rheumatoid arthritis (RA). We undertook this study to obtain morphologic evidence of subclinical atherosclerosis in RA patients. Methods We used high-resolution B-mode ultrasound to compare carotid artery intima-media wall thickness (IMT) between 53 postmenopausal women with RA and 53 controls matched by age, sex, and menopause status. No subject in either group had a history of atherosclerosis or its complications. We investigated the association between IMT and relevant clinical and therapeutic variables, including the impact of low-dose corticosteroid therapy (≤10 mg/day prednisolone). Results The mean ± SD IMT of the left and right common carotid arteries in RA patients was significantly greater than that in controls (0.77 ± 0.09 mm versus 0.68 ± 0.14 mm; P < 0.001). Early RA (duration ≤1 year) was associated with lesser IMT than was RA of longer duration (0.72 ± 0.03 mm versus 0.78 ± 0.01 mm; P < 0.04). Prednisolone use was not associated with increased IMT (0.78 ± 0.02 mm in nonusers versus 0.76 ± 0.01 mm in users; P = 0.38). Conclusion Our data indicate that RA patients have an ultrasonic marker of early atherosclerosis consistent with an increased risk for atherosclerosis.

A novel timing estimation method for OFDM systems

Abstract: We present a novel timing offset estimation method for orthogonal frequency division multiplexing(OFDM) systems. The proposed estimator is designed to avoid the ambiguity in timing offset estimation. The performance of proposed scheme is presented in terms of mean and mean-square error (MSE) sense. The simulation results show that the proposed estimator is unbiased and has significantly smaller MSE.

Adsorption Equilibria of CO2 on Zeolite 13X and Zeolite X/Activated Carbon Composite

Abstract: The adsorption equilibria of CO2 on zeolite 13X and zeolite X/activated carbon composite (Zeocarbon) were measured by a static volumetric method. The equilibrium experiments were conducted at (273.15, 293.15, 313.15, 333.15, and 353.15) K and at pressures up to 102.0 kPa for zeolite 13X and 99.7 kPa for Zeocarbon. The experimental data obtained were correlated by the Toth, UNILAN, and Sips models, which are generally used for microporous adsorbents such as zeolites and activated carbon. The isosteric enthalpies of adsorption were calculated for CO2 on both adsorbents.