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K J Chang

Publications and source records attributed to K J Chang.

At least 19 recordsLinked to original sources
PubMed2003

Electrically deactivating nearest-neighbor donor-pair defects in Si.

Based on first-principles density-functional calculations, we propose a class of nearest-neighbor donor pairs that are energetically favorable in highly n-type Si. These donor pairs comprise dopant atoms either fourfold coordinated at the nearest-neighbor distance or threefold coordinated through bond-breaking relaxations. For P and As dopants, the two defect states are very close in energy, less than 0.1 eV, while the threefold coordinated state is more stable by 0.24 eV for Sb dopants. The former state has a very deep donor level close to the valence band maximum, while the defect level lies deep inside the valence band for the latter. Thus, both the donor pairs are electrically inactive at very high doping levels, and they are suggested to be responsible for the observed saturation of carriers.

Journal Article↗
PubMed2003

Dynamics of fullerene coalescence.

Fullerene coalescence experimentally found in fullerene-embedded single-wall nanotubes under electron-beam irradiation or heat treatment is simulated by minimizing the classical action for many atom systems. The dynamical trajectory for forming a (5,5) C120 nanocapsule from two C60 fullerene molecules consists of thermal motions around potential basins and ten successive Stone-Wales-type bond rotations after the initial cage-opening process for which energy cost is about 8 eV. Dynamical paths for forming large-diameter nanocapsules with (10,0), (6,6), and (12,0) chiral indexes have more bond rotations than 25 with the transition barriers in a range of 10-12 eV.

Journal Article↗
PubMed2003

Spectral correlation in incommensurate multiwalled carbon nanotubes.

We investigate the energy spectra of clean incommensurate double-walled carbon nanotubes, and find that the overall spectral properties are described by the critical statistics similar to that known in the Anderson metal-insulator transition. In the energy spectra, there exist three different regimes characterized by Wigner-Dyson, Poisson, and semi-Poisson distributions. This feature implies that the electron transport in incommensurate multiwalled nanotubes can be either diffusive, ballistic, or intermediate between them, depending on the position of the Fermi energy.

Journal Article↗
PubMed2003

Impact of endoscopic ultrasound combined with fine-needle aspiration biopsy in the management of esophageal cancer.

BACKGROUND AND STUDY AIMS: Endoscopic ultrasound (EUS) in combination with fine-needle aspiration biopsy (FNA) is a highly accurate method for the preoperative staging of esophageal cancer. Its impact on medical decision-making and the cost of care is unknown. This prospective case series was undertaken in order to determine the impact of EUS in combination with FNA on patients' choice of therapy and on the cost of care. PATIENTS AND METHODS: Sixty consecutive patients with esophageal cancer, referred for preoperative EUS staging in a large tertiary-care academic medical center, were enrolled. The accuracy of EUS, the impact of EUS-based staging on the patients' choice of therapy, and costs were studied. RESULTS: The accuracy rates for EUS combined with FNA in tumor and lymph-node staging were 83 % and 89 %, respectively. Twenty-five patients (42 %) had EUS stage I and II and were candidates for curative surgery. Twenty-eight patients (47 %) had stage III, and seven (12 %) had stage IV. All patients with stage I had surgery, while all patients with stage IV had medical therapy. The majority (62 %) of patients with stage II had surgery, while only a minority (25 %) of patients with stage III had surgery. Thirty-six patients (60 %) underwent medical therapy. Patients' medical decisions in favor of surgical or medical therapy correlated strongly with the results of their EUS staging ( P = 0.005), but not with age, sex, or referring physicians (surgeons vs. nonsurgeons). EUS-guided therapy potentially decreased the cost of care by $ 740 424 ($ 12 340/patient) by reducing the number of thoracotomies. CONCLUSIONS: Patients' decisions regarding therapy correlated with their overall tumor staging, suggesting that the information provided by EUS played a significant role in patients' decision-making. The use of EUS in combination with FNA reduces the cost of managing patients with esophageal cancer.

Adenocarcinoma↗
PubMed2002

Seasonal prevalence of anti-Japanese encephalitis virus antibody in pigs in different regions of Taiwan.

Although the endemic season of Japanese encephalitis lasts from May through October, sporadic cases occur in other months of the year. To appreciate the real situation of Japanese encephalitis virus (JEV) activity throughout the year, a survey was conducted using hemagglutination-inhibition test to detect the presence of anti-JEV antibodies in pigs' sera, which were collected from 4 regions of Taiwan between January 2000 and January 2001. Results indicate that (1) JEV-infected pigs were found throughout the year; (2) the prevalence rates of JEV in the 4 regions in descending order were 70% in Miaoli, 59% in Hualien, 52% in Pingtung, and 49% in Nantou; (3) similar to that in 1990, the peak endemic months appeared 1 month after the date of 50% seroconversion (May 21, 2000); (4) infected pigs were present during the period from December through April as a reservoir for over-wintering of JEV; and (5) there was a suggestive evidence for the occurrence of sporadic cases of JEV during the December-April period. In conclusion, JEV propagates and is active indigenously in the winter as well as other seasons of the year.

Animals↗
PubMed2001

Magnetic quantum dot: a magnetic transmission barrier and resonator.

We study the ballistic edge-channel transport in quantum wires with a magnetic quantum dot, which is formed by two different magnetic fields B(*) and B0 inside and outside the dot, respectively. We find that the electron states located near the dot and the scattering of edge channels by the dot strongly depend on whether B(*) is parallel or antiparallel to B0. For parallel fields, two-terminal conductance as a function of channel energy is quantized except for resonances, while, for antiparallel fields, it is not quantized and all channels can be completely reflected in some energy ranges. All these features are attributed to the characteristic magnetic confinements caused by nonuniform fields.

Journal Article↗
PubMed2001

Even-odd behavior of conductance in monatomic sodium wires.

With the aid of the Friedel sum rule, we perform first-principles calculations of conductances through monatomic Na wires, taking into account the sharp tip geometry and discrete atomic structure of electrodes. We find that conductances (G) depend on the number (L) of atoms in the wires; G is G(0)( = 2e(2)/h) for odd L, independent of the wire geometry, while G is generally smaller than G(0) and sensitive to the wire structure for even L. This even-odd behavior is attributed to the charge neutrality and resonant character due to the sharp tip structure. We suggest that similar even-odd behavior may appear in other monovalent atomic wires.

Journal Article↗
PubMed2001

Structural transformation in the formation of H-induced (111) platelets in Si.

On the basis of first-principles calculations, we present a structural model for the formation of H-induced (111) platelets in Si, which involves a structural transformation from a double-layer-H2(*) configuration of H2(*) aggregates into an H-saturated internal (111) surface structure. This reaction process preferably occurs at high H plasma treatment temperatures and subsequently generates H2 molecules in the platelet voids, consistent with experiments. Our model also reveals the important features observed in (111) platelets, such as high-resolution transmission electron microscopy images, step structures, lattice dilation lengths, and H vibrational frequencies.

Journal Article↗
PubMed2001

Mechanism for the enhanced diffusion of charged oxygen ions in SiO2.

Based on real-space multigrid electronic structure calculations, we find that a double Si-O-Si bridge structure is the lowest energy configuration of interstitial oxygen ions (O(-) and O(2-)) in SiO2, where two additional Si-O bonds are formed with almost no interaction between the interstitial and host O atoms, while the peroxy linkage is the most stable structure for neutral interstitial O. We propose a diffusion mechanism of interstitial O ions generated from molecular O2 under UV radiation, and find extremely low energy barriers of 0.11--0.27 eV for migration in the form of the double-bridge structure, in good agreement with enhanced oxidation experiments.

Journal Article↗
PubMed2001

EUS in the detection of ascites and EUS-guided paracentesis.

BACKGROUND: The utility of EUS was evaluated for detection of ascites and EUS-guided FNA of ascites in patients undergoing EUS for diagnosis and staging of GI malignancies. METHODS: A series (from March 1994 to October 1997) of 571 consecutive patients who underwent upper EUS for various indications was retrospectively reviewed. Follow-up clinical information was obtained from referring physicians, subsequent CT, and telephone interviews. RESULTS: Eighty-five patients (15% of series) were found to have ascites by EUS. Six did not have CT before EUS. Pre-EUS CT identified ascites in only 14 (18%) of the 79 patients who had pre-EUS CT. Of the patients in whom CT was negative for abdominal fluid (n = 65) and who had clinical follow-up, 13 of 58 (22%) subsequently had ascites develop that were detected by CT or physical examination. Overall, 31 of the 85 patients underwent EUS-guided FNA paracentesis; the mean volume obtained was 7.9 mL (range 1-40 mL). In 5 patients, malignant ascites was diagnosed by EUS-guided FNA; in these patients surgery was avoided. CONCLUSIONS: EUS is more sensitive than CT in detecting small amounts of ascites. A significant number (22%) of patients who had ascites by EUS subsequently had ascites develop that was detectable by CT or physical examination. EUS-guided paracentesis appears to be safe and effective and can identify malignant ascites.

Ascites↗
PubMed2001

IL-6 inhibits apoptosis and retains oxidative DNA lesions in human gastric cancer AGS cells through up-regulation of anti-apoptotic gene mcl-1.

Apoptosis plays a critical role in maintaining genomic integrity by selectively removing the most heavily damaged cells from the population. Reactive oxygen species (ROS) and certain inflammatory cytokines are always elevated during the human carcinogenic process. However, the biological significance of the interplay between ROS and inflammatory cytokine remains elusive. This study demonstrates that interleukin-6 (IL-6) effectively protects gastric cancer cells from the apoptosis induced by hydrogen peroxide (H(2)O(2)). The cell death signaling JNK pathway elicited by H(2)O(2) is also inhibited by IL-6. We further found that Mcl-1, but not other Bcl-2 family members, was up-regulated by IL-6, by a substantial level over 24 h. We further transfected a mcl-1 expression vector, pCMV-mcl-1, into the AGS cells, and successfully obtained several mcl-1-overexpressing clones. Flow cytometric analysis shows that these mcl-1-overexpressing AGS cells are more resistant to the apoptosis induced by H(2)O(2) when compared with the neo control AGS cells. Consistently, the activation of the JNK pathway induced by H(2)O(2) is also blocked in mcl-1-overexpressed cells. These results indicate that the anti-apoptotic effect of IL-6 is, at least in part, due to the up-regulation of mcl-1. To our surprise, either IL-6 exposure or mcl-1 overexpression fails to reduce the level of intracellular peroxides in the AGS cells triggered by H(2)O(2). This study also determined the level of 8-hydroxydeoxyguanosine (8-OH-dGua), an indicator for oxidative DNA lesions in IL-6-treated or mcl-1-overexpressed AGS cells after treatment with H(2)O(2). Notably, our results indicate that a majority of the 8-OH-dGua is efficiently removed in the AGS cells without IL-6 treatment, whereas only approximately 50% of the 8-OH-dGua was repaired in the IL-6-treated AGS cells after 24 h. Similarly, approximately 60-70% of the 8-OH-dGua also failed to repair and was retained in the genomic DNA of the mcl-1 transfectants. Results in this study provide a novel mechanism by which up-regulation of the Mcl-1 protein by IL-6 may enhance the susceptibility to H(2)O(2)-induced oxidative DNA lesions by overriding apoptosis.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed2001

Clinicopathologic association of cyclooxygenase 1 and cyclooxygenase 2 expression in gastric adenocarcinoma.

OBJECTIVE: To evaluate the association of clinicopathologic factors and prognostic value with the expression of cyclooxygenase 1 and 2 in patients with gastric adenocarcinoma. SUMMARY BACKGROUND DATA: Epidemiologic studies have indicated that nonsteroidal antiinflammatory drugs reduce the risk of colon cancer by as much as 40% and also decrease the risk of gastric cancer. Recently, gastric cancer was found to express constitutive cyclooxygenase 1 and inducible cyclooxygenase 2 isoenzymes. Nonsteroidal antiinflammatories, which may function as cyclooxygenase inhibitors, inhibited the growth of gastric cancer cells. These two isoenzymes' expressions associated with traditional clinicopathologic factors have not been fully evaluated, and their prognostic value for determining survival in patients remains to be clarified. METHODS: Seventy-one specimens resected from patients with gastric adenocarcinoma were investigated by immunohistochemical stain against cyclooxygenase 1 and 2. The 71 specimens were divided into stain-positive and stain-negative groups. Correlations between cyclooxygenase 1 and 2 expression, various clinicopathologic factors (including vascular invasion and Helicobacter pylori infection), and prognosis were studied. RESULTS: The cyclooxygenase 2-positive group was significantly correlated with vascular invasion and H. pylori infection by univariate and multivariate analysis. In patients with cyclooxygenase 2-positive cancer, the prognosis was significantly poorer than in those with cyclooxygenase 2-negative cancer. However, multivariate analysis showed that vascular invasion, serosal invasion, and lymph node metastasis were independent prognostic factors for patients with gastric cancer, but cyclooxygenase 2 expression was not. There was no significant correlation between cyclooxygenase 1 expression and clinicopathologic factors and prognosis. CONCLUSIONS: Upregulated cyclooxygenase 2 expression was associated with H. pylori infection in gastric cancer and was also strongly correlated with positive vascular invasion, which was an independent prognostic factor for poorer survival in this study. The usefulness of cyclooxygenase 2 inhibitors in the prevention or treatment of gastric cancer remains undetermined but deserves further investigation.

Adenocarcinoma↗
PubMed2001

Breast cancer screening in Taiwan and China.

In contrast to incidence rates prevailing in women in Western countries, Chinese women in Taiwan and China are considered to have the lowest incidence of breast cancer in the world. However, in the past 20 years, breast cancer incidence in Chinese women has seen a dramatic increase of 50-100%, which strongly supports the need for breast cancer prevention and screening programs. It is also important to indicate that breast cancer in Chinese women is characterized by younger age at tumor onset. More than 50% of the total breast cancer diagnosed annually is found in premenopausal patients, creating the need to initiate breast cancer screening programs in this population. Initially, the breast cancer screening program depended on breast self-examination. Since Chinese women have relatively small breasts, it was assumed that breast cancer was easier to detect by self-examination. However, this strategy has failed. The dilemma of breast cancer screening can be summarized by the fact that Chinese have a rapidly increasing incidence of premenopausal breast cancer, while the overall incidence is still low. Therefore, since premenopausal women have denser breasts than postmenopausal women, and Chinese women have smaller breasts and a higher percentage of dense breasts, increased mammography screening frequency may be not the sole solution to increase detection in this age group. In our experience in Taiwan, the addition of breast ultrasound may be helpful. Nearly all the nonpalpable cancers detected by mammography in our women are due to microcalcifications, and ultrasound is more sensitive in detecting nonpalpable cancers; Therefore, we suggest that a screening program, based on ultrasound to detect nonpalpable cancers not associated with microcalcifications, along with mammography within a long period, may provide more effective protection for Taiwanese and Chinese women against breast cancer.

Journal Article↗
PubMed2001

Disability-adjusted life years for breast cancer patients in Taiwan.

BACKGROUND AND PURPOSE: The incidence and mortality of breast cancer in Taiwan have increased rapidly in the past several decades, but the societal impact of deaths and disabilities due to breast cancer has not been assessed. This study estimated the disability-adjusted life years (DALYs) for breast cancer patients during 1994, and compared the results with similar data from other areas of the world. METHODS: DALYs for breast cancer patients in Taiwan were calculated using the equation developed by Murray and Lopez. The incidence and mortality of breast cancer and the population structure were obtained from national statistics maintained by the Department of Health and the Ministry of the Interior. The age-specific mean survival time for breast cancer patients was estimated using the exponential distribution from incidence-mortality linkage of the incidence file at National Taiwan University Hospital and the National Mortality File maintained by the Department of Health. RESULTS: There were 11,963 years of life lost (YLL) due to breast cancer during 1994, 2677 years lived with disability (YLD), and 14,640 DALYs. The YLL and DALYs per 1000 population (1.17 and 1.44) were in the middle of the world spectrum, while the YLD value per 1000 population (0.26) was closer to those of developed countries. The proportion of DALYs contributed by younger patients (< 45 years) was higher than in developed countries and similar to those in developing countries other than Sub-Saharan Africa. The DALYs per 1000 population of women younger than 45 years of age in Taiwan were also higher than those in India, China, other regions of Asia and Islands, Sub-Saharan Africa, and the Middle Eastern Crescent. CONCLUSIONS: The disability portion (YLD) of the DALYs for breast cancer patients in Taiwan was higher than in other regions of the world. Moreover, patients younger than 45 years contributed a higher proportion of DALYs than in developed countries. The DALY value per 1000 population younger than 45 years of age was also higher than in developing countries. These results suggest that health professionals should focus more attention on programs for education, screening, and treatment of younger women.

Adolescent↗