Biomedical subjects

T W Noh

Publications and source records attributed to T W Noh.

14 recordsLinked to original sources

PubMed2006

Effect of orbital rotation and mixing on the optical properties of orthorhombic RMnO3 (R=La, Pr, Nd, Gd, and Tb).

We investigated the ab-plane absorption spectra of RMnO3 (R=La, Pr, Nd, Gd, and Tb) thin films. As the ionic radius of the R ion decreases, we observed a drastic suppression of the 2 eV peak, i.e., the intersite optical transition between spin- and orbital-aligned states across the Mott gap. We found that, in addition to orbital rotation, orbital mixing in the orbital-ordered state should play an important role in the suppression of 2 eV peak. We also found that the spectral weight of 2 eV peak is proportional to the A-type antiferromagnetic ordering temperature, which suggests that the magnetic interaction should be sensitively coupled to the orbital degree of freedom.

Journal Article↗

PubMed2006

Orbital-selective mass enhancements in multiband Ca(2-x)Sr(x)RuO4 systems analyzed by the extended Drude model.

We investigated optical spectra of quasi-two-dimensional multiband systems. The extended Drude model analysis on the -plane optical conductivity spectra indicates that the effective mass should be enhanced near . Based on the sum rule argument, we showed that the orbital-selective Mott-gap opening for the bands, the widely investigated picture, could not be the origin of the mass enhancement. We exploited the multiband effects in the extended Drude model analysis, and demonstrated that the intriguing heavy mass state near should come from the renormalization of the band.

Journal Article↗

PubMed2005

Polarization relaxation induced by a depolarization field in ultrathin ferroelectric capacitors.

Time-dependent polarization relaxation behavior induced by a depolarization field E(d) was investigated on high-quality ultrathin SrRuO3/BaTiO3/SrRuO3 capacitors. The E(d) values were determined experimentally from an applied external field to stop the net polarization relaxation. These values agree with those from the electrostatic calculations, demonstrating that a large E(d) inside the ultrathin ferroelectric layer could cause severe polarization relaxation. For numerous ferroelectric devices of capacitor configuration, this effect will set a stricter size limit than the critical thickness issue.

Journal Article↗

PubMed2004

Kinetic roughening of ion-sputtered Pd(001) surface: beyond the Kuramoto-Sivashinsky model.

We investigate the kinetic roughening of Ar+ ion-sputtered Pd(001) surface both experimentally and theoretically. In situ real-time x-ray reflectivity and in situ scanning tunneling microscopy show that nanoscale adatom islands form and grow with increasing sputter time t. Surface roughness W(t) and lateral correlation length xi(t) follow the scaling laws W(t) approximately t(beta) and xi(t) approximately t(1/z) with the exponents beta approximately 0.20 and 1/z approximately 0.20, for an ion beam energy epsilon=0.5 keV, which is inconsistent with the prediction of the Kuramoto-Sivashinsky (KS) model. We thereby extend the KS model by applying the coarse-grained continuum approach of the Sigmund theory to the order of O(inverted Delta(4),h(2)), where h is the surface height, and derive a new term of the form inverted Delta(2)(inverted Delta h)(2) which plays a decisive role in describing the observed morphological evolution of the sputtered surface.

Journal Article↗

PubMed2004

Resonant inelastic X-ray scattering of the holon-antiholon continuum in SrCuO2.

We report a resonant inelastic x-ray scattering study of charge excitations in the quasi-one-dimensional Mott insulator SrCuO2. We observe a continuum of low-energy excitations, the onset of which exhibits a small dispersion of approximately 0.4 eV. Within this continuum, a highly dispersive feature with a large sinusoidal dispersion (approximately 1.1 eV) is observed. We have also measured the optical conductivity, and studied the dynamic response of the extended Hubbard model with realistic parameters, using a dynamical density-matrix renormalization group method. In contrast to earlier work, we do not find a long-lived exciton, but rather these results suggest that the excitation spectrum comprises a holon-antiholon continuum together with a broad resonance.

Journal Article↗

PubMed2004

Optical-spectroscopic detection of spin-exchange interaction pyrochlore molybdates.

Optical spectroscopy was used to determine nearest-neighbor spin correlations in pyrochlore molybdates R2Mo2O7 (R=Y, Sm, and Nd), which exhibit ferromagnetic metal to spin-glass insulator transition as the R ion size decreases. Using an analysis based on the orbitally degenerate Hubbard model, we could estimate important physical parameters, such as the effective on-site Coulomb energy U(eff) and the Hund rule exchange coupling J(H). We demonstrated experimentally and theoretically that the effective superexchange interaction between the Mo ions depends on J(H)/U(eff), which determines the phase boundary of the magnetic ground states.

Journal Article↗

PubMed2002

Electron and orbital correlations in Ca2-xSrxRuO4 probed by optical spectroscopy.

The optical conductivity spectra of the quasi-two-dimensional Ca2-xSrxRuO4 (0.0< or =x< or =2.0) system were investigated. In the Mott insulating state, two electron correlation-induced peaks were observed about 1.0 and 1.9 eV, which could be explained using the 3-orbital Hubbard model. The low frequency peak showed a shift toward higher frequency as temperature was lowered, indicating that electron-phonon interactions play an important role in the orbital arrangements. From the systematic analysis, it was suggested that the antiferro-orbital and the ferro-orbital ordering states could coexist.

Journal Article↗

PubMed2002

Spin-orbital pattern dependent polaron absorption in manganites.

We systematically investigated optical properties of Nd1-xSrxMnO3 single crystals ( x = 0.40, 0.50, 0.55, and 0.65). They are similar in their spin-orbital (SO) disordered states at room temperature. At low temperature, the crystals enter into various SO ordered states, i.e., F-, CE-, A-, and C-type orderings, and their mid-infrared absorptions become quite different. The remarkable variation can be explained by polaron dynamics which depend on the ordering patterns. This SO pattern dependent polaron model can also explain the pseudo CE-type ordering case, demonstrating that this scheme can explain the carrier dynamics in complex SO configurations.

Journal Article↗

PubMed2002

Charge ordering fluctuation and optical pseudogap in La(1-x)Ca(x)MnO(3).

Optical spectroscopy was used to investigate the optical gap ( 2 Delta) due to charge ordering (CO) and related pseudogap developments with x and temperature ( T) in La(1-x)Ca(x)MnO(3) ( 0.48< or =x< or =0.67). Surprisingly, we found 2 Delta/k(B)T(CO) is as large as 30 for x approximately 0.5, and decreases rapidly with increasing x. Simultaneously, the optical pseudogap, possibly starting from T* far above T(CO) becomes drastically enhanced near x = 0.5, producing non-BCS T-dependence of 2 Delta with the large magnitude far above T(CO), and systematic increase of T* for x approximately 0.5. These results unequivocally indicate systematically enhanced CO correlation when x approaches 0.5 even though T(CO) decreases.

Journal Article↗

PubMed2001

Teratoid hepatoblastoma: multidirectional differentiation of stem cell of the liver.

Hepatoblastoma is the most common malignant hepatic neoplasm of childhood, showing a wide spectrum of epithelial and mesenchymal components. Teratoid hepatoblastoma, which reveals multiple lines of tissue differentiation such as mucinous epithelium, melanin pigment, endocrine differentiation, glial and mesenchymal components, has rarely been observed. We report a case of teratoid hepatoblastoma in a 22-month-old girl. She had been diagnosed with hepatoblastoma through percutaneous needle biopsy of the liver and treated with 10 chemotherapy cycles of epirubicin, VP-16 and cisplatin and with hepatic artery embolization. After 10 months, an extended left lobectomy was performed. Grossly, a multinodular, partly well-demarcated, solid mass (7 x 5 cm) with dense fibrosis and focal cystic change occupied almost the entire specimen. There was extensive necrosis due to preoperative treatment. Microscopically, the tumor showed multiple lines of differentiation, which was composed of embryonal, fetal hepatocytes and mesenchymal elements with numerous foci of osteoid. There were also other components showing endodermal, neural, melanocytic and endocrine differentiation. These teratoid components were considered relatively resistant to preoperative chemotherapy, in contrast to extensive necrosis of both embryonal and fetal hepatocytes. These teratoid features of hepatoblastoma are considered to be a multidirectional differentiation of the small epithelial cells or stem cells of the tumor.

Cell Differentiation↗

PubMed2001

Thymoma with pseudosarcomatous stroma.

Thymoma with psuedosarcomatous stroma is a recently described, rare variant of thymomas that are characterized by having a biphasic histologic pattern which consists of both an epithelial and a spindle cell stromal component. So far only 11 cases having similar histologic findings have been reported worldwide. At this time we report a case of this rare variant of thymoma which occurred in a 53-year-old Korean man. This previously healthy patient presented with coughing and an anterior mediastinal mass was then detected radiographically. Mediastinal exploration revealed a 9 x 8 x 8 cm-sized well- encapsulated, ovoid, cystic mass. Histological examination showed a biphasic neoplasm composed of anastomosing nests of epithelial cells and somewhat cellular stromal spindle cells that had advanced degenerative changes. Immunohistochemical staining using the antibodies for cytokeratins, EMA, e-cadherin, and p75NGFR showed a strong expression of these markers in the epithelial component but no expression in the spindle stromal cells. The epithelial tumor cells showed no reactivity to CD5 and L26 and a high proportion of the infiltrated lymphocytes were the cortical type that expressed CD99 and terminal deoxynucleotidyl transferase. Ultrastructural examinations revealed tonofilaments in the spindle cells. Follow up has been done for 5 years after the surgical excision and the patient has been free of disease during that period. Similar to previous reports, this patient had a benign clinical course that was unassociated with myasthenia gravis which appears to be a characteristic of this histologic variant of thymoma. However, our case also showed advanced degenerative features and we could demonstrate ultrastructural evidence of epithelial differentiation in the stromal spindle cells that were not mentioned in the previously reported cases. Based on the results of our studies, we suggest this entity is a distinct type of organotypic thymoma that shows cortical differentiation and abundant cellular stroma.

Humans↗

PubMed2000

Primary carcinoma of the fallopian tube coexisting with benign cystic teratoma of the ovary.

Primary carcinoma of the fallopian tube is a rare malignancy of the female genital tract and infrequently diagnosed before an operation. The majority of patients have extensive disease at the time of diagnosis. We have experienced incidentally a case of a carcinoma of the fallopian tube coexisting with a benign cystic teratoma of the ovary in a 25-year-old woman. We report this case with a brief review of literatures.

Adenocarcinoma, Papillary↗

PubMed2000

Lobular carcinoma in situ in sclerosing adenosis.

The initial presentation of breast malignancy as noninvasive carcinoma in an area of sclerosing adenosis is unusual. Especially, lobular carcinoma in situ in sclerosing adenosis sometimes can be a potential source of confusion with invasive lobular carcinoma. We report a case of lobular carcinoma in situ presenting in adenosis exhibiting patterns akin to invasive lobular carcinoma, thus leading to potential misdiagnosis. Overall architecture of the lesion as seen at lower power and immunohistochemistry can be useful to distinguish between sclerosing adenosis with lobular carcinoma in situ and infiltrating lobular carcinoma.

Breast Neoplasms↗

PubMedDate not supplied

Composite neuroendocrine and adenocarcinoma of the common bile duct associated with Clonorchis sinensis: a case report.

The biliary tract has neuroendocrine cells of endoderm origin similar to the gastrointestinal tract, however neuroendocrine tumors of the biliary tract are rare. We report a composite glandular-endocrine cell carcinoma of the common bile duct in a 64-year-old Korean man which was associated with Clonorchis sinensis. The patient complained of right upper quadrant abdominal pain. Several parasites of Clonorchis sinensis were removed during the percutaneous transbiliary drainage. Endoscopic retrograde cholangiopancreatography revealed a polypoid mass (3 x 3 cm) with central ulceration in the common bile duct. Pancreaticoduodenectomy was performed. Microscopic examination of the tumor revealed a composite small cell neuroendocrine carcinoma and adenocarcinoma. The small cell carcinoma component showed positive reaction to chromogranin A and neuron-specific enolase and it was located mainly in the deeper portion of the mass. The well-differentiated adenocarcinoma component showed a positive reaction to carcinoembryonic antigen and it was situated in the superficial portion of the mass. Exclusively, the small cell component metastasized to the lymph node. It is suggested that this tumor could arise from a multipotential stem cell and showed neuroendocrine and glandular differentiation and that Clonorchis sinensis could be a predisposing factor, as in cholangiocarcinoma.

Adenocarcinoma↗