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S-J Tang

Publications and source records attributed to S-J Tang.

13 recordsLinked to original sources
PubMed2006

Coherent electronic fringe structure in incommensurate silver-silicon quantum wells.

Atomically uniform silver films grown on highly doped n-type Si(111) substrates show fine-structured electronic fringes near the silicon valence band edge as observed by angle-resolved photoemission. No such fringes are observed for silver films grown on lightly doped n-type substrates or p-type substrates, although all cases exhibited the usual quantum-well states corresponding to electron confinement in the film. The fringes correspond to electronic states extending over the silver film as a quantum well and reaching into the silicon substrate as a quantum slope, with the two parts coherently coupled through an incommensurate interface structure.

Journal Article↗
PubMed2006

Umklapp-mediated quantization of electronic states in Ag films on Ge(111).

We employ angle-resolved photoemission to study the electronic structure of atomically uniform films of Ag grown on Ge(111). A new kind of quantum well state is observed near a specific emission direction away from the surface normal. In contrast with the usual quantum well state arising from electron confinement by specular reflections at the surface and interface of the film, the new kind involves retroreflections, or umklapp reflections, at the interface. It requires four reflections, instead of the usual two reflections, to complete a coherent interference path.

Journal Article↗
PubMed2006

Sublimation of atomic layers from a chromium surface.

We employ low-energy electron microscopy to study the kinetics of thermal etching, or sublimation, of Cr(001) at approximately 1100 K. Atomic layers are removed from the surface by spontaneous nucleation and growth of two-dimensional vacancy islands, by rotation of spiral steps, and by island decay. The growth rates of vacancy islands and the rotation frequencies of double spirals are measured as a function of temperature, and the results are correlated with activation barriers of surface processes. Mass transport between the surface and bulk is shown to be unimportant.

Journal Article↗
PubMed2006

Modification of surface states in ultrathin films via hybridization with the substrate: a study of Ag on Ge.

The Shockley surface state of Ag(111) develops unusual band dispersion relations for Ag films of decreasing thicknesses on Ge(111), as observed by angle-resolved photoemission. Its parabolic dispersion in the thick-film limit shifts toward higher binding energies and splits into multiple bands with dispersions that reflect the valence band structure of Ge including the heavy-hole, light-hole, and split-off bands. The results are explained in terms of a hybridization interaction between the Ag surface state and the Ge substrate states.

Journal Article↗
PubMed2005

Precut papillotomy versus persistence in difficult biliary cannulation: a prospective randomized trial.

BACKGROUND AND STUDY AIMS: Failed biliary cannulation occurs in up to 10% of patients undergoing ERCP. There is some controversy as to the safety and efficacy of using precut techniques to achieve biliary cannulation in difficult cases. To date, no randomized trial has compared the success and complication rates of precut with the rates for persistence when biliary cannulation is difficult. The aim of this study was to compare the success rates and complication rates of precut with the success rates and complication rates of persistence in cases of difficult biliary cannulation. PATIENTS AND METHODS: Patients without prior sphincterotomy who required biliary cannulation were screened. A "difficult biliary cannulation" was arbitrarily defined as failed cannulation after 12 minutes. These patients were then randomized to continue treatment by needle-knife cut over the roof of the papilla or by persistence with a non-wire-guided, single-lumen papillotome. "Primary" success was defined as deep cannulation within 15 minutes of randomization. Primary and final success rates and complication rates within 30 days after ERCP were compared. RESULTS: Over a 38-month period a total of 642 patients were screened. Patients in whom biliary cannulation was successful within a time period of 12 minutes or less formed the reference group (n = 580). The remainder of the patients were randomly assigned to the "precut" arm (n = 32) or to the "persistence" arm (n = 30). Primary success rates and complication rates were similar in the precut and persistence arms (75% and 4% respectively for the precut arm vs. 73% and 9% for the persistence arm). The final successful cannulation rate in the entire group of 642 patients was 99.5%. CONCLUSIONS: In experienced hands, precut papillotomy and persistence in cannulation are equally effective in cases of difficult cannulation, with a similar complication rate.

Abdominal Pain↗
PubMed2004

Breakup of quasiparticles in thin-film quantum wells.

Quantum well states in thin films are commonly described in terms of a quasiparticle confined in a quantum box, but this single-particle picture can fail dramatically near a substrate band edge, as shown by this angle-resolved photoemission study. Atomically uniform Ag films are prepared on Ge(111) to facilitate accurate line shape and dispersion relation measurements. A quantum well peak is observed to split into two peaks near the Ge valence band edge. The unusual line shapes are shown to be due to many-body interactions and are quantitatively explained by a Green's function calculation.

Journal Article↗
PubMed2004

Direct extraction of the Eliashberg function for electron-phonon coupling: a case study of Be(10(-)10).

We propose a systematic procedure to directly extract the Eliashberg function for electron-phonon coupling from high-resolution angle-resolved photoemission measurement. The procedure is successfully applied to the Be(10(-)10) surface, providing new insights into electron-phonon coupling at this surface. The method is shown to be robust against imperfections in experimental data and suitable for wider applications.

Journal Article↗
PubMed2004

Acidic-rich region of amyloid precursor protein induces glial cell apoptosis.

Amyloid precursor protein (APP) has several caspase cleavage sites in its C-terminal cytoplasmic domain and N-terminal extracellular domain. Caspase cleavages of APP at its cytosolic tail may result in releasing the domain and inducing cell death. During apoptosis, the N-terminal domain may also be processed at amino acids 197 and 219 by caspases leading to unmasking of an acidic-rich region (AR). In this study, AR-exposing APP was shown to inhibit cell growth after transfection into RBA-1 astrocytes and BV-2 microglial cells. The recombinant AR from residue 220 to 288 of APP (APP220-288) was produced and its biological activities were analyzed. APP220-288 induced morphological changes, cell death, and DNA fragmentation in BV-2 and RBA-1 cells. However, AR was determined to have no apparent effects in suspension cells, erythroleukemia K562 cells, and Jurkat T cells. The cytotoxicity was depending on negative charge cluster and the apoptotic activity of AR was attributed to the inhibition of cell adhesion. In BV-2 microglial cells, AR significantly stimulated Fas expression, although expressions of the pro-inflammatory cytokine genes were not detected. APP220-288 also induced nitric oxide synthase (iNOS) expression and nitric oxide (NO) production. These findings indicate that the acidic-rich domain of APP may have apoptotic activity due to inhibition of cell adhesion and induction of iNOS and Fas expressions. Moreover, unmasking the apoptosis-induced AR may activate and exacerbate glial cells which in turn lead to further progression of the death program.

Amyloid beta-Protein Precursor↗
PubMed2003

Autoantibodies to dsDNA cross-react with the arginine-glycine-rich domain of heterogeneous nuclear ribonucleoprotein A2 (hnRNP A2) and promote methylation of hnRNP A2.

OBJECTIVE: This study was designed to clarify the internalization of anti-DNA antibodies (anti-DNA) into living cells in the pathogenesis of systemic lupus erythematosus (SLE) using anti-DNA monoclonal antibodies (mAbs). METHODS: Anti-DNA mAbs 9D7, 9D7D2, 9A4, 5E3F5, 12B3H2 and 6E11E3 were prepared by a standard hybridoma procedure to determine the interaction of anti-DNA with proteins in different types of cells. RESULTS: The anti-DNA mAbs reacted with two protein antigens (35 and 50 kDa) in the cells. The 35-kDa antigen was shown to have 100% homology with hnRNP A2. The arginine-glycine-rich domain in hnRNP A2 was found to be the reaction site, and the methylation of hnRNP A2 by PRMT1 (protein arginine methyltransferase 1) was increased by anti-DNA. Moreover, anti-DNA was demonstrated to bind and internalize into the cytoplasm and nucleus. CONCLUSION: Nuclear localizing anti-DNA may cross-react with hnRNP A2 to modulate the inflammatory responses and polarize immune reactions associated with SLE.

Amino Acid Sequence↗
PubMed2002

Uvular necrosis after upper endoscopy: a case report and review of the literature.

Uvular necrosis after endotracheal intubation or upper endoscopy is rare. We report here on a case of uvular necrosis and ulceration after endoscopy. The combination of ulceration and necrosis suggests uvular ischemia during endoscopy. The uvula may have been sandwiched between the shaft of the endoscope and the gum or hard palate, or may have been pressed against the posterior pharynx, leading to prolonged ischemia and resultant ulceration and necrosis. Uvular trauma can also be caused by oral pharyngeal suction. We recommend that post-endoscopy uvular necrosis should be managed conservatively based on the patient's symptoms. In all reported cases, and in the present case as well, the uvula healed and the symptoms resolved within 2 weeks (5 - 14 days) after the procedure. The uvula regained its normal appearance. Overall, these patients should have a good clinical outcome.

Endoscopy, Gastrointestinal↗
PubMed2002

Push enteroscopy for recurrent gastrointestinal hemorrhage due to jejunal anastomotic varices: a case report and review of the literature.

Small-bowel anastomotic and adhesion-related varices can form within adhesions in the setting of mesenteric venous hypertension, arising from either mesenteric venous obstruction or portal hypertension. In evaluating gastrointestinal bleeding in patients who have had previous abdominal surgery and mesenteric venous hypertension, small-bowel anastomotic varices and adhesion-related varices should be considered. For patients with recurrent, severe melena or hematochezia, we recommend that the initial diagnostic work-up should include push enteroscopy in patients with previous small-bowel surgery. Retrograde ileoscopy should also be considered these patients to look for distal small-bowel varices. Potentially, such small-bowel varices can be identified by wireless capsule endoscopy. We report a case of recurrent gastrointestinal bleeding caused by jejunal anastomotic varices which were secondary to superior mesenteric vein occlusion following an abdominal gunshot wound. Although the treatment of segmental varices has been surgical resection, for patients with overt systemic portal hypertension, a transjugular intrahepatic portal-systemic shunt or a decompressive shunting procedure are recommended.

Adult↗