Tunneling effects on impurity spectral function in coupled asymmetric quantum wires

The impurity spectral function is studied in coupled double quantum wires at finite temperatures. Simple anisotropy in the confinement direction of the wires leads to finite non-diagonal elements of the impurity spectral function matrix. These non-diagonal elements are responsible for tunneling effects and result in pronounced extra peak in the impurity spectral function up to temperatures as high as 20 K.Comment: Accepted in Phys. Rev.

Carrier relaxation due to electron-electron interaction in coupled double quantum well structures

We calculate the electron-electron interaction induced energy-dependent inelastic carrier relaxation rate in doped semiconductor coupled double quantum well nanostructures within the two subband approximation at zero temperature. In particular, we calculate, using many-body theory, the imaginary part of the full self-energy matrix by expanding in the dynamically RPA screened Coulomb interaction, obtaining the intrasubband and intersubband electron relaxation rates in the ground and excited subbands as a function of electron energy. We separate out the single particle and the collective excitation contributions, and comment on the effects of structural asymmetry in the quantum well on the relaxation rate. Effects of dynamical screening and Fermi statistics are automatically included in our many body formalism rather than being incorporated in an ad-hoc manner as one must do in the Boltzman theory.Comment: 26 pages, 5 figure

Intersubband plasmons in quasi-one-dimensional electron systems on a liquid helium surface

The collective excitation spectra are studied for a multisubband quasi-one-dimensional electron gas on the surface of liquid helium. Different intersubband plasmon modes are identified by calculating the spectral weight function of the electron gas within a 12 subband model. Strong intersubband coupling and depolarization shifts are found. When the plasmon energy is close to the energy differences between two subbands, Landau damping in this finite temperature system leads to plasmon gaps at small wavevectors.Comment: To be published as a Rapid Communication in Phys. Rev.

Intrasubband and Intersubband Electron Relaxation in Semiconductor Quantum Wire Structures

We calculate the intersubband and intrasubband many-body inelastic Coulomb scattering rates due to electron-electron interaction in two-subband semiconductor quantum wire structures. We analyze our relaxation rates in terms of contributions from inter- and intrasubband charge-density excitations separately. We show that the intersubband (intrasubband) charge-density excitations are primarily responsible for intersubband (intrasubband) inelastic scattering. We identify the contributions to the inelastic scattering rate coming from the emission of the single-particle and the collective excitations individually. We obtain the lifetime of hot electrons injected in each subband as a function of the total charge density in the wire.Comment: Submitted to PRB. 20 pages, Latex file, and 7 postscript files with Figure

Contact endoscopy (microstomatoscopy) in oral lesions: evaluation of the method

OBJETIVO: Descrever as dificuldades da endoscopia de contato aplicada à boca e ao lábio (microestomatoscopia de contato) e aplicar nas lesões do lábio os critérios usados na endoscopia de contato de outras topografias. MÉTODO: Estudo prospectivo utilizando o endoscópio de contato Storz 8715A e o corante azul de toluidina. Vinte exames foram feitos para aprendizado da técnica e depois mais 31 (21 lesões do lábio e 10 da boca), todos exames in vivo. Os critérios avaliados foram: Celularidade, Arquitetura, Estratificação e Morfologia. RESULTADOS: A falta de nitidez, os tremores finos e o deslizamento do aparelho dificultaram o procedimento em 100% dos casos, mas permitiram um exame adequado. Os 13 diagnósticos de malignidade das lesões do lábio apresentaram todos os critérios alterados. CONCLUSÃO: as dificuldades encontradas foram o contato do aparelho com a superfície anatômica, o deslizamento do aparelho, os tremores finos e a falta de nitidez da imagem, que não inviabilizaram a realização e a interpretação do exame. Os critérios são aplicáveis às lesões da boca e do lábio inferior.BACKGROUND: 1- To describe difficulties of contact endoscopy related to mouth and lip (contact microstomatoscopy) and 2- apply the criteria used in contact endoscopy of other topographies when lip lesions are diagnosed. METHODS: A prospective study was performed with the contact endoscope Storz 8715A and toluidine blue was used. Twenty examinations were accomplished in order to learn the technique; after that, other 31 were included (21 lip lesions and 10 oral lesions), all in vivo examinations. The criteria assessed were: cellularity, architecture, stratification and morphology. RESULTS: Lack of image clearness, slight tremors and sliding of the equipment made the procedure difficult in 100% of the cases; even though, accomplishment of proper examination was obtained. The 13 cases of lip malignancy lesions had the criteria altered as a whole. CoNCLUSION: Difficulties found were the contact of the equipment with anatomic surface, the sliding of the equipment, the slight tremors, and the lack of image clearness. Nevertheless, such elements did not interrupt the accomplishment and the examination analysis. The criteria are applied to oral and lower lip lesions

Hypercalcitoninemia is not Pathognomonic of Medullary Thyroid Carcinoma

Hypercalcitoninemia has frequently been reported as a marker for medullary thyroid carcinoma. Currently, calcitonin measurements are mostly useful in the evaluation of tumor size and progression, and as an index of biochemical improvement of medullary thyroid carcinomas. Although measurement of calcitonin is a highly sensitive method for the detection of medullary thyroid carcinoma, it presents a low specificity for this tumor. Several physiologic and pathologic conditions other than medullary thyroid carcinoma have been associated with increased levels of calcitonin. Several cases of thyroid nodules associated with increased values of calcitonin are not medullary thyroid carcinomas, but rather are related to other conditions, such as hypercalcemias, hypergastrinemias, neuroendocrine tumors, renal insufficiency, papillary and follicular thyroid carcinomas, and goiter. Furthermore, prolonged treatment with omeprazole (> 2–4 months), beta-blockers, glucocorticoids and potential secretagogues, have been associated with hypercalcitoninemia. An association between calcitonin levels and chronic auto-immune thyroiditis remains controversial. Patients with calcitonin levels >100 pg/mL have a high risk for medullary thyroid carcinoma (~90%–100%), whereas patients with values from 10 to 100 pg/mL (normal values: <8.5 pg/mL for men, < 5.0 pg/mL for women; immunochemiluminometric assay) have a <25% risk for medullary thyroid carcinoma

Surgical approach to medullary thyroid carcinoma associated with multiple endocrine neoplasia type 2

We briefly review the surgical approaches to medullary thyroid carcinoma associated with multiple endocrine neoplasia type 2 (medullary thyroid carcinoma/multiple endocrine neoplasia type 2). The recommended surgical approaches are usually based on the age of the affected carrier/patient, tumor staging and the specific rearranged during transfection codon mutation. We have focused mainly on young children with no apparent disease who are carrying a germline rearranged during transfection mutation. Successful management of medullary thyroid carcinoma in these cases depends on early diagnosis and treatment. Total thyroidectomy should be performed before 6 months of age in infants carrying the rearranged during transfection 918 codon mutation, by the age of 3 years in rearranged during transfection 634 mutation carriers, at 5 years of age in carriers with level 3 risk rearranged during transfection mutations, and by the age of 10 years in level 4 risk rearranged during transfection mutations. Patients with thyroid tumor >5 mm detected by ultrasound, and basal calcitonin levels >40 pg/ml, frequently have cervical and upper mediastinal lymph node metastasis. In the latter patients, total thyroidectomy should be complemented by extensive lymph node dissection. Also, we briefly review our data from a large familial medullary thyroid carcinoma genealogy harboring a germline rearranged during transfection Cys620Arg mutation. All 14 screened carriers of the rearranged during transfection Cys620Arg mutation who underwent total thyroidectomy before the age of 12 years presented persistently undetectable serum levels of calcitonin (<2 pg/ml) during the follow-up period of 2–6 years. Although it is recommended that preventive total thyroidectomy in rearranged during transfection codon 620 mutation carriers is performed before the age of 5 years, in this particular family the surgical intervention performed before the age of 12 years led to an apparent biochemical cure