Anlaytic mean-field Hall crystal solution at nu=1/3: composite fermion like sub-bands and correlation effects

An analytic solution of the Hartree-Fock problem for a 2DEG at filling 1/3 and half an electron per unit cell is presented. The Coulomb interaction dynamically breaks the first Landau level in three narrow sub-bands, one of which is fully occupied and the other empty, as in the composite fermion model. The localized orbitals associated to the Bloch like single electron wavefunctions are nearly static, resembling the angular momentum eigenstates within a Landau level for non-interacting fermions. Strong correlations are expected owing to the large charge density overlap between neighboring plaquettes. A numerical evaluation brings the cohesive energy close to that of the best present day models. It is also found that correlations are long range, requiring over 50 particles spread over a finite sample to approach convergence. Since presently allowed exact calculations are far from this number, the question of how relevant the considered wave-function is for the description of the ground state of the 2DEG system remains open.Comment: 24 pages, 4 figures, content exposed in the: Symposium Quantum Hall Effect: "Past, Present and Future", Sttutgart, Germany, 2-5 July 2003 and in the Third Stig Lundquist Conference on Advancing Frontiers of Condensed Matter Physics 11-15 August 2003, ICTP, Trieste Ital

Un dispositivo para el control automático del cese de respuesta en el MECADOL-1 : el SS NN SN - 482

Este trabajo describe la estructura y funcionamiento de un aparato (SS NN SN- 482) diseñado y construido como solución a un problema de control de la variable "cese de respuesta" aparecido en una investigación amplia acerca del dolor y del umbral del dolor desde una perspectiva experimental. Se indican algunas de las ventajas que proporcionan las nociones de tecnología al psicólogo experimental y se insiste en el riguroso control de las variables como característica del trabajo científico básico.This paper describes the structure and functioning of a device (SS NN SN - 482) designed and made to solve a control problem of the variable "end of answer" which appeared in an important research project on pain and on threshold of pain from an experimental perspective. The paper indicates some of the advantages which technological notions provide have for the experimental psychologist and it insists on the strict control of the variables as a characteristic of basic scientific work

Assessing the oncological safety of autologous fat grafting for breast cancer

Orientadores: Aarão Mendes Pinto Neto, Luís Otávio Zanatta SarianTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Ciências MédicasResumo: Introdução: A lipoenxertia para reconstrução da mama é uma técnica efetiva, de baixa complexidade e baixo custo. Entretanto, a associação entre obesidade e câncer de mama, além de evidências laboratoriais de que as adipocinas podem estimular a proliferação celular e a diferenciação de células-tronco mesenquimais (ASC), suscitam dúvidas sobre a segurança oncológica do procedimento para a prática clínica. Objetivo: Avaliar o risco oncológico da lipoenxertia autóloga para o câncer de mama. Métodos: Esta tese trata de quatro estudos interligados. No primeiro, foi desenvolvido um modelo experimental para o estudo da lipoenxertia em ratas da raça Sprague-Dawley avaliando características adaptativas do tecido adiposo de omento pediculado por meio de avaliação macroscópica, histológica e morfologia de adipócitos. No segundo, este modelo foi aplicado para comparar o potencial oncogênico do tecido adiposo exposto a dieta hipercalórica com o procedimento de lipoenxertia, através de marcadores de inflamação crônica (CD68 em macrófagos), proliferação celular (Ki67) e níveis de PAI-1. No terceiro estudo comparamos mamas que receberam lipoenxertia de omento, de subcutâneo e as que não foram manipuladas, através de avaliação histológica, imunoistoquímica e PCR-RT de CD68, Ki67, PAI-1 e receptores de estrógeno (ER, marcador 1D5). O quarto estudo foi uma revisão sistemática da literatura sobre a utilização de tecido adiposo do omento para o tratamento das afecções mamárias. Resultados: No primeiro estudo, o tecido adiposo do omento pediculado sofreu processo adaptativo resultante de alterações no seu interstício, sem alteração morfológica dos adipócitos (p=0,27) e sem atipias celulares quando estimulado pela translocação. No segundo estudo, o tecido adiposo não manipulado exposto à dieta hipercalórica produziu proliferação celular (representada por elevação do Ki67, p=0,046) e elevação dos níveis de PAI-1 (p0,05. Na revisão sistemática foram identificados 60 estudos que envolveram 985 mulheres. Oito estudos analisaram o risco oncológico para recidiva de câncer de mama, sendo que em sete a enxertia foi realizada em estádio avançado e a recorrência local foi de 35,5% (143/403). Um destes estudos avaliou pacientes com câncer em estádio inicial (89 mulheres) e nenhuma recidiva foi identificada em follow-up médio superior a cinco anos após a reconstrução. Conclusão: Pelos estudos experimentais in vivo, identificamos o potencial oncogênico dos adipócitos nativos sem manipulação quando expostos a dieta hipercalórica. Entretanto, o tecido adiposo enxertado ou as células do sitio receptor (incluindo as células ductais) não foram capazes de mostrar qualquer alteração potencialmente oncogênica, quando analisado o processo de enxertia isoladamente. Nossos achados experimentais estão perfeitamente alinhados com as conclusões da literatura para lipoenxertia e de nossa revisão sistemática de estudos clínicos em tecido adiposo de omento, os quais sustentam a segurança oncológica da lipoenxertia para reconstrução da mamaAbstract: Introduction: Lipofilling for breast reconstruction is an effective procedure, with low complexity and low cost. However, its oncological safety was questioned when obesity was identified as a risk factor for breast cancer along with some in vitro and preclinical studies that identified the oncogenic potential of adipocytes to cellular proliferation and differentiation of adipose stromal cells (ASC). Objective: To assess of the oncological safety of autologous fat grafting for breast cancer. Method: The present research is composed by four studies. In the first one, it was proposed an experimental model for lipofilling using adipose tissue of pedicle omental flap in Sprague-Dawley rats to assess its adaptative properties through histopathological analyses and adipocyte morphology. In the second, this model was used to compare the oncogenic potential of samples of native unmanipulated adipose tissue when exposed to high-energy diet to samples of fat exposed only to the lipofilling procedure through markers of chronic inflammation (CD68 in macrophages), cellular proliferation (Ki67), and levels of PAI-1. In the third, lipofilled breasts (grafted with subcutaneous or omental fat tissue) were compared with unmanipulated breasts (control) through histopathological analyses, immunohistochemical and PCR-RT tests of CD68, Ki67, PAI-1 and 1D5 markers. The forth study was a systematic review of treatment of breast disorders with adipose tissue of pedicle omental flap. Results: In the first study, the adipose tissue of transposed pedicle omental flap underwent an adaptative transformation with intertitial changes, without changes of adipocyte morphology (p=0.27) e without cellular atypia. In the second, the unmanipulated fat exposed to high-energy diet showed cellular proliferation (overexpression of Ki67, p=0.046) and increased levels of PAI-1 (p0.05. The systematic review identified 60 studies with 985 women. Eight studies analyzed the oncologic risk for breast cancer relapse, seven of them described breast lipofilling after treatment of advanced disease and their recurrence rate was 35.5% (143/403). The eighth study in this series, analyzed 89 women treated for non-advanced disease and found no cancer recurrence during a mean follow-up longer than five years. Conclusion: Our experimental studies in vivo identified the oncogenic potential of native unmanipulated fat when exposed to a high-energy diet. However, this potential was not oberved in grafted fat or in its host microenvironment (including the ductal lobular cells) when the procedure of lipofilling was analyzed alone. Our experimental results are in accordance to clinical results reported in literature for breast lipofilling and to the clinical data identified in our systematic review for adipose tissue of pedicled omental flap. Thus, they sustain the oncological safety of fat grafting for breast reconstructionDoutoradoOncologia Ginecológica e MamáriaDoutor em Ciências da Saúd

The underlying social dynamics of paradigm shifts

We develop here a multi-agent model of the creation of knowledge (scientific progress or technological evolution) within a community of researchers devoted to such endeavors. In the proposed model, agents learn in a physical-technological landscape, and weight is attached to both individual search and social influence. We find that the combination of these two forces together with random experimentation can account for both i) marginal change, that is, periods of normal science or refinements on the performance of a given technology (and in which the community stays in the neighborhood of the current paradigm); and ii) radical change, which takes the form of scientific paradigm shifts (or discontinuities in the structure of performance of a technology) that is observed as a swift migration of the knowledge community towards the new and superior paradigm. The efficiency of the search process is heavily dependent on the weight that agents posit on social influence. The occurrence of a paradigm shift becomes more likely when each member of the community attaches a small but positive weight to the experience of his/her peers. For this parameter region, nevertheless, a conservative force is exerted by the representatives of the current paradigm. However, social influence is not strong enough to seriously hamper individual discovery, and can act so as to empower successful individual pioneers who have conquered the new and superior paradigm.Fil: Rodriguez Sickert, Carlos. Universidad del Desarrollo; ChileFil: Cosmelli, Diego. Pontificia Universidad Católica de Chile; ChileFil: Claro, Francisco. Pontificia Universidad Católica de Chile; ChileFil: Fuentes, Miguel Angel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad San Sebastián; Chil

Phase diagram of two dimensional electron gas in a perpendicular magnetic field around Landau level filling factors \nu=1 and \nu=3

The measured melting curve $T_{m}(\nu)$ between the crystal and liquid phases is analyzed using thermodynamics to extract the change of magnetization $\Delta M$ as a function of the Landau level filling factor \ $\nu,$ near $\nu=1$. \ An explanation of $\Delta M$($\nu)$ is proposed \ in terms of Skyrmions. \ Near $\nu=3$, a Wigner crystal is the most probable solid phase, experiments excluding Skyrmions.Comment: 5 pages, 4 figure

¿cuánto duraremos?

Cuando se pide a la física que se refiera al destino de la vida sobre el planeta se apela a su capacidad para predecir el futuro. Aquí cuestionamos dicha capacidad y presentamos el concepto de horizonte de credibilidad de la predicción científica, el que acota el alcance de toda afirmación acerca del futuro. En particular, las proposiciones de la cosmología acerca del devenir del entorno material que sustenta la vida humana deben leerse como afirmaciones de alcance acotado, y no como verdades finales.When physics is asked to make a statement of the end of times t he issue of its real capability for predicting the fut ure is brought about. Here we question such capability and present the concept of a credibility horizon in scientific prediction, which makes explicit the existence of a limited scope to whatsoever statement about t he future. In part icular, the proposit ions of cosmology about t he evolution of the material substrate that makes life posible, or about the end of time, must be read as statements of bounded validity and not as a final truth