Semiclassical approach to Bose-Einstein condensates in a triple well potential

We present a new approach for the analysis of Bose-Einstein condensates in a few mode approximation. This method has already been used to successfully analyze the vibrational modes in various molecular systems and offers a new perspective on the dynamics in many particle bosonic systems. We discuss a system consisting of a Bose-Einstein condensate in a triple well potential. Such systems correspond to classical Hamiltonian systems with three degrees of freedom. The semiclassical approach allows a simple visualization of the eigenstates of the quantum system referring to the underlying classical dynamics. From this classification we can read off the dynamical properties of the eigenstates such as particle exchange between the wells and entanglement without further calculations. In addition, this approach offers new insights into the validity of the mean-field description of the many particle system by the Gross-Pitaevskii equation, since we make use of exactly this correspondence in our semiclassical analysis. We choose a three mode system in order to visualize it easily and, moreover, to have a sufficiently interesting structure, although the method can also be extended to higher dimensional systems.Comment: 15 pages, 15 figure

Bloch oscillations of Bose-Einstein condensates: Breakdown and revival

We investigate the dynamics of Bose-Einstein condensates (BEC) in a tilted one-dimensional periodic lattice within the mean-field (Gross-Pitaevskii) description. Unlike in the linear case the Bloch oscillations decay because of nonlinear dephasing. Pronounced revival phenomena are observed. These are analyzed in detail in terms of a simple integrable model constructed by an expansion in Wannier-Stark resonance states. We also briefly discuss the pulsed output of such systems for stronger static fields.Comment: RevTeX4, 9 pages, 14 figure

Chaotic Quantum Decay in Driven Biased Optical Lattices

Quantum decay in an ac driven biased periodic potential modeling cold atoms in optical lattices is studied for a symmetry broken driving. For the case of fully chaotic classical dynamics the classical exponential decay is quantum mechanically suppressed for a driving frequency \omega in resonance with the Bloch frequency \omega_B, q\omega=r\omega_B with integers q and r. Asymptotically an algebraic decay ~t^{-\gamma} is observed. For r=1 the exponent \gamma agrees with $q$ as predicted by non-Hermitian random matrix theory for q decay channels. The time dependence of the survival probability can be well described by random matrix theory. The frequency dependence of the survival probability shows pronounced resonance peaks with sub-Fourier character.Comment: 7 pages, 5 figure

An algebraic solution of driven single band tight binding dynamics

The dynamics of the driven tight binding model for Wannier-Stark systems is formulated and solved using a dynamical algebra. This Lie algebraic approach is very convenient for evaluating matrix elements and expectation values. It is also shown that a dynamical invariant can be constructed. A classicalization of the tight binding model is discussed as well as some illustrating examples of Bloch oscillations and dynamical localization effects.Comment: 13 pages; revised version (changed title and sections 6,7, added references

Bound and resonance states of the nonlinear Schroedinger equation in simple model systems

The stationary nonlinear Schroedinger equation, or Gross-Pitaevskii equation, is studied for the cases of a single delta potential and a delta-shell potential. These model systems allow analytical solutions, and thus provide useful insight into the features of stationary bound, scattering and resonance states of the nonlinear Schroedinger equation. For the single delta potential, the influence of the potential strength and the nonlinearity is studied as well as the transition from bound to scattering states. Furthermore, the properties of resonance states for a repulsive delta-shell potential are discussed.Comment: 19 pages, 10 figure

Association between Vascular Remodelling and Necrotic Core in Coronary Arteries: Analysis by Intracoronary Ultrasound with Virtual Histology®

ABSTRACTBackgroundAnatomopathological studies suggest an association of positive vascular remodeling and vulnerable coronary plaques. The objective of this study was to verify whether there is a correlation between positive vascular remodeling and necrotic core in atherosclerotic coronary lesions.MethodsWe studied 270 cross sections obtained by Virtual Histology® in 30 patients who had positive remodeling in coronary artery segments with lesions > 50%, identified by coronary angiography. Seven cross sections were assessed per segment of coronary artery, including the cross section with the highest remodeling index, denominated cross section of interest (cross section 4).ResultsMean age was 60.8±8.8 years, 80% were male and 30% were diabetic. Unstable angina was the most frequent clinical presentation (56.6%) and the left anterior descending artery was the most analyzed vessel (43%). The vessel reference area was 15.5±4.9mm2 and the remodeling index in cross section 4 was 1.2±0.1. Repeated measures analysis of variance showed a higher percentage of necrotic core in the cross section of interest (P < 0.001). We observed a positive correlation of coronary artery remodeling and necrotic core (r = 0.79; P < 0.001).ConclusionsPositive coronary artery remodeling is associated to the presence of necrotic core, which characterizes vulnerable atherosclerotic plaques. The search for positive arterial remodeling may be a useful strategy for detecting vulnerable plaques before rupture

Desenvolvimento e Aplicação do CDA Introdução aos Estudos Virtuais

O presente trabalho tem o objetivo de mostrar o processo de desenvolvimento de um construto digital de aprendizagem criado pelo Laboratório de Objetos de Aprendizagem da Universidade Feevale. O artigo introduz autores que sustentam o uso de jogos digitais na educação e que serviram para embasar a metodologia utilizada na criação e validação do construto. Os resultados foram obtidos através da aplicação do projeto em um grupo de 101 estudantes dos cursos a distância da própria instituição

Multiple molecular mechanisms form a positive feedback loop driving amyloid β42 peptide-induced neurotoxicity via activation of the TRPM2 channel in hippocampal neurons

Emerging evidence supports an important role for the ROS-sensitive TRPM2 channel in mediating age-related cognitive impairment in Alzheimer’s disease (AD), particularly neurotoxicity resulting from generation of excessive neurotoxic Aβ peptides. Here we examined the elusive mechanisms by which Aβ₄₂ activates the TRPM2 channel to induce neurotoxicity in mouse hippocampal neurons. Aβ₄₂-induced neurotoxicity was ablated by genetic knockout (TRPM2-KO) and attenuated by inhibition of the TRPM2 channel activity or activation through PARP-1. Aβ₄₂-induced neurotoxicity was also inhibited by treatment with TPEN used as a Zn²⁺-specific chelator. Cell imaging revealed that Aβ₄₂-induced lysosomal dysfunction, cytosolic Zn²⁺ increase, mitochondrial Zn²⁺ accumulation, loss of mitochondrial function, and mitochondrial generation of ROS. These effects were suppressed by TRPM2-KO, inhibition of TRPM2 or PARP-1, or treatment with TPEN. Bafilomycin-induced lysosomal dysfunction also resulted in TRPM2-dependent cytosolic Zn²⁺ increase, mitochondrial Zn²⁺ accumulation, and mitochondrial generation of ROS, supporting that lysosomal dysfunction and accompanying Zn²⁺ release trigger mitochondrial Zn²⁺ accumulation and generation of ROS. Aβ₄₂-induced effects on lysosomal and mitochondrial functions besides neurotoxicity were also suppressed by inhibition of PKC and NOX. Furthermore, Aβ₄₂-induced neurotoxicity was prevented by inhibition of MEK/ERK. Therefore, our study reveals multiple molecular mechanisms, including PKC/NOX-mediated generation of ROS, activation of MEK/ERK and PARP-1, lysosomal dysfunction and Zn²⁺ release, mitochondrial Zn²⁺ accumulation, loss of mitochondrial function, and mitochondrial generation of ROS, are critically engaged in forming a positive feedback loop that drives Aβ₄₂-induced activation of the TRPM2 channel and neurotoxicity in hippocampal neurons. These findings shed novel and mechanistic insights into AD pathogenesis

p38 MAPK and JNK Antagonistically Control Senescence and Cytoplasmic p16INK4A Expression in Doxorubicin-Treated Endothelial Progenitor Cells

Patients treated with low-dose anthracyclines often show late onset cardiotoxicity. Recent studies suggest that this form of cardiotoxicity is the result of a progenitor cell disease. In this study we demonstrate that Cord Blood Endothelial Progenitor Cells (EPCs) exposed to low, sub-apoptotic doses of doxorubicin show a senescence phenotype characterized by increased SA-b-gal activity, decreased TRF2 and chromosomal abnormalities, enlarged cell shape, and disarrangement of F-actin stress fibers accompanied by impaired migratory ability. P16 INK4A localizes in the cytoplasm of doxorubicin-induced senescent EPCs and not in the nucleus as is the case in EPCs rendered senescent by different stimuli. This localization together with the presence of an arrest in G2, and not at the G1 phase boundary, which is what usually occurs in response to the cell cycle regulatory activity of p16INK4A, suggests that doxorubicin-induced p16 INK4A does not regulate the cell cycle, even though its increase is closely associated with senescence. The effects of doxorubicin are the result of the activation of MAPKs p38 and JNK which act antagonistically. JNK attenuates the senescence, p16 INK4A expression and cytoskeleton remodeling that are induced by activated p38. We also found that conditioned medium from doxorubicin-induced senescent cardiomyocytes does not attract untreated EPCs, unlike conditioned medium from apoptotic cardiomyocytes which has a strong chemoattractant capacity. In conclusion, this study provides a better understanding of the senescence of doxorubicin-treated EPCs, which may be helpful in preventing and treating late onset cardiotoxicity

Análise de colecistectomias videolaparoscópicas no Hospital de Clínicas de Porto Alegre

OBJECTIVE: Laparoscopic cholecystectomy (LC) is the treatment of choice for cholelithiasis. Our objective was to assess the results of LC in comparison with previous data published in 1994.PATIENTS AND METHODS: From 1992 to 1999, 2,300 patients were submitted to surgery at the Hospital de Clínicas de Porto Alegre. The medical records of 1,540 of these patients were assessed retrospectively. The variables evaluated were preoperative diagnosis, duration of hospital stay and of surgery, intra- and postoperative complications, conversion rate to open surgery, and anatomicopathological examination of the gallbladder.RESULTS: The most common preoperative diagnosis was of symptomatic gallstones (92%); the average hospital stay was of 3.6 ± 6 days (median of 2 days); the average duration of surgery was of 89.5 ± 38 minutes; the most frequent intraoperative complications were gallbladder rupture (7.3%), calculi in peritoneum (0.8%), and iatrogenic bile duct injury (0.2%); and the postoperative complications reported were wound infection (1.3%), retained stones (0.6%), and biliary peritonitis (0.5%). The conversion rate to open procedure was of 2.5%, and reoperation was necessary in 1.8% of cases. There was only one death (0.06%).CONCLUSION: In comparison to data from a previous experience, there has been an improvement in LC results, but additional technical improvements can still be made.&nbsp;OBJETIVO: A colecistectomia videolaparoscópica (CVL) é o tratamento preferencial da colelitíase. O objetivo deste trabalho é avaliar os resultados da CVL comparando com a experiência inicial relatada em 1994.PACIENTES E MÉTODOS: De 1992 a 1999 foram operados 2.300 pacientes no Hospital de Clínicas de Porto Alegre. Deste total foram revisados retrospectivamente 1.540 prontuários. As variáveis analisadas foram a indicação cirúrgica, o tempo de internação hospitalar e cirúrgico, as complicações trans e pós-operatórias, a taxa de conversão para cirurgia aberta e o exame anatomopatológico da vesícula biliar.RESULTADOS: A principal indicação de cirurgia foi a colelitíase sintomática (92%). O tempo de internação hospitalar foi 3,6 ± 6 dias e a mediana de 2 dias e o tempo cirúrgico médio de 89,5 ± 38 minutos. As principais complicações intra-operatórias foram a perfuração da vesícula biliar (7,3%), a queda de cálculos na cavidade (0,8%) e lesão iatrogênica de via biliar (0,2%). No pós-operatório, as complicações mais freqüentes foram a infecção de ferida operatória (1,3%), a coledocolitíase residual (0,6%) e o coleperitônio (0,5%). A taxa de conversão foi de 2,5% e de reoperação de 1,8%. Houve apenas um óbito (0,06%).CONCLUSÕES: Em relação à experiência inicial, a CVL evoluiu muito, mas ainda pode ser aprimorada tecnicamente.&nbsp;&nbsp