Branching processes and computational collapse of discretized unimodal mappings

In computer simulations of smooth dynamical systems, the original phase space is replaced by machine arithmetic, which is a finite set. The resulting spatially discretized dynamical systems do not inherit all functional properties of the original systems, such as surjectivity and existence of absolutely continuous invariant measures. This can lead to computational collapse to fixed points or short cycles. The paper studies loss of such properties in spatial discretizations of dynamical systems induced by unimodal mappings of the unit interval. The problem reduces to studying set-valued negative semitrajectories of the discretized system. As the grid is refined, the asymptotic behavior of the cardinality structure of the semitrajectories follows probabilistic laws corresponding to a branching process. The transition probabilities of this process are explicitly calculated. These results are illustrated by the example of the discretized logistic mapping.

Progressive Age-Related Changes Similar to Age-Related Macular Degeneration in a Transgenic Mouse Model

Age-related macular degeneration (AMD) is the major cause of blindness in the developed world. its pathomechanism is unknown and its late onset, complex genetics and strong environmental components have all hampered investigations. Here we demonstrate the development of an animal model for AMD that reproduces features associated with geographic atrophy, a transgenic mouse line (mcd/mcd) expressing a mutated form of cathepsin D that is enzymatically inactive thus impairing processing of phagocytosed photoreceptor outer segments in the retinal pigment epithelial (RPE) cells. Pigmentary changes indicating RPE cell atrophy and a decreased response to flash electroretinograms were observed in 11- to 12-month-old mcd/mcd mice. Histological studies showed RPE cell proliferation, photoreceptor degeneration, shortening of photoreceptor outer segments, and accumulation of immunoreactive photoreceptor breakdown products in the RPE cells. An accelerated photoreceptor cell death was detected in 12-month-old mcd/mcd mice. Transmission electron microscopy demonstrated presence of basal laminar and linear deposits that are considered to be the hallmarks of AMD. Small hard drusen associated with human age-related maculopathy were absent in the mcd/mcd mouse model at the ages analyzed. in summary, this model presents several features of AMD, thus providing a valuable tool for investigating the underlying biological processes and pathomechanism of AMD.

A crise financeira de 2008 e seus impactos na economia brasileira: uma análise sob a perspectiva de Minsky

Diante do colapso financeiro de 2008, este trabalho retoma a teoria econômica proposta por Hyman P. Minsky com o objetivo de esclarecer as circunstâncias que propiciaram uma crise financeira tão profunda. A estrutura analítica de Minsky é marcada pela Hipótese da Instabilidade Financeira, a qual aponta para fatores endógenos ao próprio sistema capitalista como o principal causador de instabilidades financeiras. Este processo, caracterizado principalmente por um avanço desfavorável no nível de endividamento dos agentes, constrói um ciclo de estágios que pode se desenvolver para uma crise financeira ou um colapso sistêmico, definidos como “Momento Minsky” e “Colapso Minsky”. Este cenário descrito por Minsky, também analisado à luz de teorias mais recentes como as de Gary A. Dymski e Alessandro Vercelli, é conhecido por “ciclo minskyano”. Ao adotar estes preceitos da análise teórica de Minsky, é possível visualizar como o processo de desregulamentação e fragilização financeira dos Estados Unidos nas décadas de 1980 e 1990 proveram condições para a crise do subprime e, posteriormente, o colapso financeiro de 2008. De maneira similar, é possível observar que a análise teórica de Minsky também é aplicável à crise que afeta a economia brasileira no final de 2008. A fragilização financeira que se inicia no Brasil poucos anos antes da crise, acentuada no setor exportador de commodities, cria a condição para o “momento Minsky brasileiro”, demonstrando que apesar das falhas da análise teórica de Minsky, que supõe uma economia fechada com características da economia estadunidense, é possível visualizar uma relação de causa e efeito da recente crise financeira com a teoria minskyana.

The East Atlantic Bluefin Tuna Fisheries: Stock Collapse or Recovery?

A discrete time, multi-gear, and age structured bio-economic model is developed for the East Atlantic bluefin tuna fisheries, a paradigmatic example of the difficulties faced in managing highly migratory fish stocks. The model is used to analyse alternative management strategies for the Regional Fisheries Management Organisation (RFMO) managing this fishery, and to investigate some of the policy implications. For the various scenarios, the optimal stock level varies between 500–800,000 tonnes, which compares with a stock level of 150,000 tonnes in 1995. In other words, there is a very strong case for rebuilding the stock. Moreover, the sustainability of the stock is threatened unless a recovery programme is implemented; indeed, the alternative may be stock collapse. Second, to rebuild the stock, Draconian measures are called for: either outright moratoria over fairly lengthy periods, or possibly a more gradual approach to steady state given by a Total Allowable Catch (TAC) at a low level for an extended period of time. Third, the cost of inefficient gear structure is very high indeed.

Análise estática não linear de um edifício em betão armado

Trabalho Final de Mestrado para obtenção do grau de Mestre em Engenharia Civil

Aids-related progressive multifocal leukoencephalopathy: a retrospective study in a referral center in São Paulo, Brazil

Few data are available about progressive multifocal leukoencephalopathy (PML) in patients with acquired immunodeficiency syndrome (AIDS) from Brazil. The objectives of this study were to describe the main features of patients with PML and estimate its frequency among AIDS patients with central nervous system (CNS) opportunistic diseases admitted to the Instituto de Infectologia Emílio Ribas, São Paulo, Brazil, from April 2003 to April 2004. A retrospective and descriptive study was performed. Twelve (6%) cases of PML were identified among 219 patients with neurological diseases. The median age of patients with PML was 36 years and nine (75%) were men. Nine (75%) patients were not on antiretroviral therapy at admission. The most common clinical manifestations were: focal weakness (75%), speech disturbances (58%), visual disturbances (42%), cognitive dysfunction (42%), and impaired coordination (42%). The median CD4+ T-cell count was 45 cells/µL. Eight (67%) of 12 patients were laboratory-confirmed with PML and four (33%) were possible cases. Eleven (92%) presented classic PML and only one case had immune reconstitution inflammatory syndrome (IRIS)-related PML. In four (33%) patients, PML was the first AIDS-defining illness. During hospitalization, three patients (25%) died as a result of nosocomial pneumonia and nine (75%) were discharged to home. Cases of PML were only exceeded by cases of cerebral toxoplasmosis, cryptococcal meningoencephalitis, and CNS tuberculosis, the three more frequent neurologic opportunistic infections in Brazil. The results of this study suggest that PML is not an uncommon HIV-related neurologic disorder in a referral center in Brazil.

Non-Progressive Leukoencephalopathy with Bilateral Temporal Cysts

We report two cases of a peculiar leukoencephalopathy with temporal cysts. Both patients have a non-progressive neurological disorder with mental retardation, microcephaly and sensorineural deafness although clinical differences between them may reflect a different aetiology. The metabolic disorders with white matter involvement and the recently described leukoencephalopathies (Van Der Knaap disease, 'vanishing white matter disease') were excluded based on clinical, biologic and imaging findings. Cytomegalovirus infection is a likely possibility in the first case although the magnetic resonance imaging picture is only partially similar to previously reported cases. Our patients are strikingly similar to the patients reported by Deonna et al. and Olivier et al. We discuss the clinical and imaging findings in our patients and the differential diagnosis considering the known disorders of the white matter in childhood.

Progressive multifocal leukoencephalopathy as an AIDS-defining condition in a patient with high CD4+ T-lymphocyte count

We present the case of a 31-year-old man with acute manifestation of progressive multifocal leukoencephalopathy (PML) as an AIDS-defining disease. The patient presented with a three-day history of neurological disease, brain lesions without mass effect or contrast uptake and a slightly increased protein concentration in cerebrospinal fluid. A serological test for HIV was positive and the CD4+ T-cell count was 427/mm³. Histological examination of the brain tissue revealed abnormalities compatible with PML. The disease progressed despite antiretroviral therapy, and the patient died three months later. PML remains an important cause of morbidity and mortality among HIV-infected patients.

Mechanical ventilation for the treatment of severe excessive dynamic airway collapse

[Excerpt] We read with interest the case report by Ismael et al1 describing a patient with Sjo¨gren’s syndrome and cystic lung disease who could not be weaned from a ventilator due to severe central excessive dynamic airway collapse (EDAC) of the lower part of the trachea and proximal bronchi. EDAC corresponds to the expiratory bulging of the tracheobronchial wall without known airway structural abnormalities, leading to a decrease of at least 50% in internal diameter.2 It is a rare and underdiagnosed entity, commonly confused with other respiratory diseases such as asthma and COPD. Although noninvasive procedures such as cervicothoracic computed tomography scan on inspiration and expiration may suggest the disorder, the accepted standard method for diagnosis is bronchoscopy.3-7 (...).

Cylindrically symmetric models of gravitational collapse to black holes: a short review

We survey results about exact cylindrically symmetric models of gravitational collapse in General Relativity. We focus on models which result from the matching of two spacetimes having collapsing interiors which develop trapped surfaces and vacuum exteriors containing gravitational waves. We collect some theorems from the literature which help to decide a priori about eventual spacetime matchings. We revise, in more detail, some toy models which include some of the main mathematical and physical issues that arise in this context, and compute the gravitational energy flux through the matching boundary of a particular collapsing region. Along the way, we point out several interesting open problems.

Quantitative study of myocardial microcirculation in arterial hypertension due to progressive inhibition of NO synthesis

OBJECTIVE: To study the quantitative changes in intramyocardial blood vessels in rats in whom nitric oxide synthesis was inhibited. METHODS: Four groups of 10 rats were studied: control (C25 and C40) and L-NAME (L25 and L40). The animals L25 and L40 received L-NAME in the dosage of 50mg/kg/day for 25 and 40 days, respectively. On days 26 and 41 the animals in groups 25 and 40 were sacrificed. Analysis of the myocardium was performed using light microscopy and stereology. RESULTS: Arterial blood pressure and heart weight increased 74.5 and 57.8% after 25 days and 90.2 and 34.6% after 40 days, respectively. Comparing the L-NAME rats with the respective controls revealed that vessel volume density decreased 31.3% after 40 days, and the vessel length-density decreased 53.5% after 25 days and 25.7% after 40 days. The mean cross-sectional area of the vessels showed an important reduction of 154.6% after 25 days. The intramyocardial vessels decreased significantly in length- density in the L-NAME animals. The mean cross-sectional area of the vessels, which normally increases during heart growth between 25 and 40 days, showed a precocious increase by the 25th day in the L-NAME rats. This suggests an increase of the size of the heart, including blood vessels. CONCLUSION: The inhibition of the NO synthesis provokes rarefaction in the intramyocardial vessels that progresses with the time of administration of L-NAME.