Boolean Models of Bistable Biological Systems

This paper presents an algorithm for approximating certain types of dynamical systems given by a system of ordinary delay differential equations by a Boolean network model. Often Boolean models are much simpler to understand than complex differential equations models. The motivation for this work comes from mathematical systems biology. While Boolean mechanisms do not provide information about exact concentration rates or time scales, they are often sufficient to capture steady states and other key dynamics. Due to their intuitive nature, such models are very appealing to researchers in the life sciences. This paper is focused on dynamical systems that exhibit bistability and are desc ribedby delay equations. It is shown that if a certain motif including a feedback loop is present in the wiring diagram of the system, the Boolean model captures the bistability of molecular switches. The method is appl ied to two examples from biology, the lac operon and the phage lambda lysis/lysogeny switch

Frequency and histopathological classification of canine mastocytoma in the casuistry (period 2000-2006) of a histopathology veterinary laboratory in Lima, Peru

El objetivo del presente estudio fue clasificar el mastocitoma de acuerdo a su grado histológico, a partir de muestras provenientes de necropsias y biopsias caninas diagnosticadas por histopatología en el Laboratorio de Patología Veterinaria de la Facultad de Medicina Veterinaria de la Universidad Nacional Mayor de San Marcos, Lima, Perú, a través de un estudio retrospectivo para el periodo 2000-2006. Se encontraron 40 casos de mastocitomas (4.5%) en 881 neoplasias caninas. Al clasificar los mastocitomas según su grado histológico se encontró que el 42.5% fueron de grado I (bien diferenciado), el 47.5% de grado II (moderadamente diferenciado) y el 10% de grado III (poco diferenciado). Asimismo, el 63.9% (23/36) de los casos se encontraron en perros Bóxer.The aim of this retrospective study was to classify mastocytomas according to histologic grade from samples of canine necropsies and biopsies diagnosed by histopathology in the Pathology Laboratory of the Faculty of Veterinary Medicine of the National University of San Marcos, Lima, Peru in the period 2000-2006. A total of 40 cases of mastocytomas were found (4.5%) in 881 neoplasms. The classification of the mastocytomas based on the histologic grade indicated that el 42.5% were of grade I (well differentiated), 47.5% of grade II (moderately differentiated) and 10% of grade III (poorly differentiated). Moreover, 63.9% (23/36) cases were found in the Boxer breed

Toric G_2 and Spin(7) holonomy spaces from gravitational instantons and other examples

Non-compact G_2 holonomy metrics that arise from a T^2 bundle over a hyper-Kahler space are discussed. These are one parameter deformations of the metrics studied by Gibbons, Lu, Pope and Stelle in hep-th/0108191. Seven-dimensional spaces with G_2 holonomy fibered over the Taub-Nut and the Eguchi-Hanson gravitational instantons are found, together with other examples. By considering the Apostolov-Salamon theorem math.DG/0303197, we construct a new example that, still being a T^2 bundle over hyper-Kahler, represents a non trivial two parameter deformation of the metrics studied in hep-th/0108191. We then review the Spin(7) metrics arising from a T^3 bundle over a hyper-Kahler and we find two parameter deformation of such spaces as well. We show that if the hyper-Kahler base satisfies certain properties, a non trivial three parameter deformations is also possible. The relation between these spaces with the half-flat structures and almost G_2 holonomy spaces is briefly discussed.Comment: 27 pages. Typos corrected. Accepted for publication in Commun.Math.Phy

Cuantificación mineralógica de cementos mediante análisis Rietveld de DRX

Existen varias técnicas para conocer la composición mineralógica de los cementos, como las fórmulas de Bogue o el conteo con microscopía. En los últimos años la técnica que ha ganado mayor aceptación es la cuantificación mediante el método Rietveld para difracción de rayos X, por sus ventajas comparativas a los demás métodos (velocidad, precisión y la posibilidad de ser aplicado a cualquier tipo de cemento). Entre las variables que pueden afectar a la reproducibilidad de los resultados, se encuentra el conocimiento y la experiencia del operario que utiliza los programas de refinamiento. Para minimizar la incidencia del operario existen protocolos de refinamiento, a veces incluidos en el programa, o como en este caso elaborados manualmente. En este trabajo se analizaron muestras de cementos y adiciones minerales con dos programas de refinamiento y se compararon los resultados entre sí, y con ensayos de fluorescencia

Prognostic value of cardiac troponin T elevation is independent of renal function and clinical findings in heart failure patients

Background: The aim of this study is to determine the prevalence and prognostic value of elevated cardiac troponin (cTnT) and its association with clinical characteristics according to renal function status in patients with stable heart failure. Methods: In a prospective observational study, 152 consecutive patients from the Heart Failure Clinic of the INCMNSZ were followed for a period of 42 months. All underwent clinical evaluation, echocardiography, and determination of body composition by electric bioimpedance to identify hypervolemia. Concentrations of cTnT were quantified by immunoassay with electrochemoluminescence and &#8805; 0.02 ng/mL levels were considered elevated. Also glomerular filtration rate (eGFR) was estimated using the Cockcroft-Gault equation. Results: Elevated cTnT was significantly associated with increased all-cause mortality in the observational period even after adjusting for eGFR < 60 mL/min/1.73 m2 and clinical findings such as hypertension, functional class, loop diuretics, angiotensin converting enzyme inhibitors, pulmonary pressure and hypervolemia in Cox regression analysis with a hazard ratio of 4.58 (95% confidence interval: 1.84&#8211;11.45). Conclusions: Heart failure patients with elevated cardiac-specific troponin T are at increased risk of death independently of the presence of chronic kidney disease. (Cardiol J 2010; 17, 1: 42-48

Phenotypic Variation and Bistable Switching in Bacteria

Microbial research generally focuses on clonal populations. However, bacterial cells with identical genotypes frequently display different phenotypes under identical conditions. This microbial cell individuality is receiving increasing attention in the literature because of its impact on cellular differentiation, survival under selective conditions, and the interaction of pathogens with their hosts. It is becoming clear that stochasticity in gene expression in conjunction with the architecture of the gene network that underlies the cellular processes can generate phenotypic variation. An important regulatory mechanism is the so-called positive feedback, in which a system reinforces its own response, for instance by stimulating the production of an activator. Bistability is an interesting and relevant phenomenon, in which two distinct subpopulations of cells showing discrete levels of gene expression coexist in a single culture. In this chapter, we address techniques and approaches used to establish phenotypic variation, and relate three well-characterized examples of bistability to the molecular mechanisms that govern these processes, with a focus on positive feedback.