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A instabilidade contínua na Guiné-Bissau
Kamilla Rizzi
Meridiano 47 : Boletim de Análise de Conjuntura em Rela??es Internacionais , 2010,
Abstract: Pouco mais de um ano após os assassinatos políticos que chocaram a comunidade internacional, uma nova tentativa de golpe militar ocorreu na Guiné-Bissau, em 1o de abril passado. A contínua instabilidade política guineense vem desde a independência, em 1973.
Comunicación mediática y consenso democrático. Una investigación sobre las transformaciones de la obligación política
Lino Rizzi
Revista mexicana de ciencias políticas y sociales , 2003,
Abstract: En este artículo, el autor realiza un análisis filosófico-político de la disociación entre la noción política de ciudadanía y la comunicación mediática, con el propósito de comprender el estatus político del derecho a la expresión pública. En el trabajo se sostiene que la comunicación ya no es más un acto político y por ello ya no conserva la característica imprescindible llamada performabilidad, que abarca la polémica, la visibilidad, la accesibilidad, la posibilidad de preguntar, de replicar y de discutir. En este tenor, el autor destaca que mientras en las constituciones la definición de ciudadanía está anclada a un carácter asociativo y discursivo, los nuevos medios de comunicación hacen posible la desarticulación de la implicación antropológica necesaria en el acto comunicativo; esto porque tal parece que la reunión pública ya no es una necesidad humana para realizar el intercambio de ideas y para formar y conformar las opiniones, pues los medios de comunicación están invadiendo este espacio. Como consecuencia, existe una contradicción entre el sistema democrático y las prácticas de comunicación sin participación pública.
The Meaning of Bell's Theorem
Anthony Rizzi
Physics , 2003,
Abstract: The import of Bell's Theorem is elucidated. The theorem's proof is illustrated both heuristically and in mathematical detail in a pedagogical fashion. In the same fashion, it is shown that the proof is correct mathematically, but it doesn't require, as is usually thought, one to abandon locality or realism.
Angular and Linear Momentum in General Relativity: Their Geometric Structure and Interrelation
Anthony Rizzi
Physics , 2002,
Abstract: Generalized definitions for angular and linear momentum are given and shown to reduce to the ADM (at spatial infinity) definitions and the definitions at null infinity in the appropriate limit. These definitions are used to express angular momentum in terms of linear momentum. The formalism allows one to see the connection with the classical and special relativitistic notions of momenta. Further, the techniques elucidate, for the first time, the geometric nature of these conserved quantities. The boosted Schwarzschild solution is used to illustrate some aspects. The definitions are useful and give insight in the region far from all masses where gravity waves are detected.
Measure contraction properties of Carnot groups
Luca Rizzi
Mathematics , 2015,
Abstract: We prove that any corank 1 Carnot group of dimension $k+1$ equipped with a left-invariant measure satisfies the MCP(K,N) iff $K \leq 0$ and $N \geq k+3$. This generalizes the well known result by Juillet for the Heisenberg group $\mathbb{H}_{2d+1}$ to a larger class of structures, which admit non-trivial abnormal minimizing curves. The number $k+3$ coincides with the geodesic dimension of the Carnot group, which we define here for a general metric space. We discuss some of its properties, and its relation with the curvature exponent (the least $N$ such that the MCP(K,N) is satisfied). We prove that, on a metric measure space, the curvature exponent is always larger than the geodesic dimension which, in turn, is larger than the Hausdorff one. When applied to Carnot groups, this result improves a previous lower bound due to Rifford. As a byproduct, we prove that a Carnot group is ideal if and only if it is fat.
Clifford Tori and the singularly perturbed Cahn-Hilliard equation
Matteo Rizzi
Mathematics , 2015,
Abstract: In this paper we construct entire solutions $u_{\varepsilon}$ to the Cahn-Hilliard equation $-\varepsilon^{2}\Delta(-\varepsilon^{2}\Delta u+W^{'}(u))+W^{"}(u)(-\varepsilon^{2}\Delta u+W^{'}(u))=0$, under the volume constraint $\int_{\mathbb{R}^{3}}(1-u_{\varepsilon})dx=4\sqrt{2}\pi^{2}$, whose nodal set approaches the Clifford Torus, that is the Torus with radii of ratio $1/\sqrt{2}$ embedded in $\mathbb{R}^{3}$, as $\varepsilon\to 0$. What is crucial is that the Clifford Torus is a Willmore hypersurface and it is non-degenerate, up to conformal transformations. The proof is based on the Lyapunov-Schmidt reduction and on careful geometric expansions of the laplacian.
The emergence of power-law distributions of inter-spike intervals characterizes status epilepticus induced by pilocarpine administration in rats
Massimo Rizzi
Quantitative Biology , 2015,
Abstract: Objective. To ascertain the existence of power-law distributions of inter-spike intervals (ISI) occurring during the progression of status epilepticus (SE), so that the emergence of critical states could be reasonably hypothesized as being part of the intrinsic nature of the SE. Methods. Status epilepticus was induced by pilocarpine administration in post-natal 21-day rats (n=8). For each animal, 24 hours of EEG from the onset of the SE were analyzed according to the analytical procedure suggested by Clauset et al. (2009) which combines maximum-likelihood fitting methods with goodness-of-fit tests based on the Kolmogorov-Smirnov statistics and likelihood ratios. The analytical procedure was implemented by the freely available R software package "poweRlaw". Time of calculations was considerably shorten by the exploitation of High-Throughput Computing technology, a.k.a. Grid Computing technology. Results. The progression of the SE is characterized by the emergence of power-law correlations of ISI whose likelihood of occurrence increases the more the time from the onset of the SE elapses. Log-normal distribution of ISI is however widely represented. Additionally, undetermined distributions of ISI are represented as well, although confined within a restricted temporal window. The final stage of SE appears dominated only by power-law and log-normal distributions of ISI. Significance. The emergence of power-law correlations of ISI concretely supports the concept of the occurrence of critical states during the progression of SE. It is reasonably speculated, as a working hypothesis, that the occurrence of power-law distributions of ISI within the early stages of the SE could be a hallmark of the establishment of the route to epileptogenesis.
Region-Based PDEs for Cells Counting and Segmentation in 3D+Time Images of Vertebrate Early Embryogenesis
Barbara Rizzi,Alessandro Sarti
International Journal of Biomedical Imaging , 2009, DOI: 10.1155/2009/968986
Abstract: This paper is devoted to the segmentation of cell nuclei from time lapse confocal microscopy images, taken throughout early Zebrafish embryogenesis. The segmentation allows to identify and quantify the number of cells in the animal model. This kind of information is relevant to estimate important biological parameters such as the cell proliferation rate in time and space. Our approach is based on the active contour model without edges. We compare two different formulations of the model equation and evaluate their performances in segmenting nuclei of different shapes and sizes. Qualitative and quantitative comparisons are performed on both synthetic and real data, by means of suitable gold standard. The best approach is then applied on a number of time lapses for the segmentation and counting of cells during the development of a zebrafish embryo between the sphere and the shield stage.
The approximability of the String Barcoding problem
Giuseppe Lancia, Romeo Rizzi
Algorithms for Molecular Biology , 2006, DOI: 10.1186/1748-7188-1-12
Abstract: The following setting was introduced by Rash and Gusfield in [1]: Given a set V of n strings v1,...,vn (representing the genomes of n known viruses), and an extra string s (representing a virus in V, but not yet classified), we aim at recognizing s as one of the known viruses through an hybridization experiment. In the experiment, we utilize a set ∏ of k probes (DNA strings) and we will are able to determine which ones are contained in s (as substrings) and which are not. The result of the experiment is therefore a binary k-vector (called, in [1] a barcode) which can be seen as the signature of s with respect to the given probes. In order for the barcode to be able to discriminate between all the viruses, it must be true that, for each pair of viruses vi, vj, with 1 ≤ i
DISE?O DE INSTRUMENTOS ECONóMICOS PARA LA INTERNALIZACIóN DE EXTERNALIDADES DE ACCIDENTES DE TRáNSITO
RIZZI,LUIS IGNACIO;
Cuadernos de economía , 2005, DOI: 10.4067/S0717-68212005012600004
Abstract: road crashes are a major source of transport externalities. based on jansson's road crashes model, this paper analyzes ways to internalize those externalities. jansson's model is extended to analyze the effect of congestion and safety variables related to vehicle and infrastructure design on crash rates and severity. the model is then used to compute the cost of road crashes externalities in chile
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