Spacecraft magnetic attitude control using approximating sequence Riccati equations

This paper presents the results of a spacecraft attitude control system based on magnetic actuators designed for low Earth orbits. The control system is designed by using a nonlinear control technique based on the approximating sequence of Riccati equations. The behavior of the satellite is discussed under perturbations and model uncertainties. Simulation results are presented when the control system is able to guide the spacecraft to the desired attitude in a variety of different conditions

Microscopic Theory, Analysis, and Interpretation of Conductance Histograms in Molecular Junctions

Molecular electronics break-junction experiments are widely used to investigate fundamental physics and chemistry at the nanoscale. Reproducibility in these experiments relies on measuring conductance on thousands of freshly formed molecular junctions, yielding a broad histogram of conductance events. Experiments typically focus on the most probable conductance, while the information content of the conductance histogram has remained unclear. Here, we develop a theory for the conductance histogram by merging the theory of force-spectroscopy with molecular conductance. To do so, we propose a microscopic model of the junction evolution under the modulation of external mechanical forces and combine it with the statistics of junction rupture and formation. Our formulation focuses on contributions to the conductance dispersion that emerge due to changes in the conductance during mechanical manipulation. The final shape of the histogram is determined by the statistics of junction rupture and formation. The procedure yields analytical equations for the conductance histogram in terms of parameters that describe the free-energy profile of the junction, its mechanical manipulation, and the ability of the molecule to transport charge. All physical parameters that define our microscopic model can be extracted from separate conductance and rupture force measurements on molecular junctions. Our theory accurately fits experimental conductance histograms and augments the information content that can be extracted from experiments. Further, the predicted behavior with respect to physical parameters can be used to design experiments with narrower conductance distribution and to test the range of validity of the model

Modal analysis of semi-enclosed basins

Abstract This paper presents a novel technique for the computation of eigenvalues and eigenvectors of partially enclosed basins such as harbours and bays. The procedure makes use of the finite element approximation of the linear shallow water equations, and converts the time-depending problem into an eigenvalues one. The main point of novelty of this research is the mathematical condition used at the boundary that separates the computational domain from the open sea. While classical techniques impose a zero surface elevation (i.e. a nodal line), here an approximate radiation condition is applied. The use of a radiation condition at the open boundary gives a quadratic eigenvalue problem that admits as solution complex eigenvalues and eigenvectors, thus describing the flow in terms of both standing and progressive waves. The new method is applied to an idealized long and narrow harbour, for which an analytical solution of long wave resonance exists, and to the harbour of Marina di Carrara (Italy), for which measurements and previous numerical computation results are available. In both cases the results show good agreement with the available data

Estudio taxonómico y ecológico del género Elaphoglossum (Elaphoglossaceae), en el Parque Nacional Yanachaga-Chemillén, Oxapampa, Pasco

Se presenta el estudio taxonómico y ecológico del género Elaphoglossum (Elaphoglossaceae) en el Parque Nacional Yanachaga-Chemillén, ubicado en la provincia de Oxapampa, departamento de Pasco. Se realizó recolectas intensivas entre los 380 y 3500 msnm. Para un mejor análisis de los resultados se agruparon las especies bajo la subdivisión del género Elaphoglossum (secciones y subsecciones) hecha por Mickel and Atehortúa (1980). Para el estudio taxonómico se elaboraron claves y descripciones para las especies. Se reporta 118 especies y 8 secciones. Las secciones más diversas son Lepidoglossa con 37 especies y Elaphoglossum con 36 especies, la sección Undulata incluyó 12 especies, las secciones Setosa y Polytrichia 11 especies, seguidas por las secciones Squamipedia (8 especies), Eximia (2 especies) y Decorata (1 especie). De las 118 especies reportadas, 36 son probables nuevos registros para el Perú y 82 son nuevos registros para el departamento de Pasco. Algunas especies se describen por primera vez de material fértil, además se dan nuevos rangos de variación morfológica para varias de ellas. En el estudio ecológico se define al rango altitudinal entre los 1700-2800 msnm como el más diverso para el género Elaphoglossum; sin embargo, existen especies restringidas a lo largo de la gradiente altitudinal, 9 especies están restringidas bajo los 1000 msnm y 5 especies sobre los 3000 msnm. La mayoría de las especies son epífitas, aunque existen especies que sólo se desarrollan sobre el suelo o rocas. Las especies que crecen a altas elevaciones suelen ser terrestres y se agrupan en matas, mientras que las especies de bajas elevaciones, son predominantemente epífitas y crecen sobre los troncos en forma de nido de ave. No se encontró una clara diferencia en la distribución altitudinal a nivel de las secciones.A study on the taxonomy and ecology of the genus Elaphoglossum (Elaphoglossaceae) in the National Park Yanachaga-Chemillén, located in the province of Oxapampa, Pasco department is presented herein. Intensive collections were carried out between 380 and 3500 meters above sea level (masl). For a better analysis of the results, the species were grouped under the subdivision of the genus Elaphoglossum made by Mickel and Atehortúa (1980). In the taxonomic study, keys and descriptions were elaborated for the species. It is reported 118 species in 8 of the 9 sections described by Mickel and Atehortúa (1980). The most diverse sections are Lepidoglossa with 37 species and Elaphoglossum with 36 species, the section Undulata reported 12 species, the sections Setosa and Polytrichia 11 species, followed by the sections Squamipedia (8 species), Eximia (2 species) and Decorata (1 species). Of the 118 reported species, 82 are new records for the department of Pasco, and 36 of them are new records for Peru, expecting some of them to be new species for science. Some species are described for the first time from fertile material and additional morphologic features is provided. In the ecological study, the altitudinal range between 1700-2800 masl is defined as the most diverse; however, there are restricted species along of the altitudinal gradient, being 9 species restricted below 1000 masl and 5 species above 3000 masl. Most of the species are epiphytes, although some species only develop on the floor or rocks. The high elevation species are usually terrestrial and group in undergrowths, while the low elevations species are predominantly epiphytes and grow on trunks in shape of bird nest. Differences in altitudinal distribution in the sections were not found.Tesi

Atypical subacute sclerosing panencephalitis: Case report

Subacute sclerosing panencephalitis (SSPE) is a progressive inflammatory disorder of the central nervous system with both poor prognosis and high mortality. the disease has been related to a persistent and aberrant measles virus infection and no effective treatment has been available. We report a case of SSPE with atypical features including seizures at onset and a fulminant course in a 8 years-old boy who had been previously immunized against measles.Univ Fed Juiz de Fora, Univ Hosp, Dept Internal Med, Neurol Serv, Juiz de Fora, MG, BrazilUniv Fed Fluminense, Niteroi, RJ, BrazilUniv Fed Juiz de Fora, Juiz de Fora, MG, BrazilUniversidade Federal de São Paulo, São Paulo, BrazilUniv Fed Rio de Janeiro, Rio de Janeiro, BrazilUniv Fed Juiz de Fora, Univ Hosp, Dept Internal Med, Juiz de Fora, MG, BrazilUniversidade Federal de São Paulo, São Paulo, BrazilWeb of Scienc

Finite Heisenbeg Groups and Seiberg Dualities in Quiver Gauge Theories

A large class of quiver gauge theories admits the action of finite Heisenberg groups of the form Heis(Z_q x Z_q). This Heisenberg group is generated by a manifest Z_q shift symmetry acting on the quiver along with a second Z_q rephasing (clock) generator acting on the links of the quiver. Under Seiberg duality, however, the action of the shift generator is no longer manifest, as the dualized node has a different structure from before. Nevertheless, we demonstrate that the Z_q shift generator acts naturally on the space of all Seiberg dual phases of a given quiver. We then prove that the space of Seiberg dual theories inherits the action of the original finite Heisenberg group, where now the shift generator Z_q is a map among fields belonging to different Seiberg phases. As examples, we explicitly consider the action of the Heisenberg group on Seiberg phases for C^3/Z_3, Y^{4,2} and Y^{6,3} quiver.Comment: 22 pages, five figure

Los Tributos: Aporte de Milagro y Guayaquil por Impuesto a la Renta

A lo largo de la historia de los tributos  existieron  cambios sustanciales en la forma de imposición y el presente trabajo trata de resumir esa historia y hace énfasis en el impuesto a la renta. Presenta un análisis porcentual de las recaudaciones de Milagro y Guayaquil con relación a la provincia del Guayas y la recaudación Global en Ecuador

Central Extensions of Finite Heisenberg Groups in Cascading Quiver Gauge Theories

Many conformal quiver gauge theories admit nonconformal generalizations. These generalizations change the rank of some of the gauge groups in a consistent way, inducing a running in the gauge couplings. We find a group of discrete transformation that acts on a large class of these theories. These transformations form a central extension of the Heisenberg group, generalizing the Heisenberg group of the conformal case, when all gauge groups have the same rank. In the AdS/CFT correspondence the nonconformal quiver gauge theory is dual to supergravity backgrounds with both five-form and three-form flux. A direct implication is that operators counting wrapped branes satisfy a central extension of a finite Heisenberg group and therefore do not commute.Comment: 25 pages, 12 figure