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Search Results: 1 - 10 of 38 matches for " Remis "
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Cytogenetic studies in Sinipta dalmani St?l (Orthoptera: acrididae). II. Effects of centric fusions on chiasma frequency and distribution
MI Remis
Genetics Selection Evolution , 1990, DOI: 10.1186/1297-9686-22-3-263
Chromosome polymorphisms in natural populations of the South American grasshopper Sinipta dalmani
Remis, Maria Isabel;
Genetics and Molecular Biology , 2008, DOI: 10.1590/S1415-47572008000100009
Abstract: six populations of sinipta dalmani from the provinces of buenos aires and entre rios (argentina) were analyzed. the populations of "el palmar" national park (entre rios) were polymorphic for pericentric inversions in pairs m4 and m7 and for a centric fusion involving pair m5 and the x chromosome. the m4 inversion remained similar over time and the karyomorphic frequencies did not depart from those expected according to the hardy-weinberg equilibrium. the analysis of chiasma frequency and distribution showed clear intra- and interchromosome effects of the different chromosome rearrangements. both inversions and centric fusions were related with total or partial crossing over restriction in heterozygous condition, leading to a genetic differentiation between rearranged and non-rearranged chromosomes. the chromosome polymorphisms analyzed herein were associated with an increase in the number of terminal chiasmata both in the rearranged chromosomes (heterozygous centric fusion and homozygous m4 inversion) and in the other chromosomes (m4 inversion). our results showed that the chromosome polymorphisms in s. dalmani may be associated with a significant decrease in genetic recombination, which may explain in part their maintenance in some areas of its geographical distribution.
Análisis de la estructura poblacional
Remis,María Isabel;
BAG. Journal of basic and applied genetics , 2011,
Abstract: the study of the population structure allows analyzing the distribution of the variability within and among natural populations interpreting the processes that shape variation. in the laboratory of genetics of the population structure of the department of ecology, genetics and evolution (f. c. e. yn., uba) intraspecific variability analysis are carried out using chromosome, molecular and morphometric markers in organisms of agronomic or evolutionary importance using species of grasshoppers and marine vertebrates as biological models. in orthoptera cytogenetic studies clarifed the mechanisms of coevolution between dispensable genomic elements (chromosomes b) and the host genome (a chromosomes) and provided the opportunity to analyze the variability associated with chromosomal rearrangements (centric fusions; pericentric inversions) which modify the number of independent linkage groups. the analysis of the relationships between morphometric and climatic/environmental variables allow inferring important aspects of the phenotypic evolution. cytogenetic and morphometric simultaneous studies analyzed the effects of the karyotype and phenotype on fitness components providing direct evidence of the adaptive significance of the chromosomal polymorphisms. studies using molecular markers (rflp, damd rapd) analyzed the genetic population structure as well as the gene fow between populations. morphometric and molecular studies (dna sequences, microsatellites) in vertebrate marine identifed genetically distinct groups of organisms that should be conserved. the emerged results interpreted the adaptive strategies of orthoptera species considered plagues as well as provided information to implement mitigation measures and plans for conservation in marine vertebrate species.
An Efficient Model-Order Reduction Approach to Low-Frequency Transmission Line Modeling
Rob F. Remis
PIER , 2010, DOI: 10.2528/PIER09123006
Abstract: In this paper we present a Lanczos-type reduction method to simulate the low-frequency response of multiconductor transmission lines. Reduced-order models are constructed in such a way that low frequencies are approximated first. The inverse of the transmission line system matrix is then required and an explicit expression for this inverse is presented. No matrix factorization needs to be computed numerically. Furthermore, computing the action of the inverse on a vector requires an () amount of work, where is the total number of unknowns, and the inverse satisfies a particular reciprocityrelated symmetry relation as well. These two properties are exploited in a Lanczos-type algorithm to efficiently construct the low-frequency reduced-order models. Numerical examples illustrate the performance of the method.
An Electric Field Volume Integral Equation Approach to Simulate Surface Plasmon Polaritons
Rob Remis,Edoardo Charbon
Advanced Electromagnetics , 2013, DOI: 10.7716/aem.v2i1.23
Abstract: In this paper we present an electric field volume integral equation approach to simulate surface plasmon propagation along metal/dielectric interfaces. Metallic objects embedded in homogeneous dielectric media are considered. Starting point is a so-called weak-form of the electric field integral equation. This form is discretized on a uniform tensor-product grid resulting in a system matrix whose action on a vector can be computed via the fast Fourier transform. The GMRES iterative solver is used to solve the discretized set of equations and numerical examples, illustrating surface plasmon propagation, are presented. The convergence rate of GMRES is discussed in terms of the spectrum of the system matrix and through numerical experiments we show how the eigenvalues of the discretized volume scattering operator are related to plasmon propagation and the medium parameters of a metallic object.
Pasado y presente del juramento Hipocrático: Análisis de su vigencia
José Antonio Remis
Revista Argentina de Radiología , 2009,
A Krylov Stability-Corrected Coordinate-Stretching Method to Simulate Wave Propagation in Unbounded Domains
Vladimir Druskin,Rob Remis
Mathematics , 2012,
Abstract: The Krylov subspace projection approach is a well-established tool for the reduced order modeling of dynamical systems in the time domain. In this paper, we address the main issues obstructing the application of this powerful approach to the time-domain solution of exterior wave problems. We use frequency independent perfectly matched layers to simulate the extension to infinity. Pure imaginary stretching functions based on Zolotarev's optimal rational approximation of the square root are implemented leading to perfectly matched layers with a controlled accuracy over a complete spectral interval of interest. A new Krylov-based solution method via stability-corrected operator exponents is presented which allows us to construct reduced-order models (ROMs) that respect the delicate spectral properties of the original scattering problem. The ROMs are unconditionally stable and are based on a renormalized bi-Lanczos algorithm. We give a theoretical foundation of our method and illustrate its performance through a number of numerical examples in which we simulate 2D electromagnetic wave propagation in unbounded domains, including a photonic waveguide example. The new algorithm outperforms the conventional finite-difference time domain method for problems on large time intervals.
José Antonio Remis,Silvina Zarlenga,Marcelo Amarillo,José Federico Remis
Revista Argentina de Radiología , 2010,
Spatial Genetic Structure and Mitochondrial DNA Phylogeography of Argentinean Populations of the Grasshopper Dichroplus elongatus
Natalia Rosetti, Maria Isabel Remis
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0040807
Abstract: Many grasshopper species are considered of agronomical importance because they cause damage to pastures and crops. Comprehension of pest population dynamics requires a clear understanding of the genetic diversity and spatial structure of populations. In this study we report on patterns of genetic variation in the South American grasshopper Dichroplus elongatus which is an agricultural pest of crops and forage grasses of great economic significance in Argentina. We use Direct Amplification of Minisatellite Regions (DAMD) and partial sequences of the cytochrome oxydase 1 (COI) mitochondrial gene to investigate intraspecific structure, demographic history and gene flow patterns in twenty Argentinean populations of this species belonging to different geographic and biogeographic regions. DAMD data suggest that, although genetic drift and migration occur within and between populations, measurable relatedness among neighbouring populations declines with distance and dispersal over distances greater than 200 km is not typical, whereas effective gene flow may occur for populations separated by less than 100 km. Landscape analysis was useful to detect genetic discontinuities associated with environmental heterogeneity reflecting the changing agroecosystem. The COI results indicate the existence of strong genetic differentiation between two groups of populations located at both margins of the Paraná River which became separated during climate oscillations of the Middle Pleistocene, suggesting a significant restriction in effective dispersion mediated by females and large scale geographic differentiation. The number of migrants between populations estimated through mitochondrial and DAMD markers suggest that gene flow is low prompting a non-homogeneous spatial structure and justifying the variation through space. Moreover, the genetic analysis of both markers allows us to conclude that males appear to disperse more than females, reducing the chance of the genetic loss associated with recent anthropogenic fragmentation of the D. elongatus studied range.
An Extended Krylov Subspace Model-Order Reduction Technique to Simulate Wave Propagation in Unbounded Domains
Vladimir Druskin,Rob Remis,Mikhail Zaslavsky
Physics , 2014, DOI: 10.1016/j.jcp.2014.04.051
Abstract: In this paper we present a novel extended Krylov subspace reduced-order modeling technique to efficiently simulate time- and frequency-domain wavefields in open complex structures. To simulate the extension to infinity, we use an optimal complex-scaling method which is equivalent to an optimized perfectly matched layer in which the frequency is fixed. Wavefields propagating in strongly inhomogeneous open domains can now be modeled as a non-entire function of the complex-scaled wave operator. Since this function contains a square root singularity, we apply an extended Krylov subspace technique to construct fast converging reduced-order models. Specifically, we use a modified version of the extended Krylov subspace algorithm as proposed by Jagels and Reichel [Linear Algebra Appl., Vol. 434, pp. 1716 - 1732, 2011], since this algorithm allows us to balance the computational costs associated with computing powers of the wave operator and its inverse. Numerical experiments from electromagnetics and acoustics illustrate the performance of the method.
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