Automated detection of block falls in the north polar region of Mars

We developed a change detection method for the identification of ice block falls using NASA's HiRISE images of the north polar scarps on Mars. Our method is based on a Support Vector Machine (SVM), trained using Histograms of Oriented Gradients (HOG), and on blob detection. The SVM detects potential new blocks between a set of images; the blob detection, then, confirms the identification of a block inside the area indicated by the SVM and derives the shape of the block. The results from the automatic analysis were compared with block statistics from visual inspection. We tested our method in 6 areas consisting of 1000x1000 pixels, where several hundreds of blocks were identified. The results for the given test areas produced a true positive rate of ~75% for blocks with sizes larger than 0.7 m (i.e., approx. 3 times the available ground pixel size) and a false discovery rate of ~8.5%. Using blob detection we also recover the size of each block within 3 pixels of their actual size

Body size in Drosophila: Genetic architecture, allometries and sexual dimorphism

Even though substantial progress has been made to elucidate the physiological and environmental factors underpinning differences in body size, little is known about its genetic architecture. Furthermore, all animal species bear a specific relationship between the size of each organ and overall body size, so different body size traits should be investigated as well as their sexual dimorphism that may have an important impact on the evolution of body size. We have surveyed 191 co-isogenic lines of Drosophila melanogaster, each one of them homozygous for a single P-element insertion, and assessed the effects of mutations on different body size traits compared to the P-element-free co-isogenic control. Nearly 60% of the lines showed significant differences with respect to the control for these traits in one or both sexes and almost 35% showed trait- and sex-specific effects. Candidate gene mutations frequently increased body size in males and decreased it in females. Among the 92 genes identified, most are involved in development and/or metabolic processes and their molecular functions principally include protein-binding and nucleic acid-binding activities. Although several genes showed pleiotropic effects in relation to body size, few of them were involved in the expression of all traits in one or both sexes. These genes seem to be important for different aspects related to the general functioning of the organism. In general, our results indicate that the genetic architecture of body size traits involves a large fraction of the genome and is largely sex and trait specific. © 2009 Macmillan Publishers Limited All rights reserved.Fil:Carreira, V.P. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Mensch, J. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Fanara, J.J. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Evolution of male genitalia: environmental and genetic factors affect genital morphology in two Drosophila sibling species and their hybrids

<p>Abstract</p> <p>Background</p> <p>The rapid evolution of genital morphology is a fascinating feature that accompanies many speciation events. However, the underlying patterns and explanatory processes remain to be settled. In this work we investigate the patterns of intraspecific variation and interspecific divergence in male genitalic morphology (size and shape) in the cactophilic sibling species <it>Drosophila buzzatii </it>and <it>D. koepferae</it>. Genital morphology in interspecific hybrids was examined and compared to the corresponding parental lines.</p> <p>Results</p> <p>Despite of being siblings, <it>D. buzzatii </it>and <it>D. koepferae </it>showed contrasting patterns of genital morphological variation. Though genitalic size and shape variation have a significant genetic component in both species, shape varied across host cacti only in <it>D. buzzatii</it>. Such plastic expression of genital shape is the first evidence of the effect of rearing substrate on genitalic morphology in <it>Drosophila</it>. Hybrid genital morphology was not intermediate between parental species and the morphological resemblance to parental strains was cross-dependent.</p> <p>Conclusion</p> <p>Our results suggest the evolution of different developmental networks after interspecific divergence and the existence of a complex genetic architecture, involving genetic factors with major effects affecting genital morphology.</p

A Langmuir multi-probe system for the characterization of atmospheric pressure arc plasmas

The 'high-pressure' atmospheric (TIG) arc plasma is studied by means of a multi-Langmuir probe system. In order to determine the appropriate regime of operation, definitions of the plasma parameters for the description of the argon arc are considered and evaluations are presented. A description of the probe basic techniques is followed by an in-depth discussion of the different regimes of probe operation. The emphasis is put on atmospheric and flowing (arc) regimes. Probe sheath theories are compared and “Nonidealities” like cooling due to plasma-probe motion and probe emission mechanisms are then described. The extensive literature review reveals that the existing probe theories are inappropriate for a use in the TIG arc, because of ‘high’ pressure (atmospheric), broad range of ionization across the arc, flowing conditions, and ultimately, to the uncertainty about onset of Local Thermodynamical Equilibrium. The Langmuir probe system is built to operate in floating and biased conditions. The present work represents the first extensive investigation of electrostatic probes in arcs where the experimental difficulties and the primary observed quantities are presented in great detail. Analysis methodologies are introduced and experimental results are presented towards a unified picture of the resulting arc structure by comparison with data from emission spectroscopy. Results from different measurements are presented and comparison is made with data on TIG arcs present in literature. Probe obtained temperatures are lower than the values obtained from emission spectroscopy and this ‘cooling’ is attributed to electron-ion recombination. However, it is believed that probes can access temperatures regions not attainable by emission spectroscopy. Only axial electric potential and electric field are obtained because of the equipotential-probe requirement. Estimations of the sheath voltage and extension are obtained and a qualitative picture of the ion and electron current densities within the arc is given.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Erosion rate of the north polar scarps of Mars based on automated detection of block falls in HiRISE images

We automatically detected ice block falls in high resolution satellite images of the north polar region of Mars, with the aim of understanding their role in erosion processes and the morphological evolution of the region. Our change detection method is based on the combination of Binary Large OBjects (BLOB)detection and machine learning and we aim to extend our investigation to all steep scarps of the margin of the north polar ice cap where suitable high resolution data exist

Geographic Patterns of Inversion Polymorphism in the Second Chromosome of the Cactophilic Drosophila buzzatii from Northeastern Argentina

The inversion polymorphisms of the cactophilic Drosophila buzzatti Patterson and Wheeler (Diptera: Drosophilidae) were studied in new areas of its distribution in Argentina. A total of thirty-eight natural populations, including 29 from previous studies, were analyzed using multiple regression analyses. The results showed that about 23% of total variation was accounted for by a multiple regression model in which only altitude contributed significantly to population variation, despite the fact that latitude and longitude were also included in the model. Also, inversion frequencies exhibited significant associations with mean annual temperature, precipitation, and atmospheric pressure. In addition, expected heterozygosity exhibited a negative association with temperature and precipitation and a positive association with atmospheric pressure. The close similarity of the patterns detected in this larger dataset to previous reports is an indication of the stability of the clines. Also, the concurrence of the clines detected in Argentina with those reported for colonizing populations of Australia suggests the involvement of natural selection as the main mechanism shaping inversion frequencies in D. buzzatii