Automatic X-ray landmark detection and shape segmentation via data-driven joint estimation of image displacements

In this paper, we propose a new method for fully-automatic landmark detection and shape segmentation in X-ray images. To detect landmarks, we estimate the displacements from some randomly sampled image patches to the (unknown) landmark positions, and then we integrate these predictions via a voting scheme. Our key contribution is a new algorithm for estimating these displacements. Different from other methods where each image patch independently predicts its displacement, we jointly estimate the displacements from all patches together in a data driven way, by considering not only the training data but also geometric constraints on the test image. The displacements estimation is formulated as a convex optimization problem that can be solved efficiently. Finally, we use the sparse shape composition model as the a priori information to regularize the landmark positions and thus generate the segmented shape contour. We validate our method on X-ray image datasets of three different anatomical structures: complete femur, proximal femur and pelvis. Experiments show that our method is accurate and robust in landmark detection, and, combined with the shape model, gives a better or comparable performance in shape segmentation compared to state-of-the art methods. Finally, a preliminary study using CT data shows the extensibility of our method to 3D data.

Limited Correlation between Expansin Gene Expression and Elongation Growth Rate

The aim of this work was to study the role of the cell wall protein expansin in elongation growth. Expansins increase cell wall extensibility in vitro and are thought to be involved in cell elongation. Here, we studied the regulation of two tomato (Lycopersicon esculentum cv Moneymaker) expansin genes,LeExp2 and LeExp18, in rapidly expanding tissues. LeExp2 was strongly expressed in the elongation zone of hypocotyls and in the faster growing stem part during gravitropic stimulation. LeExp18 expression did not correlate with elongation growth. Exogenous application of hormones showed a substantial auxin-stimulation of LeExp2 mRNA in etiolated hypocotyls and a weaker auxin-stimulation ofLeExp18 mRNA in stem tissue. Analysis of transcript accumulation revealed higher levels of LeExp2 andLeExp18 in light-treated, slow-growing tissue than in dark-treated, rapidly elongating tissue. Expansin protein levels and cell wall extension activities were similar in light- and dark-grown hypocotyl extracts. The results show a strong correlation between expansin gene expression and growth rate, but this correlation is not absolute. We conclude that elongation growth is likely to be controlled by expansin acting in concert with other factors that may limit growth under some physiological conditions.

Localized Upregulation of a New Expansin Gene Predicts the Site of Leaf Formation in the Tomato Meristem

Expansins are extracellular proteins that increase plant cell wall extensibility in vitro and are thought to be involved in cell expansion. We showed in a previous study that administration of an exogenous expansin protein can trigger the initiation of leaflike structures on the shoot apical meristem of tomato. Here, we studied the expression patterns of two tomato expansin genes, LeExp2 and LeExp18. LeExp2 is preferentially expressed in expanding tissues, whereas LeExp18 is expressed preferentially in tissues with meristematic activity. In situ hybridization experiments showed that LeExp18 expression is elevated in a group of cells, called I1, which is the site of incipient leaf primordium initiation. Thus, LeExp18 expression is a molecular marker for leaf initiation, predicting the site of primordium formation at a time before histological changes can be detected. We propose a model for the regulation of phyllotaxis that postulates a crucial role for expansin in leaf primordium initiation.

El concepto de persona en el comentario de las sentencias de Guillermo de Ockham

En un primer examen de las auctoritates Ockham formula un claro acercamiento al esquema aristotélico-boeciano y a la definición de persona como sustancia en cuanto suppositum intellectualis, definición que encuentra conveniente aplicar tanto a lo creado como a Dios. Comienza luego una discusión más próxima y contemporánea con los moderni, que está centrada, por un lado en Escoto para quien la persona se ha de definir a partir de la relación; y por otro, con santo Tomás de Aquino. “Persona", para el Aquinate, no significa una naturaleza común quidditas, ousía o sustancia segunda, por el contrario, indica al individuo: “esta carne y estos huesos" pero lo significa de un modo vago e indeterminado. Precisamente, éste es el punto que Ockham discute: qué denota esta significación indeterminada; le dedica a la cuestión un amplio análisis que lo conduce a equiparar los conceptos de naturaleza y de persona. En un paso subsiguiente Ockham propone examinar las personas in divinis: no es posible establecer in divinis ninguna diferencia o distinción; si se afirma en Dios la presencia de tres personas y de una sola naturaleza la adhesión se presta por la fe sin que medie un acercamiento racional al tema. El aparato conceptual y metafísico para abordar el problema de la persona en sede divina, ha pasado por la criba de un examen que concluye, para Ockham, en la verdadera imposibilidad de elaborar una teología trinitaria.

Ingenieros agrónomos, desarrollo rural y cultura política : reflexiones críticas en torno a la práctica de la (ex)tensión rural

En esta nota breve se analiza, desde una perspectiva crítica, la práctica de la extensión rural realizada por profesionales agrónomos en Mendoza, Argentina. En base a una amplia revisión bibliográfica y análisis documental sobre programas de desarrollo rural, analizamos los condicionamientos socio-culturales de dicha práctica, elementos que inciden sobre la concepción, ejecución y orientación de las estrategias de desarrollo promovidas por estos sujetos y sus instituciones. Así argumentamos que a pesar de los profundos cambios ocurridos en el mundo, particularmente los que afectan al mundo rural, las prácticas de los extensionistas y su concepción, continúan arraigadas a los ya viejos supuestos de la modernización y el progreso indefinido. Asimismo sostenemos que la falta de reflexividad crítica institucional retroalimenta la crisis del desarrollo rural con considerables repercusiones en sus promotores, los extensionistas. Finalmente destacamos que la reflexión sobre la práctica de la extensión rural tiene una relevancia social e institucional central, considerando que un análisis crítico de las limitaciones y posibilidades en este campo puede contribuir a orientar -y superar- los desafíos actuales y futuros.

Seawater carbonate chemistry and physiological and mechanical properties of the starfish Asterias rubens in a laboratory experiment

The increase in atmospheric CO2 due to anthropogenic activity results in an acidification of the surface waters of the oceans. Its impact will depend on the considered organisms and ecosystems. The intertidal may harbor organisms pre-adapted to the upcoming changes as they face tidal pH and temperature fluctuations. However, these environments will be more affected as shallow waters will face the highest decrease in seawater pH. In this context, the effects of reduced environmental pH on the physiology and tube feet mechanical properties of the intertidal starfish Asterias rubens, a top predator, were investigated during 15 and 27 days. A. rubens showed a respiratory acidosis with its coelomic fluid pH always lower than that of seawater. This acidosis was most pronounced at pH 7.4. Notwithstanding, the starfish showed no significant variations in RNA/DNA ratio of different tissues and in tube feet strength. However, respiration rates were significantly lower for individuals maintained at reduced seawater pH. Within the ocean acidification context, the present results suggest that A. rubens withstands the effects of reduced seawater pH, at least for medium term exposures.