652 research outputs found
Kinematic study of planetary nebulae in NGC 6822
By measuring precise radial velocities of planetary nebulae (which belong to
the intermediate age population), H II regions, and A-type supergiant stars
(which are members of the young population) in NGC 6822, we aim to determine if
both types of population share the kinematics of the disk of H I found in this
galaxy.
Spectroscopic data for four planetary nebulae were obtained with the high
spectral resolution spectrograph Magellan Inamori Kyocera Echelle (MIKE) on the
Magellan telescope at Las Campanas Observatory. Data for other three PNe and
one H II region were obtained from the SPM Catalog of Extragalactic Planetary
Nebulae which employed the Manchester Echelle Spectrometer attached to the 2.1m
telescope at the Observatorio Astron\'omico Nacional, M\'exico. In the
wavelength calibrated spectra, the heliocentric radial velocities were measured
with a precision better than 5-6 km s. Data for three additional H II
regions and a couple of A-type supergiant stars were collected from the
literature. The heliocentric radial velocities of the different objects were
compared to the velocities of the H i disk at the same position.
From the analysis of radial velocities it is found that H II regions and
A-type supergiants do share the kinematics of the H I disk at the same
position, as expected for these young objects. On the contrary, planetary
nebula velocities differ significantly from that of the H I at the same
position. The kinematics of planetary nebulae is independent from the young
population kinematics and it is closer to the behavior shown by carbon stars,
which are intermediate-age members of the stellar spheroid existing in this
galaxy. Our results are confirming that there are at least two very different
kinematical systems in NGC 6822
Atherosclerotic Plaque Segmentation Based on Strain Gradients: A Theoretical Framework
Background: Atherosclerotic plaque detection is a clinical and technological problem that has been approached by different studies. Nowadays, intravascular ultrasound (IVUS) is the standard used to capture images of the coronary walls and to detect plaques. However, IVUS images are difficult to segment, which complicates obtaining geometric measurements of the plaque. Objective: IVUS, in combination with new techniques, allows estimation of strains in the coronary section. In this study, we have proposed the use of estimated strains to develop a methodology for plaque segmentation. Methods: The process is based on the representation of strain gradients and the combination of the Watershed and Gradient Vector Flow algorithms. Since it is a theoretical framework, the methodology was tested with idealized and real IVUS geometries. Results: We achieved measurements of the lipid area and fibrous cap thickness, which are essential clinical information, with promising results. The success of the segmentation depends on the plaque geometry and the strain gradient variable (SGV) that was selected. However, there are some SGV combinations that yield good results regardless of plaque geometry such as ▽εvMises+▽εrθ, ▽εyy+▽εrr or ▽εmin+▽εTresca. These combinations of SGVs achieve good segmentations, with an accuracy between 97.10% and 94.39% in the best pairs. Conclusions: The new methodology provides fast segmentation from different strain variables, without an optimization step
On Iterated Twisted Tensor Products of Algebras
We introduce and study the definition, main properties and applications of
iterated twisted tensor products of algebras, motivated by the problem of
defining a suitable representative for the product of spaces in noncommutative
geometry. We find conditions for constructing an iterated product of three
factors, and prove that they are enough for building an iterated product of any
number of factors. As an example of the geometrical aspects of our
construction, we show how to construct differential forms and involutions on
iterated products starting from the corresponding structures on the factors,
and give some examples of algebras that can be described within our theory. We
prove a certain result (called ``invariance under twisting'') for a twisted
tensor product of two algebras, stating that the twisted tensor product does
not change when we apply certain kind of deformation. Under certain conditions,
this invariance can be iterated, containing as particular cases a number of
independent and previously unrelated results from Hopf algebra theory.Comment: 44 pages, 21 figures. More minor typos corrections, one more example
and some references adde
Un modelo de potencialidad climática para la trufa negra (Tuber melanosporum) en Teruel (España)
Black truffle (Tuber melanosporum) is an edible ectomycorrhizal mushroom whose cultivation is an economically-viable alternative in rural areas affected by depopulation. In the province of Teruel (Spain), truffle plantations occupy nowadays more than 4,500 ha, but no land use planning guidelines have been available. Species distribution models are tools that allow managers, farmers and foresters to plan ahead and make decisions with a scientific basis. The territory climatically suitable for T. melanosporum in Teruel has been predicted using a method based on the ecology field theory, previously tested in the development of distribution models for forest species. A dataset of 924 locations where black truffle has been collected in the Catalano-Aragonesa ecoregion and eight climatic parameters deeply influencing the presence and fructification of the black truffle have been considered and their corresponding habitats have been built. The distribution model, corrected under lithological criteria, has identified more than 8,000 km² as suitable for black truffle fructification in Teruel, almost 55% of the province, belonging 3,000 of them to the optimal class. This land is mainly distributed over the regions of Gúdar-Javalambre, Comunidad de Teruel and Maestrazgo. A further correction based on land-use criteria has identified more than 4,000 km² as suitable for truffle plantations, being 1,150 of them optimal. The model here presented will help to a proper planning for truffle cultivation in the province of Teruel.La trufa negra (Tuber melanosporum) es un hongo ectomicorrícico comestible cuyo cultivo supone en la actualidad una alternativa económica viable para zonas rurales afectadas gravemente por la despoblación. En la provincia de Teruel (España) hay más de 4.500 ha de plantaciones truferas, instaladas sin ningún proceso de planificación orientado a alcanzar un territorio rural ordenado. Los modelos territoriales de potencialidad o aptitud para las especies son herramientas que permiten a los gestores, agricultores y selvicultores desarrollar dicha planificación y tomar decisiones fundamentadas en un conocimiento científico lo más riguroso posible.
Utilizando un método basado en la teoría de campos aplicada a la ecología, habitual para elaborar las áreas potenciales de especies forestales vegetales, se ha determinado el territorio climáticamente apto para T. melanosporum en la provincia Teruel. Para construir este modelo se han utilizado 924 localizaciones de la ecorregión Catalano-Aragonesa. Elaborando ocho parámetros climáticos trascendentes para la fructificación de la trufa negra, se han construido sus correspondientes hábitats.
El modelo de potencialidad climática elaborado, completado con una corrección litológica, ha permitido identificar algo más de 8.000 km2 como aptos para la recolección de la trufa negra en Teruel, casi el 55% de la provincia, de los cuales 3.000 corresponden a la clase óptima y están distribuidos por las comarcas de Gúdar-Javalambre, Comunidad de Teruel y Maestrazgo. La adaptación del modelo ha permitido identificar más de 4.000 km2 como aptos para la instalación de plantaciones truferas, 1.150 de los cuales tienen potencialidad óptima.
El modelo generado en el presente trabajo permitirá la adecuada planificación territorial de la truficultura en la provincia de Teruel
Parathyroid hormone-related protein as a renal regulating factor: From Vessels to Glomeruli and Tubular Epithelium
Parathyroid hormone (PTH) and PTH-related protein (PTHrP) produce similar biological effects through the PTH/PTHrP receptor. Less is known about the physiological role of PTHrP, which was first identified as the agent of the humoral hypercalcemia of malignancy. Despite the widespread production of PTHrP in healthy individuals, the concentration of the protein is below the detectable limit of current assays, suggesting that PTHrP normally functions locally in an autocrine or paracrine manner. Thus, some differences in their biological activities have been described and they may be related to the presence of different receptors. In this regard, a second receptor that binds selectively to PTH has also been found. Recent studies have demonstrated the expression of both PTH/PTHrP receptor and protein in the renal glomeruli. Moreover, there are convincing data that support a direct role of PTH and PTHrP in modulating renal blood flow and glomerular filtration rate. This multifunctional protein, PSHrP, also has a proliferative effect on both glomerular mesangial cells and tubular epithelial cells. Increases in the expression of PTHrP have been observed in several experimental models of nephropathies, suggesting that PTHrP upregulation is a common event associated with the mechanism of renal injury and repair
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