De retibus socialibus et legibus momenti

Online Social Networks (OSNs) are a cutting edge topic. Almost everybody --users, marketers, brands, companies, and researchers-- is approaching OSNs to better understand them and take advantage of their benefits. Maybe one of the key concepts underlying OSNs is that of influence which is highly related, although not entirely identical, to those of popularity and centrality. Influence is, according to Merriam-Webster, "the capacity of causing an effect in indirect or intangible ways". Hence, in the context of OSNs, it has been proposed to analyze the clicks received by promoted URLs in order to check for any positive correlation between the number of visits and different "influence" scores. Such an evaluation methodology is used in this paper to compare a number of those techniques with a new method firstly described here. That new method is a simple and rather elegant solution which tackles with influence in OSNs by applying a physical metaphor.Comment: Changes made for third revision: Brief description of the dataset employed added to Introduction. Minor changes to the description of preparation of the bit.ly datasets. Minor changes to the captions of Tables 1 and 3. Brief addition in the Conclusions section (future line of work added). Added references 16 and 18. Some typos and grammar polishe

Técnicas SIG aplicadas al estudio del relieve de los Montes de León (NO de la Península Ibérica)

En este trabajo se presenta un método basado en el análisis de modelos digitales de elevación (MDE) a través de SIG, encaminado a realizar una cartografía preliminar de antiguas superficies de aplanamiento en los relieves que bordean la cuenca del Bierzo (oeste de la provincia de León, noroeste de la Península Ibérica). El área de estudio es un complejo sistema escalonado de niveles de aplanamiento elaborados sobre el basamento del Macizo Ibérico, constituyente de los relieves montañosos de la zona, deformado por la Orogenia Alpina durante el Cenozoico, en donde las superficies se encuentran elevadas, basculadas, fragmentadas y muy degradadas. Partiendo del MDE con paso de malla de 25 m del PNOA se realizó una caracterización general de la zona de estudio mediante la obtención de mapas derivados: pendientes, orientaciones de pendiente y sombreado, así como de la red de drenaje. Empleando la extensión EZ Profile para ArcGIS 9.3 se generaron 213 perfiles topográficos, sobre los principales cordales e interfluvios, con los que se localizaron y correlacionaron los elementos culminantes (indicios y restos de superficies de aplanamiento) presentes en toda la zona de estudio, lo que permitió reconstruir el relieve previo al desmantelamiento por parte de la red de drenaje. Una vez delimitadas las superficies de aplanamiento se procedió a su caracterización, agrupación y jerarquización, mediante el estudio de superficies de tendencia, el análisis de la red de drenaje y la relación con la actividad tectónica. Se realizó una reconstrucción teórica de cada uno de los aplanamientos a través de la interpolación de los puntos pertenecientes al antiguo relieve, generando así una superficie de tendencia de primer orden, de donde se obtuvo la orientación y pendiente de cada una de ellas. A su vez, se buscaron anomalías en los cauces de los ríos que atraviesan los aplanamientos, que pudieran indicar actividad tectónica reciente. Asimismo, se llevó a cabo un estudio de las cuencas de drenaje, sobre las que se realizaron cálculos de hipsometría y de asimetría (Factor de Asimetría). Por último, se calculó la incisión del drenaje sobre las superficies de aplanamiento cartografiadas. Como resultado se obtuvieron veinte superficies clasificadas en ocho niveles, desde los 1000m a los 2100m, en donde se observa cómo los distintos elementos de un mismo nivel se encuentran en extremos opuestos de la zona de estudio, ubicados en forma de orla perdiendo altura hacia la cuenca del Bierzo.Trabajo financiado por el proyecto de la Junta de Castilla y León LE311A12-2 y por el proyecto Consolider Ingenio 2006 CSD-2006, TopoIberia Geociencias en Iberia

Ultrathin carbon nanotube with single, double, and triple bonds

A metastable carbon nanotube with single, double, and triple bonds has been predicted from abinitio simulation. It results from the relaxation of an ideal carbon nanotube with chirality (2,1), without any potential barrier between the ideal nanotube and the new structure. Ten-membered carbon rings are formed by breaking carbon bonds between adjacent hexagons; eight-membered rings, already present in the ideal structure, become the smallest rings. This structure is stable in molecular dynamics simulations at temperatures up to 1000K. Raman, infrared, and optical absorption spectra are simulated to allow its identification in the laboratory. The structure can be described as a double helical chain with alternating single, double, and triple bonds, where the chains are bridged by single bondsThis work was supported by Grants No. SB2010-0119 (MEC), No. CTQ2010-19232 (MICIN), and No. A1/035856/11 (AECID

Accuracy of CT-based attenuation correction in bone imaging with PET/CT

Proceeding of: 2007 IEEE Nuclear Science Symposium Conference Record (NSS'07), Honolulu, Hawaii, USA, Oct. 27 - Nov. 3, 2007PET/CT has become the most comprehensive diagnostic tool in oncology imaging providing improved lesion identification and localization. Bone is a common site of metastasis and the quantitative accuracy of PET images in bone tissue is important for assessing response to therapy. The use of CT images for attenuation correction is becoming a standard procedure in these scanners. However the impact of CT-based attenuation correction (CTAC) on the accuracy of PET tracer uptake values measured in bone has not been carefully evaluated, having only been carefully studied in soft tissue. We investigated the accuracy of CTAC on PET bone images by comparing the attenuation coefficients with PET transmission scans. For this, we imaged frozen bovine femur segments in a 20x20 cm cylindrical phantom. Different regions of the bones in both images were segmented by using thresholding and erosion methods to get equivalent volume masks. Differences in linear attenuation coefficients between the two images were then calculated. We repeated this analysis using patient images from the same patient imaged on the GE Advance PET scanner and the GE Discovery STE PET/CT scanner. The impact of the errors in the linear attenuation coefficients on PET SUV measurements was evaluated by simulations using the patent images with known bone disease and elevated levels of FDG uptake in bone (e.g. SUV = 5) at disease sites. The impact of the errors in the linear attenuation coefficients was then estimated by forward projection and reconstruction, after including the effects of attenuation and attenuation correction.This work was supported in kart by Agencia Antidroga de la Comunidad de Madrid (S-SAL2007), Ministerio de Sanidad y Consumo (CIBER CB06/01/0079), and Ministerio de Industria (Programa CENIT). It was also supported in part by NIH grants R01- CA124573 and R01-CA115870

Adult cocaine-induced brain metabolic activation is altered in a sex-dependent manner by chronic periadolescent cannabinoid exposure in rats

[Poster] 4th European Molecular Imaging Meeting, Barcelona, Spain, May 27 - 30, 2009Cannabinoid exposure during the periadolescent period has been shown to augment the rates of cocaine self-administration in female but not male Wistar rats. However, how this cannabinoid history alters cocaine-induced brain activation remains unknownPublicad

Transporte y destino de residuos sólidos flotantes en la desembocadura del río matanza-riachuelo

La presencia de residuos sólidos flotantes (RSF) en ríos y arroyos urbanos impacta sobre los distintos usos, capacidades hidráulicas, calidad del agua y condiciones estéticas. En la Cuenca Matanza-Riachuelo (CMR), el transporte y destino de RSF puede perjudicar el normal funcionamiento de obras de infraestructura y elementos de observación y control ubicados en cercanías de la desembocadura en el Río de la Plata. En esta zona se encuentra implementado un sistema de limpieza de espejo de agua basado en la ubicación estratégica de barreras de retención. Ante la ocurrencia de precipitaciones significativas, estas barreras pueden colapsar permitiendo movilizar clusters de RSF cuyo destino puede resultar perjudicial. La hidrodinámica en esta zona está asociada a las condiciones hidrológicas de la CMR y a la dinámica del Río de la Plata. Para estudiarla en detalle se utilizó la combinación de dos modelos numéricos: 1) un modelo hidrológico-hidráulico de la CMR; 2) un modelo hidrodinámico del Río de la Plata Interior. Se presentan en este trabajo los resultados referidos a la evaluación de tiempos de concentración de la cuenca y los caminos de los RSF siguiendo partículas a partir de ensayos de rotura instantánea de barreras de retención.Fil: Mariano Re. Laboratorio de Hidráulica, Instituto Nacional del Agua (INA), Buenos Aires, Argentina.Fil: Pablo E. García. Laboratorio de Hidráulica, Instituto Nacional del Agua (INA), Buenos Aires, Argentina.Fil: Emilio Lecertua. Laboratorio de Hidráulica, Instituto Nacional del Agua (INA), Buenos Aires, Argentina.Fil: Ángel N. Menéndez. Laboratorio de Hidráulica, Instituto Nacional del Agua (INA), Buenos Aires, Argentina

Postnatal administration of allopregnanolone modifies glutamate release but Not BDNF content in striatum samples of rats prenatally exposed to ethanol

Ethanol consumption during pregnancy may induce profound changes in fetal CNS development. We postulate that some of the effects of ethanol on striatal glutamatergic transmission and neurotrophin expression could be modulated by allopregnanolone, a neurosteroid modulator of GABA A receptor activity. We describe the acute pharmacological effect of allopregnanolone (65 μg/kg, s.c.) administered to juvenile male rats (day 21 of age) on the corticostriatal glutamatergic pathway, in both control and prenatally ethanol-exposed rats (two ip injections of 2.9 g/kg in 24% v/v saline solution on gestational day 8). Prenatal ethanol administration decreased the K+-induced release of glutamate regarding the control group. Interestingly, this effect was reverted by allopregnanolone. Regarding BDNF, allopregnanolone decreases the content of this neurotrophic factor in the striatum of control groups. However, both ethanol alone and ethanol plus allopregnanolone treated animals did not show any change regarding control values. We suggest that prenatal ethanol exposure may produce an alteration of GABA A receptors which blocks the GABA agonist-like effect of allopregnanolone on rapid glutamate release, thus disturbing normal neural transmission. Furthermore, the reciprocal interactions found between GABAergic neurosteroids and BDNF could underlie mechanisms operating during the neuronal plasticity of fetal development.Fil: Yunes, Roberto Miguel Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto de Medicina y Biología Experimental de Cuyo; Argentina. Universidad Nacional de Cuyo. Facultad de Ciencias Medicas; ArgentinaFil: Estrella, Cecilia R.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto de Medicina y Biología Experimental de Cuyo; ArgentinaFil: García Menéndez, Sebastián Marcelo Manuel. Universidad Nacional de Cuyo. Facultad de Ciencias Medicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto de Medicina y Biología Experimental de Cuyo; ArgentinaFil: Lara, Hernán E.. Universidad de Chile; ChileFil: Cabrera Kreiker, Ricardo Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto de Medicina y Biología Experimental de Cuyo; Argentin

The imprint of global climate cycles in the Fuentillejo maar-lake record during the last 50 ka cal BP (central Spain)

We have analysed the geochemical (element analysis), mineralogical and sedimentary facies to characterize the sedimentary record in Fuentillejo maar-lake in the central Spanish volcanic field of Campo de Calatrava and thus be able to reconstruct the cyclicity of the sedimentary and paleoclimatic processes involved. The upper 20 m of core FUENT-1 show variations in clastic input and water chemistry in the lake throughout the last 50 ka cal BP. Being a closed system, the water level in this maar-lake depends primarily on the balance between precipitation and evaporatio

Detection of a putative TetR-like gene related to Mycobacterium bovis BCG growth in cholesterol using a gfp-transposon mutagenesis system

In vitro transposition is a powerful genetic tool for identifying mycobacterial virulence genes and studying virulence factors in relation to the host. Transposon shuttle mutagenesis is a method for constructing stable insertions in the genome of different microorganisms including mycobacteria. Using an IS1096 derivative, we have constructed the Tngfp, a transposon containing a promoterless green fluorescent protein (gfp) gene. This transposon was able to transpose randomly in Mycobacterium bovis BCG. Bacteria with a single copy of the gfp gene per chromosome from an M. bovis BCG::Tngfp library were analyzed and cells exhibiting high levels of fluorescence were detected by flow cytometry. Application of this approach allowed for the selection of a mutant, BCG_2177c::Tngfp (BCG-Tn), on the basis of high level of long-standing fluorescence at stationary phase. This BCG-Tn mutant showed some particular phenotypic features compared to the wild type strain, mainly during stationary phase, when cholesterol was used as a sole carbon source, thus supporting the relationships of the targeted gene with the regulation of cholesterol metabolism in this bacteria. This approach showed that Tngfp is a potentially useful tool for studying the involvement of the targeted loci in metabolic pathways of mycobacteria