1,937 research outputs found
Pattern formation in a predator-prey system characterized by a spatial scale of interaction
We describe pattern formation in ecological systems using a version of the
classical Lotka-Volterra model characterized by a spatial scale which controls
the predator-prey interaction range. Analytical and simulational results show
that patterns can emerge in some regions of the parameters space where the
instability is driven by the range of the interaction. The individual-based
implementation captures realistic ecological features. In fact, spatial
structures emerge in an erratic oscillatory regime which can contemplate
predators' extinction.Comment: 5 pages, 4 figure
Antiferromagnetism in four dimensions: search for non-triviality
We present antiferromagnetism as a mechanism capable of modifying
substantially the phase diagram and the critical behaviour of statistical
mechanical models. This is particularly relevant in four dimensions, due to the
connection between second order transition points and the continuum limit as a
quantum field theory. We study three models with an antiferromagnetic
interaction: the Ising and the O(4) Models with a second neighbour negative
coupling, and the \RP{2} Model. Different conclusions are obtained depending
on the model.Comment: 4 pages LateX. Contribution to Lat9
Global characterization and target identification of piRNAs and endo-siRNAs in mouse gametes and zygotes
44 p.-1 tab.-10 fig.A set of small RNAs known as rasRNAs (repeat-associated small RNAs) have been related to the down-regulation of Transposable Elements (TEs) to safeguard genome integrity. Two key members of the rasRNAs group are piRNAs and endo-siRNAs. We have performed a comparative analysis of piRNAs and endo-siRNAs present in mouse oocytes, spermatozoa and zygotes, identified by deep sequencing and bioinformatic analysis. The detection of piRNAs and endo-siRNAs in the spermatozoa and revealed also in zygotes, hints to their potential delivery to oocytes during fertilization. However, a comparative assessment of the three cell types indicates that both piRNAs and endo-siRNAs are mainly maternally inherited. Finally, we have assessed the role of the different rasRNA molecules in connection with amplification processes by way of the "ping-pong cycle". Our results suggest that the ping-pong cycle can act on other rasRNAs, such as tRNA- and rRNA-derived fragments, thus not only being restricted to TEs during gametogenesis. © 2014 Elsevier B.V.This work was funded by grants from The European Chemical Industry Council Long-range Research Initiative (CEFIC-LRi), from the MEDDTL (11-MRESPNRPE-9-CVS-072), France, from the CSIC (PIE 201020E016), Spain.Peer reviewe
Experimental set-up for exciting and detecting magneto-optical effects and surface plasmon resonance simultaneously
We present here an experimental set-up system to excite and measure simultaneously surface plasmon resonance (SPR) and magneto-optic signal in hybrid magneto-plasmonic systems using two independent light sources. The system can be used to excite and measure both types of SPR, localized surface plasmons in nanostructures and surface plasmon polaritons in thin films. It also allows measuring SPR in presence of magnetic fields and recording magnetooptical hysteresis loops while exciting SPR
Vulnerability and resilience of high-mountain pine forests of the Gredos range (Ávila, Spanish Central System): two thousand years of socio-ecological dynamics
RESUMEN: En este trabajo se presenta el análisis palinológico de la turbera de Pozo de la Nieve, localizada en el Parque Natural del Valle de Iruelas (Ávila), un área de alto valor sociocultural dentro de la Sierra de Gredos (Sistema Central). Con el objetivo de relacionar los cambios en el paisaje con la explotación de los recursos naturales y eventos climáticos, en primer lugar se han realizado 7 dataciones radiocarbónicas que sitúan el inicio del registro sedimentario ca. 240 cal BC. Los datos polínicos indican la existencia de un denso pinar altimontano dominado por Pinus sylvestris/nigra desde la Segunda Edad de Hierro hasta el periodo islámico. A partir del periodo cristiano las actividades antrópicas se intensifican, especialmente la ganadería en la Edad Contemporánea, lo cual conlleva la progresiva desaparición del pinar de alta montaña y el desarrollo de pastizales mediante el manejo del fuego, situación que culmina con el desarrollo del paisaje actual dominado por piornales pirófilos.ABSTRACT: We present the palynological study of Pozo de la Nieve peat bog, located in a very valuable socio-cultural placement within the Iruelas Valley Natural Park (Gredos range, Iberian Central System). We have focused in relating landscape changes to natural resources management and climatic events. Firstly, we carried out seven radiocarbon dates suggesting the origin of this record ca. 240 cal BC. The palynological data show the existence of dense high-mountain pine woodlands dominated by Pinus sylvestris/nigra from the Late Iron Age to the Muslim period. Later, from the Christian period, anthropogenic activities have intensified, especially livestock grazing in the Contemporary Age. Its consequences are the progressive disappearance of highmountain pine forests and the extension of grasslands by means of fire, which has shaped current landscape dominated by broom communities.Este trabajo ha sido financiado por el proyecto
Desirè-HAR2013-43701-P (Plan Nacional
I+D+I, Ministerio de Economía y Competitividad
de España). Sebastián Pérez Díaz está
financiado por el Programa Estatal de Promoción
del Talento y su Empleabilidad en I+D+i
en la modalidad Juan de la Cierva-Incorporación.
Mónica Ruiz Alonso está financiada por
el Programa Estatal de Promoción del Talento
y su Empleabilidad en I+D+i en la modalidad
Juan de la Cierva-Formación
Intermediate Old Star Clusters in a Young Starburst: The case of NGC 5253
We investigate the star cluster population in the outer parts of the
starburst galaxy NGC 5253 using archive images taken with the Hubble Space
Telescope's Advanced Camera for Surveys. Based on the F415W, F555W, and F814W
photometry ages and masses are estimated for bona-fide star cluster candidates.
We find three potentially massive (\ge 10 \time 10^5 \Msun) star clusters at
ages of order of 1-2 Gyr, implying, if confirmed, a high global star formation
rate in NGC 5253 during that epoch. This result underlines earlier findings
that the current star burst is just one episode in an very active dwarf galaxy.Comment: accepted for publication in MNRAS - The definitive version is (will
be) available at www.blackwell-synergy.co
Phase diagram of d=4 Ising Model with two couplings
We study the phase diagram of the four dimensional Ising model with first and
second neighbour couplings, specially in the antiferromagnetic region, by using
Mean Field and Monte Carlo methods. From the later, all the transition lines
seem to be first order except that between ferromagnetic and disordered phases
in a region including the first-neighbour Ising transition point.Comment: Latex file and 4 figures (epsfig required). It replaces the preprint
entitled "Non-classical exponents in the d=4 Ising Model with two couplings".
New analysis with more statistical data is performed. Final version to appear
in Phys. Lett.
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