A Selection Criterion for Patterns in Reaction-Diffusion Systems

Alan Turing's work in Morphogenesis has received wide attention during the past 60 years. The central idea behind his theory is that two chemically interacting diffusible substances are able to generate stable spatial patterns, provided certain conditions are met. Turing's proposal has already been confirmed as a pattern formation mechanism in several chemical and biological systems and, due to their wide applicability, there is a great deal of interest in deciphering how to generate specific patterns under controlled conditions. However, techniques allowing one to predict what kind of spatial structure will emerge from Turing systems, as well as generalized reaction-diffusion systems, remain unknown. Here, we consider a generalized reaction diffusion system on a planar domain and provide an analytic criterion to determine whether spots or stripes will be formed. It is motivated by the existence of an associated energy function that allows bringing in the intuition provided by phase transitions phenomena. This criterion is proved rigorously in some situations, generalizing well known results for the scalar equation where the pattern selection process can be understood in terms of a potential. In more complex settings it is investigated numerically. Our criterion can be applied to efficiently design Biotechnology and Developmental Biology experiments, or simplify the analysis of hypothesized morphogenetic models.Comment: 19 pages, 10 figure

Equivariant intersection cohomology of the circle actions

In this paper, we prove that the orbit space B and the Euler class of an action of the circle S^1 on X determine both the equivariant intersection cohomology of the pseudomanifold X and its localization. We also construct a spectral sequence converging to the equivariant intersection cohomology of X whose third term is described in terms of the intersection cohomology of B.Comment: Final version as accepted in RACSAM. The final publication is available at springerlink.com; Revista de la Real Academia de Ciencias Exactas, Fisicas y Naturales. Serie A. Matematicas, 201

An approach to the multidimensional assessment of food security and environmental sustainability: a vulnerability framework for the Mediterranean region

Poster presented at First International Conference on Global Food Security. Noordwijkerhout (The Netherlands), 29 Sep - 2 Oct 201

Multidimensional assessment of food security and environmental sustainability: a vulnerability framework for the Mediterranean Region [Poster]

Poster presented at Tropentag 2013. International Research on Food Security, Natural Resource Management and Rural Development. "Agricultural development within the rural-urban continuum". Stuttgart-Hohenheim (Germany), Sep 17-19 2013

An approach to the multidimensional assessment of food security and environmental sustainability: a vulnerability framework for the Mediterranean region

Poster presented at First International Conference on Global Food Security. Noordwijkerhout (The Netherlands), 29 Sep - 2 Oct 201

Portuguese migrations to South America after world war II: Extending citizenship abroad

info:eu-repo/semantics/publishedVersio

South–South student mobility: International students from Portuguese-speaking Africa in Brazil

As a complex and multi-faceted phenomenon, student mobility involves diverse actors, interests and rationalities. With the globalization of education, universities and other higher education providers have implemented strategies to recruit and attract international students, not least to increase their revenues and levels of internationalization (Findlay et al. 2017). Likewise, destination countries have acknowledged the advantages of hosting international students: financial benefits, an increase in the skilled worker pool and improvements in diplomatic relations (Riaño et al. 2018). Origin countries meanwhile identify student mobility as a means through which talented individuals can become qualified via moving to countries with well-developed higher education system (Findlay 2010). And students themselves, and their families, recognize the potential impact of an international diploma on employability, making them instrumental in establishing educational mobility imperatives at tertiary level (Alberts and Hazen 2005; Holloway et al. 2012).info:eu-repo/semantics/acceptedVersio

The very faint hard state of the persistent neutron star X-ray binary SLX 1737-282 near the Galactic centre

We report on a detailed study of the spectral and temporal properties of the neutron star low mass X-ray binary SLX 1737-282, which is located only ~1degr away from Sgr A. The system is expected to have a short orbital period, even within the ultra-compact regime, given its persistent nature at low X-ray luminosities and the long duration thermonuclear burst that it has displayed. We have analysed a Suzaku (18 ks) observation and an XMM-Newton (39 ks) observation taken 7 years apart. We infer (0.5-10 keV) X-ray luminosities in the range 3-6 x10^35erg s-1, in agreement with previous findings. The spectra are well described by a relatively cool (kTbb = 0.5 keV) black body component plus a Comptonized emission component with {\Gamma} ~1.5-1.7. These values are consistent with the source being in a faint hard state, as confirmed by the ~ 20 per cent fractional root mean square amplitude of the fast variability (0.1 - 7 Hz) inferred from the XMM-Newton data. The electron temperature of the corona is >7 keV for the Suzaku observation, but it is measured to be as low as ~2 keV in the XMM-Newton data at higher flux. The latter is significantly lower than expected for systems in the hard state. We searched for X-ray pulsations and imposed an upper limit to their semi-amplitude of 2 per cent (0.001 - 7 Hz). Finally, we investigated the origin of the low frequency variability emission present in the XMM-Newton data and ruled out an absorption dip origin. This constraint the orbital inclination of the system to 65 degr unless the orbital period is longer than 11 hr (i.e. the length of the XMM-Newton observation).Comment: 7 pages, 4 figures, 1 table. Accepted for publication in MNRA

TeV Burst of Gamma-Ray Bursts and Ultra High Energy Cosmic Rays

Some recent experiments detecting very high energy (VHE) gamma-rays above 10-20 TeV independently reported VHE bursts for some of bright gamma-ray bursts (GRBs). If these signals are truly from GRBs, these GRBs must emit a much larger amount of energy as VHE gamma-rays than in the ordinary photon energy range of GRBs (keV-MeV). We show that such extreme phenomena can be reasonably explained by synchrotron radiation of protons accelerated to \sim 10^{20-21} eV, which has been predicted by Totani (1998a). Protons seem to carry about (m_p/m_e) times larger energy than electrons, and hence the total energy liberated by one GRB becomes as large as \sim 10^{56} (\Delta \Omega / 4 \pi) ergs. Therefore a strong beaming of GRB emission is highly likely. Extension of the VHE spectrum beyond 20 TeV gives a nearly model-independent lower limit of the Lorentz factor of GRBs, as \gamma \gtilde 500. Furthermore, our model gives the correct energy range and time variability of ordinary keV-MeV gamma-rays of GRBs by synchrotron radiation of electrons. Therefore the VHE bursts of GRBs strongly support the hypothesis that ultra high energy cosmic rays observed on the Earth are produced by GRBs.Comment: Final version to appear in ApJ Lett. Emphasizing that the extremely large energy required in this model is not theoretically impossible if GRB emission is strongly beamed. References update

Cross-linguistic generalization in treatment of bilingual aphasia

For individuals who speak more than one language, aphasia following left-hemisphere stroke or focal brain injury impacts all of their languages to varying degrees. At this time, there is limited research regarding the most effective form of treatment for bilingual aphasia, specifically whether to target one or all languages. Some research has suggested that treating individuals with bilingual aphasia in their non-dominant language (L2) yields positive results in their dominant language (L1) (e.g., Edmonds & Kiran, 2006; Kiran & Roberts, 2010; Kohnert, 2004; Langanaro & Overton Venet, 2001; Marangolo et al., 2009). These findings derive from the mixed model of bilingual language distribution (de Groot, 1992) and the Complexity Account of Treatment Efficacy (CATE; Thompson et al., 2003). Per de Groot’s model, there is one semantic system with separate lexicons for each language, and the lexicons have direct access both to the semantic system and one another. The strength of the connection between each lexicon and the semantic system, and between the lexicons themselves, depends upon the individual’s proficiency level in each language. Thus, an individual more proficient in Spanish than English would have a weaker link between his/her English lexicon and the semantic system but a stronger link from the English to the Spanish lexicon. The act of speaking English could, therefore, be considered a more complex process than speaking Spanish, as the individual would rely more heavily on the link from the English to the Spanish lexicon to access the semantic system. According to CATE (Thompson, et al., 2003), training an individual on more complex tasks will yield generalization to less complex, related tasks; therefore training this individual in English (more complex process) should yield generalization to Spanish (less complex process). Edmonds and Kiran (2006) found that treating English-dominant English/Spanish bilinguals in Spanish had positive effects on their English, and that treating an equally proficient Spanish/English bilingual in Spanish had positive effects in both languages. To our knowledge, no studies have specifically examined whether it is effective to treat bilingual individuals whose non-dominant language is English in English only. Considering that fewer than 6% of AHSA-certified SLPs speak a language other than English (ASHA, 2010) while the fastest growing U.S. subgroup is comprised of elderly Hispanic individuals (ASHA, 1991), it is reasonable to assume that monolingual SLPs will increasingly be called upon to treat bilingual individuals with aphasia. The purpose of this study was to determine whether treating Spanish/English bilinguals, whose non-dominant language is English, in English would improve both of their languages