1,697 research outputs found
Phantom inflation and the "Big Trip"
Primordial inflation is regarded to be driven by a phantom field which is
here implemented as a scalar field satisfying an equation of state
, with . Being even aggravated by the weird properties
of phantom energy, this will pose a serious problem with the exit from the
inflationary phase. We argue however in favor of the speculation that a smooth
exit from the phantom inflationary phase can still be tentatively recovered by
considering a multiverse scenario where the primordial phantom universe would
travel in time toward a future universe filled with usual radiation, before
reaching the big rip. We call this transition the "big trip" and assume it to
take place with the help of some form of anthropic principle which chooses our
current universe as being the final destination of the time transition.Comment: 23 pages, 5 figures, LaTex, Phys. Lett. B (in press
Emergence and resilience of cooperation in the spatial Prisoner's Dilemma via a reward mechanism
We study the problem of the emergence of cooperation in the spatial
Prisoner's Dilemma. The pioneering work by Nowak and May showed that large
initial populations of cooperators can survive and sustain cooperation in a
square lattice with imitate-the-best evolutionary dynamics. We revisit this
problem in a cost-benefit formulation suitable for a number of biological
applications. We show that if a fixed-amount reward is established for
cooperators to share, a single cooperator can invade a population of defectors
and form structures that are resilient to re-invasion even if the reward
mechanism is turned off. We discuss analytically the case of the invasion by a
single cooperator and present agent-based simulations for small initial
fractions of cooperators. Large cooperation levels, in the sustainability
range, are found. In the conclusions we discuss possible applications of this
model as well as its connections with other mechanisms proposed to promote the
emergence of cooperation
Regeneration of plants from somatic embryos of Verticillium dahliae-resistant wild olive genotypes
Regeneration capacity, via somatic embryogenesis, of several wild olive genotypes differing in their response to Verticillium wilt (resistant genotypes Stop Vert, Out Vert, Ac4 and Ac 18 and the susceptible Ac 15) has been evaluated. To induce somatic embryogenesis, methodologies previously used in cultivated (high ratio cytokinin/auxin) or wild olive (low ratio cytokinin/auxin) were used. Obtained results revealed the importance of genotype, explant type, mineral formulation and hormonal balance in the induction process, ca. use of apical buds obtained from micropropagated shoots following the methodology of Mazri et al. (2013) in cultivated olive (4 days in liquid medium MS Âœ, 30 ”M TDZ â 0.54 ”M ANA, 8 weeks in basal medium MS Âœ, followed by subculturing in ECO basal medium supplemented with 0.5 ”M 2iP, 0.44 ”M BA and 0.25 ”M IBA) was adequate to obtain somatic embryos in 2 genotypes, Stop Vert and Ac18, but no embryogenic response was observed in the other three. An analysis of genetic stability on Stop Vert, using SSR and RAPDs markers, was carried out in embryogenic callus, plants regenerated form this callus and micropropagated shoots in comparison with the mother plant. Polymorphism was only observed in the banding pattern generated by RAPDs in one of the 10 callus samples evaluated, resulting in a variation rate of 0.07%. This is the first time in which plants have been regenerated via somatic embryogenesis in wild olive.Universidad de MĂĄlaga. Campus de Excelencia Internacional AndalucĂa Tech.
Research project: Junta de AndalucĂa P11-AGR799
Nitrogen Incorporation in CH_4-N_2 Photochemical Aerosol Produced by Far Ultraviolet Irradiation
Nitrile incorporation into Titan aerosol accompanying hydrocarbon chemistry is thought to be driven by extreme UV wavelengths (λ120ânm is presently unaccounted for in atmospheric photochemical models. We suggest that reaction with CH radicals produced from CH_4 photolysis may provide a mechanism for incorporating N into the molecular structure of the aerosol. Further work is needed to understand the chemistry involved, as these processes may have significant implications for how we view prebiotic chemistry on early Earth and similar planets. Key Words: TitanâPhotochemical aerosolâCH_4-N_2 photolysisâFar UVâNitrogen activation
Heterologous expression of AtNPR1 gene in olive for increasing fungal tolerance
The NPR1 gene encodes a key component of SAR signaling mediated by salicylic acid (SA). After a pathogen infection, the accumulation of SA releases NPR1 monomers in the cytosol that are translocated to the nucleus, activating the expression of pathogenesis-related (PR) genes. Overexpression of NPR1 has conferred resistance to fungal, viral and bacterial pathogens in several plant species. The aim of this research was to generate transgenic olive plants expressing the gene AtNPR1 from Arabidopsis thaliana to obtain material resistant to fungal pathogens. Three transgenic lines expressing AtNPR1 gene under the control of the constitutive promoter CaMV35S were obtained following the protocol of Torreblanca et al. (2010), using an embryogenic line derived from a seed of cv. Picual. Level of AtNPR1 expression in transgenic calli varied greatly among the different lines, being higher in the line NPR1-780. The elicitation of embryogenic calli in liquid medium with AS did not increase endochitinase activity, a PR protein. However, jasmonic acid induced a transient increase in chitinase activity after 24 h of treatment in all the lines, being the increment higher in transgenic NPR1 than in control. After maturation and germination of transgenic somatic embryos, plants were micropropagated and acclimated to ex vitro conditions. The expression of AtNPR1 did not alter the growth of transgenic plants neither in vitro nor in the greenhouse. Experiments are in progress to determine the resistance of transgenic AtNPR1 plants to V. dalihae and R. necatrix.Universidad de MĂĄlaga. Campus de Excelencia Internacional AndalucĂa Tech.
Research projects: Plan Nacional AGL2014-52518-C2-1-R; AGL2017-83368-C2-1-R and Junta de AndalucĂa P11-AGR799
Les diffĂ©rences sexuelles dans lâactivation cĂ©rĂ©brale durant lâaccomplissement de la tĂąche de rotation mentale chez les patients atteints de schizophrĂ©nie
Dans la population gĂ©nĂ©rale plusieurs Ă©tudes ont dĂ©montrĂ© que les hommes ont, par comparaison aux femmes, de meilleures performances dans les tĂąches de rotation mentale Ă trois dimensions. A lâaide de lâimagerie par rĂ©sonnance magnĂ©tique fonctionnelle, on a pu observer que lâexĂ©cution de cette tĂąche de rotation mentale sâaccompagnait dâune activation du cortex pariĂ©tal chez lâhomme mais du cortex prefrontal chez la femme. Ces diffĂ©rences entre les deux sexes suggĂšrent un fonctionnement neuronal diffĂ©rent dans lâapprĂ©hension des habiletĂ©s cognitives et comportementales. De fait, de nombreuses Ă©tudes ont signalĂ© des diffĂ©rences notables entre les deux sexes quant Ă leur fonctionnement cĂ©rĂ©bral tant sur le plan Ă©motionnel que de leurs habiletĂ©s visuo spatiales.
La schizophrĂ©nie est un trouble grave et persistant de la santĂ© mentale dont lâorigine est certes multifactorielle et dont les facteurs de protection sont partiellement biologiques, psychologiques et sociales. Cette maladie requiert une approche thĂ©rapeutique Ă la fois clinique mĂ©dicamenteuse, psychologique et sociale visant Ă une rĂ©intĂ©gration des malades dans leur communautĂ©. Le pronostic de cette maladie varie en fonction du sexe ainsi que les atteintes neurologiques, neuropsychologiques et socioculturelles. Il est donc surprenant que lâexploration des mĂ©canismes neuronaux sous-tendant les anomalies fonctionnelles cognitivo-comportementales nâait point, en schizophrĂ©nie, adressĂ© Ă date la fonctionnalitĂ© diffĂ©rente de lâhomme et de la femme.
Une Ă©tude pilote, rĂ©alisĂ©e dans mon laboratoire dâaccueil, ayant suggĂ©rĂ© chez le schizophrĂšne, lors du traitement cognitif de stimuli Ă©motionnels, une altĂ©ration du dimorphisme sexuel observĂ© dans la population normale, il devenait impĂ©ratif de confirmer ces observations.
Ce mĂ©moire vise Ă vĂ©rifier par rĂ©sonnance magnĂ©tique fonctionnelle lâactivitĂ© neuronale cĂ©rĂ©brale tĂ©moignant de la performance neuropsychologique de schizophrĂšnes des deux sexes et de la comparer Ă celle de sujets tĂ©moins sains appareillĂ©s pour lâĂąge, la dominance hĂ©misphĂ©rique et le statut familial socio-Ă©conomique. A cette fin, nous avons enregistrĂ©, lors dâune tĂąche de rotation mentale Ă trois dimensions, les variables neurocognitives traduisant la validitĂ© des rĂ©ponses ainsi que leur rapiditĂ© dâexĂ©cution. SimultanĂ©ment, nous avons enregistrĂ©, par rĂ©sonnance magnĂ©tique fonctionnelle, les sites dâactivation cĂ©rĂ©brale ainsi que leur degrĂ© dâactivation corticale. Les donnĂ©es expĂ©rimentales, neurocognitives et cĂ©rĂ©bro-fonctionnelles, furent analysĂ©es en comparant les deux sexes dâune part et les deux Ă©tats de santĂ© dâautre part. Les rĂ©sultats de ce mĂ©moire ont fait lâobjet de deux articles qui sont inclus.
Les rĂ©sultats obtenus confirment lâhypothĂšse dâun dimorphisme homme/femme dans la population gĂ©nĂ©rale ainsi que chez le schizophrĂšne. Ces rĂ©sultats appuient aussi lâhypothĂšse de lâaltĂ©ration, chez le schizophrĂšne, du dimorphisme observĂ© dans la population gĂ©nĂ©rale.Sex differences in visuo-spatial abilities have been well documented in the general population, but there are only a few reports in schizophrenia. The purpose of the present study was to examine potential sex differences in performance and pattern of brain activations during mental rotation in schizophrenia patients relative to control participants.
First study: ÂŹReports mainly the results of mental rotation behavioural data, collected from 17 men and 13 women with schizophrenia and the same number of healthy subjects matched for age and sex. The findings revealed the expected sex difference in the control participants (men faster and more accurate than women) and the unexpected reversal of normal sexual dimorphism in patients (women more accurate and faster than men).
Second Study: Reports mainly fMRI results investigating the neural correlates of mental rotation in men and women with schizophrenia relative to healthy controls. Thirty three schizophrenia patients (17 women and 16 men) were compared to thirty five healthy control participants (17 women and 18 men), while performing a classic mental rotation of 3-D figures. BOLD echo planar images were acquired on a 3Tesla Siemens TRIO system. Analyses were performed using SPM5 (UK Welcome Institute). Behavior data revealed a diagnosis-by-sex interaction with healthy men (HM) performing significantly better than schizophrenia men (SZ-M), and no significant difference between healthy women (HW) and schizophrenia women (SZ-W). fMRI results revealed that overall similar pattern of extensive cerebral activations (in the parietal and the prefrontal cortices) in HM and SZ-W, and deactivation during performance of the mental rotation task versus control task. In contrast, both HW and SZ-M showed much more restricted activations and deactivations in these regions.
The whole of these results suggests that sex differences in the cerebral activations during mental rotation in schizophrenia patients deviates from what we and others have observed in the general population and thus supports and extends existing evidence of a disturbed cerebral sexual dimorphism in schizophrenia. Moreover, the results emphasize the importance of including sex as a variable in neurocognitive and neuroimaging studies of schizophrenia
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