Heterogeneous Delays in Neural Networks

We investigate heterogeneous coupling delays in complex networks of excitable elements described by the FitzHugh-Nagumo model. The effects of discrete as well as of uni- and bimodal continuous distributions are studied with a focus on different topologies, i.e., regular, small-world, and random networks. In the case of two discrete delay times resonance effects play a major role: Depending on the ratio of the delay times, various characteristic spiking scenarios, such as coherent or asynchronous spiking, arise. For continuous delay distributions different dynamical patterns emerge depending on the width of the distribution. For small distribution widths, we find highly synchronized spiking, while for intermediate widths only spiking with low degree of synchrony persists, which is associated with traveling disruptions, partial amplitude death, or subnetwork synchronization, depending sensitively on the network topology. If the inhomogeneity of the coupling delays becomes too large, global amplitude death is induced

Interaction of crop load and water status on growth of olive fruit tissues and mesocarp cells

Trabajo presentado en el XXVIII International Horticultural Congress on Science and Horticulture for People (IHC2010): International Symposium on Plant Physiology from Cell to Fruit Production System, celebrado en Lisboa (Portugal) del 22 al 27 de agosto de 2010.Field-grown olive trees (Olea europaea L. ‘Leccino’) were hand-thinned at 5-6 weeks after full bloom (AFB) to establish heavy or low crop loads, and then were subjected to three irrigation regimes: a) FI, fully-irrigated with pre-dawn leaf water potential (LPWP) greater than -1.1 MPa; b) DI, deficit irrigated (LPWP between -1 and -3.3 MPa; c) SI, water stressed (LPWP higher than -4.2 MPa). Fruits were sampled at pit hardening and harvest, the mesocarp separated from the endocarp, and their fresh weight and dry weight determined. Additional fruits were fixed in FAE for anatomical studies, their mesocarp and endocarp area measured on transverse slices with an image analysis system connected to a stereo microscope. Mesocarp cell size and number were then determined by microscope after standard paraffin processing. The effect of crop load on the growth of fruit tissues was significantly influenced by the irrigation regime. Within the FI or DI treatments the mesocarp dry weight was higher at low than at high crop load. In the SI treatment, mesocarp dry and fresh weights were 180 and 200% respectively those for trees bearing high crop loads. The pulp-pit ratio was decreased by high cropping for both DI and SI treatments, but was unaffected for the fully-irrigated trees. Overall, there was a notable interaction of crop load and water status on fruit growth processes at multiple morphogenetic levels, including the absolute and relative growth of pulp and pit, mesocarp cell division and enlargement.Peer reviewe

Water deficit-induced changes in mesocarp cellular processes and the relationship between mesocarp and endocarp during olive fruit development

A field experiment was conducted during two consecutive growing seasons to determine and quantify the growth response of the olive (Olea europaea L. cv. Leccino) fruit and of its component tissues to tree water status. Pre-dawn leaf water potential (Ww) and fruit volume were measured at about weekly intervals, and fresh weight (FW) and dry weight (DW) of the fruit tissues at 15, 20 and 21 weeks after full bloom (AFB). Fruit anatomical sections were prepared at 8, 15 and 21 weeks AFB for area determinations and cell counts. Fruit volume of the well-watered trees (average Ww = 0.97 MPa) increased rapidly and reached the greatest final size, that from the most stressed (average Ww = 2.81 MPa) grew most slowly and were smallest. In general, equatorial transverse areas of the mesocarp increased with increasing Ww, and this response was more evident at 21 than at 15 weeks AFB. By 21 weeks AFB, the mesocarp of the well-watered trees reached values more than three times higher than those measured at 8 weeks AFB. The endocarp FW and DW did not increase between 15 and 21 weeks AFB. Within each sampling date the endocarp area, FW and DW responded weakly to Ww. The mesocarp-to-endocarp ratio (FW and DW) increased from 15 to 21 weeks AFB regardless of water status, mainly due to the mesocarp growth. In both years at 20 and 21 weeks AFB, low values of the mesocarp-toendocarp ratio were found with Ww below 2.5 MPa. Within the mesocarp, cell size was more responsive to water deficit than to cell number. At 8 weeks AFB, the number of cells in the mesocarp was unaffected by tree water deficit, whereas cell size decreased, although slightly, in fruits sampled from trees in which Ww was < 3.0 MPa. At 21 weeks AFB, cell size showed a linear decrease with increasing level of water deficit, whereas the number of cells at 21 weeks AFB decreased as the Ww decreased below 2.5 MPa and seemed unaffected above that range. Overall, the results clarify the complexity of the water-induced response of mesocarp and endocarp growth and cellular processes of olive fruits

Differential contributions of set-shifting and monitoring to dual-task interference

It is commonly argued that complex behaviour is regulated by a number of “executive functions” which work to co-ordinate the operation of disparate cognitive systems in the service of an overall goal. However, the identity, roles, and interactions of specific putative executive functions remain contentious, even within widely accepted tests of executive function. The authors present two experiments that use dual-task interference to provide further support for multiple distinct executive functions and to establish the differential contributions of those functions in two relatively complex executive tasks – Random Generation and the Wisconsin Card Sorting Test. Results are interpreted in terms of process models of the complex executive tasks