Aportación al conocimiento paleoecológico del Holoceno en el NW de la Península Ibérica

Se ha hecho análisis polínico de dos palcosudos enterrados bajo un yacimiento arqueológico de cultura catrexa y dt un depósito lacustre. Los tres está.n geográficamente próximos y son com:lacionablc.~ debido a la CXJSI-encia d!:.datacioncs C-14 y a datos culturales. Coll los datos polfnicos obtenidos, se ban hecho dos diagramas en los que se dcfmcn distintas etapas de vegetación dc5dc finales del Sub-Boreal al Sub-Atlántico actual. Dichas etapas son: fin Uel Sub-Boreal con boS()UC de Q¡:e~eu.r y presencia de ÚlJianea; expansión del roble a comien- 7.0s del Sub-Atlántico y presencia deAinus; fase de cultivo de COJtanta hacia 1580 B.P .; fase de máxima dcforcsucióo y fmalmcntc, fase. de cultivo dcPjnr.uA polleo analysi! of two palcosoih buricd under an arcbacological deposit o[ caHcxa culture aod Jakc dcposils was carricd out. Thc thrcc are geograpbkally close and are relatcd as tbe cOOstence of C-14 data and cultaral in(onnation preves. With the po11en data oblai.ned we dcvi.sed rwo diagrams dcfming severa! Mage..~ of vegc.tation ranging from thc cnd of lhc Sub-Boreal te thc prcscnt Sub·Atlantic. Thcse stagcs are: tbc cnd of tbc Sub-Boreal wi tb QuerroJ furcsts and thc prcsc:mx: of Ca¡ftm , u; extcrmon o( oaks at thc bcginning of thc Sub-Atlantic and the presence of Afnus; tbe Castnnea cultivation phase (rom about 1580 B.P .; the maximum deforcslation phase and lastly, cultivation ofthe Pil11tS phas

Local mean-field study of capillary condensation in silica aerogels

We apply local mean-field (i.e. density functional) theory to a lattice model of a fluid in contact with a dilute, disordered gel network. The gel structure is described by a diffusion-limited cluster aggregation model. We focus on the influence of porosity on both the hysteretic and the equilibrium behavior of the fluid as one varies the chemical potential at low temperature. We show that the shape of the hysteresis loop changes from smooth to rectangular as the porosity increases and that this change is associated to disorder-induced out-of-equilibrium phase transitions that differ on adsorption and on desorption. Our results provide insight in the behavior of $^4$He in silica aerogels.Comment: 19 figure

Honey bee visitation to sunflower: effects on pollination and plant genotype

Sunflower (Helianthus annuus L.) is an allogamic plant, which needs insects on flowering, especially the honeybees for seed production. Collecting nectar and pollen by honeybees in agricultural crops is essential to apiculture, as well as a better understanding of plant biology. The foraging behavior of Africanized Apis mellifera L. (Hymenoptera, Apidae) and its efficiency of pollination on seed yield of sunflower genotypes (open pollination and restricted pollination) were evaluated. There were peaks of visits by A. mellifera for nectar collection on the 2nd and 3rd flowering days between 7h00 and 8h30. The average density of A. mellifera during increased visitation ranged from 2.27 to 2.94 bees per capitulum. Nectar collecting bees were more frequent (2.28 bees per capitulum) than pollen collecting (0.40 bees per capitulum). On the 3rd flowering day, Helio 360 and Aguará hybrids had higher (p ≤ 0.05) number of bee visits per flower head than the other genotypes. Seed yield was 43 % higher (p ≤ 0.05) from sunflower plants that were visited by pollinator-insects compared with plants restricted to pollinators