Equivalent Circuit and AC conductivity of Sr1.75Co0.25P2O7 compound

Sr1.75Co0.25P2O7 compound was prepared by the solid-state reaction method. The impedance spectroscopy measurements were performed in the frequency and the temperature range of (209 Hz1 MHz) and (622704 K), respectively. Besides, the impedance spectra were fitted to an equivalent circuit consisting of series combination of grains and grain boundary. The AC conductivity for grain contribution is interpreted using the universal Jonschers power law. The approximation type OLPT model explains the universal behavior of the s exponent. The mechanism of conduction is probably due from the displacements of the Sr2+ ion in the tunnel-type cavities

Copepods encounter rates from a model of escape jump behaviour in turbulence

A key ecological parameter for planktonic copepods studies is their interspecies encounter rate which is driven by their behaviour and is strongly influenced by turbulence of the surrounding environment. A distinctive feature of copepods motility is their ability to perform quick displacements, often dubbed jumps, by means of powerful swimming strokes. Such a reaction has been associated to an escape behaviour from flow disturbances due to predators or other external dangers. In the present study, the encounter rate of copepods in a developed turbulent flow with intensity comparable to the one found in copepods' habitat is numerically investigated. This is done by means of a Lagrangian copepod (LC) model that mimics the jump escape reaction behaviour from localised high-shear rate fluctuations in the turbulent flows. Our analysis shows that the encounter rate for copepods of typical perception radius of ~ {\eta}, where {\eta} is the dissipative scale of turbulence, can be increased by a factor up to ~ 100 compared to the one experienced by passively transported fluid tracers. Furthermore, we address the effect of introducing in the LC model a minimal waiting time between consecutive jumps. It is shown that any encounter-rate enhancement is lost if such time goes beyond the dissipative time-scale of turbulence, {\tau}_{\eta}. Because typically in the ocean {\eta} ~ 0.001m and {\tau}_{\eta} ~ 1s, this provides stringent constraints on the turbulent-driven enhancement of encounter-rate due to a purely mechanical induced escape reaction.Comment: 11 pages, 10 figure

Transfer and accumulation of lead, zinc, cadmium and copper in plants growing in abandoned mining-district area

The analysis of the Jebel Hallouf-Sidi Bouaouane mining-district soil has shown that the surface horizons are strongly contaminated by heavy metals, especially during floods or in lee-side areas. The contents of metallic-trace elements (MTE), in the soil and two cultivated plant species, have been determined by Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES). The results show that the concentration of metals in the soil are up to 39 g. kg-1, 6.3 g. kg-1, 56 mg. kg-1 and 131 mg. kg-1, for lead (Pb), zinc (Zn), cadmium (Cd) and copper (Cu), respectively. The chemical analysis of plants: broad beans [Vicia faba (L.)] and barley [Hordeum vulgare (L.)], sampled inside the mining district, show that the roots and the upper part (leaves and stem) are enriched for Pb (up to 508 and 220 mg.kg-1, respectively), Cd (up to 8 and 5 mg.kg-1, respectively), and Zn (up to 491 and 468 mg.kg-1, respectively) when compared with similar species collected far from the contaminated site (up to 9.6 and 0.8 mg.kg-1 for Pb, up to 0.04 and 0.04 mg.kg-1 for Cd, up to 44 and 15 mg.kg-1 for Zn, respectively). Statistically, the concentration of MTE in the soils and plants of the mining area is significantly different from the concentrations of the same elements in the soils and plants of the control ones (p < 0.01). This is expressed by a strong Enrichment Coefficient (EC), which is given by the ratio between the concentration of the metal in the contaminated plant and the concentration of the same element in the similar control one. The results (up to 405, 342 and 32, respectively), indicate that the contamination has reached the first link of the food chain. However, the calculation of the translocation factor (TF), deduced from the ratio between the concentration of the metal in the outer part of the plant and the concentration of the same element in the roots, shows that, the broad beans accumulates metals in the roots (TF < 1); whereas for barley, metals are fairly distributed between the roots and the outer part (TF ≈ 1). These results suggest that the cultivated areas inside the mining district constitute a serious source of contamination of the food chain. Therefore, actions have to be taken in order to remedy this problem.Key words: MTE, contamination, transfer, soil, plant

Spatial analysis of hydrological and phytoplanktonic data of the Bay of Tunis. Multivariate cartography

A method of cartography originally used in geology was adapted to generate regionalization and to obtain 2-D maps of multivariate marine data. The ecological purpose of the method is to divide the studied area through homogeneous regions presenting common multivariate characteristics. Firstly, transformation was applied to the original matrix of hydrological parameters in order to satisfy the condition of multinormality. Then, associative analysis was used in order to produce an easy to interpret partition of sites. The level of heterogeneity between each station and the properties of each group was assessed by measuring the Bayesian probabilities. These conditional probabilities measure the chance that each site has of belonging to a predefined group of sites. Based on the geographical positions of the stations, the probability values for each group of stations were mapped using kriging interpolation algorithm. The obtained maps of iso-probabilities for the different groups of stations were used to define homogenous zones on a single map. Including the phytoplanktonic dataset afterwards, the indicator species were identified for each zone.This multivariate analysis was applied to a hydrological and phytoplanktonic dataset of the Bay of Tunis. Measures at surface were made at 17 stations, sampled monthly over 2 years. The results illustrated a partition of the bay considering four groups, two coastal and two central groups of stations. The importance of the inshore influence was demonstrated in the setting up of such a regionalization through the inflow of alluvium and other products of coastal activities. The significant presence of the toxic phytoplanktonic community in the bay suggests the need to institute a monitoring program

Variabilité des descripteurs physiques, chimiques et phytoplanctonique dans des étangs d'alevinage (station de la Deroua, Béni-Mellal, Maroc)

Dans les étangs d'alevinage à la station de la Deroua, le phytoplancton est représenté par des populations se succédant dans le temps.Ces étangs montrent une similarité vis-à-vis de la variabilité des descripteurs de la qualité de l'eau. Les résultats statistiques montrent une variabilité des paramètres physiques et chimiques dépendant des interventions anthropiques.Les deux étangs B3 et B4 présentent des groupements phytoplanctoniques plus importants avec un développement de Cyanobactéries en fin du cycle d'alevinage lié à une forte biodisponibilité du phosphore dissous.In fry ponds at Deroua farm, the phytoplankton was represented by a temporal succession of taxa groups.This study showed a similar variability of physical and chemical parameters in fishponds. The statistical analysis proved a variability of these parameters depending of human interventions.At the end of fry period, the phosphorus concentration in B3 and B4 ponds allowed a development of Cyanobacteri

Feeding mechanism and capture success of European whitefish (Coregonus lavaretus L.) larvae

Feeding success is a key factor for larval growth and survival, and is highly dependent on small-scale processes which occur during the predator-prey interaction. We studied the feeding mechanisms involved in the capture success of the European whitefish (Coregonus lavaretus) larvae using video recordings. The successful predatory sequence of this species consists of the following 5 events: encounter, pursuit (including fixation), strike, capture and ingestion. C. lavaretus larvae can exhibit an “S” shaped posture and always strikes on its prey from beyond. The mean fixation distance for wild larvae was 1.75 ± 0.71 mm and for reared larvae was 1.65 ± 0.76 mm. This distance was significantly different between failed and successful snaps, and seemed to be an important parameter to the capture success of C. lavaretus larvae. The analysis of the complexity in predator’s swimming path showed that more convoluted approaches are less likely to lead to a fruitful att

Decadal changes in water temperature and ecological time-series in Lake Geneva, Europe - detecting relationships with the subtropical Atlantic climate variability

We investigated connections between subtropical Atlantic climate variability, atmospheric conditions in the European Alpine region (45 to 47° N and 5 to 8° E) and the interannual variability of the thermal conditions in the largest body of freshwater in Western Europe (Lake Geneva). The long-term water temperature was related to climate variability by means of a multivariate regression model. Results revealed atmospheric connections that have been elusive so far, and showed that over the period from 1959 to 2000, summer thermal conditions in Lake Geneva appear tightly linked to the long-term variability of the subtropical Atlantic climate. The multivariate model revealed high skills and tight correlations, which suggest the possibility of assessing future thermal changes in Lake Geneva from the Atlantic climate variability. The implications of such climatic forcing on the functioning of the pelagic ecosystem in Lake Geneva were illustrated by analysing the long-term changes in abundance of the summer-dominant carnivorous cladocerans Bythotrephes longimanus and Leptodora kindtii during the period 1974 to 2000. Again, the multivariate model revealed high skills and excellent correlations between the interannual changes in abundance of these species and the variability of summer climate. Our approach provides a general understanding of the interrelations between large- and regional-scale climates, local environmental conditions and the ecological responses in Lake Geneva during summer, and is therefore applicable to other retrospective studies

Rendezvous of Two Robots with Constant Memory

We study the impact that persistent memory has on the classical rendezvous problem of two mobile computational entities, called robots, in the plane. It is well known that, without additional assumptions, rendezvous is impossible if the entities are oblivious (i.e., have no persistent memory) even if the system is semi-synchronous (SSynch). It has been recently shown that rendezvous is possible even if the system is asynchronous (ASynch) if each robot is endowed with O(1) bits of persistent memory, can transmit O(1) bits in each cycle, and can remember (i.e., can persistently store) the last received transmission. This setting is overly powerful. In this paper we weaken that setting in two different ways: (1) by maintaining the O(1) bits of persistent memory but removing the communication capabilities; and (2) by maintaining the O(1) transmission capability and the ability to remember the last received transmission, but removing the ability of an agent to remember its previous activities. We call the former setting finite-state (FState) and the latter finite-communication (FComm). Note that, even though its use is very different, in both settings, the amount of persistent memory of a robot is constant. We investigate the rendezvous problem in these two weaker settings. We model both settings as a system of robots endowed with visible lights: in FState, a robot can only see its own light, while in FComm a robot can only see the other robot's light. We prove, among other things, that finite-state robots can rendezvous in SSynch, and that finite-communication robots are able to rendezvous even in ASynch. All proofs are constructive: in each setting, we present a protocol that allows the two robots to rendezvous in finite time.Comment: 18 pages, 3 figure

La preferencia ecológico versus convencional en los productos lácteos: el caso del queso

Las nuevas exigencias de los consumidores hacia todo lo relacionado con la calidad y la seguridad de los productos agroalimentarios están provocando un cambio progresivo en los hábitos de compra y de consumo de dichos productos. Concretamente, en el sector lácteo los consumidores buscan cada vez más productos de mayor calidad, más sanos, naturales, ecológicos, artesanales, locales etc., y en definitiva, más saludables y respetuosos con el medioambiente. Las nuevas tendencias del consumo alimentario hacia estos nuevos productos están provocando una continua adaptación de las empresas productoras para satisfacer estas demandas y, por consiguiente, poder competir en el mercado. Dentro del sector lácteo, los productos lácteos artesanales (PLA) y sobre todo los derivados de la ganadería de pequeños rumiantes, forman parte del patrimonio de productos agroalimentarios de las regiones más desfavorecidas en muchos países de la región mediterránea. Dichos productos constituyen un recurso endógeno con un claro potencial de desarrollo, no siempre bien aprovechado y revalorizado, particularmente, en España. Varias razones tanto relacionadas con la demanda y los mercados, como con la potencialidad productiva primaria y, sobre todo, secundaria avalan dicho potencial. Analizando dicho sector, uno de los productos con un alto potencial de desarrollo es el queso artesanal. En este sentido, debido a la creciente importancia de la producción ecológica en la dieta alimentaria y la orientación progresiva de los consumidores hacia dichos productos, entre las oportunidades comerciales que se presentan para el queso, es la diferenciación hacia la calidad ecológica. No obstante, como dicha diferenciación no parece resultar suficiente para incrementar el consumo, parece de gran interés analizar la estructura de preferencias de los consumidores en relación con unos atributos del queso, y estimar la importancia relativa del atributo modo de producción (ecológica vs convencional) frente a otras características del mismo tal como el tipo de leche, el proceso de elaboración (industrial, de pequeñas industrias o artesanal) y el precio. Asimismo, se han intentado estimar los precios implícitos de las variaciones en los niveles de los diferentes atributos, básicamente, la disposición a pagar de los consumidores por la calidad ecológica frente al convencional. La información manejada en este trabajo proviene de una encuesta realizada a 263 consumidores de queso en Andalucía. El cuestionario tiene dos grandes bloques. En el primero se incluye un test de preferencias de los entrevistados hacia unos perfiles de quesos. En el segundo se recogen las características sociodemográficas y de estilo de vida de los encuestados.Instituto de Investigación y Formación Agraria IFAPA Centro Camino de Purchil, Granada. Área de Economía y Sociología Agrarias