158 research outputs found

    Paleontologia y bioestratigrafia del mioceno continental de la Cuenca de Calatayud (Zaragoza): nuevos yacimientos de micromamiferos

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    In this work we study the micromammal associations of five new sites from the basin of Calatayud: Vilueña, Torralba de Ribota 8, Montón, Armantes 14 and Belmonte. In the first four sites we have recognised the evolved species lineage of Megacricetodon primitivus-collongensis-crusafonti of the Middle Miocene that have allowed us to place them biostratigraphically with accuracy. The oldest site is Vilueña, with Megacricetodon primitivus which is a characteristic species of the C y D1 zones corresponding respectively to the Lower and Middle Aragonian. The association of Megacriceton primitivus- collongensis and Fahlbuschia koenigswaldi in Torralba de Ribota 8 is characteristic of the D zone of the Middle Aragonian. In Montón we found the transitional taxon of Megacricetodon collongensis-crusafonti which is characteristic of the F and Gl zones of the Upper Aragonian. In Armantes 14 there is the species Megacricetodon crusafonti that is characteristic of the G2 zone of the Upper Aragonian. Finally in the Belmonte site, the presence of the muridae Progonomys hispanicus, indicates its age of the Upper Vallesian, in the zone J that is characterized by that species. From a paleoenvironmental and paleoclimatic point of view, the presence in the sites of Vilueña, Torralba de Ribota 8 and Montón of the terrestrial squirrel of the genus Heteroxerus, and some gliridae of the genus Microdyromys which are not related with a wet climate, and the capacity of this last genus and also of the cricetid genus Fahlbuschia to endure high temperatures, suggest an open country environment and a climate relatively dry and warm during the most part of the Lower and Middle Aragonian and the lower part of the Upper Aragonian as was pointed out in other areas (Daams et al., 1988; Daams & van der Meulen, 1984; van der Meulen & Daams, 1992). In the Upper Aragonian faunal association of Armantes 14, it appears a gliridae of the genus Muscardinus that is considered characteristic of a humid climate, and there are no terrestrial squirrels. This is in agreement with the suggestion made by Daams et al. (op.cit.) that this age was relatively wetter than the former one. There is a fauna1 micromammal change between the Middle and the Upper Miocene, evident in the fauna1 association of the Upper Vallesian site of Belmonte in which there are no anyone of the cricetidae that were characteristic of the Middle Miocene but it appears the first muridae represented by the genus Progonomys. This has been interpreted as a climatic change towards relatively drier conditions, that went on during al1 the Upper Miocene, and also relatively colder, according to Daams et al. (op. cit.).Se dan a conocer cinco nuevos yacimientos de micromamíferos de la cuenca de Calatayud: Vilueña, Torralba de Ribota 8, Montón, Armantes 14 y Belmonte, que abarcan un período comprendido entre el Mioceno inferior y el superior. En las asociaciones faunísticas de micromamíferos de los cuatro primeros yacimientos, hemos determinado la línea evolutiva de las especies: Megacricetodon primitivus-collongensis- crusafonti del Mioceno medio, lo que nos ha permitido situarlas con gran precisión bioestratigráfica. El yacimiento bioestratigráficamente más antiguo es el de Vilueña, en el que está presente la especie Megacricetodon primitivus que es característica de las zonas C y D1 correspondientes, respectivamente, al Aragoniense inferior y medio. En Torralba de Ribota 8, la asociación de Megacriceton primitivus-collongensis y Fahlbuschia koenigswaldi es característica de la zona D del Aragoniense medio. En Montón se encuentra la forma de transición Megacricetodon collongensis-crusafonti, característica de las zonas F y G1 del Aragoniense superior. En Armantes 14 está la especie Megacricetodon crusafonti que es característica de la zona G2 del Aragoniense superior. Finalmente en el yacimiento de Belmonte, la presencia del múrido Progonomys hispanicus indica su edad del Vallesiense superior, en la zona J caracterizada por dicha especie. Desde un punto de vista paleoambiental y paleoclimático, durante el Aragoniense inferior y medio, la presencia en las asociaciones de Vilueña, Torralba de Ribota 8 y Montón de ardillas terrestres, atribuibles al género Heteroxerus, y glíridos del género Microdyromys que no están ligados a un clima húmedo, así como el carácter termófilo del glírido del género Microdyromys y del cricétido del género Fahlbuschia, hacen suponer la existencia de un medio abierto y un clima relativamente seco y cálido (Daams et al., 1988; Daams y Van der Meulen, 1984; Van der Meulen y Daams, 1992). En la asociación del Aragoniense superior de Armantes 14, sin embargo, ya aparece un glírido considerado de clima húmedo, como el género Muscardinus, y no se constata la presencia de ardillas terrestres, habiéndose interpretado esta edad como relativamente más húmeda que la precedente (Daams et al., op.cit.). La transición de las faunas del Mioceno medio al Mioceno superior en la cuenca de Calatayud (representada esta última edad por la asociación faunística del Vallesiense superior del nuevo yacimiento de Belmonte) corrobora también en esta área la existencia de un cambio faunístico con la desaparición de los taxones de cricétidos que tuvieron una gran expansión y evolución durante el Mioceno medio, frente a la llegada de nuevos inmigrantes como los múridos, representados por el género Progonomys. Estos hechos se han interpretado como resultado de un cambio climático hacia unas condiciones relativamente más secas, que continuaron durante todo el Mioceno superior, y más frías (Daams et al., op.cit.)

    Los roedores y lagomorfos del Neógeno de España

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    The studies made since the middle of the last century by many authors about the Spanish micromammal faunas of many sites have given rise at present to a good knowledge of the fossil record of the Spanish Neogene. The former synthesis works on Neogene mammals made by López et al. (1987) and Calvo et al. (1993), of the rodents by Sesé (1988) and of the lagomorphs by López (1989) shows the extraordinary fossil richness of the several Spanish geographical areas and basins (Ebro, Tajo, Calatayud-Teruel, Duero, Vallés-Penedés, Levante, Béticas). In the present work it is made a review and update synthesis on the Spanish Neogene (Miocene and Pliocene) rodents (order Rodentia) and lagomorphs (order Lagomorpha), mainly of the peninsula where there are more findings, but also of some findings made in the islands. They have been analysed, mainly from the systematical and biostratigraphical point of view, the faunas of the Neogene sites that have characteristical taxa of their asigned age. The order of the presentation of the analysis is, at a first level, by the stages or mammal ages, giving their most important characteristics, and, at a second level, analysing the most characteristical features of the faunas of each biozone that belong to each stage. These stages are: in the Miocene, the Early Lower Miocene, Ramblian, Aragonian, Vallesian and Turolian, and, in the Pliocene, the Ruscinian (Alfambrian) and Villanian. Regarding the zones, for the Miocene we follow the local biozonation more used in Spain that comprises the zones named from X to Y and from A to M, correlating them with the MN zones of the Mediterranean Neogene biozonation (Mein, 1975) that is the most used in Europe; and in the Pliocene, we used the MN 14 to MN 17 zones. They have been summarized the dates made in many sites, zones and stages, mainly since the last decade. It is pointed out the biogeographical differentiation between the Ibero-Central and the Ibero-Levant provinces during the most part of the Miocene, and their homogeinity at the end of the Miocene and during the Pliocene with the southern France in the so called Ibero-Occitanian province. It has been also indicated the main paleoenvironmental changes inferred from the micromammal faunal changes, mainly those that have been related with global changes.Los estudios realizados desde mediados del siglo pasado en España por muchos autores sobre las faunas de micromamíferos, han dado lugar a que actualmente haya un buen conocimiento del registro fósil del Neógeno español. Trabajos de síntesis anteriores a éste, como los de mamíferos del Neógeno realizados por López et al. (1987) y Calvo et al. (1993), el de roedores por Sesé (1988) y el de lagomorfos por López (1989), muestran la extraordinaria riqueza fosilífera de las diversas áreas geográficas y cuencas españolas (Ebro, Tajo, Calatayud-Teruel, Duero, Vallés Penedés, Levante, Béticas). En el presente trabajo se realiza una síntesis de revisión y actualización del registro fósil de roedores (orden Rodentia) y lagomorfos (orden Lagomorpha) del Neógeno (Mioceno y Plioceno) en España, principalmente de la península que es donde se han realizado más hallazgos, pero también de algunos realizados en las islas. Se han analizado, desde los puntos de vista sistemático y biostratigráfico principalmente, las faunas de los yacimientos neógenos que presentan taxones característicos de la edad que se les asigna. El orden de presentación de este análisis es, en un primer nivel, por pisos o edades de mamíferos, dando las características más importantes de los mismos, y, en un segundo nivel, analizando los aspectos más característicos de las faunas de las biozonas que comprende cada uno. Los pisos a que nos referimos son: en el Mioceno, la base del Mioceno Inferior, Rambliense, Aragoniense, Vallesiense y Turoliense, y, en el Plioceno, el Rusciniense (Alfambriense) y Villaniense. En cuanto a las zonas, para el Mioceno seguimos la biozonación local más utilizada en España que comprende las zonas denominadas de la X a la Y y de la A a la M, correlacionándolas con las zonas de la biozonación del Neógeno Mediterráneo (zonas MN) de Mein (1975), que es la más generalizada para toda Europa, y para el Plioceno las zonas MN 14 a MN 17. Se recogen las dataciones realizadas, especialmente desde la última década, de numerosos yacimientos, zonas y pisos. Se señala la diferenciación biogeográfica que hay durante la mayor parte del Mioceno entre la provincia Ibero-Central y la Ibero- Levantina, y la homogeneización de ambas con el sur de Francia en la denominada provincia Ibero-Occitana al final de Mioceno que continúa durante el Plioceno. Se indican también los cambios paleoambientales más importantes inferidos a partir de los cambios faunísticos de micromamíferos, sobre todo los que se relacionan con cambios globales

    Los micromamíferos (Eulipotyphla, Chiroptera, Rodentia y Lagomorpha) del yacimiento del Pleistoceno Superior de la cueva de El Sidrón (Asturias)

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    In the Late Pleistocene site of El Sidrón cave, with a date of ~ 49,000 ky, known for its numerous fossil remains of Neanderthals, some remains of micromammals were found, whose detailed study is carried out in this work. The determined faunal association is the following: Sorex araneus–Sorex coronatus, Neomys cf. fodiens, Talpa sp., Rhinolophus euryale-Rhinolophus mehelyi, Marmota cf. marmota, Eliomys quercinus, Glis glis, Arvicola terrestris, Chionomys nivalis, Microtus arvalis-Microtus agrestis, Microtus lusitanicus, Microtus oeconomus, Clethrionomys glareolus, Apodemus sylvaticus-Apodemus flavicollis and Oryctolagus cuniculus. These taxa are present in the current fauna of Asturias and Cantabrian Region except for Microtus oeconomus that disappeared from the Iberian Peninsula in historical times and is currently in northernmost Eurasian regions. The fauna of micromammals as a whole seems to indicate a predominantly open space environment, generally of certain moisture meadows and vegetation development at ground level, although there would also be wooded areas of some entity and some watercourse. The presence, although with few remains, of some thermophilic species, and the absence of cold climate indicator species, seem to indicate that the climate during the formation of the fossiliferous deposits would be relatively temperate and humid, probably similar to the current one in the area

    Zero-temperature spin-glass freezing in self-organized arrays of Co nanoparticles

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    We study, by means of magnetic susceptibility and magnetic aging experiments, the nature of the glassy magnetic dynamics in arrays of Co nanoparticles, self-organized in N layers from N=1 (two-dimensional limit) up to N=20 (three-dimensional limit). We find no qualitative differences between the magnetic responses measured in these two limits, in spite of the fact that no spin-glass phase is expected above T=0 in two dimensions. More specifically, all the phenomena (critical slowing down, flattening of the field-cooled magnetization below the blocking temperature and the magnetic memory induced by aging) that are usually associated with this phase look qualitatively the same for two-dimensional and three-dimensional arrays. The activated scaling law that is typical of systems undergoing a phase transition at zero temperature accounts well for the critical slowing down of the dc and ac susceptibilities of all samples. Our data show also that dynamical magnetic correlations achieved by aging a nanoparticle array below its superparamagnetic blocking temperature extend mainly to nearest neighbors. Our experiments suggest that the glassy magnetic dynamics of these nanoparticle arrays is associated with a zero-temperature spin-glass transition.Comment: 6 pages 6 figure

    El Aragoniense Medio y Superior en el Suroeste de Madrid: Los nuevos yacimientos de Micromamíferos del Mioceno Medio de Villaviciosa de Odón y Leganés

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    This paper discloses two new sites in the southwestern area of Madrid, Villaviciosa de Odón and Leganés, which have provided two rich micromammals associations of different ages. The micromammal association of the Villaviciosa de Odón site determined in this work is composed by the following taxa: Lagomorpha: Lagopsis peñai; Erinaceomorpha: Galerix cf. exilis; Soricomorpha: Miosorex cf. grivensis; Rodentia: Atlantoxerus sp., Microdyromys sp., Armantomys tricristatus, Megacricetodon collongensis and Democricetodon sp. This association, mainly by the evolutionary stage of Megacricetodon collongensis, corresponds to the E local biozone after Daams & Freudenthal (1988a) from the end of the Middle Aragonian which is correlated with the end of the MN 5 Unit of Mein (1975). The micromammal association of the Leganés site consists of the following taxa: Lagomorpha: Lagopsis verus; Erinaceomorpha: Galerix cf. exilis; Rodentia: Heteroxerus cf. rubricati, Armantomys sp., Megacricetodon collongensis-crusafonti and cf. Democricetodon sp. Mainly by the evolutionary stage of Megacricetodon collongensis-crusafonti this association corresponds to the G1 local biozone after Daams et al. (1999 a y b) which is correlated with the MN 6 Unit of Mein (1975). It is the only site known in Madrid of this age. Both micromammals associations suggest an open environment dominated by hard vegetation of steppe kind, and a dry and relatively warm climate.En este trabajo se dan a conocer dos nuevos yacimientos de la zona suroeste de Madrid, Villaviciosa de Odón y Leganés, que han proporcionado dos ricas asociaciones de micromamíferos de edades diferentes. La asociación de micromamíferos del yacimiento de Villaviciosa de Odón determinada en este trabajo está compuesta por los siguientes taxones: Lagomorpha: Lagopsis peñai; Erinaceomorpha: Galerix cf. exilis; Soricomorpha: Miosorex cf. grivensis; Rodentia: Atlantoxerus sp., Microdyromys sp., Armantomys tricristatus, Megacricetodon collongensis y Democricetodon sp. Por el estadio evolutivo de Megacricetodon collongensis esta asociación se incluiría en la biozona local E de Daams & Freudenthal (1988a) del final del Aragoniense Medio, correlacionable con el final de la unidad MN 5 de Mein (1975). La asociación del yacimiento de Leganés se compone de los siguientes taxones: Lagomorpha: Lagopsis verus; Erinaceomorpha: Galerix cf. exilis; Rodentia: Heteroxerus cf. rubricati, Armantomys sp., Megacricetodon collongensis-crusafonti y cf. Democricetodon sp. Por el estadio evolutivo de Megacricetodon collongensis-crusafonti se situaría en el Aragoniense Superior en la biozona local G1 de Daams et al. (1999 a y b) que se correlaciona con la unidad MN 6 de Mein (1975). Es el primer yacimiento que se conoce en Madrid de esta edad. Las asociaciones de micromamíferos de Villaviciosa de Odón y Leganés sugieren un medio fundamentalmente abierto, con predominio de la vegetación dura de tipo estepario, y un clima seco y relativamente cálido

    Ac magnetic susceptibility of a molecular magnet submonolayer directly patterned onto a microSQUID sensor

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    We report the controlled integration, via Dip Pen Nanolithography, of monolayer dots of ferritin-based CoO nanoparticles (12 Bohr magnetons) into the most sensitive areas of a microSQUID sensor. The nearly optimum flux coupling between these nanomagnets and the microSQUID improves the achievable sensitivity by a factor 100, enabling us to measure the linear susceptibility of the molecular array down to very low temperatures (13 mK). This method opens the possibility of applying ac susceptibility experiments to characterize two-dimensional arrays of single molecule magnets within a wide range of temperatures and frequencies.Comment: 4 pages 3 figure

    Enhancement of the liquefaction rate in small-scale helium liquefiers working near and above the critical point

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    Letter.-- et al.Low-temperature research laboratories with typical liquid-helium consumption of the order of tens of liters per day have greatly benefited from the recent development of small-scale liquefiers. In general, these liquefiers are based on Gifford-McMahon or pulse-tube closed-cycle refrigerators with a nominal cooling power ranging from 1 to 1.5 W at 4.2 K. The liquefaction rate for these cryocooler-based liquefiers depends on the pressure at which the helium is liquefied, although the final user conditions of the produced liquid helium are always atmospheric pressure and boiling temperature (e.g., 4.2 K at 100 kPa). Here, we show a systematic study on this effect, in which an enhancement in excess of 70% in liquefaction rate is found experimentally for pressures near and above the critical point of helium (220 kPa). We propose that the underlying mechanism for the liquefaction enhancement is based on the increase in cryocooler cooling power with temperature and the decrease of the helium enthalpy with pressure.Financial support from the Spanish Ministry of Economy and Competitiveness through Project No. IPT-2012-0442-420000, in addition to European Union FEDER funds, is gratefully acknowledged.Peer Reviewe

    Accurate measurements of small currents using a CCC with DC SQUID read out

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    The continuous miniaturisation in the semiconductor industry increases the importance of accurate measurement and control of very small currents. In the field of precision electrical measurements, cryogenic current comparators (CCCs) are used as extremely sensitive and accurate instruments for scaling currents. In an international co-operation project, a special CCC system is being developed, optimised for the measurement of extremely small currents to less than 1 pA (10−12 A). DC superconducting quantum interference device (SQUID) readout is used for monitoring the ampere-turn unbalance of the CCC. In this paper, we report on the accurate determination of the CCC and SQUID input coil inductances. Matching of these inductances is required for obtaining ultimate current resolution with the CCC. We find very good agreement between measurements of the CCC inductance at room temperature and at 4.2 K, and results from numerical calculations. The measured values for the input and mutual inductance of the SQUID sensor are in good agreement with the design values when the effect of the slit in the SQUID washer is correctly taken into account. Final current resolution of our measurement system is expected to be better than 1×10−15 A/√Hz for a CCC with 20,000 primary windings
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