81 research outputs found
SPECT: A spin-flip loaded magnetic ultracold neutron trap for a determination of the neutron lifetime
The confinement of ultracold neutrons (UCNs) in a three dimensional magnetic
field gradient trap allows for a measurement of the free neutron lifetime with
superior control over spurious loss channels and can provide a large kinetic
energy acceptance to enhance statistical sensitivity. In this paper, we present
the first successful implementation of a pulsed spin-flip based loading scheme
for a three-dimensional magnetic UCN trap. The measurements with the
SPECT experiment were performed at the pulsed UCN source of the research
reactor TRIGA Mainz. We report on detailed investigations of major systematic
effects influencing the neutron storage time, statistically limited by the size
of the recorded data set. The extracted neutron storage time constant of is compatible with, but not to be interpreted as, a
measurement of the free neutron lifetime.Comment: 15 pages, 19 figure
Influence of spin fluctuations on the superconducting transition temperature and resistivity in the t-J model at large N
Spin fluctuations enter the calculation of the superconducting transition
temperature T only in the next-to-leading order (i.e., in O(1/N) of the
1/N expansion of the t-J model. We have calculated these terms and show that
they have only little influence on the value of T obtained in the leading
order O(1/N) in the optimal and overdoped region, i.e., for dopings larger than
the instability towards a flux phase. This result disagrees with recent
spin-fluctuation mediated pairing theories. The discrepancies can be traced
back to the fact that in our case the coupling between electrons and spins is
determined by the t-J model and not adjusted and that the spin susceptibility
is rather broad and structureless and not strongly peaked at low energies as in
spin-fluctuation models. Relating T and transport we show that the
effective interactions in the particle-particle and particle-hole channels are
not simply related within the 1/N expansion by different Fermi surface averages
of the same interactin as in the case of phonons or spin fluctuations. As a
result, we find that large values for T and rather small scattering rates
in the normal state as found in the experiments can easily be reconciled with
each other. We also show that correlation effects heavily suppress transport
relaxation rates relative to quasiparticle relaxation rates in the case of
phonons but not in the case of spin fluctuations.Comment: 16 pages, 10 figures, will appear in Phys. Rev.
The World Karst Aquifer Mapping project : concept, mapping procedure and map of Europe
Karst aquifers contribute substantially to freshwater supplies in many regions of the world, but are vulnerable to contamination and difficult to manage because of their unique hydrogeological characteristics. Many karst systems are hydraulically connected over wide areas and require transboundary exploration, protection and management. In order to obtain a better global overview of karst aquifers, to create a basis for sustainable international water-resources management, and to increase the awareness in the public and among decision makers, the World Karst Aquifer Mapping (WOKAM) project was established. The goal is to create a world map and database of karst aquifers, as a further development of earlier maps. This paper presents the basic concepts and the detailed mapping procedure, using France as an example to illustrate the step-by-step workflow, which includes generalization, differentiation of continuous and discontinuous carbonate and evaporite rock areas, and the identification of non-exposed karst aquifers. The map also shows selected caves and karst springs, which are collected in an associated global database. The draft karst aquifer map of Europe shows that 21.6% of the European land surface is characterized by the presence of (continuous or discontinuous) carbonate rocks; about 13.8% of the land surface is carbonate rock outcrop
Comparação entre a ventilação com pressão positiva intermitente ou pressão controlada em equinos. Parte I: parâmetros ventilatórios e da mecânica respiratória
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Soil structural quality degradation by the increase in grazing intensity in integrated crop-livestock system
The Oldest Case of Decapitation in the New World (Lapa do Santo, East-Central Brazil)
We present here evidence for an early Holocene case of decapitation in the New World (Burial 26), found in the rock shelter of Lapa do Santo in 2007. Lapa do Santo is an archaeological site located in the Lagoa Santa karst in east-central Brazil with evidence of human occupation dating as far back as 11.7-12.7 cal kyBP (95.4% interval). An ultra-filtered AMS age determination on a fragment of the sphenoid provided an age range of 9.1-9.4 cal kyBP (95.4% interval) for Burial 26. The interment was composed of an articulated cranium, mandible and first six cervical vertebrae. Cut marks with a v-shaped profile were observed in the mandible and sixth cervical vertebra. The right hand was amputated and laid over the left side of the face with distal phalanges pointing to the chin and the left hand was amputated and laid over the right side of the face with distal phalanges pointing to the forehead. Strontium analysis comparing Burial 26's isotopic signature to other specimens from Lapa do Santo suggests this was a local member of the group. Therefore, we suggest a ritualized decapitation instead of trophy-taking, testifying for the sophistication of mortuary rituals among hunter-gatherers in the Americas during the early Archaic period. In the apparent absence of wealth goods or elaborated architecture, Lapa do Santo's inhabitants seemed to use the human body to express their cosmological principles regarding death
INVESTIGAÇÃO TEMÁTICA NA FORMAÇÃO DE PROFESSORES DE CIÊNCIAS EM PAU BRASIL-BA: COMPREENSÕES ACERCA DE UM TEMA GERADOR
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