1,714 research outputs found
Paleoenvironmental dynamics during the last 135.000 years at the Upper Jiloca basin area : the lacustrine record of "El Cañizar"
359 páginas - Tesis presentada para optar al grado de Doctor en Física Aplicada por la Universidad de ZaragozaPeer reviewe
CLIWOC multilingual meteorological dictionary
This dictionary is the first attempt to express the wealth of archaic logbook wind force terms in a form that is comprehensible to the modern-day reader. Oliver and Kington (1970) and Lamb (1982) have drawn attention to the importance of logbooks in climatic studies, and Lamb (1991) offered a conversion scale for early eighteenth century English wind force terms, but no studies have thus far pursued the matter to any greater depth. This text attempts to make good this deficiency, and is derived from the research undertaken by the CLIWOC project1 in which British, Dutch, French and Spanish naval and merchant logbooks from the period 1750 to 1850 were used to derive a global database of climatic information. At an early stage in the project it was apparent that many of the logbook weather terms, whilst conforming to a conventional vocabulary, possessed meanings that were unclear to twenty-first century readers or had changed over time. This was particularly the case for the important element of wind force; but no special plea is entered for the evolution in nautical vocabulary, which often reflected more wide-ranging changes in the respective native languages.The key objective was to translate the archaic vocabulary of the late eighteenth and early nineteenth century mariner into expressions directly comparable with the Beaufort Scale (see Appendix I). Only then could the projects scientific programme be embarked upon. This dictionary is the result of the largest undertaking into logbook studies that has yet been carried out. Several thousand logbooks from British, Dutch, French and Spanish archives were examined, and the exercise offered a unique opportunity to explore the vocabulary of the one hundred year period beginning in 1750. The logbooks from which the raw data have been abstracted range widely across the North and South Atlantic and the Indian Oceans. Only the Pacific, largely in consequence of the paucity of regular naval activity in that area, is not well represented. The range of climates encountered in this otherwise wide geographic domain gives ample opportunity for the full range of the mariners nautical weather vocabulary to be assessed, from the calms of the Equatorial regions, through the gales of the mid-latitude systems to the fearsome storms of the tropical latitudes. The Trade Winds belts, the Doldrums, the unsettled mid-latitudes, even the icy wastes of the high latitudes, are all embraced in this study. It is not here intended to pass any judgements on the climatological record of the logbooks, and this text seeks only to provide a means of understanding archaic wind force terms and, other than to indicate those items that were not commonly used, no information is given on the frequency with which different terms appeared in the logbooks. Attention is, furthermore, confined to Dutch, English, French and Spanish because these once great imperial powers were the only nations able to support wide-ranging ocean-going fleets with their attendant collections of logbooks and documents over this long period of time. The work is offered to the wider academic community in the hope that they will prove to be of as much value as it has been to the CLIWOC team
Correlation between Mn oxidation state and magnetic behavior in Mn/ZnO multilayers prepared by sputtering
Compositional, microstructural, and magnetic characterization of ZnO 30 Å/Mn x n multilayers
prepared by sputtering is presented to study the observed ferromagnetism in the Mn-ZnO system.
The nominal Mn layer thickness, x, is varied from 3 to 60 Å, while the number of bilayers, n, is
increased to maintain the total amount of Mn constant. Microstructure information was deduced
from x-ray reflectivity, Mn oxidation state was determined by x-ray absorption spectroscopy, and
magnetic properties were measured over a temperature range of 5–400 K. Magnetic behavior of
these samples is found to be related to the Mn layer thickness x. Multilayers with x 30 Å exhibit
ferromagnetism with a Curie temperature above 400 K, while mostly paramagnetic behavior is
obtained for x15 Å. Magnetic behavior is discussed in terms of electronic and structural
parameters of samples. Mn-ZnO interface effect is related to the ferromagnetic order of the samples,
but it is not a sufficient condition. The essential role of the Mn oxidation state in the magnetic
behavior of this system is pointed out. It is shown a correlation between the obtained
ferromagnetism and a Mn oxidation state close to 2+.Ministerio de Educación y Ciencias de España-MAT2003-01880 y MAT2006-0100
Quantifying Li-content for compositional tailoring of lithium ferrite ceramics
Owing to their multiple applications, lithium ferrites are relevant materials
for several emerging technologies. For instance, LiFeO2 has been spotted as an
alternative cathode material in Li-ion batteries, while LiFe5O8 is the lowest
damping ferrite, holding promise in the field of spintronics. The Li-content in
lithium ferrites has been shown to greatly affect the physical properties, and
in turn, the performance of functional devices based on these materials.
Despite this, lithium content is rarely accurately quantified, as a result of
the low number of electrons in Li hindering its identification by means of
routine materials characterization methods. In the present work, magnetic
lithium ferrite powders with Li:Fe ratios of 1:1, 1:3 and 1:5 have been
synthesized, successfully obtaining phase-pure materials (LiFeO2 and LiFe5O8),
as well as a controlled mixture of both phases. The powders have been compacted
and subsequently sintered by thermal treatment (Tmax = 1100 {\deg}C) to
fabricate dense pellets which preserve the original Li:Fe ratios. Li-content on
both powders and pellets has been determined by two independent methods: (i)
Rutherford backscattering spectroscopy combined with nuclear reaction analysis
and (ii) Rietveld analysis of powder X-ray diffraction data. With good
agreement between both techniques, it has been confirmed that the Li:Fe ratios
employed in the synthesis are maintained in the sintered ceramics. The same
conclusion is drawn from spatially-resolved confocal Raman microscopy
experiments on regions of a few microns. Field emission scanning electron
microscopy has evidenced the substantial grain growth taking place during the
sintering process - mean particle sizes rise from about 600 nm in the powders
up to 3.8(6) um for dense LiFeO2 and 10(2) um for LiFe5O8 ceramics
Epitaxial integration of CoFe₂O₄ thin films on Si (001) surfaces using TiN buffer layers
Epitaxial cobalt ferrite thin films with strong in-plane magnetic anisotropy have been grown on Si (001) substrates using a TiN buffer layer. The epitaxial films have been grown by ion beam sputtering using either metallic, CoFe₂, or ceramic, CoFe₂2O₄, targets. X-ray diffraction (XRD) and Rutherford spectrometry (RBS) in random and channeling configuration have been used to determine the epitaxial relationship CoFe₂O₄ [100]/TiN [100]/Si [100]. Mossbauer spectroscopy, in combination with XRD and RBS, has been used to determine the composition and structure of the cobalt ferrite thin films. The TiN buffer layer induces a compressive strain in the cobalt ferrite thin films giving rise to an in-plane magnetic anisotropy. The degree of in- plane anisotropy depends on the lattice mismatch between CoFe₂O₂ and TiN, which is larger for CoFe₂O₄ thin films grown on the reactive sputtering process with ceramic targets
Induced ferromagnetism in Mn3N2 phase embedded in Mn/Si3N4 multilayers
Room temperature ferromagnetism has been obtained for different sets of Mn/Si3N4 multilayers
prepared by sputtering. In order to find the most suitable conditions to stabilize the ferromagnetic
ordering in this system, the evolution of the magnetic properties has been studied for films in which
the Si3N4 layer thickness was maintained constant while that of the Mn layer was varied,
Mn tm/Si3N4 3.4 nm n, and conversely, in Mn 0.7 nm/Si3N4 tsn 43 samples, in which the Mn
layer thickness was kept constant while varying the Si3N4 layer thickness. Structural, compositional,
electronic and magnetic characterizations have been performed by means of x-ray reflectometry,
Rutherford backscattering spectrometry, x-ray photoemission spectroscopy, x-ray absorption, and
superconducting quantum interference device for further knowledge of the magnetic-structural
relationship in this system. Our results show that the peculiar magnetic behavior of these films is
mainly related to the stabilization of a slightly distorted Mn3N2 phase that is induced by the Si3N4
at the interfaces. For samples with larger Mn layer thickness, metallic Mn and Mn3N2 phases
coexist, which leads to a reduction of the total magnetization per Mn atom due to the presence of
metallic Mn. For small Mn layer thickness tm 0.86 nm, where noncontinuous Mn3N2 layers are
formed, the magnetization decreases noticeably due to the superparamagnetic size limit. It has been
found that the best conditions for the stabilization of the ferromagnetism in this system occur when
both, the manganese-rich and the silicon nitride layers, are continuous and with similar thickness,
close to 3.5 nm.Ministerio de Educación y Ciencia de España-MAT2006-01004, MAT2008-06542-C04-01, MAT2008-06765-C02-02, S-0505/MAT/0194, Consolider 2010_26400 y Nanoselect CSD2007-0004
CompareML: A Novel Approach to Supporting Preliminary Data Analysis Decision Making
There are a large number of machine learning algorithms as well as a wide range of libraries and services that allow one to create predictive models. With machine learning and artificial intelligence playing a major role in dealing with engineering problems, practising engineers often come to the machine learning field so overwhelmed with the multitude of possibilities that they find themselves needing to address difficulties before actually starting on carrying out any work. Datasets have intrinsic properties that make it hard to select the algorithm that is best suited to some specific objective, and the ever-increasing number of providers together make this selection even harder. These were the reasons underlying the design of CompareML, an approach to supporting the evaluation and comparison of machine learning libraries and services without deep machine learning knowledge. CompareML makes it easy to compare the performance of different models by using well-known classification and regression algorithms already made available by some of the most widely used providers. It facilitates the practical application of methods and techniques of artificial intelligence that let a practising engineer decide whether they might be used to resolve hitherto intractable problems. Thus, researchers and engineering practitioners can uncover the potential of their datasets for the inference of new knowledge by selecting the most appropriate machine learning algorithm and determining the provider best suited to their data
- …