232 research outputs found
Pairing mechanism in Fe pnictide superconductors
By applying an exact unitary transformation to a two-band hamiltonian which
also includes the effects due to large pnictogen polarizabilities, we show that
an attractive spin-mediated Hubbard term appears in the ,
nearest-neighbour channel. This pairing mechanism implies a singlet
superconducting order parameter in iron pnictides.Comment: 4 pages, 3 figure
Diagnosis of gastric carcinoma by classification on feature projections
Cataloged from PDF version of article.A new classification algorithm, called benefit maximizing classifier on feature projections (BCFP), is developed and applied to the problem of diagnosis of gastric carcinoma. The domain contains records of patients with known diagnosis through gastroscopy results. Given a training set of such records, the BCFP classifier learns how to differentiate a new case in the domain. BCFP represents a concept in the form of feature projections on each feature dimension separately. Classification in the BCFP algorithm is based on a voting among the individual predictions made on each feature. In the gastric carcinoma domain, a lesion can be an indicator of one of nine different Levels of gastric carcinoma, from early to late stages. The benefit of correct classification of early levels is much more than that of late cases. Also, the costs of wrong classifications are not symmetric. In the training phase, the BCFP algorithm learns classification rules that maximize the benefit of classification. In the querying phase, using these rules, the BCFP algorithm tries to make a prediction maximizing the benefit. A genetic algorithm is applied to select the relevant features. The performance of the BCFP algorithm is evaluated in terms of accuracy and running time. The rules induced are verified by experts of the domain. (C) 2004 Elsevier B.V. All rights reserved
Strong coupling between magnetic and structural order parameters in SrFe2As2
X-ray and Neutron diffraction as well as muon spin relaxation and M\"ossbauer
experiments performed on SrFeAs polycrystalls confirm a sharp first
order transition at ,K corresponding to an orthorhombic phase
distortion and to a columnar antiferromagnetic Fe ordering with a propagation
vector (1,0,1), and a larger distortion and larger size of the ordered moment
than reported for BaFeAs. The structural and the magnetic order
parameters present an remarkable similarity in their temperature dependence
from down to low temperatures, showing that both phenomena are intimately
connected. Accordingly, the size of the ordered Fe moments scale with the
lattice distortion when going from SrFeAs to BaFeAs.
Full-potential band structure calculations confirm that the columnar magnetic
order and the orthorhombic lattice distortion are intrinsically tied to each
other.Comment: 10 pages, 4 figure
Magnetic and structural transitions in layered FeAs systems: AFe2As2 versus RFeAsO compounds
Resistivity, specific heat and magnetic susceptibility measurements performed
on SrFe2As2 samples evidence a behavior very similar to that observed in
LaFeAsO and BaFe2As2 with the difference that the formation of the SDW and the
lattice deformation occur in a pronounced first order transition at T_0=205K.
Comparing further data evidences that the Fe-magnetism is stronger in SrFe2As2
and in EuFe2As2 than in the other layered FeAs systems investigated up to now.
Full potential LDA band structure calculations confirm the large similarity
between the compounds, especially for the relevant low energy Fe 3d states. The
relation between structural details and magnetic order is analyzed.Comment: 4 pages, 3 figure
Low-temperature synthesis of SmFeAsO0.7F0.3 wires with high transport critical current density
Ag-sheathed SmFeAsO0.7F0.3 (Sm-1111) superconducting wires were prepared by a
one-step solid state reaction at temperatures as low as 850~900C, instead of
commonly used temperatures of 1150~1250C. The X-ray diffraction pattern of the
as-sintered samples is well indexed on the basis of tetragonal ZrCuSiAs-type
structure. We characterized transport critical current density Jc of the
SmFeAsO0.7F0.3 wires in increasing and subsequently decreasing fields, by a
resistive four-probe method. A transport Jc as high as ~1300 A/cm^2 at 4.2 K
and self field has been observed for the first time in Sm-1111 type
polycrystalline superconductors. The Jc also shows a rapid depression in small
applied fields as well as a magnetic-history dependence, indicating weak-linked
grain boundaries. The low-temperature synthesis method can be very beneficial
to fabricating the RE-1111 iron oxynictides in a convenient and safe way.Comment: 12 pages, 3 figure
Simple Metals at High Pressure
In this lecture we review high-pressure phase transition sequences exhibited
by simple elements, looking at the examples of the main group I, II, IV, V, and
VI elements. General trends are established by analyzing the changes in
coordination number on compression. Experimentally found phase transitions and
crystal structures are discussed with a brief description of the present
theoretical picture.Comment: 22 pages, 4 figures, lecture notes for the lecture given at the Erice
course on High-Pressure Crystallography in June 2009, Sicily, Ital
Electronic structure of SrPt_4Ge_{12}: a combined photoelectron spectroscopy and band structure study
We present a combined study of the electronic structure of the
superconducting skutterudite derivative SrPt4Ge12 by means of X-ray
photoelectron spectroscopy and full potential band structure calculations
including an analysis of the chemical bonding. We establish that the states at
the Fermi level originate predominantly from the Ge 4p electrons and that the
Pt 5d shell is effectively full. We find excellent agreement between the
measured and the calculated valence band spectra, thereby validating that band
structure calculations in combination with photoelectron spectroscopy can
provide a solid basis for the modeling of superconductivity in the compounds
MPt4Ge12 (M = Sr, Ba, La, Pr) series
Al<sub>2</sub>Pt fĂŒr die Sauerstoffentwicklungsreaktion bei der Wasserspaltung: eine Strategie zur Erzeugung von MultifunktionalitĂ€t in der Elektrokatalyse
Die Herstellung von Wasserstoff durch Wasserelektrolyse ist nur möglich, wenn wirksame und stabile Katalysatoren fĂŒr die Sauerstoffentwicklungsreaktion (Oxygen Evolution Reaction, OER) verfĂŒgbar sind. Intermetallische Verbindungen mit genau definierter Kristallstruktur und elektronischen Eigenschaften sowie besonderer chemischer Bindung werden als Vorstufe fĂŒr neue Werkstoffe vorgeschlagen, die interessante katalytische Eigenschaften aufweisen. Al2Pt kristallisiert im AntiâFluoritâKristallstrukturtyp und zeigt eine stark polare chemische Bindung. Platin ist hierbei katalytisch aktiv und wird auch unter den Bedingungen der Sauerstoffentwicklungsreaktion vergleichsweise wenig aus der KatalysatoroberflĂ€che herausgelöst. Im Folgenden wird die unerwartete LeistungsfĂ€higkeit einer OberflĂ€chenâNanokompositâArchitektur beschrieben, die aus der selbstorganisierten Umwandlung der intermetallischen Vorstufe Al2Pt resultiert. Hierbei wird insbesondere das Langzeitverhalten der katalytischen AktivitĂ€t und StabilitĂ€t unter den Bedingungen der Sauerstoffentwicklungsreaktion untersucht
AFe2As2 (A = Ca, Sr, Ba, Eu) and SrFe_(2-x)TM_(x)As2 (TM = Mn, Co, Ni): crystal structure, charge doping, magnetism and superconductivity
The electronic structure and physical properties of the pnictide compound
families OFeAs ( = La, Ce, Pr, Nd, Sm), FeAs ( = Ca,
Sr, Ba, Eu), LiFeAs and FeSe are quite similar. Here, we focus on the members
of the FeAs family whose sample composition, quality and single
crystal growth are better controllable compared to the other systems. Using
first principles band structure calculations we focus on understanding the
relationship between the crystal structure, charge doping and magnetism in
FeAs systems. We will elaborate on the tetragonal to
orthorhombic structural distortion along with the associated magnetic order and
anisotropy, influence of doping on the site as well as on the Fe site, and
the changes in the electronic structure as a function of pressure.
Experimentally, we investigate the substitution of Fe in
SrFeAs by other 3 transition metals, = Mn, Co, Ni.
In contrast to a partial substitution of Fe by Co or Ni (electron doping) a
corresponding Mn partial substitution does not lead to the supression of the
antiferromagnetic order or the appearance of superconductivity. Most calculated
properties agree well with the measured properties, but several of them are
sensitive to the As position. For a microscopic understanding of the
electronic structure of this new family of superconductors this structural
feature related to the Fe-As interplay is crucial, but its correct ab initio
treatment still remains an open question.Comment: 27 pages, single colum
Analysis of parcel-based image classification methods for monitoring the activities of the Land Bank of Galicia (Spain)
[EN] The abandonment of agricultural plots entails a low economic productivity of the land and a higher vulnerability to wildfires and degradation of affected areas. In this sense, the local government of Galicia is promoting new methodologies based on high-resolution images in order to classify the territory in basic and generic land uses. This procedure will be used to control the sustainable management of plots belonging to the Land Bank. This paper presents an application study for maintaining and updating land use/land cover geospatial databases using parcel-oriented classification. The test is performed over two geographic areas of Galicia, in the northwest of Spain. In this region, forest and shrublands in mountain environments are very heterogeneous with many private unproductive plots, some of which are in a high state of abandonment. The dataset is made of high spatial resolution multispectral imagery, cadastral cartography employed to define the image objects (plots), and field samples used to define evaluation and training samples. A set of descriptive features is computed quantifying different properties of the objects, i.e. spectral, texture, structural, and geometrical. Additionally, the effect on the classification and updating processes of the historical land use as a descriptive feature is tested. Three different classification methodologies are analyzed: linear discriminant analysis, decision trees, and support vector machine. The overall accuracies of the classifications obtained are always above 90 % and support vector machine method is proved to provide the best performance. Forest and shrublands areas are especially undefined, so the discrimination between these two classes is low. The results enable to conclude that the use of automatic parcel-oriented classification techniques for updating tasks of land use/land cover geospatial databases, is effective in the areas tested, particularly when broad and well defined classes are required.The authors appreciate the collaboration and
support provided by Xunta de Galicia, Sociedade para o Desenvolvemento Comarcal de GalĂcia, and Banco de Terras de Galicia. The
financial support provided by the Spanish Ministerio de Ciencia e
InnovaciĂłn in the framework of the projects CGL2010-19591/BTE
and CGL2009-14220 is also acknowledged.Hermosilla, T.; DĂaz Manso, J.; Ruiz FernĂĄndez, LĂ.; Recio Recio, JA.; FernĂĄndez-SarrĂa, A.; FerradĂĄns Nogueira, P. (2012). Analysis of parcel-based image classification methods for monitoring the activities of the Land Bank of Galicia (Spain). Applied Geomatics. 4(4):245-255. https://doi.org/10.1007/s12518-012-0087-zS24525544Arikan M (2004) Parcel-based crop mapping through multi-temporal masking classification of landsat 7 images in Karacabey, Turkey. Int Arch Photogramm Remote Sens Spat Inf Sci 35:1085â1090Balaguer A, Ruiz LA, Hermosilla T, Recio JA (2010) Definition of a comprehensive set of texture semivariogram features and their evaluation for object-oriented image classification. Comput Geosci 36(2):231â240Balaguer-Besser A, Hermosilla T, Recio JA, Ruiz LA (2011) Semivariogram calculation optimization for object-oriented image classification. 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