Role of the conduction electrons in mediating exchange interactions in Heusler alloys

Because of large spatial separation of the Mn atoms in Heusler alloys the Mn 3d states belonging to different atoms do not overlap considerably. Therefore an indirect exchange interaction between Mn atoms should play a crucial role in the ferromagnetism of the systems. To study the nature of the ferromagnetism of various Mn-based semi- and full-Heusler alloys we perform a systematic first-principles calculation of the exchange interactions in these materials. The calculation of the exchange parameters is based on the frozen-magnon approach. The calculations show that the magnetism of the Mn-based Heusler alloys depends strongly on the number of conduction electrons, their spin polarization and the position of the unoccupied Mn 3d states with respect to the Fermi level. Various magnetic phases are obtained depending on the combination of these characteristics. The Anderson's s-d model is used to perform a qualitative analysis of the obtained results. The conditions leading to diverse magnetic behavior are identified. If the spin polarization of the conduction electrons at the Fermi energy is large and the unoccupied Mn 3d states lie well above the Fermi level, an RKKY-type ferromagnetic interaction is dominating. On the other hand, the contribution of the antiferromagnetic superexchange becomes important if unoccupied Mn 3d states lie close to the Fermi energy. The resulting magnetic behavior depends on the competition of these two exchange mechanisms. The calculational results are in good correlation with the conclusions made on the basis of the Anderson s-d model which provides useful framework for the analysis of the results of first-principles calculations and helps to formulate the conditions for high Curie temperature.Comment: 16 pages, 9 figures, 2 table

Identification of R gene genotypes in Japanese wheat cultivars

Dissertação de mestrado em Psicologia Clínica e da Saúde (Psicopatologia e Psicoterapias Dinâmicas), apresentada à Faculdade de Psicologia e de Ciências da Educação da Universidade de CoimbraA presente investigação visa explorar múltiplas variáveis (sociodemográficas, clínicas e satisfação com o suporte social) na relação com o bonding materno. O nosso principal objetivo foi perceber quais as diferenças entre as mães adultas e as mães adolescentes relativamente à forma como se vinculam (bonding) ao seu bebé, para isso procedemos às entrevistas de 57 mães, em que 29 são mães adultas e 28 são mães adolescentes. Consoante os nossos resultados, pudemos inferir que as mães adolescentes apresentam valores de bonding inferiores aos valores das mães adultas. Quando comparamos o bonding com o suporte social também verificamos que as mães adolescentes apresentam valores de perceção do suporte social inferiores aos valores das mães adultas. Deste modo, a relação mãe-bebé vai sendo fortalecida consoante aumenta a idade das mães e a perceção que as mesmas têm em relação ao suporte social.The present investigation pretends to explore multiple variables (sociodemographic, clinic, and satisfaction with social support) and its relation to maternal bonding. Our main goal was to understand which are the differences between adult mothers and teenage mothers as how they are bond to their baby. We interviewed 57 mothers, in which 29 are adult mothers and 28 are adolescent mothers. From our results, we infer that teenage mothers have lower values than adult mothers on bonding. When we compare bonding with social support we also found that teenage mothers have lower values of social support perception relatively to adult mothers. We also conclude that mother-baby relationship and social support perception will be strengthened as mothers grow older

Shape control of QDs studied by cross-sectional scanning tunneling microscopy

In this cross-sectional scanning tunneling microscopy study we investigated various techniques to control the shape of self-assembled quantum dots (QDs) and wetting layers (WLs). The result shows that application of an indium flush during the growth of strained InGaAs/GaAs QD layers results in flattened QDs and a reduced WL. The height of the QDs and WLs could be controlled by varying the thickness of the first capping layer. Concerning the technique of antimony capping we show that the surfactant properties of Sb result in the preservation of the shape of strained InAs/InP QDs during overgrowth. This could be achieved by both a growth interrupt under Sb flux and capping with a thin GaAsSb layer prior to overgrowth of the uncapped QDs. The technique of droplet epitaxy was investigated by a structural analysis of strain free GaAs/AlGaAs QDs. We show that the QDs have a Gaussian shape, that the WL is less than 1 bilayer thick, and that minor intermixing of Al with the QDs takes place.Comment: 7 pages, 10 figure

Quark condensate in nuclear matter based on Nuclear Schwinger-Dyson formalism

The effects of higher order corrections of ring diagrams for the quark condensate are studied by using the bare vertex Nuclear Schwinger Dyson formalism based on $\sigma$-$\omega$ model. At the high density the quark condensate is reduced by the higher order contribution of ring diagrams more than the mean field theory or the Hartree-Fock

Shape control of QDs studied by cross-sectional scanning tunneling microscopy

In this cross-sectional scanning tunneling microscopy study we investigated various techniques to control the shape of self-assembled quantum dots (QDs) and wetting layers (WLs). The result shows that application of an indium flush during the growth of strained InGaAs/GaAs QD layers results in flattened QDs and a reduced WL. The height of the QDs and WLs could be controlled by varying the thickness of the first capping layer. Concerning the technique of antimony capping we show that the surfactant properties of Sb result in the preservation of the shape of strained InAs/InP QDs during overgrowth. This could be achieved by both a growth interrupt under Sb flux and capping with a thin GaAsSb layer prior to overgrowth of the uncapped QDs. The technique of droplet epitaxy was investigated by a structural analysis of strain free GaAs/AlGaAs QDs. We show that the QDs have a Gaussian shape, that the WL is less than 1 bilayer thick, and that minor intermixing of Al with the QDs takes place.Comment: 7 pages, 10 figure

Expression and clinical significance of erb-B receptor family in hepatocellular carcinoma

In order to elucidate the clinical significance of the erbB family, epidermal growth factor receptor (EGF-R), c-erbB-2, c-erbB-3 and c-erbB-4 in hepatocellular carcinoma (HCC), we investigated the expression of these proteins by means of immunohistochemistry for HCC as well as adjacent noncancerous lesions. EGF-R was expressed in 68% of the HCC examined and showed correlation with the proliferating activity, stage, intrahepatic metastasis and carcinoma differentiation. c-erbB-2 was expressed in only 21% of the cases and showed no relationships with the clinicopathological parameters. c-erbB-3 protein was observed in 84% of the HCC and 38.1% of the noncancerous lesions. Its expression in HCC was equal to or greater than noncancerous lesions in 90.5% of the cases, and was related to the stage, portal invasion, cell proliferating activity, tumour size, intrahepatic metastasis and carcinoma differentiation. c-erbB-4 protein was expressed in 61.0% of HCC and in as much as 86.1% of the noncancerous lesions. Unlike the expression of c-erbB-3, that of c-erbB-4 in HCC was less than that of the adjacent noncancerous lesions in 51.2% of the cases. No statistical significance could be established between this protein expression in HCC and clinicopathological features. EGF-R and c-erbB-3 affected disease-free survival, but were not recognized as independent prognostic factors by multivariate analysis. The present study suggests that, of the four receptors, EGF-R and c-erbB-3 play important roles in the progression of HCC. © 2001 Cancer Research Campaign www.bjcancer.co

Lattice dynamics and structural stability of ordered Fe3Ni, Fe3Pd and Fe3Pt alloys

We investigate the binding surface along the Bain path and phonon dispersion relations for the cubic phase of the ferromagnetic binary alloys Fe3X (X = Ni, Pd, Pt) for L12 and DO22 ordered phases from first principles by means of density functional theory. The phonon dispersion relations exhibit a softening of the transverse acoustic mode at the M-point in the L12-phase in accordance with experiments for ordered Fe3Pt. This instability can be associated with a rotational movement of the Fe-atoms around the Ni-group element in the neighboring layers and is accompanied by an extensive reconstruction of the Fermi surface. In addition, we find an incomplete softening in [111] direction which is strongest for Fe3 Ni. We conclude that besides the valence electron density also the specific Fe-content and the masses of the alloying partners should be considered as parameters for the design of Fe-based functional magnetic materials.Comment: Revised version, accepted for publication in Physical Review