Insigths into the tribochemistry of silicon-doped carbon based films by ab initio analysis of water/surface interactions

Diamond and diamond-like carbon (DLC) are used as coating materials for numerous applications, ranging from biomedicine to tribology. Recently, it has been shown that the hydrophilicity of the carbon films can be enhanced by silicon doping, which highly improves their biocompatibility and frictional performances. Despite the relevance of these properties for applications, a microscopic understanding on the effects of silicon is still lacking. Here we apply ab initio calculations to study the interaction of water molecules with Si-incorporated C(001) surfaces. We find that the presence of Si dopants considerably increases the energy gain for water chemisorption and decreases the energy barrier for water dissociation by more than 50%. We provide a physical rational for the phenomenon by analysing the electronic charge displacements occuring upon adsorption. We also show that once hydroxylated, the surface is able to bind further water molecules much strongly than the clean surface via hydrogen-bond networks. This two-step process is consistent with and can explain the enhanced hydrophilic character observed in carbon-based films doped by silicon

Fermi surface and antiferromagnetism in the Kondo lattice: an asymptotically exact solution in d>1 Dimensions

Interest in the heavy fermion metals has motivated us to examine the quantum phases and their Fermi surfaces within the Kondo lattice model. We demonstrate that the model is soluble asymptotically exactly in any dimension d>1, when the Kondo coupling is small compared with the RKKY interaction and in the presence of antiferromagnetic ordering. We show that the Kondo coupling is exactly marginal in the renormalization group sense, establishing the stability of an ordered phase with a small Fermi surface, AFs. Our results have implications for the global phase diagram of the heavy fermion metals, suggesting a Lifshitz transition inside the antiferromagnetic region and providing a new perspective for a Kondo-destroying antiferromagnetic quantum critical point.Comment: 4 pages, 4 figures; (v2) corrected typos and added reference/acknowledgment; (v3) version as published in Physical Review Letters (July, 2007

Origin of the multiferroic spiral spin-order in the RMnO3 perovskites

The origin of the spiral spin-order in perovskite multiferroic manganites $R$MnO$_{3}$ ($RE=$ Tb or Dy) is here investigated using a two $e_{\rm g}$-orbitals double-exchange model. Our main result is that the experimentally observed spiral phase can be stabilized by introducing a relatively weak next-nearest-neighbor superexchange coupling ($\sim10$ of the nearest-neighbor superexchange). Moreover, the Jahn-Teller lattice distortion is also shown to be essential to obtain a realistic spiral period. Supporting our conclusions, the generic phase diagram of undoped perovskite manganites is obtained using Monte Carlo simulations, showing phase transitions from the A-type antiferromagnet, to the spiral phase, and finally to the E-type antiferromagnet, with decreasing size of the $R$ ions. These results are qualitatively explained by the enhanced relative intensity of the superexchanges.Comment: 6 pages, 4 figure

Lysosomes in Mouse Melanoma

The relation between melanoma growth and lysosomal enzyme activities was investigated using B-16 mouse melanoma. The tumor weight began to increase very rapidly after an induction period of 14 days. All the enzyme activities (unit/mg protein) investigated, except for succinic dehydrogenase, showed a rapid increase up to the ninth day after the transplant, then decreased. Tyrosinase and β-Glucuronidase activities showed, at the end of the 29 day growth period results that were equal to half of those recorded on the ninth day. Succinic dehydrogenase activity increased sharply up to the twenty-first day and then decreased. Acid phosphatase activity, on the other hand, was rather steady. An increase in lysosomal enzyme activities was not observed in the later stage of tumor growth, contrary to what had been expected

Degradation of Melanosomes by Lysosomes

The degradation of melanosomes by the lysosomes of the mouse liver was studied in vitro. Mice with melanoma received intraperitoneal injections of a 14C-amino acid mixture and 14C-dopa separately. Radioactive mitochondria and melanosomes were isolated from these mouse melanomas. Digestion of the 14C-amino acid labeled melanosomes and mitochondria was carried out with lysosomes isolated from the mouse liver. The progressive degradation of the protein moiety of the mitochondria was observed and also the slow but steady degradation of melanosomes. Digestion of 14C-dopa labeled melanosomes was attempted with liver lysosomes. There was no significant amount of degradation. Melanin appears to be very resistant to lysosomal digestion in vitro. It is assumed, therefore, that in the compound melanosomes, the melanosomes can be degraded by lysosomes at the protein moiety but not at the melanin moiety