7 research outputs found
Density of States of Disordered Two-Dimensional Crystals with Half-Filled Band
A diagrammatic method is applied to study the effects of commensurability in
two-dimensional disordered crystalline metals by using the particle-hole
symmetry with respect to the nesting vector P_0={\pm{\pi}/a, {\pi}/a} for a
half-filled electronic band. The density of electronic states (DoS) is shown to
have nontrivial quantum corrections due to both nesting and elastic impurity
scattering processes, as a result the van Hove singularity is preserved in the
center of the band. However, the energy dependence of the DoS is strongly
changed. A small offset from the middle of the band gives rise to disappearence
of quantum corrections to the DoS .Comment: to be published in Physical Review Letter
Effect of Substitutional Impurities on the Electronic States and Conductivity of Crystals with Half-filled Band
Low temperature quantum corrections to the density of states (DOS) and the
conductivity are examined for a two-dimensional(2D) square crystal with
substitutional impurities. By summing the leading logarithmic corrections to
the DOS its energy dependence near half-filling is obtained. It is shown that
substitutional impurities do not suppress the van Hove singularity at the
middle of the band, however they change its energy dependence strongly. Weak
disorder due to substitutional impurities in the three-dimensional simple cubic
lattice results in a shallow dip in the center of the band. The calculation of
quantum corrections to the conductivity of a 2D lattice shows that the
well-known logarithmic localization correction exists for all band fillings.
Furthermore the magnitude of the correction increases as half-filling is
approached. The evaluation of the obtained analytical results shows evidence
for delocalized states in the center of the band of a 2D lattice with
substitutional impurities
Receptor activator NF kB ligand (RANKL) and osteoprotegerin (OPG) protein expression in periodontitis
The definitive version is available at www.blackwell-synergy.com Article first published online: 26 JUN 2003Objectives and background: This study investigated the expression of key mediators that regulate differentiation of osteoclasts, receptor activator of nuclear factor κB ligand (RANKL), and its natural inhibitor, osteoprotegerin (OPG), in periodontitis. We aimed to compare the levels of the RANKL and OPG in the granulomatous tissue adjacent to areas of alveolar bone loss from patients with periodontitis to that present in tissue from patients without periodontitis. In addition, we aimed to determine the types of cells expressing these factors in these tissues and to demonstrate the expression of the osteoclastic markers, RANK and tartrate-resistant acid phosphatase (TRAP), in periodontitis. Materials and methods: Frozen biopsy specimens were analysed using specific monoclonal antibodies and were evaluated by semiquantitative analysis and digital image analysis to compare levels of RANKL and OPG protein expression. Double labelling of frozen sections with antibodies to different cell lineage specific markers was used to determine the types of cells expressing these proteins. In situ hybridization was used to detect cells expressing RANK mRNA. Results: Semiquantitative image analysis demonstrated that significantly higher levels of RANKL protein (P < 0.05) were expressed in the periodontitis tissue. Conversely, OPG protein was significantly lower (P < 0.05) in the periodontitis tissues. RANKL protein was associated with lymphocytes and macrophages. OPG protein was associated with endothelial cells in both tissues. Many leukocytes expressing RANK mRNA and TRAP were observed in periodontitis tissues. Conclusion: The change in the levels of these key regulators of osteoclast differentiation may play a major role in the bone loss seen in periodontitis.Tania Crotti, Malcolm D. Smith, Robert Hirsch, Steven Soukoulis, Helen Weedon, Maria Capone, Michael J. Ahern, David Hayne
Receptor activator NF kB ligand (RANKL) and osteoprotegerin (OPG) protein expression in periodontitis
35 NORRE SOGADE,PO BOX 2148, COPENHAGEN,
DENMARK, DK-101