Charge response function and a novel plasmon mode in graphene

Polarizability of non-interacting 2D Dirac electrons has a 1/\sqrt{qv-\omega} singularity at the boundary of electron-hole excitations. The screening of this singularity by long-range electron-electron interactions is usually treated within the random phase approximation. The latter is exact only in the limit of N -> infinity, where N is the ``color'' degeneracy. We find that the ladder-type vertex corrections become crucial close to the threshold as the ratio of the n-th order ladder term to the same order RPA contribution is (\ln|qv-\omega|)^n/N^n$. We perform analytical summation of the infinite series of ladder diagrams which describe excitonic effect. Beyond the threshold, qv>\omega, the real part of the polarization operator is found to be positive leading to the appearance of a strong and narrow plasmon resonance.Comment: 4 pages, 3 figures,typos correcte

High-Resolution Microscopy And Microanalysis In Oral Biology And Dentistry.

The oral region contains all types of mineralized tissues found in the body. Its nonnalmucosa lining exhibits a greater variation in histo-structure than found in the entire skin surface

P2Y2 nucleotide receptor activation enhances the aggregation and self-organization of dispersed salivary epithelial cells

"May 2014."Dissertation Advisor: Dr. Gary A Weisman.Includes vita.Salivary gland dysfunction affects millions of Americans whose quality of life is severely impacted by dry mouth, oral bacterial infections, poor nutrition, and other disorders that are associated with decreased saliva production. Over the past decade, progress has been made in cell-based reconstitution strategies for salivary glands. Understanding the mechanisms and signaling pathways that regulate the salivary gland reconstitution process is a necessity to enhance the ongoing efforts to develop better regenerative therapies for damaged salivary glands. The P2Y2 nucleotide receptor (P2Y2R), a G protein-coupled receptor equipotently activated by ATP and UTP, is upregulated in a variety of tissues, including salivary gland epithelium, in response to injury or stress and is proposed to play important roles in the regeneration of a variety of tissues. The results presented in this dissertation indicate that P2Y2R activation with UTP enhances the migration, aggregation and self-organization of dispersed salivary epithelial cells forming spheres that display characteristics similar to differentiated acini in salivary glands. Moreover, our data suggest that the afore- mentioned P2Y2R-mediated response s depend on the transactivation of the epidermal growth factor receptor (EGFR) via a disintegrin and metalloproteinases (ADAM10/ADAM17) and the [alpha-5 beta-1] integrin/Cdc42 Rho GTPase signaling pathway. This study sheds light on the P2Y2R as a target in salivary gl and reconstitution strategies and introduces [alpha-5 beta-1] integrin and Cdc42 as novel downstream components in the P2Y 2 R-mediated signaling network. Future studies will optimize the activation of P2Y2R-mediated signaling pathways to promote the self- organization of salivary epithelial cells into acinar-like spheres that secrete saliva components and have utility for replacement of salivary gland tissue damaged by autoimmune disease or radiation therapy used to treat head and neck cancers.Includes bibliographical references (pages 62-84)

Optical Conductivity of a Two-Dimensional Electron Liquid with Spin-Orbit Interaction

The interplay of electron-electron interactions and spin-orbit coupling leads to a new contribution to the homogeneous optical conductivity of the electron liquid. The latter is known to be insensitive to many-body effects for a conventional electron system with parabolic dispersion. The parabolic spectrum has its origin in the Galilean invariance which is broken by spin-orbit coupling. This opens up a possibility for the optical conductivity to probe electron-electron interactions. We analyze the interplay of interactions and spin-orbit coupling and obtain optical conductivity beyond RPA.Comment: 5 pages, 3 figures; final version, fig. 3 added, minor change