514 research outputs found
Partial Kekule Ordering of Adatoms on Graphene
Electronic and transport properties of Graphene, a one-atom thick crystalline
material, are sensitive to the presence of atoms adsorbed on its surface. An
ensemble of randomly positioned adatoms, each serving as a scattering center,
leads to the Bolzmann-Drude diffusion of charge determining the resistivity of
the material. An important question, however, is whether the distribution of
adatoms is always genuinely random. In this Article we demonstrate that a
dilute adatoms on graphene may have a tendency towards a spatially correlated
state with a hidden Kekule mosaic order. This effect emerges from the
interaction between the adatoms mediated by the Friedel oscillations of the
electron density in graphene. The onset of the ordered state, as the system is
cooled below the critical temperature, is accompanied by the opening of a gap
in the electronic spectrum of the material, dramatically changing its transport
properties
Point mutations of the P53 gene, human hepatocellular carcinoma and aflatoxins
The tumor suppressor p53 exerts important protective functions towards DNA-damaging agents. Its inactivation by allelic deletions or point mutations within the P53 gene as well as complex formation of wildtype p53 with cellular or viral proteins is a common and crucial event in carcinogenesis. Mutations increase the half-life of the p53 protein allowing the immunohistochemical detection and anti-p53 antibody formation. Distinct G to T point mutations in codon 249 leading to a substitution of the basic amino acid arginine by the neutral amino acid serin are responsible for the altered functionality of the mutant gene product and were originally identified in 8 of 16 Chinese and 5 of 10 African HCC patients. Both groups are frequently exposed to mycotoxin contaminations of their food. Today an average P53 gene mutation rate of 25% is assumed for high-aflatoxin B1-exposure regions. This is double the rate observed in low-aflatoxin B1-exposure countries. Although many HCC patients displaying P53 mutations also suffer from HBV infection, which itself can lead to rearrangements of P53 coding regions or induce the synthesis of viral proteins possibly interacting with p53, the specific G to T transversion within codon 249 of the P53 gene seems to directly reflect the extent of aflatoxin B1 exposure
Electronic Properties of Graphene in a Strong Magnetic Field
We review the basic aspects of electrons in graphene (two-dimensional
graphite) exposed to a strong perpendicular magnetic field. One of its most
salient features is the relativistic quantum Hall effect the observation of
which has been the experimental breakthrough in identifying pseudo-relativistic
massless charge carriers as the low-energy excitations in graphene. The effect
may be understood in terms of Landau quantization for massless Dirac fermions,
which is also the theoretical basis for the understanding of more involved
phenomena due to electronic interactions. We present the role of
electron-electron interactions both in the weak-coupling limit, where the
electron-hole excitations are determined by collective modes, and in the
strong-coupling regime of partially filled relativistic Landau levels. In the
latter limit, exotic ferromagnetic phases and incompressible quantum liquids
are expected to be at the origin of recently observed (fractional) quantum Hall
states. Furthermore, we discuss briefly the electron-phonon coupling in a
strong magnetic field. Although the present review has a dominating theoretical
character, a close connection with available experimental observation is
intended.Comment: 56 pages, 27 figures; published version with minor corrections and
updated reference
Polarized light bursts from kicked quantum rings
Non-equilibrium quantum rings emit circular polarized subterahertz radiation
with a polarization degree controllable on nano- to picosecond time scales.
This we conclude using a theory developed here for the time-dependent detection
of the circular polarization of polychromatic radiations, valid for time scales
comparable to the reciprocal of characteristic emission frequencies. The theory
is applied to driven quantum rings whereby the influence of radiative and
non-radiative processes on the properties of the emitted light is incorporated.Comment: 4 pages, 2 figures; submitted to Phys. Rev. Let
What's in a name? - A short history of coordination chemistry from then to now
This article traces the development of coordination chemistry and shows how progress in the science has been paralleled by the development of a vocabulary and nomenclature to describe new concepts, structural features and compound types
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