457 research outputs found
Three DNA polymerases, recruited by different mechanisms, carry out NER repair synthesis in human cells
Nucleotide excision repair (NER) is the most versatile DNA repair system that deals with the major UV photoproducts in DNA, as well as many other DNA adducts. The early steps of NER are well understood, whereas the later steps of repair synthesis and ligation are not. In particular, which polymerases are definitely involved in repair synthesis and how they are recruited to the damaged sites has not yet been established. We report that, in human fibroblasts, approximately half of the repair synthesis requires both polκ and polδ, and both polymerases can be recovered in the same repair complexes. Polκ is recruited to repair sites by ubiquitinated PCNA and XRCC1 and polδ by the classical replication factor complex RFC1-RFC, together with a polymerase accessory factor, p66, and unmodified PCNA. The remaining repair synthesis is dependent on polɛ, recruitment of which is dependent on the alternative clamp loader CTF18-RFC
Room-temperature ferromagnetism in graphite driven by 2D networks of point defects
Ferromagnetism in carbon-based materials is appealing for both applications
and fundamental science purposes because carbon is a light and bio-compatible
material that contains only s and p electrons in contrast to traditional
ferromagnets based on 3d or 4f electrons. Here we demonstrate direct evidence
for ferromagnetic order locally at defect structures in highly oriented
pyrolytic graphite (HOPG) with magnetic force microscopy and in bulk
magnetization measurements at room temperature. Magnetic impurities have been
excluded as the origin of the magnetic signal after careful analysis supporting
an intrinsic magnetic behavior of carbon. The observed ferromagnetism has been
attributed to originate from unpaired electron spins localized at grain
boundaries of HOPG. Grain boundaries form two-dimensional arrays of point
defects, where their spacing depends on the mutual orientation of two grains.
Depending on the distance between these point defects, scanning tunneling
spectroscopy of grain boundaries showed two intense split localized states for
small distances between defects (< 4 nm) and one localized state at the Fermi
level for large distances between defects (> 4 nm).Comment: 19 pages, 5 figure
Theory of superconductivity of carbon nanotubes and graphene
We present a new mechanism of carbon nanotube superconductivity that
originates from edge states which are specific to graphene. Using on-site and
boundary deformation potentials which do not cause bulk superconductivity, we
obtain an appreciable transition temperature for the edge state. As a
consequence, a metallic zigzag carbon nanotube having open boundaries can be
regarded as a natural superconductor/normal metal/superconductor junction
system, in which superconducting states are developed locally at both ends of
the nanotube and a normal metal exists in the middle. In this case, a signal of
the edge state superconductivity appears as the Josephson current which is
sensitive to the length of a nanotube and the position of the Fermi energy.
Such a dependence distinguishs edge state superconductivity from bulk
superconductivity.Comment: 5 pages, 2 figure
Quantum oscillations with magnetic hysteresis observed in CeTe thin films
We have performed magnetotransport measurements in CeTe thin films down
to . It is known that CeTe has two magnetic transitions at
and . A clear
Shubnikov-de-Haas (SdH) oscillation was observed at , demonstrating
the strong two-dimensional nature in this material. Below , the SdH
oscillation has two frequencies, indicating that the Fermi surface could be
slightly modulated due to the second magnetic transition. We also observed a
magnetic hysteresis in the SdH oscillation below . Especially,
there is a unique spike in the magnetoresistance at
only when the magnetic field is swept from a high enough field (more than
) to zero field.Comment: 5 pages, 4 figures, accepted for publication in Applied Physics
Letter
Clar's Theory, STM Images, and Geometry of Graphene Nanoribbons
We show that Clar's theory of the aromatic sextet is a simple and powerful
tool to predict the stability, the \pi-electron distribution, the geometry, the
electronic/magnetic structure of graphene nanoribbons with different hydrogen
edge terminations. We use density functional theory to obtain the equilibrium
atomic positions, simulated scanning tunneling microscopy (STM) images, edge
energies, band gaps, and edge-induced strains of graphene ribbons that we
analyze in terms of Clar formulas. Based on their Clar representation, we
propose a classification scheme for graphene ribbons that groups configurations
with similar bond length alternations, STM patterns, and Raman spectra. Our
simulations show how STM images and Raman spectra can be used to identify the
type of edge termination
Electron Wave Function in Armchair Graphene Nanoribbons
By using analytical solution of a tight-binding model for armchair
nanoribbons, it is confirmed that the solution represents the standing wave
formed by intervalley scattering and that pseudospin is invariant under the
scattering. The phase space of armchair nanoribbon which includes a single
Dirac singularity is specified. By examining the effects of boundary
perturbations on the wave function, we suggest that the existance of a strong
boundary potential is inconsistent with the observation in a recent scanning
tunneling microscopy. Some of the possible electron-density superstructure
patterns near a step armchair edge located on top of graphite are presented. It
is demonstrated that a selection rule for the G band in Raman spectroscopy can
be most easily reproduced with the analytical solution.Comment: 7 pages, 4 figure
A modified BlÄzka–type respirometer for the study of swimming metabolism in fishes having deep, laterally compressed bodies or unusual locomotor modes
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73888/1/j.1095-8649.2000.tb00890.x.pd
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