475 research outputs found
Functional regulation of FEN1 nuclease and its link to cancer
Flap endonuclease-1 (FEN1) is a member of the Rad2 structure-specific nuclease family. FEN1 possesses FEN, 5âČ-exonuclease and gap-endonuclease activities. The multiple nuclease activities of FEN1 allow it to participate in numerous DNA metabolic pathways, including Okazaki fragment maturation, stalled replication fork rescue, telomere maintenance, long-patch base excision repair and apoptotic DNA fragmentation. Here, we summarize the distinct roles of the different nuclease activities of FEN1 in these pathways. Recent biochemical and genetic studies indicate that FEN1 interacts with more than 30 proteins and undergoes post-translational modifications. We discuss how FEN1 is regulated via these mechanisms. Moreover, FEN1 interacts with five distinct groups of DNA metabolic proteins, allowing the nuclease to be recruited to a specific DNA metabolic complex, such as the DNA replication machinery for RNA primer removal or the DNA degradosome for apoptotic DNA fragmentation. Some FEN1 interaction partners also stimulate FEN1 nuclease activities to further ensure efficient action in processing of different DNA structures. Post-translational modifications, on the other hand, may be critical to regulate proteinâprotein interactions and cellular localizations of FEN1. Lastly, we also review the biological significance of FEN1 as a tumor suppressor, with an emphasis on studies of human mutations and mouse models
Quasiparticle picture of high temperature superconductors in the frame of Fermi liquid with the fermion condensate
A model of a Fermi liquid with the fermion condensate (FC) is applied to the
consideration of quasiparticle excitations in high temperature superconductors,
in their superconducting and normal states. Within our model the appearance of
the fermion condensate presents a quantum phase transition, that separates the
regions of normal and strongly correlated electron liquids. Beyond the phase
transition point the quasiparticle system is divided into two subsystems, one
containing normal quasiparticles and the other --- fermion condensate localized
at the Fermi surface and characterized by almost dispersionless single-particle
excitations. In the superconducting state the quasiparticle dispersion in
systems with FC can be presented by two straight lines, characterized by
effective masses and , respectively, and intersecting near
the binding energy which is of the order of the superconducting gap. This same
quasiparticle picture persists in the normal state, thus manifesting itself
over a wide range of temperatures as new energy scales. Arguments are presented
that fermion systems with FC have features of a quantum protectorate.Comment: 12 pages, Late
Algebraic Quantization, Good Operators and Fractional Quantum Numbers
The problems arising when quantizing systems with periodic boundary
conditions are analysed, in an algebraic (group-) quantization scheme, and the
``failure" of the Ehrenfest theorem is clarified in terms of the already
defined notion of {\it good} (and {\it bad}) operators. The analysis of
``constrained" Heisenberg-Weyl groups according to this quantization scheme
reveals the possibility for new quantum (fractional) numbers extending those
allowed for Chern classes in traditional Geometric Quantization. This study is
illustrated with the examples of the free particle on the circumference and the
charged particle in a homogeneous magnetic field on the torus, both examples
featuring ``anomalous" operators, non-equivalent quantization and the latter,
fractional quantum numbers. These provide the rationale behind flux
quantization in superconducting rings and Fractional Quantum Hall Effect,
respectively.Comment: 29 pages, latex, 1 figure included with EPSF. Revised version with
minor changes intended to clarify notation. Acepted for publication in Comm.
Math. Phy
Research of Gravitation in Flat Minkowski Space
In this paper it is introduced and studied an alternative theory of
gravitation in flat Minkowski space. Using an antisymmetric tensor, which is
analogous to the tensor of electromagnetic field, a non-linear connection is
introduced. It is very convenient for studying the perihelion/periastron shift,
deflection of the light rays near the Sun and the frame dragging together with
geodetic precession, i.e. effects where angles are involved. Although the
corresponding results are obtained in rather different way, they are the same
as in the General Relativity. The results about the barycenter of two bodies
are also the same as in the General Relativity. Comparing the derived equations
of motion for the -body problem with the Einstein-Infeld-Hoffmann equations,
it is found that they differ from the EIH equations by Lorentz invariant terms
of order .Comment: 28 page
Ultrasound attenuation in gap-anisotropic systems
Transverse ultrasound attenuation provides a weakly-coupled probe of momentum
current correlations in electronic systems. We develop a simple theory for the
interpretation of transverse ultrasound attenuation coefficients in systems
with nodal gap anisotropy. Applying this theory we show how ultrasound can
delineate between extended-s and d-wave scenarios for the cuprate
superconductors.Comment: Uuencode file: 4 pages (Revtex), 3 figures. Some references adde
Hidden symmetry and knot solitons in a charged two-condensate Bose system
We show that a charged two-condensate Ginzburg-Landau model or equivalently a
Gross-Pitaevskii functional for two charged Bose condensates, can be mapped
onto a version of the nonlinear O(3) -model. This implies in particular
that such a system possesses a hidden O(3) symmetry and allows for the
formation of stable knotted solitons. The results, in particular, should be
relevant to the superconducting MgB_2.Comment: This version will appear in Phys. Rev. B, added a comment on the case
when condensates in two bands do not independently conserve, also added a
figure and references to experimental papers on MgB_2 (for which our study is
relevant). Miscellaneous links on knot solitons are also available at the
homepage of one of the authors http://www.teorfys.uu.se/PEOPLE/egor/ .
Animations of knot solitons are available at
http://users.utu.fi/h/hietarin/knots/c45_p2.mp
Angle-resolved photoemission in doped charge-transfer Mott insulators
A theory of angle-resolved photoemission (ARPES) in doped cuprates and other
charge-transfer Mott insulators is developed taking into account the realistic
(LDA+U) band structure, (bi)polaron formation due to the strong electron-phonon
interaction, and a random field potential. In most of these materials the first
band to be doped is the oxygen band inside the Mott-Hubbard gap. We derive the
coherent part of the ARPES spectra with the oxygen hole spectral function
calculated in the non-crossing (ladder) approximation and with the exact
spectral function of a one-dimensional hole in a random potential. Some unusual
features of ARPES including the polarisation dependence and spectral shape in
YBa2Cu3O7 and YBa2Cu4O8 are described without any Fermi-surface, large or
small. The theory is compatible with the doping dependence of kinetic and
thermodynamic properties of cuprates as well as with the d-wave symmetry of the
superconducting order parameter.Comment: 8 pages (RevTeX), 10 figures, submitted to Phys. Rev.
Dynamic Evolution Model of Isothermal Voids and Shocks
We explore self-similar hydrodynamic evolution of central voids embedded in
an isothermal gas of spherical symmetry under the self-gravity. More
specifically, we study voids expanding at constant radial speeds in an
isothermal gas and construct all types of possible void solutions without or
with shocks in surrounding envelopes. We examine properties of void boundaries
and outer envelopes. Voids without shocks are all bounded by overdense shells
and either inflows or outflows in the outer envelope may occur. These
solutions, referred to as type void solutions, are further
divided into subtypes and
according to their characteristic behaviours across the sonic critical line
(SCL). Void solutions with shocks in envelopes are referred to as type
voids and can have both dense and quasi-smooth edges.
Asymptotically, outflows, breezes, inflows, accretions and static outer
envelopes may all surround such type voids. Both cases of
constant and varying temperatures across isothermal shock fronts are analyzed;
they are referred to as types and
void shock solutions. We apply the `phase net matching procedure' to construct
various self-similar void solutions. We also present analysis on void
generation mechanisms and describe several astrophysical applications. By
including self-gravity, gas pressure and shocks, our isothermal self-similar
void (ISSV) model is adaptable to various astrophysical systems such as
planetary nebulae, hot bubbles and superbubbles in the interstellar medium as
well as supernova remnants.Comment: 24 pages, 13 figuers, accepted by ApS
Dynamic Evolution of a Quasi-Spherical General Polytropic Magnetofluid with Self-Gravity
In various astrophysical contexts, we analyze self-similar behaviours of
magnetohydrodynamic (MHD) evolution of a quasi-spherical polytropic magnetized
gas under self-gravity with the specific entropy conserved along streamlines.
In particular, this MHD model analysis frees the scaling parameter in the
conventional polytropic self-similar transformation from the constraint of
with being the polytropic index and therefore
substantially generalizes earlier analysis results on polytropic gas dynamics
that has a constant specific entropy everywhere in space at all time. On the
basis of the self-similar nonlinear MHD ordinary differential equations, we
examine behaviours of the magnetosonic critical curves, the MHD shock
conditions, and various asymptotic solutions. We then construct global
semi-complete self-similar MHD solutions using a combination of analytical and
numerical means and indicate plausible astrophysical applications of these
magnetized flow solutions with or without MHD shocks.Comment: 21 pages, 7 figures, accepted for publication in APS
A Conformally Invariant Holographic Two-Point Function on the Berger Sphere
We apply our previous work on Green's functions for the four-dimensional
quaternionic Taub-NUT manifold to obtain a scalar two-point function on the
homogeneously squashed three-sphere (otherwise known as the Berger sphere),
which lies at its conformal infinity. Using basic notions from conformal
geometry and the theory of boundary value problems, in particular the
Dirichlet-to-Robin operator, we establish that our two-point correlation
function is conformally invariant and corresponds to a boundary operator of
conformal dimension one. It is plausible that the methods we use could have
more general applications in an AdS/CFT context.Comment: 1+49 pages, no figures. v2: Several typos correcte
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