389 research outputs found
Spatial arrangement of LD motif-interacting residues on focal adhesion targeting domain of Focal Adhesion Kinase determine domain-motif interaction affinity and specificity
Background: Leucine rich Aspartate motifs (LD motifs) are molecular recognition motifs on Paxillin that recognize LD-motif binding domains (LDBD) of a number of focal adhesion proteins in order to carry out downstream signaling and actin cytoskeleton remodeling. In this study, we identified structural features within LDBDs that influence their binding affinity with Paxillin LD motifs. Methods: Various point mutants of focal adhesion targeting (FAT) domain of Focal Adhesion Kinase (FAK) were created by moving a key Lysine residue two and three helical turns in order to match the unique conformations as observed in LDBDs of two other focal adhesion proteins, Vinculin and CCM3. Results: This led to identify a mutant of FAT domain of FAK, named as FAT(NV) (Asn992 of FAT domain was replaced by Val), with remarkable high affinity for LD1 (Kd = 1.5 µM vs no-binding with wild type) and LD2 peptides (Kd = 7.2 µM vs 63 µM with wild type). Consistently, the focal adhesions of MCF7 cells expressing FAK(NV) were highly stable (turnover rate = 1.25 × 10-5 µm2/s) as compared to wild type FAK transfected cells (turnover rate = 1.5 × 10-3 µm2/s). Conclusions: We observed that the relative disposition of key LD binding amino-acids at LDBD surface, hydrophobic burial of long Leucine side chains of LD-motifs and complementarity of charged surfaces are the key factors determining the binding affinities of LD motifs with LDBDs. General significance: Our study will help in protein engineering of FAT domain of FAK by modulating FAK-LD motif interactions which have implications in cellular focal adhesions and cell migration
A QCD motivated model for soft interactions at high energies
In this paper we develop an approach to soft scattering processes at high
energies,which is based on two mechanisms: Good-Walker mechanism for low mass
diffractionand multi-Pomeron interactions for high mass diffraction. The
pricipal idea, that allows us to specify the theory for Pomeron interactions,
is that the so called soft processes occur at rather short distances
(r^2 \propto 1 /^2 \propto \alpha'_\pom \approx 0.01 GeV^{-2}), where
perturbative QCD is valid. The value of the Pomeron slope \alpha'_\pom was
obtained from the fit to experimental data. Using this theoretical approach we
suggest a model that fits all soft data in the ISR-Tevatron energy range, the
total, elastic, single and double diffractive cross sections, including
dependence of the differential elastic cross section, and the mass dependence
of single diffraction. In this model we calculate the survival probability of
diffractive Higgs production, and obtained a value for this observable, which
is smaller than 1% at the LHC energy range.Comment: 33pp,20 figures in eps file
Odderon and Pomeron from the Vacuum Correlator Method
Glueball masses with J<=7 are computed both for C=+1 and C=-1 using the
string Hamiltonian derived in the framework of the Vacuum Correlator Method. No
fitting parameters are used, and masses are expressed in terms of string
tension and effective value of . We extend the calculations
done for J<=3 using the same Hamiltonian, which provided glueball masses in
good agreement with existing lattice data, to higher mass states. It is shown
that 3^{--}, 5^{--} and 7^{--} states lie on the odderon trajectories with the
intercept around or below 0.14. Another odderon trajectory with 3g glueballs of
Y-shape, corresponds to 11% higher masses and low intercept. These findings are
in agreement with recent experimental data, setting limits on the odderon
contribution to the exclusive reactions.Comment: 16 pages. Journal version. To be published in Phys.Lett.
Phase diagram of an Ising model with long-range frustrating interactions: a theoretical analysis
We present a theoretical study of the phase diagram of a frustrated Ising
model with nearest-neighbor ferromagnetic interactions and long-range
(Coulombic) antiferromagnetic interactions. For nonzero frustration, long-range
ferromagnetic order is forbidden, and the ground-state of the system consists
of phases characterized by periodically modulated structures. At finite
temperatures, the phase diagram is calculated within the mean-field
approximation. Below the transition line that separates the disordered and the
ordered phases, the frustration-temperature phase diagram displays an infinite
number of ``flowers'', each flower being made by an infinite number of
modulated phases generated by structure combination branching processes. The
specificities introduced by the long-range nature of the frustrating
interaction and the limitation of the mean-field approach are finally
discussed.Comment: 32 pages, 7 figure
Dirichlet sigma models and mean curvature flow
The mean curvature flow describes the parabolic deformation of embedded
branes in Riemannian geometry driven by their extrinsic mean curvature vector,
which is typically associated to surface tension forces. It is the gradient
flow of the area functional, and, as such, it is naturally identified with the
boundary renormalization group equation of Dirichlet sigma models away from
conformality, to lowest order in perturbation theory. D-branes appear as fixed
points of this flow having conformally invariant boundary conditions. Simple
running solutions include the paper-clip and the hair-pin (or grim-reaper)
models on the plane, as well as scaling solutions associated to rational (p, q)
closed curves and the decay of two intersecting lines. Stability analysis is
performed in several cases while searching for transitions among different
brane configurations. The combination of Ricci with the mean curvature flow is
examined in detail together with several explicit examples of deforming curves
on curved backgrounds. Some general aspects of the mean curvature flow in
higher dimensional ambient spaces are also discussed and obtain consistent
truncations to lower dimensional systems. Selected physical applications are
mentioned in the text, including tachyon condensation in open string theory and
the resistive diffusion of force-free fields in magneto-hydrodynamics.Comment: 77 pages, 21 figure
A spatio-temporal description of the abrupt changes in the photospheric magnetic and Lorentz-force vectors during the 2011 February 15 X2.2 flare
The active region NOAA 11158 produced the first X-class flare of Solar Cycle
24, an X2.2 flare at 01:44 UT on 2011 February 15. Here we analyze SDO/HMI
magnetograms covering a 12-hour interval centered at the time of this flare. We
describe the spatial distributions of the photospheric magnetic changes
associated with this flare, including the abrupt changes in the field vector,
vertical electric current and Lorentz force vector. We also trace these
parameters' temporal evolution. The abrupt magnetic changes were concentrated
near the neutral line and in two neighboring sunspots. Near the neutral line,
the field vectors became stronger and more horizontal during the flare and the
shear increased. This was due to an increase in strength of the horizontal
field components near the neutral line, most significant in the horizontal
component parallel to the neutral line but the perpendicular component also
increased in strength. The vertical component did not show a significant,
permanent overall change at the neutral line. The increase in total flux at the
neutral line was accompanied by a compensating flux decrease in the surrounding
volume. In the two sunspots near the neutral line the azimuthal flux abruptly
decreased during the flare but this change was permanent in only one of the
spots. There was a large, abrupt, downward vertical Lorentz force change during
the flare, consistent with results of past analyses and recent theoretical
work. The horizontal Lorentz force acted in opposite directions along each side
of neutral line, with the two sunspots at each end subject to abrupt torsional
forces. The shearing forces were consistent with field contraction and decrease
of shear near the neutral line, whereas the field itself became more sheared as
a result of the flux collapsing towards the neutral line from the surrounding
volume.Comment: DOI 10.1007/s11207-012-0071-0. Accepted for publication in Solar
Physics SDO3 Topical Issue. Some graphics missing due to 15MB limi
Mathematics of Gravitational Lensing: Multiple Imaging and Magnification
The mathematical theory of gravitational lensing has revealed many generic
and global properties. Beginning with multiple imaging, we review
Morse-theoretic image counting formulas and lower bound results, and
complex-algebraic upper bounds in the case of single and multiple lens planes.
We discuss recent advances in the mathematics of stochastic lensing, discussing
a general formula for the global expected number of minimum lensed images as
well as asymptotic formulas for the probability densities of the microlensing
random time delay functions, random lensing maps, and random shear, and an
asymptotic expression for the global expected number of micro-minima. Multiple
imaging in optical geometry and a spacetime setting are treated. We review
global magnification relation results for model-dependent scenarios and cover
recent developments on universal local magnification relations for higher order
caustics.Comment: 25 pages, 4 figures. Invited review submitted for special issue of
General Relativity and Gravitatio
The triple-pomeron regime and the structure function of the pomeron in the diffractive deep inelastic scattering at very small x
Misprints and numerical coefficients corrected, a bit of phenomenology and
one figure added. The case for the linear evolution of the unitarized structure
functions made stronger.Comment: KFA-IKP(Th)-1993-17, Landau-16/93, 46 pages, 14 figures upon request
from N.Nikolaev, [email protected]
Some Properties of a Transient New Coherent Condition of Matter Formed in High--Energy Hadronic Collisions
We investigate the dynamical possibility for the formation of a transient new
coherent condition of matter in high--energy hadronic collisions. The coherent
bosonic amplitude is characterized by a non--zero momentum and is sustained by
--wave interactions of quasi--pions in a dense fermionic medium. We make
quantitative estimates of several essential properties: the condensate momentum
and the fermionic density, the size of the coherent amplitude and the negative
energy density contributed by the condensate, a characteristic proper time for
the system to exist prior to breakdown into a few pions, and a characteristic
extension of the system over the plane perpendicular to the collision axis.
These quantities then allow us to make definite estimates of new signals: a few
pions with anomalously small transverse momenta MeV/c; and a
possible anomalous bremsstrahlung of very soft photons with characteristic
transverse momenta as low as about 4 MeV/c.Comment: 23 pages, LaTeX. A complete postscript file is available via
anonymous ftp at ttpux2.physik.uni-karlsruhe.de (129.13.102.139) as /ttp94-18
/ttp94-18.ps, Local preprint# TTP94-1
Svestka's Research: Then and Now
Zdenek Svestka's research work influenced many fields of solar physics,
especially in the area of flare research. In this article I take five of the
areas that particularly interested him and assess them in a "then and now"
style. His insights in each case were quite sound, although of course in the
modern era we have learned things that he could not readily have envisioned.
His own views about his research life have been published recently in this
journal, to which he contributed so much, and his memoir contains much
additional scientific and personal information (Svestka, 2010).Comment: Invited review for "Solar and Stellar Flares," a conference in honour
of Prof. Zden\v{e}k \v{S}vestka, Prague, June 23-27, 2014. This is a
contribution to a Topical Issue in Solar Physics, based on the presentations
at this meeting (Editors Lyndsay Fletcher and Petr Heinzel
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