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 $t$ 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 $\sigma$ and effective value of $\alpha_s$. 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 $\gamma p$ 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 $P$--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 $\leq 50$ 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