9,385 research outputs found
The Holography Hypothesis and Pre-Big Bang Cosmology
The consequences of holography hypothesis are investigated for the
Pre-big-bang string cosmological models. The evolution equations are obtained
from the tree level string effective action. It is shown that is bounded
by a constant in each case, being the entropy within the volume bounded by
the horizon of area .Comment: 11 pages, revtex, 1 eps fil
Computerized Protein Modeling and Molecular Docking Analysis of Human Proto Oncogene Tyrosine Protein Kinase YES for Discovery of Novel Lead Molecules
Human proto-oncogene tyrosine-protein kinase YES (YES) is a non receptor kinase belongs to Src family. This gene lies in close proximity to thymidylate synthase gene on chromosome 18, and a corresponding pseudogene has been found on chromosome 22. In hepatocellular carcinoma and colorectal carcinoma elevated human YES activity was observed. Inhibitors of human YES reported till date are in clinical trials and associated with several side effects. The present study was mainly aimed in homology modeling of human YES and discovery of novel lead molecules that inhibit YES kinase more efficiently with fewer side effects. Virtual screening and docking techniques were applied to identify novel lead molecule of YES kinase. As there was no reported human YES crystal structural data, the three dimensional structure of human YES was constructed based on template structure (PDB ID: 2H8H) obtained through homology search using MODELLER 9V7. The model was refined, energy minimized and assessed through PROCHECK. Active site residues of human YES were identified from the homology model in complex with template ligand AZD0530 and were further confirmed using CASTp. Five published inhibitors of YES family (Dasatinib, Bosutinib, SU6656, AZD0530 and CGP77675) were identified through literature search. High throughput virtual screening method at Ligand.Info was applied for these five inhibitors to establish a library of 1932 structural analogs. LigPrep was used to generate possible conformations of each ligand molecules from structural analog library. The ligand duplicates conformers, ligands having reactive functional group and poor ADME properties were rejected from the prepared dataset. Glide 5.5 was used to generate a grid box by picking the active site residues of human YES protein. Through sequential applications of stringent mode glide docking procedures from Glide HTVS to SP to XP respectively, 13 potential inhibitors were proposed. The docking complexes of each inhibitor with human YES protein were analyzed and lead ‘1’ molecule was identified to have higher binding affinity to human YES protein (XP Gscore: -12.07 Kcal/mol) compared to existing published inhibitors and other 12 lead molecules. The lead ‘1’ - human YES docking complex was highly stabilized through hydrogen bond network with amino acid residues Thr348, Asp358, Asp414 and Phe415. Moreover, from the results obtained we could decipher that lead ‘1’ molecule can be raised into potential inhibitors after binding assays, substantiated experimental investigations and passing several phases of clinical trials
Highly Excited Core Resonances in Photoionization of Fe XVII : Implications for Plasma Opacities
A comprehensive study of high-accuracy photoionization cross sections is
carried out using the relativistic Breit-Pauli R-matrix (BPRM) method for (hnu
+ Fe XVII --> Fe XVIII + e). Owing to its importance in high-temperature
plasmas the calculations cover a large energy range, particularly the myriad
photoexciation-of-core (PEC) resonances including the n = 3 levels not
heretofore considered. The calculations employ a close coupling wave function
expansion of 60 levels of the core ion Fe XVIII ranging over a wide energy
range of nearly 900 eV between the n = 2 and n = 3 levels. Strong coupling
effects due to dipole transition arrays 2p^5 --> 2p^4 (3s,3d) manifest
themselves as large PEC resonances throughout this range, and enhance the
effective photoionization cross sections orders of magnitude above the
background. Comparisons with the erstwhile Opacity Project (OP) and other
previous calculations shows that the currently available cross sections
considerably underestimate the bound-free cross sections. A
level-identification scheme is used for spectroscopic designation of the 454
bound fine structure levels of Fe XVII. Level-specific photoionization cross
sections are computed for all levels. In addition, partial cross sections for
leaving the core ion Fe XVII in the ground state are also obtained. These
results should be relevant to modeling of astrophysical and laboratory plasma
sources requiring (i) photoionization rates, (ii) extensive
non-local-thermodynamic-equilibrium models, (iii) total unified electron-ion
recombination rates including radiative and dielectronic recombination, and
(iv) plasma opacities. We particularly examine PEC and non-PEC resonance
strengths and emphasize their expanded role to incorporate inner-shell
excitations for improved opacities, as shown by the computed monochromatic
opacity of Fe XVII.Comment: 12 pages, 5 figures, Physical Review A (in press
Magnetic Order Beyond RKKY in the Classical Kondo Lattice
We study the Kondo lattice model of band electrons coupled to classical
spins, in three dimensions, using a combination of variational calculation and
Monte Carlo. We use the weak coupling `RKKY' window and the strong coupling
regime as benchmarks, but focus on the physically relevant intermediate
coupling regime. Even for modest electron-spin coupling the phase boundaries
move away from the RKKY results, the non interacting Fermi surface no longer
dictates magnetic order, and weak coupling `spiral' phases give way to
collinear order. We use these results to revisit the classic problem of 4f
magnetism and demonstrate how both electronic structure and coupling effects
beyond RKKY control the magnetism in these materials.Comment: 6 pages, 4 figs. Improved figures, expanded captions. To appear in
Europhys. Let
Sampling rare fluctuations of height in the Oslo ricepile model
We have studied large deviations of the height of the pile from its mean
value in the Oslo ricepile model. We sampled these very rare events with
probabilities of order by Monte Carlo simulations using importance
sampling. These simulations check our qualitative arguement [Phys. Rev. E, {\bf
73}, 021303, 2006] that in steady state of the Oslo ricepile model, the
probability of large negative height fluctuations about
the mean varies as as with
held fixed, and .Comment: 7 pages, 8 figure
Probability distribution of residence times of grains in models of ricepiles
We study the probability distribution of residence time of a grain at a site,
and its total residence time inside a pile, in different ricepile models. The
tails of these distributions are dominated by the grains that get deeply buried
in the pile. We show that, for a pile of size , the probabilities that the
residence time at a site or the total residence time is greater than , both
decay as for where
is an exponent , and values of and in the two
cases are different. In the Oslo ricepile model we find that the probability
that the residence time at a site being greater than or equal to ,
is a non-monotonic function of for a fixed and does not obey simple
scaling. For model in dimensions, we show that the probability of minimum
slope configuration in the steady state, for large , varies as where is a constant, and hence .Comment: 13 pages, 23 figures, Submitted to Phys. Rev.
Atomic data from the Iron Project.XLIII. Transition probabilities for Fe V
An extensive set of dipole-allowed, intercombination, and forbidden
transition probabilities for Fe V is presented. The Breit-Pauli R-matrix (BPRM)
method is used to calculate 1.46 x 10^6 oscillator strengths for the allowed
and intercombination E1 transitions among 3,865 fine-structure levels dominated
by configuration complexes with n <= 10 and l <= 9. These data are complemented
by an atomic structure configuration interaction (CI) calculation using the
SUPERSTRUCTURE program for 362 relativistic quadrupole (E2) and magnetic dipole
(M1) transitions among 65 low-lying levels dominated by the 3d^4 and 3d^ 4s
configurations. Procedures have been developed for the identification of the
large number of fine-structure levels and transitions obtained through the BPRM
calculations. The target ion Fe VI is represented by an eigenfunction expansion
of 19 fine-structure levels of 3d^3 and a set of correlation configurations. Fe
V bound levels are obtained with angular and spin symmetries SL\pi and J\pi of
the (e + Fe VI) system such that 2S+1 = 5,3,1, L <= 10, J <= 8 of even and odd
parities. The completeness of the calculated dataset is verified in terms of
all possible bound levels belonging to relevant LS terms and transitions in
correspondence with the LS terms. The fine-structure averaged relativistic
values are compared with previous Opacity Project LS coupling data and other
works. The 362 forbidden transition probabilities considerably extend the
available data for the E2 and M1 transtions, and are in good agreement with
those computed by Garstang for the 3d^4 transitions.Comment: 19 pages, 1 figure. This paper marks the beginning of a large-scale
effort of ab initio atomic calculations that should eventually lead to
re-calculation of accurate iron opacities. Astron. Astrophys. Suppl. Ser. (in
press
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