Gamma ray production cross sections in proton induced reactions on natural Mg, Si and Fe targets over the proton energy range 30 up to 66 MeV

Gamma-ray excitation functions have been measured for 30, 42, 54 and 66 MeV proton beams accelerated onto C + O (Mylar), Mg, Si, and Fe targets of astrophysical interest at the separate-sector cyclotron of iThemba LABS in Somerset West (Cape Town, South Africa). A large solid angle, high energy resolution detection system of the Eurogam type was used to record Gamma-ray energy spectra. Derived preliminary results of Gamma-ray line production cross sections for the Mg, Si and Fe target nuclei are reported and discussed. The current cross section data for known, intense Gamma-ray lines from these nuclei consistently extend to higher proton energies previous experimental data measured up to Ep ~ 25 MeV at the Orsay and Washington tandem accelerators. Data for new Gamma-ray lines observed for the first time in this work are also reported.Comment: 11 pages, 6 figures. IOP Institute of Physics Conference Nuclear Physics in Astrophysics VII, 28th EPF Nuclear Physics Divisional Conference, May 18-22 2015, York, U

Measurement and analysis of nuclear γ-ray production cross sections in proton interactions with Mg, Si, and Fe nuclei abundant in astrophysical sites over the incident energy range E = 30–66 MeV

The modeling of nuclear γ -ray line emission induced by highly accelerated particles in astrophysical sites (e.g., solar flares, the gas and dust in the inner galaxy) and the comparison with observed emissions from these sites needs a comprehensive database of related production cross sections. The most important reactions of protons and α particles are those with abundant target elements like C, O, N, Ne, Mg, Si, and Fe at projectile energies extending from the reaction threshold to a few hundred MeV per nucleon. In this work, we have measured γ -ray production cross section excitation functions for 30, 42, 54, and 66 MeV proton beams accelerated onto nat C , C + O (Mylar), nat Mg , nat Si , and 56 Fe targets of astrophysical interest at the Separated Sector Cyclotron (SSC) of iThemba LABS (near Cape Town, South Africa). The AFRODITE array equipped with eight Compton suppressed high-purity (HPGe) clover detectors was used to record γ -ray line energy spectra. For known, intense lines previously reported experimental data measured up to E p ≃ 25 MeV at the Washington and Orsay tandem accelerators were thus extended to higher proton energies. Our experimental data for the last three targets are reported here and discussed with respect to previous data and to the Murphy et al. compilation [Astrophys. J. Suppl. Ser. 183, 142 (2009)]

A Descriptive Analysis Of Populations Of Three-Dimensional Structures Calculated From Primary Sequences Of Proteins By Osiris

Among different ab initio approaches to calculate 3D-structures of proteins out of primary sequences, a few are using restricted dihedral spaces and empirical equations of energy as is OSIRIS. All those approaches were calibrated on a few proteins or fragments of proteins. To optimize the calculation over a larger diversity of structures, we need first to define for each sequence what are good conditions of calculations in order to choose a consensus procedure fitting most 3D-structures best. This requires objective classification of calculated 3D-structures. In this work, populations of avian and bovine pancreatic polypeptides (APP, BPP) and of calcium-binding protein (CaBP) are obtained by varying the rate of the angular dynamics of the second step of OSIRIS. Then, 3D-structures are clustered using a nonhierarchical method, SICLA, using rmsd as a distance parameter. A good clustering was obtained for four subpopulations of APP, BPP and CaBP. Each subpopulation was characterized by its barycenter, relative frequency and dispersion. For the three alpha-helix proteins, after the step 1 of OSIRIS, most secondary structures were correct but molecules have a few atomic contacts. Step 2, i.e., the angular dynamics, resolves those atomic contacts and clustering demonstrates that it generates subpopulations of topological conformers as the barycenter topologies show

Prediction Of The Antigenic Sites Of The Cystic-Fibrosis Transmembrane Conductance Regulator Protein By Molecular Modeling

Antibodies are powerful tools for studying the in situ localization and physiology of proteins. The prediction of epitopes by molecular modelling has been used successfully for the papilloma virus, and valuable antibodies have been raised [Muller et al. (1990) J. Gen. Virol., 71, 2709-2717]. We have improved the modelling approach to allow us to predict epitopes from the primary sequences of the cystic fibrosis transmembrane conductance regulator. The procedure involves searching for fragments of primary sequences likely to make amphipathic secondary structures, which are hydrophilic enough to be at the surface of the folded protein and thus accessible to antibodies. Amphipathic helices were predicted using the methods of Berzofsky, Eisenberg and Jahnig. Their hydrophobic-hydrophilic interface was calculated and drawn, and used to predict the orientation of the helices at the surface of the native protein. Amino acids involved in turns were selected using the algorithm of Eisenberg. Tertiary structures were calculated using 'FOLDING', a software developed by R. Brasseur for the prediction of small protein structures [Brasseur (1995) J. Mol. Graphics, in press]. We selected sequences that folded as turns with at least five protruding polar residues. One important property of antibodies is selectivity. To optimize the selectivity of the raised antibodies, each sequence was screened for similarity (FASTA) to the protein sequence from several databanks. Ubiquitous sequences were discarded. This approach led to the identification of 13 potential epitopes in the cystic fibrosis transmembrane conductance regulator: seven helices and six loops

The solvation concept approached by lipophily

peer reviewedThe soivent of biological media is water and interactions between water and solutes are major to explain membrane and protein structures, Therefore, mimicking solvation effects is a challenge to compute native structures of biological molecules. Lipophlly is an, experimental approach of solvation sinca it measures the parItion of a solute between two solvents, the reterence being water. In the last decade, different attempts were made to extract parameters from lipophily that will enable to describe soivation of complex molecules. We discuss here some analysis made with the atomie transfer energy and the atomic aurface parameter in the study of protein folding and protein Insertion in membranes

Nuclear γ-ray line emission induced by energetic ions in solar flares and by galactic cosmic rays

International audienceThe γ-ray spectra ol the strongest solar flares often show a broad and complex structure in the 0.1-10 MeV region sitting on a bremsstrahlung continuum. This structure is composed of several outstanding narrow lines and of thousands of unresolved narrow and broad lines forming a quasi-continuum. The major part of this emission is due to prompt deexcitation lines following nuclear interactions of accelerated light and heavy ions with the atomic nuclei composing the solar atmosphere. A similar emission is expected from interactions of galactic cosmic rays with the interstellar gas and dust. Experimental nuclear reaction studies coupled with extensive calculations have been done in the last one and a half decade at Orsay for the modelisation of this γ-ray emission. After a description of the nuclear reaction studies the analysis of one solar flare spectrum and predictions for the emission from the inner Galaxy will be presented

The Structural And Functional Organization Of H-Ns-Like Proteins Is Evolutionarily Conserved In Gram-Negative Bacteria

peer reviewedThe structural gene of the H-NS protein, a global regulator of bacterial metabolism, has been identified in the group of enterobacteria as well as in closely related bacteria, such as Erwinia chrysanthemi and Haemophilus influenzae. Isolated outside these groups, the BpH3 protein of Bordetella pertussis exhibits a low amino acid conservation with H-NS, particularly in the N-terminal domain. To obtain information on the structure, function and/or evolution of H-NS, we searched for other H-NS-related proteins in the latest databases. We found that HvrA, a trans-activator protein in Rhodobacter capsulatus, has a low but significant similarity with H-NS and H-NS-like proteins. This Gram-negative bacterium is phylogenetically distant from Escherichia coli. Using theoretical analysis (e.g. secondary structure prediction and DNA binding domain modelling) of the amino acid sequence of H-NS, StpA (an H-NS-like protein in E. coli), BpH3 and HvrA and by in vivo and in vitro experiments (e.g. complementation of various H-NS-related phenotypes and competitive gel shift assay), we present evidence that these proteins belong to the same class of DNA binding proteins. In silico analysis suggests that this family also includes SPB in R. sphaeroides, XrvA in Xanthomonas oryzae and VicH in Vibrio cholerae. These results demonstrate that proteins structurally and functionally related to H-NS are widespread in Gram-negative bacteria