Seed conservation in ex situ genebanks - genetic studies on longevity in barley

Recognizing the danger due to a permanent risk of loss of the genetic variability of cultivated plants and their wild relatives in response to changing environmental conditions and cultural practices, plant ex situ genebank collections were created since the beginning of the last century. World-wide more than 6 million accessions have been accumulated of which more than 90% are stored as seeds. Research on seed longevity was performed in barley maintained for up to 34 years in the seed store of the German ex situ genebank of the Leibniz-Institute of Plant Genetics and Crop Plant Research in Gatersleben. A high intraspecific variation was detected in those natural aged accessions. In addition three doubled haploid barley mapping populations being artificial aged were investigated to study the inheritance of seed longevity. Quantitative trait locus (QTL) mapping was based on a transcript map. Major QTLs were identified on chromosomes 2H, 5H (two) and 7H explaining a phenotypic variation of up to 54%. A sequence homology search was performed to derive the putative function of the genes linked to the QTLs

Calculation of Vibrational Line Shifts for Molecular Dimers

A method for calculating the shifts of vibrational excitation frequencies in molecular clusters is presented. It is based on second order non-degenerate perturbation theory and refers to early publications of Buckingham. The resulting formula involves off-diagonal cubic force constants thus accounting for coupling of the individual molecular normal modes. It is applied to the C-O stretching mode in methanol dimers and to all three modes in water dimers. The results are in good agreement with experimental values with exception of the ν3-mode of the donor molecule in the water dimer where the perturbation approach was found to be not adequate

A Perturbation Approach to Predict the Infrared Spectra of Small Molecular Clusters Applied to Methanol

A method for predicting splittings and shifts of bands in infrared spectra of small clusters of polyatomic molecules is presented. Based on an approach of early publications of Buckingham, the influence of the intermolecular forces on the vibrational energy levels of the constituent molecules is calculated using perturbation theory to second order. In order to describe the interaction of identical molecules, this ansatz is extended to also cover degenerate systems. In first order, a coupling of the vibrational modes of the interacting molecules occurs which leads to delocalized vibrations of all the molecules in the cluster. The second order correction of the vibrational excitation frequencies are found to be dominated by the intramolecular couplings of the normal modes due to the cubic anharmonicity of the force field. The procedures developed here are applied for the interpretation of vibrational photodissociation spectra of small methanol clusters in the region of the fundamental excitation frequency of the OH stretching mode (ν1, 3681.5 cm-1), the CH3 rocking mode (ν7, 1074.5 cm-1), and the CO stretching mode (ν8, 1033.5 cm-1). Using semiempirical models for the intermolecular potential functions, splittings and positions of the experimental bands can well be explained. The nonequivalent positions of the two molecules in the linear dimer structure give rise to two different absorption frequencies for each of the three modes of the donor and the acceptor molecule, respectively. The trimer and tetramer spectrum with only one absorption band are in agreement with the existence of symmetric planar ring structures (C3h and C4h) for these species. The pentamer spectrum which also consists of one band is explained by the occurrence of three closely spaced frequencies of an asymmetric ring. The double peak structure in the hexamer spectra can be attributed to a distorted ring structure of S6 symmetry, while the occurrence of other energetically near-degenerate isomers can be ruled out by means of their spectra

Frequency Shifts in Infrared Spectra of Ethylene Clusters

Based on structure calculations of small ethene (C2H4) clusters published previously [R. Ahlrichs et al., Z. Phys. D. 15, 341, 1990], shifts and splittings of the fundamental excitation frequency of the ν7 mode are calculated for the dimer, trimer and tetramer. Using a first order perturbation approach, we find blue shifts in the order of 1-3 cm-1 which compare well with experimental findings. It is shown that the shifts are approximately independent of the cluster size and of the isomeric structure (ring-like or chainlike) of the ethene complexes

Structure and Photodissociation Spectra of Mixed Ethene-Acetone Clusters

Infrared photodissociation spectra of the mixed complexes C2H4-CH3COCH3 and C2H4-(CH3COCH3)2 have been observed after size selecting them by scattering from a helium beam combined with mass spectrometric detection. The excitation of the v7-out of plane symmetric wagging mode of ethene near its gas phase frequency at 949.3 cm-1 with a cw-CO2 laser leads to a characteristic depletion of the cluster beam. The dissociation spectrum of the 1:1 complex can be explained by two peaks at 950.8 and 961.6 cm-1. Calculations of minimum energy configurations and band shifts based on an empirical site-site potential show that these frequencies can be attributed to the absorption of two different isomers. They correspond to the two different binding patterns of the H atoms of ethene to the O atom of acetone and those of acetone to the C-C group of ethene, respectively. For the 1:2 complex, a large peak at 958.5 cm-1 and a smaller onearound 940.5 cm-1 are found which can be explained in a similar manner by several isomers found in the structure calculations

Large scale Gd-beta-diketonate based organic liquid scintillator production for antineutrino detection

Over the course of several decades, organic liquid scintillators have formed the basis for successful neutrino detectors. Gadolinium-loaded liquid scintillators provide efficient background suppression for electron antineutrino detection at nuclear reactor plants. In the Double Chooz reactor antineutrino experiment, a newly developed beta-diketonate gadolinium-loaded scintillator is utilized for the first time. Its large scale production and characterization are described. A new, light yield matched metal-free companion scintillator is presented. Both organic liquids comprise the target and "Gamma Catcher" of the Double Chooz detectors.Comment: 16 pages, 4 figures, 5 table

Large scale Gd-beta-diketonate based organic liquid scintillator production for antineutrino detection

Over the course of several decades, organic liquid scintillators have formed the basis for successful neutrino detectors. Gadolinium-loaded liquid scintillators provide efficient background suppression for electron antineutrino detection at nuclear reactor plants. In the Double Chooz reactor antineutrino experiment, a newly developed beta-diketonate gadolinium-loaded scintillator is utilized for the first time. Its large scale production and characterization are described. A new, light yield matched metal-free companion scintillator is presented. Both organic liquids comprise the target and "Gamma Catcher" of the Double Chooz detectors.Comment: 16 pages, 4 figures, 5 table

Prototype scintillator cell for an In-based solar neutrino detector

We describe the work carried out at MPIK to design, model, build and characterize a prototype cell filled with a novel indium-loaded scintillator of interest for real-time low energy solar neutrino spectroscopy. First, light propagation in optical modules was studied with experiments and Monte Carlo simulations. Subsequently a 5 cm x 5 cm x 100 cm prototype detector was set up and the optical performances of several samples were measured. We first tested a benchmark PXE-based scintillator, which performed an attenuation length of ~ 4.2 m and a photo-electron yield of ~ 730 pe/MeV. Then we measured three In-loaded samples. At an In-loading of 44 g/l, an energy resolution of ~ 11.6 % and a spatial resolution of ~ 7 cm were attained for 477 keV recoil electrons. The long-range attenuation length in the cell was ~1.3 m and the estimated photo-electron yield ~ 200 pe/MeV. Light attenuation and relative light output of all tested samples could be reproduced reasonably well by MC. All optical properties of this system have remained stable over a period of > 1 y.Comment: 57 pages, 19 figures, 10 tables elsevier template for manuscript submission submitted to NIMA 10 February 200

Structural Transitions and Thermally Averaged Infrared Spectra of Small Methanol Clusters

Classical Monte Carlo and molecular dynamics (MD) simulations were carried out to investigate the structures, the infrared spectra, and the rigid-nonrigid transitions of small methanol clusters (CH3OH)n, n=3-6. The study was motivated by experimental results for these clusters from size specific infrared (IR) dissociation spectroscopy. The MD simulations revealed the following transitions: The trimer passes from a rigid ring configuration into a series of nonrigid open chain structures starting at 197 K. For n=4 and 5 such transitions occur between rings and rapidly fluctuating ring structures at T=357 and 243 K, respectively. For n=6 first a pure isomeric transition between the two energetically lowest isomers of S6 and C2 symmetry is found at 35 K, and then a similar transition to a nonrigid behavior as is observed for n=4 and 5 is seen at 197 K. The measured spectral display in all cases the rigid lowest energy configurations