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Production of the doubly strange H dibaryon

Description: There is much current interest in the spectroscopy of multiquark states. Predictions abound for the existence of baryonium (Q/sup 2/ anti Q/sup 2/) and six-quark dibaryon (Q/sup 6/) resonances, for instance. In the strangeness S = -2 sector of Q/sup 6/, the MIT bag model predicts a dibaryon H with quantum numbers J/sup ..pi../ = 0/sup +/, isospin I = 0, and mass M/sub H/ approx. = 2150 MeV approx. = 2M/sub ..lambda../ -80 MeV. The H has quark composition uuddss, so all quarks can occupy the ls state; it is unique in that it possesses no strong decay modes. The fact that the H mass is considerably below the ..lambda lambda.. or XiN thresholds precludes its interpretation as a deuteron-like object bound by conventional long-range meson exchange forces. The H has been searched for in the reaction p + p ..-->.. K/sup +/ + K/sup +/ + H by Carroll et al., with an upper limit of about 100 nb/sr/sup 2/ for two K/sup +/'s at +- 18/sup 0/ in the lab system. Some crude cross section estimates we have made for this process indicate much smaller cross sections than this limit. A more natural way to produce the H, in our view, is via the (K/sup -/, K/sup +/) reaction on a diproton in a nuclear target, i.e. K/sup -/ + (pp) ..-->.. K/sup +/ + H.
Date: January 1, 1982
Creator: Aerts, A.T. & Dover, C.B.
Partner: UNT Libraries Government Documents Department

The genome of black cottonwood, Populus trichocarpa (Torr.&Gray)

Description: We report the draft genome of the black cottonwood tree, Populus trichocarpa. Integration of shotgun sequence assembly with genetic mapping enabled chromosome-scale reconstruction of the genome. Over 45,000 putative protein-coding genes were identified. Analysis of the assembled genome revealed a whole-genome duplication event, with approximately 8,000 pairs of duplicated genes from that event surviving in the Populus genome. A second, older duplication event is indistinguishably coincident with the divergence of the Populus and Arabidopsis lineages. Nucleotide substitution, tandem gene duplication and gross chromosomal rearrangement appear to proceed substantially slower in Populus relative to Arabidopsis. Populus has more protein-coding genes than Arabidopsis, ranging on average between 1.4-1.6 putative Populus homologs for each Arabidopsis gene. However, the relative frequency of protein domains in the two genomes is similar. Overrepresented exceptions in Populus include genes associated with disease resistance, meristem development, metabolite transport and lignocellulosic wall biosynthesis.
Date: September 1, 2006
Creator: Tuskan, G. A.; DiFazio, S.; Jansson, S.; Bohlmann, J.; Grigoriev,I.; Hellsten, U. et al.
Partner: UNT Libraries Government Documents Department

The sequence and analysis of duplication rich human chromosome 16

Description: Human chromosome 16 features one of the highest levels of segmentally duplicated sequence among the human autosomes. We report here the 78,884,754 base pairs of finished chromosome 16 sequence, representing over 99.9% of its euchromatin. Manual annotation revealed 880 protein-coding genes confirmed by 1,637 aligned transcripts, 19 tRNA genes, 341 pseudogenes, and 3 RNA pseudogenes. These genes include metallothionein, cadherin, and iroquois gene families, as well as the disease genes for polycystic kidney disease and acute myelomonocytic leukemia. Several large-scale structural polymorphisms spanning hundreds of kilobase pairs were identified and result in gene content differences among humans. While the segmental duplications of chromosome 16 are enriched in the relatively gene poor pericentromere of the p-arm, some are involved in recent gene duplication and conversion events likely to have had an impact on the evolution of primates and human disease susceptibility.
Date: April 6, 2005
Creator: Martin, J; Han, C; Gordon, L A; Terry, A; Prabhakar, S; She, X et al.
Partner: UNT Libraries Government Documents Department