Fusion-Fission of 16O+197Au at Sub-Barrier Energies

The recent discovery of heavy-ion fusion hindrance at far sub-barrier energies has focused much attention on both experimental and theoretical studies of this phenomenon. Most of the experimental evidence comes from medium-heavy systems such as Ni+Ni to Zr+Zr, for which the compound system decays primarily by charged-particle evaporation. In order to study heavier systems, it is, however, necessary to measure also the fraction of the decay that goes into fission fragments. In the present work we have, therefore, measured the fission cross section of 16O+197Au down to unprecedented far sub-barrier energies using a large position sensitive PPAC placed at backward angles. The preliminary cross sections will be discussed and compared to earlier studies at near-barrier energies. No conclusive evidence for sub-barrier hindrance was found, probably because the measurements were not extended to sufficiently low energies.Comment: Fusion06 - Intl. Conf. on Reaction Mechanisms and Nuclear Structure at the Coulomb Barrier, San Servolo, Venezia, Italy, March 19-223, 2006 5 pages, 4 figure

Rapid purification of yeast mitochondrial DNA in high yield

A procedure is presented for the rapid isolation of mitochondrial DNA (mtDNA) in high yield from Saccharomyces cerevisiae. Yeast cells, which may be grown to late stationary phase, are broken by a combination of enzymatic and mechanical means; mtDNA is then isolated from a crude mitochondrial lysate by a single cycle of bisbenzimide-CsCl buoyant density centrifugation. mtDNA so isolated is at least 99.5% pure, and has a mean duplex molecular weight of 24.5 [middle dot] 106. In addition to mtDNA and bulk nuclear DNA, several other yeast nucleic acid species, identified as ribosomal DNA and a mixture of duplex RNAs, form discrete bands in these gradients.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23088/1/0000005.pd

Mitochondrial DNAs of Suillus: three fold size change in molecules that share a common gene order

We constructed restriction-site and gene maps for mitochondrial DNAs from seven isolates of five species of Suillus (Boletaceae, Basidiomycotina). Each mitochondrial genome exists as a single circular chromosome, ranging in size from 36 to 121 kb. Comparisons within species and between two closely related species revealed that insertions and deletions are the major form of genome change, whereas most restriction sites are conserved. Among more distantly related species, size and restriction-site differences were too great to allow precise alignments of maps, but small clusters of putatively homologous restriction sites were found. Two mitochondrial gene orders exist in the five species. These orders differ only by the relative positions of the genes for ATPase subunit 9 and the small ribosomal RNA and are interconvertible by a single transposition. One of the two gene arrangements is shared by four species whose mitochondrial DNAs span the entire size range of 36 to 121 kb. The conservation of gene order in molecules that vary over three-fold in size and share few restriction sites demonstrates a low frequency of rearrangements relative to insertions, deletions, and base substitutions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46963/1/294_2004_Article_BF00365756.pd

Location and structure of the var1 gene on yeast mitochondrial DNA: Nucleotide sequence of the 40.0 allele

Alleles of the var1 locus on yeast mitochondrial DNA specify the size of var1 ribosomal protein. We report the nucleotide sequence of a var1 allele that determines the smallest var1 protein. It contains an open reading frame of 396 codons, which we identify as the structural gene for var1 protein. The var1 protein specified by this allele has an amino acid composition in close agreement with that predicted by the DNA sequence. The var1 coding region is highly unusual: it is 89.6% AT and contains a 46 bp GC-rich palindromic cluster that accounts for 38% of the total GC residues. Our results strongly suggest that like mammalian mitochondria but unlike those from Neurospora, yeast mitochondria use AUA as a methionine codon. Comparison with the sequence of a var1 allele specifying a larger protein suggests that some size polymorphism of var1 protein results from in-frame insertions of a variable number of AAT (Asn) codons.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23885/1/0000124.pd

Monensin Improves the Effectiveness of meso-Dimercaptosuccinate when Used to Treat Lead Intoxication in Rats

Among divalent cations, the ionophore monensin shows high activity and selectivity for the transport of lead ions (Pb(2+)) across phospholipid membranes. When coadministered to rats that were receiving meso-dimercaptosuccinate for treatment of Pb intoxication, monensin significantly increased the amount of Pb removed from femur, brain, and heart. It showed a tendency to increase Pb removal from liver and kidney but had no effect of this type in skeletal muscle. Tissue levels of several physiologic (calcium, cobalt, copper, iron, magnesium, manganese, molybdenum, zinc) and nonphysiologic (arsenic, cadmium, chromium, nickel, strontium) elements were also determined after the application of these compounds. Among the physiologic elements, a number of significant changes were seen, including both rising and falling values. The size of these changes was typically around 20% compared with control values, with the largest examples seen in femur. These changes often tended to reverse those of similar size that had occurred during Pb administration. Among the nonphysiologic elements, which were present in trace amounts, the changes were smaller in number but larger in size. None of these changes appears likely to be significant in terms of toxicity, and there were no signs of overt toxicity under any of the conditions employed. Monensin may act by cotransporting Pb(2+) and OH(–) ions out of cells, in exchange for external sodium ions. The net effect would be to shuttle intracellular Pb(2+) to extracellular dimercaptosuccinic acid thereby enhancing its effectiveness. Thus, monensin may be useful for the treatment of Pb intoxication when applied in combination with hydrophilic Pb(2+) chelators

Hindrance of Heavy-ion Fusion at Extreme Sub-Barrier Energies in Open-shell Colliding Systems

The excitation function for the fusion-evaporation reaction 64Ni+100Mo has been measured down to a cross-section of ~5 nb. Extensive coupled-channels calculations have been performed, which cannot reproduce the steep fall-off of the excitation function at extreme sub-barrier energies. Thus, this system exhibits a hindrance for fusion, a phenomenon that has been discovered only recently. In the S-factor representation introduced to quantify the hindrance, a maximum is observed at E_s=120.6 MeV, which corresponds to 90% of the reference energy E_s^ref, a value expected from systematics of closed-shell systems. A systematic analysis of Ni-induced fusion reactions leading to compound nuclei with mass A=100-200 is presented in order to explore a possible dependence of the fusion hindrance on nuclear structure.Comment: 10 pages, 9 figures, Submitted to Phys. Rev.

Experimental limits on nucleon decay and ΔB=2 processes

Results from the IMB collabration to detect possible proton decay in a salt mine near Cleveland, Ohio are presented. Detection apparatus is described.(AIP)Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87900/2/1_1.pd

The search for proton decay

Following a very brief description of the theoretical developments which motivated the search for proton decay, I shall describe one of these experiments (the IMB experiment) in some detail. Then I shall compare recent results from that experiment with those from other detectors.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87399/2/321_1.pd

IMB Detector‐The first 30 Days

A large water Chernekov detector, located 2000 feet below ground, has recently been turned on. The primary purpose of the device is to measure nucleon stability to limits 100 times better than previous measurements. The properties of the detector are described along with its operating characteristics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87428/2/138_1.pd