Assessment of strength development of cemented desert soil

For highway construction or any superstructure, on dune sand, designers and construction teams must ensure that the foundation soil is stable enough to provide support for the applied loads. Sand dunes are stretched across Libyan deserts that make road construction a challenge because of the poor soil base. Replacement of such a weak soil is very expensive and not economically feasible, and, in many cases, there is no alternative soil nearby. This study used two different mix designs aimed at stabilizing the existing base course using a mix of dune sand and manufactured sand with a small percentage of Portland cement. Compaction, unconfined compressive strength and California bearing ratio tests were conducted on the treated sample with a varying cement proportion of 0%, 3%, 5% and 7% by weight. The first tests were done with a mix of 50% dune sand and 50% crushed sand that is shown to have excellent results. For a more economic design, this study also included testing of another mix design with 70% dune sand and 30% crushed sand; laboratory results show this 70%/30% mixture was appropriate to use as a base-treated material for road construction material. This mix resulted in overall superior performance. Its use will reduce the cost of road construction by saving materials and time, and it will also have lower environmental impacts in desert areas. This study has shown that the stabilization of weak material (desert sand) by using cement improves the strength characteristics of the treated soil.

Plant gene targeting and gene replacement: application to crop genetic improvement

Recent advances and limitations of using zinc finger nuclease to stimulate a high efficiency of homologous recombination, and chimeric oligonucleotides to promote single base replacement in functional genomic research and plant genetic breeding, are systematically reviewed. Approaches to improve gene targeting efficiency through molecular modification of key pathways in plant homologous recombination are also discussed.

Fitness of a Turnip Crinkle Virus Satellite RNA Correlates with a Sequence-Nonspecific Hairpin and Flanking Sequences That Enhance Replication and Repress the Accumulation of Virions

ABSTRACT satC, a satellite RNA associated with Turnip crinkle virus (TCV), enhances the ability of the virus to colonize plants by interfering with stable virion accumulation (F. Zhang and A. E. Simon, unpublished data). Previous results suggested that the motif1-hairpin (M1H), a replication enhancer on minus strands, forms a plus-strand hairpin flanked by CA-rich sequence that may be involved in enhancing systemic infection (G. Zhang and A. E. Simon, J. Mol. Biol. 326:35-48, 2003). In this study, sequence and structural requirements of the M1H were further assayed by replacing the 28-base M1H with 10 random bases and then subjecting the pool of satellite RNA to functional selection in plants. Unlike previous results with 28-base replacement sequences (G. Zhang and A. E. Simon, J. Mol. Biol. 326:35-48, 2003), only a few of the 10-base SELEX (systematic evolution of ligands by exponential enrichment) assay winners contained short motifs in their minus-sense orientation that were similar to TCV replication elements. However, all second- and third-round winning replacement sequences folded into hairpins flanked by CA-rich sequence predicted to be more stable on plus strands than minus strands. Plus strands of several of the most fit satellite RNAs contained insertions of CA-rich sequence at the base of their hairpins whose presence correlated with enhanced replication and reduced detection of virions. Deletion of the M1H resulted in no detectable virions despite very low satellite accumulation. These results support the hypothesis that a sequence-nonspecific plus-strand hairpin brings together flanking CA-rich sequences in the M1H region that confers fitness to satC by reducing the accumulation of stable virions.

Detection of a Variant Metallo-β-Lactamase, IMP-10, from Two Unrelated Strains of Pseudomonas aeruginosa and an Alcaligenes xylosoxidans Strain

ABSTRACT The gene bla IMP-10 of a variant metallo-β-lactamase, IMP-10, had a single base replacement of G by T at nucleotide 145, which led to an amino acid alteration of Val49 to Phe compared to the IMP-1 enzyme, indicating that IMP-10 was a point mutation derivative of IMP-1. Highly purified enzymes revealed that IMP-10 was different from IMP-1 in its extremely low hydrolyzing activities for penicillins, such as benzylpenicillin, ampicillin, and piperacillin.