Global impacts of land degradation

Study commissioned by the Scientific, Technical and Advisory Panel (STAP) of the Global Environment Facility (GEF) to support the development of the new GEF focal area of Land Degradatio

Environmental Education Through The Use Of Erosional Features

Article from Geographical Proceedings of 1979/80.This article is based upon teaching materials prepared for the FAO Southern Africa Training Programme (Overseas Development Group, Norwich) and in preparation for another FAC project in land use and regional planning, Central Province, Zambia

Studies on the biosynthesis of paraherquamide A and the total synthesis of (±) VM55599

2001 Summer.Includes bibliographical references.Studies that partially elucidate the biosynthetic pathway of the heptacyclic fungal metabolite, Paraherquamide A are presented. Through biosynthetic feeding experiments with stable isotope labeled compounds, it was determined that the carbon skeleton of paraherquamide A consists of three amino acids and two equivalents of dimethylallyl pyrophosphate. L-methionine was determined to be the precursor to C-29, L-tryptophan was determined to be the precursor to the oxindole moiety and L-isoleucine was determined to be the precursor to the β-hydroxy- β-methylproline ring of paraherquamide A. A subsequent feeding experiment with [5-13C3H2]-L-isoleucine indicated that L-isoleucine is converted to β-methyl-proline via a 4-electron oxidation and that the pro-S hydrogen of C-5 is retained in the oxidative cyclization. The incorporation of [1-13C]-3(S)-methyl-L-proline also indicated that L-isoleucine undergoes oxidative cyclization prior to coupling to L-tryptophan. The two dimethylallyl pyrophosphate-derived portions of paraherquamide A were found to arise via the well-known mevalonic acid pathway. In addition, it was determined that P. fellutanum, a paraherquamide A producing fungus, installs theses two dimethylallyl groups in two stereo-facially distinct manners. The C5 unit (C-19~C-23) leading to the bicyclo[2.2.2]diazaoctan ring is formed in an entirely non-stereospecific manner, while the C-5 unit (C-24~C-28) leading to the dioxepin ring is installed in a completely stereospecific manner. Only the latter observation is consistent with the mechanism of known prenylase enzymes. The first total synthesis of VM55599, a proposed precursor of paraherquamide A, was completed. Feeding experiments with doubly 13C-labeled racemic VM55599, its diastereomer and the oxidized forms of these compounds were performed on P. fellutanum. Only the diasteromer of VM55599 (244a) was incorporated. The incorporation of the bicyclic intermediate signifies that the dimethylallyl group leading to C-19~C-23 of paraherquamide A is installed prior to the dimethylallyl group leading to C-24~C-28. In addition, the incorporation 244a indicates that the oxidations of the indole ring leading to the spirooxindole and the dioxepin ring occur after the formation of the bicyclic ring system

Soil and water conservation in semi-arid Kenya

Sub-Saharan Africa is beset by an increasing population putting stringent demands on a declining resource base. Soil and water conservation (S&WC) is often seen as the primary means to arrest the inevitable decline in soil quality and maintain the productivity of farming systems upon which the majority of the populace rely for their precarious living standards. Yet S&WC programmes have a patchy record: in humid areas they may be relatively successful, but in semi-arid areas there is neither evidence of widespread adoption of S&WC nor increased production. These marginal areas, economically and climatically present the most intractable challenge to natural resource managers. This study investigates the performance of S&WC in rainfed cropping in the drier parts of Kenya, paying particular emphasis to the yield benefits and economic viability of crop production systems for the small scale and most vulnerable of the rural land users. Results are based upon a series of experiments conducted over three crop growing seasons on three soils, testing 10 S&WC based crop production systems with a monocrop of 75-day (short-season) maize (Zea mays L.: var. Makueni composite). The S&WC measures range from physical techniques of contour tillage, tied ridging and terraces to a partly biological technique of trashlines. Hand tillage was taken as the control. In this marginal environment (agro-climatic zones IV and V), the typical situation of smallscale farmers adding no fertilizer was compared with currently recommended levels of application of fertilizer and manure

Common-Value Auctions with Liquidity Needs: An Experimental Test of a Troubled Assets Reverse Auction

We experimentally test alternative auction designs suitable for pricing and removing troubled assets from banks’ balance sheets as part of the financial rescue. Many individual securities or pools of securities are auctioned simultaneously. Securities that are widely held are purchased in auctions for individual securities. Securities with concentrated ownership are purchased as pools of related securities. Each bank has private information about its liquidity need and the true common value of each security. We study bidding behavior and performance of sealed-bid uniform-price auctions and dynamic clock auctions. The clock and sealed-bid auctions resulted in similar prices. However, the clock auctions resulted in substantially higher bank payoffs, since the dynamic auction enabled the banks to better manage their liquidity needs. The clock auctions also reduced bidder error. The experiments demonstrated the feasibility of quickly implementing simple and effective auction designs to help resolve the crisis.Auctions, financial auctions, financial crisis

Sources Shared on Twitter: A Case Study on Immigration

The study, which aimed to better understand the types of information sources that users on one popular social media platform may see about a major national policy issue, finds that news organizations play a far larger role than other types of content providers, such as commentary or government sites.This is especially true in regards to one contentious issue: immigration

Indentification of the Metabolites of 3-Nitrofluoranthene and 2-Nitrofluoranthene Formed by Samonella Typhimurium Strains TA98, TA98 ND, and TA98/1, 8-DNP6

3-Nitrofluoranthene (3-NFA) and 2-nitrofluoranthene (2-NFA) are environmental pollutants produced during combustion processes, proven to be mutagenic in bacterial assays and potentially carcinogenic in mammalian species. 3-NFA was incubated with Salmonella typhimurium strain TA98 and its variants TA98 ND and TA98/1,8-DNP6, deficient in nitroreductase and transacetylase enzymes respectively. All three strains produced equal amounts of the reductive metabolite 3-aminofluoranthene (3-AFA) over six hours of incubation. The nitroreductase deficient strain TA98 ND produced the metabolite at a slower initial rate of conversion than the nitroreductase proficient TA98 and TA98/1,8-DNP6. 2-NFA incubated with TA98 and TA98 ND produced two identifiable metabolites 2-aminofluoranthene (2-AFA), and N-acetyl-2-aminofluoranthene (2-NAAFA) within 24 hours of incubation. The production of metabolites by TA98 ND was significantly slower than that of TA98. TA98/1,8-DNP5 produced only 2-AFA at slower rates than TA98. The metabolism of 2-NFA by the Salmonella strains progressed at slower rates than that of 3-NFA. This reflects the difference observed in the mutagenicity of these compounds as measured by the Ames assay (3-NFA highly mutagenic, 2-NFA slightly to moderately mutagenic).Master of Science in Public Healt

Reversible defects in natural killer and memory CD8 T cell lineages in interleukin 15-deficient mice

C57BL/6 mice genetically deficient in interleukin 15 (IL-15(-/-) mice) were generated by gene targeting. IL-15(-/-) mice displayed marked reductions in numbers of thymic and peripheral natural killer (NK) T cells, memory phenotype CD8+ T cells, and distinct subpopulations of intestinal intraepithelial lymphocytes (IELs). The reduction but not absence of these populations in IL-15(-/-) mice likely reflects an important role for IL-15 for expansion and/or survival of these cells. IL-15(-/-) mice lacked NK cells, as assessed by both immunophenotyping and functional criteria, indicating an obligate role for IL-15 in the development and functional maturation of NK cells. Specific defects associated with IL-15 deficiency were reversed by in vivo administration of exogenous IL-15. Despite their immunological defects, IL-15(-/-) mice remained healthy when maintained under specific pathogen-free conditions. However, IL-l5(-/-) mice are likely to have compromised host defense responses to various pathogens, as they were unable to mount a protective response to challenge with vaccinia virus. These data reveal critical roles for IL-15 in the development of specific lymphoid lineages. Moreover, the ability to rescue lymphoid defects in IL-15(-/-) mice by IL-15 administration represents a powerful means by which to further elucidate the biological roles of this cytokine