"Civilization arranged in chronological strata": a digital approach to the English semantic space

No abstract available

Lorentz and CPT Violation in the Higgs Sector

Colladay and Kostelecky have proposed a framework for studying Lorentz and CPT violation in a natural extension of the Standard Model. Although numerous bounds exist on the Lorentz and CPT violating parameters in the gauge boson and fermion sectors, there are no published bounds on the parameters in the Higgs sector. We determine these bounds. The bounds on the CPT-even asymmetric coefficients arise from the one-loop contributions to the photon propagator, those from the CPT-even symmetric coefficients arise from the equivalent c_{\mu\nu} coefficients in the fermion sector, and those from the CPT-odd coefficient arise from bounds on the vacuum expectation value of the Z-boson.Comment: 17 pages, 1 figure, 1 table; Clarifications and changes to text, results unchanged. References added. Version to be published in Physical Review

Chemigation

Presented at the Central Plains irrigation short course and exposition on February 4, 1997 at the Colby Community Building in Colby, Kansas

Impact assessment of food policy research a stocktaking workshop: synthesis report

"This stocktaking workshop provided an opportunity for several groups with active interest in impact assessment relating to agricultural policy research to share experiences and views about what constitutes good practice in this field. The sponsoring organizations have had a long-standing concern for the relevance and effectiveness of agricultural and food policy research in general and at IFPRI in particular. That concern has been addressed in past meetings and the time seemed right for a further stocktaking. The focus of this 2004 meeting was on impact assessment experience at IFPRI. IFPRI has, since the mid-1990s, carried out a variety of activities aimed at assessing the impact of its policy research, capacity strengthening, and policy communications programs. The workshop brought together practitioners of such impact assessment work, users of such information, as well as researchers whose activities have been the subject of impact assessment. The cogency and necessity of such impact accounting work was reaffirmed in general terms. There was constructively critical commentary on the merits of particular approaches and instruments, such as narrative recordings and more quantitative methods of attempting to measure effects of research investments. The perennial issue of challenging counterfactuals was necessarily addressed, and the practicality of experimental and quasi-experimental methods considered. The need for consistency of assessment approaches between ex post studies (which have been the bulk of IFPRI's experience to date) and ex ante assessment efforts that represent an increasing share of the assessment portfolio was also discussed. There has long been a commitment to work towards a strong impact-orientation “culture” within IFPRI; the workshop concluded that, while there has been progress in working toward mainstreaming such a culture, there is still far to go, and efforts must continue in this direction." from Author's AbstractImpact assessment, Agricultural policy, Food policy Research, Capacity strengthening, Research methods,

Molecular and biochemical investigation of the mechanisms of acclimation to chilling stress in maize seedlings

Seedlings of chilling-sensitive maize inbred G50 (Pioneer) survived poorly when exposed to a chilling stress. Acclimation or ABA treatment caused a dramatic improvement of chilling tolerance. Differences in gene expression between acclimated and unacclimated seedlings were investigated and three cDNA clones (designated car333, car30, and car757) were isolated, representing transcripts that were up-regulated during acclimation. Car30 and car757 were not homologous to any known sequence but car333 was 97.8% homologous to cat3, maize mitochondrial catalase. The up-regulation of CAT3 during acclimation suggested that chilling stress caused the generation of H[subscript]2O[subscript]2 in the mitochondria and increased catalase was needed to prevent oxidative damage. Measurement of H[subscript]2O[subscript]2 revealed a 4-fold increase in the coleoptile+leaf and mesocotyl of chilled seedlings but H[subscript]2O[subscript]2 was maintained near unchilled levels in seedlings that were acclimated before chilling. In effort to explain the acclimation-induced protection from oxidative stress, isozyme profiles of catalase, guaiacol peroxidase, superoxide dismutase, ascorbate peroxidase, and glutathione reductase were examined. None of the enzymes responded to acclimation in the coleoptile+leaf. However, examination of ascorbate and glutathione pools revealed an increased synthesis of glutathione, which might be responsible for the protection of the coleoptile+leaf from oxidative stress. In the mesocotyl, superoxide dismutase and ascorbate peroxidase were unaffected but catalase, peroxidase, and glutathione reductase were altered by acclimation. It was proposed that induction of CAT3 may serve as the first line of defense against mitochondria-generated H[subscript]2O[subscript]2. Induction of cell wall peroxidases may be responsible for the observed increase in lignin content, which would serve to improve the mechanical strength of mesocotyls and allow them to remain intact when exposed to a chilling stress. Cytosolic glutathione reductase may have been shifted to forms that were more active at low temperature. All of these changes illustrated the numerous ways that chilling tolerance was enhanced in the mesocotyl. In contrast to acclimation, the response of antioxidant enzymes to ABA was dramatically different. Despite the fact that both ABA and acclimation induced chilling tolerance, the mechanisms of action were clearly different, at least in terms of antioxidant defenses