Action research on alternative land tenure arrangements in Wenchi,Ghana: learning from ambiguous social dynamics and self-organized institutional innovation     

Samuel Adjei-Nsiah  Cees Leeuwis  Ken E. Giller  Thom W. Kuyper 《Agriculture and Human Values》2008,25(3):389-403

This study reports on action research efforts that were aimed at developing institutional arrangements beneficial for soil fertility improvement. Three stages of action research are described and analyzed. We initially began by bringing stakeholders together in a platform to engage in a collaborative design of new arrangements. However, this effort was stymied mainly because conditions conducive for learning and negotiation were lacking. We then proceeded to support experimentation with alternative arrangements initiated by individual landowners and migrant farmers. The implementation of these arrangements too ran into difficulties due to intra-family dynamics and ambiguities regarding land tenure. Further investigations to find out how ambiguities could be tackled revealed that the local actors themselves had taken initiatives towards developing institutional innovations to reduce ambiguities. However, there is still considerable scope for further development of these self-organized innovations. The article ends with a reflection on inter-disciplinary action research, where it is argued that making “mistakes” is an inherent and necessary characteristic in action research that aims to address complex social issues.

Samuel Adjei-NsiahEmail:

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Coeval large-scale magmatism in the Kalahari and Laurentian cratons during Rodinia assembly     

Hanson RE  Crowley JL  Bowring SA  Ramezani J  Gose WA  Dalziel IW  Pancake JA  Seidel EK  Blenkinsop TG  Mukwakwami J 《Science (New York, N.Y.)》2004,304(5674):1126-1129

We show that intraplate magmatism occurred 1106 to 1112 million years ago over an area of two million square kilometers within the Kalahari craton of southern Africa, during the same magnetic polarity chron as voluminous magmatism within the cratonic core of North America. These contemporaneous magmatic events occurred while the Rodinia supercontinent was being assembled and are inferred to be parts of a single large igneous province emplaced across the two cratons. Widespread intraplate magmatism during Rodinia assembly shows that mantle upwellings required to generate such provinces may occur independently of the supercontinent cycle.  相似文献   

Memory transfer   总被引：3，自引：0，他引：3  

W L Byrne  D Samuel  E L Bennett  M R Rosenzweig  E Wasserman 《Science (New York, N.Y.)》1966,153(736):658-659

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U-Pb ages from the neoproterozoic Doushantuo Formation, China   总被引：4，自引：0，他引：4  

Condon D  Zhu M  Bowring S  Wang W  Yang A  Jin Y 《Science (New York, N.Y.)》2005,308(5718):95-98

U-Pb zircon dates from volcanic ash beds within the Doushantuo Formation (China) indicate that its deposition occurred between 635 and 551 million years ago. The base records termination of the global-scale Marinoan glaciation and is coeval with similar dated rocks from Namibia, indicating synchronous deglaciation. Carbon isotopic and sequence-stratigraphic data imply that the spectacular animal fossils of the Doushantuo Formation are for the most part younger than 580 million years old. The uppermost Doushantuo Formation contains a pronounced negative carbonate carbon isotopic excursion, which we interpret as a global event at circa 551 million years ago.  相似文献   

Convergence of Campylobacter species: implications for bacterial evolution     

Sheppard SK  McCarthy ND  Falush D  Maiden MC 《Science (New York, N.Y.)》2008,320(5873):237-239

The nature of species boundaries in bacteria remains controversial. In particular, the mechanisms of bacterial speciation and maintenance in the face of frequent genetic exchange are poorly understood. Here, we report patterns of genetic exchange that show two closely related zoonotic pathogenic species, Campylobacter jejuni and Campylobacter coli, are converging as a consequence of recent changes in gene flow. Population expansion into a novel ecological niche generated by human activity is the most probable explanation for the increase in genetic exchange between these species. Bacterial speciation can therefore occur by mechanisms analogous to those seen in metazoans, where genetic diversification and incipient speciation caused by ecological factors have been reported in several genera.  相似文献   

Statement on scientific publication and security     

Atlas R  Campbell P  Cozzarelli NR  Curfman G  Enquist L  Fink G  Flanagin A  Fletcher J  George E  Hammes G  Heyman D  Inglesby T  Kaplan S  Kennedy D  Krug J  Levinson R  Marcus E  Metzger H  Morse SS  O'Brien A  Onderdonk A  Poste G  Renault B  Rich R  Rosengard A  Salzburg S  Scanlan M  Shenk T  Tabor H  Varmus H  Wimmer E  Yamamoto K;Journal Editors  Authors Group 《Science (New York, N.Y.)》2003,299(5610):1149

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Comparative genomics of trypanosomatid parasitic protozoa     

El-Sayed NM  Myler PJ  Blandin G  Berriman M  Crabtree J  Aggarwal G  Caler E  Renauld H  Worthey EA  Hertz-Fowler C  Ghedin E  Peacock C  Bartholomeu DC  Haas BJ  Tran AN  Wortman JR  Alsmark UC  Angiuoli S  Anupama A  Badger J  Bringaud F  Cadag E  Carlton JM  Cerqueira GC  Creasy T  Delcher AL  Djikeng A  Embley TM  Hauser C  Ivens AC  Kummerfeld SK  Pereira-Leal JB  Nilsson D  Peterson J  Salzberg SL  Shallom J  Silva JC  Sundaram J  Westenberger S  White O  Melville SE  Donelson JE  Andersson B  Stuart KD  Hall N 《Science (New York, N.Y.)》2005,309(5733):404-409

A comparison of gene content and genome architecture of Trypanosoma brucei, Trypanosoma cruzi, and Leishmania major, three related pathogens with different life cycles and disease pathology, revealed a conserved core proteome of about 6200 genes in large syntenic polycistronic gene clusters. Many species-specific genes, especially large surface antigen families, occur at nonsyntenic chromosome-internal and subtelomeric regions. Retroelements, structural RNAs, and gene family expansion are often associated with syntenic discontinuities that-along with gene divergence, acquisition and loss, and rearrangement within the syntenic regions-have shaped the genomes of each parasite. Contrary to recent reports, our analyses reveal no evidence that these species are descended from an ancestor that contained a photosynthetic endosymbiont.  相似文献   

Self-assembly of large and small molecules into hierarchically ordered sacs and membranes     

Capito RM  Azevedo HS  Velichko YS  Mata A  Stupp SI 《Science (New York, N.Y.)》2008,319(5871):1812-1816

We report here the self-assembly of macroscopic sacs and membranes at the interface between two aqueous solutions, one containing a megadalton polymer and the other, small self-assembling molecules bearing opposite charge. The resulting structures have a highly ordered architecture in which nanofiber bundles align and reorient by nearly 90 degrees as the membrane grows. The formation of a diffusion barrier upon contact between the two liquids prevents their chaotic mixing. We hypothesize that growth of the membrane is then driven by a dynamic synergy between osmotic pressure of ions and static self-assembly. These robust, self-sealing macroscopic structures offer opportunities in many areas, including the formation of privileged environments for cells, immune barriers, new biological assays, and self-assembly of ordered thick membranes for diverse applications.  相似文献   

Issues in biosecurity and biosafety     

Cook-Deegan RM  Berkelman R  Davidson EM  Finder S  Heitman E  Kelley MC  King NM  Moseley R  Thomas JC  Tilden SJ  Vangsnes NM 《Science (New York, N.Y.)》2005,308(5730):1867-1868

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Tracing the origin and fate of NOx in the Arctic atmosphere using stable isotopes in nitrate     

Morin S  Savarino J  Frey MM  Yan N  Bekki S  Bottenheim JW  Martins JM 《Science (New York, N.Y.)》2008,322(5902):730-732

Atmospheric nitrogen oxides (NOx =NO+ NO2) play a pivotal role in the cycling of reactive nitrogen (ultimately deposited as nitrate) and the oxidative capacity of the atmosphere. Combined measurements of nitrogen and oxygen stable isotope ratios of nitrate collected in the Arctic atmosphere were used to infer the origin and fate of NOx and nitrate on a seasonal basis. In spring, photochemically driven emissions of reactive nitrogen from the snowpack into the atmosphere make local oxidation of NOx by bromine oxide the major contributor to the nitrate budget. The comprehensive isotopic composition of nitrate provides strong constraints on the relative importance of the key atmospheric oxidants in the present atmosphere, with the potential for extension into the past using ice cores.  相似文献