863 research outputs found
Cordagalma tottoni Margulis 1993
No full textCordagalma tottoni Margulis, 1993. Diagnosis. Small, typically heart-shaped nectophores. Pedicular canal, on reaching nectosac, gives rise to only upper and lower radial canals. Lateral canals arise from the upper canal. Remarks. The original description of Cordagalma tottoni was based on fragments of a single specimen collected, using a Juday net in the 100 –0m depth zone, by the Research Vessel Vozrozhedenia on 18 th December 1986 at 35 °S 139 °W, in the middle of the South Pacific Ocean. The material was said to consist of a stem, with pneumatophore and various buds, three nectophores, two gastrozooids, and several siphosomal fragments. The type specimen has been re-examined by the present author. A problem with Margulis' (1993) description of the nectophores is that she had orientated them upside-down, such that she considered the conical lower part of the nectophore to be anterior. This apart, the only real distinguishing feature of the nectophores, the largest of which measured 3.5 mm in height and 2.5 mm in width, was that the pedicular canal, on reaching the nectosac, gave rise to only the upper and lower radial canals (Figure 12). The lateral radial canals then arose from the upper (ventral according to Margulis) canal. This, with some difficulty, was confirmed by the present author and, thus, is in contrast to the arrangement in all other Cordagalma species herein described where all the radial canals arise together from the pedicular canal. It is far from certain that the siphosomal zooids described by Margulis (1993) actually belong to the same specimen as the detached nectophores. Some of the palpons were said to have palpacles (Figure 12) while others did not. This suggests their presence and subsequent loss, which would be in marked contrast to the arrangement in other Cordagalma species, but is in accord with that found for Cardianecta parchelion gen. nov., sp. nov. described below. However, the re-examination showed that the palpons, which were attached at their bases, appeared not to possess palpacles. The loose gastrozooids had the proximal part of the tentacles attached, which bore, presumably, young tentilla with long pedicles and oval cnidobands, with a beak-shaped tip. There was said to be a single row of larger nematocysts on either side of the cnidoband, enclosing numerous smaller ones. No further details could be added. These are quite unlike the tentilla of C. ordinatum that Margulis (1993, Figure 2 E) figured but, again, those of Cardianecta parchelion gen. nov., sp. nov. are very different. The bracts of C. tottoni also were markedly different in having a transverse ridge demarcating a triangular distal facet on the upper side, and with a bracteal canal that was said to end below the middle of a strip of nematocysts running proximally from the distal tip of the bract. Finally, Margulis described the gonophores as being immature but, on re-examination, the sex of some could be determined and they all appeared to be female. It is, however, doubtful that this observation has any significance. Thus, until a complete specimen of Cordagalma tottoni is collected it is impossible to know if the siphosomal zooids described by Margulis (1993) actually belong with the nectophores. Nonetheless, the fact, since confirmed by the present author, that the lateral radial canals on the nectosac arise from the upper canal is a distinguishing feature setting this species apart from all other Cordagalma species. Distribution. Known only from a single specimen collected in superficial waters in the central South Pacific Ocean (c, 35 ° S 139 ° W). Etymology. Named for Arthur Knyvett Totton whose Synopsis of the Siphonophora, published in 1965, remains the most important work on siphonophores published to date.Published as part of P. R. Pugh, 2016, A synopsis of the Family Cordagalmatidae fam. nov. (Cnidaria, Siphonophora, Physonectae), pp. 1-64 in Zootaxa 4095 (1) on pages 16-17, DOI: 10.11646/zootaxa.4095.1.1, http://zenodo.org/record/26138
Specialty fibres and components for advanced microscopy
No full textWe investigate fibre basic functions like SHG and pulse gating. We achieved 5.2% conversion efficiency into green light with 50 W peak pump power and demonstrated in-fibre pulse gating at 1 MHz repetition rat
Lynn Margulis, architect of the endosymbiotic theory
No full textInternational audienceLynn Margulis is known as the scientist who advanced the endosymbiotic theory in the late 60’s (Sagan, 1967) and brought it from its rejection to its acceptance by the scientific community in the 80’s. Nevertheless, Margulis’ contribution was neither new, nor decisive in terms of conclusive experiments. The hypothesis of an endosymbiotic origin of chloroplast was first proposed in the late 19th century. In the 60’s, Margulis professor's Hans Ris showed convincingly that plastids contain their own genetic material and revived the endosymbiotic hypothesis (Ris & Plaut, 1962). Similar hypotheses about mitochondria were made in the early 20th century and their DNA was then discovered in the same period than plastidial DNA. The passionate 70’s debate opposing symbiotic origin supporters and opponents remained unresolved until the development of a new field of biology to which Margulis addressed much criticism: molecular phylogeny. Moreover, the aspects of the theory she was the only scientist to defend (the symbiotic origin of the microtubule system) were not confirmed after 50 years of research. One could wonder which role Margulis played in reaching the consensus.I will argue that the original contribution of Margulis lies in her efforts to contextualize the mitochondrial and plastidial nature in a complete and coherent scenario of the evolution of life on Earth, and to combine all biological disciplines (and beyond): cell biology, biochemistry, genetics, symbiosis studies, systematics, paleontology. Thanks to her, this event of life history became a cross-disciplinary subject in debate at an international level. It allowed to review scattered and sometimes seemingly contradictory data. It stimulated research into this topic, whose results contributed in turn to support the theory. Margulis started a fruitful research program. References:Ris, H., Plaut, W. 1962. Ultrastructure of DNA-containing areas in the chloroplast of Chlamydomonas. The Journal of Cell Biology 13(3): 383‐391.Sagan, L. 1967. On the origin of mitosing cells. Journal of theoretical biology 14(3): 225‐274
Lynn Margulis, architect of the endosymbiotic theory
No full textInternational audienceLynn Margulis is known as the scientist who advanced the endosymbiotic theory in the late 60’s (Sagan, 1967) and brought it from its rejection to its acceptance by the scientific community in the 80’s. Nevertheless, Margulis’ contribution was neither new, nor decisive in terms of conclusive experiments. The hypothesis of an endosymbiotic origin of chloroplast was first proposed in the late 19th century. In the 60’s, Margulis professor's Hans Ris showed convincingly that plastids contain their own genetic material and revived the endosymbiotic hypothesis (Ris & Plaut, 1962). Similar hypotheses about mitochondria were made in the early 20th century and their DNA was then discovered in the same period than plastidial DNA. The passionate 70’s debate opposing symbiotic origin supporters and opponents remained unresolved until the development of a new field of biology to which Margulis addressed much criticism: molecular phylogeny. Moreover, the aspects of the theory she was the only scientist to defend (the symbiotic origin of the microtubule system) were not confirmed after 50 years of research. One could wonder which role Margulis played in reaching the consensus.I will argue that the original contribution of Margulis lies in her efforts to contextualize the mitochondrial and plastidial nature in a complete and coherent scenario of the evolution of life on Earth, and to combine all biological disciplines (and beyond): cell biology, biochemistry, genetics, symbiosis studies, systematics, paleontology. Thanks to her, this event of life history became a cross-disciplinary subject in debate at an international level. It allowed to review scattered and sometimes seemingly contradictory data. It stimulated research into this topic, whose results contributed in turn to support the theory. Margulis started a fruitful research program. References:Ris, H., Plaut, W. 1962. Ultrastructure of DNA-containing areas in the chloroplast of Chlamydomonas. The Journal of Cell Biology 13(3): 383‐391.Sagan, L. 1967. On the origin of mitosing cells. Journal of theoretical biology 14(3): 225‐274
Lynn Margulis, architect of the endosymbiotic theory
No full textInternational audienceLynn Margulis is known as the scientist who advanced the endosymbiotic theory in the late 60’s (Sagan, 1967) and brought it from its rejection to its acceptance by the scientific community in the 80’s. Nevertheless, Margulis’ contribution was neither new, nor decisive in terms of conclusive experiments. The hypothesis of an endosymbiotic origin of chloroplast was first proposed in the late 19th century. In the 60’s, Margulis professor's Hans Ris showed convincingly that plastids contain their own genetic material and revived the endosymbiotic hypothesis (Ris & Plaut, 1962). Similar hypotheses about mitochondria were made in the early 20th century and their DNA was then discovered in the same period than plastidial DNA. The passionate 70’s debate opposing symbiotic origin supporters and opponents remained unresolved until the development of a new field of biology to which Margulis addressed much criticism: molecular phylogeny. Moreover, the aspects of the theory she was the only scientist to defend (the symbiotic origin of the microtubule system) were not confirmed after 50 years of research. One could wonder which role Margulis played in reaching the consensus.I will argue that the original contribution of Margulis lies in her efforts to contextualize the mitochondrial and plastidial nature in a complete and coherent scenario of the evolution of life on Earth, and to combine all biological disciplines (and beyond): cell biology, biochemistry, genetics, symbiosis studies, systematics, paleontology. Thanks to her, this event of life history became a cross-disciplinary subject in debate at an international level. It allowed to review scattered and sometimes seemingly contradictory data. It stimulated research into this topic, whose results contributed in turn to support the theory. Margulis started a fruitful research program. References:Ris, H., Plaut, W. 1962. Ultrastructure of DNA-containing areas in the chloroplast of Chlamydomonas. The Journal of Cell Biology 13(3): 383‐391.Sagan, L. 1967. On the origin of mitosing cells. Journal of theoretical biology 14(3): 225‐274
Lynn Margulis, architect of the endosymbiotic theory
No full textInternational audienceLynn Margulis is known as the scientist who advanced the endosymbiotic theory in the late 60’s (Sagan, 1967) and brought it from its rejection to its acceptance by the scientific community in the 80’s. Nevertheless, Margulis’ contribution was neither new, nor decisive in terms of conclusive experiments. The hypothesis of an endosymbiotic origin of chloroplast was first proposed in the late 19th century. In the 60’s, Margulis professor's Hans Ris showed convincingly that plastids contain their own genetic material and revived the endosymbiotic hypothesis (Ris & Plaut, 1962). Similar hypotheses about mitochondria were made in the early 20th century and their DNA was then discovered in the same period than plastidial DNA. The passionate 70’s debate opposing symbiotic origin supporters and opponents remained unresolved until the development of a new field of biology to which Margulis addressed much criticism: molecular phylogeny. Moreover, the aspects of the theory she was the only scientist to defend (the symbiotic origin of the microtubule system) were not confirmed after 50 years of research. One could wonder which role Margulis played in reaching the consensus.I will argue that the original contribution of Margulis lies in her efforts to contextualize the mitochondrial and plastidial nature in a complete and coherent scenario of the evolution of life on Earth, and to combine all biological disciplines (and beyond): cell biology, biochemistry, genetics, symbiosis studies, systematics, paleontology. Thanks to her, this event of life history became a cross-disciplinary subject in debate at an international level. It allowed to review scattered and sometimes seemingly contradictory data. It stimulated research into this topic, whose results contributed in turn to support the theory. Margulis started a fruitful research program. References:Ris, H., Plaut, W. 1962. Ultrastructure of DNA-containing areas in the chloroplast of Chlamydomonas. The Journal of Cell Biology 13(3): 383‐391.Sagan, L. 1967. On the origin of mitosing cells. Journal of theoretical biology 14(3): 225‐274
Margulis lemma for compact lie groups
No full textWe improve Margulis lemma for a compact connected Lie group G: there is a neighborhood U of the identity such that for any finite subgroup Gamma subset of G, U boolean AND Gamma generates an abelian group. We show that for each n, there exists an integer w(n) > 0, such that if H is a closed subgroup of a compact connected Lie group G of dimension n, then the quotient group, H / H-0, has an abelian subgroup of index <= w(n), where H-0 is the identity component of H. As an application, we show that the fundamental group of the homogeneous space G / H has an abelian subgroup of index <= w(n). We show this same property for the fundamental groups of almost non-negatively curved n-manifolds whose universal coverings are not collapsed.MathematicsSCI(E)0ARTICLE2395-40625
Lynn Margulis and the endosymbiont hypothesis: 50 years later
No full textThe 1967 article “On the Origin of Mitosing Cells” in the Journal of Theoretical Biology by Lynn Margulis (then Lynn Sagan) is widely regarded as stimulating renewed interest in the long-dormant endosymbiont hypothesis of organelle origins. In her article, not only did Margulis champion an endosymbiotic origin of mitochondria and plastids from bacterial ancestors, but she also posited that the eukaryotic flagellum (undulipodium in her usage) and mitotic apparatus originated from an endosymbiotic, spirochete-like organism. In essence, she presented a comprehensive symbiotic view of eukaryotic cell evolution (eukaryogenesis). Not all of the ideas in her article have been accepted, for want of compelling evidence, but her vigorous promotion of the role of symbiosis in cell evolution unquestionably had a major influence on how subsequent investigators have viewed the origin and evolution of mitochondria and plastids and the eukaryotic cell per se.</jats:p
On the Margulis constant for Kleinian groups
No full textAbstract. The Margulis constant for Kleinian groups is the smallest constant c such that for each discrete group G and each point x in the upper half space H 3 , the group generated by the elements in G which move x less than distance c is elementary. We take a first step towards determining this constant by proving that if f, g is nonelementary and discrete with f parabolic or elliptic of order n ≥ 3 , then every point x in H 3 is moved at least distance c by f or g where c = .1829 . . . . This bound is sharp
Food Aid and the WTO: Can New Rules Be Effective?
No full textA new Agreement on Agriculture from the Doha Development Agenda negotiations is certain to contain binding rules on food aid shipments. Negotiating parties are concerned that food aid has been used as a form of export competition policy, and they seek the use of coercive WTO legislation to prevent the disposal of surplus agricultural commodities as food aid. Current Uruguay Round food aid guidelines are contrasted with the most recent Doha Development Agenda proposals, and the prospective effectiveness of new rules is assessed. Food aid rules will be difficult to enforce within the WTO’s Dispute Settlement Understanding. Also, exogenous policy changes in donor countries are reducing the relevance of rules that target food aid as a means of surplus disposal. The future of international food aid governance in the event of a Doha Round collapse is also discussed.agricultural trade, development economics, export competition, food aid, WTO, Food Security and Poverty, International Relations/Trade, O13, O19, Q17, F13,
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