391 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
Weaknesses of Margulis and Ramanujan-Margulis Low-Density Parity-Check Codes
No full textWe report weaknesses in two algebraic constructions of low-density parity-check codes based on expander graphs. The Margulis construction gives a code with nearcodewords, which cause problems for the sum-product decoder; The RamanujanMargulis construction gives a code with low-weight codewords, which produce an error-floor
Temporal Integration Can Readily Switch Between Sublinear and Supralinear Summation
No full text Margulis, Michael and Cha-Min Tang. Temporal integration can readily switch between sublinear and supralinear summation. J. Neurophysiol. 79: 2809–2813, 1998. Temporal summation at dendrites of cultured rat hippocampal neurons was examined as a function of the interval separating two dendritic inputs. A novel method that relies on single-mode optical fibers to achieve rapid photorelease of glutamate was developed. Dendritic excitation achieved with this approach resembles that associated with miniature excitatory postsynaptic currents (mEPSCs), but the strengths, sites, and timing of the inputs can be precisely controlled. Dendritic summation deviated markedly from behavior predicted by passive cable theory. Subthreshold temporal summation varied as a triphasic function of the interpulse interval. As the interpulse interval decreased, local dendritic Na+ conductances were recruited to generate a marked transition from sublinear to supralinear summation. These results suggest that active dendritic conductances acting in concert with passive cable properties may serve to boost coincident synaptic inputs and attenuate noncoincident inputs. </jats:p
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
Dynamics, geometry, number theory: the impact of Margulis on modern mathematics/ edited by David Fisher, Dmitry Kleinbock, and Gregory Soifer.
No full textIncludes bibliographical references."Mathematicians David Fisher, Dmitry Kleinbock, and Gregory Soifer highlight in this edited collection the foundations and evolution of research by mathematician Gregory Margulis. Margulis is unusual in the degree to which his solutions to particular problems have opened new vistas of mathematics. Margulis' ideas were central, for example, to developments that led to the recent Fields Medals of Elon Lindenstrauss and Maryam Mirzhakhani. The broad goal of this volume is to introduce these areas, their development, their use in current research, and the connections between them. The foremost experts on the topic have written each of the chapters in this volume with a view to making them accessible by graduate students and by experts in other parts of mathematics"--Part I. Arithmeticity, superrigidity, normal subgroups -- Part II. Discrete subgroups -- Part III. Expanders, representations, spectral theory -- Part IV. Homogeneous dynamics.1 online resource (vi, 566 pages)
sj-docx-1-aei-10.1177_15345084221133559 – Supplemental material for A Comparison of Reading Screeners in Kindergarten: The Texas Primary Reading Inventory and Acadience Reading With English Learners and Monolingual English Speakers
No full textSupplemental material, sj-docx-1-aei-10.1177_15345084221133559 for A Comparison of Reading Screeners in Kindergarten: The Texas Primary Reading Inventory and Acadience Reading With English Learners and Monolingual English Speakers by Milena A. Keller-Margulis, Michael Matta, Lindsey Landry Pierce, Katherine Zopatti, Erin K. Reid and G. Thomas Schanding in Assessment for Effective Intervention</p
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
Spirochete attachment ultrastructure : implications for the origin and evolution of cilia
No full textThe fine structure of spirochete attachments to the plasma membrane of anaerobic protists displays variations here interpreted as legacies of an evolutionary sequence analogous to that from free-living spirochetes to undulipodia (eukaryotic "flagella" and homologous structures). Attached spirochetes form a vestment, a wriggling fringe of motile cells at the edge of the plasma membrane of unidentified cellulolytic protist cells in the hypertrophied hindgut of the digestive system of Mastotermes darwinien- sis, the large wood-feeding termite from northern Australia. From the membrane extend both undulipodia and a complex of comparably sized (10-12 μm × 0.2-0.3 μn) ectosymbiotic spirochetes that resembles unruly ciliated epithelium. In the intestines are helical (swimming) and round-body morphotypes. Round bodies (RBs) are slow or immotile spirochetes, propagules known to revert to typical swimming helices under culture conditions favorable for growth. The surfaces of both the spirochete gram-negative eubacteria and the parabasalid protists display distinctive attachment structures. The attached hypertrophied structures, some of which resemble ciliate kinetids, are found consistently at sites where the spirochete termini contact the protist plasma membranes
Cysts and symbionts of Staurojoenina assimilis Kirby from Neotermes
No full textStaurojoenina assimilis Kirby, a hindgut hypermastigote parabasalid symbiont in two kalotermitids (Neotermes mona St. John, US Virgin Islands and N. jouteli Puerto Rico) was studied live and by electron microscopy. In this first description of hypermastigote protist cysts in termite intestines we report numerous of these translucent walled spheres in a population of S. assimilis in the hindgut of one pseudergate from a Puerto Rican mangrove community. Tightly adhering, regularly spaced rod bacteria were observed on the surfaces of all live S. assimilis cells. The bacterial nature of these ectosymbiotic rods was verified by TEM and SEM. They are present on the four anterior lobes and most of the rest of the surface of this hypermastigote. The processes by which these ectosymbionts may be retained after ingestion, propagated and transported to the protist's outer membrane are suggested. The ultrastructure of other unknown symbionts, endonuclear microbes that resemble Caryococcus, perhaps pleiomorphic Gram negative bacteria, is also described
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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