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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Towards an Understanding of the Differences Between the Blepharoplasts of Mosses and Liverworts, and Comparisons With Hornworts, Biflagellate Lycopods and Charophytes: A Numerical Analysis

RENZAGLIA, KAREN S., DUCKETT, JEFFREY G. 01 January 1991 (has links)
Numerical analysis of the lengths and positions of the two basal bodies (BBs), lamellar strip (LS) and anterior mitochondrion (AM) relative to each other in mid‐ and late‐stage spermatids of mosses and liverworts reveals the existence of several well denned, but previously unrecognized, features which clearly distinguish the blepharoplasts of the two groups. The ten possible quotients were calculated from measurements of anterior BB lengths, posterior BB lengths, LS lengths, distances between the anterior tips of the BBs and distances between the transition regions of the BBs in mid‐stage spermatids of 9 mosses and 16 hepatics. These critical data may be quickly compiled from a small number of electron micrographs. A Mann‐Whitney rank order t test showed highly significant differences in 6 of the 10 quotients between the moss and liverwort taxa. The primary data for late‐stage spermatids (4 mosses, 6 liverworts) also included the length of the AM. A Wilcoxon signed rank procedure revealed that the relationship between the AM and other blepharoplast components changed significantly between mid‐ and late‐stage spermatids in mosses but not in liverworts. The clear‐cut numerical differences between the blepharoplast components in each group are related to different patterns of development namely (1) bidirectional assembly of the LS in young spermatids of liverworts versus unidirectional (anterior) elongation at the same stage in mosses (2) elongation of the posterior BB over the nucleus in mid‐stage spermatids of mosses and (3) maturational elongation of the AM in mosses. Since the differences between the blepharoplasts of mosses and liverworts become apparent only during the later stages in ontogeny and since the mode of development of basal body stagger, involving the same precisely defined patterns of proximal triplet microtubule extension, is unique to mosses and liverworts, we suggest that the two groups share a common ancestry. The blepharoplasts of all the taxa used in the calculations are illustrated in a simplified form and the ‘average’ blepharoplast for mid‐ and late‐stage spermatids of both mosses and liverworts is reconstructed from all the data presently available on the two groups. The same analysis of the blepharoplasts of hornworts, birlagellate lycopods, and charophytes highlights the differences between these groups and mosses and liverworts. Most striking is the side‐by‐side orientation of the basal bodies in hornworts and charophytes compared with the staggered arrangement in mosses, liverworts and the lycopods.
2

A Centrin Homologue Is a Component of the Multilayered Structure in Bryophytes and Pteridophytes

Vaughn, K. C., Sherman, T. D., Renzaglia, Karen S. 01 March 1993 (has links)
The multilayered structure (MLS), a component of the locomotory complex of plant sperm, has been utilized extensively by taxonomists in establishing phylogenetic relationships between the lower plants and algae. Unfortunately, there has been almost no biochemical characterization of the MLS and, in those studies that did attempt a characterization, conflicting results were obtained. We utilized antisera to the calcium-binding protein centrin to probe thin sections of the mid-stage spermatids of the anthocerote Phaeoceros laevis, the hepatic Sphaerocarpos texanus, and the pteridophyte Ceratopteris richardii embedded in L. R. White resin. The lamellar strip (LS; layers S2-S4) of the MLS in each of these species is labelled strongly with anti-centrin, but the S1 layer, composed of microtubules, is not. In Ceratopteris, centrin is also detected in the amorphous electron opaque material that connects the basal bodies of the flagella. Both the MLS and the amorphous zones are putative microtubule organizing centers. Extracts from axenic cultures of Ceratopteris subjected for electrophoresis and Western blotting revealed a reactive band at 19.3 kDa, a protein similar in molecular mass to algal centrin. These data indicate that the MLS is composed at least partially of the protein centrin or a protein antigenically-related to centrin. This report is the first electron microscopic immunocytochemical demonstration that a centrin homologue is found in land plants and that it occurs at putative microtubule organizing centers.
3

Исследование характеристик неоднородно заполненных цилиндрических линий передачи : магистерская диссертация / Investigation of the characteristics of heterogeneously filled cylindrical transmission lines

Малов, Э. Э., Malov, E. E. January 2017 (has links)
В данной работе представлены исследования характеристик металлического круглого волновода с неоднородным диэлектрическим заполнением и одномодового оптического волокна. Были построены и проанализированы частотные зависимости постоянной распространения для следующих диэлектрических структур круглого волновода: стержень, втулка, цилиндр, цилиндр с зазором, стержень с параболическим профилем изменения относительной диэлектрической проницаемости. Были рассмотрены одномодовые оптические волокна с разным профилем преломления и изучены материальная и хроматическая дисперсия одномодового волокна. / This work contains researches of characteristics of inhomogeniously filled metal circular waveguide and single-mode optical fiber. Frequency dependences of propagation constant of following dialectic structures in circular waveguide were calculated and analyzed: rod, plug, cylinder, cylinders with air gap, rod with parabolic permittivity profile. Characteristics of single-mode optical fiber with different refractive index profiles were considered, alsomaterial and chromatic dispersions were explored.

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