Ultrastructural characteristics of the reproductive organs of adult male helminth Heterakis dispar (Nematoda: Heterakidae)

Nematodes belonging to the Heterakidae family are similar in appearance and their identification causes certain difficulties. For this reason, there is a need to define new taxonomic characteristics. On the other hand, despite the fact that the nematode Heterakis dispar Schrank, 1790, included in the same family, has a wide distribution area, there is little information about the ultrastructure of the parasite. Research on the ultrastructure of the reproductive system of this helminth hase not been conducted. Parasitic worms collected from the caeca of birds were identified, following which, based on the accepted methods of electron microscopy, blocks were prepared, cut, stained, pictures and electrograms were prepared and described. In the present study, the ultrastructural characteristics of the reproductive organs (testis, seminal vesicle, vas deferens and ejaculatory duct) of the adult nematode H. dispar, a specific parasite of domestic waterfowl, were studied with the help of light and electron microscopic methods. The obtained results were compared with the structure of other studied species (H. gallinarum Gmelin, 1790 and H. spumosa Schneider, 1866) of the Heterakidae family. Firstly, it was revealed that the reproductive organs of the male nematode H. dispar are located in the pseudocoelomic cavity, which is considered a taxonomic sign of this family. As in other species of the family, the testis, seminal vesicle, and wall of the vas deferens of the male nematode H. dispar consist of a basement membrane and an epithelial layer. In addition to the basement membrane, muscular and epithelial layers, the wall of the ejaculatory duct is also composed of glandular cells in the front part of the duct. It was revealed that, in the lumen of the tubular reproductive organs of the adult male nematode H. dispar, germ-cells turn into spermatogonia in the germinal zone and spermatocytes in the growth zone of the testis, spermatids in the seminal vesicle, incomplete formed spermatozoa in the vas deferens, and fully formed spermatozoa in the ejaculatory duct of the parasite. The spicules of the parasite nematode, which are the secondary sexual organs consist of a thick cuticle on the outside, and hypodermal origin cells and processes of nerve cells (dendrites and axons) on the inside. Two processes are found on the spicules, which is not observed in other nematodes of the same family

South caucasus and a ‘New Great Game’: the communication of competition in securitised international relations

This article seeks to compare and analyse the historical and contemporary arguments concerning the existence of the brand the ‘Great Game’ in Central Asia with that of a ‘new’ Great Game in the South Caucasus, while assessing the validity and problems of using this term. The article analyses the regional state of affairs and possible impacts of the Russian factor in forging close relations between South Caucasus states and NATO. It is argued that Russia’s and NATO’s vested interests in the region rhetorically contribute to European security system in the context of the security environment after the Georgian-Russian War of 2008 and its repercussions. NATO’s presence may be interpreted as counterbalancing the Russian military presence in the region, but there are also clear limits to the alliance’s willingness to actively engage in the region, not least the reluctance to antagonize Moscow. The context of geopolitical competition may be interpreted as a ‘new’ Great Game sharing similarities with nineteenth century competition of great powers, yet a number of clear differences also exist relative to the traditional Great Game. © 2020 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group

Investigation of the quasifission process by theoretical analysis of experimental data of fissionlike reaction products

The fusion excitation function is the important quantity in planning experiments for the synthesis of superheavy elements. Its values seem to be determined by the experimental study of the hindrance to complete fusion by the observation of mass, angular and energy distributions of the fissionlike fragments. There is ambiguity in establishment of the reaction mechanism leading to the observed binary fissionlike fragments. The fissionlike fragments can be produced in the quasifission, fast fission, and fusion-fission processes which have overlapping in the mass (angular, kinetic energy) distributions of fragments. The branching ratio between quasifission and complete fusion strongly depends on the characteristics of the entrance channel. In this paper we consider a wide set of reactions (with different mass asymmetry and mass symmetry parameters) with the aim to explain the role played by many quantities on the reaction mechanisms. We also present the results of study of the $^{48}$Ca+$^{249}$Bk reaction used to synthesize superheavy nuclei with Z = 117 by the determination of the evaporation residue cross sections and the effective fission barriers $$ of excited nuclei formed along the de-excitation cascade of the compound nucleus.Comment: 21 pages, 15 figures, 2 table