Classical double-layer atoms: artificial molecules

The groundstate configuration and the eigenmodes of two parallel two-dimensional classical atoms are obtained as function of the inter-atomic distance (d). The classical particles are confined by identical harmonic wells and repel each other through a Coulomb potential. As function of d we find several structural transitions which are of first or second order. For first (second) order transitions the first (second) derivative of the energy with respect to d is discontinuous, the radial position of the particles changes discontinuously (continuously) and the frequency of the eigenmodes exhibit a jump (one mode becomes soft, i.e. its frequency becomes zero).Comment: 4 pages, RevTex, 5 ps figures, to appear in Phys.Rev.Let

Topological Defects and Non-homogeneous Melting of Large 2D Coulomb Clusters

The configurational and melting properties of large two-dimensional clusters of charged classical particles interacting with each other via the Coulomb potential are investigated through the Monte Carlo simulation technique. The particles are confined by a harmonic potential. For a large number of particles in the cluster (N>150) the configuration is determined by two competing effects, namely in the center a hexagonal lattice is formed, which is the groundstate for an infinite 2D system, and the confinement which imposes its circular symmetry on the outer edge. As a result a hexagonal Wigner lattice is formed in the central area while at the border of the cluster the particles are arranged in rings. In the transition region defects appear as dislocations and disclinations at the six corners of the hexagonal-shaped inner domain. Many different arrangements and type of defects are possible as metastable configurations with a slightly higher energy. The particles motion is found to be strongly related to the topological structure. Our results clearly show that the melting of the clusters starts near the geometry induced defects, and that three different melting temperatures can be defined corresponding to the melting of different regions in the cluster.Comment: 7 pages, 11 figures, submitted to Phys. Rev.

Phase equilibria and glass transition in colloidal systems with short-ranged attractive interactions. Application to protein crystallization

We have studied a model of a complex fluid consisting of particles interacting through a hard core and a short range attractive potential of both Yukawa and square-well form. Using a hybrid method, including a self-consistent and quite accurate approximation for the liquid integral equation in the case of the Yukawa fluid, perturbation theory to evaluate the crystal free energies, and mode-coupling theory of the glass transition, we determine both the equilibrium phase diagram of the system and the lines of equilibrium between the supercooled fluid and the glass phases. For these potentials, we study the phase diagrams for different values of the potential range, the ratio of the range of the interaction to the diameter of the repulsive core being the main control parameter. Our arguments are relevant to a variety of systems, from dense colloidal systems with depletion forces, through particle gels, nano-particle aggregation, and globular protein crystallization.Comment: 20 pages, 10 figure

Early growth, survival and litter size in Ethiopian Horro sheep

(South African J of Animal Science: 2000, 30, Supplement 1: 1-3

On the Hydrodynamic and Structural Performance of Thermoplastic Composite Ship Propellers Produced by Additive Manufacturing Method

\ua9 2024 by the authors. In the marine industry, the search for sustainable methods, materials, and processes, from the product’s design to its end-of-life stages, is a necessity for combating the negative consequences of climate change. In this context, the lightening of products is essential in reducing their environmental impact throughout their life. In addition to lightening through design, lightweight materials, especially plastic-based composites, will need to be used in new and creative ways. The material extrusion technique, one of the additive manufacturing methods, is becoming more widespread day by day, especially in the production of objects with complex forms. This prevalence has not yet been reflected in the marine industry. In this study, the performances of plastic composite propellers produced by the material extrusion technique is investigated and discussed comparatively with the help of both hydrodynamic and structural tests carried out in a cavitation tunnel and mechanical laboratory. The cavitation tunnel test and numerical simulations were conducted at a range of advance coefficients (J) from 0.3 to 0.9. The shaft rate was kept at 16 rps. The thrust and torque data were obtained using the tunnel dynamometer. Digital pictures were taken to obtain structural deformation and cavitation dynamics. The structural performance of the propellers shows that an aluminum propeller is the most rigid, while a short carbon fiber composite propeller is the most flexible. Continuous carbon fiber composite has high strength and stiffness, while continuous glass fiber composite is more cost-effective. In terms of the hydrodynamic performance of the propellers, flexibility reduces the loading on the blade, which can result in thrust and torque reduction. Overall, the efficiency of the composite propellers was similar and less than that of the rigid aluminum propeller. In terms of weight, the composite carbon propeller containing continuous fiber, which is half the weight of the metal propeller, is considered as an alternative to metal in production. These propellers were produced from a unique composite consisting of polyamide, one of the thermoplastics that is a sustainable composite material, and glass and carbon fiber as reinforcements. The findings showed that the manufacturing method and the new composites can be highly successful for producing ship components

New pseudotagmic genus of acaricaline mites (Eriophyidae, Acaricalini) from a South African palm Hyphaene coriacea and remarks on lateral opisthosomal spines and morphology of deutogynes in Eriophyoidea

A new genus, Tumescoptella n. g., with two new sympatric species Tumescoptella aculeata n. sp.and T. rotundiscuta n. sp., was found on the indigenous South African palm Hyphaene coriacea, Lala palm. Both species are described and illustrated with the aid of conventional light microscopy, confocal laser scanning microscopy and low temperature scanning electron microscopy. Additionally, a new record of Tumescoptes dicrus Meyer collected from Phoenix reclinata(Arecaceae), near Kirstenbosch Gardens (Cape Town, South Africa), is reported. Morphologically the Tumescoptella n. g. is most similar to Tumescoptes Keifer, but possesses a more reduced chaetome and more derived pseudotagmosis. Pseudotagmosis is one type of body consolidation in vagrant eriophyoids, realized through the formation of dorsal opisthosomal plates, pseudotagmata. Along with previously described pseudotagmata (prodorsum, cervix, postprodorsum, superpostprodorsum, pretelosoma, and telosoma), a new term, anteroscutum, is proposed for the complex pseudotagma formed as a fusion of the three anterior pseudotagmata (prodorsum+cervix+postprodorsum) in several phyllocoptine mites from palms. An anteroscutum is present in monotypic Scolocenus Keifer from coconut and in the new genus Tumescoptella n. g. Protogyne females of Tumescoptella n. g. have uncommonly large lateral opisthosomal spines. Along with tiny spinules, triangular cuticular plates, band-shaped processes, and areas of thickened cuticle, the lateral spines belong to a common group of serial derivatives of dorsal opisthosomal annuli. We give a brief review on variation of spine-like structures across taxa of Eriophyoidea and their morpho-functional evaluation. Contrary to protogyne females, deutogyne females of T.aculeata n. sp. lack lateral spines, and they possess a smoother topography of the anteroscutum. Morphological similarity of these deutogynes with mites of the less transformed genus Tumescoptesis in accordance with a previous hypothesis on the possible correspondence of deutogyne morphology to that of an ancestral taxon. Two hypotheses on the origin of the presumably monophyletic group of Tumescoptes-like phyllocoptines (TP) from palms, comprising genera Scolocenus, Tumescoptella n. g., Tumescoptes, and Pseudotagmus, are proposed based on morphological similarity with two groups of eriophyoid genera: (a) pseudotagmic genera associated with aboriginal Asian dicotyledonous tropical trees, and (b) South American phyllocoptines from arecoid palms.Light microscopy investigation of the mite samples from Africa was supported by research projects of ZIN RAS (#АААА-А17-117030310209-7). CLSM studies were performed at the Research park of St. Petersburg State University in the Center for Molecular and Cell Technologies (IAS 1.53.917.2016, project #109-9164) and Center for Microscopy and Microanalysis (IAS 1.52.1424.2016, project #112-8186). LT-SEM studies were performed at the Laboratory for Microscopy and Microanalysis, University of Pretoria, South Africa.The field survey to collect eriophyoid mites on Hyphaene palm species was funded by the South Africa Department of Science and Technology grant to the Agricultural Research Council in South Africa.https://www.biotaxa.org/saaam2019Forestry and Agricultural Biotechnology Institute (FABI

Leptospira interrogans serovar pomona associated with abortion in cattle : isolation methods and laboratory animal histopathology

Leptospira interrogans serovar pomona was successfully isolated from cattle urine in the western Transvaal after an abortion storm had occurred. Direct inoculation of EMJH medium proved the most successful method. The selective agent, 5-fluorouracil, was most effective in controlling contamination when used at the 0,4 mg/ml level. The strain isolated was pathogenic in hamsters, but specific lesions and the leptospirae were seen only where overwhelming infection occurred.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format

Evidence that Quadrastichodella nova (Hymenoptera: Eulophidae) is the only gall inducer among four hymenopteran species associated with seed capsules of Eucalyptus camaldulensis (Myrtaceae) in South Africa

Three chalcidoid wasp species, Megastigmus zebrinus Grissell (Torymidae), Quadrastichodella nova Girault (Eulophidae) and Leprosa milga Kim & La Salle (Eulophidae), have each been described independently as gall inducers associated with Eucalyptus species (Myrtaceae). The finding that at times they emerge together from seed capsules of river red gum (Eucalyptus camaldulensis Dehnhardt) collected at the same site in South Africa, cast doubt on the accuracy of these earlier interpretations. The current study examined the gall inducing abilities of each of the three wasp species. During geographical surveys, all three species coexisted in seed capsules at 16 of the 61 sites sampled. A study of the seasonal emergence pattern of the three species, together with a fourth, locally abundant gall associate, Aprostocetus sp., showed that Q. nova and L. milga emerge during early summer, while the remaining two species emerge in smaller numbers throughout the year. Oviposition trials on sleeved branches of E. camaldulensis, from which all insects had previously been excluded, verified that Q. nova had the ability to induce galls, while both M. zebrinus and L. milga failed to do so. Only one type of gall of characteristic structure was encountered, which repudiates the possibility of a second gall inducer, and no indication of inquilinism was found. Megastigmus zebrinus, L. milga and Aprostocetus sp. are thus more likely to be parasitoids.DNA sequences were obtained for the adults of all four these species. By matching the DNA of identified adults with that of juvenile hymenopterans in the galls, it was confirmed that all four hymenopterans species developed within the seed-capsule galls of E. camaldulensis. Regrettably, this technique failed to give a clear indication of the exact host relationships between the various gall inhabitants. By dissecting seed capsules at different stages of gall development, the origin of the gall was proven to be in the placenta of one of the locules of a flower bud, and not in a seed or ovule, as previously reported.The Agricultural Research Councilhttp://reference.sabinet.co.za/sa_epublication/entohttp://www.entsocsa.co.za/Publications.htm2017-03-30am201