102,396 research outputs found
Calidad del Semen Refrigerado de Carneros Assaf y Blackbelly
No full textChilled semen quality of Assaf and Blackbelly rams used in artificial insemination and raised in the central coast of Peru were compared. Semen was collected with an artificial vagina and diluted with Tris-fructose-egg yolk. The individual progressive motility, the membrane integrity by the hypoosmotic text (HOST), and sperm concentration in the Neubauer chamber were determined after two hours of refrigeration. The percentage values were previously transformed into ArcSen %. The Student «t» test for independent means differences between breeds was performed. Progressive individual motility was 82.36 ± 6.66 and 83.30 ± 4.92% (p>0.05) and the mass motility was 4.28 ± 0.45 and 4.06 ± 0.33 (p<0.05) for the Assaf and for Blackbelly rams, respectively. The integrity of the spermatic membrane was 83.50 ± 2.77% for Assaf and 82.56 ± 3.78% for Blackbelly (p<0.05). Sperm concentration and percentages of live and abnormal spermatozoa were similar in both breeds.Se comparó la calidad del semen refrigerado de carneros Assaf y Blackbelly utilizados en inseminación artificial y criados en la costa central del Perú. El semen fue colectado con vagina artificial y diluido en Tris-fructosa-yema de huevo. Se determinó la motilidad individual progresiva, la integridad de membrana mediante la prueba hipoosmótica (HOST) y la concentración espermática a través de la cámara de Neubauer a las dos horas de la refrigeración. Los valores porcentuales fueron transformados a ArcSeno %. Se realizaron pruebas de «t» Student para determinar diferencias de medias independientes entre las variables determinadas, según la raza. La motilidad individual progresiva fue de 82.36 ± 6.66 y 83.30 ± 4.92% (p>0.05) y la motilidad masal fue de 4.28 ± 0.45 y 4.06 ± 0.33 (p<0.05) para los carneros Assaf y Blackbelly, respectivamente. La integridad de la membrana espermática fue de 83.50 ± 2.77% para Assaf y 82.56 ± 3.78% para Blackbelly (p<0.05). La concentración espermática y los porcentajes de espermatozoides vivos y anormales fueron similares en ambas razas
THE RELATIONSHIP BETWEEN PLANT DIVERSITY AND PRODUCTIVITY IN NATURAL AND IN MANAGED GRASSLANDS
No full textAssaf TA, Beyschlag W, Isselstein J. THE RELATIONSHIP BETWEEN PLANT DIVERSITY AND PRODUCTIVITY IN NATURAL AND IN MANAGED GRASSLANDS. APPLIED ECOLOGY AND ENVIRONMENTAL RESEARCH. 2011;9(2):157-166.Despite the fact that several experiments have been conducted to explore the biodiversity-productivity relationship in synthesized and natural plant communities, the results obtained were contradictory and no clear consensus has been reached. Recent experiments that surveyed mature natural plant communities have investigated this relationship across environmental gradients, where biotic and/or abiotic factors are correlated with the observed diversity and productivity levels. We studied the effect of plant diversity on ecosystem productivity in agriculturally managed (managed at a low intensity with moderate level of disturbance) and natural (no history of management) grasslands at a within-site scale in order to minimize the confounding effect of environmental factors. We tested the effects of two diversity measures (species richness and species evenness) on productivity within-and across-sites scale. Our results indicated that this relationship was different between the natural and the managed grasslands and varied according to the diversity measure. Species richness only poorly explained the variation in productivity for the managed grasslands, while the variations in system productivity were better explained by species evenness. Interestingly, our results from the natural low productive, species poor grassland are in agreement with the results obtained from the recent experiments that artificially manipulated diversity levels and found an asymptotic increase in productivity along with increasing species richness. Our results provide additional evidence of the complex behavior that measures of species diversity that combine several aspects of diversity such as species evenness, species identity as well as the interactions among the species may be better determinants of the response of the ecosystem to biodiversity
The relationship between biodiversity and productivity in permanent grasslands and in ley system
No full text
Launch of Essential facts about Covid-19 Booklet
No full textMP 4 video; Size: 2.56GB; Duration: 1:58Please cite as: Academy of Science of South Africa (ASSAf), (2021). Launch of Essential facts about Covid-19 Booklet. [Online] Available at: http://hdl.handle.net/20.500.11911/195The booklet titled "Essential facts about Covid-19: the disease, the responses, and an uncertain future. For South African learners, teachers, and the general public" was launched as part of this webinar. View the launch video at https://www.youtube.com/watch?v=07kIfuHZztY&t=7s. The booklet itself can be accessed at http://hdl.handle.net/20.500.11911/194. The following presentations formed part of this webinar: Introduction to Booklet - Prof Anwar Suleman Mall, University of Cape Town; Vaccines and Variants - Prof Ed Rybicki, University of Cape Town; HIV and Covid-19 - Prof Quarraisha Abdool Karim, University of KwaZulu-Natal; Covid-19 and Hospitals - Prof Marc Mendelson, University of Cape Town.
The first cases of a new coronavirus (SARS CoV 2) were identified toward the end of 2019 in Wuhan, China. Over the following months, this virus spread to everywhere in the world, and by now no country has been spared the devastation from the Covid-19. During this book launch event some of the authors will highlight selected current issues relating to this pandemic: the role and future of variants, the effectiveness of vaccinations and challenges of vaccinating a sufficient fraction of the population worldwide, and more generally the relation to HIV and hospital care in South Africa.During this book launch event some of the authors highlighted selected current issues relating to this pandemic: the role and future of variants, the effectiveness of vaccinations and challenges of vaccinating a sufficient fraction of the population worldwide, and more generally the relation to HIV and hospital care in South Africa.Academy of Science of South Africa (ASSAf
The relationship between biodiversity and productivity in permanent grasslands and in ley system
No full textLetter, [Author unclear] to Paulina T. Merritt
No full textHandwritten letter to Paulina Merritt from an unknown author, October 1, 1876.
Genetic dissection of "Caulobacter crescentus" surface colonization
No full textDuring its biphasic life cycle Caulobacter crescentus switches from a planktonic to surface attached life style. This transition requires the continuous remodeling of the cell poles through the temporally and spatially coordinated assembly and disassembly of polar organelles like the flagellum, pili, and an adhesive holdfast. A genetic screen for mutants affected in surface binding and colonization led to the identification of various genes required for motility, pili, and holdfast biogenesis, suggesting a specific role for all three organelles in C. crescentus surface colonization. Several novel holdfast genes were identified, which are potentially involved in the synthesis and regulation of the polysaccharidic component of the holdfast. Quantitative surface binding studies during the C. crescentus cell cycle revealed that optimal attachment coincides with the presence of flagellum, pili, and holdfast at the same pole. This indicated that accurate temporal control of polar appendices is critical for surface colonization of C. crescentus and represents the first example for developmentally controlled bacterial surface adhesion. We have used genetic and biochemical analyzes to demonstrate that di-cyclic guanosine monophosphate (c-di-GMP) is a central regulatory compound involved in the timing of C. crescentus pole development. Mutants lacking the diguanylatecyclase PleD show a dramatic delay of holdfast formation during swarmer cell differentiation. In contrast, cells lacking the GGDEF-EAL composite protein CC0091 show premature holdfast formation, while overexpression of CC0091 also leads to a delayed appearance of holdfast. The observation that CC0091 is a c-di-GMP specific phosphodiesterase indicated that the antagonistic activities of PleD and CC0091 could be responsible for the correct timing of holdfast formation and flagellum ejection. Finally, our genetic screen identified a candidate for the c-di-GMP effector protein, which mediates holdfast synthesis in response to fluctuating levels of c-di-GMP. The glycosyltransferase CC0095 is strictly required for holdfast formation and its overexpression leads to premature holdfast synthesis. This and the observation that CC0095 is able to bind c-di-GMP lead to the hypothesis that holdfast synthesis is
regulated via allosteric control of the CC0095 glycosyltransferase. These data provide the first
example of a developmental process being regulated by the bacterial second messenger, c-di-GMP
Bending actuation of a composite liquid crystal elastomer via direct Joule heating
No full textIn this work a new bi-layered composite actuator based on a polysiloxane-based monodomain nematic Liquid Crystal Elastomer (LCE) and on a conductive PEDOT:PSS thin layer is proposed. The basic idea is to integrate electroconductive properties in the LCE and to validate the feasibility of direct actuation of the LCE by Joule heating of the conductive (and compliant) PEDOT: PSS layer. The fabrication of the actuator is achieved by depositing a thin conductive polymer layer by drop casting a PEDOT: PSS waterborne solution after having increased the LCE surface wettability with an air plasma treatment. The excellent stability of PEDOT: PSS and its mechanical properties, better matched with LCE ones compared to metals or inorganic nanoparticles used in other approaches, allowed to develop an all-organic reliable actuating composite based on thermoresponsive properties of LCE. Thermal actuation via direct Joule heating of the composite has been verified and prototypes of LCE/PEDOT:PSS bending actuators have been preliminary tested
Impact of olive pomace wastes and fungicide treatment on indigenous arbuscular mycorrhizal fungi associated with chickpea (Cicer arietinum L.) under field conditions
No full textThe effect of soil amendment with olive pomace wastes (OPW) on population and root infection of indigenous arbuscular mycorrhizal (AM) fungi associated with chickpea has been studied under field conditions. Yield components, phosphorus (P) percentage, AM spore density and root length colonization of AM fungi were recorded. We found that OPW increased biomass, seed yield, and shoot phosphorus concentration of chickpea plants. Our results also indicated that AM fungal spore population and colonization levels were substantially enhanced by the application of OPW. Fungicide applications significantly decreased both spore population and colonization length of AM fungi. We concluded that organic matter amendments potentially increased AM fungal association and hence might increase growth and yield of chickpea plants in the field
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