Disparity in the timing of vertebrate diversification events between the northern and southern hemispheres.

ABSTRACT: BACKGROUND: Climatic oscillations throughout the Quaternary had profound effects on temperate biodiversity, but the extent of Quaternary climate change was more severe in temperate regions of the northern hemisphere than in the southern hemisphere. We sought to determine whether this geographic disparity differentially influenced the timing of intraspecific diversification events within ectothermic and endothermic vertebrate species. Using published phylogenetic hypotheses, we gathered data on the oldest intraspecific diversification event within mammal, bird, freshwater fish, amphibian, and reptile species from temperate-zone areas. We then tested whether the timing of diversification events differed between hemispheres. RESULTS: Our analyses provide strong evidence that vertebrates from temperate regions of the northern hemisphere are younger than those from the southern hemisphere. However, we find little evidence to suggest that this relationship differs between endotherms versus ectotherms, or that it varies widely across the five classes of vertebrates that we considered. In addition, we find that on average, endothermic species are much younger than ectothermic species. CONCLUSION: Our findings suggest that geographic variation in the magnitude of climatic oscillations during the Quaternary led to substantial disparity in the timing of intraspecific diversification events between northern and southern hemisphere vertebrates, and that the magnitude of this divergence is largely congruent across vertebrate taxa

Characterisation and neutralisation of Aeromonas hydrophila enterotoxin in the rabbit ileal-loop model

Cell-free culture filtrates and crude enterotoxin preparations from six strains of Aeromonas hydrophiza caused the accumulation of fluid in rabbit ileal loops. This activity was due to a non-dialysable, heat and acid-labile antigenic protein and was lost when culture filtrates and crude enterotoxin preparations were heated at 60°C for 20 min. or 56°C for 30 min. respectively. Maximum activity was observed at pH 8.0-10.0; there was a gradual loss at lower pH and activity was abolished in culture filtrates held at pH 3.0 and crude enterotoxin preparations held at pH 4.0. Titration of the crude enterotoxin preparations in rabbit ileal loops showed that the ED50 (equivalent to 1 unit of toxin) was contained in 25 μg of protein; a logarithmic plot of the neutralisation coefficients against antiserum concentrations showed that one unit of antitoxin was contained in 42×10−4 ml of the antiserum

Robotic control of the seven-degree-of-freedom NASA laboratory telerobotic manipulator

A computationally efficient robotic control scheme for the NASA Laboratory Telerobotic Manipulator (LTM) is presented. This scheme utilizes the redundancy of the seven-degree-of-freedom LTM to avoid joint limits and singularities. An analysis to determine singular configurations is presented. Performance criteria are determined based on the joint limits and singularity analysis. The control scheme is developed in the framework of resolved rate control using the gradient projection method, and it does not require the generalized inverse of the Jacobian. An efficient formulation for determining the joint velocities of the LTM is obtained. This control scheme is well suited for real-time implementation, which is essential if the end-effector trajectory is continuously modified based on sensory feedback. Implementation of this scheme on a Motorola 68020 VME bus-based controller of the LTM is in progress. Simulation results demonstrating the redundancy utilization in the robotic mode are presented

To Study The Impact Of Virtual Assistant Using Artificial Intelligence In Society

As technology continues to advance, the integration of Artificial Intelligence (AI) in various domains has become increasingly prevalent. This research paper explores the transformative impact of AI in the realm of virtual assistance for research purposes. The paper delves into the development and implementation of intelligent virtual assistants, leveraging sophisticated AI algorithms and natural language processing techniques. The primary objective of this research is to investigate how AI-driven virtual assistants can enhance and streamline research workflows across diverse disciplines. The study assesses the capabilities of these virtual assistants in information retrieval, data analysis, literature review, and collaboration facilitation. Special attention is given to the adaptability of these systems to different research contexts and the customization options available for researchers. The paper also examines the challenges and ethical considerations associated with deploying AI in research assistance, addressing issues related to data privacy, bias, and the responsible use of AI technologies. Additionally, the research discusses the potential benefits of AI-driven virtual assistants, such as increased productivity, improved decision-making, and the democratization of access to research resources. Several case studies and examples of existing AI-powered virtual assistants in the research domain are analyzed to provide insights into their effectiveness and user acceptance

Proučavanje promjena frekvencije elektronskih sudara i apsorpcijskog koeficijenta u neizotropnoj atmosferi

The analytical form of absorption index appropriate to a certain range of height of the upper atmosphere plasma medium during ordinary wave propagation under quasi-transverse approximations has been utilized to develop an integral equation through Wentzel-Kramers-Brillouin method of solution. The integral equation is useful for the determination of effective electron collision frequency. Numerical results are presented graphically along with the results of some earlier work.Primjenjujemo analitički izraz za apsorpcijski koeficijent prikladan za širenje običnih elektromagnetskih valova u razmatranom rasponu visina gornje atmosferske plazme. Primijenili smo kvazi-poprečno približenje za izvod integralne jednadžbe pomoću Wentzel-Kramers-Brillouinove metode. Integralna jednadžba je pogodna za određivanje efektivne frekvencije elektronskih sudara. Načinili smo numeričke analize i ishodi se uspoređuju grafički s nekim ranijim rezultatima

Prevalence and co-infection of Toxoplasma gondii and Neospora caninum in Apodemus sylvaticus in an area relatively free of cats

The protozoan parasite Toxoplasma gondii is prevalent worldwide and can infect a remarkably wide range of hosts despite felids being the only definitive host. As cats play a major role in transmission to secondary mammalian hosts, the interaction between cats and these hosts should be a major factor determining final prevalence in the secondary host. This study investigates the prevalence of T. gondii in a natural population of Apodemus sylvaticus collected from an area with low cat density (<2·5 cats/km2). A surprisingly high prevalence of 40·78% (95% CI: 34·07%–47·79%) was observed despite this. A comparable level of prevalence was observed in a previously published study using the same approaches where a prevalence of 59% (95% CI: 50·13%–67·87%) was observed in a natural population of Mus domesticus from an area with high cat density (>500 cats/km2). Detection of infected foetuses frompregnant dams in both populations suggests that congenital transmission may enable persistence of infection in the absence of cats. The prevalences of the related parasite, Neospora caninum were found to be low in both populations (A. sylvaticus: 3·39% (95% CI: 0·12%–6·66%); M. domesticus: 3·08% (95% CI: 0·11%–6·05%)). These results suggest that cat density may have a lower than expected effect on final prevalence in these ecosystems

Tempering of Die-steels based on indigenous materials

This paper present studies on the effects of quenching temperature, tempering temperature and time on the hardness of three die steels of similar carbon contents but having increasing chromium percentages. While tempering in the range of 150°C to 400°C it was observed that hardness decreased as quenching temperature was raised. All the steels showed secondary hardening phenomenon in relation to the variables mentioned above. It was also observed that on tempering the steels above 450°C, after prior quenching from increasing temperatures, hardness gradually increased upto the quenching temperature of 1100°C, beyond which followed a decrease in hardness. This phenomenon was the decrease in hardness. This phenomenon was the same at all tempering temperatures upto 601°C, but the increase in hardness from low quenching temperatures to the maximum quenching temperature was less at 450°C than at the higher temperatures and attained a maximum at 600°C secondary hardening decreased with the increase of quenching temperatur