Morphological and parasitological variations of African lungfish, Protopterus annectens in dry and rainy seasons

This study was carried out to determine the seasonal morphological and parasitological variations of African Lung fish (Protopterus annectens) from Upper River Benue, Nigeria. Twenty specimens each of the fish samples from the two seasons were collected monthly for a period of ten months and transported fresh (alive) to the Veterinary laboratory Teaching Hospital, University of Agriculture, Makurdi in plastic jars. The fish samples were identified and sorted into male and female. The total and standard lengths measurements were recorded while the weight was measured. Length weight relationship was determined. Examination for parasites on the fish samples was carried out. Parasitic indices (prevalence (%), and mean intensity, percentage parasite load and percentage frequency of occurrence of each parasite species per location in fish were calculated. The mean total length, total body weight and condition factor of Protopterus annectens in dry season were 36.25cm±0.67, 515.60g±25.90 and 0.91±0.023, respectively while in rainy season, the mean total length, total body weight and condition factor of 34.74cm±0.63, 460.60g±24.20 and 0.91±0.019, respectively. There was no significant difference (p > 0.05) between the mean total lengths, total body weight and condition factor of the fish sample in both seasons. Out of the 400 samples of P. annectens used for the study in dry and rainy seasons, 31.75% were infested with 242 different parasites. Of the total parasites, 50.83% parasites were recorded in dry season from 67.00% infested fish samples while 48.40% parasites were recorded from 32.00% infested fish. Of the parasites species, Contracaecum sp was the most prevalent (34.15%) in dry season. This parasite accounted for 18.70% in the intestine and 15.45% in the stomach while Eustrongyloids sp was the most prevalent (27.36%) in rainy season accounting for 22.64% in the intestine and 4.72% in the stomach. The least prevalent parasite load (3.25% in dry season and 2.83% in rainy season) was recorded for Trichodina sp. Among the body organs of the fish samples, intestine recorded the highest percentage parasite load (50.41%) in dry season while stomach had the highest percentage parasite load (49.06%) in rainy season. The least (3.25% in dry season and 2.83% in rainy season) were recorded for skin. Generally, intestine had the highest percentage parasite load (98.52%) with 50.41% in dry season and 48.11% in rainy season. Female P. annectens from both seasons had more percentage parasite loads (61.79% in dry season and 53.77% in rainy season) than the male P. annectens in both seasons (38.21% in dry season and 46.23% in rainy season). There were variations in percentage parasite load among the length and weight groups of the fish samples and conclusively, higher percentage parasite load (50.83%) was recorded in dry season than the rainy season (48.40%).Keywords: Protopterus annectens, parasites, dry and rainy seasons and upper River Benu

Health systems’ responses to the roll-out of antiretroviral therapy (ART) in India: a comparison of two HIV high-prevalence settings

The government of India launched the free anti-retroviral therapy (ART) initiative in 2004 and the programme has since scaled up expansion in a phased manner. Programme authorities acknowledge problems in scale-up, yet discussions have been restricted to operational constraints, with little consideration for how local health system responses to HIV/AIDS influence the delivery of ART. This paper draws on the perspectives of key informants and people living with HIV (PLHIV) to compare delivery of ART in two ART centres in the States of Maharashtra and Andhra Pradesh at two distinct points of time. In 2005, data were collected through key informant interviews (KIIs) using interview guides and a survey of PLHIV using a semi-structured interview schedule. Differences were observed in the functioning and resources of the two centres, indicating different levels of preparedness which in turn influenced PLHIV's pathways in accessing ART. We examine these differences in the light of programme leadership, ownership and the roles of public, private and non-governmental organisation actors in HIV care. KIIs conducted during a follow-up visit in 2009 focused on changes in ART delivery. Many operational problems had been resolved; however, new challenges were emerging as a result of the increased patient load. An understanding of how ART programmes evolve within local health systems has bearing on future developments of the ART programme and must include a consideration of the wider socio-political environment within which HIV programmes are embedded

Continuous Percolation Phase Transitions of Two-dimensional Lattice Networks under a Generalized Achlioptas Process

The percolation phase transitions of two-dimensional lattice networks under a generalized Achlioptas process (GAP) are investigated. During the GAP, two edges are chosen randomly from the lattice and the edge with minimum product of the two connecting cluster sizes is taken as the next occupied bond with a probability $p$. At $p=0.5$, the GAP becomes the random growth model and leads to the minority product rule at $p=1$. Using the finite-size scaling analysis, we find that the percolation phase transitions of these systems with $0.5 \le p \le 1$ are always continuous and their critical exponents depend on $p$. Therefore, the universality class of the critical phenomena in two-dimensional lattice networks under the GAP is related to the probability parameter $p$ in addition.Comment: 7 pages, 14 figures, accepted for publication in Eur. Phys. J.

Improving tree mortality models by accounting for environmental influences

Tree-ring chronologies have been widely used in studies of tree mortality where variables of recent growth act as an indicator of tree physiological vigour. Comparing recent radial growth of live and dead trees thus allows estimating probabilities of tree mortality. Sampling of mature dead trees usually provides death-year distributions that may span over years or decades. Recent growth of dead trees (prior to death) is then computed during a number of periods, whereas recent growth (prior to sampling) for live trees is computed for identical periods. Because recent growth of live and dead trees is then computed for different periods, external factors such as disturbance or climate may influence growth rates and, thus, mortality probability estimations. To counteract this problem, we propose the truncating of live-growth series to obtain similar frequency distributions of the "last year of growth" for the populations of live and dead trees. In this paper, we use different growth scenarios from several tree species, from several geographic sources, and from trees with different growth patterns to evaluate the impact of truncating on predictor variables and their selection in logistic regression analysis. Also, we assess the ability of the resulting models to accurately predict the status of trees through internal and external validation. Our results suggest that the truncating of live-growth series helps decrease the influence of external factors on growth comparisons. By doing so, it reinforces the growth-vigour link of the mortality model and enhances the model's accuracy as well as its general applicability. Hence, if model parameters are to be integrated in simulation models of greater geographical extent, truncating may be used to increase model robustness

Adaptation of Autocatalytic Fluctuations to Diffusive Noise

Evolution of a system of diffusing and proliferating mortal reactants is analyzed in the presence of randomly moving catalysts. While the continuum description of the problem predicts reactant extinction as the average growth rate becomes negative, growth rate fluctuations induced by the discrete nature of the agents are shown to allow for an active phase, where reactants proliferate as their spatial configuration adapts to the fluctuations of the catalysts density. The model is explored by employing field theoretical techniques, numerical simulations and strong coupling analysis. For d<=2, the system is shown to exhibits an active phase at any growth rate, while for d>2 a kinetic phase transition is predicted. The applicability of this model as a prototype for a host of phenomena which exhibit self organization is discussed.Comment: 6 pages 6 figur

Gravitational Lensing at Millimeter Wavelengths

With today's millimeter and submillimeter instruments observers use gravitational lensing mostly as a tool to boost the sensitivity when observing distant objects. This is evident through the dominance of gravitationally lensed objects among those detected in CO rotational lines at z>1. It is also evident in the use of lensing magnification by galaxy clusters in order to reach faint submm/mm continuum sources. There are, however, a few cases where millimeter lines have been directly involved in understanding lensing configurations. Future mm/submm instruments, such as the ALMA interferometer, will have both the sensitivity and the angular resolution to allow detailed observations of gravitational lenses. The almost constant sensitivity to dust emission over the redshift range z=1-10 means that the likelihood for strong lensing of dust continuum sources is much higher than for optically selected sources. A large number of new strong lenses are therefore likely to be discovered with ALMA, allowing a direct assessment of cosmological parameters through lens statistics. Combined with an angular resolution <0.1", ALMA will also be efficient for probing the gravitational potential of galaxy clusters, where we will be able to study both the sources and the lenses themselves, free of obscuration and extinction corrections, derive rotation curves for the lenses, their orientation and, thus, greatly constrain lens models.Comment: 69 pages, Review on quasar lensing. Part of a LNP Topical Volume on "Dark matter and gravitational lensing", eds. F. Courbin, D. Minniti. To be published by Springer-Verlag 2002. Paper with full resolution figures can be found at ftp://oden.oso.chalmers.se/pub/tommy/mmviews.ps.g

Oscillations and dynamics in a two-dimensional prey-predator system

Using Monte Carlo simulations we study two-dimensional prey-predator systems. Measuring the variance of densities of prey and predators on the triangular lattice and on the lattice with eight neighbours, we conclude that temporal oscillations of these densities vanish in the thermodynamic limit. This result suggests that such oscillations do not exist in two-dimensional models, at least when driven by local dynamics. Depending on the control parameter, the model could be either in an active or in an absorbing phase, which are separated by the critical point. The critical behaviour of this model is studied using the dynamical Monte Carlo method. This model has two dynamically nonsymmetric absorbing states. In principle both absorbing states can be used for the analysis of the critical point. However, dynamical simulations which start from the unstable absorbing state suffer from metastable-like effects, which sometimes renders the method inefficient.Comment: 7 eps figures, Phys.Rev.E - in pres

Origins of the Ambient Solar Wind: Implications for Space Weather

The Sun's outer atmosphere is heated to temperatures of millions of degrees, and solar plasma flows out into interplanetary space at supersonic speeds. This paper reviews our current understanding of these interrelated problems: coronal heating and the acceleration of the ambient solar wind. We also discuss where the community stands in its ability to forecast how variations in the solar wind (i.e., fast and slow wind streams) impact the Earth. Although the last few decades have seen significant progress in observations and modeling, we still do not have a complete understanding of the relevant physical processes, nor do we have a quantitatively precise census of which coronal structures contribute to specific types of solar wind. Fast streams are known to be connected to the central regions of large coronal holes. Slow streams, however, appear to come from a wide range of sources, including streamers, pseudostreamers, coronal loops, active regions, and coronal hole boundaries. Complicating our understanding even more is the fact that processes such as turbulence, stream-stream interactions, and Coulomb collisions can make it difficult to unambiguously map a parcel measured at 1 AU back down to its coronal source. We also review recent progress -- in theoretical modeling, observational data analysis, and forecasting techniques that sit at the interface between data and theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue connected with a 2016 ISSI workshop on "The Scientific Foundations of Space Weather." 44 pages, 9 figure

Star Formation and Dynamics in the Galactic Centre

The centre of our Galaxy is one of the most studied and yet enigmatic places in the Universe. At a distance of about 8 kpc from our Sun, the Galactic centre (GC) is the ideal environment to study the extreme processes that take place in the vicinity of a supermassive black hole (SMBH). Despite the hostile environment, several tens of early-type stars populate the central parsec of our Galaxy. A fraction of them lie in a thin ring with mild eccentricity and inner radius ~0.04 pc, while the S-stars, i.e. the ~30 stars closest to the SMBH (<0.04 pc), have randomly oriented and highly eccentric orbits. The formation of such early-type stars has been a puzzle for a long time: molecular clouds should be tidally disrupted by the SMBH before they can fragment into stars. We review the main scenarios proposed to explain the formation and the dynamical evolution of the early-type stars in the GC. In particular, we discuss the most popular in situ scenarios (accretion disc fragmentation and molecular cloud disruption) and migration scenarios (star cluster inspiral and Hills mechanism). We focus on the most pressing challenges that must be faced to shed light on the process of star formation in the vicinity of a SMBH.Comment: 68 pages, 35 figures; invited review chapter, to be published in expanded form in Haardt, F., Gorini, V., Moschella, U. and Treves, A., 'Astrophysical Black Holes'. Lecture Notes in Physics. Springer 201