Browsing by Subject "distribution"
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- ItemOpen AccessA more general model for the intrinsic scatter in type Ia supernova distance moduli(2011) Marriner, John; Bernstein, J P; Kessler, Richard; Lampeitl, Hubert; Miquel, Ramon; Mosher, Jennifer; Nichol, Robert C; Sako, Masao; Schneider, Donald P; Smith, MathewWe describe a new formalism to fit the parameters {alpha} and {beta} that are used in the SALT2 model to determine the standard magnitudes of Type Ia supernovae (SNe Ia). The new formalism describes the intrinsic scatter in SNe Ia by a covariance matrix in place of the single parameter normally used. We have applied this formalism to the Sloan Digital Sky Survey Supernova Survey (SDSS-II) data and conclude that the data are best described by {alpha} = 0.135{sup +.033} - .017 and {beta} = 3.19{sup +0.14} - 0.24, where the error is dominated by the uncertainty in the form of the intrinsic scatter matrix. Our result depends on the introduction of a more general form for the intrinsic scatter of the distance moduli of SNe Ia than is conventional, resulting in a larger value of {beta} and a larger uncertainty than the conventional approach. Although this analysis results in a larger value of {beta} and a larger error, the SDSS data differ (at a 98% confidence level) from {beta} = 4.1, the value expected for extinction by the type of dust found in the Milky Way. We have modeled the distribution of SNe Ia in terms of their colormore » and conclude that there is strong evidence that variation in color is a significant contributor to the scatter of SNe Ia around their standard candle magnitude.« less
- ItemOpen AccessBayesian analysis of the backreaction models(2010) Kurek, Aleksandra; Bolejko, Krzysztof; Szydłowski, MarekWe present a Bayesian analysis of four different types of backreaction models, which are based on the Buchert equations. In this approach, one considers a solution to the Einstein equations for a general matter distribution and then an average of various observable quantities is taken. Such an approach became of considerable interest when it was shown that it could lead to agreement with observations without resorting to dark energy. In this paper we compare the {Lambda}CDM model and the backreaction models with type Ia supernovae, baryon acoustic oscillations, and cosmic microwave background data, and find that the former is favored. However, the tested models were based on some particular assumptions about the relation between the average spatial curvature and the backreaction, as well as the relation between the curvature and curvature index. In this paper we modified the latter assumption, leaving the former unchanged. We find that, by varying the relation between the curvature and curvature index, we can obtain a better fit. Therefore, some further work is still needed--in particular, the relation between the backreaction and the curvature should be revisited in order to fully determine the feasibility of the backreaction models to mimic dark energy.
- ItemOpen AccessDEGREE OF POLARIZATION AND SOURCE COUNTS OF FAINT RADIO SOURCES FROM STACKING POLARIZED INTENSITY(2014) Stil, J M; Keller, B W; George, S J; Taylor, A RWe present stacking polarized intensity as a means to study the polarization of sources that are too faint to be detected individually in surveys of polarized radio sources. Stacking offers not only high sensitivity to the median signal of a class of radio sources, but also avoids a detection threshold in polarized intensity, and therefore an arbitrary exclusion of source with a low percentage of polarization. Correction for polarization bias is done through a Monte Carlo analysis and tested on a simulated survey. We show that the non-linear relation between the real polarized signal and the detected signal requires knowledge of the shape of the distribution of fractional polarization, which we constrain using the ratio of the upper quartile to the lower quartile of the distribution of stacked polarized intensities. Stacking polarized intensity for NVSS sources down to the detection limit in Stokes I, we find a gradual increase in median fractional polarization that is consistent with a trend that was noticed before for bright NVSS sources, but is much more gradual than found by previous deep surveys of radio polarization. Consequently, the polarized radio source counts derived from our stacking experiment predict fewer polarized radio sources for future surveys with the Square Kilometre Array and its pathfinders.
- ItemOpen AccessDistribution and phylogenetic inference within the flightless spring katydids (Tettigoniidae: Brinckiella Chopard, 1955) in the Greater Cape Floristic Region(2022) Guta, Ricardo José; Janion-Scheepers, Charlene; Naskrecki, PiotrThe genus Brinckiella is an endemic group from the Greater Cape Floristic region (GCFR) with several undescribed species. Some of them are of conservation concern, categorized by IUCN as Endangered (EN) and Vulnerable (VU) due to their restricted distribution caused by livestock overgrazing, agriculture, and urbanization. However, data are still missing to fully assess their distribution pattern and conservation status. Moreover, although the phylogeny of katydids was recently inferred, Brinckiella was not included in that analysis. Thus, its closest relatives and evolutionary history are still unknown. This study aimed to investigate the distribution and phylogenetic inference within the genus Brinckiella, map the distribution of its species, delimit the species through taxonomy and genetics, and elucidate the phylogenetic relationship and divergence time within the genus. Specimens were collected by hand and sweep netting. Phylogenetic inference was done using the COI gene and analysed under Maximum likelihood and Bayesian inference. This study identified 13 morphospecies of Brinckiella, of which five are new, undescribed species. The genus is currently distributed in 27 vegetation types in three biomes, and apart from the Fynbos and Succulent Karoo biomes, the genus also occurs in the Azonal vegetation biome. Fynbos had the highest number of species of Brinckiella, which is likely related to the vast diversity of plant that they are associated with and probably feed on. In the Succulent Karoo the distribution of Brinckiella might be associated with seasonal plants that occur in the spring and at the beginning of summer. The genus may be monophyletic, and it split from the common ancestor shared with Holochlora fruhstorferi Carl, 1914 about 14.2 Mya, and it split again from the common ancestor shared with Isophya major Brunner von Wattenwyl, 1878, Phaneroptera gracilis Burmeister, 1838 and Kuwayamaea chinensis (Brunner von Wattenwyl, 1878) at 10.16 Mya and diverged in the late Miocene around 8.79 Mya, producing two main clades (A and B). Clade A diverged 7.85 Mya and is composed by two closely related species: B. aptera and B. mauerbergerorum, while Clade B diverged 7.24 Mya and gave rise to two lineages (L1 and L2). Brinckiella wilsoni constitutes L1, and L2 split later in the early Pliocene around 4.74 Mya, and is represented by two sister species, B. arboricola and B. sp. n. 5.
- ItemOpen AccessDoes the distribution of health care benefits in Kenya meet the principles of universal coverage?(BioMed Central Ltd, 2012) Chuma, Jane; Maina, Thomas; Ataguba, JohnBACKGROUND:The 58th World Health Assembly called for all health systems to move towards universal coverage where everyone has access to key promotive, preventive, curative and rehabilitative health interventions at an affordable cost. Universal coverage involves ensuring that health care benefits are distributed on the basis of need for care and not on ability to pay. The distribution of health care benefits is therefore an important policy question, which health systems should address. The aim of this study is to assess the distribution of health care benefits in the Kenyan health system, compare changes over two time periods and demonstrate the extent to which the distribution meets the principles of universal coverage. METHODS: Two nationally representative cross-sectional households surveys conducted in 2003 and 2007 were the main sources of data. A comprehensive analysis of the entire health system is conducted including the public sector, private-not-for-profit and private-for-profit sectors. Standard benefit incidence analysis techniques were applied and adopted to allow application to private sector services. RESULTS: The three sectors recorded similar levels of pro-rich distribution in 2003, but in 2007, the private-not-for-profit sector was pro-poor, public sector benefits showed an equal distribution, while the private-for-profit sector remained pro-rich. Larger pro-rich disparities were recorded for inpatient compared to outpatient benefits at the hospital level, but primary health care services were pro-poor. Benefits were distributed on the basis of ability to pay and not on need for care. CONCLUSIONS: The principles of universal coverage require that all should benefit from health care according to need. The Kenyan health sector is clearly inequitable and benefits are not distributed on the basis of need. Deliberate efforts should be directed to restructuring the Kenyan health system to address access barriers and ensure that all Kenyans benefit from health care when they need it.
- ItemOpen AccessHumpback whale abundance south of 60°S from three complete circumpolar sets of surveys(International Whaling Commission, 2011) Branch, Trevor AAustral summer estimates of abundance are obtained for humpback whales (Megaptera novaeangliae) in the Southern Ocean from the IWC’s IDCR and SOWER circumpolar programmes. These surveys have encircled the Antarctic three times: 1978/79–1983/84 (CPI), 1985/86–1990/91 (CPII) and 1991/92–2003/04 (CPIII), criss-crossing strata totalling respectively 64.3%, 79.5% and 99.7% of the open-ocean area south of 60°S. Humpback whales were absent from the Ross Sea, but were sighted in all other regions, and in particularly high densities around the Antarctic Peninsula, in Management Area IV and north of the Ross Sea. Abundance estimates are presented for each CP, for Management Areas, and for assumed summer feeding regions of each Breeding Stock. Abundance estimates are negatively biased because some whales on the trackline are missed and because some humpback whales are outside the survey region. Circumpolar estimates with approximate midpoints of 1980/81, 1987/88 and 1997/98 are 7,100 (CV = 0.36), 10,200 (CV = 0.30) and 41,500 (CV = 0.11). When these are adjusted simply for unsurveyed northern areas, the estimated annual rate of increase is 9.6% (95% CI 5.8–13.4%). All Breeding Stocks are estimated to be increasing but increase rates are significantly greater than zero only for those on the eastern and western coasts of Australia. Given the observed rates of increase, the current total Southern Hemisphere abundance is greater than 55,000, which is similar to the summed northern breeding ground estimates (~60,000 from 1999–2008). Some breeding ground abundance estimates are far greater, and others far lower, than the corresponding IDCR/SOWER estimates, in a pattern apparently related to the latitudinal position of the Antarctic Polar Front.
- ItemOpen AccessH i kinematics, mass distribution and star formation threshold in NGC 6822, using the SKA pathfinder KAT-7(2017) Namumba, B; Carignan, C; Passmoor, S; de Blok, W J GWe present high sensitivity H I observations of NGC 6822, obtained with the Karoo Array Telescope (KAT-7). We study the kinematics, the mass distribution and the star formation thresholds. The KAT-7 short baselines and low system temperature make it sensitive to large-scale, low surface brightness emission. The observations detected ∼ 23 per cent more flux than previous Australian Telescope Compact Array observations. We fit a tilted ring model to the H I velocity field to derive the rotation curve (RC). The KAT-7 observations allow the measurement of the rotation curve of NGC 6822 out to 5.8 kpc, ∼1 kpc further than existing measurements. NGC 6822 is seen to be dark matter dominated at all radii. The observationally motivated pseudo-isothermal dark matter (DM) halo model reproduces well the observed RC while the Navarro Frank-White DM model gives a poor fit to the data. We find the best-fitting mass-to-light ratio (M/L) of 0.12 ± 0.01 which is consistent with the literature. The modified Newtonian dynamics gives a poor fit to our data. We derive the star formation threshold in NGC 6822 using the H I and H α data. The critical gas densities were calculated for gravitational instabilities using the Toomre-Q criterion and the cloud-growth criterion. We found that in regions of star formation, the cloud-growth criterion explains star formation better than the Toomre-Q criterion. This shows that the local shear rate could be a key player in cloud formation for irregular galaxies such as NGC 6822.
- ItemOpen AccessIdentity and distribution of southern African sciaenid fish species of the genus Umbrina(2005) Hutchings, K; Griffiths, M HTwo Umbrina species, U. canariensis Valenciennes 1843 and U. robinsoni Gilchrist and Thompson 1908, are recognised from southern Africa. The latter species was hitherto believed to be a synonym of Umbrina ronchus Valenciennes 1843 (type locality Canary Islands). U. canariensis is distributed along the South Africa eastern seaboard from Cape Point to Sodwana Bay and U. robinsoni is known from False Bay to Madagascar and Oman. African Umbrina taxonomy has, however, been hindered by geographic samples that were either too few or consisted of specimens of disparate length; and as a result the identification and distribution of South African Umbrina species was confused. Morphological comparison of a large number of South African Umbrina with specimens from the type locality (Canary Islands) confirmed the identity of South African U. canariensis and allowed for an expanded description of the species. However, differences between specimens of U. ronchus and those of the second South African species (n = 251) led us to resurrect U. robinsoni (Gilchrist and Thompson 1908) as a valid name for this species. U. robinsoni differs from U. ronchus in having a smaller supraoccipital crest and thus a less steep pre-dorsal profile; a shallower preorbital bone (13–21% head length [HL] vs 21% HL); and a shorter nostril-orbit distance (2.4–6.9% HL vs 7.8–8.5% HL). Colour patterns also differ between the two species, with U. ronchus lacking the oblique, wavy, white stripes evident on the flanks of U. robinsoni. U. ronchus does not occur in South African waters, and is an eastern Atlantic species occurring from Gibraltar to Angola. Specimens from the east coast of Africa (Moçambique to Gulf of Oman) that were previously identified as U. ronchus are U. robinsoni. Differences between U. robinsoni and U. canariensis include: a lower modal number of soft dorsal fin rays, (22–27 vs 24–30); less deep body depth, (26–36% standard length [SL] vs 33–39% SL); shorter pectoral fin length (15–21% SL vs 20–25% SL); longer caudal peduncle length (26–34% SL vs 21–28% SL) and snout length (27–38% HL vs 23–32% HL); and smaller orbit diameter (14–33% HL vs 23–34% HL). Otoliths of U. robinsoni differ from those of U. canariensis in being smaller, less elongate, lacking a massive post-central umbo and having a post-dorsal spine remnant. The body colour and nature of the striping pattern on the flanks differs markedly between the species: in U. robinsoni the oblique stripes are thin, wavy, white lines; in U. canariensis the oblique stripes are thicker, nearly straight and brown; U. robinsoni also lacks the triangleshaped mark on the outer operculum and the dark pigmentation of the inner operculum that is found on U. canariensis. Spatial analysis of South African specimens collected with a variety of gear revealed U. robinsoni to be a shallow-water species found from the surf-zone to 40m, whereas U. canariensis occurs predominantly from 40 to 100m depth. Although both species occur throughout the South African eastern seaboard, U. canariensis is most common west of the Kei River, where the shelf is wider. Examination of three specimens of U. steindachneri Cadenat 1950 confirmed the presence of a fourth sub-Saharan Umbrina species that is limited to tropical West African waters from Senegal to Angola. U. steindachneri differs from the other African Umbrina in having a high number of soft dorsal rays (28–29), a greater 3rd dorsal spine length (25–27% SL) and a very pronounced and convoluted striping pattern on the flanks.
- ItemOpen AccessMeasurement of colour flow with the jet pull angle in tt¯ events using the ATLAS detector at √s = 8 TeV(2015) Aad, G; Abbott, B; Abdallah, J; Abdinov, O; Aben, R; Abolins, M; AbouZeid, O S; Abramowicz, H; Abreu, H; Abreu, R; Abulaiti, Y; Acharya, B S; Adamczyk, L; Adams, D L; Adelman, J; Adomeit, S; Adye, T; Affolder, A A; Agatonovic-Jovin, T; Agricola, J; Aguilar-Saavedra, J A; Ahlen, S P; Ahmadov, F; Aielli, G; Akerstedt, H; Åkesson, T P A; Akimov, A V; Alberghi, G L; Albert, J; Albrand, S; Alconada Verzini, M J; Aleksa, MThe distribution and orientation of energy inside jets is predicted to be an experimental handle on colour connections between the hard--scatter quarks and gluons initiating the jets. This Letter presents a measurement of the distribution of one such variable, the jet pull angle. The pull angle is measured for jets produced in tt¯ events with one W boson decaying leptonically and the other decaying to jets using 20.3 fb−1 of data recorded with the ATLAS detector at a centre--of--mass energy of s√=8 TeV at the LHC. The jet pull angle distribution is corrected for detector resolution and acceptance effects and is compared to various models.
- ItemOpen AccessOptimal placement and effect of a wind farm on load flow and protection systems in a municipal distribution network(2019) Martin, Mogamat Noer; Awodele, Kehinde O.Much research has been done on the effects of distributed generation on network characteristics. However, little research has been done on the effects of this distributed generation on current network protection schemes. An IPP has approached a South African municipality regarding the connection of a wind farm that would be connected to the municipality’s existing grid. This presented a unique opportunity to simulate and study the impact and effect that this wind farm would have on a real-life network in terms of network operation and protection schemes. This also presents the possibility of connecting the wind farm in a different configuration, possibly resulting in better network operation at a lower cost. The network optimisation in this research was done using the probability-based incremental learning (PBIL) and differential evolution (DE) optimisation techniques. These algorithms were programmed and modelled according to the desired IPP wind farm requirements using the MATLAB and MATPOWER simulation packages. The networks used in these algorithms were modelled in the text-based MATPOWER format. This research goes on to study a modified 14-bus IEEE test network in terms of network characteristics and protection performance so that an idea of the performance of the optimisation algorithms can be obtained. Protection data for the IEEE network was not available. The network was thus graded for use in this study. The research then continues to model the existing and proposed network configuration, and proposes various other points of connection to the municipal network using the PBIL and DE algorithms. These studies were conducted using the DIgSILENT PowerFactory simulation package, with the networks and protection data being modelled in this package. Network and protection performance results were recorded for each case in both networks under study. The results show that in the case of the modified IEEE network, the DE algorithm provides a better solution in terms of improving power losses while the PBIL algorithm provides a better solution in terms of improving the voltage profile. In the case of the municipality network, the DE algorithm provides the best performance, with the DE result managing to reduce power losses by 83.89% compared to the current and proposed network configurations. The overall voltage profile was also seen to improve by over 23%. The research also found that the change in fault level for the various cases are minimal. This is due to the limitation in fault current contribution imposed by the use of an inverter system connecting the wind farm to the grid. This means that, as the results shows, network grading is not very much affected by the addition of the wind farm connections. However, it is seen that the municipal network is not optimally graded in the base case. Finally, it is also seen that, though not often used in research, the MATPOWER package works well as a network simulation tool. A costing analysis was also conducted and shows that the DE solution is the most cost-effective solution, in addition to being the best-performing solution. The study recommends that the results produced by the DE algorithm be implemented instead of the proposed implementation. The municipal network should also be regraded and new protection settings should be implemented.
- ItemRestrictedAn overview of the biology of the desiccation-tolerant resurrection plant Myrothamnus flabellifolia.(Oxford University Press, 2007) Moore, John P; Lindsey, George G; Farrant, Jill M; Brandt, Wolf FMyrothamnus flabellifolia (Welw.) is a relatively large resurrection plant, a woody shrub between 0.5 m and 1.5 m tall (Sherwin et al., 1998) that grows on rock inselbergs (Porembski and Barthlott, 2000) throughout southern Africa (Weimarck, 1936; Van Wyk et al., 1997; Glen et al., 1999). The plant was first recorded in 1859 by Friedrich Welwitsch, who named the plant Myrothamnus (myron meaning aromatic and thamnos meaning bush) flabellifolia (meaning fan-like leaves) (Puff, 1978a; Glen et al., 1999), the leaves having a balsamic-like odour (Puff, 1978a; Glen et al., 1999). Weiss (1906) was the first to note the ‘miraculous manner’ with which the desiccated plant revived when supplied with water (Fig. 1A, B). Myrothamnus flabellifolia occupies an important position in traditional African folklore and medicine (Watt and Breyer-Brandwijk, 1962; Hutchings, 1996; Van Wyk et al., 1997). The Zulu name for the plant is ‘uvukwaba- file’ (wakes from the dead). The reviving ability is believed to be passed on to the ill person during treatment (Hutchings, 1996; Van Wyk et al., 1997). The plant is a geophyte possessing an extensive root system which extends into the crevices of the rocky slopes upon which it grows (Child, 1960; Glen et al., 1999). Myrothamnus flabellifolia can dehydrate its vegetative tissue, in particular its leaves, to an air-dry state. In this state, the leaves and stem segments curl and change colour from green to dullbrown (Farrant et al., 1999; Glen et al., 1999). When water is provided to the roots the plant re-hydrates its desiccated tissue and returns to its original colour and shape (Glen et al., 1999; Farrant et al., 2003). Since the last review on M. flabellifolia was written many years ago (Puff, 1978a) and since considerable work has been published in the last decade, this review focuses on recent advances in the understanding of the physiology, biochemistry and chemistry of M. flabellifolia.
- ItemOpen AccessTHE CENTRAL SLOPE OF DARK MATTER CORES IN DWARF GALAXIES: SIMULATIONS VERSUS THINGS(2011) Oh, Se-Heon; Brook, Chris; Governato, Fabio; Brinks, Elias; Mayer, Lucio; de Blok, W J G; Brooks, Alyson; Walter, FabianWe make a direct comparison of the derived dark matter (DM) distributions between hydrodynamical simulations of dwarf galaxies assuming ACDM cosmology and the observed dwarf galaxies sample from the THINGS survey in terms of (1) the rotation curve shape and (2) the logarithmic inner density slope a of mass density profiles. The simulations, which include the effect of baryonic feedback processes, such as gas cooling, star formation, cosmic UV background heating, and most importantly, physically motivated gas outflows driven by supernovae, form bulgeless galaxies with DM cores. We show that the stellar and baryonic mass is similar to that inferred from photometric and kinematic methods for galaxies of similar circular velocity. Analyzing the simulations in exactly the same way as the observational sample allows us to address directly the so-called cusp/core problem in the ACDM model. We show that the rotation curves of the simulated dwarf galaxies rise less steeply than cold dark matter rotation curves and are consistent with those of the THINGS dwarf galaxies. The mean value of the logarithmic inner density slopes alpha of the simulated galaxies' DM density profiles is similar to-0.4 +/- 0.1, which shows good agreement with alpha = -0.29 +/- 0.07 of the THINGS dwarf galaxies. The effect of non-circular motions is not significant enough to affect the results. This confirms that the baryonic feedback processes included in the simulations are efficiently able to make the initial cusps with alpha similar to-1.0 to -1.5 predicted by DM-only simulations shallower and induce DM halos with a central mass distribution similar to that observed in nearby dwarf galaxies.
- ItemOpen Access