4,299 research outputs found
Universality of Load Balancing Schemes on Diffusion Scale
We consider a system of parallel queues with identical exponential
service rates and a single dispatcher where tasks arrive as a Poisson process.
When a task arrives, the dispatcher always assigns it to an idle server, if
there is any, and to a server with the shortest queue among randomly
selected servers otherwise . This load balancing scheme
subsumes the so-called Join-the-Idle Queue (JIQ) policy and the
celebrated Join-the-Shortest Queue (JSQ) policy as two crucial
special cases. We develop a stochastic coupling construction to obtain the
diffusion limit of the queue process in the Halfin-Whitt heavy-traffic regime,
and establish that it does not depend on the value of , implying that
assigning tasks to idle servers is sufficient for diffusion level optimality
Relationships between the El-Niño Southern Oscillation and spate flows in southern Africa and Australia
International audienceThe flow records of arid zone rivers are characterised by a high degree of seasonal variability, being dominated by long periods of very low or zero flow. Discrete flow events in these rivers are influenced by aseasonal factors such as global climate forcings. The atmospheric circulations of the El-Niño Southern Oscillation (ENSO) have been shown to influence climate regimes across many parts of the world. Strong teleconnections between changing ENSO regimes and discharges are likely to be observed in highly variable arid zones. In this paper, the influence of ENSO mechanisms on the flow records of two arid zone rivers in each of Australia and Southern Africa are identified. ENSO signals, together with multi-decadal variability in their impact as identified through seasonal values of the Interdecadal Pacific Oscillation (IPO) index, are shown to influence both the rate of occurrence and the size of discrete flow episodes in these rivers. Keywords: arid zones, streamflow, spates, climate variability, ENSO, Interdecadal Pacific Oscillation, IP
Unravelling Active Galactic Nuclei
A complete flat-spectrum radio-loud sample of AGN includes a significant
fraction of Seyfert-like AGN including a NLS1. Analysis of their optical
spectra suggests that the reddest continuum colours are either associated with
AGN in nearby resolved galaxies, or distant quasars showing relatively narrow
permitted emission lines.Comment: Poster contribution presented at the Joint MPE,AIP,ESO workshop on
NLS1s, Bad Honnef, Dec. 1999, to appear in New Astronomy Reviews; also
available at http://wave.xray.mpe.mpg.de/conferences/nls1-worksho
Finite Element Flow Simulations of the EUROLIFT DLR-F11 High Lift Configuration
This paper presents flow simulation results of the EUROLIFT DLR-F11
multi-element wing configuration, obtained with a highly scalable finite
element solver, PHASTA. This work was accomplished as a part of the 2nd high
lift prediction workshop. In-house meshes were constructed with increasing mesh
density for analysis. A solution adaptive approach was used as an alternative
and its effectiveness was studied by comparing its results with the ones
obtained with other meshes. Comparisons between the numerical solution obtained
with unsteady RANS turbulence model and available experimental results are
provided for verification and discussion. Based on the observations, future
direction for adaptive research and simulations with higher fidelity turbulence
models is outlined.Comment: 52nd Aerospace Sciences Meetin
Black Hole Mass Estimates of Radio Selected Quasars
The black hole (BH) mass in the centre of AGN has been estimated for a sample
of radio-selected flat-spectrum quasars to investigate the relationship between
BH mass and radio properties of quasars. We have used the virial assumption
with measurements of the H FWHM and luminosity to estimate the central
BH mass. In contrast to previous studies we find no correlation between BH mass
and radio power in these AGN. We find a range in BH mass similar to that seen
in radio-quiet quasars from previous studies. We believe the reason that the
low BH mass radio-loud quasars have not been measured in previous studies is
due to optical selection effects which tend to miss the less optically luminous
radio-loud sources.Comment: 22 pages, 7 figures, accepted for publication in Ap
Formulation of complementary food using amaranth, chickpea and maize improves iron, calcium and zinc content
Malnutrition is the cause of the majority of deaths in children under five years old in Ethiopia. Micronutrient deficiencies such as iron, zinc and calcium, often seen in malnourished children, are major public health problems throughout Ethiopia. These deficiencies have negative consequences on the cognitive and physical development of children, and on work productivity of adults. There is, therefore, a need for sustainable methods to address iron inadequacy in complementary feeding. Animal products are a good source of iron, zinc and calcium, but due to their high costs, their consumption by most children in Ethiopia has declined. The grain amaranth grows wild in areas of Ethiopia but is considered a weed. This study, conducted in rural Ethiopia, was initiated to prepare nutrient-rich complementary food using recipes that substituted the usual maize gruel with porridge made from amaranth and chickpea flours. Using a laboratory based experimental study design, four porridges suitable for complementary feeding, with different proportions of amaranth grains, maize and chickpeas were formulated in triplicate and analyzed in triplicate for minerals including iron, and phytate levels. Mother-child pairs were recruited for acceptability testing, at the community level. Results showed adding amaranth improved the content of iron and other nutrients as compared to control porridge (100% maize) and decreased phytate levels. The lowest phytate to iron ratio (0.24) was observed in the 70% amaranth and 30% chickpea blend, and the lowest viscosity measure was also observed in this same formulation. Soaking amaranth seeds in warm (50oC) water then germinating in lemon juice-containing water at 32oC for 72 hours resulted in the lowest phytate levels. In sensory testing, all of the formulated porridges with different proportions of amaranth flour were acceptable to mothers and their children, although the red color was disliked by mothers and their children. Flavor preference was not altered; however, overall acceptability was reduced with increasing amounts of amaranth. The study indicated that a processed 70% amaranth and 30% chickpea product can be used to produce low-cost, nutrient-rich complementary food with moderate acceptability. Increased nutritional awareness, production and consumption of grain amaranth products may be the way to address mineral deficiencies including iron, in the study area.Keywords: Micronutrients, Phytates, Complementary feeding, Amaranth grain, Chickpea, Ethiopia, Iron, Zinc
Investigation of the New Local Group Galaxy VV 124
We present the results of our stellar photometry and spectroscopy for the new
Local Group galaxy VV 124 (UGC 4879) obtained with the 6-m BTA telescope. The
presence of a few bright supergiants in the galaxy indicates that the current
star formation process is weak. The apparent distribution of stars with
different ages in VV 124 does not differ from the analogous distributions of
stars in irregular galaxies, but the ratio of the numbers of young and old
stars indicates that VV 124 belongs to the rare Irr/Sph type of galaxies. The
old stars (red giants) form the most extended structure, a thick disk with an
exponential decrease in the star number density to the edge. Definitely, the
young population unresolvable in images makes a great contribution to the
background emission from the central galactic regions. The presence of young
stars is also confirmed by the [O III] emission line visible in the spectra
that belongs to extensive diffuse galactic regions. The mean radial velocity of
several components (two bright supergiants, the unresolvable stellar
population, and the diffuse gas) is v_h = -70+/-15 km/s and the velocity with
which VV 124 falls into the Local Group is v_LG = -12+/-15 km/s. We confirm the
distance to the galaxy D = 1.1+/-0.1 Mpc and the metallicity of red giants
([Fe/H] = -1.37) found by Kopylov et al. (2008).VV 124 is located on the
periphery of the Local Group approximately at the same distance from M 31 and
our Galaxy and is isolated from other galaxies. The galaxy LeoA nearest to it
is 0.5 Mpc away.Comment: 10 pages, 8 figures. Accepted for publication in Astronomy Letters
(2010, Vol. 36, No. 5, pp. 309-318
Modelling persistence in annual Australia point rainfall
Annual rainfall time series for Sydney from 1859 to 1999 is analysed. Clear evidence of nonstationarity is presented, but substantial evidence for persistence or hidden states is more elusive. A test of the hypothesis that a hidden state Markov model reduces to a mixture distribution is presented. There is strong evidence of a correlation between the annual rainfall and climate indices. Strong evidence of persistence of one of these indices, the Pacific Decadal Oscillation (PDO), is presented together with a demonstration that this is better modelled by fractional differencing than by a hidden state Markov model. It is shown that conditioning the logarithm of rainfall on PDO, the Southern Oscillation index (SOI), and their interaction provides realistic simulation of rainfall that matches observed statistics. Similar simulation models are presented for Brisbane, Melbourne and Perth.</p> <p style='line-height: 20px;'><b>Keywords: </b>Hydrological persistence,hidden state Markov models, fractional differencing, PDO, SOI, Australian rainfall</p
High-velocity OH megamasers in IRAS 20100-4156: Evidence for a Supermassive Black Hole
We report the discovery of new, high-velocity narrow-line components of the
OH megamaser in IRAS 20100-4156. Results from the Australian Square Kilometre
Array Pathfinder (ASKAP)'s Boolardy Engineering Test Array (BETA) and the
Australia Telescope Compact Array (ATCA) provide two independent measurements
of the OH megamaser spectrum. We found evidence for OH megamaser clumps at
409 and 562 km/s (blue-shifted) from the systemic velocity of the galaxy,
in addition to the lines previously known. The presence of such high velocities
in the molecular emission from IRAS 201004156 could be explained by a ~50 pc
molecular ring enclosing an approximately 3.8 billion solar mass black hole. We
also discuss two alternatives, i.e. that the narrow-line masers are dynamically
coupled to the wind driven by the active galactic nucleus or they are
associated with two separate galactic nuclei. The comparison between the BETA
and ATCA spectra provides another scientific verification of ASKAP's BETA. Our
data, combined with previous measurements of the source enabled us to study the
variability of the source over a twenty-six year period. The flux density of
the brightest OH maser components has reduced by more than a factor of two
between 1988 and 2015, whereas a secondary narrow-line component has more than
doubled in the same time. Plans for high-resolution VLBI follow-up of this
source are discussed, as are prospects for discovering new OH megamasers during
the ASKAP early science program.Comment: Accepted to MNRAS. Seven pages, three figure
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