2,625 research outputs found
The Role of Provenance Management in Accelerating the Rate of Astronomical Research
The availability of vast quantities of data through electronic archives has
transformed astronomical research. It has also enabled the creation of new
products, models and simulations, often from distributed input data and models,
that are themselves made electronically available. These products will only
provide maximal long-term value to astronomers when accompanied by records of
their provenance; that is, records of the data and processes used in the
creation of such products. We use the creation of image mosaics with the
Montage grid-enabled mosaic engine to emphasize the necessity of provenance
management and to understand the science requirements that higher-level
products impose on provenance management technologies. We describe experiments
with one technology, the "Provenance Aware Service Oriented Architecture"
(PASOA), that stores provenance information at each step in the computation of
a mosaic. The results inform the technical specifications of provenance
management systems, including the need for extensible systems built on common
standards. Finally, we describe examples of provenance management technology
emerging from the fields of geophysics and oceanography that have applicability
to astronomy applications.Comment: 8 pages, 1 figure; Proceedings of Science, 201
Enhancing the cosmic-ray mass sensitivity of air-shower arrays by combining radio and muon detectors
The muonic and electromagnetic components of air showers are sensitive to the
mass of the primary cosmic particle. The sizes of the components can be
measured with particle detectors on ground, and the electromagnetic component
in addition indirectly via its radio emission in the atmosphere. The
electromagnetic particles do not reach the ground for very inclined showers. On
the contrary, the atmosphere is transparent for the radio emission and its
footprint on ground increases with the zenith angle. Therefore, the radio
technique offers a reliable detection over the full range of zenith angles, and
in particular for inclined showers. In this work, the mass sensitivity of a
combination of the radio emission with the muons is investigated in a case
study for the site of the Pierre Auger Observatory using CORSIKA Monte Carlo
simulations of showers in the EeV energy range. It is shown, that the
radio-muon combination features superior mass separation power in particular
for inclined showers, when compared to established mass observables such as a
combination of muons and electrons or the shower maximum Xmax. Accurate
measurements of the energy-dependent mass composition of ultra-high energy
cosmic rays are essential to understand their still unknown origin. Thus, the
combination of muon and radio detectors can enhance the scientific performance
of future air-shower arrays and offers a promising upgrade option for existing
arrays
Paradoxical diffusion: Discriminating between normal and anomalous random walks
Commonly, normal diffusive behavior is characterized by a linear dependence
of the second central moment on time, , while anomalous
behavior is expected to show a different time dependence, with for
superdiffusive motions. Here we demonstrate that this kind of qualification, if
applied straightforwardly, may be misleading: There are anomalous transport
motions revealing perfectly "normal" diffusive character (), yet being non-Markov and non-Gaussian in nature. We use recently developed
framework \cite[Phys. Rev. E \textbf{75}, 056702 (2007)]{magdziarz2007b} of
Monte Carlo simulations which incorporates anomalous diffusion statistics in
time and space and creates trajectories of such an extended random walk. For
special choice of stability indices describing statistics of waiting times and
jump lengths, the ensemble analysis of paradoxical diffusion is shown to hide
temporal memory effects which can be properly detected only by examination of
formal criteria of Markovianity (fulfillment of the Chapman-Kolmogorov
equation).Comment: 8 pages, 7 figure
Tracer diffusion inside fibrinogen layers
We investigate the obstructed motion of tracer (test) particles in crowded
environments by carrying simulations of two-dimensional Gaussian random walk in
model fibrinogen monolayers of different orientational ordering. The fibrinogen
molecules are significantly anisotropic and therefore they can form structures
where orientational ordering, similar to the one observed in nematic liquid
crystals, appears. The work focuses on the dependence between level of the
orientational order (degree of environmental crowding) of fibrinogen molecules
inside a layer and non-Fickian character of the diffusion process of spherical
tracer particles moving within the domain. It is shown that in general
particles motion is subdiffusive and strongly anisotropic, and its
characteristic features significantly change with the orientational order
parameter, concentration of fibrinogens and radius of a diffusing probe.Comment: 8 pages, 12 figure
Effects of crude oil on the gastropod, tympanotomus fuscata in the Cross River Estuary, south-east Nigeria
Edible periwinkle, Tympanotonus fuscata, was collected from the Cross River estuary, allowed to acclimate to laboratory conditions for a week and then exposed to Nigerian light crude oil at different concentrations of 50ml, 100ml, and 150ml per litre of water for a period of 96 hours. Mud (80g) was added to all the 4-litre aquaria used for the experiment. The oil was thoroughly mixed with the estuarine water by stirring vigorously. During the 4-days experimental period, most of the specimens suffered suffocation and became moribund and mortality recorded. Within the first 24 hours mortality was absent in the 50ml and 100ml concentrations, although most specimens moved out of the medium by creeping up the aquaria. Specimens in the control seemed lively and unaffected by oiling throughout the duration of the experiment. Mortalities were as high as 117 out of 180 individuals during the entire experimental period, with higher concentrations recording higher mortalities. There was steady increase in mortality from 4 individuals in the first 24 hours to 12 individuals after 72 hours in the 150ml/l concentration. The LC50 values were obtained by graphical interpolation. It is concluded that the soluble fraction of the Nigerian light crude oil could be detrimental to shellfish even at a concentration as low as 1000ml/l of the estuarine water.KEYWORDS: Crude Oil, Water Soluble Fraction, Tympanotonus fuscata, Cross River estuary, Nigeria
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Human gut Bacteroides capture vitamin B12 via cell surface-exposed lipoproteins.
Human gut Bacteroides use surface-exposed lipoproteins to bind and metabolize complex polysaccharides. Although vitamins and other nutrients are also essential for commensal fitness, much less is known about how commensal bacteria compete with each other or the host for these critical resources. Unlike in Escherichia coli, transport loci for vitamin B12 (cobalamin) and other corrinoids in human gut Bacteroides are replete with conserved genes encoding proteins whose functions are unknown. Here we report that one of these proteins, BtuG, is a surface-exposed lipoprotein that is essential for efficient B12 transport in B. thetaiotaomicron. BtuG binds B12 with femtomolar affinity and can remove B12 from intrinsic factor, a critical B12 transport protein in humans. Our studies suggest that Bacteroides use surface-exposed lipoproteins not only for capturing polysaccharides, but also to acquire key vitamins in the gut
Influence of rice husk ash source variability on road subgrade properties
This study presents the influence of variability of Rice Husk Ash (RHA) on the geotechnical properties of subgrade. The subgrade soil classified as A–7–6 (Clayey soil) in the AASHTO Classification system or CL in the USCS was used. The RHA materials were obtained from Ebonyi, Enugu and Cross River States of Nigeria, respectively. The geotechnical properties investigated included consistency limits, compaction and the California Bearing Ratio (CBR) of the soil for varying RHA contents for the three different RHA sources. There was significant variability in the chemical composition of RHA, with samples from Cross River, Ebonyi and Enugu States having Silica contents of 84.55%, 76.30% and 70.12% respectively. The results obtained showed that there was a general increase in the Optimum Moisture Content (OMC) and CBR values of the soil with increase in RHA content. However, the plasticity and Maximum Dry Density (MDD) decreased with increase in RHA.Keywords: California Bearing Ratio; Consistency indices; Lateritic soil; Maximum Dry Density; Optimum Moisture Content; Rice Husk Ash; Sub-grade
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