4,480 research outputs found
Size Class Dependent Relationships between Temperature and Phytoplankton Photosynthesis-Irradiance Parameters in the Atlantic Ocean
Over the past decade, a number of methods have been developed to estimate
size-class primary production from either in situ phytoplankton pigment data or
remotely-sensed data. In this context, the first objective of this study was to compare
two methods of estimating size class specific (micro-, nano-, and pico-phytoplankton)
photosynthesis-irradiance (PE) parameters from pigment data. The second objective
was to analyse the relationship between environmental variables (temperature,
nitrate and PAR) and PE parameters in the different size-classes. A large dataset
was used of simultaneous measurements of the PE parameters (n = 1,260) and
phytoplankton pigment markers (n = 2,326), from 3 different institutes. There were no
significant differences in mean PE parameters of the different size classes between
the chemotaxonomic method of Uitz et al. (2008) and the pigment markers and
carbon-to-Chl a ratios method of Sathyendranath et al. (2009). For both methods,
mean maximum photosynthetic rates (PBm
) for micro-phytoplankton were significantly
lower than those for pico-phytoplankton and nano-phytoplankton. The mean light
limited slope (�B) for nano-phytoplankton were significantly higher than for the
other size taxa. For micro-phytoplankton dominated samples identified using the
Sathyendranath et al. (2009) method, both PBm
and �B exhibited a significant, positive
linear relationship with temperature, whereas for pico-phytoplankton the correlation
with temperature was negative. Nano-phytoplankton dominated samples showed a
positive correlation between PBm
and temperature, whereas for �B and the light saturation
parameter (Ek) the correlations were not significant. For the Uitz et al. (2008) method,
only micro-phytoplankton PBm
, pico-phytoplankton �B, nano- and pico-phytoplankton
Ek exhibited significant relationships with temperature. The temperature ranges
occupied by the size classes derived using these methods differed. The Uitz et al.
(2008) method exhibited a wider temperature range compared to those derived
from the Sathyendranath et al. (2009) method. The differences arise from the
classification of mixed populations. Based on these patterns, we therefore recommend
using the Sathyendranath et al. (2009) method to derive micro-phytoplankton PE parameters at sea water temperatures up to 8◦C during monospecific blooms and
the Uitz et al. (2008) method to derive PE parameters of mixed populations over the
temperature range from 8 to 18◦C. Both methods exhibited similar relationships between
pico-phytoplankton PE parameters and temperatures >18◦C
Fungi and some mycotoxins contaminating rice (Oryza Sativa) in Niger State, Nigeria
Study on the fungi and some mycotoxins (Aflatoxin B1 - AFB1, ochratoxin A - OTA and zearalenone -ZEN) contaminating rice (Oryza sativa) in Niger State of Nigeria was carried out. One thousand and sixty two fungi were isolated and identified from one hundred and ninety six mouldy rice samples collected from the state. The major fungal genera contaminating rice were Aspergillus, Penicillium, Fusarium,Alternaria, Mucor, Rhizopus, Trichoderma, Curvularia, elminthosporium and Cladosporium. The most prevalent fungal species on rice were .Penicillium spp., A. flavus, A. parasiticus, A. niger, Mucor spp.,Rhizopus spp. and Alternaria spp. The commonest fungal contaminants of the dry, harmattan; dry-hot and rainy seasons were A. niger, Penicillium spp. and A. flavus respectively. AFB1 was detected in 97 ofthe samples analyzed at concentrations between 20-1642 ug/kg. Fifty six of the one hundred and forty samples analyzed for OTA contained the toxin (24 – 1164 ug/kg). Zearalenone was found in ninety threeof the one hundred and ninety six mouldy rice samples analyzed at concentrations of between 24 and 1169 ug/kg. Twenty two samples were concurrently contaminated with the three toxins while sevenothers were found to contain both AFB1 and OTA. AFB1 and ZEN occurred together in twelve samples, and eight samples contained both OTA and ZEN
Cometary ions detected by the Cassini spacecraft 6.5 au downstream of Comet 153P/Ikeya-Zhang
During March-April 2002, while between the orbits of Jupiter and Saturn, the Cassini spacecraft detected a significant enhancement in pickup proton flux. The most likely explanation for this enhancement was the addition of protons to the solar wind by the ionization of neutral hydrogen in the corona of comet 153P/Ikeya-Zhang. This comet passed relatively close to the Sun-Cassini line during that period, allowing pickup ions to be carried to Cassini by the solar wind. This pickup proton flux could have been further modulated by the passage of the interplanetary counterparts of coronal mass ejections past the comet and spacecraft. The radial distance of 6.5 Astronomical Units (au) traveled by the pickup protons, and the implied total tail length of 7.5 au make this cometary ion tail the longest yet measured
Exploring Graphs with Time Constraints by Unreliable Collections of Mobile Robots
A graph environment must be explored by a collection of mobile robots. Some
of the robots, a priori unknown, may turn out to be unreliable. The graph is
weighted and each node is assigned a deadline. The exploration is successful if
each node of the graph is visited before its deadline by a reliable robot. The
edge weight corresponds to the time needed by a robot to traverse the edge.
Given the number of robots which may crash, is it possible to design an
algorithm, which will always guarantee the exploration, independently of the
choice of the subset of unreliable robots by the adversary? We find the optimal
time, during which the graph may be explored. Our approach permits to find the
maximal number of robots, which may turn out to be unreliable, and the graph is
still guaranteed to be explored.
We concentrate on line graphs and rings, for which we give positive results.
We start with the case of the collections involving only reliable robots. We
give algorithms finding optimal times needed for exploration when the robots
are assigned to fixed initial positions as well as when such starting positions
may be determined by the algorithm. We extend our consideration to the case
when some number of robots may be unreliable. Our most surprising result is
that solving the line exploration problem with robots at given positions, which
may involve crash-faulty ones, is NP-hard. The same problem has polynomial
solutions for a ring and for the case when the initial robots' positions on the
line are arbitrary.
The exploration problem is shown to be NP-hard for star graphs, even when the
team consists of only two reliable robots
ar
چکیده هدف پژوهش حاضر ارزشیابی دور ة آموزشی الکترونیکی رشته کارشناسی ارشد مهندسی فنّاوری اطلاعات دانشگاههای تربیت مدرس ،خواجه نصیر الدین طوسی و امیرکبیر بر اساس الگوی رودریک سیمز است. در این تحقیق از روش توصیفی استفاده شده است. نمون ۀ آماری پژوهش 151 نفر از دانشجویان، استادان و آموزشیاران دور ة آموزش الکترونیکی رشتۀ کارشناسی ارشد مهندسی فنّاوری اطلاعات دانشگاههای تربیت مدرس، خواجه نصیرالدین طوسی و امیرکبیر بودند. در این پژوهش پایایی پرسشنامه 93/0 به دست آمد. نتایج نشان داد که دورههای آموزش الکترونیکی در دانشگاههای خواجه نصیر و تربیت مدرس غالباً در حد نسبتاً مطلوب ارزیاب ی شده و در دانشگاه امیرکبیر وضعیت مؤلفهها در مقایسه با نتایج خواجه نصیر و تربیت مدرس مطلوب تر ارزشیابی شده است
High photosynthetic rates associated with pico and nanophytoplankton communities and high stratification index in the North West Atlantic
The biological dynamics of pelagic marine ecosystems are strongly influenced by the size structure and ecological
succession of phytoplankton, which in turn modifies photosynthetic efficiency. Variability in photosynthetic
rates is closely coupled with changes in community structure, but it is difficult to obtain coincident
data at high enough resolution to characterise these changes. In this study, we employ hierarchical cluster
analysis on chlorophyll-normalised high performance liquid chromatography (HPLC) pigment concentrations
from the North West Atlantic, to identify seasonal successional trends amongst phytoplankton populations.
Changes in phytoplankton community were also analysed as a function of mean equivalent spherical diameter
(MESD) derived from absorption measurements, photosynthetic rates, water-column stratification and temperature.
Well-mixed conditions in spring to early summer were associated with populations of large cells
containing high concentrations of fucoxanthin, chlorophyll-c1 and chlorophyll-c2 relative to chlorophyll-a (Chl
a). As stratification increased over the course of the summer, these cells were replaced by populations dominated
by chlorophyll-b, 19'-hexanoyloxyfucoxanthin, 19'-butanoyloxyfucoxanthin and divinyl chlorophyll-a, indicative
of small picophytoplankton. As stratification decreased in autumn, MESD and alloxanthin increased, suggesting
the presence of cryptophytes. Positive relationships were found between MESD and the quantum yield of
photosynthesis (φm) for 7 out of the 8 phytoplankton clusters identified, while negative relationships between
mean mixed layer photosynthetically active radiation and φm and the light limited slope of photosynthesis (αB)
were observed for 4 clusters, as a result of nutrient limitation and photo-protection. The highest photosynthetic
rates were associated with a pico & nanophytoplankton communities, which increased from spring to late
summer as stratification intensified. By contrast, diatom communities had the lowest photosynthetic rates
throughout the year. These successional patterns in the dominant phytoplankton size-class and phenology
support Margalef's mandala in terms of the relationship between turbulence and community structure. The study
sheds new light on assemblages dominated by smaller cells, under warm, stratified conditions, having higher
photosynthetic efficiencies, which has implications for the carbon flux in the NW Atlantic
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Optimization and Augmentation for Data Parallel Contour Trees
Contour trees are used for topological data analysis in scientific visualization. While originally computed with serial algorithms, recent work has introduced a vector-parallel algorithm. However, this algorithm is relatively slow for fully augmented contour trees which are needed for many practical data analysis tasks. We therefore introduce a representation called the hyperstructure that enables efficient searches through the contour tree and use it to construct a fully augmented contour tree in data parallel, with performance on average 6 times faster than the state-of-the-art parallel algorithm in the TTK topological toolkit
Parallel Peak Pruning for Scalable SMP Contour Tree Computation
As data sets grow to exascale, automated data analysis and visu- alisation are increasingly important, to intermediate human under- standing and to reduce demands on disk storage via in situ anal- ysis. Trends in architecture of high performance computing sys- tems necessitate analysis algorithms to make effective use of com- binations of massively multicore and distributed systems. One of the principal analytic tools is the contour tree, which analyses rela- tionships between contours to identify features of more than local importance. Unfortunately, the predominant algorithms for com- puting the contour tree are explicitly serial, and founded on serial metaphors, which has limited the scalability of this form of analy- sis. While there is some work on distributed contour tree computa- tion, and separately on hybrid GPU-CPU computation, there is no efficient algorithm with strong formal guarantees on performance allied with fast practical performance. We report the first shared SMP algorithm for fully parallel contour tree computation, with for- mal guarantees of O(lgnlgt) parallel steps and O(nlgn) work, and implementations with up to 10× parallel speed up in OpenMP and up to 50× speed up in NVIDIA Thrust
Control Words of String Rewriting P Systems
P systems with controlled computations have been introduced and investigated in the recent past, by assigning labels to the rules in the regions of the P system and guiding the computations by control words. Here we consider string rewriting cell-like transition P system with label assigned rules working in acceptor mode and compare the obtained family of languages of control words over the rule labels with certain well-known language families. An application to chain code picture generation is also pointed out
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