495 research outputs found
Environmental variables, pesticide pollution and meiofaunal community structure in two contrasting temporarily open/closed false bay estuaries
Environmental variables (including natural and anthropogenic stressors) and meiobenthic communities were sampled in a ‘natural’ (Rooiels) and a ‘disturbed’ (Lourens) estuary in the Western Cape, South Africa, bimonthly for 20 months. A primary aim of the study was to assess if the meiobenthic community structure is driven by different variables when comparing ‘natural’ versus ‘disturbed’ system. Due to the much smaller catchment of the Rooiels Estuary, many environmental variables were significantly different (p<0.001) from the variables in the Lourens Estuary, e.g. salinity, temperature, pH, total suspended solids, nitrate and depth. No pesticide concentrations were expected in the Rooiels Estuary due to the absence of agricultural development in the catchment. However, chlorpyrifos (8.9 µg/kg), prothiofos (22.0 µg/kg) and cypermethrin concentrations (0.42 µg/kg) were detected frequently, with the highest concentrations recorded during the summer months. Principal response curve analysis showed that temporal variability between sampling dates explained 42% of the variance in environmental variables and pesticide concentrations and spatial variability between the 2 estuaries explained 58%. Variables contributing most to the differences were higher concentrations of endosulfan, p,p-DDE and nitrate concentrations in the Lourens Estuary and larger grain size and higher salinity at the bottom in the Rooiels Estuary. In general the meiofaunal community in the Rooiels Estuary showed a significantly higher number of taxa (p<0.001), a significantly higher Shannon Wiener Diversity Index (
Drawing Planar Graphs with Few Geometric Primitives
We define the \emph{visual complexity} of a plane graph drawing to be the
number of basic geometric objects needed to represent all its edges. In
particular, one object may represent multiple edges (e.g., one needs only one
line segment to draw a path with an arbitrary number of edges). Let denote
the number of vertices of a graph. We show that trees can be drawn with
straight-line segments on a polynomial grid, and with straight-line
segments on a quasi-polynomial grid. Further, we present an algorithm for
drawing planar 3-trees with segments on an
grid. This algorithm can also be used with a small modification to draw maximal
outerplanar graphs with edges on an grid. We also
study the problem of drawing maximal planar graphs with circular arcs and
provide an algorithm to draw such graphs using only arcs. This is
significantly smaller than the lower bound of for line segments for a
nontrivial graph class.Comment: Appeared at Proc. 43rd International Workshop on Graph-Theoretic
Concepts in Computer Science (WG 2017
SNOMED CT – advances in concept mapping, retrieval, and ontological foundations. Selected contributions to the Semantic Mining Conference on SNOMED CT (SMCS 2006)
Magnetic field measurements and wind-line variability of OB-type stars
Context. The first magnetic fields in O- and B-type stars that do not belong
to the Bp-star class, have been discovered. The cyclic UV wind-line
variability, which has been observed in a significant fraction of early-type
stars, is likely to be related to such magnetic fields. Aims. We attempt to
improve our understanding of massive-star magnetic fields, and observe
twenty-five carefully-selected, OB-type stars. Methods. Of these stars we
obtain 136 magnetic field strength measurements. We present the UV wind-line
variability of all selected targets and summarise spectropolarimetric
observations acquired using the MUSICOS spectropolarimeter, mounted at the TBL,
Pic du Midi, between December 1998 and November 2004. From the average Stokes I
and V line profiles, derived using the LSD method, we measure the magnetic
field strengths, radial velocities, and first moment of the line profiles.
Results. No significant magnetic field is detected in any OB-type star that we
observed. Typical 1{\sigma} errors are between 15 and 200 G. A possible
magnetic-field detection for the O9V star 10 Lac remains uncertain, because the
field measurements depend critically on the fringe- effect correction in the
Stokes V spectra. We find excess emission in UV-wind lines, centred about the
rest wavelength, to be a new indirect indicator of the presence of a magnetic
field in early B-type stars. The most promising candidates to host magnetic
fields are the B-type stars {\delta} Cet and 6 Cep, and a number of O stars.
Conclusions. Although some O and B stars have strong dipolar field, which cause
periodic variability in the UV wind-lines, such strong fields are not
widespread. If the variability observed in the UV wind-lines of OB stars is
generally caused by surface magnetic fields, these fields are either weak
(<~few hundred G) or localised.Comment: A&A publishe
Visual/infrared interferometry of Orion Trapezium stars: Preliminary dynamical orbit and aperture synthesis imaging of the Theta 1 Orionis C system
Located in the Orion Trapezium cluster, Theta 1 Orionis C is one of the
youngest and nearest high-mass stars (O5-O7) and also known to be a close
binary system. Using new multi-epoch visual and near-infrared bispectrum
speckle interferometric observations obtained at the BTA 6 m telescope, and
IOTA near-infrared long-baseline interferometry, we trace the orbital motion of
the Theta 1 Ori C components over the interval 1997.8 to 2005.9, covering a
significant arc of the orbit. Besides fitting the relative position and the
flux ratio, we apply aperture synthesis techniques to our IOTA data to
reconstruct a model-independent image of the Theta 1 Ori C binary system.
The orbital solutions suggest a high eccentricity (e approx. 0.91) and
short-period (P approx. 10.9 yrs) orbit. As the current astrometric data only
allows rather weak constraints on the total dynamical mass, we present the two
best-fit orbits. From these orbital solutions one can be favoured, implying a
system mass of 48 M_sun and a distance to the Trapezium cluster of 434 pc. When
also taking the measured flux ratio and the derived location in the HR-diagram
into account, we find good agreement for all observables, assuming a spectral
type of O5.5 for Theta 1 Ori C1 (M=34.0 M_sun) and O9.5 for C2 (M=15.5 M_sun).
We find indications that the companion C2 is massive itself, which makes it
likely that its contribution to the intense UV radiation field of the Trapezium
cluster is non-negligible. Furthermore, the high eccentricity of the
preliminary orbit solution predicts a very small physical separation during
periastron passage (approx. 1.5 AU, next passage around 2007.5), suggesting
strong wind-wind interaction between the two O stars.Comment: 13 pages, 9 figures, Accepted for publication in Astronomy &
Astrophysic
The chemical abundance analysis of normal early A- and late B-type stars
Modern spectroscopy of early-type stars often aims at studying complex
physical phenomena. Comparatively less attention is paid to identifying and
studying the "normal" A- and B-type stars and testing how the basic atomic
parameters and standard spectral analysis allow one to fit the observations. We
wish to stablish whether the chemical composition of the solar photosphere can
be regarded as a reference for early A- and late B-type stars. We have obtained
optical high-resolution, high signal-to-noise ratio spectra of three slowly
rotating early-type stars (HD 145788, 21 Peg and pi Cet) that show no obvious
sign of chemical peculiarity, and performed a very accurate LTE abundance
analysis of up to 38 ions of 26 elements (for 21 Peg), using a vast amount of
spectral lines visible in the spectral region covered by our spectra. We
provide an exhaustive description of the abundance characteristics of the three
analysed stars with a critical review of the line parameters used to derive the
abundances. We compiled a table of atomic data for more than 1100 measured
lines that may be used in the future as a reference. The abundances we obtained
for He, C, Al, S, V, Cr, Mn, Fe, Ni, Sr, Y, and Zr are compatible with the
solar ones derived with recent 3D radiative-hydrodynamical simulations of the
solar photosphere. The abundances of the remaining studied elements show some
degree of discrepancy compared to the solar photosphere. Those of N, Na, Mg,
Si, Ca, Ti, and Nd may well be ascribed to non-LTE effects; for P, Cl, Sc and
Co, non-LTE effects are totally unknown; O, Ne, Ar, and Ba show discrepancies
that cannot be ascribed to non-LTE effects. The discrepancies obtained for O
(in two stars) and Ne agree with very recent non-LTE abundance analysis of
early B-type stars in the solar neighbourhood.Comment: Accepted for publication on Astronomy and Astrophysic
Exploring correlations between sex steroids and fatty acids and their potential roles in the induced maturation of the male European eel
[EN] The present study was undertaken to evaluate the correlations between the fatty acids in the liver and testis and the plasma levels of the hormonal steroids used during eel spermatogenesis, in order to clarify the physiological roles fatty acids play in the spermatogenetic process. The stages of testis development (S1-S5) were assessed by histological observations in order to classify the different phases of hormonally-induced spermatogenesis and evaluate the possible relationships between the hormones and fatty acids in each stage.
The highest plasma levels of 17 beta-estradiol (E2), testosterone (T) and 11-ketotestosterone (11KT) were found in S1, when spermatogonial proliferation occurs. A correlation was found between 17 alpha-20 beta-dihydroxy-4-pregnen-3- one (DHP) levels and some fatty acids during the proliferation and growing phases (S1-2), suggesting that DHP might modulate lipid metabolism in the liver during early spermatogenesis. The DHP levels increased significantly during the growing phase (S2) and remained at high levels throughout the subsequent development stages (S3-S5).
Similar to results found in mammals, our results show that in the eel there are regulatory mechanisms, including eicosapentaenoic acid (20:5-n3, EPA) and docosahexaenoic acid (22:6-n3, DHA), which act as modulators in the synthesis of androgens, particularly during the final phase of sperm maturation. Our results suggest that the fact that EPA, ARA and DHA concentrations in the eel testis remain constant/stable during spermiation could be related to the subsequent union of the spermatozoa and the egg. The findings from this research provide new insights for further studies about the possible effect of steroids on desaturase activity and highlight the importance of the effect of lipid metabolism during male eel spermatogenesis. (C) 2014 Elsevier B.V. All rights reserved.Funded by the European Community's 7th Framework Programme under the Theme 2 "Food, Agriculture and Fisheries, and Biotechnology", grant agreement no. 245257 (PRO-EEL). D. S. P. had a contract co-financed by MICINN and UPV (PTA2011-4948-I) and received a Shortterm Scientific Mission grant from COST Office (Food and Agriculture COST Action FA1205: AQUAGAMETE) to carry out the steroids analyses in Norway.Baeza Ariño, R.; Peñaranda, D.; Vilchez Olivencia, MC.; Tveiten, H.; Pérez Igualada, LM.; Asturiano Nemesio, JF. (2015). Exploring correlations between sex steroids and fatty acids and their potential roles in the induced maturation of the male European eel. Aquaculture. 435:328-335. https://doi.org/10.1016/j.aquaculture.2014.10.016S32833543
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