1,277 research outputs found
Global stability for an inverse problem in soil-structure interaction
We consider the inverse problem of determining the Winkler
subgrade reaction coefficient of a slab foundation modelled as a
thin elastic plate clamped at the boundary. The plate is loaded by
a concentrated force and its transversal deflection is measured at
the interior points. We prove a global Holder stability
estimate under (mild) regularity assumptions on the unknown
coefficient
Numerical size estimates of inclusions in Kirchhoff-Love elastic plates
The size estimates approach for Kirchhoff--Love elastic plates allows to determine upper and lower bounds of the area of an unknown elastic inclusion by measuring the work developed by applying a couple field on the boundary of the plate. Although the analytical process by which such bounds are determined is of constructive type, it leads to rather pessimistic evaluations. In this paper we show by numerical simulations how to obtain such bounds for practical applications of the method. The computations are developed for a square plate under various boundary loads and for inclusions of different position, shape and stiffness. The sensitivity of the results with respect to the relevant parameters is also analyzed
A single mutation results in diploid gamete formation and parthenogenesis in a Drosophila yemanuclein-alpha meiosis I defective mutant
<p>Abstract</p> <p>Background</p> <p>Sexual reproduction relies on two key events: formation of cells with a haploid genome (the gametes) and restoration of diploidy after fertilization. Therefore the underlying mechanisms must have been evolutionary linked and there is a need for evidence that could support such a model.</p> <p>Results</p> <p>We describe the identification and the characterization of <it>yem<sup>1</sup></it>, the first <it>yem-alpha </it>mutant allele (V478E), which to some extent affects diploidy reduction and its restoration. Yem-alpha is a member of the Ubinuclein/HPC2 family of proteins that have recently been implicated in playing roles in chromatin remodeling in concert with HIRA histone chaperone. The <it>yem<sup>1 </sup></it>mutant females exhibited disrupted chromosome behavior in the first meiotic division and produced very low numbers of viable progeny. Unexpectedly these progeny did not display paternal chromosome markers, suggesting that they developed from diploid gametes that underwent gynogenesis, a form of parthenogenesis that requires fertilization.</p> <p>Conclusions</p> <p>We focus here on the analysis of the meiotic defects exhibited by <it>yem<sup>1 </sup></it>oocytes that could account for the formation of diploid gametes. Our results suggest that <it>yem<sup>1 </sup></it>affects chromosome segregation presumably by affecting kinetochores function in the first meiotic division.</p> <p>This work paves the way to further investigations on the evolution of the mechanisms that support sexual reproduction.</p
Effects of psychological stress on skin and hair pigmentation in Polish adolescents
The effects of psychological stress, gender and age on hair and skin pigmentation levels were evaluated in the reported study. The material included Polish high-school and university students aged 18-22 (in the age range 17.50-22.49). All subjects who had sunbathed or used tanning beds or lamps, skin tanning agents, tanning extenders and/or medical agents affecting skin pigmentation during the 60 days preceding the beginning of the study were excluded. The use of hormonal contraceptives within a month prior to the study was also an excluding factor. Stress levels were evaluated by the Perceived Stress Scale (PSS-10) in the Polish adaptation, while hair and skin pigmentation levels were assessed with a dermaspectrometer (Cortex TechnologyÂź, Denmark, 2007). The study was carried out with the exclusion of the summer period. Skin pigmentation was evaluated in 395 subjects (264 women and 131 men). Hair pigmentation was analyzed in a smaller group of 351 subjects (223 women and 128 men), as some had had their hair dyed within 12 months prior to the study while in some others the hair was too short to be correctly measured. Regardless of their age, the studied women felt much more stress related to their life situation and were characterized by stronger skin pigmentation than the examined men. No sex differences were identified with regard to hair pigmentation. In the studied period of ontogenesis (18-22 years of age), hair pigmentation levels increased with age, while skin melanization remained stable. Disregarding the effects of age and sex, the level of perceived stress was negatively correlated with skin pigmentation levels; no such relationship was found for hair melanization. © 2012 Polish Anthtropological Society.Aneta Sitek, ElĆŒbieta Ć»Ä
dziĆska and Iwona Rosse
Fixed points and amenability in non-positive curvature
Consider a proper cocompact CAT(0) space X. We give a complete algebraic
characterisation of amenable groups of isometries of X. For amenable discrete
subgroups, an even narrower description is derived, implying Q-linearity in the
torsion-free case.
We establish Levi decompositions for stabilisers of points at infinity of X,
generalising the case of linear algebraic groups to Is(X). A geometric
counterpart of this sheds light on the refined bordification of X (\`a la
Karpelevich) and leads to a converse to the Adams-Ballmann theorem. It is
further deduced that unimodular cocompact groups cannot fix any point at
infinity except in the Euclidean factor; this fact is needed for the study of
CAT(0) lattices.
Various fixed point results are derived as illustrations.Comment: 33 page
Caractérisation des risques de contamination des agrosystÚmes périurbains de Dakar par les éléments traces métalliques
Lâapplication de produits rĂ©siduaires organiques (PRO) amĂ©liore la fertilitĂ© des sols, mais induit des effets nĂ©gatifs sur les agrosystĂšmes, en raison de la prĂ©sence de contaminants tels que les Ă©lĂ©ments traces mĂ©talliques (ETM). Cette Ă©tude vise Ă Ă©valuer lâinfluence de deux doses (20 et 60 T.ha-1) dâapport de boue de station dâĂ©puration STEP et de fiente de volaille sur la disponibilitĂ© de quatre ETM (Ni, Cd, Cr et Pb) dans un arenosol et un fluvisol. Une incubation de 88 jours en conditions contrĂŽlĂ©es a Ă©tĂ© conduite sur les deux sols mĂ©langĂ©s aux diffĂ©rentes doses de boue et de fiente. La disponibilitĂ© des ETM dans les sols incubĂ©s a Ă©tĂ© Ă©valuĂ©e par la technique DGT (Diffusive Gradient in Thin films). Les boues ont abaissĂ© le pH des deux sols tandis que les fientes ont alcalinisĂ© lâarenosol durant les 14 premiers jours dâincubation. Ces PRO ont augmentĂ© les concentrations de Ni, Cd, Pb et Cr disponibles dans les sols. Les disponibilitĂ©s du Ni, Cd et Pb sont plus Ă©levĂ©es dans lâarenosol que dans le fluvisol. La boue Ă 60 T.ha-1 a induit les plus fortes disponibilitĂ©s en Cd et Pb tandis que la fiente Ă 60 T.ha-1 a induit les plus fortes disponibilitĂ©s en Ni et Cr dans les deux sols.Mots clĂ©s : ElĂ©ments traces mĂ©talliques, arenosol, fluvisol, boue dâĂ©puration, fiente.  CHARACTERIZATION OF CONTAMINATION RISKS OF THE SUBURBANAGROECOSYSTEMS OF DAKAR BY TRACE ELEMENTSOrganic wastes (OW) spreading improve soil fertility, but can induce negative effects on agroecosystems, due to the presence of contaminants such as trace elements (TE). This study aims to evaluate the impacts of two doses (20 and 60 T.ha-1) of sewage sludge and poultry manure on the availability of four trace elements (Ni, Cd, Cr and Pb) in arenosol and fluvisol. Soils mixed with different doses of sewage sludge and poultry manure were incubated for 88 days under controlled conditions. The availability of trace elements in incubated soils was evaluated by the DGT (Diffusive Gradient in Thin films) technique. Sewage sludge has decreased the pH of both soils while poultry manure induced an alkalinization of arenosol during the first 14 days of incubation. OW increased Ni, Cd, Pb and Cr availability in the soils. Availability of Ni, Cd and Pb were higher in arenosol than in the fluvisol. Sewage sludge at 60 T.ha-1 induced the highest availability of Cd and Pb while the poultry manure at 60 T.ha-1 induced the highest availability of Ni and Cr in both soils.Keywords : Trace elements, arenosol, fluvisol, sewage sludge, poultry manure
Computing Volume Bounds of Inclusions by EIT Measurements
The size estimates approach for Electrical Impedance Tomography (EIT) allows
for estimating the size (area or volume) of an unknown inclusion in an
electrical conductor by means of one pair of boundary measurements of voltage
and current. In this paper we show by numerical simulations how to obtain such
bounds for practical application of the method. The computations are carried
out both in a 2D and a 3D setting.Comment: 20 pages with figure
Measurement of the Crab nebula polarization at 90 GHz as a calibrator for CMB experiments
CMB experiments aiming at a precise measurement of the CMB polarization, such
as the Planck satellite, need a strong polarized absolute calibrator on the sky
to accurately set the detectors polarization angle and the cross-polarization
leakage. As the most intense polarized source in the microwave sky at angular
scales of few arcminutes, the Crab nebula will be used for this purpose. Our
goal was to measure the Crab nebula polarization characteristics at 90 GHz with
unprecedented precision. The observations were carried out with the IRAM 30m
telescope employing the correlation polarimeter XPOL and using two orthogonally
polarized receivers. We processed the Stokes I, Q, and U maps from our
observations in order to compute the polarization angle and linear polarization
fraction. The first is almost constant in the region of maximum emission in
polarization with a mean value of alpha_Sky=152.1+/-0.3 deg in equatorial
coordinates, and the second is found to reach a maximum of Pi=30% for the most
polarized pixels. We find that a CMB experiment having a 5 arcmin circular beam
will see a mean polarization angle of alpha_Sky=149.9+/-0.2 deg and a mean
polarization fraction of Pi=8.8+/-0.2%.Comment: Accepted for publication in A&A, 9 pages, 4 figure
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