A high-wavenumber boundary-element method for an acoustic scattering problem

In this paper we show stability and convergence for a novel Galerkin boundary element method approach to the impedance boundary value problem for the Helmholtz equation in a half-plane with piecewise constant boundary data. This problem models, for example, outdoor sound propagation over inhomogeneous flat terrain. To achieve a good approximation with a relatively low number of degrees of freedom we employ a graded mesh with smaller elements adjacent to discontinuities in impedance, and a special set of basis functions for the Galerkin method so that, on each element, the approximation space consists of polynomials (of degree $\nu$) multiplied by traces of plane waves on the boundary. In the case where the impedance is constant outside an interval $[a,b]$, which only requires the discretization of $[a,b]$, we show theoretically and experimentally that the $L_2$ error in computing the acoustic field on $[a,b]$ is ${\cal O}(\log^{\nu+3/2}|k(b-a)| M^{-(\nu+1)})$, where $M$ is the number of degrees of freedom and $k$ is the wavenumber. This indicates that the proposed method is especially commendable for large intervals or a high wavenumber. In a final section we sketch how the same methodology extends to more general scattering problems

La progression des pins sur les Causses : un phénomène difficilement contrôlable ? L'exemple du Causse Méjan.

La progression du pin sylvestre et du pin noir se fait à partir de l'écotone entre le causse boisé et le causse nu des géographes et à partir de la bordure nord du causse. L'analyse des processus de reproduction, de dissémination et d'installation permet en partie d'expliquer cette structure. Il est difficile de prévoir la progression du pin dans les détails, mais il est clair qu'elle amènera les éleveurs à modifier leur systèmes d'exploitation pour maintenir des surfaces suffisantes de pâturage

Impacts of predicted climate change on recruitment at the geographical limits of Scots pine

Ongoing changes in global climate are having a significant impact on the distribution of plant species, with effects particularly evident at range limits. We assessed the capacity of Pinus sylvestris L. populations at northernmost and southernmost limits of the distribution to cope with projected changes in climate. We investigated responses including seed germination and early seedling growth and survival, using seeds from northernmost (Kevo, Finland) and southernmost (Granada, Spain) populations. Seeds were grown under current climate conditions in each area and under temperatures increased by 5 °C, with changes in precipitation of +30% or -30% with reference to current values at northern and southern limits, respectively, in a fully factorial controlled-conditions experimental design. Increased temperatures reduced germination time and enhanced biomass gain at both range edges but reduced survival at the southern range edge. Higher precipitation also increased survival and biomass but only under a southern climate. Seeds from the southern origin emerged faster, produced bigger seedlings, allocated higher biomass to roots, and survived better than northern ones. These results indicate that recruitment will be reduced at the southernmost range of the species, whereas it will be enhanced at the northern limit, and that the southern seed sources are better adapted to survive under drier conditions. However, future climate will impose a trade-off between seedling growth and survival probabilities. At the southern range edge, higher growth may render individuals more susceptible to mortality where greater aboveground biomass results in greater water loss through evapotranspiration

Plant Responses to Extreme Climatic Events: A Field Test of Resilience Capacity at the Southern Range Edge

The expected and already observed increment in frequency of extreme climatic events may result in severe vegetation shifts. However, stabilizing mechanisms promoting community resilience can buffer the lasting impact of extreme events. The present work analyzes the resilience of a Mediterranean mountain ecosystem after an extreme drought in 2005, examining shoot-growth and needle-length resistance and resilience of dominant tree and shrub species (Pinus sylvestris vs Juniperus communis, and P. nigra vs J. oxycedrus) in two contrasting altitudinal ranges. Recorded high vegetative-resilience values indicate great tolerance to extreme droughts for the dominant species of pine-juniper woodlands. Observed tolerance could act as a stabilizing mechanism in rear range edges, such as the Mediterranean basin, where extreme events are predicted to be more detrimental and recurrent. However, resistance and resilience components vary across species, sites, and ontogenetic states: adult Pinus showed higher growth resistance than did adult Juniperus; saplings displayed higher recovery rates than did conspecific adults; and P. nigra saplings displayed higher resilience than did P. sylvestris saplings where the two species coexist. P. nigra and J. oxycedrus saplings at high and low elevations, respectively, were the most resilient at all the locations studied. Under recurrent extreme droughts, these species-specific differences in resistance and resilience could promote changes in vegetation structure and composition, even in areas with high tolerance to dry conditions.This study was supported by Ministerio de Ciencia e Innovación (Spanish Government) Projects CGL2008-04794 and CGL2011-29910 to R.Z., and by grant FPU-MEC (AP2005-1561) to A. H

Seedling emergence and establishment of Pinus sylvestris in the Mongolian forest-steppe ecotone

Syftet med studien är att undersöka och beskriva pedagogers uppfattningar av hur de skapar delaktighet och inflytande, i en kommuns förskoleverksamhet och organisation.Mina frågeställningar är hur pedagogerna beskriver sina möjligheter och hinder för att få och skapa delaktighet och inflytande, samt vilka inre och yttre faktorer som finns som påverkar möjligheten för delaktighet och inflytande.För att undersöka detta har jag valt en kvalitativ forskningsansats. Jag har genomfört semistrukturerade intervjuer med sju pedagoger. Det empiriska materialet har bearbetats kvalitativt i en empirinära ansats.I resultatet såg jag att ett större fokus på processkvaliteten behöver läggas och medvetenheten behöver ökas, kring den pedagogiska dokumentationens betydelse.Sammanfattningsvis behöver den undersökta kommunens förskolor en gemensam samsyn i hela systemet i ett förståelsebaserat och tolkande perspektiv som gynnar en långsiktig och hållbar utveckling.Participation and influence in the preschool, a study with teachers in one municipality.The purpose of this study is to explore and describe teacher’s perceptions of how they create participation and influence, in a municipality´s preschool and organization.My questions are how teachers describe their opportunities and barriers to get and create participation and influence, and what internal and external factors that affecting the ability of participation and influence.To examine this, I have chosen a qualitative research approach. I have conducted semi structured interviews, with seven teachers. The empirical data have been processed in a qualitative empirical closely approach.In the result, I found that a greater focus on process quality needs to be added and awareness needs to be increased, on the pedagogic documentations significances.In conclusion, needs the municipal preschools, which have been examined, get a common consensus of the entire system in a understanding based and interpretive perspective, that support a long term and sustainable development

The operationalization of fatigue in frailty scales : a systematic review

Purpose: To identify the different fatigue items in existing frailty scales. Methods: PubMed, Web of Knowledge and PsycINFO were systematically screened for frailty scales. 133 articles were included, describing 158 frailty scales. Fatigue items were extracted and categorized in 4 fatigue constructs: “mood state related tiredness”, “general feeling of tiredness”, “activity based feeling of tiredness” and “resistance to physical tiredness”. Results: 120 fatigue items were identified, of which 100 belonged to the construct “general feeling of tiredness” and only 9 to the construct “resistance to physical tiredness”. 49,4% of the frailty scales included at least 1 fatigue item, representing 15±9,3% of all items in these scales. Fatigue items have a significantly higher weight in single domain (dominantly physical frailty scales) versus multi domain frailty scales (21±3.2 versus 10.6±9.8%, p=<0,05 ). Conclusion: Fatigue is prominently represented in frailty scales, covering a great diversity in fatigue constructs and underlying pathophysiological mechanisms by which fatigue relates to frailty. Although fatigue items were more prevalent and had a higher weight in physical frailty scales, the operationalization of fatigue leaned more towards psychological constructs. This review can be used as a reference for choosing a suitable frailty scale depending on the type of fatigue of interest

Masse des graines, capacité de dispersion et performance dans une population de Pinus sylvestris

[Departement_IRSTEA]GT [TR1_IRSTEA]32 - GECOTER / ECOFRICHInternational audienceSeed size optimization theories are generally based on the assumption that seed mass increase seedling performance and decreases seed dispersal ability. In this paper, we investigated the relationship between seed mass, wing area and seed terminal fall rates in a wind-dispersed tree, Pinus sylvestris L. and we ask whether these morphological seed measurements are related to seedling performance. We found important differences between trees in seed dimensions, but seed wing-loading (mass/area ratio) and terminal fall rate remains constant. Seed mass had a positive effect on emergence rate and seedling growth until 6 months, which did not result from any maternal effect. However, seed terminal fall rate was not related to any measurement of progeny performance. A positive correlation between seed mass and wing area lead to low variation of seed terminal fall rate and may explain the absence of relationship between seed fall rate and seedling performance.Les théories d'optimisation de la taille de la graine sont généralement basées sur l'hypothèse que la masse élevée d'une graine augmente la performance de la plantule qui en est issue, mais diminue en contrepartie sa capacité de dissémination. Nous avons cherché à déterminer la relation qui existe entre la masse de la graine, la surface de son aile et sa vitesse de chute stable chez un arbre (Pinus sylvestris) dont la dissémination se fait par le vent. Nous tentons également de savoir si ces mesures morphologiques sont associées aux performances des plantules. Tel que suggéré par l'hypothèse isométrique, nous avons constaté que la forme de la graine demeure la même lorsque la taille varie. Cette constance de la forme de la graine entraîne deux conséquences importantes : i) la masse de la graine est inversement proportionnelle à sa capacité de dissémination ; ii) les caractéristiques associées à la dissémination sont beaucoup moins variables que la masse des graines. La masse de la graine a aussi un effet positif sur le taux d'émergence et de croissance de la plantule jusqu'à six mois et cet effet n'est associé en aucune façon à un facteur d'origine familiale. Par ailleurs, le peu de variation de la vitesse de chute stable de la graine ne permet pas d'établir de relation statistique entre la capacité de dissémination de la graine et la performance de la plantul

Masse des graines, capacité de dispersion et performance dans une population de Pinus sylvestris

[Departement_IRSTEA]GT [TR1_IRSTEA]32 - GECOTER / ECOFRICHInternational audienceSeed size optimization theories are generally based on the assumption that seed mass increase seedling performance and decreases seed dispersal ability. In this paper, we investigated the relationship between seed mass, wing area and seed terminal fall rates in a wind-dispersed tree, Pinus sylvestris L. and we ask whether these morphological seed measurements are related to seedling performance. We found important differences between trees in seed dimensions, but seed wing-loading (mass/area ratio) and terminal fall rate remains constant. Seed mass had a positive effect on emergence rate and seedling growth until 6 months, which did not result from any maternal effect. However, seed terminal fall rate was not related to any measurement of progeny performance. A positive correlation between seed mass and wing area lead to low variation of seed terminal fall rate and may explain the absence of relationship between seed fall rate and seedling performance.Les théories d'optimisation de la taille de la graine sont généralement basées sur l'hypothèse que la masse élevée d'une graine augmente la performance de la plantule qui en est issue, mais diminue en contrepartie sa capacité de dissémination. Nous avons cherché à déterminer la relation qui existe entre la masse de la graine, la surface de son aile et sa vitesse de chute stable chez un arbre (Pinus sylvestris) dont la dissémination se fait par le vent. Nous tentons également de savoir si ces mesures morphologiques sont associées aux performances des plantules. Tel que suggéré par l'hypothèse isométrique, nous avons constaté que la forme de la graine demeure la même lorsque la taille varie. Cette constance de la forme de la graine entraîne deux conséquences importantes : i) la masse de la graine est inversement proportionnelle à sa capacité de dissémination ; ii) les caractéristiques associées à la dissémination sont beaucoup moins variables que la masse des graines. La masse de la graine a aussi un effet positif sur le taux d'émergence et de croissance de la plantule jusqu'à six mois et cet effet n'est associé en aucune façon à un facteur d'origine familiale. Par ailleurs, le peu de variation de la vitesse de chute stable de la graine ne permet pas d'établir de relation statistique entre la capacité de dissémination de la graine et la performance de la plantul

Modèles de recrutement dans des populations en expansion de Pinus sylvestris et Pinus nigra dans des pelouses abandonnées : mesurer la dispersion par le vent à courte et longue distance

[Departement_IRSTEA]GT [TR1_IRSTEA]32 - GECOTER / ECOFRICHAccurate predictions about woody plant invasions require estimation of demographic and dispersal parameters in low-density expanding populations. In particular, long-distance dispersal has been recognized as a key determinant of population expansion rate. Empirical measurements of the shape of the tail of dispersal curves remain however rare.We used inverse modelling to estimate the fecundity and dispersal parameters in an expanding population of Pinus sylvestris and of Pinus nigra in the Causse Méjan, Southern France. Empirical models such as the generalized exponential distribution, the bivariate Student's distribution and mixed discrete models were compared. Only mixed discrete dispersal kernels fitted adequately the data, thus suggesting that tree dispersal is a composite process including simple descent dispersal and rare uplifting events. The others candidate models strongly underestimated the tail of the dispersal curve. Although a higher seed terminal fall velocity, Pinus nigra exhibited much higher dispersal ability than Pinus sylvestris. This demonstrates the limit of biological attributes such as seed morphology to predict dispersal ability. The timing and duration of the dispersal period, and its relation to climatic and wind conditions, may play a major role on achievable dispersal distance.Our results lead to the prediction of a faster spread rate of non-native Pinus nigra, compared to native Pinus sylvestris. In the study area, most plantations of Pinus nigra become sexually-mature, thus possibly leading to a very fast expansion to the adjacent grasslands in relation to decreasing impact of grazing.Une bonne prédiction des invasions ligneuses requiert l'estimation de paramètres démographiques et de dispersion dans des populations à faible densité et en cours d'expansion. En particulier, la dispersion à longue distance est reconnue comme un paramètre déterminant de la vitesse d'expansion d'une population. Cependant, les mesures expérimentales de la courbe complète de dispersion sont rares. Nous avons utilisé la modélisation inverse pour estimer la fécondité et les sparamètres de dispersion dans une population en expansion de Pinus sylvestris (pin sylvestre) et of Pinus nigra (pin noir) sur le Causse Méjean, France. Des modèles empiriques comme la distribution exponentielle généralisée, la distribution bivariée de Student et des modèles mixtes discrets ont été comparés. Seul le modèle mixte discret montre une bonne adéquation avec les données de terrain, suggérant ainsi que la dispersion des pins est un processus composite incluant des événements normaux de dispersion et des événements rares liés à des vents violents. Les autres modèles sous-estiment fortement la queue de la courbe de dispersion. Bien qu'il ait une vitesse terminale de chute plus forte, Pinus nigra a démontré une capacité de dispersion beacoup plus forte que Pinus sylvestris. Cela illustre les limites de l'utilisation d'attributs biologiques simples comme la morphologie des graines pour prédire la capacité de dispersion d'une espèce. La période et la durée de la prédiode de dispersion, en relation avec les conditions climatiques et de vent, pourraient jouer un rôle majeur dans la dispersion réelle. Nos résultats conduisent à prédire une vitesse d'expansion plus rapide pour Pinus nigra (introduite sur le Causse) que pour Pinus sylvestris (espèce autochtone). La plupart des plantations de pin noir arrivant à maturité sexuelle, cela pourrait conduire à une vitesse d'expansion rapide sur les pelouses situées à proximité, dans un contexte de pâturage extensif