3,929 research outputs found
Pseudo-rotations of the open annulus
In this paper, we study pseudo-rotations of the open annulus, \emph{i.e.}
conservative homeomorphisms of the open annulus whose rotation set is reduced
to a single irrational number (the angle of the pseudo-rotation). We prove in
particular that, for every pseudo-rotation of angle , the rigid
rotation of angle is in the closure of the conjugacy class of . We
also prove that pseudo-rotations are not persistent in topology for any
.Comment: 25 page
Lack of increased availability of root-derived C may explain the low N2O emission from low N-urine patches
Urine deposition on grassland causes significant N2O losses, which in some cases may result from increased denitrification stimulated by labile compounds released from scorched plant roots. Two 12-day experiments were conducted in 13C-labelled grassland monoliths to investigate the link between N2O production and carbon mineralization following application of low rates of urine-N. Measurements of N2O and CO2 emissions from the monoliths as well as ÎŽ13C signal of evolved CO2 were done on day -4, -1, 0, 1, 2, 4, 5, 6 and 7 after application of urine corresponding to 3.1 and 5.5 g N m-2 in the first and second experiment, respectively. The ÎŽ13C signal was also determined for soil organic matter, dissolved organic C and CO2 evolved by microbial respiration. In addition, denitrifying enzyme activity (DEA) and nitrifying enzyme activity (NEA) were measured on day -1, 2 and 7 after the first urine application event. Urine did not affect DEA, whereas NEA was enhanced 2 days after urine application. In the first experiment, urine had no significant effect on the N2O flux, which was generally low (-8 to 14 ÎŒg N2O-N m-2 h-1). After the second application event, the N2O emission increased significantly to 87 ÎŒg N2O-N m-2 h-1 and the N2O emission factor for the added urine-N was 0.18 %. However, the associated 13C signal of soil respiration was unaffected by urine. Consequently, the increased N2O emission from the simulated low N-urine patches was not caused by enhanced denitrification stimulated by labile compounds released from scorched plant roots
Some fossil ginkgophytes and a possible vojnovskyalean element from the Glossopteris flora of Vereeniging, Transvaal
Main articleA short historical review is given of previously described sites where plant fossils
occur in Lower Karroo beds at Vereeniging in the Southern Transvaal. Reference is made to the importance of these sites because of the outstanding discoveries made here in the past. Some new material from the same sites is described and several unusual elements in the Glossopteris flora of Vereeniging are recorded for the first time.
Leaves of a plant not previously recorded from Gondwanaland are provisionally
described under the term cf. Nephropsis on account of a strong resemblance to leaves of
the Russian Permian genus Nephropsis Zalessky.
The remaining specimens in the assemblage are tentatively placed in the genera
Ginkgoites Seward and Psygmophyllum Schimper respectively. Owing to the paucity of
material, type numbers are assigned in certain cases, instead of specific names. Specific
identification is attempted, however, in the case of four of the specimens, which are
provisionally assigned to Psygmophyllum kidstoni Seward.Non
On some "northern" elements in the Lower Gondwana flora of Vereeniging, Transvaal
Main articleA small assemblage of plant elements from the Lower Permian of Vereeniging, in the southern Transvaal, is described here. The assemblage is constituted of form-genera normally only found in the palaeo floristic regions of the northern hemisphere. The genera concerned are: Pecopteris (Asterotheca), Cladophlebis, Sphenophyllum and Psygmophyllum. The intermingling of these "Northern" elements with
the Glossopteris flora of Vereeniging serves to illustrate the mixed nature of this flora. Reference is made to similar mixed Gondwana floras elsewhere in Africa and also in South America.Non
Connected Choice and the Brouwer Fixed Point Theorem
We study the computational content of the Brouwer Fixed Point Theorem in the
Weihrauch lattice. Connected choice is the operation that finds a point in a
non-empty connected closed set given by negative information. One of our main
results is that for any fixed dimension the Brouwer Fixed Point Theorem of that
dimension is computably equivalent to connected choice of the Euclidean unit
cube of the same dimension. Another main result is that connected choice is
complete for dimension greater than or equal to two in the sense that it is
computably equivalent to Weak K\H{o}nig's Lemma. While we can present two
independent proofs for dimension three and upwards that are either based on a
simple geometric construction or a combinatorial argument, the proof for
dimension two is based on a more involved inverse limit construction. The
connected choice operation in dimension one is known to be equivalent to the
Intermediate Value Theorem; we prove that this problem is not idempotent in
contrast to the case of dimension two and upwards. We also prove that Lipschitz
continuity with Lipschitz constants strictly larger than one does not simplify
finding fixed points. Finally, we prove that finding a connectedness component
of a closed subset of the Euclidean unit cube of any dimension greater or equal
to one is equivalent to Weak K\H{o}nig's Lemma. In order to describe these
results, we introduce a representation of closed subsets of the unit cube by
trees of rational complexes.Comment: 36 page
Investigating an Ethical Approach to Genetically Modified Crops in Environmental Educational Processes
Genetically modified (GM) crops gained attention in southern Africa in the context of broader debates about the struggle for food security and poverty alleviation to achieve sustainable development. The prospects of GM crops as a technological innovation have provoked numerous debates and environmental concern groups have challenged their use. Environmental educatorsâ concern for greater ethical practices regarding environmental issues can be applied to the subject of GM crops. This article focuses on the perceptions of environmental educators regarding the use of GM crops towards sustainable development. Interviews were conducted with a small group of environmental educators to gain some insight into their perceptions. The interviews reflected some contextual relevance of GM crops, understanding of the concepts âGM cropsâ and âsustainable developmentâ as well as four unique themes. These emphasise the plurality of the GM crops issue and the importance thereof in working towards an ethical approach in environmental educational processes
Wave identification and separation on seismic data
In order to study the influence of the sea-floor on the oceanic acoustic wave
propagation, we try to qualify the energetic contributions of the waves which
propagate in the subsurface compared to the water propagating modes . The treated
shallow water data have been recorded in the Beaulieu Bay (Mediterranean Sea) .
A realistic propagation model is obtained by successive comparisons between field
and simulated data. Most of the time delays and amplitudes of the dominant waves
can be explained if some velocity gradients are included in the sediments layers
models. The presented method consists to define the separation parameters from
the propagation model to extract the dominant waves from the field data .Afin d'Ă©tudier l'influence du fond marin sur la propagation acoustique ocĂ©anique ultra basse frĂ©quence UBF (< 100 Hz), on cherche Ă Ă©valuer les contributions Ă©nergĂ©tiques des ondes se propageant dans le sous-sol par rapport aux modes de propagation dans l'eau Ă partir de donnĂ©es sismiques obtenues en eaux peu profondes dans la baie de Beaulieu (mer MĂ©diterranĂ©e). Les comparaisons successives entre la section sismique expĂ©rimentale et une simulation de la section conduisent Ă l'Ă©laboration d'un modĂšle de propagation rĂ©aliste du site oĂč les temps d'arrivĂ©es et les amplitudes des diffĂ©rentes ondes s'expliquent Ă condition d'introduire un gradient de vitesse dans la couche de sĂ©diments. La mĂ©thode dĂ©veloppĂ©e consiste Ă sĂ©parer les ondes dominantes de la section expĂ©rimentale Ă partir du modĂšle de propagatio
Enhancing ICT for Inclusive Human Development in Sub-Saharan Africa
âThis study assesses if increasing information and communication technology (ICT) enhances inclusive human development in a sample of 49 countries in Sub-Saharan Africa for the period 2000-2012. The empirical evidence present in this study, is based on instrumental variable Tobit regressions, in order to account for simultaneity and the limited range in the dependent variable. In the interest of increasing room for policy implications and controlling for the unobserved heterogeneity, the analysis is decomposed into the fundamental characteristics that human development based on: income levels, legal origins, religious dominations, political stability, landlockedness and resource-wealth. Our findings show that policies designed to boost ICT (mobile phone, internet, telephone) penetration will increase inclusive development in the post-2015 sustainable development agenda. The degree of positive responsiveness of inclusive development to ICT varies across fundamental characteristics of human development and ICT dynamics. The study has substantial policy relevance because the adoption and/or penetration rate of ICT can be influenced by policy to achieve inclusive development outcomes. Further policy implications are also discussed
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