2,441 research outputs found
Three-dimensional, lifting wings of minimum drag in hypersonic flow
Three-dimensional lifting wings of minimum drag in hypersonic flo
Three-dimensional Wings of Maximum Lift-to- Drag Ratio in Hypersonic Flow
Optimizing lift-to-drag ratio of slender, flat-top wing of given planform in hypersonic flow by using variational calculus method
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Enactivism and ethnomethodological conversation analysis as tools for expanding Universal Design for Learning: the case of visually impaired mathematics students
Blind and visually impaired mathematics students must rely on accessible materials such as tactile diagrams to learn mathematics. However, these compensatory materials are frequently found to offer students inferior opportunities for engaging in mathematical practice and do not allow sensorily heterogenous students to collaborate. Such prevailing problems of access and interaction are central concerns of Universal Design for Learning (UDL), an engineering paradigm for inclusive participation in cultural praxis like mathematics. Rather than directly adapt existing artifacts for broader usage, UDL process begins by interrogating the praxis these artifacts serve and then radically re-imagining tools and ecologies to optimize usability for all learners. We argue for the utility of two additional frameworks to enhance UDL efforts: (a) enactivism, a cognitive-sciences view of learning, knowing, and reasoning as modal activity; and (b) ethnomethodological conversation analysis (EMCA), which investigates participantsâ multimodal methods for coordinating action and meaning. Combined, these approaches help frame the design and evaluation of opportunities for heterogeneous students to learn mathematics collaboratively in inclusive classrooms by coordinating perceptuo-motor solutions to joint manipulation problems. We contextualize the thesis with a proposal for a pluralist design for proportions, in which a pair of students jointly operate an interactive technological device
The footprint of large scale cosmic structure on the ultra-high energy cosmic ray distribution
Current experiments collecting high statistics in ultra-high energy cosmic
rays (UHECRs) are opening a new window on the universe. In this work we discuss
a large scale structure model for the UHECR origin which evaluates the expected
anisotropy in the UHECR arrival distribution starting from a given astronomical
catalogue of the local universe. The model takes into account the main
selection effects in the catalogue and the UHECR propagation effects. By
applying this method to the IRAS PSCz catalogue, we derive the minimum
statistics needed to significatively reject the hypothesis that UHECRs trace
the baryonic distribution in the universe, in particular providing a forecast
for the Auger experiment.Comment: 21 pages, 14 figures. Reference added, minor changes, matches
published versio
Maximum Lift-to-drag Ratio of a Slender, Flat-top, Hypersonic Body
Maximum lift-drag ratio of slender, flat top, hypersonic body assuming modified Newtonian pressure distribution and constant surface averaged skin friction coefficien
Primordial Nucleosynthesis: from precision cosmology to fundamental physics
We present an up-to-date review of Big Bang Nucleosynthesis (BBN). We discuss
the main improvements which have been achieved in the past two decades on the
overall theoretical framework, summarize the impact of new experimental results
on nuclear reaction rates, and critically re-examine the astrophysical
determinations of light nuclei abundances. We report then on how BBN can be
used as a powerful test of new physics, constraining a wide range of ideas and
theoretical models of fundamental interactions beyond the standard model of
strong and electroweak forces and Einstein's general relativity.Comment: 148 pages, 66 figures, revised version accepted by Physics Report
Pichia pastoris Fep1 is a [2Fe-2S] protein with a Zn finger that displays an unusual oxygen-dependent role in cluster binding
Fep1, the iron-responsive GATA factor from the methylotrophic yeast Pichia pastoris, has been characterised both in vivo and in vitro. This protein has two Cys(2)-Cys(2) type zinc fingers and a set of four conserved cysteines arranged in a Cys-X-5-Cys-X-8-Cys-X-2-Cys motif located between the two zinc fingers. Electronic absorption and resonance Raman spectroscopic analyses in anaerobic and aerobic conditions indicate that Fep1 binds iron in the form of a [2Fe-2S] cluster. Site-directed mutagenesis shows that replacement of the four cysteines with serine inactivates this transcriptional repressor. Unexpectedly, the inactive mutant is still able to bind a [2Fe-2S] cluster, employing two cysteine residues belonging to the first zinc finger. These two cysteine residues can act as alternative cluster ligands selectively in aerobically purified Fep1 wild type, suggesting that oxygen could play a role in Fep1 function by causing differential localization of the [Fe-S] cluster
Dosage compensation in birds
AbstractThe Z and W sex chromosomes of birds have evolved independently from the mammalian X and Y chromosomes [1]. Unlike mammals, female birds are heterogametic (ZW), while males are homogametic (ZZ). Therefore male birds, like female mammals, carry a double dose of sex-linked genes relative to the other sex. Other animals with nonhomologous sex chromosomes possess âdosage compensationâ systems to equalize the expression of sex-linked genes. Dosage compensation occurs in animals as diverse as mammals, insects, and nematodes, although the mechanisms involved differ profoundly [2]. In birds, however, it is widely accepted that dosage compensation does not occur [3â5], and the differential expression of Z-linked genes has been suggested to underlie the avian sex-determination mechanism [6]. Here we show equivalent expression of at least six of nine Z chromosome genes in male and female chick embryos by using real-time quantitative PCR [7]. Only the Z-linked ScII gene, whose ortholog in Caenorhabditis elegans plays a crucial role in dosage compensation [8], escapes compensation by this assay. Our results imply that the majority of Z-linked genes in the chicken are dosage compensated
Effects of non-standard neutrino-electron interactions on relic neutrino decoupling
We consider the decoupling of neutrinos in the early Universe in presence of
non-standard neutral current neutrino-electron interactions (NSI). We first
discuss a semi-analytical approach to solve the relevant kinetic equations and
then present the results of fully numerical and momentum-dependent
calculations, including flavor neutrino oscillations. We present our results in
terms of both the effective number of neutrino species (N_eff) and the impact
on the abundance of He-4 produced during Big Bang Nucleosynthesis. We find
that, for NSI parameters within the ranges allowed by present laboratory data,
non-standard neutrino-electron interactions do not essentially modify the
density of relic neutrinos nor the bounds on neutrino properties from
cosmological observables, such as their mass. Nonetheless, the presence of
neutrino-electron NSI may enhance the entropy transfer from electron-positron
pairs into neutrinos instead of photons, up to a value of N_eff=3.12. This is
almost three times the correction to N_eff=3 that appears for standard weak
interactions.Comment: 23 pages, 5 figures. To be published in NP
Estrutura dos contratos de integração na suinocultura de Santa Catarina.
bitstream/CNPSA/15857/1/publicacao_o333i3k.pdfPublicado também no site Engormix, 21 fev. 2011
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