2,799 research outputs found
Directional Variations of the Non-Gaussianity Parameter f_NL
We investigate local variations of the primordial non-Gaussianity parameter
f_NL in the WMAP data, looking for possible influence of foreground
contamination in the full-sky estimate of f_NL. We first improve the needlet
bispectrum estimate in (Rudjord et al. 2009) on the full-sky to f_NL= 73 +/- 31
using the KQ75 mask on the co-added V+W channel. We find no particular values
of f_NL estimates close to the galactic plane and conclude that foregrounds are
unlikely to affect the estimate of f_NL in the V and W bands even for the
smaller KQ85 mask. In the Q band however, we find unexpectedly high values of
f_NL in local estimates close to the galactic mask, as well as significant
discrepancies between Q band estimates and V/W band estimates. We therefore
conclude that the Q band is too contaminated to be used for non-Gaussianity
studies even with the larger KQ75 mask. We further noted that the local f_NL
estimates on the V+W channel are positive on all equatorial bands from the
north to the south pole. The probability for this to happen in a universe with
f_NL = 0 is less than one percent.Comment: 6 pages, 2 figures, included section on non-Gaussian maps, references
adde
Temperature and Polarization CMB Maps from Primordial non-Gaussianities of the Local Type
The forthcoming Planck experiment will provide high sensitivity polarization
measurements that will allow us to further tighten the f_NL bounds from the
temperature data. Monte Carlo simulations of non-Gaussian CMB maps have been
used as a fundamental tool to characterize non-Gaussian signatures in the data,
as they allow us to calibrate any statistical estimators and understand the
effect of systematics, foregrounds and other contaminants. We describe an
algorithm to generate high-angular resolution simulations of non-Gaussian CMB
maps in temperature and polarization. We consider non-Gaussianities of the
local type, for which the level of non-Gaussianity is defined by the
dimensionless parameter, f_NL. We then apply the temperature and polarization
fast cubic statistics recently developed by Yadav et al. to a set of
non-Gaussian temperature and polarization simulations. We compare our results
to theoretical expectations based on a Fisher matrix analysis, test the
unbiasedness of the estimator, and study the dependence of the error bars on
f_NL. All our results are in very good agreement with theoretical predictions,
thus confirming the reliability of both the simulation algorithm and the fast
cubic temperature and polarization estimator.Comment: 14 pages, 9 figures, revised version accepted by PRD, minor changes
and acknowledgements adde
Assessing the Effectiveness of a Learning Community Course Design to Improve the Math Performance of First-Year Students
National attention is focused on the persistent high failure rates for students enrolled in math courses, and the search for strategies to change these outcomes is on. This study used a mixed-method research design to assess the effectiveness of a learning community course designed to improve the math performance levels of first-year students. Results suggested that investing resources into learning community programs that help students meet collegiate-level math course demands helps promote academic success in math courses and eases students’ college transitions. Participants in the math learning communities reported significantly higher rates of using academic supports, engaging in campus activities, and understanding general education learning outcomes compared to a quasi-control group of students enrolled in the same math courses. Math learning community participants enrolled in introductory algebra courses had higher levels of math performance compared to nonparticipants
Single photon thermal ionization of C60
We report on experiments which show that C60 can ionize in an indirect, quasi-thermal boiloff process
after absorption of a single photon. The process involves a large number of incoherently excited valence
electrons and yields electron spectra with a Boltzmann distribution with temperatures exceeding 10^4 K.
It is expected to be present for other molecules and clusters with a comparatively large number of valence
electrons. The astrophysical consequences are briefly discussed
Lattice Boltzmann Method for mixtures at variable Schmidt number
When simulating multicomponent mixtures via the Lattice Boltzmann Method, it
is desirable to control the mutual diffusivity between species while
maintaining the viscosity of the solution fixed. This goal is herein achieved
by a modification of the multicomponent Bhatnagar-Gross-Krook (BGK) evolution
equations by introducing two different timescales for mass and momentum
diffusion. Diffusivity is thus controlled by an effective drag force acting
between species. Numerical simulations confirm the accuracy of the method for
neutral binary and charged ternary mixtures in bulk conditions. The simulation
of a charged mixture in a charged slit channel show that the conductivity and
electro-osmotic mobility exhibit a departure from the Helmholtz-Smoluchowski
prediction at high diffusivity.Comment: 18 pages, 6 figure
Projeto de trabalho e ensino de ciências: uma relação entre conhecimentos e situações cotidianas
Dissertação (mestrado) - Universidade Federal de Santa Catarina. Programa de Pós-Graduação em Educação Científica e TecnológicaNa atualidade há uma grande confusão quando se discute sobre as variadas metodologias baseadas no desenvolvimento de projetos no ambiente escolar. Simultaneamente há a proposição dos órgãos governamentais para que se aplique um ensino baseado em projetos e que se desenvolva habilidades no ensino de ciências. Neste contexto, nos questionamos até que ponto os estudantes conseguem aproximar o conhecimento cotidiano do conhecimento científico através dos Projetos de Trabalho. Assim, objetivamos verificar se os Projetos de Trabalho oferecem meios para que estudantes da 8ª série do Ensino Fundamental consigam desenvolver as habilidades propostas pela teoria dos Projetos de Trabalho e o conhecimento científico escolar. Também buscamos verificar se os Projetos de Trabalho oferecem meios para que estudantes da 8ª série do Ensino Fundamental consigam aplicar os conhecimentos e habilidades apreendidos na disciplina de ciências em outras situações do seu cotidiano. Para tanto, elaboramos e desenvolvemos uma seqüência didática baseada na metodologia de Projetos de Trabalho, por meio da qual buscamos identificar o desenvolvimento de alguns conhecimentos científicos escolares e de algumas habilidades e a possível transferência destes para outras situações do cotidiano dos alunos. Como resultado, apontamos que a metodologia baseada nos Projetos de Trabalho proporciona o desenvolvimento da compreensão de que a ciência ajuda a interpretar o mundo que nos cerca, mas principalmente podemos inferir sobre o desenvolvimento de algumas habilidades tais como: argumentar, relacionar, identificar, decidir e apresentar
Simulating Hard Rigid Bodies
Several physical systems in condensed matter have been modeled approximating
their constituent particles as hard objects. The hard spheres model has been
indeed one of the cornerstones of the computational and theoretical description
in condensed matter. The next level of description is to consider particles as
rigid objects of generic shape, which would enrich the possible phenomenology
enormously. This kind of modeling will prove to be interesting in all those
situations in which steric effects play a relevant role. These include biology,
soft matter, granular materials and molecular systems. With a view to
developing a general recipe for event-driven Molecular Dynamics simulations of
hard rigid bodies, two algorithms for calculating the distance between two
convex hard rigid bodies and the contact time of two colliding hard rigid
bodies solving a non-linear set of equations will be described. Building on
these two methods, an event-driven molecular dynamics algorithm for simulating
systems of convex hard rigid bodies will be developed and illustrated in
details. In order to optimize the collision detection between very elongated
hard rigid bodies, a novel nearest-neighbor list method based on an oriented
bounding box will be introduced and fully explained. Efficiency and performance
of the new algorithm proposed will be extensively tested for uniaxial hard
ellipsoids and superquadrics. Finally applications in various scientific fields
will be reported and discussed.Comment: 36 pages, 17 figure
Large-area inventory of species composition using airborne laser scanning and hyperspectral data
5openInternationalInternational coauthor/editorTree species composition is an essential attribute in stand-level forest management inventories and remotely sensed data might be useful for its estimation. Previous studies on this topic have had several operational drawbacks, e.g., performance studied at a small scale and at a single tree-level with large fieldwork costs. The current study presents the results from a large-area inventory providing species composition following an operational area-based approach. The study utilizes a combination of airborne laser scanning and hyperspectral data and 97 field sample plots of 250 m2 collected over 350 km2 of productive forest in Norway. The results show that, with the availability of hyperspectral data, species-specific volume proportions can be provided in operational forest management inventories with acceptable results in 90% of the cases at the plot level. Dominant species were classified with an overall accuracy of 91% and a kappa-value of 0.73. Species-specific volumes were estimated with relative root mean square differences of 34%, 87%, and 102% for Norway spruce (Picea abies (L.) Karst.), Scots pine (Pinus sylvestris L.), and deciduous species, respectively. A novel tree-based approach for selecting pixels improved the results compared to a traditional approach based on the normalized difference vegetation index.openØrka, Hans Ole; Hansen, Endre Hofstad; Dalponte, Michele; Gobakken, Terje; Næsset, ErikØrka, H.O.; Hansen, E.H.; Dalponte, M.; Gobakken, T.; Næsset, E
- …