309 research outputs found
Generating socially appropriate tutorial dialog
Analysis of student-tutor coaching dialogs suggest that good human tutors attend to and attempt to influence the motivational state of learners. Moreover, they are sensitive to the social face of the learner, and seek to mitigate the potential face threat of their comments. This paper describes a dialog generator for pedagogical agents that takes motivation and face threat factors into account. This enables the agent to interact with learners in a socially appropriate fashion, and foster intrinsic motivation on the part of the learner, which in turn may lead to more positive learner affective states
Petrografia e Geoquímica do Complexo Migmatítico de Bemposta (Zona Centro Ibérica, NE de Portugal)
ABSTRACT: The Bemposta Migmatite Complex (CMB) belong to the Central-Iberian Zone, NE Portugal. It is a high-grade metamorphic belt composed by metasediments of Ediacarian-Lower Cambrian age affected by partial melting during the second Variscan deformation event (D2). The anatexis culminated with intrusion of syn-tardi-D2 leucogranite sills in the CMB. Field and petrographic evidence suggest that the anatexis of the metasediments was controlled by muscovite dehydration-melting reactions. On the other hand, the stromatic leucosomes show that they were probably produced at a slightly deeper structural level (through biotite dehydration-melting reactions) and subsequently injected in these lithologies. The geochemical data reveals that leucosomes no longer correspond to the original melt compositions. During melt migration and ascent, they underwent fractional crystallization and accumulation of K-feldspar. Syn-tardi-D2 leucogranites that intrude CMB were most likely produced by higher degrees of partial melting. They have fractionated compositions and variable degrees of contamination with residual accessory mineral phases. Thus, CMB is interpreted as a Migmatite Injection Complex, where anatectic melts produced at slightly deeper levels were accumulated.RESUMO: O Complexo Migmatítico de Bemposta (CMB) situa-se na Zona Centro Ibérica (NE Portugal) correspondendo a um cinturão metamórfico de alto grau, composto por metassedimentos do Ediacariano-Câmbrico Inferior afetados por fusão parcial durante a segunda fase de deformação Varisca (D2). A anatexia destas rochas culminou com a intrusão de leucogranitos sin-tardi-D2 do tipo sill. As evidências de campo em consonância com a petrografia sugerem que a anatexia dos metassedimentos foi controlada pela reação de desidratação da moscovite. Os leucossomas mostram evidências de terem sido produzidos em níveis estruturais inferiores (através da reação da desidratação da biotite) e subsequentemente injetados nestas litologias. Os dados de geoquímica revelam que os leucossomas durante a sua ascensão foram afetados por cristalização fracionada e acumulação de feldspato potássico. Os leucogranitos sin-tardi-D2 que intruem o CMB resultaram de altas taxas de fusão e possuem composições equivalentes a magmas afetados por cristalização fracionada, contaminados por minerais acessórios residuais. Assim, o CMB é interpretado como um Complexo Migmatítico de Injeção, onde os líquidos anatéticos produzidos em profundidade se acumularam.info:eu-repo/semantics/publishedVersio
Multiwavelength Studies of Young OB Associations
We discuss how contemporary multiwavelength observations of young
OB-dominated clusters address long-standing astrophysical questions: Do
clusters form rapidly or slowly with an age spread? When do clusters expand and
disperse to constitute the field star population? Do rich clusters form by
amalgamation of smaller subclusters? What is the pattern and duration of
cluster formation in massive star forming regions (MSFRs)? Past observational
difficulties in obtaining good stellar censuses of MSFRs have been alleviated
in recent studies that combine X-ray and infrared surveys to obtain rich,
though still incomplete, censuses of young stars in MSFRs. We describe here one
of these efforts, the MYStIX project, that produced a catalog of 31,784
probable members of 20 MSFRs. We find that age spread within clusters are real
in the sense that the stars in the core formed after the cluster halo. Cluster
expansion is seen in the ensemble of (sub)clusters, and older dispersing
populations are found across MSFRs. Direct evidence for subcluster merging is
still unconvincing. Long-lived, asynchronous star formation is pervasive across
MSFRs.Comment: 22 pages, 9 figures. To appear in "The Origin of Stellar Clusters",
edited by Steven Stahler, Springer, 2017, in pres
Association Of Bartonella Species With Wild And Synanthropic Rodents In Different Brazilian Biomes
Bartonella spp. comprise an ecologically successful group of microorganisms that infect erythrocytes and have adapted to different hosts, which include a wide range of mammals, besides humans. Rodents are reservoirs of about two-thirds of Bartonella spp. described to date; and some of them have been implicated as causative agents of human diseases. In our study, we performed molecular and phylogenetic analyses of Bartonella spp. infecting wild rodents from five different Brazilian biomes. In order to characterize the genetic diversity of Bartonella spp., we performed a robust analysis based on three target genes, followed by sequencing, Bayesian inference, and maximum likelihood analysis. Bartonella spp. were detected in 25.6% (117/457) of rodent spleen samples analyzed, and this occurrence varied among different biomes. The diversity analysis of gltA sequences showed the presence of 15 different haplotypes. Analysis of the phylogenetic relationship of gltA sequences performed by Bayesian inference and maximum likelihood showed that the Bartonella species detected in rodents from Brazil was closely related to the phylogenetic group A detected in other cricetid rodents from North America, probably constituting only one species. Last, the Bartonella species genogroup identified in the present study formed a monophyletic group that included Bartonella samples from seven different rodent species distributed in three distinct biomes. In conclusion, our study showed that the occurrence of Bartonella bacteria in rodents is much more frequent and widespread than previously recognized. © 2016, American Society for Microbiology. All Rights Reserved.82247154716
Heterotic Compactification, An Algorithmic Approach
We approach string phenomenology from the perspective of computational
algebraic geometry, by providing new and efficient techniques for proving
stability and calculating particle spectra in heterotic compactifications. This
is done in the context of complete intersection Calabi-Yau manifolds in a
single projective space where we classify positive monad bundles. Using a
combination of analytic methods and computer algebra we prove stability for all
such bundles and compute the complete particle spectrum, including gauge
singlets. In particular, we find that the number of anti-generations vanishes
for all our bundles and that the spectrum is manifestly moduli-dependent.Comment: 36 pages, Late
Caracterização da produção agroecológica do sul do Rio Grande do Sul e sua relação com a mecanização agrícola.
A agricultura agroecológica tem-se destacado como uma das alternativas de renda para os pequenos agricultores devido à crescente busca por parte da população por alimentação mais saudável. No Rio Grande do Sul, a Associação Regional de Produtores Agroecológicos da Região Sul (Arpasul), constituída por 48 famílias, é representativa do processo de produção e de comercialização de produtos agroecológicos, servindo como referencial para o presente estudo. O objetivo principal deste trabalho foi o levantamento das necessidades dos produtores agroecológicos
em relação à mecanização agrícola. As informações obtidas foram baseadas no sistema de produção utilizado, sendo caracterizados aspectos referentes à propriedade, às operações agrícolas e às necessidades específicas de máquinas e implementos. Por meio deste estudo, foi evidenciada a carência no atendimento das demandas específicas, na área de máquinas agrícolas para esse segmento, podendo servir como referencial para o desenvolvimento de novas máquinas e/ou aperfeiçoamento das existentes. A semeadora de milho e feijão foi a máquina que a maioria dos agricultores pesquisados indicou como sua maior necessidade
On the role of the magnetic dipolar interaction in cold and ultracold collisions: Numerical and analytical results for NH() + NH()
We present a detailed analysis of the role of the magnetic dipole-dipole
interaction in cold and ultracold collisions. We focus on collisions between
magnetically trapped NH molecules, but the theory is general for any two
paramagnetic species for which the electronic spin and its space-fixed
projection are (approximately) good quantum numbers. It is shown that dipolar
spin relaxation is directly associated with magnetic-dipole induced avoided
crossings that occur between different adiabatic potential curves. For a given
collision energy and magnetic field strength, the cross-section contributions
from different scattering channels depend strongly on whether or not the
corresponding avoided crossings are energetically accessible. We find that the
crossings become lower in energy as the magnetic field decreases, so that
higher partial-wave scattering becomes increasingly important \textit{below} a
certain magnetic field strength. In addition, we derive analytical
cross-section expressions for dipolar spin relaxation based on the Born
approximation and distorted-wave Born approximation. The validity regions of
these analytical expressions are determined by comparison with the NH + NH
cross sections obtained from full coupled-channel calculations. We find that
the Born approximation is accurate over a wide range of energies and field
strengths, but breaks down at high energies and high magnetic fields. The
analytical distorted-wave Born approximation gives more accurate results in the
case of s-wave scattering, but shows some significant discrepancies for the
higher partial-wave channels. We thus conclude that the Born approximation
gives generally more meaningful results than the distorted-wave Born
approximation at the collision energies and fields considered in this work.Comment: Accepted by Eur. Phys. J. D for publication in Special Issue on Cold
Quantum Matter - Achievements and Prospects (2011
Genome-wide association study in an admixed case series reveals IL12A as a new candidate in Behçet Disease
Introduction: The etiology of Behçet's disease (BD) is unknown, but widely considered an excessive T-cell mediated inflammatory response in a genetically susceptible host. Recent genomewide association studies (GWAS) have shown limited number of novel loci-associations. The rarity and unequal distribution of the disease prevalence amongst different ethnic backgrounds have hampered the use of GWAS in cohorts of mixed ethnicity and sufficient sample size. However, novel statistical approaches have now enabled GWAS in admixed cohorts. Methods: We ran a GWAS on 336 BD cases and 5,843 controls. The cases consisted of Western Europeans, Middle Eastern and Turkish individuals. Participants from the Generation R study, a multiethnic birth cohort in Rotterdam, The Netherlands were used as controls. All samples were genotyped and data was combined. Linear regression models were corrected for population stratification using Genomic Principal Components and Linear Mixed Modelling. Meta-analysis was performed on selected results previously published. Results: We identified SNPs associated at genome-wide significant level mapping to the 6p21.33 (HLA) region. In addition to this known signal two potential novel associations on chromosomes 6 and 18 were identified, yet with low minor allele frequencies. Extended metaanalysis reveal a GWS association with the IL12A variant rs17810546 on chromosome 3. Discussion: We demonstrate that new statistical techniques enable GWAS analyses in a limited sized cohort of mixed ethnicity. After implementation, we confirmed the central role of the HLA region in the disease and identified new regions of interest. Moreover, we validated the association of a variant in the IL2A gene by meta-analysis with previous work. These findings enhance our
Interstellar MHD Turbulence and Star Formation
This chapter reviews the nature of turbulence in the Galactic interstellar
medium (ISM) and its connections to the star formation (SF) process. The ISM is
turbulent, magnetized, self-gravitating, and is subject to heating and cooling
processes that control its thermodynamic behavior. The turbulence in the warm
and hot ionized components of the ISM appears to be trans- or subsonic, and
thus to behave nearly incompressibly. However, the neutral warm and cold
components are highly compressible, as a consequence of both thermal
instability in the atomic gas and of moderately-to-strongly supersonic motions
in the roughly isothermal cold atomic and molecular components. Within this
context, we discuss: i) the production and statistical distribution of
turbulent density fluctuations in both isothermal and polytropic media; ii) the
nature of the clumps produced by thermal instability, noting that, contrary to
classical ideas, they in general accrete mass from their environment; iii) the
density-magnetic field correlation (or lack thereof) in turbulent density
fluctuations, as a consequence of the superposition of the different wave modes
in the turbulent flow; iv) the evolution of the mass-to-magnetic flux ratio
(MFR) in density fluctuations as they are built up by dynamic compressions; v)
the formation of cold, dense clouds aided by thermal instability; vi) the
expectation that star-forming molecular clouds are likely to be undergoing
global gravitational contraction, rather than being near equilibrium, and vii)
the regulation of the star formation rate (SFR) in such gravitationally
contracting clouds by stellar feedback which, rather than keeping the clouds
from collapsing, evaporates and diperses them while they collapse.Comment: 43 pages. Invited chapter for the book "Magnetic Fields in Diffuse
Media", edited by Elisabete de Gouveia dal Pino and Alex Lazarian. Revised as
per referee's recommendation
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