121,425 research outputs found
A test of arm-induced star formation in spiral galaxies from near-IR and H imaging
We have imaged a sample of 20 spiral galaxies in H and in the
near-infrared K band (2.2 um), in order to determine the location and strength
of star formation in these objects with respect to perturbations in the old
stellar population. We have found that star formation rates are significantly
enhanced in the vicinity of K band arms. We have also found that this
enhancement in star formation rate in arm regions correlates well with a
quantity that measures the relative strengths of shocks in arms. Assuming that
the K band light is dominated by emission from the old stellar population, this
shows that density waves trigger star formation in the vicinity of spiral arms.Comment: 6 pages, 1 figure, accpeted for publication in MNRA
Sublattice asymmetry of impurity doping in graphene: A review
In this review we highlight recent theoretical and experimental work on
sublattice asymmetric doping of impurities in graphene, with a focus on
substitutional Nitrogen dopants. It is well known that one current limitation
of graphene in regards to its use in electronics is that in its ordinary state
it exhibits no band gap. By doping one of its two sublattices preferentially it
is possible to not only open such a gap, which can furthermore be tuned through
control of the dopant concentration, but in theory produce quasi-ballistic
transport of electrons in the undoped sublattice, both important qualities for
any graphene device to be used competetively in future technology. We outline
current experimental techniques for synthesis of such graphene monolayers and
detail theoretical efforts to explain the mechanisms responsible for the
effect, before suggesting future research directions in this nascent field.Comment: 20 pages, 4 figures. Accepted for publication in Beilstein Journal of
Nanotechnolog
Vector unparticle contributions to lepton g-2
The generic unparticle propagator may be modified in two ways. Breaking the
conformal symmetry effectively adds a mass term to the propagator, while
considering vacuum polarization corrections adds a width-like term. Both of
these modifications result naturally from the coupling of the unparticle to
standard model (SM) fields. We explore how these modifications to the
propagator affect the calculation of the lepton anomalous magnetic moment using
an integral approximation of the propagator that is accurate for
, where is the unparticle dimension. We find that for this
range of and various values of the conformal breaking scale , the
value of calculated when allowing various SM fermions to run in the
unparticle self-energy loops does not significantly deviate from the value of
when the width term is ignored. We also investigate the limits on a
characteristic mass scale for the unparticle sector as a function of and
.Comment: 16 pages, 11 figures, 2 tables. Included neutrinos in loops. Added
reference
ecp: An R Package for Nonparametric Multiple Change Point Analysis of Multivariate Data
There are many different ways in which change point analysis can be
performed, from purely parametric methods to those that are distribution free.
The ecp package is designed to perform multiple change point analysis while
making as few assumptions as possible. While many other change point methods
are applicable only for univariate data, this R package is suitable for both
univariate and multivariate observations. Estimation can be based upon either a
hierarchical divisive or agglomerative algorithm. Divisive estimation
sequentially identifies change points via a bisection algorithm. The
agglomerative algorithm estimates change point locations by determining an
optimal segmentation. Both approaches are able to detect any type of
distributional change within the data. This provides an advantage over many
existing change point algorithms which are only able to detect changes within
the marginal distributions
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Learning In the Visual Arts and the Worldviews of Young Children
This paper reports a research study into the effects of rich,sustained visual arts instruction on 103inner city 9-year-olds in two major US cities. We use the lenses of social learning theory, theories of motivation and self-efficacy, and recentresearch on artistic thinking to investigate the programs' effects on children's self-beliefs and creative thinking. The study enlisted a pre -- post measure,treatment-comparison group design along with structured observations of participant andcomparison group classrooms. The arts students made significant comparative gains on a selfefficacy scale and on an 'originality' subscale of a standard creativity test. These effects are attributed to children's engagement in art and to the social organization of instruction includingreinforcing peer and student -- adult relationships. Relationships between self-efficacy beliefs andtendencies to think originally are explored
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