21,961 research outputs found
Clear and Compress: Computing Persistent Homology in Chunks
We present a parallelizable algorithm for computing the persistent homology
of a filtered chain complex. Our approach differs from the commonly used
reduction algorithm by first computing persistence pairs within local chunks,
then simplifying the unpaired columns, and finally applying standard reduction
on the simplified matrix. The approach generalizes a technique by G\"unther et
al., which uses discrete Morse Theory to compute persistence; we derive the
same worst-case complexity bound in a more general context. The algorithm
employs several practical optimization techniques which are of independent
interest. Our sequential implementation of the algorithm is competitive with
state-of-the-art methods, and we improve the performance through parallelized
computation.Comment: This result was presented at TopoInVis 2013
(http://www.sci.utah.edu/topoinvis13.html
Size-dependent bandgap and particle size distribution of colloidal semiconductor nanocrystals
A new analytical expression for the size-dependent bandgap of colloidal
semiconductor nanocrystals is proposed within the framework of the finite-depth
square-well effective mass approximation in order to provide a quantitative
description of the quantum confinement effect. This allows one to convert
optical spectroscopic data (photoluminescence spectrum and absorbance edge)
into accurate estimates for the particle size distributions of colloidal
systems even if the traditional effective mass model is expected to fail, which
occurs typically for very small particles belonging to the so-called strong
confinement limit. By applying the reported theoretical methodologies to CdTe
nanocrystals synthesized through wet chemical routes, size distributions are
inferred and compared directly to those obtained from atomic force microscopy
and transmission electron microscopy. This analysis can be used as a
complementary tool for the characterization of nanocrystal samples of many
other systems such as the II-VI and III-V semiconductor materials.Comment: 9 pages, 5 figure
Temperature dependence of antiferromagnetic susceptibility in ferritin
We show that antiferromagnetic susceptibility in ferritin increases with
temperature between 4.2 K and 180 K (i. e. below the N\'{e}el temperature) when
taken as the derivative of the magnetization at high fields (
Oe). This behavior contrasts with the decrease in temperature previously found,
where the susceptibility was determined at lower fields ( Oe). At
high fields (up to Oe) the temperature dependence of the
antiferromagnetic susceptibility in ferritin nanoparticles approaches the
normal behavior of bulk antiferromagnets and nanoparticles considering
superantiferromagnetism, this latter leading to a better agreement at high
field and low temperature. The contrast with the previous results is due to the
insufficient field range used ( Oe), not enough to saturate the
ferritin uncompensated moment.Comment: 7 pages, 7 figures, accepted in Phys. Rev.
Effective Monopoles within Thick Branes
The monopole mass is revealed to be considerably modified in the thick
braneworld paradigm, and depends on the position of the monopole in the brane
as well. Accordingly, the monopole radius continuously increases, leading to an
unacceptable setting that can be circumvented when the brane thickness has an
upper limit. Despite such peculiar behavior, the quantum corrections accrued --
involving the classical monopole solution -- are shown to be still under
control. We analyze the monopole's peculiarities also taking into account the
localization of the gauge fields. Furthermore, some additional analysis in the
thick braneworld context and the similar behavior evinced by the topological
string are investigated.Comment: 7 pages, 1 figur
Produção de alecrim de tabuleiro utilizando diferentes doses de adubação orgânica em condição de estresse hÃdrico.
Suplemento. Edição dos Anais do 52 Congresso Brasileiro de Olericultura, Salvador, jul. 2012
Shifted loops and coercivity from field imprinted high energy barriers in ferritin and ferrihydrite nanoparticles
We show that the coercive field in ferritin and ferrihydrite depends on the
maximum magnetic field in a hysteresis loop and that coercivity and loop shifts
depend both on the maximum and cooling fields. In the case of ferritin we show
that the time dependence of the magnetization also depends on the maximum and
previous cooling fields. This behavior is associated to changes in the
intra-particle energy barriers imprinted by these fields. Accordingly, the
dependence of the coercive and loop shift fields with the maximum field in
ferritin and ferrihydrite can be described within the frame of a
uniform-rotation model considering a dependence of the energy barrier with the
maximum and the cooling fields.Comment: 8 pages, 5 figures. Accepted for publication in Phys. Rev. B. Final
version with improved writing and figure
Otimização da concentração de misturas de herbicidas considerando a resistência de plantas daninhas.
I CMAC Sudeste
- …