1,551 research outputs found
A simple algorithm for optimization and model fitting: AGA (asexual genetic algorithm)
Context. Mathematical optimization can be used as a computational tool to
obtain the optimal solution to a given problem in a systematic and efficient
way. For example, in twice-differentiable functions and problems with no
constraints, the optimization consists of finding the points where the gradient
of the objective function is zero and using the Hessian matrix to classify the
type of each point. Sometimes, however it is impossible to compute these
derivatives and other type of techniques must be employed such as the steepest
descent/ascent method and more sophisticated methods such as those based on the
evolutionary algorithms. Aims. We present a simple algorithm based on the idea
of genetic algorithms (GA) for optimization. We refer to this algorithm as AGA
(Asexual Genetic Algorithm) and apply it to two kinds of problems: the
maximization of a function where classical methods fail and model fitting in
astronomy. For the latter case, we minimize the chi-square function to estimate
the parameters in two examples: the orbits of exoplanets by taking a set of
radial velocity data, and the spectral energy distribution (SED) observed
towards a YSO (Young Stellar Object). Methods. The algorithm AGA may also be
called genetic, although it differs from standard genetic algorithms in two
main aspects: a) the initial population is not encoded, and b) the new
generations are constructed by asexual reproduction. Results. Applying our
algorithm in optimizing some complicated functions, we find the global maxima
within a few iterations. For model fitting to the orbits of exoplanets and the
SED of a YSO, we estimate the parameters and their associated errors.Comment: 10 pages, 8 figures, Astronomy and Astrophysics (in press
Gender of authors in the Mexican Journal of Behavior Analysis: changes over time [GÉNERO DE LOS AUTORES DE LA REVISTA MEXICANA DE ANÁLISIS DE LA CONDUCTA: CAMBIOS A TRAVÉS DEL TIEMPO]
The Mexican Journal of Behavior Analysis was examined from 1975 to 2018 to determine the proportion of authorship by women and men. Data were compiled and assessed for the percentage of authorship, percentage of first-authored publications, percentage of publications with at least one woman, and percentage of publications with at least one man. From the journal’s inception to 2018, women and men accounted for 33% and 67% of authorship, respectively. The data suggest that women’s participation, based on percentages of total authorship, has increased across time.
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Con el propósito de determinar la proporción de autores mujeres y hombres, se analizaron los artículos publicados en la Revista Mexicana de Análisis de la Conducta de 1975 a 2018. Con base en los datos recopilados, se evaluó el porcentaje de artículos publicados, el porcentaje de artículos publicados como primer autor, el porcentaje de publicaciones con al menos una mujer como autora y el porcentaje de publicaciones con al menos un hombre como autor. Desde la creación de la revista hasta 2018, las mujeres y los hombres conformaron el 33% y el 67% de los autores, respectivamente. Con base en los porcentajes del total de publicaciones, los datos sugieren que la participación de las mujeres de hecho ha aumentado a través del tiempo
Gender of Authors in the Brazilian Journal of Behavior Analysis [Gênero dos autores na Revista Brasileira de Análise do Comportamento]
We examined publication records in the Brazilian Journal of Behavior Analysis from 2005 through 2020 to determine the participation of women and men as contributing authors. We assessed the following variables: authorship (in general), first authors, articles with at least one woman, articles with at least one man, articles with both men and women, single-author articles, and authors with more than 10 publications. We identified 281 articles, with a total of 732 listed authors. Women and men were listed as authors 361 (49%) and 368 (50%) times, respectively. Women accounted for 43% of articles as first authors, and 69% of articles listed at least one woman as an author. These data are discussed and compared to data from other behavior-analytic journals.
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Examinamos o registro de publicação, de 2005 a 2020, do Revista Brasileira de Análise do Comportamento para determinar a participação de mulheres e homens como autores colaboradores. Foram avaliadas as seguintes variáveis: autoria (em geral), primeiros autores, artigos com pelo menos uma mulher, artigos com pelo menos um homem, artigos de ambos os sexos, artigos de autoria única e autores com mais de 10 publicações. Identificamos 281 artigos, com um total de 732 autores listados. Mulheres e homens foram listados como autores 361 (49%) e 368 (50%) vezes, respectivamente. As mulheres representaram 43% dos artigos como primeiros autores e 69% dos artigos listaram pelo menos uma mulher como autora. Esses dados são discutidos e comparados com dados de outros periódicos analíticos comportamentais
Modelling the fear of crime
How secure people feel in a particular region is
obviously linked to the actual crime suffered in that
region but the exact relationship between crime and
its fear is quite subtle. Two regions may have the
same crime rate but their local perception of security
may differ. Equally, two places may have the same
perception of security even though one may have a
significantly lower crime rate. Furthermore, a negative
perception might persist for many years, even when
crime rates drop. Here, we develop a model for the
dynamics of the perception of security of a region
based on the distribution of crime suffered by the
population using concepts similar to those used for
opinion dynamics. Simulations under a variety of
conditions illustrate different scenarios and help us
determine the impact of suffering more, or less,
crime. The inhomogeneous concentration of crime
together with a memory loss process is incorporated
into the model for the perception of security, and
results explain why people are often more fearful than
actually victimized; why a region is perceived as being
insecure despite a low crime rate; and why a decrease
in the crime rate might not significantly improve the
perception of security
Binding-incompetent adenovirus facilitates molecular conjugate-mediated gene transfer by the receptor-mediated endocytosis pathway
Molecular conjugate vectors may be constructed that accomplish high efficiency gene transfer by the receptor-mediated endocytosis pathway. In order to mediate escape from lysosomal degradation, we have incorporated adenoviruses into the functional design of the conjugate. In doing so, however, we have introduced an additional ligand, which can bind to receptors on the cell surface, undermining the potential for cell specific targeting. To overcome this, we have treated the adenovirus with a monoclonal anti-fiber antibody, which renders the virus incapable of binding to its receptor. The result is a multi-functional molecular conjugate vector, which has preserved its binding specificity while at the same time being capable of preventing lysosomal degradation of endosome-internalized conjugate-DNA complexes. This finding indicates that adenoviral binding is not a prerequisite for adenoviral-mediated endosome disruption
The Circumstellar Structure and Excitation Effects around the Massive Protostar Cepheus A HW 2
We report SMA 335 GHz continuum observations with angular resolution of
~0.''3, together with VLA ammonia observations with ~1'' resolution toward Cep
A HW 2. We find that the flattened disk structure of the dust emission observed
by Patel et al. is preserved at the 0.''3 scale, showing an elongated structure
of ~$0.''6 size (450 AU) peaking on HW 2. In addition, two ammonia cores are
observed, one associated with a hot-core previously reported, and an elongated
core with a double peak separated by ~1.''3 and with signs of heating at the
inner edges of the gas facing HW 2. The double-peaked ammonia structure, as
well as the double-peaked CH3CN structure reported previously (and proposed to
be two independent hot-cores), surround both the dust emission as well as the
double-peaked SO2 disk structure found by Jimenez-Serra et al. All these
results argue against the interpretation of the elongated dust-gas structure as
due to a chance-superposition of different cores; instead, they imply that it
is physically related to the central massive object within a disk-protostar-jet
system.Comment: 12 pages, 3 figures; accepted for publication in the Astrophysical
Journa
1.3 mm Polarized emission in the circumstellar disk of a massive protostar
We present the first resolved observations of the 1.3 mm polarized emission from the disk-like structure surrounding the high-mass protostar Cepheus A HW2. These CARMA data partially resolve the dust polarization, suggesting a uniform morphology of polarization vectors with an average position angle of 57° ± 6° and an average polarization fraction of 2.0% ± 0.4%. The distribution of the polarization vectors can be attributed to (1) the direct emission of magnetically aligned grains of dust by a uniform magnetic field, or (2) the pattern produced by the scattering of an inclined disk. We show that both models can explain the observations, and perhaps a combination of the two mechanisms produces the polarized emission. A third model including a toroidal magnetic field does not match the observations. Assuming scattering is the polarization mechanism, these observations suggest that during the first few 104 years of high-mass star formation, grain sizes can grow from1 mm to several 10s μm.Fil: Fernandez Lopez, Manuel. Provincia de Buenos Aires. Gobernación. Comision de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomia; ArgentinaFil: Stephens, I. W.. Harvard-Smithsonian Center for Astrophysics; Estados Unidos. Boston University; Estados Unidos. University of Illinois; Estados UnidosFil: Girart, J. M.. Harvard-Smithsonian Center for Astrophysics; Estados Unidos. Institut de Ciències de l’Espai; EspañaFil: Looney, L.. University of Illinois; Estados UnidosFil: Curiel, S.. Universidad Nacional Autónoma de México; MéxicoFil: Segura Cox, D.. University of Illinois; Estados UnidosFil: Eswaraiah, C.. National Tsing Hua University; República de ChinaFil: Lai, S. P.. National Tsing Hua University; República de Chin
Multi-filter transit observations of WASP-39b and WASP-43b with three San Pedro M\'artir telescopes
Three optical telescopes located at the San Pedro M\'artir National
Observatory were used for the first time to obtain multi-filter defocused
photometry of the transiting extrasolar planets WASP-39b and WASP-43b. We
observed WASP-39b with the 2.12m telescope in the U filter for the first time,
and additional observations were carried out in the R and I filters using the
0.84m telescope. WASP-43b was observed in VRI with the same instrument, and in
the i filter with the robotic 1.50m telescope. We reduced the data using
different pipelines and performed aperture photometry with the help of custom
routines, in order to obtain the light curves. The fit of the light curves
(1.5--2.5mmag rms), and of the period analysis, allowed a revision of the
orbital and physical parameters, revealing for WASP-39b a period ( days) which is seconds larger than
previously reported. Moreover, we find for WASP-43b a planet/star radius
() which is larger in the i filter
with respect to previous works, and that should be confirmed with additional
observations. Finally, we confirm no evidence of constant period variations in
WASP-43b.Comment: 13 pages, 7 figures, accepted in PASP, scheduled for the February 1,
2015 issu
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