944 research outputs found
Nonperturbative Quantum Physics from Low-Order Perturbation Theory
The Stark effect in hydrogen and the cubic anharmonic oscillator furnish
examples of quantum systems where the perturbation results in a certain
ionization probability by tunneling processes. Accordingly, the perturbed
ground-state energy is shifted and broadened, thus acquiring an imaginary part
which is considered to be a paradigm of nonperturbative behavior. Here we
demonstrate how the low order coefficients of a divergent perturbation series
can be used to obtain excellent approximations to both real and imaginary parts
of the perturbed ground state eigenenergy. The key is to use analytic
continuation functions with a built in analytic structure within the complex
plane of the coupling constant, which is tailored by means of Bender-Wu
dispersion relations. In the examples discussed the analytic continuation
functions are Gauss hypergeometric functions, which take as input fourth order
perturbation theory and return excellent approximations to the complex
perturbed eigenvalue. These functions are Borel-consistent and dramatically
outperform widely used Pad\'e and Borel-Pad\'e approaches, even for rather
large values of the coupling constant.Comment: 5 pages, 3 figures, PDFLaTe
The impact of cultural dissonance and acculturation orientations on immigrant students' academic performance
Indexación: Scopus; Scielo; Redalyc.Prior research has documented meaningful differences between school
performance of immigrant and native students. Multicultural education has been
associated with academic failure of foreign students. e aim of this study was to examine
the impact of a set of psychosocial variables on the perceived academic achievement
of first generation immigrant adolescents from public secondary schools in Northern
Spain. Results showed that 46% of the variability in foreign students’ perceived academic
performance was explained by home-school cultural dissonance. We also explored the
impact of acculturation orientation to separation, perception of discrimination from
teachers, school adjustment, and psychological well-being in academic performance.
Any multicultural education context should take into account psychosocial adjustment,
given its influence on academic performance of all studentsSe han hallado diferencias significativas entre el rendimiento académico de
los inmigrantes y el de los estudiantes nativos. Sin embargo, hay una escasa evidencia
acerca de los aspectos psicosociales de este fenómeno. El objetivo de este estudio fue
examinar el impacto de un conjunto de variables psicosociales: disonancia cultural y
orientaciones de aculturación en el rendimiento académico percibido de adolescentes
inmigrantes de primera generación de centros de Educación Secundaria en el Norte
de España. Los resultados mostraron que alrededor del 46% de la variabilidad en el
rendimiento era explicada por la disonancia cultural entre escuela y hogar. Cualquier
contexto de educación multicultural ha de tomar en consideración el ajuste psicosocial,
dada su influencia en el rendimiento académico de los estudiantes.http://www.redalyc.org/jatsRepo/647/64753989003/index.htm
Sex-biased differences in the effects of host individual, host population and environmental traits driving tick parasitism in red deer
The interactions between host individual, host population, and environmental factors modulate parasite abundance in a given host population. Since adult exophilic ticks are highly aggregated in red deer (Cervus elaphus) and this ungulate exhibits significant sexual size dimorphism, life history traits and segregation, we hypothesized that tick parasitism on males and hinds would be differentially influenced by each of these factors. To test the hypothesis, ticks from 306 red deer-182 males and 124 females-were collected during 7 years in a red deer population in south-central Spain. By using generalized linear models, with a negative binomial error distribution and a logarithmic link function, we modeled tick abundance on deer with 20 potential predictors. Three models were developed: one for red deer males, another for hinds, and one combining data for males and females and including "sex" as factor. Our rationale was that if tick burdens on males and hinds relate to the explanatory factors in a differential way, it is not possible to precisely and accurately predict the tick burden on one sex using the model fitted on the other sex, or with the model that combines data from both sexes. Our results showed that deer males were the primary target for ticks, the weight of each factor differed between sexes, and each sex specific model was not able to accurately predict burdens on the animals of the other sex. That is, results support for sex-biased differences. The higher weight of host individual and population factors in the model for males show that intrinsic deer factors more strongly explain tick burden than environmental host-seeking tick abundance. In contrast, environmental variables predominated in the models explaining tick burdens in hinds
Fast Summation of Divergent Series and Resurgent Transseries in Quantum Field Theories from Meijer-G Approximants
We demonstrate that a Meijer-G-function-based resummation approach can be
successfully applied to approximate the Borel sum of divergent series, and thus
to approximate the Borel-\'Ecalle summation of resurgent transseries in quantum
field theory (QFT). The proposed method is shown to vastly outperform the
conventional Borel-Pad\'e and Borel-Pad\'e-\'Ecalle summation methods. The
resulting Meijer-G approximants are easily parameterized by means of a
hypergeometric ansatz and can be thought of as a generalization to arbitrary
order of the Borel-Hypergeometric method [Mera {\it et al.} Phys. Rev. Lett.
{\bf 115}, 143001 (2015)]. Here we illustrate the ability of this technique in
various examples from QFT, traditionally employed as benchmark models for
resummation, such as: 0-dimensional theory, with degenerate
minima, self-interacting QFT in 0-dimensions, and the computation of one- and
two-instanton contributions in the quantum-mechanical double-well problem.Comment: 18 pages, 9 figures, PDFTe
Chileans facing immigration: Relations between orientations of acculturation, perception of threat and social well-being in the great concepcion
Indexación: Scopus; Scielo; Redalyc.En Chile, el aumento sostenido de la inmigración extranjera ha impactado en
la construcción de nuevas formas de relación social. Si bien los procesos aculturativos han
sido estudiados desde la perspectiva de los inmigrantes por numerosas investigaciones,
los miembros de las sociedades receptoras han recibido menor atención. Este trabajo
tiene como propósito identificar las preferencias de aculturación de N=553 chilenos,
y verificar sus relaciones con la percepción de amenaza y el bienestar social. Contrario
a lo esperado, el individualismo aculturativo se asoció con un menor grado de
amenaza percibida y una mejor evaluación del propio funcionamiento social que el
integracionismo. Estos hallazgos son relacionados con la incorporación de modelos de
ciudadanÃa promovidos por la ideologÃa neoliberal en el Chile post-dictatorial.In Chile, the sustained increase of migratory flows is producing an important
impact on building new forms of social relations. Acculturation processes have been
studied from immigrant’s perspective by numerous studies, but host majority members
has received less attention from scholars. is study aimed to verify relations between
acculturation preferences of N=553 Chilean participants, their social well-being and
perceived threat. Results showed that, contrary as expected, individualism was positively
linked with better social functioning and less perceived threat than integrationism,
suggesting the impact of neoliberal ideology on post-dictatorial Chilean culture.http://www.redalyc.org/jatsRepo/647/64753989005/index.htm
Source blending effects on microlensing time-histograms and optical depth determination
Source blending in microlensing experiments is known to modify the Einstein
time of the observed events. In this paper, we have conducted Monte-Carlo
calculations, using the analytical relationships derived by Han (1999) to
quantify the effect of blending on the observed event time distribution and
optical depth. We show that short-time events are affected significantly by
source blending and that, for moderately blended sources, the optical depth
is globally overestimated, because of an underestimation of the
exposure. For high blending situations, on the opposite, blending leads to an
{\it under}estimation of the optical depth. Our results are in agreement with
the most recent optical depth determinations toward the Galactic Center of the
MACHO collaboration (Popowski et al. 2004) and the OGLE-II collaboration (Sumi
et al. 2005) that use clump giants (less affected by the blending effect) as
sources. The blending-corrected, lower optical depth toward the Galactic Bulge
is now in good agreement with the value inferred from galactic models,
reconciling theoretical and observational determinations.Comment: Accepted in Astronomy Astrophysics. Note that these calculations were
conducted in 2001, prior to the recent DIA analyses mentioned in the
references (see Alibert, Y. SF2A-conference, 2001
- …