272 research outputs found
A shooting argument approach to a sharp type solution for nonlinear degenerate Fisher-KPP equations
In this paper we prove the existence and uniqueness of a travelling-wave solution of sharp type for the degenerate (at u = 0) parabolic equation where D is a strictly increasing function and g is a function which generalizes the kinetic part of the classical Fisher-KPP equation. The original problem is transformed into the proper travelling-wave variables, and then a shooting argument is used to show the existence of a saddle-saddle heteroclinic trajectory for a critical value, c*>0, of the speed c of an autonomous system of ordinary differential equations. Associated with this connection is a sharp-type solution of the nonlinear partial differential equation
A review on travelling wave solutions of one-dimensional reaction diffusion equations with non-linear diffusion term
In this paper we review the existence of different types of travelling wave solutions of degenerate non-linear reaction-diffusion equations of the form for different density-dependent diffusion coefficients D and kinetic part g. These include the non-linear degenerate generalized Fisher-KPP and the Nagumo equations. Also, we consider an equation whose diffusion coefficient changes sign as the diffusive substance increases. This describes a diffusive-aggregative process. In this case the travelling wave solutions are explored and the ill-posedness of two boundary-value problems associated with the above equation is stated
Superiorization: An optimization heuristic for medical physics
Purpose: To describe and mathematically validate the superiorization
methodology, which is a recently-developed heuristic approach to optimization,
and to discuss its applicability to medical physics problem formulations that
specify the desired solution (of physically given or otherwise obtained
constraints) by an optimization criterion. Methods: The underlying idea is that
many iterative algorithms for finding such a solution are perturbation
resilient in the sense that, even if certain kinds of changes are made at the
end of each iterative step, the algorithm still produces a
constraints-compatible solution. This property is exploited by using permitted
changes to steer the algorithm to a solution that is not only
constraints-compatible, but is also desirable according to a specified
optimization criterion. The approach is very general, it is applicable to many
iterative procedures and optimization criteria used in medical physics.
Results: The main practical contribution is a procedure for automatically
producing from any given iterative algorithm its superiorized version, which
will supply solutions that are superior according to a given optimization
criterion. It is shown that if the original iterative algorithm satisfies
certain mathematical conditions, then the output of its superiorized version is
guaranteed to be as constraints-compatible as the output of the original
algorithm, but it is superior to the latter according to the optimization
criterion. This intuitive description is made precise in the paper and the
stated claims are rigorously proved. Superiorization is illustrated on
simulated computerized tomography data of a head cross-section and, in spite of
its generality, superiorization is shown to be competitive to an optimization
algorithm that is specifically designed to minimize total variation.Comment: Accepted for publication in: Medical Physic
Percepción de niños y niñas del papel social de hombres y mujeres en la Ciudad de México
En la familia se enseñan los papeles sociales de hombres y mujeres, de tal
manera que las actitudes, conductas y tipo de relaciones estarán determinadas por
el ambiente social en el que cada persona se desarrolle, muchas veces manifestando
las diferencias entre hombres y mujeres como desigualdades. El objetivo de este
trabajo fue analizar si niños y niñas de la Ciudad de México conviven en la igualdad
o bien, ya asumen una desigualdad social entre hombres y mujeres. Se estudiaron
300 niños y niñas de 4 a 9 años de edad, utilizando el Inventario Expectativas de
Vida. Los resultados muestran que los conceptos que tienen los niños y las niñas,
reflejan las creencias del papel social de hombres y mujeres del entorno social y
cultural que les rodea y que, desde edades de desarrollo tempranas, las concepciones
de desigualdad se van enseñando y formando en la vida cotidiana.Is in the family where occurs the teaching of men and women social skills
performance, this is why all attitudes, behaviors and relations are determined,
taking place from the social environment where each person grows, many times
showing men and women differences as inequalities. This paper objective’s been to
analyze if boys and girls from Mexico City live together in equality or if they carry
out their own inequality social skills concepts between men and woman. The study
came from 300 boys and girls 4 to 9 years old; we used the Life Expectations
Inventory. The results showed the conception that boys and girls have, and manifest
the social skills performs mirror believes of men and women from their social and
cultural atmospheres encircles, plus indicates how this inequalities in men and
woman are teach in early years in every day life
¿Cómo resuelven los problemas los directores eficaces? Un estudio de directores de primaria mexicanos en su primer año de servicio
Desde principios del siglo pasado, la investigación sobre eficacia escolar realizada en los países anglosajones ha demostrado consistentemente el impacto del director en la mejora y cambio de la escuela (por ejemplo, Murphy, 2006). En iberoamérica, el interés por el tema es más reciente. Diversos trabajos realizados en la región (Murillo, 2003) confirman que la gestión, la dirección de los centros escolares o liderazgo, según se le quiera denominar, es un factor clave en la eficacia escolar. A raíz de estos hallazgos, las políticas educativas han puesto más atención al papel del director. En la región el país pionero ha sido España; existen trabajos desde la década de los 70 (por ejemplo, Baquero, 1971); en los 90 destacan el trabajo de Sacristán(1995), y el de Murillo, Barrio y Pérez Albó (1999).
El estado de la investigación en Latinoamérica sobre la dirección escolar se refleja en el número monográfico dedicado a la dirección de la Revista Electrónica Iberoamericana sobre Calidad, Eficacia y Cambio en Educación (2006). En el caso mexicano, entre las pocas investigaciones empíricas mexicanas destacan la de Pastrana (1997); Loera y colaboradores ( 2001), y la de Fierro (2006). Como se aprecia, la investigación en la región es escasa. En el medio internacional, el interés por el estudio de la dirección escolar en el nivel básico se ha enfocado a los directores de primer año de servicio. Investigaciones anglosajonas señalan que el primer año de los directores en el cargo es, en cierto sentido, traumático (Hobson, 2003).
Los nuevos directores experimentan sentimientos de soledad y aislamiento; enfrentan múltiples tareas y algunos deben lidiar con el legado del antiguo director. En un estudio reciente realizado con directores de primaria en su primer año de servicio, Slater, García Garduño, y López-Gorosave (2007) encontraron problemas semejantes. Esta investigación es parte de un proyecto internacional enfocado a estudiar la preparación, motivación y problemas que enfrentan los directores de escuelas primarias en su primer año de servicio, en México y en otros países. Lo que aún no se ha investigado es cómo resuelven los problemas los directores de primer ingreso eficaces, por lo que se decidió hacer un nuevo análisis de la información recabada con directores de primaria mexicanos, con el propósito de identificar las estrategias utilizadas en la resolución de los problemas. Las técnicas y métodos de recopilación de datos incluyeron grupos de enfoque, registro de incidentes críticos y entrevistas en profundidad. El análisis permitió identificar algunas estrategias que emplean los directores eficaces en la solución o manejo de problemas: buscan alentar; guían con el ejemplo; siempre comunican; se anticipan a los problemas, intervienen lo más rápido posible, buscan persuadir y dan seguimiento a la evolución de los casos difíciles
Ultraviolet-A Light and Riboflavin Therapy for Acanthamoeba Keratitis: A Case Report
Purpose: To report ultraviolet-A (UV-A) light treatment in a patient with Acanthamoeba keratitis (AK). Methods: Interventional case report. A standard protocol for ultraviolet corneal therapy, with a power emission of 3 mW/cm2 and a wavelength of 370 nm, was used. The protocol included an 8-nm bandwidth at a 54-mm distance measured with a collimation system of diodes as well as a protective shield of riboflavin in a case of documented AK. Results: A 54-year-old female patient with AK, showing no therapeutic response to a wide variety of topical antimicrobial agents and with a visual acuity of 20/400, was treated with UV-A therapy. The patient displayed a favourable response in the first 24 h after treatment, with improvement of symptoms, visual acuity (to 20/200) and biomicroscopy cornea with haze degree I. By the third week post-treatment, the patient was symptom-free. Her visual acuity was 20/30, and the affected cornea was clear. Five months after treatment, there had been no recurrence, and her vision was 20/20. Conclusions: Treatment with UV-A light was an effective therapy in this case of AK
Galaxy and Mass Assembly (GAMA): The interplay between galaxy mass, SFR, and heavy element abundance in paired galaxy sets
© 2021 2020 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society. We study the star formation rate (SFR), stellar mass (M∗), and the gas metallicity (Z) for 4636 galaxy pairs using the Galaxy And Mass Assembly (GAMA) survey. Our galaxy pairs lie in a redshift range of 0 250 km s-1 and high multiplicity
Use of a Simulation Model to Develop Feeding Strategies for Cattle at Pasture in Small Scale Dairy Farming Systems in the Highlands of Central Mexico: Methodological Frame Work
The massive relic galaxy NGC 1277 is dark matter deficient. From dynamical models of integral-field stellar kinematics out to five effective radii
According to the CDM cosmology, present-day galaxies with stellar
masses should contain a sizable fraction of
dark matter within their stellar body. Models indicate that in massive
early-type galaxies (ETGs) dark matter should account for of the
dynamical mass within five effective radii (). Most massive ETGs
have been shaped through a two-phase process: the rapid growth of a compact
core was followed by the accretion of an extended envelope through mergers. The
exceedingly rare galaxies that have avoided the second phase, the so-called
relic galaxies, are thought to be the frozen remains of the massive ETG
population at . The best relic galaxy candidate discovered to date
is NGC 1277, in the Perseus cluster. We used deep integral field GCMS data to
revisit NGC 1277 out to an unprecedented radius of 6 kpc (corresponding to ). By using Jeans anisotropic modelling we find a negligible dark
matter fraction within (; two-sigma
confidence level), which is in tension with the expectation. Since the lack of
an extended envelope would reduce dynamical friction and prevent the accretion
of an envelope, we propose that NGC 1277 lost its dark matter very early or
that it was dark matter deficient ab initio. We discuss our discovery in the
framework of recent proposals suggesting that some relic galaxies may result
from dark matter stripping as they fell in and interacted within galaxy
clusters. Alternatively, NGC 1277 might have been born in a high-velocity
collision of gas-rich proto-galactic fragments, where dark matter left behind a
disc of dissipative baryons. We speculate that the relative velocities of
required for the latter process to happen were
possible in the progenitors of the present-day rich galaxy clusters.Comment: Accepted for publication in A&
- …