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 $u_1 = [D(u)u_x]_x + g(u)$ 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 $u(x,t) = \phi(x - ct)$ of degenerate non-linear reaction-diffusion equations of the form $u_t = [D(u)u_x]_x + g(u)$ 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

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 $\Lambda$CDM cosmology, present-day galaxies with stellar masses $M_\star>10^{11} {\rm M}_\odot$ 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 $\sim60\%$ of the dynamical mass within five effective radii ($5 R_{\rm e}$). 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 $z\gtrsim2$. 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 $5 R_{\rm e}$). By using Jeans anisotropic modelling we find a negligible dark matter fraction within $5 R_{\rm e}$ ($f_{\rm DM}(5 R_{\rm e})<0.05$; 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 $\approx2000 {\rm km/s}$ 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&