794 research outputs found
WKB Approximation to the Power Wall
We present a semiclassical analysis of the quantum propagator of a particle
confined on one side by a steeply, monotonically rising potential. The models
studied in detail have potentials proportional to for ; the
limit would reproduce a perfectly reflecting boundary, but at
present we concentrate on the cases and 2, for which exact
solutions in terms of well known functions are available for comparison. We
classify the classical paths in this system by their qualitative nature and
calculate the contributions of the various classes to the leading-order
semiclassical approximation: For each classical path we find the action ,
the amplitude function and the Laplacian of . (The Laplacian is of
interest because it gives an estimate of the error in the approximation and is
needed for computing higher-order approximations.) The resulting semiclassical
propagator can be used to rewrite the exact problem as a Volterra integral
equation, whose formal solution by iteration (Neumann series) is a
semiclassical, not perturbative, expansion. We thereby test, in the context of
a concrete problem, the validity of the two technical hypotheses in a previous
proof of the convergence of such a Neumann series in the more abstract setting
of an arbitrary smooth potential. Not surprisingly, we find that the hypotheses
are violated when caustics develop in the classical dynamics; this opens up the
interesting future project of extending the methods to momentum space.Comment: 30 pages, 8 figures. Minor corrections in v.
Medida de magnetorresistencia en la manganita La0.65Sr0.35Mn03
Se describe la implementación del sistema de medida de magnetorresistencia con base en el método de cuatro puntas para determinar la resistividad eléctrica y su correspondiente variación ante la presencia de un campo magnético paralelo o antiparalelo al flujo de corriente, este campo es generado por un imán permanente controlando su intensidad mediante la distancia a la cual se acerca y la resistividad se registra mediante el multímetro DMM4065 para temperatura ambiente. Se analizan los efectos de los contactos, la rotación de los puntos de inyección de corriente y el registro de voltaje, el efecto de Lorentz provocado por el campo magnético terrestre y la precisión de las medidas. Se realiza la medida de magnetorresistencia en la manganita magnetorresistiva La0.65Sr0.35Mn03, describiendo además la preparación por el método sol-gel de este compuest
Efecto de siete bioestimulantes sobre la “gota” (Phytophthora infestans (Mont.) de Bary) y la productividad en papa criolla amarilla (Solanum tuberosum Grupo Phureja)
La papa criolla amarilla es una importante opción agrícola para los pequeños sistemas productivos del departamento de Nariño, no obstante presenta predisposición al patógeno Phytophthora infestans, para el cual existen otras medidas de mitigación aparte del manejo convencional. Por consiguiente, el objetivo del presente trabajo fue comprobar el efecto de la aplicación de bioestimulantes, sobre la severidad del patógeno, el rendimiento y sus componentes. Se utilizó un diseño de bloques completos al azar con nueve tratamientos y tres repeticiones, evaluando a siete bioestimulates que corresponden a: aminoácidos, Ascophyllum nodosum, Lactobacillus+Trichoderma, ácidos orgánicos, fosfitos de potasio, silicio y preparado artesanal, con aplicaciones foliares en cuatro etapas fenológicas del cultivo de papa. Encontrando efecto de fosfitos de potasio, Lactobacillus+Trichoderma, Ascophyllum nodosum y aminoácidos, con menores porcentajes de severidad de P. infestans, en comparación con el Testigo absoluto y preparado artesanal en diferentes etapas de evaluación, siendo los fosfitos de potasio el bioestimulante de mayor duración. Se determinó alta correlación con efecto negativo entre la severidad y número de tubérculos grandes, número de tubérculos medianos y el rendimiento y efecto positivo con el número de tubérculos muy pequeños, con grados de asociación de -0,84, -0,72, -0,80 y 0,49% respectivamente. Encontrando que el incremento de 1% de severidad, disminuyó en 0,04 el número de tubérculos grandes y medianos y aumentó en 0,05 el número de tubérculos muy pequeños, reduciendo finalmente en 0,12 t.ha-1 el rendimiento. Los tratamientos más productivos fueron fosfitos de potasio y Testigo comercial, siendo éste último el de mayor viabilidad económica
Assertion-based Analysis via Slicing with ABETS
[EN] We present ABETS, an assertion-based, dynamic analyzer that helps diagnose errors in Maude programs. ABETS uses slicing to automatically create reduced versions of both a run's execution trace and executed program, reduced versions in which any information that is not relevant to the bug currently being diagnosed is removed. In addition, ABETS employs runtime assertion checking to automate the identification of bugs so that whenever an assertion is violated, the system automatically infers accurate slicing criteria from the failure. We summarize the main services provided by ABETS, which also include a novel assertionbased facility for program repair that generates suitable program fixes when a state invariant is violated. Finally, we provide an experimental evaluation that shows the performance and effectiveness of the system.This work has been partially supported by the EU (FEDER) and Spanish MINECO grant TIN2015-69175-C4-1-R, and by Generalitat Valenciana PROMETEOII/2015/013. J. Sapina was supported by FPI-UPV grant SP2013-0083.Alpuente Frasnedo, M.; Frechina, F.; Sapiña Sanchis, J.; Ballis, D. (2016). Assertion-based Analysis via Slicing with ABETS. Theory and Practice of Logic Programming. 16(5):515-532. https://doi.org/10.1017/S1471068416000375S51553216
Regimes hídricos e doses de fósforo em cafeeiro.
O trabalho objetivou estudar os crescimentos vegetativo e reprodutivo e a produtividade de cafeeiro sob três regimes hídricos e quatro doses de adubação fosfatada, no segundo ano após a poda, em solo de Cerrado. A cultivar utilizada foi a Catuaí Rubi MG 1192, Coffea arabica L., com 7.143 plantas ha-1. Os regimes hídricos aplicados foram: sem suspensão da irrigação, feita o ano todo (I); e a partir de 24/6/07, com suspensão da irrigação por 70 dias (SI70); e com suspensão da irrigação por 109 dias (SI109). Os tratamentos SI70 e SI109 foram interrompidos por uma chuva de 12 mm (1.o/10/07), que visualmente induziu a floração. As quatro doses anuais de adubação fosfatada foram: 0 (P0), 100 (P100), 200 (P200) e 400 (P400) kg de P2O5 ha-1. O delineamento experimental foi o de blocos completos ao acaso com o regime hídrico na parcela e a dose de fósforo na subparcela, com três repetições. As doses de fósforo (P200) e (P400) proporcionaram aumento no comprimento e área foliar de ramos, número de frutos e na produtividade de grãos. Os regimes hídricos SI70 e SI109 proporcionaram as maiores porcentagens de frutos cereja e a maior e menor produtividade de grãos respectivamente
Virtual Teams in The University: A Critical Literature Review and A Research Agenda
The incentives for the internationalization of universities and the digitalization of teaching driven by the situation of COVID-19 have increased the operation of virtual work teams in higher education institutions, both in terms of groups of students and groups of researchers. The objective of this study is to explore the evolution of academic research concerning virtual teams within university settings, aiming to delineate prominent research trajectories and outline a prospective agenda for future inquiry in this domain. This work involved a systematic review of the literature in the WoS and Scopus databases to identify what, when, who, where and how virtual teams in universities have been researched. The PRISMA method was used to guide the data collection process. Forty-seven articles were identified as relevant for analysis. Despite the significant development of academic research on virtual teams since the end of the last century, the necessary attention has still not been given to the specific case of virtual teams in universities. Most of the research has been conducted in the United States; however, previous research reveals that cultural aspects are relevant variables in the performance and efficiency of virtual teams, so it is advisable to extend this type of research to other countries and cultural contexts. In addition, we can also see that most of the works identified have analysed work teams formed by students, and there are very few studies on virtual teams of researchers, despite the importance of these teams in the context of encouraging the internationalization of research networks. Moreover, the review of the content of the articles as well as the future lines of research have been organized around a life cycle model, considering three categories: inputs, operating process and outputs-results. The second category is the most developed to date
Una guía para el estudio de nanopartículas magnéticas de óxidos de hierro con aplicaciones biomédicas. Parte I
In this paper, a theoretical and experimental review of main physical properties of magnetic nanoparticles with application in magnetic hyperthermia is presented. In this way, this work has been divided in two parts: In part I, corresponding with this article, a detailed theoretical review about the particles properties and the physical laws that govern them, such as magnetization, interparticles interactions and structuring in colloidal suspensions. In the Part II, subjects such as nanoparticles synthesis, physical characterization and modeling, experimental determination of heat dissipation under radiofrequency fields, and its correlation with the current modells will be presented. This work is intended as a guide because what is expressed therein gives a series of important guidelines to take into account when making a research on magnetic nanoparticles.El siguiente artículo corresponde a una revisión teórica y experimental sobre las las principales propiedades físicas de un sistema de nanopartículas magnéticas con aplicaciones en el tratamiento del cáncer por hipertermia magnética. Así, se divide el mismo en dos partes: en la primera parte, correspondiente a esta entrega, se realiza una revisión teórica detallada sobre las principales propiedades de las nanopartículas, y las leyes físicas que las rigen, tales como magnetización, interacciones entre partículas y su ordenamiento en suspensiones coloidales. En una segunda entrega, se tratarán temas como la síntesis de nanopartículas, técnicas y modelos de caracterización física y medidas experimentales de disipación de calor bajo campos de radiofrecuencia, y su correlación con los modelos mostrados en este articulo. Se presenta este trabajo como una guía ya que ofrece una serie de pautas importantes para tener en cuenta al momento de realizar una investigación en nanopartículas magnéticas
- …