Radio observations of evaporating objects in the Cygnus OB2 region

We present observations of the Cygnus OB2 region obtained with the Giant Metrewave Radio Telescope (GMRT) at frequencies of 325 and 610 MHz. In this contribution we focus on the study of proplyd-like objects (also known as free-floating evaporating gas globules or frEGGs) that typically show an extended cometary morphology. We identify eight objects previously studied at other wavelengths and derive their physical properties by obtaining their optical depth at radio-wavelengths. Using their geometry and the photoionization rate needed to produce their radio-continuum emission, we find that these sources are possibly ionized by a contribution of the stars Cyg OB2 #9 and Cyg OB2 #22. Spectral index maps of the eight frEGGs were constructed, showing a flat spectrum in radio frequencies in general. We interpret these as produced by optically thin ionized gas, although it is possible that a combination of thermal emission, not necessarily optically thin, produced by a diffuse gas component and the instrument response (which detects more diffuse emission at low frequencies) can artificially generate negative spectral indices. In particular, for the case of the Tadpole we suggest that the observed emission is not of non-thermal origin despite the presence of regions with negative spectral indices in our maps.Fil: Isequilla, Natacha Laura. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Fernandez Lopez, Manuel. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Benaglia, Paula. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Ishwara Chandra, C. H.. National Center For Radio Astrophysics; IndiaFil: del Palacio, Santiago. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentin

Metamagnetic Transition in UCoAl Probed by Thermoelectricity Measurements

We report field and temperature dependent measurements of the thermoelectric power (TEP) and the Nernst effect in the itinerant metamagnet UCoAl. The magnetic field is applied along the easy magnetization c-axis in the hexagonal crystal structure. The metamagnetic transition from the paramagnetic phase at zero field to the field induced ferromagnetic (FM) state is of first order at low temperatures and becomes a broad crossover above the critical temperature $T^{\star}_{M} \sim 11$ K. The field-dependence of the TEP reveals that the effective mass of the hole carriers changes significantly at the metamagnetic transition. The TEP experiment reflects the existence of different carrier types in good agreement with band structure calculations and previous Hall effect experiments. According to the temperature dependence of the TEP, no Fermi liquid behavior appears in the paramagnetic state down to 150 mK, but is achieved only in the field induced ferromagnetic state.Comment: 5 pages, 4 figure

The rational expectations hypothesis: An assessment from Popper's philosophy

The rational expectations hypothesis (REH) is the standard approach to expectations formation in macroeconomics. We discuss its compatibility with two strands of Karl Popper's philosophy: his theory of knowledge and learning, and his "rationality principle" (RP). First, we show that the REH is utterly incompatible with the former. Second, we argue that the REH can nevertheless be interpreted as a heuristic device that facilitates economic modeling and, consequently, it may be justified along the same lines as Popper's RP. We then argue that, our position as to the resolution of this paradox notwithstanding, Popper's philosophy provides a metatheoretical framework with which we can evaluate the REH. Within this framework, the REH can be viewed as a heuristic device or strategy that fulfils the same function as, for instance, the optimizing assumption. However, we believe that the REH imparts a serious methodological bias, since, by implying that macroeconomic instability is caused exclusively by "exogenous" shocks that randomly hit the economy, it precludes the analysis of any sources of inherent instability caused by the making of (nonrandom) errors by individuals, and hence it favors the creation of an institutional configuration that may be ill suited to address this type of instability

Popper's "rationality principle" reconsidered

Popper recognizes that there are, at least, two versions of his "Rationality Principle" (RP) yet he does not explain either how they relate to other parts of his works or which version social scientists should adopt. We argue that Popper's formulation of RP can be upgraded by explicitly considering the conjectural nature of all knowledge and the subjective nature of the "facts" of the social sciences. Next, we examine several areas of Popper's work as well as some of Hayek's ideas and conclude that, had Popper reflected on these issues he would probably recommended social scientists to adopt the 'subjectivist' version of RP

La modelización macroeconómica en el enfoque keynesiano: una reconstrucción popperiana

We review Keynes´s attempt to deal with the `problem of induction´ since his Treatise on Probability and then argue that Popper´s `solution´ to the former, known as Popper´s evolutionary of knowledge and learning, is compatible with Keynes´s adoption of a conventional theory of knowledge in his later economic writings. We also argue that Keynes´s macro-theory as it appears in both his General Theory and his 1937 QJE paper can be (re)interpreted as an instance of a reformulated version of the `subjectivist´ version of Popper´s `Rationality Principle´ (RPs) according to which agents´ behaviour is appropriate or adequate to the problem-situation as the theorist believes that agents believe the former is. A number of further results follow from the previous arguments.Repasamos el intento de Keynes de abordar el "problema de la inducción" en su Treatise on Probability y señalamos que la solución propuesta por Popper al mismo, conocido como la teoría popperiana del conocimiento y el aprendizaje es compatible con la adopción por parte de Keynes de una teoría convencionalista del conocimiento en su última etapa. También señalamos que la Teoría General y su artículo del año 1937 en el QJE pueden ser interpretados como un caso concreto de la versión `subjetivista´ del "Principio de Racionalidad" Popperiano, de acuerdo con el cual el comportamiento de los agentes económicos es adecuado al problema-situación tal y como el modelizador cree que los agentes perciben este último. De esta interpretación obtenemos una serie de resultados adicionales.DecanatoFac. de Ciencias Económicas y EmpresarialesTRUEunpu

Some Reflections on Popper's approach to Rationality and its implications for the Social Sciences

Existen dos nociones distintas sobre la racionalidad humana en la obra filosófica de Popper: la derivada de la teoría popperiana del conocimiento y el aprendizaje (TPCA) y la noción implícita en su propuesta metodológica para las Ciencias Sociales conocida como "Análisis Situacional" (AS). Este ensayo realiza un análisis crítico detallado de la relación entre estas dos nociones y de sus implicaciones para las ciencias sociales. En concreto, el ensayo aborda: (i) las diferencias entre TPCA y las versiones "objetivista" y "subjetivista" de AS, (ii) la distinción propuesta por Schumpeter entre la "racionalidad del observador y la "racionalidad del observado" y (iii) los argumentos de Hayek sobre la naturaleza de los "hechos" en las Ciencias Sociales.There are two different notions of human rationality in Popper´s work: the notion that stems from his evolutionary theory of knowledge and learning (PTKL), and the notion embodied in his methodological proposal for the social sciences known as `Situational Analysis´ (SA). This essay provides an in-depth critical analysis of the relation between these two approaches and its implications for the social sciences. In particular, we focus on (i) the difference between PTKL and both the `objectivist´ and `subjectivist´ version of SA, (ii) Schumpeter´s distinction between the `rationality of the observer´ and the `rationality in the observed´, and (iii) Hayek´s arguments about the nature of the `facts´ of the social sciences.DecanatoFac. de Ciencias Económicas y EmpresarialesTRUEpu

La macroeconomía ortodoxa a la luz de Popper

Macroeconomics has been dominated over the last four decades by the Rational Expectations Hypothesis (REH) which implies that economies are inherently stable. REH is a key element of the New Neoclassical Synthesis (NNS) macroeconomic model which has also played a dominant role in theory and policy analysis over the last two decades. We analyse REH in light of Popper´s evolutionary theory of knowledge and learning. We claim that the latter provides macroeconomics with an epistemological and ontological foundation that, unlike REH, takes full account of human fallibility and upon which economists can build a more useful macroeconomic theory.La macroeconomía ortodoxa ha estado dominada durante las últimas cuatro décadas por la llamada “hipótesis de expectativas racionales” (HER) que conlle-va el supuesto implícito de que las economías de mercado son inherentemente estables. A su vez, la HER constituye un elemento esencial de la llamada “Nueva Síntesis Neoclásica” en macroeconomía que también ha desempeñado un papel dominante tanto en la teoría macroeconómica como en la política económica durante las últimas dos décadas. En este trabajo analizamos la HER a la luz de la teoría popperiana del conocimiento y el aprendizaje y afirmamos que esta última dota a la teoría macro-económica de unos fundamentos epistemológicos y ontológicos que, a diferencia de la HER, incorporan plenamente el concepto de falibilidad humana y sobre los cuales los economistas pueden construir una teoría macroeconómica más útil.DecanatoFac. de Ciencias Económicas y EmpresarialesTRUEunpu