Indeterminacy with No-Income-Effect Preferences and Sector-Specific Externalities

We examine a two-sector real business cycle model with sector-specific externalities in the production of distinct consumption and investment goods. In addition, the household utility is postulated to exhibit no income effect on the demand for leisure. Unlike in the one-sector counterpart, we show that equilibrium indeterminacy can result with sufficiently high returns-to-scale in the production of investment goods. We also find that the smaller the labor supply elasticity, the lower the threshold level of returns-to-scale needed for generating indeterminacy and sunspots. This finding turns out to be exactly the opposite of that in all existing RBC-based indeterminacy studies.Indeterminacy, Income Effect, Sector-Specific Externalities

On the Penrose Inequality for general horizons

For asymptotically flat initial data of Einstein's equations satisfying an energy condition, we show that the Penrose inequality holds between the ADM mass and the area of an outermost apparent horizon, if the data are restricted suitably. We prove this by generalizing Geroch's proof of monotonicity of the Hawking mass under a smooth inverse mean curvature flow, for data with non-negative Ricci scalar. Unlike Geroch we need not confine ourselves to minimal surfaces as horizons. Modulo smoothness issues we also show that our restrictions on the data can locally be fulfilled by a suitable choice of the initial surface in a given spacetime.Comment: 4 pages, revtex, no figures. Some comments added. No essential changes. To be published in Phys. Rev. Let

“The feeling of fear was not from my student, but from myself”: A pre-service teacher’s shift from traditional to problem-posing second language pedagogy in a Mexican youth prison

This era of globalization, capitalism, and economic progress has given rise to mass incarceration, as a considerable number of youths in developing and developed countries live behind bars in detention facilities without appropriate educational support. Educators in these facilities deposit knowledge, through traditional pedagogical approaches, under systemic oppression and surveillance deemed necessary for safety and security. This study investigated implementations of Freire’s (2000) problem-posing pedagogy using a participatory action research (PAR) approach through the lens of critical theory. Two of the co-authors helped develop a Freirean language teaching program in an urban youth prison in Mexico, centering student teachers’ critical self-awareness by providing them with opportunities to reflect on their identity, life experiences, and reality while teaching in prison. Through critical, autoethnographic self-reflections of a bilingual teacher candidate on her teaching practices, this study provides insights into how the teacher was impacted by the problem-posing pedagogy and how it was reflected in her transformation to a critical, loving teacher and student progress. This research embraces a humanistic approach to teaching incarcerated youth in Mexico through care and courage by supporting them as students, as well as by empowering their voices and thoughts. Building a learning community, where students and teachers create respectful human connections through dialogue and discussions on language, culture, and lived experiences, is portrayed in this research as essential

Observation of dispersive wave emission by temporal cavity solitons

We examine a coherently-driven, dispersion-managed, passive Kerr fiber ring resonator and report the first direct experimental observation of dispersive wave emission by temporal cavity solitons. Our observations are in excellent agreement with analytical predictions and they are fully corroborated by numerical simulations. These results lead to a better understanding of the behavior of temporal cavity solitons under conditions where higher-order dispersion plays a significant role. Significantly, since temporal cavity solitons manifest themselves in monolithic microresonators, our results are likely to explain the origins of spectral features observed in broadband Kerr frequency combs.Comment: 4 pages, 3 figure

Isometric Representations of Totally Ordered Semigroups

Let S be a subsemigroup of an abelian torsion-free group G. If S is a positive cone of G, then all C*-algebras generated by faithful isometrical non-unitary representations of S are canonically isomorphic. Proved by Murphy, this statement generalized the well-known theorems of Coburn and Douglas. In this note we prove the reverse. If all C*-algebras generated by faithful isometrical non-unitary representations of S are canonically isomorphic, then S is a positive cone of G. Also we consider G = Z\times Z and prove that if S induces total order on G, then there exist at least two unitarily not equivalent irreducible isometrical representation of S. And if the order is lexicographical-product order, then all such representations are unitarily equivalent.Comment: February 21, 2012. Kazan, Russi

How many photons are needed to distinguish two transparencies?

We give a bound on the minimum number of photons that must be absorbed by any quantum protocol to distinguish between two transparencies. We show how a quantum Zeno method in which the angle of rotation is varied at each iteration can attain this bound in certain situations.Comment: 5 pages, 4 figure