Corruption, growth and ethnolinguistic fractionalization: a theoretical model

This paper analyzes the existing relationship between ethnolinguistic fractionalization, corruption and the growth rate of a country. We provide a simple theoretical model. We show that a non-linear relationship between fractionalization and corruption exists: corruption is high in homogeneous or very fragmented countries, but low where fractionalization is intermediate. In fact, when ethnic diversity is intermediate, constituencies act as a checkand balance device to limit ethnically-based corruption. Consequently, the relationship between fractionalization and growth rate is also non-linear: growth is high in the�middle range of ethnic diversity, low in homogeneous or very fragmented countries.

Role of an intermediate state in homogeneous nucleation

We explore the role of an intermediate state (phase) in homogeneous nucleation phenomenon by examining the decay process through a doubly-humped potential barrier. As a generic model we use the fourth- and sixth-order Landau potentials and analyze the Fokker-Planck equation for the one-dimensional thermal diffusion in the system characterized by a triple-well potential. In the low temperature case we apply the WKB method to the decay process and obtain the decay rate which is accurate for a wide range of depth and curvature of the middle well. In the case of a deep middle well, it reduces to a doubly-humped-barrier counterpart of the Kramers escape rate: the barrier height and the curvature of an initial well in the Kramers rate are replaced by the arithmetic mean of higher(or outer) and lower(or inner) partial barriers and the geometric mean of curvatures of the initial and intermediate wells, respectively. It seems to be a universal formula. In the case of a shallow-enough middle well, Kramers escape rate is alternatively evaluated within the standard framework of the mean-first-passage time problem, which certainly supports the WKB result. The criteria whether or not the existence of an intermediate state can enhance the decay rate are revealed.Comment: 9pages, 11figure

A vulnerability approach to the definition of the middle class

Measurement of the middle class has recently come to the center of policy debate in middle-income countries as they search for the potential engines of growth and good governance. This debate assumes, first, that there is a meaningful definition of class, and second, that thresholds that define relatively homogeneous groups in terms of pre-determined sociological characteristics can be found empirically. This paper aims at proposing a view of the middle class based on vulnerability to poverty. Following this approach the paper exploits panel data to determine the amount of comparable income -- associated with a low probability of falling into poverty -- which could define the lower bound of the middle class. The paper looks at absolute thresholds, challenging the view that people above the poverty line are actually part of the middle class. The estimated lower threshold is used in cross-section surveys to quantify the size and the evolution of middle classes in Chile, Mexico, and Peru over the past two decades. The first relevant feature relates to the fact that the proposed thresholds lie around the 60th percentile of the distribution. The evidence also shows that the middle class has increased significantly in all three countries, suggesting that a higher number of households face lower probabilities of falling into poverty than they did in the 1990s. There is an important group of people, however, which cannot be defined as middle class from this perspective, but are not eligible for poverty programs according to traditional definitions of poverty.Rural Poverty Reduction,Inequality,Regional Economic Development,Urban Partnerships&Poverty,Services&Transfers to Poor

Fano manifolds of Calabi-Yau Hodge type

International audienceWe introduce and we study a class of odd dimensional compact complex manifolds whose Hodge structure in middle dimension looks like that of a Calabi-Yau threefold. We construct several series of interesting examples from rational homogeneous spaces with special properties

A Case for Student Teacher Placement as Preparation for Future Urban Educators

Do schools of education effectively train young, white, and middle-class teacher candidates to work in urban classrooms? How can schools of education prepare teachers and future teachers for classrooms that are diverse in terms of race/ethnicity, nationality, social class, language and other differences (Nieto, 2004) Classrooms that used to be homogeneous are now diverse, yet the predominant face and gender of the teacher has remained the same. Dramatic inequalities exist in the access that students around the globe have to an excellent, high quality education; inequalities that are lamentably too frequently based on race, social class, language, and other differences (Orfield, 2001). Using data from a descriptive survey, this paper will draw from the experience of eleven teacher candidates in racially diverse urban elementary schools through their first year of teaching to provide recommendations for future program improvements to strengthen existing teacher education programs internationally. Using both qualitative surveys and descriptive statistics, this research strives to answer the question of how to educate the strongest teacher candidates for urban classrooms worldwide

Quantum critical behavior and trap-size scaling of trapped bosons in a one-dimensional optical lattice

We study the quantum (zero-temperature) critical behaviors of confined particle systems described by the one-dimensional (1D) Bose-Hubbard model in the presence of a confining potential, at the Mott insulator to superfluid transitions, and within the gapless superfluid phase. Specifically, we consider the hard-core limit of the model, which allows us to study the effects of the confining potential by exact and very accurate numerical results. We analyze the quantum critical behaviors in the large trap-size limit within the framework of the trap-size scaling (TSS) theory, which introduces a new trap exponent theta to describe the dependence on the trap size. This study is relevant for experiments of confined quasi 1D cold atom systems in optical lattices. At the low-density Mott transition TSS can be shown analytically within the spinless fermion representation of the hard-core limit. The trap-size dependence turns out to be more subtle in the other critical regions, when the corresponding homogeneous system has a nonzero filling f, showing an infinite number of level crossings of the lowest states when increasing the trap size. At the n=1 Mott transition this gives rise to a modulated TSS: the TSS is still controlled by the trap-size exponent theta, but it gets modulated by periodic functions of the trap size. Modulations of the asymptotic power-law behavior is also found in the gapless superfluid region, with additional multiscaling behaviors.Comment: 26 pages, 34 figure

Phase-space structure of two-dimensional excitable localized structures

In this work we characterize in detail the bifurcation leading to an excitable regime mediated by localized structures in a dissipative nonlinear Kerr cavity with a homogeneous pump. Here we show how the route can be understood through a planar dynamical system in which a limit cycle becomes the homoclinic orbit of a saddle point (saddle-loop bifurcation). The whole picture is unveiled, and the mechanism by which this reduction occurs from the full infinite-dimensional dynamical system is studied. Finally, it is shown that the bifurcation leads to an excitability regime, under the application of suitable perturbations. Excitability is an emergent property for this system, as it emerges from the spatial dependence since the system does not exhibit any excitable behavior locally.Comment: 10 pages, 9 figure

A Critical Exploratory Analysis of Black Girls\u27 Achievement in 8th grade U.S. History

The purpose of this study was to utilize an ethnically homogeneous design to examine Black female student U.S. History content-specific knowledge. The study aims to elucidate the importance of single-group analyses as an alternative to between-group comparative designs. The present study utilized a critical, quantitative, descriptive research design to examine the achievement of Black girls in U.S. History from a strength-based and growth-focused perspective. The study contributes to the literature on Black girls’ achievement by applying a quantitative approach to intersectional research. This study utilized two subsamples of Black 8th grade girls from the 2006 and 2010 National Assessment of Educational Progress (N = 4,490). Mean differences in Black girls’ specialized U.S. History content knowledge were assessed using both descriptive statistics and an analysis of variance (ANOVA). The results indicate statistically significant growth overall, and on the democracy and world role domains. Data also indicate that scores on the democracy and culture domains were statistically significantly higher than scores on the technology and world role domains. This study provides implications for middle grades U.S. History achievement and the specific needs of Black girls