Regional Evolutions

macroeconomics, regional evolutions

Wage Dynamics: Reconciling Theory and Evidence

U.S. macroeconomic evidence shows a negative relation between the rate of change of wages and unemployment. In contrast, most theories of wage determination imply a negative relation between the level of wages and unemployment. In this paper, we ask whether one can reconcile the empirical evidence with theoretical wage relations. We reach three main conclusions. First, we derive the condition under which the two can indeed be reconciled. We show the constraints that such a condition imposes on the determinants of workers' reservation wages as well as the relative importance of workers' outside options as opposed to match specific productivity in wage determination. Second, in the light of this condition, we reinterpret the presence of an "error correction" term in macroeconomic wage relations for most European economies but not in the United States. Third, we show that whether this condition holds or not has important implications for the effects of a number of variables -- from real interest rates to oil prices to payroll taxes -- on the natural rate of unemployment.

Inference and Evaluation of the Multinomial Mixture Model for Text Clustering

In this article, we investigate the use of a probabilistic model for unsupervised clustering in text collections. Unsupervised clustering has become a basic module for many intelligent text processing applications, such as information retrieval, text classification or information extraction. The model considered in this contribution consists of a mixture of multinomial distributions over the word counts, each component corresponding to a different theme. We present and contrast various estimation procedures, which apply both in supervised and unsupervised contexts. In supervised learning, this work suggests a criterion for evaluating the posterior odds of new documents which is more statistically sound than the "naive Bayes" approach. In an unsupervised context, we propose measures to set up a systematic evaluation framework and start with examining the Expectation-Maximization (EM) algorithm as the basic tool for inference. We discuss the importance of initialization and the influence of other features such as the smoothing strategy or the size of the vocabulary, thereby illustrating the difficulties incurred by the high dimensionality of the parameter space. We also propose a heuristic algorithm based on iterative EM with vocabulary reduction to solve this problem. Using the fact that the latent variables can be analytically integrated out, we finally show that Gibbs sampling algorithm is tractable and compares favorably to the basic expectation maximization approach

What We Know and Do Not Know About the Natural Rate of Unemployment

Over the past three decades, a large amount of research has attempted to identify the determinants of the natural rate of unemployment. It is this body of work we assess in this paper. We reach two main conclusions. First, there has been considerable theoretical progress over the past 30 years. A framework has emerged. We present it, and show how it can be used to think for example about the relation between technological progrss and unemployment. Second, empirical knowledge lags behind. Economists do not have a good quantitative understanding of the determinants of the natural rate, either across time or across countries. We look at two issues, the relation of wages to unemployment, and the risk of European unemployment.

Mineral Contamination from Cemetery Soils: Case Study of Zandfontein Cemetery, South Africa

The burial of coffins may pose an environmental and health hazard since the metals that are used in coffin-making may corrode or degrade into harmful toxins. These may leach into the surrounding soils and groundwater. Very little research has been conducted world-wide on the mineral contamination potential of cemeteries, and virtually none in South Africa. The aim of the study is to determine whether burial practices affect the mineral content of soils in cemeteries. This was done by comparing the mineral concentrations of soils within the Zandfontein Cemetery in Tshwane (Gauteng, South Africa) to those off-site as well as those in zones with high burial loads with those zones with fewer burials. Twenty three soil samples were collected from various sites on- and off-site and analyzed for 31 minerals using ICP-AES. It was found that mineral concentrations of soils within the Zandfontein Cemetery were considerably higher than those off-site. Soil samples in multiple burials blocks also have elevated metal concentrations. These excess metals are probably of anthropogenic origin associated with burial practices and could pose an environmental and human health hazard. Strict monitoring of water quality in boreholes in the vicinity of the cemetery is recommended

A matrix model for the topological string II: The spectral curve and mirror geometry

In a previous paper, we presented a matrix model reproducing the topological string partition function on an arbitrary given toric Calabi-Yau manifold. Here, we study the spectral curve of our matrix model and thus derive, upon imposing certain minimality assumptions on the spectral curve, the large volume limit of the BKMP "remodeling the B-model" conjecture, the claim that Gromov-Witten invariants of any toric Calabi-Yau 3-fold coincide with the spectral invariants of its mirror curve.Comment: 1+37 page

Electric-Field-Induced Mott Insulating States in Organic Field-Effect Transistors

We consider the possibility that the electrons injected into organic field-effect transistors are strongly correlated. A single layer of acenes can be modelled by a Hubbard Hamiltonian similar to that used for the kappa-(BEDT-TTF)(2)X family of organic superconductors. The injected electrons do not necessarily undergo a transition to a Mott insulator state as they would in bulk crystals when the system is half-filled. We calculate the fillings needed for obtaining insulating states in the framework of the slave-boson theory and in the limit of large Hubbard repulsion, U. We also suggest that these Mott states are unstable above some critical interlayer coupling or long-range Coulomb interaction.Comment: 9 pages, 7 figure

Perspectives in Fundamental Physics in Space

We discuss the fundamental principles underlying the current physical theories and the prospects of further improving their knowledge through experiments in space.Comment: Gravitational waves, gravitomagnetism, Equivalence Principle, Antimatter, Pioneer Anomaly, Lorentz invariance. To appear in IAA - Acta Astronautica Journal (2006

Advances in Human-Protein Interaction - Interactive and Immersive Molecular Simulations

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