Long-Time Evolution of Gas-Free Disc Galaxies in Binary Systems

We present the results of several detailed numerical N-body simulations of the dynamical interactions of two equal mass disc galaxies. Both galaxies are embedded in spherical halos of dark matter and contain central bulges. Our analysis of the dynamical evolution of the binary system focuses on the morphological evolution of the stellar distribution of the discs. The satellite galaxy has coplanar or polar disc orientation in relation to the disc of the primary galaxy and their initial orbits are prograde eccentric ($e=0.1$, $e=0.4$ or $e=0.7$). Both galaxies have mass and size comparable to the Milky Way. We show that the merger of the two disc galaxies, depending on the relative orientation of the discs, can yield either a disc or lenticular remnant, instead of an elliptical one. These are the first simulations in the literature to show the formation of S0-like galaxies from protracted binary galaxy interactions. Additionally, we demonstrate that the time to merger increases linearly with the initial apocentric distance between the galaxies, and decreases with the initial orbital eccentricity. We also show that the tidal forces of the discs excite transient $m=1$ and $m=2$ wave modes, i.e., lopsidedness, spiral arms, and bars. However, after the merging of the discs, such instabilities fade completely, and the remnant is thicker and bigger than the original discs. The maximum relative amplitude of these waves is at most about 15 times greater compared to the control case. of these two wave modes. Finally, the disc settles down quickly, after the merger, in less than one outer disc rotation period.Comment: 23 pages, 3 tables and 16 figures. Accepted for publication in A&

Non-agricultural land use and land reform: theory and evidence from Brazil

This paper examines the effect of nonagricultural land use on agrarian organization and land reform, providing a simple model to determine its policy implications and some evidence on its importance. It is argued that, if land-rental market is imperfect, there is a role for redistributive land policies and the following implications hold: (i) land reform is more probable to enhance efficiency in a low-wage economy; (ii) such policies should aim small farmers instead of landless people, obtaining land from large landholders. Empirical evidence suggests this is a relevant issue in Brazil, specially during periods of high macroeconomic instability.land reform; land use; agricultural development

Land taxes in a Latin American context

Since Henry George (1839-1897) economists have been arguing that a tax on unim- proved land is an ideal tax on e¢ ciency grounds. Output taxes, on the other hand, have distortional e¤ects on the economy. This paper shows that under asymmetric information output tax might be used along with land tax in order to implement the optimal taxation scheme in a Latin-American context, i.e., in an economy with imperfect land-rental market, non-agricultural land use and non-revenue objectives of land taxation. Also, we show that: (i) schemes based on land taxes alone might not be implementable; and (ii) tax evasion is more acute among large landholders.Optimal taxation, tax evasion, land use.

Financial constraints, migration and inequality

Although the self-selection of emigrants is determined by di¤erences in the returns to education, according to the celebrated Roy model, empirical evidence suggests that migrants tend to be favorably selected. This paper argues that financial con- straints might be useful to explain this controversy. These constraints might impose positive correlations between (i) wealth and education, and (ii) wealth and migra- tion, implying a positive bias in the empirical results. We also show that high levels of migration premium and return to education in the source country explain the migration of middle-class individuals, a situation in which migration increases in- equality in the home country.migration, financial constraints, self-selection, human capital

BIOECONOMIC MANAGEMENT OF RED SWAMP CRAYFISH (PROCAMBARUS CLARKII) IN THE PRESENCE OF ENVIRONMENTAL EXTERNALITIES

Red swamp crayfish (Procambarus clarkii) is a valuable renewable resource which creates significant negative externalities to its environment. Crayfish can cause severe crop damage by burrowing in fields and using irrigation systems to spread. These crayfish are resistant to normal dosages of pesticides which are harmful to fish and birds, can endure months of dryness, and live in a low oxygen environment. This paper presents a simple bioeconomic model for optimal use of the red swamp crayfish accounting for its value in consumption, adapting Plourde's (1970) model to include the negative externalities.Resource /Energy Economics and Policy,

¿Por qué nos estamos enfermando?

Pese a los avances de la medicina, las técnicas modernas de exámenes dediagnósticos y el eficiente sistema de producción y abastecimiento de alimentos,los índices de enfermedades crónicas y degenerativas son cada vez másalarmantes en todo el mundo. Este artículo propone una reflexión a la preguntade por qué nos estamos enfermando, a partir de una visión Epigenética y dela constatación que nuestra microbiota intestinal es considerada un órgano(virtual) en nuestro organismo. La alimentación basada predominantemente enplantas, ayuda en la mantención de la salud previniendo enfermedades, por losnutrientes y compuestos funcionales que entrega y además por ser fuente de prey probióticos, garantizando así el equilibrio de la flora intestinal.Palabras claves: Epigenética, salud, microbiota intestinal, alimentación basadaen plantas

ANÁLISE DA EVOLUÇÃO DAS ÁREAS VERDES URBANAS – VILA NOVA – JOINVILLE/SC

Este artigo apresenta uma avaliação da evolução das áreas verdes urbanas do perímetro amostral do município de Joinville no lapso temporal compreendido entre os anos de 1989 e 2007. É realizada uma análise do modo com que essas transformações ocorreram, como foram alterados os limites das referidas áreas e de que modo que essas modificações se relacionaram com a legislação pertinente – quer seja ela municipal, estadual e nacional. Dentro dessa análise, é considerada, de maneira especial, a influência do Plano Diretor na conformação dessas áreas verdes urbanas