El Colegio de México

Aluminum (Al) is the most abundant metal in the earth's crust, but its availability depends on soil pH. Despite this abundance, Al is not considered an essential element and so far no experimental evidence has been put forward for a biological role. In plants and other organisms, Al can have a beneficial or toxic effect, depending on factors such as, metal concentration, the chemical form of Al, growth conditions and plant species. Here we review recent advances in the study of Al in plants at physiological, biochemical and molecular levels, focusing mainly on the beneficial effect of Al in plants (stimulation of root growth, increased nutrient uptake, the increase in enzyme activity, and others). In addition, we discuss the possible mechanisms involved in improving the growth of plants cultivated in soils with acid pH, as well as mechanisms of tolerance to the toxic effect of Al.

In this paper, we use data from the Mexico and U.S. population censuses to examine who migrates from Mexico to the United States and how the skills and economic performance of these individuals compare to those who remain in Mexico.We test Borjas' negative-selection hypothesis that in poor countries the individuals with the strongest incentive to migrate to rich countries are those with relatively low skill levels.We find that 1) Mexican immigrants, while much less educated than U.S. natives, are on average more educated than residents of Mexico, and 2) were Mexican immigrants in the United States to be paid according to current skill prices in Mexico they would tend to occupy the middle and upper portions of Mexico's wage distribution.These results are inconsistent with the negative-selection hypothesis and suggest, instead, that in terms of observable skills there is intermediate or positive selection of immigrants from Mexico.The results also suggest that migration abroad may raise wage inequality in Mexico.

This study has two objectives. First, it uses time-series techniques (including unit root tests) to reexamine the classic Prebisch-Singer hypothesis that the relative prices of primary commodities, in terms of manufactured goods, are characterized by secular deterioration. Second, commodity price movements are decomposed into permanent and cyclical components using the Beveridge and Nelson (1981) technique. The latter information is valuable when assessing the viability of commodity stabilization funds and formulating countercyclical macroeconomic policy responses to commodity booms and busts. Copyright 1989 by Royal Economic Society.

BACKGROUND: Denture stomatitis is associated to Candida albicans, different bacteria and other co-factors such as an acid pH, a carbohydrate ingestion increase, different systemic illnesses and pharmacological treatments. OBJECTIVE: The aim of this study was to determine Candida albicans, Staphylococcus aureus and Streptococcus mutans prevalence in the mucous membrane and prosthesis of patients with and without atrophic denture stomatitis and its relationship with other potential clinical co-factors. STUDY DESIGN: Saliva was collected from 105 patients (62 female and 43 male) wearing dental prosthesis in order to measure their pH. Oral samples of the mucous membrane and the internal surface of dental prosthesis were taken with sterile cotton to proceed with the microbiological study. The identification of the isolated microorganisms was performed using conventional microbiological methods. RESULTS: Diabetes and Hypertension were the most frequent systemic illnesses. High carbohydrate ingestion was observed in numerous patients. Atrophic denture stomatitis was reported in 50 patients and the pH average in saliva was of 5.2. The presence of C albicans, S. aureus and S. mutans in the mucous membrane and prosthesis was of 51.4%, 52.4% and 67.6%, respectively. C. albicans was isolated in 66.7% from the prosthesis, whereas S. aureus and S. mutans were isolated in 49.5% of those same prosthesis. C. albicans was isolated in 86% of the patients with atrophic denture stomatitis and S. aureus was isolated in a similar percentage (84% of patients). The isolation of S. mutans was less frequent, and it was observed in 16% of the oral samples of these patients. CONCLUSIONS: C. albicans, S. aureus and S. mutans frequently colonize the oral mucous of patients wearing dental prosthesis. This illness-bearing condition is more frequent in patients with denture stomatitis, even though dental prosthesis colonization is lower than in the oral mucous.

Commodity crop expansion, for both global and domestic urban markets, follows multiple land change pathways entailing direct and indirect deforestation, and results in various social and environmental impacts. Here we compare six published case studies of rapid commodity crop expansion within forested tropical regions. Across cases, between 1.7% and 89.5% of new commodity cropland was sourced from forestlands. Four main factors controlled pathways of commodity crop expansion: (i) the availability of suitable forestland, which is determined by forest area, agroecological or accessibility constraints, and land use policies, (ii) economic and technical characteristics of agricultural systems, (iii) differences in constraints and strategies between small-scale and large-scale actors, and (iv) variable costs and benefits of forest clearing. When remaining forests were unsuitable for agriculture and/or policies restricted forest encroachment, a larger share of commodity crop expansion occurred by conversion of existing agricultural lands, and land use displacement was smaller. Expansion strategies of large-scale actors emerge from context-specific balances between the search for suitable lands; transaction costs or conflicts associated with expanding into forests or other state-owned lands versus smallholder lands; net benefits of forest clearing; and greater access to infrastructure in already-cleared lands. We propose five hypotheses to be tested in further studies: (i) land availability mediates expansion pathways and the likelihood that land use is displaced to distant, rather than to local places; (ii) use of already-cleared lands is favored when commodity crops require access to infrastructure; (iii) in proportion to total agricultural expansion, large-scale actors generate more clearing of mature forests than smallholders; (iv) property rights and land tenure security influence the actors participating in commodity crop expansion, the form of land use displacement, and livelihood outcomes; (v) intensive commodity crops may fail to spare land when inducing displacement. We conclude that understanding pathways of commodity crop expansion is essential to improve land use governance.

Pigmentocracies--the fruit of the multiyear Project on Ethnicity Race in Latin America (PERLA)--is a richly revealing analysis of contemporary attitudes toward ethnicity race in Brazil, Colombia, Mexico, Peru, four of Latin America's most populous nations. Based on extensive, original sociological anthropological data generated by PERLA, this landmark study analyzes ethnoracial classification, inequality, discrimination, as well as public opinion about Afro-descended indigenous social movements policies that foster greater social inclusiveness, all set within an ethnoracial history of each country. A once-in-a-generation examination of contemporary ethnicity, this book promises to contribute in significant ways to policymaking public opinion in Latin America. Edward Telles, PERLA's principal investigator, explains that profound historical political forces, including multiculturalism, have helped to shape the formation of ethnic identities the nature of social relations within across nations. One of Pigmentocracies's many important conclusions is that unequal social economic status is at least as much a function of skin color as of ethnoracial identification. Investigators also found high rates of discrimination by color ethnicity widely reported by both targets and witnesses. Still, substantial support across countries was found for multicultural-affirmative policies--a notable result given that in much of modern Latin America race ethnicity have been downplayed or ignored as key factors despite their importance for earlier nation-building.

This article analyzes immigrant incorporation and transnational participation as gendered experiences. The results indicate that the incorporation of immigrants is a complex process affected negatively by class and racial exclusion and positively by their knowledge of U.S. society. The analysis also indicates that incorporation and transnational participation are concurrent and intertwined processes. Our results show that gender matters in the analysis of immigrant incorporation. The experiences of immigrant men and women share a lot in common as they confront similar challenges, but are also affected differently by the most relevant factors in the process of incorporation and transnational participation.

A milk production and digestibility trial with 32 cows (2 X 2 factorial with 8 cows per treatment) was conducted to test animal response to varying rumen degradation of dietary starch and protein. Four rations (barley-cottonseed, barley-brewers dried grains, milo-cottonseed, and milobrewers dried grains) were compared in early lactation cows fed 65% concentrate and 35% forage for 60 d. Digestibilities of starch were higher for barley than milo diets; whereas, those for organic matter were higher for cottonseed meal than brewers dried grains. Milk production was highest on barley-cottonseed with mean adjusted values of (kg/d): 37.4, 34.9, 34.2, and 34.6 for respective treatments. Dry matter intakes were not different among rations. Milk fat was higher on milo than barley with respective diets averaging (%): 3.1, 2.9, 3.4, and 3.6, and resulting in lowest FCM for the barley-brewers dried grains diet. Milk protein was not altered by treatment. These data suggest that responses to varying protein degradability can be altered by rate of starch breakdown in the rumen.

It is well recognised that unsafe abortions have significant implications for women's physical health; however, women's perceptions and experiences with abortion-related stigma and disclosure about abortion are not well understood. This paper examines the presence and intensity of abortion stigma in five countries, and seeks to understand how stigma is perceived and experienced by women who terminate an unintended pregnancy and influences her subsequent disclosure behaviours. The paper is based upon focus groups and semi-structured in-depth interviews conducted with women and men in Mexico, Nigeria, Pakistan, Peru and the United States (USA) in 2006. The stigma of abortion was perceived similarly in both legally liberal and restrictive settings although it was more evident in countries where abortion is highly restricted. Personal accounts of experienced stigma were limited, although participants cited numerous social consequences of having an abortion. Abortion-related stigma played an important role in disclosure of individual abortion behaviour.

Objetivos: Presentar un resumen de la versión del 2007 de la guía de la Asociación Europea de Urología (EAU) para el cáncer de próstata (CaP). Métodos: Se realizó por un grupo de trabajo una revisión de los nuevos datos presentes desde 2004 hasta 2007 en la literatura. Las guías han sido actualizadas y el nivel de evidencia/grado de recomendación ha sido añadido al texto basándose en una revisión sistemática de la literatura, que incluía una búsqueda de las bases de datos online y revisiones bibliográficas. Resultados: Una versión completa está disponible en la EAU Office o en www.uroweb.org. El método diagnóstico de elección es la biopsia sistematizada de la próstata bajo control ecográfico. El tratamiento activo es el recomendado en la mayoría de los pacientes con enfermedad localizada y una larga esperanza de vida, siendo la prostatectomía radical superior a la vigilancia ("watchful waiting") en un ensayo randomizado prospectivo. La prostatectomía radical con preservación de bandeletas es la técnica de elección en la enfermedad órgano-confinada; el bloqueo androgénico neoadyuvante no ha demostrado una mejoría en las variables de resultados. La radioterapia debe realizarse con al menos 72 Gy en el CaP de bajo riesgo y con 78 Gy en el de intermedio - alto riesgo. El bloqueo androgénico en monoterapia es el estándar del tratamiento en el CaP metastásico; el bloqueo androgénico intermitente podría ser un tratamiento alternativo en pacientes seleccionados. El seguimiento se basa principalmente en los niveles de PSA y en la anamnesis específica de la enfermedad, estando las pruebas de imagen sólo indicadas cuando aparecen los síntomas. La quimioterapia con docetaxel ha surgido como el tratamiento de referencia para el CaP metastásico hormonorefractario. Conclusiones: El conocimiento en el campo del CaP está rápidamente cambiando. Estas guías de la EAU resumen los hallazgos más recientes y los aplican a la práctica clínica.

In Mexico, as in most Latin American countries with indigenous populations, it is commonly believed that European phenotypes are preferred to mestizo or indigenous phenotypes. However, it is hard to test for such racial biases in the labor market using official statistics since race can only be inferred from native language. The experiment consisted on sending fictitious curriculums responding to job advertisements with randomized information of the applicants. The resumes included photographs representing three distinct phenotypes: Caucasian, mestizo, and indigenous. We find that indigenous looking females are discriminated against, but the effect is not present for males.

Chagas disease is a leading cause of heart disease affecting approximately 10 million people in Latin America and elsewhere worldwide. The two major drugs available for the treatment of Chagas disease have limited efficacy in Trypanosoma cruzi-infected adults with indeterminate (patients who have seroconverted but do not yet show signs or symptoms) and determinate (patients who have both seroconverted and have clinical disease) status; they require prolonged treatment courses and are poorly tolerated and expensive. As an alternative to chemotherapy, an injectable therapeutic Chagas disease vaccine is under development to prevent or delay Chagasic cardiomyopathy in patients with indeterminate or determinate status. The bivalent vaccine will be comprised of two recombinant T. cruzi antigens, Tc24 and TSA-1, formulated on alum together with the Toll-like receptor 4 agonist, E6020. Proof-of-concept for the efficacy of these antigens was obtained in preclinical testing at the Autonomous University of Yucatan. Here the authors discuss the potential for a therapeutic Chagas vaccine as well as the progress made towards such a vaccine, and the authors articulate a roadmap for the development of the vaccine as planned by the nonprofit Sabin Vaccine Institute Product Development Partnership and Texas Children's Hospital Center for Vaccine Development in collaboration with an international consortium of academic and industrial partners in Mexico, Germany, Japan, and the USA.

Truncations of tau protein at aspartic acid421 (D421) and glutamic acid391 (E391) residues are associated with neurofibrillary tangles (NFTs) in the brains of Alzheimer disease (AD) patients. Using immunohistochemistry with antibodies to D421- and E391-truncated tau (Tau-C3 and MN423, respectively), we correlated the presence of NFTs composed of these truncated tau proteins with clinical and neuropathologic parameters in 17 AD and 23 non-AD control brains. The densities of NFTs composed of D421- or E391-truncated tau correlated with clinical dementia index and Braak staging in AD. Glutamic acid391 tau truncation was prominent in the entorhinal cortex, whereas D421 truncation was prominent in the subiculum, suggesting that NFTs composed of either D421- or E391-truncated tau may be formed mutually exclusively in these areas. Both truncations were associated with the prevalence of the apolipoprotein E epsilon4 allele. By double labeling, intact tau in NFTs was commonly associated with D421-cleaved tau but not with E391-truncated tau; D421-cleaved tau was never associated with E391-truncated tau. These results indicate that tau is not randomly proteolyzed at different domains, and that proteolysis occurs sequentially from the C-terminus to inner regions of tau in AD progression. Identification of NFTs composed of tau at different stages of truncation may facilitate assessment of neurofibrillary pathology in AD.

"Migration reshapes rural economies in ways that may go beyond the contribution of migrant remittances to household income. Consumption and investment expenditures by migrant-sending households may transmit some of the impacts of migration to others inside and outside the rural economy, and they also may shape the potential effects of migration within the source household. Numerous studies have attempted to quantify the impact of migrant remittances on expenditures in migrant-sending households following one of two approaches. The first asks how migrant remittances are spent. It has the advantage of being simple but the significant disadvantage of ignoring the fungibility of income from migrant and nonmigrant sources. Remittances almost certainly have indirect effects on expenditures by way of their contribution to households' total budgets. The second uses a regression approach that considers remittances as an explanatory variable, in addition to total income and other controls, in a household expenditure demand system. It has the advantage of enabling one to test whether remittances affect expenditures in ways that are independent of their contribution to total income. But it does not take into account other ways, besides remittances, in which migration may influence expenditure patterns in households with migrants. It also may suffer from econometric bias resulting from the endogeneity of migration and remittance receipts. The same variables may simultaneously affect both remittances and household expenditures, and unless one controls for this, biased estimates may result. "--World Bank web site

Abstract Independent lines of research on urbanization, urban areas, and carbon have advanced our understanding of some of the processes through which energy and land uses affect carbon. This synthesis integrates some of these diverse viewpoints as a first step toward a coproduced, integrated framework for understanding urbanization, urban areas, and their relationships to carbon. It suggests the need for approaches that complement and combine the plethora of existing insights into interdisciplinary explorations of how different urbanization processes, and socio‐ecological and technological components of urban areas, affect the spatial and temporal patterns of carbon emissions, differentially over time and within and across cities. It also calls for a more holistic approach to examining the carbon implications of urbanization and urban areas, based not only on demographics or income but also on other interconnected features of urban development pathways such as urban form, economic function, economic‐growth policies, and other governance arrangements. It points to a wide array of uncertainties around the urbanization processes, their interactions with urban socio‐institutional and built environment systems, and how these impact the exchange of carbon flows within and outside urban areas. We must also understand in turn how carbon feedbacks, including carbon impacts and potential impacts of climate change, can affect urbanization processes. Finally, the paper explores options, barriers, and limits to transitioning cities to low‐carbon trajectories, and suggests the development of an end‐to‐end, coproduced and integrated scientific understanding that can more effectively inform the navigation of transitional journeys and the avoidance of obstacles along the way.

fPlates 1-15 follow index; plate 16 is in pocket] PLATE 1, 2. Early Cambrian-1 fauna. 3. Early Cambrian-2 fauna. 4. Early Cambrian-3 fauna; Middle Cambrian-1 fauna. 5. Middle Cambian-1 fauna. 6. Middle Cambrian-1, -2 fauna; Dresbachian-1 fauna. 7-9. Dresbachian-2 fauna. 10. Dresbachian-2 fauna; Franconian-1 fauna. 11-13. Franconian-2 fauna. 14. Franconian-2 fauna; Trempealeauan-1 fauna. 15. Trempealeauan-1, -2 fauna. 16. Stratigraphic occurrences of trilobites in measure*, sections, east-central Alaska and immediately adjacent Canada. FIGURE 1. Index map showing outcrop areas of Cambrian rocks in eastern Alaska and immediately adjacent parts of Cana da ___--______--_____-____

This paper describes and analyzes the characteristics of the process of economic convergence among the states and regions of Mexico during the 1940-95 period. We derive two main results from our study. First, regional disparities in Mexico declined at a rate of 1, 2 percent per year between 1940 and 1995. This rate is too low when compared to the experiences of other countries and it has been insufficient to reduce the marked regional inequality that has characterized the country since 1940. Second, we identified that the process of regional convergence in Mexico has really taken place in two stages: in the first one, from 1940 through 1960, there was a relatively rapid process of regional convergence in Mexico. During the second stage, from 1960 through 1995, the convergence process suddenly stopped and it even began to revert itself. This paper ends with a brief discussion about some alternative explanations for such pattern of regional development.// Este trabajo delinea y analiza las características del proceso de convergencia económica entre los estados regiones de México durante el período de 1940-1995. De nuestro análisis se infieren dos resultados principales. Primero las disparidades regionales en México se han reducido a una tasa de 1.2% por año entre 1940 y 1995. Esta tasa de convergencia es muy baja cuando se le compara con las experiencias de otros países, y ha sido claramente insuficiente para reducir la marcada desigualdad regional que ha caracterizado al país desde 1940. Segundo, se identificaron dos fases claramente diferenciadas del proceso de convergencia regional: la primera de ellas, de 1940 a 1960, se caracterizó por un proceso relativamente rápido de convergencia regional; durante la segunda fase, de 1960 a 1995, este proceso se detuvo de manera súbita e incluso mostró cierta tendencia a revertirse. El trabajo termina con un breve análisis de algunas explicaciones posibles de esta pauta de desarrollo regional.

This paper studies a central aspect of optimal income taxation as modelled in Mirrlees' original paper on the topic (identical leisure/consumption preferences, qualitatively homogeneous "skills" in production), namely, whether given concave utilitarianism alone the optimal marginal income tax will be non-negative. A well-known positive answer to this question (in weak inequality form) was given in the said paper which, however, we show requires additive separability of individual utility (in the ordinal and cardinal senses). Our main result here is to derive the required (strict) positivity of the marginal tax under weak conditions, slightly wider than noninferiority of consumption and leisure, with preferences otherwise arbitrary.

K-means clustering and principal component analysis (PCA) are widely used in water quality analysis and management. Nevertheless, numerous studies have pointed out that K-means with the squared Euclidean distance is not suitable for high-dimensional datasets. We evaluate a methodology (K-means based on PCA) for water quality evaluation. It is based on the PCA method to reduce the dataset from high dimensional to low for the improvement of K-means clustering. For this, a large dataset of 28 hydrogeochemical variables and 582 wells in the coastal aquifer are classified with K-means clustering for high dimensional and K-means clustering based on PCA. The proposed method achieved increased quality cluster cohesion according to the average Silhouette index. It ranged from 0.13 for high dimensional k-means clustering to 5.94 for K-means based on PCA and the practical spatial geographic information systems (GIS) evaluation of clustering indicates more quality results for K-means clustering based on PCA. K-means based on PCA identified three hydrogeochemical classes and their sources. High salinity was attributed to seawater intrusion and the mineralization process, high levels of heavy metals related to domestic-industrial wastewater discharge and low heavy metals concentrations were associated with industrial wastewater punctual discharges. This approach allowed the demarcation of natural and anthropogenic variation sources in the aquifer and provided greater certainty and accuracy to the data classification.

Abstract An analysis of nationally representative panel data from rural Mexico, with observations in years 2002, 2007, and 2010, suggests that the same shift out of farm work that characterized U.S. labor history is well underway in Mexico. Meanwhile, the demand for agricultural labor in Mexico is rising. In the future, U.S. agriculture will compete with Mexican farms for a dwindling supply of farm labor. Since U.S. domestic workers are unwilling to do farm work and the United States can feasibly import farm workers from only a few countries in close geographic proximity, the agricultural industry will eventually need to adjust production to use less labor. The decline in foreign labor supply to farms in the United States ultimately will need to be accompanied by farm labor conservation, switching to less labor intensive crops and technologies, and labor management practices that match fewer workers with more farm jobs.