Calcium Triplet Synthesis

We present theoretical equivalent widths for the sum of the two strongest lines of the Calcium Triplet, CaT index, in the near-IR, using evolutionary techniques and the most recent models and observational data for this feature in individual stars. We compute the CaT index for Single Stellar Populations (instantaneous burst, standard Salpeter-type IMF) at four metallicities, Z=0.004, 0.008, 0.02 (solar) and 0.05, and ranging in age from very young bursts of star formation (few Myr) to old stellar populations, up to 17 gyr, representative of globular clusters, elliptical galaxies and bulges of spirals. The interpretation of the observed equivalent widths of CaT in different stellar systems is discussed. Composite-population models are also computed as a tool to interpret the CaT detections in star-forming regions, in order to disantangle between the component due to Red Supergiants stars, RSG, and the underlying, older, population. CaT is found to be an excellent metallicity-indicator for populations older than 1 Gyr, practically independent of the age. We discuss its application to remove the age- metallicity degeneracy, characteristic of all studies of galaxy evolution based on the usual integrated indices (both broad band colors and narrow band indices). The application of the models computed here to the analysis of a sample of elliptical galaxies will be discussed in a forthcoming paper (Gorgas et al. 1998).Comment: 17 pages, 7 figures, to be published in A&

A treacherous journey through Latin America: The plight of Black African and Haitian migrants forced to remain in Mexico

The growing presence of Black African and Haitian migrants in Mexico poses a new set of challenges to a country that is already struggling to recognize the presence of Afro-Mexicans and where mestizaje still dominates the national discourse on race. Due to restrictive U.S. and Mexican immigration policies since 2016, many of these migrants have found themselves forced to remain in a country they had only intended to transit through on their journey northward to the U.S. Mexico has only recently taken the necessary steps to recognize its Afro-Mexican population which had been marginalized and erased from history. This paper aims to shed light on the specific issues affecting Black, non-Spanish speaking migrants in Mexico due to their intersecting identities by using a mixed-methods approach. It analyzes 86 responses obtained from an online survey administered in Spanish to Afro-Mexicans in order to learn about their experiences as Black Mexicans and to draw a connection between their experiences as Black Mexicans and those of Black African and Haitian migrants in Mexico. It also draws on 23 in-depth semi-structured interviews conducted in French and English with Black African and Haitian migrants in Tijuana and Mexico City and analyzes U.S. and Mexican immigration policies affecting these communities. Black African and Haitian migrants face challenges due to their status as migrants, their race in a country where the majority of the population is not Black and their lack of Spanish which hinders their access to services and makes navigating Mexico harder. Appropriate measures should be taken by the Mexican government to provide assistance and support to these Black African and Haitian migrants, whose intersecting identities increase their vulnerabilities

Does red blood cell distribution width (RDW) improve evaluation of microcytic anaemias?

Abstract The red cell distribution width (RDW) is an index of the variation in red cells size (anisocytosis). A study was conducted to examine the validity of using RDW in improving classification of microcytic anaemias. A total of 300 blood samples collected from a patient population aged 3 months to 55 years who were referred for haemoglobin electrophoresis were examined at The Aga Khan University Hospital (AKUH). On complete blood count, initially 200 patients (66.6%) were found to have hypochromic microcytic anaemia. Following haemoglobin electrophoresis 41% (821200) patients were diagnosed to have thalassemia minor and 59% (1181200) had hypochromic microcytic anaemia with either a normal haemoglobin paltern or an abnormal haemoglobin. The mean (± SD) RDW estimated in 250 apparently healthy Pakistani population was 14 (+ 1.5%). Elevated RDW of 23% was present in 94% (110/118) of the patients with hypochromic microcytic anaemia due to other causes, whereas 48% (39/82) of the patients with thalassemia minor had elevated RDW of 16%. Also, of the 82 thalassemia minor, 28 patients had normal haemoglobin level, of which 6 had elevated RDW and of the 54 with low haemoglobin level, 35 had elevated RDW. RDW was normal in 41 patients with thalassemia minor trait. Our results suggest that RDW alone cannot be used as a reliable indicator to distinguish between thalassemia minor and other causes of microcytosis (JPMA 43:149, 1993)