The transformation of the aluminum-zinc eutectoid alloy at subcritical temperatures

Interest in the mechanism of the austenite eutectoid transformation in iron-carbon alloys, especially as produced by the isothermal sub-critical techniques introduced by Davenport and Bain, has resulted in the application of similar heat treatment studies to the eutectoid transformations in other alloy systems. The study of the eutectoid transformation is of both fundamental and industrial interest because past experience has shown that these studies yielded much information concerning the nature and mechanism of the changes in eutectoid alloys during the decomposition of the phase stable at high temperatures and has also contributed much toward the development of new properties to be attained by heat treatment methods never before attempted. The desire of the author to know more about the exact nature of eutectoid transformations, in general, and to study, in particular, the transformation in a system which had heretofore been only partially investigated has led to choice of this research topic. Therefore, the object of this investigation is to attempt to determine the rate of transformation of the aluminum - zinc eutectoid alloy (79.0% zinc) at several subcritical temperatures. A number of more or less reliable methods have been used for the study of the rate of transformation of austenite at subcritical temperatures. The author began this research with the intention of utilizing the technique of Davenport and Bain in which the progress of transformation is followed by metallographic examination. However, the method was discarded as impractical because of the nature of the transformation. In this particular eutectoid alloy, the decomposition of the solid solution which is stable at high temperatures is manifested by the evolution of heat. The author has attempted to establish the onset and completion of transformation by measurement of this heat evolution against time and, from this data, to construct a Time-Temperature-Transformation curve for the alloy --Introduction, pages 1-2

Prevalence of Undiagnosed Hypoxemia in Adults and Children in an Under-Resourced District Hospital in Zambia

Background: In adequately resourced clinical environments, diagnosis of hypoxemia via pulse oximetry is routine. Unfortunately, pulse oximetry is rarely utilized in under-resourced hospitals in developing countries. Aim: The prevalence of undiagnosed hypoxemia among adults and children with illnesses other than pneumonia in these environments remains poorly described. Methods: This cross-sectional analysis of the prevalence of hypoxemia was conducted in Kapiri Mposhi, Zambia, at the 60-bed District Hospital, which serves a population of 320,000. The resting room air oxygen saturations of two consecutive samples of all adult and pediatric inpatients were measured in December 2008 and March 2009 using handheld pulse oximetry. Hypoxemia was defined as resting room air SpO$_{2}$ less than 90%. Results: A total of 192 patients were enrolled: 68 young children (<5 years old), 15 older children (5-17 years old), and 109 adults (≥18 old). Five young children (7%), 0 older children (0%), and 10 adults (9%) were hypoxemic. No hypoxemic patients were receiving oxygen therapy at the time of diagnosis. Pneumonia, tuberculosis, and malnutrition were the most common conditions among those with hypoxemia. Oximetry data changed clinical management in all observed cases of hypoxemia and several cases of normoxemia, leading to application of supplemental oxygen, initiation of further diagnostic testing, prolongation of inpatient stay, or expedited discharge home. Conclusions: Undiagnosed hypoxemia is present among inpatients at this district hospital in rural Zambia with high prevalence in both adults and young children. These results support routine screening for hypoxemia in similar facilities in both age groups. Further investigation is warranted into the clinical impact and cost-effectiveness of pulse oximetry, provision of oxygen concentrators, and training on their use in developing countries

Maternal concentration of polychlorinated biphenyls and dichlorodiphenyl dichlorethylene and birth weight in Michigan fish eaters: a cohort study

BACKGROUND: Studies on maternal exposure to polychlorinated biphenyls (PCBs) reported inconsistent findings regarding birth weight: some studies showed no effect, some reported decreased birth weight, and one study found an increase in weights. These studies used different markers of exposure, such as measurement of PCBs in maternal serum or questionnaire data on fish consumption. Additionally maternal exposures, such as dichlorodiphenyl-dichloroethylene (DDE), which are related to PCB exposure and may interfere with the PCB effect, were rarely taken into account. METHODS: Between 1973 and 1991, the Michigan Department of Community Health conducted three surveys to assess PCB and DDE serum concentrations in Michigan anglers. Through telephone interviews with parents, we gathered information on the birth characteristics of their offspring, focusing on deliveries that occurred after 1968. We used the maternal organochlorine (OC) measurement closest to the date of delivery as the exposure. Although one mother may have contributed more than one child, serum concentrations derived from measurements in different surveys could vary for different children from the same mother. The maternal DDE and PCB serum concentrations were categorized as follows: 0 -< 5 microg / L, 5 -< 15 microg / L, 15 -< 25 microg / L, ≥25 microg / L. Using repeated measurement models (Generalized Estimation Equation), we estimated the adjusted mean birth weight controlling for gender, birth order, gestational age, date of delivery as well as maternal age, height, education, and smoking status. RESULTS: We identified 168 offspring who were born after 1968 and had maternal exposure information. We found a reduced birth weight for the offspring of mothers who had a PCB concentration ≥25 microg / L (adjusted birth weight = 2,958 g, p = 0.022). This group, however, was comprised of only seven observations. The association was not reduced when we excluded preterm deliveries. The birth weight of offspring was increased in women with higher DDE concentrations when controlling for PCBs; however, this association was not statistically significant. CONCLUSION: Our results contribute to the body of evidence that high maternal serum PCB concentration may reduce the birth weight in offspring. However, only a small proportion of mothers may actually be exposed to PCB concentrations ≥25 microg / L