X-ray Imaging of Alloy Solidification: Crystal Formation,Growth, Instability and Defects

Synchrotron and laboratory-based X-ray imaging techniques have been increasingly used for in situ investigations of alloy solidification and other metal processes. Several reviews have been published in recent years that have focused on the development of in situ X-ray imaging techniques for metal solidification studies. Instead, this work provides a comprehensive review of knowledge provided by in situ X-ray imaging for improved understanding of solidification theories and emerging metal processing technologies. We first review insights related to crystal nucleation and growth mechanisms gained by in situ X-ray imaging, including solute suppressed nucleation theory of α-Al and intermetallic compound crystals, dendritic growth of α-Al and the twin plane re-entrant growth mechanism of faceted Fe-rich intermetallics. Second, we discuss the contribution of in situ X-ray studies in understanding microstructural instability, including dendrite fragmentation induced by solute-driven, dendrite root re-melting, instability of a planar solid/liquid interface, the cellular-to-dendritic transition and the columnar-to-equiaxed transition. Third, we review investigations of defect formation mechanisms during near-equilibrium solidification, including porosity and hot tear formation, and the associated liquid metal flow. Then, we discuss how X-ray imaging is being applied to the understanding and development of emerging metal processes that operate further from equilibrium, such as additive manufacturing. Finally, the outlook for future research opportunities and challenges is presented.     

Twin anemia‐polycythemia sequence with suspected cardiac dysfunction

We present a case of twin anemia‐polycythemia sequence diagnosed postnatally with suspected chronic stress on the heart in the donor twin.     

Twins: a test of the equal environments assumption

We asked a sample of 343 adult same-sex twin pairs a number of questions about the similarity of their social environment during childhood and early adolescence. A factor analysis of their responses indicated that their common environment was derived from two sources, one being similar treatment "imposed" upon them by their parents, the other being "elicited" by the twins' similar interests and behavior. Monozygotic (MZ) twins reported experiencing more similar "imposed" and "elicited" environments than dizygotic (DZ) twins. The extent of imposed similar treatment received during childhood and early adolescence was unrelated to either MZ or DZ twins' current behavioral similarity, as indicated by absolute intrapair differences in their Neuroticism, Anxiety, and Depression scores. Similar treatment imposed upon MZ twins on the basis of their zygosity alone is therefore not a threat to the validity of the twin method.     

Genetic factors and susceptibility to falls in older women

OBJECTIVES: To determine whether genetic influences account for individual differences in susceptibility to falls in older women. DESIGN: Prospective twin cohort study. SETTING: Research laboratory and residential environment. PARTICIPANTS: Ninety-nine monozygotic (MZ) and 114 dizygotic (DZ) female twin pairs aged 63 to 76 from the Finnish Twin Cohort study. MEASUREMENTS: The participants recorded their falls on a calendar for an average+/-standard deviation of 344+/-41 days. Reported falls were verified via telephone interview, and circumstances, causes, and consequences of the fall were asked about. RESULTS: The total number of falls was 434, of which 188 were injurious; 91 participants had two or more falls. Casewise concordance was 0.61 (95% confidence interval (CI)=0.49-0.72) for MZ twins and 0.49 (95% CI=0.37-0.62) for DZ twins for at least one fall, 0.38 (95% CI=0.23-0.53) for MZ and 0.33 (95% CI=0.17-0.50) for DZ twins for at least one injurious fall, and 0.43 (95% CI=0.26-0.60) for MZ and 0.36 (95% CI=0.17-0.55) for DZ twins for recurrent falls. On average, the proportion of familial influences accounting for the individual differences in susceptibility to at least one fall was 30% and to recurrent falls was 40%; nongenetic familial and nonfamilial factors alone accounted for susceptibility to at least one injurious fall. CONCLUSION: In community-dwelling older women, familial factors underlie the risk of falling but not the risk of injurious falls.     

Can color difference on the maternal side of the placenta distinguish between acute peripartum twin–twin transfusion syndrome and twin anemia–polycythemia sequence?

ObjectiveTo investigate the color difference between two placental shares in monochorionic placentas with acute peripartum twin–twin transfusion syndrome (TTTS) and twin anemia–polycythemia sequence (TAPS).MethodsWe evaluated all digital pictures of TAPS, acute peripartum TTTS and a control group of uncomplicated monochorionic placentas examined at our center. We determined the color intensity of the individual placental share on the maternal side of each monochorionic placenta using an image–processing program and calculated the color difference ratio (CDR).ResultsDigital pictures of 5 acute peripartum TTTS, 25 TAPS and 54 control group placentas were included in this study. The median CDR in acute peripartum TTTS was significantly lower compared to TAPS placentas, 1.20 (inter-quartile range (IQR) 1.05–1.20) and 2.50 (IQR 1.85–3.34), respectively (p < 0.01), and was comparable to the control group (CDR 1.11, IQR 1.05–1.22).ConclusionTAPS placentas have a higher CDR compared to acute peripartum TTTS placentas. Examining color difference on the maternal side of the placenta might help distinguish between acute peripartum TTTS and TAPS.