The Extreme Scattering Event Toward PKS 1741-038: VLBI Images

(Abridged) We report multi-epoch VLBI observations of the source PKS 1741-038 as it underwent an extreme scattering event. Observations at four epochs were obtained, and images were produced at three of these. During the event the source consisted of a dominant, compact component, essentially identical to the structure seen outside the event. However, the source's diameter increased slightly at 13 cm during the ESE. An increase in the source's diameter is inconsistent with a simple refractive model. We also see no evidence for ESE-induced substructure within the source or the formation of multiple images, as would occur in a strongly refractive lens. However, a model in which the decrease in flux density during the ESE occurs solely because of stochastic broadening within the lens requires a larger broadening diameter during the ESE than is observed. Thus, the ESE toward 1741-038 involved both stochastic broadening and refractive defocussing within the lens. If the structure responsible for the ESE has a size of order 1 AU, the level of scattering within an ESE lens may be a factor of 10^7 larger than that in the ambient medium. A filamentary structure could reduce the difference between the strength of scattering in the lens and ambient medium, but we conclude that, if ESEs arise from filamentary structures, they occur when the filamentary structures are seen lengthwise. We predict the amount of pulse broadening that would result from a comparable lens passing in front of a pulsar. The pulse broadening would be no more than 1.1 microseconds, consistent with the lack of pulse broadening detected during ESEs toward the pulsars PSR B1937+21 and PSR J1643-1224.Comment: 19 pages, LaTeX2e with AASTeX-4.0, 1 LaTeX table and 5 figures in 9 PostScript files, to be published in the ApJ, minor change in Figures 2a, 3a, and 4a to correct a labe

The pheno-genotypic characteristics of infantile acute leukemia in a regional cancer center from South India

Introduction: Acute leukemia (AL) is uncommon in infants, with an annual incidence of 30 per million live births. They have peculiar biological characteristics. Although remarkable progress is seen in treatment of childhood AL, infantile AL remains a resistant subset with a dismally low 4-year survival of 35%. Objectives: To study the morphological, immunophenotypic, and cytogenetic features of infantile AL. A retrospective study of AL cases in children from birth up to 1 year of age, presenting to the departments of pediatric oncology and hematopathology between January 2010 and April 2015, was conducted. Results: Thirty-eight cases of infantile AL were included. The mean age at presentation was 10.2 months, and a female preponderance (M–F ratio: 0.65:1) was noted. Hyperleukocytosis (total white cell count >50 × 109/mm3) was seen in 13 (39.4%) cases. Immunophenotyping done in 31 cases showed pre-B acute lymphoblastic leukemia (B ALL) in 18 (58%), pre-T ALL in three (9.7%), and acute myeloid leukemia (AML) in 10 (32.3%). CD10 positivity was seen in 12 (57.1%) cases of ALL. Cytogenetic study done in 34 cases showed AML with recurrent genetic abnormalities in four. Mixed lineage leukemia (11q23) abnormality was seen in three cases of ALL. Two cases of AML were associated with trisomy 21. One case with features of AML M7 in a 4-day-old baby turned out to be transient abnormal myelopoiesis on follow-up. Conclusion: Literature on infantile AL from Indian studies is scarce compared to the available Western literature. Hence an epidemiological study of AL cases was done with review of literature, in an attempt to understand their pheno-genotypic features that influence their behavior. This may help in standardizing the treatment of these rare cases