Chromatic periodic activity down to 120 megahertz in a fast radio burst.

Fast radio bursts (FRBs) are extragalactic astrophysical transients1 whose brightness requires emitters that are highly energetic yet compact enough to produce the short, millisecond-duration bursts. FRBs have thus far been detected at frequencies from 8 gigahertz (ref. 2) down to 300 megahertz (ref. 3), but lower-frequency emission has remained elusive. Some FRBs repeat4-6, and one of the most frequently detected, FRB 20180916B7, has a periodicity cycle of 16.35 days (ref. 8). Using simultaneous radio data spanning a wide range of wavelengths (a factor of more than 10), here we show that FRB 20180916B emits down to 120 megahertz, and that its activity window is frequency dependent (that is, chromatic). The window is both narrower and earlier at higher frequencies. Binary wind interaction models predict a wider window at higher frequencies, the opposite of our observations. Our full-cycle coverage shows that the 16.3-day periodicity is not aliased. We establish that low-frequency FRB emission can escape the local medium. For bursts of the same fluence, FRB 20180916B is more active below 200 megahertz than at 1.4 gigahertz. Combining our results with previous upper limits on the all-sky FRB rate at 150 megahertz, we find there are 3-450 FRBs in the sky per day above 50 Jy ms. Our chromatic results strongly disfavour scenarios in which absorption from strong stellar winds causes FRB periodicity. We demonstrate that some FRBs are found in 'clean' environments that do not absorb or scatter low-frequency radiation.

Longitudinal relations between skin tone and self-esteem in African American girls.

We examined developmental changes in self-esteem from late childhood to late adolescence in African American girls (N = 124), comparing skin tone groups. Girls completed a measure of self-esteem when they were in Grades 5, 7, 10, and 12, and in Grade 12 their skin tone was rated on a 3-point scale (1 = Light, 2 = Medium, 3 = Dark). Girls with lighter skin reported higher self-esteem than dark and medium-toned girls in Grades 5 and 7, and their self-esteem remained high across the seven years of the study. The self-esteem of dark- and medium-skinned girls increased in high school such that at Grade 12, medium-skinned girls had higher self-esteem than dark-skinned girls, who did not differ from light-skinned girls. The results are discussed in terms of theory-building on the topic of colorism. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

A composite noninvasive index correlates with liver fibrosis scores in post-Fontan patients: Preliminary findings.

OBJECTIVE: We hypothesized that clinic-based, hepatic-ultrasound, elastography measurements, either alone or in combination with other noninvasive variables, might correlate with liver-biopsy fibrosis scores in patients post-Fontan. METHODS: Between March 2012 and February 2017, we identified patients post-Fontan that underwent elective cardiac catheterization and simultaneous transvenous hepatic biopsy. From this group, we selected patients that met inclusion criteria for liver-ultrasound, shear-wave elastography. Utilizing the results of elastography, laboratory testing, and time post-Fontan, we constructed a composite Fontan hepatic index as a sum of elastography measurements in kilopascals, model for end-stage liver disease excluding INR scores, and the square root of the number of years post-Fontan. Further, we analyzed correlations between Fontan hepatic index values and fibrosis scores from hepatic biopsy. RESULTS: We identified a total of 79 post-Fontan patients that underwent cardiac catheterization and liver biopsy. Of the 79 patients, 53 met inclusion criteria, and 32 consented to undergo hepatic-ultrasound elastography. Of the 32 that underwent elastography, data from 30 patients was used for analysis. We found no statistically significant differences in demographics, laboratory values, or cardiac catheterization data between the 30 included patients and the 21 that did not participate. Utilizing data from the 30 included patients, we found a strong, highly statistically significant correlation between the Fontan hepatic index values and total fibrosis scores (R = 0.8, P < .00001). However, the cohort size prevented reliable discriminating cut-off values for the range of total fibrosis scores. CONCLUSIONS: In a small cohort of patients post-Fontan, preliminary findings suggest that the composite Fontan hepatic index might be a clinically useful, noninvasive method of serially monitoring for hepatic fibrosis. Further studies, with large patient cohorts, are necessary to validate our findings and develop clinically useful discriminatory cutoff values.

Bidirectional influence between African American mothers' and children's racial centrality from elementary through high school.

For many African Americans, racial identity is an important aspect of their individual identity. We explored developmental change and stability of individual differences in the racial centrality of African American youths and their mothers as well as the relation between maternal and child racial centrality across time. African American youths (N = 380) and mothers completed surveys when youths were in grades 5, 7, 10, and 12. Mean levels of youths' racial centrality did not increase or decrease across the 7 years of the study. The stability of individual differences in youths' racial centrality increased across time, reaching adult levels by high school. Cross-lagged panel analyses showed relations between mothers' and children's racial centrality in middle adolescence but not in early and late adolescence. Results document that the importance of race to the personal identities of African American youths does not show normative developmental change across adolescence, and only minimal change is linked to maternal influence. (PsycINFO Database Record

Inequitable Chronic Lead Exposure: A Dual Legacy of Social and Environmental Injustice.

Both historic and contemporary factors contribute to the current unequal distribution of lead in urban environments and the disproportionate impact lead exposure has on the health and well-being of low-income minority communities. We consider the enduring impact of lead through the lens of environmental justice, taking into account well-documented geographic concentrations of lead, legacy sources that produce chronic exposures, and intergenerational transfers of risk. We discuss the most promising type of public health action to address inequitable lead exposure and uptake: primordial prevention efforts that address the most fundamental causes of diseases by intervening in structural and systemic inequalities.

Intergroup Cooperation in Common Pool Resource Dilemmas.

Fundamental problems of environmental sustainability, including climate change and fisheries management, require collective action on a scale that transcends the political and cultural boundaries of the nation-state. Rational, self-interested neoclassical economic theories of human behavior predict tragedy in the absence of third party enforcement of agreements and practical difficulties that prevent privatization. Evolutionary biology offers a theory of cooperation, but more often than not in a context of discrimination against other groups. That is, in-group boundaries are necessarily defined by those excluded as members of out-groups. However, in some settings human's exhibit behavior that is inconsistent with both rational economic and group driven cooperation of evolutionary biological theory. This paper reports the results of a non-cooperative game-theoretic exercise that models a tragedy of the commons problem in which groups of players may advance their own positions only at the expense of other groups. Students enrolled from multiple universities and assigned to different multi-university identity groups participated in experiments that repeatedly resulted in cooperative outcomes despite intergroup conflicts and expressions of group identity. We offer three possible explanations: (1) students were cooperative because they were in an academic setting; (2) students may have viewed their instructors as the out-group; or (3) the emergence of a small number of influential, ethical leaders is sufficient to ensure cooperation amongst the larger groups. From our data and analysis, we draw out lessons that may help to inform approaches for institutional design and policy negotiations, particularly in climate change management.

Comparison of amniotic and intramembranous unidirectional permeabilities in late-gestation sheep.

OBJECTIVE: Amniotic fluid volume is regulated by the intrinsic modulation of intramembranous absorption. However, neither the mechanisms nor the rate-limiting barriers of this transport are known. We tested the hypothesis that the amnion is the rate-limiting barrier of intramembranous absorption by comparing unidirectional permeabilities of the amnion in vitro and the intramembranous pathway in vivo. STUDY DESIGN: Unidirectional permeabilities to 99m technetium pertechnate or [14 C]inulin of fresh ovine amnion were measured in vitro in a Ussing chamber; the permeability-surface area products were calculated by the multiplication of the permeabilities by gestational age-specific amniotic surface areas. Unidirectional permeabilities of the intramembranous pathway of the 2 tracers were calculated from solute fluxes between amniotic fluid and fetal blood in chronically catheterized late-gestation fetal sheep. Statistical comparisons included t -tests, least squares regression, analysis of variance, and analysis of covariance. RESULTS: In the isolated amnion in vitro, the ratio of permeabilities in the amniotic fluid to chorionic direction and the reverse direction was not significantly different from unity for 99m technetium pertechnate (1.03+/-0.10 [SE]; n=7) or [14 C]inulin (1.10+/-0.17; n=7). In contrast, in the in vivo preparation, the ratio of intramembranous permeabilities outward from the amniotic fluid and the reverse direction was greater than unity for 99m technetium pertechnate (2.10+/-0.34; n=8; P=.014) and [14 C]inulin (4.68+/-1.24; n=7; P=.025). The permeability-surface area product of 99m technetium pertechnate (2.18+/-0.79 mL/min) of the isolated amnion was similar to the in vivo intramembranous permeability (n=8) in the amniotic fluid to fetal blood direction (1.42+/-0.34 mL/min) and greater than that in the reverse direction (0.84+/-0.25 mL/min; P=.046). The permeability-surface area product of [14 C]inulin of the amnion (0.53+/-0.20 mL/min) was similar to intramembranous permeability (n=7) in the amniotic fluid to fetal blood (0.68+/-0.15 mL/min) direction and greater than that in the reverse direction (0.22+/-0.06 mL/min; P=.0097). CONCLUSION: Solute transport across the ovine amnion depends on solute size and appears to be limited only by the amnion's passive diffusional properties. In vivo intramembranous transport similarly depends on solute size but is not exclusively a passive diffusional process because it is primarily unidirectional outward from the amniotic fluid. Although it is a major barrier, the amnion is not the only barrier and does not appear to be responsible for the unidirectional nature of intramembranous absorption. Thus, unidirectionality appears to be imparted by nonpassive mechanisms in non-amnion tissues, which most likely includes vesicular transport within the endothelial cells of the intramembranous microvessels.