Disentangling Selection from Causation in the Empirical Association between Crime and Adolescent Work

Researchers consistently find that youths who work longer hours during high school tend to have higher rates of crime and substance use. On the basis of this and other research showing the negative developmental impact of an "intensive" work commitment during high school, the National Research Council (1998) recommended that federal lawmakers place limits on the maximum number of hours per week that teenagers are allowed to work during the school year. However, recent empirical research demonstrates the possibility of severe bias due to failure to control for unobserved sources of heterogeneity. I take advantage of two unique characteristics of the National Longitudinal Survey of Youth 1997 to assess the veracity of the claim that longer work hours are causally related to elevated involvement in crime and substance use. First, since the same respondents are followed over a period of five years, I use individual fixed effects to adjust for the omission of relevant time-stable covariates. Second, I exploit state-to-state variation in the restrictiveness of child labor laws governing the number of hours per week allowed during the school year, and the fact that these restrictions are relaxed (and eventually expire) with increasing age. In this modelbased on a fixed-effects instrumental variables (FEIV) estimatoridentification of the "work intensity effect" on problem behavior is predicated on exogenous within-individual variation in school-year work hours attributable to the easing of child labor restrictions as youths age out of their legal status as minors. The attractiveness of the FEIV estimator is its ability to eliminate bias in the estimated "work intensity effect" due to omitted stable and dynamic variables. The model thus provides an especially powerful test of the thesis that intensive employment during the school year causally aggravates involvement in problem behavior. The empirical results demonstrate that longer work hours are associated with a significant decrease in adolescent crime, contrary to virtually all prior research. The results for adolescent substance use are mixed, suggesting the possibility that longer work hours either increase or have no effect on substance use, depending on whether a fixed-effects or first-differences procedure is implemented

Transgressive segregation reveals mechanisms of Arabidopsis immunity to Brassica-infecting races of white rust (Albugo candida)

Arabidopsis thaliana accessions are universally resistant at the adult leaf stage to white rust (Albugo candida) races that infect the crop species Brassica juncea and Brassica oleracea. We used transgressive segregation in recombinant inbred lines to test if this apparent species-wide (nonhost) resistance in A. thaliana is due to natural pyramiding of multiple Resistance (R) genes. We screened 593 inbred lines from an Arabidopsis multiparent advanced generation intercross (MAGIC) mapping population, derived from 19 resistant parental accessions, and identified two transgressive segregants that are susceptible to the pathogen. These were crossed to each MAGIC parent, and analysis of resulting F2 progeny followed by positional cloning showed that resistance to an isolate of A. candida race 2 (Ac2V) can be explained in each accession by at least one of four genes encoding nucleotide-binding, leucine-rich repeat (NLR) immune receptors. An additional gene was identified that confers resistance to an isolate of A. candida race 9 (AcBoT) that infects B. oleracea. Thus, effector-triggered immunity conferred by distinct NLR-encoding genes in multiple A. thaliana accessions provides species-wide resistance to these crop pathogens

Transgressive segregation reveals mechanisms of Arabidopsis immunity to Brassica-infecting races of white rust (Albugo candida)

Arabidopsis thaliana accessions are universally resistant at the adult leaf stage to white rust (Albugo candida) races that infect the crop species Brassica juncea and Brassica oleracea. We used transgressive segregation in recombinant inbred lines to test if this apparent species-wide (nonhost) resistance in A. thaliana is due to natural pyramiding of multiple Resistance (R) genes. We screened 593 inbred lines from an Arabidopsis multiparent advanced generation intercross (MAGIC) mapping population, derived from 19 resistant parental accessions, and identified two transgressive segregants that are susceptible to the pathogen. These were crossed to each MAGIC parent, and analysis of resulting F 2 progeny followed by positional cloning showed that resistance to an isolate of A. candida race 2 (Ac2V) can be explained in each accession by at least one of four genes encoding nucleotide-binding, leucine-rich repeat (NLR) immune receptors. An additional gene was identified that confers resistance to an isolate of A. candida race 9 (AcBoT) that infects B. oleracea. Thus, effector-triggered immunity conferred by distinct NLR-encoding genes in multiple A. thaliana accessions provides species-wide resistance to these crop pathogens

Constraining emissions of volatile organic compounds from western US wildfires with WE-CAN and FIREX-AQ airborne observations

The impact of biomass burning (BB) on the atmospheric burden of volatile organic compounds (VOCs) is highly uncertain. Here we apply the GEOS-Chem chemical transport model (CTM) to constrain BB emissions in the western US at ~25 km resolution. Across three BB emission inventories widely used in CTMs, the total of 14 modeled BB VOC emissions in the western US agree with each other within 30&ndash;40 %. However, emissions for individual VOC differ by up to a factor of 5 (i.e., lumped &ge; C4 alkanes), driven by the regionally averaged emission ratios (ERs) among inventories. We further evaluate GEOS-Chem simulations with aircraft observations made during WE-CAN (Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen) and FIREX-AQ (Fire Influence on Regional to Global Environments and Air Quality) field campaigns. Despite being driven by different global BB inventories or applying various injection height assumptions, GEOS-Chem simulations underpredict observed vertical profiles by a factor of 3&ndash;7. The model shows small-to-no bias for most species in low/no smoke conditions. We thus attribute the negative model biases mostly to underestimated BB emissions in these inventories. Tripling BB emissions in the model reproduces observed vertical profiles for primary compounds, i.e., CO, propane, benzene, and toluene. However, it shows no-to-less significant improvements for oxygenated VOCs, particularly formaldehyde, formic acid, acetic acid, and lumped &ge; C3 aldehydes, suggesting the model is missing secondary sources of these compounds in BB-impacted environments. The underestimation of primary BB emissions in inventories is likely attributable to underpredicted amounts of effective dry matter burned, rather than errors in fire detection, injection height, or ERs. We cannot rule out potential sub-grid uncertainties (i.e., not being able to fully resolve fire plumes) in the nested GEOS-Chem which could explain the model negative bias partially, though the back-of-the-envelope calculation and evaluation using longer-term ground measurements help increase the argument of the dry matter burned underestimation. The ERs of the 14 BB VOCs implemented in GEOS-Chem account for about half of the total 161 measured VOCs (~75 versus 150 ppb ppm-1). This reveals a significant amount of missing reactive organic carbon in widely-used BB emission inventories. Considering both uncertainties in effective dry matter burned and unmodeled VOCs, we infer that BB contributed up to 10 % in 2019 and 45 % in 2018 (240 and 2040 GgC) of the total VOC primary emission flux in the western US during these two fire seasons, compared to only 1&ndash;10 % in the standard GEOS-Chem.</p

Sea surface temperature signatures of oceanic internal waves in low winds

Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 112 (2007): C06014, doi:10.1029/2006JC003947.In aerial surveys conducted during the Tropical Ocean–Global Atmosphere Coupled Ocean-Atmosphere Response Experiment and the low-wind component of the Coupled Boundary Layer Air-Sea Transfer (CBLAST-Low) oceanographic field programs, sea surface temperature (SST) variability at relatively short spatial scales (O(50 m) to O(1 km)) was observed to increase with decreasing wind speed. A unique set of coincident surface and subsurface oceanic temperature measurements from CBLAST-Low is used to investigate the subsurface expression of this spatially organized SST variability, and the SST variability is linked to internal waves. The data are used to test two previously hypothesized mechanisms for SST signatures of oceanic internal waves: a modulation of the cool-skin effect and a modulation of vertical mixing within the diurnal warm layer. Under conditions of weak winds and strong insolation (which favor formation of a diurnal warm layer), the data reveal a link between the spatially periodic SST fluctuations and subsurface temperature and velocity fluctuations associated with oceanic internal waves, suggesting that some mechanism involving the diurnal warm layer is responsible for the observed signal. Internal-wave signals in skin temperature very closely resemble temperature signals measured at a depth of about 20 cm, indicating that the observed internal-wave SST signal is not a result of modulation of the cool-skin effect. Numerical experiments using a one-dimensional upper ocean model support the notion that internal-wave heaving of the warm-layer base can produce alternating bands of relatively warm and cool SST through the combined effects of surface heating and modulation of wind-driven vertical shear.We gratefully acknowledge funding for this research from the Office of Naval Research through the CBLAST Departmental Research Initiative (grants N00014-01-1-0029, N00014-05-10090, N00014-01-1-0081, N00014-04-1-0110, N00014-05-1-0036, N00014-01-1-0080) and the Secretary of the Navy/Chief of Naval Operations Chair (grant N00014-99-1-0090)

Methyl Jasmonate Regulates Podophyllotoxin Accumulation in Podophyllum hexandrum by Altering the ROS-Responsive Podophyllotoxin Pathway Gene Expression Additionally through the Down Regulation of Few Interfering miRNAs

Podophylloxin (ptox), primarily obtained from Podophyllum hexandrum, is the precursor for semi-synthetic anticancer drugs viz. etoposide, etopophos, and teniposide. Previous studies established that methyl jasmonate (MeJA) treated cell culture of P. hexandrum accumulate ptox significantly. However, the molecular mechanism of MeJA induced ptox accumulation is yet to be explored. Here, we demonstrate that MeJA induces reactive oxygen species (ROS) production, which stimulates ptox accumulation significantly and up regulates three ROS-responsive ptox biosynthetic genes, namely, PhCAD3, PhCAD4 (cinnamyl alcohol dehydrogenase), and NAC3 by increasing their mRNA stability. Classic uncoupler of oxidative phosphorylation, carbonylcyanide m-chlorophenylhydrazone, as well as H2O2 treatment induced the ROS generation and consequently, enhanced the ptox production. However, when the ROS was inhibited with NADPH oxidase inhibitor diphenylene iodonium and Superoxide dismutase inhibitor diethyldithio-carbamic acid, the ROS inhibiting agent, the ptox production was decreased significantly. We also noted that, MeJA up regulated other ptox biosynthetic pathway genes which are not affected by the MeJA induced ROS. Further, these ROS non-responsive genes were controlled by MeJA through the down regulation of five secondary metabolites biosynthesis specific miRNAs viz. miR172i, miR035, miR1438, miR2275, and miR8291. Finally, this study suggested two possible mechanisms through which MeJA modulates the ptox biosynthesis: primarily by increasing the mRNA stability of ROS-responsive genes and secondly, by the up regulation of ROS non-responsive genes through the down regulation of some ROS non-responsive miRNA

Constraints from observations and modeling on atmosphere-surface exchange of mercury in eastern North America

Atmosphere-surface exchange of mercury, although a critical component of its global cycle, is currently poorly constrained. Here we use the GEOS-Chem chemical transport model to interpret atmospheric Hg-0 (gaseous elemental mercury) data collected during the 2013 summer Nitrogen, Oxidants, Mercury and Aerosol Distributions, Sources and Sinks (NOMADSS) aircraft campaign as well as ground-and ship-based observations in terms of their constraints on the atmosphere-surface exchange of Hg-0 over eastern North America. Model-observation comparison suggests that the Northwest Atlantic may be a net source of Hg-0, with high evasion fluxes in summer (our best sensitivity simulation shows an average oceanic Hg-0 flux of 3.3 ng m(-2) h(-1) over the Northwest Atlantic), while the terrestrial ecosystem in the summer of the eastern United States is likely a net sink of Hg-0 (our best sensitivity simulation shows an average terrestrial Hg-0 flux of -0.6 ng m(-2) h(-1) over the eastern United States). The inferred high Hg-0 fluxes from the Northwest Atlantic may result from high wet deposition fluxes of oxidized Hg, which are in turn related to high precipitation rates in this region. We also find that increasing simulated terrestrial fluxes of Hg-0 in spring compared to other seasons can better reproduce observed seasonal variability of Hg-0 concentration at ground-based sites in eastern North America.Peer reviewe

Serum neurofilament dynamics predicts neurodegeneration and clinical progression in presymptomatic Alzheimer's disease

Neurofilament light chain (NfL) is a promising fluid biomarker of disease progression for various cerebral proteopathies. Here we leverage the unique characteristics of the Dominantly Inherited Alzheimer Network and ultrasensitive immunoassay technology to demonstrate that NfL levels in the cerebrospinal fluid (n = 187) and serum (n = 405) are correlated with one another and are elevated at the presymptomatic stages of familial Alzheimer's disease. Longitudinal, within-person analysis of serum NfL dynamics (n = 196) confirmed this elevation and further revealed that the rate of change of serum NfL could discriminate mutation carriers from non-mutation carriers almost a decade earlier than cross-sectional absolute NfL levels (that is, 16.2 versus 6.8 years before the estimated symptom onset). Serum NfL rate of change peaked in participants converting from the presymptomatic to the symptomatic stage and was associated with cortical thinning assessed by magnetic resonance imaging, but less so with amyloid-β deposition or glucose metabolism (assessed by positron emission tomography). Serum NfL was predictive for both the rate of cortical thinning and cognitive changes assessed by the Mini-Mental State Examination and Logical Memory test. Thus, NfL dynamics in serum predict disease progression and brain neurodegeneration at the early presymptomatic stages of familial Alzheimer's disease, which supports its potential utility as a clinically useful biomarker