We report O
2/Ar ratios (a constraint on net community production) and the triple isotopic composition of dissolved O
2 (a constraint on gross primary production) in samples collected from the ...surface mixed layer on 23 Southern Ocean transits. Samples were collected at 1–2° meridional resolution during the austral summer. Methodological limitations notwithstanding, the results constrain the net/gross production ratio, net O
2 production, and gross O
2 production at unprecedented resolution throughout the Southern Ocean mixed layer. Gross O
2 production rates inferred from the oxygen triple isotopes are greater than production rates calculated from a model based on remotely sensed chlorophyll. This result agrees with previous
18O and
14C incubations along 170°W. O
2/Ar ratios exceeding saturation are consistently observed within the Subantarctic and Polar Frontal Zones south of New Zealand and Australia, showing that a net autotrophic community predominates during austral summer. Lower O
2/Ar values are observed within the Drake Passage and Antarctic Zone, suggesting unresolved influences of low net community production, net heterotrophy, and upwelling of O
2-undersaturated waters. In autotrophic waters of the austral summer mixed layer, ratios of net community production/gross O
2 production scatter about 0.13, corresponding to
f ratios of ∼0.25. Net community/gross O
2 production ratios show no meridional gradient across the Antarctic Circumpolar Current, suggesting that an approximately constant fraction of gross primary productivity is regenerated or exported. Our calculated net O
2 production rates are in satisfactory agreement with comparable published estimates. Net and gross O
2 production rates are highest in the Subantarctic and decline to the south, paralleling the well-known trend of chlorophyll
a concentrations. In an analysis of variance of net O
2 production and gross O
2 production with other environmental variables, the strongest correlations are between net O
2 production and sea surface temperature (SST) (direct correlation), climatological NO
3
− (inverse correlation), and estimates of primary productivity derived from a remote sensing (direct correlation). These trends are as expected if aerosol iron input is the most important influence on production. They are unexpected if upwelling-derived SiO
2 and iron are the leading influence or if lower SSTs promote greater export in this region.
Linear stability methods were applied to a biomechanical model of the human musculoskeletal spine to investigate effects of reflex gain and reflex delay on stability. Equations of motion represented ...a dynamic 18 degrees-of-freedom rigid-body model with time-delayed reflexes. Optimal muscle activation levels were identified by minimizing metabolic power with the constraints of equilibrium and stability with zero reflex time delay. Muscle activation levels and associated muscle forces were used to find the delay margin, i.e., the maximum reflex delay for which the system was stable. Results demonstrated that stiffness due to antagonistic co-contraction necessary for stability declined with increased proportional reflex gain. Reflex delay limited the maximum acceptable proportional reflex gain, i.e., long reflex delay required smaller maximum reflex gain to avoid instability. As differential reflex gain increased, there was a small increase in acceptable reflex delay. However, differential reflex gain with values near intrinsic damping caused the delay margin to approach zero. Forward-dynamic simulations of the fully nonlinear time-delayed system verified the linear results. The linear methods accurately found the delay margin below which the nonlinear system was asymptotically stable. These methods may aid future investigations in the role of reflexes in musculoskeletal stability.
The purpose of this study was to identify and determine the influence of perceived intrinsic barriers to physical activity among mothers living in rural areas.
Mothers were identified through a study ...of child-parent dyads in the predominantly rural states of New Hampshire and Vermont. Using a telephone interview, we asked mothers (n = 1691) about their level of physical activity and assessed eight potential barriers to physical activity. Data were analyzed using chi-square tests, t tests, and analysis of variance (ANOVA) comparisons for groups within each variable. We used multiple regression analysis to assess associations between perceived barriers to physical activity and self-reported levels of physical activity.
Each barrier was inversely associated with physical activity. Multivariate models that included terms for all potential barriers and covariates identified three barriers associated with lower levels of physical activity: lack of self-discipline, lack of time, and lack of interest.
Rural mothers are less likely to be physically active if they identify lack of self-discipline, time, or interest as barriers, suggesting that they have difficulty prioritizing exercise for themselves. Interventions aimed at increasing physical activity for mothers should specifically consider these barriers. One possible solution may be to support infrastructure that facilitates active living as the default option, to remove the issue of having to purposefully engage in physical activity as a separate aspect of a mother's life.
Most studies of attention-deficit hyperactivity disorder (ADHD) youth have obtained data from the perspective of either children or parents, but not both simultaneously. The purpose of this study was ...to examine child and parent perspectives on parenting in a large community-based sample of children with and without ADHD. We identified children in grades 4–6 and their parents through surveys administered to a random sample of public schools. We used multivariable logistic regression to determine independent associations between child and parent characteristics and the presence of ADHD while controlling for covariates and clustering by school. Sufficient data were achieved for 2,509 child/parent dyads. Ten percent of youths (
n
= 240) had been diagnosed with ADHD. Compared with those without ADHD, those with ADHD were more commonly male (67.9 vs. 48.0 %,
p
< .001) and age 12 or over (16.3 vs. 10.3 %). After adjusting for covariates and clustering, compared to children without ADHD, children with ADHD were significantly more likely to report lower self-regulation (OR = 0.68, 95 % CI = 0.53, 0.88) and higher levels of rebelliousness (OR = 2.00, 95 % CI = 1.52, 2.69). Compared with parents whose children did not have ADHD, parents of children with ADHD rated their overall parental efficacy substantially lower (OR = 0.23, 95 % CI = 0.15, 0.33). However, child assessment of parenting style was similar by ADHD. Despite the internal challenges community-based youth with ADHD face, many parents of ADHD youth exhibit valuable parental skills from the perspective of their children. Feedback of this information to parents may improve parental self-efficacy, which is known to be positively associated with improved ADHD outcomes.
As advanced reactor concepts challenge the accuracy of current modeling technologies, a higher-fidelity depletion calculation is necessary to model time-dependent core reactivity properly for ...accurate cycle length and safety margin determinations. The recent integration of CINDER90 into the MCNPX Monte Carlo radiation transport code provides a completely self-contained Monte Carlo-linked depletion capability. Two advances have been made in the latest MCNPX capability based on problems observed in prereleased versions: continuous-energy collision density tracking and adequate fission yield selection.
Prereleased versions of the MCNPX depletion code calculated the reaction rates for (n,2n), (n,3n), (n,p), and (n,α) by matching the MCNPX steady-state 63-group flux with 63-group cross sections inherent in the CINDER90 library and then collapsing to one-group collision densities for the depletion calculation. The accuracy of this procedure is therefore dictated by the adequacy of the 63-group energy structure of the cross-section set to accurately capture the spectrum of a specific model. Different types of models would therefore require different types of cross-section energy group structure. MCNPX 2.6.A eliminates this dependency by using the continuous-energy reaction rates determined during the MCNPX steady-state calculation to calculate energy-integrated collision rates to be used by CINDER90.
MCNPX 2.6.A now also determines the proper fission yield to be used by the CINDER90 code for the depletion calculation. The CINDER90 code offers a thermal, fast, and high-energy fission yield for each fissile isotope contained in the CINDER90 data file. MCNPX 2.6.A determines which fission yield to use for a specified problem by calculating the integral fission rate for the defined energy boundaries (thermal, fast, and high energy), determining which energy range contains the majority of fissions, and then selecting the appropriate fission yield for the energy range containing the majority of fissions.
The MCNPX depletion capability enables complete, relatively easy-to-use depletion calculations in a single Monte Carlo code. This study focuses on the methodology development of the two improvements described here. Further improvements are under development to enhance the usefulness of this new capability.
Runs of the anadromous American shad Alosa sapidissima in the Lehigh River, a major tributary to the west shore of the Delaware River, were blocked by construction of dams during the 1820s. ...Completion of two fish ladders in 1994 opened up the lower 39 km to migratory fish. Hatchery‐reared American shad larvae, marked by immersion in tetracycline antibiotics, have been stocked in the Lehigh River since 1985. From 1995 to 2000, hatchery‐origin (marked) American shad made up 73–98% of the adult shad collected in the Lehigh River upriver of the first dam. The contribution of Lehigh River hatchery‐marked adult shad in the Delaware River was 5–15% at Raubsville, 10 km downriver from the mouth of the Lehigh River, and 0–4% at Smithfield Beach, 53 km upstream from the mouth of the Lehigh River. These results demonstrated that American shad migrating into the Lehigh River were not a random assortment of shad from the Delaware River population. When the downstream Delaware River samples were segregated laterally on the east and west sides of the river, the sample on the west side had a significantly higher proportion of Lehigh River marks (8–15%) than the sample on the east side (2–7%), indicating that the returning Lehigh River hatchery‐marked adults preferred the side of the Delaware River influenced by the Lehigh River. Our results suggest that efforts to restore American shad above dams should include some transplant strategy to expedite recolonization.
Mixed layer seawater samples from the Southern Ocean were analyzed for the triple oxygen isotope composition (δ17O and δ18O) of dissolved O2 and the ratio of O2 to Ar. δ17O and δ18O together ...constrain the mass independent anomaly in O2, and hence the fraction of photosynthetic O2 in the dissolved O2 pool. Assuming oxygen in the mixed layer is at steady state, we calculate ratios of the gross photosynthetic O2 production rate to the O2 air–sea gas exchange rate, and ratios of net to gross O2 production rates. With estimates of the O2 gas exchange rate from a wind speed parameterization, we determine absolute in situ rates of gross and net O2 production. Based on the net/gross production ratios and δ18O of dissolved O2, we calculate a value for the 18O fractionation factor associated with marine respiration in the Southern Ocean mixed layer of 0.978 (an isotope effect of 22‰). The study regions cover latitudes between ∼45°S and the ice edge at: (1) 175°E in December 1999, (2) 145°E in December 2000, and (3) 145°E in January 2001. At both meridians, gross O2 production decreases to the south. At 145°E, rates of net O2 production follow the same pattern, while at 175°E these rates are consistently low at all latitudes. In December, gross and net O2 production rates are both higher at 145°E than at 175°E. Gross O2 production at 145°E was similar in December and January, but net O2 production decreased by ∼50%. Net/gross C production ratios, calculated by scaling O2 production rates, are lower than estimates of the 15N f-ratio, determined as the ratio of 15NO3− uptake to 15NO3−+15NH4+ uptake in 15N incubations. They are also lower than ef-ratios predicted by the model of Laws et al. (Global Biogeochem. Cycles 14 (2000a) 1231) at the temperatures of the Southern Ocean. The differences in the measurements could be due to natural interannual and spatial variability or the differences in metabolic rates measured and modeled, and the fundamental assumptions required by each technique.
This study validated a whole‐otolith aging method using known‐age American shad Alosa sapidissima from the Delaware River system. Although scale ages are commonly used in autecological and assessment ...studies of American shad, scale ages from the same fish could not be validated. New data reported here used known‐aged otoliths and scales available from shad marked by oxytetracycline as larvae in a hatchery and recaptured as adults on or near their spawning ground. A subset of whole otoliths were examined and annuli—defined as a pair of translucent and opaque bands—were counted using males and females ranging in age from 3 to 9 years. The reading and interpretation of annuli by the more experienced reader were accurate with respect to the known age, whether measured as the percent agreement (PA = 80%) or Chang's coefficient of variation (CV = 3.11). The use of otoliths provided more accurate results than scales obtained from the same fish (PA = 46%; CV = 7.84). A second reader, who had no previous experience with this species, had lower performance scores but also performed better with otoliths; this demonstrated the need for training and testing when using the whole‐otolith aging method. Growth modeling using ages of known‐age juveniles and adults confirmed dimorphic growth. Females grew larger than males (von Bertalanffy L∞ = 552 and 495‐mm FL, respectively). The maximum age observed for females was only slightly older than males (9 versus 8 years). The superiority of the otolith‐based age method makes it difficult to compare our results with older, scale‐based demographic studies, but it represents an improved method for generating ages for future stock assessments.
As a contribution to the study of equatorial Pacific biogeochemistry, we measured the O
2
/Ar ratio and the triple isotope composition (
18
O,
17
O, and
16
O) of O
2
along six meridional lines in the ...equatorial Pacific (8°N–8°S at 95°W, 110°W, 125°W, 140°W, 155°W, and 170°W). O
2
/Ar ratios and δ
18
O were close to equilibrium values within the mixed layer and followed the general trend of increasing δ
18
O with decreasing O
2
/Ar at greater depths. The
17
Δ (≈δ
17
O–0.5δ
18
O) constrains the fraction of photosynthetic O
2
;
17
Δ was slightly elevated with respect to equilibrium within the mixed layer due to local photosynthetic production. In aphotic zone waters above 250 m depth the average
17
Δ values were higher than in the mixed layer. There are four sources of this photosynthetic signal in the dark ocean: production in the euphotic zone prior to subduction in the distant source regions, production below the mixed layer during travel to the equatorial zone, diapycnal mixing with shallower waters bearing photosynthetic O
2
, and accumulation of photosynthetic O
2
produced at very low rates below the 1% light level. Our results also constrain biological production rates within the mixed layer at several locations along 95°W and 110°W. Our average rate of
14
C production (53 ± 34 mmol C m
−2
d
−1
) agreed well with other estimates in the equatorial Pacific, while our average rate of net C production (6.9 ± 6.2 mmol C m
−2
d
−1
) and
f
ratio (0.12 ± 0.11) were somewhat lower than other estimates. Adding δ
18
O and
17
Δ as tracers to three‐dimensional biogeochemical ocean GCMs and comparing results with observations will extend our understanding of metabolic rates in the study region.
Cating's method of using scales to age American shad (Alosa sapidissima) has been the standard for more than 50 years. However, the only validation of this method is for ages 4–6 in the Connecticut ...River. To test the method for these—and older—age classes in another river, we obtained scales from 52 known‐age fish from two Pennsylvania rivers and had 13 experienced biologists estimate ages using Cating's method. Each biologist read the scale impressions twice, and these readings were then assessed in terms of precision, accuracy, and bias. Percent agreement between estimates for the same scale set (precision) ranged from 50.0 to 76.5%. Percent agreement between estimated age and known age (accuracy) was highest for ages 3–6 (33.7–48.5%), markedly lower for age‐7 (12.1%), and lowest for age‐8 fish (3.9%). Ages of the youngest fish were often overestimated, and those of the oldest fish were typically underestimated (bias). Therefore, Cating's method is not applicable to American shad in these Pennsylvania rivers. In fact, this scale‐ageing method has never been validated across all ages for any American shad stock. Thus, we recommend against using age‐based techniques to assess stocks of American shad until further age‐validation studies have been completed.
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