215 research outputs found
An integral model based on slender body theory, with applications to curved rigid fibers
We propose a novel integral model describing the motion of curved slender
fibers in viscous flow, and develop a numerical method for simulating dynamics
of rigid fibers. The model is derived from nonlocal slender body theory (SBT),
which approximates flow near the fiber using singular solutions of the Stokes
equations integrated along the fiber centerline. In contrast to other models
based on (singular) SBT, our model yields a smooth integral kernel which
incorporates the (possibly varying) fiber radius naturally. The integral
operator is provably negative definite in a non-physical idealized geometry, as
expected from PDE theory. This is numerically verified in physically relevant
geometries. We propose a convergent numerical method for solving the integral
equation and discuss its convergence and stability. The accuracy of the model
and method is verified against known models for ellipsoids. Finally, a fast
algorithm for computing dynamics of rigid fibers with complex geometries is
developed
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Assisting students struggling with mathematics: Response to intervention (RtI) for elementary and middle schools.
Taking early action may be key to helping students struggling with mathematics. The eight recommendations in this guide are designed to help teachers, principals, and administrators use Response to Intervention for the early detection, prevention, and support of students struggling with mathematics
Dixdc1 Is a Critical Regulator of DISC1 and Embryonic Cortical Development
The psychiatric illness risk gene Disrupted in Schizophrenia-1 (DISC1) plays an important role in brain development; however, it is unclear how DISC1 is regulated during cortical development. Here, we report that DISC1 is regulated during embryonic neural progenitor proliferation and neuronal migration through an interaction with DIX domain containing-1 (Dixdc1), the third mammalian gene discovered to contain a Disheveled-Axin (DIX) domain. We determined that Dixdc1 functionally interacts with DISC1 to regulate neural progenitor proliferation by co-modulating Wnt-GSK3β/β-catenin signaling. However, DISC1 and Dixdc1 do not regulate migration via this pathway. During neuronal migration, we discovered that phosphorylation of Dixdc1 by cyclin-dependent kinase 5 (Cdk5) facilitates its interaction with the DISC1-binding partner Ndel1. Furthermore, Dixdc1 phosphorylation and its interaction with DISC1/Ndel1 in vivo is required for neuronal migration. Together, these data reveal that Dixdc1 integrates DISC1 into Wnt-GSK3β/β-catenin-dependent and -independent signaling pathways during cortical development and further delineate how DISC1 contributes to neuropsychiatric disorders.Human Frontier Science Program (Strasbourg, France) (Long-Term Fellowship)Natural Sciences and Engineering Research Council of Canada (Postdoctoral Fellowship)National Alliance for Research on Schizophrenia and Depression (U.S.) (Young Investigator Award)National Institutes of Health (U.S.) (Grant NS37007
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Ontogenetic patterns and temperature-dependent growth rates in early life stages of Pacific cod (Gadus macrocephalus)
Pacific cod (Gadus macrocephalus)is an important component of fisheries and food webs in the North Pacific Ocean and Bering Sea. However, vital rates of early life stages of this species have yet to be described in detail. We determined the thermal sensitivity of growth rates of embryos, pref lexion and postf lexion larvae, and postsettlement juveniles. Growth rates (length and mass) at each ontogenetic stage were measured in three replicate tanks at four to five temperatures. Nonlinear regression was used to obtain parameters for independent stage-specific growth functions and a unified size- and temperature-dependent growth function. Specific growth rates increased with temperature at all stages and generally decreased with increases in body size. However, these analyses revealed a departure from a strict size-based allometry in growth patterns, as reduced growth rates were observed among pref lexion larvae: the reduction in specific growth rate between embryos and free-swimming larvae was greater than expected based on body size differences. Growth reductions in the preflexion larvae appear to be associated with increased metabolic rates and the transition from endogenous to exogenous feeding. In future studies, experiments should be integrated across life transitions
to more clearly define intrinsic ontogenetic and size-dependent growth patterns because these are critical for evaluations of spatial and temporal variation in habitat quality.Keywords: Codfish, Growth, Environmental aspect
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Effect of temperature and tissue type on fatty acid signatures of two species of North Pacific juvenile gadids: A laboratory feeding study
The utility of the fatty acid biomarker (FAB) approach in fisheries ecology is limited by our understanding of how biotic and abiotic factors determine dietary markers in fish tissues. An 8-week laboratory experiment was conducted on two species of juvenile gadids (Pacific cod, Gadus macrocephalus and walleye Pollock, Theragra chalcogramma) reared at 3 °C or 9 °C and fed a diet enriched with either oils of marine origin or terrestrial plant origin. Non-linear models were fitted to investigate how tissue type and temperature mediated the proportion of FABs in fish. Across temperatures, fatty acid (FA) profiles were similar for both species of gadids. FAs also showed high temporal sensitivity across temperatures, and were evident in fish after only one week of feeding. Pacific cod held at 9 °C and fed a terrestrial plant oil (TPO) enriched diet had significantly higher C₁₈ polyunsaturated FAs (PUFAs) in their liver than cod held at 3 °C after one week, but this temperature effect diminished as tissues reached equilibrium with their diet. C₁₈ PUFAs were significantly higher in liver than in muscle.Differential proportions of C₁₈ PUFAs among tissues provide temporal patterns that may help with disentangling the timing of offshore– inshore nursery migrations in juvenile fish. Calibration coefficients were determined to explain the relationship between FAs in the diet and FAs in fish tissues. These coefficients will support future development of quantitative estimates of diet in juvenile low-fat fish.Keywords: Juvenile, Cod, Pollock, Fatty acid, Biomarker, Temperatur
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Role of temperature on lipid/fatty acid composition in Pacific cod (Gadus macrocephalus) eggs and unfed larvae
During early development, oviparous fish species must use finite lipid and fatty acid (FA) reserves for both catabolism and structural components. In cold environments, developing fish have the additional constraint of maintaining membrane fluidity for metabolic efficiency (homeoviscous adaptation), resulting in further demand on lower melting point FAs like n-3 polyunsaturated fatty acids (PUFAs). To examine whether marine fish embryos physiologically adapt to changing temperature environments, we incubated Pacific cod (Gadus macrocephalus) eggs at 5 temperatures (0, 2, 4, 6, and 8 °C) in the laboratory and sampled them repeatedly during development to measure changes in lipid/FA composition. Pacific cod embryos increased n-3 PUFA content during the egg stage in all temperature treatments, with the possible exception of 0 °C, where poor survival and hatch success limited our ability for continued sampling. At the beginning of the hatch cycle, free-swimming embryos shifted from lipogenesis to lipid catabolism. The rates of lipogenesis and catabolism were temperature dependent, and the distinct increase in unsaturated fatty acids at temperatures <8 °C was consistent with homeoviscous adaptation theory. However, with the possible exception of embryos at 0 °C, the relative amounts of essential fatty acids (e.g., EPA, DHA, AA) were conserved in a similar manner across incubation temperatures. Collectively, these data suggest Pacific cod are capable of homeoviscous adaptation but cannot tolerate temperatures approaching 0 °C despite their possible ability to biosynthesize PUFAs from other energetic sources
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Temperature-dependent growth and behavior of juvenile Arctic cod (Boreogadus saida) and co-occurring North Pacific gadids
The thermal sensitivity of Arctic fish species is poorly understood, yet such data are a critical component of forecasting and understanding ecosystem impacts of climate change. In this study, we experimentally measured temperature-dependent growth and routine swim activity in the juvenile stage of two Arctic gadids (Arctic cod, Boreogadus saida and saffron cod, Eleginus gracilis) and two North Pacific gadids (walleye pollock, Gadus chalcogrammus and Pacific cod, Gadus macrocephalus) over a 6-week growth period across five temperatures (0, 5, 9, 16 and 20°C). Arctic cod demonstrated a cold-water, stenothermic response in that there was relatively high growth at 0°C (0.73 % day⁻¹), near-maximal growth at 5°C (1.35 % day⁻¹) and negative impacts on activity, growth and survival at 16 °C. In contrast, saffron cod demonstrated a warmer-water, eurythermic response, and temperature had a positive effect on growth and condition beyond 16°C. However, despite these distinct thermal responses, walleye pollock and Pacific cod grew 2–3 times faster than Arctic gadids across a relatively broad temperature range above 5°C. These results, coupled with possible northward expansion by both Pacific cod and walleye pollock, suggest Arctic cod are highly vulnerable to continued climate change in the Arctic, especially in coastal areas of the Beaufort and Chukchi Seas where temperatures already exceed 14°C in the summer growth period.This is the publisher’s final pdf. The article is copyrighted by the US Government and published by Springer. It can be found at: http://link.springer.com/journal/300Keywords: Climate change, Saffron cod, Walleye pollock, Thermal sensitivity, Pacific cod, Biogeograph
Combined effects of crude oil exposure and warming on eggs and larvae of an arctic forage fish
Climate change, along with environmental pollution, can act synergistically on an organism to amplify adverse effects of exposure. The Arctic is undergoing profound climatic change and an increase in human activity, resulting in a heightened risk of accidental oil spills. Embryos and larvae of polar cod (Boreogadus saida), a key Arctic forage fish species, were exposed to low levels of crude oil concurrently with a 2.3 °C increase in water temperature. Here we show synergistic adverse effects of increased temperature and crude oil exposure on early life stages documented by an increased prevalence of malformations and mortality in exposed larvae. The combined effects of these stressors were most prevalent in the first feeding larval stages despite embryonic exposure, highlighting potential long-term consequences of exposure for survival, growth, and reproduction. Our findings suggest that a warmer Arctic with greater human activity will adversely impact early life stages of this circumpolar forage fish
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