598 research outputs found
Changes to the airâsea flux and distribution of radiocarbon in the ocean over the 21st century
We investigate the spatiotemporal evolution of radiocarbon (Î14C) in the ocean over the 21st century under different scenarios for anthropogenic CO2 emissions and atmospheric CO2 and radiocarbon changes using a 3âD ocean carbon cycle model. Strong decreases in atmospheric Î14C in the highâemission scenario result in strong outgassing of 14C over 2050â2100, causing Î14C spatial gradients in the surface ocean and vertical gradients between the surface and intermediate waters to reverse sign. Surface Î14C in the subtropical gyres is lower than Î14C in Pacific Deep Water and Southern Ocean surface water in 2100. In the lowâemission scenario, ocean Î14C remains slightly higher than in 1950 and relatively constant over 2050â2100. Over the next 20 years we find decadal changes in Î14C of â30â° to +5â° in the upper 2 km of the ocean, which should be detectable with continued hydrographic surveys. Our simulations can help in planning future observations, and they provide a baseline for investigating natural or anthropogenic changes in ocean circulation using ocean Î14C observations and models
Changes in oceanic radiocarbon and CFCs since the 1990s
Anthropogenic perturbations from fossil fuel burning, nuclear bomb testing, and chlorofluorocarbon (CFC) use have created useful transient tracers of ocean circulation. The atmospheric 14C/C ratio (â14C) peaked in the early 1960s and has decreased now to pre-industrial levels, while atmospheric CFC-11 and CFC-12 concentrations peaked in the early 1990s and early 2000s, respectively, and have now decreased by 10%â20%. We present the first analysis of a decade of new observations (2007 to 2018â2019) and give a comprehensive overview of the changes in ocean â14C and CFC concentration since the WOCE surveys in the 1990s. Surface ocean â14C decreased at a nearly constant rate from the 1990â2010s (20â°/decade). In most of the surface ocean â14C is higher than in atmospheric CO2 while in the interior ocean, only a few places are found to have increases in â14C, indicating that globally, oceanic bomb 14C uptake has stopped and reversed. Decreases in surface ocean CFC-11 started between the 1990 and 2000s, and CFC-12 between the 2000â2010s. Strong coherence in model biases of decadal changes in all tracers in the Southern Ocean suggest ventilation of Antarctic Intermediate Water was enhanced from the 1990 to the 2000s, whereas ventilation of Subantarctic Mode Water was enhanced from the 2000 to the 2010s. The decrease in surface tracers globally between the 2000 and 2010s is consistently stronger in observations than in models, indicating a reduction in vertical transport and mixing due to stratification
Changes in Oceanic Radiocarbon and CFCs Since the 1990s
Anthropogenic perturbations from fossil fuel burning, nuclear bomb testing, and chlorofluorocarbon (CFC) use have created useful transient tracers of ocean circulation. The atmospheric 14C/C ratio (â14C) peaked in the early 1960s and has decreased now to preâindustrial levels, while atmospheric CFCâ11 and CFCâ12 concentrations peaked in the early 1990s and early 2000s, respectively, and have now decreased by 10%â20%. We present the first analysis of a decade of new observations (2007 to 2018â2019) and give a comprehensive overview of the changes in ocean â14C and CFC concentration since the WOCE surveys in the 1990s. Surface ocean â14C decreased at a nearly constant rate from the 1990â2010s (20â°/decade). In most of the surface ocean â14C is higher than in atmospheric CO2 while in the interior ocean, only a few places are found to have increases in â14C, indicating that globally, oceanic bomb 14C uptake has stopped and reversed. Decreases in surface ocean CFCâ11 started between the 1990 and 2000s, and CFCâ12 between the 2000â2010s. Strong coherence in model biases of decadal changes in all tracers in the Southern Ocean suggest ventilation of Antarctic Intermediate Water was enhanced from the 1990 to the 2000s, whereas ventilation of Subantarctic Mode Water was enhanced from the 2000 to the 2010s. The decrease in surface tracers globally between the 2000 and 2010s is consistently stronger in observations than in models, indicating a reduction in vertical transport and mixing due to stratification
Eccentric exercise slows in vivo microvascular reactivity during brief contractions in human skeletal muscle
Unaccustomed exercise involving eccentric contractions results in muscle soreness and an overall decline in muscle function, however, little is known about the effects of eccentric exercise on microvascular reactivity in human skeletal muscle. Fourteen healthy men and women performed eccentric contractions of the dorsiflexor muscles in one leg, while the contralateral leg served as a control. At baseline, and 24 and 48 h after eccentric exercise, the following were acquired bilaterally in the tibialis anterior muscle: 1) transverse relaxation time (T2)-weighted magnetic resonance images to determine muscle cross-sectional area (mCSA) and T2; 2) blood oxygen level-dependent (BOLD) images during and following brief, maximal voluntary contractions (MVC) to monitor the hyperemic responses with participants positioned supine in a 3T magnet; 3) muscle strength; and 4) pain pressure threshold. Compared with the control leg, eccentric exercise resulted in soreness, decline in strength (âŒ20%), increased mCSA (âŒ7%), and prolonged T2 (âŒ7%) at 24 and 48 h ( P < 0.05). The BOLD response to a brief MVC was altered 24 and 48 h after eccentric exercise, such that time-to-peak (âŒ35%, P < 0.05) and time-to-half-recovery (âŒ23%, P < 0.05) were prolonged. The altered contraction-induced hyperemic response suggests slowed microvascular reactivity and altered matching of O2 delivery to O2 utilization within muscle tissue showing signs of muscle damage. These changes in microvascular regulation after eccentric exercise may impede rapid adjustments in muscle blood flow at exercise onset and during activities involving brief bursts of muscle activation, which may impair O2 delivery and contribute to reduced muscle function after eccentric exercise. </jats:p
Resisted adduction in hip neutral is a superior provocation test to assess adductor longus pain:an experimental pain study
The criterion of long-standing groin pain diagnoses in athletes usually relies on palpation and clinical tests. An experimental pain model was developed to examine the clinical tests under standardized conditions. Pain was induced by hypertonic saline injected into the proximal adductor longus (AL) tendon or rectus femoris (RF) tendon in 15 healthy male participants. Isotonic saline was injected contralaterally as a control. Pain intensity was assessed on a visual analog scale (VAS). Resisted hip adduction at three different angles and trunk flexion were completed before, during, and after injections. Pain provocation in the presence of experimental pain was recorded as a true positive compared with pain provocation in the non-pain conditions. Similar peak VAS scores were found after hypertonic saline injections into the AL and RF and both induced higher VAS scores than isotonic saline (P<0.01). Adduction at 0° had the greatest positive likelihood ratio (+LR=2.8, 95%CI: 1.09-7.32) with 45° (-LR=0.0, 95%CI: 0.00-1.90) and 90° (-LR=0.0, 95%CI: 0.00-0.94) having the lowest negative LR. This study indicates that the 0° hip adduction test resisted at the ankles optimizes the diagnostic procedure without compromising diagnostic capacity to identify experimental groin pain. Validation in clinical populations is warranted
Corticomotor excitability reduction induced by experimental pain remains unaffected by performing a working memory task as compared to staying at rest
Experimental pain inhibits primary motor cortex (M1) excitability. Attenuating pain-related inhibition of M1 excitability may be useful during rehabilitation in individuals with pain. One strategy to attenuate M1 excitability is to influence prefrontal and premotor cortex activity. Working memory tasks, e.g. the two-back task (TBT), engage prefrontal and premotor cortices and may influence M1 excitability. We hypothesized that performing the TBT during pain would influence pain-related changes in M1 excitability. Participants (n = 28) received rigorous training in the TBT before baseline testing. Experimental pain was induced by injecting hypertonic saline into the first dorsal interosseous (FDI) muscle. Participants rated pain intensity on a 0â10 numerical rating scale (NRS) every second min until pain-resolved (PR) during the performance of the TBT (n = 14) or during REST (n = 14). In the TBT, letters were presented pseudo-randomly, and accuracy and reaction time to identified letters corresponding to letters shown two times back were recorded. M1 excitability was assessed using transcranial magnetic stimulation. Motor-evoked potentials (MEPs) were recorded at baseline, and at PR, PR + 10, PR + 20, and PR + 30Â min. Four minutes after hypertonic saline injection, the pain NRS scores were higher in the TBT group than the REST group (p = 0.009). No time x group interaction was found for MEPs (p = 0.73), but a main effect of time (p < 0.0005) revealed a reduction of MEPs at PR up until PR + 30 (p < 0.008). The TBT accuracy improved at PR + 30 in both groups (p = 0.019). In conclusion, the pain-induced reduction in corticomotor excitability was unaffected by performing a working memory task, despite greater pain in the TBT group
Designing optimal greenhouse gas observing networks that consider performance and cost
Emission rates of greenhouse gases (GHGs) entering into the atmosphere can be
inferred using mathematical inverse approaches that combine observations from
a network of stations with forward atmospheric transport models. Some
locations for collecting observations are better than others for constraining
GHG emissions through the inversion, but the best locations for the inversion
may be inaccessible or limited by economic and other non-scientific factors.
We present a method to design an optimal GHG observing network in the
presence of multiple objectives that may be in conflict with each other. As a
demonstration, we use our method to design a prototype network of six
stations to monitor summertime emissions in California of the potent GHG
1,1,1,2-tetrafluoroethane (CH<sub>2</sub>FCF<sub>3</sub>, HFC-134a). We use a
multiobjective genetic algorithm to evolve network configurations that seek
to jointly maximize the scientific accuracy of the inferred HFC-134a
emissions and minimize the associated costs of making the measurements. The
genetic algorithm effectively determines a set of "optimal" observing
networks for HFC-134a that satisfy both objectives (i.e., the Pareto
frontier). The Pareto frontier is convex, and clearly shows the tradeoffs
between performance and cost, and the diminishing returns in trading one for
the other. Without difficulty, our method can be extended to design optimal
networks to monitor two or more GHGs with different emissions patterns, or to
incorporate other objectives and constraints that are important in the
practical design of atmospheric monitoring networks
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