A model analysis of climate and CO2 controls on tree growth in a semi-arid woodland

We used a light-use efficiency model of photosynthesis coupled with a dynamic carbon allocation and tree-growth model to simulate annual growth of the gymnosperm Callitris columellaris in the semi-arid Great Western Woodlands, Western Australia, over the past 100 years. Parameter values were derived from independent observations except for sapwood specific respiration rate, fine-root turnover time, fine-root specific respiration rate and the ratio of fine-root mass to foliage area, which were estimated by Bayesian optimization. The model reproduced the general pattern of interannual variability in radial growth (tree-ring width), including the response to the shift in precipitation regimes that occurred in the 1960s. Simulated and observed responses to climate were consistent. Both showed a significant positive response of tree-ring width to total photosynthetically active radiation received and to the ratio of modeled actual to equilibrium evapotranspiration, and a significant negative response to vapour pressure deficit. However, the simulations showed an enhancement of radial growth in response to increasing atmospheric CO2 concentration (ppm) ([CO2]) during recent decades that is not present in the observations. The discrepancy disappeared when the model was recalibrated on successive 30-year windows. Then the ratio of fine-root mass to foliage area increases by 14% (from 0.127 to 0.144 kg C m-2) as [CO2] increased while the other three estimated parameters remained constant. The absence of a signal of increasing [CO2] has been noted in many tree-ring records, despite the enhancement of photosynthetic rates and water-use efficiency resulting from increasing [CO2]. Our simulations suggest that this behaviour could be explained as a consequence of a shift towards below-ground carbon allocation

Mechanical Evidence of the Orbital Angular Momentum to Energy Ratio of Vortex Beams

We measure, in a single experiment, both the radiation pressure and the torque due to a wide variety of propagating acoustic vortex beams. The results validate, for the first time directly, the theoretically predicted ratio of the orbital angular momentum to linear momentum in a propagating beam. We experimentally determine this ratio using simultaneous measurements of both the levitation force and the torque on an acoustic absorber exerted by a broad range of helical ultrasonic beams produced by a 1000-element matrix transducer array. In general, beams with helical phase fronts have been shown to contain orbital angular momentum as the result of the azimuthal component of the Poynting vector around the propagation axis. Theory predicts that for both optical and acoustic helical beams the ratio of the angular momentum current of the beam to the power should be given by the ratio of the beam’s topological charge to its angular frequency. This direct experimental observation that the ratio of the torque to power does convincingly match the expected value (given by the topological charge to angular frequency ratio of the beam) is a fundamental result

Evidence Use in Congress: Options for Charting a New Direction; Volume 2

Lawmakers in Congress have expressed a growing interest in the promise of evidence-based policymaking. Bipartisan legislation has been pursued in Congress that would encourage the use of evidence to improve outcomes for key education, health, workforce, and other federal programs. These past legislative initiatives suggest growing potential for the wider use of evidence to better inform congressional decision-making in the future. However, key challenges remain for fostering a stronger culture of evidence in Congress. This stronger culture will be necessary to fully realize the potential benefits of evidence-based policymaking

The effect of different concentrations of tween-20 combined with rice husk silica on the stability of o/w emulsion: A kinetic study

Emulsion is a thermodynamically unstable system which undergoes destabilization with time. The destabilization kinetics of "food grade" oil-in-water (O/W) emulsions in the presence of both tween-20 and rice husk silica as emulsifiers were studied. Rice husk silica concentration of 2.5% was combined with various concentrations of tween-20 from 0.1 to 1%. Oil phase fraction was 20% relative to the aqueous phase. Emulsification was conducted using a rotor-stator homogenizer at 20,000 rpm. The emulsions tended to destabilize with time. Their destabilization rates were studied using zero order and first order kinetic models. In general, the kinetics of O/W emulsion destabilization followed first order model. Different concentrations of tween-20 combined with rice husk silica influenced the destabilization rate of o/w emulsions. Destabilization rates of emulsions stabilized using mixed emulsifiers of 1% tween-20 and 2.5% silica were ~50 times and ~3 times lower compared to those stabilized using silica alone and tween-20 alone, respectively