Size-Resolved Particle Fluxes and Vertical Gradients over and in a Sparse Pine Forest

Although a number of flux data sets indicate apparent upward fluxes of particles over forests, the causes of such fluxes remain only partially understood. Using data collected during the 2011 BEACHON experiment, it is shown that over one third of fluxes of both sub- and super-30-nm diameter particles over this sparse pine forest are upward. Quadrant analysis, timescale analysis using a particle dynamics model, and frequency power spectra of particle concentrations demonstrate that, in this environment, the morning upward fluxes tend to be associated with downward “sweeps” of particle depleted air during break down of the nocturnal inversion, and it is the most common mechanism resulting in upward fluxes of particle size distributions with diameters above 30 nm. Upward fluxes of particles later in the day are more strongly linked to “ejections” of particle enriched air from the canopy that are attributable to growth of fairly recently nucleated particles by both addition of oxidation products of biogenic volatile organic compounds and coagulation. This mechanism appears to dominate upward fluxes of sub-30-nm particles, although the resulting destabilization of the particle size distribution can result in upward fluxes of larger particles. Vertical gradients of particle size distribution above, through, and below the canopy are also analyzed to investigate the size dependence of canopy uptake of particles and indicate that, in accord with wind tunnel analyses, penetration efficiencies are lower for smaller geometric mean diameters (～15–20 nm) and increase with diameter up to approx. 80 nm (the largest diameter considered here).

Copyright 2013 American Association for Aerosol Research     

Faster integer-feasibility in mixed-integer linear programs by branching to force change

Branching in mixed-integer (or integer) linear programming requires choosing both the branching variable and the branching direction. This paper develops a number of new methods for making those two decisions either independently or together with the goal of reaching the first integer-feasible solution quickly. These new methods are based on estimating the probability of satisfying a constraint at the child node given a variable/direction pair. The surprising result is that the first integer-feasible solution is usually found much more quickly when the variable/direction pair with the smallest probability of satisfying the constraint is chosen. This is because this selection forces change in many candidate variables simultaneously, leading to an integer-feasible solution sooner. Extensive empirical results are given.     

Climate change impacts on wind energy: A review

Expansion of wind energy installed capacity is poised to play a key role in climate change mitigation. However, wind energy is also susceptible to global climate change. Some changes associated with climate evolution will likely benefit the wind energy industry while other changes may negatively impact wind energy developments, with such ‘gains and losses’ depending on the region under consideration. Herein we review possible mechanisms by which global climate variability and change may influence the wind energy resource and operating conditions, summarize some of the tools that are being employed to quantify these effects and the sources of uncertainty in making such projections, and discuss results of studies conducted to date. We present illustrative examples of research from northern Europe. Climate change analyses conducted for this region, which has shown considerable penetration of wind energy, imply that in the near-term (i.e. to the middle of the current century) natural variability exceeds the climate change signal in the wind energy resource and extreme wind speeds, but there will likely be a decline in icing frequency and sea ice both of which will tend to benefit the wind energy industry. By the end of the twenty-first century there is evidence for small magnitude changes in the wind resource (though the sign of the change remains uncertain), for increases in extreme wind speeds, and continued declines in sea ice and icing frequencies. Thus the current state-of-the-art suggests no detectable change in the wind resource or other external conditions that could jeopardize the continued exploitation of wind energy in northern Europe, though further research is needed to provide greater confidence in these projections.     

Toxoplasma gondii: dithiol-induced Ca2+ flux causes egress of parasites from the parasitophorous vacuole

Ca2+ is an essential activator of motility in the obligate intracellular parasite Toxoplasma gondii. Ca2+ ionophore A23187 and intracellular microinjection of Ca2+ initiate motility of parasites residing in parasitophorous vacuoles (PV). The source of Ca2+ and the mechanism by which it activates motility in vivo remain uncertain. Exposure of the parasites to dithiothreitol (DTT) can activate egress of previously nonmotile intravacuolar parasites within 60 sec. DTT is also known to activate both isoforms of the highly concentrated nucleoside triphosphate hydrolase (NTPase) produced by T. gondii. Using an adherent cell analysis system (ACAS) for Ca2+ imaging, a brief 15-50% increase in intra-PV fluorescence ratio was observed after exposure of infected fibroblasts to 5 mM DTT. Chelation of intracellular Ca2+ with BAPTA-AM and extracellular Ca2+ with EGTA blocked the DTT effect; however, this chelation did not prevent the activation of parasites nor the Ca2+ response to the Ca2+ ionophore ionomycin, suggesting that the Ca2+ that activates motility may reside near or within the parasite itself. This result demonstrates that an increase in Ca2+ within the vacuole precedes the onset of motility and the correlation of the DTT effect on motility and tachyzoite NTPase suggests that NTPase activation may be involved in the Ca2+ flux.