Measuring Work of Adhesion of Polystyrene Microspheres

Particle adhesion is relevant in fields ranging from aerospace and energy to civil engineering and medicine. The functions of aerodynamic surfaces, heat exchangers, solar panels, ventilation systems, and blood vessels are affected by the buildup of particulates on their surfaces. Direct measurement of the adhesive force between a particle and a surface is key to understanding and mitigating particle fouling. Approaches such as the Johnson-Kendall-Roberts (JKR) and Derjaguin-Muller-Toporov (DMT) models offer a first approximation of the forces involved but do not account for non-idealities like roughness or plastic deformation. Experimental measurements of adhesive forces often deviate significantly from predictions. One approach to measure adhesion is the colloidal probe technique, which uses a particle attached to the tip of an atomic force microscope (AFM) cantilever. The particle is touched to a surface and then withdrawn and a pull-off force (FPO) determined by cantilever deflection. FPO can be used to estimate work of adhesion (Wa) and other properties from existing models. We describe a new method for producing colloidal probes using wax as an adhesive to attach micrometer-scale spheres to AFM tips. This method can be used with a range of particles and minimizes the potential for changes to the particle surface chemistry or geometry from exposure to heat, chemicals, radiation, or external forces. Particle attachment to AFM tips is robust and reversible, allowing old particles to be replaced with new ones in a few minutes. Pull-off measurements using polystyrene (PS) particles, pristine and modified with myristyltrimethylammonium bromide (14-TAB), were collected from various substrates to demonstrate the viability of this technique and investigate the impact of particle surface modification

Climate Change Decreases Nitrogen Pools and Mineralization Rates in Northern Hardwood Forests

Nitrogen (N) supply often limits the productivity of temperate forests and is regulated by a complex mix of biological and climatic drivers. In excess, N is linked to a variety of soil, water, and air pollution issues. Here, we use results from an elevation gradient study and historical data from the long-term Hubbard Brook Ecosystem Study (New Hampshire, USA) to examine relationships between changes in climate, especially during winter, and N supply to northern hardwood forest ecosystems. Low elevation plots with less snow, more soil freezing, and more freeze/thaw cycles supported lower rates of N mineralization than high elevation plots, despite having higher soil temperatures and no consistent differences in soil moisture during the growing season. These results are consistent with historical analyses showing decreases in rates of soil N mineralization and inorganic N concentrations since 1973 that are correlated with long-term increases in mean annual temperature, decreases in annual snow accumulation, and a increases in the number of winter thawing degree days. This evidence suggests that changing climate may be driving decreases in the availability of a key nutrient in northern hardwood forests, which could decrease ecosystem production but have positive effects on environmental consequences of excess N

Increasing risk of Amazonian drought due to decreasing aerosol pollution

The Amazon rainforest plays a crucial role in the climate system, helping to drive atmospheric circulations in the tropics by absorbing energy and recycling about half of the rainfall that falls on it. This region (Amazonia) is also estimated to contain about one-tenth of the total carbon stored in land ecosystems, and to account for one-tenth of global, net primary productivity. The resilience of the forest to the combined pressures of deforestation and global warming is therefore of great concern, especially as some general circulation models (GCMs) predict a severe drying of Amazonia in the twenty-first century. Here we analyse these climate projections with reference to the 2005 drought in western Amazonia, which was associated with unusually warm North Atlantic sea surface temperatures (SSTs). We show that reduction of dry-season (July–October) rainfall in western Amazonia correlates well with an index of the north–south SST gradient across the equatorial Atlantic (the 'Atlantic N–S gradient'). Our climate model is unusual among current GCMs in that it is able to reproduce this relationship and also the observed twentieth-century multidecadal variability in the Atlantic N–S gradient, provided that the effects of aerosols are included in the model. Simulations for the twenty-first century using the same model3, 8 show a strong tendency for the SST conditions associated with the 2005 drought to become much more common, owing to continuing reductions in reflective aerosol pollution in the Northern Hemisphere

Characterization of lab-based swarms of Anopheles gambiae mosquitoes using 3D-video tracking

Abstract Mosquito copulation is a crucial determinant of its capacity to transmit malaria-causing Plasmodium parasites as well as underpinning several highly-anticipated vector control methodologies such as gene drive and sterile insect technique. For the anopheline mosquitoes responsible for African malaria transmission, mating takes place within crepuscular male swarms which females enter solely to mate. However, the mechanisms that regulate swarm structure or that govern mate choice remain opaque. We used 3D-video tracking approaches and computer vision algorithms developed for the study of other complex biological systems to document swarming behavior of a lab-adapted Anopheles gambiae line in a lab-based setting. By reconstructing trajectories of individual mosquitoes lasting up to 15.88 s, in swarms containing upwards of 200 participants, we documented swarm-like behavior in both males and females. In single sex swarms, encounters between individuals were fleeting ( 0.75 s;  2.5 s). We also documented several examples of apparent male-male mating competition. These findings represent the first steps towards a more detailed and quantitative description of swarming and courtship behavior in one of the most important vectors of malaria

Supplemental Material, GSJ739610_suppl_mat - Spine Surgeon Treatment Variability: The Impact on Costs

<p> Supplemental Material, GSJ739610_suppl_mat for Spine Surgeon Treatment Variability: The Impact on Costs by Matthew D. Alvin, Daniel Lubelski, Ridwan Alam, Seth K. Williams, Nancy A. Obuchowski, Michael P. Steinmetz, Jeffrey C. Wang, Alfred J. Melillo, Amit Pahwa, Edward C. Benzel, Michael T. Modic, Robert Quencer, and Thomas E. Mroz in Global Spine Journal </p

The contribution of terrestrial sources and sinks to trends in the seasonal cycle of atmospheric carbon dioxide

We characterized decadal changes in the amplitude and shape of the seasonal cycle of atmospheric CO_2 with three kinds of analysis. First, we calculated the trends in the seasonal cycle of measured atmospheric CO_2 at observation stations in the National Oceanic and Atmospheric Administration Climate Monitoring and Diagnostic Laboratory network. Second, we assessed the impact of terrestrial ecosystems in various localities on the mean seasonal cycle of CO_2 at observation stations using the Carnegie‐Ames‐Stanford Approach terrestrial biosphere model and the Goddard Institute for Space Studies (GISS) atmospheric tracer transport model. Third, we used the GISS tracer model to quantify the contribution of terrestrial sources and sinks to trends in the seasonal cycle of atmospheric CO_2 for the period 1961–1990, specifically examining the effects of biomass burning, emissions from fossil fuel combustion, and regional increases in net primary production (NPP). Our analysis supports results from previous studies that indicate a significant positive increase in the amplitude of the seasonal cycle of CO_2 at Arctic and subarctic observation stations. For stations north of 55°N the amplitude increased at a mean rate of 0.66% yr^(−1) from 1981 to 1995. From the analysis of ecosystem impacts on the mean seasonal cycle we find that tundra, boreal forest, and other northern ecosystems are responsible for most of the seasonal variation in CO_2 at stations north of 55°N. The effects of tropical biomass burning on trends in the seasonal cycle are minimal at these stations, probably because of strong vertical convection in equatorial regions. From 1981 to 1990, fossil fuel emissions contributed a trend of 0.20% yr^(−1) to the seasonal cycle amplitude at Mauna Loa and less than 0.10% yr^(−1) at stations north of 55°N. To match the observed amplitude increases at Arctic and subarctic stations with NPP increases, we find that north of 30°N a 1.7 Pg C yr^(−1) terrestrial sink would be required. In contrast, over regions south of 30°N, even large NPP increases and accompanying terrestrial sinks would be insufficient to account for the increase in high‐latitude amplitudes