Tempo-spatial patterns of PM2.5 measured using a portable particulate monitor around a mine complex in Canada's Arctic.

Mining activities in Canada's pristine Arctic (e.g., driving on unpacked roads, blasts, rock grinding, diesel combustion, and garbage incineration) could add local sources of airborne fine particulate matter with a diameter of < 2.5 µm (PM2.5) to their surrounding area. The increase in PM2.5 above the background level around a mine represents a potential disturbance to caribou. To quantify the spatial distribution of the elevated PM2.5, we investigated three different sampling schemes to measure PM2.5 concentration using a portable monitor. We found that the best sampling scheme was to use the regional background PM2.5 as the reference and analyze the anomaly of PM2.5 measured at sites around the mine complex from the background level. The regional background PM2.5 values were measured at the Daring Lake Tundra Research Station during 2018 and 2019. Our results indicated that the background PM2.5 was not a low and constant value but varied with rain events, wind direction, and the impacts of forest fire smoke. After excluding periods affected by forest fires smokes, we found the background PM2.5 was close to 0 µg m-3 for the first few hours after rain, and then increased logistically with the time after rain (tar) to the maximum of 5 (or 10) µg m-3 when the wind came from the north (or south) of the NW-SE axis. The NW-SE axis in western Canada divides the tundra north with few anthropogenic PM2.5 sources from the forested south with many PM2.5 sources from forest fire smokes and human activities. Analyses of PM2.5 anomaly from the background (i.e., PM2.5 measured at a site around the mining complex-the background level at the corresponding tar and wind direction) revealed that the zone of elevated PM2.5 around the mine (Zepm) expanded with tar. In the first few hours after rain, PM2.5 was close to 0 everywhere except within meters of a source (e.g., a truck exhaust) in the downwind direction. During tar = 6 to 96 h, Zepm expanded to 6.3 km in the downwind direction when the wind came from south of the NW-SE axis. A similar result was found in the downwind direction when the wind came from north of the NW-SE axis, with Zepm = 4.4 km. In the upwind direction, the value of Zepm was much smaller, being 0.7 km (or 1.0 km) when the wind came from the north (or south) of the NW-SE axis. For the period of tar between 96 and 192 hours, Zepm further expanded to 21.2 km when the wind from the south of the NW-SE axis. The results from this study indicated that this reference paradigm that uses the regional background PM2.5 as the reference in combination with a portable PM2.5 monitor worked well for quantifying the tempo-spatial patterns of PM2.5 at locations in remote and mostly pristine Arctic. However, their effectiveness for other regions needs further investigation.

A biomechanical comparison of periprosthetic femoral fracture fixation in normal and osteoporotic cadaveric bone.

Several techniques are described for fixation of Vancouver B1 femoral shaft fractures after total hip arthroplasty. Twenty-four femurs were scanned by dual x-ray absorptiometry scanned and matched for bone mineral density. Femurs were implanted with a cemented simulated total hip prosthesis with a simulated periprosthetic femur fracture distal to the stem. Fractures were fixed with Synthes (Paoli, Pa) 12-hole curved plates and 4 different constructs proximally. Each construct was loaded to failure in axial compression. Constructs with locking and nonlocking screws demonstrated equivalent loads at failure and were superior in load at failure compared with cables. Cable constructs failed proximally. No proximal failures occurred in specimens fixed with screws and cables. A combination of locked or nonlocked screws and supplemental cable fixation is recommended for the treatment of Vancouver B1 periprosthetic femur fractures.

Possible role of relativistic effects in the plasticity of the coordination geometry of cadmium(II). A voltammetric study of the stability of the complexes of cadmium(II) with 12-crown-4,15-crown-5 and 18-crown-6 in aqueous solution and the structures of [Cd(benzo-18-crown-6)(NCS)(2)] and [K(18-crown-6)][Cd(SCN)(3)].

A differential pulse voltammetric study of complexes of Cd(II) and Pb(II) with crown ethers is reported. Measured log K(1) values for Cd(II) with 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane), 15-crown-5 (1,4,7,10,13-pentaoxacyclopentadecane), and 12-crown-4 (1,4,7,10-tetraoxacyclododecane) are respectively 2.53 (+/-0.06), 1.97 (+/-0.07), and 1.72 (+/-0.08) and for Pb(II) with 18-crown-6 is 4.17 (+/-0.03), all at 25 degrees C in 0.1 M LiNO(3). Cd(II) is smaller than is usually associated with strong bonding with crown ethers. The high log K(1) values for Cd(2+) with crown ethers found here are discussed in terms of distortion of Cd(II) by relativistic effects. The resulting plasticity of the coordination geometry of the Cd(II) ion allows it to meet the metal ion size requirements of all the crown ethers, allowing high log K(1) values to occur. Crystal structures for [Cd(bz-18-crown-6)(SCN)(2)] (1) (bz-18-crown-6 = benzo-1,4,7,10,13,16-hexaoxacyclooctadecane) and [K(18-crown-6)][Cd(SCN)(3)] (2) are reported. 1 was triclinic, space group P1, a = 8.5413(2), b = 10.0389(2), and c = 13.4644(2) A, alpha = 94.424(1), beta = 102.286(1), and gamma = 93.236(1) degrees, Z = 2, and final R = 0.023. 2 was orthorhombic, space group Cmc2(1), a = 14.7309(3), b = 15.1647(3), and c = 10.6154(2) A, Z = 4, and final R = 0.020. In 1, the Cd occupies the cavity of the bz-18-crown-6 with long average Cd-O bond lengths of 2.65 A and is N-bonded to the thiocyanates with short average Cd-N bonds of 2.12 A. In [Cd(bz-18-crown-6)(SCN)(2)], the linear coordination involving the Cd and the two N-bonded thiocyanate groups in 1 is discussed in terms of the role of relativistic effects in the tendency to linear coordination geometry in group 12 metal ions. In 2 Cd forms a polymeric structure involving thiocyanate bridges between Cd atoms and K(+) occupies the cavity of the crown ether. 2 highlights the fact that cadmium is almost never S-bonded to thiocyanate except in bridging thiocyanates.