Ecological effects of particulate matter.

Atmospheric particulate matter (PM) is a heterogeneous material. Though regulated as un-speciated mass, it exerts most effects on vegetation and ecosystems by virtue of the mass loading of its chemical constituents. As this varies temporally and spatially, prediction of regional impacts remains difficult. Deposition of PM to vegetated surfaces depends on the size distribution of the particles and, to a lesser extent, on the chemistry. However, chemical loading of an ecosystem may be determined by the size distribution as different constituents dominate different size fractions. Coating with dust may cause abrasion and radiative heating, and may reduce the photosynthetically active photon flux reaching the photosynthetic tissues. Acidic and alkaline materials may cause leaf surface injury while other materials may be taken up across the cuticle. A more likely route for metabolic uptake and impact on vegetation and ecosystems is through the rhizosphere. PM deposited directly to the soil can influence nutrient cycling, especially that of nitrogen, through its effects on the rhizosphere bacteria and fungi. Alkaline cation and aluminum availability are dependent upon the pH of the soil that may be altered dramatically by deposition of various classes of PM. A regional effect of PM on ecosystems is linked to climate change. Increased PM may reduce radiation interception by plant canopies and may reduce precipitation through a variety of physical effects. At the present time, evidence does not support large regional threats due to un-speciated PM, though site-specific and constituent-specific effects can be readily identified. Interactions of PM with other pollutants and with components of climate change remain important areas of research in assessment of challenges to ecosystem stability.

Isometry of the anterior cruciate ligament: an intraoperative perspective.

The emphasis our society places on physical fitness has produced an ever increasing number of injuries to the anterior cruciate ligament (ACL). To successfully replace the anterior cruciate deficient knee, physicians need to determine the "ideal" location for the femoral tunnel. In the search to find this "isometric point," if there is one, we draw attention to the origin of the distal fascicles of the anterior cruciate from the lateral femoral condyle. Visualizing this surgical landmark can facilitate and expedite accurate placement of the isometric device and thus influence the results of the surgical procedure. Also, magnetic resonance imaging may help the surgeon in locating the origin of the ACL.