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The history of the Black Mountains in North Carolina and the southern
Spruce-Fir ecosystem has been fraught with widespread forest decline since the
mid 1960’s. Balsam Woolly Adelgid attacks and acidic deposition were two of the
most recognized causes of decline. Uncertainty arose about the future of these
forests, and projections were made regarding the endangerment or extinction of
the endemic Fraser fir ([Pursh] Poiret). This study analyzed data sets from a permanent plot network in the Black Mountains
dating 1985, 2002, and 2012. Indications that the Fraser fir population is
stabilizing from a “boom-bust” cycle of population growth and has entered the
stem exclusion stage of forest stand development are evident. Fir live stem density increased more than 250% from 1985 to
2002, and then declined 40% by 2012 at the highest elevations in the forest.
Overall, fir appeared to be more impacted on western facing slopes than eastern
ones. The population of red spruce experienced a steady decrease in live stem
counts, but an increase in live basal area through all years, and at all
elevation classes (1675 m, 1830 m, and 1980 m), indicating a normal progression through stand development. Red spruce
was also most negatively impacted on western facing slopes. Live stem density
was significantly higher (P < 0.001) than eastern plots, but live
basal area was similar between the two aspects. Atmospheric deposition
concentrations of the four main acidic molecules at Mt. Mitchell all peaked in
1998, but decreased by 2012. These reductions, occurring shortly after
tightened regulations in the 1990 amendments to the Clean Air Act may have
potential implications for increased forest resilience.
A cradle-to-grave life cycle assessment is done to identify the environmental impacts of chromated copper arsenate (CCA)-treated timber used for highway guard rail posts, to understand the processes that contribute to the total impacts, and to determine how the impacts compare to the primary alternative product, galvanized steel posts. Guard rail posts are the supporting structures for highway guard rails. Transportation engineers, as well as public and regulatory interests, have increasing need to understand the environmental implications of guard rail post selection, in addition to factors such as costs and service performance. This study uses a life cycle inventory (LCI) to catalogue the input and output data from guard rail post manufacture, service life, and disposition, and a life cycle impact assessment (LCIA) to assess anthropogenic and net greenhouse gas (GHG), acidification, smog, ecotoxicity, and eutrophication potentially resulting from life cycle air emissions. Other indicators of interest also are tracked, such as fossil fuel and water use. Comparisons of guard rail post products are made at a functional unit of one post per year of service. This life cycle assessment (LCA) finds that the manufacture, use, and disposition of CCA-treated wood guard rails offers lower fossil fuel use and lower anthropogenic and net GHG emissions, acidification, smog potential, and ecotoxicity environmental impacts than impact indicator values for galvanized steel posts. Water use and eutrophication impact indicator values for CCA-treated guard rail posts are greater than impact indicator values for galvanized steel guard rail posts.
Creosote-treated wooden railroad crossties have been used for more than a century to support steel rails and to transfer load from the rails to the underlying ballast while keeping the rails at the correct gauge. As transportation engineers look for improved service life and environmental performance in railway systems, alternatives to the creosote-treated wooden crosstie are being considered. This paper compares the cradle-to-grave environmental life cycle assessment (LCA) results of creosote-treated wooden railroad crossties with the primary alternative products: concrete and plastic composite (P/C) crossties. This LCA includes a life cycle inventory (LCI) to catalogue the input and output data from crosstie manufacture, service life, and disposition, and a life cycle impact assessment (LCIA) to evaluate greenhouse gas (GHG) emissions, fossil fuel and water use, and emissions with the potential to cause acidification, smog, ecotoxicity, and eutrophication. Comparisons of the products are made at a functional unit of 1.61 kilometers (1.0 mile) of rail-road track per year. This LCA finds that the manufacture, use, and disposition of creosote-treated wooden railroad crossties offers lower fossil fuel and water use and lesser environmental impacts than competing products manufactured of concrete and P/C.
and screw constructs are routinely used in the treatment of long bone
fractures. Despite considerable advancements in technology and techniques,
there can still be complications in the healing of long bone fractures.
Non-unions, delayed unions, and hardware failures are common complications observed
in clinical practice following open reduction and internal fixation of
fractures . Potential causes of these adverse clinical effects may be disruptive
to the periosteal and endosteal blood supply, stress shielding effects, and
inadequate mechanical stability. The goal of the present study was to explore
the effect of screw position on the fracture healing and formation of new bone
tissue with mechanoregulatory algorithms in a computational model. An idealized
poroelastic 3D finite element (FE) model of a femur with a 5 mm fracture gap,
including a plate-screw construct was developed. Nineteen different plate-screw
combinations, created by varying the number and position of screws within the
plate, were created to identify a construct with the most favourable attributes
for fracture healing. The first phase of the study evaluated constructs through
mechanical stress analyses to identify those constructs with high loadsupport
capability. The second phase of the study evaluated healing and bone formation
with a biphasic mechanoregulatory algorithm to simulate tissue differentiation
for fixation within selected constructs. The results of our analysis demonstrated
a 4-screw symmetrical construct with the largest distance between screws to
provide the most favourable balance of stability and optimized conditions to
promote fracture healing.