2,181 research outputs found
Serendipitous Data Following a Severe Windstorm in an Old-Growth Pine Stand
Reliable dimensional data for old-growth pine-dominated forests in the Gulf Coastal Plain of Arkansas are hard to find, but sometimes unfortunate circumstances provide good opportunities to acquire this information. On July 11, 2013, a severe thunderstorm with high winds struck the Levi Wilcoxon Demonstration Forest (LWDF) near Hamburg, Arkansas. This storm uprooted or snapped dozens of large pines and hardwoods and provided an opportunity to more closely inspect these rare specimens. For instance, the largest tree killed in this event, a loblolly pine (Pinus taeda), was 105 cm in diameter at breast height, 39.3 m tall, and if the tree had been sound would have yielded 3,803 board feet (Doyle log rule) of lumber. Gross board foot volume yield was also estimated from two other recently toppled large pines, an 85-cm-DBH loblolly and an 86-cm-DBH shortleaf pine (Pinus echinata), which tallied 2,430 and 2,312 board feet Doyle, respectively. A number of the other wind thrown pines on the LWDF were sound enough to count their rings for a reasonable (± 2-5 years) estimate of their ages. The stump of the fallen national champion shortleaf pine had 168 rings, and counts from other pines toppled by this storm had from 68 to 198 rings. We also searched for a new champion shortleaf pine using a LiDAR canopy height model of the LWDF to narrow our search. This preliminary assessment produced a number of targets that exceeded 40 m in height; further field checking of the tallest of these trees found that these were loblolly pines up to about 44 m. We eventually found shortleaf pines between 37 and 41 m tall, with diameters of up to 85 cm, indicating that the LWDF could still contain the Arkansas state champion
Multiscale fluid--particle thermal interaction in isotropic turbulence
We use direct numerical simulations to investigate the interaction between
the temperature field of a fluid and the temperature of small particles
suspended in the flow, employing both one and two-way thermal coupling, in a
statistically stationary, isotropic turbulent flow. Using statistical analysis,
we investigate this variegated interaction at the different scales of the flow.
We find that the variance of the fluid temperature gradients decreases as the
thermal response time of the suspended particles is increased. The probability
density function (PDF) of the fluid temperature gradients scales with its
variance, while the PDF of the rate of change of the particle temperature,
whose variance is associated with the thermal dissipation due to the particles,
does not scale in such a self-similar way. The modification of the fluid
temperature field due to the particles is examined by computing the particle
concentration and particle heat fluxes conditioned on the magnitude of the
local fluid temperature gradient. These statistics highlight that the particles
cluster on the fluid temperature fronts, and the important role played by the
alignments of the particle velocity and the local fluid temperature gradient.
The temperature structure functions, which characterize the temperature
fluctuations across the scales of the flow, clearly show that the fluctuations
of the fluid temperature increments are monotonically suppressed in the two-way
coupled regime as the particle thermal response time is increased. Thermal
caustics dominate the particle temperature increments at small scales, that is,
particles that come into contact are likely to have very large differences in
their temperature. This is caused by the nonlocal thermal dynamics of the
particles..
Irreversibility-inversions in 2 dimensional turbulence
In this paper we consider a recent theoretical prediction (Bragg \emph{et
al.}, Phys. Fluids \textbf{28}, 013305 (2016)) that for inertial particles in
2D turbulence, the nature of the irreversibility of the particle-pair
dispersion inverts when the particle inertia exceeds a certain value. In
particular, when the particle Stokes number, , is below a certain
value, the forward-in-time (FIT) dispersion should be faster than the
backward-in-time (BIT) dispersion, but for above this value, this
should invert so that BIT becomes faster than FIT dispersion. This non-trivial
behavior arises because of the competition between two physically distinct
irreversibility mechanisms that operate in different regimes of . In
3D turbulence, both mechanisms act to produce faster BIT than FIT dispersion,
but in 2D turbulence, the two mechanisms have opposite effects because of the
flux of energy from the small to the large scales. We supplement the
qualitative argument given by Bragg \emph{et al.} (Phys. Fluids \textbf{28},
013305 (2016)) by deriving quantitative predictions of this effect in the short
time limit. We confirm the theoretical predictions using results of inertial
particle dispersion in a direct numerical simulation of 2D turbulence. A more
general finding of this analysis is that in turbulent flows with an inverse
energy flux, inertial particles may yet exhibit a net downscale flux of kinetic
energy because of their non-local in-time dynamics
Bacterial Quality of Private Water Wells in Clark County, Arkansas
Most private water wells in Clark County appeared to be contaminated by bacteria, apparently entering the wells from surface water seepage. Eighteen to 24% of the wells investigated were positive for fecal contamination. Deeper wells were less often contaminated. More than one-half of the wells sampled exceeded recommended limits of inorganic chemicals for safe potable water. High concentrations of iron and manganese were most common, exceeding recommended limits in more than 40% of the well
Distribution and Efficiency of Hydrocarbon-Oxidizing Bacteria in a Freshwater Reservoir
Hydrocarbon-oxidizing bacteria were identified from three stations on DeGray Reservoir, Arkansas. The organisms were primarily gram-negative rods representing 9 taxa and 37 biotypes Pseudomonas spp. were the most common isolates. The largest populations were found in areas most frequently used by boaters, although seasonal fluctuations were apparent during the spring and fall. The degradation of outboard motor oil by the five most rapidly growing isolates was studied. Each species had a different decomposition profile, and substrate oxidation rates were variable Acinetobacter calcoaceticus var. anitratus was the most efficient decomposer
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