176,888 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
Living Close to Your Neighbors: The Importance of Both Competition and Facilitation in Plant Communities
Recent work has demonstrated that competition and facilitation likely operate jointly in plant communities, but teasing out the relative role of each has proven difficult. Here we address how competition and facilitation vary with seasonal fluctuations in environmental conditions, and how the effects of these fluctuations change with plant ontogeny. We planted three sizes of pine seedlings (Pinus strobus) into an herbaceous diversity experiment and measured pine growth every two weeks for two growing seasons. Both competition and facilitation occurred at different times of year between pines and their neighbors. Facilitation was important for the smallest pines when environmental conditions were severe. This effect decreased as pines got larger. Competition was stronger than facilitation overall and outweighed facilitative effects at annual time scales. Our data suggest that both competition and the counter‐directional effects of facilitation may be more common and more intense than previously considered
Understanding High Temperature Superconductors: Progress and Prospects
I review progress in measurements of the dynamic spin susceptibility in the
normal state which yield a new phase diagram and discuss microscopic
calculations which yield qualitative, and in many cases, quantitative agreement
with the measured changes in the quasiparticle, transport, magnetotransport,
and optical properties of the cuprate superconductors as one varies doping and
temperature provided one describes the systems as nearly anti-ferromagnetic
Fermi liquids in which the effective magnetic interaction between planar
quasiparticles mirrors the dynamic spin susceptibility measured in NMR and INS
experiments. Together with the demonstration that the NAFL pairing potential
leads inexorably to a d_x2-y2,pairing state, this work provides a "proof of
concept" for the NAFL description of high Tc materials. I review Eliashberg
calculations of the mean-field behavior found in overdoped systems and discuss
the extent to which the crossovers to pseudoscaling and pseudogap behavior
found in the effective magnetic interaction and quasiparticle behavior in the
optimally doped and underdoped systems may be derived microscopically. I
conclude with a tentative scenario for the dependence of Tc on doping level and
imperfections in different systems.Comment: 6 pages, 1 figure. To appear in a special issue of Physica C of the
M2S-HTSC-V Conference held Feb. 28-Mar. 4, 1997, in Beijing, Chin
Nearly Antiferromagnetic Fermi Liquids: A Progress Report
I describe recent theoretical and experimental progress in understanding the
physical properties of the two dimensional nearly antiferromagnetic Fermi
liquids (NAFL's) found in the normal state of the cuprate superconductors. In
such NAFL's, the magnetic interaction between planar quasiparticles is strong
and peaked at or near the commensurate wave vector, . For
the optimally doped and underdoped systems, the resulting strong
antiferromagnetic correlations produce three distinct magnetic phases in the
normal state: mean field above , pseudoscaling between and
, and pseudogap below . I present arguments which suggest that the
physical origin of the pseudogap found in the quasiparticle spectrum below
is the formation of a precursor to a spin-density-wave-state, describe
the calculations based on this scenario of the dynamical spin susceptibility,
Fermi surface evolution, transport, and Hall effect, and summarize the
experimental evidence in its support.Comment: LATEX + PS figures. To appear in the proceedings of the
Euroconference on "Correlations in Unconventional Quantum Liquids," Evora,
Portugal, October 199
N-body description of Debye shielding and Landau damping
This paper brings further insight into the recently published N-body
description of Debye shielding and Landau damping [Escande D F, Elskens Y and
Doveil F 2014 Plasma Phys. Control. Fusion 57 025017]. Its fundamental equation
for the electrostatic potential is derived in a simpler and more rigorous way.
Various physical consequences of the new approach are discussed, and this
approach is compared with the seminal one by Pines and Bohm [Pines D and Bohm D
1952 Phys. Rev. 85 338--353].Comment: invited talk to 42nd EPS conference on plasma physics (Lisbon, 2015),
submitted to Plasma Physics and Controlled Fusio
Book Review: Siva in the Forest of Pines: An Essay on Sorcery and Self-Knowledge
A review of Siva in the Forest of Pines: An Essay on Sorcery and Self-Knowledge by Don Handelman and David Shulman
Pines Calyx Earth Tube Performance
In temperate climates earth tubes achieve increased comfort in summer and the pre-heating of inlet air in winter, reducing the requirement for cooling and heating. This strategy was adopted to pre-temper air entering a small conference centre building in Kent, UK. The earth tube is about 16m long comprising a concrete pipe with an internal diameter of 0.6m. The pipe is located approximately 1.5m below ground level. A very low energy fan at the outlet end draws air through the tube and pushes it through a heat exchanger before it is distributed via ducts in the building. This paper reports on the results of monitoring the earth tube temperatures and air velocities under different weather conditions. Temperature sensors were positioned externally and at both ends of the earth tube. An anemometer was fixed in place 4m from the inlet end. This ‘fixed’ anemometer in the earth tube was calibrated and the velocity profile of the air flow in the tube was established. The air in the tube was found to have an almost uniform velocity profile, which is likely to be caused by the considerable turbulence created by changes in the direction of the tube, and the dimensions of the pipe relative to the flow rate. This indicates that the system was well-designed to maximise the heat exchange potential of the duct. The energy contribution of the earth in pre-heating and pre-cooling the air has been calculated at approximately 500W for each degree Kelvin raised or lowered, compared to only 18W power consumed by the fans. This demonstrates that earth tubes can make a very significant contribution to providing heating and cooling, with very low carbon emissions. Earth tubes are a durable and low-cost method of providing resilience in the face of climate change
Menthol mouth rinsing: An applied perspective
With the Tokyo Olympics rapidly approaching, and increasing global temperatures, applied nutrition practitioners and supporting scientists are looking for ways to physiologically cool their athletes, but the value of perceptual cooling is also gaining a profile; menthol mouth swilling is one such strategy. This article provides a brief synopsis of menthol research to date,
followed by a reflection of how we have used menthol mouth rinsing to complement anIro nman™ triathlete’s event nutrition strategy, and concludes by highlighting ethical concerns with menthol mouth rinsing
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