2,532 research outputs found
The Development of Ecological Functions in Created Forested Wetlands
Wetland mitigation has become a 2.4 billion dollar per year industry in the U.S. and in Virginia it leads to the replacement of 77 ha of palustrine forested wetlands (PFWs) per year with mitigation wetlands, including created forested wetlands (CFWs). Mitigation hinges on the idea that compensation wetlands lead to āno net loss of wetland functionā when compared to impacted wetlands. We assessed the functions of provision of habitat and biogeochemical functions associated with production of biomass, the retention and removal of nutrients and the accumulation of soil C over 8 years in seven CFWs of approximately 11 and 20 years and compared them to natural reference wetlands (NRWs). CFW plant communities were similar to NRWs in all measured parameters in the herbaceous and shrub/sapling strata and in all strata combined. However, non-native dominance showed a significant positive linear relationship with CFW age. In the tree strata, 11 year old (yo) CFWs had lower richness than NRWs and both age classes of CFWs had lower FQI than NRWs. NRWs held 10 to 20 times more carbon in woody biomass than CFWs. Tree species composition was significantly different between CFWs and NRWs, however NRW trees were similar to CFW saplings. 11 yo CFWs held lower percentages of C, N and P and had higher Db than NRWs in both the 0-10 and 10-20 cm depth. 20 yo CFWs developed similar levels of %C, %P, bulk density (Db), and nutrient ratios in the surface and displayed rapid increases in %C and %N over 8 years. However, CFWs offered 45% lower soil total soil C storage and 50% lower %N. Furthermore, all CFWs stored lower nutrient levels than NRWs in the 10-20 cm soil depth. We found that FQI correlated positively with total C accumulation rates in woody biomass and soil C, indicating that biogeochemical function and the provision of habitat can be complimentary in CFWs. Finally, 11 and 20 yo CFWs adhered to the regulatory performance standards established for Virginia in terms of stems per ha and wetland indicator status, but all wetlands (including NRWs) failed to achieve \u3c5% non-native species cover
Turbulence, spatial transport, and heating of the solar wind
A phenomenological theory describes radial evolution of plasma turbulence in the solar wind from 1 to 50 astronomical units. The theory includes a simple closure for local anisotropic magnetohydrodynamic turbulence, spatial transport, and driving by large-scale shear and pickup ions. Results compare well to plasma and magnetic field data from the Voyager 2 spacecraft, providing a basis for a concise, tractable description of turbulent energy transport in a variety of astrophysical plasmas
Tragedy of the common canal
This paper uses laboratory experiments to investigate the effects of alternative solutions to a common-pool resource with a unidirectional flow. The focus is on the comparative economic efficiency of communications, bilateral āCoasianā bargaining, auctions and price-based allocations. All treatments improve allocative efficiency relative to a baseline environment. Communication and bilateral bargaining are not generally as effective as market allocations. An exogenously imposed, optimal fee results in the greatest efficiency gain, followed by auction allocations that determine the usage fee endogenously.externalities, experiments, auctions, Coasian bargaining, common pool resource
Defective hierarchical porous copper-based metal-organic frameworks synthesised via facile acid etching strategy
Introducing hierarchical pore structure to microporous materials such as
metal-organic frameworks (MOFs) can be beneficial for reactions where the rate
of reaction is limited by low rates of diffusion or high pressure drop. This
advantageous pore structure can be obtained by defect formation, mostly via
post-synthetic acid etching, which has been studied extensively on water-stable
MOFs. Here we show that a water-unstable HKUST-1 MOF can also be modified in a
corresponding manner by using phosphoric acid as a size-selective etching agent
and a mixture of dimethyl sulfoxide and methanol as a dilute solvent.
Interestingly, we demonstrate that the etching process which is time- and
acidity- dependent, can result in formation of defective HKUST-1 with extra
interconnected hexagonal macropores without compromising on the bulk
crystallinity. These findings suggest an intelligent scalable synthetic method
for formation of hierarchical porosity in MOFs that are prone to hydrolysis,
for improved molecular accessibility and diffusion for catalysis.Comment: 14 pages, 8 figure
Heating the outer heliosphere by pickup protons
There is a growing body of literature that demonstrates the ability of a turbulent cascade within the solar wind to heat the thermal protons. Several sources of energy are required to accomplish the observed heating. Wind shear and shocks originating with the multiple source of wind plasma heat the wind inside ā½AU. However, beyond this distance little is left of these sources and all that remains is the energy injected into the plasma by the pickup of newborn protons originating from interstellar neutrals. Recent advances in the theory of wave excitation by the newborn protons allows us to return to the published heating theory and remove a previously unexplained parameterization of the heating due to pickup protons. Furthermore, recent observational evidence suggests that large-scale correlations between the wind speed and the proton temperature exist into the distant outer heliosphere that motivate an attempt to connect the two within the structure of the heating theory
Quantifying Mangrove Canopy Regrowth and Recovery after Hurricane Irma with Large-Scale Repeat Airborne Lidar in the Florida Everglades
Increased Thymic B Cells but Maintenance of Thymic Structure, T Cell Differentiation and Negative Selection in Lymphotoxin-Ī± and TNF Gene-Targeted Mice
TNF, lymphotoxin (LT) and their receptors are expressed constitutively in the thymus. It
remains unclear whether these cytokines play a role in normal thymic structure or function.
We have investigated thymocyte differentiation, selection and thymic organogenesis in gene
targeted mice lacking LTĪ±, TNF, or both (TNF/LTĪ±-/-). The thymus was normal in
TNF/LTĪ±-/- mice with regard to cell yields and stromal architecture. Detailed analysis of Ī±Ī²
and Ī³Ī“ T cell-lineage thymocyte subsets revealed no abnormalities, implying that neither TNF
nor LT play an essential role in T cell differentiation or positive selection. The number and
distribution of thymic CD11c+ dendritic cells was also normal in the absence of both TNF and
LTĪ±. A three-fold increase in B cell numbers was observed consistently in the TNF/LTĪ±-/-
thymus. This phenotype was due entirely to the LTĪ± deficiency and associated with changes
in the hemopoietic compartment, rather than the thymic stromal compartment of LTĪ±-/- mice.
Finally, specific VĪ²8+ T cell deletion within the thymus following intrathymic injection of
staphylococcal enterotoxin B (SEB) was TNF/LT independent. Thus, despite the presence of
these cytokines and their receptors in the normal thymus, there appears no essential role for
either TNF or LT in development of organ structure or for those processes associated with T
cell repertoire selection
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