51 research outputs found
A Study on the Active Induction Control of Upstream Wind Turbines for total power increases
In this study, the effect of active induction control of upstream wind turbines is investigated. Two scaled wind turbines having a rotor diameter of 1 m with a spacing of four times of the rotor diameter were used to experimentally validate the concept. Also, an in-house c code was used to simulate the same two wind turbines and see if the experimental observations can be obtained. From the experiment, approximately 0.81% increase of total power could be observed. Although the simulation results were not exactly the same as the experimental results but the shape was similar and the maximum power increase of 0.27% was predicted. Also from further simulation using NREL 5MW wind turbines instead of scaled wind turbines with realistic ambient turbulence intensity, it was found that the power increase could become more than 1%
Cosmological Luminosity Evolution of QSO/AGN Population
We apply the observed optical/X-ray spectral states of the Galactic black
hole candidates (GBHCs) to the cosmological QSO luminosity evolution under the
assumptions that QSOs and GBHCs are powered by similar accretion processes and
that their emission mechanisms are also similar. The QSO luminosity function
(LF) evolution in various energy bands is strongly affected by the spectral
evolution which is tightly correlated with the luminosity evolution. We
generate a random sample of QSOs born nearly synchronously by allowing the QSOs
to have redshifts in a narrow range around an initial high redshift, black hole
masses according to a power-law, and mass accretion rates near Eddington rates.
The QSOs evolve as a single long-lived population on the cosmological time
scale. The pure luminosity evolution results in distinct luminosity evolution
features due to the strong spectral evolution. Most notably, different energy
bands (optical/UV, soft X-ray, and hard X-ray) show different evolutionary
trends and the hard X-ray LF in particular shows an apparent reversal of the
luminosity evolution (from decreasing to increasing luminosity) at low
redshifts, which is not seen in the conventional pure luminosity evolution
scenario without spectral evolution. The resulting mass function of black holes
(BHs), which is qualitatively consistent with the observed QSO LF evolution,
shows that QSO remnants are likely to be found as BHs with masses in the range
10**8-5x10**10 solar masses. The long-lived single population of QSOs are
expected to leave their remnants as supermassive BHs residing in rare, giant
elliptical galaxies.Comment: 9 pages, 2 figures, ApJ
Effects of human demand on conservation planning for biodiversity and ecosystem services
Safeguarding ecosystem services and biodiversity is critical to achieving sustainable development. To date, ecosystem services quantification has focused on the biophysical supply of services with less emphasis on human beneficiaries (i.e., demand). Only when both occur do ecosystems benefit people, but demand may shift ecosystem service priorities toward human-dominated landscapes that support less biodiversity. We quantified how accounting for demand affects the efficiency of conservation in capturing both human benefits and biodiversity by comparing conservation priorities identified with and without accounting for demand. We mapped supply and benefit for 3 ecosystem services (flood mitigation, crop pollination, and nature-based recreation) by adapting existing ecosystem service models to include and exclude factors representing human demand. We then identified conservation priorities for each with the conservation planning program Marxan. Particularly for flood mitigation and crop pollination, supply served as a poor proxy for benefit because demand changed the spatial distribution of ecosystem service provision. Including demand when jointly targeting biodiversity and ecosystem service increased the efficiency of conservation efforts targeting ecosystem services without reducing biodiversity outcomes. Our results highlight the importance of incorporating demand when quantifying ecosystem services for conservation planning
Ecology and economics of using native managed bees for almond pollination
Native managed bees can improve crop pollination, but a general framework for evaluating the associated economic costs and benefits has not been developed. We conducted a costâbenefit analysis to assess how managing blue orchard bees (Osmia lignaria Say [Hymenoptera: Megachildae]) alongside honey bees (Apis mellifera Linnaeus [Hymenoptera: Apidae]) can affect profits for almond growers in California. Specifically, we studied how adjusting three strategies can influence profits: (1) number of released O. lignaria bees, (2) density of artificial nest boxes, and (3) number of nest cavities (tubes) per box. We developed an ecological model for the effects of pollinator activity on almond yields, validated the model with published data, and then estimated changes in profits for different management strategies. Our model shows that almond yields increase with O. lignaria foraging density, even where honey bees are already in use. Our costâbenefit analysis shows that profit ranged from âUS2,800/ acre given different combinations of the three strategies. Adding nest boxes had the greatest effect; we predict an increase in profit between low and high nest box density strategies (2.5 and 10 boxes/acre). In fact, the number of released bees and the availability of nest tubes had relatively small effects in the high nest box density strategies. This suggests that growers could improve profits by simply adding more nest boxes with moderate number of tubes in each. Our approach can support grower decisions regarding integrated crop pollination and highlight the importance of a comprehensive ecological economic framework for assessing these decisions
Asymmetric Supernovae, Pulsars, Magnetars, and Gamma-Ray Bursts
We outline the possible physical processes, associated timescales, and
energetics that could lead to the production of pulsars, jets, asymmetric
supernovae, and weak gamma-ray bursts in routine circumstances and to a
magnetar and perhaps stronger gamma-ray burst in more extreme circumstances in
the collapse of the bare core of a massive star. The production of a
LeBlanc-Wilson MHD jet could provide an asymmetric supernova and result in a
weak gamma-ray burst when the jet accelerates down the stellar density gradient
of a hydrogen-poor photosphere. The matter-dominated jet would be formed
promptly, but requires 5 to 10 s to reach the surface of the progenitor of a
Type Ib/c supernova. During this time, the newly-born neutron star could
contract, spin up, and wind up field lines or turn on an alpha-Omega dynamo. In
addition, the light cylinder will contract from a radius large compared to the
Alfven radius to a size comparable to that of the neutron star. This will
disrupt the structure of any organized dipole field and promote the generation
of ultrarelativistic MHD waves (UMHDW) at high density and Large Amplitude
Electromagnetic Waves (LAEMW) at low density. The generation of the these waves
would be delayed by the cooling time of the neutron star about 5 to 10 seconds,
but the propagation time is short so the UMHDW could arrive at the surface at
about the same time as the matter jet. In the density gradient of the star and
the matter jet, the intense flux of UMHDW and LAEMW could drive shocks,
generate pions by proton-proton collision, or create electron/positron pairs
depending on the circumstances. The UMHDW and LAEMW could influence the
dynamics of the explosion and might also tend to flow out the rotation axis to
produce a collimated gamma-ray burst.Comment: 31 pages, LaTeX, revised for referee comments, accepted for ApJ, July
10 issu
Disaggregating the evidence linking biodiversity and ecosystem services
Ecosystem services (ES) are an increasingly popular policy framework for connecting biodiversity with human well-being. These efforts typically assume that biodiversity and ES covary, but the relationship between them remains remarkably unclear. Here we analyse \u3e500 recent papers and show that reported relationships differ among ES, methods of measuring biodiversity and ES, and three different approaches to linking them (spatial correlations, management comparisons and functional experiments). For spatial correlations, biodiversity relates more strongly to measures of ES supply than to resulting human benefits. For management comparisons, biodiversity of ù ⏠service providers\u27 predicts ES more often than biodiversity of functionally unrelated taxa, but the opposite is true for spatial correlations. Functional experiments occur at smaller spatial scales than management and spatial studies, which show contrasting responses to scale. Our results illuminate the varying dynamics relating biodiversity to ES, and show the importance of matching management efforts to the most relevant scientific evidence
Formation of Millisecond Pulsars from Accretion Induced Collapse and Constraints on Pulsar Gamma Ray Burst Models
We study accretion induced collapse of magnetized white dwarfs as an origin
of millisecond pulsars. We apply magnetized accretion disk models to the
pre-collapse accreting magnetic white dwarfs and calculate the white dwarf spin
evolution. If the pulsar magnetic field results solely from the flux-frozen
fossil white dwarf field, a typical millisecond pulsar is born with a field
strength . The uncertainty in the field strength is
mainly due to the uncertain physical parameters of the magnetized accretion
disk models. A simple correlation between the pulsar spin and the
magnetic field , , is
derived for a typical accretion rate \sim 5\times 10^{-8}M_{\sun}/yr. This
correlation remains valid for a wide pre-collapse physical conditions unless
the white dwarf spin and the binary orbit are synchronized prior to accretion
induced collapse. We critically examine the possibility of spin-orbit
synchronization in close binary systems. Using idealized homogeneous ellipsoid
models, we compute the electromagnetic and gravitational wave emission from the
millisecond pulsars and find that electromagnetic dipole emission remains
nearly constant while millisecond pulsars may spin up rather than spin down as
a result of gravitational wave emission. We also derive the physical conditions
under which electromagnetic emission from millisecond pulsars formed by
accretion induced collapse can be a source of cosmological gamma-ray bursts. We
find that relativistic beaming of gamma-ray emission and precession of
gamma-ray emitting jets are required unless the dipole magnetic field strengths
are G; such strong dipole fields are in excess of those allowed from
the accretion induced collapse formation process except in spin-orbit
synchronization.Comment: 36 pages, AASLATEX, 4 ps figures, Ap
Biodiversity offsets may miss opportunities to mitigate impacts on ecosystem services
© The Ecological Society of America Biodiversity offsets are most commonly used to mitigate the adverse impacts of development on biodiversity, but some offsets are now also designed to support ecosystem services (ES) goals. Here, we assemble a global database of biodiversity offsets (n = 70) to show that 41% already take ES into consideration, with the objective of enhancing cultural, regulating, and provisioning services. We found that biodiversity offsets were more likely to consider ES when (1) development projects reported impacts on services, (2) offsets had voluntary biodiversity goals, and (3) conservation organizations were involved. However, offsets that considered ES were similar in design (eg offsetting approach, extent, and location) to offsets focused solely on biodiversity, suggesting that including ES goals may represent an attempt to strengthen community support for development projects, rather than to offset known ES impacts. We also found that 34% of all offsets displaced people and negatively affected livelihoods. Therefore, when biodiversity and ES are linked, current practices may not actually improve outcomes, instead incurring additional costs to communities and companies
Speciation of Cu-Oxo Clusters in Ferrierite for Selective Oxidation of Methane to Methanol
Cu-oxo nanoclusters in Cu-exchanged zeolites oxidize methane to methanol via a three-step process. Cu-exchanged ferrierite shows high reactivity to this selective oxidation at both ambient and elevated methane pressures. The active sites are dimeric Cu clusters located in the eight-membered channels of ferrierite, containing two oxygen atoms with different reactivities. Combining in situ ultravioletâvisible (UVâvis), X-ray absorption spectroscopy (XAS), and Raman spectroscopy, it is shown that the active site is a [Cu2O2]2+ cluster stabilized at pairs of negatively charged aluminum oxygen tetrahedra. This cluster is able to oxidize up to two methane molecules at elevated methane chemical potential
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