2,646 research outputs found
Phylogeography of New Zealand’s coastal benthos
During the past 30 years, 42 molecular studies have been undertaken in New Zealand to examine the phylogeography of coastal benthic invertebrates and plants. Here, we identify generalities and/or patterns that have emerged from this research and consider the processes implicated in generating genetic structure within populations. Studies have used various molecular markers and examined taxonomic groups with a range of life histories and dispersal strategies. Genetic disjunctions have been identified at multiple locations, with the most frequently observed division occurring between northern and southern populations at the top of the South Island. Although upwelling has been implicated as a cause of this disjunction, oceanographic evidence is lacking and alternative hypotheses exist. A significant negative correlation between larval duration and genetic differentiation (r2 = 0.39, P < 0.001, n = 29) across all studies suggests that larval duration might be used as a proxy for dispersal potential. However, among taxa with short larval durations (<10 days) there was greater variability in genetic differentiation than among taxa with longer pelagic periods. This variability implies that when larval duration is short, other factors may determine dispersal and connectivity among populations. Although there has been little congruence between the phylogeographic data and recognised biogeographic regions, recent research has resolved population subdivision at finer spatial scales corresponding more closely with existing biogeographic classifications. The use of fast-evolving and ecologically significant molecular markers in hypothesis-driven research could further improve our ability to detect population subdivision and identify the processes structuring marine ecosystems
Do wind turbines pose roll hazards to light aircraft?
Wind energy accounted for 5.6 % of all electricity generation
in the United States in 2016. Much of this development has occurred in rural
locations, where open spaces favorable for harnessing wind also serve general
aviation airports. As such, nearly 40 % of all United States wind turbines exist
within 10 km of a small airport. Wind turbines generate electricity by
extracting momentum from the atmosphere, creating downwind wakes
characterized by wind-speed deficits and increased turbulence. Recently, the
concern that turbine wakes pose hazards for small aircraft has been used to
limit wind-farm development. Herein, we assess roll hazards to small aircraft
using large-eddy simulations (LES) of a utility-scale turbine wake. Wind-generated
lift forces and subsequent rolling moments are calculated for hypothetical
aircraft transecting the wake in various orientations. Stably and neutrally
stratified cases are explored, with the stable case presenting a possible
worst-case scenario due to longer-persisting wakes permitted by lower ambient
turbulence. In both cases, only 0.001 % of rolling moments experienced by
hypothetical aircraft during down-wake and cross-wake transects lead to an
increased risk of rolling.</p
Report of the Working Group on the Composition of Ultra High Energy Cosmic Rays
For the first time a proper comparison of the average depth of shower maximum
() published by the Pierre Auger and Telescope Array Observatories
is presented. The distributions measured by the Pierre Auger
Observatory were fit using simulated events initiated by four primaries
(proton, helium, nitrogen and iron). The primary abundances which best describe
the Auger data were simulated through the Telescope Array (TA) Middle Drum (MD)
fluorescence and surface detector array. The simulated events were analyzed by
the TA Collaboration using the same procedure as applied to their data. The
result is a simulated version of the Auger data as it would be observed by TA.
This analysis allows a direct comparison of the evolution of with energy of both data sets. The
measured by TA-MD is consistent with a preliminary simulation of the Auger data
through the TA detector and the average difference between the two data sets
was found to be .Comment: To appear in the Proceedings of the UHECR workshop, Springdale USA,
201
Grace DAKASEP alkaline battery separator
The Grace DAKASEP separator was originally developed as a wicking layer for nickel-zinc alkaline batteries. The DAKASEP is a filled non-woven separator which is flexible and heat sealable. Through modification of formulation and processing variables, products with a variety of properties can be produced. Variations of DAKASEP were tested in Ni-H2, Ni-Zn, Ni-Cd, and primary alkaline batteries with good results. The properties of DAKASEP which are optimized for Hg-Zn primary batteries are shown in tabular form. This separator has high tensile strength, 12 micron average pore size, relatively low porosity at 46-48 percent, and consequently moderately high resistivity. Versions were produced with greater than 70 percent porosity and resistivities in 33 wt percent KOH as low as 3 ohm cm. Performance data for Hg-Zn E-1 size cells containing DAKASEP with the properties shown in tabular form, are more reproducible than data obtained with a competitive polypropylene non-woven separator. In addition, utilization of active material is in general considerably improved
Seasonal variability of wake impacts on US mid-Atlantic offshore wind plant power production
The mid-Atlantic will experience rapid wind plant development due to its promising wind resource located near large population centers. Wind turbines and wind plants create wakes, or regions of reduced wind speed, that may negatively affect downwind turbines and plants. We evaluate wake variability and annual energy production with the first yearlong modeling assessment using the Weather Research and Forecasting model, deploying 12 MW turbines across the domain at a density of 3.14 MW km−2, matching the planned density of 3 MW km−2. Using a series of simulations with no wind plants, one wind plant, and complete build-out of lease areas, we calculate wake effects and distinguish the effect of wakes generated internally within one plant from those generated externally between plants. We also provide a first step towards uncertainty quantification by testing the amount of added turbulence kinetic energy (TKE) by 0 % and 100 %. We provide a sensitivity analysis by additionally comparing 25 % and 50 % for a short case study period. The strongest wakes, propagating 55 km, occur in summertime stable stratification, just when New England's grid demand peaks in summer. The seasonal variability of wakes in this offshore region is much stronger than the diurnal variability of wakes. Overall, yearlong simulated wake impacts reduce power output by a range between 38.2 % and 34.1 % (for 0 %–100 % added TKE). Internal wakes cause greater yearlong power losses, from 29.2 % to 25.7 %, compared to external wakes, from 14.7 % to 13.4 %. The overall impact is different from the linear sum of internal wakes and external wakes due to non-linear processes. Additional simulations quantify wake uncertainty by modifying the added amount of turbulent kinetic energy from wind turbines, introducing power output variability of 3.8 %. Finally, we compare annual energy production to New England grid demand and find that the lease areas can supply 58.8 % to 61.2 % of annual load. We note that the results of this assessment are not intended to make nor are they suitable to make commercial judgments about specific wind projects.</p
An interactive atlas for marine biodiversity conservation in the Coral Triangle
An online atlas of the Coral Triangle region of the Indo-Pacific
biogeographic realm was developed. This online atlas consists of the three
interlinked parts: (1) Biodiversity Features; (2) Areas of Importance for
Biodiversity Conservation; (3) recommended priorities for Marine Protected
Area (MPA) Network Expansion (http://www.marine.auckland.ac.nz/CTMAPS).
The first map, Biodiversity Features, provides comprehensive data on the
region's marine protected areas and biodiversity features, threats, and
environmental characteristics. The second provides spatial information on
areas of high biodiversity conservation values, while the third map shows
priority areas for expanding the current Coral Triangle MPA network. This
atlas provides the most comprehensive biodiversity datasets that have been
assembled for the region. The datasets were retrieved and generated
systematically from various open-access sources. To engage a wider audience
and to raise participation in biodiversity conservation, the maps were
designed as an interactive and online atlas. This atlas presents
representative information to promote a better understanding of the key
marine and coastal biodiversity characteristics of the region and enables the
application of marine biodiversity informatics to support marine
ecosystem-based management in the Coral Triangle region.</p
National Geodetic Satellite Program, Part II: Smithsonian Astrophysical Observatory
A sequence of advances in the determination of geodetic parameters presented by the Smithsonian Astrophysical Observatory are described. A Baker-Nunn photographic system was used in addition to a ruby-laser ranging system to obtain data for refinement of geodetic parameters. A summary of the data employed to: (1) derive coordinates for the locations of various tracking stations; and (2) determine the gravitational potential of the earth, is presented
Assessing variability of wind speed: comparison and validation of 27 methodologies
Because wind resources vary from year to year, the
intermonthly and interannual variability (IAV) of wind speed is a key
component of the overall uncertainty in the wind resource assessment
process, thereby creating challenges for wind farm operators and owners. We
present a critical assessment of several common approaches for calculating
variability by applying each of the methods to the same 37-year monthly
wind-speed and energy-production time series to highlight the differences
between these methods. We then assess the accuracy of the variability
calculations by correlating the wind-speed variability estimates to the
variabilities of actual wind farm energy production. We recommend the robust
coefficient of variation (RCoV) for systematically estimating variability,
and we underscore its advantages as well as the importance of using a
statistically robust and resistant method. Using normalized spread metrics,
including RCoV, high variability of monthly mean wind speeds at a location
effectively denotes strong fluctuations of monthly total energy generation,
and vice versa. Meanwhile, the wind-speed IAVs computed with annual-mean
data fail to adequately represent energy-production IAVs of wind farms.
Finally, we find that estimates of energy-generation variability require 10±3 years of monthly mean wind-speed records to achieve a 90 %
statistical confidence. This paper also provides guidance on the spatial
distribution of wind-speed RCoV.</p
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Implementation and assessment of turbine wake models in the Weather Research and Forecasting model for both mesoscale and large-eddy simulation
Flow dynamics in large wind projects are influenced by the turbines located within. The turbine wakes, regions characterized by lower wind speeds and higher levels of turbulence than the surrounding free stream flow, can extend several rotor diameters downstream, and may meander and widen with increasing distance from the turbine. Turbine wakes can also reduce the power generated by downstream turbines and accelerate fatigue and damage to turbine components. An improved understanding of wake formation and transport within wind parks is essential for maximizing power output and increasing turbine lifespan. Moreover, the influence of wakes from large wind projects on neighboring wind farms, agricultural activities, and local climate are all areas of concern that can likewise be addressed by wake modeling. This work describes the formulation and application of an actuator disk model for studying flow dynamics of both individual turbines and arrays of turbines within wind projects. The actuator disk model is implemented in the Weather Research and Forecasting (WRF) model, which is an open-source atmospheric simulation code applicable to a wide range of scales, from mesoscale to large-eddy simulation. Preliminary results demonstrate the applicability of the actuator disk model within WRF to a moderately high-resolution large-eddy simulation study of a small array of turbines
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