476 research outputs found
Three Algorithms for a Class of Multidimensional Assignment Problems
The assignment problem of matching the elements of two sets at some cost or to some benefit is well known and can be solved in polynomial time. However, many applications, particularly those in remote sensing and computer vision, require matching elements from more than two sets at some cost. Such problems are called multidimensional assignment problems and are known to be NP-hard. For time-critical applications and nontrivial multidimensional assignment problems, fast near-optimal algorithms are the only alternative. This paper compares three such algorithms: greedy, limited branch and bound, and Lagrangian relaxation
Global patterns in seagrass herbivory: Why, despite existing evidence, there are solid arguments in favor of latitudinal gradients in seagrass herbivory
© 2020, Coastal and Estuarine Research Federation. The ecological paradigm that biological interactions are more intense in the tropics than in temperate or polar regions has existed since the mid-twentieth century, but several recent meta-analyses have provided scant evidence for latitudinal gradients in the intensity of herbivory. This contradictory evidence led us to carefully review the data and results of several of those papers that failed to find latitudinal gradients in rates of seagrass herbivory. To re-evaluate the arguments around the presence or absence of latitudinal gradients in herbivory in seagrass, we began by expanding the selection criteria to include more studies to compare the published latitudinal range of seagrass occurrences with the latitudes in which seagrass herbivory has been studied. We also compared the latitudinal range of known seagrass herbivores with the distribution of studies on seagrass herbivory. Finally, we investigated studies that provided seasonal data on net primary production and standing stock of seagrasses, which allowed an assessment of the relative amounts of production that could enter the seagrass grazing food web among latitudes and climatic regimes. Consistent with recent meta-analyses, we found little latitudinal effect on grazing rates. However, we argue that the following factors are likely to confound these findings and potentially mask latitudinal trends in seagrass herbivory: (1) the paucity of data available to test latitudinal trends in grazing rates at high latitudes; (2) the mismatch between the geographic distribution of important grazers and studies on seagrass herbivory; (3) the paucity of experimental studies from areas with little or no herbivory because few researchers would initiate a study on something not observed to be occurring; (4) the high level of seasonality in seagrass production in high latitudes, where seagrass production is very low or nonexistent in winter months; (5) the fact that temperate areas with Mediterranean climates behave very differently than temperate areas at similar latitudes with much greater seasonality, thereby making latitude a much less informative independent variable than annual range in temperature; and (6) anthropogenic disturbances, including the overharvesting to functional extinction of large seagrass herbivores in both temperate and tropical regions. Thus, while we currently cannot discount the lack of a latitudinal gradient in grazing intensity, we argue that the intensity of grazing is likely to be greater in the tropics than high-latitude regions where the carrying capacity of seagrass meadows is far less stable. Either way, there are clear gaps in our knowledge and ability to evaluate the role of grazing in seagrass ecosystems and inform future efforts to conserve and restore these extraordinarily valuable ecosystems
Chapman-Enskog method and synchronization of globally coupled oscillators
The Chapman-Enskog method of kinetic theory is applied to two problems of
synchronization of globally coupled phase oscillators. First, a modified
Kuramoto model is obtained in the limit of small inertia from a more general
model which includes ``inertial'' effects. Second, a modified Chapman-Enskog
method is used to derive the amplitude equation for an O(2) Takens-Bogdanov
bifurcation corresponding to the tricritical point of the Kuramoto model with a
bimodal distribution of oscillator natural frequencies. This latter calculation
shows that the Chapman-Enskog method is a convenient alternative to normal form
calculations.Comment: 7 pages, 2-column Revtex, no figures, minor change
Irregular silviculture and stand structural effects on the plant community in an ancient semi-natural woodland
Plants associated with traditional forms of coppice management are affected by changes in, or cessation of, stand management which produce differences in structure, usually in the direction of high forest. The habitat structure, ground flora richness, and composition of an ancient woodland in southern England were compared across three distinct management treatments: traditional Coppice (the cyclical cutting of underwood on rotations), Limited Intervention (representing the effective cessation of management), and Irregular High Forest silviculture (a form of continuous cover forestry using single and small group selective tree harvesting). Coppice and Irregular silviculture showed a more complex woody stand structure whereas Limited Intervention was strongly correlated with closed-canopy, single-storied structures and no developing understorey. Increased bramble Rubus fruticosus cover was strongly associated with Irregular silviculture, bare ground mostly with the limited intervention closed-canopy stands. Distinct plant-habitat associations were identified across stand management types with the greatest differences between Limited Intervention and the two active interventions. Overall vascular plant species and Coppice group species were lowest in Limited Intervention stands. Using ancient woodland indicator and Coppice plant species and groups, we found a similar community pattern between Coppice and Irregular silviculture. More ancient woodland species were accommodated within the comparatively heterogenous woodland habitat associated with active silvicultural interventions of Coppice and Irregular High Forest management. The study indicates that the introduction of Irregular silviculture as practiced here can conserve most ancient woodland and Coppice plants associated with traditional coppicing, a practice which has declined significantly in the UK since the late 19th Century
Catalogue of squat lobsters of the world (Crustacea: Decapoda: Anomura-families Chirostylidae, Galatheidae and Kiwaidae)
220 páginas, 5 figuras, 1 tabla.[EN] This adaptation text reproduces Anexo I of the dissertation “Results”: Sistemática e historia evolutiva de la Familia Galatheidae (Crustacea: Anomura) en el Pacífico Sur, of Patricia Cabezas (2010) http://hdl.handle.net/10261/134771[ES] Este artículo es una adaptación del Anexo I de la tesis doctoral: Sistemática e historia evolutiva de la Familia Galatheidae (Crustacea: Anomura) en el Pacífico Sur, of Patricia Cabezas (2010) http://hdl.handle.net/10261/134771Taxonomic and ecological interest in squat lobsters has grown considerably over the last two decades. A checklist of the
870 current valid species of squat lobsters of the world (families Chirostylidae, Galatheidae and Kiwaidae) is presented.
The compilation includes the complete taxonomic synonymy and geographical distribution of each species plus type
information (type locality, repository and registration number). The numbers of described species in the world’s major
ocean basins are summarised.Peer reviewe
Atmospheric Density Uncertainty Quantification for Satellite Conjunction Assessment
Conjunction assessment requires knowledge of the uncertainty in the predicted
orbit. Errors in the atmospheric density are a major source of error in the
prediction of low Earth orbits. Therefore, accurate estimation of the density
and quantification of the uncertainty in the density is required. Most
atmospheric density models, however, do not provide an estimate of the
uncertainty in the density. In this work, we present a new approach to quantify
uncertainties in the density and to include these for calculating the
probability of collision Pc. For this, we employ a recently developed dynamic
reduced-order density model that enables efficient prediction of the
thermospheric density. First, the model is used to obtain accurate estimates of
the density and of the uncertainty in the estimates. Second, the density
uncertainties are propagated forward simultaneously with orbit propagation to
include the density uncertainties for Pc calculation. For this, we account for
the effect of cross-correlation in position uncertainties due to density errors
on the Pc. Finally, the effect of density uncertainties and cross-correlation
on the Pc is assessed. The presented approach provides the distinctive
capability to quantify the uncertainty in atmospheric density and to include
this uncertainty for conjunction assessment while taking into account the
dependence of the density errors on location and time. In addition, the results
show that it is important to consider the effect of cross-correlation on the
Pc, because ignoring this effect can result in severe underestimation of the
collision probability.Comment: 15 pages, 6 figures, 5 table
Marine Biodiversity in the Australian Region
The entire Australian marine jurisdictional area, including offshore and sub-Antarctic islands, is considered in this paper. Most records, however, come from the Exclusive Economic Zone (EEZ) around the continent of Australia itself. The counts of species have been obtained from four primary databases (the Australian Faunal Directory, Codes for Australian Aquatic Biota, Online Zoological Collections of Australian Museums, and the Australian node of the Ocean Biogeographic Information System), but even these are an underestimate of described species. In addition, some partially completed databases for particular taxonomic groups, and specialized databases (for introduced and threatened species) have been used. Experts also provided estimates of the number of known species not yet in the major databases. For only some groups could we obtain an (expert opinion) estimate of undiscovered species. The databases provide patchy information about endemism, levels of threat, and introductions. We conclude that there are about 33,000 marine species (mainly animals) in the major databases, of which 130 are introduced, 58 listed as threatened and an unknown percentage endemic. An estimated 17,000 more named species are either known from the Australian EEZ but not in the present databases, or potentially occur there. It is crudely estimated that there may be as many as 250,000 species (known and yet to be discovered) in the Australian EEZ. For 17 higher taxa, there is sufficient detail for subdivision by Large Marine Domains, for comparison with other National and Regional Implementation Committees of the Census of Marine Life. Taxonomic expertise in Australia is unevenly distributed across taxa, and declining. Comments are given briefly on biodiversity management measures in Australia, including but not limited to marine protected areas
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How home cooking methods and appliances affect the GHG emissions of food
Food is widely acknowledged as a significant contributor to climate change. Yet, estimates of food-related greenhouse gas emissions frequently consider supply chain stages only up to farm gate or regional distribution centres. Here, we estimate greenhouse gas emissions associated with different cooking methods and appliances in the UK. Data on current cooking practices were collected through a survey with more than 700 respondents. Results reveal that home cooking accounts for as much as 61% of total emissions associated with specific foods, and that this can be substantially reduced through alternative, readily available cooking practices
Benchmarking global biodiversity of decapod crustaceans (Crustacea: Decapoda)
A new assessment of the global biodiversity of decapod Crustacea (to 31 December 2022) records 17,229 species in 2,550 genera and 203 families. These figures are derived from a well-curated dataset maintained on the online platform DecaNet, a subsidiary of the World Register of Marine Species (WoRMS). Distinct phases are recognised in the discovery process (as measured by species descriptions) corresponding to major historical and geopolitical time periods, with the current rate of species descriptions being more than three times higher than in the Victorian age of global exploration. Future trends are briefly explored, and it is recognised that a large number of species remain to be discovered and described
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