100 research outputs found
Beyond the Lamppost: Optimal Prevention and Control of the Brown Treesnake in Hawaii
In this paper, an integrated model for the prevention and control of an invasive species is developed. The generality of the model allows it to be used for both existing and potential threats to the system of interest. The deterministic nature of arrivals in the model allows for a clear examination of the tradeoffs inherent when choosing between prevention and control strategies. We illuminate how optimal expenditure paths change in response to various biological and economic parameters for the case of the Brown treesnake in Hawaii. Results suggest that it is more advantageous to spend money finding the small population of snakes as they occur than attempting to prevent all future introductions. Like the drunk that looks for his keys only where the light is, public policy may fail to look âbeyond the lamppostâ for snakes that have already arrived but have not yet been detected. Actively searching for a potential population of snakes rather than waiting for an accidental discovery may save Hawaii tens to hundreds of millions of dollars in future damages, interdiction expenditures, and control costs.invasive species, brown tree snake, Boiga irregularis, prevention and control, Hawaii
In-plane structure and ordering at liquid sodium surfaces and interfaces from ab initio molecular dynamics
Atoms at liquid metal surfaces are known to form layers parallel to the
surface. We analyze the two-dimensional arrangement of atoms within such layers
at the surface of liquid sodium, using ab initio molecular dynamics (MD)
simulations based on density functional theory. Nearest neighbor distributions
at the surface indicate mostly 5-fold coordination, though there are noticeable
fractions of 4-fold and 6-fold coordinated atoms. Bond angle distributions
suggest a movement toward the angles corresponding to a six-fold coordinated
hexagonal arrangement of the atoms as the temperature is decreased towards the
solidification point. We rationalize these results with a distorted hexagonal
order at the surface, showing a mixture of regions of five and six-fold
coordination. The liquid surface results are compared with classical MD
simulations of the liquid surface, with similar effects appearing, and with ab
initio MD simulations for a model solid-liquid interface, where a pronounced
shift towards hexagonal ordering is observed as the temperature is lowered
Economic analysis of the proposed rule to prevent arrival of new genetic strains of the rust fungus Puccinia psidii in Hawaiâi
Reports were scanned in black and white at a resolution of 600 dots per inch and were converted to text using Adobe Paper Capture Plug-in.Since its first documented introduction to Hawaiâi in 2005, the rust fungus P. psidii has already severely damaged Syzygium jambos (Indian rose apple) trees and the federally-endangered Eugenia koolauensis (nioi). Fortunately, the particular strain has yet to cause serious damage to âĆhiâa, which comprises roughly 80% of the stateâs native forests and covers 400,000 ha. Although the rust has affected less than 5% of Hawaiiâs âĆhiâa trees thus far, the introduction of more virulent strains and the genetic evolution of the current strain are still possible. Since the primary pathway of introduction is Myrtaceae plant material imported from outside the state, potential damage to âohiâa can be minimized by regulating those high-risk imports. We discuss the economic impact on the stateâs florist, nursery, landscaping, and forest plantation industries of a proposed rule that would ban the import of non-seed Myrtaceae plant material and require a one-year quarantine of seeds. Our analysis suggests that the benefits to the forest plantation industry of a complete ban on non-seed material would likely outweigh the costs to other affected sectors, even without considering the reduction in risk to âĆhiâa. Incorporating the value of âĆhiâa protection would further increase the benefit-cost ratio in favor of an import ban
The insider view: tackling disabling practices in higher education institutions
This paper reports on research about the experiences of disabled staff members in UK universities, drawing on eleven semi-structured interviews with disabled staff in one university, alongside a group auto ethnography conducted by the first four authors, all of whom identified as disabled academics. Disability is generally considered to be predominantly an issue for students, both in practice and in the literature. By contrast, taking a social practice approach, we focused on the barriers faced by disabled employees, both overt and hidden. We found that disability was still viewed as a medical problem, and that disabled members of staff faced considerable extra labour in organising their own supports. We were often made to feel that we were unwanted and that we were âmisfitsâ in the institution. This paper contributes to theory by showing how social practices can become exclusionary, and how interconnections between practices matter. We discuss ways in which ableism, based on the ideal of âindividualâ excellence, creates barriers for disabled staff. In the global context of Higher Education, the increasing marketization of universities in higher income countries creates a difficult climate for the values of inclusion
Surface layering of liquids: The role of surface tension
Recent measurements show that the free surfaces of liquid metals and alloys
are always layered, regardless of composition and surface tension; a result
supported by three decades of simulations and theory. Recent theoretical work
claims, however, that at low enough temperatures the free surfaces of all
liquids should become layered, unless preempted by bulk freezing. Using x-ray
reflectivity and diffuse scattering measurements we show that there is no
observable surface-induced layering in water at T=298 K, thus highlighting a
fundamental difference between dielectric and metallic liquids. The
implications of this result for the question in the title are discussed.Comment: 5 pages, 4 figures, to appear in Phys. Rev. B. 69 (2004
Atomic layering at the liquid silicon surface: a first- principles simulation
We simulate the liquid silicon surface with first-principles molecular
dynamics in a slab geometry. We find that the atom-density profile presents a
pronounced layering, similar to those observed in low-temperature liquid metals
like Ga and Hg. The depth-dependent pair correlation function shows that the
effect originates from directional bonding of Si atoms at the surface, and
propagates into the bulk. The layering has no major effects in the electronic
and dynamical properties of the system, that are very similar to those of bulk
liquid Si. To our knowledge, this is the first study of a liquid surface by
first-principles molecular dynamics.Comment: 4 pages, 4 figures, submitted to PR
Density Distribution in the Liquid Hg-Sapphire Interface
We present the results of a computer simulation study of the liquid density
distribution normal to the interface between liquid Hg and the reconstructed
(0001) face of sapphire. The simulations are based on an extension of the
self-consistent quantum Monte Carlo scheme previously used to study the
structure of the liquid metal-vapor interface. The calculated density
distribution is in very good agreement with that inferred from the recent
experimental data of Tamam et al (J. Phys. Chem. Lett. 1, 1041-1045 (2010)). We
conclude that, to account for the difference in structure between the liquid
Hg-vapor and liquid-Hg-reconstructed (0001) Al2O3 interfaces, it is not
necessary assume there is charge transfer from the Hg to the Al2O3. Rather, the
available experimental data are adequately reproduced when the van der Waals
interactions of the Al and O atoms with Hg atoms and the exclusion of electron
density from Al2O3 via repulsion of the electrons from the closed shells of the
ions in the solid are accounted for.Comment: 26 pages, 11 figure
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