8,166 research outputs found
The Alberta Oil Sands
The Alberta oil sands near Ft. McMurray, Alberta, have been estimated by many to contain at least 300,000,000,000 bbls of oil, and would therefore be classed as the largest potential oil field in the world. The oil sand deposit is considered to be non-marine in origin and consists mainly of very fine-grained, angular, quartz grains with the viscous oil acting as a binding agent. Lenticular beds of clay and extensive cross-bedding indicates deltaic conditions with intermittent flooding periods during deposition. Extensive research has shown that the problems of extraction, transportation, plant design and location are surmountable, and oil production from the sands is forseeable in the near future
Documentation for the machine-readable version of the SAO-HD-GC-DM cross index version 1983
An updated and extended machine readable version of the Smithsonian Astrophysical Observatory star catalog (SAO) is described. A correction of all errors which were found since preparation of the original catalog which resulted from misidentifications and omissions of components in multiple star systems and missing Durchmusterung numbers (the common identifier) in the SAO Catalog are included and component identifications from the Index of Visual Double Stars (IDS) are appended to all multiple SAO entries with the same DM numbers, and lower case letter identifiers for supplemental BD stars are added. A total of 11,398 individual corrections and data additions is incorporated into the present version of the cross index
Efficient algorithms for rigid body integration using optimized splitting methods and exact free rotational motion
Hamiltonian splitting methods are an established technique to derive stable
and accurate integration schemes in molecular dynamics, in which additional
accuracy can be gained using force gradients. For rigid bodies, a tradition
exists in the literature to further split up the kinetic part of the
Hamiltonian, which lowers the accuracy. The goal of this note is to comment on
the best combination of optimized splitting and gradient methods that avoids
splitting the kinetic energy. These schemes are generally applicable, but the
optimal scheme depends on the desired level of accuracy. For simulations of
liquid water it is found that the velocity Verlet scheme is only optimal for
crude simulations with accuracies larger than 1.5%, while surprisingly a
modified Verlet scheme (HOA) is optimal up to accuracies of 0.4% and a fourth
order gradient scheme (GIER4) is optimal for even higher accuracies.Comment: 2 pages, 1 figure. Added clarifying comments. Accepted for
publication in the Journal of Chemical Physic
Mapping quantum-classical Liouville equation: projectors and trajectories
The evolution of a mixed quantum-classical system is expressed in the mapping
formalism where discrete quantum states are mapped onto oscillator states,
resulting in a phase space description of the quantum degrees of freedom. By
defining projection operators onto the mapping states corresponding to the
physical quantum states, it is shown that the mapping quantum-classical
Liouville operator commutes with the projection operator so that the dynamics
is confined to the physical space. It is also shown that a trajectory-based
solution of this equation can be constructed that requires the simulation of an
ensemble of entangled trajectories. An approximation to this evolution equation
which retains only the Poisson bracket contribution to the evolution operator
does admit a solution in an ensemble of independent trajectories but it is
shown that this operator does not commute with the projection operators and the
dynamics may take the system outside the physical space. The dynamical
instabilities, utility and domain of validity of this approximate dynamics are
discussed. The effects are illustrated by simulations on several quantum
systems.Comment: 4 figure
Different male vs. female breeding periodicity helps mitigate offspring sex ratio skews in sea turtles
The implications of climate change for global biodiversity may be profound with those species with little capacity for adaptation being thought to be particularly vulnerable to warming. A classic case of groups for concern are those animals exhibiting temperature-dependent sex-determination (TSD), such as sea turtles, where climate warming may produce single sex populations and hence extinction. We show that, globally, female biased hatchling sex ratios dominate sea turtle populations (exceeding 3:1 in >50% records), which, at-a-glance, reiterates concerns for extinction. However, we also demonstrate that more frequent breeding by males, empirically shown by satellite tracking 23 individuals and supported by a generalized bio-energetic life history model, generates more balanced operational sex ratios (OSRs). Hence, concerns of increasingly skewed hatchling sex ratios and reduced population viability are less acute than previously thought for sea turtles. In fact, in some scenarios skewed hatchling sex ratios in groups with TSD may be adaptive to ensure optimum OSRs.<br /
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Social media reveals consistently disproportionate tourism pressure on a threatened marine vertebrate
Establishing how wildlife viewing pressure is distributed across individual animals within a population can inform the management of this activity, and ensure targeted individuals or groups are sufficiently protected. Here, we used social media data to quantify whether tourism pressure varies in a loggerhead sea turtle Caretta caretta population and elucidate the potential implications. Laganas Bay (Zakynthos, Greece) supports both breeding (migratory, and hence transient) and foraging (resident) turtles, with turtle viewing representing a major component of the tourism industry. Social media entries spanning two seasons (April to November, 2018 and 2019) were evaluated, and turtles were identified via photo-identification. For the 2 years, 1684 and 2105 entries of 139 and 122 unique turtles were obtained from viewings, respectively (boats and underwater combined). However, while residents represented less than one-third of uniquely identified turtles, they represented 81.9 and 87.9% of all entries. Even when the seasonal breeding population was present (May to July), residents represented more than 60% of entries. Notably, the same small number of residents (<10), mostly males, were consistently viewed in both years; however, different individuals were targeted by boats versus underwater. Thus, turtles appear to remain in the area despite high viewing intensity, possibly indicating low disturbance. However, photo-identification records revealed a high risk of propeller and boat strike to residents (30%) leading to trauma and mortality. To reduce this threat, we recommend the compulsory use of propeller guards for all boats, compliance with speed regulations and the creation of temporary ‘refuge’ zones for resident animals at viewing hotspots, with these suggestions likely being relevant for other wildlife with similar population dynamics. In conclusion, social media represents a useful tool for monitoring individuals at a population scale, evaluating the pressure under which they are placed, and providing sufficient data to refine wildlife viewing guidelines and/or zoning. © 2020 The Authors. Animal Conservation published by John Wiley & Sons Ltd on behalf of Zoological Society of Londo
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