Learning in the Repeated Secretary Problem

In the classical secretary problem, one attempts to find the maximum of an unknown and unlearnable distribution through sequential search. In many real-world searches, however, distributions are not entirely unknown and can be learned through experience. To investigate learning in such a repeated secretary problem we conduct a large-scale behavioral experiment in which people search repeatedly from fixed distributions. In contrast to prior investigations that find no evidence for learning in the classical scenario, in the repeated setting we observe substantial learning resulting in near-optimal stopping behavior. We conduct a Bayesian comparison of multiple behavioral models which shows that participants' behavior is best described by a class of threshold-based models that contains the theoretically optimal strategy. Fitting such a threshold-based model to data reveals players' estimated thresholds to be surprisingly close to the optimal thresholds after only a small number of games

Tidal rectification and frontal circulation on the sides of Georges Bank

Using Wright and Loder\u27s (l985a,b) depth-dependent tidal rectification model and Garrett and Loder\u27s (1981) diagnostic frontal circulation model, predictions of the residual circulation associated with the topographic rectification of tidal currents and the summertime density field on the northwestern and open ocean sides of Georges Bank are made and compared with observations. In general, the estimates of both wintertime and summertime along-isobath currents are in qualitative agreement with observations, but the agreement between predicted and observed cross-isobath currents is poor. The circulation associated with tidal rectification is primarily along isobaths in an anticyclonic sense around the Bank at all depths. The cross-isobath circulation is much weaker and, in the Eulerian specification, is dominated by two cells with opposing current directions. However, a significant Stokes velocity is predicted such that the along-isobath Lagrangian current is generally less than its Eulerian counterpart, and the cross-isobath Lagrangian current is sometimes in the opposite direction to its Eulerian counterpart. Both the along-isobath and cross-isobath currents associated with tidal rectification are predicted to be significantly stronger in summer than in winter due to a reduction in the strength of friction as a result of reduced wind stress and increased density stratification.An additional contribution to the anticyclonic circulation around Georges Bank is associated directly with the summertime tidal front around the Bank. This flow component is predicted to form a second intense along-isobath jet on the northwestern side, slightly off-bank of that due to tidal rectification, and a broader flow on the open ocean side. The associated cross-isobath circulation is predicted to be much weaker than the along-isobath circulation, with a general on-bank bottom flow on both sides of the Bank

Automated tagging of environmental data using a novel SKOS formatted environmental thesaurus

There is increasing need to use the widest range of data to address issues of environmental management and change, which is reflected in increasing emphasis from government funding agencies for better management and access to environmental data. Bringing together different environmental datasets to confidently enable integrated analysis requires reference to common standards and definitions, which are frequently lacking in environmental data, due to the broad subject area and lack of metadata. Automatic inclusion within datasets of controlled vocabulary concepts from publicly available standard vocabularies facilitates accurate annotation and promotes efficiency of metadata creation. To this end, we have developed a thesaurus capable of describing environmental chemistry datasets. We demonstrate a novel method for tagging datasets, via insertion of this thesaurus into a Laboratory Information Management System, enabling automated tagging of data, thus promoting semantic interoperability between tagged data resources. Being web available, and formatted using the Simple Knowledge Organisation System (SKOS) semantic standard, this thesaurus is capable of providing links both to and from other relevant thesauri, thus facilitating a linked data approach. Future developments will see extension of the thesaurus by the user community, in terms of both concepts included and links to externally hosted vocabularies. By employing a Linked Open Data approach, we anticipate that Web-based tools will be able to use concepts from the thesaurus to discover and link data to other information sources, including use in national assessment of the extent and condition of environmental resources

Meeting the challenge of environmental data publication: an operational infrastructure and workflow for publishing data

Here we describe the defined workflow and its supporting infrastructure, which are used by the Natural Environment Research Council’s (NERC) Environmental Information Data Centre (EIDC) (http://​eidc.​ceh.​ac.​uk/​) to enable publication of environmental data in the fields of ecology and hydrology. The methods employed and issues discussed are also relevant to publication in other domains. By utilising a clearly defined workflow for data publication, we operate a fully auditable, quality controlled series of steps permitting publication of environmental data. The described methodology meets the needs of both data producers and data users, whose requirements are not always aligned. A stable, logically created infrastructure supporting data publication allows the process to occur in a well-managed and secure fashion, while remaining flexible enough to deal with a range of data types and user requirements. We discuss the primary issues arising from data publication, and describe how many of them have been resolved by the methods we have employed, with demonstrable results. In conclusion, we expand on future directions we wish to develop to aid data publication by both solving problems for data generators and improving the end-user experience

Implementation of a workflow for publishing citeable environmental data: successes, challenges and opportunities from a data centre perspective

In recent years, the development and implementation of a robust way to cite data have encouraged many previously sceptical environmental researchers to publish the data they create, thus ensuring that more data than ever are now open and available for re-use within and between research communities. Here, we describe a workflow for publishing citeable data in the context of the environmental sciences—an area spanning many domains and generating a vast array of heterogeneous data products. The processes and tools we have developed have enabled rapid publication of quality data products including datasets, models and model outputs which can be accessed, re-used and subsequently cited. However, there are still many challenges that need to be addressed before researchers in the environmental sciences fully accept the notion that datasets are valued outputs and time should be spent in properly describing, storing and citing them. Here, we identify current challenges such as citation of dynamic datasets and issues of recording and presenting citation metrics. In conclusion, whilst data centres may have the infrastructure, tools, resources and processes available to publish citeable datasets, further work is required before large-scale uptake of the services offered is achieved. We believe that once current challenges are met, data resources will be viewed similarly to journal publications as valued outputs in a researcher’s portfolio, and therefore both the quality and quantity of data published will increase

Observations of Above-Surface Littoral Foraging in Two Sea Ducks, Barrow's Goldeneye, Bucephala islandica, and Surf Scoter, Melanitta perspicillata, in Coastal Southwestern British Columbia

Barrow's Goldeneyes (Bucephala islandica) and Surf Scoters (Melanitta perspicillata) were observed on four separate occasions, by three different observers, foraging on Bay Mussels (Mytilus trossulus) above the water surface. This unique foraging behaviour could be attributed to diurnal spring tides and reduced lower intertidal mussel abundance

Comparison of the interactions in the rare gas hydride and Group 2 metal hydride anions

We study both the rare gas hydride anions, RG–H− (RG = He–Rn) and Group 2 (Group IIa) metal hydride anions, MIIaH− (MIIa = Be–Ra), calculating potential energy curves at the CCSD(T) level with augmented quadruple and quintuple basis sets, and extrapolating the results to the basis set limit. We report spectroscopic parameters obtained from these curves; additionally, we study the Be–He complex. While the RG–H− and Be–He species are weakly bound, we show that, as with the previously studied BeH− and MgH− species, the other MIIaH− species are strongly bound, despite the interactions nominally also being between two closed shell species: M(ns2) and −(1s2). We gain insight into the interactions using contour plots of the electron density changes and population analyses. For both series, the calculated dissociation energy is significantly less than the ion/induced-dipole attraction term, confirming that electron repulsion is important in these species; this effect is more dramatic for the MIIaH− species than for RG–H−. Our analyses lead us to conclude that the stronger interaction in the case of the MIIaH− species arises from sp and spd hybridization, which allows electron density on the MIIa atom to move away from the incoming H−

Evidence for a Molecular Cloud Origin for Gamma-Ray Bursts: Implications for the Nature of Star Formation in the Universe

It appears that the majority of rapidly-, well-localized gamma-ray bursts with undetected, or dark, optical afterglows, or `dark bursts' for short, occur in clouds of size R > 10L_{49}^{1/2} pc and mass M > 3x10^5L_{49} M_{sun}, where L is the isotropic-equivalent peak luminosity of the optical flash. We show that clouds of this size and mass cannot be modeled as a gas that is bound by pressure equilibrium with a warm or hot phase of the interstellar medium (i.e., a diffuse cloud): Such a cloud would be unstable to gravitational collapse, resulting in the collapse and fragmentation of the cloud until a burst of star formation re-establishes pressure equilibrium within the fragments, and the fragments are bound by self-gravity (i.e., a molecular cloud). Consequently, dark bursts probably occur in molecular clouds, in which case dark bursts are probably a byproduct of this burst of star formation if the molecular cloud formed recently, and/or the result of lingering or latter generation star formation if the molecular cloud formed some time ago. We then show that if bursts occur in Galactic-like molecular clouds, the column densities of which might be universal, the number of dark bursts can be comparable to the number of bursts with detected optical afterglows: This is what is observed, which suggests that the bursts with detected optical afterglows might also occur in molecular clouds. We confirm this by modeling and constraining the distribution of column densities, measured from absorption of the X-ray afterglow, of the bursts with detected optical afterglows: We find that this distribution is consistent with the expectation for bursts that occur in molecular clouds, and is not consistent with the expectation for bursts that occur in diffuse clouds. More...Comment: Accepted to The Astrophysical Journal, 22 pages, 6 figures, LaTe