GreenPhylDB v2.0: An improved database for plant functional genomics

Poster presented at 2009 Annual Research Meeting of the Generation Challenge Programme. Bamako (Mali), 20-23 September 200

Efficiency and Technological Change in Health Care Services in Ontario

This paper presents productivity measurement results for hospital services using panel data for Ontario hospitals between 2003 and 2006. The study uses the Malmquist Productivity index (MPI) obtained through the application of Data Envelopment Analysis (DEA) which is decomposed into efficiency change (ECH), i.e., movement towards the best practice frontier and technological change (TCH), i.e., movement of the frontier itself (Färe et al. [12]). The study also uses kernel density estimation techniques for analysis of efficiency distributions of the productivity scores and their components across different types of hospitals (e.g. small /large and rural /urban) and over time. Our results suggest that in addition to average productivity it is important to examine distributions of productivity and of its components which we find differs by hospital type and over time. We find that productivity growth occurred mostly through improvement in technology and in spite of declining efficiency. The results provide useful insight into the underlying mechanisms of observed changes in overall productivity, in technological change and in technical efficiency change in this vital sector of the health care market.

Locating Depots for Capacitated Vehicle Routing

We study a location-routing problem in the context of capacitated vehicle routing. The input is a set of demand locations in a metric space and a fleet of k vehicles each of capacity Q. The objective is to locate k depots, one for each vehicle, and compute routes for the vehicles so that all demands are satisfied and the total cost is minimized. Our main result is a constant-factor approximation algorithm for this problem. To achieve this result, we reduce to the k-median-forest problem, which generalizes both k-median and minimum spanning tree, and which might be of independent interest. We give a (3+c)-approximation algorithm for k-median-forest, which leads to a (12+c)-approximation algorithm for the above location-routing problem, for any constant c>0. The algorithm for k-median-forest is just t-swap local search, and we prove that it has locality gap 3+2/t; this generalizes the corresponding result known for k-median. Finally we consider the "non-uniform" k-median-forest problem which has different cost functions for the MST and k-median parts. We show that the locality gap for this problem is unbounded even under multi-swaps, which contrasts with the uniform case. Nevertheless, we obtain a constant-factor approximation algorithm, using an LP based approach.Comment: 12 pages, 1 figur

Adding a new station and a road link to a road-rail network in the presence of modal competition

In this paper we study the problem of locating a new station on an existing rail corridor and a new junction on an existing road network, and connecting them with a new road segment under a budget constraint. We consider three objective functions and the corresponding optimization problems, which are modeled by means of mixed integer non-linear programs. For small instances, the models can be solved directly by a standard solver. For large instances, an enumerative algorithm based on a discretization of the problem is proposed. Computational experiments show that the latter approach yields high quality solutions within short computing times.This research was done while one of the co-authors (Federico Perea) was enjoying a research stay funded by the Spanish Ministerio de Educacion y Ciencia, under program Jose Castillejo. This research was partially funded by the Canadian Natural Sciences and Engineering Research Council under grant 39682-10, by the Spanish Ministerio de Educacion, Ciencia e Innovacion/FEDER under grant MTM2009-14243, by the Spanish Ministerio de Economia y Competitividad/FEDER under grant MTM2012-37048, and by the Junta de Andalucia/FEDER under grants P09-TEP-5022 and FQM-5849. This support is gratefully acknowledged. Special thanks are due to the referees for their valuable comments and to Javier Fernandez and Lorenzo jaro, from the Spanish railway infrastructure management company ADIF, for providing some of the necessary data for the case study.Perea Rojas Marcos, F.; Mesa López-Colmenar, JA.; Laporte, G. (2014). Adding a new station and a road link to a road-rail network in the presence of modal competition. Transportation Research Part B: Methodological. 68:1-16. https://doi.org/10.1016/j.trb.2014.05.015S1166

A re-interpretation of the Triangulum-Andromeda stellar clouds: a population of halo stars kicked out of the Galactic disk

The Triangulum-Andromeda stellar clouds (TriAnd1 and TriAnd2) are a pair of concentric ring- or shell-like over-densities at large $R$ ($\approx$ 30 kpc) and $Z$ ($\approx$ -10 kpc) in the Galactic halo that are thought to have been formed from the accretion and disruption of a satellite galaxy. This paper critically re-examines this formation scenario by comparing the number ratio of RR Lyrae to M giant stars associated with the TriAnd clouds with other structures in the Galaxy. The current data suggest a stellar population for these over-densities ($f_{\rm RR:MG} < 0.38$ at 95% confidence) quite unlike any of the known satellites of the Milky Way ($f_{\rm RR:MG} \approx 0.5$ for the very largest and $f_{\rm RR:MG} >>1$ for the smaller satellites) and more like the population of stars born in the much deeper potential well inhabited by the Galactic disk ($f_{\rm RR:MG} < 0.01$). N-body simulations of a Milky-Way-like galaxy perturbed by the impact of a dwarf galaxy demonstrate that, in the right circumstances, concentric rings propagating outwards from that Galactic disk can plausibly produce similar over-densities. These results provide dramatic support for the recent proposal by Xu et al. (2015) that, rather than stars accreted from other galaxies, the TriAnd clouds could represent stars kicked-out from our own disk. If so, these would be the first populations of disk stars to be found in the Galactic halo and a clear signature of the importance of this second formation mechanism for stellar halos more generally. Moreover, their existence at the very extremities of the disk places strong constraints on the nature of the interaction that formed them.Comment: 27 pages, 8 figures; published in MNRA