1,281 research outputs found
A tutorial on estimator averaging in spatial point process models
Assume that several competing methods are available to estimate a parameter
in a given statistical model. The aim of estimator averaging is to provide a
new estimator, built as a linear combination of the initial estimators, that
achieves better properties, under the quadratic loss, than each individual
initial estimator. This contribution provides an accessible and clear overview
of the method, and investigates its performances on standard spatial point
process models. It is demonstrated that the average estimator clearly improves
on standard procedures for the considered models. For each example, the code to
implement the method with the R software (which only consists of few lines) is
provided
Averaging of density kernel estimators
Averaging provides an alternative to bandwidth selection for density kernel estimation. We propose a procedure to combine linearly several kernel estimators of a density obtained from different, possibly data-driven, bandwidths. The method relies on minimizing an easily tractable approximation of the integrated square error of the combination. It provides, at a small computational cost, a final solution that improves on the initial estimators in most cases. The average estimator is proved to be asymptotically as efficient as the best possible combination (the oracle), with an error term that decreases faster than the minimax rate obtained with separated learning and validation samples. The performances are tested numerically, with results that compare favorably to other existing procedures in terms of mean integrated square errors
Proximal ulna comminuted fractures: Fixation using a double-plating technique
SummaryIntroductionComminuted fractures of the proximal ulna are severe injuries often associated with bone and ligament injuries of the elbow joint (Monteggia lesion, radial head fractures, dislocation of the elbow). The treatment of these fractures is very demanding and the functional results often fairly mediocre due to associated injuries. Based on a single-center retrospective study, we report the results of the treatment of these fractures fixed using a double-plate technique. The aim was to evaluate the feasibility and reliability of this fixation mode and to compare it with other fractures series using a single plate fixation (in terms of bone union, elbow joint function, and complications stemming from the plates).Patients and methodsEighteen patients sustained a comminuted proximal ulna fracture between 2002 and 2006. The fractures were associated in five cases with a Monteggia type lesion, in two cases with elbow dislocation, and in four cases with a Mason 3 radial head fracture. Four patients had an open fracture. These comminuted ulna fractures included nine Mayo Clinic IIIB fractures. Bone fixation was performed with two third-cylinder tubular plates, one plate on each side of the proximal ulna. This allows more versatile solutions for screw insertion. Functional assessment (according to Broberg and Morrey) and radiological evaluation (bone healing) were provided at 6Â months and at the longest follow-up by an independent surgeon.ResultsSixteen of 18Â patients achieved bone union. No septic complications occurred and no hardware removal was required on patient request. In 67% of the cases, the Morrey score indicated excellent or good results with a mean score of 82.DiscussionThere are no reports in the literature on the technical point of fixation concerning complex fractures of the ulna. Two plates mean the possibility of twice the number of screw insertions for epiphyseal reconstruction . This fixation remains easy to perform and provides stable anatomic reconstruction of the ulna.Level of evidenceLevel IV. Retrospective study
Thermodynamics of aggregation of two proteins
We investigate aggregation mechanism of two proteins in a thermodynamically
unambiguous manner by considering the finite size effect of free energy
landscape of HP lattice protein model. Multi-Self-Overlap-Ensemble Monte Carlo
method is used for numerical calculations. We find that a dimer can be formed
spontaneously as a thermodynamically stable state when the system is small
enough. It implies the possibility that the aggregation of proteins in a cell
is triggered when they are confined in a small region by, for example, being
surrounded by other macromolecules.We also find that the dimer exhibits a
transition between unstable state and metastable state in the infinite system.Comment: jpsj2.cls, 7 pages, 14 figures; misconfigurations of Fig.Nos.
correcte
Power-Law Distributions in a Two-sided Market and Net Neutrality
"Net neutrality" often refers to the policy dictating that an Internet
service provider (ISP) cannot charge content providers (CPs) for delivering
their content to consumers. Many past quantitative models designed to determine
whether net neutrality is a good idea have been rather equivocal in their
conclusions. Here we propose a very simple two-sided market model, in which the
types of the consumers and the CPs are {\em power-law distributed} --- a kind
of distribution known to often arise precisely in connection with
Internet-related phenomena. We derive mostly analytical, closed-form results
for several regimes: (a) Net neutrality, (b) social optimum, (c) maximum
revenue by the ISP, or (d) maximum ISP revenue under quality differentiation.
One unexpected conclusion is that (a) and (b) will differ significantly, unless
average CP productivity is very high
Environmental Effects on Cephalopod Life History and Fisheries
Editorial de un número especial de la Revista Aquatic Living ResourcesThe present collection of papers arises from a theme session on “Cephalopod Stocks: Review, Analyses, Assessment, and Sustainable Management” at the 2004 ICES Annual Science Conference, Vigo, Spain.
The original proposal for the theme session was justified by the availability of much unpublished information on cephalopod
biology and fisheries arising from various CEC-funded R&D projects during the last 15 years. The theme session also related directly to the EC-funded Concerted Action: CEPHSTOCK (Q5CA-2002-00962), and provided a route for dissemination of the review and synthesis work carried out under this project. The theme session was intended to facilitate the wider dissemination and publication of these results, with the long-term aim of informing future management decisions for the major fished stocks of cephalopods in European waters.
Any future European research programme, related to cephalopod biology and fisheries, will need to take into account of knowledge acquired on cephalopod populations. The theme session aimed to attract scientists working on cephalopod stocks outside the NE Atlantic as well as those from ICES countries. The scope of the theme session was:
• The current state of knowledge on exploited cephalopods (biology, fisheries, environmental relationships, stock identity) in European waters;
• Current fishery data collection, stock assessment and management practices for cephalopod capture fisheries world-wide;
• The current status of cephalopod culture and the prospects for commercial aquaculture;
• Socio-economic issues related to cephalopod fisheries;
• Current knowledge of aspects of cephalopod biology and ecology related to their suitability as resource species for capture and culture fisheries, and assessment of environmental factors which affect the immuno-competence and physiology of cephalopods;
• Assessment and management options for currently unregulated cephalopod fisheries.
The theme session attracted 28 oral presentations and 12 posters that could be broadly divided into those more concerned
with biology and ecology, and those focusing on fisheries. Some of these presentations appear elsewhere, e.g. Guerra et al. (2005)
on giant squid strandings. The selection of papers presented in Aquatic Living Resources vol. 18, No. 4, 2005, “Environmental effects on cephalopod life history and fisheries”, illustrates how cephalopod studies could contribute to a development of an ecosystem approach to fisheries management (FAO 2003), by analysing a series of environmental effects operating at different scales.
Environmental effects on life histories The life-cycle characteristics of cephalopods contribute the main reasons for the large inter-annual fluctuations of population densities (Boyle and Boletzky 1996). In teleost fishes differences in biological parameters have been analysed in relation to fishing, considered sometimes as the main environmental impact (Rochet et al. 2000). As a first step to transposing this approach to cephalopods, substantial biological data sets and new statistical approaches are applied to answer questions about squid life history.
Vidal et al. evaluated the influence of food supply on yolk utilization, metabolism and growth of paralarvae of Loligo vulgaris
reynaudii while Smith et al. re-examined historical life history data to infer the relationships between nutritional state, growth and maturation in Loligo forbesi. Moreno et al. examined differences in age, size-at-maturity and reproductive investment in different cohorts of Loligo vulgaris in relation to environmental influences.
Consequences of such influences on cohort success have to be analysed taking into account the spatial organization of fished
populations. Walters et al. (2004) encouraged this approach presenting “spatial life history trajectories” which involve nested designs or time-stepping structures
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