21 research outputs found
On the probabilistic min spanning tree Problem
We study a probabilistic optimization model for min spanning tree, where any vertex vi of the input-graph G(V,E) has some presence probability pi in the final instance GâČ â G that will effectively be optimized. Suppose that when this ârealâ instance GâČ becomes known, a spanning tree T, called anticipatory or a priori spanning tree, has already been computed in G and one can run a quick algorithm (quicker than one that recomputes from scratch), called modification strategy, that modifies the anticipatory tree T in order to fit G âČ. The goal is to compute an anticipatory spanning tree of G such that, its modification for any G âČ â G is optimal for G âČ. This is what we call probabilistic min spanning tree problem. In this paper we study complexity and approximation of probabilistic min spanning tree in complete graphs under two distinct modification strategies leading to different complexity results for the problem. For the first of the strategies developed, we also study two natural subproblems of probabilistic min spanning tree, namely, the probabilistic metric min spanning tree and the probabilistic min spanning tree 1,2 that deal with metric complete graphs and complete graphs with edge-weights either 1, or 2, respectively
A sharp image or a sharp knife: norms for the modality-exclusivity of 774 concept-property items
According to recent embodied cognition theories, mental concepts are represented by modality-specific sensory-motor systems. Much of the evidence for modality-specificity in conceptual processing comes from the property-verification task. When applying this and other tasks, it is important to select items based on their modality-exclusivity. We collected modality ratings for a set of 387 properties, each of which was paired with two different concepts, yielding a total of 774 concept-property items. For each item, participants rated the degree to which the property could be experienced through five perceptual modalities (vision, audition, touch, smell, and taste). Based on these ratings, we computed a measure of modality exclusivity, the degree to which a property is perceived exclusively through one sensory modality. In this paper, we briefly sketch the theoretical background of conceptual knowledge, discuss the use of the property-verification task in cognitive research, provide our norms and statistics, and validate the norms in a memory experiment. We conclude that our norms are important for researchers studying modality-specific effects in conceptual processing
Large-scale unit commitment under uncertainty: an updated literature survey
The Unit Commitment problem in energy management aims at finding the optimal production schedule of a set of generation units, while meeting various system-wide constraints. It has always been a large-scale, non-convex, difficult problem, especially in view of the fact that, due to operational requirements, it has to be solved in an unreasonably small time for its size. Recently, growing renewable energy shares have strongly increased the level of uncertainty in the system, making the (ideal) Unit Commitment model a large-scale, non-convex and uncertain (stochastic, robust, chance-constrained) program. We provide a survey of the literature on methods for the Uncertain Unit Commitment problem, in all its variants. We start with a review of the main contributions on solution methods for the deterministic versions of the problem, focussing on those based on mathematical programming techniques that are more relevant for the uncertain versions of the problem. We then present and categorize the approaches to the latter, while providing entry points to the relevant literature on optimization under uncertainty. This is an updated version of the paper "Large-scale Unit Commitment under uncertainty: a literature survey" that appeared in 4OR 13(2), 115--171 (2015); this version has over 170 more citations, most of which appeared in the last three years, proving how fast the literature on uncertain Unit Commitment evolves, and therefore the interest in this subject
Determining Rank in the Presence of Error
The problem of determining rank in the presence of error occurs in a number of applications. The usual approach is to compute a rank-revealing decomposition and make a decision about the rank by examining the small elements of the decomposition. In this paper we look at three commonly use decompositions: the singular value decomposition, the pivoted QR decomposition, and the URV decomposition
Dietary changes needed to improve diet sustainability: are they similar across Europe ?
International audienc
Measuring and Influencing Physical Activity with Smartphone Technology: A Systematic Review
Background Rapid developments in technology have
encouraged the use of smartphones in physical activity
research, although little is known regarding their effectiveness
as measurement and intervention tools.
Objective This study systematically reviewed evidence
on smartphones and their viability for measuring and
influencing physical activity.
Data Sources Research articles were identified in September
2013 by literature searches in Web of Knowledge,
PubMed, PsycINFO, EBSCO, and ScienceDirect.
Study Selection The search was restricted using the terms
(physical activity OR exercise OR fitness) AND (smartphone*
OR mobile phone* OR cell phone*) AND (measurement
OR intervention). Reviewed articles were
required to be published in international academic peerreviewed
journals, or in full text from international scientific
conferences, and focused on measuring physical
activity through smartphone processing data and influencing people to be more active through smartphone
applications.
Study Appraisal and Synthesis Methods Two reviewers
independently performed the selection of articles and
examined titles and abstracts to exclude those out of scope.
Data on study characteristics, technologies used to objectively
measure physical activity, strategies applied to
influence activity; and the main study findings were
extracted and reported.
Results A total of 26 articles (with the first published in
2007) met inclusion criteria. All studies were conducted in
highly economically advantaged countries; 12 articles
focused on special populations (e.g. obese patients). Studies
measured physical activity using native mobile features,
and/or an external device linked to an application. Measurement
accuracy ranged from 52 to 100 % (n = 10
studies). A total of 17 articles implemented and evaluated
an intervention. Smartphone strategies to influence physical
activity tended to be ad hoc, rather than theory-based
approaches; physical activity profiles, goal setting, realtime
feedback, social support networking, and online
expert consultation were identified as the most useful
strategies to encourage physical activity change. Only five
studies assessed physical activity intervention effects; all
used step counts as the outcome measure. Four studies
(three preâpost and one comparative) reported physical
activity increases (12â42 participants, 800â1,104 steps/
day, 2 weeksâ6 months), and one case-control study
reported physical activity maintenance (n = 200 participants;[
10,000 steps/day) over 3 months.
Limitations Smartphone use is a relatively new field of
study in physical activity research, and consequently the
evidence base is emerging.
Conclusions Few studies identified in this review considered
the validity of phone-based assessment of physical activity. Those that did report on measurement properties
found average-to-excellent levels of accuracy for different
behaviors. The range of novel and engaging intervention
strategies used by smartphones, and user perceptions on
their usefulness and viability, highlights the potential such
technology has for physical activity promotion. However,
intervention effects reported in the extant literature are
modest at best, and future studies need to utilize randomized
controlled trial research designs, larger sample sizes,
and longer study periods to better explore the physical
activity measurement and intervention capabilities of
smartphones