1,266 research outputs found
Simulating leaching losses following incorporation of grass and grass-clover leys
Dynamic simulation models can be useful tools for predicting the residual effect of leys, but only if they have been calibrated and validated appropriately for this particular situation. The BIOMOD project has aimed at expanding, calibrating and validating two Danish dynamic simulation models, namely FASSET and Daisy, for a range of crop rotational situations occurring in organic farming. Here we report on the calibration results for an extensive experiment with residual effect and nitrate leaching following grass-clover leys
Processor Allocation for Optimistic Parallelization of Irregular Programs
Optimistic parallelization is a promising approach for the parallelization of
irregular algorithms: potentially interfering tasks are launched dynamically,
and the runtime system detects conflicts between concurrent activities,
aborting and rolling back conflicting tasks. However, parallelism in irregular
algorithms is very complex. In a regular algorithm like dense matrix
multiplication, the amount of parallelism can usually be expressed as a
function of the problem size, so it is reasonably straightforward to determine
how many processors should be allocated to execute a regular algorithm of a
certain size (this is called the processor allocation problem). In contrast,
parallelism in irregular algorithms can be a function of input parameters, and
the amount of parallelism can vary dramatically during the execution of the
irregular algorithm. Therefore, the processor allocation problem for irregular
algorithms is very difficult.
In this paper, we describe the first systematic strategy for addressing this
problem. Our approach is based on a construct called the conflict graph, which
(i) provides insight into the amount of parallelism that can be extracted from
an irregular algorithm, and (ii) can be used to address the processor
allocation problem for irregular algorithms. We show that this problem is
related to a generalization of the unfriendly seating problem and, by extending
Tur\'an's theorem, we obtain a worst-case class of problems for optimistic
parallelization, which we use to derive a lower bound on the exploitable
parallelism. Finally, using some theoretically derived properties and some
experimental facts, we design a quick and stable control strategy for solving
the processor allocation problem heuristically.Comment: 12 pages, 3 figures, extended version of SPAA 2011 brief announcemen
Snacking patterns among Chilean children and adolescents: Is there potential for improvement?
Objective: To examine snacking patterns, food sources and nutrient profiles of snacks in low- and middle-income Chilean children and adolescents. Design: Cross-sectional. Dietary data were collected via 24 h food recalls. We determined the proportion of snackers, snacks per day and energy from top food and beverage groups consumed. We compared the nutrient profile (energy, sodium, total sugars and saturated fat) of snacks v. meals. Setting: South-east region of Chile. Participants: Children and adolescents from two cohorts: the Food Environment Chilean Cohort (n 958, 4-6 years old) and the Growth and Obesity Cohort Study (n 752, 12-14 years old). Results: With a mean of 2·30 (se 0·03) snacks consumed daily, 95·2 % of children and 89·9 % of adolescents reported at least one snacking event. Snacks contributed on average 1506 kJ/d (360 kcal/d) in snacking children and 2218 kJ/d (530 kcal/d) in snacking adolescents (29·0 and 27·4 % daily energy contribution, respectively). Grain-based desserts, salty snacks, other sweets and desserts, dairy foods and cereal-based foods contributed the most energy from snacks in the overall sample. For meals, cereal-based foods, dairy beverages, meat and meat substitutes, oils and fats, and fruits and vegetables were the top energy contributors. Conclusions: Widespread snacking among Chilean youth provides over a quarter of their daily energy and includes foods generally considered high in energy, saturated fat, sodium and/or total sugars. Future research should explore whether snacking behaviours change as the result of Chile's national regulations on food marketing, labelling and school environments
Analytical approximation of the stress-energy tensor of a quantized scalar field in static spherically symmetric spacetimes
Analytical approximations for and of a
quantized scalar field in static spherically symmetric spacetimes are obtained.
The field is assumed to be both massive and massless, with an arbitrary
coupling to the scalar curvature, and in a zero temperature vacuum state.
The expressions for and are divided into
low- and high-frequency parts. The contributions of the high-frequency modes to
these quantities are calculated for an arbitrary quantum state. As an example,
the low-frequency contributions to and are
calculated in asymptotically flat spacetimes in a quantum state corresponding
to the Minkowski vacuum (Boulware quantum state). The limits of the
applicability of these approximations are discussed.Comment: revtex4, 17 pages; v2: three references adde
Examining Chile's unique food marketing policy: TV advertising and dietary intake in preschool children, a pre- and post- policy study
Background: The Chilean government implemented the first phase of a comprehensive marketing policy in 2016, restricting child-directed marketing of products high in energy, total sugars, sodium or saturated fat (hereafter âhigh-inâ). Objectives: To examine the role that high-in TV food advertising had in the effect of the policy on consumption of high-in products between 2016 and 2017. Methods: Dietary data were obtained from 24-hour diet recall measured in 2016 (n = 940) and 2017 (n = 853), pre- and post-policy, from a cohort of 4 to 6 years children. Television use was linked to analyses of food advertisements to derive individual-level estimates of exposure to advertising. A multilevel mediation analysis examined direct and indirect effects of the policy through advertising exposure. Results: Children's high-in food consumption and advertising exposure declined significantly from 2016 to 2017 (P <.01). Consumption changes were not significantly mediated by changes in advertising exposure, which might suggest other elements of the Chilean Law potentially driving decreases in consumption to a greater extent than TV ads. Conclusions: Preschoolers' exposure to high-in advertising and consumption of high-in products decreased post-policy. Further research is needed to understand how marketing changes will relate to dietary changes after full implementation of the law and in the long term
Logarithmic Corrections in Dynamic Isotropic Percolation
Based on the field theoretic formulation of the general epidemic process we
study logarithmic corrections to scaling in dynamic isotropic percolation at
the upper critical dimension d=6. Employing renormalization group methods we
determine these corrections for some of the most interesting time dependent
observables in dynamic percolation at the critical point up to and including
the next to leading correction. For clusters emanating from a local seed at the
origin we calculate the number of active sites, the survival probability as
well as the radius of gyration.Comment: 9 pages, 3 figures, version to appear in Phys. Rev.
TV advertising and dietary intake in adolescents: a pre- and post- study of Chileâs Food Marketing Policy
Background: The first phase of a comprehensive marketing policy was implemented in Chile in 2016. The policy restricted child-directed marketing of foods and beverages considered high in energy, total sugars, sodium or saturated fat (âhigh-inâ). The objective of this study was to examine the role of high-in TV food advertising as a mediator in the association between policy implementation and consumption of high-in foods and beverages between 2016 and 2017. Methods: Dietary data were from 24-hour diet recalls collected in 2016 and 2017 in a cohort of 12â14 y children (n = 721). Television use was assessed concurrently and linked to analyses of food advertisements on broadcast and paid television to derive individual-level estimates of exposure to high-in food advertising. A multilevel mediation analysis examined direct and indirect effects of the policy through advertising exposure. Results: Following the policy implementation, high-in advertising exposure was significantly reduced (p < 0.01). High-in food intake decreased in adolescents with lower levels, but not higher levels, of high-in advertising at baseline. We did not find evidence of mediation by changes in high-in ad exposure. Conclusions: Adolescentsâ exposure to high-in TV advertising decreased after the 2016 implementation of the Chilean Food Labeling and Marketing Law. However, evidence that changes in advertisement mediated dietary changes was not found. Further research is needed to understand how marketing changes will relate to dietary changes after full implementation of the law and in the long term
Motion of Inertial Observers Through Negative Energy
Recent research has indicated that negative energy fluxes due to quantum
coherence effects obey uncertainty principle-type inequalities of the form
|\Delta E|\,{\Delta \tau} \lprox 1\,. Here is the magnitude of
the negative energy which is transmitted on a timescale . Our main
focus in this paper is on negative energy fluxes which are produced by the
motion of observers through static negative energy regions. We find that
although a quantum inequality appears to be satisfied for radially moving
geodesic observers in two and four-dimensional black hole spacetimes, an
observer orbiting close to a black hole will see a constant negative energy
flux. In addition, we show that inertial observers moving slowly through the
Casimir vacuum can achieve arbitrarily large violations of the inequality. It
seems likely that, in general, these types of negative energy fluxes are not
constrained by inequalities on the magnitude and duration of the flux. We
construct a model of a non-gravitational stress-energy detector, which is
rapidly switched on and off, and discuss the strengths and weaknesses of such a
detector.Comment: 18pp + 1 figure(not included, available on request), in LATEX,
TUPT-93-
Kelp forest distribution in the Nordic region
Kelp forests are productive coastal ecosystems that provide a range of ecosystem services. Mapping the distribution and area occupied by kelp forests is a critical step to identify their ecosystem functions and services, including their role in the carbon cycle, and to detect changes in their distribution. We compiled quantitative data of the dominant genera Laminaria and Saccharina across the Nordic region, allowing us to separate kelp forests (areas with dense or moderately dense kelp coverage) from occurrences of single or few individuals. By fitting boosted regression trees to the compiled data, we modelled and predicted the distribution of kelp forests across the Nordic region. Despite the large scale of the analyses, the models captured well the kelpsâ environmental affinities and predicted the presence of kelp forests with high accuracy. Dense kelp forests are found along the rocky shores of all the Nordic countries, except in the brackish Baltic Sea, with largest areas in Norway, Greenland and Iceland. The results of this study set the scene for future studies on the importance of kelp forests in the Nordic region, including their contribution to the marine carbon budget.Kelp forest distribution in the Nordic regionpublishedVersio
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