7,574 research outputs found
Evaluation of models to predict the stoichiometry of volatile fatty acid profiles in rumen fluid of lactating Holstein cows
Volatile fatty acids (VFA), produced in the rumen by microbial fermentation, are the main energy source for ruminants. The VFA profile, particularly the nonglucogenic (acetate, Ac; butyrate, Bu) to glucogenic (propionate, Pr) VFA ratio (NGR), is associated with effects on methane production, milk composition, and energy balance. The aim of this study was to evaluate extant rumen VFA stoichiometry models for their ability to predict in vivo VFA molar proportions. The models were evaluated using an independent data set consisting of 101 treatments from 24 peer-reviewed publications with lactating Holstein cows. All publications contained a full diet description, rumen pH, and rumen VFA molar proportions. Stoichiometric models were evaluated based on root mean squared prediction error (RMSPE) and concordance correlation coefficient (CCC) analysis. Of all models evaluated, the 1998 Friggens model had the lowest RMSPE for Ac and Bu (7.2 and 20.2% of observed mean, respectively). The 2006 Bannink model had the lowest RMSPE and highest CCC for Pr (14.4% and 0.70, respectively). The 2008 Bannink model had comparable predictive performance for Pr to that of the 2006 Bannink model but a larger error due to overall bias (26.2% of MSPE). The 1982 Murphy model provided the poorest prediction of Bu, with the highest RMSPE and lowest CCC (24.6% and 0.15, respectively). The 1988 Argyle and Baldwin model had the highest CCC for Ac with an intermediate RMSPE (0.47 and 8.0%, respectively). The 2006 Sveinbjörnsson model had the highest RMSPE (13.9 and 34.0%, respectively) and lowest CCC (0.31 and 0.40, respectively) for Ac and Pr. The NGR predictions had the lowest RMSPE and highest CCC in the 2 models of Bannink, whereas the lowest predictive performance was in the 2006 Sveinbjörnsson model. It appears that the type of VFA produced is not a simple linear relationship between substrate inputs and pH as currently represented. The analysis demonstrates that most rumen VFA stoichiometric approaches explain a large part of the variation in VFA molar proportions among diets, in particular for Ac, whereas predictive power for Pr and Bu differ largely among approaches. The move toward feed evaluation systems based on animal response might necessitate an improved representation of rumen fermentation, focused on improving our understanding of VFA proportions in diets that vary from the mean
An indicator of the multiple equilibria regime of the Atlantic meridional overturning circulation
Recent model results have suggested that there may be a scalar indicator ? monitoring whether the Atlantic meridional overturning circulation (MOC) is in a multiple equilibrium regime. The quantity ? is based on the net freshwater transport by the MOC into the Atlantic basin. It changes sign as soon as the steady Atlantic MOC enters the multiple equilibrium regime because of an increased freshwater input in the northern North Atlantic. This paper addresses the issue of why the sign of ? is such a good indicator for the multiple equilibrium regime. Changes in the Atlantic freshwater budget over a complete bifurcation diagram and in finite amplitude perturbation experiments are analyzed in a global ocean circulation model. The authors show that the net anomalous freshwater transport into or out of the Atlantic, resulting from the interactions of the velocity perturbations and salinity background field, is coupled to the background (steady state) state freshwater budget and hence to ?. The sign of ? precisely shows whether this net anomalous freshwater transport is stabilizing or destabilizing the MOC. Therefore, it can indicate whether the MOC is in a single or multiple equilibrium regime.<br/
Complementing CO2 emission reduction by solar radiation management might strongly enhance future welfare
Abstract. Solar radiation management (SRM) has been proposed as a means to reduce
global warming in spite of high greenhouse-gas concentrations and to lower the chance
of warming-induced tipping points. However, SRM may cause economic damages and its
feasibility is still uncertain. To investigate the trade-off between these (economic) gains and
damages, we incorporate SRM into a stochastic dynamic integrated assessment model and
perform the first rigorous costâbenefit analysis of sulfate-based SRM under uncertainty,
treating warming-induced climate tipping and SRM failure as stochastic elements.
We find that within our model, SRM has the potential to greatly enhance future welfare and
merits being taken seriously as a policy option. However, if only SRM and no
CO2 abatement is used, global warming is not stabilised and will exceed 2âK.
Therefore, even if successful, SRM can not replace but only complement
CO2 abatement. The optimal policy combines CO2
abatement and modest SRM and succeeds in keeping global warming below 2âK
A review of mathematical functions for the analysis of growth in poultry
Poultry industries face various decisions in the production cycle that affect the profitability of an operation. Predictions of growth when the birds are ready for sale are important factors that contribute to the economy of poultry operations. Mathematical functions called âgrowth functionsâ have been used to relate body weight (W) to age or cumulative feed intake. These can also be used as response functions to predict daily energy and protein dietary requirements for maintenance and growth (France et al., 1989). When describing growth versus age in poultry, a fixed point of inflexion can be a limitation with equations such as the Gompertz and logistic. Inflexion points vary depending on age, sex, breed and type of animal, so equations such as the Richards and LĂłpez are generally recommended. For describing retention rate against daily intake, which generally does not exhibit an inflexion point, the monomolecular would appear the function of choice
Effects of diamagnetic levitation on bacterial growth in liquid
Diamagnetic levitation is a technique that uses a strong, spatially-varying magnetic field to levitate diamagnetic materials, such as water and biological cells. This technique has the potential to simulate aspects of weightlessness, on the Earth. In common with all ground-based techniques to simulate weightlessness, however, there are effects introduced by diamagnetic levitation that are not present in space. Since there have been few studies that systematically investigate these differences, diamagnetic levitation is not yet being fully exploited. For the first time, we critically assess the effect of diamagnetic levitation on a bacterial culture in liquid. We used a superconducting magnet to levitate growing bacterial cultures for up to 18 hours, in a series of experiments to determine the effect of diamagnetic levitation on all phases of the bacterial growth cycle. We find that diamagnetic levitation increases the rate of population growth in a liquid culture. The speed of sedimentation of the bacterial cells to the bottom of the container is considerably reduced. Further experiments and microarray gene analysis show that the growth enhancement is due to greater oxygen availability in the magnetically levitated sample. We demonstrate that the magnetic field that levitates the cells also induces convective stirring in the liquid, an effect not present in microgravity. We present a simple theoretical model, showing how the paramagnetic force on dissolved oxygen can cause the liquid to become unstable to convection when the consumption of oxygen by the bacteria generates an oxygen concentration gradient. We propose that this convection enhances oxygen availability by transporting oxygen around the sample. Since convection is absent in space, these results are of significant importance and timeliness to researchers considering using diamagnetic levitation to explore weightless effects on living organisms and a broad range of other topics in the physical and life sciences
Dimensional crossover of the fundamental-measure functional for parallel hard cubes
We present a regularization of the recently proposed fundamental-measure
functional for a mixture of parallel hard cubes. The regularized functional is
shown to have right dimensional crossovers to any smaller dimension, thus
allowing to use it to study highly inhomogeneous phases (such as the solid
phase). Furthermore, it is shown how the functional of the slightly more
general model of parallel hard parallelepipeds can be obtained using the
zero-dimensional functional as a generating functional. The multicomponent
version of the latter system is also given, and it is suggested how to
reformulate it as a restricted-orientation model for liquid crystals. Finally,
the method is further extended to build a functional for a mixture of parallel
hard cylinders.Comment: 4 pages, no figures, uses revtex style files and multicol.sty, for a
PostScript version see http://dulcinea.uc3m.es/users/cuesta/cross.p
Healthiness from Duality
Healthiness is a good old question in program logics that dates back to
Dijkstra. It asks for an intrinsic characterization of those predicate
transformers which arise as the (backward) interpretation of a certain class of
programs. There are several results known for healthiness conditions: for
deterministic programs, nondeterministic ones, probabilistic ones, etc.
Building upon our previous works on so-called state-and-effect triangles, we
contribute a unified categorical framework for investigating healthiness
conditions. We find the framework to be centered around a dual adjunction
induced by a dualizing object, together with our notion of relative
Eilenberg-Moore algebra playing fundamental roles too. The latter notion seems
interesting in its own right in the context of monads, Lawvere theories and
enriched categories.Comment: 13 pages, Extended version with appendices of a paper accepted to
LICS 201
Phase behaviour of charged colloidal sphere dispersions with added polymer chains
We study the stability of mixtures of highly screened repulsive charged
spheres and non-adsorbing ideal polymer chains in a common solvent using free
volume theory. The effective interaction between charged colloids in an aqueous
salt solution is described by a screened-Coulomb pair potential, which
supplements the pure hard-sphere interaction. The ideal polymer chains are
treated as spheres that are excluded from the colloids by a hard-core
interaction, whereas the interaction between two ideal chains is set to zero.
In addition, we investigate the phase behaviour of charged colloid-polymer
mixtures in computer simulations, using the two-body (Asakura-Oosawa pair
potential) approximation to the effective one-component Hamiltonian of the
charged colloids. Both our results obtained from simulations and from free
volume theory show similar trends. We find that the screened-Coulomb repulsion
counteracts the effect of the effective polymer-mediated attraction. For
mixtures of small polymers and relatively large charged colloidal spheres, the
fluid-crystal transition shifts to significantly larger polymer concentrations
with increasing range of the screened-Coulomb repulsion. For relatively large
polymers, the effect of the screened-Coulomb repulsion is weaker. The resulting
fluid-fluid binodal is only slightly shifted towards larger polymer
concentrations upon increasing the range of the screened-Coulomb repulsion. In
conclusion, our results show that the miscibility of dispersions containing
charged colloids and neutral non-adsorbing polymers increases, upon increasing
the range of the screened-Coulomb repulsion, or upon lowering the salt
concentration, especially when the polymers are small compared to the colloids.Comment: 25 pages,13 figures, accepted for publication on J.Phys.:Condens.
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