5,442 research outputs found
Short relaxation times but long transient times in both simple and complex reaction networks
When relaxation towards an equilibrium or steady state is exponential at
large times, one usually considers that the associated relaxation time ,
i.e., the inverse of that decay rate, is the longest characteristic time in the
system. However that need not be true, and in particular other times such as
the lifetime of an infinitesimal perturbation can be much longer. In the
present work we demonstrate that this paradoxical property can arise even in
quite simple systems such as a chain of reactions obeying mass action kinetics.
By mathematical analysis of simple reaction networks, we pin-point the reason
why the standard relaxation time does not provide relevant information on the
potentially long transient times of typical infinitesimal perturbations.
Overall, we consider four characteristic times and study their behavior in both
simple chains and in more complex reaction networks taken from the publicly
available database "Biomodels." In all these systems involving mass action
rates, Michaelis-Menten reversible kinetics, or phenomenological laws for
reaction rates, we find that the characteristic times corresponding to
lifetimes of tracers and of concentration perturbations can be much longer than
Farm-level Acreage Allocation under Risk
We model the area allocation decision problem for a fixed size crop farm under random yields and prices for a risk-averse farmer. We assume that in the short run, the variable input expenses are fixed per hectare and per crop (an assumption that is motivated by our data). Therefore the cost function depends only on the non-stochastic area allocation. The first order conditions of the model involve integrals across functions of random variables that do not in general have closed form solutions. Numerical simulation techniques are used to calibrate the parameters of the cost function. The two sources of randomness, price and yield, are combined into a single random variable, the yield-in-value. Based on examination of panels of yield-in-value data, we assume independence across the yield-in-value distributions and that the farmers know these distributions. We have modeled the sugar quota constraint, the Common Agricultural Policy subsidies and set-aside, and one Agri-Environmental Measure called "buffer zone".Risk and Uncertainty,
Overview of the coordinated ground-based observations of Titan during the Huygens mission
Coordinated ground-based observations of Titan were performed around or during the Huygens atmospheric probe mission at Titan on 14 January 2005, connecting the momentary in situ observations by the probe with the synoptic coverage provided by continuing ground-based programs. These observations consisted of three different categories: (1) radio telescope tracking of the Huygens signal at 2040 MHz, (2) observations of the atmosphere and surface of Titan, and (3) attempts to observe radiation emitted during the Huygens Probe entry into Titan's atmosphere. The Probe radio signal was successfully acquired by a network of terrestrial telescopes, recovering a vertical profile of wind speed in Titan's atmosphere from 140 km altitude down to the surface. Ground-based observations brought new information on atmosphere and surface properties of the largest Saturnian moon. No positive detection of phenomena associated with the Probe entry was reported. This paper reviews all these measurements and highlights the achieved results. The ground-based observations, both radio and optical, are of fundamental importance for the interpretation of results from the Huygens mission
Design Thinking and Participation: Lessons Learned from Three Case Studies
This paper examines how design thinking and serious games approaches can be used to support participation through the analysis of three case studies. Indeed we will analyze these approaches in three different contexts: (i) a state-owned multi-utilities company; (ii) a political party; (iii) an information system strategic committee. Our analysis framework relies on the concepts of "perceived usefulness" and "perceived ease of use" and we will use it to discuss the lessons learned. Our main finding is that these approaches really contributing in making complex and abstract matters more "tangible" and thus understandable.participation; design thinking; serious games; case study; perceived usefulness
Recommended from our members
Nonparametric specification analysis of dynamic parametric models
Time series parametric models generally cater to a particular objective, such as forecasting, and it is therefore desirable to judge such models solely on the basis of their performance in the fullfillment of that objective. We propose a specification testing procedure which concentrates power on the parametric model's ability to estimate a set of characteristics of the finite dimensional distributions of the process. It is based on the comparison between a nonparametric estimate of the said characteristic and its parametric boot-strap analogue. Applications of this principle are proposed for the assessment of recursive dynamic models in the estimation of conditional means and conditional quantiles for mixing processes and for the estimation of dependence in long memory processes
Multi-input Multi-output Farm-level Cost Function: A Comparison of Least Squares and Entropy Estimators
We introduce a modification of the quadratic-Leontieff multi-output cost function that is particularly suitable for the data of the Farm Accountancy Data Network. We present least squares and entropy estimates of that function and compare their results for a sample of crop farms. Our results are encouraging for the use of entropy estimators in cases in which farms are not assumed to share the same technology. Our approach can be seen as an extension of the Positive Mathematical Programming approach (Howitt, 1995). The extension consists in an explicit specification of inputs in the cost function and in the possibility of modeling several farms simultaneously.cost function, least squares estimator, entropy estimator, heterogeneity, Farm Management, C3, D61, Q12,
Steroid substrate-induced epimerase mechanism in the active site of the human 11β-hydroxysteroid dehydrogenase type 1
Cytochrome P4507B1 7[alpha]-hydroxylates dehydroepiandrosterone (DHEA), epiandrosterone (EpiA) and 5[alpha]-androstane-3[beta],17[beta]-diol (Adiol). 11[beta]-Hydroxysteroid dehydrogenase type 1 (11[beta]-HSD1) interconverts 7[alpha]- and 7[beta]- forms. Whether the inter-conversion proceeds through oxido-reductive steps or epimerase activity is investigated. Experiments using ^3^H-labeled 7[beta]-hydroxy-DHEA, 7[beta]-hydroxy-EpiA and 7[beta]-hydroxy-Adiol show the ^3^H-label to accumulate in 7-oxo-DHEA trap but neither in 7-oxo-EpiA nor 7-oxo-Adiol traps. Computed models of 7-oxygenated steroids dock in the active site of 11[beta]-HSD1 either in a flipped or turned form relative to cortisone and cortisol. 7-Oxo-steroid reduction in 7[alpha]- or 7[beta]-hydroxylated derivatives results from either turned or flipped forms. 11[beta]-HSD1 incubation in H~2~^18^O medium with each 7-hydroxysteroid did not incorporate ^18^O in 7-hydroxylated derivatives of EpiA and Adiol independently of the cofactor used. Thus oxido-reductive steps apply for the interconversion of 7[alpha]- and 7[beta]-hydroxy-DHEA through 7-oxo-DHEA. Epimerisation may proceed on the 7-hydroxylated derivatives of EpiA and Adiol through a mechanism involving the cofactor and Ser170
Validation of Spherical Fourier-Bessel power spectrum analysis with lognormal simulations and eBOSS DR16 LRG EZmocks
Tuning into the bass notes of the large-scale structure requires careful
attention to geometrical effects arising from wide angles. The spherical
Fourier-Bessel (SFB) basis provides a harmonic-space coordinate system that
fully accounts for all wide-angle effects. To demonstrate the feasibility of
the SFB power spectrum, in this paper we validate our SFB pipeline by applying
it to lognormal, and both complete and realistic EZmock simulations that were
generated for eBOSS DR16 LRG sample. We include redshift space distortions and
the local average effect (aka integral constraint). The covariance matrix is
obtained from 1000 EZmock simulations, and inverted using eigenvalue
decomposition.Comment: 20 pages, 16 figure
- …