1,986 research outputs found
Epi-Consistency of Convex Stochastic Programs
This paper presents consistency results for sequences of optimal solutions to convex stochastic optimization problems constructed from empirical data. Very few additional assumptions are required because of the special properties of convexity and empirical measures; nevertheless the results are broadly applicable to many situations arising in stochastic programming
Charged lepton contributions to the solar neutrino mixing and theta_13
A charged lepton contribution to the solar neutrino mixing induces a
contribution to theta_13, barring cancellations/correlations, which is
independent of the model building options in the neutrino sector. We illustrate
two robust arguments for that contribution to be within the expected
sensitivity of high intensity neutrino beam experiments. We find that the case
in which the neutrino sector gives rise to a maximal solar angle (the natural
situation if the hierarchy is inverse) leads to a theta_13 close to or
exceeding the experimental bound depending on the precise values of theta_12,
theta_23, an unknown phase and possible additional contributions. We finally
discuss the possibility that the solar angle originates predominantly in the
charged lepton sector. We find that the construction of a model of this sort is
more complicated. We comment on a recent example of natural model of this type.Comment: 10 pages, 1 figur
Plant perfomance across latitude: the role of plasticity and local adaltation in aquatic plant
Geographic variation can lead to the evolution of different local varieties within a given species, therefore influencing its distribution and genetic structure. We investigated the contribution of plasticity and local adaptation to the performance of a common aquatic plant (Potamogeton pectinatus) in contrasting climates, using reciprocal transplants at three experimental sites across a latitudinal cline in Europe. Plants from 54 genets, originally collected from 14 populations situated within four climatic regions (sub- arctic, cold temperate, mild temperate, and mediterranean) were grown in three different localities within three of these regions (cold temperate, Nor way; mild temperate, The Netherlands; mediterranean, Spain). Tuber production was highest for the mild-temperate genets, irrespective of locality where the genets were grown. Selection coefficients indicated that populations at the European center of the species distribution perform better than all other populations, at all sites. However, marginal populations showed changes in life-histor y traits, such as compressed life cycles in the north and true perenniality in the south, that may allow them to perform better locally, at the limits of their distribution range. Our results thus suggest that local adaptation may overlap spatially with center–peripher y gra- dients in performance caused by genetic factors (such as genetic drift and inbreeding in range-marginal populations).Peer reviewe
Stochastic approach to molecular interactions and computational theory of metabolic and genetic regulations
Binding and unbinding of ligands to specific sites of a macromolecule are one
of the most elementary molecular interactions inside the cell that embody the
computational processes of biological regulations. The interaction between
transcription factors and the operators of genes and that between ligands and
binding sites of allosteric enzymes are typical examples of such molecular
interactions. In order to obtain the general mathematical framework of
biological regulations, we formulate these interactions as finite Markov
processes and establish a computational theory of regulatory activities of
macromolecules based mainly on graphical analysis of their state transition
diagrams. The contribution is summarized as follows: (1) Stochastic
interpretation of Michaelis-Menten equation is given. (2) Notion of
\textit{probability flow} is introduced in relation to detailed balance. (3) A
stochastic analogy of \textit{Wegscheider condition} is given in relation to
loops in the state transition diagram. (4) A simple graphical method of
computing the regulatory activity in terms of ligands' concentrations is
obtained for Wegscheider cases.Comment: 20 pages, 13 figure
On the fraction of dark matter in charged massive particles (CHAMPs)
From various cosmological, astrophysical and terrestrial requirements, we
derive conservative upper bounds on the present-day fraction of the mass of the
Galactic dark matter (DM) halo in charged massive particles (CHAMPs). If dark
matter particles are neutral but decay lately into CHAMPs, the lack of
detection of heavy hydrogen in sea water and the vertical pressure equilibrium
in the Galactic disc turn out to put the most stringent bounds. Adopting very
conservative assumptions about the recoiling velocity of CHAMPs in the decay
and on the decay energy deposited in baryonic gas, we find that the lifetime
for decaying neutral DM must be > (0.9-3.4)x 10^3 Gyr. Even assuming the
gyroradii of CHAMPs in the Galactic magnetic field are too small for halo
CHAMPs to reach Earth, the present-day fraction of the mass of the Galactic
halo in CHAMPs should be < (0.4-1.4)x 10^{-2}. We show that redistributing the
DM through the coupling between CHAMPs and the ubiquitous magnetic fields
cannot be a solution to the cuspy halo problem in dwarf galaxies.Comment: 21 pages, 2 figures. To appear in JCA
Epistemic and social scripts in computer-supported collaborative learning
Collaborative learning in computer-supported learning environments typically means that learners work on tasks together, discussing their individual perspectives via text-based media or videoconferencing, and consequently acquire knowledge. Collaborative learning, however, is often sub-optimal with respect to how learners work on the concepts that are supposed to be learned and how learners interact with each other. One possibility to improve collaborative learning environments is to conceptualize epistemic scripts, which specify how learners work on a given task, and social scripts, which structure how learners interact with each other. In this contribution, two studies will be reported that investigated the effects of epistemic and social scripts in a text-based computer-supported learning environment and in a videoconferencing learning environment in order to foster the individual acquisition of knowledge. In each study the factors ‘epistemic script’ and ‘social script’ have been independently varied in a 2×2-factorial design. 182 university students of Educational Science participated in these two studies. Results of both studies show that social scripts can be substantially beneficial with respect to the individual acquisition of knowledge, whereas epistemic scripts apparently do not to lead to the expected effects
Come to the dark side! The role of functional traits in shaping dark diversity patterns of south-eastern European hoverflies
1. Dark diversity represents the set of species that can potentially inhabit a given area under particular ecological conditions, but are currently 'missing' from a site. This concept allows characterisation of the mechanisms determining why species are sometimes absent from an area that seems ecologically suitable for them. 2. The aim of this study was to determine the dark diversity of hoverflies in south-eastern Europe and to discuss the role of different functional traits that might increase the likelihood of species contributing to dark diversity. Based on expert opinion, the Syrph the Net database and known occurrences of species, the study estimated species pools, and observed and dark diversities within each of 11 defined vegetation types for 564 hoverfly species registered in south-eastern Europe. To detect the most important functional traits contributing to species being in dark diversity across different vegetation types, a random forest algorithm and respective statistics for variable importance were used. 3. The highest dark diversity was found for southwest Balkan sub-Mediterranean mixed oak forest type, whereas the lowest was in Mediterranean mixed forest type. Three larval feeding modes (saproxylic, and phytophagous on bulbs or roots) were found to be most important for determining the probability of a species contributing to hoverfly dark diversity, based on univariate correlations and random forest analysis. 4. This study shows that studying dark diversity might provide important insights into what drives community assembly in south-eastern European hoverflies, especially its missing components, and contributes to more precise conservation prioritisation of both hoverfly species and their habitats.Peer reviewe
Self-referencing spectral interferometric probing of the onset time of relativistic transparency in intense laser-foil interactions
Irradiation of an ultrathin foil target by a high intensity laser pulse drives collective electron motion and the generation of strong electrostatic fields, resulting in ultrabright sources of high-order harmonics and energetic ions. The ion energies can be significantly enhanced if the foil undergoes relativistic self-induced transparency during the interaction, with the degree of enhancement depending in part on the onset time of transparency. We report on a simple and effective approach to diagnose the time during the interaction at which the foil becomes transparent to the laser light, providing a route to optically controlling and optimizing ion acceleration and radiation generation. The scheme involves a self-referencing approach to spectral interferometry, in which coherent transition radiation produced at the foil rear interferes with laser light transmitted through the foil. The relative timing of the onset of transmission with respect to the transition radiation generation is determined from spectral fringe spacing and compared to simultaneous frequency-resolved optical gating measurements. The results are in excellent agreement, and are discussed with reference to particle-in-cell simulations of the interaction physics and an analytical model for the onset time of transparency in ultrathin foils
Higher Twist Distribution Amplitudes of the Nucleon in QCD
We present the first systematic study of higher-twist light-cone distribution
amplitudes of the nucleon in QCD. We find that the valence three-quark state is
described at small transverse separations by eight independent distribution
amplitudes. One of them is leading twist-3, three distributions are twist-4 and
twist-5, respectively, and one is twist-6. A complete set of distribution
amplitudes is constructed, which satisfies equations of motion and constraints
that follow from conformal expansion. Nonperturbative input parameters are
estimated from QCD sum rules.Comment: 29 pages, 4 figures, eqn in (3.19) corrected, table 3 accordingly
changed, some typos fixe
Pre-main-sequence Lithium Depletion
In this review I briefly discuss the theory of pre-main-sequence (PMS) Li
depletion in low-mass (0.075<M<1.2 Msun) stars and highlight those uncertain
parameters which lead to substantial differences in model predictions. I then
summarise observations of PMS stars in very young open clusters, clusters that
have just reached the ZAMS and briefly highlight recent developments in the
observation of Li in very low-mass PMS stars.Comment: 8 pages, invited review at "Chemical abundances and mixing in stars
in the Milky Way and its satellites", eds. L. Pasquini, S. Randich. ESO
Astrophysics Symposium (Springer-Verlag
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