Composite Gaussian process models for emulating expensive functions

A new type of nonstationary Gaussian process model is developed for approximating computationally expensive functions. The new model is a composite of two Gaussian processes, where the first one captures the smooth global trend and the second one models local details. The new predictor also incorporates a flexible variance model, which makes it more capable of approximating surfaces with varying volatility. Compared to the commonly used stationary Gaussian process model, the new predictor is numerically more stable and can more accurately approximate complex surfaces when the experimental design is sparse. In addition, the new model can also improve the prediction intervals by quantifying the change of local variability associated with the response. Advantages of the new predictor are demonstrated using several examples.Comment: Published in at http://dx.doi.org/10.1214/12-AOAS570 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

Dynamics of subpicosecond dispersion-managed soliton in a fibre: A perturbative analysis

A model is studied which describes a propagation of a subpicosecond optical pulse in dispersion-managed fibre links. In the limit of weak chromatic dispersion management, the model equation is reduced to a perturbed modified NLS equation having a nonlinearity dispersion term. By means of the Riemann--Hilbert problem, a perturbation theory for the soliton of the modified NLS equation is developed. It is shown in the adiabatic approximation that there exists a unique possibility to suppress the perturbation-induced shift of the soliton centre at the cost of proper matching of the soliton width and nonlinearity dispersion parameter. In the next-order approximation, the spectral density of the radiation power emitted by a soliton is calculated.Comment: 16 pages, 3 figures, to appear in J. Mod. Optic

The growth of ICT4D:impact in educational system in developing countries

Abstract. Problems in developing countries have been an issue for a long time. ICT4D was initiated to solve these problems, at least to ease the current problems to make living standard a bit better. ICT4D stands for information and communication for development, which uses advanced technology to bring opportunities for the people in many fields, such as in education. The term “developing countries” is hard to define, since it is defined by people from developed countries, but in this thesis, I will go through the definition and variables that defines the term. People think that money could solve the problem, but in fact it cannot stop the problems, but by using it to educate people, we can make use of the knowledge learned and thus improve people’s future. In this thesis, I will introduce ICT4D and the evolution of ICT4D, what kind of changes it has gone through to become what it is now. I will also define developing countries from few points of views and also defining human development index (HDI) and means for a better living standard. Next, I will talk about the education and how it could improve the living standard when implementing it properly and how ICT4D is having and could have an impact on the education in developing countries. Also, I will introduce few challenges that could be problematic but not impossible to solve and how huge of a digital divide is between developing and development countries. All of these affect the educational system in developing countries, and is considered as a highly important matters in digital economy, fortunately we have many movements such as ICT4D to tackle these issuesTiivistelmä. Kehitysmaiden ongelmat ovat olleet keskusteluaiheena jo pitkään. ICT4D-liike pantiin alulle ratkaisemaan näitä ongelmia tai ainakin helpottamaan nykyisiä ongelmia parantaakseen ihmisten elintasoa hieman paremmaksi. ICT4D tarkoittaa “tietoa ja viestintää kehitykselle”, jonka tarkoituksena on käyttää edistynyttä teknologiaa tarjoamaan mahdollisuuksia ihmisille monilla aloilla, kuten koulutusaloilla. “Kehitysmaat” käsitteenä on vaikea määritellä, sillä sana “kehitysmaat” ovat määritelleet maat, joissa teknologia on nykyaikaista ja arkipäiväistä. Tässä opinnäytetyössä käyn kuitenkin läpi ne muuttujat, jotka määrittelevät kyseisen termin. Monet ajattelevat, että raha voisi ratkaista näitä ongelmia, mutta tämä ei kuitenkaan ole totta, vaikkakin ongelmat helpottuvat hetkeksi, ongelma on vielä olemassa. Vain kouluttamalla ihmisiä ja hyödyntämällä nykyteknologiaa ja oppimaamme tietoa, voimme ratkaista ongelmia kehitysmaissa. Tässä työssä käyn läpi termin ICT4D:n ja sen evoluution, sekä millaisia ​​muutoksia se on käynyt läpi tullakseen sellaiseksi kuin se nyt on. Aion määritellä myös kehitysmaat muutamasta näkökulmasta ja myös inhimillisen kehityksen indeksin (HDI) ja keinoja paremman elintason saavuttamiseksi. Seuraavaksi opinnäytetyössäni puhun koulutuksesta ja kuinka se voisi parantaa kehitysmaiden elintasoa, kun sitä pannaan täytäntöön sopivalla tavalla ja miten ICT4D voi vaikuttaa kehitysmaiden koulutukseen. Aion myös esitellä muutamia haasteita, jotka voivat olla ongelmallisia, mutta joita ei ole mahdotonta ratkaista, ja miten valtava digitaalinen kuilu on kehittyneiden maiden ja kehitysmaiden välillä. Kaikki mainitut asiat vaikuttavat kehitysmaiden koulutusjärjestelmään, ja näitä pidetään erittäin tärkeänä digitaalitalouden aikana, onneksemme meillä on monia liikkeitä, kuten ICT4D, jotka ovat valmiita ratkaisemaan näitä ongelmia

Dynamics of localization in a waveguide

This is a review of the dynamics of wave propagation through a disordered N-mode waveguide in the localized regime. The basic quantities considered are the Wigner-Smith and single-mode delay times, plus the time-dependent power spectrum of a reflected pulse. The long-time dynamics is dominated by resonant transmission over length scales much larger than the localization length. The corresponding distribution of the Wigner-Smith delay times is the Laguerre ensemble of random-matrix theory. In the power spectrum the resonances show up as a 1/t^2 tail after N^2 scattering times. In the distribution of single-mode delay times the resonances introduce a dynamic coherent backscattering effect, that provides a way to distinguish localization from absorption.Comment: 18 pages including 8 figures; minor correction

Excitonic ferromagnetism in the hexaborides

A ferromagnet with a small spontaneous moment but with a high Curie temperature can be obtained by doping an excitonic insulator made from a spin triplet exciton condensate. Such a condensate can occur in a semimetal with a small overlap or a semiconductor with a small bandgap. We propose that it is responsible for the unexpected ferromagnetism in the doped hexaboride material Ca_{1-x}La_xB_6.Comment: 4 pages, 3 figure

Temperature dependent photoluminescence of single CdS nanowires

Temperature dependent photoluminescence (PL) is used to study the electronic properties of single CdS nanowires. At low temperatures, both near-band edge (NBE) photoluminescence (PL) and spatially-localized defect-related PL are observed in many nanowires. The intensity of the defect states is a sensitive tool to judge the character and structural uniformity of nanowires. As the temperature is raised, the defect states rapidly quench at varying rates leaving the NBE PL which dominates up to room temperature. All PL lines from nanowires follow closely the temperature-dependent band edge, similar to that observed in bulk CdS.Comment: 11 pages, 4 figure

High-temperature magnetic anomaly in the Kitaev hyperhoneycomb compound β-Li2IrO3

We report the existence of a high-temperature magnetic anomaly in the three-dimensional Kitaev candidate material, β-Li2IrO3. Signatures of the anomaly appear in magnetization, heat capacity, and muon spin relaxation measurements. The onset coincides with a reordering of the principal axes of magnetization, which is thought to be connected to the onset of Kitaev-like correlations in the system. The anomaly also shows magnetic hysteresis with a spatially anisotropic magnitude that follows the spin-anisotropic exchange anisotropy of the underlying Kitaev Hamiltonian. We discuss possible scenarios for a bulk and impurity origin

Composition chimique, dégradabilité in sacco et produits de fermentation in vitro de la fétuque élevée (Festuca arundinacea

Objectifs : En vue d’une sélection pour une utilisation comme aliment pour bétail, vingt quatre écotypes de fétuque élevée (Festuca arundinacea) provenant du milieu naturel du nord de la Belgique ont été étudiés afin d’en déterminer la valeur nutritionnelle.Méthodologie et Résultats : La composition chimique, la dégradabilité in sacco et les incubations in vitro ont été réalisés. Un mouton adulte fistulé au niveau du rumen a été utilisé pour la détermination de la dégradabilité in sacco des écotypes et les incubations in vitro. La teneur moyenne en MAT (8,0% MS) des 24 écotypes étudiés est faible. Les écotypes de Festuca arundinacea présentent en moyenne une meilleure dégradabilité potentielle (a + b) (82,7%) que les fourrages tropicaux Pennisetum purpureum (64,9%) et Tripsacum laxum (66,8%) mais moindre que les fourrages tempérés (Lolium perenne : 90,5%). Festuca arundinacea a présenté une production élevée de propionate (234.7 Gmol/mmol AGV totaux).Conclusion : Les meilleurs de la collection de 24 écotypes de F. arundinacea ont été identifiés pour une utilisation comme aliment pour bétail. Les teneurs en MAT trouvées pour la fétuque élevée sont comparables à celles des fourrages tropicaux qui sont généralement plus pauvres en protéine que les fourrages tempérés ; ce qui représente un handicap pour leur ingestion volontaire. Ces résultats impliquent d’une part qu’il faut une supplémentation en azote pour les pâturages de Festuca arundinacea et d’autre part l’exploitation des pâturages à la fétuque élevée au stade avant frutification. Par ailleurs, la culture en association de fétuque élevée et légumineuses est également une solution envisageable. Une variabilité a été notée entre les écotypes de Festuca arundinacea qui en moyenne présentent une meilleure dégradabilité que les fourrages tropicaux, mais moindres que les fourrages tempérés. Cet avantage de la fétuque élevée sur les fourrages tropicaux se consolide par une production élevée d’acide propionique et faible d’acide acétique comparables à celles des fourrages tempérés ; ce qui est très intéressant car le propionate peut générer du glucose, un des facteurs limitant pour la production laitière.Mots clés: Festuca arundinacea, écotype, azote ammoniacal, dégradabilité in sacco, méthane, acides gras volatile