Sequential Quasi-Monte Carlo

We derive and study SQMC (Sequential Quasi-Monte Carlo), a class of algorithms obtained by introducing QMC point sets in particle filtering. SQMC is related to, and may be seen as an extension of, the array-RQMC algorithm of L'Ecuyer et al. (2006). The complexity of SQMC is $O(N \log N)$, where $N$ is the number of simulations at each iteration, and its error rate is smaller than the Monte Carlo rate $O_P(N^{-1/2})$. The only requirement to implement SQMC is the ability to write the simulation of particle $x_t^n$ given $x_{t-1}^n$ as a deterministic function of $x_{t-1}^n$ and a fixed number of uniform variates. We show that SQMC is amenable to the same extensions as standard SMC, such as forward smoothing, backward smoothing, unbiased likelihood evaluation, and so on. In particular, SQMC may replace SMC within a PMCMC (particle Markov chain Monte Carlo) algorithm. We establish several convergence results. We provide numerical evidence that SQMC may significantly outperform SMC in practical scenarios.Comment: 55 pages, 10 figures (final version

Isotopic techniques to measure N2O, N2 and their sources

GHG emissions are usually the result of several simultaneous processes. Furthermore, some gases such as N2 are very difficult to quantify and require special techniques. Therefore, in this chapter, the focus is on stable isotope methods. Both natural abundance techniques and enrichment techniques are used. Especially in the last decade, a number of methodological advances have been made. Thus, this chapter provides an overview and description of a number of current state-of-theart techniques, especially techniques using the stable isotope 15N. Basic principles and recent advances of the 15N gas flux method are presented to quantify N2 fluxes, but also the latest isotopologue and isotopomer methods to identify pathways for N2O production. The second part of the chapter is devoted to 15N tracing techniques, the theoretical background and recent methodological advances. A range of different methods is presented from analytical to numerical tools to identify and quantify pathway-specific N2O emissions. While this chapter is chiefly concerned with gaseous N emissions, a lot of the techniques can also be applied to other gases such as methane (CH4), as outlined in Sect. 5.3

Doing Gender Im Technisch-Naturwissen-Schaftlichen Bereich

Für die Lösung des Nachwuchsproblems in den Technikwissenschaften spielt die Gewinnung von Frauen eine zentrale Rolle. Die in der Expertise dargestellten Befunde verdeutlichen dreierlei: (1) In den Natur- und Technikwissenschaften "verliert" man Frauen sehr früh im Lebensverlauf. (2) Wie beim Durchlauf eines Trichters (leaking pipeline) verringert sich mit jeder Bildungs- und Karrierestufe die Anzahl von Frauen in diesen Fächern und Berufen. (3) Die Erhöhung des Interesses für Technikwissenschaften von Mädchen und Frauen ist nicht nur "ein Problem" für das Bildungssystem, sondern ganz wesentlich auch des Arbeitsmarktes. Die Befunde der Expertise zeigen, dass es unbedingt notwendig ist, jungen Frauen, die in technischen Berufen gut ausgebildet sind, eine höhere Chance als bisher zu geben, (a) ihren Beruf aus dem Bereich Mathematik, Informatik, Naturwissenschaften, Technik (im Folgenden kurz: MINT) auszuüben und (b) dies auch mit den gleichen Gratifikationen wie Männer. Diese Herausforderung muss - und zwar unabhängig von der Nachfrage nach neuem Personal in technischen Berufen - schnell gemeistert werden, wenn Wirtschaft und Politik ein ernst gemeintes Interesse an "Frauen in MINT-Berufen" besitzen

Electrochemical behavior of ammonia at Ni/Ni(OH)2 electrode

The electrochemical oxidation of ammonia was investigated on a Ni/Ni(OH)(2) electrode prepared by potential cycling of a Ni electrode in 1 M NaClO4. It was found that oxidation of ammonia is strongly pH dependent and proceeds mainly at pH values above 7. This indicates that NH3 rather than NH4+ is oxidized on nickel electrodes. Oxidation of ammonia occurs in the potential region of Ni(II)/Ni(III) redox activity resulting in formation of a clear peak. Ni/Ni(OH)(2) is not deactivated during ammonia oxidation even at high ammonia concentrations. A considerable fraction of the ammonia was oxidized to nitrate (11%), while the rest were gaseous nitrogen compounds. It is postulated that nitrogen was formed via a mechanism involving direct electron transfer from ammonia to the anode whereas the formation of nitrate involved oxygen transfer from water to an ammonia molecule. (C) 2009 Elsevier B.V. All rights reserved

Human resource management in US subsidiaries in Europe and Australia: centralisation or autonomy?

We explore determinants of subsidiary autonomy in setting human resource management (HRM) practices within US-parented multinational enterprises (MNEs), in Europe and Australia. We examine both the effect of strategic context and the effect of the institutional location of the subsidiary. We find that US MNEs show greater centralisation of control over HRM where the subsidiary faces global markets, in coordinated market economies vs liberal market economies, and where union density is low