Optimal Adaptive Control Methods for Structurally Varying Systems

The problem of simultaneously identifying and controlling a time-varying, perfectly-observed linear system is posed. The parameters are assumed to obey a Markov structure and are estimated with a Kalman filter. The problem can be solved conceptually by dynamic programming, but even with a quadratic loss function the analytical computations cannot be carried out for more than one step because of the dual nature of the optimal control law. All approximations to the solution that have been proposed in the literature, and two approximations that are presented here for the first time are analyzed. They are classified into dual and non-dual methods. Analytical comparison is untractable; hence Monte Carlo simulations are used. A set of experiments is presented in which five non-dual methods are compared. The numerical results indicate a possible ordering among these approximations.

The Effect of Voting Advice Applications (VAAs) on Political Preferences - Evidence from a Randomized Field Experiment

Can online Voting Advice Applications (VAAs) that match voters to candidates and parties based on issue congruence influence voters’ political preferences? To address this question, we conducted a field experiment with University students during the 2011 Swiss federal elections and examine whether voters who used the Swiss VAA smartvote prior to the elections were more likely to adapt their initial party preferences. smartvote is an online web tool that enables voters to match their issue preferences to those of parties and candidates running for office, providing voters with custom made voting recommendations. Moreover, the tool allows voters to visualize their political position in the political landscape and compare their position to the political offer. The VAA gives unprecedented access to detailed political information and lets voters systematically compare electoral alternatives. Given these unique opportunities offered by the VAA, we analyze whether the revelation of “objective” preferences by the voting recommendation initiates changes in “subjective” preferences of voters. Decades of research on political behavior indicate that voters’ knowledge of and interest in politics is fairly limited and that political preferences are therefore highly amenable to (additional) information. Hence, we expect that voters who have their policy matches revealed by smartvote to be more likely to reconsider previously held convictions and consequently show changes in their political preference structure. We argue that VAAs can reinforce and rearrange pre-existing preferences. Employing the common political preference measure of an individual’s propensity to vote (ptv) for specific parties, we ascertain whether the smartvote voting recommendation caused voters to adapt their ptv scores for the running parties in the election. To empirically test these assumptions, we conducted a randomized field experiment during the 2011 Swiss federal elections among 2’000 University students in Switzerland. The treatment group received * Contact: [email protected] an email invitation to use smartvote before elections, providing survey participants with a personalized login for the website. The control group did not receive such an invitation. We measured the baseline characteristics and political preferences of both groups before and after the elections by means of an online survey. Given the randomized treatment assignment and the panel structure of the experiment, the data allows us to estimate the causal effect of smartvote use on political preferences. Due to non-compliance in the sample, we identify local average treatment effects for compliers. We find significant changes in the awarded scores for the top party preference among smartvote users. The assigned ptv score for the top party preferences increases significantly among those voters who used smartvote. Among those who changed their top party ptv score, most remained with the same party choice. Thus, in case of the most preferred party, smartvote use seems to reinforce pre-existing preferences. We do not only find a strengthening of the top party preference but also a multiplication thereof. Voters who consulted the tool report higher likelihoods for considering alternative choice options at elections. smartvote users, compared to non-users, are significantly more likely to change their initial preferences from a single most favored party to multiple highly preferred parties. In other words, being exposed to detailed information about vote alternatives seems to incline voters to consider these alternative options more closely and include the closest ones as part of their future choice set. These systematic shifts among smartvote users present empirical evidence for a causal effect of VAA use on political preferences

XenDB: Full length cDNA prediction and cross species mapping in Xenopus laevis

BACKGROUND: Research using the model system Xenopus laevis has provided critical insights into the mechanisms of early vertebrate development and cell biology. Large scale sequencing efforts have provided an increasingly important resource for researchers. To provide full advantage of the available sequence, we have analyzed 350,468 Xenopus laevis Expressed Sequence Tags (ESTs) both to identify full length protein encoding sequences and to develop a unique database system to support comparative approaches between X. laevis and other model systems. DESCRIPTION: Using a suffix array based clustering approach, we have identified 25,971 clusters and 40,877 singleton sequences. Generation of a consensus sequence for each cluster resulted in 31,353 tentative contig and 4,801 singleton sequences. Using both BLASTX and FASTY comparison to five model organisms and the NR protein database, more than 15,000 sequences are predicted to encode full length proteins and these have been matched to publicly available IMAGE clones when available. Each sequence has been compared to the KOG database and ~67% of the sequences have been assigned a putative functional category. Based on sequence homology to mouse and human, putative GO annotations have been determined. CONCLUSION: The results of the analysis have been stored in a publicly available database XenDB . A unique capability of the database is the ability to batch upload cross species queries to identify potential Xenopus homologues and their associated full length clones. Examples are provided including mapping of microarray results and application of 'in silico' analysis. The ability to quickly translate the results of various species into 'Xenopus-centric' information should greatly enhance comparative embryological approaches. Supplementary material can be found at

Analytic approximations to the phase diagram of the Jaynes-Cummings-Hubbard model with application to ion chains

We discuss analytic approximations to the ground state phase diagram of the homogeneous Jaynes-Cummings-Hubbard (JCH) Hamiltonian with general short-range hopping. The JCH model describes e.g. radial phonon excitations of a linear chain of ions coupled to an external laser field tuned to the red motional sideband with Coulomb mediated hopping or an array of high-$Q$ coupled cavities containing a two-level atom and photons. Specifically we consider the cases of a linear array of coupled cavities and a linear ion chain. We derive approximate analytic expressions for the boundaries between Mott-insulating and superfluid phases and give explicit expressions for the critical value of the hopping amplitude within the different approximation schemes. In the case of an array of cavities, which is represented by the standard JCH model we compare both approximations to numerical data from density-matrix renormalization group (DMRG) calculations.Comment: 9 pages, 5 figures, extended and corrected second versio

Divergence in seasonal hydrology across northern Eurasia: Emerging trends and water cycle linkages

Discharge from large Eurasia rivers increased during the 20th century, yet much remains unknown regarding details of this increasing freshwater flux. Here, for the three largest Eurasian basins (the Ob, Yenisei, and Lena) we examine the nature of annual and seasonal discharge trends by investigating the flow changes along with those for precipitation, snow depth, and snow water equivalent. On the basis of a multiperiod trend analysis and examination of station data, we propose two characteristic regimes to explain the long‐term discharge increase from these large Eurasian rivers. Over the early decades from approximately 1936 to 1965, annual precipitation correlates well with annual discharge, and positive discharge trends are concurrent with summer/fall discharge increases. The latter decades were marked by a divergence between winter/spring flows, which increased, amid summer/fall discharge declines. A comparison of cold season precipitation (CSP) and spring discharge trends across subbasins of the Ob, Yenisei, and Lena shows limited agreement with one precipitation data set but good agreement (R2 \u3e 0.90) when a second is used. While natural variability in the Arctic system tends to mask these emerging trends, spatial and temporal changes can generally be characterized by increased solid precipitation, primarily to the north, along with a drier hydrography during the warm season