Smoothness of stabilisers in generic characteristic

Let $R$ be a commutative unital ring. Given a finitely-presented affine $R$-group $G$ acting on a finitely-presented $R$-scheme $X$ of finite type, we show that there is a prime $p_0$ so that for any $R$-algebra $k$ which is a field of characteristic $p > p_0$, the centralisers in $G_k$ of all subsets $U \subseteq X(k)$ are smooth. We prove this using the Lefschetz principle together with careful application of Gr\"{o}bner basis techniques.Comment: 15 page

The Lyman-alpha forest and WMAP year three

A combined analysis of Cosmic Microwave Background (CMB) and Lyman-a forest data allows to constrain the matter power spectrum from small scales of about 1 Mpc/h all the way to the horizon scale. The long lever arm and complementarity provided by such an analysis has previously led to a significant tightening of the constraints on the shape and the amplitude of the power spectrum of primordial density fluctuations. We present here a combined analysis of the WMAP three year results with Lyman-a forest data. The amplitude of the matter power spectrum sigma_8 and the spectral index ns inferred from the joint analysis with high resolution Lyman-a forest data and low resolution Lyman-a forest data as analyzed by Viel & Haehnelt (2006) are consistent with the new WMAP results to within 1 sigma. The joint analysis with the mainly low resolution data as analysed by McDonald et al. (2005) suggests a value of sigma_8 which is ~ 2 sigma higher than that inferred from the WMAP three year data alone. The joint analysis of the three year WMAP and the Lyman-a forest data also does not favour a running of the spectral index. The best fit values for a combined analysis of the three year WMAP data, other CMB data, 2dF and the Lyman-a forest data are (sigma_8, ns) = (0.78\pm 0.03,0.96 \pm 0.01).Comment: 5 pages, 4 figs, 2 tables. MNRAS letters in pres

Problem equivalence and necessary conditions of relaxed dynamic programming type in optical control

Imperial Users onl

A Mobile App Delivering a Gamified Battery of Cognitive Tests Designed for Repeated Play (OU Brainwave): App Design and Cohort Study

Background: Mobile phone and tablet apps are an increasingly common platform to collect data. A key challenge for researchers has been participant “buy-in” and participant attrition for designs requiring repeated testing. Objective: The objective of this study was to develop and asses the utility of 1 – 2 minute versions of both classic and novel cognitive tasks within a user focussed and driven mobile phone and tablet app designed to encourage repeated play. Methods: A large sample (N = 13,979 at first data collection) participated in multiple, self-paced, sessions of working memory (N-back), spatial cognition (Mental rotation), sustained attentional focus (Persistent Vigilance task), and split attention (Multiple object tracking) tasks along with an implementation of a novel action learning task. A full morningness-eveningness questionnaire was also included. Data was collected across an 18 month period. While the app prompted reengagement at set intervals, each participant was free to repeatedly complete each task as many times as they wished. Results: We found a significant relationship between morningness and age (r = 0.298, n = 12755, p Conclusions: Using extremely short testing periods and permitting participants to decide their own level of engagement - both in terms of which gamified task they played, and how many sessions they completed - we were able to collect a substantial and valid dataset. We suggest that the success of OU brainwave should inform future research oriented apps - particularly in issues around balancing participant engagement with data fidelity

In silico generation of novel, drug-like chemical matter using the LSTM neural network

The exploration of novel chemical spaces is one of the most important tasks of cheminformatics when supporting the drug discovery process. Properly designed and trained deep neural networks can provide a viable alternative to brute-force de novo approaches or various other machine-learning techniques for generating novel drug-like molecules. In this article we present a method to generate molecules using a long short-term memory (LSTM) neural network and provide an analysis of the results, including a virtual screening test. Using the network one million drug-like molecules were generated in 2 hours. The molecules are novel, diverse (contain numerous novel chemotypes), have good physicochemical properties and have good synthetic accessibility, even though these qualities were not specific constraints. Although novel, their structural features and functional groups remain closely within the drug-like space defined by the bioactive molecules from ChEMBL. Virtual screening using the profile QSAR approach confirms that the potential of these novel molecules to show bioactivity is comparable to the ChEMBL set from which they were derived. The molecule generator written in Python used in this study is available on request.Comment: in this version fixed some reference number

Do Stationary Risk Premia Explain It All? Evidence from the Term Struct

Most studies of the expectations theory of the term structure reject the model. However, the significance of the rejections depend strongly upon the form of the test. In this paper, we use the pattern of rejection across maturities to back out the implied behavior of time-varying risk premia and/or market forecasts. We then use a new technique to test whether stationary risk premia alone can be responsible for these rejections. Surprisirj1y, this test is rejected for short maturities up to 6 months, suggesting that time-varying risk premia do not explain it all. We also describe hew this method can be used to test other asset pricing relationships.

Do Expected Shifts in Inflation Policy Affect Real Rates?

This paper presents a new explanation for the negative correlation between ex post real interest rates and inflation found in earlier empirical studies. We begin by showing that there is a strong negative correlation between the permanent movements in ex post real interest rates and inflation. We argue that such a correlation can arise when people incorporate anticipated shifts in inflation policy into their expectations. Under these circumstances, a shift to lower (higher) inflation will lead to systematically higher (lower) ex post real rates. Using new time series techniques we are able to reject the hypothesis that nominal interest rates were unaffected by anticipated switches in inflation policy in the post-war era. To evaluate the impact of these switches, we then calculate the effects of inflationary expectations upon real rates using a Markov switching model of inflation. Inflation forecasts based upon the estimates of this rational model behave similarly to inflation forecasts from the Livingston survey. When ex ante real interest rates are identified with the Markov models of inflation, we find that ex ante real interest rate does not contain permanent shocks, nor is it related to permanent shocks in inflation.

Trends in Expected Returns in Currency and Bond Markets

Under conventional notions about rational expectations and market efficiency, expected returns differ from the actual expost returns by a forecast error that is uncorrelated with current information. In this paper, we describe how small departures from conventional notions of rational expectations and market efficiency can produce trends in excess returns. These trends are in addition to the trends typically found in the level of asset prices themselves. We report strong evidence for the presence of additional trends in excess foreign exchange and bond returns. We also estimate the additional trend component in excess returns on foreign exchange and find that it varied between -.8% and 1% for one month returns and between -6% and 8% for three month returns.

Light stops, blind spots, and isospin violation in the MSSM

In the framework of the MSSM, we examine several simplified models where only a few superpartners are light. This allows us to study WIMP--nucleus scattering in terms of a handful of MSSM parameters and thereby scrutinize their impact on dark matter direct-detection experiments. Focusing on spin-independent WIMP--nucleon scattering, we derive simplified, analytic expressions for the Wilson coefficients associated with Higgs and squark exchange. We utilize these results to study the complementarity of constraints due to direct-detection, flavor, and collider experiments. We also identify parameter configurations that produce (almost) vanishing cross sections. In the proximity of these so-called blind spots, we find that the amount of isospin violation may be much larger than typically expected in the MSSM. This feature is a generic property of parameter regions where cross sections are suppressed, and highlights the importance of a careful analysis of the nucleon matrix elements and the associated hadronic uncertainties. This becomes especially relevant once the increased sensitivity of future direct-detection experiments corners the MSSM into these regions of parameter space.Comment: 38 pages, 15 figures. v2: expanded text in Sec. 3 concerning relic density and (g-2)_mu constraints, clarified text on isospin violation. Fig. 1 is new, minor changes to Figs. 3,4,10. References added, journal versio