Offline to Online Conversion

We consider the problem of converting offline estimators into an online predictor or estimator with small extra regret. Formally this is the problem of merging a collection of probability measures over strings of length 1,2,3,... into a single probability measure over infinite sequences. We describe various approaches and their pros and cons on various examples. As a side-result we give an elementary non-heuristic purely combinatoric derivation of Turing's famous estimator. Our main technical contribution is to determine the computational complexity of online estimators with good guarantees in general.Comment: 20 LaTeX page

Narrowband Searches for Continuous and Long-duration Transient Gravitational Waves from Known Pulsars in the LIGO-Virgo Third Observing Run

Isolated neutron stars that are asymmetric with respect to their spin axis are possible sources of detectable continuous gravitational waves. This paper presents a fully coherent search for such signals from eighteen pulsars in data from LIGO and Virgo's third observing run (O3). For known pulsars, efficient and sensitive matched-filter searches can be carried out if one assumes the gravitational radiation is phase-locked to the electromagnetic emission. In the search presented here, we relax this assumption and allow both the frequency and the time derivative of the frequency of the gravitational waves to vary in a small range around those inferred from electromagnetic observations. We find no evidence for continuous gravitational waves, and set upper limits on the strain amplitude for each target. These limits are more constraining for seven of the targets than the spin-down limit defined by ascribing all rotational energy loss to gravitational radiation. In an additional search, we look in O3 data for long-duration (hours-months) transient gravitational waves in the aftermath of pulsar glitches for six targets with a total of nine glitches. We report two marginal outliers from this search, but find no clear evidence for such emission either. The resulting duration-dependent strain upper limits do not surpass indirect energy constraints for any of these targets. © 2022. The Author(s). Published by the American Astronomical Society

Comparison of the effective temperatures, gravities and helium abundances of DAO white dwarfs from Balmer and Lyman line studies

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2004 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.The use of observations of the hydrogen Balmer absorption series is a well-established method of determining the surface gravity and effective temperature (Teff) of white dwarfs. In situations where the Balmer lines cannot be used it is possible to use the hydrogen Lyman series instead. However, previous studies by Barstow et al. have shown that for DAs (hydrogen-rich, no helium) hotter than ∼50 000 K the Lyman lines systematically yield higher values of Teff than the Balmer lines. Analysis of optical and FUSE spectra of 16 DAO white dwarfs (hybrid hydrogen/helium) demonstrates that temperatures measured using the different data sets continue to diverge at even higher temperatures, and in three extreme cases Teff derived from the Lyman lines is in excess of 120 000 K. These discrepancies are observed to decrease at lower gravities and luminosities. Helium abundances were also determined from the strength of He ii lines in the two wavelength regimes. These agree well, even though the temperatures differ considerably, with the exception of two DAO+M dwarf binaries. For these, the change in the measured helium abundance may result from the different times at which the objects were observed in the two wavelength regimes.PPARC, UKPPARC - Advanced FellowshipNAS

Regulation of anti-herbivore defence by Fucus vesiculosus in response to various cues

1 We examined whether the marine macroalga Fucus vesiculosus induces defences herbivory and, if so, which factors trigger this induction. In addition, we assessed whether induced defences are reduced after consumption stops. 2 Induced effects were measured as changes in palatability rather than changes in the chemistry of the algae. We also tested for reductions in growth rate to determine whether induced defence incurs metabolic costs. 3 We tested whether direct grazing, feeding on neighbouring plants, clipping and pre- sence of a non-grazing herbivore could trigger induction. The isopod Idotea baltica and the gastropod Littorina littorea were used as herbivores. 4 Both direct feeding of I. baltica and feeding on neighbouring plants induced chemical defence in E vesiculosus, whereas the snail L. Iittorea only induced defence by direct grazing. Simulated herbivory (clipping), or the presence of herbivores without grazing, did not lead to defence induction. All induced defences were reversed within 2 weeks of consumption ending. 5 Thus, F. vesiculosus differentiates between physical damage and natural herbivory. Furthermore, feeding by I. baltica on F. vesiculosus releases signals that trigger neigh- bouring Fucus individuals to induce defence. 6 We found no evidence that metabolic costs incurred as a consequence of induced defence were sufficient to lead to growth reduction. 7 This algal species demonstrates defence plasticity (i.e. induction and reduction of anti-herbivore defences 'on demand'), with the response depending on both grazer identity and grazing pattern matter