On the identification of normal modes of oscillation from observations of the solar periphery

The decomposition of solar oscillations into their constituent normal modes requires a knowledge of both the spatial and temporal variation of the perturbation to the Sun's surface. The task is especially difficult when only limited spatial information is available. Observations of the limb darkening function, for example, are probably sensitive to too large a number of modes to permit most of the modes to be identified in a power spectrum of measurements at only a few points on the limb, unless the results are combined with other data. A procedure was considered by which the contributions from quite small groups of modes to spatially well resolved data obtained at any instant can be extracted from the remaining modes. Combining these results with frequency information then permits the modes to be identified, at least if their frequencies are low enough to ensure that modes of high degree do not contribute substantially to the signal

Using learned action models in execution monitoring

Planners reason with abstracted models of the behaviours they use to construct plans. When plans are turned into the instructions that drive an executive, the real behaviours interacting with the unpredictable uncertainties of the environment can lead to failure. One of the challenges for intelligent autonomy is to recognise when the actual execution of a behaviour has diverged so far from the expected behaviour that it can be considered to be a failure. In this paper we present further developments of the work described in (Fox et al. 2006), where models of behaviours were learned as Hidden Markov Models. Execution of behaviours is monitored by tracking the most likely trajectory through such a learned model, while possible failures in execution are identified as deviations from common patterns of trajectories within the learned models. We present results for our experiments with a model learned for a robot behaviour

Systematic reviews for policy

The authors argue that learning from existing evidence is a key skill both for researchers and policy makers. However, how do you go about accomplishing this? What are the key approaches, and how do you make the right choices? Additionally, what are the common pitfalls? This chapter gives the reader a guide to best practice in systematic reviews

Probing Solar Convection

In the solar convection zone acoustic waves are scattered by turbulent sound speed fluctuations. In this paper the scattering of waves by convective cells is treated using Rytov's technique. Particular care is taken to include diffraction effects which are important especially for high-degree modes that are confined to the surface layers of the Sun. The scattering leads to damping of the waves and causes a phase shift. Damping manifests itself in the width of the spectral peak of p-mode eigenfrequencies. The contribution of scattering to the line widths is estimated and the sensitivity of the results on the assumed spectrum of the turbulence is studied. Finally the theoretical predictions are compared with recently measured line widths of high-degree modes.Comment: 26 pages, 7 figures, accepted by MNRA

Prospects for Measuring Differential Rotation in White Dwarfs Through Asteroseismology

We examine the potential of asteroseismology for exploring the internal rotation of white dwarf stars. Data from global observing campaigns have revealed a wealth of frequencies, some of which show the signature of rotational splitting. Tools developed for helioseismology to use many solar p-mode frequencies for inversion of the rotation rate with depth are adapted to the case of more limited numbers of modes of low degree. We find that the small number of available modes in white dwarfs, coupled with the similarity between the rotational-splitting kernels of the modes, renders direct inversion unstable. Accordingly, we adopt what we consider to be plausible functional forms for the differential rotation profile; this is sufficiently restrictive to enable us to carry out a useful calibration. We show examples of this technique for PG 1159 stars and pulsating DB white dwarfs. Published frequency splittings for white dwarfs are currently not accurate enough for meaningful inversions; reanalysis of existing data can provide splittings of sufficient accuracy when the frequencies of individual peaks are extracted via least-squares fitting or multipeak decompositions. We find that when mode trapping is evident in the period spacing of g modes, the measured splittings can constrain dOmega/dr.Comment: 26 pages, 20 postscript figures. Accepted for publication in The Astrophysical Journa

Farmland pricing in an inflationary economy with implications for public policy

While the importance of the price of land in agricultural production and policy is well recognised, land price formation is a process not well understood. The study reported here was aimed at an examination of the cause and implications of farmland price inflation in New Zealand over the past 20 or so years. The report attempts to isolate some of the factors other than annual earnings that could explain the sudden increase in the market value of farmland during an inflationary period.Ministry of Agriculture and Fisherie

Enabling knowledge brokerage intermediaries to be evidence-informed

TARGET AUDIENCE: What Works Centres; other intermediary brokerage agencies; their funders and users; and researchers of research use. BACKGROUND: Knowledge brokerage and knowledge mobilisation (KM) are generic terms used to describe activities to enable the use of research evidence to inform policy, practice and individual decision making. Knowledge brokerage intermediary (KBI) initiatives facilitate such use of research evidence. This debate paper argues that although the work of KBIs is to enable evidence-informed decision making (EIDM), they may not always be overt and consistent in how they follow the principles of EIDM in their own practice. KEY POINTS FOR DISCUSSION: Drawing on examples from existing brokerage initiatives, four areas are suggested where KBIs could be more evidence-informed in their work: (1) needs analysis: evidence-informed in their analysis of where and how the KBI can best contribute to the existing evidence ecosystem; (2) methods and theories of change: evidence-informed in the methods that the KBI uses to achieve its goals; (3) evidence standards: credible standards for making evidence claims; and (4) evaluation and monitoring: evidence-informed evaluation of their own activities and contribution to the knowledge base on evidence use. For each of these areas, questions are suggested for considering the extent that the principles are being followed in practice. CONCLUSIONS AND IMPLICATIONS: KBIs work with evidence but they may not always be evidence-informed in their practice. KBIs could benefit from more overtly attending to the extent that they apply the logic of EIDM to how they work. In doing so, KBIs can advance both the study, and practice, of using research evidence to inform decision making

Thermonuclear Burning on the Accreting X-Ray Pulsar GRO J1744-28

We investigate the thermal stability of nuclear burning on the accreting X-ray pulsar GRO J1744-28. The neutron star's dipolar magnetic field is <3\times 10^{11} G if persistent spin-up implies that the magnetospheric radius is less than the co-rotation radius. After inferring the properties of the neutron star, we study the thermal stability of hydrogen/helium burning and show that thermonuclear instabilities are unlikely causes of the hourly bursts seen at very high accretion rates. We then discuss how the stability of the thermonuclear burning depends on both the global accretion rate and the neutron star's magnetic field strength. We emphasize that the appearance of the instability (i.e., whether it looks like a Type I X-ray burst or a flare lasting a few minutes) will yield crucial information on the neutron star's surface magnetic field and the role of magnetic fields in convection. We suggest that a thermal instability in the accretion disk is the origin of the long (~300 days) outburst and that the recurrence time of these outbursts is >50 years. We also discuss the nature of the binary and point out that a velocity measurement of the stellar companion (most likely a Roche-lobe filling giant with m_K>17) will constrain the neutron star mass.Comment: 19 pages, 3 PostScript figures, uses aaspp4.sty and epsfig.sty, to appear in the Astrophysical Journa