A transient Markov chain with finitely many cutpoints

We give an example of a transient reversible Markov chain that almost surely has only a finite number of cutpoints. We explain how this is relevant to a conjecture of Diaconis and Freedman and a question of Kaimanovich. We also answer Kaimanovich's question when the Markov chain is a nearest-neighbor random walk on a tree.Comment: Published in at http://dx.doi.org/10.1214/193940307000000365 the IMS Collections (http://www.imstat.org/publications/imscollections.htm) by the Institute of Mathematical Statistics (http://www.imstat.org

Active teacher selection for reinforcement learning from human feedback

Reinforcement learning from human feedback (RLHF) enables machine learning systems to learn objectives from human feedback. A core limitation of these systems is their assumption that all feedback comes from a single human teacher, despite querying a range of distinct teachers. We propose the Hidden Utility Bandit (HUB) framework to model differences in teacher rationality, expertise, and costliness, formalizing the problem of learning from multiple teachers. We develop a variety of solution algorithms and apply them to two real-world domains: paper recommendation systems and COVID-19 vaccine testing. We find that the Active Teacher Selection (ATS) algorithm outperforms baseline algorithms by actively selecting when and which teacher to query. The HUB framework and ATS algorithm demonstrate the importance of leveraging differences between teachers to learn accurate reward models, facilitating future research on active teacher selection for robust reward modeling

The breaking of quantum double symmetries by defect condensation

In this paper, we study the phenomenon of Hopf or more specifically quantum double symmetry breaking. We devise a criterion for this type of symmetry breaking which is more general than the one existing in the literature, and therefore extends the number of possible breaking patterns that can be described consistently. We start by recalling why the extended symmetry notion of quantum double algebras is an optimal tool when analyzing a wide variety of two dimensional physical systems including quantum fluids, crystals and liquid crystals. The power of this approach stems from the fact that one may characterize both ordinary and topological modes as representations of a single (generally non-Abelian) Hopf symmetry. In principle a full classification of defect mediated as well as ordinary symmetry breaking patterns and subsequent confinement phenomena can be given. The formalism applies equally well to systems exhibiting global, local, internal and/or external (i.e. spatial) symmetries. The subtle differences in interpretation for the various situations are pointed out. We show that the Hopf symmetry breaking formalism reproduces the known results for ordinary (electric) condensates, and we derive formulae for defect (magnetic) condensates which also involve the phenomenon of symmetry restoration. These results are applied in two papers which will be published in parallel.Comment: 65 pages, 7 figures, correction in table 3, updated reference

Further Evidence for Intrinsic Redshifts in Normal Spiral Galaxies

Evidence from galaxy absolute magnitudes, linear diameters, and HyperLeda images is presented which strongly supports the interpretation that some normal spiral galaxies can contain large non-cosmological (intrinsic) redshifts in excess of 5000 km s-1.Comment: 17 pages, Astrophysics&Space Science - Accepted for publicatio

High levels of childhood obesity observed among 3- to 7-year-old New Zealand Pacific children is a public health concern.

This cross-sectional, community-based survey was designed to assess attained growth and body composition of 3- to 7-y-old Pacific children (n = 21 boys and 20 girls) living in Dunedin, New Zealand, and to examine nondietary factors associated with the percentage of body fat. Fat mass, lean tissue mass and the percentage of body fat were measured using dual energy X-ray absorptiometry. One trained anthropometrist also measured height, weight, skinfolds (triceps, subscapular) and circumferences (mid-upper arm, chest, waist, calf). Compared with the National Center for Health Statistics and National Health and Examination Surveys I and II reference data, these Pacific children were tall and heavy for their age with high arm-muscle-area-for-height. Median (quartiles) Z-scores for height and BMI-for-age and arm-muscle-area-for-height were 1.33 (0.60, 2.15), 1.20 (0.74, 4.43) and 1.09 (0.63, 1.85), respectively. Their median (quartile) percentage of body fat was 21.8% (15.0, 35.5) of which 38.5% was located in the trunk. The estimated percentage of children classified as obese ranged from 34 to 49% depending on the criterion used. Over 60% of the children had levels of trunk fat above 1 SD of reported age- and sex-specific Z-scores for New Zealand children. The nondietary factors examined (hours of television viewing and hours playing organized sports, as reported by parents) were not associated with variations in the percentage of body fat, after adjusting for age, sex and birth weight. These extremely high levels of obesity and truncal fat among very young New Zealand children will have major public health implications as these children age

Near-infrared [Fe II] emission from supernova remnants and the supernova rate of starburst galaxies

In an effort to better calibrate the supernova rate of starburst galaxies as determined from near-IR [Fe II] features, we report on a [Fe II] 1.644 microns line-imaging survey of a sample of 42 optically-selected SNRs in M33. A wide range of [Fe II] luminosities are observed within our sample (from less than 6 to 695 L_sun). Our data suggest that the bright [Fe II] SNRs are entering the radiative phase and that the density of the local ISM largely controls the amount of [Fe II] emission. We derive the following relation between the [Fe II] 1.644 microns line luminosity of radiative SNRs and the electronic density of the postshock gas, n_e: L_[Fe II] (L_sun) ~ 1.1 n_e (cm^-3). We also find a correlation in our data between L_[Fe II] and the metallicity of the shock-heated gas, but the physical interpretation of this result remains inconclusive, as our data also show a correlation between the metallicity and n_e. The dramatically higher level of [Fe II] emission from SNRs in the central regions of starburst galaxies is most likely due to their dense environments, although metallicity effects might also be important. The typical [Fe II]-emitting lifetime of a SNR in the central regions of starburst galaxies is found to be of the order of 10^4 yr. On the basis of these results, we provide a new empirical relation allowing the determination of the current supernova rate of starburst galaxies from their integrated near-IR [Fe II] luminosity.Comment: 13 pages, 5 figures; accepted for publication in MNRA

XMMU J0541.8-6659, a new supernova remnant in the Large Magellanic Cloud

The high sensitivity of the XMM-Newton instrumentation offers the opportunity to study faint and extended sources in the Milky Way and nearby galaxies such as the Large Magellanic Cloud (LMC) in detail. The ROSAT PSPC survey of the LMC has revealed more than 700 X-ray sources, among which there are 46 supernova remnants (SNRs) and candidates. We have observed the field around one of the most promising SNR candidates in the ROSAT PSPC catalogue, labelled [HP99] 456 with XMM-Newton, to determine its nature. We investigated the XMM-Newton data along with new radio-continuum, near infrared and optical data. In particular, spectral and morphological studies of the X-ray and radio data were performed. The X-ray images obtained in different energy bands reveal two different structures. Below 1.0 keV the X-ray emission shows the shell-like morphology of an SNR with a diameter of ~73 pc, one of the largest known in the LMC. For its thermal spectrum we estimate an electron temperature of (0.49 +/- 0.12)keV assuming non-equilibrium ionisation. The X-ray images above 1.0 keV reveal a less extended source within the SNR emission, located ~1' west of the centre of the SNR and coincident with bright point sources detected in radio-continuum. This hard component has an extent of 0.9' (i.e. ~13 pc at a distance of ~50 kpc) and a non-thermal spectrum. The hard source coincides in position with the ROSAT source [HP99] 456 and shows an indication for substructure. We firmly identify a new SNR in the LMC with a shell-like morphology and a thermal spectrum. Assuming the SNR to be in the Sedov phase yields an age of ~23 kyr. We explore possible associations of the hard non-thermal emitting component with a pulsar wind nebula (PWN) or background active galactic nuclei (AGN).Comment: 8 pages, 7 figures, accepted for publication in Astronomy and Astrophysic

Bragg guiding of domain-like nonlinear modes and kink arrays in lower-index core structures

We introduce a novel class of stable nonlinear modes trapped in a lower-index film core sandwiched between two optical lattices, or in the cylindrical core of a radial lattice, imprinted in defocusing media. Such family of nonlinear modes transforms into defect lattice solitons when the core width is sufficiently small or into an array of kinks when the width is large enough. We find that higher-order modes with multiple zeros inside the guiding core can be stable in one-dimensional settings.Comment: 12 pages, 3 figures, to appear in Optics Letter

Rational design of p-type thermoelectric PbTe: temperature dependent sodium solubility

We develop a solid understanding of the temperature-dependent solubility of sodium in p-type PbTe, the most efficient thermoelectric material. The maximum solubility of sodium telluride (NaTe) in PbTe is measured to be 1.4 ± 0.3 at% and the heat of solution is evaluated as 26^(+19)_(−11) kJ mol^(−1) that addresses fundamental issues regarding the formation of nano-precipitates

Physical activity outcomes in afterschool programs: A group randomized controlled trial

Afterschool programs (ASPs) across the US are working towards achieving the standard of all children accumulating 30minutes of moderate-to-vigorous physical activity (MVPA) during program time. This study describes the two-year impact of an intervention designed to assist ASPs meeting the 30min/d MVPA standard