Solution of Orthopositronium lifetime Puzzle

The intrinsic decay rate of orthopositronium formed in ${\rm SiO_2}$ powder is measured using the direct $2\gamma$ correction method such that the time dependence of the pick-off annihilation rate is precisely determined. The decay rate of orthopositronium is found to be $7.0396\pm0.0012 (stat.)\pm0.0011 (sys.)\mu s^{-1}$, which is consistent with our previous measurements with about twice the accuracy. Results agree well with the $O(\alpha^2)$ QED prediction, and also with a result reported very recently using nanoporous film

Experiences of European Engineering Students and Academics in the UK: Findings of an Exploratory Mixed-Methods Study

In the UK Higher Education, 20% of all academic engineering staff and 12% of engineering students are European nationals. There has been much discussion about the impact of the UK’s departure from the European Union in current and future relationships. However, prior to this study, no data on the impact of Brexit on engineering education and research, from the perspective of European students and academics, had been collected. This study explores the impact of Brexit on European engineering students and academics experiences in UK Higher Education Institutions – their motivations to study and work in the UK, mobility, funding, and career prospects. The study adopted an exploratory mixed methods design. It began with a primary qualitative phase, where a diverse sample of 9 European engineering students and 15 academics were interviewed to explore their experiences following the Brexit decision. The key issues identified in this phase, via inductive and thematic analysis, were then explored in the following quantitative phase of the study, with a larger sample of European nationals – 89 engineering students and 104 academics – in an online survey. The UK’s engineering education is still attractive to a majority of European students and academics. However, changes in financial support for students, restrictions on freedom of movement and access to research funding are key decision factors when considering staying or leaving the UK. The findings of the study are also relevant for understanding the impacts on engineering research collaborations between the UK and higher education institutions in Europe

The Longitudinal Development of Movement Competency in Young High-Level Golfers

The aim of this study was to longitudinally monitor movement competency of golfers in a talent development program. Thirty-six golfers were included in the study (24 males, 12 females); on entry the mean age was 14.38 ± 2.88 years and mean handicap was 6. Participants completed the Golf Movement Screen (GMS). Data was collected annually at the start of each off-season in the program, providing three testing occasions over a two-year period. Total GMS score significantly improved (all p < 0.05) year-on year from 41 ± 13 on entry, to 52 ± 13 in year 1, and 63 ± 14 in year 2. Handicap also significantly improved from 6 ± 5 on entry to 2 ± 4 in year 2 (p < 0.05). Significant improvements were found in 7 of the 10 exercises between entry and year 1, and 9 of the 10 exercises between entry and year 2 (all p < 0.05), while scores for the remaining exercise were high on entry and remained stable. The findings suggest that golfers in a talent development program are able to improve their movement competency, and that the GMS has the sensitivity to detect these changes

HST color-magnitude diagrams of 74 galactic globular clusters in the HST F439W and F555W bands

We present the complete photometric database and the color-magnitude diagrams for 74 Galactic globular clusters observed with the HST/WFPC2 camera in the F439W and F555W bands. A detailed discussion of the various reduction steps is also presented, and of the procedures to transform instrumental magnitudes into both the HST F439W and F555W flight system and the standard Johnson B and V systems. We also describe the artificial star experiments which have been performed to derive the star count completeness in all the relevant branches of the color magnitude diagram. The entire photometric database and the completeness function will be made available on the Web immediately after the publication of the present paper.Comment: 21 pages, 77 figures. High resolution version of this paper can be retrived at http://dipastro.pd.astro.it/globular

On the HI-Hole and AGB Stellar Population of the Sagittarius Dwarf Irregular Galaxy

Using two HST/ACS data-sets that are separated by ~2 years has allowed us to derive the relative proper-motion for the Sagittarius dwarf irregular (SagDIG) and reduce the heavy foreground Galactic contamination. The proper-motion decontaminated SagDIG catalog provides a much clearer view of the young red-supergiant and intermediate-age asymptotic giant branch populations. We report the identification of 3 Milky Way carbon-rich dwarf stars, probably belonging to the thin disk, and pointing to the high incidence of this class at low Galactic latitudes. A sub-group of 4 oxygen-rich candidate stars depicts a faint, red extension of the well-defined SagDIG carbon-rich sequence. The origin of these oxygen-rich candidate stars remains unclear, reflecting the uncertainty in the ratio of carbon/oxygen rich stars. SagDIG is also a gas-rich galaxy characterized by a single large cavity in the gas disk (HI-hole), which is offset by ~360 pc from the optical centre of the galaxy. We nonetheless investigate the stellar feedback hypothesis by comparing the proper-motion cleaned stellar populations within the HI-hole with appropriately selected comparison regions, having higher HI densities external to the hole. The comparison shows no significant differences. In particular, the centre of the HI-hole (and the comparison regions) lack stellar populations younger than ~400 Myr, which are otherwise abundant in the inner body of the galaxy. We conclude that there is no convincing evidence that the SagDIG HI-hole is the result of stellar feedback, and that gravitational and thermal instabilities in the gas are the most likely mechanism for its formation.Comment: Accepted for publication in A&A, 11 pages, 6 jpeg figure

Extra dimensions and invisible decay of orthopositronium

We point out that some models with infinite additional dimension(s) of Randall-Sundrum type predict the disappearance of orthopositronium (o-Ps) into additional dimension(s). The experimental signature of this effect is the o-Ps -> invisible decay of orthopositronium which may occur at a rate within three orders of magnitude of the present experimental upper limit. This result enhances existing motivations for a more sensitive search for this decay mode and suggests additional directions for testing extra dimensions in non accelerator experiments.Comment: 3 pages, to appear in Phys. Rev.

An Age Difference of 2 Gyr between a Metal-Rich and a Metal-Poor Globular Cluster

Globular clusters trace the formation history of the spheroidal components of both our Galaxy and others, which represent the bulk of star formation over the history of the universe. They also exhibit a range of metallicities, with metal-poor clusters dominating the stellar halo of the Galaxy, and higher metallicity clusters found within the inner Galaxy, associated with the stellar bulge, or the thick disk. Age differences between these clusters can indicate the sequence in which the components of the Galaxy formed, and in particular which clusters were formed outside the Galaxy and later swallowed along with their original host galaxies, and which were formed in situ. Here we present an age determination of the metal-rich globular cluster 47 Tucanae by fitting the properties of the cluster white dwarf population, which implies an absolute age of 9.9 (0.7) Gyr at 95% confidence. This is about 2.0 Gyr younger than inferred for the metal-poor cluster NGC 6397 from the same models, and provides quantitative evidence that metal-rich clusters like 47 Tucanae formed later than the metal-poor halo clusters like NGC 6397.Comment: Main Article: 10 pages, 4 figures; Supplementary Info 15 pages, 5 figures. Nature, Aug 1, 201