507 research outputs found
Spontaneous Octahedral Tilting in the Cubic Inorganic Caesium Halide Perovskites CsSnX and CsPbX (X = F, Cl, Br, I)
The local crystal structures of many perovskite-structured materials deviate
from the average space group symmetry. We demonstrate, from lattice-dynamics
calculations based on quantum chemical force constants, that all the
caesium-lead and caesium-tin halide perovskites exhibit vibrational
instabilities associated with octahedral titling in their high-temperature
cubic phase. Anharmonic double-well potentials are found for zone-boundary
phonon modes in all compounds with barriers ranging from 108 to 512 meV. The
well depth is correlated with the tolerance factor and the chemistry of the
composition, but is not proportional to the imaginary harmonic phonon
frequency. We provide quantitative insights into the thermodynamic driving
forces and distinguish between dynamic and static disorder based on the
potential-energy landscape. A positive band gap deformation (spectral
blueshift) accompanies the structural distortion, with implications for
understanding the performance of these materials in applications areas
including solar cells and light-emitting diodes
The case for Tai Chi in the repertoire of strategies to prevent falls among older people
Falls among older people is a global public health issue. In this article, Dr Samuel Nyman of Bournemouth University Dementia Research Institute, and Professor Dawn Skelton, Institute for Applied Health Research, Glasgow Caledonian University highlight the effectiveness of Tai Chi as an alternative strategy to physiotherapy to combat this issue
A Massive Galaxy in its Core Formation Phase Three Billion Years After the Big Bang
Most massive galaxies are thought to have formed their dense stellar cores at
early cosmic epochs. However, cores in their formation phase have not yet been
observed. Previous studies have found galaxies with high gas velocity
dispersions or small apparent sizes but so far no objects have been identified
with both the stellar structure and the gas dynamics of a forming core. Here we
present a candidate core in formation 11 billion years ago, at z=2.3.
GOODS-N-774 has a stellar mass of 1.0x10^11 Msun, a half-light radius of 1.0
kpc, and a star formation rate of 90[+45-20]Msun/yr. The star forming gas has a
velocity dispersion 317+-30 km/s, amongst the highest ever measured. It is
similar to the stellar velocity dispersions of the putative descendants of
GOODS-N-774, compact quiescent galaxies at z~2 and giant elliptical galaxies in
the nearby Universe. Galaxies such as GOODS-N-774 appear to be rare; however,
from the star formation rate and size of the galaxy we infer that many star
forming cores may be heavily obscured, and could be missed in optical and
near-infrared surveys.Comment: To appear in Natur
The Spatial Extent and Distribution of Star Formation in 3D-HST Mergers at z~1.5
We present an analysis of the spatial distribution of star formation in a
sample of 60 visually identified galaxy merger candidates at z>1. Our sample,
drawn from the 3D-HST survey, is flux-limited and was selected to have high
star formation rates based on fits of their broad-band, low spatial resolution
spectral energy distributions. It includes plausible pre-merger (close pairs)
and post-merger (single objects with tidal features) systems, with total
stellar masses and star formation rates derived from multi-wavelength
photometry. Here we use near-infrared slitless spectra from 3D-HST which
produce Halpha or [OIII] emission line maps as proxies for star-formation maps.
This provides a first comprehensive high-resolution, empirical picture of where
star formation occurred in galaxy mergers at the epoch of peak cosmic star
formation rate. We find that detectable star formation can occur in one or both
galaxy centres, or in tidal tails. The most common case (58%) is that star
formation is largely concentrated in a single, compact region, coincident with
the centre of (one of) the merger components. No correlations between star
formation morphology and redshift, total stellar mass, or star formation rate
are found. A restricted set of hydrodynamical merger simulations between
similarly massive and gas-rich objects implies that star formation should be
detectable in both merger components, when the gas fractions of the individual
components are the same. This suggests that z~1.5 mergers typically occur
between galaxies whose gas fractions, masses, and/or star formation rates are
distinctly different from one another.Comment: Accepted for publication in MNRAS, 16 pages, 10 figure
Feasibility of trial procedures for a randomised controlled trial of a community based group exercise intervention for falls prevention for visually impaired older people: the VIOLET study
Background Visually impaired older people (VIOP) have a higher risk of falling than their sighted peers, and are likely to avoid physical activity. The aim was to adapt the existing Falls Management Exercise (FaME) programme for VIOP, delivered in the community, and to investigate the feasibility of conducting a definitive randomised controlled trial (RCT) of this adapted intervention. Methods Two-centre randomised mixed methods pilot trial and economic evaluation of the adapted group-based FaME programme for VIOP versus usual care. A one hour exercise programme ran weekly over 12 weeks at the study sites (Newcastle and Glasgow), delivered by third sector (voluntary and community) organisations. Participants were advised to exercise at home for an additional two hours over the week. Those randomised to the usual activities group received no intervention. Outcome measures were completed at baseline, 12 and 24 weeks. The potential primary outcome was the Short Form Falls Efficacy Scale – International (SFES-I). Participants’ adherence was assessed by reviewing attendance records and self-reported compliance to the home exercises. Adherence with the course content (fidelity) by instructors was assessed by a researcher. Adverse events were collected in a weekly phone call. Results Eighteen participants, drawn from community-living VIOP were screened; 68 met the inclusion criteria; 64 participants were randomised with 33 allocated to the intervention and 31 to the usual activities arm. 94% of participants provided data at the 12 week visit and 92% at 24 weeks. Adherence was high. The intervention was found to be safe with 76% attending nine or more classes. Median time for home exercise was 50 min per week. There was little or no evidence that fear of falling, balance and falls risk, physical activity, emotional, attitudinal or quality of life outcomes differed between trial arms at follow-up. Conclusions The intervention, FaME, was implemented successfully for VIOP and all progression criteria for a main trial were met. The lack of difference between groups on fear of falling was unsurprising given it was a pilot study but there may have been other contributory factors including suboptimal exercise dose and apparent low risk of falls in participants. These issues need addressing for a future trial
A theoretical study of the Pnma and R3m phases of Sb2S3, Bi2S3, and Sb2Se3
[EN]
We report a comparative theoretical study of the Pnma and R3m phases of Sb2S3, Bi2S3, and Sb2Se3 close to ambient pressure. Our enthalpy calculations at 0 K show that at ambient pressure the R3m (tetradymite-like) phase of Sb2Se3 is energetically more stable than the Pnma phase, contrary to what is observed for Sb2S3 and Bi2S3, and irrespective of the exchange-correlation functional employed in the calculations. The result for Sb2Se3 is in contradiction to experiments in which all three compounds are usually grown in the Pnma phase. This result is further confirmed by free-energy calculations taking into account the temperature dependence of unit-cell volumes and phonon frequencies. Lattice dynamics and elastic tensor calculations further show that both the Pnma and R3m phases of Sb2Se3 are dynamically and mechanically stable at zero applied pressure. Since these results suggest that the formation of the R3m phase of Sb2Se3 should be feasible under close to ambient conditions, we provide a theoretical crystal structure and simulated Raman and infrared spectra to help in its identification. We also discuss the results of the two published works that have claimed to have synthesized tetradymite-like Sb2Se3. Finally, the stability of the R3m phase across the three group-15 A(2)X(3) sesquichalcogenides is analysed based on their van der Waals gap and X-X in-plane geometry.This publication is part of the MALTA Consolider Team network (RED2018-102612-T) (MINECO/AEI/10.13039/501100003329), and is supported by I + D + i project PID2019-106383GB41/42/43 (MCIN/AEI/10.13039/501100011033), by the PROMETEO/2018/123(EFIMAT) and CIPROM/2021/075 (GREENMAT) projects (Generalitat Valenciana), and by the European Union Horizon 2020 research and innovation programme under a Marie Sklodowska-Curie grant agreement (785789-COMEX). E. L. d. S., A. M., and P. R.-H. acknowledge computing time provided on the MALTA-Cluster at the University of Oviedo and on the MareNostrum facility through Red Espanola de Supercomputacion (RES) with technical support provided by the Barcelona Supercomputing Center (QCM-2018-3-0032). E. L. d. S. also acknowledges the Network of Extreme Conditions Laboratories (NECL), financed by FCT and co-financed by NORTE 2020 through the Portugal 2020 and FEDER programmes. J. M. S. is grateful to UK Research and Innovation for the support of a Future Leaders Fellowship (MR/T043121/1) and to the University of Manchester for the previous support of a Presidential Fellowship.Da Silva, EL.; Skelton, JM.; RodrÃguez-Hernández, P.; Muñoz, A.; Santos, MC.; MartÃnez-GarcÃa, D.; Vilaplana Cerda, RI.... (2022). A theoretical study of the Pnma and R3m phases of Sb2S3, Bi2S3, and Sb2Se3. Journal of Materials Chemistry C. 10(40):15061-15074. https://doi.org/10.1039/d2tc01484j1506115074104
Acceptability of novel lifelogging technology to determine context of sedentary behaviour in older adults
<strong>Objective:</strong> Lifelogging, using body worn sensors (activity monitors and time lapse photography) has the potential to shed light on the context of sedentary behaviour. The objectives of this study were to examine the acceptability, to older adults, of using lifelogging technology and indicate its usefulness for understanding behaviour.<strong> </strong><strong>Method:</strong> 6 older adults (4 males, mean age: 68yrs) wore the equipment (ActivPAL<sup>TM</sup> and Vicon Revue<sup>TM</sup>/SenseCam<sup>TM</sup>) for 7 consecutive days during free-living activity. The older adults’ perception of the lifelogging technology was assessed through semi-structured interviews, including a brief questionnaire (Likert scale), and reference to the researcher's diary. <strong>Results:</strong> Older adults in this study found the equipment acceptable to wear and it did not interfere with privacy, safety or create reactivity, but they reported problems with the actual technical functioning of the camera. <strong>Conclusion:</strong> This combination of sensors has good potential to provide lifelogging information on the context of sedentary behaviour
3D-HST: A wide-field grism spectroscopic survey with the Hubble Space Telescope
We present 3D-HST, a near-infrared spectroscopic Treasury program with the
Hubble Space Telescope for studying the processes that shape galaxies in the
distant Universe. 3D-HST provides rest-frame optical spectra for a sample of
~7000 galaxies at 1<z<3.5, the epoch when 60% of all star formation took place,
the number density of quasars peaked, the first galaxies stopped forming stars,
and the structural regularity that we see in galaxies today must have emerged.
3D-HST will cover 3/4 (625 sq.arcmin) of the CANDELS survey area with two
orbits of primary WFC3/G141 grism coverage and two to four parallel orbits with
the ACS/G800L grism. In the IR these exposure times yield a continuum
signal-to-noise of ~5 per resolution element at H~23.1 and a 5sigma emission
line sensitivity of 5x10-17 erg/s/cm2 for typical objects, improving by a
factor of ~2 for compact sources in images with low sky background levels. The
WFC3/G141 spectra provide continuous wavelength coverage from 1.1-1.6 um at a
spatial resolution of ~0."13, which, combined with their depth, makes them a
unique resource for studying galaxy evolution. We present the preliminary
reduction and analysis of the grism observations, including emission line and
redshift measurements from combined fits to the extracted grism spectra and
photometry from ancillary multi-wavelength catalogs. The present analysis
yields redshift estimates with a precision of sigma(z)=0.0034(1+z), or
sigma(v)~1000 km/s. We illustrate how the generalized nature of the survey
yields near-infrared spectra of remarkable quality for many different types of
objects, including a quasar at z=4.7, quiescent galaxies at z~2, and the most
distant T-type brown dwarf star known. The CANDELS and 3D-HST surveys combined
will provide the definitive imaging and spectroscopic dataset for studies of
the 1<z<3.5 Universe until the launch of the James Webb Space Telescope.Comment: Replacement reflects version now accepted by ApJS. A preliminary data
release intended to provide a general illustration of the WFC3 grism data is
available at http://3dhst.research.yale.edu
- …