48 research outputs found
The experience of open access youth work: the voice of young people
This research explores young people’s experiences of open access youth work and identifies what they consider to be its value. The detailed analysis of the data, achieved through focus groups, revealed that ‘association’ was a key driver of engagement. It also highlighted the support system the youth club creates amongst the peers. The young people also valued the relationships they form with youth workers and acknowledge the support and guidance offered to them which better enables them to reflect on and navigate their complex lives. Young people also valued the acceptance they feel from the community developed in the youth space. It provided comfort and reassurance when at times they do not feel like they fit in anywhere else. This research offers a significant counter to the tide of current targeted youth work policy which is resulting in the demise of a provision which, judged by the findings from this research, appears to be highly valued by, and beneficial to, young people
Formation of artificial Fermi surfaces with a triangular superlattice on a conventional two dimensional electron gas
In nearly free electron theory the imposition of a periodic electrostatic
potential on free electrons creates the bandstructure of a material, determined
by the crystal lattice spacing and geometry. Imposing an artificially designed
potential to the electrons confined in a GaAs quantum well makes it possible to
engineer synthetic two-dimensional band structures, with electronic properties
different from those in the host semiconductor. Here we report the fabrication
and study of a tuneable triangular artificial lattice on a GaAs/AlGaAs
heterostructure where it is possible to transform from the original GaAs
bandstructure and Fermi surface to a new bandstructure with multiple artificial
Fermi surfaces simply by altering a gate bias. For weak electrostatic potential
modulation magnetotransport measurements reveal quantum oscillations from the
GaAs two-dimensional Fermi surface, and classical oscillations due to these
electrons scattering from the artificial lattice. Increasing the strength of
the modulation reveals new quantum oscillations due to the formation of
multiple artificial Fermi surfaces, and ultimately to new classical
oscillations of the electrons from the artificial Fermi surface scattering from
the superlattice modulation. These results show that low disorder gate-tuneable
lateral superlattices can be used to form artificial two dimensional crystals
with designer electronic properties.Comment: 19 pages, 6 figure
Tuning the bandstructure of electrons in a two-dimensional artificial electrostatic crystal in GaAs quantum wells
The electronic properties of solids are determined by the crystal structure
and interactions between electrons, giving rise to a variety of collective
phenomena including superconductivity, strange metals and correlated
insulators. The mechanisms underpinning many of these collective phenomena
remain unknown, driving interest in creating artificial crystals which
replicate the system of interest while allowing precise control of key
parameters. Cold atoms trapped in optical lattices provide great flexibility
and tunability [1, 2], but cannot replicate the long range Coulomb interactions
and long range hopping that drive collective phenomena in real crystals. Solid
state approaches support long range hopping and interactions, but previous
attempts with laterally patterned semiconductor systems were not able to create
tunable low disorder artificial crystals, while approaches based on Moire
superlattices in twisted two-dimensional (2D) materials [3, 4] have limited
tunability and control of lattice geometry. Here we demonstrate the formation
of highly tunable artificial crystals by superimposing a periodic electrostatic
potential on the 2D electron gas in an ultrashallow (25 nm deep) GaAs quantum
well. The 100 nm period artificial crystal is identified by the formation of a
new bandstructure, different from the original cubic crystal and unique to the
artificial triangular lattice: transport measurements show the Hall coefficient
changing sign as the chemical potential sweeps through the artificial bands.
Uniquely, the artificial bandstructure can be continuously tuned from parabolic
free-electron bands into linear graphene-like and flat kagome-like bands in a
single device. This approach allows the formation arbitrary geometry 2D
artificial crystals, opening a new route to studying collective quantum states.Comment: 30 pages, 11 figure
Geometric control of universal hydrodynamic flow in a two dimensional electron fluid
Fluid dynamics is one of the cornerstones of modern physics and has recently
found applications in the transport of electrons in solids. In most solids
electron transport is dominated by extrinsic factors, such as sample geometry
and scattering from impurities. However in the hydrodynamic regime Coulomb
interactions transform the electron motion from independent particles to the
collective motion of a viscous `electron fluid'. The fluid viscosity is an
intrinsic property of the electron system, determined solely by the
electron-electron interactions. Resolving the universal intrinsic viscosity is
challenging, as it only affects the resistance through interactions with the
sample boundaries, whose roughness is not only unknown but also varies from
device to device. Here we eliminate all unknown parameters by fabricating
samples with smooth sidewalls to achieve the perfect slip boundary condition,
which has been elusive both in molecular fluids and electronic systems. We
engineer the device geometry to create viscous dissipation and reveal the true
intrinsic hydrodynamic properties of a 2D system. We observe a clear transition
from ballistic to hydrodynamic electron motion, driven by both temperature and
magnetic field. We directly measure the viscosity and electron-electron
scattering lifetime (the Fermi quasiparticle lifetime) over a wide temperature
range without fitting parameters, and show they have a strong dependence on
electron density that cannot be explained by conventional theories based on the
Random Phase Approximation
Prevalence, Distribution, and Impact of Mild Cognitive Impairment in Latin America, China, and India: A 10/66 Population-Based Study
A set of cross-sectional surveys carried out in Cuba, Dominican Republic, Peru, Mexico, Venezuela, Puerto Rico, China, and India reveal the prevalence and between-country variation in mild cognitive impairment at a population level
Packages of Care for Dementia in Low- and Middle-Income Countries
In the fifth in a series of six articles on packages of care for mental disorders in low- and middle-income countries, Martin Prince and colleagues discuss the treatment of dementia
Safety and efficacy of the ChAdOx1 nCoV-19 vaccine (AZD1222) against SARS-CoV-2: an interim analysis of four randomised controlled trials in Brazil, South Africa, and the UK.
BACKGROUND: A safe and efficacious vaccine against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), if deployed with high coverage, could contribute to the control of the COVID-19 pandemic. We evaluated the safety and efficacy of the ChAdOx1 nCoV-19 vaccine in a pooled interim analysis of four trials. METHODS: This analysis includes data from four ongoing blinded, randomised, controlled trials done across the UK, Brazil, and South Africa. Participants aged 18 years and older were randomly assigned (1:1) to ChAdOx1 nCoV-19 vaccine or control (meningococcal group A, C, W, and Y conjugate vaccine or saline). Participants in the ChAdOx1 nCoV-19 group received two doses containing 5 × 1010 viral particles (standard dose; SD/SD cohort); a subset in the UK trial received a half dose as their first dose (low dose) and a standard dose as their second dose (LD/SD cohort). The primary efficacy analysis included symptomatic COVID-19 in seronegative participants with a nucleic acid amplification test-positive swab more than 14 days after a second dose of vaccine. Participants were analysed according to treatment received, with data cutoff on Nov 4, 2020. Vaccine efficacy was calculated as 1 - relative risk derived from a robust Poisson regression model adjusted for age. Studies are registered at ISRCTN89951424 and ClinicalTrials.gov, NCT04324606, NCT04400838, and NCT04444674. FINDINGS: Between April 23 and Nov 4, 2020, 23 848 participants were enrolled and 11 636 participants (7548 in the UK, 4088 in Brazil) were included in the interim primary efficacy analysis. In participants who received two standard doses, vaccine efficacy was 62·1% (95% CI 41·0-75·7; 27 [0·6%] of 4440 in the ChAdOx1 nCoV-19 group vs71 [1·6%] of 4455 in the control group) and in participants who received a low dose followed by a standard dose, efficacy was 90·0% (67·4-97·0; three [0·2%] of 1367 vs 30 [2·2%] of 1374; pinteraction=0·010). Overall vaccine efficacy across both groups was 70·4% (95·8% CI 54·8-80·6; 30 [0·5%] of 5807 vs 101 [1·7%] of 5829). From 21 days after the first dose, there were ten cases hospitalised for COVID-19, all in the control arm; two were classified as severe COVID-19, including one death. There were 74 341 person-months of safety follow-up (median 3·4 months, IQR 1·3-4·8): 175 severe adverse events occurred in 168 participants, 84 events in the ChAdOx1 nCoV-19 group and 91 in the control group. Three events were classified as possibly related to a vaccine: one in the ChAdOx1 nCoV-19 group, one in the control group, and one in a participant who remains masked to group allocation. INTERPRETATION: ChAdOx1 nCoV-19 has an acceptable safety profile and has been found to be efficacious against symptomatic COVID-19 in this interim analysis of ongoing clinical trials. FUNDING: UK Research and Innovation, National Institutes for Health Research (NIHR), Coalition for Epidemic Preparedness Innovations, Bill & Melinda Gates Foundation, Lemann Foundation, Rede D'Or, Brava and Telles Foundation, NIHR Oxford Biomedical Research Centre, Thames Valley and South Midland's NIHR Clinical Research Network, and AstraZeneca
Safety and efficacy of the ChAdOx1 nCoV-19 vaccine (AZD1222) against SARS-CoV-2: an interim analysis of four randomised controlled trials in Brazil, South Africa, and the UK
Background
A safe and efficacious vaccine against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), if deployed with high coverage, could contribute to the control of the COVID-19 pandemic. We evaluated the safety and efficacy of the ChAdOx1 nCoV-19 vaccine in a pooled interim analysis of four trials.
Methods
This analysis includes data from four ongoing blinded, randomised, controlled trials done across the UK, Brazil, and South Africa. Participants aged 18 years and older were randomly assigned (1:1) to ChAdOx1 nCoV-19 vaccine or control (meningococcal group A, C, W, and Y conjugate vaccine or saline). Participants in the ChAdOx1 nCoV-19 group received two doses containing 5 × 1010 viral particles (standard dose; SD/SD cohort); a subset in the UK trial received a half dose as their first dose (low dose) and a standard dose as their second dose (LD/SD cohort). The primary efficacy analysis included symptomatic COVID-19 in seronegative participants with a nucleic acid amplification test-positive swab more than 14 days after a second dose of vaccine. Participants were analysed according to treatment received, with data cutoff on Nov 4, 2020. Vaccine efficacy was calculated as 1 - relative risk derived from a robust Poisson regression model adjusted for age. Studies are registered at ISRCTN89951424 and ClinicalTrials.gov, NCT04324606, NCT04400838, and NCT04444674.
Findings
Between April 23 and Nov 4, 2020, 23 848 participants were enrolled and 11 636 participants (7548 in the UK, 4088 in Brazil) were included in the interim primary efficacy analysis. In participants who received two standard doses, vaccine efficacy was 62·1% (95% CI 41·0–75·7; 27 [0·6%] of 4440 in the ChAdOx1 nCoV-19 group vs71 [1·6%] of 4455 in the control group) and in participants who received a low dose followed by a standard dose, efficacy was 90·0% (67·4–97·0; three [0·2%] of 1367 vs 30 [2·2%] of 1374; pinteraction=0·010). Overall vaccine efficacy across both groups was 70·4% (95·8% CI 54·8–80·6; 30 [0·5%] of 5807 vs 101 [1·7%] of 5829). From 21 days after the first dose, there were ten cases hospitalised for COVID-19, all in the control arm; two were classified as severe COVID-19, including one death. There were 74 341 person-months of safety follow-up (median 3·4 months, IQR 1·3–4·8): 175 severe adverse events occurred in 168 participants, 84 events in the ChAdOx1 nCoV-19 group and 91 in the control group. Three events were classified as possibly related to a vaccine: one in the ChAdOx1 nCoV-19 group, one in the control group, and one in a participant who remains masked to group allocation.
Interpretation
ChAdOx1 nCoV-19 has an acceptable safety profile and has been found to be efficacious against symptomatic COVID-19 in this interim analysis of ongoing clinical trials