4,739 research outputs found
High precision quantum control of single donor spins in silicon
The Stark shift of the hyperfine coupling constant is investigated for a P
donor in Si far below the ionization regime in the presence of interfaces using
Tight-binding and Band Minima Basis approaches and compared to the recent
precision measurements. The TB electronic structure calculations included over
3 million atoms. In contrast to previous effective mass based results, the
quadratic Stark coefficient obtained from both theories agrees closely with the
experiments. This work represents the most sensitive and precise comparison
between theory and experiment for single donor spin control. It is also shown
that there is a significant linear Stark effect for an impurity near the
interface, whereas, far from the interface, the quadratic Stark effect
dominates. Such precise control of single donor spin states is required
particularly in quantum computing applications of single donor electronics,
which forms the driving motivation of this work.Comment: 5 pages, 2 figure
Mitigating impacts of the COVID-19 pandemic on primary and lower secondary children during school closures: a rapid evidence review
BACKGROUND:
To control the spread of the SARS-CoV-2 virus during the COVID-19 pandemic, UK schools were closed and education activity was undertaken at home resulting in considerable disruption to children’s education.
AIMS:
To identify and assess evidence of harms caused to primary and lower secondary pupils during this time and identify mitigation strategies relevant to those harms.
METHODS:
A rapid evidence review tailored to delivery at pace, drawing on UK evidence for harms and relevant mitigation strategies.
FINDINGS ON HARM:
There is evidence that the patterns of disruption to education during the pandemic have impacted on children’s learning and attainment, mental health and wellbeing, physical health and nutrition and increased exposure to risk especially for those children living in potentially dangerous domestic settings. Although the quality of the evidence is uneven, it is clear that children living in poverty have been most affected, in particular through food insecurity and conditions triggering stress and anxiety in the home, alongside their more limited opportunities to access digital resources for learning, or indeed outside space for physical activity. Attempts to distinguish harms that impact in the short term from longer lasting harms may take time. It also requires schools to have access to contextually relevant diagnostic tools they can use to assess the range of harms in need of redress in their local context.
FINDINGS ON MITIGATION STRATEGIES:
We found no evidence for mitigation strategies directly relevant to the harms experienced by children due to school closures under COVID-19. Mitigation strategies suggested in the UK often derived their evidence of efficacy from circumstances quite unlike the prolonged patterns of disruption to education that COVID has caused. Most were designed to address the needs of a few pupils struggling under normal circumstances and were not able to demonstrate their relevance at scale. We therefore examined the primary literature on recovery from unplanned school closures in other countries focused on school-based strategies that had been evaluated as effective under similar conditions.
CONCLUSION:
We found some evidence of a range of harms but little research evidence on relevant mitigation strategies and an absence of evidence on those strategies that schools themselves have adopted since re-opening, tailored to local needs. Such mitigation strategies may be highly relevant for system learning, and it is important to document and evaluate their efficacy, and indeed learn from them. Closing schools during the pandemic has revealed the importance of schools in safeguarding children. School staff should be given the training and resources to be able to identify children at risk and refer pupils to appropriate services if necessary
Multiwavelength Observations of a Flare from Markarian 501
We present multiwavelength observations of the BL Lacertae object Markarian
501 (Mrk 501) in 1997 between April 8 and April 19. Evidence of correlated
variability is seen in very high energy (VHE, E > 350 GeV) gamma-ray
observations taken with the Whipple Observatory gamma-ray telescope, data from
the Oriented Scintillation Spectrometer Experiment of the Compton Gamma-Ray
Observatory, and quicklook results from the All-Sky Monitor of the Rossi X-ray
Timing Explorer while the Energetic Gamma-Ray Experiment Telescope did not
detect Mrk 501. Short term optical correlations are not conclusive but the
U-band flux observed with the 1.2m telescope of the Whipple Observatory was 10%
higher than in March. The average energy output of Mrk 501 appears to peak in
the 2 keV to 100 keV range suggesting an extension of the synchrotron emission
to at least 100 keV, the highest observed in a blazar and ~100 times higher
than that seen in the other TeV-emitting BL Lac object, Mrk 421. The VHE
gamma-ray flux observed during this period is the highest ever detected from
this object. The VHE gamma-ray energy output is somewhat lower than the 2-100
keV range but the variability amplitude is larger. The correlations seen here
do not require relativistic beaming of the emission unless the VHE spectrum
extends to >5 TeV.Comment: 10 pages, 2 figures, accepted for publication in ApJ Letter
Very High Energy gamma-ray observations of Mrk 501 using TACTIC imaging gamma-ray telescope during 2005-06
In this paper we report on the Markarian 501 results obtained during our TeV
-ray observations from March 11 to May 12, 2005 and February 28 to May
7, 2006 for 112.5 hours with the TACTIC -ray telescope. During 2005
observations for 45.7 hours, the source was found to be in a low state and we
have placed an upper limit of 4.62 10 photons cm
s at 3 level on the integrated TeV -ray flux above 1 TeV
from the source direction. However, during the 2006 observations for 66.8h,
detailed data analysis revealed the presence of a TeV -ray signal from
the source with a statistical significance of 7.5 above
1 TeV. The time averaged differential energy spectrum of the
source in the energy range 1-11 TeV is found to match well with the power law
function of the form () with and .Comment: 16 pages and 8 Figures Accepted for publication in the Journal of
Physics
Stochastically Realized Observables for Excitonic Molecular Aggregates
We show that a stochastic approach enables calculations of the optical
properties of large 2-dimensional and nanotubular excitonic molecular
aggregates. Previous studies of such systems relied on numerically
diagonalizing the dense and disordered Frenkel Hamiltonian, which scales
approximately as for dye molecules. Our approach scales
much more efficiently as , enabling quick study of
systems with a million of coupled molecules on the micron size scale. We
calculate several important experimental observable including the optical
absorption spectrum and density of states, and develop a stochastic formalism
for the participation ratio. Quantitative agreement with traditional matrix
diagonalization methods is demonstrated for both small- and intermediate-size
systems. The stochastic methodology enables the study of the effects of
spatial-correlation in site energies on the optical signatures of large 2D
aggregates. Our results demonstrate that stochastic methods present a path
forward for screening structural parameters and validating experiments and
theoretical predictions in large excitonic aggregates.Comment: 11 pages, 7 figures, as submitted to JP
The purpose of mess in action research: building rigour though a messy turn
Mess and rigour might appear to be strange bedfellows. This paper argues that the purpose of mess is to facilitate a turn towards new constructions of knowing that lead to transformation in practice (an action turn). Engaging in action research - research that can disturb both individual and communally held notions of knowledge for practice - will be messy. Investigations into the 'messy area', the interface between the known and the nearly known, between knowledge in use and tacit knowledge as yet to be useful, reveal the 'messy area' as a vital element for seeing, disrupting, analysing, learning, knowing and changing. It is the place where long-held views shaped by professional knowledge, practical judgement, experience and intuition are seen through other lenses. It is here that reframing takes place and new knowing, which has both theoretical and practical significance, arises: a 'messy turn' takes place
Pharmacologic Inhibition of COX-1 and COX-2 in Influenza A Viral Infection in Mice
BACKGROUND: We previously demonstrated that cyclooxygenase (COX)-1 deficiency results in greater morbidity and inflammation, whereas COX-2 deficiency leads to reduced morbidity, inflammation and mortality in influenza infected mice. METHODOLOGY/PRINCIPAL FINDINGS: We investigated the effects of COX-1 and COX-2 inhibitors in influenza A viral infection. Mice were given a COX-1 inhibitor (SC-560), a COX-2 inhibitor (celecoxib) or no inhibitor beginning 2 weeks prior to influenza A viral infection (200 PFU) and throughout the course of the experiment. Body weight and temperature were measured daily as indicators of morbidity. Animals were sacrificed on days 1 and 4 post-infection and bronchoalveolar lavage (BAL) fluid was collected or daily mortality was recorded up to 2 weeks post-infection. Treatment with SC-560 significantly increased mortality and was associated with profound hypothermia and greater weight loss compared to celecoxib or control groups. On day 4 of infection, BAL fluid cells were modestly elevated in celecoxib treated mice compared to SC-560 or control groups. Viral titres were similar between treatment groups. Levels of TNF-alpha and G-CSF were significantly attenuated in the SC-560 and celecoxib groups versus control and IL-6 levels were significantly lower in BAL fluid of celecoxib treated mice versus control and versus the SC-560 group. The chemokine KC was significantly lower in SC-560 group versus control. CONCLUSIONS/SIGNIFICANCE: Treatment with a COX-1 inhibitor during influenza A viral infection is detrimental to the host whereas inhibition of COX-2 does not significantly modulate disease severity. COX-1 plays a critical role in controlling the thermoregulatory response to influenza A viral infection in mice
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