735 research outputs found
Structural properties of a calcium aluminosilicate glass from molecular-dynamics simulations: A finite size effects study
We study a calcium aluminosilicate glass of composition
(SiO)-(AlO)-(CaO) by means of
molecular-dynamics (MD) simulations, using a potential made of two-body and
three-body interactions. In order to prepare small samples that can
subsequently be studied by first-principles, the finite size effects on the
liquid dynamics and on the glass structural properties are investigated. We
find that finite size effects affect the Si-O-Si and Si-O-Al angular
distributions, the first peaks of the Si-O, Al-O and Ca-O pair correlation
functions, the Ca coordination and the oxygen atoms environment in the smallest
system (100 atoms). We give evidence that these finite size effects can be
directly attributed to the use of three-body interactions.Comment: 36 pages, 14 figures. Journal of Chem. Phys., in pres
A Survey of Employee Perceptions of Information Privacy in Organizations
In this study of employees in five multinational corporations, assessment was made of (a) employees\u27 beliefs regarding the types of personal information stored their companies, (b) the accuracy of those perceptions, (c) reactions to various internal and external uses of this personal information, and (d) evaluations of the companies\u27 information handling policies and practices
Building and sustaining Work Engagement â A participatory action intervention to increase Work Engagement in nursing staff
This study evaluated whether a participatory action research intervention with nursing staff on
acute care older people NHS wards in the UK was effective for increasing work engagement.
Mediation analyses between job resources, (social support, influence in decision-making), job
demands, work-related needs (autonomy, competence, relatedness), and work engagement
explored the presumed psychological mechanisms underlying the intervention. A nonrandomised,
matched control group, pre-test, post-test design involved three intervention and
five control wards. A significant decrease in relatedness, and a borderline significant decrease
in competence, was observed in the intervention group compared to the control group, with no
effect on work engagement (N=45). Work-related needs mediated between resources and
work engagement, supporting the Job Demands-Resources model and Self-Determination
Theory as an underlying explanatory theory. Intervention implementation was difficult,
highlighting the need for participant and organisational readiness for change, and strong
management support. This is the first known study to apply participatory techniques to
increase work engagement in nursing staff and explore the underlying explanatory
psychological mechanisms, offering a novel means of taking work engagement research
forward. Crucially, it highlights the challenges involved in intervention research and the
importance of including evaluations of intervention implementation alongside statistical
evaluations to avoid erroneous conclusions
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Neutrinos below 100 TeV from the southern sky employing refined veto techniques to IceCube data
Many Galactic sources of gamma rays, such as supernova remnants, are expected to produce neutrinos with a typical energy cutoff well below 100 TeV. For the IceCube Neutrino Observatory located at the South Pole, the southern sky, containing the inner part of the Galactic plane and the Galactic Center, is a particularly challenging region at these energies, because of the large background of atmospheric muons. In this paper, we present recent advancements in data selection strategies for track-like muon neutrino events with energies below 100 TeV from the southern sky. The strategies utilize the outer detector regions as veto and features of the signal pattern to reduce the background of atmospheric muons to a level which, for the first time, allows IceCube searching for point-like sources of neutrinos in the southern sky at energies between 100 GeV and several TeV in the muon neutrino charged current channel. No significant clustering of neutrinos above background expectation was observed in four years of data recorded with the completed IceCube detector. Upper limits on the neutrino flux for a number of spectral hypotheses are reported for a list of astrophysical objects in the southern hemisphere
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Time-Integrated Neutrino Source Searches with 10Â Years of IceCube Data.
This Letter presents the results from pointlike neutrino source searches using ten years of IceCube data collected between April 6, 2008 and July 10, 2018. We evaluate the significance of an astrophysical signal from a pointlike source looking for an excess of clustered neutrino events with energies typically above âŒ1ââTeV among the background of atmospheric muons and neutrinos. We perform a full-sky scan, a search within a selected source catalog, a catalog population study, and three stacked Galactic catalog searches. The most significant point in the northern hemisphere from scanning the sky is coincident with the Seyfert II galaxy NGC 1068, which was included in the source catalog search. The excess at the coordinates of NGC 1068 is inconsistent with background expectations at the level of 2.9Ï after accounting for statistical trials from the entire catalog. The combination of this result along with excesses observed at the coordinates of three other sources, including TXS 0506+056, suggests that, collectively, correlations with sources in the northern catalog are inconsistent with background at 3.3Ï significance. The southern catalog is consistent with background. These results, all based on searches for a cumulative neutrino signal integrated over the 10 years of available data, motivate further study of these and similar sources, including time-dependent analyses, multimessenger correlations, and the possibility of stronger evidence with coming upgrades to the detector
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A Search for MeV to TeV Neutrinos from Fast Radio Bursts with IceCube
We present two searches for IceCube neutrino events coincident with 28 fast radio bursts (FRBs) and 1 repeating FRB. The first improves on a previous IceCube analysis - searching for spatial and temporal correlation of events with FRBs at energies greater than roughly 50 GeV - by increasing the effective area by an order of magnitude. The second is a search for temporal correlation of MeV neutrino events with FRBs. No significant correlation is found in either search; therefore, we set upper limits on the time-integrated neutrino flux emitted by FRBs for a range of emission timescales less than one day. These are the first limits on FRB neutrino emission at the MeV scale, and the limits set at higher energies are an order-of-magnitude improvement over those set by any neutrino telescope
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Search for sources of astrophysical neutrinos using seven years of icecube cascade events
Low-background searches for astrophysical neutrino sources anywhere in the sky can be performed using cascade events induced by neutrinos of all flavors interacting in IceCube with energies as low as âŒ1 TeV. Previously we showed that, even with just two years of data, the resulting sensitivity to sources in the southern sky is competitive with IceCube and ANTARES analyses using muon tracks induced by charge current muon neutrino interactions - especially if the neutrino emission follows a soft energy spectrum or originates from an extended angular region. Here, we extend that work by adding five more years of data, significantly improving the cascade angular resolution, and including tests for point-like or diffuse Galactic emission to which this data set is particularly well suited. For many of the signal candidates considered, this analysis is the most sensitive of any experiment to date. No significant clustering was observed, and thus many of the resulting constraints are the most stringent to date. In this paper we will describe the improvements introduced in this analysis and discuss our results in the context of other recent work in neutrino astronomy
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Efficient propagation of systematic uncertainties from calibration to analysis with the SnowStorm method in IceCube
Efficient treatment of systematic uncertainties that depend on a large number of nuisance parameters is a persistent difficulty in particle physics and astrophysics experiments. Where low-level effects are not amenable to simple parameterization or re-weighting, analyses often rely on discrete simulation sets to quantify the effects of nuisance parameters on key analysis observables. Such methods may become computationally untenable for analyses requiring high statistics Monte Carlo with a large number of nuisance degrees of freedom, especially in cases where these degrees of freedom parameterize the shape of a continuous distribution. In this paper we present a method for treating systematic uncertainties in a computationally efficient and comprehensive manner using a single simulation set with multiple and continuously varied nuisance parameters. This method is demonstrated for the case of the depth-dependent effective dust distribution within the IceCube Neutrino Telescope
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