64 research outputs found
Limitations in the determination of surface emission distributions on comets through modelling of observational data -- A case study based on Rosetta observations
The European Space Agency's (ESA) Rosetta mission has returned a vast data
set of measurements of the inner gas coma of comet 67P/Churyumov-Gerasimenko.
These measurements have been used by different groups to determine the
distribution of the gas sources at the nucleus surface. The solutions that have
been found differ from each other substantially and illustrate the degeneracy
of this issue. It is the aim of this work to explore the limitations that
current gas models have in linking the coma measurements to the surface. In
particular, we discuss the sensitivity of Rosetta's ROSINA/COPS, VIRTIS, and
MIRO instruments to differentiate between vastly different spatial
distributions of the gas emission from the surface. We have applied a state of
the art 3D DSMC gas dynamics code to simulate the inner gas coma of different
models that vary in the fraction of the surface that contains ice and in
different sizes of active patches. These different distributions result in jet
interactions that differ in their dynamical behaviour. We have found that
ROSINA/COPS measurements by themselves cannot detect the differences in our
models. While ROSINA/COPS measurements are important to constrain the regional
inhomogeneities of the gas emission, they can by themselves not determine the
surface emission distribution of the gas sources to a spatial accuracy of
better than a few hundred metres (400 m). Any solutions fitting the ROSINA/COPS
measurements is hence fundamentally degenerate, be it through a forward or
inverse model. Only other instruments with complementary measurements can
potentially lift this degeneracy as we show here for VIRTIS and MIRO. Finally,
as a by-product, we have explored the effect of our activity distributions on
lateral flow at the surface that may be responsible for some of the observed
aeolian features.Comment: Icarus (in press
Gas flow in near surface comet like porous structures: Application to 67P/Churyumov-Gerasimenko
We performed an investigation of a comet like porous surface to study how sub-surface sublimation with subsequent flow through the porous medium can lead to higher gas temperatures at the surface. A higher gas temperature of the emitted gas at the surface layer, compared to the sublimation temperature, will lead to higher gas speeds as the gas expands into the vacuum thus altering the flow properties on larger scales (kilometres away from the surface). Unlike previous models that have used modelled artificial structures, we used Earth rock samples with a porosity in the range 24 – 92 % obtained from X-ray micro computed tomography (micro-CT) scans with resolution of some μm. Micro-CT scanning technology provides 3D images of the pore samples. The direct simulation Monte Carlo (DSMC) method for the rarefied gas dynamics is directly applied on the digital rock samples in an unstructured mesh to determine the gas densities, temperatures and speeds within the porous medium and a few centimetres above the surface. The thicknesses of the rock samples were comparable to the diurnal thermal skin depth (5cm). H2O was assumed to be the outgassing species. We correlated the coma temperatures and other properties of the flow with the rock porosities. The results are discussed as an input to analysis of data from the Microwave Instrument on Rosetta Orbiter (MIRO) on the 67P/Churyumov-Gerasimenko
Surveillance quality correlates with surgical site infection rates in knee and hip arthroplasty and colorectal surgeries: A call to action to adjust reporting of SSI rates.
OBJECTIVE
The incidence of surgical site infections may be underreported if the data are not routinely validated for accuracy. Our goal was to investigate the communicated SSI rate from a large network of Swiss hospitals compared with the results from on-site surveillance quality audits.
DESIGN
Retrospective cohort study.
PATIENTS
In total, 81,957 knee and hip prosthetic arthroplasties from 125 hospitals and 33,315 colorectal surgeries from 110 hospitals were included in the study.
METHODS
Hospitals had at least 2 external audits to assess the surveillance quality. The 50-point standardized score per audit summarizes quantitative and qualitative information from both structured interviews and a random selection of patient records. We calculated the mean National Healthcare Safety Network (NHSN) risk index adjusted infection rates in both surgery groups.
RESULTS
The median NHSN adjusted infection rate per hospital was 1.0% (interquartile range [IQR], 0.6%-1.5%) with median audit score of 37 (IQR, 33-42) for knee and hip arthroplasty, and 12.7% (IQR, 9.0%-16.6%), with median audit score 38 (IQR, 35-42) for colorectal surgeries. We observed a wide range of SSI rates and surveillance quality, with discernible clustering for public and private hospitals, and both lower infection rates and audit scores for private hospitals. Infection rates increased with audit scores for knee and hip arthroplasty (P value for the slope = .002), and this was also the case for planned (P = .002), and unplanned (P = .02) colorectal surgeries.
CONCLUSIONS
Surveillance systems without routine evaluation of validity may underestimate the true incidence of SSIs. Audit quality should be taken into account when interpreting SSI rates, perhaps by adjusting infection rates for those hospitals with lower audit scores
Water vapor deposition from the inner gas coma onto the nucleus of Comet 67P/Churyumov-Gerasimenko
Rosetta has detected water ice existing on the surface of Comet 67P/Churyumov-Gerasimenko in various types of features. One of particular interest is the frost-like layer observed at the edge of receding shadows during the whole mission, interpreted as the recondensation of a thin layer of water ice. Two possible mechanisms, (1) subsurface ice sublimation and (2) gas coma deposition, have been proposed for producing this recondensation process and diurnal cycles of water ice. Previous studies have demonstrated both mechanisms based on simplified models. More precise and modern models are yet insufficient when addressing the gas-coma-deposition mechanism. We aim to study the recondensation from the inner water gas coma of the 67P/Churyumov-Gerasimenko with more physical constraints including the OSIRIS images, nucleus shape model, and insolation conditions. We compute, for the first time, the backflux distributions from the coma with various boundary conditions. Numerical simulations of this gas-coma-deposition process show that the equivalent water ice deposition can be up to several microns in an hour of accumulation time close to the perihelion passage, which is comparable with the simulation results of the other subsurface-ice sublimation mechanism
Antimicrobial prophylaxis administration after umbilical cord clamping in cesarean section and the risk of surgical site infection: a cohort study with 55,901 patients.
BACKGROUND
The World Health Organization (WHO) recommends administration of surgical antimicrobial prophylaxis (SAP) in cesarean section prior to incision to prevent surgical site infections (SSI). This study aimed to determine whether SAP administration following cord clamping confers an increased SSI risk to the mother.
METHODS
Study design: Cohort.
SETTING
75 participating Swiss hospitals, from 2009 to 2018.
PARTICIPANTS
A total of 55,901 patients were analyzed.
MAIN OUTCOME MEASURES
We assessed the association between SAP administration relative to incision and clamping and the SSI rate, using generalized linear multilevel models, adjusted for patient characteristics, procedural variables, and health-care system factors.
RESULTS
SAP was administered before incision in 26'405 patients (47.2%) and after clamping in 29,496 patients (52.8%). Overall 846 SSIs were documented, of which 379 (1.6% [95% CI, 1.4-1.8%]) occurred before incision and 449 (1.7% [1.5-1.9%]) after clamping (p = 0.759). The adjusted odds ratio for SAP administration after clamping was not significantly associated with an increased SSI rate (1.14, 95% CI 0.96-1.36; p = 0.144) when compared to before incision. Supplementary and subgroup analyses supported these main results.
CONCLUSIONS
This study did not confirm an increased SSI risk for the mother in cesarean section if SAP is given after umbilical cord clamping compared to before incision
The impact of public health interventions on the future prevalence of ESBL-producing Klebsiella pneumoniae: a population based mathematical modelling study.
BACKGROUND
Future prevalence of colonization with extended-spectrum betalactamase (ESBL-) producing K. pneumoniae in humans and the potential of public health interventions against the spread of these resistant bacteria remain uncertain.
METHODS
Based on antimicrobial consumption and susceptibility data recorded during > 13 years in a Swiss region, we developed a mathematical model to assess the comparative effect of different interventions on the prevalence of colonization.
RESULTS
Simulated prevalence stabilized in the near future when rates of antimicrobial consumption and in-hospital transmission were assumed to remain stable (2025 prevalence: 6.8% (95CI%:5.4-8.8%) in hospitals, 3.5% (2.5-5.0%) in the community versus 6.1% (5.0-7.5%) and 3.2% (2.3-4.2%) in 2019, respectively). When overall antimicrobial consumption was set to decrease by 50%, 2025 prevalence declined by 75% in hospitals and by 64% in the community. A 50% decline in in-hospital transmission rate led to a reduction in 2025 prevalence of 31% in hospitals and no reduction in the community. The best model fit estimated that 49% (6-100%) of observed colonizations could be attributable to sources other than human-to-human transmission within the geographical setting.
CONCLUSIONS
Projections suggests that overall antimicrobial consumption will be, by far, the most powerful driver of prevalence and that a large fraction of colonizations could be attributed to non-local transmissions
Better Operating Room Ventilation as Determined by a Novel Ventilation Index is Associated with Lower Rates of Surgical Site Infections.
OBJECTIVE
To assess the impact of operating room (OR) ventilation quality on surgical site infections (SSI) using a novel ventilation index.
SUMMARY BACKGROUND DATA
Previous studies compared laminar air flow with conventional ventilation, thereby ignoring many parameters that influence air flow properties.
METHODS
In this cohort study, we surveyed hospitals participating in the Swiss SSI surveillance and calculated a ventilation index for their ORs, with higher values reflecting less turbulent air displacement. For procedures captured between 01/2017-12/2019, we studied the association between ventilation index and SSI rates using linear regression (hospital-level analysis) and with the individual SSI risk using generalized linear mixed-effects models (patient-level analysis).
RESULTS
We included 47 hospitals (182 ORs). Among the 163'740 included procedures, 6791 SSIs were identified. In hospital-level analyses, a 5-unit increase in the ventilation index was associated with lower SSI rates for knee and hip arthroplasty (-0.41 infections per 100 procedures, CI -0.69 to -0.13), cardiac (-0.89, -1.91 to 0.12), and spine surgeries (-1.15, -2.56 to 0.26). Similarly, patient-level analyses showed a lower SSI risk with each 5-unit increase in ventilation index (adjusted odds ratio 0.71, CI 0.58 to 0.87 for knee and hip; 0.72, 0.49 to 1.06 for spine; 0.82, 0.69 to 0.98 for cardiac surgery). Higher index values were mainly associated with a lower risk for superficial and deep incisional SSIs.
CONCLUSIONS
Better ventilation properties, assessed with our ventilation index, are associated with lower rates of superficial and deep incisional SSIs in orthopedic and cardiac procedures. OR ventilation quality appeared to be less relevant for other surgery types
Better operating room ventilation as determined by a novel ventilation index is associated with lower rates of surgical site infections
OBJECTIVE: The aim was to assess the impact of operating room (OR) ventilation quality on surgical site infections (SSIs) using a novel ventilation index.
BACKGROUND: Previous studies compared laminar air flow with conventional ventilation, thereby ignoring many parameters that influence air flow properties.
METHODS: In this cohort study, we surveyed hospitals participating in the Swiss SSI surveillance and calculated a ventilation index for their ORs, with higher values reflecting less turbulent air displacement. For procedures captured between January 2017 and December 2019, we studied the association between ventilation index and SSI rates using linear regression (hospital-level analysis) and with the individual SSI risk using generalized linear mixed-effects models (patient-level analysis).
RESULTS: We included 47 hospitals (182 ORs). Among the 163,740 included procedures, 6791 SSIs were identified. In hospital-level analyses, a 5-unit increase in the ventilation index was associated with lower SSI rates for knee and hip arthroplasty (-0.41 infections per 100 procedures, 95% confidence interval: -0.69 to -0.13), cardiac (-0.89, -1.91 to 0.12), and spine surgeries (-1.15, -2.56 to 0.26). Similarly, patient-level analyses showed a lower SSI risk with each 5-unit increase in ventilation index (adjusted odds ratio 0.71, confidence interval: 0.58-0.87 for knee and hip; 0.72, 0.49-1.06 for spine; 0.82, 0.69-0.98 for cardiac surgery). Higher index values were mainly associated with a lower risk for superficial and deep incisional SSIs.
CONCLUSIONS: Better ventilation properties, assessed with our ventilation index, are associated with lower rates of superficial and deep incisional SSIs in orthopedic and cardiac procedures. OR ventilation quality appeared to be less relevant for other surgery types
ORIGO: A mission concept to challenge planetesimal formation theories
Comets are generally considered among the most pristine objects in our Solar System. There have thus been significant efforts to understand these bodies. During the past decades, we have seen significant progress in our theoretical understanding of planetesimal/cometesimals (the precursors of comets) formation. Recent space missions—such as ESA’s Rosetta mission to comet 67P/Churyumov-Gerasimenko—have provided observations claimed by proponents of different comet formation theories to validate their scenarios. Yet, no single formation paradigm could be definitively proven. Given the importance of understanding how the first bodies in our Solar System formed, we propose a dedicated mission to address this issue. ORIGO will deliver a lander to the surface of a cometary nucleus where it will characterise the first five m of the subsurface. With remote sensing instruments and the deployment of payload into a borehole, we will be able to study the physico-chemical structure of ancient, unmodified material. The mission has been designed to fit into the ESA M-class mission budget
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