29 research outputs found
A Businger Mechanism for Intermittent Bursting in the Stable Boundary Layer
No full textHigh-resolution large-eddy simulations of the Antarctic very stable boundary layer reveal a mechanism for systematic and periodic intermittent bursting. A nonbursting state with a boundary layer height of just 3 m is alternated by a bursting state with a height of ≈5 m. The bursts result from unstable wave growth triggered by a shear-generated Kelvin–Helmholtz instability, as confirmed by linear stability analysis. The shear at the top of the boundary layer is built up by two processes. The upper, quasi-laminar layer accelerates due to the combined effect of the pressure force and rotation by the Coriolis force, while the lower layer decelerates by turbulent friction. During the burst, this shear is eroded and the initial cause of the instability is removed. Subsequently, the interfacial shear builds up again, causing the entire sequence to repeat itself with a time scale of ≈10 min. Despite the clear intermittent bursting, the overall change of the mean wind profile is remarkably small during the cycle. This enables such a fast erosion and recovery of the shear. This mechanism for cyclic bursting is remarkably similar to the mechanism hypothesized by Businger in 1973, with one key difference. Whereas Businger proposes that the flow acceleration in the upper layer results from downward turbulent transfer of high-momentum flow, the current results indicate no turbulent activity in the upper layer, hence requiring another source of momentum. Finally, it would be interesting to construct a climatology of shear-generated intermittency in relation to large-scale conditions to assess the generality of this Businger mechanism.Atmospheric Remote Sensin
Antibody Response against SARS-CoV-2 and Seasonal Coronaviruses in Nonhospitalized COVID-19 Patients
No full textThere is strong interest in the nature of the neutralizing antibody response against SARS-CoV-2 in infected individuals. For vaccine development, it is especially important which antibodies confer protection against SARS-CoV-2, if there is a phenomenon called antibody-dependent enhancement (ADE) of infection, and if there is cross-protection by antibodies directed against seasonal coronaviruses
Release of Immunomodulatory Ebola Virus Glycoprotein-Containing Microvesicles Is Suppressed by Tetherin in a Species-Specific Manner
No full textSummary: The Ebola virus glycoprotein (EBOV-GP) forms GP-containing microvesicles, so-called virosomes, which are secreted from GP-expressing cells. However, determinants of GP-virosome release and their functionality are poorly understood. We characterized GP-mediated virosome formation and delineated the role of the antiviral factor tetherin (BST2, CD317) in this process. Residues in the EBOV-GP receptor-binding domain (RBD) promote GP-virosome secretion, while tetherin suppresses GP-virosomes by interactions involving the GP-transmembrane domain. Tetherin from multiple species interfered with GP-virosome release, and tetherin from the natural fruit bat reservoir showed the highest inhibitory activity. Moreover, analyses of GP from various ebolavirus strains, including the EBOV responsible for the West African epidemic, revealed the most efficient GP-virosome formation by highly pathogenic ebolaviruses. Finally, EBOV-GP-virosomes were immunomodulatory and acted as decoys for EBOV-neutralizing antibodies. Our results indicate that GP-virosome formation might be a determinant of EBOV immune evasion and pathogenicity, which is suppressed by tetherin. : Nehls et al. demonstrate that the glycoprotein of the highly pathogenic Ebola virus is incorporated into secretory vesicles, called GP-virosomes, to dampen the immune response and capture neutralizing antibodies. The lack of replication competence and the incorporation of antigenically intact GP might qualify GP-virosomes as safe vaccine candidates. Keywords: Ebola virus, glycoprotein, microvesicles, virosome, exosome, tetherin, immune modulation, immune evasion, antiviral immune response, neutralizing antibod
Surgical Safety Checklists in Operative Medicine in Switzerland
No full textObjective: Despite the known positive impact of surgical checklists on morbidity and mortality rates, data on the implementation of checklists in Swiss operating rooms as well as the resulting experiences are missing. The present study evaluated the general use and design of checklists in operative medicine in Switzerland, the difficulties in introduction and the subjective impact on adverse events.
Methods: An anonymous national survey of directors of adult departments in operative medicine in Switzerland was conducted during spring 2011. They were identified from the database of the Swiss college of surgeons (fmCh). The survey included questions about the use, type and content of the used checklists, the prevention of mixing up patients and the awareness of wrong site surgery.
Results: Overall, 237/799 (29.7%) surveys were returned. At the time of the survey, 172/233 (73.8%) departments used surgical checklists (4 missing values). The median time needed for collecting data per patient was 60 (range 10-600) seconds. In all, 46/161 (28.6%) participants reported a subjective decrease of adverse events after the introduction of a surgical checklist (11 missing values). Out of 217 respondents, 62 (28.6%) knew of one event and 87 (40.1%) of more than one event of wrong site surgery (20 missing values).
Conclusions: There is still room for improvement in the use of surgical checklists, which impresses, in regard to the time needed for data collection per patient, and which is not excessively time-consuming. However, acceptance problems of the majority of respondents during the introduction phase of surgical checklists vanished over time. [Arch Clin Exp Surg 2012; 1(3.000): 158-167
Measurements of Dry Deposition of No2 to A Dutch Heathland Using the Eddy‐Correlation Technique
No full textNO2 was deposited at a constant rate of 0.02 μg m-2s -1 for nearly all of the measuring period. The deposition velocity maintained a mean value of 1 mm s-1 throughout with minimum values nearing zero and maximum values of 3.5 mm s-1. There was no diurnal variation in canopy resistances to NO2. Mean values were 548 s m-1 and 400 s m-1 with and without the inclusion of several brief periods when the resistance increased markedly. Finally, a simulation of the cumulative sampling method was performed on the data set as described in Businger and Oncley (1990). They calculated a constant of proportionality, b, and showed it to have a value of 0.6 when considering heat and water-vapour fluxes. A value of b was calculated for NO2 flux using the data set presented here and was found to be 0.58. -from Author
Scalar flux profile relationships over the open ocean
No full textAuthor Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 109 (2004): C08S09, doi:10.1029/2003JC001960.The most commonly used flux-profile relationships are based on Monin-Obukhov (MO) similarity theory. These flux-profile relationships are required in indirect methods such as the bulk aerodynamic, profile, and inertial dissipation methods to estimate the fluxes over the ocean. These relationships are almost exclusively derived from previous field experiments conducted over land. However, the use of overland measurements to infer surface fluxes over the ocean remains questionable, particularly close to the ocean surface where wave-induced forcing can affect the flow. This study investigates the flux profile relationships over the open ocean using measurements made during the 2000 Fluxes, Air-Sea Interaction, and Remote Sensing (FAIRS) and 2001 GasEx experiments. These experiments provide direct measurement of the atmospheric fluxes along with profiles of water vapor and temperature. The specific humidity data are used to determine parameterizations of the dimensionless gradients using functional forms of two commonly used relationships. The best fit to the Businger-Dyer relationship [ Businger, 1988 ] is found using an empirical constant of a q = 13.4 ± 1.7. The best fit to a formulation that has the correct form in the limit of local free convection [e.g., Wyngaard, 1973 ] is found using a q = 29.8 ± 4.6. These values are in good agreement with the consensus values from previous overland experiments and the Coupled Ocean-Atmosphere Response Experiment (COARE) 3.0 bulk algorithm [ Fairall et al., 2003 ]; e.g., the COARE algorithm uses empirical constants of 15 and 34.2 for the Businger-Dyer and convective forms, respectively. Although the flux measurements were made at a single elevation and local similarity scaling is applied, the good agreement implies that MO similarity is valid within the marine atmospheric surface layer above the wave boundary layer.The FAIRS work was supported by the
Office of Naval Research grant N00014-00-1-0403 while the GasEx work
was supported by the National Science Foundation grant OCE-9986724
Update Offshore Wind Atlas: Implementing a variable sea surface roughness
No full textIn 2005 the Energy research Centre of the Netherlands (ECN) published its first version of the Offshore Wind Atlas of the Dutch part of the North Sea [3]. This version has been updated and improved using longer time series and another approach for the calculation of the roughness of the sea surface. In contradiction to other Wind Atlases which are based on measurements [28], use is made of data from the Numerical Weather Prediction model Hirlam. Measurements of wind speeds and directions are only used to validate the Wind Atlas. For the Offshore Wind Atlas, the Hirlam data is interpolated where for the vertically interpolation use is made of the Businger-Dyer profiles in combination with the Monin-Obukhov length [3]. One of the required parameters for the interpolation is the surface roughness. For land, it can be assumed constant while for sea it is variable. In the previous version of the Offshore Wind Atlas, the sea surface roughness has been determined using Charnock’s relation [9], where the so-called Charnock parameter is constant. In the new version, the equation of Hsu is introduced which states that the Charnock parameter is variable and dependent on the wave steepness i.e. the wave height divided by the wave length [19]. Assuming that the North Sea is a shallow sea and using the general wave equation, which relates the sea depth and wave length to the phase velocity of the waves, it was found that the wave steepness can be rewritten in a fraction of the wave height over the wave period multiplied by the square root of the sea depth times the gravitational acceleration. These quantities are derived from measured values which are interpolated to the location of interest. Using this approach, it is tried to improve the prediction of the wind speed distributions for a given location and altitude. Using wind measurements at several locations it was found that adding the wave data to the computations show a small improvement in the estimation of the wind speed distribution compared to the previous version of the Offshore Wind Atlas. For each measurement location and method, a two parameter Weibull distribution has been made, after which a comparison was done between the various shape and scale parameters. Generally, the scale parameter was overestimated by both versions of the Offshore Wind Atlas compared to the measurements. The cause of this behavior might be found in the data used to make the Atlas. The shape parameter is well predicted by the new version of the Offshore Wind Atlas due to the use of wave data. The influence of the wave data is found to be larger for lower altitudes than for higher altitudes. Besides Weibull distributions, also maps with average wind speeds are given by the Offshore Wind Atlas which are compared to older mapsAerospace Engineerin
Students' View of Evidence-Based Medicine: A Survey in Switzerland
No full textObjective: Training in Evidence-based medicine (EBM) has been implemented in Swiss medical schools for the last 8 to 10 years. Still, there is little known about the undergraduates' perception of EBM and Medical Statistics.
Methods: Between February and July 2007, fifth- to sixth-year medical students during surgical clerkship at 15 adult surgical departments in German-speaking Switzerland were asked to participate in an anonymous survey. At the end of the surgical clerkship each student received a self-administered questionnaire on EBM. It included questions concerning the perception of the practical use of EBM, eight multiple-choice questions regarding the statistical literacy and 26 questions about the view of Science and Scientific Methods.
Results: A total of 185/344 (53.8%) medical students participated in the study. On a seven-point Likert scale, the importance of teaching and knowledge in EBM was rated as high (5.7+/-1.1 and 5.9+/-1.0). The subjective knowledge on EBM was considered moderate on a five-point Likert scale (3.4+/-1.0), corresponding with the median percentage knowledge score of 33 (range 0-47). The frequency of literature research and number of publications as co-author proved to be the only significant predictors for a higher knowledge in EBM and Medical Statistics of medical students (p=0.01). The attitude toward Science was good with a total score for the value of Science and research of 80.0 +/- 8.3 out of a maximum of 130. The main impediments for using EBM were lack of time (57/165, 35%), ignorance (36/165, 22%), and difficulties in integration into everyday life (32/165, 19%).
Conclusions: Medical students in Switzerland were aware of their moderate knowledge in EBM and Medical Statistics and aimed for an improvement. More courses in EBM and journal clubs must be introduced and access to information resources must be ensured with an early introduction in search engines (i.e. MEDLINE, Cochrane Library, etc.). A general strengthening of the knowledge on EBM and Medical Statistics among medical students may be a good way of educating the critical number of academic physicians and establishing a foundation for their future academic environment. [Arch Clin Exp Surg 2012; 1(1.000): 34-40
Update Offshore Wind Atlas: Implementing a variable sea surface roughness
No full textIn 2005 the Energy research Centre of the Netherlands (ECN) published its first version of the Offshore Wind Atlas of the Dutch part of the North Sea [3]. This version has been updated and improved using longer time series and another approach for the calculation of the roughness of the sea surface. In contradiction to other Wind Atlases which are based on measurements [28], use is made of data from the Numerical Weather Prediction model Hirlam. Measurements of wind speeds and directions are only used to validate the Wind Atlas. For the Offshore Wind Atlas, the Hirlam data is interpolated where for the vertically interpolation use is made of the Businger-Dyer profiles in combination with the Monin-Obukhov length [3]. One of the required parameters for the interpolation is the surface roughness. For land, it can be assumed constant while for sea it is variable. In the previous version of the Offshore Wind Atlas, the sea surface roughness has been determined using Charnock’s relation [9], where the so-called Charnock parameter is constant. In the new version, the equation of Hsu is introduced which states that the Charnock parameter is variable and dependent on the wave steepness i.e. the wave height divided by the wave length [19]. Assuming that the North Sea is a shallow sea and using the general wave equation, which relates the sea depth and wave length to the phase velocity of the waves, it was found that the wave steepness can be rewritten in a fraction of the wave height over the wave period multiplied by the square root of the sea depth times the gravitational acceleration. These quantities are derived from measured values which are interpolated to the location of interest. Using this approach, it is tried to improve the prediction of the wind speed distributions for a given location and altitude. Using wind measurements at several locations it was found that adding the wave data to the computations show a small improvement in the estimation of the wind speed distribution compared to the previous version of the Offshore Wind Atlas. For each measurement location and method, a two parameter Weibull distribution has been made, after which a comparison was done between the various shape and scale parameters. Generally, the scale parameter was overestimated by both versions of the Offshore Wind Atlas compared to the measurements. The cause of this behavior might be found in the data used to make the Atlas. The shape parameter is well predicted by the new version of the Offshore Wind Atlas due to the use of wave data. The influence of the wave data is found to be larger for lower altitudes than for higher altitudes. Besides Weibull distributions, also maps with average wind speeds are given by the Offshore Wind Atlas which are compared to older maps.Aerospace Engineerin
