Identification of Intermediates in the Reaction Pathway of SO2_{2} on the CaO Surface: From Physisorption to Sulfite to Sulfate

The interaction of CaO and Ca(OH)$_{2}$ with solvated or gaseous SO$_{2}$ plays a crucial role in the corrosion of urban infrastructure by acid rain or in the removal of SO$_{2}$ from flue gas. We carried out a combined spectroscopic and theoretical investigation on the interaction of SO$_{2}$ with a CaO(001) single crystal. First, the surface chemistry of SO$_{2}$ was investigated at different temperatures using polarization-resolved IR reflection absorption spectroscopy. Three species were identified, and an in-depth density functional theory study was carried out, which allowed deriving a consistent picture. Unexpectedly, low temperature exposure to SO$_{2}$ solely yields a physisorbed species. Only above 100 K, the transformation of this weakly bound adsorbate first to a chemisorbed sulfite and then to a sulfate occurs, effectively passivatating the surface. Our results provide the basis for more efficient strategies in corrosion protection of urban infrastructure and in lime-based desulfurization of flue gas

Elimination of Domain Boundaries Accelerates Diffusion in MOFs by an Order of Magnitude: Monolithic Metal‐Organic Framework Thin Films Epitaxially Grown on Si(111) Substrates

Many properties of the emerging class of metal-organic frameworks (MOFs) depend crucially on defect concentrations, as in case of other solids. In order to provide reference systems with nearly perfect structure and low defect density, a procedure to grow MOFs epitaxially on cm-sized Si(111) single crystals is developed. The crystalline metal-organic thin films are in high registry with the substrate\u27s crystal lattice, as demonstrated by synchrotron-based grazing incidence X-ray diffraction (GI-XRD) experiments. The corresponding reduction of MOF defect density is shown to have striking effects on the properties of these porous frameworks. The most pronounced difference concerns mass transport. An increase in the diffusion coefficient of guest molecules by one order of magnitude relative to the same MOF materials with normal defect densities is observed

Key characteristics impacting survival of COVID-19 extracorporeal membrane oxygenation

Background Severe COVID-19 induced acute respiratory distress syndrome (ARDS) often requires extracorporeal membrane oxygenation (ECMO). Recent German health insurance data revealed low ICU survival rates. Patient characteristics and experience of the ECMO center may determine intensive care unit (ICU) survival. The current study aimed to identify factors affecting ICU survival of COVID-19 ECMO patients. Methods 673 COVID-19 ARDS ECMO patients treated in 26 centers between January 1st 2020 and March 22nd 2021 were included. Data on clinical characteristics, adjunct therapies, complications, and outcome were documented. Block wise logistic regression analysis was applied to identify variables associated with ICU-survival. Results Most patients were between 50 and 70 years of age. PaO2/FiO2 ratio prior to ECMO was 72 mmHg (IQR: 58–99). ICU survival was 31.4%. Survival was significantly lower during the 2nd wave of the COVID-19 pandemic. A subgroup of 284 (42%) patients fulfilling modified EOLIA criteria had a higher survival (38%) (p = 0.0014, OR 0.64 (CI 0.41–0.99)). Survival differed between low, intermediate, and high-volume centers with 20%, 30%, and 38%, respectively (p = 0.0024). Treatment in high volume centers resulted in an odds ratio of 0.55 (CI 0.28–1.02) compared to low volume centers. Additional factors associated with survival were younger age, shorter time between intubation and ECMO initiation, BMI > 35 (compared to < 25), absence of renal replacement therapy or major bleeding/thromboembolic events. Conclusions Structural and patient-related factors, including age, comorbidities and ECMO case volume, determined the survival of COVID-19 ECMO. These factors combined with a more liberal ECMO indication during the 2nd wave may explain the reasonably overall low survival rate. Careful selection of patients and treatment in high volume ECMO centers was associated with higher odds of ICU survival

Reaktion von CaO und Ca(OH)2_{\rm 2} - Einkristallen mit Schwefeldioxid in der UHV-IRRAS

Im Rahmen dieser Dissertation wurde die Reaktion der Calciumoxid (001)- und der Calciumhydroxid (001)-Einkristalloberfläche mit Schwefeldioxid unter Ultrahochvakuumbedingungen mittels Infrarot-Reflexions-Absorptions-Spektroskopie beobachtet. Dabei wurde für SO$_{\rm 2}$ auf CaO (001) ein dreischrittiger Reaktionspfad bestehend aus Physisorption und zwei temperaturabhängigen Umwandlungen in Chemisorbate gefunden, während auf der Ca(OH)$_{\rm 2}$ (001)-Oberfläche die Physisorption von SO$_{\rm 2}$ mit einer Vorzugsorientierung von im Mittel 23° gegenüber der Flächennormale identifiziert werden konnte

Experiments on the aerodynamic behaviour of square cylinders with rounded corners at Reynolds numbers up to 12 million

The influence of the angle of incidence and corner radius on the aerodynamics of square-section cylinders is studied by means of wind tunnel experiments. Two different corner radii (r∕D=0.16 and 0.29) were investigated at three angles of incidence (alpha=0deg, −22.5deg and −45deg). Steady and unsteady global forces and local surface pressures were measured in the high-pressure wind tunnel in Göttingen. The Reynolds number was varied up to values as high as 12x10^6, thereby spanning the known flow state regimes up to high transcritical. The results demonstrated that a decrease of the cylinder’s bluffness induced lower maximum drag coefficients and r.m.s. values, as well as higher Strouhal numbers in all flow state regimes. Furthermore, the critical Reynolds numbers shifted to significantly lower values. For the cylinder configurations at alpha=0deg no upper transition or transcritical flow state was present up to ReD=12 million. A decrease in the angle of incidence resulted in a significant reduction of the length of the supercritical flow state, a shift of the drag force, Strouhal number and base pressure to higher values and an increase of the critical Reynolds numbers. The cylinders at non-zero angles of incidence all displayed a clear critical flow state, at which two discontinuous transitions were observed, accompanied by jumps in the CD and CL values and the Strouhal number. Only three out of six studied configurations experienced hysteresis, where for the high corner radius configuration at alpha=0deg a particularly broad hysteresis effect was measured

Experimental investigation on the combined effects of surface roughness and corner radius for square cylinders at high Reynolds numbers up to 10^7

In this study, the aerodynamics of 2D, slightly rough, square-section cylinders with rounded corners is experimentally investigated for Reynolds numbers up to about 12 × 10^6. The cylinders have a mean relative surface roughness of k/D = 1 × 10^−3, a corner radius of either r/D = 0.16 or 0.29 and are positioned at an angle of incidence of 0° or −45° in cross-flow direction. The results show that a larger corner radius induces lower drag coefficients and higher vortex shedding frequencies for all flow regimes, but at lower shedding intensities. Changing the angle of incidence from 0° to −45° results in all coefficients and the wake profile to become nearly independent of the Reynolds number. The critical flow state furthermore shifts to higher Reynolds numbers and decreases in length, whereas the supercritical flow state reduces to a single point. An increase of the surface roughness height from k/D = 5 × 10^−6 to k/D = 1 × 10^−3 induces a shift of the flow regimes towards significantly lower Reynolds numbers. The values of the coefficients show a lower dependency on the Reynolds number in all flow regimes, whereas in the upper transition a strong recovery of all coefficients towards subcritical values takes place

Investigation of the steady and unsteady forces acting on a pair of circular cylinders in crossflow up to ultra-high Reynolds numbers

Measurements of the steady and unsteady forces acting on a pair of circular cylinders in crossflow are performed from subcritical up to ultra-high Reynolds numbers. The two cylinders with equal diameters d are arranged inline at two centre-to-centre distances: S/d = 2.8 and 4. The trend of the drag curve for the upstream cylinder Cd1(Re) at both distances is similar to that for a single circular cylinder. The development of the drag curves Cd2(Re, S/d = 2.8, 4) of the downstream cylinder is inverse to that of the upstream cylinder. For both cylinder spacing values, the drag on the downstream cylinder is negative for subcritical Reynolds numbers, increases abruptly to positive values at the beginning of the supercritical regime, and shows a significant dip at transcritical Reynolds numbers. This drag inversion indicates that the critical distance Sc decreases sharply in the supercritical Reynolds number range. For S/d = 2.8 at Re to 10E7, the downstream cylinder experiences once more a thrust force. The curve of the Strouhal number St(Re) of the downstream cylinder for S/d = 4 is very close to that of a single cylinder. For Reynolds numbers of Re = 1×10E6 - 7×10E6, the Strouhal numbers have nearly equal values of St = 0.22 - 0.24 for both distances. This is followed by a branching. For Re to 10E7 and the case S/d = 2.8, the Strouhal numbers dip at St = 0.17. However, for S/d = 4, they increase up to St = 0.27. In the supercritical range, two peaks occur in the power spectra for the large distance S/d = 4. Based on a wavelet analysis, we can conclude that the low-frequency mode, which does not occur for a single cylinder, is an interference effect

Experimental investigation on the flow around single and tandem cylinder configurations at Reynolds numbers from 40.000 up to 12 million

Steady and unsteady force measurements and surface pressure measurements on cylinders in single and tandem configurations were performed for Reynolds numbers from sub- up to transcritical values. The smooth and rough cylinders, either with a square cross-section and rounded edges or with a circular cross-section, represent typical column shapes for large floating offshore structures. The measurements were conducted in the DNW High Pressure Wind Tunnel in Göttingen, a specialized high Reynolds number facility. The aerodynamic forces on the cylinder were measured using a both sided piezo-electric balance. For the tandem cases, only the forces on the downstream cylinder were measured due to restrictions of the test setup. In addition to the unsteady force measurements the time-mean surface pressures at two locations on the cylinders were obtained. As a supplement, a pressure rake was used to measure the time-mean pressure and thus velocity distribution in the wake of the (downstream) cylinder. Variations of the Reynolds number were possible over almost three orders of magnitude in the range from Re = 4·10^4 up to 12·10^6 by changing the free stream flow velocity and the total pressure. In case of the square cross-section cylinders the dependence of the aerodynamic forces and surface pressures on the Reynolds number were investigated for various angles of incidence � and for two non-dimension surface roughness values of O(10^−6) and O(10^−3). At the maximum angle of incidence the blockage did not exceed 13%. For the tandem configurations the distance between the centers of the cylinders had a value of 4.0 and 5.6 times the diameter for the square cylinders and of 2.8 and 4.0 times the diameter for the circular cylinders. For all configurations drastic changes of the global values as function of the Reynolds number were observed