Wind tunnel experiments were performed to quantify the drag reduction on a wind turbine airfoil partially or fully covered with riblets. A full-scale 2.5 MW wind turbine airfoil section, typical for ...the near tip, was placed in the free stream flow of the wind tunnel at the Saint Anthony Falls Laboratory, University of Minnesota. Various sizes and geometries of experimental riblets were provided by 3M Company and tested at angles of attack ranging from 0° ≤ α ≤ 10° (0.25 ≤ CL ≤ 1.14) and at a Reynolds number of Re = 2.2 × 106. Mean drag was measured via wake survey (momentum deficit) and with a sensitive force balance. Lift was measured directly from the force balance. Tests included the cases of complete and partial riblet coverage on the wing. Results indicated that riblets could provide an overall reduction of skin friction drag, and that the amount of the decrease varied with riblet height and geometry. Partial riblet coverage appears in some cases more efficient than its complete coverage counterpart. The percentage of drag the riblets reduced varied greatly and in some cases the riblets were even detrimental to the airfoil. The most efficient riblet for a completely covered airfoil was found to be the V-groove shape of 100 μm height. It produced a reduction of roughly 6% in the operational range expected in a turbine airfoil. On the other hand, the most efficient riblet size for partial coverage was also a V-groove shape and seemed to shift slightly to a smaller peak height of 80 μm. This configuration produced a reduction of roughly 4% in the range of angle of attack that is typical for operation in the field. The average non-dimensional square root of the groove cross-section, l+, defined in terms of the drag coefficient at design angle of attack for the optimum riblet configuration in the fully coverage case was found to be l+≈10, which is very close to the optimum value found for planar surfaces. Based on our results we propose a formulation for the optimum riblet size in airfoil considering the mean drag coefficient and chord length Reynolds number. Even though the optimum full coverage case showed better performance that the partial case, the additional drag reduction benefit may be offset by the additional application cost.
► Experiments were performed to quantify the drag reduction on a wind turbine using riblets. ► Results indicated that riblets could provide a reduction of skin friction drag. ► The amount of the drag decrease varied with riblet height and geometry. ► Maximum drag reduction of 6% was obtained in the operational range expected in a turbine airfoil. ► Based on our results we propose a formulation for the optimum riblet size in airfoils.
The fundamental properties of turbulent flow around a perfectly staggered wind farm are investigated in a wind tunnel. The wind farm consisted of a series of 10 rows by 2–3 columns of miniature wind ...turbines spaced 5 and 4 rotor diameters in the streamwise and spanwise directions respectively. It was placed in a boundary-layer flow developed over a smooth surface under thermally neutral conditions. Cross-wire anemometry was used to obtain high resolution measurements of streamwise and vertical velocity components at various locations within and above the wind farm. The results show that the staggered configuration is more efficient in terms of momentum transfer from the background flow to the turbines compared to the case of an aligned wind turbine array under similar turbine separations in the streamwise and spanwise directions. This leads to improved power output of the overall wind farm. A simplified analysis suggests that the difference in power output between the two configurations is on the order of 10%. The maximum levels of turbulence intensity in the staggered wind farm were found to be very similar to that observed in the wake of a single wind turbine, differing substantially with that observed in an aligned configuration with similar spacing. The dramatic changes in momentum and turbulence characteristics in the two configurations show the importance of turbine layout in engineering design. Lateral homogenization of the turbulence statistics above the wind farm allows for the development of simple parametrizations for the adjustment of flow properties, similar to the case of a surface roughness transition. The development of an internal boundary layer was observed at the upper edge of the wind farm within which the flow statistics are affected by the superposition of the ambient flow and the flow disturbance induced by the wind turbines. The adjustment of the flow in this layer is much slower in the staggered situation (with respect to its aligned counterpart), implying a change in the momentum/power available at turbine locations. Additionally, power spectra of the streamwise and vertical velocity components indicate that the signature of each turbine-tip vortex structure persists to locations deep within the wind farm.
•Significant detrimental effect of workforce reduction on mental health and life satisfaction.•Evidence for fear of job loss acting as mediator.•Indirect econometric approach robust to reverse ...causality.•Heterogeneous effect with respect to psychological health.
We examine the link between workforce reduction, subjective job insecurity, and mental health using individual level panel data for private-sector employees in Germany. We first estimate the effect of firm-level workforce reductions on mental health, finding a strong, negative, and statistically significant relationship. We then extensively examine the role of subjective job insecurity as mediating variable and its importance relative to other possible channels for the effect of workforce reduction on mental health. Eventually, as an extension to our analysis, we use life satisfaction as alternative outcome variable.
This study presents credible estimates for the causal effect of BMI growth on employment among the obese. By exploring random assignment of a weight-loss intervention based on monetary rewards, I ...provide convincing evidence that weight loss positively affects the employment prospects of obese women but not of obese men. Consistent with this, significant effects of weight loss on proxy variables for labor productivity are found only for obese women.
Huntington’s disease (HD) is a genetic neurodegenerative disorder caused by an expanded polyglutamine (polyQ) domain near the N-terminus of the huntingtin (htt) protein. Expanded polyQ leads to htt ...aggregation. The first 17 amino acids (Nt17) in htt comprise a lipid-binding domain that undergoes a number of posttranslational modifications that can modulate htt toxicity and subcellular localization. As there are three lysines within Nt17, we evaluated the impact of lysine acetylation on htt aggregation in solution and on model lipid bilayers. Acetylation of htt-exon1(51Q) and synthetic truncated htt-exon 1 mimicking peptides (Nt17-Q35-P10-KK) was achieved using a selective covalent label, sulfo-N-hydroxysuccinimide (NHSA). With this treatment, all three lysine residues (K6, K9, and K15) in Nt17 were significantly acetylated. N-terminal htt acetylation retarded fibril formation in solution and promoted the formation of larger globular aggregates. Acetylated htt also bound lipid membranes and disrupted the lipid bilayer morphology less aggressively compared with the wild-type. Computational studies provided mechanistic insights into how acetylation alters the interaction of Nt17 with lipid membranes. Our results highlight that N-terminal acetylation influences the aggregation of htt and its interaction with lipid bilayers.
Background
The COVID-19 pandemic has led to widespread cancelation of electively scheduled surgeries, including for colorectal, pancreatic, and gastric cancer. The American College of Surgeons and ...the Society of Surgical Oncology have released guidelines for triage of these procedures. We seek to synthesize available evidence on delayed resection and oncologic outcomes, while also providing a critical assessment of the released guidelines.
Methods
A systematic review was conducted to identify literature between 2005 and 2020 investigating the impact of time to surgery on oncologic outcomes in colorectal, pancreatic, and gastric cancer.
Results
For colorectal cancer, 1066 abstracts were screened and 43 papers were included. In primarily resected colon cancer, delay over 30 to 40 days is associated with lower survival. In rectal cancer, time to surgery over 7 to 8 weeks following neoadjuvant therapy is associated with decreased survival. Three hundred ninety-four abstracts were screened for pancreatic cancer and nine studies were included. Two studies demonstrate increased unexpected progression with delayed surgery over 30 days. Out of 633 abstracts screened for gastric cancer, six studies were included. No identified study demonstrated worse survival with increased time to surgery.
Conclusion
Moderate evidence suggests that delayed resection of colorectal cancer worsens survival; the impact of time to surgery on gastric and pancreatic cancer outcomes is uncertain. Early resection of gastrointestinal malignancies provides the best chance for curative therapy. During the COVID-19 pandemic, prioritization of procedures should account for available evidence on time to surgery and oncologic outcomes.
Chronic stress and little physical activity play an increasing role in dominant civilization diseases. The positive contribution of nature to health has been examined in a multitude of studies. The ...ambition of this study is to review the present state of international research on exposure to forests and its specific effects on human health, particularly stress-reducing effects. The review focusses on research in Asia and Germanspeaking countries (GSC) in Europe, distinguishing between forest benefits for physical and mental well-being. Considering the objective of the EU Forest Action Plan (FAP) to contribute to quality of life by improving the social dimensions of forests, it also examines and compares the forest strategies and programmes of GSC. With regard to plan implementation at national levels, attention is drawn to preventive health care aspects. The results are discussed and challenges, especially for forestry in GSC, are deduced.
Oxygen activation at the active sites of FeFe hydrogenases has been proposed to be the initial step of irreversible oxygen-induced inhibition of these enzymes. On the basis of a first theoretical ...study into the thermodynamics of O2 activation Inorg. Chem. 2009, 48, 7127 we here investigate the kinetics of possible reaction paths at the distal iron atom of the active site by means of density functional theory. A sequence of steps is proposed to either form a reactive oxygen species (ROS) or fully reduce O2 to water. In this reaction cascade, two branching points are identified where water formation directly competes with harmful oxygen activation reactions. The latter are water formation by O-O bond cleavage of a hydrogen peroxide-bound intermediate competing with H2O2 dissociation and CO2 formation by a putative iron-oxo species competing with protonation of the iron-oxo species to form a hydroxyo ligand. Furthermore, we show that proton transfer to activated oxygen is fast and that proton supply to the active site is vital to prevent ROS dissociation. If sufficiently many reduction equivalents are available, oxygen activation reactions are accelerated, and oxygen reduction to water becomes possible.
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