Bubble Drag Reduction Requires Large Bubbles Verschoof, Ruben A; van der Veen, Roeland C A; Sun, Chao ...
Physical review letters,
2016-Sep-02, Letnik:
117, Številka:
10
Journal Article
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In the maritime industry, the injection of air bubbles into the turbulent boundary layer under the ship hull is seen as one of the most promising techniques to reduce the overall fuel consumption. ...However, the exact mechanism behind bubble drag reduction is unknown. Here we show that bubble drag reduction in turbulent flow dramatically depends on the bubble size. By adding minute concentrations (6 ppm) of the surfactant Triton X-100 into otherwise completely unchanged strongly turbulent Taylor-Couette flow containing bubbles, we dramatically reduce the drag reduction from more than 40% to about 4%, corresponding to the trivial effect of the bubbles on the density and viscosity of the liquid. The reason for this striking behavior is that the addition of surfactants prevents bubble coalescence, leading to much smaller bubbles. Our result demonstrates that bubble deformability is crucial for bubble drag reduction in turbulent flow and opens the door for an optimization of the process.
The ubiquity of turbulent flows in nature and technology makes it of utmost importance to fundamentally understand turbulence. Kolmogorov's 1941 paradigm suggests that for strongly turbulent flows ...with many degrees of freedom and large fluctuations, there would only be one turbulent state as the large fluctuations would explore the entire higher dimensional phase space. Here we report the first conclusive evidence of multiple turbulent states for large Reynolds number, Re = O(10(6)) (Taylor number Ta = O(10(12))) Taylor-Couette flow in the regime of ultimate turbulence, by probing the phase space spanned by the rotation rates of the inner and outer cylinder. The manifestation of multiple turbulent states is exemplified by providing combined global torque- and local-velocity measurements. This result verifies the notion that bifurcations can occur in high-dimensional flows (that is, very large Re) and questions Kolmogorov's paradigm.
In the Leidenfrost effect, liquid drops deposited on a hot surface levitate on a thin vapor cushion fed by evaporation of the liquid. This vapor layer forms a concave depression in the drop ...interface. Using laser-light interference coupled to high-speed imaging, we measured the radius, curvature, and height of the vapor pocket, as well as nonaxisymmetric fluctuations of the interface for water drops at different temperatures. The geometry of the vapor pocket depends primarily on the drop size and not on the substrate temperature.
A drop impacting on a solid surface deforms before the liquid makes contact with the surface. We directly measure the time evolution of the air layer profile under the droplet using high-speed color ...interferometry, obtaining the air layer thickness before and during the wetting process. Based on the time evolution of the extracted profiles obtained at multiple times, we measure the velocity of air exiting from the gap between the liquid and the solid, and account for the wetting mechanism and bubble entrapment. The present work offers a tool to accurately measure the air layer profile and quantitatively study the impact dynamics at a short time scale before impact.
We experimentally investigate the splashing mechanism of a millimeter-sized ethanol drop impinging on a structured solid surface, composed of micropillars, through side-view and top-view high-speed ...imaging. By increasing the impact velocity, we can tune the impact outcome from a gentle deposition to a violent splash, at which tiny droplets are emitted as the liquid sheet spreads laterally. We measure the splashing threshold for different micropatterns and find that the arrangement of the pillars significantly affects the splashing outcome. In particular, directional splashing in the direction in which air flows through the pattern is possible. Our top-view observations of impact dynamics reveal that entrapped air is responsible for the splashing. Indeed, by lowering the pressure of the surrounding air we show that we can suppress the splashing in the explored parameter regime.
In the unbundled national electricity markets in Europe, the balancing market is the institutional arrangement that deals with the balancing of electricity demand and supply. This paper presents a ...framework for policy makers that identifies the relevant design variables and performance criteria that play a role in the design and analysis of European balancing markets. We outline the full extent of the design challenge through a discussion of trade-offs among performance criteria, uncertain effects of design variables, and the many inter-linkages between the balancing market and the electricity market at large. Policy makers can address the balancing market design challenge by adopting a structured approach in which design variables, performance criteria, market conditions, system developments, and resultant market incentives are explicitly considered.
•A balancing market design framework shows the spectrum of variables and criteria.•The design challenge is shown by discussing trade-offs, effects and interlinkages.•We arrive at principles for policy making on electricity balancing market design.•We conclude that the framework can support a systematic design approach.
Data from the Genetic Association Information Network (GAIN) genome-wide association study (GWAS) in major depressive disorder (MDD) were used to explore previously reported candidate gene and ...single-nucleotide polymorphism (SNP) associations in MDD. A systematic literature search of candidate genes associated with MDD in case-control studies was performed before the results of the GAIN MDD study became available. Measured and imputed candidate SNPs and genes were tested in the GAIN MDD study encompassing 1738 cases and 1802 controls. Imputation was used to increase the number of SNPs from the GWAS and to improve coverage of SNPs in the candidate genes selected. Tests were carried out for individual SNPs and the entire gene using different statistical approaches, with permutation analysis as the final arbiter. In all, 78 papers reporting on 57 genes were identified, from which 92 SNPs could be mapped. In the GAIN MDD study, two SNPs were associated with MDD: C5orf20 (rs12520799; P=0.038; odds ratio (OR) AT=1.10, 95% CI 0.95-1.29; OR TT=1.21, 95% confidence interval (CI) 1.01-1.47) and NPY (rs16139; P=0.034; OR C allele=0.73, 95% CI 0.55-0.97), constituting a direct replication of previously identified SNPs. At the gene level, TNF (rs76917; OR T=1.35, 95% CI 1.13-1.63; P=0.0034) was identified as the only gene for which the association with MDD remained significant after correction for multiple testing. For SLC6A2 (norepinephrine transporter (NET)) significantly more SNPs (19 out of 100; P=0.039) than expected were associated while accounting for the linkage disequilibrium (LD) structure. Thus, we found support for involvement in MDD for only four genes. However, given the number of candidate SNPs and genes that were tested, even these significant may well be false positives. The poor replication may point to publication bias and false-positive findings in previous candidate gene studies, and may also be related to heterogeneity of the MDD phenotype as well as contextual genetic or environmental factors.
The imbalance pricing mechanism is an important design variable within European-type electricity balancing markets that determines the incentives given to so-called Balance Responsible Parties (BRPs) ...to balance their electricity production and consumption portfolio. To analyze the impact of alternative imbalance pricing mechanisms on balancing market performance, an agent-based model has been built, in which the BRPs are the agents that decide autonomously in each round on their balancing strategy based on results in past rounds. Six alternative mechanisms are analyzed. It is concluded that aiming for a small long position is generally the preferable BRP strategy. Different imbalance pricing mechanisms lead to comparable system imbalances, but single pricing results in the lowest imbalance costs for the BRPs and for the market as a whole.
► We model the impact of the imbalance pricing mechanism in balancing markets. ► The six alternative mechanisms analyzed result in different imbalance costs. ► The effect of alternative mechanisms on system imbalances is very similar. ► Single pricing leads to the lowest imbalance costs for the market. ► Balance Responsible Parties opt for small and positive individual imbalances.
Prostate cancer patients with locoregional lymph node disease at diagnosis (N1M0) still have a limited prognosis despite the improvements provided by aggressive curative intent multimodal ...locoregional external beam radiation therapy (EBRT) with systemic androgen deprivation therapy (ADT). Although some patients can be cured and the majority of patients have a long survival, the 5-year biochemical failure rate is currently 29-47%.
LuLu-PSMA-617 has shown impressive clinical and biochemical responses with low toxicity in salvage setting in metastatic castration-resistant prostate cancer. This study aims to explore the combination of standard EBRT and ADT complemented with a single administration of
LuLu-PSMA-617 in curative intent treatment for N1M0 prostate cancer. Hypothetically, this combined approach will enhance EBRT to better control macroscopic tumour localizations, and treat undetected microscopic disease locations inside and outside EBRT fields.
The PROQURE-I study is a multicenter prospective phase I study investigating standard of care treatment (7 weeks EBRT and 3 years ADT) complemented with one concurrent cycle (three, six, or nine GBq) of systemic
LuLu-PSMA-617 administered in week two of EBRT. A maximum of 18 patients with PSMA-positive N1M0 prostate cancer will be included. The tolerability of adding
LuLu-PSMA-617 will be evaluated using a Bayesian Optimal Interval (BOIN) dose-escalation design. The primary objective is to determine the maximum tolerated dose (MTD) of a single cycle
LuLu-PSMA-617 when given concurrent with EBRT + ADT, defined as the occurrence of Common Terminology Criteria for Adverse Events (CTCAE) v 5.0 grade three or higher acute toxicity. Secondary objectives include: late toxicity at 6 months, dosimetric assessment, preliminary biochemical efficacy at 6 months, quality of life questionnaires, and pharmacokinetic modelling of
LuLu-PSMA-617.
This is the first prospective study to combine EBRT and ADT with
LuLu-PSMA-617 in treatment naïve men with N1M0 prostate cancer, and thereby explores the novel application of
LuLu-PSMA-617 in curative intent treatment. It is considered likely that this study will confirm tolerability as the combined toxicity of these treatments is expected to be limited. Increased efficacy is considered likely since both individual treatments have proven high anti-tumour effect as mono-treatments.
ClinicalTrials, NCT05162573 . Registered 7 October 2021.
This study explores the predictive power of interaction terms between the risk adjusters in the Dutch risk equalization (RE) model of 2014. Due to the sophistication of this RE‐model and the ...complexity of the associations in the dataset (N = ~16.7 million), there are theoretically more than a million interaction terms. We used regression tree modelling, which has been applied rarely within the field of RE, to identify interaction terms that statistically significantly explain variation in observed expenses that is not already explained by the risk adjusters in this RE‐model. The interaction terms identified were used as additional risk adjusters in the RE‐model. We found evidence that interaction terms can improve the prediction of expenses overall and for specific groups in the population. However, the prediction of expenses for some other selective groups may deteriorate. Thus, interactions can reduce financial incentives for risk selection for some groups but may increase them for others. Furthermore, because regression trees are not robust, additional criteria are needed to decide which interaction terms should be used in practice. These criteria could be the right incentive structure for risk selection and efficiency or the opinion of medical experts.
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