Bubbly Turbulent Drag Reduction Is a Boundary Layer Effect

In turbulent Taylor-Couette flow, the injection of bubbles reduces the overall drag. On the other hand, rough walls enhance the overall drag. In this work, we inject bubbles into turbulent Taylor-Couette flow with rough walls (with a Reynolds number up to 4×105), finding an enhancement of the dimensionless drag as compared to the case without bubbles. The dimensional drag is unchanged. As in the rough-wall case no smooth boundary layers can develop, the results demonstrate that bubbly drag reduction is a pure boundary layer effec

Challenges to the implementation of fiscal sustainability measures

Purpose: Fiscal sustainability is high on the global political agenda. Yet, implementing the needed performance-orientation throughout public-sector organizations remains problematic. Such implementation seems to run counter to deep-seated social structures. In this paper the aim is to shed light via key change agents' views on these social structures at the management level during the implementation of a performance-based budgeting scheme. Design/methodology/approach: The authors analyzed documentary data and conducted in-depth, semi-structured interviews with key change agents operative within central government ministries in The Netherlands. The data were analyzed using a structurational approach to identify the enablers and barriers to performance-based budgeting implementation. Findings: In total, 29 social enablers and barriers to performance-based budgeting implementation were derived. These were categorized into: Context, Autonomy, Traditional beliefs, Influence on results, and Top management support. Based on these categories five propositions were developed on how social structures enable and constrain performance-based budgeting implementation among public managers. Research limitations/implications: The study was executed in one country in a specific period in time. Although the problems with performance-based budgeting exist over the globe, research is needed to study whether similar social structures enable and impede implementation. Social implications: Policy makers and change agents aiming to improve fiscal sustainability by budgeting reform need to consider the found social structures. Where possible they could strengthen enablers and design specific comprehensive measures to tackle the barriers identified. Originality/value: This paper provides insight and develops knowledge on the social structures that enable and constrain performance-based budgeting, which in turn improves fiscal sustainability

Catalytic reforming of glycerol in supercritical water over bimetallic Pt-Ni catalyst

Catalytic reforming of pure glycerol for the production of hydrogen at low temperature and short residence times in supercritical water was investigated using a bimetallic Pt–Ni catalyst supported on alumina. Initial tests were carried out to study the reforming activity of bimetallic Pt–Ni catalysts by reforming different model compounds having different carbon numbers in supercritical water at 400–450 °C. The influence of different operating parameters such as reaction temperature, initial feed concentration, location of the catalyst bed, and weight hourly space velocity on the carbon to gas conversion and product gas distribution is studied. Continuous experiments were carried out using a fixed bed reactor for a temperature range of 380–500 °C, feed concentrations of up to 20 wt %, at space velocities of up to 45 h–1. The product gas mainly consisted of CO2, H2 and alkanes (CH4 and C2H6) and the liquid effluent after the reaction primarily consisted of unconverted glycerol, 1,2-propanediol, and ethanol, with trace amounts of acetaldehyde, ethanol, and 1,3-propanediol. A comparison of the reforming activity of the catalyst and process with respect to the feedstock characteristics was made by comparing the carbon to gas conversion and product distribution for pure and crude glycerol. The carbon to gas conversion and the product gas distribution of pure and crude glycerol are comparable. Complete conversion of 15 wt % (pure) glycerol in water to gaseous products was achieved at 450–500 °C and the product gas mainly consisted of H2, CO2, and CH4. However, whereas the catalyst deactivated rapidly with crude glycerol, for pure glycerol the catalyst showed stable performance for a long duration run up to 85 h, indicating that catalyst deactivation by for example, coke formation in the gasification reaction system is not a major issue. It is anticipated that with a proper catalyst support material, the gasification of concentrated aqueous glycerol streams can be developed into a viable proces

Applying Laser Doppler Anemometry inside a Taylor-Couette geometry - Using a ray-tracer to correct for curvature effects

In the present work it will be shown how the curvature of the outer cylinder affects Laser Doppler anemometry measurements inside a Taylor-Couette apparatus. The measurement position and the measured velocity are altered by curved surfaces. Conventional methods for curvature correction are not applicable to our setup, and it will be shown how a ray-tracer can be used to solve this complication. By using a ray-tracer the focal position can be calculated, and the velocity can be corrected. The results of the ray-tracer are verified by measuring an a priori known velocity field, and after applying refractive corrections good agreement with theoretical predictions are found. The methods described in this paper are applied to measure the azimuthal velocity profiles in high Reynolds number Taylor-Couette flow for the case of outer cylinder rotation

Tunneling and propagation of vacuum bubbles on dynamical backgrounds

In the context of bubble universes produced by a first-order phase transition with large nucleation rates compared to the inverse dynamical time scale of the parent bubble, we extend the usual analysis to non-vacuum backgrounds. In particular, we provide semi-analytic and numerical results for the modified nucleation rate in FLRW backgrounds, as well as a parameter study of bubble walls propagating into inhomogeneous (LTB) or FLRW spacetimes, both in the thin-wall approximation. We show that in our model, matter in the background often prevents bubbles from successful expansion and forces them to collapse. For cases where they do expand, we give arguments why the effects on the interior spacetime are small for a wide range of reasonable parameters and discuss the limitations of the employed approximations.Comment: 29 pages, 8 figures, typos corrected, matches published versio

Residual quadrupolar couplings observed in 7 Tesla deuterium MR spectra of skeletal muscle

Purpose: Deuterium metabolic imaging could potentially be used to investigate metabolism in skeletal muscle noninvasively. However, skeletal muscle is a tissue with a high degree of spatial organization. In this study, we investigated the effect of incomplete motional averaging on the naturally abundant deuterated water signal in 7 Tesla deuterium spectra of the lower leg muscles and the dependence on the angle between the muscle fibers and the main magnetic field B0, as determined by DTI. Methods: Natural abundance deuterium MRSI measurements of the right lower leg muscles were performed at 7 Tesla. Three subjects were scanned in a supine position, with the right leg parallel with the B0 field. One subject was scanned twice; during the second scan, the subject was laying on his right side and the right knee was bent such that the angle between the right lower leg and B0 was approximately 45°. DTI was performed in the same subjects in the same positions at 3 Tesla to determine muscle fiber angles. Results: We observed splittings in the natural abundance deuterated water signal. The size of the splittings varied between different muscles in the lower leg but were mostly similar among subjects for each muscle. The splittings depended on the orientation of the muscle fibers with respect to the main magnetic field B0. Conclusion: Partial molecular alignment in skeletal muscle leads to residual deuteron quadrupolar couplings in deuterated water, the size of which depends on the angle between the muscle fibers and B0

DEcreased Cognitive functiON, NEurovascular CorrelaTes and myocardial changes in women with a history of pre-eclampsia (DECONNECT):research protocol for a cross-sectional pilot study

Introduction Pre-eclampsia is a hypertensive disorder affecting up to 8% of pregnancies. After pre-eclampsia, women are at increased risk of cognitive problems, and cerebrovascular and cardiovascular disorders. These sequelae could result from microvascular dysfunction persisting after pre-eclampsia. This study will explore differences in cerebral and myocardial microvascular function between women after pre-eclampsia and women after normotensive gestation. We hypothesise that pre-eclampsia alters cerebral and myocardial microvascular functions, which in turn are related to diminished cognitive and cardiac performance. Methods and analysis The cross-sectional € DEcreased Cognitive functiON, NEurovascular CorrelaTes and myocardial changes in women with a history of pre-eclampsia' (DECONNECT) pilot study includes women after pre-eclampsia and controls after normotensive pregnancy between 6 months and 20 years after gestation. We recruit women from the Queen of Hearts study, a study investigating subclinical heart failure after pre-eclampsia. Neuropsychological tests are employed to assess different cognitive domains, including attention, processing speed, and cognitive control. Cerebral images are recorded using a 7 Tesla MRI to assess blood-brain barrier integrity, perfusion, blood flow, functional and structural networks, and anatomical dimensions. Cardiac images are recorded using a 3 Tesla MRI to assess cardiac perfusion, strain, dimensions, mass, and degree of fibrosis. We assess the effect of a history of pre-eclampsia using multivariable regression analyses. Ethics and dissemination This study is approved by the Ethics Committee of Maastricht University Medical Centre (METC azM/UM, NL47252.068.14). Knowledge dissemination will include scientific publications, presentations at conferences and public forums, and social media. Trial registration number NCT02347540.</p

Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at sqrt(s) = 7 TeV with the ATLAS experiment

This paper describes an analysis of the angular distribution of W->enu and W->munu decays, using data from pp collisions at sqrt(s) = 7 TeV recorded with the ATLAS detector at the LHC in 2010, corresponding to an integrated luminosity of about 35 pb^-1. Using the decay lepton transverse momentum and the missing transverse energy, the W decay angular distribution projected onto the transverse plane is obtained and analysed in terms of helicity fractions f0, fL and fR over two ranges of W transverse momentum (ptw): 35 < ptw < 50 GeV and ptw > 50 GeV. Good agreement is found with theoretical predictions. For ptw > 50 GeV, the values of f0 and fL-fR, averaged over charge and lepton flavour, are measured to be : f0 = 0.127 +/- 0.030 +/- 0.108 and fL-fR = 0.252 +/- 0.017 +/- 0.030, where the first uncertainties are statistical, and the second include all systematic effects.Comment: 19 pages plus author list (34 pages total), 9 figures, 11 tables, revised author list, matches European Journal of Physics C versio

Observation of a new chi_b state in radiative transitions to Upsilon(1S) and Upsilon(2S) at ATLAS

The chi_b(nP) quarkonium states are produced in proton-proton collisions at the Large Hadron Collider (LHC) at sqrt(s) = 7 TeV and recorded by the ATLAS detector. Using a data sample corresponding to an integrated luminosity of 4.4 fb^-1, these states are reconstructed through their radiative decays to Upsilon(1S,2S) with Upsilon->mu+mu-. In addition to the mass peaks corresponding to the decay modes chi_b(1P,2P)->Upsilon(1S)gamma, a new structure centered at a mass of 10.530+/-0.005 (stat.)+/-0.009 (syst.) GeV is also observed, in both the Upsilon(1S)gamma and Upsilon(2S)gamma decay modes. This is interpreted as the chi_b(3P) system.Comment: 5 pages plus author list (18 pages total), 2 figures, 1 table, corrected author list, matches final version in Physical Review Letter