The interaction between a turbulent boundary layer flow and compliant surfaces is investigated experimentally. Three viscoelastic coatings with different material stiffnesses are used to identify the ...general surface response to the turbulent flow conditions. For the softest coating, the global force measurements show two obvious regimes of interaction with an indicated transition at $U_b/C_t\sim 3.5$, where $U_b$ is the bulk flow velocity and $C_t$ is the coating shear velocity. The one-way coupled regime shows friction values comparable to those of the rigid wall, while the two-way coupled regime indicate a significant increase in fluid friction. Within the one-way coupled regime for $U_b/C_t>1.2$, the flow measurements show a low level of two-way coupling represented by the change of the velocity profile as well as the increase in the Reynolds stresses in the near-wall region. This is supported by the surface deformation measurements. Initially, the turbulent flow structures induce only an imprint on the coating surface, while a change in surface response occurs when the surface wave propagation velocity $c_w$ equals the shear wave velocity of the coating $C_t$ (i.e. $c_w/C_t\sim 1$). Above $U_b/C_t>1.2$, a growth in wavelength is observed with increasing flow velocity, most probably due to the surface wave formation generated downstream the pressure features of the flow. The surface response is stable and correlates with the high-intensity turbulent pressure fluctuations in the turbulent boundary layer, with a wave propagation velocity $c_w\sim 0.7\unicode{x2013}0.8$ $U_b$. Within the two-way coupled regime, additional fluid motions and a downward shift in the logarithmic region of the velocity profile are observed due to substantial surface deformation and confirm the frictional drag increase. Another type of surface response is initiated by phase-lag instability in combination with surface undulations that start to protrude the viscous sublayer, where the propagation velocity of surface wave trains is $c_w\sim 0.17\unicode{x2013}0.18$ $U_b$.
Open cluster kinematics with Gaia DR2 Soubiran, C.; Cantat-Gaudin, T.; Romero-Gómez, M. ...
Astronomy and astrophysics (Berlin),
11/2018, Letnik:
619
Journal Article
Recenzirano
Odprti dostop
Context. Open clusters are very good tracers of the evolution of the Galactic disc. Thanks to Gaia, their kinematics can be investigated with an unprecedented precision and accuracy. Aims. The ...distribution of open clusters in the 6D phase space is revisited with Gaia DR2. Methods. The weighted mean radial velocity of open clusters was determined, using the most probable members available from a previous astrometric investigation that also provided mean parallaxes and proper motions. Those parameters, all derived from Gaia DR2 only, were combined to provide the 6D phase-space information of 861 clusters. The velocity distribution of nearby clusters was investigated, as well as the spatial and velocity distributions of the whole sample as a function of age. A high-quality subsample was used to investigate some possible pairs and groups of clusters sharing the same Galactic position and velocity. Results. For the high-quality sample of 406 clusters, the median uncertainty of the weighted mean radial velocity is 0.5 km s−1. The accuracy, assessed by comparison to ground-based high-resolution spectroscopy, is better than 1 km s−1. Open clusters nicely follow the velocity distribution of field stars in the close solar neighbourhood as previously revealed by Gaia DR2. As expected, the vertical distribution of young clusters is very flat, but the novelty is the high precision to which this can be seen. The dispersion of vertical velocities of young clusters is at the level of 5 km s−1. Clusters older than 1 Gyr span distances to the Galactic plane of up to 1 kpc with a vertical velocity dispersion of 14 km s−1, typical of the thin disc. Five pairs of clusters and one group with five members might be physically related. Other binary candidates that have been identified previously are found to be chance alignments.
Sound velocity errors often lead to distortion of seafloor topography in multibeam bathymetric data processing. The current method of sound velocity profile (SVP) inversion has the problems of small ...application scope of the inversed equivalent sound velocity profile (ESVP) and terrain distortion calculated by inversed SVP under the condition of water depth consistency constraint in overlapping line area. In this paper, we propose a method of SVP inversion using the Empirical Orthogonal Function (EOF) and Differential Evolution (DE) algorithm. Firstly, EOF is used to decompose the SVP matrix, then the water depth discrepancy between the check line and the main survey line is used as the objective function instead of the discrepancy of overlapping line area, and DE is used to find the optimal time coefficient, and finally, the SVP is reconstructed to correct the seabed topography. The method was verified by experiments in shallow and mid-deep water, and the mean absolute and standard deviation of the corrected bathymetric discrepancy values are about 50% of those before correction.
Introduction: Growth impairment is a known adverse event (AE) of corticosteroids in children. This study aimed to assess the effect of once‐daily (QD) inhaled fluticasone furoate (FF) versus placebo ...on growth velocity over 1 year in prepubertal children with well‐controlled asthma.Materials and Methods: This randomized, double‐blind, parallel‐group, placebo‐controlled, multicenter study (NCT02889809) included prepubertal children, aged 5 to <9 years (boys), and 5 to <8 years (girls), with ≥6 months' asthma history. Children received inhaled placebo QD plus background open‐label montelukast QD for a 16‐week run‐in period and were then randomized 1:1 to receive inhaled FF 50 μg QD or placebo QD (whilst continuing background open‐label montelukast) for a 52‐week treatment period. The primary endpoint was the difference in growth velocity (cm/year) over the treatment period. Other growth endpoints were measured, as were incidence of AEs and asthma exacerbation. Growth analyses included all intent‐to‐treat (ITT) participants with ≥3 post‐randomization, on‐treatment clinic visit height assessments (GROWTH population).Results: Of 644 children in the run‐in period, 477 (mean age 6.2 years, 63% male) entered the 52‐week treatment period (ITT population: FF N = 238, placebo N = 239; GROWTH population: N = 457 FF N = 231; placebo N = 226). The least‐squares mean difference in growth velocity for FF versus placebo was –0.160 cm/year (95% confidence interval: –0.462, 0.142). There were no new safety signals.Conclusions: Over 1 year, FF 50 μg QD had a minimal effect on growth velocity versus placebo, with no new safety signals.
This study evaluated the velocity-selective (VS) MRA with different VS labeling modules, including double refocused hyperbolic tangent, eight-segment B1-insensitive rotation, delay alternating with ...nutation for tailored excitation, Fourier transform-based VS saturation, and Fourier transform-based inversion.
These five VS labeling modules were evaluated first through Bloch simulations, and then using VSMRA directly on various cerebral arteries of healthy subjects. The relative signal ratios from arterial ROIs and surrounding tissues as well as relative arteria-tissue contrast ratios of different methods were compared.
Double refocused hyperbolic tangent and eight-segment B1-insensitive rotation showed very similar labeling effects. Delay alternating with nutation for tailored excitation yielded high arterial signal but with residual tissue signal due to the spatial banding effect. Fourier transform-based VS saturation with half the time of other techniques serves as an efficient nonsubtractive VSMRA method, but the remaining tissue signal still obscured some small distal arteries that were delineated by other subtraction-based VSMRA, allowing more complete cancelation of static tissue. Fourier transform-based inversion produced the highest arterial signal in VSMRA with minimal tissue background.
This is the first study that angiographically compared five different VS labeling modules. Their labeling characteristics on arteries and tissue and implications for VSMRA and VS arterial spin labeling are discussed.
Understanding the motion of particles in very dense granular flows is crucial for comprehending the dynamics of many geological phenomena, and advancing our knowledge of granular material physics. We ...conduct transparent ring shear experiments to directly observe the granular motion under relatively high‐pressure conditions, and find that the granular velocity non‐linearly decays, forming an approximately 7‐particle‐diameter‐thick localized shear band. A fitting curve underlying non‐local physics can be used to well predict velocity profile geometries that are almost independent of normal stress and shear velocity. Moreover, experimental results show monotonically decreasing granular kinetic temperature, which may be caused by energy dissipation due to more inelastic contacts under high confining pressures. The variation of granular temperature will significantly influence the local yield stress and rheological properties, which may lead to inhomogeneous fluidity of the material and thus to shear localization in very dense granular flows.
Plain Language Summary
Understanding how particles move under high pressure is essential for studying various geological phenomena and advancing our understanding of granular material physics. In this study, transparent ring shear experiments are conducted to observe the motion of granular particles in very dense granular flows under high normal stress. It is found that the velocity distribution progressively decays and forms a shear band with a width of approximately 7 particle diameters. We suggest an equation that can well predict the velocity profile both of the quasi‐linear velocity in the fast‐moving shear zone and the exponential velocity curve in the slow‐motion region. Furthermore, we analyze the distribution of particle velocity fluctuation and particle density across the sample. Near the moving plate, the particle velocity fluctuation is more intense and the particle density is lower, gradually decreasing far from the moving plate. This phenomenon may be caused by energy dissipation due to inelastic contact between particles. The mechanical properties of the granular material are influenced by these variations in velocity fluctuation and particle density. Thus, this leads to an inhomogeneous shear strain rate and promotes the formation of shear zones under relatively high‐pressure conditions.
Key Points
A nonlinearly decayed velocity profile and spontaneous shear localization are observed in plane shear granular flows under high normal stress
The monotonically decayed granular temperature may lead to inhomogeneities in very dense granular flows and thus to shear localization
The length scale of the non‐local model in very dense granular flows is estimated based on experimental observation
Abstract
The roughness property of rocks is significant in engineering studies due to their mechanical and hydraulic performance and the possibility of quantifying flow velocity and predicting the ...performance of wells and rock mass structures. However, the study of roughness in rocks is usually carried out through 2D linear measurements (through mechanical profilometer equipment), obtaining a coefficient that may not represent the entire rock surface. Thus, based on the hypothesis that it is possible to quantify the roughness coefficient in rock plugs reconstructed three-dimensionally by the computer vision technique, this research aims to an alternative method to determine the roughness coefficient in rock plugs. The point cloud generated from the 3D model of the photogrammetry process was used to measure the distance between each point and a calculated fit plane over the entire rock surface. The roughness was quantified using roughness parameters (
$$R_a$$
R
a
) calculated in hierarchically organized regions. In this hierarchical division, the greater the quantity of division analyzed, the greater the detail of the roughness. The main results show that obtaining the roughness coefficient over the entire surface of the three-dimensional model has peculiarities that would not be observed in the two-dimensional reading. From the 2D measurements, mean roughness values (
$$R_a$$
R
a
) of
$$0.35\,\upmu \hbox {m}$$
0.35
μ
m
and
$$0.235\,\upmu \hbox {m}$$
0.235
μ
m
were obtained for samples 1 and 2, respectively. By the same method, the results of the
$$R_a$$
R
a
coefficient applied three-dimensionally over the entire rocky surface were at most
$$0.165\,\upmu \hbox {m}$$
0.165
μ
m
and
$$0.166\,\upmu \hbox {m}$$
0.166
μ
m
, respectively, showing the difference in values along the surface and the importance of this approach.
Surface waves are widely used in near-surface geophysics and provide a noninvasive way to determine near-surface structures. By extracting and inverting dispersion curves to obtain local 1D S-wave ...velocity profiles, multichannel analysis of surface waves (MASW) has been proven as an efficient way to analyze shallow-seismic surface waves. By directly inverting the observed waveforms, full-waveform inversion (FWI) provides another feasible way to use surface waves in reconstructing near-surface structures. This paper provides a state of the art review of MASW and shallow-seismic FWI and a comparison of both methods. A two-parameter numerical test is performed to analyze the nonlinearity of MASW and FWI, including the classical, the multiscale, the envelope-based, and the amplitude-spectrum-based FWI approaches. A checkerboard model is used to compare the resolution of MASW and FWI. These numerical examples show that classical FWI has the highest nonlinearity and resolution among these methods, while MASW has the lowest nonlinearity and resolution. The modified FWI approaches have an intermediate nonlinearity and resolution between classical FWI and MASW. These features suggest that a sequential application of MASW and FWI could provide an efficient hierarchical way to delineate near-surface structures. We apply the sequential-inversion strategy to two field data sets acquired in Olathe, Kansas, USA, and Rheinstetten, Germany, respectively. We build a 1D initial model by using MASW and then apply the multiscale FWI to the data. High-resolution 2D S-wave velocity images are obtained in both cases, whose reliabilities are proven by borehole data and a GPR profile, respectively. It demonstrates the effectiveness of combining MASW and FWI for high-resolution imaging of near-surface structures.
Continuous monitoring of blood pressure, an essential measure of health status, typically requires complex, costly, and invasive techniques that can expose patients to risks of complications. ...Continuous, cuffless, and noninvasive blood pressure monitoring methods that correlate measured pulse wave velocity (PWV) to the blood pressure via the Moens–Korteweg (MK) and Hughes Equations, offer promising alternatives. The MK Equation, however, involves two assumptions that do not hold for human arteries, and the Hughes Equation is empirical, without any theoretical basis. The results presented here establish a relation between the blood pressure P and PWV that does not rely on the Hughes Equation nor on the assumptions used in the MK Equation. This relation degenerates to the MK Equation under extremely low blood pressures, and it accurately captures the results of in vitro experiments using artificial blood vessels at comparatively high pressures. For human arteries, which are well characterized by the Fung hyperelastic model, a simple formula between P and PWV is established within the range of human blood pressures. This formula is validated by literature data as well as by experiments on human subjects, with applicability in the determination of blood pressure from PWV in continuous, cuffless, and noninvasive blood pressure monitoring systems.
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