Pressure fluctuations and interfacial robustness in turbulent flows over superhydrophobic surfaces

Superhydrophobic surfaces can entrap gas pockets within their grooves when submerged in water. Such a mixed-phase boundary is shown to result in an effective slip velocity on the surface, and has promising potential for drag reduction and energy-saving in hydrodynamic applications. The target flow regime, in most such applications, is a turbulent flow. Previous analyses of this problem involved direct numerical simulations of turbulence with the superhydrophobic surface modelled as a flat boundary, but with a heterogeneous mix of slip and no-slip boundary conditions corresponding to the surface texture. Analysis of the kinematic data from these simulations has helped to establish the magnitude of drag reduction for various texture topologies. The present work is the first investigation that, alongside a kinematic investigation, addresses the robustness of superhydrophobic surfaces by studying the load fields obtain from data from direct numerical simulations (DNS). The key questions at the focus of this work are: does a superhydrophobic surface induce a different pressure field compared to a flat surface? If so, how does this difference scale with system parameters, and when does it become significant that it can deform the air–water interface and potentially rapture the entrapped gas pockets? To this end, we have performed DNS of turbulent channel flows subject to superhydrophobic surfaces over a wide range of texture sizes spanning values from $L^{+}=6$ to $L^{+}=155$ when expressed in terms of viscous units. The pressure statistics at the wall are decomposed into two contributions: one coherent, caused by the stagnation of slipping flow hitting solid posts, and one time-dependent, caused by overlying turbulence. The results show that the larger texture size intensifies the contribution of stagnation pressure, while the contribution from turbulence is essentially insensitive to $L^{+}$. The two-dimensional stagnation pressure distribution at the wall and the pressure statistics in the wall-normal direction are found to be self-similar for different $L^{+}$. The scaling of the induced pressure and the consequent deformations of the air–water interface are analysed. Based on our results, an upper bound on the texture wavelength is quantified that limits the range of robust operation of superhydrophobic surfaces when exposed to high-speed flows. Our results indicate that when the system parameters are expressed in terms of viscous units, the main parameters controlling the problem are $L^{+}$ and a Weber number based on inner dimensions; We obtain good collapse when all our results are expressed in wall units, independently of the Reynolds number.This work was supported by the Office of Naval Research under grant 3002451214. The authors greatly appreciate the Kwanjeong Educational Foundation for the funding support for Jongmin Seo.This is the author accepted manuscript. The final version is available from Cambridge University Press via http://dx.doi.org/10.1017/jfm.2015.57

Recent transformation of intertidal environments under a sea-level rise scenario: Examples from northern Spain

The transformation of two intertidal environments from northern Spain during the last 150 years shows an evolution from a tidal flat into a salt marsh environment, with an intermediate transitional stage. The environment of deposition was reconstructed based on benthic foraminifera and sand content. Sediments were put into a temporal framework using short-lived radioisotope activities and heavy metal concentrations. The observed natural evolution responds to the availability of abundant sediment and the current sea-level rise scenario, where intertidal environments are trying to adapt to increasing flooding periods by accreting sediment rapidly. © 2019 Sociedad Geologica de Espana. All rights reserved.This research was funded by the Mi nistry of Economy and Competitiveness of Spain (CGL2013-41083-P), the University of the Basque Country UPV/EHU (UFI11/09), and the Basque Government (IT976-16). Ane García-Artola was funded by the Basque Government (BFI08.180). Miriam Torrontegui Aguado carried out the micropalaeontological analysis of the PR core and Eduardo Leorri (East Carolina University, USA) helped in the field. We thank Juan Usera (Universitat de Valèn-cia), an anonymous reviewer, and Manuel Díaz Azpiroz (Assistant Editor) for their valuable comments. This work represents contribution #29 of the Geo-Q Zentroa Research Unit (Joaquín Gómez de Llarena Laboratory)

Metallic spin-glasses beyond mean-field: An approach to the impurity-concentration dependence of the freezing temperature

A relation between the freezing temperature ($T^{}_{\rm g}$) and the exchange couplings ($J^{}_{ij}$) in metallic spin-glasses is derived, taking the spin-correlations ($G^{}_{ij}$) into account. This approach does not involve a disorder-average. The expansion of the correlations to first order in $J^{}_{ij}/T^{}_{\rm g}$ leads to the molecular-field result from Thouless-Anderson-Palmer. Employing the current theory of the spin-interaction in disordered metals, an equation for $T^{}_{\rm g}$ as a function of the concentration of impurities is obtained, which reproduces the available data from {\sl Au}Fe, {\sl Ag}Mn, and {\sl Cu}Mn alloys well.Comment: 4 figures. This is a strongly revised version, where several aspects have been improved, and the equation for the freezing temperature has been refined. It is equivalent to the published version in J. Phys.: Condens. Matter 25 (2013) 13600

Higher order Jordan Osserman Pseudo-Riemannian manifolds

We study the higher order Jacobi operator in pseudo-Riemannian geometry. We exhibit a family of manifolds so that this operator has constant Jordan normal form on the Grassmannian of subspaces of signature (r,s) for certain values of (r,s). These pseudo-Riemannian manifolds are new and non-trivial examples of higher order Osserman manifolds

Elemental Abundances of Kepler Objects of Interest in APOGEE. I. Two Distinct Orbital Period Regimes Inferred from Host Star Iron Abundances

The Apache Point Observatory Galactic Evolution Experiment (APOGEE) has observed $\sim$600 transiting exoplanets and exoplanet candidates from \textit{Kepler} (Kepler Objects of Interest, KOIs), most with $\geq$18 epochs. The combined multi-epoch spectra are of high signal-to-noise (typically $\geq$100) and yield precise stellar parameters and chemical abundances. We first confirm the ability of the APOGEE abundance pipeline, ASPCAP, to derive reliable [Fe/H] and effective temperatures for FGK dwarf stars -- the primary \textit{Kepler} host stellar type -- by comparing the ASPCAP-derived stellar parameters to those from independent high-resolution spectroscopic characterizations for 221 dwarf stars in the literature. With a sample of 282 close-in ($P<100$ days) KOIs observed in the APOGEE KOI goal program, we find a correlation between orbital period and host star [Fe/H] characterized by a critical period, $P_\mathrm{crit}$= $8.3^{+0.1}_{-4.1}$ days, below which small exoplanets orbit statistically more metal-enriched host stars. This effect may trace a metallicity dependence of the protoplanetary disk inner-radius at the time of planet formation or may be a result of rocky planet ingestion driven by inward planetary migration. We also consider that this may trace a metallicity dependence of the dust sublimation radius, but find no statistically significant correlation with host $T_\mathrm{eff}$ and orbital period to support such a claim.Comment: 18 Pages, Accepted to A

The post-common-envelope binary central star of the planetary nebula PN G283.7-05.1

We present the discovery and characterisation of the post-common-envelope central star system in the planetary nebula PN G283.7-05.1. Deep images taken as part of the POPIPlaN survey indicate that the nebula may possess a bipolar morphology similar to other post-common-envelope planetary nebulae. Simultaneous light and radial velocity curve modelling reveals that the newly discovered binary system comprises a highly irradiated M-type main-sequence star in a 5.9-hour orbit with a hot pre-white dwarf. The nebular progenitor is found to have a particularly low mass of around 0.4 M, making PN G283.7-05.1 one of only a handful of candidate planetary nebulae that is the product of a common-envelope event while still on the red giant branch. In addition to its low mass, the model temperature, surface gravity, and luminosity are all found to be consistent with the observed stellar and nebular spectra through comparison with model atmospheres and photoionisation modelling. However, the high temperature (Teff ∼ 95 kK) and high luminosity of the central star of the nebula are not consistent with post-RGB evolutionary tracks

The minimal-span channel for rough-wall turbulent flows

Roughness predominantly alters the near-wall region of turbulent flow while the outer layer remains similar with respect to the wall shear stress. This makes it a prime candidate for the minimal-span channel, which only captures the near-wall flow by restricting the spanwise channel width to be of the order of a few hundred viscous units. Recently, Chung et al. (J. Fluid Mech., vol. 773, 2015, pp. 418-431) showed that a minimal-span channel can accurately characterise the hydraulic behaviour of roughness. Following this, we aim to investigate the fundamental dynamics of the minimal-span channel framework with an eye towards further improving performance. The streamwise domain length of the channel is investigated with the minimum length found to be three times the spanwise width or 1000 viscous units, whichever is longer. The outer layer of the minimal channel is inherently unphysical and as such alterations to it can be performed so long as the near-wall flow, which is the same as in a full-span channel, remains unchanged. Firstly, a half-height (open) channel with slip wall is shown to reproduce the near-wall behaviour seen in a standard channel, but with half the number of grid points. Next, a forcing model is introduced into the outer layer of a half-height channel. This reduces the high streamwise velocity associated with the minimal channel and allows for a larger computational time step. Finally, an investigation is conducted to see if varying the roughness Reynolds number with time is a feasible method for obtaining the full hydraulic behaviour of a rough surface. Currently, multiple steady simulations at fixed roughness Reynolds numbers are needed to obtain this behaviour. The results indicate that the non-dimensional pressure gradient parameter must be kept below 0.03-0.07 to ensure that pressure gradient effects do not lead to an inaccurate roughness function. An empirical costing argument is developed to determine the cost in terms of CPU hours of minimal-span channel simulations a priori. This argument involves counting the number of eddy lifespans in the channel, which is then related to the statistical uncertainty of the streamwise velocity. For a given statistical uncertainty in the roughness function, this can then be used to determine the simulation run time. Following this, a finite-volume code with a body-fitted grid is used to determine the roughness function for square-based pyramids using the above insights. Comparisons to experimental studies for the same roughness geometry are made and good agreement is observed.This work was partly funded through the Multi ow program by the European Research Council. Computational time was granted under the Victoria Life Sciences Computational Initiative, which is supported by the Victorian Government, Australia

Photoprotective compounds as early markers to predict holm oak crown defoliation in declining Mediterranean savannahs

This research was mainly funded by the Spanish Government through the IBERYCA project (CGL2017-84723-P) and its associated FPI scholarship BES-2014-067971 (to M.E.-V.). It was further supported by the BC3 María de Maeztu excellence accreditation (MDM-2017-0714; the Spanish Government) and by the BERC 2018-2021 and the UPV/EHU-GV IT-1018-16 program (Basque Government). Additionally, this research was further supported through the ‘Juan de la Cierva program’ (the Spanish Government to M.V.; (IJCI-2017-34640).) and two projects funded by the Romanian Ministry of Education and Research through UEFISCDI (NATIvE, PN-III-P1-1.1-PD- 2016-0583 and REASONING, PN-III-P1-1.1-TE-2019-1099 to A.-M.H.)

Current practices and challenges in adaptation of clinical guidelines : A qualitative study based on semistructured interviews

Funding YS is funded by China Scholarship Council (No 201707040103).Altres ajuts: CSC/201707040103Objective This study aims to better understand the current practice of clinical guideline adaptation and identify challenges raised in this process, given that published adapted clinical guidelines are generally of low quality, poorly reported and not based on published frameworks. Design A qualitative study based on semistructured interviews. We conducted a framework analysis for the adaptation process, and thematic analysis for participants' views and experiences about adaptation process. Setting Nine guideline development organisations from seven countries. Participants Guideline developers who have adapted clinical guidelines within the last 3 years. We identified potential participants through published adapted clinical guidelines, recommendations from experts, and a review of the Guideline International Network Conference attendees' list. Results We conducted ten interviews and identified nine adaptation methodologies. The reasons for adapting clinical guidelines include developing de novo clinical guidelines, implementing source clinical guidelines, and harmonising and updating existing clinical guidelines. We identified the following core steps of the adaptation process (1) selection of scope and source guideline(s), (2) assessment of source materials (guidelines, recommendations and evidence level), (3) decision-making process and (4) external review and follow-up process. Challenges on the adaptation of clinical guidelines include limitations from source clinical guidelines (poor quality or reporting), limitations from adaptation settings (lacking resources or skills), adaptation process intensity and complexity, and implementation barriers. We also described how participants address the complexities and implementation issues of the adaptation process. Conclusions Adaptation processes have been increasingly used to develop clinical guidelines, with the emergence of different purposes. The identification of core steps and assessment levels could help guideline adaptation developers streamline their processes. More methodological research is needed to develop rigorous international standards for adapting clinical guidelines

Electrically-driven phase transition in magnetite nanostructures

Magnetite (Fe$_{3}$O$_{4}$), an archetypal transition metal oxide, has been used for thousands of years, from lodestones in primitive compasses[1] to a candidate material for magnetoelectronic devices.[2] In 1939 Verwey[3] found that bulk magnetite undergoes a transition at T$_{V}$ $\approx$ 120 K from a high temperature "bad metal" conducting phase to a low-temperature insulating phase. He suggested[4] that high temperature conduction is via the fluctuating and correlated valences of the octahedral iron atoms, and that the transition is the onset of charge ordering upon cooling. The Verwey transition mechanism and the question of charge ordering remain highly controversial.[5-11] Here we show that magnetite nanocrystals and single-crystal thin films exhibit an electrically driven phase transition below the Verwey temperature. The signature of this transition is the onset of sharp conductance switching in high electric fields, hysteretic in voltage. We demonstrate that this transition is not due to local heating, but instead is due to the breakdown of the correlated insulating state when driven out of equilibrium by electrical bias. We anticipate that further studies of this newly observed transition and its low-temperature conducting phase will shed light on how charge ordering and vibrational degrees of freedom determine the ground state of this important compound.Comment: 17 pages, 4 figure