Roles of gas in capillary filling of nanoslits

Control and understanding of flows inside fabricated nanochannels is rich in potential applications, but nanoscale physics of fluids remains to be clarified even for the simple case of spontaneous capillary filling. This paper reports an experimental and modelling investigation of the role of gas on the capillary filling kinetics slowdown in nanoslits (depth going from 20 nm to 400 nm) compared to Washburn's prediction. First, the role of gas through the usually observed trapped bubbles during a nanoslits capillary filling is analysed thanks to experiments realized with water, ethanol and silicone oil in siliconglass nanochannels. Bubbles are trapped only when slit depth is below a liquid-dependent threshold. This is interpreted as possible contact line pinning strength varying with wettability. Stagnant trapped bubbles lifetime is investigated for the three liquids used. Experimental results show that bubbles are first compressed because of the increasing local liquid pressure. Once the gas bubble pressure is sufficiently high, gas dissolution induces the final bubble collapse. Influence of the bubbles' presence on the capillary filling kinetics is analysed by estimating viscous resistance induced by the bubbles using an effective medium approach (Brinkman approximation). Surprisingly, the bubbles' presence is found to have a very minor effect on nanoslits capillary filling kinetics. Second, the transient gas pressure profile between the advancing meniscus and the channel exit is computed numerically taking into account gas compressibility. A non-negligible over-pressure ahead of the meniscus is found for nano-scale slit capillary filling. Considering the possible presence of precursor films, reducing cross-section for gas flow, leads to a capillary filling kinetics slowdown comparable to the ones measured experimentally

Deep Learning for scalp High Frequency Oscillations Identification

Since last 2 decades, High Frequency Oscillations (HFOs) are studied as a promising biomarker to localize the epileptogenic zone of patients with refractory focal epilepsy. As HFOs visual detection is time consuming and subjective, automatization of HFO detection is required. Most HFO detectors were developed on invasive electroencephalograms (iEEG) whereas scalp electroencephalograms (EEG) are used in clinical routine. In order HFO detection can benefit to more patients, scalp HFO detectors has to be developed. However, HFOs identification in scalp EEG is more challenging than in iEEG since scalp HFOs are of lower rate, lower amplitude and more likely to be corrupted by several sources of artifacts than iEEG HFOs. The main goal of this study is to explore the ability of deep learning architecture to identify scalp HFOs from the remaining EEG signal. Hence, a binary classification Convolutional Neural Network (CNN) is learned to analyze High Density Electroencephalograms (HD-EEG). EEG signals are first mapped into a 2D time-frequency image, several color definitions are then used as an input for the CNN. Experimental results show that deep learning allows simple end-to-end learning of preprocessing, feature extraction and classification modules while reaching competitive performance

Attenuating through Aid the Vulnerability to Price Shocks

The purpose of this paper is to examine what kind of global measures may be efficiently implemented to help the developing countries to face price shocks, avoiding the past failures, which needs to take into account the long term trend of the markets. Firstly, we recall the nature of the vulnerability to price shocks: this legitimates to make the dampening of these shocks a reasonable goal for the development cooperation policy. Then, we consider the rationality of some international schemes of insurance or of guarantee which could be implemented through international assistance for countries facing price shocks: this assistance should be provided on a macroeconomic level, in particular through debt management, and on a microeconomic level, for instance through an insurance for the producers. The general principle underlying our proposals is that international assistance can enable developing countries to face price shocks, while taking into account the market signals, by offering a guarantee to these countries provided they respect some management rules.

Nanobubbles and gas dynamics during capillary filling of nanochannels

This paper focuses on capillary filling at the nanoscale where deviations to the Washburn’s classical theory are observed. Imbibition experiments in microfabricated silicon-glass nanochannels with low aspect ratio (width >> depth and depths going from 400 nm down to 20 nm) are performed for several liquids. In all cases, as predicted by the Washburn’s law, liquid invasion front location evolves as the square root of time. However, filling kinetics slowdown compared to the Washburn’s law is measured in nanochannels for depths below ~ 100 nm. Furthermore, below a liquid-dependent depth threshold, we observe spontaneous bubbles formation behind the advancing meniscus. Bubbles dynamics (formation conditions and lifetime) are analyzed thanks to our experimental data involving several liquids and nanochannels depths. Viscous resistance induced by the bubbles presence is estimated using an effective medium approach. Conjointly, gas flow ahead of the advancing meniscus is modeled considering the gas as viscous and compressible. Influence of these effects on the filling kinetics is discussed

Water-sediment exchanges control microbial processes associated with leaf litter degradation in the hyporheic zone: a microcosm study

The present study aimed to experimentally quantify the influence of a reduction of surface sediment permeability on microbial characteristics and ecological processes (respiration and leaf litter decomposition) occurring in the hyporheic zone (i.e. the sedimentary interface between surface water and groundwater). The physical structure of the water-sediment interface was manipulated by adding a 2-cm layer of coarse sand (unclogged systems) or fine sand (clogged systems) at the sediment surface of slow filtration columns filled with a heterogeneous gravel/sand sedimentary matrix. The influence of clogging was quantified through measurements of hydraulic conductivity, water chemistry, microbial abundances and activities and associated processes (decomposition of alder leaf litter inserted at a depth of 9 cm in sediments, oxygen and nitrate consumption by microorganisms). Fine sand deposits drastically reduced hydraulic conductivity (by around 8-fold in comparison with unclogged systems topped by coarse sand) and associated water flow, leading to a sharp decrease in oxygen (reaching less than 1 mg L(-1) at 3 cm depth) and nitrate concentrations with depth in sediments. The shift from aerobic to anaerobic conditions in clogged systems favoured the establishment of denitrifying bacteria living on sediments. Analyses performed on buried leaf litter showed a reduction by 30% of organic matter decomposition in clogged systems in comparison with unclogged systems. This reduction was linked to a negative influence of clogging on the activities and abundances of leaf-associated microorganisms. Finally, our study clearly demonstrated that microbial processes involved in organic matter decomposition were dependent on hydraulic conductivity and oxygen availability in the hyporheic zone

Triassic alkaline magmatism of the Hawasina Nappes: Post-breakup melting of the Oman lithospheric mantle modified by the Permian Neotethyan Plume

International audienceMiddle to Late Triassic lavas were sampled within three tectonostratigraphic groups of the Hawasina Nappes in the Oman Mountains. They are predominantly alkali basalts and trachybasalts, associated with minor sub-alkaline basalts, trachyandesites, trachytes and rhyolites. Their major, trace elements and Nd-Pb isotopic compositions are very similar to those of the Permian plume-related high-Ti basalts which also occur in the Hawasina Nappes. The Triassic lavas derive from low-degree melting of an enriched OIB-type mantle source, characterized by εNdi = 0.3-5.3 and (206Pb/204Pb)i = 16.96-19.31 (for t = 230 My). With time, melting depths decreased from the garnet + spinel to the spinel lherzolite facies and the degree of melting increased. The oldest are distinguished from the others by unradiogenic Nd and Pb signatures, with εNdi = − 4.5 to − 1.2 and (206Pb/204Pb)i = 16.35-17.08, which we attribute to their contamination by Arabo-Nubian lower crust. The lavas likely derived from the Oman lithospheric mantle, the original DMM-HIMU signature of which was overprinted during its pervasive metasomatism by the Permian plume-related melts. We suggest that these lavas were emplaced during post-breakup decompression-triggered melting in the Middle Triassic during global kinematic reorganization of the Tethyan realm