The collapse of a bubble of radius R_{o} at the surface of a liquid generating a liquid jet and a subsequent first drop of radius R is universally scaled using the Ohnesorge number ...Oh=μ/(ρσR_{o})^{1/2} and a critical value Oh^{*} below which no droplet is ejected; ρ, σ, and μ are the liquid density, surface tension, and viscosity, respectively. First, a flow field analysis at ejection yields the scaling of R with the jet velocity V as R/l_{μ}∼(V/V_{μ})^{-5/3}, where l_{μ}=μ^{2}/(ρσ) and V_{μ}=σ/μ. This resolves the scaling problem of curvature reversal, a prelude to jet formation. In addition, the energy necessary for the ejection of a jet with a volume and averaged velocity proportional to R_{o}R^{2} and V, respectively, comes from the energy excess from the total available surface energy, proportional to σR_{o}^{2}, minus the one dissipated by viscosity, proportional to μ(σR_{o}^{3}/ρ)^{1/2}. Using the scaling variable φ=(Oh^{*}-Oh)Oh^{-2}, it yields V/V_{μ}=k_{v}φ^{-3/4} and R/l_{μ}=k_{d}φ^{5/4}, which collapse published data since 1954 and resolve the scaling of R and V with k_{v}=16, k_{d}=0.6, and Oh^{*}=0.043 when gravity effects are negligible.
The ability to manipulate and sort droplets is a fundamental issue in droplet-based microfluidics. Various lab-on-a-chip applications can only be realized if droplets are systematically categorized ...and sorted. These micron-sized droplets act as ideal reactors which compartmentalize different biological and chemical reagents. Array processing of these droplets hinges on the competence of the sorting and integration into the fluidic system. Recent technological advances only allow droplets to be actively sorted at the rate of kilohertz or less. In this review, we present state-of-the-art technologies which are implemented to efficiently sort droplets. We classify the concepts according to the type of energy implemented into the system. We also discuss various key issues and provide insights into various systems.
This review presents the fundamentals of different active methods for sorting droplets in microfluidics.
Flavonoids are new promising potential natural compounds for treating Alzheimer's disease (AD). Actually most promising drugs for symptomatic treatment of AD are acetylcholinesterase inhibitors ...(AChEI). Flavonoids with AChE inhibitory activity and due to their well known antioxidant activity could be new multipotent drugs for AD treatment. This work focuses on natural and synthetic flavonoids inhibitors of the enzyme acetylcholinesterase (AChE). Over, all this review refers to 128 flavonoids, which are classified in chemical structure, and summarizes 64 references.
Dripping, jetting and tip streaming Montanero, J M; Gañán-Calvo, A M
Reports on progress in physics,
09/2020, Letnik:
83, Številka:
9
Journal Article
Recenzirano
Odprti dostop
Dripping, jetting and tip streaming have been studied up to a certain point separately by both fluid mechanics and microfluidics communities, the former focusing on fundamental aspects while the ...latter on applications. Here, we intend to review this field from a global perspective by considering and linking the two sides of the problem. First, we present the theoretical model used to study interfacial flows arising in droplet-based microfluidics, paying attention to three elements commonly present in applications: viscoelasticity, electric fields and surfactants. We review both classical and current results of the stability of jets affected by these elements. Mechanisms leading to the breakup of jets to produce drops are reviewed as well, including some recent advances in this field. We also consider the relatively scarce theoretical studies on the emergence and stability of tip streaming in open systems. Second, we focus on axisymmetric microfluidic configurations which can operate on the dripping and jetting modes either in a direct (standard) way or via tip streaming. We present the dimensionless parameters characterizing these configurations, the scaling laws which allow predicting the size of the resulting droplets and bubbles, as well as those delimiting the parameter windows where tip streaming can be found. Special attention is paid to electrospray and flow focusing, two of the techniques more frequently used in continuous drop production microfluidics. We aim to connect experimental observations described in this section of topics with fundamental and general aspects described in the first part of the review. This work closes with some prospects at both fundamental and practical levels.
The reliable generation of micron-sized droplets is an important process for various applications in droplet-based microfluidics. The generated droplets work as a self-contained reaction platform in ...droplet-based lab-on-a-chip systems. With the maturity of this platform technology, sophisticated and delicate control of the droplet generation process is needed to address increasingly complex applications. This review presents the state of the art of active droplet generation concepts, which are categorized according to the nature of the induced energy. At the liquid/liquid interface, an energy imbalance leads to instability and droplet breakup.
This review presents the state of the art of active microfluidic droplet generation concepts.
Graphene is an excellent material for long-distance spin transport but allows little spin manipulation. Transition-metal dichalcogenides imprint their strong spin–orbit coupling into graphene via the ...proximity effect, and it has been predicted that efficient spin-to-charge conversion due to spin Hall and Rashba–Edelstein effects could be achieved. Here, by combining Hall probes with ferromagnetic electrodes, we unambiguously demonstrate experimentally the spin Hall effect in graphene induced by MoS2 proximity and for varying temperatures up to room temperature. The fact that spin transport and the spin Hall effect occur in different parts of the same material gives rise to a hitherto unreported efficiency for the spin-to-charge voltage output. Additionally, for a single graphene/MoS2 heterostructure-based device, we evidence a superimposed spin-to-charge current conversion that can be indistinguishably associated with either the proximity-induced Rashba–Edelstein effect in graphene or the spin Hall effect in MoS2. By a comparison of our results to theoretical calculations, the latter scenario is found to be the most plausible one. Our findings pave the way toward the combination of spin information transport and spin-to-charge conversion in two-dimensional materials, opening exciting opportunities in a variety of future spintronic applications.
ABSTRACT
We present the first application of deep neural networks to the semantic segmentation of cosmological filaments and walls in the large-scale structure of the universe. Our results are based ...on a deep convolutional neural network (CNN) with a U-Net architecture trained using an existing state-of-the-art manually guided segmentation method. We successfully trained and tested a U-Net with a Voronoi model and an N-body simulation. The predicted segmentation masks from the Voronoi model have a Dice coefficient of 0.95 and 0.97 for filaments and masks, respectively. The predicted segmentation masks from the N-body simulation have a Dice coefficient of 0.78 and 0.72 for walls and filaments, respectively. The relatively lower Dice coefficient in the filament mask is the result of filaments that were predicted by the U-Net model but were not present in the original segmentation mask. Our results show that for a well-defined data set such as the Voronoi model the U-Net has excellent performance. In the case of the N-body data set, the U-Net produced a filament mask of higher quality than the segmentation mask obtained from a state-of-the art method. The U-Net performs better than the method used to train it, being able to find even the tenuous filaments that the manually guided segmentation failed to identify. The U-Net presented here can process a 5123 volume in a few minutes and without the need of complex pre-processing. Deep CNN have great potential as efficient and accurate analysis tools for the next generation large-volume computer N-body simulations and galaxy surveys.
The photophysical properties of films of organic–inorganic lead halide perovskites under different ambient conditions are herein reported. We demonstrate that their luminescent properties are ...determined by the interplay between photoinduced activation and darkening processes, which strongly depend on the atmosphere surrounding the samples. We have isolated oxygen and moisture as the key elements in each process, activation and darkening, both of which involve the interaction with photogenerated carriers. These findings show that environmental factors play a key role in the performance of lead halide perovskites as efficient luminescent materials.
Contrary to the common view voids have very complex internal structure and dynamics. Here, we show how the hierarchy of structures in the density field inside voids is reflected by a similar ...hierarchy of structures in the velocity field. Voids defined by dense filaments and clusters can de described as simple expanding domains with coherent flows everywhere except at their boundaries. At scales smaller than the void radius the velocity field breaks into expanding subdomains corresponding to subvoids. These subdomains break into even smaller sub-subdomains at smaller scales resulting in a nesting hierarchy of locally expanding domains.
The ratio between the magnitude of the velocity field responsible for the expansion of the void and the velocity field defining the subvoids is approximately one order of magnitude. The small-scale components of the velocity field play a minor role in the shaping of the voids but they define the local dynamics directly affecting the processes of galaxy formation and evolution.
The super-Hubble expansion inside voids makes them cosmic magnifiers by stretching their internal primordial density fluctuations allowing us to probe the small scales in the primordial density field. Voids also act like time machines by 'freezing' the development of the medium-scale density fluctuations responsible for the formation of the tenuous web of structures seen connecting protogalaxies in computer simulations. As a result of this freezing haloes in voids can remain 'connected' to this tenuous web until the present time. This may have an important effect in the formation and evolution of galaxies in voids by providing an efficient gas accretion mechanism via coherent low-velocity streams that can keep a steady inflow of matter for extended periods of time.
We report on the numerical analysis of solar absorption enhancement in organic–inorganic halide perovskite films embedding plasmonic gold nanoparticles. The effect of particle size and concentration ...is analyzed in realistic systems in which random particle location within the perovskite film and the eventual formation of dimers are also taken into account. We find a maximum integrated solar absorption enhancement of ∼10% in perovskite films of 200 nm thickness and ∼6% in 300 nm films, with spheres of radii 60 and 90 nm, respectively, in volume concentrations of around 10% in both cases. We show that the presence of dimers boosts the absorption enhancement up to ∼12% in the thinnest films considered. Absorption reinforcement arises from a double contribution of plasmonic near-field and scattering effects, whose respective weight can be discriminated and evaluated from the simulations.
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