- May 2022
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In this case, the band broadens rapidly in the first few centimeters of the channel as indicated by the asymmetry of the trace acquired 2 cm downstream from the inlet (blue trace in Fig. 4C). The traces acquired further downstream are noticeably more symmetrical; this change indicates a transition to diffusive broadening. Note that, by reducing the mixing length, the SHM will also reduce Deff(8, 26).
Compared to Poiseuille flow in a rectangular channel, the SHM achieved fluid mixing faster and within a shorter channel length. In addition, in the herringbone ridge mixer, the axial dispersion, i.e. spread of a plug introduced into the channel, is greatly reduced.
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In Fig. 3E, we see that Δy90 increases linearly with ln(Pe) for large Pe, as expected for chaotic flows.
The authors demonstrated that the channel length required to achieve 90% mixing increases with the natural logarithm of the Peclet number (as opposed to being directly proportional) at high flow rates. Since log(x) grows much slower than x, the channel length required to achieve full mixing remains small, even at high flow rates, when chaotic mixing methods (such as the one demonstrated in this work) are used.
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Chaotic flows will also exist in the laminar shear flow in the boundary layer of an extended flow over a surface that presents the staggered herringbone structure. This stirring of the boundary layer should enhance the rates of diffusion-limited reactions at surfaces (e.g., electrode reactions) and heat transfer from solids into bulk flows.
Here the authors describe some possible applications that could benefit from this work. One specific application described is diffusion limited reactions which might happen at a surface such as those between an electrode and electrolytes in solution or between immobilized antibodies and antigens in solution. A previous annotation mentions a protein detection mechanism from blood samples which is dependent on a diffusion limited reaction.
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offers a general solution to the problem of mixing fluids in microfluidic systems. The simplicity of its design allows it to be integrated easily into microfluidic structures with standard microfabrication techniques.
The authors have proven that they have created a novel mixing technique which is more effective that standard diffusion mixing, easier to integrate into other microfluidic structurers than current mixing techniques, and doesn't require any complicated active device components.
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- Mar 2022
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The mixing length in a simple microchannel would be Δym ∼ Pe ×l = 100 cm. On the basis of Fig. 3D, the mixing length in the SHM would be, Δym ∼ 1 cm. Furthermore, increasing the flow speed by a factor of 10 (i.e., toPe = 105) will increase the mixing length in the SHM to Δym ∼ 1.5 cm. With the same change in flow speed, the mixing length in the absence of stirring will increase 10-fold, to Δym ∼ 103 cm.
The SHM demonstrated a shorter mixing length and remained significantly less impacted by an increase in flow speed compared to a simple microchannel.
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This design adds a negligible resistance to flow relative to that of a simple channel of the same dimensions
This method of mixing can be adapted to most microfluidic devices as it has a negligible effect on the overall flow characteristics.
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- Feb 2022
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The experiments presented in Fig. 4 demonstrate that, by stirring the fluid in the cross section of the flow, the SHM (Fig. 4C) reduces the extent of the initial, rapid broadening of a band of material relative to that in an unstirred flow (Fig. 4B).
In the SHM, mixed fluid spreads less along the channel (Fig 4C) in comparison to the unstirred flow (Fig 4B).
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- Feb 2018
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Second, if anti-ISIS agencies are insufficiently active in countermeasures and hence the overall rate at which they fragment pro-ISIS clusters becomes too small—specifically, if the aggregate fragmentation rate vfrag < (NlnN)–1—then pro-ISIS support will grow exponentially fast into one super-aggregate (fig. S11).
The rationale here is that if anti-ISIS agencies do not shut down smaller aggregates at a sufficient rate, these aggregates will merge (coalesce) into bigger ones, which will be harder to shut down. Eventually, this process will repeat until a "super-aggregate" is formed, which will be very hard to shut down.
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The data show that operational pro-ISIS and protest narratives develop through self-organized online aggregates, each of which is an ad hoc group of followers of an online page created through Facebook or its global equivalents, such as ВКонтакте (VKontakte) at http://vk.com/
An account page created on Facebook or VKontakte can be marked as an "organization". These pages are often used for informal organizations or groups of people interested in a particular subject. In the case of pro-ISIS aggregates, the pages contain material expressing a strong allegiance to ISIS and are followed by people interested in such material.
In the Supplementary Material, the authors point out that pages containing ISIS-related content are almost imediately shut down on Facebook and that such pages experience longer lifetimes on VKontakte.
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