1,592 research outputs found
Surface Roughness and Hydrodynamic Boundary Conditions
We report results of investigations of a high-speed drainage of thin aqueous
films squeezed between randomly nanorough surfaces. A significant decrease in
hydrodynamic resistance force as compared with predicted by Taylor's equation
is observed. However, this reduction in force does not represents the slippage.
The measured force is exactly the same as that between equivalent smooth
surfaces obeying no-slip boundary conditions, but located at the intermediate
position between peaks and valleys of asperities. The shift in hydrodynamic
thickness is shown to be independent on the separation and/or shear rate. Our
results disagree with previous literature data reporting very large and
shear-dependent boundary slip for similar systems.Comment: Revised versio
Random-roughness hydrodynamic boundary conditions
We report results of lattice Boltzmann simulations of a high-speed drainage
of liquid films squeezed between a smooth sphere and a randomly rough plane. A
significant decrease in the hydrodynamic resistance force as compared with that
predicted for two smooth surfaces is observed. However, this force reduction
does not represent slippage. The computed force is exactly the same as that
between equivalent smooth surfaces obeying no-slip boundary conditions, but
located at an intermediate position between peaks and valleys of asperities.
The shift in hydrodynamic thickness is shown to depend on the height and
density of roughness elements. Our results do not support some previous
experimental conclusions on very large and shear-dependent boundary slip for
similar systems.Comment: 4 pages, 4 figure
Electro-osmosis on anisotropic super-hydrophobic surfaces
We give a general theoretical description of electro-osmotic flow at striped
super-hydrophobic surfaces in a thin double layer limit, and derive a relation
between the electro-osmotic mobility and hydrodynamic slip-length tensors. Our
analysis demonstrates that electro-osmotic flow shows a very rich behavior
controlled by slip length and charge at the gas sectors. In case of uncharged
liquid-gas interface, the flow is the same or inhibited relative to flow in
homogeneous channel with zero interfacial slip. By contrast, it can be
amplified by several orders of magnitude provided slip regions are uniformly
charged. When gas and solid regions are oppositely charged, we predict a flow
reversal, which suggests a possibility of huge electro-osmotic slip even for
electro-neutral surfaces. On the basis of these observations we suggest
strategies for practical microfluidic mixing devices. These results provide a
framework for the rational design of super-hydrophobic surfaces.Comment: 4 pages, 4 figures; submitted to PRL Revised version: several
references added, typos corrected. Supplementary file was restructured, the
second part of the original EPAPS was removed and is supposed to be published
as a separate pape
Transverse flow in thin superhydrophobic channels
We provide some general theoretical results to guide the optimization of
transverse hydrodynamic phenomena in superhydrophobic channels. Our focus is on
the canonical micro- and nanofluidic geometry of a parallel-plate channel with
an arbitrary two-component (low-slip and high-slip) coarse texture, varying on
scales larger than the channel thickness. By analyzing rigorous bounds on the
permeability, over all possible patterns, we optimize the area fractions, slip
lengths, geometry and orientation of the surface texture to maximize transverse
flow. In the case of two aligned striped surfaces, very strong transverse flows
are possible. Optimized superhydrophobic surfaces may find applications in
passive microfluidic mixing and amplification of transverse electrokinetic
phenomena.Comment: 4 page
Social and economic space compression in border areas: the case of the Northwestern Federal District
The so-called "compression" of social and economic space has been the subject of quite a few studies in the past decades. There are two principle types of compression: communicative, that is, associated with the development of transport and information systems, and physical, manifested in the rapid decrease of the number of new territories to explore. While physical and communicative compression are interrelated, they have different spatial expressions depending on geographical conditions, economic, environmental, historical, and political characteristics of the region. The authors identify the patterns of communicative and physical space compression using comparative mapping, statistical and historical research methods, and a model showing the spatial differentiation of regional socioeconomic characteristics in the Northwestern Federal District. The study focuses on border areas, where the following key manifestations of compression have been identified: transport connectivity, level of agriculture development, and depopulation. All these indicators of space compression process are studied at the municipal level. The authors identify the key features of socioeconomic space compression for the border areas of the Russian Northwest
Application of Crowdsourcing Technology In Terms Of Digitization of Supply Chain Strategy
Abstract— The article presents the study on the problem of crowdsourcing application in terms of digital development of supply chain strategy. The purpose of this study is to develop the algorithm of application of crowdsourcing technology in terms of digitalization of supply chain strategy in socio-economic processes. The application of crowdsourcing technology facilitates the search for the most effective solutions to enterprise’s problems, minimizing the time-related and financial costs for their development. In the framework of this study, the methods of analysis, comparative analysis, generalization, decomposition were used. The novelty of the research is in the detailed examination of the crowdsourcing technology, comprehensive description of the algorithm of its functioning with application in addressing various tasks of supply chain strategy. The findings of the study can help enterprises to elaborate the workflow supply chain management with regard to public opinion
Effective slip over superhydrophobic surfaces in thin channels
Superhydrophobic surfaces reduce drag by combining hydrophobicity and
roughness to trap gas bubbles in a micro- and nanoscopic texture. Recent work
has focused on specific cases, such as striped grooves or arrays of pillars,
with limited theoretical guidance. Here, we consider the experimentally
relevant limit of thin channels and obtain rigorous bounds on the effective
slip length for any two-component (e.g. low-slip and high-slip) texture with
given area fractions. Among all anisotropic textures, parallel stripes attain
the largest (or smallest) possible slip in a straight, thin channel for
parallel (or perpendicular) orientation with respect to the mean flow. For
isotropic (e.g. chessboard or random) textures, the Hashin-Strikman conditions
further constrain the effective slip. These results provide a framework for the
rational design of superhydrophobic surfaces.Comment: 4+ page
Prevalence of suicidal behaviours and its correlates in Latvian general population : 2019-2020
publishersversionPeer reviewe
- …