1,157 research outputs found
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
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
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
A method for calculating the productivity of cable communications networks
A probabilistic-mathematical instrument was used to develop a method fo
Interannual variability of the Black Sea Proper oxygen and nutrients regime: The role of climatic and anthropogenic forcing
The Black Sea is a unique, stratified, enclosed ocean basin of great importance. The water column provides a wealth of information concerning aerobic-anaerobic biogeochemistry, the responses of which can have links to anthropogenic and climatic forcing. Herein, we synthesize dissolved oxygen (DO) and nutrient data (phosphate, dissolved inorganic nitrogen (DIN), and silicate) for the period 1984-2010 received in the northeastern and western areas of the Sea. In the subsequent analysis we discuss the role of anthropogenic and climatic forcing in the context of the Black Sea oxic layer and oxic/anoxic interface characteristics.The DO concentration in the surface layer and in the Cold Intermediate Layer (CIL) decreased in warm periods and increased in cold periods, correlating to North Atlantic Oscillation (NAO) index variation. The biogeochemical regime of the Black Sea oxygenated upper layer has notably changed since 1999. After 1999 DO concentration in the CIL decreased by 20% while the concentrations in the surface layer changed very little. This provides evidence that the CIL waters were not fully replenished during the winters of the last decade.The nutrient concentrations (DIN and phosphate) in the surface layer decreased significantly in the 2000s compared with the 1980s-1990s. This decrease is regarded as improvement of the Black Sea ecosystem state. Oxygen and nutrient dynamics in the middle pycnocline have been decoupled since 1999. Presently physical (climatic) forcing is the dominant affecting factor controlling the Sea oxygen and nitrogen regime. © 2013 Elsevier Ltd
Tensorial slip of super-hydrophobic channels
We describe a generalization of the tensorial slip boundary condition,
originally justified for a thick (compared to texture period) channel, to any
channel thickness. The eigenvalues of the effective slip length tensor,
however, in general case become dependent on the gap and cannot be viewed as a
local property of the surface, being a global characteristic of the channel. To
illustrate the use of the tensor formalism we develop a semi-analytical theory
of an effective slip in a parallel-plate channel with one super-hydrophobic
striped and one hydrophilic surface. Our approach is valid for any local slip
at the gas sectors and an arbitrary distance between the plates, ranging from a
thick to a thin channel. We then present results of lattice Boltzmann
simulations to validate the analysis. Our results may be useful for extracting
effective slip tensors from global measurements, such as the permeability of a
channel, in experiments or simulations.Comment: 12 pages, 7 figure
The haunted delimitation of subjectivity in the Work of Nicolas Abraham
Kinesin-like calmodulin binding protein (KCBP), a Kinesin-14 family motor protein, is involved in the structural organization of microtubules during mitosis and trichome morphogenesis in plants. The molecular mechanism of microtubule bundling by KCBP remains unknown. KCBP binding to microtubules is regulated by Ca(2+)-binding proteins that recognize its C-terminal regulatory domain. In this work, we have discovered a new function of the regulatory domain. We present a crystal structure of an Arabidopsis KCBP fragment showing that the C-terminal regulatory domain forms a dimerization interface for KCBP. This dimerization site is distinct from the dimerization interface within the N-terminal domain. Side chains of hydrophobic residues of the calmodulin binding helix of the regulatory domain form the C-terminal dimerization interface. Biochemical experiments show that another segment of the regulatory domain located beyond the dimerization interface, its negatively charged coil, is unexpectedly and absolutely required to stabilize the dimers. The strong microtubule bundling properties of KCBP are unaffected by deletion of the C-terminal regulatory domain. The slow minus-end directed motility of KCBP is also unchanged in vitro. Although the C-terminal domain is not essential for microtubule bundling, we suggest that KCBP may use its two independent dimerization interfaces to support different types of bundled microtubule structures in cells. Two distinct dimerization sites may provide a mechanism for microtubule rearrangement in response to Ca(2+) signaling since Ca(2+)- binding proteins can disengage KCBP dimers dependent on its C-terminal dimerization interface
Effect of Statins (Zocor) on Oxygen-Dependent Processes in Muscle Tissue and Erythrocytes in Animals with Hypercholesterolemia
Background. Statin therapy may be accompanied by a toxic effect on skeletal muscle and liver cells, the molecular mechanisms of which have not yet been fully understood.Aim. To clarify the peculiarities of changes in the oxygen transport function of erythrocytes and antioxidant mechanisms in erythrocytes and muscles of animals with prolonged administration of statins (simvastatin).Materials and methods. The study was conducted on outbred male rats, which during the experiment were randomly assigned to following groups: the control group contained animals on a common ration of the vivarium, the group of comparison – animals with induced hypercholesterolemia, the main group – animals with induced hypercholesterolemia treated with simvastatin. In erythrocytes and muscle tissue of animals, indicators characterizing the state of antioxidant defense and carbohydrate metabolism were determined.The results. The experiment showed that the administration of simvastatin to animals was characterized by aggravation of hypoxia due to hypercholesterolemia, as indicated by a sharp increase in the concentration of 2,3-BPG and lactate in erythrocytes of animals, as well as a significant decrease in the activity of G6PD. In the muscle tissue of animals, there was a decrease in the concentration of pyruvic acid and lactate relative to the comparison group, which indicates their intensive participation in metabolic processes.Conclusion. Based on the data obtained, it can be assumed that the peculiarity of the action of statins in erythrocytes is the increased oxygen delivery to the tissues, which in muscles was accompanied by a decrease in the level of oxidized products. At the same time, against the background of the use of statins, despite the positive direction of adaptive reactions, signs of oxidative stress remain, which is documented by the imbalance of the SOD-catalase system and a decrease in the activity of glutathione-dependent reaction
Lattice Boltzmann simulations in microfluidics: probing the no-slip boundary condition in hydrophobic, rough, and surface nanobubble laden microchannels
In this contribution we review recent efforts on investigations of the effect
of (apparent) boundary slip by utilizing lattice Boltzmann simulations. We
demonstrate the applicability of the method to treat fundamental questions in
microfluidics by investigating fluid flow in hydrophobic and rough
microchannels as well as over surfaces covered by nano- or microscale gas
bubbles.Comment: 11 pages, 6 figure
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