1,165 research outputs found
Drag force on a sphere moving towards an anisotropic super-hydrophobic plane
We analyze theoretically a high-speed drainage of liquid films squeezed
between a hydrophilic sphere and a textured super-hydrophobic plane, that
contains trapped gas bubbles. A super-hydrophobic wall is characterized by
parameters (texture characteristic length), and (local slip
lengths at solid and gas areas), and and (fractions of solid
and gas areas). Hydrodynamic properties of the plane are fully expressed in
terms of the effective slip-length tensor with eigenvalues that depend on
texture parameters and (local separation). The effect of effective slip is
predicted to decrease the force as compared with expected for two hydrophilic
surfaces and described by the Taylor equation. The presence of additional
length scales, , and , implies that a film drainage can be much
richer than in case of a sphere moving towards a hydrophilic plane. For a large
(compared to ) gap the reduction of the force is small, and for all textures
the force is similar to expected when a sphere is moving towards a smooth
hydrophilic plane that is shifted down from the super-hydrophobic wall. The
value of this shift is equal to the average of the eigenvalues of the
slip-length tensor. By analyzing striped super-hydrophobic surfaces, we then
compute the correction to the Taylor equation for an arbitrary gap. We show
that at thinner gap the force reduction becomes more pronounced, and that it
depends strongly on the fraction of the gas area and local slip lengths. For
small separations we derive an exact equation, which relates a correction for
effective slip to texture parameters. Our analysis provides a framework for
interpreting recent force measurements in the presence of super-hydrophobic
surface.Comment: 9 pages, 5 figures, submitted to PRE; EPAPS file include
Link Graph Analysis for Adult Images Classification
In order to protect an image search engine's users from undesirable results
adult images' classifier should be built. The information about links from
websites to images is employed to create such a classifier. These links are
represented as a bipartite website-image graph. Each vertex is equipped with
scores of adultness and decentness. The scores for image vertexes are
initialized with zero, those for website vertexes are initialized according to
a text-based website classifier. An iterative algorithm that propagates scores
within a website-image graph is described. The scores obtained are used to
classify images by choosing an appropriate threshold. The experiments on
Internet-scale data have shown that the algorithm under consideration increases
classification recall by 17% in comparison with a simple algorithm which
classifies an image as adult if it is connected with at least one adult site
(at the same precision level).Comment: 7 pages. Young Scientists Conference, 4th Russian Summer School in
Information Retrieva
An Energy-efficient Live Video Coding and Communication over Unreliable Channels
In the field of multimedia communications there exist many important applications where live or real-time video data is captured by a camera, compressed and transmitted over the channel which can be very unreliable and, at the same time, computational resources or battery capacity of the transmission device are very limited. For example, such scenario holds for video transmission for space missions, vehicle-to-infrastructure video delivery, multimedia wireless sensor networks, wireless endoscopy, video coding on mobile phones, high definition wireless video surveillance and so on. Taking into account such restrictions, a development of efficient video coding techniques for these applications is a challenging problem.
The most popular video compression standards, such as H.264/AVC, are based on the hybrid video coding concept, which is very efficient when video encoding is performed off-line or non real-time and the pre-encoded video is played back. However, the high computational complexity of the encoding and the high sensitivity of the hybrid video bit stream to losses in the communication channel constitute a significant barrier of using these standards for the applications mentioned above.
In this thesis, as an alternative to the standards, a video coding based on three-dimensional discrete wavelet transform (3-D DWT) is considered as a candidate to provide a good trade-off between encoding efficiency, computational complexity and robustness to channel losses. Efficient tools are proposed to reduce the computational complexity of the 3-D DWT codec. These tools cover all levels of the codec’s development such as adaptive binary arithmetic coding, bit-plane entropy coding, wavelet transform, packet loss protection based on error-correction codes and bit rate control. These tools can be implemented as end-to-end solution and directly used in real-life scenarios. The thesis provides theoretical, simulation and real-world results which show that the proposed 3-D DWT codec can be more preferable than the standards for live video coding and communication over highly unreliable channels and or in systems where the video encoding computational complexity or power consumption plays a critical role
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