30 research outputs found
Channeling of particles and associated anomalous transport in a 2D complex plasma crystal
Implications of recently discovered effect of channeling of upstream extra
particles for transport phenomena in a two-dimensional plasma crystal are
discussed. Upstream particles levitated above the lattice layer and tended to
move between the rows of lattice particles. An example of heat transport is
considered, where upstream particles act as moving heat sources, which may lead
to anomalous heat transport. The average channeling length observed was 15 - 20
interparticle distances. New features of the channeling process are also
reported
Wake-mediated propulsion of an upstream particle in two-dimensional plasma crystals
The wake-mediated propulsion of an "extra" particle in a channel of two
neighboring rows of a two-dimensional plasma crystal, observed experimentally
by Du et al. [Phys. Rev. E 89, 021101(R) (2014)], is explained in simulations
and theory. We use the simple model of a pointlike ion wake charge to reproduce
this intriguing effect in simulations, allowing for a detailed investigation
and a deeper understanding of the underlying dynamics. We show that the
nonreciprocity of the particle interaction, owing to the wake charges, is
responsible for a broken symmetry of the channel that enables a persistent
self-propelled motion of the extra particle. We find good agreement of the
terminal extra-particle velocity with our theoretical considerations and with
experiments.Comment: 7 pages, 4 figures, PRL (https://journals.aps.org/prl/), updated
version with correct author affiliation
Network analysis of 3D complex plasma clusters in a rotating electric field
Network analysis was used to study the structure and time evolution of driven
three-dimensional complex plasma clusters. The clusters were created by
suspending micron-size particles in a glass box placed on top of the rf
electrode in a capacitively coupled discharge. The particles were highly
charged and manipulated by an external electric field that had a constant
magnitude and uniformly rotated in the horizontal plane. Depending on the
frequency of the applied electric field, the clusters rotated in the direction
of the electric field or remained stationary. The positions of all particles
were measured using stereoscopic digital in-line holography. The network
analysis revealed the interplay between two competing symmetries in the
cluster. The rotating cluster was shown to be more cylindrical than the
nonrotating cluster. The emergence of vertical strings of particles was also
confirmed.Comment: 9 pages, 9 figures; corrected Fig.4 and typo
Network analysis of 3D complex plasma clusters
Network analysis was used to study the structure and time evolution of driven
three-dimensional complex plasma clusters. The clusters were created by suspending
micron-size particles in a glass box placed on top of the rf electrode in
a capacitively coupled discharge. The particles were highly charged and manipulated
by an external electric �eld that had a constant magnitude and rotated
uniformly in the horizontal plane. Depending on the frequency of the applied electric
�eld, the clusters rotated in the direction of the electric �eld or remained stationary.
The three-dimensional positions of all particles were measured using stereoscopic
digital in-line holography.
The network approach was used to elucidate the structural changes in the cluster
consisting only of a very limited number of particles (64). The Analysis revealed an
interplay between two competing symmetries in the cluster. Spherical and cylindrical
ordering of the particles was examined by comparing network measures of the
experimental data with null models. The null models were arti�cial data with a certain
number of points in perfectly spherical order, and the rest in cylindrical order.
The well established network measures local connectivity, clustering coe�cient and
average path length were considered. Network analysis of the clusters showed
that the rotating cluster was more cylindrical than the nonrotating cluster.
These �ndings were in agreement with the estimate of the radial con�nement
with the aid of a dynamical force balance. Neglecting friction and inertial forces due
to the low particle velocities in the cluster, the pro�le of the electrical con�nement
could be estimated by calculating the repulsing Yukawa-type interaction between
the particles. The radial con�nement was shown to be stronger in the case of cluster
rotation, increasing the cylindricity of the cluster.
The emergence of vertical strings of particles was also con�rmed by using a network
analysis. While the traditional method of a �xed threshold has limitations such
as erroneously including passing by particles and a somewhat arbitrary threshold,
community �nding algorithms yield a more elegant approach of �nding structures
in complex systems. With the aid of multislice networks, it is possible to examine
the whole time series at once and thus resolve the time evolution of the strings.
As we demonstrated, network analysis is a powerful tool to analyze the structure
of complex plasma clusters and may have numerous applications in other complex
systems where the characertization of the spatial structure plays a vital role.
Novel Biodegradable Polymeric Microparticles Facilitate Scarless Wound Healing by Promoting Re-epithelialization and Inhibiting Fibrosis
Despite decades of research, the goal of achieving scarless wound healing remains elusive. One of the approaches, treatment with polymeric microcarriers, was shown to promote tissue regeneration in various in vitro models of wound healing. The in vivo effects of such an approach are attributed to transferred cells with polymeric microparticles functioning merely as inert scaffolds. We aimed to establish a bioactive biopolymer carrier that would promote would healing and inhibit scar formation in the murine model of deep skin wounds. Here we characterize two candidate types of microparticles based on fibroin/gelatin or spidroin and show that both types increase re-epithelialization rate and inhibit scar formation during skin wound healing. Interestingly, the effects of these microparticles on inflammatory gene expression and cytokine production by macrophages, fibroblasts, and keratinocytes are distinct. Both types of microparticles, as well as their soluble derivatives, fibroin and spidroin, significantly reduced the expression of profibrotic factors Fgf2 and Ctgf in mouse embryonic fibroblasts. However, only fibroin/gelatin microparticles induced transient inflammatory gene expression and cytokine production leading to an influx of inflammatory Ly6C+ myeloid cells to the injection site. The ability of microparticle carriers of equal proregenerative potential to induce inflammatory response may allow their subsequent adaptation to treatment of wounds with different bioburden and fibrotic content
Three-dimensional structure of a string-fluid complex plasma
Three-dimensional structure of complex (dusty) plasmas was investigated under
long-term microgravity conditions in the International-Space-Station-based
Plasmakristall-4 facility. The microparticle suspensions were confined in a
polarity-switched dc discharge. The experimental results were compared to the
results of the molecular dynamics simulations with the interparticle
interaction potential represented as a superposition of isotropic Yukawa and
anisotropic quadrupole terms. Both simulated and experimental data exhibited
qualitatively similar structural features indicating the bulk liquid-like order
with the inclusion of solid-like strings aligned with the axial electric field.
Individual strings were identified and their size spectrum was calculated. The
decay rate of the size spectrum was found to decrease with the enhancement of
string-like structural features
Morphology and Chemical Composition of Silicon Carbide Surface in Interaction with Titanium Alloy under Micro-Scratching Conditions
The article describes features of the wear site morphology formation during micro-scratching of a titanium alloy by a silicon carbide crystal in comparison with a corundum crystal. The initial shape of the crystal top and the rate of micro-scratching were assumed to be constant. No lubricating or cooling process media were used. External factors: micro-scratch depth and cutting path length. The chemical composition of wear sites was studied using micro-x-ray spectral analysis. The content of chemical elements in the surface layer of silicon carbide and adhered metal was studied at separate points and by area scanning. The accelerating voltage of the excitation electrons was changed in the range from 5 to 20 kV. The concentration of chemical elements on the surface of the wear site was determined immediately after micro-scratching and after removing the adhered metal by etching. The regularities of changes in the concentration of chemical elements depending on the accelerating voltage of the excitation electrons were determined
Tracking and Linking of Microparticle Trajectories During Mode-Coupling Induced Melting in a Two-Dimensional Complex Plasma Crystal
In this article, a strategy to track microparticles and link their trajectories adapted to the study of the melting of a quasi two-dimensional complex plasma crystal induced by the mode-coupling instability is presented. Because of the three-dimensional nature of the microparticle motions and the inhomogeneities of the illuminating laser light sheet, the scattered light intensity can change significantly between two frames, making the detection of the microparticles and the linking of their trajectories quite challenging. Thanks to a two-pass noise removal process based on Gaussian blurring of the original frames using two different kernel widths, the signal-to-noise ratio was increased to a level that allowed a better intensity thresholding of different regions of the images and, therefore, the tracking of the poorly illuminated microparticles. Then, by predicting the positions of the microparticles based on their previous positions, long particle trajectories could be reconstructed, allowing accurate measurement of the evolution of the microparticle energies and the evolution of the monolayer properties
Photophoretic force on microparticles in complex plasmas
Experimental observations are presented of unusual (‘abnormal’) microparticles, having trajectories very different from those of the majority of microparticles in the particle cloud in PK-3 Plus chamber (on board the International Space Station). To quantitatively study the mechanism driving this ‘irregular’ motion, we performed a series of experiments with quasi-two-dimensional complex
plasmas in a modified GEC RF reference cell in a ground-based laboratory. The results show that the average particle velocity increases with illumination laser power, particularly for the ‘abnormal’ particles. We suggest that the photophoretic force provides an important contribution to the drive, and briefly discuss the mechanism leading to this effect. Optical microscopy results indicate that the ‘abnormal’ particles could be those having deformations or defects on their surface
The relation between the geometric parameters of grinding powders grains measured by laser diffraction and light-microscopical methods
The studies were conducted on grinding powders of black silicon carbide with F180-F60 grit produced by Volzhsky Abrasive Plant. The length, width, perimeter, area and reduced diameter of the grain area were determined by light-microscopical method, the equivalent diameter by the laser diffraction method. The distribution laws of geometric parameters are determined. A direct proportional relationship between the mean equivalent diameter and the average geometric parameters of the grain fractions (length, width, perimeter, equivalent diameter) and the power-law dependence with the average area of the grain fractions have been establishe