Vladimir I. Stadnichuk

Nonlinear-optical probing of nanosecond ferroelectric switching

It is demonstrated that the switching dynamics of the ferroelectric polarization in thin Ba(SrTi)O3 (BST) films can be followed by optical second harmonic generation with a time resolution that is only limited by the gating electronics. It is shown that the characteristic time of electric-field induced polarization switching in 70 nm BST films is less than τ=5 ns.

Size distribution of particles in Saturn’s rings from aggregation and fragmentation

Significance Although it is well accepted that the particle size distribution in Saturn’s rings is not primordial, it remains unclear whether the observed distribution is unique or universal, that is, whether it is determined by the history of the rings and details of the particle interaction or whether the distribution is generic for all planetary rings. We show that a power-law size distribution with large-size cutoff, as observed in Saturn’s rings, is universal for systems where a balance between aggregation and disruptive collisions is steadily sustained. Hence, the same size distribution is expected for any ring system where collisions play a role, like the Uranian rings, the recently discovered rings of Chariklo and Chiron, and possibly rings around extrasolar objects. Saturn’s rings consist of a huge number of water ice particles, with a tiny addition of rocky material. They form a flat disk, as the result of an interplay of angular momentum conservation and the steady loss of energy in dissipative interparticle collisions. For particles in the size range from a few centimeters to a few meters, a power-law distribution of radii, ∼r−q with q≈3, has been inferred; for larger sizes, the distribution has a steep cutoff. It has been suggested that this size distribution may arise from a balance between aggregation and fragmentation of ring particles, yet neither the power-law dependence nor the upper size cutoff have been established on theoretical grounds. Here we propose a model for the particle size distribution that quantitatively explains the observations. In accordance with data, our model predicts the exponent q to be constrained to the interval 2.75≤q≤3.5. Also an exponential cutoff for larger particle sizes establishes naturally with the cutoff radius being set by the relative frequency of aggregating and disruptive collisions. This cutoff is much smaller than the typical scale of microstructures seen in Saturn’s rings.

Microbial alkaloid staurosporine induces formation of nanometer-wide membrane tubular extensions (cytonemes, membrane tethers) in human neutrophils

In the present work, we demonstrate that microbial alkaloid staurosporine (STS) and Ro 31-8220, structurally related to STS protein kinase C inhibitor, caused development of membrane tubular extensions in human neutrophils upon adhesion to fibronectin-coated substrata. STS-induced tubular extensions interconnected neutrophils in a network and bound serum-opsonized bacteria Salmonella enterica serovar Typhimurium. The diameter of STS-induced extensions varied in the range 160-200 nm. The extensions were filled with cytoplasm and covered with membrane, as they included fluorescent cytoplasmic and lipid dyes. Neither protein kinase C inhibitors H-7 and bisindolylmaleimide VII, nor tyrosine protein kinase inhibitors tyrphostin AG 82 and genistein caused such extensions formation. Supposedly, STS induces membrane tubular extension formation promoting actin cytoskeleton depolymerization or affecting NO synthesis.

Membrane tubules attach Salmonella Typhimurium to eukaryotic cells and bacteria

Using scanning electron microscopy techniques we measured the diameter of adhesive tubular appendages of Salmonella enterica serovar S. Typhimurium. The appendages interconnected bacteria in biofilms grown on gallstones or coverslips, or attached bacteria to host cells (human neutrophils). The tubular appendage diameter of bacteria of virulent flagellated C53 strain varied between 60 and 70 nm, thus considerably exceeding in size of flagella or pili. Nonflagellated bacteria of mutant SJW 880 strain in biofilms grown on gallstones or coverslips were also interconnected by 60-90-nm tubular appendages. Transmission electron microscopy studies of thin sections of S. Typhimurium biofilms grown on agar or coverslips revealed numerous fragments of membrane tubular and vesicular structures between bacteria of both flagellated and nonflagellated strains. The membrane structures had the same diameter as tubular appendages observed by scanning electron microscopy, indicating that tubular appendages might represent membrane tubules (tethers). Previously, we have shown that neutrophils can contact cells and bacteria over distance via membrane tubulovesicular extensions (TVE) (cytonemes). The present electron microscopy study revealed the similarities in size and behavior of bacterial tubular appendages and neutrophil TVE. Our data support the hypothesis that bacteria establish long-range adhesive interactions via membrane tubules.

Proteome analysis identified human neutrophil membrane tubulovesicular extensions (cytonemes, membrane tethers) as bactericide trafficking

BACKGROUND Following adhesion to fibronectin neutrophils can develop membrane tubulovesicular extensions (TVEs) that can be 200nm wide and several cell diameters long. TVEs attach neutrophils to the other cells, substrata or bacteria over distance. To understand the physiological significance of TVEs we performed proteome analysis of TVE content in neutrophils plated to fibronectin in the presence of compounds known to induce TVE formation (nitric oxide donor diethylamine NONOate, 4-bromophenacyl bromide, cytochalasin D). METHODS Development of TVEs was confirmed by scanning electron microscopy. TVEs were disrupted following removal of inductors and biochemical, high-performance liquid chromatography and mass spectrometry investigations were employed to characterize the proteins within the incubation media. RESULTS TVE disruption released (a) the granular bactericides lactoferrin, lipocalin, myeloperoxidase, cathepsin G and defensins; (b) energy metabolism enzymes; (c) actin cytoskeleton proteins; (d) S100 proteins; and (e) annexin 1. CONCLUSIONS The data confirm that TVEs represent a means of secretory bactericide trafficking, where the protrusions fuse with the plasma membrane upon neutrophil adhesion or extend from the cell surface when fusion is impaired. It is proposed that proteins abundantly presented in TVE (energy metabolism enzymes, actin cytoskeleton and S100 proteins, annexin 1) play an important role in fusion of TVE with the plasma membrane. GENERAL SIGNIFICANCE Our study confirms TVEs as neutrophil secretory protrusions that make direct contacts with cells and bacteria over distance. The membrane-packed content and outstanding length of TVEs might allow targeted neutrophil secretion of aggressive bactericides over a long distance without dilution or injury to surrounding tissues.

Membrane tubulovesicular extensions (cytonemes): secretory and adhesive cellular organelles.

In this review, we summarized data on the formation and structure of the long and highly adhesive membrane tubulovesicular extensions (TVEs, membrane tethers or cytonemes) observed in human neutrophils and other mammalian cells, protozoan parasites and bacteria. We determined that TVEs are membrane protrusions characterized by a uniform diameter (130–250 nm for eukaryotic cells and 60–90 nm for bacteria) along the entire length, an outstanding length and high rate of development and a high degree of flexibility and capacity for shedding from the cells. This review represents TVEs as protrusions of the cellular secretory process, serving as intercellular adhesive organelles in eukaryotic cells and bacteria. An analysis of the physical and chemical approaches to induce TVEs formation revealed that disrupting the actin cytoskeleton and inhibiting glucose metabolism or vacuolar-type ATPase induces TVE formation in eukaryotic cells. Nitric oxide is represented as a physiological regulator of TVE formation.

Inhibition of the GTPase dynamin or actin depolymerisation initiates outward plasma membrane tubulation/vesiculation (cytoneme formation) in neutrophils

In a previous study, we demonstrated that human neutrophils can develop membrane tubulovesicular extensions (TVEs) that are 160–250 nm in width and several micrometres long. These extensions, or cytonemes, are capable of establishing long‐range contacts with other cells or bacteria. Cytonemes consist of membrane tubules and vesicles of a uniform diameter aligned in a row. The mechanism of membrane tubulation/vesiculation to form cytonemes remains unknown. Upon endocytosis, the GTPase dynamin and an intact actin cytoskeleton are required for endocytic vesicles scission from the plasma membrane.

Anderson acceleration method of finding steady-state particle size distribution for a wide class of aggregation–fragmentation models

Abstract A fast numerical method of finding steady-state distributions of particles sizes for a wide class of aggregation–fragmentation models, including the models with a source of monomers is developed. The method is based on a fast evaluation scheme for large sets of non-linear Smoluchowski-type ODE with an application of the Anderson acceleration method of the fixed point iterations. In the numerical tests of the suggested approach we demonstrate that huge sets of non-linear ODE may be solved with high precision in terms of Euclidian norm of the residual in modest times with use of a regular desktop computer. We compare our numerical solutions with the known analytical results for the steady-state distributions as well as with the other fast numerical schemes and prove the high accuracy of the novel method and its significant superiority with respect to the existing fast numerical method of solution of the addressed problems.

Smoluchowski aggregation–fragmentation equations: Fast numerical method to find steady-state solutions

In this paper, we propose an efficient and fast numerical method of finding a stationary solution of large systems of aggregation–fragmentation equations of Smoluchowski type for concentrations of reacting particles. This method is applicable when the stationary concentrations steeply decrease with increasing aggregate size, which is fulfilled for the most important cases. We show that under rather mild restrictions, imposed on the kernel of the Smoluchowski equation, the following numerical procedure may be used: First, a complete solution for a relatively small number of equations (a “seed system”) is generated and then the result is exploited in a fast iterative scheme. In this way the new approach allows to obtain a steady-state solution for rather large systems of equations, by orders of magnitude faster than the standard schemes.

Time-delayed nonlinear optical systems: temporal instability and cooperative chaotic dynamics

We present the results of numerical simulation of a nonlinear optical system with a time-delayed feedback which exhibits spatio-temporal chaotic states. The model incldues three main phenomena governing the system: temporal delay, diffusion and diffraction. We focused our attention on the statistical properties of this system and analyzed the join action of mentioned phenomena, features of spatial spectra in wide range of parameters, scaling relations. We found that under certain conditions powers spectrum of phase fluctuations in chaotic states monotonically decreases as a function of spatial frequency. This causes us to anticipate that such class of optical system can be used for an artificial optical turbulence simulation.