Designing the 3D electrostatic microgenerator

This paper discusses the design and simulation of a 3D electrostatic generator, one part of power supply component of the self-powered microsystem [1], which is able to provide enough energy to power up smart sensor chains. In this case the most suitable method to gather enough electrical energy is so-called energy harvesting principle [2], [3]. The designed generator is based on electrostatic converter and uses the principle of conversion of non-electric energy into electrical energy by periodical modification of gap between electrodes of a capacitor [4]. The structure is designed and modeled as three-dimensional silicon based MEMS. Innovative approach involving the achievement of very low resonant frequency of the structure (around 100 Hz) using the modified long cantilever design, minimal area of the chip, the ability to work in all 3 axes of coordinate system and the ability to be tuned to reach desired parameters shows further development.     

Distribution of Overjump Functionals of a Semicontinuous Homogeneous Process with Independent Increments

We establish relations for the distributions of functionals associated with an overjump of a process (t) with continuously distributed jumps of arbitrary sign across a fixed level x > 0 (including the zero level x = 0 and infinitely remote level x ). We improve these relations in the case where the distributions of maxima and minima of (t) may have an atom at zero. The distributions of absolute extrema of semicontinuous processes are defined in terms of these atomic probabilities and the cumulants of the corresponding monotone processes.     

Behavior of risk processes with random premiums after ruin and a multivariate ruin function

We establish relations for the distribution of functionals associated with the behavior of a risk process with random premiums after ruin and for a multivariate ruin function. __________ Translated from Ukrains’kyi Matematychnyi Zhurnal, Vol. 59, No. 11, pp. 1473–1484, November, 2007.     

Bioactivity Performance of Pure Mg after Plasma Electrolytic Oxidation in Silicate-Based Solutions

The biodegradable metals, including magnesium (Mg), are a convenient alternative to permanent metals but fast uncontrolled corrosion limited wide clinical application. Formation of a barrier coating on Mg alloys could be a successful strategy for the production of a stable external layer that prevents fast corrosion. Our research was aimed to develop an Mg stable oxide coating using plasma electrolytic oxidation (PEO) in silicate-based solutions. 99.9% pure Mg alloy was anodized in electrolytes contained mixtures of sodium silicate and sodium fluoride, calcium hydroxide and sodium hydroxide. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), contact angle (CA), Photoluminescence analysis and immersion tests were performed to assess structural and long-term corrosion properties of the new coating. Biocompatibility and antibacterial potential of the new coating were evaluated using U2OS cell culture and the gram-positive Staphylococcus aureus (S. aureus, strain B 918). PEO provided the formation of a porous oxide layer with relatively high roughness. It was shown that Ca(OH)₂ was a crucial compound for oxidation and surface modification of Mg implants, treated with the PEO method. The addition of Ca²⁺ ions resulted in more intense oxidation of the Mg surface and growth of the oxide layer with a higher active surface area. Cell culture experiments demonstrated appropriate cell adhesion to all investigated coatings with a significantly better proliferation rate for the samples treated in Ca(OH)₂-containing electrolyte. In contrast, NaOH-based electrolyte provided more relevant antibacterial effects but did not support cell proliferation. In conclusion, it should be noted that PEO of Mg alloy in silicate baths containing Ca(OH)₂ provided the formation of stable biocompatible oxide coatings that could be used in the development of commercial degradable implants.     

Impact of Electrospinning Parameters and Post-Treatment Method on Antibacterial and Antibiofilm Activity of Chitosan Nanofibers

Chitosan, a natural biopolymer, is an ideal candidate to prepare biomaterials capable of preventing microbial infections due to its antibacterial properties. Electrospinning is a versatile method ideally suited to process biopolymers with minimal impact on their physicochemical properties. However, fabrication parameters and post-processing routine can affect biological activity and, therefore, must be well adjusted. In this study, nanofibrous membranes were prepared using trifluoroacetic acid and dichloromethane and evaluated for physiochemical and antimicrobial properties. The use of such biomaterials as potential antibacterial agents was extensively studied in vitro using Staphylococcus aureus and Escherichia coli as test organisms. The antibacterial assay showed inhibition of bacterial growth and eradication of the planktonic cells of both E. coli and S. aureus in the liquid medium for up to 6 hrs. The quantitative assay showed a significant reduction in bacteria cell viability by nanofibers depending on the method of fabrication. The antibacterial properties of these biomaterials can be attributed to the structural modifications provided by co-solvent formulation and application of post-treatment procedure. Consequently, the proposed antimicrobial surface modification method is a promising technique to prepare biomaterials designed to induce antimicrobial resistance via antiadhesive capability and the biocide-releasing mechanism.     

Compound Poisson Processes with Two-Sided Reflection

We consider a compound oscillating Poisson process with two-sided reflection. This process is defined by an upper-semicontinuous compound Poisson process (t) and its functionals, namely the first-exit time of (t) from an interval and the first-exit time of (t) across the upper and lower levels. We study the main characteristics of this oscillating process in terms of the potential and resolvent of the process (t) introduced by Korolyuk. For this purpose, we refine the Pecherskii identities and some other results for upper-semicontinuous Poisson processes.     

Behavior of classical risk processes after ruin and a multivariate ruin function

We establish relations for the distribution of functionals associated with the behavior of a classical risk process after ruin and a multivariate ruin function. __________ Translated from Ukrains’kyi Matematychnyi Zhurnal, Vol. 59, No. 10, pp. 1339–1352, October, 2007.     

On the Exit of One Class of Random Walks from an Interval

We consider a random walk for which the characteristic function of jumps ξ _k satisfies the condition of almost semicontinuity. The problem of the exit of random walks S _n of this type from a finite interval is studied. __________ Translated from Ukrains'kyi Matematychnyi Zhurnal, Vol. 57, No. 9, pp. 1209–1217, September, 2005.