New Materials Based on Polyvinylpyrrolidone-Containing Copolymers with Ferromagnetic Fillers

The article investigates the peculiarities of the effect of ferromagnetic fillers (FMFs) of various natures (Ni, Co, Fe, FeCo, SmCo₅) on the formation of the structure and properties of 2-hydroxyethylmethacrylate (HEMA) with polyvinylpyrrolidone (PVP) copolymers. The composites were characterized using FTIR-spectroscopy, SEM, DMTA, magnetometry of vibrating samples, specific electrical resistivity studies, and mechanical and thermophysical studies. The formation of a grafted spatially crosslinked copolymer (pHEMA-gr-PVP) was confirmed and it was established that the FMF introduction of only 10 wt.% into the copolymer formulation increased the degree of crosslinking of the polymer network by three times. The surface hardness of composites increased by 20–25%. However, the water content decreased by 16–18% and lay within 42–43 wt.%, which is a relatively high number. The heat resistance of dry composites was characterized by Vicat softening temperature, which was 39–42 °C higher compared to the unfilled material. It was established that the obtained composites were characterized by a coercive force of 200 kA × m⁻¹ and induction of a magnetic field at the poles of 4–5 mT and 10–15 mT, respectively. The introduction of FMF particles into pHEMA-gr-PVP copolymers, which, in the dry state, are dielectrics, provides them with electrical conductivity, which was evaluated by the specific volume resistance. Depending on the FMF nature and content, as well as their orientation in the magnetic field, the resistance of filled materials could be regulated within 10²–10⁶ Ohm·m. Therefore, the modification of HEMA with PVP copolymers by ferromagnetic fillers of various natures provides the possibility of obtaining materials with unique predicted properties and expands the fields of their use, for instance as magnetic sorbents for various applications, as well as the possibilities associated with their being electrically conductive materials that can respond by changing of electrical conductivity, depending on various factors.     

Adaptive Optimal Designs for Dose-Finding Studies with Time-to-Event Outcomes

We consider optimal design problems for dose-finding studies with censored Weibull time-to-event outcomes. Locally D-optimal designs are investigated for a quadratic dose–response model for log-transformed data subject to right censoring. Two-stage adaptive D-optimal designs using maximum likelihood estimation (MLE) model updating are explored through simulation for a range of different dose–response scenarios and different amounts of censoring in the model. The adaptive optimal designs are found to be nearly as efficient as the locally D-optimal designs. A popular equal allocation design can be highly inefficient when the amount of censored data is high and when the Weibull model hazard is increasing. The issues of sample size planning/early stopping for an adaptive trial are investigated as well. The adaptive D-optimal design with early stopping can potentially reduce study size while achieving similar estimation precision as the fixed allocation design.     

Correction to: Closed‑suction drainage in thoracolumbar spinal surgery–clinical routine without evidence? a systematic review

European Spine Journal -     

The Formation of Cr-Al Spinel under a Reductive Atmosphere

In the present work, for the first time, the possibility of formation of CrAl₂O₄ was shown from the equimolar mixture of co-precipitated Al₂O₃ and Cr₂O₃ oxides under a reductive environment. The crystallographic properties of the formed compound were calculated using the DICVOL procedure. It was determined that it has a cubic crystal structure with space group Fd-3m and a unit cell parameter equal to 8.22(3) Å. The formed CrAl₂O₄ is not stable under ambient conditions and easily undergoes oxidation to α-Al₂O₃ and α-Cr₂O₃. The overall sequence of the phase transformations of co-precipitated oxides leading to the formation of spinel structure is proposed.     

Assessment of Technological Capabilities for Forming Al-C-B System Coatings on Steel Surfaces by Electrospark Alloying Method

In this paper, the possibility of applying the electrospark alloying (ESA) method to obtain boron-containing coatings characterised by increased hardness and wear resistance is considered. A new method for producing such coatings is proposed. The method consists in applying grease containing aluminium powder and amorphous boron to the surface to be treated and subsequently processing the obtained surface using the ESA method by a graphite electrode. The microstructural analysis of the Al-C-B coatings on steel C40 showed that the surface layer consists of several zones, the number and parameters of which are determined by the energy conditions of the ESA process. Durametric studies showed that with an increase in the discharge energy influence, the microhardness values of both the upper strengthened layer and the diffusion zone increased to W_p = 0.13 J, Hµ = 6487 MPa, and W_p = 4.9 J, Hµ = 12350 MPa, respectively. The results of X-ray diffraction analysis indicate that at the discharge energies of 0.13 and 0.55 J, the phase composition of the coating is represented by solid solutions of body-centred cubic lattice (BCC) and face-centred cubic lattice (FCC). The coatings obtained at W_p = 4.9 J were characterised by the presence of intermetallics Fe₄Al₁₃ and borocementite Fe₃ (CB) in addition to the solid solutions. The X-ray spectral analysis of the obtained coatings indicated that during the electrospark alloying process, the surface layers were saturated with aluminium, boron, and carbon. With increasing discharge energy, the diffusion zone increases; during the ESA process with the use of the discharge energy of 0.13 J for steel C40, the diffusion zone is 10–15 μm. When replacing a substrate made of steel C40 with the same one material but of steel C22, an increase in the thickness of the surface layer accompanied by a slight decrease in microhardness is observed as a result of processing with the use of the ESA method. There were simulated phase portraits of the Al-C-B coatings. It is shown that near the stationary points in the phase portraits, one can see either a slowing down of the evolution or a spiral twisting of the diffusion-process particle.     

Acid-Sensing Ion Channels: Focus on Physiological and Some Pathological Roles in the Brain

Acid-sensing ion channels (ASICs) are Na⁺-permeable ion channels activated by protons and predominantly expressed in the nervous system. ASICs act as pH sensors leading to neuronal excitation. At least eight different ASIC subunits (including ASIC1a, ASIC1b, ASIC2a, ASIC2b, ASIC3, ASIC4, ASIC5) are encoded by five genes (ASIC1-ASIC5). Functional ASICs assembled in the plasma membrane are homo- or heteromeric trimers. ASIC1a-containing trimers are of particular interest as, in addition to sodium ions, they also conduct calcium ions and thus can trigger or regulate multiple cellular processes. ASICs are widely but differentially expressed in the central and peripheral nervous systems. In the mammalian brain, a majority of neurons express at least one ASIC subunit. Several recent reviews have summarized findings of the role of ASICs in the peripheral nervous system, particularly in nociception and proprioception, and the structure-function relationship of ASICs. However, there is little coverage on recent findings regarding the role of ASICs in the brain. Here we review and discuss evidence regarding the roles of ASICs: (i) as postsynaptic receptors activated by protons co-released with glutamate at glutamatergic synapses; (ii) as modulators of synaptic transmission at glutamatergic synapses and GABAergic synapses; (iii) in synaptic plasticity, memory and learning; (iv) in some pathologies such as epilepsy, mood disorders and Alzheimer''s disease.