Search

The present study is focused on the structural phase transition in (La,Ce)Pd2Al2−xGax investigated by low temperature X-ray powder diffraction. All parent compounds crystallize in the tetragonal CaBe2Ge2 structure type (P4/nmm, 129) at room temperature and undergo structural phase transitions at low temperatures. Rietveld analysis of the measured patterns shows that the low temperature structures of (La,Ce)Pd2Al2 and (La,Ce)Pd2Ga2 have the same space groups and Wyckoff positions, but exhibit different magnitude of distortion and different characteristics of the structural transition. A small continuously appearing distortion is present in the Al parent compounds while the Ga ones exhibit a large discontinuously appearing distortion. These low temperature structures can be described using the C m m e , 67 space group which is translationengleiche subgroup of the tetragonal P 4 / n m m , 129 space group. The concentration dependence of the temperature where the distortion occurs has a minimum or is almost suppressed at a concentration of x ∼ 0.4 (cerium series) and x ∼ 1.6 (lanthanum series). To support our experimental findings we also present density function theory calculations which confirm the structural stability as experimentally observed. We discuss the impact of structural properties in the studied series on the previously observed development of physical properties such as superconductivity and magnetic excitations in neutron scattering spectra.

Fluoride conversion coating was applied on wrought AZ61 magnesium alloy by the immersion of alloy in Na[BF4] molten salt. Two different temperatures 430 °C and 450 °C, and different treatment times of 0.5; 2 and 8 h were used for the coating preparation. The surface morphology and the cross-sections of the coatings were investigated by scanning electron microscopy, focused ion beam cutting and energy-dispersive X-ray spectroscopy. The electrochemical corrosion characteristics of coated material varied with processing conditions. A significant improvement of electrochemical corrosion properties of the AZ61 magnesium alloy coated with fluoride conversion coatings was revealed by the potentiodynamic tests and electrochemical impedance spectroscopy.

Laser welding accompanied by tungsten inert gas welding was applied for 3 mm thick high strength low alloy S460MC steel butt joining with the aim to study the effect of arc electric current on weld cooling rate and thus weld microstructure and mechanical properties. Preheating realized by the arc decreased microhardness peaks in coarse-grained heat affected zone while strength properties were not degraded. Dissimilar S460MC to DC01 mild steel welds were performed with different positions of tungsten electrode towards the laser beam trajectory to maintain uniform weld profile.

Among a large group of R2T2X intermetallics (R = rare earth, T = transition element, X = p-metal) crystallizing in the Shastry-Sutherland-like tetragonal structure, Ce2Pd2In represents a rare example of Ce-based ferromagnet, reached, however via an antiferromagnetic phase stable at higher temperatures. Here we describe the development of magnetism in Ce2Pd2In under external hydrostatic and uniaxial pressure, monitored by means of electrical resistivity, magnetization, and AC magnetic susceptibility experiments on a high-quality single crystal. The experiments prove a stability of the 4f magnetism in pressures up to 3 GPa. At these pressures only slightly reduced spontaneous magnetization in the FM state and enhanced electrical resistivity with signs of Kondo lattice behavior are observed. The AFM Neel temperature (TN = 4.65 K) is essentially pressure independent, while the Curie temperature (TC = 4.16 K at ambient pressure) significantly decreases under hydrostatic pressure. The fact that the ferromagnetic phase can be re-entered in weak magnetic fields (0.05 T) proves that the two types of magnetic order are effectively degenerate. Interestingly, TC is not affected by uniaxial pressure applied along the tetragonal c-axis, TN value exhibits only a weak decrease of 0.25 K GPa−1 under such uniaxial pressure. The crystal structure of Ce2Pd2In exhibits a strongly anisotropic thermal expansion with anomalous expansion of the c-parameter with decreasing T. Modest size of magnetostriction effects, observed by dilatometry at ambient pressure, indicates only regular magnetovolume interactions.

Field-assisted sintering is a modern approach to novel magnesium materials preparation; however, it is unclear whether it is better to sinter green compact or loose powder. This work focuses on preparing bulk materials from loose and cold-compacted magnesium powder through a field-assisted sintering technique – spark plasma sintering (SPS). Green compacts were prepared under a series of compacting pressures from 100 MPa to 500 MPa. SPS was performed at 400 °C, 500 °C, and 600 °C applying additional pressure of 100 MPa during the sintering process. Prepared materials were analysed regarding their microstructure, hardness, and microhardness and through the three-point bending test and fractography. The green compacts porosity decreased with increased cold-compaction pressure. The SPS positively affected porosity and mechanical properties only in loose powder and the lowest cold-compacted green compacts. Increasing cold compaction pressure of the green compacts above 200 MPa is therefore unfavourable for further SPS processing.

Solid dispersion is considered one of the most successful strategies for improving the dissolution and absorption of poorly water-soluble APIs. The primary focus of this study was to investigate the effects of methods of solid dispersion preparation on the pharmaceutically important physicochemical properties of a product based on Soluplus ® as the polymer carrier and febuxostat as the model BCS II API. The methods of preparation evaluated were based on melt and solvent mechanisms. The samples prepared were evaluated by modulated differential scanning calorimetry, solid state NMR, Raman spectroscopy, XRPD, scanning electron microscopy, and BET analysis. Differences among the solid dispersions obtained by the specific methods and their mechanisms were clearly observed in in-vitro testing. The dissolution behaviour was shown to be influenced not only by particle characteristics such as the size and specific surface area, but also by the interactions between the API and the polymer matrix on the molecular level (e.g. non-covalent interactions). The set of measurements showed that similar methods of preparation do not lead to solid dispersion systems of similar characteristics. Surprisingly, similar dissolution profiles were found in samples prepared by very different methods although their physical-chemical characteristics differed significantly, and vice versa.

The presence of mitochondria and related organelles in every studied eukaryote supports the view that mitochondria are essential cellular components. Here, we report the genome sequence of a microbial eukaryote, the oxymonad Monocercomonoides sp., which revealed that this organism lacks all hallmark mitochondrial proteins. Crucially, the mitochondrial iron-sulfur cluster assembly pathway, thought to be conserved in virtually all eukaryotic cells, has been replaced by a cytosolic sulfur mobilization system (SUF) acquired by lateral gene transfer from bacteria. In the context of eukaryotic phylogeny, our data suggest that Monocercomonoides is not primitively amitochondrial but has lost the mitochondrion secondarily. This is the first example of a eukaryote lacking any form of a mitochondrion, demonstrating that this organelle is not absolutely essential for the viability of a eukaryotic cell.

Our study is focused on superconductivity in LaPt2Al2 compound. Specific heat and electrical resistivity measurements reveal a superconducting state below 0.57 K. Superconducting behaviour is in agreement with the weak coupling limit of BCS theory. The electronic Sommerfeld coefficient and equilibrium volume were described by first principles methods. The calculated electron phonon constant, λ = 0.48 , using the McMillan formula is small. The crystal lattice of LaPt2Al2 is described by the orthorhombic space group C m m e . Polarisation contrast microscopy reveals a domain structure, which is the result of a symmetry lowering structural transition above room temperature.

The structure, kinetics and thermodynamics of formation of unconventional fluoride conversion coating on wrought AZ61 magnesium alloy are described in this work. Fluoride conversion coating was prepared by immersion of the specimens of AZ61 magnesium alloy into Na[BF4] molten salt at 410, 420, 430, 440 and 450 °C for 0.5, 1, 2, 4, 8, 12, 24 and 36 h. Testing methods, such as scanning electron microscopy, focused ion beam cutting and transmission electron microscopy were used for the morphology analysis, chemical composition and microstructure investigation of the fluoride conversion coating. It was found that the coating was composed of the primary MgF2 and secondary Na[MgF3] layer. The growth mechanism of the primary coating layer was described by the empirical kinetic method. The apparent activation energy and pre-exponential factor, estimated from the Arrhenius plot, are 82.87 kJ·mol−1 and 8.22 s−1, respectively. The kinetic analysis of the coating growth indicates that the process is driven by the parabolic rate law of the stationary one-dimensional diffusion at 410 °C. The Jander equation of the stationary three-dimensional diffusion describes the coating growth at higher investigated temperatures.

The hybrid laser-tungsten inert gas welding technology was applied to butt weld 3-mm-thick S460MC and S700MC high-strength low-alloy steel sheets. The intent of low-current arc addition was to preheat the material to reduce extremely fast cooling rate accompanying laser welding. High-cycle fatigue tests were performed to evaluate the effect of welding conditions on fatigue behavior of S460MC and S700MC laser and hybrid welds. Both base materials exhibit approximately the same fatigue limit. However, corresponding samples with the weld behaved significantly different under cyclic loading. We demonstrated that the drop of their fatigue lifetime is caused by the combination of microstructural changes and especially by the presence of surface notches resulting from the welding process. The two series of both steels were tested to reveal the contribution of induced surface roughness and microstructural changes itself. The first one was in the as-welded condition. The second one had a smooth surface resulting from surface layer grinding after the welding. It was found, that the geometric notches created by the welding process are the determining factor in case of both tested steels. Testing of the ground samples showed, that in case of S460MC steel, the application of pre-heat did not improve the fatigue properties. On the other hand, the performed fatigue tests showed improved fatigue limit of ground series samples of the pre-heated S700MC steel, when compared with the conventional laser welding.

A nanofibrous membrane carrier for nearly water insoluble drug diosmin was formulated. The aim of this study was to evaluate the drug release and dissolution properties in an aqueous buffer of pH 7.8, and to compare the suitability of the drug carrier with the available drug forms and screen diosmin absorption extent. The membranes were produced from HPC/PVA/PEO-drug water solutions and then evaluated by SEM and DSC measurements. The results showed that diosmin was incorporated within the nanofibers in an amorphous state, and/or as a solid dispersion. The results of in vitro release experiments excerpt a very fast release of the drug, followed by the formation of an over saturated solution and partial precipitation of the drug (a “spring” effect). The enormous increases in dissolution of the drug from a nanofibrous carrier, compared to a micronized and crystalline form, was achieved. The in vivo bioavailability study carried out on rats showed higher initial drug plasma levels and higher AUC values after administration of the nanofibrous drug formulation, compared to the micronized form. The results of the study demonstrated that the improvement of the diosmin in vitro dissolution also brought the enhanced in vivo absorption extent of the drug.

The paper offers an analysis of the corrosion process of the AZ61 magnesium alloy protected with the unconventionally prepared fluoride conversion coating using Na[BF4] salt melt. The protection of the magnesium alloy with the coating was shown to vary depending on the preparation temperature (430 and 450 °C) and coating time (0.5, 2 and 8 h). Lower coating temperature and shorter coating times offer lower protection of the material against corrosion. Similar corrosion mechanism was observed for all the damaged specimens. Migration of the species from the SBF to the substrate through the coating resulted in the coating damage due to the H2 evolution and corrosion products creation following with more pronounced corrosion attack of the substrate. However, no signs of the corrosion attack were observed when the coating was prepared at 430 °C for 8 h and at 450 °C for 2 and 8 h even after 168 h of exposure of the specimen to the simulated body fluid solution at 37 ± 2 °C.

Sublingual administration of active pharmaceutical substances is in principle favourable for rapid onset of drug action, ready accessibility and avoidance of first pass metabolism. This administration could prove very useful in the treatment of migraines, thus two frequently used drugs were selected for our study. Sumatriptan succinate, naproxen, and its salt as well as combinations of these were incorporated into nanofibrous membranes via the electrospinning process. DSC measurements proved that the resulted membranes contained non-crystalline drug forms. SEM imaging approved good homogeneity of diameter and shape of the membrane nanofibres. The nanofibrous membranes always showed the rapid and mutually independent release of the tested drugs. The drugs exhibited very high differences in sublingual permeation rates in vitro, but the rates of both substances were increased several times using nanofibrous membranes as the drug carrier in comparison to drug solutions. The released drugs subsequently permeated through sublingual mucosa preferentially as non-ionized moieties. The prepared nanofibrous membranes proved very flexible and mechanically resistant. With their drug load capacity of up to 40% of membrane mass, they could be very advantageous for the formulation of sublingual drug delivery systems.

Cyclic deformation behavior and fatigue life of squeeze-cast AZ31 magnesium alloy was studied under stress amplitude-control at room temperature. Low and high cycle fatigue tests with engineering stress amplitudes in the range from 40 to 110 MPa were conducted. Analysis of hysteresis curves was performed. Tension–compression asymmetry of hysteresis loops was not observed; the alloy exhibited cyclic hardening in tension and compression. The fatigue life in the low cycle fatigue region was expressed by Wohler and derived Manson–Coffin curves. Experimental data in both, the low and high cycle fatigue regions were fitted by means of regression functions. S–N curves exhibited a smooth transition from the low to the high cycle fatigue regions and significant scattering of experimental points was observed. Furthermore, metallographic and fractographic analyses were performed. Crack initiation occurred from the specimen surface or on clusters of secondary particles; the region of final fracture was characterized by a transgranular ductile fracture. It can be concluded that the fatigue properties of squeeze cast magnesium alloy AZ31 are significantly improved comparing to materials prepared by common methods of casting. Squeeze casting also enables the cost-effective fabrication of complicatedly shaped parts.

The purpose of this work was to develop a novel approach to transdermal permeation enhancer design, based on utilizing some favorable properties of their metabolites. As an example of this concept, a series of carbamic acid salts of tranexamic acid (TXA) esters was synthesized, because TXA was previously shown to improve skin barrier homeostasis. Enhancement activities of 1% TXA derivatives dispersed in both hydrophilic and lipophilic vehicles were evaluated in vitro using human skin and theophylline as a model drug. Dispersed in an aqueous donor vehicle, the dodecyl ester showed the enhancement ratio (ER) of 4.3+/-0.9, which is almost 2 times higher than that of 1-dodecylazepan-2-one (Azone; 2.2+/-0.7). From an isopropyl-myristate suspension, the decyl ester was the most effective enhancer (4.9+/-1.4), while Azone was inactive. Decomposition of the carbamate in a slightly acidic environment was shown by FTIR; hydrolysis of the pertinent ester by porcine esterase was monitored by TLC and HPLC. Biodegradable enhancers of this type could mediate easier and faster recovery of the skin barrier after transdermal delivery through the action of the released TXA.

Novel transdermal permeation enhancers related to stratum corneum ceramides were investigated. The synthesis of a series of simple compounds based on two selected amino acids, l -serine and glycine, and their enhancement activities are reported. Glycine derivative 3 enhanced the permeation of theophylline through human skin in vitro 12.5±0.5 times. The relationships between properties of the polar head of the compounds and their activity are discussed.