Variations In Surface Morphology Research Articles

Fractal variation of three-dimensional surface topography during sliding wear under mixed elastohydrodynamic lubrication

The surface morphology variation of the friction pair during the wear process directly affects the local lubrication effect and contact strength, and this variation is difficult to quantify in mixed lubrication. In this study, a numerical simulation and characterization model method of sliding wear surface morphology evolution based on deterministic elastohydrodynamic lubrication (EHL) model and surface three-dimensional morphology fractal method is established. The effectiveness of the lubrication model is verified by the film thickness measurement, and the actual surface wear coefficient is obtained through the wear experiment. On this basis, the variation of surface morphology and fractal parameters in the sliding wear process is investigated, and the effect of contact load and sliding speed on surface lubrication characteristics and fractal parameters is analyzed. The results show: wear will cause the higher wave peaks on the ground surface to be gradually worn away and the fine structure of the surface is reduced, and the fractal dimension of the morphology is therefore reduced. In addition, the contact area ratio and contact load ratio, as well as the coefficient of friction and surface evolution under different loads and sliding speeds are consistent.

Strike-slip faulting on Titan: Modeling tidal stresses and shear failure conditions due to pore fluid interactions

Expressions of strike-slip faulting are well documented on multiple ocean worlds (e.g., Europa, Enceladus, and Ganymede) and the motion along these faults is thought to be driven by variations in diurnal tidal stresses. Titan exhibits a complex and dynamic geology with a varied surface morphology developed from fluvial, aeolian, and possible cryovolcanic and tectonic activity. However, observational data are currently limited and no clear strike-slip indicators have been identified so far. Nevertheless, the inferred presence of a porous ice layer saturated with liquid hydrocarbons in Titan's shallow subsurface provides a unique environment for studying zones of frictional weakness, shear heating, and the promotion of cryovolcanism. This study examines Titan's ability to host shear deformation mechanisms, including considerations for how the presence of near-surface liquid hydrocarbons and the crustal porosity of ice significantly reduce the resistance to shear failure of strike-slip faults in flexed areas under maximum diurnal tidal stresses. We conduct a sensitivity analysis of Titan's shear failure tendencies, given optimal failure conditions that may exist due to pore fluid interactions, and we examine the possibility for strike-slip tectonics guided by Coulomb failure laws and tidal stress mechanisms. Using the SatStress tidal stress model for a Titan-appropriate rheology, we compute the diurnal tidal stress tensor and resolve shear and normal stresses onto a suite of fault orientations. We adopt plausible coefficients of friction and include the effect of a hydrostatic pore fluid pressure gradient for Titan. At shallow fault depths (< 1 km) and for optimally oriented faults, this exploratory model suggests shear failure is achievable under diurnal tidal stress conditions subject to such pore fluid pressures, especially in the polar regions. Our results suggest that under these conditions, shear failure is not only possible, but may be an active deformation mechanism on the surface and in the subsurface of Titan, and could potentially serve as a pathway for the exchange of surface and subsurface materials through shear heating mechanisms. Moreover, the inference of conditions supporting strike-slip tectonism on Titan could have important implications for future Dragonfly observations and for future studies directed at better understanding the structural development of the surfaces of icy moons.

Geologic Mapping and Age Determinations of Tsiolkovskiy Crater

Tsiolkovskiy is a ~200 km diameter crater presenting one of the few mare deposits of the lunar far side. In this work, we perform a geological study of the crater by means of morpho-stratigraphic and color-based spectral mappings, and a detailed crater counting age determination. The work aims at characterizing the surface morphology and compositional variation observed from orbital data including the Lunar Reconnaissance Orbiter Wide Angle Camera and Clementine UVVIS Warped Color Ratio mosaics, and attempts a reconstruction of the evolutionary history of the Tsiolkovskiy crater through both relative and absolute model age determinations. The results show a clear correlation between the geologic and spectral units and an asymmetric distribution of these units reflecting the oblique impact origin of the crater. Crater counts performed using the spectral units identified on the smooth crater floor returned distinct age ranges, suggesting the occurrence of at least three different igneous events, generating units characterized by particular compositions and/or degree of maturity. This work demonstrates the scientific value of Tsiolkovskiy crater for a better understanding of the volcanic evolution of the Moon and, in particular, of its far side.

Boron doped diamond thin films for the electrochemical detection of SARS-CoV-2 S1 protein

Amidst a global pandemic, a precise and widely accessible rapid detection method is needed for accurate diagnosis and contact tracing. The lack of this technology was exposed through the outbreak of SARS-CoV-2 beginning in 2019. This study sets the foundation for the development of a boron doped diamond (BDD)-based impedimetric sensor. While specifically developed for use in the detection of SARS-CoV-2, this technology uses principles that could be adapted to detect other viruses in the future. Boron doped polycrystalline diamond electrodes were functionalized with a biotin-streptavidin linker complex and biotinylated anti-SARS-CoV-2 S1 antibodies. Electrodes were then incubated with the S1 subunit of the SARS-CoV-2 spike surface protein, and an electrical response was recorded using the changes to the electrode's charge transfer resistance (Rct), measured through electrochemical impedance spectroscopy (EIS). Detectable changes in the Rct were observed after 5-min incubation periods with S1 subunit concentrations as low as 1 fg/mL. Incubation with Influenza-B Hemagglutinin protein resulted in minimal change to the Rct, indicating specificity of the BDD electrode for the S1 subunit of SARS-CoV-2. Detection of the S1 subunit in a complex (cell culture) medium was also demonstrated by modifying the EIS protocol to minimize the effects of sample matrix binding. BDD films of varying surface morphologies were investigated, and material characterization was used to give insight into the microstructure-performance relationship of the BDD sensing surface.

Unusual Surface Texture, Dimensions and Morphology Variations of Chiral and Single Crystals**

AbstractWe demonstrate here a unique metallo‐organic material where the appearance and the internal crystal structure are in contradiction. The egg‐shaped (ovoid) crystals have a brain‐like texture. Although these micro‐sized crystals are monodispersed; like fingerprints their grainy surfaces are never exactly alike. Remarkably, our X‐ray and electron diffraction studies unexpectedly revealed that these structures are single‐crystals comprising a continuous coordination network of two differently shaped homochiral channels. By using the same building blocks under different reaction conditions, a rare series of crystals have been obtained that are uniquely rounded in their shape. In stark contrast to the brain‐like crystals, these isostructural and monodispersed crystals have a comparatively smooth appearance. The sizes of these crystals vary by several orders of magnitude.

Unusual Surface Texture, Dimensions and Morphology Variations of Chiral and Single Crystals**

We demonstrate here a unique metallo-organic material where the appearance and the internal crystal structure are in contradiction. The egg-shaped (ovoid) crystals have a brain-like texture. Although these micro-sized crystals are monodispersed; like fingerprints their grainy surfaces are never exactly alike. Remarkably, our X-ray and electron diffraction studies unexpectedly revealed that these structures are single-crystals comprising a continuous coordination network of two differently shaped homochiral channels. By using the same building blocks under different reaction conditions, a rare series of crystals have been obtained that are uniquely rounded in their shape. In stark contrast to the brain-like crystals, these isostructural and monodispersed crystals have a comparatively smooth appearance. The sizes of these crystals vary by several orders of magnitude.

Modeling the feedbacks between surface ablation and morphological variations on debris-covered Baltoro Glacier in the central Karakoram

Recent studies show that many debris-covered glaciers exhibit high-magnitude differential thinning despite the presence of supraglacial debris. Existing studies have not adequately explored the variability in surface ablation, morphology, and related feedback mechanisms that incorporate topographically controlled surface irradiance and debris transport. In this study, we address these issues using a radiation-driven surface ablation model that more fully characterizes ablation dynamics by accounting for temporally-linked radiative forcing, surface geomorphological evolution and gravitational debris flux. Simulation results based on Baltoro Glacier in the central Karakoram indicate the following: 1) A debris-covered glacier can exhibit high spatial variability in surface ablation due to heterogeneous debris thickness and debris transport. A bare-ice glacier given similar initial conditions, has higher overall ablation but exhibits much less variability. 2) The topographic influence on surface ablation is non-negligible because glacier-surface topography controls irradiance and gravitational debris flux. The overall ablation on a debris-covered glacier tends to increase in response to high-frequency topographic variations due to the larger area with thin debris cover. In contrast, a bare-ice glacier exhibits decreased overall ablation in response to high-frequency topographic variations due to its high sensitivity to topographic shading. 3) Gravity-driven surface debris flux plays an important role in local debris thickness redistribution, which regulates ablation rates over the ablation season. 4) Surface ablation dynamics on a debris-covered glacier is regulated by active system couplings and feedbacks between surface morphology, melt and debris transport. Consequently, certain locations on a debris-covered glacier may be more sensitive to radiative forcing than previously thought. Simulation results suggest that nonlinear feedback responses may permit debris-covered glacier subsystems to be very sensitive to radiative forcing, thereby causing significant morphological changes to the glacier surface.

InN crystal habit, structural, electrical, and optical properties affected by sapphire substrate nitridation in N-polar InN/InAlN heterostructures

Indium nitride (InN) is a very promising direct bandgap semiconductor material for near-infrared optoelectronic devices and high speed transistors, however InN growth is much more challenging compared to other III-N semiconductors. In this study we analysed the impact of pre-growth vicinal c-plane sapphire substrate nitridation on the electrical, optical, and strucutral properties of N-polar InN/InAlN heterostructures and the InN crystal habit. While a short cool-down nitridation phase resulted in a high quality InAlN layer and low quality InN layer, it was the opposite for a long cool-down nitridation phase. A trade-off between the electrical and optical properties was observed: the short nitridation cool-down produced InN layers with a higher electron mobility of 629 cm2 V−1 s−1 and low photoluminescence (PL) emission, and the long one resulted in InN with a ∼21% lower electron mobility of 497 cm2 V−1s−1 but strong PL emission. Also, a very different InN crystal habit was observed for either case. The short nitridation cool-down was conducive to the formation of a continuous layer consisting mostly of coalesced downward-pointing hexagonal pyramids, while the long one led to a layer of upward-pointing hexagonal pyramids. The local decomposition of an AlON layer produced by sapphire nitridation and variations in the InAlN surface morphology resulting in a preferential attraction of growth species and localised change in the surface free energy contributions were most likely responsible for these observations. Our results also suggest N-polar buffer layers are likely to produce coalesced InN layers with a high electron mobility, while metal-polar buffer layers may facilitate the growth of high crystal quality pyramidal InN with a strong optical response.

Numerical and analytical investigation on meltpool temperature of laser-based powder bed fusion of IN718

Prediction of meltpool features in Laser-Based Powder Bed Fusion (LB-PBF) is a complex non-linear multiple phase dynamic problem. In this investigation, numerical simulations and analytical models are offered to predict meltpool temperature and to provide a methodology to estimate melt track quality. By determining the meltpool temperature, different rheological phenomena including recoil pressure can be controlled. Recoil pressure is known to drive the keyhole and conduction modes in LB-PBF which is an important factor to qualify the melt track. A numerical simulation was carried out using Discrete Element Method (DEM) with a range of process parameters and absorptivity ratios; allowing observation of the variation of meltpool temperature and free surface morphology, as calculated by the volume-of-fluid (VOF) method. A spatially thermophysical-based analytical model is developed to estimate meltpool temperature, based on LB-PBF process parameters and thermophysical properties of the material. These results are compared with experimentally observed meltpool depth for IN718 specimens and found to have a good accuracy. The numerical and analytic results show good agreement in the conduction mode to estimate the meltpool temperature and related phenomena such as recoil pressure to control the melt track and layering quality. The analytical model does not accurately predict the keyhole mode which may be explained by evaporation of chemical elements in the examined material.

Green Three-Step Electrodeposition of Mn+3 Rich Layered δ-Phase MnO2 Nanofibers on Silicon and Epitaxial Graphene-Silicon Carbide Heterostructures

Mixed valence manganese oxides (MnOx) have attracted significant research interest in recent years due to the easily reversible redox reactions between manganese oxidation states (Mn+2, Mn+3, and Mn+4)1 which enable applications in catalysis2, energy storage3, and gas sensing4. Of the manganese oxides manganese dioxide (MnO2) has been of particular interest due to its wide variety of synthesized structural polymorphs ((β)1x1 tunnel5, (α)1x2 tunnel5 (γ) spinel5, (δ) layered5) which allow for enhanced control over the available surface area and reactive properties of MnO2. Among these structural polymorphs, the α and δ phases exhibit mixed-valence character with Mn+3 defects being found throughout the crystal structure5. Mn+3 defects have been found to increase the catalytic activity of MnO2 making its presence desirable6. Hexagonal δ-MnO2, in particular, contains a large number of Mn+3 ions as the interlayer contains Mn+2/+3 ions to neutralize the layer charge from Mn+3 lattice defects7. However, the controlled synthesis of hexagonal δ-MnO2 has proven challenging and often relies on the use of harsh chemicals1, high temperatures1, and long reaction times1. These methods also rely on permanganate salts1 as the manganese precursor, which leads to the formation of monoclinic δ-MnO2 and significantly reduces the number of Mn+3 defects in the crystal lattice. In this work, we present the green facile synthesis of high Mn+3 content hexagonal δ-MnO2 via electrodeposition on both silicon(Si) and epitaxial graphene/silicon carbide(EG/SiC) substrates. The electrodeposition was carried out in a three-electrode electrochemical cell with an Ag/AgCl reference electrode, a Pt counter electrode, and the substrate (Si or EG/SiC) as the working electrode utilizing a 100mM manganese acetate solution. The electrodeposition process contained three steps, an initial pulse at the oxidation potential to seed the surface with oxygen, a second pulse at the reduction potential to deposit manganese on the surface, and a third pulse at the oxidation potential to oxidize the deposited manganese, with the potentials determined by cyclic voltammetry. The resulting δ-MnO2 thin films were then characterized through Raman spectroscopy, X-Ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy(AFM) to determine its crystalline phase and surface morphology. Raman spectroscopy(Fig. 1) confirmed the formation of MnO2 on both substrates due to the presence of Raman peaks between 650-640cm-1,8 575-585cm-1,8, and 490-510cm-1,8, which are associated with the Mn-O symmetric stretching bond8, the Mn-O stretching bond in the basal plane8, and Mn-O stretching bond in the [MnO6] octehedra8. The formation of the δ phase is confirmed by the presence of a weak peak at 130cm-1,2 consistent with the literature. The observed 9cm-1 redshift of the 490-510cm-1,6 between Si and SiC substrates is associated with the weakening Mn-O stretching bond on Si, which combined with the strengthening of the peak at 600-620cm-1 indicates that the growth on Si contains a higher rate of Mn+3defects2,8. XPS corroborated this result and indicated that the manganese in the δ-MnO2 deposited on EG/SiC had an average oxidation state of 3.3. The AFM images indicated that the surface was made up of nanofibrous nanoparticles, with the deposition on Si exhibiting significantly larger nanofibers (Fig 2.). SEM confirmed this (Fig. 3) and indicated that the deposition on EG/SiC was made up of microplates ~40umx40um in size, which was not observed in the deposition on Si. We believe this variation in surface morphology is due to interactions between SiC and MnO2, which are not present when δ-MnO2 is grown on Si. The reactivity of the deposited δ-MnO2 was then tested by depositing 4 Ti/Au (30nm/120nm) contacts on the δ-MnO2/EG/SiC heterostructures to form a simple gas sensor, which was tested against 5ppm NO2, 5ppm NH3, 1000ppm IPA, and 1000ppm methanol. The sensor displayed a remarkably fast response/ recovery time of 3.8s/2.2s to NH3 and 3.4/6.0s to NO2(Fig. 4), demonstrating the high reactive potential of the δ-MnO2 thin films. This reactivity demonstrates that our electrodeposited δ-MnO2 provides a good candidate for use in other applications of MnO2 such as energy storage and catalysis.

Physicochemical and functional characteristics of polysaccharides from okra extracted by using ultrasound at different frequencies

In this study, single- (SFU) and dual-frequency (DFU) ultrasounds were used to extract polysaccharides from okra (Abelmoschus esculentus (L.) Moench) pods (OPSs), and the physicochemical characteristics, functional properties, and in vitro biological activities of the OPSs were comparatively evaluated. Results showed that ultrasonic extractions at different frequencies led to remarkable variations in extraction yields, chemical components, monosaccharide compositions, molecular weights (MWs), surface morphologies, and rheological properties of the OPSs but hardly affected their preliminary structural features and thermal stabilities. The OPS obtained through DFU at 40/60 kHz with the lowest MWs (0.85–14.93 × 105 Da) and highest polyphenol content (7.38%) as well as loosest network structures showed superior antioxidant, cholesterol absorption and nitrite ion absorption capacities than the other OPSs, and the OPS extracted through SFU at 20 kHz with the highest carboxylate content (76.08%), MWs (7.28–32.83 × 105 Da) and degree of esterification (30.7%) exhibited higher bile acid-binding capacity than the other OPSs.

Antimicrobial and antioxidant properties of biosynthesized of NiO nanoparticles using Raphanus sativus (R. sativus) extract

The aim of this study was to explore the antibacterial and antioxidant efficacy of nickel oxide nanoparticles (NiO NPs). The Raphanus sativus (R. sativus) extract mediated NiO NPs were calcined at 100, 300, 600 and 900 ℃ in a muffle furnace for 3 h. The increased intensity of diffraction bands in the X-ray diffraction (XRD) spectrum suggest that the degree of crystallinity increases with increasing calcination temperature. The desired elements was depicted in the energy dispersive X-rays (EDX) spectrum confirm the purity of the NiO Sample. The variation in surface morphology and increase in the particles size from 12.78 to 51.42nm was determined from the transmission electron microscope (TEM) micrographs. The shift toward higher wavelength was observed in the diffuse reflectance spectroscopy (DRS) spectra with increasing calcination temperature, results into a clear decrease in band gap from 3.12 to 2.86 eV. The presence of hydroxyl group along with other organic moieties were confirm through Fourier transform infrared (FTIR) spectroscopy analysis. The biological potential of the calcined NiO NPs was examined during the antibacterial and antioxidant experiments. The antibacterial effect of NiO NPs was studied using the agar well diffusion process, and the ABTS free radical scavenging potential of NiO NPs was also assessed. The activity of NiO NPs calcined at 100 °C is greater than that of those calcined at higher temperatures.

Comparative taxonomic variation in fruits and seeds' surface morphology among populations of alpine Rosa sericea complex (Rosaceae).

In this research, the fruits and seeds' surface morphological features and their taxonomic significance were determined. Additionally, useful traits for delimitation of taxa of Rosa sericea complex were studied. In this research, three taxa of the complex R. sericea, R. omeiensis, and R. sikangensis have been studied. A total of 41 populations and 130 specimens of seeds, and 35 populations and 168 specimens of fruits from 10 different geographical regions of southwest China have been examined. The surface micro-morphological characters of the seeds have been studied through scanning electron microscopy to distinguish important characteristics of the complex taxa. Forty-four different qualitative and quantitative characteristics were observed. Principal component analysis was used to simplify and elucidate the relationship between the studied characters of different population based on the morphology of fruits and seeds' features. Moreover, the numerical taxonomic characters and their variation with elevation have been studied in these species. The most interesting characters observed on the surface of the seeds were stomata, and trichomes, for which density was more at the dorsal and ventral parts, while rarely present on the lateral parts. The fruits and seeds' surface morphology of the studied species was complicated and some variation in the characters, that is, persistent calyx shape, the shape of fruits and seeds, stomata shape, and trichomes size were found significant for delimitation of taxa in the complex. The purpose of this study is to identify the taxa of R. sericea complex based on fruits and seeds' morphological characters, and identification keys.

Supercritical water gasification of wheat straw: Composition of reaction products and kinetic study

Supercritical water gasification (SCWG) technology is a potential technology to convert solid wastes to hydrogen rich gas products. But the gasification mechanism of real biomass in SCW is unclear due to its complicated composition and unique properties of SCW. In this paper, the gasification experiment of wheat straw in SCW was conducted in a quartz tube batch reactor, and the gasification properties was analyzed through researching the variation of gas yield, composition, liquid products and surface morphology of biochar to help understand the gasification mechanism. Besides, the reaction kinetic model of wheat straw was established to provide guidance for the acceleration of its gasification. The results illustrated that the increase of reaction time can enhance the gasification obviously (CGE increased by 37% as time extended from 1 min to 15 min) and temperature became the limitation factor after 15min. Higher temperature can increase the hydrogen yield obviously, which was raised by 7.2 mol/kg within 100 °C temperature increment, and the highest hydrogen yield was 12.88 mol/kg at 700 °C, 30 min. Kinetic study illustrated that the decomposition of PAHs was the rate-controlling step of wheat straw, activation energy of which was the highest, 427.13 kJ mol−1.

Dissolution of Different Reservoir Rocks by Organic Acids in Laboratory Simulations: Implications for the Effect of Alteration on Deep Reservoirs

Organic acids are important agents in the alteration of deep reservoirs. It is difficult, however, to assess the impact of organic acid alteration on deep reservoirs because different dissolution processes may occur during diagenesis. This study simulated the dissolution of three different types of reservoir rocks by acetic acid in a closed system and compared the mineral and elemental composition, surface morphology, pore structure, and water chemistry variations of the initial and altered samples. The study demonstrated that both micrite and sucrosic dolostone are strongly dissolved, losing about 20%–30% of their initial rock sample weights. Observation under SEM showed that the limestone dissolved homogenously, whereas the dolostone showed honeycomb-like dissolution. Both carbonate samples showed the development of large voids, including holes and cavities of micrometer scale, but nanopores of various sizes were blocked. In contrast, lithic arkose was heterogeneously altered, losing a weight proportion of about 13% by dissolution of calcite cement. These micrometer-scale microfissures were developed, but those nanometer-scale pores just varied in a narrow range of sizes. The volume increase in all three reservoir types is mainly attributed to the dissolution of carbonate minerals. In deep reservoirs, in situ generated organic acids can enlarge existing cavities in carbonates and develop microfissures in sandstones. The microfissure porosity in sandstone is limited but can increase through other geological processes such as overpressure. More importantly, these acids can maintain the acidity of pore waters, inhibit the precipitation of dissolved minerals, and help to preserve reservoir porosity. Although temperature plays an insignificant role in laboratory simulations, it influences both the generation and destruction processes of organic acids in deep reservoirs on geologic time scales and, thus, warrants further attention. The results provide a basis for recognizing the typical patterns of organic acid dissolution on different reservoir rocks and further suggest the potential role of organic acids in the formation and preservation of secondary porosity in deeply buried reservoirs.

Experimental and theoretical studies on the surface morphology variation of a Ni substrate by graphene growth

As graphene grows on a metal substrate, step bunching and terrace formation occur due to thermodynamic instability. Variation in the terrace–step bunching morphology is caused by graphene–metal interaction. The mechanism for this morphological variation was elucidated in terms of the crystal lattice matching by the observation of step bunching formation using in situ scanning electron microscopy and analysis of the crystal orientation of the same microscopic field using electron backscatter diffraction. The cross-sectional structure was also observed using transmission electron microscopy (TEM). These combined methods enable a reliable analysis of the step bunching region. The lattice matching was also evaluated according to the 0-lattice theory. From the structural analysis using TEM and the application of the 0-lattice theory, the graphene-covered surface was confirmed to consist of good and poor lattice-matching regions. The steps ejected from the terrace region piled up in the poor lattice-matching region to form a low Miller index plane. It was concluded that step flow occurs on the good lattice-matching region and steps are piled up and arranged very closely on the poor matching region based on the lattice-matching evaluation by the 0-lattice theory.

Light Scattering from Rough Silver Surfaces: Modeling of Absorption Loss Measurements.

We consider two series of experimental setups of multilayered Ag/ZnO thin films with varying surface morphologies given by atomic force microscopy images. The absorption loss under diffuse scattering is studied theoretically by applying a combination of the scattering matrix approach with diffraction theory for randomly nanotextured interfaces. Our modeling is in excellent agreement with the respective measurements. The theoretical approach is applicable to a wide range of wavelengths, surface morphologies, and materials for both measured and computed rough surface morphologies.

Aging of PVDF and PES ultrafiltration membranes by sodium hypochlorite: Effect of solution pH

Sodium hypochlorite (NaClO) is a commonly applied cleaning agent for ultrafiltration membranes in water and wastewater treatment. Long-term exposure to NaClO might change the properties and performance of polymeric membranes, and ultimately shorten membrane lifespan. Active species in NaClO solution vary with solution pH, and the aging effects can change depending on the membrane material. In this study, the aging of polyvinylidene fluoride (PVDF) and polyethersulfone (PES) membranes by NaClO at pH 3–11 was investigated by examining variations in chemical composition, surface charge, surface morphology, mechanical strength, permeability, and retention ability. Polyvinyl pyrrolidone (PVP), which was blended in both membranes, was oxidized and dislodged due to NaClO aging at all investigated pH values, but the oxidation products and dislodgement ratio of PVP varied with solution pH. For the PVDF membrane, NaClO aging at pH 3–11 caused a moderate increase in permeability and decreased retention due to the oxidation and release of PVP. The tensile strength decreased only at pH 11 because of the defluorination of PVDF molecules. For the PES membrane, NaClO aging at all investigated pH resulted in chain scission of PES molecules, which was favored at pH 7 and 9, potentially due to the formation of free radicals. Therefore, a decrease in tensile strength and retention ability, as well as an increase in permeability, occurred in the PES membrane for NaClO aging at pH 3–11. Overall, the results can provide a basis for selecting chemical cleaning conditions for PVDF and PES membranes.

Mehanizmi i morfologije kavitacionog oštećenja čelika Nionikral 70

Broken test tubes for low-cycle fatigue testing of Nionicral 70 (NN-70) parent material (PM) steel and simulated heat-affected zones (SHAZ) were used to produce samples for cavitation resistance testing. Ultrasonic vibrational cavitation method (stationary sample method) was applied for testing in laboratory conditions. The test conditions and procedure, sample preparation and interpretation of results are defined by ASTM G32. The surfaces of the NN-70 PM and SHAZ steel samples were exposed to cavitation and damage monitoring over time. Measuring the weight loss of samples on the analytical balance after a certain time allowed us to determine the cavitation velocity as a measure of the material's resistance to the effect of cavitation. Scanning electron microscopy (SEM) was applied to monitor variations in surface morphology with changing test time. On the basis of the results of the cavitation resistance test, the morphologies of the surface damage for different exposure times of the cavitation of PM and SHAZ steel NN-70 samples were analyzed, as well as the mechanisms that led to the damage of the sample surfaces.

Putative crayfish burrows from the Upper Triassic Grabowa Formation of southern Poland

The present paper provides the first description of natural casts of arthropod- made burrows recovered from the continental Upper Triassic Grabowa Formation in the southern Poland. Casts' general morphologies and nature of cast- forming sediments – all corroborate the conclusion that the casts are of open tubular burrows once communicated with the surface and subsequently passively infilled with sediments. Despite their fragmentary and ex situ preservation, some of the casts represent branched structures and horizontal components of the original burrows. The surficial morphology is smooth or displays features like: scrap marks, scratches, knobby textures, metameric body parts' impressions, nodes and elongated coiled imprints. Branching, horizontal components and most of the surficial features (excluding nodes and elongated coiled imprints) are assignable to activity of arthropods, possibly crayfish. One specimen displays features known from lungfish burrows. The observed smooth to sculptured variation of surface morphology is likely a function of substrate water saturation – burrowers lived in a phreatic and vadose zones of the groundwater profile and dug within softground and firmground substrates, respectively.