Rapidly growing 3D printing of hydrogels requires network materials which combine enhanced mechanical properties and printability. One of the most promising approaches to strengthen the hydrogels ...consists of the incorporation of inorganic fillers. In this paper, the rheological properties important for 3D printability were studied for nanocomposite hydrogels based on a rigid network of percolating halloysite nanotubes embedded in a soft alginate network cross-linked by calcium ions. Particular attention was paid to the effect of polymer cross-linking on these properties. It was revealed that the system possessed a pronounced shear-thinning behavior accompanied by a viscosity drop of 4-5 orders of magnitude. The polymer cross-links enhanced the shear-thinning properties and accelerated the viscosity recovery at rest so that the system could regain 96% of viscosity in only 18 s. Increasing the cross-linking of the soft network also enhanced the storage modulus of the nanocomposite system by up to 2 kPa. Through SAXS data, it was shown that at cross-linking, the junction zones consisting of fragments of two laterally aligned polymer chains were formed, which should have provided additional strength to the hydrogel. At the same time, the cross-linking of the soft network only slightly affected the yield stress, which seemed to be mainly determined by the rigid percolation network of nanotubes and reached 327 Pa. These properties make the alginate/halloysite hydrogels very promising for 3D printing, in particular, for biomedical purposes taking into account the natural origin, low toxicity, and good biocompatibility of both components.
This study presents preparing and characterization of polyacrylonitrile (PAN) fibers containing various content of tetraethoxysilane (TEOS) incorporated via mutual spinning solution or emulsion using ...wet and mechanotropic spinning methods. It was shown that the presence of TEOS in dopes does not affect their rheological properties. The coagulation kinetics of complex PAN solution was investigated by optical methods on the solution drop. It was shown that during the interdiffusion process phase separation occurs and TEOS droplets form and move in the middle of the dope's drop. Mechanotropic spinning induces the TEOS droplets to move to the fiber periphery. The morphology and structure of the fibers obtained were investigated by scanning and transmission electron microscopy, as well as X-ray diffraction methods. It was shown that during fiber spinning stages the transformation of the TEOS drops into solid silica particles takes place as a result of hydrolytic polycondensation. This process can be characterized as the sol-gel synthesis. The formation of nano-sized (3-30 nm) silica particles proceeds without particles aggregation, but in a mode of the distribution gradient along the fiber cross-section leading to the accumulation of the silica particles either in the fiber center (wet spinning) or in the fiber periphery (mechanotropic spinning). The prepared composite fibers were carbonized and according to XRD analysis of carbon fibers, the clear peaks corresponding to SiC were observed. These findings indicate the useful role of TEOS as a precursor agent for both, silica in PAN fibers and silicon carbide in carbon fibers that has potential applications in some advanced materials with high thermal properties.
The Venus Monitoring Camera (VMC) acquired a set of ultraviolet (UV) images during the Venus Express mission unprecedented in its duration from May 2006 to September 2013. Here we present the results ...of digital tracking of the cloud features in the upper cloud layer at latitudes 25–75°S using images from 257 orbits with the best spatial coverage. The method relies on analysis of correlations between pairs of UV images separated in time. The bulk of data processed allows us to clarify the reasons why the mid-latitude jet is not always present in latitudinal wind profiles. Comparing VMC images with wind velocity fields we found a relationship between cloud morphology at middle latitudes and the circulation. The vector field in middle latitudes depends on the presence of a contrast global streak in the cloud morphology tilted with respect to latitude circles. The angle of the flow deflection (the angle between the wind velocity and latitudinal circles) and the difference of the zonal velocity on the opposite sides of the streak are in direct relationship to the angle between the streak and latitude circles. During such orbits the jet bulge does not appear in the latitudinal profile of the zonal wind component. Otherwise a zonal flow with small changes of the meridional velocity dominates in middle latitudes and manifests itself as a jet bulge. The relationship between the cloud cover morphology and circulation peculiarities can be attributed to the motion of global cloud features, like the Y-feature. We prepared plots of zonal and meridional velocities averaged with respect to the entire observation period. The average zonal velocity has a diurnal maximum at 15:00 local solar time and at 40°S. The meridional velocity reaches its maximum between 13:00 and 16:00 and at 50°S. The velocities obtained by the digital method are in good agreement with results of the visual method in the middle latitudes published earlier by Khatuntsev et al. (2013).
•Digital correlation method of cloud features tracking.•Relationship between the cloud morphology and atmospheric circulation.•Dependence of the cloud top wind speed on local solar time and cloud top altitude.
The Thermal InfraRed channel in honor of professor Vassili Ivanovich Moroz (TIRVIM) of the Atmospheric Chemistry Suite onboard ExoMars Trace Gas Orbiter has continuously monitored the Martian ...atmosphere from 13 March 2018 until 2 December 2019, covering almost a complete Martian Year (MY). In the nadir mode of observations, infrared spectra obtained by TIRVIM in the spectral range 600–1,300 cm−1 permit retrievals of vertical temperature profiles from the surface up to 60 km of altitude, surface temperatures and column aerosol optical depths. Here we report the retrieved atmospheric thermal structure and the column dust content during the global dust storm (GDS) of MY 34 monitored from Ls = 182.2° to Ls = 211.8° (Solar Longitude), capturing the evolution of the GDS and the response of the atmospheric thermal structure to the changing dust loading. The global storm caused asymmetric atmosphere heating, predominantly in the southern hemisphere, and changed diurnal contrast of atmospheric thermal structure. We also observe a reduced diurnal contrast of surface temperatures at the peak of the GDS.
Plain Language Summary
The thermal radiation emitted by Mars in the spectral range 7.7–16.7 μm was measured by the Atmospheric Chemistry Suite Thermal InfraRed channel in honor of professor Vassili Ivanovich Moroz (ACS TIRVIM) onboard ExoMars Trace Gas Orbiter. The nadir spectra carry information about the temperature of the atmosphere at different altitudes thanks to a deep CO2 absorption present around 15 μm. Also, the dust loading can be found from the 9‐μm silicate absorption, and the surface temperature can be estimated at 7 μm where the atmosphere is mostly transparent. We follow the evolution of these parameters during the strong global dust storm of Martian Year (MY) 34 (2018). The peculiarity of the ACS TIRVIM data set is the exceptionally dense coverage providing a new look at this otherwise well‐studied dust event.
Key Points
Atmospheric thermal structure and dust content on Mars are retrieved from Atmospheric Chemistry Suite Thermal InfraRed channel nadir measurements in the spectral range 7.7–16.7 μm
The 2018 global dust storm covered the entire planet and caused an asymmetric heating of the atmosphere with a hotter southern hemisphere
We observe a reduced diurnal contrast of surface temperatures and a changed contrast of atmospheric thermal structure during the storm
To make tissue engineering a truly effective tool, it is necessary to understand how the patterns of specific tissue development are modulated by and depend on the artificial environment. Even the ...most advanced approaches still do not fully meet the requirements of practical engineering of tracheobronchial epithelium. This study aimed to test the ability of the synthetic and natural nonwoven scaffolds to support the formation of morphological sound airway epithelium including the basement membrane (BM). We also sought to identify the potential role of fibroblasts in this process. Our results showed that nonwoven scaffolds are generally suitable for producing well-differentiated tracheobronchial epithelium (with cilia and goblet cells), while the structure and functionality of the equivalents appeared to be highly dependent on the composition of the scaffolds. Unlike natural scaffolds, synthetic ones supported the formation of the epithelium only when epithelial cells were cocultured with fibroblasts. Fibroblasts also appeared to be obligatory for basal lamina formation, regardless of the type of the nonwoven material used. However, even in the presence of fibroblasts, the synthetic scaffolds were unable to support the formation of the epithelium and of the BM (in particular, basal lamina) as effectively as the natural scaffolds did.
The design and performance features of an IR Fourier-transform spectrometer for studying the Martial atmosphere in the spectrum range of 600–5500 cm
–1
during the ExoMars-2016 mission are described. ...The obtained spectral resolution is in agreement with the theoretical value (0.2 cm
–1
); the threshold of the instrument sensitivity is approximately 0.1 mW/(m
2
sr cm
–1
).
A strongly nonmonotonic temperature dependence of the magnetoresistance in (CoFeB)
x
(LiNbO
y
)
100 –
x
film nanocomposites (
x
≈ 40–48 at %) is observed in the temperature range of 3–250 K at the ...magnetic field up to 14 T near the percolation threshold on its insulating side. The magnetoresistance has a minimum at 40 K and increases steeply on cooling. Such behavior of the magnetoresistance is attributed to the coexistence of superferromagnetic regions with exchange-coupled granules separated by regions with superparamagnetic granules in the nanocomposite. In this case, an increase in the negative magnetoresistance at
T
> 40 K is due to the destruction of superferromagnetic ordering, whereas an increase in the magnetoresistance at
T
< 40 K is related to the processes involving simultaneous elastic tunneling via the chains of granules. At the saturation of the magnetization, an additional negative contribution arises, which is probably due to the quantum interference effects. At
T
< 4 K, a double-well shape of the field dependence of the magnetoresistance is observed, which could be attributed to the effect of a positive contribution that competes with the negative magnetoresistance.
Highly porous polymer materials have been studied a lot for applications in biotechnology and biomedicine, because of their high surface area and percolated pore structure. Varying processing ...conditions, in this study, can tune the morphology, mechanical, and physicochemical characteristics of the materials. In the present work, cross‐linked poly(vinyl alcohol)‐based freeze‐dried sponges linked by glutaraldehyde are studied. The current study analyzes the influence of cooling speed on the sponge's morphology and mechanical properties. Complex analysis of the tests carried out shows agreement in morphology, surface area, equilibrium degree of swelling, and mechanical properties of the sponges with dependence on the amount of cross‐linking agent and freezing conditions.
The adhesive properties of scaffolds, which primarily depend on the chemical and structural features of their surface, play an important role in the tissue engineering. The cell adhesion of ...dissociated primary neuronal culture to isotropic and anisotropic nonwoven and sponge polylactide scaffolds was studied by fluorescence and environmental scanning electron microscopy. Neurons extracted from neonatal mouse brain showed improved adhesion on all types of scaffolds after the plasma treatment. The most pronounced effect was observed for non-oriented scaffolds.
Abstract
A simulator of lunar soil and lunar dust has been developed, designed for modeling various engineering processes in terrestrial conditions. The elemental and granulometric compositions of ...the simulator were studied using X-ray fluorescence analysis, scanning electron microscopy and laser light scattering. The resulting material will be used in the future to simulate thermophysical processes when creating lunar power generating plants. The finely dispersed component of the simulator based on basalt wool will be used to study the filtration of lunar dust.
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