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31.
Plastic immersed heat exchangers are used in various applications where chemically neutral and noncorrosive equipment is required. Their potential competitors, namely, polymeric hollow‐fiber bundles, were investigated. Three different fiber bundles were tested as immersed coolers of a hot reservoir. Two types of polypropylene hollow fibers with various outside diameters were employed. Fibers were twisted with different curvature to achieve better distribution and improve natural convection on their outer surface. Calculation by experimental results was compared with the equation for natural convection across the horizontal cylinder, which overestimates heat transfer coefficients and can be applied for only rough estimation. Experimentally achieved pressure drops agreed well with theoretical prediction for laminar flow. 相似文献
32.
Slobodan D. Dolić Dragana J. Jovanović Krisjanis Smits Biljana Babić Milena Marinović-Cincović Slavica Porobić Miroslav D. Dramićanin 《Ceramics International》2018,44(15):17953-17961
Monoclinic scheelite-type BiVO4 is currently considered as one of the most promising non-titania photocatalysts, wheras tetragonal zircon-type BiVO4 is still poorly understood. Herein, a new and simple synthetic approach was applied and nanostructured single-phase zircon-type BiVO4 was successfully prepared by a controllable ethylene-glycol colloidal route. In addition, nanostructured monoclinic scheelite-type BiVO4 powders were also fabricated through annealing of the as-prepared samples. A comparative study of the two BiVO4 polymorphs was conducted and it turned out that the novel synthetic approach had a significant impact on porosity and photocatalytic performance of zircon-structured BiVO4. All the prepared materials, as-prepared and annealed, were mesoporous, while measured values of specific surface area of some zircon-structured samples (~34?m2/g) were ~7 times higher than those reported thus far for this phase. Interestingly, for the first time, zircon-type BiVO4, previously considered to be a poor photocatalyst, exhibited a better overall performance in degradation of methyl orange compared to monoclinic scheelite-type BiVO4. Hence, it could be expected that the here-presented synthesis and observations will both arouse interest in scarcely studied tetragonal zircon-type BiVO4 and facilitate as well as speed up further research of its properties. 相似文献
33.
Ta?ana?Vacková Jaroslav?Kratochvíl Aleksandra?Ostafinska Sabina?Krej?íková Martina?Nevoralová Miroslav?SloufEmail authorView authors OrcID profile 《Polymer Bulletin》2017,74(2):445-464
Crystallization kinetics of polycaprolactone (PCL) filled with TiO2-based particles (TiX) was shown to depend on the TiX particle type and concentration, which were associated with a slight polymer matrix degradation. The partially degraded, shorter, and more mobile polymer chains increased the overall crystallization rate at the initial stage of crystallization, while at the later stages, the non-nucleating TiX particles acted as a sterical hindrance, slowing down the crystallization process. The PCL/TiX composites were prepared by melt-mixing and contained 2.5 and 5 wt% of the filler. The investigated TiX particles included isometric anatase microparticles (mTiO2) and titanate nanotubes with high-aspect ratio (TiNT). Light and electron microscopy showed very homogeneous dispersion of the mTiO2 particles in the PCL matrix, while the TiNT formed large agglomerates. In situ polarized light microscopy displayed faster isothermal crystallization of all PCL/TiX composites, but the micrographs indicated that the TiX particles did not act as nucleation centres. Isothermal DSC experiments, evaluated in terms of Avrami theory, confirmed the PLM results and showed that the overall rate of isothermal crystallization increased in the following order: PCL <PCL/TiNT <PCL/mTiO2. Non-isothermal DSC and rheological measurements revealed the correlation between the crystallization rate and the polymer matrix degradation—the well-dispersed mTiO2 particles with high specific surface caused the highest PCL degradation and, consequently, the earliest start of non-isothermal crystallization as well as the fastest isothermal crystallization. Microindentation hardness measurements confirmed that the partial degradation of the polymer matrix did not have a significant impact on the mechanical performance of PCL/mTiO2 composites. 相似文献
34.
Nikola Vitković Miloš Stojković Vidosav Majstorović Miroslav Trajanović Jelena Milovanović 《CIRP Annals》2018,67(1):177-180
Bone scaffolds provide a structural support for tissue development. Existing bone scaffolds are mainly characterized by complex porous designs whose shortcomings are a low level of permeability for growing tissue, and a difficult design customization. Scaffolds with nucleuses (rods or lattices) as basic elements should improve bone regeneration and enable higher design flexibility. In this paper, we present two new methods for building 3D geometrical models of personalized scaffolds, which are based on method of anatomical features. Methods are demonstrated in the case of scaffold for the mandible bone. This approach greatly reduces the designer effort and time, while enabling easy personalization of scaffolds’ shape and geometry. 相似文献
35.
Zdeňka Sedláková Josef Pleštil Josef Baldrian Miroslav Šlouf Pavel Holub 《Polymer Bulletin》2009,63(3):365-384
A series of novel polystyrene and poly(butyl methacrylate) montmorillonites (MMT-Na) nanocomposite latexes have been successfully
prepared by emulsion polymerization. First of all, chemical modification of MMT-Na with a reactive coupling agent (MMT-QS)
has been employed for the synthesis of hybrids. Subsequently, in situ seeded emulsion polymerization of hydrophobic vinyl
monomers, such as butyl methacrylate and styrene, using sodium dodecyl sulfate (SDS) and ammonium persulfate (APS) as surfactant
and initiator, respectively, were used for nanocomposite preparation. This technique allowed preparing of stable nanocomposite
latexes with high (30–45 wt.%) solids contents and with loading of inorganic particles up to 5 wt.%. The prepared wet dispersions
were subsequently characterized by light scattering method. In order to characterize the microstructure of the clay layers,
and that of the organoclay in polystyrene and poly(butyl methacrylate) nanocomposites, wide and small angle X-ray analyses
(WAXS, SAXS) and transmission electron microscopy (TEM) techniques were used. 相似文献
36.
The effect of polydispersity on dilute solution properties and microphase separation of polydisperse high-molecular-weight (Mw > 105 g mol−1) polystyrene-block-poly(styrene-co-acrylonitrile) diblock copolymers, PS-block-P(S-co-AN), was studied in this work. For experiments, a series of diblock copolymers with variable weight fractions of acrylonitrile units (wAN = 0.08-0.29) and length of block P(S-co-AN) was synthesized using nitroxide-mediated radical polymerization (NMP) technique, namely, by chain extension of nitroxide-terminated polystyrene (PS-TEMPO). According to light scattering and viscometry measurements in dilute tetrahydrofuran (THF) solutions the studied diblock copolymers assumed random coil conformation with the values of characteristic structure factor Rg/Rh = 1.50-1.76. It was found that polydisperse diblock copolymers being in strong segregation limit (SSL) self-assembled into microphase-separated ordered morphologies at ordinary temperature. The long periods of lamellar microdomains were larger compared to theoretical predictions for hypothetical monodisperse diblock copolymers. It was demonstrated by means of SAXS and TEM that a transition from a lamellar (LAM) to irregular face-centered-cubic (FCC) morphology occurred with increasing volume fraction of P(S-co-AN) block. 相似文献
37.
Leandar Litov Peicho Petkov Miroslav Rangelov Nevena Ilieva Elena Lilkova Nadezhda Todorova Elena Krachmarova Kristina Malinova Anastas Gospodinov Rossitsa Hristova Ivan Ivanov Genoveva Nacheva 《International journal of molecular sciences》2021,22(19)
Our objective is to reveal the molecular mechanism of the anti-inflammatory action of low-molecular-weight heparin (LMWH) based on its influence on the activity of two key cytokines, IFNγ and IL-6. The mechanism of heparin binding to IFNγ and IL-6 and the resulting inhibition of their activity were studied by means of extensive molecular-dynamics simulations. The effect of LMWH on IFNγ signalling inside stimulated WISH cells was investigated by measuring its antiproliferative activity and the translocation of phosphorylated STAT1 in the nucleus. We found that LMWH binds with high affinity to IFNγ and is able to fully inhibit the interaction with its cellular receptor. It also influences the biological activity of IL-6 by binding to either IL-6 or IL-6/IL-6Rα, thus preventing the formation of the IL-6/IL-6Rα/gp130 signalling complex. These findings shed light on the molecular mechanism of the anti-inflammatory action of LMWH and underpin its ability to influence favourably conditions characterised by overexpression of these two cytokines. Such conditions are not only associated with autoimmune diseases, but also with inflammatory processes, in particular with COVID-19. Our results put forward heparin as a promising means for the prevention and suppression of severe CRS and encourage further investigations on its applicability as an anti-inflammatory agent. 相似文献
38.
Jan Rybnicek Ralf Lach Monika Lapcikova Josef Steidl Zdenek Krulis Wolfgang Grellmann Miroslav Slouf 《应用聚合物科学杂志》2008,109(5):3210-3223
Binary and ternary blends of PC, ABS, and PMMA were studied. The blends were produced from original and recycled materials by melt mixing in a wide range of compositions. Instrumented Charpy impact testing, tensile testing, rheology investigations, and electron microscopy were carried out to determine the relationship between the deformation and fracture behavior, blend composition, morphology, and processing parameters. Resistance against unstable crack propagation was evaluated using the concepts of J‐integral and crack‐tip‐opening displacement (CTOD). The transition from ductile elastic‐plastic to brittle‐linear elastic fracture behavior was observed in the case of PC/ABS/PMMA blend at 10% of PMMA. Reprocessing had only a slight influence on the deformation and fracture behavior of the recycled blends. The blends produced from recycled materials proved to be competitive with the original pure materials. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008 相似文献
39.
Mingjun Liu Miroslav Petro Jean M. J. Fréchet S. A. Haque Hsien-Chang Wang 《Polymer Bulletin》1999,43(1):51-58
Summary Poly(propylene imine) dendrimers with amino chain ends have been used for the preparation of hydrophobic star polymers with hydrophilic dendritic cores. The unsaturated end groups of polyisobutylene (PIB) were transformed into reactive anhydride end groups by an “ene” reaction with maleic anhydride, and the resulting functionalized PIB was then reacted with dendrimers to afford dendrimer-PIB star copolymers. Received: 20 May 1999/Accepted: 17 June 1999 相似文献
40.
Miroslav Sahul Martin Sahul Ján Lokaj L’ubomír Čaplovič Petr Nesvadba 《Journal of Materials Engineering and Performance》2018,27(11):5665-5674
Explosive welding of titanium Grade 1 to AW7075 aluminum alloy arranged in parallel setup was performed. The annealing of produced bimetals at the temperatures of 450, 500 and 550 °C for times ranging from 20 to 100 h was carried out after explosive welding. The produced bimetal was characteristic by its wavy interface typical for that bonding process. Increase in the microhardness at the interface was recorded due to work hardening. Delamination of titanium Grade 1 flyer sheet was firstly observed when annealing temperature of 500 °C for 40 h was carried out. Annealing at 550 °C also resulted in delamination of upper sheet. The intermetallic compound (IMC) layer was observed at the interface after annealing of bimetals. The higher the annealing temperature and time, the higher the thickness of continuous IMC layer. The maximum measured thickness of IMC layer averaged 13 µm. Energy dispersive x-ray spectroscopy (EDS) and x-ray diffraction (XRD) analyses revealed that the interface layer is consisted of Al18Ti2Mg3 IMC. Microhardness at the interface increased dramatically up to 439 HV0.1 after annealing of bimetal due to the presence of above-mentioned IMC. 相似文献