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31.
Flame dynamics under various backpressures in a model scramjet with and without a cavity flameholder
Flame dynamics under various backpressure conditions were experimentally investigated using direct flame visualization, high-speed CH* chemiluminescence imaging, and wall pressure measurements. The stagnation pressure and temperature used in the present study were 100 kPa and 2500 K, respectively, with a freestream Mach number of 4.5. Rectangular scramjet models with and without a cavity were used to explore the effects of the cavity on flame dynamics when operating in scramjet mode, ramjet mode, and unstart. The flow rate of the ethylene jet was varied to impose backpressures corresponding to each operation mode. For both models, reverse flame propagation was observed for ramjet mode and unstart. For ramjet mode, flame fluctuation occurred within the isolator due to the coupling of fluid dynamics and combustion. The presence of a cavity enhanced combustion and reduced flame fluctuation in both scram and ramjet mode. The cavity promoted unstart because of the greater heat release from combustion. Further research using spatially resolved diagnostic techniques is needed to identify the flame locations for ramjet mode and unstart. 相似文献
32.
Kyung Hak Kim Jin Kyoung Park Sang Hyuk Im Bum Jun Park 《Particle & Particle Systems Characterization》2021,38(4):2100006
Waterproof light-emitting perovskite–polymer composite microparticles are synthesized by a continuous one-step microfluidic reactor, which enables in situ production of metal halide perovskite nanoparticles (MHP-NPs) by the ligand-assisted reprecipitation process (LARP) and the encapsulation of MHP-NPs by UV cross-linking polymerization in the microfluidic channel. Successful encapsulation of MHP-NPs in polymer microparticles is attributed to the co-dispersion of an LARP solution and UV polymerizable solution in an aqueous continuous phase within the microfluidic channel, in which N,N-dimethylformamide, in co-dispersion droplets, is continuously extracted to the aqueous medium upon UV polymerization. MHP-NPs–polymer composite microparticles show enhanced stability against air and moisture. 相似文献
33.
Solvent-free and high yielding one-pot synthesis of 1,8-dioxodecahydroacridine and polyhydroquinoline derivatives have been described through Hantzsch condensation of various aldehydes, ammonium acetate with cyclic 1,3-dicarbonyl compounds and ethyl acetoacetate in a very simple, efficient, and environmentally benign method using ascorbic acid as a nontoxic organocatalyst. 相似文献
34.
The crystallization behavior and fine structure of poly(butylene succinate) (PBS) nanocomposites with intercalation (30B20) and exfoliation (30BM20) morphologies, respectively, were investigated via isothermal crystallization testing and synchrotron small-angle X-ray scattering (SAXS). The dynamic viscosity of 30BM20 was markedly increased due to favorable interactions between the PBS matrix and the urethane group on the clay surface. However, 30BM20 showed similar crystallization rates to that of homo PBS because the surface urethane modification for 30BM20 precluded PBS matrix from the metallic group into clay to difficult in contact with each other, resulting in a reduced nucleation activity for the metallic group. SAXS profiles revealed that the long period and amorphous region size for 30B20 drastically decreased during isothermal crystallization. Meanwhile, 30BM20 was similar to those of homo PBS. This result also supports the above explanation for isothermal crystallization behavior. Considering all results in total, the introduction of a urethane modification considerably enhanced the physical properties of PBS but caused delayed crystallization rates. 相似文献
35.
Protegrin‐1 (PG‐1) belongs to the family of antimicrobial peptides. It interacts specifically with the membrane of a pathogen and kills the pathogen by releasing its cellular contents. To fully understand the energetics governing the orientation of PG‐1 in different membrane environments and its effects on the physicochemical properties of the peptide and membrane bilayers, we have performed the potential of mean force (PMF) calculations as a function of its tilt angle at four distinct rotation angles in explicit membranes composed of either DLPC (1,2‐dilauroylphosphatidylcholine) or POPC (1‐palmitoyl‐2‐oleoylphosphatidylcholine) lipid molecules. The resulting PMFs in explicit lipid bilayers were then used to search for the optimal hydrophobic thickness of the EEF1/IMM1 implicit membrane model in which a two‐dimensional PMF in the tilt and rotation space was calculated. The PMFs in explicit membrane systems clearly reveal that the energetically favorable tilt angle is affected by both the membrane hydrophobic thickness and the PG‐1 rotation angle. Local thinning of the membrane around PG‐1 is observed upon PG‐1 tilting. The thinning is caused by both hydrophobic mismatch and arginine‐lipid head group interactions. The two‐dimensional PMF in the implicit membrane is in good accordance with those from the explicit membrane simulations. The ensemble‐averaged Val16 15N and 13CO chemical shifts weighted by the two‐dimensional PMF agree fairly well with the experimental values, suggesting the importance of peptide dynamics in calculating such ensemble properties for direct comparison with experimental observables. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010 相似文献
36.
Ji Sun Im Tae-Sung Bae Young-Seak Lee 《Journal of Physics and Chemistry of Solids》2011,72(10):1175-1179
ZrO2-embedded carbon fibers were prepared for use as an electromagnetic interference (EMI) shielding material by electrospinning and heat treatment methods. Structural changes were observed in the ZrO2 and in the carbon structures by XRD and Raman spectroscopy, respectively. During heat treatment, XRD analysis results revealed a transition from a monoclinic structure to a tetragonal structure in ZrO2 and a graphitization in the structural formation of carbon fibers was observed by Raman spectroscopy. It was observed that these structural changes in the ZrO2 and the carbon fibers improved the real and imaginary permittivities by a factor of more than 3.5. The EMI shielding efficiency (SE) improved along with the permittivity with higher treatment temperatures and greater amounts of embedded ZrO2; the highest average EMI SE achieved was 31.79 dB in 800-8500 MHz. The heat treatment played an important role in the improvements in the permittivity and in the EMI SE because of the heat-induced structural changes of the ZrO2-embedded electrospun carbon fibers. We suggest that the EMI shielding of the fibers is primarily due to the absorption of electromagnetic waves, which prevents secondary EMI by reflection of electromagnetic waves. 相似文献
37.
Jiyeon Lee Dahye Im Yajie Liu Jing Fang Xibao Tian Minsu Kim Prof. Wen-Bin Zhang Prof. Jongcheol Seo 《Angewandte Chemie (International ed. in English)》2023,62(51):e202314980
A technique combining ion mobility spectrometry-mass spectrometry (IMS-MS) and supercharging electrospray ionization (ESI) has been demonstrated to differentiate protein chemical topology effectively. Incorporating as many charges as possible into proteins via supercharging ESI allows the protein chains to be largely unfolded and stretched, revealing their hidden chemical topology. Different chemical topologies result in differing geometrical sizes of the unfolded proteins due to constraints in torsional rotations in cyclic domains. By introducing new topological indices, such as the chain-length-normalized collision cross-section (CCS) and the maximum charge state (zM) in the extensively unfolded state, we were able to successfully differentiate various protein chemical topologies, including linear chains, ring-containing topologies (lasso, tadpole, multicyclics, etc.), and mechanically interlocked rings, like catenanes. 相似文献
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40.
Kyung‐Moo Shin Tungalag Dong Kouji Yazawa Seung‐Soon Im Yoshio Inoue 《Journal of Polymer Science.Polymer Physics》2008,46(9):879-891
The inclusion complexes (ICs) of unmodified natural and methylated α‐cyclodextrins (CDs) with biodegradable polymers, polyethylene glycol and poly(ε‐caprolactone), were prepared by two methods, that is, the one using water and the other using chloroform as the solvent for the respective CDs. The ICs obtained were characterized by IR, WAXD, DSC, and 13C CP/MAS NMR. It was found that the possibility and the phenomena of IC formation could be varied with the degree of methyl substitution of CD as well as the type of solvents used. Methylated α‐CDs showed the prominent characteristics of IC formation with polymers in the case where chloroform was used than in the case where water was used as the solvent for CDs, while vice versa in the case of native α‐CD. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 879–891, 2008 相似文献