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排序方式: 共有186条查询结果,搜索用时 125 毫秒
91.
92.
Abstract Laminated reinforced plastics using carbon or silica fabrics and phenolic resins are widely used for ablative liners of rocket nozzles and for other applications requiring protection of structural elements in a high thermal environment. Under cyclic heating conditions, the phenolic resin chars, thereby providing ablation cooling; on cool-down, cracks and/or delaminations result in the majority of applications. On a reheat cycle, as in a multistart engine or other pulsed environment, a burn-through or other catastrophic failure may occur in the cracked areas. 相似文献
93.
Mullen DG Borgmeier EL Fang M McNerny DQ Desai A Baker JR Orr BG Holl MM 《Macromolecules》2010,43(16):6577-6587
Partial acetylation of the amine-terminated poly(amidoamine) dendrimer has been used in the preparation of dendrimer particles conjugated with a wide variety of functional ligands including targeting moieties, therapeutic agents, and dye molecules. The effectiveness of mass transport during the partial acetylation reaction was found to have a major effect on subsequent distributions of dendrimer-ligand components and to be a major source of inconsistency between batches. This study has broad implications for a wide range of nanoparticle-ligand systems because it demonstrates that conjugates with the same mean ligand-particle ratios can have completely different distribution profiles. 相似文献
94.
[reaction: see text] (R)-[(tolBINAP)Pt(NC(6)F(5))(2)][SbF(6)](2) (5) catalyzes the highly enantioselective Prins reaction between 2-allylphenols and glyoxylate esters. Other Lewis acid catalysts favor glyoxylate-ene products. 相似文献
95.
96.
B.V. Pond C. Mullen I. Suarez J. Kessler K. Briggs S.E. Young M.J. Coggiola D.R. Crosley H. Oser 《Applied physics. B, Lasers and optics》2007,86(4):735-742
We report studies using laser photoionization and time-of-flight mass spectrometry to detect several explosive-related compounds
(ERCs). The ultimate goal of this work is the detection of buried land mines through their chemical signatures. Resonantly
enhanced multiphoton ionization using jet expansion cooling, with a nanosecond pulse laser, results in complete photofragmentation
of the parent ERC and appearance only of the NO+ ion, which forms all of the detected signal. This will also occur for compounds naturally occurring in the environment, such
as NO2 or peroxyacetylnitrate, rendering too many false alarms for this approach to be viable. Therefore, two other techniques were
evaluated. Single-photon ionization with nanosecond pulses in the vacuum ultraviolet is shown to produce only the parent ion,
and is probably the most suitable choice. For 2,4-dinitrobenzene we find a limit of detection of about 40 ppb, for a signal
to noise ratio of 3. This may be sufficient for land-mine detection, but improvement is likely with future work. Nonresonant
multiphoton ionization in the ultraviolet with a femtosecond laser produces fragmentation but retains some parent ERC ion
signal. The limit of detection is similar to that of single-photon ionization but it is harder to implement with lasers now
commercially available. Future directions are outlined.
PACS 07.07.Df; 33.80.Rv; 82.80.Ms; 82.80.Rt 相似文献
97.
98.
99.
Z. Ding D. W. Bullock P. M. Thibado V. P. LaBella Kieran Mullen 《Surface science》2003,540(2-3):491-496
The GaAs(0 0 1) surface is observed to evolve from being perfectly flat to a surface half covered with one-monolayer high spontaneously formed GaAs islands. The dynamics of this process are monitored with atomic-scale resolution using scanning tunneling microscopy. Surprisingly, pit formation dominates the early stages of island formation. Insight into the nucleation process is reported. 相似文献
100.
Brian D. Mullen Chau N. Tang Robson F. Storey 《Journal of polymer science. Part A, Polymer chemistry》2003,41(13):1978-1991
The synthesis, characterization, and ring‐opening polymerization of a new cyclic carbonate monomer containing an allyl ester moiety, 5‐methyl‐5‐allyloxycarbonyl‐1,3‐dioxan‐2‐one (MAC), was performed for the first time. MAC was synthesized in five steps in good yield beginning from the starting material, 2,2‐bis(hydroxymethyl)propionic acid. Subsequent polymerization and copolymerizations of the new cyclic carbonate with rac‐lactide (rac‐LA) and ?‐caprolactone (CL) were attempted. Rac‐LA copolymerized well with MAC, but CL copolymerizations produced insoluble products. Oligomeric macroinitiators of MAC and rac‐LA were synthesized from stannous ethoxide, and both macroinitiators were used for the controlled ring‐opening polymerization of rac‐LA. The polymerization kinetics were examined by monitoring the disappearance of the characteristic C? O ring stretch of the monomer at 1240 cm?1 with real‐time in situ Fourier transform infrared spectroscopy. Postpolymerization oxidation reactions were conducted to epoxidize the unsaturated bonds of the MAC‐functionalized polymers. Epoxide‐containing polymers may allow further organic transformations with various nucleophiles, such as amines, alcohols, and carboxylic acids. NMR was used for microstructure identification of the polymers, and size exclusion chromatography and differential scanning calorimetry were used to characterize the new functionalized poly(ester‐carbonates). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1978–1991, 2003 相似文献