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991.
Gary L. Hagnauer 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(1):385-408
Polydichlorophosphazene (NPC12)X is unique as a synthetic precursor for poly(organo)phosphazenes [1–6] and presents special problems in polymerization studies because of branching, crosslinking, and cyclization reactions and in characterization due to the polymer's hydrolytic instability. This paper reviews the literature and discusses problem areas and recent advances relating to polydichlorophosphazene polymerization. Melt, solution, and irradiation polymerization reactions and mechanisms are discussed. Previously unpublished results are presented, and current research efforts and areas for future investigation are considered. 相似文献
992.
The intensities of X-rays from muonic atoms formed in low pressure Ne, O2, N2, He, and H2 gas was measured. For the pressure chosen external electron refilling can be neglected. Absolute yields were extracted and
compared to results of cascade calculations. Knowledge of the yields of the circular X-ray transitions allows an in situ efficiency
calibration of X-ray detectors down to energies of 1.5 keV.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
993.
James D Kubicki Gary P Halada Prashant Jha Brian L Phillips 《Chemistry Central journal》2009,3(1):10-29
Background
Quantum mechanical calculations were performed on a variety of uranium species representing U(VI), U(V), U(IV), U-carbonates, U-phosphates, U-oxalates, U-catecholates, U-phosphodiesters, U-phosphorylated N-acetyl-glucosamine (NAG), and U-2-Keto-3-doxyoctanoate (KDO) with explicit solvation by H2O molecules. These models represent major U species in natural waters and complexes on bacterial surfaces. The model results are compared to observed EXAFS, IR, Raman and NMR spectra. 相似文献994.
The link between standards and research may not be clearcut. However, in this article the authors argue that there is a notable relationship between standards and research, one that is cyclical in nature. Using the standards for school mathematics developed by the National Council of Teachers of Mathematics (NCTM) as a case in point, the authors examine how NCTM's standards have influenced the agenda for mathematics education research and stimulated research on the impact of those standards. In turn, this and other research played a significant role in the development of NCTM's new Principles and Standards for School Mathematics. The authors conclude with a discussion of ways in which the Principles and Standards may continue this cyclical relationship in coming years, potentially promoting investigation of new research areas and systematic research on the impact of standards. 相似文献
995.
996.
Wei Chen Tao Wang Gary C. Lickfield 《Journal of Polymer Science.Polymer Physics》2007,45(14):1821-1833
The flexibility of molecular structures of rubber materials was evaluated using molecular modeling techniques to develop new crosslink agents which improve deformation recovery of cellulose without significant loss of the mechanical strength. Among the studied structures Poly(propylene oxide) (PPO) pentamer appears to be the most flexible and coiled one. Our calculation results showed that, cellulose crosslinked with PPO pentamers had similar deformation recovery to that crosslinked with DMDHEU. No conformation transitions were observed in these crosslinks when cellulose models were extended to 15% strain, which is consistent with the previous result that conformation transitions in crosslinks should be avoided upon extension to achieve a good recovery on crosslinked cellulose. In addition, PPO crosslinks did not significantly affect the breaking strain of cellulose based upon the cavity volume calculations, and they helped to remove the stress concentration among cellulose chains as suggested by the results of hydrogen bonding analysis. Thus, breaking strength of cellulose might not be significantly affected by PPO crosslinks as well. The preliminary experimental results confirmed above observations. Therefore, PPO pentamer appears to be a promising elastomeric backbone structure of crosslinking agents. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1821–1833, 2007 相似文献
997.
Hin‐Koon Woo Eden P. Go Linh Hoang Sunia A. Trauger Benjamin Bowen Gary Siuzdak Trent R. Northen 《Rapid communications in mass spectrometry : RCM》2009,23(12):1849-1855
Mass spectrometry has become an indispensable tool for the global study of metabolites (metabolomics), primarily using electrospray ionization mass spectrometry (ESI‐MS). However, many important classes of molecules such as neutral lipids do not ionize well by ESI and go undetected. Chemical derivatization of metabolites can enhance ionization for increased sensitivity and metabolomic coverage. Here we describe the use of tris(2,4,6,‐trimethoxyphenyl)phosphonium acetic acid (TMPP‐AA) to improve liquid chromatography (LC)/ESI‐MS detection of hydroxylated metabolites (i.e. lipids) from serum extracts. Cholesterol which is not normally detected from serum using ESI is observed with attomole sensitivity. This approach was applied to identify four endogenous lipids (hexadecanoyl‐sn‐glycerol, dihydrotachysterol, octadecanol, and alpha‐tocopherol) from human serum. Overall, this approach extends the types of metabolites which can be detected using standard ESI‐MS instrumentation and demonstrates the potential for targeted metabolomics analysis. Published in 2009 by John Wiley & Sons, Ltd. 相似文献
998.
Experimental Techniques - 相似文献
999.