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951.
Balram Dhawan Derek Redmore 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):41-47
Abstract Treatment of aminoalkanols 1 with phosphorous acid and formaldehyde in presence of conc. hydrochloric acid gave mixtures of [(2-hydroxy alkyl)imino] dimethylene diphosphonic acids 3 and 4-(phosphonomethyl)-2-hydroxy-2-oxo-1,4,2-oxazaphosphorinanes 2 from which 2 were isolated as crystalline solids. Similar treatment of 2-amino-2-methyl-1,3-propanediol 8 gave a complex mixture from which dimethylene diphosphonic acid of 5-amino-5-methyl-1,3-dioxane 9 was isolated. 2-Aminoethanethiol, when subjected to phosphonomethylation. gave an unexpected novel quarternary nitrogen product 11. N-Alkylaminoalkanols 4 on phosphonomethylation gave 3:1 mixtures of [N-alkyl-N-(2-hydroxyalkyl)amino] methane phosphonic acid 6 and N-alkyl-2-hydroxy-2-oxo-1,4,2-oxazaphosphorinane 5. Treatment of the crude mixtures of 5 and 6 with aqueous sodium hydroxide gave disodium salts of [N-alkyl-N-(2-hydroxyalkyl)amino] methanephosphonic acid 7. The ratio of the cyclic to the open chain structures obtained as well as the formation of any unexpected novel products is dependent on the structure of the aminoalkanol that is phosphonomethylated. The 1H, 13C and 31P spectra are reported for all new compounds. 相似文献
952.
Balram Dhawan Derek Redmore 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3-4):215-220
Abstract Reaction of pentaerythritol 1 with 1, 2 or 3 equivalents of diethyl phosphorochloridate 2 yielded pentaerythritol tris(diethyl phosphate) 5. Treatment of pentaerythritol with 4 or more equivalents of 2 gave pentaerythritol tetrakis(diethyl phosphate) 6. Transesterification of 5 and 6 with trimethylsilyl chloride and sodium iodide in acetonitrile followed by treatment with water gave pentaerythritol tris (dihydrogen phosphate) 7 and pentaerythritol tetrakis(dihydrogen phosphate) 8 respectively. Pentaerythritol bis(dihydrogen phosphate) 9 was prepared by the hydrolysis of 3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro [5,5] undecane 3,9-dioxide 10. The compounds 7,8 and 9 were isolated as anilinium salts and characterized by 1H, 13C and 31P NMR spectra. 相似文献
953.
We demonstrate that porous fibers in addition to low loss and high confinement, have near zero dispersion for 0.5-1 THz resulting in reduced terahertz signal degradation compared to microwires. We also show for the first time that these new fibers can be designed, introducing asymmetrical sub-wavelength airholes within the core, to achieve high birefringence ≈0.026. This opens up the potential for realization of novel polarization preserving fibers in the terahertz regime. 相似文献
954.
Probe interval graphs (PIGs) are used as a generalization of interval graphs in physical mapping of DNA. G=(V,E) is a probe interval graph (PIG) with respect to a partition (P,N) of V if vertices of G correspond to intervals on a real line and two vertices are adjacent if and only if their corresponding intervals intersect and at least one of them is in P; vertices belonging to P are called probes and vertices belonging to N are called non-probes. One common approach to studying the structure of a new family of graphs is to determine if there is a concise family of forbidden induced subgraphs. It has been shown that there are two forbidden induced subgraphs that characterize tree PIGs. In this paper we show that having a concise forbidden induced subgraph characterization does not extend to 2-tree PIGs; in particular, we show that there are at least 62 minimal forbidden induced subgraphs for 2-tree PIGs. 相似文献
955.
956.
Justin I. McIntyre Mathew Cooper April J. Carman Theodore W. Bowyer Anthony Day Derek Haas James C. Hayes Tom R. Heimbigner Charlie Hubbard Kevin Litke Michael Ripplinger Brian Schrom Reynold Suarez 《Journal of Radioanalytical and Nuclear Chemistry》2009,282(3):755-759
Absolute efficiency calibration of radiometric detectors is frequently difficult and requires careful detector modeling and accurate knowledge of the radioactive source used. In the past we have calibrated the β–γ coincidence detector of the Automated Radioxenon Sampler/Analyzer (ARSA) using a variety of sources and techniques which have proven to be less than desirable (Reeder et al., J Radioanal Nucl Chem, 235, 1989). A superior technique has been developed that uses the conversion-electron (CE) and X-ray coincidence of 131mXe to provide a more accurate absolute gamma efficiency of the detector. The 131mXe is injected directly into the beta cell of the coincident counting system and no knowledge of absolute source strength is required. In addition, 133Xe is used to provide a second independent means to obtain the absolute efficiency calibration. These two data points provide the necessary information for calculating the detector efficiency and can be used in conjunction with other noble gas isotopes to completely characterize and calibrate the ARSA nuclear detector. In this paper we discuss the techniques and results that we have obtained. 相似文献
957.
Thomas J. Manning Amy Feldman Michael Anderson Leri Atwater Brent Lesile Derek Lovingood Anna Lee McRae Rob Stapleton Kim Riddle Jun Lui Thomas Vickers Naresh Dalal Lambertus J. van de Burgt 《The Chemical Educator》2001,6(4):238-246
The blend of nanotechnology and material science is often beyond the scope of undergraduate laboratories. Through undergraduate research, graphite-intercalated compounds have been incorporated in the production of carbon-based nanostructures. Based on this work a series of exploratory exercises were designed for the undergraduate physical chemistry laboratory emphasizing nanostructure material science. This rapidly expanding area of science and technology can be introduced at an undergraduate level using a high temperature oven to produce nanostructure samples that are analyzed by Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy at research university laboratories, infrared spectroscopy, and a bomb calorimeter. In these experiments we use samples of pure graphite, fluorinated graphite, and lanthanum oxide to induce the formation of nanostructures. An overview of fullerenes, nanotubes, boron nitride and Si nanostructures, other carbon forms, graphite-intercalated compounds, and the storage of hydrogen in nanotubes are provided in an appendix. Several extensions of the laboratory are proposed. 相似文献
958.
959.
960.
We prove that a finitely generated group G is virtually free if and only if there exists a generating set for G and k > 0 such that all k-locally geodesic words with respect to that generating set are geodesic.
Received: 30 October 2006 相似文献