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71.
Lindsey?Gillian?MackayEmail author C.?Peter?Taylor Richard?Bruce?Myors Ruth?Hearn Bernard?King 《Accreditation and quality assurance》2003,8(5):191-194
The selection of an appropriate isotope dilution mass spectrometry technique for the practical application of this potentially primary method of analysis is highly important. The NARL approach for the application of the exact matching double isotope dilution mass spectrometry technique developed by Henrion is presented. NARL's approach utilises exact matching to minimise the effect of measurement biases within the method but also includes the thorough examination of all other biasing factors. The approach has been successfully tested in international CCQM intercomparisons with other national metrology institutes. 相似文献
72.
Computations are performed on the interaction specificities of tetramethylammonium (TMA) for double-stranded oligonucleotides held in the B conformation. The effects of base sequence and chain length are investigated. In the short oligomers (helices formed from dinucleoside monophosphates and trinucleoside diphosphates), the interaction energies of TMA are larger in the major groove of (dG)n · (dC)n than in the minor groove of either (dA)n · (dT)n or (dA—dT)n. Upon lengthening the oligomers, and owing to the gradual shaping of the grooves of the helix and cumulative effect of the phosphates, TMA is shown to increasingly favor the minor groove of (dA)n · (dT)n with respect to the major groove of (dG)n · (dC)n, with a sizeable energy difference computed at the pentanucleoside hexaphosphate level. The binding of TMA in the minor groove of (dA)n · (dT)n involves stabilizing contacts with several sites, on the bases and on the deoxyriboses. Configurations locating the cation closer to the thymine strand are slightly preferred over configurations locating it closer to the adenine strand. 相似文献
73.
Manuel A. Fernandes Marcus Layh Bernard Omondi 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(7):o384-o385
The title compound, C10H11N, displays a crystallographic mirror plane that incorporates all the non‐H atoms, as well as the H atoms attached to the aromatic ring. The isocyano group is almost linear and shows an N[triple‐bond]C bond distance of 1.158 (3) Å. 相似文献
74.
The NaF-AlF(3) system with additions of CaF(2) and MgF(2) has been studied with Raman and vapor pressure measurements for 3 >/= CR (NaF/AlF(3) molar ratio) >/= 1 and up to 50 mol % additive. The results show that the binary melt can be described using the two equilibria AlF(6)(3)(-) = AlF(6)(2)(-) + F(-) and AlF(5)(2)(-) = AlF(4)(-) + F(-) with equilibrium constants 0.25 and 0.05, respectively, at 1293 K. Both reactions have positive reaction enthalpies. The first equilibrium is strongly shifted to the right resulting in a melt mixture with very low AlF(6)(3)(-) concentrations even at the Na(3)AlF(6) composition. Evidence for nonideal mixing of anions was found. For the ternaries, models based on Raman data are presented and compared with vapor pressure measurements. Good agreement is observed when association between the additives, CaF(2) or MgF(2), with the AlF(5)(2)(-) ions in the melt was considered. This association could be experimentally observed through a band broadening and a slight shift in the AlF(5)(2)(-) band frequency. Our vapor pressures and Raman data both indicate that MgF(2) clearly acts as an acid when added to NaF-AlF(3) melts of any composition. When CaF(2) is added, a slight decrease of vapor pressure occurs. Raman data indicate a decrease of AlF(4)(-) concentration, corresponding to a dissociation of CaF(2) with liberation of F(-) ions. All these results are, however, very much dependent on the initial melt composition. These data are explained in terms of acid-base, dilution, and association reactions of the solute with the solvent. 相似文献
75.
Bernard W. TaylorIII Arthur J. Keown Allen G. Greenwood 《The Journal of the Operational Research Society》1983,34(5):379-390
The decision-making process involved in the procurement of military weapon systems, although quite critical and complex, still encompasses the basic characteristics of a capital budgeting problem. Given a number of expenditure items and a limited budget, it is desired to procure those weapon systems that will achieve the goals and objectives of the government and/or military in the most efficient manner. Since these objectives are typically numerous and diverse, traditional decision-making techniques are not applicable. As such, integer goal programming is suggested as a technique to be employed to determine the number of military aircraft to be procured, given conflicting expenditure, budget and effectiveness goals. This method is demonstrated via a case example in which the solution results are presented. 相似文献
76.
The nonintercalative binding of an aliphatic and an aromatic bisguanylhydrazone (BGH) to the minor groove of double-stranded (dA-dT)
n
oligomers is investigated by means of theoretical computations. The preferred binding arrangements of both BGHs are stabilized by a number of H-bonding interactions with sites O2(T), N3(A) and o1 on the two strands, and require limited conformational rearrangements of the BGHs around their C-C single bonds. The intermolecular interaction energy is larger with the aliphatic BGH than with the aromatic one. The energy difference is, however, considerably reduced when the oligomer is lengthened: it passes from 16.1 kcal/mole at the heptamer level, to 7.9 kcal/mole at the undecamer level and to 4.6 kcal/mole when each strand of the undecamer is flanked with a complementary complete helical turn of phosphates, on both the 3 and 5 termini.The interaction energies of the BGHs with water molecules in the first hydration shell are, however, also larger with the aliphatic BGH, than with the aromatic BGH. This energy difference is further enhanced when one considers also the water molecules in the second shell. It becomes greater than the difference in the interaction energy of the two BGHs with (dA-dT)
n
for large values of n. When the dehydration energy of BGHs is taken into account the overall energy balance is then more favorable for the interaction of the aromatic than of the aliphatic BGH with the polynucleotide. This last conclusion is in agreement with experimental results. 相似文献
77.
78.
79.
Diels-Alder adducts were formed in the lead tetraacetate oxidations of substituted cyclic hydrazides of furan, pyridazine and pyrrole dicarboxylic acids in the presence of 1,3-cyclo-hexadiene or 1,3-cyclopentadiene. The products resulting were furo[3,4-g]pyridazino[1,2-a]-pyridazine-6,10-diones, pyridazino[4,5-g]pyridazino[1,2-a]pyridazine-6,11-diones, and pyrrolo-[3,4-g]pyridazino[1,2-a]pyridazine-6,10-diones, respectively. Some hydrogenations and ring opening reactions were studied. 相似文献
80.
Emmanuel Beyou Pierre Babin Bernard Bennetau Jacques Dunogues Dominique Teyssie Sylvie Boileau 《Journal of polymer science. Part A, Polymer chemistry》1994,32(9):1673-1681
Unsaturated perfluoroalkyl esters derived from undecylenic acid: CH2?CH? (CH2)8? COO? CH2? CH2? RF (with RF?C6F13, 2a and RF?C8F17, 2b ) and C8F17? (CH2)10? COO? CH2? CH?CH2, 2c were prepared with excellent yields. Their hydrosilylation by methylhydrodimethylsiloxane copolymers of various Si? H contents gives new fluorinated polysiloxanes which were examined by 1H- and 13C-NMR, GPC, differential scanning calorimetry, and optical polarizing microscopy. Polymers derived from compounds 2a and 2b exhibit mesomorphic structures. © 1994 John Wiley & Sons, Inc. 相似文献