Relaxation phenomena due tos—d exchange interaction of dilute iron in molybdenum

It is demonstrated that the localized magnetic moments of Fe in Mo which undergo spin compensation at low temperatures vias—d exchange interaction (Kondo-effect) also exhibit, at temperaturesT>T _k , relaxation phenomena in the Mössbauer spectra due to the same exchange interaction. Utilizing the Korringa relation, the product of the exchange parameterJ and the density of statesp(? _F is estimated to be ¦Jp(? _F )¦=0.008. At low temperatures, however, deviations from this relation have been observed. The relaxation rate becomes temperature independent and decreases with increasing external magnetic field.     

Preferred electron-impact elimination of two CHO groups from A triapentafulvalenequinone. Formation of a triafulvalene radical cation?

The mass spectral fragmentations of 1,2-diphenyl- and 1,2-di (phenyl-d₅)-4,5-benzotriapentafulvalene-3,6-quinone indicate the preferred elimination of two CHO groups with the formation of triafulvalene radical cations.     

Microprocessor ratemeter for kinetic determinations

A simple, compact, easy-to-implement microprocessor ratemeter for kinetic determinations based on initial rate, fixed time, and variable time is presented. The hardware and software are such that the ratemeter can be used with almost any transducer or instrument to monitor reactions in a wide variety of chemical systems. The performance of the ratemeter is demonstrated by its application to the determination of phosphorus by stoppedflow spectrometry, glucose by amperometry, and alkaline phosphatase activity in control sera by visible spectrophotometry.     

1H and 13C n.m.r. study of butatriene-bis-tricarbonyliron complexes. Assignment of geometric orientation by comparative J(CCCH) values

A number of substituted butatriene-bis-tricarbonyliron complexes have been studied by ¹³C and ¹H n.m.r. spectroscopy. Long range coupling values, J(CCCH), have confirmed chemical shift results that methyl and phenyl groups assume opposite orientations at the coordinated double bonds with the methyl group preferentially trans to carbon and the phenyl group preferentially trans to iron.     

A better step-off algorithm for the knapsack problem

The knapsack problem, maximize Σ^m_{i = 1}c_ix_i when Σ^m_{i = 1}a_ix_i?b for integers x_i?0, can be solved by the classical step-off algorithm. The algorithm develops a series of feasible solutions with ever-increasing objective values. We make a change in the problem so that the step-off algorithm produces a series of solutions of not necessarily increasing objective values. A point is reached when no better solutions can be found and the calculation is stopped.     

Formation of hexacoordinate complexes of PhCCSiF3 with 2,2'-bipyridine and with 1,10-phenanthroline through intermolecular silicon...nitrogen interactions

Bidentate intermolecular Si...N interactions were utilized to form new hypervalent complexes of trifluoro-phenylethynyl-silane with 2,2'-bipyridine and with 1,10-phenanthroline. X-ray structures obtained for these complexes display a somewhat distorted octahedral geometry about the silicon atom. Binding constants ranging from 170 to 1600 M(-1) at 25 degrees C in CDCl3 were measured for the formation of these complexes, suggesting that such hypervalent complexes of silicon could be used as new motifs in supramolecular chemistry.     

Quantitative optical imaging of the pharmacokinetics of fluorescent-specific antibodies to tumor markers through tissuelike turbid media

Fluorescent optical imaging of tumors deep within tissue depends on specific binding of antibodies to the tumors' surface markers. These fluorescent antibodies propagating in the vicinity of the tumor can be attached to and (or) diffused away from it. We illustrate application of a new tool, based on the random-walk theory in turbid media, for extracting the pharmacokinetics of these fluorescent antibodies by data deconvolution, excluding the effect of upper turbid tissue layers.     

Application of synchronous fluorescence to parchment characterization

A nondestructive method for quantitative parchment characterization and sensitive indication of its deterioration stage was developed. Synchronous fluorescence (SF) measurements were applied for the first time to parchment samples. The method provides detailed spectral features, which are useful for parchment characterization. The discrimination of parchment samples into groups (modern, historical, and artificially aged) was successfully performed. The SF spectra could be resolved into specific fluorophores, which were related to the parchment condition. The spectral data indicate a continuous change in the collagen-to-gelatin ratio during the aging process. Depth-resolved synchronous fluorescence spectra were also measured. The data indicate that parchments possess a layered structure, and the dominant fluorophore in the upper layer is different from those in the lower layers. Layer-resolved profiling allows for quantifying the contribution of each fluorophore in each given layer. This way, significant differences between modern, artificially aged, and historical samples can be observed.     

151Eu mössbauer spectroscopy studies of substituted EuBa2Cu3O7 systems

Mössbauer spectroscopy studies of¹⁵¹ Eu in EuBa₂Cu₃O₇, EuBa₂Cu₃O₆, EuBa₂Cu₃O₆S, EuBaKCu₃O₇, EuBa₂Cu_2.5Fe_0.5O₇, Eu_0.5Pr_0.5Ba₂Cu₃O₇, Eu_1.25Ba_1.75Cu₃O₇ and EuCaBaCu₃O₇ at several temperatures have been performed. The major conclusions are; All substitutions affect the Eu quadrupole interaction (10–20%). Substitution of 0 by S increases the Eu quadrupole interaction by 15% and increases η from 0.3 to 0.8 which proves that S substitutes oxygen in the immediate neighbourhood of the rare earth ions. In EuCaBaCu₃O₇ the quadrupole interaction is larger by 80% than in EuBa₂Cu₃O₇, proving that in this structure Eu occupies predominantly the Ba sites.