Magnetic structure variation in manganese-oxide clusters

Negative-ion photoelectron spectroscopy and ab initio simulations are used to study the variation in magnetic structure in Mn(x)O(y) (x = 3, 4[semicolon] y = 1, 2) clusters. The ferrimagnetic and antiferromagnetic ground-state structures of Mn(x)O(y) are 0.16-1.20 eV lower in energy than their ferromagnetic isomers. The presence of oxygen thus stabilizes low-spin isomers relative to the preferred high-spin ordering of bare Mn(3) and Mn(4). Each cluster has a preferred overall magnetic moment, and no evidence is seen of competing states with different spin multiplicities. However, non-degenerate isomags, which possess the same spin multiplicity but different arrangements of local moments, do contribute additional features and peak broadening in the photoelectron spectra. Proper accounting for all possible isomags is shown to be critical for accurate computational prediction of the spectra.     

Quantitative Estimation: One, Two, or Three Abilities?

The mathematics education literature refers to 3 types of quantitative estimation skill: numerosity, measurement, and computational estimation. The psychometric literature includes a confusing array of tests intended to define quantitative estimation. This study examined relations among tests for numerosity, measurement, and computational estimation, and recognized tests for numerical facility and quantitative reasoning using principal components analysis. 2 components were identified. The first component aligned computational estimation with numerical facility and general quantitative reasoning. The second component included the tests of numerosity and measurement estimation. It was suggested that this second component might be related to spatial ability. Implications for mathematics education and assessment are discussed.     

Slowing down of gamma photons

Hyperfine Interactions - By a transformation to a rotating reference system, a nuclear level mixing scheme is equivalent to a scheme with pure quadrupole splitting and a strong RF-drive between...     

Synchrotron Mössbauer reflectometry using stroboscopic detection

The concept of the heterodyne/stroboscopic detection of nuclear resonance scattering of synchrotron radiation is extended to the grazing incidence geometry. Model calculations for an antiferromagnetic [⁵⁷Fe/Cr]₂₀ multilayer are shown and discussed. Principles and methodological aspects of stroboscopic synchrotron Mössbauer reflectometry are briefly reviewed.     

Isotopic metrology of carbon dioxide. I. Interlaboratory comparison and empirical modeling of inlet equilibration time,inlet pressure,and ion source conductance

We report a pilot study of high-precision differential isotope ratio measurements made on replicate samples of pure carbon dioxide using three instruments of identical manufacture. Measurement protocols were designed to explore the effects of sample size, ion source conductance, and inlet changeover equilibration time on the raw measurements. Our goal was better understanding of factors that influence these measurements in order to establish procedures for highly reproducible and accurate determinations of Reference Material (RM) isotopic compositions. Evaluation and modeling of reported data illuminated effects consistent with two instrumental memory sources--one short-lived (t((1/2)) approximately 10 s) and the other long-lived (t((1/2)) approximately 6-10 min), uncompensated by normal background measurements--that can significantly influence measurements made by the dual inlet method. These biases, proportional to the difference in isotopic compositions between the measured sample and reference gases, decrease in magnitude with increasing sample size, source conductance, and equilibration time. We observed biases as high as 0.1 per thousand per 10 per thousand difference between sample and reference gases. These memory sources may be responsible for measured delta(13)C values of RMs generally being highly reproducible within any single laboratory but less reproducible among independent laboratories. The magnitude of the bias is consistent with the ranges of delta(13)C values reported in prior laboratory intercomparisons. Uncertainties are most likely due to high and variable long-lived memory among the instruments tested.     

THE EFFECT OF DIFFERENTIATION ON PHOTOSENSITIZER UPTAKE BY HL60 CELLS

The capability of human promyelocytic leukemia cells HL60 to be induced to differentiate to various stages along the monocytic or myelocytic pathway was exploited for investigation of the uptake of selected photo-sensitizers by diverse types of cells of the same origin. The results showed that there was no substantial difference in photofrin uptake between noninduced HL60 cells, immature monocytes, immature neutrophils and cells differentiated along the eosinophilic pathway. In contrast, HL60 cells differentiated into macrophages (HL609) exhibited markedly increased photofrin uptake, which was further enhanced by their pretreatment with bacterial lipopolysaccharide. Similar results were obtained with other photosensitizers tested: di-and tetrasulfonated aluminum phthalocyanines (AIPcS₂ and AIPcS₄), tetrasulfonated zinc phthalocyanine (ZnPcS₄), tetraphenylporphine tetrasulfonate (TPPS₄) and benzoporphyrin derivative monoacid (BPD). Despite marked differences in the state of self-aggregation and other chemical properties of these compounds, the degree of their preferential uptake by HL60 PH cells showed very little variation. In a typical experiment, the uptake of these photosensitizers by HL60 PH cells was four to five times higher than the uptake by noninduced HL60 cells. In addition to the fluorometric assay employed in most of the experiments, cellular concentration of AlPcS₄ was determined by measurement of elementary aluminum using atomic absorption spectroscopy.     

Investigation of the Montmorillonite clay-catalyzed [1,3] shift reaction of 3-methyl-2-butenyl phenyl ether

The [1,3] shift reaction of 3-methyl-2-butenyl phenyl ether was catalyzed more effectively by Montmorillonite K10 clay than Montmorillonite KSF clay, and proceeded with greatest ortho-selectivity in carbon tetrachloride at room temperature.     

Intramolekulare Basenkoordination je nach Bedarf: Der 1-(Dimethylaminoethyl)-2,3,4,5-tetramethylcyclopentadienyl-Ligand in der Komplexchemie von s-, p-, d- und f-Block-Elementen

The synthesis of cyclopentadienyl complexes containing the polydentate C₅Me₄(CH₂CH₂NMe₂) ligand is described. The compounds (C₅Me₄CH₂CH₂NMe₂)₂M (M = Ca, Sm), (C₅Me₄CH₂CH₂ NMe₂)AIEt₂, [(C₅Me₄CH₂CH₂NMe₂)M(CO)₂]₂ (M = Mo, Fe) and [(C₅Me₄CH₂CH₂NMe₂)Fe(CO)₂]⁺BF₄^± are obtained by standard procedures. Except for the dimeric metal carbonyls, all cyclopentadienyl compounds are characterized by an additional intramolecular coordination of the nitrogen atom in the side chain.     

A local intercomparison study of ESR dosimetry using tooth enamel

Using electron spin resonance (ESR), tooth enamel is a possible dosimeter in case of a radiation accident. To check the present status of this technique, we conducted a local intercomparison study. We irradiated several samples of tooth enamel with a⁶⁰Co source. Three institutes in Belgium and The Netherlands recorded the ESR signal of the samples. The results of the measurements and the methods used are compared. It is concluded that ESR on tooth enamel can be a useful technique in accident dosimetry, provided further research is done.     

Magnetic resonance study of Rh complexes in AgCl microcrystals

X-ray or UV irradiation at room temperature of Rh3+ doped AgCl emulsion powders leads to the production of three paramagnetic Rh2+ related centres, labeled R4, R5 and R6. A combined X and Q band electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) study allowed the determination of a nearly complete structural model for these centres. In the X band ENDOR spectra of R4 and R5 interactions of the unpaired electron with nearby protons have been identified, indicating that for these centres Cl- ligands have been exchanged by H2O or OH-. The R6 centre, identified as a (RhCl6)4- complex, has been found to be fundamentally different from the dominant centre in large Rh2+ doped AgCl single crystals grown from the melt. The results are compared with recent work by other researchers in the same field.