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A Square Well Atomic Potential: NO2 Treated Iron-Doped ZSM-5 Zeolite

Treating iron-doped ZSM-5 zeolite with NO₂ produced a complete change in the parameters of its ⁵⁷Fe Mössbauer spectrum. The intensity of the absorption showed a dramatic decrease at 40–70 K with smooth, but anharmonic, behavior above this temperature. The results can be interpreted in terms of the modification of the iron environment to form an approximately square-well potential. This results in an asymmetric potential in which the iron becomes frozen in one region at low temperatures.     

61Ni Mössbauer spectra of fine Ni particles

We report the first measurements of fine Ni particles from⁶¹Ni Mössbauer spectroscopy. The average hyperfine field of the 10 nm particles at 4.2K is measured to be 7.7(4) T, compared to the measured value for Ni foil of 7.5(3) T. Application of an external field of 6 T to the fine particles causes a reduction of the hyperfine splitting to 1.5(6) T, a consequence of the negative hyperfine field at Ni nuclei. These results are discussed in terms of fine particle effects.     

Experimental measurements and computational modeling of the flow field in an idealized human oropharynx

The velocity field in the central sagittal plane of an idealized representation of the human oropharynx (HOP) during steady inspiration, simulating oral inhalation through an inhaler mouthpiece, was measured experimentally using endoscopic particle image velocimetry (PIV). Measurements were made at three flow rates: 15, 30, and 90 L/min, which correspond to a wide range of physiological conditions. Extensive tests were performed to verify the veracity of the PIV data. The flow was also modeled computationally using Reynolds-averaged Navier–Stokes (RANS) computational fluid dynamics (CFD) methods. The PIV data clearly indicate the complex nature of HOP flow, with three-dimensionality and several regions of separation and recirculation evident. Comparison of the experimental and computational results shows that, although the RANS CFD reproduces the basic features of the flow, it does not adequately capture the increased viscous effects at lower Reynolds numbers. The results demonstrate the need for more development and validation of CFD modeling, in particular RANS methods, in these flows.     

Axisymmetric stagnation point flow and mass transfer for power-law fluids

The boundary-layer equations for axisymmetric stagnation point flow of a power-law fluid are solved by a similarity transformation, and values of the wall shear rate are obtained. Theoretical expressions for local and average Sherwood numbers are derived from the convective diffusion equation for systems with high Schmidt numbers. The results can be used to predict diffusion coefficients of dilute species in fluids with specified power-law characteristics.     

A unified treatment of electromagnetic decays,electroproduction, and pair production in e+e− annihilation for hadrons of arbitrary spin

We gather together in a unified notation formulas for electromagnetic decay rates of resonances and cross sections for electroproduction and e⁺e^? annihilation for all those processes which can be expressed in terms of matrix elements of the electromagnetic current between single particle (or resonant) helicity states. We show in complete generality how to decompose such helicity matrix elements into form factors which are free of all kinematic singularities and constraints simultaneously at both physical thresholds, and relate them to the familiar multipole moments and to some others which have been used in data analysis. Tables are given of the form factor decomposition of the helicity matrix elements for many cases of actual and potential practical interest.     

A monte carlo method for factorization

We describe briefly a novel factorization method involving probabilistic ideas.     

Mössbauer spectroscopic studies of haemosiderins from different sources

Mössbauer spectra obtained from the haemosiderin isolated from ironoverloaded horse and reindeer spleen and liver show superparamagnetic behaviour with a much lower transition temperature than haemosiderin from iron-overloaded human spleen. These data clearly indicate the existence of different forms of haemosiderin, which are primarily distinguishable by Mössbauer spectroscopy.