Absorption Imaging of Ultracold Atoms on Atom Chips

Imaging ultracold atomic gases close to surfaces is an important tool for the detailed analysis of experiments carried out using atom chips. We describe the critical factors that need be considered, especially when the imaging beam is purposely reflected from the surface. In particular we present methods to measure the atom-surface distance, which is a prerequisite for magnetic field imaging and studies of atom surface-interactions.Comment: 12 pages, 8 figures. v2 contains updated figures, modifications to tex

Reduction of NOx and Particulate Emissions in the Diesel Combustion Process

A model of the combustion and emission formation processes was formulated to identify modifications to combustion process parameters with potential for reducing NOx and particulate emissions in a diesel engine. The model was calibrated using data from an experimental, single-cylinder, direct injection diesel engine. Several combustion system modifications were made to the engine that reduced NOx and particulate emissions. The model was used to estimate the changes in the combustion process parameters responsible for the reductions observed. After calibration, the model was used to evaluate the effects of a wide range of modifications to the combustion process parameters on NOx and particulate emissions. These results were used to estimate changes in the combustion process parameters required to approach the objectives assumed for the 1991 Federal emission regulations for heavy-duty diesel engines. A reduction in the lubricating oil contribution to the particulate emissions was also projected to be required to approach the 1991 objectives.</jats:p

Phase-object approximation in small-angle neutron scattering experiments on silicon gratings

The phase-object approximation for neutron scattering based on a onedimensional dynamic forward scattering theory is discussed and used to calculate the differential cross section of an object. It is shown that this approximation is valid in ultra-small-angle neutron scattering (USANS) and spin-echo small-angle neutron scattering (SESANS) experiments on silicon gratings. In the weak scattering limit, the phase-object approximation reduces to the kinematic or first Born approximation. The spatial coherence function is used to describe instrumental resolution effects. Measurements on three different instruments are in good agreement with calculation results. In the experiment with a time-of-flight SESANS instrument, the effect of Pendello¨sung with object size is observed