Molecular velocity auto-correlation of simple liquids observed by NMR MGSE method

The velocity auto-correlation spectra of simple liquids obtained by the NMR method of modulated gradient spin echo show features in the low frequency range up to a few kHz, which can be explained reasonably well by a $t^{-3/2}$ long time tail decay only for non-polar liquid toluene, while the spectra of polar liquids, such as ethanol, water and glycerol, are more congruent with the model of diffusion of particles temporarily trapped in potential wells created by their neighbors. As the method provides the spectrum averaged over ensemble of particle trajectories, the initial non-exponential decay of spin echoes is attributed to a spatial heterogeneity of molecular motion in a bulk of liquid, reflected in distribution of the echo decays for short trajectories. While at longer time intervals, and thus with longer trajectories, heterogeneity is averaged out, giving rise to a spectrum which is explained as a combination of molecular self-diffusion and eddy diffusion within the vortexes of hydrodynamic fluctuations.Comment: 8 pages, 6 figur

Collusion Theory in Search of Robust Themes: A Comment on Switgard Feuerstein's Survey

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46450/1/10842_2005_Article_4870.pd

Human-capital investment and the wage gap

According to empirical studies, the relation between the relative wage of skilled workers and their relative supply is U-shaped. This finding is explained by the effect of technological change on the incentives for human-capital investments made by heterogeneous individuals. (orig.)Available from TIB Hannover: RN 6136(307) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Influence of fuel injection parameters on combustion-induced noise in a small diesel engine

In this paper, the effects of fuel injection parameters on combustion-induced noise in a small single-cylinder direct-injection diesel engine used in a generator set are described. A range of fuel injection parameters, including injection timing and injection quantity, was explored to understand their influence on combustion-induced noise by studying their effect on in-cylinder pressure development. Fourier analysis was performed to understand the effects of changing combustion characteristics on in-cylinder pressure levels in different frequency ranges. In addition, time–frequency analysis was used to understand the changes in the combustion chamber resonance effects under different injection settings. Finally, overall engine noise levels were measured to confirm the changes as predicted by the in-cylinder pressure analysis. Results suggest that retarding main injection has the largest impact on reducing noise. When using split injection, earlier preinjection and larger preinjection quantities tend to result in lower noise.C.S. Bhat, P.H. Meckl, J.S. Bolton and J. Abraha