Backward pion-nucleon scattering

A global analysis of the world data on differential cross sections and polarization asymmetries of backward pion-nucleon scattering for invariant collision energies above 3 GeV is performed in a Regge model. Including the $N_\alpha$, $N_\gamma$, $\Delta_\delta$ and $\Delta_\beta$ trajectories, we reproduce both angular distributions and polarization data for small values of the Mandelstam variable $u$, in contrast to previous analyses. The model amplitude is used to obtain evidence for baryon resonances with mass below 3 GeV. Our analysis suggests a $G_{39}$ resonance with a mass of 2.83 GeV as member of the $\Delta_{\beta}$ trajectory from the corresponding Chew-Frautschi plot.Comment: 12 pages, 16 figure

Condensation of zinc vapor in a supersonic carrier gas

A study of the condensation of a metal vapor in an inert carrier gas is made. Superheated zinc vapor is generated in a hot shot wind tunnel in a helium carrier gas and expanded in a converging-diverging nozzle. Static pressure measurements along the length of the nozzle are made to determine the location of the onset of condensation. A conical nominal Mach 5 (helium) nozzle is employed. The amount of supercooling before the onset of condensation is found to be approximately 430 K, measured along the isentrope over a range of initial zinc mass fractions of .35 to .70 for saturation partial pressures of zinc between 10 psia and 70 psia. The measurements are compared with results of an analysis based on the classical liquid drop model of nucleation. The computed results agree reasonably well with the measurements.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41794/1/10494_2004_Article_BF00382286.pd

Control of urea hydrolysis and nitrification in soil by chemicals - Prospects and problems

A review is made of the recent work to assess the prospects of regulating urea hydrolysis and nitrification processes in soils by employing chemicals that can retard urea hydrolysis and nitrification. The possible benefits from control of nitrogen transformations in terms of conserving and enhancing fertilizer nitrogen efficiency for crop production and the problems associated with their use with regard to N metabolism of plants have also been discussed with examples. Prospects of using cheap and effective indigenous materials and chemicals for control of urea hydrolysis and nitrification under specific soil situations appear eminent in improving the fertilizer nitrogen efficiency. Urease inhibitors may be helpful in reducing problems associated with ammonia volatilization if this is not offset by leaching of urea. On the other hand retardation of nitrification appears useful in reducing losses that accompany nitrification due to leaching and denitrification, and with the plants that metabolize equally well with relatively higher amounts of NH4–N may be more effective in improving the utilization of fertilizer N under these situation