Temperature dependence of pressure broadening of NH3 perturbed by H2 and N2

The temperature dependence of pressure broadening of 134 rovibrational transitions of several branches in the ν₄ and 2ν₂ bands of ammonia perturbed by H₂ and N₂ has been measured using a high-resolution Fourier transform spectrometer. The temperature range covered during the experiments was between 235 and 296 K. The pressure-broadening linewidths were obtained using the method of multipressure fitting to the measured shapes of the lines. These broadenings were also calculated using a semiclassical model leading to a reasonable agreement with the observations and reproduces well the strong systematic experimental J and K quantum number dependencies. The retrieved values of the linewidths, along with those previously determined from the spectra at room temperature, were used to derive the temperature dependence of both H₂ and N₂ broadening of NH₃ lines. The broadening coefficients were shown to fit closely the well-known exponential law. For both experimental and theoretical results, the temperature exponent n has been obtained. Careful inspection of the experimental values shows that, contrary to the linewidths, the coefficient n is nearly K independent within each J multiplet. Also for a given J it does not seem to exhibit any noticeable variation with the type of rotational transition. On the other hand, the calculated n values exhibit a strong J and K systematic dependencies. n increases with K for a given J, decreases with J for a given K and are independent of the type of rotational transition.     

Contemplating Criteria for Science Education Reform: The Case of the Olympia School District

Proposals for current reform in science education elaborate national standards and a plethora of state-level interpretations commonly labeled as curriculum or learning frameworks. The purpose of this case study was to examine the dynamics of the science curriculum reform process in one of the first school districts to use the Georgia Framework for Learning Mathematics and Science as a basis for their reform initiative. The paper describes the ways in which members of the Olympia School District's Science Curriculum Committee participated in the science curriculum reform process, as well as their personal beliefs about the criteria needed for reform to take place. The results highlight the nature of metaphors guiding reform efforts; the influence of social, historical, economic, and political forces on the reform process; the use of local and professional languages as discourses for communicating about reform; and the complex power relations that influence the micropolitics of reform in the Olympia School District. This study has important implications for other teachers and school districts engaged in standards-based science curriculum reform. It points to the need for reform to include reflection and analysis of the role of teachers in the reform process and consideration of the purpose of science education reform in society.     

Rheological behaviour and shear thickening exhibited by aqueous CTAB micellar solutions

In this experimental work we carefully investigate the rheological behaviour and in particular the shear thickening exhibited by aqueous micellar solutions of CTAB with NaSal as added counterion. We are particularly interested in the evolution of the critical shear rate (at which shear thickening occurs) versus C _D , the surfactant concentration. We show that , at fixed salt concentration C _S , increases with C _D following a power law evolution with a positive exponent of + 5.8. On the other hand we show that if the ratio C _D / C _S is fixed, decreases with C _D with a negative exponent of -2.0. Nevertheless investigations of the zero shear viscosity indicate that in all situations (implying variation of the surfactant concentration C _D , or the salt concentration C _S or the temperature) is a decreasing function of the length of the micelles. All these evolutions are compatible with a gelation mechanism which could possibly be associated with entanglement effects of large interacting flowing structures. Received: 3 March 1998 / Revised: 16 June 1998 / Accepted: 3 July 1998