Beating the System: Course Structure and Student Strategies in a Traditional Introductory Undergraduate Physics Course for Nonmajors

The purpose of this study was to describe relationships among instructor and student goals, course design, and student strategies for learning physics in a traditional introductory undergraduate physics course for nonmajors. The procedures included 16 hours ofnonparticipant observation, during which detailed field notes and photographs were taken and documents were collected. Audiotaped open-ended interviews were given to instructors and students, and all students participated in a limited survey. The data were analyzed using qualitative methods of the Chicago School. Results indicated that both differing goals of students and instructors and the structure of the course inhibited the understanding of physics and were conducive to students engaging in unexpected behaviors designed to help them successfully pass the course. The consequences of the structure of the course and subsequent student behaviors inhibited their understanding and appreciation of physics and deterred them from enrolling in further science courses. The paper includes implications for teaching introductory college physics.     

Dynamic SIMS analysis of cryo-prepared biological and geological specimens

The modification of a dynamic magnetic sector secondary ion mass spectrometry (SIMS) instrument to permit the analysis of frozen biological and geological samples is described. The SIMS instrument used for this study combines SIMS analysis with the generation of ion-induced secondary electron images, allowing direct superposition of the SIMS image onto the image of cellular structures. Secondary ion maps have been acquired with sub-micron resolution, permitting the characterisation of sub-cellular elemental distributions in plant cells and human fibroblast cells, as well as the distribution of chemical impurities at grain boundaries in polar ice samples. This cryo-preparation technique clearly extends the applicability of SIMS analysis to a wide range of samples.     

Microviscosity of dilute latex + gelatin dispersions determined by dynamic light-scattering

The microviscosity of dilute latex + gelatin dispersions has been studied by dynamic light-scattering at gelatin concentrations up to 1.0 wt % and temperatures in the range 8–45 °C. The change in mean particle diffusion coefficient following a rapid quench correlates strongly with the change in bulk shear viscosity of the gelatin solution. Slow thermal studies of latex + gelatin exhibit hysteresis effects which are mirrored by bulk viscometry data for gelatin solutions at the same concentration.     

Direct evaluation of DLVO theory for predicting long-range forces between a yeast cell and a surface

Using a combined gradient optical trap and evanescent wave light-scattering force-measurement technique, long-range colloidal forces were measured between a single Candida albicans yeast cell and a flat, bare glass surface in electrolyte concentrations ranging from 0.1 to 100 mM NaCl. The Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was compared to experimentally measured equilibrium force curves and found to provide a close approximation to the decay length of the measured forces for electrolyte concentrations up to about 0.23 mM NaCl. At higher electrolyte concentrations (>/=0.5 mM NaCl), decay lengths of force curves in experimental measurements were consistently longer than Debye lengths calculated from the electrolyte concentrations. In electrolyte concentrations of 10 and 100 mM NaCl, most cells attached rapidly, which prevented measurements of long-range forces. The small fraction of cells remaining unattached in these higher electrolyte concentrations displayed purely repulsive forces. These results show that the DLVO theory accurately describes cell-surface interactions when the Debye length is in the range of 20-30 nm but underpredicts the decay length of the interactions at higher electrolyte concentrations.     

Some factors responsible for high ionic conductivity in simple solid compounds

The ionic conductivities, activation energies for mobility, and crystal structures of solid electrolytes are reviewed. The high conductivity of a group of compounds containing simple anions is examined in some detail.For a solid to possess high ionic conductivity there must be: (a) an excess of acceptable lattice sites for the mobile ion, (b) only a small energy difference between the ordered and disordered distribution of the mobile ions over these sites, and (c) a low heat of activation for movement of the mobile ion. These conditions are most readily realized when the cations are monovalent and stable in both 4-coordinated (tetrahedral) and 3-coordinated configurations. Since only Ag^I and Cu^I satisfy these requirements, their nearly unique conduction properties become understandable. Moreover, these requirements appear to be satisfied only with highly polarizable anions; a characteristic of the anions present in the good conductors.     

X-ray photoelectron spectroscopic studies of electrode surfaces using a new controlled transfer technique: Part II. Results for a molybdenum electrode and the curve fitting procedure

The surface of molybdenum metal was examined by XPS after exposure to gaseous and liquid systems and after electrochemical treatment. The latter being conducted in a specially designed electrochemical cell situated in a vacuum chamber attached to the main spectrometer chamber. The results show that a clean molybdenum metal surface is unaffected by oxygen gas and deoxygenated sulphuric acid. It was slightly oxidized by deoxygenated water and appreciably oxidized by oxygenated water. The Mo(VI) oxide is not observed after cathodic polarisation.     

Stability and rheology of emulsions containing sodium caseinate: combined effects of ionic calcium and alcohol

We have investigated the combined effect of ionic calcium and ethanol on the visual creaming behavior and rheology of sodium caseinate-stabilized emulsions (4 wt% protein, 30 vol% oil, pH 6.8, mean droplet diameter 0.4 microm). A range of ionic calcium concentrations, expressed as a calcium/caseinate molar ratio R, was adjusted prior to homogenization and varying concentrations of ethanol were added shortly after homogenization. A stability map was produced on the basis of visual creaming behavior over a minimum period of 8 h for different calcium/caseinate/ethanol emulsion compositions. A single narrow stable (noncreaming) region was identified, indicating limited cooperation between calcium ions and ethanol. The shear-thinning behavior of the caseinate-stabilized emulsions is typical of systems undergoing depletion flocculation. Addition of calcium ions and/or ethanol was found to lead to a pronounced reduction in viscosity and the onset of Newtonian flow. The state of aggregation was correlated with emulsion microstructure from confocal laser scanning microscopy. Time-dependent rheology (18 h) with a density-matched oil phase (1-bromohexadecane) revealed that the visually stable emulsions were time-independent low-viscosity fluids. Surface coverage data showed that increasing amounts of caseinate were associated with the oil-water interface with increasing R and ethanol content. A decrease in free calcium ions in the aqueous phase with moderate increases in R and ethanol content was observed, which is consistent with greater calcium-caseinate binding (aggregation). Ostwald ripening occurred at the high-ethanol emulsion compositions that were stable to depletion flocculation. While the coarsening rate was low, this can account for the cream plug formation observed during gravity creaming experiments. The caseinate emulsion with no ionic calcium or ethanol exhibits depletion flocculation from excess nonadsorbed caseinate submicelles. Addition of calcium ions reduces the submicelle number density via specific calcium-binding in the aqueous phase (fewer, larger calcium-caseinate aggregates) and at the droplet surface (increased surface coverage). Nonspecific ethanol-induced (calcium-dependent) caseinate submicelle aggregation in the bulk phase and on the droplet surface (increased surface coverage) culminates in a reduction in the number density of caseinate submicelles. A narrow window of inhibition of depletion flocculation occurs in systems containing both calcium ions and ethanol, both species combining to aggregate the protein and so reduce the density of free submicelles.     

An adsorption effect on the gel strength of dilute gelatin-stabilized oil-in-water emulsions

The incorporation of emulsion oil droplets into a gelatin gel leads to an initial increase in shear modulus at 25 °C for a gelatin concentration of 8 wt % but an initialdecrease for a concentration of 5 wt %. The latter result is consistent with a net lowering of the gelatin concentration available for gelation in the aqueous phase due to adsorption at the oil-water interface.