Dynamics of hydrogen bromide dissolution in the ground and excited states.

The dissolution of acids is one of the most fundamental solvation processes, and an important issue is the nature of the hydration complex resulting in ion pair formation. We used femtosecond pump-probe spectroscopy to show that five water molecules are necessary for complete dissolution of a hydrogen bromide molecule to form the contact ion pair H+.Br-(H2O)n in the electronic ground state. In smaller mixed clusters (n < 5), the ion pair formation can be photoinduced by electronic excitation.

To Matrix, Network, or Hierarchy: That Is the Question.

The authors present a structural analysis of three spatial diagrams-matrices, networks, and hierarchies-that specifies 10 properties on which these diagrammatic representations are hypothesized to differ: global structure, building block, number of sets, item/link constraints, item distinguishability, link type, absence of a relation, linking relations, path, and traversal. Each property has a "value" for each diagram, and these property values constitute the applicability conditions for the representations. Twenty-three college students (computer science majors and math educators) selected the type of diagram they thought would be most efficient for organizing the information in each of 18 short scenarios and verbally justified the reasons for their selections. The verbal protocols were coded with respect to the structural analysis. Both the representation selection and verbal justification data provided strong support for the structural analysis. Additionally, a factor analysis of students' justifications indicated that the organization of their knowledge is consistent with the structural analysis. Students' use of the structural properties to select appropriate representations and to justify those selections indicates that the structural analysis has psychological force.

Femtosecond cluster studies of the solvated 7-azaindole excited state double-proton transfer.

Presented here are femtosecond pump-probe studies on the water-solvated 7-azaindole dimer, a model DNA base pair. In particular, studies are presented that further elucidate the nature of the reactive and nonreactive dimers and also provide new insights establishing that the excited state double-proton transfer in the dimer occurs in a stepwise rather than a concerted manner. A major question addressed is whether the incorporation of a water molecule with the dimer results in the formation of species that are unable to undergo excited state double-proton transfer, as suggested by a recent study reported in the literature [Nakajima, A., Hirano, M., Hasumi, R., Kaya, K., Watanabe, H., Carter, C. C., Williamson, J. M. & Miller, T. (1997) J. Phys. Chem. 101, 392-398]. In contrast to this earlier work, our present findings reveal that both reactive and nonreactive dimers can coexist in the molecular beam under the same experimental conditions and definitively show that the clustering of water does not induce the formation of the nonreactive dimer. Rather, when present with a species already determined to be a nonreactive dimer, the addition of water can actually facilitate the occurrence of the proton transfer reaction. Furthermore, on attaining a critical hydration number, the data for the nonreactive dimer suggest a solvation-induced conformational structure change leading to proton transfer on the photoexcited half of the 7-azaindole dimer.

Evidence for abstract, schematic knowledge of three spatial diagram representations.

Spatial diagram representations such as hierarchies, matrices, and networks are important tools for thinking. Our data suggest that college students possess abstract schemas for these representations that include at least rudimentary information about their applicability conditions. In Experiment 1, subjects were better able to select the appropriate spatial diagram representation for a problem when cued to use general category information in memory about those representations than when cued to use specific example problems given during the experiment. The results of Experiment 2 showed that the superior performance in the general category condition was not based on a comparison of the test problems with examples in memory. The results of Experiment 3 showed that the superior performance was not due to learning that occurred during the experiment or to transfer appropriate processing. The General Discussion section considers the nature of students' representation schemas and the question of why college students have only rudimentary schemas for common and widely applicable diagrammatic representations.

Variable colonial phenotypic expression and comparison to nuclei number in Blastomyces dermatitidis.

We examined colonial phenotypes of five isolates of Blastomyces dermatitidis at 33, 35 and 37 degrees C on four growth media. Three different colony types were identified: yeast, mycelial, and a mixed type consisting of both yeast and mycelia. Each isolate varied in its ability to grow on the different media and at different temperatures, and in the types of colonies it produced in the various temperature-media combinations. Quantification of the number of nuclei per yeast cell by fluorescent staining revealed no correlation between the number of nuclei per cell and the colonial phenotype. These results indicate that the colonial phenotype of B. dermatitidis varies with the isolate as well as with temperature and culture medium, but is not correlated with the number of nuclei per yeast. These findings could provide a start towards typing B. dermatitidis isolates.