This study examined an experiential avoidance conceptualization of depressive rumination in 3 ways: 1) associations among questionnaire measures of rumination, experiential avoidance, and fear of emotions; 2) performance on a dichotic listening task that highlights preferences for non-depressive material; and 3) psychophysiological reactivity in an avoidance paradigm modeled after the one used by Borkovec and colleagues (1993) in their examination of worry. One hundred and thirty eight undergraduates completed questionnaire measures and participated in a clinical interview to diagnose current and past episodes of depression. Of those, 100 were randomly assigned to a rumination or relaxation induction condition and participated in a dichotic listening task, rumination/relaxation induction, and depression induction. Questionnaire measures confirmed a relationship between rumination status and avoidance; however, no significant effects were found in the dichotic listening task. Psychophysiological measures indicated no difference in physiological response to a depression induction among high ruminators (HR). However, low ruminators (LR) in the relaxation condition exhibited a larger IBI response than LR in the rumination condition. Overall, these results provide partial support for an avoidance conceptualization of depressive rumination. Implications of these findings are discussed.

Disturbance has many effects on ecological communities, and it is often suggested that disturbance can affect species diversity by altering competitive outcomes. However, disturbance regimes have many distinct aspects that may act, and interact, to influence species diversity. While there are many theoretical models of disturbance‐prone communities, few have specifically documented how interactions between different aspects of a disturbance regime change competitive outcomes. Here, we present a model of two plant species subject to disturbance which we then use to examine species coexistence over varying levels of two aspects of disturbance: frequency, and spatial extent (i.e., area disturbed). We show that the competitive outcome is affected differently by changes in each aspect and that the effect of disturbance frequency on species coexistence depends strongly on the spatial extent of the disturbance, and vice versa. We classify the nature of these interactions between disturbance frequency and extent on the basis of the shape of the resulting coexistence regions in a frequency–extent parameter plane. Our results illustrate that different types of interaction can result from differences in life‐history traits that control species‐specific sensitivity to frequency and extent of disturbance. Thus, our analysis shows that the various aspects of disturbance must be carefully considered in concert with the life‐history traits of the community members in order to assess the consequences of disturbance.

We develop a reversible colloidal system of silica nanoparticles whose state of aggregation is controlled reproducibly from a state of fully dispersed nanoparticles to that of a colloidal gel and back. The surface of silica nanoparticles is coated with various amino silanes to identify a silane capable of forming a monolayer on the surface of the particles without causing irreversible aggregation. Of the three silanes used in this study, N-[3-(trimethoxysilyl)propyl]ethylenediamine was found to be capable of producing monolayers up to full surface coverage without inducing irreversible aggregation of the nanoparticles. At near full surface coverage the electrokinetic behavior of the functionalized silica is completely determined by that of the aminosilane. At acidic pH the ionization of the amino groups provides electrosteric stabilization and the system is fully dispersed. At basic pH, the dispersion state is dominated by the hydrophobic interaction between the uncharged aminosilane chains in the aqueous environment and the system forms a colloidal gel. At intermediate pH values the dispersion state is dominated by the balance between electrostatic and hydrophobic interactions, and the system exists in clusters whose size is determined solely by the pH. The transformation between states of aggregation is reversible and a reproducible function of pH. The rate of gelation can be controlled to be as fast as minutes while deaggregation is much slower and takes several hours to complete.

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