The ABCs of PDAs.

The popularity of personal digital assistants (PDAs) continues to rise, due mostly to the convenience and reliability they offer caregivers.

Sorting out bacterial viability with optical tweezers.

We have developed a method, using laser, optical tweezers and direct microscopic analysis of reproductive potential and membrane integrity, to assess single-cell viability in a stationary-phase Escherichia coli population. It is demonstrated here that a reduction in cell integrity, determined by using the fluorescent nucleic acid stain propidium iodide, correlated well with a reduction in cell proliferating potential during the stationary-phase period studied. Moreover, the same cells that exhibited reduced integrity were found to be the ones that failed to divide upon nutrient addition. A small but significant number of the intact cells (496 of 7,466 [6.6%]) failed to replicate. In other words, we did not find evidence for the existence of a large population of intact but nonculturable cells during the stationary-phase period studied but it is clear that reproductive ability can be lost prior to the loss of membrane integrity. In addition, about 1% of the stationary-phase cells were able to divide only once upon nutrient addition, and in a few cases, only one of the two cells produced by division was able to divide a second time, indicating that localized cell deterioration, inherited by only one of the daughters, may occur. The usefulness of the optical trapping methodology in elucidating the mechanisms involved in stationary-phase-induced bacterial death and population heterogeneity is discussed.

Internal/external locus of control, self-esteem, and parental verbal interaction of at-risk black male adolescents.

We investigated the relationship between three factors--internal/external locus of control, self-esteem, and parental verbal interaction--for at-risk Black male adolescents in the United States. Forty-two male students in Grades 6, 7, and 8 who had been identified by their teachers as being at risk completed the Locus of Control Scale for Children (Nowicki & Strickland, 1973), the Self-Esteem Inventory (Coopersmith, 1967), and the Verbal Interaction Questionnaire (Blake, 1991). A moderate positive relationship found between self-esteem and parental verbal interaction was consistent with a previous finding for White high school students. A moderate negative relationship found between locus of control and self-esteem differed from a previous finding of no significant relationship for Black elementary children. A weak, yet significant, negative relationship was found between locus of control and parental verbal interaction.

Sex differences in shock motivated behaviors, activity, and discrimination learning of northern grasshopper mice (Onychomys leucogaster).

Sex differences in the behavior of the highly predatory northern grasshopper mouse (Onychomys leucogaster) were investigated in a series of eight experiments. Female mice acquired two-way avoidance behavior more slowly, but passive avoidance more rapidly, than males. Females also buried a shock probe more completely than males and showed more escape behavior during open field testing. There were no sex differences in flinch-jump thresholds or escape from electric shock, general activity levels, or acquisition and reversal of a position discrimination. It is suggested that the sex differences in aversively motivated behavior result from an increased tendency of females to respond defensively to focal sources of aversive stimuli. The enhanced defensiveness of females may be an adaptation to higher levels of pup predation resulting from the large territories required by their predatory specialization and their association with other, more abundant, rodent species.

[Effects of quingestanol acetate on the histology, histochemistry and ultrastructure of the endometrium]. / Effets de l'acetate de quingestanol sur l'histologie, l'histochimie et l'ultrastructure de l'endomètre.

According to studies carried out using the optical microscope and the electron microscope quingestanol acetate, which is a powerful progestagen, modified significantly the histology and the histochemistry of the endometrium. The mechanisms of transport across the cellular membranes are not changed, but probably there is competition between the oestrogens at the binding sites as a result of which the synthesis of proteins and hydrocarbons is changed. This in turn provokes the formation of aggregations of platelets in the blood vessels and cellular degeneration starting from the onset of the cycle. The contraceptive efficiency of quingestanol acetate when it is administered by itself is due to alterations in cellular biology which it brings about at the level of the endometrium as well as due to its inhibitory effect on gonadotropins.