RESUMEN
We report on laser cooling of a large fraction of positronium (Ps) in free flight by strongly saturating the 1^{3}S-2^{3}P transition with a broadband, long-pulsed 243 nm alexandrite laser. The ground state Ps cloud is produced in a magnetic and electric field-free environment. We observe two different laser-induced effects. The first effect is an increase in the number of atoms in the ground state after the time Ps has spent in the long-lived 2^{3}P states. The second effect is one-dimensional Doppler cooling of Ps, reducing the cloud's temperature from 380(20) to 170(20) K. We demonstrate a 58(9)% increase in the fraction of Ps atoms with v_{1D}<3.7×10^{4} ms^{-1}.
RESUMEN
Our understanding of postpartum anxiety (PPA) in fathers is limited, despite the negative consequences of anxiety on the father and child. Offspring contact reduces PPA in mothers; however, parallel investigations in fathers has gone unaddressed. Adult neurogenesis in the dentate gyrus (DG) contributes to anxiety regulation and is altered during the postpartum period, yet the effects of fatherhood on the production, or survival, of newborn cells in the DG, and the role of adult neurogenesis in PPA regulation, have not been examined. Using the biparental California mouse (Peromyscus californicus), we examined the relationships among postnatal day, anxiety-like behavior and adult neurogenesis in fathers. We hypothesized that attenuated anxiety-like behavior and enhanced adult neurogenesis would be observed when father-offspring contact was increased. We observed a reduction in anxiety-like behavior on the elevated plus-maze, but only at PND 16, a time of peak pup retrieval. Fatherhood reduced 1-week survival of newborn cells; however, surviving cells were maintained until 2 weeks postpartum. In contrast, non-fathers experienced a significant reduction in the survival of newborn cells between 1 and 2 weeks postpartum. Fatherhood also increased the numbers of newborn cells that expressed a neuronal phenotype. Collectively, these findings suggest that offspring interaction contributes to reductions in anxiety-like behavior and the maintenance of newborn neurons in the DG of fathers. These data contribute to our knowledge of the postpartum affective state in fathers, findings that may contribute to improved health of both the father and offspring.