Multimodal transition and stochastic antiresonance in squid giant axons

The experimental data of N. Takahashi, Y. Hanyu, T. Musha, R. Kubo, and G. Matsumoto, Physica D \textbf{43}, 318 (1990), on the response of squid giant axons stimulated by periodic sequence of short current pulses is interpreted within the Hodgkin-Huxley model. The minimum of the firing rate as a function of the stimulus amplitude $I_0$ in the high-frequency regime is due to the multimodal transition. Below this singular point only odd multiples of the driving period remain and the system is highly sensitive to noise. The coefficient of variation has a maximum and the firing rate has a minimum as a function of the noise intensity which is an indication of the stochastic coherence antiresonance. The model calculations reproduce the frequency of occurrence of the most common modes in the vicinity of the transition. A linear relation of output frequency vs. $I_0$ for above the transition is also confirmed.Comment: 5 pages, 9 figure

Direct Detection of Galactic Halo Dark Matter

The Milky Way Galaxy contains a large, spherical component which is believed to harbor a substantial amount of unseen matter. Recent observations indirectly suggest that as much as half of this ``dark matter'' may be in the form of old, very cool white dwarfs, the remnants of an ancient population of stars as old as the Galaxy itself. We conducted a survey to find faint, cool white dwarfs with large space velocities, indicative of their membership in the Galaxy's spherical halo component. The survey reveals a substantial, directly observed population of old white dwarfs, too faint to be seen in previous surveys. This newly discovered population accounts for at least 2% of the halo dark matter. It provides a natural explanation for the indirect observations, and represents a direct detection of Galactic halo dark matter.Comment: 13 pages, 4 figures, 1 table. Note added after Science Express online publication: This text reflects the correction of a few typographical errors in the online version of the table. It also includes the new constraint on the calculation of d_max which accounts for the fact that the survey could not have detected stars with proper motions below 0.33 arcseconds per year. Published online at ScienceExpress www.sciencemag.org 22 March 2001; 10.1126/science.1059954; To appear in Science 27 April 200

What about the men? Perinatal experiences of men of color whose partners were at risk for preterm birth, a qualitative study.

BACKGROUND:Preterm birth in the United States is associated with maternal clinical factors such as diabetes, hypertension and social factors including race, ethnicity, and socioeconomic status. In California, 8.7% of all live births are preterm, with African American and Black families experiencing the greatest burden. The impact of paternal factors on birth outcomes has been studied, but little is known about the experience of men of color (MOC). The purpose of this study was to explore the experiences of MOC who are partners to women at medical and social risk for preterm birth. METHODS:This study used a qualitative research design and focus group methods. The research was embedded within an existing study exploring experiences of women of color at risk for preterm birth conducted by the California Preterm Birth Initiative. RESULTS:Twelve MOC participated in the study and among them had 9 preterm children. Four themes emerged from thematic analysis of men's experiences: (1) "Being the Rock": Providing comfort and security; (2) "It's a blessing all the way around": Keeping faith during uncertainty; (3) "Tell me EVERYTHING": Unmet needs during pregnancy and delivery; (4) "Like a guinea pig": Frustration with the healthcare system. Participants identified many barriers to having a healthy pregnancy and birth including inadequate support for decision making, differential treatment, and discrimination. CONCLUSIONS:This study shows novel and shared narratives regarding MOC experiences during pregnancy, birth, and postpartum periods. Healthcare providers have an essential role to acknowledge MOC, their experience of discrimination and mistrust, and to assess needs for support that can improve birth outcomes. As MOC and their families are at especially high social and medical risk for preterm birth, their voice and experience should be central in all future research on this topic

Dynamic behaviors in directed networks

Motivated by the abundance of directed synaptic couplings in a real biological neuronal network, we investigate the synchronization behavior of the Hodgkin-Huxley model in a directed network. We start from the standard model of the Watts-Strogatz undirected network and then change undirected edges to directed arcs with a given probability, still preserving the connectivity of the network. A generalized clustering coefficient for directed networks is defined and used to investigate the interplay between the synchronization behavior and underlying structural properties of directed networks. We observe that the directedness of complex networks plays an important role in emerging dynamical behaviors, which is also confirmed by a numerical study of the sociological game theoretic voter model on directed networks