A low fraction of nitrogen in molecular form in a dark cloud.

Nitrogen is the fifth most abundant element in the Universe. In the interstellar medium, it has been thought to be mostly molecular (N2). However, N2 has no observable rotational or vibrational transitions, so its abundance in the interstellar medium remains poorly known. In comets, the N2 abundance is very low, while the elemental nitrogen abundance is deficient with respect to the solar value. Moreover, large nitrogen isotopic anomalies are observed in meteorites and interstellar dust particles. Here we report the N2H+ (and by inference the N2) abundance inside a cold dark molecular cloud. We find that only a small fraction of nitrogen in the gas phase is molecular, with most of it being atomic. Because the compositions of comets probably reflect those of dark clouds, this result explains the low N2 abundance in comets. We argue that the elemental nitrogen abundance deficiency in comets can be understood if the atomic oxygen abundance is lower than predicted by present chemical models. Furthermore, the lack of molecular nitrogen in molecular clouds explains the nitrogen anomalies in meteorites and interstellar dust particles, as nitrogen fractionation is enhanced if gaseous nitrogen is atomic.

Internal structure of a cold dark molecular cloud inferred from the extinction of background starlight.

Stars and planets form within dark molecular clouds, but little is understood about the internal structure of these clouds, and consequently about the initial conditions that give rise to star and planet formation. The clouds are primarily composed of molecular hydrogen, which is virtually inaccessible to direct observation. But the clouds also contain dust, which is well mixed with the gas and which has well understood effects on the transmission of light. Here we use sensitive near-infrared measurements of the light from background stars as it is absorbed and scattered by trace amounts of dust to probe the internal structure of the dark cloud Barnard 68 with unprecedented detail. We find the cloud's density structure to be very well described by the equations for a pressure-confined, self-gravitating isothermal sphere that is critically stable according to the Bonnor-Ebert criteria. As a result we can precisely specify the physical conditions inside a dark cloud on the verge of collapse to form a star.

Absence epilepsy: early prognostic signs.

We have studied 124 children with typical absence epilepsy. The onset of symptoms was in 12% under 4 years, in 51% between 4-8 years and in 37% above 8 years. The F:M ratio was 2:1 in children under 4 years versus 1:1 above 8 years. Absences alone occurred in 82% and absences followed or preceded by generalized tonic-clonic seizures (GTCS) in 6.5% and 11%, respectively. Simple absences were not seen in children under 4 years and were more frequent (14%) in the 4-8 years age group. Family history was positive for epilepsy in 20% and febrile convulsion in 7%. Sixteen percent had a positive past history of febrile convulsions. All patients showed bilateral, synchronous spike-wave discharges from 2.5 to 4 c/s. Lateralized spikes, spike-slow wave complexes were found in 27%. Photosensitivity was present in 18% and was marked in 12%. Monotherapy with sodium valproate or ethosuximide (91% SV) was successful in 85% of patients with absences alone and 68% of the absences with GTCS. Only 2% were not fully controlled either on monotherapy or polytherapy. Treatment was withdrawn in 41 patients and 13 relapsed. We have identified four factors associated with relapses: (a) poor initial response to treatment, (b) lateralized focal EEG abnormality and/or marked photosensitivity, (c) the evolution to myoclonic epilepsy, and (d) early withdrawal of AED (< 3 years).

[Health education in sexuality and family planning. A experience]. / Educación para la salud en sexualidad y planificación familiar. Una experiencia.

We present an educational health experience in Sexuality and Family Planning, carried out jointly by health care professionals in a Health Care Center and by teachers at a Job Training School within its area, with three groups of students, mostly adolescents. Four sessions were conducted: Sexual education: sexuality and health. Sexual relations. Family relations. Family planning. Evaluation of the previous sessions. In each session, there was a presentation made by the teacher/expert, after which working groups of 4-5 students were formed. Finally, everyone came together again to discuss their work. In each session, several group techniques were used to motivate a higher degree participation, lower inhibition, and deepen mutual contacts. Results have been positive, both for students and teachers, with an increase in knowledge, a variation in attitudes towards the subject, and because it was something different from everyday studies.

The formation of sunlike stars.

Understanding how stars like the sun formed constitutes one of the principal challenges confronting modern astrophysics. In recent years, advances in observational technology, particularly at infrared and millimeter wavelengths, have produced an avalanche of critical data and unexpected discoveries about the process of star formation, which is blocked from external view at optical and shorter wavelengths by an obscuring blanket of interstellar dust. Fueled by this new knowledge, a comprehensive empirical picture of stellar genesis is beginning to emerge, laying the foundations for a coherent theory of the birth of sunlike stars.