RESUMEN
It is thought that neutron stars in low-mass binary systems can accrete matter and angular momentum from the companion star and be spun-up to millisecond rotational periods. During the accretion stage, the system is called a low-mass X-ray binary, and bright X-ray emission is observed. When the rate of mass transfer decreases in the later evolutionary stages, these binaries host a radio millisecond pulsar whose emission is powered by the neutron star's rotating magnetic field. This evolutionary model is supported by the detection of millisecond X-ray pulsations from several accreting neutron stars and also by the evidence for a past accretion disc in a rotation-powered millisecond pulsar. It has been proposed that a rotation-powered pulsar may temporarily switch on during periods of low mass inflow in some such systems. Only indirect evidence for this transition has hitherto been observed. Here we report observations of accretion-powered, millisecond X-ray pulsations from a neutron star previously seen as a rotation-powered radio pulsar. Within a few days after a month-long X-ray outburst, radio pulses were again detected. This not only shows the evolutionary link between accretion and rotation-powered millisecond pulsars, but also that some systems can swing between the two states on very short timescales.
RESUMEN
INTRODUCTION: Organ transplantation is often the only possible treatment to save the lives of patients with end-stage organ failure. Limiting factors include failure to notify in cases of patients with brain death, the inefficient procurement and distribution of organs, the lack of specific educational policies for health care professionals, lack of knowledge on the organ transplantation process, and family refusal for organ donation. OBJECTIVE: To evaluate the knowledge of students enrolled in different undergraduate university courses in Rio de Janeiro on the regulations and strategies governing transplant organ donation in Brazil. METHODS: This qualitative, observational study used a 10-item questionnaire aimed at obtaining data on respondents' general knowledge regarding organ donation and transplantation. The questionnaire was applied using either a printed or an electronic version developed on Google Forms and was completed anonymously. RESULTS: Overall, 587 questionnaires were completed. The participants were divided into 3 groups according to their field of study: 256 (43.6%) from courses related to arts and humanities, 159 (27.1%) from science and technology-related courses, and 172 (29.3%) from the biomedical field. Most respondents (396; 67.5%) were unaware of the criteria required to be an organ transplant donor. CONCLUSION: There is a significant lack of knowledge among university students on issues related to the organ donation and transplantation process in Brazil.