ABSTRACT
Nova explosions are caused by global thermonuclear runaways triggered in the surface layers of accreting white dwarfs1-3. It has been predicted4-6 that localized thermonuclear bursts on white dwarfs can also take place, similar to type-I X-ray bursts observed in accreting neutron stars. Unexplained rapid bursts from the binary system TV Columbae, in which mass is accreted onto a moderately strong magnetized white dwarf from a low-mass companion, have been observed on several occasions in the past 40 years7-11. During these bursts, the optical/ultraviolet luminosity increases by a factor of more than three in less than an hour and fades in around ten hours. Fast outflows have been observed in ultraviolet spectral lines7, with velocities of more than 3,500 kilometres per second, comparable to the escape velocity from the white dwarf surface. Here we report on optical bursts observed in TV Columbae and in two additional accreting systems, EI Ursae Majoris and ASASSN-19bh. The bursts have a total energy of approximately 10-6 times than those of classical nova explosions (micronovae) and bear a strong resemblance to type-I X-ray bursts12-14. We exclude accretion or stellar magnetic reconnection events as their origin and suggest thermonuclear runaway events in magnetically confined accretion columns as a viable explanation.
ABSTRACT
BACKGROUND: Central venous oxygen saturation (ScvO2) remains the gold standard surrogate for tissue oxygen extraction in paediatric cardiac surgery. Near-infrared spectroscopy (NIRS) has been developed as a non-invasive diagnostic tool for regional oxygen saturation. The aim was to compare regional oxygen saturation measured by NIRS with ScvO2 in postoperative paediatric cardiac patients. METHODS: In this prospective study, we included newborns and infants younger than 45 days undergoing heart surgery. We recorded continuous ScvO2 and NIRS regional saturation placed on the forehead (B) and right flank (S) for 48 h postoperatively. A Bland-Altman's analysis was used to assess the agreement between these measurements. RESULTS: A total of 23 patients were included with a median age of 12 days (2-46) and median weight of 3.1 kg (2.3-4.47). The mean difference (MD) ScvO2- B NIRS was 10.45% with limits of agreement (LOA) -17.23 to 38.13% and ScvO2- S NIRS MD 7.16% with LOA: -25.51 to 39.84%. The single ventricle ScvO2- S NIRS subgroup had MD within ± 5%; however, wide LOA was observed. The remaining subgroups showed MD nearly above ± 5%, with wide LOA. CONCLUSIONS: The regional oxygen saturation of brain and kidney did not match ScvO2 as estimation of global tissue perfusion. Nevertheless, NIRS may still provide information regarding regional circulation that may help in the management of neonatal cardiac surgery patients.