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Eight planetary nebulae (PNe) are known to emit OH and/or H2O masers, but there is no report of an SiO maser in this type of objects. We present a search for SiO masers in 16 confirmed and candidate PNe, carried out with the Australia Telescope Compact Array. We found no evidence of association between SiO masers and PNe in our data. Previous detections of thermal SiO emission in PNe show that these molecules can be present in gas phase in this type of objects, but it is not yet clear whether they can be found where the physical conditions are appropriate for maser pumping. We suggest that the best candidates for a new search would be PNe showing high-velocity outflows.
Planetary nebulae (PNe) harbouring masers of H2O (H2OPNe) and/or OH (OHPNe) are thought to be nascent PNe. They are extremely scarce, and so far only eight members are know to date. Here we explain our current effort to identify new H2OPNe and/or OHPNe. We report IRAS 07027–7934 as a new bona fine OHPN. Its 1612 MHz OH spectrum seems to be changing from double- to single-peaked since the redshifted emission has vanished almost completely, and the 1667 MHz OH maser emission has disappeared. For the OHPN Vy 2-2, we found that its central star is unexpectedly carbon (C)-rich, has a low-mass progenitor, and could be a post-common envelope binary system. Moreover, we confirm Vy 2-2 as a nascent PN. We speculate that low-mass C-rich central stars in post-common envelope systems could be a common end of H2OPNe and OHPNe.
Neurofibromatosis (NF) is an autosomal dominant disorder encompassing several distinct genetic defects with overlapping clinical features. This chapter focuses on the main genetic, clinical, pathological, and radiological features of neurofibromatosis type 1 (NF1). The cerebrovascular manifestations of NF1 include cerebral ischemia, intracranial hematoma, and subarachnoidal hemorrhage. Recurrent strokes can occur in the same or in different territories. Every large or medium-sized artery can be affected, and some patients have multiple stenoses of intracranial vessels combined with stenoses or occlusion of extracranial vessel. Hemispheric territorial infarction is a common stroke manifestation. Ocular involvement may present with retinal ischemia or global ocular ischemia. Angiography, time-of-flight magnetic resonance angiography (TOF-MRA) and Color duplex and spectral Doppler ultrasonography are useful diagnostic modalities for revealing the vascular complications of NF1. Neurosurgical revascularization in patients with moyamoya syndrome has been shown to reduce the risk of first-ever and recurrent stroke and transient ischemic attack (TIA).
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