Good covers are algorithmically unrecognizable

A good cover in R^d is a collection of open contractible sets in R^d such that the intersection of any subcollection is either contractible or empty. Motivated by an analogy with convex sets, intersection patterns of good covers were studied intensively. Our main result is that intersection patterns of good covers are algorithmically unrecognizable. More precisely, the intersection pattern of a good cover can be stored in a simplicial complex called nerve which records which subfamilies of the good cover intersect. A simplicial complex is topologically d-representable if it is isomorphic to the nerve of a good cover in R^d. We prove that it is algorithmically undecidable whether a given simplicial complex is topologically d-representable for any fixed d \geq 5. The result remains also valid if we replace good covers with acyclic covers or with covers by open d-balls. As an auxiliary result we prove that if a simplicial complex is PL embeddable into R^d, then it is topologically d-representable. We also supply this result with showing that if a "sufficiently fine" subdivision of a k-dimensional complex is d-representable and k \leq (2d-3)/3, then the complex is PL embeddable into R^d.Comment: 22 pages, 5 figures; result extended also to acyclic covers in version

3,4-Methylenedioxymethamphetamine (MDMA) neurotoxicity in rats: a reappraisal of past and present findings

RATIONALE: 3,4-Methylenedioxymethamphetamine (MDMA) is a widely abused illicit drug. In animals, high-dose administration of MDMA produces deficits in serotonin (5-HT) neurons (e.g., depletion of forebrain 5-HT) that have been interpreted as neurotoxicity. Whether such 5-HT deficits reflect neuronal damage is a matter of ongoing debate. OBJECTIVE: The present paper reviews four specific issues related to the hypothesis of MDMA neurotoxicity in rats: (1) the effects of MDMA on monoamine neurons, (2) the use of “interspecies scaling” to adjust MDMA doses across species, (3) the effects of MDMA on established markers of neuronal damage, and (4) functional impairments associated with MDMA-induced 5-HT depletions. RESULTS: MDMA is a substrate for monoamine transporters, and stimulated release of 5-HT, NE, and DA mediates effects of the drug. MDMA produces neurochemical, endocrine, and behavioral actions in rats and humans at equivalent doses (e.g., 1–2 mg/kg), suggesting that there is no reason to adjust doses between these species. Typical doses of MDMA causing long-term 5-HT depletions in rats (e.g., 10–20 mg/kg) do not reliably increase markers of neurotoxic damage such as cell death, silver staining, or reactive gliosis. MDMA-induced 5-HT depletions are accompanied by a number of functional consequences including reductions in evoked 5-HT release and changes in hormone secretion. Perhaps more importantly, administration of MDMA to rats induces persistent anxiety-like behaviors in the absence of measurable 5-HT deficits. CONCLUSIONS: MDMA-induced 5-HT depletions are not necessarily synonymous with neurotoxic damage. However, doses of MDMA which do not cause long-term 5-HT depletions can have protracted effects on behavior, suggesting even moderate doses of the drug may pose risks

Emergent tracheostomy during the pandemic of COVID-19: Slovenian National Recommendations

Purpose: Emergent tracheostomy under local anaesthesia is a reliable method of airway management when orotracheal intubation is not possible. COVID-19 is spread through aerosol making the emergent tracheostomy a high-risk procedure for surgeons. The surgical establishment of the air conduit in emergency scenarios must be adjusted for safety reasons. Methods: To establish the Slovenian National Guidelines for airway management in cannot intubate—cannot ventilate situations in COVID-19 positive patients. Results: Good communication and coordination between surgeon and anaesthesiologist is absolutely necessary. Deep general anaesthesia, full muscle relaxation and adequate preoxygenation without intubation are initial steps. The surgical cricothyrotomy is performed quickly, the thin orotracheal tube is inserted, the cuff is inflated and ventilation begins. Following patient stabilisation, the conversion to the tracheostomy is undertaken with the following features: skin infiltration with vasoconstrictor, a vertical incision, avoidance of electrical devices in favour of classical manners of haemostasis, the advancement of the tube towards the carina, performing the tracheal window in complete apnoea following adequate oxygenation, the insertion of non-fenestrated canulla attached to a heat and moisture exchanger, the fixation of canulla with stitches and tapes, and the cricothyrotomy entrance closure. Appropriate safety equipment is equally important. Conclusion: The goal of the guidelines is to make the procedure safer for medical teams, without harming the patients. Further improvements of the guidelines will surely appear as COVID-19 is a new entity and there is not yet much experience in handling it