1,427 research outputs found
On Graph Refutation for Relational Inclusions
We introduce a graphical refutation calculus for relational inclusions: it
reduces establishing a relational inclusion to establishing that a graph
constructed from it has empty extension. This sound and complete calculus is
conceptually simpler and easier to use than the usual ones.Comment: In Proceedings LSFA 2011, arXiv:1203.542
Simulations of secondary Farley-Buneman instability driven by a kilometer-scale primary wave: anomalous transport and formation of flat-topped electric fields
Since the 1950s, high frequency and very high frequency radars near the magnetic equator have frequently detected strong echoes caused ultimately by the FarleyâBuneman instability (FBI) and the gradient drift instability (GDI). In the 1980s, coordinated rocket and radar campaigns made the astonishing observation of flatâtopped electric fields coincident with both meterâscale irregularities and the passage of kilometerâscale waves. The GDI in the daytime E region produces kilometerâscale primary waves with polarization electric fields large enough to drive meterâscale secondary FBI waves. The meterâscale waves propagate nearly vertically along the largeâscale troughs and crests and act as VHF tracers for the largeâscale dynamics. This work presents a set of hybrid numerical simulations of secondary FBIs, driven by a primary kilometerâscale GDIâlike wave. Meterâscale density irregularities develop in the crest and trough of the kilometerâscale wave, where the total electric field exceeds the FBI threshold, and propagate at an angle near the direction of total Hall drift determined by the combined electric fields. The meterâscale irregularities transport plasma across the magnetic field, producing flatâtopped electric fields similar to those observed in rocket data and reducing the largeâscale wave electric field to just above the FBI threshold value. The selfâconsistent reduction in driving electric field helps explain why echoes from the FBI propagate near the plasma acoustic speed.NSF grants PHY-1500439 and AGS-1755350 and NASA grant NNX14AI13G supported the research presented in this work. This work used TACC and XSEDE computational resources supported by the National Science Foundation grant ACI-1053575. This paper did not use any data; simulation runs are archived on the TACC Ranch system. The authors thank one anonymous reviewer for helpful comments. (PHY-1500439 - NSF; AGS-1755350 - NSF; NNX14AI13G - NASA; ACI-1053575 - National Science Foundation)Published version2019-07-0
How Does SARS-CoV-2 Affect the Central Nervous System? A Working Hypothesis
Interstitial pneumonia was the first manifestation to be recognized as caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2); however, in just a few weeks, it became clear that the coronavirus disease-2019 (COVID-19) overrun tissues and more body organs than just the lungs, so much so that it could be considered a systemic pathology. Several studies reported the involvement of the conjunctiva, the gut, the heart and its pace, and vascular injuries such as thromboembolic complications and Kawasaki disease in children and toddlers were also described. More recently, it was reported that in a sample of 214 SARS-CoV-2 positive patients, 36.4% complained of neurological symptoms ranging from non-specific manifestations (dizziness, headache, and seizures), to more specific symptoms such hyposmia or hypogeusia, and stroke. Older individuals, especially males with comorbidities, appear to be at the highest risk of developing such severe complications related to the Central Nervous System (CNS) involvement. Neuropsychiatric manifestations in COVID-19 appear to develop in patients with and without pre-existing neurological disorders. Growing evidence suggests that SARS-CoV-2 binds to the human Angiotensin-Converting Enzyme 2 (ACE2) for the attachment and entrance inside host cells. By describing ACE2 and the whole Renin Angiotensin Aldosterone System (RAAS) we may better understand whether specific cell types may be affected by SARS-CoV-2 and whether their functioning can be disrupted in case of an infection. Since clear evidences of neurological interest have already been shown, by clarifying the topographical distribution and density of ACE2, we will be able to speculate how SARS-CoV-2 may affect the CNS and what is the pathogenetic mechanism by which it contributes to the specific clinical manifestations of the disease. Based on such evidences, we finally hypothesize the process of SARS-CoV-2 invasion of the CNS and provide a possible explanation for the onset or the exacerbation of some common neuropsychiatric disorders in the elderly including cognitive impairment and Alzheimer disease
Anastrepha species (Diptera: Tephritidae), their hosts and parasitoids in the extreme north of Brazil.
O presente trabalho foi realizado em cinco municĂpios do Estado de Roraima, Brasil, com o objetivo de registrar a ocorrĂȘncia de espĂ©cies de Anastrepha, suas plantas hospedeiras e parasitoides. Foram coletados frutos carnosos de 21 espĂ©cies pertencentes a 10 famĂlias botĂąnicas de setembro/2007 a setembro/2008. Foram identificadas 10 espĂ©cies de Anastrepha (Anastrepha bahiensis Lima e Anastrepha montei Lima foram registradas pela primeira vez em Roraima) e cinco espĂ©cies de parasitoides (4 Braconidae e 1 Figitidae). Doryctobracon areolatus (SzĂ©pligeti) foi o parasitoide mais abundante
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