Flamelet tabulation methods for solid fuel combustion with fuel-bound nitrogen

This work develops flamelet tabulation methods for solid fuel combustion with and without fuel-bound nitrogen based on computations in particle-laden counterflow flames. The proposed flamelet tabulation methods for NO prediction are evaluated for two different coal types. The results show that extracting the NO mass fraction from the flamelet library directly results in significant discrepancies in the studied fuel nitrogen-free flame, while reasonable predictions can be obtained by using the same method in the fuel-bound nitrogen flames for both coal types. In contrast, solving a transport equation for the NO mass fraction tends to improve the NO prediction. The NO concentration is well predicted by splitting the NO source term into a formation part and a rescaled consumption part. The best NO prediction is obtained by extracting the formation part and the rescaled consumption part with a modified reaction progress variable

Moyamoya vasculopathie: Diagnostiek en chirurgische behandlung

Samenvatting: Moyamoya vasculopathie is een zeldzame cerebrovasculaire aandoening met een onbekende etiologie die wordt gekenmerkt door een progressieve, bilaterale stenose van het distale gedeelte van de arteria carotis interna en van de proximale arteria cerebri anterior en media. Patiënten presenteren zich meestal met een ‘transient ischaemic attack’, herseninfarct of, meer zeldzaam, met een intracerebrale bloeding. Daarnaast kunnen er cognitieve stoornissen bestaan. Hoewel deze zeldzame aandoening voornamelijk in Oost-Azië voorkomt, wordt moyamoya steeds vaker gediagnosticeerd in de westerse wereld, vooral bij kinderen en jong volwassenen. Gerandomiseerde klinische trials ontbreken, maar er zijn sterke aanwijzingen dat neurochirurgisch ingrijpen door middel van directe, indirecte of gecombineerde revascularisatie de cerebrale perfusie verbetert en de kans op herseninfarcten verkleint. Herkenning van deze zeldzame progressieve intracraniële vaatziekte is belangrijk voor tijdige verwijzing naar een vasculair neurochirurgisch centrum. Summary: Moyamoya vasculopathy is a rare cerebrovascular disorder of unknown etiology. In moyamoya disease, progressive bilateral stenosis of the distal portion of the internal carotid artery and proximal anterior and middle cerebral artery occurs. Patients usually present with transient ischemic attack or stroke and, more rarely, with intracerebral haemorrhage. Additionally, there may be cognitive impairment. Although this rare disorder is mostly seen in Eastern Asia, moyamoya is increasingly recognised in the Western world, especially in children and young adults. Randomised clinical trials have not been performed but there are strong indications that neurosurgical intervention through direct, indirect or combined revascularisationcsurgery improves cerebral perfusion and reduces the risk of ischaemic stroke. Recognition of this rare progressive intracranial vascular disease is important to allow timely referral to a neurovascular center

Carrier-phase DNS of detailed NOx formation in early-stage pulverized coal combustion with fuel-bound nitrogen

Carrier-phase direct numerical simulation of detailed NOx formation in pulverized coal flames (PCC) with fuel-bound nitrogen is conducted in a 3D temporally evolving mixing layer setup where Lagrangian particles (Colombian bituminous coal) in an air stream (upper half of the domain) mix with the products of lean volatile/air combustion in the lower stream. The release of fuel-N is represented by ammonia, hydrogen cyanide, and a lumped nitrogenated tar (pyridine). Devolatilization is modeled by fitting a 2-step pyrolysis approach to the detailed heterogeneous PoliMi kinetics. A comprehensive homogeneous mechanism including all standard pathways of NOx and pyridine oxidation is adopted. Results show a partition of NO in two distinct branches of scatter plots of NO mass fraction vs. volatile mixture fraction after flame establishment, corresponding to NO in the lower stream flame region and hot spots near the upper stream. The contribution of NO2, prompt, and thermal mechanisms to total NOx is limited in the early stages of PCC. The main source of NO is fuel-N, with NH being the most important precursor. Pyridine plays an important role for NO production in the upper stream through CN formed from CHCHCN. CN and ammonia oxidation have the highest contribution to NH production. Regarding NO destruction, NO reactions with HCCO, CHi and C through the reburn process constitute the largest share. NO conversion to N2O by NH followed by conversion of N2O to N2 and NO+N→N2+O are the two most important pathways directly reducing NO to N2

Contralateral improvement of cerebrovascular reactivity and TIA frequency after unilateral revascularization surgery in moyamoya vasculopathy

OBJECTIVE: Moyamoya vasculopathy is a rare, often bilateral disease characterized by progressive stenosis and occlusion of the distal internal carotid artery, leading to a progressive deterioration of cerebrovascular reactivity (CVR) and increased risk of transient ischemic attacks (TIAs), infarction and hemorrhage. Surgical revascularization is a widely accepted symptomatic treatment, often performed bilaterally in one or two stages. To possibly further optimize treatment strategy, we investigated the effect of unilateral revascularization surgery on the CVR of, and TIA frequency originating from, the contralateral hemisphere. METHODS: From our database of 143 moyamoya vasculopathy patients we selected those with bilateral disease, who underwent hemodynamic imaging ([15O]H2O positron emission tomography (PET)-CT with acetazolamide challenge) before and 14 months (median) after unilateral revascularization. We evaluated CVR in three regions per hemisphere, and averaged these per hemisphere for statistical comparison. Conservatively treated patients were showed as a comparison group. To examine TIA frequency, we selected patients who presented with TIAs that (also) originated from the contralateral - not to be operated - hemisphere. We scored changes in CVR and TIA frequency of the ipsilateral and contralateral hemisphere over time. RESULTS: Seven surgical and seven conservative patients were included for CVR comparison. Of the 20 scored contralateral regions in the surgical group, 15 showed improved CVR after unilateral revascularization, while 5 remained stable. The averaged scores improved significantly for both hemispheres. In conservatively treated patients, however, only 3 of the 20 scored regions improved in the least-affected (contralateral) hemispheres, and 9 deteriorated. From the 6 patients with contralateral TIAs at presentation, 4 had a decreased TIA frequency originating from the contralateral hemisphere after unilateral surgery, while 2 patients remained stable. CONCLUSION: Both CVR and TIA frequency in the contralateral hemisphere can improve after unilateral revascularization surgery in bilateral MMV