Nonlinear Aspects of Combustion Instability in Liquid Propellant Rocket Motors. Second Yearly Progress Report for the Period 1 June 1961 to 31 May 1962

Combustion instability in liquid-propellant rocket engine

Commentary

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Giovani generazioni tra idee, parole e immagini di future famiglie

Nella certezza delle diffuse incertezze che stanno accompagnando la nostra società in questi ultimi anni, pure amplificate dalla pandemia, l’intenzione di formare una famiglia sembra, in ogni modo, rientrare nei progetti di vita per la maggior parte dei giovani. In tale cornice, il contributo rielabora le riflessioni svolte da studenti universitari, ai quali è stato chiesto di provare a definire il loro concetto di famiglia, per poi procedere con un esercizio di immaginazione di quella che loro stessi intenderanno costituire, anche alla luce della passata situazione pandemica. Partire, dunque, dalle parole dei giovani, intercettarne e decodificarne i significati e le direzioni di senso, può divenire una preziosa occasione di ri- flessione pedagogica, finalizzata all’avviamento di percorsi progettuali nei quali generare spazi di mediazione tra persone, famiglie e società

Particle formation in premixed ethylene-benzene flames: An experimental and modeling study

Abstract In this work soot formation was studied in laminar premixed flames of binary ethylene-benzene mixtures varying throughout the composition range from pure ethylene to pure benzene keeping constant the equivalence ratio (φ = 2) and obtaining a very similar maximum temperature (Tmax around 1750 K). In such way, it was possible to study for the first time the effect of binary aliphatic-aromatic fuel mixtures composition on the sooting behavior in comparable combustion conditions. In-situ optical techniques (laser induced incandescence and fluorescence) and ex-situ particle size distribution (PSD) measured downstream of the flame front, as well as modeling by means of a multi-sectional method, were applied. PSD profiles showed that particles with sizes less than 10 nm decrease as benzene percentage in the feed mixture increases, disappearing for benzene percentages above 30%. Conversely, large aggregates grow towards sizes larger than 100 nm when benzene concentration is increased. A non-linear effect of the benzene content in the binary fuel mixture on soot particle concentration was observed by laser induced incandescence, and confirmed by the multi-sectional model. In particular soot formation was found to increase more than linear up to 50% then leveled off to reincrease linearly from 80% to 100%. On the contrary, particles smaller than 10 nm at the end of the flame rapidly decreased for benzene percentages larger than 30%. From reaction rate analysis, the formation of gas-phase polycyclic aromatic hydrocarbons (PAH) and high-molecular mass aromatics precursors was found to be significantly large already for fuel mixtures featured by low benzene amounts (from 10 up to 40–50%). The enhanced aromatic precursor formation, combined with the abundance of acetylene mainly coming from the dehydrogenation of ethylene as predominant component of the binary fuel mixture, appeared to be responsible for the non-linear effect of ethylene-benzene composition on particle formation, particularly significant up to 40–50% of benzene. This finding has a considerable importance as regards the exploitation of highly-aromatic fuels as well as to foresee the soot emission for effect of the aromatic presence in natural and synthetic fuels used in practical combustion systems

The effect of butanol isomers on the formation of carbon particulate matter in fuel-rich premixed ethylene flames

Abstract The effect of the butanol isomers on carbon particulate matter formation was studied by substituting up to 20% of the total carbon of ethylene, fed to premixed flames with different equivalence ratios, with the four butanol isomers. Soot and condensed-phase nanostructures were tracked by means of particle size distribution (PSD) measurements and laser induced emission spectroscopy, namely fluorescence and incandescence. Butanol isomers, especially t-butanol, significantly reduced the total amount and the size of the soot particles, whereas a negligible effect was detected on condensed-phase nanostructures. PSDs were measured along with the aromaticity and functionalities of the carbon particulate matter thermophoretically sampled in the highest equivalence ratio condition. No significant differences were found among the different butanol isomers neither in the soot aggregate size, as measured by size exclusion chromatography, nor in the aromaticity, as evaluated by Raman and UV–vis spectroscopy, of the particulate matter. Conversely, FTIR analysis showed that carbon particulate matter produced from 1-butanol and t-butanol-doped flames contained larger amounts of oxygen in form of C = O, C–O–C and OH functionalities. However, most of the differences in the oxygen functionalities disappeared after dichloromethane (DCM) treatment, suggesting that these oxygenated moieties belong to the condensed-phase nanostructures, soluble in DCM, rather than to soot particles

Numerical Investigation on the Effect of the Oxymethylene Ether-3 (OME3) Blending Ratio in Premixed Sooting Ethylene Flames

Synthetic fuels, especially oxygenated fuels, which can be used as blending components, make it possible to modify the emission properties of conventional fossil fuels. Among oxygenated fuels, one promising candidate is oxymethylene ether-3 (OME3). In this work, the sooting propensity of ethylene (C2H4) blended with OME3 is numerically investigated on a series of laminar burner-stabilized premixed flames with increasing amounts of OME3, from pure ethylene to pure OME3. The numerical analysis is performed using the Conditional Quadrature Method of Moments combined with a detailed physico-chemical soot model. Two different equivalence ratios corresponding to a lightly and a highly sooting flame condition have been investigated. The study examines how different blending ratios of the two fuels affect soot particle formation and a correlation between OME3 blending ratio and corresponding soot reduction is established. The soot precursor species in the gas-phase are analyzed along with the soot volume fraction of small nanoparticles and large aggregates. Furthermore, the influence of the OME3 blending on the particle size distribution is studied applying the entropy maximization concept. The effect of increasing amounts of OME3 is found to be different for soot nanoparticles and larger aggregates. While OME3 blending significantly reduces the amount of larger aggregates, only large amounts of OME3, close to pure OME3, lead to a considerable suppression of nanoparticles formed throughout the flame. A linear correlation is identified between the OME3 content in the fuel and the reduction in the soot volume fraction of larger aggregates, while smaller blending ratios may lead to an increased number of nanoparticles for some positions in the flame for the richer flame condition

Effect of counterion on the catalytic activity of NHC-gold(I) in A3 coupling reactions

Synthetic A3-coupling represents an efficient and environmentally convenient procedure for the production of propargylamines, relevant intermediates for the preparation of pharmacologically active substances. Gold(I) complexes of general formula NHC-Au-X have been synthesized, characterized, and tested in the A3-coupling reaction of benzaldehyde, piperidine and phenylacetylene on varying the anionic fragment X as halogenide (Cl, Br, I), acetate (OAc), hexafluorophosphate (PF6) or phenylacetylide (-C≡CPh), with 5-dichloro[N-methyl, N’(2-hydroxy-2-phenyl)ethyl imidazole-2-ylidene as NHC ligand. The kinetic profiles were interpreted with DFT (Density Functional Theory) studies on bond dissociation energies (BDE) of the counterion as well as on the relative stability of the neutral NHC-Au-X complexes with respect to their ionic forms [Au(NHC)2]+[AuX2]-

Optical Coherence Tomography after Carotid Stenting: Rate of Stent Malapposition, Plaque Prolapse and Fibrous Cap Rupture According to Stent Design

ObjectivesThis study aims to evaluate the rate of stent malapposition, plaque prolapse and fibrous cap rupture detected by optical coherence tomography (OCT) imaging according to carotid stent design.DesignIt was a prospective single-centre study.Materials and methodsForty consecutive patients undergoing protected carotid artery stenting (CAS) and high-definition OCT image acquisition were enrolled in the study. OCT frames were analysed off-line, in a dedicated core laboratory by two independent physicians. Cross-sectional OCT images within the stented segment of the internal carotid artery were evaluated at 1-mm intervals for the presence of strut malapposition, plaque prolapse and fibrous cap rupture according to stent design.ResultsClosed-cell design stents (CC) were used in 17 patients (42.5%), open-cell design stents (OC) in 13 (32.5%) and hybrid design stents (Hyb) in 10 (25%). No procedural or post-procedural neurological complications occurred (stroke/death 0% at 30 days). On OCT analysis the frequencies of malapposed struts were higher with CC compared to OC and Hyb (34.5% vs 15% and 16.3%, respectively; p < 0.01). Plaque prolapse was more frequent with OC vs CC (68.6% vs 23.3%; p < 0.01) and vs Hyb stents (30.8%; p < 0.01). Significant differences were also noted in the rates of fibrous cap rupture between CC and OC (24.2% vs 43.8%; p < 0.01), and between CC and Hyb (24.2% vs 39.6%; p < 0.01), but not between OC and Hyb stents (p = 0.4).ConclusionIntravascular OCT after CAS revealed that micro-defects after stent deployment are frequent and are related to the design of implanted stents. Stent malapposition is more frequent with CC stents, while plaque prolapse is more common with OC stents.It remains, however, unknown whether these figures now detected with OCT are of any clinical and prognostic significance

Triterpenoids from vitellaria paradoxa stem barks reduce nitrite levels in lps-stimulated macrophages

open7siVitellaria paradoxa C. F. Gaertn is widely used in African traditional medicine as an anti-inflammatory remedy to treat rheumatism, gastric problems, diarrhea, and dysentery. The phyto-chemical investigation of the ethyl acetate extract of V. paradoxa stem bark collected in Burkina Faso led to the isolation of eight known and two triterpenes undescribed to date (7 and 10), in the free alcohol form or as acetyl and cinnamyl ester derivatives. The stereostructures of the new compounds were elucidated using HR-ESIMS and 1D and 2D NMR data. The isolated compounds were evaluated in vitro for their inhibitory effect on nitrite levels on murine macrophages J774 stimulated with the lipopolysaccharide (LPS). Among all the compounds tested, lupeol cinnamate (3) and betulinic acid (5) showed a beneficial effect in reducing nitrite levels produced after LPS stimulation.openSirignano C.; Nadembega P.; Poli F.; Romano B.; Lucariello G.; Rigano D.; Taglialatela-Scafati O.Sirignano C.; Nadembega P.; Poli F.; Romano B.; Lucariello G.; Rigano D.; Taglialatela-Scafati O

How to combine CTA, 99mTc-WBC SPECT/CT, and [18F]FDG PET/CT in patients with suspected abdominal vascular endograft infections?

Purpose - We aimed at comparing Tc-99m-HMPAO white blood cells (Tc-99m-WBC) scintigraphy, 18fluorine-fluorodeoxyglucose ([F-18]FDG) positron emission tomography/computed tomography (PET/CT) and CT angiography (CTA) in patients with suspected abdominal vascular graft or endograft infection (VGEI). Moreover, we attempted to define a new visual score for interpreting [F-18]FDG PET/CT scans aiming at increasing its specificity. Methods - We prospectively compared Tc-99m-WBC SPECT/CT, [F-18]FDG PET/CT, and CTA in 26 patients with suspected abdominal VGEI. WBC scans were performed and interpreted according to EANM recommendations. [F-18]FDG PET/CT studies were assessed with both qualitative (Sah's scale and new visual score) and semi-quantitative analyses. CTA images were interpreted according to MAGIC criteria. Microbiology, histopathology or a clinical follow-up of at least 24 months were used to achieve final diagnosis. Results - Eleven out of 26 patients were infected. [F-18]FDG PET/CT showed 100% sensitivity and NPV, with both scoring systems, thus representing an efficient tool to rule out the infection. The use of a more detailed scoring system provided statistically higher specificity compared to the previous Sah's scale (p = 0.049). Tc-99m-WBC SPECT/CT provided statistically higher specificity and PPV than [F-18]FDG PET/CT, regardless the interpretation criteria used and it can be, therefore, used in early post-surgical phases or to confirm or rule out a PET/CT finding. Conclusions - After CTA, patients with suspected late VGEI should perform a [F-18]FDG PET/CT given its high sensitivity and NPV. However, given its lower specificity, positive results should be confirmed with Tc-99m-WBC scintigraphy. The use of a more detailed scoring system reduces the number of Tc-99m-WBC scans needed after [F-18]FDG PET/CT. Nevertheless, in suspected infections within 4 months from surgery, Tc-99m-WBC SPECT/CT should be performed as second exam, due to its high accuracy in differentiating sterile inflammation from infection