Thermoacoustically driven flame motion and heat release variation in a swirl-stabilized gas turbine burner investigated by LIF and chemiluminescence

Laser-induced fluorescence and chemiluminescence, both phase-locked to the dominant acoustic oscillation, are used to investigate phenomena related to thermoacoustic instability in a swirl-stabilized industrial scale gas turbine burner. The observed sinusoidal phase-averaged flame motion in axial (main flow) direction is analyzed using different schemes for defining the flame position. Qualitative agreement between experimental data and theoretical analysis of the observed flame motion is obtained, interpreted as originating primarily from variation of the burning velocity. The heat release variation during an acoustic cycle is determined from the sinusoidally varying total OH* chemiluminescence intensit

Identification of H2_2CCC as a diffuse interstellar band carrier

We present strong evidence that the broad, diffuse interstellar bands (DIBs) at 4881 and 5450\,\AA are caused by the B\,^1B$_1$\,$\leftarrow$\,X\,^1A$_1$ transition of H$_2$CCC (l-C$_3$H$_2$). The large widths of the bands are due to the short lifetime of the B\,^1B$_1$ electronic state. The bands are predicted from absorption measurements in a neon matrix and observed by cavity ring-down in the gas phase and show exact matches to the profiles and wavelengths of the two broad DIBs. The strength of the 5450\,\AA DIB leads to a l-C$_3$H$_2$ column density of $\sim5\times10^{14}$ cm$^{-2}$ towards HD\,183143 and $\sim2\times10^{14}$\,cm$^{-2}$ to HD\,206267. Despite similar values of $E$($B-V$), the 4881 and 5450\,\AA DIBs in HD\,204827 are less than one third their strength in HD\,183143, while the column density of interstellar C$_3$ is unusually high for HD\,204827 but undetectable for HD\,183143. This can be understood if C$_3$ has been depleted by hydrogenation to species such as l-C$_3$H$_2$ towards HD\,183143. There are also three rotationally resolved sets of triplets of l-C$_3$H$_2$ in the 6150$-$6330\,\AA region. Simulations, based on the derived spectroscopic constants and convolved with the expected instrumental and interstellar line broadening, show credible coincidences with sharp, weak DIBs for the two observable sets of triplets. The region of the third set is too obscured by the $\alpha$-band of telluric O$_2$.Comment: 22 pages, 9 figure

Characterizing Long COVID in Children and Adolescents

ImportanceMost research to understand postacute sequelae of SARS-CoV-2 infection (PASC), or long COVID, has focused on adults, with less known about this complex condition in children. Research is needed to characterize pediatric PASC to enable studies of underlying mechanisms that will guide future treatment.ObjectiveTo identify the most common prolonged symptoms experienced by children (aged 6 to 17 years) after SARS-CoV-2 infection, how these symptoms differ by age (school-age [6-11 years] vs adolescents [12-17 years]), how they cluster into distinct phenotypes, and what symptoms in combination could be used as an empirically derived index to assist researchers to study the likely presence of PASC.Design, setting, and participantsMulticenter longitudinal observational cohort study with participants recruited from more than 60 US health care and community settings between March 2022 and December 2023, including school-age children and adolescents with and without SARS-CoV-2 infection history.ExposureSARS-CoV-2 infection.Main outcomes and measuresPASC and 89 prolonged symptoms across 9 symptom domains.ResultsA total of 898 school-age children (751 with previous SARS-CoV-2 infection [referred to as infected] and 147 without [referred to as uninfected]; mean age, 8.6 years; 49% female; 11% were Black or African American, 34% were Hispanic, Latino, or Spanish, and 60% were White) and 4469 adolescents (3109 infected and 1360 uninfected; mean age, 14.8 years; 48% female; 13% were Black or African American, 21% were Hispanic, Latino, or Spanish, and 73% were White) were included. Median time between first infection and symptom survey was 506 days for school-age children and 556 days for adolescents. In models adjusted for sex and race and ethnicity, 14 symptoms in both school-age children and adolescents were more common in those with SARS-CoV-2 infection history compared with those without infection history, with 4 additional symptoms in school-age children only and 3 in adolescents only. These symptoms affected almost every organ system. Combinations of symptoms most associated with infection history were identified to form a PASC research index for each age group; these indices correlated with poorer overall health and quality of life. The index emphasizes neurocognitive, pain, and gastrointestinal symptoms in school-age children but change or loss in smell or taste, pain, and fatigue/malaise-related symptoms in adolescents. Clustering analyses identified 4 PASC symptom phenotypes in school-age children and 3 in adolescents.Conclusions and relevanceThis study developed research indices for characterizing PASC in children and adolescents. Symptom patterns were similar but distinguishable between the 2 groups, highlighting the importance of characterizing PASC separately for these age ranges

Distributions d'énergie cinétique de la dissociation d'ions du Fluoroéthène et du 1,1-difluoroéthène.

The unimolecular dissociation of energy-selected fluoroethene and 1,1-difluoroethene ions has been investigated by threshold photoelectron photoion coincidence TPEPICO) technique. The breakdown diagrams of the 1,1-difluorethene and fluoroethene have been recorded between 13-22 eV. From time-of-flight (TOF) spectra, complete distributions of the kinetic energy released (KERD) in the dissociation of these energy-selected ions have been derived. For the HF-loss reaction channel, the KERD peaks at about 200 meV for low excitation energies but becomes thermal at higher excitation energies. For the F-loss channel, the KERD peaks at zero kinetic energy for low excitation energies but at about 200 meV for high excitation energy. The analysis of the KERD provides evidence that consecutive fragmentation takes place for the 1,1-difluoroethene at energies above 19 eV

Réactions statistiques et non-statistiques dans les ions Fluorométhane sélectionnés en énergie.

The unimolécular reactions of the fluoromethane ion have been investigated by the threshold photoelectron photoion coincidence technique (TPIPECO). The breakdown curves have been measured in the energy range between the adiabatic ionization potential of 12.53 eV and 21 eV. In this enery range the formation of the CH2F+, CHF+, CH2+, CH3+, and CF+ fragment ions is observed. The appearance energies (AE) for these ions at 300K are 13.2, 13.91, 13.93, 14.51 and <17.7 eV respectively. The 0K threshold energy for the formation of CH2F+ ions is 13.37 eV. Two different pathways for the unimolecular reaction of the fluoromethane ion can be distinguished.The reaction proceeding through the electronic ground state of the ion is entirely statistical. In contrast to this the reaction occurring through the first electronic excited state shows non-statistical behaviour. The two pathways are distinguished via the kinetic energy released in the respective dissociation channels. While all thermodynamically allowed reaction channels are observed on the ion ground state potential, the first excited state seems to decay predominantly by F loss reaction

Les réactions élémentaires des ions 1,1-Difluoroéthène sélectionnés en énergie.

The dissociative photoionization dynamics of 1,1-difluoroethene has been investigated by TPEPICO using synchrotron radiation. The breakdown diagram has been build. The attention has been focussed on C2HF+ (HF-loss) channel

Réaction chimique dans l'agrégat ionisé constitué de 1,1-Difluoroéthène et d'Argon.

The preparation conditions of 1,1-difluoroethene-Ar clusters has been investigated by photoionization using synchrotron radiation. The nature of the products has been identified by a quadrupole mass spectrometer