Frequency shifting of pulsed narrow-band laser light in a multipass Raman cell

A multipass cell is described which allows efficient stimulated Raman frequency shifting for low pump laser intensities and low gas pressures. The latter is important for Raman shifting of narrow-band Fourier-transform limited light pulses (Δv=75 MHz). It is shown that frequency broadening of the Raman shifted light can be largely avoided in the Dicke narrowing regime at low pressures. For 75 MHz pump pulses and an H2 density of 2.5 amagat we found a negligible broadening to 90 MHz of the stimulated Stokes light. This is far below the value of 250 MHz expected from spontaneous emission. The narrow-band Stokes pulses achieved in CO2 enabled us to measure the pressure shift coefficient (-0.71×10-2 cm-1/amagat) of this gas. It is demonstrated, for the example of benzene, that our technique provides a very practical light source for high resolution molecular spectroscopy

Effect of angiotensin-converting enzyme inhibitor and angiotensin receptor blocker initiation on organ support-free days in patients hospitalized with COVID-19

IMPORTANCE Overactivation of the renin-angiotensin system (RAS) may contribute to poor clinical outcomes in patients with COVID-19. Objective To determine whether angiotensin-converting enzyme (ACE) inhibitor or angiotensin receptor blocker (ARB) initiation improves outcomes in patients hospitalized for COVID-19. DESIGN, SETTING, AND PARTICIPANTS In an ongoing, adaptive platform randomized clinical trial, 721 critically ill and 58 non–critically ill hospitalized adults were randomized to receive an RAS inhibitor or control between March 16, 2021, and February 25, 2022, at 69 sites in 7 countries (final follow-up on June 1, 2022). INTERVENTIONS Patients were randomized to receive open-label initiation of an ACE inhibitor (n = 257), ARB (n = 248), ARB in combination with DMX-200 (a chemokine receptor-2 inhibitor; n = 10), or no RAS inhibitor (control; n = 264) for up to 10 days. MAIN OUTCOMES AND MEASURES The primary outcome was organ support–free days, a composite of hospital survival and days alive without cardiovascular or respiratory organ support through 21 days. The primary analysis was a bayesian cumulative logistic model. Odds ratios (ORs) greater than 1 represent improved outcomes. RESULTS On February 25, 2022, enrollment was discontinued due to safety concerns. Among 679 critically ill patients with available primary outcome data, the median age was 56 years and 239 participants (35.2%) were women. Median (IQR) organ support–free days among critically ill patients was 10 (–1 to 16) in the ACE inhibitor group (n = 231), 8 (–1 to 17) in the ARB group (n = 217), and 12 (0 to 17) in the control group (n = 231) (median adjusted odds ratios of 0.77 [95% bayesian credible interval, 0.58-1.06] for improvement for ACE inhibitor and 0.76 [95% credible interval, 0.56-1.05] for ARB compared with control). The posterior probabilities that ACE inhibitors and ARBs worsened organ support–free days compared with control were 94.9% and 95.4%, respectively. Hospital survival occurred in 166 of 231 critically ill participants (71.9%) in the ACE inhibitor group, 152 of 217 (70.0%) in the ARB group, and 182 of 231 (78.8%) in the control group (posterior probabilities that ACE inhibitor and ARB worsened hospital survival compared with control were 95.3% and 98.1%, respectively). CONCLUSIONS AND RELEVANCE In this trial, among critically ill adults with COVID-19, initiation of an ACE inhibitor or ARB did not improve, and likely worsened, clinical outcomes. TRIAL REGISTRATION ClinicalTrials.gov Identifier: NCT0273570

On Polyodontes maxillosus

Volume: 4Start Page: 332End Page: 33

Analyse de la bande 2 ν4 de 12CH4

The analysis of the 2 ν4 band of 12CH4 is performed by introducting the A1 sub-level in interaction with the others sub-levels already taken into account. With 12 new parameters added to those already known for the ground and ν4 states the standard deviation obtained is 0.027 cm-1 on the 206 lines observed at 100 K with J ≤ 7.L'analyse de la bande 2 ν4 de 12CH4 est reprise en introduisant le sous-niveau A1 en interaction avec les sous-niveaux précédemment considérés. Avec 12 nouveaux paramètres s'ajoutant à ceux déjà obtenus pour les niveaux de base et ν4, l'écart quadratique moyen obtenu est de 0,027 cm-1 sur les 206 transitions attribuées dans le spectre à 100 K pour J ≤ 7

Collisional effects in the stimulated Raman Q branch of O2 and O2-N2

11 pags., 5 figs., 9 tabs.The fundamental isotropic Raman Q branch of oxygen at pressures up to 2 atm and for temperatures between 295 and 1350 K has been recorded using stimulated Raman gain spectroscopy (SRGS) for collisions with oxygen and nitrogen. The line broadening and line shifting coefficients have been determined for several rotational quantum numbers (up to N = 55 at 1350 K). The temperature dependence of these coefficients has also been studied for most of the rotational lines. The line parameters (widths and shifts) have been then calculated a priori through a semiclassical model. A good agreement between experimental and theoretical data has been observed. Another theoretical approach based on fitting and scaling law has been used to calculate the line broadening coefficients. It is shown that a modified exponential energy gap model (MEG) and an energy corrected sudden law (ECS) for the state-to-state rotationally inelastic rates, account for the rotational and temperature dependences of the observed linewidths. With regard to the energy corrected sudden law, the best results are obtained when the basis rate constants are modeled with a hybrid exponential-power fitting law (EP). The line broadening and shifting coefficients of the oxygen-nitrogen mixture are very close to those found for pure oxygen. © 1992 American Institute of Physics.This research was supported by the Centre National de la Recherche Scientifique, Paris, the Ministere de I'Education Nationale, the Conseil Regional de Bourgogne and by a scientific cooperation program (no. 17) between France and Spain

Détermination des constantes scalaires de l'état de base de SF 6

From analysis of the ν2 Raman band the molecular constants of the ground state of SF6 have been determined : B0 = 0.091 11 ± 0.000 05 cm-1, D0 = (0.16 ± 0.08) 10-7 cm-1.A partir de l'analyse de la bande Raman ν2 de SF6, les constantes scalaires de l'état de base ont pu être déterminées : B0 = 0,091 11 ± 0,000 05 cm-1, D0 = (0,16 ± 0,08) 10-7 cm-1

Rétrécissement collisionnel dans N2 mis en évidence par diffusion Raman stimulée

We demonstrate the reduction of the Doppler broadening of the self-perturbed N2 molecule at room temperature due to the change in the velocity during collision. The study is done in stimulated backward Raman scattering where the Doppler width is significantly increased over foreward scattering. The Galatry profile is found suitable for the study of this phenomenon and allows us to determine the value of the diffusion constant as D = 0.13 cm2 s-1 atm-1. Our work shows that an error of about 10 % is made in the collisional width by neglecting the Doppler narrowing.Nous mettons en évidence la réduction de la largeur Doppler due au changement de vitesse des molécules lors des collisions pour la molécule N2 autoperturbée à la température ambiante. Cette étude est faite en diffusion Raman stimulée, dans le cas où les faisceaux pompe et sonde se propagent en sens inverse, augmentant ainsi considérablement la largeur Doppler. Le modèle de Galatry s'est avéré satisfaisant pour étudier ce phénomène et nous a permis de mesurer la constante de diffusion (D = 0,13 cm 2 s-1 atm-1). Ce travail montre qu'une erreur de 10 % environ serait commise sur la largeur collisionnelle si l'on négligeait le rétrécissement Doppler

Observation de transitions de la molécule 29SiH4 dans le spectre Raman stimulé de la bande ν1 du silane en abondance naturelle

The stimulated Raman spectrum of silane has been recorded between 2 183 and 2 187 cm-1 with the Raman spectrometer of Dijon which has an instrumental resolution of 0.0025 cm-1. The resolution of the spectrum, essentially limited by the Doppler broadening, is about 0.006 cm -1 at 7.5 torr pressure. In this study we assigned transitions which belong to 29 SiH4 and we measured the isotopic shift of ν1 band origins for isotopic species 28SiH 4 and 29SiH4.Le spectre Raman stimulé du silane a été enregistré entre 2 183 et 2 187 cm-1 sur le spectromètre Raman de Dijon, dont la résolution instrumentale est de 0,0025 cm-1. La résolution du spectre essentiellement limitée par l'effet Doppler est de 0,006 cm-1 à une pression de 7,5 torr. Cette étude a permis de mettre en évidence des transitions appartenant à l'espèce isotopique 29SiH4 et de mesurer le déplacement isotopique entre les centres de la bande ν1 pour les espèces 28SiH4 et 29SiH4

Enhancement of Sensitivity in High-Resolution Stimulated Raman-Spectroscopy of Gases - Application to the 2v2 (1285 cm-1) Band of CO2

0377-048

Study of the Density and Temperature Dependences of the Vibrational Raman Transition in Compressed Liquid N2

0021-9606Accurate values of linewidth and line shift in the isotropic vibrational Raman spectrum of compressed liquid N2 have been obtained by using inverse Raman spectroscopy. Experiments have been performed for eight isotherms, from the normal boiling point to the critical point temperatures of N2, the number density varying between the value on the coexistence line, and the maximum value of 2.1 x 10^22 cm-3. Minima of the linewidth have been observed above 86 K, showing the increasing influence of vibration-rotation coupling (motional narrowing) competing with the broadening due to pure vibrational dephasing. Moreover, for the first time, maxima of the red line shifts have been found, exhibiting increasing values as temperature increases. As far as the linewidth is concerned, the comparison with two existing models shows that negative interference of the attractive and repulsive forces must be taken into account for obtaining reasonable agreement between the experimental and theoretical parameters. The experimental density dependence of the linewidth can be described well enough with the Schweizer-Chandler model by taking only into account a soft-core, hard-sphere approximation for the calculation of the radial distribution functions. In the case of the frequently shifts, there is only qualitative agreement between the experimental and theoretical density dependences for the effective repulsive contributions calculated within the framework of the Schweizer-Chandler model