Laboratory measurements in the energy range 0.02–1 eV of the rate constants of ion–molecule reactions involving CS +

International audienceThe energy dependence of the total rate constant and of the branching ratios of the reactions of CS+ with O2, H2, and CH4 have been determined in the energy range 0.02–1 eV by the drift tube mass spectrometer technique. The reaction CS++O2 proceeds through three primary steps giving OCS+, SO+, and O+2 with branching ratios of 0.7, 0.2, and 0.1, respectively, at low energy (<0.025 eV) and 0.4, 0.1, and 0.5 at high energy (0.38 eV). The secondary ions OCS+ and SO+ do not react with O2. The overall rate constant is energy independent (8±2)10−11 cm3 s−1, but the elementary steps leading to OCS+ and SO+ decrease in rate with increasing energy while the charge transfer reaction increase in rate. The reactions of CS+ with H2 and CH4 form HCS+; the first reaction is found to have an energy independent rate constant of (3.8±1)10−10 cm3 s−1 and the second has a measured rate constant which increases from 5.10−10 cm3 s−1 at the lowest energy studied (0.2 eV) to 1.10−9 cm3 s−1 at 1 eV. HCS+ does not react rapidly with H2 or CH

REACTION CH3+ + NH3 - EVOLUTION DES PRODUITS EN FONCTION DE LA CONCENTRATION DE NH3

Nous avons utilisé un tube à dérive à introduction sélective (T.D.S.M.) (1) pour l'étude de la réaction CH+3 + NH3 dans une gamme d'énergie comprise entre 0,04 eV et 1 eV. Les ions CH3+ sont produits à partir de CH4 dans une source à bombardement électronique puis sélectionnés parmi les fragments ionisés à l'aide d'un spectromètre de masse avant leur introduction dans le tube à dérive d'une longueur effective de 56,5 mm. L'ammoniac est introduit dans le tube à différentes dilutions dans l'hélium utilisé comme gaz vecteur. La gamme de pression dans le tube est comprise entre 0,3 e t 0,7 Torr. Afin de diminuer l'état d'excitation des ions l'introduction se fait à basse énergie (2 à 3 eV). L'énergie des électrons ionisants dans la source contribue à l'excitation des ions initiaux, elle a été abaissée à la valeur minimale compatible avec un niveau de signal suffisant (20 eV)

Does Accelerometry at the Centre of Mass Accurately Predict the Gait Energy Expenditure in Patients with Hemiparesis?

International audienceBackground: The aim of this study was to compare energy expenditure (EE) predicted by accelerometery (EEAcc) with indirect calorimetry (EEMETA) in individuals with hemiparesis. Methods: Twenty-four participants (12 with stroke and 12 healthy controls) performed a six-minute walk test (6MWT) during which EEMETA was measured using a portable indirect calorimetry system and EEACC was calculated using Bouten’s equation (1993) with data from a three-axis accelerometer positioned between L3 and L4. Results: The median EEMETA was 9.85 [8.18;11.89] W·kg−1 in the stroke group and 5.0 [4.56;5.46] W·kg−1 in the control group. The median EEACC was 8.57 [7.86;11.24] W·kg−1 in the control group and 8.2 [7.05;9.56] W·kg−1 in the stroke group. The EEACC and EEMETA were not significantly correlated in either the control (p = 0.8) or the stroke groups (p = 0.06). The Bland–Altman method showed a mean difference of 1.77 ± 3.65 W·kg−1 between the EEACC and EEMETA in the stroke group and −2.08 ± 1.59 W·kg−1 in the controls. Conclusions: The accuracy of the predicted EE, based on the accelerometer and the equations proposed by Bouten et al., was low in individuals with hemiparesis and impaired gait. This combination (sensor and Bouten’s equation) is not yet suitable for use as a stand-alone measure in clinical practice for the evaluation of hemiparetic patients

Restricted daytime feeding attenuates reentrainment of the circadian melatonin rhythm after an 8-h phase advance of the light_dark cycle

It is well established that in the absence of photic cues, the circadian rhythms of rodents can be readily phase-shifted and entrained by various nonphotic stimuli that induce increased levels of locomotor activity (i.e., benzodiazepines, a new running wheel, and limited food access). In the presence of an entraining light-dark (LD) cycle, however, the entraining effects of nonphotic stimuli on (parts of) the circadian oscillator are far less clear. Yet, an interesting finding is that appropriately timed exercise after a phase shift can accelerate the entrainment of circadian rhythms to the new LD cycle in both rodents and humans. The present study investigated whether restricted daytime feeding (RF) (1) induces a phase shift of the melatonin rhythm under entrained LD conditions and (2) accelerates resynchronization of circadian rhythms after an 8-h phase advance. Animals were adapted to RF with 2-h food access at the projected time of the new dark onset. Before and at several time points after the 8-h phase advance, nocturnal melatonin profiles were measured in RF animals and animals on ad libitum feeding (AL). In LD-entrained conditions, RF did not cause any significant changes in the nocturnal melatonin profile as compared to AL. Unexpectedly, after the 8-h phase advance, RF animals resynchronized more slowly to the new LD cycle than AL animals. These results indicate that prior entrainment to a nonphotic stimulus such as RF may "phase lock" the circadian oscillator and in that way hinder resynchronization after a phase shif