Phase change-related variations of dome shape in Eucalyptus urophylla x Eucalyptus grandis shoot apical meristems

International audienceShoot apical meristem (SAM) domes derived from five different outdoor and in vitro sources of juvenile and mature Eucalyptus urophylla x Eucalyptus grandis akin genotypes were compared. Overall measurements of SAM dome height H and diameter D ranged from 2 to 35 µm and 20 to 80 µm, notwithstanding significant differences according to the various physiological origins of plant material investigated. SAM domes from the mature trees ?Mat? were taller than those from the rejuvenated ministock plants ?Rej?; from the in vitro microcuttings ?IVM? of the same clone, and also from the in vitro juvenile seedlings ?IVJ?, whereas outdoor seedlings ?Juv? SAM domes exhibited intermediate height. SAM domes from the rejuvenated material ?Rej?, from the in vitro mature ?IVM? and juvenile ?IVJ? origins were also narrower than those from the outdoor seedlings ?Juv? and to lesser extent than those from the mature trees ?Mat?. Overall the mature source ?Mat? displayed bigger and somehow sharper hemispherical domes than those from ?Rej? and ?Juv?, physiologically more juvenile, or those from the in vitro origins ?IVM ? and ?IVJ? which looked flatter and smaller. SAM dome height, diameter D and H/D values varied also significantly according to shoot apex status. More specifically, H, D and H/D SAM differences between the five origins were not significant when SAM were in their more organogenic stage, to become more salient as leaf structures started to elongate and to differentiate. This was particularly obvious for mature tree ?Mat? SAM dome shapes which showed at this stage much higher H/D values than the other SAM sources. Additionally, a shape index S used for characterizing more accurately dome shape confirmed these trends. These observations provide additional arguments to the view that juvenility in trees become more and more time and space restricted as ageing increases in the course of time during the ontogenetical process, to be ultimately confined to the more organogenic phases of SAM, from which shoot characteristics derive

Détection de la nucléation de cristaux de glace au voisinage d'une bulle de cavitation

International audienceThe application of power ultrasound in liquids produces thousands of bubbles. This phenomenon is called acoustic cavitation. The bubbles formed do not have the same size, their oscillations are not in phase, and their spatial density in the fluid is very not homogeneous: this phenomenon is thus very complex and involves multiple variables which are very difficult to isolate. Even if the phenomenon is chaotic, its macroscopic effects on the nucleation and growth of of ice crystals in undercooled solutions are noticeable. These effects have a crucial importance for industrial applications such as freezing and lyophilisation (also called freeze drying) of pharmaceutics products. Although the effects of ultrasound on crystallization are well-known, their physical origin remains unclear. Multi-bubble experiments do not give any hint in the microscopic mechanisms involved. Therefore, in order to isolate the main actor of these effects, this study aims at creating and observing a single cavitation bubble. To do so, a cubic levitation cell with optical glass walls was build. In this cell, in order to maintain a single bubble levitating, a pressure wave is imposed by a piezoelectric ceramic glued to the base of the cell. A piezoelectric microphone is also glued on the lateral wall in order to record the bubble response, which is strongly linked to the bubble dynamics. The presence or appearance of any foreign body near the levitating bubble may perturb the latter and alter the periodicity of its oscillation. We wish to exploit this loss of periodicity for early detection of crystals nucleation near the bubble. As a preliminary step, to simulate the later, a micro-fiber of diameter smaller than 50 μm is approached to the bubble. By performing an autocorrelation study of the microphone signal, we can detect the perturbation of the periodicity of the bubble dynamics. In a second step, crystallization experiments will be conducted, and the detection principle will be used to trigger the recording of images in the early phase of the crystals formation.L'application des ultrasons de puissance dans un liquide produit des milliards de bulles. Ce phénomène est appelé cavitation acoustique. Les bulles formées ne font pas toutes la même taille, leurs oscillations ne sont pas en phase, et leur densité spatiale dans le fluide est très inhomogène: ce phénomène très complexe implique donc de nombreuses variables difficiles à isoler. Même si le phénomène est chaotique, ses effets macroscopiques sur la nucléation et la croissance des cristaux de glace dans une solution sous-refroidie sont notables. Ces effets sont d'une importance capitale pour des applications industrielles comme la congélation ou la lyophilisation. Bien que les effets des ultrasons sur la cristallisation soient réputés, leur origine reste mal connue. Les expériences impliquant des milliards de bulles ne fournissent aucune piste sur les mécanismes microscopiques mis en jeu. Afin d'isoler l'acteur essentiel de ces effets, l'étude menée vise à créer et observer une bulle unique de cavitation. Pour cela, une cellule de lévitation carrée en verre a été conçue. Dans cette cellule, pour maintenir une bulle unique en lévitation, une onde de pression est imposée par un piézoélectrique positionné à la base de la cellule. Un microphone est collé sur une face latérale afin d'enregistrer sa réponse qui est fortement liée à la dynamique de la bulle. Lorsque un corps étranger apparaît ou s'approche de la bulle, il la perturbe et affecte sa périodicité. Nous souhaitons exploiter cette perturbation pour détecter la formation des premiers cristaux au voisinage de la bulle. Dans un premier temps, afin de simuler cette perturbation, une micro-fibre de diamètre inférieur à 50 µm est approchée de la bulle. L'étude de l'auto-corrélation du signal du microphone nous permet de détecter la perturbation engendrée sur la périodicité de la dynamique de bulle. Dans un second temps, des expériences de cristallisation seront menées, et le principe de détection sera alors mis à profit pour déclencher l'enregistrement d'images dans la phase initiale de formation des cristaux

Perturbation of a radially oscillating single-bubble by a micron-sized object

A single bubble oscillating in a levitation cell is acoustically monitored by a piezo-ceramics microphone glued on the cell external wall. The correlation of the filtered signal recorded over distant cycles on one hand, and its harmonic content on the other hand, are shown to carry rich information on the bubble stability and existence. For example, the harmonic content of the signal is shown to increase drastically once air is fully dissociated in the bubble, and the resulting pure argon bubble enters into the upper branch of the sonoluminescence regime. As a consequence, the bubble disappearance can be unambiguously detected by a net drop in the harmonic content. On the other hand, we perturb a stable sonoluminescing bubble by approaching a micron-sized fiber. The bubble remains unperturbed until the fiber tip is approached within a critical distance, below which the bubble becomes unstable and disappears. This distance can be easily measured by image treatment, and is shown to scale roughly with 3–4 times the bubble maximal radius. The bubble disappearance is well detected by the drop of the microphone harmonic content, but several thousands of periods after the bubble actually disappeared. The delay is attributed to the slow extinction of higher modes of the levitation cell, excited by the bubble oscillation. The acoustic detection method should however allow the early detection and imaging of non-predictable perturbations of the bubble by foreign micron-sized objects, such as crystals or droplets

Prediction of the acoustic and bubble fields in insonified freeze-drying vials

The acoustic field and the location of cavitation bubble are computed in vials used for freeze-drying, insonified from the bottom by a vibrating plate. The calculations rely on a nonlinear model of sound propagation in a cavitating liquid [Louisnard, Ultrason. Sonochem., 19, (2012) 56-65]. Both the vibration amplitude and the liquid level in the vial are parametrically varied. For low liquid levels, a threshold amplitude is required to form a cavitation zone at the bottom of the vial. For increasing vibration amplitudes, the bubble field slightly thickens but remains at the vial bottom, and the acoustic field saturates, which cannot be captured by linear acoustics. On the other hand, increasing the liquid level may promote the formation of a secondary bubble structure near the glass wall, a few centimeters below the free liquid surface. These predictions suggest that rather complex acoustic fields and bubble structures can arise even in such small volumes. As the acoustic and bubble fields govern ice nucleation during the freezing step, the final crystal’s size distribution in the frozen product may crucially depend on the liquid level in the vial

Performance of Small Cluster Surveys and the Clustered LQAS Design to estimate Local-level Vaccination Coverage in Mali

<p>Abstract</p> <p>Background</p> <p>Estimation of vaccination coverage at the local level is essential to identify communities that may require additional support. Cluster surveys can be used in resource-poor settings, when population figures are inaccurate. To be feasible, cluster samples need to be small, without losing robustness of results. The clustered LQAS (CLQAS) approach has been proposed as an alternative, as smaller sample sizes are required.</p> <p>Methods</p> <p>We explored (i) the efficiency of cluster surveys of decreasing sample size through bootstrapping analysis and (ii) the performance of CLQAS under three alternative sampling plans to classify local VC, using data from a survey carried out in Mali after mass vaccination against meningococcal meningitis group A.</p> <p>Results</p> <p>VC estimates provided by a 10 × 15 cluster survey design were reasonably robust. We used them to classify health areas in three categories and guide mop-up activities: i) health areas not requiring supplemental activities; ii) health areas requiring additional vaccination; iii) health areas requiring further evaluation. As sample size decreased (from 10 × 15 to 10 × 3), standard error of VC and ICC estimates were increasingly unstable. Results of CLQAS simulations were not accurate for most health areas, with an overall risk of misclassification greater than 0.25 in one health area out of three. It was greater than 0.50 in one health area out of two under two of the three sampling plans.</p> <p>Conclusions</p> <p>Small sample cluster surveys (10 × 15) are acceptably robust for classification of VC at local level. We do not recommend the CLQAS method as currently formulated for evaluating vaccination programmes.</p

Hyperoxemia and excess oxygen use in early acute respiratory distress syndrome : Insights from the LUNG SAFE study

Publisher Copyright: © 2020 The Author(s). Copyright: Copyright 2020 Elsevier B.V., All rights reserved.Background: Concerns exist regarding the prevalence and impact of unnecessary oxygen use in patients with acute respiratory distress syndrome (ARDS). We examined this issue in patients with ARDS enrolled in the Large observational study to UNderstand the Global impact of Severe Acute respiratory FailurE (LUNG SAFE) study. Methods: In this secondary analysis of the LUNG SAFE study, we wished to determine the prevalence and the outcomes associated with hyperoxemia on day 1, sustained hyperoxemia, and excessive oxygen use in patients with early ARDS. Patients who fulfilled criteria of ARDS on day 1 and day 2 of acute hypoxemic respiratory failure were categorized based on the presence of hyperoxemia (PaO2 > 100 mmHg) on day 1, sustained (i.e., present on day 1 and day 2) hyperoxemia, or excessive oxygen use (FIO2 ≥ 0.60 during hyperoxemia). Results: Of 2005 patients that met the inclusion criteria, 131 (6.5%) were hypoxemic (PaO2 < 55 mmHg), 607 (30%) had hyperoxemia on day 1, and 250 (12%) had sustained hyperoxemia. Excess FIO2 use occurred in 400 (66%) out of 607 patients with hyperoxemia. Excess FIO2 use decreased from day 1 to day 2 of ARDS, with most hyperoxemic patients on day 2 receiving relatively low FIO2. Multivariate analyses found no independent relationship between day 1 hyperoxemia, sustained hyperoxemia, or excess FIO2 use and adverse clinical outcomes. Mortality was 42% in patients with excess FIO2 use, compared to 39% in a propensity-matched sample of normoxemic (PaO2 55-100 mmHg) patients (P = 0.47). Conclusions: Hyperoxemia and excess oxygen use are both prevalent in early ARDS but are most often non-sustained. No relationship was found between hyperoxemia or excessive oxygen use and patient outcome in this cohort. Trial registration: LUNG-SAFE is registered with ClinicalTrials.gov, NCT02010073publishersversionPeer reviewe

Characteristics of Acacia mangium shoot apical meristems in natural and in vitro conditions in relation to heteroblasty

PDF version of the authors can be published in January 2013International audienceMorphological and histocytological characteristics of Acacia mangium shoot apical meristems (SAMs) were assessed in natural and in vitro conditions in relation to heteroblasty. In the natural environment, SAMs with a mature-phyllode morphology were much bigger, contained more cells with larger vacuolated area, or vacuome, and lower nucleoplasmic ratios than those from the juvenile type (Juv). In these latter, nuclei appeared more voluminous, evenly and lightly stained, with clearly distinguishable nucleolei and less abundant chromocenters. In vitro, where reversions from mature to juvenile morphological traits do occur unpredictably, heteroblasty was less obvious in the SAM characteristics examined. In vitro SAMs corresponding to the juvenile and mature types showed similarities with outdoor Juv SAMs, but could be distinguished from these latter by a much larger vacuome that might be induced by the culture conditions. These findings encourage pursuing the investigations at the chromatin and nucleolus level in SAM zones where heteroblasty-related differences have been detected