Assessment of AlGaN/AlN superlattices on GaN nanowires as active region of electron-pumped ultraviolet sources.

In this paper, we describe the design and characterization of 400 nm long (88 periods) Al x Ga1-x N/AlN (0 ≤ x ≤ 0.1) quantum dot superlattices deposited on self-assembled GaN nanowires for application in electron-pumped ultraviolet sources. The optical performance of GaN/AlN superlattices on nanowires is compared with the emission of planar GaN/AlN superlattices with the same periodicity and thickness grown on bulk GaN substrates along the N-polar and metal-polar crystallographic axes. The nanowire samples are less sensitive to nonradiative recombination than planar layers, attaining internal quantum efficiencies (IQE) in excess of 60% at room temperature even under low injection conditions. The IQE remains stable for higher excitation power densities, up to 50 kW cm-2. We demonstrate that the nanowire superlattice is long enough to collect the electron-hole pairs generated by an electron beam with an acceleration voltage V A = 5 kV. At such V A, the light emitted from the nanowire ensemble does not show any sign of quenching under constant electron beam excitation (tested for an excitation power density around 8 kW cm-2 over the scale of minutes). Varying the dot/barrier thickness ratio and the Al content in the dots, the nanowire peak emission can be tuned in the range from 340 to 258 nm.

Microwave Thermoablation of Colorectal Liver Metastases Close to Large Hepatic Vessels Under Pringle Maneuver Minimizes the "Heat Sink Effect".

BACKGROUND: Liver resection and thermoablation are the mainstay of the surgical management of colorectal liver metastases (CRLM). The main limitation of thermoablation is the "heat-sink" effect for nodules next to large vessels. Herein, we report the preliminary results of microwave ablation (MWA) with associated Pringle maneuver to overcome this flaw. METHODS: From November 2017, we performed intraoperative MWA with Pringle maneuver for nodules ≤3 cm with immediate proximity to large vessels (distance ≤ 5 mm, diameter ≥ 3 mm). We collected characteristics of nodules, surgical procedures and postoperative morbidity. Diameter of the ablation area, especially the ablative minimal margin, was calculated for each nodule. Recurrence was also evaluated. RESULTS: Nineteen patients underwent MWA with Pringle maneuver for 23 nodules. Nineteen (83%) ablated nodules were located in segments VI, VII and VIII, and one nodule was in segment I. Median size of nodules was 15 mm (10-21). No deaths occurred. Six patients (38%) experienced complications, among them only one was subsequent to the thermal ablation. Ablative minimal margin was ≥5 mm for 19 (83%) nodules. Margin was not sufficient for four nodules, among them only 2/23 cases (8.7%) of in situ recurrence occurred after 12 months of median follow-up. CONCLUSIONS: In this preliminary study, MWA with Pringle maneuver was associated with a low related morbidity rate and favorable oncological outcome, especially when the radiological minimal margin was sufficient.

Colonization pressure as a risk factor of ICU-acquired multidrug resistant bacteria: a prospective observational study.

The primary objective of this study was to evaluate the impact of colonization pressure on intensive care unit (ICU)-acquired multidrug resistant bacteria (MDRB). All patients hospitalized for more than 48 h in the ICU were included in this prospective observational study. MDRB were defined as methicillin resistant Staphylococcus aureus, Pseudomonas aeruginosa resistant to ceftazidime or imipenem, Gram-negative bacilli producing extended-spectrum beta-lactamases (ESBL), and all strains of Acinetobacter baumannii and Stenotrophomonas maltophilia. Colonization pressure was daily calculated in the three participating ICUs. Univariate and multivariate analyses were used to determine risk factors for ICU-acquired MDRB. Two hundreds and four (34%) of the 593 included patients acquired an MDRB during their ICU stay. Multivariate analysis identified colonization pressure as an independent risk factor for ICU-acquired MDRB (OR (95% CI) 4.18 (1.03-17.01), p = 0.046). Other independent risk factors for ICU-acquired MDRB were mechanical ventilation (3.08 (1.28-7.38), p = 0.012), and arterial catheter use (OR, 3.04 (1.38-6.68), p = 0.006). ICU-acquired MDRB were associated with increased mortality, duration of mechanical ventilation, and ICU stay. However, ICU-acquired MDRB was not independently associated with ICU-mortality. Colonization pressure is an independent risk factor for acquiring MDRB in the ICU.

YAG:Ce nanoparticle lightsources.

We investigate the luminescence properties of 10 nm yttrium aluminum garnet (YAG) nanoparticles doped with Ce ions at 0.2%, 4% and 13% that are designed as active probes for scanning near-field optical microscopy. They are produced by a physical method without any subsequent treatment, which is imposed by the desired application. The structural analysis reveals the amorphous nature of the particles, which we relate to some compositional defects as indicated by the elemental analysis. The optimum emission is obtained with a doping level of 4%. The emission of the YAG nanoparticles doped at 0.2% is strongly perturbed by the crystalline disorder whereas the 13% doped particles hardly exhibit any luminescence. In the latter case, the presence of Ce(4+) ions is confirmed, indicating that the Ce concentration is too high to be incorporated efficiently in YAG nanoparticles in the trivalent state. By a unique procedure combining cathodoluminescence and Rutherford backscattering spectrometry, we demonstrate that the enhancement of the particle luminescence yield is not proportional to the doping concentration, the emission enhancement being larger than the Ce concentration increase. Time-resolved photoluminescence reveals the presence of quenching centres likely related to the crystalline disorder as well as the presence of two distinct Ce ion populations. Eventually, nano-cathodoluminescence indicates that the emission and therefore the distribution of the doping Ce ions and of the defects are homogeneous.

Shells of crystal field symmetries evidenced in oxide nano-crystals.

By the use of a point charge model based on the Judd-Ofelt transition theory, the luminescence from Eu(3+) ions embedded in Gd(2)O(3) clusters is calculated and compared to the experimental data. The main result of the numerical study is that without invoking any other mechanisms such as crystal disorder, the pure geometrical argument of the symmetry breaking induced by the particle surface has an influence on the energy level splitting. The modifications are also predicted to be observable in realistic conditions where unavoidable size dispersion has to be taken into account. The emission spectrum results from the contribution of three distinct regions; a cluster core, a cluster shell and the very surface, the latter being almost completely quenched in realistic conditions. Eventually, by detailing the spectra of the ions embedded at different positions in the cluster we get an estimate of about 0.5 nm for the extent of the crystal field induced Stark effect. Due to the similarity between Y (2)O(3) and Gd(2)O(3), these results also apply to Eu(3+) doped Y(2)O(3) nanoparticles.

Use, timing and factors associated with tracheal intubation in septic shock: a prospective multicentric observational study.

BACKGROUND: No recommendation exists about the timing and setting for tracheal intubation and mechanical ventilation in septic shock. PATIENTS AND METHODS: This prospective multicenter observational study was conducted in 30 ICUs in France and Spain. All consecutive patients presenting with septic shock were eligible. The use of tracheal intubation was described across the participating ICUs. A multivariate analysis was performed to identify parameters associated with early intubation (before H8 following vasopressor onset). RESULTS: Eight hundred and fifty-nine patients were enrolled. Two hundred and nine patients were intubated early (24%, range 4.5-47%), across the 18 centers with at least 20 patients included. The cumulative intubation rate during the ICU stay was 324/859 (38%, range 14-65%). In the multivariate analysis, seven parameters were significantly associated with early intubation and ranked as follows by decreasing weight: Glasgow score, center effect, use of accessory respiratory muscles, lactate level, vasopressor dose, pH and inability to clear tracheal secretions. Global R-square of the model was only 60% indicating that 40% of the variability of the intubation process was related to other parameters than those entered in this analysis. CONCLUSION: Neurological, respiratory and hemodynamic parameters only partially explained the use of tracheal intubation in septic shock patients. Center effect was important. Finally, a vast part of the variability of intubation remained unexplained by patient characteristics. Trial registration Clinical trials NCT02780466, registered on May 23, 2016. https://clinicaltrials.gov/ct2/show/NCT02780466?term=intubatic&draw=2&rank=1.

Facile and rapid synthesis of highly luminescent nanoparticles via pulsed laser ablation in liquid.

This paper demonstrates the usefulness of pulsed laser ablation in liquids as a fast screening synthesis method able to prepare even complex compositions at the nanoscale. Nanoparticles of Y2O3:Eu3+, Lu2O2S:Eu3+, Gd2SiO5:Ce3+, Lu3TaO7:Gd3+ and Tb3+ are successfully synthesized by pulsed laser ablation in liquids. The phase and stoichiometries of the original materials are preserved while the sizes are reduced down to 5-10 nm. The optical properties of the materials are also preserved but show some small variations and some additional structures which are attributed to the specificities of the nanoscale (internal pressure, inhomogeneous broadening, surface states, etc).

Fluorescent oxide nanoparticles adapted to active tips for near-field optics.

We present a new kind of fluorescent oxide nanoparticle (NP) with properties well suited to active-tip based near-field optics. These particles with an average diameter in the 5-10 nm range are produced by low energy cluster beam deposition (LECBD) from a YAG:Ce3+ target. They are studied by transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), cathodoluminescence, near-field scanning optical microscopy (NSOM) and fluorescence in the photon-counting mode. Particles of extreme photo-stability as small as 10 nm in size are observed. These emitters are validated as building blocks of active NSOM tips by coating a standard optical tip with a 10 nm thick layer of YAG:Ce3+ particles directly in the LECBD reactor and by subsequently performing NSOM imaging of test surfaces.

Observation of chemiluminescence induced by hydrodynamic cavitation in microchannels.

We have performed hydrodynamic cavitation experiments with an aqueous luminol solution as the working fluid. Light emission, together with the high frequency noise which characterizes cavitation, was emitted by the two-phase flow, whereas no light emission from luminol was recorded in the single phase liquid flow. Light emission occurs downstream transparent microdiaphragms. The maximum level of the recorded signal was around 180 photons per second with flow rates of 380 µl/s, that corresponds to a real order of magnitude of the chemiluminescence of 75,000 photons per second. The yield of emitted photons increases linearly with the pressure drop, which is proportional to the square of the total flow rate. Chemiluminescence of luminol is a direct and a quantitative demonstration of the presence of OH hydroxyl radicals created by hydrodynamic cavitation. The presented method could be a key to optimize channel geometry for processes where radical production is essential.

A fatal endocarditis case due to an emerging bacterium: Moraxella nonliquefaciens.

Moraxella nonliquefaciens is a Gram-negative coccobacillus considered as a commensal organism from the upper respiratory tract, with low pathogenic potential. The phenotypical conventional identification is difficult and the matrix-assisted laser desorption/ionization time-of-flight technology has increased the resolution of identification of this bacterium. We report a fatal case of endocarditis due to M. nonliquefaciens whose identification was confirmed by 16S rRNA, and we review the literature on this pathogen in endocarditis.

Impact of a targeted isolation strategy at intensive-care-unit-admission on intensive-care-unit-acquired infection related to multidrug-resistant bacteria: a prospective uncontrolled before-after study.

Isolation of patients with multidrug resistant (MDR) bacteria is recommended to reduce cross-transmission of these bacteria. However, isolation of critically ill patients has several negative side effects. Therefore, we hypothesized that a targeted isolation strategy, based on the presence of at least one risk factor for MDR bacteria, would be not inferior to a systematic isolation strategy at intensive-care unit (ICU) admission. This prospective before-after study was conducted in a mixed ICU, during two 12-month periods, separated by a 1-month 'wash-out' period. During the before period, isolation was systematically performed in all patients at admission. During the after period, isolation was only performed in patients with at least one risk factor for MDR bacteria at admission. During the two periods, routine screening for MDR bacteria was performed at ICU admission, and isolation prescription was modified after receipt of screening result. Primary outcome was the percentage of patients with ICU-acquired infection (ICUAI) related to MDR bacteria, measured from ICU admission until ICU discharge or day 28, whatever happens first. A total of 1221 patients were included. No significant difference was found in ICUAI related to MDR bacteria (85 of 585 (14.5%) vs. 84 of 636 (13.2%) patients, risk difference, -1.3%, 95% confidence interval [-5.2 to 2.6%]) between the two periods, confirming the non-inferiority hypothesis. Our results suggest that targeted isolation of patients at ICU admission is not inferior to systematic isolation, regarding the percentage of patients with ICUAI related to MDR bacteria. Further randomized controlled multicentre studies are needed to confirm our results.

Synthesis and properties of europium-based phosphors on the nanometer scale: Eu2O3, Gd2O3:Eu, and Y2O3:Eu.

Nanocrystals of oxides containing europium as the main constituent or as a doping element in RE2O3 ( RE=Y, Gd) have been prepared by direct oxide precipitation in high-boiling polyalcohol solutions and characterized by high-resolution TEM, absorption spectroscopy, and luminescence spectroscopy. The samples obtained consisted of concentrated and colloidally stable suspensions of luminescent oxide nanoparticles with an average grain diameter in the range 2-5 nm. The nanoparticles were found to be highly crystalline despite their ultrasmall size and the low temperature of 180 degrees C applied during the synthesis. Upon UV excitation, the red luminescence relative to the 5D0-->7Fn transition within the cubic form of RE2O3 exhibits some important differences from that usually found in bulk materials.

Thin film growth using hetero embryo: demonstration on pyrochlore phase.

The paper reports the possible use of nanoparticles embedded in amorphous host as hetero embryos in order to grow complex crystalline phases as thin film. Demonstration is performed in the prototypical case of pyrochlore phase Gd(2)Ti(2)O(7) grown from Gd(2)O(3) nanoparticles embedded in TiO(2) matrix at low temperature. As embryos, two kinds of nanoparticles are compared: clusters deposited by low energy cluster beam deposition (LECBD) and nanostructured films elaborated by sol-gel process. The growth has been analyzed by X-ray diffraction and transmission electron microscopy. Furthermore, the nanoparticles have been doped with Eu(3+) luminescence probes in order to follow the nucleation mechanisms at the atomic scale. It is shown that the size, shape, and composition of hetero embryos and as well their interfaces are of paramount importance to enhance the formation of complex materials, such as pyrochlore. By this mean, the first step in classical nucleation science, controlling the height of the energetic barrier, is skipped and the synthesis conditions can be eased.

Development of an x-ray imaging system for the Laser Megajoule (LMJ).

This imaging system aims at recording images of the core size and shape of an imploding deuterium-tritium (DT) microballoon on LMJ inertial confinement fusion (ICF) experiments. Image acquisition is difficult due to the harsh surrounding created by the fusion reaction, which affects system specifications. This one is made of a scintillator, an optical relay, and a CCD camera shielded from the surrounding. The system was tested on different facilities at CEA/DIF, where a spatial resolution of 120 µm was achieved and gamma dose up to 20 rad effects were measured. Setup and performed test are described.

Quantum confinement effect on Gd2O3 clusters.

The evolution of the gap of a nanoscaled insulator material, namely, Gd(2)O(3), has been observed by means of vacuum ultraviolet excitation spectra of a dopant (Eu(3+)). The nanoparticles have been synthesized by the low energy cluster beam deposition technique and grown afterward by different annealing steps. A gap shift towards the blue is observed, similar to what is observed in semiconductor nanoparticles. Despite the strong ionic character of the material, the evolution exhibits a behavior similar to covalent materials. The evolution of the gap for Gd(2)O(3) follows the same empiric rule that has been derived for semiconductors (ZnO, CuBr, Si, and CdS). It shows that, in spite of the strong ionic character of the material (0.9 on the scale of Phillips), the amount of covalency is important enough for creating a significant delocalization of the electron with regard to its hole.

Structural transition in rare earth oxide clusters.

Size effects, such as structure transition, have been reported in small clusters of alkali halide compounds. We extend the study to rare earth sesquioxide (Gd(2)O(3)) clusters which are as ionic as the alkali halide compounds, but have a more complicated structure. In a clean and controlled environment (ultra high vacuum), such particles are well crystallized, facetted and tend to adopt a rhombic dodecahedron shape. This indicates the major role of highly ionic bonds in preserving the crystal lattice even at small sizes (a few lattice parameter). Based on both cathodo-luminescence and transmission electron microscopy, we report the existence of a structural transition from bcc to monoclinic at small sizes.