Resonant Raman scattering of core-shell GaN/AlN nanowires.

We have analyzed the electron-phonon coupling in GaN/AlN core-shell nanowires by means of Raman scattering excited at various wavelengths in the ultraviolet spectral range (335, 325 and 300 nm) and as a function of the AlN shell thickness. The detailed analysis of the multi-phonon spectra evidences important differences with excitation energy. Under 325 and 300 nm excitation the Raman process is mediated by the allowedA1(LO) phonon mode, where the atoms vibrate along the NW axis. Considering its selection rules, this mode is easily accessible in backscattering along the wurtzitecaxis. Interestingly, for 335 nm excitation the scattering process is instead mediated by theE1(LO) phonon mode, where atoms vibrate in thec-plane and that is forbidden in this configuration. This change is ascribed to the band anticrossing caused by the uniaxial strain imposed by the AlN shell and the proximity, at this particular excitation energy, of real electronic transitions separated by the energy of the longitudinal optical phonon modes. The energy and character of the electronic bands can be tuned by varying the AlN shell thickness, a degree of freedom unique to core-shell nanowires. The interpretation of the experimental results is supported by calculations of the electronic transitions of GaN under uniaxial strain performed within the framework of ak · pmodel.

Impact of kinetics on the growth of GaN on graphene by plasma-assisted molecular beam epitaxy.

The growth of GaN on graphene by molecular beam epitaxy was investigated. The most stable epitaxial relationship, i.e. [00.1]-oriented grains, is obtained at high temperature and N-rich conditions, which match those for nanowire growth. Alternatively, at moderate temperature and Ga-rich conditions, several metastable orientations are observed at the nucleation stage, which evolve preferentially towards [00.1]-oriented grains. The dependence of the nucleation regime on growth conditions was assigned to Ga adatom kinetics. This statement is consistent with the calculated graphene/GaN in-plane lattice coincidence and supported by a combination of transmission electron microscopy, x-ray diffraction, photoluminescence, and Raman spectroscopy experiments.

Optical contrast of 2D InSe on SiO2/Si and transparent substrates using bandpass filters.

The particular optical and electronic properties recently reported for 2D InSe depict this 2D material as being very versatile for future electronic and optoelectronic devices with tunable and optimized functionalities. For its fundamental study and the development of practical applications, rapid and accurate identification methods of atomically thin InSe are essential. Here, we demonstrate an enhancement of the optical contrast between InSe nanosheets and the underlying SiO2/Si substrate by illuminating with a 40 nm wide bandpass filter centered at 500 nm. Moreover, we study the optical contrast of 2D InSe on transparent substrates. Our results suggest that a good optical contrast is achieved for transparent substrates with low real refractive indices such as LiF or a viscoelastic polydimethylsiloxane stamp. In this case, an optimum optical contrast would be achieved by using a bandpass filter centered at 450 nm. These results can be very useful for speeding up the continuously growing research on 2D InSe and its applications.

Assessment of Polarity in GaN Self-Assembled Nanowires by Electrical Force Microscopy.

In this work, we demonstrate the capabilities of atomic force microscopies (AFMs) for the nondestructive determination of the polarity of GaN nanowires (NWs). Three complementary AFMs are analyzed here: Kelvin probe force microscopy (KPFM), light-assisted KPFM, and piezo-force microscopy (PFM). These techniques allow us to assess the polarity of individual NWs over an area of tens of µm(2) and provide statistics on the polarity of the ensemble with an accuracy hardly reachable by other methods. The precise quantitative analysis of the tip-sample interaction by multidimensional spectroscopic measurements, combined with advanced data analysis, has allowed the separate characterization of electrostatic and van der Waals forces as a function of tip-sample distance. Besides their polarity, the net surface charge density of individual NWs was estimated.

Growth, structural and optical properties of AlGaN nanowires in the whole composition range.

We report on the growth of AlxGa1-xN nanowires by plasma-assisted molecular beam epitaxy for x in the 0.3-0.8 range. Based on a combination of macro- and micro-photoluminescence, Raman spectroscopy, x-ray diffraction and scanning electron microscopy experiments, it is shown that the structural and optical properties of AlGaN NWs are governed by the presence of compositional fluctuations associated with strongly localized electronic states. A growth model is proposed, which suggests that, depending on growth temperature and metal adatom density, macroscopic composition fluctuations are mostly of kinetic origin and are directly related to the nucleation of the AlGaN nanowire section on top of the GaN nanowire base which is used as a substrate.

The structural properties of GaN/AlN core-shell nanocolumn heterostructures.

The growth and structural properties of GaN/AlN core-shell nanowire heterostructures have been studied using a combination of resonant x-ray diffraction, Raman spectroscopy and high resolution transmission electron microscopy experiments. For a GaN core of 20 nm diameter on average surrounded by a homogeneous AlN shell, the built-in strain in GaN is found to agree with theoretical calculations performed using a valence force field model. It is then concluded that for an AlN thickness up to at least 12 nm both core and shell are in elastic equilibrium. However, in the case of an inhomogeneous growth of the AlN shell caused by the presence of steps on the sides of the GaN core, plastic relaxation is found to occur. Consistent with the presence of dislocations at the GaN/AlN interface, it is proposed that this plastic relaxation, especially efficient for AlN shell thickness above 3 nm, is promoted by the shear strain induced by the AlN inhomogeneity.

The structural properties of GaN insertions in GaN/AlN nanocolumn heterostructures.

The strain state of 1 and 2.5 nm thick GaN insertions in GaN/AlN nanocolumn heterostructures has been studied by means of a combination of high resolution transmission electron microscopy, Raman spectroscopy and theoretical modeling. It is found that 2.5 nm thick GaN insertions are partially relaxed, which has been attributed to the presence of dislocations in the external AlN capping layer, in close relationship with the morphology of GaN insertions and with the AlN capping mechanism. The observed plastic relaxation in AlN is consistent with the small critical thickness expected for GaN/AlN radial heterostructures.

Optimal dose of sufentanil in children for intubation after sevoflurane induction without neuromuscular block.

BACKGROUND: We studied 63 ASA I children (age 2-8 yr) to determine the sufentanil dose needed to facilitate intubation under excellent conditions after inhalation induction with various end-tidal concentrations of sevoflurane without neuromuscular block. METHODS: Subjects were allocated randomly to receive sevoflurane end-tidal concentrations (e'(sevo)) of 2.5%, 3%, or 3.5%. Anaesthesia was induced with sevoflurane 6% without nitrous oxide for 2 min, and then inspired sevoflurane concentration was adjusted to keep e'(sevo) at 2.5%, 3%, or 3.5% according to the group. Subjects received i.v. sufentanil according to an 'up and down' design. Tracheal intubation by direct laryngoscopy was performed 6 min after sufentanil injection. Intubation was considered successful, if intubation conditions were excellent as determined by the laryngoscopist. RESULTS: The ED(50) [effective dose for 50% of subjects; mean (sd)] of sufentanil required for excellent intubation conditions was 0.6 (0.12), 0.32 (0.10), or 0.11 (0.07) microg kg(-1) for e'(sevo) of 2.5%, 3%, or 3.5%, respectively. Using logistic analysis, the 95% effective dose (ED(95)) of sufentanil was 1.02 [95% confidence intervals (CI) 0.31-1.74] microg kg(-1), 0.58 (95% CI 0.17-0.99) microg kg(-1), or 0.28 (95% CI 0.04-0.52) microg kg(-1) for e'(sevo) of 2.5%, 3%, or 3.5%, respectively. CONCLUSIONS: Excellent intubation conditions could be obtained in children after inhalation induction with low sevoflurane concentrations and adjuvant sufentanil.

The I-gel, a single-use supraglottic airway device with a non-inflatable cuff and an esophageal vent: an observational study in children.

BACKGROUND: The I-gel is a new single-use supraglottic airway device with a non-inflatable cuff. It is composed of a thermoplastic elastomer and a soft gel-like cuff that adapts to the hypopharyngeal anatomy. Like the LMA-ProSeal, it has an airway tube and a gastric drain tube. Little is known about its efficiency in pediatric anesthesia. METHODS: Fifty children above 30 kg, ASA I-II, undergoing a short-duration surgery were included in this prospective, observational study. We evaluated ease in inserting the I-gel, seal pressure, gastric leak, complications during insertion and removal, ease in inserting the gastric tube and ventilatory parameters during positive pressure ventilation. RESULTS: All devices were inserted at the first attempt. The mean seal pressure was 25 cmH(2)O. There was no gastric inflation and gastric tube insertion was achieved in all cases. The results appear similar to those in a previous study concerning laryngeal mask airway in terms of leak pressure and complication rates. CONCLUSION: Because the I-gel has a very good insertion success rate and very few complications, it seems to be an efficient and safe device for pediatric airway management.

X-ray absorption near-edge structure of GaN with high Mn concentration grown on SiC.

By means of x-ray absorption near-edge structure (XANES) several Ga(1-x)Mn(x)N (0.03

A new single use supraglottic airway device with a noninflatable cuff and an esophageal vent: an observational study of the i-gel.

BACKGROUND: The i-gel is a new single-use supraglottic airway device with a noninflatable cuff and an esophageal vent. METHOD: In this prospective, observational study, we evaluated the i-gel in 71 women. RESULTS: Insertion success rate was 97%. Insertion was easy and performed at the first attempt in every patient. Mean seal pressure was 30 +/- 7 cm H(2)O, and average peak pressure was 11 +/- 3 cm H(2)O. The gastric tube was inserted in 100% of cases. Only one case of coughing and one mild sore throat occurred. CONCLUSION: The i-gel is a reliable, easily inserted airway device that provides an adequate seal with a low morbidity rate.

Intubation of infants with Pierre Robin syndrome: the use of the paraglossal approach combined with a gum-elastic bougie in six consecutive cases.

Infants with Pierre Robin syndrome are known to be difficult to intubate. We evaluated the paraglossal approach combined with a gum elastic bougie for intubation of these infants. Whilst under general anaesthesia, a conventional laryngoscopy was performed; if it failed to obtain a laryngoscopic grade I or II view, intubation was attempted using a paraglossal approach and a gum elastic bougie. Six consecutive infants were studied. Conventional laryngoscopy failed in all infants whilst the paraglossal approach combined with a gum elastic bougie was successful in five of the cases. The paraglossal approach combined with a gum elastic bougie made intubation easy in most children with severe Pierre Robin syndrome and difficult laryngoscopy. Therefore we recommend this as the first line for airway management in such children. However, a fibreoptic bronchoscope and an anaesthetist trained in fibreoptic intubation must still be present when dealing with severe Pierre Robin syndrome infants.

Therapeutic efficacy of intra-cochlear administration of methylprednisolone after acoustic trauma caused by gunshot noise in guinea pigs.

The therapeutic efficacy of cochlear infusion of methylprednisolone (MP) after an impulse noise trauma (170dB SPL peak) was evaluated in guinea pigs. The compound action potential threshold shifts were measured over a 14 days recovery period after the gunshot exposure. For each animal, one of the cochlea was perfused directly into the scala tympani with MP during 7 days via a mini-osmotic pump, whereas the other cochlea was not pump-implanted. The functional study of hearing was supplemented by histological analysis. Forty eight hours after the trauma, significant differences between auditory threshold shifts in the implanted and non-implanted ears were observed for frequencies above 8kHz. At day 7, the difference was significant for only one frequency and no difference was observed after 14 days recovery. Cochleograms showed that the hair cell losses were significantly lower in the MP treated ears. This work indicates that direct infusion of MP into perilymphatic space accelerates hearing recovery, reduces hair cell losses after impulse noise trauma but does not limit permanent threshold shifts.

[Inhalation induction with sevoflurane in paediatrics: what is new?]. / Induction au masque facial avec le sévoflurane chez l'enfant: le point sur les nouvelles modalités.

The delay for loss of consciousness can be shortened by using high concentration sevoflurane > 6% and by adding N2O during inhalation induction with sevoflurane in paediatrics. Mean time for tracheal tube insertion is lower than 5 min in the majority of studies. This shorter delay is not associated with any significant increase in clinical side effects. However, recent studies have demonstrated the epileptogenic effect of high effect site sevoflurane concentration (occurrence of spike wave on the EEG). Inhalation induction with high alveolar sevoflurane concentration is questionable mainly when it is associated with hyperventilation. Positive pressure ventilation or pressure support ventilation make it possible to maintain normocapnia and to monitor FeSevo. Adding a narcotic decreases the target cerebral concentration required to perform tracheal intubation and consequently the risk of spike wave occurrence.

[Oropharyngeal ulcers following anaesthesia with the laryngeal tube S]. / Ulcérations oropharyngées suite à l'utilisation d'un tube laryngé S.

We report a case of acute tongue and uvula ulcerations consecutive to the use of a laryngeal tube Sonda (LTS) for airway management. The LTS was used during general anaesthesia for hysteroscopy and resection of endometrial hyperplasia. No trouble occurred during LTS insertion and anaesthesia. Symptomatic treatment provided complete resolution within a few days. This event points out the potential risk of more serious lesions.

[Clinical study of the laryngeal mask in paediatric. Comparison of the LMA-ProSeal and LMA-classic]. / Etude clinique du masque laryngé en pédiatrie. Comparaison du LMA-classic et du LMA-ProSeal taille 2 et 2,5.

OBJECTIVES: To compare the Classic laryngeal mask airway (MLC) and the ProSeal LMA (MLP), size 2 and 2.5 in terms of ease of insertion, leak pressure and side effects during insertion and extraction in the recovery room. STUDY TYPE: Randomised prospective. MATERIAL AND METHOD: All children between 10 and 30 kg scheduled for general anaesthesia with laryngeal mask (ML) were included. There was no imposed protocol for the anaesthesia. The ML size was determined according to the child's weight. The MLC was inserted using the standard technique. The MLP was inserted following the recommendations, with or without the handle according to the operator's choice. The data analysed were: insertion type, ease of insertion of the mask, of the nasogastric tube (SG), number of attempts of mask insertion, complications, gastric leaks. RESULTS: One hundred (and) twenty children were included. There was no statistical difference in terms of difficulty of insertion, number of failed attempts, leak pressure or side effects. The use of the handle did not make insertion easier. Insertion of a nasogastric tube was possible in 92% cases. CONCLUSION: MLP is as easy to use in children as the MLC. MLP has the advantage of allowing rapid access to the stomach. It seems that the MLP is safer since its correct position is confirmed by easy gastric tube insertion.

Role of residue Glu152 in the discrimination between transfer RNAs by tyrosyl-tRNA synthetase from Bacillus stearothermophilus.

Residue Glu152 of tyrosyl-tRNA synthetase (TyrTS) from Bacillus stearothermophilus is close to phosphate groups 73 and 74 of tRNATyr in the structural model of their complex. TyrTS(E152A), a mutant synthetase carrying the change of Glu152 to Ala, was toxic when overproduced in Escherichia coli. The toxicity strongly increased with the growth temperature. It was measured by the ratios of the efficiencies with which the producing cells plated in induced or repressed conditions and at 30 degrees C or 37 degrees C. TyrTS(E152Q), TyrTS(E152D) and the wild-type synthetase were not toxic in conditions where TyrTS(E152A) was toxic. The toxicity of TyrTS(E152A) was abolished by additional mutations of the synthetase that prevent the binding of tRNATyr but not by a mutation that prevents the formation of Tyr-AMP. Because TyrTS(E152A) was active for the aminoacylation of tRNATyr, its toxicity could only be due to faulty interactions with non-cognate tRNAs, either their non-productive binding or their mischarging with tyrosine. TyrTS(E152A) and TyrTS(E152Q) mischarged tRNAPhe and tRNAVal in vitro with tyrosine unlike TyrTS(E152D) or the wild-type enzyme. Thus, several features of the side-chain in position 152 of TyrTS, including its negative charge, are important for the rejection of non-cognate tRNAs. TyrTS(E152A), TyrTS(E152D) and TyrTS(E152Q) had similar steady-state kinetics parameters for the charging of tRNATyr with tyrosine in vitro, with kcat/KM ratios improved 2.5 times relative to the wild-type synthetase. We conclude that the side-chain of residue Glu152 weakens the binding of TyrTS to tRNATyr and prevents its interaction with non-cognate tRNAs.

[Occurrence of epileptiform crisis in child under sevoflurane anaesthesia]. / Survenue d'une crise épileptiforme avec le sévoflurane chez un enfant.

A case report is presented of an unknown epileptic child, who developed convulsive movements during inhalation of 3.9% sevoflurane for 45 minutes associated with moderate hyperventilation. Epilepsy was discovered on the EEG, which was performed postoperatively.

[Induction of anaesthesia with target-controlled inhalation of sevoflurane in adults with the ZEUS anaesthesia machine]. / Induction par inhalation de sévoflurane à objectif de concentration chez l'adulte avec le respirateur ZEUS.

OBJECTIVES: To evaluate if the new anaesthesia platform ZEUS (Dräger Medical) allows the induction of anaesthesia with target-controlled inhalation of sevoflurane. STUDY DESIGN: Prospective clinical study. PATIENTS: Adult ASA I or II patients scheduled for elective surgery under general anaesthesia. METHODS: After preoxygenation during 3 min at 100% oxygen, patients were asked to breathe normally; the target end-tidal concentration of sevoflurane was fixed at 4% without priming of the circuit. Sufentanil (target concentration 0.5 ng/ml) was administered 40 s after. RESULTS: Ten patients (48+/-22 yrs) were included. Sevoflurane was detected in the circuit after 36+/-5 s; the target end-tidal concentration of sevoflurane was obtained at 130+/-19 s. Loss of consciousness was observed after 119+/-7 s. The induction was achieved in all patients without any incident. CONCLUSION: This new anaesthesia system make available the induction of anaesthesia with sevoflurane without priming of the circuit.

[Clinical evaluation of the single use Laryngeal Tube in adults: the LTD]. / Evaluation clinique chez l'adulte du tube laryngé à usage unique: le LTD.

OBJECTIVES: The Laryngeal Tube (LT) is a supra-laryngeal device indicated to manage upper airway during anaesthesia. Leak pressures were lately reported higher for the LT as compared to the LMA. A recent study found a small amount of proteinaceous material on LMA after classical sterilization suggesting a risk of contamination by unconventional transmissible agents (prions). The aim of this study was to evaluate the effectiveness of the single use Laryngeal Tube: the LTD. STUDY DESIGN: Prospective study realized after ethical committee agreement and patient consent for participation. PATIENTS AND METHODS: Adults, ASA score< or =3, 18 to 75-year-old, without upper airway abnormality or difficult intubation criteria, anaesthesia< or =2 h, free access to patient's head and LTD. The following criteria were evaluated: easiness of insertion, assisted (AV), controlled (CV) and spontaneous ventilation (SV); leak pressure (LP) 5 and 15 min after insertion; complications during anaesthesia conducted with propofol and remifentanil under bispectral index monitoring. RESULTS: 55 patients were included; only one failure was reported at insertion. AV and CV were easy, SV difficult in 4 patients with chin lift necessary for adequate ventilation. LP was 28.92+/-8.4 and 30.87+/-8.68 cmH2O 5 and 15 min after insertion respectively. No major incident was noticed throughout the study. CONCLUSION: the use of the LTD was easy and successful. Moreover the LTD totally excluded the risk of contamination by unconventional transmissible agents.