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.

International Cancer Genome Consortium Data Portal--a one-stop shop for cancer genomics data.

The International Cancer Genome Consortium (ICGC) is a collaborative effort to characterize genomic abnormalities in 50 different cancer types. To make this data available, the ICGC has created the ICGC Data Portal. Powered by the BioMart software, the Data Portal allows each ICGC member institution to manage and maintain its own databases locally, while seamlessly presenting all the data in a single access point for users. The Data Portal currently contains data from 24 cancer projects, including ICGC, The Cancer Genome Atlas (TCGA), Johns Hopkins University, and the Tumor Sequencing Project. It consists of 3478 genomes and 13 cancer types and subtypes. Available open access data types include simple somatic mutations, copy number alterations, structural rearrangements, gene expression, microRNAs, DNA methylation and exon junctions. Additionally, simple germline variations are available as controlled access data. The Data Portal uses a web-based graphical user interface (GUI) to offer researchers multiple ways to quickly and easily search and analyze the available data. The web interface can assist in constructing complicated queries across multiple data sets. Several application programming interfaces are also available for programmatic access. Here we describe the organization, functionality, and capabilities of the ICGC Data Portal.

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.

["Difficult intubation" workshops : impact on knowledge and practices]. / Ateliers "intubation difficile": impact sur les connaissances et les pratiques.

OBJECTIVES: To evaluate the impact of difficult intubation workshops on airway management knowledge and daily medical practice in anaesthesiology. STUDY DESIGN: Prospective survey. METHODS: The participants to the workshops accredited by the French college of anaesthesiologists (Cfar) in 2003 were invited to answer to MCQ before, immediately and three months after the course. They also completed a questionnaire provided during the workshop and three months later, focusing on medical practice and their own organization in the area of difficult intubation before and after the workshop. RESULTS: One hundred seven participants responded to the immediate evaluation (MCQ and questionnaire) whereas 32 responded to the delayed evaluation performed three months later. A subjective scale was used to assess the level of knowledge in difficult intubation (0: lowest level, 10 highest level). The mean score for subjective knowledge considering difficult intubation was 4.7+/-2.3 before the course and 6.9+/-1.6 at 3 months (P<0.001). The mean scores attributed to MCQ were not different before and after the workshops. Participants expected complementary practical training (65%) and theoretical courses (40%). Delayed evaluation revealed that 25/32 participants had to deal with difficult intubation during their clinical practice after the workshop, but 3 cases (12%) could not be managed with success. Defects could be observed in terms of organization: no difficult airway trolley (22%), no predefined difficult airway algorithm (66%), and information: no written information given to the difficult airway patient (44%), and no information given to the difficult airway patient's home doctor (91%). DISCUSSION: These results showed that difficult intubation remains a real problem for anaesthesiologists. They also revealed differences between subjective and objective knowledge and pointed out defects in terms of organization and management which should be improved.

[Which anaesthesia for children undergoing MRI? An Internet survey in the French university hospitals]. / Quelle anesthésie pour les IRM en pédiatrie? Résultats d'une enquête par Internet dans les CHU de France.

OBJECTIVE: To investigate the procedures used by French anaesthesiologists in children undergoing MRI. METHODS: A questionnaire was sent by Internet to every university hospital in France. Information concerning the specialty of the doctor in charge of the child, the age of the children, premedication, airway control, the agents used, presence of a specific recovery room, length of hospitalization and number of children undergoing MRI was obtained. RESULTS: Out of the 28 hospitals contacted, one did not reply and two did not perform anaesthesia for MRI. In 80% of cases, paediatric anaesthesiologists were in charge of the children. Only one team applied an age limit and performed sedation only in children over 10 kg. Specific monitoring for MRI was used by all teams. Premedication was given in 52% of cases. Parents were present during induction in 52% of cases. Sevoflurane was used in 52%, propofol in 40% and propofol with sufentanil in 8%. Presence of a venous line is systematic in 92% of cases. Intubation is systematic in 36% of cases, laryngeal mask in 20%, one or the other in 24%, and face mask and/or oral canula in 20%. The most widely used ventilation mode is spontaneous breathing (52%). All children go to the recovery room, which was close to the MRI unit in only 48% of cases and was less than 1 hour away in 72%. In 83% of cases, MRI is performed on a day-case basis and the number of procedures varies from 4 to 30 per week. CONCLUSION: While there is no standard anaesthetic protocol in France for children undergoing MRI, only specialist teams undertake such procedures.

Pressure support ventilation during fibreoptic intubation under propofol anaesthesia.

GOAL OF THE STUDY: To assess the benefit of pressure support ventilation during fibreoptic intubation performed under propofol anaesthesia in patients having an anticipated difficult intubation. PROCEDURES: Thirty-two patients with ENT cancer, and having at least two criteria for anticipated difficult intubation were prospectively included. All patients received topical lidocaine 2% and propofol by plasma target control infusion (initial target concentration 3 microg ml(-1), then adjusted to maintain loss of consciousness without apnoea). They were randomly assigned between two groups: spontaneous breathing (SB) or pressure support ventilation (with a support level set at 10 cm H(2)O) both using Fi(o(2))=1. Conditions for fibreoptic intubation, respiratory parameters (pulse oxymetry, ventilatory frequency, tidal volume and PetCO2 after intubation) and haemodynamic parameters were recorded. RESULTS: Patient characteristic data and intubation conditions were similar between both groups. All patients had a successful fibreoptic intubation and none needed a rescue procedure because of desaturation. In spite of a longer duration of intubation, PE'CO2 after intubation was lower and tidal volume during intubation was higher with pressure support ventilation than in SB patients [38.1 (4.2) vs 42.3 (4.7) mm Hg and 371 (139) vs 165 (98) ml, respectively]. Desaturation episodes were observed in two SB patients conversely to no episode during pressure support ventilation, probably because of the higher minute ventilation. CONCLUSION: Pressure support represents a useful method to improve ventilation during fibreoptic intubation under propofol anaesthesia in patients with an anticipated difficult intubation.

Pressure-controlled ventilation is superior to volume-controlled ventilation with a laryngeal mask airway in children.

BACKGROUND: This prospective, randomized, crossover study had two purposes: first, to determine whether pressure-controlled ventilation (PCV) is safer than volume-controlled ventilation (VCV) by preventing gastric insufflation in children ventilated through an laryngeal mask airway (LMA); second, to assess whether the measurement of LMA leak pressure (P(leak)) is useful for preventing leakage during positive pressure ventilation (PPV). METHODS: Forty-one, 2 to 15-year-old children underwent general anesthesia with an LMA. The expiratory valve was set at 30 cmH(2)O and P(leak) was measured using constant gas flow. Children were randomly ventilated using PCV or VCV for 5 min in order to reach a P(ET)CO(2) not exceeding 45 mm Hg, and then they were ventilated with the alternative mode. If the target P(ET)CO(2) could not be obtained in one mode, we switched to the other. If both modes failed, children were intubated. Tidal volumes, P(ET)CO(2) and airway pressures were noted and compared between modes. Gastric insufflation was checked by epigastric auscultation. RESULTS: PCV provided more efficient ventilation than VCV, as targeted P(ET)CO(2) was obtained without gastric insufflation using PCV in all cases except one, whereas VCV failed in three cases. No gastric insufflation occurred when ventilating below peak. CONCLUSIONS: These findings suggest that in the age group studied, PCV is more efficient than VCV for controlled ventilation with a laryngeal mask. Gastric insufflation did not occur with this mode.

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.