How Adsorbed Oxygen Atoms Inhibit Hydrogen Dissociation on Tungsten Surfaces.

Hydrogen molecules dissociate on clean W(110) surfaces. This reaction is progressively inhibited as the tungsten surface is precovered with oxygen. We use density functional theory and ab initio molecular dynamics to rationalize, at the atomic scale, the influence of the adsorbed O atoms on the H2 dissociation process. The reaction probability is calculated for kinetic energies below 300 meV and different O nominal coverages. We show that the adsorbed O atoms act as repulsive centers that modulate the dynamics of the impinging H2 molecules by closing dissociation pathways. In agreement with existing experimental information, H2 dissociation is absent for an O coverage of half a monolayer. The results show that the influence of O adsorbates on the dissociation dynamics on W(110) goes much beyond the blocking of possible H adsorption sites. Adsorbed O atoms create a sort of chemical shield at the surface that prevents further approach and dissociation of the H2 molecules.

Chemical reaction thresholds according to classical-limit quantum dynamics.

Classical-limit quantum dynamics is used to explain the origin of the quantum thresholds of chemical reactions from their classical dynamics when these are vibrationally nonadiabatic across the interaction region. This study is performed within the framework of an elementary model of chemical reaction that mimics the passage from the free rotation of the reagents to the bending vibration at the transition state to the free rotation of the products.

From mothership to drip-and-ship: Effects of staff shortages at a comprehensive stroke center.

BACKGROUND: Mechanical thrombectomy (MT) has been shown to be effective in the acute phase of ischemic stroke. Current data suggests that the drip-and-ship and mothership telestroke models are equally effective for its administration. We describe the consequences of changing the telestroke model due to staff shortages in a comprehensive stroke center (Besançon), which was replaced by a more distant one (Dijon). METHODS: We conducted a retrospective analysis of all patients referred for MT from January 2015 to December 2018. We analyzed the time between symptom onset and arrival in the angiography suite. We also calculated number of thrombectomies divided by number of days on call, and rate of thrombectomies relative to the number of strokes in each group. RESULTS: In Besançon, 205 patients underwent an MT procedure, versus 43 patients in Dijon. A further four patients were transferred to Dijon but not treated. The time from symptom onset to arrival in the angiography suite was longer for Dijon; 334min versus 281min for Besançon (p<0.001). The percentage of thrombectomies performed per day on call was higher for Besançon: 18.6% versus 13.2% in Dijon (p=0.026). CONCLUSIONS: Over the study period, the time from symptom onset to angiography suite was longer for patients who were transferred to Dijon. The period in which the Besançon hospital experienced the greatest lack of personnel corresponded to a decrease in the number of MTs performed.

Statistical properties of quantum probability fluctuations in complex-forming chemical reactions.

The energy dependence of quantum complex-forming reaction probabilities is well known to involve sharp fluctuations, but little seems to be known about their amplitudes. We develop here, for triatomic reactions, an analytical approach of their statistical distribution. This approach shows that the fluctuation amplitudes depend essentially on the number of available quantum states in the reagent and product channels. Moreover, the more numerous the product states, the more efficiently the fluctuations of their populations compensate each other when they add up to give the reaction probability. The predictions of our approach appear to be in good quantitative agreement with quantum scattering calculations for the prototypical reaction H+ + H2.

When Classical Trajectories Get to Quantum Accuracy: The Scattering of H2 on Pd(111).

When elementary reactive processes occur at such low energies that only a few states of reactants and/or products are available, quantum effects strongly manifest and the standard description of the dynamics within the classical framework fails. We show here, for H2 scattering on Pd(111), that by pseudoquantizing in the spirit of Bohr the relevant final actions of the system, along with adequately treating the diffraction-mediated trapping of the incoming wave, classical simulations achieve an unprecedented agreement with state-of-the-art quantum dynamics calculations.

Theoretical Study of Barrierless Chemical Reactions Involving Nearly Elastic Rebound: The Case of S(1D) + X2, X = H, D.

For some values of the total angular momentum consistent with reaction, the title processes involve nonreactive trajectories proceeding through a single rebound mechanism during which the internal motion of the reagent diatom is nearly unperturbed. When such paths are in a significant amount, the classical reaction probability is found to be markedly lower than the quantum mechanical one. This finding was recently attributed to an unusual quantum effect called diffraction-mediated trapping, and a semiclassical correction was proposed in order to take into account this effect in the classical trajectory method. In the present work, we apply the resulting approach to the calculation of opacity functions as well as total and state-resolved integral cross sections (ICSs) and compare the values obtained with exact quantum ones, most of which are new. As the title reactions proceed through a deep insertion well, mean potential statistical calculations are also presented. Seven values of the collision energy, ranging from 30 to 1127 K, are considered. Two remarkable facts stand out: (i) The corrected classical treatment strongly improves the accuracy of the opacity function as compared to the usual classical treatment. When the entrance transition state is tight, however, those trajectories crossing it with a bending vibrational energy below the zero point energy must be discarded. (ii) The quantum opacity function, particularly its cutoff, is finely reproduced by the statistical approach. Consequently, the total ICS is also very well described by the two previous approximate methods. These, however, do not predict state-resolved ICSs with the same accuracy, proving thereby that (i) one or several genuine quantum effects involved in the dynamics are missed by the corrected classical treatment and (ii) the dynamics are not fully statistical.

Adult moyamoya angiopathy in Bourgogne-Franche-Comté: Epidemiology, diagnosis and management.

INTRODUCTION: Moyamoya angiopathy (MMA) is a progressive steno-occlusive disease of the distal internal carotid arteries mainly described in Asia. It induces the development of collateral vascular networks to reduce chronic cerebral hypoperfusion. Symptoms depend on the patient's age in Asia: children are at greater risk of transient or constituted ischemic events, whereas adults are more exposed to hemorrhagic stroke. Data from the literature seem to show that the pattern of MMA in western countries differs from that in Asia. MATERIAL AND METHODS: A retrospective study of patients with MMA was conducted in Bourgogne-Franche-Comté (mid-eastern France). Clinical data (symptoms, risk factors, age at diagnosis, number and timing of recurrences, type of treatment) as well as radiological data (angiographic findings, Suzuki's grade) were analyzed. RESULTS: Seventeen adult patients (9 men, 53%) were followed at the university hospitals of Besançon and Dijon from 2009 to 2016. Fourteen patients (83%) had bilateral disease. The mean age at diagnosis was 49 years (±16), 83% of the patients were Caucasian and 17% originated from Maghreb. Only 17% of the hemispheres had a hemorrhagic form. Ischemic form was more frequent before diagnosis with transient ischemic attack (24% of patients) and stroke (83% of patients). With medical treatment, 9 patients suffered from stroke recurrence (53% of patients) with an average delay of 22.7±34 months. Three patients (18%) had combined surgical management by encephelo-synangiosis and superficial temporal artery-to-middle cerebral artery (STA-MCA) anastomosis, without symptom recurrence after treatment with an average follow up of 14 months. CONCLUSION: MMA remains a rare cerebrovascular disease in Europe and requires multidisciplinary care. Epidemiological analysis showed differences with the Asian population, especially the predominance of ischemic forms in adults.

Semiclassical initial value theory of rotationally inelastic scattering: Some remarks on the phase index in the interaction picture.

This paper deals with the treatment of quantum interferences in the semiclassical initial value theory of rotationally inelastic scattering in the interaction picture. Like many semiclassical methods, the previous approach involves a phase index related to sign changes of a Jacobian whose square root is involved in the calculations. It is shown that replacing the original phase index by a new one extends the range of applicability of the theory. The resulting predictions are in close agreement with exact quantum scattering results for a model of atom-rigid diatom collision involving strong interferences. The developments are performed within the framework of the planar rotor model, but are readily applicable to three-dimensional collisions.

Chemical & Nano-mechanical Study of Artificial Human Enamel Subsurface Lesions.

White lesions represent an early phase of caries formation. 20 human sound premolars were subjected to pH cycling procedure to induce subsurface lesions (SLs) in vitro. In addition, 2 teeth with naturally developed white spot lesions (WSLs) were used as references. All specimens characterized by confocal Raman microscopy being used for the first time in examining white & subsurface lesions and providing a high resolution chemical and morphological map based on phosphate peak intensity alterations at 960 cm-1. Nanoindentation technique was used to measure Hardness (H) and Young's modulus (E) of enamel. Phosphate map of examined samples exhibited presence of intact surface layer (ISL) followed by severe depletion in (PO43-) peak in the area corresponding to the body of the lesion. In all examined groups, the mechanical properties of enamel were decreased in lesion area and found to be inversely related to penetration depth of indenter owing to enamel hierarchical structure. By combining the above two techniques, we linked mechanical properties of enamel to its chemical composition and ensured that the two methods are highly sensitive to detect small changes in enamel composition. Further work is required to bring these two excellent tools to clinical application to perceive carious lesions at an early stage of development.

Moya-Moya syndrome after cranial radiation for optic glioma with NF1. Case report and literature review of syndromic cases.

INTRODUCTION: Moya-Moya angiopathy is a neurovascular disease that predisposes to ischemic or hemorrhagic strokes. It is generated by a steno-occlusion of the terminal portion of the internal carotid arteries, which induces the development of abnormal neovessels in the deep regions of the brain. Some pathologies such as sickle cell disease, Down syndrome or Graves' disease may be associated with Moya-Moya angiopathy. These syndromic forms harbor several differences compared with idiopathic Moya-Moya disease. CASE REPORT: We report the case of a young patient who presented with a syndromic form of Moya-Moya angiopathy after cranial radiation therapy for an optic glioma associated with type 1 neurofibromatosis treated by combined revascularization. We discuss the particularities of syndromic forms, in their presentation and management based on a review of the literature. CONCLUSION: Many diseases can be associated with Moya-Moya syndrome. Symptomatic patients should undergo surgery, but the risk of postoperative complications appears to be greater than that encountered in patients with non-syndromic Moya-Moya angiopathy.

Full-Dimensional Theory of Pair-Correlated HNCO Photofragmentation.

Full-dimensional semiclassical dynamical calculations combining classical paths and Bohr quantization of product internal motions are reported for the prototype photofragmentation of isocyanic acid in the S1 state. These calculations allow one to closely reproduce for the first time key features of state-of-the-art imaging measurements at photolysis wavelengths of 201 and 210 nm while providing insight into the underlying dissociation mechanism. Quantum scattering calculations being beyond reach for most polyatomic fissions, pair-correlated data on these processes are much more often measured than predicted. Our theoretical approach can be used to fill this gap.

[Closed claims in obstetrics: A study based on French Sham insurance data]. / Sinistralité en obstétrique dans les hôpitaux publics français: données Sham.

OBJECTIVE: The aim of this study was to analyze the medicolegal claims related to obstetrics in French hospitals. MATERIAL AND METHODS: We did retrospective study on insurance claims provided by Sham insurances and which has been settled by a court over a 3-year period (2004-2006). RESULTS: We analyzed 66 closed claims that occurred between 1983 and 2005 in French hospitals (54 general hospitals and 12 academic). The average time between the declaration of the claim and the court conviction was 6 years. The average amount of compensation per claim was 500,000 €. The damage occurred during vaginal delivery (n=44), planned (n=5) or unplanned (n=4) cesarean. The more often claims are fetal asphyxia (n=24) or shoulder dystocia (n=8). The consequences are very important: cerebral palsy (16), death of the newborn (12), death of the mother (2) or brachial plexus injuries (6). CONCLUSION: The causes identified by the expert are always multifactorial with generally a misdiagnosis (n=27), a decision making error (n=36), a care error by the midwife (n=21) and/or a delay in medical care (n=13). These data should help strengthen the quality approach in obstetrics.

Semiclassical Wigner theory of photodissociation in three dimensions: Shedding light on its basis.

The semiclassical Wigner theory (SCWT) of photodissociation dynamics, initially proposed by Brown and Heller [J. Chem. Phys. 75, 186 (1981)] in order to describe state distributions in the products of direct collinear photodissociations, was recently extended to realistic three-dimensional triatomic processes of the same type [Arbelo-González et al., Phys. Chem. Chem. Phys. 15, 9994 (2013)]. The resulting approach, which takes into account rotational motions in addition to vibrational and translational ones, was applied to a triatomic-like model of methyl iodide photodissociation and its predictions were found to be in nearly quantitative agreement with rigorous quantum results, but at a much lower computational cost, making thereby SCWT a potential tool for the study of polyatomic reaction dynamics. Here, we analyse the main reasons for this agreement by means of an elementary model of fragmentation explicitly dealing with the rotational motion only. We show that our formulation of SCWT makes it a semiclassical approximation to an approximate planar quantum treatment of the dynamics, both of sufficient quality for the whole treatment to be satisfying.

Totally extraperitoneal (TEP) endoscopic inguinal hernia repair with TAP (transversus abdominis plane) block as a day-case: a prospective cohort study.

BACKGROUND: Totally extraperitoneal (TEP) endoscopic inguinal hernia repair is indicated for recurrent and bilateral inguinal hernias and traditionally is performed under general anesthesia. However, interventions that minimize pain and reduce opioid consumption have certain advantages for patients by avoiding side effects such as nausea and vomiting. The transversus abdominis plane (TAP) block has been used to minimize pain in a diverse range of surgical procedures but its safety on patients undergoing TEP repair has yet to be investigated. AIM: To assess the results of outpatient TEP repair with TAP block without curare. METHODS: Consecutive patients undergoing elective TEP procedure were prospectively enrolled. Patients in two institutes received a similar anesthetic, surgical, and analgesic treatment protocol. RESULTS: Fifty consecutive day-case patients were included in this series. The TEP repair was successful in 49 patients and there was one conversion to transabdominal pre-peritoneal (TAPP) endoscopic inguinal hernia repair. The mean duration of surgery was 20min for unilateral hernia and 40min for bilateral hernia. CONCLUSION: These preliminary results suggest that day-case endoscopic hernia repair (TEP) with TAP block without curare is effective, safe, reproducible and can be proposed in all patients.

Insights into the semiclassical Wigner treatment of bimolecular collisions.

The semiclassical Wigner treatment of bimolecular collisions, proposed by Lee and Scully on a partly intuitive basis [J. Chem. Phys. 73, 2238 (1980)], is derived here from first principles. The derivation combines Heller's ideas [J. Chem. Phys. 62, 1544 (1975); ibid. 65, 1289 (1976); ibid. 75, 186 (1981)], the backward picture of molecular collisions [L. Bonnet, J. Chem. Phys. 133, 174108 (2010)] and the microreversibility principle.

New insights into the semiclassical Wigner treatment of photodissociation dynamics.

The semiclassical Wigner treatment of Brown and Heller [J. Chem. Phys. 1981, 75, 186] is applied to direct triatomic (or triatomic-like polyatomic) photodissociations with the aim of accurately predicting final state distributions at relatively low computational cost, and having available a powerful interpretative tool. For the first time, the treatment takes rotational motions into account. The proposed formulation closely parallels the quantum description as far as possible. An approximate version is proposed, which is still accurate while numerically much more efficient. In addition to being weighted by usual vibrational Wigner distributions, final phase space states appear to be weighted by new rotational Wigner distributions. These densities have remarkable structures clearly showing that classical trajectories most contributing to rotational state j are those reaching the products with a rotational angular momentum close to [j(j + 1)](1/2) (in ℏ units). The previous methods involve running trajectories from the reagent molecule onto the products. The alternative backward approach [L. Bonnet, J. Chem. Phys., 2010, 133, 174108], in which trajectories are run in the reverse direction, is shown to strongly improve the numerical efficiency of the most rigorous method in addition to being state-selective, and thus, ideally suited to the description of state-correlated distributions measured in velocity imaging experiments. The results obtained by means of the previous methods are compared with rigorous quantum results in the case of Guo's triatomic-like model of methyl iodide photodissociation [J. Chem. Phys., 1992, 96, 6629] and close agreement is found. In comparison, the standard method of Goursaud et al. [J. Chem. Phys., 1976, 65, 5453] is only semi-quantitative.

High-harmonic transient grating spectroscopy of NO2 electronic relaxation.

We study theoretically and experimentally the electronic relaxation of NO(2) molecules excited by absorption of one ∼400 nm pump photon. Semiclassical simulations based on trajectory surface hopping calculations are performed. They predict fast oscillations of the electronic character around the intersection of the ground and first excited diabatic states. An experiment based on high-order harmonic transient grating spectroscopy reveals dynamics occurring on the same time scale. A systematic study of the detected transient is conducted to investigate the possible influence of the pump intensity, pump wavelength, and rotational temperature of the molecules. The quantitative agreement between measured and predicted dynamics shows that, in NO(2), high harmonic transient grating spectroscopy encodes vibrational dynamics underlying the electronic relaxation.