Effect of the surface model on the theoretical description of the chemisorption of atomic hydrogen on Cu(001)

Adsorption at surfaces can be modelled using a periodic supercell approach or using finite clusters. For many systems and properties these models are complementary and often the most productive way to work is to use a combination of these techniques. If reliable data is to be obtained it is essential that convergence is achieved with respect to the size of supercell and cluster. This work discusses the convergence of chemisorption properties of H on Cu(001) with respect to the cluster size. To this end calculations of the H binding energy and equilibrium distance, are reported for cluster models of increasing size containing up to 77 metal atoms. Likewise, periodic slab model calculations are used to provide the corresponding values towards which the cluster approach should converge. In many previous studies of a wide variety of systems it has been established that computed equilibrium distances converge rapidly with respect to cluster size. Here, a systematic study of the dependence on cluster size shows that, for adsorption in the 4-fold site, convergence is not achieved even for very large clusters. The reason for this poor convergence is seen to be the inability of the cluster model to reproduce accurately the charge density and electrostatic potential of the crystalline surface

Evaluation of appendicitis risk prediction models in adults with suspected appendicitis

Background Appendicitis is the most common general surgical emergency worldwide, but its diagnosis remains challenging. The aim of this study was to determine whether existing risk prediction models can reliably identify patients presenting to hospital in the UK with acute right iliac fossa (RIF) pain who are at low risk of appendicitis. Methods A systematic search was completed to identify all existing appendicitis risk prediction models. Models were validated using UK data from an international prospective cohort study that captured consecutive patients aged 16–45 years presenting to hospital with acute RIF in March to June 2017. The main outcome was best achievable model specificity (proportion of patients who did not have appendicitis correctly classified as low risk) whilst maintaining a failure rate below 5 per cent (proportion of patients identified as low risk who actually had appendicitis). Results Some 5345 patients across 154 UK hospitals were identified, of which two‐thirds (3613 of 5345, 67·6 per cent) were women. Women were more than twice as likely to undergo surgery with removal of a histologically normal appendix (272 of 964, 28·2 per cent) than men (120 of 993, 12·1 per cent) (relative risk 2·33, 95 per cent c.i. 1·92 to 2·84; P < 0·001). Of 15 validated risk prediction models, the Adult Appendicitis Score performed best (cut‐off score 8 or less, specificity 63·1 per cent, failure rate 3·7 per cent). The Appendicitis Inflammatory Response Score performed best for men (cut‐off score 2 or less, specificity 24·7 per cent, failure rate 2·4 per cent). Conclusion Women in the UK had a disproportionate risk of admission without surgical intervention and had high rates of normal appendicectomy. Risk prediction models to support shared decision‐making by identifying adults in the UK at low risk of appendicitis were identified

Combining molecular dynamics and ab initio quantum-chemistry to describe electron transfer reactions in electrochemical environments

A theoretical model is presented aimed to provide a detailed microscopic description of the electron transfer reaction in an electrochemical environment. The present approach is based on the well-known two state model extended by the novelty that the energy of the two states involved in the electron transfer reaction is computed quantum mechanically as a function of the solvent coordinate, as defined in the Marcus theory, and of the intensity of an external electric field. The solvent conformations defining the reaction coordinate are obtained from classical molecular dynamics and then transferred to the quantum mechanical model. The overall approach has been applied to the electron transfer between a chloride anion and a single crystal Cu(100) electrode. It is found that the solvent exerts a strong influence on the equilibrium geometry of the halide and hence on the relative energy of the two states involved in the electron transfer reaction. Finally, both solvent fluctuations and external field facilitate the electron transfer although solvent effects have a stronger influence

Développement d'un détecteur sans temps mort sensible en temps et en position (application à l'étude des collisions de petits agrégats d'argon Ar+n sur une cible d'argon)

Nous avons développé un nouveau système de détection sans temps mort, résolu en temps et en position et basé sur des galettes de microcanaux. Le principe de ce détecteur est de coupler deux systèmes de détection indépendants qui observent le même événement pour aboutir à leur localisation sans temps mort. Le premier système est constitué d'une caméra CCD capable de fournir l'information position. Le deuxième est constitué d'une carte de numérisation pour enregistrer le signal temps issu des galettes de microcanaux. Le lien entre ces deux systèmes est assuré par une anode constituée de deux lignes à retard, placées derrière les galettes de microcanaux, capable de fournir les deux informations temps et position mais d'une façon moins précise. Ce détecteur opérant au kHz permet d'atteindre une résolution spatiale de 100 m et temporelle de 100 ps.Nous avons étudié la fragmentation induite par collision des petits agrégats d'argon (Ar2+ et Ar3+) avec une cible d'argon atomique dans la gamme des énergies du keV. Toutes les voies de fragmentation : la dissociation induite par collision (CID) et l'échange de charge dissociatif (DCT) sont analysées par la corrélation vectorielle de tous les fragments détectés en coïncidence. En particulier, nous avons montré que le processus DCT dépendait fortement de l'énergie interne initiale de l'agrégat (i.e. du défaut de résonance). La comparaison de diverses observables mesurées en collision Ar2+-Ar et Ar3+-Ar nous a conduit à conclure que les agrégats Ar3+ produits dans notre source ont majoritairement la structure d'un dimère chargé (Ar2+) autour duquel orbite un troisième atome peu lié.The aim of this work is the development of a fast multi-hit position and time sensitive detector with zero dead-time for heavy particles in the keV energy range. This new type of detector makes use of a micro-channel plates MCP assembly and combines a detection based on delay line anode with a simultaneous particle imaging provided by CCD-camera. The time pickup accuracy is enhanced by digitalizing the MCP biasing signal. This detector, operating at kHz repetition rate, allows a position resolution better than 100 m and a time resolution better than 100 ps to be achieved.We have studied the fragmentation induced by collision of small ionic argon clusters (Ar2+ and Ar3+) with an atomic argon target at keV energies range. All the fragmentation channels: collision induced dissociation (CID) and dissociative charge transfer (DCT) have been analysed by the method of vectorial correlation of all the fragments detected in coincidence. The importance of electronic processes in these collision systems is demonstrated through various results. The dependence of the electron transfer on the initial internal energy of the cluster has been stressed out. Ar3+ has been found to be mainly formed of a strongly bound Ar2+ core surrounded by loosely linked Ar atom.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Incidence and predictors of bleeding in ACS patients treated with PCI and prasugrel or ticagrelor: An analysis from the RENAMI registry

OBJECTIVES To evaluate "real life" incidence and independent predictors of major bleeding defined in ACS patients treated with PCI and current standard antithrombotic therapy with prasugrel or ticagrelor. METHODS AND RESULTS The RENAMI project is a multicenter retrospective observational registry enrolling 4424 patients with ACS treated with PCI and prasugrel or ticagrelor plus aspirin. Primary endpoint was MACE (major adverse cardiovascular events). Secondary endpoints included each component of MACE, cardiovascular death (CV death), recurrence of ACS (reACS) and stroke. Eighty three (1.8%) patients developed out of hospital major bleedings after 14.1 ± 6.2 months. These patients had higher rates of MACE (14.5% vs 4.4%; p = 0.001) and of all-cause death (11% vs 2.1%; p 75 years (OR 2.00; 95% CI 1.18-3.41; p = 0.010) and female sex (OR 1.66; 95% CI 1.02-2.70; p = 0.041). BARC 3-5 bleeding was independently associated with all-cause mortality (OR 3.46; 95% CI 1.64-7.31; p 0.001). CONCLUSION In ACS patients treated with PCI and ticagrelor or prasugrel, BARC 3-5 bleedings despite being uncommon negatively impacted on prognosis. Old and female patients are at increased risk, offering clinical indications for tailoring dual antiplatelet therapy