Correlated detection of neutral and charged fragments in collision induced fragmentation of molecular clusters

accepté dans International Journal of Mass SpectrometryWe report on collision induced fragmentation of isolated molecular nanosystems studied with an event by event detection technique including the correlated detection of both neutral and charged fragments. This work focuses on the dissociation induced by collisional excitation without ionisation and electron-capture. Two molecular cluster cations are investigated: the collision of protonated hydrogen clusters at 60keV/amu with helium targets and that of protonated water clusters at 8keV with an argon gas. In addition to the molecular evaporation process the dissociation channel leading to the production of the H3+ or H3O+ molecular cations (loss of all the molecules) is observed with an unexpected abundance. The cross section for the production of these cations is observed to increase with the number of molecules in the cluster. Such an increase cannot be associated with the direct collisional excitation of the cation core of the cluster

Charge-Transfer Induced Dissociation in the H+(H2O)3-Ar collisions observed with the COINTOF mass spectrometer

Electron-capture in collisions of singly charged protonated water cluster H+(H2O)3, ions with Ar atoms is studied at the impact energy of 8 keV in the frame of the COrrelated Ion and Neutral fragments Time-Of-Flight, COINTOF, technique. In contrast to methods based only on the detection of the charged fragments, dissociation induced by collisional-excitation and electron-capture induced dissociation can be simultaneously recorded in the present set-up. Time of flight measurement of both neutral and corresponding charged species resulting from the charge-exchange process leads to the direct observation of the dissociation of the neutralized protonated water cluster. Thus, the present COINTOF method provides new valuable insights into the collision processes through the detection of produced neutral fragments. Moreover, it opens new possibilities to measure kinetic energy release also in the dissociation of the produced neutrals, which is our future endeavour in the development of the presented COINTOF set up

Probing the liquid-t-gas like phase transition in a cluster via a caloric curve

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Reply to the comment on direct experimental evidence for a negative heat capacity in the liquid to gas phase transition in hydrogen cluster ions backbending of the caloric curve

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Total partial and electron-capture cross sections for ionization of water vapor by 20-150 keV protons

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Collision induced cluster fragmentation: From fragment size distributions to the caloric curve

IPMInternational audienceWe report on a cluster fragmentation study involving collisions of high-energy (60 keV/amu) H3+(H2)m hydrogen cluster ions (m=9, 11) with atomic helium or fullerenes. The experimental characterisation of the cluster fragmentation not only by the average fragment size distribution but also by a statistical analysis of the fragmentation events has become possible owing to a recently developed multi-coincidence technique in which all the fragments of all collisions occurring in the experiment are mass analysed on an event-by-event basis. By selecting specific decay reactions we can start after the energizing collision with a microcanonical cluster ion ensemble of fixed excitation energy. From the respective fragment distributions for these selected decay reactions we derive corresponding temperatures of the decaying cluster ions. The relation between this temperature and the excitation energy (caloric curve) exhibits the typical prerequisites of a first order phase transition in a finite system, in the present case signalling the transition from a bound cluster type situation to the free gas phase

Femoral deficiency reconstruction using a hydroxyapatite-coated locked modular stem. A series of 43 total hip revisions

SummaryIntroductionWe report a continuous prospective series of patients operated on for total hip prosthesis femoral component loosening involving a bone defect. Reconstruction was performed using a hydroxyapatite-coated locked modular stem. The study's objective was to assess medium term clinical and X-ray results obtained with this original concept.Materials and methodsThe patients included received a REEF® (DePuy) femoral implant for aseptic loosening or loosening associated with a periprosthetic fracture. Implantation was systematically accompanied by an extended trochanteric osteotomy (ETO). Patients were followed up prospectively by clinical and X-ray examination. Their loosening was graded at inclusion according to Vives’ classification as revised by SOFCOT in 1999. Analysis focused on actuarial implant survivorship, dislocation and the bone/implant interface.ResultsForty-three hips were included: mean follow-up was 58.2 months (12–92) and mean age at surgery was 72.4 years (37–94). The main indications were severe bone loss rated grade III (n=15) or IV (n=16) according to the SOFCOT classification. There was one long-term failure, involving implant fracture secondary to nonunion of the femoral shaft. Mean Postel and Merle d’Aubigné (PMA) clinical assessment score increased from six preoperatively to 14.5 at end of follow-up. X-ray analysis found no stem migration by end of follow-up. There was consistent consolidation of the ETO around the stem, except in one case of stem fracture which evolved into tight nonunion. In terms of metaphyseal integration, five patients showed radiolucency without evolution over follow-up, and eight had severe calcar cortical atrophy at end of follow-up. Mean 5-year actuarial survivorship was 97.7±2.3%, with a 2% incidence of dislocation.DiscussionThe complications rate was low, and results were comparable with those reported in the literature. The study confirmed the interest of the extended trochanteric osteotomy exposure and the effectiveness of the hydroxyapatite-coated interlocked modular stem concept in the treatment of hip prosthesis loosening with femoral bone loss (involving or not the cortex). On analysis, the one case of failure does not proscribe the surgical technique employed. Implant osseointegration was difficult to analyze. The extent of the surgical approach and of its corresponding sequels, combined with the complexity of adjusting the implant, however, restrict this surgical option indications to level III and IV cases of femoral loosening.Level of evidence: level IV; therapeutic study

Electron-loss and target ionization cross sections for water vapor by 20-150 keV neutral atomic hydrogen impact

A complete set of cross sections is reported for the ionization of water molecules by neutral atomic hydrogen impact at velocities of the order of the Bragg peak. The measured relative cross sections are normalized by comparison with proton impact results for the same target conditions and previous absolute data. Event by event coincidence analysis of the product ions and the projectile enables partial cross sections for target ionization and target plus projectile ionization to be determined, as well as total cross sections for electron loss reactions.Comment: To be published in Chemical Physics Letter

Is nasal carriage of the main acquisition pathway for surgical-site infection in orthopaedic surgery?

International audienceThe endogenous or exogenous origin of , responsible for orthopaedic surgical-site infections (SSI), remains debated. We conducted a multicentre prospective cohort study to analyse the respective part of exogenous contamination and endogenous self-inoculation by during elective orthopaedic surgery. The nose of each consecutive patient was sampled before surgery. Strains of isolated from the nose and the wound, in the case of SSI, were compared by antibiotypes or pulsed-field gel electrophoresis (PFGE). A total of 3,908 consecutive patients undergoing orthopaedic surgery were included. Seventy-seven patients developed an SSI (2%), including 22 related to (0.6%). was isolated from the nose of 790 patients (20.2%) at the time of surgery. In the multivariate analysis, nasal carriage was found to be a risk factor for SSI in orthopaedic surgery. However, only nine subjects exhibiting SSI had been found to be carriers before surgery: when compared, three pairs of strains were considered to be different and six similar. In most cases of SSI, either an endogenous origin could not be demonstrated or pre-operative nasal colonisation retrieved a strain that was different from the one recovered from the surgical sit

Event by event analysis of collision induced cluster ion fragmentation: sequential monomer evaporation versus fission reactions

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