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Context. Meteoroid impacts are an important source of neutral atoms in the exosphere of Mercury. Impacting particles of size smaller than 1 cm have been proposed to be the major contribution to exospheric gases. However, our knowledge of the fluxes and impact velocities of different sizes is based on old extrapolations of similar quantities on Earth. Aims. We compute by means of N-body numerical integrations the orbital evolution of a large number of dust particles supposedly produced in the Main Belt. They migrate inward under the effect of drag forces until they encounter a terrestrial planet or eventually fall into the Sun. From our numerical simulations, we compute the flux of particles hitting Mercury's surface and the corresponding distribution of impact velocities. Methods. The orbital evolution of dust particles of different sizes is computed with a numerical code based on a physical model developed previously by Marzari & Vanzani (1994, A&A, 283, 275). It includes the effects of Poynting-Robertson drag, solar wind drag, and planetary perturbations. A precise calibration of the particle flux on Mercury has been performed by comparing our model predictions for dust infall on to Earth with observational data. Results. We provide predictions of the flux to different size particles impacting Mercury and their collisional velocity distribution. We compare our results with previous estimates and we find that these collisional velocities are lower but that the fluxes are significantly higher.

Mass accretion rate on Earth is an important tool to discriminate the extraterrestrial nature of particles or isotopes found in different environments on the ground. In this context, the knowledge of the micrometeoroid flux arriving in our atmosphere is a key parameter and it needs to be calibrated. We provide a new calibration of the flux of submillimeter particles impacting the Earth in the mass range from 10 −9 to 10 −4 g, derived by computing a specific scaling law for impact craters on the Long Duration Exposure Facility (LDEF). We use the hydrocode iSALE to calculate the outcome of impacts on LDEF, adopting realistic impact velocities for dust particles derived from the numerical integration of their trajectories assuming either asteroidal or cometary origin. We estimate a particle mass accretion rate of (7.4 ± 1.0) × 10 6 kg yr −1 if the Main Belt is assumed as the major source of dust, while it reduces to (4.2 ± 0.5) × 10 6 kg yr −1 if cometary dust dominates. These values agree with the estimates provided by independent measurements made on ice core and ocean sediments and based on the abundance of some elements in the samples.

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Background and study aims In recent years, it has been reported that early Barrett’s and esophagogastric junction (EGJ) neoplasia can be effectively and safely treated using endoscopic mucosal resection (EMR) and endoscopic submucosal dissection (ESD). Multiband mucosectomy (MBM) appears to be the safest EMR method. The aim of this systematic review is to assess the safety and efficacy of MBM compared with ESD for the treatment of early neoplasia in Barrett’s or at the EGJ. Methods A literature review of studies published up to May 2013 on EMR and ESD for early Barrett’s esophagus (BE) neoplasia and adenocarcinoma at the EGJ was performed through MEDLINE, EMBASE and the Cochrane Library. Results on outcome parameters such as number of curative resections, complications and procedure times are compared and reported. Results A total of 16 studies met the inclusion criteria for analysis in this study. There were no significant differences in recurrence rates when comparing EMR (10/380, 2.6 %) to ESD (1/333, 0.7 %) (OR 8.55; 95 %CI, 0.91 – 80.0, P = 0.06). All recurrences after EMR were treated with additional endoscopic resection. The risks of delayed bleeding, perforation and stricture rates in both groups were similar. The procedure was considerably less time-consuming in the EMR group (mean time 36.7 min, 95 %CI, 34.5 – 38.9) than in the ESD group (mean time 83.3 min, 95 %CI, 57.4 – 109.2). Conclusions The MBM technique for EMR is as effective as ESD when comparing outcomes related to recurrence and complication rates for the treatment of early Barrett’s or EGJ neoplasia. The MBM technique is considerably less time-consuming.