RESUMO
Free-electron lasers (FELs) currently represent a step forward on time-resolved investigations on any phase of matter through pump-probe methods involving FELs and laser beams. That class of experiments requires an accurate spatial and temporal superposition of pump and probe beams on the sample, which at present is still a critical procedure. More efficient approaches are demanded to quickly achieve the superposition and synchronization of the beams. Here, we present what we believe is a novel technique based on an integrated device allowing the simultaneous characterization and the fast spatial and temporal overlapping of the beams, reducing the alignment procedure from hours to minutes.
RESUMO
Multi-walled carbon nanotubes (CNTs) have been grown in situ on a SiO 2 substrate and used as gas sensors. For this purpose, the voltage response of the CNTs as a function of time has been used to detect H 2 and CO 2 at various concentrations by supplying a constant current to the system. The analysis of both adsorptions and desorptions curves has revealed two different exponential behaviours for each curve. The study of the characteristic times, obtained from the fitting of the data, has allowed us to identify separately chemisorption and physisorption processes on the CNTs.
RESUMO
Since 1992 we have performed laparoscopic cholecystectomy with 3 trocars (10, 10 and 5 mm) while most surgeons use 4. In our 10 years of experience a total of 1,243 cholecystectomies have been performed with the 3-trocar technique. The overall conversion rate is 0.75%. In 5.7% of cases we used a fourth trocar in order to avoid anatomical difficulties or to perform intraoperative cholangiography. All interventions are technically feasible, even in sclerotic cholecystitis and in emergency operations. We describe this technique which can be considered an economic and cosmetically satisfying alternative, that is safe and effective for the patient and easy to perform for the surgeon.
