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M Borromeo

Publications and source records attributed to M Borromeo.

9 recordsLinked to original sources
PubMed2002

String ratchets: ac driven asymmetric kinks.

We simulated numerically the time evolution of a one-kink bearing, damped elastic string sitting on noiseless periodic substrates of two types: (I) asymmetric, time independent, (II) symmetric, periodically deformable. An asymmetric kink subjected to an ac drive is shown to drift steadily with finite average speed independent of its initial kinetic conditions. In the overdamped regime the resulting net kink transport can be attributed to the rectification of the Brownian motion of a pointlike particle with oscillating mass. For intermediate to low damping completely different features show up, due to the finite size of the objects being transported; in particular, the kink current hits a maximum for an optimal value of the damping constant, resonates at the kink internal-mode frequency and, finally, reverses sign within a certain range of the drive parameters.

Journal Article↗
PubMed2002

Deterministic ratchets: route to diffusive transport.

The rectification efficiency of an underdamped ratchet operated in the adiabatic regime increases according to a scaling current-amplitude curve as the damping constant approaches a critical threshold; below threshold the rectified signal becomes extremely irregular and eventually its time average drops to zero. Periodic (locked) and diffusive (fully chaotic) trajectories coexist on fine tuning the amplitude of the input signal. The transition from regular to chaotic transport in noiseless ratchets has been studied numerically.

Journal Article↗
PubMed2000

Backward-to-forward jump rates on a tilted periodic substrate

Driven diffusion of a Brownian particle along a one-dimensional lattice is investigated numerically on decreasing its damping constant. The notions of multiple jumps, jump reversal, and backward-to-forward rates are discussed in detail. In particular, we conclude that in the underdamped limit backward jumps are suppressed relative to forward jumps more effectively than previously assumed. The dependence of such a drive-controlled mechanism on the damping constant and the temperature is interpreted analytically.

Journal Article↗
PubMed1989

Campylobacter pylori--a role in non-ulcer dyspepsia?

Non-ulcer dyspepsia (NUD) is a common complaint in which no systematic illness or organic proximal alimentary tract disease can be identified. The pathophysiology of NUD is probably heterogeneous. Eighty-two subjects with NUD were studied in a prospective randomized placebo-controlled study to assess the efficacy of colloidal bismuth subcitrate (CBS) chewable tablets at a dose of four tablets daily for 1 month. The role of Campylobacter pylori and associated histological gastritis was evaluated. Sixty-one percent of NUD patients had C. pylori in the gastric antrum compared with 25% of age-matched controls. C. pylori was associated with acute and chronic inflammation (P less than 0.001) in the antrum. C. pylori was cleared in 59% of CBS-treated subjects compared with only 4% placebo (P less than 0.05). Both acute and chronic inflammation improved in subjects cleared of bacteria. Clearance of C. pylori and histological improvement was associated with a significant decrease in symptoms. In C. pylori negative subjects improvement in symptoms occurred in both the placebo and active treatment groups. This study would suggest that C. pylori and associated histological gastritis may play a role in non-ulcer dyspepsia.

Adult↗