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Mario Salerno

Publications and source records attributed to Mario Salerno.

14 recordsLinked to original sources
PubMed2006

Discrete nonlinear Schrödinger equations with arbitrarily high-order nonlinearities.

A class of discrete nonlinear Schrödinger equations with arbitrarily high-order nonlinearities is introduced. These equations are derived from the same Hamiltonian using different Poisson brackets and include as particular cases the saturable discrete nonlinear Schrödinger equation and the Ablowitz-Ladik equation. As a common property, these equations possess three kinds of exact analytical stationary solutions for which the Peierls-Nabarro barrier is zero. Several properties of these solutions, including stability, discrete breathers, and moving solutions, are investigated.

Journal Article↗
PubMed2006

Discrete soliton ratchets driven by biharmonic fields.

Directed motion of topological solitons (kinks or antikinks) in the damped and ac-driven discrete sine-Gordon system is investigated. We show that if the driving field breaks certain time-space symmetries, the soliton can perform unidirectional motion. The phenomenon resembles the well known effects of ratchet transport and nonlinear harmonic mixing. Direction of the motion and its velocity depends on the shape of the ac drive. Necessary conditions for the occurrence of the effect are formulated. In comparison with the previously studied continuum case, the discrete case shows a number of new features: nonzero depinning threshold for the driving amplitude, locking to the rational fractions of the driving frequency, and diffusive ratchet motion in the case of weak intersite coupling.

Journal Article↗
PubMed2005

Analytical approach to soliton ratchets in asymmetric potentials.

We use soliton perturbation theory and collective coordinate ansatz to investigate the mechanism of soliton ratchets in a driven and damped asymmetric double sine-Gordon equation. We show that, at the second order of the perturbation scheme, the soliton internal vibrations can couple effectively, in presence of damping, to the motion of the center of mass, giving rise to transport. An analytical expression for the mean velocity of the soliton is derived. The results of our analysis confirm the internal mode mechanism of soliton ratchets proposed in [Phys. Rev. E 65, 025602(R) (2002)].

Journal Article↗
PubMed2005

Double parametric resonance for matter-wave solitons in a time-modulated trap.

We analyze the motion of solitons in a self-attractive Bose-Einstein condensate, loaded into a quasi-one-dimensional parabolic potential trap, which is subjected to time-periodic modulation with an amplitude epsilon and frequency Omega. First, we apply the variational approximation, which gives rise to decoupled equations of motion for the center-of-mass coordinate of the soliton, xi (t), and its width a (t). The equation for xi (t) is the ordinary Mathieu equation (ME) (it is an exact equation that does not depend on the adopted ansatz), the equation for a (t) being a nonlinear generalization of the ME. Both equations give rise to the same map of instability zones in the (epsilon,Omega) plane, generated by the parametric resonances (PRs), if the instability is defined as the onset of growth of the amplitude of the parametrically driven oscillations. In this sense, the double PR is predicted. Direct simulations of the underlying Gross-Pitaevskii equation give rise to a qualitatively similar but quantitatively different stability map for oscillations of the soliton's width a (t). In the direct simulations, we identify the soliton dynamics as unstable if the instability (again, realized as indefinite growth of the amplitude of oscillations) can be detected during a time comparable with, or smaller than, the lifetime of the condensate (therefore accessible to experimental detection). Two-soliton configurations are also investigated. It is concluded that multiple collisions between solitons are elastic, and they do not affect the instability borders.

Journal Article↗
PubMed2005

Is physical training contraindicated in patients with deep vein thrombosis during cardiac rehabilitation?

Deep vein thrombosis is a potential complication in patients admitted to cardiac rehabilitation programs after acute coronary syndromes, episodes of acute congestive heart failure, and cardiac revascularization. A common clinical problem in these patients is to decide whether to start or continue physical training or not, given the risk of pulmonary embolism. Until definite evidence becomes available, careful patient selection and inpatient supervision may avoid the a priori withdrawal of such an important core component of cardiac rehabilitation programs.

Contraindications↗
PubMed2004

Deep vein thrombosis among patients entering cardiac rehabilitation after coronary artery bypass surgery.

BACKGROUND: Little information is available about the prevalence of deep vein thrombosis (DVT) after discharge from cardiac surgery units and its impact on rehabilitation programs. OBJECTIVES: To estimate the rate of DVT, in relation to different thromboprophylaxis strategies, in patients with a recent coronary artery bypass graft (CABG) entering cardiac rehabilitation. METHODS: Two hundred seventy consecutive patients admitted to three rehabilitation facilities after CABG surgery from 19 cardiac surgery units (male patients, 81%; mean +/- SD age, 64 +/- 9 years; interval after operation, 4 to 19 days) underwent serial leg venous ultrasound examination on admission to three rehabilitative units. RESULTS: At admission, antiplatelet treatment was present in all patients except 10 with absolute contraindications. In 171 patients (63%), heparin prophylaxis (low-molecular-weight heparin once daily, 87%; unfractionated heparin twice daily, 13%) was reported, limited to the early postoperative period (< or = 3 days) in 102 patients (38%). DVT was detected in 47 patients (17.4%). The rate of proximal and isolated distal DVT was 2.6% (7 cases) and 14.8% (40 cases), respectively. DVT was complicated in two cases (0.7%) by symptomatic pulmonary embolism, fatal in one case (0.4%). Clots were found in the leg contralateral to the saphenous vein harvest site in half of all DVT cases. Forty-three DVT cases (91%) were diagnosed at admission, while serial ultrasound testing allowed diagnosis of an additional 4 distal DVT cases. At multivariate analysis, female sex (p < 0.001) and length of stay in the surgery unit > 8 days (p < 0.05) were independently associated with risk of DVT in the rehabilitation setting. The adoption of heparin prophylaxis until discharge predicted the absence of DVT after adjustment for immobility (p < 0.05). CONCLUSIONS: This study showed a high rate of DVT in patients entering cardiac rehabilitation after CABG surgery. Wearing unilateral graded compression stockings after CABG surgery had limited efficacy, as clots were often localized in legs contralateral to the saphenous vein harvest site.

Coronary Artery Bypass↗
PubMed2004

Upper extremity deep vein thrombosis and pulmonary embolism after coronary bypass surgery: a case report and preliminary results from a prospective study evaluating patients during cardiac rehabilitation.

A 78-year-old woman with unstable angina underwent coronary bypass surgery with complete cardiac revascularization and no immediate postoperative complications. Six days after surgery, during hospitalization for cardiac rehabilitation, the patient developed severe respiratory distress and pulmonary embolism was diagnosed. Color duplex ultrasound revealed the presence of concomitant upper extremity deep vein thrombosis (UEDVT), ipsilateral to the site of placement of a central venous line, in the absence of lower extremity deep vein thrombosis. We describe this case and provide preliminary data from a prospective observational study evaluating the prevalence of catheter-related UEDVT and symptomatic pulmonary embolism (55 and 1.4% respectively) in a series of 71 consecutive coronary bypass surgery patients admitted to a cardiac rehabilitation facility. Catheter-related UEDVT and pulmonary embolism may complicate coronary bypass surgery and should be taken into consideration when managing patients after surgery.

Aged↗
PubMed2004

Newly diagnosed carotid atherosclerosis in patients with coronary artery disease admitted for cardiac rehabilitation.

BACKGROUND: The association of coronary artery disease (CAD) with carotid artery disease has been well documented. However, data focusing on CAD patients participating in cardiac rehabilitation programs are lacking. We studied the prevalence of newly diagnosed carotid artery disease in CAD patients admitted for cardiac rehabilitation. METHODS: We performed carotid ultrasonography in 168 angiographically confirmed CAD patients admitted to two facilities. Patients with previous cerebrovascular episodes or carotid imaging were excluded. RESULTS: Out of 168 patients considered (mean age 65 +/- 8 years; males 76%; chronic stable angina as the reason for cardiac rehabilitation 34%, silent ischemia 14%, and acute coronary syndrome 52%), 149 (89%) were found to have carotid atherosclerosis. Carotid atherosclerosis was present in 83, 87, 89, and 93% of patients with one-, two- and three-vessel disease and left main stem CAD respectively. Patients with severe CAD (i.e. three-vessel or left main stem) had a higher prevalence of > or = 50% carotid stenosis as compared to patients without severe CAD (26 vs 8%, p < 0.05). Severe CAD had a high negative (92%) and a low positive (26%) predictive value for the presence of > or = 50% carotid stenosis. CONCLUSIONS: Silent and previously undetected carotid atherosclerosis is frequent in CAD patients admitted for cardiac rehabilitation. The absence of severe CAD reflects the absence of > or = 50% carotid stenosis.

Aged↗
PubMed2003

Stable two-dimensional dispersion-managed soliton.

The existence of a dispersion-managed soliton in two-dimensional nonlinear Schrödinger equation with periodically varying dispersion has been explored. The averaged equations for the soliton width and chirp are obtained which successfully describe the long time evolution of the soliton. The slow dynamics of the soliton around the fixed points for the width and chirp are investigated and the corresponding frequencies are calculated. Analytical predictions are confirmed by direct partial differential equation (PDE) and ordinary differential equation (ODE) simulations. Application to a Bose-Einstein condensate in optical lattice is discussed. The existence of a dispersion-managed matter-wave soliton in such system is shown.

Journal Article↗
PubMed2003

Prevalence and prevention of venous thromboembolism in patients with acute exacerbations of COPD.

BACKGROUND: Little information exists on the prevalence and prevention of deep vein thrombosis (DVT) and pulmonary embolism (PE) in patients admitted for acute exacerbations of chronic obstructive pulmonary disease (COPD). OBJECTIVE: To review available literature, we performed a Medline search on papers published on this topic between 1966 and 2003. DATA SYNTHESIS: Pulmonary emboli have been frequently found (up to 30% of cases) in autoptic series that included patients who died from acute exacerbation of COPD, while the real incidence of PE during exacerbation has never been prospectively evaluated by large-scale clinical studies. Diagnosis of concomitant PE in these patients is often missed because symptoms of acute exacerbation of COPD may mimic PE, and non-invasive evaluation by pulmonary scintigraphy or CT scan is less specific. Even if not fatal, undetected and untreated PE may lead to long-term morbidity from pulmonary hypertension and predispose to recurrent venous thromboembolism (VTE). DVT of the lower extremities affects about 10% of patients with acute exacerbation of COPD at admission, but the rate is likely to be underestimated. The results of clinical trials conducted on general medical patients, including COPD patients, indicate that unfractionated heparin (UH) and low molecular weight heparin (LMWH) significantly reduce VTE rates. However, subgroup data on COPD patients are generally not available. In a single randomised, controlled trial specifically conducted on COPD patients, nadroparin reduced the rate of DVT from 28% to 15% without affecting mortality. CONCLUSIONS: Despite a substantial lack of consistent data, VTE appears as a major threat to patients admitted for acute exacerbation of COPD, and pharmacologic prophylaxis should be considered in all high risk situations. However, methodologically rigorous studies in this setting are still needed.

Acute Disease↗
PubMed2002

Soliton ratchetlike dynamics by ac forces with harmonic mixing.

The possibility of unidirectional motion of a kink (topological soliton) of a dissipative sine-Gordon equation in the presence of ac forces with harmonic mixing (at least biharmonic) and of zero mean, is presented. The dependence of the kink mean velocity on system parameters is investigated numerically and the results are compared with a perturbation analysis based on a point-particle representation of the soliton. We find that first order perturbative calculations lead to incomplete descriptions, due to the important role played by the soliton-phonon interaction in establishing the phenomenon. The role played by the temporal symmetry of the system in establishing soliton dc motions that resemble usual soliton ratchets, is also emphasized. In particular, we show the existence of an asymmetric internal mode on the kink profile that couples to the kink translational mode through the damping in the system. Effective soliton transport is achieved when the internal mode and the external force get phase locked. We find that for kinks driven by biharmonic drivers consisting of the superposition of a fundamental driver with its first odd harmonic, the transport arises only due to this internal mode mechanism, while for biharmonic drivers with even harmonic superposition, also a point-particle contribution to the drift velocity is present. The phenomenon is robust enough to survive the presence of thermal noise in the system and can lead to several interesting physical applications.

Journal Article↗
PubMed2002

Soliton ratchets.

The mechanism underlying the soliton ratchet, both in absence and in presence of noise, is investigated. We show the existence of an asymmetric internal mode on the soliton profile that couples, through the damping in the system, to the soliton translational mode. Effective soliton transport is achieved when the internal mode and the external force are phase locked. We use as a working model a generalized double sine-Gordon equation. The phenomenon is expected to be valid for generic soliton systems.

Journal Article↗
PubMed2002

Efficacy of a short-course intensive rehabilitation program in patients with moderate-to-severe intermittent claudication.

BACKGROUND: Many rehabilitation programs for intermittent claudication include physical training for several months, since the outcome of short-course protocols is still unclear. The aim of this study was to evaluate the efficacy of a short course of exercise therapy in patients with moderate-to-severe intermittent claudication in terms of walking distance variations. METHODS: Twenty-six patients (males 88%, mean age 59 +/- 8 years, ankle-brachial index < or = 0.8 and < or = 0.5 before and after exercise respectively) were evaluated. Moderate-to-severe stenoses or occlusions were localized at color Doppler scanning of the abdominal aorta/iliac arteries and femoral/popliteal/tibial arteries in 15 and 31% of patients respectively, while in 54% of cases both the proximal and distal sites were involved. The initial and absolute claudication distances were recorded by means of the constant treadmill test (3 km/hour speed, 0% grade) at the time of presentation and after a short-course comprehensive rehabilitation program (4 week duration) including physical training, educational intervention, psychological support, and cardiovascular risk management. RESULTS: At the end of the program, 1 patient (4%) became asymptomatic (walked > 1000 m without pain). In 25 patients who still developed pain, the average increase in the initial claudication distance was 132% (from 75 to 174 m). Among these, 20 patients (77%) were still unable to complete the treadmill test due to maximal claudication pain, but the absolute claudication distance increased by 87% from 204 to 381 m (p < 0.05). No cardiovascular complication occurred during the study period. Major clinical variables failed to predict an unsatisfactory increase in walking capacity. CONCLUSIONS: Short-course training programs enhance the walking ability even in patients with moderate-to-severe intermittent claudication and seem to be well tolerated, supporting their widespread use in rehabilitation centers.

Aged↗