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Biomedical subjects

L Moriconi

Publications and source records attributed to L Moriconi.

At least 19 recordsLinked to original sources
PubMed2005

Langevin simulation of the chirally decomposed sine-Gordon model.

A large class of quantum and statistical field theoretical models, encompassing relevant condensed matter and non-Abelian gauge systems, are defined in terms of complex actions. As the ordinary Monte Carlo methods are useless in dealing with these models, alternative computational strategies have been proposed along the years. The Langevin technique, in particular, is known to be frequently plagued with difficulties such as strong numerical instabilities or subtle ergodic behavior. Regarding the chirally decomposed version of the sine-Gordon model as a prototypical case for the failure of the Langevin approach, we devise a truncation prescription in the stochastic differential equations which yields numerical stability and is assumed not to spoil the Berezinskii-Kosterlitz-Thouless transition. This conjecture is supported by a finite size scaling analysis, whereby a massive phase ending at a line of critical points is clearly observed for the truncated stochastic model.

Journal Article↗
PubMed2004

Stochastic perturbations in vortex-tube dynamics.

A dual lattice vortex formulation of homogeneous turbulence is developed, within the Martin-Siggia-Rose field theoretical approach. It consists of a generalization of the usual dipole version of the Navier-Stokes equations, known to hold in the limit of vanishing external forcing. We investigate, as a straightforward application of our formalism, the dynamics of closed vortex tubes, randomly stirred at large length scales by Gaussian stochastic forces. We find that besides the usual self-induced propagation, the vortex tube evolution may be effectively modeled through the introduction of an additional white-noise correlated velocity field background. The resulting phenomenological picture is closely related to observations previously reported from a wavelet decomposition analysis of turbulent flow configurations.

Journal Article↗
PubMed2004

Statistics of intense turbulent vorticity events.

We investigate statistical properties of vorticity fluctuations in fully developed turbulence, which are known to exhibit a strong intermittent behavior. Taking as the starting point the Navier-Stokes equations with a random force term correlated at large scales, we obtain in the high Reynolds number regime a closed analytical expression for the probability distribution function of an arbitrary component of the vorticity field. The central idea underlying the analysis consists in the restriction of the velocity configurational phase-space to a particular sector where the rate of strain and the rotation tensors can be locally regarded as slow and fast degrees of freedom, respectively. This prescription is implemented along the Martin-Siggia-Rose functional framework, whereby instantons and perturbations around them are taken into account within a steepest-descent approach.

Journal Article↗
PubMed2003

Extended self-similarity in the two-dimensional metal-insulator transition.

We show that extended self-similarity, a scaling phenomenon first observed in classical turbulent flows, holds for a two-dimensional metal-insulator transition that belongs to the universality class of random Dirac fermions. Deviations from multifractality, which in turbulence are due to the dominance of diffusive processes at small scales, appear in the condensed-matter context as a large-scale, finite-size effect related to the imposition of an infrared cutoff in the field theory formulation. We propose a phenomenological interpretation of extended self-similarity in the metal-insulator transition within the framework of the random beta-model description of multifractal sets. As a natural step, our discussion is bridged to the analysis of strange attractors, where crossovers between multifractal and nonmultifractal regimes are found and extended self-similarity turns out to be verified as well.

Journal Article↗
PubMed2002

Circulation-strain sum rule in stochastic magnetohydrodynamics.

We study probability density functions (PDFs) of the circulation of velocity and magnetic fields in magnetohydrodynamics, computed for a circular contour within inertial range scales. The analysis is based on the instanton method as adapted to the Martin-Siggia-Rose field theory formalism. While in the viscous limit the expected Gaussian behavior of fluctuations is indeed verified, the case of vanishing viscosity is not suitable of a direct saddle-point treatment. To study the latter limit, we take into account fluctuations around quasistatic background fields, which allows us to derive a sum rule relating PDFs of the circulation observables and the rate of the strain tensor. A simple inspection of the sum rule definition leads straightforwardly to the algebraic decay rho(Gamma)-1/Gamma(2) at the circulation PDF tails.

Journal Article↗
PubMed1999

Effects of oral administration of heparan sulphate in the rat remnant kidney model.

Heparins are useful for the protection of residual renal function in several nephropathies, but the anticoagulant action and the need of parenteral administration are two main drawbacks limiting their use in chronic renal failure patients. Heparan sulphate (HS) is a heparin-like mucopolysaccharide devoid of anticoagulant action and active orally. In this study, the effects of HS oral administration have been evaluated in 18 subtotally nephrectomized rats;18 untreated remnant kidney rats served as control. No mortality was observed in the HS-treated rats, whereas in the control rats the survival rate was 72.2% at 18 weeks. At the end of the study, HS-treated rats showed lower urinary protein excretion (44 +/- 22 vs. 80 +/- 54 mg/24 h, p < 0.01), lower urea plasma levels (75 +/- 34 vs. 134 +/- 105 mg/dl, p < 0.01) and higher creatinine clearance (66 +/- 15 vs. 47 +/- 21 ml/min. 10(2), p < 0.05) than control rats. Remnant kidney weight (2.3 +/- 1.1 vs. 1.3 +/- 0.2 g, p < 0.01) and heart weight (1.3 +/- 0.2 vs. 1.1 +/- 0.1 g, p < 0.05) were greater in the control than in the HS-treated rats, as well as the systemic blood pressure values (167 +/- 19 vs. 115 +/- 32 mm Hg, respectively, p < 0.001). The remnant kidney histological examination in the HS-treated rats showed a lower prevalence of glomerular sclerosis, mesangial proliferation, and a much less evident tubulointerstitial damage than in controls. The antiproliferative and anti-inflammatory actions of HS together with its protective action on the endothelium are the putative mechanisms that could account for our findings. In conclusion, the present study supports evidence of an antiproteinuric and a renoprotective effect of orally administered HS in subtotally nephrectomized rats. This is in keeping with the well-known effects exerted also by other heparins, but the effectiveness of an orally available heparin-like product in this animal model could suggest the possibility of a clinical use also in progressing chronic renal failure patients.

Administration, Oral↗
PubMed1997

Predictors of renal outcome in diffuse proliferative glomerulonephritis in systemic lupus erythematosus.

The occurrence of nephritis is considered to be the most important factor influencing the prognosis in systemic lupus erythematosus (SLE). Despite the apparent histological similarity of the lesions, however, patients with diffuse proliferative glomerulonephritis (DPGN) may exhibit different outcomes. A retrospective study was carried out on 81 SLE patients with DPGN to evaluate the prognostic significance of different clinical, serological and histological variables; in particular, 95 renal biopsies were re-evaluated and the activity and chronicity indices for the patients were determined. A positive correlation was observed between the presence of chronic lesions on renal biopsy and a poor renal outcome (< 0.001). Moreover, in the repeat biopsies the patients with a poor outcome showed a higher degree of chronic lesions. Active lesions and other clinical and serological parameters did not correlate with the outcome.

Adolescent↗
PubMed1994

Selective techniques of apheresis in polyneuropathy associated with monoclonal gammopathy of undetermined significance.

Three cases affected by peripheral neuropathy associated to monoclonal gammopathy of undetermined significance (MGUS) were treated by using selective apheretic techniques, chosen on the basis of the serological characteristics of the gammopathy. Double filtration plasmapheresis was used in the first two cases, respectively affected by gammopathy of IgM type, kappa chains, and IgG type, lambda chains; protein A immunoadsorption in Case 3 with IgG type, lambda chains. Apheretic sessions were performed for three-four months, in association with low-dose immunosuppressive therapy. Clear and stable improvement of the neuropathy over 12-month follow-up period was observed both from a clinical and electrophysiological point of view. It is concluded that in peripheral neuropathy associated with MGUS selective techniques of apheresis can prove useful both in obtaining positive results and in avoiding the collateral effect of the original plasma exchange.

Adult↗
PubMed1993

Cryoglobulinemic membranoproliferative glomerulonephritis associated with hepatitis C virus.

A striking association between hepatitis C virus (HCV) and mixed cryoglobulinemia (MC) has been reported by various authors, regardless of the presence of chronic hepatitis. The aim of this study is to evaluate the prevalence of HCV-related markers in cryoglobulinemic membranoproliferative glomerulonephritis (MPGN) which is one of the most severe complications of MC. Antibodies against HCV have been detected by second-generation Chiron ELISA and RIBA in 26/26 (100%) cryoglobulinemic MPGN. In addition, serum HCV RNA, expression of the ongoing viral replication, was present in 7/7 patients by the polymerase chain reaction technique. The high percentage of anti-HCV seropositivity suggests that this virus may play an important role in the pathogenesis of this immunemediated glomerulonephritis.

Cryoglobulinemia↗
PubMed1993

Low-antigen-content diet in the treatment of patients with IgA nephropathy.

Since dietary macromolecular antigens can be involved in the pathogenesis of IgA nephropathy (IgAN), the effect of a low-antigen-content diet was evaluated in 21 patients (10 women, 11 men, mean age 27.7 +/- 10 years) with immunohistochemical findings of active IgAN. The diet was followed for a 14-24-week period (mean 18.8 +/- 6); in all cases the effects of the treatment were evaluated by clinical and serological parameters, and in 11 patients also by repeat renal biopsy. After dietetic therapy a significant reduction of urinary proteins was recorded (P < 0.001); in particular, heavy proteinuria (> 1 g/day), present in 12 cases during the 6 months preceding the treatment, was markedly reduced or disappeared in 11. At post-treatment control biopsy mesangial and parietal deposits of immunoglobulins, complement C5 fraction and fibrinogen were significantly reduced. The improvement of the objective parameters such as heavy proteinuria, a strong predictor of a poor prognosis, and of immunohistochemical alterations indicate that a low-antigen diet can positively affect patients with IgAN. These results could be ascribed to a reduction of nephritogenic food antigen input and to a putative functional restoration of the mononuclear phagocytic system.

Adolescent↗