15 research outputs found
Untargeted NMR Metabolomics Reveals Alternative Biomarkers and Pathways in Alkaptonuria
Alkaptonuria (AKU) is an ultra-rare metabolic disease caused by the accumulation of homogentisic acid (HGA), an intermediate product of phenylalanine and tyrosine degradation. AKU patients carry variants within the gene coding for homogentisate-1,2-dioxygenase (HGD), which are responsible for reducing the enzyme catalytic activity and the consequent accumulation of HGA and formation of a dark pigment called the ochronotic pigment. In individuals with alkaptonuria, ochronotic pigmentation of connective tissues occurs, leading to inflammation, degeneration, and eventually osteoarthritis. The molecular mechanisms underlying the multisystemic development of the disease severity are still not fully understood and are mostly limited to the metabolic pathway segment involving HGA. In this view, untargeted metabolomics of biofluids in metabolic diseases allows the direct investigation of molecular species involved in pathways alterations and their interplay. Here, we present the untargeted metabolomics study of AKU through the nuclear magnetic resonance of urine from a cohort of Italian patients; the study aims to unravel molecular species and mechanisms underlying the AKU metabolic disorder. Dysregulation of metabolic pathways other than the HGD route and new potential biomarkers beyond homogentisate are suggested, contributing to a more comprehensive molecular signature definition for AKU and the development of future adjuvant treatment. © 2022 by the authors
Is Quantum Chaos Weaker Than Classical Chaos?
We investigate chaotic behavior in a 2-D Hamiltonian system - oscillators
with anharmonic coupling. We compare the classical system with quantum system.
Via the quantum action, we construct Poincar\'{e} sections and compute Lyapunov
exponents for the quantum system. We find that the quantum system is globally
less chaotic than the classical system. We also observe with increasing energy
the distribution of Lyapunov exponts approaching a Gaussian with a strong
correlation between its mean value and energy.Comment: text (LaTeX) + 7 figs.(ps
Chaos in effective classical and quantum dynamics
We investigate the dynamics of classical and quantum N-component phi^4
oscillators in the presence of an external field. In the large N limit the
effective dynamics is described by two-degree-of-freedom classical Hamiltonian
systems. In the classical model we observe chaotic orbits for any value of the
external field, while in the quantum case chaos is strongly suppressed. A
simple explanation of this behaviour is found in the change in the structure of
the orbits induced by quantum corrections. Consistently with Heisenberg's
principle, quantum fluctuations are forced away from zero, removing in the
effective quantum dynamics a hyperbolic fixed point that is a major source of
chaos in the classical model.Comment: 6 pages, RevTeX, 5 figures, uses psfig, changed indroduction and
conclusions, added reference
Quantum Chaos at Finite Temperature
We use the quantum action to study quantum chaos at finite temperature. We
present a numerical study of a classically chaotic 2-D Hamiltonian system -
harmonic oscillators with anharmonic coupling. We construct the quantum action
non-perturbatively and find temperature dependent quantum corrections in the
action parameters. We compare Poincar\'{e} sections of the quantum action at
finite temperature with those of the classical action.Comment: Text (LaTeX), Figs. (ps
Quantum Chaos Versus Classical Chaos: Why is Quantum Chaos Weaker?
We discuss the questions: How to compare quantitatively classical chaos with
quantum chaos? Which one is stronger? What are the underlying physical reasons
Riemannian theory of Hamiltonian chaos and Lyapunov exponents
This paper deals with the problem of analytically computing the largest
Lyapunov exponent for many degrees of freedom Hamiltonian systems. This aim is
succesfully reached within a theoretical framework that makes use of a
geometrization of newtonian dynamics in the language of Riemannian geometry. A
new point of view about the origin of chaos in these systems is obtained
independently of homoclinic intersections. Chaos is here related to curvature
fluctuations of the manifolds whose geodesics are natural motions and is
described by means of Jacobi equation for geodesic spread. Under general
conditions ane effective stability equation is derived; an analytic formula for
the growth-rate of its solutions is worked out and applied to the
Fermi-Pasta-Ulam beta model and to a chain of coupled rotators. An excellent
agreement is found the theoretical prediction and the values of the Lyapunov
exponent obtained by numerical simulations for both models.Comment: RevTex, 40 pages, 8 PostScript figures, to be published in Phys. Rev.
E (scheduled for November 1996
Study of dynamic buckling in droppers of high-speed railway line catenary during pantograph passage|Studio del dynamic buckling nei pendini conduttori di una catenaria AV al passaggio del pantografo
The dynamical actions to which the catenary dropper is subjected during the pantograph passage can become very relevant for high speeds of railway vehicle. In some very rare and isolated cases, premature failure of the dropper positioned near the suspension and/or near the auto tensioning devices in catenaries for High Speed (HS) operation has been observed. In order to understand the phenomenon, an analysis developed in several activities was carried out, including numerical analyses and in line and in laboratory experimental activities. A final phase of the investigation was dedicated to the development of a prototype of a dropper specifically designed on the basis of the results obtained from this study with the aim of improving the dropper fatigue behaviour. The new dropper could be used in critical points of the overhead line, such as near the suspension and/or near the auto tensioning devices