1,721,014 research outputs found

    Covariant momentum map thermodynamics for parametrized field theories

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    A general-covariant statistical framework capable of describing classical fluctuations of the gravitational field is a thorny open problem in theoretical physics, yet ultimately necessary to understand the nature of the gravitational interaction, and a key to quantum gravity. Inspired by Souriau's symplectic generalization of the Maxwell-Boltzmann-Gibbs equilibrium in Lie group thermodynamics, we investigate a space-time-covariant formulation of statistical mechanics for parametrized first-order field theories, as a simplified model sharing essential general covariant features with canonical general relativity. Starting from a covariant multi-symplectic phase space formulation, we define a general-covariant notion of Gibbs state in terms of the covariant momentum map associated with the lifted action of the diffeomorphisms group on the extended phase space. We show how such a covariant notion of equilibrium encodes the whole information about symmetry, gauge and dynamics carried by the theory, associated with a canonical spacetime foliation, where the covariant choice of a reference frame reflects in a Lie algebra-valued notion of local temperature. We investigate how physical equilibrium, hence time evolution, emerges from such a state and the role of the gauge symmetry in the thermodynamic description

    Multi-symplectic Lie Group Thermodynamics for Covariant Field Theories

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    We propose a multi-symplectic generalisation of Souriau’s Lie group thermodynamics for first order parametrised classical field theories. A new notion of general covariant Gibbs state functional is defined in terms of the multi-momentum map associated to the lifted action of the diffeomorphisms group on the fields extended phase space. We elaborate on the use of such functional toward a covariant statistical mechanic description of fully constrained field theories, at the crossroad between geometrical methods and information theory

    Dynamics of pantographic sheet around the clamping region: experimental and numerical analysis

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    The experimental and numerical analyses of the linear time-invariant dynamical behavior of the clamping region of a 2D pantographic material are presented. The experimental observations of the clamping area, obtained by means of a specialized stereo microscope, are compared with the results of a second gradient linear model enforcing the same symmetries as the system microstructure

    La nefrolitiasi nelle malattie intestinali

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    Intestinal diseases may cause the formation of urinary stones through changes in the metabolism of oxalate, calcium, and uric acid. The oxalate that is excreted into urine comes from the catabolism of ascorbic acid and some amino acids or from intestinal absorption of food oxalate. Calcium is absorbed by the gut after the stimulation of active vitamin D and is excreted by the kidney under the control of the bone/parathyroid hormone axis. Uric acid is generated by the oxidation of exogenous and endogenous purine bases, is excreted by the kidney through glomerular filtration/tubular secretion, and is soluble in alkaline urine. Several data indicate that patients with inflammatory bowel diseases are at high risk of urinary stones containing calcium-oxalate salt or uric acid. Calcium-oxalate stones are caused by colonic oxalate hyperabsorption (secondary to intestinal dysfunction) or by parenteral nutrition. Uric acid stones are typical of patients with severe diarrhea and/or intestinal neostomy, that is, in patients with hyperconcentrated acidic urine. Relationships between malabsorptive intestinal diseases and urinary stones are less well defined. Preventive countermeasures are not the same for all disorders. Hyperoxaluria should be controlled by diets with a low content of lipids and oxalate but supplemented with calcium and probiotics. The presence of hyperconcentrated acidic urine should be controlled by correct hydration and administration of citrate

    Spectral properties of 2D pantographic metamaterial: Experimental results

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    Preliminary results of the first experimental investigation of the spectral properties of a 2D pantographic material are presented and discussed. The observed eigenfrequencies and deflection shapes are compatible with the numerical predictions presented in previous numerical studies
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