arXiv subjects

Piero Chiarelli

Publications and source records attributed to Piero Chiarelli.

24 records · Page 2Linked to original sources

arXiv2013

The density maximum of He4 at the lambda point modeled by the stochastic quantum hydrodynamic analogy

The lambda point in liquid He4 is a well established phenomenon acknowledged as an example of Bose-Einstain condensation. This is generally accepted, but there are serious discrepancies between the theory and experimental results, namely the lower value of the transition temperature Tl and the negative value of dTl /dP. These discrepancies can be explained in term of the quantum stochastic hydrodynamic analogy (QSHA). The QSHA shows that at the He4I\textregisteredHe4II superfluid transition the quantum coherence length lc becomes of order of the distance up to which the wave function of a couple of He4 atoms extends itself. In this case, the He42 state is quantum and the quantum pseudo-potential brings a repulsive interaction that leads to the negative dTl /dP behavior. This fact overcomes the difficulty to explain the phenomenon by introducing a Hamiltonian inter-atomic repulsive potential that would obstacle the gas-liquid transition.

cond-mat.other↗

arXiv2012

The Schrödinger equation and its generalized analogs derived by the quantum hydrodynamic representation

The derivation of the Schrödinger-like equations from the system of equations of the quantum hydrodynamic analogy (QHA) is analyzed in presence of fluctuations. If in absence of fluctuation each QHA solution can be tracked back to the equivalent one of the Schrödinger problem, in presence of fluctuations the work shows that the ensemble of solution of the QHA equations is wider than the Schrödinger one and the tracking-back procedure from the QHA problem to the original Schrödinger equation is not generally possible. The break-down of the mathematical correspondence is inspected and correlated to the characteristics of the states. Finally, the paper shows that if the form of Schrödinger equation is generalized, the QHA stochastic case as well as its classical limit can be translated into a Schrödinger-like representation.

quant-ph↗

arXiv2012

Poroelastic longitudinal wave equation for soft living tissues

Making use of the poroelastic theory for hydrated polymeric matrices, the ultrasound (US) propagation in a gel medium filled by spherical cells is studied . The model describes the connection between the poroelastic structure of living means and the propagation behavior of the acoustic waves. The equation of fast compressional wave, its phase velocity and its attenuation as a function of the elasticity, porosity and concentration of the cells into the gel external matrix are investigated. The outcomes of the theory agree with the measurements done on PVA gel scaffolds inseminated by porcine liver cells at various concentrations. The model is promising in the quantitative non-invasive estimation of parameters that could asses the change in the tissue structure, composition and architecture.

cond-mat.soft↗

arXiv2012

Polyelectrolyte intelligent gels. Design and applications

In this chapter polyelectrolyte intelligent gels are examined along three broad lines. The effects of different physical, chemical and biological stimuli on gels response are analysed and mechanisms of response are outlined. The broad range of biomedical applications of smart gels is reviewed and limits and perspectives of the proposed techniques and devices are crititically discussed. Finally, continuous modelling of gel electromechanochemistry is described, providing quantitative tools to assess swelling equilibrium conditions and coupled kinetics.

cond-mat.soft↗

arXiv2012

High frequency poroelastic waves in hydrogels

In this work a continuum model for high frequency poroelastic longitudinal waves in hydrogels is presented. A viscoelastic force describing the interaction between the polymer network and the bounded water present in such materials is introduced. The model is tested by means of ultrasound wave speed and attenuation measurements in polyvinylalcohol hydrogel samples. The theory and experiments show that ultrasound attenuation decreases linearly with the increase of the water volume fraction "β" of the hydrogel. The introduction of the viscoelastic force between the bounded water and the polymer network leads to a bi-phasic theory showing an ultrasonic fast wave attenuation that can vary as a function of the frequency with a non-integer exponent in agreement with the experimental data in literature. When β tends to 1 (100% of interstitial water) due to the presence of bounded water in the hydrogel, the ultrasound phase velocity acquires higher value than that of pure water. The ultrasound speed gap at β = 1 is confirmed by the experimental results that show that it increases in less cross-linked gel samples that own a higher concentration of bounded water.

cond-mat.soft↗

arXiv2012

Is the quantum hydrodynamic analogy more general than the Schroedinger approach?

The quantum hydrodynamic analogy (QHA), equivalent to the Schrödinger equation, is investigated and extended to the stochastic case. The investigation shows that in addition to reproducing the standard quantum mechanics the QHA model is able to generally describe the quantum stochastic dynamics leading to the dissipative Schrödinger equation given by Kostin [55] as a particular case. The inspection shows that the QHA is well suited for the treatment of problems where local noise (spatially distributed one) is introduced. In this case the analysis shows that the bi-univocal correspondence between the QHA and the Schrödinger approach breaks down and that the states described by the QHA do not have their corresponding ones into the Schrödinger description.

quant-ph↗