Polytechnic University of Milan

About: Polytechnic University of Milan is a education organization based out in Milan, Italy. It is known for research contribution in the topics: Finite element method & Population. The organization has 18231 authors who have published 58416 publications receiving 1229711 citations. The organization is also known as: PoliMi & L-NESS.

Heart rate variability and its sympatho-vagal modulation

Abstract: The activity of sinus node pacemaker cells is under continuous regulation mainly effected by neural mechanisms. Hence the study of the variability of heart period, especially when assessed in the frequency domain with spectral analysis, was proposed about 15 years ago [l] as a probe for the evaluation of its autonomic control. Initially three spectral components of heart rate variability (HRV) were defined, while the factors considered as modulating them included sympathetic and parasympathetic activities, humoral factors such as the renin-angiotensin system or complex patterns like thermoregulation. On the basis of (i) an attempt to analyse cardiovascular neural regulation in closed-loop conditions, (ii) a different spectral methodology using autoregressive algorithms [21, (iii> simultaneous spectral analysis of both heart rate and arterial pressure variabilities providing the possibility of calculating crossspectra and their coherence, we reached the conclusion that only two spectral components were soundly analysable in a time span of a few hundred cycles-i.e., the time series usually selected to afford an adequate number of events, adequate stationarity and some appraisal of dynamic changes [3]. Hence, apart from a very low frequency (VLF) component [41, short-term variability appeared to consist mainly of an oscillation at low frequency (LF), usually around 0.1 Hz largely related to vasomotor activity, and of a high frequency (HF) oscillation, related to respiratory activity and under control conditions often around 0.25 Hz. Since our initial studies [2], we observed that the power of the LF component was percentually increased during manoeuvres exciting sympathetic activity while HF was

The Classical Nature of Thermal Conduction in Nanofluids

Abstract: We show that a large set of nanofluid thermal conductivity data falls within the upper and lower Maxwell bounds for homogeneous systems. This indicates that the thermal conductivity of nanofluids is largely dependent on whether the nanoparticles stay dispersed in the base fluid, form large aggregates, or assume a percolating,fractal confguration. The experimental data, which are strikingly analogous to those in most solid composites and liquid mixtures, provide strong evidence for the classical nature of thermal conduction in nanofluids.

Physical models of size-dependent nanofilament formation and rupture in NiO resistive switching memories.

Abstract: NiO films display unipolar resistance switching characteristics, due to the electrically induced formation and rupture of nanofilaments. While the applicative interest for possible use in highly dense resistance switching memory (RRAM) is extremely high, switching phenomena pose strong fundamental challenges in understanding the physical mechanisms and models. This work addresses the set and reset mechanisms for the formation and rupture of nanofilaments in NiO RRAM devices. Reset is described in terms of thermally-accelerated diffusion and oxidation processes, and its resistance dependence is explained by size-dependent Joule heating and oxidation. The filament is described as a region with locally-enhanced doping, resulting in an insulator-metal transition driven by structural and chemical defects. The set mechanism is explained by a threshold switching effect, triggering chemical reduction and a consequent local increase of metallic doping. The possible use of the observed resistance-dependent reset and set parameters to improve the memory array operation and variability is finally discussed.

Asymptotic behavior of a Cahn-Hilliard-Navier-Stokes system in 2D

Abstract: We consider a model for the flow of a mixture of two homogeneous and incompressible fluids in a two-dimensional bounded domain. The model consists of a Navier–Stokes equation governing the fluid velocity coupled with a convective Cahn–Hilliard equation for the relative density of atoms of one of the fluids. Endowing the system with suitable boundary and initial conditions, we analyze the asymptotic behavior of its solutions. First, we prove that the initial and boundary value problem generates a strongly continuous semigroup on a suitable phase-space which possesses the global attractor A . Then we establish the existence of an exponential attractors E . Thus A has finite fractal dimension. This dimension is then estimated from above in terms of the physical parameters. Moreover, assuming the potential to be real analytic and in absence of volume forces, we demonstrate that each trajectory converges to a single equilibrium. We also obtain a convergence rate estimate in the phase-space metric.