90 research outputs found
A Formal Approach to Cyber-Physical Attacks
We apply formal methods to lay and streamline theoretical foundations to
reason about Cyber-Physical Systems (CPSs) and cyber-physical attacks. We focus
on %a formal treatment of both integrity and DoS attacks to sensors and
actuators of CPSs, and on the timing aspects of these attacks. Our
contributions are threefold: (1) we define a hybrid process calculus to model
both CPSs and cyber-physical attacks; (2) we define a threat model of
cyber-physical attacks and provide the means to assess attack
tolerance/vulnerability with respect to a given attack; (3) we formalise how to
estimate the impact of a successful attack on a CPS and investigate possible
quantifications of the success chances of an attack. We illustrate definitions
and results by means of a non-trivial engineering application
Drying research From physical and biological mechanisms to breakthrough innovation
Drying research From physical and biological mechanisms to breakthrough innovation. STLOpenday
Torsional oscillation monitoring by means of a magnetoelastic resonator: modeling and experimental functionalization to measure viscosity of liquids
A new application of a high sensitivity magnetoelastic resonator able to measure period and dampingconstant of low frequency torsional oscillation is described and validated by experimental tests. Thesensitive parameter is the amplitude of resonant magnetoelastic waves in the soft ferromagnetic core(Fe62.5Co6Ni7.5Zr6Cu1Nb2B15amorphous ribbon). The theoretical model of the device has been developed,correlating torsional oscillations to the friction force applied by the fluid in which they occur. Thus,an accurate indirect evaluation of fluid viscosity has been demonstrated. The main prerogative of theproposed sensor is to work without contact with the oscillating mechanism. As experimental validation,viscosity of UHT milk was measured versus different fat content. The experimental comparison with astandard rheometer demonstrates the new device competitiveness in the measure of low viscosity fluidsat low share rate. Moreover, the detected behaviors at increasing temperature are in agreement withprevious literature. In perspective, the new magnetoelastic resonators application can be very ductileand effective in on-line monitoring of viscosity change with time to control composition, degradation orcontamination of liquids
Ultrasound pulse echo analysis of blood aggregation in microfluidics
International audienceBlood aggregation occurs when erythrocytes, red blood cells (RBC), agglutinate together into compact stacks of cells called rouleaux. Blood aggregation can then be compared to a liquid-gel transition that appears at low flow regime, and is responsible of the high value of the blood viscosity at low shear rate. This paper will present a physical device that can detect the appearing of this liquid-gel transition using the transmission and reflection properties of ultrasonic waves. In order to detect the liquid-gel transition in resting blood we use the property of an ultrasonic shear wave (5 MHz) to be transmitted or reflected at a glass-liquid interface that is populated with RBC. The setup, as sketched in Figure1, is made of a piezoelectric transducer, a PZT stack that is bonded on the bottom face of a glass cylinder that acts as an acoustic delay line [1]. A burst of signal (2µs) is sent by the PZT toward the glass coverslip, travels through the delay line, bounces at the interfaces and returns with a delay to the PZT where it is detected. Amplitudes of the echo is then compared to input signal in order to extract a reflexion coefficient (r). Experiments are performed both on droplets of healthy blood deposited on glass coverslips and in PDMS microfluidic circuits at low flow strength and at rest. In particular, a spiral shaped microchip, as can be seen in Figure 2, is used both to mimic a vascular network (160x150µm section channels) and to expose a large surface (about 25 mm2) of the sample to the ultrasonic signal [2]. The detection of r over time is coupled with observations of RBCs behaviour during the sample desiccation by optical microscopy to elucidate the dynamics of the drying process of blood. All measurements are carried out at controlled temperature (25 °C) and relative humidity (30-60%). Note that the acoustic power (<1pJ) sent to the blood is small and does not interact with cells through acoustophoresis mechanisms. (a) (b) Figure 1: (a) Schematic (not to scale) of the ultrasound pulse echo setup for the analysis of liquid gel transition in steady blood flow due to red blood cells aggregation. (b) Photograph of the spiral shaped microfluidic circuit bonded on a microscope glass blade a coupled to an ultrasonic pulse echo system. The spiral channel is 160μm wide, 150μm for a total diameter of diameter of 6mm
Lyapunov exponents of heavy particles in turbulence
Lyapunov exponents of heavy particles and tracers advected by homogeneous and
isotropic turbulent flows are investigated by means of direct numerical
simulations. For large values of the Stokes number, the main effect of inertia
is to reduce the chaoticity with respect to fluid tracers. Conversely, for
small inertia, a counter-intuitive increase of the first Lyapunov exponent is
observed. The flow intermittency is found to induce a Reynolds number
dependency for the statistics of the finite time Lyapunov exponents of tracers.
Such intermittency effects are found to persist at increasing inertia.Comment: 4 pages, 4 figure
Numerical simulations of aggregate breakup in bounded and unbounded turbulent flows
Breakup of small aggregates in fully developed turbulence is studied by means
of direct numerical simulations in a series of typical bounded and unbounded
flow configurations, such as a turbulent channel flow, a developing boundary
layer and homogeneous isotropic turbulence. The simplest criterion for breakup
is adopted, whereas aggregate breakup occurs when the local hydrodynamic stress
, with being the energy dissipation
at the position of the aggregate, overcomes a given threshold
, which is characteristic for a given type of aggregates.
Results show that the breakup rate decreases with increasing threshold. For
small thresholds, it develops a universal scaling among the different flows.
For high thresholds, the breakup rates show strong differences between the
different flow configurations, highlighting the importance of non-universal
mean-flow properties. To further assess the effects of flow inhomogeneity and
turbulent fluctuations, theresults are compared with those obtained in a smooth
stochastic flow. Furthermore, we discuss the limitations and applicability of a
set of independent proxies.Comment: 15 pages, 12 figures, Refinded discussion in Section 2.1, results
unchange
Isotropy vs anisotropy in small-scale turbulence
The decay of large-scale anisotropies in small-scale turbulent flow is
investigated. By introducing two different kinds of estimators we discuss the
relation between the presence of a hierarchy for the isotropic and the
anisotropic scaling exponents and the persistence of anisotropies. Direct
measurements from a channel flow numerical simulation are presented.Comment: 7 pages, 2 figure
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