3,913 research outputs found
Supershear Rayleigh waves at a soft interface
We report on the experimental observation of waves at a liquid foam surface
propagating faster than the bulk shear waves. The existence of such waves has
long been debated, but the recent observation of supershear events in a
geophysical context has inspired us to search for their existence in a model
viscoelastic system. An optimized fast profilometry technique allowed us to
observe on a liquid foam surface the waves triggered by the impact of a
projectile. At high impact velocity, we show that the expected subshear
Rayleigh waves are accompanied by faster surface waves that can be identified
as supershear Rayleigh waves.Comment: 4 pages, 4 figures, 2 supplementary video
The spatio-temporal spectrum of turbulent flows
Identification and extraction of vortical structures and of waves in a
disorganised flow is a mayor challenge in the study of turbulence. We present a
study of the spatio-temporal behavior of turbulent flows in the presence of
different restitutive forces. We show how to compute and analyse the
spatio-temporal spectrum from data stemming from numerical simulations and from
laboratory experiments. Four cases are considered: homogeneous and isotropic
turbulence, rotating turbulence, stratified turbulence, and water wave
turbulence. For homogeneous and isotropic turbulence, the spectrum allows
identification of sweeping by the large scale flow. For rotating and for
stratified turbulence, the spectrum allows identification of the waves, precise
quantification of the energy in the waves and in the turbulent eddies, and
identification of physical mechanisms such as Doppler shift and wave absorption
in critical layers. Finally, in water wave turbulence the spectrum shows a
transition from gravity-capillary waves to bound waves as the amplitude of the
forcing is increased.Comment: Added new references and analysi
The spatio-temporal spectrum of turbulent flows
Identification and extraction of vortical structures and of waves in a disorganised flow is a mayor challenge in the study of turbulence. We present a study of the spatio-temporal behavior of turbulent flows in the presence of different restitutive forces. We show how to compute and analyse the spatio-temporal spectrum from data stemming from numerical simulations and from laboratory experiments. Four cases are considered: homogeneous and isotropic turbulence, rotating turbulence, stratified turbulence, and water wave turbulence. For homogeneous and isotropic turbulence, the spectrum allows identification of sweeping by the large-scale flow. For rotating and for stratified turbulence, the spectrum allows identification of the waves, precise quantification of the energy in the waves and in the turbulent eddies, and identification of physical mechanisms such as Doppler shift and wave absorption in critical layers. Finally, in water wave turbulence the spectrum shows a transition from gravity-capillary waves to bound waves as the amplitude of the forcing is increased.Fil: Clark Di Leoni, Patricio. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Ciudad Universitaria. Instituto de FĂsica de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de FĂsica de Buenos Aires; ArgentinaFil: Cobelli, Pablo Javier. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Ciudad Universitaria. Instituto de FĂsica de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de FĂsica de Buenos Aires; ArgentinaFil: Mininni, Pablo Daniel. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Ciudad Universitaria. Instituto de FĂsica de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de FĂsica de Buenos Aires; Argentin
Fourier analysis of wave turbulence in a thin elastic plate
The spatio-temporal dynamics of the deformation of a vibrated plate is
measured by a high speed Fourier transform profilometry technique. The
space-time Fourier spectrum is analyzed. It displays a behavior consistent with
the premises of the Weak Turbulence theory. A isotropic continuous spectrum of
waves is excited with a non linear dispersion relation slightly shifted from
the linear dispersion relation. The spectral width of the dispersion relation
is also measured. The non linearity of this system is weak as expected from the
theory. Finite size effects are discussed. Despite a qualitative agreement with
the theory, a quantitative mismatch is observed which origin may be due to the
dissipation that ultimately absorbs the energy flux of the Kolmogorov-Zakharov
casade.Comment: accepted for publication in European Physical Journal B see
http://www.epj.or
A nonparametric approach for model individualization in an artificial pancreas
The identification of patient-tailored linear time invariant glucose-insulin models is investigated for type 1 diabetic patients, that are characterized by a substantial inter-subject variability. The individualized linear models are identified by considering a novel kernel-based nonparametric approach and are compared with a linear time invariant average model in terms of prediction performance by means of the coefficient of determination, fit, positive and negative max errors, and root mean squared error. Model identification and validation are based on in-silico data collected from the adult virtual population of the UVA/Padova simulator. The data generation involves a protocol designed to produce a sufficient input excitation without compromising patient safety, compatible also with real life scenarios. The identified models are exploited to synthesize an individualized Model Predictive Controller (MPC) for each patient, which is used in an Artificial Pancreas to maintain the blood glucose concentration within an euglycemic range. The MPC used in several clinical studies, synthesized on the basis of a non-individualized average linear time invariant model, is also considered as reference. The closed-loop control performance is evaluated in an in-silico study on the adult virtual population of the UVA/Padova simulator in a perturbed scenario, in which the MPC is blind to random variations of insulin sensitivity in each virtual patient. © 2015, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved
Design, construction and validation of an instrumented particle for the lagrangian characterization of flows. Application to gravity wave turbulence
The design and application of an instrumented particle for the lagrangian
characterization of turbulent free surface flows is presented in this study.
This instrumented particle constitutes a local measurement device capable of
measuring both its instantaneous 3D translational acceleration and angular
velocity components, as well as recording them on an embarked removeable memory
card. A lithium ion polymer battery provides the instrumented particle with up
to 8 hours of autonomous operation. Entirely composed of commercial off the
shelf electronic components, it features accelerometer and gyroscope sensors
with a resolution of 16 bits for each individual axis, and maximum data
acquisition rates of 1 and 8 kHz, respectively, as well as several user
programmable dynamic ranges. Its ABS 3D printed body takes the form of a 36 mm
diameter hollow sphere, and has a total mass of (19.6 0.5) g. Controlled
experiments, carried out to calibrate and validate its performance showed good
agreement when compared to reference techniques. In order to assess the
practicality of the instrumented particle, we apply it to the statistical
characterization of floater dynamics in experiments of surface wave turbulence.
In this feasibility study, we focused our attention on the distribution of
acceleration and angular velocity fluctuations as a function of the forcing
intensity. The IP's motion is also simultaneously registered by a 3D particle
tracking velocimetry (PTV) system, for the purposes of comparison. Beyond the
results particular to this study case, it constitutes a proof of both the
feasibility and potentiality of the IP as a tool for the experimental
characterization of particle dynamics in such flows
Response to Comment on "Minimal and Maximal Models to Quantitate Glucose Metabolism: Tools to Measure, to Simulate and to Run in Silico Clinical Trials"
We thank Eichenlaub and coworkers for their interesting letter to the editor entitled Comment on “Minimal and Maximal Models to Quantitate Glucose Metabolism: Tools to Measure, to Simulate and to Run in Silico Clinical Trials.”1 When developing the original model,2 we acknowledged that the need of fixing SG (fractional glucose effectiveness) to a population value was an important limitation of the method. To test the implication of this assumption on the model-derived insulin sensitivity, SI , we performed an extensive validation work against independent techniques, including glucose clamp3 and multiple tracer experiment,4 and we were able to prove that SI is well correlated with model-independent indices. Eichenlaub and coworkers’ overlook the SI validation studies3,4 that fully address their concerns: the correlation was 0.81 P < .001 with clamp in 10 normal and 11 impaired glucose tolerant subjects3 and 0.86, P < .0001 with the multiple tracer experiment in 88 healthy individuals.4 Therefore, their critiques cannot be sustained in the face of such a large body of validation evidence. [...
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