31 research outputs found
Avalanche statistics during coarsening dynamics
We study the coarsening dynamics of a two dimensional system via lattice
Boltzmann numerical simulations. The system under consideration is a biphasic
system consisting of domains of a dispersed phase closely packed together in a
continuous phase and separated by thin interfaces. Such system is elastic and
typically out of equilibrium. The equilibrium state is attained via the
coarsening dynamics, wherein the dispersed phase slowly diffuses through the
interfaces, causing domains to change in size and eventually rearrange
abruptly. The effect of rearrangements is propagated throughout the system via
the intrinsic elastic interactions and may cause rearrangements elsewhere,
resulting in intermittent bursts of activity and avalanche behaviour. Here we
aim at quantitatively characterizing the corresponding avalanche statistics
(i.e. size, duration, inter-avalanche time). Despite the coarsening dynamics is
triggered by an internal driving mechanism, we find quantitative indications
that such avalanche statistics displays scaling-laws very similar to those
observed in the response of disordered materials to external loads
Analysis of the heat transfer fluctuations in the Rayleigh-B\'enard convection of concentrated emulsions with finite-size droplets
Employing numerical simulations, we provide an accurate insight into the of
heat transfer mechanisms in the Rayleigh-B\'enard convection of concentrated
emulsions with finite-size droplets. We focus on the unsteady dynamics
characterizing the thermal convection of these complex fluids close to the
transition from conductive to convective states, where the heat transfer
phenomenon, expressed in terms of the Nusselt number Nu, is characterized by
pronounced fluctuations triggered by collective droplets motion [Pelusi et al.,
Soft Matter 17(13), 3709 - 3721 (2021)]. By systematically increasing the
droplet concentration, we show how these fluctuations emerge along with the
segregation of ``extreme events" in the boundary layers, causing intermittent
bursts in the heat flux fluctuations. Furthermore, we quantify the extension
and the duration of the coherent droplet motion accompanying
these extreme events via a suitable statistical analysis involving the droplets
displacements. We show how the increase in droplet concentration results in a
power-law behaviour of the probability distribution function of and
and how this outcome is robust at changing the analysis protocol.
Our work offers a comprehensive picture, linking macroscopic heat transfer
fluctuations with the statistics of droplets at the mesoscale.Comment: 10 pages, 7 figure
A sharp interface approach for wetting dynamics of coated droplets and soft particles
The wetting dynamics of liquid particles, from coated droplets to soft
capsules, holds significant technological interest. Motivated by the need to
simulate liquid metal droplet with an oxidize surface layer, in this work we
introduce a computational scheme that allows to simulate droplet dynamics with
general surface properties and model different levels of interface stiffness,
describing also cases that are intermediate between pure droplets and capsules.
Our approach is based on a combination of the immersed boundary (IB) and the
lattice Boltzmann (LB) methods. Here, we validate our approach against the
theoretical predictions in the context of shear flow and static wetting
properties and we show its effectiveness in accessing the wetting dynamics,
exploring the ability of the scheme to address a broad phenomenology.Comment: 14 pages, 6 figure
Suspensions of viscoelastic capsules: effect of membrane viscosity on transient dynamics
Membrane viscosity is known to play a central role in the transient dynamics
of isolated viscoelastic capsules by decreasing their deformation, inducing
shape oscillations and reducing the loading time, that is, the time required to
reach the steady-state deformation. However, for dense suspensions of capsules,
our understanding of the influence of the membrane viscosity is minimal. In
this work, we perform a systematic numerical investigation based on coupled
immersed boundary -- lattice Boltzmann (IB-LB) simulations of viscoelastic
spherical capsule suspensions in the non-inertial regime. We show the effect of
the membrane viscosity on the transient dynamics as a function of volume
fraction and capillary number. Our results indicate that the influence of
membrane viscosity on both deformation and loading time strongly depends on the
volume fraction in a non-trivial manner: dense suspensions with large surface
viscosity are more resistant to deformation but attain loading times that are
characteristic of capsules with no surface viscosity, thus opening the
possibility to obtain richer combinations of mechanical features
Rayleigh–Bénard convection of a model emulsion: anomalous heat-flux fluctuations and finite-size droplet effects
We present mesoscale numerical simulations of Rayleigh-B\'enard (RB)
convection in a two-dimensional model emulsion. The systems under study are
constituted of finite-size droplets, whose concentration Phi_0 is
systematically varied from small (Newtonian emulsions) to large values
(non-Newtonian emulsions). We focus on the characterisation of the heat
transfer properties close to the transition from conductive to convective
states, where it is known that a homogeneous Newtonian system exhibits a steady
flow and a time-independent heat flux. In marked contrast, emulsions exhibit a
non-steady dynamics with fluctuations in the heat flux. In this paper, we aim
at the characterisation of such non-steady dynamics via detailed studies on the
time-averaged heat flux and its fluctuations. To understand the time-averaged
heat flux, we propose a side-by-side comparison between the emulsion system and
a single-phase (SP) system, whose viscosity is constructed from the shear
rheology of the emulsion. We show that such local closure works well only when
a suitable degree of coarse-graining (at the droplet scale) is introduced in
the local viscosity. To delve deeper into the fluctuations in the heat flux, we
propose a side-by-side comparison between a Newtonian emulsion and a
non-Newtonian emulsion, at fixed time-averaged heat flux. This comparison
elucidates that finite-size droplets and the non-Newtonian rheology cooperate
to trigger enhanced heat-flux fluctuations at the droplet scales. These
enhanced fluctuations are rooted in the emergence of space correlations among
distant droplets, which we highlight via direct measurements of the droplets
displacement and the characterisation of the associated correlation function.
The observed findings offer insights on heat transfer properties for confined
systems possessing finite-size constituents.Comment: 15 pages, 22 figures. arXiv admin note: substantial text overlap with
arXiv:2010.02139, arXiv:2010.0213
Body mass index rather than the phenotype impacts precocious ultrasound cardiovascular risk markers in polycystic ovary syndrome
Objective
Research into cardiovascular disease (CV) prevention has demonstrated a variety of ultrasound (US) markers predicting risk in the general population but which have been scarcely used for polycystic ovary syndrome (PCOS). Obesity is a major factor contributing to CV disease in the general population, and it is highly prevalent in PCOS. However, it is still unclear how much risk is attributable to hyperandrogenism. This study evaluates the most promising US CV risk markers in PCOS and compares them between different PCOS phenotypes and BMI values.
Design
Women fulfilling the Rotterdam criteria for PCOS were recruited from our outpatient clinic for this cross-sectional study.
Methods
Participants (n\u2009=\u2009102) aged 38.9 \ub1 7.4 years were stratified into the four PCOS phenotypes and the three BMI classes (normal-weight, overweight, obese). They were assessed for clinical and biochemical parameters together with the following US markers: coronary intima-media thickness (cIMT), flow-mediated vascular dilation (FMD), nitroglycerine-induced dilation (NTG), and epicardial fat thickness (EFT).
Results
There was no statistical difference among the four phenotypes in terms of cIMT, FMD, NTG or EFT, however all the US parameters except NTG showed significant differences among the three BMI classes. Adjusting for confounding factors in multiple regression analyses, EFT retained the greatest direct correlation with BMI and cIMT remained directly correlated but to a lesser degree.
Conclusions
This study showed that obesity rather than the hyperandrogenic phenotype negatively impacts precocious US CV risk markers in PCOS. In addition, EFT showed the strongest association with BMI, highlighting its potential for estimating CV risk in PCOS
Management of Pediatric Urinary Tract Infections: A Delphi Study
Urinary tract infection (UTI) is one of the most common infectious diseases in the pediatric population and represents a major cause of antibiotic consumption and hospitalization in children. Considering the ongoing controversies on the management of pediatric UTI and the challenges due to increasing antimicrobial resistance, the aim of the present study was to evaluate the level of agreement on UTI management in pediatric age in Emilia-Romagna Region, Italy, and to assess on the basis of recent studies whether there is the need to change current recommendations used by primary care pediatricians, hospital pediatricians, and pediatric surgeons in everyday clinical practice to possibly improve outcomes. This consensus provides clear and shared indications on UTI management in pediatric age, based on the most updated literature. This work represents, in our opinion, the most complete and up-to-date collection of statements on procedures to follow for pediatric UTI, in order to guide physicians in the management of the patient, standardize approaches, and avoid abuse and misuse of antibiotics. Undoubtedly, more randomized and controlled trials are needed in the pediatric population to better define the best therapeutic management in cases with antimicrobial resistance and real usefulness of long-term antibiotic prophylaxis
PROPOSAL OF A MILLIMETER-WAVE ANTENNA ARRAY FOR CUBESATS
This paper describes the preliminary phase of design of a microstrip antenna array composed by subarrays, intended to be mounted on a CubeSat operating in the millimeter-wave frequency range. A three-step procedure is described, consisting in the development of the single-element, of the subarray and of the complete array. Different configurations of the subarray and of the complete array are investigated and mutually compared
TLBfind: a Thermal Lattice Boltzmann code for concentrated emulsions with FINite-size Droplets
In this paper, we present TLBfind, a GPU code for simulating the
hydrodynamics of droplets along with a dynamic temperature field. TLBfind
hinges on a two-dimensional multi-component lattice Boltzmann (LB) model
simulating a concentrated emulsion with finite-size droplets evolving in a
thermal convective state, just above the transition from conduction to
convection. The droplet concentration of the emulsion system is tenable, and at
the core of the code lies the possibility to measure a large number of physical
observables characterising the flow and droplets. Furthermore, TLBfind includes
a parallel implementation on GPU of the Delaunay triangulation useful for the
detection of droplets' plastic rearrangements, and several types of boundary
conditions, supporting simulations of channels with structured rough walls