We address the problem of data augmentation in a rotating turbulence set-up, a paradigmatic challenge in geophysical applications. The goal is to reconstruct information in two-dimensional (2D) cuts ...of the three-dimensional flow fields, imagining spatial gaps present within each 2D observed slice. We evaluate the effectiveness of different data-driven tools, based on diffusion models (DMs), a state-of-the-art generative machine learning protocol, and generative adversarial networks (GANs), previously considered as the best-performing method both in terms of point-wise reconstruction and the statistical properties of the inferred velocity fields. We focus on two different DMs recently proposed in the specialized literature: (i) RePaint, based on a heuristic strategy to guide an unconditional DM for flow generation by using partial measurements data, and (ii) Palette, a conditional DM trained for the reconstruction task with paired measured and missing data. Systematic comparison shows that (i) DMs outperform the GAN in terms of the mean squared error and/or the statistical accuracy; (ii) Palette DM emerges as the most promising tool in terms of both point-wise and statistical metrics. An important property of DMs is their capacity for probabilistic reconstructions, providing a range of predictions based on the same measurements, enabling uncertainty quantification and risk assessment.
We apply formal methods to lay and streamline theoretical foundations to reason about Cyber-Physical Systems (CPSs) and physics-based attacks, i.e., attacks targeting physical devices. We focus on a ...formal treatment of both integrity and denial of service attacks to sensors and actuators of CPSs, and on the timing aspects of these attacks. Our contributions are fourfold. (1) We define a hybrid process calculus to model both CPSs and physics-based attacks. (2) We formalise a threat model that specifies MITM attacks that can manipulate sensor readings or control commands to drive a CPS into an undesired state; we group these attacks into classes and provide the means to assess attack tolerance/vulnerability with respect to a given class of attacks, based on a proper notion of most powerful physics-based 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. (4) We illustrate our definitions and results by formalising a non-trivial running example in U
PPAAL
SMC, the statistical extension of the U
PPAAL
model checker; we use U
PPAAL
SMC as an automatic tool for carrying out a static security analysis of our running example in isolation and when exposed to three different physics-based attacks with different impacts.
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, whereby aggregate breakup occurs when the local hydrodynamic stress
${\it\sigma}\sim {\it\varepsilon}^{1/2}$
, with
${\it\varepsilon}$
being the energy dissipation at the position of the aggregate, overcomes a given threshold
${\it\sigma}_{cr}$
, which is characteristic for a given type of aggregate. Results show that the breakup rate decreases with increasing threshold. For small thresholds, it develops a scaling behaviour 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, the results are compared with those obtained in a smooth stochastic flow. Furthermore, we discuss the limitations and applicability of a set of independent proxies.
The breakup of inertial, solid aggregates in an incompressible, homogeneous and isotropic three-dimensional turbulent flow is studied by means of a direct numerical simulation, and by a Lagrangian ...tracking of the aggregates at varying Stokes number and fluid-to-particle density ratio. Within the point-particle approximation of the Maxey–Riley–Gatignol equations of motion, we analyze the statistics of the time series of shear and drag stresses, which are here both deemed as responsible for aggregate breakup. We observe that, regardless of the Stokes number, the shear stresses produced by the turbulent velocity gradients similarly impact the breakup statistics of inertial and neutrally buoyant aggregates, and dictate the breakup rate of loose aggregates. When the density ratio is different from unity, drag stresses become dominant and are seen to be able to cause to breakup of also the most resistant aggregates. A transition from a shear-dominated to a drag-dominated breakup regime is observed, and a power-law is seen to well describe the breakup rate of loose aggregates regardless of their inertia. The present work assesses the role of shear and drag stresses on aggregate breakup and computes breakup rates to be possibly used in population balance models.
•Breakup of inertial aggregates is studied by DNS and Lagrangian tracking.•Different approaches for measuring breakup rates in numerical experiments.•Transition from shear to drag dominated breakup at increasing Stokes number.•Breakup of heavy and light aggregates is dictated by drag stresses.
On the vortex dynamics in fractal Fourier turbulence Lanotte, Alessandra S.; Malapaka, Shiva Kumar; Biferale, Luca
The European physical journal. E, Soft matter and biological physics,
04/2016, Letnik:
39, Številka:
4
Journal Article
Recenzirano
Odprti dostop
.
Incompressible, homogeneous and isotropic turbulence is studied by solving the Navier-Stokes equations on a reduced set of Fourier modes, belonging to a fractal set of dimension
D
. By tuning the ...fractal dimension parameter, we study the dynamical effects of Fourier decimation on the vortex stretching mechanism and on the statistics of the velocity and the velocity gradient tensor. In particular, we show that as we move from
D
= 3 to
D
∼ 2.8 , the statistics gradually turns into a purely Gaussian one. This result suggests that even a mild fractal mode reduction strongly depletes the stretching properties of the non-linear term of the Navier-Stokes equations and suppresses anomalous fluctuations.
Graphical abstract
We apply formal methods to lay and streamline theoretical foundations to reason about Cyber-Physical Systems (CPSs) and cyber-physical attacks. We focus on 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.
•Correct management of end-of-life tires and waste plastics is critical, but both wastes can be an excellent addition to pavement materials.•The structural transformation of crumb rubber into ...devulcanized rubber (DVR) can solve the high-viscosity typical of rubberized bitumen, but its performance is poor.•Composites of devulcanized tire rubber and waste plastics can enhance bitumen performance while using two waste materials at the same time.•The rutting and fatigue cracking performance of bitumen modified with these composites is comparable to heavily SBS-modified bitumen, aka high-polymer modified bitumen.
Devulcanized rubber (DVR) and waste plastics have been studied separately as bitumen modifiers, but their individual drawbacks prevent full implementation in the field. In this paper, two pelletized composites produced by coupling DVR with waste low-density polyethylene (LDPE) and polypropylene (PP) were investigated. Linear viscoelastic properties, rutting, and fatigue cracking performance were evaluated, and results were compared to those obtained on neat and polymer-modified bitumen with high styrene-butadiene-styrene content (HiPMB). The non-recoverable creep compliance was reduced with the increasing addition of DVR with either LDPE or PP, and the modified bitumen can be classifiable as “E” grade like the common HiPMB. Bitumen modified with DVR-LDPE compounds showed the best fatigue cracking performance overall, and can fully replace the industrial HiPMB. The implications of these results go beyond the sole performance improvement since these compounds can significantly reduce the environmental impact of road construction by using two waste materials simultaneously.
Display omitted
Patients' quality of life (QoL), facial nerve (FN), and cochlear nerve (CN) (if conserved) functions should be pursued as final outcomes of vestibular schwannoma (VS) surgery. In regard to FN ...function, different morphologic and neurophysiological factors have been related to postoperative outcomes. The aim of the current retrospective study was to investigate the impact of these factors on the short- and long-term FN function after VS resection. The combination of preoperative and intraoperative factors resulted in designing and validating a multiparametric score to predict short- and long-term FN function.
A single-center retrospective analysis was performed for patients harboring non-syndromic VS who underwent surgical resection in the period 2015-2020. A minimum follow-up period of 12 months was considered among the inclusion criteria. Morphological tumor characteristics, intraoperative neurophysiological parameters, and postoperative clinical factors, namely, House-Brackmann (HB) scale, were retrieved in the study. A statistical analysis was conducted to investigate any relationships with FN outcome and to assess the reliability of the score.
Seventy-two patients with solitary primary VS were treated in the period of the study. A total of 59.8% of patients showed an HB value < 3 in the immediate postoperative period (T1), reaching to 76.4% at the last follow-up evaluation. A multiparametric score, Facial Nerve Outcome Score (FNOS), was built. The totality of patients with FNOS grade A showed an HB value < 3 at 12 months, decreasing to 70% for those with FNOS grade B, whereas 100% of patients with FNOS grade C showed an HB value ≥ 3. The ordinal logistic regression showed three times increasing probability to see an HB value ≥ 3 at 3-month follow-up for each worsening point in FNOS score Exp(B), 2,999; p < 0.001 that was even more probable Exp(B), 5.486; p < 0.001 at 12 months.
The FNOS score resulted to be a reliable score, showing high associations with FN function both at short- and long-term follow-up. Although multicenter studies would be able to increase its reproducibility, it could be used to predict the FN damage after surgery and the potential of restoring its function on the long-term period.
Hydrocephalus is a commonly encountered pathology in the neurosurgical practice. Since the first permanent ventriculo-subarachnoid-subgaleal shunt described by Mikulicz in 1893, there were multiple ...attempts to find solutions for draining the excess production/less reabsorption of the cerebrospinal fluid (CSF) from the brain. Nowadays, the most common technique is the ventriculoperitoneal shunt (VPS), whereas the ventriculoatrial shunt (VAS) is applied only in some rare conditions. To date there are still no specific guidelines or strong evidence in literature that guide the surgeon in the choice between the two methods, and the decision usually relies on the confidence and expertise of the surgeon. Considering the lack of established recommendations, this systematic review and meta-analysis aims to evaluate the effectiveness and safety of these two shunting techniques. This systematic review was conducted following the PRISMA protocol (Preferred Reporting Items for Systematic Reviews and Meta-Analyses). No chronological limits of study publications were included. Prospective and retrospective clinical studies, and reports of case series with at least five patients per group and reporting data on comparison between VAS and VPS techniques were eligible for inclusion. Nine studies reporting 3197 patients meeting the inclusion and exclusion criteria were identified and included in the quantitative synthesis. The risk of shunt dysfunction/obstruction was significantly lower in the VAS group odds ratio (OR) 0.49, 95%-CI 0.34–0.70, I2 0%. The risk of infection was not significantly different between the two groups (OR 1.02, 95%-CI 0.59–1.74, I2 0%). The risk of revision was not significantly different between the two groups; however, the heterogeneity between the studies was significant (OR 0.73, 95%-CI 0.36–1.49, I2 91%). Additionally, the risk of death was not significantly different between the two groups; however, the heterogeneity between the studies was high (OR 1.93, 95%-CI 0.81–4.62, I2 64%). VAS remains a safe surgical alternative for hydrocephalus. The results of this study highlight a lower risk of shunt dysfunction/obstruction variable in the VAS group, with no significant statistical differences regarding the occurrence of at least one infection-related complication. In consequence, the choice between these two techniques must be tailored to the specific characteristics of the patient.Protocol Registration: The review protocol was registered and published in Prospective Register of Systematic Reviews (PROSPERO) (www.crd.york.ac.uk/PROSPERO) website with registration number: CRD42023479365.
PDF
