Ash plume properties retrieved from infrared images: a forward and inverse modeling approach

We present a coupled fluid-dynamic and electromagnetic model for volcanic ash plumes. In a forward approach, the model is able to simulate the plume dynamics from prescribed input flow conditions and generate the corresponding synthetic thermal infrared (TIR) image, allowing a comparison with field-based observations. An inversion procedure is then developed to retrieve ash plume properties from TIR images. The adopted fluid-dynamic model is based on a one-dimensional, stationary description of a self-similar (top-hat) turbulent plume, for which an asymptotic analytical solution is obtained. The electromagnetic emission/absorption model is based on the Schwarzschild's equation and on Mie's theory for disperse particles, assuming that particles are coarser than the radiation wavelength and neglecting scattering. [...] Application of the inversion procedure to an ash plume at Santiaguito volcano (Guatemala) has allowed us to retrieve the main plume input parameters, namely the initial radius $b_0$, velocity $U_0$, temperature $T_0$, gas mass ratio $n_0$, entrainment coefficient $k$ and their related uncertainty. Moreover, coupling with the electromagnetic model, we have been able to obtain a reliable estimate of the equivalent Sauter diameter $d_s$ of the total particle size distribution. The presented method is general and, in principle, can be applied to the spatial distribution of particle concentration and temperature obtained by any fluid-dynamic model, either integral or multidimensional, stationary or time-dependent, single or multiphase. The method discussed here is fast and robust, thus indicating potential for applications to real-time estimation of ash mass flux and particle size distribution, which is crucial for model-based forecasts of the volcanic ash dispersal process.Comment: 41 pages, 13 figures, submitted pape

A semi-implicit, second-order-accurate numerical model for multiphase underexpanded volcanic jets

Abstract. An improved version of the PDAC (Pyroclastic Dispersal Analysis Code, Esposti Ongaro et al., 2007) numerical model for the simulation of multiphase volcanic flows is presented and validated for the simulation of multiphase volcanic jets in supersonic regimes. The present version of PDAC includes second-order time- and space discretizations and fully multidimensional advection discretizations in order to reduce numerical diffusion and enhance the accuracy of the original model. The model is tested on the problem of jet decompression in both two and three dimensions. For homogeneous jets, numerical results are consistent with experimental results at the laboratory scale (Lewis and Carlson, 1964). For nonequilibrium gas–particle jets, we consider monodisperse and bidisperse mixtures, and we quantify nonequilibrium effects in terms of the ratio between the particle relaxation time and a characteristic jet timescale. For coarse particles and low particle load, numerical simulations well reproduce laboratory experiments and numerical simulations carried out with an Eulerian–Lagrangian model (Sommerfeld, 1993). At the volcanic scale, we consider steady-state conditions associated with the development of Vulcanian and sub-Plinian eruptions. For the finest particles produced in these regimes, we demonstrate that the solid phase is in mechanical and thermal equilibrium with the gas phase and that the jet decompression structure is well described by a pseudogas model (Ogden et al., 2008). Coarse particles, on the other hand, display significant nonequilibrium effects, which associated with their larger relaxation time. Deviations from the equilibrium regime, with maximum velocity and temperature differences on the order of 150 m s−1 and 80 K across shock waves, occur especially during the rapid acceleration phases, and are able to modify substantially the jet dynamics with respect to the homogeneous case

An application of parallel computing to the simulation of volcanic eruptions

A parallel code for the simulation of the transient 3D dispersal of volcanic particles produced by explosive eruptions is presented. The model transport equations, based on the multiphase flow theory, describe the atmospheric dynamics of the gas-particle mixture ejected through the volcanic crater. The numerics is based on a finite-volume discretization scheme and a pressure-based iterative non-linear solver suited to compressible multiphase flows. The code has been parallelized by adopting an ad hoc domain partitioning scheme that enforces the load balancing. An optimized communication layer has been built over the Message-Passing Interface. The code proved to be remarkably efficient on several high-performance platforms and makes it possible to simulate fully 3D eruptive scenarios on realistic volcano topography

Neutron spectrometry at various altitudes in atmosphere by passive detector technique

A new experimental system, constituted by passive detectors, has been developed to measure neutron spectra at various altitudes in the atmosphere. The knowledge of the neutron spectrum is required to evaluate with a good accuracy the neutron contribution to the total dose, due to the cosmic ray exposure, in fact the flux-to-dose conversion factors strongly depend on neutron energy. Moreover, in many dosimetric applications, as the dose evaluation to the aircrew in service on intercontinental flights, the passive system is not only the most convenient but it is often the unique technique. The experimental system is constituted by the passive bubble detector BD100R, polycarbonate foils, polycarbonate bottles, sensitive in low and intermediate neutron energy range, and the bismuth stack, sensitive in the high energy range. Experimental data were obtained in high mountain measurements at Matterhorn (3600 m altitude, 46 N ) and Chacaltaya (5230 m altitude, 16 S), during flights at 12000 m and on board of stratospheric balloons at 38000 m. All the spectra obtained show, as expected, the evaporation peak around 1 MeV and the second direct bump around 100 MeV; the results, different in the neutron flux intensity, confirm the satisfactory sensitivity of this experimental technique

Ash plume properties retrieved from infrared images: a forward and inverse modeling approach

We present a coupled fluid-dynamic and electromagnetic model for volcanic ash plumes. In a forward approach, the model is able to simulate the plume dynamics from prescribed input flow conditions and generate the corresponding synthetic thermal infrared (TIR) image, allowing a comparison with field-based observations. An inversion procedure is then developed to retrieve ash plume properties from TIR images. The adopted fluid-dynamic model is based on a one-dimensional, stationary description of a self-similar (top-hat) turbulent plume, for which an asymptotic analytical solution is obtained. The electromagnetic emission/absorption model is based on the Schwarzschild's equation and on Mie's theory for disperse particles, assuming that particles are coarser than the radiation wavelength and neglecting scattering. In the inversion procedure, model parameters space is sampled to find the optimal set of input conditions which minimizes the difference between the experimental and the synthetic image. Two complementary methods are discussed: the first is based on a fully two-dimensional fit of the TIR image, while the second only inverts axial data. Due to the top-hat assumption (which overestimates density and temperature at the plume margins), the one-dimensional fit results to be more accurate. However, it cannot be used to estimate the average plume opening angle. Therefore, the entrainment coefficient can only be derived from the two-dimensional fit. Application of the inversion procedure to an ash plume at Santiaguito volcano (Guatemala) has allowed us to retrieve the main plume input parameters, namely the initial radius $b_0$, velocity $U_0$, temperature $T_0$, gas mass ratio $n_0$, entrainment coefficient $k$ and their related uncertainty. Moreover, coupling with the electromagnetic model, we have been able to obtain a reliable estimate of the equivalent Sauter diameter $d_s$ of the total particle size distribution. The presented method is general and, in principle, can be applied to the spatial distribution of particle concentration and temperature obtained by any fluid-dynamic model, either integral or multidimensional, stationary or time-dependent, single or multiphase. The method discussed here is fast and robust, thus indicating potential for applications to real-time estimation of ash mass flux and particle size distribution, which is crucial for model-based forecasts of the volcanic ash dispersal process

New development: Directly elected mayors in Italy: creating a strong leader doesn’t mean creating strong leadership

More than 20 years after their introduction, directly elected mayors are key players in Italian urban governance. This article explains the main effects of this reform on local government systems and provides lessons for other countries considering directly elected mayors

Environmental DNA assessment of airborne plant and fungal seasonal diversity

Environmental DNA (eDNA) metabarcoding and metagenomics analyses can improve taxonomic resolution in biodiversity studies. Only recently, these techniques have been applied in aerobiology, to target bacteria, fungi and plants in airborne samples. Here, we present a nine-month aerobiological study applying eDNA metabarcoding in which we analyzed simultaneously airborne diversity and variation of fungi and plants across five locations in North and Central Italy. We correlated species composition with the ecological characteristics of the sites and the seasons. The most abundant taxa among all sites and seasons were the fungal genera Cladosporium, Alternaria, and Epicoccum and the plant genera Brassica, Corylus, Cupressus and Linum, the latter being much more variable among sites. PERMANOVA and indicator species analyses showed that the plant diversity from air samples is significantly correlated with seasons, while that of fungi varied according to the interaction between seasons and sites. The results consolidate the performance of a new eDNA metabarcoding pipeline for the simultaneous amplification and analysis of airborne plant and fungal particles. They also highlight the promising complementarity of this approach with more traditional biomonitoring frameworks and routine reports of air quality provided by environmental agencies

Antibacterial rifampicin-loaded electrospun polycaprolactone membranes for ureteral regeneration

Author of the study: Nowadays partial or complete ureteral loss following resection or injuries of various etiology is managed with different surgical techniques involving local tissue flaps or autologous tissues interposition. In the last years ureteral tissue engineering using membranes, tubular scaffolds or decellularized matrices has shown promising results for ureteral substitution. The aim of this study is to evaluate the use of antibacterial electrospun polycaprolactone/ rifampicin (PCL/RIF) membranes for the production of ureteral scaffolds with antibacterial properties. Materials and methods: Electrospinning processwas used to produce the membranes that were subsequently impregnated with rifampicin. Membranes stability was evaluated by immersion in Simulated Body Fluid (SBF) at 37 °C. Mechanical properties were evaluated by uniaxial tensile tests, Young’s modulus was calculated for each sample. UV spectrophotometry was used to evaluate in vitro release of rifampicin. The ability of PCL/Rif membranes to sustain cell adhesion and proliferation was evaluated by seeding human urothelial bladder carcinoma cells on the membranes. In order to investigate the antibacterial effect of PCL/Rif membranes, in vitro antibacterial tests were performed using bacterial strains belonging to the “ESKAPE” group. Results: PCL/Rif membranes are characterized by a random distribution of fibers with an average diameter of 0.52 μm.Water contact angle for PCL and PCL/Rif membranes is around 125° and decreases to 0° after air-plasma treatment. When culture medium is used as testing fluid PCL and PCL/Rif contact angles are 116° and 12° respectively. Membranes are deformable up to 300% of their initial dimension and possess an elastic Young modulus of about 20 kPa; after 3 weeks membranes gain the property to sustain a 100% deformation before rupture. The 72% of rifampicin load is released by the membranes in the first 24 hours. Proliferation assay showed a seven-fold increase of cell number adhered on the membranes after 7 days of culture. At the same time in presence of PCL/Rif membranes, rates of bacterial proliferation inhibition ranged from 75 to 94% compared to controls. Conclusions: PCL/Rif membranes represent a promising starting point in the production of ureteral scaffolds with antibacterial properties for ureteral substitution

Improving pre-operative planning of robot assisted nephron sparing surgery using three-dimensional anatomical model

Introduction Despite the introduction of robot-assisted surgery in daily clinical practice, complex renal masses are still challenging even for expert surgeon. In this scenario 3D anatomical models and augmented reality represent valuable tools for the surgeon. Materials and methods We present a challenging case where PN was mandatory to preserve the overall renal function. The patient was 69 years old, with indwelling catheter for BPH and Parkinson disease. After a single episode of hematuria with negative cystoscopy, a cT1N0M0 renal cancer was diagnosed (38 mm maximum diameter). Pre-operative three-dimensional (3D) model was obtained. After multidisciplinary discussion robot-assisted partial nephrectomy was proposed. The surgery was planned according to the anatomical model. Results Before the procedure a 7Ch single loop ureteral stent was placed. The surgery was carried out in 220 minutes. Selective ischaemia was perfomed for 24 minutes. Estimated blood loss was 400cc. No post-operative complications were observed. Ureteral stent was removed 4 days after the surgery. Definitive histological examination described a pG2-3 T1a Nx R0 clear cell renal carcinoma. Conclusion In selected cases 3D model result to be a useful tool for the pre-operative planning of the surgery

A Short Counterexample Property for Safety and Liveness Verification of Fault-tolerant Distributed Algorithms

Distributed algorithms have many mission-critical applications ranging from embedded systems and replicated databases to cloud computing. Due to asynchronous communication, process faults, or network failures, these algorithms are difficult to design and verify. Many algorithms achieve fault tolerance by using threshold guards that, for instance, ensure that a process waits until it has received an acknowledgment from a majority of its peers. Consequently, domain-specific languages for fault-tolerant distributed systems offer language support for threshold guards. We introduce an automated method for model checking of safety and liveness of threshold-guarded distributed algorithms in systems where the number of processes and the fraction of faulty processes are parameters. Our method is based on a short counterexample property: if a distributed algorithm violates a temporal specification (in a fragment of LTL), then there is a counterexample whose length is bounded and independent of the parameters. We prove this property by (i) characterizing executions depending on the structure of the temporal formula, and (ii) using commutativity of transitions to accelerate and shorten executions. We extended the ByMC toolset (Byzantine Model Checker) with our technique, and verified liveness and safety of 10 prominent fault-tolerant distributed algorithms, most of which were out of reach for existing techniques.Comment: 16 pages, 11 pages appendi