Pore-scale modeling of fluid-particles interaction and emerging poromechanical effects

A micro-hydromechanical model for granular materials is presented. It combines the discrete element method (DEM) for the modeling of the solid phase and a pore-scale finite volume (PFV) formulation for the flow of an incompressible pore fluid. The coupling equations are derived and contrasted against the equations of conventional poroelasticity. An analogy is found between the DEM-PFV coupling and Biot's theory in the limit case of incompressible phases. The simulation of an oedometer test validates the coupling scheme and demonstrates the ability of the model to capture strong poromechanical effects. A detailed analysis of microscale strain and stress confirms the analogy with poroelasticity. An immersed deposition problem is finally simulated and shows the potential of the method to handle phase transitions.Comment: accepted in Int. Journal for Numerical and Analytical Methods in Geomechanic

Physical and numerical modelling of sand liquefaction in waves interacting with a vertical wall

International audienceWave induced liquefaction at a coastal structure is studied. Experiments in a glass-wall flume filled with a partially saturated bed of light-weight sediment are presented. Periodic waves and single wave loadings are simulated. For large enough wave conditions an excess pore pressure is recorded within the soil and a liquefaction threshold is reached. Velocity fields obtained from video recordings display large zones of the bed that behave as a fluid. Phases of soil compaction and dilatation are identified. Moreover, a Discrete Element Method - Pore-scale Finite Volume model is used to simulate the wave-sediment interactions. The computation of the coupling between the flow and the motion of the particles enables to reproduce the excess pore pressure that lead to liquefaction and the progressive compaction of the bed

Adaptively Secure Single Secret Leader Election from DDH

Single Secret Leader Election protocols (SSLE, for short) allow a group of users to select a random leader so that the latter remains secret until she decides to reveal herself. Thanks to this feature, SSLE can be used to build an election mechanism for proof-of-stake based blockchains. In particular, a recent work by Azouvi and Cappelletti (ACM AFT 2021) shows that in comparison to probabilistic leader election methods, SSLE-based proof-of-stake blockchains have significant security gains, both with respect to grinding attacks and with respect to the private attack. Yet, as of today, very few concrete constructions of SSLE are known. In particular, all existing protocols are only secure in a model where the adversary is supposed to corrupt participants before the protocol starts -- an assumption that clashes with the highly dynamic nature of decentralized blockchain protocols. In this paper we make progress in the study of SSLE by proposing new efficient constructions that achieve stronger security guarantees than previous work. In particular, we propose the first SSLE protocol that achieves adaptive security. Our scheme is proven secure in the universal composability model and achieves efficiency comparable to previous, less secure, realizations in the state of the art

The future direction of imaging in prostate cancer: MRI with or without contrast injection

Background: Multiparametric MRI (mpMRI) is the "state of the art" management tool for patients with prostate cancer (PCa) suspicion. The role of non-contrast MRI is investigated to move toward a more personalized, less invasive, and highly cost-effective PCa diagnostic workup. Objective: To perform a non-systematic review of the existing literature to highlight strength and flaws of performing non-contrast MRI, and to provide a critical overview of the international scientific production on the topic. Materials and methods: Online databases (Medline, PubMed, and Web of Science) were searched for original articles, systematic review and meta-analysis, and expert opinion papers. Results: Several investigations have shown comparable diagnostic accuracy of biparametric (bpMRI) and mpMRI for the detection of PCa. The advantage of abandoning contrast-enhanced sequences improves operational logistics, lowering costs, acquisition time, and side effects. The main limitations of bpMRI are that most studies which compared the non-contrast and contrast MRI come from centers with high expertise that might not be reproducible in the general community setting; besides, reduced protocols might be insufficient for estimation of the intra- and extra-prostatic extension and regional disease. The mentioned observations suggest that low quality mpMRI for the general population, might represent the main shortage to overcome. Discussion: Non-contrast MRI future trends are likely represented by PCa screening and the application of artificial intelligence (AI) tools. PCa screening is still a controversial topic and bpMRI, and has become one of the most promising diagnostic applications, as it is a more sensitive test for PCa early detection, compared to serum PSA level test. Also, AI applications and radiomic have been the object of several studies investigating PCa detection using bpMRI, showing encouraging results. Conclusion: Today, the accessibility to MRI for early detection of PCa is a priority. Results from prospective, multicenter, multireader and paired validation studies are needed to provided evidence supporting its role in the clinical practice

On the Impossibility of Algebraic Vector Commitments in Pairing-Free Groups

Vector Commitments allow one to (concisely) commit to a vector of messages so that one can later (concisely) open the commitment at selected locations. In the state of the art of vector commitments, algebraic constructions have emerged as a particularly useful class, as they enable advanced properties, such as stateless updates, subvector openings and aggregation, that are for example unknown in Merkle-tree-based schemes. In spite of their popularity, algebraic vector commitments remain poorly understood objects. In particular, no construction in standard prime order groups (without pairing) is known. In this paper, we shed light on this state of affairs by showing that a large class of concise algebraic vector commitments in pairing-free, prime order groups are impossible to realize. Our results also preclude any cryptographic primitive that implies the algebraic vector commitments we rule out, as special cases. This means that we also show the impossibility, for instance, of succinct polynomial commitments and functional commitments (for all classes of functions including linear forms) in pairing-free groups of prime order

Safety and comfort of domestic bortezomib injection in real-life experience

Despite novel agents, multiple myeloma is still an incurable disease, especially for elderly and frail patients, who are difficult to manage for concomitant comorbidities as the therapeutic options are limited and the response to chemotherapy is often short. We report our evaluations upon safety and efficacy of domestic subcutaneous bortezomib in elderly and frail patients candidate to bortezomib-melphalan-prednisone (VMP) regimen. We confirmed that overall incidence of adverse events, including peripheral neuropathy, was low, and in no case required admission to emergency service, contributing to reduce the rate of therapy discontinuation. These results confirm the effectiveness and safety of subcutaneous bortezomib, in a real-life-experience, and define a new possibility of safe auto-administration in a comfortable domestic setting. We suggest that domestic treatment can significantly improve the quality of life of the patients, avoiding unnecessary transfer to the hospital without reducing treatment efficacy

Biparametric prostate MRI: impact of a deep learning-based software and of quantitative ADC values on the inter-reader agreement of experienced and inexperienced readers

Objective To investigate the impact of an artificial intelligence (AI) software and quantitative ADC (qADC) on the inter-reader agreement, diagnostic performance, and reporting times of prostate biparametric MRI (bpMRI) for experienced and inexperienced readers. Materials and methods A total of 170 multiparametric MRI (mpMRI) of patients with suspicion of prostate cancer (PCa) were retrospectively reviewed by one experienced and one inexperienced reader three times, following a wash-out period. First, only the bpMRI sequences, including T2-weighted imaging (T2WI), diffusion-weighted imaging (DWI) sequences, and apparent diffusion coefficient (ADC) maps, were used. Then, bpMRI and quantitative ADC values were used. Lastly, bpMRI and the AI software were used. Inter-reader agreement between the two readers and between each reader and the mpMRI original reports was calculated. Detection rates and reporting times were calculated for each group. Results Inter-reader agreement with respect to mpMRI was moderate for bpMRI, Quantib, and qADC for both the inexperienced (weighted k of 0.42, 0.45, and 0.41, respectively) and the experienced radiologists (weighted k of 0.44, 0.46, and 0.42, respectively). Detection rate of PCa was similar between the inexperienced (0.24, 0.26, and 0.23) and the experienced reader (0.26, 0.27 and 0.27), for bpMRI, Quantib, and qADC, respectively. Reporting times were lower for Quantib (8.23, 7.11, and 9.87 min for the inexperienced reader and 5.62, 5.07, and 6.21 min for the experienced reader, for bpMRI, Quantib, and qADC, respectively). Conclusions AI and qADC did not have a significant impact on the diagnostic performance of both readers. The use of Quantib was associated with lower reporting times

Multi-criteria environmental and economic impact assessment of wire arc additive manufacturing

Wire arc additive manufacturing (WAAM) is a fusion- and wire-based additive manufacturing technology which has gained industrial interest for the production of medium-to-large components with high material deposition rates. However, in-depth studies on performance indicators that incorporate economic and environmental sustainability still have to be carried out. The first aim of the paper has been to quantify the performance metrics of WAAM based manufacturing approaches, while varying the size and the deposited material of the component. The second aim has been to propose a multi-criteria decision-analysis mapping to compare the combined impacts of products manufactured by means of the WAAM-based approach and machinin

Wire arc additive manufacturing of Ti-6Al-4V components: the effects of the deposition rate on the cradle-to-gate economic and environmental performance

Wire Arc Additive Manufacturing (WAAM) is a direct energy deposition process based on a wire-shaped metal feedstock which is melted by means of an electric arc to produce and/or repair components in a layer-wise manner. WAAM has shown to be suitable for producing large components, in particular those with a near-to-net shape, at relatively high productivity levels. The aim of this work has been to assess the effects of the WAAM deposition rate on economic and environmental sustainability metrics. A life cycle assessment has been performed under cradleto-gate system boundaries. Three components, with different geometrical characteristics (i.e., dimensions, masses, and solid-to-cavity ratios) and made of Ti-6Al-4V, have been considered as case studies. The effects of different deposition rates have been evaluated on the Cumulative Energy Demand, CO2 emissions, manufacturing times and costs. The conventional manufacturing route for the production of the same components, that is, machining from massive workpieces, has been considered as a benchmark for a process performance comparison. The results show that an increase in the deposition rate determines a significant reduction (up to 25%, on average) in the production time and, consequently, in the manufacturing costs

Low cancer yield in pi-rads 3 upgraded to 4 by dynamic contrast-enhanced mri. is it time to reconsider scoring categorization

Objectives: To evaluate MRI diagnostic performance in detecting clinically significant prostate cancer (csPCa) in peripheral-zone PI-RADS 4 lesions, comparing those with clearly restricted diffusion (DWI-score 4), and those with equivocal diffusion pattern (DWI-score 3) and positive dynamic contrast-enhanced (DCE) MRI. Methods: This observational prospective study enrolled 389 men referred to MRI and, if positive (PI-RADS 3 with PSA-density [PSAD] ≥ 0.15 ng/mL/mL, 4 and 5), to MRI-directed biopsy. Lesions with DWI-score 3 and positive DCE were classified as "PI-RADS 3up," instead of PI-RADS 4. Univariable and multivariable analyses were implemented to determine features correlated to csPCa detection. Results: Prevalence of csPCa was 14.5% and 53.3% in PI-RADS categories 3up and 4, respectively (p < 0.001). MRI showed a sensitivity of 100.0%, specificity 40.9%, PPV 46.5%, NPV 100.0%, and accuracy 60.9% for csPCa detection. Modifying the threshold to consider MRI positive and to indicate biopsy (same as previously described, but PI-RADS 3up only when associated with elevated PSAD), the sensitivity changed to 93.9%, specificity 57.2%, PPV 53.0%, NPV 94.8%, and accuracy 69.7%. Age (p < 0.001), PSAD (p < 0.001), positive DWI (p < 0.001), and PI-RADS score (p = 0.04) resulted in independent predictors of csPCa. Conclusions: Most cases of PI-RADS 3up were false-positives, suggesting that upgrading peripheral lesions with DWI-score 3 to PI-RADS 4 because of positive DCE has a detrimental effect on MRI accuracy, decreasing the true prevalence of csPCa in the PI-RADS 4 category. PI-RADS 3up should not be upgraded and directed to biopsy only if associated with increased PSAD. Key points: • As per PI-RADS v2.1 recommendations, in case of a peripheral zone lesion with equivocal diffusion-weighted imaging (DWI score 3), but positive dynamic contrast-enhanced (DCE) MRI, the overall PI-RADS score should be upgraded to 4. • The current PI-RADS recommendation of upgrading PI-RADS 3 lesions of the peripheral zone to PI-RADS 4 because of positive DCE decreased clinically significant prostate cancer detection rate in our series. • According to our results, the most accurate threshold for setting indication to prostate biopsy is PI-RADS 3 or PI-RADS 3 with positive DCE both associated with increased PSA density