Energetic Balance in the Debonding of a Reinforcing Stringer: Effect of the Substrate Elasticity

An effective way to strengthen deteriorated concrete or masonry structures is to glue to them, at critical regions, strips or plates made of Fiber Reinforced Polymers (FRP). The reliability of this technique depends upon interfacial adhesion, whose performance is usually evaluated through an energetic balance, assuming that the support is rigid. The present study analyzes the contact problem between reinforcement and substrate, both assumed to be linear elastic. The solution of the resulting integro-differential equations is expressed in terms of Chebyshev polynomials. A generalization to this problem of the Crack Closure Integral Method developed by Irwin allows to calculate the energy release rate associated with the debonding of the stiffener. Energetic balance `a la Griffith emphasizes the role played by the length of the stiffener and the deformation of the substrate, predicting load vs. displacement curves that, in agreement with experimental measurements, exhibit a snap-back phase

Cohesive debonding of a stiffener from an elastic substrate

To strengthen concrete or masonry, a modern technique uses adherent strips made of Fiber Reinforced Polymer (FRP). A model problem for this is here considered, represented by an elastic stiffener pulled at one end, in adhesive contact with an elastic half space in generalized plane stress. An analytical solution is developed under the hypothesis `a la Baranblatt that cohesive adhesion forces remain active between the two materials when relative slip occurs (provided this is less than a critical value), so that the stress singularity predicted by the theory of elasticity in the case of perfect bonding is removed. We find that the bond length beyond which no further increase of strength could be achieved, referred to as the effective bond length, coincides in practice with the ultimate length of the cohesive zone, i.e., its maximal extension prior that the critical slip limit is attained. The debonding process in a pull-out experiment is analyzed in detail. Results are in better agreement with experimental data than those obtainable with traditional models, which neglect as a rule the deformation of the substrat

Face morphing detection in the presence of printing/scanning and heterogeneous image sources

Face morphing represents nowadays a big security threat in the context of electronic identity documents as well as an interesting challenge for researchers in the field of face recognition. Despite of the good performance obtained by state-of-the-art approaches on digital images, no satisfactory solutions have been identified so far to deal with cross-database testing and printed-scanned images (typically used in many countries for document issuing). In this work, novel approaches are proposed to train Deep Neural Networks for morphing detection: in particular generation of simulated printed-scanned images together with other data augmentation strategies and pre-training on large face recognition datasets, allowed to reach state-of-the-art accuracy on challenging datasets from heterogeneous image sources

Filaments of the radio cosmic web: opportunities and challenges for SKA

The detection of the diffuse gas component of the cosmic web remains a formidable challenge. In this work we study synchrotron emission from the cosmic web with simulated SKA1 observations, which can represent an fundamental probe of the warm-hot intergalactic medium. We investigate radio emission originated by relativistic electrons accelerated by shocks surrounding cosmic filaments, assuming diffusive shock acceleration and as a function of the (unknown) large-scale magnetic fields. The detection of the brightest parts of large ($>10 \rm Mpc$) filaments of the cosmic web should be within reach of the SKA1-LOW, if the magnetic field is at the level of a $\sim 10$ percent equipartition with the thermal gas, corresponding to $\sim 0.1 \mu G$ for the most massive filaments in simulations. In the course of a 2-years survey with SKA1-LOW, this will enable a first detection of the "tip of the iceberg" of the radio cosmic web, and allow for the use of the SKA as a powerful tool to study the origin of cosmic magnetism in large-scale structures. On the other hand, the SKA1-MID and SKA1-SUR seem less suited for this science case at low redshift ($z \leq 0.4$), owing to the missing short baselines and the consequent lack of signal from the large-scale brightness fluctuations associated with the filaments. In this case only very long exposures ($\sim 1000$ hr) may enable the detection of $\sim 1-2$ filament for field of view in the SKA1-SUR PAF Band1.Comment: 10 pages, 4 figures, to appear in Proceedings of 'Advancing Astrophysics with the SKA (AASKA14) - Cosmic Magnetism' Chapter

On the Detachment of FRP Stiffeners from Brittle-Elastic Substrates

Fiber Reinforced Polymers (FRP) are commonly used for strengthening and rehabilitation of concrete or masonry structures, by gluing strips or plates made of this material on the surface of the weak material. Experimental studies have provided evidence that the main failure mode is the debonding of the FRP stiffener from the support, triggered by high stress concentrations at the extremities of the stiffener. Fracture propagates firstly parallel to the interface and then in the substrate, until complete separation between the two adherents occurs. Final failure is often characterized by the detachment of a wedge-shaped portion of the substrate, which remains bonded to the FRP strip. In order to describe the whole process, the model problem considered here is that of a finite thin elastic stiffener, bonded to an elastic half-space in generalized plane stress, pulled at one end by an axial force. The thickness of the stiffener is supposed very small, so that its bending stiffness can be considered negligible and only shear stresses act at the interface. On the contrary to the common assumptions of current models, the elastic deformations of the substrate are not neglected here: this is the main novelty of the proposed approach. Compatibility equations between the stiffener and the substrate allow to write a singular integral equation for the contact problem, whose solution can then be obtained through an expansion in Chebyshev's series. The debonding process in pure mode II is supposed to be activated by an energetic balance, i.e., when the release of elastic strain energy equals the surface energy associated with material separation. If the bond is perfect, the theory of elasticity predicts stress singularities at both ends of the stiffener. The shear stresses in a neighborhood of the singularity at the loaded end of the FRP strip is sufficient to counterbalance, in practice, the whole load applied, while the experimental evidence shows instead an effective bond length (EBL), over which the load transfer occurs gradually. To solve this inconsistency, in a second model a cohesive zone has been introduced at the loaded end of the stiffener, where slippage can occur according to an interface constitutive law, until a limit slip value is reached. Following an approach “à là” Barenblatt, the length of this zone is found by imposing that the stress intensity factor is null at the transition zone between the completely bonded part and the cohesive part, so to annihilate the stress singularity. There is a maximal reachable length of this cohesive zone, in which cohesive forces counterbalance, in practice, all the applied load, and which, therefore, can be referred to as the EBL. It can be also demonstrated that the second singularity at the free end of the stiffener plays a minor role, being negligible the load associated with it. In order to describe the phenomenon of the wedge-shaped fracturing of concrete, a fracture mechanics problem “à là” Griffith has been considered for the substrate, assuming the crack propagation occurs in steps of finite length (quanta), of the same order of the intrinsic material length scale. From the energetic and tensional competition between the failure of the adhesive joint and the fracturing of the substrate, it has been possible to determine a critic propagation angle which coincides with the characteristic angle of the detached wedge-shaped bulb. Results obtained from the analytical models are in very good agreement with the experimental results

Detecting Morphing Attacks via Continual Incremental Training

Scenarios in which restrictions in data transfer and storage limit the possibility to compose a single dataset -- also exploiting different data sources -- to perform a batch-based training procedure, make the development of robust models particularly challenging. We hypothesize that the recent Continual Learning (CL) paradigm may represent an effective solution to enable incremental training, even through multiple sites. Indeed, a basic assumption of CL is that once a model has been trained, old data can no longer be used in successive training iterations and in principle can be deleted. Therefore, in this paper, we investigate the performance of different Continual Learning methods in this scenario, simulating a learning model that is updated every time a new chunk of data, even of variable size, is available. Experimental results reveal that a particular CL method, namely Learning without Forgetting (LwF), is one of the best-performing algorithms. Then, we investigate its usage and parametrization in Morphing Attack Detection and Object Classification tasks, specifically with respect to the amount of new training data that became available.Comment: Paper accepted in IJCB 2023 conferenc

Template co-updating in multi-modal human activity recognition systems

Multi-modal systems are quite common in the context of human activity recognition; widely used RGB-D sensors (Kinect is the most prominent example) give access to parallel data streams, typically RGB images, depth data, skeleton information. The richness of multimodal information has been largely exploited in many works in the literature, while an analysis of their effectiveness for incremental template updating has not been investigated so far. This paper is aimed at defining a general framework for unsupervised template updating in multi-modal systems, where the different data sources can provide complementary information, increasing the effectiveness of the updating procedure and reducing at the same time the probability of incorrect template modifications

Factor Structure, Reliability, and Validity of the Therapist Response Questionnaire

open4noThe aim of this study was to examine the stability of the factor structure and psychometric properties of the Therapist Response Questionnaire (Betan, Heim, Zittel Conklin, & Westen, 2005; Zittel Conklin & Westen, 2003), a clinician report instrument able to measure the clinician's emotional reactions to the patient in psychotherapy. A national sample of psychiatrists and clinical psychologists (N = 332) of psychodynamic and cognitive-behavioral orientation completed the Therapist Response Questionnaire, as well as the Shedler-Westen Assessment Procedure-200 (Westen & Shedler, 1999a, 1999b), to assess personality disorders and level of psychological functioning, regarding a patient currently in their care. They also administered the Symptom Checklist-90-Revised (Derogatis, 1994) to the patients. Exploratory and confirmatory factor analyses revealed 9 distinct countertransference factors that were similar to 8 dimensions identified in the original version of the measure: (a) helpless/inadequate, (b) overwhelmed/disorganized, (c) positive/satisfying, (d) hostile/angry, (e) criticized/devalued, (f) parental/protective, (g) special/overinvolved, (h) sexualized, and (i) disengaged. These scales showed excellent internal consistencies and good validity. They were especially able to capture the quality and intensity of emotional states that therapists experience while treating personality-disordered patients, as well as to better differentiate them; additionally, they tapped into the complexity of clinicians' reactions toward patients experiencing severe psychiatric symptomatology. Results seem to confirm that Therapist Response Questionnaire is a valid and reliable instrument that allows to evaluate patterns of countertransference responses in clinically sensitive and psychometrically robust ways, regardless of therapists' orientations. The clinical and research implications of these findings are addressed. (PsycINFO Database RecordopenTanzilli, Annalisa; Colli, Antonello; Del Corno, Franco; Lingiardi, VittorioTanzilli, Annalisa; Colli, Antonello; Del Corno, Franco; Lingiardi, Vittori