Grenzflächenverhalten zwischen Faserverbundwerkstoffen und quasi-spröden Oberflächen

The use of externally glued fiber-reinforced polymers (FRP) as reinforcement to overcome the tensile deficiency of quasi-brittle elements (e.g. concrete beams, shear walls, masonry arches) has gained great popularity during the last years. Experimental and theoretical studies demonstrated that, when the FRP-substrate joint is mostly stressed in shear, one of the princiapal failure mechanisms is the debonding. It occurs when the shear capacity of the system is reached and a crack develops underneath the bond plane a few millimeters inside the substrate, causing the detachment of the composite element. In the present work the interface behavior of FRP joints is studied by means of experimental and numerical studies. A new single-lap test setup is proposed allowing to stably follow, for the first time, the entire equilibrium path of this kind of reinforcement. The proposed setup is then adopted to study the bond performances of FRPs applied on both concrete and masonry. The test results highlight a dependence of the global behavior from the initial bonded length and suggest the presence of non-negligible stresses orthogonal to the bonding plane. Also, comparing the results on concrete and on masonry, it is shown how, for this latter kind of substrates, the behavior is strongly influenced by the material texture and composition. To reproduce the changes in behavior observed during the experimental campaign, a novel cohesive zone model that accounts for the presence and the coupling between normal and tangential stresses is proposed and validated. Furthermore, the problem of the fatigue failure for this joints is studied and a new thermodynamically consistent numerical model that couples damage and plasticity under pure shear conditions is formulated. The numerical simulations coming from the two proposed models are compared to experimental results coming from the performed tests as well as from the available literature. Moreover, the improvements with respect to the models to date available are highlighted. Finally, taking advantage of new experimental studies and starting from theoretical considerations, a modified practical design formula for the debonding capacity for FRP reinforcements applied on masonry substrates is proposed and calibrated over a large database of results collected form the literature.Der Einsatz außen geklebter Faserverbundwerkstoffe (fiber-reinforced polymers, FRP) als Verstärkung, um die Schwäche quasi-spröder Elemente bei Zugbelastung zu überwinden, hat in den letzten Jahren an großer Aufmerksamkeit gewonnen. Experimentelle und theoretische Studien haben gezeigt, dass wenn die FKV-Substrat-Verbindung überwiegend auf Schub belastet wird, die Ablösung eine der hauptsächlichen Versagenskriterien ist. Diese tritt auf, wenn die Schubtragfähigkeit des Systems erreicht ist und sich ein Riss unterhalb der Klebfläche, wenige Millimeter innerhalb des Substrats ausbreitet und die Ablösung des Verbundelements bewirkt. In der vorliegenden Arbeit wird das Grenzflächenverhalten von FRP-Verbindungen mittels experimenteller und numerischer Studien untersucht. Eine neue Zugscherversuchsanordnung wird vorgeschlagen, die es erstmalig für diese Art von Verstärkung ermöglicht, der gesamten Kraft-Weg-Kurve stabil zu folgen. Der vorgeschlagene Aufbau wird genutzt, um die Klebergebnisse von Faser-Kunststoff-Verbunden zu untersuchen, die sowohl auf Beton als auch Mauerwerken appliziert werden. Die Testergebnisse zeigen eine Abhängigkeit des globalen Verhaltens von der initialen Länge der Klebung auf und deuten auf das Vorhandensein nicht unerheblicher Spannungen senkrecht zur Klebfläche hin. Um die Veränderungen im Verhalten zu reproduzieren, die während der experimentellen Testreihen beobachtet wurde, wird ein neuartiges Kohäsivzonenmodell vorgeschlagen und validiert, welches das Vorhandensein und die Koppelung zwischen Normal- und Tangentialspannungen berücksichtigt. Außerdem wird das Problem der Materialermüdung für diese Verbindungen untersucht und ein neues, thermodynamisch konsistentes, numerisches Modell formuliert, das Schaden und Plastizität unter reinen Scherbedingungen koppelt. Die numerischen Simulationen auf Basis der beiden vorgeschlagenen Modelle werden mit experimentellen Ergebnissen aus den durchgeführten Tests sowie der verfügbaren Literatur verglichen. Außerdem werden die Verbesserungen im Vergleich zu aktuell verfügbaren Modellen dargestellt. Zum Schluss wird - den Vorteil neuer experimenteller Studien ausnutzend und mit theoretischen Überlegungen als Ausgangspunkt - eine modifizierte, praxistaugliche Berechnungsformel für die Schubtragfähigkeit von FRP-Verstärkungen, die auf Mauerwerk-Substraten appliziert werden, vorgeschlagen und mit Hilfe einer großen Datenbank aus Ergebnissen in der Literatur kalibriert

Data-Driven Rate-Dependent Fracture Mechanics

We extend the model-free data-driven paradigm for rate-independent fracture mechanics proposed in Carrara et al. (2020), Data-driven Fracture Mechanics, Comp. Meth. App. Mech. Eng., 372 to rate-dependent fracture and sub-critical fatigue. The problem is formulated by combining the balance governing equations stemming from variational principles with a set of data points that encodes the fracture constitutive behavior of the material. The solution is found as the data point that best satisfies the meta-stability condition as given by the variational procedure and following a distance minimization approach based on closest-point-projection. The approach is tested on different setups adopting different types of rate-dependent fracture and fatigue models affected or not by white noise.Comment: Submitted for Review in Journal of Mechanics and Physics of Solids (JMPS

Phase-field modeling of brittle fracture in heterogeneous bars

We investigate phase-field modeling of brittle fracture in a one-dimensional bar featuring a continuous variation of elastic and/or fracture properties along its axis. Our main goal is to quantitatively assess how the heterogeneity in elastic and fracture material properties influences the observed behavior of the bar, as obtained from the phase-field modeling approach. The results clarify how the elastic limit stress, the peak stress and the fracture toughness of the heterogeneous bar relate to those of the reference homogeneous bar, and what are the parameters affecting these relationships. Overall, the effect of heterogeneity is shown to be strictly tied to the non-local nature of the phase-field regularization. Finally, we show that this non-locality may amend the ill-posedness of the sharp-crack problem in heterogeneous bars where multiple points compete as fracture locations

Autonomic and circulatory alterations persist despite adequate resuscitation in a 5-day sepsis swine experiment.

Autonomic and vascular failures are common phenotypes of sepsis, typically characterized by tachycardia despite corrected hypotension/hypovolemia, vasopressor resistance, increased arterial stiffness and decreased peripheral vascular resistance. In a 5-day swine experiment of polymicrobial sepsis we aimed at characterizing arterial properties and autonomic mechanisms responsible for cardiovascular homeostasis regulation, with the final goal to verify whether the resuscitation therapy in agreement with standard guidelines was successful in restoring a physiological condition of hemodynamic profile, cardiovascular interactions and autonomic control. Twenty pigs were randomized to polymicrobial sepsis and protocol-based resuscitation or to prolonged mechanical ventilation and sedation without sepsis. The animals were studied at baseline, after sepsis development, and every 24 h during the 3-days resuscitation period. Beat-to-beat carotid blood pressure (BP), carotid blood flow, and central venous pressure were continuously recorded. The two-element Windkessel model was adopted to study carotid arterial compliance, systemic vascular resistance and characteristic time constant τ. Effective arterial elastance was calculated as a simple estimate of total arterial load. Cardiac baroreflex sensitivity (BRS) and low frequency (LF) spectral power of diastolic BP were computed to assess autonomic activity. Sepsis induced significant vascular and autonomic alterations, manifested as increased arterial stiffness, decreased vascular resistance and τ constant, reduced BRS and LF power, higher arterial afterload and elevated heart rate in septic pigs compared to sham animals. This compromised condition was persistent until the end of the experiment, despite achievement of recommended resuscitation goals by administered vasopressors and fluids. Vascular and autonomic alterations persist 3 days after goal-directed resuscitation in a clinically relevant sepsis model. We hypothesize that the addition of these variables to standard clinical markers may better profile patients' response to treatment and this could drive a more tailored therapy which could have a potential impact on long-term outcomes

Sun-induced chlorophyll fluorescence and photochemical reflectance index improve remote-sensing gross primary production estimates under varying nutrient availability in a typical Mediterranean savanna ecosystem

Este estudio investiga las diferentes actuaciones de ópticas sobre los índices para estimar la producción primaria bruta (GPP) del estrato herbáceo de una sabana mediterránea con diferente disponibilidad de nitrógeno (N) y de fósforo (P). La fluorescencia de la clorofila inducida por el sol sobre el rendimiento calculado en 760 nm (FY760), escala de índice de reflectancia fotoquímica (sPRI), MERIS terrestre (índice de clorofila MTCI) y el índice de vegetación de diferencia normalizada (NDVI) fueron calculadas desde cerca de la superficie y las mediciones de espectroscopia de campo recolectados se hicieron utilizando espectrómetros de alta resolución espectral, que abarcan las regiones del infrarrojo cercano visible. La GPP fue medida utilizando cámaras de dosel en las mismas localidades muestreadas por los espectrómetros. Hemos probado si la eficiencia del uso de los modelos de luz (LUE) impulsados por cantidades de teledetección (RSMs) pueden hacer un mejor seguimiento de los cambios en la GPP causada por fuentes de nutrientes en comparación con aquellos impulsados exclusivamente por datos meteorológicos (MM). En particular, comparamos los espectáculos de diferentes formulaciones de RSM -basándose en la utilización de FY760 o sPRI como proxy para LUE y NDVI MTCI o como una fracción de la radiación fotosintéticamente activa absorbida (APAR f)- con las clásicas de MM. Los resultados mostraron mayor GPP en la N -parcelas experimentales fertilizadas durante el período de crecimiento. Estas diferencias en la GPP desaparecieron en el período de secado, cuando los efectos de la senescencia enmascarada contiene diferencias de potencial debido a la planta N. Por consiguiente, MTCI estaba estrechamente relacionada con la media de la planta N, contenida a través de tratamientos (r2 D 0:86, p < 0:01), porque estaba mal relacionados con GPP (r2 D 0:45, p < 0:05). Por el contrario sPRI y FY760 se correlacionaban bien con GPP durante todo el período de medición. Los resultados revelaron que la relación entre el GPP y FY760 no es única en los tratamientos, pero no se ve afectada por la disponibilidad de N. Los resultados de un análisis de validación cruzada mostró que el MM (AICcv D 127, MEcv D 0:879) superó a RSM (AICcv D 140, MEcv D 0:8737,) cuando la humedad del suelo fue utilizada para restringir la dinámica estacional de LUE. Sin embargo, el análisis residual demostró que las predicciones de GPP con MM son inexactas cuando no revela explícitamente unas variables climáticas en cambios relacionados con el parámetro de nutrientes LUE. Estos resultados sugieren que RSM es un medio valioso para diagnosticar los efectos inducidos por los nutrientes en la actividad fotosintética.This study investigates the performances of different optical indices to estimate gross primary production (GPP) of herbaceous stratum in a Mediterranean savanna with different nitrogen (N) and phosphorous (P) availability. Sun-induced chlorophyll fluorescence yield computed at 760 nm (Fy760), scaled photochemical reflectance index (sPRI), MERIS terrestrial-chlorophyll index (MTCI) and normalized difference vegetation index (NDVI) were computed from near-surface field spectroscopy measurements collected using high spectral resolution spectrometers covering the visible near-infrared regions. GPP was measured using canopy chambers on the same locations sampled by the spectrometers. We tested whether light-use efficiency (LUE) models driven by remote-sensing quantities (RSMs) can better track changes in GPP caused by nutrient supplies compared to those driven exclusively by meteorological data (MM). Particularly, we compared the performances of different RSM formulations – relying on the use of Fy760 or sPRI as a proxy for LUE and NDVI or MTCI as a fraction of absorbed photosynthetically active radiation (f APAR) – with those of classical MM. Results showed higher GPP in the N-fertilized experimental plots during the growing period. These differences in GPP disappeared in the drying period when senescence effects masked out potential differences due to plant N content. Consequently, although MTCI was closely related to the mean of plant N content across treatments (r2 D 0:86, p < 0:01), it was poorly related to GPP (r2 D 0:45, p < 0:05). On the contrary sPRI and Fy760 correlated well with GPP during the whole measurement period. Results revealed that the relationship between GPP and Fy760 is not unique across treatments, but it is affected by N availability. Results from a cross-validation analysis showed that MM (AICcv D 127, MEcv D 0:879) outperformed RSM (AICcv D 140, MEcv D 0:8737) when soil moisture was used to constrain the seasonal dynamic of LUE. However, residual analyses demonstrated that GPP predictions with MM are inaccurate whenever no climatic variable explicitly reveals nutrient-related changes in the LUE parameter. These results suggest that RSM is a valuable means to diagnose nutrient-induced effects on the photosynthetic activity.Trabajo financiado por: Alexander von Humboldt Foundation y la Max Planck Research AwardpeerReviewe

Flat band separation and robust spin-Berry curvature in bilayer kagome metals

Kagome materials have emerged as a setting for emergent electronic phenomena that encompass different aspects of symmetry and topology. It is debated whether the XV$_6$Sn$_6$ kagome family (where X is a rare earth element), a recently discovered family of bilayer kagome metals, hosts a topologically non-trivial ground state resulting from the opening of spin-orbit coupling gaps. These states would carry a finite spin-Berry curvature, and topological surface states. Here, we investigate the spin and electronic structure of the XV$_6$Sn$_6$ kagome family. We obtain evidence for a finite spin-Berry curvature contribution at the center of the Brillouin zone, where the nearly flat band detaches from the dispersing Dirac band because of spin-orbit coupling. In addition, the spin-Berry curvature is further investigated in the charge density wave regime of ScV$_6$Sn$_6$, and it is found to be robust against the onset of the temperature-driven ordered phase. Utilizing the sensitivity of angle resolved photoemission spectroscopy to the spin and orbital angular momentum, our work unveils the spin-Berry curvature of topological kagome metals, and helps to define its spectroscopic fingerprint.Comment: 21 pages, 4 figure

Observation of termination-dependent topological connectivity in a magnetic Weyl Kagome lattice

The research leading to these results has received funding from the European Union’s Horizon 2020 research and innovation program under Marie Skłodowska-Curie Grant Agreement 897276. The authors gratefully acknowledge the Gauss Centre for Supercomputing e.V. (https://www.gauss-centre.eu) for funding this project by providing computing time on the GCS Supercomputer SuperMUC-NG at Leibniz Supercomputing Centre (https://www.lrz.de). The authors are grateful for funding support from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy through the Würzburg-Dresden Cluster of Excellence on Complexity and Topology in Quantum Matter ct.qmat (EXC 2147, Project 390858490), through FOR 5249-449872909 (Project P5), and through the Collaborative Research Center SFB 1170 ToCoTronics (Project 258499086). The authors greatly acknowledge the Diamond Light Source that supported the entire micro-ARPES experiment and corresponding costs. The Flatiron Institute is a division of the Simons Foundation. P.D.C.K. and C.B. gratefully acknowledge support from The Leverhulme Trust via Grant RL-2016-006.Engineering surfaces and interfaces of materials promises great potential in the field of heterostructures and quantum matter designers, with the opportunity to drive new many-body phases that are absent in the bulk compounds. Here, we focus on the magnetic Weyl kagome system Co3Sn2S2 and show how for the terminations of different samples the Weyl points connect differently, still preserving the bulk-boundary correspondence. Scanning tunneling microscopy has suggested such a scenario indirectly, and here, we probe the Fermiology of Co3Sn2S2 directly, by linking it to its real space surface distribution. By combining micro-ARPES and first-principles calculations, we measure the energy-momentum spectra and the Fermi surfaces of Co3Sn2S2 for different surface terminations and show the existence of topological features depending on the top-layer electronic environment. Our work helps to define a route for controlling bulk-derived topological properties by means of surface electrostatic potentials, offering a methodology for using Weyl kagome metals in responsive magnetic spintronics.Publisher PDFPeer reviewe

Surgical Antimicrobial Prophylaxis in Patients of Neonatal and Pediatric Age Undergoing Orthopedic and Hand Surgery: A RAND/UCLA Appropriateness Method Consensus Study

Surgical site infections (SSIs) represent a potential complication in any type of surgery and can occur up to one year after the procedure in the case of implant placement. In the field of orthopedic and hand surgery, the rate of SSIs is a relevant issue, considering the need for the placement of synthesis devices and the type of some interventions (e.g., exposed fractures). This work aims to provide guidance on the management of peri-operative antibiotic prophylaxis for the pediatric and neonatal population undergoing orthopedic and hand surgery in order to standardize the management of patients and to reduce, on the one hand, the risk of SSI and, on the other, the development of antimicrobial resistance. The following scenarios were considered: (1) bloodless fracture reduction; (2) reduction of unexposed fracture and grade I and II exposed fracture; (3) reduction of grade III exposed fracture or traumatic amputation; (4) cruel fracture reduction with percutaneous synthesis; (5) non-traumatic amputation; (6) emergency intact skin trauma surgery and elective surgery without synthetic media placement; (7) elective orthopedic surgery with prosthetic and/or synthetic media placement and spinal surgery; (8) clean elective hand surgery with and without bone involvement, without use of synthetic means; (9) surgery of the hand on an elective basis with bone involvement and/or with use of synthetic means. This manuscript has been made possible by the multidisciplinary contribution of experts belonging to the most important Italian scientific societies and represents, in our opinion, the most complete and up-to-date collection of recommendations regarding the behavior to be adopted in the peri-operative setting in neonatal and pediatric orthopedic and hand surgery. The specific scenarios developed are aimed at guiding the healthcare professional in practice to ensure the better and standardized management of neonatal and pediatric patients, together with an easy consultation

Colorectal surgery in Italy during the Covid19 outbreak: a survey from the iCral study group

Background The COVID19 pandemic had a deep impact on healthcare facilities in Italy, with profound reorganization of surgical activities. The Italian ColoRectal Anastomotic Leakage (iCral) study group collecting 43 Italian surgical centers experienced in colorectal surgery from multiple regions performed a quick survey to make a snapshot of the current situation. Methods A 25-items questionnaire was sent to the 43 principal investigators of the iCral study group, with questions regard- ing qualitative and quantitative aspects of the surgical activity before and after the COVID19 outbreak. Results Two-thirds of the centers were involved in the treatment of COVID19 cases. Intensive care units (ICU) beds were partially or totally reallocated for the treatment of COVID19 cases in 72% of the hospitals. Elective colorectal surgery for malignancy was stopped or delayed in nearly 30% of the centers, with less than 20% of them still scheduling elective colo- rectal resections for frail and comorbid patients needing postoperative ICU care. A significant reduction of the number of colorectal resections during the time span from January to March 2020 was recorded, with significant delay in treatment in more than 50% of the centers. Discussion Our survey confirms that COVID19 outbreak is severely affecting the activity of colorectal surgery centers partici- pating to iCral study group. This could impact the activity of surgical centers for many months after the end of the emergency

Chronic constipation diagnosis and treatment evaluation: The "CHRO.CO.DI.T.E." study

Background: According to Rome criteria, chronic constipation (CC) includes functional constipation (FC) and irritable bowel syndrome with constipation (IBS-C). Some patients do not meet these criteria (No Rome Constipation, NRC). The aim of the study was is to evaluate the various clinical presentation and management of FC, IBS-C and NRC in Italy. Methods: During a 2-month period, 52 Italian gastroenterologists recorded clinical data of FC, IBS-C and NRC patients, using Bristol scale, PAC-SYM and PAC-QoL questionnaires. In addition, gastroenterologists were also asked to record whether the patients were clinically assessed for CC for the first time or were in follow up. Diagnostic tests and prescribed therapies were also recorded. Results: Eight hundred seventy-eight consecutive CC patients (706 F) were enrolled (FC 62.5%, IBS-C 31.3%, NRC 6.2%). PAC-SYM and PAC-QoL scores were higher in IBS-C than in FC and NRC. 49.5% were at their first gastroenterological evaluation for CC. In 48.5% CC duration was longer than 10 years. A specialist consultation was requested in 31.6%, more frequently in IBS-C than in NRC. Digital rectal examination was performed in only 56.4%. Diagnostic tests were prescribed to 80.0%. Faecal calprotectin, thyroid tests, celiac serology, breath tests were more frequently suggested in IBS-C and anorectal manometry in FC. More than 90% had at least one treatment suggested on chronic constipation, most frequently dietary changes, macrogol and fibers. Antispasmodics and psychotherapy were more frequently prescribed in IBS-C, prucalopride and pelvic floor rehabilitation in FC. Conclusions: Patients with IBS-C reported more severe symptoms and worse quality of life than FC and NRC. Digital rectal examination was often not performed but at least one diagnostic test was prescribed to most patients. Colonoscopy and blood tests were the "first line" diagnostic tools. Macrogol was the most prescribed laxative, and prucalopride and pelvic floor rehabilitation represented a "second line" approach. Diagnostic tests and prescribed therapies increased by increasing CC severity