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Background: Complications of atrial fibrillation (AF) include ischemic events originating within the left atrial appendage (LAA), a protrusion of the left atrium with variable morphological characteristics. The role of the patient specific morphology and pathological haemodynamics on the risk of ischemia remains unclear. Methods: This work performs a comparative assessment of the hemodynamic parameters among patient-specific LAA morphologies through fluid-structure interaction computational analyses. Three LAA models per each of the four commons patient-specific morphological families (chicken wing, cactus, windsock, and cauliflower) were analysed. Mechanical properties of the tissue were based on experimental uniaxial tests on a young pig's heart. Boundary conditions were imposed based on clinical assessments of filling and emptying volumes. Sinus rhythm and atrial fibrillation operative conditions were simulated and analysed. Results: For each model, the effect of morphological and functional parameters, such as the number of trabeculae and LAA stroke volume, over the hemodynamics established into the appendage was analysed. Comparison between results obtained in healthy and diseased conditions suggested the introduction of a new parameter to quantify the risk of thrombosis, here called blood stasis factor (BSF). This is defined as the LAA surface area which permanently experiences levels of shear strain rate inferior to a threshold value, set to 5 s−1 (BSF5). Conclusions: This work suggests that the current morphological classification is unsuitable to evaluate the probability of thrombus formation. However, hemodynamic parameters easy to determine from clinical examinations, such as normalised stroke volume, LAA orifice flow rate and presence of extensive trabeculations can identify departures from healthy hemodynamics in AF and support a more systematic stratification of the thromboembolic risk.

This paper describes an innovative methodology to calibrate EM simulators oriented to monolithic microwave integrated circuit design. The proposed approach allows one to accurately estimate the substrate characteristics without realizing expensive on-wafer structures that require a large substrate area. We will demonstrate how the proposed approach ultimately results in higher EM simulation accuracy, describing and quantifying the limitations that arise from commonly adopted calibration procedures for EM simulators. Authors

Inversion of the left atrial appendage is a rare phenomenon, which may occur during the de-airing maneuvers associated to routinely performed surgery procedures, such as cardiopulmonary bypass or left ventricular assist device implantation. In this case, the body of the inverted appendage can obstruct the mitral valve leading to severe complications. The mechanisms are still poorly known, and more specific studies are needed to better understand its causes and identify mitigating strategies. The current study attempts to gain a better comprehension of the conditions and the factors favourable to left atrial appendage inversion. Four patient specific appendage morphologies, obtained from computerised tomography and representative of the main typologies commonly used for the appendage classification (chicken wing, cactus, cauliflower, and windsock), were used for the study. The numerical models were subjected to the same loading pattern, made of subsequent different pressure curves. Results show that the morphologies invert and recover their original anatomical configuration at different pressure loads, indicating that their tendency to invert is associated to their specific morphological features. Moreover, the analysis highlights that, although restoring the physiological left atrium pressure is not sufficient to induce appendage recovery, pressures well below the ventricular ones can induce the return to the natural configuration. All models recovered the anatomical configuration at pressures well below the ventricular pressure (about 100 mmHg), suggesting that basic trans-catheter maneuvers, e.g. producing temporary mitral regurgitation, could be attempted to correct the appendage configuration, prior to opt for more invasive surgical approaches.

A promising reduction of costs, consumption and environmental impact for infrastructures exploiting Radio-over-Fiber systems can be given by the use of Vertical Cavity Surface Emitting Lasers operating in the first optical transmission window (i.e., 850nm) and by the re-use of already installed G.652 fiber. However, the effectiveness of this combination of elements is strongly dependent on the presence of intermodal dispersion, produced mainly by the bi-modal propagation in the G.652 when operating in the first window. However, in principle, the excitation of each mode strictly depends on the coupling conditions, such as relative alignment and tilting between fiber and VCSEL, and the input field of the latter. The numerical and experimental analysis performed in this work shows the impact of different coupling conditions on the two-mode excitation focusing on its impact on multimode effects such as intermodal dispersion and modal noise.

High survival of the nematode Contracaecum rudolphii in European eel, Anguilla anguilla L. despite an extensive recruitment of immune cells in granulomas is described. A total of 39 eel specimens captured in Canneviè lagoon (Northern Adriatic Sea, Italy) was obtained from local fishermen. The fish were examined for the presence of endoparasitic helminths. Twenty-six eels (67%) harbored third-stage larvae (L3) of Contracaecum rudolphii A and the intensity of infection ranged from 1 to 100 parasites per fish (mean 11.4). A total of 296 larvae were counted and 293 were alive and encysted in the serosa (primarily on external surface of the rectum) as conspicuous granulomas, appearing as white nodules. Histological sections showed a granuloma formed around an individual larva and consisted of three concentric cell layers, containing numerous mast cells (MCs), fibroblasts, macrophages, and epithelioid cells. Encysted larvae were also present in other layers of the intestinal wall, including the mucosa, where recruitment of macrophage aggregates in lamina propria was documented. Immunohistochemical investigations, applying eight antibodies raised against immune cell markers, revealed histamine and serotonin in MCs and inducible-nitric oxide synthase and toll-like receptor-2 in macrophages surrounding the parasite larvae. The study indicates that this innate cellular response in the eel has a chronic inflammatory character and keeps the nematode larvae arrested in a state allowing both host tolerance and parasite survival. The European eel serves as prey for birds and the high survival of C. rudolphii A larvae in the eel indicates that this fish species is a good paratenic host for the parasite allowing completion of its life cycle in birds.

Description of granuloma formation ell infected by the nematode larvae C. rudolphii

In this paper, the experimental verification of suitable input harmonic injection to achieve class F operating conditions in class bfC (under pinch-off) biased active devices is discussed. In detail, it is demonstrated that by generating a third harmonic component V_g, 3 with a proper phase relationship with respect to the fundamental one V_g, 1, it is possible to change the phase of the resulting output harmonic components, and in particular of the third one I_D, 3, thus generating the proper squaring of the output voltage. Experimental results at device level have shown an improvement in terms of output power and efficiency from 2.24W to 3.00W and from 72.2% to 79.3%, respectively. The proposed approach could play a key role in the maximization of the achievable efficiency of Doherty power amplifiers, where the auxiliary branch needs to be biased in class C for a exploitation of the architecture.

In this paper, we experimentally investigate the effects of degradation observed on 0.15-& mu;m GaN HEMT devices when operating under realistic power amplifier conditions. The latter will be applied to the devices under test (DUT) by exploiting a low-frequency load-pull characterization technique that provides information consistent with RF operation, with the advantage of revealing electrical quantities not directly detectable at high frequency. Quantities such as the resistive gate current, play a fundamental role in the analysis of technology reliability. The experiments will be carried out on DUTs of the same periphery considering two different power amplifier operations: a saturated class-AB condition, that emphasizes the degradation effects produced by high temperatures due to power dissipation, and a class-E condition, that enhances the effects of high electric fields. The experiments will be carried out at 30 & DEG;C and 100 & DEG;C, and the results will be compared to evaluate how a specific RF condition can impact on the device degradation. Such a kind of comparison, to the authors' knowledge, has never been carried out and represents the main novelty of the present study.

In this work, we describe the complete design flow of a 1.3–3.3-GHz active balun, exploited to generate a high-voltage swing differential local oscillator (LO) signal driving a highly linear doubly balanced resistive ring mixer. Both the LO active balun and the mixer are integrated into a -band single chip monolithic microwave integrated circuits (MMIC) downconverter for the state-of-the-art telecom satellites. System performance has been maximized designing the different circuits by a holistic approach, which considers a non 50- environment. The experimental validation is carried out by means of an ad hoc time-domain load–pull test bench and shows that the LO active balun provides two quasi-sinusoidal, 180 out-phased, signals with 2.4-V peak-to-peak voltage to the input ports of the mixer over a very high-impedance loading condition.

The 15th century cross-vaults of the medieval Modena Cathedral (UNESCO site) consist of intricate patches of different masonry portions bound by three types of lime mortars and at least two types of gypsum mortars. Such anomalous structure suggests multiple repair works over time after damaging earthquakes. The absolute dating of lime mortars (14C) and bricks (TL) integrated with the pollen record of mortars allowed to clarify the construction and restoration history of the vaults and to link the repairs to the earthquake chronology for the area. The results reveal that the original construction of the vaults (1404–1454) was carried out using lime mortar binding reused Roman and medieval older bricks. Lime mortar was used also for later repairs caused by earthquakes in the 16th and 17th centuries. Gypsum mortars were then used to entirely rebuild some vaults and to repair others in the 18th and 19th centuries. The study indicates that unexpected damage could be revealed by the detailed chronology of masonry binders. These data represent fundamental steps to implement earthquake risk assessments and strengthening projects of ancient buildings.

In this paper we experimentally analyze two of the most controversial classes of operation, i.e., class E and class F-1, often misinterpreted, due to the necessity of an exciting waveform different from a pure sinusoidal or distorted sinusoidal signal. As a matter of fact, without a proper shaping of the input signal these classes of operation give rise to very poor amplifier performance that can lead to erroneous conclusions.

In this paper, we present a method for characterizing and analysing GaN-based FET devices. The measurement technique, named Dynamic Bias, is presented here using its oscilloscope-based implementation. Some practical issues in implementing such a measurement technique with an oscilloscope will be discussed, and solutions to overcome these problems will be presented. The analysis is carried out using both simulations and measurements. Experimental results are shown for a 0.15 \mu m GaN HEMT device with 300-\mu m periphery.

Background: A large majority of thrombi causing ischemic complications under atrial fibrillation (AF) originate in the left atrial appendage (LAA), an anatomical structure departing from the left atrium, characterized by a large morphological variability between individuals. This work analyses the hemodynamics simulated for different patient-specific models of LAA by means of computational fluid–structure interaction studies, modeling the effect of the changes in contractility and shape resulting from AF. Methods: Three operating conditions were analyzed: sinus rhythm, acute atrial fibrillation, and chronic atrial fibrillation. These were simulated on four patient-specific LAA morphologies, each associated with one of the main morphological variants identified from the common classification: chicken wing, cactus, windsock, and cauliflower. Active contractility of the wall muscle was calibrated on the basis of clinical evaluations of the filling and emptying volumes, and boundary conditions were imposed on the fluid to replicate physiological and pathological atrial pressures, typical of the various operating conditions. Results: The LAA volume and shear strain rates were analyzed over time and space for the different models. Globally, under AF conditions, all models were well aligned in terms of shear strain rate values and predicted levels of risk. Regions of low shear rate, typically associated with a higher risk of a clot, appeared to be promoted by sudden bends and focused at the trabecule and the lobes. These become substantially more pronounced and extended with AF, especially under acute conditions. Conclusion: This work clarifies the role of active and passive contraction on the healthy hemodynamics in the LAA, analyzing the hemodynamic effect of AF that promotes clot formation. The study indicates that local LAA topological features are more directly associated with a thromboembolic risk than the global shape of the appendage, suggesting that more effective

This study is aimed at investigating the performance of an advanced GaN HEMT technology for millimeter-wave applications. Both DC and frequency-dependent measurements are performed on three multifinger on-wafer 0.15-µm transistors with different gate widths at different ambient temperatures for foreseeing GaN technology capability when applications require challenging frequency operation.

Optical transmitters based on Vertical Cavity Surface Emitting Lasers operating in the first optical window (FW-VCSELs) constitute an attractive option to realize Green Radio over Fiber (RoF) systems, due to their low energy consumption. In addition, these devices can take advantage of the widespread existing infrastructures realized on G.652 Standard Single Mode Fibers (SSMF) to develop low-cost RoF connections while remaining transparent for the presently transmitted Fiber-To-The-Home services, which exploit the second and third optical windows. Within this context, the use of simple butt-coupling between FW-VCSELs and SSMF should be a desirable feature, which however is theoretically exposed to possible drawbacks of poor efficiency and two-mode propagation effects. Through a detailed experimental activity referred to commercial high-performance multi- and single-mode FW-VCSELs, it is shown how to optimize their butt-coupling configuration to SSMF reducing the mentioned drawbacks and consider this solution suitable for 5G-and-beyond low-cost Green RoF applications.

Green and low-cost radio-over-fiber infrastructures for the capillary distribution of millimeter-wave signals can straightforwardly be developed through the use of low-consumption devices and the re-use of current deployed fibers. In particular, green infrastructures could be achieved by using Gallium-Arsenide Vertical Cavity Surface Emitting Lasers (VCSELs) operating around 850nm together with the standard G.652 fiber of 9-micron core diameter (SSMF) already installed inside building for providing internet connection via the Fiber-To-The-Home (FTTH) technology. In this context, the use of simple butt-coupling between VCSEL and SSMF is an attractive option in view of the targeted low-cost of the final system. However, all the commercial and currently available VCSELs are designed to be coupled with multimode fibers for short length datacom applications, and the coupling with SSMF is typically not optimized. In this work, we investigate the practicability of butt-coupling between high-performance multimode and singlemode VCSELs and SSMF, in view of 5G-And-beyond Radio over Fiber applications.

In this paper, reliability issues in Gallium Nitride (GaN) HEMTs are empirically investigated. To this purpose, stress measurements were carried out on a microwave transistor under realistic load-line conditions exploiting a nonlinear load-pull setup operating at few megahertz. Although the characterization strategy was applied on a 150-nm GaN technology, it has general validity and, as will be demonstrated by the reported experimental results, can be successfully applied to evaluate the maturity of the investigated technology processes.

In this paper, a model extraction technique suitable for GaN transistors with very large periphery is described. The technique is based on the accurate nonlinear model extraction of a reference size device that is then scaled to a larger periphery preserving its original accuracy. The proposed model has been extensively validated with microwave nonlinear load-pull measurements and with the design of a 200-W S-band power amplifier.

This paper describes the efficiency-limiting factors resulting from transistor current source in the case of class-F and inverse class-F (F-1) operations under saturated region. We investigated the influence of knee voltage and gate-voltage clipping behaviors on drain efficiency as limiting factors for the current source. Numerical analysis using a simplified transistor model was carried out. As a result, we have demonstrated that the limiting factor for class-F-1 operation is the gate-diode conduction rather than knee voltage. On the other hand, class-F PA is restricted by the knee voltage effects. Furthermore, nonlinear measurements carried out on a GaN HEMT validate our analytical results.

In this paper, a single-chip front-end (SCFE) operating in Ku-band (12–17 GHz) is presented. It is designed exploiting a GaN on SiC technology featured by 150 nm gate length provided by UMS foundry. This MMIC integrates high power and low noise amplification functions enabled by a single-pole double-throw (SPDT) switch, occupying a total area of 20 mm2. The transmitting chain (Tx) presents a 39 dBm output power, a power added efficiency (PAE) higher than 30% and a 22 dB power gain. The receive path (Rx) offers a low noise figure (NF) lower than 2.8 dB with 25 dB of linear gain. The Rx port output power leakage is limited on chip to be below 15 dBm even at high compression levels. Finally, a complete characterization of the SCFE in the Rx and Tx modes is presented, also showing the measurement of the recovery time in the presence of large-signal interferences.

Nonlinear modeling of GaN HEMTs is a challenging task especially when accurate predictions are desired under nonlinear dynamic operation. This is mainly due to the dispersion phenomena affecting state-of-the-art devices that must be accurately characterized and correctly accounted for during the development of their nonlinear model. The challenge becomes harder as frequency, power and circuit complexity increase as being demanded by the marketplace for the upcoming 5G-related applications. In this paper, nonlinear measurement techniques are discussed which allow the accurate characterization of microwave GaN HEMTs under actual operating conditions. The paper also discusses how to use these measurements in the extraction phase of nonlinear models highlighting the benefits of their adoption for modeling purposes.

Dealing with high-power operation (i.e., >100 W) is extremely critical to power-amplifier designers due to the lack of accurate transistor models of multicell (i.e., powerbar) devices. The reason is twofold: from one side, it is extremely difficult to characterize high-power transistors (e.g., device instability, thermal issues, microwave instrumentation costs, and measurement uncertainty that drastically increases with the investigated power level); and from the other side, the scaling proprieties of the model, moving from the unit-cell device to the multicell one, are inherently poor due to the different passive access structures to the active-device area. In this article, for the first time, an accurate modeling technique oriented to multicell devices is described, which allows one to extract a compact model of a multicell transistor showing similar prediction accuracy of the unit-cell one. Our assumptions have been widely demonstrated in the manuscript by a comprehensive characterization campaign from small-to large-signal operations carried out on both the unit-and multicell devices.

We present a measurement technique for the characterization of the degradation in microwave transistors. The time-domain setup operates in the megahertz range to set a realistic load-line for the device. Data on the degradation of a microwave transistor are reported.

New system architectures oriented to more and more challenging performance for the next generations of mobile devices demand for an accurate design of integrated circuits. The power amplifier is one of the most critical components in an RF system and the need for high performance has focused the designer attention to complex architectures, such as the Doherty power amplifier (DPA). In its most common implementations, the design requires transistor models showing high-accuracy levels under different classes of operation. In this work, we investigate the possibility of achieving the required level of accuracy for the transistor current-generator model using a set of measurements performed under the different classes of operation that mimic realistic device operation and use them for the model optimization. The developed approach is fully validated on a 28-GHz MMIC DPA, showing good agreement with the measured results.

The BRAIN (Botanical Records of Archaeobotany Italian Network) database and network was developed by the cooperation of archaeobotanists working on Italian archaeological sites. Examples of recent research including pollen or other plant remains in analytical and synthetic papers are reported as an exemplar reference list. This paper retraces the main steps of the creation of BRAIN, from the scientific need for the first research cooperation to the website which has a free online access since 2015.