•The influence of temperature on DC–DC converter devices properties is considered.•An electro-thermal design method for PV power optimizer converters is proposed.•The electro-thermal design method ...proposed is applied to DR boost and SR boost.•Efficiency results of the designed SR converter and DR converters are presented.
Photovoltaic (PV) systems can operate in presence of not uniform working conditions caused by continuously changing temperature and irradiance values and mismatching and shadowing phenomena. The more the PV system works in these conditions, the more its energy performances are negatively affected. Distributed Maximum Power Point Tracking (DMPPT) converters are now increasingly used to overcome this problem and to improve PV applications efficiency. A DMPPT system consists in a DC–DC converters equipped with a suitable controller dedicated to the Maximum Power Point Tracking (MPPT) of a single PV module. It is arranged either inside the junction-box or in a separate box close to the PV generator. Many power optimizers are now commercially available. In spite of different adopted DC–DC converter topologies, the shared interests of DMPPT systems designers are the high efficiency and reliability values. It is worth noting that to obtain so high performances converters, electronic components have to be carefully selected between the whole commercial availability and appropriately matched together. In this scenario, an electro-thermal design methodology is proposed and a reliability study by means of the Military Handbook 217F is carried out.
The developed DMPPT converters design method is constituted by many steps. In fact, beginning from installation site, PV generators and load data, this process selects power optimizers commercially available devices and it verifies their electro-thermal behavior to the aim to identify a set of suitable components for DMPPT applications. Repeating this process many times, many different feasible solutions can be found. An elaboration step follows to the “optima” power optimizer recognition among the whole obtained converters. In this case, a multi-objective optimization, consisting in the maximization of the solutions European efficiency and in the minimization of their cost, is executed and all not dominated solutions with respect to at least one of the two objectives are selected. The strength of the described method is represented by accurate PV generators and optimizer devices models. In detail, in the developed models particular attention is reserved to the thermal factor and to the quantification of the temperature action on devices parameters and performances. In fact, in such multiple and continuous changing working conditions, the temperature influence on components behavior can considerably vary their properties causing the whole converter performances worsening. The other important aspect, the converter reliability, is estimated by the reliability prediction model Military Handbook 217F.
The proposed tool is applied to Diode Rectification (DR) boosts and Synchronous (SR) boosts design. To completely characterize the obtained solutions their efficiency, cost and reliability performances are evaluated. In detail, Pareto fronts in terms of European efficiency and cost are identified for the SR and DR cases. Among the whole not dominated solutions, a SR converter characterized by a European efficiency of 97.1% and a DR boost characterized by a European efficiency of 95.5% are chosen. Their cost is comparable and equal about to $11. Then their reliability performances are evaluated by means of the Military Handbook 217F Notice 2. The carried out analysis shows that, for the same device cost, the SR solution represents the best one if efficiency is the most critical aspect. DR boost is, instead, the optimum solution if reliability represents the tighter requirement.
The proposed DMPPT converters methodology permits to design families of feasible power optimizers. This process is applied to two boost versions, so two sets of power optimizers are obtained and a trade-off solution is chosen for each set. To correctly select the more suitable optimizer, a characterization in terms of efficiency, cost and reliability is carried out. In detail, the SR optimizer is characterized by lower losses and higher efficiency than the DR one. On the other hand, the DR boost results more reliable than the SR converter. So the optimum solution has to be chosen on the base of the most critical requirement.
The developed method can represent a useful tool to design DMPPT optimizers able to assure high level performances in terms of economical and technical aspects. It can be applied to many commercially available PV generators and, without loss of generality, it can be used with different DC–DC converter topologies.
SUMMARY
Microseismic monitoring is a primary tool for understanding and tracking the progress of mechanical processes occurring in active rock fracture systems. In geothermal or hydrocarbon fields or ...along seismogenic fault systems, the detection and location of microseismicity facilitates resolution of the fracture system geometry and the investigation of the interaction between fluids and rocks, in response of stress field perturbations. Seismic monitoring aims to detect locate and characterize seismic sources. The detection of weak signals is often achieved at the cost of increasing the number of false detections, related to transient signals generated by a range of noise sources, or related to instrumental problems, ambient conditions or human activity that often affect seismic records. A variety of fast and automated methods has been recently proposed to detect and locate microseismicity based on the coherent detection of signal anomalies, such as increase in amplitude or coherent polarization, at dense seismic networks. While these methods proved to be very powerful to detect weak events and to reduce the magnitude of completeness, a major problem remains to discriminate among weak seismic signals produced by microseismicity and false detections. In this work, the microseimic data recorded along the Irpinia fault zone (Southern Apennines, Italy) are analysed to detect weak, natural earthquakes using one of such automated, migration-based, method. We propose a new method for the automatic discrimination of real vs false detections, which is based on empirical data and information about the detectability (i.e. detection capability) of the seismic network. Our approach allows obtaining high performances in detecting earthquakes without requiring a visual inspection of the seismic signals and minimizing analyst intervention. The proposed methodology is automated, self-updating and can be tuned at different success rates.
A coherence-based earthquake detection technique was applied to continuous (1 year) waveform data recorded along the Irpinia fault system (Southern Italy). The earthquake detection was performed ...using coherent P- and S-wave arrivals recorded by the dense seismic network operating in Irpinia and assuming a local velocity model. We applied a strategy to simultaneously detect and locate earthquakes and to discriminate among true and false detections using an automated and fast procedure, able to process 1 year of data in ~ 1.75 days. The final catalogue of automatically retrieved earthquakes shows a performance improvement with respect to the standard monitoring practices, with an increase in the number of detected small events of about a factor three with respect to the automatic Earth-worm Binder implemented in ISNet and decreases in completeness magnitude of almost half unit magnitude.
A modern digital seismic network, with many stations optimally distributed on the earthquake causative seismic zone, enables detection of very low magnitude earthquakes and determination of their ...source parameters. It is essential to associate to such kind of networks procedures to analyze the huge amount of continuously recorded data for monitoring the space-time-magnitude evolution of natural and/or induced seismicity. Hence, the demand for near-real-time, automated data collection and analysis procedures for assisting seismic network operators in carrying out microearthquake monitoring is growing. In response to this need, we designed a computational software platform, TREMOR, for fast and reliable detection and characterization of seismicity recorded by a dense local seismic network. TREMOR integrates different open-source seismological algorithms for earthquake signal detection, location, and source characterizations in a fully automatic workflow. We applied the platform in play-back mode to the continuous waveform data recorded during 1 month at the Japanese Hi-net seismic network in the Nagano region (Japan) and compared the resulting catalog with the Japan Meteorological Agency bulletin in terms of number of detections, location pattern and magnitudes. The results show that the completeness magnitude of the new seismic catalog decreased by 0.35 units of the local magnitude scale and consequently the number of events increased by about 60% with respect to the available catalog. Moreover, the fault plane solutions resulted coherent with the stress regime of the region, and the Vp/Vs ratio well delineated the main structural features of the area. According to our results, TREMOR has shown to be a valid tool for investigating and studying earthquakes, especially to identify and monitor natural or induced micro-seismicity.
We present the first seismic imaging of the crustal volume affected by the March-April 2021 Thessaly sequence by applying a 3D seismic tomography to the aftershocks recorded by an unprecedented ...number of stations. The results, in terms of V
P
, V
S
, and V
P
/V
S
ratio and earthquakes’ location parameters, depict blind fluid-filled inherited structures within the Northern Thessaly seismic gap. The tomographic images highlight the basal detachment accommodating the Pelagonian nappe onto the carbonate of the Gavrovo unit. The high V
P
/V
S
(>1.85) where most of the seismicity occurs increases from SE to NW, showing possible fluid accumulation in the NW edge of the seismogenic volume that could have contributed to the sequence evolution. The aftershock relocations correlate well with the fault planes of the three mainshocks proposed by several geodetic models, but also show additional possible faults sub-parallel and antithetical to the main structures, not to be overlooked for future seismic risk mitigation.
The pathogenesis of thrombocytopenia in chronic hepatitis is not well known. This study evaluated the relationship between liver injury, serum thrombopoietin, splenomegaly and thrombocytopenia in ...chronic viral hepatitis. Two hundred and nine patients were enrolled, 85 with splenomegaly and 124 without. Thrombocytopenia was present in 71% and 23% of patients with or without splenomegaly respectively. In subjects with low platelet count, those with splenomegaly showed significantly lower platelet numbers than those without splenomegaly. The spleen size correlated with portal hypertension. An inverse correlation between spleen size and platelet count was observed (r = −0·54; P < 0·0001). In patients without splenomegaly, thrombocytopenia was associated with the grade of fibrosis; platelet counts were the highest in patients with fibrosis 0–2, lower in those with grade 3 (P < 0·008) and lowest in those with grade 4 (P < 0·05). These findings were independent of demographic and biochemical characteristics, hepatic necroinflammatory activity, portal hypertension and splenomegaly. Patients with normal platelet counts showed higher thrombopoietin levels than those with low platelet counts (P < 0·0001). An inverse correlation between thrombopoietin levels and fibrosis grade was observed (r = − 0·50; P < 0·0001). Median thrombopoietin levels were 58 and 27 pg/ml for fibrosis grade 0–1 and grade 4 respectively (P < 0·001). These data indicate that advanced hepatic fibrosis, causing an altered production of thrombopoietin and portal hypertension, plays the central role in the pathogenesis of thrombocytopenia in chronic viral hepatitis.
Improving the knowledge of seismogenic faults requires the integration of geological, seismological, and geophysical information. Among several analyses, the definition of earthquake focal mechanisms ...plays an essential role in providing information about the geometry of individual faults and the stress regime acting in a region. Fault plane solutions can be retrieved by several techniques operating in specific magnitude ranges, both in the time and frequency domain and using different data.
The severe acute respiratory syndrome Coronarovirus-2 associated still causes a significant number of deaths and hospitalizations mainly by the development of respiratory failure. We aim to validate ...lung ultrasound score in order to predict mortality and the severity of the clinical course related to the need of respiratory support.
In this prospective multicenter hospital-based cohort study, all adult patients with diagnosis of SARS-CoV-2 infection, performed by real-time reverse transcription polymerase chain reaction were included. Upon admission, all patients underwent blood gas analysis and lung ultrasound by expert operators. The acquisition of ultrasound scan was performed on 12 peculiar anatomic landmarks of the chest. Lung ultrasound findings were classified according to a scoring method, ranging 0 to 3: Score 0: normal A-lines. Score 1: multiple separated B-lines. Score 2: coalescent B-lines, alteration of pleural line. Score 3: consolidation area.
One thousand and seven patients were included in statistical analysis (male 62.4 %, mean age 66.3). Oxygen support was needed in 811 (80.5 %) patients. The median ultrasound score was 24 and the risk of having more invasive respiratory support increased in relation to higher values score computed. Lung ultrasound score showed negative strong correlation (rho: -0.71) with the P/F ratio and a significant association with in-hospital mortality (OR 1.11, 95 %CI 1.07–1.14; p < 0.001), even after adjustment with the following variables (age, sex, P/F ratio, SpO2, lactate, hypertension, chronic renal failure, diabetes, and obesity).
The novelty of this research corroborates and validates the 12-field lung ultrasound score as tool for predicting mortality and severity clinical course in COVID-19 patients. Baseline lung ultrasound score was associated with in-hospital mortality and requirement of intensive respiratory support and predict the risk of IOT among COVID-19 patients.
The role of steatosis in the progression of liver damage in chronic hepatitis C (CHC) was studied. Enrolled were 180 consecutive liver biopsy-proven CHC patients and 41 additional subjects with a ...known duration of infection. We evaluated the histological activity index (HAI), grade of fibrosis and steatosis, body mass index (BMI; kg/m2), distribution of body fat, HCV genotype, and levels of HCV RNA. Eighty six (48%) patients showed steatosis, and a higher prevalence was observed in genotype 3a infection (P < .01). A correlation between the grade of steatosis and fibrosis was observed (P < .001). Fibrosis was also associated with age (P < .001). After adjusting for age, the association between steatosis and fibrosis remained significant. The grade of steatosis also correlated with the HAI (P < .007) with a significant increase in periportal necrosis. No relation was found between steatosis and age, gender, iron storage, or levels of HCV RNA. Patients with a high grade of steatosis (>30%) showed higher serum levels of γ-GT and ALT (P < .001). Overall, steatosis was not significantly associated to BMI. Analysis by single genotype showed a significant association between the grade of steatosis and BMI in type 1 infection r = .689; P < .001) and with levels of HCV RNA in type 3a infection r = .786; P < .001). Visceral fat distribution rather than BMI proved to be associated with steatosis (P < .001). Data obtained from patients with a known date of infection confirmed that steatosis grades 3-4 were associated with a higher annual rate of fibrosis progression, and showed that alcohol and steatosis act together in increasing fibrosis (P < .05). Our data indicate that steatosis is an important cofactor in increasing liver necroinflammatory activity and in accelerating fibrosis in CHC. Visceral obesity and genotype 3a play a role in the development of steatosis. (HEPATOLOGY 2001;33:1358-1364.)
•Higher-, middle-, and lower-income individuals showed differences in terms of well-being experiences in urban parks in Bogotá.•Middle-income individuals in Bogotá reported higher levels of ...well-being from park experience.•Use of urban parks and psychological variables were relevant predictors of well-being in an integrated model.•Different psychological mechanisms linking park experience to well-being emerged across the three income groups.
Studies on the positive effects of contact with nature have been mainly conducted in European countries, North America, and Australia, whereas the experience of nature for people living in other countries is still to be adequately investigated. Investigation of the beneficial effects of nature is particularly important in dense urban areas characterized by heavy environmental stress-related problems, like crowding and noise, and for people suffering from income-related well-being inequalities. To contribute to filling this gap, the present study investigated the effects of contact with urban parks on well-being among residents in Bogotá, Colombia. A questionnaire was administered to an opportunistic sample of 398 respondents (300 of which were completed and used in the analyses) in parks located in three districts differing in socio-economic status. The residents of these districts were representative of the upper, middle, and lower income groups. The questions asked about the use of green areas and related psychological variables, such as human-nature interdependence, connectedness to nature, perceived restorative and affective qualities attributed to the park, emotions experienced, and overall well-being derived from the park experience. The results showed higher levels of well-being for people in the middle-income group and a relevant role of nature-related activities and psychological variables in explaining such beneficial outcomes. Differences in the mechanisms leading to well-being also emerged for the three income groups. Theoretical and practical implications of the study are discussed.
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