196,105 research outputs found
Surface-wave velocity measurements of shear stiffness of moving earthflows
No full textEarthflows are a flow-like movement of plastic clayey soils characterized by long periods of slow motion (at rates averaging a few meters per year or less) alternated with short periods of rapid surges at high velocity (up to meters per hour). During rapid surges, most earthflows move over a long distance with a fluid-like behavior. Although the generation of flow-type failures is an important issue for hazard assessment, our knowledge is limited by the difficulty of monitoring the process in the field. This has led to different explanations for rapid earthflows including high pore–pressure generation along the basal slip surface, pervasive shearing, or material fluidization. One key question is whether or not earthflows can fluidize through remolding and water entrainment. If this occurs, the material can change from plastic to fluid as the soil moisture increases, causing the landslide to move as a viscous flow; if not, the material remains in a plastic state and, as suggested by many authors, the flow-like morphology shown by earthflows would result by distributed internal shears rather than real mass flow. In this study, we provide the first answer to this question by measuring the shear stiffness of four large active earthflows in the Northern Apennines of Italy. Shear stiffness was measured using two geophysical techniques, the multichannel analysis of surface waves (MASW) and the passive refraction microtremors (ReMi). Measurements were carried out just a few days after the mobilization of the landslides and repeated in the following 2–3 years to evaluate the change of elastic properties with time. Field data show that soon after the mobilization, earthflows are characterized by very low values of shear stiffness (about 5–15 MPa), typical of soft clay soils with the high-void ratio. Shear stiffness then increases 4–5 times in the following months (up to 40–60 MPa) as the earthflows slow down and the material consolidates. These data indicate that during a rapid movement, earthflows undergo a dramatic increase of porosity and water content that probably drive the transition from a solid to a fluid-like state
Continuous monitoring of surface wave velocity at the Montevecchio earthflow (Forlì-Cesena Province, Northern Apennines)
No full textThe Montevecchio landslide is an active earthflow in the province of Forlì-Cesena (Northern Apennines of Italy). In the last few years, this landslide reactivated several times. In order to investigate the landslide dynamics, two monitoring systems were installed by combining 3 permanent GPS stations (to measure landslide movement) and 4 geophones (to evaluate surface-wave velocity). In this paper we present the monitoring data collected during the last reactivation of the landslide (24th - 25th of May 2015). The geophones data show a clear relationship between surface-wave velocity (Vr) and displacement rate. In particular, a decrease of Vr value was observed just before an increase of velocity, while higher Vr values were detected when the landslide was slowing down. Moreover, a pressure sensor, buried at low depth beside the geophones, showed an increase in pore water pressure before the failure in correspondence of the critical rainfall event, and while the displacement rate increased the pore water pressure had a positive value (above the ground level), probably due to the undrained compression of the landslide material
Kinematic Segmentation and Velocity in Earth Flows: A Consequence of Complex Basal-slip Surfaces
No full textAbstractWe investigated relations between geomorphic structures, movement velocity, and basal-slip surface geometry within individual kinematic domains of two large earth flows in the Apennine Mountains of southern Italy: the “Montaguto” earth flow and the “Mount Pizzuto” earth flow. Our analyses indicated that the earth flows are composed of distinct kinematic zones characterized by specific deformational patterns and longitudinal velocity profiles. Variations in velocity within individual kinematic zones is controlled by the geometry of the basal-slip surface, and, in particular by local variations in slope angle. Slip-surface geometry and slope also seem to control the density of extensional structures in driving earth-flow elements
Electromagnetic field observations by the DEMETER satellite in connection with the 2009 L’Aquila earthquake
No full textTo define a background in the electromagnetic emissions above seismic regions, it is necessary to define the statistical distribution of the wave energy in the absence of seismic activity and any other anomalous input (e.g. solar forcing). This paper presents a completely new method to determine both the environmental and instrumental backgrounds applied to the entire DEMETER satellite electric and magnetic field data over L'Aquila. Our technique is based on a new data analysis tool called ALIF (adaptive local iterative filtering, Cicone et al., 2016; Cicone and Zhou, 2017; Piersanti et al., 2017b). To evaluate the instrumental background, we performed a multiscale statistical analysis in which the instantaneous relative energy (εrel), kurtosis, and Shannon entropy were calculated. To estimate the environmental background, a map, divided into 1° × 1° latitude–longitude cells, of the averaged relative energy (εrel), has been constructed, taking into account the geomagnetic activity conditions, the presence of seismic activity, and the local time sector of the satellite orbit. Any distinct signal different (over a certain threshold) from both the instrumental and environmental backgrounds will be considered as a case event to be investigated. Interestingly, on 4 April 2009, when DEMETER flew exactly over L'Aquila at UT = 20:29, an anomalous signal was observed at 333Hz on both the electric and magnetic field data, whose characteristics seem to be related to pre-seismic activity
Total solar irradiance during the last five centuries
No full textThe total solar irradiance (TSI) varies on timescales of minutes to centuries. On short timescales it varies due to the superposition of intensity fluctuations produced by turbulent convection and acoustic oscillations. On longer timescales, it changes due to photospheric magnetic activity, mainly because of the facular brightenings and dimmings caused by sunspots. While modern TSI variations have been monitored from space since the 1970s, TSI variations over much longer periods can only be estimated either using historical observations of magnetic features, possibly supported by flux transport models, or from the measurements of the cosmogenic isotope (e.g., 14C or 10Be) concentrations in tree rings and ice cores. The reconstruction of the TSI in the last few centuries, particularly in the 17th/18th centuries during the Maunder minimum, is of primary importance for studying climatic effects. To separate the temporal components of the irradiance variations, specifically the magnetic cycle from secular variability, we decomposed the signals associated with historical observations of magnetic features and the solar modulation potential Φ by applying an empirical mode decomposition algorithm. Thus, the reconstruction is empirical and does not require any feature contrast or field transport model. The assessed difference between the mean value during the Maunder minimum and the present value is ≃2.5 W m−2. Moreover it shows, in the first half of the last century, a growth of ≃1.5 W m−2, which stops around the middle of the century to remain constant for the next 50 years, apart from the modulation due to the solar cycle
Acquired digital fibrokeratoma: First observation by high-resolution skin ultrasound and line-field confocal optical coherence tomography
No full textAuthors' reply to: ‘Generalized pustular figurate erythema first report in two COVID-19 patients on hydroxychloroquine’
No full textPrediction of sunspot and plage coverage for solar cycle 25
No full textSolar variability occurs over a broad range of spatial and temporal scales, from the Sun's brightening over its lifetime to the fluctuations commonly associated with magnetic activity over minutes to years. The latter activity includes most prominently the 11 yr sunspot solar cycle and its modulations. Space weather events, in the form of solar flares, solar energetic particles, coronal mass ejections, and geomagnetic storms, have long been known to approximately follow the solar cycle occurring more frequently at solar maximum than solar minimum. These events can significantly impact our advanced technologies and critical infrastructures, making the prediction for the strength of future solar cycles particularly important. Several methods have been proposed to predict the strength of the next solar cycle, cycle 25, with results that are generally not always consistent. Most of these methods are based on the international sunspot number time series, or other indicators of solar activity. We present here a new approach that uses more than 100 yr of measured fractional areas of the visible solar disk covered by sunspots and plages and an empirical relationship for each of these two indices of solar activity in even-odd cycles. We anticipate that cycle 25 will peak in 2024 and will last for about 12 yr, slightly longer than cycle 24. We also found that, in terms of sunspot and plage areas coverage, the amplitude of cycle 25 will be substantially similar or slightly higher than cycle 24
Upadacitinib in Moderate-to-Severe Atopic Dermatitis: Real-Life Study of Long-Term Efficacy, Safety and Correlation Between Clinical Effectiveness and Subjective Perception of Disease
No full textAn Updated Algorithm Integrated With Patient Data for the Differentiation of Atypical Nevi From Early Melanomas: the idScore 2021
No full textIntroduction: It is well known that multiple patient-related risk factors contribute to the development of cutaneous melanoma, including demographic, phenotypic and anamnestic factors. Objectives: We aimed to investigate which MM risk factors were relevant to be incorporated in a risk scoring-classifier based clinico-dermoscopic algorithm. Methods: This retrospective study was performed on a monocentric dataset of 374 atypical melanocytic skin lesions sharing equivocal dermoscopic features, excised in the suspicion of malignancy. Dermoscopic standardized images of 258 atypical nevi (aN) and 116 early melanomas (eMM) were collected along with objective lesional data (i.e., maximum diameter, specific body site and body area) and 7 dermoscopic data. All cases were combined with a series of 10 MM risk factors, including demographic (2), phenotypic (5) and anamnestic (3) ones. Results: The proposed iDScore 2021 algorithm is composed by 9 variables (age, skin phototype I/II, personal/familiar history of MM, maximum diameter, location on the lower extremities (thighs/legs/ ankles/back of the feet) and 4 dermoscopic features (irregular dots and globules, irregular streaks, blue gray peppering, blue white veil). The algorithm assigned to each lesion a score from 0 to 18, reached an area under the ROC curve of 92% and, with a score threshold ≥ 6, a sensitivity (SE) of 98.2% and a specificity (SP) of 50.4%, surpassing the experts in SE (+13%) and SP (+9%).Conclusions: An integrated checklist combining multiple anamnestic data with selected relevant dermoscopic features can be useful in the differential diagnosis and management of eMM and aN exhibiting with equivocal features
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