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The Cinque Torri Group (The Dolomites): analysis of past and present-day gravitational phenomena by laser scanning and numerical modeling
Full text linkMany sites in the Dolomites are endangered by mountain slope instabilities, whose effects can lead to exposure of both human life and infrastructures to landslide hazard.
In cases of reactivated or active landslides, the knowledge of the past gravitational phenomena can allow an indirect analysis of the present slope setting, therefore leading to an explanation of the triggering factors of the instability. In this cognitive process, the first step is the characterization of geometry and rock material properties of the studied unstable slope.
Among the wide variety of gravitational phenomena, the Deep Seated Gravitational Slope Deformations (DSGSDs) still represent an open issue in terms of triggering factors and slope behavior.
This study concerns the analysis of the dynamics that govern an unstable rock group named Cinque Torri, placed in the Dolomites (Eastern Alps, Italy). The rock group is an articulated system of carbonatic monoliths located in a very important touristic area, therefore characterized by a significant risk. The involved instability phenomena represent an example of lateral spreading developed over a larger DSGSD. After the recent fall of a monolith of more than 10 000 m3, a scientific study began to monitor the more unstable sectors and to characterize the past and present movements as a fundamental tool for predictions of future movements and hazard assessment.
The present research outlines how the geomorphology of the area is strongly influenced by the tectonic structures that resulted from the Alpine orogeny and the geotechnical contrast between lithologies. This DSGSD is mainly influenced by the contact of lithologies with different rheological attitudes. The setting is represented by a plastic bed mainly made up by mudstone layers, and above a dolomite cliff roof, which is extremely tectonized and separated in various rocky towers of different dimensions.
Attempting to achieve greater insight in the ongoing lateral spreading, a method aimed at producing a quantitative analysis of occurred rotations has been developed, applied and validated.
The introduction of numerical modeling as last stage of the research aims to investigate the present- day slope instability mechanisms, and indirectly to support the outcomes of the analyzed rotations. In particular, the combined use of the distinct-element and the finite-element codes allows a modeling of the stress-strain relations within the slope
and the control exerted by both discrete structures and rock-mass strength. Moreover, these codes provide a powerful method to assess the influence of the controlling factors on the overall instability.
This research project is articulated in following steps:
1. Recognition and characterization of the main discontinuity systems through the use of laser scanner datasets (terrestrial, TLS, and aerial laser scanner, ALS), and their validation through traditional field measurements.
2. Rock properties classification through field surveys and laboratory analyses.
3. Geophysical investigations (Electrical Resistivity Tomography and passive seismic reliefs) aimed to discern the buried structural setting of the slope.
4. Use of the experimental software packages Coltop-3D (Jaboyedoff, 2007) and PCM (Vosselman, 2004) on TLS/ALS data, to discriminate the tectonic influence on local
rock instability phenomena and provide a complete geometrical characterization of rock discontinuities respectively.
5. Structural correlation among the spreaded rock monoliths.
6. Estimation of the rotational components of the lateral spreading, in order to predict future instabilities and to interprete the buried features of the DSGSD.
7. Numerical modeling of the DSGSD based on a distinct element code (UDEC, 4.1).
and a finite element code (Plaxis, 8.5). In order to create a conceptual model of the present and future instabilities, a comparison of the results of the modeling and the interpretation of the rotational component analysis is achieved.
In particular, the most significant achievement of this thesis concerns the role of rock discontinuities for indirect analysis of the initial slope conditions by providing a novel methodology for rotational movements computation based on laser scanner data
treatment.
The input data frame is based on the accurate geometrical survey of the Cinque Torri area obtained by laser scanning. In June 2008, the Cinque Torri rock group was observed by using a long-range TLS and an ALS. The survey was performed covering a surface of about 22 km2. In this way, a multi-scale model of the unstable rocky group and its surroundings is derived.
The results of the proposed methodology allows a primary identification of the tectonic fabric on the spread rock sectors in terms of representativeness of joint families inside the group with respect to a reference frame fixed on the external stable areas. Both bedding planes and representative joint-sets are used to derive the Euler angles that describe the rotational components of the lateral spreading. On the basis of these results, a new interpretation of the phenomena is achieved. The variations from the regional trend provide a kinematic description of the past gravitational movement of the Cinque Torri group, which can be interpreted as initially controlled by the inherited tectonic features and subsequently differentiated into sectors. After such a differentiation, the movements are most likely induced by deep seated ground deformation and local topographic anomalies related to the lateral spreading development. The geophysical data allow a confirmation and a completion of these interpretations. In particular, these data show that the tectonic action in the Cinque Torri area produced substantial changes in the strata bedding orientation which may have favored tilts and rotations of the uppermost brittle carbonates. At a final stage, in order to decipher slope behavior, a reliable slope model is derived from accurate geometrical surveys of the outcropped rocks, analysis of compositional, mechanical and physical properties of the involved lithotypes. The slope modeling shows that three major factors control the behavior of the Cinque Torri DSGSD: (i) the monolith weight; (ii) the stratigraphical heterogeneity, and (iii) the inclination of strata. Twodimensional finite difference and distinct-element modeling indicate small
displacements of the overall DSGSD, confirming the typical velocities of this type oflandslide. These computations provide a model able to describe the geometries and gravitational mechanisms acting within the investigated slope.
The results of the field observations, rotational components analysis and numerical models suggest that the Cinque Torri DSGSD involves a complex mechanism with a rotational component of the movement, and a probable differentiation of the sliding surface of the DSGSD into segments with different amounts of rotation. In addition, the plastic deformation within the cohesive layers induces tilts, rotations and displacements of the topmost monoliths.The results achieved during this research provide a comprehensive scheme of geometries and processes acting within the Cinque Torri slope. The obtained information can be used for hazard assessment purposes.IL territorio dolomitico è spesso interessato da fenomeni franosi di diversa entità che possono coinvolgere comunità e infrastrutture. Da ciò deriva la necessità di valutare costantemente le condizioni di instabilità, dunque di rischio, delle aree montane, al fine di poter predisporre adeguate misure di salvaguardia. Come dimostrato nella presente tesi di dottorato, l’analisi dei processi gravitativi avvenuti nel passato può essere importante per la comprensione dei fenomeni attuali o recenti, sia in termini di processo, sia in termini di volumi coinvolti. In genere, i fenomeni gravitativi possono essere decifrati attraverso il riconoscimento di un criterio geometrico che relazioni le porzioni di pendio mobilitate dal processo gravitativo, e che perciò fornisca indicazioni sull’assetto del pendio antecedente l’instabilità. Al fine di una corretta analisi delle dinamiche di versante è perciò fondamentale definire inizialmente geometrie e proprietà delle litologie che caratterizzano il pendio instabile.
Tra i molteplici fenomeni gravitativi esistenti in natura, le Deformazioni Gravitative Profonde di Versante (DGPV) rappresentano tutt’oggi un argomento di ampia discussione.
La presente tesi di dottorato si occupa dell’analisi dei fenomeni instabilità nell’area turistica del gruppo Cinque Torri (Dolomiti bellunesi, Alpi orientali, Italia). Un'ipotesi avvalorata dai precedenti studi vede il pendio su cui poggia il gruppo roccioso coinvolto da un processo di DGPV ampio, la cui espressione superficiale è rappresentata dall’espandimento laterale dei torrioni dolomitici a monte. Il recente crollo della Torre Trephor, uno dei monoliti carbonatici che costituiscono il gruppo, avvenuto nel 2004, ha dato inizio ad un complesso studio scientifico concernente il monitoraggio dei settori più instabili e la caratterizzazione dei fenomeni d’instabilità attuali e passati come strumento di predizione e valutazione della pericolosità dell’area.
Le attività di ricerca si inseriscono in questo quadro come strumento di analisi approfondita delle dinamiche passate e in atto dell’espandimento laterale delle Cinque Torri. I processi gravitativi, così come la geomorfologia dell’area esaminata, sono strettamente legati all’assetto tettonico locale e alle caratteristiche meccaniche delle litologie ivi presenti. Difatti la DGPV dell’area Cinque Torri trova origine dal contrasto di competenza fra litologie a comportamento fragile (livelli carbonatici) e litologie a comportamento duttile (livelli marnosi).
Il punto chiave della ricerca vede lo sviluppo di una nuova metodologia di analisi basata sulla trattazione di dati geometrici derivati da acquisizioni laser scanner.
Nella fase finale di ricerca, l’introduzione di modelli numerici promuove un’analisi delle dinamiche in atto nel pendio offrendo uno strumento di validazione delle interpretazioni ottenute dall’analisi dei dati geometrici. Inoltre, l’approccio numerico permette la valutazione del grado di influenza di alcuni fattori predisponenti la DGPV in esame.
Le fasi del progetto di ricerca volte alla caratterizzazione di forme e processi nell’area in esame, possono essere così riassunte:
1. Identificazione dei principali sistemi di discontinuità degli affioramenti rocciosi attraverso l’uso di dati laser scanner (terrestre e aereo) e successiva validazione attraverso rilievi tradizionali di campagna;
2. Classificazione delle proprietà delle litologie coinvolte ottenuta da rilievi di campagna e prove di laboratorio;
3. Indagini geofisiche (tomografia elettrica e rilievi di sismica passiva) per l’identificazione indiretta dell’assetto strutturale del sottosuolo.
4. Utilizzo del pacchetto software sperimentale Coltop-3D (Jaboyedoff, 2007) per la caratterizzazione delle discontinuità e distinzione tra discontinuità tettoniche e gravitative e, inoltre, introduzione del software sperimentale PCM (Vosselman, 2004) per la caratterizzazione geometrica delle principali famiglie di discontinuità come criterio di confronto con il dato di campagna;
5. Correlazione strutturale tra monoliti rocciosi;
6. Calcolo delle componenti rotazionali dell’espandimento laterale in atto, allo scopo di predire future instabilità e di interpretare le strutture sepolte;
7. Modellazione numerica della DGPV, realizzata attraverso codici di calcolo agli elementi disstinti (UDEC, 4.1) e agli elementi finiti (Plaxis, 8.5). Paragonando i risultati ottenuti dalla modellazione numerica e le interpretazioni derivate dall’analisi delle componenti rotazionali si è potuto così ottenere un modello concettuale delle instabilità attuali e future.
In particolare, il risultato più significativo di questa tesi riguarda l’utilizzo dei rapporti geometrici esistenti fra le discontinuità tettoniche per l’analisi indiretta dei movimenti gravitativi. Infatti, attraverso l’analisi del dato laser scanner sono state ricostruite le componenti rotazionali dei movimenti che hanno determinato l’attuale assetto del gruppo Cinque Torri. Alla base di questa innovativa trattazione c’è il rilievo geometrico ad alta risoluzione, ottenuto attraverso l’impiego di tecniche laser scanner. Nel giugno 2008 infatti, la geometria del gruppo Cinque Torri è stata acquisita totalmente grazie un laser scanner terrestre (LST) a lunga portata ed inoltre un’acquisizione laser da aereo ha permesso di completare l’informazione geometrica sulle aree circostanti il gruppo roccioso. La combinazione dei due tipi di dato ha garantito la creazione di un modello geometrico multi-scala dell’area, con particolare attenzione alla rappresentazione di superfici planari sia orizzontali, sia verticali. Grazie a questo metodo sono state identificate le famiglie di discontinuità esistenti in ciascun monolite, successivamente correlate con dei set di riferimento estratti da affioramenti rocciosi esterni alla DGPV. Da tali correlazioni sono state poi dedotte le componenti angolari di spostamento dei set individuati rispetto a quelli di riferimento, fornendo le basi per nuova interpretazione dei fenomeni gravitativi in atto. Dai risultati della ricerca si evince che le dinamiche del pendio sono inizialmente controllate dalle principali direttrici tettoniche, che di fatto hanno frammentato il gruppo roccioso secondo chiare leggi geometriche. In una fase successiva la suddivisione del gruppo e l'allontanamento dei monoliti sono indotti dalla DGPV e da anomalie locali topografiche (legate con buona probabilità alla sviluppo dell’espandimento laterale).
Questa interpretazione ha trovato riscontro nei risultati delle indagini geofisiche condotte nell’area in studio. Tali indagini hanno evidenziato il quadro tettonico del pendio sottostante il gruppo Cinque Torri, mettendo in luce dislocazioni metriche verticali subite dalla stratigrafia. E' ragionevole ipotizzare che questi gradini strutturali influenzino in parte le rotazioni e i basculamenti in atto nel gruppo Cinque Torri.
L’ultima parte della tesi è dedicata alla modellazione numerica del pendio, realizzata attraverso l’uso dell’accurato modello geometrico fornito dalle acquisizioni laser scanner e dai risultati delle prove di laboratorio e di campagna attuate per la caratterizzazione delle litologie coinvolte. La modellazione numerica ha evidenziato che i fattori che maggiormente influenzano l’instabilità del pendio in studio risiedono nell’azione della forza peso agente sul pendio ad opera dei monoliti, nell’eterogeneità stratigrafica e nell’inclinazione degli strati. Inoltre, i risultati di tali modelli numerici confermano le interpretazioni dedotte dallo studio delle componenti rotazionali sulla geometria della DGPV.
In conclusione la tesi proposta fornisce un modello interpretativo dei fenomeni gravitativi dell’area Cinque Torri, che coinvolgono deformazioni gravitative profonde con componente pseudo-circolare e significative deformazioni plastiche all’interno degli strati marnosi. Queste ultime inducono basculamenti, rotazioni e traslazioni nelle porzioni sommitali del pendio, in altre parole, l’espandimento laterale.
L’insieme dei risultati così raggiunto fornisce un quadro nuovo per l’identificazione dei controlli strutturali e la comprensione dei processi agenti all’interno del pendio Cinque Torri, da cui un valido strumento per la valutazione e mitigazione del rischio
Laser scanning-based recognition of rotational movements on a deep seated gravitational instability: the Cinque Torri case (North-Eastern Italian Alps).
No full textThe Cinque Torri group (Cortina d'Ampezzo, Italy) is an articulated system of unstable carbonatic rock monoliths located in a very important tourism area and therefore characterized by a significant risk. The instability phenomena involved represent an example of lateral spreading developed over a larger deep seated gravitational slope deformation (DSGSD) area. After the recent fall of a monolith of more than 10000 m3, a scientific study was initiated to monitor the more unstable sectors and to characterize the past movements as a fundamental tool for predicting future movements and hazard assessment. To achieve greater insight on the ongoing lateral spreading process, a method for a quantitative analysis of rotational movements associated with the lateral spreading has been developed, applied and validated. The method is based on: i) detailed geometrical characterization of the area by means of laser scanner techniques; ii) recognition of the discontinuity sets and definition of a reference frame for each set, iii) correlation between the obtained reference frames related to a specific sector and a stable external reference frame, and iv) determination of the 3D rotations in terms of Euler angles to describe the present settlement of the Cinque Torri system with respect to the surrounding stable areas. In this way, significant information on the processes involved in the fragmentation and spreading of a former dolomitic plateau into different rock cliffs has been gained. The method is suitable to be applied to similar case studies
Reconstruction of the dynamic in a fatal traffic accident with prolonged dragging of the victim
No full textThe post-mortem examination of victims of fatal road crashes and the reconstruction of the dynamic of traffic accidents are fundamental in vehicular homicides, where the degree of negligence/careless of the driver has to be established. Here we present a case in which a pedestrian was dragged along an SUV for 3.5 km, until the vehicle was parked at the house of the driver, arising the suspect of vehicular manslaughter and failure to provide assistance. On the basis of death scene investigation, analysis of video recording from a surveillance camera, post-mortem computerized tomography (PMCT) and complete post-mortem examination, including gross and microscopical findings, the accident was reconstructed as a frontal collision between the right portion of the bumper and the right side of the body of a standing pedestrian, with deformation of the bumper and production of a metal sheet hook; secondary run-over the right feet, cranio-facial trauma against the bodywork of the vehicle and hooking of the right hand of the victim to the metal sheet; prolonged dragging of the pedestrian over the road surface and severe bleeding. A multidisciplinary-multimodal methodology, including PMCT, allowed to assess the cause of death as hemorrhagic shock, suggested that the victim would have likely survived if the vehicle had stopped, and is increasingly recommendable in fatal road accidents
Micro computed tomography features of laryngeal fractures in a case of fatal manual strangulation
No full textCases of subtle fatal neck compression are often complicated by the lack of specificity of the post-mortem signs of asphyxia and by the lack of clear signs of neck compression.Herein we present a forensic case of a 45-year-old schizophrenic patient found on the floor of the bedroom of a psychiatric ward in cardiopulmonary arrest and who died after two days in a vegetative state. The deposition of the roommate of the deceased, who claimed responsibility for the killing of the victim by neck compression, was considered unreliable by the prosecutor.Autopsy, toxicological analyses, and multi-slice computed tomography (MSCT), micro computed tomography (micro-CT) and histology of the larynx complex were performed. Particularly, micro-CT analysis of the thyroid cartilage revealed the bilateral presence of ossified triticeous cartilages and the complete fragmentation of the right superior horn of the thyroid, but it additionally demonstrated a fracture on the contralateral superior horns, which was not clearly diagnosable at MSCT. On the basis of the evidence of intracartilaginous laryngeal hemorrhages and bilateral microfracture at the base of the superior horns of the larynx, the death was classified as a case of asphyxia due to manual strangulation.Micro-CT was confirmed as a useful tool in cases of subtle fatal neck compression, for the detection of minute laryngeal cartilage fractures, especially in complex cases with equivocal findings on MSCT. © 2016 Elsevier Ireland Ltd
Suicidal Smothering by Rubber Latex Gloves and Handkerchief
No full textAsphyxial deaths are common in forensic practice, being sustained by a variety of mechanisms that cause an oxygen deficiency to the brain. Several classification models have been proposed in the literature, the most recent one being that of the International Network for Forensic Research Group (INFOR). This report describes an unusual case of suffocation where the obstruction of the airways was caused by a gag formed of three latex gloves and a handkerchief. The manner of death (differential diagnosis between homicide and suicide) and the different alternatives of classification are discussed
Investigations on alluvial deposits through borehole stratigraphy, radiocarbon dating and passive seismic technique (Carnic Alps, NE Italy)
Full text linkAlluvial sediment investigations provide fundamental tools to infer the processes that control geomorphological
evolution of mountain environments. By analyzing sediment stratigraphy in depth, it is possible to retrieve the
source, the geology, the time of deposition, the relative distance travelled by material as well as to distinguish
among different type of transport (i.e., gravitational, fluvial or glacial).
In this work, we present a combination of log stratigraphy, radiocarbon dating and geophysical surveys carried out
on the valley floor of the But River (Carnic Alps, North East Italy). The But River basin drains an area of 326 km2
with a range in elevation from 2769 to 323 m a.s.l.; the bedrock mainly consists of carbonates and quartz arenites
with minor inclusions of effusive rocks. After Pleistocene the gravitational deposits from mountain slopes have
impounded the But River several times. In particular, we analyzed a sector of the upper portion of the But valley
close to the confluence of the Moscardo Torrent, frequently affected by debris flows.
A borehole was drilled in the But River floodplain, at the intersection with the Moscardo Torrent alluvial fan,
down to a depth of 80 m. The analysis of the core samples allowed discerning three sedimentary levels rich in clay
and organic materials, which testify the presence of small dam lakes, originated from the Moscardo debris-flow
deposits. Three samples of wood and plant debris were collected from 13, 14 and 23 m of depth, respectively. They
were analyzed through radiocarbon dating in order to determine the age of the lakes and, thus, to infer the activity
of the debris flows building the Moscardo cone. The calibrated ages of the 3 samples are close to the younger limit
of the radiocarbon method indicating a fast aggradation of the valley floor, starting from a period ranging between
1450 - 1632 AD. Historical maps and documents confirm the presence of the lakes until 19th century and they
permit to assess their extent and the maximum depths.
Two passive seismic campaigns were carried out near the borehole site and along the But valley at different elevations.
The aim was to investigate the depth of the buried bedrock and therefore to indirectly characterize the
thickness of alluvial deposits. We calibrated the fundamental frequency of each site by constraining average shear
velocity of the alluvial sediments close to the borehole site with known stratigraphy. Eight HVSR (Horizontal to
Vertical Spectral Ratio, Nakamura, 1989) were carried out, and thus a first sketch of the buried valley floor along
a longitudinal profile of about 5 km was depicted. The values of the derived bedrock depth allow to quantify the
differences in thickness between the alluvial deposits and the Moscardo Torrent fan deposits. This information
helps to address the contribution of the debris-flow processes in damming the upper But River during the last five
centuries.
The results confirm the role of debris-flow deposits from the Moscardo Torrent in shaping the morphology of the
valley floor of But River and show suitability of an integrated approach, encompassing log stratigraphy, geophysical
surveys and analysis of historical documents, for gaining insights on the evolution of alpine valleys
Micro computed tomography features of laryngeal fractures in a case of fatal manual strangulation
No full textCases of subtle fatal neck compression are often complicated by the lack of specificity of the post-mortem signs of asphyxia and by the lack of clear signs of neck compression. Herein we present a forensic case of a 45-year-old schizophrenic patient found on the floor of the bedroom of a psychiatric ward in cardiopulmonary arrest and who died after two days in a vegetative state. The deposition of the roommate of the deceased, who claimed responsibility for the killing of the victim by neck compression, was considered unreliable by the prosecutor. Autopsy, toxicological analyses, and multi-slice computed tomography (MSCT), micro computed tomography (micro-CT) and histology of the larynx complex were performed. Particularly, micro-CT analysis of the thyroid cartilage revealed the bilateral presence of ossified triticeous cartilages and the complete fragmentation of the right superior horn of the thyroid, but it additionally demonstrated a fracture on the contralateral superior horns, which was not clearly diagnosable at MSCT. On the basis of the evidence of intracartilaginous laryngeal hemorrhages and bilateral microfracture at the base of the superior horns of the larynx, the death was classified as a case of asphyxia due to manual strangulation. Micro-CT was confirmed as a useful tool in cases of subtle fatal neck compression, for the detection of minute laryngeal cartilage fractures, especially in complex cases with equivocal findings on MSCT
Rainfall thresholds for the possible initiation of shallow landslides in the Italian Alps
No full textAbstract Rainfall-induced shallow landslides are frequent in the Italian Alps, where they cause severe economic damages and loss of life. The prediction of rainfall-induced slope failures is of utmost importance for civil protection purposes and relies upon the definition of physically based or empirical rainfall thresholds. Reliable empirical rainfall thresholds require a large amount of information on the geographical and temporal location of past rainfall events that caused the observed mass movements. We have compiled a catalogue listing 453 rainfall events that have triggered landslides in the Italian Alps in the 13-year period 2000-2012. For the purpose, we searched national and local newspapers, blogs, technical reports, historical databases, and scientific journals. In the catalogue, for each rainfall event that triggered one or more failures, the information includes: (i) landslide geographical position, (ii) date of the landslide occurrence, (iii) landslide type (if available from the source of information), and (iv) rainfall information. Using the available information, we calculated the cumulated amount (E) and the duration (D) of the rainfall that likely caused the documented slope failures. We exploited the catalogue to calculate new ED threshold curves and their associated uncertainties for the Italian Alps adopting a frequentist approach. To define seasonal rainfall thresholds, we also investigated the monthly distribution of the landslides. The new thresholds are compared with similar curves in the same general area. We expect the results of our study to improve the ability to forecast shallow landslides in the Italian Alps and, more generally, in the wider Alpine regio
Traumatic fatal aortic rupture in motorcycle drivers
No full textTraumatic fatal aortic rupture (FAR) is a common finding in victims of motor vehicle crashes (MVC), but its aetiology and mechanisms of production remain an issue of major concern, above all in motorcyclists. This study reports a series of cases obtained from a retrospective analysis of traumatic FARs occurring in motorcycle drivers, with the aim of defining the injury patterns and correlating them with the mechanisms of FAR production. Circumstantial, autopsy and histology data were collected through a retrospective analysis of post mortem examinations performed at the Institute of Legal Medicine of the University of Padova between 2014 and 2016. Among 151 traffic related victims, 8 were motorcycle drivers and displayed traumatic FAR and were thus included in the study. In 7 cases, the presence of abdominal/thoracic injuries suggested that the external compression due to the accident was at least a concurrent cause of FAR, being the predominant mechanism of aortic injury in 4 cases, through the “osseous pinch” or the “waterhammer effect” mechanisms. Our study highlights the well-known role of “preventative forensic pathology”, which has become routinary in traffic medicine since many years, also for defining the points of impact and the injury patterns of motorcyclists sustaining traumatic FAR, thereby facilitating the development of new prevention strategies and devices. Further studies, however, are needed in order to widen the investigated population and to estimate the real number of victims for which traumatic FAR might hypothetically be prevented with specific countermeasures. © 2017 Elsevier B.V
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