1,721,149 research outputs found
Dynamics of a seismogenic fault subject to variable strain rate
Full text linkThe behaviour of seismogenic faults is generally investigated under the assumption that they are subject to a constant strain rate. We consider the effect of a slowly variable strain rate on the recurrence times of earthquakes generated by a single fault. To this aim a spring-block system is employed as a low-order analog of the fault. Two cases are considered: a sinusoidal oscillation in the driver velocity and a monotonic change from one velocity value to another. In the first case, a study of the orbit of the system in the state space suggests that the seismic activity of the equivalent fault is organized into cycles that include several earthquakes and repeat periodically. Within each cycle the recurrence times oscillate about an average value equal to the recurrence period for constant strain rate. In the second case, the recurrence time changes gradually from the value before the transition to the value following it. Asymptotic solutions are also given, approximating the case when the amplitude of the oscillation or of the monotonic change is much smaller than the average driver velocity and the period of oscillation or the duration of the transition is much longer than the recurrence times of block motions. If the system is not isolated but is subject to perturbations in stress, the perturbation anticipates or delays the subsequent earthquake. The effects of stress perturbations in the two cases of strain rate oscillations and monotonic change are considered
Role of viscous dissipation in the dynamics of lava flows with power-law rheology
No full textWe model a lava flow as a one-dimensional flow of a pseudoplastic fluid with viscous dissipation. The flow is horizontally unbounded and is driven downslope by the gravity force. We consider a power-law constitutive equation and we take into account the temperature dependence of the rheological parameters. Given an effusion rate and an initial temperature at the eruption vent, the flow is assumed to cool down by heat radiation. We calculate the heat produced by viscous dissipation as a function of lava temperature and effusion rate. The cooling rate is calculated as a function of the surface temperature and flow rate. Viscous dissipation reduces the cooling rate by an amount which is independent of flow rate. We evaluate the effect of viscous dissipation on the flow thickness and velocity. The effect of dissipation is to decrease the flowthickness and to increase the flowvelocity. The effect on flow thickness is greater for smaller flow rates, while the effect on velocity is greater for larger effusion rates. In principle, themodel provides a method for estimating the flowrate fromin-field measurements of distances and temperatures
DETECTION BY MONTECARLO SIMULATIONS OF LOCKED ZONES AT DEPTH ON THE FAULT PLANE OF THE COLFIORITO SEQUENCE (CENTRAL ITALY)
No full textRiconoscimento con il metodo Montecarlo di zone bloccate sul piano di faglia della sequenza di Colfiorito (Italia Centrale)
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Anemie in lavoratori esposti a piombo: attualità della diagnosi differenziale
No full textL’esposizione professionale a piombo metallico (Pb) è
in grado di determinare anemia per valori di piombemia >50 μg/dl,
ormai poco frequenti nei Paesi industrializzati. Soprattutto in zone
ad alta endemia per anemie extraprofessionali, quali la β-Talassemia e la anemia sideropenica, è invece discretamente probabile
riscontrare in lavoratori esposti al metallo altre forme di anemia.
Queste devono essere correttamente inquadrate dal punto di visto etiologico, sia per un adeguato indirizzo terapeutico sia per le
evidenti ricadute medico-legali. L’obiettivo di questo studio è stato di verificare se, in lavoratori maschi esposti a piombo, una attenta
valutazione dei parametri dell’esame emocromocitometrico e dei
comuni indicatori di esposizione e di effetto del Pb sull’eme, possa
permettere di discriminare le forme più comuni di anemia
riscontrabili nella popolazione in età lavorativa dell’Italia meridionale. Sono stati esaminati 68 lavoratori professionalmente esposti a dosi medio-basse di Pb e, come gruppo di controllo, 59
lavoratori di un’azienda alimentare. Su campioni di sangue venoso prelevati da tali lavoratori è stato eseguito un esame
emocromocitometrico completo e la determinazione dei livelli di piombemia e di zincoprotoporfirina. Sono risultati portatori di
anemia (Hb<13g/dl) sei lavoratori esposti a piombo ed un lavoratore non esposto. La valutazione ragionata dei parametri di laboratorio
ha portato ad individuare, tra i lavoratori esposti a Pb, quattro soggetti con elevata probabilità di trait β-talassemico e due lavoratori con anemia saturnina. Sulla base dei dati di letteratura,
inoltre, è stato elaborato un algoritmo diagnostico che sembrerebbe capace di discriminare i casi di anemia di origine saturnina da quelli
da altra causa nei lavoratori esposti a Pb esaminati in questo studio
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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