12,370 research outputs found
Turning waves and breakdown for incompressible flows
We consider the evolution of an interface generated between two immiscible
incompressible and irrotational fluids. Specifically we study the Muskat and
water wave problems. We show that starting with a family of initial data given
by (\al,f_0(\al)), the interface reaches a regime in finite time in which is
no longer a graph. Therefore there exists a time where the solution of
the free boundary problem parameterized as (\al,f(\al,t)) blows-up: \|\da
f\|_{L^\infty}(t^*)=\infty. In particular, for the Muskat problem, this result
allows us to reach an unstable regime, for which the Rayleigh-Taylor condition
changes sign and the solution breaks down.Comment: 15 page
Optimal path shape for range-only underwater target localization using a Wave Glider
Underwater localization using acoustic signals is one of the main components in a navigation system for an autonomous underwater vehicle (AUV) as a more accurate alternative to dead-reckoning techniques. Although different methods based on the idea of multiple beacons have been studied, other approaches use only one beacon, which reduces the system’s costs and deployment complexity. The inverse approach for single-beacon navigation is to use this method for target localization by an underwater or surface vehicle. In this paper, a method of range-only target localization using a Wave Glider is presented, for which simulations and sea tests have been conducted to determine optimal parameters to minimize acoustic energy use and search time, and to maximize location accuracy and precision. Finally, a field mission is presented, where a Benthic Rover (an autonomous seafloor vehicle) is localized and tracked using minimal human intervention. This mission shows, as an example, the power of using autonomous vehicles in collaboration for oceanographic research.Peer ReviewedPostprint (author's final draft
Secular variations of magma source compositions in the North Patagonian batholith from the Jurassic to Tertiary: Was mélange melting involved?
This study of Sr-Nd initial isotopic ratios of plutons from the North Patago nian batholith (Argentina and Chile) revealed that a secular evolution spanning
180 m.y., from the Jurassic to Neogene, can be established in terms of magma
sources, which in turn are correlated with changes in the tectonic regime. The
provenance and composition of end-member components in the source of mag mas are represented by the Sr-Nd initial isotopic ratios (87Sr/86Sr and 143Nd/144Nd)
of the plutonic rocks. Our results support the interpretation that source compo sition was determined by incorporation of varied crustal materials and trench
sediments via subduction erosion and sediment subduction into a subduction
channel mélange. Subsequent melting of subducted mélanges at mantle depths
and eventual reaction with the ultramafic mantle are proposed as the main causes
of batholith magma generation, which was favored during periods of fast conver gence and high obliquity between the involved plates. We propose that a parental
diorite (= andesite) precursor arrived at the lower arc crust, where it underwent
fractionation to yield the silicic melts (granodiorites and granites) that formed
the batholiths. The diorite precursor could have been in turn fractionated from
a more mafic melt of basaltic andesite composition, which was formed within
the mantle by complete reaction of the bulk mélanges and the peridotite. Our
proposal follows model predictions on the formation of mélange diapirs that
carry fertile subducted materials into hot regions of the suprasubduction mantle
wedge, where mafic parental magmas of batholiths originate. This model not
only accounts for the secular geochemical variations of Andean batholiths, but it
also avoids a fundamental paradox of the classical basalt model: the absence of
ultramafic cumulates in the lower arc crust and in the continental crust in general
Psychobiological Aspects of Panic Disorder
Anxiety is a useful warning sign that helps an individual face potential or real danger. At appropriate levels, it serves as a warning for the presence of internal or external threats, causing a person to be alert and prepare to deal appropriately with such situations. Moreover, moderate levels of anxiety can lead to improved performance in several activities. However, anxiety becomes pathological when its duration is excessively long or its intensity is extremely high and leads to significant suffering and distress. In such cases, anxiety is appropriately described as part of a pathological response, characterizing an anxiety disorder. The historical concept of a unitary anxiety disorder has been replaced by a heterogeneous group of psychopathologies with different etiologies. Panic disorder is a complex anxiety disorder that involves both recurrent, unexpected panic attacks, and persistent concern about having additional attacks. The present chapter reviews current psychobiological perspectives in the etiology and treatment of panic disorder. The first section describes the current classification of this anxiety disorder. We then explore possible neural circuitry associated with panic disorder. Finally, the chapter addresses current treatment approaches, considering the efficacy of different forms of psychotherapy and pharmacological treatments
Permo-Carboniferous magmatism in the core of Pangaea (Southern Pyreness): a possible linkange between the Variscan and Cimmerian cycles?
In southern Europe and the western Mediterranean, Permo-Carboniferous magmatism is well represented in areas
of Iberia, the Alps, Sardinia and the Balkan Peninsula. In Iberia, the magmatism that has been related to the
Variscan orogeny is associated with syn-orogenic events at ca. 350-315 Ma and post-orogenic at ca. 310-295
Ma. In the southern Pyrenees there is Permo-Carboniferous sedimentary basins with a significant volume of
rhyolitic ignimbrites and andesitic flows. The Erill Castell-Estac, Cadà and Castellar de n’Hug basins are spatially
associated with the BoÃ, Montellá and Vielha granites and the Cardet dacitic dykes emplaced in Variscan basement
rocks. U-Pb SHRIMP dating of zircons extracted from these granites, an andesitic flow, a dacitic dyke and six
ignimbrites, revealed that magmatism was active from ca. 304 Ma to ca. 266 Ma. The scattering of zircon ages
in each sample shows that the history of melt crystallization was prolonged and complex. The reported ages of
the magmatic activity for the Southern Pyrenees in the range ca. 304-283 Ma (this study) fit in well with the
time interval of magmatism related to the early North-dipping subduction of the Western Paleotethys Ocean, the
subsequent development of Iberian orocline (Variscan cycle), and the large-scale bending and blocking of the
Paleotethys Ocean subduction at East of Iberia.In paleogeographic reconstructions of the Permo-Carboniferous, Iberia is located in the core of Pangaea to the
east of the probable Rheic Ocean suture and near the western end of the subduction zone of the Paleotethys
Ocean. The emplacement in Iberia of granites with ca. 310-278 Ma age occurred after the collision of Laurussia
and Gondwana, when the subduction of the Rheic Ocean was inactive. From a Variscan-cycle perspective, the
Permo-Carboniferous magmatism of the Pyrenees has been considered as post-orogenic. However, global paleogeographic
reconstructions put Iberia in between the Rheic Ocean suture and the still active subduction zone of the
Western Paleotethys Ocean. Therefore, the Permo-Carboniferous magmatism of Iberia, from a Cimmerian-cycle
perspective, may have accompanied the closing of the Paleotethys Ocean. During this stage of the evolution of
Pangaea, the east of Iberia was geologically affected by the active subduction zone of the Paleotethys Ocean. The
period ca. 310-285 Ma is marked by the development of an orocline that extends from Iberia to Armorica. The
northwards subduction of the western corner of Paleotethys probably caused orocline formation and consequent
large-scale bending and blocking of Paleotethys subduction immediately east of Iberia. The Permo-Carboniferous
magmatism of Iberia, coeval with this tectonic evolution, shows a mixed imprint of subduction and delamination
geochemical signatures. Although this may seem controversial, in our view the magmatic activity preserved in
the Southern Pyrenees could provide the missing link between the development of the Iberian orocline and the
continued subduction of easternmost segments of the Paleotethys Ocean (Cimmerian cycle) during the evolution
of Pangaea
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Is hazard perception ability culturally specific? A cross-cultural comparison between China, Spain and the UK
Hazard perception refers to a driver’s ability to spot hazards on the road in time to make a safe manoeuvre to avoid collision. Such a test is now part of the formal licencing procedure in the UK and in parts of Australia. But can such tests be successfully exported to other countries to reduce traffic fatalities?
The aim of this project is to study whether hazard perception skill is culturally specific by comparing UK, Spanish and Chinese drivers across clips filmed in all three countries. Data collection was set-up in the respective countries in collaboration with the University of Granada (Spain) and Tsinghua University (China). Participants had to watch 30 video clips filmed from the driver’s perspective (10 filmed in each of the three countries). Two variants of the test were created: a typical hazard perception test (with full clips requiring speeded responses to hazards), and a hazard prediction task (or 'What Happens Next?' task), where the film ends immediately prior to the hazard onset. This latter test removes the confound of individual hazard thresholds, as participants could successfully report 'what happens next' without judging whether it posed a hazard to them. All videos contained a variety of hazardous situations (or precursors to hazards) reflecting the particular driving environment of each country.
Three hundred participants across the 3 countries were tested, evenly divided between learner and experienced drivers. The differences between the culturally-specific tests in their ability to discriminate between driver groups will be discussed in regards to the potential for employing hazard perception testing in diverse geographical locations and cultures
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