1,721,074 research outputs found
Isotopic evidence for chaotic imprint in upper mantle heterogeneity
No full textThe intrinsic structure of the isotope data set of samples from the Mid-Atlantic Ridge and East Pacific Rise, believed to represent the isotopic composition of their mantle source, reveals a close relationship between sample spatial distribution and their geochemical features. The spatial distribution of their isotopic heterogeneity is self-similar on a scale between 5000 and 6000 km (about 1/6 of Earth's circumference), suggesting a self-organized structure for the underlying mantle. This implies the imprint of chaotic mantle processes, induced by mantle flow and likely related to an early phase of highly dynamic behavior of the Earth's mantle. The size of the identified self-organized region reflects the large length scale of upper mantle chemical variability, and it is likely frozen since the Proterozoic. The geochemical heterogeneity of the asthenosphere along the ridges is believed to record a transition in the thermal conditions of the Earth's mantle and to be reflected in the l = 6 peak expansion of several geophysical observables
A new approach to the Guillotine Cutting Problem
No full textDIP. DI MATEMATICA P. E A., UNIVERSITA` DI PADOV
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
A new model for estimating deep-level magma ascent rates from thermobarometry: an example From Mt. Etna and implications for deep-seated magma dehydration
No full textWe propose a method to estimate deep-level magma ascent rates, and potentially, the depths of initial magma dehydration, using pressure
and temperature (P-T) estimates from mineral-liquid thermobarometers, and cooling rates inferred from Crystal Size Distribution
theory. Ascent rates can be ascertained by recognizing that the slope of a given P-T path (dP/dT), rates of cooling (dT/dt), and
magma ascent rates (dP/dt) are interrelated, and ascent velocity, v, is given as: v = 1 ⎛dP⎞ ⎛dT⎞, where Ú is magma density and
Ú g ⎝dT⎠ ⎝dt ⎠
g is the acceleration due to gravity. Preliminary applications of this method are provided for Mt. Etna lava flows, where both dP/dT
and dT/dt have been well characterized based on, respectively, clinopyroxene thermobarometry, and clinopyroxene CSDs (the latter
yields dT/dt = 2×10-6). Deep-level (>20 km) magma ascent rates range from effectively 0 (where clinopyroxene P-T estimates form a
cluster, and so dP/dT ≈ 0), to about 10 m/hr for flows that yield very steep P-T trajectories. Many lava flows at Mt. Etna yield P-T paths
that follow a hydrous (3% water) clinopyroxene saturation surface, as calculated by pMELTS (Ghiorso et alii 2002), which closely approximates
water contents obtained from melt inclusions; these slopes yield ascent rates of ~1 m/hr, and are comparable to the very
slowest rates derived for magma effusion or vapor-driven ascent (~0.001 to > 0.2 m/s, or 3.6 to 720 m/hr). The initiation of such upward
movements, however slow, may be key to understanding eruption triggering mechanisms. At Mt. Etna, certain flows exhibit two
kinds of clinopyroxene crystallization behavior: from a single flow, those clinopyroxenes that form at the greatest depths either follow
a clinopyroxene saturation surface (as calculated from pMELTS) or cluster along such a curve, but clinopyroxenes from these
same flows that yield more shallow depth estimates fall on near-vertical P-T paths. Such changes in slope appear to indicate an acceleration
of upward magma transport, which may be due to the initiation of deep-level magma dehydration
Plume-related magmatism in collision zones: examples from the Tertiary-Quaternary magmatism in Italy.
No full textFrom late Cretaceous to present time, an extensive magmatic activity developed both in Europe and northern Africa, showing a progressive transition with time from calc-alkaline to Na-rich alkaline features in areas tightly connected with subduction systems (Morocco, Algeria, Tunisia, Spain, Italy), while Na-rich basalts and basanites, with minor tholeiitic volcanics, occur at extensional tectonic settings, both associated or not to orogenic dynamics (Valencia trough, Pannonian, Alboran, Tyrrhenian, and Aegean basins, Pantelleria-Etna-Iblean area, Veneto Province, Cenozoic Rift System). The widespread alkaline magmatism in the European and circum Mediterranean area shows a uniform HIMU-DMM type signature which has been recently ascribed to a mantle contamination episode triggered by the rise of the Central Atlantic Plume (CAP) head since Cretaceous time (Piromallo et al., 2008).
The occurrence of a HIMU-DMM component within lavas originated in collision environments such as the Veneto Volcanic Province in NE Alps (related to the Tertiary convergence of Europe and Africa plates) or the Roman Magmatic Province (related to the Cenozoic Adria subduction) might be explained in terms of slab breakoff (Macera et al., 2008; Gasperini et al., 2002). Evidence for slab breakoff in these areas comes from seismic tomography (Piromallo and Faccenna, 2004) and geophysical modeling consisting in evaluating the time evolution of buoyancy of oceanic and continental lithosphere during subduction with both constant and time-varying convergence rates (Macera et al., 2008). If the subducted slab intercepts a hot mantle diapir rising from the frayed plume head, the corresponding part of the slab is heated and therefore softened. The softening effect is enhanced if the slab includes continental material. The combination of changes in negative buoyancy caused by continental subduction, and softening of a part of the slab caused by slab-plume interaction, may act as a regulator for the time of slab breakoff and consequently for the time and type variations of magmatism in the overriding lithosphere above a subduction zone. In the Alpine region, we assume that the plume material interacted with the subducting slab causing its heating, softening, and finally its detachment. Ensuing upwelling of plume material through the resulting plate window is supposed to be the responsible for partial melting in the lithospheric mantle wedge and/or decompression melting of the ascending plume material.
Plume-related volcanism in subduction zones is possible either before the subducted slab intercepts plume head material , or after slab breakoff. The above considerations provide a framework for the occurrence of plume-related and calc-alkaline magmatism in the southeastern Alps and probably in other similar tectonic settings such as the Central Europe Magmatic Province. The heat released by the hot mantle component to the overriding mantle wedge contributed to its partial melting and production of calc-alkaline mafic magmas. The latter additionally favored the genesis of calc-alkaline felsic magmas through partial melting of the lower crust by underplating. A quantitative approach based on mixing calculations on Sr-Nd and Pb isotopes support these hypotheses
Preliminary Study of Optimized Metasurface Matching Layer in Near Field
No full textElectromagnetic devices often require the maximization of the transmitted field, especially for biomedical applications. The employment of a matching layer can reduce the reflections at the air/skin interface, but it is often realized without design guidelines and it may result bulky. On the other hand, introducing a metasurface can improve user's comfort. A rigorous procedure to find the parameters of the matching layer, also comprising the metasurface, can help in its design. Here, we extend the analytical optimization procedure of our previous works by considering a real patch antenna instead of a short dipole. An experimental setup for retrieving the electric field inside a tissue-mimicking phantom is also presented. Three cases are considered: no matching layer, dielectric-only matching layer and metasurface matching layer. The preliminary results show a good agreements with the theoretical ones
Preliminary Study On Novel 3D Printed Radio-Frequency Pressure Sensor
No full textPressure sensors are exploited in a wide range of applications, from industry to healthcare. In the state of the art, pressure sensors convert mechanical energy into electric energy and often they may result difficult to realize. However, recent advances in Additive Manufacturing (AM) allows to create customized low-cost devices in short time. Here we present an initial study for the realization of a pressure sensor based on radio-frequency, consisting of a flexible substrate and a single antenna. Different loads are placed upon the proposed system, in order to measure the correspondent changes in the reflection coefficient of the antenna. Two different substrates are realized with different printing settings. Preliminary measurements show that when the load is increased, the resonant frequency of the antenna is shifted to lower values. Some considerations about the relation between printing parameters (infill density and infill pattern) and substrate deformation are also given
Matching Layer Design for Far-Field and Near-Field Penetration Into a Multilayered Lossy Media
No full textThe remarkable spreading of medical devices relying on electromagnetic (EM) fields stimulates a deeper analysis of their interactions with the human body. The electric field generated by a radio-frequency (RF) source, such as an antenna, can be transmitted inside biological tissues and used in disease treatment, rehabilitation, and noninvasive imaging. In this context, it is important to facilitate the penetration of the electric field inside tissues. Matching layers (MLs) consisting of dielectric media or impedance surfaces provide an approach to maximize the field penetration. However, the presence of a source in close proximity to the body complicates the EM analysis and the design of such a structure. Here, we analyze an analytical method based on the wave-transmission-chain matrix and the wave-impedance concept, as defined by Schelkunoff for near-field sources. Examples of the usefulness of this approach in designing an ML that could improve the penetration of the electric field inside tissues are presented. The results obtained analytically are finally compared with those of a full-wave solver, showing good agreement
Analytical Approach to Matching Layer Design for Electric Field Maximization in Biological Tissues
No full textThe electromagnetic waves transmission inside biological tissues can be useful in several biomedical applications, such as rehabilitation and microwave imaging. In this context, an important point is to design a matching layer to enhance the penetration of the electric field into a target tissue. Here we present an analytical method to design a matching layer under the near-field regime, i.e. when the electromagnetic source, as for instance a short dipole antenna, lies in the proximity of the body. In particular, two cases are examined: when the matching layer only consists of a dielectric slab, and when it is composed by a metasurface printed on a dielectric substrate. The proposed approach is based on the wave-transmission chain matrix and on the Schelkunoff's definition of wave impedance to consider the source. The body is modeled as a multilayered planar medium. An optimization procedure based on a stochastic algorithm is applied to determine the parameters of the matching layer which could realize the maximum electric field transmission inside the muscle. These parameters are then used to simulate the overall system with a numerical software. The results show that the matching layer comprising the metasurface is the most effective solution in terms of electric field maximization and dimensions of the substrate
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