420 research outputs found
TDOA–based Localization in Two Dimensions: the Bifurcation Curve
No full textIn this paper, we complete the study of the geometry of the TDOA map that encodes the
noiseless model for the localization of a source from the range differences between three receivers
in a plane, by computing the Cartesian equation of the bifurcation curve in terms of the positions of
the receivers. From that equation, we can compute its real asymptotic lines. The present manuscript
completes the analysis of [12]. Our result is useful to check if a source belongs or is closed to the
bifurcation curve, where the localization in a noisy scenario is ambiguous
Multistage metasomatism in ultrahigh-pressure mafic rocks from the North Dabie Complex (China)
No full textRelease of metamorphic fluids within the slab and/or from the slab to the mantle wedge in subduction environments can produce important metasomatic effects. Ultrahigh-pressure (UHP) metasomatised rocks represent ideal materials to study the element exchange at pressures corresponding to sub-arc depths in subduction zones. We present a petrologic and geochemical study of eclogites (s.l.) from the Dabie Mountains (China). The investigated samples were collected in the North Dabie Complex, where eclogite-facies rocks are significantly overprinted by granulite-facies metamorphism and partial melting. The studied eclogites are included in meta-lherzolitic bodies, which are in turn hosted by leucocratic gneisses. The textural relations among the various rock-forming minerals enabled us to identify several re-crystallisation stages. The peak (UHP) paragenesis consists of
garnet, clinopyroxene and rutile. UHP garnet and clinopyroxene display oriented inclusions of polycrystalline rods of rutile + ilmenite and of albite, K–Ba-feldspar and quartz, respectively. Garnet and clinopyroxene are both rimmed by an inclusion free zone that formed after the peak, still at high-pressure conditions. Such optical zoning does not correspond to a difference in major element concentrations between garnet core and rim. This observation provides evidence that the major element composition of garnet was reset during exhumation, thus preventing thermobarometric determination of peak metamorphic conditions. Further
decompression is documented by the formation of limited ilmenite+amphibole and granulite-facies coronas consisting of
clinopyroxene, orthopyroxene, plagioclase and amphibole around garnet. In order to investigate the stability of observed mineral parageneses, a series of reconnaissance piston cylinder synthesis experiments were carried out in an identical bulk composition.
The experimental study indicates that the peak metamorphic paragenesis is stable at P∼3.5 GPa and T≥750–800 °C. The
petrological study, combined with bulk-rock and mineral trace element analyses, provides evidence of intense metasomatism
affecting these eclogites. The bulk-rock major and trace element compositions indicate that the eclogites derive from basaltic protoliths with MORB and E-MORB affinity. Compared with such basalts, the studied rocks show strong depletion in SiO2 and alkalis and enrichment in MgO and FeO. These features likely derive from element exchange with ultramafic rocks prior to subduction, possibly related with the influx of Si-depleted and Mg-enriched fluids produced during the serpentinisation of the associated lherzolitic rocks. On the other hand, the trace element bulk-rock compositions show strong enrichment in Cs, Ba and Pb. The same characteristic enrichment and fractionation is recorded by peak metamorphic clinopyroxene but not in retrograde amphibole. Therefore, influx of crustal fluids transporting LILE and light elements must have occurred during subduction at UHP conditions. This stage likely records the tectonic coupling of the mafic–ultramafic rocks with the associated crustal rock units and provides evidence of LILE mobility between different slab components
Polyphase inclusions in garnet–orthopyroxenite (Dabie Shan, China) as monitors for metasomatism and fluid-related trace element transfer in subduction zone peridotite
No full textThe ultrahigh-pressure (UHP) Maowu Ultramafic Complex (Dabie Shan, China) is hosted by coesite-bearing gneisses. Textural and geochemical data demonstrate that garnet-orthopyroxenites within the ultramafic complex derive from garnet-harzburgite precursors that have been metasomatised at peak UHP conditions (4.0 ± 1.0 GPa, 750 ± 50 °C) by the addition of a silica- and incompatible trace element-rich fluid phase (hydrous melt), sourced from the associated crustal rocks. This metasomatism produced poikilitic orthopyroxene with high LREE and Ni contents and inclusion-rich garnet porphyroblasts. Solid polyphase primary inclusions within peak metamorphic garnet display negative crystal shapes and constant volume ratios of infilling mineral phases. Experimental homogenisation of these inclusions at conditions close to the estimated metamorphic peak demonstrates that the polyphase inclusions derive from trapped solute-rich aqueous fluids. The trace element characteristics of the experimentally re-homogenised inclusions include high LREE contents, a pronounced enrichment in LILE, with spikes of Cs, Ba, Pb and high U/Th. The investigated UHP garnet-orthopyroxenites from Maowu represent a natural laboratory to constrain the trace element transfer from the subducted crust to the mantle wedge at sub-arc depths. The observed textures and chemical characteristics provide evidence for the infiltration of a felsic hydrous melt into garnet-peridotite, a circumstance comparable to expected interaction of sediment-derived melts with mantle wedge peridotites in subduction zones. The SiO2 and Al2O3 component of the hydrous melt reacted with olivine to form replacive orthopyroxene and new garnet. The neoblastic orthopyroxene is able to accommodate some of the LREE, whereas the H2O and LILE component of the melt were partitioned into a residual aqueous fluid phase. Remnants of such an aqueous fluid were trapped in the garnet and formed the polyphase inclusions. The trace element pattern of these inclusions is very similar to the incompatible element enrichment observed in arc lavas. We suggest that the residual fluid produced by the peridotite/hydrous melt reaction is able to transfer the characteristic LILE signature from the subducted sediments to the locus of partial melting in the mantle wedge. Moreover, this study provides evidence that polyphase inclusions are important tools for constraining the nature and composition of UHP fluid
A comprehensive analysis of the geometry of TDOA maps in localization problems
No full textIn this paper we consider the well-established problem of time
differences of arrival (TDOA)-based source localization and propose a
comprehensive analysis of its solution for arbitrary sensor measurement and
placement. More specifically, we define the TDOA map from the physical
space of source locations to the space of range measurements (TDOAs), in the
specific case of three receivers in 2D space. We then study the identifiability
of the model, giving a complete analytical characterization of the image of
this map and its invertibility. This analysis has been conducted in a completely
mathematical fashion, using many different tools which make it valid for every
sensor configuration. These results are the first step toward the solution of
more general problems involving, for example, a larger number of sensors,
uncertainty in their placement, or lack of synchronization
Innovative unattended SEM-EDS analysis for asbestos fiber quantification
No full textScanning electron microscopy with energy dispersive spectrometry (SEM-EDS) is the only affordable analytical
technique that can discriminate both morphology and elemental composition of inorganic fibers. SEM-EDS is
indeed required to quantify asbestos in confounding natural matrixes (e.g. ophiolites), but is also time-consuming,
operator dependent, and strongly relies on the stochastic distribution of the fibers on the filter surface.
The balance between analytical time/cost and the method sensibility allows only about 0.5% of the filter to be
analyzed, strongly affecting the statistical significance of results. To improve sensitivity and precision and enhance
productivity, an unattended quantitative measurement of the asbestos fibers by SEM-EDS is proposed. The
method identifies the particle shape first and determines their chemical composition later, saving EDS analytical
time. Our approach was tested on four asbestos standards and the relative error on replicated measurements
was< 10%. The proposed unattended method quantifies asbestos in natural confounding matrix, also with a
very low asbestos content
Simulating voting rule reforms for the Italian parliament. An economic perspective
No full textThe aim of this paper is to contribute to the debate about the electoral rules in Italy. In particular, we simulate some voting rules to test what is the best electoral system on the basis of a utility function that takes into account two indices: representativeness and governability. As long as governability is important, a mixed member system (75% plurality, 25% proportional representation) outperforms the others. Our tool is the software ALEX4.1.Italian Parliament, electoral system, simulations
Les roches alpines dans l'outillage poli néolithique de la France méditerranéenne
No full textThe only alpine rocks found among the Neolithic polished tools of the French Mediterranean zone and a few perialpine areas are glaucophane rocks, s.l. éclogites and jadeilites. Serpentinites were used in western Switzerland and the Jura only. The areas containing primary and secondary outcrops of these rocks have been determined. A serie of arguments allows the authors to assert that essentially secondary deposits were exploited in the Neolithic. An analysis of the way these rocks are represented among the tools has evidenced various methods of circulating materials (raw materials, blanks or end-products ?) : a regional circulation for glaucophane rocks, a long-distance circulation for s.l. éclogites and probably jadéitites. Different flows of circulation have been considered for the latter two. Some arguments in favour of a Ligurian origin for the s.l. eclogite tools in southern France are presented.Les seules roches alpines rencontrées dans l'outillage poli néolithique de la zone méditerranéenne de la France et de quelques régions périalpines sont les roches à glaucophane, les éclogites s.l. et les jadéitites. Les serpentinites n'ont été employées qu'en Suisse occidentale et dans le Jura. Les zones d'affleurements primaires et secondaires de ces roches ont été déterminées. Un certain nombre d'arguments permet d'affirmer que ce sont essentiellement les gisements secondaires qui ont été exploités au Néolithique. L'analyse de la distribution de ces roches dans l'outillage a permis la mise en évidence de divers modes de circulation des matériaux (roches, ébauches ou objets finis ?) : circulation régionale pour les roches à glaucophane, circulation sur de grandes distances pour les éclogites s.l. et probablement les jadéitites. Différents courants de circulation ont été envisagés pour ces deux dernières. Des arguments en faveur d'une origine ligure des outils en éclogite s.l. du Sud de la France sont présentés.Ricq de Bouard Monique, Compagnoni Roberto, Desmons Jacqueline, Fedele Francesco. Les roches alpines dans l'outillage poli néolithique de la France méditerranéenne. In: Gallia préhistoire, tome 32, 1990. pp. 125-149
The Algebro-geometric Study of Range Maps
No full textLocalizing a radiant source is a problem of great interest to many scientific and technological research areas. Localization based on range measurements is at the core of technologies such as radar, sonar and wireless sensor networks. In this manuscript, we offer an in-depth study of the model for source localization based on range measurements obtained from the source signal, from the point of view of algebraic geometry. In the case of three receivers, we find unexpected connections between this problem and the geometry of Kummer’s and Cayley’s surfaces. Our work also gives new insights into the localization based on range differences
Letter
No full textRe: Ilgren EB, Pooley FD, Kumiya YM, Hoskins JA Critical reappraisal of Balangero chrysotile and mesothelioma risk. Epidemiology Biostatistics and Public Health. 2015; 12:e10125-
On the statistical model of source localization based on Range Difference measurements
No full textIn this work we study the statistical model of source localization based on Range Difference measurements, under the assumption of Gaussian noise on the data. Our analysis is based on a previous work of the same authors concerning the localization in a noiseless scenario. We investigate the case of planar localization of a source using a minimal configuration of three non aligned receivers. We have four curved exponential families corresponding to four different, non disjoint, regions of the feasible set. For each family we solve Maximum Likelihood Estimation (MLE). This requires to find the projection of a point on a set of segments and arcs of ellipse. Then, we perform the analytic study of the localization accuracy. In particular, we give formulas for mean square error and bias of MLE, depending on the displacement vectors. We validate the results through Monte Carlo simulations, in a given setup of the receivers. As the set of feasible measurements is a semialgebraic variety, this investigation makes use of techniques from Algebraic Statistics and Information Geometry
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