263 research outputs found
Iron ore deposits in the central Southern Alps (Lombardy, Italy): lithostratigraphic and metallogenic reassessment
No full textThe central Southern Alps host a very extensive metallogenic province including different metalliferous districts which are characterised by the prevailing presence of Fe, Pb-Zn ores, fluorite, and barite. The dominant iron district showing siderite-ankerite and minor hematite and sulphides is strictly space- and time-controlled. It runs from east to west, between Lake Lugano and Lake Iseo (Giudicarie Line), and includes several iron deposits, both of syngenetic-stratiform and epigenetic vein and dissemination type (fig. 1; tabs. 1, 2, 3). Such deposits were formed during a metallogenic epoch involving the Ordovician-Silurian upper portion of the crystalline basement and the volcano-sedimentary cover formations defined, from bottom to top, by: (i) the Carboniferous-Lower Permian Basal Conglomerate Fm, (ii) the Lower Permian Collio Fm, (iii) the Upper Permian Verrucano Lombardo Fm, (iv) the Lower Triassic Servino Fm. Concerning ore genesis (the depositional environment, transport of hydrothermal fluids, generation of hydrothermal ore fluids and constituents) of the syngenetic-strati form iron mineralization in the different lithostratigraphic sequences, the following observations can be deduced: (a) the presence of a common sub-littoral marine coastal to more distal depositional environment which was CO2-rich and locally hypersaline. This was set in a shallow carbonate-producing shelf zone with contributions of terrigenous as well as magmatogenic material. Local environments include lacustrine and evaporitic (upper member of the Collio Formation), together with a continental alluvial environment for the placer deposit of the >; (b) with respect to iron concentration in the depositional sites, there is evidence for a cyclic transport mechanism by hydrothermal systems, strictly connected to synsedimentary transtensive tectonics; (c) the generation of hydrothermal iron-enriched fluids can be referred to the dissolved content of both accessory and essential iron-bearing minerals of pre-existing rocks, leached and transported under suitable Eh-pH conditions. The genetic points common to epigenetic vein and disseminated mineralization are: (a) fault systems and fractures and permeable lithologies such as conglomerates, sandstones, cataclasites can act as suitable sites of deposition; (b) because of the spatial relationships existing between the epigenetic deposits and the late-Hercynian heat engines, the main mobilisation of the metal solutions (of meteoric, metamorphic and diagenetic origin) can be assumed to be hydrothermal >; a minor remobilization > of meteoric waters and chiefly of syn- to late-diagenetic hydrothermal fluids entirely affects every iron formation, especially the Servino Fm, which marks the upper limit of the iron metallogenesis; (c) the iron source can be envisaged in the leaching of any kind of pre-existing rocks, including the iron formations occurring within the sequence. On the question of iron source, the metal zoning of the basement of the Southern Central Alps can be taken into account (BRIGO & OMENETTO, 1979). Such basement is defined, from west to east, respectively, by a Au-zone (Strona Ceneri Zone), a Fe-zone (central Southern Alps), a pyrite-zone (Trentino Alto Adige Region), and a Cu-pyrite-zone (Cadore-Belluno Province). With respect to a general picture of the iron metallogenesis in the Alps, it is important to notice (BRIGO, 1998) that the deposits in the central Southern Alps are correlated with the iron deposits of the >, Styria, in the Northern Grauwacken Zone (THALMANN, 1979; SCHULZ et alii, 1997). On taking the recent investigations of the Authors into account, together with a critical literature revision of geology and of ore geology (JERVIS, 1873; CURIONI, 1877; CORNELIUS, 1916; STELLA, 1921; PENTA, 1952; MICHELETTI, 1954; GILLIERON, 1959; ASSERETO & CASATI, 1965; OMENETTO & BRIGO, 1974; FRIZZO & OMENETTO, 1974; FUMASOLI, 1974; BRIGO & OMENETTO, 1979; BERTOTTI et alii, 1993; CASSINIS el alii, 1997; SCIUNNACH et alii, 1999; SPALLA & GOSSO, 1999; SPALLA et alii, 1999; JADOUL et alii, 2000; SPALLA et alii, 2000), as well as an important re-evaluation of the extensive series of scientific works of historical, technological and archaeological nature (MAIRONI DA PONTE, 1803; ARRIGONI, 1840; CESA BIANCHI, 1874; FRUMENTO, 1952-1963; SQUARZINA, 1960; COLOMBO, 1976; TIZZONI, 1994-1995, 1997), it is possible to attain considerable evidence for a general theory concerning the origin of stratiform iron-bearing mineralizations or stratigraphic markers in different geological units especially occurring in the crystalline basement. As a consequence, the extension of this iron-bearing district in the Alps consisting of a dense distribution of small concentrations attains about 1900 km(2); such a pattern accounts for the presence of intense mining, metallurgical and artisanal activities which have taken place beginning from a remote origin until the first half of the XXth century, accounting for the present world-wide important social and economic position of Lombardy region
Optimal Projection Filters
No full textWe present the two new notions of projection of a stochastic differential
equation (SDE) onto a submanifold, as developed in Armstrong, Brigo e Rossi
Ferrucci (2019, 2018): the Ito-vector and Ito-jet projections. This allows one
to systematically and optimally develop low dimensional approximations to high
dimensional SDEs using differential geometric techniques. Our new projections
are based on optimality arguments and yield a well-defined ``optimal''
approximation to the original SDE in the mean-square sense. We also show that
the earlier Stratonovich projection satisfies an optimality criterion that is
more ad hoc and less natural than the criteria satisfied by the new
projections. As an application, we consider approximating the solution of the
non-linear filtering problem within a given manifold of densities, using either
the Hellinger or direct metrics and related Information Geometry
structures on the space of densities. The Stratonovich projection had yielded
the projection filters studied in Brigo, Hanzon and Le Gland (1998, 1999),
while the new projections lead to the optimal projection filters. The optimal
projection filters have been introduced in Armstrong, Brigo e Rossi Ferrucci
(2019), where numerical examples for the Gaussian case are given and where they
are compared to more traditional nonlinear filters.Comment: arXiv admin note: text overlap with arXiv:1610.0388
"you Are Older, although You Do Not Know That": Time, Consciousness, and Memory in "a Kind of Alaska" by Harold Pinter (1930-2008)
No full text"A Kind of Alaska"is a one-act play by the British playwright and Nobel Prize winner Harold Pinter (1930-2008), based on the book Awakenings by the neurologist Oliver Sacks (1933-2015). This play, first performed in 1982, is centered around the character of Deborah, a middle-aged woman, struck by encephalitis lethargica ("sleeping sickness") at the age of 16, who wakes up after 29 years of apparent sleep following the injection of an unnamed drug. This article analyzes how Pinter's drama investigated the mysterious and fascinating relationship between time, memory, and consciousness. The term "awakenings,"chosen by Sacks himself, clearly refers to the restoration of voluntary motor function in patients with postencephalitic parkinsonism who responded to levodopa. However, it also suggests that these patients had an impairment of awareness. Actually, beyond the acute phase, subjects with postencephalitic parkinsonism were not sleeping but severely akinetic and therefore probably aware of the passage of time. Oliver Sacks probably did not entirely recognize the intrinsic contradiction between prolonged sleep (with consequent impairment of awareness and subjective "time gap") of the acute lethargic phase and the severe akinesia with preserved awareness of the time-passing characteristic of postencephalitic parkinsonism. This confusion was further compounded by Harold Pinter in his play
The socio-cultural legacy of encephalitis lethargica and its representation in popular and mass culture
No full textWe propose an analysis of the socio-cultural legacy of encephalitis lethargica and post-encephalitic parkinsonism, and of their representations outside the scientific literature. Over the years, these conditions have been depicted in various ways, fueling a series of reflections on consciousness, time and memory. These representations have gradually flanked and partly overlapped the historical dimension of the disease. Encephalitis lethargica, in its core of historical reality, and its multiple representations constitute an inseparable and fascinating combination that continues to influence, even if in a subtle way, our way of looking at sleep, consciousness, memory, and our brain
Jean-Martin Charcot (1825-1893) and the first description of the "Alice in Wonderland Syndrome"
No full textThe "Alice in Wonderland Syndrome" is a neurological disorder characterized by visual or somatic disturbances frequently associated with migraine. The first documented description of this syndrome is that of a patient with macrosomatognosia and migraine with aura evaluated by Jean-Martin Charcot (1825- 1893) during a lecture given on November 22, 1887 at the Salpêtrière. Although at the time this condition was unknown, Charcot attributed the complex of symptoms to migraine with aura and sensory epilepsy. This diagnosis, although questionable, correctly suggested the presence of a cortical excitability disorder of areas responsible for processing and perception of sensory stimuli
Ipereccitabilità della corteccia visiva primaria nelle epilessie generalizzate idiopatiche associate a fotosensibilità: Uno studio mediante stimolazione magnetica transcranica | [Visual cortex hyperexcitability in idiopathic generalized epilepsies with photosensitivity: A TMS study]
No full textIn this study we aimed to investigate the excitability of both the primary motor cortex and the primary visual cortex in patients affected by idiopatic generalized epilepsy (IGE) with/without photosensitivity. Using transcranial magnetic stimulation we determined the resting motor threshold (rMT) and the phosphene threshold (PT) in 33 patients with IGEs (8 with photosensitivity), compared with 12 healthy controls. An inversion of the PT/rMT ratio (PT/rMT ratio <1) was found in 87.5% epileptic patients with photosensitivity. All patients with active epilepsy and photosensitivity showed this inversion. The differences in the PT/rMT ratio of epilepsy patients with photosensitivity and those of healthy controls (p=0.007) and with epilepsy patients without photosensitivity (p=0.016) were statistically significant. 91.7% of the controls reported phosphenes, compared with 45.5% of patients with idiopathic generalized epilepsy (p=0.015). Phosphenes were reported more frequently among epilepsy patients with photosensitivity (87.5%) than in patients with active epilepsy without photosensitivity (30.8%) (p=0.038) and with patients with epilepsy in remission without photosensitivity (33.3%) (p=0.054). No differences were found between epilepsy patients with photosensitivity and controls (p=0.648). The marked decrease in PT and the high phosphene prevalence in epilepsy patients with photosensitivity indicate a regional hyperexcitability of the primary visual cortex. Results of our study argue therefore against the presence of homogeneously distributed hyperexcitability in idiopathic generalized epilepsies associated with photosensitivity. If confirmed by further studies, transcranial magnetic stimulation with the assessment of rMT and PT might be a useful and fascinating method with which to study pathophysiological mechanisms underlying photosensitivity
“Chi l’ha detto?”. Un caso emblematico di errata attribuzione
No full textThis article discusses the real authorship of a sentence erroneously attributed to Giovanni Battista Morgagni (1682-1771) but actually by the French physician François Joseph Victor Broussais (1772-1838). This exemplary case shows how a single erroneous attribution risks being reproposed over time, consolidating itself in the scientific literature, so much to replace the original authorship with an erroneous one. It follows the absolute necessity to always and rigorously verify the accuracy of a sentence attributed to a certain author, both in form and in content, as well as in its real authorship.In questo articolo si presenta e discute la reale paternità di una frase erroneamente attribuita a Giovanni Battista Morgagni (1682-1771) e in realtà del medico francese François Joseph Victor Broussais (1772-1838). Questo caso emblematico evidenzia come una singola attribuzione errata rischi di essere riproposta nel tempo consolidandosi nella lettera-tura scientifica, tanto da sostituire la paternità originaria con una erronea. Ne consegue l’assoluta necessità di verificare sempre e in maniera rigorosa l’accuratezza di un’espressione attribuita a un autore, sia nella forma che nel contenuto, oltre che nella sua reale paternità
Coexistence of two distinct benign EEG variants in the same subject.
No full textRhythmic temporal theta bursts of drowsiness (RTTD), also known as "psychomotor variant", and subclinical rhythmic EEG discharge of adults (SREDA) are two EEG patterns of uncertain significance that occur without any correlation with epilepsy. Each of these patterns has been described to occur alone and in the literature there are no previous reports of co-occurrence of the two distinct benign EEG variants in the same patient. We describe the coexistence of RTTD and SREDA in EEG recordings from the same subject. Although the coexistence of two distinct EEG variants in the same patient is a rarity, these patterns are not so infrequently encountered when present alone and should thus be promptly recognised in order to avoid misdiagnosis of epilepsy due to an over-interpretation of normal sharp patterns
Common Correlation and Calibrating the Lognormal Forward Rate Model
No full text1997 three papers that introduced very similar lognormal diffusion processes for interest rates appeared virtuously simultaneously. These models, now commonly called the 'LIBOR models' are based on either lognormal diffusions of forward rates as in Brace, Gatarek & Musiela (1997) and Miltersen, Sandermann & Sondermann (1997) or lognormal diffusions of swap rates, as in Jamshidian (1997). The consequent research interest in the calibration of the LIBOR models has engendered a growing empirical literature, including many papers by Brigo and Mercurio, and Riccardo Rebonato (www.fabiomercurio.it and www.damianobrigo.it and www.rebonato.com). The art of model calibration requires a reasonable knowledge of option pricing and a thorough background in statistics - techniques that are quite different to those required to design no-arbitrage pricing models. Researchers will find the book by Brigo and Mercurio (2001) and the forthcoming book by Rebonato (2002) invaluable aids to their understanding.
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