3,056 research outputs found
Polar cap absorption events of November 2001 at Terra Nova Bay, Antarctica
Polar cap absorption (PCA) events recorded during November 2001 are investigated by observations of ionospheric absorption of a 30MHz riometer installed at Terra Nova Bay (Antarctica), and of solar proton flux, monitored by the NOAA-GOES8 satellite in geo-synchronous orbit. During this period three solar proton events (SPE) on 4, 19 and 23 November occurred. Two of these are among the dozen most intense events since 1954 and during the current solar cycle (23rd), the event of 4 November shows the greatest proton flux at energies &gt;10MeV. Many factors contribute to the peak intensity of the two SPE biggest events, one is the Coronal Mass Ejection (CME) speed, other factors are the ambient population of SPE and the shock front due to the CME. During these events absorption peaks of several dB (~20dB) are observed at Terra Nova Bay, tens of minutes after the impact of fast halo CMEs on the geomagnetic field. </p><p style="line-height: 20px;"> Results of a cross-correlation analysis show that the first hour of absorption is mainly produced by 84–500MeV protons in the case of the 4 November event and by 15–44MeV protons for the event of 23 November, whereas in the entire event the contribution to the absorption is due chiefly to 4.2–82MeV (4 November) and by 4.2–14.5MeV (23 November). Good agreement is generally obtained between observed and calculated absorption by the empirical flux-absorption relationship for threshold energy <i>E<sub>0</sub></i>=10MeV. From the residuals one can argue that other factors (e.g. X-ray increases and geomagnetic disturbances) can contribute to the ionospheric absorption.<br><br><b>Key words.</b> Ionosphere (Polar Ionosphere, Particle precipitation) – Solar physics (Flares and mass ejections
Paleomagnetic constraints on the Plio-Pleistocene geodynamic evolution of the external central-northern Apennines (Italy)
We report on new paleomagnetic results obtained from 27 sites sampled in the Plio-Pleistocene sequences at the external front of the central-northern Apennines. Previous analyses of Miocene (Messinian) sediments indicated that the present shape of the northern Apenninic arc is due to the oroclinal bending of an originally straight belt oriented around N320° and that vertical axis rotations accompanied the migration of the thrust fronts toward the Adriatic
foreland [F. Speranza et al., J. Geophys. Res. 102 (1997) 3153-3166]. We tried to provide new paleomagnetic constraints for the timing and rates of the oroclinal bending process during the Pliocene and the Pleistocene. The results suggest that CCW rotations observed in the northern part of the studied area are possibly younger than 3 Ma. No regional rotation is recorded in the Pliocene and Pleistocene sediments from the southern part of the study area, analogously to the Messinian sediments of the 'Acquasanta' domain of Speranza et al. [F. Speranza et al., J. Geophys. Res. 102 (1997) 3153-3166]. A local significant CCW rotation (23° ± 10°) is identified in the Early Pleistocene sediments that crop out along the Adriatic coast between Ascoli and Pescara, indicating differential motion of the thrust sheets. This rotation must be younger than 1.43 Ma
Noninvasive Evaluation of Abdominal Fat and Liver Changes Following Progressive Weight Loss in Severely Obese Patients Treated with Laparoscopic Gastric Bypass.
Proper orthogonal decomposition of solar photospheric motions
The spatio-temporal dynamics of the solar photosphere is studied by
performing a Proper Orthogonal Decomposition (POD) of line of sight velocity
fields computed from high resolution data coming from the MDI/SOHO instrument.
Using this technique, we are able to identify and characterize the different
dynamical regimes acting in the system. Low frequency oscillations, with
frequencies in the range 20-130 microHz, dominate the most energetic POD modes
(excluding solar rotation), and are characterized by spatial patterns with
typical scales of about 3 Mm. Patterns with larger typical scales of 10 Mm, are
associated to p-modes oscillations at frequencies of about 3000 microHz.Comment: 8 figures in jpg in press on PR
GNSS data filtering optimization for ionospheric observation
In the last years, the use of GNSS (Global Navigation Satellite Systems) data has been gradually increasing, for both scientific studies
and technological applications. High-rate GNSS data, able to generate and output 50-Hz phase and amplitude samples, are commonly
used to study electron density irregularities within the ionosphere. Ionospheric irregularities may cause scintillations, which are rapid and
random fluctuations of the phase and the amplitude of the received GNSS signals.
For scintillation analysis, usually, GNSS signals observed at an elevation angle lower than an arbitrary threshold (usually 15 , 20 or
30 ) are filtered out, to remove the possible error sources due to the local environment where the receiver is deployed. Indeed, the signal
scattered by the environment surrounding the receiver could mimic ionospheric scintillation, because buildings, trees, etc. might create
diffusion, diffraction and reflection.
Although widely adopted, the elevation angle threshold has some downsides, as it may under or overestimate the actual impact of
multipath due to local environment. Certainly, an incorrect selection of the field of view spanned by the GNSS antenna may lead to
the misidentification of scintillation events at low elevation angles.
With the aim to tackle the non-ionospheric effects induced by multipath at ground, in this paper we introduce a filtering technique,
termed SOLIDIFY (Standalone OutLiers IDentIfication Filtering analYsis technique), aiming at excluding the multipath sources of
non-ionospheric origin to improve the quality of the information obtained by the GNSS signal in a given site. SOLIDIFY is a statistical
filtering technique based on the signal quality parameters measured by scintillation receivers. The technique is applied and optimized on
the data acquired by a scintillation receiver located at the Istituto Nazionale di Geofisica e Vulcanologia, in Rome. The results of the
exercise show that, in the considered case of a noisy site under quiet ionospheric conditions, the SOLIDIFY optimization maximizes
the quality, instead of the quantity, of the data.Published2552–25622A. Fisica dell'alta atmosferaJCR Journa
Metabolic and nutritional status changes after 10% weight loss in severely obese patients treated with laparoscopic surgery vs integrated medical treatment
Intrawell stochastic resonance versus interwell stochastic resonance in underdamped bistable systems
We show that, for periodically driven noisy underdamped bistable systems, an intrawell stochastic resonance can exist, together with the conventional interwell stochastic resonance, resulting in a double maximum in the power spectral amplitude at the forcing frequency as a function of the noise intensity. The locations of the maxima correspond to matchings of deterministic and stochastic time scales in the system. In this paper we present experimental evidence of these phenomena and a phemonological nonadiabatic description in terms of a noise-controlled nonlinear dynamic resonance
An Optimal Execution Problem with Market Impact
We study an optimal execution problem in a continuous-time market model that
considers market impact. We formulate the problem as a stochastic control
problem and investigate properties of the corresponding value function. We find
that right-continuity at the time origin is associated with the strength of
market impact for large sales, otherwise the value function is continuous.
Moreover, we show the semi-group property (Bellman principle) and characterise
the value function as a viscosity solution of the corresponding
Hamilton-Jacobi-Bellman equation. We introduce some examples where the forms of
the optimal strategies change completely, depending on the amount of the
trader's security holdings and where optimal strategies in the Black-Scholes
type market with nonlinear market impact are not block liquidation but gradual
liquidation, even when the trader is risk-neutral.Comment: 36 pages, 8 figures, a modified version of the article "An optimal
execution problem with market impact" in Finance and Stochastics (2014
Geomagnetic polar observatories: the role of Concordia station at Dome C, Antarctica
A geomagnetic observatory is a permanent facility where magnetic
declination and inclination are recorded in conjunction with the temporal
evolution of the magnetic field components. Polar regions are
scarcely covered by observational points then the contributions from observatories
located there are particularly relevant. The geomagnetic observatory
at Concordia station, Dome C - Antarctica is located in the
inner part of the continent, its position is favorable for two key reasons,
i) data are unaltered by the "coastal effect” and ii) crustal effect
is negligible due to the thickness, almost 3 km, of ice coverage. Nevertheless,
these latter conditions imply an unconsidered aspect which
characterizes the entire station and every structure laying on the ice
surface: the dome on which Concordia station resides is sliding horizontally
and moving vertically with a velocity of few millimeter to
centimeters per year as indicated by independent geodetic observations.
This slow and continuous movement has a puzzling effect on the
trend of horizontal components of the magnetic field, sampled in a
time window of a decade since the establishing of the observatory in
2005.During the International Polar Year (2007-2009) the observatory
was upgraded with new equipment fulfilling the requirements of the
Intermagnet consortium, and becoming an observatory member in
2011. In this paper are illustrated the strategy adopted to track any possible
displacement of the observatory reference points (i.e. the azimuth
mark, the pillar position) and all the ordinary and extraordinary actions
required for collecting high quality data
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