1,722,029 research outputs found
Il nucleo terrestre: il cuore magnetico della Terra
No full textIl campo magnetico terrestre è una proprietà intrinseca del nostro pianeta e di altri oggetti del
sistema solare. Il Sole stesso possiede un forte campo magnetico che si inverte quasi ciclicamente
ogni 10-11 anni; tale comportamento è visibile attraverso la medesima ciclicità delle macchie solari
che denotano sulla superficie l’intensa attività magnetica della nostra stella.
Il campo magnetico terrestre è importantissimo per la vita sulla Terra. Esso protegge il pianeta dalle
particelle cariche provenienti dal Sole: con la sua presenza si oppone alla forza di questo vento
solare che altrimenti spazzerebbe via gran parte dell’atmosfera terrestre, così come probabilmente è
già avvenuto in passato con l’atmosfera di Marte.Published43-50ope
Translated origin spherical cap harmonic analysis
No full textThe method of spherical cap harmonic analysis (SCHA), due to Haines (1985) is appropriate for regional geomagnetic field modelling as it includes the required potential field constraints and, for a given number of model parameters, describes shorter wavelength features than a global spherical harmonic model. If the origin of the coordinate system is moved from the centre of the Earth towards the surface then the Earth's surface is no longer equidistant from the origin. At the Earth's surface the minimum wavelength described by a SCH model in the new coordinate system is smaller at the centre of the region than at the edge. This method of
translated origin spherical cap harmonic analysis (TOSCA) has been applied to regional field modelling for Italy. The method is able to take advantage of the dense distribution of data at the centre of region and the model effectively smooths towards the periphery. The performance of the TOSCA model is discussed in relation to a model derived using conventional SCHA.Published253-263N/A or not JCRreserve
Translated origin spherical cap harmonic analysis
No full textThe method of spherical cap harmonic analysis (SCHA), due to Haines (1985) is appropriate for regional geomagnetic field modelling as it includes the required potential field constraints and, for a given number of model parameters, describes shorter wavelength features than a global spherical harmonic model. If the origin of the coordinate system is moved from the centre of the Earth towards the surface then the Earth's surface is no longer equidistant from the origin. At the Earth's surface the minimum wavelength described by a SCH model in the new coordinate system is smaller at the centre of the region than at the edge. This method of
translated origin spherical cap harmonic analysis (TOSCA) has been applied to regional field modelling for Italy. The method is able to take advantage of the dense distribution of data at the centre of region and the model effectively smooths towards the periphery. The performance of the TOSCA model is discussed in relation to a model derived using conventional SCHA.Published253-263N/A or not JCRreserve
Oriente e occidente nella decorazione come linguaggio complesso, dalle "Zelliges" nel "Khatem" al "Drakslingor" celtico
No full textAre we going towards a global planetary magnetic change?
No full textThe dipolar part of the geomagnetic field has been decaying rapidly during the last few hundreds of years. In addition to this classical argument, from Information theory applied to geomagnetism, there are some evidences that the recent Earth magnetic field is showing characteristics typical of a reversal in progress. If this is true, many scientific and environmental questions will arise. For instance, it will be of particular interest to monitor the time-space dynamics the South Atlantic Anomaly, where the magnetic field is strongly reduced (a sort of "planetary magnetic hole"). Here we find one of the most favourite places where Low Earth Orbiting (LEO) satellites are lost or present some damages, due to the vicinity of "clouds" of electric particles (Van Allen belts) to the Earth's surface. The decay of the field will also decrease the screening effect to the solar wind and cosmic charges, so enhancing the cosmic radiation illuminating our planet: possible negative consequences are expected in terms of increase of skin cancers. Also important will be the study of the possible evolution of the core dynamics that will be generating this specific condition of the geomagnetic field.PublishedMalta, September 11-13, 20081.6. Osservazioni di geomagnetismo3.3. Geodinamica e struttura dell'interno della Terra3.4. Geomagnetismoope
Are we going towards a global planetary magnetic change?
No full textThe dipolar part of the geomagnetic field has been decaying rapidly during the last few hundreds of years. In addition to this classical argument, from Information theory applied to geomagnetism, there are some evidences that the recent Earth magnetic field is showing characteristics typical of a reversal in progress. If this is true, many scientific and environmental questions will arise. For instance, it will be of particular interest to monitor the time-space dynamics the South Atlantic Anomaly, where the magnetic field is strongly reduced (a sort of "planetary magnetic hole"). Here we find one of the most favourite places where Low Earth Orbiting (LEO) satellites are lost or present some damages, due to the vicinity of "clouds" of electric particles (Van Allen belts) to the Earth's surface. The decay of the field will also decrease the screening effect to the solar wind and cosmic charges, so enhancing the cosmic radiation illuminating our planet: possible negative consequences are expected in terms of increase of skin cancers. Also important will be the study of the possible evolution of the core dynamics that will be generating this specific condition of the geomagnetic field.PublishedMalta, September 11-13, 20081.6. Osservazioni di geomagnetismo3.3. Geodinamica e struttura dell'interno della Terra3.4. Geomagnetismoope
Power-law frequency distribution of H/V spectral ratio of seismic signals: Evidence for a critical crust.
No full textVisual cryptography schemes with perfect reconstruction of black pixels
No full textA (k,n)-threshold visual cryptography scheme ((k,n)-threshold VCS, for short) is a method to encode a secret image SI into n shadow images called shares such that any k or more shares enable the "visual" recovery of the secret image, but by inspecting less than k shares one cannot gain any information on the secret image. The "visual" recovery consists of xeroxing the shares onto transparencies, and then stacking them. Any k shares will reveal the secret image without any cryptographic computation. Visual cryptography schemes are characterized by two parameters: The pixel expansion, which is the number of subpixels each pixel of the original image is encoded into, and the contrast which measures the "difference" between a black and a white pixel in the reconstructed image. In this paper we analyze visual cryptography schemes in which the reconstruction of black pixels is perfect, that is, all the subpixels associated to a black pixel are black. We show that the minimum pixel expansion of such schemes can be simply computed by solving a suitable linear programming problem. Moreover, we give a construction for (3,n)-threshold VCS and a construction for (n - 1,n)-threshold VCS. These two constructions improve on the best previously known constructions with respect to the pixel expansion. © 1998 Elsevier Science Ltd. All rights reserved
A Design Methodology for Commercial Aircraft Formation Flight Plans with Minimal Fuel Consumption
No full textThis article deals with the problem of fuel saving in the design of flight plans for a formation flight connecting a given set of departure and arrival airports. Fuel savings occur when aircraft form proper flight formations during the cruise phase to take advantage of the induced drag reduction of the trailing aircraft. A procedure is provided to list all possible flight formation options for a plan with any number of flights. The option with the lowest fuel consumption is determined using a low-fidelity model of the fuel consumption of an aircraft flying at a constant speed and altitude, in a no-wind condition. The model exhibits the same accuracy in terms of ground tracks of the flights and fuel consumption calculation as compared to high-fidelity models that integrate nonlinear aircraft dynamics. Thus, a significant reduction in computational effort is achieved, while maintaining the same effectiveness
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