Theoretical accuracy of synthetic aperture sonar micronavigation using a displaced phase-center antenna     

Bellettini  A. Pinto  M.A. 《Oceanic Engineering, IEEE Journal of》2002,27(4):780-789

The Cramer-Rao lower bounds on the cross-track translation and rotation of a displaced phase-center antenna (DPCA) in the slant range plane between two successive pings (known as DPCA sway and yaw in what follows) are computed, assuming statistically homogeneous backscatter. These bounds are validated using experimental data from a 118-182-kHz sonar, showing an accuracy of the order of 20 microns on the ping-to-ping cross-track displacements. Next, the accuracy required on the DPCA sway and yaw in order to achieve a given synthetic aperture sonar (SAS) beampattern specification, specified by the expected SAS array gain, is computed as a function of the number P of pings in the SAS. Higher accuracy is required when P increases to counter the accumulation of errors during the integration of the elementary ping-to-ping estimates: the standard deviation must decrease as P/sup -1/2/ for the DPCA sway and P/sup -3/2/ for the yaw. Finally, by combining the above results, the lower bounds on DPCA micronavigation accuracy are established. These bounds set an upper limit to the SAS length achievable in practice. The maximum gain Q in cross-range resolution achievable by a DPCA micronavigated SAS is computed as a function of the key SAS parameters. These theoretical predictions are compared with simulations and experimental results.  相似文献   

Prediction of Stellar Atmospheric Parameters using Instance-Based Machine Learning and Genetic Algorithms   总被引：1，自引：0，他引：1  

J. Federico Ramírez  Olac Fuentes  Ravi K. Gulati 《Experimental Astronomy》2001,12(3):163-178

In this article we present a method for the automated prediction of stellar atmospheric parameters from spectral indices. This method uses a genetic algorithm (GA) for the selection of relevant spectral indices and prototypical stars and predicts their properties, using the k-nearest neighbors method (KNN). We have applied the method to predict the effective temperature, surface gravity, metallicity, luminosity class and spectral class of stars from spectral indices. Our experimental results show that the feature selection performed by the genetic algorithm reduces the running time of KNN up to 92%, and the predictive accuracy error up to 35%. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

The Ferrara hard X-ray facility for testing/calibrating hard X-ray focusing telescopes     

Gianluca Loffredo  Filippo Frontera  Damiano Pellicciotta  Alessandro Pisa  Vito Carassiti  Stefano Chiozzi  Federico Evangelisti  Luca Landi  Michele Melchiorri  Stefano Squerzanti 《Experimental Astronomy》2005,20(1-3):413-420

We will report on the current configuration of the X-ray facility of the University of Ferrara recently used to perform reflectivity tests of mosaic crystals and to calibrate the experiment JEM–X aboard Integral. The facility is now located in the technological campus of the University of Ferrara in a new building (named LARIX laboratory= ̳LARge ̳Italian ̳X-ray facility) that includes a tunnel 100 m long with, on the sides, two large experimental rooms. The facility is being improved for determining the optical axis of mosaic crystals in Laue configuration, for calibrating Laue lenses and hard X-ray mirror prototypes.  相似文献   

A simulation tool for high data-rate acoustic communication in ashallow-water, time-varying channel     

Bjerrum-Niese  C. Bjorno  L. Pinto  M.A. Quellec  B. 《Oceanic Engineering, IEEE Journal of》1996,21(2):143-149

The paper discusses the development of a simulation tool to model high data-rate acoustic communication in shallow water. The simulation tool is able to generate synthetic time series of signals received at a transducer array after transmission across a shallow-water communication channel. The simulation tool is suitable for testing advanced signal processing techniques for message recovery. A channel model has been developed based on the physical aspects of the acoustic channel. Special emphasis has been given to fluctuations of the signal transmission caused by time-varying multipath effects. At shorter ranges, the temporal variations are dominated by acoustic scattering from the moving sea surface. Therefore, the channel model produces a coherence function which may be interpreted as a time-varying reflection coefficient for the surface scattered acoustical path. A static, range-independent ray model identifies the significant multipaths, and the surface path is modulated with the time-varying reflection coefficient. The advantages and limitations of the channel model are discussed and assumptions necessary to overcome the limitations are emphasised. Based on the assumptions, an algorithm has been developed and implemented to model how a binary message will be modulated when transmitted by a transducer, is distorted in the channel and finally is received by a transducer array  相似文献   

Design of shallow foundations under tensile loading for transmission line towers: An overview     

M.P. Pacheco  F.A.B. Danziger  C. Pereira Pinto   《Engineering Geology》2008,101(3-4):226-235

Tensioned foundations are common in civil engineering applications such as transmission towers, harbors, offshore structures, basement slabs under pressure, industrial equipment, etc. Procedures for the design of tensioned foundations are discussed in this paper, including specific recommendations for more common transmission tower foundations. Starting from a distinction between shallow and deep modes of failure, the paper presents the most common failure mechanisms for shallow failure in tension, including procedures for calculation of foundation tensile capacity under vertical and inclined loading. Emphasis is given to the influence of the strength of the compacted backfill compared to the strength of the natural soil, including presentation of results of full-scale loading tests.  相似文献   

Internal colonisation, hegemony and coercion: Investigating migration to Southern Lazio, Italy, in the 1930s     

Federico Caprotti 《Geoforum》2008,39(2):942-957

This paper investigates the Italian fascist regime’s use of internal colonisation as part of a wider ruralisation policy aimed at promoting population growth, curbing rural-urban migration, staunching emigration, and halting the spread of industrial urbanisation. By focusing on the case study of the Pontine Marshes, the paper demonstrates how, through targeted selection procedures aimed at displacing defined social and political undesirables, migrants were chosen and effectively coerced into migrating to the “fascist” landscape of the marshes. The area, reclaimed and developed in the 1930s, was celebrated as a sign of the regime’s engineering and social success. The paper utilises Antonio Gramsci’s thought on hegemony, and argues that the overt use of coercion hints at the fact that fascism, although ideologically totalitarian and hegemonic, was contested. Although statisticians, demographers and state bureaucrats were organised and institutionalised in the construction of hegemony based on consent, fascism based itself more in coercion than in passive consent in the case of internal colonisation.  相似文献   

Stratigraphic framework of gas accumulations in the Ría de Pontevedra (NW Spain)     

Ruth Durán  Soledad García-Gil  Raquel Diez  Federico Vilas 《Geo-Marine Letters》2007,27(2-4):77-88

Knowledge of marine geological environments in which shallow gas is accumulating is becoming increasingly important in global studies of climate change because a measurable proportion of the total methane source comes from continental margins. Previous studies have revealed that coastal environments represent important geological environments where microbial methane is being generated, is accumulating, and is being released. In the Ría de Pontevedra, at least 4.5 km² of seafloor in the innermost part of the ría is underlain by sediments containing natural gas. Seismic interpretation contributes new findings for the definition of periods and geological environments in which the gas could have been generated, and is accumulating and released in the Ría de Pontevedra. Groundtruthing the seismic data (facies, environments) makes it possible to identify favourable geological environments for gas generation in the sedimentary infill of the Ría de Pontevedra. Sequence stratigraphy based on high-resolution seismic profiles and post-Last Glacial Maximum sea-level records makes it possible to establish the stratigraphic architecture of the ría and to define the periods in which gas could have been generated. The results of this study show that the sedimentary infill is composed of a fifth-order sequence developed since the Last Glacial Maximum. Within this sequence, gas appears to have accumulated in the Holocene deposits associated with the latest transgressive and highstand system tracts. Seismic analysis shows that gas could have been generated in different geological environments in the Ría de Pontevedra. If coastal environments at times of lower sea level were similar to those of the present, organic-rich mud deposits (deposited mainly in lakes, estuaries and floodplains) could have survived transgression and remained buried as potential gas sources in the inner part of the ría.  相似文献   

Late Pleistocene vertebrate-bearing deposits at San Teodoro Cave (North-Eastern Sicily): Preliminary data on faunal diversification and chronology     

Laura Bonfiglio  Daniela Esu  Gabriella Mangano  Federico Masini  Daria Petruso  Michele Soligo  Paola Tuccimei   《Quaternary International》2008,190(1):26

This paper deals with the chronology and the possible correlations among levels of different excavated areas in the Pleistocene vertebrate-bearing deposits at the large San Teodoro Cave (North-Eastern Sicily). Two trenches have been excavated along the eastern side of the cave, located at a distance from the entrance, respectively, of 8 m (α trench) and 28 m (β trench) and at different depths. Lithological features, biometrical data from small mammals and ecological data from molluscs point to similar environmental conditions for the α trench deposits and those located along the eastern wall of the cave in the eastern part of the β trench. The same evidence, and the taphonomic features of large mammals, points to different environmental conditions and perhaps to different ages for the deposits located in the western part of the β trench. The survival of elephants in Sicily up to 32,000 years ago is a new significant result of the ²³⁰Th/²³⁴U dating carried out from a concretionary stratum from the β trench and represents the youngest elephant survival in the western Mediterranean islands.  相似文献   

A calibration system for superconducting gravimeters     

Vladimiro Achilli  Paolo Baldi  Giuseppe Casula  Mario Errani  Sergio Focardi  Marco Guerzoni  Federico Palmonari  Giuseppe Raguní 《Journal of Geodesy》1995,69(2):73-80

A new method for the calibration of a superconducting gravity meter is described, in which a 273 Kg annular mass is placed around the meter and is moved up and down. The geometry of the apparatus is easy to model and the accuracy in the computation of the gravity variation induced by the mass, 6.7µgal, is limited only by the accuracy in the knowledge of value of the gravitational constant. Measurements done in 91 and 92 for the calibration of the instrument GWR-T015 are described. The calibration factor has been determined with a precision of about 0.3%.  相似文献   

Origin and thermal evolution of icy satellites     

Angioletta Coradini  Costanzo Federico  Olivier Forni  Gianfranco Magni 《Surveys in Geophysics》1995,16(4):533-591

The paper reviews the problem of formation and evolution of the so-called regular satellites of the giant planets, and it consists of two parts: the first describes the possible origin of the satellites, the second studies their evolution, attempting to stress the relations of the present status of the satellites with their evolutionary history.The formation of regular satellite systems around giant planets is probably related to the formation of the central planet. Some characteristics of regular satellite systems are quite similar, and suggest a common origin in a disk present around the central body. This disk can originate through different mechanisms which we will describe, paying attention to the so-called accretion disk model, in which the satellite-forming material is captured. The disk phase links the formation of the primary body with the formation of satellites. The subsequent stages of the disk's evolution can lead first to the formation of intermediate size bodies, and through the collisional evolution of these bodies, to the birth of satellite embryos able to gravitationally capture smaller bodies.Given the scenario in which icy satellites may be formed by homogeneous accretion of planetesimals made of a mixtures of ice and silicates, if no melting occurs during accretion, the satellites have a homogeneous ice-rock composition. For the smaller satellites this homogeneous structure should not be substantially modified; only sporadic local events, such as large impacts, can modify the surface structure of the smaller satellites. For the larger satellites, if some degree of melting appears during accretion, a differentiation of the silicate part occurs, the amount of differentiation and hence the core size depending on the fraction of gravitational potential energy retained during the accumulation process. Melting and differentiation soon after the accretion, for the larger satellites, could also depend on the convective evolution in presence of phase transitions and generate an intermediate rock layer, considerably denser than the underlying, still homogeneous core, and unstable to overturning on a geologic time scale. Moreover the liquid water mantle could be a transient feature because the mantle would freeze over several hundred million years. For these large bodies the stable configuration is expected to be one consisting of a silicate core and a mantle of mixed rock and ice.  相似文献