排序方式： 共有37条查询结果，搜索用时 15 毫秒
1.
2.
P. Bergamini G. Bonelli A. Paizis L. Tommasi M. Uslenghi R. Falomo G. Tondello 《Experimental Astronomy》2000,10(4):457-471
The scientific performance evaluation of a photon countingimaging system is presented. The detector is constituted by an ICCD camera with RbTe photocathode(optimized for UV radiation), and dedicated electronics for the acquisition and analysis ofthe events. For each photon event on the CCD, a real-time centroid calculation is performed, inorder to reach spatial resolution down to 25 m FWHM. The system has been tested usingthe 182 cm telescope of the Asiago Observatory.A standard stars field through U Johnson filter,and the Crab pulsar (PSR 0531+21) were observed. From the photometric data, relative magnitudes of the standard stars have been derived, showing a goodlinearity of the detector in the range of flux under consideration, as expected fromprevious laboratory measurements.The pulsar's data have been processed by FFT and epoch foldingtechniques to testthe detector's timing performances in the highest resolutionmode (4.512 ms).These observations show that a space resolved time analysis ofperiodic sources can be performed with 10-7 s accuracy. 相似文献
3.
Constantinos C. Repapis Petros P. Mimoglou Vicky V. Dimakopoulou Ioannis N. Psycharis Ioannis M. Taflampas 《地震工程与结构动力学》2020,49(5):479-497
The special interest produced by near-field directivity records and their effect on structural response has given a new significance in the velocity time history, its pulse-like content, and relevant parameters and indices. Recent research has shown that directivity pulses inherent in these records govern the linear and the nonlinear response of a wide range of structures. Based on this observation, it is suggested in this paper that a truncated ground motion, limited to the duration of the predominant velocity pulse, can be efficiently used to predict the structural response, instead of the base motion with the total duration, reducing significantly the required runtimes. The proposed methodology is verified for a series of medium to high rise reinforced concrete buildings, for which nonlinear time-history analyses are performed for a vast suite of pulse-like near-field records applied as base excitations with their total duration and the proposed truncated one. Comparison of the results for the response displacements and forces shows very good agreement, permitting the acceptance of the pulse duration as the efficient strong motion time interval of the original record, which determines the response and, thus, it can be used for nonlinear structural analyses. 相似文献
4.
Constantinos Tsingas Thierry Brizard Abdulaziz Al Muhaidib 《Geophysical Prospecting》2019,67(6):1557-1570
Although narrow-azimuth towed-streamer data provide good image quality for structural interpretation, it is generally accepted that for wide-azimuth marine surveys seabed receivers deliver superior seismic reflection measurements and seismically derived reservoir attributes. However, seabed surveys are not widely used due to the higher acquisition costs when compared to streamer acquisition. In recent years, there have been significant engineering efforts to automate receiver deployment and retrieval in order to minimize the cost differential and conduct cost-efficient seabed receiver seismic surveys. These engineering efforts include industrially engineered nodes, nodes on a rope deployment schemes and even robotic nodes, which swim to and from the deployment location. This move to automation is inevitable, leading to robotization of seismic data acquisition for exploration and development activities in the oil and gas industry. We are developing a robotic-based technology, which utilizes autonomous underwater vehicles as seismic sensors without the need of using a remotely operated vehicle for deployment and retrieval. In this paper, we describe the autonomous underwater vehicle evolution throughout the project years from initial heavy and bulky nodes to fully autonomous light and flexible underwater receivers. Results obtained from two field pilot tests using different generations of autonomous underwater vehicles indicate that the seismic coupling, and navigation based on underwater acoustics are very reliable and robust. 相似文献
5.
Application of the revised universal soil loss equation model on landslide prevention. An example from N. Euboea (Evia) Island, Greece 总被引：5，自引：2，他引：3
Dimitrios Rozos Hariklia D. Skilodimou Constantinos Loupasakis George D. Bathrellos 《Environmental Earth Sciences》2013,70(7):3255-3266
This study aims to evaluate the application of the Revised Universal Soil Loss Equation (RUSLE) on predicting of sites susceptible to slope failures caused by the soil erosion. It was carried out at the northern part of Euboea Island presenting one of the highest frequencies of landslide occurrence in Greece. All required datasets for the application of the RUSLE model were engaged to compile a potential soil erosion map of the study area. In addition, historical slope failure data were used to evaluate the produced map. Moreover, the frequency ratio statistical analysis was applied for the verification of the soil erosion map. The results showed a satisfactory agreement between the soil erosion intensity zones and distribution of landslides events. Therefore, the RUSLE model can be applied for the localization of sites susceptible to landslides that were prepared or triggered by the soil erosion. Finally, taking under consideration the contribution of erosion mechanisms over the landslides manifestation, a combination of measures were proposed for preventing and supporting these catastrophic phenomena. 相似文献
6.
7.
P. Savolainen D. C. Hannikainen O. Vilhu A. Paizis J. Nevalainen P. Hakala 《Monthly notices of the Royal Astronomical Society》2009,393(2):569-578
We have fitted ∼200 RXTE and INTEGRAL spectra of the neutron star (NS) low-mass X-ray binary (LMXB) GX 9+9 from 2002 to 2007 with a model consisting of a disc blackbody and another blackbody representing the spreading layer (SL), i.e. an extended accretion zone on the NS surface as opposed to the more traditional disc-like boundary layer. Contrary to theory, the SL temperature was seen to increase towards low SL luminosities, while the approximate angular extent had a nearly linear luminosity dependency. Comptonization was not required to adequately fit these spectra. Together with the ∼ 70° upper bound of inclination implied by the lack of eclipses, the best-fitting normalization of the accretion disc blackbody component implies a distance of ∼10 kpc, instead of the usually quoted 5 kpc. 相似文献
8.
L. Sidoli P. Romano L. Ducci A. Paizis G. Cusumano V. Mangano H. A. Krimm S. Vercellone D. N. Burrows J. A. Kennea N. Gehrels 《Monthly notices of the Royal Astronomical Society》2009,397(3):1528-1538
We report on new X-ray outbursts observed with Swift from three Supergiant Fast X-ray Transients (SFXTs): XTE J1739−302, IGR J17544−2619 and IGR J08408−4503. XTE J1739−302 underwent a new outburst on 2008 August 13, IGR J17544−2619 on 2008 September 4 and IGR J08408−4503 on 2008 September 21. While the XTE J1739−302 and IGR J08408−4503 bright emission triggered the Swift /Burst Alert Telescope, IGR J17544−2619 did not, thus we could perform a spectral investigation only of the spectrum below 10 keV. The broad-band spectra from XTE J1739−302 and IGR J08408−4503 were compatible with the X-ray spectral shape displayed during the previous flares. A variable absorbing column density during the flare was observed in XTE J1739−302 for the first time. The broad-band spectrum of IGR J08408−4503 requires the presence of two distinct photon populations, a cold one (∼0.3 keV) most likely from a thermal halo around the neutron star and a hotter one (1.4–1.8 keV) from the accreting column. The outburst from XTE J1739−302 could be monitored with a very good sampling, thus revealing a shape which can be explained with a second wind component in this SFXT, in analogy to what we have suggested in the periodic SFXT IGR J11215−5952. The outburst recurrence time-scale in IGR J17544−2619 during our monitoring campaign with Swift suggests a long orbital period of ∼150 d (in a highly eccentric orbit), compatible with what previously observed with INTEGRAL . 相似文献
9.
Woodon Jeong Constantinos Tsingas Mohammed S. Almubarak 《Geophysical Prospecting》2020,68(5):1523-1539
A number of deblending methods and workflows have been reported in the past decades to eliminate the source interference noise recorded during a simultaneous shooting acquisition. It is common that denoising algorithms focusing on optimizing coherency and weighting down/ignoring outliers can be considered as deblending tools. Such algorithms are not only enforcing coherency but also handling outliers either explicitly or implicitly. In this paper, we present a novel approach based on detecting amplitude outliers and its application on deblending based on a local outlier factor that assigns an outlier-ness (i.e. a degree of being an outlier) to each sample of the data. A local outlier factor algorithm quantifies outlier-ness for an object in a data set based on the degree of isolation compared with its locally neighbouring objects. Assuming that the seismic pre-stack data acquired by simultaneous shooting are composed of a set of non-outliers and outliers, the local outlier factor algorithm evaluates the outlier-ness of each object. Therefore, we can separate the data set into blending noise (i.e. outlier) and signal (i.e. non-outlier) components. By applying a proper threshold, objects having high local outlier factors are labelled as outlier/blending noise, and the corresponding data sample could be replaced by zero or a statistically adequate value. Beginning with an explanation of parameter definitions and properties of local outlier factor, we investigate the feasibility of a local outlier factor application on seismic deblending by analysing the parameters of local outlier factor and suggesting specific deblending strategies. Field data examples recorded during simultaneous shooting acquisition show that the local outlier factor algorithm combined with a thresholding can detect and attenuate blending noise. Although the local outlier factor application on deblending shows a few shortcomings, it is consequently noted that the local outlier factor application in this paper obviously achieves benefits in terms of detecting and attenuating blending noise and paves the way for further geophysical applications. 相似文献
10.
Constantinos I. Cartalis 《Earth, Moon, and Planets》1991,52(2):131-144
A new method is developed to determine the concentration profiles of chemical species from satellite measurements. The method takes into account the interaction of photochemical and radiative processes in the stratosphere and is applied for chemical species (nitric oxide and nitrogen dioxide) experiencing large diurnal changes. It is found that if the interaction of the photochemical and radiative processes is neglected, that is if the temporal and spatial variations of NO and NO2 are not considered in the radiative transfer calculations, the resulting errors for the concentration profiles for altitudes less than 20 km reach 100 and 5% respectively, for both sunset and sunrise. A photochemical scheme is developed capable of providing the mixing ratio profiles of NO and NO2 for different latitudes, altitudes and seasons and a retrieval code combining an iterative inversion algorithm, working from top of the atmosphere downwards, and a parameterization of the variability of NO and NO2 is also constructed. The method is used to examine the accuracy of the retrieval of the vertical concentration profiles and the new results show that the recovered profiles are in good agreement (error 5–15%) with measured profiles (WMO, 1985) and reflect the trends of NO and NO2 at sunset and sunrise. 相似文献