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231.
Barbara Calcinai Carlo Cerrano Nozomu Iwasaki & Giorgio Bavestrello 《Marine Ecology》2008,29(2):273-279
Precious corals represent peculiar substrata for several species of boring sponges that exploit their carbonatic scleraxis, strongly decreasing their commercial value. Here we describe a new species of the genus Alectona from Japan recorded in a colony of Paracorallium japonicum (Kishinouye, 1903). The spicular complement of the new species consists of diactinal spicules covered by mushroom-like tubercles, often modified into styloid forms, and fusiform amphiasters with two or sometimes four verticils, each generally made up of six short tubercled rays. A complete survey of the literature on boring sponges recorded in precious corals in the Mediterranean Sea and Pacific Ocean indicates that the species of the family Alectonidae are the most strictly associated to this kind of substratum. Their world distribution, in fact, partially or totally overlap that of their coral hosts. 相似文献
232.
Giorgio Bartolini Alessandro Messeri Daniele Grifoni Daniele Mannini Simone Orlandini 《Theoretical and Applied Climatology》2014,118(1-2):147-157
Global warming alters the hydrological cycle since a rise in temperature leads to an increase in the moisture-holding capacity of the atmosphere at a rate of about 7 %/°C. This fact can influence the global, but also local characteristics of precipitation, such as total amount and intensity. Therefore, it is important to study changes in rainfall regime in regions with complex orography, like Tuscany, where there are strong spatial gradients in precipitation amounts. The aim of this study is to look for temporal change in precipitation from 1955 to 2007 searching for spatial differences. Daily data of 21 meteorological stations were analyzed to identify trends in seasonal and annual precipitation indices. Cluster analysis applied to principal components was applied to identify homogeneous groups of stations. A decrease in precipitation was observed at annual time scale, during winter and spring, especially in northwestern areas. Wet days highlighted a decrease in all of Tuscany, due to the same seasons. In northern Tuscany, the decrease in rainfall amount was mainly determined by a lower frequency of rainy events which in turn caused a decrease in the occurrence of extreme daily precipitation events (75th, 90th, and 95th percentile). In central-southern Tuscany, no significant changes were observed except for an increase in precipitation fraction, due to extreme events and in mean daily total amount for wet days. These results are consistent with recent findings for the Mediterranean area and confirm the usefulness of cluster analysis for the analysis of the spatial distribution of precipitation. 相似文献
233.
Jacopo Belfi Nicolò Beverini Filippo Bosi Giorgio Carelli Angela Di Virgilio Dmitri Kolker Enrico Maccioni Antonello Ortolan Roberto Passaquieti Fabio Stefani 《Journal of Seismology》2012,16(4):757-766
The ring laser gyroscope ??G-Pisa?? has been taking data inside the Virgo interferometer central area with the aim of performing high sensitivity measurements of rotations in the vertical as well as in the horizontal orientation. We discuss the main characteristics of the instrument, describing its mechanical design and presenting the measured sensitivity limit. By applying a simple effective model for the laser gyroscope, we show that the stability of the sensor above 10?s of integration time is mainly limited by backscattering effects. The horizontal rotation rate signal is also compared with the signals recorded by the Virgo environmental monitoring system and by a biaxial mechanical tiltmeter rigidly fixed on top of the gyrolaser mounting frame. 相似文献
234.
Eleazar Padrón Pedro A. Hernández Nemesio M. Pérez Theofilos Toulkeridis Gladys Melián José Barrancos Giorgio Virgili Hirochika Sumino Kenji Notsu 《Bulletin of Volcanology》2012,74(6):1509-1519
Measurements of visible and diffuse gas emission were conducted in 2006 at the summit of Sierra Negra volcano, Galapagos, with the aim to better characterize degassing after the 2005 eruption. A total SO2 emission of 11?±?2?t day?1 was derived from miniature differential optical absorption spectrometer (mini-DOAS) ground-based measurements of the plume emanating from the Mini Azufral fumarolic area, the most important site of visible degassing at Sierra Negra volcano. Using a portable multigas system, the H2S/SO2, CO2/SO2, and H2O/SO2 molar ratios in the Mina Azufral plume emissions were found to be 0.41, 52.2, and 867.9, respectively. The corresponding H2O, CO2, and H2S emission rates were 562, 394, and 3?t day?1, respectively. The total output of diffuse CO2 emissions from the summit of Sierra Negra volcano was 990?±?85?t day?1, with 605?t day?1 being released by a deep source. The diffuse-to-plume CO2 emission ratio was about 1.5. Mina Azufral fumaroles released gasses containing 73.6?mol% of H2O; the main noncondensable components amounted to 97.4?mol% CO2, 1.5?mol% SO2, 0.6?mol% H2S, and 0.35?mol%?N2. The higher H2S/SO2 ratio values found in 2006 as compared to those reported before the 2005 eruption reveal a significant hydrothermal contribution to the fumarolic emissions. 3He/4He ratios measured at Mina Azufral fumarolic discharges showed values of 17.88?±?0.25?R A , indicating a mid-ocean ridge basalts (MORB) and a Galapagos plume contribution of 53 and 47?%, respectively. 相似文献
235.
Indoor GNSS signals are typically received with poor signal-to-noise ratio, which impairs the acquisition stage of common
global positioning system (GPS) receivers. Extending the coherent integration time increases the acquisition sensitivity,
but the data-bit-rate limits the maximum achievable performance. Non-coherent processing also improves the detection performance,
but indoor signals require a large amount of accumulations resulting in significant squaring loss. Moreover, both strategies
have high computational complexity which fixes demanding requirements for stand alone mass-market terminals operating in real
time. A sensitivity–complexity trade-off is therefore mandatory. Assisted-GPS, which is included in 3GPP specifications, reduces the overall acquisition complexity and enhances sensitivity. In this paper
we describe a low-complexity-assisted data-wipe-off technique that enables the high-sensitivity acquisition of GPS signals.
The method is based on the acquisition of the strongest signal in order to obtain information that eases the acquisition of
the weaker ones. The analysis also addresses sources of sensitivity loss, such as Doppler effects and local oscillator inaccuracies.
A test campaign with real signals and integration times up to 2 s validates the method, demonstrating the effectiveness of
the proposed technique in indoor environments. 相似文献
236.
The spatial variability of bed particles of a gravel-bed channel is analysed and treated experimentally in order to simulate the effects of the arrangement of coarse bed elements on the flow resistance law. For the studied bed patterns, characterized by the concentration Γ of coarser elements arranged on the bed layer, a particle arrangement parameter α is proposed. The α parameter is useful for estimating the intercept b0 of the semi-logarithmic flow resistance law deduced by flume measurements carried out for the hydraulic condition of large-scale and transition roughness. The differences between the experimental friction factor parameter values and the ones calculated by the proposed semi-logarithmic relationship are explained by the ratio between the Shields parameter and its critical value. The analysis shows that estimates of the friction factor parameter are not improved by introducing the Froude number into the flow resistance law. © 1997 by John Wiley & Sons, Ltd. 相似文献
237.
Analysis of refracturing in horizontal wells: Insights from the poroelastic displacement discontinuity method
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Ali Rezaei Giorgio Bornia Mehdi Rafiee Mohamed Soliman Stephen Morse 《国际地质力学数值与分析法杂志》2018,42(11):1306-1327
In this paper, a fully coupled 2‐dimensional poroelastic displacement discontinuity method is used to investigate the refracturing process in horizontal wells. One of the objectives of refracturing is to access new reserves by adding new hydraulic fractures in zones that were bypassed in the initial fracturing attempt. Pore pressure depletion in the vicinity of old fractures directly affects the state of stress and eventually the propagation of newly created hydraulic fractures. Thus, a poroelastic analysis is required to identify guidelines for the refracturing process, in particular to understand the extension of the pore pressure depletion, and eventually, the orientation of new as well as old fractures. We propose a fully coupled approach to model the whole process of child fracture propagation in a depleted area between 2 parent fractures in the same wellbore. This approach omits the need of using multistep workflow that is regularly used to model the process. The maximum tensile stress criterion (σ criterion) is used for hydraulic fracture propagation. The proposed method is verified using available analytical solutions for total stress and pore pressure loading modes on a line fracture in drained and undrained conditions. Then, test cases of multifractured horizontal wells are studied to calculate the time evolution of the stress and pore pressure fields around old fractures and to understand the effect of these fields on the propagation path of newly created fractures. Finally, the effect of the pore pressure depletion on the propagation path of the newly created fractures in the bypassed area of the same wellbore is studied. The results show that the depleted areas around old fractures are highly affected by the extent and severity of the stress redistribution and pore pressure depletion. It is observed that a successful creation of new fractures may only happen in certain time frames. The results of this study provide new insights on the behavior of newly created fractures in depleted zones. They also clarify the relationship between stress change and pore pressure depletion in horizontal wells. 相似文献
238.
According to historical reports, the north-eastern coastal sector of the volcanic Pantelleria Island (Sicily Channel, Italy) was uplifted up to 1.0 m a.s.l. in the year preceding the October 1891 offshore eruptive event. To better understand the nature and timing of coastal uplift, a detailed survey of morphological and biological indicators of raised palaeo-shorelines has been carried out along the island coastline. This survey identified raised palaeo-shoreline levels at three elevation ranges: 2.5–4.2 m a.s.l. (highest), 1.5–2.7 m a.s.l. (intermediate) and 0.4–1.0 m a.s.l. (lowest). Radiocarbon dating on samples of corals and vermetids placed tight temporal constraints on the uplifting of the raised shorelines. In general, they indicate that the north-eastern sector of the island, centred on the area of Cala del Gadir, has undergone major uplifting, tilting the island towards the southwest from 900 years ago. Applying accurate corrections for sea-level variations, the total amount of volcano-tectonic uplift can be estimated. Uplift rates up to 5 mm/a suggest that the vertical deformation was caused by inflation processes related to magmatic intrusion along feeding fissures. 相似文献
239.
Hydrogeology of the Nurra Region, Sardinia (Italy): basement-cover influences on groundwater occurrence and hydrogeochemistry 总被引:2,自引:0,他引:2
Giorgio Ghiglieri Giacomo Oggiano Maria Dolores Fidelibus Tamiru Alemayehu Giulio Barbieri Antonio Vernier 《Hydrogeology Journal》2009,17(2):447-466
The Nurra district in the Island of Sardinia (Italy) has a Palaeozoic basement and covers, consisting of Mesozoic carbonates, Cenozoic pyroclastic rocks and Quaternary, mainly clastic, sediments. The faulting and folding affecting the covers predominantly control the geomorphology. The morphology of the southern part is controlled by the Tertiary volcanic activity that generated a stack of pyroclastic flows. Geological structures and lithology exert the main control on recharge and groundwater circulation, as well as its availability and quality. The watershed divides do not fit the groundwater divide; the latter is conditioned by open folds and by faults. The Mesozoic folded carbonate sequences contain appreciable amounts of groundwater, particularly where structural lows are generated by synclines and normal faults. The regional groundwater flow has been defined. The investigated groundwater shows relatively high TDS and chloride concentrations which, along with other hydrogeochemical evidence, rules out sea-water intrusion as the cause of high salinity. The high chloride and sulphate concentrations can be related to deep hydrothermal circuits and to Triassic evaporites, respectively. The source water chemistry has been modified by various geochemical processes due to the groundwater–rock interaction, including ion exchange with hydrothermal minerals and clays, incongruent solution of dolomite, and sulphate reduction. 相似文献
240.
A new genus and species of percoid fish, Hendrixella grandei gen. & sp. nov. is described from the upper Ypresian limestone of Monte Bolca, Italy. It is based on four well-preserved
specimens that show an elongate and slender body and a unique combination of features, including possession of 11 + 13 vertebrae,
two series of intermuscular bones, fused haemal spine of third preural centrum, caudal fin with 17 principal rays and 11 upper
and eight lower procurrent rays, predorsal formula 0/0/1 + 1/1/, two separated dorsal fins with rayless pterygiophore in-between,
and a single supernumerary spine in both dorsal and anal fins. Due to this unique combination of features, Hendrixella cannot be placed within any existing fossil or extant percoid families and it is placed incertae sedis in the Percoidei. The possession of two series of intermuscular bones represents an unambiguous autapomorphy of Hendrixella. A comparative analysis of the distribution of intermusculars among percomorph fishes indicates that the intermuscular bones
of the upper series can be homologized with the epineurals and those of the lower series are the homologs of the epicentrals
of non-acanthomorphs. 相似文献