On the time-dependent effects in advancing tunnels     

Jamshid Ghaboussi  Giancarlo Gioda 《国际地质力学数值与分析法杂志》1977,1(3):249-269

A finite element study is presented of the short-term effects that develop when a tunnel is driven in a ground showing viscous behaviour associated with the deviatoric deformations. Axisymmetric conditions around the tunnel centreline are assumed and the process of excavation is simulated by means of a step-by-step time incremental technique. The Kelvin's model is used to approximate the medium creep behaviour and a simple procedure is presented that allows the determination of the creep model constants from the laboratory test data. Various rates of advancing, the presence of an unsupported zone close to the tunnel face and the temporary interruption of the excavation process are considered. For the viscous model and the analytical technique used, simple, approximate relationships are presented for the displacements around the tunnel and the overexcavation volume as functions of the rate of excavation advancing.  相似文献   

Adiabatic chaos in the spin–orbit problem     

Giancarlo Benettin  Massimiliano Guzzo  Valerio Marini 《Celestial Mechanics and Dynamical Astronomy》2008,101(1-2):203-224

We provide evidences that the angular momentum of a symmetric rigid body in a spin–orbit resonance can perform large scale chaotic motions on time scales which increase polynomially with the inverse of the oblateness of the body. This kind of irregular precession appears as soon as the orbit of the center of mass is non-circular and the angular momentum of the body is far from the principal directions with minimum (maximum) moment of inertia. We also provide a quantitative explanation of these facts by using the theory of adiabatic invariants, and we provide numerical applications to the cases of the 1:1 and 1:2 spin–orbit resonances.  相似文献   

Relationships between Nutrient Enrichment and Benthic Function: Local Effects and Spatial Patterns     

Mohamed A. Abdelrhman  Giancarlo Cicchetti 《Estuaries and Coasts》2012,35(1):47-59

Eutrophication-induced changes to benthic faunal activities are problems of significant ecological impact, affecting global nutrient budgets as well as local trophic connections. We address the question of how nitrogen loads to estuarine embayments alter the bioturbation activities of benthic fauna. Specifically, we related local benthic activities to calculated local nitrogen concentrations for 22 northeastern US estuaries. These local nitrogen concentrations were derived from the calculated nitrogen loading for the embayment together with the spatial distribution of the local flushing time. Our results showed a maximum bioturbation rate at intermediate nitrogen concentrations or a “hump-shaped” pattern of response. This behavior was evident in all embayments that had a range of concentrations including low, intermediate, and high values. Embayments where sampling did not include this full range did not show this behavior. This work provides methods and guidance to help managers make decisions concerning the effects of nitrogen loading on the activities and well-being of benthic fauna in coastal embayments. The novelty of this approach lies in identifying the response of bioturbation to nitrogen loading in many systems, without costly and time-consuming speciation of benthic fauna, and also in rapidly identifying embayments and aquatic areas with vulnerable fauna. These results are ecologically significant in supporting the hypothesis that benthic organism abundance and activity will peak at mid-levels of nitrogen due to the interplay of food availability and oxygen levels, noting that the critical levels of these factors differ among water bodies.  相似文献   

The thermal stability of sideronatrite and its decomposition products in the system Na2O–Fe2O3–SO2–H2O     

Gennaro Ventruti  Fernando Scordari  Giancarlo Della Ventura  Fabio Bellatreccia  Alessandro F. Gualtieri  Andrea Lausi 《Physics and Chemistry of Minerals》2013,40(8):659-670

The thermal stability of sideronatrite, ideally Na₂Fe³⁺(SO₄)₂(OH)·3(H₂O), and its decomposition products were investigated by combining thermogravimetric and differential thermal analysis, in situ high-temperature X-ray powder diffraction (HT-XRPD) and Fourier transform infrared spectroscopy (HT-FTIR). The data show that for increasing temperature there are four main dehydration/transformation steps in sideronatrite: (a) between 30 and 40 °C sideronatrite transforms into metasideronatrite after the loss of two water molecules; both XRD and FTIR suggest that this transformation occurs via minor adjustments in the building block. (b) between 120 and 300 °C metasideronatrite transforms into metasideronatrite II, a still poorly characterized phase with possible orthorhombic symmetry, consequently to the loss of an additional water molecule; X-ray diffraction data suggest that metasideronatrite disappears from the assemblage above 175 °C. (c) between 315 and 415 °C metasideronatrite II transforms into the anhydrous Na₃Fe(SO₄)₃ compound. This step occurs via the loss of hydroxyl groups that involves the breakdown of the [Fe³⁺(SO₄)₂(OH)] _∞ ^2? chains and the formation of an intermediate transient amorphous phase precursor of Na₃Fe(SO₄)₃. (d) for T > 500 °C, the Na₃Fe(SO₄)₃ compound is replaced by the Na-sulfate thenardite, Na₂SO₄, plus Fe-oxides, according to the Na₃Fe³⁺(SO₄)₃ → 3/2 Na₂(SO₄) + 1/2 Fe₂O₃ + SO_x reaction products. The Na–Fe sulfate disappears around 540 °C. For higher temperatures, the Na-sulfates decomposes and only hematite survives in the final product. The understanding of the thermal behavior of minerals such as sideronatrite and related sulfates is important both from an environmental point of view, due to the presence of these phases in evaporitic deposits, soils and sediments including extraterrestrial occurrences, and from the technological point of view, due to the use of these materials in many industrial applications.  相似文献   

The Relation Among Seismic Activity, Volcanic Rock Emplacement and Bouguer Anomalies in Italy     

Giancarlo Scalera 《Natural Hazards》1997,15(2-3):165-181

A digitization has been performed of all volcanic rock fragments, main thrust fronts and fold axes from the 'Synthetic Structural Kinematic Map' as well as of all intrasedimentary magnetic bodies from the map of Cassano et al. These two maps complement each other, and the buried magnetized bodies fill the gaps of volcanic rocks in various regions e.g. in Tuscany. Some other major gaps can be found along the Northern Apennines, the Central and Southern Apennines and the Calabrian arc. A comparison of a map representing the 'Log C – seismic macrozonation index' to the pattern of all volcanic rocks, reveals that more seismic energy is released in those areas where volcanic rocks are absent or where their continuity in space is interrupted. Furthermore seismic activity is inhibited in those areas where minimum values of Bouguer anomalies are recorded.  相似文献   

Assessment of toxicological status of a SW Mediterranean segment population of striped dolphin (Stenella coeruleoalba) using skin biopsy     

M. Cristina Fossi  Letizia Marsili  Giancarlo Lauriano  Caterina Fortuna  Simone Canese  Stefania Ancora  Claudio Leonzio  Teresa Romeo  Ruben Merino  Esteban Abad  Begoa Jimnez 《Marine environmental research》2004,58(2-5):269

Various studies have revealed high concentrations of contaminants such as organochlorines (OCs) and heavy metals in Mediterranean cetaceans. A geographical trend of contamination (PCBs and DDTs) has been found for striped dolphin (Stenella coeruleoalba). In this study we used a non-lethal approach (skin biopsy) to investigate bioaccumulation of OCs, including polychlorobiphenyls (PCBs), DDTs, polychlorodibenzo-p-dioxins (PCDDs), polychlorodibenzofurans (PCDFs), trace elements (Hg, Cd, Pb) and CYP1A activity (BPMO) in nine striped dolphins sampled in the Aeolian area (Sicily – Italy) in summer 2002. The arithmetic mean value of BPMO activity in this group was 43.46 AUF/g tissue/h. This value is approximately 3 times and 5 times lower, respectively, than the value found in the Ionian and in the Ligurian groups. Skin biopsies of striped dolphins emerged as a suitable material for assessing the toxicological status of the various Mediterranean groups.  相似文献   

Size matters more than method: Visual quadrats vs photography in measuring human impact on Mediterranean rocky reef communities     

Valeriano Parravicini  Carla Morri  Giada Ciribilli  Monica Montefalcone  Giancarlo Albertelli  Carlo Nike Bianchi 《Estuarine, Coastal and Shelf Science》2009,81(3):359-367

The performances of two commonly used non-destructive sampling procedures for rocky benthic assemblages (i.e. photography and visually assessed quadrats) were compared. A damaging human activity, date mussel (Lithophaga lithophaga) harvesting (DMH), was chosen. Directly impacted sites were compared with reference conditions (controls). Both visual quadrats and photography were equally able to detect differences between impacted situations and controls. However, visual quadrats showed high variability among replicates and estimated higher species richness for controls, while photography did so for impacts. Pooling photos in a ‘sum photo quadrat’ showed that differences between the two methods are due to sampling unit size rather than sampling procedure itself. As a small sampling unit is unavoidable with photography, visual quadrats should be preferred in investigating shallow rocky reefs for their larger size; however, longer working time underwater with quadrats does not allow for numerous replicates. Pooling many photos to reach sampling sizes comparable with those of quadrats may be a valid alternative to reconcile image resolution and areal coverage.  相似文献   

High‐resolution topography and anthropogenic feature extraction: testing geomorphometric parameters in floodplains          下载免费PDF全文

Giulia Sofia  Giancarlo Dalla Fontana  Paolo Tarolli 《水文研究》2014,28(4):2046-2061

In floodplains, anthropogenic features such as levees or road scarps, control and influence flows. An up‐to‐date and accurate digital data about these features are deeply needed for irrigation and flood mitigation purposes. Nowadays, LiDAR Digital Terrain Models (DTMs) covering large areas are available for public authorities, and there is a widespread interest in the application of such models for the automatic or semiautomatic recognition of features. The automatic recognition of levees and road scarps from these models can offer a quick and accurate method to improve topographic databases for large‐scale applications. In mountainous contexts, geomorphometric indicators derived from DTMs have been proven to be reliable for feasible applications, and the use of statistical operators as thresholds showed a high reliability to identify features. The goal of this research is to test if similar approaches can be feasible also in floodplains. Three different parameters are tested at different scales on LiDAR DTM. The boxplot is applied to identify an objective threshold for feature extraction, and a filtering procedure is proposed to improve the quality of the extractions. This analysis, in line with other works for different environments, underlined (1) how statistical parameters can offer an objective threshold to identify features with varying shapes, size and height; (2) that the effectiveness of topographic parameters to identify anthropogenic features is related to the dimension of the investigated areas. The analysis also showed that the shape of the investigated area has not much influence on the quality of the results. While the effectiveness of residual topography had already been proven, the proposed study underlined how the use of entropy can anyway provide good extractions, with an overall quality comparable to the one offered by residual topography, and with the only limitation that the extracted features are slightly wider than the investigated one. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Urban seagrass: status of Posidonia oceanica facing the Genoa city waterfront (Italy) and implications for management     

Montefalcone M  Albertelli G  Morri C  Bianchi CN 《Marine pollution bulletin》2007,54(2):206-213

A system of five adjacent Posidonia oceanica meadows facing the waterfront of Genoa city (Ligurian Sea, NW Mediterranean) was investigated over different spatial scales (meters-kilometers) using three environmental indices: conservation index (CI), substitution index (SI) and phase-shift index (PSI). CI revealed differences mostly at large spatial scale, distinguishing the poor condition of the meadows closest to Genoa centre and harbour from the comparatively healthy condition of the farthest meadows. SI showed differences mostly at small spatial scale (i.e., within meadows), suggesting the influence of local factors in the re-colonisation of regressed meadows by the seagrass Cymodocea nodosa and/or the invasive alga Caulerpa racemosa. Mapping of PSI showed that the meadows closest to Genoa centre and harbour have undergone a nearly total phase shift and have no real potential for recovery: attempts to re-establish P. oceanica there might be a waste of time and money. On the contrary, the meadows farthest from Genoa centre and harbour showed a comparatively low level of phase shift and could still fully recover given specific management actions.  相似文献   

GIS morphometric indicators for the analysis of sediment dynamics in mountain basins     

Lorenzo Marchi  Giancarlo Dalla Fontana 《Environmental Geology》2005,48(2):218-228

Watershed management and headwater reconstruction programs require a reliable knowledge of sediment dynamics. Geographical Information Systems (GIS) provide the framework for the implementation of different complex techniques for the assessment of shallow landsliding and erosion processes in mountain basins. This paper presents some morphometric indicators aimed at erosion and sediment delivery analysis. The proposed indicators can be easily derived from medium to fine resolution Digital Elevation Models (DEM). Applications conducted in Eastern Italian Alps have shown the adequateness of the proposed approach to address erosion and sediment-related problems. The analysis considered the classification of sediment source areas with regard to their activity, the comparison between drainage basins having different morphological characteristics and the topographic control on sediment transport capacity, with a particular attention to the identification of channel reaches characterised by a low sediment transport capacity.  相似文献