The operational sex ratio of the sea urchin Paracentrotus lividus populations: the case of the Mediterranean marine protected area of Ustica Island (Tyrrhenian Sea, Italy)     

Paola Gianguzza  Fabio Badalamenti  Fabrizio Gianguzza  Chiara Bonaviri  & Silvano Riggio 《Marine Ecology》2009,30(1):125-132

We investigated, with a series of field and laboratory observations, the possible effect of the starfish Marthasteria glacialis predation on the operational sex ratio (OSR), i.e. the number of sexually mature males divided by the total number of sexually mature adults of both sexes at any one time, of the edible sea urchin Paracentrotus lividus . The OSR was estimated three times during the sea urchin summer spawning period (July 2004, June 2005 and July 2006) on barren substrates of Ustica Island Marine Protected Area (Southern Tyrrhenian Sea, Italy). Four sites were selected: two characterized by high M. glacialis density (take zone C) and two controls with low starfish density (no-take zone A). Mature sea urchins were independently collected by SCUBA diving and sexed. The adult sex ratio was skewed towards males at high M. glacialis density sites, whereas it was balanced (1:1) at predator low-density sites. Results of sex-selective feeding experiments in the laboratory showed that females of P. lividus were more vulnerable to M. glacialis predation. These outcomes underline the possible importance of M. glacialis in regulating the OSR of P. lividus populations.  相似文献   

Compound and hybrid clinothems of the last lowstand Mid-Adriatic Deep: Processes,depositional environments,controls and implications for stratigraphic analysis of prograding systems     

Fabiano Gamberi  Claudio Pellegrini  Giacomo Dalla Valle  Daniele Scarponi  Kevin Bohacs  Fabio Trincardi 《Basin Research》2020,32(2):363-377

Clinoforms with a range of scales are essential elements of prograding continental margins. Different types of clinoforms develop during margin growth, depending on combined changes in relative sea level, sediment supply and oceanographic processes. In studies of continental margin stratigraphy, trajectories of clinoform ‘rollover’ points are often used as proxies for relative sea-level variation and as predictors of the character of deposits beyond the shelf-break. The analysis of clinoform dynamics and rollover trajectory often suffers from the low resolution of geophysical data, the small scale of outcrops with respect to the dimensions of clinoform packages and low chronostratigraphic resolution. Here, through high-resolution seismic reflection data and sediment cores, we show how compound clinoforms were the most common architectural style of margin progradation of the late Pleistocene lowstand in the Adriatic Sea. During compound clinoform development, the shoreline was located landward of the shelf-break. It comprised a wave-dominated delta to the west and a barrier and back-barrier depositional system in the central and eastern area. Storm-enhanced hyperpycnal flows were responsible for the deposition of a sandy lobe in the river mouth, whereas a heterolithic succession formed elsewhere on the shelf. The storm-enhanced hyperpycnal flows built an apron of sand on the slope that interrupted an otherwise homogeneous progradational mudbelt. Locally, the late lowstand compound clinoforms have a flat to falling shelf-break trajectory. However, the main phase of shelf-break bypass and basin deposition coincides with a younger steeply rising shelf-break trajectory. We interpret divergence from standard models, linking shelf-break trajectory to deep-sea sand deposition, as resulting from a great efficiency of oceanographic processes in reworking sediment in the shelf, and from a high sediment supply. The slope foresets had a large progradational attitude during the late lowstand sea-level rise, showing that oceanographic processes can inhibit coastal systems to reach the shelf-edge. In general, our study suggests that where the shoreline does not coincide with the shelf-break, trajectory analysis can lead to inaccurate reconstruction of the depositional history of a margin.  相似文献   

A systematic analysis of the XMM-Newton background: III. Impact of the magnetospheric environment     

Simona Ghizzardi  Martino Marelli  David Salvetti  Fabio Gastaldello  Silvano Molendi  Andrea De Luca  Alberto Moretti  Mariachiara Rossetti  Andrea Tiengo 《Experimental Astronomy》2017,44(3):273-285

A detailed characterization of the particle induced background is fundamental for many of the scientific objectives of the Athena X-ray telescope, thus an adequate knowledge of the background that will be encountered by Athena is desirable. Current X-ray telescopes have shown that the intensity of the particle induced background can be highly variable. Different regions of the magnetosphere can have very different environmental conditions, which can, in principle, differently affect the particle induced background detected by the instruments. We present results concerning the influence of the magnetospheric environment on the background detected by EPIC instrument onboard XMM-Newton through the estimate of the variation of the in-Field-of-View background excess along the XMM-Newton orbit. An important contribution to the XMM background, which may affect the Athena background as well, comes from soft proton flares. Along with the flaring component a low-intensity component is also present. We find that both show modest variations in the different magnetozones and that the soft proton component shows a strong trend with the distance from Earth.  相似文献   

Probabilistic performance‐based optimum design of seismic isolation for a California high‐speed rail prototype bridge          下载免费PDF全文

Yong Li  Joel P. Conte 《地震工程与结构动力学》2018,47(2):497-514

Previous comparison studies on seismic isolation have demonstrated its beneficial and detrimental effects on the structural performance of high‐speed rail bridges during earthquakes. Striking a balance between these 2 competing effects requires proper tuning of the controlling design parameters in the design of the seismic isolation system. This results in a challenging problem for practical design in performance‐based engineering, particularly when the uncertainty in seismic loading needs to be explicitly accounted for. This problem can be tackled using a novel probabilistic performance‐based optimum seismic design (PPBOSD) framework, which has been previously proposed as an extension of the performance‐based earthquake engineering methodology. For this purpose, a parametric probabilistic demand hazard analysis is performed over a grid in the seismic isolator parameter space, using high‐throughput cloud‐computing resources, for a California high‐speed rail (CHSR) prototype bridge. The derived probabilistic structural demand hazard results conditional on a seismic hazard level and unconditional, i.e., accounting for all seismic hazard levels, are used to define 2 families of risk features, respectively. Various risk features are explored as functions of the key isolator parameters and are used to construct probabilistic objective and constraint functions in defining well‐posed optimization problems. These optimization problems are solved using a grid‐based, brute‐force approach as an application of the PPBOSD framework, seeking optimum seismic isolator parameters for the CHSR prototype bridge. This research shows the promising use of seismic isolation for CHSR bridges, as well as the potential of the versatile PPBOSD framework in solving probabilistic performance‐based real‐world design problems.  相似文献   

Shake table testing of an elevator system in a full‐scale five‐story building          下载免费PDF全文

Xiang Wang  Tara C. Hutchinson  Rodrigo Astroza  Joel P. Conte  José I. Restrepo  Matthew S. Hoehler  Waldir Ribeiro 《地震工程与结构动力学》2017,46(3):391-407

This paper investigates the seismic performance of a functional traction elevator as part of a full‐scale five‐story building shake table test program. The test building was subjected to a suite of earthquake input motions of increasing intensity, first while the building was isolated at its base and subsequently while it was fixed to the shake table platen. In addition, low‐amplitude white noise base excitation tests were conducted while the elevator system was placed in three different configurations, namely, by varying the vertical location of its cabin and counterweight, to study the acceleration amplifications of the elevator components due to dynamic excitations. During the earthquake tests, detailed observation of the physical damage and operability of the elevator as well as its measured response are reported. Although the cabin and counterweight sustained large accelerations because of impact during these tests, the use of well‐restrained guide shoes demonstrated its effectiveness in preventing the cabin and counterweight from derailment during high‐intensity earthquake shaking. However, differential displacements induced by the building imposed undesirable distortion of the elevator components and their surrounding support structure, which caused damage and inoperability of the elevator doors. It is recommended that these aspects be explicitly considered in elevator seismic design. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

A hybrid optimization scheme for self-potential measurements due to multiple sheet-like bodies in arbitrary 2D resistivity distributions     

Iraklis Giannakis  Panagiotis Tsourlos  Costas Papazachos  George Vargemezis  Antonios Giannopoulos  Nikos Papadopoulos  Fabio Tosti  Amir Alani 《Geophysical Prospecting》2019,67(7):1948-1964

Self-potential is a passive geophysical method that can be applied in a straightforward manner with minimum requirements in the field. Nonetheless, interpretation of self-potential data is particularly challenging due to the inherited non-uniqueness present in all potential methods. Incorporating information regarding the target of interest can facilitate interpretation and increase the reliability of the final output. In the current paper, a novel method for detecting multiple sheet-like targets is presented. A numerical framework is initially described that simulates sheet-like bodies in an arbitrary 2D resistivity distribution. A scattered field formulation based on finite differences is employed that allows the edges of the sheet to be independent of the grid geometry. A novel analytical solution for two-layered models is derived and subsequently used to validate the accuracy of the proposed numerical scheme. Lastly, a hybrid optimization is proposed that couples linear least-squares with particle-swarm optimization in order to effectively locate the edges of multiple sheet-like bodies. Through numerical and real data, it is proven that the hybrid optimization overcomes local minimal that occurs in complex resistivity distributions and converges substantially faster compared to traditional particle-swarm optimization.  相似文献   

Linear dynamic modeling of a uni‐axial servo‐hydraulic shaking table system     

J. P. Conte  T. L. Trombetti 《地震工程与结构动力学》2000,29(9):1375-1404

This paper focuses on the development of a linear analytical model (even though servo‐hydraulic actuation systems are inherently non‐linear, especially for large amplitude simulations — near the performance capacity of the system — linearized models proved experimentally to be quite effective overall in capturing the salient features of shaking table dynamics) of a uni‐axial, servo‐hydraulic, stroke controlled shaking table system by using jointly structural dynamics and linear control theory. This model incorporates the proportional, integral, derivative, feed‐forward, and differential pressure gains of the control system. Furthermore, it accounts for the following physical characteristics of the system: time delay in the servovalve response, compressibility of the actuator fluid, oil leakage through the actuator seals and the dynamic properties of both the actuator reaction mass and test structure or payload. The proposed model, in the form of the total shaking table transfer function (i.e. between commanded and actual table motions), is developed to account for the specific characteristics of the Rice University shaking table. An in‐depth sensitivity study is then performed to determine the effects of the table control parameters, payload characteristics, and servovalve time delay upon the total shaking table transfer function. The sensitivity results reveal: (a) a potential strong dynamic interaction between the oil column in the actuator and the payload, and (b) the very important effect of the servovalve time delay upon the total shaking table transfer function. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

A discriminatory diagram of massive versus stratified deposits based on the sedimentation and bedload transportation rates. Experimental investigation and application to pyroclastic density currents     

Pierfrancesco Dellino  Fabio Dioguardi  Domenico Maria Doronzo  Daniela Mele 《Sedimentology》2020,67(4):2013-2039

Dense gas-particle jets similar to collapsing eruption columns were generated by large-scale experiments. The column collapse resulted in a ground-hugging current forming stratified layers with bedding similar to natural pyroclastic density current deposits. At the impact of the collapsing column on the ground, a thick, massive bed was formed due to a high sedimentation rate that dumped turbulence due to high clast concentration. Down-current, flow expansion favoured turbulence and dilute gas-particle current that formed thin rippled layers deposited under traction. Experiments fed with fine ash (median size 0·066 mm) formed deposits without tractional structures, because fine particles, as other sedimentary fine material, is cohesive and exposes a limited surface to the shear stress. Experimental outcomes show that massive beds are formed where the sedimentation rate per unit width S_rw exceeds the bedload transportation rate Q_b by two orders of magnitude. A lower ratio generates traction at the base of the flow and formation of shear structures that increase in wavelength and height with a decreasing flux. This study presents a diagram that provides a useful addition for facies analysis of pyroclastic density currents, provided that deposits representing sustained sedimentation can be identified in the field. In the diagram a decrease in the S_rw/Q_b ratio corresponds to an increase in bedform size. Application of the diagram for hazard assessment purposes allows the reconstruction of the mass eruption rate of the Agnano–Monte Spina eruption at Campi Flegrei, which is the main variable defining the intensity of past eruptions, and of the Bingham rheology of the massive underflow of the Mercato pyroclastic density current at Vesuvius.  相似文献