True amplitude elastic Gaussian beam imaging of multicomponent walkaway vertical seismic profiling data

We develop the true‐amplitude prestack migration of multicomponent data based on the use of elastic Gaussian beams for walkaway vertical seismic profile (VSP) acquisition systems. It consists in a weighted summation of multishot data with specific weights, computed by tracing elastic Gaussian beams from each imaging point of the target area towards the sources and receivers. Each pair of beams may be connected with either a pair of P‐rays (PP‐image) or the P‐ray towards sources and the S‐ray to receivers (PS‐image) and is uniquely determined by dip (the angle of the bisector between the rays and the vertical direction) and opening (the angle between the rays) angles. Shooting from the bottom towards the acquisition system helps to avoid well‐known troubles, in particular multipathing for the imaging conditions in complex velocity models. The ability to fix the dip angle and implement summation over opening angles leads to the so‐called selective images that contain mostly interfaces with desired slopes. On the other hand, a set of images computed for a range of opening angles by summation over all available dip angles is used as input of an AVO‐like inversion procedure for the recovery of elastic parameters. The feasibility of this imaging procedure is verified by synthetic data for 2D realistic elastic models.     

Optimal implicit staggered‐grid finite‐difference schemes based on the sampling approximation method for seismic modelling

We propose new implicit staggered‐grid finite‐difference schemes with optimal coefficients based on the sampling approximation method to improve the numerical solution accuracy for seismic modelling. We first derive the optimized implicit staggered‐grid finite‐difference coefficients of arbitrary even‐order accuracy for the first‐order spatial derivatives using the plane‐wave theory and the direct sampling approximation method. Then, the implicit staggered‐grid finite‐difference coefficients based on sampling approximation, which can widen the range of wavenumber with great accuracy, are used to solve the first‐order spatial derivatives. By comparing the numerical dispersion of the implicit staggered‐grid finite‐difference schemes based on sampling approximation, Taylor series expansion, and least squares, we find that the optimal implicit staggered‐grid finite‐difference scheme based on sampling approximation achieves greater precision than that based on Taylor series expansion over a wider range of wavenumbers, although it has similar accuracy to that based on least squares. Finally, we apply the implicit staggered‐grid finite difference based on sampling approximation to numerical modelling. The modelling results demonstrate that the new optimal method can efficiently suppress numerical dispersion and lead to greater accuracy compared with the implicit staggered‐grid finite difference based on Taylor series expansion. In addition, the results also indicate the computational cost of the implicit staggered‐grid finite difference based on sampling approximation is almost the same as the implicit staggered‐grid finite difference based on Taylor series expansion.     

Displacement interaction among energy piles bearing on stiff soil strata

This study presents an analysis of the displacement interaction among general configurations of energy piles bearing on stiff soil strata that are subjected to thermal loads. This work integrates recent analyses investigating the displacement interaction among predominantly floating energy piles subjected to thermal loads in deep uniform soil deposits. To address this challenge, design charts for energy piles resting on either infinitely or finitely rigid soil strata are presented, applied and validated for the analysis of the vertical displacement of predominantly end-bearing energy pile groups subjected to thermal loads using the interaction factor method.     

Nematopsis N. Sp. (Sporozoa: Gregarinia) in Perna canaliculus (note)

Spores of a new species of Nematopsis have been found in the green‐lipped mussel Perna canaliculus Gmelin. This is the first record of a sporozoan parasite of a New Zealand shellfish.     

Fecundity in the marine spiny lobster Jasus verreauxi (H. Milne Edwards) (Crustacea: Decapoda: Palinuridae)

Fecundity in Jasus verreauxi (H. Milne Edwards, 1851) has been studied by a detailed investigation of (a) the total weight of eggs carried by female specimens, (b) the average number of eggs per 1 g sample, and (c) the total number of eggs carried by females. In mid October 1966, 217 females “in berry” (that is, carrying external eggs) were examined and measured at Spirits Bay, New Zealand. The fecundity study is based on the results obtained from 21 selected specimens, with carapace lengths from 15.5 cm to 23.5 cm.

A direct relation was found between the total weight of eggs carried and increase in carapace length. The total weight of eggs carried varied from about 51 g to 238 g for carapace lengths of 15.5 cm to 23.5 cm. No correlation was shown between the average number of eggs per 1 g sample and increase in carapace length. Considerable variation was noted in the number of eggs per 1 g sample, which ranged from a low count of 6,453 eggs to a high count of 8,341 eggs. The total number of eggs carried by female J. verreauxi was found to be related to an increase in carapace length. Furthermore, increase in fecundity per relative carapace length increase was noted to be greater in smaller specimens than in larger specimens. The total number of eggs carried ranged from about 385,000 for a carapace length of 15.5 cm to 1,940,000 for a carapace length of 23.5 cm.

Fecundity, as measured by the total weight of eggs carried and the total number of eggs produced, was found to be much higher in J. verreauxi than in several Jasus species previously studied by other workers.     

Ventilation and oxygen consumption in the spotted stargazer Genyagnus monopterygius †

As with other benthic fish which bury themselves in sand, in Genyagnus monopterygius it is the branchiostegal apparatus which makes the major contribution to ventilation of the gills. The prolonged abduction of the branchiostegal membranes draws water in through the mouth, and exhaled water moves away from the fish through mucus‐lined channels in the sand. The steady and continuous flow of water during ventilation may avoid detection of the stargazer by prey or predators. Associated with its sluggish habits and the low gill surface area available for gas exchange, Genyagnus has a low rate of oxygen consumption (15.8 ml kg^‐1 h^‐1 for a 100 g fish at 17°C). At partial pressures of oxygen (PO2) below 6 kPa (45 mm Hg) oxygen consumption is reduced, but the fish does not emerge from the sand until the PO2 falls below 2 kPa. There is evidence that the fish can sustain an oxygen debt. Respiration in the stargazer is discussed in relation to the fish's ability to withstand temporary hypoxia when it is stranded above the water level in the intertidal zone.     

Recruitment,habitat selection and larval photoresponse of Paraleucilla magna (Porifera,Calcarea) in Rio de Janeiro,Brazil

Little is known about the recruitment and behaviour of sponge larvae, especially of the class Calcarea. The calcareous sponge Paraleucilla magna is very common in Southeast Brazil, where it is considered a cryptogenic species. This study quantified recruitment rates in shaded and illuminated habitats for 2 years in Rio de Janeiro, Brazil, and analyzed larval photoresponses of this species. Four structures, each containing a shaded and an illuminated surface, were exchanged every 3 months for 2 years. The number of recruits was quantified on each plate. In the laboratory, larvae of P. magna were placed in half‐shaded Petri dishes and the number of settlers in each side was counted after 24 h. Paraleucilla magna recruited continuously throughout the experiment. Recruits occurred in greater abundance on shaded surfaces than on illuminated surfaces, and the larvae were negatively phototactic in vitro. Despite the possible influence of other factors in the recruitment of sponges (such as sedimentation, competition and predation), the prevalence of P. magna in shaded habitats may also be related to larval choice.     

New Viscoplastic Model for Design Analysis of Tunnels in Squeezing Conditions

Summary  This paper is intended to describe the SHELVIP (Stress Hardening ELastic VIscous Plastic) model, a new viscoplastic constitutive law which has been developed to incorporate the most important features of behaviour observed in tunnels excavated in severe to very severe squeezing conditions. This model couples the elastoplastic and time-dependent behaviour by using a plastic yield surface, as frequently adopted in tunnel design analysis, and the definition of a state of overstress referred to a viscoplastic yield surface. The model is formulated in all its detailed aspects. The related analytical closed-form solution for representing triaxial creep deformations is developed. Also developed is an incremental numerical solution for describing the triaxial stress–strain behaviour under constant strain rate conditions. The model is shown to fit very satisfactorily the results of creep tests on clay shales and relaxation tests on coal specimens, as recently performed for design analysis of tunnels in squeezing conditions. Correspondence: D. Debernardi, Department of Structural and Geotechnical Engineering, Politecnico di Torino, Torino, Italy     

Stress–Strain Behaviour of Flowable Fill

Flowable fill is a self-levelling and self-compacting, cementitious material which is primarily used as a backfill. It is a mixture of fine aggregates, small amount of cement, water and a by-product material. In this present experimental study, three industrial by-products namely fly ash, rice husk ash and quarry dust were used as constituent materials in flowable fill. Mix proportions were developed for different combination of these industrial by-products, in addition to small amount of cement content. The main objective of the present investigation is to study the stress–strain behaviour of these mixes, namely unconfined compressive strength (UCS), strain corresponding to peak stress, strain corresponding to fracture and modulus of elasticity. In addition, several mixes were tested for few other properties such as flowability, density, water-absorption and volume changes. The range of strengths, strains and moduli of elasticity obtained for these flowable fill mixtures represents different types of clay soils ranging from soft clays to very stiff clays. Thus, industrial by-products such as fly ash, rice husk ash and quarry dust can be beneficially added in flowable fill that offers comparable strengths to soils used for conventional fills and many other low-strength applications.     

弹性波传播数值模拟的区域分裂法

本文针对弹性波波场传播的数学模型,提出了一种基于有限元和有限差分耦合的区域分裂方法．它有灵活的网格剖分,克服了单纯用差分方法对区域的依赖性,可以适用于曲边地表;达到同样精度所需的计算量比有限元方法小;并易于实现并行计算．数值实验表明了算法的有效性．