Changes in reproduction for subtropical cutlassfish Trichiurus japonicus reflect variation in temperature and population demography

Many subtropical fishes spawn multiple batches throughout a year. To understand plasticity in their reproductive output, we evaluated variation in oocyte size and batch fecundity for an exploited subtropical cutlassfish, Trichiurus japonicus, between two temperature periods (warm vs. cold) on the NE and SW coasts of Taiwan, northwestern Pacific. Given greater temperature variability on NE compared with SW coast, we hypothesized greater changes between warm and cold periods in oocyte size and fecundity for T. japonicus on the NE coast. We found opposite changes in sizes of ripe oocytes between periods (cold > warm on the NE but warm > cold on the SW coast) but consistent patterns in batch fecundity between coasts (warm > cold). Furthermore, the between-period patterns in female length were consistent on both coasts (warm > cold). The differential between-period patterns in oocyte size were related to potential adaptive responses to differential thermal environments between coasts, whereas the changes in fecundity mainly involved plastic processes (e.g., changes in population demography or movement). Together, our findings suggest that variability of temperature and maternal effects underlie recruitment variability of T. japonicus.     

Slip monitoring of a dip-slope and runout simulation by the discrete element method: a case study at the Huafan University campus in northern Taiwan

Slope failure is a widely observed phenomenon in the mountainous areas in Taiwan due to rainy climatic and fragile geological conditions. Landslides easily occur after intense rainfall, especially from typhoons, and, accordingly, cause a great loss of human life and property. At the northern end of the Western Foothill belt in northern Taiwan, Huafan University is founded on a dip-slope about 20° toward the southwest composed of early Miocene alternations of sandstone and shale. Data from continuous monitoring using inclinometers and groundwater gauges reveal that 6–10 mm/month of slope creeping occurs, and a potential sliding surface is then detected about 10–40 m beneath the slope surface. To understand the potential runout process of the dip-slope failure at the campus, particle flow code 3D models based on a discrete element method are applied in this study. Results of the simulation reveal a critical value of the friction coefficient to be 0.13 and that more than 90% of the campus buildings will slide down in 100 s when the friction coefficient is reduced to half the critical value. The weakening of the shear zone due to the rise of groundwater during rainstorms is assumed to be the main factor. Some suggestions for preventing landslide disasters are to construct catchpits to drain runoff and lower the groundwater table and to install a sufficient number of ground anchors and retaining walls to stabilize the slope.     

Effects of principal stress rotation on wave-induced soil response in a poro-elastoplastic sandy seabed

In this study, a constitutive model is developed in order to investigate wave–seabed interactions. This model takes into account the impact of principal stress rotation (PSR) and is based on the generalized plasticity theory, in which plastic strain generated by PSR is considered an additional item in the constitutive relationship of soil. The normalized loading direction and plastic flow direction were determined based on the stress tensor invariant. Comparisons between the present model and previous Hollow Cylinder Apparatus tests and geotechnical centrifugal wave tests show good agreement. Numerical results show the effects of PSR on predictions of liquefaction potential due to: (a) the cumulative impact of plastic strain in the seafloor and (b) the buildup of pore pressure. Parametric study shows that the model parameters, including the wave and seabed parameters, have significant effects on the wave-induced soil liquefaction.

     

Model experiments for propellant embedded rock anchors

Summary Propellant embedded anchors can be used to secure offshore platforms by rapidly anchoring them in seafloor rock. Field tests conducted by the U.S. Navy showed inconsistent results. A more promising approach seems to be modelling of anchor penetration and pullout resistance in jointed rock based on first principles.In this paper, physical model tests are described with which the physical phenomena are investigated and which will serve as a basis for predictive analytical models. The laboratory experiments, conducted with fasteners to model the anchors and with jointed and intact rock models made from gypsum, showed that basic intact material properties, joint configuration and individual joint properties influence penetration and pullout resistance. If the behavior is brittle, penetration is accompanied by cracking, otherwise ductile continuum deformation occurs. Jointing affects cracking in that closer joint spacing restricts cracking to fewer joint bounded plates but increases the number of cracks in the individual plate. The increased cracking intensity leads to a reduced pullout resistance.For purposes of analytical modelling, one can therefore, in a first step, build upon established relations between intact meterial, joint geometry and individual joint characteristics.     

Application of sub-image multiresolution analysis of Ground-penetrating radar data in a study of shallow structures

Fourier-based algorithms originally developed for the processing of seismic data are applied routinely in the Ground-penetrating radar (GPR) data processing, but these conventional methods of data processing may result in an abundance of spurious harmonics without any geological meaning. We propose a new approach in this study based essentially on multiresolution wavelet analysis (MRA) for GPR noise suppression. The 2D GPR section is similar to an image in all aspects if we consider each data point of the GPR section to be an image pixel in general. This technique is an image analysis with sub-image decomposition. We start from the basic image decomposition procedure using conventional MRA approach and establish the filter bank accordingly. With reasonable knowledge of data and noise and the basic assumption of the target, it is possible to determine the components with high S/N ratio and eliminate noisy components. The MRA procedure is performed further for the components containing both signal and noise. We treated the selected component as an original image and applied the MRA procedure again to that single component with a mother wavelet of higher resolution. This recursive procedure with finer input allows us to extract features or noise events from GPR data more effectively than conventional process.To assess the performance of the MRA filtering method, we first test this method on a simple synthetic model and then on experimental data acquired from a control site using 400 MHz GPR system. A comparison of results from our method and from conventional filtering techniques demonstrates the effectiveness of the sub-image MRA method, particularly in removing ringing noise and scattering events. Field study was carried out in a trenched fault zone where a faulting structure was present at shallow depths ready for understanding the feasibility of improving the data S/N ratio by applying the sub-image multiresolution analysis. In contrast to the conventional methods, the MRA sub-image filtering technique provides an overall improvement in image quality of the data as shown in the field study.     

Winter Distribution of Diatom Assemblages in the East China Sea

We examined the spatial distributional relationships between diatom assemblages and water types during the winter in the East China Sea. Principal component analysis was used to identify two water types and two diatom assemblages in the study area. Coastal water types along the mainland China coastline had low temperature and salinity levels, but high nitrate levels. The shelf-mixing water type in the rest of the study area had higher temperatures and salinities and lower levels of nitrate. Diatom assemblage distribution was not spatially consistent with water type. The Kuroshio assemblage had a large standing stock, distributed along the surface of the shelf break. This assemblage is likely the result of Kuroshio surface water coming into contact with nutrient-rich water in the shelf area, triggering proliferation of certain diatom species. A background assemblage with low standing stock level persisted over the entire study area in both coastal water and the shelf-mixing water types. Our results support previous research: the background assemblage is due to poor growth conditions such as the convection of water during winter; there were no significant seasonal variations in the species composition.     

Oscillatory soil response and liquefaction in an unsaturated layered seabed

The subject of wave-induced soil response in a real seabed has attracted the attention of geotechnical and coastal engineers over the last three decades, for which several basic theories have been developed. However, the evaluation of soil liquefaction has not been attempted theoretically in a seabed with multiple sub-layers, in which homogeneity in soil properties can be assumed within each layer. In this study, a semi-analytical approach is presented for obtaining solutions for the pore pressure and effective stresses in a non-cohesive layered seabed of finite thickness subject to a system of three-dimensional waves. Based on the numerical results for a layered seabed, influences of soil characteristics (relative layer thickness, permeability ratio and shear modulus) on seabed responses are described. Special attention is given to the effect of placing a coarser material as a top layer for protecting an underlayer of finer sediment. Although only a three-layered seabed is explicitly solved in this study, the procedure outlined can readily be extended to a multi-layered soil system. The three-dimensional solutions can also be applied to the two-dimensional progressive or standing wave systems.