Numerical study on the flow characteristics of tidal jets induced by a tidal-jet-generator

The flow characteristics of tidal jets induced by a Tidal-Jet Generator (TJG) are investigated using a finite-difference numerical scheme, named Navier–Stokes (NS)–Marker and Cell (MAC)-TIDE, based on the fully 3D NS equations. The TJG is an enclosed rectangular breakwater, which has vertical opening and a large enclosed volume inside. During both phases of tide, strong and uni-directional jets can be obtained locally from the inlet of the TJG, due to the water level difference between the inner and outer sides of TJG.The computed results are extensively compared with three other independently developed numerical models; 3D-ADI, DVM, and CIP-CSF. These models are based on quasi-3D, 2D depth-averaged, and fully 3D NS equations, respectively. It is seen that the present fully 3D numerical model NS–MAC-TIDE can predict the maximum intensity of inlet velocity with higher accuracy than the other numerical models when compared with the empirical function proposed from the experiments. The numerical simulations based on NS–MAC-TIDE can reproduce successfully the processes of generation, development, and dissipation of tidal jets. The effects of gap opening on the main characteristics of the tidal jet flow are assessed. Through numerical assessment, it is also clearly demonstrated that the residual time of a pollutant distributed around the front of the TJG can be decreased by significant amount due to the locally induced tidal jet. The TJG can thus utilize tidal energy for water purification in local marine environment by providing a flushing mechanism.     

Distribution of caustic-crossing intervals for Galactic binary-lens microlensing events

Detection of caustic crossings of binary-lens gravitational microlensing events is important because by detecting them one can obtain useful information about both the lens and the source star. In this paper, we compute the distribution of the intervals between two successive caustic crossings, f ( t _cc), for Galactic bulge binary-lens events to investigate the observational strategy for the optimal detection and resolution of caustic crossings. From this computation, we find that the distribution is highly skewed towards short t _cc and peaks at t _cc∼1.5 d. For the maximal detection of caustic crossings, therefore, prompt initiation of follow-up observations for intensive monitoring of events will be important. We estimate that, under the strategy of the current follow-up observations with a second caustic-crossing preparation time of ∼2 d, the fraction of events with resolvable caustic crossing is ∼80 per cent. We find that if the follow-up observations can be initiated within 1 d after the first caustic crossing by adopting more aggressive observational strategies, the detection rate can be improved to ∼90 per cent.     

Characterizing the effect of heavy metal contamination on marine mussels using metabolomics

Marine mussels (Mytilus) are widely used as bioindicators to measure pollution in marine environments. In this study, (1)H NMR spectroscopy and multivariate statistical analyses were used to differentiate mussel groups from a heavy metal-polluted area (Onsan Bay) and a clean area (Dokdo area). Principal component analysis and orthogonal projection to latent structure-discriminant analysis revealed significant separation between extracts of mussels from Onsan Bay and from the Dokdo area. Organic osmolytes (betaine and taurine) and free amino acids (alanine, arginine, glutamine, phenylalanine, and threonine) were more highly accumulated in Onsan Bay mussels compared with Dokdo mussels. These results demonstrate that NMR-based metabolomics can be used as an efficient method for characterizing heavy metal contamination derived from polluted area compared to clean area and to identify metabolites related to environments that are contaminated with heavy metals.     

Copepod feeding in a coastal area of active tidal mixing: diel and monthly variations of grazing impacts on phytoplankton biomass

This study examined monthly feeding rates and grazing impact on phytoplankton biomass, as well as diel feeding rhythms of four key copepod species in a tidally well mixed estuary (Asan Bay, Korean Peninsula). Monthly ingestion rates estimated based on gut pigment analysis were closely associated with their peak densities, but not with phytoplankton biomass, implying high ingestion may be related to reproductive output for population growth. The three smaller copepods, Acartia hongi, Acartia pacifica and Paracalanus parvus, showed feeding preference for smaller phytoplankton (<20 μm) with higher clearance rates, whereas the larger Calanus sinicus preferred larger phytoplankton. Acartia pacifica and P. parvus showed distinct increased nocturnal feeding rates as measured with gut fluorescence, whereas A. hongi showed no significant day–night differences. Copepod diel feeding patterns were not associated with food quantity, and endogenous physiological rhythm might be hypothesized as responsible for the observed diel feeding patterns. Grazing impact on phytoplankton biomass by the four copepods in the estuary was on average 8% (range 0.2–29.8%) of the phytoplankton standing stock, similar to values reported in other coastal waters. Very high copepod abundances but low daily carbon ration (<20% for all copepods) provided by feeding on phytoplankton indicate that copepods also grazed on other non‐phytoplankton foods in Asan Bay.     

Evaluation of seismic behaviour of Cheomseongdae using dynamic centrifuge model test

Cheomseongdae is known to be the oldest astronomical observatory in Asia. According to historical records, the Gyeongju area, where Cheomseongdae is located, suffered from numerous medium‐scale earthquakes. Cheomseongdae has a masonry structure, which is apparently vulnerable to horizontal dynamic loads such as earthquakes. However, despite its appearance, features such as the filler of the lower half, inner irregular‐shaped stones which can induce high frictional resistance, eight long horizontal tie stones inside the artefact, and a grid of interlocking headstones increase its resistance to horizontal dynamic loads. Dynamic centrifuge model tests were performed on Cheomseongdae in order to evaluate the seismic response characteristics of this architectural heritage structure. Model tests were executed on two 1/15‐scale models: one which was an exact duplicate of the original Cheomseongdae and the other without the long horizontal tie stones and grid of interlocking headstones. On the basis of the amplification patterns in the time and frequency domains, the differences in seismic behaviour between the two Cheomseongdae models, and a broken stone at the 19th layer during tests, the long horizontal tie stones and headstones were found to increase the seismic resistance within Cheomseongdae and provide a glimpse of the ‘seismic design’ of our ancestors. Copyright © 2014 John Wiley & Sons, Ltd.     

Wavenumber of the guided wave supported by a thin resistive layer in marine controlled‐source electromagnetics

This paper discusses the asymptotic behaviour of the electromagnetic fields received on the sea‐bed (target response), as well as the fields distributed inside a thin resistive target, generated by a horizontal electric dipole above the sea‐bed in marine controlled‐source electromagnetics for hydrocarbon exploration. It is found that the guided wave supported by a thin resistive target can be expressed as a single‐mode exponential function. A simple closed‐form expression is derived to relate the single‐mode wavenumber of the guided wave to the model parameters: the resistivity and thickness of the target layer, the sea‐bed resistivity and the frequency. When the air‐wave is removed, the guided wave is dominant among the fields received on the sea‐bed at far offset. Hence the wavenumber of the guided wave can be calculated from the fields measured on the sea‐bed. The closed‐form expression can then be used to invert the target property from the calculated wavenumber and hence, can be considered as a hydrocarbon indicator.     

Ambiguous Hydraulic Heads and 14C Activities in Transient Regional Flow

A regional flow and transport model is used to explore the implications of significant variability in Pleistocene and Holocene climates on hydraulic heads and ¹⁴C activity. Simulations involve a 39 km slice of the Death Valley Flow System through Yucca Mountain toward the Amargosa Desert. The long-time scale over which infiltration has changed (tens-of-thousands of years) is matched by the large physical extent of the flow system (many tens-of-kilometers). Estimated paleo-infiltration rates were estimated using a juniper pollen percentage that extends from the last interglacial (LIG) period (approximately 120 kyrbp) to present. Flow and ¹⁴C transport simulations show that groundwater flow changes markedly as a function of paleoclimate. At the last glacial maximum (LGM, 21 kyrbp), the recharge to the flow system was about an order-of-magnitude higher than present, and water table was more than 100 m higher. With large basin time constants, flow is complicated because hydraulic heads at a given location reflect conditions of the past, but at another location the flow may reflect present conditions. This complexity is also manifested by processes that depend on flow, for example ¹⁴C transport. Without a model that accounts for the historical transients in recharge for at least the last 20,000 years, there is no simple way to deconvolve the ¹⁴C dates to explain patterns of flow.     

LH-moment estimation of Wakeby distribution with hydrological applications

This article discusses the method of higher-order L-moment (LH-moment) estimation for the Wakeby distribution (WAD), and describes and formulates details of parameter estimation using LH-moments for WAD. Monte Carlo simulation is performed, to illustrate the performance of the LH-moment method via heavy-tail quantiles (over all quantiles) using WAD. The LH-moment method proves as useful and effective as the L-moment approach in handling data that follow WAD, and it is then applied to annual maximum flood and wave height data.