The sediment-water interface increment due to the complex burrows of macrofauna in a tidal flat

The architecture of macrofaunal burrows and the total area of the sediment-water interface created by biogenic structure were investigated in the Donggeomdo tidal flat on the west coast of Korea. Resin casting methods were applied to recover burrows of four dominant species, Macrophthalmus japonicus, Cleistostoma dilatatum, Perinereis aibuhitensis, and Periserrula leucophryna, and whole burrows within the casting area at three sites in different tidal levels.P. leucophryna excavated the largest burrow in terms of a surface area among them. In the case of whole burrow casting, the space occupied by the biogenic structure was extended into deeper and expanded more greatly at the higher tidal level. In the uppermost flat, the burrow wall surface area within sediment was more extensive than the sediment surface area. Increased oxygen supply through the extended interface could enhance the degradation rates of organic carbon and also change the pathways of degradation. Quantifying the relationship between the extended interface and mineralization rate and pathway requires more extensive study.     

Some stability properties of large-scale baroclinic flows with nonlinear zonal current profile

The stability properties of a baroclinic zonal current with nonlinear velocity profile are investigated. The integral method is applied to the governing eigenvalue equation having the vertical velocity as the dependent variable. Expressed in terms of the Rossby number and the Richardson number, stability criteria, unstable regions in the complexc plane, and the upper bound of the unstable wave growth rate are found. Some differences in the results are noted between the present model and the quasi-geostrophic streamfunction model, particularly in connection with the effect of the velocity profile curvature termU _zz . It is conjectured in the present model that, depending on extreme behaviors ofU _zz , the propagation speed of unstable waves can be greater thanU _max or smaller thanU _min .     

Robust adaptive control of underactuated ships on a linear course with comfort

This paper addresses an important problem in ship control application—the robust stabilization of underactuated ships on a linear course with comfort. Specifically, we develop a multivariable controller to stabilize ocean surface ships without a sway actuator on a linear course and to reduce roll and pitch simultaneously. The controller adapts to unknown parameters of the ship and constant environmental disturbances induced by wave, ocean current and wind. It is also robust to time-varying environmental disturbances, time-varying change in ship parameters and other motions of the ship such as surge and heave. The roll and pitch can be made arbitrarily small while the heading angle and sway are kept to be in reasonably small bounds. The controller development is based on Lyapunov’s direct method and backstepping technique. A Lipschitz continuous projection algorithm is used to update the estimate of the unknown parameters to avoid the parameters’ drift due to time-varying environmental disturbances. Simulations on a full-scale catamaran illustrate the effectiveness of our proposed controller.     

Geophysical and geochemical observations on actively seeping hydrocarbon gases on the south-eastern Yellow Sea continental shelf

In the southeastern Yellow Sea, active seepage of hydrocarbon gases has been observed by high-resolution (3.5 kHz) seismic profiling both in 1987 and 2001, occurring through a large number of plumes from the topmost pre-Holocene sedimentary layer. It is strong enough to compensate for current speed, extending vertically up to the sea surface. The gas seepage often appears to be explosive to form craters and diapirs, although pockmarks are rare due to the redistribution of mobile palimpsest sands. In core-top seawater and sediments, the gases are characterized by high amounts of C₂, homogenous ¹³C₁ values and a large difference (19.7 on average) between ¹³C₁ (–55.2 to –53.6 PDB) and ¹³C₂ (–36.8 to –32.5 PDB) values. The gases are considered to be generated with a smaller amount of C₁ at the early thermal cracking stage of labile source materials, after which the C₂ gas is enriched in ¹³C by diffusion or biological alternation at the generation or accumulation site. The homogenous ¹³C₁ values may be one of the geochemical characteristics of gases acquired at depth which are less altered in the case of rapid diffusive gas migration to the seafloor.     

Bacterioplankton growth and production at the Louisiana hydrocarbon seeps

The growth rate and potential production of bacterioplankton in cold hydrocarbon seeps located along the Louisiana coast were determined using a pulse-labeling technique. Surprisingly, community doubling times are on the order of 1.1 h, which compares to laboratory-grown cultures. We also found that there are differences in growth rates on relatively small geographic scales, suggesting the influence of site-specific geological features (e.g., gas hydrate mounds). Proceeding downslope to deeper waters, methane-oxidizing bacteria appeared to play a more significant role in community productivity. These preliminary experiments indicated, quite unexpectedly, that water column microbes are growing at a more rapid rate than in any other marine system so far studied and that methane may serve as a primary nutrient (carbon) source in these seep-associated microbial assemblages.     

Evaluation of bending moments and shear forces at unit connections of very large floating structures using hydroelastic and rigid body analyses

This paper investigates the characteristics of bending moments, shear forces and stresses at unit connections of very large floating structures (VLFS) under wave loads. The responses of VLFS are calculated by solving multi-body motion equation considering hydroelasticity and connection stiffness. Hydroelastic responses are calculated by the direct method. Higher-order boundary element method (HOBEM) is used for fluid analysis and finite element method (FEM) is introduced for structural analysis. The equation of motion is modified to describe the unit connections by employing spring elements. Bending moments and shear forces at the connections are obtained from the dynamic equilibrium condition for pressures and inertia forces. Two types of VLFS units such as tandem arranged units and side-by-side arranged units are considered in the numerical examples. The influences of connection stiffness, wave frequency and heading angle on responses of VLFS are investigated through the numerical examples. Rigid body analysis along with hydroelastic analysis is also carried out in the numerical analysis and comparison of those two approaches is discussed.     

Robust and adaptive path following for underactuated autonomous underwater vehicles

This paper proposes a nonlinear robust adaptive control strategy to force a six degrees of freedom underactuated underwater vehicle with only four actuators to follow a predefined path at a desired speed despite of the presence of environmental disturbances and vehicle’s unknown physical parameters. The proposed controller is designed using Lyapunov’s direct method, the popular backstepping and parameter projection techniques. The closed loop path following errors can be made arbitrarily small. Interestingly, it is shown that our developed control strategy is easily extendible to situations of practical importance such as parking and point-to-point navigation. Numerical simulations are provided to illustrate the effectiveness of the proposed methodology.     

Formation and distribution of manganese nodule deposit in the northwestern margin of Clarion-Clipperton fracture zones,northeast equatorial Pacific

In the northwestern margin of the Clarion and Clipperton fracture zones, manganese nodules are latitudinally variable in character, resulting from the progressive (re)generation of nodules since the Oligocene as the Pacific Plate migrates northwestward beneath the equatorial production zone. Complemented by the surface water productivity, bottom current activities have concentrated nodules in the Oligocene to Miocene siliceous clay. Resedimentation processes on nodules form three types of nodules with concentric structures and 10 Å-manganaterich bottoms, by periodically causing the diagenetic growth of nodules within the topmost sediment layer.     

硫酸皮肤素寡糖的分离与制备

利用软骨素酶 ABC (Chondroitinase ABC,EC4 .2 .2 .4 )对硫酸皮肤素 (Dermatan Sul-fate,DS)进行控制降解。对得到的混合寡糖首先采用低压凝胶渗透色谱 (L PGPC)进行分级 ,然后对每一组分再利用强阴离子交换高压液相色谱 (SAX- HPL C)进行分离 ,最终制备出聚合度为 2 ,4 ,6 ,8,10 ,12的寡糖纯品。寡糖纯度采用 SAX- HPL C,毛细管电泳 (CE)以及聚丙烯酰胺凝胶电泳(PAGE)进行检验 ,结构采用电喷雾离子化质谱 (ESI- MS)以及核磁共振波谱 (NMR)技术确定