Physical experiments are used to investigate the influence of the Coriolis forces on flow structures in channelized turbidity currents, and their implication for the evolution of straight and sinuous submarine channels. Initial tests were used to determine whether or not saline density currents are a good surrogate for particle-laden currents. Results imply that this assumption is valid when turbidity currents are weakly-depositional and have similar velocity and turbulence structures to saline density currents. Second, the controls of Coriolis forces on flow structures in straight channel sections are compared with two mathematical models: Ekman boundary layer dynamics and the theory of Komar [1969]. Ekman boundary layer dynamics prove to be a more suitable description of flow structures in rotating turbidity currents and should be used to derive flow parameters from submarine channels systems that are subjected to Coriolis forces. The significance of Coriolis forces for submarine channel systems were determined by evaluating the dimensionless Rossby number RoW. The Rossby number is defined as the ratio of the flow velocity, U, of a turbidity current to the channel width, W, and the rotation rate of the Earth represented by the Coriolis parameter, f. Coriolis forces are very significant for channel systems with RoW ≤ O(1). Third, the effect of Coriolis forces on the internal flow structure in sinuous submarine channels is considered. Since previous studies have only considered pressure gradient and centrifugal forces, the Coriolis force provides a crucial contribution to the lateral momentum balance in channel bends. In a curved channel, both the Rossby number RoW and the ratio of the channel curvature radius R to the channel width W, determine whether Coriolis forces affect the internal flow structure. The results demonstrate that Coriolis forces can cause a significant shift of the density interface and the downstream velocity core of channelized turbidity currents. The sediment transport regime in high-latitude channel systems, which have RoW << R/W, is therefore strongly influenced by Coriolis forces. Finally, these findings are incorporated into a conceptual model describing the evolution of submarine channels at different latitudes. For instance, the Northern Hemisphere channels have a distinctly higher right levee system and migrate predominantly to the left side and generally exhibit a low sinuosity. In contrast, low latitude channel systems have RoW >> R/W so that centrifugal forces are more dominant. This results in more sinuous submarine channel systems with varying levee asymmetries in subsequent channel bends. In conclusion, Coriolis forces are negligible around the equator but should be considered in high latitude systems, particularly when RoW ~ O(1) and RoW << R/W.

No description available.

No description available.

In the current study, behavioral responses of several species of calanoid copepods to mimics of oceanographic structure were observed and evaluated in the context of foraging and aggregation. Zooplankton distributions in oceanic habitats are often attributed to physical forcing; however, physical factors only act to drive ecological patterns at large scales (m to km). At fine to intermediate scales (cm to m) zooplankton behavior is believed to govern observed distributions, but the mechanisms and ecological significance of these behaviors are not well understood. In a water column, biological activity is often concentrated into one or a few regions, called thin layers, on the order of a meter thick, and zooplankton, such as copepods, must be able to reliably locate and exploit these patches for survival. Thin layers commonly are associated with oceanic structure such as flow gradients, fluid density jumps, or chemical composition gradients. Utilization of mechanosensory or chemosensory cues associated with thin layers may increase foraging success, thus translating into a significant ecological advantage. A laboratory apparatus was developed to create isolated and combined thin layer properties. Copepods then were exposed to laboratory mimics of thin layers. All of the tested species of copepods exhibited behavioral responses associated with area-restricted search behavior to one of the physical gradients (flow velocity or fluid density), but not both. Similar responses were observed for chemical exudate layer experiments and included increased proportional residence times, swimming speeds, and turn frequency. Food layers induced feeding responses from all tested species (increased proportional residence time, decreased swimming speed). Responses to various combinations of gradients were not fully synergistic, but suggested that some copepods employ a cue hierarchy to locate food-rich areas. Velocity or density gradients acted as initial cues for narrowing search regions, while chemical exudates induced responses that strengthened or removed the initial reactions. A simple foraging model was used to illustrate how such behavioral changes can lead to observed aggregations at larger temporal and spatial scales. Consequently, these results suggest that individual responses to oceanographic structure may have far reaching influence on population dynamics, succession, and biodiversity in coastal and pelagic ecosystems.

In general, a PEMFC was assembled by using a number of locked bolts. But this assembly will cause concentrated loads existed on the upper and lower portions of the end plates, so that the pressure distributed non-uniformly at the internal structures in the PEMFC and thus causing uneven distributed deformations of flow-channel plates. This phenomenon may lead to the leak of reaction gas, and causing not only the decrease of the efficiency of PEMFC, but also the increase of the dangerous. If the fuel cell size getting smaller, the influence may be more severely. The main aim of this study is to simulate the response of a micro-PEMFC numerically by utilizing a 3-D FEM model while the micro-PEMFC was assembled by three pairs of bolts along the upper and lower portions, respectively, of the end plates. The effects of different bolts locking sequences on the deformation and pressure distributions at flow-channel plates and on the porosity of gas diffusion layers in the micro-PEMFC were investigated. The simulated results showed that if one locked the middle bolt either on the upper or lower portion first, then the obtained uniformities of warpage, deformation, von Mises stress and porosity were superior than the corresponding obtained results if one locked either one of the four corner bolts first. Also, among the three pairs of bolts used for assembling the cell, the first locking bolt of the first pair of locking bolts and the first locking bolt of the rest of two pairs of locking bolts were suggested on the reverse portions of the end plates.

Omni-directional acoustic wave source interactions with a rough seabed with a continuously varying density and sound speed in a fluid-like sediment layer. The acoustic properties in the sediment layer possess an exponential type of variation in density and one of the three classes of sound speed profiles, which are constant,~$k^2$-linear, or inverse-square variations. Analytical solution of mean field. The mean field reflection coefficients corresponding to the aforementioned density and sound speed profiles for various frequencies, roughness parameters, are numberically generated and analyzed. Physical interpretations are provided for various results. This simple model characterizes two important features of sea floor, including seabed roughness, sediment inhomogenieties, therefore, provide a canonical analysis in seabed acoustics.

This thesis presents a critical reading of the multilayeredness in contemporary cities through the case of Divanyolu, main road of the historical istanbul. The ground in this case displays the fragmented character, so in order to follow the discontinuities in the morphological, economical, cultural and also hypothetic structures / this study will concentrate on the confrontation of layers within the framework of modernization process in the city. Beyond many possible discussions questioning the multiplicity of Istanbul, this study aims to encompass the specific character of the modernization process observed in Divanyolu. Furthermore, the information derived from the evaluation can suggest an exemplary framework for the new grounds in the multilayered sites, which is actually the other aim of the study. Within this framework, Divanyolu is chosen as a major urban case to discuss the complexity of the stratified ground. It was an example of a stratified ground being the main thoroughfare of the Ottoman Capital, which formed the important network from the Topkapi Palace to the Edirne Gate. The road has been the stage for the modernization process beginning from the 19th century to the present. With the different stage modernization process, the ground displayed the fragmented character. In this thesis, the main dynamics of this partial transformation will be evaluated.

A hull-mounted 38-kHz phased-array acoustic Doppler current profiler (ADCP) was used to acoustically survey the continental margin of the northern Gulf of Mexico (GOM) during 6 cruises in 2002-2003. This is the first backscatter survey with a 38-kHz ADCP in the Gulf of Mexico. ADCPs have been used as a proxy to measure the volume backscatter return from plankton in the water column, however previous studies were restricted to the upper 200 to 300 meters due to the relatively high frequency of operation (150-300 kHz) of the transducers. In addition to measuring deep water current velocities, the 38-kHz phased-array ADCP can measure Relative Acoustic Backscatter Intensity (RABI) as deep as 1000 meters. The daytime depth of the main deep scattering layer at 400 to 500 meters was resolved, and locally high backscatter intensity can be seen down to 800 meters. The objectives were to determine how to analyze RABI from the instrument to resolve scattering layers, and then to seek secondary deep scattering layers of potential prey species below the main deep scattering layer, from 600 to 800 meters in the feeding range for Gulf of Mexico sperm whales. Based on RABI from the 38-kHz ADCP, secondary DSLs in sperm whale diving range were more commonly recorded over the continental shelf than in the deep basin region of the Gulf of Mexico. The daytime depths of migrating plankton showed variation depending on physical circulation features (cyclone, anticyclone, proximity to Mississippi river, and Loop Current) present. Vertical migrations compared between concurrently running 38 and 153-kHz ADCPs showed an overlap of acoustic scatterers recorded by the two instruments, however the 153-kHz instrument has much finer vertical resolution. Vertical migration rates were calculated and simultaneous net tow samples from one of the cruises was used to compare abundance estimates by the two methods.

The liquid-crystal display because matches to the method is different , common has the TN monitor , the STN monitor , and the MVA monitor . Because these match to the method difference , therefore liquid crystal molecule pretilt angle is also different . Present liquid crystal molecule pretilt angle choice way includes : (1) Chooses the different polyimide material , after specific rubded intensity , but produces specific pretilt angle. (2) Uses low pretilt angle the polyimide material , mixes high pretilt angle according to the different proportion the polyimide material , but achieved accent of the pretilt angle changes . But in this research proposed double alignment layers , takes the first floor by homotropic layers , uses homogenous layers does for the upper formation , the surface free energy of the alignment layer can be easily controlled by adjusting the thickness of the top polyimide layer, similarly may achieve the accent to change liquid crystal molecule pretilt angle the effect . And may compensate the liquid crystal display to be insufficient because of rubbed polyimide , but has the question which dark condition is exposed , has a higher contrast gradient . Because this experiment scope accent changes the effect in liquid crystal molecule higher pretilt angle good , also kneading board various regions liquid crystal molecule pretilt the angle uniformity is higher , therefore may effectively apply on various types homotropic liquid crystal display component , for example: MVA , VA-STN , DSTN liquid-crystal display .

The design and method of cell assembly plays an important role in the performance of PEM fuel cell. The cell assembly will affect the contact behavior between the bipolar plates, flow-channel plates, gas diffusion layers (GDLs) and membrane electrode assembly (MEA). From the past studies, it was noted that the flow-channel plates in the cell will be deformed while the cell was assembled by locking with bolts. This phenomenon may lead to leakage of fuels, high contact resistance and malfunctioning of the cells. The main aim of this research is to study the variation of the deformation mode of the flow-channel plat in a micro-PEM fuel cell assembly subjected to different bolts locking sequences. The commercial FEM package, ANSYS, was adopted to model the three-dimensional single micro-PEMFC FEM model and the numerical simulation analyses were performed. The effect of the bolts locking sequence on the deformations of flow-channel plate in the micro-PEMFC was presented. A most properly bolts locking sequence was proposed also.