Oxygen transport across the benthic boundary layer: from a 1-D to a 3-D view

The sediment-water interface is a fascinating environment.Bordering the dynamic processes between hydrosphere andgeosphere, it is the gate-keeper for the benthic-pelagiccoupling of carbon and nutrient cycles in aquatic ecosystems.In this region boundary layer hydrodynamics interact withtransport processes across the interface, organic matterdeposited on the sediment surface supports and focuses thebiological activity to a thin veneer teeming with life, and steepchemical gradients provide diverse zones for biological andgeochemical processes.Just as the earth surface appears flat when viewed fromorbit, the sediment surface appears flat when we read mostbiogeochemical literature which describes it with only avertical axis. However, many aspects of sediment biology andgeochemistry require a three-dimensional view to understandtheir essential properties. We need novel approaches withgreater information capacity to study the spatial structures ofbiota, environments, and processes. To stimulate thedevelopment of such approaches, this short review will discuss some of the small-scale characteristics of the benthic boundarylayer, and illustrates the 3-D world of the sea floor based onrecent progress in analytical and experimental techniques. Thefew examples used are taken mostly from the work of our owngroup since brevity forces us to neglect the excellent work ofmany colleagues

Scale-based surface understanding using diffusion smoothing

The research discussed in this thesis is concerned with surface understanding from the viewpoint of recognition-oriented, scale-related processing based on surface curvatures and diffusion smoothing. Four problems below high level visual processing are investigated: 1) 3-dimensional data smoothing using a diffusion process; 2) Behaviour of shape features across multiple scales, 3) Surface segmentation over multiple scales; and 4) Symbolic description of surface features at multiple scales. In this thesis, the noisy data smoothing problem is treated mathematically as a boundary value problem of the diffusion equation instead of the well-known Gaussian convolution, In such a way, it provides a theoretical basis to uniformly interpret the interrelationships amongst diffusion smoothing, Gaussian smoothing, repeated averaging and spline smoothing. It also leads to solving the problem with a numerical scheme of unconditional stability, which efficiently reduces the computational complexity and preserves the signs of curvatures along the surface boundaries. Surface shapes are classified into eight types using the combinations of the signs of the Gaussian curvature K and mean curvature H, both of which change at different scale levels. Behaviour of surface shape features over multiple scale levels is discussed in terms of the stability of large shape features, the creation, remaining and fading of small shape features, the interaction between large and small features and the structure of behaviour of the nested shape features in the KH sign image. It provides a guidance for tracking the movement of shape features from fine to large scales and for setting up a surface shape description accordingly. A smoothed surface is partitioned into a set of regions based on curvature sign homogeneity. Surface segmentation is posed as a problem of approximating a surface up to the degree of Gaussian and mean curvature signs using the depth data alone How to obtain feasible solutions of this under-determined problem is discussed, which includes the surface curvature sign preservation, the reason that a sculptured surface can be segmented with the KH sign image alone and the selection of basis functions of surface fitting for obtaining the KH sign image or for region growing. A symbolic description of the segmented surface is set up at each scale level. It is composed of a dual graph and a geometrical property list for the segmented surface. The graph describes the adjacency and connectivity among different patches as the topological-invariant properties that allow some object's flexibility, whilst the geometrical property list is added to the graph as constraints that reduce uncertainty. With this organisation, a tower-like surface representation is obtained by tracking the movement of significant features of the segmented surface through different scale levels, from which a stable description can be extracted for inexact matching during object recognition

Digital relief generation from 3D models

It is difficult to extend image-based relief generation to high-relief generation, as the images contain insufficient height information. To generate reliefs from three-dimensional (3D) models, it is necessary to extract the height fields from the model, but this can only generate bas-reliefs. To overcome this problem, an efficient method is proposed to generate bas-reliefs and high-reliefs directly from 3D meshes. To produce relief features that are visually appropriate, the 3D meshes are first scaled. 3D unsharp masking is used to enhance the visual features in the 3D mesh, and average smoothing and Laplacian smoothing are implemented to achieve better smoothing results. A nonlinear variable scaling scheme is then employed to generate the final bas-reliefs and high-reliefs. Using the proposed method, relief models can be generated from arbitrary viewing positions with different gestures and combinations of multiple 3D models. The generated relief models can be printed by 3D printers. The proposed method provides a means of generating both high-reliefs and bas-reliefs in an efficient and effective way under the appropriate scaling factors

Network Behavior in Thin Film Growth Dynamics

We present a new network modeling approach for various thin film growth techniques that incorporates re-emitted particles due to the non-unity sticking coefficients. We model re-emission of a particle from one surface site to another one as a network link, and generate a network model corresponding to the thin film growth. Monte Carlo simulations are used to grow films and dynamically track the trajectories of re-emitted particles. We performed simulations for normal incidence, oblique angle, and chemical vapor deposition (CVD) techniques. Each deposition method leads to a different dynamic evolution of surface morphology due to different sticking coefficients involved and different strength of shadowing effect originating from the obliquely incident particles. Traditional dynamic scaling analysis on surface morphology cannot point to any universal behavior. On the other hand, our detailed network analysis reveals that there exist universal behaviors in degree distributions, weighted average degree versus degree, and distance distributions independent of the sticking coefficient used and sometimes even independent of the growth technique. We also observe that network traffic during high sticking coefficient CVD and oblique angle deposition occurs mainly among edges of the columnar structures formed, while it is more uniform and short-range among hills and valleys of small sticking coefficient CVD and normal angle depositions that produce smoother surfaces.Comment: 11 pages, 9 figures, revtex

Network Behavior in Thin Film Growth Dynamics

Understanding patterns and components in thin film growth is crucial for many engineering applications. Further, the growth dynamics (e.g., shadowing and re-emission effects) of thin films exist in several other natural and man-made phenomena. Recent work developed network science techniques to study the growth dynamics of thin films and nanostructures. These efforts used a grid network model (i.e. viewing of each point on the thin film as an intersection point of a grid) via Monte Carlo simulation methods to study the shadowing and re-emission effects in the growth. These effects are crucial in understanding the relationships between growth dynamics and the resulting structural properties of the film to be grown. In this dissertation, we use a cluster-based network model with Monte Carlo simulation method to study these effects in thin film growth. We use image processing to identify clusters of points on the film and establish a network model of these clusters. Monte Carlo simulations are used to grow films and dynamically track the trajectories of re-emitted particles. We treat the points on the film substrate and cluster formations from the deposition of adatoms / particles on the surface of the substrate as the nodes of network, and movement of particles between these points or clusters as the traffic of the network. Then, graph theory is used to study various network statistics and characteristics that would explain various important phenomena in the thin film growth. We compare the cluster-based results with the grid-based results to determine which method is better suited to study the underlying characteristics of the thin film. Based on the clusters and the points on the substrate, we also develop a network traffic model to study the characteristics and phenomena like fractal behavior in the count and inter-arrival time of the particles. Our results show that the network theory of the growth process explains some of the underlying phenomena in film growth better than the existing theoretical and statistical models

Aerodynamic Synthesis of a Centrifugal Impeller Using CFD and Measurements

The performance and flow structure in an unshrouded impeller of approximately 4:1 pressure ratio is synthesized on the basis of a detailed analysis of 3D viscous CFD results and aerodynamic measurements. A good data match was obtained between CFD and measurements using laser anemometry and pneumatic probes. This solidified the role of the CFD model as a reliable representation of the impeller internal flow structure and integrated performance. Results are presented showing the loss production and secondary flow structure in the impeller. The results indicate that while the overall impeller efficiency is high, the impeller shroud static pressure recovery potential is underdeveloped leading to a performance degradation in the downstream diffusing element. Thus, a case is made for a follow-on impeller parametric design study to improve the flow quality. A strategy for aerodynamic performance enhancement is outlined and an estimate of the gain in overall impeller efficiency that might be realized through improvements to the relative diffusion process is provided

3D digital relief generation.

This thesis investigates a framework for generating reliefs. Relief is a special kind of sculptured artwork consisting of shapes carved on a surface so as to stand out from the surrounding background. Traditional relief creation is done by hand and is therefore a laborious process. In addition, hand-made reliefs are hard to modify. Contrasted with this, digital relief can offer more flexibility as well as a less laborious alternative and can be easily adjusted. This thesis reviews existing work and offers a framework to tackle the problem of generating three types of reliefs: bas reliefs, high reliefs and sunken reliefs. Considerably enhanced by incorporating gradient operations, an efficient bas relief generation method has been proposed, based on 2D images. An improvement of bas relief and high relief generation method based on 3D models has been provided as well, that employs mesh representation to process the model. This thesis is innovative in describing and evaluating sunken relief generation techniques. Two types of sunken reliefs have been generated: one is created with pure engraved lines, and the other is generated with smooth height transition between lines. The latter one is more complex to implement, and includes three elements: a line drawing image provides a input for contour lines; a rendered Lambertian image shares the same light direction of the relief and sets the visual cues and a depth image conveys the height information. These three elements have been combined to generate final sunken reliefs. It is the first time in computer graphics that a method for digital sunken relief generation has been proposed. The main contribution of this thesis is to have proposed a systematic framework to generate all three types of reliefs. Results of this work can potentially provide references for craftsman, and this work could be beneficial for relief creation in the fields of both entertainment and manufacturing