A Technology‐Enhanced Learning Environment for an Optical Fiber Communications Course*

This paper describes a technology‐enhanced learning environment for an undergraduate course on Optical Fiber Communications ( http:ctle.colorado.edunsf2000 ).     

Corrosion behavior of plasma-sprayed coatings on a Ni-base superalloy in Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>-60 Pct V<Subscript>2</Subscript>O<Subscript>5</Subscript> environment at 900 °C

The shrouded plasma spray process was used to deposit NiCrAlY, Ni-20Cr, Ni₃Al, and Stellite-6 metallic coatings on a Ni-based superalloy (62Ni-23Cr-1.48Al-0.80Mn-0.37Si-0.10Cu-0.025C-bal Fe). NiCrAlY was used as a bond coat in all cases. Hot corrosion studies were conducted on uncoated as well as plasma-spray-coated superalloy specimens after exposure to molten salt at 900 °C under cyclic conditions. The thermogravimetric technique was used to establish the kinetics of corrosion. X-ray diffraction (XRD), scanning electron microscopy/energy-dispersive X-ray analysis (SEM/EDAX) and electron-probe microanalysis techniques were used to analyze the corrosion products. The uncoated superalloy suffered accelerated corrosion in the form of intense spalling of the scale. The NiCrAlY coated specimen showed a minimum weight gain, whereas the Stellite-6 indicated a maximum weight gain among the coatings studied. All the coatings were found to be successful in developing resistance against hot corrosion, which may be attributed to the formation of oxides, and spinels of nickel, aluminum, chromium, or cobalt.     

Design considerations for developing biodegradable and bioabsorbable magnesium implants

The integration of biodegradable and bioabsorbable magnesium implants into the human body is a complex undertaking that faces major challenges. Candidate biomaterials must meet both engineering and physiological requirements to ensure the desired properties. Historically, efforts have been focused on the behavior of commercial magnesium alloys in biological environments and their resultant effect on cell-mediated processes. Developing causal relationships between alloy chemistry and microstructure, and effects as a cellular behavior can be a difficult and time-intensive process. A systems design approach has the power to provide significant contributions in the development of the next generation of magnesium alloy implants with controlled degradability, biocompatibility, and optimized mechanical properties, at reduced time and cost. This approach couples experimental research with theory and mechanistic modeling for the accelerated development of materials. The aim of this article is to enumerate this strategy, design considerations, and hurdles for developing new cast magnesium alloys for use as biodegradable implant materials.     

SONET implementation

The status of the synchronous optical network (SONET) infrastructure development and deployment are examined to see whether or not they meet original expectations. Issues arising from deployment, such as the use of new features and the necessary support from operations systems, and future directions of SONET are discussed. These future trends include digital cross connect systems (DCSs), SONET ring architectures, and hybrid ring-DCS networks. New SONET services are also discussed     

Trackability as a cue for potential obstacle identification and 3-D description

In many man-made environments, obstacles in the path of a mobile robot can be characterized asshallow, that is, they have relatively small extent in depth compared to the distance from the camera. We present a framework for segmenting shallow structures from their background over a sequence of images. Shallowness is first quantified asaffine describability. This is embedded in a tracking system within which hypothesized model structures undergo a cycle of prediction and model-matching. Structures emerge either as shallow or nonshallow based on theiraffine trackability. Two major contributions of this work are (i) aggregate object tracking based on 3-D motion and structure constraints in constrast with traditional primitive feature tracking based on image motion heuristics, and (ii) use of temporal behavior for object segmentation and 3-D reconstruction.     

Dynamic directional gradient vector flow for snakes.

Snakes, or active contour models, have been widely used in image segmentation. However, most present snake models do not discern between positive and negative step edges. In this paper, a new type of dynamic external force for snakes named dynamic directional gradient vector flow (DDGVF) is proposed that uses this information for better performance. It makes use of the gradients in both x and y directions and deals with the external force field for the two directions separately. In snake deformation, the DDGVF field is utilized dynamically according to the orientation of snake in each iteration. Experimental results demonstrate that the DDGVF snake provides a much better segmentation than GVF snake in situations when edges of different directions are present which pose confusion for segmentation.     

Minimum concave cost multicommodity network design

The minimum concave cost multicommodity network design problem (MCMNDP) arises in many application areas, such as transportation planning, energy distribution systems and especially in the design of both packet and circuit switching backbone networks. Exact concave cost optimization algorithms have been developed but they are applicable only if the network size is small. Therefore, MCMNDP is usually solved using non-exact iterative methods. In this paper, such heuristic techniques proposed within the context of circuit switching and packet switching network design are evaluated in detail. Following a comprehensive literature survey, Yaged’s linearization, Minoux’s greedy and Minoux’s accelerated greedy methods have been selected for the circuit switching network design case for further investigation. Minoux’s greedy methods are found to create routes that include cycles causing degradation in the quality of the solution; therefore, we propose a simple but effective modification scheme as a cycle elimination strategy. Similarly, but within the context of packet switching network design, Gerla and Kleinrock’s concave branch elimination, Gersht’s greedy, and Stacey’s concave link elimination methods have been selected for further investigation. All of these methods consider aggregate flows on each link, simultaneously re-routing more than one commodity in one step. In this paper, we propose an alternative disaggregate approach, where only one commodity is handled at a time. Our final proposal is the adaptation of the algorithms proposed for circuit switching network design to the packet switching case. Then an extensive comparative computational study is performed for a number of networks and cost structures to help establish the best method with respect to time and solution quality. Our computational results have shown that the performances of the MCMNDP algorithms heavily depend on the network type and the cost structure. The results have also revealed that our proposed modification to Minoux greedy to eliminate cycles leads to considerable improvements and our proposed disaggregate approach gives the best result in some networks with certain cost structures.