This is a two-part series to model scaling of heat transfer surfaces by calcium carbonate based on the first conservation principle approach. In Part I, general physical and chemical processes in CaCO3 fouling are described and a single-species model is proposed whereby only Ca+2 species transport needs to be of concern. The deposition process is assumed to be controlled by the two processes of mass transport to and crystallization reaction on the heat transfer surface. The model is then used to solve for CaCo3 scaling in a laminar falling film system and to assess which of the two types of prevailing reaction rate expressions is more appropriate for the CaCO3 fouling analysis. The predicted deposition rate, scale thickness, and its profile are compared with experimental data. The comparison shows that the single-species model yields satisfactory predictions only for a limited range of concentrations. It reveals that the type of reaction rate expression used in the single-species model is less accurate than the other type used in the multispecies model. The latter is described in Part II of the series.
Although peer-to-peer (P2P) streaming can efficiently deliver live video content to large user populations, existing applications often suffer from limited video quality, periodic hiccups, and high delays. To overcome some of the limitations of today's unstructured (mesh-based) designs, we have developed and deployed FastMesh-SIM, a novel P2P streaming system that leverages proxies, push-mechanism and IP multicast to achieve lower playback delay and better stream continuity. Having control over a real P2P streaming system also gives us a rare opportunity to conduct controlled experiments where we vary major design parameters (e.g., push vs. pull delivery, IP multicast support, streaming rate, and video segment size) under a range of operating conditions (e.g., dynamics of peer churn, and different network configurations), while collecting detailed, fine-granular measurements (e.g., the various components of end-to-end delay). Analysis of the measurement data, consisting of seven trials of streaming several live TV channels for more than 100 hours to 140 peers, sheds light on how design decisions and the operating environment affect important performance metrics. Our experiments show that a push-based, proxy-P2P system can achieve low delay and good video quality, though network bottlenecks on long-haul connections can sometimes cause disruptions in a global deployment. Theory-practice gaps observed from the data are also discussed. Large-scale, global experiments are now being carried out.
This annual report summarizes the work accomplished on rewetting of monogroove heat pipe in space station. Specifically, theoretical and experimental investigations of the rewetting characteristics of thin liquid films over unheated and heated capillary grooved plates were performed. To investigate the effect of gravity on rewetting, the grooved surface was placed in upward and downward facing positions. Profound gravitational effects were observed as the rewetting velocity was found to be higher in the upward than in the downward facing orientation. The difference was even greater with higher initial plate temperatures. With either orientation, it was found that the rewetting velocity increased with the initial plate temperature. But when the temperature was raised above a rewetting temperature, the rewetting velocity decreased with the initial plate temperature. Hydrodynamically controlled and heat conduction controlled rewetting models were then presented to explain and to predict the rewetting characteristics in these two distinct regions. The predicted rewetting velocities were found to be in good agreement with experimental data with elevated plate temperatures.
The CCITT (ITU-IT) has decided that the B-ISDN services of the future will be supported by asynchronous transfer mode (ATM), since it can offer the benefits of statistical multiplexing to bursty traffic, thus bringing down costs. There has been a considerable body of research done on the problem of congestion control in ATM networks, and several different approaches have been investigated. A four-level approach is proposed to the very specific problem of transporting MPEG encoded real-time video over ATM, and it is argued that this is consistent with current research results and directions. Then, using a real video source and the simplest option in the MPEG standard, the intra-frame coding, we experimentally evaluate alternatives for the implementation of the lower three levels, and show that the approach appears feasible.
The solution for thermally developing Poiseuille flow with scattering is obtained by using the method of collocation. The results show that scattering tends to decrease radiation component without affecting the convective component at low optical thicknesses. For moderate to high values of optical thicknesses, both the convective and radiation components are reduced. The relative effect of scattering both on convective and radiation Nusselt numbers appears to be unaffected by a change in the surface emissivity. A significant feature of combined radiation-convection in thermally developing flows appears to be that the total Nusselt number increases downstream of position of minimum rather than approaching an asymptotic value as is the case with corresponding pure convection. Another departure in the behavior appears to be the lack of existence of similarity in the temperature profiles, particularly at low values of conduction-radiation parameter.
Locality classification is an important component to enable location-based services. It entails two sequential queries: 1) whether a target is within the site or not, i.e., inside/outside region decision, and 2) if so, which area in the region the target is located, i.e., area classification. Locality classification is hence more coarse-grained and efficient as compared with pinpointing the exact target location in the region. The classification problem is challenging, because fingerprints may not exist outside the region for training. Furthermore, the target may sample an incomplete RSSI vector due to, say, random signal noise, momentary occlusion, or scanning duration. The algorithm also has to be computationally efficient. We propose INOA, a scalable and practical locality classification overcoming the above challenges. INOA may serve as a plug-in before any fingerprint-based localization, and can be incrementally extended to cover new areas or regions for large-scale deployment. Its preprocessor cherry-picks only those discriminating access points, which greatly enhances computational efficiency and accuracy. By formulating a “one-class” classifier using ensemble learning, INOA accurately decides whether the target is within the region or not. Extensive experimental trials in different sites validate the high efficiency and accuracy of INOA, without the need of full RSSI vectors collected at the target.
In near video-on-demand, requests for the same movie arriving within a period of time are grouped together (i.e., batched) and served with a single multicast stream; thereby reducing the bandwidth requirement compared with the unbatched case. We consider here that the use of a multicast channel comes with a cost. Since delayed users may cancel their requests while being batched, this uncollected revenue has to be appropriately balanced with the channel usage cost in order to achieve maximum profit. We address profit issues for a number of batching schemes. In the window-based schemes, users are batched for a fixed period of time before they are served; in the batch-size based scheme, users are served once a certain number of them are collected. We study the system profit in terms of user reneging behavior, movie popularity, and multicast channel cost. By combining the advantages of the window-based and the batch-size based schemes, we introduce a scheme which adapts to the fluctuating request rate to achieve high profit.
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