Fullerene photoelectrochemical solar cells

The photoelectrochemistry of single crystal C₆₀ and fullerene photoelectrochemical solar cells is studied. Illuminated and immersed, C₆₀ is shown to drive oxidation of several solution-phase redox couples. Utilization of a photoelectrochemical solid/liquid junction, rather than solid-state photovoltaic junction, improves the observed photocurrent. Utilization of a single crystal, rather than a polycrystalline film, of C₆₀ decreases dark current to the extent that light-driven charge transfer dominates. The spectral response and current-voltage behaviour in several electrolytes is studied. A low-power fullerene photoelectrochemical solar cell, utilizing a regenerative polyiodide and ferri/ferrocyanide redox couple, is demonstrated.     

Fault-tolerant VLSI sorters

Parallel sorting algorithms have been proposed for VLSI implementation. Random defects in the silicon wafer and fabrication errors render processors in the wafer faulty, and may cause these algorithms to fail despite a significant number of nonfaulty processors. This paper presents twofault-tolerant pipelined sorting algorithms that would work on a wafer comprised of faulty and nonfaulty processors. Both the algorithms useO(n) processors and requireO(n) time to sortn elements.P. J. Varman's research was supported by an IBM Faculty Development Award, I. V. Ramakrishnan's by the ONR Grant N00014-84-K-0530 and NSF Grant ECS-84-04399, and D. S. Fussell's by NSF Grant MCS-8104017.     

An OSPF topology server: design and evaluation

In large scale, operational Internet protocol networks, creating timely, accurate and network-wide views of the intradomain topology is a fundamental problem. Topical network backbones consist of hundreds of routers, which establish routing adjacencies with one another through static configuration and dynamic routing protocols, such as open shortest path first (OSPF). We describe the design of an OSPF topology server which tracks intradomain topology, by passively and safely listening into OSPFs reliable flooding mechanism, or by pushing and pulling information from the routers via the simple network management protocol. We provide a detailed evaluation and comparison of the two approaches in terms of operational issues, reliability and timeliness of information     

Photoaction, temperature and O2 depletion effects in fullerene photoelectrochemical solar cells

It is demonstrated that higher temperature and C₆₀ oxygen depletion increase the photocurrent of fullerene photoelectrochemical solar cells (PEC). Fullerene/iodide electrolyte PEC consisting of intrinsic single crystal C₆₀ in either aqueous 3 M KI, 0.01 M I₂, or 0.1 M tetrabutyl ammonium iodide, 0.3 M LiClO₄ in acetonitrile solution, drive regenerative photoinduced iodide oxidation. The photocurrent is increased by an order of magnitude (to 6.4 μA/cm² under 100 mW/cm² illumination) by an increase of the aqueous cell temperature from 24°C to 82°C. A similar order of magnitude increase in photocurrent is accomplished by O₂ depletion pretreatment (24 h at 400°C in Ar) of the C₆₀ to improve conductivity. However, this latter treatment also irreversibly increases the cell dark current. The spectral action of single crystal C₆₀ is also probed, through the generated photoelectrochemical current in iodide, ferricyanide and sulfuric electrolytes as a function of wavelength. Band edges are observed at 720 nm (1.7 eV) and 560 nm (2.2 eV), and a substantial peak photocurrent response occurs at 395 nm (3.1 eV) and decreases at shorter wavelengths.     

Transaction models for Web accessibility

The Web has evolved into a dominant digital medium for conducting many types of online transactions such as shopping, paying bills, making travel plans, etc. Such transactions typically involve a number of steps spanning several Web pages. For sighted users these steps are relatively straightforward to do with graphical Web browsers. But they pose tremendous challenges for visually impaired individuals. This is because screen readers, the dominant assistive technology used by visually impaired users, function by speaking out the screen’s content serially. Consequently, using them for conducting transactions can cause considerable information overload. But usually one needs to browse only a small fragment of a Web page to do a step of a transaction (e.g., choosing an item from a search results list). Based on this observation this paper presents a model-directed transaction framework to identify, extract and aurally render only the “relevant” page fragments in each step of a transaction. The framework uses a process model to encode the state of the transaction and a concept model to identify the page fragments relevant for the transaction in that state. We also present algorithms to mine such models from click stream data generated by transactions and experimental evidence of the practical effectiveness of our models in improving user experience when conducting online transactions with non-visual modalities.     

Transporting compressed video over ATM networks with explicit-ratefeedback control

We propose a scheme for transmission of variable bit rate (VBR) compressed video for interactive applications using the explicit-rate congestion-control mechanisms proposed for the available bit rate (ABR) service in asynchronous transfer mode networks. Compressed video is inherently bursty, with rate fluctuations over both short and long time scales. This source behavior can be accommodated by the ABR service, since the explicit-rate scheme allows sources to request varying amounts of bandwidth over time. Moreover, when the bandwidth demand cannot be met, the network provides feedback indicating the bandwidth currently available to a connection. In our scheme, the video source rate is matched to the available bandwidth by modifying the quantization level used during compression. We use trace-driven simulations to examine how effective the enhanced explicit-rate scheme is in “rate matching” between the network and the source and the effect on end-to-end delay. We also look at the sensitivity of the proposed scheme to the estimates of the network round-trip times and to inaccuracies in the rate requests made by sources     

Compression based clustering technique for enhancing accuracy in web scale videos

Multimedia Tools and Applications - Detection and clustering of commercial advertisements plays an important role in multimedia indexing also in the creation of personalized user content. In...     

Comparison of dicarboxylic acids as complexing agents for abrasive-free chemical mechanical planarization of copper

Abrasive particles used in chemical mechanical planarization (CMP) of copper often agglomerate and cause scratches on the finished surface. Abrasive-free CMP offers a feasible solution to this problem, and our present work examines four dicarboxylic acids (oxalic, malonic, succinic and glutaric, with increasing carbon chain lengths) as possible complexing agents for such a chemically dominated CMP process. At pH 3.0-4.0, oxalic and malonic acids are most effective for abrasive-free Cu removal. The rates of Cu dissolution and polish (with or without abrasives) are correlated with pH dependent distributions of mono-anionic (for oxalic and malonic) and neutral (for succinic and glutaric) acid species. The surface morphologies of a Cu wafers obtained by abrasive-free CMP in these acids also are more defect free and flat compared to those obtained using abrasives.     

Data envelopment analysis for weight derivation and aggregation in the analytic hierarchy process

Data envelopment analysis (DEA) is proposed in this paper to generate local weights of alternatives from pair-wise comparison judgment matrices used in the analytic hierarchy process (AHP). The underlying assumption behind the approach is explained, and some salient features are explored. It is proved that DEA correctly estimates the true weights when applied to a consistent matrix formed using a known set of weights. DEA is further proposed to aggregate the local weights of alternatives in terms of different criteria to compute final weights. It is proved further that the proposed approach, called DEAHP in this paper, does not suffer from rank reversal when an irrelevant alternative(s) is added or removed.