Showing papers by "Indian Institute of Technology Bombay published in 2002"

Keyword searching and browsing in databases using BANKS

Abstract: With the growth of the Web, there has been a rapid increase in the number of users who need to access online databases without having a detailed knowledge of the schema or of query languages; even relatively simple query languages designed for non-experts are too complicated for them. We describe BANKS, a system which enables keyword-based search on relational databases, together with data and schema browsing. BANKS enables users to extract information in a simple manner without any knowledge of the schema or any need for writing complex queries. A user can get information by typing a few keywords, following hyperlinks, and interacting with controls on the displayed results. BANKS models tuples as nodes in a graph, connected by links induced by foreign key and other relationships. Answers to a query are modeled as rooted trees connecting tuples that match individual keywords in the query. Answers are ranked using a notion of proximity coupled with a notion of prestige of nodes based on inlinks, similar to techniques developed for Web search. We present an efficient heuristic algorithm for finding and ranking query results.

Interactive deduplication using active learning

Abstract: Deduplication is a key operation in integrating data from multiple sources. The main challenge in this task is designing a function that can resolve when a pair of records refer to the same entity in spite of various data inconsistencies. Most existing systems use hand-coded functions. One way to overcome the tedium of hand-coding is to train a classifier to distinguish between duplicates and non-duplicates. The success of this method critically hinges on being able to provide a covering and challenging set of training pairs that bring out the subtlety of deduplication function. This is non-trivial because it requires manually searching for various data inconsistencies between any two records spread apart in large lists.We present our design of a learning-based deduplication system that uses a novel method of interactively discovering challenging training pairs using active learning. Our experiments on real-life datasets show that active learning significantly reduces the number of instances needed to achieve high accuracy. We investigate various design issues that arise in building a system to provide interactive response, fast convergence, and interpretable output.

Refined plate theory and its variants

Abstract: Thedevelopmentofa newree ned platetheoryand its two simplevariantsisgiven. Thetheorieshavestrongcommonality withtheequationsofclassicalplatetheory (CPT).However,unlikeCPT,thesetheoriesassumethatlateral and axial displacements have bending and shear components such that bending components do not contribute toward shearforces and, likewise, shearing components do not contribute toward bending moments. The theory and one of its variants are variationally consistent, whereasthesecond variant isvariationally inconsistent and usesthe relationships between moments, shear forces, and loading. It should be noted that, unlike any other ree ned plate theory, thegoverning equation as well as the expressions for moments and shear forces associated with thisvariant areidentical tothoseassociated withtheCPT,savefortheappearanceofasubscript. Theeffectivenessofthetheory and itsvariantsisdemonstratedthroughanexample. Surprisingly,theanswersobtained by boththevariantsofthe theory, one of which is variationally consistent and the other one is inconsistent, are same. The numerical example studied, therefore, not only brings out the effectiveness of the theories presented, but also, albeit unintentionally, supports the doubts, e rst raised by Levinson, about the so called superiority of variationally consistent methods.

Accelerated focused crawling through online relevance feedback

Abstract: The organization of HTML into a tag tree structure, which is rendered by browsers as roughly rectangular regions with embedded text and HREF links, greatly helps surfers locate and click on links that best satisfy their information need Can an automatic program emulate this human behavior and thereby learn to predict the relevance of an unseen HREF target page wrt an information need, based on information limited to the HREF source page? Such a capability would be of great interest in focused crawling and resource discovery, because it can fine-tune the priority of unvisited URLs in the crawl frontier, and reduce the number of irrelevant pages which are fetched and discarded

1.6 Ga U-Pb zircon age for the Chorhat Sandstone, lower Vindhyan, India: Possible implications for early evolution of animals

Abstract: Bedding-plane markings in the Chorhat Sandstone (lower Vindhyan), central India, were recently interpreted as burrows produced by triploblastic animals. Because the rocks were thought to be older than 1000 Ma, these structures were regarded as the oldest fossil evidence for metazoan life. However, the biological origin of the markings has been questioned, as has their age. Current age estimates are based on K-Ar, Rb-Sr, and fission- track dates, though some contentious evidence suggests that the rocks may be only 540 Ma. Here we provide the first robust age data for the lower Vindhyan by using SHRIMP (sensitive, high-resolution ion microprobe) U-Pb zircon geochronology to date silicified tuffs bounding the Chorhat Sandstone. Our results show that the sediments were deposited between 1628 ± 8 Ma and 1599 ± 8 Ma. If the Chorhat markings are burrows left by worm-like animals, then our data suggest that complex metazoans had evolved before 1600 Ma, 1 b.y. before the “Cambrian explosion” when animals rapidly diversified and became ecologically dominant. However, given the doubts expressed about the origin of the bedding-plane structures, as well as the surprisingly “old” age of the host rocks, further studies are urgently required to provide supportive evidence.

Hybrid systems through natural product leads: An approach towards new molecular entities

Abstract: Hybrid systems are constructs of different molecular entities, natural or unnatural, to generate functional molecules in which the characteristics of various components are modulated, amplified or give rise to entirely new properties. These hybrids can be designed from carefully selected components either through domain integration of key structural/ functional features or via straightforward covalent linkages. Some of the recently reported hybrid systems based on steroid, carbohydrate, C60-fullerene platforms, amongst others, mainly crafted with the object of enhancement of the therapeutical spectrum, will be discussed.

Perturbation of Microtubule Polymerization by Quercetin through Tubulin Binding: A Novel Mechanism of Its Antiproliferative Activity†

Abstract: The dietary flavonoid quercetin has a broad range of biological activities, including potent antitumor activity against several types of tumors. Recently, it has been shown that quercetin inhibits cancer cells proliferation by depleting cellular microtubules and perturbing cellular microtubule functions. However, the direct interactions of quercetin with tubulin and microtubules have not been examined so far. Here, we found that quercetin inhibited polymerization of microtubules and depolymerized microtubules made from purified tubulin in vitro. The binding of quercetin with tubulin was studied using quercetin fluorescence and intrinsic tryptophan fluorescence of tubulin. Quercetin bound to tubulin at a single site with a dissociation constant of 5-7 microM, and it specifically inhibited colchicine binding to tubulin but did not bind at the vinblastine site. In addition, quercetin perturbed the secondary structure of tubulin, and the binding of quercetin stimulated the intrinsic GTPase activity of soluble tubulin. Further, quercetin stabilized tubulin against decay and protected two cysteine residues of tubulin toward chemical modification by 5,5'-dithiobis-2-nitrobenzoic acid. Our data demonstrated that the binding of quercetin to tubulin induces conformational changes in tubulin and a mechanism through which quercetin could perturb microtubule polymerization dynamics has been proposed. The data suggest that quercetin inhibits cancer cells proliferation at least in part by perturbing microtubule functions through tubulin binding.

The structure of broad topics on the Web

Abstract: The Web graph is a giant social network whose properties have been measured and modeled extensively in recent years. Most such studies concentrate on the graph structure alone, and do not consider textual properties of the nodes. Consequently, Web communities have been characterized purely in terms of graph structure and not on page content. We propose that a topic taxonomy such as Yahoo! or the Open Directory provides a useful framework for understanding the structure of content-based clusters and communities. In particular, using a topic taxonomy and an automatic classifier, we can measure the background distribution of broad topics on the Web, and analyze the capability of recent random walk algorithms to draw samples which follow such distributions. In addition, we can measure the probability that a page about one broad topic will link to another broad topic. Extending this experiment, we can measure how quickly topic context is lost while walking randomly on the Web graph. Estimates of this topic mixing distance may explain why a global PageRank is still meaningful in the context of broad queries. In general, our measurements may prove valuable in the design of community-specific crawlers and link-based ranking systems.

Proxy-based acceleration of dynamically generated content on the world wide web: an approach and implementation

Abstract: As Internet traffic continues to grow and web sites become increasingly complex, performance and scalability are major issues for web sites. Web sites are increasingly relying on dynamic content generation applications to provide web site visitors with dynamic, interactive, and personalized experiences. However, dynamic content generation comes at a cost --- each request requires computation as well as communication across multiple components.To address these issues, various dynamic content caching approaches have been proposed. Proxy-based caching approaches store content at various locations outside the site infrastructure and can improve Web site performance by reducing content generation delays, firewall processing delays, and bandwidth requirements. However, existing proxy-based caching approaches either (a) cache at the page level, which does not guarantee that correct pages are served and provides very limited reusability, or (b) cache at the fragment level, which requires the use of pre-defined page layouts. To address these issues, several back end caching approaches have been proposed, including query result caching and fragment level caching. While back end approaches guarantee the correctness of results and offer the advantages of fine-grained caching, they neither address firewall delays nor reduce bandwidth requirements.In this paper, we present an approach and an implementation of a dynamic proxy caching technique which combines the benefits of both proxy-based and back end caching approaches, yet does not suffer from their above-mentioned limitations. Our dynamic proxy caching technique allows granular, proxy-based caching where both the content and layout can be dynamic. Our analysis of the performance of our approach indicates that it is capable of providing significant reductions in bandwidth. We have also deployed our proposed dynamic proxy caching technique at a major financial institution. The results of this implementation indicate that our technique is capable of providing order-of-magnitude reductions in bandwidth and response times in real-world dynamic Web applications.

Aggregate Planning in Supply Chains by Pinch Analysis

Abstract: This work presents a novel extension of the targeting methods from pinch analysis to aggregate planning in supply chains. Aggregate planning aims at meeting demand over a specified time horizon in a way that maximizes profit through optimal levels of production, capacity, subcontracting, inventory, and stockouts. It is demonstrated how minimum production rates for a given demand forecast may be targeted through composite curves on a time versus material quantity plot. The grand composite curve (GCC) representation may be conveniently used to depict how surpluses and shortages in inventory fluctuate over time. The pinch corresponds to the point of minimum lead time and zero inventory. An example problem is used to illustrate the approach. The initial aggregate plan from pinch analysis exactly matches the solution reported in literature obtained by solving a linear programming formulation. On the other hand, the final aggregate plans from the pinch targeting method are superior to the solution in literature, as they are more realistic. It may be concluded that the production composite determined by the pinch targeting method provides either the best aggregate plan or an excellent starting point to reduce computational time for a solution by mixed integer linear programming.

The structure of broad topics on the web

Abstract: The Web graph is a giant social network whose properties have been measured and modeled extensively in recent years. Most such studies concentrate on the graph structure alone, and do not consider textual properties of the nodes. Consequently, Web communities have been characterized purely in terms of graph structure and not on page content. We propose that a topic taxonomy such as Yahoo! or the Open Directory provides a useful framework for understanding the structure of content-based clusters and communities. In particular, using a topic taxonomy and an automatic classifier, we can measure the background distribution of broad topics on the Web, and analyze the capability of recent random walk algorithms to draw samples which follow such distributions. In addition, we can measure the probability that a page about one broad topic will link to another broad topic. Extending this experiment, we can measure how quickly topic context is lost while walking randomly on the Web graph. Estimates of this topic mixing distance may explain why a global PageRank is still meaningful in the context of broad queries. In general, our measurements may prove valuable in the design of community-specific crawlers and link-based ranking systems.

Structure–property correlation in discontinuously reinforced aluminium matrix composites as a function of relative particle size ratio

Abstract: Metal matrix composites made by a powder metallurgy route often exhibit clustering of the reinforcements due to geometrical reasons. The clustering tendency was studied in 2124 Al/30 v/o SiCp composites as a function of relative particle size ratio between the matrix and reinforcement particles. Dry blended composite powders, with different RPS ratios, were vacuum hot-pressed and microstructures were examined to assess the uniformity of the microstructure by measuring the local area fraction of the constituents. It was found that a decrease in RPS ratio resulted in an increase in strength as well as ductility, as a result of improved distribution of the SiCp. The improved response to the homogenisation treatment, observed in the composite with lower RPS ratio, is attributed to the smaller diffusion path length for the alloying element.

Power System State Estimation

Abstract: Secure and economic operation is an important requirement of modern power systems. This is achieved through a hierarchical control system incorporating both local and centralized control.

Anionic metal–organic and cationic organic layer alternation in the coordination polymers [{M(BTEC)(OH2)4}·{C4H12N2}·4H2O]n (M = Co, Ni, and Zn; BTEC = 1,2,4,5-benzenetetracarboxylate)

Abstract: New coordination polymers [{M(BTEC)(OH2)4}·{C4H12N2}·4H2O]n (BTEC = 1,2,4,5-benzenetetracarboxylate) (M = Co 1; Ni 2; Zn 3) have been synthesized starting from the respective transition metal salts, 1,2,4,5-benzenetetracarboxylic acid and piperazine hexahydrate. The highly-crystalline compounds, which are insoluble in water as well as common organic solvents, have been characterized in the solid-state with the aid of elemental analysis, IR and diffuse reflectance UV-visible spectroscopy, and TGA/DTA measurements. The molecular structures of all the compounds have been determined in the solid-state by X-ray diffraction studies; all the three compounds are isomorphous and crystallize in centerosymmetric triclinic space group. The molecular structures are made up of extensively hydrogen-bonded alternating layers of anionic {M(BTEC)(OH2)4}n coordination polymer and piperazinium dications. The extended structure formed in the solid-state due to extensive inter-layer O–H⋯O and N–H⋯O hydrogen bonds incorporate four water molecules per unit cell. The water molecules present in the polymeric network can be easily removed at fairly low temperatures. Heating 1 or 2 to approximately 60–70 °C in a vacuum (0.1 mmHg) for 12 h results in the elimination of three water molecules as evidenced by elemental analysis. Similar results were obtained from the thermogravimetric studies. The dehydration process is accompanied by a colour change in the case of compounds 1 and 2. Exposure of the dehydrated sample to ammonia results in the uptake of three equivalents of ammonia molecules. However, the methane gas adsorption studies carried out on dehydrated sample did not show the presence of a porous structure.

DMS atmospheric concentrations and sulphate aerosol indirect radiative forcing: a sensitivity study to the DMS source representation and oxidation

Abstract: The global sulphur cycle has been simulated using a general circulation model with a focus on the source and oxidation of atmospheric dimethylsulphide (DMS). The sensitivity of atmospheric DMS to the oceanic DMS climatology, the parameterisation of the sea-air transfer and to the oxidant fields have been studied. The importance of additional oxidation pathways (by O3 in the gas- and aqueous-phases and by BrO in the gas phase) not incorporated in global models has also been evaluated. While three different climatologies of the oceanic DMS concentration produce rather similar global DMS fluxes to the atmosphere at 24–27 Tg S yr−1, there are large differences in the spatial and seasonal distribution. The relative contributions of OH and NO3 radicals to DMS oxidation depends critically on which oxidant fields are prescribed in the model. Oxidation by O3 appears to be significant at high latitudes in both hemispheres. Oxidation by BrO could be significant even for BrO concentrations at sub-pptv levels in the marine boundary layer. The impact of such refinements on the DMS chemistry onto the indirect radiative forcing by anthropogenic sulphate aerosols is also discussed.

A new algorithm for discrete-time sliding-mode control using fast output sampling feedback

Abstract: This paper presents a new approach for sliding-mode control (SMC) of discrete-time systems using the reaching law approach together with the fast output sampling (FOS) feedback technique. This method does not need the system states for feedback as it makes use of only the output samples for designing the controller. Thus, this methodology is more practical and easy to implement. A numerical example demonstrates the design technique. Simulation results show that the proposed FOS SMC technique produces the same results as obtained by state feedback SMC technique.