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11.
Exploring spatial datasets with histograms 总被引:2,自引:0,他引:2
Chengyu Sun Nagender Bandi Divyakant Agrawal Amr El Abbadi 《Distributed and Parallel Databases》2006,20(1):57-88
As online spatial datasets grow both in number and sophistication, it becomes increasingly difficult for users to decide whether
a dataset is suitable for their tasks, especially when they do not have prior knowledge of the dataset. In this paper, we
propose browsing as an effective and efficient way to explore the content of a spatial dataset. Browsing allows users to view the size of
a result set before evaluating the query at the database, thereby avoiding zero-hit/mega-hit queries and saving time and resources.
Although the underlying technique supporting browsing is similar to range query aggregation and selectivity estimation, spatial
dataset browsing poses some unique challenges. In this paper, we identify a set of spatial relations that need to be supported
in browsing applications, namely, the contains, contained and the overlap relations. We prove a lower bound on the storage required to answer queries about the contains relation accurately at a given resolution. We then present three storage-efficient approximation algorithms which we believe
to be the first to estimate query results about these spatial relations. We evaluate these algorithms with both synthetic
and real world datasets and show that they provide highly accurate estimates for datasets with various characteristics.
Recommended by: Sunil Prabhakar
Work supported by NSF grants IIS 02-23022 and CNF 04-23336. An earlier version of this paper appeared in the 17th International
Conference on Data Engineering (ICDE 2001). 相似文献
12.
DeTienne D.H. Gray G.R. Agrawal G.P. Lenstra D. 《Quantum Electronics, IEEE Journal of》1997,33(5):838-844
Most of the previous treatments of semiconductor lasers subject to optical feedback from a phase-conjugate mirror (PCM) have assumed that the PCM responds instantaneously. Furthermore, the mechanism responsible for phase conjugation does not usually enter into the analysis. In this paper, we derive the time-dependent reflectivity of a PCM created through nondegenerate four-wave mixing in a Kerr-type nonlinear medium. The resulting laser dynamics are compared with the case of the ideal PCM, as a function of the external-cavity length, the PCM reflectivity, and the PCM interaction depth. The PCM with a significant interaction depth tends to suppress otherwise chaotic output and produces pulses whose repetition rate is tunable by varying PCM reflectivity. At high feedback levels, it stabilizes the laser output. We use the circle-map formalism to explain our numerical results 相似文献
13.
H.U. Khan K.M. Agrawal M. Anwar S.P. Nautiyal B.S. Rawat 《Petroleum Science and Technology》1998,16(1):145-166
Lubricating oil base stocks differ greatly in their chemical composition and consequently in their physical properties and applications. Influence of waxes and various hydrocarbon type constituents viz saturates and aromatic components on the viscosity and shear stress as a function of temperature in different lube oil base stocks has been studied in the present paper. 相似文献
14.
Identification of critical erosion prone areas in the small agricultural watershed using USLE,GIS and remote sensing 总被引:10,自引:1,他引:9
In the present study, Karso watershed of Hazaribagh, Jharkhand State, India was divided into 200 × 200 grid cells and average
annual sediment yields were estimated for each grid cell of the watershed to identify the critical erosion prone areas of
watershed for prioritization purpose. Average annual sediment yield data on grid basis was estimated using Universal Soil
Loss Equation (USLE). In general, a major limitation in the use of hydrological models has been their inability to handle
the large amounts of input data that describe the heterogeneity of the natural system. Remote sensing (RS) technology provides
the vital spatial and temporal information on some of these parameters. A recent and emerging technology represented by Geographic
Information System (GIS) was used as the tool to generate, manipulate and spatially organize disparate data for sediment yield
modeling. Thus, the Arc Info 7.2 GIS software and RS (ERDAS IMAGINE 8.4 image processing software) provided spatial input
data to the erosion model, while the USLE was used to predict the spatial distribution of the sediment yield on grid basis.
The deviation of estimated sediment yield from the observed values in the range of 1.37 to 13.85 percent indicates accurate
estimation of sediment yield from the watershed. 相似文献
15.
Multishell Carrier Transport in Multiwalled Carbon Nanotubes 总被引:1,自引:0,他引:1
Agrawal S. Raghuveer M.S. Ramprasad R. Ramanath G. 《Nanotechnology, IEEE Transactions on》2007,6(6):722-726
Understanding carrier transport in carbon nanotubes (CNTs) and their networks is important for harnessing CNTs for device applications. Here, we report multishell carrier transport in individual multiwalled CNTs, and films of randomly dispersed multiwalled CNTs, as a function of electric field and temperature. Electrical measurements and first-principles density functional theory calculations indicate transport across CNT shells. Intershell conduction occurs across an energy barrier range of 60-250 meV in individual CNTs, and ~ 60 meV in CNT networks. In both cases, the conductance behavior can be explained based upon field-enhanced carrier injection and defect-enhanced transport, as described by the Poole-Frenkel model. 相似文献
16.
This paper introduces an analytical model to investigate the energy efficiency of the IEEE 802.11 distributed coordinated
function (DCF). This model not only accounts for the number of contending nodes, the contention window, but also the packet
size, and the channel condition. Based on this model, we identify the tradeoff in choosing optimum parameters to optimize
the energy efficiency of DCF in the error-prone environment. The effects of contention window and packet size on the energy
efficiency are examined and compared for both DCF basic scheme and DCF with four-way handshaking. The maximum energy efficiency
can be obtained by combining both the optimal packet size and optimal contention window. To validate our analysis, we have
done extensive simulations in ns-2, and simulation results seem to match well with the presented analytical results.
The Ohio Board of Regents Doctoral Enhancements Funds and the National Science Foundation under Grant CCR 0113361 have supported
this work.
Xiaodong Wang received his B.S. degree in communication engineering from Beijing Information Technical Institute of China in 1995, and
his M.S. degree in electric engineering from Beijing University of Aeronautics and Astronautics of China in 1998. He joined
China Telecom in 1998 where he worked on communication protocols for telecommunication. From June 2000 to July 2002, he worked
on GSM base station software development at Bell-labs China, Beijing, China. Currently he is a Ph.D. student in Computer Engineering
at University of Cincinnati. His research activities include wireless MAC protocols, energy saving for wireless sensor networks.
He is a student member of the IEEE.
Jun Yin received the BS degree in automatic control from Dalian Railway Institute of China in 1997, and the MS degree in flight control
from Beijing University of Aeronautics and Astronautics of China in 2001. Since 2001 she has been a Ph.D. student in the OBR
Research Center for Distributed and Mobile Computing at the University of Cincinnati. Her research interests include performance
evaluation of 802.11 MAC protocol, wireless ad hoc networks and sensor networks. She is a student member of the IEEE.
Dharma P.Agrawal IEEE Fellow, 1987; ACM Fellow, 1998; AAAS Fellow, 2003 Dr. Agrawal is the Ohio Board of Regents Distinguished Professor of
Computer Science and Computer Engineering in the department of Electrical and Computer Engineering and Computer Science, University
of Cincinnati, OH. He has been a faculty member at Wayne State University, (1977–1982) and North Carolina State University
(1982–1998). He has been a consultant to the General Dynamics Land Systems Division, Battelle, Inc., and the U. S. Army. He
has held visiting appointment at AIRMICS, Atlanta, GA, and the AT&T Advanced Communications Laboratory, Whippany, NJ. He has
published a number of papers in the areas of Parallel System Architecture, Multi computer Networks, Routing Techniques, Parallelism
Detection and Scheduling Techniques, Reliability of Real-Time Distributed Systems, Modeling of C-MOS Circuits, and Computer
Arithmetic. His recent research interest includes energy efficient routing, information retrieval, and secured communication
in ad hoc and sensor networks, effective handoff handling and multicasting in integrated wireless networks, interference analysis
in piconets and routing in scatternet, use of smart directional antennas (multibeam) for enhanced QoS, Scheduling of periodic
real-time applications and automatic load balancing in heterogeneous workstation environment. He has four approved patents
and three patent filings in the area of wireless cellular networks. 相似文献
17.
We consider a system comprising of a single bottleneck switch/node that is fed by N independent Markov-modulated fluid sources. There is a fixed propagation delay incurred by the traffic between these sources and the switch. We assume that the switch sends periodic feedback in the form of a single congestion indicator bit. This feedback also incurs a fixed propagation delay in reaching the sources. Upon reaching the sources (or the access controllers associated with the sources), this congestion indicator bit is used to choose between two rates for the excess traffic, high or low, possibly depending on the state of that source. The switch employs a threshold mechanism based on its buffer level to discard excess traffic. We show that the stationary distribution of this system satisfies a set of first-order linear differential equations along with a set of split boundary conditions. We obtain an explicit solution to these using spectral decomposition. To this end we investigate the related eigenvalue problem. Based on these results we investigate the role of delayed feedback vis-a-vis various time-constants and traffic parameters associated with the system. In particular, we identify conditions under which the feedback scheme offers significant improvement over the open-loop scheme 相似文献
18.
A version control mechanism is proposed that enhances the modularity and extensibility of multiversion concurrency control algorithms. The multiversion algorithms are decoupled into two components: version control and concurrency control. This permits modular development of multiversion protocols and simplifies the task of proving the correctness of these protocols. A set of procedures for version control is described that defines the interface with the version control component. It is shown that the same interface can be used by the database actions of both two-phase locking and time-stamp concurrency control protocols to access multiversion data. An interesting feature of the framework is that the execution of read-only transactions becomes completely independent of the underlying concurrency control implementation. Unlike other multiversion algorithms, read-only transactions in this scheme do not modify any version-related information, and therefore do not interfere with the execution of read-write transactions. The extension of the multiversion algorithms to a distributed environment becomes very simple 相似文献
19.
20.
Energy minimization and design for testability 总被引:6,自引:0,他引:6
Srimat T. Chakradhar Vishwani D. Agrawal Michael L. Bushnell 《Journal of Electronic Testing》1994,5(1):57-66
The problem of fault detection in general combinational circuits is NP-complete. The only previous result on identifying easily testable circuits is due to Fujiwara who gave a polynomial time algorithm for detecting any single stuck fault inK-bounded circuits. Such circuits may only contain logic blocks with no more thanK input lines and the blocks are so connected that there is no reconvergent fanout among them. We introduce a new class of combinational circuits called the (k, K)-circuits and present a polynomial time algorithm to detect any single or multiple stuck fault in such circuits. We represent the circuit as an undirected graphG with a vertex for each gate and an edge between a pair of vertices whenever the corresponding gates have a connection. For a (k, K)-circuit,G is a subgraph of ak-tree, which, by definition, cannot have a clique of size greater thank+1. Basically, this is a restriction on gate interconnections rather than on the function of gates comprising the circuit. The (k, K)-circuits are a generalization of Fujiwara'sK-bounded circuits. Using the bidirectional neural network model of the circuit and the energy function minimization formulation of the fault detection problem, we present a test generation algorithm for single and multiple faults in (k, K)-circuits. This polynomial time aggorithm minimizes the energy function by recursively eliminating the variables. 相似文献