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Document ranking on weight-partitioned signature files

ACM TRANSACTIONS ON INFORMATION SYSTEMS 1996年第2期14卷 109-137页

作者： Lee, DL Ren, LM Ohio State Univ. Columbus

A signature file organization, called the weight-partitioned signature file, for supporting document ranking is proposed. It employs multiple signature files, each of which corresponds to one term frequency, to represent terms with different term frequencies. Words with the same term frequency in a document are grouped together and hashed into the signature file corresponding to that term frequency. This eliminates the need to record the term frequency explicitly for each word. We investigate the effect of false drops on retrieval effectiveness if they are not eliminated in the search process. We have shown that false drops introduce insignificant degradation on precision and recall when the false-drop probability is below a certain threshold. This is an important result since false-drop elimination could become the bottleneck in systems using fast signature file search techniques. We perform an analytical study on the performance of the weight-partitioned signature file under different search strategies and configurations. An optimal formula is obtained to determine for a fixed total storage overhead the storage to be allocated to each partition in order to minimize the effect of false drops on document ranks. Experiments were performed using a document collection to support the analytical results.

关键词： design experimentation performance access method document retrieval information retrieval signature file superimposed coding text retrieval

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Suitability analysis of practical directional algorithms for use in directional comparison bus protection based on IEC61850 process bus

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IET GENERATION TRANSMISSION & DISTRIBUTION 2011年第2期5卷 199-208页

作者： Zadeh, M. R. D. Sidhu, T. S. Klimek, A. Univ Western Ontario Dept Elect & Comp Engn London ON Canada Powertech Labs Inc Vancouver BC Canada

A directional comparison bus protection can provide a high-speed bus fault clearing in an IEC61850 process-bus environment. This technique is based on fault direction for each circuit connected to the protected bus. Compared to biased current differential protection, the loss of accurate time synchronisation of the individual merging units does not cause the bus protection based on directional comparison to lose security. The suitability of various practical directional techniques is investigated from the viewpoint of directional comparison bus protection for an IEC61850 process bus. A modification in the superimposed directional algorithm for bus protection is proposed to overcome the major problems resulted from breaker operations. As a part of this modification, a new technique is proposed to determine the bus voltage from feeder voltages to avoid the need for an additional three-phase CVT on the bus. PSCAD/EMTDC and MATLAB are utilised to simulate the power system and various directional algorithms, respectively. Results are reported and compared.

关键词： ALGORITHMS ELECTRIC fault location ELECTRIC circuits superimposed coding ELECTRIC power ELECTRICAL engineering BUS conductors (Electricity)

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Fine structural features of radio-frequency radiation of the solar flare of February 12, 2010

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GEOMAGNETISM AND AERONOMY 2014年第4期54卷 406-415页

作者： Chernov, G. P. Fomichev, V. V. Gorgutsa, R. V. Markeev, A. K. Sobolev, D. E. Hillaris, A. Alissandrakis, K. Russian Acad Sci IZMIRAN Pushkov Inst Terr Magnetism Ionosphere & Radio Wa Troitsk 142190 Moscow Oblast Russia Univ Ioannina Dept Phys Sect Astrogeophys GR-45110 Ioannina Greece Univ Athens Dept Phys Sect Astrophys Astron & Mech Zografos 15784 Greece

Solar radio emission records received at the IZMIRAN spectrograph (25-270 MHz) during the solar flare event of February 12, 2010 are analyzed. Different fine structures were observed in three large groups of type III bursts against a low continuum. According to data from the Nancay radioheliograph, sources of all three groups of bursts were located in one active region, 11046, and their emissions were accompanied by soft X-ray bursts (GOES satellite): C7.9 at 0721 UT, B9.6 at 0940 UT, and M8.3 at 1125 UT. After the first group of bursts, classical fiber bursts were observed in combination with reverse-drift fiber bursts with unusual arc drift. After the third (the most powerful) group, stable second-length pulsations and slow-drift fiber bursts were observed, the instantaneous frequency bands of which were an order of magnitude larger than the frequency band of classical fiber bursts, and the frequency drift was several times lower. More complex fiber bursts were observed in the weakest group in the time range 0940:39-0942:00 UT. They were narrow-band (similar to 0.5 MHz) fiber bursts, periodically recurring in a narrow frequency band (5-6 MHz) during several seconds. The presence of many chaotically drifting ensembles of fibers, crossing and superimposing on one another, is a feature of this event. It is assumed that occurrence of these structures can be connected with the existence of many small shock fronts behind the leading edge of a coronal mass ejection.

关键词： RADIATION RADIO frequency SOLAR flares superimposed coding FIBER lasers

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Index structures for efficiently accessing fuzzy data including cost models and measurements

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FUZZY SETS AND SYSTEMS 1999年第1期108卷 11-37页

作者： Boss, B Helmer, S Univ Mannheim Lehrstuhl Prakt Informat 3 D-68131 Mannheim Germany Robert Bosch GmbH FV SLD D-60326 Frankfurt Germany

Recently, the call for database management systems (DBMS) with uncertainty capabilities is getting stronger. Many of the existing approaches to modeling uncertainty in database management systems are based on the theory of fuzzy sets. High performance is a necessary precondition for the acceptance of such systems by end users. However, performance issues have been quite neglected in research on fuzzy DBMS so far. Tn this article they are addressed explicitly. We propose new index structures for fuzzy DBMS based on the well known technique of superimposed coding together with detailed cost models. The correctness of the cost models as well as the efficiency of the index structures proposed is validated by a number of measurements on experimental fuzzy databases. (C) 1999 Elsevier Science B.V. All rights reserved.

关键词： information storage and retrieval fuzzy database management systems fuzzy information retrieval fuzzy object oriented database management systems index structures cost analysis superimposed coding

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A NEW SIGNATURE APPROACH FOR RETRIEVAL OF DOCUMENTS FROM FREE-TEXT DATABASES

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INFORMATION PROCESSING & MANAGEMENT 1992年第2期28卷 153-163页

作者： TAVAKOLI, N RAY, A UNIV N CAROLINA DEPT COMP SCICHARLOTTENC 28223 USA

Among the techniques used for retrieval of information from free-text or document databases, signature methods have proven to be more efficient in terms of storage overhead and processing speed. Signature methods, however, present the problem of "false drops" in which a document is identified but does not satisfy the user query. In the signature approaches such as Word Signature, and superimposed coding, the number of false drops is directly related to the hashing function selected, signature size, and number of signature buffers used for each document. Hashing functions also generate collisions, which will result in false drops. In addition, these signature methods do not take into account the length of the words or the positional information of the characters that constitute the word. The use of "Don't Care Characters" in the queries, therefore, is not possible. This paper presents a new signature approach in which the sizes of the signature files are dependent on the number of unique symbols in the alphabet, and therefore for all documents containing English text, the size is constant. The signature generated in this technique maintains the positional information of characters and therefore allows for Don't Care Characters to be used in the queries. Implementation results and comparison of this technique to the superimposed coding method is presented.

关键词： SIGNATURE FALSE DROP INVERSION superimposed coding FULL-TEXT

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On the probability distribution of superimposed random codes

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IEEE TRANSACTIONS ON INFORMATION THEORY 2008年第7期54卷 3206-3210页

作者： Guenther, Bernd Beilstein Inst D-60487 Frankfurt Germany Univ Frankfurt D-6000 Frankfurt Germany Univ Washington Seattle WA 98195 USA

In this correspondence, a systematic study of the probability distribution of superimposed random codes is presented through the use of generating functions. Special attention is paid to the cases of either uniformly distributed but not necessarily independent or nonuniform but independent bit structures. Recommendations for optimal coding strategies are derived.

关键词： database indexing false drop estimates generating functions probability distribution superimposed coding

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On physical-layer security for primary system in underlay cognitive radio networks

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IET NETWORKS 2018年第2期7卷 68-73页

作者： Xie, Ping Zhang, Moli Zhang, Gaoyuan Zheng, Ruijuan Xing, Ling Wu, Qingtao Henan Univ Sci & Technol Informat Engn Coll Luoyang 471023 Peoples R China

In this study, the authors consider the physical-layer security for transmission in underlay cognitive radio networks, where consisting of a primary source-destination pair, a secondary transmitter-receiver pair and a common eavesdropper (E). To transmit data in a secure and reliable manner, they propose a transmission protocol for an underlay cognitive radio network. In particular, the secondary user is allowed to operate on the primary spectrum bandwidth when the interference threshold is satisfied. To protect the transmission confidentiality of primary system, PS node transmits a signal, which is linearly combined with the jamming signal (as artificial noise) and expectation signal, to interfere E. Furthermore, they propose a superimposed coding to combine with the artificial noise and expectation signal at PS node. We also analyse the performance of the proposed transmission protocol. We obtain the outage probability of secondary and primary systems. Simultaneously, they derive the closed-form expression of intercept probability for primary system. In addition, they verify the performance of their proposed transmission protocol by numerical experiment. The numerical results show that their proposed transmission protocol not only has the better outage performance for secondary system but also has the better intercept performance for primary system.

关键词： cognitive radio jamming telecommunication security protocols telecommunication network reliability probability encoding radio receivers radio transmitters outage performance intercept probability closed-form expression superimposed coding expectation signal artificial noise jamming signal PS node transmission confidentiality interference threshold primary spectrum bandwidth transmission protocol common eavesdropper secondary transmitter-receiver pair primary source-destination pair underlay cognitive radio networks primary system physical-layer security

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Nanoscopy with more than 100,000 'doughnuts'

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NATURE METHODS 2013年第8期10卷 737-+页

作者： Chmyrov, Andriy Keller, Jan Grotjohann, Tim Ratz, Michael d'Este, Elisa Jakobs, Stefan Eggeling, Christian Hell, Stefan W. Max Planck Inst Biophys Chem Dept NanoBiophoton D-37077 Gottingen Germany Univ Gottingen Dept Neurol Gottingen Germany

We show that nanoscopy based on the principle called RESOLFT (reversible saturable optical fluorescence transitions) or nonlinear structured illumination can be effectively parallelized using two incoherently superimposed orthogonal standing light waves. The intensity minima of the resulting pattern act as 'doughnuts', providing isotropic resolution in the focal plane and making pattern rotation redundant. We super-resolved living cells in 120 mm x 100 mm-sized fields of view in <1 s using 116,000 such doughnuts.

关键词： FLUORESCENCE NONLINEAR optics RESOLUTION (Optics) LIGHTING superimposed coding ROTATIONAL motion

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PEEKABIT COMPUTER OFFSPRING OF PUNCHED CARD PEEKABOO FOR NATURAL LANGUAGE SEARCHING

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COMMUNICATIONS OF THE ACM 1968年第9期11卷 595-&页

作者： HUTTON, FC Union Carbide Corporation Oak Ridge Tennessee

The 'peekaboo' idea from punched card information retrieval methods has been mated with the idea of superimposed punching to produce a programming technique which cuts computer run time in half on a test search of 33,000 subject index entries. A search program using the device has been operational since late 1963. As an item is entered in the store, an 18-byte mask is created from the item's meaningful words using the inclusive OR operation. If, at search time, the logical product (using the AND operation) of this mask and a similarly constructed question mask is not equal to the question mask, then one or more question words are not present in the store item. An equality is inconclusive; the words of the store item must be unpacked and compared with question words. The present store is made up of over 600,000 subject index entries estimated to average 60 characters each. Longer texts, such as abstracts, could be handled by multiple masks. [ABSTRACT FROM AUTHOR]

关键词： computer search information compaction natural language searching peekaboo superimposed coding text searching

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Prediction of 3D Transversal Patterns in Packed-Bed Reactors Using a Reduced 2D Model: Oscillatory Kinetics

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INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH 2010年第21期49卷 10558-10564页

作者： Nekhamkina, Olga Sheintuch, Moshe Technion Israel Inst Technol Dept Chem Engn IL-32000 Haifa Israel

We have recently showed the formation of transversal patterns in a 3D cylindrical reactor in which an exothermic first-order reaction of Arrhenius kinetics occurs with variable catalytic activity. Under these oscillatory kinetics, the system exhibits a planar front (ID) solution, with the front position oscillating in the axial direction, while in the 3D case, three types of transversal patterns can emerge: rotating fronts, oscillating fronts with superimposed transversal (nonrotating) oscillations, and mixed rotating oscillating fronts. In the present study, we analyze the possible reduction of the 3D model to a 2D cylindrical shell model to predict patterns. We map bifurcation diagrams showing domains of different modes using the reactor radius (R) as a bifurcation parameter and show that the front divergence and the domains of the kn-mode pattern in the 3D model [corresponding to the transversal eigenfunction J(k)(mu(kn)r) exp(ik0), in which is the Bessel function of the first kind] can be predicted by those of the one wave in the 2D model using the linear transformation R(3D) = mu(kn)R(2D).

关键词： FIXED bed reactors OSCILLATING chemical reactions CHEMICAL kinetics ARRHENIUS equation BIFURCATION theory EIGENFUNCTIONS BESSEL functions superimposed coding CHEMICAL engineering CHEMICAL reactors

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