Das MINERVA-Projekt: Datenbankselektion für Peer-to-Peer-Websuche     

Matthias Bender  Sebastian Michel  Gerhard Weikum und Christian Zimmer 《Informatik - Forschung und Entwicklung》2005,20(3):152-166

Zusammenfassung In diesem Artikel wird MINERVA pr?sentiert, eine prototypische Implementierung einer verteilten Suchmaschine basierend auf einer Peer-to-Peer (P2P)-Architektur. MINERVA setzt auf die in der P2P-Welt verbreitete Technik verteilter Hash-Tabellen auf und benutzt diese zum Aufbau eines verteilten Verzeichnisses. Peers in unserem Ansatz entsprechen v?llig autonomen Benutzern mit ihren lokalen Suchm"oglichkeiten, die bereit sind, ihr lokales Wissen und ihre lokalen Suchm?glichkeiten im Rahmen einer Kollaboration zur Verfügung zu stellen. Wir formalisieren unsere Systemarchitektur und beschreiben das zentrale Problem einer effizienten Suche nach vielversprechenden Peers für eine konkrete Anfrage innerhalb des Verbundes. Wir greifen dabei auf existierende Methoden zurück and passen diese an unseren Systemkontext an. Wir pr?sentieren Experimente auf realen Daten, die verschiedene dieser Ans?tze vergleichen. Diese Experimente zeigen, dass die Qualit?t der Ans?tze variiert und untermauern damit die Wichtigkeit und den Einfluss einer leistungsstarken Methode zur Auswahl guter Datenbanken. Unsere Experimente deuten an, dass eine geringe Anzahl sorgf?ltig ausgew?hlter Datenbanken typischerweise bereits einen Gro?teil aller relevanten Ergebnisse des Gesamtsystems liefert.

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This paper presents the MINERVA project that protoypes a distributed search engine based on P2P techniques. MINERVA is layered on top of a Chord-style overlay network and uses a powerful crawling, indexing, and search engine on every autonomous peer. We formalize our system model and identify the problem of efficiently selecting promising peers for a query as a pivotal issue. We revisit existing approaches to the database selection problem and adapt them to our system environment. Measurements are performed to compare different selection strategies using real-world data. The experiments show significant performance differences between the strategies and prove the importance of a judicious peer selection strategy. The experiments also present first evidence that a small number of carefully selected peers already provide the vast majority of all relevant results.

CR Subject Classification H.4,H.3.3,H3.4  相似文献   

Das MINERVA-Projekt: Datenbankselektion für Peer-to-Peer-Websuche     

Matthias Bender  Sebastian Michel  Gerhard Weikum  Christian Zimmer 《Informatik - Forschung und Entwicklung》2005,12(5):152-166

In diesem Artikel wird MINERVA pr?sentiert, eine prototypische Implementierung einer verteilten Suchmaschine basierend auf einer Peer-to-Peer (P2P)-Architektur. MINERVA setzt auf die in der P2P-Welt verbreitete Technik verteilter Hash-Tabellen auf und benutzt diese zum Aufbau eines verteilten Verzeichnisses. Peers in unserem Ansatz entsprechen v?llig autonomen Benutzern mit ihren lokalen Suchm"oglichkeiten, die bereit sind, ihr lokales Wissen und ihre lokalen Suchm?glichkeiten im Rahmen einer Kollaboration zur Verfügung zu stellen. Wir formalisieren unsere Systemarchitektur und beschreiben das zentrale Problem einer effizienten Suche nach vielversprechenden Peers für eine konkrete Anfrage innerhalb des Verbundes. Wir greifen dabei auf existierende Methoden zurück and passen diese an unseren Systemkontext an. Wir pr?sentieren Experimente auf realen Daten, die verschiedene dieser Ans?tze vergleichen. Diese Experimente zeigen, dass die Qualit?t der Ans?tze variiert und untermauern damit die Wichtigkeit und den Einfluss einer leistungsstarken Methode zur Auswahl guter Datenbanken. Unsere Experimente deuten an, dass eine geringe Anzahl sorgf?ltig ausgew?hlter Datenbanken typischerweise bereits einen Gro?teil aller relevanten Ergebnisse des Gesamtsystems liefert.  相似文献   

Targets for research in library education: Edited by Harold Borko. Chicago, 1973, American Library Association, 293 pp     

Michel J. Menou 《Information processing & management》1977,13(3):201-202

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Influence of a conservative sleep management strategy during a solo Pacific Ocean crossing on anxiety and perceived fatigue: a case study     

Hagin V  Gonzales BR  Candau RB  Groslambert A 《Journal of sports sciences》2012,30(4):395-402

The aim of this case study was to determine whether a sailor's deliberate choice of a conservative strategy to manage sleep deprivation would allow him to cross the Pacific Ocean and to minimize his state of anxiety and perceived fatigue. The participant, who had more than 10 years' sailing experience in severe conditions, was tested on a small catamaran without any living quarters during a solo Pacific Ocean crossing. Estimations of sleep hours, state anxiety, and perceived fatigue were self-reported by the sailor on a daily basis using a specific questionnaire. The most important finding is that the sailor's deliberate sleep strategy, 5.4 h sleep per day (24% less than on-shore), was enough to keep his anxiety and perceived fatigue within acceptable limits and enabled him to achieve his goal, which was the first crossing of the Pacific Ocean on a catamaran of less than 6 m. In conclusion, our results suggest that the sailor observed in the present case study was able to minimize anxiety and perceived fatigue with adequate sleep to optimize his performance, security, and to achieve his goal.  相似文献   

A comparison of time-motion performance between age groups in judo matches     

Miarka B  Panissa VL  Julio UF  Del Vecchio FB  Calmet M  Franchini E 《Journal of sports sciences》2012,30(9):899-905

The aim of this study was to compare time-motion indicators during judo matches performed by athletes from different age groups. The following age groups were analysed: Pre-Juvenile (13-14 years, n = 522), Juvenile (15-16 years, n = 353); Junior (19 years, n = 349) and Senior (>20 years, n = 587). The time-motion indicators included: Total Combat Time, Standing Combat Time, Displacement Without Contact, Gripping Time, Groundwork Combat Time and Pause Time. Analysis of variance (ANOVA) one-way and the Tukey test, as well as the Kruskal-Wallis test and Mann-Whitney (for non-parametric data), were conducted, using P < 0.05 as significance level. The results showed that all analysed groups obtained a median of 7 (first quantile - 3, third quantile - 12) sequences of combat/pause cycles. In total time of combat, the result was: for Total Combat Time, Standing Combat Time and Gripping Time: Pre-Juvenile and Senior were significantly longer than Juvenile and Junior. Considering Displacement Without Contact, Junior was significantly longer than all other age groups. For Groundwork Combat Time, Senior was significantly longer than all other age groups and Pre-Juvenile was longer than Junior. These results can be used to improve the physiological performance in intermittent practices, as well as technical-tactical training during judo sessions.  相似文献   

Characterizing the mechanical parameters of forward and backward falls as experienced in snowboarding     

Schmitt KU  Wider D  Michel FI  Brügger O  Gerber H  Denoth J 《Sports biomechanics / International Society of Biomechanics in Sports》2012,11(1):57-72

Wrist injuries are frequently observed after falls in snowboarding. In this study, laboratory experiments mimicking forward and backward falls were analysed. In six different falling scenarios, participants self-initiated falls from a static initial position. Eighteen volunteers conducted a total of 741 trials. Measurements were taken for basic parameters describing the kinematics as well as the biomechanical loading during impact, such as impact force, impact acceleration, and velocity. The effective mass affecting the wrist in a fall also was determined. The elbow angle at impact showed a more extended arm in backward falls compared to forward falls, whereas the wrist angle at impact remained similar in forward and backward falls. The study results suggest a new performance standard for wrist guards, indicating the following parameters to characterize an impact: an effective mass acting on one wrist of 3-5 kg, an impact angle of 75 degrees of the forearm relative to the ground, and an impact velocity of 3 m/s.  相似文献   

Write when hot — submit when not: seasonal bias in peer review or acceptance?     

Shaul SHALVI  Matthijs BAAS  Michel J. J. HANDGRAAF  Carsten K.W. DE DREU 《Learned Publishing》2010,23(2):117-123

At a top psychology journal, Psychological Science (PS), submissions peak during the summer months. We tested whether this seasonal submission bias decreases the likelihood of a paper being accepted in that period. Month of submission data was obtained for all 575 publications in PS for the period 2003–2006. Whereas submissions to PS were higher in the summer, there was no evidence that most accepted publications were originally submitted in the summer. Thus, contributors submit to PS when the likelihood of acceptance is the lowest – creating their own entrance barrier. A similar seasonal pattern was not identified for Personality and Social Psychology Bulletin, another top psychology journal. Using the Web of Knowledge database, we further assessed whether overcoming the seasonal entrance barrier influences the number of citations a paper receives in subsequent years. We discuss the possibility that the different rejections policies in the two journals, employing desk rejections or not, may explain this discrepancy, and explore a range of alternative hypotheses.  相似文献   

Citing-side normalization of journal impact: A robust variant of the Audience Factor     

Michel Zitt 《Journal of Informetrics》2010,4(3):392-406

The principle of a new type of impact measure was introduced recently, called the “Audience Factor” (AF). It is a variant of the journal impact factor where emitted citations are weighted inversely to the propensity to cite of the source. In the initial design, propensity was calculated using the average length of bibliography at the source level with two options: a journal-level average or a field-level average. This citing-side normalization controls for propensity to cite, the main determinant of impact factor variability across fields. The AF maintains the variability due to exports–imports of citations across field and to growth differences. It does not account for influence chains, powerful approaches taken in the wake of Pinski–Narin's influence weights. Here we introduce a robust variant of the audience factor, trying to combine the respective advantages of the two options for calculating bibliography lengths: the classification-free scheme when the bibliography length is calculated at the individual journal level, and the robustness and avoidance of ad hoc settings when the bibliography length is averaged at the field level. The variant proposed relies on the relative neighborhood of a citing journal, regarded as its micro-field and assumed to reflect the citation behavior in this area of science. The methodology adopted allows a large range of variation of the neighborhood, reflecting the local citation network, and partly alleviates the “cross-scale” normalization issue. Citing-side normalization is a general principle which may be extended to other citation counts.  相似文献   

Scaling-up Sustainable Land Management Practices through the Concept of the Rural Resource Centre: Reconciling Farmers' Interests with Research Agendas     

Takoutsing Bertin  Tchoundjeu Zacharie  Degrande Ann  Asaah Ebenezar  Tsobeng Alain 《The Journal of Agricultural Education and Extension》2013,19(5):463-483

Abstract

Purpose: Formal agricultural research has generated vast amount of knowledge and fundamental insights on land management, but their low adoption has been attributed to the use of public extension approach. This research aims to address whether and how full participation of farmers through the concept of Rural Resource Centre (RRC) provides new insights for the development of alternative and farmers-based extension methods.

Design/Methodology/Approach: Using the Concept of RRC, this research assesses the role of farmers in on-farm demonstrations and scaling-up of land management practices, and investigates effective ways to enhance beneficial interactions between researchers, extension workers and farmers in view of improving adoption.

Findings: The findings suggest that farmers can effectively participate in demonstrations and scaling-up of agricultural practices. This participation is enhanced by judicious incentives such as higher crop yields that motivate farmers and influence adoption. The current success of the approach stems from the fact that farmers, extension workers and researchers jointly implement the activities and their different aims were achieved simultaneously: scientific results for researchers, better agricultural practices for extension workers, and economic success and free choice for farmers.

Practical implications: This research concludes that farmers have the capacities to play an innermost role in demonstrations and scaling-up of agricultural practices. However, there is a need to build and strengthen their capacities to facilitate their participation and contribution.

Originality/Value: The article demonstrates the value of the preponderant role of farmers in on-farm demonstrations and scaling-up practices by exhibiting the beneficial interactions between researchers, extension workers and farmers.  相似文献   

General Growth Mixture Analysis of Adolescents' Developmental Trajectories of Anxiety: The Impact of Untested Invariance Assumptions on Substantive Interpretations     

Alexandre J. S. Morin  Christophe Maïano  Benjamin Nagengast  Herbert W. Marsh  Julien Morizot  Michel Janosz 《Structural equation modeling》2013,20(4):613-648

Substantively, this study investigates potential heterogeneity in the developmental trajectories of anxiety in adolescence. Methodologically, this study demonstrates the usefulness of general growth mixture analysis (GGMA) in addressing these issues and illustrates the impact of untested invariance assumptions on substantive interpretations. This study relied on data from the Montreal Adolescent Depression Development Project (MADDP), a 4-year follow-up of more than 1,000 adolescents who completed the Beck Anxiety Inventory each year. GGMA models relying on different invariance assumptions were empirically compared. Each of these models converged on a 5-class solution, but yielded different substantive results. The model with class-varying variance–covariance matrices was retained as providing a better fit to the data. These results showed that although elevated levels of anxiety might fluctuate over time, they clearly do not represent a transient phenomenon. This model was then validated in relation to multiple predictors (mostly related to school violence) and outcomes (grade-point average, school dropout, depression, loneliness, and drug-related problems).  相似文献