Popular Ensemble Methods: An Empirical Study

An ensemble consists of a set of individually trained classifiers (such as neural networks or decision trees) whose predictions are combined when classifying novel instances. Previous research has shown that an ensemble is often more accurate than any of the single classifiers in the ensemble. Bagging (Breiman, 1996c) and Boosting (Freund and Shapire, 1996; Shapire, 1990) are two relatively new but popular methods for producing ensembles. In this paper we evaluate these methods on 23 data sets using both neural networks and decision trees as our classification algorithm. Our results clearly indicate a number of conclusions. First, while Bagging is almost always more accurate than a single classifier, it is sometimes much less accurate than Boosting. On the other hand, Boosting can create ensembles that are less accurate than a single classifier -- especially when using neural networks. Analysis indicates that the performance of the Boosting methods is dependent on the characteristics of the data set being examined. In fact, further results show that Boosting ensembles may overfit noisy data sets, thus decreasing its performance. Finally, consistent with previous studies, our work suggests that most of the gain in an ensemble's performance comes in the first few classifiers combined; however, relatively large gains can be seen up to 25 classifiers when Boosting decision trees

Options for transporting Russian gas to Western Europe: A game-theoretic simulation analysis

This paper examines the perspectives of Russian gas exports to Western Europe and the strategic options of the CIS gas transiting countries, namely Ukraine and Belarus. The development of a new transit corridor through Belarus (the Yamal-Europe pipeline), depriving Ukraine of its former monopoly, has modified the situation profoundly. The thrust of the paper is an analysis of nthe strategies that Ukraine and Belarus may pursue in transiting Russian gas: non-cooperative duopoly, cooperative duopoly, and individual or collective cooperation with Russia. Using a demand function for Western European gas imports from Russia, we estimate prices and quantities for gas transit, the expected profits for Russia, Ukraine, and Belarus, and the resulting import prices for Western Europe. The results indicate that Ukraine suffers a loss of several hundred million USD annually from the market entry of Belarus, Belarus has an incentive to increase its gas transit capacity to at least 56 billion cubic meters, and Russia's profits increase, in particular when it unites its gas sector with Belarus and Ukraine. For Western Europe, all scenarios indicate an increase in welfare through the new pipeline, but also an increasing importance of gas imports from Russia. -- Der Beitrag untersucht die Perspektiven russischer Gasexporte nach Westeuropa und die strategischen Optionen der Gastransitländer Ukraine und Belarus. Durch den Neu- und Ausbau eines Gastransitkorridors durch Belarus (die Jamal-Europa-Pipeline) geht die bisherige Monopolstellung der Ukraine als Transitland verloren. Ziel der Arbeit ist die Modellierung und Quantifizierung unterschiedlicher Wettbewerbsstrategien, wie das nichtkooperative Duopol, das kooperative Duopol, oder die individuelle bzw. kollektive Kooperation der Transitländer mit Russland. Hierfür werden Exportpreise und mengen sowie die resultierenden Gewinne der Spieler geschätzt. Durch den Markteintritt von Belarus ergeben sich erhebliche Verluste für die Ukraine, während sich Belarus mit einem Ausbau seiner Kapazitäten auf 56 Mrd. m3 noch besser stellt. Russlands Gewinne steigen insbesondere durch die vertikale Integration der belarussischen und ukrainischen Gassektoren. Für Westeuropa legen die Ergebnisse erhebliche Wohlfahrtsgewinne durch den Pipelineausbau nahe, gleichzeitig aber auch eine gestiegene Abhängigkeit von Gasimporten aus Russland.Gas,pipelines,strategic behavior,CIS,Russia

The vascularity of the kidney as influenced by sensory impulses

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Nanofriction mechanisms derived from the dependence of friction on load and sliding velocity from air to UHV on hydrophilic silicon

This paper examines friction as a function of the sliding velocity and applied normal load from air to UHV in a scanning force microscope (SFM) experiment in which a sharp silicon tip slides against a flat Si(100) sample. Under ambient conditions, both surfaces are covered by a native oxide, which is hydrophilic. During pump-down in the vacuum chamber housing the SFM, the behavior of friction as a function of the applied normal load and the sliding velocity undergoes a change. By analyzing these changes it is possible to identify three distinct friction regimes with corresponding contact properties: (a) friction dominated by the additional normal forces induced by capillarity due to the presence of thick water films, (b) higher drag force from ordering effects present in thin water layers and (c) low friction due to direct solid-solid contact for the sample with the counterbody. Depending on environmental conditions and the applied normal load, all three mechanisms may be present at one time. Their individual contributions can be identified by investigating the dependence of friction on the applied normal load as well as on the sliding velocity in different pressure regimes, thus providing information about nanoscale friction mechanisms

Limb imaging of the Venus O2 visible nightglow with the Venus Monitoring Camera

We investigated the Venus O2 visible nightglow with imagery from the Venus Monitoring Camera on Venus Express. Drawing from data collected between April 2007 and January 2011, we study the global distribution of this emission, discovered in the late 70s by the Venera 9 and 10 missions. The inferred limb-viewing intensities are on the order of 150 kiloRayleighs at the lower latitudes and seem to drop somewhat towards the poles. The emission is generally stable, although there are episodes when the intensities rise up to 500 kR. We compare a set of Venus Monitoring Camera observations with coincident measurements of the O2 nightglow at 1.27 {\mu}m made with the Visible and Infrared Thermal Imaging Spectrometer, also on Venus Express. From the evidence gathered in this and past works, we suggest a direct correlation between the instantaneous emissions from the two O2 nightglow systems. Possible implications regarding the uncertain origin of the atomic oxygen green line at 557.7 nm are noted.Comment: 7 pages, 3 figure

Lost or Fond? Effects of Nostalgia on Sad Mood Recovery Vary by Attachment Insecurity

Nostalgia involves a fond recollection of people and events lost to time. Growing evidence indicates that nostalgia may ameliorate negative affective states such as loneliness and boredom. However, the effect of nostalgia on sadness is unknown, and there is little research on how social connectedness might impact nostalgia\u27s effects. Grounded in a theoretical framework whereby people with lower levels of attachment insecurity benefit more from nostalgia, we exposed participants to a mortality-related sad mood and then randomly assigned them to reflect on a nostalgic or an ordinary event memory. We examined changes in mood and electrodermal activity (EDA) and found that nostalgic versus ordinary event memories led to a blunted recovery from sad mood, but that this effect was moderated by degree of attachment insecurity, such that participants with low insecurity benefited from nostalgia whereas people with high insecurity did not. These findings suggest that nostalgia\u27s benefits may be tied to the degree of confidence one has in one\u27s social relationships