2,748 research outputs found
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 GastransitlĂ€nder 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 TransitlĂ€nder mit Russland. HierfĂŒr werden Exportpreise und mengen sowie die resultierenden Gewinne der Spieler geschĂ€tzt. Durch den Markteintritt von Belarus ergeben sich erhebliche Verluste fĂŒr die Ukraine, wĂ€hrend sich Belarus mit einem Ausbau seiner KapazitĂ€ten auf 56 Mrd. m3 noch besser stellt. Russlands Gewinne steigen insbesondere durch die vertikale Integration der belarussischen und ukrainischen Gassektoren. FĂŒr Westeuropa legen die Ergebnisse erhebliche Wohlfahrtsgewinne durch den Pipelineausbau nahe, gleichzeitig aber auch eine gestiegene AbhĂ€ngigkeit von Gasimporten aus Russland.Gas,pipelines,strategic behavior,CIS,Russia
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
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