406 research outputs found
Ist der Einsatz des Rektumballons in der Strahlentherapie des Prostatakarzinoms von klinischer Relevanz?
Ist der Einsatz des Rektumballons in der Strahlentherapie des Prostatakarzinoms im Hinblick
auf strahleninduzierte Nebenwirkungen von klinischer Relevanz? Material und Methoden: Vergleich von zwei Patientenkollektiven mit jeweils 51 Patienten unter äquivalenter3-D-Konformationsbestrahlung (Gesamtdosis 70,2 – 72 Gy, Einzelfraktionsdosis 1,8-2,0 Gy, 3-Feld-Technik) des lokalisierten Prostatakarzinoms. Eine Gruppe wurde unter täglichen Einbringens eines intrarektalen Ballons bestrahlt. Ergebnisse: Unter Ballonapplikation traten vermehrt akute rektale Nebenwirkungen (Schmerzen und Blutungen) auf. Eine Signifikanz im 95%-Konfidenzintervall wurde nicht erreicht. Insgesamt konnte bezüglich rektaler oder vesicaler Nebenwirkungen kein statistisch signifikanter Unterschied erhoben werden. Schlussfolgerung: Ein Benefit durch eine intrarektale Ballonapplikation konnte nicht festgestellt werden
Toward Interpretable Deep Reinforcement Learning with Linear Model U-Trees
Deep Reinforcement Learning (DRL) has achieved impressive success in many
applications. A key component of many DRL models is a neural network
representing a Q function, to estimate the expected cumulative reward following
a state-action pair. The Q function neural network contains a lot of implicit
knowledge about the RL problems, but often remains unexamined and
uninterpreted. To our knowledge, this work develops the first mimic learning
framework for Q functions in DRL. We introduce Linear Model U-trees (LMUTs) to
approximate neural network predictions. An LMUT is learned using a novel
on-line algorithm that is well-suited for an active play setting, where the
mimic learner observes an ongoing interaction between the neural net and the
environment. Empirical evaluation shows that an LMUT mimics a Q function
substantially better than five baseline methods. The transparent tree structure
of an LMUT facilitates understanding the network's learned knowledge by
analyzing feature influence, extracting rules, and highlighting the
super-pixels in image inputs.Comment: This paper is accepted by ECML-PKDD 201
Selfish Network Creation with Non-Uniform Edge Cost
Network creation games investigate complex networks from a game-theoretic
point of view. Based on the original model by Fabrikant et al. [PODC'03] many
variants have been introduced. However, almost all versions have the drawback
that edges are treated uniformly, i.e. every edge has the same cost and that
this common parameter heavily influences the outcomes and the analysis of these
games.
We propose and analyze simple and natural parameter-free network creation
games with non-uniform edge cost. Our models are inspired by social networks
where the cost of forming a link is proportional to the popularity of the
targeted node. Besides results on the complexity of computing a best response
and on various properties of the sequential versions, we show that the most
general version of our model has constant Price of Anarchy. To the best of our
knowledge, this is the first proof of a constant Price of Anarchy for any
network creation game.Comment: To appear at SAGT'1
Greedy Selfish Network Creation
We introduce and analyze greedy equilibria (GE) for the well-known model of
selfish network creation by Fabrikant et al.[PODC'03]. GE are interesting for
two reasons: (1) they model outcomes found by agents which prefer smooth
adaptations over radical strategy-changes, (2) GE are outcomes found by agents
which do not have enough computational resources to play optimally. In the
model of Fabrikant et al. agents correspond to Internet Service Providers which
buy network links to improve their quality of network usage. It is known that
computing a best response in this model is NP-hard. Hence, poly-time agents are
likely not to play optimally. But how good are networks created by such agents?
We answer this question for very simple agents. Quite surprisingly, naive
greedy play suffices to create remarkably stable networks. Specifically, we
show that in the SUM version, where agents attempt to minimize their average
distance to all other agents, GE capture Nash equilibria (NE) on trees and that
any GE is in 3-approximate NE on general networks. For the latter we also
provide a lower bound of 3/2 on the approximation ratio. For the MAX version,
where agents attempt to minimize their maximum distance, we show that any
GE-star is in 2-approximate NE and any GE-tree having larger diameter is in
6/5-approximate NE. Both bounds are tight. We contrast these positive results
by providing a linear lower bound on the approximation ratio for the MAX
version on general networks in GE. This result implies a locality gap of
for the metric min-max facility location problem, where n is the
number of clients.Comment: 28 pages, 8 figures. An extended abstract of this work was accepted
at WINE'1
Correlation of the Cd-to-Te ratio on CdTe surfaces with the surface structure
We report here that reconstruction on (100), (1lIlA, and (1l1lB CdTe surfaces is either C(2X2), (2X2), and (l X I) or (2X I), (l X I), and (l X I) when they are Cd or Te stabilized, respectively. There is a mixed region between Cd and Te stabilization in which the reflected high-energy electron-diffraction (RHEED) patterns contain characteristics of both Cd- and Te-stabilized surfaces. We have also found that the Cd-to-Te ratio of the x-ray photoelectron intensities of their 3d core levels is about 20% larger for a Cd-stabilized (1lIlA, (1lIlB, or (100) CdTe surface than for a Te-stabilized one. According to a simple model calculation, which was normalized by means of the photoelectron intensity ratio of a Cd-stabilized (lll)A and aTe-stabilized (1l1lB CdTe surface, the experimental data for CdTe surfaces can be explained by a linear dependence of the photoelectron-intensity ratio on the fraction of Cd in the uppermost monatomic layer. This surface composition can be correlated with the surface structure, i.e., the corresponding RHEED patterns. This correlation can in turn be employed to determine Te and Cd evaporation rates. The Te reevaporation rate is increasingly slower for the Te-stabilized (Ill) A, (l1l)B, and (100) surfaces, while the opposite is true for Cd from Cd-stabilized (Ill) A and (Ill)B surfaces. In addition, Te is much more easily evaporated from all the investigated surfaces than is Cd, if the substrate is kept at normal molecular-beam-epitaxy growth temperatures ranging from 2oo·C to 300 ·C
Improving the Accuracy of a Two-Stage Algorithm in Evolutionary Product Unit Neural Networks for Classification by Means of Feature Selection
This paper introduces a methodology that improves the accuracy
of a two-stage algorithm in evolutionary product unit neural networks
for classification tasks by means of feature selection. A couple
of filters have been taken into consideration to try out the proposal.
The experimentation has been carried out on seven data sets from the
UCI repository that report test mean accuracy error rates about twenty
percent or above with reference classifiers such as C4.5 or 1-NN. The
study includes an overall empirical comparison between the models obtained
with and without feature selection. Also several classifiers have
been tested in order to illustrate the performance of the different filters
considered. The results have been contrasted with nonparametric statistical
tests and show that our proposal significantly improves the test
accuracy of the previous models for the considered data sets. Moreover,
the current proposal is much more efficient than a previous methodology
developed by us; lastly, the reduction percentage in the number of inputs
is above a fifty five, on average.MICYT TIN2007-68084-C02-02MICYT TIN2008-06681-C06-03Junta de AndalucĂa P08-TIC-374
The band structure of BeTe - a combined experimental and theoretical study
Using angle-resolved synchrotron-radiation photoemission spectroscopy we have
determined the dispersion of the valence bands of BeTe(100) along ,
i.e. the [100] direction. The measurements are analyzed with the aid of a
first-principles calculation of the BeTe bulk band structure as well as of the
photoemission peaks as given by the momentum conserving bulk transitions.
Taking the calculated unoccupied bands as final states of the photoemission
process, we obtain an excellent agreement between experimental and calculated
spectra and a clear interpretation of almost all measured bands. In contrast,
the free electron approximation for the final states fails to describe the BeTe
bulk band structure along properly.Comment: 21 pages plus 4 figure
Probabilistic modeling and machine learning in structural and systems biology
This supplement contains extended versions of a selected subset of papers presented at the workshop PMSB 2007, Probabilistic Modeling and Machine Learning in Structural and Systems Biology, Tuusula, Finland, from June 17 to 18, 2006
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