Refine
Year of publication
Document Type
- Preprint (759)
- Article (402)
- Working Paper (119)
- Doctoral Thesis (93)
- Diploma Thesis (47)
- Conference Proceeding (41)
- Book (37)
- Bachelor Thesis (36)
- diplomthesis (28)
- Report (25)
Has Fulltext
- yes (1619)
Is part of the Bibliography
- no (1619)
Keywords
Institute
- Informatik (1619) (remove)
Im Jahr 1993 schlug A. Shamir Protokolle zur Erstellung digitaler Unterschriften vor, die auf rationalen Funktionen kleinen Grades beruhen. D. Coppersmith, J. Stern und S. Vaudenay präsentierten die ersten Angriffe auf die Verfahren. Diese Angriffe können den geheimen Schlüssel nicht ermitteln. Für eine der von Shamir vorgeschlagenen Varianten zeigen wir, wie der geheime Schlüssel ermittelt werden kann. Das zweite Signaturschema von Shamir hängt von der Wahl einer algebraischen Basis ab. Eine besondere Bedeutung haben Basen, deren Elemente polynomiale Terme vom Grad 2 sind. Wir analysieren die Struktur der algebraischen Basen. Für den hervorgehobenen Spezialfall kann eine vollständige Klassifikation durchgeführt werden.
Digitale Kompetenzen von Hochschullehrenden messen : Validierungsstudie eines Kompetenzrasters
(2018)
Der Beitrag beschreibt die Entwicklung eines Kompetenzrasters zur Erfassung digitaler Kompetenzen von Hochschullehrenden und stellt Ergebnisse der Validierung des Rasters vor. Dazu werden die Ergebnisse eines Pre-Tests (N=90) unter Teilnehmenden eines E-LearningQualifizierungsangebots inferenzstatistisch ausgewertet. Zusätzlich werden zur äußeren Validierung des Kompetenzrasters Ergebnisse mit Aussagen der Befragungsteilnehmer*innen verglichen, die mit Hilfe qualitativer Methoden aus E-Portfolios gewonnen wurden. Die skalenanalytischen Befunde erbrachten für sechs der acht Subdimensionen digitaler Kompetenz eindeutige, einfaktorielle Lösungen mit guten Varianzaufklärungen. Die Subskalen verfügen über hohe interne Konsistenzen. Zwei Dimensionen trennen sich faktorenanalytisch in weitere Subtests auf, die sich im Test ebenfalls als reliabel erweisen. Zur Validität des Kompetenzrasters konnten durch Zusammenhänge mit Aussagen aus E-Portfolios positive Belege gesammelt werden.
The production of J/ψ and ψ(2S) was measured with the ALICE detector in Pb-Pb collisions at the LHC. The measurement was performed at forward rapidity (2.5<y<4) down to zero transverse momentum (pT) in the dimuon decay channel. Inclusive J/ψ yields were extracted in different centrality classes and the centrality dependence of the average pT is presented. The J/ψ suppression, quantified with the nuclear modification factor (RAA), was studied as a function of centrality, transverse momentum and rapidity. Comparisons with similar measurements at lower collision energy and theoretical models indicate that the J/ψ production is the result of an interplay between color screening and recombination mechanisms in a deconfined partonic medium, or at its hadronization. Results on the ψ(2S) suppression are provided via the ratio of ψ(2S) over J/ψ measured in pp and Pb-Pb collisions.
The production of J/ψ and ψ(2S) was measured with the ALICE detector in Pb-Pb collisions at the LHC. The measurement was performed at forward rapidity (2.5<y<4) down to zero transverse momentum (pT) in the dimuon decay channel. Inclusive J/ψ yields were extracted in different centrality classes and the centrality dependence of the average pT is presented. The J/ψ suppression, quantified with the nuclear modification factor (RAA), was studied as a function of centrality, transverse momentum and rapidity. Comparisons with similar measurements at lower collision energy and theoretical models indicate that the J/ψ production is the result of an interplay between color screening and recombination mechanisms in a deconfined partonic medium, or at its hadronization. Results on the ψ(2S) suppression are provided via the ratio of ψ(2S) over J/ψ measured in pp and Pb-Pb collisions.
The production of J/ψ and ψ(2S) was measured with the ALICE detector in Pb-Pb collisions at the LHC. The measurement was performed at forward rapidity (2.5<y<4) down to zero transverse momentum (pT) in the dimuon decay channel.
Inclusive J/ψ yields were extracted in different centrality classes and the centrality dependence of the average pT is presented. The J/ψ suppression, quantified with the nuclear modification factor (RAA), was studied as a function of centrality, transverse momentum and rapidity. Comparisons with similar measurements at lower collision energy and theoretical models indicate that the J/ψ production is the result of an interplay between color screening and recombination mechanisms in a deconfined partonic medium, or at its hadronization. Results on the ψ(2S) suppression are provided via the ratio of ψ(2S) over J/ψ measured in pp and Pb-Pb collisions.
Die Integration von Dienstgüte-Vorkehrungen in objektorientierte Verteilungsinfrastrukturen befähigt Anwendungsentwickler, den Verteilungs-induzierten Problemen verteilter Systeme zu begegnen. Im Rahmen dieser Arbeit wurde die generische Einbettung von Dienstgüte-Vorkehrungen in verteilte Objektsysteme untersucht und ein Lösungsansatz präsentiert. Zunächst wurde eine Analyse der für das Dienstgüte-Management notwendigen Aufgaben vorgestellt. Ausgehend von einem verteilten Objektmodell wurde untersucht, wie Dienstgüte-Vorkehrungen integriert werden können. Dienstgüte-Vorkehrungen stellen bei einem zugrundeliegenden Ob- jektmodell nicht-einkapselbare Verantwortlichkeiten dar. Die enge Bindung der Dienstgüte-Vorkehrungen an einen Dienst führt so zu Vermaschungen in den Strukturen der Implementierung. Damit ist die getrennte Wieder- verwendung beider erschwert. Zusätzlich werden unterschiedliche Abstrak- tionen vermischt. Die aspektorientierte Programmierung (AOP) behandelt solche Vermaschungen. Dienstgüte wurde bei der Integration in ein verteil- tes Objektmodell als ein Aspekt im Sinne der AOP klassifiziert. Ausgehend von den Anforderungen an das Dienstgüte-Management wur- de ein Rahmenwerk auf Basis eines verteilten Objektmodells entworfen. Der in dieser Arbeit dargestellte Schwerpunkt liegt auf der Spezifikation von Dienstgüte-Charakteristiken und deren Umsetzung in die Implementie- rungssprache der Anwendungsobjekte. Für die Unterstützung der Ende-zu- Ende-Dienstgüte-Erbringung ist der Einbezug von Dienstgüte-Vorkehrun- gen des Netzwerks, Betriebssystems oder spezieller Bibliotheken notwendig. Die resultierende Hierarchie von Dienstgüte-Mechanismen wird durch die vorgestellte Integration in eine Verteilungsinfrastruktur unterstützt. Durch die Integration der Dienstgüte-Spezifikation in die Schnittstel- lenbeschreibungssprache erlaubt das Rahmenwerk einen aspektorientierten Ansatz ohne die Einführung weiterer Sprachen zur Spezifikation oder Im- plementierung. Die Spezifikation von Dienstgüte-Charakteristiken in der erweiterten IDL wird in spezielle Entwurfsmuster in der Zielsprache umge- setzt. Diese Entwurfsmuster separieren die Anwendungsobjekte weitgehend von den Dienstgüte-Vorkehrungen. Die auf der Ebene der Anwendungsobjekte generierten Vorlagen für die Dienstgüte-Vorkehrungen können durch einen modifizierten bzw. schon da- für ausgelegten Verteilungsinfrastrukturkern in das System integriert wer- den. Eine einheitliche statische Schnittstelle erlaubt einen einfachen re- effektiven Ansatz. So ist der Zugriff auf Dienstgüte-Vorkehrungen tieferer Schichten wie auch die Integration anwendungsspezifischer Dienstgüte-Vor- kehrungen auf der Netzwerkschicht möglich. Das Rahmenwerk bietet somit eine klare Trennung der Verantwortlich- keiten, die sowohl Anwendungsentwickler wie auch Dienstgüte-Implemen- tierer unterstützt. Die aus der Schnittstellenbeschreibungssprache generier- ten Einheiten stellen für die Anwendungsobjekte eine Abstraktion dar, die sowohl die Verteilungsaspekte wie auch die Dienstgüte-Vorkehrungen ein- fach nutzbar anbietet und von der zugrundeliegenden Plattform isoliert. Eine sich aus dieser Arbeit ergebende Fragestellung besteht in der Er- weiterung und Verallgemeinerung des aspektorientierten Ansatzes. Die im Rahmen der Analyse betrachteten Dienstgüte-Charakteristiken sind aus dem systemnahen Bereich und insbesondere aus der Betrachtung typi- scher Probleme in verteilten Systemen und den daraus erwachsenen Anwen- dungsanforderungen gewonnen. Nicht-funktionale Aspekte der Dienster- bringung lassen sich weiter fassen. So kann ausgehend von den bereitge- stellten Abstraktionen untersucht werden, inwieweit auf Anwendungsebe- ne nicht-funktionale Eigenschaften in ähnlicher Weise einbettbar sind. Im Rahmen dieser Arbeit wurde beispielsweise eine Dienstgüte-Charakteristik zur Parallelisierung von Berechnungen realisiert. Eine anwendungsbezogene Dienstgüte-Charakteristik könnte numerische Optimierungen realisieren, die von den reinen mathematischen Operationen zu trennen ist. Andere Beispiele aus der Multimedia-Kategorie sind durch die Qualität einer Au- dio-Übertragung gegeben. So kann bei einer geringen Bandbreite durch die Kompression der Daten eine bessere Qualität der Audiowiedergabe ereicht werden, als durch Übertragung der Rohdaten. Die Kompressionsrate kann von der Anwendung isoliert und durch entsprechende Dienstgüte-Mecha- nismen realisiert werden. Qualitätsunterschiede ergeben sich durch mögli- che verlustbehaftete Kompression und de notwendigen Anforderungen an Hardware- oder Software-Unterstützung. Andere Kriterien für die Qualität lassen sich weniger leicht vor der Anwendung verbergen. Die Wiedergabe von Stereo- oder Mono-Audiodaten erfordert entsprechende Anwendungen und auch Ausstattungen der Endgeräte. Im Kontext dieser Arbeit wurde ein Objektmodell betrachtet, das eine starke Bindung zwischen Schnittstellen und Objekten besitzt. Insbeson- deren wurde bei der Umsetzung der Schnittstellenbeschreibungssprache in die Zielsprache eine Umsetzung gewählt, die Dienste als Objekte reprä- sentiert. Involviert die Diensterbringung verschiedene Objekte, kann nur ein Objekt als Stellvertreter all dieser Dienste den Service anbieten. Dieses Objekt ist für die Einhaltung von Dienstgüte-Vereinbarungen mit Klien- ten verantwortlich. Innerhalb der Objekte, die den Service realisieren, sind für die Dienstgüte-Erbringung dann ggf. weitere interne Dienstgüte-Vor- kehrungen zu etablieren. Komponentenmodelle versprechen hier einen all- gemeineren Ansatz, der die Integration von Dienstgüte-Vorkehrungen loh- nenswert erscheinen lässt. Zum einen unterstützen Komponentenmodelle definierte Schnittstellen zur Interaktion zwischen den beteiligten Objek- ten einer Komponente, und zum anderen bieten Komponenten eine über die Schnittstellenbeschreibungssprache hinausgehende Beschreibung ihrer Funktionalität in einer Komponentenspezifikation. Diese Komponentenspe- zifikation verspricht einen guten Ansatz, um Dienstgüte-Spezifikationen der Komponenten zu integrieren. Neben den beiden bislang beschriebenen Forschungsrichtungen, die je- weils ein Rahmenwerk für das Dienstgüte-Management voraussetzen und darauf aufbauen, existieren innerhalb des in der Arbeit vorgestellten Rah- menwerkes weitere offene Forschungsfragen. Die Ausgestaltung von Preisen bei der Vergabe von Ressourcen und die damit verbundenen Richtlinien für die Vergabe und auch den Entzug stellen noch kein abgeschlossenes Gebiet dar. Hier ist der Einbezug anderer Disziplinen vielversprechend. Preisrichtlinien für manche Ressourcen, die bei Nicht-Nutzung verfallen wie Netzwerkkapazität sind Gegenstand der Forschung in der Betriebs- wirtschaftslehre. Die Gestaltung von Vergaberichtlinien, insbesondere aber die Festlegung von Vergütungen bei Nichterbringung eines festgesetzten Dienstgüte-Niveaus oder Kompensationen bei dem Entzug von Ressourcen mit einer damit einhergehenden Verletzung der Dienstgüte-Vereinbarung, wirft rechtliche Fragen über die Gültigkeit solcher Richtlinien auf. Weitere, nicht-interdisziplinäre Fragestellungen, ergeben sich aus der Frage der Wiederverwendbarkeit und Dokumentation von Dienstgüte-Vor- kehrungen im Rahmenwerk. Die Erstellung eines Katalogs mit einem ein- heitlichen Aufbau wie es bei Entwurfsmustern üblich ist verspricht eine geeignete Dokumentationsform. Allerdings muss eine solche Dokumentati- on zwei Zielgruppen gerecht werden. Zum einen sind dies Anwendungsent- wickler, die eine gegebene Dienstgüte-Implementierung anwenden wollen und Informationen für die Nutzung und Anpassung der Anwendung benö- tigen und zum anderen Dienstgüte-Entwickler, die auf bereits existierende transportspezifische Dienstgüte-Mechanismen aufbauen. Für die hier skizzierten Forschungsrichtungen ist ein Rahmenwerk für das Dienstgüte-Management unerlässlich. Das in dieser Arbeit vorgestellte Rahmenwerk bietet eine gute Ausgangsbasis.
The first measurement of e+e− pair production at mid-rapidity (|ηe| < 0.8) in pp collisions at s√=7 TeV with ALICE at the LHC is presented. The dielectron production is studied as a function of the invariant mass (mee < 3.3 GeV/c2), the pair transverse momentum (pT,ee < 8 GeV/c), and the pair transverse impact parameter (DCAee), i.e., the average distance of closest approach of the reconstructed electron and positron tracks to the collision vertex, normalised to its resolution. The results are compared with the expectations from a cocktail of known hadronic sources and are well described when PYTHIA is used to generate the heavy-flavour contributions. In the low-mass region (0.14 < mee < 1.1 GeV/c2), prompt and non-prompt e+e− sources can be separated via the DCAee. In the intermediate-mass region (1.1 < mee < 2.7 GeV/c2), a double-differential fit to the data in mee and pT,ee and a fit of the DCAee distribution allow the total cc¯¯ and bb¯¯¯ cross sections to be extracted. Two different event generators, PYTHIA and POWHEG, can reproduce the shape of the two-dimensional mee and pT,ee spectra, as well as the shape of the DCAee distribution, reasonably well. However, differences in the cc¯¯ and bb¯¯¯ cross sections are observed when using the generators to extrapolate to full phase space. Finally, the ratio of inclusive to decay photons is studied via the measurement of virtual direct photons in the transverse-momentum range 1 < pT < 8 GeV/c. This is found to be unity within the statistical and systematic uncertainties and consistent with expectations from next-to-leading order perturbative quantum chromodynamic calculations.
The first measurement of e+e− pair production at mid-rapidity (|ηe| < 0.8) in pp collisions at s√=7 TeV with ALICE at the LHC is presented. The dielectron production is studied as a function of the invariant mass (mee < 3.3 GeV/c2), the pair transverse momentum (pT,ee < 8 GeV/c), and the pair transverse impact parameter (DCAee), i.e., the average distance of closest approach of the reconstructed electron and positron tracks to the collision vertex, normalised to its resolution. The results are compared with the expectations from a cocktail of known hadronic sources and are well described when PYTHIA is used to generate the heavy-flavour contributions. In the low-mass region (0.14 < mee < 1.1 GeV/c2), prompt and non-prompt e+e− sources can be separated via the DCAee. In the intermediate-mass region (1.1 < mee < 2.7 GeV/c2), a double-differential fit to the data in mee and pT,ee and a fit of the DCAee distribution allow the total cc¯¯ and bb¯¯¯ cross sections to be extracted. Two different event generators, PYTHIA and POWHEG, can reproduce the shape of the two-dimensional mee and pT,ee spectra, as well as the shape of the DCAee distribution, reasonably well. However, differences in the cc¯¯ and bb¯¯¯ cross sections are observed when using the generators to extrapolate to full phase space. Finally, the ratio of inclusive to decay photons is studied via the measurement of virtual direct photons in the transverse-momentum range 1 < pT < 8 GeV/c. This is found to be unity within the statistical and systematic uncertainties and consistent with expectations from next-to-leading order perturbative quantum chromodynamic calculations.
The first measurements of dielectron production at midrapidity (|ηc|<0.8) in proton-proton and proton-lead collisions at sNN−−−√ = 5.02 TeV at the LHC are presented. The dielectron cross section is measured with the ALICE detector as a function of the invariant mass mee and the pair transverse momentum pT,ee in the ranges mee < 3.5 GeV/c2 and pT,ee < 8.0 GeV/c2, in both collision systems. In proton-proton collisions, the charm and beauty cross sections are determined at midrapidity from a fit to the data with two different event generators. This complements the existing dielectron measurements performed at s√ = 7 and 13 TeV. The slope of the s√ dependence of the three measurements is described by FONLL calculations. The dielectron cross section measured in proton-lead collisions is in agreement, within the current precision, with the expected dielectron production without any nuclear matter effects for e+e− pairs from open heavy-flavor hadron decays. For the first time at LHC energies, the dielectron production in proton-lead and proton-proton collisions are directly compared at the same sNN−−−√ via the dielectron nuclear modification factor RpPb. The measurements are compared to model calculations including cold nuclear matter effects, or additional sources of dielectrons from thermal radiation.
The first measurements of dielectron production at midrapidity (|ηc|<0.8) in proton-proton and proton-lead collisions at sNN−−−√ = 5.02 TeV at the LHC are presented. The dielectron cross section is measured with the ALICE detector as a function of the invariant mass mee and the pair transverse momentum pT,ee in the ranges mee < 3.5 GeV/c2 and pT,ee < 8.0 GeV/c2, in both collision systems. In proton-proton collisions, the charm and beauty cross sections are determined at midrapidity from a fit to the data with two different event generators. This complements the existing dielectron measurements performed at s√ = 7 and 13 TeV. The slope of the s√ dependence of the three measurements is described by FONLL calculations. The dielectron cross section measured in proton-lead collisions is in agreement, within the current precision, with the expected dielectron production without any nuclear matter effects for e+e− pairs from open heavy-flavor hadron decays. For the first time at LHC energies, the dielectron production in proton-lead and proton-proton collisions are directly compared at the same sNN−−−√ via the dielectron nuclear modification factor RpPb. The measurements are compared to model calculations including cold nuclear matter effects, or additional sources of dielectrons from thermal radiation.
The first measurements of dielectron production at midrapidity (|ηc|<0.8) in proton-proton and proton-lead collisions at sNN−−−√ = 5.02 TeV at the LHC are presented. The dielectron cross section is measured with the ALICE detector as a function of the invariant mass mT,ee and the pair transverse momentum pT,ee in the ranges mT,ee < 3.5 GeV/c2 and mT,ee < 8.0 GeV/c2, in both collision systems. In proton-proton collisions, the charm and beauty cross sections are determined at midrapidity from a fit to the data with two different event generators. This complements the existing dielectron measurements performed at s√ = 7 and 13 TeV. The slope of the s√ dependence of the three measurements is described by FONLL calculations. The dielectron cross section measured in proton-lead collisions is in agreement, within the current precision, with the expected dielectron production without any nuclear matter effects for e+e− pairs from open heavy-flavor hadron decays. For the first time at LHC energies, the dielectron production in proton-lead and proton-proton collisions are directly compared at the same sNN−−−√ via the dielectron nuclear modification factor RpPb. The measurements are compared to model calculations including cold nuclear matter effects, or additional sources of dielectrons from thermal radiation.
The first measurement of e+e− pair production at mid-rapidity (|ηe| < 0.8) in pp collisions at s√=7 TeV with ALICE at the LHC is presented. The dielectron production is studied as a function of the invariant mass (mee < 3.3 GeV/c2), the pair transverse momentum (pT,ee < 8 GeV/c), and the pair transverse impact parameter (DCAee), i.e., the average distance of closest approach of the reconstructed electron and positron tracks to the collision vertex, normalised to its resolution. The results are compared with the expectations from a cocktail of known hadronic sources and are well described when PYTHIA is used to generate the heavy-flavour contributions. In the low-mass region (0.14 < mee < 1.1 GeV/c2), prompt and non-prompt e+e− sources can be separated via the DCAee. In the intermediate-mass region (1.1 < mee < 2.7 GeV/c2), a double-differential fit to the data in mee and pT,ee and a fit of the DCAee distribution allow the total cc¯¯ and bb¯¯¯ cross sections to be extracted. Two different event generators, PYTHIA and POWHEG, can reproduce the shape of the two-dimensional mee and pT,ee spectra, as well as the shape of the DCAee distribution, reasonably well. However, differences in the cc¯¯ and bb¯¯¯ cross sections are observed when using the generators to extrapolate to full phase space. Finally, the ratio of inclusive to decay photons is studied via the measurement of virtual direct photons in the transverse-momentum range 1 < pT < 8 GeV/c. This is found to be unity within the statistical and systematic uncertainties and consistent with expectations from next-to-leading order perturbative quantum chromodynamic calculations.
The first measurement of the e+e− pair production at midrapidity and low invariant mass in central Pb−Pb collisions at sNN−−−√=5.02 TeV at the LHC is presented. The yield of e+e− pairs is compared with a cocktail of expected hadronic decay contributions in the invariant mass (mee) and pair transverse momentum (pT,ee) ranges mee<3.5 GeV/c2 and pT,ee<8 GeV/c. For 0.18<mee<0.5 GeV/c2 the ratio of data to the cocktail of hadronic contributions without ρ mesons amounts to 1.42±0.12 (stat.)±0.17 (syst.)±0.12 (cocktail) and 1.44±0.12 (stat.)±0.17 (syst.)+0.17−0.21 (cocktail), including or not including medium effects in the estimation of the heavy-flavor background, respectively. It is consistent with predictions from two different models for an additional contribution of thermal e+e− pairs from the hadronic and partonic phases. In the intermediate-mass range (1.2<mee<2.6 GeV/c2), the pair transverse impact parameter of the e+e− pairs (DCAee) is used for the first time in Pb−Pb collisions to separate displaced dielectrons from heavy-flavor hadron decays from a possible (thermal) contribution produced at the interaction point. The data are consistent with a suppression of e+e− pairs from cc¯¯ and an additional prompt component. Finally, the first direct-photon measurement in the 10% most central Pb−Pb collisions at sNN−−−√=5.02 TeV is reported via the study of virtual direct photons in the transverse momentum range 1<pT<5 GeV/c. A model including prompt photons, as well as photons from the pre-equilibrium and fluid-dynamic phases, can reproduce the result, while being at the upper edge of the data uncertainties.
The first measurement of the e+e− pair production at low lepton pair transverse momentum (pT,ee) and low invariant mass (mee) in non-central Pb−Pb collisions at sNN−−−√=5.02 TeV at the LHC is presented. The dielectron production is studied with the ALICE detector at midrapidity (|ηe|<0.8) as a function of invariant mass (0.4≤mee<2.7 GeV/c2) in the 50−70% and 70−90% centrality classes for pT,ee<0.1 GeV/c, and as a function of pT,ee in three mee intervals in the most peripheral Pb−Pb collisions. Below a pT,ee of 0.1 GeV/c, a clear excess of e+e− pairs is found compared to the expectations from known hadronic sources and predictions of thermal radiation from the medium. The mee excess spectra are reproduced, within uncertainties, by different predictions of the photon−photon production of dielectrons, where the photons originate from the extremely strong electromagnetic fields generated by the highly Lorentz-contracted Pb nuclei. Lowest-order quantum electrodynamic (QED) calculations, as well as a model that takes into account the impact-parameter dependence of the average transverse momentum of the photons, also provide a good description of the pT,ee spectra. The measured ⟨p2T,ee⟩−−−−−√ of the excess pT,ee spectrum in peripheral Pb−Pb collisions is found to be comparable to the values observed previously at RHIC in a similar phase-space region.
The first measurement of the e+e− pair production at low lepton pair transverse momentum (pT,ee) and low invariant mass (mee) in non-central Pb−Pb collisions at sNN−−−√=5.02 TeV at the LHC is presented. The dielectron production is studied with the ALICE detector at midrapidity (|ηe|<0.8) as a function of invariant mass (0.4≤mee<2.7 GeV/c2) in the 50−70% and 70−90% centrality classes for pT,ee<0.1 GeV/c, and as a function of pT,ee in three mee intervals in the most peripheral Pb−Pb collisions. Below a pT,ee of 0.1 GeV/c, a clear excess of e+e− pairs is found compared to the expectations from known hadronic sources and predictions of thermal radiation from the medium. The mee excess spectra are reproduced, within uncertainties, by different predictions of the photon−photon production of dielectrons, where the photons originate from the extremely strong electromagnetic fields generated by the highly Lorentz-contracted Pb nuclei. Lowest-order quantum electrodynamic (QED) calculations, as well as a model that takes into account the impact-parameter dependence of the average transverse momentum of the photons, also provide a good description of the pT,ee spectra. The measured ⟨p2T,ee⟩−−−−−√ of the excess pT,ee spectrum in peripheral Pb−Pb collisions is found to be comparable to the values observed previously at RHIC in a similar phase-space region.
The first measurement of the e+e− pair production at low lepton pair transverse momentum (pT,ee) and low invariant mass (mee) in non-central Pb−Pb collisions at sNN−−−√=5.02 TeV at the LHC is presented. The dielectron production is studied with the ALICE detector at midrapidity (|ηe|<0.8) as a function of invariant mass (0.4≤mee<2.7 GeV/c2) in the 50−70% and 70−90% centrality classes for pT,ee<0.1 GeV/c, and as a function of pT,ee in three mee intervals in the most peripheral Pb−Pb collisions. Below a pT,ee of 0.1 GeV/c, a clear excess of e+e− pairs is found compared to the expectations from known hadronic sources and predictions of thermal radiation from the medium. The mee excess spectra are reproduced, within uncertainties, by different predictions of the photon−photon production of dielectrons, where the photons originate from the extremely strong electromagnetic fields generated by the highly Lorentz-contracted Pb nuclei. Lowest-order quantum electrodynamic (QED) calculations, as well as a model that takes into account the impact-parameter dependence of the average transverse momentum of the photons, also provide a good description of the pT,ee spectra. The measured ⟨p2T,ee⟩−−−−−√ of the excess pT,ee spectrum in peripheral Pb−Pb collisions is found to be comparable to the values observed previously at RHIC in a similar phase-space region.
The measurement of dielectron production is presented as a function of invariant mass and transverse momentum (pT) at midrapidity (|ye|<0.8) in proton-proton (pp) collisions at a centre-of-mass energy of s√=13 TeV. The contributions from light-hadron decays are calculated from their measured cross sections in pp collisions at s√=7 TeV or 13 TeV. The remaining continuum stems from correlated semileptonic decays of heavy-flavour hadrons. Fitting the data with templates from two different MC event generators, PYTHIA and POWHEG, the charm and beauty cross sections at midrapidity are extracted for the first time at this collision energy: dσcc¯/dy|y=0=974±138(stat.)±140(syst.) μb and dσbb¯/dy|y=0=79±14(stat.)±11(syst.) μb using PYTHIA simulations and dσcc¯/dy|y=0=1417±184(stat.)±204(syst.) μb and dσbb¯/dy|y=0=48±14(stat.)±7(syst.) μb for POWHEG. These values, whose uncertainties are fully correlated between the two generators, are consistent with extrapolations from lower energies. The different results obtained with POWHEG and PYTHIA imply different kinematic correlations of the heavy-quark pairs in these two generators. Furthermore, comparisons of dielectron spectra in inelastic events and in events collected with a trigger on high charged-particle multiplicities are presented in various pT intervals. The differences are consistent with the already measured scaling of light-hadron and open-charm production at high charged-particle multiplicity as a function of pT. Upper limits for the contribution of virtual direct photons are extracted at 90% confidence level and found to be in agreement with pQCD calculations.
The measurement of dielectron production is presented as a function of invariant mass and transverse momentum (pT) at midrapidity (|ye|<0.8) in proton-proton (pp) collisions at a centre-of-mass energy of s√=13 TeV. The contributions from light-hadron decays are calculated from their measured cross sections in pp collisions at s√=7 TeV or 13 TeV. The remaining continuum stems from correlated semileptonic decays of heavy-flavour hadrons. Fitting the data with templates from two different MC event generators, PYTHIA and POWHEG, the charm and beauty cross sections at midrapidity are extracted for the first time at this collision energy: dσcc¯/dy|y=0=974±138(stat.)±140(syst.) μb and dσbb¯/dy|y=0=79±14(stat.)±11(syst.) μb using PYTHIA simulations and dσcc¯/dy|y=0=1417±184(stat.)±204(syst.) μb and dσbb¯/dy|y=0=48±14(stat.)±7(syst.) μb for POWHEG. These values, whose uncertainties are fully correlated between the two generators, are consistent with extrapolations from lower energies. The different results obtained with POWHEG and PYTHIA imply different kinematic correlations of the heavy-quark pairs in these two generators. Furthermore, comparisons of dielectron spectra in inelastic events and in events collected with a trigger on high charged-particle multiplicities are presented in various pT intervals. The differences are consistent with the already measured scaling of light-hadron and open-charm production at high charged-particle multiplicity as a function of pT. Upper limits for the contribution of virtual direct photons are extracted at 90% confidence level and found to be in agreement with pQCD calculations.
Die wahrscheinlich beste Entscheidung : wie Online-Algorithmen mit der unsicheren Zukunft rechnen
(2018)
Lohnt es sich, als Skianfänger in einem schneeunsicheren Jahr Skier zu kaufen? Oder ist es günstiger, sie zu mieten? Oft müssen wir Entscheidungen treffen, ohne genügend Informationen über die Zukunft zu haben. Das gilt in noch größerem Maße für Rechnersysteme, die große Datenmengen verarbeiten und schnelle Entscheidungen treffen müssen. Damit sie trotz einer Vielzahl von Unsicherheiten erfolgreich arbeiten können, entwickeln Informatiker OnlineAlgorithmen.
Large language models have become widely available to the general public, especially due to ChatGPT's release. Consequently, the AI community has invested much effort into recreating language models of the same caliber as ChatGPT, since the latter is still a technical blackbox. This thesis aims to contribute to that cause by proposing R.O.B.E.R.T., a Robotic Operating Buddy for Efficiency, Research and Teaching. In doing so, it presents a first implementation of a lightweight environment which produces tailor-made, instruction-following language models with a heavy focus on conversational capabilities that instruct themselves into a given domain-context. Within this environment, the generation of datasets, the fine-tuning process and finally the inference of a unique R.O.B.E.R.T. instance are all carried out as part of an automated pipeline.
Interacting with the environment to process sensory information, generate perceptions, and shape behavior engages neural networks in brain areas with highly varied representations, ranging from unimodal sensory cortices to higher-order association areas. Recent work suggests a much greater degree of commonality across areas, with distributed and modular networks present in both sensory and non-sensory areas during early development. However, it is currently unknown whether this initially common modular structure undergoes an equally common developmental trajectory, or whether such a modular functional organization persists in some areas—such as primary visual cortex—but not others. Here we examine the development of network organization across diverse cortical regions in ferrets of both sexes using in vivo widefield calcium imaging of spontaneous activity. We find that all regions examined, including both primary sensory cortices (visual, auditory, and somatosensory—V1, A1, and S1, respectively) and higher order association areas (prefrontal and posterior parietal cortices) exhibit a largely similar pattern of changes over an approximately 3 week developmental period spanning eye opening and the transition to predominantly externally-driven sensory activity. We find that both a modular functional organization and millimeter-scale correlated networks remain present across all cortical areas examined. These networks weakened over development in most cortical areas, but strengthened in V1. Overall, the conserved maintenance of modular organization across different cortical areas suggests a common pathway of network refinement, and suggests that a modular organization—known to encode functional representations in visual areas—may be similarly engaged in highly diverse brain areas.
Significance Different areas of the mature brain encode vastly different representations of the world. This study shows that a modular functional organization where nearby neurons participate in similar functional networks is shared across different brain areas not only during early development, but also as the brain matures where it remains a shared feature that shapes neural activity. The largely conserved trajectory of developmental changes across brain areas suggests that similar circuit mechanisms may drive this maturation. This implies that the large literature on developing cortical circuits, which is largely focused on sensory areas, may also apply more broadly, and that perturbations during development that impinge on any such shared mechanisms may produce deficits that extend across multiple brain systems.
This thesis will first introduce in more detail the Bayesian theory and its use in integrating multiple information sources. I will briefly talk about models and their relation to the dynamics of an environment, and how to combine multiple alternative models. Following that I will discuss the experimental findings on multisensory integration in humans and animals. I start with psychophysical results on various forms of tasks and setups, that show that the brain uses and combines information from multiple cues. Specifically, the discussion will focus on the finding that humans integrate this information in a way that is close to the theoretical optimal performance. Special emphasis will be put on results about the developmental aspects of cue integration, highlighting experiments that could show that children do not perform similar to the Bayesian predictions. This section also includes a short summary of experiments on how subjects handle multiple alternative environmental dynamics. I will also talk about neurobiological findings of cells receiving input from multiple receptors both in dedicated brain areas but also primary sensory areas. I will proceed with an overview of existing theories and computational models of multisensory integration. This will be followed by a discussion on reinforcement learning (RL). First I will talk about the original theory including the two different main approaches model-free and model-based reinforcement learning. The important variables will be introduced as well as different algorithmic implementations. Secondly, a short review on the mapping of those theories onto brain and behaviour will be given. I mention the most in uential papers that showed correlations between the activity in certain brain regions with RL variables, most prominently between dopaminergic neurons and temporal difference errors. I will try to motivate, why I think that this theory can help to explain the development of near-optimal cue integration in humans. The next main chapter will introduce our model that learns to solve the task of audio-visual orienting. Many of the results in this section have been published in [Weisswange et al. 2009b,Weisswange et al. 2011]. The model agent starts without any knowledge of the environment and acts based on predictions of rewards, which will be adapted according to the reward signaling the quality of the performed action. I will show that after training this model performs similarly to the prediction of a Bayesian observer. The model can also deal with more complex environments in which it has to deal with multiple possible underlying generating models (perform causal inference). In these experiments I use di#erent formulations of Bayesian observers for comparison with our model, and find that it is most similar to the fully optimal observer doing model averaging. Additional experiments using various alterations to the environment show the ability of the model to react to changes in the input statistics without explicitly representing probability distributions. I will close the chapter with a discussion on the benefits and shortcomings of the model. The thesis continues whith a report on an application of the learning algorithm introduced before to two real world cue integration tasks on a robotic head. For these tasks our system outperforms a commonly used approximation to Bayesian inference, reliability weighted averaging. The approximation is handy because of its computational simplicity, because it relies on certain assumptions that are usually controlled for in a laboratory setting, but these are often not true for real world data. This chapter is based on the paper [Karaoguz et al. 2011]. Our second modeling approach tries to address the neuronal substrates of the learning process for cue integration. I again use a reward based training scheme, but this time implemented as a modulation of synaptic plasticity mechanisms in a recurrent network of binary threshold neurons. I start the chapter with an additional introduction section to discuss recurrent networks and especially the various forms of neuronal plasticity that I will use in the model. The performance on a task similar to that of chapter 3 will be presented together with an analysis of the in uence of different plasticity mechanisms on it. Again benefits and shortcomings and the general potential of the method will be discussed. I will close the thesis with a general conclusion and some ideas about possible future work.
Programmable hardware in the form of FPGAs found its place in various high energy physics experiments over the past few decades. These devices provide highly parallel and fully configurable data transport, data formatting, and data processing capabilities with custom interfaces, even in rigid or constrained environments. Additionally, FPGA functionalities and the number of their logic resources have grown exponentially in the last few years, making FPGAs more and more suitable for complex data processing tasks. ALICE is one of the four main experiments at the LHC and specialized in the study of heavy-ion collisions. The readout chain of the ALICE detectors makes use of FPGAs at various places. The Read-Out Receiver Cards (RORCs) are one example of FPGA-based readout hardware, building the interface between the custom detector electronics and the commercial server nodes in the data processing clusters of the Data Acquisition (DAQ) system as well as the High Level Trigger (HLT). These boards are implemented as server plug-in cards with serial optical links towards the detectors. Experimental data is received via more than 500 optical links, already partly pre-processed in the FPGAs, and pushed towards the host machines. Computer clusters consisting of a few hundred nodes collect, aggregate, compress, reconstruct, and prepare the experimental data for permanent storage and later analysis. With the end of the first LHC run period in 2012 and the start of Run 2 in 2015, the DAQ and HLT systems were renewed and several detector components were upgraded for higher data rates and event rates. Increased detector link rates and obsolete host interfaces rendered it impossible to reuse the previous RORCs in Run 2.
This thesis describes the development, integration, and maintenance of the next generation of RORCs for ALICE in Run 2. A custom hardware platform, initially developed as a joint effort between the ALICE DAQ and HLT groups in the course of this work, found its place in the Run 2 readout systems of the ALICE and ATLAS experiments. The hardware fulfills all experiment requirements, matches its target performance, and has been running stable in the production systems since the start of Run 2. Firmware and software developments for the hardware evaluation, the design of the board, the mass production hardware tests, as well as the operation of the final board in the HLT, were carried out as part of this work. 74 boards were integrated into the HLT hardware and software infrastructure, with various firmware and software developments, to provide the main experimental data input and output interface of the HLT for Run 2. The hardware cluster finder, an FPGA-based data pre-processing core from the previous generation of RORCs, was ported to the new hardware. It has been improved and extended to meet the experimental requirements throughout Run 2. The throughput of this firmware component could be doubled and the algorithm extended, providing an improved noise rejection and an increased overall mean data compression ratio compared to its previous implementation. The hardware cluster finder forms a crucial component in the HLT data reconstruction and compression scheme with a processing performance of one board equivalent to around ten server nodes for comparable processing steps in software.
The work on the firmware development, especially on the hardware cluster finder, once more demonstrated that developing and maintaining data processing algorithms with the common low-level hardware description methods is tedious and time-consuming. Therefore, a high-level synthesis (HLS) hardware description method applying dataflow computing at an algorithmic level to FPGAs was evaluated in this context. The hardware cluster finder served as an example of a typical data processing algorithm in a high energy physics readout application. The existing and highly optimized low-level implementation provided a reference for comparisons in terms of throughput and resource usage. The cluster finder algorithm could be implemented in the dataflow description with comparably little effort, providing fast development cycles, compact code and at, the same time, simplified extension and maintenance options. The performance results in terms of throughput and resource usage are comparable to the manual implementation. The dataflow environment proved to be highly valuable for design space explorations. An integration of the dataflow description into the HLT firmware and software infrastructure could be demonstrated as a proof of concept. A high-level hardware description could ease both the design space exploration, the initial development, the maintenance, and the extension of hardware algorithms for high energy physics readout applications.
Particle identification is an important feature of the ALICE detector at the LHC. In particular, for particle identification via the time-of-flight technique, the precise determination of the event collision time represents an important ingredient of the quality of the measurement. In this paper, the different methods used for such a measurement in ALICE by means of the T0 and the TOF detectors are reviewed. Efficiencies, resolution and the improvement of the particle identification separation power of the methods used are presented for the different LHC colliding systems (pp , p-Pb and Pb-Pb) during the first period of data taking of LHC (Run 1).
Particle identification is an important feature of the ALICE detector at the LHC. In particular, for particle identification via the time-of-flight technique, the precise determination of the event collision time represents an important ingredient of the quality of the measurement. In this paper, the different methods used for such a measurement in ALICE by means of the T0 and the TOF detectors are reviewed. Efficiencies, resolution and the improvement of the particle identification separation power of the methods used are presented for the different LHC colliding systems (pp , p-Pb and Pb-Pb) during the first period of data taking of LHC (Run 1).
Particle identification is an important feature of the ALICE detector at the LHC. In particular, for particle identification via the time-of-flight technique, the precise determination of the event collision time represents an important ingredient of the quality of the measurement. In this paper, the different methods used for such a measurement in ALICE by means of the T0 and the TOF detectors are reviewed. Efficiencies, resolution and the improvement of the particle identification separation power of the methods used are presented for the different LHC colliding systems (pp , p-Pb and Pb-Pb) during the first period of data taking of LHC (Run 1).
Future operation of the CBM detector requires ultra-fast analysis of the continuous stream of data from all subdetector systems. Determining the inter-system time shifts among individual detector systems in the existing prototype experiment mCBM is an essential step for data processing and in particular for stable data taking. Based on the input of raw measurements from all detector systems, the corresponding time correlations can be obtained at digital level by evaluating the differences in time stamps. If the relevant systems are stable during data taking and sufficient digital measurements are available, the distribution of time differences should display a clear peak. Up to now, the outcome of the processed time differences is stored in histograms and the maximum peak is considered, after the evaluation of all timeslices of a run leading to significant run times. The results presented here demonstrate the stability of the synchronicity of mCBM systems. Furthermore it is illustrated that relatively small amounts of raw measurements are sufficient to evaluate corresponding time correlations among individual mCBM detectors, thus enabling fast online monitoring of them in future online data processing.
Poster presentation: The analysis of neuronal processes distributed across multiple cortical areas aims at the identification of interactions between signals recorded at different sites. Such interactions can be described by measuring the stability of phase angles in the case of oscillatory signals or other forms of signal dependencies for less regular signals. Before, however, any form of interaction can be analyzed at a given time and frequency, it is necessary to assess whether all potentially contributing signals are present. We have developed a new statistical procedure for the detection of coincident power in multiple simultaneously recorded analog signals, allowing the classification of events as 'non-accidental co-activation'. This method can effectively operate on single trials, each lasting only for a few seconds. Signals need to be transformed into time-frequency space, e.g. by applying a short-time Fourier transformation using a Gaussian window. The discrete wavelet transform (DWT) is used in order to weight the resulting power patterns according to their frequency. Subsequently, the weighted power patterns are binarized via applying a threshold. At this final stage, significant power coincidence is determined across all subgroups of channel combinations for individual frequencies by selecting the maximum ratio between observed and expected duration of co-activation as test statistic. The null hypothesis that the activity in each channel is independent from the activity in every other channel is simulated by independent, random rotation of the respective activity patterns. We applied this procedure to single trials of multiple simultaneously sampled local field potentials (LFPs) obtained from occipital, parietal, central and precentral areas of three macaque monkeys. Since their task was to use visual cues to perform a precise arm movement, co-activation of numerous cortical sites was expected. In a data set with 17 channels analyzed, up to 13 sites expressed simultaneous power in the range between 5 and 240 Hz. On average, more than 50% of active channels participated at least once in a significant power co-activation pattern (PCP). Because the significance of such PCPs can be evaluated at the level of single trials, we are confident that this procedure is useful to study single trial variability with sufficient accuracy that much of the behavioral variability can be explained by the dynamics of the underlying distributed neuronal processes.
Human lymph nodes play a central part of immune defense against infection agents and tumor cells. Lymphoid follicles are compartments of the lymph node which are spherical, mainly filled with B cells. B cells are cellular components of the adaptive immune systems. In the course of a specific immune response, lymphoid follicles pass different morphological differentiation stages. The morphology and the spatial distribution of lymphoid follicles can be sometimes associated to a particular causative agent and development stage of a disease. We report our new approach for the automatic detection of follicular regions in histological whole slide images of tissue sections immuno-stained with actin. The method is divided in two phases: (1) shock filter-based detection of transition points and (2) segmentation of follicular regions. Follicular regions in 10 whole slide images were manually annotated by visual inspection, and sample surveys were conducted by an expert pathologist. The results of our method were validated by comparing with the manual annotation. On average, we could achieve a Zijbendos similarity index of 0.71, with a standard deviation of 0.07.
Paging is one of the most prominent problems in the field of online algorithms. We have to serve a sequence of page requests using a cache that can hold up to k pages. If the currently requested page is in cache we have a cache hit, otherwise we say that a cache miss occurs, and the requested page needs to be loaded into the cache. The goal is to minimize the number of cache misses by providing a good page-replacement strategy. This problem is part of memory-management when data is stored in a two-level memory hierarchy, more precisely a small and fast memory (cache) and a slow but large memory (disk). The most important application area is the virtual memory management of operating systems. Accessed pages are either already in the RAM or need to be loaded from the hard disk into the RAM using expensive I/O. The time needed to access the RAM is insignificant compared to an I/O operation which takes several milliseconds.
The traditional evaluation framework for online algorithms is competitive analysis where the online algorithm is compared to the optimal offline solution. A shortcoming of competitive analysis consists of its too pessimistic worst-case guarantees. For example LRU has a theoretical competitive ratio of k but in practice this ratio rarely exceeds the value 4.
Reducing the gap between theory and practice has been a hot research issue during the last years. More recent evaluation models have been used to prove that LRU is an optimal online algorithm or part of a class of optimal algorithms respectively, which was motivated by the assumption that LRU is one of the best algorithms in practice. Most of the newer models make LRU-friendly assumptions regarding the input, thus not leaving much room for new algorithms.
Only few works in the field of online paging have introduced new algorithms which can compete with LRU as regards the small number of cache misses.
In the first part of this thesis we study strongly competitive randomized paging algorithms, i.e. algorithms with optimal competitive guarantees. Although the tight bound for the competitive ratio has been known for decades, current algorithms matching this bound are complex and have high running times and memory requirements. We propose the algorithm OnlineMin which processes a page request in O(log k/log log k) time in the worst case. The best previously known solution requires O(k^2) time.
Usually the memory requirement of a paging algorithm is measured by the maximum number of pages that the algorithm keeps track of. Any algorithm stores information about the k pages in the cache. In addition it can also store information about pages not in cache, denoted bookmarks. We answer the open question of Bein et al. '07 whether strongly competitive randomized paging algorithms using only o(k) bookmarks exist or not. To do so we modify the Partition algorithm of McGeoch and Sleator '85 which has an unbounded bookmark complexity, and obtain Partition2 which uses O(k/log k) bookmarks.
In the second part we extract ideas from theoretical analysis of randomized paging algorithms in order to design deterministic algorithms that perform well in practice. We refine competitive analysis by introducing the attack rate
parameter r, which ranges between 1 and k. We show that r is a tight bound on the competitive ratio of deterministic algorithms.
We give empirical evidence that r is usually much smaller than k and thus r-competitive algorithms have a reasonable performance on real-world traces. By introducing the r-competitive priority-based algorithm class OnOPT we obtain a collection of promising algorithms to beat the LRU-standard. We single out the new algorithm RDM and show that it outperforms LRU and some of its variants on a wide range of real-world traces.
Since RDM is more complex than LRU one may think at first sight that the gain in terms of lowering the number of cache misses is ruined by high runtime for processing pages. We engineer a fast implementation of RDM, and compare it
to LRU and the very fast FIFO algorithm in an overall evaluation scheme, where we measure the runtime of the algorithms and add penalties for each cache miss.
Experimental results show that for realistic penalties RDM still outperforms these two algorithms even if we grant the competitors an idealistic runtime of 0.
The thesis in general deals with CORBA, the Common Object Request Broker Architecture. More specifically, it takes a look at the server-side, where object adapters exist to aid the developer in implementing objects and in dealing with request processing. The new Portable Object Adapter was recently added to the CORBA 2.2 standard. My task was the implementation of the POA in MICO and the examination if (a) the POA specification is sensible and (b) in which areas it improves over the old Basic Object Adapter. After introducing distributed platforms in general and CORBA in particular, the thesis' main two chapters are a detailed abstract examination ("Design") of the POA design and their relization ("Implementation"), highlighting the potential trouble spots, persistence and collocation.
Syntactic coindexing restrictions are by now known to be of central importance to practical anaphor resolution approaches. Since, in particular due to structural ambiguity, the assumption of the availability of a unique syntactic reading proves to be unrealistic, robust anaphor resolution relies on techniques to overcome this deficiency.
This paper describes the ROSANA approach, which generalizes the verification of coindexing restrictions in order to make it applicable to the deficient syntactic descriptions that are provided by a robust state-of-the-art parser. By a formal evaluation on two corpora that differ with respect to text genre and domain, it is shown that ROSANA achieves high-quality robust coreference resolution. Moreover, by an in-depth analysis, it is proven that the robust implementation of syntactic disjoint reference is nearly optimal. The study reveals that, compared with approaches that rely on shallow preprocessing, the largely nonheuristic disjoint reference algorithmization opens up the possibility/or a slight improvement. Furthermore, it is shown that more significant gains are to be expected elsewhere, particularly from a text-genre-specific choice of preference strategies.
The performance study of the ROSANA system crucially rests on an enhanced evaluation methodology for coreference resolution systems, the development of which constitutes the second major contribution o/the paper. As a supplement to the model-theoretic scoring scheme that was developed for the Message Understanding Conference (MUC) evaluations, additional evaluation measures are defined that, on one hand, support the developer of anaphor resolution systems, and, on the other hand, shed light on application aspects of pronoun interpretation.
We study the descriptional complexity of cellular automata (CA), a parallel model of computation. We show that between one of the simplest cellular models, the realtime-OCA. and "classical" models like deterministic finite automata (DFA) or pushdown automata (PDA), there will be savings concerning the size of description not bounded by any recursive function, a so-called nonrecursive trade-off. Furthermore, nonrecursive trade-offs are shown between some restricted classes of cellular automata. The set of valid computations of a Turing machine can be recognized by a realtime-OCA. This implies that many decidability questions are not even semi decidable for cellular automata. There is no pumping lemma and no minimization algorithm for cellular automata.
Mit der Smart Learning Infrastruktur wurde ein neuartiges didaktisches Konzept für Kurse in der Weiterbildung entwickelt. Diese Infrastruktur ist vielfältig anwendbar. Erste Analysen von Kursen zeigen, dass TeilnehmerInnen, die alle Übungen korrekt abgearbeitet haben, eine bessere Note erreichen als die Durchschnittsnote. Dieser Beitrag beschreibt ein Konzept für ein Gamification-Modul, welches mit spielerischen Elementen möglichst frühzeitig dazu animiert, alle Übungen eines Kurses korrekt und mit Verstand abzuarbeiten.
Wie eine "Heilslehre" überzieht der Begriff "Digitalisierung" fast alle Lebensbereiche – natürlich auch den Bildungsbereich. Gerade wir Informatiker*innen sind gefordert, diese Wege der Bildungstransformation mitzugestalten. Wir zusammen mit den Erziehungswissenschaftler*innen und Psychologen*innen müssen identifizieren, aufzeigen und vorbildlich umsetzen, was sinnvoll und möglich ist. Wir sind diejenigen, die die Bedingungen des Gelingens und auch die der Irrwege erforschen und aufzeigen müssen. Digitalisierungswahnsinn brauchen wir nicht!
Die 16. Jahrestagung DeLFI 2018 der Fachgruppe eLearning der Gesellschaft für Informatik e. V. findet vom 10. bis 13.September 2018 an der Johann Wolfgang Goethe – Universität, Frankfurt am Main statt, gemeinsam mit der 8. Tagung für Hochschuldidaktik der Informatik HDI 2018. ...
Algorithms for the Maximum Cardinality Matching Problem which greedily add edges to the solution enjoy great popularity. We systematically study strengths and limitations of such algorithms, in particular of those which consider node degree information to select the next edge. Concentrating on nodes of small degree is a promising approach: it was shown, experimentally and analytically, that very good approximate solutions are obtained for restricted classes of random graphs. Results achieved under these idealized conditions, however, remained unsupported by statements which depend on less optimistic assumptions.
The KarpSipser algorithm and 1-2-Greedy, which is a simplified variant of the well-known MinGreedy algorithm, proceed as follows. In each step, if a node of degree one (resp. at most two) exists, then an edge incident with a minimum degree node is picked, otherwise an arbitrary edge is added to the solution.
We analyze the approximation ratio of both algorithms on graphs of degree at most D. Families of graphs are known for which the expected approximation ratio converges to 1/2 as D grows to infinity, even if randomization against the worst case is used. If randomization is not allowed, then we show the following convergence to 1/2: the 1-2-Greedy algorithm achieves approximation ratio (D-1)/(2D-3); if the graph is bipartite, then the more restricted KarpSipser algorithm achieves the even stronger factor D/(2D-2). These guarantees set both algorithms apart from other famous matching heuristics like e.g. Greedy or MRG: these algorithms depend on randomization to break the 1/2-barrier even for paths with D=2. Moreover, for any D our guarantees are strictly larger than the best known bounds on the expected performance of the randomized variants of Greedy and MRG.
To investigate whether KarpSipser or 1-2-Greedy can be refined to achieve better performance, or be simplified without loss of approximation quality, we systematically study entire classes of deterministic greedy-like algorithms for matching. Therefore we employ the adaptive priority algorithm framework by Borodin, Nielsen, and Rackoff: in each round, an adaptive priority algorithm requests one or more edges by formulating their properties---like e.g. "is incident with a node of minimum degree"---and adds the received edges to the solution. No constraints on time and space usage are imposed, hence an adaptive priority algorithm is restricted only by its nature of picking edges in a greedy-like fashion. If an adaptive priority algorithm requests edges by processing degree information, then we show that it does not surpass the performance of KarpSipser: our D/(2D-2)-guarantee for bipartite graphs is tight and KarpSipser is optimal among all such "degree-sensitive" algorithms even though it uses degree information merely to detect degree-1 nodes. Moreover, we show that if degrees of both nodes of an edge may be processed, like e.g. the Double-MinGreedy algorithm does, then the performance of KarpSipser can only be increased marginally, if at all. Of special interest is the capability of requesting edges not only by specifying the degree of a node but additionally its set of neighbors. This enables an adaptive priority algorithm to "traverse" the input graph. We show that on general degree-bounded graphs no such algorithm can beat factor (D-1)/(2D-3). Hence our bound for 1-2-Greedy is tight and this algorithm performs optimally even though it ignores neighbor information. Furthermore, we show that an adaptive priority algorithm deteriorates to approximation ratio exactly 1/2 if it does not request small degree nodes. This tremendous decline of approximation quality happens for graphs on which 1-2-Greedy and KarpSipser perform optimally, namely paths with D=2. Consequently, requesting small degree nodes is vital to beat factor 1/2.
Summarizing, our results show that 1-2-Greedy and KarpSipser stand out from known and hypothetical algorithms as an intriguing combination of both approximation quality and conceptual simplicity.
In this talk we presented a novel technique, based on Deep Learning, to determine the impact parameter of nuclear collisions at the CBM experiment. PointNet based Deep Learning models are trained on UrQMD followed by CBMRoot simulations of Au+Au collisions at 10 AGeV to reconstruct the impact parameter of collisions from raw experimental data such as hits of the particles in the detector planes, tracks reconstructed from the hits or their combinations. The PointNet models can perform fast, accurate, event-by-event impact parameter determination in heavy ion collision experiments. They are shown to outperform a simple model which maps the track multiplicity to the impact parameter. While conventional methods for centrality classification merely provide an expected impact parameter distribution for a given centrality class, the PointNet models predict the impact parameter from 2–14 fm on an event-by-event basis with a mean error of −0.33 to 0.22 fm.
FIFO is the most prominent queueing strategy due to its simplicity and the fact that it only works with local information. Its analysis within the adversarial queueing theory however has shown, that there are networks that are not stable under the FIFO protocol, even at arbitrarily low rate. On the other hand there are networks that are universally stable, i.e., they are stable under every greedy protocol at any rate r < 1. The question as to which networks are stable under the FIFO protocol arises naturally. We offer the first polynomial time algorithm for deciding FIFO stability and simple-path FIFO stability of a directed network, answering an open question posed in [1, 4]. It turns out, that there are networks, that are FIFO stable but not universally stable, hence FIFO is not a worst case protocol in this sense. Our characterization of FIFO stability is constructive and disproves an open characterization in [4].
Various static analyses of functional programming languages that permit infinite data structures make use of set constants like Top, Inf, and Bot, denoting all terms, all lists not eventually ending in Nil, and all non-terminating programs, respectively. We use a set language that permits union, constructors and recursive definition of set constants with a greatest fixpoint semantics in the set of all, also infinite, computable trees, where all term constructors are non-strict. This internal report proves decidability, in particular DEXPTIME-completeness, of inclusion of co-inductively defined sets by using algorithms and results from tree automata and set constraints, and contains detailed proofs. The test for set inclusion is required by certain strictness analysis algorithms in lazy functional programming languages and could also be the basis for further set-based analyses.
Static analysis of different non-strict functional programming languages makes use of set constants like Top, Inf, and Bot denoting all expressions, all lists without a last Nil as tail, and all non-terminating programs, respectively. We use a set language that permits union, constructors and recursive definition of set constants with a greatest fixpoint semantics. This paper proves decidability, in particular EXPTIMEcompleteness, of subset relationship of co-inductively defined sets by using algorithms and results from tree automata. This shows decidability of the test for set inclusion, which is required by certain strictness analysis algorithms in lazy functional programming languages.
It is well known that first order uni cation is decidable, whereas second order and higher order unification is undecidable. Bounded second order unification (BSOU) is second order unification under the restriction that only a bounded number of holes in the instantiating terms for second order variables is permitted, however, the size of the instantiation is not restricted. In this paper, a decision algorithm for bounded second order unification is described. This is the fist non-trivial decidability result for second order unification, where the (finite) signature is not restricted and there are no restrictions on the occurrences of variables. We show that the monadic second order unification (MSOU), a specialization of BSOU is in sum p s. Since MSOU is related to word unification, this is compares favourably to the best known upper bound NEXPTIME (and also to the announced upper bound PSPACE) for word unification. This supports the claim that bounded second order unification is easier than context unification, whose decidability is currently an open question.
The knowledge of the material budget with a high precision is fundamental for measurements of direct photon production using the photon conversion method due to its direct impact on the total systematic uncertainty. Moreover, it influences many aspects of the charged-particle reconstruction performance. In this article, two procedures to determine data-driven corrections to the material-budget description in ALICE simulation software are developed. One is based on the precise knowledge of the gas composition in the Time Projection Chamber. The other is based on the robustness of the ratio between the produced number of photons and charged particles, to a large extent due to the approximate isospin symmetry in the number of produced neutral and charged pions. Both methods are applied to ALICE data allowing for a reduction of the overall material budget systematic uncertainty from 4.5% down to 2.5%. Using these methods, a locally correct material budget is also achieved. The two proposed methods are generic and can be applied to any experiment in a similar fashion.
The knowledge of the material budget with a high precision is fundamental for measurements of direct photon production using the photon conversion method due to its direct impact on the total systematic uncertainty. Moreover, it influences many aspects of the charged-particle reconstruction performance. In this article, two procedures to determine data-driven corrections to the material-budget description in ALICE simulation software are developed. One is based on the precise knowledge of the gas composition in the Time Projection Chamber. The other is based on the robustness of the ratio between the produced number of photons and charged particles, to a large extent due to the approximate isospin symmetry in the number of produced neutral and charged pions. Both methods are applied to ALICE data allowing for a reduction of the overall material budget systematic uncertainty from 4.5% down to 2.5%. Using these methods, a locally correct material budget is also achieved. The two proposed methods are generic and can be applied to any experiment in a similar fashion.
The knowledge of the material budget with a high precision is fundamental for measurements of direct photon production using the photon conversion method due to its direct impact on the total systematic uncertainty. Moreover, it influences many aspects of the charged-particle reconstruction performance. In this article, two procedures to determine data-driven corrections to the material-budget description in ALICE simulation software are developed. One is based on the precise knowledge of the gas composition in the Time Projection Chamber. The other is based on the robustness of the ratio between the produced number of photons and charged particles, to a large extent due to the approximate isospin symmetry in the number of produced neutral and charged pions. Both methods are applied to ALICE data allowing for a reduction of the overall material budget systematic uncertainty from 4.5% down to 2.5%. Using these methods, a locally correct material budget is also achieved. The two proposed methods are generic and can be applied to any experiment in a similar fashion.
Data structures and advanced models of computation on big data : report from Dagstuhl seminar 14091
(2014)
This report documents the program and the outcomes of Dagstuhl Seminar 14091 "Data Structures and Advanced Models of Computation on Big Data". In today's computing environment vast amounts of data are processed, exchanged and analyzed. The manner in which information is stored profoundly influences the efficiency of these operations over the data. In spite of the maturity of the field many data structuring problems are still open, while new ones arise due to technological advances.
The seminar covered both recent advances in the "classical" data structuring topics as well as new models of computation adapted to modern architectures, scientific studies that reveal the need for such models, applications where large data sets play a central role, modern computing platforms for very large data, and new data structures for large data in modern architectures.
The extended abstracts included in this report contain both recent state of the art advances and lay the foundation for new directions within data structures research.
Data driven automatic model selection and parameter adaptation – a case study for septic shock
(2004)
In bioinformatics, biochemical pathways can be modeled by many differential equations. It is still an open problem how to fit the huge amount of parameters of the equations to the available data. Here, the approach of systematically learning the parameters is necessary. This paper propose as model selection criterion the least complex description of the observed data by the model, the minimum description length. For the small, but important example of inflammation modeling the performance of the approach is evaluated.